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Injecting Inter-Layers and the Built-in Potential of Blue Polymer Light-Emitting Diodes

Published online by Cambridge University Press:  21 March 2011

Thomas M. Brown ,
Ian S. Millard ,
David J. Lacey ,
Jeremy H. Burroughes ,
Richard H. Friend  and
Franco Cacialli
Thomas M. Brown
Affiliation:
Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK.
Ian S. Millard
Affiliation:
CDT Ltd, Greenwich House, Madingley Road, Cambridge, CB3 OHJ, UK.
David J. Lacey
Affiliation:
CDT Ltd, Greenwich House, Madingley Road, Cambridge, CB3 OHJ, UK.
Jeremy H. Burroughes
Affiliation:
CDT Ltd, Greenwich House, Madingley Road, Cambridge, CB3 OHJ, UK.
Richard H. Friend
Affiliation:
Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK. CDT Ltd, Greenwich House, Madingley Road, Cambridge, CB3 OHJ, UK.
Franco Cacialli
Affiliation:
Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK.
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Abstract

The semiconducting-polymer/injecting-electrode heterojunction plays a crucial part in the operation of organic solid state devices. In polymer light-emitting diodes (LEDs), a common fundamental structure employed is Indium-Tin-Oxide/Polymer/Al. However, in order to fabricate efficient devices, alterations to this basic structure have to be carried out. The insertion of thin layers, between the electrodes and the emitting polymer, has been shown to greatly enhance LED performance, although the physical mechanisms underlying this effect remain unclear. Here, we use electro-absorption measurements of the built-in potential to monitor shifts in the barrier height at the electrode/polymer interface. We demonstrate that the main advantage brought about by inter-layers, such as poly(ethylenedioxythiophene)/poly(styrene sulphonic acid) (PEDOT:PSS) at the anode and Ca, LiF and CsF at the cathode, is a marked reduction of the barrier to carrier injection. The electro- absorption results also correlate with the electroluminescent characteristics of the LEDs.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 660: Symposia JJ – Organic Electronic & Photonic Materials and Devices , 2000 , JJ6.9
Copyright
Copyright © Materials Research Society 2001

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