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 CsPbI 3 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 CsPbI 3 films and lower the phase transition temperature. Systematic investigation reveals that the CdI 2 incorporation could promote Cs + transfer and significantly reduce the CsPbI 3 phase transition temperature from 190 to 130 °C; meanwhile, Pb(SCN) 2 addition significantly improves the low-temperature-annealed CsPbI 3 crystal quality, even surpassing high-temperature-annealed perovskite films. Optimized CsPbI 3 films exhibit low defect density, weak nonradiative recombination, and high phase stability. Consequently, rigid CsPbI 3 solar cells achieve a champion power conversion efficiency (PCE) of 22.3%, while flexible CsPbI 3 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 CsPbI 3 perovskite films and perovskite solar cell (PSC) devices, typically suitable for flexible photovoltaics.