1. Key Laboratory of Advanced Display and System Applications of Ministry of Education, Shanghai University, 149 Yanchang Road, Shanghai 200072, P. R. China
2. Institute of Advanced Energy, Kyoto University, Uji, Kyoto 611-0011, Japan
3. Department of Physics and Astronomy and Wright Center for Photovoltaics Innovation and Commercialization, The University of Toledo, Toledo, Ohio 43606, United States