1. Biomolecular and organic electronics, Department of Physics, Chemistry and Biology (IFM), Linkoping University, 58183 Linkoping, Sweden
2. Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China
3. Institut für Angewandte Photophysik, Technische Universität Dresden, 01069 Dresden, Germany