1. Shenzhen Research Institute, Renewable Energy Conversion and Storage Center, College of Electronic Information and Optical Engineering, Nankai University, Tianjin 300350, P. R. China
2. Analysis and Measurement Center, Tianjin University, Tianjin 300072, P. R. China
3. Institute for Composites Science Innovation, School of Materials Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, P. R. China
4. Department of Physics, East China Normal University, Shanghai 200062, P. R. China