Highly Luminescent CsPbX₃ (X=Cl, Br, I) Nanocrystals Achieved by a Rapid Anion Exchange at Room Temperature

Cesium lead halide perovskite (CsPbX₃ ) nanocrystals (NCs) exhibit an excellent photoelectric performance, which is directly governed by fine-tuning of the composition and preparation of materials with a special phase structure and morphology. However, it is still facing challenges to achieve highly stable and luminescent CsPbX₃ NCs at room temperature. Herein, we report on a novel exchange reaction, in which metal halides MX₂ (M=Zn, Mg, Cu, or Ca; X=Cl, Br, or I) solids act as anion source to directly prepare CsPbX₃ NCs at room temperature without any pretreatment. Introducing small amount of oleic acid or oleylamine speed up the exchange reaction through different promotion mechanisms. Oleic acid coordinates to the surface of the NCs, which increases the reaction activity, and oleylamine greatly enhances the dissolution of ZnCl₂ . XRD and TEM tests demonstrate that the cubic phase structure and the morphology of the parent CsPbX₃ were well preserved. Moreover, the band-gap energies and photoluminescence (PL) spectra were readily tunable over the entire visible spectral region of λ=406-685 nm. Our findings could open up the possibilities of using metal halide solids as new anion sources to prepare high-quality CsPbX₃ NCs at room temperature.