Anion Exchange Reaction of CsPbBr3 Perovskite Nanocrystals: Affinity of Halide Ion Matters

The affinity of chloride/iodide ions to replace the lattice sites of bromide ions in the CsPbBr3 nanocrystals by anion exchange reactions is investigated. In the presence of an equal number of iodide and chloride ions, the absorption and emission of lead halide perovskites are found to be red-shifted as a result of the preferential anion exchange with the iodide ions. In order to initiate the anion exchange reactions with the chloride ions from a mixture of chloride and iodide ions, a minimum of 66 % of chloride ions, is essential to observe a significant change. The differential affinity of chloride/iodide ions to substitute bromide ions in CsPbBr3 perovskite is also substantiated using density functional theory (DFT) calculation. Understanding the interactions in the crystal structure of lead halide perovskites can give directions to tune the material properties in the nanoscale for various applications in science and technology.