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 (DA) 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-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 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.