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Thermally crosslinked hole-transporting layers for cascade hole-injection and effective electron-blocking/exciton-confinement in phosphorescent polymer light-emitting diodes

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4 Author(s)
Niu, Yu-Hua ; Department of Materials Science and Engineering, University of Washington, Box 352120, Seattle, Washington 98195-2120 ; Liu, Michelle S. ; Ka, Jae-Won ; Jen, Alex K.-Y.

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A bilayer hole-injection/transport structure was prepared by thermally crosslinking two separate hole-transport layers (HTL). The resulting films possess excellent optical quality and solvent resistance. Cascade hole-injection and effective electron-blocking/exciton confinement can be achieved for light-emitting diodes (LEDs) using blue phosphorescent emitters, such asbis(4,6-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate. The first HTL was based on tetraphenyldiamine (TPD) has its highest occupied molecular orbit (HOMO) level lies at -5.3 eV, and the second HTL with 4,4,4-tri(N-carbazolyl)triphenylamine has its HOMO level lies at -5.7 eV. The preliminary results from blue LEDs using these cascade HTLs showed much improved device performance than those only use a single layer hole-transporting polymer.

Published in:

Applied Physics Letters  (Volume:88 ,  Issue: 9 )