Structural, optical and impurity-absorption properties of CdS thin films deposited by a chemical bath using four cadmium sources

Abstract

This study examines the effects of four cadmium sources on the properties of cadmium sulfide (CdS) thin films prepared using chemical bath methods. The reaction solutions used cadmium acetate, cadmium sulfate, cadmium iodide and cadmium chloride as cadmium sources. The surface morphology, crystal structure, optical properties and impurities absorption of CdS films were analyzed. The CdS films deposited with different Cd sources showed similar crystalline structures and surface morphologies. In addition, the Cd film band gaps differed unobviously. Measurements made with Fourier transform infrared spectrum showed that CN bonds were the main impurities absorbed in the CdS films. After the CdS films had been annealed at 120 °C in air, the CN peak intensity for cadmium acetate, cadmium sulfate and cadmium chloride decreased while the CN peak intensity for cadmium iodide increased. We found that the performance of a copper indium gallium selenide (CIGS) solar cell was influenced by the Cd sources; this was especially true for the fill factor (FF). Higher values of CN bonds absorption yielded lower values of FF and conversion efficiency of CIGS solar cells. Among the four tested Cd sources, cadmium acetate and cadmium sulfate proved much more suitable as Cd sources for depositing CdS thin films.