1. State Key Laboratory of Polymer Physics and Chemistry, Beijing National Laboratory for Molecular Sciences, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, 100190 Beijing, P. R. China
2. University of Chinese Academy of Sciences, 100049 Beijing, P. R. China
3. State Key Laboratory of Photovoltaic Science and Technology, Trina Solar, Changzhou, 213031, China
4. CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, 100190 Beijing, China
5. School of Materials Science and Engineering, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Tianjin University and Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300350, P. R. China
6. School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan, Shandong 250100, P. R. China