Sputter-Deposited WOx and MoOx for Hole Selective Contacts

Reactive sputter deposited tungsten and molybdenum oxide (WO_x, MoO_x) thin films are tested for their ability to form a hole selective contact for Si wafer based solar cells. A characterization approach based on analyzing the band bending induced in the c-Si absorber and the external and implied open-circuit voltage of test structures was used. It is shown that the oxygen partial pressure allows to tailor the selectivity to some extent and that a direct correlation between induced band bending and hole selectivity exists. Although the selectivity of the sputtered films is inferior to the reference films deposited by thermal evaporation, these results demonstrate a good starting point for further optimizations of sputtered WO_x and MoO_x towards higher work functions to improve the hole selectivity.