Optical and electrical properties of thin films grown by spray pyrolysis

Polycrystalline films of Sn2S3 compound were prepared on glass substrates by the spray pyrolysis technique at a substrate temperature of 270 ∘C using tin chloride (SnCl2) and thiourea (Cs(NH2)2) solutions with a concentration of 0.1 M. The X-ray diffraction pattern reveals an orthorhombic structure and an average grain size equal to 130 Å. The optical properties of the films were studied using optical transmittance and reflectance measurements over the wavelength range 200–2500 nm. The variation of refractive index n and extinction coefficient k with photon energy are reported. The dispersion of the refractive index in Sn2S3 is analysed using the concept of a single oscillator. The values of oscillator energy E 0 and dispersion energy E d are determined to be 3.98 eV and 13.5 eV, respectively. The optical constants confirm that the Sn2S3 thin films have a direct band gap of 2 eV. A value of 4.35×10−3 (Ω cm)−1 for the room temperature conductivity is found using the four-probe method.