Fluorinated thienyl side chain and benzo[1,2-b:4,5-b′]bis(selenophene) core-based A–D–A-type multifunctional small molecule as a high-performance acceptor and non-volatile solid additive

Two-dimensional (2D) aromatic side-chain conjugation effectively alleviates the efficiency bottlenecks of A–D–A small-molecule acceptors (SMAs). However, the rational design of selenium-based SMAs with 2D conjugated side chains and their dual functions as active acceptors and non-volatile additives in binary OSCs remains underexplored. Herein, using synergistic selenium-substituted core and 2D conjugated aromatic side-chain engineering, a series of inner selenium-substituted fused-ring A–D–A-type SMAs (BDSeCl, T-BDSeCl, and FT-BDSeCl), having one benzo[1,2-b:4,5-b′]bis(selenophene) (BDSe)-based central core, but without side chains, and with thienyl and fluorinated thienyl modified side chains, were successfully synthesized, respectively. Compared with BDSeCl, T-BDSeCl and FT-BDSeCl exhibit slightly widened bandgaps yet more ordered solid-state aggregation via slightly twisted 2D conjugated aromatic side chains. Single-crystal results confirm that T-BDSeCl and FT-BDSeCl adopt more planar conformations than BDSeCl, stabilized by intramolecular S⋯Se noncovalent interactions. More importantly, favourable J-type aggregation, shortened π–π stacking distances, and enhanced π–π electronic coupling are achieved in the FT-BDSeCl crystal, thereby affording enhanced crystallinity and more efficient charge transport channels. The FT-BDSeCl-based blend films present highly ordered face-on packing, continuous fibrous networks, and optimal phase separation, enabling efficient exciton dissociation and balanced charge transport. PM6:FT-BDSeCl binary OSCs achieve a top-tier PCE of 14.13%, outperforming PM6:T-BDSeCl (13.44%) and PM6:BDSeCl (12.36%) counterparts, and this efficiency represents one of the best results for 2D conjugated aromatic side chain-modified A–D–A SMAs. Beyond serving as a high-performance photovoltaic acceptor, FT-BDSeCl also acts as a superior non-volatile solid additive to boost the efficiency of D18:L8-BO OSCs from 18.44% to 19.77% in comparison with T-BDSeCl. This work demonstrates that the BDSe-fused-core and fluorinated 2D conjugated aromatic side chain synergistic molecular engineering can effectively optimize molecular conformation, crystal packing, and blend morphology, offering a reliable molecular design strategy for high-efficiency A–D–A type selenium-based small-molecule OSC materials.