1. Institute of Applied Technology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, P. R. China
2. University of Science and Technology of China, Hefei 230026, P. R. China
3. Henan Key Laboratory of Photovoltaic Materials, Henan University, Kaifeng 475004, P. R. China
4. Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structural Materials of Guangdong Province, Shantou University, Shantou 515063, P. R. China
5. Beijing National Laboratory for Condensed Matter Physics and CAS Key Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, P. R. China