The effect of sulfur on the phase formation of Cu2ZnSnS4 solar cell material

Non-stoichiometry compositions of Cu2Zn1.5Sn1.2S4+x (CZTS) bulk alloys were prepared by the thermal molten technique and characterized by X-ray diffraction (XRD), Raman spectroscopy, Transmission electron microscopy (TEM), Electron probe micro analysis (EPMA) and UV-vis absorbance spectroscopy. The results indicate that the secondary phases such as Cu2S, ZnS and SnS etc., are present as identified by XRD and Raman spectroscopy in the lower sulfur content alloys. However, the pure CZTS kesterite phase was obtained in sulfur excess (ie, x=0.4) composition. The backscattered electron images confirm that the transition from a multiphase formation in the alloy to a single phase formation. A direct band gap of about 1.22 eV has been estimated from UV-vis absorbance spectra studies, and this is close to the optimum value of best solar cell efficiency.