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Abstract: Wide-band gap chalcopyrite semiconductors have a great interest due to their potential application in multi-junction thin film solar cells or as window layers. Polycrystalline CuAl x Ga1−x Se2 (CAGS) thin films have been prepared by selenization of evaporated metallic precursor layers on bare and Mo-coated soda lime glass substrates. The optical properties of CAGS films of 2 thicknesses have been analyzed by spectrophotometry in the visible-infrared (VIS-IR) and the compositional characteristics have been studied by energy dispersive analysis of X-rays (EDAX) and X-ray photoelectron spectroscopy (XPS). The optical transmission increases and the band gap energy shifts toward higher values as the Al content increases, which indicates the partial substitution of Ga by Al. The dependence of the band gap with the composition has resulted to be nonlinear and a bowing parameter of b =0.62 and b =0.54 for 0.6μm and 1.1μm-CAGS samples, respectively, has been obtained. XPS data have shown an Al, Ga and Se composition gradient in depth and a surface strongly oxidized. However, XPS reveals that the Cu composition remains constant in depth and the oxidation is relatively low in bulk increasing slightly in the interface with Mo/SLG. Moreover, samples with high Al content reveal a higher contribution of CuO in depth. [Copyright &y& Elsevier]

Abstract: Wide-bandgap quaternary semiconductor chalcopyrites can be of interest for photovoltaic application. Novel CuAl x Ga1−x Se2 (CAGS) (0≤ x ≤1) thin films have been achieved by selenization of evaporated metallic precursor layers in a wide range of Al content and for several film thicknesses. Influence of Al incorporation, x, and film thickness on the structural, electrical and morphological properties of the samples have been studied. Polycrystalline CAGS thin films have been obtained reproducibly with chalcopyrite structure. The lattice parameters, a and c, and the average crystallite size decreased with the increase of Al amount, x. All films showed random orientation with the degree of randomness reduced for increasing x values. All samples show photoconductivity and resistivities ranging from 101 to 104 Ωcm depending on the film thickness and x value. Resistivity values increase and thermoelectric coefficient decreases with the increase of Al proportion, x. Surface morphology was studied by SEM images and roughness measurements. Grain size and the arithmetic average roughness decreases with the increase of x and with the decrease of film thickness. [Copyright &y& Elsevier]