Engineering Low-Temperature CsPbI ₃ Crystallization via Synergistic Regulation Strategy for Efficient Inorganic Perovskite Solar Cells

A high-temperature annealing process is beneficial for improving CsPbI3 crystallinity but detrimental to its application in flexible and tandem devices. Regarding this challenge, we propose a synergistic regulation strategy to simultaneously enhance the crystallinity of blade-coated CsPbI3 films and lower the phase transition temperature. Systematic investigation reveals that the CdI2 incorporation could promote Cs+ transfer and significantly reduce the CsPbI3 phase transition temperature from 190 to 130 °C; meanwhile, Pb(SCN)2 addition significantly improves the low-temperature-annealed CsPbI3 crystal quality, even surpassing high-temperature-annealed perovskite films. Optimized CsPbI3 films exhibit low defect density, weak nonradiative recombination, and high phase stability. Consequently, rigid CsPbI3 solar cells achieve a champion power conversion efficiency (PCE) of 22.3%, while flexible CsPbI3 devices present 18.6% PCE. Good operational photostability is also obtained with over 90% of the initial PCE retained after 500 h. This work demonstrates a universal low-temperature fabrication strategy to realize stable and high-quality black-phase CsPbI3 perovskite films and perovskite solar cell (PSC) devices, typically suitable for flexible photovoltaics.