Effect of Substrate Temperature on Optical Properties of Spray Pyrolytic Cadmium Sulphide Thin Films

Abstract

Cadmium sulphide (CdS) thin films were prepared by chemical spray pyrolysis technique on micro-slide glasses using cadmium acetate and thiourea as precursors. The substrate temperature was varied in the range of 250°C- 350°C. The prepared films were annealed at 500°C for 1hour. The effects of substrate temperature and annealing on the optical properties of the films were investigated. The films were characterized using UVVisible Spectrophotometer. The absorption and transmission spectra revealed that the transmission increases with wavelength, while the absorbance reduces as the wavelength increases in the visible region. The optical band gaps of the films were found to be 2.26eV, 2.07eV and 1.88eV with deposition temperature of 250°C, 300°C and 350°C, respectively. It was observed that the refractive index of the thin film obtained reduces as the substrate temperature increases and that annealing reduces the refractive index of the cadmium sulphide thin film. These findings show that cadmium sulphide is one of the most promising materials to be used as a window layer in hetero-junction thin film solar cells. It is also of good interest for its applications in some optoelectronic devices, like photoresistor and photodiode.

Keywords:Cadmium sulphide, Spray pyrolysis, Thin film, Annealing, Optical properties.