Ultrastable CsPbBr₃@CsPb₂Br₅@TiO₂ Composites for Photocatalytic and White Light-Emitting Diodes

Although cesium halide lead (CsPbX₃, X = Cl, Br, I) perovskite quantum dots (QDs) have excellent photovoltaic properties, their unstable characteristics are major limitations to application. Previous research has demonstrated that the core-shell structure can significantly improve the stability of CsPbX₃ QDs and form heterojunctions at interfaces, enabling multifunctionalization of perovskite materials. In this article, we propose a convenient method to construct core-shell-structured perovskite materials, in which CsPbBr₃@CsPb₂Br₅ core-shell micrometer crystals can be prepared by controlling the ratio of Cs⁺/Pb²⁺ in the precursor and the reaction time. The materials exhibited enhanced optical properties and stability that provided for further postprocessing. Subsequently, CsPbBr₃@CsPb₂Br₅@TiO₂ composites were obtained by coating a layer of dense TiO₂ nanoparticles on the surfaces of micrometer crystals through hydrolysis of titanium precursors. According to density functional theory (DFT) calculations and experimental results, the presence of surface TiO₂ promoted delocalization of photogenerated electrons and holes, enabling the CsPbBr₃@CsPb₂Br₅@TiO₂ composites to exhibit excellent performance in the field of photocatalysis. In addition, due to passivation of surface defects by CsPb₂Br₅ and TiO₂ shells, the luminous intensity of white light-emitting diodes prepared with the materials only decayed by 2%-3% at high temperatures (>100 °C) when working for 24 h.