Methylammonium-Mediated Crystallization of Cesium-Based 2D/3D Perovskite toward High-Efficiency Light-Emitting Diodes

2D/3D perovskites have been successfully applied to high-efficiency light-emitting diodes (LEDs) due to their large exciton binding energy (Eb) caused by the quantum and dielectric confinements. Thermal annealing and antisolvent treatments are usually executed in order to promote the crystallization and film quality of perovskites, which add complexity to the device fabrication process. Here, the Cesium-based 2D/3D perovskite was prepared by introducing an ammonium halide benzamidine hydrochloride (BMCl) as the additive. By further introducing an appropriate amount of MABr and PbBr2, BM2(Cs1-xMAxPbBr3)n-1PbBr4 crystals can be formed rapidly without any additional treatments, whilst inhibiting the formation of unfavorable Cs4PbBr6 phase. The optimized 2D/3D perovskite based LEDs achieved a maximum luminance of 12367 Cd/m2, current efficiency of 17.4 Cd/A, and EQE of 5.2%. Our results suggest that appropriate perovskite crystallization can be achieved at room temperature by the regulation of precursor solut...