Mesoporous Perovskite Solar Cells: Material Composition, Charge-Carrier Dynamics, and Device Characteristics

We report on our investigations on charge transport and recombination in TiO₂-based mesoporous solar cells using PbI₂ and various perovskite compositions, including CH₃NH₃PbI₃, CH₃NH₃PbI₂Br, CH₃NH₃PbIBr₂, and CH₃NH₃PbBr₃. The mesoporous TiO₂ film is about 650 nm thick. Electron microscopy measurements show that no perovskite capping layer is formed on the top surface of the TiO₂ film. Intensity-modulated photocurrent/photovoltage spectroscopies show that the electron diffusion coefficient and recombination lifetime are governed by the underlying mesoporous TiO₂ film and thus do not depend on the perovskite composition. However, replacing the perovskite absorber with PbI₂ leads to a diffusion coefficient that is about a factor of 5 slower than that in perovskite-based devices. We also find that TiCl₄ treatment of the mesoporous TiO₂ film prior to device fabrication substantially reduces the charge recombination kinetics in mesoporous perovskite solar cells.