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Complementary hydrogen bonding enables efficient and mechanically robust polymer solar cells

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Complementary hydrogen bonding enables efficient and mechanically robust polymer solar cells

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Content COMPLEMENTARY HYDROGEN BONDING ENABLES EFFICIENT AND
MECHANICALLY ROBUST POLYMER SOLAR CELLS
by
Qingpei Wan
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(CHEMISTRY)
May 2025
Copyright 2025 Qingpei Wan

ii
Dedication
To my family and friends

iii
Acknowledgments
First and foremost, I would want to express my gratitude to my parents for their unwavering
love and support throughout my life. I know that this would not have been possible without your
support, and you both have inspired me in so many ways.
Further, I would like to sincerely thank Prof. Barry C. Thompson, my adviser, for his
continuous support and guiding during my doctoral studies. This task would never have been
completed without his help in every stages. I really appreciate all of your help and patience
throughout the previous five years.
Additionally, I would like to acknowledge the members of my PhD committee Prof. Chao
Zhang and Prof. Wei Wu, for their insightful comments and encouragement. I also wish to express
my gratitude for the assistance I received from the collaborative work I completed with Professors
Mark E. Thompson, Bumjoon J. Kim and Taek-Soo Kim. I would also greatly thank the rest of the
group members for their collaborative effort during my graduate studies. To Dr. Gobalasingham,
Dr. Ekiz, Dr. Melenbrink, Dr. Pankow, Dr. Samal, Dr. Ye, Dr. Das, Dr. Kazerouni and Dr. Schmitt,
thanks for your patience guiding me throughout my research when we were colleagues. Many
thanks for supporting me for always providing helpful suggestions and help with instruments as
well as general lab questions. I also thank all the present members of the research group. Tanin
Hooshmand, Grace Castillo, Timothy Bennett, Steven Sheppard, Dhairya Patel, and Sarah
Karabadjakyan thanks for being the most knowledgable and supportive colleagues and friends.
Apart from the academic support, I would like to specially thank the support and understading
from my wife Xiaoyi Guo over the past five years. I could not be writing this without all of your
support and I cannot begin to express my gratitude for you.

iv
The work in this dissertation would not have been possible without the assistance of the
following individuals: Dr. Liwei Ye (molecule synthesis in Chapters 2), Soodeok Seo (materials
characterization and device fabrication in Chapter 3, 4), Hyerinn Jeon (materials characterization
and device fabrication in Chapter 4), Sun-Woo Lee (mechanical properties measurments in
Chapter 3) and Eun Sung Oh (mechanical properties measurments in Chapter 4).

v
Table of Contents
DEDICATION.................................................................................................................... ii
ACKNOWLEDGMENTS .................................................................................................iii
LIST OF TABLES...........................................................................................................viii
LIST OF FIGURES ............................................................................................................ x
LIST OF SCHEMES ...................................................................................................... xvii
ABSTRACT...................................................................................................................xviii
CHAPTER 1: CONTROL OF PROPERTIES THROUGH HYDROGEN BONDING
INTERACTIONS IN CONJUGATED POLYMERS ........................................................ 1
1.INTRODUCTION ............................................................................................................. 1
2. COMMON H-BONDING FUNCTIONAL GROUPS IN CPS .................................................. 6
2.1. Hydroxyl Group................................................................................................... 6
2.2. Amide and Carbamate groups............................................................................ 16
2.3. Urea functional groups....................................................................................... 32
2.4. Thymine functional groups................................................................................ 40
3. OTHER H-BONDING FUNCTIONAL GROUPS USED IN CPS ............................................ 49
4. CONCLUSION AND OUTLOOK ..................................................................................... 52
5. REFERENCES .............................................................................................................. 56
CHAPTER 2: UNPRECEDENTED EFFICIENCY INCREASE IN A TERNARY
POLYMER SOLAR CELL EXHIBITING POLYMER-MEDIATED
POLYMORPHISM OF A NON-FULLERENE ACCEPTOR......................................... 68

vi
2.1 INTRODUCTION......................................................................................................... 68
2.2 RESULTS AND DISCUSSION....................................................................................... 70
2.3 CONCLUSION............................................................................................................ 81
2.4 REFERENCES ............................................................................................................ 83
CHAPTER 3: HIGH PERFORMANCE INTRINSICALLY STRETCHABLE
POLYMER SOLAR CELL WITH RECORD EFFICIENCY AND
STRETCHABILITY ENABLED BY THYMINE FUNCTIONALIZED
TERPOLYMER................................................................................................................ 89
3.1 INTRODUCTION......................................................................................................... 89
3.2 RESULTS AND DISCUSSION....................................................................................... 90
3.3 CONCLUSION............................................................................................................ 98
3.4 REFERENCES .......................................................................................................... 100
CHAPTER 4: POLYMER ACCEPTOR WITH HYDROGEN BONDING
FUNCTIONALITY FOR EFFICIENT AND MECHANICALLY
ROBUST TERNARY ORGANIC SOLAR CELLS ...................................................... 107
4.1 INTRODUCTION....................................................................................................... 107
4.2 RESULTS AND DISCUSSION..................................................................................... 111
4.4 REFERENCES .......................................................................................................... 127
BIOGRAPHICAL SKETCH .......................................................................................... 134
APPENDIX A................................................................................................................. 135
A.1 MATERIALS AND METHODS .................................................................................. 135
A.2 CHARACTERIZATION (UV, CV, GIXRD AND DSC).............................................. 139

vii
A.3 OPV PERFORMANCE ............................................................................................. 143
APPENDIX B................................................................................................................. 146
B.1 MATERIALS AND METHODS................................................................................... 146
B.2 CHARACTERIZATION ............................................................................................. 159
B.3 PREVIOUS REPORT ................................................................................................. 167
B.4 REFERENCE ........................................................................................................... 170
APPENDIX C................................................................................................................. 173
C.1 MATERIALS AND METHODS................................................................................... 173
C.2 CHARACTERIZATION ............................................................................................. 176

viii
List of Tables
Table 2-1 Photovoltaic Properties of PTQ10:NFA:PC61BM Ternary Blend BHJ
Solar Cells......................................................................................................................... 78
Table 3-1 Photovoltaic Properties of PD:L8-BO blends in rigid solar cells..................... 99
Table 4-1 Material properties of PM6 PD, Y6-BO SMA and the two PAs used in
this study ......................................................................................................................... 112
Table 4-2 Photovoltaic parameters of OSCs................................................................... 116
Table 4-3 Morphological properties of blend films........................................................ 121
Table A-1 Mismatch Factor, corrected current, calculated current and EQE
error calculation
......................................................................................................................................... 138
Table A-2 PTQ10, IDID and PC61BM blending test under the same devices
fabricating conditions (o-DCB)
......................................................................................................................................... 140
Table B-2 Photovoltaic properties of PD:L8-BO blend in rigid solar cell
......................................................................................................................................... 156
Table B-3 SCLC mobilities of the PD:L8-BO blends.
......................................................................................................................................... 156
Table B-4 Domain size (d) and coherence length (LC) estimated from GIWAXS
linecut profiles of PD:L8-BO blend films. ...................................................................... 158
Table B-5 Tensile properties of the PD:L8-BO blend films ........................................... 159
Table B-6 Device structures, mechanical and photovoltaic performances of previously
reported IS-PSCs and this work. The PCE80% values were estimated by interpolation
of the data reported in the papers.................................................................................... 160

ix
Table C-1 Tensile properties of the neat PA films
......................................................................................................................................... 183
Table C-2 The specific viscosity (ηsp) of pure chloroform (CF) solvent, N2200 CF
solution (10 mg mL-1
), and N2200-ThyDap CF solution (10 mg mL-1
)
......................................................................................................................................... 184
Table C-3 Photovoltaic parameters of OSCs with 20 wt% PA
......................................................................................................................................... 184
Table C-4 SCLC electron mobilities of the pristine PA films.
......................................................................................................................................... 185
Table C-5 SCLC mobilities of blend films.
......................................................................................................................................... 185
Table C-6 Tensile properties of the blend films with 20 wt% PA
......................................................................................................................................... 188

x
List of Figures
Figure 1-1 Representative H bond incorporated functional groups.................................. 25
Figure 1-2 Representative hydroxyl functionalized CPs (P1 to P17)............................... 26
Figure 1-3 Overview of the conversion of a film of a parent ester polymer to a
hydroxyl polymer. Reproduced with permission. [44] Copyright 2022, American
Chemical Society. ............................................................................................................. 28
Figure 1-4 Schematic illustration of the formation of helical nanofibers in P13.
The blue and red colors represent the P3HT block and P3HHT block, respectively.
Reproduced with permission. [66] Copyright 2018, Royal Society of Chemistry. ............ 33
Figure 1-5 Representative amide and carbamate functionalized CPs (P18 to P45) ......... 37
Figure 1-6 Stannylation of the thiophene with secondary amide ..................................... 41
Figure 1-7 GIWAXS of P24 before and after annealing at 200 °C for 10 min.
Reproduced with permission. [76] Copyright 2015, American Chemical Society............. 43
Figure 1-8 Illustration of the treatments used for healing conjugated polymer
films after stretching (top). AFM phase images for damaged and healed films of P37
(middle). Transfer curves and field-effect mobility of damaged and healed films of P37
(bottom). Reproduced with permission.[50] Copyright 2016, Springer Nature. ................ 46
Figure 1-9 Representative benzene-based urea functionalized CPs (P46 to P50)........... 49
Figure 1-10 Illustration of fluorescence turn-on sensing of anions based on the
disassembly of P47. Reproduced with permission.[93] Copyright 2012, American
Chemical Society. ............................................................................................................. 52
Figure 1-11 Representative thymine functionalized CPs (P58 to P70) ............................ 56
Figure 1-12 (a) illustration of thymine resonance structures and (b) the thymine-

xi
thymine dimer. .................................................................................................................. 57
Figure 1-13 Two representative thymine functionalized monomer syntheses.[111,118]...... 58
Figure 1-14 (a) Device structure and (b) image of the intrinsically stretchable
PSC (IS-PSC). (c) J−V curves of the IS-PSCs with PM7 and PM7-Thy (P70)-based
blends. (d) Normalized PCE of IS-PSCs during stretching. Reproduced with
permission. [118] Copyright 2023, American Chemical Society........................................ 63
Figure 1-15 Representative Upy and adenine based CPs. ................................................ 66
Figure 2-1 Structures and corresponding HOMO and LUMO energy levels of PTQ10,
IDID, and PC61BM ........................................................................................................... 77
Figure 2-2 Relative Increase in Jsc and PCE with respect to the best binary cell in
literature ............................................................................................................................ 79
Figure 2-3 GIXRD patterns of thin film with IDID and the blend with PTQ10 from
2θ=6 to 14 degrees............................................................................................................ 81
Figure 2-4 DSC thermograms of (a) PTQ10, IDID, and PTQ10/IDID (1:0.3, w/w)
upon heating (down) and cooling (up) with endo down (b) enlarged figure of pink
rectangle at the position of Tc. .......................................................................................... 83
Figure 2-5 (a) UV-Vis and (b) PL spectra of PTQ10, PC61BM (1:1.2) binary and
PTQ10, PC61BM, IDID (1:1.2:0.3) ternary....................................................................... 86
Figure 3-1 (a) Chemical Structure of PM7-ThyX, Q-Thy and (b) Thin film UV-vis
spectra of PDs.................................................................................................................... 96
Figure 3-2 (a) J-V curves of PD:L8-BO-based blends in the rigid PSC architecture.
(b) Gaussian distribution of PCEs of the PSCs................................................................. 98
Figure 3-3 GIWAXS in-plane linecuts of the PD: L8-BO blend films........................... 100

xii
Figure 3-4 (a) Optical microscope images of PM7:L8-BO and PM7-Thy10:L8-BO
blend films after 3 and 10% strain, respectively. (b) Stress-strain curves of the
different blend films measured by the pseudo free-standing tensile tests ...................... 101
Figure 3-5 (a) Device structure and (b) active image of the intrinsically-stretchablePSC (IS-PSC). (c) J-V curves of the IS-PSCs based on the PM7- and
PM7-Thy10-based blends. (d) Normalized PCE of IS-PSCs during stretching. ............ 101
Figure 3-6 Photovoltaic parameters of IS-PSCs and their strain values at 80% of
their initial PCE............................................................................................................... 102
Figure 4-1 (a) Molecular structures of two polymer additives, N2200-ThyDap
and N2200. (b) Depiction of interaction between the Thy and Dap unit.
(c) Molecular structures of PM6 PD and Y6-BO SMA. ................................................. 111
Figure 4-2 (a) Normalized thin film UV-Vis spectra and (b) energy levels of the
materials used in this study. (c) The second heating cycle and the first cooling cycle
from differential scanning calorimeter (DSC) of the N2200 and N2200-ThyDap.
(d) Stress-Strain curve of neat PA films. (e) Optical microscopy (OM) pristine film
images during tensile tests. ............................................................................................. 113
Figure 4-3 Photovoltaic performance of PM6:Y6-BO OSCs with polymer additives;
(a) J-V curves. (b) PCE distribution with Gaussian fitting. (c) EQE response spectra.
(d) Jph vs. Veff curves....................................................................................................... 116
Figure 4-4 (a) Stress-Strain curves of PM6:Y6-BO binary blend and PM6:Y6-BO:PA
ternary blends (wt% value of PA indicates the weight of PA compared to (PA + SMA)
weight). (b) OM images of blend films during tensile tests. .......................................... 119
Figure 4-5 (a) GIXS spectra of PM6:Y6-BO binary and PM6:Y6-BO:PA ternary

xiii
films along the IP direction and (b) OOP direction. (c) Lorentz-correlated resonance
soft X-ray scattering (RSoXS) profiles of blend films. .................................................. 121
Figure A-0 synthesisi of IDID ........................................................................................ 132
Figure A-00 1
HNMR Of IDID ........................................................................................ 133
Figure A-1 UV-Vis absorption spectra of IDID thin film spin-coated from chloroform
and placed in a N2 for 30 minutes.................................................................................. 134
Figure A-2 CV scan of IDID film, ELUMO = Eg
opt - EHOMO.............................................. 134
Figure A-3 GIXRD patterns of thin film processed from o-DCB with blend of PTQ10
and IDID with/without thermal annealing (120°C for 20mins)...................................... 135
Figure A-4 GIXRD patterns of thin films of IDIC (processed from chloroform
with annealing) and PTQ10:IDIC (processed from o-DCB as cast)............................... 135
Figure A-5 GIXRD patterns of thin film processed from chloroform with blend of
PTQ10 and IDID with/without thermal annealing (120°C for 20mins)......................... 136
Figure A-6 DSC thermograms of the blend PTQ10 and IDID (1:0.3) during heating
cycle with higher temperature scanning ......................................................................... 136
Figure A-7 DSC thermograms of enlarged figure of pink rectangle at the position
of Tc, neat IDID (red), blend of PTQ10 and IDID (1:0.3) (blue) ................................... 137
Figure A-8 DSC thermograms of neat IDIC and blend with PTQ10 (1:0.3, w/w)
processed from o-DCB upon heating.............................................................................. 137
Figure A-9 GIXRD patterns of thin film of PTQ10: PC61BM binary and PTQ10:
IDID: PC61BM ternary blend.......................................................................................... 138
Figure A-10 External Quantum Efficiency of the corresponding binary
(PTQ10: PC61BM=1:1.2) and ternary blends (PTQ10: FRSM: PC61BM=1:0.3:1.2)..... 139

xiv
Figure A-11 J-V Curve of the corresponding binary (PTQ10: PC61BM=1:1.2) and
ternary blends (PTQ10: FRSM: PC61BM=1:0.3:1.2) ..................................................... 139
Figure B-1 1
H NMR spectrum of Q-Thy monomer (CDCl3) ......................................... 147
Figure B-2 1
H NMR spectra of PM7-Thy5..................................................................... 148
Figure B-3 1
H NMR spectra of PM7-Thy10................................................................... 149
Figure B-4 1
H NMR spectra of PM7-Thy20................................................................... 150
Figure B-5 1
H NMR spectra (Aromatic region) of concentration dependent (1 mM,
5 mM, and 10 mM) Q-Thy in CDCl3 and the corresponding protons and peaks labeled
as a, b, and c.................................................................................................................... 151
Figure B-6 1
H NMR spectra of concentration dependent (1 mM, 5 mM, and 10 mM)
Q-Thy in CDCl3 .............................................................................................................. 151
Figure B-7 Solution UV-vis spectra of PDs in chloroform solution. .............................. 152
Figure B-8 Cyclic voltammetry of PDs and ferrocene reference. ................................... 153
Figure B-9 (a) Chemical Structure of PM7-ThyX, L8-BO SMA, and the H-bonding
between the Thymine molecule. (b) UV-vis spectra of PDs in thin film state.
(c) Energy levels of PDs and L8-BO SMA. .................................................................... 154
Figure B-10 EQE spectra of the rigid PSCs.................................................................... 155
Figure B-11 Relationship between the Veff and Jph ......................................................... 155
Figure B-12 2D images of GIWAXS PD neat films. ...................................................... 157
Figure B-13 GIWAXS lincuts of pristine constituents along the (a) IP direction and
(b) OOP direction............................................................................................................ 157
Figure B-14 2D images of GIWAXS PD:L8-BO blend films......................................... 157
Figure B-15 GIWAXS linecut profiles in the out-of-plane direction of PD:L8-BO

xv
blend films. ..................................................................................................................... 158
Figure B-16 Previously reported intrinsically stretchable polymer solar cells (IS-PSC)
and this work................................................................................................................... 159
Figure C-1 1
H NMR spectrum of Compound 2.............................................................. 172
Figure C-2 1
H NMR spectrum of T-Dap monomer........................................................ 173
Figure C-3 1
H NMR spectrum of N2200-ThyDap. ........................................................ 174
Figure C-4 1
H NMR spectra (from 3.3 ppm to 4.8 ppm) of N2200-ThyDap versus
N2200.............................................................................................................................. 175
Figure C-5 1
H NMR spectrum (from 3.3 ppm to 5.1 ppm) of N2200-ThyDap to
calculate the molar ratio between the Thy, Dap, and NDI functions.............................. 176
Figure C-6 Aromatic region 1
H NMR spectra of pristine Q-Thy, T-Dap, and Q-Thy:
T-Dap mixture in CDCl3 at R.T...................................................................................... 177
Figure C-6b Full 1
H NMR spectra of pristine Q-Thy, T-Dap, and Q-Thy: T-Dap
mixture in CDCl3 at R.T. ................................................................................................ 178
Figure C-7 Solution UV-Vis spectra of materials used in this study.............................. 179
Figure C-8 Cyclic voltammetry of materials used in study. ........................................... 180
Figure C-9 2D GIXS images of neat materials in the thin film state.............................. 181
Figure C-10 (a) In-plane and (b) out-of-plane linecuts of GIXS spectra of neat PA
films. ............................................................................................................................... 182
Figure C-11 (a) In-plane and (b) out-of-plane linecuts of GIXS spectra of neat PM6
PD and Y6-BO SMA....................................................................................................... 182
Figure C-12 Specific viscosity (ηsp) of pure chloroform (CF) solvent, N2200 CF
solution (10 mg mL-1
), and N2200-ThyDap CF solution (10 mg mL-1
)......................... 183

xvi
Figure C-13 (a) Molecular structure, (b) density functional theory (DFT) simulation
calculated structure, and (c) electrostatic potential map of N2200 (The DFT
simulation was used at the B3LYP/6-31G(d,p) level. To simplify the calculation,
the trimer form of the N2200 was modeled and side chains at NDI were simplified
as ethyl)........................................................................................................................... 186
Figure C-14 (a) Molecular structure, (b) DFT simulation calculated structure,
and (c) electrostatic potential map of N2200-ThyDap (The DFT simulation was used
at the B3LYP/6-31G(d,p) level and side chains at NDI were simplified as ethyl)......... 187
Figure C-15 Stress-Strain curve of PM6:Y6-BO binary blend and PM6:Y6-BO:PA
ternary blend (wt% value of PA indicates the weight of PA compared to (PA + SMA)
weight). ........................................................................................................................... 188
Figure C-16 2D GIXS images of blend films. ................................................................ 189

xvii
List of Schemes
Scheme B-1 Synthetic scheme for monomer and polymer donors (PDs). ...................... 141
Scheme C-1 Synthetic scheme for the T-Dap monomer and N2200-ThyDap polymer
acceptor (PA)................................................................................................................... 165

xviii
Abstract
The field of polymer solar cells (PSCs) has been growing rapidly over the last five years, and
significant effort has been put into developing new materials such as non-fullerene acceptors
(NFAs), device engineering, and comprehensive understanding of structure function relationships.
Currently, single-junction organic solar cells exhibit remarkable power conversion efficiencies
(PCEs) of more than 19%. Discovering and designing novel materials to further improve the
efficiency and mechanical reliability is essential to the commercialization of organic solar cells.
In contrast to fullerene acceptors, NFAs such as ITIC and Y6 lead to crystalline domains in
solid-state films that can crystallize in a variety of polymorphs depending on the processing
conditions. Different crystalline phases can result in various structural, optical, and electrical
properties, which potentially can affect device performance. Therefore, polymorphism is a critical
design parameter for semiconducting properties and even minor changes in crystal packing can
result in differentiation of electronic properties by orders of magnitude. Additionally, for future
commercialization of PSCs, it is crucial to design stretchable systems with both high efficiency
and mechanical robustness, as mechanical stress is a major factor causing device failure. A very
limited range of molecular design strategies such as introducing flexible non-conjugated spacers
into the polymer donors (PD) have been developed for high performance and mechanically robust
PSCs. Introducing Hydrogen-bonding (H-bonding) into conjugated polymers (CPs) has been a
broadly exploited but still represents an emerging strategy capable of tuning a range of properties
encompassing solubility, crystallinity, electronic properties, solid-state morphology and stability,
as well as mechanical properties and self-healing properties.
In this dissertation, a ternary polymer solar cell with a polymer donor-mediated polymoprh of
a novel NFA is presented to offer a new direction to improve the PCEs of PSCs. More importantly,

xix
several H-bonding molecular desgin strategies for PDs with the aim to improve the mechanical
reliability of PSC’s are also presented.
Chapter 1 provides an overview of classes of H-bonding CPs (assorted by the different Hbond functional groups), the synthetic methods to introduce the corresponding H-bond functional
groups and the impact of H-bonding in CPs on corresponding electronic and materials properties.
Recent advances in addressing the trade-off between electronic performance and mechanical
durability are also highlighted. Furthermore, insights into future directions and prospects for Hbonded CPs are discussed. This chapter provides the background for the reseach on the novel Hbonded CPs molecular desgin strategies in details in Chapters 3-4.
In Chapter 2, using a new NFA 2,2'-((4,4,9,9-tetrahexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b']
dithiophene-2,7-diyl) bis(methaneylylidene)) bis(1H-indene-1,3(2H)-dione), referred to IDID, as
the third component, we observed the appearance of a polymorph of IDID when it was introduced
into a PTQ10: PC61BM binary blend and this ternary blend solar cell showed a significant
improvement in efficiency from 3.38% to 6.04%. This relative increase (with respect to the best
binary cell) is nearly 80% which is the highest among all the reported organic ternary blends to
the best of our knowledge. Specifically, IDID was found to be nucleated by the host polymer donor
PTQ10 under the assistance of the processing solvent to form a distinct polymorph, as proven by
the grazing incidence X-Ray diffraction (GIXRD), differential scanning calorimetry (DSC), and
supported by surface energy measurements. More interestingly, IDID, as a third component in the
PTQ10: PC61BM system, was found to outperform the structurally similar NFA IDIC, which only
boosted the efficiency from 3.38% to 3.55% in ternary polymer solar cells. This work highlights
polymer-mediated polymorphism in NFAs as an important consideration in the selection of
components for and optimization of OSCs.

xx
In Chapter 3, a novel thymine side chain terminated 6,7-difluoro-quinoxaline (Q-Thy)
monomer was designed and used to synthesize a series of fully conjugated PDs (PM7-Thy5, PM7-
Thy10, PM7-Thy20) featuring Q-Thy. The Q-Thy units, capable of inducing dimerizable Hbonding, enable strong intermolecular PD assembly and highly efficient and mechanically robust
PSCs. The PM7-Thy10:SMA blend demonstrates a combination of high PCE >17% in rigid
devices and excellent stretchability (crack-on-set value >13.5%). More importantly, PM7-Thy10-
based intrinsically stretchable polymer solar cells IS-PSCs show an unprecedented combination of
PCE (13.7%) and ultrahigh mechanical durability (maintaining 80% of initial PCE after 43.1%
strain) illustrating promising potential for commercialization in wearable applications.
In Chapter 4, to overcome the limitation arising from using rigid and highly crystalline smallmolecule acceptors (SMAs) which limits the mechanical robustness of PSCs, a stretchable and
conjugated polymer acceptor (PA, N2200-ThyDap) was synthesized and introduced as the third
component to the benchmark polymer donor (PD):SMA system PM6:Y6-BO. N2200-ThyDap was
designed to incorporate H-bonding into the N2200 PA backbone using thymine (Thy) and
diaminopyrazine (Dap) units and the neat film shows excellent stretchability (crack onset strain
(COS) = 28.2%) compared to the PA of similar molecular weight without H-bonding (N2200, COS
= 1.5%). The N2200-ThyDap incorporated ternary system (PM6:Y6-BO:N2200-ThyDap) exhibits
a higher PCE (16.4%) than the reference binary (PM6:Y6-BO, PCE = 15.4%) and the N2200
incorporated control ternary system (PCE = 14.7%). The PM6:Y6-BO:N2200-ThyDap ternary
blend film achieves higher stretchability (COS = 4.8%) than the PM6:Y6-BO binary (COS = 2.1%)
and PM6:Y6-BO:N2200 ternary (COS = 2.4%) films. It is likely that a stronger intermolecular
interaction enabled by N2200-ThyDap leads to a higher photovoltaic performance and improved

xxi
stretchability. This study highlights the importance of conjugated polymer additive design in the
realization of high-performance and stretchable ternary OSCs.

1
Chapter 1: Control of Properties Through Hydrogen Bonding Interactions in
Conjugated Polymers
1.Introduction
Conjugated polymers (CPs) are a type of polymer with optical, semiconducting/conducting,
and/or electrochemical properties that have been developed for use in a number of electronic
applications. They are a low-cost organic materials family that can be solution processed, suitable
for roll-to-roll (R2R) production, and can be used in lightweight, flexible and stretchable device
applications.[1–5] The electrical and physical properties of CPs can be easily modified based on
their synthetic tunability. With synthetic customization, physical properties, such as solubility and
crystallinity as well as electrical properties including charge transport and light absorption, can be
regulated to satisfy the corresponding application of interest. This has led to their successful use
in applications such as organic photovoltaics (OPV)[6–9], organic field effect transistors (OFET)[10–
12], organic light emitting diodes (OLED)[13], electrochromic devices[14], organic electrochemical
transistors (OECT)[15–17], chemical sensors[18], biological applications[19–23], and photocatalysis[24–
27].
Hydrogen bonds (H-bonds), as a class of noncovalent/secondary bonds, are a special type of
dipole-dipole attraction formed by a hydrogen atom lying between two strongly electronegative
atoms. A hydrogen atom can be shared between a covalently bonded donor (X) and a free acceptor
(Y) with electron lone pairs and H-bonding is typically denoted as X-H···Y.[28] The most common
(X, Y) atoms that can participate in H-bonds are N, O, and F. The energy of an H-bond typically
can range from 1 to 40 kcal/mol and is influenced by the geometry, environment, and nature of the
participating donor and acceptor atoms.[29] H-bonds have dynamic properties owing to their
reversible bonding associations and broadly adjustable binding affinities.[30] From simple water

2
molecules to delicate biological macromolecules, H-bonds, as the most common noncovalent
interactions, occur in nature (e.g. DNA, proteins, and carbohydrates).
Molecular design based on H-bonds has been successfully applied to synthetic materials such
as elastomers, organic framework functional materials and electroactive polymers, leading to the
remarkable development of synthetic H-bonding materials.[31–34] Elastomers are a type of material
that can be dramatically deformed when subjected to an external force and partially or entirely
recover if the stress is removed. Elastomers often face repeated stresses, resulting in unexpected
degradation, cracking, and even macroscopic fracture. The ability of elastomers to self-heal is
crucial to extend service life time and improve their use safety. Hydrogen bonding plays an
important role in the design of self-healing electroactive elastomers due to the intrinsically
dynamic nature and self-healing elastomers based on multiple hydrogen-bonding interactions can
largely recover to their initial mechanical properties and electrical performance.[35–39] H-bonded
organic frameworks (HOFs) are a novel class of porous crystalline materials that self-assemble
from organic or metal-organic building blocks through intermolecular hydrogen-bonding
interactions and HOFs offer several unique characteristics such as mild synthesis conditions,
solution processability, self-healing, and regeneration as H-bonds are weaker than the coordinate
and covalent bonds utilized to produce metal organic frameworks (MOFs) and covalent organic
frameworks (COFs).[33] Thanks to the flexible and highly reversible nature of hydrogen bonds,
HOFs can be used as a customizable platform for the development of functional materials with
significantly increased structural diversity in many applications such as fluorescent sensing, gas
separation and storage, heterogeneous catalysis, and membrane-based applications.[33]
Introducing H-bonding into CPs has been a broadly exploited strategy since H-bonds can tune
a range of properties from solubility and crystallinity, to electronic properties, and morphological

3
stability, as well as mechanical and self-healing properties.
[32,40,41] Different H-bonding group are
utilized to tailor the properties that benefit the corresponding application of interest. Polar H-bonds
can promote aqueous solubility of CPs and facilitate polymer-aqueous phase interaction.[42–45] As
a type of directional intermolecular interaction, H-bonds can significantly affect the conformation
as well as optical and physical properties of the polymers involved. For instance, H-bonds can
assist molecules to self-assemble, offering the material a more ordered and crystalline structure in
the solid state. Different levels and motifs of crystallinity will result in significantly different
electronic properties as can be advantagous or detrimental depending on the given application. For
instance, OFETs benefit from a more aligned and crystalline structure that can enhance the charge
transport whereas OPVs require a mixed amorphous phase.[46,47] Stable solid-state morphology has
also been an important parameter for devices to maintain excellent performance under external
stimuli such as temperature fluctuations. H-bonds embedded in the solid-state can act as physical
cross-link sites to lock the morphology thus maintaining the initial and optimal morphology.[48,49]
Due to the reversible nature of H-bonds, physical cross-link sites are also capable of acting as
energy dissipation centers to absorb external mechanical stress and thus improve the mechanical
reliability.[50] A central challenge in CPs is to combine excellent electrical performance with robust
mechanical reliability. A few representative examples demonstrate the effectiveness of using Hbonds to address this important trade-off in organic electronics. Bao et al. utilized amide containing
spacers in CPs to realize OFETs with a high mobility of 1.12 cm2 V−1
s
−1 at 100% strain along the
direction perpendicular to the strain.[50] Kim et al. found an amide spacer incorporated CP donor
enabling for intrinsically stretchable organic solar cells (IS-OSC) with a high power conversion
efficiency (PCE) of 12.7% and excellent stretchability (PCE retention of >80% of the initial value
at 32% strain).[51] Likewise, Thompson et al. reported a thymine incorporated fully conjugated CP

4
donor that further improved the PCE of IS-OSC to 13.7% with a PCE retention of >80% of the
initial value at 43% strain, which significantly exceeded the 30% applied stress requirement for
wearable electronics.[52]
Although a few reviews examining the scope of H-bonding in CPs have been published, most
heavily focus on one specific application and the corresponding device performance.[32,40] In this
review, recent advances in H-bonded CPs (assorted by the different H-bond functional groups, as
shown in Figure 1-1) are broadly reviewed, including the synthetic method to introduce the
corresponding H-bonding functional groups, as well as the impact of H-bonding on the
corresponding materials properties.
Other than self-complementary hydrogen bonding in Figure 1-1, specific-complementary
hydrogen bonding between distinct, mutually interacting groups is also an important category. This
is analgous to the base-pairing hydrogen bonding that defines the structure of DNA and RNA. For
instance, thymine (Thy) and diaminopyrazine (Dap) is a pair explored in synthetic systems. Thy
and Dap display specific-complementary H-bonding and are able to form strong multi-point Hbonds, which have been widely used in supramolecular assembly and molecular recognition.[53–55]
Although specific-complementary hydrogen bonding has been applied in CPs, only a few
examples exist, which will briefly be discussed in the thymine section.

5
Figure 1-1 Representative H bond incorporated functional groups

6
2. Common H-Bonding Functional Groups in CPs
2.1. Hydroxyl Group
Figure 1-2 Representative hydroxyl functionalized CPs (P1 to P17)

7
2.1.1. Overview of the Hydroxyl Group and representative CPs
Hydroxyl groups are the simplest functional group that exhibits H-bonding effects and consists
of an oxygen atom which with two lone pairs covalently bonded to a hydrogen atom. The oxygen
atom with strong electronegativity can act as the H-bond donor (X) for the H bond definition XH···Y. The oxygen atom of another hydroxyl group can act as the H-bond acceptor (Y). Alcohols
and phenols are representative examples. If other electronegative atoms are present in the system,
it is also possible to function as the H bond acceptor for hydroxyl groups.
[48] Generally, introducing
hydroxyl groups into CPs significantly increases the hydrophilicity of the polymer which will
benefit applications that require interaction with aqueous media.[42–44] The most common location
of the hydroxyl group in CPs is in the side chain and representative hydroxyl incorporated CPs are
shown in Figures 1-2.
2.1.2. Synthetic Approaches for introducing Hydroxyl Groups into CPs
Post-polymerization functionalization is the most common strategy used to incorporate
hydroxyl groups into CPs. Jen et al. synthesized P2-P4 by Suzuki polymerization to form a
precursor fluorene polymer with terminal chlorines on the side chains and followed by treatment
with diethanolamine to perform the substitution to realize the target polymers.[43] Wang et al.
reported the fluorene homopolymer P5 with a similar strategy using a precursor polymer with
terminal bromide as the reactive site.[42] Kim et al. synthesized the fluorene polymer P6 with an
ethyl hydroxyl trialkyl ammonium salt via the quaternarization of bromoethanol with the precursor
polymer containing the tertiary amine.[56]

8
In an alternative post-polymerization strategy, Reynolds et al. synthesized the parent ester
polymer of P7-P9 by Direct Arylation Polymerization (DArP) under the Fagnou-derived condition
(Pd(OAc)2/K2CO3/PivOH/DMAc).[57] The parent ester polymer was cast on a glass substrate and
the hydroxyl group was generated via ester hydrolysis using a strongly basic KOH solution to form
P7-P9, as shown in the Figure 1-3.
[44] Rondeau-Gagné et al. reported the asymmetric hydroxyl
group incorporated isoindigo-based copolymer P11.
[58] The tert-butyldimethylsilyl (TBS) group
protected parent polymer of P11 was synthesized by Stille polymerization and was deprotected
under mild acidic condition yielding the hydroxyl group. Similarly, Katz et al. synthesized P12 by
Grignard metathesis (GRIM) polymerization with the TBS protected monomer tert-butyl(2,5-
dibromothiophen-3-6)methoxy)-dimethylsilane and deprotected to form the hydroxyl group after
the polymerization.[59] Qiu et al. protected the side chain hydroxyl group by tetrahydropyran (THP)
and synthesized parent diblock copolymers (BCPs) via GRIM polymerization followed by
deprotection to form the poly(3-hexylthiophene)-b-poly[3-(6-hydroxy)hexylthiophene] (P3HT-bP3HHT) BCPs (P13).[60] Kawai et al. synthesized the precursor polymer P15 via GRIM
polymerization and treated with BBr3 to carry out the transformation from the methoxy group to
the hydroxyl group (P14).[61]
Figure 1-3 Overview of the conversion of a film of a parent ester polymer to a hydroxyl polymer.
Reproduced with permission. [44] Copyright 2022, American Chemical Society.

9
Interestingly, there exist a few CPs synthesized by directly polymerizing monomers bearing
hydroxyl groups. Huang et al. reported the synthesis of P1 and similar fluorene polymers without
hydroxyl groups by Yamamoto polymerization and were able to achieve number-average
molecular weight (Mn) of 24.7 kg/mol.[62] Wang et al. conducted oxidative copolymerization with
hydroxyl terminated thiophene in the presence of FeCl3 to give P16.
[63] Luo et al. grafted glycidol
onto the EDOT and electrochemically polymerized on glassy carbon electrodes(GCE). [64]
Ultimately, post-polymerization functionalization has the advantage of excluding the effect of
the hydroxyl group during the polymerization, so different types of polymerizations such as GRIM,
Suzuki, Stille and DArP have been applied to hydroxyl incorporated CPs precursor polymer
synthesis. Additionally, the quality of the polymer such as molecular weight and defects should be
nearly identical to the precursor polymer. However, the reaction of converting to the hydroxyl
group after polymerization might be a tedious step, especially when complete conversion is
needed. Considering that most polymer NMR signals are broad and offer limited information, in
most of the cases, the presence of the hydroxyl group after post-polymerization reaction is
qualitatively (not quantitatively) confirmed.
2.1.3. Materials Properties of Hydroxyl Group functionalized CPs
After introducing the hydroxyl group, CPs typically exhibit poor solubility in non-polar
aromatic solvents such as toluene compared to CPs without the hydroxyl group. A more polar
solvent such as THF or DMF often provides good solubility for the hydroxyl group functionalized
CPs, due to the formation of hydrogen bonds between the polymer and solvent. Huang et al.
utilized this property and prepared an H-bonded CP gel (P1/toluene gels via supramolecular selfassembly behavior) by a heating-cooling process where a P1 toluene solution with a concentration

10
of 25 mg/ml was heated to 80°C for 10 min and then cooled to room temperature by standing for
30 hours.[62] Huang et al conducted a solvent effect study on P1 gel formation and found the solvent
immobile organogel was able to form in non-polar or low polarity solvents, such as
dichloromethane (DCM), chloroform (CHCl3), 1,2-dichloroethane (DCE), toluene,
bromobenzene, chlorobenzene, and 1,2-dichlorobenzene, but was not able to form in polar aprotic
solvents, such as DMF, 1,4-dioxane, and THF.[62] Additionally, Huang et al. showed that the
emission color of P1 supramolecular thin films can be dynamically tuned from blue to yellow via
selecting different types of solvent and Mn because these two factors significantly affect the
aggregation of P1. [62]
Hydroxyl functionalized CPs combine the advantages of conjugated polyelectrolytes and
traditional neutral surfactants,[43] which allow them to be processed from environmentally-friendly
alcohol solutions. The polar groups on their side chains can also facilitate electron injection from
high work-function metal cathodes because hydroxyl groups can interact with high work-function
metals to form a positive interfacial dipole between the cathode and the electron transporting layer
(ETL), which results in a reduced injection barrier at the interface.[43] Jen et al developed P2-P4
with different electron donating/withdrawing monomers and applied them as electron injecting
layers in Polymer light-emitting diodes (PLEDs).[43] Owing to the advantage of the polar hydroxyl
group and the interaction with the metal electrode, these polymers modified the work function
(WF) of the metal electrode, aligning the energy levels of the electrode and active layer in organic
photovoltaics (OPV) which ensures energy level alignment for effective charge extraction.
Additionally, the issue of the difference between the hydrophilic metal surface and the
hydrophobic OPV active layer can be addressed because the polymer interlayer can reduce
interfacial tension. Wang et al. combined the active layers including high-performing acceptor and

11
donor polymers (all polymer solar cells) with P5 as an interlayer and found the power conversion
efficiency (PCE) was increased from 2.7% (without P5) to 5.3% (with P5), which is comparable
with the conventional devices with LiF/Al.[42] More interestingly, Kim et al. found that P6, as the
interfacial layer, led to an even greater PCE improvement than the non-hydroxyl star interlayer
polymer PFN-BT because the OPV device with P6 had a lower series resistance. Specifically,
OPV devices with PTB7-Th as the donor and PC71BM as the acceptor and P6 as the interfacial
layer exhibited an average PCE of 10.5% while the same device with PFN-BT exhibited an average
PCE of 9.6%.[56]
In addition to enabling interfacial layers, hydroxyl groups can also can play a critical role in
CP doping. Ponder Jr. et al reported that the electrical conductivity of chemically doped CP films
was significantly increased after post-processing side chain removal of the parent ester polymers
of P7-P9 and demonstrated the increase in electrical conductivity is mainly due to an increase in
charge carrier density and reduction in carrier localization that occurs after side chain removal.
[44]
The polarity of the hydroxyl groups on P7-P9 also offers aqueous electrochemical compatibility.
Impressively, P9 exhibits an exceptional electrical conductivity (∼700 S/cm), which is better than
all previously reported glycol-based CPs. Additionally, Reynolds et al. showed that short hydroxyl
substituents (P7) can afford facile doping and high volumetric capacitance (C*) in saline-based
electrolytes and long polar side chains are not required.
[45] The hydroxyl groups on the side chain
can act as both hydrogen bond donors and acceptors. The hydrogen bonds formed in aqueous
media can benefit the polymer-electrolyte interactions and facilitate the uptake of hydrated ions,
which might induce special polymer-electrolyte interactions in aqueous media that are not
observed for the other glyme side chains.[45] Therefore, P7 has the highest C* (106 ± 7 F cm−3
)
across the entire voltage range compared to other glyme side chains polymers.

12
Luo et al. designed and synthesized a novel conducting polymer P10 by electrochemical
polymerization.[64] The excellent antifouling properties of the surface of P10 were demonstrated
by cell attachment studies with both human cervical carcinoma (HeLa) cells and Michigan Cancer
Foundation-7 (MCF-7) cells. Nearly full coverages of HeLa and MCF-7 cells were observed on
PEDOT surfaces whereas a very limited number of cells attached to the PEDOT-HPG (P10)
surfaces, which showed the PEDOT-HPG (P10) surface can effectively resist the nonspecific cell
attachment. Luo et al proposed that the good antifouling capability mainly arises from the
prominent hydrophilicity due to the presence of glycol groups on the polymer, which helps to form
a hydration layer between proteins and the electrode surface thus creating a barrier that inhibits the
adsorption of proteins and other contaminants.
Rondeau-Gagné et al reported the isoindigo-based polymer P11 with improved processability
in alcohol-based solvents. P11 demonstrated the highest average mobility (2.49 × 10−4
cm
2 V−1
s
−1
) when processed in 20% v/v o-anisole/n-BuOH in thin film organic field-effect transistors
thanks to the hydroxyl moieties.[58] Additionally, P11 thin film coupling with an fluorescein
isothiocyanate (FTIC) probe using dibutyltindilaurate demonstrated that the terminal hydroxyl
groups are capable of solid-state post-functionalization towards the development of
multifunctional organic electronics. [58]
Katz et al. studied the sensing properties of P12 as a bioreceptor in organic electrochemical
transistors (OECT) since hydroxyl groups target hydrogen bonds between the polymer films and
biomolecules, which can aid the immobilization of the biomolecules and create larger sensing
signals.[59] Although the sensitivity of P12 is relatively small, it exhibits better specificity since the
smaller Vth change for both the anti-human Immunoglobulin G (IgG) and myelin basic protein

13
(MBP) pair and bovine serum albumin (BSA) and IgG pair has been observed and the signal
change of pure P12 only comes from the specific binding between antibody and antigen.
In addition to homopolymers and alternating copolymers, hydroxyl groups have also been
applied to block copolymers. Qiu et al. synthesized P13 BCPs with different block ratios which
can be cross-linked since hydroxyl groups are crosslinked during thermal annealing by releasing
water.[60] The obtained BCPs formed microphase separated structures due to the different polarities
of the two blocks. After thermal annealing at 200 °C, the cross-linking of the hydroxyl block
disturbed the microphase separated structure and the roughness of films increased and the degree
of crystallization greatly improved, which is caused by the rearrangement of the non-crosslinked
parts. It was also demonstrated that cross-linking during thermal annealing at 200 °C not only
improved the degree of crystallization but also the ductility of films.
[60] Qiu et al also investigated
the crystallization, microphase separation and photophysical properties of P13 BCPs in mixed
solvents.[65] After adding 20% methanol into pyridine solution, nanofibers were observed. When
the volume ratio of methanol/pyridine was 40: 60, the nanofibers disappeared and ordered
spherical micelles started to be seen. Since methanol is a poorer solvent for the hydrocarbon side
chain block than the hydroxyl side chain, the block with hydroxyl groups was more swollen and
became larger in volume than hydrocarbon block while adding methanol. Eventually, the BCPs
transformed into spherical micelles with the hydrocarbon side chain block as the core surrounded
by the hydroxyl side chain block corona to minimize the interfacial energy. Further increasing the
ratio to 70: 30, the spherical micelles aggregated to a much larger size.
Peng et al prepared one-dimensional (1D) helical nanofibers through the self-assembly of P13
in an aged pyridine solution and proposed that such helical nanofibers were formed by the π-π

14
interaction between rigid polythiophene backbones plus the hydrogen-bonding interactions
between the polar hydroxyl groups of the side chains, as shown in Figure 1-4.
[66] More
interestingly, the Young’s modulus of such helical fibers is about 5.16 GPa, which is about two
times higher than the P3HT films characterized by the peak force quantitative nanomechanical
(PF-QNM) method and the field effect mobility of these helical fibers is as high as 0.034 cm2 V-1
s
-1
.
Figure 1-4 Schematic illustration of the formation of helical nanofibers in P13. The blue and red
colors represent the P3HT block and P3HHT block, respectively. Reproduced with permission. [66]
Copyright 2018, Royal Society of Chemistry.
Temperature-dependent infrared (FTIR) spectroscopy measurements were conducted to prove
hydrogen bonding in the solid state polymer film of P13.
[66] The –OH stretching vibration of the
initial film appeared at 3335 cm-1 and gradually blue-shifted to the vibration peak at 3495 cm-1
as
the temperature increased, which was mainly due to the splitting of the hydrogen bonds and
hydroxyl groups becoming free –OH groups.
[67]
Takagi et al. supported the intramolecular hydrogen bonding between pyridine and the
hydroxyl groups via DFT calculations on model compounds and found a significant red-shift of
the absorption maxima from 476 nm (P15) to 662 nm (P14), which is mainly caused by formation
of intramolecular hydrogen bonding.[61] Wang et al. designed and synthesized P16 and P17

15
polythiophene-tamoxifen conjugates for intracellular molecule-targeted binding and inactivation
of protein for growth inhibition of MCF-7 cancer cells by incorporating the small molecule drug
into the side chain of the conjugated polymer.[63] The hydroxyl side chain thiophene moiety not
only acted as the key reactive site to be converted into other important functional group (i.e.
Tamoxifen) but also can improve the hydrophilicity when it is on the polymer chain.

16
2.2. Amide and Carbamate groups

17

18
Figure 1-5 Representative amide and carbamate functionalized CPs (P18 to P45)

19
2.2.1. Overview of Amide and Carbamate Groups and Representative CPs
Secondary amides are the most commonly used amide groups to introduce H bonding into
polymers because the hydrogen atom in the -NH group is positive enough to form a H bonding
with a lone pair on the oxygen atom of another amide group (the N atom covalently bonded with
the H serves as the H bonding donor X and the O atom from the carbonyl group of a different
secondary amide will serve as the H bonding acceptor Y in the scheme X-H···Y). Generally,
introducing an amide or carbamate group into CPs can effectively tune features such as
crystallinity, molecular packing, and mechanical properties of the polymer. Most commonly amide
and carbamate groups are introduced into the side chain of CPs and representative amide and
carbamate incorporated CPs are shown in Figure 1-5.
2.2.2. Synthetic Approaches for introducing Amide and Carbamate Groups into CPs
Generally, the synthesis of amide and carbamate functionalized monomers followed by
polymerization is the most common strategy for incorporation into CPs and most often the amide
or carbamate group is found on an aryl-halide monomer. Specifically, this corresponds to the two
polymerization strategies of terpolymerization and perfectly alternative polymerization. In the
terpolymeization approach, typically a benchmark polymer serves as the parent polymer and an
amide or carbamate functionalized monomer is used as the third monomer. The content of group
incorporated is directly tuned by the ratio of the amide or carbamate containing monomer that is
added into the polymerization and representative polymers include P28, P33, P37-P38, and P39-
P41.
[50,51,68–70] Most of these polymers are achieved by traditional cross-coupling polymerization
such as Suzuki or Stille polymerization under conditions very similar to the parent polymer since

20
the ratio of the incorporated amide or carbamate monomer is generally relatively low (from 5%mol
to 30%mol). For instance, Huang et al. synthesized P22 by Yamamoto polymerization.[71] A very
clear trend from the synthesis of these polymers is that nearly all of the amide or carbamate
polymers with higher loading (e.g. ≥ 20%mol) have a lower Mn than the analogous polymers with
lower loading (e.g. ~5%mol). As the ratio of the amide or carbamate monomer is increased, the
solubility very likely decreases. Typically, an optimal and balanced ratio (between 5%mol and 30
%mol) is used considering the application of the polymers.
A perfectly alternating polymerization strategy includes the amide or carbamate functionalized
monomer as the only co-monomer such as P29-P32, P34-P36 and P42-P43.
[72–75] It is worth noting
that the amide and carbamate functionalized perfectly alternative polymers P29-P32 and P34-P36
all have a reasonable molecular weight (with Mn higher than 50kg mol-1
). P42 and P43 have lower
molecular weight (10-15 kg mol-1
) and this might be due to the end capping effect which introduces
monobromo or monostannyl compound to stop the chain growing. Significantly, Bao et al. and
Rondeau-Gagné et al. were able to conduct the stannylation of thiophene via lithium
diisopropylamide (LDA) in the presence of the N-H bond in the secondary amide, as shown in
Figure 1-6.
[50,75]
Post polymerization functionalization is another method used to introduce amide and
carbamate groups into CPs. Huang et al. synthesized tert-butoxycarbonyl (t-Boc) substituted
indigo, isoindigo and diketopyrrolopyrrole (DPP) acceptor units and conducted the thermal
treatment of P24-P26 films at 200 °C for 10 min to deprotect the t-Boc side groups and form the
amide groups.
[76] Thermogravimetric (TGA) analysis indicated a two-step thermal decomposition
of these copolymers and the first weight loss occurred at ∼190 °C which arose from the elimination

21
of the t-Boc groups. FT-IR spectroscopy indicated the original stretching vibration band of C=O
from t-Boc at ∼1700 cm−1 disappeared and the new characteristic band of C=O of the lactam moiety
shifted to slightly smaller wavenumbers, which supports the nearly complete deprotection of the
t-Boc groups. Additionally, a new band appeared at ∼3450 cm−1 after thermal treatment, which
corresponds to the N−H···O=C hydrogen bonding resulting from the lactam structures. Zhu et al.
utilized a similar post-polymerization method to prepare the P23 and P27.
[77,78]
Oxidative polymerization and DArP have also been utilized to polymerize amide
functionalized monomers. Mei et al. conducted FeCl3 mediated oxidative polymerization with a
ProDOT monomer to obtain polymers P18 and P19 although the molecular weight of the resulting
polymers is slightly lower than 10kg/mol.[79] Thompson et al. utilized DArP to synthesize P21
with an Mn of up to 15.4 kg/mol and yields of up to 90% by polymerizing the corresponding
monomer 5-bromo-N-hexyl-N-methylthiophene-3-carboxamide.
[80] Interestingly, the optimal
DArP condition for P21 cannot be directly applied to secondary amide polymer P20 and 1
H NMR
studies show impurities in the aliphatic region which can be the result of N-arylation of the
secondary amide. Thompson et al then employed a modified condition using Pd(OAc)2 with P(tBu)2Me-HBF4 as a ligand and K2CO3 a base to synthesize P20 successfully with a satisfactory Mn
(11.6 kDa). Importantly, the 1
H NMR exhibited no apparent impurity in the aliphatic region, and
the N−H resonance (δ 5.82 ppm) remains after polymerization. However, H-bonding between
secondary amides likely resulted in a fraction of insoluble polymer that caused a lower yield for
the polymerization compared with P21.
As an alternative approach, the reaction between a hydroxyl end group and an isocyanate group
can form secondary amides in the polymer backbone. For instance, Lipomi et al. synthesized P44

22
and P45 via the polyaddition between a diketopyrrolopyrrole (DPP) block, and the poly(εcaprolactone) (PCL) block using DPP diol blocks and hexamethylene diisocyanate.
[81]
2.2.3. Materials Properties of Amide and Carbamate Functionalized CPs
The materials properties of amide and carbamate functionalized CPs can be classified into two
categories. The first category is related to engendering aqueous solubility/compatibility since most
CPs have a hydrophobic nature but as amide and carbamate groups are polar functional groups,
hydrophilic character is introduced. For instance, Mei et al. found that the presence of amide
groups in polymer side chains can facilitate redox switching in aqueous electrolytes while
preserving a high electrochromic contrast. [79] Additionally, the presence of the amide group was
found to reduce the oxidation onset from 0.3 V to 0.15 V and the absorbance spectra of P18
exhibited a red-shifted λmax value and absorbance onset compared to the polymer without the amide
group, most likely stemming from H-bonding induced ordering.[79] Similar impacts on solubility
have also been observed by Thompson et al with demonstration that P20 and P21 can be processed
using green polar solvents such as ethanol and 1-butanol.[80] Generally, an extremely high loading
or nearly a full loading of amide groups in the side chains is required to realize aqueous solubility.
Although both hydroxyl and amide groups were reported for use as functional groups intended to
increase aqueous solubility/compatibility, hydroxyl groups are significantly more commonly used
than amides. The hydrogen bond generated from hydroxyl groups is typically stronger than the
hydrogen bond formed in the amide and carbamate group since the oxygen atom is more
electronegative than the nitrogen atom.[82,83] Therefore, introducing the hydroxyl group will likely
have a more significant impact on the aggregation, crystallinity and solid state behavior of the
polymer than the amide and carbamate group.

23
Figure 1-6 Stannylation of the thiophene with secondary amide [50,75]
The second category is related to using H-bonding in secondary amides to tune aspects such
as crystallinity and mechanical properties. Huang et al. found that physical cross-links via
interchain H-bonds were able to facilitate chain entanglement and aggregation in solution via
dynamic light scattering (DLS) and rheological measurements. Additionally, increasingly
pronounced diffraction peaks were observed in wide-angle X-ray scattering (WAXS) as the ratio
of the amide functionalized monomer increased indicating that H-bonds are favorable for
promoting long-range-order in P22.
[71] Huang et al. also demonstrated that polymers with a higher
ratio of secondary amide have better mechanical properties and the enhanced toughness mainly
results from the interchain network assisted by H-bonding interactions and the resulting energydissipation centers derived from the rigid crystalline nanodomain.[84]
Huang et al. also reported significantly improved field effect hole mobility of P24-P26
copolymers after forming the amide group through deprotection of t-Boc side groups.[76] The
increase in mobility upon annealing is correlated with an increase in the intensity of the sharp
reflections (GIWAXS) for the thermally annealed films, which indicates substantially improved
intermolecular packing, as shown in Figure 1-7. H-bonding from the amide group partially

24
contributes to this improved molecular ordering and improved packing generally induces higher
charge carrier mobility. Huang et al also investigated the photovoltaic performance of bulk
heterojunction solar cells by blending the polymers P24-P26 with [6,6]- phenyl C71 butyric acid
methyl ester (PCBM) but did not find a significant increase in the power conversion efficiency
(PCE) after annealing, which might be due to significant phase separation and coarsening of the
film morphology.[76] Similarly, Zhu et al observed a strong bathochromic shift in the UV–vis
spectra and narrower bandgap in the H-bonded polymer P23 and the electron mobility of P23 was
0.01 cm2 V−1
s
−1 which was about 40 times higher than the precursor with a mobility of 2.4 × 10−4
cm
2 V−1
s
−1
.
[77] Zhu et al also applied this strategy to an isoindigo polymer.[78]
The DPP unit is one of the key building blocks for high performance OFETs since the first
thiophene-flanked DPP-based polymer semiconductor was reported and showed hole mobility (µh)
of 0.1 cm2 V−1
s
−1 and electron mobility (µe) up to 0.09 cm2 V−1
s
−1
, respectively.[85] Introducing
an H-bonding unit such as secondary amide into the side chain of DPP unit is a prevailing strategy.
Rondeau-Gagné et al. found that incorporation of a small amount (5 mol%) of DPP monomer with
amide side chains (P33) enabled a maximum hole mobility of 2.46 cm2 V−1
s
−1 in OFET devices.[69]
Interestingly, Rondeau-Gagné et al. also found that side-chain engineering with amide moieties
reduced the crystallinity of the DPP polymers in the thin film state, which is in contrast to other
polymers, but significantly influenced the mechanical properties of the DPP-polymers by
improving their stretchability and lowering the elastic modulus. P33 with 10% H-bonding side
chains can be stretched up to 75% elongation without any nanoscale cracks on a PDMS substrate
and damaged films could be recovered after chlorobenzene solvent vapor annealing and thermal
annealing.[86] Oh et al. reported the well-defined alternating donor-acceptor polymers P34-P36 by
synthesizing the branched carbamate-based DPP monomer which not only provided structural

25
regularity with moderate H-bonding but also guaranteed sufficient solubility.[74] Thin films of P36
demonstrated the highest mechanical stability, maintaining their electrical and molecular packing
characteristics under strains of up to 100% and showing a healing property.
Chen et al. incorporated poly (acrylate amide) (PAAm) side chains along with octyldecane
(OD) into isoindigo–bithiophene conjugated copolymers to construct the intrinsically stretchable
polymer P28.
[68] The soft and bulky PAAm side chains improved the morphology of the thin film
surface under strain and the stretchability and mobility were improved by combining hydrogen
bonding with the soft acrylate unit. The experimental results demonstrated that with 5-10%
PAAm5 (5 repeat unit of poly (acrylate amide)) improved crystallinity and stretchability were
observed but higher numbers of repeat units of PAAm led to poor crystallinity and lower charge
carrier mobility due to the bulkiness of the side chains, which disrupted the molecular stacking.
Figure 1-7 GIWAXS of P24 before and after annealing at 200 °C for 10 min. Reproduced with
permission. [76] Copyright 2015, American Chemical Society.
In addition to intermolecular H-bonding, intramolecular H bonding within the polymer
backbone has also been studied using amide groups. Rondeau-Gagné et al. synthesized P42 and
P43 by incorporating pyrazine or benzene moieties flanked by thiophenes with pendant amide side
chains and the orientation and type of H-bonds were carefully controlled by using either pyrazine

26
(P42) or benzene (P43) in the polymer backbone.[75] Interestingly, P42 has a maximum mobility
of 0.162 cm2 V−1
s
−1
, which is three orders of magnitude greater than P43 and the P42-based OFET
devices also had a good Ion/Ioff current ratio (105
) and low threshold voltage, which is likely due to
the more planar polymer chains and better solid-state morphology induced by the intramolecular
H-bonds. Surprisingly, despite being more crystalline and more rigid due to the more planar
polymer chains, P42 was found to be a softer material (tensile modulus of 361 MPa) than P43
(tensile modulus of 501MPa), which is explained by the presence of intermolecular H-bonds in
P43 which also act as cross-linking sites resulting in stiffer materials.
Similarly, Zhang et al. synthesized the pyridine-thieno[3,2-b]thiophene-pyridine building
block and the weak intramolecular noncovalent interactions enabled a rigid co-planar structure
with extended π-conjugation, and a tight lamellar arrangement in the solid state.[72] P29 had a ptype field-effect mobility of 0.17 cm2 V−1
s
−1 and P30 based polymer solar cells exhibited a notable
power conversion efficiency of 10.8%. Zhang et al. also synthesized the thiophene-pyrazinethiophene building blocks with carbamate substituents where intramolecular hydrogen bonds were
able to form within the polymer backbone.[73] Interestingly, the PCE of the devices based on P32
with intramolecular hydrogen bonds was 5-8%, while the PCE of the devices based on P31 with
intermolecular hydrogen bonds was 0.1%, which is attributed to the higher bimolecular
recombination, geminate recombination and reduced face-on orientation of the blend.
Surprisingly, polymers with similar backbones with intramolecular hydrogen bonding exhibit
significantly better performance in both OFET and OPV devices. In OFETs, intramolecular
hydrogen bonding functionality in P42 shows three orders of magnitude greater hole mobility than
the intermolecular hydrogen bonding in P43. In OPVs, intramolecular hydrogen bonding in P32

27
enables a PCE of 5-8% while the intermolecular hydrogen bonding in P31 leads to a PCE of only
0.1%. Intramolecular hydrogen bonding likely generates more planar polymer chains and
improved solid-state morphology, which can lead to improved face-on orientation.
Amide-based derivatives such as 2,6-pyridine dicarboxamide (PDCA) have also been
introduced into CPs to construct intrinsically stretchable and healable semiconducting layers.
[50]
Bao et al. introduced the PDCA building block to synthesize P37 (10%mol PDCA) and P38
(10%mol PDCA) with methylation of amide group as a the reference polymer.
[50] The reason why
PDCA was chosen to introduce H-bonding within the flexible polymer backbone is because it
contains two amide groups with moderate hydrogen-bonding strength, allowing the formation of
a polymer network without significantly increasing the material's tensile modulus. Interestingly,
although intermolecular hydrogen bonding was supposed to effectively cross-link the polymers,
which is anticipated to increase the elastic modulus of the polymer film, it appears that reducing
the rigidity of the conjugated polymer backbone had a greater effect on the elastic modulus of the
polymer semiconductor film and this lead to both P37 and P38 having a lower modulus than the
perfectly alternating parent DPP polymer.
Bao et al. found that when applying strains up to 100%, the average field-effect mobility of
P37 decreased from 1.32 cm2 V−1
s
−1 to 0.11 cm2 V−1
s
−1 along the direction of applied strain and
after releasing the applied strain, the mobility was observed to recover to 1.00 cm2 V−1
s
−1
.
[50]
When strain was applied perpendicularly, the mobility of P37 is maintained at >1 cm2 V−1
s
−1 even
up to 100% strain. As a control, P38 exhibited decreased stretchability, with a crack onset strain
of approximately 25%. The healing ability of P37 was demonstrated via combined thermal and
solvent annealing, which promoted the most efficient healing of the polymer films and a complete

28
disappearance of the nanocracks within the damaged films, as well as an almost complete recovery
of the average field-effect mobility to 1.13 cm2 V−1
s
−1
, as shown in Figure 1-8.
[50] Fully
stretchable OTFTs based on P37 were fabricated and the majority of the devices had field-effect
mobilities in the 10-1
cm
2 V−1
s
−1 range with >105 on/off current ratio.
Figure 1-8 Illustration of the treatments used for healing conjugated polymer films after stretching
(top). AFM phase images for damaged and healed films of P37 (middle). Transfer curves and fieldeffect mobility of damaged and healed films of P37 (bottom). Reproduced with permission.[50]
Copyright 2016, Springer Nature.
In order to investigate the electrical performance of the transistors under various mechanical
strain conditions to verify their stretchability, the fabricated fully stretchable devices were mounted

29
on human limbs to undergo a series of common movements such as arm folding, hand twisting,
and elbow stretching to test the device tolerance. Under all of these conditions, P37 based fully
stretchable OTFTs maintained an average mobility of >0.1 cm2 V−1
s
−1
.
Bao et al also inserted the PDCA moiety into the side chain of a DPP-based CP to synthesize
P40. By comparing with the reference P41, it was determined that PDCA in the side chains
produced almost quantitative formation of intermolecular H-bonding even at low PDCA content
(10 mol%).[70] Attenuated total-reflectance Fourier transformation infrared spectroscopy (ATRFTIR) was conducted to analyze differences in intermolecular H-bonding between the PDCA unit
in the side chain and the backbone of the polymer since broad IR peaks in the amide region are
typically attributed to bound protons, whereas sharp peaks at higher wavenumbers are typically
attributed to free NH groups.[70].
When PDCA units are located in the side chains (P40), almost all of the N-H signals are in the
H-bonding state (3327 cm-1
) even at only 10 mol%.[70] In comparison, polymers with PDCA units
within the backbone only achieve a high degree of bonding at 60 mol% and films made of
backbone incorporated PDCA (P37) showed a clearer evolution in the intensity and position of the
C=O stretching with a higher amount of PDCA in the structure.[70] It is also worth noting that
pyridine moieties in the PDCA unit may also contribute to improved mechanical properties by
participating in intra- and intermolecular hydrogen bonding.
Kim et al. synthesized P39 by introducing the amide incorporated N1
, N3
-bis((5-bromothiophen-2-yl)methyl)isophthalamide (PhAm) unit into the benchmark polymer donor PM6 for
organic photovoltaics.
[51] The incorporation of PhAm into the PM6 backbone gradually increased
the relative intensity of the (0-0) peak (I0-0) to the (0-1) peak (I0-1) in the solution UV-vis profiles

30
and the GIWAXS results of the pristine film indicated P39 had tighter packing and larger crystals
than the reference PM6, which is attributed to improved intermolecular interaction between
polymer chains due to H-bonding from the amide groups in the PhAm unit. Interestingly, the
maximum PCEs (PCEmaxs) of the binary OPVs increased from 15.47% (PM6) to 17.45% (P39
with 10%PhAm) in rigid devices when blending with the non-fullerene acceptor (NFA) Y7, which
is caused by the improved charge transport and crystallinity resulting from the intermolecular
amide H-bonding.[51]
Intrinsically Stretchable Organic Solar Cells (IS-OSCs) with all-stretchable layers were
constructed to compare the photovoltaic and mechanical properties of the blends based on P39 .
[51]
The initial PCE of the P39 based IS-OSC (PCE of 12.73%) was higher than the PM6 based ISOSC (PCE of 11.05%) and the strain at PCE80% of the P39 based IS-OSC was 32%, whereas it was
only 15% for the PM6 based device.
The mechanical properties of the blend films were investigated using pseudo-free-standing
tensile tests and the PM6:Y7 blend exhibited highly brittle mechanical properties with a COS of
only 1.8% whereas the P39: Y7 had a COS of 13.8%. Even at 2% strain, the PM6:Y7 blend showed
a sharp crack while the P39:Y7 blend showed plastic deformation with no crack even at 10%
strain.[51] The P39 based blend achieved a high PCE while also improving stretchability and this
successfully addressed the common trade-off relationship between these two parameters.

31
2.3. Urea functional groups
Figure 1-9 Representative benzene-based urea functionalized CPs (P46 to P50)

32
2.3.1. Overview of the Urea Group and Representative CPs
The urea group is well known for strong H-bonding and directionality because the two N-H
protons can interact with the oxygen of another carbonyl group. Both lone pairs on the oxygen
atom in the carbonyl group can participate in the H bonding to form urea-urea dimers (Figure 1-
9). The urea-urea dimer possesses two relatively stable rotamers with dihedral angles of 0°
(coplanar) or 90° (perpendicular).[87] Urea-urea dimerization can change interchain interactions,
allowing tunability of semiconducting polymer properties and it can also cause polymers to form
more organized domains as well as improved polymer domain interconnection.[88] The urea-urea
dimer is also a sufficient recognition component for a guest molecule to perform the size-selective
molecular recognition.[89–91] Additionally, the urea functional group can be conveniently installed
with a small number of synthetic steps. Similar to amide and carbamate groups, urea groups are
most often introduced into the side chain of the CPs and representative urea functionalized CPs
are shown in Figures 1-9.
2.3.2. Synthetic Approaches for introducing Urea Groups into CPs
Similar to the amide group, the design and synthesis of urea functionalized monomers
preceding direct polymerization is the most common strategy. The most typical method to
synthesize the urea group is to perform an addition reaction between an amine (R-NH2) and
isocynate (R-NCO) while triphosgene can also be used as the linking moiety to react with an amine
(R-NH2) to form the urea group. P46 was synthesized by the conventional rhodium-catalyzed
alkyne polymerization using the catalyst [Rh(BPh4)(nbd)] with the monomer bearing the urea
group.[92] P47 was synthesized via a copper(I)-mediated oxidative coupling polymerization of the
corresponding urea functionalized monomer with a molecular weight of 14kg/mol.[93]

33
P48, P49 and P50 were synthesized by Sonogashira polymerization.[95,96] P51-P57 were
polymerized with the Stille polymerization and nearly all the urea groups were incorporated in the
aryl-halogen monomer.
[88,94,97–99] Notably, the Mn decreased for the Stille-derived polymers as the
ratio of urea monomer increased. For instance, Rondeau-Gagné et al. showed that the Mn of P55
decreased from 13kg/mol to 8-9 kg/mol as the ratio of the urea monomer increased up to 20%mol.
More clearly, the weight average molecular weight (Mw) decreased from 60-75kg/mol to 18-
35kg/mol, which indicates that the presence of urea is less favorable for forming long chain
polymers. Additionally, Fang et al. showed that conducting Sonogashira polymerization directly
in the presence of the urea group led to a relatively low Mn (about 5kg/mol) for P49, which is
caused by precipitation during solution-phase synthesis due to the rigid nature of polymer P49.
Fang et al. adopted the H-bond masking technique and synthesized the precursor polymer P50
with high molecular weight (Mn = 32kg/mol) then converted into a higher molecular weight batch
of P49 in the solid state with thermal cleavage of the Boc protecting group.[95]
2.3.3. Materials Properties of Urea functionalized CPs
The application of urea functionalized CPs can be classified across three categories: (i)
molecular binding of anions (ii) solid-state morphology tuning of CPs and (iii) mechanical
property tuning. Anions not only play an important role in biological, industrial, and environmental
processes, but are also essential in many areas of chemical research such as functional materials,
transmembrane transport, and catalysis.[89] Therefore, selective binding and sensing of anions by
synthetic materials has become an important field of supramolecular chemistry. The application
of molecular recognition of anions is mainly through the coordination/binding of urea groups with
anionic guests and it has been demonstrated that urea can chelate an anion via two directed Hbonds.[90] Use of a CP backbone as a scaffold for the urea anion receptor not only acts as a signaling

34
component that allows for a colorimetric response but can also increase the anion-binding affinity
through the cooperative recognition of multiple spatially arranged urea groups.[91] For example, a
THF solution of P46 was pale yellow with an absorption around 400 nm but when tetra-nbutylammonium acetate (CH3CO2
-
) was added, the color of the polymer solution immediately
became red, demonstrating the polymer's colorimetric response capabilities. The observed color
shift was mainly attributed to an increase in the length of the main chain conjugation and the
conformational change in the polymer main chain caused by CH3CO2
-
binding to the urea
receptors. Other anions, such as F-
, Cl- Br-
, I-
, HSO4
-
, NO3
- and N3
-
, produced different changes in
the absorption.
Figure 1-9 Illustration of fluorescence turn-on sensing of anions based on the disassembly of P47.
Reproduced with permission.[93] Copyright 2012, American Chemical Society.

35
P47 with an alkyne based conjugated backbone exhibited similar anion detection behavior.
Here, anion-recognition prompted disassembly of P47 aggregates was revealed to be the
mechanism of the observed fluorescence turn-on, as shown in Figure 1-10.
[93] To demonstrate this
turn-on fluorescence sensor, Kakuchi et al. measured the fluorescence of P47 in the presence of
various anions and most of the polymer solutions showed intense fluorescence emission when
anions were added.
[93]
Urea groups have also been inserted into CPs in both the backbone and in the side chain to
tune morphology and crystallinity. Vanden Bout et al. synthesized P48 and investigated the folding
of the CPs at the single molecule level.[96] Based on single molecule excitation polarization
spectroscopy, it was found that urea-containing side-chains have higher folding order and it was
hypothesized that the red-shift of 0.06 eV in the 0-0 absorption peak for the urea-containing
polymer is due to the backbone planarization caused by a highly organized urea-containing
polymer structure. Fang et al. tuned the solubility between P49 and P50 by chemically blocking
and rebuilding the preorganized intramolecular hydrogen bonds, which resulted in a stiff laddertype conformation for P49 from the precursor P50 in thin films via in situ thermal treatment.[95]
Zhang et al. reported the synthesis of P52 and found that adding urea groups in the alkyl side
chains improved OFET hole mobility after thermal annealing.[88] It worth noting that the mobility
increased by incorporating more urea group and P52 with about 10mol% urea, gave the highest
mobility of 13.1 cm2 V−1
s
−1
. Zhang et al. ascribed this improvement to the increased lamellar
packing order of the alkyl chains where each has the urea group and modest inter-chain stacking.
Introducing hydrogen bonding into the side chain of DPP polymers to construct high performance
OFETs is a widely explored approach. The amide based DPP polymer (P33) achieved a maximum
hole mobility of 2.46 cm2 V−1
s
−1 while the urea based DPP polymer (P52) enabled an impressive

36
hole mobility of 13.1 cm2 V−1
s
−1
. This is perhaps due to the stronger and more directional
hydrogen bonding in the urea group when compared to the amide group, leading to a higher
crystallinity and more ordered structure in the thin film state, thus strongly enhancing charge
transport. However, the higher crystallinity induced by the introduction of urea group might be
detrimental to the mechanical properties while the amide based polymers might avoid this potential
trade off.
More interestingly, introducing urea groups into the alkyl side chains also has a positive impact
on the photovoltaic performance of the blend with P52 donor and PC71BM acceptor. Zhang et al.
found that the urea groups may help P52 assemble into nanofibers and the PC71BM acceptor
aggregate in a more ordered fashion, as proven by the micro-phase separation observed in AFM
images. Therefore, the P52: PC71BM blend exhibited PCE between 6-7% while most of the
reference and control polymers gave PCE close to or lower than 5%.[88] Similarly, Rondeau-Gagné
et al. synthesized P55 by inserting the urea group into the side chain of the isoindigo-based
polymers (P56 with linear hydrocarbon side chain as a control) and observed the trend that the
OFETs made from polymer with 20% urea moieties had higher average hole mobility (0.032 cm2
V−1
s
−1
) than P56 with 20% dodecyl side chains (0.0073 cm2 V−1
s
−1
).[98] Additionally, Deshmukh
et al. also introduced the urea group as a conjugation break spacer (CBS) into the backbone of the
isoindigo-based polymers (P57).[99]
Since the urea group enables H-bonding, the impact of the urea group on mechanical properties
of CPs is also very interesting. Bao et al. synthesized P53 and P54 to investigate the impact of
urea on the mechanical properties of DPP-based CPs and found that the CPs with urea groups
generated greater polymer chain aggregation and crystallinity in thin films, which lead to a higher

37
modulus and crack on-set strain.[94] Furthermore, the rDoC (relative degree of crystallinity) of the
stretched thin film with the greatest crack on-set strain experienced nearly no decrease in the ratio,
indicating the predominant energy dissipation process is the breaking of dynamic H-bonds. On the
other hand, other less stretchy polymer films based on the amide analogues, released the strain
energy by breaking the crystalline domain, as demonstrated by a significant decrease in rDoC.[94]
P54 exhibited slightly higher modulus than P53 which might be due to more oxygen atoms that
potentially can participate in H-bond formation.
Importantly, Bao et al also summarized four strain energy dissipation mechanisms in Hbonding functionalized CPs: (1) breakage of H-bonding sites, (2) reorientation and alignment of
crystalline domains, (3) chain extension and alignment in amorphous regions, (4) breaking of
crystalline domains.[94] In addition, both P53 and P54 have higher mobility than the control
polymer without H-bonding because of their substantially higher crystallinity and distributed Hbonding domain caused by the urea group. P53 and P54 also demonstrated the ability to maintain
charge transport properties in fully stretched transistors. Interestingly, Gu et al. investigated the
urea side chain incorporated DPP polymer P51 and discovered a significant difference in ductility
where urea functionalization leads in a 50% loss in strain at failure.[97] P51 exhibited an impressive
crack onset (COS) of ~50% with the film-on-elastomer (FOE) measurement while a low COS with
the film-on-water (FOW) measurement.[97] Depending on the measurement conditions, P51
displayed both low and high ductility, which suggests that two competing mechanisms - potentially
high crystallinity, which reduces ductility, and energy dissipation via hydrogen bonding, which
increases ductility - determine its mechanical performance.[97] P51 was found to experience a fastinitial swelling in the aqueous environment and the strong hydrogen bond interaction of urea
moieties with water is assumed to be the reason of the initial fast swelling.

38
Due to the symmetrical and triatomic intermolecular geometry between urea moieties [94], they
can produce strong H-bonding interaction energy, which can cause directed crystallization and
also possibly cause a lack of stress tolerance if the plasticization of the urea group with water
molecules happens. It worth highlighting the stark mechanical difference between two urea
incorporated DPP polymers P51 (side chain) and P53 (backbone).[94,97] Furthermore, it should be
considered that in order to incorporate the urea group into the backbone of DPP CPs, P53
consequently has certain content of conjugation break spacer which can be an important variable
that needs to be considered since breaking the conjugation generally will lead to lower elastic
modulus and improved ductility.[100–108] Overall, this stark mechanical difference also offers a good
lesson that the future of intrinsically stretchable CP design needs to be carefully evaluated since
side chain engineering and backbone engineering using the same urea group can bring completely
opposite results.

39
2.4. Thymine functional groups

40
Figure 1-10 Representative thymine functionalized CPs (P58 to P70)
2.4.1. Overview of the Thymine Group and representative CPs
Thymine is a well-known nucleobase in the nucleic acid DNA. Inspired by biological
macromolecules, the introduction of thymine into synthetic polymers is an interesting molecular
design strategy (Figure 1-11). Importantly, the N-3 proton of thymine is more acidic than the NH proton of an amide group due to the two adjacent carbonyl groups rendering this an imide type
functionality. Additionally, the basicity of C=O bond which participates in the dimerization at the
C-4 of thymine, is stronger than the typical carbonyl group since the oxygen bonded to C-4 is
conjugated with N-1 via C-5, C-6 double bond according to its resonance structure, as shown in
Figure 1-12. These effect induce thymine to have a significantly stronger tendency to selfdimerize (dimerization constant about 15 M-1
) than other common H-bonding functional groups
that have been widely adopted into CPs (i.e. amide group with dimerization constant about 5 M1
).[109] Nearly all thymine functionalized CPs have been synthesized by direct polymerization with
the thymine functionalized monomer and in all cases, the thymine unit was introduced into the
side chain in order to maintain the conjugation of the backbone and maximize the H-bonding
interaction.
Figure 1-11 (a) illustration of thymine resonance structures and (b) the thymine-thymine dimer.
2.4.2. Synthetic Approaches for Introducing Thymine Groups into CPs

41
As direct polymerization of thymine functionalized monomers is the dominant approach,
synthetic strategies can be subdivided into two steps: (i) monomer design and synthesis and (ii)
polymerization. The thymine functionalized monomers for P58, P60 and P63-69 were synthesized
using traditional SN2 reactions which involve the reaction between an alkyl-halide and thymine (5-
Methylpyrimidine-2,4(1H,3H)-dione).[110–114] Interestingly, Yamaguchi et al. synthesized the
thymine analogous monomer (alloxazine-6,9-diyl unit) of P59 by a condensation between the
alloxane and 1,4-dibromo-2,3-diaminobenzene.[115] Son et al. synthesized 1-(6-hydroxyhexyl)-5-
methylpyrimidine-2,4(1H,3H)-dione as the thymine source and performed the Steglich
Esterification with 2,5-dibromothiophene-3-carboxylic acid to synthesize the thymine
functionalized monomer for P61.
[116] Thompson et al. designed the thymine side chain terminated
6,7-difluoro-quinoxaline (Q-Thy) monomer based on the benchmark acceptor unit 5,8-dibromo6,7-difluoroquinoxalin-2-ol [117] starting with the most commonly used thymine source in the
supramolecular field (thymine-1-acetic acid) and synthesized P70.
[118] Two representative
synthetic routes for the synthesis of thymine functionalized monomers are shown in Figure 1-13.
It has been demonstrated that using thymine-1-acetic acid as the thymine source rather than direct
alkylation can avoid side reactions and purification issues caused by tautomers such as N-3
alkylation and O-alkylation products, potentially significantly widening the scope of
substrates.[119,120]

42
Figure 1-12 Two representative thymine functionalized monomer syntheses.[111,118]
P61, P64 and P70 were synthesized by the Stille polymerization and P65-P69 were
synthesized by Sonogashira polymerization. In general, the Mn of terpolymers starts decreasing as
the ratio of thymine functional monomer is increased. For instance, the Mn of P64 decreased from
95kg/mol to 30kg/mol with 5 mol% loading of thymine monomer.[113] The Mn of P70 decreased to
the half of the original Mn without thymine when the incorporated ratio of thymine monomer was
20%.[118] The Mn of P61 significantly decreased from 52.6 kg/mol to 11.9kg/mol as the ratio of
thymine monomer increased from 0% to 20%.[116] It is suggested that the decreased Mn of the
terpolymers could be mainly attributed to palladium-thymine interference during
polymerization.[121] It is also worth highlighting that with P58, P59 and P60 every repeat unit has
a thymine group and reasonable molecular weights were still achieved.
[110,111,115] Interestingly, in
these case, all were polymerized in polar solvents. For instance, polymerization of P58 was in
THF, P59 was on THF/NMP and P60 was in DMF.
2.4.3. Materials Properties of Thymine Functionalized CPs
Similar to the urea group, the application of thymine functionalized CPs can be classified into
three categories: (i) molecular recognition (ii) morphology tuning and (iii) mechanical impact.

43
Since one of the signature advantages of thymine is molecular recognition with a
complementary H-bonding unit such as adenine, utilizing thymine functionalized CPs to identify
other moieties with corresponding complementary H-bonding is very common. For instance,
Wang et al. synthesized a novel CP nanogel carrier based on P58 and successfully developed triple
hydrogen bonded drug conjugation, which allowed long-term drug release with improved drugloading efficiency, stability, and biocompatibility.[110] Qin et al. also investigated the impact of
molecular recognition between thymine based P3HT analogous polymers and diaminopyridine
functionalized fullerene.[122–124]
Yamaguchi et al. found that P59 has photoluminescence in solution at 581 nm and that
photoluminescence decreased with the addition of nucleosides including adenosine (A) and
guanosine (G) and with metal ions such as Cu(I), Cu(II), and Zn(II).[115] It was proposed that the
drop of PL intensity caused by the addition of nucleosides and metal salts is very likely due to
electron transfer from the originally excited polymer to the complexes formed by hydrogen
bonding between the polymer alloxazine unit and the nucleoside. Zhang et al. found Pd(II) and
Hg(II) ions can be independently integrated into P64 polymer thin films via air-water interface
coordination and that FETs based on these thin films responded sensitively and selectively to CO
and H2S, respectively.[113] It worth highlighting the CO with a low concentration of 10 ppb can be
detected by P64-Pd(II)-based FETs which only incorporate 5mol% thymine monomer, whereas
H2S with a concentration of 1 ppb can be detected by FETs using P64-Hg(II) thin films.[113]
Due to the strong tendency of thymine to dimerize, introducing thymine into the side chain of
CPs generally has a significant impact on the solid-state morphology. Zhang et al compared P62
and P63 and found that H-bonding from thymine facilitated assembly into highly ordered

44
structures, which improved intermolecular charge transfer and enabled a nearly five-times higher
hole mobility as compared to the polymer without the thymine group.[112] More interestingly,
Zhang et al observed a broad N-H peak between 3100 and 3680 cm-1 in the IR and found the
magnitude of the broad peak dramatically increased after five minutes of thermal annealing at 140
°C, which indicates the as-cast P63 film has free thymine groups which become H-bonded during
thermal annealing. Walter et al. found that the inclusion of thymine significantly increased hole
mobility as P60 has a hole mobility of µh of 7.2 × 10−6 cm
2 V−1
s
−1 which is significantly higher
than the alkyl side chain control polymer with the µh of 3.9 × 10−8 cm
2 V−1
s
−1
. The observed
improvement in mobility was ascribed to close and well-organized packing.
[111]
Jia et al. revealed that the incorporation of physical crosslinking based on thymine H-bonding
can assist self-assembly, suppressing severe aggregation of chromophores in thin films and
provides improved electroluminescent performance in PLEDs.[114] As such, the
photoluminescence and electroluminescence of P65-P69 were greatly improved over non-thymine
control polymers. Zhang et al. also observed that P64 has higher mobility (9.1 × 10−6 cm
2 V−1
s
−1
)
than the analogous CP without thymine and ascribed this enhancement to the improved
crystallinity.[113] Similar to the trend between amide and urea, a relatively stronger hydrogen
bonding interaction in a thymine-based DPP polymer (P64) also exhibited a higher maximum hole
mobility of 9.1 cm2 V−1
s
−1 compared to the amide based DPP polymer (P33). The GIWAXS
results show that the inclusion of thymine groups in the side chains improves the lamellar packing.
For instance, scattering signals up to the fourth order were seen in the out-of-plane direction for
P64 thin films due to lamellar stacking of side chains while, in comparison, the corresponding
(100) and (200) signals for the non-thymine control polymer thin films were found to be weak and
broad. Furthermore, the lamellar stacking signals for P64 thin films are sharper than for the pure

45
alkyl side chain polymer thin films and with a smaller full width at half-maxima. In fact, the
improved crystallinity is most likely due to the development of H-bonding between the thymine
groups, which also causes the polymer chains to pack more tightly.
Since thymine enables strong dimerizable H-bonding, the impact of thymine on the mechanical
properties of CPs is also gaining significant attention. Son et al. found the COS of neat polymer
P61 significantly increased as the ratio of the thymine incorporated monomer increased based on
the film-on-elastomer method.[116] The crystal coherence length LC(100) and LC(200) values for P61
blend films with the nonfullerene acceptor IT4F [125] are clearly higher than the LC(100) and LC(200)
values of the blend film using the non-thymine control copolymers, which is likely the result of
H-bonding between the thymine units. However, the PCE in OPV of the P61 blend film decreased
from 13.4% to less than 12% as the ratio of the thymine incorporated monomer increased in the
polymer. Importantly, as thymine content was increased the molecular weight significantly
decreased from about 50kg/mol to about 10kg/mol, which can have significant impact on the PCE
since a significantly lower Mn can cause a different blend morphology, molecular packing and
domain sizes.[126,127]
Also focusing on thymine-functionalized CPs in OPV, Thompson et al. observed a similar
trend with a blend of P70 and small molecule NFA L8-BO[128] showing significantly larger LC (200)
(13.0 nm), LC(010) (2.9 nm) and smaller d010 (3.72 Å) than the blend with PM7 control polymer
without thymine [129] which showed LC (200) of 8.4 nm, LC(010) of 2.3 nm, and a π−π stacking distance
d010 of 3.79 Å.
[118] More interestingly, the P70 blend exhibit a higher PCE than the PM7 blend and
this is attributed to improved crystallinity in P70 enable by thymine induced H-bonding and better
mixing between P70 and the acceptor in the blend, which leads to enhanced charge generation,

46
higher hole mobility and PCE.
[130,131] Film-on-water measurements were conducted to evaluate the
impact of thymine functionalization on the mechanical properties of the blend.[118] The P70 blend
exhibited a COS of 13.7% and a toughness of 4.5 MJ m3
, which are 5 and 9 times greater than the
COS and toughness of the PM7 blend, respectively. Additionally, film-on-elastomer with
TPU/PEDOT:PSS/active layer architecture has been measured and the P70 based blend exhibited
significantly higher mechanical durability.
In order to highlight the improved mechanical properties, the P70 blend was introduced to an
intrinsically stretchable polymer solar cell (IS-PSC) with a TPU/PEDOT:PSS/active
layer/Interfacial layer/EGaIn device architecture. Prior to stretching, the P70-based IS-PSC
outperformed the PM7-based IS-PSC with PCE of 13.7%, owing to increased Jsc and FF. The PCE
of the PM7-based IS-PSC decreased sharply at 10% strain, and the strain at PCE80% was 16.5%
while the PM7-Thy10-based IS-PSC, demonstrated much improved stretchability with a strain at
PCE80% of 43.1%, as shown in Figure 1-14.
Interestingly, both the amide based polymer (P39) and thymine based polymer (P70) were
examined in OPV devices. A Similar trend in enhanced crystallinity in the NFA blends were
observed in both cases. P70 has the stronger H-bonding thymine functional group but it worth
noting that although P39 is an amide based polymer, it has two equivalents of H-bonding group
relative to P70. As a result, both polymers exhibited improved intermolecular interaction that led
to a tighter packing and larger crystals in the blend and benefited the PCE. More encouragingly,
both polymers showed significantly improved COS in the blend that might indicate that they are
subject to the strain energy dissipation mechanism for breakage of H-bonding sites.

47
Figure 1-13 (a) Device structure and (b) image of the intrinsically stretchable PSC (IS-PSC). (c)
J−V curves of the IS-PSCs with PM7 and PM7-Thy (P70)-based blends. (d) Normalized PCE of ISPSCs during stretching. Reproduced with permission. [118] Copyright 2023, American Chemical
Society.
In a related approach, Son et al. introduced melamine into a P61 blend with NFA IT4F to
investigate the self-healing property via molecular cross linking between thymine and
melamine.[116] One melamine molecule can bind with three thymine groups and this enables selfhealing since self-healing occurs via polymer matrix reorganization, which is accompanied by the
regeneration of dynamic bonds such as H-bonds and the tangling of polymer chains at the damaged
interfaces.[132] Specifically, nanocracks in P61 based BHJ films disappeared after adding the
melamine with the assistance of thermal treatment. However, the PCE of the corresponding selfhealable blends decreased from 13% to less than 11%, which also indicates the difficulty in
addressing the trade-off between outstanding photovoltaic performance and excellent self-healing
properties. Therefore, the performance of self-healable OPV needs to be improved further with the

48
goal of obtaining a high photovoltaic performance (i.e. PCE > 17%) as well as an excellent selfhealing property (excellent maximum recoverable strain and PCE) simultaneously.
3. Other H-bonding Functional Groups used in CPs
Due to very limited examples of the corresponding H-bonding functionalized CPs, other Hbonding CPs based on groups such as adenine and ureidopyrimidone are briefly reviewed in this
section. Adenine, also a well-known nucleobase in the nucleic acid DNA, has been introduced into
CPs. For instance, Walter et al. introduced adenine into benzo[1,2-b:4,5-b’]-dithio-phene (BDT)
based CPs and this led to a significant red shift in absorption due to the strong molecular
assembly.[133] Kilbey et al. synthesized an adenine-functionalized thiophene-based alternating
copolymer via Direct Arylation Polymerization.
[134] It worth highlighting that the primary amine
in adenine was protected by the Boc group since adenine can strongly bind with the palladium
metal center. Kilbey et al. found the interchain H-bonding via adenine can significantly improve
the packing of the copolymer, which resulted in a 70 °C increase in glass transition temperature
compared to the unfunctionalized control polymer. Additionally, the nucleobase's ability to bind
heavy metal ions resulted in a substantial fluorescence suppression (>90%) upon addition of Cu2+
ions, which represented a high Stern-Volmer constant. Subsequently, Kilbey et al. conducted a
facile one-pot synthetic method including Direct Arylation Polymerization followed by Boc
deprotection to create an adenine-containing poly(alkylthiophene) P71 (Figure 1-15) by careful
temperature control, which eliminated unnecessary purification and isolation steps and allowed
the overall synthesis to become more efficient and feasible with the production of higher molecular
weight polymers.[135] Jiang et al. introduced adenine into the side chain of a fluorene-based
polymer and found that the adenine unit could improve the interaction between the surface of the
polymer photocatalyst and water molecules by forming hydrogen bonds, which significantly

49
increased the hydrophilicity and distribution of the resulting polymer photocatalyst in the
photocatalytic reaction solution.[136] As a result, the adenine-functionalized fluorene polymer
exhibited a high photocatalytic activity under UV-Vis irradiation with a hydrogen evolution rate
(HER) of 25.21 mmol g-1
h-1
, which is significantly higher than the control polymer without the
adenine group (6.53 mmol g-1 h-1
).[136] More impressively, the fluorene based polymer with
adenine demonstrated an outstanding HER of 21.93 mmol g-1 h-1 under visible light (λ > 420 nm)
without the inclusion of a Pt co-catalyst.
Since Meijer et al. first reported the ureidopyrimidinone (Upy) unit in 1997 [137], the UPy unit
and its derivatives have been introduced to many fields based on the advantages of ease of
synthesis, available starting materials and high association constant.[138–142] For example, Son et al.
introduced the Upy unit into the side chain of a BDT-based polymer P72 (Figure 1-15) and found
that H-bonding between polymer side chains can efficiently maintain the ordered polymer packing
patterns under applied strain.[143] As such, the TFT device with Upy maintained a relatively high
mobility of 5.8 × 10-3 cm
2 V−1
s
−1 in the direction perpendicular to the strain direction due to the
increased crystallinity of the polymer whereas the device based on the control polymer showed a
dramatic decrease in hole mobility under strain from 1.0 × 10−2
cm
2 V−1
s
−1 to 5.6 × 10-3 cm
2 V−1
s
−1 due to morphological changes and cracking of the film.[143] Verduzco et al. synthesized Upyterminated CPs by reacting hydroxyl or primary amine terminated parent CPs with reactive
isocyanate Upy group and found that the quadruple hydrogen bonding interactions can be exploited
to prevent micrometer-scale phase separation within the blend consisting a CP and an insulating
polymer under thermal annealing.[144] Specifically, different from the unmodified polymer blends,
the blends of UPy-terminated CPs do not exhibit micrometer-scale phase separation even after
extended thermal annealing (i.e. 160 °C with 16h). Additionally, photoluminescence experiments

50
indicate the UPy modification can promote the PL quenching in the donor and acceptor polymer
solutions, owing to hydrogen-bonding associations that lower the average distance for energy and
electron transfer. Verduzco et al. further investigated the photovoltaic performance of the Upyterminated polymer-polymer blend and found a slight increase in power conversion efficiency.[145]
Impedance analysis of polymer-blend OPVs identified an increase in both charge transport and
charge recombination resistance in the annealed OPVs, which indicates the UPy modification
strategy can be an effective approach to reduce macro-phase separation, optimize the interfacial
electrical characteristics in polymer/polymer blends and generate high-performance photovoltaic
devices. Qiu et al. inserted the ring-like quadruple H-bonding UPy unit into the backbone of a
DPP-based polymer resulting in the breakdown of the backbone's conjugation with simultaneous
strong H-bond inclusion, which improved the mechanical properties.[146]
Figure 1-14 Representative Upy and adenine based CPs.
Fluorination is a widely used design strategy in the CP field. [147] As an electronegative atom,
fluorine can act as the hydrogen bond acceptor and there exist examples where fluorine atoms on
CPs participate in the hydrogen bonding.[148] However, the fluorine atom on the CPs will mostly

51
likely affect the conformation of CPs via the secondary interaction rather than actual hydrogen
bonding.
[149–155] Therefore, this review is not focus on fluorine-based CPs.
Carboxylic acids are one of the hydrogen bonding functional groups that have been introduced
into CPs. Katz et al. found that carboxylic acid-functionalized amphiphilic polythiophenes
exhibited a higher stability and better pH sensitivity than P3HT in aqueous solution.[156] You et al.
reported a random polythiophene with 50% mol% thermocleavable tertiary ester side chain.[157]
After thermal annealing treatment, which led to the cleavage of the tertiary ester group, the
carboxylic acid based polythiophene demonstrated significantly improved π–π stacking, which led
to greater charge mobility. Further, these carboxylic acid functional polythiophenes in the solid
state have considerably enhanced stretchability and the sensors based on these carboxylic acid
polythiophenes not only detect humidity and ethanol but also light and heat energy owing to the
hydrogen bonding resulting from the carboxylic acid group. Additionally, carboxylic acid groups
are critical in designing CPs for dye-sensitized solar cells because the CPs must adhere to the
nanostructured TiO2 surface via the interaction between the polar carboxylic acid units with the
metal oxide surface.[158] Overall though, carboxylic acid based CPs have limited examples and
applications and therefore this review is not focus on carboxylic acid based hydrogen bonding in
CPs.
4. Conclusion and Outlook
Different types of H-bonding functional groups used in the CP field and representative CPs
have been presented. The synthetic methods for introducing the corresponding H-bond functional
groups into CPs have also been highlighted. Generally, introducing H-bonding into CPs increases
the hydrophilicity. Further, the creation of strong noncovalent H-bonds within polymer thin films

52
results in not only in more ordered and crystalline structures due to the molecular assembly, but
also the powerful aggregation and enhanced packing, which can benefit charge transport within
and between polymer chains. Therefore, H-bonded CPs with excellent charge-transport properties
have been achieved. Additionally, H-bonding groups distributed in the polymer films can act as
physical crosslinking sites due to the reversible nature of the non-covalent bonds, which can
significantly impact the mechanical properties of polymer films. It has been demonstrated that it
is possible to address the trade-off between mechanical robustness and electronic or photovoltaic
performance by utilizing the H-bonding strategy.
Looking forward, several aspects of H-bonding CPs need to be expanded upon to further
realize the full potential impact of this approach. Specifically: (i) A greater variety of different
types of H-bonding groups should be considered since the majority of the H-bonding strategies in
CPs are limited to the secondary amides, carbamates, and urea groups. Although H-bonding groups
have been demonstrated as a successful design strategy for certain applications, other H bonding
groups such as triple and quadruple H-bonding groups could offer greater control over properties.
For instance, the UPy unit has a significantly higher association constants than most of the
hydrogen bonding groups reported for use in CPs. It will be interesting to thoroughly understand
the impact of the UPy unit on the morphology, aggregation, electrical and mechanical properties
of CPs. Additionally, systematicly investigating hydrogen bonding groups with different strengths
but on identical polymer backbones will offer better understating of the impact of hydrogen
bonding groups on fundamental properties and in the context of varying applications. (ii) The
scope of the substrate where H-bonding group are attached needs to be significantly expanded.
The CP field has a broad diversity of monomers ranging from strong electron donating units to the
strong electron deficient units. However, nearly all the substrates with H-bond groups are based

53
on very simple moieties such as thiophene, fluorene (or carbozole), and diketopyrrolopyrrole. Only
a very few existing examples such as the 6,7-difluoro-quinoxaline (Q-Thy) are based on state-ofthe-art monomer units. Some benchmark moieties such as C8-BTBT, naphthalene diimide,
fluorobenzotriazole (FTAZ), NFAs such as Y6 and its derivatives should be considered since the
functionalization of benchmark units with hydrogen bonding groups is an underutilized approach.
(iii) Successfully polymerizing high molecular weight CPs with H-bonding groups is still
challenging regardless of the transition metal cross-coupling used (Stille, Suzuki, Sonogashira and
DArP). Molecular weight, as one of the intrinsic and decisive factors, plays a key role in
determining the properties of CPs. Although solubility is a concern for high molecular weight CPs,
most of the H-bonding functionalized terpolymers are not able to reach this stage because the Hbonding groups are very likely to interact with the transition metal catalyst and interfere with the
catalytic cycle during polymerization. It is still very challenging to develop a general direct
polymerization condition than can overcome this drawback. Systematic investigations of
polymerization conditions including optimizing the diverse methods (i.e. Suzuki, Stille, DArP and
postpolymerization) and the details such as catalysts, ligands and solvents are needed. (iv) More
elucidation and understanding of the role and impact of the H-bonds in CPs is needed to assist
future molecular design. For instance, introducing H-bonds into a DPP-based polymer decreased
the modulus while an increased modulus was observed in other polymers. Moreover, introducing
urea groups into the side chain versus the backbone of DPP polymers caused two completely
opposite results. (v) More aspects of existing applications should receive greater attention rather
than only focusing on the impact on morphology and mechanical properties. For instance, utilizing
the coordination between anion and specific hydrogen bond to construct CP-based chemical
sensors. Additionally, introducing hydrogen bonding into CPs generally will improve the

54
hydrophilicity and this might benefit CPs when utilized as the photocatalyst for water splitting.
Overall, H-bonding groups have shown tremendous potential to tailor electronic and physical
properties in CPs. However, there is much work to do to further elucidate structure-property
relationships and to fully and broadly exploit the potential of this approach.

55
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67
Chapter 2: Unprecedented Efficiency Increase in a Ternary Polymer Solar Cell Exhibiting
Polymer-Mediated Polymorphism of a Non-Fullerene Acceptor
2.1 Introduction
Polymer solar cells (PSCs) with bulk heterojunction (BHJ) photoactive layers have received
significant attention in recent decades due to their notable strengths for enabling large-area
fabrication of flexible solar cells via low-cost solutions coating processes.1–3,4 Ternary organic
solar cells consisting of three components in a single active layer have been identified as a simple
and low-cost approach for increasing the power conversion efficiency (PCE) and stability of these
devices.
5–7,8 Thanks to the rapid development of non-fullerene acceptors (NFAs) over the last five
years, the efficiencies of binary organics solar cells have surpassed 18%.9–13 By combining the
ternary strategy with the NFAs, the efficiencies of single junction organic solar cells are
approaching the 19% landmark. 14–16 Indeed, the four ternary models developed among fullerene
systems, such as cascade charger transfer,17,18 energy transfer,19 parallel-like,20 and the alloy
model,21–25 have been successfully applied to NFA-based organic solar cells. For instance, two
NFAs with similar fused backbones have been reported to combine and form an alloy acceptor,
which effectively addresses the trade-off between photocurrent and voltage and thus maximizes
the performance.26–28
In contrast to fullerene acceptors, NFAs such as ITIC and Y6 lead to crystalline domains in
the solid-state films that can crystallize in a variety of polymorphs depending on the processing
conditions.29,30 Different crystalline phases can result in various structural, optical, and electrical
properties, which potentially can affect device performance. For instance, Pfannmöller et al.31
revealed that when the polymer PBDB-T acts to nucleate the NFA ITIC, it leads to the formation
of a distinct polymorph under the assistance of DIO additive and thermal annealing. The PBDB-

68
T:ITIC blend with the nucleated ITIC polymorph exhibited an 8.5% PCE whereas the blend
without the nucleated polymorph exhibited only a 5.6% PCE. Polymorphism is a critical design
parameter for semiconducting properties and even minor changes in crystal packing can result in
differentiation of electronic properties by orders of magnitude.
32–34,29 Despite significant progress
in building NFA-based ternary solar cells, in the majority of cases the intrinsic and unique
crystalline properties of NFAs such as polymorphism have been ignored.
In this letter, inspired by the design strategy presented by Hou et al 35,36, a new NFA named
2,2'-((4,4,9,9-tetrahexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b'] dithiophene-2,7-diyl)
bis(methaneylylidene)) bis(1H-indene-1,3(2H)-dione) and referred to as IDID (Figure 2-1), has
been designed and synthesized. We observed a significantly enhanced PCE in a ternary PSC based
on PTQ1037 :PC61BM upon addition of IDID. Specifically, the relative increase in PCE of this
ternary blend was found to be nearly 80% (with respect to the best binary blend) which, to the best
of our knowledge, is the highest among all reported ternary blends.6,38,39 Importantly, relative to
pristine IDID films, we found the formation of a distinct IDID polymorph nucleated by PTQ10
under the assistance of the processing solvent in the ternary solar cells. Additionally, this
PTQ10:IDID:PC61BM ternary blend performs significantly better than the analogous blend with
IDIC as a control. These results indicate that polymorphism in NFAs, as dictated by interaction
with the host polymer, represents an important aspect that needs to be considered when designing
and constructing a ternary polymer solar cell, both in terms of component selection and processing
optimization.

69
2.2 Results and Discussion
PTQ10 was selected as the donor in this study because it has been demonstrated as the high
efficiency and low-cost polymer donor 37 We adopted PC61BM as the acceptor in the parent binary
system and maintained the same polymer:fullerene (1:1.2) ratio for all blends so that the only
variable is the third component NFA. The chemical structures of the host donor PTQ10, acceptor
PC61BM, and the third component IDID are shown in Figure 2-1. The synthetic route to the novel
IDID is described in the supporting information. Specifically, the precursor IDT-CHO was
synthesized according to previous literature 40 and then reacted with 1H-Indene-1,3(2H)-dione
under basic conditions to perform the Knoevenagel condensation. The optical and electrochemical
characteristics used to determine the HOMO and LUMO energies of IDID are shown in Figure A1 and A-2. The HOMO and LUMO energy levels of PTQ10 and PC61BM were adopted from the
literature.21,37
Figure 2-1 Structures and corresponding HOMO and LUMO energy levels of PTQ10, IDID, and
PC61BM

70
Organic solar cells were prepared with the conventional architecture ITO /PEDOT:PSS
/PTQ10: NFA: PC61BM /Al. All of the PSCs in this study were processed from o-DCB without
post-treatment or additives and were fabricated and measured in air without any encapsulation
(average 35% humidity). Binary OSCs made from PTQ10 and PC61BM gave the reasonable PCE
of 3.38% (Table 1) with a Voc of 0.858 V, both being similar to literature reports.41 Ternary devices
with a ratio of PTQ10:IDID:PC61BM =1:0.3:1.2 achieved a significantly higher PCE of 6.04%,
owing to simultaneous increases in Voc (0.928 V), Jsc (11.5 mA/cm2
) and fill factor (FF) (57%).
Since the fused ring backbone and part of the end group of IDID are identical to the representative
NFA IDIC,42 we adopted the use of IDIC as a third component as a control. Interestingly, using
IDIC as a third component under the same composition and conditions led to only a slight
improvement in efficiency from 3.38% to 3.55% with a Jsc of 8.5 mA/cm2
, Voc of 0.806 V, and a
FF of 52%, as shown in Table 2-1. The introduction of IDIC didn’t significantly increase the
efficiency and even led to a lower open circuit voltage. For reference, Welch et al reported a Voc
of 0.52V and PCE of 3.4% when fabricating the PTQ10:IDIC binary cells with a conventional
architecture and measuring in air.43 In addition, we measured binary blend solar cells of
PTQ10:IDID and IDID:PC61BM as controls and the results are shown in Table A-2. IDID:PC61BM
showed no measurable photovoltaic effect, possibly due to the inability to generate a uniform film.
The binary PTQ10:IDID resulted in a PCE of only 0.06%, which might due to the high miscibility
of PTQ10 and IDID (vide infra).
To contextualize the relative increase in PCE observed upon addition of IDID to the
PTQ10:PC61BM binary blend, we compared increases in Jsc and PCE between host binary and
ternary systems from the literature,6,38,39 and the results are shown in Figure 2-2. The relative
improvement of Jsc is more than 40% and the relative improvement of PCE is close to 80%. Both

71
of these increases are better than all the reported ternary blends in literature, to the best of our
knowledge.
Table 2-1 Photovoltaic Properties of PTQ10:NFA:PC61BM Ternary Blend BHJ Solar Cells
PTQ10: NFA: PC61BM Jsc
(mA/cm2
)
Voc
(V)
FF
(%)
PCE
(%)
1:0:1.2a 8.0 0.858 49 3.38
1:0.3(IDID):1.2a 11.5 0.928 57 6.04
1:0.3(IDIC):1.2a 8.5 0.806 52 3.55
a Devices were fabricated with standard conventional architecture ITO/PEDOT:PSS/Active
layer/Al, Processed and measured in air without any encapsulations, Posttreatment and additive
free, Averages over 7 pixels
Figure 2-2 Relative Increase in Jsc and PCE with respect to the best binary cell in literature
To better understand the role of IDID in these ternary solar cells, characterization of the active
layer was pursued. Grazing incidence X-ray diffraction (GIXRD) was used to investigate the

72
crystallinity of the different components and blends under processing conditions identical to those
used for solar cells active layers with the exception of the neat IDID film which was processed
from chloroform since it did not form a film using o-DCB. Neat IDID processed from chloroform
with 20 minutes of thermal annealing at 120 °C shows a (100) lamellar peak with 2θ of 8.8 degrees,
as shown in Figure 2-3. When IDID was blended with the donor PTQ10 (1:0.3, w/w) with o-DCB
as the processing solvent used for devices under as-cast conditions, the lamellar peak of IDID
shifted significantly to 2θ of 9.4 degrees, implying that the molecular packing became more
compact after blending with PTQ10 since the d100 decreased from 10.0Å to 9.4Å. Additionally,
both the stronger peak intensity and the narrower full width at half the maximum (FWHM)
indicated an enhanced crystallinity. Crystalline size calculated from the Scherrer equation
increased from 7.6nm to 10.7nm for the IDID film and blend film respectively. Thus, we propose
that the third component NFA IDID, with the assistance of the processing solvent o-DCB, is likely
nucleated by the host donor PTQ10 and forms a distinct polymorph. In order to examine this
assumption, we first thermally annealed the PTQ10:IDID blend film (1:0.3, w/w) with the same
annealing condition for neat IDID. As a result, the intensity of the IDID lamellar peak clearly
decreased, as shown in Figure 2-3. Correspondingly, the intensity of the PTQ10 lamellar peak
increased, as shown in the full GIXRD spectrum (Figures A-3 in the Supporting Information).
These observations are consistent with evidences used by Bao et al 44,45 to prove the formation of
a new polymorph which are typically metastable and require less activation energy to form,
whereas the most thermodynamically stable form is the last to appear.30,32 The more compact
structure of the NFA polymorph in the polymer blend may be due to alignment between the
polymer and small molecule due to polymer-mediated nucleation of the novel polymorph.46

73
Figure 2-3 GIXRD patterns of thin film with IDID and the blend with PTQ10 from 2θ=6 to 14
degrees
Interestingly, when we applied the same experiments with IDIC, we did not observe a
consequence indicative of any special interaction between IDIC and PTQ10, and the intensity of
the peaks of the as-cast NFA were clearly suppressed upon blending with PTQ10 as shown in
Figure A-4, which matches the observation reported by Li et al. 37 We also studied the PTQ10:IDID
blend processed from chloroform for direct comparison to the neat IDID film. The un-annealed
chloroform blend did not show a lamellar peak for IDID. The lamellar peak for IDID was observed
in the blend after annealing (Figure A-5), but no peak shift relative to IDID film was observed,
indicating the lack of polymorph formation in this case. This observation highlights the important
role of the processing solvent in the formation of the unique polymorph.

74
In order to further confirm the nucleation between the host polymer donor and the NFA,
Differential Scanning Calorimetry (DSC) was employed to evaluate the molecular interaction in
all blends. As seen in Figure 2-4a, PTQ10 did not show any phase transitions during the heating
and cooling cycles between 20°C to 220°C, which matches the literature since the melting point
of PTQ10 is close to 360°C.47 Considering the melting point of PTQ10 is in a range which might
cause NFA to decompose, we avoided this melting temperature in our DSC study. The DSC trace
of neat IDID showed a sharp melting temperature (Tm) and a crystallization temperature (Tc) of
151.8°C and 67.2 °C, respectively. However, when IDID was blended with PTQ10 with the ratio
(1:0.3, w/w) and processed with solvent o-DCB, no endothermic peak was observed during the
heating cycle between 20°C to 220°C but there existed a new endothermic peak at 234.9°C as
shown in Figure A-6, which could correspond to the newly formed polymorph of IDID.
Additionally, we observed that the crystallization temperature (Tc) of the blend during the cooling
cycle shifted slightly to a higher temperature of 69.7°C, as shown in Figure 2-4b. This increased
crystallization temperature during the cooling cycle has been widely used in polymer blending
studies to demonstrate a nucleation effect.48 For instance, blending of styrene-ethylene-propylenestyrene (SEPS) triblock copolymer with high-density polyethylene (HDPE) induces a slight shift
of Tc for HDPE to a higher value,49 which is similar to the behavior of PTQ10 and IDID reported
here. Additionally, after blending with SEPS, the GIXRD peak of HDPE also shifts to a higher
angle50, which matches our GIXRD observations for PTQ10 and IDID. The nucleation effect of
SEPS on HDPE as measured by DSC and GIXRD is analogous to our observations with
PTQ10/IDID, which supports the nucleation effect of PTQ10 on IDID to form a distinct
polymorph.

75
Figure 2-4 DSC thermograms of (a) PTQ10, IDID, and PTQ10/IDID (1:0.3, w/w) upon heating
(down) and cooling (up) with endo down (b) enlarged figure of pink rectangle at the position of Tc.
As an additional signature of a nucleation effect, a higher crystallization temperature tail is
usually observed, along with an overall shift in the peak towards higher temperature,
51 which is
also observed in our study (77.1°C versus 80.0°C, Figure A-7). Therefore, we propose that the host
donor PTQ10 nucleates IDID to form a distinct polymorph as assisted by processing in o-DCB.
Since IDIC is the control NFA in this study, we adopted the same DSC analysis for the

76
PTQ10/IDIC blend processed under the same condition as the IDID blend. The results are shown
in Figure A-8 in the Supporting Information. IDIC has a high melting point, which was observed
to decrease after blending with PTQ10. This matches the IDIC melting point depression behavior
previously reported.
52
Since the fabricated organic solar cells consist of three components, with the host acceptor
PC61BM accounting for roughly half of the active layer, we further investigated whether this
nucleation mediated polymorph of IDID does exist in an actual device active layer. First, the
GIXRD of the ternary blend PTQ10:IDID:PC61BM (1:0.3:1.2) clearly showed a peak at 2θ of 9.4
degrees which is identical to the lamellar peak of the IDID polymorph (2θ of 9.4 degrees). Within
this region, the control host binary device did not show any peaks (Figures A-9 in the Supporting
Information). Second, we measured the surface energy of these compounds based on the two liquid
method (Wu model) to investigate the potential interaction between each compound in the ternary
blend.53 The surface energy of PTQ10 is 21.4 mN/m with a 107.4° water contact angle and 94.9°
glycerol contact angle, which is very close to the value reported by Wantz et al and the water
contact angle is nearly the same.41 The surface energy of IDID is 21.7 mN/m with the water contact
angle at 101.1° and glycerol contact angle at 90.5°. Since PC61BM has a high surface energy of
27.6 mN/m,
54 PTQ10 and IDID have a strong possibility of mixing with each other in the ternary
blend, which supports our PTQ10:IDID:PC61BM (1:0.3:1.2) ternary GIXRD observations. This
further supports that the ternary blend in the device has the unique polymorph caused by the
nucleation between PTQ10 and IDID. In contrast, IDIC’s surface energy is 25.6 mN/m with the
water contact angle at 97.6° and glycerol contact angle at 84.6°. As such, for the IDIC ternary
blend, IDIC should preferentially mix with PC61BM because of the relatively close surface energy

77
and this agrees with the reported alloy acceptor formation between fullerene acceptors and NFA
acceptors.55
In order to further understand this ternary system and explore the reasons behind the enhanced
performance, Ultraviolet-Visible spectroscopy (UV-Vis) have been conducted to compare the
PTQ10: PC61BM (1:1.2) binary and PTQ10: PC61BM: IDID (1:1.2:0.3) ternary blend. Both binary
and ternary films were prepared under the organic solar cell device fabrication conditions, with the
thickness about 60nm. As shown in the thin film UV spectroscopy in Figure 2-5a, the binary
PTQ10:PC61BM blend has a slightly higher absorption coefficient before 500nm, which matches
the External Quantum Efficiency (EQE) in Figure A-10 since the EQE of the binary is higher than
the ternary in this region. However, beyond 500nm, the PTQ10:PC61BM:IDID(0.3) ternary blend
clearly has a much higher absorption coefficient and the edge slightly shifts to longer wavelength,
which might be due to the absorption of IDID itself (in Figure A-1). These two factors are also
reflected by the EQE in Figure A-10. First, the EQE of the ternary blend is obviously higher than
the binary blend after 500nm, which could be correlated to the higher absorption coefficient.
Second, compared to the binary, the edge of the EQE of the ternary blend is slightly red-shifted as
well. As such, the improvement in absorption affected by the addition of IDID can contribute to
the enhanced Jsc that is observed.
Since the polymer PTQ10 and IDID have similar absorption and the emission of polymer
PTQ10 is mainly at 600nm-850nm56, we conducted a Photoluminescence(PL) study to compare
the binary and ternary blends, as shown in Figure 2-5b. Interestingly, the photoluminescence (PL)
between 600nm and 850nm was further quenched after adding the third component IDID, which
suggests improved charger transfer between PTQ10, IDID and PC61BM.57,58 Since the surface
energy of PTQ10 and IDID are nearly the same, the introduced third component is expected to

78
mainly interact with PTQ10. As we already demonstrated in the manuscript via GIXRD and DSC,
IDID is nucleated in the presence of the host donor PTQ10 to form a special polymorph in the
ternary blend. Because the polymer PTQ10 is able to induce IDID to form a new polymorph, a
special molecular alignment is expected at the interface between the PTQ10 and IDID to promote
this nucleation. For instance, Pfannmöller et al.31 showed that ITIC formed a new polymorph after
thermal annealing because ITIC was able to dock to the polymer PBDB-T and nucleate and grow.
Therefore, we infer that the interface between PTQ10 and IDID in the actual ternary blend will be
different from the polymer-fullerene interface in the binary blend, and the further quenching in PL
is mainly related to this special interface, which will lead to more efficient charge transfer and thus
higher Jsc. These observations also match what Pfannmöller et al. reported.31

79
Figure 2-5 (a) UV-Vis and (b) PL spectra of PTQ10, PC61BM (1:1.2) binary and PTQ10, PC61BM,
IDID (1:1.2:0.3) ternary

80
We have also measured Space-Charge-Limited Current (SCLC) mobility of the binary and
ternary blends to further compare the charge transport property. The data overview, hole/electron
mobility ratio, and representative J-V curve are shown in Figure A-12, A-13 and Table A-4. Adding
IDID leads to decreased hole mobility from 9.8 × 10-5 cm
2 V-1 S-1 to 2.7 × 10-5 cm
2 V-1 S-1 in the
ternary blend, which is similar to the result reported by Cho et al.59 Cho et al. observed the hole
mobility was continuously decreasing when introducing the third component NFA IDT2BR into
the PPDT2FBT: PCBM binary blend. They ascribed the decreased hole mobility to the presence
of IDT2BR in the hole-transporting region. This impact is likely significantly stronger in our case
since IDID and PTQ10 have similar surface energy and IDID can be nucleated by the holetransporting polymer PTQ10. Interestingly, we found the electron mobility in our ternary blend
was slightly improved from 1.1 × 10-5 cm
2 V-1 S-1 to 1.3 × 10-5 cm
2 V-1 S-1while Cho et al. observed
a decreased electron mobility and they ascribed it to the low electron mobility of NFA compared
with PCBM. We propose the slightly improved electron mobility in our ternary blend is mainly
due to the enhanced crystallinity of IDID, which might benefit the charge transport and compensate
for its intrinsic low electron mobility.
31 Importantly, the µh/µe ratio of the ternary blend (2.0) is
significantly better than the binary blend (8.9). This shows that adding the IDID can also balance
the charge transport, thus leading to a higher fill factor (FF). Additionally, the open-circuit voltage
(Voc) of the ternary blend was increased from 0.86V to 0.93V upon addition of IDID.
2.3 Conclusion
In summary, we designed and synthesized a new NFA IDID based on a 1H-Indene-1,3(2H)-
dione end group and demonstrated a novel ternary blend where the host polymer donor showed a
nucleation effect on IDID and induced IDID to form a new polymorph. Compared with IDIC,
IDID has a much lower surface energy and is expected to more strongly interact with the host

81
donor within the ternary blend. GIXRD and the DSC measurements confirmed the unique
polymorph of IDID resulting from the o-DCB assisted nucleation between the host donor PTQ10
and third component IDID. More importantly, we observed a close to 80% relative increase in PCE
for this ternary blend, which is a new record for PCE improvement when transitioning from a
binary to a ternary blend. Importantly, this enhancement is significantly higher than a control with
IDIC even though IDIC has been shown to be one of the best performing NFAs and the NFAfullerene co-acceptor strategy has been widely used for the state-of-the-art. Thus, this work
suggests the intrinsic ability of NFAs to form polymorphs must be taken into account when
selecting components for ternary blend solar cells and in the optimization of processing conditions.

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Chapter 3: High Performance Intrinsically Stretchable Polymer Solar Cell with Record
Efficiency and Stretchability Enabled by Thymine Functionalized Terpolymer
3.1 Introduction
Polymer solar cells (PSCs) have gained increasing attention for enabling production of flexible
solar cells via low-cost solution coating methods.1–5 The power conversion efficiencies (PCEs) of
PSCs have exceeded 18% due to recently developed polymer donors (PD) and small molecule
acceptors (SMAs).6–14 For future commercialization of PSCs, it is crucial to design stretchable
systems with both high efficiency and mechanical robustness, as mechanical stress is a major factor
causing device failure.15,16 As nearly all high performance PSCs are composed of fully conjugated
rigid PDs and SMAs, these PSCs suffer from low stretchability (i.e. crack onset strain (COS) <
3%).17–19 A limited range of molecular design strategies such as introducing flexible nonconjugated spacers into the PD have been developed for high performance and mechanically robust
PSCs.20–25 However, this strategy can sacrifice charge transport.26 Additionally, non-conjugated
spacers are typically incorporated as random comonomers resulting in a randomized distribution
of conjugation lengths, which limits reproducible synthesis.27–30
Another strategy to increase the stretchability of conjugated polymers is embedding dynamic
bonding (i.e., hydrogen bonding (H-bonding)).31,32 For example, the nucleobase thymine, has been
introduced into polymers to enhance their mechanical properties due to strong dimerizable Hbonding between thymine units.
33–36 Specifically, the N-3 proton and carbonyl at C-4 induce a
stronger tendency towards self-dimerization in thymine than other common H-bonding groups
such as amides.37–40 Additionally, introducing H-bonding functional groups in the side chain
preserves full conjugation of the backbone. Hence, an intrinsically fully-conjugated thymine side

89
chain incorporated PD based on PM741 is an attractive target for high performance, stretchable, and
reproducible PSCs.
36,42
3.2 Results and Discussion
Herein, we report a facile synthetic method to incorporate thymine into the side chain of the
benchmark electron deficient unit 5,8-dibromo-6,7-difluoroquinoxalin-2-ol43 and report a new
monomer Q-Thy. Using thymine-1-acetic acid as the thymine source rather than direct alkylation
of thymine is found to avoid complications resulting from tautomers and thus potentially
significantly expanding the scope of substrates.44–46 We designed three new random terpolymer
donors, named PM7-ThyX (Figure 3-1a) incorporating X= 5, 10, 20 mol% of the Q-Thy as the
third monomer. Interestingly, we found PM7-Thy10 is not only able to achieve a higher PCE
(17.1%) than PM7 (16.0%) but also exhibits a significantly higher COS (13.7%) and toughness
(4.50 MJ m-3
) than PM7 (2.6% and 0.52 MJ m-3
) when blending with the SMA L8-BO10.
Furthermore, a PM7-Thy10-based intrinsically stretchable polymer solar cell (IS-PSC) showed
much higher PCE (13.7%) and mechanical durability (strain at the 80% of initial PCE (PCE80%) =
43.1%) than the PM7-based IS-PSC (PCE = 11.3% and strain at PCE80% = 16.5%). Both the PCE
and stretchability of the PM7-Thy10-based IS-PSC are the highest among all reported high
performance IS-PSCs. These findings illustrate a novel PD molecular design strategy that involves
copolymerizing a third monomer with an H-bonding side chain and demonstrate that it is possible
to outperform the parent polymer while simultaneously increasing the mechanical reliability of
PSCs without sacrificing a fully conjugated backbone. This design strategy promises broad
applicability to other benchmark copolymers and opens a new avenue for high performance
stretchable PSCs.

90
Figure 3-1 (a) Chemical Structure of PM7-ThyX, Q-Thy and (b) Thin film UV-vis spectra
of PDs
The synthetic route to PM7-ThyX polymers is shown in Scheme B-1. The number-average
molecular weight (Mn) of PM7-ThyX terpolymers are in a similar range (162-186 kg mol-1
) except
for PM7-Thy20 (Table B-1). The lower molecular weight of PM7-Thy20 may be due to

91
interference during polymerization between palladium and the large amount of thymine.35,36,47 1
H
NMR spectra confirmed the presence of thymine groups in the terpolymers with a peak at ~4.4
ppm (Figures B2-B4). Additionally, a concentration-dependent 1
H NMR study on Q-Thy was
conducted to demonstrate that thymine-functionalized terpolymers are capable of forming
intermolecular H-bonds (Figures B5-B6) since most of the 1
H NMR signals of polymers are broad
and offer limited information.33,48 A gradual shift of the N-3 proton was observed and the
difference in chemical shift between 1-10 mM is ~0.22 ppm, which matches the literature.33,49 The
optical properties of the PDs are shown in Figure 3-1b and Figure B-7. Compared with PM7, PM7-
ThyX PDs showed red shifted absorption. The λmaxfilm of PM7 is 598 nm while λmaxfilm of PM7-
Thy PDs range from 609-611 nm. Additionally, all PM7-ThyX PDs show an enhanced vibronic
peak with a higher 0-0/0-1 intensity ratio than PM7 (0.99) of 1.08 for all PM7-ThyX PDs. The
enhanced vibronic peaks indicate more ordered interchain packing, likely resulting from Hbonding.35 The LUMO/HOMO energy levels of all the PDs aligned well with those of the L8-BO
SMA for efficient charge transfer (Figure B-9).
Photovoltaic properties were investigated by blending PDs with L8-BO in PSCs with a
conventional architecture (detailed fabrication is in the supporting information). The J-V curves
and corresponding device performance are shown in Figure 3-2 and Table 3-1. As a control, the
PM7:L8-BO PSC showed a maximum PCE (PCEmax) of 16.0% with an open-circuit voltage (Voc)
of 0.91 V, short-circuit current density (Jsc) of 24.3 mA cm-2 and fill factor (FF) of 0.74.
Interestingly, PM7-Thy10 PSCs exhibited a superior PCEmax of 17.1% with higher Jsc (25.6 mA
cm-2
) and FF (0.76) than the other blends. PM7-Thy20 devices with higher Thy ratio exhibited
decreased PCE, indicating an optimal 10 mol% of Q-Thy. The Gaussian distributions in Figure 3-
2b indicate that all PSCs have a similar range of PCEs. The calculated Jsc values estimated from

92
external quantum efficiency (EQE) are well matched with the Jsc values in PSCs within 2% error
(Figure B-10 and Table B-2).
Figure 3-2 (a) J-V curves of PD:L8-BO-based blends in the rigid PSC architecture. (b) Gaussian
distribution of PCEs of the PSCs
Charge generation and transport properties were investigated to better understand the origin of
the differing photovoltaic performances. First, exciton dissociation probabilities (P(E,T)s) were
extracted from photocurrent density (Jph) versus effective voltage (Veff), as shown in Figure B-11.
PM7-Thy10:L8-BO had the highest value (over 96%), which indicates better charge generation
ability than the other PSCs. Second, the space charge limited current (SCLC) method was
employed to compare the charge mobilities (Table B-5). The electron mobilities (µe) of all PD:L8-
BO blends were in a similar range at 3.7-4.0 × 10-4
cm
2 V-1
s
-1
, whereas there was a distinct

93
difference in hole mobility (µh) values depending on the PD. The µh value linearly increased with
Q-Thy content, where values of PM7, PM7-Thy5, and PM7-Thy10-based blends were 1.8, 2.8,
and 4.2 × 10-4
cm
2 V-1
s
-1
, respectively. The relative lower µh value (3.0 × 10-4
cm
2 V s-1
) of the
PM7-Thy20-based blend is ascribed to its lower Mn.
36 Additionally, the PM7-Thy10-based blend
exhibited the most balanced mobility ratio (µh/µe) at 1.07 compared to PM7 (0.47), PM7-Thy5
(0.85), and PM7-Thy20 (0.81). The higher hole mobility and well balanced mobility of the PM7-
Thy10 blend supports the highest FF value (0.76) among the PSCs.50,51
Table 3-1 Photovoltaic Properties of PD:L8-BO blends in rigid solar cells
PDs:
L8-BO (1:1.2)
Jsc
(mA cm-2
)
Voc
(V)
FF
(%)
PCEavg
(%)
PCEmax
(%)
PM7 24.35 0.91 0.74 15.84 16.01
PM7-Thy5 23.76 0.89 0.72 14.89 15.39
PM7-Thy10 25.64 0.88 0.76 16.83 17.05
PM7-Thy20 21.96 0.90 0.72 14.08 14.34
Grazing incidence wide angle X-ray scattering (GIWAXS) was performed on the pristine PDs
and blend films to better understand the effect of introducing Q-Thy into PM7. The GIWAXS
spectra of neat PM7-ThyX PD films showed clear (200) peaks along the in-plane (IP) direction
while the PM7 film showed a relatively poorly defined (200) peak (Figures B12-B13). H-bonding
between thymine groups might be responsible for this sharp and distinct (200) peak in the PM7-
ThyX films.35,52 For instance, Zhang et al, observed a similar trend where a film of pure alkyl side
chain polymers exhibited a weak and broad (200) scattering peak while the thymine side chain
analogues showed a sharper (200) peak.35
Blend films for GIWAXS measurements were prepared under the conditions used for PSC
fabrication. PM7-ThyX-based blends showed larger crystal sizes and more closely packed
structures than the PM7-based blend as shown in Figure 3-3, Figures B14-B15, and Table B-3.

94
Crystal coherence lengths (LCs) were estimated based on the (200) and (010) peaks, respectively,
using the Scherrer equation.53 When compared to the PM7:L8-BO blend (LC(200) = 8.4 nm, LC(010)
= 2.3 nm, and π-π stacking distance (d010)= 3.79 Å), the PM7-Thy10:L8-BO blend had
significantly larger Lc(200)= 13.0 nm, Lc(010)= 2.9 nm and smaller d010= 3.72 Å. The enhanced
crystalline properties of the PM7-Thy10:L8-BO blend indicate strong intermolecular assembly
attributed to H-bonding, which should benefit charge transport and increase Jsc in PSCs.54,55
A pseudo free-standing tensile testing method was employed to investigate the mechanical
properties of the PD:L8-BO blend thin films. The results are shown in Figure 3-4 and Table B4.5657 The PM7:L8-BO blend exhibited brittle mechanical properties with low COS of 2.6% and
toughness of 1.96 MJ m-3
. In contrast, the PM7-Thy5:L8-BO blend had much higher COS of 6.1%,
which was further increased to a COS of 13.7% and toughness of 4.50 MJ m-3 for the PM7-
Thy10:L8-BO blend, which are 5 and 9 times higher than the COS and toughness of the PM7:L8-
BO blend, respectively. Figure 3-4a presents an image of the PM7:L8-BO blend after the tensile
test, illustrating that the blend cracked before reaching 3% strain. In stark contrast, even at 10%
strain, the PM7-Thy10:L8-BO blend experienced plastic deformations without any cracking as
evidenced by wrinkled features. The higher COS value and toughness of PM7-ThyX-based blends
are expected to result from robust intermolecular interaction mainly attributed to strong
intermolecular H-bonding.

95
Figure 3-3 GIWAXS in-plane linecuts of the PD: L8-BO blend films
Figure 3-4 (a) Optical microscope images of PM7:L8-BO and PM7-Thy10:L8-BO blend films after
3 and 10% strain, respectively. (b) Stress-strain curves of the different blend films measured by the
pseudo free-standing tensile tests

96
Figure 3-5 (a) Device structure and (b) active image of the intrinsically-stretchable-PSC (IS-PSC).
(c) J-V curves of the IS-PSCs based on the PM7- and PM7-Thy10-based blends. (d) Normalized
PCE of IS-PSCs during stretching.
Figure 3-6 Photovoltaic parameters of IS-PSCs and their strain values at 80% of their initial PCE
a
Average values were estimated from 5 independent devices
To highlight the impact of the excellent mechanical properties of the PM7-Thy10-based blend,
we fabricated IS-PSCs using PM7-based and PM7-Thy10-based blends. The detailed fabrication
process is similar to previous reports and described in the supporting information,58,59 where the
layers were different from rigid PSCs because all layers must possess stretchability60 (Figure 3-

97
5a-b). The PM7-Thy10-based IS-PSC showed superior PCE (13.7%) to the PM7-based IS-PSC
(11.3%) prior to stretching. The higher PCE of PM7-Thy10 is explained by a higher Jsc and FF
(Table 3-2). Importantly, there was a contrast in the stretchability of the IS-PSCs. For accurate
measurements, the PCE change of IS-PSCs during stretching was obtained using an active layer
mask to ensure the same cell area. The PM7-based IS-PSC showed a sharp decrease in PCE after
10% strain and the strain at 80% of initial PCE was 16.5% (Figure 3-5d). In contrast, the PM7-
Thy10-based IS-PSC showed significantly enhanced stretchability with a strain at PCE80% of
43.1%. This difference is attributed to stretchability of the active layer as the other layers are all
same. Importantly, the PM7-Thy10-based IS-PSC shows a combination of champion stretchability
and PCE among all reported high performance IS-PSCs (Figure B-16 and Table B-6). Therefore,
PM7-Thy10 successfully addresses the trade-off between mechanical robustness and photovoltaic
performance.61–64
3.3 Conclusion
In summary, we demonstrated IS-PSCs with both high performance and stretchability by
designing a series of H-bonding incorporated PM7-ThyX PDs. The PM7-Thy PDs exhibited
stronger aggregation and enhanced crystalline properties attributed to H-bonding assisted
intermolecular assembly between the thymine groups. In particular, the impact of H-bonding was
maximized for the PM7-Thy10-based blend which showed a higher Jsc and FF with a superior PCE
of 17.1% compared to the PM7 blend with a PCE of 16.0%. Additionally, the COS value of the
PM7-Thy10 blend was dramatically improved to 13.7%, which was 5 times higher than the PM7
blend. Importantly, PM7-Thy10 based IS-PSCs showed a record PCE (13.7%) and stretchability
(strain at PCE80%= 43.1%) among all reported IS-PSCs. As such, we report an effective design
principle for future wearable electronics.

98

99
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Chapter 4: Polymer Acceptor with Hydrogen Bonding Functionality for Efficient and
Mechanically Robust Ternary Organic Solar Cells
4.1 Introduction
Organic solar cells (OSCs) have been of interest as the power source for wearable electronics
due to their remarkable advantages of being lightweight, semi-transparent, and flexible. Over the
past few years, the development of polymer donors (PDs) and small molecule acceptors (SMAs)
for the active layer of OSCs has enabled rapid improvement in the OSC efficiency, now exceeding
18-19% power conversion efficiency (PCE).1-17 PDs and SMAs containing multiple fused rings are
generally used to enhance light absorption and charge transport in OSCs, leading to higher
efficiency. However, these rigid structures lead to poor stretchability in their blend films due to
their crystalline properties. Typically, the crack onset strain (COS) value of high-performance
PD:SMA blend films is less than 3%.18, 19 Therefore, it is necessary to introduce a novel strategy
for the simultaneous improvement of mechanical and electrical properties in OSCs.
Ternary strategies have been demonstrated as a successful and simple method to satisfy
differing demands for properties in OSC.20-22 The introduction of a third ductile component into
PD:SMA binary blends can be an effective and straightforward strategy to enhance the overall
stretchability of the films. As an example, soft materials such as flexible elastomers (i.e.
poly(dimethylsiloxane) (PDMS), or styrene–ethylene–butylene–styrene (SEBS)) were introduced
to PD:SMA blends to augment the stretchability of the blend film.23-25 Although these elastomers
have a much higher stretchability (COS > 100%) than the PD or SMA, introducing such elastomers
as the third component has two serious drawbacks. First, such elastomers generally exhibit
insulating properties due to their non-conjugated structures, so a higher portion of these elastomers

107
will very likely reduce the PCE of OSCs.23, 25 Second, these elastomers show poor molecular
compatibility with the PD or SMA, and therefore tend to cause large scale phase separation.
25
Cracks under mechanical stress usually occur at the interface of the elastomer and the brittle
PD:SMA and within the delicate SMA domain, so these strategies show clear limits.19 Thus, the
focus has been on introducing additional electronically active components such as conjugated
polymers into PD:SMA blends to prevent crack propagation. Among such conjugated polymer
additives, using naphthalene diimide (NDI)-based polymers as the third component is an attractive
method due to excellent electron mobility and complementary absorption to state-of-the-art
PD:SMA blends. For instance, Lee et al. investigated the effect of an NDI-based polymer additive
on PCE and COS in OSCs using poly[[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-
bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)] (P(NDI2OD-T2), N2200) with ultra-high
molecular weight (Mw > 250 kg mol-1
).18 By optimizing the content of N2200 in the active layer,
they demonstrated that a proper ratio of N2200 can increase the PCE and COS simultaneously.
However, achieving synthetic control for very high Mw for a broad range of different types of
polymers presents a significant practical challenge. The use of such high-Mw polymers can also be
a challenge due to limited processability resulting from reduced solubility. Additionally, it is well
known that N2200 with a low Mw has a negative impact on OSCs because NDI-based polymers
cannot act as tie molecules in the active layer if the molecular weight is not high enough.
26, 27 Thus,
it is important to develop a more generally accessible additive design for electronically active
polymers with enhanced molecular interaction (such as intrachain and interchain interactions) for
PD:SMA blends.
Introducing functional groups exhibiting dynamic bonding into a conjugated polymer is a
simple and effective strategy to enhance the intermolecular interaction and stretchability of

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materials. Among several dynamic bonds, hydrogen bonding (H-bonding) is a plausible candidate
due to its strong bonding energy (10–40 kJ mol−1
), which is significantly higher than other
secondary interactions (dipole-based interactions (2–20 kJ mol−1
) or London dispersion forces
(0.05–10 kJ mol−1
)).28-31 The effects of H-bonding in organic field-effect transistors (OFETs) and
OSCs are well demonstrated.32, 33 For instance, Liu et al. demonstrated that an amide H-bonding
functionalized polymer (PCTZ-T) can achieve higher hole mobility (µh = 1.98 cm2 V-1
s
-1
) than
the reference polymer (µh = 0.076 cm2 V-1
s
-1
) due to the enhanced intermolecular interaction in
OFETs.
34 As another example, Lee et al. designed a new PD with an amide H-bonding spacer in
the polymer backbone.35 They investigated the intermolecular interaction in the PD:SMA blend
and the stretchability of the blend films. Interestingly, the H-bonding functionalized PD (PhAm)
showed enhanced intermolecular interaction with the Y7 SMA and exhibited higher stretchability
(COS of PhAm:Y7 blend film = 13.8%) than the PM6:Y7 reference blend (COS = 1.8%). From
these studies, it is clear that H-bonding functionalized polymers can enhance the overall molecular
interactions and contribute to improvement in electrical and mechanical properties.
Herein, we report a new stretchable polymer acceptor (PA) additive for ternary blends, N2200-
ThyDap, which comprises an NDI-based backbone and the H-bonding functionalities Thymine
(Thy) and Diaminopyrazine (Dap). Thy and Dap are two complementary H-bonding groups that
are able to form strong multi-point H-bonds, which have been widely used in supramolecular
assembly and molecular recognition.36-38 We introduce this polymer acceptor into the well-known
binary OSC blend system consisting of the poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophene2-yl)-benzo[1,2-b:4,5-b′]-dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)-
benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione)) (PM6) donor and 2,2′-((2Z,2′Z)-((12,13-bis(2-
butyloctyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-

109
e]thieno[2′,3′:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno[2′,3′:4,5]thieno[3,2-b]indole-2,10-
diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-
diylidene))dimalononitrile (Y6-BO) SMA.39, 40 Notably, the PM6:Y6-BO:N2200-ThyDap ternary
blend showed a higher photovoltaic performance (PCE = 16.4%) than the PM6:Y6-BO binary
blend (PCE = 15.4%) or the analogues PM6:Y6-BO:N2200 blend (PCE = 14.7%). Furthermore,
the ternary PM6:Y6-BO:N2200-ThyDap system exhibited enhanced mechanical properties (COS
= 4.8%) relative to the reference PM6:Y6-BO binary (COS = 2.1%) and N2200 containing ternary
blend (COS = 2.4%).

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4.2 Results and Discussion
4.2-1. Polymer Design, Synthesis and Characterization
Figure 4-1 (a) Molecular structures of two polymer additives, N2200-ThyDap and N2200. (b)
Depiction of interaction between the Thy and Dap unit. (c) Molecular structures of PM6 PD and Y6-
BO SMA.
To investigate the impact of H-bonding functionality in an electronically active ternary
additive on OSC performance, reference polymer N220041 and H-bonding incorporated NDIbased polymer (N2200-ThyDap) were synthesized (Figure 4-1a and Figures 4-1-4). Thymine
and diaminopyrazine functional groups were introduced to the N2200 polymer backbone to afford
H-bonding ability to the PA. N2200-ThyDap was synthesized by Stille polycondensation of 6-

111
((5,8-dibromo-6,7-difluoroquinoxalin-2-yl)oxy)hexyl-2-(5-methyl-2,4-dioxo-3,4-
dihydropyrimidin-1(2H)-yl)acetate (Q-Thy),42 the novel monomer 6-((2,6-
dihexanamidopyrimidin-4-yl)oxy)hexyl-2,5-dibromothiophene-3-carboxylate (T-Dap), 4,9-
dibromo-2,7-bis(2-octyldodecyl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (NDI),
and 5,5'-bis(trimethylstannyl)-2,2'-bithiophene. Detailed information about the synthesis of the
novel T-Dap monomer and N2200-ThyDap is described in the Supporting Information. N2200
and N2200-ThyDap were synthesized with similar number-average molecular weight (Mn) (Table
4-1). The dibromo monomers, Q-Thy, T-Dap, and NDI, were used in a molar feed ratio of 0.05,
0.05, and 0.90, respectively. The 1
H nuclear magnetic resonance (NMR) spectrum of N2200-
ThyDap was measured to calculate the actual molar ratio between the functional groups, which is
nearly the same as the feed ratio (Figure C-5).
Table 4-1 Material properties of PM6 PD, Y6-BO SMA and the two PAs used in this study
Material
Mn (Ð)
a
[kg mol-1
]
λmaxsol b
[nm]
λmaxfilm c
[nm]
εmaxfilm c
[× 104 cm−1
]
Eg
opt d
[eV]
Tm
e
[
o
C]
∆Hm
e
[J g-1
]
PM6 132 (2.1) 611 615 7.8 1.83 - -
N2200 18.9 (2.1) 648 702 3.9 1.46 307 7.1
N2200-
ThyDap 18.5 (2.5) 694 696 3.5 1.49 299 5.6
Y6-BO - 733 810 12.5 1.40 - -
a
Determined by gel permeation chromatography (GPC) using 80 o
C ortho-dichlorobenzene and calibrated
with the polystyrene standards; b
Measured from the UV-Vis spectra in chloroform solution; c
Measured
from the UV-Vis film spectra; d
Estimated from the film UV-Vis spectra using Eg
opt = 1240/λ; e
Measured
from the second cycle using differential scanning calorimetry.

112
Figure 4-1b depicts the well-known H-bonding interaction between Thy and Dap functional
groups. The capacity for H-bonding interaction between Thy and Dap units is supported by the 1
H
NMR peak shift in monomer mixtures (Figure C-6a and C-6b). In this case, all the N-H protons
including the two N-H protons from T-Dap and the N-H proton from Q-Thy clearly exhibited peak
shifts after mixing the two monomers together. Specifically, the two N-H protons of T-Dap shift
from 9.54 ppm and 9.06 ppm to 9.47 ppm and 8.88 ppm, respectively. Additionally, the signature
downfield shift of the thymine N-H proton in the Thy-Dap complex is observed from 8.01 ppm to
8.42 ppm.43, 44 N2200-ThyDap was designed as a third component for OSC active layers with the
intention of inducing strong inter and intramolecular H-bonding interactions, which can benefit
the overall stretchability of the blend film by acting as tie-molecules. PM6 and Y6-BO were
selected as PD and SMA for the reference binary blend due to their excellent absorption properties
and mobility (Figure 4-1c).
40

113
Figure 4-2 (a) Normalized thin film UV-Vis spectra and (b) energy levels of the materials used in
this study. (c) The second heating cycle and the first cooling cycle from differential scanning
calorimeter (DSC) of the N2200 and N2200-ThyDap. (d) Stress-Strain curve of neat PA films. (e)
Optical microscopy (OM) pristine film images during tensile tests.
We first investigated the properties of the individual components of N2200 and N2200-
ThyDap. Both N2200 and N2200-ThyDap showed complementary absorption with PM6 PD and
Y6-BO SMA (Figure 4-2a and C-7). The absorption coefficient values of N2200 and N2200-
ThyDap at 700 nm were similar, 3.9 and 3.5 × 104 cm−1
, respectively. This indicates that
introducing Thy and Dap units into N2200 does not have a significant impact on the absorption
ability of N2200. The energy levels of all materials were estimated using the cyclic voltammetry

114
(CV) (Figure 4-2b and C-8). N2200 and N2200-ThyDap showed a similar highest occupied
molecular orbital energy level (N2200 = − 5.95 eV and N2200-ThyDap = − 5.96 eV). Importantly,
both PAs showed well-aligned energy levels with the PM6 PD.
DSC and grazing incidence X-ray scattering (GIXS) were performed to compare the crystalline
properties of the two PAs (Figure 4-2c and Figure C-9-C-11). First, the thermal properties of the
neat PAs in the bulk state were investigated by DSC. The second heating cycle and first cooling
cycle in DSC were used. Interestingly, N2200 showed an enhanced crystalline transition compared
to N2200-ThyDap where N2200 showed a higher melting temperature (Tm = 307 o
C) and melting
enthalpy (∆Hm = 7.1 J g−1
) than N2200-ThyDap (Tm = 299 o
C and ∆Hm = 5.6 J g−1
). The crystalline
properties in the thin film state were compared using the GIXS spectra of neat PA films (Figure
C-10). N2200 showed a sharp and distinct (100) peak along the in-plane (IP) direction and (010)
peak along the out-of-plane (OOP) direction as well as a (200) peak along the IP direction,
indicating a highly ordered packing arrangement in N2200.
45, 46 In comparison, N2200-ThyDap
showed more poorly defined packing. We infer that randomized incorporation of functionalized
quinoxaline and ester-thiophene units diminish the ability of N2200-ThyDap to crystallize as
effectively as the more structurally regular N2200.
41, 47 Further, the NDI unit has a significantly
larger and more planar structure than both the quinoxaline and ester-thiophene units and most NDI
based polymers tend to generate significant crystallization.48, 49 Therefore, partial replacement of
the NDI unit with quinoxaline and ester-thiophene units in the polymer backbone could lead to a
less crystalline polymer and have some degree of impact on polymer properties even in the absence
of Thy and Dap functional side chains. Additionally, the regio-random placement of the side chains
of Q-Thy and T-Dap likely plays a role in reducing order relative to N2200. Consequently, we

115
expect that the N2200-ThyDap film would include a larger fraction of amorphous domains
compared to the N2200 film, as evidenced by GIXS and DSC.
The tensile property of the neat PA films was examined to investigate the impact of Thy and
Dap groups of the N2200-ThyDap on their stretchability.15, 18, 50-57 In order to exclude the impact
of the substrate and elucidate the intrinsic tensile properties of the neat PA films, a pseudo freestanding tensile test method was performed to obtain the stress-strain curve and measure the elastic
moduli (E), COS, and toughness (Figure 4-2d-e and Table C-1).
51 N2200-ThyDap exhibited a
18-fold enhanced stretchability (COS = 28.2%) compared to N2200 (COS = 1.5%) (Figure 4-2d
and Table C-1). Accordingly, the toughness value of N2200-ThyDap film (7.2 MJ m−3
) is 72 times
greater than N2200 film (0.1 MJ m-3
). As shown in OM images of the neat PA films during
stretching (Figure 4-2e), the N2200 film showed breaks before the plastic deformation region
(COS < 3%), whereas N2200-ThyDap film exhibited plastic deformation during stretching and
much higher mechanical strength.18, 27, 58 Considering the Mn of N2200 and N2200-ThyDap is
similar (~19 kg mol−1
), the improved stretchability of the N2200-ThyDap film is mainly attributed
to enhanced intermolecular interaction stemming from the introduction of Thy and Dap functional
groups. The reversible breakage and formation of H-bonding interactions likely contributes to
stress dissipation during mechanical stretching.59, 60 Partial replacement of NDI units with
randomly distributed quinoxaline and ester-thiophene units in N2200-ThyDap indeed reduces the
overall crystallinity of the PA, which might also benefit the mechanical properties due to the
relatively less crystalline polymer phases. We measured the viscosity values (ηsp) of pure
chloroform (CF, processing solvent), N2200 CF solution in 10 mg mL-1 concentration, and N2200-
ThyDap CF solution in 10 mg mL-1 concentration (Figure C-12 and Table C-2). It was found that
N2200-ThyDap solution (1.58 mPa·s) showed higher viscosity than N2200 solution (0.65 mPa·s).

116
This result supports the higher intermolecular interaction between N2200-ThyDap than N2200
through the hydrogen bonding of Thy and Dap units.
4.2-2. Photovoltaic and Electrical Properties of Blend Films
Figure 4-3 Photovoltaic performance of PM6:Y6-BO OSCs with polymer additives; (a) J-V curves.
(b) PCE distribution with Gaussian fitting. (c) EQE response spectra. (d) Jph vs. Veff curves.

117
Table 4-2 Photovoltaic parameters of OSCs.
System
Weight Ratio
(PD:SMA:PA)
Voc
[V]
Jsc
[mA cm−2
]
cal. Jsc
[mA cm−2
]
FF
PCEavga
[%]
PCEmax
[%]
PM6:Y6-BO 1:1.2:0 0.81 25.94 25.56 0.73 15.28 15.41
PM6:Y6-BO:
N2200
1:1.08:0.12 0.84 25.38 25.32 0.69 14.28 14.65
PM6:Y6-BO:
N2200-ThyDap
1:1.08:0.12 0.85 27.56 27.10 0.70 16.26 16.36
a
Average values were calculated from at least 10 different cells.
The photovoltaic and electrical properties of OSCs were investigated by comparing the
PM6:Y6-BO binary system with PM6:Y6-BO:PA ternary systems using a conventional device
configuration as described in the Supporting Information. In the ternary system, the weight ratio
between the PD and the sum of (SMA+PA) was fixed as 1:1.2. Thus, the discussed PA percentages
in the OSC blends correspond to the weight percentage of PA in the total acceptor (SMA and PA).
For instance, a blend with 10 wt% of the PA indicates a PM6:Y6-BO:PA weight ratio of 1:1.08:0.12.
The current density-voltage (J-V) curves and detailed photovoltaic performance of the devices
were analyzed, as shown in Figure 4-3a and Table 4-2. The PM6:Y6-BO binary reference showed
a PCE of 15.41%, with open-circuit voltage (Voc), short-circuit current density (Jsc), and fill factor
(FF) values of 0.81 V, 25.94 mA cm-2
, and 0.73, respectively. This PCE value is similar to
previously reported results.
61 Interestingly, the PM6:Y6-BO blend system with incorporation of
10 wt% of N2200-ThyDap exhibited an enhanced PCE of 16.36% with a higher Jsc value of 27.56
mA cm-2
. However, the performance of the PM6:Y6-BO:N2200 10 wt% blend exhibited reduced
PCE and Jsc with values of 14.65% and 25.38 mA cm-2
, respectively. In comparison, the ternary
blends containing 20 wt% of PA showed lower PCE than the cases with 10 wt% of PA (Table C-

118
3). This result agrees well with the PCE trend of the PM6:Y6-BO:N2200 with low Mn (less than
20 kg mol-1
) of N2200 additives.18 The 20 wt% N2200-ThyDap ternary blend showed Jsc = 26.30
mA cm-2 and PCE =14.14% while the 20 wt% N2200 ternary blend showed PCE = 13.14% and Jsc
= 23.27 mA cm-2
. The Gaussian PCE distributions for the 10 wt% OSCs in Figure 4-3b show that
each system has minimal deviation in PCE values. From the external quantum efficiency (EQE)
spectra displayed in Figure 4-3c, the PM6:Y6-BO:N2200-ThyDap based OSC showed higher
EQE response in the absorption range of the SMA (650-900 nm) compared to the other blends. All
calculated Jsc values from EQE were well matched with the device Jsc within an error margin of
2%.
The primary photovoltaic parameter contributing to enhanced PCE in the PM6:Y6-BO:N2200-
ThyDap ternary blend OSC is the enhanced Jsc value compared with other blends. To understand
the increase in Jsc caused by introducing N2200-ThyDap, the charge generation and transport
properties of the OSCs were investigated (Figure 4-3d and Table C4-C5). First, the exciton
dissociation probability (P(E,T)) of OSCs was determined from photocurrent density (Jph) versus
effective voltage (Veff). The P(E,T) values were calculated by dividing the Jph under short-circuit
conditions by the saturated current density (Jsat) at Veff = 3 V.62 The introduction of N2200-ThyDap
into the PM6:Y6-BO blend resulted in the highest P(E,T) value of 96.9% among the all blends,
contributing to the observed highest Jsc. This result indicates that introducing N2200-ThyDap into
the active layer facilitates exciton dissociation at the interface between donor and acceptor.
. To elucidate the origin of the high Jsc in the N2200-ThyDap incorporated OSC, density
functional theory (DFT) simulation at the B3LYP/6-31G (d,p) level was performed on N2200 and
N2200-ThyDap (Figure C-13 and C-14). We compared the electrostatic potential (ESP) and the
dipole moment between N2200 and N2200-ThyDap. Interestingly, N2200-ThyDap exhibited a

119
significantly higher dipole moment (6.53 debye) than N2200 (2.37 debye) due to the polar Hbonding incorporated side chains, as shown in Figure C-13c and C-14c. We postulate this higher
dipole moment of N2200-ThyDap facilitates more efficient exciton dissociation.63, 64
Electron mobilities (µe) of the pristine PAs and blend films, as well as hole (µh) mobilities of
the blend systems were analyzed by the space-charge-limited current (SCLC) method (Table C4
and C5).65 For the neat PA films, the µe of N2200 and N2200-ThyDap were 6.71 × 10-5 and 4.70 ×
10-5 cm
2 V-1
s
-1
, respectively. For blend films, the µe values of PM6:Y6-BO, PM6:Y6-BO:N2200,
and PM6:Y6-BO:N2200-ThyDap were 1.24 × 10-4
, 1.76 × 10-4 and 9.69 × 10-5 cm
2 V-1
s
-1
, which
implies comparable electron mobilities. We additionally compared the ratio between the µh and µe
values of the blend systems. Well-balanced mobility values are associated with higher FF values.66,
67 The PM6:Y6-BO:N2200-ThyDap ternary blend showed the most balanced charge transport
ability (µh/µe = 1.29) compared to PM6:Y6-BO binary (µh/µe = 1.58) and PM6:Y6-BO:N2200
ternary blend (µh/µe = 1.64) which explains the high Jsc and FF values of the PM6:Y6-BO:N2200-
ThyDap ternary blend-based OSC.
4.2-3. Mechanical and Morphological Properties of Blend Films

120
Figure 4-4 (a) Stress-Strain curves of PM6:Y6-BO binary blend and PM6:Y6-BO:PA ternary blends
(wt% value of PA indicates the weight of PA compared to (PA + SMA) weight). (b) OM images of
blend films during tensile tests.
Table 4-3 Tensile properties of the blend films.
Blend
(Weight Ratio)
Ea
[GPa]
COSa
[%]
Toughnessa
[MJ m-3
]
PM6:Y6-BO
(1:1.2)
0.90 ± 0.02 2.10 ± 0.30 0.22 ± 0.09
PM6:Y6-BO:N2200
(1:1.08:0.12)
0.81 ± 0.02 2.42 ± 0.14 0.30 ± 0.02
PM6:Y6-BO:N2200-ThyDap
(1:1.08:0.12)
0.76 ± 0.01 4.81 ± 0.72 0.75 ± 0.31
We have also compared the stretchability of the blend films, which is one of the most important
properties for application in wearable devices.15, 50-57 The stretchability of the blend films were
also estimated from a pseudo free-standing tensile test to quantify elastic moduli (E), COS, and
toughness (Figure 4-4, Table 4-3, Figure C-15 and Table C-6). The blend films were prepared

121
using the same conditions as for the active layer preparation in OSC fabrication. The PM6:Y6-BO
blend film presented a brittle property due to the rigid chemical structures, showing a COS of only
2.1%.18 The incorporation of 10 wt% of N2200 into the blend slightly increased the stretchability
(COS = 2.4%) likely because the pristine COS value of the N2200 PA film (COS = 2.1%) shows
higher stretchability than the pristine Y6-BO film (COS ~ 0%).68 In comparison, introducing the
H-bonding functionalized PA significantly increased the stretchability of the blend film where
PM6:Y6-BO:N2200-ThyDap showed COS of 4.8%. The small fraction (10 wt%) and relatively
low Mn of the PA additive in the ternary blend likely dilutes the impact of H-bonding postulated to
account for the high COS in pristine N2200-ThyDap films. Indeed, the content of H-bonding
groups in the blend film is small since N2200-ThyDap is the third and minority component.
However, even a small content of H-bonding groups can dramatically change polymer properties.
For instance, Chen et al. introduced only two thymine units into the chain ends of a polymer and
found the toughness of the thymine incorporated polymer (155.17 MPa) was 80 times higher than
the reference polymer (1.9 MPa).
69 In result, the enhanced stretchability of PM6:Y6-BO:N2200-
ThyDap compared to the other blends is still attributed to the enhanced intermolecular interactions
of N2200-ThyDap within the blend through introduction of Thy and Dap functional
groups.
35,42,59,70 To support this hypothesis, we compared the stretchability of the 20 wt% PA
incorporated films (Figure C-15 and Table C-6). Here, the 20 wt% N2200 incorporated ternary
blend film showed a similar stretchability (COS = 2.5%) compared with the 10 wt% N2200
incorporated blend film (COS = 2.4%). However, 20 wt% of N2200-ThyDap led to a higher
stretchability (COS = 5.5%) compared to 10 wt% of N2200-ThyDap (COS = 4.8%). These results
demonstrate that the reversible and dynamic bonding within the blend film likely improved
mechanical robustness, resulting in higher COS values.35, 42

122
Interestingly, although the low molecular weight H-bonded N2200-ThyDap exhibits an
excellent COS (~ 30%), the toughness of the N2200-ThyDap (7.2 MJ m-3
) is only a bit higher than
half of the value for the high molecular weight N2200 (12.0 MJ m-3
) from previously reported
results.18 We hypothesize that both COS and toughness are critical for a third component that will
be introduced into the blend. The high molecular weight N2200 not only has an excellent COS but
also has significantly higher toughness. Additionally, as shown previously, high Mn N2200 can act
as a ‘tie molecule’ in ternary blend films, which can effectively dissipate strain energy during
stretching.18 An optimal study should be based on an extremely high molecular weight N2200 with
H-bonding features, which is however a synthetic challenge.

123
Figure 4-5 (a) GIXS spectra of PM6:Y6-BO binary and PM6:Y6-BO:PA ternary films along the IP
direction and (b) OOP direction. (c) Lorentz-correlated resonance soft X-ray scattering (RSoXS)
profiles of blend films.
Table 4-3 Morphological properties of blend films.
Blend (Weight Ratio)
d010a
[Å]
Lc(010)a
[nm]
Domain Sizeb
[nm]
√TSIb
PM6:Y6-BO (1:1.2) 3.5 2.1 18 0.89
PM6:Y6-BO:N2200 (1:1.08:0.12) 3.5 4.0 21 0.99
PM6:Y6-BO: N2200-ThyDap (1:1.08:0.12) 3.5 2.0 21 1.00
a
Estimated from the GIXS profiles of blend films along the OOP direction. b
Estimated from the RSoXS
profiles of all blend at the 285.0 eV. √TSI indicates the intensity the relative domain purity, estimated
from the total scattering intensity of the RSoXS profiles.

124
We compared the blend morphology using GIXS and RSoXS of all blend films (Figure 4-5,
Figure C-16 and Table 4-4). All films were prepared using the same conditions as for OSC
fabrication. For the blend GIXS, we compared the (010) peak along the OOP direction because all
materials showed distinct (100) peak along the IP direction and (010) peak along the OOP direction
(Figure C-10 and C-11). The d010 and Lc(010) values were calculated using the Scherrer equation.71
The introduction of N2200 into the PM6:Y6-BO blend resulted in an increased Lc(010) value (from
2.1 nm (PM6:Y6-BO) to 4.0 nm (PM6:Y6-BO:N2200)). On the other hand, the PM6:Y6-
BO:N2200-ThyDap ternary blend showed similar Lc(010) (2.0 nm) values compared to PM6:Y6-
BO binary blend due to the weaker crystalline nature of N2200-ThyDap compared to N2200. We
compared the domain size and purity of all blends using RSoXS profiles (Figure 4-5c). In the
RSoXS profiles, all blends showed similar small domain size (from 17 to 22 nm) and domain
purity (from 0.89 to 1). This indicates that incorporated 10 wt% of N2200 and N2200-ThyDap in
the ternary blend did not significantly affect the phase-separated nature of the ternary blend.
Further, all blends showed appropriate domain sizes and purities for efficient charge generation
and transport. From the combined results, it was found that the use of N2200-ThyDap additives is
helpful in bridging isolated domains of the SMAs by H-bond assisted intermolecular interactions
and in providing more amorphous behavior compared to that of N2200.72 This contributes to
simultaneous increases in the stretchability and PCE of the ternary OSC.

125
4.3. CONCLUSIONS
In this study, we developed the new PA N2200-ThyDap based on N2200 but containing Thy and
Dap functionalized monomers. Introducing N2200-ThyDap as a third component into the
PM6:Y6-BO PD:SMA binary blend OSC (PCE = 15.4%) led to an enhanced performance
(PM6:Y6-BO:N2200-ThyDap, PCE = 16.4%). Improved charge dissociation due to enhanced
intermolecular interaction within the PM6:Y6-BO:N2200-ThyDap ternary blend enables higher
photovoltaic parameters of Jsc and PCE. Additionally, the PM6:Y6-BO:N2200-ThyDap ternary
blend film showed higher stretchability (COS = 4.8%) compared to the reference PM6:Y6-BO
blend (COS = 2.1%) and PM6:Y6-BO:N2200 ternary blend film (COS = 2.4%). This enhancement
is attributed to the excellent stretchability of neat N2200-ThyDap (COS = 28.2%) likely stemming
from enhanced intermolecular interaction compared to neat N2200 film (COS = 1.5%) that have a
comparable Mn to N2200-ThyDap. Therefore, the introduction of an H-bonding capable N2200-
ThyDap PA into the PD:SMA blend enabled concurrently improved electrical and mechanical
properties. As such, this work establishes an approach to the design of polymer additive
components in ternary blends for stretchable OSCs for use in wearable applications.

126
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64. Kim, G.-U.; Sun, C.; Lee, D.; Choi, G.-S.; Park, J. S.; Seo, S.; Lee, S.; Choi, D.-Y.; Kwon,
S.-K.; Cho, S.; Kim, Y.-H.; Kim, B. J., Effect of the Selective Halogenation of Small Molecule
Acceptors on the Blend Morphology and Voltage Loss of High-Performance Solar Cells. Adv.
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Hexylthiophene). Phys. Rev. B 2004, 70, 235207.
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132
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133
Biographical Sketch
Qingpei Wan received his B.E. in applied chemistry from the Shenzhen University in 2016 and
earned his Master of Science degree in Materials Engineering from the University of Southern
California in 2018. Currently, he is performing his Ph.D. studies under the guidance of Prof. Barry
C. Thompson at the University of Southern California. His research is centered on the design,
synthesis and application of organic functional materials for organic electronics.

134
Appendix A
Chapter 2: Unprecedented Efficiency Increase in a Ternary Polymer Solar Cell Exhibiting
Polymer-Mediated Polymorphism of a Non-Fullerene Acceptor
A.1 Materials and Methods
All reagent and solvents from commercial sources were used without further purification,
unless otherwise note. All reactions were performed under dry N2 in glassware that was pre-dried
in oven, unless otherwise noted. 1
HNMR spectra were recorded in CDCl3 on a Varian Mercury
400NMR Spectrometer. PTQ10 and IDIC were synthesized according to the reported literatures.
The PTQ10 has a number average molecular weight (Mn) of 15.3kg/mol and a PDI of 3.0.
For polymer thin-film measurements, solutions were spin-coated onto pre-cleaned glass slides
from the solutions with the corresponding solvent. Typically, neat films were processed from
chloroform with 7mg/ml and the conditions for blend films were identical as the device processing
conditions. UV-Vis absorption spectra were obtained on an Agilent Cary 60 spectrophotmeter.
The thickness of the thin films and grazing-incidence X-ray diffraction (GIXRD) measurements
were obtained using a Rigaku Diffractometer Ultima IV using radiation source (λ=1.54 Å) in the
reflectivity and grazing-incidence mode, respectively.
Surface energy studies of neat films were performed on a Rame-Hart Instrument Co. contact
angle goniometer model 290-F1 and analyzed using Surface energy (two liquids) tool implemented
in DROPimage 2.4.05 software. Water and glycerol were used as the two solvents in the two-liquid
model to measure the contact angle and average surface energy values were calculated from Wu
model.

135
Cyclic Voltammetry (CV) was performed on Princeton Applied Research VersaStat3
potentiostat under control of VersaStudio Software. A standard three-electrode cell based on a Pt
wire working electrode, a silver wire pseudo reference electrode (calibrated vs Fc/Fc+ which is
taken as 5.1eV vs vacuum), and a Pt wire counter electrode was purged with nitrogen and
maintained under a nitrogen atmosphere during all measurements. Anhydrous acetonitrile was
purchased from VWR, and TBAPF6 (0.1M) was used as the supporting electrolyte. Films were
made by spin coating the solutions over cleaned ITO substrate and dried over nitrogen prior to
measurement.
Differential scanning calorimetry (DSC) was performed on Perkin Elmer DSC 8000 and TA
instrument Q2000 with 10 °C/min scanning rate. The DSC samples were prepared with dropcasting the solution on a pre-cleaned glass slides. The slides were fully dried in the dark and
nitrogen environment for a different amount of period depending on the solvents. The dried
materials were remove from the slide and transferred to the DSC sample container. All the
temperatures reported in DSC were identified by the instrument.
Device Fabrication and Characterization. All devices were fabricated and characterized in air.
ITO-coated glass substrates (10 Ω/sq, Thin Film Devices Inc.) were cleaned in a sonication bath
sequentially in detergent, deionized water, tetrachloroethylene, acetone, and isopropyl alcohol,
then dried overnight in a nitrogen stream. A thin layer of PEDOT:PSS (Clevios PH500. Filtered
with a 0.45 µm) poly(vinylidene fluoride) syringe filter-Pall Life Sciences was first spin-coated on
the precleaned ITO-coated glass substrates and baked at 120°C for 50 min under vacuum. Binary
solution and ternary solutions in o-DCB were prepared with the polymer concentration of
10mg/ml. The solutions were stirred overnight to completely dissolve in the solvent at 60°C. Then,
the solutions were spin-coated on the top of the PEDOT:PSS layer. After casting the active layers,

136
the films were dried under N2 for 30 min and then placed in the vacuum chamber for aluminum
deposition. Finally, the substrates were exposed to high vacuum (< 2.5 × 10-6 Torr), and aluminum
(100nm) was thermally evaporated at 3-5 Å/s using s Denton Benchtop Turbo IV Coating System
onto the active layer through shadow masks to define the active area of the devices as 5.18mm2
.
The current-voltage (I-V) characteristics of the devices were measured under ambient conditions
using a Keithley 2400 source-measurement unit.
Synthesis of Compound IDID
Figure A-0 synthesis of IDID
An oven dried three-neck flask was vacuum backfilled three times and charged with 200 mg
of 1 (0.303mmol, 1eq.) and 440 mg of 2 (0.3mmol, 10eq.). Then 30 ml of dry chloroform were
added in one portion followed by adding 0.5ml trimethylamine. The mixture was then keep at
room temperature for overnight and poured into water, extracted with chloroform (3x30ml), dried
over MgSO4, filtered and concentrated in vacuo. The crude product was purified by column
chromatography and recrystallization to yield the desired product as a purple solid in 70% yield.
(195.2mg)

137
Figure A-00 1
HNMR Of IDID

138
A.2 Characterization (UV, CV, GIXRD and DSC)
Figure A-1 UV-Vis absorption spectra of IDID thin film spin-coated from chloroform and placed in
a N2 for 30 minutes
Figure A-2 CV scan of IDID film, ELUMO = Eg
opt - EHOMO

139
Figure A-3 GIXRD patterns of thin film processed from o-DCB with blend of PTQ10 and IDID
with/without thermal annealing (120°C for 20mins)
Figure A-4 GIXRD patterns of thin films of IDIC (processed from chloroform with annealing) and
PTQ10:IDIC (processed from o-DCB as cast)

140
Figure A-5 GIXRD patterns of thin film processed from chloroform with blend of PTQ10 and IDID
with/without thermal annealing (120°C for 20mins)
Figure A-6 DSC thermograms of the blend PTQ10 and IDID (1:0.3) during heating cycle with
higher temperature scanning

141
Figure A-7 DSC thermograms of enlarged figure of pink rectangle at the position of Tc, neat IDID
(red), blend of PTQ10 and IDID (1:0.3) (blue)
Figure A-8 DSC thermograms of neat IDIC and blend with PTQ10 (1:0.3, w/w) processed from oDCB upon heating

142
Figure A-9 GIXRD patterns of thin film of PTQ10: PC61BM binary and PTQ10: IDID: PC61BM
ternary blend
A.3 OPV Performance
Table A-1 Mismatch Factor, corrected current, calculated current and EQE error calculation
PTQ10: FRSM:
PC61BM
MM
(Mismatch
Factor)
Jsc
(mA/cm2
)
J(correcte
d)
(mA/cm2
)
J(EQE)
(mA/c
m
2
)
Error
(%)
1:0:1.2 0.99 8.12 8.20 8.10 1.2
1:0.3(IDID):1.2 1.0 10.7 10.7 10.3 3.8
1:0.3(IDIC):1.2 0.94 7.86 8.36 8.55 2.2

143
Figure A-10 External Quantum Efficiency of the corresponding binary (PTQ10: PC61BM=1:1.2)
and ternary blends (PTQ10: FRSM: PC61BM=1:0.3:1.2)
Figure A-11 J-V Curve of the corresponding binary (PTQ10: PC61BM=1:1.2) and ternary blends
(PTQ10: FRSM: PC61BM=1:0.3:1.2)

144
Table A-2 PTQ10, IDID and PC61BM blending test under the same devices fabricating conditions (oDCB)
a Jsc from solar simulator; b no homogeneous films
Blend Jsc
(mA/cm
2
)
Voc
(V)
FF
(%)
PCE(%)
PTQ10: IDID 0.3a 0.92 0.19 0.06
IDID: PC61BMb
- - - -

145
Appendix B
Chapter 3: High Performance Intrinsically Stretchable Polymer Solar Cell with Record
Efficiency and Stretchability Enabled by Thymine Functionalized Terpolymer
B.1 Materials and Methods
Synthesis of monomer and polymer donors
N N
OH
F F
Br Br
N N
O
F F
Br Br
O
3
O
N
NH
O
O
1.
2. Q-Thy
HO OH
3
DIAD
N
NH
O
O
O
OH
DCC, DMAP
1

146
Scheme B-1 Synthetic scheme for monomer and polymer donors (PDs).
(1) Synthesis of Q-Thy monomer
The first step is adapted from the reported literature.1 (200 mg, 0.588 mmol) 5,8-dibromo-6,7-
difluoroquinoxalin-2-ol (Compound 1), triphenylphosphine (177 mg, 0.676 mmol),, and 1,6-
hexanediol (104 mg, 0.882 mmol) were added to a 50 ml three-neck round bottom flask under N2.
Anhydrous THF (35 ml), DIAD (148 mg, 0.735 mmol) was added to the reaction mixture and the
reaction was heated at reflux for 18 h. After cooling, the reaction was quenched with DI water and
extracted in CHCl3. The organic layer was dried over MgSO4 and the solvent was removed after
filtering. The crude product was running through a flash column and used for next step without
further purifications. An oven dried three-neck flask was vacuum backfilled three times and
S
S
S C2H5
C4H9
C2H5
C4H9
S
O O
S
S
S
S
Cl
Cl
C4H9 C2H5
C4H9
C2H5
Sn Sn Br Br
N N
O
F F
Br Br
O
3
O
N
NH
O
O
+ +
BDT-T-Cl BDD Q-Thy
S
S
S
S
Cl
Cl
C4H9 C2H5
C4H9
C2H5
S
S
S C2H5
C4H9
C2H5
C4H9
S S
S
S
S
Cl
Cl
C4H9 C2H5
C4H9
C2H5
F F
N N
O
O
O
N
NH
O
O
3
1-x x
O O
PM7-ThyX (X=0, 5, 10, 20mol%)
Pd(PPh3)4 o-xylene/DMF

147
charged with the crude product from previous step (320 mg, 0.72 mmol), thymine-1-acetic acid
(132.5 mg, 0.72 mmol.), DCC (148.5 mg, 0.72 mmol) and DMAP (8.5 mg, 0.072 mmol). Then 35
ml of dry dichloromethane were added in one portion. The mixture was then keep at room
temperature for overnight and poured into water, extracted with CHCl3 (3x30 ml), dried over
MgSO4, filtered and concentrated in vacuo. The crude product was purified by column
chromatography to yield the desired product as a white solid in a 20% yield over two steps. (72.1
mg). 1
HNMR (500 MHz, CDCl3) δ (ppm): 8.52 (s, 1H), 8.09 (s, 1H), 6.93 (s, 1H), 4.59 (t 2H),
4.43 (s, 2H), 4.22 (t, 2H), 1.94 (s, 3H), 1.91 (m, 2H), 1.72 (m, 2H), 1.47 (m, 2H), 1.26 (m, 2H).
(2) Synthesis of PM7-Thy5
(4,8-bis(5-(2-ethylhexyl)-4-chlorothiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene-2,6-
diyl)bis(trimethylstannane) (BDT-T-Cl) monomer (48.6 mg, 0.05 mmol), 1,3-bis(4-(2-ethylhexyl)
thiophen-2-yl)-5,7-bis(2-alkyl)benzo [1,2-c:4,5-c’]dithiophene-4,8-dione (BDD) monomer (36.4
mg, 0.0475 mmol), Q-Thy monomer (1.51 mg, 0.0025 mmol), and Pd(PPh3)4 (2.5 mg, 0.005 mmol)
were added into a 15 ml Schlenk tube. The mixture of o-xylene (2 ml) and DMF (0.2 ml) was
added under N2 and the solution was degassed for 10 min. The mixture was reacted for 5 hrs in oil
bath at 120 °C and precipitated in methanol and purified by soxhlet under methanol, hexane, and
chlorobenzene. The chlorobenzene fraction was precipitated in methanol (40 mg, 69%). (Numberaverage molecular weight Mn = 186.1 kg mol-1
, Ð = 2.0)
(3) Synthesis of PM7-Thy10
BDT-T-Cl monomer (48.6 mg, 0.05 mmol), BDD monomer (34.5 mg, 0.045 mmol), Q-Thy

148
monomer (3.0 mg, 0.005 mmol) and Pd(PPh3)4 (2.5 mg, 0.005 mmol) were added into a 15 ml
Schlenk tube. Reaction and purification processes are identical as PM7-Thy5. Obtained 42 mg,
Yield = 71%. Mn = 167.6 kg mol-1
, Ð = 2.0
(4) Synthesis of PM7-Thy20
BDT-T-Cl monomer (48.6 mg, 0.05 mmol), (BDD) monomer (30.6 mg, 0.04 mmol), Q-Thy
monomer (6.0 mg, 0.01 mmol) and Pd(PPh3)4 (2.5 mg, 0.005 mmol) were added into a 15 ml
Schlenk tube. Reaction and purification processes are identical as PM7-Thy5. Obtained 39 mg
Yield = 70%. Mn = 99.2 kg mol-1
, Ð = 1.3
Materials: Clevios P VP (AI 4083, Heraeus Co.) was used as a hole-transporting layer in rigid
PSCs and IS-PSCs. The thermoplastic polyurethane (TPU) (AFEL Co.) and Clevios PH1000
(Heraeus Co.) were used as a substrate and bottom electrode in IS-PSCs, respectively. All reagent
and solvents from commercial sources were used without further purification, unless otherwise
noted. All reactions were performed under dry N2 in glassware that was pre-dried in oven, unless
otherwise noted.
Characterizations: 1
H NMR spectra of monomers were recorded in CDCl3 on a Varian Mercury
400NMR Spectrometer at 25 °C. The 1
H NMR spectra of PM7-ThyX series PDs were measured
in 1,1,2,2-Tetrachloroethane-d2 solution and recorded on a Varian Mercury 600NMR
Spectrometer at 100 °C. The Mn and Ð of PDs were measured using gel permeation

149
chromatography (GPC) at 80 o
C by using 1,2-dichlorobenzene as eluent. The GPC measurement
was calibrated using a polystyrene standard. UV-1800 spectrophotometer was used to measure the
aggregation properties of solutions and thin films at room temperature. EC-Lab software with VSP
from BioLogic Science Instruments Co. was used to measure the energy levels of PDs, using
ferrocene as a reference. The Ag/AgCl and Pt electrodes were used as the reference electrode and
counter electrode during the cyclic voltammetry measurement. The crystalline properties of neat
PD films and PD:L8-BO blend films were determined using GIXS analyses, measured at the 3C
beamline in Pohang Accelerator Laboratory. The external quantum efficiency (EQE) spectra were
measured by the K3100 IQX instrument (McScience Inc.) using the xenon arc lamp as a light
source. The intensity of the xenon arc lamp was standardized with an optical chopper (MC 200
Thorlabs) and filtered by a monochromator filter from Newport Co.
Fabrication of PSCs and measurement: Indium tin-oxide (ITO) coated glass was washed in order
of acetone, de-ionized water, and isopropyl alcohol with ultrasonic process. The washed ITO was
dried in the 80 o
C oven to remove the residual solvent. The ITO was treated with ozone-plasma
for 10 min and AI4083 was spin coated on the ITO at 3500 rpm for 30 sec. The AI4083-coated
ITO was annealed at 150 o
C for 15 min. The active layer solution was prepared by weighing the
PD:L8-BO as 9 mg/ml concentration (weight ratio between PD:L8-BO = 1:1.2) in chloroform. The
1-chloronaphtalene was used as the solvent additive as the 0.4 vol% of active layer solution. The
active layer solution was stirred at 55 o
C for 1 hr and spin-coated on the ITO at 2500 rpm for 30
sec. The thickness of active layer for all systems were in 90 – 100 nm range, measured by the
atomic force microscopy (AFM). The spin-coated ITOs were annealed at 100 o
C for 10 min. The
poly[(9,9-bis(3′-((N,N-dimethyl)-nethylammonium)propyl)-2,7-fluorene)-alt-5,5′-bis-(2,2′-

150
thiophene)-2,6-naphthalene-1,4,5,8-tetracaboxylic-N,N′di(2ethylhexyl)imide] dibromide
(PNDIT-F3N-Br) was used for the electron transporting layer and dissolved in methanol as 1
mg/ml concentration. The PNDIT-F3N-Br solution was spin-coated at 3000 rpm for 30 sec. The
Ag (120 nm) was used as the electrode and deposited under high vacuum (~10-6 Torr) using
evaporation chamber. The optical microscopy (OM) was used to measure the area of mask used
during the photovoltaic parameters measurement. The area of mask was 0.04 cm2
. Keithley 2400
SMU instrument was used to measure the photovoltaic efficiency of the PSCs under an Air Mass
1.5 G solar simulator (100 mW cm−2
, solar simulator: K201 LAB55, McScience Inc.), satisfying
the Class AAA, ASTM Standards. K801SK302 (McScience Inc.) was used as a standard silicon
reference cell.
Fabrication ofIntriscially-Stretchable PSCs(IS-PSCs): The IS-PSCs with a device configuration
(TPU/modified PH1000/AI4083/photoactive layers/(PNDIT-F3N-Br)/eutectic
gallium−indium(EGaIn)) were fabricated. The modified PH1000 solution containing dimethyl
sulfoxide (DMSO) 5 vol%, 3-Glycidoxypropyltrimethoxysilane(GOPS) 0.15 vol%, and
fluorosurfactant 0.5 vol% was stirred overnight. Then, the modified PH1000 was spin-coated at
1000 rpm for 30 sec on the ozone plasma-treated TPU substrate and baked to 110 °C for 20 min
in air. Next, AI4083 hole transporting layer was spin-coated at 3500 rpm for 30 sec on the
PH1000/TPU and dried to 100 °C for 15 min. The preparation of active layer solutions and thermal
annealing process were same as the rigid-PSC fabrication. Then, a PNDIT-F3N-Br solution in
methanol with 1 mg/mL concentration was spun-cast at 3000 rpm for 30 sec. Finally, EGaIn liquid

151
metal was sprayed through a deposition mask to complete the IS-PSC fabrication. The PCE
measurement during the stretching was performed using 0.04 cm2 mask.
Space-charge-limited current (SCLC) measurements: Hole mobilities of neat PD films and blend
films, and electron mobilities of the blend films were measured using the SCLC method. The
device structure for measuring hole mobility was ITO/PEDOT:PSS/active layer (PD:L8-BO
blend)/Au. ITO/zinc oxide/ active layer (PD: L8-BO blend)/poly[(9,9-bis(3′-(N,Ndimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN)/Al structure was used
for the measurement of electron mobility. The PD:L8-BO blend films were prepared under the
same conditions as described for the fabrication of PSCs. A voltage range from 0 to 6 V was
applied to gauge the current-voltage measurements and then fitted by the Mott-Gurney equation.
JSCLC =
!
"
��$�
&'
()
ε0 represents the permittivity of free space (8.85 × 10-14 F cm-1
), ε is the relative dielectric constant
of the polymer films, µ is the mobility of the charge carrier, V is the calculated potential across the
SCLC device (V = Vapplied - Vbi - Vr, which Vbi is the potential of built-in state and Vr is the degree
of voltage drop). The thickness of films was measured by AFM.
Pseudo-freestanding tensile test: In the pseudo free-standing tensile method, the films were
prepared under the same condition as the PSC fabrications. The films were spin-casted onto the
polystyrene sulfonic acid-coated glass substrate, and cut into a dog-bone shape by a femtosecond
laser. Then, the films were floated onto the water surface, and attached to the grips by Van-der

152
Waals interactions. The strain was applied with a fixed strain rate (0.8 ×10-3 s
-1
), and the tensile
load values were measured by a load cell with high resolution (LTS-10GA, KYOWA, Japan).
Elastic modulus was calculated using the least square method for the slope of the linear region in
the stress-strain curve within 0.5 % strain.
Supplementary Figures & Tables
Figure B-1 1
H NMR spectrum of Q-Thy monomer (CDCl3)
9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
f1 (ppm)
-5
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
1.83
2.26
2.19
1.98
3.36
2.18
2.17
2.18
1.00
0.85
0.82
1.26
1.47
1.72
1.91
1.94
4.22
4.43
4.59
6.93
8.08
8.52

153

154
Figure B-2 1
H NMR spectra of PM7-Thy5

155
Figure B-3 1
H NMR spectra of PM7-Thy10

156
Figure B-4 1
H NMR spectra of PM7-Thy20

157
Figure B-5 1
H NMR spectra (Aromatic region) of concentration dependent (1 mM, 5 mM, and 10
mM) Q-Thy in CDCl3 and the corresponding protons and peaks labeled as a, b, and c.
Figure B-6 1
H NMR spectra of concentration dependent (1 mM, 5 mM, and 10 mM) Q-Thy in
CDCl3

158
B.2 Characterization
Figure B-7 Solution UV-vis spectra of PDs in chloroform solution.

159
Figure B-8 Cyclic voltammetry of PDs and ferrocene reference.

160
Figure B-9 (a) Chemical Structure of PM7-ThyX, L8-BO SMA, and the H-bonding between the
Thymine molecule. (b) UV-vis spectra of PDs in thin film state. (c) Energy levels of PDs and L8-BO
SMA.

161
Table B-1 Molecular and electronic properties of the PDs in this study.
PD
Mn (Ð)
(kg mol-
)
a
λmaxsol
(nm)b
λmaxfilm
(nm)c
Eg
opt
(eV)d
EHOMO
(eV)e
ELUMO
(eV)f
PM7 162.3 (2.4) 600 598 1.83 −5.67 −3.84
PM7-Thy5 186.1 (2.0) 610 611 1.84 −5.63 −3.79
PM7-Thy10 167.6 (2.0) 610 611 1.84 −5.63 −3.79
PM7-Thy20 99.2 (1.3) 606 609 1.85 −5.65 −3.80
a)Estimated from the gel permeation chromatograph (GPC) in 80 o
C o-dichlorobenzene with
polystyrene standard. b)Measured from the dilute chloroform solution. c)Measured from the spincoated film from the chloroform solution. d)Calculated from the film UV-vis spectra using Eg
opt =
1240/λ.
e) Estimated from the CV spectra and using EHOMO = −4.8 eV − (Eonset
Polymer −
Eonset
Ferrocene). f) Calculated using ELUMO = EHOMO + Eg
opt.
Figure B-10 EQE spectra of the rigid PSCs

162
Figure B-11 Relationship between the Veff and
Jph

163
Table B-2 Photovoltaic properties of PD:L8-BO blend in rigid solar cell
PD
Voc
[V]
Jsc
[mA cm -1
]
Calcd. Jsc a)
[mA cm -1
]
FF PCEavg
b) PCEmax
PM7 0.91 24.35 24.01 0.74 15.84 16.01
PM7-Thy 5 0.89 23.76 23.48 0.72 14.89 15.39
PM7-Thy 10 0.88 25.64 25.32 0.76 16.83 17.05
PM7-Thy 20 0.90 21.96 22.10 0.72 14.08 14.34
a)
Calculated Jsc values from the EQE spectra. b)Average values estimated from at least 10
devices
Table B-3 SCLC mobilities of the PD:L8-BO blends.
PD µh [cm2 V−1 s
−1
] µe [cm2 V−1 s
−1
] µh/µe
PM7 1.8 × 10−4 3.8 × 10−4 0.47
PM7-Thy5 2.8 × 10−4 4.0 × 10−4 0.85
PM7-Thy10 4.2 × 10−4 3.9 × 10−4 1.07
PM7-Thy20 3.0 × 10−4 3.7 × 10−4 0.81

164
Figure B-12 2D images of GIWAXS PD neat films.
Figure B-13 GIWAXS line-cuts of pristine constituents along the (a) IP direction and (b) OOP
direction.

165
Figure B-14 2D images of GIWAXS PD:L8-BO blend films.
Figure B-15 GIWAXS linecut profiles in the out-of-plane direction of PD:L8-BO blend films.

166
Table B-4 Domain size (d) and coherence length (LC) estimated from GIWAXS linecut profiles of
PD:L8-BO blend films.
Blend
d(200)
[Å]a)
Lc(200)
[nm] a)
d(010)
[Å]b)
Lc(010)
[nm]b)
PM7:L8-BO 9.26 8.4 3.79 2.3
PM7-Thy 5:L8-BO 9.93 12.0 3.76 2.6
PM7-Thy 10:L8-BO 9.92 13.0 3.72 2.9
PM7-Thy 20:L8-BO 10.04 10.0 3.78 2.3
Table B-5 Tensile properties of the PD:L8-BO blend films
Blend E
[Gpa]
COS
[%]
Toughness
[MJ/m³]
PM7:L8-BO 1.96 2.6 0.52
PM7-Thy 5:L8-BO 1.31 6.1 1.54
PM7-Thy 10:L8-BO 2.25 13.7 4.50
B.3 Previous report

167
Figure B-16 Previously reported intrinsically stretchable polymer solar cells (IS-PSC) and this
work
Table B-6 Device structures, mechanical and photovoltaic performances of previously reported ISPSCs and this work. The PCE80% values were estimated by interpolation of the data reported in the
papers
Year Device structure Active Layer
PCE
[%]
Strain at PCE80%
[%] Ref.
2012
UV/O3-treated
PDMS/PEDOT:PSS/Active
Layer/EGaIn
P3HT:PCBM ~1 - [2]
2013 PDMS/PEDOT:PSS/
Active Layer/EGaIn
P3HT:PCBM 0.59 - [3] P3DDT:PCBM 0.29 -
2016 PU/PEDOT:PSS/PEI/Active
Layer/PEDOT:PSS/PU P3HpT:PCBM 1.25 - [4]
2017
PUA-AgNW/
SWNT/PEDOT:PSS/Active
Layer/PEIE/SWNT/
AgNW-PUA
PTB7-Th:
PC71BM 2.90 - [5]
2017
3M tape/PEI/Ag/PH1000/
Active Layer/EGaIn
PTB7-Th:
PCBM 5.32 8.1 [6]

168
PTB7-Th:N2200 2.02 20.2
2018
3M tape/
PEDOT:PSS/
Active Layer/
PFN-NBR/EGaIn
PTB7-Th:N2200 2.02 20.2
[7]
PTB7-Th:
ITIC 1.66 10.4
PTB7-Th:
P(NDI2HD-T) 3.00 15.7
2019
Ag mesh/PEDOT:PSS/
Active Layer/
PEIE/Ag/Parylene
PTzNTz: PC71BM 9.70 7.7 [8]
2021 PDMS/PH1000/
Active Layer/EGaIn
PBDB-T:
PCE10:N2200
(1.2:0.8:1)
6.33 11.2 [9]
2021
TPU/PH1000/
AI4083/Active Layer/
PNDIT-F3N-Br/EGaIn
PM6:Y7 11.2 12.4
PM6:PCBM 5.7 5.1 [10]
PCE12:N2200 5.0 42.3
2021 TPU/AgNW/PEDOT:PSS/
Active Layer/EGaIn
PTB7-Th:
IEICO-4F 10.1 12.0 [11]
2022
TPU/PH1000/
AI4083/Active Layer/
PNDIT-F3N-Br/EGaIn
PM6:Y7:N2200
(1:0.8:0.2) 11.71 19.9 [12]
2022
TPU/PH1000/
AI4083/Active Layer/
PNDIT-F3N-Br/EGaIn
PhAm5:Y7 12.76 31.6 [13]
2022
TPU/PH1000/
AI4083/Active Layer/
PNDIT-F3N-Br/EGaIn
PM6-OEG5:
BTP-eC9 12.05 22.0 [14]
2022
TPU/GL:PH1000/
AI4083/Active Layer/
PNDIT-F3N-Br/EGaIn
PM6:Y6:5wt% BAC
(crosslinker) 13.40 20.0 [15]
2022
TPU/PH1000/
AI4083/Active Layer/
PNDIT-F3N-Br/EGaIn
PBDB-T:PYFS-Reg 10.64 36.7 [16]
2023
TPU-AgNWs/PEDOT:PSS/
Active Layer/
Azo-AgNWs-AZO
PM6:BTP-eC9 10.90 9.9 [17]
2023
TPU/PH1000/
AI4083/Active Layer/
PNDIT-F3N-Br/EGaIn
PM7-Thy10:L8-BO 13.69 43.1 This
Work

169
B.4 Reference
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Designing Simple Conjugated Polymers for Scalable and Efficient Organic Solar Cells.
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(2) Lipomi, D. J.; Lee, J. A.; Vosgueritchian, M.; Tee, B. C.-K.; Bolander, J. A.; Bao, Z.
Electronic Properties of Transparent Conductive Films of PEDOT:PSS on Stretchable
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(3) Savagatrup, S.; Makaram, A. S.; Burke, D. J.; Lipomi, D. J. Mechanical Properties of
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C. Intrinsically Stretchable Nanostructured Silver Electrodes for Realizing Efficient Strain
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(7) Hsieh, Y.-T.; Chen, J.-Y.; Fukuta, S.; Lin, P.-C.; Higashihara, T.; Chueh, C.-C.; Chen, W.-
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21712–21720.
(8) Jiang, Z.; Fukuda, K.; Huang, W.; Park, S.; Nur, R.; Nayeem, Md. O. G.; Yu, K.; Inoue, D.;
Saito, M.; Kimura, H.; Yokota, T.; Umezu, S.; Hashizume, D.; Osaka, I.; Takimiya, K.;
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J.; Lee, J.-Y. Intrinsically Stretchable Organic Solar Cells with Efficiencies of over 11%. ACS
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(11) Wang, Z.; Xu, M.; Li, Z.; Gao, Y.; Yang, L.; Zhang, D.; Shao, M. Intrinsically Stretchable
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(12) Lee, J.; Kim, G.; Kim, D. J.; Jeon, Y.; Li, S.; Kim, T.; Lee, J.; Kim, B. J. IntrinsicallyStretchable, Efficient Organic Solar Cells Achieved by High-Molecular-Weight, ElectroActive Polymer Acceptor Additives. Adv. Energy Mater. 2022, 12 (28), 2200887.
(13) Lee, J.; Seo, S.; Lee, S.; Kim, G.; Han, S.; Phan, T. N.; Lee, S.; Li, S.; Kim, T.; Lee, J.; Kim,
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Donors Featuring Hydrogen-Bonding Spacers. Adv. Mater. 2022, 34 (50), 2207544.
(14) Lee, J.; Lim, C.; Lee, S.; Jeon, Y.; Lee, S.; Kim, T.; Lee, J.; Kim, B. J. Intrinsically Stretchable
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10.1039.D2EE03096A

172
Appendix C
Chapter 4: Polymer Acceptor with Hydrogen Bonding Functionality for Efficient and
Mechanically Robust Ternary Organic Solar Cells
C.1 Materials and Methods
The PM6 polymer donor (PD) and Y6-BO small molecule accepter (SMA) were purchased the
Derthon Co. and used in the active layer of organic solar cell (OSC) without additional purification.
The Clevios P VP (AI 4083) was purchased from the Heraeus Co. and used as the hole-transporting
layer in OSC fabrication. All reagents and solvents from commercial sources were used without
further purification, unless otherwise noted. All reactions were performed under dry N2 in
glassware that was oven dried, unless otherwise noted.
Synthesis of monomer and N2200-ThyDap

173
Scheme C-1 Synthetic scheme for the T-Dap monomer and N2200-ThyDap polymer acceptor (PA).
(1) Synthesis of Compound 2
Compound 1 was synthesized according to the reported literature.
1 (168 mg, 0.588 mmol) of
Compound 1, triphenylphosphine (177 mg, 0.676 mmol), and 1,6-hexanediol (104 mg, 0.882
mmol) were added to a 50 mL three-neck round bottom flask under N2. Anhydrous THF (35 mL),
and DIAD (148 mg, 0.735 mmol) was added to the reaction mixture and the reaction was
conducted at room temperature (R.T.) for 18 hr. After cooling, the reaction was quenched with

174
deionized (DI) water and extracted in CHCl3. The organic layer was dried over MgSO4 and the
solvent was removed after filtering. The crude product was purified by column chromatography
to yield the desired product as a colorless oil in an 85% yield (224.5 mg). 1
H nuclear magnetic
resonance (NMR) (500 MHz, CDCl3) δ (ppm): 7.34 (s, 1H), 4.28 (t, 2H), 3.41 (t, 2H), 1.89 (m,
2H), 1.76 (m, 2H), 1.49 (m, 4H)
(2) Synthesis of T-Dap monomer
Compound 3 was synthesized according to the reported literature.
2 (264 mg, 0.588 mmol) of
Compound 2, (189 mg, 0.588 mmol) of Compound 3, and Cs2CO3 (191 mg, 0.588 mmol) were
added to a 50 mL three-neck round bottom flask under N2. Anhydrous N, N-Dimethylformamide
(DMF) (30 mL) was added to the reaction mixture and the reaction was conducted at 80 °C for 18
hr. After cooling, the reaction was quenched with DI water, extracted in CHCl3, and then washed
with DI water. The organic layer was dried over MgSO4 and the solvent was removed after
filtering. The crude product was purified by column chromatography to yield the desired product
as a white solid in a 30% yield (121.8 mg). 1
H NMR (500 MHz, CDCl3) δ (ppm): 9.54 (s, 1H, NH), 9.06 (s, 1H, N-H), 7.35 (s, 1H), 7.34 (s, 1H), 4.29 (t, 2H), 4.28 (t, 2H), 2.89 (t, 2H), 2.45 (t,
2H), 1.78-1.71 (m, 10H), 1.35 (m, 10H), 0.90 (m, 6H)

175
(3) Synthesis of N2200-ThyDap
4,9-Dibromo-2,7-bis(2-octyldodecyl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone
(NDI) monomer (44.3 mg, 0.045 mmol), 1,1 ′ -[2,2 ′ -Bithiophene]-5,5 ′ -diylbis[1,1,1-
trimethylstannane] monomer (24.6 mg, 0.05 mmol), Q-Thy monomer (1.5 mg, 0.0025 mmol), TDap monomer (1.7 mg, 0.0025 mmol) and Pd2(dba)3 (1.2 mg) and P(o-tol)3 (2.4 mg) were added
into a 15 mL Schlenk tube. The mixture of toluene (2 mL) was added under N2 and the solution
was degassed for 10 min. The mixture was reacted for 48 hr in oil bath at 120 °C and precipitated
in methanol and purified by soxhlet under methanol, hexane, and chloroform. The chloroform
fraction was precipitated in methanol (35 mg, 95%). (Number-average molecular weight (Mn) =
18.5 kg mol-1
, Ð = 2.5)
C.2 Characterization
1
H NMR spectra of monomers were recorded in CDCl3 on a Varian Mercury 400 NMR
Spectrometer at 25 °C. The 1
H NMR spectra of N2200 and N2200-ThyDap PAs were measured in
CDCl3 solution and recorded on a Varian Mercury 500 NMR Spectrometer at 25 °C. The Mn and
dispersity values of PM6 PD and PAs were measured using gel permeation chromatography (GPC)
at 80 o
C using ortho-dichlorobenzene as the eluent, which was calibrated with polystyrene
standard. UV-1800 spectrophotometer was used to measure the absorption properties of materials
used in study at the room temperature. EC-Lab software with VSP from BioLogic Science
Instruments Co. was used to measure the energy levels of materials used in active layer, using
ferrocene as a reference. Ag/AgCl and Pt electrodes were used as the reference electrode and

176
counter electrode during the cyclic voltammetry measurement. The crystalline properties of neat
materialfilms and blend films were determined using GIXS analyses, measured at the 3C beamline
in Pohang Accelerator Laboratory. The specific viscosity (ηsp) values were measured using an
Anton Paar MCR 302 parallel plate rheometer, applying a constant shear rate (100 s−1
) with a
measuring time of 10 s per point at room temperature. The external quantum efficiency (EQE)
spectra were measured using the K3100 IQX instrument (McScience Inc.) using the xenon arc
lamp as a light source. The intensity of the xenon arc lamp was standardized with an optical
chopper (MC 200 Thorlabs) and filtered by a monochromator filter (Newport). Optical microscopy
(OM) images of blend films were obtained from the NX10 (Park Systems). The resonance soft Xray scattering (RSoXS) of blend films was estimated from the Advanced Light Source (USA) with
the 285.0 eV beam intensity. Atomic force microscopy (AFM) from Bruker (NX10) was used to
measure the thickness of films.
Fabrication of OSCs and measurement: OSCs with a conventional device configuration (indium
tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/active
layer/2,9-bis(3-((3-(dimethylamino)propyl)amino)propyl)anthra[2,1,9-def:6,5,10-
d'e'f']diisoquinoline-1,3,8,10(2H,9H)-tetraone (PDINN)/Ag) were fabricated through the
following procedures. ITO-coated glass was washed in order of acetone, DI water, and isopropyl
alcohol with ultrasonic process. The cleaned ITO was dried in the 80 o
C oven under ambient
conditions to eliminate the residual solvent and treated with ozone-plasma for 10 min. The spincoating process was carried out with PEDOT:PSS solution (Clevios, AI4083) on the ITO substrate

177
at 3000 rpm for 30 sec, and then the AI4083-coated ITO was thermally annealed at 165 o
C for 15
min. The active layer solution for the PM6:Y6-BO blend system consisting the 1:1.2 weight ratio
of donor to acceptor was prepared as 16.0 mg mL-1 concentration in chloroform (CF). With the
incorporation of PAs into the blend system, the active layer solutions were dissolved in CF with an
optimized condition (PD:(SMA:PA) blend ratio = 1:1.2, concentration = 13.5 mg mL-1
). The 1-
chloronaphtalene (CN) was added as a solvent additive at a concentration of 0.5 vol% for each
active layer solution. The resulting active layer solution was stirred at 55 o
C for 1 hr and spincoated onto the ITO substrate at 1900 rpm for 30 sec. The thickness of the active layer in all
systems was determined to be within the range of 110-120 nm range, as measured using AFM.
The spin-coated active layer on the substrate was annealed at 100 o
C for 5 min. For the electron
transporting layer, the PDINN was dissolved in methanol at 1mg mL-1 and spin-coated on the
active layer/substrate at 3000 rpm for 30 sec. Lastly, Ag (120 nm) was deposited using an
evaporation chamber under the high vacuum conditions (~10-6 Torr). The area of active layer of
all systems was 0.04 cm2
, confirmed by the OM measurement. The photovoltaic efficiency of the
OSCs was measured using Keithley 2400 SMU instrument under an Air Mass 1.5 G solar simulator
(100 mW cm−2
, solar simulator: K201 LAB55, McScience Inc.), meeting the Class AAA, ASTM
Standards. A standard silicon reference cell, specifically the K801SK302 model by McScience
Inc., was used for precise calibration of solar irradiance.
Space-charge-limited current (SCLC) measurements: The hole mobilities (µh) for blend films
and the electron mobilities (µe) of the neat PA films and blend films were estimated from the SCLC

178
method. For measuring µh values of devices, the device structure was ITO/PEDOT:PSS/active
layer (PM6:Y6-BO blend or PM6:Y6-BO:PA blend)/Au. For measuring µe values of devices, the
device configuration of ITO/zinc oxide (ZnO)/active layer (PM6:Y6-BO blend or PM6:Y6-BO:PA
blend) or pristine PA /poly[9,9-bis(3′-(N,N-dimethyl)-N-ethylammoinium-propyl-2,7-fluorene)-
alt-2,7-(9,9-dioctylfluorene)]dibromide (PFN-Br)/Al was used. The preparation for active layers
followed the same conditions as those described for the OSC fabrications. The current-voltage
measurements were conducted with the applied voltage range of 0 to 6 V, and the obtained results
were fitted using the Mott-Gurney law.
J =
!*+*,-&'
"()
where J denotes the current density, εr represents the relative dielectric constant of the films, ε0
exhibits the permittivity of free space (8.85 × 10-14 F cm-1
), µ is the charge carrier (hole or electron)
mobility, V is the calculated potential across the SCLC device (V = Vapplied - Vbi - Vr, where Vbi is
the built-in state potential and Vr is the voltage drop resulting from resistance), and L is the
thickness of the blend or pristine films measured by AFM.
Pseudo free-standing tensile test: In the pseudo free-standing tensile method, the blend films were
prepared under the same condition as the OSC fabrications. All films were spin-coated with the
similar thickness (~100 nm). The thickness of sample was measured using AFM. The films were
spin-casted onto the polystyrene sulfonic acid-coated glass substrate, and cut into a dog-bone shape
by a femtosecond laser. Then, the films were floated onto the water surface, and attached to the

179
grips by Van-der Waals interactions. The strain was applied with a fixed strain rate (0.8 × 10-3 s
-
1
), and the tensile load values were measured by a load cell with high resolution (LTS-10GA,
KYOWA, Japan). Elastic modulus (E) was calculated using the least square method for the slope
of the linear region in the stress-strain curve within 0.5% strain.

180
Supplementary Figures & Tables
Figure C-1 1
H NMR spectrum of Compound 2.

181
Figure C-2 1
H NMR spectrum of T-Dap monomer.

182
Figure C-3 1
H NMR spectrum of N2200-ThyDap.

183
Figure C-4 1
H NMR spectra (from 3.3 ppm to 4.8 ppm) of N2200-ThyDap versus N2200.

184
Figure C-5 1
H NMR spectrum (from 3.3 ppm to 5.1 ppm) of N2200-ThyDap to calculate the molar
ratio between the Thy, Dap, and NDI functions.

185
Figure C-6a Aromatic region 1
H NMR spectra of pristine Q-Thy, T-Dap, and Q-Thy:T-Dap
mixture in CDCl3 at R.T.

186
Figure C-6b Full 1
H NMR spectra of pristine Q-Thy, T-Dap, and Q-Thy: T-Dap mixture in CDCl3
at R.T.

187
Figure C-7 Solution UV-Vis spectra of materials used in this study.

188
Figure C-8 Cyclic voltammetry of materials used in study.

189
Figure C-9 2D GIXS images of neat materials in the thin film state.

190
Figure C-10 (a) In-plane and (b) out-of-plane linecuts of GIXS spectra of neat PA films.
Figure C-11 (a) In-plane and (b) out-of-plane linecuts of GIXS spectra of neat PM6 PD and Y6-BO
SMA.

191
Table C-1 Tensile properties of the neat PA films
Material Ea
[GPa]
COSa
[%]
Toughnessa
[MJ m-3
]
N2200 0.42 ± 0.04 1.51 ± 0.17 0.05 ± 0.02
N2200-ThyDap 0.47 ± 0.04 28.20 ± 1.23 7.23 ± 0.44
a
Average values were obtained from at least 3 different films.
Figure C-12 Specific viscosity (ηsp) of pure chloroform (CF) solvent, N2200 CF solution (10 mg mL1
), and N2200-ThyDap CF solution (10 mg mL-1
).

192
Table C-2 The specific viscosity (ηsp) of pure chloroform (CF) solvent, N2200 CF solution (10 mg mL1
), and N2200-ThyDap CF solution (10 mg mL-1
)
Material
ηsp
[mPa∙s]
Pure chloroform 0.57
N2200 CF solution 0.65
N2200-ThyDap CF solution 1.58
Table C-3 Photovoltaic parameters of OSCs with 20 wt% PA
System
Weight
Ratio
(PD:SMA:PA
)
Voc
[V]
Jsc
[mA cm2
]
FF
PCEavga
[%]
PCEmax
[%]
PM6:Y6-BO 1:1.2:0 0.81 25.94 0.73 15.28 15.41
PM6:Y6-BO:
N2200
1:0.96:0.24 0.84 23.27 0.68 12.85 13.14
PM6:Y6-BO:
N2200-ThyDap
1:0.96:0.24 0.85 26.30 0.64 13.55 14.14
a
Average values were calculated from at least 10 different cells.

193
Table C-4 SCLC electron mobilities of the pristine PA films.
Material µe
a
[cm2 V-1 s
-1
]
N2200 6.71 × 10-5
N2200-ThyDap 4.70 × 10-5
a
Average values were obtained from at least 3 different SCLC devices.
Table C-5 SCLC mobilities of blend films.
Blend
(Weight Ratio)
µe
a
[cm2 V-1 s
-1
]
µh
a
[cm2 V-1 s
-1
] µh/µe
PM6:Y6-BO
(1:1.2)
1.24 × 10-4 1.96 × 10-4 1.58
PM6:Y6-BO:N2200
(1:1.08:0.12)
1.76 × 10-4 2.88 × 10-4 1.64
PM6:Y6-BO:N2200-ThyDap
(1:1.08:0.12)
9.69 × 10-5 1.25 × 10-4 1.29
a
Average values were obtained from at least 3 different SCLC devices.

194
Figure C-13 (a) Molecular structure, (b) density functional theory (DFT) simulation calculated
structure, and (c) electrostatic potential map of N2200 (The DFT simulation was used at the
B3LYP/6-31G(d,p) level. To simplify the calculation, the trimer form of the N2200 was modeled and
side chains at NDI were simplified as ethyl).

195
Figure C-14 (a) Molecular structure, (b) DFT simulation calculated structure, and (c) electrostatic
potential map of N2200-ThyDap (The DFT simulation was used at the B3LYP/6-31G(d,p) level and
side chains at NDI were simplified as ethyl).

196
Figure C-15 Stress-Strain curve of PM6:Y6-BO binary blend and PM6:Y6-BO:PA ternary blend
(wt% value of PA indicates the weight of PA compared to (PA + SMA) weight).
Table C-6 Tensile properties of the blend films with 20 wt% PA
Blend
(Weight Ratio)
Ea
[GPa]
COSa
[%]
Toughnessa
[MJ m-3
]
PM6:Y6-BO
(1:1.2)
0.90 ± 0.02 2.10 ± 0.30 0.22 ± 0.09
PM6:Y6-BO:N2200
(1:0.96:0.24)
0.81 ± 0.02 2.46 ± 0.15 0.37 ± 0.05
PM6:Y6-BO:N2200-ThyDap
(1:0.96:0.24)
0.72 ± 0.02 5.48 ± 1.07 0.87 ± 0.37
a
Average values were obtained from at least 3 different cells.

197
Figure C-16 2D GIXS images of blend films.

Abstract (if available)

Abstract The field of polymer solar cells (PSCs) has been growing rapidly over the last five years, and significant effort has been put into developing new materials such as non-fullerene acceptors (NFAs), device engineering, and comprehensive understanding of structure function relationships. Currently, single-junction organic solar cells exhibit remarkable power conversion efficiencies (PCEs) of more than 19%. Discovering and designing novel materials to further improve the efficiency and mechanical reliability is essential to the commercialization of organic solar cells.
In contrast to fullerene acceptors, NFAs such as ITIC and Y6 lead to crystalline domains in solid-state films that can crystallize in a variety of polymorphs depending on the processing conditions. Different crystalline phases can result in various structural, optical, and electrical properties, which potentially can affect device performance. Therefore, polymorphism is a critical design parameter for semiconducting properties and even minor changes in crystal packing can result in differentiation of electronic properties by orders of magnitude. Additionally, for future commercialization of PSCs, it is crucial to design stretchable systems with both high efficiency and mechanical robustness, as mechanical stress is a major factor causing device failure. A very limited range of molecular design strategies such as introducing flexible non-conjugated spacers into the polymer donors (PD) have been developed for high performance and mechanically robust PSCs. Introducing Hydrogen-bonding (H-bonding) into conjugated polymers (CPs) has been a broadly exploited but still represents an emerging strategy capable of tuning a range of properties encompassing solubility, crystallinity, electronic properties, solid-state morphology and stability, as well as mechanical properties and self-healing properties.
In this dissertation, a ternary polymer solar cell with a polymer donor-mediated polymoprh of a novel NFA is presented to offer a new direction to improve the PCEs of PSCs. More importantly, several H-bonding molecular desgin strategies for PDs with the aim to improve the mechanical reliability of PSC’s are also presented.
Chapter 1 provides an overview of classes of H-bonding CPs (assorted by the different H-bond functional groups), the synthetic methods to introduce the corresponding H-bond functional groups and the impact of H-bonding in CPs on corresponding electronic and materials properties. Recent advances in addressing the trade-off between electronic performance and mechanical durability are also highlighted. Furthermore, insights into future directions and prospects for H-bonded CPs are discussed. This chapter provides the background for the reseach on the novel H-bonded CPs molecular desgin strategies in details in Chapters 3-4.
In Chapter 2, using a new NFA 2,2'-((4,4,9,9-tetrahexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b'] dithiophene-2,7-diyl) bis(methaneylylidene)) bis(1H-indene-1,3(2H)-dione), referred to IDID, as the third component, we observed the appearance of a polymorph of IDID when it was introduced into a PTQ10: PC61BM binary blend and this ternary blend solar cell showed a significant improvement in efficiency from 3.38% to 6.04%. This relative increase (with respect to the best binary cell) is nearly 80% which is the highest among all the reported organic ternary blends to the best of our knowledge. Specifically, IDID was found to be nucleated by the host polymer donor PTQ10 under the assistance of the processing solvent to form a distinct polymorph, as proven by the grazing incidence X-Ray diffraction (GIXRD), differential scanning calorimetry (DSC), and supported by surface energy measurements. More interestingly, IDID, as a third component in the PTQ10: PC61BM system, was found to outperform the structurally similar NFA IDIC, which only boosted the efficiency from 3.38% to 3.55% in ternary polymer solar cells. This work highlights polymer-mediated polymorphism in NFAs as an important consideration in the selection of components for and optimization of OSCs.
In Chapter 3, a novel thymine side chain terminated 6,7-difluoro-quinoxaline (Q-Thy) monomer was designed and used to synthesize a series of fully conjugated PDs (PM7-Thy5, PM7-Thy10, PM7-Thy20) featuring Q-Thy. The Q-Thy units, capable of inducing dimerizable H-bonding, enable strong intermolecular PD assembly and highly efficient and mechanically robust PSCs. The PM7-Thy10:SMA blend demonstrates a combination of high PCE >17% in rigid devices and excellent stretchability (crack-on-set value >13.5%). More importantly, PM7-Thy10-based intrinsically stretchable polymer solar cells IS-PSCs show an unprecedented combination of PCE (13.7%) and ultrahigh mechanical durability (maintaining 80% of initial PCE after 43.1% strain) illustrating promising potential for commercialization in wearable applications.
In Chapter 4, to overcome the limitation arising from using rigid and highly crystalline small-molecule acceptors (SMAs) which limits the mechanical robustness of PSCs, a stretchable and conjugated polymer acceptor (PA, N2200-ThyDap) was synthesized and introduced as the third component to the benchmark polymer donor (PD):SMA system PM6:Y6-BO. N2200-ThyDap was designed to incorporate H-bonding into the N2200 PA backbone using thymine (Thy) and diaminopyrazine (Dap) units and the neat film shows excellent stretchability (crack onset strain (COS) = 28.2%) compared to the PA of similar molecular weight without H-bonding (N2200, COS = 1.5%). The N2200-ThyDap incorporated ternary system (PM6:Y6-BO:N2200-ThyDap) exhibits a higher PCE (16.4%) than the reference binary (PM6:Y6-BO, PCE = 15.4%) and the N2200 incorporated control ternary system (PCE = 14.7%). The PM6:Y6-BO:N2200-ThyDap ternary blend film achieves higher stretchability (COS = 4.8%) than the PM6:Y6-BO binary (COS = 2.1%) and PM6:Y6-BO:N2200 ternary (COS = 2.4%) films. It is likely that a stronger intermolecular interaction enabled by N2200-ThyDap leads to a higher photovoltaic performance and improved stretchability. This study highlights the importance of conjugated polymer additive design in the realization of high-performance and stretchable ternary OSCs.

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Creator Wan, Qingpei (author)

Core Title Complementary hydrogen bonding enables efficient and mechanically robust polymer solar cells

School College of Letters, Arts and Sciences

Degree Doctor of Philosophy

Degree Program Chemistry

Degree Conferral Date 2025-05

Publication Date 01/31/2025

Defense Date 01/27/2025

Publisher Los Angeles, California (original), University of Southern California (original), University of Southern California. Libraries (digital)

Tag complementary hydrogen bonding,mechanical property,OAI-PMH Harvest,polymer solar cells

Format theses (aat)

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Thompson, Barry (committee chair), Wu, Wei (committee member), Zhang, Chao (committee member)

Creator Email qingpeiw@usc.edu,wanqingpei@126.com

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Document Type Dissertation

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