1. Department of Physics, Chemistry and Biology (IFM)Linköping University SE-58183 Linköping Sweden
2. Guangzhou Key Laboratory of Vacuum Coating Technologies and New Energy MaterialsPhysics DepartmentJinan University 510632 Guangzhou PR China
3. Laboratory of Organic ElectronicsDepartment of Science and TechnologyLinköping University SE-60174 Norrköping Sweden
4. Wallenberg Wood Science CenterLinköping University SE-60174 Norrköping Sweden