1. Henan Key Laboratory of Photovoltaic Materials, School of Future Technology, Henan University, Kaifeng 475004, P. R. China
2. Tianjin Key Laboratory of Organic Solar Cells and Photochemical Conversion, Department of Applied Chemistry, Tianjin University of Technology, Tianjin 300384, P. R. China
3. Institute of Solid State Physics, HFIPS, Chinese Academy of Sciences, Hefei 230031, P. R. China