1. Energy Harvesting Research Group, SUPA, School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS, UK
2. Department of Physics, SUPA, University of Strathclyde, Glasgow G4 0NG, UK
3. Materials Sciences Division, Lawrence Berkeley National Laboratory, California 94720, USA
4. Materials Science and Engineering Department, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
5. Organic Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews Fife, KY16 9SS, UK
6. Department of Engineering, University of Exeter, North Park Road, EX4 4QF Exeter, UK
7. Molecular Foundry, Lawrence Berkeley National Laboratory, California 94720, USA