Dresden 2003 – wissenschaftliches Programm
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CPP: Chemische Physik und Polymerphysik
CPP 20: POSTER A
CPP 20.59: Poster
Montag, 24. März 2003, 19:00–21:00, ZEU/250
Metal versus Polymer Electrodes in Organic Devices: Energy Level Alignment, Hole Injection, and Structure — •Norbert Koch1, Bert Nickel2, Jacques Ghijsen3, Andreas Elschner4, Jean-Jacques Pireaux3, and Antoine Kahn2 — 1Institut für Physik, Humboldt-Universität zu Berlin, D-10115 Berlin — 2Princeton Materials Institute, Princeton University, Princeton, NJ 08544, USA — 3LISE, FUNDP, B-5000 Namur, Belgium — 4H.C. Starck GmbH, c/o Bayer AG Uerdingen, D-47829 Krefeld
We have investigated the electronic, structural, and charge injection properties of interfaces formed between three conjugated organic materials, i.e., N,N’-bis-(1-naphthyl)-N,N’-diphenyl1-1,1-biphenyl1-4,4’-diamine (NPB), pentacene, p-sexiphenyl, and two high work function electrode materials, i.e., gold and the conducting polymer poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS). Ultraviolet photoelectron spectroscopy shows that the hole injection barrier between the three organic materials and PEDOT/PSS is lower by 0.6-1.0 eV as compared to Au, despite a similar work function of the pristine electrode material surfaces (ca. 5 eV). This very large difference is due to an effective change of the metal work function due to the deposition of organic molecules. Model device structures show much higher current densities for hole injection from PEDOT/PSS than from Au. Hole injection from Au for NPB devices is independent of deposition sequence and substrate. Pentacene devices exhibit significant asymmetries in that respect, due to a strong dependence of the preferred molecular orientation on the substrate.