Enhanced physicochemical properties of ZnTe thin films as potential buffer layer in solar cell applications

The Cd-based solar cells possess rear contact problem in superstrate device architecture, which may be eliminated by inserting a suitable buffer layer of zinc telluride (ZnTe) films of appropriate thickness between CdTe absorber and Cu/Au metal contacts. The present work meticulously reports the influence of annealing on the physicochemical properties of ZnTe thin films where ZnTe films were grown employing electron beam thermal evaporation technique and subsequently annealed for 1 h in air ambient and vacuum in 100-300 degrees C temperature range with an interval of 100 degrees C. Structural analysis reveals that as-grown and air/vacuum annealed ZnTe films have (111) preferred reflection with zinc blende structure of cubic phase (except 300 degrees C air annealed films) and grain size is boosted from 22 to 40 nm with annealing. The direct optical energy band gap is estimated in range of 2.25-2.84 eV and 2.65-2.87 eV for air and vacuum annealing, respectively. The contacts between the film surface and the TCO layer showed ohmic behavior as revealed by the I-V characteristics. The EDS results confirmed ZnTe thin film deposition and FESEM micrographs of air annealed films demonstrated the grain growth. The AFM images of vacuum annealed films showed hill-like topographies where hill density and RMS surface roughness reduced with annealing. The findings warrant that 100 degrees C air annealed ZnTe thin films could be employed as an efficient buffer layer and rear contact material to the Cd-based solar cell devices.