First evidence of macroscale single crystal ion exchange found in lead halide perovskites

Ion exchange is classified as a reaction that may be performed among nanocrystals. Here, we discovered that methylammonium lead bromide macroscale perovskite single crystals may exchange ions with the environment while maintaining their original morphology. Iodide replaced bromide and was detected even in the very center of a previously pure macroscale MAPbBr₃ single crystal. Additionally, the entrance of chloride into the crystal is energetically favorable and most bromides were exchanged, yet kinetic factors hindered Cs⁺ entry and Pb²⁺ by Sn²⁺ substitution. Furthermore, grinding different single crystals together revealed swift I/Br exchange. Clear differences in comparison with nanomaterials, along with density functional theory calculations, shed light on the nature of ion-exchange reactions in perovskite single crystals. This work provides first evidence of these halide exchange reactions in macroscale perovskite single crystals. These results offer a new perspective on ion-exchange reaction and pave a path toward synthesis of inhomogeneous single crystals. (Figure presented.).