Thermal annealing induced physical properties of ZnSe thin films for buffer layer in solar cells

This article is dedicated to the study on the influence of thermal annealing on the physical properties of ZnSe thin films in order to seek a suitable alternative Cd-free window layer for developing high efficiency CdTe and CIGS solar cells. ZnSe films having thickness 300 nm were deposited onto glass and ITO substrates employing e-beam evaporation technique and then thermal annealing was undertaken in temperature range of 373-573 K with an interval of 100 K. The structural studies show that films are having cubic phase with (111) predominant peak and grain size corresponding to the preferred peak is observed to vary with annealing. The optical parameters like absorbance, transmittance, extinction coefficient, refractive index were also evaluated. The transmittance of films is found to vary and 573 K annealed films have shown maximum transmittance. The optical energy band gap was found to increase with annealing from 1.97 eV to 2.47 eV. Electrical analysis revealed the linear relationship between current and voltage indicating ohmic nature of the contacts. The results are also correlated with the surface morphology of the thin ZnSe films while the presence of Zn and Se peaks in EDAX spectra confirmed the film deposition.