1. Complex Materials and Devices, Department of Physics, Chemistry and Biology (IFM), Linköping University, 581 83 Linköping, Sweden
2. Centre for Advanced Materials, Heidelberg University, Im Neuenheimer Feld 225, 69120 Heidelberg, Germany
3. Physics, Faculty of Science and Engineering, Åbo Akademi University, Porthansgatan 3, 20500 Turku, Finland
4. Biomolecular and Organic Electronics, Department of Physics, Chemistry and Biology (IFM), Linköping University, 581 83 Linköping, Sweden