1. School of Microelectronics Fudan University Shanghai 200433 China
2. Shanghai Synchrotron Radiation Facility (SSRF) Shanghai Advanced Research Institute & Shanghai Institute of Applied Physics Chinese Academy of Sciences Shanghai 201204 China
3. State Key Laboratory of Photovoltaic Science and Technology Fudan University Shanghai 200433 China
4. Hangzhou Institute of Technology Xidian University Hangzhou 311200 China
5. Department of Physics The Chinese University of Hong Kong Shatin New Territories Hong Kong 999077 China
6. Key Laboratory of Advanced Display and System Applications of Ministry of Education Shanghai University Shanghai 200072 China