Berlin 2005 – wissenschaftliches Programm
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SYOO: Organic Optoelectronics and Photonics
SYOO 2: Optoelectronic Properties
SYOO 2.3: Vortrag
Montag, 7. März 2005, 12:00–12:15, TU C130
Work Function Independent Hole Injection Barriers Between Pentacene and Conducting Polymers — •Norbert Koch1, Andreas Elschner2, Robert L. Johnson3, and Jürgen P. Rabe1 — 1Humboldt-Universität zu Berlin, Institut f. Physik, Newtonstr. 15, D-12489 Berlin — 2H. C. Starck GmbH, c/o Bayer AG, D-51368 Leverkusen — 3Universität Hamburg, Institut f. Experimentalphysik, D-22761 Hamburg
The interface formation between conducting polymers, containing poly(3,4-ethylenedioxythiophene) (PEDT) and sulfonate moieties, and pentacene was studied by ultraviolet photoelectron spectroscopy (UPS) and atomic force microscopy. By employing in situ polymerized PEDT, PEDT with sulfonate moieties on the side chain, and dispersions of PEDT and poly(styrenesulfonic acid), the work function Φ of pristine polymer films could be varied from 4.25 - 5.15 eV. After the deposition of pentacene UPS results show that the hole injection barrier Δ at interfaces between these polymers and pentacene (ca. 0.35 eV) is virtually independent of the initial Φ. This is in marked contrast to interfaces between metals and pentacene, where Δ varies significantly with metal Φ. A chemical reaction between pentacene and PEDT cations is proposed to lead to a pinning of pentacene molecular levels relative to the Fermi-level. These results are of paramount relevance for novel conductive polymers: increasing conductive polymer Φ does not implicitly lead to smaller Δ.