1. Guangzhou Key Laboratory of Vacuum Coating Technologies and New Energy Materials Guangdong Provincial Engineering Technology Research Center of Vacuum Coating Technologies and New Energy Materials Siyuan Laboratory Department of Physics Jinan University Guangzhou 510632 P. R. China
2. Institute for Electric Light Sources School of Information Science and Technology Fudan University Shanghai 200433 P. R. China
3. Laboratory of Organic Electronics Department of Science and Technology Linköping University 60174 Norrköping Sweden
4. Institute of Polymer Optoelectronic Materials and Devices State Key Laboratory of Luminescent Materials and Devices South China University of Technology Guangzhou 510640 P. R. China