Introducing Ion Migration and Light-Induced Secondary Ion Redistribution for Phase-Stable and High-Efficiency Inorganic Perovskite Solar Cells.

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 CsPbI, is reported for high-efficiency and phase-stable CsPbI-based solar cells. Characterizations demonstrate that the bromide ion can migrate from the surface into the bulk of CsPbI, mitigating the nonuniform depth distribution of iodide in the CsPbI 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 CsPbI-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.