1. CAS Center for Excellence in Nanoscience, Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 101400, P. R. China
2. School of Nanoscience and Engineering, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
3. Siyuan Laboratory, Guangdong Provincial Engineering Technology Research Center of Vacuum Coating Technologies and New Energy Materials, Department of Physics, Jinan University, Guangzhou, Guangdong 510632, P. R. China
4. Georgia Institute of Technology, Atlanta, Georgia 30332-0245, United States
5. Guangzhou Institute of Blue Energy, Knowledge City, Huangpu District, Guangzhou 510555, China
6. Yonsei Frontier Lab, Yonsei University, Seoul 03722, Republic of Korea