Method to control the optical properties: Band gap energy of mixed halide Organolead perovskites

Abstract In this work, we studied the effect of varying the volume of mixed halide perovskites on the structural, morphological and optical properties of deposited thin films. A two-step process of spin coating and dipping technique was employed so as to enhance deposition of the films. The samples were subjected to heat treatment after each deposition cycle in order to increase the crystalinity and grain size of the films. The band gap, refractive index, dielectric constant and optical conductivity of the mixed halide perovskites were calculated. The single term Wemple DiDomenico oscillator formulae were applied in determining the expression of the parameter n below the optical band gap in relation to the energy. A significant observation in this study was that the band gap of mixed halide perovskites was extremely lowered compared to the high band energy of its halide perovskite, which reveals the band gap alteration effect of mixed halide perovskites. The refractive index and dielectric constant of the halide and mixed halide perovkites showed results in the wavelength range of 300–600 nm, which is significant for photovoltaic materials .