1. Beijing National Laboratory for Condensed Matter Physics Renewable Energy Laboratory Institute of Physics Chinese Academy of Sciences (CAS) Beijing 100190 P. R. China
2. School of Physical Sciences University of Chinese Academy of Sciences Beijing 100049 P. R. China
3. State Key Laboratory of New Ceramics and Fine Processing School of Materials Science and Engineering Tsinghua University Beijing 100084 China
4. State Key Laboratory of Organic Electronics and Information Displays and Institute of Advanced Materials Nanjing University of Posts & Telecommunications Nanjing 210023 China
5. Songshan Lake Materials Laboratory Dongguan Guangdong 523808 P. R. China
6. Center of Materials Science and Optoelectronics Engineering University of Chinese Academy of Sciences Beijing 100049 P. R. China