Effect of Anionic Substitution of S by Se in CZTSSe Films Prepared from Electron Beam Evaporation

Abstract

Abstract Cu2ZnSnSxSe4-x (CZTSSe) is a prominent candidate as a photon absorber layer in solar cell owing to its earth abundant constituents and high absorption coefficient with tunable bandgap. In this study, the effect of metallic stacking order and anionic substitution of S by Se on the properties of CZTSSe is investigated by varying the S/Se ratio. CZT metallic precursor films with stacking sequences SLG/Sn/Zn/Cu and SLG/Cu/Sn/Zn/Cu are fabricated on soda lime glass substrate by using electron beam evaporation of elemental metallic precursors. In order to obtain CZTSSe films with various S/Se ratio, the films are annealed in the presence of elemental S and Se environment with various ratio of elemental S and Se powder at 550 °C for 1 hour at a ramping rate of 10 °C/min with N2 as a carrier gas. The effect of variation of S/Se powder on crystallinity, morphology and composition of the films are confirmed through X-Ray diffraction, Raman spectroscopy, FEGSEM and EDS analysis. The optical bandgap of the films is estimated to decrease with increasing Se content in the films. The Se incorporation is noticed the highest in case of SLG/Sn/Zn/Cu stack and its bandgap is found to be decreasing from 1.53 to 1.2 eV with increasing Se content.