1. Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing101400, P. R. China
2. Center on Nanoenergy Research, School of Physical Science and Technology, Guangxi University, Nanning, 530004, P. R. China
3. Hunan Key Laboratory for Super Microstructure and Ultrafast Process, School of Physics and Electronics, Central South University, Changsha, 410083, P. R. China
4. Hunan Key Laboratory of Nanophotonics and Devices, School of Physics and Electronics, Central South University, Changsha, 410083, P. R. China
5. School of Nanoscience and Technology, University of Chinese Academy of Sciences, Beijing100049, P. R. China
6. Shandong Zhongke Naneng Energy Technology Co., Ltd., Dongying, 257061, P. R. China
7. Georgia Institute of Technology, Atlanta, Georgia30332-0245, United States