Formation of donor-acceptor complex by co-deposition of Zn-tetra-phenyl-porphyrin and C: molecular interaction and charge transfer time of excited charges.

paolo, vilmercati1; castellarin-cudia, carla1; petaccia, luca1; silvano, lizzit1; guillermo, zampieri2; rossanna, larciprete1; luigi, sangaletti1; stefania, pagliara1; albano, cossaro1; alberto, verdini1; alberto, morgante1; cinzia, cepek1; andrea, goldoni1 1Italy; 2Argentina

The technology for the production of efficient and low cost solar cells is routing the basic research through the study of organic molecules that mime efficient biological processes such as the chlorophyllian synthesis. In this process the chlorophyll is a light to current converter for the sugar to oxygen and carbon dioxide synthesis to occur. So chlorophyll-like molecules are good candidate for light to current conversion in devices, i.e. solar cells. For this reason we are studying complexes made by porphyrin (chlorophyll like molecules) that are good light absorber and charge donors, and fullerene C, that is a good charge acceptor, to create a local p-n junction where the pophyrin excited electron can rapidly delocalize to the fullerene braking the exciton. We demonstrate that a donor-acceptor complex where the molecules self-assemble in a local ordered fashion can be formed by co-evaporating in UHV two molecular beams of Zn-tetra-phenyl-porphyrin and C, respectively, on the Si(110) surface. Using linearly polarized synchrotron radiation we performed photoemission (UPS and XPS) and polarization dependent x-ray absorption to characterize the electronic states and the relative molecular orientations. Finally, resonant photoemission is used to probe, with chemical sensitivity, the time scale of the excited charge delocalization.

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