1. Cavendish Laboratory; University of Cambridge; J.J. Thomson Avenue Cambridge CB3 0HE UK
2. Department of Materials Science and Metallurgy; University of Cambridge; Charles Babbage Road Cambridge CB3 0FS UK
3. Biomolecular and Organic Electronics; IFM; Linköping University; Linköping 58183 Sweden
4. Department of Engineering; University of Cambridge; J.J. Thomson Avenue Cambridge CB3 0FA UK
5. Department of Chemistry; National University of Singapore; 3 Science Drive 3 S117543 Singapore
6. Solar Energy Research Institute of Singapore; National University of Singapore; 7 Engineering Drive 1 S117574 Singapore