Efficient and Stable CsPbI Inorganic Perovskite Photovoltaics Enabled by Crystal Secondary Growth.

Defect-triggered phase degradation is generally considered as the main issue that causes phase instability and limited device performance for CsPbI inorganic perovskites. Here, a defect compensation in CsPbI 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 perovskite. Upon solid-state reaction, the Br ions can diffuse over the entire CsPbI perovskite layer to heal the undercoordinated Pb 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 ] octahedra. The carrier dynamics confirm that this crystal secondary growth can realize defect compensation in CsPbI . The as-achieved defect-compensated CsPbI not only improves the charge dynamics but also enhances the photoactive phase stability. Finally, the CsPbI -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.