1. Key Laboratory
of Novel Thin Film Solar Cells, Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, 230031 Hefei, P. R. China
2. School of Materials Science and Engineering, Hefei University of Technology, Hefei 230031, China
3. Beijing National Laboratory for Molecular Sciences, Key
Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China