The optimization of a Mo bilayer and its application in Cu(In, Ga)Se2 solar cells

Abstract

Molybdenum (Mo) back contact films for Cu(In, Ga)Se2 (CIGS) solar cells are deposited on soda-lime glass (SLG) substrates by direct current (DC) magnetron sputtering with a Mo target in a pure Ar atmosphere. The effect of the DC power (in the range, 100–500W) and the sputtering pressure (in the range, 0.2–1.8Pa) on the morphology, the electrical resistivity, the optical reflectance and the adhesive properties of Mo films is determined. The optimum properties for the Mo bilayer are obtained. The quality of the SLG/Mo bilayers/CIGS samples that are selenized at 560°C is confirmed to be dense and relatively smooth, with very good adherence. No cracking or peeling off is observed after selenization. The X-ray diffraction patterns for the CIGS absorbers film have a chalcopyrite crystal structure with a preferred orientation of (112), (204)/(220) and (312)/(116). The chemical composition of the Cu-In-Ga precursor films and CIGS absorbers are determined using X-ray fluorescence spectroscopy. The secondary ion mass spectroscopy surface chemical analysis for the CIGS films shows that the Ga element moves away from the surface and accumulates at the bottom of the sample and Se diffuses into the Mo surface, which indicates the possible completion of selenization. The CIGS solar cells that are produced have a maximum photo-conversion efficiency of 12.83%.