1. Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials; Key Laboratory of Cluster Science Ministry of Education of China; School of Chemistry and Chemical Engineering Beijing Institute of Technology Beijing 100081 P. R. China
2. School of Materials Science and Engineering Beijing Institute of Technology Beijing 100081 P. R. China
3. Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education Department of Chemistry Tsinghua University Beijing 100084 P. R. China