Toward Enhanced Organic Solar Cells Based on BTA-Based Materials: The Role of Donor–Acceptor Design with Identical Central Units

Constructing organic photovoltaic donor and acceptor materials with identical functional units represents an effective strategy to enhance the performance of organic solar cells (OSCs). In this study, we designed and synthesized a near-infrared asymmetric fused-ring electron acceptor (FREA), BTA-m-S-2Cl, which incorporates the electron-deficient benzotriazole (BTA) unit as its core. Owing to the well-matched energy levels and complementary light absorption between PBDF-NS (a previously reported polymer donor incorporating BTA as the central unit) and BTA-m-S-2Cl, the blended system exhibits improved exciton dissociation and charge transport. Consequently, OSCs based on PBDF-NS:BTA-m-S-2Cl achieve an impressive open-circuit voltage ( V oc ) of 0.857 V, a short-circuit current density ( J sc ) of 27.36 mA/cm 2, and a fill factor (FF) of 77.9%, yielding an outstanding power conversion efficiency (PCE) of 18.27%, significantly surpassing the 16.93% efficiency of the benzothiadiazole (BT)-based acceptor (LC301) and marking the highest PCE for BTA-based OSCs. These findings demonstrate that designing FREAs with functional units identical to those of the donor facilitates optimized energy level alignment, thereby balancing V oc and J sc to achieve high-performance OSCs.