Effect of vacuum annealing on structural, morphological and optical properties of Sn2Sb2S5thin films with different thicknesses

Abstract

Sn2Sb2S5 thin films in thickness of 100–900 nm were deposited on unheated glass substrates using thermal evaporation method and annealed in vacuum at temperature of 200 °C for 2 h. X-ray diffraction spectra indicated that all the Sn2Sb2S5 samples are polycrystalline in nature having orthorhombic structure. The various structural parameters, such as, crystalline size, dislocation density, strain and texture coefficient 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 as-deposited and post-annealed films have been determined from the analysis of the transmittance and reflectance spectral data over the wavelength range 300–1800 nm. All the Sn2Sb2S5 thin films before and after annealing have relatively high absorption coefficient between 104 and 105 cm−1 in the visible spectral range. The optical band gap was found to decrease, from 1.72 to 1.5 eV for samples before annealing and from 172 to 1.46 eV for samples annealed in vacuum, with increasing films thickness in the 100–900 nm range.