Monitoring interface traps in operating organic light-emitting diodes using impedance spectroscopy

L. S.C. Pingree, M. T. Russell, T. J. Marks, M. C. Hersam*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


Electronic trap densities at the indium tin oxide (ITO)/hole transport layer (HTL) interface in operating organic light-emitting diodes (OLEDs) are characterized in situ using impedance spectroscopy. For OLEDs with a high density of active trap states, negative values of the frequency derivative of resistance are clearly observable for frequencies on the order of 10 kHz, whereas positive values are observed when the trap density is low With this technique, it is revealed that the trap density is minimized via the introduction of a TPD-Si2 (4,4′-bis[(p-trichlorosilylpropylphenyl) phenylamino]-biphenyl) passivation layer at the ITO/HTL interface or by the application of large electric fields during device operation. Furthermore, impedance spectroscopy illustrates that the ITO/HTL interface is not a simple series resistance when traps are present since they are shown not to contribute to high frequency conduction. Overall, this paper demonstrates that the parasitic effects of interface traps can mask the underlying negative capacitive transport in OLEDs and presents a technique capable of monitoring the trap density of buried interfaces in organic electronic devices.

Original languageEnglish (US)
Pages (from-to)4783-4787
Number of pages5
JournalThin Solid Films
Issue number11
StatePublished - Apr 9 2007


  • Indium tin oxide
  • Negative capacitance
  • Optoelectronic devices
  • Surface and interface states

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Metals and Alloys
  • Materials Chemistry


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