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Investigations on the Aluminum/Para-Hexaphenyl Interface in Light Emitting Devices

Published online by Cambridge University Press:  10 February 2011

N. Koch ,
L.-M. Yu ,
J.-L. Guyaux ,
Y. Morciaux ,
G. Leising ,
J.-J. Pireaux  and
G. Demoustier
N. Koch
Affiliation:
Institut für Festkörperphysik, Technische Universität Graz, A-8010 Graz, Austria
L.-M. Yu
Affiliation:
L.I.S.E., University of Namur, B-5000 Namur, Belgium
J.-L. Guyaux
Affiliation:
L.I.S.E., University of Namur, B-5000 Namur, Belgium
Y. Morciaux
Affiliation:
L.A.R.N., University of Namur, B-5000 Namur, Belgium
G. Leising
Affiliation:
Institut für Festkörperphysik, Technische Universität Graz, A-8010 Graz, Austria
J.-J. Pireaux
Affiliation:
L.I.S.E., University of Namur, B-5000 Namur, Belgium
G. Demoustier
Affiliation:
L.A.R.N., University of Namur, B-5000 Namur, Belgium
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Abstract

Blue light emitting devices (LED) with para-hexaphenyl (PHP) as the active material and aluminum as cathode exhibit very high quantum efficiencies. To further optimize device performance it is crucial to understand the physical properties of the involved interfaces. We have performed Rutherford-Backscattering experiments on actual devices to show the importance of oxygen in the interface formation at the cathode as this leads to the formation of a layer of AlxOy between PHP and aluminum. In devices, where the organic film is exposed to air before the metal electrode is evaporated, an insulating layer on the metal-side therefore is inherent. It has been shown that the introduction of an intermediate layer between active material and electrodes results in a higher quantum efficiency of the LED, the most common concepts being charge-transport-layers, or insulators on the other hand. Our results underline the need for a better control of the LED processing. Ultraviolet- and X-ray photoelectron spectroscopy in situ growth studies of thin aluminum films on PHP have been made to reveal the change in the electronic structure of the active medium in a LED in the absence of oxygen. Also the direct interaction of oxygen with this organic material is investigated by photoelectron spectroscopy.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 488: Symposium J – Electrical, Optical & Magnetic Properties of Organic IV , 1997 , 509
Copyright
Copyright © Materials Research Society 1998

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