1. Department of Applied Physics, School of Physics and Electronics Hunan University Changsha 410082 China
2. School of Materials Science and Engineering Hunan Provincial Key Laboratory of Advanced Materials for New Energy Storage and Conversion Hunan University of Science and Technology Xiangtan 411201 China
3. Hunan Provincial Key Laboratory of Flexible Electronic Materials Genome Engineering School of Physics and Electronic Science Changsha University of Science and Technology Changsha 410114 China