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Proceedings Paper

Bright and efficient blue light-emitting diodes based on conjugated polymer blends
Author(s): Leonidas C. Palilis; David G. Lidzey; Michael Redecker; Donal D. C. Bradley; Michael Inbasekaran; Edmund P. Woo; Weishi W. Wu
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Paper Abstract

We report on the fabrication and properties of single layer blue light-emitting diodes (LEDs) based on conjugated polymer blends. We have used poly(9,9-dioctylfluorene) (PFO) as the host and a hole transport triarylamine/fluorene copolymer as the guest. Despite the fact that the photoluminescence quantum efficiency of the blend is lower compared than that of the host and guest polymers on their own, an enhancement in both the electroluminescence quantum and power efficiency is seen for the blend. This observation indicates that the hole transport material leads to a significant improvement in hole injection and transport and a greatly improved charge carrier balance factor. A careful comparison of the photoluminescence and the electroluminescence spectra reveals that more emission originates from the guest polymer for electroluminescence than for photoluminescence. This can be rationalized by the expectation that both Forster transfer and charge transfer from the host to the guest occur under electrical operation of the device. Only Forster transfer is expected for optical excitation. A much higher brightness and a lower turn on and operating voltage is achieved for the blend. The emission from our optimized blue single layer LED reaches a maximum brightness of 1550 cd/m2 and has a maximum external quantum efficiency of .4% and a maximum power efficiency of 0.3 lm/W.

Paper Details

Date Published: 17 December 1999
PDF: 15 pages
Proc. SPIE 3797, Organic Light-Emitting Materials and Devices III, (17 December 1999); doi: 10.1117/12.372734
Show Author Affiliations
Leonidas C. Palilis, Univ. of Sheffield (United States)
David G. Lidzey, Univ. of Sheffield (United Kingdom)
Michael Redecker, Univ. of Sheffield (Germany)
Donal D. C. Bradley, Univ. of Sheffield (United Kingdom)
Michael Inbasekaran, Dow Chemical Co. (United States)
Edmund P. Woo, Dow Chemical Co. (United States)
Weishi W. Wu, Dow Chemical Co. (United States)

Published in SPIE Proceedings Vol. 3797:
Organic Light-Emitting Materials and Devices III
Zakya H. Kafafi, Editor(s)

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