thermal annealing influence over optical properties of thermally evaporated sns/cds bilayer thin films

Thin films of tin sulfide/cadmium sulfide (sns/cds) were prepared by thermal evaporation method at room temperature on a glass substrate and then annealed at different temperature with the aim of optimizing the optical properties of the material for use in photovoltaic solar cell devices. the effect of annealing on optical properties of sns/cds film was studied in the temperature range of 100 to 400 °c with steps of 100 °c. the films were characterized by optical absorption spectra. the optical constants such as band gap, refractive index (n) and extinction coefficient (k) were calculated on different annealing temperature and in the wavelength range of 250 nm to 750 nm. analysis of the optical absorption coefficient demonstrated the presence of direct optical transition and the corresponding band gap values showed enhancement as deposition annealing temperature increased. the energy band gap in the range 2.20 ev – 3.18 ev has been obtained for a film as-deposited which increases clearly with increasing annealing temperature. the refractive index and extinction coefficient both decrease notably with increasing annealing temperature.