High‐Efficiency Organic Solar Cells Enabled by Non‐Fullerene Acceptors with Benzimidazole as the Central Core

Abstract Electron‐deficient central core plays a crucial role in the construction of efficient Y‐series non‐fullerene acceptors (NFAs). Here, fused‐ring benzimidazole (BIm) served as a central core for the first time to yield a new NFA named MZ‐1 and its structural analogue named MZ‐2, which is obtained by replacing the methyl group on the 2C position of BIm in MZ‐1 with trifluoromethyl group. Compared with MZ‐1, MZ‐2 shows obviously blue‐shifted absorption and lowers the highest occupied molecular orbital (HOMO) energy level that is more matched to that of polymer donor PM6. Benefiting from the more efficient charge transport and favorable microphase separation morphology of the active layer, the acceptor MZ‐2‐based device affords an excellent power conversion efficiency (PCE) of 17.31% along with a high open‐circuit voltage (V_oc) of 0.903 V, a short‐circuit current density (J_sc) of 26.32 mA cm⁻² and a fill factor (FF) of 72.83%, which is remarkably superior to that of MZ‐1‐based devices with PCE of 10.70%. This study offers valuable insight into the design of acceptors to enrich Y series NFAs for high‐performance organic solar cells (OSCs).