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 (CsPbX₃ (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 CsPbX₃ system remains a challenge. In this study, we introduce an optimized hot-injection method for the epitaxial growth of the CsPb₂X₅ substrate on CsPbX₃ surfaces, achieved by precisely controlling the reaction time and the ratio of lead halide precursors. The synthesized CsPbX₃/CsPb₂X₅ 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 CsPb₂X₅ and the (11¯0) plane of CsPbX₃, facilitating the formation of high-quality type-I heterojunctions. Furthermore, introducing Cl^- and I^- significantly alters the surface energy of CsPb₂X₅'s (110) plane, leading to an evolutionary morphological shift of grains from circular to square microplates. Benefiting from the passivation of CsPb₂X₅, the composites exhibit enhanced optical properties and stability. Subsequently, the white light-emitting diode prepared using the CsPbX₃/CsPb₂X₅ 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.