Bright Luminescent Surface States on the Edges of Wide-bandgap Two-dimensional Lead Halide Perovskite

Abstract

Three-dimensional lead halide perovskites have surprised people for their defect-tolerant electronic and optical properties, two-dimensional lead halide layered structures exhibit even more puzzling phenomena: luminescent edge states in Ruddlesden-Popper perovskites and conflicting reports of highly luminescent versus non-emissive CsPb${}_{\text{2}}$Br${}_{\text{5}}$. In this work, we report the observation of bright luminescent surface states on the edges of CsPb${}_{\text{2}}$Br${}_{\text{5}}$ microplatelets. We prove that green surface emission makes wide-bandgap single crystal CsPb${}_{\text{2}}$Br${}_{\text{5}}$ highly luminescent. Using polarized Raman spectroscopy and atomic-resolution transmission electron microscopy, we further prove that polycrystalline CsPb${}_{\text{2}}$Br${}_{\text{5}}$ is responsible for the bright luminescence. We propose that these bright edge states originate from corner-sharing clusters of PbBr${}_{\text{6}}$ in the distorted regions between CsPb${}_{\text{2}}$Br${}_{\text{5}}$ nanocrystals. Because metal halide octahedrons are building blocks of perovskites, our discoveries settle a long-standing controversy over the basic property of CsPb${}_{\text{2}}$Br${}_{\text{5}}$ and open new opportunities to understand, design and engineer perovskite solar cells and other optoelectronic devices.

† Equal contributions * Corresponding author. E-mail: [email protected] (J.M.B.); [email protected] (Z.M.W.)