Cs₄PbBr₆/CsPbBr₃ Perovskite Composites with Near-Unity Luminescence Quantum Yield: Large-Scale Synthesis, Luminescence and Formation Mechanism, and White Light-Emitting Diode Application

All-inorganic perovskites have emerged as a new class of phosphor materials owing to their outstanding optical properties. Zero-dimensional inorganic perovskites, in particular the Cs₄PbBr₆-related systems, are inspiring intensive research owing to the high photoluminescence quantum yield (PLQY) and good stability. However, synthesizing such perovskites with high PLQYs through an environment-friendly, cost-effective, scalable, and high-yield approach remains challenging, and their luminescence mechanisms has been elusive. Here, we report a simple, scalable, room-temperature self-assembly strategy for the synthesis of Cs₄PbBr₆/CsPbBr₃ perovskite composites with near-unity PLQY (95%), high product yield (71%), and good stability using low-cost, low-toxicity chemicals as precursors. A broad range of experimental and theoretical characterizations suggest that the high-efficiency PL originates from CsPbBr₃ nanocrystals well passivated by the zero-dimensional Cs₄PbBr₆ matrix that forms based on a dissolution-crystallization process. These findings underscore the importance in accurately identifying the phase purity of zero-dimensional perovskites by synchrotron X-ray technique to gain deep insights into the structure-property relationship. Additionally, we demonstrate that green-emitting Cs₄PbBr₆/CsPbBr₃, combined with red-emitting K₂SiF₆:Mn⁴⁺, can be used for the construction of WLEDs. Our work may pave the way for the use of such composite perovskites as highly luminescent emitters in various applications such as lighting, displays, and other optoelectronic and photonic devices.