Regulating Crystallinity and Miscibility via Ternary Strategy Triggers Efficient All-Small-Molecule Organic Solar Cells

All-small-molecule OSCs (ASM-OSCs) have garnered significant attention for their inherent advantages, including low batch-to-batch variations and well-defined molecular structures. However, their power conversion efficiencies (PCEs) are relatively inferior, mainly imputed to the challenges in controlling active layer morphologies. Herein, FSBTSeHR, a small-molecule donor (SMD) was added to the B1:BTP-eC9 blend. FSBTSeHR exhibits high crystallinity, improving the molecular packing in the ternary blend. Furthermore, FSBTSeHR has better miscibility with the host donor B1 than with BTP-eC9, leading to a proper nanoscale phase separation morphology in the ternary active layer. The optimized active layer morphology facilitates charge transport and extraction while suppressing charge recombination in ternary devices. Transient absorption spectroscopy (TAS) reveals a rapid exciton dissociation and diffusion process in the blend of B1:FSBTSeHR:BTP-eC9, which is consistent with its improved morphology. Thus, the ternary device obtained a remarkable PCE (17.04%), which is one of the highest values in ASM-OSCs to date.