Date of Award
Master of Science
Shirin Movaghgharnezhad for the master of science degree in mechanical engineering, presented on November 6, 2017, at Southern Illinois University Carbondale. TITLE: Electrodeposition of CuGaS2 from Aqueous and Non-Aqueous Electrolyte Mixtures MAJOR PROFESSOR: Dr. Ian I. Suni Electrodeposition of CuGaS2 from aqueous and non-aqueous electrolyte mixtures is reported in this work. Acetonitrile complexation is used to shift the reduction potential of Cu (II) in the cathodic direction. With the presence of 50% acetonitrile, the difference between the peak reduction currents of Cu (II) and Ga (III) during cyclic voltammetry is only 140 mV, whereas the standard reduction potentials of the individual components in aqueous electrolytes differ by 870 mV. When all components are present in the electrolyte, a new reduction peak obtained in cyclic voltammograms at −260 mV and pH 2.7 that is anodically shifted relative to the cathodic peaks when only one component is present. According to the composition, and morphology analysis at deposition potential -260 mV vs. Ag/AgCl for 15 minutes from aqueous and non-aqueous solutions of 10 mM Ga(NO3)3, 0.5 CuSO4, 1 mM Na2S, 100 mM LiClO4 and a 50-50 mixture of water and acetonitrile at pH 2.7 was found to be the optimum condition to obtain stoichiometric CuGaS2 thin films. In addition, oxygen incorporation in the electrodeposit is observed, because electrodeposition of stoichiometric CuGaS2 appears to be immediately followed by Ga oxidation. The sample were annealed at temperature 300°C in Ar atmosphere for 2 hours to improve crystallinity and reduce the extent of oxidation. Thin film analysis by EDX, top-view SEM, and also cross-sectional SEM were also performed to determine the elemental ratio of Cu:Ga:S, thin film morphology, and thin film thickness, respectively. This material has potential application in solar cells. The EDX analysis of copper gallium sulfide thin films at different potentials and different gallium solution phase concentration were also performed.
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