1. Materials and Device Engineering Group, Department of Information Technology and Electrical Engineering, ETH Zurich, 8092 Zurich, Switzerland
2. IEK-5 Photovoltaik, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
3. Faculty of Engineering and CENIDE, University of Duisburg-Essen, Carl-Benz-Str. 199, 47057 Duisburg, Germany