1. Faculty of Engineering; University of Duisburg-Essen and CENIDE, Bismarckstr. 81; 47057 Duisburg Germany
2. Institute for Solar Energy Research, Hameln/Emmerthal GmbH (ISFH); Am Ohrberg 1; 31860 Emmerthal Germany
3. Institute of Electronic Materials and Devices; University of Hannover, Schneiderberg 32; 30167 Hannover Germany