Phase Evolution Kinetics in Additive‐Free 19.75% Organic Photovoltaics Empowered by Solvent Vapor Annealing

Organic photovoltaics (OPVs) are fundamentally constrained by suboptimal molecular packing and interfacial recombination within bulk heterojunction architectures. While solvent vapor annealing (SVA) presents a promising morphology‐regulation strategy, its kinetic mechanisms in state‐of‐the‐art polymer donor/non‐fullerene acceptor systems remain obscured by empirical post‐processing approaches. Through time‐resolved analysis of hierarchical assembly dynamics in PM6:BO‐4Cl blends, we elucidate the kinetic superiority of SVA intervention. Transient absorption spectroscopy uncovers that 30‐s SVA treatment accelerates exciton dissociation to τ 1 = 0.48 ps while reducing trap‐state density by 35%, synergistically enabling a high‐power conversion efficiency (PCE) of 19.06% in binary devices. Depth‐profiling technique, in situ UV‐vis, and GIWAXS analysis collaboratively demonstrate that SVA balances domain purity and interfacial distribution, effectively mitigating non‐radiative recombination. Extending this kinetic‐controlled strategy to ternary PM6:D18:L8‐BO systems achieve a high PCE of 19.75%—which is among the highest efficiency reported for additive‐free OPVs. This study reveals the mechanism of SVA regulating interface dynamics and phase evolution, providing a mechanistic understanding and controllable process path for high‐performance organic photovoltaics.