Dresden 2011 – scientific programme

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O: Fachverband Oberflächenphysik

O 10: Metal substrates: Adsorption of organic / bio molecules II

O 10.8: Talk

Monday, March 14, 2011, 16:45–17:00, TRE Phy

Exciton dynamics at oligothiophene / Au(111) interfaces — •Erwan Varene, Isabel Martin, Christopher Bronner, Lea Bogner und Petra Tegeder — Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany

Semiconducting materials based on organic molecules or polymers are promising candidates for applications in electronic devices such as organic photovoltaic cells. The electronic structure and carrier dynamics at interfaces between organic semiconductors and inorganic substrates are the most fundamental issues in order to understand the functionalities of organic films. Time-resolved two-photon photoemission (2PPE) spectroscopy is employed to determine the electronic structure, charge carrier dynamics and energetics at the sexithiophene (6T)/Au(111) interface. We found the HOMO and HOMO-1 to be located at -0.8 and -1.5 eV, respectively and two 6T-derived unoccupied states at 2.1 eV and 3.0 eV with respect to the Fermi level which we assign to the LUMO and LUMO +1. In addition an exciton state possessing a binding energy of 0.9 eV is observed. The timescale for the exciton breakup exhibits a strong 6T coverage dependency, i.e., the exciton lifetime increases with increasing coverage. For instance at a coverage 12 ML the decay times are around 700 fs for the fast component and ~ 5 ps for the slow component.