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 center dot 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 center dot 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.