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 (Jsc). 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 Jsc 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.