Compact nanostructured TiO2 deposited by aerosol spray pyrolysis for the hole-blocking layer in a CH3NH3PbI3 perovskite solar cell

Abstract Layers of crystalline TiO 2 were prepared using aerosol spray pyrolysis at different deposition temperatures and times. The effects of the deposition parameters on the structural, morphological and optical properties were investigated. The extent of the crystallinity and surface morphology of TiO 2 depended very much on the growth temperatures. At a gas flow rate of 5 l/min, an inhomogeneous morphology with a cauliflower-like feature was observed for the films sprayed at 375 °C whereas they became denser and homogenous with the quality of both crystallization and diameters becoming better when the sprayed temperature was being increased up to 450 °C. The optical band gap of the TiO 2 films was found to decrease from 3.66 to 3.61 eV as the film thicknesses was increased from 80 to 450 nm. The refractive index for electromagnetic waves having wavelengths between 450 and 800 nm varied between 2.0 and 2.12 for the films with thickness of 250–360 nm. There was a significant decrease to 1.93 when the thickness of the films was 450 nm. A layer of the sprayed-on TiO 2 was then used as the hole-blocking layer in an organic-inorganic CH 3 NH 3 PbI 3 perovskite based solar cell. A state-of-the-art transmission electron microscopy (TEM) technique for sample preparation was carried out using a dual focused ion beam (FIB) to investigate vertical morphology of the devices. It was found that the devices having the optimized thickness of the sprayed-on TiO 2 displayed the power conversion efficiency (PCE) of 6.24%.