2D Cs2PbI2Cl2 Nanosheets for Holistic Passivation of Inorganic CsPbI2Br Perovskite Solar Cells for Improved Efficiency and Stability

Inorganic CsPbI 2 Br perovskite solar cells (PSCs) have gained enormous research interest due to their excellent thermal and light stabilities. However, their unsatisfactory power-conversion efficiency and poor intrinsic phase stability remain roadblocks to their further development. Herein, Cs 2 PbI 2 Cl 2 nanosheets (NSs) with the Ruddlesden–Popper (RP) structure are synthesized, and an NSs/CsPbI 2 Br/NSs heterostructure is employed to enhance both the stability and efficiency of CsPbI 2 Br solar cells. The novel Cs 2 PbI 2 Cl 2 NSs can not only passivate the top and bottom surfaces of the perovskite film and top surface of the TiO 2 film but also enhance the stability of the perovskite film. Based on the heterostructured NSs/CsPbI 2 Br/NSs inorganic perovskite film, the efficiency of the CsPbI 2 Br PSCs is improved from 15.02% to 16.65%. Moreover, the unencapsulated CsPbI 2 Br devices with the NSs/CsPbI 2 Br/NSs heterostructure sustain over 90% of their original efficiencies after being exposed to ambient conditions (≈25 °C and ≈35% RH) for 648 h. Both the UV-light-soaking stability (100 mW cm −1 365 nm UV light) and thermal stability ( T = 85 °C) of the optimized devices are dramatically improved in comparison with their counterparts with only a 3D active layer. Therefore, this work promotes the application of RP inorganic perovskite nanocrystals in a range of perovskite optoelectronic devices.