Spatially Resolved Local Electronic Properties of 2D Lead Halide Perovskite Single Crystals Studied by X-Ray Photoemission Electron Microscopy

Recently, research on the edge states of 2D lead halide perovskites (LHPs) has been attracting much attention. The lower-energy edge state (LES) is believed to provide an efficient pathway for the dissociation of photoexcited excitons. However, the mechanism of the LES formation remains controversial, and studies that establish precisely the local electronic properties are lacking. Herein, the first study of spatially resolved electronic structures in 2D LHP single-crystal flakes by X-ray photoemission electron microscopy is presented, specifically identifying the contribution from the edge area. The results show that blueshifts occur in the Pb 5d core-level peaks at the edge area compared to the interior area with much less difference in I 4d core-level peaks. The shift becomes more pronounced as n varies from 1 to 3 (approximate to 0.2-1.0 eV). This phenomenon is attributed to the surface restructuring of the edge area induced by the release of mechanical strain through lattice expansion. This work provides an important reference on the origin of the LES of 2D LHPs and is beneficial for future optoelectronic device applications.