1. Department of Physics and the Centre for Plastic Electronics; Imperial College London; London SW7 2AZ UK
2. Department of Physics; National Technical University of Athens; Athens GR-15780 Greece
3. Department of Materials and the Centre for Plastic Electronics; Imperial College London; Royal School of Mines; London SW7 2AZ UK
4. Department of Chemistry and the Centre for Plastic Electronics; Imperial College London; London SW7 2AZ UK
5. Department of Physics; Laboratory of Applied Physics; Aristotle University of Thessaloniki; Thessaloniki 54124 Greece
6. Division of Physical Sciences and Engineering and KAUST Solar Centre; King Abdullah University of Science and Technology (KAUST); Thuwal 23955-6900 Saudi Arabia