1 Key Laboratory of Computational Physical Sciences (Ministry of Education), State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, Shanghai 200433, People's Republic of China and National Renewable Energy Laboratory, Golden, Colorado 80401, USA.
2 National Renewable Energy Laboratory, Golden, Colorado 80401, USA.
3 Department of Applied Physics, Nanjing University of Science and Technology, Nanjing, Jiangsu 210094, People's Republic of China.
4 Key Laboratory of Computational Physical Sciences (Ministry of Education), State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, Shanghai 200433, People's Republic of China.