Cs-Pb-Br Core-shell Perovskite Microcrystals for Stability Improvement

Lead halide perovskite nanocrystals (LHP NCs) have been developed since 2014. Due to their intrinsic ionic salts and lead-halogen composition, they have high molar absorbance coefficient, high defect tolerance, and ultra-fast carrier mobility, and their material structure and optical properties can be precisely controlled through ion exchange, which have aroused great research interest of scientific researchers as well as new thinking on the ion salt nanocrystal. Among LHP NCs family, CsPbBr3 NCs are quite outstanding as they exhibit better luminescence properties, etc. They also demonstrate promising application prospects in the fields of optoelectronic devices, photovoltaics, and photocatalysis, occupying a central position in the current research of LHP NCs. However, their lack of stability to external elements, including light, humidity, and heat limits their use in practical applications. Heterostructure development is one of several approaches to overcome these limits. Combining two or more materials at the nanoscale results in new heteronanocrystals that outperform the pure material. To improve the stability of LHP NCs against environmental stress, core-shell NCs can be created by growing a shell on the surface of core NCs, drawing inspiration from chalcogenide semiconductor NCs. In this sense, there are multiple organic materials (e.g., phenylpropylammonium bromide and polymethyl methacrylate) and inorganic materials (such as NaBr, TiO2, and metal chalcogenides, as well as perovskites, e.g., Cs4PbBr6, CsPb2Br5, and Rb4PbBr6) used for covering a perovskite core. In this paper, the most promising approach involves coating perovskite NCs (PeNCs) with a crystalline perovskite shell by in situ synthesis, resulting in high-density NCs with a perovskite/perovskite core-shell configuration. This efficiently corrects the lattice mismatch between the core and shell. Because of its indirect band gap, photoluminescence (PL) intensity, water resistance, and minimum lattice mismatch with CsPbBr3 NCs, 0D Cs4PbBr6 and 2D CsPb2Br5 perovskite materials are thought to be promising coating materials. The changes in luminescence properties and stability were studied and the application of the composite material in the field of anti-counterfeiting was studied. This paper describes the synthesis and characterisation of two core-shell structures based on CsPbBr3 NCs, with a particular focus on enhancing their stability and physical properties. The research successfully achieved the in situ formation of a protective shell on the surface of CsPbBr3 NCs using a simple room-temperature synthesis method, thereby overcoming lattice mismatch issues arising from stepwise synthesis. Research into this system not only aids in understanding interfacial chemistry but also provides strategies for the low-cost synthesis of stable luminescent materials. This resolves the issue of the extremely complex fabrication process for core-shell structures, which is prone to generating interface defects and incomplete passivation, thereby leading to variations in their optical properties. Notably, in-situ spectroscopic and structural techniques were employed to investigate the exceptional performance of the synthesised core-shell structures under high-temperature and water immersion challenges. This demonstrates the critical role of the core-shell architecture in CsPbBr3 NCs, effectively passivating the crystals while substantially enhancing environmental stability.