1. Department of Physics, Department of Materials Science and Engineering, and Department of Biomedical Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon 999077, Hong Kong, China
2. Institute for Energy Research, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, China
3. Yunnan Provincial Rural Energy Engineering Key Laboratory, Yunnan Normal University, Kunming 650500, Yunnan, China