A Dithienopyrazine-BasedWide Band Gap Polymer Donorfor Efficient Organic Solar Cells

Developing a wide band gap polymer donor is highly important for realizing high-performance organic solar cells (OSCs). Herein, we are the first to utilize the dithienopyrazine (DTPz) electron-accepting (A) unit to construct novel D–A type copolymers, namely, DTPz-1 and DTPz-2, using benzodithiophene (BDT) and benzodifuran (BDF) as the copolymerizing electron-donating (D) units, respectively. Compared with DTPz-1, DTPz-2 exhibits a cascade energy level with nonfullerene acceptors (NFAs) of L8-BO, proper phase separation scale, strong molecular packing, and high charge mobility. As a result, the device based on DTPz-2/L8-BO achieves a higher power conversion efficiency (PCE) of 15.03% compared with DTPz-1/L8-BO, which has a PCE of 8.14%. This study not only provides a new A structural unit for fabricating high-efficiency D–A type polymer donors but also proves that BDF may be more suitable than classic BDT when designing certain D–A type photovoltaic donors.