Halogenation-Regulated Electron-Phonon Coupling Stabilizes Delocalized Excitation Toward High-Performance Organic...

Non-radiative energy loss remains a critical limitation to further improving the efficiency of organic solar cells (OSCs), as charge generation is typically governed by charge-transfer (CT) states that intrinsically suffer from non-radiative recombination. Intra-moiety excitation (i-EX), a delocalized excitation capable of dissociating within acceptor domains, provides an alternative pathway that can reduce CT-mediated loss. However, its molecular regulation and intrinsic photophysical characteristics remain unclear. In this work, the competition between CT- and i-EX-mediated charge generation pathways is systematically regulated by halogen substitution, where enhanced i-EX contribution suppresses CT-related spin-triplet recombination and substantially reduces non-radiative energy loss. Increasing halogen atomic numbers from fluorine to iodine promotes i-EX formation while suppressing CT participation. Reduced CT involvement diminishes spin-triplet recombination, leading to decreased non-radiative energy loss. Meanwhile, heavier halogen substitution weakens electron-phonon coupling and stabilizes delocalized excitations against vibration-induced dissipation, enabling efficient i-EX-mediated charge generation at room temperature. By balancing i-EX generation and CT processes, the brominated acceptor achieves 20.3% power conversion efficiency in binary OSCs and over 21% in ternary OSCs. This work reveals a clear structure-property relationship for stabilizing delocalized excitations and minimizing energy loss toward high-efficiency OSCs.