Study of optical, structural and morphological properties on Cd-free buffer materials

In_xSe_y, Ga_xSe_y and ZnSe thin films deposited by different methods such as coevaporation, physical evaporation and close spaced sublimation methods, were characterized through X-ray diffraction (XRD), transmittance and atomic force microscopy (AFM) measurements. These materials are an attractive alternative to the CdS buffer layer in the development of CIGS and CdTe based solar cells. This work has focused on studying the influence of the preparation method and film thickness on the optical gap, morphology and crystallographic phases of the above mentioned compounds. The studies revealed that the indium selenide films grow mainly in the γ-In₂S₃ phase, the zinc selenide films grow in the ZnSe phase and the gallium selenide grows in the phases δ-GaSe and β-Ga₂Se₃. With the exception of the ZnSe films deposited by CSS method, in the rest of the studied films, a marked effect of the thickness on their optical gap was observed, Eg. For samples of InSe, GaSe and ZnSe with a thickness of about 3.5 μm, Eg values were found of 1.9, 2.5 and 2.6 eV respectively