1. Department of Materials and Food, University of Electronic Science and Technology of China Zhongshan Institute, Zhongshan 528402, P. R. China
2. School of Optoelectronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu 610054, P. R. China
3. School of Materials and Energy, University of Electronic Science and Technology of China, Chengdu 610054, P. R. China