Dresden 2017 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 22: Organic Electronics and Photovoltaics II: Doping
HL 22.7: Talk
Monday, March 20, 2017, 17:00–17:15, ZEU 260
Redox-Potentials Outperform Ionization Energy / Electron Affinity for Predicting Ion Pair Formation in Molecular Electrical Doping — •Berthold Wegner1, Lutz Grubert2, Dennis Chercka3, Andreas Opitz4, Stefan Hecht2, Klaus Müllen3, and Norbert Koch1,4 — 1Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin, Germany — 2Institut für Chemie, Humboldt-Universität zu Berlin, Berlin, Germany — 3Max-Planck-Institut für Polymerforschung, Mainz, Germany — 4Institut für Physik & IRIS Adlershof, Humboldt-Universität zu Berlin, Berlin, Germany
Electrical doping with strong molecular donors and acceptors is a key technological component to control the charge carrier density and Fermi level of organic semiconductors. While commonly ionization energy / electron affinity values (measured on thin films via ultraviolet / inverse photoelectron spectroscopy) are employed to guide the selection of molecular dopants for organic hosts, we find strong indications that redox-potentials (measured in solution via cyclic voltammetry) are indeed better suited. A set of donor-acceptor systems, both in solution and in thin films, is studied using structurally similar molecules. Our results show that redox-potentials provide a useful basis to predict ion pair formation in the studied systems, while ionization energies / electron affinities fail to provide such a basis. This is ascribed to the molecular length scale dopant-host interaction well described by local redox events at the molecule-electrode interface, whereas thin film ionization and affinity level measurements include collective and long-range solid state properties.