"Study the physical properties of ZnIn2Se4 for photovoltaic applications"

Abstract

ZnIn2Se4 has been prepared by fusion of stoichiometric quantities of pure elements in vacuum sealed silica tubes, which were left at 1323 ± 5 K for10 h , then cooled to room temperature over 48h. Thin films of different thicknesses have been deposited onto pre-cleaned and un-heated glass and /or quartz substrates using thermal evaporation under vacuum better than 10−4 Pa. The deposition rate was kept un-varied at 20Å/s. Structural characterization of bulk as well as deposited films have been carried out using Energy dispersive x-ray analysis (EDX) , x-ray diffraction (XRD), scanning electron microscope (SEM) and atomic force microscope (AFM). The obtained results proved the bulk stoichiometry similar to the percentage of the elemental constituents. The deposited films showed nano-crystalline nature with average crystallite size 20 nm. The increase of the annealing temperature affect both the crystallite size and the surface roughness of the deposited films. At annealing temperature 623 K, the mean radius of particles decreased from 70 nm to 20 nm, and the surface roughness decreased from 1.41 nm to 1.20 nm. The refractive index n and the extinction coefficient k have been computed from the spectrophotometric measured spectral transmittance and reflectance and were found to be thickness independent. Analysis of the absorption coefficient results revealed the existence of allowed direct and indirect transitions with optical energy gaps of 2.21eV and 1.71eV, respectively. At high annealing temperature (623 K), the value of indirect band gap remained nearly unchanged, while the direct band gap increased to 2.41eV.