Defect-Related Broadband Emission in Two-Dimensional Lead Bromide Perovskite Microsheets

Low-dimensional hybrid lead halide perovskites (LHPs) with broadband emission (BE) have been developed as promising candidates for single-source white-light-emitting diodes. However, the underlying origin of such BE is poorly understood. Herein, dual-emissive [NH3(CH2)(8)NH3]PbBr4 perovskite microsheets (PMSs) with good dispersibility are successfully prepared. Besides the general narrowband emission (NE) originating from free excitons, BE (similar to 522 nm) is generated under a Br-poor condition, which is not observed in the single-crystal sample. Unlike self-trapped exciton emission, the BE observed in PMSs is experimentally determined to be related to bromide vacancies (V-Br), thereby exhibiting quasisaturation under high excitation intensity. Femto-second transient absorption spectroscopy first shows that the trapping time of the photogenerated electrons by acceptor-like VBr- is similar to 15 ps, slower than that by surface defects (<1 ps). This study provides new insight into the underlying mechanism of BE and an effective approach to manipulating the optical properties of 2D perovskites.