Effective Preparation of Nanoscale CH₃NH₃PbI₃ Perovskite Photosensitizers for Mesoporous TiO₂-Based Solar Cells by Successive Precursor Layer Adsorption and Reaction Process

Nanoscale CH₃NH₃PbI₃ perovskite sensitizers are grown by delivering each precursor successively onto the surface of mesoporous (meso) TiO₂ electrodes. Using Pb(NO₃)₂ ions as a lead(II) source and CH₃NH₃I (MAI) for methylammonium and iodide sources, repetitive cycles of the two dipping steps are successful in growing few nanometer-sized MAPbI₃ gradually on the TiO₂ surface inside the meso-TiO₂ film. However, some aggregates are observed on the top surface of the meso-TiO₂ film due to slight dissolution of PbI₂ and its accumulation/reaction with MAI at the top surface of the meso-TiO₂ film. To solve this inhomogeneity of the deposition, a nondestructive multiple deposition route for nanoscale MAPbI₃ is suggested as a successive precursor layer adsorption and reaction (SPLAR) process where, from the second cycle of deposition, PbI₂ is delivered with the help of an ionic liquid compound dissolved in dichloromethane. With this new Pb precursor in less-polar solvents, nanoscale MAPbI₃ sensitizers are grown without dissolution of preformed perovskites or formation of some aggregates at the top surface. After the third cycle of SPLAR deposition, about 7.0 nm–sized MAPbI₃ sensitizers are prepared and display enhanced photovoltaic performance (7.18 ± 0.31%) compared with devices obtained from only one cycle (5.74 ± 0.30%).