1. Institute for Solar Energy Research Hamelin (ISFH); Am Ohrberg 1 31860 Emmerthal Germany
2. Heraeus Deutschland GmbH CoKG; HEB-EC; Chempark Leverkusen 51368 Leverkusen Germany
3. Department of Solar Energy; Institute of Solid-State Physics; Leibniz Universität Hannover; Appelstr. 2 30167 Hannover Germany