Poly(benzodithiophene) Homopolymer for High-Performance Polymer Solar Cells with Open-Circuit Voltage of Near 1 V: A Superior Candidate To Substitute for Poly(3-hexylthiophene) as Wide Bandgap Polymer

Abstract

Conjugated homopolymers can be synthesized more simply and reproducibly at lower cost than widely developing donor–acceptor (D–A) alternating copolymers. However, except for well-known poly(3-hexylthiophene) (P3HT), almost no successful homopolymer-based polymer solar cells (PSCs) have been reported because of their relatively wide band gap and unoptimized energy levels that limit the values of short circuit current (JSC) and open-circuit voltage (VOC) in PSCs. Herein, we report the development of poly(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b’]dithiophene) (PBDTT) homopolymer that has high light absorption coefficients and nearly perfect energy alignment with that of [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). Therefore, we were able to produce high-performance PSCs with the power conversion efficiency (PCE) of 6.12%, benefiting from both high VOC (0.93 V) and JSC (11.95 mA cm–2) values. To the best of our knowledge, this PCE value is one of the highest values reported for the homo...