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Proceedings Paper

Improving the efficiency and stability of organic light-emitting devices using mixed emitting layers
Author(s): Zoran D. Popovic; Hany Aziz; Carl P. Tripp; Nan-Xing Hu; Ah-Mee Hor; Gu Xu
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Paper Abstract

We studied an organic light emitting device (OLED) involving electroluminescence from a mixed layer consisting of a hole transport material (HTM) and an emitting electron transport material (ETM) and including thin electron and hole injection contacts. A naphthyl-substituted benzidine derivative (NPB) and tris (8-hydroxyquinoline) aluminum (ALQ3) are used as the HTM and the emitting ETM, respectively. Following a control-experiment approach, the efficiency and the operational lifetime of OLEDs adopting the new structure are compared to those of conventional bilayer devices made of the same materials and fabricated under the same conditions. Efficiency is calculated from the luminance-current density-voltage characteristics. Lifetime tests are carried at constant current density in dry air. Photoluminescence is used to detect changes in the quantum efficiency of the ALQ3 on mixing with the HTL. Compared to a conventional bilayer device, the new device structure leads to approximately 50 percent higher efficiency and an order of magnitude increase in the operational lifetime. The higher efficiency is attributed to (i) reduced leakage of charge carrier to the electrodes, (ii) exciton confinement away from the metal cathode, and (iii) higher quantum efficiency of the emitting electron transport material due to mixing with the hole transport material. Possible reasons for the higher stability are also discussed.

Paper Details

Date Published: 16 December 1998
PDF: 6 pages
Proc. SPIE 3476, Organic Light-Emitting Materials and Devices II, (16 December 1998);
Show Author Affiliations
Zoran D. Popovic, Xerox Research Ctr. of Canada (Canada)
Hany Aziz, McMaster Univ. (Canada)
Carl P. Tripp, Xerox Research Ctr. of Canada (Canada)
Nan-Xing Hu, Xerox Research Ctr. of Canada (Canada)
Ah-Mee Hor, Xerox Research Ctr. of Canada (Canada)
Gu Xu, McMaster Univ. (Canada)


Published in SPIE Proceedings Vol. 3476:
Organic Light-Emitting Materials and Devices II
Zakya H. Kafafi, Editor(s)

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