Effect of the concentration of Cu²⁺ in the electrolytes on CuInS₂ thin films

CuInS₂ thin film, CuIn₁₁S₁₇ thin film and a mixture of both were formed on ITO glass substrates by sulfurizing Cu-In-S precursors which were electrodeposited in the electrolytes solutions with different Cu²⁺ concentrations. The properties of the thin films were characterized by X-ray diffraction (XRD), scanning electron micrographs (SEM) and energy dispersive spectroscopy (EDS). The experiment results indicate that while keeping the In³⁺ and S₂O_32- concentrations fixed, the concentration of Cu²⁺ has significant influence on the chemical composition, morphology and crystal structure of the resulting thin films. With a proper Cu²⁺ concentration, a single-phase polycrystalline CuInS₂ thin film can be achieved with ideal stoichiometry and a suitable band gap of 1.5 eV, which will be used as the absorber layer of a thin film solar cell in further work.