Cation exchange for thin film lead iodide perovskite interconversion

We demonstrate that we can convert hybrid perovskites between methylammonium lead iodide (MAPbI ₃ ) and formamidinium lead iodide (FAPbI ₃ ) by immersion in solutions of MA or FA iodide at room temperature. The cations diffuse uniformly throughout the bulk films, forming an alloy rather than a bi-layer. Furthermore, this demonstrates good organic cation mobility in these materials.