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

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 ( J SC ) and open-circuit voltage ( V OC ) 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-C 71 -butyric acid methyl ester (PC 71 BM). Therefore, we were able to produce high-performance PSCs with the power conversion efficiency (PCE) of 6.12%, benefiting from both high V OC (0.93 V) and J SC (11.95 mA cm –2 ) values. To the best of our knowledge, this PCE value is one of the highest values reported for the homopolymer donor-based PSCs. Significantly, the optimized condition of the device was achieved without any solvent additive or thermal treatment. Therefore, PBDTT is a promising candidate to take over the role of P3HT in tandem solar cells and ternary blend solar cells.