1. Department of Physics and Astronomy; University of Turku; FI-20014 Turku Finland
2. Ioffe Physical-Technical Institute; Russian Academy of Sciences; St. Petersburg 194021 Russian Federation
3. Renewable Energy; Helmholtz-Zentrum Berlin für Materialien und Energie GmbH; Hahn-Meitner-Platz 1 D-14109 Berlin Germany
4. Department of Chemistry; University of Turku; FI-20014 Turku Finland
5. Optoelectronics Research Centre; Tampere University of Technology; FI-33101 Tampere Finland