Effect of zinc doping on the optoelectronic properties of cadmium sulphide (CdS) thin films deposited by chemical bath deposition by utilising an alternative sulphur precursor

Abstract

CdS is commonly used as a window layer in solar cell structure and is deposited by different growth techniques. In this study, a source-dependent comparative analysis on chemical bath deposition-grown CdS thin film focusing on different sulphur sources, namely, thiourea (NH2SCNH2) and N-methylthiourea (NH2CSNHCH3), was conducted. Moreover, the effect of Zn2+ doping on as-grown CdS film from the abovementioned sulphur sources was examined. Results reveal that the optical transmittance increases with the increase in zinc concentration. The optical bandgap ranges from 2.35 eV to 2.45 eV whilst thiourea is used as sulphur source, and the bandgap ranges from 2.2 eV to 2.4 eV whilst N-methylthiourea (NMT hereinafter) is utilised. Notably, the electrical properties are independent of the difference in sulphur sources. Zn2+-doped CdS thin films with NMT as sulphur source exhibit ideal optoelectrical properties for the usage as window layers in solar cell device applications.