Tuning Linker Rigidity in Dimeric Acceptors Enables Efficient Organic Solar Cells

Organic solar cells (OSCs) based on nonfullerene acceptors have achieved remarkable efficiency improvements, yet the structure–property relationships of oligomeric acceptors, particularly the role of π-bridge rigidity in governing molecular packing and device physics, remain insufficiently understood. Here, we report two dimeric acceptors, DY-TT and DY-T-T, constructed from an identical monomeric backbone but featuring distinct π-bridge linkers to elucidate the impact of linker rigidity on photovoltaic performance. Compared with the more rigid DY-TT containing a fused bithiophene linker, the DY-T-T acceptor with a more flexible bithiophene linker exhibits a slightly narrower optical bandgap and more favorable energy-level alignment. In the corresponding PM6-based blends, DY-T-T enables enhanced charge generation and a more optimized phase-separated morphology. Moreover, the PM6:DY-T-T blend shows more coherent molecular packing and reduced trap-assisted recombination, which are attributed to its moderate conformational flexibility. As a result, the DY-T-T-based device delivers an improved power conversion efficiency of 18.92%, outperforming the DY-TT counterpart (17.90%) with simultaneously improved short-circuit current density and fill factor. These findings demonstrate that rational modulation of linker rigidity represents an effective molecular design strategy for advancing high-performance oligomeric acceptors in OSCs.