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International Journal of Photoenergy
Volume 2012, Article ID 581421, 8 pages
Research Article

Improvement of Power Efficiency in Phosphorescent White Organic Light-Emitting Diodes Using p-Doped Hole Transport Layer

Department of Electrical Engineering and Computer Science, Inter-University Semiconductor Research Center, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-744, Republic of Korea

Received 14 July 2011; Revised 12 October 2011; Accepted 13 October 2011

Academic Editor: Raghu N. Bhattacharya

Copyright © 2012 Hyunkoo Lee 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.


We investigated the optical and electrical properties of molybdenum trioxide- (MoO3-) doped (1,1-bis[(di-4-tolylamino)phenyl]cyclohexane) (TAPC) films with different doping concentrations. Based on our results, we have fabricated white organic light emitting diodes (WOLEDs) with multi-emitting layer structures that consist of 1,3-bis(9-carbazolyl)benzene as a host and three phosphorescent dopants: iridium(III) bis[4,6-difluorophenyl]-pyridinato-N, C 2 ] picolinate as a blue dopant, bis(2-phenylbenxothiozolato-N, C 2 )iridium(III) (acetylacetonate) as an orange dopant, and bis(1-phenylisoquinoline) (acetylacetonate) iridium(III) as a red dopant. We improved the power efficiency and decreased driving voltage of WOLEDs by employing a MoO3-doped TAPC layer as a hole transport layer. The MoO3-doped TAPC layer lowers the driving voltage by about 1.2 V and increases the power efficiency from 6 . 2 l m W 1 to 7 . 9 l m W 1 at 1 , 0 0 0 c d m 2 , an approximately 27.4% increase. Furthermore, the WOLED has a high color-rendering index, which is about 86 with the Commission Internationale de l’Eclairage 1931 chromatic coordinates of (0.4303, 0.3893) and correlated color temperature of 3008 K.