Enhanced Luminescence and Stability of Cesium Lead Halide Perovskite CsPbX₃ Nanocrystals by Cu²⁺-Assisted Anion Exchange Reactions

Inorganic CsPbX₃ perovskite nanocrystals (NCs) have exhibited great optical properties, such as tunable emission wavelength, narrow emission line-widths, and high photoluminescent quantum yields. However, the unstable crystal structure of perovskite CsPbX₃ NCs lead to a deterioration in optical performance. In this work, it is demonstrated that inorganic perovskite NCs, including CsPbCl₃ and CsPbBr_3-xCl_x NCs with excellent photoluminescence quantum yield and optical stability can be improved via anion exchange reaction treated with a new halide precursor consisting of copper halide- (CuX₂-) oleylamine (OLA) complexes. Unlike traditional perovskite synthesized processes for better crystalline structures operated at high temperatures, this work offers an economical method operable at the room temperatures. The treated CsPbX₃ perovskite nanocrystals were characterized by in situ photoluminescence (PL) spectra and in situ X-ray diffraction (XRD). Cu²⁺ ions were only absorbed on the surface of perovskite NCs confirmed by the X-ray absorption spectroscopy (XAS) analysis. Density functional theory calculation explained that the origin of high stability and good crystallinity for treated perovskite NCs stemmed from adsorption of CuCl₂ on perovskite's surface to passivate defect sites during the recrystallization process.