The role of surface plasmons in organic light-emitting diodes

• Published in: IEEE journal of selected topics in quantum electronics Vol. 8; no. 2; pp. 378 - 386
• Main Authors: Hobson, P.A., Wasey, J.A.E., Sage, I., Barnes, W.L.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.03.2002; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Cathodes; Electroluminescence; Light-emitting diodes; Mathematical models; Microcavities; Numerical models; Optical coupling; Optical losses; Optical surface waves; Organic light emitting diodes; Plasmons; Polymers; Stimulated emission; Wavelength measurement; Wavelengths
• ISSN: 1077-260X; 1558-4542
• DOI: 10.1109/2944.999193

Organic light-emitting diodes typically take the form of an optical microcavity in which one layer is a metallic cathode. Coupling between emissive species in the light emitting layer and surface plasmon (SP) modes associated with the metallic cathode result in a loss of efficiency; an aspect often discussed but not so far fully quantified. Here we numerically model the extent of this problem, both for organic light-emitting diodes based on small molecules (Alq/sub 3/) and those based on conjugated polymers (MEH-PPV). We show that SP modes can significantly detract from device efficiency, particularly those based on small molecules. We then report measurements of photo- and electroluminescence from organic light-emitting diodes incorporating wavelength scale periodic structure. These data demonstrate the existence of the SP modes in organic light-emitting diodes. Finally we consider ways in which the problems associated with SPs might be overcome, and may even be turned to advantage.