Harmonizing A‑Site Cation Incorporation With Conductive Grain‑Boundary Bridging for Durable Perovskite Solar Cells.

While perovskite solar cells (PSCs) have achieved significant progress in power conversion efficiency (PCE), their commercialization remains hindered by a critical challenge: irreversible efficiency degradation during device operation, primarily caused by the spontaneous degradation of the perovskite layer. The root of this issue lies in the initial heterogeneity of the mixed-cation perovskite films, which accelerates localized phase segregation and defect proliferation under light and electrical stress. Current solutions balancing halide-Pb2+ interactions with additives commonly fail to resolve the intrinsic cation-PbI2 affinity disparity; moreover, additives are typically insulating, creating charge transport bottlenecks at grain boundaries. Herein, we developed a coordination‑chemistry‑based crystallization kinetics modulation strategy using 4,4'‑dichlorodiphenyl sulfone (DCPSO). It balances the disparate crystallization kinetics of components with varying coordination capacities, yielding a highly uniform initial phase distribution that fundamentally suppresses degradation pathways from compositional heterogeneity. Additionally, the D-π-A conjugated structure of DCPSO provides good conductivity, alleviating carrier accumulation at grain boundaries and optimizing energy level alignment. The champion device achieves a PCE of 25.75% with excellent long term operational stability. Through molecular design, this work enables synergistic regulation of crystallization kinetics and electrical properties, offering an effective materials strategy and mechanistic insights to simultaneously tackle efficiency and stability challenges.