Edge Effect on the Population of Free Carriers and Excitons in Single-Crystal CH3NH3PbBr3 Perovskite Nanomaterials

The spatial distribution of free carriers and excitons in perovskite micro-/nanostructures is currently a major topic of debate. They have been reported to coexist with spatial separation in individual perovskite grains and films. It is revealed that free carriers and excitons in single-crystal CH3NH3PbBr3 perovskite microplatelets can spatially overlap; however, the distribution is such that the edges can be entirely occupied by the former, while the interior is occupied only by the latter. This is further confirmed in single-crystal CH3NH3PbBr3 perovskite microstrips, in which only free carriers are observed. These results may be attributable to electrostatic potential fluctuations on the edges, which can promote electron-hole separation so that they do not bind to form excitons. Microscopic I-V measurements demonstrate that the microplatelet edges and the microstrips show current densities of more than 260 and 340 A cm(-2) in a dark environment under 1.2 V bias voltage, respectively. It is suggested that these findings mean that such microstructures hold promise for the development of novel perovskite micro-/nanostructure-based optoelectronic devices with interesting photoconductive properties such as high photoluminescence intensity, longer excited-state lifetime, high conductivity, large saturation current densities, and suppressed hysteresis effects (smaller open voltages).