Regensburg 2013 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 8: Charge Transfer Effects in Molecular Materials II (jointly with BP, CPP, HL)
DS 8.7: Hauptvortrag
Montag, 11. März 2013, 17:00–17:30, H40
The role of intermolecular hybridization in molecular electrical doping — •Ingo Salzmann1, Georg Heimel1, Henry Méndez1, Andreas Opitz1, Patrick Barkowski1, Martin Oehzelt2,1, Katrein Sauer1, and Norbert Koch1,2 — 1Humboldt Universität zu Berlin — 2Helmholtz Zentrum Berlin, Germany
Molecular electrical doping of functional organic semiconductor (OSC) films is typically done by the admixture of strong molecular donors/acceptors as dopants. In a recent combined experimental and theoretical study on prototypical OSC/dopant pairs we showed that positive polarons, evidencing the common perception of direct electron transfer between the highest occupied molecular orbital (HOMO) of the OSC and the lowest unoccupied molecular orbital (LUMO) of the p-dopant, are not observed in ultraviolet photoelectron spectroscopy even at considerable dopant ratios [1]. Instead of mutual ionization leading to singly occupied states, frontier molecular orbital hybridization between the OSC-HOMO and the dopant-LUMO occurs forming a doubly occupied bonding and an empty anti-bonding supramolecular hybrid orbital with a reduced fundamental gap, which is tunable by the acceptor strength. As all available states are occupied following Fermi-Dirac statistics, only a fraction of the hybrids is ionized at room temperature rationalizing the high dopant concentrations in practical applications. From this model, controlling the degree of hybridization emerges as strategy for the design of future improved molecular dopants in organic electronic devices.
I. Salzmann, G. Heimel et al., Phys. Rev. Lett. 108, 035502, 2012.