Achieving 16% Efficiency for Polythiophene Organic Solar Cells with a Cyano‐Substituted Polythiophene

Abstract Polythiophenes (PTs) are promising electron donors in organic solar cells (OSCs) due to their simple structures and excellent synthetic scalability. However, the device performance of PT‐based OSCs is rather poor due mainly to large photon energy losses and an unfavorable active layer morphology. Herein, the authors report a new PT, which is abbreviated as P5TCN‐2F and features cyano‐group substituents for high‐efficiency OSCs. The cyano‐group endows P5TCN‐2F with a deep‐lying highest occupied molecular orbital energy level, which thereby contributed to high open‐circuit voltage in OSCs as a result of reduced non‐radiative recombination energy loss. Moreover, the cyano‐group leads to strong interchain interaction, improved polymer crystallinity, and appropriate miscibility with the prevailing non‐fullerene acceptors. Consequently, P5TCN‐2F offers over 15% power conversion efficiency when blended with various Y‐series non‐fullerene acceptors (Y6, Y6‐BO, eC9, and L8‐BO). Particularly, a champion efficiency of 16.1% is obtained by the P5TCN‐2F:Y6 blend, which is largely higher than that of any previous PT‐based OSCs. Moreover, the average figure of merit of the active layer based on P5TCN‐2F is much superior to that of benzodithiophene‐based polymers. These results suggest the renaissance of PT‐based OSCs and have opened an avenue to access high‐performance materials for the large‐scale production of OSC modules.