Charge-selective-contact-dependent halide phase segregation in CsPbIBr2 perovskite solar cells and its correlation to device degradation

Abstract

All-inorganic perovskite CsPbIBr2 has emerged as one of promising candidates for perovskite solar cells (PSCs) due to its feasible thermal stability and relatively narrow bandgap. However, the current CsPbIBr2 PSCs are generally faced with serious halide phase segregation issues. Herein, halide phase segregation phenomenon of CsPbIBr2 films grown on the typical electron transporting layer (ETL) and hole transporting layer (HTL) of CsPbIBr2 PSCs are studied. We show that such a phenomenon is reversible and can be fully recovered for CsPbIBr2 film grown on TiO2 ETL. However, a plenty of iodide ions are captured by surficial oxygen-vacancy defects of NiOx HTL, which hinders the recovery of halide phase segregation of CsPbIBr2 film on it. Thus, halide phase segregation has a margin influence on photoelectric conversion properties and stability of CsPbIBr2 film on TiO2 ETL, while it significantly damages the photoelectric conversion characters and stability of CsPbIBr2 film on NiOx HTL. Our work indicates that the obstacles caused by halide phase segregation of CsPbIBr2 films could be overcome by optimizing the charge transporting layer, and it suggests a promising strategy to further improve the performance and stability of CsPbIBr2 PSCs.