Optical properties of the perovskite films deposited on meso-porous TiO_2 by one step and hot casting techniques

摘要

In this work, CH3NH3PbI3 is coated on meso-porous TiO2 films via one step method (OSM) and hot casting technique (HCT). The optical properties of the solution-processed organic inorganic halide perovskite layers deposited on meso-structured TiO2 scaffolds are investigated using UV-Vis reflectance and transmittance spectroscopies at the wavelength range of 400-900 nm. Optical parameters including refractive index, extinction coefficient, real and imaginary parts of the dielectric constants, optical conductivity and direct and indirect optical band gaps are calculated and compared for the perovskite films created by above mentioned methods. Optical band gaps are determined from the absorption coefficient values using Tauc's power law. The obtained values of direct band gap for two perovskite films are close to each other (1.56 and 1.58 eV for perovskite layer deposited by OSM and HCT respectively). For both prepared films, the difference between direct and indirect band gaps is 60 meV which is in very good agreement with that reported in literature. In addition to the difference between the perovskite morphology, the optical absorption of perovskite layers created by the HCT is less than that of layers prepared by OSM and therefore the amount of generated photo current is less. This is the main reason that causes the efficiency of perovskite solar cells prepared by HCT (3.0%) is similar to 38% less than that of cells created by OSM (4.15%).