Effect of substrate and Zn doping on the structural, optical and electrical properties of CdS thin films prepared by CBD method

Abstract

CdS is an important and useful material for photovoltaic applications. In this paper, pure CdS and Zn-doped CdS (CdS:Zn) thin film were fabricated on glass and ITO substrate using chemical bath deposition (CBD) method, to systematically investigate the effect of substrate and Zn concentration on the crystallization behavior, and optical and electrical properties of the CdS thin films by X-ray diffraction, atomic force microscope, X-ray photoelectron spectroscopic, Raman scattering, UV–vis spectrophotometer, and transportation measurement system. The results indicated that no matter what substrate was used, whether glass or ITO substrate, the crystal structure of CdS thin film is always hexagonal phase with (002) as the preferential orientation. And CdS thin film deposited on ITO substrate have a good crystallinity and its morphology is very compact and uniformity. For doping thin films, the results revealed that Zn element has been successfully doped into the lattice of CdS thin film and the position of (002) diffraction peak shifted monotonically from 26.6° to 26.97° with the increase of Zn concentration. Finally, optical and electrical properties were discussed. The optical band gap for the CdS:Zn thin films is bigger than that of the pure CdS thin film, and suitable Zn doping can improve the electrical conductivity of thin film. Our results indicate the CdS:Zn thin films fabricated via CBD method may be more suitable for the application in optoelectronic devices, such as the window layer for cadmium telluride and copper zinc tin sulfide solar cell.