Crystallization Pathway Dictates Performance: Unraveling Microstructural Evolution toward Efficient and Stable Inorganic Perovskite Solar Cells

The crystallization evolution in solution-processed films is critical to the performance and stability of perovskite solar cells. However, the crystallization kinetics of all-inorganic perovskites remain poorly understood due to experimental challenges in observing polycrystalline cluster kinetics during annealing. Using temperature-controlled laser scanning confocal microscopy, we performed in situ monitoring during annealing. Results show that enhanced dicoumarol (DIC)–perovskite precursor interactions promote spontaneous formation of DIC-Cs + [PbI 3- x Br x ] − (δ-phase) heterogeneous seeds. This suppresses solvent-dominated intermediate phases and promotes solvent volatilization. The effective diffusion activation energy increased from 24.5 to 26.9 kJ mol –1, significantly retarding crystal growth. The average cluster growth rate decreased from 320 to 237 nm s –1 . The resulting CsPbI 3- x Br x films exhibit high crystallinity, reduced trap density, and extended carrier lifetime, enabling a power conversion efficiency of 22.14% and improved environmental stability. This work provides direct in situ insights into cluster growth, guiding the use of heterogeneous seeds for high-quality all-inorganic perovskite films.