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Proceedings Paper

High-efficiency fluorescent white organic light-emitting diodes using double hole-transporting-layers
Author(s): Jwo-Huei Jou; Shih-Ming Shen; Cheng-Chung Chen; Yu-Chiao Chung; Chun-Jan Wang; Mao-Feng Hsu; Wei-Ben Wang; Ming-Hsuan Wu; Chih-Jie Yang; Chi-Ping Liu
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Paper Abstract

High-efficiency fluorescent white organic light-emitting diodes (OLED) were fabricated by using double holetransporting- layers (HTLs), poly(3,4-ethylene- dioxythiophene)-poly-(styrenesulfonate) (PEDOT) and N,N'-bis-(1- naphthyl)-N,N'-diphenyl-1,10-biphenyl-4-4'-diamine (NPB). The diodes were composed of a single emissive-layer (EML), with 0.5 wt% red 4-(dicyanomethylene)-2-tbutyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran doped in a mixed-host of 25% trans-1,2-bis(6-(N,N-di-p-tolylamino)-Naphthalene-2-yl)ethene and 75% 1-butyl-9,10-naphthaleneanthracene. The device structure comprised a 125 nm anode layer of indium tin oxide, a 25 nm first HTL of PEDOT, a 0 to 10 nm second HTL of NPB, a 30 nm EML, a 40 nm electron-transporting-layer of 2,2',2"-(1,3,5-benzenetriyl)-tris(1- phenyl-1-H-benzimidazole), a 1 nm electron-injection-layer of lithium fluoride and a 150 nm cathode layer of aluminum. With the addition of a 7.5 nm second HTL (NPB), the resultant power-efficiency at 100 cd/m2, for example, was increased from 11.9 to 18.9 lm/W, an improvement of 59%. The improvement was even more marked at 1,000 cd/m2, i.e. that the power-efficiency was increased from 9.1 to 16.5 lm/W, an improvement of 81%. The marked efficiency improvement may be attributed to a better balance of carrier-injection in the desired emissive zone since the addition of the NPB layer in between the first HTL and the EML may have effectively reduced the injection of excessive holes into the EML due to the relatively high energy-barrier to hole, which was 0.5 eV, at the interface of the two HTLs. The resultant hole-blocking function was plausibly more effective at higher voltage so that comparatively much less holes would be injected into the EML, leading to a much better balanced carrier-injection and consequently a higher efficiency-improvement at the higher brightness.

Paper Details

Date Published: 16 April 2008
PDF: 8 pages
Proc. SPIE 6999, Organic Optoelectronics and Photonics III, 69992S (16 April 2008); doi: 10.1117/12.779509
Show Author Affiliations
Jwo-Huei Jou, National Tsing Hua Univ. (Taiwan)
Shih-Ming Shen, National Tsing Hua Univ. (Taiwan)
Cheng-Chung Chen, National Tsing Hua Univ. (Taiwan)
Yu-Chiao Chung, National Tsing Hua Univ. (Taiwan)
Chun-Jan Wang, National Tsing Hua Univ. (Taiwan)
Mao-Feng Hsu, National Tsing Hua Univ. (Taiwan)
Wei-Ben Wang, National Tsing Hua Univ. (Taiwan)
Ming-Hsuan Wu, National Tsing Hua Univ. (Taiwan)
Chih-Jie Yang, National Tsing Hua Univ. (Taiwan)
Chi-Ping Liu, National Tsing Hua Univ. (Taiwan)

Published in SPIE Proceedings Vol. 6999:
Organic Optoelectronics and Photonics III
Paul L. Heremans; Michele Muccini; Eric A. Meulenkamp, Editor(s)

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