1. Key Laboratory for Renewable Energy; Chinese Academy of Sciences; Beijing Key Laboratory for New Energy Materials and Devices; Institute of Physics; Chinese Academy of Sciences; Beijing 100190 P. R. China
2. School of Physical Sciences; University of Chinese Academy of Sciences; Beijing 100049 P. R. China
3. State Key Lab of Advanced Technologies for Materials Synthesis and Processing; Wuhan University of Technology; Wuhan 430070 China