1. Faculty of Materials Science and Applied Chemistry, Riga Technical University, P. Valdena Str. 3, LV-1048, Riga, Latvia
2. Latvian Institute of Organic Synthesis, Aizkraukles Str. 21, Riga LV-1006, Latvia
3. Institute of Solid State Physics, University of Latvia, Kengaraga Str. 8, LV-1063, Riga, Latvia
4. Laboratory of Organic Electronics, Department of Science and Technology, Linköping University, SE-60174 Norrköping, Sweden
5. Department of Physics and Astronomy, Uppsala University, SE-751 20 Uppsala, Sweden
6. Department of Electrical Engineering, Yuan Ze University, Chungli 32003, Taiwan