Observation and implication of halide exchange beyond CsPbX ₃ perovskite nanocrystals

Anion exchange between pre-synthesized all-inorganic nanocrystals with a perovskite structure is a promising approach to tune their chemical composition and optical properties. Herein we have reported the first study of internanocrystal anion exchange reactionsin the cesium lead halide family, including CsPbX ₃ , Cs ₄ PbX ₆ and CsX, and we found that the anion exchange dynamics is highly dependent on their crystalline phase. In stark contrast to the fast rate in CsPbX ₃ , cesium based non-perovskite NCs display much slower halide mobility. The reaction time is increased to several hours in Cs ₄ PbX ₆ and days in CsX, respectively. Furthermore, we confirm that mixing these NCs with the same halide but different structures will induce halide diffusion from Cs ₄ PbX ₆ NCs and CsX NCs to CsPbX ₃ NCs. This feature can be explored to utilize the Cs ₄ PbX ₆ NCs and CsX NCs as a halide source to improve the photoluminescence efficiency and colloidal stability of CsPbX ₃ NCs.