Characterization of Perovskite Obtained from Two-Step Deposition on Mesoporous Titania.

The properties of perovskite films are sensitive to the fabrication method, which plays a crucial role in the performance of perovskite solar cell. In this work, we fabricate organo-lead iodide perovskite on mesoporous TiO2 films through two different two-step deposition methods, respectively, for the purpose of studying the crystal growth of perovskite film and its effect on light harvesting efficiency, defect density, charge extraction rate, and energy levels. The crystal growth exerts a significant influence on the morphology and hence the film properties, which are found to correlate with the performance of solar cells. It is found that vapor deposition of methylammonium iodide in the PbI2 lattice gives a more complete coverage on mesoporous TiO2 with a flatter surface and Fermi level closer to the middle of the band-gap, resulting in higher light absorption in the visible spectral region, lower defect density, and faster charge extraction, as compared to the sequential solution deposition. For this reason, the vapor-processed perovskite film achieves higher short-circuit photocurrent and power conversion efficiency than the solution-processed film.