Composition-Dependent Energy Splitting between Bright\nand Dark Excitons in Lead Halide Perovskite Nanocrystals

Abstract

Perovskite semiconductor\nnanocrystals with different compositions\nhave shown promise for applications in light-emitting devices. Dark\nexcitonic states may suppress light emission from such nanocrystals\nby providing an additional nonradiative recombination channel. Here,\nwe study the composition dependence of dark exciton dynamics in nanocrystals\nof lead halides by time-resolved photoluminescence spectroscopy at\ncryogenic temperatures. The presence of a spin-related dark state\nis revealed by magneto-optical spectroscopy. The energy splitting\nbetween bright and dark states is found to be highly sensitive to\nboth halide elements and organic cations, which is explained by considering\nthe effects of size confinement and charge screening, respectively,\non the exchange interaction. These findings suggest the possibility\nof manipulating dark exciton dynamics in perovskite semiconductor\nnanocrystals by composition engineering, which will be instrumental\nin the design of highly efficient light-emitting devices.