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A donor polymer based on 3-cyanothiophene, a structurally simple unit, is synthesized for organic solar cells, which exhibited prominent power conversion efficiency and excellent batch-to-batch reproducibility in a wide molecular weight range.

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 opencircuit 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.

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