Morphological Modulation by Solid Additive Enables High‐Efficiency Organic Solar Cells with Extended Exciton Diffusion

Comprehensive Summary The active layer of organic solar cells (OSCs), which processed from volatile and toxic solvents, poses significant challenges for the spontaneous formation of an optimal morphology during the film‐forming process. Herein, a non‐halogenated solid additive, diphenyl disulfide (DPDS), is employed to enhance the exciton dynamics and photovoltaic performance of OSCs through a two‐step aggregation process. Detailed characterization reveals that intermolecular interactions between DPDS and the structural units of L8‐BO lead to more pronounced fibrillation of acceptor, a reduced π‐π stacking distance, and an extended exciton diffusion length. The ternary OSCs incorporating DPDS additive achieve a power conversion efficiency (PCE) of 19.3% and a fill factor of 80.3%, significantly outperforming the control devices. Notably, the ternary devices processed from both non‐halogenated solvent and additive demonstrate no significant loss compared to its halogenated counterparts. This study provides new insights into additive‐directed morphology control and offers a promising strategy for the development of high‐performance OSCs.