1. Institute of Inorganic Chemistry, University of Cologne, Greinstrasse 6, 50939 Cologne, Germany
2. Institute of Physics 2, University of Cologne, Zülpicher strasse 77, 50937 Cologne, Germany
3. Graduate School of Engineering, Toin University of Yokohama, 1614 Kuroganecho, Aoba, Yokohama, Kanagawa 225-8503, Japan
4. IEK-5 Photovoltaik, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
5. Laboratoire des Solides Irradiés, Ecole Polytechnique, CNRS, CEA/DRF/IRAMIS, Institut Polytechnique de Paris, 91128 Palaiseau Cedex, France
6. Faculty of Engineering and Natural Sciences, Tampere University, P.O. Box 541, FI-33101 Tampere, Finland
7. Faculty of Engineering and CENIDE, University of Duisburg-Essen, Carl-Benz-Strasse 199, 47057 Duisburg, Germany