Suppressing Intermediate-Phase Heterogeneity Enables Efficient and Stable CsPbI₃ Solar Cells

All-inorganic CsPbI₃ perovskite solar cells are promising for durable photovoltaics owing to their superior resistance to thermal decomposition and halide segregation compared with hybrid counterparts. However, their photovoltaic performance remains hampered by poor crystalline quality arising from heterogeneous intermediate-phase evolution and nonuniform crystallization kinetics. Herein, an intermediate-phase homogenization strategy is developed to fabricate uniform CsPbI₃ films, wherein calcium ascorbate regulates the intermediate phases through synergistic interactions with perovskite components-including electrostatic interactions, hydrogen bonding, and coordination bonding. This modulation approach effectively suppresses the formation of Cs₄PbI₆ intermediates and redirects the intermediate from a heterogeneous Cs₄PbI₆/DMAPbI₃ mixture toward a predominant Cs_xDMA_1-xPbI₃(Asc) intermediate, yielding high-quality CsPbI₃ films with improved structural and energetic homogeneity, as well as enhanced stability. The modified p-i-n CsPbI₃ solar cells achieve a champion power conversion efficiency of 22.08%, among the highest reported for inverted CsPbI₃ devices. Unencapsulated devices retain 97% of their initial efficiency after 1000 h of maximum power point tracking under 1 sun illumination at 40 ± 5°C in N₂ and 94% after aging at 85°C for 500 h in N₂. This work demonstrates the effectiveness of suppressing crystallization-kinetic heterogeneity for homogeneous perovskite films, offering a general strategy for rationally fabricating high-performance thin-film optoelectronic devices.