Structurally Locked A–D–A-Type Medium-Bandgap-Small-Molecule Donors for Low-Cost and High-Efficiency All-Small-Molecule Organic Solar Cells

The development of high-performance polymer donors and fused-ring small-molecule donors (SMDs) for organic solar cells is often hindered by complex multiple-step synthesis and high synthetic complexity, restricting their figure of merit (FOM). In this study, we reported two simple medium-bandgap A-D-A-type SMDs, AW-01 and AW-02, featuring the same dialkoxybenzene as a central core and two indanedione as terminal electron withdrawing units, but differed in π-linkers in their donor units (thiophene for AW-01 and ethylenedioxythiophene for AW-02). Both donors were synthesized via a facile four-step synthetic route using direct C-H arylation and Knoevenagel condensation reactions without hazardous reagents. An intramolecular noncovalent interaction strategy was employed to enhance molecular planarity; notably, AW-02 exhibits multiple O···S and O···H interactions, leading to backbone rigidification and J-aggregation. AW-02 shows complementary absorption with the Y6 acceptor over 450-900 nm and suitable energy level alignment. The nonhalogen solvent-processed all-small-molecule OSCs based on AW-02/Y6 achieved a high PCE of 15.11%, significantly outperforming AW-01 (7.49%). The superior performance of AW-02 is primarily attributed to its higher Jsc and FF, arising from enhanced charge transport, balanced hole and electron mobilities, low radiative energy losses, and reduced trap-assisted recombination, matching the highest efficiencies reported for additive-free binary SMD-based OSCs. This work demonstrates a promising strategy for developing simple, low-cost, and highly efficient SMDs for future scalable ASM-OSCs, highlighting their potential to replace high-efficiency polymer donors and fused SMDs.