One-Step Preparation of High-Stability CsPbX₃/CsPb₂X₅ Composite Microplates with Tunable Emission

The core–shell structure is an effective means to improve the stability and optoelectronic properties of cesium lead halide (CsPbX 3 (X = Cl, Br, I)) perovskite quantum dots (QDs). However, confined by the ionic radius differences, developing a core–shell packaging strategy suitable for the entire CsPbX 3 system remains a challenge. In this study, we introduce an optimized hot-injection method for the epitaxial growth of the CsPb 2 X 5 substrate on CsPbX 3 surfaces, achieved by precisely controlling the reaction time and the ratio of lead halide precursors. The synthesized CsPbX 3 /CsPb 2 X 5 composite microplates exhibit an emission light spectrum that covers the entire visible range. Crystallographic analyses and density functional theory (DFT) calculations reveal a minimal lattice mismatch between the (002) plane of CsPb 2 X 5 and the (1 1 ¯ 0) plane of CsPbX 3, facilitating the formation of high-quality type-I heterojunctions. Furthermore, introducing Cl – and I – significantly alters the surface energy of CsPb 2 X 5 ’s (110) plane, leading to an evolutionary morphological shift of grains from circular to square microplates. Benefiting from the passivation of CsPb 2 X 5, the composites exhibit enhanced optical properties and stability. Subsequently, the white light-emitting diode prepared using the CsPbX 3 /CsPb 2 X 5 composite microplates has a high luminescence efficiency of 136.76 lm/W and the PL intensity decays by only 3.6% after 24 h of continuous operation.