Interface engineering using a perovskite derivative phase for efficient and stable CsPbBr3 solar cells

Inorganic perovskite materials have great potential for application in optoelectronic devices, especially solar cells, due to their outstanding photoelectric properties and high stability. In this work, we demonstrated CsPbBr3 inorganic perovskite solar cells (PSCs) composed of a derivative-phase CsPb2Br5 for the first time by precisely controlling the film thickness of precursor materials. The presence of CsPb2Br5 at the interface of CsPbBr3 crystals can increase the grain size of the inorganic perovskite and effectively passivate grain defects and the electron transport layer. The derivative phase will lower the energy barrier and reduce the carrier recombination in the active layer. Remarkably, this self-passivation results in a respectable power conversion efficiency (PCE) of 8.34% with a CsBr : PbBr2 ratio of 1 : 1.1. Besides, the device exhibits a superior stability for more than 1000 h without any degradation. Insights into the derivative phase formation and self-passivation mechanisms are demonstrated, providing a novel approach to improve the performance of perovskite solar cells.