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Structure-function studies of random and semi-random poly(3-hexyl thiophene) copolymers

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Structure-function studies of random and semi-random poly(3-hexyl thiophene) copolymers

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STRUCTURE-FUNCTION STUDIES OF RANDOM AND SEMI-RANDOM POLY(3-
HEXYL THIOPHENE) COPOLYMERS

By

Jenna B Howard

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)

December 2016

Copyright 2016 Jenna B Howard
ii
DEDICATION

To my grandmother, mother, and my sister.

iii
ACKNOWLEDGEMENTS

I owe special thanks to my advisor, Prof. Barry C. Thompson, for his unwavering support
during the past five years. His guidance has helped shape my skills as a scientist and a
colleague for those I work with. Barry is an incredibly patient, humble mentor with great
leadership and enthusiasm that which everyone should aspire to. I’m grateful for our
conversations and the group of people he has brought together.

I would like to thank Prof. Mark E. Thompson, Prof. Surya Prakash, Prof. Chao Zhang,
and Prof Aiichiro Nakano for being members of my screening and qualification exam
committee. And I would like to thank Michele Dea, Katie McKissick, Magnolia Benitez,
David Hunter, Jessy May, Carole Phillips, Allan Kershaw, Frank Devlin, and Ross Lewis
for their help during my time at USC.

For their scientific expertise and guidance on key measurements in my research: Drs.
Malancha Gupta, Scott Siedel, and Prof. Travis Williams. I also want to thank those who
supported and guided me through my teaching experiences at USC: Dr. Jennifer Moore,
Prof. Thieo E. Hogen-Esch, Prof. Travis Williams, Prof. Kyung Jung, Dr. Thomas
Bertolini, and Dr. Rebecca Broyer.

I’m very grateful to the members of Barry’s research group. Thanks to Drs. Beate
Burkhart, Peter Khylabich, and Andrey Rudenko for everything they taught me and for
serving as such great role models. My deepest appreciation goes to Seyma Ekiz for her
dedication to our joint projects and her endlessly joyful spirit. Many days were made
iv
better thanks to her effortless ability to light up a room and bring a smile to everyone’s
face; I will cherish our friendship. I will miss standing lunchtimes and regular discussions
with Betsy Melenbrink about almost anything under the sun. Betsy’s dedication to
exploring the world and making it a better place through public service is unmatched by
most. Thank you to Dr. Bing Xu, Dr. Sangtaik Noh, Alia Latif, Nemal Gobalasingham,
and Robert Pankow. I will miss our gatherings, the lawn games, impossible charade
clues, hilarious white-elephant gift exchanges, and I hope we may all solve another maze
room together again.

Thank you to the friends I met at USC: Anna Dawsey, Janet Olsen, and Lena Hoober-
Burkhardt. I’m grateful to know you and I’m inspired by your hard work and
determination, I only wish our busy lives could let us spend more time together. Thank
you to my closest friends outside of USC for all the coffee dates, good food and wine, the
great board games, and best company I could ask for: Dave Matos, Tara Waugh, Robyn
Schneider, Anne Meyer, Jenny Rogers, Tiffany and Rick Loverd, Dan and Kim Lifschitz,
Aaron Ensweiler, and Lydia Carmany.

My family has been my most constant support throughout my education. Thank you to
my beautiful, smart, and artistic sister, June, for all of her encouragement. Thank you to
my mother, Judith, for her unconditional love and strength when life isn’t easy. Thank
you to my grandmother, Fannie, for always reminding me that my education can never be
taken away.
v
I nearly quadrupled the size of my family when I married my husband, Ari, almost a year
ago. Thank you to the Lubet and Schoeneman families for your love and support. In
particular, thank you to Dana, Bonnie, Cheryl, Mark, Steve, Linda, Eric, Janet, Gammy,
Jewel, Elliot, Jenny, Alan, and Alyssa.

Ari, your boundless energy both exhausts and refreshes me. Everyday with you is fun and
our life is never boring. You are the best co-parent to our dogs and a good chef, errand
runner, and laundry man when my time is in high demand. Thank you for being the best
partner and having my back whenever I need it, not just when I need it most. Thank you
for sharing your virtues of patience, forgiveness, and love.

vi
TABLE OF CONTENTS

DEDICATION ……………………………………………………………………………ii

ACKNOWLEDGEMENTS ……………………………………………………………...iii

LIST OF TABLES …………………………………………………………………..viii

LIST OF FIGURES……………………………………………………………………....ix

ABSTRACT ……………………………………………………………………………..xv

CHATPER 1 Random and Semi-Random Polymers for Organic Photovoltaics …….1
1.1 Poly(3-hexyl thiophene) for Organic Solar Cells …………………….1
1.2 Classification of Random and Semi-Random P3HT based systems …….4
1.3 Fine-tuning Random P3HT Polymers …………………………………….8
1.4 Semi-Random P3HT Donor-Acceptor Polymers………………………..14
1.5 Learning More About Semi-Random Donor-Acceptor Polymers……….23
1.6 References for Chapter 1………………………………………………...24

CHAPTER 2 Fine Tuning Surface Energy of Poly(3-hexyl thiophene) by Heteroatom
Modification of the Alkyl Side Chains …………………………………………...27
2.1 Introduction …………………………………………………………...27
2.2 Results and Discussion…………………………………………………..29
2.3 Conclusion……………………………………………………………….39
2.4 References for Chapter 2………………………………………………...40

CHAPTER 3 Surface Energy Modification of Semi-Random P3HTT-DPP …...44
3.1 Introduction …………………………………………………………...44
3.2 Results and Discussion …………………………………………...45
3.3 Conclusion …………………………………………………………...53
3.4 References for Chapter 3 …………………………………………...54

CHAPTER 4 Investigation of Random Copolymer Analogs of a Semi-Random
Conjugated Polymer Incorporating Thienopyrazine …………………………………...57
4.1 Introduction …………………………………………………………...57
4.2 Results and Discussion …………………………………………...58
4.2.1 Synthesis …………………………………………………...58
4.2.2 Structural Characterization …………………………………...62
4.2.3 Optical and Electrochemical Properties …………………...67
4.2.4 Morphology Characterization …………………………………...69
4.2.5 Thermal Properties………………………………………………73
4.3 Conclusion …………………………………………………………...74
4.4 References …………………………………………………………...75

vii

BIBLIOGRAPHY …………………………………………………………………...78

APPENDIX 1 Fine Tuning Surface Energy of Poly(3-hexyl thiophene) by Heteroatom
Modification of the Alkyl Side Chains …………………………………………...88
A1.1 Materials and Methods …………………………………………...88
A1.2 Synthesis …………………………………………………………...92
A1.3 Polymer Characterization ………………………………………….100
A1.4 References Appendix 1 ………………………………………….110

APPENDIX 2 Surface Energy Modification of Semi-Random P3HTT-DPP ….111
A2.1 Synthesis ………………………………………………………….111
A2.2 Polymer Characterization ………………………………………….113
A2.3 Device Fabrication and Characterization ………………………….118
A2.4 References Appendix 2 ………………………………………….119

APPENDIX 3 Investigation of Random Copolymer Analogs of a Semi-Random
Conjugated Polymer Incorporating Thienopyrazine ………………………………….120
A3.1 Synthesis ………………………………………………………….120
A3.2 Polymer Characterization ………………………………………….129
A3.3 References Appendix 3 ………………………………………….140

viii
LIST OF TABLES

Table 1.1. Molecular weights (Đ), electrochemical HOMO values, optical band
gaps, and SCLC mobilities of P3HT and random P3HT copolymers....………………....9

Table 1.2. Photovoltaic properties of P3HT and random P3HT copolymers…………...10

Table 1.3. Molecular weights (Đ), electrochemical HOMO values, optical band
gaps, and SCLC mobilities of P3HT semi-random D-A copolymers…………………...14

Table 1.4. Photovoltaic properties of P3HT and semi-random P3HT D-A
copolymers……………………………………………………………………….………15

Table 1.5. Molecular weights (Đ), electrochemical HOMO values, optical band
gaps, and SCLC mobilities of P3HT semi-random D-A copolymers…………………....18

Table 1.6. Photovoltaic properties of semi-random P3HT D-A copolymers……….…...19
Table 2.1. Molecular weights (PDI), electrochemical HOMO values, HOMO values,
optical band gaps, and SCLC mobilities of P3HT, P3HT-co-FHT and P3HT-co-MET
polymers……..…………………………………………………………………………...36

Table 3.1. Molecular weights (Đ), electrochemical HOMO values, optical band
gaps, and SCLC mobilities of P3HTT-DPP, P3HTMETT-DPP, and P3HTFHTT-DPP
polymers…………………………………………………………………………….……48

Table 3.2. Photovoltaic Properties of P3HTT-DPP, P3HTMETT-DPP, and
P3HTFHT-DPP...………………………………………………………………………...52

Table 4.1. Molecular weights (PDI), electrochemical HOMO values, HOMO values,
optical band gaps, and SCLC mobilities of random and semi-random P3HT based
polymers……..…………………………………………………………………………...61

Table A1.1. Calculated surface energy measurements with standard deviations of
polymers using the one-liquid method and Wu Model……...………………………….102

Table A2.1. Surface energy data of semi-random polymers. …………………………..117

ix
LIST OF FIGURES

Figure 1.1 Structures of P3HT and P3AT. ……………………………………………….1

Figure 1.2. Structures of P3TI, PTPD3T, and PffBT-T3(1,2)-2. ………………………...2

Figure 1.3. Stille polycondensation of P3HT-TP (random copolymer) and P3HTT-TP
(semi-random copolymer) from monomer sources. ……………………………………...4

Figure 1.4. Semi-alternating copolymer bonding scheme. ………………………………6

Figure 1.5. Stille polycondensation of P3HT random copolymers. ……………………..8

Figure 1.6. Semi-random P3HT D-A copolymer structures. …………………………...13

Figure 1.7. Semi-random dual acceptor P3HT D-A copolymer structures. …………...15

Figure 1.8. Semi-random P3HT D-A copolymer structures. …………………………...19

Figure 2.1. Synthesis of comonomer 4 and 7. ………………………………………….31

Figure 2.2. Stille polycondensation of P3HT-coFHT and P3HT-co-MET. ……………32

Figure 2.3. Surface energy of P3HT-co-MET (blue) and P3HT-co-FHT (red)
polymers measured from a) as cast thin films and b) thermally annealed
thin films. P3HT-co-MET and P3HT films were annealed at 100 °C, P3HT-co-FHT
films were annealed at 150 °C....………………………………………………………...33

Figure 2.4. Absorption profiles of a) as-cast P3HT-co-FHT, and b) as-cast
P3HT-co-MET films; i) P3HT, ii) P3HT90-co-FHT10, iii) P3HT80-co-FHT20,
iv) P3HT70-co-FHT30, v) P3HT60-co-FHT40, vi) P3HT50-co-FHT50, vii) P3HT90-co-
MET10, viii) P3HT80-co-MET20, ix) P3HT70-co-MET30, x) P3HT60-co-MET40,
and xi) P3HT50-co-MET50…………………………………………………………...…...35

Figure 2.5. GIXRD data of a) P3HT-co-FHT and b)P3HT-co-MET annealed films;
i) P3HT, ii) P3HT90-co-FHT10, iii) P3HT80-co-FHT20, iv) P3HT70-co-FHT30,
v) P3HT60-co-FHT40, vi) P3HT50-co-FHT50, vii) P3HT90-co-MET10, viii) P3HT80-co-
MET20, ix) P3HT70-co-MET30, x) P3HT60-co-MET40, and xi) P3HT50-co-MET50……...37

Figure 3.1. Stille polycondensation of a) P3HTFHTT-DPP, b) P3HTMETT-DPP,
and c) P3HTT-DPP…..…………………………………………………………………..47

Figure 3.2. Absorption profiles of P3HTT-DPP (black), P3HTMETT-DPP (blue),
and P3HTFHTT-DPP (red)..……………………………………………………………..49

x
Figure 3.3. GIXRD data of P3HTT-DPP (black), P3HTMETT-DPP (blue), and
P3HTFHTT-DPP (red)……...…………………………………………………………...50

Figure 3.4. Photoluminescence spectra of P3HTT-DPP (black), P3HTMETT-DPP
(blue), and P3HTFHTT-DPP (red).……………………………………………………...51

Figure 4.1. Synthesis of unsymmetrical dimethylthienopyrazine monomer, 2…….…...59

Figure 4.2. Stille Polycondensation of sr-P3HTT-TP, r-P3HTT-TP, r-P3HT-TP, r-
P3HTT-10%, and r-P3HTT-20%.......…………………………………………………...60

Figure 4.3. Stacked
1
H NMR Spectra of sr-P3HTT-TP (bottom, red), r-P3HTT-TP
(middle, green), and r-P3HT-TP (top, blue)...…………………………………………...63

Figure 4.4. Comparison of monomer linkages found in semi-random and random
thienopyrazine polymers. …………………………………………………………...64

Figure 4.5. Stacked
1
H NMR Spectra of sr-P3HTT-TP (bottom, red), r-P3HTT-TP
(middle, green), and r-P3HT-TP (top, blue). …………………………………………...65

Figure 4.6. UV-Vis Absorption profiles of sr-P3HTT-20% (black), r-P3HTT-20%
(blue), r-P3HTT-10% (aqua), r-P3HT-TP (purple), r-P3HTT-TP (green), and sr-
P3HTT-TP (red) polymers. …………………………………………………………...68

Figure 4.7. GIXRD profiles of P3HT (black), r-P3HTT-10% (aqua), r-P3HTT-20%
(blue), sr-P3HTT-20% (brown), r-P3HT-TP (purple), r-P3HTT-TP (green), and sr-
P3HTT-TP (red) polymers. …………………………………………………………...70

Figure 4.8. Comparison of long-range linkage patterns in a) semi-random and
b) random polymers...…………………………………………………………………...70

Figure A1.1 Synthesis of (5-bromo-4-(4,4,5,5,6,6,7,7,7-nonafluoroheptyl)thiophen-2-
yl)trimethylstannane, 4. …………………………………………………………...92

Figure A1.2 Synthesis of (5-bromo-4-(2-(2-methoxyethoxy)ethyl)thiophen-2-
yl)trimethylstannane, 7. …………………………………………………………...94

Figure A1.3. Stille polycondensation of P3HT-co-FHT and P3HT-co-MET random
polymers. …………………………………………………………………………...96

Figure A1.4.
1
H NMR of P3HT-co-FHT and P3HT Polymers. Singlet at 2.10 ppm is
acetone and 1.50 ppm is water. …………………………………………………...98

Figure A1.5.
1
H NMR of P3HT-co-MET and P3HT Polymers. ………………….100

Figure A1.6. Surface energy as calculated by the One-Liquid Model for as cast
xi
(solid line) and thermally annealed (dotted line) thin films of P3HT-co-MET (blue)
and P3HT-co-FHT (red)….…………………………………………………………….100

Figure A1.7. Surface energy as calculated by the harmonic mean Wu Model for
a) as cast and b) thermally annealed thin films of P3HT-co-MET (blue) and
P3HT-co-FHT (red)…………………………………………………………………….101

Figure A1.8. Absorption profiles of a) annealed P3HT-co-FHT, and b) annealed
P3HT-co-MET films; i) P3HT, ii) P3HT90-co-FHT10, iii) P3HT80-co-FHT20, iv)
P3HT70-co-FHT30, v) P3HT60-co-FHT40, vi) P3HT50-co-FHT50, vii) P3HT90-co-
MET10, viii) P3HT80-co-MET20, ix) P3HT70-co-MET30, x) P3HT60-co-MET40, and
xi) P3HT50-co-MET50….………………………………………………………………...102

Figure A1.9. Photoluminescence responses of a) as cast and b) annealed P3HT-co-
FHT films; c) as cast and d) annealed P3HT-co-MET; black) P3HT, blue) P3HT90-co-
FHT10 or P3HT90-co-MET10, orange) P3HT60-co-FHT40 or P3HT60-co-MET40, red)
P3HT50-co-FHT50 or P3HT50-co-MET50.……………………………………………….103

Figure A1.10. GIXRD data of a) as-cast P3HT-co-FHT and b) as cast P3HT-co-MET
films; i) P3HT, ii) P3HT90-co-FHT10, iii) P3HT80-co-FHT20, iv) P3HT70-co-FHT30, v)
P3HT60-co-FHT40, and vi) P3HT50-co-FHT50. vii) P3HT90-co-MET10, viii) P3HT80-co-
MET20, ix) P3HT70-co-MET30, x) P3HT60-co-MET40, and xi) P3HT50-co-MET50…....104

Figure A1.11. P3HT90-co-FHT10 Film CV. ………………………………………….105

Figure A1.12. P3HT90-co-FHT10 Solution CV. ………………………………….105

Figure A1.13. P3HT80-co-FHT20 Film CV. ………………………………………….105

Figure A1.14. P3HT80-co-FHT20 Solution CV. ………………………………….105

Figure A1.15. P3HT70-co-FHT30 Film CV. ………………………………………….105

Figure A1.16. P3HT70-co-FHT30 Solution CV. ………………………………….106

Figure A1.17. P3HT60-co-FHT40 Film CV. ………………………………………….106

Figure A1.18. P3HT60-co-FHT40 Solution CV. ………………………………….106

Figure A1.19. P3HT50-co-FHT50 Film CV. ………………………………………….106

Figure A1.120. P3HT50-co-FHT50 Solution CV. ………………………………….106

Figure A1.21. P3HT90-co-MET10 Film CV. ………………………………………….107

xii
Figure A1.22. P3HT90-co-MET10 Solution CV. ………………………………….107

Figure A1.23. P3HT80-co-MET20 Film CV. ………………………………………….107

Figure A1.24. P3HT80-co-MET20 Solution CV. ………………………………….107

Figure A1.25. P3HT70-co-MET30 Film CV. ………………………………………….107

Figure A1.26. P3HT70-co-MET30 Solution CV. ………………………………….107

Figure A1.27. P3HT60-co-MET40 Film CV. ………………………………………….108

Figure A1.28. P3HT60-co-MET40 Solution CV. ………………………………….108

Figure A1.29. P3HT50-co-MET50 Film CV. ………………………………………….108

Figure A1.30. P3HT50-co-MET50 Solution CV. ………………………………….108

Figure A1.31. P3HT Film CV. ………………………………………………….108

Figure A1.32 P3HT90-co-FHT10 DSC trace. ………………………………………….109

Figure A1.33 P3HT80-co-FHT20 DSC trace. ………………………………………….109

Figure A1.34 P3HT70-co-FHT30 DSC trace. ………………………………………….109

Figure A1.35 P3HT60-co-FHT40 DSC trace. ………………………………………….109

Figure A1.36 P3HT50-co-FHT50 DSC trace. ………………………………………….109

Figure A1.37 P3HT90-co-MET10 DSC trace. ………………………………………….109

Figure A1.38 P3HT80-co-MET20 DSC trace. ………………………………………….110

Figure A1.39 P3HT70-co-MET30 DSC trace. ………………………………………….110

Figure A1.40 P3HT60-co-MET40 DSC trace. ………………………………………….110

Figure A1.41 P3HT50-co-MET50 DSC trace. ………………………………………….110

Figure A2.1. Copolymerizations of P3HTFHTT-DPP, P3HTMETT-DPP, and
P3HTT-DPP polymers...……………………………………………………………….111

Figure A2.2.
1
H NMR of P3HTFHT-DPP in CDCl3. ………………………….113

Figure A2.3.
1
H NMR of P3HTMETT-DPP in CDCl3. ………………………….114
xiii

Figure A2.4.
1
H NMR of P3HTT-DPP in CDCl3. ………………………………….115

Figure A2.5. P3HTFHTT-DPP CV trace. ………………………………………….116

Figure A2.6. P3HTMETT-DPP CV trace. ………………………………………….116

Figure A2.7. P3HTT-DPP CV trace. ………………………………………………….116

Figure A2.8 P3HTFHTT-DPP DSC trace. ………………………………………….117

Figure A2.9 P3HTMETT-DPP DSC trace. ………………………………………….117

Figure A2.10. P3HTT-DPP DSC trace. ………………………………………….117

Figure A3.1. Synthesis of 5-bromo-2,3-dimethyl-thieno[3,4-b]pyrazine, 1. ………….120

Figure A3.2. Copolymerizations of P3HT based random and semi-random
polymers………………………………………………………………………………..122

Figure A3.3. sr-P3HTT-TP
1
H NMR spectrum. ………………………………….123

Figure A3.4. r-P3HTT-TP
1
H NMR spectrum. ………………………………….124

Figure A3.5. r-P3HT-TP
1
H NMR spectrum. ………………………………….125

Figure A3.6. r-P3HTT-10%
1
H NMR spectrum. ………………………………….126

Figure A3.7. r-P3HTT-20%
1
H NMR spectrum. ………………………………….127

Figure A3.8. sr-P3HTT-20%
1
H NMR spectrum. ………………………………….128

Figure A3.9. Selective excitation at 2.82 ppm of r-P3HT-TP. ………………….129

Figure A3.10. Selective excitation at 2.72 ppm of r-P3HT-TP. ………………….130

Figure A3.11. Selective excitation at 2.72 ppm zoomed in, r-P3HT-TP. ………….131

Figure A3.12. Selective excitation at 2.68 ppm, r-P3HT-TP. ………………….132

Figure A3.13. Selective excitation at 2.70 ppm, sr-P3HTT-TP. ………………….133

Figure A3.14. Selective excitation at 2.68 ppm, r-P3HTT-TP. ………………….134

Figure A3.15. Selective excitation at 2.72 ppm, r-P3HTT-TP. ………………….135

xiv
Figure A3.16. Absorption profiles of P3HT (orange), r-P3HTT-10% (light blue), r-
P3HTT-20% (dark blue), sr-P3HTT-20% (black). ………………………………….136

Figure A3.17 sr-P3HTT-TP film CV. ………………………………………….137

Figure A3.18 r-P3HTT-TP film CV. ………………………………………….137

Figure A3.19 r-P3HT-TP film CV. ………………………………………….137

Figure A3.20 r-P3HTT-10% film CV. ………………………………………….137

Figure A3.21 r-P3HTT-20% film CV. ………………………………………….138

Figure A3.22 sr-P3HTT-20% film CV. ………………………………………….138

Figure A3.23 P3HT film CV. ………………………………………………….138

Figure A3.24 sr-P3HTT-TP DSC trace. ………………………………………….139

Figure A3.25 r-P3HTT-TP DSC trace. ………………………………………….139

Figure A3.26 r-P3HT-TP DSC trace. ………………………………………….139

Figure A3.27 r-P3HTT-10% DSC trace. ………………………………………….139

Figure A3.28 r-P3HTT-20% DSC trace. ………………………………………….140
Figure A3.29 sr-P3HTT-20% DSC trace. ………………………………………….140

xv

ABSTRACT

Conjugated polymers are promising semi-conducting materials for use in organic
photovoltaics such as solar cells, field effect transistors, and light emitting diodes.
Polymer photovoltaics are attractive because they are lightweight, flexible, and easy to
integrate into existing infrastructure. Polymer active layers are also solution processable,
making large-scale roll-to-roll manufacturing possible and lowering manufacturing costs
of solar cells.
The focus of this dissertation is structure-function relationships in random and
semi-random conjugated polymers based on regio-regular poly (3-hexyl thiophene)
(P3HT). Semi-random polymers largely comprise 3-hexyl thiophene and small feed ratios
of electron-poor acceptors, leading to low band gaps and broad absorption profiles.
Meanwhile, desirable properties of P3HT are still maintained: high hole mobilites, good
polymer:fullerene miscibility, and semi-crystallinity.
Semi-random polymers have also been used in ternary blend solar cells, which
utilize two polymer donors and one fullerene acceptor. Two polymer donors with
complementary absorption profiles can boost short-circuit currents (JSC). Moreover,
polymer pairs that exhibit good miscibility or compatibility have also benefited from a
composition-dependent open-circuit voltage (VOC). The synergistic effects of additive
light absorption and composition-tuned voltage can lead to an over all improved solar cell
device efficiency.
Compositional tuning of VOC is attributed intimate mixing of the polymer donors.
Polymer:polymer miscibility can be predicted by surface energies of the respective
materials, which is an easily measured physical parameter. Chapter 2 focuses on
xvi
modulating the surface energy of random P3HT copolymers through side chain
engineering. New P3HT-like polymer families containing either semi-fluoro alkyl or
oligo-ether side chains are prepared and characterized. Optical and electronic properties
are virtually identical to P3HT while surface energy is finely tuned with comonomer
composition.
Subsequently, chapter 3 applies the synthetic model used for P3HT to tune the
surface energy of semi-random polymer containing diketopyrrolopyrrole (P3HTT-DPP).
Similarly, optical and electronic properties are maintained and surface energy is tuned.
Small changes in lamellar packing and melt transitions are observed. The resulting
polymers are optimized in photovoltaic devices showing that oligo-ether side chain
polymer (P3HTMETT-DPP) maintains similar performance. However, the semi-fluoro
alkyl polymer (P3HTFHTT-DPP) required lower polymer solution concentrations for
thin film processing, resulting in a lower JSC and overall efficiency.
Lastly, differences in linkage patterns of random and semi-random donor-acceptor
polymers based on thienopyrazine (P3HTT-TP) are investigated in chapter 4. This study
suggests that restricted linkage patterns, like those in semi-randoms, are necessary for
favoring push-pull behavior and strong intramolecular charge transfer (ICT) absorption
bands. Random and semi-random analogs also demonstrate differences in frontier orbital
levels, thermal properties, semi-crystallinity, and lamellar packing.

1
CHAPTER 1 Random and Semi-Random Polymers for
Organic Photovoltaics

1.1 Poly(3-hexyl thiophene) for Organic Solar Cells

Poly(3-hexyl thiophene) (P3HT) is one of the most widely studied conjugated
polymer systems for organic photovoltaics (OPV) to date.
1,2
It is often viewed as a “fruit
fly” material well suited for fundamental investigation, and is less often considered a
state-of-the-art or high-performing material (Figure 1.1). Since the introduction of
poly(3-alkylthiophenes) (P3AT) in 1985, nearly every optical, electronic, and physical
property of P3HT has been elucidated. Early research of P3HT attributes its good solar
cell performance to its primary qualities: simple total synthesis, solubility in a wide range
of solvents, semi-crystallinity, fullerene miscibility, and ability to form bicontinuous
networks in bulk heterojunctions (BHJ). These properties enable high hole mobilities.
3

One key disadvantage of P3HT is its narrow absorption profile, which limits the short-
circuit current (J
sc
) attainable in solar cells. The efficiency of polymer-fullerene solar
cells is directly proportional to the J
sc
, and is therefore related to the polymer’s optical
band gap. This relationship has, in large part, driven the field of OPV research towards
designing low-band gap polymers with broader absorption.
4,5

Figure 1.1. Structures of P3HT and P3AT.

2
Low-band gap polymers are most commonly prepared from a donor-acceptor (D-
A) approach, in which electron rich monomers are copolymerized with electron-poor
monomers.
6
Many state-of-the-art polymers are perfectly alternating structures
comprising symmetrical, fused heteroaromatic rings. However, 3-alkyl thiophenes (3AT)
have not been entirely retired from use. Some recently reported high-performing
polymers include P3TI,
7
PTPD3T,
8
and PffBT-T3(1,2)-2
9
(Figure 1.2). Alternating D-A
polymers have flourished in organic photovoltaic research, but new monomer discovery
is relatively latent. At present, a great majority of backbone permutations have been
realized under the 1:1 donor:acceptor ratio.
10

Figure 1.2. Structures of P3TI, PTPD3T, and PffBT-T3(1,2)-2.
To this end, random and semi-random donor-acceptor systems are a valuable
approach for tuning band gaps, charge mobility, and polymer miscibility. Few research
teams have successfully investigated random analogs of alternating D-A polymers,
11,12

3
which suggests that some D-A polymers may benefit from careful refinement backbone
structure. Important design parameters of random systems, such as ideal D-A ratios and
sequence distribution, are a primary focus of research. Semi-random polymers are
exclusively 3AT based, renewing interest in P3HT-like polymers.
Semi-random P3HT based polymers for use in organic solar cells were first
reported in 2011.
13
The motivation behind semi-random polymers is joining desirable
properties of P3HT and narrow band gaps of alternating D-A polymers. Semi-random
polymers are prepared via Stille polycondensation conditions whereby 80% of the
monomer feed ratio comprises 3-hexyl thiophene, leading to their solution processability
and fullerene miscibility. The remaining 20% incorporates an electron-poor monomer
and thiophene, which engenders smaller band gaps. New families of random P3HT
copolymers also selectively tune properties by careful side chain modification. Likewise,
random P3HT systems have been applied to semi-random polymers to further modulate
frontier energy levels.
This introduction surveys structure-function relationships, photovoltaic properties,
and broader impacts of random and semi-random P3HT polymers. Modularity of 3AT
monomers and bonding schemes will be discussed as valuable tools for designing P3HT-
like polymers with higher efficiencies attainable by the parent homopolymer.

1.2 Classification of Random and Semi-Random P3HT based systems
Semi-random polymers are unique compared to random and perfectly alternating
backbones. Restricted linkage patterns allows for the backbone to comprise primarily 3-
hexyl thiophene with low, randomized incorporation of an acceptor (Figure 1.3).

4
Selecting monomer units bearing specific complementary functional groups necessary for
aryl-aryl bond formation controls linkage patterns in random and semi-random
polymerizations. Stille polycondensation, one of the most widely utilized polymerizations
for conjugated polymers, requires an aryl bromide and stannyl group.
14
As depicted in
Figure 1.3, random polymers can be obtained by selectively preparing each monomer to
have both a bromo and stannyl functional group (AB functionalized). Semi-random
polymers diverge from the random structure by utilizing three monomers with non-
identical functionalization: AB, AA (distannyl), and BB (dibromo).

Figure 1.3. Stille polycondensation of P3HT-TP (random copolymer) and P3HTT-TP
(semi-random copolymer) from monomer sources.

Random polymers prepared from AB functionalized monomers ensure regio-
regularity, an important property in P3ATs,
15
while allowing for precise control over
monomer ratios. This bonding structure is beneficial for tuning specific properties of
P3ATs, such as frontier orbital levels,
16–18
optical absorption,
19
and miscibility.
20

5
Currently, studies of completely randomized analogs of perfectly alternating D-A
polymers are limited.
3,12
Recent studies present poor photovoltaic performance, which is
attributed to charge carrier traps and acceptor-acceptor linkages in the polymer
backbone.
21
Thus, random systems are proven to be effective for fine-tuning specific
electronic and physical properties, but are not ideal for push-pull D-A polymers.
One reason there are few examples of random D-A polymers is due to limited
synthetic precedence unsymmetrical, or AB functionalized, acceptor monomers.
Moreover, many acceptor monomers do not form stable organo-lithium intermediates
required for forming stannyl compounds. To date, a di-stannyl diketopyrrolopyrrole
(DPP)
22
and difluoro-benzothiadiazole (ffBTD)
23
have been prepared. Still, many rely on
di-bromo and di-boronic ester functionalized monomers to prepare random D-A polymers
via Suzuki polycondensation. The aforementioned drawbacks of random D-A polymers
can be resolved by a semi-random bonding structure. Three distinct sets of functionalized
monomers (AB, AA, and BB) are used in semi-random copolymerizations. Here, simple
di-bromo functionalized acceptor monomers can be used, preventing acceptor-acceptor
linkages. This strategy also ensures maintenance of regioregularity of 3AT (AB
monomer) and a random dispersion of D-A chromophores.
It should be noted that acceptor-acceptor linkages can be avoided in D-A
polymers by utilizing an AA
D1
/BB
D2
/BB
A1
or a AA
D1
/BB
A1
/BB
A2
system where 1) all
monomers are symmetric, 2) AA
D1
and BB
D2
are electron-rich, donor monomers, but not
necessarily identical, 4) BB
A1
and BB
A2
are di-bromo acceptor monomers, also not
necessarily identical, and 3) overall ratio of AA functional groups is equal to di-bromo
(BB) functional groups (Figure 1.4). This bonding scheme is more generally referred to

6
as a random polymer, despite the implication of both regular and restricted linkage
patterns.
12,24–27
Namely, these bonding schemes are “semi-alternating” in nature: AA
D1
is
alternating while BB monomers are randomly distributed. The AB/AA/BB semi-random
bonding scheme is distinct from AA/BB/BB systems; AA and BB monomers must be
stoichiometrically balanced to each other, but their combined feed ratio can be modified
with respect to the AB monomer. In this case, no particular monomer is restricted to an
alternating fashion and AA and BB monomers can still be randomly distributed through
the backbone. Moreover, semi-alternating copolymerizations are not regio-selective while
regio-regularity is maintained for AB monomers in semi-random copolymers. To date,
most semi-random P3AT D-A polymers have feed ratios of AA and BB ranging from 5
to 15% each, maintaining an overall ratio of 70 to 90% 3-alkyl thiophene.

Figure 1.4. Semi-alternating copolymer bonding scheme.

7
The modularity and scope of semi-random D-A polymers is realized by
considering the structure into two main parts: 1) a 3-alkyl thiophene that is AB
functionalized and comprises a majority of the backbone, and 2) an electron-poor
acceptor monomer that is BB functionalized and stoichiometrically balanced by di-
stannyl thiophene. The availability of di-bromo acceptor monomers is diverse. More
recent studies expand knowledge on simple acceptor modifications such as changes in
solubilizing groups, backbone fluorination, or identity of flanking aromatic substituents.
Similarly, the library of AB 3AT monomers is also expanding to include simple
structures that can tune a wide array of polymer properties. Semi-random polymers
facilitate highly desirable donor-acceptor interactions, but are not limited by 1:1 ratio or
semi-alternating linkage patterns. Thus, the semi-random D-A platform is ripe for
expansive investigation.

1.3 Fine-tuning Random P3HT Polymers
Before surveying the field of semi-random D-A polymers, a brief history of
random P3HT copolymers will be presented. Random P3HT co-monomers comprise a
thiophene ring and a modified functional group in the 3-position. Random
copolymerization is achieved by Stille polycondensation and availability of AB
functionalized monomers. While alkyl thiophenes
18
are prepared through a standard
lithiation and subsequent stannylation procedure, other polar functional groups are
obtained through a magnesiated intermediate (Figure 1.5).
19,20,28
Specifically, the
commercially available Knöchel-Hauser base (2,2,6,6-tetramethylpiperdinylmagesium
chloride lithium chloride complex, TMPMgCl!LiCl) is utilized for selective formation of

8
the required organo-magensium intermediates, facilitating the complete synthesis of
previously unreported monomers. The remarkable functional group tolerance of
TMPMgCl!LiCl expands the scope of functionalized thiophenes available for region-
regular polycondensations. In all cases, feed ratios of the copolymers were confirmed by
1
H NMR spectroscopy and each copolymer family was fully characterized optically and
electronically.

Figure 1.5. Stille polycondensation of P3HT random copolymers.

9
Table 1.1. Molecular weights (Đ), electrochemical HOMO values, optical band gaps, and
SCLC mobilities of P3HT and random P3HT copolymers.
Polymer
M
n
(kDa)
(Đ)

HOMO (eV)
(film; solution)

E
g

(eV)

µ
h
(cm
2
V
-1
s
-1
)

P3HT 24.2 (2.7) -5.17; -5.25 1.90 2.30 x10
-4

P3HT
90
-co-EHT
10
21.3 (2.5) -5.30; -5.25 1.90 1.77 x10
-4

P3HT
75
-co-EHT
25
26.1 (2.5) -5.43; -5.30 1.90 1.39 x10
-4

P3HT
50
-co-EHT
50
40.1 (2.0) -5.48; -5.32 1.90 1.07 x10
-4

P3EHT 22.1 (2.9) -5.57; -5.28 2.00 2.87 x10
-5

P3HT-CNT-5% 11.0 (1.9) -5.30 1.90 1.51 x10
-4

P3HT-CNT-10% 12.0 (2.4) -5.31 1.88 1.03 x10
-4

P3HT-CNT-15% 10.0 (2.1) -5.34 1.90 8.54 x10
-5

P3HT-CNT-20% 14.0 (2.1) -5.31 1.87 6.15 x10
-5

P3HT-CNT-EHT (15:15) 9.6 (2.5) -5.38 1.90 1.14 x10
-4
P3HT-CNT-EHT (20:20) 8.1 (2.2) -5.43 1.90 0.69 x10
-4

P3HT-CNT-EHT (25:25) 6.4 (1.8) -5.55 1.89 0.44 x10
-4

P3CNT-EHT (50:50) 4.3 (1.5) -5.78 1.90 0.16 x10
-4

P3HT
90
-co-3HOT
10
19.5 (2.1) -5.13 1.85 3.00 x10
-4

P3HT
75
-co-3HOT
25
19.4 (2.6) -5.07 1.77 6.80 x10
-5

P3HT
50
-co-3HOT
50
11.9 (3.0) -4.96 1.70 1.00 x10
-5

Modification of solubilizing side chains is known to have considerable effects on
the photovoltaic properties of conjugated polymers.
13,14,17
However, by 2010, relatively
few controlled studies had been completed to carefully sift through electronic, optical,

10
and physical effects when linear alkyl chains are replaced with branched analogs. This
considerable gap in literature served as motivation for using P3HT and poly(3-(2-
ethylhexyl)thiophene) (P3EHT) as a case study. Burkhart and coworkers prepared the
aforementioned homopolymers and a series of random copolymers with varied ratios of
monomers (10, 25, and 50% of 3-(2-ethylhexyl)thiophene).
18
A notable result from this
study is the impact of branched alkyl chains on HOMO levels of polymers and V
OC
of
photovoltaic devices.
Solution and film CV experiments revealed that the HOMO level of polymers in
the solid state dropped with increasing content of the branched alkyl chain, but
maintained relatively the same in solution (Table 1.1). This change in solid-state HOMO
level was reflected by an inverse correlation to measured V
OC
, whereby the value trended
between 0.60 (P3HT) and 0.90 V (P3EHT). Specifically, P3HT
75
-co-EHT
25
benefited
from increased V
OC
(0.69 V), similar J
SC
to P3HT (9.85 mA/cm
2
), with an overall
efficiency of 3.85% (Table 1.2). In summary, band gaps of the random copolymers were
unchanged compared to P3HT and the polymers maintained regio-regularity and semi-
crystallinity, suggesting random incorporation of small amounts of a modified 3-alkyl
thiophene monomer is an effective method for selectively tuning specific properties.

Table 1.2. Photovoltaic properties of P3HT and random P3HT copolymers.
Polymer (Polymer:PC
61
BM Ratio) J
SC
(mA/cm
2
)
c
V
OC
(V) FF PCE (%)
P3HT (1:1) 9.67 0.60 0.60 3.48
P3HT
90
-co-EHT
10
(1:0.8) 9.26 0.63 0.51 2.80
P3HT
75
-co-EHT
25
(1:0.8) 9.85 0.69 0.57 3.85

11
Table 1.2 Continued
Polymer (Polymer:PC
61
BM Ratio) J
SC
(mA/cm
2
)
c
V
OC
(V) FF PCE (%)
P3HT
50
-co-EHT
50
(1:3.5) 2.52 0.85 0.35 0.74
P3EHT (1:3.0) 2.54 0.90 0.36 0.83
P3HT-CNT-5% (1:1) 7.02 0.72 0.58 2.96
P3HT-CNT-10% (1:1.3) 8.16 0.75 0.55 3.33
P3HT-CNT-15% (1:1.3) 7.56 0.81 0.55 3.28
P3HT-CNT-EHT (15:15) (1:1.3) 8.02 0.83 0.54 3.60

P3HT-CNT-EHT (20:20) (1:1.3) 8.23 0.84 0.46 3.20
P3HT-CNT-EHT (25:25) (1:0.8) 7.12 0.88 0.42 2.60
P3CNT-EHT (50:50) (1:0.9) 2.36 0.91 0.38 0.80

Random incorporation of branched ethyl-hexyl side chains is an effective method
for modulating the HOMO between 100 to 300 mV without major impacts to desirable
properties of P3HT. Subsequent studies include models for tuning HOMO levels of
random P3HT copolymers by using electron donating or withdrawing functionalities – 3-
hexyloxy (3HOT) and 3-cyanothiophene (3CNT), respectively. The latter case study
demonstrates that small feed ratios of 3CNT effectively lowers the HOMO (Table 1.1),
maintains regio-regularity, semi-crystallinity, solution-processability, and fill factors of
0.55 and greater (Table 1.2).
28
However, P3HT-CNT-20% was found not to be soluble
enough for device fabrication. To this end, Rudenko and coworkers combined both 3EHT
and 3CNT to overcome solubility restrictions associated with 3CNT ratios greater than
15%.
17
Polymers with 3CNT ratios of 15, 20, 25, and 50%, with matching 3EHT ratios,

12
were sufficiently soluble for full characterization and device fabrication (Table 1.2). The
synergistic effects of 3EHT and 3CNT contributed towards a overall lower HOMO level
of P3HT-CNT-EHT terpolymers compared to P3HT-CNT copolymers. Levels as deep as
-5.55 and -5.78 eV were attainable with the combined comonomer approach due to the
solubility imparted by the branched ethyl-hexyl side chain.
The previously mentioned 3HOT monomer was utilized in random P3HT
copolymers to promote the opposite effect on HOMO levels.
19
Alkyloxy thiophenes have
been previously studied and characterized, demonstrating lower band gaps and raised
HOMO levels compared to 3AT analogs of homopolymers
30
and alternating D-A
polymers.
31
Previously, only one case of a regio-regular random copolymer, prepared by
GRIM polymerization, had been reported.
32
Random P3HT-co-3HOT polymers are
consistent with reported optical and electronic effects; the decrease in HOMO level and
band gap could be tuned with varying the composition of 3HOT (Table 1.1).
The availability of AB functionalized 3HOT monomers via a magnesiated
intermediate facilitated a new achievement with semi-random D-A polymers. Small
incorporations of 3HOT monomers in place of some of the 3HT feed ratio offered
another handle for finely tuning electronic and optical properties of semi-random D-A
polymers.

1.4 Semi-Random P3HT Donor-Acceptor Polymers
The first report of semi-random P3HT D-A polymers focused on characterizing
polymer properties resulting from small feed ratios of dibromo functionalized acceptors;
benzothiadiazole (BTD) and thienopyrazine (TP).
13
Polymerizations of reported semi-

13
random P3HT D-A polymers are highly reproducible, easily isolated via precipitation,
and purified using standard Soxhlet extraction techniques (Figure 1.6). The resulting
polymers, P3HTT-BTD and P3HTT-TP, exhibited broadened absorption profiles and
reduced band gaps from 1.91 eV (P3HT) to 1.62 and 1.36 eV, respectively, and nearly
identical hole mobilities as P3HT (Table 1.3).

Figure 1.6. Semi-random P3HT D-A copolymer structures.
Absorption breadth could be extended into near IR, and a lower band gap of 1.27
eV could be obtained if both acceptor units were incorporated, where BTD and TP each
comprised 8.75% of the overall feed ratio in P3HTT-TP-BTD (Figure 1.7, Table 1.3).
Semi-random polymers containing BTD maintained semi-crystallinity, as determined by

14
GIXRD. Despite promising properties, photovoltaic device performances suffered from
poor J
SC
and FF, suggesting continued study of alternative donor-acceptor systems would
be necessary (Table 1.4).
Table 1.3. Molecular weights (Đ), electrochemical HOMO values, optical band gaps, and
SCLC mobilities of P3HT semi-random D-A copolymers.
Polymer M
n
(kDa) (Đ)
HOMO
(eV) (film)
E
g
(eV) µ
h
(cm
2
V
-1
s
-1
)
P3HT 24.2 (2.7) -5.17 1.90 2.30 x10
-4

P3HTT 47.8 (1.75) -5.29 1.96 8.21 x10
-5

P3HTT-BTD

15.3 (2.45) -5.41 1.62 2.06 x10
-4

P3HTT-TP 16.6 (2.35) -5.23 1.36 2.50 x10
-4

P3HTT-TP-BTD 16.3 (2.05) -5.11 1.27 2.35 x10
-4

P3HTT-DPP-5% 19.0 (2.8) -5.20 1.52 1.1 x10
-4

P3HTT-DPP-10% 24.6 (2.3) -5.20 1.51 2.3 x10
-4

P3HTT-DPP-15% 17.6 (2.9) -5.20 1.46 1.3 x10
-4

P3HTT-TPD-10% 22.6 (2.0) -5.40 1.82 0.8 x10
-4

P3HTT-TPD-15% 12.1 (2.1) -5.40 1.80 0.7 x10
-4
P3HT-TPD-DPP (1:1) 11.7 (2.9) -5.35 1.48 1.5 x10
-4

P3HT-TPD-DPP (1:2) 12.7 (3.4) -5.30 1.50 1.6 x10
-4

P3HT-TPD-DPP (2:1) 19.7 (3.1) -5.30 1.47 1.9 x10
-4

P3HTT-BTD-TPD 16.8 (3.0) -5.40 1.64 1.5 x10
-4

P3HTT-BTD-DPP 15.4 (3.4) -5.22 1.47 1.9 x10
-4

P3HTT-TP-TPD 12.6 (3.3) -5.29 1.32 1.3 x10
-4

P3HTT-TP-DPP 22.8 (2.4) -5.14 1.32 1.1 x10
-4

15

Figure 1.7. Semi-random dual acceptor P3HT D-A copolymer structures.

Table 1.4. Photovoltaic properties of P3HT and semi-random P3HT D-A copolymers.
Polymer (Polymer:PC
61
BM Ratio) J
SC
(mA/cm
2
)
c
V
OC
(V) FF PCE (%)
P3HT (1:1) 9.67 0.60 0.60 3.48
P3HTT-BTD (1:1.5) 2.87 0.79 0.33 0.75
P3HTT-TP (1:0.8) 3.22 0.44 0.50 0.71
P3HTT-TP-BTD (1:0.8) 3.04 0.39 0.37 0.43
P3HTT-DPP-5% (1:1) 9.57 0.66 0.58 3.60
P3HTT-DPP-10% (1:1.3) 14.62 0.59 0.64 5.53
P3HTT-DPP-15% (1:2.6) 14.28 0.51 0.65 4.66
P3HTT-TPD-10% (1:1.5) 5.38 0.72 0.58 2.22

P3HTT-TPD-15% (1:1.3) 5.33 0.68 0.56 2.02

16
Table 1.4 Continued
Polymer (Polymer:PC
61
BM Ratio) J
SC
(mA/cm
2
)
c
V
OC
(V) FF PCE (%)
P3HT-TPD-DPP (1:1) (1:1.7) 15.26 0.51 0.64 4.93
P3HT-TPD-DPP (1:2) (1:1.5) 11.67 0.55 0.62 3.94
P3HT-TPD-DPP (2:1) (1:2.0) 16.37 0.50 0.61 4.92
P3HTT-BTD-TPD (1:1.3) 6.89 0.58 0.62 2.48
P3HTT-BTD-DPP (1:1.1) 10.91 0.50 0.55 2.97
P3HTT-TP-TPD (1:1.1) 4.56 0.36 0.48 0.78
P3HTT-TP-DPP (1:1.3) 7.94 0.36 0.48 1.37

Shortly thereafter, high efficiencies were obtained from semi-random polymers
utilizing DPP (Figure 1.6).
33
The overall ratio of DPP was optimized at 10%, where 5%
and 15% feed ratios only exhibited small improvements in photovoltaic performance
compared to P3HT (Table 1.4). Hole-mobilities, semi-crystallinity, and near 1:1
polymer:fullerene blending ratios were maintained close to that of P3HT for the P3HTT-
DPP-10% semi-random polymer. Overall efficiency was optimized to 4.94% where the
photovoltaic device benefited from a greater J
SC
imparted by the absorption breadth of the
polymer; P3HTT-DPP-10% was later optimized to reach 5.7% PCE.
34
DPP is an ideal
acceptor unit for the semi-random D-A platform because of its simple synthesis, high
planarity, high charge carrier mobility, and multiple sites for further modifications
(aromatic flanking units, alkyl side chains).
Dual-acceptor semi-random polymers with DPP have also been characterized and
useful for identifying donor/acceptor combinations. The previously mentioned P3HTT-
TP-BTD was unprecedented in its strong and uniform light absorption from 400 – 1000

17
nm. Thienopyrroledione (TPD) was copolymerized as a secondary acceptor to DPP, with
varied TPD:DPP ratios and maintaining an overall acceptor content of 15% (Figure
1.7).
34
Dual-acceptor semi-random P3HTT-TPD-DPP polymers exhibited good
photovoltaic performance with efficiencies approaching 5% and improved J
SC
compared
to P3HTT-DPP polymers (Table 1.4).
Both TPD and DPP acceptors were utilized in dual-acceptor semi-random
polymer studies with previously known BTD and TP acceptors to prepare P3HTT-BTD-
TPD, P3HTT-BTD-DPP, P3HTT-TP-TPD, and P3HTT-TP-DPP (Figure 1.7).
35
The
resulting BTD and TP containing polymers also exhibited broadened absorption profiles
with improved photovoltaic performances compared to P3HTT-TP-BTD, although
P3HTT-TPD-DPP still exceeded in performance (Table 1.4).
Dual-acceptor semi-random polymers are an effective route towards
improvements on absorption breadth of P3HT based systems. Accordingly, dual-donor
systems were also investigated as a potential avenue for improving polymer properties
through maximizing push-pull character in the polymer backbone. Dithienopyrrole
(DTP), a strong donor monomer, was copolymerized to semi-random P3HTT-DTP and
semi-random D-A polymers; P3HTT-DPP-DTP, P3HTT-BTD-DTP, and P3HTT-TP-
DTP (Figure 1.8).
36
Absorption profiles and band gaps were relatively unchanged from
semi-random D-A polymers without DTP (Table 1.5). However, HOMO levels were
significantly higher for DTP polymers with BTD and TP, suggesting the LUMO shifted
concomitantly. Accordingly, photovoltaic performances of DTP containing polymers
were lower than semi-random P3HTT-BTD and P3HTT-TP, which can be attributed to
the smaller LUMO
ACCEPTOR
to HOMO
DONOR
offset and effectively lower V
OC
. P3HTT-

18
DPP-DTP photovoltaic efficiency was greater than other DTP containing polymers, but
could still benefit from continued optimization to better match or surpass J
SC
and FF of
P3HTT-DPP (Table 1.6)

Table 1.5. Molecular weights (Đ), electrochemical HOMO values, optical band gaps, and
SCLC mobilities of P3HT semi-random D-A copolymers.
Polymer M
n
(kDa) (Đ)
HOMO
(eV) (film)
E
g
(eV) µ
h
(cm
2
V
-1
s
-1
)
P3HTT-DPP-DTP 19.6 (3.6) -5.18 1.47 1.40 x10
-4

P3HTT-BTD-DTP 20.0 (2.8) -5.15 1.61 6.21 x10
-5

P3HTT-TP-DTP

21.2 (3.0) -5.05 1.38 7.03 x10
-5

P3HTT-HOT-DPP (75:5) 14.7 (3.1) -5.14 1.46 2.80 x10
-4

P3HTT-HOT-DPP (70:10) 18.5 (2.7) -5.11 1.44 2.00 x10
-5

P3HTT-HOT-DPP (65:15) 14.7 (2.9) -5.07 1.43 7.80 x10
-5

P3HTT-HOT-DPP (60:20) 15.8 (2.6) -4.98 1.41 2.3 x10
-5

P3HTT-HOT-DPP (40:40) 5.3 (3.82) -4.93 1.35 4.4 x10
-5

19

Figure 1.8. Semi-random P3HT D-A copolymer structures.
Table 1.6. Photovoltaic properties of semi-random P3HT D-A copolymers.
Polymer (Polymer:PC
61
BM Ratio) J
SC
(mA/cm
2
)
c
V
OC
FF PCE
P3HTT-DPP-DTP (1:1) 10.77 0.53 0.50 2.83
P3HTT-BTD-DTP (1:1) 1.48 0.47 0.31 0.21
P3HTT-TP-DTP (1:1) 1.81 0.35 0.28 0.18
P3HTT-HOT-DPP (75:5) (1:1) 12.64 0.53 0.57 3.79
P3HTT-HOT-DPP (70:10) (1:1) 11.02 0.45 0.53 2.64
P3HTT-HOT-DPP (65:15) (1:1) 10.92 0.40 0.48 2.11
P3HTT-HOT-DPP (60:20) (1:1) 8.65 0.37 0.47 1.51
P3HTT-HOT-DPP (40:40) (1:1) 4.89 0.23 0.36 0.40

20
Incorporation of the DTP donor monomer was achieved by via BB, or di-bromo,
functionalized monomer, which dictates that there are no direct linkages between DTP
and DPP. Alternatively, modification of the 3HT monomer with AB functionalization is a
route towards facilitating direct linkages between stronger donor monomers and DPP. Xu
and coworkers utilized the previously described 3HOT monomer to prepare P3HTT-
HOT-DPP semi-random polymers with varying ratios of 3HT to 3HOT (Figure 1.8).
19

While incorporation of DTP appeared to have minimal impact on the HOMO level and
band gap of P3HTT-DPP-DTP, small feed ratios of 3HOT both increased HOMO levels
and lowered band gaps. Ten percent of 3HOT in P3HTT-HOT-DPP was associated with
a 90 mV increase in HOMO level and decrease from 1.49 to 1.44 eV band gap (Table
1.5). Further increase of 3HOT content continues to raised HOMO levels and lower band
gaps of the semi-random D-A polymers, consistent with random P3HT-co-3HOT
polymer trends.
The increased HOMO levels of P3HT-HOT-DPP polymers trends inversely to the
observed V
OC
of photovoltaic devices, leading to lower overall efficiencies with
increasing content of 3HOT (Table 1.6). For 5 – 15% 3HOT content, J
SC
was maintained
above 10 mA/cm
2
, but the devices did not appear to benefit from the slightly extended
absorption onset of 3HOT polymers. Fill factors also fell slightly, possibly due to
changes in polymer chain packing indicated by GIXRD measurements, resulting in poor
morphologies. Moreover, oxidative instability of polymer films in ambient testing
conditions could not be ruled out. However, characterization of the P3HTT-HOT-DPP
family reveals that frontier orbital levels of semi-random polymers can be finely tuned
through careful monomer selection.

21
To date, many acceptor monomers and few modified 3-alkyl thiophene monomers
have been studied in semi-random P3HT-based D-A polymers. Yet previous work has
suggested the semi-random platform is ripe for both further investigation and
improvements upon existing benchmark efficiencies. One of the significant contributions
of semi-random polymers to the current mechanistic understanding of charge generation
and separation is use in ternary blend solar cells.
37
One design limitation inherent to
polymer:fullerene BHJ solar cells is the compromise between attainable J
SC
and V
OC
;
attempts to lower band-gaps and broaden profile absorption is often met with smaller
energetic offsets of LUMO
ACCEPTOR
and HOMO
DONOR
, and subsequently lower V
OC
.
Shortly after determining that V
OC
of solar cells could actually be tuned in a two fullerene
acceptor, one polymer donor BHJ ternary blends,
38
Khlyabich and coworkers blended
two polymer donors, P3HT-co-EHT and P3HTT-DPP, with one fullerene acceptor,
PCBM, to prepare a range of devices between the binary cases. A nearly linear trend was
established between V
OC
and content of P3HT-co-EHT, which has a lower-lying HOMO
than P3HTT-DPP.
37,39
The ternary blend solar cells benefited from higher J
SC
, derived
from the complementary absorption profiles of the two polymer donors, thus select
ternary blends achieved a higher overall efficiency compared to the binary cases.
Since, ternary blend solar cells have been widely investigated for other polymer
donors. However, there are cases in which the V
OC
is pinned to the lower value associated
with the smaller LUMO
ACCEPTOR
and HOMO
DONOR
offset. Polymer-polymer miscibility
has been identified as a key factor in determining the compatibility of donors for ternary
blend systems.
40,41
Miscibility of the previously investigated blends is attributed to the
random copolymer effect, which is achieved through random incorporation of common

22
comonomers in polymer structures.
42
As such, semi-random polymers are uniquely
suitable for use in ternary blend solar cells, due in part to their highly modular,
randomized structures. Additionally, surface energy is often used as a figure of merit for
predicting polymeric materials that are miscible, and has been investigated in tuning and
pinned V
OC
ternary blends.
40
Systems that benefit from V
OC
tuning utilize polymer
donors with similar surface energies. Conversely, ternary blends that have pinned V
OC

utilize polymer donors with dissimilar surface energies.
40

Seemingly, surface energy is a physical parameter that could be modified in
polymers with simple changes in the primary structure. To date, modular control over
surface energy in conjugated polymers is unexplored. Likewise, surface energy
measurements are not a part of standard characterization efforts of conjugated polymers.
Considering the previously established routes for optical and electronic modifications
through small changes in functional groups, surface energy modification of specific
polymer targets appears feasible.

1.5 Learning more about Semi-Random Donor-Acceptor Polymers
The semi-random D-A polymer platform in combination with ternary blend solar
cells is a powerful method for realizing tunable polymers with simple, low cost synthesis
and higher efficiency solar cells. In summary, semi-random and random polymer
properties are easily modulated through simple changes in monomer structures and fine
control over monomer feed ratios.
Inspired by the previously explored semi-random systems, this thesis is focused
on illuminating structure-function relationships in primary, secondary and tertiary

23
structures of conjugated polymers. Specifically, direct comparisons between completely
randomized and semi-random donor-acceptor polymers are investigated to determine the
impact of linkage patterns on properties. This study is possible through alternative
functionalization methods to prepare AB-type monomers that were previously
unreported. In addition, methods for surface energy modification of polymers through the
use of hydrophilic and hydrophobic functionalities are explored as an effort to expand
upon working knowledge of ternary blend solar cells. Polymer families with identical
optical and electronic properties, but with different surface energies, will be described.
All together, the research presented here serves to expand upon the fundamental
knowledge in semi-random polymer structures and to introduce new methods for surface
energy modification of polymers towards ternary blend solar cells.

1.6 References

(1) Sista, P.; Luscombe, C. K. In P3HT Revisited – From Molecular Scale to Solar Cell
Devices; Ludwigs, S., Ed.; Advances in Polymer Science; Springer Berlin
Heidelberg, 2014; pp 1–38.

(2) Marrocchi, A.; Lanari, D.; Facchetti, A.; Vaccaro, L. Energy Environ. Sci. 2012, 5
(9), 8457–8474.

(3) Khlyabich, P. P.; Burkhart, B.; Rudenko, A. E.; Thompson, B. C. Polymer 2013, 54
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(4) Zhenan Bao. In Polymers for Microelectronics and Nanoelectronics; ACS
Symposium Series; American Chemical Society, 2004; Vol. 874, pp 1–14.

(5) Bundgaard, E.; Krebs, F. C. Solar Energy Materials and Solar Cells 2007, 91 (11),
954–985.

(6) Beaujuge, P. M.; Fréchet, J. M. J. J. Am. Chem. Soc. 2011, 133 (50), 20009–20029.

(7) Wang, E.; Ma, Z.; Zhang, Z.; Vandewal, K.; Henriksson, P.; Inganäs, O.; Zhang, F.;
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24
(8) Guo, X.; Zhou, N.; Lou, S. J.; Smith, J.; Tice, D. B.; Hennek, J. W.; Ortiz, R. P.;
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Marks, T. J. Nat Photon 2013, 7 (10), 825–833.

(9) Hu, H.; Jiang, K.; Yang, G.; Liu, J.; Li, Z.; Lin, H.; Liu, Y.; Zhao, J.; Zhang, J.;
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14157.

(10) Po, R.; Bianchi, G.; Carbonera, C.; Pellegrino, A. Macromolecules 2015, 48 (3),
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(11) Nielsen, C. B.; Ashraf, R. S.; Schroeder, B. C.; D’Angelo, P.; Watkins, S. E.; Song,
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(12) Kang, T. E.; Choi, J.; Cho, H.-H.; Yoon, S. C.; Kim, B. J. Macromolecules 2016, 49
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(13) Burkhart, B.; Khlyabich, P. P.; Cakir Canak, T.; LaJoie, T. W.; Thompson, B. C.
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(14) Carsten, B.; He, F.; Son, H. J.; Xu, T.; Yu, L. Chem. Rev. 2011, 111 (3), 1493–1528.

(15) Osaka, I.; McCullough, R. D. Acc. Chem. Res. 2008, 41 (9), 1202–1214.

(16) Khlyabich, P. P.; Rudenko, A. E.; Thompson, B. C. J. Polym. Sci. Part A: Polym.
Chem. 2014, 52 (8), 1055–1058.

(17) Rudenko, A. E.; Khlyabich, P. P.; Thompson, B. C. J. Polym. Sci. Part A: Polym.
Chem. 2015, 1526–1536.

(18) Burkhart, B.; Khlyabich, P. P.; Thompson, B. C. Macromolecules 2012, 45 (9),
3740–3748.

(19) Xu, B.; Noh, S.; Thompson, B. C. Macromolecules 2014, 47 (15), 5029–5039.

(20) Howard, J. B.; Noh, S.; Beier, A. E.; Thompson, B. C. ACS Macro Lett. 2015, 725–
730.

(21) Li, W.; Hendriks, K. H.; Wienk, M. M.; Janssen, R. A. J. Acc. Chem. Res. 2016, 49
(1), 78–85.

(22) Hu, X.; Zuo, L.; Fu, W.; Larsen-Olsen, T. T.; Helgesen, M.; Bundgaard, E.;
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15710–15716.

25
(23) Jheng, J.-F.; Lai, Y.-Y.; Wu, J.-S.; Chao, Y.-H.; Wang, C.-L.; Hsu, C.-S. Adv.
Mater. 2013, 25 (17), 2445–2451.

(24) Kang, T. E.; Kim, K.-H.; Kim, B. J. J. Mater. Chem. A 2014, 2 (37), 15252–15267.

(25) Braunecker, W. A.; Oosterhout, S. D.; Owczarczyk, Z. R.; Kopidakis, N.; Ratcliff,
E. L.; Ginley, D. S.; Olson, D. C. ACS Macro Lett. 2014, 3 (7), 622–627.

(26) Hendriks, K. H.; Heintges, G. H. L.; Wienk, M. M.; Janssen, R. A. J. J. Mater.
Chem. A 2014, 2 (42), 17899–17905.

(27) Deng, P.; Wu, B.; Lei, Y.; Cao, H.; Ong, B. S. Macromolecules 2016, 49 (7), 2541–
2548.

(28) Khlyabich, P. P.; Rudenko, A. E.; Thompson, B. C. J. Polym. Sci. Part A: Polym.
Chem. 2014, 52 (8), 1055–1058.

(29) Mei, J.; Bao, Z. Chem. Mater. 2014, 26 (1), 604–615.

(30) Hu, X.; Xu, L. Polymer 2000, 41 (26), 9147–9154.

(31) Guo, X.; Ortiz, R. P.; Zheng, Y.; Kim, M.-G.; Zhang, S.; Hu, Y.; Lu, G.; Facchetti,
A.; Marks, T. J. J. Am. Chem. Soc. 2011, 133 (34), 13685–13697.

(32) Shi, C.; Yao, Y.; Yang; Pei, Q. J. Am. Chem. Soc. 2006, 128 (27), 8980–8986.

(33) Khlyabich, P. P.; Ng, C. F.; Thompson, B. C. Macromolecules 2011, 44 (13), 5079–
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(34) Burkhart, B.; Khlyabich, P. P.; Thompson, B. C. ACS Macro Lett. 2012, 1 (6), 660–
666.

(35) Burkhart, B.; Khlyabich, P. P.; Thompson, B. C. Macromol. Chem. Phys. 2013, 214
(6), 681–690.

(36) Burkhart, B.; Khlyabich, P. P.; Thompson, B. C. J. Photon. Energy 2012, 2 (1),
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(37) Khlyabich, P. P.; Burkhart, B.; Thompson, B. C. J. Am. Chem. Soc. 2012, 134 (22),
9074–9077.

(38) Khlyabich, P. P.; Burkhart, B.; Thompson, B. C. J. Am. Chem. Soc. 2011, 133 (37),
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(39) Street, R. A.; Davies, D.; Khlyabich, P. P.; Burkhart, B.; Thompson, B. C. J. Am.
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26

(40) Khlyabich, P. P.; Rudenko, A. E.; Burkhart, B.; Thompson, B. C. ACS Appl. Mater.
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(41) Khlyabich, P. P.; Rudenko, A. E.; Street, R. A.; Thompson, B. C. ACS Appl. Mater.
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27
CHAPTER 2 Fine Tuning Surface Energy of Poly(3-hexyl
thiophene) by Heteroatom Modification of the Alkyl Side
Chains
2.1 Introduction
Conjugated polymers are promising materials for low-cost, solution processable devices
such as organic solar cells and field effect transistors.
1
The structure-function
relationships of conjugated polymers have been widely explored to elucidate high
performing donor materials for organic photovoltaic (OPV) applications. Systematic
modification of the polymer’s primary structure to tune HOMO/LUMO levels and optical
band gaps is well understood through considering donor-acceptor push-pull effects and
chain packing.
2
To date, many features such as alternating,
3–5
random,
6,7
and semi-random
donor-acceptor structures,
8,9
backbone planarity,
10
and side-chains
5,6,11,12
have been tools
for manipulating polymer properties towards optimized short circuit currents (J
SC
) and
open circuit voltages (V
OC
).
13,14
Additionally, several studies have focused on how
primary polymer structure can influence polymer-fullerene interactions in binary bulk
heterojunction (BHJ) solar cells for optimized charge separation and transport.
15
Specific
arrangements and lengths of side chains have also been utilized to control fullerene
miscibility and intercalation.
16–18
Significant progress in this field of research has pushed
single-layer BHJ solar cells with state-of-the-art donor materials to record efficiencies in
the range of 8 – 10%.
19

An emerging class of devices, known as ternary blend solar cells, utilizes either two
acceptors and one donor (D:A1
x
A2
(1-x)
)
20
or two donors with one acceptor (D1
x
D2
(1-x)
:A),
21

where x represents the composition range from 0 to 1. More typically, ternary blends with
two donors have been found to benefit from enhanced J
SC
due to complementary

28
absorption, and composition-dependent V
OC
derived from the synergistic donor
materials.
22
Recently, we reported that polymer compatibility between two polymer donor
materials is a significant factor in the formation of previously described organic alloys,
leading to an intermediate V
OC
rather than a lower, pinned value that would suggest hole-
trapping in the highest lying HOMO.
23
The organic alloy model suggests that two donors
or acceptors experience an averaging of frontier orbitals when there is miscibility
between the materials. Specifically, the random-copolymer effect
24
supports polymers
pairs that demonstrated alloying behavior; which are random or semi-random, based on
common comonomers, and exhibit co-crystallization behavior. More generally, similar
surface energy was attributed as a key figure of merit for predicting pairs of polymers
that may be used synergistically together in a ternary blend system. In the case of
dissimilar surface energies, devices fabricated with blends containing two donors, up to
95% composition of the lower-lying HOMO polymer, showed pinning to the V
OC

corresponding to that of the other higher-lying HOMO polymer. Whereas devices
incorporating two donor materials with similar surface energies showed a
compositionally dependent V
OC
.
23
Surface energy can be correlated with a material’s
Flory Huggins interaction parameter (χ) which is used to characterize polymer-polymer
interactions.
25
Several recent studies have included surface energy measurements and
indicate it as a strong predictor of material compatibility in organic photovoltaics.
26–34

Currently, features of conjugated polymer primary structure and their influence on
surface energy remains widely unexplored, even though such information may be a
useful tool for predicting favorable candidates for binary and especially ternary blend
solar cells. Moreover, a modular method for tuning the surface energy of existing state-

29
of-the-art conjugated polymers without altering their desirable optical and electronic
properties may enable more pairing options for ternary blends from well-known polymers
with complementary absorption profiles and different HOMO levels. While a handful of
successful ternary blend systems have been identified,
20,21,35–37
little is known about the
influence of primary structure on cooperative effects in these materials, which has
prompted the need for a better understanding and control of polymer-polymer
interactions and blending.
20–22

2.2 Results and Discussion
P3HT is a well-known conjugated polymer used in BHJ solar cells, with a simple
primary structure that may be manipulated for studying surface energy as an isolated
variable. With the goal of maintaining the optical and electronic properties of P3HT, the
alkyl side chains were identified as a point of modification towards tuning surface
energy. Previous studies have established that small incorporation of a comonomer into a
regio-regular copolymer can fine tune specific polymer properties while maintaining the
desirable properties of P3HT.
6,8,9
In the present case, the alkyl chains were modified to
contain varying amounts of fluorine or oxygen atoms to induce hydrophobic or
hydrophilic interactions, respectively, and directly control the surface energy. Precise
control of the comonomer compositions allows for tuning of the surface energy.
Modification of the alkyl chain was executed with a spacer of at least two carbons in
length to diminish any electronic effects from the heteroatoms on the conjugated
backbone.

30
Synthesis of comonomer, 4 (Figure 2.1), was achieved from modified literature
procedures,
38
via a Wittig coupling, followed by hydrogenation, electrophilic bromination
and finally a lithiation and subsequent stannylation. Comonomer 7 (Figure 2.1) was also
prepared following modifications of previous literature procedures
39
by an electrophilic
bromination followed by a Williamson-ether synthesis. Intermediate 6 could not be
stannylated via the 5-lithiated intermediate, which led to inseparable isomers, but rather a
5-magnesiated intermediate generated from the Knochel-Hauser base.
40,41
To the best of
our knowledge, this is the first report of both of the final monomers with the 5-position
functionalized with a trimethyl tin group. To date, the previously reported monomer
precursors 3 and 6, and similar monomer structures with longer oligoether or semi or per-
fluoroalkyl chains, have been used in oligomer syntheses,
38,42
GRIM,
43,44
oxidative,
45
or
electropolymerizations
46–48
to form homopolymers.
Comonomers 4 and 7 were subsequently copolymerized in 10 – 50% feed ratio
with 2-bromo-3-hexyl-5-(trimethylstannyl) thiophene under Stille polycondensation
conditions (Figure 2.2, M
n
and PDI reported in Table 2.1.) Proton NMR spectra of the
polymers support the feed ratios and composition of the comonomers (Figure A1.4 and
A1.5). Polymers containing a semi-fluoro alkyl chain are designated as P3HT
X
-co-
FHT
100-X
with x representing percent composition of 3-hexyl thiophene. Likewise,
polymers containing a methoxy-ethoxy-ethyl chain are designated as P3HT
X
-co-MET
100-
X
. This is the first report of regio-regular, random P3HT-co-FHT. While Bilkay and
coworkers44 previously reported P3HT-co-MET via GRIM with different feed ratios,
this is the first report of P3HT-co-MET via Stille polycondensation, which is made
possible by successful stannylation to prepare monomer 7. P3HT-co-FHT polymers

31
exhibited decreasing solubility in o-DCB with increasing content of the comonomer, to
the extent that P3HT
50
-co-FHT
50
was not sufficiently soluble for GPC analysis. For this
reason, we chose only compare up to 50% composition for both polymer families.

Figure 2.1. Synthesis of comonomer 4 and 7.

32

Figure 2.2. Stille polycondensation of P3HT-coFHT and P3HT-co-MET.
Critically, surface energies of the polymers were determined using a contact angle
goniometer. Contact angle measurements of water on pristine, as-cast polymer films
revealed that P3HT-co-FHT polymer surface energy steadily decreases with increasing
content of the semi-fluoro alkyl thiophene monomer (Figure 2.3a). Incorporation of the
comonomer up to 50% resulted in surface energy as low as 14.2 mN/m compared to
P3HT at 19.9 mN/m for as cast blends. This trend is also observed in thermally annealed
polymer films (Figure 2.3b), however P3HT-co-FHT polymers with 10-30% FHT
composition appear to have roughly the same surface energy as P3HT. This is perhaps
due to a change in content of fluoro side chains at the polymer film surface relative to the
bulk after thermal annealing. In contrast, polymers containing methoxy-ethoxy-ethylene
side chains gradually increased in surface energy, up to 27.0 mN/m and 26.3 mN/m at
50% comonomer composition for as cast and annealed films, respectively (Figure 2.3).

33

Figure 2.3. Surface energy of P3HT-co-MET (blue) and P3HT-co-FHT (red) polymers
measured from a) as cast thin films and b) thermally annealed thin films. P3HT-co-MET
and P3HT films were annealed at 100 °C, P3HT-co-FHT films were annealed at 150 °C.
Surface energy calculations based on a two-liquid approach, using water and
glycerol, with the Wu Model were also completed and the data is available in the SI
(Figure A1.7). While our previous research and others have utilized the Wu Model,
23,26,29–
31
here, we choose to present the one-liquid method due to previously reported large
variations in surface energy measurements with the two-liquid method when the pair of
testing liquids does not include a completely dispersive and compatible solvent that can
be used consistently for all samples.
49,50
Many material studies of surface energy utilize
diiodomethane as the dispersive solvent, which poses solubilizing problems during the
measurement of the solid conjugated polymer films. Previous measurements of
conjugated polymers, including our own, have opted to use glycerol as the dispersive
solvent for the two-liquid method, however glycerol may pose a solubilizing problem for
the P3HT-co-MET polymer family. As such, the one-liquid method with water is found
to be most applicable to this study.

34
While the desired effect on surface energy was clearly demonstrated, importantly
the optical and electronic properties were found to be unaffected by side chain identity
and composition. The optical properties of the resulting polymers were characterized by
UV-Vis, specifically to explore effects of comonomer composition on polymer band gap
and absorption coefficient in films cast from chloroform. Absorption profiles for both
P3HT-co-MET and P3HT-co-FHT families are P3HT-like, with lower absorption
coefficients for both as cast (Figure 2.4) and annealed films (Figure A1.8) relative to
P3HT. Absorption coefficients for all P3HT-co-FHT polymers increase and vibronic
shoulders are more prominent after thermal annealing, (Figure A1.8a). P3HT-co-MET
polymers absorption coefficients remain the same after annealing, with the exception of
P3HT
50
-co-MET
50
, which decreases slightly. All P3HT-co-MET polymers absorption
maxima blue shift between 20 – 30 nm after annealing. Strikingly, some polymers, such
as P3HT
60
-co-MET
40
and P3HT
50
-co-MET
50
bear prominent vibronic shoulders in the as-
cast blends where others do not (Figure 2.4b).
The absorption coefficient decreases could be explained given the volume of the
polymeric material, as polymers containing a higher content of the heteroatom chains
(both of which are seven atoms in length) spatially contain less chromophore than that of
P3HT with six-carbon alkyl chains. Alternatively, the presence of heteroatom alkyl
chains may induce varied packing compared to that of P3HT, which would be reflected
the in absorption profiles and maxima.
46
The differences in absorption coefficient and
maxima were investigated by GIXRD and discussed later. P3HT
60
-co-MET
40
and P3HT
50
-
co-MET
50
polymers feature vibronic shoulders in as cast blends, similar to what is seen
for P3HT films after annealing (Figure 2.4b), suggesting self-organization within the

35
films without the need for thermal or solvent vapor annealing. Optical band gaps, derived
from absorption onset of films, of all polymers are 1.9 eV (Table 2.1), unchanged by the
alkyl chain modification.

Figure 2.4. Absorption profiles of a) as-cast P3HT-co-FHT, and b) as-cast P3HT-co-
MET films; i) P3HT, ii) P3HT
90
-co-FHT
10
, iii) P3HT
80
-co-FHT
20
, iv) P3HT
70
-co-FHT
30
,
v) P3HT
60
-co-FHT
40
, vi) P3HT
50
-co-FHT
50
, vii) P3HT
90
-co-MET
10
, viii) P3HT
80
-co-
MET
20
, ix) P3HT
70
-co-MET
30
, x) P3HT
60
-co-MET
40
, and xi) P3HT
50
-co-MET
50
.

36
Table 2.1. Molecular weights (PDI), electrochemical HOMO values, HOMO values,
optical band gaps, and SCLC mobilities of P3HT, P3HT-co-FHT and P3HT-co-MET
polymers.
Polymer
M
n
(kDa)
(PDI)
a

HOMO (eV)
(film
b
; solution
c
)

E
g

(eV)
µ
h

(cm
2
V
-1
s
-1
)
e

T
m
; T
c

(°C)
P3HT 25.7 (2.6) 5.24; 5.25 1.9 8.10 x10-5 221; 186
P3HT
90
-co-FHT
10
41.8 (1.7) 5.30; 5.30 1.9 1.02 x10-5 221; 187
P3HT
80
-co-FHT
20
42.9 (1.7) 5.30; 5.29 1.9 7.98 x10-5 231; 205
P3HT
70
-co-FHT
30
40.9 (1.8) 5.28; 5.30 1.9 2.86 x10-5 236; 216
P3HT
60
-co-FHT
40
29.1 (1.8) 5.27; 5.30 1.9 1.46 x10-5 233; 213
P3HT
50
-co-FHT
50
- 5.30; 5.30 1.9 5.45 x10-5 239; 221
P3HT
90
-co-MET
10
23.6 (2.0) 5.29; 5.29 1.9 3.45 x10-5 - ; -
P3HT
80
-co-MET
20
21.0 (2.0) 5.29; 5.29 1.9 1.35 x10-5 - ; 109
P3HT
70
-co-MET
30
14.5 (2.3) 5.27; 5.30 1.9 2.38 x10-5 - ; 124
P3HT
60
-co-MET
40
9.9 (1.6) 5.25; 5.29 1.9 1.78 x10-5 - ; 99
P3HT
50
-co-MET
50
8.5 (1.4) 5.29; 2.58 1.9 1.51 x10-5 - ; 115
a
Determined by SEC with polystyrene standards and o-DCB eluent.
b
Cyclic voltammetry (vs Fc/Fc
+
) in
chloroform, 0.1 M TBABF
4
.
c
Cyclic voltammetry (vs Fc/Fc
+
) in acetonitrile, 0.1 M TBAPF
6
.
d

Calculated from the absorption band edge in thin films, E
g
= 1240/λ
edge
.
e
Measured for neat, as cast
polymer films.
f
The absence of a T
m
or T
c
is indicated by “-.”

Additionally, CV was completed for comparison of HOMO energy levels of the
polymers (Table 2.1). Both solution and film CVs were examined; all P3HT-co-FHT and
P3HT-co-MET polymers measured between 5.25 to 5.30 eV, with no observable trend
within each family. Analysis of optical and electronic data suggests that both families of
polymers exhibit band gaps, absorption profiles and solid-state HOMO levels that are
virtually identical to that of P3HT. These P3HT-like properties were likely maintained by

37
the incorporation of a carbon-spacer to physically decouple the heteroatoms from the
backbone conjugation.
As previously mentioned, the UV-Vis study of the P3HT-co-FHT and P3HT-co-
MET polymers revealed some variance in absorption coefficient and maxima. For a full
comparison, all P3HT-co-MET and P3HT-co-FHT families were studied using GIXRD
to gain insight into these differences. The GIXRD d-spacings of P3HT-co-FHT as cast
and annealed films indicate a larger spacing in lamellar packing as the content of the FHT
comonomer is increased (Figure 2.5a and Figure A1.10a), and the intensity of all signals
increases after thermal annealing. Interestingly, the d-spacings for P3HT-co-MET
polymers are similar to that of P3HT for both as cast and annealed films (Figure 2.5b and
Figure A1.10b) while intensity of the signal increases with higher contents of the
comonomer; all signals also increase after thermal annealing.

Figure 2.5. GIXRD data of a) P3HT-co-FHT and b)P3HT-co-MET annealed films; i)
P3HT, ii) P3HT
90
-co-FHT
10
, iii) P3HT
80
-co-FHT
20
, iv) P3HT
70
-co-FHT
30
, v) P3HT
60
-co-
FHT
40
, vi) P3HT
50
-co-FHT
50
, vii) P3HT
90
-co-MET
10
, viii) P3HT
80
-co-MET
20
, ix)
P3HT
70
-co-MET
30
, x) P3HT
60
-co-MET
40
, and xi) P3HT
50
-co-MET
50
.

38
The larger spacing in lamellar packing of P3HT-co-FHT polymers is consistent
with our hypothesis that the side-chains spatially expend greater volumes, coherent with a
lower absorption coefficient relative to P3HT. However, as cast P3HT-co-MET polymer
films have an opposite trend compared to P3HT-co-FHT polymers, where the absorption
coefficient increases with MET monomer content. By comparison, the MET side chain
lacks hydrogen atoms relative to an alkyl or semi-fluoro alkyl chain, which may
counteract the longer chain length and allow for tighter packing, which is supported by
the greater intensity of the peaks as MET content increases. Additionally, hole-mobilities
measured by SCLC were slightly higher for P3HT
60
-co-MET
40
and P3HT
50
-co-MET
50

compared to P3HT in as cast films (Table 2.1). GIXRD data considered together with the
observed blue-shift in annealed films indicates that P3HT-co-MET polymers may have
some unusual packing which may be responsible for absorption coefficient and maxima
differences.
Analysis of the UV-Vis absorption profiles and GIXRD data of annealed films
also suggests differences in thermal transitions that were further explored by DSC.
Thermally annealed films (100 °C) of P3HT-co-MET polymers have a blue-shifted
absorption maxima and vibronic shoulder (Figure A1.8b) and GIXRD measurements
indicate a greater degree of crystallinity of each annealed polymer film compared to
P3HT (Figure 2.5b). In contrast, P3HT-co-FHT polymers exhibited vibronic shoulders
and increased crystallinities comparable to P3HT only after thermal annealing at 150 °C
(Figure A1.10a). The milder thermal annealing conditions of P3HT-co-MET required to
enhance film crystallinity, compared to P3HT-co-FHT polymers, suggests a difference in
thermal transitions. A DSC study indicated that the P3HT-co-MET polymer family has

39
lower temperature thermal transitions, and P3HT-co-FHT polymers have a higher
transition, compared to P3HT (Table 2.1, Figure A1.32 – Figure A1.41). These findings
are consistent with previously reported thermal behavior of 3-alkyl thiophene
homopolymers featuring oligo ether
51
or semi fluoro alkyl side chains.
52,53

Lastly, photoluminescence spectra of selected samples were obtained (Figure
A1.9) for further comparison. Spectra of P3HT-co-FHT polymers have the same profile
as P3HT, with increase in photoluminescence with increasing content of comonomer,
indicating a decrease in non-radiative quenching pathways. We attribute the decrease in
quenching to the larger lamellar spacings of the polymer chains observed in GIXRD of
P3HT-co-FHT polymers. Interestingly, P3HT-co-MET polymers are less emissive than
P3HT in as cast films, indicating higher quenching with the comonomer present. Higher
quenching in these films may be consistent with our hypothesis that these polymers can
pack tighter than P3HT. Moreover, the annealed film PL spectra of P3HT-co-MET
polymers exhibit a blue shift, consistent with the UV-Vis measurements.
2.3 Conclusion
In summary, simple chemical modification of monomer alkyl side chains and
direct control of their overall composition in conjugated copolymers is an effective
method for the fine-tuning of surface energy while maintaining optical and electronic
properties. This is the first report of a family of conjugated polymers with a tuned and
composition dependent surface energy profile. The synthetic approaches employed here
allow for the preparation of newly reported stannylated monomers and random
copolymers, via Stille polycondensation. These results indicate that incorporation of

40
varying amounts of fluorine or oxygen atoms in the alkyl side chains of other well-known
conjugated polymers may be an effective tool for modifying surface energies, polymer
compatibility, and engendering alloy formation for the further investigation and
exploitation of ternary blend organic solar cells.
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44
CHAPTER 3 Surface Energy Modification of Semi-
Random P3HTT-DPP
3.1 Introduction
Bulk heterojunction (BHJ) organic solar cells incorporating conjugated polymers
are a promising platform for harvesting energy with the promise of low cost and short
pay back time.
1,2
Commonly, a binary system is utilized in the active layer of BHJ solar
cells, comprising a polymer donor and fullerene acceptor.
3
Today, efficiencies for single-
layer BHJ devices have exceeded 10%, reaching near-theoretical limits.
4
Higher
efficiencies may be attained with multiple active layers connected in a series, or tandem
solar cell devices, whereby V
OC
is additive across the junctions. However, J
SC
is limited
to the lowest current of the junctions.
5
Single layer devices offer more simple fabrication
methods compared to their tandem cell counterparts.
In the past five years ternary blends, a new class of BHJ solar cells, have gained
rapid interest and widespread research effort due to unique device properties.
6,7

Specifically, ternary blends incorporating two polymer donors and one fullerene acceptor
demonstrate cumulative J
SC
and composition-dependent V
OC
, reflective of the relative
content of the polymer donors.
8–13
Initial consideration of the respective frontier orbital
levels would suggest V
OC
should be pinned to the lowest possible value between
polymer/fullerene pairs. While this behavior is observed in some cases,
14–16
many recent
cases have demonstrated un-pinned V
OC
and ultimately a ternary blend device with
higher J
SC
and overall improved efficiency compared to the binary cases.
12,13,15,17

Trending, or tuning, of V
OC
in ternary blends is intriguing and has become the center of
extensive study and theory to elucidate electronic and structural evidence to expand upon
working hypotheses.
18–20
Recent work has pointed to an organic-alloy model which
45
suggests polymer-compatibility and intimate mixing of polymer donors is essential to
facilitate V
OC
tuning. It is suggested that V
OC
tuning derives from an averaging of frontier
orbitals, thereby minimizing hole-trapping effects in higher lying HOMO.
9,17,21,22

Surface energy, γ, of polymers has been indicated as a potential key figure of
merit,
15,17
and is an easily measured physical parameter, for identifying potential pairs of
polymer donors for ternary blends. Chapter 1 described a modular method for modifying
the surface energy of P3HT by random incorporation of oligo-ether or semi-fluoro alkyl
side chains.
23
Modified polymers exhibited increased or decreased surface energy by
incorporation of oligo-ether or semi-fluoro alkyl chains, respectively, while maintaining
desirable optical and electronic properties. This provides a potential handle for
controlling compatibility of known state-of-the-art polymers. P3HT is a simple
conjugated polymer, which served well for careful analysis of the effects of side chain
modification. However, this method has not yet been studied in higher performing
polymers that are of interest for ternary blends; nor have the solution processing methods
for optimum device performance been explored.
3.2 Results and Discussion
A new family of semi-random P3HTT-DPP polymers with modified surface
energy profiles was prepared utilizing the previously described method in Chapter 1
(Figure 3.1). Semi-random P3HTT-DPP comprises mostly 3HT monomer with small feed
ratios of DPP acceptor, thus maintains several desirable P3HT properties, but with
improved optical absorption.
24
Previous investigations of ternary blend devices have
frequently incorporated P3HTT-DPP, making it an ideal target for surface energy
modification and subsequent characterization.
8,9,15,22
In the present case, new semi-
46
random polymers P3HTMETT-DPP and P3HTFHTT-DPP, where the monomer feed
ratios were 40% 3-hexyl thiophene, 10% thiophene, 10% DPP, and 40% 3-
methoxyethoxythiophene (MET) or 3-nonafluoroheptylthiophene (FHT), respectively,
were prepared via Stille polycondensation (Figure 3.1, M
n
and Đ reported in Table 3.1).
Monomers were prepared via literature procedures without modification.
23
Proton NMR
spectra of polymers reflects the monomer feed ratios and composition (Figure A2.2 –
A2.3). Previously described P3HTT-DPP utilizes an 80% feed ratio of 3-
hexylthiophene.
24

Surface energies of the resulting polymers were determined with a contact angle
goniometer by measuring contact angles of water on pristine as-cast polymer films.
Consistent with the P3HT model,
23
P3HTT-DPP, P3HTMETT-DPP, and P3HTFHTT-
DPP surface energies were determined to be 20.6, 25.7, and 15.0 mN/m, respectively
(Table 3.1). P3HTMETT-DPP is particularly interesting due to its increased surface
energy, which approaches those of fullerenes such as PCBM. While surface energy
measurements are not reported for many conjugated polymers, most of the known values
generally range from 20.0 to 30.0 mN/m.
25–30

47

Figure 3.1. Stille polycondensation of a) P3HTFHTT-DPP, b) P3HTMETT-DPP, and c)
P3HTT-DPP.

48
Table 3.1. Molecular weights (Đ), electrochemical HOMO values, optical band gaps, and
SCLC mobilities of P3HTT-DPP, P3HTMETT-DPP, and P3HTFHTT-DPP polymers.
Polymer
M
n
(kDa)
(Đ)
a

HOMO
(eV)
(film)
b

E
g

(eV)
c

µ
h

(cm
2
V
-1
s
-1
)
d

T
m
; T
c

(°C)
γ
(mN/m)
e

P3HTT-DPP 13.5 (5.2) 5.23 1.51 1.47x10
-4
214; 210 20.6
P3HTMETT-DPP 16.2 (3.1) 5.21 1.51 1.43x10
-4
209; 190 25.7
P3HTFHTT-DPP 10.9 (3.1) 5.27 1.51 0.64x10
-4
255; 238 15.0
a
Determined by SEC with polystyrene standards and o-DCB eluent.
b
Cyclic voltammetry (vs Fc/Fc
+
) in
acetonitrile, 0.1 M TBAPF
6
.
c
Calculated from the absorption band edge in thin films, E
g
= 1240/λ
edge
.
d
Measured for neat, as cast polymer films.
f
Measured for neat, as cast polymer films.

Electronic and optical properties of the modified polymers were found to be
virtually identical to P3HTT-DPP. Film CV measurements indicated HOMO levels of
P3HTMETT-DPP and P3HTFHTT-DPP to be within experimental error of P3HTT-DPP
(Table 3.1). UV-Vis spectra of the polymers exhibited band gaps ranging from 1.50 to
1.53. Notably, the absorptivity of the intramolecular charge transfer (ICT) band of
P3HTMETT-DPP is more broad and intense than P3HTT-DPP, while the π-π band is less
intense (Figure 3.2). Additionally, the peak positions of the ICT bands and absorption
onset of P3HTMETT-DPP have a minor red-shift (~6 nm) compared to both P3HTT-DPP
and P3HTFHTT-DPP. This suggests greater donor-acceptor electronic interactions in
P3HTMETT-DPP and may also indicate a higher degree of order or closer chain packing
compared to the alkyl and semi-fluoro alkyl polymers.
49

Figure 3.2. Absorption profiles of P3HTT-DPP (black), P3HTMETT-DPP (blue), and
P3HTFHTT-DPP (red).
Analysis of GIXRD data is consistent with UV-Vis findings and the P3HT model
study, indicating similar effects of incorporating heteroatom modified alkyl chains
(Figure 3.3). Simply, the P3HT and P3HTT-DPP polymers with semi-fluoro alkyl chains
are less crystalline compared to regular alkyl chain polymers and have greater lamellar
packing distances. Conversely, oligo-ether chain incorporation yields more crystalline
polymers with tighter packing.

50

Figure 3.3. GIXRD data of P3HTT-DPP (black), P3HTMETT-DPP (blue), and
P3HTFHTT-DPP (red).

Like previous photoluminescence studies of modified P3HT polymers,
P3HTFHTT-DPP is more emissive than P3HTT-DPP, where as, P3HTMETT-DPP is less
emissive (Figure 3.4). This is attributed to either a decrease or increase, respectively, of
nonradiative quenching pathways. More over, P3HTMETT-DPP emission is slightly red-
shifted, consistent with the UV-Vis absorption patterns. Analysis of thermal transitions of
the polymers is also consistent with general findings for semi-fluoro alkyl and oligo-ether
side-chain polymers. P3HTFHTT-DPP exhibited and increased T
m
and T
c
while
P3HTMETT-DPP transitions were decreased compared to P3HTT-DPP (Table 3.1).
Many previously studied conjugated polymers bearing oligo-ether groups have unsuitably
low thermal transitions.
31
Here, P3HTMETT-DPP has only marginally lower thermal
transitions compared to its aliphatic parent analog, which are appropriate for photovoltaic
devices.
51

Figure 3.4. Photoluminescence spectra of P3HTT-DPP (black), P3HTMETT-DPP (blue),
and P3HTFHTT-DPP (red).
Overall, this new family of semi-random P3HTT-DPP based polymers bear ideal
optical, electronic, and physical properties desired for polymer solar cells. Binary BHJ
solar cells (ITO/PEDOT:PSS/polymer:PC
61
BM/Al) were prepared individually
optimized. Thin film processing conditions were carried out by simple solvent annealing
of the polymer:PCBM blend after spin coating.
The semi-fluoro alkyl analog has poor solubility in o-DCB, but solubility
improves with chlorobenzene, chloroform, and tetrahydrofuran. Optimal film processing
conditions and device performance was observed when P3HTFHTT-DPP was solubilized
in chloroform at low polymer concentrations (4 mg/mL). Understandably, the J
SC
for this
polymer is lower than P3HTMETT-DPP due to the lower concentration of light
absorbing material and relatively thinner film (Table 3.2). Higher ratios of fullerene to
polymer (2:1) were needed to optimize P3HTFHTT-DPP devices. It should be noted that
the surface energy of PCBM is higher (27.6 mN/m).
15
It is likely that more fullerene was
52
needed to promote donor-acceptor interaction and overcome self-aggregation of PCBM.
Historically, fluoro-alkyl polymers are inherently interesting due to their high thermal
stabilities.
32,33
However, these polymers suffer from limited compatibility with higher
boiling point solvents. Here, it’s demonstrated that random incorporation of semi-fluoro
alkyl monomers with an overall monomer content of 40% or below is an effective
method for preparing polymers with higher melting points and lower surface energy,
while still achieving device performance with FF greater than 0.50. It is likely that feed
ratios of 50% or greater of fluoro alkyl monomers is not advantageous as many
previously reported polymers were not sufficiently soluble for complete characterization.

Table 3.2. Photovoltaic Properties of P3HTT-DPP, P3HTMETT-DPP, and P3HTFHT-
DPP.
Polymer (Polymer:PCBM Ratio) J
SC
(mA/cm
2
)
c
V
OC
(V) FF PCE (%)
P3HTT-DPP (1:1.3)
a
11.69 0.61 0.59 4.14
P3HTMETT-DPP (1:1.3)
a
10.17 0.59 0.52 3.08
P3HTFHTT-DPP (1:2)
b
5.36 0.66 0.54 1.91
a
Spin-coated from o-dichlorobenzene, dried under N
2
before aluminum deposition.
b
Spin-coated from
chloroform, dried under N
2
before aluminum deposition.
c
Mismatch corrected.

The oligo-ether analog is easily processed with the same conditions as P3HTT-
DPP. The J
SC
and V
OC
of P3HTMETT-DPP is similar to P3HTT-DPP, suggesting that
incorporation of oligo-ether solubilizing groups is a viable method for modification of
conjugated polymers without detriment to current or voltage of the working device (Table
3.2). Previous work from Wang and coworkers has also utilized oligo-ether side chains
53
on alternating polymers to achieve closer π-π packing and demonstrated remarkable
improvement of device parameters via processing with a non-halogenated solvent:
methoxy benzene (MOB).
34
In the present study, MOB did not sufficiently solubilize
P3HTMETT-DPP for thin film processing. The fill factor of o-DCB processed films
suggests there is more room for improvement in processing conditions, or perhaps for a
more precise tuning of the oligo-ether monomer feed ratio. We predict that continued
study of oligo-ether side chains in conjugated polymers will reveal new processing
methods ideal for backbones comprising predominantly hydrocarbons, and side chains
featuring hydrophilic moieties. These polymers are unique from non-polar systems that
are nearly ubiquitous in conjugated polymer research,
31,35
and lack a more comprehensive
understanding of processing methods.
3.3 Conclusion
In summary, the modular method described in Chapter 1 was applied for tuning
surface energy of semi-random P3HTT-DPP. In this work, modified polymers retain
desirable characteristics for photovoltaic application. P3HTFHTT-DPP suffers from
lower solubility in solvents commonly used for conjugated polymers, and thus requires
lower polymer concentrations in thin film processing. P3HTMETT-DPP maintains
similar photovoltaic performance under identical processing conditions. Ongoing work
includes surface energy modification of alternating copolymers and incorporation of the
presented polymers in ternary blends to explore polymer-polymer compatibility.

54
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(24) Khlyabich, P. P.; Ng, C. F.; Thompson, B. C. Macromolecules 2011, 44 (13),
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(25) Khlyabich, P. P.; Rudenko, A. E.; Street, R. A.; Thompson, B. C. ACS Appl.
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(26) Huang, J.-H.; Hsiao, Y.-S.; Richard, E.; Chen, C.-C.; Chen, P.; Li, G.; Chu, C.-W.;
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57
CHAPTER 4 Investigation of Random Copolymer
Analogs of a Semi-Random Conjugated Polymer Incorporating
Thienopyrazine
4.1 Introduction
Organic photovoltaics offer a promise of low-cost, large area, and flexible
electronic devices through the use of conjugated polymer active layers.
1,2
The backbones
of conjugated polymers have been extensively investigated, yielding a broad range of
linkage patterns, including homopolymers, random,
3–7
alternating,
8
and block
copolymers.
9,10
Explicit design choices within these major architectures, such as identity
of D-A monomers
11,12
and side chain engineering,
13
allow for precise tuning of desirable
properties such as absorption breadth, frontier orbital levels, solubility, and polymer self-
organization. Of the previously mentioned backbone architectures, a perfectly alternating
D-A polymer structure is popular for achieving low band gaps and improved efficiencies
in solar cells.
12,14,15
However, many of these systems exhibit red-shifted absorption,
sacrificing short-wavelength photons.
16,17
More recently, a new class of semi-random
polymers have successfully incorporated multiple, distinct and randomized chromophores
that exhibit broadened absorption profiles.
18–21
Semi-random polymers based on regio-
regular P3HT have additional unique design advantages. Specifically, due to the large 3-
hexyl thiophene content, resulting polymers retain many of the desirable properties of
P3HT such as semi-crystallinity, good solubility in common processing solvents, and
favorable polymer:fullerene ratios in devices.
Semi-random polymers are unique from random copolymers due to their
restricted linkage patterns.
20
Previous work on rr-P3HT based semi-random polymers,
small amounts of electron-poor acceptor monomers, such as DPP,
18,22
BTD,
23
TP,
20
and

58
TPD,
19
are incorporated into the polymer backbone while maintaining upwards of 80%
overall content of 3-hexyl thiophene. The previously reported semi-random P3HT based
polymers were prepared via Stille polycondensation, utilizing trimethylstannyl (A
functionality) and bromo (B functionality) groups for aryl-aryl bond formation. In order
to stoichiometrically balance the dibromo functionalized acceptor monomers (BB
functionality) 2,5-di(trimethylstannyl)thiophene is used (AA functionality). Meanwhile,
the classic 2-bromo-5-trimethylstannyl-3-hexylthiophene is retained for regio-regularity
(AB functionality). This specific choice in linkage patterns excludes acceptor-acceptor
linkages and ensures that the acceptor is randomly distributed through the polymer
backbone. Polymers of this design exhibit broadened absorption profiles, decreased band
gaps, and OPV efficiencies exceeding 5%. Previous work from Braunecker and
coworkers has investigated differences between semi-random and well-defined
alternating polymers.
24
However, 3-alkyl thiophene based semi-random polymers have
yet to be directly compared to entirely random analogs. It is not known whether the same
optical, electronic or structural features will be observed if the polymer backbone is
comprised entirely of monomers, in the same feed ratios, with only AB functionalities.
4.2 Results and Discussion
4.2.1 Synthesis
This work investigates if restricted linkage patterns in semi-random polymers are
necessary to obtain the desirable optical and electronic effects. Additionally, what role an
AA versus AB functionalized thiophene spacer imparts is investigated. To explore the
differences between semi-random and completely random co-polymer systems based on
P3HT, we chose to prepare a series of P3HTT-TP copolymers. Previously, nearly

59
identical semi-random polymers were prepared and characterized, incorporating
thienopyrazine without the methyl solubilizing groups.
20
The thienopyrazine monomer
was specifically identified for this study because to date, it’s the only acceptor monomer
with synthetic precedence for bearing AB style functionalization. Rasmussen and
coworkers recently demonstrated dimethyl and dihexyl-thienopyrazine monomers could
be functionalized unsymmetrically with bromo, trimethylsilane, and trimethylstannyl
moieties.
25
While the desired 2-bromo-5-trimethylstannyl isomer was not presented in
their work, it inspired the synthetic work presented here to obtain an AB functionalized
dimethylthienopyrazine (Figure 4.1). The unfunctionalized monomer, prepared via
literature conditions without modification, was mono-brominated with NBS to yield 1.
The final monomer, 2, was prepared from magnesiated intermediate using the Knochel-
Hauser base, and subsequent stannylation. Syntheses of alternative AB functionalized
acceptor monomers, such as DPP, were attempted using a wide array of organo-metallic
bases, however, pure monomers could not be isolated for the purpose of polymerizations.
The remaining monomers needed for this study were also prepared from literature
conditions without modification.

Figure 4.1. Synthesis of unsymmetrical dimethylthienopyrazine monomer, 2.

60

Figure 4.2. Stille Polycondensation of sr-P3HTT-TP, r-P3HTT-TP, r-P3HT-TP, r-
P3HTT-10%, and r-P3HTT-20%.
Polymers were prepared via Stille polycondensation (Figure 4.2), precipitated in
methanol, washed with methanol and hexanes in a Soxhlet extractor, collected in
chloroform and finally precipiated in methanol again before collection by filtration.

61
Semi-random polymers and random polymers are designated with either “sr-“ or “r-“,
respectively, before their acronyms. Accordingly, sr-P3HTT-TP was prepared with AA
functionalized dimethylthienopyrazine, where as r-P3HTT-TP was prepared with AB
functionalized monomer 2. Additionally, random polymers were prepared without either
AB thiophene (r-P3HT-TP) or dimethylthienopyrazine monomers (r-P3HTT) for further
comparison. Lastly, a semi-random P3HTT polymer was prepared using both AA and BB
functionalized thiophene (sr-P3HTT-20%). P3HT was prepared from literature
conditions without modification. All polymers containing dimethylthienopyrazine had TP
monomer feed ratios of 10%; therefore, 3-hexylthiophene monomer feed ratios were
either 80 or 90% depending if the thiophene monomer was also present in the given case.
Two varieties of r-P3HTT were synthesized, r-P3HTT-10% and r-P3HTT-20%,
whereby the feed ratio of 2-bromo-5-(trimethylstannyl)thiophene was 10 and 20%,
respectively. All polymer M
n
and Đ were determined by GPC and reported in Table 4.1.

Table 4.1. Molecular weights (PDI), electrochemical HOMO values, HOMO values,
optical band gaps, and SCLC mobilities of random and semi-random P3HT based
polymers.
Polymer M
n
(kDa) (PDI)
a

HOMO (eV)
(film)
b

E
g
(eV)
c
T
m
; T
c
(°C)
P3HT 16.5 (1.93) 5.25 1.90 221; 186
r-P3HTT-10% 28.2 (1.99) 5.21 1.93 190; 151
r-P3HTT-20% 26.8 (1.99) 5.29 1.93 151; 89
sr-P3HTT-20% 38.6 (3.29) 5.33 1.93 117; 112

62
Table 4.1 Continued
Polymer M
n
(kDa) (PDI)
a

HOMO (eV)
(film)
b

E
g
(eV)
c
T
m
; T
c
(°C)
r-P3HT-TP 14.9 (4.18) 5.40 1.38 213; 165
r-P3HTT-TP 14.8 (3.96) 5.28 1.38 188; 134
sr-P3HTT-TP 17.0 (4.76) 5.23 1.50 202; 199
a
Determined by SEC with polystyrene standards and o-DCB eluent.
b
Cyclic voltammetry (vs Fc/Fc
+
) in
acetonitrile, 0.1 M TBAPF
6
.
c
Calculated from the absorption band edge in as-cast thin films, E
g
=
1240/λ
edge
.

4.2.2 Structural Characterization
Proton NMR analysis supported the monomer feed ratios and also provided some
of the first evidence of unique structural differences between semi-random and random
P3HTT-TP polymers, specifically in the alkyl proton region from 2.5 to 3.0 ppm (Figure
4.3, full spectra available in Appendix 3). Notably, the methyl peaks from
dimethylthienopyrazine in sr-P3HTT-TP appear as a singlet at 2.70 ppm, whereas there
are two distinct singlets, with nearly equal integration, at 2.72 and 2.68 ppm for r-
P3HTT-TP and r-P3HT-TP. This difference suggests that the methyl groups on the TP
monomers are experiencing different electronic environments along the backbone of the
polymer. This may be due to 3-hexylthiophene and dimethylthienopyrazine linkages that
are distinct in connectivity between the semi-random and random polymer cases (Figure
4.4). When considering the possible monomer linkages, the semi-random scheme ensures
that dimethylthienopyrazine has only two bond forming scenarios: 1)
dimethylthienopyrazine to the 5-position of 3-hexylthiophene (TP-3HT) and 2) thiophene
to dimethylthienopyrazine (T-TP), whereby the 2 and 5-position of thiophene are

63
equivalent. However, the random scheme does facilitate bonding of
dimethylthienopyrazine to both the 2 and 5-position of 3-hexylthiophene (3HT-TP and
TP-3HT, respectively). Therefore TP-3HT and 3HT-TP are not equivalent monomer
sequences. While this appears ostensibly minor, these linkages are distinct due to the
steric hindrance imposed between the hexyl chain and methyl group of 3HT and TP. It is
noted that TP-TP linkages are also possible in the random polymer cases, but the
occurrence of these linkages should be low considering the thienopyrazine monomer has
only a 10% feed ratio. A proton signal in the spectrum due to this linkage pattern would
be low and difficult to resolve from overlapping peaks.

Figure 4.3. Stacked
1
H NMR Spectra of sr-P3HTT-TP (bottom, red), r-P3HTT-TP
(middle, green), and r-P3HT-TP (top, blue).
Another area of interest in
1
H NMR spectra of the TP containing polymers is in
the aromatic region from 6.5 to 7.6 ppm (Figure 4.5). Peaks within this region are sharper
and better defined in the semi-random case compared to the random polymers.
Additionally, the singlet at 7.48 ppm for sr-P3HTT-TP is more intense than the singlets
at 7.50 ppm for random TP polymers. To investigate these differences further, selective

64
1D-NOESY NMR experiments were performed on TP based polymers (Figures A3.9-
A3.15). The nuclear overhauser effect (NOE) was famously used to discern 3D structural
information on biological macromolecules by Wüthrich and coworkers, earning the
Nobel Prize in Chemistry in 2002.
26
NOE signals can be obtained on macromolecules
when protons are near enough in space that a selective excitation of one results in a
change of spin polarization, due to cross-relaxation, of the other. Considering the linkage
patterns presented in Scheme 3, it may be predicted that selective excitation of methyl
protons on dimethylthienopyrazine would give rise to a NOE signal of the closest protons
– namely the aryl proton of either 3-hexyl thiophene or thiophene, seen in TP-3HT or TP-
T linkages, respectively. An NOE signal of another methyl proton associated with the
dimethyl thienopyrazine unit would suggest that the two methyl groups of the same
monomer have distinct electronic environments.

Figure 4.4. Comparison of monomer linkages found in semi-random and random
thienopyrazine polymers.

65

Figure 4.5. Stacked
1
H NMR Spectra of sr-P3HTT-TP (bottom, red), r-P3HTT-TP
(middle, green), and r-P3HT-TP (top, blue).
Selective excitation of the methylene bridge peak of 3-hexylthiophene, the most
abundant monomer, at 2.81 ppm was performed, which acquired NOE signals of nearby
protons (Figure A3.9). This experiment serves as a control to ensure optimal experiment
conditions (mixing time, temperature, scans), and to set a benchmark for maximum NOE
enhancement expected for these polymers, as dimethylthienopyrazine only comprises
10% of the backbone. Three NOE signals can be observed: an aryl signal at 6.99 ppm
with 1.57% relative enhancement to the excited signal, and two methyl bridge signals at
1.74 and 1.46 ppm with 0.30 and 0.23% relative enhancement, respectively. Turning to
characterizing dimethylthienopyrazine, selective excitation of the methyl protons is
necessary.
First, selective excitation of the methyl proton singlet at 2.70 ppm, which is
associated with TP in sr-P3HTT-TP, acquires a NOE signal at 7.49 ppm (Figure A3.13),
suggesting the sharp singlet at 7.49 ppm in the
1
H NMR spectrum is due to TP-3HT or T-
TP linkages seen in Scheme 3. Next, selective excitation of the methyl proton signal at

66
2.68 ppm, in the r-P3HT-TP spectrum, acquires NOE signal of both the neighboring
methyl proton (2.72 ppm) and two signals in the aromatic region (7.12 and 6.99 ppm),
presumably the aryl protons of 3-hexyl thiophene (Figure A3.12). However, selective
excitation of the methyl proton signal at 2.72 ppm of the same polymer leads only to
NOE signal of the methyl proton at 2.68 ppm (Figures A3.10-A3.11). This suggests the
methyl protons associated with 2.68 and 2.72 ppm are nearby to each other, presumably
on the same monomer unit. Moreover the former experiences an electronic environment
associated with the TP-3HT linkage while the later experiences an electronic
environment associated with the 3HT-TP linkage (Figure 4.4). We propose that the
methyl proton at 2.72 ppm does not acquire NOE signals of any of the methylene bridge
signals of the hexyl chain of 3HT because of steric repulsion induced by the rotation
required to bring said protons near to each other in physical space (Figure 4.4).
Lastly, selective excitation of either methyl signal of r-P3HTT-TP did not
acquire any NOE signal in the aromatic region (Figures A3.9-A3.15). Perhaps the variety
of TP linkages is too diffuse, compared to r-P3HT-TP and sr-P3HTT-TP, to result in a
correlation by NOE spectroscopy. These various enhanced signals could be interpreted to
indicate the presence of specific linkages in random and semi-random systems, such as
TP-3HT, 3HT-TP, or TP-TP bonds, however the presented experiments do not yield a
complete description on monomer sequence distribution in poly-disperse semi-random
and random polymer chains. Nevertheless, the NOE experiments do support our findings
from
1
H NMR that semi-random and random polymers of the same monomer ratios are
structurally distinct from one another.

67
4.2.3 Optical and Electrochemical Properties
Previous studies of polymers related by content, but differentiated by backbone
structure, indicate distinct difference in optical and electronic properties.
24,27
Cyclic
voltammetry was used to investigate differences in HOMO levels of the polymers (Table
4.1). Measurements of P3HT, sr-P3HTT, and sr-P3HTT-TP are consistent with
previously reported values.
20
Notably, r-P3HT-TP exhibits a deeper HOMO level than
the other D-A polymers, while r-P3HTT-TP is intermediate to sr-P3HTT-TP. Recently,
Marks and coworkers demonstrated that thiophene catenation in D-A polymers was
effective in raising HOMO levels, where as polymers with lower acceptor:thiophene
ratios had lower-lying HOMOs due to larger degrees of backbone torsion.
28
This is a
viable explanation for the same behavior observed in r-P3HT-TP, where 3HT-TP
connections (Figure 4.4) may also induce some backbone torsion. In the case of r-
P3HTT-TP, these linkages are still possible, incorporation of thiophene could relieve
these sterics effects, thereby raising the observed HOMO level. Lastly, the sr-P3HTT-TP
polymer linkages dictate that thienopyrazine will not have the same 3HT-TP steric
occurences, so a higher-lying HOMO is also observed.
Absorption profiles of the polymer films were measured by UV-Vis (Figure 4.6),
and band gaps were extracted from absorption onsets (Table 4.1). Most notably, sr-
P3HTT-TP bears a stronger ICT absorption band compared to random analogs
containing thienopyrazine. The prominent ICT band absorption in sr-P3HTT-TP
compared to random analogs suggests a stronger push-pull donor-acceptor character in
the backbone. The reduced donor-acceptor interaction in random analogs could be due to
the presence of acceptor-acceptor linkages, which is permitted in the randomized bonding

68
scheme. This suggests that the semi-random polymer bonding scheme better favors
donor-acceptor interaction. Kim and coworkers
29
demonstrated that a randomized analog
of a perfectly alternating donor-acceptor copolymer exhibited a weakened and broadened
ICT absorption band, much like the presented system here. Furthermore, several cases
have been presented in literature whereby acceptor-acceptor linkages were either
permitted or present due to homocoupling in polymers.
30–32
Weakened ICT absorption
bands of random thienopyrazine polymers could also result from disruption of effective
conjugation lengths in D-A segments due to steric interactions of 3HT-TP linkages.

Figure 4.6. UV-Vis Absorption profiles of sr-P3HTT-20% (black), r-P3HTT-20%
(blue), r-P3HTT-10% (aqua), r-P3HT-TP (purple), r-P3HTT-TP (green), and sr-
P3HTT-TP (red) polymers.

69
Absorption profiles of P3HTT polymers are similar to P3HT, with lower
absorptivities (Figure A3.16). The lower absorptivity of r-P3HTT-10% compared to sr-
P3HTT-20% and r-P3HTT-20% polymers may be attributed to larger lamellar packing,
which is supported by GIXRD measurements. Moreover, the sr-P3HTT-20% lacks a
vibronic shoulder that is present in random P3HTT polymers, suggesting lower
crystallinity relative to r-P3HTT-10% and r-P3HTT-20%.
4.2.4 Morphologhy Characterization
GIXRD was used to determine relative crystallinity and spacing of neat polymer
films (Figure 4.7). The sr-P3HTT-20% polymer is less crystalline than both r-P3HTT
polymers and P3HT, yet has roughly the same peak position as r-P3HTT-20%.
Crystallinity increases with r-P3HTT-10% and is higher in r-P3HTT-20%. The peak
position of r-P3HTT-10% is at a lower 2θ than both P3HTT-20% polymers, and more
close to that of P3HT, suggesting P3HTT-20% polymers have closer lamellar packing
compared to r-P3HT-10%. Perhaps this is due to less alkyl chains per backbone in the
20% polymer, allowing the chains to pack slightly closer. The relative crystallinities and
d-spacings of the P3HTT polymers is consistent with the UV-Vis findings where
absorptivity is lower for r-P3HTT-10%, absorptivities are nearly equal for sr-P3HTT-
20% and r-P3HTT-20%, and sr-P3HTT-20% lack a vibronic feature.

70

Figure 4.7. GIXRD profiles of P3HT (black), r-P3HTT-10% (aqua), r-P3HTT-20%
(blue), sr-P3HTT-20% (brown), r-P3HT-TP (purple), r-P3HTT-TP (green), and sr-
P3HTT-TP (red) polymers.

Figure 4.8. Comparison of long-range linkage patterns in a) semi-random and b) random
polymers.

71
The comparison of r- and sr-P3HTT polymer GIXRD results provides clear
context for the comparison of r and sr-P3HTT-TP. Crystallinity and peak position of r-
P3HT-TP is lower than r-P3HTT-TP, which is consistent with the finding that reducing
the amount of thiophene in random cases will reduce crystallinity and increase packing
distance. Lastly, sr-P3HTT-TP shows no signal in GIXRD, which is consistent with that
sr-P3HTT-20% was lower in crystallinity than its random analogue. Interestingly, DSC
analysis revealed that sr-P3HTT-TP has shallow and narrow melt and crystallization
thermal transitions, suggesting semi-crystallinity (Table 4.1, Figure A3.24). Additional
spin-coating conditions with varied solvents, polymer concentrations, and annealing
conditions were tested for sr-P3HTT-TP, yet no peaks were observed in GIXRD
measurements for neat films. Perhaps crystallites of sr-P3HTT-TP have a different
preference for face-on versus edge-on orientation compared to random analogs. It’s also
possible that crystalline domains of sr-P3HTT-TP are small and diffuse – which is
supported by the magnitude and width of the thermal transitions relative to other
polymers in this study.
Close examination of probable long-range linkage patterns in random and semi-
random polymers provides insight and reasonable explanation for reduced crystallinity,
among other notable differences, observed in semi-random polymers (Figure 4.8). It
should be noted that previously characterized semi-random polymers containing acceptor
units such as DPP, benzothiadiazole, and thienopyrroledione, were found to have semi-
crystalline features in GIXRD measurements.
18,20,23
Both sr-P3HTT-20% and sr-
P3HTT-TP were found to lack semi-crystallinity in the same previous studies. Semi-

72
crystallinity may be imparted on other semi-random polymers when the acceptor
monomer is known to be highly planar and favor backbone rigidity.
30,33,34

Semi-random thienopyrazine polymers based on 3-alkyl thiophenes are unique
from random polymers, evidenced by the previously discussed optical and electronic
properties, which can be attributed to long-range ordering induced by the alkyl chains. In
the semi-random case, AA (thiophene, T) and BB (dimethylthienopyrazine, TP)
functionalized monomers facilitate the opportunity for an AB monomer (3-hexyl
thiophene, 3HT) to bond on either side, and does not necessitate that an AA monomer
will always be linked to a BB monomer to form T-TP bonds (Figure 4.8b). In fact, the
occurrence of T-TP bonds is likely lower than TP-3HT or T-3HT, simply by considering
that 3HT makes up 80% of the monomer feed ratio. Thus, the following tri-mers are
present in the semi-random backbone: 3HT-T-3HT and 3HT-TP-3HT. In this scenario,
the direction of the alkyl chain swaps in order for the complementary functional groups to
undergo Stille condensation: either the hexyl chains surrounding the thiophene will point
towards one another or the hexyl chains surrounding the thienopyrazine (or thiophene in
the sr-P3HTT-20% polymer) will point away from each other.
This change in directionality introduces two effects that have consequences in the
physical and optical properties of the resulting polymer. First, when the hexyl chains are
pointing inwardly, one can imagine planarity and effective conjugation length being
disrupted, as the backbone would rotate to relieve steric effects. This particular linkage
occurrence is key to understanding the decrease in crystallinity as measured by GIXRD
for semi-random polymers. Second, when acceptor monomers are introduced into the
backbone (first and third row in Figure 4.8a), the long-range alkyl chain ordering is either

73
pointing in one direction or outwardly in opposite directions. This effectively creates
more unique chromophores involving the electron-poor monomer. Bearing in mind, this
scheme does not account for many other possible chromophores due to linking of
multiple thienopyrazines in a short range (3HT-TP-3HT-3HT-TP, for example).
In comparison to the r-P3HT-TP and r-P3HTT-TP polymers (Figure 4.8a),
incorporation of thienophene or thienopyrazine into the backbone does not necessitate a
change in alkyl chain direction because all monomers are AB functionalized. It is likely
that the higher probable occurrence of unique donor-acceptor chromophores, with
randomly alternating alkyl chain direction is a feature contributing to the increased
absorption in the ICT band of sr-P3HTT-TP compared to r-P3HT-TP and r-P3HTT-TP
polymers.
4.2.5 Thermal Properties
Analysis of polymer thermal transitions is also consistent with consideration long-
range of linkage patterns (Table 4.1). First, comparing the P3HTT series to P3HT,
35
the
T
m
and T
c
decrease as the content of thiophene relative to 3-hexyl thiophene is increased,
suggesting less energy is needed to overcome rotational barriers throughout the backbone
due to the lower content of side chains. This trend is also consistent in the comparison of
r-P3HT-TP and r-P3HTT-TP, whereby higher content of thiophene is associated with
lower thermal transitions. By comparison, sr-P3HTT-20% has lower transitions relative
to r-P3HTT-20%, possibly due to higher probability of long-range ordering disruption
discussed earlier. However, this specific trend is not the same for sr-P3HTT-TP and r-
P3HTT-TP. While both are lower than r-P3HT-TP, possibly due to their higher
thiophene content, its possible that the semi-random polymer maintains higher thermal

74
transitions than the random analog because the steric effect of 3HT-TP linkages (Figure
4.4) is more impactful on lowering energy barriers for rotation.

4.3 Conclusion
In summary, the synthesis of a family of semi-random and random 3-hexyl
thiophene and thienopyrazine based polymers was achieved through the careful
preparation and selection of AB, AA, and BB functionalized monomers. Remarkably, we
have determined the functional role of the 2,5-di(trimethylstannyl) thiophene in semi-
random polymers as it serves to stoichiometrically balance di-bromo acceptor monomers,
but also disrupts long-range alkyl chain ordering and effectively raises HOMO levels.
This relationship was otherwise difficult to discern without careful study of random
analogs of semi-random polymers. Consideration of possible linkage patterns in random
versus semi-random systems is valuable in understanding significant differences
observed in electronic, optical, and physical properties of the resulting polymers. The
design parameters of 3-alkyl thiophene based semi-random polymers is fortuitous due to
the ease of preparation of di-brominated acceptor monomers, and the linkage patterns
lending to the formation of multiple, randomly orientated chromophores through-out the
polymer backbone, favors donor-acceptor interaction, and increases long-wave length
absorption. Ongoing studies include how to improve upon the current design to achieve
broader absorption profiles, higher molecular weight polymers, and overall improved
device performance to make semi-random polymers more competitive with their
perfectly alternating counterparts.

75
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88
APPENDIX 1 Fine Tuning Surface Energy of Poly(3-hexyl
thiophene) by Heteroatom Modification of the Alkyl Side Chains

A1.1 Materials and Methods
All reagents from commercial sources were used without further purification, unless otherwise
noted. All reactions were performed under dry N
2
, unless otherwise noted. All dry reactions were
performed with glassware that was flamed under high vacuum and backfilled with N
2
. Flash
chromatography was performed using a Teledyne CombiFlash R
f

instrument in combination with
RediSep R
f

normal phase disposable columns. Solvents were purchased from VWR and used
without further purification except for THF, which was dried over sodium/benzophenone before
being distilled.

All compounds were characterized by
1
H NMR (400 MHz) and
13
C NMR (100 MHz) on a
Mercury 400. Polymer
1
H NMRs (500 MHz) were obtained on a Varian VNMRS-500. For
polymer molecular weight determination, polymer samples were dissolved in HPLC grade o-
dichlorobenzene at a concentration of 0.5 mg/ml, briefly heated and then allowed to turn to room
temperature prior to filtering through a 0.2 µm PTFE filter. SEC was performed using HPLC
grade o-dichlorobenzene at a flow rate of 1 ml/min on one 300 x 7.8 mm TSK-Gel GMH
H R
-H
column (Tosoh Corporation) at 70 °C using a Viscotek GPC Max VE 2001 separation module
and a Viscotek TDA 305 RI detector. The instrument was calibrated vs. polystyrene standards
(1,050 – 3,800 000 g/mol) and data was analyzed using OmniSec 4.6.0 software.

Cyclic voltammetry was collected using an EG&G instruments Model 263A potentiostat under
the control of PowerSuite Software. A standard three electrode cell based on a Pt wire working
89
electrode, a silver wire pseudo reference electrode (calibrated vs. Fc/Fc
+
which is taken as 5.1 eV
vs. vacuum)

and a Pt wire counter electrode was purged with nitrogen and maintained under
nitrogen atmosphere during all measurements. Acetonitrile and chloroform were distilled over
CaH
2

prior to use. Tetrabutyl ammonium hexafluorophosphate (0.1 M) was used as the
supporting electrolyte for polymer films. Polymer films were made by repeatedly dipping the Pt
wire in a 1% (w/w) polymer solution in chloroform or o-dichlorobenzene and dried under
nitrogen prior to measurement. Polymer solutions were prepared in chloroform at a concentration
of 0.1 mg/mL and tetrabutyl ammonium tetrafluoroborate (0.1 M) was used as the supporting
electrolyte.
Surface energy studies of the neat polymers film were performed on Ramé-Hart Instrument Co.
contact angle goniometer model 290-F1 and analyzed using Surface Energy (one liquid) tool
implemented in DROPimage 2.4.05 software. Polymer films were prepared from 10 mg/ml
chloroform solutions, spin-coated on the pre-cleaned glass slides. Water and glycerol were used
as two solvents in the two-liquid model to measure the contact angle and harmonic mean Wu
90
model

was used to calculate the average surface energy values for each film according to
following set of equations:
where Z
w
and Z
g
are the contacts angles with water and glycerol, respectively; γ
tot
is the total
surface energy, γ
p
and γ
d
are the polar and dispersive surface energy components.
Mobility was measured using a hole-only device configuration of ITO/PEDOT:PSS/Polymer/Al
in the space charge limited current regime. The dark current was measured under ambient
conditions. At sufficient potential the mobilities of charges in the device can be determined by
fitting the dark current to the model of SCL current and described by equation 4:
2
0 3
9
8
SCLC R
V
J
L
εεµ = (4),
where J
SCLC
is the current density, ε
0
is the permittivity of space, ε
R
is the dielectric constant of
the polymer (assumed to be 3), µ is the zero-field mobility of the majority charge carriers, V is
the effective voltage across the device (V = V
applied
– V
bi
– V
r
), and L is the polymer layer
thickness. The series and contact resistance of the hole-only device (16 – 20 Ω) was measured
using a blank (ITO/PEDOT/Al) configuration and the voltage drop due to this resistance (V
r
) was
subtracted from the applied voltage. The built-in voltage (V
bi
), which is based on the relative
work function difference of the two electrodes, was also subtracted from the applied voltage. The
built-in voltage can be determined from the transition between the ohmic region and the SCL
region and is found to be about 0.6 V.

All steps of device fabrication and testing were performed in air. ITO-coated glass substrates (10
Ω/ ☐, Thin Film Devices Inc.) were sequentially cleaned by sonication in detergent, de-ionized
water, tetrachloroethylene, acetone, and isopropyl alcohol, and dried in a nitrogen stream. A thin
91
layer of PEDOT:PSS (Baytron
®
P VP AI 4083, filtered with a 0.45 μm PVDF syringe filter –
Pall Life Sciences) was first spin-coated on the pre-cleaned ITO-coated glass substrates and
baked at 130 ºC for 60 minutes under vacuum. Solutions of polymers were prepared in
chloroform solvent at a concentration of 10 mg/ml and stirred for overnight. Subsequently, the
polymer active layer was spin coated (with a 0.45 µm PTFE syringe filter [Pall Life Sciences] for
P3HT and P3HT-co-MET polymers and 0.45 µm Nylon syringe filter [VWR International] for
P3HT-co-FHT polymers) on top of the PEDOT:PSS layer. Upon spin coating of polymers, films
were first placed to the N
2
cabinet for 30 min and then placed in the vacuum chamber for
aluminum deposition. At the final stage, the substrates were pumped down to high vacuum (<
9×10
-7
Torr) and aluminum (100 nm) was thermally evaporated at 3 – 4 Å/sec using a Denton
Benchtop Turbo IV Coating System onto the active layer through shadow masks to define the
active area of the devices as 5.18 mm
2
.

For thin film measurements, polymers were spin coated onto pre-cleaned glass slides from
chloroform solutions; 10 mg/mL for UV-Vis, 5 mg/mL for PL (with a 0.45 µm PTFE syringe
filter [Pall Life Sciences] for P3HT and P3HT-co-MET polymers and 0.45 µm Nylon syringe
filter [VWR International] for P3HT-co-FHT polymers). UV-vis absorption spectra were
obtained on a Perkin- Elmer Lambda 950 spectrophotometer. INSERT PL MEASUREMENT
INFO. The thickness and crystallinity of the thin films and GIXRD measurements were obtained
using Rigaku Diffractometer Ultima IV using Cu Kα radiation source (λ= 1.54 Å) in the
reflectivity and grazing incidence X-Ray diffraction mode, respectively.

92
A1.2 Synthetic Procedures
Synthetic procedures for the synthesis of 2-bromo-5-trimethyltin-3-hexylthiopehene and poly(3-
hexyl thiophene) were used without modifications as reported in the literature.
1
Synthesis of
compounds 3 and 6 were modified from literature.

Figure A1.1 Synthesis of (5-bromo-4-(4,4,5,5,6,6,7,7,7-nonafluoroheptyl)thiophen-2-
yl)trimethylstannane, 4.
3-(4,4,5,5,6,6,7,7,7-nonafluorohept-1-en-1-yl)thiophene (1). A phosphonium ylide was
generated by adding PPh
3
in one portion to a solution of 1H,1H, 2H, 2H-nonafluorohexyl iodide
(11.34g, 30.3 mmol) in DMF (15 mL). The solution was heated to 105 °C for 24 hours. After
cooling the reaction mixture, the solvent was removed by vacuum distillation to yield viscous
yellow oil. Dioxane/water (9:1, 170 mL) was added, followed by 3-carboxyaldehyde thiophene
(3.39 g, 30.3 mmol) and K
2
CO
3
(5.44 g, 39.4 mmol). The reaction mixture was refluxed for 24
hours, cooled and extracted with CHCl
3
. The organic layer was washed with water three times
and brine three times, dried over Na
2
SO
4
and concentrated in vacuo to yellow oil. The crude
material was purified on a column with hexanes to yield clear and faint yellow oil (8.82 g, 85%
yield), then carried onto hydrogenation.
1
H NMR: (400 MHz, CDCl
3
) δ 7.43 (dd, 1H), 7.18, (dd,
1H), 7.05 (dd, 1H), 6.74 (dd, 1H), 5.69 (dt, 1H), 3.15 (td, 2H).

3-(4,4,5,5,6,6,7,7,7-nonafluoroheptyl)thiophene (2). To a solution of methanol (40 mL) and 1
(5.00 g, 14.6 mmol) in a 3-necked RBF fitted with a condenser, stir bar, and rubber septa with a
93
vent needle at the top of the condenser, dry Pd/C 10% (550 mg, 10% w/w) was carefully added.
To a separate 3-necked RBF fitted with an addition funnel and rubber septa, NaBH
4
was added
with a stir bar. A solution of methanol and acetic acid (10% v/v solution) was added to the
addition funnel. A cannula was place to connect the atmosphere of the NaBH
4
vessel to the
solution of 1. The solution was heated to 50 °C with vigorous stirring while the acidic methanol
solution was set to slowly add to the NaBH
4
, allowing hydrogen gas to bubble through the
solution. Progress of the reaction mixture was monitored by sampling aliquots by
1
H NMR, and
was typically complete after 24 h. The reaction mixture was concentrated in vacuo and Pd/C was
filtered off through a pad of Celite. The crude material was purified on a column with hexanes to
yield a clear, colorless oil (4.61 g, 92% yield).
1
H NMR: (400 MHz, CDCl
3
) δ 7.28 (dd, 1H),
6.97, (dd, 1H), 6.95 (dd, 1H), 2.74 (t, 2H), 2.09 (m, 2H), 1.96 (m, 2H).

2-bromo-3-(4,4,5,5,6,6,7,7,7-nonafluoroheptyl)thiophene (3). To a solution of 2 (2.57 g, 7.47
mmol) and acetic acid (0.6 M, 12.5 mL), freshly recrystallized NBS (1.46 g, 8.23 mmol) was
added in one portion. The reaction mixture was left to stir at room temperature for 24 h and then
transferred to a separatory funnel with ether and water. The organic layer was washed with 2 M
NaOH
aq
three times, dried with MgSO
4
and concentrated in vacuo to yellow oil. The crude
material was purified on silica column with hexanes followed by a vacuum distillation to yield
clear and colorless oil (2.17 g, 69% yield).
1
H NMR: (400 MHz, CDCl
3
) δ 7.24 (d, 1H), 6.81, (d,
1H), 2.69 (t, 2H), 2.09 (m, 2H), 1.91 (m, 2H).

(5-bromo-4-(4,4,5,5,6,6,7,7,7-nonafluoroheptyl)thiophen-2-yl)trimethylstannane 4. To a
solution of diisopropylamine (0.76 mL, 5.40 mmol) and THF at -78 °C, n-BuLi (1.6 M, 2.83 mL,
94
4.353 mmol) was added drop wise and left to stir for 15 minutes. The solution was warmed to
room temperature for 15 minutes, then subsequently cooled to -78 °C. The LDA solution was
then cannulated to a solution of 3 (1.88 g, 4.40 mmol) and THF at -78 °C. The reaction mixture
was left to stir for 1 h, then trimethyl tin chloride (1.0 M, 5.40 mL, 5.40 mmol) was added drop
wise at -78 °C. The final solution was left to slowly warm to room temperature overnight. The
reaction mixture was transferred to a separatory funnel with ether and water. The organic layer
was washed with diluted HCl
aq
three times, dried over Na
2
SO
4
, and concentrated in vacuo to red
oil. The crude material was vacuum distilled to yield clear, faint yellow oil (1.33 g, 52% yield).
1
H NMR: (400 MHz, CDCl
3
) δ 6.85 (s, 1H), 2.68 (t, 2H), 2.11 (m, 2H), 1.92 (m, 2H), 0.36 (s,
9H);
13
C NMR: (500 MHz, CDCl
3
) δ 140.91, 139.00, 135.73, 114.32, 30.29, 29.86, 29.04, 28.40,
22.59, 20.53, 14.07, -8.26.

Figure A1.2 Synthesis of (5-bromo-4-(2-(2-methoxyethoxy)ethyl)thiophen-2-
yl)trimethylstannane, 7.
2-(2-bromothiophen-3-yl)ethan-1-ol (5). To a solution of 2(3-thienyl)ethanol (3.46 g, 27.0
mmol) in THF (34 mL) at 0 °C, freshly recrystrallized NBS (5.00 g, 28.1 mmol) was slowly
added. The reaction mixture was covered from light and left to slowly warm to room temperature
overnight. After 24 h, reaction mixture was transferred into a separatory funnel with ether and
water. The organic layer was washed with water three times, dried over MgSO
4
and concentrated
in vacuo to brown oil. The extract was eluted through a silica column with 8:2 hexanes to ethyl
acetate solvent, concentrated to an oil, then vacuum distilled to yield a clear and colorless oil
95
(4.88 g, 87% yield).
1
H NMR: δ 7.20 (d, 1H), 6.85 (d, 1H), 3.77 (t, 2H), 2.82 (t, 2H);
13
C NMR:
δ 138.03, 128.59, 125.65, 110.28, 61.90, 32.74.

2-bromo-3-(2-(2-methoxyethoxy)ethyl)thiophene (6). Freshly powdered KOH (3.96 g, 70.7
mmol) was added to a solution of 5 (4.88 g, 23.6 mmol), 2-chloroethylmethyl ether (5.57 g, 58.9
mmol), and Aliquat 336 (0.3 mL). The reaction mixture was left to stir for 4 days at 80 °C.
Reaction mixture was cooled to room temperature and transferred into a separatory funnel with
ether and water. The organic layer was washed three times with dilute HCl
(aq)
, dried over
MgSO
4
, then concentrated to a yellow oil. Extract eluted through a silica column with 9:1
hexanes to ethyl acetate solution, concentrated to an oil, then vacuum distilled to yield a clear
and colorless oil (3.18 g, 51% yield).
1
H NMR: δ 7.18 (d, 1H), 6.86 (d, 1H), 3.64 (t, 2H), 3.55
(m, 4H), 3.38 (s, 3H), 2.89 (t, 2H);
13
C NMR: δ 138.20, 128.62, 125.31, 109.92, 71.91, 70.25,
70.11, 59.08, 29.64.

(5-bromo-4-(2-(2-methoxyethoxy)ethyl)thiophen-2-yl)trimethylstannane (7). A solution of 6
(1.48g, 5.58 mmol) in THF (11.2 mL) was cooled to -78 °C followed by the dropwise addition of
TMP MgCl LiCl in THF/Toluene solution (0.65 M, 9.45 mL). The reaction mixture was stirred
at -78 °C for 3 h, followed by the dropwise addition of trimethyl tin chloride in hexanes solution
(1.0 M, 6.14 mL), then slowly warmed to room temperature over night. The reaction mixture was
transferred to a separatory funnel with ether and water. The organic layer was washed with water
three times, dried over MgSO
4
, then concentrated to a red oil. Extract was vacuum distilled to
yield a clear and yellow oil (1.62 g, 69% yield).
1
H NMR:
13
C NMR:
1
H NMR: δ 6.92 (s, 1H),
96
3.65 (t, 2H), 3.56 (m, 4H), 3.39 (s, 3H), 2.90 (t, 2H);
13
C NMR: δ 139.16, 138.27, 136.61,
114.55, 71.95, 70.40, 70.09, 59.10, 29.66, -8.23.

Figure A1.3. Stille polycondensation of P3HT-co-FHT and P3HT-co-MET random polymers.

Stille Copolymerizations for P3HT-co-FHT Polymers. Monomers 4 and 2-bromo-5-
trimethyltin-3-hexylthiopehene were added to 3-necked RBFs at varied molar ratios via syringe.
Dry DMF (0.04 M) was added via syringe followed by quickly adding palladium
tetrakis(triphenyphosphine) Pd(PPh
3
)
4
(0.04 eq) in one portion. The solution was degassed with
N
2
for 20 m, then heated to 95 °C for 24 h. Reaction mixtures were cooled to room temperature
and precipitated into cold stirring methanol, followed by addition of ammonium hydroxide.
Polymers were decanted into a thimble and purified via Soxhlet extraction with methanol,
97
hexanes, dichloromethane and then collected in chloroform. Polymer chloroform solutions were
concentrated in vacuo and precipitated in cold MeOH and collected via filtration.

P3HT-co-FHT-10%: Yield: 31% (69 mg).
1
H NMR (500 MHz, CDCl
3
) δ 2.83 (m, 0.11H), 2.74
(m, 1H).

P3HT-co-FHT-20%: Yield: 46% (104 mg).
1
H NMR (500 MHz, CDCl
3
) δ 2.83 (m, 0.26H),
2.74 (m, 1H).

P3HT-co-FHT-30%: Yield: 45% (102 mg).
1
H NMR (500 MHz, CDCl
3
) δ 2.83 (m, 0.41H),
2.74 (m, 1H).

P3HT-co-FHT-40%: Yield: 53% (130 mg).
1
H NMR (500 MHz, CDCl
3
) δ 2.83 (m, 0.64H),
2.74 (m, 1H).

P3HT-co-FHT-50%: Yield: 59% (146 mg).
1
H NMR (500 MHz, CDCl
3
) δ 2.83 (m, 0.95H),
2.74 (m, 1H).
98

Figure A1.4.
1
H NMR of P3HT-co-FHT and P3HT Polymers. Singlet at 2.10 ppm is acetone and
1.50 ppm is water.

Stille Copolymerizations for P3HT-co-MET Polymers. Monomers 7 and 2-bromo-5-
trimethyltin-3-hexylthiopehene were added to 3-necked RBFs at varied molar ratios via syringe.
Dry DMF (0.04 M) was added via syringe followed by quickly adding palladium
tetrakis(triphenyphosphine) Pd(PPh
3
)
4
(0.04 eq) in one portion. The solution was degassed with
N
2
for 20 m, then heated to 95 °C for 48 - 120 h. Reaction mixtures were cooled to room
temperature and precipitated into cold stirring methanol, followed by addition of ammonium
hydroxide. Polymers were decanted into a thimble and purified via Soxhlet extraction with
99
methanol, hexanes, and then collected in chloroform. Polymer chloroform solutions were
concentrated in vacuo and precipitated in cold MeOH and collected via filtration.

P3HT-co-MET-10%: Yield: 31% (56 mg).
1
H NMR (500 MHz, CDCl
3
) δ 3.80 (m, 0.17H), 3.67
(m, 0.17H), 3.59 (m, 0.17H), 3.41 (s, 0.26H), 3.14 (m, 0.15H), 2.82 (m, 1.61H).

P3HT-co-MET-20%: Yield: 15% (36 mg).
1
H NMR (500 MHz, CDCl
3
) δ 3.80 (m, 0.33H), 3.67
(m, 0.35H), 3.59 (m, 0.35H), 3.41 (s, 0.54H), 3.14 (m, 0.31H), 2.82 (m, 1.49H).

P3HT-co-MET-30%: Yield: 16% (32 mg).
1
H NMR (500 MHz, CDCl
3
) δ 3.80 (m, 0.56H), 3.67
(m, 0.56H), 3.59 (m, 0.58H), 3.41 (s, 0.86H), 3.14 (m, 0.51H), 2.82 (m, 1.32H).

P3HT-co-MET-40%: Yield: 37% (79 mg).
1
H NMR (500 MHz, CDCl
3
) δ 3.80 (m, 0.79H), 3.67
(m, 0.81H), 3.59 (m, 0.84H), 3.41 (s, 1.26H), 3.14 (m, 0.73H), 2.82 (m, 1.04H).

P3HT-co-MET-50%: Yield: 24% (50 mg).
1
H NMR (500 MHz, CDCl
3
) δ 3.80 (m, 0.93H), 3.67
(m, 1.04H), 3.59 (m, 1.03H), 3.41 (s, 1.46H), 3.14 (m, 0.87H), 2.82 (m, 0.84H).

100

Figure A1.5.
1
H NMR of P3HT-co-MET and P3HT Polymers.
A1.2 Polymer Characterization

One Liquid Model Data

Figure A1.6. Surface energy as calculated by the One-Liquid Model for as cast (solid line) and
thermally annealed (dotted line) thin films of P3HT-co-MET (blue) and P3HT-co-FHT (red).
101

Wu Model Data

Figure A1.7. Surface energy as calculated by the harmonic mean Wu Model for a) as cast and b)
thermally annealed thin films of P3HT-co-MET (blue) and P3HT-co-FHT (red).

a
b
a
102

Table A1.1. Calculated surface energy measurements with standard deviations of polymers
using the one-liquid method and Wu Model.

Polymer
One-Liquid Surface Energy Wu Model Surface Energy
As Cast Annealed As Cast Annealed
P3HT 19.94 ± 0.27 18.73 ± 0.32 19.78 ± 0.73 21.37 ± 0.87
P3HT
90
-co-FHT
10
18.09 ± 0.23 17.94 ± 0.06 17.39 ± 0.34 17.20 ± 0.87
P3HT
80
-co-FHT
20
17.46 ± 0.11 18.21 ± 0.02 16.85 ± 0.72 15.97 ± 0.95
P3HT
70
-co-FHT
30
16.92 ± 0.19 18.13 ± 0.43 15.39 ± 0.47 15.36 ± 0.42
P3HT
60
-co-FHT
40
16.03 ± 0.15 17.19 ± 0.54 13.61 ± 0.13 14.62 ± 0.94
P3HT
50
-co-FHT
50
14.17 ± 0.21 15.67 ± 0.92 12.27 ± 0.14 13.85 ± 0.53
P3HT
90
-co-MET
10
21.17 ± 0.09 20.99 ± 0.12 18.18 ± 0.10 20.53 ± 0.34
P3HT
80
-co-MET
20
22.86 ± 0.21 22.84 ± 0.29 18.97 ± 0.24 22.44 ± 0.61
P3HT
70
-co-MET
30
24.09 ± 0.18 24.05 ± 0.26 19.86 ± 0.13 21.62 ± 0.45
P3HT
60
-co-MET
40
25.05 ± 0.26 25.62 ± 0.19 20.70 ± 0.29 22.21 ± 0.33
P3HT
50
-co-MET
50
27.02 ± 0.08 26.34 ± 0.05 22.34 ± 0.14 22.53 ± 0.27

UV-Vis Spectroscopy

Figure A1.8. Absorption profiles of a) annealed P3HT-co-FHT, and b) annealed P3HT-co-MET
films; i) P3HT, ii) P3HT
90
-co-FHT
10
, iii) P3HT
80
-co-FHT
20
, iv) P3HT
70
-co-FHT
30
, v) P3HT
60
-
co-FHT
40
, vi) P3HT
50
-co-FHT
50
, vii) P3HT
90
-co-MET
10
, viii) P3HT
80
-co-MET
20
, ix) P3HT
70
-co-
MET
30
, x) P3HT
60
-co-MET
40
, and xi) P3HT
50
-co-MET
50
.

b
a
103
Photoluminescence

Figure A1.9. Photoluminescence responses of a) as cast and b) annealed P3HT-co-FHT films; c)
as cast and d) annealed P3HT-co-MET; black) P3HT, blue) P3HT
90
-co-FHT
10
or P3HT
90
-co-
MET
10
, orange) P3HT
60
-co-FHT
40
or P3HT
60
-co-MET
40
, red) P3HT
50
-co-FHT
50
or P3HT
50
-co-
MET
50
.

a
b
c d
104
GIXRD

Figure A1.10. GIXRD data of a) as-cast P3HT-co-FHT and b) as cast P3HT-co-MET films; i)
P3HT, ii) P3HT
90
-co-FHT
10
, iii) P3HT
80
-co-FHT
20
, iv) P3HT
70
-co-FHT
30
, v) P3HT
60
-co-FHT
40
,
and vi) P3HT
50
-co-FHT
50
. vii) P3HT
90
-co-MET
10
, viii) P3HT
80
-co-MET
20
, ix) P3HT
70
-co-MET
30
,
x) P3HT
60
-co-MET
40
, and xi) P3HT
50
-co-MET
50
.

105
Cyclic Voltammetry

Figure A1.11. P3HT
90
-co-FHT
10
Film CV Figure A1.12. P3HT
90
-co-FHT
10
Solution CV

Figure A1.13. P3HT
80
-co-FHT
20
Film CV Figure A1.14. P3HT
80
-co-FHT
20
Solution CV

106

Figure A1.15. P3HT
70
-co-FHT
30
Film CV Figure A1.16. P3HT
70
-co-FHT
30
Solution CV

Figure A1.17. P3HT
60
-co-FHT
40
Film CV Figure A1.18. P3HT
60
-co-FHT
40
Solution CV

Figure A1.19. P3HT
50
-co-FHT
50
Film CV Figure A1.20. P3HT
50
-co-FHT
50
Solution CV
107

Figure A1.21. P3HT
90
-co-MET
10
Film CV Figure A1.22. P3HT
90
-co-MET
10
Solution CV

Figure A1.23. P3HT
80
-co-MET
20
Film CV Figure A1.24. P3HT
80
-co-MET
20
Solution CV

Figure A1.25. P3HT
70
-co-MET
30
Film CV Figure A1.26. P3HT
70
-co-MET
30
Solution CV
108

Figure A1.27. P3HT
60
-co-MET
40
Film CV Figure A1.28. P3HT
60
-co-MET
40
Solution CV

Figure A1.29. P3HT
50
-co-MET
50
Film CV Figure A1.30. P3HT
50
-co-MET
50
Solution CV

Figure A1.31. P3HT Film CV
109
Differential Scanning Calorimetry

Figure A1.32 P3HT
90
-co-FHT
10
DSC trace. Figure A1.33 P3HT
80
-co-FHT
20
DSC trace.

Figure A1.34 P3HT
70
-co-FHT
30
DSC trace. Figure A1.35 P3HT
60
-co-FHT
40
DSC trace.

Figure A1.36 P3HT
50
-co-FHT
50
DSC trace. Figure A1.37 P3HT
90
-co-MET
10
DSC trace.
110

Figure A1.38 P3HT
80
-co-MET
20
DSC trace. Figure A1.39 P3HT
70
-co-MET
30
DSC trace.

Figure A1.40 P3HT
60
-co-MET
40
DSC trace. Figure A1.41 P3HT
50
-co-MET
50
DSC trace.

References

(1) Burkhart, B.; Khlyabich, P. P.; Cakir Canak, T.; LaJoie, T. W.; Thompson, B. C.
Macromolecules 2011, 44 (6), 1242–1246.

111
APPENDIX 2 Surface Energy Modification of Semi-Random
P3HTT-DPP

A2.1 Synthesis
Synthetic procedures for the synthesis of 2-bromo-5-trimethyltin-3-hexylthiopehene, 2,5-
bis(trimethyltin)thiophene, (5-bromo-4-(4,4,5,5,6,6,7,7,7-nonafluoroheptyl)thiophen-2-
yl)trimethylstannane, (5-bromo-4-(2-(2-methoxyethoxy)ethyl)thiophen-2-yl)trimethylstannane
(7), 2,5-Diethylhexyl-3,6-bis(5-bromothiophene-2-yl)pyrrolo[3,4-c]-pyrrole-1,4-dione, were used
without modifications as reported in the literature.
1,2

Figure A2.1. Copolymerizations of P3HTFHTT-DPP, P3HTMETT-DPP, and P3HTT-DPP
polymers.
112
Stille Copolymerizations for P3HTT-DPP Polymers. Monomers 2-bromo-5-trimethyltin-3-
hexylthiopehene (n), 2,5-bis(trimethyltin)thiophene (o), and 2,5-Diethylhexyl-3,6-bis(5-
bromothiophene-2-yl)pyrrolo[3,4-c]-pyrrole-1,4-dione (p) were added to 3-necked RBFs at varied
molar ratios (n = 0.8 for P3HTT-DPP, or n = 0.4 eq for P3HTFHT-DPP and P3HTMETT-DPP, o
= 0.1 eq, p = 0.1 eq.) Comonomer (5-bromo-4-(4,4,5,5,6,6,7,7,7-nonafluoroheptyl)thiophen-2-
yl)trimethylstannane or (5-bromo-4-(2-(2-methoxyethoxy)ethyl)thiophen-2-yl)trimethylstannane
was added at a molar ratio of 0.4 eq for semi-fluoro alkyl and oligoether co-polymers,
respectively. Dry DMF (0.04 M) was added via syringe followed by quickly adding palladium
tetrakis(triphenyphosphine) (0.04 eq) in one portion. The solution was degassed with N
2
for 20 m,
then heated to 95 °C for 48 h. Reaction mixtures were cooled to room temperature and
precipitated into stirring methanol, followed by addition of ammonium hydroxide. Polymers were
decanted into a thimble and purified via Soxhlet extraction with methanol, hexanes,
dichloromethane and then collected in chloroform. Polymer chloroform solutions were
concentrated in vacuo and precipitated in cold MeOH and collected via filtration.
P3HTFHTT-DPP: m = 0.4, n = 0.4, o = 0.1, p = 0.1. Yield 64% (171 mg). M
n
= 10.9 kDa, Đ =
3.06.
1
H NMR (600 MHz, CDCl
3
) δ 8.91 (s, 0.10H), 7.32 (s, 0.13H), 7.17 – 7.14 (m, 0.20H), 7.00
(s, 0.30H), 4.10 – 4.04 (m, 0.20H), 2.95 (m, 0.34H), 2.82 (m, 0.40H), 2.72 (m, 0.08H), 2.60 (m,
0.03H), 2.20 (m, 0.37H), 2.05 – 1.96 (m, 0.51H), 1.74 – 1.72 (m, 0.47H), 1.48 – 1.28 (m, 2.76H),
0.96 – 0.89 (m, 1.40H).
P3HTMETT-DPP: m = 0.4, n = 0.4, o = 0.1, p = 0.1. Yield 79% (240 mg). M
n
= 16.2 kDa, Đ =
3.13.
1
H NMR (600 MHz, CDCl
3
) δ 8.91 (s, 0.10H), 7.34 (s, 0.72H), 7.17 – 6.93 (m, 0.43H), 4.08
(m, 0.23H), 3.81 (m, 0.37H), 3.67 (m, 0.38H), 3.58 (m, 0.37H), 3.41 (s, 0.54H), 3.12 (m, 0.33H),
113
2.94 (m, 0.04H), 2.83 (m, 0.34H), 2.60 (m, 0.04H), 1.97 (m, 0.12H), 1.74 (m, 0.36H), 1.50 – 1.28
(m, 2.41H), 0.97 – 0.90 (m, 1.35H).
P3HTT-DPP: n = 0.8, o = 0.1, p = 0.1. Yield 64% (118 mg). M
n
= 13.5 kDa, Đ = 5.20.
1
H NMR
(600 MHz, CDCl
3
) δ 8.91 (s, 0.10H), 7.32 (s, 0.08H), 7.17 (d, 0.20H), 7.00 (s, 0.34H), 4.10 –
4.04 (m, 0.19H), 2.82 (m, 0.78H), 2.60 (m, 0.05H), 1.96 (m, 0.10H), 1.72 (m, 0.93H), 1.48 – 1.28
(m, 3.93H), 0.89 (m, 2.13H).

A2.2 Polymer Characterization

1
H NMR of Polymers:

Figure A2.2.
1
H NMR of P3HTFHT-DPP in CDCl
3
.

114

Figure A2.3.
1
H NMR of P3HTMETT-DPP in CDCl
3
.

115

Figure A2.4.
1
H NMR of P3HTT-DPP in CDCl
3
.

116
Cyclic Voltammetry:

Figure A2.5. P3HTFHTT-DPP CV trace. Figure A2.6. P3HTMETT-DPP CV trace.

Figure A2.7. P3HTT-DPP CV trace.

117
Differential Scanning Calorimetry:

Figure A2.8 P3HTFHTT-DPP DSC trace. Figure A2.9 P3HTMETT-DPP DSC trace.

Figure A2.10. P3HTT-DPP DSC trace.

Surface Energy Data
Table A2.1. Surface energy data of semi-random polymers.
Polymer
One-Liquid Surface
Energy
Wu Model Surface
Energy
As Cast As Cast
P3HTT-DPP 18.7 ± 0.32 20.6 ± 0.70
P3HTMETT-DPP 29.1 ± 0.39 25.7 ± 0.25
P3HTFHTT-DPP 15.9 ± 0.09 15.0 ±1.16

118
A2.3 Device Fabrication and Characterization
All steps of device fabrication and testing were performed in air. ITO-coated glass
substrates (10 Ω/ ☐, Thin Film Deivces Inc.) were sequentially cleaned by sonication in
detergent, de-ionised water, tetrachloroethylene, acetone, and isopropyl alcohol, and dried in a
nitrogen stream. A thin layer of PEDOT:PSS (Baytron® P VP AI 4083, filtered with a 0.45 µm
PVDF syringe filter – Pall Life Sciences) was first spin-coated on the pre-cleaned ITO-coated
glass substrate and annealed at 130 °C for 60 minutes under vacuum. Polymer:fullerene solutions
were prepared in o-dichlorobenzene or chloroform and stirred for 24 hours at 40 °C. The
polymer:PC
61
BM active layer was spin-coated (with a 0.45 µm PTFE syringe filter – Whatman)
on top of the PEDOT:PSS layer. The P3HTT-DPP: PC
61
BM film was spin-coated from o-
dichlorobenzene solution (10 mg/mL in P3HTT-DPP, 1:1.3 w/w polymer:PC
61
BM ratio). The
P3HTMETT-DPP: PC
61
BM film was spin-coated from o-dichlorobenzene solution (11 mg/mL in
P3HTMETT-DPP, 1:1.3 w/w polymer:PC
61
BM ratio). The P3HTFHTT-DPP: PC
61
BM film was
spin-coated from chloroform solution (4 mg/mL in P3HTFHTT-DPP, 1:2 w/w polymer:PC
61
BM
ratio). Films were placed in a nitrogen cabinet for 20 minutes before being transferred to a
vacuum chamber. The substrates were pumped down to a high vacuum and aluminum (100 nm)
was thermally evaporated at 3 – 4 Å/s using a Denton Benchtop Turbo IV Coating System onto
the active layer through shadow masks to define the active area of the devices are 5.2 mm
2

P3HTT-DPP and P3HTMETT-DPP devices and 4.7 mm
2
for P3HTFHTT-DPP devices.
The current-voltage (I-V) characteristics of the photovoltaic devices were measured under
ambient conditions using a Keithley 2400 source-measurement unit. An Oriel® Sol3A class AAA
solar simulator with xenon lamp (450 Watt) and an AM 1.5G filter was used as the solar
simulator. An Oriel PV reference cell system 91150V was used as the reference cell. To calibrate
119
the light intensity of the solar simulator (to 100 mW/cm
2
), the power of the xenon lamp was
adjusted to make the short-circuit current (J
SC
) of the reference cell under simulated sun light as
high as it was under the calibration condition. Spectral mismatch corrections were performed for
each device according to previously described conditions.
1

A 2.4 References
(1) Khlyabich, P. P.; Ng, C. F.; Thompson, B. C. Macromolecules 2011, 44 (13), 5079–5084.
(2) Howard, J. B.; Noh, S.; Beier, A. E.; Thompson, B. C. ACS Macro Lett. 2015, 725–730.

120
APPENDIX 3 Investigation of Random Copolymer Analogs
of a Semi-Random Conjugated Polymer Incorporating
Thienopyrazine
A3.1 Synthesis
Synthetic procedures for the synthesis of 2-bromo-5-trimethyltin-3-
hexylthiopehene, poly(3-hexyl thiophene), 2,5-bis(trimethyltin)thiophene, 2-bromo-5-
(trimethylstannyl)thiophene, 2,3-dimethyl-thieno[3,4-b]pyrazine, and 5,7-dibromo-2,3-
dimethyl-thieno[3,4-b]pyrazine were used without modifications as reported in the
literature.
1,2

Figure A3.1. Synthesis of 5-bromo-2,3-dimethyl-thieno[3,4-b]pyrazine, 1.

5-bromo-2,3-dimethyl-thieno[3,4-b]pyrazine (1). 2,3-dimethyl-thieno[3,4-b]pyrazine
(337.7 mg, 2.06 mmol) was dissolved in DMF (41 mL, 0.05 M) and cooled to -20 °C. A
solution of NBS (384.8 mg, 2.16 mmol) in DMF (20 mL) was added slowly over the
course of 2 h. The reaction mixture was covered from light and left to stir overnight and
warm to RT. The reaction mixture was extracted with ether and washed with water
several times. The organic layer was dried with MgSO
4
and subsequently concentrated in
vacuo to an orange solid. The extract was purified via flash chromatography with DCM
then dried in a dessicator (318.5 mg, 64% yield).
1
H NMR: (400 MHz, CDCl
3
) δ 8.01 (s,
121
1H) 2.62 (s, 3H), 2.61 (s, 3H).
13
C NMR: (500 MHz, CDCl
3
) δ 154.57, 153.90, 141.11,
139.61, 115.88, 104.34, 23.73, 23.41.

5-bromo-2,3-dimethyl-7-(trimethylstannyl)thieno[3,4-b]pyrazine (2). Compound 1
(178.5 mg, 0.735 mmol) was dissolved in THF (5 mL, 0.15 M) and cooled to -78 °C
followed by the dropwise addition of TMP MgCl LiCl in THF/Toluene solution (1.0 M,
1.10 mL). Reaction mixture was left to stir for 3 hours at -78 °C followed by dropwise
addition of trimethyl tin chloride in hexanes solution (1.0 M, 1.6 mL). Reaction mixture
was left to stir overnight and warm to RT. Reaction mixture was extracted with ether and
washed with water and brine several times. The organic layer was dried over MgSO
4
and
concentrated in vacuo. The extract was dissolved in chloroform and passed through a
celite plug, pretreated with triethylamine, and concentrated in vacuo to an orange solid
(300 mg, 95%).
1
H NMR: (500 MHz, CDCl
3
) δ 2.64 (s, 3H), 2.60 (s, 3H), 0.50 (s, 9H).
13
C NMR: (500 MHz, CDCl
3
) δ 152.10, 128.43, 128.38, 128.26, 125.65, 115.51, 23.68,
23.50, 7.59.

122

Figure A3.2. Copolymerizations of P3HT based random and semi-random polymers.

General Procedure for Stille Copolymerizations for P3HTT, P3HTT-TP and P3HT-
TP Polymers. Monomers were dissolved in dry DMF at an overall concentration of 0.04
M, followed by addition of 4 mol % of Pd(PPh
3
)
4
in one portion. The solution was
degassed for 20 minutes with nitrogen, then heated to 95 °C for 48 hours. The reaction
mixture was cooled to room temperature and precipitated in stirring methanol followed
by addition of 5 mL NH
4
OH. The polymer was then filtered into a soxhlet thimble and
123
purified via soxhlet extraction using MeOH, followed by hexanes. Polymers were
collected in hot chloroform, concentrated in vacuo, then precipitated in cold stirring
methanol. Polymers were then vacuum filtered and dried in a dessicator.

sr-P3HTT-TP. Yield 69% (107.7 mg).
1
H NMR: (500 MHz, CDCl
3
) δ 7.48 (s, 0.25 H),
7.13 (s, 0.19 H), 7.06 (s, 0.24 H), 7.00 (s, 0.44 H), 2.84 (t, 1.77 H), 2.70 (s, 0.75 H), 2.XX
(m, 0.15H), 1.73 (m, 1.94 H), 0.94 (t, 3.00 H)

Figure A3.3. sr-P3HTT-TP
1
H NMR spectrum.

124
r-P3HTT-TP. Yield 61% (96.6 mg).
1
H NMR: (500 MHz, CDCl
3
) δ 7.50 (s, 0.11 H),
7.14 (s, 0.17 H), 7.07 (s, 0.40 H), 6.99 (s, 0.52 H), 2.XX (m, 0.18H), 2.82 (t, 1.56 H),
2.72 – 2.68 (s, 0.55 H), 2.XX (m, 0.21H), 1.73 (m, 1.99 H), 0.93 (t, 3.00 H)

Figure A3.4. r-P3HTT-TP
1
H NMR spectrum.

125
r-P3HT-TP. Yield 92% (147.4 mg).
1
H NMR: (500 MHz, CDCl
3
) δ 7.50 (s, 0.16 H),
7.09 - 6.99 (s, 0.83 H), 2.XX (m, 0.32H), 2.82 (t, 1.56 H), 2.72 – 2.68 (s, 0.55 H), 2.XX
(m, 0.23H), 1.73 (m, 2.04 H), 0.93 (t, 3.00 H)

Figure A3.5. r-P3HT-TP
1
H NMR spectrum.

126
r-P3HTT-10%. Yield 88% (191 mg).
1
H NMR: (500 MHz, CDCl
3
) δ 7.14 (s, 0.14 H),
7.07 (s, 0.19 H), 6.99 (s, 0.88 H), 2.82 (t, 1.97 H), 1.72 (m, 2.01 H), 0.93 (t, 3.00 H)

Figure A3.6. r-P3HTT-10%
1
H NMR spectrum.

127
r-P3HTT-20%. Yield 49% (80.8 mg).
1
H NMR: (500 MHz, CDCl
3
) δ 7.13 (s, 0.29 H),
7.07 (s, 0.31 H), 6.99 (s, 0.88 H), 2.82 (t, 1.99 H), 1.72 (m, 2.07 H), 0.93 (t, 3.00 H)

Figure A3.7. r-P3HTT-20%
1
H NMR spectrum.

128
sr-P3HTT-20%. Yield 71% (137.8 mg).
1
H NMR: (500 MHz, CDCl
3
) δ 7.13 (s, 0.23 H),
7.08 (s, 0.25 H), 7.00 (s, 0.94 H), 2.82 (t, 2.08 H), 1.73 (m, 2.11 H), 0.94 (t, 3.00 H)

Figure A3.8. sr-P3HTT-20%
1
H NMR spectrum.

129
A3.2 Polymer Characterization
1
H 1D-NOESY Spectroscopy

Figure A3.9. Selective excitation at 2.82 ppm of r-P3HT-TP.
130

Figure A3.10. Selective excitation at 2.72 ppm of r-P3HT-TP.
131

Figure A3.11. Selective excitation at 2.72 ppm zoomed in, r-P3HT-TP.
132

Figure A3.12. Selective excitation at 2.68 ppm, r-P3HT-TP.
133

Figure A3.13. Selective excitation at 2.70 ppm, sr-P3HTT-TP.
134

Figure A3.14. Selective excitation at 2.68 ppm, r-P3HTT-TP.

135

Figure A3.15. Selective excitation at 2.72 ppm, r-P3HTT-TP.

136

UV-Vis Spectroscopy

Figure A3.16. Absorption profiles of P3HT (orange), r-P3HTT-10% (light blue), r-
P3HTT-20% (dark blue), sr-P3HTT-20% (black).

137
Cyclic Voltammetry

Figure A3.17 sr-P3HTT-TP film CV. Figure A3.18 r-P3HTT-TP film CV.

Figure A3.19 r-P3HT-TP film CV. Figure A3.20 r-P3HTT-10% film CV.

138

Figure A3.21 r-P3HTT-20% film CV. Figure A3.22 sr-P3HTT-20% film CV.

Figure A3.23 P3HT film CV.

139
Differential Scanning Calorimetry

Figure A3.24 sr-P3HTT-TP DSC trace. Figure A3.25 r-P3HTT-TP DSC trace.

Figure A3.26 r-P3HT-TP DSC trace. Figure A3.27 r-P3HTT-10% DSC trace.

140

Figure A3.28 r-P3HTT-20% DSC trace. Figure A3.29 sr-P3HTT-20% DSC trace.

A3.3 References
(1) Burkhart, B.; Khlyabich, P. P.; Cakir Canak, T.; LaJoie, T. W.; Thompson, B. C.
Macromolecules 2011, 44 (6), 1242–1246.
(2) Wen, L.; Heth, C. L.; Rasmussen, S. C. Phys. Chem. Chem. Phys. 2014, 16 (16),
7231–7240.

Abstract (if available)

Abstract Conjugated polymers are promising semi-conducting materials for use in organic photovoltaics such as solar cells, field effect transistors, and light emitting diodes. Polymer photovoltaics are attractive because they are lightweight, flexible, and easy to integrate into existing infrastructure. Polymer active layers are also solution processable, making large-scale roll-to-roll manufacturing possible and lowering manufacturing costs of solar cells. ❧ The focus of this dissertation is structure-function relationships in random and semi-random conjugated polymers based on regio-regular poly (3-hexyl thiophene) (P3HT). Semi-random polymers largely comprise 3-hexyl thiophene and small feed ratios of electron-poor acceptors, leading to low band gaps and broad absorption profiles. Meanwhile, desirable properties of P3HT are still maintained: high hole mobilites, good polymer:fullerene miscibility, and semi-crystallinity. ❧ Semi-random polymers have also been used in ternary blend solar cells, which utilize two polymer donors and one fullerene acceptor. Two polymer donors with complementary absorption profiles can boost short-circuit currents (JSC). Moreover, polymer pairs that exhibit good miscibility or compatibility have also benefited from a composition-dependent open-circuit voltage (VOC). The synergistic effects of additive light absorption and composition-tuned voltage can lead to an over all improved solar cell device efficiency. ❧ Compositional tuning of VOC is attributed intimate mixing of the polymer donors. Polymer:polymer miscibility can be predicted by surface energies of the respective materials, which is an easily measured physical parameter. Chapter 2 focuses on modulating the surface energy of random P3HT copolymers through side chain engineering. New P3HT-like polymer families containing either semi-fluoro alkyl or oligo-ether side chains are prepared and characterized. Optical and electronic properties are virtually identical to P3HT while surface energy is finely tuned with comonomer composition. ❧ Subsequently, chapter 3 applies the synthetic model used for P3HT to tune the surface energy of semi-random polymer containing diketopyrrolopyrrole (P3HTT-DPP). Similarly, optical and electronic properties are maintained and surface energy is tuned. Small changes in lamellar packing and melt transitions are observed. The resulting polymers are optimized in photovoltaic devices showing that oligo-ether side chain polymer (P3HTMETT-DPP) maintains similar performance. However, the semi-fluoro alkyl polymer (P3HTFHTT-DPP) required lower polymer solution concentrations for thin film processing, resulting in a lower JSC and overall efficiency. ❧ Lastly, differences in linkage patterns of random and semi-random donor-acceptor polymers based on thienopyrazine (P3HTT-TP) are investigated in chapter 4. This study suggests that restricted linkage patterns, like those in semi-randoms, are necessary for favoring push-pull behavior and strong intramolecular charge transfer (ICT) absorption bands. Random and semi-random analogs also demonstrate differences in frontier orbital levels, thermal properties, semi-crystallinity, and lamellar packing.

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Asset Metadata

Creator Howard, Jenna B. (author)

Core Title Structure-function studies of random and semi-random poly(3-hexyl thiophene) copolymers

School College of Letters, Arts and Sciences

Degree Doctor of Philosophy

Degree Program Chemistry

Publication Date 10/31/2016

Defense Date 10/31/2016

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

Tag conjugated polymers,OAI-PMH Harvest,organic photovoltaics,random polymers,semi-random polymers

Format application/pdf (imt)

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Thompson, Barry C. (committee chair), Nakano, Aiichiro (committee member), Thompson, Mark E. (committee member)

Creator Email jbhoward@usc.edu,jenna.b.howard@gmail.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c40-318168

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Document Type Dissertation

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Rights Howard, Jenna B.

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Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the a...

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