Admittance spectroscopy of Indium Tin Oxide (ITO)-poly(3,4- ethylenedioxythiophene) (PEDOT)-polyfluorene-Al organic light emitting diodes is analyzed by varying PEDOT dispersion. Loss-frequency diagrams show one or two peaks. The results have been interpreted by using the Nicollian and Brews admittance model. Single level and multi level interface state distributions are found for each kind of PEDOT. Surface state density is about 1011 eV-1cm-2 for all distributions while the interface time constant varies between 471 s and 220 ns. Good agreement is found between experimental data and analytical model. The combined effect of PEDOT conductivity and the inferred interface state density is analyzed and discussed. © 2011 American Institute of Physics.
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