In conventional architecture for a copper/indium/gallium/selenium (“CIGS”) thin film solar cell, the thin film stack generally consists of a substrate, a molybdenum (“Mo”) thin film layer as a back contact layer (a.k.a., back electrode), and a CIGS thin film layer as the absorber layer. The structure further includes a buffer layer of CdS, for example, then followed by a top electrode layer. Such conventional structure is formed by first depositing the molybdenum thin film layer over the substrate. The CIGS thin film absorber layer is formed by deposition of a Cu/In/Ga (CIG) intermetallic precursor layer on the Mo thin film layer and followed by selenization and optionally sulfurization of the CIG precursor in a furnace, thus, converting the CIG precursor layer into the final CIGS/S layer. However, the resulting CIGS/S layer formed on the molybdenum thin film layer often exhibit voids at the interface between the CIGS/S layer and the molybdenum layer accompanied by delamination or peeling of the CIGS/S layer.
Cu/Ga intermetallic compounds may be formed at the Mo/precursor interface. These intermetallic compounds are believed to result in void formation at the interface. The voids between the CIGS absorber layer and the back contact layer are undesirable because they weaken the interface between the Mo back contact layer and the CIGS absorber layer.
All drawing are schematic and are not to scale and they are not intended to show actual dimensions.