Efficient and Stable CsPbI3 Inorganic Perovskite Photovoltaics Enabled by Crystal Secondary Growth

Abstract Defect‐triggered phase degradation is generally considered as the main issue that causes phase instability and limited device performance for CsPbI 3 inorganic perovskites. Here, a defect compensation in CsPbI 3 perovskite through crystal secondary growth of inorganic perovskites is demonstrated, and highly efficient inorganic photovoltaics are realized. This secondary growth is achieved by a solid‐state reaction between a bromine salt and defective CsPbI 3 perovskite. Upon solid‐state reaction, the Br − ions can diffuse over the entire CsPbI 3 perovskite layer to heal the undercoordinated Pb 2+ and conduct certain solid‐state I/Br ion exchange reaction, while the organic cations can potentially heal the Cs + cation vacancies through coupling with [PbI 6 ] 4− octahedra. The carrier dynamics confirm that this crystal secondary growth can realize defect compensation in CsPbI 3 . The as‐achieved defect‐compensated CsPbI 3 not only improves the charge dynamics but also enhances the photoactive phase stability. Finally, the CsPbI 3 ‐based solar cell delivers 20.04% efficiency with excellent operational stability. Overall, this work proposes a novel concept of defect compensation in inorganic perovskites through crystal secondary growth induced by solid‐state reaction that is promising for various optoelectronic applications.