Regensburg 2010 – scientific programme
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DS: Fachverband Dünne Schichten
DS 17: [CPP] Organic Electronics and Photovoltaics II (Joint Session DS/CPP/HL/O)
DS 17.2: Talk
Tuesday, March 23, 2010, 14:00–14:15, H37
The Localized Nature of Charge Transfer in F4TCNQ-Doped Thiophene-Based Donor Polymers — •Patrick Pingel1, Lingyun Zhu2, Kue Surk Park1, Jörn-Oliver Vogel1, Silvia Janietz3, Eung-Gun Kim2, Jürgen P. Rabe1, Jean-Luc Brédas2, and Norbert Koch1 — 1Department of Physics, Humboldt University Berlin, Germany — 2School of Chemistry and Biochemistry, and Center for Organic Photonics and Electronics, Georgia Institute of Technology, USA — 3Fraunhofer IAP, Potsdam, Germany
Recently, polymer layers exhibited exceptionally high conductivities upon p-type doping with the molecular acceptor tetrafluorotetracyanoquinodimethane (F4TCNQ). Here, we present experimental and theoretical results on blend layers of F4TCNQ and a series of poly(3-hexylthiophene-co-dithienyltetrafluorobenzene) (P3HT-TFT) copolymers with systematically varied TFT content. Regardless of the amount of TFT in the donor polymer, we find that only a single charge transfer (CT) species is formed, which we assign to the interaction of F4TCNQ with an oligothiophene segment of the main chain. The degree of CT remains constant, even if the dopant concentration is increased up to a point, where closely neighbouring CT complexes exist at the same uninterrupted thiophene segment. Our findings show that the CT between F4TCNQ and an oligothiophene segment has a localized, isolated nature, possibly comprising less than five connected thiophene units. Thus, CT is dictated by the local electronic structure on the nm scale, rather than depending, e.g., on the macroscopic ionization potential determined from photoemission methods.