1. Institute of Solid State Physics and Key Laboratory of Photovoltaic and Energy Conservation Materials, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui 230031, P. R. China
2. The Key Laboratory of Functional Molecular Solids, Ministry of Education, Anhui Normal University, Wuhu, Anhui 241002, P. R. China
3. School of Mechatronics and Vehicle Engineering, Chongqing Jiaotong University, Chongqing 400074, P. R. China