Se activity and its effect on Cu(In,Ga)Se2 photovoltaic thin films



We study some physical properties of CuIn1–xGax Se2 thin-films fabricated by evaporation from elemental sources under various Selenium environments. Specifically, thin-films were fabricated under growth conditions such as Se deficiency, near stoichiometry and excess Se during coevaporation to investigate the impact of the Se environment on absorber film properties and ultimately the device performance. We determine the chemical activity of Se in the evaporation process has a strong influence on film macrostructure (prefered orientation) and microstructure, particularly at the grain and grain boundary level. It is shown that the optoelectronic properties at grain boundaries are affected by the Se environment used resulting in absorber thin-films with distictive defect distribution and defect density. Consequently, the performance of the solar cells fabricated from those films is also affected by the Se environment. These effects on solar cell performance and absorber properties are reported in a (i) structural analysis of the CuIn1–xGax Se2/Mo/glass samples by X-ray and electron backscattering techniques; (ii) optolectronic radiative characteristics of the absorbers by cathode luminescence and photoluminescence studies and (iii) current–voltage, quantum efficiency and capacitance–voltage measurements for the solar cells made from the absorbers fabricated under the pre prescribed Se growth conditions. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)