Jpn. J. Appl. Phys. 43 (2004) pp. L1226-L1228  |Previous Article| |Next Article|  |Table of Contents|
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Letter

Improved Performance of Electrophosphorescent Organic Light-emitting Diode by Graded Doped Emissive Layer

Gangtie Lei, Liduo Wang and Yong Qiu

Key Laboratory of Organic-Optoelectronics & Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084, China

(Received June 28, 2004; accepted July 16, 2004; published September 3, 2004)

We report a blue electrophosphorescent organic light-emitting diode (PHOLED) with performance improved by designing a graded doped emissive layer. The graded doped emissive layer is formed by doping a guest material, bis[(4,6-difluorophenyl)-pyridinato-N, C2'] (picolinato) Ir(III) (FIrpic), in the host material, N, N'-dicarbazolyl-1, 4-dimethene-benzene (DCB), with a gradient increase in concentration. The graded doped emissive layer PHOLED shows a peak power efficiency of 15.4 cd/A and a maximum brightness of 35000 cd/m2, a sharp increase compared to the conventional PHOLED which has a peak power efficiency of 8.7 cd/A and a maximum brightness of 17000 cd/m2. It is also noted that the efficiency of the graded doped device dropped slowly at high current density. We attribute this improvement mainly to the fact that the concentration distribution of guest material is in accord with that of electrons in the devices and the carrier recombination zone is adjusted away from the electrodes.

URL: http://jjap.jsap.jp/link?JJAP/43/L1226/
DOI: 10.1143/JJAP.43.L1226
KEYWORDS:electrophosphorescence, organic light-emitting diode, graded doped emissive layer


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