Abstract
The ternary compound CuInS2 is attractive for solar cells due to its band gap of 1.54 eV which borders the optimum value necessary for conversion of a solar spectrum. Recently, works on thin film cells based on this material (ZnO/CuInS2) has been reported to show efficiency as high as 11.4%.
In this paper, the orientation and the morphology of CuInS2 sprayed films are determined by the means of X-ray diffraction and scanning electron microscopy. Sprayed CuInS2 films deposited onto a transparent Pyrex substrate with standard fabrication parameters show a chalcopyrite structure with a preferential orientation (112). A model based on the calculation of the relative dielectric function epsilon has been performed in order to obtain the profile of variation of this parameter and to understand the optical behavior of this material via its transmittance and reflectance in visible and near-infrared regions (0.35-2.5 mu m). In the same way, considering the inhomogeneous material CuInS2 containing air inclusions and defaults in bulk as an effective medium, we explain the lack of the interference fringes in experimental spectra of R(lambda) and T(lambda) and estimate the density of these inclusions at about 20%.
The study shows that analysis of the optical properties is a good method to assess the quality of a sprayed CuInS2 thin film in order to use it as an absorber in photovoltaic cells. (C) 2009 Elsevier B.V. All rights reserved.