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Controlled Injection of Holes into ALQ3 Based Oleds by Means of An Oxidized Transport Layer

Published online by Cambridge University Press:  15 March 2011

Mathew K. Mathai ,
Keith A. Higginson ,
Bing R. Hsieh  and
Fotios Papadimitrakopoulos
Mathew K. Mathai
Affiliation:
Nanomaterials Optoelectronics Laboratory, Department of Chemistry, Polymer Program, Institute of Materials Science, 97 North Eagleville Road, University of Connecticut, Storrs, CT 06269
Keith A. Higginson
Affiliation:
Triton Systems, Inc., 200 Turnpike Rd, Chelmsford, MA 01824
Bing R. Hsieh
Affiliation:
Canon R&D Center Americas, Inc., 3300 North First Street, 3rd FL, San Jose, CA 95134
Fotios Papadimitrakopoulos*
Affiliation:
Nanomaterials Optoelectronics Laboratory, Department of Chemistry, Polymer Program, Institute of Materials Science, 97 North Eagleville Road, University of Connecticut, Storrs, CT 06269
*
To whom correspondence should be addressed: Tel: (860)-486-3447, Fax: (860)-486-4745, Email: [email protected]
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Abstract

In this paper we report a method for tuning the extent of hole injection into the active light emitting tris- (8-hydroxyquinoline) aluminum (Alq3) layer in organic light emitting diodes (OLEDs). This is made possible by modifying the indium tin oxide (ITO) anode with an oxidized transport layer (OTL) comprising a hole transporting polycarbonate of N,N'-bis(3-hydroxymethyl)-N,N'-bis(phenyl) benzidine and diethylene glycol (PC-TPB-DEG) doped with varying concentrations of antimonium hexafluoride salt of N,N,N',N'-tetra-p-tolyl-4,4'-biphenyldiamine (TMTPD+ SbF6 -). The conductivity of the OTL can be changed over three orders of magnitude depending on salt loading. The analysis of hole and electron current variations in these devices indicates that optimizing the conductivity of the OTL enables the modulation of hole injection into the Alq3 layer. The bipolar charge transport properties for OLEDs in which the interfacial carrier injection barriers have been minimized, are governed by the conductivities of the respective layers and in this case it is shown that the variable conductivity of the OTL does allow for better control of the same. Accordingly, varying the concentration of holes in the device indicates that beyond an optimum concentration of holes, further hole injection results in the formation of light quenching cationic species and the initiation of oxidative degradation processes in the Alq3 layer, thus accelerating the intrinsic degradation of these devices. The variable conductivity of the OTL can hence be used to minimize the occurrence of these processes.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 708: Symposium BB – Organic Optoelectronic Materials, Processing and Devices , 2001 , BB3.27
Copyright
Copyright © Materials Research Society 2002

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References

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