1. Laboratory for Thin Films and Photovoltaics, Empa - Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, Dübendorf 8600, Switzerland
2. Department of Physics, Center for Optoelectronics Engineering Research, Yunnan University, Kunming, Yunnan 650091, China
3. Department of Materials Science and Engineering, University of Toronto, Toronto, Ontario M5S 3E4, Canada
4. Ecole Polytechnique Fédérale de Lausanne (EPFL), Institute of Electrical and Microengineering (IEM), Photovoltaics and Thin-Film Electronics Laboratory, Rue de la Maladière 71b, Neuchâtel 2002, Switzerland