Small-Molecule Acceptor with Unsymmetric Substituents and Fused Rings for High-Performance Organic Solar Cells with Enhanced Mobility and Reduced Energy Losses

A new unsymmetric small-molecule acceptor (SMA) BTPOSe-4F was designed by unsymmetric structure modification to Y6 with an alkyl upper side chain replaced by an alkoxy side chain and a sulfur atom in its central fused ring replaced by a selenium atom, for the application as an acceptor to fabricate organic solar cells (OSCs). BTPOSe-4F exhibits a higher lowest unoccupied molecular orbital (LUMO) energy level, a reduced nonradiation energy loss, and better charge extraction properties in its binary OSCs with a higher Voc of 0.886. Furthermore, the ternary OSCs with the addition of PC71BM demonstrated a higher power conversion efficiency (PCE) of 17.33% with Voc of 0.890 V. This work reveals that the unsymmetric modification strategy can further give impetus to the photovoltaic performance promotion of OSCs for Y6-series SMAs.