1. Department of Chemistry and Centre for Plastic Electronics, Imperial College London, London W12 0BZ, U.K.
2. State Key Laboratory of Polymer Physics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
3. Electrical Engineering Division, Department of Engineering, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA, U.K.
4. Heeger Center for Advanced Materials and Research Institute for Solar and Sustainable Energies, Gwangju Institute of Science and Technology, Gwangju 61005, Republic of Korea
5. SPECIFIC, College of Engineering, Swansea University, Bay Campus, Fabian Way, Swansea SA1 8EN, U.K.