Incorporation of alkylthio side chains on benzothiadiazole-based non-fullerene acceptors enables high-performance organic solar cells with over 16% efficiency

Y6-type non-fullerene acceptors (NFAs) with an acceptor-donor-acceptor '-donor-acceptor (A-D-A '-D-A) structure have been very popular in the field of organic solar cells (OSCs) due to their excellent performances. In this study, two novel NFAs, BTPS-4F and BTPS-4Cl were designed by incorporating undecylthio side chains into a thienothiophene moiety and connecting it to two different halogenated 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile end groups (2F-IC and 2Cl-IC) respectively. When blended with a donor polymer, PM6, BTPS-4F-based devices achieved a high power conversion efficiency (PCE) of up to 16.2% with an open-circuit voltage (V-OC) of 0.82 V, a short-circuit current density (J(SC)) of 25.2 mA cm(-2) and a fill factor (FF) of 0.78, while BTPS-4Cl-based devices achieved an inferior PCE of 13.5%. This is the first time alkylthio chains are employed on Y6-like NFAs to achieve high-performance OSCs. Subsequent characterization showed that the upshifted energy level of BTPS-4F and the better intermolecular packing in PM6:BTPS-4F blends are the major reasons for the enhanced performance of BTPS-4F-based devices over BTPS-4Cl-based ones. This work provides high-performance non-fullerene acceptors for OSCs and demonstrates a promising molecular design strategy that can effectively regulate their energy levels and morphology.