Enhanced efficiency of multilayer organic light-emitting diodes with a low-refractive index hole-transport layer: An effect of improved outcoupling?

Anne Köhnen, Malte Christian Gather, Nina Riegel, Philipp Zacharias, Klaus Meerholz

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)

Abstract

The authors report on an internal device modification for multilayerorganic light-emitting diodes(OLEDs) with enhanced efficiency that promises high compatibility with conventional manufacturing processes. By copolymerization of a hole-conducting monomer with a compound possessing a lower refractive index, a hole-transport layer with reduced optical density but slightly reduced hole-transport properties is formed. MultilayerOLEDs based on this reduced-index layer show a 25% increased efficiency compared to reference devices. The results are compared to optical simulations of the dipole emission from thin organic films. It is found that the efficiency improvement is only to some extent due to enhanced outcoupling resulting directly from the reduced refractive index but primarily due to a change of the width of the emission zone.
Original languageEnglish
Pages (from-to)113501
Number of pages3
JournalApplied Physics Letters
Volume91
Issue number11
DOIs
Publication statusPublished - 10 Sept 2007

Keywords

  • Organic light emitting diodes
  • Refractive index
  • MULTILAYERS
  • ELECTROLUMINESCENCE
  • CATHODES

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