Phthalimide additive-promoted ambient fabrication of inorganic CsPbI2Br perovskite for highly efficient and stable solar cells

Iodine-rich inorganic halide perovskites (CsPbI3 and CsPbI2Br) hold a great promise for emerging perovskite solar cells due to their excellent optoelectronic properties. Nevertheless, the current high-performance iodine-rich perovskite films for PSCs are usually fabricated in inert condition. It is still a great challenge to prepare high-quality iodine-rich perovskite films under realistic ambient conditions. Herein, we demonstrate a simple and feasible strategy for fabricating high-quality CsPbI2Br perovskite film in fully ambient air by introducing phthalimide (PTM) additive into the CsPbI2Br precursor. The PTM introduction protects the CsPbI2Br precursor from the unwanted phase transition and retards the crystallization of perovskite, which greatly ameliorates the perovskite crystallization process and prevents the perovskite from the moisture damage. When an appropriate amount of PTM is introduced, a stable CsPbI2Br perovskite film with high crystallinity and large grains is obtained in ambient air. The fabricated carbon-based CsPbI2Br perovskite solar cell achieves a high efficiency of 13.95%. In addition, the unencapsulated device displays an excellent stability with 91% of the initial efficiency maintaining after 14 days aging under ambient air.