Suppressing Electron–Phonon Coupling via Solid Additives for High‐Performance Organic Solar Cells

ABSTRACT The strong electron–phonon coupling in organic photovoltaic materials significantly impedes exciton transport and promotes charge recombination, thereby exerting a detrimental effect on the overall performance of organic solar cells (OSCs). Mitigating electron–phonon coupling is therefore essential for developing high‐performance OSCs. In this work, we introduce two solid additives, 1‐bromo‐3‐chloronaphthalene (BCN‐1) and 1‐chloro‐3‐bromonaphthalene (BCN‐2), into the bulk heterojunction active layer to address this fundamental challenge. We demonstrate that BCN‐2 effectively suppresses high‐frequency lattice vibrations, which minimizes electron–phonon scattering and thereby promotes efficient and long‐range exciton diffusion. As a result, the BCN‐2 processed devices exhibit prolonged exciton lifetime and superior charge carrier mobility compared to the control devices. These synergistic improvements in photophysical properties such as charge transport, contribute to a remarkable power conversion efficiency of 19.72% in the PM6:L8‐BO‐based OSCs. This work underscores the suppression of electron–phonon coupling as a critical and general strategy for advancing the performance of organic photovoltaic devices.