Formation of transparent and ohmic ZnO:Al/MoSe2 contacts for bifacial Cu(In,Ga)Se2 solar cells and tandem structures

Cu(In,Ga)Se2 layers are fabricated by thermal coevaporation on transparent ZnO:Al films. A thin opaque Mo interlayer inserted between the ZnO:Al and the Cu(In,Ga)Se2 film transforms the rectifying ZnO:Al/CIGS interface into an ohmic contact. Transparency of the ZnO:Al/Mo backcontact is achieved by depositing an additional NaF precursor, which catalyses the redox selenisation of the opaque Mo to transparent MoSe2 during the Cu(In,Ga)Se2 evaporation process. Cu(In,Ga)Se2 solar cells with efficiencies up to 13.4% are fabricated on transparent ZnO:Al/MoSe2 backcontacts.