Three-Step Sequential Solution Deposition of PbI2-Free CH3NH3PbI3 Perovskite

We demonstrate a three-step sequential solution process to prepare PbI₂-free CH₃NH₃PbI₃ perovskite films. In this three-step method, a thermally unstable stoichiometric PbI₂·CH₃NH₃Cl precursor film is first deposited on the mesoporous TiO₂ substrate, followed by thermal decomposition to form PbI₂, which is finally converted into CH₃NH₃PbI₃ by dipping in a regular isopropanol solution of CH₃NH₃I at room temperature. In comparison to the two-step approach using similar processing conditions, the three-step method enables the formation of the PbI₂ film through the thermal decomposition of the PbI₂·CH₃NH₃Cl precursor film. This facilitates a rapid conversion of PbI₂ to CH₃NH₃PbI₃ without any traceable residue PbI₂ in the final conversion step, leading to an improved device performance.