Identifying the Bandgap of Two-dimensional Perovskite CsPb₂Br₅

CsPb₂Br₅ is a 2D perovskite where single layer Cs acts as a spacer, monolayer PbBr₆ octahedrons are edge shared. Although CsPb₂Br₅ was synthesized more than 10 years ago, only recently it began to draw a lot of attention. Despite extensive research over past two years, its fundamental bandgap and basic electronic and optical properties still remain controversial: is this a wide bandgap indirect semiconductor or a direct bandgap material with strong green luminescence at ~520 nm? In this talk, I will discuss the reason for different observations and present our result of the bandgap investigation of CsPb₂Br₅.