Role of [Cu]/[In] Molar Ratio in Controlling Structural, Morphological and Optical Properties of Sprayed CuInS 2 Thin Films

Abstract

CuInS2 thin films were deposited by chemical spray pyrolysis from aqueous solutions containing CuCl2, InCl. and thiourea at substrate temperature of 300°C and annealed at 500°C in air. [Cu]/[In] molar ratio was varied from 0.8 to 1.4 in precursor solution. The influence of [Cu]/[In] molar ratio on structural, morphological and optical properties of CuInS2 thin films was investigated. X-ray diffraction analysis shows that all the films have chalcopyrite structure with the preferential orientation along (112) plane. CuInS2 films with indium excess have poor crystallinity and consist of large quantity of small particles while copper-rich films exhibit good crystallinity with large grains. The best film crystallinity is obtained for [Cu]/[In] = 1.2. The scanning electron microscopy and atomic force microscopy images indicated that [Cu]/[In] molar ratio has a strong influence on the microstructure and surface morphology of the films. It was observed that films obtained with [Cu]/[In] ratio of 0.8 are porous. But films surface became gradually dense with increase in [Cu]/[In] molar ratio. As consequence films roughness decreased from 236.12 nm to 110.30 nm. Optical analysis shows that all the films have good absorbance in the visible. The optical absorbance of films is found to increase with increase in [Cu]/[In] molar ratio.