1. Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
2. Physics Department, Free University of Berlin, Arnimallee 14, 14195 Berlin, Germany
3. Laboratory for Thin Films and Photovoltaics, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland
4. Institut für Optik und Atomare Physik, Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany
5. Institute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, Switzerland