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Solution processed functional chalcogenide thin films and their molecular solutes from thiol-amine inks
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Solution processed functional chalcogenide thin films and their molecular solutes from thiol-amine inks
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Content
Solution Processed Functional Chalcogenide Thin Films and Their Molecular Solutes from
Thiol-Amine Inks
Kristopher M. Koskela
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfilment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(CHEMISTRY)
August 2022
Copyright 2022 Kristopher M. Koskela
ii
Acknowledgements
The work presented herein would not be possible without the immense support of
my advisors, family, peers and friends. First, I would like to thank my Ph. D. advisor, Prof.
Richard Brutchey. You provided me not just the motivation to perform the science I want,
but the resources and guidance through several successful projects and the opportunities to
share this work at several conferences. I want to thank you for all the meaningful advice in
and out of science, and all the scientific prowess you have granted me over my five years
at USC. I lastly want to thank you for the several nominations to awards, specifically the
Chemistry Departments Research Impact Award which highlighted my scientific work and
makes it all feel worth it.
Next, I would like to thank the National Science Foundation, Solid State and
Materials Chemistry Program for research grants to conduct my thesis work. The financial
support allowed me the opportunity to dedicate my full time to chemical research and
sharing my results at several conferences.
I would like to now express my appreciation to my dissertation committee; Prof.
Richard Brutchey, Prof. Brent Melot, Prof. Mike Inkpen, Prof. Barry Thompson, and
finally Prof. John Platt. You all have been essential in my growth as a materials scientist
and education as a chemist. I would like to thank Prof. Brent Melot for his helpful insights
in classes and as a major collaborator in a high impact research project. I would next like
to thank another major collaborator, Prof. Travis Williams, for his insights, guidance, and
scientific contributions to my thesis capstone project. I have thoroughly enjoyed our fruitful
conversations and guidance through this defining project in my scientific journey.
Now, I would like to thank all Brutchey Lab members, past and present. I would
like to thank my original ‘Alkahest’ mentor, Dr. Carrie McCarthy for her guidance when I
joined the lab. I would like to thank former post–docs Dr. Patrick Cottingham and Dr. Lucia
Mora–Tamez for your scientific prowess and continued friendships. I would like to thank
Bryce Tappan, one of the smartest people I have ever met, your scientific insights are
limitless and I thank you immensely. I would next like to thank my long-time office mate,
Dr. Sara Smock for our daily chats and your numerous insights into NMR. I would like to
thank Lanja Karadaghi and Emily Williamson for the hilarious shenanigans and laughs
over the last four years of my Ph. D. Lastly, I would like to thank Kyle Crans, Marissa
Strumolo, and Allison Forsberg for allowing me to be one of your mentors in lab. I hope
the things I have passed down are helpful and I cannot wait to see the things you all publish!
I would next like to thank everyone from my undergrad that started my scientific
journey. I have immense gratitude to Dr. Andrea Steiger, one of my organic chemistry TAs
who opened my eyes to chemical research and gave me the confidence and
recommendation to pursue undergrad research. Without you, who knows where I would
have ended up. I would like to thank Prof. Jim Hutchison, my undergraduate research
iii
advisor who offered me a research position, the resources and funding to conduct
meaningful research and the financial resources to further my research contributions
through almost three full years. I would like to thank my undergrad mentors, Dr. Adam
Jansons and Dr. Brandon Crockett, the guidance and scientific expertise you taught me
allowed me to be a successful scientist in grad school and beyond. I would like to also
thank you both for the continued guidance through grad school and beyond. The thanks to
those from my undergrad years would not be complete without the biggest shoutout to Dr.
Tatiana Zaikova, your daily inspirations and guidance is unquantifiable and priceless. I
would like to further my thanks to the rest of the Hutch Lab Drs: Kenyon Plummer,
Samantha Young, Susan Cooper, Meredith Sharps, Jaclyn Kellon, Brantly Fulton and
finally Dr. Aurora Ginzberg. You all were instrumental in my growth as a chemist in some
of my most formative years.
To Allie, you have no idea the amount of gratitude and love I have for you. The
support you have given me, the patience you have had with me to endure not only your
own Ph. D but as the partner of someone getting their own, is monumental. We have grown
as humans and scientists alike and I cannot wait for what the future has in store for both of
us, we deserve it! I would like to thank the rest of your family, Mark, Tiffany, Claire,
Brooke and Rachel for all the laughs and support through these turbulent years.
Lastly, I would like to thank my family. To my parents, Gina and Will, I dedicate
my thesis to you. You have no idea the amount of support you have given me to be the
person I am today. Without you, I would not have been to do any of this. The amount of
support needed to raise a child and support them through 28+ years of life to finally receive
their Ph. D. is priceless. The sacrifices you both made will never be forgotten and would
take over a lifetime to pay back. I am a reflection of the blood, sweat, and tears you endured
to make sure I was as successful as I could be, I am eternally thankful. To my brother
Emilliano and sister Nicole, I would like to thank you for the support and words of
encouragement through my decade of schooling.
iv
Table of Contents
Acknowledgements ii
List of Tables viii
List of Figures x
Abstract xx
Chapter 1 – Introduction 1
1.1 – Abstract 1
1.2 – Solution Deposition of Thin Films 1
1.3 – Bulk Metal Chalcogenide Dissolution 6
1.4 – Bulk Metal Dissolution 9
1.5 – Metal Salt Dissolution 11
1.6 – Comparing Bulk Sn, SnO, SnS, and SnSe Dissolution 14
1.7 – Film Impurities from Alkahest Method 16
1.8 – New Applications of Alkahest Solutions 17
1.9 – Outstanding Questions 19
1.10 – Conclusions 20
1.11 – References 21
Chapter 2 – Kinetics and Mechanistic Details of Bulk ZnO Dissolution Using a
Thiol–Imidazole System 32
2.1 – Abstract 32
2.2 – Introduction 33
2.3 – Results and Discussion 35
2.3.1 – Identification of Molecular Solute 35
2.3.2 – Dissolution Kinetics 40
v
2.3.3 – Rate Law and Derivation 49
2.3.4 – Proposed Mechanism of Dissolution 51
2.3.5 – Zincite Mineral Dissolution 61
2.3.6 – Thermal Decomposition 64
2.4.1 – Characterization 66
2.4.2 – Density Functional Theory 67
2.5 – Conclusions 68
2.6 – Data Availability 69
2.7 – References 69
Chapter 3 – Polymorphic Control of Solution Processed Cu2SnS3 Films with Varying
Thiol–Amine Ink Formulation 76
3.1 – Abstract 76
3.2 – Introduction 76
3.3 – Results and Discussion 78
3.4 – Experimental 98
3.4.1 – General Considerations 98
3.4.2 – Ink Formulations and Processing 98
3.4.3 – Organic Content Determination 99
3.4.4 – Structural and Optical Characterization 100
3.4.5 – Molecular Solute Identification 101
3.4.6 – Photoelectrochemical Measurements 102
3.5 – Conclusions 102
3.6 – References 103
vi
Chapter 4 – Solution Deposition of a Bournonite CuPbSbS3 Semiconductor Thin Film
from the Dissolution of Bulk Materials with a Thiol–Amine Solvent Mixture 110
4.1 – Abstract 110
4.2 – Introduction 111
4.3 – Results and Discussion 113
4.4 – Experimental 133
4.4.1 – General Considerations 133
4.4.2 – Synthetic Ink Preparation 134
4.4.3 – Thin Film Deposition 134
4.4.4 – Natural Bournonite Ink Preparation 135
4.4.5 – Materials Characterization 135
4.4.6 – Property Measurements 137
4.5 – Conclusions 138
4.6 – References 139
Chapter 5 – Solution Processing Cu3BiS3 Absorber Layers with a Thiol-Amine Solvent
Mixture 147
5.1 – Abstract 147
5.2 – Introduction 147
5.3 – Results and Discussion 150
5.4 – Experimental 168
5.4.1 – General Considerations 168
5.4.2 – Bulk Precursor Dissolution 168
5.4.3 – Solution Processing 169
5.4.4 – Structural and Optical Characterization 169
vii
5.4.5 – Property Measurements 171
5.4.6 – Band Gap Determination from ILD Method 172
5.5 – Conclusions 173
5.6 – References 174
Appendix A – Solution Processing of a (Ag,Na)BiS2 Solid Solution using a Thiol–Amine
Solvent System 181
A.1 – Introduction 181
A.2 – Results and Discussion 182
A.3 – Experimental 191
A.3.1 – General Considerations 191
A.3.2 – Synthetic Ink Preparation 192
A.3.3 – Bulk Powder Recovery 192
A.3.4 – AgBiS2 Thin Film Deposition 192
A.3.5 – Organic Content Determination 193
A.3.6 – Structural and Optical Characterization 193
A.4 – Conclusions 194
A.5 – References 195
Full Bibliography 202
viii
List of Tables
Table 2.1. Eyring data for the dissolution of ZnO at various temperatures. Error statistics for
DH
‡
and DS
‡
derived from the analysis performed in ref. 34.
Table 2.2. Room-temperature electrolytic conductivity measurements in acetonitrile under
flowing nitrogen between two Pt wires. The measurements were run in triplicate
for accuracy at 100 mV applied potential.
Table 2.3. Description of intermediate geometries. For 2’, 3, and 3’ the sulfur atom of the
bound thiophenolate ligand coordinates to more than one zinc center on the surface.
The bond distance to the second zinc atom is provided in parentheses. Apart from
structure 3, all ligands are bound to the same Zn atom in intermediate states. In 3,
the only converged optimization calculation yields a structure in which one of the
two thiophenol ligands is bound to a second, neighboring Zn atom.
Table 3.1. Structural parameters of tetragonal () Cu2SnS3 extracted from Rietveld analysis.
Table 3.2. Structural parameters of orthorhombic (Cmc21) Cu2SnS3 extracted from Rietveld
analysis.
Table 3.3. Peak positions and peak splitting from the high-resolution XP spectra of tetragonal
Cu2SnS3 drop-casted on Si and annealed at 330 °C.
Table 3.4. Peak positions and peak splitting from the high-resolution XP spectra of
orthorhombic Cu2SnS3 drop-casted on Si and annealed at 330 °C.
Table 4.1. Structural parameters of phase-pure bournonite CuPbSbS3 extracted from Rietveld
analysis.
Table 4.2. Peak positions and peak splitting from the high-resolution XPS spectra of
CuPbSbS3 thin films on Si/SiO2 before in situ Ar
+
ion beam milling.
Table 4.3. Peak positions and peak splitting from the high-resolution XPS spectra of
CuPbSbS3 thin films on Si/SiO2 after in situ Ar
+
ion beam milling.
Table 5.1. Structural parameters of phase–pure orthorhombic Cu3BiS3 extracted from Rietveld
analysis.
Table 5.2. Peak positions and peak splitting from the high–resolution XPS spectra of
Cu3BiS3 thin films on Si/SiO2.
Table A.1. Structural refinement parameters extracted from Rietveld refinement for AgBiS2.
Table A.2. Structural refinement parameters extracted from Rietveld refinement for NaBiS2.
ix
Table A.3. Peak positions and peak splitting from the high-resolution XPS spectra of AgBiS2
thin films on Si annealed at 400 °C.
x
List of Figures
Figure 1.1. A comprehensive list of the types of soluble bulk precursors in alkahest solutions
published in the literature. Precursors dissolved in thiourea or thioglycolic acid are
omitted.
Figure 1.2. a) Examples of various bulk solids dissolved in thiol-amine mixtures. b) Powder
X-ray diffraction pattern of solution-processed CoSe2 from the dissolution of bulk
Co and Se in ME–en with a representative marcasite crystal structure shown as the
inset. c) Polarization curve of a CoSe2 thin film overlayed on top of an SEM image
of solution-deposited CoSe2. d) J-V curves of bilayer structured Cu-poor and Cu-
graded CZTSSe solar cells. e) Cross-section SEM image of a Cu-graded CZTSSe
solar cell with a bilayer absorber structure. f) Power factor (sS
2
) of Cu2Se thin films
deposited on polyimide substrates at different temperatures. g) Cross-sectional
SEM image of Cu2Se deposited on an Al2O3 substrate. Adapted, with permission
from, [12,22,25-27].
Figure 1.3. a) Negative ion mode ESI-MS of Sb2S3 dissolved in ME–en (1:40 vol/vol) with the
structure of the molecular stibanate found at m/z = 272.9 shown as the inset. b) DLS
pattern of polymeric and molecular Sb2Te3 solutions. SEM images of thin films
derived from c) polymeric Sb-Te and d) molecular Sb2Te3 precursors. e) Schematic
illustration of the procedure to produce molecular telluroantimonate precursors for
thin film deposition on flexible polyimide substrates. Adapted, with permission
from [38,42].
Figure 1.4. a) Photographs of In-thiolates isolated and dissolved in various organic solvents
(DMSO, DMF, FA, MeCN, and 2-methoxyethanol (2-MOE)). b) Proposed
dissolution pathway for In metal in dithiol-monoamine solutions. c) Negative ion
mode ESI-MS analysis of CuCl (top) and CuCl2 (bottom) dissolved in PT–BA (1:1
mol/mol) solutions. d) Photographs of CuCl and CuCl2 dissolved in a PT–BA
solution. Adapted, with permission from, [18,62].
Figure 1.5. a) Photographs of bulk zero-valent Sn, SnO, and SnS dissolved in thiol-amine
solutions. b) Solution
119
Sn NMR spectra of Sn, SnO, and SnS dissolved in EDT−en
giving a single resonance at δ119Sn = 217 ppm. c) Proposed structure of the
[(EDT)2Sn(II)]
2–
molecular solute from the dissolution of bulk elemental Sn, SnO
and SnS in EDT–en. Adapted, with permission from [68].
Figure 1.6. a) Generality of the approach of installing dissolved bulk semiconductors onto the
surface of CdSe nanocrystals. b) Stibanate ligands installed on CdSe nanocrystals,
CdS/CdSe core/shell nanocrystals, and Pt nanocrystals. c) Solution absorption
spectra of CdSe nanocrystals before and after ligand exchange with dissolved
semiconductors. d) Photocurrent response for ligand-exchanged CdSe nanocrystal
films heat treated to 300 °C and as-prepared CdSe films heat treated to 150 °C
during a potential scan from -300 to +300 mV relative to a Pt pseudoreference
electrode with chopped 472 nm illumination. e) Figure of merit (ZT) for SnTe
xi
nanocomposite prepared with thiocyanate (black) and CdSe (blue) surface modified
SnTe nanocrystals. f) Annular dark field (ADF) scanning transmission electron
microscopy (STEM) micrograph of SnTe@CdSe nanocrystals and the
corresponding STEM electron energy loss spectroscopy (EELS) elemental
composition maps: Sn (red), Te (green), Cd (blue), and Se (yellow). Adapted, with
permission from [38,40].
Figure 2.1. Powder XRD pattern of polycrystalline ZnO powder starting material (99.99%,
Alfa Aesar) indexed to the wurtzite crystal structure.
Figure 2.2. SEM micrograph of polycrystalline ZnO powder starting material (99.99%, Alfa
Aesar).
Figure 2.3. Representative photographs of synthetic polycrystalline ZnO powder dissolution in
MeIm and acetonitrile a) before thiophenol addition and (b) after thiophenol
addition and full dissolution.
Figures 2.4. Solution
1
H NMR of 4 in acetonitrile-d3.
Figure 2.5. Solution
13
C NMR of 4 in acetonitrile-d3.
Figure 2.6. FT-IR spectrum of 4 (KBr).
Figure 2.7. ORTEP plot of the X-ray crystal structure of Zn(SPh)2(MeIm)2 (4).
Figure 2.8 Solution
1
H NMR of 4 in acetonitrile-d3 after being exposed to air for 7 d (21 ˚C,
20-90 %RH). The peak at 2.25 ppm corresponds to H2O.
Figure 2.9. Stacked room-temperature solution
1
H NMR spectra in acetonitrile-d3 of the
aromatic region, methyl, and H2O peaks for aliquots taken as a function of time
from the dissolution of ZnO with MeIm (3 eq) and thiophenol (2.4 eq) at 75 °C.
Acetonitrile-d2 is labeled as *.
Figure 2.10. Plot of ZnO dissolution at 30 °C with concentration of 4 in solution vs. time.
Dissolution was performed with 2.4 eq thiophenol and 3 equiv MeIm relative to
ZnO. Zero-order dissolution kinetics are seen through completion of dissolution.
Figure 2.11. Plot of ZnO dissolution at 40 °C with concentration of 4 in solution vs. time.
Dissolution was performed with 2.4 eq thiophenol and 3 equiv MeIm relative to
ZnO. Zero-order dissolution kinetics are seen through completion of dissolution.
Figure 2.12. Plot of ZnO dissolution at 55 °C with concentration of 4 in solution vs. time.
Dissolution was performed with 2.4 eq thiophenol and 3 equiv MeIm relative to
ZnO. Zero-order dissolution kinetics are seen through completion of dissolution.
xii
Figure 2.13. Plot of ZnO dissolution at 75 °C with concentration of 4 in solution vs. time.
Dissolution was performed with 2.4 eq thiophenol and 3 equiv MeIm relative to
ZnO. Zero-order dissolution kinetics are seen through completion of dissolution.
Figure 2.14. Plot of ZnO dissolution at 75 °C with concentration of 4 in solution vs. time.
Dissolution was performed with stoichiometric thiophenol (2.05 eq) and MeIm
(2.05 eq) relative to ZnO. Zero-order dissolution kinetics are seen through
completion of dissolution.
Figure 2.15. Log-log plot of rate of ZnO dissolution vs. MeIm concentration at 40 °C, where
MeIm is present in excess (from 2.4-4.0 eq relative to ZnO). Zero-order dissolution
kinetics are seen through completion of dissolution.
Figure 2.16. Log-log plot of rate of ZnO dissolution vs. thiophenol concentration at 40°C, where
thiophenol is present in excess (from 2.4-4.8 eq relative to ZnO). Zero-order
dissolution kinetics are seen through completion of dissolution.
Figure 2.17. Log-log plot of solvent volume vs. rate of ZnO dissolution (75 °C).
Figure 2.18. Eyring plot derived from the dissolution of ZnO with MeIm (3 eq) and thiophenol
(2.4 eq) in acetonitrile-d3 from 30-75 °C.
Figure 2.19. Hammett plot corresponding to ZnO dissolution reaction at 40 °C with 2.4 eq of
para-substituted thiophenol and 3 eq of MeIm with respect to ZnO.
Figure 2.20. a) Solution
1
H NMR spectra of the aromatic region of a fully dissolved reaction
mixture of ZnO with MeIm (3 eq) and thiophenol (2.4 eq) in acetonitrile-d3. This
reaction proceeds readily to form 4. b) Upon addition of a more electron rich 4-
bromothiophenol at 75 °C, the displacement of the thiophenolate ligands for 4-
bromothiophenolate ligands with the formation of Zn(SPhBr)2(MeIm)2 by the
appearance of the resonances at d = 7.24 and 7.06 ppm and the concomitant
disappearance of thiophenolate protons at d = 7.36, 6.95 and 6.86 ppm. We see the
relative intensities of free thiophenol also increase at d = 7.30, 7.26 and 7.17 ppm
after the addition of 4-bromothiophenol.
Figure 2.21. Proposed cycle for product evolution from a surface reactive site. Note that a
second equivalent of MeIm enters the reaction in the conversion of 3 to 4, but this
step is kinetically invisible, so it does not enter the model.
Figure 2.22. FT-IR spectra of the sulfhydryl region showing the n(S–H) stretch of thiophenol
before and after addition of MeIm in acetonitrile (NaCl plates).
Figure 2.23. FT-IR spectra showing the n(C–S) stretch of thiophenol before and after addition
of MeIm in acetonitrile (NaCl plates).
xiii
Figure 2.24. FT-IR spectra showing the n(C–H) and n(S–H) stretching region (KBr). ZnO was
mixed with thiophenol at 75 °C, washed and dried under high vacuum overnight at
room temperature.
Figure 2.25. FT-IR spectra showing the n(S–C) stretching region (KBr). ZnO was mixed with
thiophenol at 75 °C, washed and dried under high vacuum overnight at room
temperature.
Figure 2.26. FT-IR spectra showing the n(C–H) stretching region (KBr). ZnO was mixed with
MeIm at 75 °C, washed and dried under high vacuum overnight at room
temperature.
Figure 2.27. a) Calculated Gibbs free energies (DG) at 30 °C associated with formation of
possible intermediate steps constituting dissolution of bulk ZnO with thiophenol
and MeIm, calculated using a reference (ZnO)12 cluster model (B3LYP functional,
def2-SVP basis with def2-ECP on zinc). The most favorable pathway is depicted
in blue and unfavorable intermediates are shown in red. b) Intermediate geometries:
1 and 1’ represent binding of thiophenol (with concomitant Zn–OH formation) and
MeIm to (ZnO)12, respectively. Structures 2 and 2’ represent binding of MeIm and
thiophenol (with H2O removal) to 1, respectively. Structures 3 and 3’ represent
binding of thiophenol (with H2O removal) and MeIm to 2, respectively. Structure
4 refers to the molecular solute state corresponding to formation of the
experimentally verified Zn(SPh)2(MeIm)2 complex. Model visualizations are
created using the Envision package.
40
The potential energy representation is created
using the ‘Energy Leveller’ program developed by Furness.
41
Figure 2.28. Powder XRD pattern of polycrystalline ZnS powder starting material (99.99%,
Sigma-Aldrich) indexed to the sphalerite crystal structure.
Figure 2.29. SEM micrograph of polycrystalline ZnS powder starting material (99.99%, Sigma-
Aldrich).
Figure 2.30.
1
H NMR spectra of the aromatic region of aliquots from the reaction of ZnS with
MeIm (3 eq) and thiophenol (2.4 eq) in acetonitrile-d3 at 75 °C demonstrating lack
of dissolution.
Figure 2.31. Stacked
1
H NMR spectra of the aromatic region of aliquots from the dissolution of
Zn metal with MeIm (3 eq) and diphenyl disulfide (2.4 eq) in acetonitrile-d3 at 75
°C. This reaction readily proceeds to form 4, as evidenced by the appearance of the
bound thiophenolate protons at d = 7.36, 6.95, 6.86 ppm. Resonances at d = 7.56,
7.38 and 7.30 represent aromatic protons of diphenyl disulfide.
Figure 2.32. Powder XRD pattern of natural zincite mineral powder indexed to the wurtzite
crystal structure. A photograph of the as-received mineral sample is shown as the
inset.
xiv
Figure 2.33. Representative photographs of natural zincite dissolution in MeIm and acetonitrile
a) before thiophenol addition and b) after thiophenol addition and full dissolution.
Figure 2.34.
1
H NMR spectrum of the aromatic region from the dissolution of natural zincite
mineral with MeIm (3 eq) and thiophenol (2.4 eq) in acetonitrile-d3 at 75 °C after
full dissolution. This reaction readily proceeds to form 4, as evidenced by the
appearance of the bound thiophenolate protons at d = 7.36, 6.95, 6.86 ppm.
Figure 2.35. TGA trace of the thermal decomposition of 4.
Figure 2.36. Powder XRD pattern of the thermal decomposition product of 4 annealed at 600 °C
for 30 h, indexed to cubic sphalerite ZnS.
Figure 3.1. a) TGA trace and derivative curve of a dried EDT/en ink that yields tetragonal
Cu2SnS3, demonstrating a decomposition endpoint of < 350 ˚C. Inset is a picture of
the ink with Cu2S and SnO dissolved in EDT/en (1:4 vol/vol). b) TGA trace and
derivative curve of a dried merc/en ink that yields orthorhombic Cu2SnS3,
demonstrating a decomposition endpoint of < 350 ˚C. Inset is a picture of the
combined ink with Cu2S and SnO dissolved in merc/en (1:4 vol/vol).
Figure 3.2. FT-IR spectra of the inks dried at 100 ˚C and annealed to 330 ˚C confirming loss
of organic species for a) tetragonal and b) orthorhombic Cu2SnS3.
Figure 3.3. a) Rietveld refinement of the XRD data corresponding to Cu2SnS3 resulting from
the EDT/en ink, confirming that the tetragonal unit cell is the appropriate structural
model for this polymorph (c
2
1.69, wR 2.29%; a = 5.43 Å, c = 10.69 Å, V = 315.19
Å
3
). (λ = 1.5406 Å) b) Structure of disordered tetragonal Cu2SnS3. c) Rietveld
refinement of XRD data corresponding to Cu2SnS3 resulting from the merc/en ink,
confirming that the orthorhombic Cmc21 unit cell is the appropriate structural
model for the metastable polymorph (c
2
2.18, wR 4.02%, a = 11.46 Å, b = 6.63 Å,
c = 6.32 Å, V = 479.95 Å
3
). (λ = 1.5406 Å) d) Structure of ordered orthorhombic
Cu2SnS3. Sulfur atoms are yellow, tin atoms are silver, and copper atoms are blue.
Figure 3.4 a) Rietveld refinement of the zinc blende phase using the cubic unit cell (c
2
3.56,
wR 3.32%, a = 5.46 Å). (λ = 1.5406 Å) b) Structural representation of disordered
cubic Cu2SnS3. Sulfur atoms are yellow, tin atoms are silver, and copper atoms are
blue.
Figure 3.5. a) Rietveld refinement of the wurtzite phase using the disordered P63mc unit cell
(c
2
3.05, wR 4.754%, a = 3.78 Å, c = 6.44 Å). (λ = 1.5406 Å) b) Structural
representation of disordered wurtzite Cu2SnS3.
Figure 3.6. Powder XRD diffraction pattern of the orthorhombic Cu2SnS3 polymorph annealed
to 550 °C, indexed to a simulated cubic zinc blende structure.
xv
Figure 3.7. Raman spectra using 532 nm excitation of a) tetragonal and b) orthorhombic
Cu2SnS3 films drop-casted and annealed at 330 °C.
Figure 3.8. Top-down SEM micrographs of tetragonal Cu2SnS3 at a) 350 and b) 250,000´ drop-
casted on Si and annealed at 330 °C.
Figure 3.9. Top-down SEM micrographs of orthorhombic Cu2SnS3 at a) 350 and b) 250,000´
drop-casted on Si and annealed at 330 °C.
Figure 3.10. XPS survey scan of tetragonal Cu2SnS3 drop casted on Si and annealed to 330 °C.
Figure 3.11. XPS survey scan of orthorhombic Cu2SnS3 drop casted on Si and annealed to
330 °C.
Figure 3.12. High-resolution XP spectra of a) Cu 2p, b) Sn 3d, and c) S 2p regions of tetragonal
Cu2SnS3 drop-casted on Si and annealed at 330 °C.
Figure 3.13. High-resolution XP spectra of a) Cu 2p, b) Sn 3d, and c) S 2p regions of
orthorhombic Cu2SnS3 drop-casted on Si and annealed at 330 °C.
Figure 3.14. Kubelka–Munk functions of absorption data to estimate direct optical band gaps
for a) tetragonal and b) orthorhombic polymorphs of Cu2SnS3. Transient
photocurrent response of solution-processed c) tetragonal and d) orthorhombic
films of Cu2SnS3 deposited on FTO substrates in 0.1 M Na2S/0.01 M sulfur (aq)
electrolyte under a potential of -600 mV vs Pt pseudoreference electrode using
chopped AM1.5 light.
Figure 3.15. Negative ion mode ESI-MS of Cu2S dissolved in a) EDT/en and b) merc/en. TGA
traces and derivative curves of a dried c) Cu2S EDT/en ink and d) Cu2S merc/en
ink.
Figure 3.16. Negative ion mode ESI-MS of SnO dissolved in a) EDT/en and b) merc/en. TGA
trace and derivative curve of a dried c) SnO EDT/en ink and d) SnO merc/en ink.
Figure 4.1. Crystal structure of bournonite CuPbSbS3 (space group Pmn21).
Figure 4.2. a) Photograph of the synthetic ink prepared from the dissolution of bulk CuO, PbO,
and Sb2S3 powders in a 1:4 (vol/vol) mixture of EDT and en alongside a 1 cm
2
CuPbSbS3 thin film. b) TGA trace of the dried ink showing an endpoint of
decomposition < 350 ˚C. c) FT-IR spectra of the ink dried at 100 ˚C under vacuum
and annealed to 400 ˚C under flowing nitrogen.
Figure 4.3. a) Ex situ powder XRD patterns of a dropcast ink annealed to various temperatures
and times showing the phase evolution of CuPbSbS3 indexed with CuSbS2 and PbS.
b) Powder XRD pattern of dropcast ink annealed to 400 ˚C for 30 min showing
xvi
substantial PbS and CuSbS2 impurities. c) Powder XRD pattern of dropcast ink
annealed to 450 ˚C for 12 h showing reduced PbS and CuSbS2 impurities.
Figure 4.4. Powder XRD pattern of phase-pure CuPbSbS3 drop-cast from the ink and annealed
to 450 ˚C, with the results from a Rietveld refinement to the orthorhombic Pmn21
structure. Cross marks (+) represent experimental data points and pink tick marks
represent individual reflections of the bournonite structure with the difference
pattern shown below in blue. (l = 1.5406 Å; Rwp = 4.96%; c
2
= 2.48)
Figure 4.5. Raman spectra of a 570 nm CuPbSbS3 thin film on glass annealed to 450 °C for
20 min, along with a blank borosilicate substrate.
Figure 4.6. XPS survey scan of thin film CuPbSbS3 on Si/SiO2 before in situ Ar
+
ion beam
milling.
Figure 4.7. XPS survey scan of thin film CuPbSbS3 on Si/SiO2 after in situ Ar
+
ion beam
milling.
Figure 4.8. High-resolution XPS spectra for a) Cu 2p before in situ Ar
+
ion beam milling, and
b) Cu 2p after milling.
Figure 4.9. High-resolution XPS spectra for a) Pb 4f before in situ Ar
+
ion beam milling, and
b) Pb 4f after milling.
Figure 4.10. High-resolution XPS spectra for a) Sb 3d before in situ Ar
+
ion beam milling, and
b) Sb 3d after milling.
Figure 4.11. High-resolution XPS spectra for a) S 2p before in situ Ar
+
ion beam milling, and b)
S 2p after milling.
Figure 4.12. a,b) Natural bournonite sample obtained from the Los Angeles County Natural
History Museum (catalog number: NHMLA 67450, mined from Chihuahua,
Mexico), and c) powder XRD pattern of natural sample indexed to CuPbSbS3
(PDF: 01-073-5993). Inset shows fully dissolved ink.
Figure 4.13. Photograph of CuPbSbS3 inks prepared from the dissolution of CuO, PbO, and
Sb2S3 in a 1:4 (v/v) mixture of EDT and en (left), and an ink of a natural bournonite
sample (right) dissolved in the same solvent mixture with the same concentration
(~60 mg mL
–1
). Solid components of inks are shown in front of vials.
Figure 4.14. Powder XRD pattern of ink of natural bournonite sample annealed to 450 ˚C for
96 h and indexed to CuPbSbS3 (PDF: 01-073-5993) and PbS (PDF: 01-077-0244).
Figure 4.15. a) Cross-sectional SEM micrograph of a CuPbSbS3 thin film deposited on a
borosilicate glass substrate. b) Plot of absorption coefficient (a) as a function of
xvii
wavelength, and c) Tauc plot extrapolated to estimate a direct optical band gap of
1.24 eV.
Figure 4.16. Cross-sectional SEM image of a ~1 µm CuPbSbS3 thin film derived from 3 coats
spun at 2000 rpm and annealed to 390 ˚C for 10 min between each coat.
Figure 4.17. Transmittance spectra in the integrating sphere using a 570 nm thin film of
CuPbSbS3.
Figure 4.18. Resistivity (r) of a CuPbSbS3 thin film as a function of temperature.
Figure 4.19. Representative resistivity measurements on different solution processed bournonite
thin film samples. Plots are representative of semiconducting nature of CuPbSbS3.
Resistances were collected until ohmic contact was lost (data omitted).
Figure 4.20. Photoresponse at 25 ˚C under ambient conditions of a CuPbSbS3 thin film deposited
on FTO. The device was tested under chopped white light at a potential of -500
mV. A 300 W Xenon arc lamp calibrated to AM1.5G illumination was employed
for this measurement. Arrows indicate when light was turned on or off.
Figure 4.21. Powder XRD pattern of aikinite CuPbBiS3 ink annealed to 450 °C for 48 h and
indexed to CuPbBiS3 (PDF: 01-071-0643) and PbS (PDF: 01-077-0244).
Figure 5.1. Crystal structure of wittichenite Cu3BiS3 (space group P212121), from PDF exp. 43-
1479.
Figure 5.2. a) Semiconductor ink containing bulk CuO and Bi2S3 dissolved in a 1:4 (vol/vol)
mixture of EDT and en next to a Cu3BiS3 thin film. b) Thermogravimetric analysis
trace of the dried ink demonstrating a decomposition endpoint of < 350 ˚C. (c) FT-
IR spectra of the ink dried at 150 ˚C and a thin film heated to 400 ˚C confirming
loss of organic species.
Figure 5.3. Cross-sectional SEM image at a) 25,000x and b) 100,000x magnification of a 490-
nm Cu3BiS3 thin film deposited from three coats spun at 2500 rpm and annealed to
400 ˚C for 10 min between each coat.
Figure 5.4. Rietveld refinement to the orthorhombic P212121 structure of the powder X-ray
diffraction pattern of phase pure Cu3BiS3. Open circles are experimental data,
purple tick marks are individual reflections of the wittichenite structure, and the
difference pattern is given in blue. (RWP = 4.30%; G.O.F. = 2.14).
Figure 5.5. Raman spectrum (532 nm excitation) of a 490-nm Cu3BiS3 thin film deposited on
a Si/SiO2 substrate annealed to 400 °C for 20 min.
Figure 5.6. XPS survey scan of Cu3BiS3 thin film on Si/SiO2.
xviii
Figure 5.7. High-resolution XPS spectrum of Cu 2p region.
Figure 5.8. High resolution XPS spectrum of Bi 4f and S 2p spectral region.
Figure 5.9. High resolution XPS spectrum of S 2s region.
Figure 5.10. Transmittance spectrum of a 490-nm thin film of Cu3BiS3 deposited on a
borosilicate glass substrate.
Figure 5.11. Absorption coefficient as a function of incident photon energy for a 490-nm thin
film of Cu3BiS3 deposited on a borosilicate glass substrate.
Figure 5.12. Inverse logarithmic derivative (ILD) plot (maroon data points) of a 490 nm thin
film deposited on a borosilicate glass substrate. ILD plot uses absorption spectra
that derived from transmittance data. The dashed black line represents the linear
regression that was used to estimate the optical band gap from the ILD plot using
values from 2.0-3.5 eV. From this, the optical band gap was determined to be 1.47
eV and the m value derived was 0.98.
Figure 5.13. Resistivity (r) of a 490 nm Cu3BiS3 thin film as a function of temperature.
Figure 5.14. Linear sweep voltammogram of p-type Cu3BiS3 at 10 mV s
–1
with chopped
simulated AM1.5G light every 10 s in contact with N2-saturated 0.1 M Eu(NO3)3
(aq).
Figure 5.15. Transient photocurrent response of solution-processed Cu3BiS3 thin film deposited
on FTO substrates in N2-saturated 0.1 M Eu(NO3)3 (aq) under a potential of -800
mV vs Ag|AgCl (3 M KCl).
Figure 5.16. Stability test of p-type Cu3BiS3 in contact with N2-saturated 0.1 M Eu(NO3)3 (aq)
at -800 mV vs Ag½AgCl. The light was turned off and back on at ca. 5, 10, and 15
min where sharp photocurrent decreases are observed.
Figure A.1. a) Representative photographs of Ag1–xNaxBiS2 solid solution inks (left to right:
AgBiS2, Ag0.75Na0.25BiS2, Ag0.50Na0.50BiS2, Ag0.25Na0.75BiS2, NaBiS2).
Thermogravimetric analysis traces of the dried b) AgBiS2 and c) NaBiS2 inks
demonstrating a decomposition endpoint of < 350 ˚C.
Figure A.2. FT-IR spectra of a) AgBiS2 and b) NaBiS2 inks dried to 150 °C and annealed at
400 °C, confirming the decomposition and complete loss of the organic species.
Figure A.3. a) Experimental powder X–ray diffraction patterns of Ag1–xNaxBiS2 solid solutions.
b) Stacked plot of peak shift at 2q = ~31° showing 100% intensity peak shifting to
higher 2q values with the alloying of Na
+
. c) Vegard’s law plot showing linear
lattice and volume expansions with alloying of Na
+
.
xix
Figure A.4. Rietveld refinements of a) AgBiS2 (G.O.F. = 2.14, wR = 8.96%) and b) NaBiS2
(G.O.F. = 2.52, wR 3.64%). l = 1.5406.
Figure A.5. a) Top–down scanning electron microscopy (SEM) image of the spin coated 175
nm AgBiS2 thin film deposited on Si substrate at 5000´ (scale bar = 10 mm). Side–
on SEM images of AgBiS2 thin film at b) 35,000´ (scale bar = 2 mm) and c)
100,000´ (scale bar = 500 nm).
Figure A.6. a) Raman spectrum, b) absorption coefficient and c) Tauc plot of 175 nm AgBiS2
thin film deposited on borosilicate glass at 400 °C.
Figure A.7. XPS survey scan of AgBiS2 thin film on Si and annealed to 400 °C.
Figure A.8. High-resolution XPS spectra of a) Ag 3d region, b) Bi 4f and S 2p, and c) S 2s
spectral regions.
xx
Abstract
The solution phase deposition of molecular inks into phase pure and alloyed semiconductor
thin films for functional devices is of importance to replace deposition techniques reliant on high
vacuum and high temperature annealing (i.e., chemical vapor deposition, physical vapor
deposition, etc.). In chapter 1, the current progress of one class of molecular inks, thiol-amine –
“alkahest”, is presented. The current progress of understanding the identity of molecular solutes
and how it dictates the phase(s) and quality of the resulting materials will be addressed as well as
outstanding questions and future directions. In chapter 2, we discuss the dissolution of bulk ZnO
in a model thiol-imidazole solvent system where the dissolution kinetics was tracked
experimentally, and a mechanism of dissolution was proposed that was supported with DFT
calculations. In chapter 3, we present the polymorphic control of two different Cu2SnS3
semiconductor films by simply switching the identity of the thiol in alkahest solvent mixtures and
a mechanism of polymorph control is suggested. In the following chapters, environmentally stable
sulfosalts as replacements for perovskites, bournonite (CuPbSbS3) (chapter 4) and wittichenite
(Cu3BiS3) (chapter 5) are solution processed into functional thin films using the alkahest and their
structural and optical properties are investigated. Finally, in the appendix, a Ag1–xNaxBiS2 solid
solution is solution processed and high quality semiconducting AgBiS2 thin films are presented.
In summary, by leveraging alkahest solutions to fine tune ink compositions and identifying
resulting molecular solutes and dissolution/decomposition pathways, high quality semiconductors
can be solution deposited with control over phase-purity, polymorph, and doping/alloying (solid
solution.
Chapter 1. Introduction*
*Published – Koskela, K. M.; Strumolo, M. J.; Brutchey, R. L. Trends Chem. 2021, 3, 1061–
1073.
1.1 Abstract
Solution deposition of thin films has garnered interest as a replacement for vacuum
deposition techniques due to its scalability and lower cost. While hydrazine processing offered an
alternative to vacuum deposition, its commercialization is limited due to its toxicity and explosive
nature. Binary thiol-amine mixtures (“alkahests”) have proven usage in the dissolution of a wide
range of inexpensive, bulk solids to give inks. Intensive study of dissolution, solute speciation, and
decomposition mechanisms have bridged the quality gap between hydrazine-processed and
vacuum deposited thin films, but analogous studies for thiol-amine mixtures are nascent. Here, we
outline recent progress made in identifying the molecular solutes from bulk solid dissolution in
thiol-amine solutions. New applications and potential areas of future study are highlighted.
1.2 Solution Deposition of Thin Films
Semiconductor thin films are used for a wide-range of technologically relevant devices,
including thermoelectrics, photovoltaics, and electrocatalysts.
1-4
Traditional deposition methods,
such as chemical vapor deposition and atomic layer deposition, require high vacuum, high
temperatures, and specialized equipment for large-scale production.
1
In contrast, solution
deposition generally utilizes lower temperatures and can be used with high-throughput techniques,
such as spray coating and roll-to-roll printing, making it more cost effective and scalable.
2,5,6
A
promising method for the solution deposition of semiconductor thin films is the use of molecular
inks, which can produce atomically homogenous thin films with good functionality (e.g., high
2
solar cell power conversion efficiencies).
7,8
Molecular inks can be prepared by the dissolution of
discrete molecular complexes or by the dissolution of bulk solids. Typically, discrete molecular
complexes possess high solubility but are more expensive. Alternatively, the dissolution of bulk
solids may be cheaper, but bulk inorganic solids often have very low solubilities in standard
solvents.
3,7,8
In 2004, Mitzi and coworkers introduced hydrazine as a potent solvent that
successfully co-dissolved several binary metal chalcogenides in the presence of chalcogen to
produce inks that led to highly efficient solution-deposited solar cells.
5
While this system is
effective, hydrazine is toxic and explosive, which limit its scalability.
5,9
Moreover, the dissolution
of bulk materials in hydrazine has been limited to metal chalcogenides.
More recently, alternate solvent systems have been explored, including a binary thiol-
amine mixture coined the “alkahest” introduced by Brutchey and coworkers in 2013.
10
The
alkahest is less toxic than hydrazine yet possesses high solvent power. Over 100 bulk solids,
including metal chalcogenides, metal oxides, and zero-valent metals, have been dissolved with this
system at room temperature and ambient pressure with solubilities of up to 30-35 wt% (as
compared to 40-45 wt% for hydrazine-based inks, with respect to metal precursor dissolved)
(Figures 1.1, 1.2a).
2,5,9,11-13
Dissolution using the alkahest is not only energetically favorable, but
kinetically favorable as well. For example, Ma et al. were able to dissolve bulk Cu2S in an alkahest
mixture in a matter of minutes, whereas analogous dissolution in hydrazine took several days.
14,15
The alkahest generally consists of short chain thiols and primary amines, both of which are
sufficiently volatile to produce homogenous thin films of the desired metal chalcogenide upon
solution deposition and mild annealing (270–350 °C).
2,10,16
Alternatively, once molecular solutes
are produced by the alkahest, they can be isolated by precipitation or by evaporating the excess
solvent and then re-dissolved in more conventional organic solvents for solution processing, such
3
as DMSO, DMF, or acetonitrile.
17,18
Thin films developed by the alkahest have been used for a
variety of applications, such as electrocatalysts (Figure 1.2b,c),
19-23
solar cells (Figure 1.2d,e),
24,25
and thermoelectrics (Figure 1.2f,g)
26,27
with performances comparable to hydrazine fabricated
devices. For example, the champion power conversion efficiencies for alkahest-processed
Cu(In,Ga)(S,Se)2 (CIGSSe) and Cu2ZnSnSe4 (CZTSSe) solar cells are 16.4% and 12.5%,
respectively.
24,25
The champion hydrazine processed device efficiencies are 18.1% and 12.6%,
respectively.
28,29
The alkahest has also been used to fabricate devices for other applications, such
as photodetectors
30
, wearable devices
31
, and neuromorphic devices.
32
As highlighted above, the alkahest solvent system has shown remarkable solvent power for
a wide range of bulk solids to solution deposit thin films for functional devices. To drive device
functionality and efficiency even higher, careful consideration of the identity and decomposition
properties of the resulting molecular solutes is needed to optimize thin film deposition. With a
fundamental understanding of the mechanisms of dissolution and the resulting molecular species
between different types of precursors (e.g., metals, metal chalcogenides, metal salts, etc.), future
studies can provide insight into decomposition mechanisms with alkahest solvent systems from
well-characterized molecular systems. The information garnered from these types of studies will
lead to further tailoring of ink compositions with possibilities for isolating and redispersing
molecular species in more polar/weakly coordinating solvents or purifying the solutes for higher
quality material deposition or tailored thermal decomposition. For high efficiency devices, the
number of impurities in the final materials must be limited for the commercialization of these
solvent systems.
4
Figure 1.1. A comprehensive list of the types of soluble bulk precursors in alkahest solutions as
of May 2022. Precursors dissolved in thiourea or thioglycolic acid are omitted.
5
Figure 1.2. a) Examples of various bulk solids dissolved in thiol-amine mixtures. b) Powder X-
ray diffraction pattern of solution-processed CoSe2 from the dissolution of bulk Co and Se in ME–
en with a representative marcasite crystal structure shown as the inset. c) Polarization curve of a
CoSe2 thin film overlayed on top of an SEM image of solution-deposited CoSe2. d) J-V curves of
bilayer structured Cu-poor and Cu-graded CZTSSe solar cells. e) Cross-section SEM image of a
Cu-graded CZTSSe solar cell with a bilayer absorber structure. f) Power factor (sS
2
) of Cu2Se thin
films deposited on polyimide substrates at different temperatures. g) Cross-sectional SEM image
of Cu2Se deposited on an Al2O3 substrate. Adapted, with permission from, [12,22,25-27].
While hydrazine has several issues with its scalability as a solvent, the insights gained from
this literature should not be overlooked. Metal chalcogenide devices processed from hydrazine
still represent the state-of-the-art for most solution processed metal chalcogenide materials. This
is due in large part to the extensive study of the mechanisms of dissolution, identities of the
6
molecular solutes, as well as the molecular condensation and decomposition mechanisms for thin
film formation;
33-37
for example, the methodologies garnered in these studies have pushed
hydrazine processed CIGSSe solar cells beyond 18% power conversion efficiency.
28
While in-
depth investigation into hydrazine processing has narrowed the gap between vacuum- and
solution-processed devices, these types of studies are not as prevalent for alkahest systems. A
review of bulk solid dissolution highlighting the resulting molecular solutes and their dissolution
mechanisms is lacking. Herein, we will focus on the recent insights gained from bulk solid
dissolution in alkahest systems and how these results have improved material deposition processes
and motivated new applications. We will first review the current understanding of metal, metal
chalcogenide, and metal salt dissolution in alkahest systems along with their resulting molecular
solutes, and how fundamental understanding of dissolution can further improve device fabrication
processes and efficiencies. We will then review how this knowledge has driven new applications,
such as using the alkahest to engineer nanocrystal surfaces.
38-40
Finally, we will highlight the open
questions on the fundamental understanding of dissolution and decomposition mechanisms for
alkahest systems and how this knowledge can lead to improved device fabrication and novel
applications.
1.3 Bulk Metal Chalcogenide Dissolution
The first report of metal chalcogenide dissolution with an alkahest solvent system came
from Webber et al. in 2013, where nine bulk V2VI3 (As2Ch3, Sb2Ch3, Bi2Ch3, where Ch = S, Se,
Te) chalcogenides were dissolved in a 1:10 (vol/vol) mixture of 1,2-ethanedithiol (EDT) and
ethylenediamine (en) at room temperature and ambient pressure.
10
Several of the materials were
dissolved within minutes. Initial attempts were made to understand alkahest dissolution through
7
several control experiments. Besides the case of As2S3, which is known to dissolve in neat
amines,
41
the dissolution of all other V2VI3 chalcogenides will not proceed without thiol. It was
concluded that the maximum solvent power was reached using 1,2-chelating dithiols and 1,2-
chelating diamines, but mixtures of monothiols and monoamines also showed appreciable solvent
power for metal chalcogenides.
10
Adding EDT to en (1:10 vol/vol) resulted in a ~15,000× increase
in electrolytic conductivity through the formation of ammonium thiolates in solution.
10
To be a
true molecular solution, the inks must be free of particles. Dynamic light scattering (DLS) can be
used to elucidate the solvodynamic size of species in solution and can confirm when inks are fully
dissolved molecular solutions. In the case of these nine bulk V2VI3 chalcogenides, those solutions
tested (Sb2Se3 and Bi2S3) gave molecule solutes after full dissolution.
10
In the case of the Sb2Te3
dissolution, a polymeric Sb-Te species (>10 nm in diameter) rather than a molecular species was
observed by DLS, which required the use of superhydride to fully reduce the species into a
molecular solution that was processable for flexible devices (Figure 1.3).
42
The first attempt to identify the resulting molecular solutes in an alkahest solvent system
came from Buckley et al. who probed the identity of molecular stibanates from the dissolution of
bulk Sb2S3 in mercaptoethanol (ME) and en (1:40 vol/vol).
38
By using negative ion mode
electrospray ionization mass spectrometry (ESI-MS), a mixture of four different mono- or
binuclear stibanate species were identified with anionic ME ligands (Figure 1.3a). Inductively-
coupled plasma atomic emission spectroscopy (ICP-AES) analysis of the dried ink found excess
C and N that were attributed to en, with a broad n(N–H) FT-IR stretch at 3300 cm
–1
suggesting
that protonated en acts as a counter cation to the stibanates. To confidently identify the molecular
species, careful consideration of previously reported metal-thiolate species is helpful. For example,
the ion cluster assigned to [(SC2H4O)Sb(SC2H4O)]
–
is analogous to the molecular stibanate
8
produced from the reaction of Sb(OiPr)3 and ME, which yields the neutral trigonal pyramidal
complex (SC2H4O)Sb(SC2H4OH), where one ME ligand forms a five-membered, dianionic chelate
ring and the other ME ligand binds unidentate through a thiolate;
43
indeed, there is excellent
agreement between the n(S–C), n(C–O), and n(Sb–OC) FT-IR bands of this complex and the
observed [(SC2H4O)Sb(SC2H4O)]
–
.
In the case of bulk Sb2Te3 dissolution in EDT and en (1:10 vol/vol), molecular products
were precipitated with the addition of acetonitrile after reduction with superhydride (Figure
1.3b,e); the resulting molecular solute possessed an Sb:Te ratio of ~2:7 by energy-dispersive X-
ray spectroscopy (EDS).
42
Based on the elemental composition, the authors speculate that one
possible form of this solute could be the previously reported Sb2Te7
4–
binuclear cluster synthesized
in hydrazine.
44
This cluster was further treated with tri-n-octylphosphine (TOP) to abstract excess
Te as TOP=Te, with the resulting antimony complex being soluble in polar solvents. This isolated
purified molecular cluster led to dense, specularly reflective thin films that were processable on
flexible polyimide substrates (Figure 1.3d,e), whereas the polymeric Sb-Te products prior to
superhydride reductive gave poor film quality (Figure 1.3c).
42
Similarly, for bulk Ag2S dissolution
in EDT and en (1:10 vol/vol), the resulting solutes change from being Ag-rich (with a Ag:S ratio
of 2:1) to Ag-poor (with a Ag:S ratio of 2:3) after precipitation with acetonitrile. The exclusion of
the unidentified Ag-rich solutes led to greatly improved film morphologies.
31
Additional studies
on the exact mechanism of metal chalcogenide dissolution are warranted to possibly direct the
formation of various advantageous molecular solute(s) and further optimize film deposition based
on this information.
9
Figure 1.3. a) Negative ion mode ESI-MS of Sb2S3 dissolved in ME–en (1:40 vol/vol) with the
structure of the molecular stibanate found at m/z = 272.9 shown as the inset. b) DLS pattern of
polymeric and molecular Sb2Te3 solutions. SEM images of thin films derived from c) polymeric
Sb-Te and d) molecular Sb2Te3 precursors. e) Schematic illustration of the procedure to produce
molecular telluroantimonate precursors for thin film deposition on flexible polyimide substrates.
Adapted, with permission from [38,42].
1.4 Bulk Metal Dissolution
Bulk metal dissolution from alkahest mixtures was first reported by Zhao et al., in which
bulk Cu and In powders were dissolved in EDT and en, whereas Ga dissolution required the
addition of bulk Se for full dissolution.
45
A subsequent study by Zhang et al. reported a wider
elemental range of bulk metal dissolution (i.e., Cu, In, Sn, and Zn) from a binary mixture of EDT
and butylamine (BA) or hexylamine (HA), in which binary metal chalcogenides were recovered
using EDT as the only sulfur source and added chalcogen was not needed for dissolution.
46
To
better understand the mechanism of dissolution with alkahest mixtures for zero-valent metals,
Agrawal and coworkers attempted to isolate and identify the molecular solutes in Cu and In
dissolved in mixtures of EDT and HA (1:10 vol/vol).
18
Using these isolated species, they
redispersed the solutes in DMSO for more benign solution deposition and device fabrication.
18
Both resulting Cu- and In-thiolates were isolated by evaporating the fully dissolved EDT-HA
solutions (e.g., Figure 1.4a). The isolated species were analyzed using ESI-MS, X-ray absorption
spectroscopy (XAS), and solution NMR spectroscopy. The isolated In-thiolates were found to be
10
in the In
3+
oxidation state with average bond distances matching well with In–S bonds and EXAFS
In K-edge showing a local coordination number of four.
18
Coupled with ESI-MS, it was concluded
that the most plausible molecular solute structure was [In(S2C2H4)2]
–
.
1
H,
13
C, and 2D coupled
1
H-
13
C NMR spectroscopy corroborated the identity of the molecular species in solution as bis(1,2-
ethanedithiolate)indium(III). It has been previously reported that In-dithiolate complexes
decompose to In2S3 whereas In-monothiolates afford InS.
47
In the case of Cu dissolution, the
identification of the molecular species was more complex. XAS confirmed the exclusive presence
of Cu
+
with a coordination number of three, and the large masses observed in ESI-MS suggests
high nuclearity Cu-thiolate clusters with 2-8 Cu atoms.
18
As previously reported in unrelated
studies on Cu-thiolate clusters, several possible geometries and structures are possible
48-50
and
without direct single-crystal XRD data, the exact identity of the Cu-thiolates in amine-thiol
mixtures is still unresolved. Moreover, a mechanism for In metal dissolution was proposed from
gaseous product analysis, where the exothermic, oxidative dissolution of zero-valent In is driven
by irreversible H2 gas evolution (Figure 1.4b).
18
For the dissolution of bulk metals, redox reactions with elemental chalcogens are typically
needed for processes akin to surface tarnishing. In the early 1990s, Rauchfuss et al. explored the
dissolution of bulk metals through an oxidative dissolution process.
51-54
Bulk Cu metal was
dissolved in the presence of sulfur with the assistance of donor solvents yielding metal complexes
with donor solvent and polysulfide ligands.
51
This work was expanded to several other metals (i.e.,
Fe, Mg, Mn, Ni and Zn) with various donor solvents (N-methylimidazole (MeIm), pyridine (py),
tetramethylethylenediamine (TMEDA), 4-(dimethylamino)pyridine).
52,53
It was shown that in the
case of Zn dissolution, the resulting Zn(TMEDA)S6 molecular complex can be decomposed to
yield cubic ZnS.
54
The dissolution of metals with sulfur and donor solvents proceeds through
11
oxidation of the metal by the chalcogen with the strong donor-solvent interaction stabilizing the
resulting molecular complex.
51-53
This chemistry was recently revisited by Wang and co-workers
for the dissolution of bulk elemental Sn and Pb, where molecular dichalcogenides serve the same
role as elemental chalcogens.
55,56
For example, diphenyl diselenide oxidizes both metallic Pb and
Sn to give discrete Pb
2+
and Sn
2+
thiolate complexes, suggesting an oxidative addition reaction
analogous to the mechanism proposed by Rauchfuss.
55,56
In the case of Pb dissolution, the
molecular solute was isolated and analyzed by single crystal XRD that gives confirmation of a
four-coordinate geometry about Pb with two selenolate ligands and two donor solvent ligands (i.e.,
Pb(L)2(SePh)2, where L = py, ½ en).
56
The isolated Pb species are structurally similar to previously
reported four-coordinate (py)2Pb(SeC5F5)2 and Pb(SeCH2CH2NMe2)2 complexes.
57,58
These
molecular solutes derived from Pb dissolution can be thermally decomposed to give PbSe, PbTe,
and PbSexTe1–x when using diphenyl diselenide, ditelluride, or a combination of the two,
respectively.
55
Along the same lines, SnSe and SnTe phases can be returned when diphenyl
diselenide or ditelluride are used, respectively, to dissolve Sn metal in the presence of en, py,
DMSO, or butylamine (BA).
55
These examples suggest that zero-valent metal dissolution with
thiol-amine solutions may be occurring through oxidative dissolution from the presence of
adventitious disulfides, which are commonly found in thiols as oxidation products.
1.5 Metal Salt Dissolution
While metal chalcogenide and zero-valent metal dissolution have been studied more
extensively, alkahest solutions have also been shown to dissolve a wide range of metal salts (e.g.,
metal acetates, acetylacetonates, halides) that return metal chalcogenide materials upon thermal
annealing.
59-61
Murria et al. identified the speciation of molecular solutes from the dissolution of
12
both CuCl and CuCl2 in 1-propanthiol (PT) and BA solutions (1:1 mol/mol) using ESI high-
resolution tandem mass spectrometry, synchrotron XAS, and Raman spectroscopy.
62
When
dissolving CuCl and CuCl2 in PT and BA, almost identical MS spectra were observed that suggest
a mixture of various Cu-thiolate and chloride complexes that give the same colored solutions
(Figure 1.4c,d). XAS suggested the exclusive presence of Cu
+
in solution, even for the dissolution
of CuCl2.
62
While no Cu-amine complexes were found by ESI, various sized butylammonium
chloride adducts ([C4H9NH3
+
]n[Cl
–
]n+1) were observed as by-products.
62
The proposed Cu-
thiolate, chloride, and mixed thiolate chloride species were corroborated with quantum chemical
calculations and are similar to previously calculated Cu-thiolate structures.
63,64
The observation of
Cu
2+
reduction to Cu
+
has also been observed in other alkahest processed chalcogenide materials
where Cu
2+
precursors are reduced in the final annealed material as evidenced by high-resolution
XPS.
11
These findings are in agreement with previous reports that suggest Cu
2+
reduces to Cu
+
in
the presence of thiols, forming disulfides;
65,66
Cu(I) disulfide complexes are thermodynamically
favored over Cu(II) µ-thiolates.
67
When these solutions were annealed to 80 °C to generate thin
films, the only crystalline products detected were n-butylammonium chloride salts.
62
While
amorphous Cu-S species were detected by Raman at 80 °C with the addition of elemental sulfur,
no crystalline products were detected even when the thin films were annealed to 350 °C with or
without added sulfur.
62
The authors posit that chloride impurities, observed in the molecular
solutes, are inhibiting crystallization of copper sulfide phases. The use of chloride salts has also
led to complications in the fabrication of CIGSSe solar cells.
60
When using GaCl3 as the Ga source,
or a combination of InCl3 and CuCl salts with Ga(acac)3, GaCl3 was always found in the precursor
ink.
60
Upon annealing these inks, the low volatilization temperature of GaCl3 led to significant Ga
loss in the final films, which was only negated by severely increasing the amount of Ga in the
13
precursor ink or simply by using non-chloride metal precursor salts. While a wide variety of
precursors have been dissolved in thiol-amine solutions, and several molecular solutes have been
identified or postulated, direct comparisons between a single metal with analogous bulk solids is
lacking. These types of studies can be beneficial for understanding element-specific dissolution
and coordination chemistry in these solvent systems, and for subsequent thin film optimization
(see section 1.6).
14
Figure 1.4. a) Photographs of In-thiolates isolated and dissolved in various organic solvents
(DMSO, DMF, FA, MeCN, and 2-methoxyethanol (2-MOE)). b) Proposed dissolution pathway
for In metal in dithiol-monoamine solutions. c) Negative ion mode ESI-MS analysis of CuCl (top)
and CuCl2 (bottom) dissolved in PT–BA (1:1 mol/mol) solutions. d) Photographs of CuCl and
CuCl2 dissolved in a PT–BA solution. Adapted, with permission from, [18,62].
1.6 Comparing Bulk Sn, SnO, SnS, and SnSe Dissolution
To identify the molecular solutes of the same metal using different bulk solid precursors,
Buckley et al. dissolved Sn, SnO, and SnS in a mixture of EDT and en (1:10 vol/vol) to give
identically colored solutions free of scattering (Figure 1.5a).
68
Using solution
119
Sn NMR, a single
15
and identical resonance at d119Sn = 217 ppm was observed for each precursor solution, suggesting
a single molecular solute that lacks any JSn-Sn coupling (Figure 1.5b).
68
This chemical shift is
indicative of four-coordinate Sn in a sulfur environment, as
119
Sn NMR is extremely sensitive to
coordination environment.
68-71
Several control experiments were performed to confidently identify
the molecular solute. For example, the independently prepared, neutral (EDT)2Sn(IV) complex
exhibits a chemical shift of d119Sn = -263 ppm in the presence of en; this chemical shift window is
indicative of six-coordinate species. Indeed, negative ion mode ESI-MS suggests en chelation to
Sn with the main ion cluster corresponding to [Sn(EDT)2en]
–
. As such, this suggests the molecular
solute is a four-coordinate [(EDT)2Sn(II)]
2–
species (Figure 1.5c), which was corroborated by a
DFT calculation of the gas-phase
119
Sn NMR chemical shift. When these inks were annealed, all
three returned crystalline and phase-pure SnS with identical optical band gaps.
68
When comparing Sn containing molecular solutes in alkahest solutions with those
identified in hydrazine dissolution, several similarities are observed. The well-defined structures
of Sn(IV) thiostannates (i.e., [Sn2S6]
4–
, [Sn4Se6]
4–
, [Sn4S10]
4–
, [Sn4Se10]
4–
) found in hydrazine
provide characteristic vibrational and absorption spectroscopic handles.
5,13,34,72-74
In a recent study
by Heo et al., compositionally phase-impure thin films of Sn(S,Se) were obtained from the
decomposition of inks derived from bulk SnSe dissolved in EDT and en (1:10 vol/vol).
17
A
purification step was performed whereby acetonitrile was used to precipitate solute species, which
were identified as [Sn4Se6]
4–
and [Sn4Se10]
4–
using Raman and UV-vis spectroscopies. By using
these isolated solutes and redispersing them in en, highly textured, mirror-like thin films of phase-
pure SnSe were fabricated after annealing to 400 °C.
17
16
Figure 1.5. a) Photographs of bulk zero-valent Sn, SnO, and SnS dissolved in thiol-amine
solutions. b) Solution
119
Sn NMR spectra of Sn, SnO, and SnS dissolved in EDT−en giving a single
resonance at δ119Sn = 217 ppm. c) Proposed structure of the [(EDT)2Sn(II)]
2–
molecular solute from
the dissolution of bulk elemental Sn, SnO and SnS in EDT–en. Adapted, with permission from
[68].
1.7 Film Impurities from Alkahest Method
Minimizing impurities and defects will lead to higher quality thin film fabrication,
ultimately opening the door to commercially competitive devices. While it is known that layers
fabricated from nanocrystal inks leave large carbonaceous impurities from the decomposition of
long chain aliphatic ligands, alkahest inks can reduce carbon impurities. It has been seen that
carbon impurities ultimately affect grain size and device performance (i.e., in CIGSSe solar cells);
therefore, it is important to minimize the amount of carbon in the final films.
45,75
In an early study,
the decomposition of an alkahest ink consisting of dissolved In, Ga, and Se in EDT and en led to
trace carbon impurities that restricted the growth of large grain CIGSe films.
45
More recently,
annealing strategies utilizing rapid thermal annealing (RTP) have been adapted to promote large
grain CIGSe formation throughout the entire absorber layer using alkahest inks for deposition.
75,76
It has been suggested in a recent study by Deshmukh et al. that their CIGSe inks prepared by the
alkahest contain no carbon impurities upon device fabrication.
77
Another possible limitation of alkahest inks is the incorporation of sulfur, from thiol
decomposition, during the crystallization of selenide and telluride thin films. Webber et al.
17
reported the incorporation of ~2 at% S upon decomposition and crystallization of a Sb2Se3 ink at
350 °C.
10
In the case of Sb2Se3, incorporation of sulfide impurities can be circumvented by using
bulk elemental Sb and Se in inks containing EDT and en, where no sulfur impurities were detected
by EDS upon recovery of the thin film.
78
While design strategies to avoid impurities in the final
materials can be gleaned from these results, decomposition mechanisms from well-characterized
molecular solutes are needed to obtain a better understanding of these effects. In the case of
CIGSSe inks in thiol-amine solvent mixtures, the amount of sulfur in the final thin film can be
severely limited upon high temperature selenization.
60,75
1.8 New Applications of Alkahest Solutions
Drawing inspiration from the hydrazine dissolution literature, the molecular solutes in
alkahest solutions can also facilitate phase-transfer ligand exchange on colloidal nanocrystals and
subsequently act as a molecular glue or solder between the nanocrystals in thin films.
38-40
The first
application of nanocrystal ligand exchange using alkahest solutions came from Buckley et al.,
where molecular stibanates (vide supra), in addition to dissolved As2S3, As2Se3, Sb2Se3, SnS, and
ZnS species, were used to replace bulky organic ligands on the surface of CdSe, CdS/CdSe
core/shell, and Pt nanocrystals (Figure 1.6a,b).
38
Absorption spectra of the ligand-exchanged CdSe
and CdS/CdSe core/shell nanocrystals showed little-to-no spectral changes in the position of the
exciton peak, indicating the particles are not etched (Figure 1.6c). A >25-fold increase in the
electrochemical photocurrent density was measured when installing the molecular stibinates on
CdSe nanocrystals because of better nanocrystal-nanocrystal coupling (Figure 1.6d). This
methodology was extended to colloidal PbS nanocrystals by Ibáñez et al., where elemental S and
Te were separately dissolved in mixtures of EDT and en and used to exchange the oleate-capped
18
surfaces of PbS nanocrystals.
39
It was shown that after thermal annealing, PbS nanocrystals treated
with dissolved sulfur complexes increased the carrier concentration in nanocrystal-derived dense
pellets by over an order of magnitude. Conversely, when PbS nanocrystals were treated with
dissolved Te complexes, carrier concentrations decreased by an order of magnitude. Such an
approach could therefore be used to tune transport in nanocrystal solids for applications in
thermoelectrics and optoelectronics. Ibáñez et al. expanded on this strategy by installing alkahest-
dissolved elemental Cd and Se onto the surfaces of SnTe nanocrystals.
40
It was proposed that the
solution of Cd and Se dissolved in EDT and en consisted of (Cd2Se3)n
2n–
or CdSe2
2–
chalcogenidocadmates by extension to the analogous solutes in hydrazine solutions;
40,79,80
however, these species were not characterized. When these materials were pressed and annealed,
CdSe surface alloying led to an increased Seebeck coefficient and power factor that also yielded
nanoinclusions of CdSe in the SnTe matrix. Resulting band engineering (i.e., wider band gap,
diminished energy separation between light-hole band and heavy hole-band) led to a higher ZT
than analogous thiocyanate-treated SCN-SnTe nanocrystals (Figure 1.6e).
40
Surface alloying with
Cd in the SnTe nanocrystals was confirmed through annular dark field (ADF) scanning
transmission electron microscopy (STEM) that showed amorphous coverage of Cd on SnTe
nanocrystals (Figure 1.6f). These types of studies using alkahest-derived solutes for nanocrystal
surface engineering are gaining traction; this methodology can be used to replace hydrazine
elsewhere, such as using In-chalcogenidometallates (such as In2Se4
2–
or others)
to ligand exchange
CdSe nanocrystals.
81
19
Figure 1.6. a) Generality of the approach of installing dissolved bulk semiconductors onto the
surface of CdSe nanocrystals. b) Stibanate ligands installed on CdSe nanocrystals, CdS/CdSe
core/shell nanocrystals, and Pt nanocrystals. c) Solution absorption spectra of CdSe nanocrystals
before and after ligand exchange with dissolved semiconductors. d) Photocurrent response for
ligand-exchanged CdSe nanocrystal films heat treated to 300 °C and as-prepared CdSe films heat
treated to 150 °C during a potential scan from -300 to +300 mV relative to a Pt pseudoreference
electrode with chopped 472 nm illumination. e) Figure of merit (ZT) for SnTe nanocomposite
prepared with thiocyanate (black) and CdSe (blue) surface modified SnTe nanocrystals. f) Annular
dark field (ADF) scanning transmission electron microscopy (STEM) micrograph of SnTe@CdSe
nanocrystals and the corresponding STEM electron energy loss spectroscopy (EELS) elemental
composition maps: Sn (red), Te (green), Cd (blue), and Se (yellow). Adapted, with permission
from [38,40].
1.9 Outstanding Questions
To further the field, a series of outstanding questions were postulated to potentially
motivate new fields of study: How will prior studies of bulk material dissolution in solvent systems
such as hydrazine drive future studies of molecular solute isolation and identification in thiol-
amine mixtures? How can well-characterized molecular solutes be leveraged for insights into
kinetic and thermodynamic mechanisms of dissolution of bulk solids? What differences in
dissolution mechanisms are expected for different bulk solids (i.e., metals vs. metal oxides vs.
20
metal chalcogenides), or when using different polymorphs of the same material? Can future studies
of well-characterized molecular solutes be used to understand thiol-amine ink decomposition
mechanisms so that knowledge can be leveraged to give higher-quality thin film morphologies?
Can the information gained from dissolution studies be leveraged to drive new applications of
thiol-amine mixtures, such as selective etching (or dissolution), material recycling, or other
metallurgical processes?
1.10 Conclusions
In a short amount of time, binary combinations of thiol and amines have become an
incredibly useful solvent mixture for the facile dissolution of a wide range of bulk solids that are
generally thought to be insoluble under standard conditions. This has enabled a large palette of
inks to be developed for the solution deposition of metal chalcogenide thin films with controllable
compositions and functionality. To further improve the effectiveness of alkahest chemistry for the
solution deposition of thin films, careful consideration must be given to the identity of dissolved
molecular solutes and their subsequent effect on the resulting material properties to close the
quality gap with hydrazine-processed thin films. Future studies should be devoted to developing a
chemical understanding of the dissolution mechanisms with different types of starting solids, such
as bulk metal chalcogenides and oxides, and more focused efforts on the direct characterization of
resulting solutes (e.g., by single crystal X-ray diffraction rather than indirect MS methods where
ionization may affect the solute identity) and potential deleterious byproducts. With structurally
well-defined molecular solutes in hand, studying their subsequent decomposition to metal
chalcogenides will enable further optimization of thin film deposition (see section 1.9). To keep
21
pace with rapidly evolving solution deposition techniques, findings from these types of studies
could ultimately lead to state-of-the-art materials or devices with competitive functionality.
1.11 References
(1) Matthews, P. D.; McNaughter, P. D.; Lewis, D. J.; O’Brien, P. Shining a Light on
Transition Metal Chalcogenides for Sustainable Photovoltaics. Chem. Sci. 2017, 8, 4177-4187.
(2) McCarthy, C. L.; Brutchey, R. L. Solution Processing of Chalcogenide Materials Using
Thiol–Amine ‘‘Alkahest’’ Solvent Systems. Chem. Commun. 2017, 53, 4888-4902.
(3) Jo, S.; Choo, S.; Kim, F.; Heo, S. H.; Son, J. S. Ink Processing for Thermoelectric Materials
and Power-Generating Devices. Adv. Mater. 2019, 31, 1804930.
(4) McCarthy, C. L.; Brutchey, R. L. Preparation of Electrocatalysts Using a Thiol–Amine
Solution Processing Method. Dalton Trans. 2018, 47, 5137-5143.
(5) Mitzi, D. B.; Kosbar, L. L.; Murray, C. E.; Copel, M.; Afazi, A. High-Mobility Ultrathin
Semiconducting Films Prepared by Spin Coating. Nature 2004, 428, 299-303.
(6) Suresh, S.; Uhl, A. R. Present Status of Solution-Processing Routes for Cu(In,Ga)(S,Se)2
Solar Cell Absorbers. Adv. Energy Mater. 2021, 11, 2003743.
(7) Habas, S. E.; Platt, H. A. S.; van Hest, M. F. A. M.; Ginley, D. S. Low-Cost Inorganic
Solar Cells: From Ink to Printed Device. Chem. Rev. 2010, 110, 6571-6594.
(8) Clark, J. A.; Murray, A.; Lee, J.-m.; Autrey, T. S.; Collord, A. D.; Hillhouse, H. W.
Complexation Chemistry in N,N-Dimethylformamide-Based Molecular Inks for Chalcogenide
Semiconductors and Photovoltaic Devices. J. Am. Chem. Soc. 2019, 141, 298-308.
22
(9) Mitzi, D. B. Solution Processing of Chalcogenide Semiconductors via Dimensional
Reduction, Solution Processing of Inorganic Materials (Mitzi, D. B.) 2008, pp.77-108, John Wiley
& Sons.
(10) Webber, D. H.; Brutchey, R. L. Alkahest for V2VI3 Chalcogenides: Dissolution of Nine
Bulk Semiconductors in a Diamine-Dithiol Solvent Mixture. J. Am. Chem. Soc. 2013, 135, 15722-
15725.
(11) Koskela, K. M.; Melot, B. C.; Brutchey, R. L. Solution Deposition of a Bournonite
CuPbSbS3 Semiconductor Thin Film from the Dissolution of Bulk Materials with a Thiol-Amine
Solvent Mixture. J. Am. Chem. Soc. 2020, 142, 6173-6179.
(12) McCarthy, C. L.; Webber, D. H.; Schueller, E. C.; Brutchey, R. L. Solution-Phase
Conversion of Bulk Metal Oxides to Metal Chalcogenides Using a Simple Thiol-Amine Solvent
Mixture. Angew. Chem., Int. Ed. 2015, 54, 8378-8381.
(13) Mitzi, D. B. Synthesis, Structure, and Thermal Properties of Soluble Hydrazinium
Germanium(IV) and Tin(IV) Selenide Salts. Inorg. Chem. 2005, 44, 3755-3761.
(14) Ma, Y.; Vartak, P. B.; Nagaraj, P.; Wang, R. Y. Thermoelectric Properties of Copper
Chalcogenide Alloys Deposited via the Solution-Phase using a Thiol-Amine Solvent Mixture. RSC
Adv. 2016, 6, 99905-99913.
(15) Mitzi, D. B.; Yuan, M.; Liu, W.; Kellock, A. J.; Jay Chey, S.; Deline, V.; Schrott, A. G. A
High-Efficiency Solution-Deposited Thin-Film Photovoltaic Device. Adv. Mater. 2008, 20, 3657-
3662.
(16) Albalawneh, G.; Ramli, M. Review-Solution Processing of CIGSe Solar Cells Using
Simple Thiol-Amine Solvents Mixture: A Review. ECS J. Solid State Sci. Technol. 2020, 9,
061013.
23
(17) Heo, S. H.; Jo, S.; Kim, H. S.; Choi, G.; Song, J. Y.; Kang, J.-Y.; Park, N.-J.; Ban, H. W.;
Kim, F.; Jeong, H.; Jung, J.; Jang, J.; Lee, W. B.; Shin, H.; Son, J. S. Composition Change-Driven
Texturing and Doping in Solution-Processed SnSe Thermoelectric Thin Films. Nat. Commun.
2019, 10, 864.
(18) Zhao, X.; Deshmukh, S. D.; Rokke, D. J.; Zhang, G.; Wu, Z.; Miller, J. T.; Agrawal, R.
Investigating Chemistry of Metal Dissolution in Amine-Thiol Mixtures and Exploiting it Toward
Benign Ink Formulation for Metal Chalcogenide Thin Films. Chem. Mater. 2019, 31, 5674-5682.
(19) Liu, F.; Zhu, J.; Hu, L.; Zhang, B.; Yao, J.; Nazeeruddin, M. K.; Grätzel, M.; Dai, S. Low-
Temperature, Solution-Deposited Metal Chalcogenide Films as Highly Efficient Counter
Electrodes for Sensitized Solar Cells. J. Mater. Chem. A 2015, 3, 6315-6323.
(20) Lui, F.; Zhu, J.; Wei, J.; Lv, M.; Xu, Y.; Zhou, L.; Hu, L.; Dai, S. Earth-Abundant Cu2SnSe3
Thin Film Counter Electrode for High-Efficiency Quantum Dot-Sensitized Solar Cells. J. Power
Sources 2015, 292, 7-14.
(21) Zhao, X.; Jiang, J.; Xue, Z.; Yan. C.; Mu, T. An Ambient Temperature, CO2-Assisted
Solution Processing of Amorphous Cobalt Sulfide in a Thiol/Amine Based Quasi-Ionic Liquid for
Oxygen Evolution Catalysis. Chem. Commun. 2017, 53, 9418-9421.
(22) McCarthy, C. L.; Downes, C. A.; Schueller, E. C.; Abuyen, K.; Brutchey, R. L. Method
for the Solution Deposition of Phase-Pure CoSe2 as an Efficient Hydrogen Evolution Reaction
Electrocatalyst. ACS Energy Lett. 2016, 1, 607-611.
(23) McCarthy, C. L.; Downes, C. A.; Brutchey, R. L. Room Temperature Dissolution of Bulk
Elemental Ni and Se for Solution Deposition of a NiSe2 HER Electrocatalyst. Inorg. Chem. 2017,
56, 10143-10146.
24
(24) Zhao, Y.; Yuan, S.; Chang, Q.; Zhou, Z.; Kou, D.; Zhou, W.; Qi, Y.; Wu, S. Controllable
Formation of Ordered Vacancy Compound for High Efficiency Solution Processed Cu(In,Ga)Se2
Solar Cells. Adv. Funct. Mater. 2021, 31, 2007928.
(25) Zhao, Y.; Zhao, X.; Kou, D.; Zhou, W.; Zhou, Z., Yuan, S.; Qi, Y.; Zheng, Z.; Wu, S. Local
Cu Component Engineering to Achieve Continuous Carrier Transport for Enhanced Kesterite
Solar Cells. ACS Appl. Mater. Interfaces 2021, 13, 795-805.
(26) Lin, Z.; He, Q.; Yin, A.; Xu, Y.; Wang, C.; Ding, M.; Cheng, H.-C.; Papandrea, B.; Huang,
Y.; Duan, X. Cosolvent Approach for Solution-Processable Electronic Thin Films. ACS Nano
2015, 9, 4398-4405.
(27) Lin, Z.; Hollar, C.; Kang, J. S.; Yin, A.; Wang, Y.; Shiu, H.-Y.; Huang, Y.; Hu, Y.; Zhang,
Y.; Duan, X. A Solution Processable High-Performance Thermoelectric Copper Selenide Thin
Film. Adv. Mater. 2017, 29, 1606662.
(28) Zhang, T.; Yang, Y.; Liu, D.; Tse, S. C.; Cao, W.; Feng, Z.; Chen, S.; Qian, L. High
Efficiency Solution-Processed Thin-Film Cu(In,Ga)(Se,S)2 Solar Cells. Energy Environ. Sci.
2016, 9, 3674-3681.
(29) Wang, W.; Winkler, M. T.; Gunawan, O.; Gokmen, T.; Todorov, T. K.; Zhu, Y.; Mitzi, D.
B. Device Characteristics of CZTSSe Thin-Film Solar Cells with 12.6% Efficiency. Adv. Energy
Mater. 2014, 4, 1301465.
(30) Hasan, M. R.; Arinze, E. S.; Singh, A. K.; Oleshko, V. P.; Guo, S.; Rani, A.; Cheng, Y.;
Kalish, I.; Zaghloul, M. E.; Rao, M. V.; Nguyen, N. V.; Motayed, A.; Davydov, A. V.; Thon, S.
M.; Debnath, R. An Antimony Selenide Molecular Ink for Flexible Broadband Detectors. Adv.
Electron. Mater. 2016, 2, 1600182.
25
(31) Jo, S.; Cho, S.; Yang, U. J.; Hwang, G.-S.; Baek, S.; Kim, S.-H.; Heo, S. H.; Kim, J.-Y.;
Choi, M. K.; Son, J. S. Solution-Processed Stretchable Ag2S Semiconductor Thin Films for
Wearable Self-Powered Nonvolatile Memory. Adv. Mater. 2021, 33, 2100066.
(32) Harikesh, P. C.; Surendran, A.; Ghosh, B.; John, R. A.; Moorthy, A.; Yantara, N.; Salim,
T.; Thirumal, K.; Leong, W. L.; Mhaisalkar, S.; Mathews, N. Cubic NaSbS2 as an Ionic-Electronic
Coupled Semiconductor for Switchable Photovoltaic and Neuromorphic Device Applications.
Adv. Mater. 2020, 32, 1906976.
(33) Bob, B.; Lei, B.; Chung, C.-H.; Yang, W.; Hsu, W.-C.; Duan, H.-S.; Hou, W. W.-J.; Li, S.-
H.; Yang, Y. The Development of Hydrazine-Processed Cu(In,Ga)(Se,S)2 Solar Cells. Adv. Energy
Mater. 2012, 2, 504-522.
(34) Nørby, P.; Overgaard, J.; Christensen, P. S.; Richter, B.; Song, X.; Dong, M.; Han, A.;
Skibsted, J.; Iversen, B. B.; Johnsen, S. (NH4)4Sn2S6·3H2O: Crystal Structure, Thermal
Decomposition, and Precursor for Textured Thin Film. Chem. Mater. 2014, 26, 4494-4504.
(35) Chung, C.-H.; Li, S.-H.; Lei, B.; Yang, W.; Hou, W. W.; Bob, B.; Yang, Y.; Identification
of the Molecular Precursors for Hydrazine Solution Processed CuIn(Se,S)2 Films and Their
Interactions. Chem. Mater. 2011, 23, 964-969.
(36) Yang, B.; Xue, D.-J.; Leng, M.; Zhong, J.; Wang, L.; Song, H.; Zhou, Y.; Tang, J.
Hydrazine Solution Processed Sb2S3, Sb2Se3 and Sb2(S1-xSex)3 Film: Molecular Precursor
Identification, Film Fabrication and Band Gap Tuning. Sci. Rep. 2015, 5, 10978.
(37) Yang, W.; Duan, H.-S.; Cha, K. C.; Hsu, C.-J.; Hsu, W.-C.; Zhou, H.; Bob, B.; Yang, Y.
Molecular Solution Approach to Synthesize Electronic Quality Cu2ZnSnS4 Thin Films. J. Am.
Chem. Soc. 2013, 135, 6915-6920.
26
(38) Buckley, J. J.; Greaney, M. J.; Brutchey, R. L. Ligand Exchange of Colloidal CdSe
Nanocrystals with Stibanates Derived from Sb2S3 Dissolved in a Thiol-Amine Mixture. Chem.
Mater. 2014, 26, 6311-6317.
(39) Ibáñez, M.; Hasler, R.; Liu, H.; Dobrozhan, O.; Nazarenko, O.; Cadavid, D.; Cabot, A.;
Kovalenko, M. V. Tuning p-type Transport in Bottom-Up-Engineered Nanocrystalline Pb
Chalcogenides Using Alkali Metal Chalcogenides as Capping Ligands. Chem. Mater. 2017, 29,
7093-7097.
(40) Ibáñez, M.; Hasler, R.; Genc, A.; Liu, Y.; Kuster, B.; Schuster, M.; Dobrozhan, O.;
Cadavid, D.; Arbiol, J.; Cabot, A.; Kovalenko, M. V. Ligand-mediated band engineering in
bottom-up assembled SnTe nanocomposites for thermoelectric energy conversion. J. Am. Chem.
Soc. 2019, 141, 8025-8029.
(41) Slang, S.; Palka, K.; Loghina, L.; Kovalskiy, A.; Jain, H.; Vlcek, M. Mechanism of the
dissolution of As-S chalcogenide glass in n-butylamine and its influence on the structure of spin
coated layers. J. Non-Cryst Solids 2015, 426, 125-131.
(42) Jo, S.; Park, S. H.; Shin, H.; Oh, I.; Heo, S. H.; Ban, H. W.; Jeong, H.; Kim, F.; Choo, S.;
Gu, D. H.; Baek, S.; Cho, S.; Kim, J. S.; Kim, B.-S.; Lee, J. E.; Song, S.; Yoo, J.-W.; Song, J. Y.;
Son, J. S. Soluble telluride-based molecular precursor for solution-processed high-performance
thermoelectrics. ACS Appl. Energy Mater. 2019, 2, 4582-4589.
(43) Gupta, A. K. S.; Bohra, R.; Mehrota, R. C.; Das, K. Heterocyclic compounds containing
antimony 1. Synthesis, physiochemical properties, crystal and molecular structure of 2-(b-
hydroxyethylthio)1,3,2-oxathiastibolane. Inorg. Chim. Acta 1990, 170, 191-197.
27
(44) Kovalenko, M. V.; Spokoyny, B.; Lee, J.-S.; Scheele, M.; Weber, A.; Perera, S.; Landry,
D.; Talapin, D. V. Semiconductor Nanocrystals Functionalized with Antimony Telluride Zintl Ions
for Nanostructured Thermoelectrics. J. Am. Chem. Soc. 2010, 132, 6686-6695.
(45) Zhao, D.; Tian, Q.; Zhou, Z.; Wang, G.; Meng, Y.; Kou, D.; Zhou, W.; Pan, D.; Wu, S.
Solution-Deposited Pure Selenide CIGSe Solar Cells from Elemental Cu, In, Ga, and Se. J. Mat.
Chem A 2015, 3, 19263.
(46) Zhang, R.; Cho, S.; Lim, D. G.; Hu, X.; Stach, E. A.; Handwerker, C. A.; Agrawal, R.
Metal-Metal Chalcogenide Molecular Precursors to Binary, Ternary, and Quaternary Metal
Chalcogenide Thin Films for Electronic Devices. Chem. Commun. 2016, 52, 5007-5010.
(47) Nomura, R.; Inazawa, S.; Kanaya, K.; Matsuda, H. Thermal Decomposition of
Butylindium Thiolates and Preparation of Indium Sulfide Powders. Appl. Organomet. Chem. 1989,
3, 195-197.
(48) Pickering, I. J.; George, G. N.; Dameron, C. T.; Kurz, B.; Winge, D. R.; Dance, I. G. X-
Ray Absorption Spectroscopy of Cuprous-Thiolate Clusters in Proteins and Model Systems. J. Am.
Chem. Soc. 1993, 115, 9498-9505.
(49) Pushie, M. J.; Zhang, L.; Pickering, I. J.; George, G. N. The Fictile Coordination Chemistry
of Cuprous-Thiolate Sites in Copper Chaperones. Biochim. Biophys. Acta, Bioenerg. 2012, 1817,
938-947.
(50) Rao, C. P.; Dorfman, J. R.; Holm, R. H. Synthesis and Structural Systematics of Ethane-
1,2-Dithiolato Complexes. Inorg. Chem. 1986, 25, 428-439.
(51) Ramli, E.; Rauchfuss, T. B.; Stern, C. L. Inception of Copper Polysulfide Clusters in the
Reaction of Copper and Sulfur in Donor Solvents: Polysulfide Complexes as the Link Between
Molecular and Nonmolecular Metal Sulfides. J. Am. Chem. Soc. 1990, 112, 4043-4044.
28
(52) Dev, S.; Ramli, E.; Rauchfuss, T. B.; Stern, C. L. Direct Approaches to Zinc
Polychalcogenide Chemistry: ZnS6(N-MeIm)2 and ZnSe4(N-MeIm)2. J. Am. Chem. Soc. 1990,
112, 6385-6386.
(53) Dev, S.; Ramli, E.; Rauchfuss, T. B.; Wilson, S. R. Synthesis and Structure of [M(N-
Methylimidazole)6]S8 (M = Mn, Fe, Ni, Mg). Polysulfide Salts Prepared by the Reaction N-
Methylimidazole + Metal Powder + Sulfur. Inorg. Chem. 1991, 30, 2514-2519.
(54) Verma, A. K.; Rauchfuss, T. R.; Wilson, S. R. Donor Solvent Mediated Reactions of
Elemental Zinc and Sulfur, sans Explosion. Inorg. Chem. 1995, 34, 3072-3078.
(55) Wang, Z.; Ma, Y.; Vartak, P. B.; Wang, R. Y. Precursors for PbTe, PbSe, SnTe, and SnSe
Synthesized Using Diphenyl Dichalcogenides. Chem. Comm. 2018, 54, 9055-9058.
(56) Vartak, P. B.; Wang, Z.; Groy, T. L.; Trovitch, R. J.; Wang, R. Y. Solution and Solid-State
Characterization of PbSe Precursors. ACS Omega 2020, 5, 1949-1955.
(57) Holligan, K.; Rogler, P.; Rehe, D.; Pamula, M.; Kornienko, A. Y.; Emge, T. J.; Krogh-
Jespersen, K.; Brennan, J. G. Copper, Indium, Tin, and Lead Complexes with Fluorinated
Selenolate Ligands: Precursors to MSex. Inorg. Chem. 2015, 54, 8896-8904.
(58) Kedernath, G.; Kumbhare, L. B.; Dey, S.; Wadawale, A. P.; Jain, V. K.; Dey, G. K. b-
Functionalized Ethylchalcogenolate Complexes of Lead (II): Synthesis, Structures and Their
Conversion into Lead Chalcogenide Nanoparticles. Polyhedron 2009, 28, 2749-2753.
(59) Zhang, R.; Szczepaniak, S. M.; Carter, N. J.; Handwerker, C. A.; Agrawal, R. A Versatile
Solution Route to Efficient Cu2ZnSn(S,Se)4 Thin-Film Solar Cells. Chem. Mater. 2015, 27, 2114-
2120.
29
(60) Zhao, X.; Lu, M.; Koeper, M. J.; Agrawal, R. Solution-Processed Sulfur Depleted Cu(In,
Ga)Se2 Solar Cells Synthesized from a Monoamine-Dithiol Solvent Mixture. J. Mater. Chem. A
2016, 4, 7390-7397.
(61) Wu. W.-Y.; Ong, X.; Bhatnagar, S.; Chan, Y. Thermochromism from Ultrathin Colloidal
Sb2Se3 Nanowires Undergoing Reversible Growth and Dissolution in an Amine-Thiol Mixture.
Adv. Mater. 2019, 31, 1806164.
(62) Murria. P.; Miskin, C. K.; Boyne, R.; Cain. L. T.; Yerabolu, R.; Zhang, R.; Wegener, E.
C.; Miller, J. T.; Kenttamaa, H. I.; Agrawal, R. Speciation of CuCl and CuCl2 Thiol-Amine
Solutions and Characterization of Resulting Films: Implications for Semiconductor Device
Fabrication. Inorg. Chem. 2017, 56, 14396-14407.
(63) Howell, J. A. S. Structure and Bonding in Cyclic Thiolate Complexes of Copper, Silver
and Gold. Polyhedron 2006, 25, 2993-3005.
(64) Kacprzak, K. A.; Lopez-Acevedo, O.; Hakkinen, H.; Gronbeck, H. Theoretical
Characterization of Cyclic Thiolated Copper, Silver, and Gold Clusters. J. Phys. Chem. C 2010,
114, 13571-13576.
(65) Hellinga, H. W. (1990) Construction of a Blue Copper Analogue Through Iterative
Rational Protein Design Cycles Demonstrates Principles of Molecular Recognition in Metal Center
Formation. J. Am. Chem. Soc. 1990, 120, 10055-10066.
(66) Smith, R. C.; Reed, V. D.; Hill, W. E. Oxidation of Thiols by Copper(II). Phosphorus,
Sulfur Silicon Relat. Elem. 1994, 90, 147-154.
(67) Ording-Wenker, E. C. M.; van der Plas, M.; Siegler, M. A.; Bonnet, S.; Bickelhaupt, F. M.;
Guerra, C. F.; Bouwman, E. Thermodynamics of the Cu
II
μ-Thiolate and Cu
I
Disulfide
30
Equilibrium: A Combined Experimental and Theoretical Study. Inorg. Chem. 2014, 53, 8494-
8504.
(68) Buckley, J. J., McCarthy, C. L.; Del Pilar-Albaladejo, J.; Rasul, G.; Brutchey, R. L.
Dissolution of Sn, SnO, and SnS in a Thiol-Amine Solvent Mixture: Insights into the Identity of
the Molecular Solutes for Solution-Processed SnS. Inorg. Chem. 2016, 55, 3175-3180.
(69) Davies, A. G.; Slater, S. D.; Povey, D. C.; Smith, G. W. The Structures of 2,2-Diakyl-1,3,2-
Dithiastannolanes. J. Organomet. Chem. 1988, 352, 283-294.
(70) Casella, G.; Ferrante, F.; Saielli, G. Karplus-Type Dependence of Vicinal
119
Sn-
13
C and
119
Sn-
1
H Spin-Spin Couplings in Organotin(IV) Derivatives: A DFT Study. Eur. J. Org. Chem.
2009, 2009, 3526-3534.
(71) Wang, L.; Kefalidis, C. E.; Roisnel, T.; Sinbandhit, S.; Maron, L.; Carpentier, J.-F.;
Sarazin, Y. Structure vs
119
Sn NMR Chemical Shift in Three-Coordinated Tin(II) Complexes:
Experimental Data and Predictive DFT Computations. Organometallics 2015, 34, 2139-2150.
(72) Liu, S.; Sun, P.; Shen, Y.; Han, J.; Sun, H.; Jia, D. Lanthanide(III) Complexes with μ-SnSe4
and μ-Sn2Se6 Linkers: Solvothermal Syntheses and Properties of New Ln(III) Selenidostannates
Decorated with Linear Polyamine. Z. Naturforsch. B 2017, 72, 231-240.
(73) Hsu, W.-C.; Bob, B.; Wang, W.; Chung, C.-H.; Yang, Y. Reaction Pathways for the
Formation of Cu2ZnSn(Se,S)4 Absorber Materials from Liquid-Phase Hydrazine-Based Precursor
Inks. Energy Environ. Sci. 2012, 5, 8564-8571.
(74) Pirani, A. M.; Mercier, H. P. A.; Dixon, D. A.; Bormann, H.; Schrobilgen, G. J. Syntheses,
Vibrational Spectra, and Theoretical Studies of the Adamantanoid Sn4Ch10
4-
(Ch=Se, Te) Anions:
X-ray Crystal Structures of [18-Crown-6- K]4[Sn4Se10]·5en and [18-Crown-6-
K]4[Sn4Te10]·3en·2THF. Inorg. Chem. 2001, 40, 4823-4829.
31
(75) Arnou, P.; van Hest, M. F. A. M.; Cooper, C. S.; Malkov, A. V.; Walls, J. M.; Bowers, J.
W. Hydrazine-Free Solution-Deposited CuIn(S,Se)2 Solar Cells by Spray Deposition of Metal
Chalcogenides. ACS Appl. Mater. Interfaces 2016, 8, 11893-11897.
(76) Zhao, D.; Fan, Q.; Tian, Q.; Zhou, Z.; Meng, Y.; Kou, D.; Zhou, W.; Wu, S. Eliminating
Fine-Grained Layers in Cu(In,Ga)(S,Se)2 Thin Films for Solution-Processed High Efficiency Solar
Cells. J. Mater. Chem. A 2016, 4, 13476.
(77) Deshmukh, S. D.; Rokke, D. J.; Kisslinger, K.; Agrawal, R. Investigating the Potential of
Amine-Thiol Solvent System for High Efficiency CuInSe2 Device. 2020 47
th
IEEE Photovoltaic
Specialists Conference (PVSC), 2020, 0818-0820.
(78) Webber, D. H.; Buckley, J. J.; Antunez, P. D.; Brutchey, R. L. Facile Dissolution of
Selenium and Tellurium in a Thiol-Amine Solvent System Under Ambient Conditions. Chem. Sci.
2014, 5, 2498-2502.
(79) Dolzhnikov, D. S.; Zhang, H.; Jang, J.; Son. J. S.; Panthani, M. G.; Shibata, T.;
Chattopadhyay, S.; Talapun, D. V. Composition-Matched Molecular “Solders” for
Semiconductors. Science 2015, 347, 425-428.
(80) Hudson, M. H.; Dolzhnikov, D. S.; Filatov, A. S.; Janke, E. M.; Jang, J.; Lee, B.; Sun, C.;
Talapin, D. V. New Forms of CdSe: Molecular Wires, Gels, and Ordered Mesoporous Assemblies.
J. Am. Chem. Soc. 2017, 139, 3368−3377.
(81) Kovalenko, M. V.; Scheele M.; Talapin, D. V. Colloidal Nanocrystals with Molecular
Metal Chalcogenide Surface Ligands. Science 2010, 324, 1417-1420.
32
Chapter 2. Kinetics and Mechanistic Details of Bulk ZnO Dissolution Using a Thiol-
Imidazole System*
*Published – Koskela, K. M.; Quiton, S. J.; Sharada, S. M.; Williams, T. J.; Brutchey, R. L. Chem.
Sci. 2022, 13, 3208–3215.
2.1 Abstract
Oxide dissolution is important for metal extraction from ores and has become an attractive
route for the preparation of inks for thin film solution deposition; however, oxide dissolution is
often kinetically challenging. While binary “alkahest” systems comprised of thiols and N-donor
species, such as amines, are known to dissolve a wide range of oxides, the mechanism of
dissolution and identity of the resulting solute(s) remain unstudied. Here, we demonstrate facile
dissolution of both bulk synthetic and natural mineral ZnO samples using an “alkahest” that
operates via reaction with thiophenol and 1-methylimidazole (MeIm) to give a single,
pseudotetrahedral Zn(SPh)2(MeIm)2 molecular solute identified by X-ray crystallography. The
kinetics of ZnO dissolution were measured using solution
1
H NMR, and the reaction was found to
be zero-order in the presence of excess ligands, with more electron withdrawing para-substituted
thiophenols resulting in faster dissolution. A negative entropy of activation was measured by
Eyring analysis, indicating associative ligand binding in, or prior to, the rate determining step.
Combined experimental and computational surface binding studies on ZnO reveal stronger,
irreversible thiophenol binding compared to MeIm, leading to a proposed dissolution mechanism
initiated by thiol binding to the ZnO surface with the liberation of water, followed by alternating
MeIm and thiolate ligand additions, and ultimately cleavage of the ligated zinc complex from the
ZnO surface. Design rules garnered from the mechanistic insight provided by this study should
inform the dissolution of other bulk oxides into inks for solution processed thin films.
33
2.2 Introduction
Macroelectronics represent a growing industry with a market value of $16.1 billion (USD)
in 2020 that is estimated to reach $39.1 billion by 2027.
1
Chemical vapor deposition (CVD) and
physical vapor deposition (PVD) are the two most common methods for depositing large area thin
films for macroelectronics applications. These methods are capable of depositing very high-quality
films but are hampered by relatively expensive processing equipment and intensive energy usage
due to the combination of ultra-low vacuum pressures and high temperatures needed for
deposition. Solution processing using semiconductor inks, on the other hand, has the potential to
reduce module costs with its relatively low energy usage.
2,3
Solution processing also opens up
avenues for new device architectures, such as easier deposition on non-planar and irregular
substrates for wearable and mobile power generating devices.
4
An attractive route for producing
semiconductor inks for solution processing is through the dissolution of inexpensive, bulk metal
oxides.
5
More generally, oxide dissolution is important for the extraction of metals from ores, but
many oxides dissolve so slowly that they are effectively insoluble even under thermodynamically
favorable conditions.
6,7
In turn, the use of extremely hazardous conditions and reagents that
generate large amounts of ensuing waste have posed problems for commercial metallurgic
processes.
8
In 2013, Webber and Brutchey developed a versatile binary solvent system consisting of a
short chain thiol (e.g., 1,2-ethanedithiol) and an amine (e.g., 1,2-ethylenediamine) that is capable
of dissolving and recovering nine different V2VI3 chalcogenides.
9
Owing to its high reactivity,
they termed this solvent system an “alkahest”; the alkahest has been subsequently shown to
dissolve over 100 bulk materials, ranging from metals to metal chalcogenides to metal oxides.
10
Indeed, the alkahest is known to dissolve a wide range of bulk metal oxides, including, but not
34
limited to, Ag2O, As2O3, Bi2O3, CdO, Cu2O, CuO, In2O3, GeO2, MnO, PbO, Sb2O3, SeO2, SnO,
and ZnO.
5,11-16
Through a mild dissolve and recover approach, the alkahest solvent system returns
phase-pure binary metal chalcogenide thin films from dissolved oxide precursors; for example,
semiconductor inks for metal sulfide thin films can be derived from dissolved metal oxides, where
the sulfur source is the thiol component of the alkahest. Moreover, phase-pure, complex multinary
semiconductors can also be solution processed by simply dissolving multiple bulk precursors in
the proper stoichiometric ratios with the alkahest solvent system.
13
In the same way,
compositionally controlled alloyed semiconductors can be solution processed by tuning the ink
formulation.
5,11
The alkahest solvent system returns functional thin films that have proven useful
in a multitude of applications, including solar cells,
17-18
photodetectors,
19
thermoelectrics,
20
neuromorphic devices,
21
electrocatalysts,
22
and it has also been used to engineer the surfaces of
colloidal nanocrystals.
23-25
This approach has the potential to be translated to large-scale solution
processing.
14
While the alkahest has been widely adopted for device fabrication because of the simplicity
of the approach, the fundamental mechanism of oxide dissolution using this solvent couple has yet
to be explored. In a conceptually related, but fundamentally different, system, Rauchfuss et al.
reported on the dissolution of bulk metal powders through oxidative corrosion. In that work, an N-
donor solvent assisted the dissolution of Cu powder in the presence of sulfur.
26
This chemistry was
expanded to include the dissolution of other zero-valent bulk transition metals including Fe, Mg,
Mn, Ni and Zn,
27-29
and has been recently revisited for the oxidative dissolution of metallic Pb and
Sn using molecular dichalcogenides.
30,31
In the particular case of metallic Zn powder, dissolution
occurs via addition of N-donor solvents and elemental sulfur to yield a defined molecular solute,
which is a pseudo-tetrahedral ZnS6(L)2 complex (where L = ½ tetramethylethylenediamine, 4-
35
(dimethylamino)pyridine). These complexes can be thermally annealed under nitrogen to yield
ZnS.
29
Based on this precedent, we sought to determine whether bulk ZnO dissolution in an
alkahest solvent system might give a similarly well-defined molecular solute through a non-
oxidative dissolution process. Thus, we present the dissolution of bulk ZnO via reaction with 1-
methylimidazole (MeIm) and thiophenol. Whilst previous attempts to identify the products of
alkahest dissolution have relied on indirect methods,
23,32,33
we unambiguously identify the
molecular solute resulting from ZnO dissolution using direct crystallographic methods, which then
enabled us to use
1
H NMR to measure the dissolution kinetics. The kinetic analysis of ZnO
dissolution in this thiol-imidazole solution allows us to propose, for the first time, a plausible
mechanism for alkahest dissolution.
2.3 Results and Discussion
2.3.1 Identification of Molecular Solute
Synthetic, polycrystalline wurtzite ZnO powder (BET surface area 8 m
2
g
–1
) (Figures 2.1,
2.2) was reacted with stoichiometric amounts of MeIm and thiophenol in acetonitrile (75 °C, 1
atm). After stirring for 8 h, the ZnO dissolution was complete, giving a colorless, optically clear
solution that is free of scattering (Figure 2.3). Importantly, the bulk ZnO powder does not dissolve
in acetonitrile solutions of MeIm or thiophenol alone; that is, the combination of the two alkahest
components is needed for dissolution. Slow evaporation of the fully dissolved reaction solution
yielded analytically pure, yellow crystals of a neutral Zn(SPh)2(MeIm)2 complex (4). The air-
stable crystals of 4 were isolated and characterized by single crystal X-ray diffraction, FT-IR and
NMR spectroscopy (Figures 2.4-2.6). Compound 4 crystallizes in the monoclinic space group
C121, where zinc is in a pseudotetrahedral coordination environment bound to nitrogen atoms of
36
two MeIm ligands and sulfur atoms of two thiophenolate ligands (Figure 2.7). The solution
1
H
NMR spectrum of isolated crystals of 4 in acetonitrile-d3 matches that of the fully dissolved
reaction mixture. We can therefore conclude that the molecular solute in the crude reaction mixture
is a single species that unambiguously matches that of isolated complex 4; this allows us to track
the temporal evolution of the molecular solute during ZnO dissolution by solution
1
H NMR
spectroscopy (vide infra). Upon dissolution, the solution remains stable over the course of at least
one week when exposed to air (i.e., 21 °C, 20-90 %RH) with no precipitation or significant color
change observed. The solution
1
H NMR spectrum of 4 in the dissolved reaction mixture also
remains unchanged over this time (Figure 2.8).
Figure 2.1. Powder XRD pattern of polycrystalline ZnO powder starting material (99.99%, Alfa
Aesar) indexed to the wurtzite crystal structure.
20 40 60
2-Theta (°)
Intensity (a.u.)
ZnO
37
Figure 2.2. SEM micrograph of polycrystalline ZnO powder starting material (99.99%, Alfa
Aesar).
Figure 2.3. Representative photographs of synthetic polycrystalline ZnO powder dissolution in
MeIm and acetonitrile a) before thiophenol addition and b) after thiophenol addition and full
dissolution.
38
Figures 2.4. Solution
1
H NMR of 4 in acetonitrile-d3.
Figure 2.5. Solution
13
C{
1
H} NMR of 4 in acetonitrile-d3.
39
Figure 2.6. FT-IR spectrum of 4 (KBr).
Figure 2.7. ORTEP plot of the X-ray crystal structure of Zn(SPh)2(MeIm)2 (4).
1000 2000 3000 4000
0
20
40
60
Wavenumber (cm
-1
)
Transmittance (%)
ν(C–H)
ν(C–S)
δ(C–H)
ν(C–N)
ν(C–H)
40
Figure 2.8. Solution
1
H NMR of 4 in acetonitrile-d3 after being exposed to air for 7 d (21 ˚C, 20-
90 %RH). The peak at 2.25 ppm corresponds to H2O.
2.3.2 Dissolution Kinetics
The ZnO dissolution kinetics were probed by performing the reaction in acetonitrile-d3 and
removing aliquots, filtering away unreacted ZnO, and monitoring the aliquots by solution
1
H NMR
as both a function of reaction time and temperature. The amounts of MeIm (3 eq) and thiophenol
(2.4 eq) were chosen relative to ZnO to observe the reaction kinetics when the reagents are present
in excess. In practice, oxide dissolution with thiols and N-donor solvents is always performed with
the two reagents in stoichiometric excess.
5
Here, non-labile binding of thiolate to the zinc center
of 4 is observed by
1
H NMR, with clear chemical shift differences between the bound and unbound
aromatic thiophenolate and thiophenol resonances, respectively (Figure 2.9). For example, the
peak intensity for the doublet corresponding to bound ortho-thiophenolate protons (d = 7.36 ppm)
increases with time as the concentration of 4 builds, while a concomitant decrease of free
41
thiophenol is observed (i.e., multiplets at d = 7.31, 7.26, and 7.17 ppm). Labile MeIm binding to
zinc is observed by a gradual downfield shift of the peaks as the concentration of 4 increases with
time (e.g., the downfield shift of the proton in the 2-position of MeIm between 7.41-7.51 ppm).
Along with the disappearance of free thiophenol and the appearance of 4, we were also able to
observe the release of a stoichiometric amount of H2O derived from liberated ZnO lattice oxygen
during the dissolution reaction (Figure 2.9).
Figure 2.9. Stacked room-temperature solution
1
H NMR spectra in acetonitrile-d3 of the aromatic
region, methyl, and H2O peaks for aliquots taken as a function of time from the dissolution of ZnO
with MeIm (3 eq) and thiophenol (2.4 eq) at 75 °C. Acetonitrile-d2 is labeled as *.
In order to determine the thermodynamic parameters of ZnO dissolution, the reaction was
performed at a series of temperatures between 30-75 °C. At all temperatures, we observe a linear
decrease in the concentration of thiophenol (and a linear increase in the concentration of 4) with
42
time by
1
H NMR, indicative of a zero-order reaction with the rate constant increasing with
increasing dissolution temperature, respectively confirmed by log-log and Eyring analyses
(Figures 2.10-2.13). Thus, thiophenol loading on the ZnO surface appears kinetically invisible.
This can be explained by rapid saturation of thiol ligation to the ZnO surface under the high
thiophenol concentrations used for dissolution. When thiophenol and MeIm were made
stoichiometric relative to ZnO, under otherwise identical dissolution conditions, the reaction
remains zero order (Figure 2.14). When the concentrations of MeIm (2.4-4.0 eq) and thiophenol
(2.4-4.8 eq) were independently varied into excess with all other reaction conditions being held
constant, we see that ZnO dissolution also remains zero order, displaying no rate dependence on
MeIm or thiophenol concentration (Figures 2.15, 2.16 and 2.3.3 Rate Law and Derivation).
However, in a dilution experiment where both ligand concentrations are made scarce, we observe
an overall reaction order of about two, as illustrated in a log-log plot with slope of 1.8 (Figure
2.17), which we hypothesize to correspond to the binding of two ligands to each zinc center
released from the ZnO surface in or prior to the rate determining step (vide infra). A rate law can
be derived from a steady-state treatment of reactive sites on the ZnO surface that is first order in
thiophenol with positive kinetic dependence on MeIm (2.3.3 Rate Law and Derivation), which
is consistent with the experimentally observed overall reaction order between 1-2 when the surface
is not saturated. To obtain the thermodynamic activation energy parameters for ZnO dissolution,
we constructed an Eyring plot using the rate data recorded from 30-75 °C. We find a DH
‡
of 27.4(5)
kJ mol
–1
and a DS
‡
of -259.8(3) J (mol•K)
–1
(Figure 2.18, Table 2.1).
34
A statistically significant,
negative DS
‡
suggests associative binding to the ZnO surface by one or more ligands in, or prior
to, the rate determining step.
43
Figure 2.10. Plot of ZnO dissolution at 30 °C with concentration of 4 in solution vs. time.
Dissolution was performed with 2.4 eq thiophenol and 3 equiv MeIm relative to ZnO. Zero-order
dissolution kinetics are seen through completion of dissolution.
Figure 2.11. Plot of ZnO dissolution at 40 °C with concentration of 4 in solution vs. time.
Dissolution was performed with 2.4 eq thiophenol and 3 equiv MeIm relative to ZnO. Zero-order
dissolution kinetics are seen through completion of dissolution.
0 5000 10000 15000 20000
0.00
0.02
0.04
0.06
0.08
Time (s)
Concentration of 4 (mol L
-1
)
Rate: 3.09x10
-6
mol L
-1
s
-1
R
2
: 0.99
0 10000 20000 30000
0.00
0.05
0.10
0.15
Time (s)
Concentration of 4 (mol L
-1
)
Rate: 4.80x10
-6
mol L
-1
s
-1
R
2
: 0.99
44
Figure 2.12. Plot of ZnO dissolution at 55 °C with concentration of 4 in solution vs. time.
Dissolution was performed with 2.4 eq thiophenol and 3 equiv MeIm relative to ZnO. Zero-order
dissolution kinetics are seen through completion of dissolution.
Figure 2.13. Plot of ZnO dissolution at 75 °C with concentration of 4 in solution vs. time.
Dissolution was performed with 2.4 eq thiophenol and 3 equiv MeIm relative to ZnO. Zero-order
dissolution kinetics are seen through completion of dissolution.
0 10000 20000
0.00
0.05
0.10
0.15
Time (s)
Concentration of 4 (mol L
-1
)
Rate: 7.65x10
-6
mol L
-1
s
-1
R
2
: 0.99
0 5000 10000
0.00
0.05
0.10
0.15
Time (s)
Concentration of 4 (mol L
-1
)
Rate: 1.48x10
-5
mol L
-1
s
-1
R
2
: 0.99
45
Figure 2.14. Plot of ZnO dissolution at 75 °C with concentration of 4 in solution vs. time.
Dissolution was performed with stoichiometric thiophenol (2.05 eq) and MeIm (2.05 eq) relative
to ZnO. Zero-order dissolution kinetics are seen through completion of dissolution.
Figure 2.15. Log-log plot of rate of ZnO dissolution vs. MeIm concentration at 40 °C, where MeIm
is present in excess (from 2.4-4.0 eq relative to ZnO). Zero-order dissolution kinetics are seen
through completion of dissolution.
0 5000 10000
0.00
0.05
0.10
Time (s)
Concentration of 4 (mol L
-1
)
Rate: 6.82x10
-6
mol L
-1
s
-1
R
2
: 0.99
-0.7 -0.6 -0.5 -0.4 -0.3
-5.6
-5.4
-5.2
-5.0
Log (MeIm conc.)
Log (Rate)
Slope: -0.03
R
2
: 0.01
46
Figure 2.16. Log-log plot of rate of ZnO dissolution vs. thiophenol concentration at 40°C, where
thiophenol is present in excess (from 2.4-4.8 eq relative to ZnO). Zero-order dissolution kinetics
are seen through completion of dissolution.
Figure 2.17. Log-log plot of solvent volume vs. rate of ZnO dissolution (75 °C).
-0.7 -0.6 -0.5 -0.4 -0.3
-5.8
-5.6
-5.4
-5.2
-5.0
Log (Thiophenol conc.)
Log (Rate)
Slope: -0.12
R
2
: 0.32
-3.0 -2.5 -2.0 -1.5
-6
-5
-4
Log (Solvent Volume)
Log (Rate)
Slope: -1.81
R
2
: 0.98
47
Figure 2.18. Eyring plot derived from the dissolution of ZnO with MeIm (3 eq) and thiophenol
(2.4 eq) in acetonitrile-d3 from 30-75 °C.
Table 2.1. Eyring data for the dissolution of ZnO at various temperatures. Error statistics for DH
‡
and DS
‡
derived from the analysis performed in ref. 34.
Temperature
(°C)
Rate (mol L
-1
s
-1
) Error in rate
(mol L
-1
s
-1
)
Rln(k/T) - Rln(kB/h)
(J/mol•K)
DH
‡
error
(J/mol•K)
1
DS
‡
error
(J/mol•K)
1
30 3.09´10
-6
4.53´10
-8
-350.54 0.48 1.25
40 4.80´10
-6
1.61´10
-7
-347.14 1.01 2.86
55 7.65´10
-6
1.99´10
-7
-343.66 0.79 2.23
75 1.48´10
-6
4.67´10
-7
-338.64 0.95 2.68
Next, a series of para-substituted thiophenols (i.e., 4-bromo-, 4-methyl-, and 4-
methoxythiophenol) was investigated to probe how the electron donating or withdrawing
substituents would affect the ZnO dissolution rate. We observe that electron donating groups (i.e.,
4-methyl- and 4-methoxythiophenol) slow down the reaction, whereas the electron withdrawing
group (4-bromothiophenol) speeds up the reaction (Figure 2.19). In competition experiments
where a free para-substituted thiophenol was titrated into a fully dissolved ZnO reaction mixture,
a less electron-rich thiol displaces a more electron-rich thiolate off the zinc center (Figure 2.20).
2.8 3.0 3.2 3.4
-355
-350
-345
-340
-335
1000/T (K
-1
)
Rln(k/T) - Rln(k
B
/h)
y = -27.45x - 259.83
R² = 0.9977
48
These data are consistent with a polarized Zn–S bond, which is strengthened by increased
polarization of the covalent bond. Replacing MeIm with 5-chloro-1-methylimidazole also allows
for complete ZnO dissolution with thiophenol that is qualitatively faster than with the unsubstituted
analogue; however, the dissolution kinetics are complex and are no longer zero order as with
MeIm.
Figure 2.19. Hammett plot corresponding to ZnO dissolution reaction at 40 °C with 2.4 eq of
para-substituted thiophenol and 3 eq of MeIm with respect to ZnO.
-0.4 -0.2 0.0 0.2 0.4
0.6
0.7
0.8
0.9
1.0
1.1
1.2
σ
Log (k/k
H
)
-Br
-H -CH
3
-OCH
3
49
Figure 2.20. a) Solution
1
H NMR spectra of the aromatic region of a fully dissolved reaction
mixture of ZnO with MeIm (3 eq) and thiophenol (2.4 eq) in acetonitrile-d3. This reaction proceeds
readily to form 4. b) Upon addition of electron poor 4-bromothiophenol at 75 °C, the displacement
of the thiophenolate ligands for 4-bromothiophenolate ligands with the formation of
Zn(SPhBr)2(MeIm)2 by the appearance of the resonances at d = 7.24 and 7.06 ppm and the
concomitant disappearance of thiophenolate protons at d = 7.36, 6.95 and 6.86 ppm. We see the
relative intensities of free thiophenol also increase at d = 7.30, 7.26 and 7.17 ppm after the addition
of 4-bromothiophenol.
2.3.3 Rate Law and Derivation
We have observed two kinetic regimes for dissolution of ZnO under the reported
conditions. In cases where ligands are abundant, rate conforms to a Michaelis-Menten saturation
kinetics model, where the apparent catalyst models a reactive site on the ZnO surface. In cases
where ligand is scarce, the saturation model loses relevance, and we treat the system with a steady-
state approximation.
50
Key: Ref = ZnO surface; 1 = binding of thiophenol (with concomitant Zn–OH formation) to ZnO;
2 = binding of MeIm to 1, as labeled in Figure 2.27.
Figure 2.21. Proposed cycle for product evolution from a surface reactive site. Note that a second
equivalent of MeIm enters the reaction in the conversion of 3 to 4, but this step is kinetically
invisible, so it does not enter the model.
Derivation of the steady-state rate law.
Rate definition: =−
!
!"
[]=
#
[][RSH]
Equilibrium between 1 and 2:
[]
[]
=
(
)
!"
[*+,-]
Steady-state approximation on [Ref]:
#
[][RSH]=
(
[][RSH]
[]
[]
=
1
#
1
$
Total reactive sites [Zn]tot: [Zn]
232
=[]+[]+[]=[][
1
#
1
$
+
(
)
!"
[*+,-]
+1]
Three-term rate law: =
1
#
[45]
%&%
[678]
[
'
#
'
$
9
$
(
!"
[*+,-]
9(]
Assuming that k1 >> k2 (i.e., conversion of 2 is rate limiting):
=
1
#
[45]
%&%
[678]
[
$
(
!"
[*+,-]
9(]
This rate law accounts for first order dependance on thiol and partial positive dependance on
methylimidazole, as observed when the reaction is diluted.
1 2
Ref
Keq
MeIm
k
2
k
1
Rate Limiting
RSH
Fast
RSH
51
Assuming that Keq[Im] << 1 (i.e., [1] is more abundant than [2]):
=
#
[Zn]
232
[RSH][MeIm]
This assumption is not reasonable in scarce ligand conditions, which is consistent with observation
of only partial order on [MeIm] in a dilution experiment.
2.3.4 Proposed Mechanism of Dissolution
To propose a mechanism of dissolution, several additional experiments were conducted to
probe reactions at the surface and in solution. We first conducted FT-IR and conductivity
experiments of thiophenol and MeIm in the absence of ZnO to probe the extent of thiophenol
deprotonation and determined that MeIm does not cause significant deprotonation of thiophenol
in acetonitrile. When thiophenol and MeIm are mixed, the resulting FT-IR spectrum clearly shows
the weak sulfhydryl n(S–H) stretching band at 2560 cm
–1
is still present, with no significant change
in the n(S–C) stretching frequencies at 680-700 cm
–1
when compared to the FT-IR spectrum of
neat thiophenol (Figure 2.22, 2.23). We also observe no significant increase in electrolytic
conductivity upon addition of thiophenol to a solution of MeIm in acetonitrile (Table 2.2), unlike
what was previously reported for other thiol-amine combinations.
9
Taken together, this suggests
that thiophenol is not deprotonated by MeIm in this system. This is consistent with pKa values in
water, where thiophenol (pKa = 8.2) would not be expected to be completely deprotonated by
MeIm (pKa = 7.3-7.8).
35,36
As such, we expect thiophenol to be the reagent that approaches and
binds to the ZnO surface, rather than an anionic thiophenolate.
An FT-IR spectrum collected on a sample of ZnO that had been stirred with thiophenol
(without MeIm) at 75 °C, rinsed, and dried clearly shows the presence of aromatic n(C–H) bands
from thiophenol at 2560 cm
–1
, the absence of the sulfhydryl n(S–H) band, and the presence of n(S–
52
C) stretching frequencies at 680-700 cm
–1
(Figure 2.24, 2.25).
An analogous experiment with
MeIm (without thiophenol) does not return any diagnostic FT-IR bands from MeIm on the ZnO
surface after rinsing and drying (Figure 2.26). We conclude from these FT-IR experiments that
thiophenol binds irreversibly to the virgin ZnO surface and MeIm does not.
Typically, in heterogenous dissolution chemistry, cleavage of the pre-coordinated complex
is the rate determining step for metal oxide dissolution.
37-39
Computational analysis using density
functional theory was performed to develop a semi-quantitative description of possible
intermediates in the mechanism of ZnO dissolution with thiophenol and MeIm. Figure 2.27
depicts the intermediate structures and results of this analysis by considering each of the different
combinations of ligand binding events that could lead to the liberation of 4 from the ZnO surface,
and Table 2.3 provides a description of the surface-bound ligands in intermediate states and key
bond distances. Based on calculated ligand binding energies in Figure 2.27, the following
sequence of steps is proposed: The first ligand binding event to the zinc center is
thermodynamically favorable, with thiophenol binding (and concomitant Zn–OH formation) to
give structure 1 favored by 29.6 (29.1) kJ mol
–1
over MeIm binding at 30 °C (75 °C). For the
second ligand binding event, there is a strong preference for MeIm coordination to give structure
2, which is thermodynamically downhill from structure 1 by 105.8 (97.9) kJ mol
–1
, whereas the
alternative binding by a second thiophenol is more energetically neutral. The third ligand binding
event is thermodynamically uphill by 102.8 (102.0) kJ mol
–1
, with the binding of a second
thiophenol (to give structure 3) being strongly preferred over the binding of a second MeIm. We
propose based on kinetics data that this conversion of 2 to 3 is rate-limiting. The final ligand
binding event is thermodynamically downhill by 604.0 (595.1) kJ mol
–1
to give the experimentally
verified solute 4.
53
Figure 2.22. FT-IR spectra of the sulfhydryl region showing the n(S–H) stretch of thiophenol
before and after addition of MeIm in acetonitrile (NaCl plates).
Figure 2.23. FT-IR spectra showing the n(C–S) stretch of thiophenol before and after addition of
MeIm in acetonitrile (NaCl plates).
2000 2500 3000
Wavenumber (cm
-1
)
Transmittance (a.u.)
ν(S–H)
Thiophenol
Thiophenol
+ MeIm
600 700 800 900 1000
Wavenumber (cm
-1
)
Transmittance (a.u.)
ν(C–S)
Thiophenol
Thiophenol
+ MeIm
54
Table 2.2. Room-temperature electrolytic conductivity measurements in acetonitrile under
flowing nitrogen between two Pt wires. The measurements were run in triplicate for accuracy at
100 mV applied potential.
Sample Voltage (V) Current (A)
MeIm 0.1 5.98´10
-10
MeIm 0.1 5.66´10
-10
MeIm 0.1 7.55´10
-10
MeIm titrated w/ thiophenol 0.1 6.03´10
-8
MeIm titrated w/ thiophenol 0.1 5.39´10
-8
MeIm titrated w/ thiophenol 0.1 5.23´10
-8
Figure 2.24. FT-IR spectra showing the n(C–H) and n(S–H) stretching region (KBr). ZnO was
mixed with thiophenol at 75 °C, washed and dried under high vacuum overnight at room
temperature.
2000 2500 3000 3500 4000
Wavenumber (cm
-1
)
Transmittance (a.u.)
Thiophenol
ZnO +
Thiophenol
ν(S–H) ν(C–H)
55
Figure 2.25. FT-IR spectra showing the n(S–C) stretching region (KBr). ZnO was mixed with
thiophenol at 75 °C, washed and dried under high vacuum overnight at room temperature.
Figure 2.26. FT-IR spectra showing the n(C–H) stretching region (KBr). ZnO was mixed with
MeIm at 75 °C, washed and dried under high vacuum overnight at room temperature.
600 700 800 900 1000
Wavenumber (cm
-1
)
Transmittance (a.u.)
Thiophenol
ZnO +
Thiophenol
ν(C–S)
2000 2500 3000 3500 4000
Wavenumber (cm
-1
)
Transmittance (a.u.)
ZnO + MeIm
MeIm
ν(C–H)
56
Figure 2.27. a) Calculated Gibbs free energies (DG) at 30 °C associated with formation of possible
intermediate steps constituting dissolution of bulk ZnO with thiophenol and MeIm, calculated
using a reference (ZnO)12 cluster model (B3LYP functional, def2-SVP basis with def2-ECP on
zinc). The most favorable pathway is depicted in blue and unfavorable intermediates are shown in
red. b) Intermediate geometries: 1 and 1’ represent binding of thiophenol (with concomitant Zn–
OH formation) and MeIm to (ZnO)12, respectively. Structures 2 and 2’ represent binding of MeIm
and thiophenol (with H2O removal) to 1, respectively. Structures 3 and 3’ represent binding of
thiophenol (with H2O removal) and MeIm to 2, respectively. Structure 4 refers to the molecular
solute state corresponding to formation of the experimentally verified Zn(SPh)2(MeIm)2 complex.
Model visualizations are created using the Envision package.
40
The potential energy representation
is created using the ‘Energy Leveller’ program developed by Furness.
41
57
Table 2.3. Description of intermediate geometries. For 2’, 3, and 3’ the sulfur atom of the bound
thiophenolate ligand coordinates to more than one zinc center on the surface. The bond distance
to the second zinc atom is provided in parentheses. Apart from structure 3, all ligands are bound
to the same Zn atom in intermediate states. In 3, the only converged optimization calculation yields
a structure in which one of the two thiophenol ligands is bound to a second, neighboring Zn atom.
Label Ligands
DG (kJ mol
–1
) at
30 °C, 75 °C
Zn–S (Å) Zn–N (Å) Zn–O (Å)
1 PhSH -119.9, -112.9 2.280 - 1.900, 1.961
1’ MeIm -90.2, -83.8 - 2.075 1.923, 2.004
2 PhSH, MeIm -225.7, -210.8 2.372 2.124 1.924, 2.004
2’ PhSH, PhSH -104.0, -96.4
2.281, 2.610
(2.357)
- 1.984, 1.996
3 2 PhSH, MeIm -122.9, -108.8
2.301, 2.793
(2.347)
2.044 1.926
3’ PhSH, 2 MeIm -58.3, -37.3
2.440
(2.660)
2.100, 2.064 1.855
4 2 PhSH, 2 MeIm -726.9, -703.9 2.338, 2.312 2.114, 2.116 -
Taken in concert with the kinetic analysis and ligand binding studies, these data suggest
that the first thiophenol binding is rapid, irreversible, and kinetically invisible. This gives rise to a
thiolate-coated oxide surface that has reversible MeIm binding. The equilibrium of MeIm-bound
and -unbound zinc monothiolates behave like a resting state of the system, and both appear in the
kinetics (vide supra), as in the case of a pre-equilibrium system. Reversible imidazole coordination
is then followed by the rate determining step involving the addition of a second equivalent of
thiophenol; the transition state has high covalent character as indicated by the low DH
‡
of 27 kJ
mol
–1
relative to the associated bond strengths. A measured DG
‡
of 118 kJ mol
–1
at 75 °C is fit to
a late rate-determining transition state for the formation of 3, according to its energy relative to 2
and 3. Following reaction of the second thiolate ligand, binding of the second MeIm and
dissociation of 4 from the surface ensue rapidly to return a zinc oxide surface. These steps do not
appear in the kinetics.
58
Analogous dissolution reactions with polycrystalline sphalerite ZnS powder (BET surface
area 15 m
2
g
–1
) (Figure 2.28, 2.29) do not readily proceed under otherwise identical conditions
(Figure 2.30). The formation of strong HO–H bonds of water (BDE = 497 kJ mol
–1
) from the
liberation of ZnO lattice oxygen appears to be a thermodynamic driver for the dissolution reaction
(ZnO lattice energy = 4142 kJ mol
–1
; melting point = 1975 ˚C).
42
For the analogous dissolution of
ZnS, the liberation of lattice sulfur would lead to the formation of weaker HS–H bonds (BDE =
381 kJ mol
–1
) that are too energetically neutral to drive the reaction (with a lower ZnS lattice
energy = 3619 kJ mol
–1
; melting point = 1185 ˚C).
42
Given the lower lattice energy of sphalerite
ZnS as compared to wurtzite ZnO, this suggests that the more facile ZnO dissolution is
thermodynamically driven by water formation. Moreover, even though various zero-valent bulk
metals have previously been dissolved in alkahest solvent systems,
32,43
metallic Zn powder does
not dissolve in freshly distilled and air-free thiophenol and MeIm. This is not surprising given the
lack of an oxidizing agent in the system, and this result reveals that previous reports of metal
dissolution are likely enabled by adventitious disulfide from oxidized thiols. For the analogous
dissolution of bulk Zn powder, diphenyl disulfide can be employed for oxidative dissolution
instead of thiophenol; in this case, 4 is also the single product of dissolution by
1
H NMR (Figure
2.31).
59
Figure 2.28. Powder XRD pattern of polycrystalline ZnS powder starting material (99.99%,
Sigma-Aldrich) indexed to the sphalerite crystal structure.
Figure 2.29. SEM micrograph of polycrystalline ZnS powder starting material (99.99%, Sigma-
Aldrich).
20 40 60
2-Theta (°)
Intensity (a.u.)
ZnS
60
Figure 2.30.
1
H NMR spectra of the aromatic region of aliquots from the reaction of ZnS with
MeIm (3 eq) and thiophenol (2.4 eq) in acetonitrile-d3 at 75 °C demonstrating lack of dissolution.
61
Figure 2.31. Stacked
1
H NMR spectra of the aromatic region of aliquots from the dissolution of
Zn metal with MeIm (3 eq) and diphenyl disulfide (2.4 eq) in acetonitrile-d3 at 75 °C. This reaction
readily proceeds to form 4, as evidenced by the appearance of the bound thiophenolate protons at
d = 7.36, 6.95, 6.86 ppm. Resonances at d = 7.56, 7.38 and 7.30 represent aromatic protons of
diphenyl disulfide.
2.3.5 Zincite Mineral Dissolution
To further assess the utility of the alkahest solvent system for oxide dissolution, we
acquired a natural zincite (ZnO) mineral sample to see if it would also dissolve and yield the same
molecular solute 4 (Figure 2.32). The orange-colored mineral sample was ground in a mortar and
pestle and analyzed by powder XRD where it was indexed to phase-pure wurtzite ZnO (Figure
2.32). An analogous dissolution among zincite, thiophenol, and MeIm readily proceeds under
identical conditions as the synthetic ZnO powder, also yielding an optically clear, colorless, free
flowing ink after 24 h of dissolution at 75 °C that is qualitatively identical to the synthetic ZnO
62
ink (Figure 2.33). The equivalent formation of 4 as the sole molecular solute from zincite mineral
dissolution was confirmed by
1
H NMR (Figure 2.34). The dissolution of zincite further
demonstrates the versatility of the alkahest to dissolve naturally occurring oxide ores.
Figure 2.32. Powder XRD pattern of natural zincite mineral powder indexed to the wurtzite crystal
structure. A photograph of the as-received mineral sample is shown as the inset.
63
Figure 2.33. Representative photographs of natural zincite dissolution in MeIm and acetonitrile a)
before thiophenol addition and b) after thiophenol addition and full dissolution.
64
Figure 2.34.
1
H NMR spectrum of the aromatic region from the dissolution of natural zincite
mineral with MeIm (3 eq) and thiophenol (2.4 eq) in acetonitrile-d3 at 75 °C after full dissolution.
This reaction readily proceeds to form 4, as evidenced by the appearance of the bound
thiophenolate protons at d = 7.36, 6.95, 6.86 ppm.
2.3.6 Thermal Decomposition
Alkahests are generally useful for the deposition of metal chalcogenides from the
dissolution of metal oxides. In the absence of added chalcogen, the product is the analogous metal
sulfide. In the case of ZnO dissolution with thiophenol and MeIm, the resulting ink is therefore
expected to yield ZnS. Along these lines, we tracked the thermal decomposition of the molecular
solute 4 by thermogravimetric analysis (TGA). The TGA trace of isolated crystals of 4 shows an
onset of decomposition at ca. 125 °C that is complete by 600 °C (Figure 2.35). The ceramic yield
(22.5%) from TGA for the thermal decomposition of 4 to give ZnS closely matches the expected
65
value (21.7%). Isolated crystals of 4 were then thermally decomposed and annealed at 600 °C for
30 h, and the resulting material was analyzed by powder X-ray diffraction (Figure 2.36). The
resulting diffraction pattern indexes well to cubic sphalerite ZnS, and an integrated energy
dispersive X-ray spectrum of the annealed material demonstrates the presence of nearly
stoichiometric amounts of zinc and sulfur (Zn/S = 1:0.82).
Figure 2.35. TGA trace of the thermal decomposition of 4.
200 400 600
0
50
100
Temperature (°C)
Mass %
66
Figure 2.36. Powder XRD pattern of the thermal decomposition product of 4 annealed at 600 °C
for 30 h, indexed to cubic sphalerite ZnS.
2.4.1 Characterization
Powder X-ray diffraction (XRD) patterns were collected using a Rigaku Miniflex600
operated at 40 mA and 35 kV, in the 2θ range of 10−70° using Cu Kα radiation (λ = 1.5406 Å).
Thermal gravimetric analysis (TGA) was performed on a TA Instruments TGA Q50 instrument
and samples were run in an alumina crucible under a flowing nitrogen atmosphere with a heating
rate of 5 ˚C min
–1
. Fourier transform infrared (FT-IR) spectra were measured on a Bruker Vertex
80 spectrometer. Liquid FT-IR samples were taken between NaCl salt plates and solid samples
were crushed and pressed into a pellet with KBr. Scanning electron microscopy (SEM) was
performed on a Thermo Scientific Helios G4 PFIB UXe equipped with an Oxford UltimMax 170
silicon drift detector X-ray energy dispersive spectroscopy (EDS) system. Brunauer-Emmett-
Teller (BET) measurements were performed on a Nova 2200e surface area and pore size analyzer
(Quantachrome Instruments, Inc.). Samples were degassed overnight at 180 °C under vacuum prior
to measurements. Solution NMR spectra were taken on a Varian VNMRS 600 spectrometer with
20 40 60
2-Theta (°)
Intensity (a.u.)
Sphalerite ZnS
67
10,000 scans for
13
C{
1
H} NMR spectra. The change in room-temperature electrical conductivity
on adding thiophenol to MeIm in acetonitrile was qualitatively assessed by measuring the
resistance between two Pt wires submerged in a nitrogen-purged cuvette of liquid using a G.W.
Instec LCR-816 meter (1.275 V, 2 kHz AC output).
2.4.2 Density Functional Theory
Calculations were carried out in the gas phase using the Q-Chem ab initio quantum
chemistry software
44
with the B3LYP
45,46
density functional approximation, def2-SVP basis set,
and corresponding def2-ECP effective core potential.
47
To determine the role of dispersion, single
point energy calculations using the D3 correction with Becke-Johnson damping
48
are carried out
for structures optimized at the B3LYP level of theory.
A cluster model approximation for ZnO is created using the 24-atom (ZnO)12 geometry
identified by Chen and coworkers.
49
Minimum energy structures are calculated and verified via
vibrational analysis for possible intermediates that must be traversed to remove a zinc atom from
(ZnO)12 and generate Zn(SPh)2(MeIm)2, H2O, and (ZnO)11. As the energetics emerging from
cluster model approximations are sensitive to cluster deformations, only the zinc atom
coordinating to ligands and its nearest oxygen neighbors are allowed to relax in these steps. The
energy of the Zn(SPh)2(MeIm)2 complex is calculated using the (ZnO)12 reference by removing
one zinc and one oxygen atom instead of (ZnO)11. This is because (ZnO)12 and (ZnO)11 have very
different minimum energy geometries and using the former as reference enables us to minimize
energy changes arising from cluster deformations. Gibbs free energies (DG), calculated at both 35
and 75 °C, are used to identify the most viable steps for ZnO dissolution. For free energy
68
calculations, it is assumed that, upon binding to the (ZnO)12 cluster, ligands lose all translational
and rotational degrees of freedom.
2.5 Conclusions
In summary, we probed bulk ZnO (in both synthetic and natural mineral form) dissolution
using an alkahest solvent system with thiophenol and MeIm in acetonitrile. A discrete molecular
solute was isolated and unambiguously identified using direct methods as a neutral
pseudotetrahedral Zn(SPh)2(MeIm)2 complex. Concomitant with the formation of the molecular
solute, we obtained the first experimental evidence of stoichiometric water formation by
1
H NMR
from the liberation of ZnO lattice oxygen. A negative entropy of activation was measured by
Eyring analysis, indicating associative ligand binding in, or prior to, the rate determining step,
which is supported by DFT. The high ZnO lattice energy does not appear to dominate the
dissolution mechanism, but rather dissolution appears to be thermodynamically driven by the
strong HO–H bond formation for water. Based on this model study, it seems that metal oxides are
more appropriate for kinetically facile dissolution to generate a semiconductor ink than the
analogous metal sulfides, and this matches what has been empirically observed in previously
reported alkahest dissolutions. Generally, metal oxides are more easily dissolved than the
analogous metal sulfides in alkahest systems, where most reported sulfides have lower maximum
solubility than the corresponding oxides.
5,9
We also observe that in alkahest systems, most oxides
dissolve almost instantaneously whereas sulfides may take elevated temperatures and extended
times for full dissolution.
5,9,11,12,32
A second design rule gleaned from this study to aid in the
formulation of semiconductor inks is that the rate of dissolution increased by using a more
electron-withdrawing thiol. This may help in cases where oxide dissolution appears to be
69
kinetically inert. The mechanistic understanding of oxide dissolution, such as the one garnered
here in a model ZnO system, will inform future studies for solution processing metal chalcogenide
thin films with alkahest ink formulations.
2.6 Data availability
Crystallographic data for 4 has been deposited at the Cambridge Crystallographic Data
Centre under CCDC 2115109.
2.7 References
(1) Global Thin-film Semiconductor Deposition Industry 2020–2027, Reportlinker 2020.
(2) Uhl, A. R.; Rajagopal, A.; Clark, J. A.; Murray, A.; Feurer, T.; Buecheler, S.; Jen A. K.-
Y.; Hillhouse, H. W. Solution–Processed Low-Bandgap CuIn(S,Se)2 Absorbers for High-
Efficiency Single–Junction and Monolithic Chalcopyrite-Perovskite Tandem Solar Cells. Adv.
Energy Mater. 2018, 8, 1801254.
(3) Cha, M.; Da, P.; Wang, J.; Wang, W.; Chen, Z.; Xiu, F.; Zheng, G.; Wang, Z.-S. Enhancing
Perovskite Solar Cell Performance by Interface Engineering Using CH3NH3Br0.9I2.1 Quantum
Dots. J. Am. Chem. Soc. 2016, 138, 8581–8587.
(4) Yun, M. J.; Cha, S. I.; Seo, S. H.; Lee, D. Y. Highly Flexible Dye-Sensitized Solar Cells
Produced by Sewing Textile Electrodes on Cloth. Sci. Rep. 2014, 4, 5322.
(5) McCarthy, C. L.; Webber, D. H.; Schueller, E. C.; Brutchey, R. L. Solution-Phase
Conversion of Bulk-Metal Oxides to Metal Chalcogenides Using a Simple Thiol–Amine Solvent
Mixture. Angew. Chem., Int. Ed. 2015, 54, 8378–8381.
70
(6) Wickham, D. G.; Mark, J.; Knox, K. Metal Iron(III) Oxides. Inorganic Syntheses 1967, 9,
152–156.
(7) Jones, C. F.; Segall, R. L.; Smart, R. St. C.; Turner, P. S. Semiconducting Oxides. The
Effect of Prior Annealing Temperature on Dissolution Kinetics of Nickel Oxide. J. Chem. Soc.,
Faraday Trans. 1 1977, 73, 1710−1720.
(8) Richter, J.; Ruck, M. Synthesis and Dissolution of Metal Oxides in Ionic Liquids and Deep
Eutectic Solvents. Molecules 2020, 25, 78.
(9) Webber, D. H.; Brutchey, R. L. Alkahest V2VI3 Chalcogenides: Dissolution of Nine
Semiconductors in a Diamine–Dithiol Solvent Mixture. J. Am. Chem. Soc. 2013, 135,
15722−15725.
(10) Koskela, K. M.; Strumolo, M. J.; Brutchey, R. L. Progress of Thiol-Amine ‘Alkahest’
Solutions for Thin Film Deposition. Trends Chem. 2021, 3, 1061–1073.
(11) McCarthy, C. L.; Brutchey, R. L. Solution Deposited Cu2BaSnS4-xSex from a Thiol–Amine
Solvent Mixture. Chem. Mater. 2018, 30, 304−308.
(12) Koskela, K. M.; Tadle, A. C.; Chen K.; Brutchey, R. L. Solution Processing Cu3BiS3
Absorber Layers with a Thiol–Amine Solvent Mixture. ACS Appl. Energy Mater. 2021, 4, 11026–
11031.
(13) Koskela, K. M.; Melot, B. C.; Brutchey, R. L. Solution Deposition of a Bournonite
CuPbSbS3 Semiconductor Thin Film from the Dissolution of Bulk Materials with a Thiol–Amine
Solvent Mixture. J. Am. Chem. Soc. 2020, 142, 6173−6179.
(14) McCarthy, C. L.; Brutchey, R. L. Solution Processing of Chalcogenide Materials Using
Thiol–Amine “Alkahest” Solvent Systems. Chem. Commun. 2017, 53, 4888−4902.
71
(15) Zhang, T.; Zhang, L.; Yin, Y.; Jiang, C.; Li, S.; Zhu, C.; Chen, T. A Thiol–Amine Mixture
for Metal Oxide Towards Device Quality Metal Chalcogenides. Sci. China Mater. 2019, 62, 899–
906.
(16) Wu, W.-Y.; Xu, Y.; Ong, X.; Bhatnagar, S.; Chan, Y. Thermochromism from Ultrathin
Colloidal Sb2Se3 Nanowires Undergoing Reversible Growth and Dissolution in an Amine–Thiol
Mixture. Adv. Mater. 2019, 31, 1806164.
(17) Zhao, Y.; Yuan, S.; Chang, Q.; Zhou, Z.; Kou, D.; Zhou, W.; Qi, Y.; Wu, S. Controllable
Formation of Ordered Vacancy Compound for High Efficiency Solution Processed Cu(In,Ga)Se2
Solar Cells. Adv. Func. Mater. 2021, 31, 2007928.
(18) Zhao, Y.; Zhao, X.; Kou, D.; Zhou, W.; Zhou, Z.; Yuan, S.; Qi, Y.; Zheng, Z.; Wu, S.
Local Cu Component Engineering to Achieve Continuous Carrier Transport for Enhanced
Kesterite Solar Cells. ACS Appl. Mater. Interfaces 2021, 13, 795–805.
(19) Hasan, M. R.; Arinze, E. S.; Singh, A. K.; Oleshko, V. P.; Guo, S.; Rani, A.; Cheng, Y.;
Kalish, I.; Zaghloul, M. E.; Rao, M. V.; Nguyen, N. V.; Motayed, A.; Davydov, A. V.; Thon, S.
M.; Debnath, R. An Antimony Selenide Molecular Ink for Flexible Broadband Detectors. Adv.
Electron. Mater. 2016, 2, 1600182.
(20) Ma, Y.; Vartak, P. B.; Nagaraj, P.; Wang, R. Y. Thermoelectric Properties of Copper
Chalcogenide Alloys Deposited via the Solution–Phase using a Thiol–Amine Solvent Mixture.
RSC Adv., 2016, 6, 99905–99913.
(21) Harikesh, P. C.; Surendran, A.; Ghosh, B.; John, R. A.; Moorthy, A.; Yantara, N.; Salim,
T.; Thirumal, K.; Leong, W. L.; Mhaisalkar, S.; Mathews, N. Cubic NaSbS2 as an Ionic-Electronic
Coupled Semiconductor for Switchable Photovoltaic and Neuromorphic Device Applications.
Adv. Mater. 2020, 32, 1906976.
72
(22) McCarthy, C. L.; Downes, C. A.; Schueller, E. C.; Abuyen, K.; Brutchey, R. L. Method
for the Solution Deposition of Phase–Pure CoSe2 as an Efficient Hydrogen Evolution Reaction
Electrocatalyst. ACS Energy Lett. 2016, 1, 607−611.
(23) Buckley, J. J.; Greaney, M. J.; Brutchey, R. L. Ligand Exchange of Colloidal CdSe
Nanocrystals with Stibanates Derived from Sb2S3 Dissolved in a Thiol–Amine Mixture. Chem.
Mater. 2014, 26, 6311−6317.
(24) Ibáñez, M.; Hasler, R.; Genç, A.; Liu, Y.; Kuster, B.; Schuster, M.; Dobrozhan, O.;
Cadavid, D.; Arbiol, J.; Cabot, A.; Kovalenko, M. Ligand–Mediated Band Engineering in Bottom–
Up Assembled SnTe Nanocomposites for Thermoelectric Energy Conversion. J. Am. Chem. Soc.
2019, 141, 8025–8029.
(25) Liu, Y.; Calcabrini, M.; Yu, Y.; Lee, S.; Chang, C.; David, J.; Ghosh, T.; Spadaro, M. C.;
Xie, C.; Cojocaru- Mirédin, O.; Arbiol, J.; Ibáñez, M. Defect Engineering in Solution–Processed
Polycrystalline SnSe Leads to High Thermoelectric Performance. ACS Nano 2022, 16, 78–88.
(26) Ramli, E.; Rauchfuss, T. B.; Stern, C. L. Interception of Copper Polysulfide Clusters in the
Reaction of Copper and Sulfur in Donor Solvents: Polysulfide Complexes as the Link Between
Molecular and Nonmolecular Metal Sulfides. J. Am. Chem. Soc. 1990, 112, 4043−4044.
(27) Dev, S.; Ramli, E.; Rauchfuss, T. B.; Stern, C. L. Direct Approaches to Zinc
Polychalcogenide Chemistry: ZnS6(N–MeIm)2 and ZnSe4(N–MeIm)2. J. Am. Chem. Soc. 1990,
112, 6385−6386.
(28) Dev, S.; Ramli, E.; Rauchfuss, T. B.; Wilson, S. R. Synthesis and Structure of [M(N-
Methylimidazole)6]S8 (M = Manganese, Iron, Nickel, Magnesium). Polusulfide Salts Prepared by
the Reaction N-Methylimidazole + Metal Powder + Sulfur. Inorg. Chem. 1991, 30, 2514–2519.
73
(29) Verma, A. K.; Rauchfuss, T. B.; Wilson, S. R. Donor Solvent Mediated Reaction of
Elemental Zinc and Sulfur, sans Explosion. Inorg. Chem. 1995, 34, 3072−3078.
(30) Wang, Z.; Ma, Y.; Vartak, P. B.; Wang, R. Y. Precursors for PbTe, PbSe, SnTe and SnSe
Synthesized Using Diphenyl Dichalcogenides. Chem. Commun. 2018, 54, 9055−9058.
(31) Vartak, P. B.; Wang, Z.; Groy, T. L.; Trovitch, R. J.; Wang, R. Y. Solution and Solid–State
Characterization of PbSe Precursors. ACS Omega 2020, 5, 1949–1955.
(32) Buckley, J. J.; McCarthy, C. L.; Del Pilar-Albaladejo, J.; Rasul, G.; Brutchey, R. L.
Dissolution of Sn, SnO, and SnS in a Thiol–Amine Solvent Mixture: Insights into the Identity of
the Molecular Solutes for Solution–Processed SnS. Inorg. Chem. 2016, 55, 3175−3180.
(33) Lowe, J. C.; Wright, L. D.; Eremin, D. B.; Burykina, J. V.; Martens, J.; Plasser, F.;
Ananikov, V. P.; Bowers, J. W.; Malkov, A. V. Solution Processed CZTS Solar Cells Using Thiol–
Amine System: Understanding the Dissolution Process and Device Fabrication. J. Mater. Chem.
C 2020, 8, 10309–10318.
(34) Williams, T. J.; Kershaw, A. D.; Li, V.; Wu, X. An Inversion Recovery NMR Kinetics
Experiment. J. Chem. Educ. 2011, 88, 665−669.
(35) Pascal, I.; Tarbell, D. S. The Kinetics of the Oxidation of a Mercaptan to the Corresponding
Disulfide by Aqueous Hydrogen Peroxide. J. Am. Chem. Soc. 1957, 79, 6015–6020.
(36) Chae, T.-Y.; Row, S.-W.; Yoo, K.-S.; Lee, S.-D.; Lee, D.-W. Hydrogenation of
Isophthalonitrile with 1–Methylimidazole as an Effective Solvent for m–Xylenediamine
Production. Bull. Korean Chem. Soc. 2006, 27, 361–362.
(37) Casey, W. H.; Ludwig, C. The Mechanism of Dissolution of Oxide Minerals. Nature 1996,
381, 506–509.
74
(38) Blesa, M. A.; Weisz, A. D.; Morando, P. J.; Salfity, J. A.; Magaz, G. E.; Regazzoni, A. E.
The Interaction of Metal Oxide Surfaces with Complexing Agents Dissolved in Water. Coord.
Chem. Rev. 2000, 196, 31–63.
(39) Suter, D.; Banwart, S.; Stumm, W. Dissolution of Hydrous Iron (III) Oxides by Reductive
Mechanisms. Langmuir 1991, 7, 809–813.
(40) Manby, F. R.; Miller III, T. F.; Bygrave, P. J.; Ding, F.; Dresselhaus, T.; Batista-Romero,
F. A.; Buccheri, A.; Bungey, C.; Lee, S. J. R.; Meli, R.; Miyamoto, K.; Steinmann, C.; Tsuchiya,
T.; Welborn, M.; Wiles, T.; Williams, Z. entos: A Quantum Molecular Simulation Package. 2019,
DOI: 10.26434/chemrXiv:7762646.v2.
(41) Furness, W. 2017, https://github.com/JFurness1/EnergyLeveller/ (accessed October 2021).
(42) Luo, Y. R. Comprehensive Handbook of Chemical Bond Energies, CRC Press, Boca Raton,
FL, 2007.
(43) Zhao, D.; Tian, Q.; Zhou, Z.; Wang, G.; Meng, Y.; Kou, D.; Zhou, W.; Pan, D.; Wu, S.
Solution–Deposited Pure Selenide CIGSe Solar Cells from Elemental Cu, In, Ga, and Se. J. Mater.
Chem. A. 2015, 3, 19263–19267.
(44) Epifanovsky, E.; Gilbert, A. T. B.; Feng, X.; et al. Software for the Frontiers of Quantum
Chemistry: An Overview of Developments in the Q–Chem 5 Package. J. Chem. Phys. 2021, 155,
084801.
(45) Becke, A. D. Density-Functional Thermochemistry. III. The Role of Exact Exchange. J.
Chem. Phys. 1993, 98, 5648.
(46) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. Ab Initio Calculation of
Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force Fields. J.
Phys. Chem. 1994, 98, 11623−11627.
75
(47) Weigend, F.; Ahlrichs, R. Balanced Basis Sets of Split Valence, Triple Zeta Valence and
Quadruple Zeta Valence Quality for H to Rn: Design and Assessment of Accuracy. Phys. Chem.
Chem. Phys. 2005, 7, 3297–3305.
(48) Grimme, S.; Ehrlich, S.; Goerigk, L. Effect oft he Damping Function in Dispersion
Corrected Density Functional Theory. J. Comput. Chem. 2011, 32, 1456–1465.
(49) Chen, M.; Straatsma, T. P.; Fang, Z.; Dixon, D. A. Structural and Electronic Property Study
of (ZnO)n, n ≤ 168: Transition from Zinc Oxide Molecular Clusters to Ultrasmall Nanoparticles.
J. Phys. Chem. C 2016, 120, 20400–20418.
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Chapter 3. Polymorphic Control of Solution Processed Cu2SnS3 Films with Varying Thiol–
Amine Ink Formulation
3.1 Abstract
There is increasing demand for well characterized molecular inks that lead to phase-pure
solution processed semiconductor films. Within the Cu–Sn–S phase space, Cu2SnS3 is a sulfosalt
that belongs to the I2-IV-VI3 class of semiconductors and crystallizes in several different
polymorphs. We report the ability of thiol-amine solvent mixtures to co-dissolve inexpensive bulk
Cu2S and SnO precursors to generate free-flowing semiconductor inks. Upon mild annealing,
polymorphic control over phase-pure tetragonal (space group ) and orthorhombic (Cmc21)
Cu2SnS3 films was realized by simply switching the identity of the thiol (i.e., 1,2-ethanedithiol vs.
2-mercaptoethanol, respectively). Solution processed polymorph control is dictated by the
strengths of the resulting molecular metal-thiolate complexes and their subsequent decomposition
temperatures. The p-type tetragonal and orthorhombic Cu2SnS3 films possess direct optical band
gaps of 0.94 and 0.88 eV, respectively, and strong photoelectrochemical current responses. Design
rules garnered from the decomposition and mass spectrometry studies should inform the
decomposition and subsequent polymorph control of other thiol-amine inks for solution processed
films.
3.2 Introduction
Ternary Cu2SnS3 is a more Earth abundant replacement for current thin film solar
absorbers, such as CdTe and Cu(In,Ga)(S,Se)2 (CIGS), while still possessing favorable
optoelectronic properties.
1–3
Cu2SnS3 belongs to the class of I2-IV-VI3 semiconductors that
possesses high optical absorption coefficients (>10
5
cm
-1
), p-type conductivity, and tunable direct
band gaps from 0.9–1.8 eV.
3–6
Several different Cu2SnS3 syntheses for applications ranging from
77
solar cells
7–11
to photocatalysts
12-14
have been reported. The I2-IV-VI3 stoichiometry of Cu2SnS3
exists in several different crystal structures on the bulk Cu–Sn–S phase diagram, including
monoclinic (Cc), tetragonal () and cubic ().
15,16
The monoclinic structure where all sulfur atoms
are tetrahedrally bonded to four cations is isomorphic to the Cu2SiS3 structure type.
16
The cubic
zinc blende polymorph has symmetry and the tetragonal stannite polymorph (supercell of zinc
blende) has symmetry if ternary Cu2SnS3 crystallizes with varying degrees of disorder on the
cation sublattice.
16
Cu2SnS3 has also been reported to form a metastable hexagonal wurtzite
(P63mc) phase in colloidal nanocrystals, but this purported polymorph does not exist on the bulk
Cu–Sn–S bulk phase diagram.
1,3,14,15,17
The structural polymorph of a material directly affects its electronic and optical properties;
therefore, synthetic phase control over both thermodynamic and metastable polymorphs may allow
for property tuning.
18,19
For example, metastable wurtzite-like Cu2ZnSn(S1–xSex)4 nanocrystals
have wider band gap tunability compared to the thermodynamic kesterite phase in the same
compositional range.
20
While colloidal nanocrystal syntheses allow for the formation of metastable
phases on bulk phase diagrams, or the isolation of phases previously unknown in bulk, the
utilization of these nanocrystals in functional devices is hampered by the insulating nature of the
organic surface ligands. Methods used to remove ligands for devices involve complex ligand
exchanges or thermally decomposing the ligands, which can leave large carbonaceous impurities
in the absorber layer and at interfaces.
21,22
No direct solution deposition of metastable Cu2SnS3
thin films using molecular inks has been previously reported.
In 2013, our group developed a simple and versatile “alkahest” solvent system consisting
of a short chain thiol (e.g., 1,2-ethanedithiol, mercaptoethanol, etc.) and an amine (e.g., 1,2-
ethylenediamine) that has been shown to dissolve over 100 bulk materials, including oxides,
78
chalcogenides, and metals. This dissolution process yields molecular inks that are amenable to
solution processing; upon solution processing and mild heating, phase-pure metal chalcogenide
thin films can be recovered.
23,24
The alkahest solvent system has been leveraged to solution process
high efficiency solar cells,
25,26
electrocatalysts,
27,28
and a few reports of nanostructured devices,
such as tremella-like SnS2 and Sb2Se3 nanowires.
29,30
While compositional control in multinary
chalcogenide semiconductors can be achieved by simply tuning the solute formulation of alkahest-
derived inks,
31,32
polymorphic phase control has yet to be demonstrated. Herein, we report phase
control over two different tetragonal and orthorhombic Cu2SnS3 structural polymorphs by simply
tuning the ink formulation (i.e., thiol choice of 1,2-ethanedithiol or mercaptoethanol). We propose
an alternate orthorhombic structure (Cmc21) for the metastable Cu2SnS3 phase, with a hexagonally
close-packed S
2–
sublattice, that is isostructural with orthorhombic Ag2GeS3.
33
To the best of our
knowledge, this is the first example where the metastable Cu2SnS3 polymorph has been observed
outside the context of colloidal nanocrystals. The preparation of the two phase pure Cu2SnS3
polymorphs using alkahest inks, and their characterization, are discussed in detail.
3.3 Results and Discussion
To formulate a typical ink to yield tetragonal Cu2SnS3, bulk powders of Cu2S and SnO
were mixed in a 1:1 (mol/mol) stoichiometric ratio in EDT/en (1:4 vol/vol) with an overall
concentration of ca. 20 mg mL
–1
. The bulk precursors may be dissolved together or separately to
return the tetragonal phase. Bulk Cu2S and SnO powders both have overall solubility limits of 10-
15 wt% in EDT/en (1:4 vol/vol) mixtures under ambient conditions (1 atm, 25 °C). The inks were
stirred at 30 °C for 2 h to yield a free-flowing, optically clear orange-brown ink free of scattering.
The ink was stable for multiple days under inert atmosphere conditions, as indicated by the lack
79
of color change and solid precipitates. To formulate a typical ink to yield orthorhombic Cu2SnS3,
bulk powders of Cu2S and SnO were added separately in a 1:1 (mol/mol) ratio in a mixture of
merc/en (1:4 vol/vol) with an overall concentration of ca. 20 mg mL
–1
in each ink. The bulk Cu2S
and SnO powders have solubility limits of 10-15 wt% and 5-10 wt%, respectively, in merc/en (1:4
vol/vol) mixtures under ambient conditions (1 atm, 25 °C). The SnO ink in merc/en was stirred at
30 °C for 2 h to yield a free flowing, optically clear, and colorless ink free of scattering. The Cu2S
ink in merc/en was a faint light brown color, optically clear, and free of scattering after dissolving
under the same conditions. Both Cu2S and SnO inks were stable for multiple days under inert
atmosphere conditions, as described above. Right before annealing, the two Cu2S and SnO inks in
merc/en were mixed to form a stable, almost colorless, and optically clear ink. When the bulk
precursors were co-dissolved in merc/en, mixed phase products were recovered upon annealing.
While the bulk Cu2S and SnO precursors returned phase-pure tetragonal and orthorhombic phases
(vide infra), using different combinations of oxides and sulfides (i.e., CuO, CuS, Cu2O, SnS, and
SnS2) also returned the tetragonal and orthorhombic polymorphs when using EDT/en and merc/en,
respectively.
Thermogravimetric analysis (TGA) was employed to determine the endpoint of organic
volatilization and molecular solute decomposition for dried inks from both EDT/en and merc/en
solvent combinations (Figure 3.1). Organic mass loss begins ca. 120 °C and mass loss ends at
temperatures < 350 °C for both inks. In the EDT/en ink, the strongest IR bands belong to
deprotonated EDT (675 cm
–1
ν(C–S) stretch, 1430 cm
−1
d(CH2) bend).
24,34
In the merc/ink, the
strongest IR bands belong to merc and/or en (665 cm
–1
ν(C–S), 1008 cm
−1
d(CH2), 1048 cm
–1
ν(C–
C), 1410 cm
−1
d(CH2)) (Figure 3.2).
35
80
Figure 3.1. a) TGA trace and derivative curve of a dried EDT/en ink that yields tetragonal
Cu2SnS3, demonstrating a decomposition endpoint of < 350 ˚C. Inset is a picture of the ink with
Cu2S and SnO dissolved in EDT/en (1:4 vol/vol). b) TGA trace and derivative curve of a dried
merc/en ink that yields orthorhombic Cu2SnS3, demonstrating a decomposition endpoint of < 350
˚C. Inset is a picture of the combined ink with Cu2S and SnO dissolved in merc/en (1:4 vol/vol).
Figure 3.2. FT-IR spectra of the inks dried at 100 ˚C and annealed to 330 ˚C confirming loss of
organic species for a) tetragonal and b) orthorhombic Cu2SnS3.
The resulting dark gray materials after solution deposition and annealing to 330 °C were
confirmed to be phase-pure tetragonal and orthorhombic Cu2SnS3 by powder X-ray diffraction
from the EDT/en and merc/en inks, respectively. Rietveld refinements were employed to
determine the proper space group for each phase. For the Cu2SnS3 resulting from the EDT/en ink,
there are three phases that are possible candidates (i.e., monoclinic, tetragonal, cubic) and their
diffraction patterns only differ slightly by minor reflections. Representations of the crystal
81
structures used for refinements are supplied in the Supporting Information. To assess the phase of
Cu2SnS3 resulting from the EDT/en ink, powder XRD data sets were refined against the
monoclinic (Cc), tetragonal (), and cubic () zinc blende crystal structures. In the first refinement,
the monoclinic phase failed to converge. In the second refinement, the disordered tetragonal phase
in which the Cu and Sn atoms are randomly distributed over a singly occupied Wyckoff position
led to a refinement with a reduced c
2
of 1.69 and a wR of 2.29% (Figure 3.3a, Table 3.1). The
Rietveld refinement to the tetragonal structure returned lattice constants of a = 5.4267(6) Å and c
= 10.6869(3) Å with a unit cell volume of V = 314.72(8) Å
3
, which match well to previously
reported values for bulk tetragonal Cu2SnS3 (a = 5.41 Å, c = 10.82 Å, V = 316.68 Å).
36
In the third
refinement, we simulated a disordered cubic zinc blende structure in which the Cu and Sn atoms
are randomly distributed over the Zn site as there are no published zinc blende structures in the
ICSD; this refinement returned a slightly worse reduced c
2
of 3.56 and a wR of 3.32% (Figure
3.4).
82
Figure 3.3. a) Rietveld refinement of the XRD data corresponding to Cu2SnS3 resulting from the
EDT/en ink, confirming that the tetragonal unit cell is the appropriate structural model for this
polymorph (c
2
1.69, wR 2.29%; a = 5.43 Å, c = 10.69 Å, V = 315.19 Å
3
). (λ = 1.5406 Å)
b) Structure of disordered tetragonal Cu2SnS3. c) Rietveld refinement of XRD data corresponding
to Cu2SnS3 resulting from the merc/en ink, confirming that the orthorhombic Cmc21 unit cell is
the appropriate structural model for the metastable polymorph (c
2
2.18, wR 4.02%, a = 11.46 Å,
b = 6.63 Å, c = 6.32 Å, V = 479.95 Å
3
). (λ = 1.5406 Å) d) Structure of ordered orthorhombic
Cu2SnS3. Sulfur atoms are yellow, tin atoms are silver, and copper atoms are blue.
83
Table 3.1. Structural parameters of tetragonal () Cu2SnS3 extracted from Rietveld analysis.
Atom Mult. x y z Frac. Uiso
Sn1 4 0.00000 0.50000 0.25000 0.1649 0.02270
Cu1 4 0.00000 0.50000 0.25000 0.2160 0.02322
Sn2 2 0.00000 0.00000 0.50000 0.1538 0.05255
Cu2 2 0.00000 0.00000 0.50000 0.1672 0.05684
Cu3 2 0.00000 0.00000 0.00000 0.4031 0.01006
S1 8 0.25625 0.25625 0.12715 0.3934 0.03402
Table 3.2. Structural parameters of orthorhombic (Cmc21) Cu2SnS3 extracted from Rietveld
analysis.
Atom Mult. x y z Frac. Uiso
Cu1 8 0.17001 0.83422 0.98810 0.9954 0.01538
S1 8 0.17757 0.84400 0.35204 1.0417 0.01393
Sn1 4 0.00000 0.31625 0.96892 0.9898 0.00950
S2 4 0.00000 0.30922 0.36476 0.9416 0.02614
Space Group
a = b (Å) 5.4267(6)
c (Å) 10.6869(3)
V (Å
3
) 314.72(8)
a = b = g 90°
Rwp 2.288%
Space Group Cmc21
a (Å)
b (Å)
11.4569(4)
6.6268(9)
c (Å) 6.3215(7)
V (Å
3
) 479.958
a = b = g 90°
Rwp 4.018%
84
Figure 3.4 a) Rietveld refinement of the zinc blende phase using the cubic unit cell (c
2
3.56, wR
3.32%, a = 5.46 Å). (λ = 1.5406 Å) b) Structural representation of disordered cubic Cu2SnS3.
Sulfur atoms are yellow, tin atoms are silver, and copper atoms are blue.
The Cu2SnS3 resulting from the merc/en ink yields a distinctly wurtzite-like diffraction
pattern. This polymorph has previously only been observed in colloidal nanocrystals and has been
assumed to adopt a hexagonal wurtzite (P63mc) structure that does not exist on the bulk Cu–Sn–S
bulk phase diagram.
1,3,14,15,17
The disordered wurtzite polymorph derives from the ZnS wurtzite
structure, where Cu
+
and Sn
4+
randomly occupy the Zn site with a 2:1 ratio, respectively. However,
there are no known published structures for wurtzite Cu2SnS3. A simulated wurtzite cell with Cu
and Sn randomly distributed (2:1 ratio, respectively) on the Zn site, preserving the sulfur positions,
returned a reduced c
2
of 5.25 and a wR of 4.54% (Figure 3.5). Tetrahedrally bonded ternary I-III-
VI2 sulfides with hexagonal S
2–
sublattices, such as wurtzite-like CuInS2 and AgInS2, are known
to possess cation ordering and not adopt a true disordered wurtzite structure.
37,38
This led us to
consider whether there are any known I2-IV-VI3 materials with hexagonal S
2–
sublattices, which
revealed the orthorhombic polymorph (Cmc21) of Ag2GeS3. This structure is similar to the wurtzite
structure type with a hexagonal close packed S
2–
sublattice, but with the major distinction being
that there is ordering of the Ag
+
and Ge
4+
cations. We simulated the Cmc21 structure type by
replacing the Ag
+
and Ge
4+
cations with Cu
+
and Sn
4+
and allowed the cell and atoms to relax using
85
DFT calculations. This structure type resulted in an improved refinement with a reduced c
2
of 2.18
and wR of 4.02% (Figure 3.3b, Table 3.2). The refinement returned lattice parameters of a =
11.4569(4) Å, b = 6.6268(9) Å, c = 6.3215(7) Å, V = 479.958 Å
3
, matching quite well to the
simulated crystal structure (a = 11.45 Å, b = 6.62 Å, c = 6.34, V = 480.56 Å
3
). This suggests a
degree of cation ordering in our wurtzite-like Cu2SnS3 polymorph due to fitting of minor
reflections and intensity mismatch of the difference curve at 2q = 47.9°. Wurtzite Cu2SnS3 has
been previously reported to undergo a phase transition to the zinc blende polymorph at elevated
temperatures (>500 °C).
3
Our orthorhombic polymorph was similarly annealed at 550 °C and
confirmed to relax to the cubic zinc blende polymorph (Figure 3.6).
Figure 3.5. a) Rietveld refinement of the wurtzite phase using the disordered P63mc unit cell (c
2
3.05, wR 4.754%, a = 3.78 Å, c = 6.44 Å). (λ = 1.5406 Å) b) Structural representation of disordered
wurtzite Cu2SnS3.
86
Figure 3.6. Powder XRD diffraction pattern of the orthorhombic Cu2SnS3 polymorph annealed to
550 °C, indexed to a simulated cubic zinc blende structure.
The Rietveld refinements for the tetragonal and orthorhombic Cu2SnS3 polymorphs were
not improved with the addition of any binary Cu2–xS, SnS, or SnS2 phases, suggesting that both
materials are phase pure. Average grain sizes of 11.0 and 68.0 nm for the tetragonal and
orthorhombic polymorphs, respectively, were extracted from refinements. Raman spectroscopy
was used to corroborate the phase purity of the solution processed tetragonal and orthorhombic
Cu2SnS3 materials. For the tetragonal polymorph, a Raman active mode at 324 cm
–1
matches well
to spectra previously reported for tetragonal Cu2SnS3 (Figure 3.7a).
37
The orthorhombic
polymorph has Raman active modes at 291 and 314 cm
–1
that match well to previously reported
“wurtzite” Cu2SnS3 (Figure 3.7b).
3
Neither have Raman active modes from potential binary
impurities, such as Cu2–xS, SnS, or SnS2.
40
20 40 60
2-Theta (°)
Intensity (a.u.)
Cubic Cu
2
SnS
3
87
Figure 3.7. Raman spectra using 532 nm excitation of a) tetragonal and b) orthorhombic Cu2SnS3
films drop-casted and annealed at 330 °C.
The broadness of the XRD peaks and small grain sizes indicate potential nanostructuring
of the resulting solution processed Cu2SnS3 films. Scanning electron microscopy (SEM) images
of drop-casted tetragonal and orthorhombic Cu2SnS3 films on Si substrates confirm the presence
of nanostructured grains (Figures 3.8,9). While the metastable phase has only been observed as
ligand stabilized colloidal nanocrystals, the SEM images coupled with the FT-IR spectra prove the
solution deposition of ligand-less orthorhombic Cu2SnS3 directly from molecular thiol–amine
solutions. SEM–EDS was used to assess the average elemental composition on the same drop
casted films. From an average of four different wide spot analyses each, elemental compositions
of Cu1.79Sn0.98S3.00 (Cu/(Cu+Sn) = 0.64) for the tetragonal polymorph and Cu1.93Sn1.19S3.00
(Cu/(Cu+Sn) = 0.63) for the orthorhombic polymorph were obtained. These stoichiometries are in
the range of previously reported tetragonal and “wurtzite” samples as Cu2SnS3 is known to possess
wide compositional variations as the Cu/(Cu+Sn) ratio can be tuned from 0.26-0.72 for the
tetragonal polymorph and 0.49-0.81 for the “wurtzite” polymorph.
1
88
Figure 3.8. Top-down SEM micrographs of tetragonal Cu2SnS3 at a) 350 and b) 250,000´ drop-
casted on Si and annealed at 330 °C.
Figure 3.9. Top-down SEM micrographs of orthorhombic Cu2SnS3 at a) 350 and b) 250,000´
drop-casted on Si and annealed at 330 °C.
X-ray photoelectron spectroscopy was used to gain insights into the valence states of the
tetragonal and orthorhombic polymorphs. Survey scans of drop casted tetragonal and
orthorhombic Cu2SnS3 on Si substrates that had been exposed to atmospheric oxygen are provided
in Figures 3.10 and 3.11. High-resolution spectra of the Cu 2p, Sn 3d, and S 2p regions of the
tetragonal Cu2SnS3 are given in Figure 3.12, and the corresponding peak fittings are given in
Table 3.3. The Cu 2p region can be fit with a single set of doublets at 952.0 and 932.2 eV with a
splitting of 19.8 eV, consistent with an assignment of Cu
+
in our tetragonal Cu2SnS3. The Sn 3d
region can be fit with two sets of doublets each with a splitting of 8.4 eV. The lower binding energy
peaks at 494.8 eV and 486.4 eV (full width at half max (FWHM) of 0.78 eV) match well to Sn
4+
–
89
S.
39
The smaller, higher binding energy doublet at 495.2 eV and 486.8 eV (FWHM of 1.75 eV)
most likely corresponds to amorphous surface oxide or other non–stoichiometric tin oxides (SnOx)
due to Sn–O having a higher binding energy than corresponding Sn–S as well as amorphous oxides
displaying larger FWHM values.
41
This is reasonable to expect as our materials were exposed to
atmospheric oxygen several times during processing and travel for measurements, consistent with
the presence of an O 1s peak in the XPS survey scan. The S 2p spectrum is fit well by a doublet
with a splitting of 1.2 eV and S 2p3/2 component at 161.4 eV. This is consistent with an assignment
of an S
2–
metal sulfide.
32,42
The doublet at higher binding energies corresponds to oxidized surface
species. Thus, XPS analysis confirms the expected formal valence states of the tetragonal
polymorph to be (Cu
2+
)2(Sn
4+
)(S
2–
)3. High-resolution spectra of the Cu 2p, Sn 3d, and S 2p regions
of the orthorhombic phase are given in Figure 3.13, and the corresponding peak fittings are given
in Table 3.4. The Cu 2p region can also be fit with a single set of doublets indicating a single Cu
+
environment, matching prior literature.
1,3,32,39,42
The Sn 3d spectrum was also fit with two sets of
doublets corresponding to Sn
4+
in a sulfide environment, but the peaks corresponding to surface
oxide are much larger relative to the Sn–S peaks when compared to the tetragonal phase.
1,3
The S
2p region can also be fit two sets of doublets, each with a splitting of 1.2 eV, which matches well
to prior literature for a S
2–
metal sulfide environment.
1,3,32,39,42
90
Figure 3.10. XPS survey scan of tetragonal Cu2SnS3 drop casted on Si and annealed to 330 °C.
Figure 3.11. XPS survey scan of orthorhombic Cu2SnS3 drop casted on Si and annealed to 330 °C.
0 500 1000
Binding Energy (eV)
Intensity (a.u.)
O KLL
Cu 2p
Cu 2s
Cu LMM
O 1s
S 2p
Cu 3s
Cu 3p
Sn 3d
C 1s
S 2s
0 500 1000
Binding Energy (eV)
Intensity (a.u.)
O KLL
Cu 2p
Cu 2s
Cu LMM
O 1s
S 2p
Cu 3s
Cu 3p
Sn 3d
C 1s
S 2s
91
Figure 3.12. High-resolution XP spectra of a) Cu 2p, b) Sn 3d, and c) S 2p regions of tetragonal
Cu2SnS3 drop-casted on Si and annealed at 330 °C.
Table 3.3. Peak positions and peak splitting from the high-resolution XP spectra of tetragonal
Cu2SnS3 drop-casted on Si and annealed at 330 °C.
Element Peak Splitting
(eV)
Peak ID Binding Energy
(eV)
Cu 19.8 2p1/2 952.0
2p3/2 932.2
Sn 8.4 3d3/2 494.8
3d5/2 486.4
Sn (surface SnOx) 8.4 3d3/2 495.2
3d5/2 486.8
S 1.2 2p1/2 162.6
2p3/2 161.4
S (oxidized surface
species)
1.2 2p1/2 163.7
2p3/2 162.5
92
Figure 3.13. High-resolution XP spectra of a) Cu 2p, b) Sn 3d, and c) S 2p regions of orthorhombic
Cu2SnS3 drop-casted on Si and annealed at 330 °C.
Table 3.4. Peak positions and peak splitting from the high-resolution XP spectra of orthorhombic
Cu2SnS3 drop-casted on Si and annealed at 330 °C.
Element Peak Splitting
(eV)
Peak ID Binding Energy
(eV)
Cu 19.8 2p1/2 952.0
2p3/2 932.2
Sn 8.4 3d3/2 494.8
3d5/2 486.4
Sn (surface SnOx) 8.4 3d3/2 495.2
3d5/2 486.8
S 1.2 2p1/2 162.6
2p3/2 161.4
S (oxidized surface
species)
1.2 2p1/2 163.2
2p3/2 162.0
93
The optical band gap of the resulting tetragonal and orthorhombic polymorphs were
measured by UV-vis-NIR spectroscopy (Figure 3.14a,b). Similar direct optical band gaps of Eg,dir
= 0.94 eV and 0.88 eV for the tetragonal and orthorhombic polymorphs of Cu2SnS3, respectively,
were determined by extrapolating the square of the linear portion of the Kubelka–Munk treated
diffuse reflectance spectra. These band gaps lie within the range of previously reported
experimental values for both tetragonal and “wurtzite” nanocrystals.
1,3,17,39
To demonstrate the
potential of these films as photoactive solar absorbers, transient photocurrent response
measurements were performed with the two nanostructured polymorphs drop casted on FTO. The
measurements were performed in an electrolyte solution of 0.1 M Na2S/0.01 M sulfur dissolved in
deionized water with Pt–wire counter and pseudoreference electrodes and the Cu2SnS3/FTO as the
working electrode. With chopped illumination from a standard laboratory solar simulator,
controlled potential electrolysis performed with an applied potential of -600 mV yielded stable
photocurrents of ~30 and ~60 μA cm
−2
for the tetragonal and orthorhombic phases, respectively
(Figure 3.14c,d). The same measurements performed at positive applied potentials did not return
a photocurrent, which confirms the p-type nature of these materials.
3–6
94
Figure 3.14. Kubelka–Munk functions of absorption data to estimate direct optical band gaps for
a) tetragonal and b) orthorhombic polymorphs of Cu2SnS3. Transient photocurrent response of
solution-processed c) tetragonal and d) orthorhombic films of Cu2SnS3 deposited on FTO
substrates in 0.1 M Na2S/0.01 M sulfur (aq) electrolyte under a potential of -600 mV vs Pt
pseudoreference electrode using chopped AM1.5 light.
To better understand the influence of ink formulation on Cu2SnS3 polymorph
determination, we employed TGA and negative ion mode electrospray ionization mass
spectrometry (ESI-MS) to study differences between the Cu2S and SnO inks with EDT/en and
merc/en. While ESI-MS is an indirect method, it is effective in gaining insights into identities of
possible molecular solutes formed in thiol-amine inks.
24,43
TGA has been utilized to monitor
decomposition temperatures of metal thiolates, which are known to decompose over a wide
temperature range (100-350+ °C) depending on the identity of the metal (e.g., Cu, Sn, In, etc.) and
thiol used.
44–48
Photographs of the Cu2S inks in EDT/en and merc/en are supplied as insets of
95
Figure 3.15a,b, showing major color differences between the two, with the EDT/en ink being dark
orange/brown and the merc/en ink being virtually colorless. Direct-injection ESI-MS was
conducted to gain insights into the differences in the molecular solutes resulting from Cu2S
dissolution in EDT/en and merc/en. The negative ion mode ESI-MS data in Figure 3.15a,b reveal
distinct differences in the major ions between the Cu2S EDT/en and merc/en inks. In the EDT/en
ink, the major ion peak at m/z = 246.9 was attributed to [Cu(C2H4S2)2]
–
(or [Cu(EDT)2]
–
), with the
rest of the major ions attributed to different copper thiolate complexes. In the merc/en ink, the
major ion peak at m/z = 776.7 was attributed to the polynuclear copper cluster [Cu5(C2H5OS)6]
–
(or [Cu5(merc)6]
–
). Derivative curves of TGA traces of these dried Cu2S inks with EDT/en and
merc/en show differences between the high-temperature mass loss events (Figure 3.15c,d). The
mass loss event attributed to the decomposition of copper thiolates is larger in the EDT/en ink
(27%) and occurs at higher temperatures (305 °C) relative to the merc/en ink (12%, 264 °C). This
is consistent with the parent ion in the ESI-MS for the Cu2S ink with EDT/en having 2 eq of
EDT/Cu whereas the parent ion in the ESI-MS for the ink with merc/en has 1.2 eq merc/Cu.
Moreover, EDT is expected to bind more strongly to copper as a bidentate X2-type ligand, whereas
merc is expected to bind less strongly in a bidentate or monodentate fashion as either an XL-type
or X-type ligand, respectively.
For the SnO EDT/en and merc/en inks, the same ESI-MS and TGA studies were conducted
(Figure 3.16). While the ink colors were similar for dissolved SnO, the TGA mass loss/difference
curves (Figure 3.16a,b) trend with the Cu and ternary inks where merc/en shows larger mass loss
at lower temperatures. Negative mode ESI-MS spectra show similarities where all the major ions
are attributed to analogous Sn-EDT or Sn-merc complexes (Figure 3.16c,d). The initial mass
losses in the EDT/en ink ca. 190 °C is attributed to volatilization of excess thiol/ start of Sn-thiolate
96
decomposition while the larger mass loss at ca. 325 °C is attributed to the decomposition of more
tightly bound Sn-thiolates. For the merc/en ink, the mass loss at ca. 208 °C is due to volatilization
of the thiol/ start of Sn-thiolate decomposition with the mass loss at ca. 328 °C due to the complete
decomposition of Sn-thiolates. While the Sn-thiolates between the two inks decompose at roughly
the same temperature, the relative mass losses between them are consistent with the ternary and
Cu2S inks (majority of merc/en metal thiolates decomposing at lower temperatures). The negative
mode ESI-MS show a major ion at m/z = 396.8 matching to [SnH(C2H4S2)3]
–
(or [SnH(EDT)3]
–
)
with the rest of the major peaks corresponding to other Sn-EDT complexes for the SnO EDT/en
ink and the major ions at m/z = 650.8 and 618.8 matching well to [Sn2HO2(C2H4OS)5]
–
(or
[Sn2HO2(merc)5]
–
) and [Sn2H(C2H4OS)5]
–
(or [Sn2H(merc)5]
–
), respectively, for the SnO merc/en
ink. The rest of the peaks identified match well to other various Sn-merc complexes.
Taken in concert, we hypothesize that the binding strength of the metal thiolates between
the two inks and subsequent differences in decomposition temperatures leads to the polymorphic
control of our nanostructured ternary Cu2SnS3 films. The larger mass loss at lower temperatures
for the merc/en ink from the decomposition of weakly bonded Cu-merc and Sn-merc metal thiolate
complexes seeds the growth of the metastable wurtzite-like polymorph. Whereas the Cu-EDT and
Sn-EDT complexes formed in the EDT/en inks decompose in higher amounts and at higher
temperatures due to the more tightly bound EDT ligands to the metal centers forming the
thermodynamic tetragonal phase upon decomposition.
97
Figure 3.15. Negative ion mode ESI-MS of Cu2S dissolved in a) EDT/en and b) merc/en. TGA
traces and derivative curves of a dried c) Cu2S EDT/en ink and d) Cu2S merc/en ink.
98
Figure 3.16. Negative ion mode ESI-MS of SnO dissolved in a) EDT/en and b) merc/en. TGA
trace and derivative curve of a dried c) SnO EDT/en ink and d) SnO merc/en ink.
3.4 Experimental
3.4.1 General Considerations
All materials were used as received. 1,2-Ethylenediamine (en, 99.5%), 2-mercaptoethanol
(merc, 99%), and copper(I) sulfide (Cu2S, 99.99%) were purchased from Sigma Aldrich. 1,2-
Ethanedithiol (EDT, 98+%), and tin(II) oxide (SnO, 99%) were purchased from Alfa Aesar.
3.4.2 Ink Formulations and Processing
To generate the ink for tetragonal Cu2SnS3, 9.95 mg (0.063 mmol) Cu2S and 8.42 mg
(0.063 mmol) SnO were added to 0.2 mL EDT and 0.8 mL en and allowed to stir for 2 h at 30 °C.
Full dissolution is observed to occur within minutes. If the EDT/en (1:4 vol/vol) solvent mixture
solidifies, gentle heating will resolubilize the solution. To generate the ink for orthorhombic
99
Cu2SnS3, 9.95 mg (0.063 mmol) Cu2S and 8.42 mg (0.063 mmol) SnO were added separately to
0.1 mL merc and 0.4 mL en and allowed to dissolve for up to 2 h at 30 °C under magnetic stirring
before finally being combined after full dissolution right before deposition and annealing.
Inks to produce the tetragonal and orthorhombic polymorphs of Cu2SnS3 were drop casted
onto fluorine-doped tin oxide (FTO), Si, or borosilicate glass substrates that were cleaned by
sequential sonication in methanol, acetone, and isopropyl alcohol for 15 min each before being
blown dry using pressurized nitrogen gas. Before deposition, the substrates were ozone cleaned
for 15 min. Finally, 20 mL of ink was deposited onto 1´1 cm
2
precut substrates and the tip of the
pipette was used to spread the ink across the full substrate without allowing the tip of the syringe
to touch the surface of the substrate. Films were annealed identically under flowing nitrogen to
330 °C and allowed to cool naturally to room temperature.
3.4.3 Organic Content Determination
Thermal gravimetric analysis (TGA) was performed on a TA Instruments TGA Q50
instrument and samples were run in an alumina crucible under a flowing nitrogen atmosphere with
a heating rate of 5 ˚C min
–1
. The TGA samples were prepared by drying the ink in an alumina
crucible to 100 ˚C under a flowing nitrogen atmosphere in an aluminum annealing chamber prior
to TGA analysis to avoid excess corrosion of the thermocouple in the TGA. FT-IR spectra were
collected on an Agilent Cary 630 spectrometer by diamond attenuated total reflection (ATR). The
samples were prepared by drop casting the inks onto glass substrates and drying to 100 ˚C before
annealing to 330 ˚C under a flowing stream of nitrogen and transferring the Cu2SnS3 to the crystal.
100
3.4.4 Structural and Optical Characterization
Powder X–ray diffraction (XRD) patterns were collected using a Rigaku Ultima IV
diffractometer operated at 44 mA and 40 kV, in the 2 range of 10-70˚ using Cu K radiation (
= 1.5406 Å). For powder diffraction studies, inks were drop cast on a glass substrate and dried to
350 °C in an aluminum annealing chamber under flowing nitrogen. The powders were removed
from the glass substrate and ground in an agate mortar. For structural refinements, the step size
and collection time were 0.01˚ (0.05˚) and 3 s (10 s) step
–1
, respectively. All patterns were recorded
under ambient conditions. Rietveld refinements were carried out using the General Structure
Analysis System II (GSAS-2) software package. The following parameters were refined: (1) scale
factor, (2) background (modeled using a shifted Chebyshev polynomial function), (3) peak shape,
(4) lattice constants, (5) fractional atomic coordinates of the Cu, Sn, and S atoms constrained by
the site symmetry, (6) preferred orientation using a spherical harmonic model, and (7) isotropic
thermal parameters for each chemical species. The Rwp and c
2
indicators were employed to assess
the quality of the refined structural models. Diffuse reflectance UV-vis-NIR transmittance
spectroscopy was performed on a Perkin Elmer Lambda 950 equipped with a 150-mm integrating
sphere. 12 mg of sample was mixed with 350 mg of BaO and placed in a solid sample holder.
Scanning electron microscopy/ energy dispersive X-ray spectroscopy (SEM–EDS) was performed
using a FEI Helios G4 P-FIB at 20 kV. Top surface micrographs were acquired via SEM using a
beam current of 0.8 nA and an accelerating voltage of 5 kV. Raman spectra were conducted on
samples deposited on Si substrates annealed to 330 °C. Spectra were recorded for 1 min using an
average of three scans using a Horiba XploRA confocal Raman microscope with 532 nm
excitation. The Raman microscope was covered with a black tarp to reduce ambient light exposure.
X-ray photoelectron spectroscopy (XPS) was performed using a Kratos Axis Ultra X-ray
101
photoelectron spectrometer with a monochromatic aluminum anode (1486.6 eV). An operating
current of 5 mA and voltage of 12 kV with a step size of 0.1 eV and a pass energy of 20 eV was
used to acquire 20 high resolution scans for each element. An operating current of 5 mA and
voltage of 12 kV with a step size of 1 eV and pass energy of 80 eV was used to acquire 5 survey
scans for each sample. Pressure in the analysis chamber < 1´10
–9
Torr. XPS was performed on
Cu2SnS3 thin films deposited on Si substrates.
3.4.5 Molecular Solute Identification
Electrospray ionization mass spectrometry (ESI-MS) samples were prepared from fully
dissolved solutions of Cu2S or SnO (20 mg mL
–1
, 1:4 (vol/vol) EDT/en or merc/en) diluted with
DMSO to ca. 1 µM. Solutions were mixed right before injection into the MS instrument to avoid
possible decomposition of products. Samples were injected through the main nebulizer using a
syringe pump, fitted with a 500 μL Hamilton syringe (1750RN) at 5 μL min
–1
flow rate. Mass
spectra were measured using Agilent 6545 qToF instrument equipped with dual AJS electrospray
ionization source operating in negative ion mode with following ionization parameters: Capillary
voltage 3.5 kV, nozzle voltage 0.0 kV, nitrogen was applied as a nebulizer gas 35 psi, sheath gas
12 L min
−1
, 275 °C, dry gas 10 L min
−1
, 300 °C, and collision gas. For external calibration and
tuning a low-concentration tuning mix solution by Agilent Technologies was utilized at 10:1
further dilution. Spectra were recorded in m/z 50-2000 range. All the mass spectra were recorded
at 1 Hz.
102
3.4.6 Photoelectrochemical Measurements
Photoelectrochemical measurements were performed on FTO substrates (Sigma Aldrich)
with a conductivity of ca. 7 Ω sq
–1
that were cut into 0.5´2.5 cm
2
pieces and cleaned as described
above. Kapton tape was used to mask off a portion of the substrate for electrode contact.
Photoelectrochemical responses for both polymorphs of Cu2SnS3 were performed using a BASi
Epsilon-EC potentiostat. A 3-neck flask was used with a Pt-wire counter electrode and a Pt-wire
pseudoreference electrode. The working electrodes were tetragonal and orthorhombic Cu2SnS3
films drop-casted on FTO-coated glass and annealed to 330 °C. The tetragonal Cu2SnS3 electrode
was further annealed at 550 °C to improve the rigidity of the working electrode and prevent
delamination during measurements. An aqueous 0.1 M Na2S/ 0.01 M sulfur electrolyte was made
from nitrogen-sparged deionized water. For photoelectrochemical experiments, a standard
laboratory white light placed ca. 15 cm from the samples was used to illuminate the working
electrode. The total illumination areas of the tetragonal and orthorhombic Cu2SnS3 working
electrodes were ~0.75 cm
2
.
3.5 Conclusions
In summary, we have demonstrated the ability of the alkahest solvent system to allow for
polymorph control in solution processed tetragonal and orthorhombic Cu2SnS3 films by simply
switching the identity of the thiol. When employing EDT/en as the solvents, the
thermodynamically preferred tetragonal phase is recovered upon mild annealing. When the
identity of the thiol is switched to merc, a metastable wurtzite-like orthorhombic polymorph is
recovered. The solution processed polymorph control is due the relative strengths of the formed
molecular metal-thiolates in solution. Metal-EDT complexes are much more stable and require
103
increased temperatures for complete decomposition and crystallization whereas metal-merc
complexes decompose and crystallize at lower temperatures leading to more facile crystallization
of the kinetic metastable polymorph. The p-type tetragonal and orthorhombic films possess direct
optical band gaps of 0.94 and 0.88 eV, respectively, and strong photocurrent responses. Design
rules garnered from the decomposition and mass spectrometry studies should inform the
decomposition and subsequent polymorph control of other thiol-amine inks for solution processed
thin films.
3.6 References
(1) Liu, X.; Wang, X.; Swihart, M. T. Composition-Dependent Crystal Phase, Optical
Properties, and Self-Assembly of Cu−Sn−S Colloidal Nanocrystals. Chem. Mater. 2015, 27,
1342−1348.
(2) Kolny-Olesiak, J.; Weller, H. Synthesis and Application of Colloidal CuInS2
Semiconductor Nanocrystals. ACS Appl. Mater. Interfaces 2013, 5, 12221−12237.
(3) Ghorpade, U. V.; Suryawanshi, M. P.; Shin, S. W.; Kim, I.; Ahn, S. K.; Yun, J. H.; Jeong,
C.; Kolekar, S. S.; Kim, J. H. Colloidal Wurtzite Cu2SnS3 (CTS) Nanocrystals and Their
Applications in Solar Cells. Chem. Mater. 2016, 28, 3308.
(4) Kanai, A.; Toyonaga, K.; Chino, K.; Katagiri, H.; Araki, H. Fabrication of Cu2SnS3 Thin-
Film Solar Cells with Power Conversion Efficiency of over 4%. Jpn. J. Appl. Phys. 2015, 54,
08KC06.
(5) Berg, D. M.; Djemour, R.; Gutay, L.; Zoppi, G.; Siebentritt, S.; Dale, P. J. Thin Film Solar
Cells based on the Ternary Compound Cu2SnS3. Thin Solid Films 2012, 520, 6291−6294.
104
(6) Avellaneda, D.; Nair, M. T. S.; Nair, P. K. Cu2SnS3 and Cu4SnS4 Thin Films via Chemical
Deposition for Photovoltaic Application. J. Electrochem. Soc. 2010, 157, D346−D352.
(7) Lee, J. Y.; Kim, I. Y.; Surywanshi, M. P.; Ghorpade, U. V.; Lee, D. S.; Kim, J. H.
Fabrication of Cu2SnS3 Thin Film Solar Cells using Cu/Sn Layered Metallic Precursors Prepared
by a Sputtering Process. Sol. Energy 2017, 145, 27–32.
(8) Suryawanshi, M. P.; Ghorpade, U. V.; Shin, S. W.; Pawar, S. A.; Kim, I. Y.; Hong, C. W.;
Wu, M.; Patil, P. S.; Moholkar, A. V.; Kim, J. H. A Simple Aqueous Precursor Solution Processing
of Earth-Abundant Cu2SnS3 Absorbers for Thin-Film Solar Cells. ACS Appl. Mater. Interfaces
2016, 8, 11603– 11614.
(9) Li, J.; Xue, C.; Wang, Y.; Jiang, G. Liu, W.; Zhu, C. Cu2SnS3 Solar Cells Fabricated by
Chemical Bath Deposition–Annealing of SnS/Cu Stacked Layers. Sol. Energy Mater. Sol. Cells
2016, 144, 281–288.
(10) Tiwari, D.; Chaudhuri, T. K.; Shripathi, T.; Deshpande, U.; Rawat, R. Non-Toxic, Earth-
Abundant 2% Efficient Cu2SnS3 Solar Cell Based on Tetragonal Films Direct-Coated from Single
Metal-Organic Precursor Solution. Sol. Energy Mater. Sol. Cells 2013, 113, 165–170.
(11) Marquez Prieto, J. A.; Levcenko, S.; Just, J.; Hampel, H.; Forbes, I.; Pearsall, N. M.; Unold,
T. Earth Abundant Thin Film Solar Cells from Co-Evaporated Cu2SnS3 Absorber Layers. J. Alloys
Compd. 2016, 689, 182–186.
(12) Vadivel, S.; Maruthamani, D.; Paul, B.; Dhar, S. S.; Habibi-Yangjeh, A.; Balachandran,
S.; Saravanakumar, B.; Selvakumar, A.; Selvam, K. Biomolecule-Assisted Solvothermal Synthesis
of Cu2SnS3 Flowers/RGO Nanocomposites and Their Visible-Light-Driven Photocatalytic
Activities. RSC Adv. 2016, 6, 74177–74185.
105
(13) Guo, Y.; Yin, X.; Yang, Y.; Que, W. Construction of ZnO/Cu2SnS3 Nanorod Array Films
for Enhanced Photoelectrochemical and Photocatalytic Activity. RSC Adv. 2016, 6, 104041–
104048.
(14) Sun, W.; Ye, Y.; You, Y.; Xu, J. A Top-Down Synthesis of Wurtzite Cu2SnS3 Nanocrystals
for Efficient Photoelectrochemical Performance. J. Mater. Chem. A 2018, 6, 8221−8226.
(15) Fiechter, S.; Martinez, M.; Schmidt, G.; Henrion, W.; Tomm, Y. Phase Relations and
Optical Properties of Semiconducting Ternary Sulfides in the System Cu–Sn–S. J. Phys. Chem.
Solids 2003, 64, 1859–1862.
(16) Zhai, Y.-T.; Chen, S.; Yang, J.-H.; Xiang, H.-J.; Gong, X.-G.; Walsh, A.; Kang, J.; Wei,
S.-H. Structural Diversity and Electronic Properties of Cu2SnX3 (X = S, Se): A First-Principles
Investigation. Phys. Rev. B 2011, 84, 075213.
(17) Liu, Q.; Zhao, Z.; Lin, Y.; Guo, P.; Li, S.; Pan, D.; Ji, X. Alloyed (ZnS)x(Cu2SnS3)1–x and
(CuInS2)x(Cu2SnS3)1–x Nanocrystals with Arbitrary Composition and Broad Tunable Band Gaps.
Chem. Comm. 2011, 47, 964–966.
(18) Fan, F.-J.; Wu, L.; Gong, M.; Liu, G.; Wang, Y.-X.; Yu, S.-H.; Chen, S.; Wang, L.-W.;
Gong, X.-G. Composition and Band Gap Tunable Synthesis of Wurtzite-Derived
Cu2ZnSn(S1−xSex)4 Nanocrystals: Theoretical and Experimental Insights. ACS Nano 2013, 7,
1454−1463.
(19) Singh, A.; Singh, S.; Levcenko, S.; Unold, T.; Laffir, F.; Ryan, K. M. Compositionally
Tunable Photoluminescence Emission in Cu2ZnSn(S1−xSex)4 Nanocrystals. Angew. Chem., Int. Ed.
2013, 52, 9120−9124.
106
(20) Zhang, X.; Guo, G.; Ji, C.; Huang, K.; Zha, C.; Wang, Y.; Shen, L.; Gupta, A.; Bao, N.
Efficient Thermolysis Route to Monodisperse Cu2ZnSnS4 Nanocrystals with Controlled Shape and
Structure. Sci. Rep. 2015, 4, 5086.
(21) Kovalenko, M. V.; Scheele, V.; Talapin, D. V. Colloidal Nanocrystals with Molecular
Metal Chalcogenide Surface Ligands. Science 2009, 324, 1417–1420.
(22) Tang, J.; Kemp, K. W.; Hoogland, S.; Jeong, K. S.; Liu, H.; Levina, L.; Furukawa, M.;
Wang, X. H.; Debnath, R.; Cha, D. K.; Chou, K. W.; Fischer, A.; Amassian, A.; Asbury, J. B.;
Sargent, E. H. Colloidal-Quantum-Dot Photovoltaic using Ligand Passivation. Nat. Mater. 2011,
10, 765–771.
(23) Webber, D. H.; Brutchey, R. L. Alkahest V2VI3 Chalcogenides: Dissolution of Nine
Semiconductors in a Diamine–Dithiol Solvent Mixture. J. Am. Chem. Soc. 2013, 135,
15722−15725.
(24) Koskela, K. M.; Strumolo, M. J.; Brutchey, R. L. Progress of Thiol-Amine ‘Alkahest’
Solutions for Thin Film Deposition. Trends Chem. 2021, 3, 1061–1073.
(25) Zhao, Y.; Yuan, S.; Chang, Q.; Zhou, Z.; Kou, D.; Zhou, W.; Qi, Y.; Wu, S. Controllable
Formation of Ordered Vacancy Compound for High Efficiency Solution Processed Cu(In,Ga)Se2
Solar Cells. Adv. Funct. Mater. 2021, 31, 2007928.
(26) Zhao, Y.; Zhao, X.; Kou, D.; Zhou, W.; Zhou, Z., Yuan, S.; Qi, Y.; Zheng, Z.; Wu, S. Local
Cu Component Engineering to Achieve Continuous Carrier Transport for Enhanced Kesterite
Solar Cells. ACS Appl. Mater. Interfaces 2021, 13, 795-805.
(27) McCarthy, C. L.; Downes, C. A.; Schueller, E. C.; Abuyen, K.; Brutchey, R. L. Method
for the Solution Deposition of Phase-Pure CoSe2 as an Efficient Hydrogen Evolution Reaction
Electrocatalyst. ACS Energy Lett. 2016, 1, 607-611.
107
(28) McCarthy, C. L.; Downes, C. A.; Brutchey, R. L. Room Temperature Dissolution of Bulk
Elemental Ni and Se for Solution Deposition of a NiSe2 HER Electrocatalyst. Inorg. Chem. 2017,
56, 10143-10146.
(29) Zuo, Y.; Li, J.; Yu, X.; Du, R.; Zhang, T.; Wang, X.; Arbiol, J.; Llorca, J.; Cabot, A. A
SnS2 Molecular Precursor for Conformal Nanostructured Coatings. Chem. Mater. 2020, 32, 2097–
2106.
(30) Hasan, M. R.; Arinze, E. S.; Singh, A. K.; Oleshko, V. P.; Guo, S.; Rani, A.; Cheng, Y.;
Kalish, I.; Zaghloul, M. E.; Rao, M. V.; Nguyen, N. V.; Motayed, A.; Davydov, A. V.; Thon, S.
M.; Debnath, R. An Antimony Selenide Molecular Ink for Flexible Broadband Detectors. Adv.
Electron. Mater. 2016, 2, 1600182.
(31) McCarthy, C. L.; Brutchey, R. L. Solution Deposited Cu2BaSnS4-xSex from a Thiol–Amine
Solvent Mixture. Chem. Mater. 2018, 30, 304−308.
(32) Koskela, K. M.; Melot, B. C.; Brutchey, R. L. Solution Deposition of a Bournonite
CuPbSbS3 Semiconductor Thin Film from the Dissolution of Bulk Materials with a Thiol–Amine
Solvent Mixture. J. Am. Chem. Soc. 2020, 142, 6173−6179.
(33) Nagel, A.; Range, K.J. Verbindungsbildung im System Ag2 S-Ge Se2-Ag I. Zeitschrift fuer
Naturforschung, Teil B: Anorganische Chemie, Organische Chemie 1978, 33, 1461–1464. (ICSD:
41711)
(34) Hayashi, M.; Shiro, Y.; Oshima, T.; Murata, H. The Vibrational Assignment, Rotational
Isomerism and Force Constants of 1,2- Ethanedithiol. Bull. Chem. Soc. Jpn. 1965, 38, 1734−1740.
(35) Nandy, S. K.; Mukherjee, D. K.; Roy, S. B.; Kastha, G. S. Vibrational Spectra and
Rotational Isomerism in 2-Mercaptoethanol. Can. J. Chem. 1973, 51, 1139.
108
(36) Chen, X.; Wada, H.; Sato, A.; Mieno, M. Synthesis, Electrical Conductivity, and Crystal
Structure of Cu4Sn7S16 and Structure Refinement of Cu2SnS3. J. Solid State Chem. 1998, 139, 144–
151.
(37) Ng, M. T.; Boothroyd, C. B.; Vittal, J. J. One-Pot Synthesis of New-Phase AgInSe2
Nanorods, J. Am. Chem. Soc. 2006, 128, 7118–7119.
(38) Shen, X.; Hernandez-Pagan, E. A.; Zhou, W.; Puzyrev, Y. S.; Idrobo, J.-C.; Macdonald, J.
E.; Pennycock, S. J.; Pantelides, S. T. Interlaced Crystals having a Perfect Bravais Lattice and
Complex Chemical Order Revealed by Real-Space Crystallography. Nat. Comm. 2014, 5, 5431.
(39) Tiwari, D.; Chaudhuri, T. K.; Shripathi, T.; Deshpande, U. Synthesis of Earth-Abundant
Cu2SnS3 Powder using Solid State Reaction. J. Phys. Chem. Solids 2014, 75, 410–415.
(40) Cheng, A.-J.; Manno, M.; Khare, A.; Leighton, C.; Campbell, S. A.; Aydil, E. S. Imaging
and Phase Identification of Cu2ZnSnS4 Thin Films Using Confocal Raman Spectroscopy. J. Vac.
Sci. Technol., A 2011, 29, 051203.
(41) Ge, J.; Yan, Y. Synthesis and Characterization of Photoelectrochemical and Photovoltaic
Cu2BaSnS4 Thin Films and Solar Cells. J. Mater. Chem. C 2017, 5, 6406−6419.
(42) Koskela, K. M.; Tadle, A. C.; Chen K.; Brutchey, R. L. Solution Processing Cu3BiS3
Absorber Layers with a Thiol–Amine Solvent Mixture. ACS Appl. Energy Mater. 2021, 4, 11026–
11031.
(43) Koskela, K. M.; Quiton, S. J.; Sharada, S. M.; Williams, T. J.; Brutchey, R. L. Kinetics and
Mechanistic Details of Bulk ZnO Dissolution Using a Thiol-Imidazole System. Chem. Sci. 2022,
13, 3208–3215.
(44) Zhuang, Z.; Lu, X.; Peng, Q.; Li, Y. A Facile “Dispersion–Decomposition” Route to Metal
Sulfide Nanocrystals. Chem. Eur. J. 2011, 17, 10445–10452.
109
(45) Heo, J.; Kim, G.-H.; Jeong, J.; Yoon, Y. J.; Seo, J. H.; Walker, B.; Kim, J. Y. Clean
Thermal Decomposition of Tertiary-Alkyl Metal Thiolates to Metal Sulfides: Environmentally-
Benign, Non-Polar Inks for Solution-Processed Chalcopyrite Solar Cells. Sci. Rep. 2016, 6, 36608.
(46) Kino, T.; Kuzuya, T.; Itoh, K.; Sumiyama, K.; Wakamatsu, T.; Ichidate, M. Synthesis of
Chalcopyrite Nanoparticles via Thermal Decomposition of Metal-Thiolate. Mat. Trans. 2008, 49,
435–438.
(47) Kuyuza, T.; Yamamuro, S.; Hihara, T.; Sumiyama, K. Water-Free Synthesis of
Monodisperse Cu2S Nanocrystals. Chem. Lett. 2004, 33, 352–353.
(48) Barone, G.; Chaplin, T.; Hibbert, T. G.; Kana, A. T.; Mahon, M. F.; Molloy, K. C.;
Worsley, I. D.; Parkin, I. P.; Price, L. S. Synthesis and Thermal Decomposition Studies of Homo-
and Heteroleptic Tin(IV) Thiolates and Dithiocarbamates: Molecular Precursors for Tin Sulfides.
J. Chem. Soc., Dalton Trans. 2002, 1085–1092.
110
Chapter 4. Solution Deposition of a Bournonite CuPbSbS3 Semiconductor Thin Film from
the Dissolution of Bulk Materials with a Thiol-Amine Solvent Mixture*
*Published – Koskela, K. M.; Melot, B. C.; Brutchey, R. L. J. Am. Chem. Soc. 2020, 142, 6173–
6179.
4.1 Abstract
There is a considerable interest in the exploration of new solar absorbers that are
environmentally stable through the visible and possess a polar crystal structure. Bournonite
CuPbSbS3 is a naturally occurring sulfosalt mineral that crystallizes in the non-centrosymmetric
Pmn21 space group and possesses an optimal band gap for single junction solar cells; however, the
synthetic literature on this quaternary semiconductor is sparse and it has yet to be deposited and
studied as a thin film. Here we describe the ability of a binary thiol-amine solvent mixture to
dissolve the bulk bournonite mineral as well as inexpensive bulk CuO, PbO, and Sb2S3 precursors
at room temperature and ambient pressure to generate an ink. The synthetic compound ink derived
from the dissolution of the bulk binary precursors in the right stoichiometric ratios yields phase-
pure thin films of CuPbSbS3 upon solution deposition and annealing. The resulting semiconductor
thin films possess a direct optical band gap of 1.24 eV, an absorption coefficient ~10
5
cm
–1
through
the visible, carrier mobility in the range of 0.01-2.4 cm
2
(V•s)
–1
, and carrier concentrations of 10
18
– 10
20
cm
–3
. These favorable optoelectronic properties suggest CuPbSbS3 thin films are excellent
candidates for solar absorbers.
111
4.2 Introduction
The discovery of hybrid lead halide perovskite solar absorbers has garnered massive
attention because of their high power conversion efficiencies in solar cells, which are now in excess
of 23%, in addition to their ability to be inexpensively solution processed.
1-3
The high power
conversion efficiencies realized for these hybrid lead halide perovskites can be attributed, in part,
to their long minority carrier lifetimes (~280 ns)
4
and diffusion lengths (up to ~175 µm).
5
It has
been suggested that the presence of polar domains within MAPbI3 (MA = methylammonium) help
facilitate the low recombination rates and subsequent spatial separation of charge carriers.
6
Unfortunately, devices based on hybrid lead halide perovskites suffer from environmental
instability issues and short device lifetimes (under ambient conditions) because of moisture
sensitivity.
7
As such, there is interest in the discovery of new thin film solar absorber candidates
that possess greater environmental stability.
In a recent study by Wallace et al., the authors screened nearly 200 naturally occurring
multinary minerals to identify dark colored materials (translating to suitable band gaps Eg = 1.0-
1.7 eV) that also assume crystal structures with a polar point group.
8
By screening for naturally
occurring minerals, the resulting materials possess thermodynamic stability and should not have
the same environmental instability issues inherent to hybrid lead halide perovskites. Polar
structures may decrease exciton binding energies and reduce recombination rates in the material;
moreover, a polar crystal structure may minimize the chance of dipole-disallowed transitions and
a corresponding reduction in oscillator strength at the absorption onset for direct band gap
materials.
8-10
One of the resulting materials that satisfied the selection criteria out of the naturally
occurring multinary minerals that were screened was bournonite CuPbSbS3. Bournonite CuPbSbS3
is a sulfosalt mineral (Strunz 2.GA.50), which crystallizes in the orthorhombic Pmn21 space group
112
with experimentally reported band gaps from 1.20 eV
11
to 1.31 eV
12
that are optimal for single
junction solar cells. Structurally, bournonite is derivative of the naturally occurring stibnite (Sb2S3)
structure, where the Pb
2+
cations alternately occupy the Sb
3+
positions, and Cu
+
occupies
tetrahedral holes to charge compensate (Figure 4.1).
8,13
The synthetic literature on CuPbSbS3 is
sparse, with only a handful of solid-state syntheses
11,14,15
and one solvothermal synthesis having
been reported thusfar.
12
The solid-state syntheses of CuPbSbS3 are energy intensive – requiring
annealing temperatures >550 ˚C and annealing times >30 d – and result in bulk material with
persistent binary PbS impurities.
14,15
To date, this material has not been deposited or studied in
thin film form, which is needed for future application work.
Figure 4.1. Crystal structure of bournonite CuPbSbS3 (space group Pmn21).
With respect to thin film deposition, solution methods (e.g., spin coating, spray coating,
etc.) have the potential to significantly reduce deposition costs over more traditional and energy
intensive physical vapor deposition methods.
16,17
Solution processable molecular inks are known
113
to give excellent film homogeneity;
18-20
however, the dissolution of inexpensive bulk material
precursors is significantly hampered by the general insolubility of these materials in typical
solvents. In response, we developed an “alkahest” solvent system that utilizes a binary mixture of
short chain thiols and amines that is capable of dissolving over 100 bulk materials, including bulk
metals, metal chalcogenides, and metal oxides.
21-27
The resulting inks return phase-pure
chalcogenide thin films upon solution deposition and mild annealing through a dissolve and
recover approach, making it potentially suitable for large-scale solution processing.
27
Indeed, thiol-
amine inks have been effectively utilized for the solution deposition of small area chalcopyrite and
kesterite-based solar cells with excellent power conversion efficiencies.
28-30
The relatively mild
conditions required for thin film deposition from the thiol-amine inks is particularly promising for
sulfosalt materials in order to minimize reaction with back contact materials, such as Mo, in thin
film solar cell architectures.
31
Herein, we are the first to demonstrate the deposition of bournonite
CuPbSbS3 thin films. The viability of the resulting solution-processed thin films as absorber layers
is assessed with a combination of optical and electrical measurements.
4.3 Results and Discussion
Bulk powders of CuO, PbO, and Sb2S3 (1.0:1.0:0.53 mol/mol/mol, respectively) were
mixed as solid precursors to formulate the compound CuPbSbS3 ink by dissolution in a 1:4
(vol/vol) binary solvent system comprised of ethanedithiol (EDT) and ethylenediamine (en),
respectively, giving an overall concentration of ~60 mg of total solids per mL of solvent. In this
solvent mixture of 1:4 (vol/vol) EDT and en, CuO, PbO, and Sb2S3 have approximate room
temperature and ambient pressure solubility limits of 10-15, 20-30, and 25-30 wt%, respectively.
It has been shown that bulk oxide precursors fully dissolve, with the likely by-product being water,
114
and transform into the corresponding sulfide with the thiol acting as a sulfur source.
32
All of the
ink components were added together and stirred at room temperature and ambient pressure, giving
full dissolution in < 20 min to yield an optically clear, free-flowing orange-brown solution (Figure
4.2a). The ink was stable (i.e., free from precipitates and color change) both in air and under inert
atmosphere for several weeks at room temperature.
Thermogravimetric analysis (TGA) indicated an endpoint of decomposition of the dried
ink well before 350 ˚C (Figure 4.2b), while the associated FT-IR bands attributable to organic
species from the thiol-amine solvent system disappear upon heating the dried ink from 100 to
400 ˚C, corroborating the thermal volatilization and decomposition of organic content (Figure
4.2c). The strongest IR bands in the spectrum of the ink dried to 100 ˚C correspond to EDT (i.e.,
2970 cm
–1
ν(C−H) stretch, 2930 cm
−1
ν(C−H) stretch, and 1430 cm
−1
d(CH2) bend).
33
The
sulfhydryl ν(S−H) stretching band is noticeably absent from the FT-IR spectrum of the dried ink,
which is in agreement with previous reports that showed complete deprotonation of EDT in thiol-
amine inks.
22,26
This is also confirmed by the shift of the ν(C–S) stretch from 699 cm
–1
for
protonated EDT to 675 cm
–1
in the ink.
26
No significant IR bands were observed above 3000 cm
−1
,
where the ν(N–H) stretches are expected, indicating that en may be mostly absent in the ink after
drying at 100 ˚C.
115
Figure 4.2. a) Photograph of the synthetic ink prepared from the dissolution of bulk CuO, PbO,
and Sb2S3 powders in a 1:4 (vol/vol) mixture of EDT and en alongside a 1 cm
2
CuPbSbS3 thin
film. b) TGA trace of the dried ink showing an endpoint of decomposition < 350 ˚C. c) FT-IR
spectra of the ink dried at 100 ˚C under vacuum and annealed to 400 ˚C under flowing nitrogen.
While the TGA and FT-IR data suggest that annealing to temperatures between 350-400
˚C is sufficient to remove the volatile organic content and decomposition products from the ink,
powder X-ray diffraction (XRD) studies revealed that higher annealing temperatures are required
to recover phase-pure CuPbSbS3. The phase evolution of bulk, drop-cast films of CuPbSbS3 was
tracked by ex situ powder XRD as a function of time and temperature (Figure 4.3). At low
temperatures and early times (i.e., 330 ˚C, 30 min) the predominant phases present were binary
PbS and ternary CuSbS2 with a minor fraction of bournonite CuPbSbS3. By increasing the
annealing temperature and time (i.e., 450 ˚C, 12 h), the amount of PbS and CuSbS2 gradually
decrease to yield an increasing fraction of CuPbSbS3, presumably via solid-state reaction (CuSbS2
+ PbS ® CuPbSbS3). A dark gray material was recovered after annealing the drop-cast dried ink
to 450 ˚C for 96 h, which was confirmed to be phase-pure orthorhombic CuPbSbS3 by powder
XRD, as shown in Figure 4.4. Rietveld refinement of the XRD pattern using the Pmn21 space
group gives lattice parameters of a = 7.8158(58), b = 8.1515(17), and c = 8.6729(54) Å, and a unit
cell volume of V = 552.5634(34) Å
3
. These values are in close agreement with the previously
116
reported values for synthetic bulk bournonite (i.e., a = 7.810, b = 8.150, and c = 8.701 Å; V =
553.85 Å
3
).
14
A table of refinement parameters are listed in Table 4.1
Figure 4.3. a) Ex situ powder XRD patterns of a dropcast ink annealed to various temperatures
and times showing the phase evolution of CuPbSbS3 indexed with CuSbS2 and PbS. b) Powder
XRD pattern of dropcast ink annealed to 400 ˚C for 30 min showing substantial PbS and CuSbS2
impurities. c) Powder XRD pattern of dropcast ink annealed to 450 ˚C for 12 h showing reduced
PbS and CuSbS2 impurities.
117
Figure 4.4. Powder XRD pattern of phase-pure CuPbSbS3 drop-cast from the ink and annealed to
450 ˚C, with the results from a Rietveld refinement to the orthorhombic Pmn21 structure. Cross
marks (+) represent experimental data points and pink tick marks represent individual reflections
of the bournonite structure with the difference pattern shown below in blue. (l = 1.5406 Å; Rwp =
4.96%; c
2
= 2.48)
Table 4.1. Structural parameters of phase-pure bournonite CuPbSbS3 extracted from Rietveld
analysis.
Atom Multiplicity Occupancy x y z Uiso (Å
2
)
Cu1 4 1.0 0.25038(9) 0.26601(5) 0.40833(1) 0.0167(7)
Pb1 2 1.0 0.0 0.07523(4) 0.994008 0.0102(9)
Pb2 2 1.0 0.0 0.44129(3) 0.67268(6) 0.00100
Sb1 2 1.0 0.0 0.92307(8) 0.54000(1) 0.00100
Sb2 2 1.0 0.0 0.50855(9) 0.15134(9) 0.00100
S1 2 1.0 0.0 0.22264(8) 0.28514(1) 0.00100
S2 2 1.0 0.0 0.75425(5) 0.75841(6) 0.00100
S3 4 1.0 0.24232(8) 0.10121(2) 0.64531(3) 0.00100
S4 4 1.0 0.26614(8) 0.58338(3) 0.45166(7) 0.00100
Space Group Pmn21
a (Å) 7.8158(58)
b (Å) 8.1515(17)
c (Å) 8.6729(54)
V (Å
3
) 552.5634(34)
a = b = g 90˚
Rwp 4.96%
c
2
2.48
118
As seen with quaternary chalcogenides, such as kesterite and stannite, X-ray diffraction is
not always sufficient to assess phase purity of thin film samples.
34,35
Therefore, Raman
spectroscopy was also used to evaluate the phase purity of our CuPbSbS3 thin films (Figure 4.5).
Using a 785 nm excitation wavelength, Raman bands corresponding to bournonite Sb-S bending
modes were observed at 332 cm
-1
and 297 cm
-1
and a lattice mode at 198 cm
-1
that match well with
a naturally occurring single crystal sample.
36
Thin films of CuSbS2 have Raman active modes at
ca. 250 cm
-1
and 350 cm
-1
and thin films of PbS have Raman active modes at 161 cm
-1
, and 263
cm
-1
.
37-39
The absence of CuSbS2 and PbS Raman active modes further supports the phase purity
of our CuPbSbS3 thin films.
Figure 4.5. Raman spectra of a 570 nm CuPbSbS3 thin film on glass annealed to 450 °C for 20
min, along with a blank borosilicate substrate.
With antimony being present in the largest excess in the ink formulation that returns phase-
pure CuPbSbS3, it is likely volatilized during annealing as Sb2S3, as has been observed with other
200 400 600
Wavenumber (cm
-1
)
Intensity (a.u.)
332 cm
-1
198 cm
-1
1h Glass Substrate
Raman Spectra
3 Point Data Smooth
1 h Thin Film
CuPbSbS
3
Raman
Spectra
297
cm
-1
119
multinary antimony-containing sulfides.
40
Inductively coupled plasma optical emission
spectroscopy (ICP-OES) was used to quantify the elemental composition of the resulting phase-
pure, solution-deposited bournonite. An elemental stoichiometry of Cu1.03Pb1.05Sb1.00S3 was
calculated from an average of four analyses. The pseudo-binary PbS–CuSbS2 phase diagram
allows for non-stoichiometry in the range of 46-52 mol% PbS in bournonite, which is within the
experimental stoichiometry of our material.
41
X-ray photoelectron spectroscopy (XPS) was used
to gain information on the valence states of ions in the CuPbSbS3 thin films. A survey scan of a
CuPbSbS3 thin film on Si/SiO2 that had been exposed to ambient conditions is provided in the
Supporting Information (Figure 4.6). The high-resolution spectra and corresponding peak fittings
for the Cu 2p, Pb 4f, Sb 3d, and S 2p regions are given in Figure 4.8a, 4.9a, 4.10a, and 4.11a,
respectively, and the fitted peak positions and peak splitting values for each high-resolution
spectrum are given in Table 4.2. The Cu 2p region can be fit with a single doublet of peaks centered
at 951.3 eV and 931.5 eV that indicates a single Cu
+
environment for copper in the material. This
is consistent with the peak splitting and binding energies for Cu
+
in other quaternary
chalcogenides.
26,42
The lack of strong satellites suggests that there is no significant amount of Cu
2+
in the material, indicating that Cu
2+
in the solid CuO precursor is reduced to Cu
+
upon dissolution
and annealing.
26,42,43
The Pb 4f region can be fit with two sets of doublets, each with a splitting of
~4.8 eV. The observation of two different lead environments has been similarly reported for
PbS,
44,45
with the higher binding energy doublet for CuPbSbS3 (centered at 143.0 and 138.1 eV)
being attributed to oxidized lead species (PbOx) on the surface and the lower binding energy
doublet (centered at 142.7 and 137.9 eV) being attributed to Pb
2+
in a sulfide environment.
Likewise, the Sb 3d region can be fit with two sets of doublets, each with a splitting of ~9.3 eV.
The observation of two distinct environments for antimony has previously been observed in bulk
120
Sb2S3 thin films;
46
here, the appearance of a doublet centered at 539.5 and 529.9 eV is associated
with SbxOy surface species and the doublet centered at 538.3 and 529.0 eV is assigned to Sb
3+
in a
sulfide environment. In the S 2p region, a doublet and a singlet can be deconvoluted from the high-
resolution spectrum. The doublet has a splitting of 1.1 eV which is attributed to the 2p1/2 and 2p3/2
of S
2–
and a broad singlet centered at 163.1 eV assigned to surface oxidation (i.e., SOx).
42
Thus,
XPS analysis verifies the valence states in the material to be Cu
+
Pb
2+
Sb
3+
(S
2–
)3 with evidence for
surface oxides. The observation of surface oxides can be corroborated with the appearance of an
O 1s peak in the survey scan. It is reasonable to observe surface oxides by XPS since our solution-
deposited CuPbSbS3 was not kept in an air-free environment after annealing and amorphous
surface oxides would not be observed by XRD. To determine the extent of oxides present in our
thin films, an in situ Ar+ ion beam treatment was done for 5 min to etch away a few nanometers
of the thin film surface. A survey spectrum of the etched thin film is provided in Figure 4.7. As
can be seen by the Cu 2p, Pb 4f, Sb 3d, and S 2p regions in Figure 4.8b, 4.9b, 4.10b, and 4.11b,
respectively, only slight reductions in oxide peaks are observed, which suggests oxide impurities
may be persistent throughout the thin film using these processing conditions (fitted peak positions
and peak splitting values are given in Table 4.3).
121
Figure 4.6. XPS survey scan of thin film CuPbSbS3 on Si/SiO2 before in situ Ar
+
ion beam milling.
Figure 4.7. XPS survey scan of thin film CuPbSbS3 on Si/SiO2 after in situ Ar
+
ion beam milling.
0 500 1000
Binding Energy (eV)
Intensity (a.u.)
Sb MNN
O KLL
Sb 3s
Cu 2p
Sb 3p
Pb 4p
Cu LMM
O 1s
Sb 3d
Pb 4d
C 1s
S 2s
S 2p
Pb 4f
Sb 2p
Cu 3p, Sb 4p
Pb 5d, Sb 4d 0 500 1000
Binding Energy (eV)
Intensity (a.u.)
Sb MNN
O KLL
Sb 3s
Cu 2p
Sb 3p
Pb 4p
Cu LMM
O 1s
Sb 3d
Pb 4d
C 1s
S 2s
S 2p
Pb 4f
Sb 2p
Cu 3p, Sb 4p
Pb 5d, Sb 4d
122
Figure 4.8. High-resolution XPS spectra for a) Cu 2p before in situ Ar
+
ion beam milling, and b)
Cu 2p after milling.
Figure 4.9. High-resolution XPS spectra for a) Pb 4f before in situ Ar
+
ion beam milling, and b) Pb
4f after milling.
123
Figure 4.10. High-resolution XPS spectra for a) Sb 3d before in situ Ar
+
ion beam milling, and b)
Sb 3d after milling.
Figure 4.11. High-resolution XPS spectra for a) S 2p before in situ Ar
+
ion beam milling, and b) S
2p after milling.
124
Table 4.2. Peak positions and peak splitting from the high-resolution XPS spectra of CuPbSbS3
thin films on Si/SiO2 before in situ Ar
+
ion beam milling.
Element Peak Splitting
(eV)
Peak ID Binding Energy
(eV)
Cu 19.8 2p1/2 951.3
2p3/2 931.5
Pb 4.8 4f5/2 142.7
4f7/2 137.9
Pb (surface PbOx) 4.9 4f5/2 143.0
4f7/2 138.1
Sb 9.3 3d3/2 538.3
3d5/2 529.0
Sb (surface SbxOy) 9.6 3d3/2 539.5
3d5/2 529.9
S 1.1 2p1/2 162.5
2p3/2 161.4
S (surface SOx)
2p 163.1
125
Table 4.3. Peak positions and peak splitting from the high-resolution XPS spectra of CuPbSbS3
thin films on Si/SiO2 after in situ Ar
+
ion beam milling.
Element Peak Splitting
(eV)
Peak ID Binding Energy
(eV)
Cu 19.8 2p1/2 951.3
2p3/2 931.5
Pb 4.8 4f5/2 142.7
4f7/2 137.9
Pb (surface PbOx) 4.9 4f5/2 143.0
4f7/2 138.1
Sb 9.3 3d3/2 538.3
3d5/2 529.0
Sb (surface SbxOy) 9.5 3d3/2 539.4
3d5/2 529.9
S 1.1 2p1/2 162.5
2p3/2 161.4
S (surface SOx)
2p 163.1
To extend the versatility of the thiol-amine solvent system, a natural mineral sample of
bournonite mined from Chihuahua, Mexico was obtained from the Natural History Museum of
Los Angeles. A ground sample of the natural mineral appeared phase pure by powder XRD
(Figure 4.12). An ink containing 60 mg mL
–1
of the natural bournonite sample was fully dissolved
in a 1:4 (vol/vol) mixture of EDT and en, respectively, at room temperature over 12 h. The resulting
ink is an optically clear and free-flowing orange-brown solution that is qualitatively identical to
126
the synthetic ink derived from the dissolution of CuO, PbO, and Sb2S3 (Figure 4.13). Drop-cast
bulk films of the dried ink were annealed at 450 ˚C for 96 h under conditions identical to those
used for the synthetic ink. Interestingly, this returned crystalline CuPbSbS3 with a significant PbS
impurity (Figure 4.14). Taken with the existing literature on synthetic bulk CuPbSbS3,
14
this result
reinforces the difficulty of isolating phase-pure bournonite even when starting from a seemingly
phase-pure naturally occurring mineral. This highlights the versatility of the thiol-amine solvent
system to fine tune synthetic ink compositions for the recovery of phase-pure multinary
chalcogenides by easily tuning the ratios of the bulk binary ink constituents.
Figure 4.12. a,b) Natural bournonite sample obtained from the Los Angeles County Natural
History Museum (catalog number: NHMLA 67450, mined from Chihuahua, Mexico), and c)
powder XRD pattern of natural sample indexed to CuPbSbS3 (PDF: 01-073-5993). Inset shows
fully dissolved ink.
127
Figure 4.13. Photograph of CuPbSbS3 inks prepared from the dissolution of CuO, PbO, and Sb2S3
in a 1:4 (v/v) mixture of EDT and en (left), and an ink of a natural bournonite sample (right)
dissolved in the same solvent mixture with the same concentration (~60 mg mL
–1
). Solid
components of inks are shown in front of vials.
Figure 4.14. Powder XRD pattern of ink of natural bournonite sample annealed to 450 ˚C for 96 h
and indexed to CuPbSbS3 (PDF: 01-073-5993) and PbS (PDF: 01-077-0244).
To demonstrate the utility of the alkahest to give high-quality thin films, a 2´ concentrated
ink (120 mg/mL) was used to solution deposit 3 coats onto a glass substrate via spin coating at
20 40 60
2-Theta (°)
Intensity (a.u.)
CuPbSbS
3
PbS
Natural Bournonite
ink annealed to 450
°C for 96 h
128
3000 rpm for 1 min with annealing to 390 ˚C between coats and a final anneal to 450 ˚C for 20
min.
While phase-pure CuPbSbS3 thin films can be obtained by annealing to 390 ˚C for 10 min,
improved grain density in the thin films was achieved by annealing to 450 ˚C for 20 min (Figure
4.15a and 4.16). Phase-pure CuPbSbS3 thin films are obtained at lower temperatures than the bulk,
drop cast films (i.e., 450 ˚C, 96 h for bulk, drop cast films vs 390 ˚C, 10 min for spin coated thin
films). The differences in annealing times between bulk and thin films can be explained by solid-
state diffusion in a thin film proceeding more readily than in a bulk powder. In the bulk, solid-state
diffusion is limiting, whereas for thin films the formation of the desired phase is nucleation
limited.
47
If the thin films are annealed at 450 ˚C for extended times (i.e., > 60 min), PbS and
CuSbS2 impurity phases begin to appear, suggesting that the CuPbSbS3 thin film disproportionates
at high temperatures and extended annealing times. Solution deposition results in specularly
reflective thin films of CuPbSbS3 that are dark gray in color and free from imperfections (i.e., pin
holes, microcracks, edge effects, striations). Cross-sectional scanning electron microcopy (SEM)
was used to assess film thickness. The resulting thin films possessed an average thickness of 565
nm.
129
Figure 4.15. a) Cross-sectional SEM micrograph of a CuPbSbS3 thin film deposited on a
borosilicate glass substrate. b) Plot of absorption coefficient (a) as a function of wavelength, and
c) Tauc plot extrapolated to estimate a direct optical band gap of 1.24 eV.
Figure 4.16. Cross-sectional SEM image of a ~1 µm CuPbSbS3 thin film derived from 3 coats
spun at 2000 rpm and annealed to 390 ˚C for 10 min between each coat.
130
Figure 4.17. Transmittance spectra in the integrating sphere using a 570 nm thin film of
CuPbSbS3.
The absorption coefficient and optical band gap of the resulting CuPbSbS3 was measured
by UV-vis-NIR spectroscopy. An absorption spectrum derived from transmittance data (Figure
4.17) and the optical band gap from recovered powder using an integrating sphere are provided in
Figure 4.15b and 4.15c, respectively. An absorption coefficient of a = 3.0 ´ 10
4
cm
–1
at 826 nm
(1.5 eV) rises to a = 1.1 ´ 10
5
cm
–1
at 516 nm (2.4 eV) for a 570 nm thick thin film. A direct
optical band gap of Eg,dir = 1.24 eV was determined after extrapolating the square of the linear
portion of the diffuse reflectance spectrum (Figure 4.15c); this band gap lies within the range of
previously reported experimental values for bournonite (ca. 1.20 eV to 1.31 eV)
11,12
and is slightly
lower than the theoretically predicted value (1.41 eV)
8
.
The electronic transport properties of the resulting CuPbSbS3 thin films were studied using
the Van der Pauw geometry, with measurements performed in a physical property measurement
system (PPMS). Measurements were conducted in the temperature range of 10-300 K, with the
resistivity as a function of temperature behaving like a typical intrinsic semiconductor (Figures
400 600 800 1000
0
10
20
30
40
Wavelength (nm)
%T
131
4.18, 4.19). Depending on the film, ranging in thickness from 562-570 nm, carrier concentrations
were found to be between 6.2 ´ 10
18
– 3.5 ´ 10
20
cm
–3
with the associated carrier mobilities ranging
from 0.01-2.4 cm
2
(V•s)
–1
. These values are in the lower range of previously reported values for
solution processed hybrid lead iodide perovskite thin films (e.g., 0.2-71 cm
2
(V•s)
–1
),
48
but are
consistent with CuPbSbS3 being a heavily doped p-type semiconductor. Hall measurements and
the p-type conductivity are very sensitive to the processing conditions. Natural samples of
bournonite have been reported to have n-type conductivity but density functional theory
calculations suggest n-type behavior in CuPbSbS3 to be highly unlikely.
13,49
The high carrier
concentrations may be due to small off-stoichiometry in the solution-processed films or oxide
defects trapped between the spun-coated layers, as the inks and films are exposed to air during
film processing as evident by oxides in the XPS data before and after in situ Ar
+
ion beam milling.
Carrier concentrations of solution processed and vacuum deposited quaternary Cu2ZnSn(S,Se)4
semiconductors have shown carrier concentrations ranging from 10
17
to 10
19
cm
–3
attributed to
differences in grain structures/boundaries and incorporated impurities, with carrier concentrations
reported as high as 3.1´10
20
cm
–3
.
34,35
Figure 4.18. Resistivity (r) of a CuPbSbS3 thin film as a function of temperature.
132
Figure 4.19. Representative resistivity measurements on different solution processed bournonite
thin film samples. Plots are representative of semiconducting nature of CuPbSbS3. Resistances
were collected until ohmic contact was lost (data omitted).
There is a single report on the Hall coefficient of a single crystal of bournonite collected in
the range from 277-833 K,
11
but the electronic properties of phase-pure thin films of bournonite
have not been explored. To further evaluate the potential use of this material for solar energy
conversion, the photoresponse of a CuPbSbS3 thin film device was tested. The CuPbSbS3 absorber
layer was spin coated on a patterned fluorine-doped SnO2 (FTO) substrate with a lateral spacing
of ~20 μm. The device was exposed to chopped white light by an AM1.5G filtered 300 W xenon
arc lamp under ambient conditions and yielded a photoresponse of >225 nA at a potential of -500
mV (Figure 4.20). The electronic properties of our thin films, combined with their high absorption
coefficient, and near-optimal direct band gap suggest that CuPbSbS3 deposited with this thiol-
amine method may yield suitable absorber layers for photovoltaic devices given the proper
deposition conditions and device architecture.
50
133
Figure 4.20. Photoresponse at 25 ˚C under ambient conditions of a CuPbSbS3 thin film deposited
on FTO. The device was tested under chopped white light at a potential of -500 mV. A 300 W
Xenon arc lamp calibrated to AM1.5G illumination was employed for this measurement. Arrows
indicate when light was turned on or off.
4.4 Experimental
4.4.1 General Considerations
All materials were used as received. 1,2-Ethylenediamine (en, 99.5%), copper(II) oxide
(CuO, 99.99%), lead(II) oxide (PbO, 99.999%), and antimony(III) sulfide (Sb2S3, 99.995%) were
purchased from Sigma Aldrich. 1,2-Ethanedithiol (EDT, 98+%) was purchased from Alfa Aesar.
Copper, lead, and antimony ICP standards (1000 ppm in 2% aqueous nitric acid) were purchased
from Perkin Elmer. A natural sample of the mineral bournonite (catalog no. 67450; mined from
Chihuahua, Mexico) was obtained from the Natural History Museum of Los Angeles County.
0 5 10 15
-5400
-5200
-5000
-4800
Time (min)
Current (nA)
Light
On
Light
Off
134
4.4.2 Synthetic Ink Preparation
For the preparation of a typical ink, 9.9 mg (0.124 mmol) CuO, 25.9 mg (0.116 mmol)
PbO, and 22.5 mg (0.066 mmol) Sb2S3 were stirred together in a mixture of 0.2 mL EDT and 0.8
mL en for 12 h at 25 ˚C under ambient conditions. Full dissolution occurred, resulting in an
optically clear, free-flowing orange-brown solution. For spin coating, a 2´ concentrated ink was
formulated using 9.9 mg (0.124 mmol) CuO, 25.9 mg (0.116 mmol) PbO, and 22.5 mg (0.066
mmol) Sb2S3 in a mixture of 0.1 mL EDT and 0.4 mL en, likewise resulting in an optically clear,
free-flowing orange-brown solution. If the solvents solidified upon the initial addition to the bulk
precursors, a heat gun was used to solubilize the ink.
4.4.3 Thin Film Deposition
Films were spin coated on 1 cm
2
borosilicate glass substrates that were cleaned by
sequential bath sonication in acetone, isopropyl alcohol, and deionized water (20 min each),
followed by drying under flowing nitrogen. The 2´ concentrated ink was spin coated onto the
substrate using a Laurell Technologies Corporation WS400Ez-6NPPLITE single-wafer spin
processor at 3000 rpm for 1 min under a flowing nitrogen atmosphere. In between coats, the films
were annealed at 390 ˚C for 10 min in a temperature-controlled aluminum annealing chamber
under flowing nitrogen and allowed to cool naturally to room temperature before the next coat of
ink was applied. After 3 coats, the films were annealed to 450 ˚C in a tube furnace under flowing
nitrogen for 20 min and allowed to naturally cool to room temperature. Films were exposed to air
between coats.
135
4.4.4 Natural Bournonite Ink Preparation
60 mg of the natural bournonite sample was crushed with an agate mortar and pestle and
subsequently stirred in a mixture of 0.2 mL EDT and 0.8 mL en for 12 h at 25 ˚C. This resulted in
full dissolution giving an optically clear, orange-brown solution. The ink was drop cast onto a
borosilicate glass substrate and subsequently annealed to 350 ˚C in a temperature-controlled
aluminum annealing chamber under flowing nitrogen for 20 min before cooling to room
temperature. The bulk material was then annealed to 450 ˚C in a tube furnace under flowing
nitrogen for 96 h and allowed to naturally cool to room temperature.
4.4.5 Material Characterization
Thermal gravimetric analysis (TGA) was performed on a TA Instruments TGA Q50
instrument and samples were run in an alumina crucible under a flowing nitrogen atmosphere with
a heating rate of 5 ˚C min
–1
. The TGA samples were prepared by drying the ink in an alumina
crucible to 140 ˚C under a flowing nitrogen atmosphere in an aluminum annealing chamber prior
to TGA analysis to avoid excess corrosion of the thermocouple in the TGA. Fourier transform
infrared (FT-IR) spectra were measured on a Bruker Vertex 80 spectrometer. The samples were
prepared by drop casting the CuPbSbS3 ink onto a ZnSe window and drying to 100 ˚C before
annealing to 450 ˚C under a flowing stream of nitrogen. FT-IR spectra were background corrected
with ~20 iterations. Powder X-ray diffraction (XRD) patterns were collected using a Rigaku
Miniflex600 operated at 40 mA and 35 kV, in the 2q range of 10-70˚ using Cu Ka radiation (l =
1.5406 Å). For powder diffraction studies, inks were drop cast on a glass slide and dried to 330-
390 °C in an aluminum annealing chamber under flowing nitrogen. The powders were collected
from the glass slide using a razor blade and crushed in an agate mortar and pestle before being put
136
into alumina crucible for annealing at elevated temperatures in a tube furnace under flowing
nitrogen. For structural refinements, the step size and collection time were 0.05˚ and 3 s step
–1
,
respectively. All patterns were recorded under ambient conditions. Rietveld refinements were
carried out using the General Structure Analysis System (GSAS) software package. The following
parameters were refined: (1) scale factor, (2) background (modeled using a shifted Chebyschev
polynomial function), (3) peak shape (modeled using a modified Thompson-Cox-Hastings pseudo-
Voigt function), (4) lattice constants (a, b, c), (5) fractional atomic coordinates of the Cu, Pb, Sb,
and S atoms constrained by the site symmetry, (6) preferred orientation using a spherical harmonic
model, and (7) isotropic thermal parameters for each chemical species. The Rwp and c
2
indicators
were employed to assess the quality of the refined structural models. UV-vis-NIR transmittance
spectroscopy was performed on a Perkin Elmer Lambda 950 equipped with a 150-mm integrating
sphere. The thin film on glass was placed in front of the integrating sphere. Scanning electron
microscopy (SEM) was performed on a JEOL JSM-7001F scanning electron microscope with an
operating voltage of 10 kV. The films were scored with a diamond scribe and broke in half before
they were sputtered with argon before SEM imaging. Inductively-coupled plasma optical emission
spectroscopy (ICP-OES) was performed on an iCap 7400 ICP. All powder samples were digested
with 2 mL of concentrated nitric acid and subsequently diluted to 25 mL with Millipore water in a
volumetric flask. Copper, lead, and antimony ICP standards were prepared at different
concentrations (0.1 ppm, 0.8 ppm, 2 ppm, 5 ppm, 10 ppm) to construct a five-point calibration
curve from which the sample concentrations of Cu, Pb, and Sb could be determined. Raman spectra
were conducted on 570 nm bournonite thin films on glass substrates annealed to 450 °C for 20 min
using a Horiba XploRA confocal Raman microscope with 785 nm excitation. The Raman
microscope was covered with a black tarp to reduce ambient light exposure. X-ray photoelectron
137
spectroscopy (XPS) was performed using a Kratos Axis Ultra X-ray photoelectron spectrometer
with a monochromatic aluminum anode. An operating current of 5 mA and voltage of 12 kV with
a step size of 0.1 eV, a pass energy of 20 eV, and a pressure range of 9 ´ 10
–8
– 1 ´ 10
–9
Torr was
used to acquire 20 high resolution scans for each element. XPS was done on thin films deposited
on Si/SiO2 substrates using the solution deposition method described in the main text. In situ Ar
+
ion beam milling was done for 5 min.
4.4.6 Property Measurements
Temperature and magnetic field-dependent electrical conductivity measurements were
performed on thin films of CuPbSbS3 (ranging in median thickness from 562-570 nm) on a 1 cm
2
borosilicate glass substrate. The film was argon sputtered with a Cressington Sputter Coater 108
(Liverpool, UK) for 90 s to remove the surface oxide layer that arises from exposing the sample
to air in order to establish better ohmic contacts. Copper leads were immediately affixed at each
corner of the thin film using a conductive silver paint (Ted Pella, Inc.). The sample was mounted
in a Quantum Design Physical Properties Measurement System (PPMS), which was used to control
the sample temperature and apply a magnetic field of 10000 Oe. Data were collected using a
Keithley 2182A nanovoltmeter and a Keithley 6220 current source, controlled by a Keithley 7065
Hall effect card. Photoconductivity measurements were performed on a basic device architecture:
Fluorine doped tin oxide (FTO) (~500 nm)/ CuPbSbS3 / FTO (500 nm). The absorber layer was
deposited on a glass substrate patterned with parallel FTO electrodes with a spacing of ~20 μm
that was pre-cleaned as described in the main text. The cleaned FTO substrates were masked with
Kapton tape to leave bare FTO for the electrode connections and the CuPbSbS3 absorber layer was
deposited as described in the main text. The Kapton mask was peeled off and the final anneal to
138
450 °C / 20 min was done without Kapton tape (decomposition temperature of polyimide ~400
°C). Photoconductivity measurements were performed in air at 25 °C using a Keithley 2420
Sourcemeter (sensitivity = 100 pA) in the dark and under white light illumination from an AM1.5G
filtered 300 W xenon arc lamp (Asahi Spectra HAL-320W).
4.5 Conclusions
In summary, we have demonstrated the ability of our alkahest solvent system to solution
process high-quality thin films of bournonite CuPbSbS3 under mild conditions from an ink
comprised of dissolved bulk CuO, PbO, and Sb2S3 in EDT and en. Having the ability to fine tune
the compound ink composition by simply adjusting the stoichiometry of the bulk precursors allows
for the deposition of phase-pure CuPbSbS3. While the same thiol-amine solvent mixture is capable
of dissolving naturally occurring bournonite, this ink returns CuPbSbS3 with PbS impurities
similar to previously reported solid-state syntheses.
The resulting CuPbSbS3 thin films possess a direct optical band gap of 1.24 eV and a high
absorption coefficient in the visible range of ~10
5
cm
–1
. Electronic measurements confirm that the
solution-processed CuPbSbS3 thin film has mobilities in the range of 0.01-2.4 cm
2
(V•s)
–1
and
carrier concentrations of 10
18
–10
20
cm
–3
. This highlights the potential use of bournonite as an
absorber layer in thin film solar cells and demands further study. First generation solar cells of
bournonite solution processed by the dithiocarbamate (DTC) inks with efficiencies exceeding
2.65% further prove the utility of bournonite as a potential solar absorber.
51,52
This method should be generalizable to the solution deposition of other multinary
semiconductor thin films, including compositionally related I-IV-V-VI2 semiconductors such as
CuPbBiS3. Aikinite CuPbBiS3 is another naturally occurring sulfosalt mineral that has recently
139
been identified through the screening of ~800 materials from the Materials Project Database for
favorable properties for potential photovoltaic absorbers.
53
Indeed, preliminary results show that
the same thiol-amine solvent mixture is capable of dissolving a mixture of bulk CuO, PbO, and
Bi2S3 precursors. This unoptimized compound ink returned a mixture of the desired crystalline
CuPbBiS3 phase (Pnma) with a slight PbS impurity upon annealing at 450 ˚C for 48 h (Figure
4.21). These combined results highlight the promise of the alkahest method for the solution
deposition of sulfosalt absorber layers for photovoltaics.
Figure 4.21. Powder XRD pattern of aikinite CuPbBiS3 ink annealed to 450 °C for 48 h and
indexed to CuPbBiS3 (PDF: 01-071-0643) and PbS (PDF: 01-077-0244).
4.6 References
(1) Haegel, N. M.; Margolis, R.; Buonassisi, T.; Feldman, D.; Froitzheim, A.; Garabedian, R.;
Green, M.; Glunz, S.; Henning, H.-M.; Holder, B.; Kaizuka, I.; Kroposki, B.; Matsubara, K.; Niki,
S.; Sakurai, K.; Schindler, R. A.; Tumas, W.; Weber, E. R.; Wilson, G.; Woodhouse, M.; Kurtz,
S. Terawatt-Scale Photovoltaics: Trajectories and Challenges. Science 2017, 356, 141–143.
20 40 60
2-Theta (°)
Intensity (a.u.)
Aikinite (CuPbBiS
3
) PDF:
01-071-0643
CuPbBiS
3
ink annealed at 450
°C for 48 hours
Galena (PbS) PDF: 01-077-0244
140
(2) Shin, S. S.; Yeom, E. J.; Yang, W. S.; Hur, S.; Kim, M. G.; Im, J.; Seo, J.; Noh, J. H.; Seok,
S. I. Colloidally Prepared La-Doped BaSnO3 Electrodes for Efficient, Photostable Perovskite Solar
Cells. Science 2017, 356, 167–171.
(3) Green, M. A.; Ho-Baillie, A.; Snaith, H. J. The Emergence of Perovskite Solar Cells. Nat.
Photonics 2014, 8, 506–514.
(4) Stranks, S. D.; Eperon, G. E.; Grancini, G.; Menelaou, C.; Alcocer, M. J. P.; Leijtens, T.;
Herz, L. M.; Petrozza, A.; Snaith, H. J. Electron-Hole Diffusion Lengths Exceeding 1 Micrometer
in an Organometal Trihalide Perovskite Absorber. Science 2013, 342, 341–344.
(5) Dong, Q.; Fang, Y.; Shao, Y.; Mulligan, P.; Qiu, J.; Cao L.; Huang, J. Electron-Hole
Diffusion Lengths > 175 μm in Solution-Grown CH3NH3PbI3 Single Crystals. Science 2015, 347,
967–970.
(6) Frost, J. M.; Butler, K. T.; Brivio, F.; Hendon, C. H.; van Schilfgaarde, M.; Walsh, A.
Atomistic Origins of High-Performance in Hybrid Halide Perovskite Solar Cells. Nano Lett. 2014,
14, 2584–2590.
(7) Song, Z.; Abate, A.; Watthage, S. C.; Liyanage, G. K.; Phillips, A. B.; Steiner, U.; Graetzel,
M.; Heben, M. J. Perovskite Solar Cell Stability in Humid Air: Partially Reversible Phase
Transitions in the PbI2‐CH3NH3I‐H2O System. Adv. Energy Mater. 2016, 6, 1600846.
(8) Wallace, S. K.; Svane, K.; Huhn, W. P.; Zhu, T.; Mitzi, D. B.; Blum, V.; Walsh, A.
Candidate Photoferroic Absorber Materials for Thin-Film Solar Cells from Naturally Occurring
Minerals: Enargite, Stephanite, and Bournonite. Sustain. Energy Fuels 2017, 1, 1339−1350.
(9) Ganose, A. M.; Savory, C. N.; Scanlon, D. O. Beyond Methylammonium Lead Iodide:
Prospects for the Emergent Field of ns2 Containing Solar Absorbers. Chem. Commun. 2017, 53,
20–44.
141
(10) Yu, L.; Zunger, A. Identification of Potential Photovoltaic Absorbers Based on First-
Principles Spectroscopic Screening of Materials. Phys. Rev. Lett. 2012, 108, 068701.
(11) Bairamova, S. T.; Bagieva, M. R.; Agapashaeva, S. M.; Aliev, O. M. Synthesis and
Properties of Structural Analogs of the Mineral Bournonite. Inorg. Mater. 2011, 47, 345–348.
(12) Wei, K.; Martin, J.; Salvador, J. R.; Nolas, G. S. Synthesis and Characterization of
Bournonite PbCuSbS3 Nanocrystals. Cryst. Growth Des. 2015, 15, 3762–3766.
(13) Durant, B.; Parkinson, B. A. Photovoltaic Response of Naturally Occurring
Semiconducting Sulfide Minerals. 2016 IEEE 43rd Photovoltaic Specialists Conference; IEEE:
New York, 2016; pp 2774-2779.
(14) Dong, Y.; Khabibullin, A. R.; Wei, K.; Salvador, J. R.; Nolas, G. S.; Woods, L. M.
Bournonite PbCuSbS3: Stereochemically Active Lone-Pair Electrons that Induce Low Thermal
Conductivity. ChemPhysChem 2015, 16, 3264–3270.
(15) Frumar, M.; Kala, T.; Horak, J. Growth and Some Physical Properties of Semiconducting
CuPbSbS3 Crystals. J. Cryst. Growth 1973, 20, 239−244.
(16) Eslamian, M. Inorganic and Organic Solution-Processed Thin Film Devices. Nano-Micro
Lett. 2017, 9, 3.
(17) Mitzi, D. B. Solution-Processed Inorganic Semiconductors. J. Mater. Chem. 2004, 14,
2355-2365.
(18) Mitzi, D. B.; Kosbar, L. L.; Murray, C. E.; Copel, M.; Afzali, A. High-Mobility Ultrathin
Semiconducting Films Prepared by Spin Coating. Nature 2004, 428, 299-303.
(19) Mitzi, D. B.; Yuan, M.; Liu, W.; Kellock, A. J.; Chey, S. J.; Deline, V.; Schrott, A. G. A
High‐Efficiency Solution‐Deposited Thin‐Film Photovoltaic Device. Adv. Mater. 2008, 20, 3657-
3662.
142
(20) Mitzi, D. B. Solution Processing of Chalcogenide Semiconductors via Dimensional
Reduction. Adv. Mater. 2009, 21, 3141-3158.
(21) Webber, D. H.; Brutchey, R. L. Alkahest for V2VI3 Chalcogenides: Dissolution of Nine
Bulk Semiconductors in a Diamine-Dithiol Solvent Mixture. J. Am. Chem. Soc. 2013, 135,
15722−15725.
(22) Webber, D. H.; Buckley, J. J.; Antunez, P. D.; Brutchey, R. L. Facile Dissolution of
Selenium and Tellurium in a Thiol−amine Solvent Mixture under Ambient Conditions. Chem. Sci.
2014, 5, 2498−2502.
(23) Antunez, P. D.; Torelli, D. A.; Yang, F.; Rabuffetti, F. A.; Lewis, N. S.; Brutchey, R. L.
Low Temperature Solution-Phase Deposition of SnS Thin Films. Chem. Mater. 2014, 26,
5444−5446.
(24) McCarthy, C. L.; Webber, D. H.; Schueller, E. C.; Brutchey, R. L. Solution-Phase
Conversion of Bulk Metal Oxides to Metal Chalcogenides Using a Simple Thiol−Amine Solvent
Mixture. Angew. Chem., Int. Ed. 2015, 54, 8378−8381.
(25) McCarthy, C. L.; Cottingham, P.; Abuyen, K.; Schueller, E. C.; Culver, S. P.; Brutchey, R.
L. Earth Abundant CuSbS2 Thin Films Solution Processed from Thiol−Amine Mixtures. J. Mater.
Chem. C 2016, 4, 6230−6233.
(26) McCarthy, C. L.; Brutchey, R. L. Solution Deposited Cu2BaSnS4–xSex from a Thiol–Amine
Solvent Mixture. Chem. Mater. 2018, 30, 304–308.
(27) McCarthy, C. L.; Brutchey, R. L. Solution Processing of Chalcogenide Materials Using
Thiol−Amine “Alkahest” Solvent Systems. Chem. Commun. 2017, 53, 4888−4902.
143
(28) Zhao, X.; Lu, M.; Koeper, M. J.; Agrawal, R. Solution-Processed Sulfur Depleted
Cu(In,Ga)Se2 Solar Cells Synthesized from a Monoamine-Dithiol Solvent Mixture. J. Mater.
Chem. A 2016, 4, 7390-7397.
(29) Yang, Y.; Wang, G.; Zhao, W.; Tian, Q.; Huang, L.; Pan, D. Solution-Processed Highly
Efficient Cu2ZnSnSe4 Thin Film Solar Cells by Dissolution of Elemental Cu, Zn, Sn, and Se
Powders. ACS Appl. Mater. Interfaces 2015, 7, 460-464.
(30) Arnou, P.; van Hest M. F. A. M.; Cooper, C. S.; Malkov, A. V.; Walls, J. M.; Bowers, J.
W. Hydrazine-Free Solution-Deposited CuIn(S,Se)2 Solar Cells by Spray Deposition of Metal
Chalcogenides. ACS Appl. Mater. Interfaces 2016, 8, 11893-11897.
(31) Dittrich, A.; Bieniok, A.; Brendel, U.; Grodzicki, M.; Topa, D. Sulfosalts – A New Class
of Compound Semiconductors for Photovoltaic Applications. Thin Solid Films 2007, 515, 5745-
5750.
(32) Buckley, J. J.; McCarthy, C. L.; Pilar-Albaladejo, J. D.; Rasul, G.; Brutchey, R. L.
Dissolution of Sn, SnO, SnS in a Thiol-Amine Solvent Mixture: Insights into the Identity of the
Molecular Solutes for Solution-Processed SnS. Inorg. Chem. 2016, 55, 3175-3180.
(33) Hayashi, M.; Shiro, Y.; Oshima, T.; Murata, H. The Vibrational Assignment, Rotational
Isomerism and Force Constants of 1,2- Ethanedithiol. Bull. Chem. Soc. Jpn. 1965, 38, 1734−1740.
(34) Mitzi, D. B.; Gunawan, O.; Todorov, T. K.; Wang, K.; Guha, S. The Path Towards a High-
Performance Solution-Processed Kesterite Solar Cell. Sol. Energy Mater. Sol. Cells 2011, 95,
1421−1436.
(35) Chen, S.; Walsh, A.; Gong, X. G.; Wei, S. H. Classification of Lattice Defects in the
Kesterite Cu2ZnSnS4 and Cu2ZnSnSe4 Earth-Abundant Solar Cell Absorbers. Adv. Mater. 2013,
25, 1522-1539.
144
(36) Kharbish, S.; Libowitzky, E.; Beran, A. Raman Spectra of Isolated and Interconnnected
Pyramidal XS3 Groups (X = Sb, Bi) in Stibnite, Bismuthinite, Kermesite, Stephanite and
Bournonite. Eur. J. Mineral 2009, 21, 325-333.
(37) Baker, J.; Kumar, R. S.; Sneed, D.; Connolly, A.; Zhang, Y.; Velisavljevic, N.; Paladugu,
J.; Pravica, M.; Chen, C.; Cornelius, A.; Zhao, Y. Pressure Induced Structural Transitions in
CuSbS2 and CuSbSe2 Thermoelectric Compounds. J. Alloys Compd. 2015, 643, 186– 194.
(38) Thiruvenkadam, S.; Rajesh, A. L. Effect of Temperature on Structural and Optical
Properties of Spray Pyrolysed CuSbS2 Thin Films for Photovoltaic Applications. Int. J. Sci. Eng.
Res. 2014, 5, 248-251.
(39) Rajashree, C.; Balu, A. R. Tuning the Physical Properties of PbS Thin Films Towards
Optoelectronic Applications Through Ni Doping. Optik 2016, 127, 8892-8898.
(40) McClary, S. A.; Balow, R. B.; Argawal, R. Role of Annealing Atmosphere on the Crystal
Structure and Composition of Tetrahedrite-Tennantite Alloy Nanoparticles. J. Mater. Chem. C.
2018, 6, 10538-10546.
(41) Aliyev, O. M.; Ajdarova, D. S.; Bayramova, S. T.; Aliyeva, S. I.; Ragimova, V. M.
Nonstoichiometry in PbCuSbS3 Compound. Azerbaijan Chem. J. 2016, 2, 51-54.
(42) Ge, J.; Yan, Y. Synthesis and Characterization of Photoelectrochemical and Photovoltaic
Cu2BaSnS4 Thin Films and Solar Cells. J. Mater. Chem. C 2017, 5, 6406−6419.
(43) Moulder, J. F.; Stickle, W. F.; Sobol, P. E.; Bomben, K. D. Handbook of X-Ray
Photoelectron Spectroscopy; Chastain, J., Ed.; Physical Electronics Division, Perkin-Elmer Corp.:
Eden Prairie, MN, 1979.
(44) Hardman, S. J. O.; Graham, D. M.; Stubbs, S. K.; Spencer, B. F.; Seddon, E. A.; Fung, H.
T.; Gardonio, S.; Sirotti, F.; Silly, M. G.; Akhtar, J.; O’Brien, P.; Binks, D. J.; Flavell, W. R.
145
Electronic and Surface Properties of PbS Nanoparticles Exhibiting Efficient Multiple Exciton
Generation. Phys. Chem. Chem. Phys. 2011, 13, 20275−20283.
(45) Cant, D. J. H.; Syres, K. L.; Lunt, P. J. B.; Radtke, H.; Treacy, J.; Thomas, P. J.; Lewis, E.
A.; Haigh, S. J.; O’Brien, P.; Schulte, K.; Bondino, F.; Magnano, E.; Flavell, W. R.; Surface
Properties of Nanocrystalline PbS Films Deposited at the Water–Oil Interface: A Study of
Atmospheric Aging. Langmuir 2015, 31, 1445-1453.
(46) Godel, K. C.; Roose, B.; Sadhanala, A.; Vaynzof, Y.; Pathak, S. K.; Steiner, U. Partial
Oxidation of the Absorber Layer Reduces Charge Carrier Recombination in Antimony Sulfide
Solar Cells. Phys. Chem. Chem. Phys. 2017, 19, 1425.
(47) Novet, T.; Johnson, D. C. New Synthetic Approach to Extended Solids: Selective Synthesis
of Iron Silicides via the Amorphous State. J. Am. Chem. Soc. 1991, 113, 3398−3403.
(48) Herz, L. M. Charge-Carrier Mobilities in Metal Halide Perovskites: Fundamental
Mechanisms and Limits. ACS Energy Lett. 2017, 2, 1539−1548.
(49) Faghaninia, A.; Guodong, Y.; Aydemir, U.; Wood, M.; Chen, W.; Rignanese, G.-M.;
Snyder, G. J.; Hautier, G.; Jain, A. A Computational Assessment of the Electronic, Thermoelectric,
and Defect Properties of Bournonite (CuPbSbS3) and Related Substitutions. Phys. Chem. Chem.
Phys. 2017, 19, 6743-6756.
(50) Wallace, S. K.; Butler, K. T.; Hinuma, Y.; Walsh, A. Finding a Junction Partner for
Candidate Solar Cell Absorbers Enargite and Bournonite from Electronic Band and Lattice
Matching. J. Appl. Phys. 2019, 125, 055703.
(51) Liu, Y.; Yang, B.; Zhang, M.; Xia, B.; Chen, C.; Liu, X.; Zhong, J.; Xiao, Z.; Tang, J.
Bournonite CuPbSbS3: An Electronically-3D, Defect-Tolerant, and Solution-Processable
Semiconductor for Efficient Solar Cells. Nano Energy 2020, 71, 104574.
146
(52) Zhang, M.; Liu, Y.; Yang, B.; Lin, X.; Lu, Y.; Zheng, J.; Chen, C.; Tang, J. Efficiency
Improvement of Bournonite CuPbSbS3 Solar Cells via Crystallinity Enhancement. ACS Appl.
Mater. Interfaces 2021, 13, 13273–13280.
(53) Fabini, D. H.; Koerner, M.; Seshadri, R. Candidate Inorganic Photovoltaic Materials from
Electronic Structure-Based Optical Absorption and Charge Transport Proxies. Chem. Mater. 2019,
31, 1561−1574.
147
Chapter 5. Solution Processing Cu3BiS3 Absorber Layers with a Thiol-Amine Solvent
Mixture*
*Published – Koskela, K. M.; Tadle, A. C.; Chen K.; Brutchey, R. L. ACS Appl. Energy Mater.
2021, 4, 11026–11031.
5.1 Abstract
There is a need to develop more Earth abundant, less toxic, and more environmentally
stable solar absorbers as the market demand for solar cells increases. Wittichenite (Cu3BiS3) is a
sulfosalt mineral that belongs to the Cu3MCh3 (M = Sb, Bi; Ch = S, Se) family of materials.
Cu3BiS3 contains bismuth, a non-toxic heavy metal that has a 6s
2
electronic structure akin to halide
perovskites that have demonstrated excellent properties, and the sulfosalt crystallizes in the
P212121 space group with a near-optimal band gap for single junction thin film solar cells. We
report the utility of thiol-amine solvent mixtures to dissolve inexpensive bulk CuO and Bi2S3
precursors to produce a free-flowing semiconductor ink. Good quality and phase pure Cu3BiS3
thin films were solution processed from this ink upon mild annealing. The p-type thin films possess
a direct band gap of 1.47 eV with a high absorption coefficient through the visible (~10
5
cm
–1
),
carrier mobilities in the range of 0.4-90 cm
2
(V•s)
–1
, and a strong photoelectrochemical current
response. The optoelectronic properties of Cu3BiS3 thin films deposited using this thiol-amine
chemistry suggest it is a favorable candidate as a solution processable solar absorber.
5.2 Introduction
With the increasing demand for solar energy conversion, there is a need for more Earth
abundant, less toxic, and more environmentally stable solar absorbers.
1
State-of-the-art
photovoltaics, such as CdTe and Cu(In,Ga)(S,Se)2 (CIGS), have appreciable power conversion
148
efficiencies >20%, but are made up of toxic (i.e., Cd) or low Earth abundance elements (i.e., In,
Ga, Te).
2,3
Recently, hybrid lead halide perovskite solar cells have demonstrated remarkable power
conversion efficiencies > 22%, but, aside from containing lead, they possess significant challenges
due to their intrinsic environmental instabilities to air and moisture.
4
Halide perovskite materials
belong to a broader class of solar absorbers containing high-Z ns
2
cations.
4
Materials containing
ns
2
cations have been theorized and demonstrated to have large band dispersions (good
hybridization) that lead to high carrier mobility,
5
defect tolerance,
6
and enhanced dielectric
constants
6
leading to improved carrier transport.
Chalcogenide solar absorbers containing ns
2
lone pairs (e.g., those with Sn
2+
, Sb
3+
, Bi
3+
cations) hold promise as photovoltaic materials, including SnS,
7
CuSbS2,
8
and Sb2S3.
9
Looking to
other compositional variants of ns
2
-containing chalcogenide solar absorbers, there is promise
within the Cu-Bi-S phase space, such as CuBiS2 and Cu3BiS3.
10
The Cu3MCh3 system (where, M
= Sb, Bi and Ch = S, Se) is a potentially interesting material family for photovoltaic applications.
11
Wittichenite, the known sulfosalt mineral phase (Strunz 2.GA.20) of Cu3BiS3, is
thermodynamically stable due to its natural occurrence and crystallizes in the orthorhombic
P212121 space group.
12
The crystal structure is composed of trigonal pyramidal BiS3 units that have
6s
2
lone pairs at the cap and are corner sharing with trigonal planar CuS3 units forming continuous
chains parallel to [001] and sheets normal to the [010] plane (Figure 5.1).
12
Density functional
theory (DFT) calculations suggest Cu3BiS3 has a higher absorption coefficient than either CIGS
or Cu2ZnSnS4 (CZTS).
13
DFT also suggests that the valence band maximum (VBM) consists
mostly of Cu d and S p states with little impact from Bi s states, while the conduction band
minimum (CBM) consists of mostly Bi p and S p antibonding states.
11
Wittichenite contains
bismuth, which is a green heavy element due to its low toxicity/environmental impact and relative
149
Earth abundance, where Bi reserves total 370,000 tons whereas In reserves total 15,000 tons
(>300,000 tons when considering Zn co-deposits or lower quality ores that are more difficult and
expensive to extract).
14-17
Figure 5.1. Crystal structure of wittichenite Cu3BiS3 (space group P212121), from PDF exp. 43-
1479.
Thin films of wittichenite Cu3BiS3 have been deposited by physical vapor deposition
methods, including sputtering
18,19
and thermal evaporation,
11,20
but these methods are generally
much more energy intensive and costly than solution processing.
21
While Cu3BiS3 thin films have
been solution deposited with non-vacuum based techniques, such as spray pyrolysis,
22,23
electrodeposition,
24,25
and chemical bath deposition,
26,27
the solution deposition of Cu3BiS3 thin
films is still challenged by the need for pre-synthesized, non-commercially available precursors,
23
extra post-deposition sulfurization steps,
24-27
amorphous films,
28
low absorption coefficients (<10
5
cm
–1
),
29
and/or films with high band gaps (>1.6 eV).
22,30
To overcome some of the general issues
with solution processing of chalcogenides, our group reported a binary solvent mixture (termed an
150
“alkahest”) comprised of thiols and amines that dissolves in excess of 100 different bulk materials,
including metals, metal oxides, and metal chalcogenides, to form solution processable
semiconductor inks.
31-37
A simple dissolve and recover approach can be used to produce
chalcogenide thin films through solution deposition and mild annealing. In the absence of an
external chalcogen source, the thiol acts as a competent sulfur source to produce polycrystalline
metal sulfides. This thiol-amine method has been utilized for the solution deposition of both CIGS
and CZTS solar cells with competitive power conversion efficiencies.
38-40
Here, we report the
utility of thiol-amine solvent mixtures to dissolve CuO and Bi2S3 precursors to form an ink, which
was solution processed to give phase-pure Cu3BiS3 thin films under mild annealing conditions.
The thin films were assessed as solar absorber layers with a combination of optical, electronic, and
photoelectrochemical measurements.
5.3 Results and Discussion
To formulate the Cu3BiS3 semiconductor ink, as-purchased bulk powders of CuO and Bi2S3
were mixed in a 6:1 (mol/mol) ratio, respectively, and then dissolved in a mixture of ethanedithiol
(EDT) and ethylenediamine (en) (1:4 vol/vol, respectively), with an overall solute concentration
of 75 mg mL
–1
. Different combinations of oxides and sulfides (e.g., Cu2O, Cu2S, Bi2O3) may also
return phase pure Cu3BiS3, but CuO and Bi2S3 were chosen as bulk precursors due to these
precursors yielding qualitatively better-quality thin films. The bulk powders of CuO and Bi2S3
both have approximate solubility limits in solvent combination of 10-15 wt% at 25 °C (1 atm).
The semiconductor ink was stirred at 30 °C for 10 h to yield an optically clear, free flowing, burnt
orange solution that does not scatter light (Figure 5.2a). The resulting ink was stable and
precipitate-free when kept under ambient conditions for several days.
151
Figure 5.2. a) Semiconductor ink containing bulk CuO and Bi2S3 dissolved in a 1:4 (vol/vol)
mixture of EDT and en next to a Cu3BiS3 thin film. b) Thermogravimetric analysis trace of the
dried ink demonstrating a decomposition endpoint of < 350 ˚C. c) FT-IR spectra of the ink dried
at 150 ˚C and a thin film heated to 400 ˚C confirming loss of organic species.
Thermogravimetric analysis (TGA) was used to determine an endpoint of volatilization
and decomposition for the solution deposited and dried ink. The dried ink begins mass loss at ca.
150 °C and it was found that mass loss terminated < 350 °C (Figure 5.2b). The loss of the organic
species upon annealing the dried ink from 150 to 400 °C was corroborated using FT-IR
spectroscopy (Figure 5.2c). IR bands were not observed in the dried ink above 3000 cm
−1
, where
ν(N–H) stretches are expected, suggesting that en, or protonated ammonium species, may be
mostly absent after heating the ink to 150 ˚C. The strong IR bands of EDT present in the dried ink
(i.e., at 2930 cm
−1
ν(C−H), 1420 cm
−1
d(CH2), and 675 cm
-1
ν(C–S)) are completely absent from
the film after annealing to 400 °C.
35,37
To demonstrate the effectiveness of EDT-en to solution process high-quality Cu3BiS3 thin
films, the ink was used to sequentially deposit three identical coats by spin coating with a 400 °C
anneal between each coat. The solution deposition procedure returned dark gray, specularly
reflective polycrystalline thin films of Cu3BiS3 that are free of pinholes, microcracks, and other
152
imperfections (e.g., edge effects or striations). A cross-sectional scanning electron microscopy
image of a Cu3BiS3 thin film formed by depositing three coats of the semiconductor ink on Si/SiO2
returns a 490 nm mean film thickness (Figure 5.3).
Figure 5.3. Cross-sectional SEM image at a) 25,000x and b) 100,000x magnification of a 490-nm
Cu3BiS3 thin film deposited from three coats spun at 2500 rpm and annealed to 400 ˚C for 10 min
between each coat.
The dark gray material resulting from annealing to 400 °C was phase pure orthorhombic
Cu3BiS3, as confirmed by powder X-ray diffraction (Figure 5.4). Rietveld refinement of the
resulting diffraction pattern using the orthorhombic P212121 space group returns lattice constants
of a = 7.70410(8), b = 10.41840(10), and c = 6.71624(7) Å, with a unit cell volume of V =
539.075(6) Å
3
(Table 5.1). The refinement was not improved with the addition of any additional
ternary phases (i.e., CuBiS2) or binary phases of copper or bismuth sulfides, and the lattice
constants for Cu3BiS3 agree with the values for bulk wittichenite (i.e., a = 7.723(10), b =
10.395(10), and c = 6.716(5) Å; V = 539.16 Å
3
).
12
Raman spectroscopy corroborated the single
phase nature of the resulting Cu3BiS3 thin film (Figure 5.5). Four Raman active modes were
observed at 150, 248, 278, and 468 cm
–1
, which match well with spectra previously reported for
wittichenite.
11,41-43
Importantly, no Raman active bands were observed for any potential binary
153
impurities of CuS,
44
Cu2–xS,
45
or Bi2S3,
46
or potential ternary phases such as CuBiS2.
47
ICP-OES
was used to assess the elemental composition of the solution processed films. By averaging four
separate analyses, the elemental stoichiometry of the resulting thin films was Cu2.84B1.00S3; this is
in the range of copper deficiencies that have been previously published for Cu3BiS3.
24,48
Figure 5.4. Rietveld refinement to the orthorhombic P212121 structure of the powder X-ray
diffraction pattern of phase pure Cu3BiS3. Open circles are experimental data, purple tick marks
are individual reflections of the wittichenite structure, and the difference pattern is given in blue.
(RWP = 4.30%; G.O.F. = 2.14).
20 40 60
2-Theta (°)
Intensity (a.u.)
Experiment
Difference
Calculated
Cu
3
BiS
3
Background
154
Table 5.1. Structural parameters of phase-pure orthorhombic Cu3BiS3 extracted from Rietveld
analysis.
Atom Mult. x y z Frac.
Bi1 4 0.19716 -0.24401 0.12860 1
Cu1 4 0.35179 0.40167 0.13762 1
Cu2 4 0.19037 0.10470 0.07838 1
Cu3 4 0.05727 0.46445 -0.02628 1
S1 4 -0.44584 0.24619 0.10918 1
S2 4 -0.31767 0.43669 -0.40779 1
S3 4 -0.32136 0.06949 -0.41380 1
Atom U11 U22 U33 U12 U13 U23
Bi1 0.0022 0.0011 0.0087 0.0158 0.0059 0.0133
Cu1 0.0284 0.0091 0.0218 0.0312 0.0328 0.0537
Cu2 0.0450 0.0056 0.0689 0.0161 0.0077 0.0443
Cu3 0.0025 0.0129 0.0594 0.0069 0.0248 0.0300
S1 0.0454 0.0603 0.0233 0.0050 0.0165 0.0621
S2 0.0673 0.0011 0.0724 0.0152 0.0274 0.0623
S3 0.0370 0.0051 0.0817 0.0135 0.0706 0.0433
Space Group P212121
a (Å) 7.70410(8)
b (Å) 10.41840(10)
c (Å) 6.71624(7)
V (Å
3
) 539.075(6)
a = b = g 90˚
Rwp 4.30%
155
Figure 5.5. Raman spectrum (532 nm excitation) of a 490-nm Cu3BiS3 thin film deposited on a
Si/SiO2 substrate annealed to 400 °C for 20 min.
X-ray photoelectron spectroscopy (XPS) was employed to interrogate the valence states in
our Cu3BiS3 thin films. A fitting procedure was used to accurately analyze the peaks, as most
Cu3BiS3 thin films reported in the literature lack robust fitting of the peaks, possibly due to the Bi
4f and S 2p peak overlap or poor signal to noise.
25,43,49
An XPS survey scan of the Cu3BiS3 thin
film that was exposed to air is given in the Supporting Information (Figure 5.6). High-resolution
Cu 2p, Bi 4f and S 2p, and S 2s spectra and their corresponding peak fittings are given in Figures
5.7-5.9, respectively. In addition, the peak positions and spin orbit coupling splitting values are
tabulated in Table 5.2. It is observed that the Cu 2p spectral region is best fit with a single set of
doublets at 952.0 and 932.2 eV (peak splitting 19.8 eV), which corresponds to a single Cu
+
environment in our Cu3BiS3 thin film, and is consistent with a single Cu
+
environment in
previously reported Cu3BiS3 thin films deposited by thermal evaporation and surface cleaned by
100 200 300 400 500
Raman Shift (cm
-1
)
Intensity (a.u.)
468 cm
-1
278 cm
-1
150 cm
-1
248 cm
-1
156
Ar
+
ion sputtering for several hours under vacuum.
11,50
Surface oxidation of copper would return
characteristic peaks at higher binding energy,
51
and as none are seen, we can confirm that no
significant degree of surface copper oxidation has occurred under the film processing conditions.
The Bi 4f and S 2p spectra were fit using three sets of doublets. Two doublets correspond
to two different Bi species, both with a splitting of 5.3 eV. The larger doublet at 163.4 and 158.1
eV corresponds to Bi
3+
in a sulfide environment,
52
and is consistent with other Cu3BiS3
samples.
11,25
The smaller doublet at 163.9 and 158.6 eV corresponds to possible surface oxidized
Bi species that may be an additional amorphous and/or non-stoichiometric oxide species on the
surface due to Bi2O3 having a higher binding energy (~159.1 eV) than the fitted peak (158.6 eV).
52
A third doublet with a 1.2 eV splitting is attributed to sulfide S 2p peaks.
53
Due to overlap in the
Bi 4f and S 2p spectra, additional peak fitting was conducted on the S 2s region to further analyze
the sulfur species on the Cu3BiS3 surface. A singlet observed at 225.8 eV agrees with Cu3BiS3
films deposited by thermal evaporation and surface cleaned by Ar
+
ion sputtering, as no other
studies have rigorously fit the peaks of the S 2s region.
11
A second singlet with lower intensity at
higher binding energies was also fit and this may correspond to carbon contaminated sulfur species
on the surface from air exposure.
11,54
The amount of surface contaminated sulfur and oxidic Bi
species can be reduced through surface Ar
+
ion sputtering,
11
but our films show lower amounts of
contaminated surface species compared to other reported Cu3BiS3 samples,
11,25,43,49
even when
exposed to atmospheric conditions.
157
Figure 5.6. XPS survey scan of Cu3BiS3 thin film on Si/SiO2.
Figure 5.7. High-resolution XPS spectrum of Cu 2p region.
0 500 1000
Binding Energy (eV)
Intensity (a.u.)
O KLL
Cu 2p
Cu 2s
Bi 4f
S 2p
Cu LMM
O 1s
Bi 4d
C 1s
S 2s
Cu 3s
Cu 3p
Bi 5d
930 940 950 960
Binding Energy (eV)
Intensity (a.u.)
Cu 2p
3/2
Cu 2p
1/2
158
Figure 5.8. High resolution XPS spectrum of Bi 4f and S 2p spectral region.
160 165
Binding Energy (eV)
Intensity (a.u.)
Bi 4f
7/2
Bi 4f
5/2
BiO
x
BiO
x
S 2p
1/2
S 2p
3/2
159
Figure 5.9. High resolution XPS spectrum of S 2s region.
220 225 230 235
Binding Energy (eV)
Intensity (a.u.)
S 2s
Atmospheric
contaminated
Sulfur species
160
Table 5.2. Peak positions and peak splitting from the high-resolution XPS spectra of Cu3BiS3
thin films on Si/SiO2.
Element Peak Splitting
(eV)
Peak ID Binding Energy
(eV)
Cu 19.8 2p1/2 952.0
2p3/2 932.2
Bi 5.3 4f5/2 163.4
4f7/2 158.1
Bi (surface BiOx) 5.3 4f5/2 163.9
4f7/2 158.6
S 1.2 2p1/2 162.6
2p3/2 161.4
S
2s 225.8
S (surface carbon
contamination)
2s 226.7
The band gap and absorption coefficient of the resulting Cu3BiS3 thin films were measured
by UV-vis-NIR spectroscopy (Figures 5.10, 5.11). An absorption coefficient a = 5.0 ´ 10
4
cm
–1
(1.46 eV) was derived from the transmittance spectrum of the resulting 490-nm thick Cu3BiS3 thin
film annealed to 400 ˚C, which increases to a = 1.1 ´ 10
5
cm
–1
(2.2 eV). The band gap of our
solution deposited thin film samples was measured using the inverse logarithmic (ILD) method,
which was first proposed by Jarosińksi et al. and is derived from the Tauc method.
55
By using
absorbance data as inputs, the ILD method provides accurate determinations of semiconductor
band gaps and has been shown to have several advantages over the more commonly used Tauc or
161
McLean methods (See section 5.4.6). We applied the ILD method to absorption data derived from
transmittance spectrum of a 490 nm Cu3BiS3 thin film (Figure 5.12). The experimental band gap
of the Cu3BiS3 thin films was determined to be 1.47 eV. This optical band gap lies well within the
previously reported experimentally reported band gaps for Cu3BiS3 (1.10–1.80 eV).
30
The reciprocal of the line of best fit from the linear regression of the ILD plot gives the
exponential factor (m), which informs the type of electronic transition. Wittichenite Cu3BiS3 has
been calculated and experimentally confirmed to be a direct band gap semiconductor.
30
From this,
one would expect an exponential factor m of 0.5 (slope of 2) for a direct band gap semiconductor.
Importantly, Jarosińksi et al. shows that for direct band gap thin film samples of TiO2 and MoS2,
the exponential factor yielded values of 1 because of the polycrystalline nature of the sputtered
films, which affects the effective dimension and dispersion relations of the thin films.
55
We find a
similar m value of 0.98. From our experimental band gap and m value, we conclude our Cu3BiS3
thin films can be described as a direct band gap semiconductor.
162
Figure 5.10. Transmittance spectrum of a 490-nm thin film of Cu3BiS3 deposited on a borosilicate
glass substrate.
500 1000 1500
0
20
40
60
80
Wavelength (nm)
% Transmittance
163
Figure 5.11. Absorption coefficient as a function of incident photon energy for a 490-nm thin film
of Cu3BiS3 deposited on a borosilicate glass substrate.
1 2 3
0.0
0.5
1.0
Energy (eV)
α (10
5
cm
-1
)
164
Figure 5.12. Inverse logarithmic derivative (ILD) plot (maroon data points) of a 490 nm thin film
deposited on a borosilicate glass substrate. ILD plot uses absorption spectra that derived from
transmittance data. The dashed black line represents the linear regression that was used to estimate
the optical band gap from the ILD plot using values from 2.0-3.5 eV. From this, the optical band
gap was determined to be 1.47 eV and the m value derived was 0.98.
Electrical conductivity of the Cu3BiS3 thin films was measured using the Van der Pauw
geometry over the temperature range of 170-300 K. Temperature-dependent resistivity
measurements suggest the resulting thin films behave like intrinsic semiconductors, where
resistivity decreases with heating (Figure 5.13). A positive Hall coefficient with a carrier
concentration of 4.2´10
17
cm
–3
was found at 300 K, indicating the p-type nature of our Cu3BiS3
thin films. The carrier concentrations decreased to 2.2´10
13
cm
–3
upon cooling to 170 K while
carrier mobilities ranged from 0.4-90 cm
2
(V•s)
–1
across the same temperature range. These values
are consistent with those previously reported for thermally evaporated Cu3BiS3 thin films, with a
carrier concentration of 2´10
16
cm
–3
and carrier mobility of 4 cm
2
(V•s)
–1
.
20
1 2 3
0.0
0.5
1.0
1.5
2.0
2.5
hν (eV)
Δhν / Δln(αhν)
165
Figure 5.13. Resistivity (r) of a 490 nm Cu3BiS3 thin film as a function of temperature.
The potential of using Cu3BiS3 as an effective solar absorber was further studied using
transient photocurrent response measurements. The Cu3BiS3 thin films were interrogated in
aqueous 0.1 M Eu(NO3)3, where the Eu
3+
ions serve as the sacrificial oxidant. A calibrated
AM1.5G filtered 300 W xenon arc lamp was used to measure the photocurrent response of the
Cu3BiS3 with a graphite rod counter electrode and a Ag|AgCl reference electrode. Linear sweep
voltammetry under chopped illumination shows cathodic photocurrent, which increases at
potentials negative of -400 mV vs Ag|AgCl (Figure 5.14), further supporting the assignment of
these Cu3BiS3 thin films as p-type semiconductors. The transient photocurrent response of a
Cu3BiS3 thin film under chopped illumination at a fixed potential of -800 mV vs Ag|AgCl is given
in Figure 5.15. This controlled potential electrolysis gave photocurrent densities >80 μA cm
−2
;
this current density exceeds those measured for p-type Cu3BiS3 thin films prepared by
150 200 250 300
0
50
100
150
Temperature (K)
Resistivity (Ω m)
166
electrodeposition, which gave photocurrent densities of ~10 μA cm
−2
at -350 mV vs Ag|AgCl under
AM1.5G illumination.
25
To prove the photocurrent response resulted from Eu
3+
reduction and not
photocorrosion, we tested the photocurrent response over a 20 min period and found the response
to be steady at 60 μA cm
−2
(Figure 5.16).
Figure 5.14. Linear sweep voltammogram of p-type Cu3BiS3 at 10 mV s
–1
with chopped simulated
AM1.5G light every 10 s in contact with N2-saturated 0.1 M Eu(NO3)3 (aq).
-900 -800 -700 -600 -500 -400
-5
-4
-3
-2
-1
0
Potential vs Ag/AgCl (mV)
Current Density (mA/cm
2
)
Light On
Light Off
167
Figure 5.15. Transient photocurrent response of solution-processed Cu3BiS3 thin film deposited
on FTO substrates in N2-saturated 0.1 M Eu(NO3)3 (aq) under a potential of -800 mV vs Ag|AgCl
(3 M KCl).
0 50 100
-1950
-1900
-1850
-1800
-1750
Time (s)
Current Density (μA/cm
2
)
Light On
Light Off
80 μA/cm
2
168
Figure 5.16. Stability test of p-type Cu3BiS3 in contact with N2-saturated 0.1 M Eu(NO3)3 (aq) at
-800 mV vs Ag½AgCl. The light was turned off and back on at ca. 5, 10, and 15 min where sharp
photocurrent decreases are observed.
5.4 Experimental
5.4.1 General Considerations
Bismuth(III) sulfide (Bi2S3, 99.995%), copper(II) oxide (CuO, 99.99%), and 1,2-
ethylenediamine (en, 99.5%) were bought from Sigma Aldrich. 1,2-Ethanedithiol (EDT, 98+%)
was bought from Alfa Aesar. ICP standards for Cu and Bi (1000 ppm, 2% HNO3) were bought
from Perkin Elmer. Europium(III) nitrate pentahydrate (99.8%) was bought from Strem. All
reagents were used as received.
5.4.2 Bulk Precursor Dissolution
To generate the semiconductor ink, 18.1 mg (0.228 mmol) CuO and 19.4 mg (0.038 mmol)
Bi2S3 were dissolved in 0.1 mL EDT and 0.4 mL en with stirring at 30 ˚C for 10 h under air (1
0 500 1000
-2200
-2000
-1800
Time (s)
Current Density (μA/cm
2
)
Light On
Light Off
169
atm). If the solvents solidified upon addition to the bulk solid precursors, gentle heating can be
used to re-liquify the ink.
5.4.3 Solution Processing
Thin films were solution processed by spin coating onto ca. 1 cm
2
borosilicate glass,
fluorine doped tin oxide (FTO), or silicon substrates that were pre-cleaned by bath sonication in
acetone, isopropanol, and then ethanol (each for 10 min). The final ink (75 mg mL
–1
) was spin
coated onto the substrate at 2500 rpm for 1 min under N2. The films were heated to 400 ˚C under
N2 in between coats, and allowed to return to room temperature before the next layer was
deposited.
5.4.4 Structural and Optical Characterization
Powder X-ray diffraction (XRD) patterns were collected using a Rigaku Miniflex600
operated at 40 mA and 35 kV, in the 2q range of 10-70˚ using Cu Ka radiation (l = 1.5406 Å).
For powder diffraction studies, inks were drop cast on a glass slide and dried to 350 °C in an
aluminum annealing chamber under flowing nitrogen. The powders were collected from the glass
slide using a razor blade and crushed in an agate mortar and pestle before being put into alumina
crucible for annealing at elevated temperatures in a tube furnace under flowing nitrogen. Bulk
powder samples were annealed for 8 h at 400 °C. For structural refinements, the step size and
collection time were 0.01˚ and 3 s step
–1
, respectively. All patterns were recorded under ambient
conditions. Rietveld refinements were carried out using the General Structure Analysis System II
(GSAS-2) software package. The following parameters were refined: (1) scale factor, (2)
background (modeled using a shifted Chebyshev polynomial function), (3) peak shape, (4) lattice
170
constants (a, b, c), (5) fractional atomic coordinates of the Cu, Bi, and S atoms constrained by the
site symmetry, (6) preferred orientation using a spherical harmonic model, and (7) isotropic
thermal parameters for each chemical species. The Rwp and G.O.F. indicators were employed to
assess the quality of the refined structural models. UV-vis-NIR transmittance spectroscopy was
performed on a Perkin Elmer Lambda 950 equipped with a 150-mm integrating sphere. The thin
film on glass was placed in front of the integrating sphere and transmittance spectra was collected
to obtain the absorption coefficient. Thermal gravimetric analysis (TGA) was performed on a TA
Instruments TGA Q50 instrument and samples were run in an alumina crucible under a flowing
nitrogen atmosphere with a heating rate of 5 ˚C min
–1
. The TGA samples were prepared by drying
the ink in an alumina crucible to 140 ˚C under a flowing nitrogen atmosphere in an aluminum
annealing chamber prior to TGA analysis to avoid excess corrosion of the thermocouple in the
TGA. FT-IR spectra were measured on a Bruker Vertex 80 spectrometer. The samples were
prepared by drop casting the Cu3BiS3 ink onto a ZnSe window and drying to 150 ˚C before
annealing to 400 ˚C under a flowing stream of nitrogen. Scanning electron microscopy (SEM) was
performed on a JEOL JSM-7001F scanning electron microscope with an operating voltage of 10
kV . The films were scored with a diamond scribe and broke in half before SEM imaging.
Inductively-coupled plasma optical emission spectroscopy (ICP-OES) was performed on an iCap
7400 ICP. All powder samples were digested with 2 mL of concentrated nitric acid and
subsequently diluted to 25 mL with Millipore water in a volumetric flask. Copper and bismuth ICP
standards were prepared at different concentrations (10 ppm, 20 ppm, 40 ppm, 60 ppm, 100 ppm)
to construct a five-point calibration curve from which the sample concentrations of Cu and Bi
could be determined. Raman spectra were conducted on 490 nm wittichenite thin films on Si/SiO2
substrates annealed to 400 °C. Spectra were recorded for 1 min using an average of three scans
171
using a Horiba XploRA confocal Raman microscope with 532 nm excitation. The Raman
microscope was covered with a black tarp to reduce ambient light exposure. X-ray photoelectron
spectroscopy (XPS) was performed using a Kratos Axis Ultra X-ray photoelectron spectrometer
with a monochromatic aluminum anode. An operating current of 5 mA and voltage of 12 kV with
a step size of 0.1 eV , a pass energy of 20 eV , and a pressure range of 9´10
–8
– 1´10
–9
Torr was used
to acquire 20 high resolution scans for each element. XPS was done on thin films deposited on
Si/SiO2 substrates using the solution deposition method described in the main text.
5.4.5 Property Measurements
Conductivity measurements were performed on Cu3BiS3 thin films (490 nm average
thickness) deposited on a 1 cm
2
borosilicate substrates. Cu leads were attached to the four corners
of the square thin film with colloidal Ag paste (Ted Pella, Inc.). A Quantum Design Physical
Properties Measurement System (PPMS) regulated the thin film temperature and applied a
magnetic field of 10000 Oe. A Keithley 2182A nanovoltmeter and a Keithley 6220 current source,
controlled by a Keithley 7065 Hall effect card, were used to collect the conductivity data.
Photoelectrochemical measurements were performed with FTO slides (Sigma Aldrich) with a
conductivity of ca. 7 Ω sq
–1
that were cut into 0.5´2.5 cm
2
pieces and were cleaned as described
above. Kapton tape was used to mask off a portion of the substrate for electrode contact. Films of
Cu3BiS3 were prepared as described above. Silver paint was used to attach a silver wire to the
unmasked FTO substrate. Loctite epoxy was applied over the wire and around the edges of the
film to mask these areas from solution and the electrodes were allowed to dry for 24 h before use.
Photocurrent response measurements of the Cu3BiS3 thin films were collected with a VersaSTAT
3 potentiostat. The two-chambered glass photoelectrochemical cell contained a graphite rod
172
counter electrode (Graphite Machining, Inc., Grade NAC-500 purified, < 10 ppm ash level), a
Ag|AgCl (3 M KCl) reference electrode, and a Cu3BiS3 thin film on FTO-coated glass as the
working electrode. The working and reference electrodes were placed in one chamber, which is
separated from the counter electrode chamber by a fine porosity glass frit. The electrolyte consisted
of aqueous 0.1 M Eu(NO3)3 as the sacrificial oxidant. The solution was sparged with N2 via
bubbling for 10 min before the experiments, and then N2 was continuously flowed over the head
space during the experiments. Simulated sunlight from an AM1.5G filtered 300 W xenon arc lamp
(Asahi Spectra HAL-320W) was used to illuminate the sample from dark conditions.
5.4.6 Band Gap Determination from ILD Method Derivation
55
Taking the natural log of the Tauc equation (eq 1) yields eq 3, where α is the absorption
coefficient, h is Planck’s constant, ν is the frequency of light, a is a constant, Eg is the intrinsic
band gap, and m is a constant with different assigned values depending on the dispersion of the
valence and conduction bands.
(1)
(2)
(3)
Taking the derivative of eq 3 with respect to the independent variable hν gives eq 5.
(4)
(5)
Taking the inverse of eq 5,
173
(6)
Distributing 1/m in eq 6 yields eq 7. Both the values of m and Eg can be found without prior
knowledge of the electronic structure of the material.
(7)
5.5 Conclusions
We showed the utility of thiol-amine solvent mixtures to solution process phase pure
Cu3BiS3 thin films using a semiconductor ink prepared by dissolving bulk CuO and Bi2S3 powders
in the proper stoichiometric ratio. The resulting thin films possess a direct band gap Eg = 1.47 eV
with a high absorption coefficient through the visible spectrum of a = 10
5
cm
–1
. We investigated
the properties of the Cu3BiS3 thin films and confirmed that the electronic properties and
photocurrent responses rival prior thin films of Cu3BiS3 prepared by other deposition methods.
The alkahest method has shown to be a reliable solution-based route for other high
efficiency multinary chalcogenide thin film solar cells. We believe solution-processed Cu3BiS3
absorber layers, with its stable photocurrent response, highlight the potential for this material in
solar energy conversion applications, including as potential photocatalysts or photodetectors.
174
5.6 References
(1) Polman, A.; Knight, M.; Garnett, E. C.; Ehrler, B.; Sinke, W. C. Photovoltaic Materials:
Present Efficiencies and Future Challenges. Science 2016, 352, aad4424.
(2) Fthenakis, V. M.; Morris, S. C.; Moskowitz, P. D.; Morgan, D. L. Toxicity of Cadmium
Telluride, Copper Indium Diselenide, and Copper Gallium Diselenide. Prog. Photovoltaics 2000,
7, 489–497.
(3) Razykov, T. M.; Ferekides, C. S.; Morel, D.; Stefanakos, E.; Ullal, H. S.; Upadhyaya, H.
M. Solar Photovoltaic Electricity: Current Status and Future Prospects. Sol. Energy 2011, 85,
1580–1608.
(4) Ganose, A. M.; Savory, C. N.; Scanlon, D. O. Beyond Methylammonium Lead Iodide:
Prospects for the Emergent field of ns
2
Containing Solar Absorbers. Chem. Commun. 2017, 53,
20−44.
(5) Du, M. H. Efficient Carrier Transport in Halide Perovskites: Theoretical Perspectives. J.
Mater. Chem. A 2014, 2, 9091–9098.
(6) Sun, J.; Singh, D. J. Electronic Properties, Screening, and Efficient Carrier Transport in
NaSbS2. Phys. Rev. Appl. 2017, 7, 024015.
(7) Sinsermsuksakul, P.; Sun, L.; Lee, S. W.; Park, H. H.; Kim, S. B.; Yang, C.; Gordon, R.
G. Overcoming Efficiency Limitations of SnS-based Solar Cells. Adv. Energy Mater. 2014, 4,
1400496.
(8) Banu, S.; Ahn, S. J.; Ahn, S. K.; Yoon, K.; Cho, A. Fabrication and Characterization of
Cost-Efficient CuSbS2 Thin Film Solar Cells Using Hybrid Inks. Sol. Energy Mater. Sol. Cells
2016, 151, 14–23.
175
(9) Choi, Y. C.; Lee, D. U.; Noh, J. H.; Kim, E. K.; Seok, S. I. Highly Improved Sb2S3
Sensitized-Inorganic Organic Heterojunction Solar Cells and Quantification of Traps by Deep-
Level Transient Spectroscopy. Adv. Funct. Mater. 2014, 24, 3587−3592.
(10) Sugaki, A.; Shima, H. Phase Relations of the Cu2S-Bi2S3 System. Technol. Rep. Yamaguchi
Uni. 1972, 1, 71–85.
(11) Whittles, T. J.; Veal, T. D.; Savory, C. N.; Yates, P. J.; Murgatroyd, P. A. E.; Gibbon, J.
T.; Birkett, M.; Potter, R. J.; Major, J. D.; Durose, K.; Scanlon, D. O.; Dhanak, V. R. Band
Alignments, Band Gap, Core Levels, and Valence Band States in Cu3BiS3 for Photovoltaics. ACS
Appl. Mater. Interfaces 2019, 11, 27033–27047.
(12) Kocman, V.; Nuffield, E. W. The Crystal Structure of Wittichenite, Cu3BiS3. Acta Cryst.
1973, 29, 2528−2535.
(13) Kumar, M.; Persson, C. Cu3BiS3 as a Potential Photovoltaic Absorber with High Optical
Efficiency. Appl. Phys. Lett. 2013, 102, 062109.
(14) Mohan, R. Green Bismuth. Nat. Chem. 2010, 2, 336.
(15) Mineral Commodity Summaries 2016; U.S. Geological Survey, U.S. Government Printing
Office: Washington, DC, 2016, 36–81.
(16) Lokanc, M.; Eggert, R.; Redlinger, M. The Availability of Indium: The Present, Medium
Term, and Long Term. National Renewable Energy Laboratory Report; U.S. Department of
Energy: Golden, CO, 2015.
(17) Cao, J.; Choi, C. H.; Zhao, F. Agent-Based Modeling for By-Product Metal Supply–A Case
Study on Indium. Sustainability 2021, 13, 7881.
(18) Gerein, N. J.; Haber, J. A. Synthesis of Cu3BiS3 Thin Films by Heating Metal and Metal
Sulfide Precursor Films under Hydrogen Sulfide. Chem. Mater. 2006, 18, 6289−6296.
176
(19) Gerein, N. J.; Haber, J. A. One-Step Synthesis and Optical and Electrical Properties of Thin
Film Cu3BiS3 for Use as a Solar Absorber in Photovoltaic Devices. Chem. Mater. 2006, 18, 6297–
6302.
(20) Mesa, F.; Gordillo, G.; Dittrich, T.; Ellmer, K.; Baier, R.; Sadewasser, S. Transient Surface
Photovoltage of p-Type Cu3BiS3. Appl. Phys. Let. 2010, 96, 082113.
(21) Mitzi, D. B. Solution-Processed Inorganic Semiconductors. J. Mater. Chem. 2004, 14,
2355–2365.
(22) Liu, S.; Wang, X.; Nie, L.; Chen, L.; Yuan, R. Spray Pyrolysis Deposition of Cu3BiS3 Thin
Films. Thin Solid Films 2015, 585, 72–75.
(23) Pai, N.; Lu, J.; Senevirathna, D. C.; Chesman, A. S. R.; Gengenbach, T.; Chatti, M.; Bach,
U.; Andrews, P. C.; Spiccia, L.; Cheng, Y.-B.; Simonov, A. N. Spray Deposition of AgBiS2 and
Cu3BiS3 Thin Films for Photovoltaic Applications. J. Mater. Chem. C 2018, 6, 2483–2494.
(24) Colombara, D.; Peter, L. M.; Hutchings, K.; Rodgers, K. D.; Schafer, S.; Dufton, J. T. R.;
Islam, M. S. Formation of Cu3BiS3 Thin Films via Sulfurization of Bi-Cu Metal Precursors. Thin
Solid Films 2012, 520, 5165–5171.
(25) Kamimura, S.; Beppu, N.; Sasaki, Y.; Tsubota, T.; Ohno, T. Platinum and Indium Sulfide-
Modified Cu3BiS3 Photocathode for Photoelectrochemical Hydrogen Evolution. J. Mater. Chem.
A 2017, 5, 10450−10456.
(26) Deshmukh, S. G.; Patel, S. J.; Patel, K. K.; Panchal, A. K.; Kheraj, V. Effect of Annealing
Temperature on Flowerlike Cu3BiS3 Thin Films Grown by Chemical Bath Deposition. J. Electron.
Mater. 2017, 46, 5582–5588.
(27) Deshmukh, S. G.; Panchal, A. K.; Kheraj, V. Development of Cu3BiS3 Thin Films by
Chemical Bath Deposition Route. J. Mater. Sci., Mater. Electron. 2017, 28, 11926–11933.
177
(28) Deshmukh, S. G.; Kheraj, V.; Karande, K. J.; Panchal, A. K.; Deshmukh, R. S. Hierarchical
Flower-Like Cu3BiS3 Thin Film Synthesis with Non-Vacuum Chemical Bath Deposition
Technique. Mater. Res. Express 2019, 6, 084013.
(29) Li, J.; Han, X.; Zhao, Y.; Li, J.; Wang, M.; Dong, C. One-Step Synthesis of Cu3BiS3 Thin
Films by a Dimethyl Sulfoxide (DMSO)-Based Solution Coating Process for Solar Cell
Application. Sol. Energy Mater. Sol. Cells 2018, 174, 593−598.
(30) Deshmukh, S. G.; Kheraj, V. A Comprehensive Review on Synthesis and Characterizations
of Cu3BiS3 Thin Films for Solar Photovoltaics. Nanotechnol. Environ. Eng. 2017, 2, 1–12.
(31) Webber, D. H.; Brutchey, R. L. Alkahest for V2VI3 Chalcogenides: Dissolution of Nine
Bulk Semiconductors in a Diamine-Dithiol Solvent Mixture. J. Am. Chem. Soc. 2013, 135,
15722−15725.
(32) Antunez, P. D.; Torelli, D. A.; Yang, F.; Rabuffetti, F. A.; Lewis, N. S.; Brutchey, R. L.
Low Temperature Solution-Phase Deposition of SnS Thin Films. Chem. Mater. 2014, 26,
5444−5446.
(33) McCarthy, C. L.; Webber, D. H.; Schueller, E. C.; Brutchey, R. L. Solution-Phase
Conversion of Bulk Metal Oxides to Metal Chalcogenides Using a Simple Thiol-Amine Solvent
Mixture. Angew. Chem., Int. Ed. 2015, 54, 8378−8381.
(34) McCarthy, C. L.; Cottingham, P.; Abuyen, K.; Schueller, E. C.; Culver, S. P.; Brutchey, R.
L. Earth Abundant CuSbS2 Thin Films Solution Processed from Thiol-Amine Mixtures. J. Mater.
Chem. C 2016, 4, 6230−6233.
(35) McCarthy, C. L.; Brutchey, R. L. Solution Deposited Cu2BaSnS4-xSex from a Thiol-Amine
Solvent Mixture. Chem. Mater. 2018, 30, 304−308.
178
(36) McCarthy, C. L.; Brutchey, R. L. Solution Processing of Chalcogenide Materials Using
Thiol-Amine “Alkahest” Solvent Systems. Chem. Commun. 2017, 53, 4888−4902.
(37) Koskela, K. M.; Melot, B. C.; Brutchey, R. L. Solution Deposition of a Bournonite
CuPbSbS3 Semiconductor Thin Film from the Dissolution of Bulk Materials with a Thiol-Amine
Solvent Mixture. J. Am. Chem. Soc. 2020, 142, 6173–6179.
(38) Zhao, X.; Lu, M.; Koeper, M. J.; Agrawal, R. Solution-Processed Sulfur Depleted
Cu(In,Ga)Se2 Solar Cells Synthesized from a Monoamine-Dithiol Solvent Mixture. J. Mater.
Chem. A 2016, 4, 7390-7397.
(39) Arnou, P.; van Hest, M. F. A. M.; Cooper, C. S.; Malkov, A. V.; Walls, J. M.; Bowers, J.
W. Hydrazine-Free Solution-Deposited CuIn(S,Se)2 Solar Cells by Spray Deposition of Metal
Chalcogenides. ACS Appl. Mater. Interfaces 2016, 8, 11893–11897.
(40) Uličná, S.; Arnou, P.; Abbas, A.; Togay, M.; Welch, L. M.; Bliss, M.; Malkov, V.; Walls,
J. M.; Bowers, J. W. Deposition and Application of a Mo-N Back Contact Diffusion Barrier
Yielding a 12.0% Efficiency Solution-Processed CIGS Solar Cell Using a Thiol-Amine Solvent
System. J. Mater. Chem. A 2019, 7, 7042–7052.
(41) Yakushev, M. V.; Maiello, P.; Raadik, T.; Shaw, M. J.; Edwards, P. R.; Krustok, J.;
Mudryi, A. V.; Forbes, I.; Martin, R. W. Electronic and Structural Characterisation of Cu3BiS3
Thin Films for the Absorber Layer of Sustainable Photovoltaics. Thin Solid Films 2014, 562, 195–
199.
(42) Yan, C.; Gu, E.; Liu, F.; Lai, Y.; Li, J.; Liu, Y. Colloidal Synthesis and Characterization
of Wittichenite Copper Bismuth Sulphide Nanocrystals. Nanoscale 2013, 5, 1789–1792.
(43) Zhong, J.; Xiang, W.; Cai, Q.; Liang, X. Synthesis, Characterization and Optical Properties
of Flower-Like Cu3BiS3 Nanorods. Mater. Lett. 2012, 70, 63–66.
179
(44) Hurma, T.; Kose, S. XRD Raman Analysis and Optical Properties of CuS Nanostructured
Film. Optik 2016, 127, 6000−6006.
(45) Shuai, X.; Shen, W.; Hou, Z.; Ke, S.; Xu, C.; Jiang, C.; A Versatile Chemical Conversion
Synthesis of Cu2S Nanotubes and the Photovoltaic Activities for Dye-Sensitized Solar Cell.
Nanoscale Res. Lett. 2014, 9, 1–7.
(46) Kaltenhauser, V.; Rath, T.; Haas, W.; Torvisco, A.; Müller, S. K.; Friedel, B.; Kunert, B.;
Saf, R.; Hofer, F.; Trimmel, G. Bismuth Sulphide-Polymer Nanocomposites from a Highly Soluble
Bismuth Xanthate Precursor. J. Mater. Chem. C 2013, 1, 7825–7832.
(47) Wang, J. J.; Akgul, M. Z.; Bi, Y.; Christodoulou, S.; Konstantatos, G. Low-Temperature
Colloidal Synthesis of CuBiS2 Nanocrystals for Optoelectronic Devices. J. Mater. Chem. A 2017,
5, 24621−24625.
(48) Hernádez-Mota, J.; Espíndola-Rodríguez, M.; Sánchez, Y.; López, I.; Peña, Y.; Saucedo,
E. Thin Film Photovoltaic Devices Prepared with Cu3BiS3 Ternary Compound. Mater. Sci.
Semicond. Process. 2018, 87, 37–43.
(49) Murali, B.; Madhuri, M.; Krupanidhi, S. B. Near-Infrared Photoactive Cu3BiS3 Thin Films
by Co-Evaporation. J. Appl. Phys. 2014, 115, 173109.
(50) Lebugle, A.; Axelsson, U.; Nyholm, R.; Mårtensson, N. Experimental L and M Core Level
Binding Energies for the Metals
22
Ti to
30
Zn. Phys. Scr. 1981, 23, 825–827.
(51) Biesenger, M. C.; Lau, L. W. M.; Gerson, A. R.; Smart, R. S. C. Resolving Surface
Chemical States in XPS Analysis of First Row Transition Metals, Oxides, and Hydroxides: Sc, Ti,
V, Cu, Zn. Appl. Surf. Sci. 2010, 257, 887–898.
(52) Debies, T. P.; Rabalais, J. W. X-Ray Photoelectron Spectra and Electronic Structure of
Bi2X3 (X = O, S, Se, Te) Chem. Phys. 1977, 20, 277–283.
180
(53) Ge, J.; Yan, Y. Synthesis and Characterization of Photoelectrochemical and Photovoltaic
Cu2BaSnS4 Thin Films and Solar Cells. J. Mater. Chem. C 2017, 5, 6406−6419.
(54) Lindberg, B. J.; Hamrin, K.; Johansson, G.; Gelius, U.; Fahlman, A.; Nordling, C.;
Siegbahn, K. Molecular Spectroscopy by Means of ESCA II. Sulfur Compounds. Correlation of
Electron Binding Energy with Structure. Phys. Scr. 1970, 1, 286–298.
(55) Jarosiński, Ł.; Pawlak, J.; Al-Ani, S. K. J. Inverse Logarithmic Derivative Method for
Determining the Energy Gap and the Type of Electron Transitions as an Alternative to the Tauc
Method. Opt. Mater. 2019, 88, 667–673.
181
Appendix. Solution Processing of a (Ag,Na)BiS2 Solid Solution using a Thiol–Amine Solvent
System
A.1 Introduction
Ionic lead halide perovskites (i.e., CsPbBr, (CH3NH3)Pb(Br,I)3, etc.) have revolutionized
a wide-array of optoelectronic applications, including solar absorption
1–3
and light emission.
4–6
But these materials have several potential drawbacks that have limited their adoption in
commercial applications, such as environmental instability due to air/moisture and the toxicity of
Pb.
7
Perovskites belong to a broader class of materials containing ns
2
electrons, such as those
containing Pb
2+
, Sb
3+
, and Bi
3+
.
8,9
These materials have a good defect tolerance due to a high
dielectric constant and contain a heavy element for strong spin–orbit coupling.
10,11
The strong
hybridization (band dispersion) of this class of materials leads to the high carrier mobilities,
11–13
high defect tolerances,
10,14,15
and enhanced dielectric constants which allows highly efficient
carrier transport.
10,14,16
These properties have led to interesting applications in ionic–electronic
coupled materials such as neuromorphic devices.
8,17–20
Beyond lead perovskites, an interesting class of ns
2
containing semiconductors is the cubic
ternary APnE2 (A = Na, Li, K, Ag, Cs, Rb ; Pn = Sb, Bi; E = S, Se) family of materials, which have
shown promise due to the lower toxicity of Bi and Sb as compared to Pb.
21
This class of materials
has found applications in thermoelectrics,
22
and most recently, colloidal AgBiS2 nanocrystals have
been leveraged to produce high efficiency ultrathin solar cells exceeding 9%.
23
Solution processed
AgBiS2 thin films have also been used to produce high-quality photodetectors.
24
Another
interesting material in this cubic ternary material family is the alkali-metal containing NaBiS2.
NaBiS2 semiconductors have been synthesized as ligand stabilized colloidal nanocrystals
25–27
and
several other syntheses have been reported including hydrothermal,
28,29
solvothermal,
30,31
and solid
182
state.
32,33
Solid solutions of Na(Bi,La)S2 have been synthesized in the solid state showing the wide
compositional range of this cubic ternary system.
34
Due to the similar ionic radii and oxidation
states between Ag
+
(Shannon–Prewitt ionic radius: 115 pm) and Na
+
(102 pm) and the cubic crystal
structure (space group) of the two parent phases (AgBiS2 and NaBiS2), a full solid solution may
be accessible, but to the best of our knowledge, no such report exists.
While solid state syntheses have demonstrated wide solid solution compositional tuning of
a NaBiS2-based system, the use of these materials in devices is hampered due the inability to
process bulk powders. Syntheses of ligand stabilized nanocrystals allow for solution processing of
devices, but the efficiency of these devices is reduced due to the insulating nature of the organic
ligands on the nanocrystal surface.
35,36
Nanocrystal syntheses are also limited in forming solid
solutions due to the different reactivities of precursors leading to possible formation of impurity
phases. Here we present the solution processing and characterization of bulk Ag1–xNaxBiS2 solid
solutions and the solution processing of high-quality AgBiS2 thin films using the thiol-amine
alkahest system.
A.2 Results and Discussion
To produce the bulk powders of the Ag1–xNaxBiS2 solid solution, Ag2O, Na2S, and Bi2S3
were mixed stoichiometrically (1–x:x:1 mol/mol/mol, respectively) and dissolved in a 1:10
(vol/vol) binary solvent system made up of ethanedithiol (EDT) and ethylenediamine (en),
respectively, giving an overall concentration of ~90 mg of total solids per mL of solvent. Ag2O
and Na2S both have room temperature solubilities of 15-20 wt% and Bi2S3 has a room temperature
solubility of 10-15 wt%. Different combinations of oxides and sulfides (e.g., Ag2O, Ag2S, Na2S,
Na2O, Bi2S3, Bi2O3) may also return phase pure Ag1–xNaxBiS2, but Ag2O, Na2S, and Bi2S3 were
183
chosen as bulk precursors due to these precursors yielding qualitatively higher-quality thin films.
The semiconductor inks were stirred at 30 °C overnight to yield an optically clear, free flowing,
bright orange solution that does not scatter light (Figure A.1a). The resulting inks were stable and
precipitate-free when kept under ambient conditions for several days.
Figure A.1. a) Representative photographs of Ag1–xNaxBiS2 solid solution inks (left to right:
AgBiS2, Ag0.75Na0.25BiS2, Ag0.50Na0.50BiS2, Ag0.25Na0.75BiS2, NaBiS2). Thermogravimetric
analysis traces of the dried b) AgBiS2 and c) NaBiS2 inks demonstrating a decomposition endpoint
of < 350 ˚C.
Thermogravimetric analysis (TGA) was used to determine an endpoint of volatilization
and decomposition for the solution deposited and dried inks. The AgBiS2 and NaBiS2 inks begin
mass loss at ca. 150 °C and it was found that mass loss terminated < 350 °C for both inks (Figure
A.1b,c). The loss of the organic species upon annealing the dried ink from 150 to 400 °C was
corroborated using FT-IR spectroscopy for both inks (Figure A.2). The IR bands observed in the
dried ink are due to metal–thiolate complexes and residual EDT. Upon annealing to 400 °C, both
the AgBiS2 and NaBiS2 inks showed an absence of organic IR bands, confirming complete
decomposition.
184
Figure A.2. FT-IR spectra of a) AgBiS2 and b) NaBiS2 inks dried to 150 °C and annealed at
400 °C, confirming the decomposition and complete loss of the organic species.
To prove the versatility of thiol-amine alkahest mixtures to solution process phase-pure
Ag1–xNaxBiS2 solid solutions, bulk powders of AgBiS2, Ag0.75Na0.25BiS2, Ag0.50Na0.50BiS2,
Ag0.25Na0.75BiS2, NaBiS2 were drop-casted on borosilicate glass substrates and annealed to 400
°C. Figure A.3a shows the powder X–ray diffraction patterns of the full solid solution and
analogous peak shift at 2q = ~31° (Figure A.3b). These peaks match well to the cubic rock salt
space group. The Vegard’s plot using experimental compositional data (SEM–EDS) and the lattice
parameter calculated from the 100 % intensity peak at 2q = ~31° is plotted in Figure A.3c. From
this data, we confirmed the formation of a full solid solution between AgBiS2 and NaBiS2 without
any noticeable deviation of Vegard’s law. Rietveld refinements of the two parent phases, AgBiS2
and NaBiS2 are plotted in Figures A.4a and A.4b, respectively. The structural refinement
parameters are given in Tables A.1 and A.2, respectively. The AgBiS2 refinement returned a
G.O.F. of 2.14, wR of 8.96% and a lattice parameter of a = 5.6266(3) Å. This matches well to
previously reported bulk AgBiS2 with lattice parameter a = 5.65 Å.
47
The NaBiS2 refinement
returned a G.O.F. of 2.52, wR of 3.64% and a lattice parameter of a = 5.7766(1) Å, matching well
185
to previously reported bulk NaBiS2 (a = 5.76 Å).
48
The optical band gaps of the Ag1–xNaxBiS2 solid
solutions were derived from diffuse reflectance data treated with the Kubelka–Munk function and
extrapolating the linear region of the plot. Direct optical band gaps of the bulk powders are plotted
in Figure A.5 showing near-linear band gap tunability of 500 meV. Direct optical band gaps of
0.82 eV and 1.30 eV for bulk AgBiS2 and NaBiS2, respectively, match well to previously reported
experimental literature.
26,49
Figure A.3. a) Experimental powder X–ray diffraction patterns of Ag1–xNaxBiS2 solid solutions.
b) Stacked plot of peak shift at 2q = ~31° showing 100% intensity peak shifting to higher 2q values
with the alloying of Na
+
. c) Vegard’s law plot showing linear lattice and volume expansions with
alloying of Na
+
.
186
Figure A.4. Rietveld refinements of a) AgBiS2 (G.O.F. = 2.14, wR = 8.96%) and b) NaBiS2
(G.O.F. = 2.52, wR 3.64%). l = 1.5406.
Table A.1. Structural refinement parameters extracted from Rietveld refinement for AgBiS2.
Atom Mult. x y z Frac. Uiso
Ag1 4 0.0 0.0 0.0 0.4964 0.02854
Bi1 4 0.0 0.0 0.0 0.4978 0.01369
S1 4 0.5 0.5 0.5 1.1275 0.04031
Space Group Fmm
a (Å) = b (Å) = c (Å) 5.6266(3)
a = b = g 90˚
Rwp
G.O.F.
Reduced
8.96%
2.14
4.57
187
Table A.2. Structural refinement parameters extracted from Rietveld refinement for NaBiS2.
Atom Mult. x y z Frac. Uiso
Na1 4 0.0 0.0 0.0 0.5 0.13664
Bi1 4 0.0 0.0 0.0 0.5 0.02022
S1 4 0.5 0.5 0.5 1 0.01530
Using the same inks as described above, thin films of AgBiS2 were spin coated on Si
substrates at 3000 rpm for 30 s and annealed to 400 °C under flowing N2 and allowed to cool
naturally to room temperature. Three success coats were applied to yield an average film thickness
of 175 nm. Scanning electron microscopy images in Figure A.5 show high-quality thin films free
of microcracks and pinholes. The SEM images show smooth surface roughness which is further
proved by the mirror-like reflection of our thin films. Raman spectroscopy was employed to prove
the phase purity of our thin films and a single Raman band at 256 cm
-–1
matches prior literature
(Figure A.6a) for Bi–S modes.
50
The absorption coefficient derived from transmittance data is
plotted in Figure A.6b. A high absorption coefficient of a = 1.3´10
5
cm
–1
is reached by 1.4 eV
and a direct optical band gap of 1.00 eV is derived from Tauc treatment of the absorption data
(Figure A.6c). A blue shifted band gap compared to the bulk powders is due to smaller nano–sized
grains in the thin films. This is possible as colloidal AgBiS2 nanocrystals exhibit a direct band gap
of 1.3 eV.
23
Space Group Fmm
a (Å) = b (Å) = c (Å) 5.7766(1)
a = b = g 90˚
Rwp
G.O.F.
Reduced
3.64%
2.52
6.34
188
Figure A.5. a) Top–down scanning electron microscopy (SEM) image of the spin coated 175 nm
AgBiS2 thin film deposited on Si substrate at 5000´ (scale bar = 10 mm). Side–on SEM images of
AgBiS2 thin film at b) 35,000´ (scale bar = 2 mm) and c) 100,000´ (scale bar = 500 nm).
Figure A.6. a) Raman spectrum, b) absorption coefficient and c) Tauc plot of 175 nm AgBiS2 thin
film deposited on borosilicate glass at 400 °C.
X-ray photoelectron spectroscopy (XPS) was used to gauge the valence states of our spin
coated 175 nm AgBiS2 thin film deposited on a Si substrate and annealed to 400 °C. A survey scan
of our thin films that were exposed to ambient conditions is plotted in Figure A.7. High-resolution
XPS spectra of the Ag 3d, Bi 4f/S 2p, and S 2s regions are plotted in Figures A.8a–c, respectively,
and the corresponding peak fittings are given in Table A.3. The Ag 3d region can be fit with a
single set of doublets at 367.5 and 373.5 eV (splitting = 6.0 eV). These match well to a single Ag
+
environment and agree with prior literature for AgBiS2.
22
The Bi 4f region can be fit with two sets
of doublets each with a splitting 5.3 eV. The first set of doublets at 158.5 eV and 163.8 eV match
well to Bi
3+
in a sulfide environment and match well to previously reported AgBiS2 samples.
40,22
189
The second set of doublets at 159.0 and 164.3 eV most likely correspond to Bi
3+
in an oxide
environment or non-stoichiometric bismuth oxides on the surface.
22,24,40
A third doublet with a 1.2
eV splitting is attributed to sulfide S 2p peaks and agrees with previous experimental reports of
AgBiS2.
22,24,40
The S 2s region was investigated due to the peak overlap of the Bi 4f and S 2p peaks
and difficulty in assigning minor peaks in the S 2p region. The singlet at 225.7 eV corresponds to
sulfur in a sulfide (S
2–
) environment and the singlet at higher binding energy (227.0 eV)
corresponds to atmospheric contaminated sulfur species.
40,51
Together, XPS confirms the valence
states of our spin coated thin films as Ag
+
Bi
3+
(S
2–
)2.
Figure A.7. XPS survey scan of AgBiS2 thin film on Si and annealed to 400 °C.
0 500 1000
Binding Energy (eV)
Intensity (a.u.)
Bi 4f
S 2p
Bi 4d
C 1s
S 2s
Bi 5d
Ag 3d
190
Figure A.8. High-resolution XPS spectra of a) Ag 3d region, b) Bi 4f and S 2p, and c) S 2s spectral
regions.
191
Table A.3. Peak positions and peak splitting from the high-resolution XPS spectra of AgBiS2 thin
films on Si annealed at 400 °C.
Element Peak Splitting
(eV)
Peak ID Binding Energy
(eV)
Ag 6.0 3d3/2 373.5
3d5/2 367.5
Bi 5.3 4f5/2 163.8
4f7/2 158.5
Bi (surface BiOx) 5.3 4f5/2 164.3
4f7/2 159.0
S 1.2 2p1/2 162.6
2p3/2 161.4
S
2s 225.7
S (surface carbon
contamination)
2s 227.0
A.3 Experimental
A.3.1 General Considerations
All materials were used as received. 1,2-Ethylenediamine (en, 99.5%), bismuth(III) sulfide
(Bi2S3, 99.995%), and sodium(I) sulfide (Na2S, 99%) were purchased from Sigma Aldrich. 1,2–
192
Ethanedithiol (EDT, 98+%) and silver(I) oxide (Ag2O, 99%) was purchased from Alfa Aesar. All
reagents used as received.
A.3.2 Synthetic Ink Preparation
To generate the AgBiS2 semiconductor ink, 14.5 mg (0.063 mmol) Ag2O and 32.2 mg
(0.063 mmol) Bi2S3 were dissolved in 0.05 mL EDT and 0.5 mL en with stirring at 30 ˚C overnight
under air (1 atm). If the solvents solidified upon addition to the bulk solid precursors, gentle heating
can be used to re-liquify the ink. To generate the NaBiS2 semiconductor ink, 4.9 mg (0.063 mmol)
Na2S and 32.2 mg (0.063 mmol) Bi2S3 were dissolved in 0.05 mL EDT and 0.5 mL en with stirring
at 30 ˚C overnight under air (1 atm). To make the solid solution inks, stoichiometric amounts of
Ag2O and Na2S were added to form Ag0.75Na0.25BiS2, Ag0.50Na0.50BiS2, and Ag0.25Na0.75BiS2.
A.3.3 Bulk Powder Recovery
Bulk powders were solution processed by drop casting onto borosilicate glass substrates.
The bulk powders were heated to 400 ˚C under N2 and allowed to cool naturally before recovering
the powders by scraping a glass side with a razor blade and grinding the powders with an agate
mortar and pestle before measurements.
A.3.4 AgBiS2 Thin Film Deposition
Thin films were solution processed by spin coating onto ca. 1 cm
2
borosilicate glass or Si
substrates that were pre-cleaned by bath sonication in methanol, acetone, and then isopropyl
alcohol (each for 10 min). The final ink (90 mg mL
–1
) was spin coated onto the substrate at 2500
193
rpm for 1 min under N2. The films were heated to 400 ˚C under N2 in between coats and allowed
to return to room temperature before the next layer was deposited.
A.3.5 Organic Content Determination
Thermal gravimetric analysis (TGA) was performed on a TA Instruments TGA Q50
instrument and samples were run in an alumina crucible under a flowing nitrogen atmosphere with
a heating rate of 5 ˚C min
–1
. The TGA samples were prepared by drying the ink in an alumina
crucible to 100 ˚C under a flowing nitrogen atmosphere in an aluminum annealing chamber prior
to TGA analysis to avoid excess corrosion of the thermocouple in the TGA. FT-IR spectra were
measured on a Bruker Vertex 80 spectrometer. The samples were prepared by drop casting the
AgBiS2 and NaBiS2 ink onto a ZnSe window and drying to 150 ˚C before annealing to 400 ˚C
under a flowing stream of nitrogen.
A.3.6 Structural and Optical Characterization
Powder X–ray diffraction (XRD) patterns were collected using a Rigaku Ultima IV
diffractometer operated at 44 mA and 40 kV, in the 2q range of 10-70˚ using Cu Ka radiation (l
= 1.5406 Å). For powder diffraction studies, inks were drop cast on a glass slide and dried to 400
°C in an aluminum annealing chamber under flowing nitrogen. The powders were collected from
the glass slide using a razor blade and crushed in an agate mortar. For structural refinements, the
step size and collection time were 0.01˚ and 3 s step
–1
, respectively. All patterns were recorded
under ambient conditions. Rietveld refinements were carried out using the General Structure
Analysis System II (GSAS-2) software package. The following parameters were refined: (1) scale
factor, (2) background (modeled using a shifted Chebyshev polynomial function), (3) peak shape,
194
(4) lattice constants (a), (5) fractional atomic coordinates of the Cu, Sn, and S atoms constrained
by the site symmetry, (6) preferred orientation using a spherical harmonic model, and (7) isotropic
thermal parameters for each chemical species. The Rwp and wR indicators were employed to assess
the quality of the refined structural models. Diffuse reflectance UV-vis-NIR transmittance
spectroscopy was performed on a Perkin Elmer Lambda 950 equipped with a 150-mm integrating
sphere. 12 mg of sample was mixed with 350 mg of BaO and placed in a solid sample holder.
Scanning electron microscopy/ energy dispersive X-ray spectroscopy (SEM–EDS) was performed
using a FEI Helios G4 P-FIB at 20 kV. Top surface micrographs were acquired via SEM using a
beam current of 0.8 nA and an accelerating voltage of 5 kV. Raman spectra were conducted on
samples deposited on Si substrates annealed to 400 °C. Spectra were recorded for 1 min using an
average of three scans using a Horiba XploRA confocal Raman microscope with 532 nm
excitation. The Raman microscope was covered with a black tarp to reduce ambient light exposure.
X-ray photoelectron spectroscopy (XPS) was performed using a Kratos Axis Ultra X-ray
photoelectron spectrometer with a monochromatic aluminum anode (1486.6 eV). An operating
current of 5 mA and voltage of 12 kV with a step size of 0.1 eV and a pass energy of 20 eV was
used to acquire 20 high resolution scans for each element. An operating current of 5 mA and
voltage of 12 kV with a step size of 1 eV and pass energy of 80 eV was used to acquire 5 survey
scans for each sample. Pressure in the analysis chamber < 1E-9 Torr. XPS was done on thin films
deposited on Si substrates.
A.4 Conclusions
In conclusion, we solution deposited the full Ag1–xNaxBiS2 solid solution in the bulk from
thiol–amine (‘alkahest’) solvent mixtures with direct band gap tunability of 0.5 eV (0.8–1.3 eV)
195
and further proved the versatility of alkahest solvent mixtures to solution deposit high-quality
AgBiS2 thin films. We characterized the inks and resulting bulk solid solutions and thin films with
TGA, FT-IR, XRD, XPS, UV-vis, and Raman spectroscopy.
A.5 References
(1) Haegel, N. M.; Margolis, R.; Buonassisi, T.; Feldman, D.; Froitzheim, A.; Garabedian, R.;
Green, M.; Glunz, S.; Henning, H.- M.; Holder, B.; Kaizuka, I.; Kroposki, B.; Matsubara, K.; Niki,
S.; Sakurai, K.; Schindler, R. A.; Tumas, W.; Weber, E. R.; Wilson, G.; Woodhouse, M.; Kurtz,
S. Terawatt-Scale Photovoltaics: Trajectories and Challenges. Science 2017, 356, 141−143.
(2) Shin, S. S.; Yeom, E. J.; Yang, W. S.; Hur, S.; Kim, M. G.; Im, J.; Seo, J.; Noh, J. H.; Seok,
S. I. Colloidally Prepared La-Doped BaSnO3 Electrodes for Efficient, Photostable Perovskite Solar
Cells. Science 2017, 356, 167−171.
(3) Green, M. A.; Ho-Baillie, A.; Snaith, H. J. The Emergence of Perovskite Solar Cells. Nat.
Photonics 2014, 8, 506−514.
(4) Zhu, F.; Men, L.; Guo, Y.; Zhu, Q.; Bhattacharjee, U.; Goodwin, P. M.; Petrich, J. W.;
Smith, E. A.; Vela, J. Shape Evolution and Single Particle Luminescence of Organometal Halide
Perovskite Nanocrystals. ACS Nano 2015, 9, 2948–2959.
(5) Swarnkar, A.; Marshall, A. R.; Sanehira, E. M.; Chernomordik, B. D.; Moore, T. D.;
Christians, J. A.; Chakrabarti, T.; Luther, J. M. Quantum Dot–Induced Phase Stabilization of a-
CsPbI3 Perovskite for High-Efficiency Photovoltaics. Science 2016, 354, 92–95.
(6) Protesescu, L.; Yakunin, S.;. Bodnarchuk, M. I.; Bertolotti, F.; Masciocchi, N.; Guagliardi,
A.; Kovalenko, M. V. Monodisperse Formamidinium Lead Bromide Nanocrystals with Bright and
Stable Green Photoluminescence. J. Am. Chem. Soc. 2016, 138,14202–14205.
196
(7) Song, Z.; Abate, A.; Watthage, S. C.; Liyanage, G. K.; Phillips, A. B.; Steiner, U.; Graetzel,
M.; Heben, M. J. Perovskite Solar Cell Stability in Humid Air: Partially Reversible Phase
Transitions in the PbI2-CH3NH3I-H2O System. Adv. Energy Mater. 2016, 6, 1600846.
(8) Ganose, A. M.; Savory, C. N.; Scanlon, D. O. Beyond Methylammonium Lead Iodide:
Prospects for the Emergent Field of ns
2
Containing Solar Absorbers. Chem. Commun. 2017, 53,
20−44.
(9) Ran, Z.;. Wang, X. J.; Li, Y. W.; Yang, D. W.; Zhao, X. G.; Biswas, K.; Singh, D. J.;
Zhang, L. G. Bismuth and Antimony-Based Oxyhalides and Chalcohalides as Potential
Optoelectronic Materials. npj Comput. Mater. 2018, 4, 14.
(10) Brandt, R. E.; Stevanovic, V.; Ginley, D. S.; Buonassisi, T. Identifying Defect-Tolerant
Semiconductors with High Minority-Carrier Lifetimes: Beyond Hybrid Lead Halide Perovskites.
MRS Commun. 2015, 5, 265.
(11) Du, M. H. Efficient Carrier Transport in Halide Perovskites: Theoretical Perspectives. J.
Mater. Chem. A 2014, 2, 9091.
(12) Yu, Y.; Zunger, A. Identification of Potential Photovoltaic Absorbers Based on First-
Principles Spectroscopic Screening of Materials. Phys. Rev. Lett. 2012, 108, 068701.
(13) Yu, L.; Kokenyesi, R. S.; Keszler, D. A.; Zunger, A. Inverse Design of High Absorption
Thin-Film Photovoltaic Materials. Adv. Energy Mater. 2013, 3, 43–48.
(14) Sun, J.; Singh, D. J. Electronic Properties, Screening and Efficient Carrier Transport in
NaSbS2. Phys. Rev. Appl. 2017, 7, 024015.
(15) Du, M. H.; Singh, D. J. Enhanced Born charge and Proximity to Ferroelectricity in
Thallium Halides. Phys. Rev. B 2010, 81, 144114.
197
(16) Brandt, R. E.; Poindexter, J. R.; Gorai, P.; Kurchin, R. C.; Hoye, R. L. Z.; Nienhaus, L.;
Wilson, M. W. B.; Polizzotti, J. A.; Sereika, R.; Zaltauskas, R.; Lee, L. C.; MacManus-Driscoll, J.
L.; Bawendi, M.; Stevanovic, V.; Buonassisi, T. Searching for Defect-Tolerant Photovoltaic
Materials: Combined Theoretical and Experimental Screening. Chem. Mater. 2017, 29, 4667–
4674.
(17) Harikesh, P. C.; Surendran, A.; Ghosh, B.; John, R. A.; Moorthy, A.; Yantara, N.; Salim,
T.; Thirumal, K.; Leong, W. L.; Mhaisalkar, S.; Mathews, N. Cubic NaSbS2 as an Ionic-Electronic
Coupled Semiconductor for Switchable Photovoltaic and Neuromorphic Device Applications.
Adv. Mater. 2020, 32, 1906976.
(18) Xiao, Z.; Yuan, Y.; Shao, Y.; Wang, Q.; Dong, Q.; Bi, C.; Sharma, P.; Gruverman, A.;
Huang, J. Giant Switchable Photovoltaic Effect in Organometal Trihalide Perovskite Devices. Nat.
Mater. 2015, 14, 193.
(19) Harikesh, P. C.; Wu, B.; Ghosh, B.; John, R. A.; Lie, S.; Thirumal, K.; Wong, L. H.; Sum,
T. C.; Mhaisalkar, S.; Mathews, N. Doping and Switchable Photovoltaic Effect in Lead-Free
Perovskites Enabled by Metal Cation Transmutation. Adv. Mater. 2018, 30, 1802080.
(20) John, R. A.; Yantara, N.; Ng, Y. F.; Narasimman, G.; Mosconi, E.; Meggiolaro, D.;
Kulkarni, M. R.; Gopalakrishnan, P. K.; Nguyen, C. A.; Angelis, F. D.; Mhaisalkar, S. G.; Basu,
A.; Mathews, N. Ionotronic Halide Perovskite Drift-Diffusive Synapses For Low-Power
Neuromorphic Computation. Adv. Mater. 2018, 30, 1805454.
(21) Mohan, R. Green Bismuth. Nature Chem 2010, 2, 336–336.
(22) Guin, S. N.; Biswas, K. Cation Disorder and Bond Anharmonicity Optimize the
Thermoelectric Properties in Kinetically Stabilized Rocksalt AgBiS 2 Nanocrystals. Chem. Mater.
2013, 25, 3225–3231.
198
(23) Wang, Y.; Kavanaugh, S. R.; Burgués-Ceballos, I.; Walsh, A.; Scanlon, D. O.;
Konstantatos, G. Cation Disordered Engineering Yields AgBiS2 Nanocrystals with Enhanced
Optical Absorption for Efficient Ultrathin Solar Cells. Nat. Photonics 2022, 16, 235–241.
(24) van Embden, J.; Della Gaspera, E. Ultrathin Solar Absorber Layers of Silver Bismuth
Sulfide from Molecular Precursors. ACS Appl. Mater. Interfaces 2019, 11, 16674–16682.
(25) Guo, J.; Ge, Z.; Hu, M.; Qin, P.; Feng, J. Facile Synthesis of NaBiS 2 Nanoribbons as a
Promising Visible Light-Driven Photocatalyst. Phys. Status Solidi RRL 2018, 12, 1800135.
(26) Rosales, B. A.; White, M. A.; Vela, J. Solution-Grown Sodium Bismuth Dichalcogenides:
Toward Earth-Abundant, Biocompatible Semiconductors. J. Am. Chem. Soc. 2018, 140, 3736–
3742.
(27) Yang, C.; Wang, Z.; Wu, Y.; Lv, Y.; Zhou, B.; Zhang, W.-H. Synthesis, Characterization,
and Photodetector Application of Alkali Metal Bismuth Chalcogenide Nanocrystals. ACS Appl.
Energy Mater. 2019, 2, 182–186.
(28) Kang, Sumin; Hong, Yonghoon; Jeon, Youngjin. A Facile Synthesis and Characterization
of Sodium Bismuth Sulfide (NaBiS2) under Hydrothermal Condition. Bulletin of the Korean
Chemical Society 2014, 35, 1887–1890.
(29) Wang, H.; Xie, Z.; Wang, X.; Jia, Y. NaBiS2 as a Novel Indirect Bandgap Full Spectrum
Photocatalyst: Synthesis and Application. Catalysts 2020, 10, 413.
(30) Fei, H.; Feng, Z.; Liu, X. Novel Sodium Bismuth Sulfide Nanostructures: A Promising
Anode Materials for Sodium-Ion Batteries with High Capacity. Ionics 2015, 21, 1967–1972.
(31) Koutavarapu, R.; Lee, G.; Babu, B.; Yoo, K.; Shim, J. Visible-Light-Driven Photocatalytic
Activity of Tiny ZnO Nanosheets Anchored on NaBiS2 Nanoribbons via Hydrothermal Synthesis.
J Mater Sci: Mater Electron 2019, 30, 10900–10911.
199
(32) Park, Y.; Mccarthy, T. J.; Sutorlk, A. C.; Kanatzidis, M. G.; Gillan, E. G. Synthesis of
Ternary Chalcogenides in Molten Polychalcogenide Salts: α-KCuQ4 , KAuS5 , NaBiS2 , KFeQ2
(Q = S, Se). Inorganic Syntheses; Murphy, D. W., Interrante, L. V., Eds.; John Wiley & Sons, Inc.:
Hoboken, NJ, USA, 2007; pp 88–95.
(33) Gabrelian, B. V.; Lavrentyev, A. A.; Nikiforov, I. Ya. To the Explanation of the “White”
Line in the X-Ray K-Absorption Spectrum of Sulfur in NaBiS2. Bull. Russ. Acad. Sci. Phys. 2009,
73, 1001–1003.
(34) BaQais, A.; Tymińska, N.; Le Bahers, T.; Takanabe, K. Optoelectronic Structure and
Photocatalytic Applications of Na(Bi,La)S2 Solid Solutions with Tunable Band Gaps. Chem.
Mater. 2019, 31, 3211–3220.
(35) Kovalenko, M. V.; Scheele, V.; Talapin, D. V. Colloidal Nanocrystals with Molecular
Metal Chalcogenide Surface Ligands. Science 2009, 324, 1417–1420.
(36) Tang, J.; Kemp, K. W.; Hoogland, S.; Jeong, K. S.; Liu, H.; Levina, L.; Furukawa, M.;
Wang, X. H.; Debnath, R.; Cha, D. K.; Chou, K. W.; Fischer, A.; Amassian, A.; Asbury, J. B.;
Sargent, E. H. Colloidal-Quantum-Dot Photovoltaic using Ligand Passivation. Nat. Mater. 2011,
10, 765–771.
(37) Webber, D. H.; Brutchey, R. L. Alkahest V2VI3 Chalcogenides: Dissolution of Nine
Semiconductors in a Diamine–Dithiol Solvent Mixture. J. Am. Chem. Soc. 2013, 135,
15722−15725.
(38) Koskela, K. M.; Strumolo, M. J.; Brutchey, R. L. Progress of Thiol-Amine ‘Alkahest’
Solutions for Thin Film Deposition. Trends Chem. 2021, 3, 1061–1073.
200
(39) McCarthy, C. L.; Downes, C. A.; Schueller, E. C.; Abuyen, K.; Brutchey, R. L. Method
for the Solution Deposition of Phase-Pure CoSe2 as an Efficient Hydrogen Evolution Reaction
Electrocatalyst. ACS Energy Lett. 2016, 1, 607-611.
(40) Koskela, K. M.; Tadle, A. C.; Chen K.; Brutchey, R. L. Solution Processing Cu3BiS3
Absorber Layers with a Thiol–Amine Solvent Mixture. ACS Appl. Energy Mater. 2021, 4, 11026–
11031.
(41) Koskela, K. M.; Melot, B. C.; Brutchey, R. L. Solution Deposition of a Bournonite
CuPbSbS3 Semiconductor Thin Film from the Dissolution of Bulk Materials with a Thiol–Amine
Solvent Mixture. J. Am. Chem. Soc. 2020, 142, 6173−6179.
(42) McCarthy, C. L.; Webber, D. H.; Schueller, E. C.; Brutchey, R. L. Solution-Phase
Conversion of Bulk-Metal Oxides to Metal Chalcogenides Using a Simple Thiol–Amine Solvent
Mixture. Angew. Chem., Int. Ed. 2015, 54, 8378–8381.
(43) McCarthy, C. L.; Brutchey, R. L. Solution Deposited Cu2BaSnS4-xSex from a Thiol–Amine
Solvent Mixture. Chem. Mater. 2018, 30, 304−308.
(44) Zhao, Y.; Yuan, S.; Chang, Q.; Zhou, Z.; Kou, D.; Zhou, W.; Qi, Y.; Wu, S. Controllable
Formation of Ordered Vacancy Compound for High Efficiency Solution Processed Cu(In,Ga)Se2
Solar Cells. Adv. Func. Mater. 2021, 31, 2007928.
(45) Zhao, Y.; Zhao, X.; Kou, D.; Zhou, W.; Zhou, Z.; Yuan, S.; Qi, Y.; Zheng, Z.; Wu, S.
Local Cu Component Engineering to Achieve Continuous Carrier Transport for Enhanced
Kesterite Solar Cells. ACS Appl. Mater. Interfaces 2021, 13, 795–805.
(46) Hasan, M. R.; Arinze, E. S.; Singh, A. K.; Oleshko, V. P.; Guo, S.; Rani, A.; Cheng, Y.;
Kalish, I.; Zaghloul, M. E.; Rao, M. V.; Nguyen, N. V.; Motayed, A.; Davydov, A. V.; Thon, S.
201
M.; Debnath, R. An Antimony Selenide Molecular Ink for Flexible Broadband Detectors. Adv.
Electron. Mater. 2016, 2, 1600182.
(47) Wernick, J. Constitution of the AgSbS2-PbS, AgBiS2-PbS, and AgBiS2-AgBiSe2 Systems.
Am. Mineral. 1960, 45, 591.
(48) Peresh, E. Yu.; Golovei, M. I.; Berul’, S. I. Preparation and Certain Properties of Alkali
Metal Metathiobismuthites. Inorg. Mat. 1971, 7, 27–30.
(49) Rathore, E.; Juneja, R.; Culver, S. P.; Minafra, N.; Singh, A. K.; Zeier, W. G.; Biswas, K.
Origin of Ultralow Thermal Conductivity in n-Type Cubic Bulk AgBiS2: Soft Ag Vibrations and
Local Structure Distortion Induced by the Bi 6s
2
Lone Pair. Chem. Mater. 2019, 31, 2106–2113.
(50) Wu, Y.; Wan, L.; Zhang, W.; Li, X.; Fang, J. In Situ Grown Silver Bismuth Sulfide
Nanorod Arrays and Their Application to Solar Cells. CrysEngComm. 2019, 21, 3137.
(51) Whittles, T. J.; Veal, T. D.; Savory, C. N.; Yates, P. J.; Murgatroyd, P. A. E.; Gibbon, J.
T.; Birkett, M.; Potter, R. J.; Major, J. D.; Durose, K.; Scanlon, D. O.; Dhanak, V. R. Band
Alignments, Band Gap, Core Levels, and Valence Band States in Cu3BiS3 for Photovoltaics. ACS
Appl. Mater. Interfaces 2019, 11, 27033–27047.
202
Full Bibliography
(1) Albalawneh, G.; Ramli, M. Review-Solution Processing of CIGSe Solar Cells Using
Simple Thiol-Amine Solvents Mixture: A Review. ECS J. Solid State Sci. Technol. 2020, 9,
061013.
(2) Aliyev, O. M.; Ajdarova, D. S.; Bayramova, S. T.; Aliyeva, S. I.; Ragimova, V. M.
Nonstoichiometry in PbCuSbS3 Compound. Azerbaijan Chem. J. 2016, 2, 51-54.
(3) Antunez, P. D.; Torelli, D. A.; Yang, F.; Rabuffetti, F. A.; Lewis, N. S.; Brutchey, R. L.
Low Temperature Solution-Phase Deposition of SnS Thin Films. Chem. Mater. 2014, 26,
5444−5446.
(4) Arnou, P.; van Hest, M. F. A. M.; Cooper, C. S.; Malkov, A. V.; Walls, J. M.; Bowers, J.
W. Hydrazine-Free Solution-Deposited CuIn(S,Se)2 Solar Cells by Spray Deposition of Metal
Chalcogenides. ACS Appl. Mater. Interfaces 2016, 8, 11893–11897.
(5) Avellaneda, D.; Nair, M. T. S.; Nair, P. K. Cu2SnS3 and Cu4SnS4 Thin Films via Chemical
Deposition for Photovoltaic Application. J. Electrochem. Soc. 2010, 157, D346−D352.
(6) Bairamova, S. T.; Bagieva, M. R.; Agapashaeva, S. M.; Aliev, O. M. Synthesis and
Properties of Structural Analogs of the Mineral Bournonite. Inorg. Mater. 2011, 47, 345–348.
(7) Baker, J.; Kumar, R. S.; Sneed, D.; Connolly, A.; Zhang, Y.; Velisavljevic, N.; Paladugu,
J.; Pravica, M.; Chen, C.; Cornelius, A.; Zhao, Y. Pressure Induced Structural Transitions in
CuSbS2 and CuSbSe2 Thermoelectric Compounds. J. Alloys Compd. 2015, 643, 186– 194.
(8) Banu, S.; Ahn, S. J.; Ahn, S. K.; Yoon, K.; Cho, A. Fabrication and Characterization of
Cost-Efficient CuSbS2 Thin Film Solar Cells Using Hybrid Inks. Sol. Energy Mater. Sol. Cells
2016, 151, 14–23.
203
(9) BaQais, A.; Tymińska, N.; Le Bahers, T.; Takanabe, K. Optoelectronic Structure and
Photocatalytic Applications of Na(Bi,La)S2 Solid Solutions with Tunable Band Gaps. Chem.
Mater. 2019, 31, 3211–3220.
(10) Barone, G.; Chaplin, T.; Hibbert, T. G.; Kana, A. T.; Mahon, M. F.; Molloy, K. C.;
Worsley, I. D.; Parkin, I. P.; Price, L. S. Synthesis and Thermal Decomposition Studies of Homo-
and Heteroleptic Tin(IV) Thiolates and Dithiocarbamates: Molecular Precursors for Tin Sulfides.
J. Chem. Soc., Dalton Trans. 2002, 1085–1092.
(11) Becke, A. D. Density-Functional Thermochemistry. III. The Role of Exact Exchange. J.
Chem. Phys. 1993, 98, 5648.
(12) Berg, D. M.; Djemour, R.; Gutay, L.; Zoppi, G.; Siebentritt, S.; Dale, P. J. Thin Film Solar
Cells based on the Ternary Compound Cu2SnS3. Thin Solid Films 2012, 520, 6291−6294.
(13) Biesenger, M. C.; Lau, L. W. M.; Gerson, A. R.; Smart, R. S. C. Resolving Surface
Chemical States in XPS Analysis of First Row Transition Metals, Oxides, and Hydroxides: Sc, Ti,
V, Cu, Zn. Appl. Surf. Sci. 2010, 257, 887–898.
(14) Blesa, M. A.; Weisz, A. D.; Morando, P. J.; Salfity, J. A.; Magaz, G. E.; Regazzoni, A. E.
The Interaction of Metal Oxide Surfaces with Complexing Agents Dissolved in Water. Coord.
Chem. Rev. 2000, 196, 31–63.
(15) Bob, B.; Lei, B.; Chung, C.-H.; Yang, W.; Hsu, W.-C.; Duan, H.-S.; Hou, W. W.-J.; Li, S.-
H.; Yang, Y. The Development of Hydrazine-Processed Cu(In,Ga)(Se,S)2 Solar Cells. Adv. Energy
Mater. 2012, 2, 504-522.
204
(16) Brandt, R. E.; Poindexter, J. R.; Gorai, P.; Kurchin, R. C.; Hoye, R. L. Z.; Nienhaus, L.;
Wilson, M. W. B.; Polizzotti, J. A.; Sereika, R.; Zaltauskas, R.; Lee, L. C.; MacManus-Driscoll, J.
L.; Bawendi, M.; Stevanovic, V.; Buonassisi, T. Searching for Defect-Tolerant Photovoltaic
Materials: Combined Theoretical and Experimental Screening. Chem. Mater. 2017, 29, 4667–
4674.
(17) Brandt, R. E.; Stevanovic, V.; Ginley, D. S.; Buonassisi, T. Identifying Defect-Tolerant
Semiconductors with High Minority-Carrier Lifetimes: Beyond Hybrid Lead Halide Perovskites.
MRS Commun. 2015, 5, 265.
(18) Buckley, J. J., McCarthy, C. L.; Del Pilar-Albaladejo, J.; Rasul, G.; Brutchey, R. L.
Dissolution of Sn, SnO, and SnS in a Thiol-Amine Solvent Mixture: Insights into the Identity of
the Molecular Solutes for Solution-Processed SnS. Inorg. Chem. 2016, 55, 3175-3180.
(19) Buckley, J. J.; Greaney, M. J.; Brutchey, R. L. Ligand Exchange of Colloidal CdSe
Nanocrystals with Stibanates Derived from Sb2S3 Dissolved in a Thiol–Amine Mixture. Chem.
Mater. 2014, 26, 6311−6317.
(20) Cant, D. J. H.; Syres, K. L.; Lunt, P. J. B.; Radtke, H.; Treacy, J.; Thomas, P. J.; Lewis, E.
A.; Haigh, S. J.; O’Brien, P.; Schulte, K.; Bondino, F.; Magnano, E.; Flavell, W. R.; Surface
Properties of Nanocrystalline PbS Films Deposited at the Water–Oil Interface: A Study of
Atmospheric Aging. Langmuir 2015, 31, 1445-1453.
(21) Cao, J.; Choi, C. H.; Zhao, F. Agent-Based Modeling for By-Product Metal Supply–A Case
Study on Indium. Sustainability 2021, 13, 7881.
(22) Casella, G.; Ferrante, F.; Saielli, G. Karplus-Type Dependence of Vicinal
119
Sn-
13
C and
119
Sn-
1
H Spin-Spin Couplings in Organotin(IV) Derivatives: A DFT Study. Eur. J. Org. Chem.
2009, 2009, 3526-3534.
205
(23) Casey, W. H.; Ludwig, C. The Mechanism of Dissolution of Oxide Minerals. Nature 1996,
381, 506–509.
(24) Cha, M.; Da, P.; Wang, J.; Wang, W.; Chen, Z.; Xiu, F.; Zheng, G.; Wang, Z.-S. Enhancing
Perovskite Solar Cell Performance by Interface Engineering Using CH3NH3Br0.9I2.1 Quantum
Dots. J. Am. Chem. Soc. 2016, 138, 8581–8587.
(25) Chae, T.-Y.; Row, S.-W.; Yoo, K.-S.; Lee, S.-D.; Lee, D.-W. Hydrogenation of
Isophthalonitrile with 1–Methylimidazole as an Effective Solvent for m–Xylenediamine
Production. Bull. Korean Chem. Soc. 2006, 27, 361–362.
(26) Chen, M.; Straatsma, T. P.; Fang, Z.; Dixon, D. A. Structural and Electronic Property Study
of (ZnO)n, n ≤ 168: Transition from Zinc Oxide Molecular Clusters to Ultrasmall Nanoparticles.
J. Phys. Chem. C 2016, 120, 20400–20418.
(27) Chen, S.; Walsh, A.; Gong, X. G.; Wei, S. H. Classification of Lattice Defects in the
Kesterite Cu2ZnSnS4 and Cu2ZnSnSe4 Earth-Abundant Solar Cell Absorbers. Adv. Mater. 2013,
25, 1522-1539.
(28) Chen, X.; Wada, H.; Sato, A.; Mieno, M. Synthesis, Electrical Conductivity, and Crystal
Structure of Cu4Sn7S16 and Structure Refinement of Cu2SnS3. J. Solid State Chem. 1998, 139, 144–
151.
(29) Cheng, A.-J.; Manno, M.; Khare, A.; Leighton, C.; Campbell, S. A.; Aydil, E. S. Imaging
and Phase Identification of Cu2ZnSnS4 Thin Films Using Confocal Raman Spectroscopy. J. Vac.
Sci. Technol., A 2011, 29, 051203.
(30) Choi, Y. C.; Lee, D. U.; Noh, J. H.; Kim, E. K.; Seok, S. I. Highly Improved Sb2S3
Sensitized-Inorganic Organic Heterojunction Solar Cells and Quantification of Traps by Deep-
Level Transient Spectroscopy. Adv. Funct. Mater. 2014, 24, 3587−3592.
206
(31) Chung, C.-H.; Li, S.-H.; Lei, B.; Yang, W.; Hou, W. W.; Bob, B.; Yang, Y.; Identification
of the Molecular Precursors for Hydrazine Solution Processed CuIn(Se,S)2 Films and Their
Interactions. Chem. Mater. 2011, 23, 964-969.
(32) Clark, J. A.; Murray, A.; Lee, J.-m.; Autrey, T. S.; Collord, A. D.; Hillhouse, H. W.
Complexation Chemistry in N,N-Dimethylformamide-Based Molecular Inks for Chalcogenide
Semiconductors and Photovoltaic Devices. J. Am. Chem. Soc. 2019, 141, 298-308.
(33) Colombara, D.; Peter, L. M.; Hutchings, K.; Rodgers, K. D.; Schafer, S.; Dufton, J. T. R.;
Islam, M. S. Formation of Cu3BiS3 Thin Films via Sulfurization of Bi-Cu Metal Precursors. Thin
Solid Films 2012, 520, 5165–5171.
(34) Davies, A. G.; Slater, S. D.; Povey, D. C.; Smith, G. W. The Structures of 2,2-Diakyl-1,3,2-
Dithiastannolanes. J. Organomet. Chem. 1988, 352, 283-294.
(35) Debies, T. P.; Rabalais, J. W. X-Ray Photoelectron Spectra and Electronic Structure of
Bi2X3 (X = O, S, Se, Te) Chem. Phys. 1977, 20, 277–283.
(36) Deshmukh, S. D.; Rokke, D. J.; Kisslinger, K.; Agrawal, R. Investigating the Potential of
Amine-Thiol Solvent System for High Efficiency CuInSe2 Device. 2020 47
th
IEEE Photovoltaic
Specialists Conference (PVSC), 2020, 0818-0820.
(37) Deshmukh, S. G.; Kheraj, V. A Comprehensive Review on Synthesis and Characterizations
of Cu3BiS3 Thin Films for Solar Photovoltaics. Nanotechnol. Environ. Eng. 2017, 2, 1–12.
(38) Deshmukh, S. G.; Kheraj, V.; Karande, K. J.; Panchal, A. K.; Deshmukh, R. S. Hierarchical
Flower-Like Cu3BiS3 Thin Film Synthesis with Non-Vacuum Chemical Bath Deposition
Technique. Mater. Res. Express 2019, 6, 084013.
(39) Deshmukh, S. G.; Panchal, A. K.; Kheraj, V. Development of Cu3BiS3 Thin Films by
Chemical Bath Deposition Route. J. Mater. Sci., Mater. Electron. 2017, 28, 11926–11933.
207
(40) Deshmukh, S. G.; Patel, S. J.; Patel, K. K.; Panchal, A. K.; Kheraj, V. Effect of Annealing
Temperature on Flowerlike Cu3BiS3 Thin Films Grown by Chemical Bath Deposition. J. Electron.
Mater. 2017, 46, 5582–5588.
(41) Dev, S.; Ramli, E.; Rauchfuss, T. B.; Stern, C. L. Direct Approaches to Zinc
Polychalcogenide Chemistry: ZnS6(N-MeIm)2 and ZnSe4(N-MeIm)2. J. Am. Chem. Soc. 1990,
112, 6385-6386.
(42) Dev, S.; Ramli, E.; Rauchfuss, T. B.; Wilson, S. R. Synthesis and Structure of [M(N-
Methylimidazole)6]S8 (M = Mn, Fe, Ni, Mg). Polysulfide Salts Prepared by the Reaction N-
Methylimidazole + Metal Powder + Sulfur. Inorg. Chem. 1991, 30, 2514-2519.
(43) Dittrich, A.; Bieniok, A.; Brendel, U.; Grodzicki, M.; Topa, D. Sulfosalts – A New Class
of Compound Semiconductors for Photovoltaic Applications. Thin Solid Films 2007, 515, 5745-
5750.
(44) Dolzhnikov, D. S.; Zhang, H.; Jang, J.; Son. J. S.; Panthani, M. G.; Shibata, T.;
Chattopadhyay, S.; Talapun, D. V. Composition-Matched Molecular “Solders” for
Semiconductors. Science 2015, 347, 425-428.
(45) Dong, Q.; Fang, Y.; Shao, Y.; Mulligan, P.; Qiu, J.; Cao L.; Huang, J. Electron-Hole
Diffusion Lengths > 175 μm in Solution-Grown CH3NH3PbI3 Single Crystals. Science 2015, 347,
967–970.
(46) Dong, Y.; Khabibullin, A. R.; Wei, K.; Salvador, J. R.; Nolas, G. S.; Woods, L. M.
Bournonite PbCuSbS3: Stereochemically Active Lone-Pair Electrons that Induce Low Thermal
Conductivity. ChemPhysChem 2015, 16, 3264–3270.
(47) Du, M. H. Efficient Carrier Transport in Halide Perovskites: Theoretical Perspectives. J.
Mater. Chem. A 2014, 2, 9091.
208
(48) Du, M. H.; Singh, D. J. Enhanced Born charge and Proximity to Ferroelectricity in
Thallium Halides. Phys. Rev. B 2010, 81, 144114.
(49) Durant, B.; Parkinson, B. A. Photovoltaic Response of Naturally Occurring
Semiconducting Sulfide Minerals. 2016 IEEE 43rd Photovoltaic Specialists Conference; IEEE:
New York, 2016; pp 2774-2779.
(50) Epifanovsky, E.; Gilbert, A. T. B.; Feng, X.; et al. Software for the Frontiers of Quantum
Chemistry: An Overview of Developments in the Q–Chem 5 Package. J. Chem. Phys. 2021, 155,
084801.
(51) Eslamian, M. Inorganic and Organic Solution-Processed Thin Film Devices. Nano-Micro
Lett. 2017, 9, 3.
(52) Fabini, D. H.; Koerner, M.; Seshadri, R. Candidate Inorganic Photovoltaic Materials from
Electronic Structure-Based Optical Absorption and Charge Transport Proxies. Chem. Mater. 2019,
31, 1561−1574.
(53) Faghaninia, A.; Guodong, Y.; Aydemir, U.; Wood, M.; Chen, W.; Rignanese, G.-M.;
Snyder, G. J.; Hautier, G.; Jain, A. A Computational Assessment of the Electronic, Thermoelectric,
and Defect Properties of Bournonite (CuPbSbS3) and Related Substitutions. Phys. Chem. Chem.
Phys. 2017, 19, 6743-6756.
(54) Fan, F.-J.; Wu, L.; Gong, M.; Liu, G.; Wang, Y.-X.; Yu, S.-H.; Chen, S.; Wang, L.-W.;
Gong, X.-G. Composition and Band Gap Tunable Synthesis of Wurtzite-Derived
Cu2ZnSn(S1−xSex)4 Nanocrystals: Theoretical and Experimental Insights. ACS Nano 2013, 7,
1454−1463.
(55) Fei, H.; Feng, Z.; Liu, X. Novel Sodium Bismuth Sulfide Nanostructures: A Promising
Anode Materials for Sodium-Ion Batteries with High Capacity. Ionics 2015, 21, 1967–1972.
209
(56) Fiechter, S.; Martinez, M.; Schmidt, G.; Henrion, W.; Tomm, Y. Phase Relations and
Optical Properties of Semiconducting Ternary Sulfides in the System Cu–Sn–S. J. Phys. Chem.
Solids 2003, 64, 1859–1862.
(57) Frost, J. M.; Butler, K. T.; Brivio, F.; Hendon, C. H.; van Schilfgaarde, M.; Walsh, A.
Atomistic Origins of High-Performance in Hybrid Halide Perovskite Solar Cells. Nano Lett. 2014,
14, 2584–2590.
(58) Frumar, M.; Kala, T.; Horak, J. Growth and Some Physical Properties of Semiconducting
CuPbSbS3 Crystals. J. Cryst. Growth 1973, 20, 239−244.
(59) Fthenakis, V. M.; Morris, S. C.; Moskowitz, P. D.; Morgan, D. L. Toxicity of Cadmium
Telluride, Copper Indium Diselenide, and Copper Gallium Diselenide. Prog. Photovoltaics 2000,
7, 489–497.
(60) Furness, W. 2017, https://github.com/JFurness1/EnergyLeveller/ (accessed October 2021).
(61) Gabrelian, B. V.; Lavrentyev, A. A.; Nikiforov, I. Ya. To the Explanation of the “White”
Line in the X-Ray K-Absorption Spectrum of Sulfur in NaBiS2. Bull. Russ. Acad. Sci. Phys. 2009,
73, 1001–1003.
(62) Ganose, A. M.; Savory, C. N.; Scanlon, D. O. Beyond Methylammonium Lead Iodide:
Prospects for the Emergent Field of ns2 Containing Solar Absorbers. Chem. Commun. 2017, 53,
20–44.
(63) Ge, J.; Yan, Y. Synthesis and Characterization of Photoelectrochemical and Photovoltaic
Cu2BaSnS4 Thin Films and Solar Cells. J. Mater. Chem. C 2017, 5, 6406−6419.
(64) Gerein, N. J.; Haber, J. A. One-Step Synthesis and Optical and Electrical Properties of Thin
Film Cu3BiS3 for Use as a Solar Absorber in Photovoltaic Devices. Chem. Mater. 2006, 18, 6297–
6302.
210
(65) Gerein, N. J.; Haber, J. A. Synthesis of Cu3BiS3 Thin Films by Heating Metal and Metal
Sulfide Precursor Films under Hydrogen Sulfide. Chem. Mater. 2006, 18, 6289−6296.
(66) Ghorpade, U. V.; Suryawanshi, M. P.; Shin, S. W.; Kim, I.; Ahn, S. K.; Yun, J. H.; Jeong,
C.; Kolekar, S. S.; Kim, J. H. Colloidal Wurtzite Cu2SnS3 (CTS) Nanocrystals and Their
Applications in Solar Cells. Chem. Mater. 2016, 28, 3308.
(67) Global Thin-film Semiconductor Deposition Industry 2020–2027, Reportlinker 2020.
(68) Godel, K. C.; Roose, B.; Sadhanala, A.; Vaynzof, Y.; Pathak, S. K.; Steiner, U. Partial
Oxidation of the Absorber Layer Reduces Charge Carrier Recombination in Antimony Sulfide
Solar Cells. Phys. Chem. Chem. Phys. 2017, 19, 1425.
(69) Green, M. A.; Ho-Baillie, A.; Snaith, H. J. The Emergence of Perovskite Solar Cells. Nat.
Photonics 2014, 8, 506−514.
(70) Grimme, S.; Ehrlich, S.; Goerigk, L. Effect oft he Damping Function in Dispersion
Corrected Density Functional Theory. J. Comput. Chem. 2011, 32, 1456–1465.
(71) Guin, S. N.; Biswas, K. Cation Disorder and Bond Anharmonicity Optimize the
Thermoelectric Properties in Kinetically Stabilized Rocksalt AgBiS 2 Nanocrystals. Chem. Mater.
2013, 25, 3225–3231.
(72) Guo, J.; Ge, Z.; Hu, M.; Qin, P.; Feng, J. Facile Synthesis of NaBiS 2 Nanoribbons as a
Promising Visible Light-Driven Photocatalyst. Phys. Status Solidi RRL 2018, 12, 1800135.
(73) Guo, Y.; Yin, X.; Yang, Y.; Que, W. Construction of ZnO/Cu2SnS3 Nanorod Array Films
for Enhanced Photoelectrochemical and Photocatalytic Activity. RSC Adv. 2016, 6, 104041–
104048.
211
(74) Gupta, A. K. S.; Bohra, R.; Mehrota, R. C.; Das, K. Heterocyclic compounds containing
antimony 1. Synthesis, physiochemical properties, crystal and molecular structure of 2-(b-
hydroxyethylthio)1,3,2-oxathiastibolane. Inorg. Chim. Acta 1990, 170, 191-197.
(75) Habas, S. E.; Platt, H. A. S.; van Hest, M. F. A. M.; Ginley, D. S. Low-Cost Inorganic
Solar Cells: From Ink to Printed Device. Chem. Rev. 2010, 110, 6571-6594.
(76) Haegel, N. M.; Margolis, R.; Buonassisi, T.; Feldman, D.; Froitzheim, A.; Garabedian, R.;
Green, M.; Glunz, S.; Henning, H.- M.; Holder, B.; Kaizuka, I.; Kroposki, B.; Matsubara, K.; Niki,
S.; Sakurai, K.; Schindler, R. A.; Tumas, W.; Weber, E. R.; Wilson, G.; Woodhouse, M.; Kurtz,
S. Terawatt-Scale Photovoltaics: Trajectories and Challenges. Science 2017, 356, 141−143.
(77) Hardman, S. J. O.; Graham, D. M.; Stubbs, S. K.; Spencer, B. F.; Seddon, E. A.; Fung, H.
T.; Gardonio, S.; Sirotti, F.; Silly, M. G.; Akhtar, J.; O’Brien, P.; Binks, D. J.; Flavell, W. R.
Electronic and Surface Properties of PbS Nanoparticles Exhibiting Efficient Multiple Exciton
Generation. Phys. Chem. Chem. Phys. 2011, 13, 20275−20283.
(78) Harikesh, P. C.; Surendran, A.; Ghosh, B.; John, R. A.; Moorthy, A.; Yantara, N.; Salim,
T.; Thirumal, K.; Leong, W. L.; Mhaisalkar, S.; Mathews, N. Cubic NaSbS2 as an Ionic-Electronic
Coupled Semiconductor for Switchable Photovoltaic and Neuromorphic Device Applications.
Adv. Mater. 2020, 32, 1906976.
(79) Harikesh, P. C.; Wu, B.; Ghosh, B.; John, R. A.; Lie, S.; Thirumal, K.; Wong, L. H.; Sum,
T. C.; Mhaisalkar, S.; Mathews, N. Doping and Switchable Photovoltaic Effect in Lead-Free
Perovskites Enabled by Metal Cation Transmutation. Adv. Mater. 2018, 30, 1802080.
212
(80) Hasan, M. R.; Arinze, E. S.; Singh, A. K.; Oleshko, V. P.; Guo, S.; Rani, A.; Cheng, Y.;
Kalish, I.; Zaghloul, M. E.; Rao, M. V.; Nguyen, N. V.; Motayed, A.; Davydov, A. V.; Thon, S.
M.; Debnath, R. An Antimony Selenide Molecular Ink for Flexible Broadband Detectors. Adv.
Electron. Mater. 2016, 2, 1600182.
(81) Hayashi, M.; Shiro, Y.; Oshima, T.; Murata, H. The Vibrational Assignment, Rotational
Isomerism and Force Constants of 1,2- Ethanedithiol. Bull. Chem. Soc. Jpn. 1965, 38, 1734−1740.
(82) Hellinga, H. W. (1990) Construction of a Blue Copper Analogue Through Iterative
Rational Protein Design Cycles Demonstrates Principles of Molecular Recognition in Metal Center
Formation. J. Am. Chem. Soc. 1990, 120, 10055-10066.
(83) Heo, J.; Kim, G.-H.; Jeong, J.; Yoon, Y. J.; Seo, J. H.; Walker, B.; Kim, J. Y. Clean
Thermal Decomposition of Tertiary-Alkyl Metal Thiolates to Metal Sulfides: Environmentally-
Benign, Non-Polar Inks for Solution-Processed Chalcopyrite Solar Cells. Sci. Rep. 2016, 6, 36608.
(84) Heo, S. H.; Jo, S.; Kim, H. S.; Choi, G.; Song, J. Y.; Kang, J.-Y.; Park, N.-J.; Ban, H. W.;
Kim, F.; Jeong, H.; Jung, J.; Jang, J.; Lee, W. B.; Shin, H.; Son, J. S. Composition Change-Driven
Texturing and Doping in Solution-Processed SnSe Thermoelectric Thin Films. Nat. Commun.
2019, 10, 864.
(85) Hernádez-Mota, J.; Espíndola-Rodríguez, M.; Sánchez, Y.; López, I.; Peña, Y.; Saucedo,
E. Thin Film Photovoltaic Devices Prepared with Cu3BiS3 Ternary Compound. Mater. Sci.
Semicond. Process. 2018, 87, 37–43.
(86) Herz, L. M. Charge-Carrier Mobilities in Metal Halide Perovskites: Fundamental
Mechanisms and Limits. ACS Energy Lett. 2017, 2, 1539−1548.
213
(87) Holligan, K.; Rogler, P.; Rehe, D.; Pamula, M.; Kornienko, A. Y.; Emge, T. J.; Krogh-
Jespersen, K.; Brennan, J. G. Copper, Indium, Tin, and Lead Complexes with Fluorinated
Selenolate Ligands: Precursors to MSex. Inorg. Chem. 2015, 54, 8896-8904.
(88) Howell, J. A. S. Structure and Bonding in Cyclic Thiolate Complexes of Copper, Silver
and Gold. Polyhedron 2006, 25, 2993-3005.
(89) Hsu, W.-C.; Bob, B.; Wang, W.; Chung, C.-H.; Yang, Y. Reaction Pathways for the
Formation of Cu2ZnSn(Se,S)4 Absorber Materials from Liquid-Phase Hydrazine-Based Precursor
Inks. Energy Environ. Sci. 2012, 5, 8564-8571.
(90) Hudson, M. H.; Dolzhnikov, D. S.; Filatov, A. S.; Janke, E. M.; Jang, J.; Lee, B.; Sun, C.;
Talapin, D. V. New Forms of CdSe: Molecular Wires, Gels, and Ordered Mesoporous Assemblies.
J. Am. Chem. Soc. 2017, 139, 3368−3377.
(91) Hurma, T.; Kose, S. XRD Raman Analysis and Optical Properties of CuS Nanostructured
Film. Optik 2016, 127, 6000−6006.
(92) Ibáñez, M.; Hasler, R.; Genc, A.; Liu, Y.; Kuster, B.; Schuster, M.; Dobrozhan, O.;
Cadavid, D.; Arbiol, J.; Cabot, A.; Kovalenko, M. V. Ligand-mediated band engineering in
bottom-up assembled SnTe nanocomposites for thermoelectric energy conversion. J. Am. Chem.
Soc. 2019, 141, 8025-8029.
(93) Ibáñez, M.; Hasler, R.; Liu, H.; Dobrozhan, O.; Nazarenko, O.; Cadavid, D.; Cabot, A.;
Kovalenko, M. V. Tuning p-type Transport in Bottom-Up-Engineered Nanocrystalline Pb
Chalcogenides Using Alkali Metal Chalcogenides as Capping Ligands. Chem. Mater. 2017, 29,
7093-7097.
214
(94) Jarosiński, Ł.; Pawlak, J.; Al-Ani, S. K. J. Inverse Logarithmic Derivative Method for
Determining the Energy Gap and the Type of Electron Transitions as an Alternative to the Tauc
Method. Opt. Mater. 2019, 88, 667–673.
(95) Jo, S.; Cho, S.; Yang, U. J.; Hwang, G.-S.; Baek, S.; Kim, S.-H.; Heo, S. H.; Kim, J.-Y.;
Choi, M. K.; Son, J. S. Solution-Processed Stretchable Ag2S Semiconductor Thin Films for
Wearable Self-Powered Nonvolatile Memory. Adv. Mater. 2021, 33, 2100066.
(96) Jo, S.; Choo, S.; Kim, F.; Heo, S. H.; Son, J. S. Ink Processing for Thermoelectric Materials
and Power-Generating Devices. Adv. Mater. 2019, 31, 1804930.
(97) Jo, S.; Park, S. H.; Shin, H.; Oh, I.; Heo, S. H.; Ban, H. W.; Jeong, H.; Kim, F.; Choo, S.;
Gu, D. H.; Baek, S.; Cho, S.; Kim, J. S.; Kim, B.-S.; Lee, J. E.; Song, S.; Yoo, J.-W.; Song, J. Y.;
Son, J. S. Soluble telluride-based molecular precursor for solution-processed high-performance
thermoelectrics. ACS Appl. Energy Mater. 2019, 2, 4582-4589.
(98) John, R. A.; Yantara, N.; Ng, Y. F.; Narasimman, G.; Mosconi, E.; Meggiolaro, D.;
Kulkarni, M. R.; Gopalakrishnan, P. K.; Nguyen, C. A.; Angelis, F. D.; Mhaisalkar, S. G.; Basu,
A.; Mathews, N. Ionotronic Halide Perovskite Drift-Diffusive Synapses For Low-Power
Neuromorphic Computation. Adv. Mater. 2018, 30, 1805454.
(99) Jones, C. F.; Segall, R. L.; Smart, R. St. C.; Turner, P. S. Semiconducting Oxides. The
Effect of Prior Annealing Temperature on Dissolution Kinetics of Nickel Oxide. J. Chem. Soc.,
Faraday Trans. 1 1977, 73, 1710−1720.
(100) Kacprzak, K. A.; Lopez-Acevedo, O.; Hakkinen, H.; Gronbeck, H. Theoretical
Characterization of Cyclic Thiolated Copper, Silver, and Gold Clusters. J. Phys. Chem. C 2010,
114, 13571-13576.
215
(101) Kaltenhauser, V.; Rath, T.; Haas, W.; Torvisco, A.; Müller, S. K.; Friedel, B.; Kunert, B.;
Saf, R.; Hofer, F.; Trimmel, G. Bismuth Sulphide-Polymer Nanocomposites from a Highly Soluble
Bismuth Xanthate Precursor. J. Mater. Chem. C 2013, 1, 7825–7832.
(102) Kamimura, S.; Beppu, N.; Sasaki, Y.; Tsubota, T.; Ohno, T. Platinum and Indium Sulfide-
Modified Cu3BiS3 Photocathode for Photoelectrochemical Hydrogen Evolution. J. Mater. Chem.
A 2017, 5, 10450−10456.
(103) Kanai, A.; Toyonaga, K.; Chino, K.; Katagiri, H.; Araki, H. Fabrication of Cu2SnS3 Thin-
Film Solar Cells with Power Conversion Efficiency of over 4%. Jpn. J. Appl. Phys. 2015, 54,
08KC06.
(104) Kang, Sumin; Hong, Yonghoon; Jeon, Youngjin. A Facile Synthesis and Characterization
of Sodium Bismuth Sulfide (NaBiS2) under Hydrothermal Condition. Bulletin of the Korean
Chemical Society 2014, 35, 1887–1890.
(105) Kedernath, G.; Kumbhare, L. B.; Dey, S.; Wadawale, A. P.; Jain, V. K.; Dey, G. K. b-
Functionalized Ethylchalcogenolate Complexes of Lead (II): Synthesis, Structures and Their
Conversion into Lead Chalcogenide Nanoparticles. Polyhedron 2009, 28, 2749-2753.
(106) Kharbish, S.; Libowitzky, E.; Beran, A. Raman Spectra of Isolated and Interconnnected
Pyramidal XS3 Groups (X = Sb, Bi) in Stibnite, Bismuthinite, Kermesite, Stephanite and
Bournonite. Eur. J. Mineral 2009, 21, 325-333.
(107) Kino, T.; Kuzuya, T.; Itoh, K.; Sumiyama, K.; Wakamatsu, T.; Ichidate, M. Synthesis of
Chalcopyrite Nanoparticles via Thermal Decomposition of Metal-Thiolate. Mat. Trans. 2008, 49,
435–438.
(108) Kocman, V.; Nuffield, E. W. The Crystal Structure of Wittichenite, Cu3BiS3. Acta Cryst.
1973, 29, 2528−2535.
216
(109) Kolny-Olesiak, J.; Weller, H. Synthesis and Application of Colloidal CuInS2
Semiconductor Nanocrystals. ACS Appl. Mater. Interfaces 2013, 5, 12221−12237.
(110) Koskela, K. M.; Melot, B. C.; Brutchey, R. L. Solution Deposition of a Bournonite
CuPbSbS3 Semiconductor Thin Film from the Dissolution of Bulk Materials with a Thiol–Amine
Solvent Mixture. J. Am. Chem. Soc. 2020, 142, 6173−6179.
(111) Koskela, K. M.; Quiton, S. J.; Sharada, S. M.; Williams, T. J.; Brutchey, R. L. Kinetics and
Mechanistic Details of Bulk ZnO Dissolution Using a Thiol-Imidazole System. Chem. Sci. 2022,
13, 3208–3215.
(112) Koskela, K. M.; Strumolo, M. J.; Brutchey, R. L. Progress of Thiol-Amine ‘Alkahest’
Solutions for Thin Film Deposition. Trends Chem. 2021, 3, 1061–1073.
(113) Koskela, K. M.; Tadle, A. C.; Chen K.; Brutchey, R. L. Solution Processing Cu3BiS3
Absorber Layers with a Thiol–Amine Solvent Mixture. ACS Appl. Energy Mater. 2021, 4, 11026–
11031.
(114) Koutavarapu, R.; Lee, G.; Babu, B.; Yoo, K.; Shim, J. Visible-Light-Driven Photocatalytic
Activity of Tiny ZnO Nanosheets Anchored on NaBiS2 Nanoribbons via Hydrothermal Synthesis.
J Mater Sci: Mater Electron 2019, 30, 10900–10911.
(115) Kovalenko, M. V.; Scheele, V.; Talapin, D. V. Colloidal Nanocrystals with Molecular
Metal Chalcogenide Surface Ligands. Science 2009, 324, 1417–1420.
(116) Kovalenko, M. V.; Spokoyny, B.; Lee, J.-S.; Scheele, M.; Weber, A.; Perera, S.; Landry,
D.; Talapin, D. V. Semiconductor Nanocrystals Functionalized with Antimony Telluride Zintl Ions
for Nanostructured Thermoelectrics. J. Am. Chem. Soc. 2010, 132, 6686-6695.
(117) Kumar, M.; Persson, C. Cu3BiS3 as a Potential Photovoltaic Absorber with High Optical
Efficiency. Appl. Phys. Lett. 2013, 102, 062109.
217
(118) Kuyuza, T.; Yamamuro, S.; Hihara, T.; Sumiyama, K. Water-Free Synthesis of
Monodisperse Cu2S Nanocrystals. Chem. Lett. 2004, 33, 352–353.
(119) Lebugle, A.; Axelsson, U.; Nyholm, R.; Mårtensson, N. Experimental L and M Core Level
Binding Energies for the Metals
22
Ti to
30
Zn. Phys. Scr. 1981, 23, 825–827.
(120) Lee, J. Y.; Kim, I. Y.; Surywanshi, M. P.; Ghorpade, U. V.; Lee, D. S.; Kim, J. H.
Fabrication of Cu2SnS3 Thin Film Solar Cells using Cu/Sn Layered Metallic Precursors Prepared
by a Sputtering Process. Sol. Energy 2017, 145, 27–32.
(121) Li, J.; Han, X.; Zhao, Y.; Li, J.; Wang, M.; Dong, C. One-Step Synthesis of Cu3BiS3 Thin
Films by a Dimethyl Sulfoxide (DMSO)-Based Solution Coating Process for Solar Cell
Application. Sol. Energy Mater. Sol. Cells 2018, 174, 593−598.
(122) Li, J.; Xue, C.; Wang, Y.; Jiang, G. Liu, W.; Zhu, C. Cu2SnS3 Solar Cells Fabricated by
Chemical Bath Deposition–Annealing of SnS/Cu Stacked Layers. Sol. Energy Mater. Sol. Cells
2016, 144, 281–288.
(123) Lin, Z.; He, Q.; Yin, A.; Xu, Y.; Wang, C.; Ding, M.; Cheng, H.-C.; Papandrea, B.; Huang,
Y.; Duan, X. Cosolvent Approach for Solution-Processable Electronic Thin Films. ACS Nano
2015, 9, 4398-4405.
(124) Lin, Z.; Hollar, C.; Kang, J. S.; Yin, A.; Wang, Y.; Shiu, H.-Y.; Huang, Y.; Hu, Y.; Zhang,
Y.; Duan, X. A Solution Processable High-Performance Thermoelectric Copper Selenide Thin
Film. Adv. Mater. 2017, 29, 1606662.
(125) Lindberg, B. J.; Hamrin, K.; Johansson, G.; Gelius, U.; Fahlman, A.; Nordling, C.;
Siegbahn, K. Molecular Spectroscopy by Means of ESCA II. Sulfur Compounds. Correlation of
Electron Binding Energy with Structure. Phys. Scr. 1970, 1, 286–298.
218
(126) Liu, F.; Zhu, J.; Hu, L.; Zhang, B.; Yao, J.; Nazeeruddin, M. K.; Grätzel, M.; Dai, S. Low-
Temperature, Solution-Deposited Metal Chalcogenide Films as Highly Efficient Counter
Electrodes for Sensitized Solar Cells. J. Mater. Chem. A 2015, 3, 6315-6323.
(127) Liu, Q.; Zhao, Z.; Lin, Y.; Guo, P.; Li, S.; Pan, D.; Ji, X. Alloyed (ZnS)x(Cu2SnS3)1–x and
(CuInS2)x(Cu2SnS3)1–x Nanocrystals with Arbitrary Composition and Broad Tunable Band Gaps.
Chem. Comm. 2011, 47, 964–966.
(128) Liu, S.; Sun, P.; Shen, Y.; Han, J.; Sun, H.; Jia, D. Lanthanide(III) Complexes with μ-SnSe4
and μ-Sn2Se6 Linkers: Solvothermal Syntheses and Properties of New Ln(III) Selenidostannates
Decorated with Linear Polyamine. Z. Naturforsch. B 2017, 72, 231-240.
(129) Liu, S.; Wang, X.; Nie, L.; Chen, L.; Yuan, R. Spray Pyrolysis Deposition of Cu3BiS3 Thin
Films. Thin Solid Films 2015, 585, 72–75.
(130) Liu, X.; Wang, X.; Swihart, M. T. Composition-Dependent Crystal Phase, Optical
Properties, and Self-Assembly of Cu−Sn−S Colloidal Nanocrystals. Chem. Mater. 2015, 27,
1342−1348.
(131) Liu, Y.; Calcabrini, M.; Yu, Y.; Lee, S.; Chang, C.; David, J.; Ghosh, T.; Spadaro, M. C.;
Xie, C.; Cojocaru- Mirédin, O.; Arbiol, J.; Ibáñez, M. Defect Engineering in Solution–Processed
Polycrystalline SnSe Leads to High Thermoelectric Performance. ACS Nano 2022, 16, 78–88.
(132) Liu, Y.; Yang, B.; Zhang, M.; Xia, B.; Chen, C.; Liu, X.; Zhong, J.; Xiao, Z.; Tang, J.
Bournonite CuPbSbS3: An Electronically-3D, Defect-Tolerant, and Solution-Processable
Semiconductor for Efficient Solar Cells. Nano Energy 2020, 71, 104574.
(133) Lokanc, M.; Eggert, R.; Redlinger, M. The Availability of Indium: The Present, Medium
Term, and Long Term. National Renewable Energy Laboratory Report; U.S. Department of
Energy: Golden, CO, 2015.
219
(134) Lowe, J. C.; Wright, L. D.; Eremin, D. B.; Burykina, J. V.; Martens, J.; Plasser, F.;
Ananikov, V. P.; Bowers, J. W.; Malkov, A. V. Solution Processed CZTS Solar Cells Using Thiol–
Amine System: Understanding the Dissolution Process and Device Fabrication. J. Mater. Chem.
C 2020, 8, 10309–10318.
(135) Lui, F.; Zhu, J.; Wei, J.; Lv, M.; Xu, Y.; Zhou, L.; Hu, L.; Dai, S. Earth-Abundant Cu2SnSe3
Thin Film Counter Electrode for High-Efficiency Quantum Dot-Sensitized Solar Cells. J. Power
Sources 2015, 292, 7-14.
(136) Luo, Y. R. Comprehensive Handbook of Chemical Bond Energies, CRC Press, Boca Raton,
FL, 2007.
(137) Ma, Y.; Vartak, P. B.; Nagaraj, P.; Wang, R. Y. Thermoelectric Properties of Copper
Chalcogenide Alloys Deposited via the Solution–Phase using a Thiol–Amine Solvent Mixture.
RSC Adv., 2016, 6, 99905–99913.
(138) Manby, F. R.; Miller III, T. F.; Bygrave, P. J.; Ding, F.; Dresselhaus, T.; Batista-Romero,
F. A.; Buccheri, A.; Bungey, C.; Lee, S. J. R.; Meli, R.; Miyamoto, K.; Steinmann, C.; Tsuchiya,
T.; Welborn, M.; Wiles, T.; Williams, Z. entos: A Quantum Molecular Simulation Package. 2019,
DOI: 10.26434/chemrXiv:7762646.v2.
(139) Marquez Prieto, J. A.; Levcenko, S.; Just, J.; Hampel, H.; Forbes, I.; Pearsall, N. M.; Unold,
T. Earth Abundant Thin Film Solar Cells from Co-Evaporated Cu2SnS3 Absorber Layers. J. Alloys
Compd. 2016, 689, 182–186.
(140) Matthews, P. D.; McNaughter, P. D.; Lewis, D. J.; O’Brien, P. Shining a Light on
Transition Metal Chalcogenides for Sustainable Photovoltaics. Chem. Sci. 2017, 8, 4177-4187.
(141) McCarthy, C. L.; Brutchey, R. L. Preparation of Electrocatalysts Using a Thiol–Amine
Solution Processing Method. Dalton Trans. 2018, 47, 5137-5143.
220
(142) McCarthy, C. L.; Brutchey, R. L. Solution Deposited Cu2BaSnS4–xSex from a Thiol–Amine
Solvent Mixture. Chem. Mater. 2018, 30, 304–308.
(143) McCarthy, C. L.; Brutchey, R. L. Solution Processing of Chalcogenide Materials Using
Thiol−Amine “Alkahest” Solvent Systems. Chem. Commun. 2017, 53, 4888−4902.
(144) McCarthy, C. L.; Cottingham, P.; Abuyen, K.; Schueller, E. C.; Culver, S. P.; Brutchey, R.
L. Earth Abundant CuSbS2 Thin Films Solution Processed from Thiol−Amine Mixtures. J. Mater.
Chem. C 2016, 4, 6230−6233.
(145) McCarthy, C. L.; Downes, C. A.; Brutchey, R. L. Room Temperature Dissolution of Bulk
Elemental Ni and Se for Solution Deposition of a NiSe2 HER Electrocatalyst. Inorg. Chem. 2017,
56, 10143-10146.
(146) McCarthy, C. L.; Downes, C. A.; Schueller, E. C.; Abuyen, K.; Brutchey, R. L. Method
for the Solution Deposition of Phase–Pure CoSe2 as an Efficient Hydrogen Evolution Reaction
Electrocatalyst. ACS Energy Lett. 2016, 1, 607−611.
(147) McCarthy, C. L.; Webber, D. H.; Schueller, E. C.; Brutchey, R. L. Solution-Phase
Conversion of Bulk Metal Oxides to Metal Chalcogenides Using a Simple Thiol-Amine Solvent
Mixture. Angew. Chem., Int. Ed. 2015, 54, 8378-8381.
(148) McClary, S. A.; Balow, R. B.; Argawal, R. Role of Annealing Atmosphere on the Crystal
Structure and Composition of Tetrahedrite-Tennantite Alloy Nanoparticles. J. Mater. Chem. C.
2018, 6, 10538-10546.
(149) Mesa, F.; Gordillo, G.; Dittrich, T.; Ellmer, K.; Baier, R.; Sadewasser, S. Transient Surface
Photovoltage of p-Type Cu3BiS3. Appl. Phys. Let. 2010, 96, 082113.
(150) Mineral Commodity Summaries 2016; U.S. Geological Survey, U.S. Government Printing
Office: Washington, DC, 2016, 36–81.
221
(151) Mitzi, D. B. Solution Processing of Chalcogenide Semiconductors via Dimensional
Reduction, Solution Processing of Inorganic Materials (Mitzi, D. B.) 2008, pp.77-108, John Wiley
& Sons.
(152) Mitzi, D. B. Solution Processing of Chalcogenide Semiconductors via Dimensional
Reduction. Adv. Mater. 2009, 21, 3141-3158.
(153) Mitzi, D. B. Solution-Processed Inorganic Semiconductors. J. Mater. Chem. 2004, 14,
2355–2365.
(154) Mitzi, D. B. Synthesis, Structure, and Thermal Properties of Soluble Hydrazinium
Germanium(IV) and Tin(IV) Selenide Salts. Inorg. Chem. 2005, 44, 3755-3761.
(155) Mitzi, D. B.; Gunawan, O.; Todorov, T. K.; Wang, K.; Guha, S. The Path Towards a High-
Performance Solution-Processed Kesterite Solar Cell. Sol. Energy Mater. Sol. Cells 2011, 95,
1421−1436.
(156) Mitzi, D. B.; Kosbar, L. L.; Murray, C. E.; Copel, M.; Afzali, A. High-Mobility Ultrathin
Semiconducting Films Prepared by Spin Coating. Nature 2004, 428, 299-303.
(157) Mitzi, D. B.; Yuan, M.; Liu, W.; Kellock, A. J.; Chey, S. J.; Deline, V.; Schrott, A. G. A
High‐Efficiency Solution‐Deposited Thin‐Film Photovoltaic Device. Adv. Mater. 2008, 20, 3657-
3662.
(158) Mohan, R. Green Bismuth. Nat. Chem. 2010, 2, 336.
(159) Moulder, J. F.; Stickle, W. F.; Sobol, P. E.; Bomben, K. D. Handbook of X-Ray
Photoelectron Spectroscopy; Chastain, J., Ed.; Physical Electronics Division, Perkin-Elmer Corp.:
Eden Prairie, MN, 1979.
(160) Murali, B.; Madhuri, M.; Krupanidhi, S. B. Near-Infrared Photoactive Cu3BiS3 Thin Films
by Co-Evaporation. J. Appl. Phys. 2014, 115, 173109.
222
(161) Murria. P.; Miskin, C. K.; Boyne, R.; Cain. L. T.; Yerabolu, R.; Zhang, R.; Wegener, E.
C.; Miller, J. T.; Kenttamaa, H. I.; Agrawal, R. Speciation of CuCl and CuCl2 Thiol-Amine
Solutions and Characterization of Resulting Films: Implications for Semiconductor Device
Fabrication. Inorg. Chem. 2017, 56, 14396-14407.
(162) Nagel, A.; Range, K.J. Verbindungsbildung im System Ag2 S-Ge Se2-Ag I. Zeitschrift fuer
Naturforschung, Teil B: Anorganische Chemie, Organische Chemie 1978, 33, 1461–1464. (ICSD:
41711)
(163) Nandy, S. K.; Mukherjee, D. K.; Roy, S. B.; Kastha, G. S. Vibrational Spectra and
Rotational Isomerism in 2-Mercaptoethanol. Can. J. Chem. 1973, 51, 1139.
(164) Ng, M. T.; Boothroyd, C. B.; Vittal, J. J. One-Pot Synthesis of New-Phase AgInSe2
Nanorods, J. Am. Chem. Soc. 2006, 128, 7118–7119.
(165) Nomura, R.; Inazawa, S.; Kanaya, K.; Matsuda, H. Thermal Decomposition of
Butylindium Thiolates and Preparation of Indium Sulfide Powders. Appl. Organomet. Chem. 1989,
3, 195-197.
(166) Nørby, P.; Overgaard, J.; Christensen, P. S.; Richter, B.; Song, X.; Dong, M.; Han, A.;
Skibsted, J.; Iversen, B. B.; Johnsen, S. (NH4)4Sn2S6·3H2O: Crystal Structure, Thermal
Decomposition, and Precursor for Textured Thin Film. Chem. Mater. 2014, 26, 4494-4504.
(167) Novet, T.; Johnson, D. C. New Synthetic Approach to Extended Solids: Selective Synthesis
of Iron Silicides via the Amorphous State. J. Am. Chem. Soc. 1991, 113, 3398−3403.
(168) Ording-Wenker, E. C. M.; van der Plas, M.; Siegler, M. A.; Bonnet, S.; Bickelhaupt, F. M.;
Guerra, C. F.; Bouwman, E. Thermodynamics of the Cu
II
μ-Thiolate and Cu
I
Disulfide
Equilibrium: A Combined Experimental and Theoretical Study. Inorg. Chem. 2014, 53, 8494-
8504.
223
(169) Pai, N.; Lu, J.; Senevirathna, D. C.; Chesman, A. S. R.; Gengenbach, T.; Chatti, M.; Bach,
U.; Andrews, P. C.; Spiccia, L.; Cheng, Y.-B.; Simonov, A. N. Spray Deposition of AgBiS2 and
Cu3BiS3 Thin Films for Photovoltaic Applications. J. Mater. Chem. C 2018, 6, 2483–2494.
(170) Park, Y.; Mccarthy, T. J.; Sutorlk, A. C.; Kanatzidis, M. G.; Gillan, E. G. Synthesis of
Ternary Chalcogenides in Molten Polychalcogenide Salts: α-KCuQ4 , KAuS5 , NaBiS2 , KFeQ2
(Q = S, Se). Inorganic Syntheses; Murphy, D. W., Interrante, L. V., Eds.; John Wiley & Sons, Inc.:
Hoboken, NJ, USA, 2007; pp 88–95.
(171) Pascal, I.; Tarbell, D. S. The Kinetics of the Oxidation of a Mercaptan to the Corresponding
Disulfide by Aqueous Hydrogen Peroxide. J. Am. Chem. Soc. 1957, 79, 6015–6020.
(172) Peresh, E. Yu.; Golovei, M. I.; Berul’, S. I. Preparation and Certain Properties of Alkali
Metal Metathiobismuthites. Inorg. Mat. 1971, 7, 27–30.
(173) Pickering, I. J.; George, G. N.; Dameron, C. T.; Kurz, B.; Winge, D. R.; Dance, I. G. X-
Ray Absorption Spectroscopy of Cuprous-Thiolate Clusters in Proteins and Model Systems. J. Am.
Chem. Soc. 1993, 115, 9498-9505.
(174) Pirani, A. M.; Mercier, H. P. A.; Dixon, D. A.; Bormann, H.; Schrobilgen, G. J. Syntheses,
Vibrational Spectra, and Theoretical Studies of the Adamantanoid Sn4Ch10
4-
(Ch=Se, Te) Anions:
X-ray Crystal Structures of [18-Crown-6- K]4[Sn4Se10]·5en and [18-Crown-6-
K]4[Sn4Te10]·3en·2THF. Inorg. Chem. 2001, 40, 4823-4829.
(175) Polman, A.; Knight, M.; Garnett, E. C.; Ehrler, B.; Sinke, W. C. Photovoltaic Materials:
Present Efficiencies and Future Challenges. Science 2016, 352, aad4424.
(176) Protesescu, L.; Yakunin, S.;. Bodnarchuk, M. I.; Bertolotti, F.; Masciocchi, N.; Guagliardi,
A.; Kovalenko, M. V. Monodisperse Formamidinium Lead Bromide Nanocrystals with Bright and
Stable Green Photoluminescence. J. Am. Chem. Soc. 2016, 138,14202–14205.
224
(177) Pushie, M. J.; Zhang, L.; Pickering, I. J.; George, G. N. The Fictile Coordination Chemistry
of Cuprous-Thiolate Sites in Copper Chaperones. Biochim. Biophys. Acta, Bioenerg. 2012, 1817,
938-947.
(178) Rajashree, C.; Balu, A. R. Tuning the Physical Properties of PbS Thin Films Towards
Optoelectronic Applications Through Ni Doping. Optik 2016, 127, 8892-8898.
(179) Ramli, E.; Rauchfuss, T. B.; Stern, C. L. Interception of Copper Polysulfide Clusters in the
Reaction of Copper and Sulfur in Donor Solvents: Polysulfide Complexes as the Link Between
Molecular and Nonmolecular Metal Sulfides. J. Am. Chem. Soc. 1990, 112, 4043-4044.
(180) Ran, Z.;. Wang, X. J.; Li, Y. W.; Yang, D. W.; Zhao, X. G.; Biswas, K.; Singh, D. J.;
Zhang, L. G. Bismuth and Antimony-Based Oxyhalides and Chalcohalides as Potential
Optoelectronic Materials. npj Comput. Mater. 2018, 4, 14.
(181) Rao, C. P.; Dorfman, J. R.; Holm, R. H. Synthesis and Structural Systematics of Ethane-
1,2-Dithiolato Complexes. Inorg. Chem. 1986, 25, 428-439.
(182) Rathore, E.; Juneja, R.; Culver, S. P.; Minafra, N.; Singh, A. K.; Zeier, W. G.; Biswas, K.
Origin of Ultralow Thermal Conductivity in n-Type Cubic Bulk AgBiS2: Soft Ag Vibrations and
Local Structure Distortion Induced by the Bi 6s
2
Lone Pair. Chem. Mater. 2019, 31, 2106–2113.
(183) Razykov, T. M.; Ferekides, C. S.; Morel, D.; Stefanakos, E.; Ullal, H. S.; Upadhyaya, H.
M. Solar Photovoltaic Electricity: Current Status and Future Prospects. Sol. Energy 2011, 85,
1580–1608.
(184) Richter, J.; Ruck, M. Synthesis and Dissolution of Metal Oxides in Ionic Liquids and Deep
Eutectic Solvents. Molecules 2020, 25, 78.
225
(185) Rosales, B. A.; White, M. A.; Vela, J. Solution-Grown Sodium Bismuth Dichalcogenides:
Toward Earth-Abundant, Biocompatible Semiconductors. J. Am. Chem. Soc. 2018, 140, 3736–
3742.
(186) Shen, X.; Hernandez-Pagan, E. A.; Zhou, W.; Puzyrev, Y. S.; Idrobo, J.-C.; Macdonald, J.
E.; Pennycock, S. J.; Pantelides, S. T. Interlaced Crystals having a Perfect Bravais Lattice and
Complex Chemical Order Revealed by Real-Space Crystallography. Nat. Comm. 2014, 5, 5431.
(187) Shin, S. S.; Yeom, E. J.; Yang, W. S.; Hur, S.; Kim, M. G.; Im, J.; Seo, J.; Noh, J. H.; Seok,
S. I. Colloidally Prepared La-Doped BaSnO3 Electrodes for Efficient, Photostable Perovskite Solar
Cells. Science 2017, 356, 167−171.
(188) Shuai, X.; Shen, W.; Hou, Z.; Ke, S.; Xu, C.; Jiang, C.; A Versatile Chemical Conversion
Synthesis of Cu2S Nanotubes and the Photovoltaic Activities for Dye-Sensitized Solar Cell.
Nanoscale Res. Lett. 2014, 9, 1–7.
(189) Singh, A.; Singh, S.; Levcenko, S.; Unold, T.; Laffir, F.; Ryan, K. M. Compositionally
Tunable Photoluminescence Emission in Cu2ZnSn(S1−xSex)4 Nanocrystals. Angew. Chem., Int. Ed.
2013, 52, 9120−9124.
(190) Sinsermsuksakul, P.; Sun, L.; Lee, S. W.; Park, H. H.; Kim, S. B.; Yang, C.; Gordon, R.
G. Overcoming Efficiency Limitations of SnS-based Solar Cells. Adv. Energy Mater. 2014, 4,
1400496.
(191) Slang, S.; Palka, K.; Loghina, L.; Kovalskiy, A.; Jain, H.; Vlcek, M. Mechanism of the
dissolution of As-S chalcogenide glass in n-butylamine and its influence on the structure of spin
coated layers. J. Non-Cryst Solids 2015, 426, 125-131.
(192) Smith, R. C.; Reed, V. D.; Hill, W. E. Oxidation of Thiols by Copper(II). Phosphorus,
Sulfur Silicon Relat. Elem. 1994, 90, 147-154.
226
(193) Song, Z.; Abate, A.; Watthage, S. C.; Liyanage, G. K.; Phillips, A. B.; Steiner, U.; Graetzel,
M.; Heben, M. J. Perovskite Solar Cell Stability in Humid Air: Partially Reversible Phase
Transitions in the PbI2‐CH3NH3I‐H2O System. Adv. Energy Mater. 2016, 6, 1600846.
(194) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. Ab Initio Calculation of
Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force Fields. J.
Phys. Chem. 1994, 98, 11623−11627.
(195) Stranks, S. D.; Eperon, G. E.; Grancini, G.; Menelaou, C.; Alcocer, M. J. P.; Leijtens, T.;
Herz, L. M.; Petrozza, A.; Snaith, H. J. Electron-Hole Diffusion Lengths Exceeding 1 Micrometer
in an Organometal Trihalide Perovskite Absorber. Science 2013, 342, 341–344.
(196) Sugaki, A.; Shima, H. Phase Relations of the Cu2S-Bi2S3 System. Technol. Rep. Yamaguchi
Uni. 1972, 1, 71–85.
(197) Sun, J.; Singh, D. J. Electronic Properties, Screening, and Efficient Carrier Transport in
NaSbS2. Phys. Rev. Appl. 2017, 7, 024015.
(198) Sun, W.; Ye, Y.; You, Y.; Xu, J. A Top-Down Synthesis of Wurtzite Cu2SnS3 Nanocrystals
for Efficient Photoelectrochemical Performance. J. Mater. Chem. A 2018, 6, 8221−8226.
(199) Suresh, S.; Uhl, A. R. Present Status of Solution-Processing Routes for Cu(In,Ga)(S,Se)2
Solar Cell Absorbers. Adv. Energy Mater. 2021, 11, 2003743.
(200) Suryawanshi, M. P.; Ghorpade, U. V.; Shin, S. W.; Pawar, S. A.; Kim, I. Y.; Hong, C. W.;
Wu, M.; Patil, P. S.; Moholkar, A. V.; Kim, J. H. A Simple Aqueous Precursor Solution Processing
of Earth-Abundant Cu2SnS3 Absorbers for Thin-Film Solar Cells. ACS Appl. Mater. Interfaces
2016, 8, 11603– 11614.
(201) Suter, D.; Banwart, S.; Stumm, W. Dissolution of Hydrous Iron (III) Oxides by Reductive
Mechanisms. Langmuir 1991, 7, 809–813.
227
(202) Swarnkar, A.; Marshall, A. R.; Sanehira, E. M.; Chernomordik, B. D.; Moore, T. D.;
Christians, J. A.; Chakrabarti, T.; Luther, J. M. Quantum Dot–Induced Phase Stabilization of a-
CsPbI3 Perovskite for High-Efficiency Photovoltaics. Science 2016, 354, 92–95.
(203) Tang, J.; Kemp, K. W.; Hoogland, S.; Jeong, K. S.; Liu, H.; Levina, L.; Furukawa, M.;
Wang, X. H.; Debnath, R.; Cha, D. K.; Chou, K. W.; Fischer, A.; Amassian, A.; Asbury, J. B.;
Sargent, E. H. Colloidal-Quantum-Dot Photovoltaic using Ligand Passivation. Nat. Mater. 2011,
10, 765–771.
(204) Thiruvenkadam, S.; Rajesh, A. L. Effect of Temperature on Structural and Optical
Properties of Spray Pyrolysed CuSbS2 Thin Films for Photovoltaic Applications. Int. J. Sci. Eng.
Res. 2014, 5, 248-251.
(205) Tiwari, D.; Chaudhuri, T. K.; Shripathi, T.; Deshpande, U. Synthesis of Earth-Abundant
Cu2SnS3 Powder using Solid State Reaction. J. Phys. Chem. Solids 2014, 75, 410–415.
(206) Tiwari, D.; Chaudhuri, T. K.; Shripathi, T.; Deshpande, U.; Rawat, R. Non-Toxic, Earth-
Abundant 2% Efficient Cu2SnS3 Solar Cell Based on Tetragonal Films Direct-Coated from Single
Metal-Organic Precursor Solution. Sol. Energy Mater. Sol. Cells 2013, 113, 165–170.
(207) Uhl, A. R.; Rajagopal, A.; Clark, J. A.; Murray, A.; Feurer, T.; Buecheler, S.; Jen A. K.-
Y.; Hillhouse, H. W. Solution–Processed Low-Bandgap CuIn(S,Se)2 Absorbers for High-
Efficiency Single–Junction and Monolithic Chalcopyrite-Perovskite Tandem Solar Cells. Adv.
Energy Mater. 2018, 8, 1801254.
(208) Uličná, S.; Arnou, P.; Abbas, A.; Togay, M.; Welch, L. M.; Bliss, M.; Malkov, V.; Walls,
J. M.; Bowers, J. W. Deposition and Application of a Mo-N Back Contact Diffusion Barrier
Yielding a 12.0% Efficiency Solution-Processed CIGS Solar Cell Using a Thiol-Amine Solvent
System. J. Mater. Chem. A 2019, 7, 7042–7052.
228
(209) Vadivel, S.; Maruthamani, D.; Paul, B.; Dhar, S. S.; Habibi-Yangjeh, A.; Balachandran,
S.; Saravanakumar, B.; Selvakumar, A.; Selvam, K. Biomolecule-Assisted Solvothermal Synthesis
of Cu2SnS3 Flowers/RGO Nanocomposites and Their Visible-Light-Driven Photocatalytic
Activities. RSC Adv. 2016, 6, 74177–74185.
(210) van Embden, J.; Della Gaspera, E. Ultrathin Solar Absorber Layers of Silver Bismuth
Sulfide from Molecular Precursors. ACS Appl. Mater. Interfaces 2019, 11, 16674–16682.
(211) Vartak, P. B.; Wang, Z.; Groy, T. L.; Trovitch, R. J.; Wang, R. Y. Solution and Solid–State
Characterization of PbSe Precursors. ACS Omega 2020, 5, 1949–1955.
(212) Verma, A. K.; Rauchfuss, T. R.; Wilson, S. R. Donor Solvent Mediated Reactions of
Elemental Zinc and Sulfur, sans Explosion. Inorg. Chem. 1995, 34, 3072-3078.
(213) Wallace, S. K.; Butler, K. T.; Hinuma, Y.; Walsh, A. Finding a Junction Partner for
Candidate Solar Cell Absorbers Enargite and Bournonite from Electronic Band and Lattice
Matching. J. Appl. Phys. 2019, 125, 055703.
(214) Wallace, S. K.; Svane, K.; Huhn, W. P.; Zhu, T.; Mitzi, D. B.; Blum, V.; Walsh, A.
Candidate Photoferroic Absorber Materials for Thin-Film Solar Cells from Naturally Occurring
Minerals: Enargite, Stephanite, and Bournonite. Sustain. Energy Fuels 2017, 1, 1339−1350.
(215) Wang, H.; Xie, Z.; Wang, X.; Jia, Y. NaBiS2 as a Novel Indirect Bandgap Full Spectrum
Photocatalyst: Synthesis and Application. Catalysts 2020, 10, 413.
(216) Wang, J. J.; Akgul, M. Z.; Bi, Y.; Christodoulou, S.; Konstantatos, G. Low-Temperature
Colloidal Synthesis of CuBiS2 Nanocrystals for Optoelectronic Devices. J. Mater. Chem. A 2017,
5, 24621−24625.
229
(217) Wang, L.; Kefalidis, C. E.; Roisnel, T.; Sinbandhit, S.; Maron, L.; Carpentier, J.-F.;
Sarazin, Y. Structure vs
119
Sn NMR Chemical Shift in Three-Coordinated Tin(II) Complexes:
Experimental Data and Predictive DFT Computations. Organometallics 2015, 34, 2139-2150.
(218) Wang, W.; Winkler, M. T.; Gunawan, O.; Gokmen, T.; Todorov, T. K.; Zhu, Y.; Mitzi, D.
B. Device Characteristics of CZTSSe Thin-Film Solar Cells with 12.6% Efficiency. Adv. Energy
Mater. 2014, 4, 1301465.
(219) Wang, Y.; Kavanaugh, S. R.; Burgués-Ceballos, I.; Walsh, A.; Scanlon, D. O.;
Konstantatos, G. Cation Disordered Engineering Yields AgBiS2 Nanocrystals with Enhanced
Optical Absorption for Efficient Ultrathin Solar Cells. Nat. Photonics 2022, 16, 235–241.
(220) Wang, Z.; Ma, Y.; Vartak, P. B.; Wang, R. Y. Precursors for PbTe, PbSe, SnTe and SnSe
Synthesized Using Diphenyl Dichalcogenides. Chem. Commun. 2018, 54, 9055−9058.
(221) Webber, D. H.; Brutchey, R. L. Alkahest for V2VI3 Chalcogenides: Dissolution of Nine
Bulk Semiconductors in a Diamine-Dithiol Solvent Mixture. J. Am. Chem. Soc. 2013, 135, 15722-
15725.
(222) Webber, D. H.; Buckley, J. J.; Antunez, P. D.; Brutchey, R. L. Facile Dissolution of
Selenium and Tellurium in a Thiol−amine Solvent Mixture under Ambient Conditions. Chem. Sci.
2014, 5, 2498−2502.
(223) Wei, K.; Martin, J.; Salvador, J. R.; Nolas, G. S. Synthesis and Characterization of
Bournonite PbCuSbS3 Nanocrystals. Cryst. Growth Des. 2015, 15, 3762–3766.
(224) Weigend, F.; Ahlrichs, R. Balanced Basis Sets of Split Valence, Triple Zeta Valence and
Quadruple Zeta Valence Quality for H to Rn: Design and Assessment of Accuracy. Phys. Chem.
Chem. Phys. 2005, 7, 3297–3305.
230
(225) Wernick, J. Constitution of the AgSbS2-PbS, AgBiS2-PbS, and AgBiS2-AgBiSe2 Systems.
Am. Mineral. 1960, 45, 591.
(226) Whittles, T. J.; Veal, T. D.; Savory, C. N.; Yates, P. J.; Murgatroyd, P. A. E.; Gibbon, J.
T.; Birkett, M.; Potter, R. J.; Major, J. D.; Durose, K.; Scanlon, D. O.; Dhanak, V. R. Band
Alignments, Band Gap, Core Levels, and Valence Band States in Cu3BiS3 for Photovoltaics. ACS
Appl. Mater. Interfaces 2019, 11, 27033–27047.
(227) Wickham, D. G.; Mark, J.; Knox, K. Metal Iron(III) Oxides. Inorganic Syntheses 1967, 9,
152–156.
(228) Williams, T. J.; Kershaw, A. D.; Li, V.; Wu, X. An Inversion Recovery NMR Kinetics
Experiment. J. Chem. Educ. 2011, 88, 665−669.
(229) Wu, W.-Y.; Xu, Y.; Ong, X.; Bhatnagar, S.; Chan, Y. Thermochromism from Ultrathin
Colloidal Sb2Se3 Nanowires Undergoing Reversible Growth and Dissolution in an Amine–Thiol
Mixture. Adv. Mater. 2019, 31, 1806164.
(230) Wu, Y.; Wan, L.; Zhang, W.; Li, X.; Fang, J. In Situ Grown Silver Bismuth Sulfide
Nanorod Arrays and Their Application to Solar Cells. CrysEngComm. 2019, 21, 3137.
(231) Wu. W.-Y.; Ong, X.; Bhatnagar, S.; Chan, Y. Thermochromism from Ultrathin Colloidal
Sb2Se3 Nanowires Undergoing Reversible Growth and Dissolution in an Amine-Thiol Mixture.
Adv. Mater. 2019, 31, 1806164.
(232) Xiao, Z.; Yuan, Y.; Shao, Y.; Wang, Q.; Dong, Q.; Bi, C.; Sharma, P.; Gruverman, A.;
Huang, J. Giant Switchable Photovoltaic Effect in Organometal Trihalide Perovskite Devices. Nat.
Mater. 2015, 14, 193.
231
(233) Yakushev, M. V.; Maiello, P.; Raadik, T.; Shaw, M. J.; Edwards, P. R.; Krustok, J.;
Mudryi, A. V.; Forbes, I.; Martin, R. W. Electronic and Structural Characterisation of Cu3BiS3
Thin Films for the Absorber Layer of Sustainable Photovoltaics. Thin Solid Films 2014, 562, 195–
199.
(234) Yan, C.; Gu, E.; Liu, F.; Lai, Y.; Li, J.; Liu, Y. Colloidal Synthesis and Characterization
of Wittichenite Copper Bismuth Sulphide Nanocrystals. Nanoscale 2013, 5, 1789–1792.
(235) Yang, B.; Xue, D.-J.; Leng, M.; Zhong, J.; Wang, L.; Song, H.; Zhou, Y.; Tang, J.
Hydrazine Solution Processed Sb2S3, Sb2Se3 and Sb2(S1-xSex)3 Film: Molecular Precursor
Identification, Film Fabrication and Band Gap Tuning. Sci. Rep. 2015, 5, 10978.
(236) Yang, C.; Wang, Z.; Wu, Y.; Lv, Y.; Zhou, B.; Zhang, W.-H. Synthesis, Characterization,
and Photodetector Application of Alkali Metal Bismuth Chalcogenide Nanocrystals. ACS Appl.
Energy Mater. 2019, 2, 182–186.
(237) Yang, W.; Duan, H.-S.; Cha, K. C.; Hsu, C.-J.; Hsu, W.-C.; Zhou, H.; Bob, B.; Yang, Y.
Molecular Solution Approach to Synthesize Electronic Quality Cu2ZnSnS4 Thin Films. J. Am.
Chem. Soc. 2013, 135, 6915-6920.
(238) Yang, Y.; Wang, G.; Zhao, W.; Tian, Q.; Huang, L.; Pan, D. Solution-Processed Highly
Efficient Cu2ZnSnSe4 Thin Film Solar Cells by Dissolution of Elemental Cu, Zn, Sn, and Se
Powders. ACS Appl. Mater. Interfaces 2015, 7, 460-464.
(239) Yu, L.; Kokenyesi, R. S.; Keszler, D. A.; Zunger, A. Inverse Design of High Absorption
Thin-Film Photovoltaic Materials. Adv. Energy Mater. 2013, 3, 43–48.
(240) Yu, Y.; Zunger, A. Identification of Potential Photovoltaic Absorbers Based on First-
Principles Spectroscopic Screening of Materials. Phys. Rev. Lett. 2012, 108, 068701.
232
(241) Yun, M. J.; Cha, S. I.; Seo, S. H.; Lee, D. Y. Highly Flexible Dye-Sensitized Solar Cells
Produced by Sewing Textile Electrodes on Cloth. Sci. Rep. 2014, 4, 5322.
(242) Zhai, Y.-T.; Chen, S.; Yang, J.-H.; Xiang, H.-J.; Gong, X.-G.; Walsh, A.; Kang, J.; Wei,
S.-H. Structural Diversity and Electronic Properties of Cu2SnX3 (X = S, Se): A First-Principles
Investigation. Phys. Rev. B 2011, 84, 075213.
(243) Zhang, M.; Liu, Y.; Yang, B.; Lin, X.; Lu, Y.; Zheng, J.; Chen, C.; Tang, J. Efficiency
Improvement of Bournonite CuPbSbS3 Solar Cells via Crystallinity Enhancement. ACS Appl.
Mater. Interfaces 2021, 13, 13273–13280.
(244) Zhang, R.; Cho, S.; Lim, D. G.; Hu, X.; Stach, E. A.; Handwerker, C. A.; Agrawal, R.
Metal-Metal Chalcogenide Molecular Precursors to Binary, Ternary, and Quaternary Metal
Chalcogenide Thin Films for Electronic Devices. Chem. Commun. 2016, 52, 5007-5010.
(245) Zhang, R.; Szczepaniak, S. M.; Carter, N. J.; Handwerker, C. A.; Agrawal, R. A Versatile
Solution Route to Efficient Cu2ZnSn(S,Se)4 Thin-Film Solar Cells. Chem. Mater. 2015, 27, 2114-
2120.
(246) Zhang, T.; Yang, Y.; Liu, D.; Tse, S. C.; Cao, W.; Feng, Z.; Chen, S.; Qian, L. High
Efficiency Solution-Processed Thin-Film Cu(In,Ga)(Se,S)2 Solar Cells. Energy Environ. Sci.
2016, 9, 3674-3681.
(247) Zhang, T.; Zhang, L.; Yin, Y.; Jiang, C.; Li, S.; Zhu, C.; Chen, T. A Thiol–Amine Mixture
for Metal Oxide Towards Device Quality Metal Chalcogenides. Sci. China Mater. 2019, 62, 899–
906.
(248) Zhang, X.; Guo, G.; Ji, C.; Huang, K.; Zha, C.; Wang, Y.; Shen, L.; Gupta, A.; Bao, N.
Efficient Thermolysis Route to Monodisperse Cu2ZnSnS4 Nanocrystals with Controlled Shape and
Structure. Sci. Rep. 2015, 4, 5086.
233
(249) Zhao, D.; Fan, Q.; Tian, Q.; Zhou, Z.; Meng, Y.; Kou, D.; Zhou, W.; Wu, S. Eliminating
Fine-Grained Layers in Cu(In,Ga)(S,Se)2 Thin Films for Solution-Processed High Efficiency Solar
Cells. J. Mater. Chem. A 2016, 4, 13476.
(250) Zhao, D.; Tian, Q.; Zhou, Z.; Wang, G.; Meng, Y.; Kou, D.; Zhou, W.; Pan, D.; Wu, S.
Solution–Deposited Pure Selenide CIGSe Solar Cells from Elemental Cu, In, Ga, and Se. J. Mater.
Chem. A. 2015, 3, 19263–19267.
(251) Zhao, X.; Deshmukh, S. D.; Rokke, D. J.; Zhang, G.; Wu, Z.; Miller, J. T.; Agrawal, R.
Investigating Chemistry of Metal Dissolution in Amine-Thiol Mixtures and Exploiting it Toward
Benign Ink Formulation for Metal Chalcogenide Thin Films. Chem. Mater. 2019, 31, 5674-5682.
(252) Zhao, X.; Jiang, J.; Xue, Z.; Yan. C.; Mu, T. An Ambient Temperature, CO2-Assisted
Solution Processing of Amorphous Cobalt Sulfide in a Thiol/Amine Based Quasi-Ionic Liquid for
Oxygen Evolution Catalysis. Chem. Commun. 2017, 53, 9418-9421.
(253) Zhao, X.; Lu, M.; Koeper, M. J.; Agrawal, R. Solution-Processed Sulfur Depleted
Cu(In,Ga)Se2 Solar Cells Synthesized from a Monoamine-Dithiol Solvent Mixture. J. Mater.
Chem. A 2016, 4, 7390-7397.
(254) Zhao, Y.; Yuan, S.; Chang, Q.; Zhou, Z.; Kou, D.; Zhou, W.; Qi, Y.; Wu, S. Controllable
Formation of Ordered Vacancy Compound for High Efficiency Solution Processed Cu(In,Ga)Se2
Solar Cells. Adv. Funct. Mater. 2021, 31, 2007928.
(255) Zhao, Y.; Zhao, X.; Kou, D.; Zhou, W.; Zhou, Z.; Yuan, S.; Qi, Y.; Zheng, Z.; Wu, S.
Local Cu Component Engineering to Achieve Continuous Carrier Transport for Enhanced
Kesterite Solar Cells. ACS Appl. Mater. Interfaces 2021, 13, 795–805.
(256) Zhong, J.; Xiang, W.; Cai, Q.; Liang, X. Synthesis, Characterization and Optical Properties
of Flower-Like Cu3BiS3 Nanorods. Mater. Lett. 2012, 70, 63–66.
234
(257) Zhu, F.; Men, L.; Guo, Y.; Zhu, Q.; Bhattacharjee, U.; Goodwin, P. M.; Petrich, J. W.;
Smith, E. A.; Vela, J. Shape Evolution and Single Particle Luminescence of Organometal Halide
Perovskite Nanocrystals. ACS Nano 2015, 9, 2948–2959.
(258) Zhuang, Z.; Lu, X.; Peng, Q.; Li, Y. A Facile “Dispersion–Decomposition” Route to Metal
Sulfide Nanocrystals. Chem. Eur. J. 2011, 17, 10445–10452.
(259) Zuo, Y.; Li, J.; Yu, X.; Du, R.; Zhang, T.; Wang, X.; Arbiol, J.; Llorca, J.; Cabot, A. A
SnS2 Molecular Precursor for Conformal Nanostructured Coatings. Chem. Mater. 2020, 32, 2097–
2106.
Abstract (if available)
Abstract
The solution phase deposition of molecular inks into phase pure and alloyed semiconductor thin films for functional devices is of importance to replace deposition techniques reliant on high vacuum and high temperature annealing (i.e., chemical vapor deposition, physical vapor deposition, etc.). In chapter 1, the current progress of one class of molecular inks, thiol-amine – “alkahest”, is presented. The current progress of understanding the identity of molecular solutes and how it dictates the phase(s) and quality of the resulting materials will be addressed as well as outstanding questions and future directions. In chapter 2, we discuss the dissolution of bulk ZnO in a model thiol-imidazole solvent system where the dissolution kinetics was tracked experimentally, and a mechanism of dissolution was proposed that was supported with DFT calculations. In chapter 3, we present the polymorphic control of two different Cu2SnS3 semiconductor films by simply switching the identity of the thiol in alkahest solvent mixtures and a mechanism of polymorph control is suggested. In the following chapters, environmentally stable sulfosalts as replacements for perovskites, bournonite (CuPbSbS3) (chapter 4) and wittichenite (Cu3BiS3) (chapter 5) are solution processed into functional thin films using the alkahest and their structural and optical properties are investigated. Finally, in the appendix, a Ag1–xNaxBiS2 solid solution is solution processed and high quality semiconducting AgBiS2 thin films are presented. In summary, by leveraging alkahest solutions to fine tune ink compositions and identifying resulting molecular solutes and dissolution/decomposition pathways, high quality semiconductors can be solution deposited with control over phase-purity, polymorph, and doping/alloying (solid solution.
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Solution processed functional chalcogenide thin films and their molecular solutes from thiol-amine inks
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Chemistry
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