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Applied Physics Letters / Volume 93 / Issue 2 / ORGANIC ELECTRONICS AND PHOTONICS
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Appl. Phys. Lett. 93, 023309 (2008); http://dx.doi.org/10.1063/1.2955527 (3 pages)

Reduced efficiency roll-off in phosphorescent organic light emitting diodes at ultrahigh current densities by suppression of triplet-polaron quenching

F. X. Zang1, T. C. Sum1, A. C. H. Huan1, T. L. Li2, W. L. Li2, and Furong Zhu3

1Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore
2Key Laboratory of Excited State Processes, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, People’s Republic of China and Graduate School of Chinese Academy of Sciences, Beijing 100039, People’s Republic of China
3Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602, Singapore

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(Received 15 April 2008; accepted 14 June 2008; published online 18 July 2008)

High-performance phosphorescent organic light emitting devices with reduced efficiency roll-off at ultrahigh current densities were realized. The devices were Ir(ppy)3-based phosphorescent organic light emitting diodes that employed 1,3-bis[2-(2,2′-bipyridine-6-yl)-1,3,4-oxadiazo-5-yl]benzene as a high mobility electron transfer layer. The device’s brightness was enhanced while the efficiency roll-off was reduced. The device exhibits high current efficiency (21 cd/A) at high brightness (80 000 cd/m2), with a maximum luminescence of 136 000 cd/m2 at over 1 A/m2 (with an efficiency of 13 cd/A). This reduction in efficiency roll-off is attributed to the suppression of the triplet-polaron quenching rate through balancing the charge carrier ratio in the device.

© 2008 American Institute of Physics

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KEYWORDS and PACS

Keywords

brightness, current density, luminescence, organic light emitting diodes, organic semiconductors, phosphorescence, polarons, triplet state

PACS

ARTICLE DATA

Digital Object Identifier
http://dx.doi.org/10.1063/1.2955527

PUBLICATION DATA

ISSN

0003-6951 (print)  
1077-3118 (online)

Publisher

$abstract.society.value is a Member of CrossRef American Institute of Physics

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Figures (click on thumbnails to view enlargements)

FIG.1
Chemical structures of (a) Bpy-OXD and (b) 2-TNATA. (c) A schematic of the device configuration.

FIG.1 Download High Resolution Image (.zip file) | Export Figure to PowerPoint

FIG.2
The current-voltage and voltage-brightness relationship of ITO/2TNATA/NPB/TCTA/CBP:Ir(ppy)3 (6%)/ hole block and ETLs (1,2,4)/LiF/Al. (Devices 1: BCP 40 nm; 2: Bpy-OXD 40 nm; 4: BCP/Alq3 10/30 nm).

FIG.2 Download High Resolution Image (.zip file) | Export Figure to PowerPoint

FIG.3
(a) Current density–current efficiency relationship of devices 1–4. The Inset shows a close-up of the initial current density–current efficiency relationship. (b) A schematic illustrating the dynamic interplay between the exciton and h+ formation processes, and TTA and TP quenching processes.

FIG.3 Download High Resolution Image (.zip file) | Export Figure to PowerPoint

FIG.4
(a) Luminescence–current efficiency curve of devices 1–4. (b) Graph of the current efficiency–electric field relationship for device 3 (BCP/Bpy-OXD) and device 4 (BCP/Alq3).

FIG.4 Download High Resolution Image (.zip file) | Export Figure to PowerPoint



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