Field dependent negative capacitance in small-molecule organic light-emitting diodes

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

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

Frequency dependent charge transport in organic light-emitting diodes, including marked negative capacitance (NC), is reproduced through an equivalent circuit model. The robustness of the model is tested through impedance spectroscopy characterization as a function of bias changes and layer thickness modifications. Correlations with current-voltage measurements reveal that the NC occurs once trap assisted space charge limited transport is reached. Through variation of the organic layer thicknesses, the magnitude of the NC response can be precisely tuned. In particular, increasing the thickness of the electron transport layer increases the NC magnitude, whereas hole transport layer thickness modifications have little effect on the magnitude of NC. Subsequent modeling indicates that alterations in the distribution of the electric field across the individual organic layers account for the observed variations in NC. In addition, it is found that the time constants for the inductive elements of the model increase with applied bias, unlike their capacitive counterparts, suggesting that an accumulation of charge at the organic/organic interface is responsible for both the increasing NC and redistribution of the applied field.

Original languageEnglish
Article number044502
JournalJournal of Applied Physics
Volume100
Issue number4
DOIs
Publication statusPublished - 2006

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light emitting diodes
capacitance
molecules
equivalent circuits
electrical measurement
time constant
space charge
traps
impedance
electric fields
spectroscopy
electrons

ASJC Scopus subject areas

  • Physics and Astronomy (miscellaneous)
  • Physics and Astronomy(all)

Cite this

Field dependent negative capacitance in small-molecule organic light-emitting diodes. / Pingree, L. S C; Russell, M. T.; Marks, Tobin J; Hersam, Mark C.

In: Journal of Applied Physics, Vol. 100, No. 4, 044502, 2006.

Research output: Contribution to journalArticle

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