1. Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, P. R. China
2. CAS Key Laboratory of Renewable Energy, Guangzhou 510640, P. R. China
3. Guangdong Provincial Key Laboratory of New and Renewable Energy Research and Development, Guangzhou 510640, P. R. China
4. University of Chinese Academy of Sciences, Beijing 100049, China