Thermally Stable Molybdenum Oxide Hole-Selective Contacts Deposited using Spatial Atomic Layer Deposition

Sub-stoichiometric MoO_x has been identified as a viable replacement to p-type a-Si:H in hole-selective contacts to c-Si solar cells. Many groups have observed a strong tendency for the electrical properties of MoO_x-based contacts to degrade during the standard contact formation anneal due to the addition of O vacancies in the MoO_x. These O vacancies create defect levels within the bandgap and lowers the work function of the MoO_x, which in turn affects the efficiency of hole-conduction through the contact. In this paper, we grow a thin tunneling SiO_x layer over p-type c-Si via UV-ozone treatment, followed by a thin (~5 nm) MoO_x deposited using spatial atomic layer deposition. We show that the use of the high work function (5.01 eV) Nickel, as a replacement to the Aluminum contact, not only assists in efficient hole-transport, but also forms a thermally stable contact up to temperatures of 300°C with contact resistivities below 10 mΩ-cm².