Regensburg 2016 – scientific programme
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DS: Fachverband Dünne Schichten
DS 55: Organic Thin Films III
DS 55.6: Talk
Friday, March 11, 2016, 11:00–11:15, H8
The energy levels in hole-doped molecular semiconductors — •Patrick Amsalem1, Stefanie Winkler1,2, Johannes Frisch1, Martin Oehzelt1,2, Georg Heimel1, and Norbert Koch1,2 — 1Institut für Physik & IRIS Adlershof, Humboldt-Universität zu Berlin — 2Helmholtz-Zentrum Berlin für Materialien und Energie GmbH
Understanding the energy level alignment in doped organic thin films is crucial in order to achieve rational design in opto-electronic organic devices. Here, we rely on interface doping phenomena as occurring at electrode / buffer layer / organic semiconductor to hole-dope a ultra-thin film C60 [1]. The present system is investigated by direct and inverse photoemission measurements and theoretical calculations based on density functional theory. The obtained results reveal a picture which differs strongly from the traditionally conceived one, i.e. where the energy levels consist of singly occupied molecular states lying within the energy gap of the semiconductor [2]. Instead, here we demonstrate that the on-site Coulomb repulsion splits the partially unoccupied frontier molecular level in the p-doped systems into two sub-levels [1]. The role of inter-site Coulomb interaction between molecular ions and neighbor molecules is further addressed and helps providing a complete picture of the electronic structure of molecular semiconductors in the presence of excess charges [1]. [1] S. Winkler, P. Amsalem, J. Frisch, M. Oehzelt, G. Heimel, N. Koch, Materials Horizons 2 (2015) 427. [2] J. L. Bredas and G. B. Street, Acc. Chem. Res. 18 (1985) 309.