Assessment for Anion-Exchange Reaction in CsPbX₃ (X = Cl, Br, I) Nanocrystals from Bond Strength of Inorganic Salt

Anion exchange via inorganic halide precursors is a highly efficient protocol to tune the chemical composition and optoelectronic properties of colloidal cesium lead halide perovskite (CsPbX₃, X = Cl, Br, I) nanocrystals (NCs). However, a simple predication rule of precursors is lacking owing to limited understanding of these used halide compounds. Here, we first use the inorganic magnesium halide (MgX₂) as a precursor to understand the halide exchange in CsPbBr₃ NCs. The samples with Br^- exchanged with Cl^- or I^- display a perfect preservation of cubic morphology, good stability, and high photoluminescence quantum yield. Then, by selecting a series of inorganic metal halide salts with different bond strength as precursors, we further find that the reaction exhibits thermal dynamic driving characteristics and the small energy difference in bonding strength between metal-X in halide salt and Pb-Br in CsPbBr₃ NCs is advantageous for the anion exchange according to the vacancy diffusion mechanism. These findings illustrate an easy way to assess the feasibility of the anion-exchange reaction, significantly promoting the synthesis of compositionally diverse metal halide perovskite NCs with various optoelectronic properties.