1. Department of Materials Science, University of Milano-Bicocca and INSTM, Via R. Cozzi 55, I-20125 Milan, Italy
2. CHOSE (Centre for Hybrid and Organic Solar Energy), Department of Electronic Engineering, University of Rome Tor Vergata, Via del Politecnico 1, I-00133 Rome, Italy
3. Department of Materials Science, University of Milano-Bicocca, Via R. Cozzi 55, I-20125 Milan, Italy