Structural properties of bi-layer Molybdenum Thin-film deposited by RF magnetron sputtering for CZTS solar cells

CZTS (Copper Zinc Tin Sulfide) is a propitious absorber material for photovoltaic applications and gaining popularity for its material abundances and non-toxicity. In order to get good adhesion with substrate and at the same time low film resistivity, bi-layer Molybdenum (Mo) thin-films are frequently used as back electrode in substrate-structured CZTS based Thin-film Solar Cells (TFSCs). In a bi-layer structured Mo film, usually a thin high-pressure (HP) bottom layer serves to give better adhesion and a thick low-pressure (LP) top layer shown lower film resistivity. In this work, structural study of two different stacks (total 1μm film thickness) of HP layer and LP layer for both as-deposited and Vacuum Thermal Annealing (VTA) @560°Cfor 45 minutes were performed. Crystals were more oriented along [200] plane instead of [110] plane and oxidation at the Mo surface were observed for thicker bottom layer. It has been found that, for thinner bottom layer, not only increased crystallite size (from 19.27 nm to 21.26 nm for as-deposited and VTA treated case respectively), but also compressive stressed Mo films were found. It is evident that this bi-layer Mo thin-film is suitable for CZTS solar cell fabrication.