Unusual blue shift of cathodoluminescence in lead bromine perovskite single crystals

Understanding the surface properties of hybrid lead-based perovskites is of great importance for improving their optoelectronic performance in perovskite-based devices. In this study, we investigated the differences between the surface and bulk optical properties of CH3NH3PbBr3 (MAPbBr3) single crystals in the wide temperature range. Depth-resolved cathodoluminescence was employed to probe the near-surface region at a depth of a few nanometers. Using the same single crystal, we also measured photoluminescence spectra under excitation with a 405 nm laser. In both experiments, we observed a peak near the bandgap and found that the cathodoluminescence peak was blue shifted by approximately 30 meV relative to the photoluminescence peak. This increase in the bandgap near the surface may be attributed to charge separation occurring in the surface region, which generates an electric field. Our modeling of the temperature dependence of the cathodoluminescence peak positions, which takes into account the electric field in the surface layer, showed good agreement with the experimental data. These findings provide insights into the unique surface effects that are important for optimizing the properties of halide perovskites for efficient solar energy harvesting and optoelectronic applications.