1. Department of Materials Science and L-NESS, University of Milano-Bicocca, Via Cozzi 55, I-20125 Milan, Italy
2. School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom
3. Laboratory of Organic Electronics, Department of Science and Technology, Linköping University, Norrköping SE-601 74, Sweden
4. Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo Da Vinci, 32, 20133 Milano, Italy
5. Institute for Microelectronics and Microsystems (CNRIMM), Via Piero Gobetti 101, 40129 Bologna, Italy
6. Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom