Elimination of hole injection barriers by conducting polymer anodes in polyfluorene light-emitting diodes

Paul A. Lane, Paul J. Brewer, Jingsong Huang, Donal D.C. Bradley, John C. DeMello

Research output: Contribution to journalArticlepeer-review

37 Scopus citations

Abstract

We have measured the built-in potential of a series of polyfluorene- containing light-emitting diodes (LEDs) by electroabsorption spectroscopy. When the anode incorporates a layer of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS), the inferred anode work function is equal to the ionization potential of the emissive polyfluorene. This result requires that the Fermi level of PEDOT:PSS is pinned to the highest occupied molecular orbital of the emissive polymer. Pinning of the anode Fermi level eliminates the injection barrier to holes and explains the low turn-on bias of polymer LEDs that incorporate PEDOT:PSS. We attribute this phenomenon to electron trapping at the interface between PEDOT:PSS and the emissive layer. © 2006 U.S. Government.
Original languageEnglish (US)
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume74
Issue number12
DOIs
StatePublished - Oct 2 2006
Externally publishedYes

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