Berlin 2008 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 19: Organic Interfaces (SYSA 6)
DS 19.8: Vortrag
Mittwoch, 27. Februar 2008, 16:30–16:45, H 2013
Hole injection barrier optimization at ITO/organic interfaces modified with strong molecular acceptors — •Ralf-Peter Blum1, Benjamin Bröker1, Steffen Duhm1, Antje Vollmer2, Ralph Rieger3, Hans Joachim Räder3, Klaus Müllen3, Jürgen P. Rabe1, and Norbert Koch1 — 1Institut für Physik, Humboldt-Universität zu Berlin, Newtonstrasse 15, D-12489 Berlin, Germany — 2Berliner Elektronenspeicherring-Gesellschaft für Synchrotronstrahlung mbH, D-12489 Berlin, Germany — 3Max Planck Institut for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany
The hole injection barriers at interfaces between N,N'-diphenyl-N,N'-bis(1-naphthyl)-1-1'biphenyl-4,4''diamine (α-NPD) and chemically modified ITO substrates have been studied by ultraviolet photoelectron spectroscopy (UPS). A decreased hole injection barrier was achieved by an appropriate arrangement of oriented dipoles, formed by chemisorption of strong electron acceptors, i.e., tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) or hexacyano-hexaazatriphenylene [HAT-(CN)]. In both cases thin acceptor layers induce coverage dependent work function shifts of more than 1 eV, thereby modifying the barrier to hole injection into α-NPD by up to 0.4 eV. We observed a linear dependence of the hole injection barrier versus the work function of modified ITO substrates. However, we find constant hole injection barriers for substrate work functions greater than 5.1 eV caused by localized states at the interface. This work is financially supported by the European Community project "IControl" (EC-STREP-033197).