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Research Letters in Materials Science
Volume 2009, Article ID 503042, 4 pages
Research Letter

Polymer Light-Emitting Diodes Efficiency Dependence on Bipolar Charge Traps Concentration

1Departamento de Física, Universidade de Trás-os-Montes e Alto Douro, Apartado 1013, 5001-801 Vila Real, Portugal
2Instituto de Telecomunicações, Instituto Superior Técnico, Avenida Rovisco Pais, 1049-001 Lisboa, Portugal
3Departamento de Engenharia Química e Biológica, Instituto Superior Técnico, Avenida Rovisco Pais, 1049-001 Lisboa, Portugal

Received 10 February 2009; Accepted 8 July 2009

Academic Editor: Maria Loi

Copyright © 2009 Luis Morgado et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The efficiency of light-emitting diodes (LEDs) based on poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-1,4-benzo- { 2, 1 -3 } -thiadiazole)], F8BT, is optimized upon simultaneous doping with a hole and an electron trapping molecule, namely, N, N -Bis(3-methylphenyl)-N, N -diphenylbenzidine and 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole, respectively. It is shown that, for devices with poly(3,4-ethylene dioxythiophene) doped with polystyrene sulfonic acid as hole-injection layer material and magnesium cathodes, the efficiency is nearly doubled (from ca. 2.5 to 3.7 cd/A) upon doping with ca. 0.34% by weight of both compounds.