1. Department of Physics Center for Materials Science and Nanotechnology University of Oslo P.O.Box 1048, Blindern Oslo N‐0316 Norway
2. Central Laboratory of Solar Energy and New Energy Sources Bulgarian Academy of Science Blvd. Tzarigradsko shosee 72 Sofia 1784 Bulgaria
3. Department of Thin Film Physics Institute of Technical Physics and Materials Science P.O. Box 49, EK MFA Budapest 1525 Hungary