Potentiostatic electrochemical deposition and characterization of Zinc Sulphide (ZnS) thin films for application as window layer in solar cells

Abstract

This study addresses the persistence challenge of the toxicity associated with cadmium sulphide (CdS) thin films, typically synthesised via chemical bath deposition technique and used as window layers of thin film solar cells. Three-electrode potentiostatic electrochemical deposition technique was used to synthesize zinc sulphide (ZnS) thin films from aqueous solution of zinc acetate and sodium thiosulphate penta-hydrate as a source of zinc and sul phur respectively. The thin films were characterized using Field Emission Scanning Electron Microscope (FESEM) to study their morphology, X-Ray Diffractometer (XRD) to determine the structure of the samples, UV-Visible spec trometer (UV-Visible) to obtain the optical properties of the thin films, four-point probes to determine their resis tivity/conductivity, Hall effect measurement to determine their conductivity type and two-point probes to study their I-V characteristics. The results obtained revealed that, the ZnS thin films were non-uniform but pin-hole free with average particle size of 4.18 μm, polycrystalline with zinc blende cubic structure. The thin film exhibited high transmittance in the visible region and the band gap is 2.94 eV. It is an n-type semiconductor with conductivity of 4.43 × 103 Ω-1cm-1. The I-V characteristics of ITO/ZnS/Ag structure is linear which implies that the junction be tween the ITO/ZnS and ZnS/Ag are ohmic. The study therefore concludes that, zinc sulphide thin films synthesized using three-electrode potentiostatic technique is a suitable material for window layer of a thin film solar cells. Thus, it was recommended that ZnS thin films deposited via three-electrode potentiostatic deposition technique should be employed as a window layer in thin film solar cells to obtain environmental benign solar cells.