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

TL;DR

This study reveals bright luminescent surface states on the edges of wide-bandgap CsPb2Br5 microplatelets, attributed to polycrystalline regions and corner-sharing PbBr6 clusters, clarifying prior controversies and opening new avenues for optoelectronic applications.

Contribution

The paper demonstrates the existence of bright edge luminescence in CsPb2Br5 and attributes it to polycrystalline regions and structural clusters, providing new insights into perovskite surface states.

Findings

Bright luminescent surface states observed on CsPb2Br5 edges.

Polycrystalline regions responsible for the luminescence.

Edge states originate from corner-sharing PbBr6 clusters.

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.