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 MAPbI(3) 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 MAPbI(3) 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 MAPbI(3) 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 MAPbI(3) sensitizers are prepared and display enhanced photovoltaic performance (7.18 +/- 0.31%) compared with devices obtained from only one cycle (5.74 +/- 0.30%).