1. Department of Materials Science and State Key Laboratory of Molecular Engineering of Polymers, Fudan University, Shanghai 200433, China.
2. Electrical Engineering Department, University at Buffalo, The State University of New York, Buffalo, NY 14260, USA.
3. School of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China.
4. Department of Physics, Fudan University, Shanghai 200433, China.