Mesoporous perovskite solar cells: material composition, charge-carrier dynamics, and device characteristics

We report on our investigations on charge transport and recombination in TiO(2)-based mesoporous solar cells using PbI(2) and various perovskite compositions, including CH(3)NH(3)PbI(3), CH(3)NH(3)PbI(2)Br, CH(3)NH(3)PbIBr(2), and CH(3)NH(3)PbBr(3). The mesoporous TiO(2) film is about 650 nm thick. Electron microscopy measurements show that no perovskite capping layer is formed on the top surface of the TiO(2) film. Intensity-modulated photocurrent/photovoltage spectroscopies show that the electron diffusion coefficient and recombination lifetime are governed by the underlying mesoporous TiO(2) film and thus do not depend on the perovskite composition. However, replacing the perovskite absorber with PbI(2) leads to a diffusion coefficient that is about a factor of 5 slower than that in perovskite-based devices. We also find that TiCl(4) treatment of the mesoporous TiO(2) film prior to device fabrication substantially reduces the charge recombination kinetics in mesoporous perovskite solar cells.