Introducing Ion Migration and Light-Induced Secondary Ion Redistribution for Phase-Stable and High-Efficiency...

Inorganic halide perovskites have been demonstrated as a promising alternative for light absorption because of their improved thermal stability compared with organic-inorganic halide perovskites. However, low power conversion efficiency and phase instability are major hindrances to their application. Here, a straightforward approach, by adding a layer of CsBr on the top of CsPbI₃, is reported for high-efficiency and phase-stable CsPbI₃-based solar cells. Characterizations demonstrate that the bromide ion can migrate from the surface into the bulk of CsPbI₃, mitigating the nonuniform depth distribution of iodide in the CsPbI₃ absorber and passivating the bulk defects. Impressively, the light illumination can induce secondary-ion redistribution, which is identified as a crucial process to further enhance the carrier extraction efficiency, strengthen the lattice stability, and improve the film homogenization. Accordingly, a high efficiency of 17% is obtained for the CsPbI₃-based solar cell. Moreover, the unencapsulated device exhibits remarkable phase stability, maintaining 93% of its initial efficiency under room temperature after being stored in the nitrogen glovebox for over 5000 h.