1. Department of Inorganic Chemistry, University of Cologne, Greinstr. 6, 50939 Cologne,
Germany
2. Department of Electronics, Universitat de Barcelona, Marti i Franquès 1,
08028 Barcelona, Spain
3. Catalonia Institute for Energy Research, IREC, Jardins de les Dones de Negre
1, 08930 Sant Adrià de Besòs, Barcelona, Spain
4. TEM-MAT, Scientific and Technological
Centers, (CCiT), Universitat de Barcelona, Sole i Sabaris 1, 08028 Barcelona, Spain