1. Institute of Electronic Devices; University of Wuppertal; Rainer-Gruenter-Str. 21 42119 Wuppertal Germany
2. Chair of Large Area Optoelectronics; University of Wuppertal; Rainer-Gruenter-Str. 21 42119 Wuppertal Germany
3. Institute of Materials Science; Surface Science Division; Darmstadt University of Technology; Petersenstraße 32 64287 Darmstadt Germany
4. Molecular Materials and Nanosystems; Institute of Complex Molecular Systems; Eindhoven University of Technology; P.O. Box 513 5600 MB Eindhoven The Netherlands