1. Institute for Solar Energy Research Hamelin (ISFH), Am Ohrberg 1, 31860 Emmerthal, Germany
2. Peter-Gruenberg Institute 7 and JARA-FIT, Forschungszentrum Juelich, 52428 Juelich, Germany
3. MESA+ Institute for Nanotechnology, University of Twente, Faculty of Science and Technology, 7500 AE Enschede, The Netherlands