1. School of Materials and Energy, National Center for International Research on Photoelectric and Energy Materials, Yunnan University, Kunming 650091, China
2. Department of Physics, Fudan University, Shanghai 200433, China
3. Department of Physics, Center for Optoelectronics Engineering Research, Yunnan University, 650091 Kunming, China
4. Eco-Materials and Renewable Energy Research Center (ERERC), College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093, China