DC reactive sputtering of aluminium doped zinc oxide films for solar modules controlled by target voltage

Reactive sputtering is an option to further reduce costs associated with the deposition of the transparent front contact in chalcopyrite-based solar modules. In view of the difficulties reported in scaling-up reactive ZnO sputtering we have chosen a simple and robust approach. It is comprised of a dual magnetron operated in DC/DC mode, a constant oxygen flow and the process is controlled by target voltage. After process optimisation, the optical and electrical properties of the reactively sputtered films are comparable to those of reference films (RF-sputtered from ceramic targets). Likewise, the efficiency of monolithically integrated CuInS2-based module test structures is not affected by the modified ZnO process.