Effect of thickness on structural and optical properties of vacuum-deposited Sn2Sb2S5 thin films

Sn2Sb2S5 thin films in thickness of 100 to 900 nm were deposited on glass substrates using thermal evaporation method. XRD indicated that all the Sn2Sb2S5 samples are polycrystalline in nature having orthorhombic structure. The various structural parameters such as crystalline size (D), dislocation density (), strain (epsilon) and texture coefficient TC (hkl) were calculated and the surface morphology of the films was also analyzed. The optical constants, i.e., refractive index, absorption coefficient and optical band gap of the deposited films have been determined from the analysis of the transmittance and reflectance spectral data over the wavelength range 300-1800nm. The averages transmittance for all films is over 80% in the near infrared spectral range. Furthermore, the absorption coefficient of Sn2Sb2S5 thin films was evaluated and found to be in the range 10(4)-10(5)cm(-1) in the UV. However, the optical band gap was found to decrease from 1.72 to 1.5eV when the thickness of films increases.