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 CsxDMA1-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.