VUV photoemission using synchrotron light: a tool for characterising surfaces and interfaces occurring in OLEDs

Jacques Ghijsen 1Robert L. Johnson 4Andreas Elschner 3Norbert Koch 2

1. University of Namur, Laboratoire Interdisciplinaire de Spectroscopie Electronique (LISE), 61 rue de Bruxelles, Namur 5000, Belgium
2. Humboldt-Universität, Newtonstr. 15, Berlin 12489, Germany
3. H.C. Starck GmbH, c/o Bayer AG Uerdingen, Krefeld, Germany
4. University of Hamburg, Institute for Experimental Physics, Luruper Chausse 149, Hamburg D-22761, Germany

Abstract

In principle, organic light-emitting diodes (OLEDs) just need one layer of appropriate material sandwiched between two metal electrodes in order to create light when the device is polarized. Real life is more complicated: in order to create a long-lived (> 10,000 hr) and efficient device (tens of lm/W), it is necessary to use more complex structures involving additional layers. Just as with more conventional inorganic devices, it is important to monitor the interfaces in order to identify possible reactions between the materials involved, to check for interdiffusion, and to determine the alignment of electronic levels.

Photoelectron spectroscopy is a well-suited technique for addressing these questions. Because the interfaces encountered in such devices often involve a metal on one side and an oligomer or a polymer on the other side, it is in many cases convenient to use a tuneable light source in order to balance properly the photoemission cross sections of the different levels involved in the valence band.

The use of the technique will be illustrated by considering the case of pentacene and low-work-function metals (samarium and alkali metals), in the cases of the growth of a metal film on pentacene as well as the deposition of pentacene on metal. This will be put in parallel with a study of interfaces with high-work-function materials, such as gold or poly(3,4-ethylenedioxythiophene/polystyrenosulfonate, and three different conjugated organic materials: N,N'-bis-(1-naphthyl)-N,N'-diphenyl1-1,1biphenyl1-4,4'-diamine, para-sexiphenyl, and pentacene.

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Presentation: invited oral at E-MRS Fall Meeting 2003, Pre-School of Symposium B, by Jacques Ghijsen
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-06-17 14:35
Revised:   2009-06-08 12:55
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