1. Department of Physics and Centre for Plastic ElectronicsImperial College London London SW7 2AZ UK
2. School of Physics and AstronomyQueen Mary University of London London E1 4NS UK
3. IEK5-PhotovoltaicsForschungszentrum Jülich 52425 Jülich Germany
4. Faculty of Engineering and CENIDEUniversity of Duisburg-Essen Carl-Benz-Str. 199 47057 Duisburg Germany