Over 17% Efficiency Binary Organic Solar Cells with Photoresponses Reaching 1000 nm Enabled by Selenophene-Fused Nonfullerene Acceptors

Nonfullerene acceptors (NFAs) have played an important role in the development of organic solar cells. However, the optical absorption of most NFAs is limited within 600-900 nm, prohibiting further improvement of short-circuit current density (J_sc). To alleviate this problem, a fused-ring π-core BzS was designed by combining weakly electron-withdrawing benzotriazole (Bz) and strongly electron-donating selenophene together. Besides, the length of N-alkyl chain on the Bz moiety was engineered to tune the morphology, affording two NFAs mBzS-4F and EHBzS-4F. Both NFAs possess an absorption edge approaching 1000 nm, as resulted from the enhanced intramolecular charge transfer in conjunction with efficient intra- and intermolecular interactions. Binary photovoltaic devices based on PM6:mBzS-4F showed a power conversion efficiency of 17.02% with a very high J_sc of 27.72 mA/cm² and a low energy loss of 0.446 eV. This work provides a strategy for future design of efficient NIR-responsive materials.