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Proceedings Paper

Origin of efficient hole injection from conducting polymer anodes into organic light-emitting diodes
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Paper Abstract

We studied hole injection from the conducting polymer blend poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) by optical spectroscopy and characterization of organic light-emitting diodes (OLEDs). Electroabsorption (EA) spectroscopy was used to measure the built-in potential of polyfluorene-based OLEDs with indium tin oxide (ITO) or poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) anodes. Although the work function of PEDOT:PSS is 5.1 eV, the inferred anode work function matches the ionization potential of the emitting polymer. We conclude that the Fermi level at the PEDOT:PSS/polyfluorene interface is pinned to the highest-occupied molecular orbital (HOMO) of the emitting polymer, permitting efficient hole injection. To test this hypothesis, we fabricated OLEDs using the archetypical molecular semiconductor, tris(8-hydroxyquinoline) aluminum (III) (Alq3). Although the anticipated hole injection barrier is 0.7 eV, OLEDs with Alq3 deposited onto PEDOT:PSS operate at a lower bias and higher power efficiency than OLEDs with a hole transport layer. The quantum efficiency of single layer Alq3 and rubrene-doped Alq3 devices is equal to that of multi-layer devices, showing that EL is not quenched by PEDOT:PSS.

Paper Details

Date Published: 17 September 2007
PDF: 10 pages
Proc. SPIE 6643, Physical Chemistry of Interfaces and Nanomaterials VI, 664307 (17 September 2007); doi: 10.1117/12.742676
Show Author Affiliations
Paul A. Lane, Naval Research Lab. (United States)
Paul J. Brewer, Imperial College, London (United Kingdom)
Gary P. Kushto, Naval Research Lab. (United States)
Zakya H. Kafafi, Naval Research Lab. (United States)
John C. de Mello, Imperial College, London (United Kingdom)

Published in SPIE Proceedings Vol. 6643:
Physical Chemistry of Interfaces and Nanomaterials VI
Piotr Piotrowiak; Garry Rumbles, Editor(s)

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