1. Experimentelle Physik 2 Technische Universität Dortmund 44227 Dortmund Germany
2. Ioffe Institute Russian Academy of Sciences St. Petersburg 194021 Russia
3. P. N. Lebedev Physical Institute of the Russian Academy of Sciences Moscow 119991 Russia
4. Laboratory of Inorganic Chemistry Department of Chemistry and Applied Biosciences ETH Zürich Zürich CH‐8093 Switzerland
5. Laboratory for Thin Films and Photovoltaics Empa‐Swiss Federal Laboratories for Materials Science and Technology Dübendorf CH‐8600 Switzerland