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

Paul A. Lane; Paul J. Brewer; Gary P. Kushto; Zakya H. Kafafi; John C. de Mello

doi:10.1117/12.742676

17 September 2007 Origin of efficient hole injection from conducting polymer anodes into organic light-emitting diodes

Paul A. Lane, Paul J. Brewer, Gary P. Kushto, Zakya H. Kafafi, John C. de Mello

Proceedings Volume 6643, Physical Chemistry of Interfaces and Nanomaterials VI; 664307 (2007) https://doi.org/10.1117/12.742676
Event: NanoScience + Engineering, 2007, San Diego, California, United States

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.

Citation Download Citation

Paul A. Lane, Paul J. Brewer, Gary P. Kushto, Zakya H. Kafafi, and John C. de Mello "Origin of efficient hole injection from conducting polymer anodes into organic light-emitting diodes", Proc. SPIE 6643, Physical Chemistry of Interfaces and Nanomaterials VI, 664307 (17 September 2007); https://doi.org/10.1117/12.742676

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