Preparation and properties of polycrystalline CdSxTe1-x thin films for solar cells

The structural, optical and electrical properties of US. Te1-x. thin films prepared by co-evaporation of powders of US and CdTe have been studied by x-ray diffraction, atomic force microscopy and optical transmittance spectra measurements. Results show that the as-deposited CdSx Te1-x. thin films are homogeneous, adherent and compact on the glass slides substrates without pinhole and that their conductivity is n-type for x >= 0.5 and p-type for x < 0.5. X-ray diffraction has been used to determine the phase and lattice parameters, indicating that the CdSxTe1-x thin films are polycrystalline and show highly preferential orientation. The predominant direct optical transitions were observed and the variation of the optical energy gap E-g is nonlinear with x. Given the values of lattice parameter and optical energy gap, the exact composition of the phase change at x = 0.25 has been determined. The films are of a cubic phase for x < 0. 25, and hexagonal for x > 0.25. After annealing there is no change in the structure of the films with a slight decrease in optical energy gap. Finally, a new structure of CdS/CdTe/ZnTe/ZnTe:Cu/An solar cells with a CdSx Te1-x buffer layer has been proposed.