1. Adolphe Merkle Institute, University of Fribourg, CH 1700 Fribourg, Switzerland
2. Institute for Photovoltaics (ipv), University of Stuttgart, Pfaffenwaldring 47, 70569 Stuttgart, Germany
3. Helmholtz Young Investigator Group FRONTRUNNER, IEK5-Photovoltaik, Forschungszentrum Jülich, 52425 Jülich, Germany