CuAl _xGa _1-xSe ₂ thin films for photovoltaic applications: Structural, electrical and morphological analysis

Wide-bandgap quaternary semiconductor chalcopyrites can be of interest for photovoltaic application. Novel CuAl _xGa _1-xSe ₂ (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 10 ¹ to 10 ⁴ Ω cm 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.