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 bythermal evaporation method at room temperature on a glass substrate and then annealedat different temperature with the aim of optimizing the optical properties of the materialfor use in photovoltaic solar cell devices. The effect of annealing on optical propertiesof SnS/CdS film was studied in the temperature range of 100 to 400 °C with steps of100 °C. The films were characterized by optical absorption spectra. The opticalconstants such as band gap, refractive index (n) and extinction coefficient (k) werecalculated on different annealing temperature and in the wavelength range of 250 nm to750 nm. Analysis of the optical absorption coefficient demonstrated the presence ofdirect optical transition and the corresponding band gap values showed enhancement asdeposition 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 withincreasing annealing temperature. The refractive index and extinction coefficient bothdecrease notably with increasing annealing temperature.