1. Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
2. School of Engineering, The Australian National University, Canberra Australian Capital Territory 2600, Australia
3. IEK5-Photovoltaik, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany