Sputtering of metal oxide tunnel junctions for tandem solar cells

Broken gap metal oxide tunnel junctions have been created for the first time by sputtering. Using a ceramic ZnO-SnO₂ target and a reactively sputtered copper target we created ZnSnO₃ and Cu₂O for the n-type and p-type layers, respectively. The band structure of the respective materials have theoretical work functions which line up with the band structure for tandem CIGS-based solar cell applications. As-deposited films demonstrated a dependence of the I-V profile with post-deposition Rapid Thermal Anneal (RTA) and substrate selection. Total junction specific contact resistances under 1Ω-cm² have been achieved.