Characterization of spray deposited ternary ZnS_xSe_(1-x) thin films for solar cell buffers

This paper reports on cadmium free, environment friendly, industrially beneficial, chemically sprayed ZnS_xSe_(1-x) (ZSS) thin films with tunable band gap which is suitable for various optoelectronic applications including buffer layer in solar cells. Chemically sprayed ZSS thin films with x ranging from 0 to 1 were studied extensively by adopting the characterization techniques like X-ray diffractometry (XRD), Scanning electron microscopy with energy dispersive spectroscopy (SEM-EDAX), Ultraviolet – visible (UV–VIS), Photoluminescence (PL) and Raman spectroscopies in order to assess the suitability of the formed thin film for the buffer layer applications. XRD analysis was done to determine various parameters like lattice constant, crystallite size, strain and dislocation density. From lattice constant, Vegard's law was also verified and compared the composition estimation with EDAX data. Refractive index was compared using Vandemme model with the values obtained using reflectance data. Photoluminescence and Raman spectra were analyzed to get an insight on structural defects, which have major role in deciding the electrical properties. Electrical properties were assessed by estimating carrier concentration, carrier mobility and electrical resistivity by adopting Van der Pauw technique. Based on structural, optical and electrical properties, sample with x = 0.4 is suggested for the buffer layer application in CIGS based solar cells, which produces minimum lattice mismatch with considerably high optical transmittance and electrical conductance.