Impedance spectroscopy of single- and double-layer polymer light-emitting diode

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Abstract
Ac electrical properties of the heterostructured polymer light-emitting diode consisting of poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH–PPV) and sodium sulfonated polystyrene (SSPS) ionomer are studied. It is found that the carrier in SSPS is not the ion but the electron, and the conduction mechanism seems to be a space-charge limited current with exponential trap distribution. Based on the results of the impedance analysis, we propose a microscopic model to explain the enhancement of the electroluminescence efficiency of the indium tin oxide/MEH–PPV/SSPS/Al structure.