1. Institute for Solar Energy Research Hamelin; Am Ohrberg 1 D-31860 Emmerthal Germany
2. Institute for Solid State Physics; Leibniz Universität Hannover; Appelstr. 4 D-30167 Hannover Germany
3. Institute of Electronic Materials and Devices; Leibniz Universität Hannover; Schneiderberg 32 D-30167 Hannover Germany
4. centrotherm pv AG; Vahrenwalder Str. 269A D-30179 Hannover Germany