High-Performance D–A Copolymer Donor Based on Difluoroquinoxaline A-Unit with Alkyl-Chlorothiophene Substituents for Polymer Solar Cells

Side chain engineering with fluorine substitution is widely used to enhance photovoltaic performance of polymer donors in the research field of polymer solar cells (PSCs). However, fluorine substitution has disadvantages of complicated synthesis and high cost. Herein, we synthesized a novel D-A copolymer donor PBQ9 based on difluoroquinoxaline A-unit with chlorine substitution on its alkyl-thiophene side chains instead of fluorine substitution in the polymer donor PBQ6, which greatly shortens the synthetic route and reduces the cost. Interestingly, the optimized binary PSC with PBQ9 as polymer donor and m-TEH as acceptor demonstrated a high power conversion efficiency (PCE) of 18.81% (certified PCE of 18.33% by National Institute of Metrology, China) with a high fill factor of 80.59%, and the photovoltaic performance of the PSCs is insensitive to the different batches of the polymer donor. The results indicate that PBQ9 is a high-performance polymer donor and that chlorine substitution is an effective strategy to improve photovoltaic performance and reduce the cost of polymer donors.