Linker‐Mediated Trade‐Off Between Acceptor Aggregation and Donor–Acceptor Mixing Enables Organic Solar Cells With Efficiencies Exceeding 20.5%

Small‐molecule acceptors (SMAs) bearing steric substituents suppress excessive aggregation‐induced nonradiative energy loss (Δ E nrad ), but this strategy often compromises charge transport by disrupting π‐orbital overlap and blend morphology. This trade‐off remains a key limitation to further improving photovoltaic efficiency. Here, we probe this dilemma through linkage‐topology engineering by incorporating highly crystalline and luminescent 3,6‐dichlorocarbazole units into SMA backbones. Through systematic linker variation, we tune acceptor self‐aggregation and donor/acceptor intermolecular interactions, thereby mitigating this intrinsic trade‐off. By modulating molecular linkage mode from a direct C─N connection (CHC‐1) to a flexible methylene bridge (CHC‐2) and a rigid carbonyl bridge (CHC‐3), we achieve orthogonal control over acceptor aggregation and donor/acceptor interfacial coupling. Notably, carbonyl‐bridged CHC‐3 shows the weakest acceptor self‐association, but the strongest donor/acceptor coupling with PM6. This combination suppresses charge‐transfer‐state nonradiative recombination and optimizes film‐forming kinetics, leading to an improved vertical composition gradient and a refined surface morphology. Consequently, CHC‐3‐based binary and ternary devices achieve PCEs of 18.79% and 20.58%, respectively, with a markedly reduced Δ E nrad of 0.204 eV. This work establishes linkage‐topology engineering as an effective strategy for balancing luminescence efficiency, charge transport, and morphology in sterically modified SMAs.