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Fluorinated Poly(N-vinylcarbazole) Host for Triplet Energy Confinement on Phosphorescent Emitter in Organic Light-emitting Diodes

Published online by Cambridge University Press:  31 January 2011

Yukitami Mizuno ,
Isao Takasu ,
Shuichi Uchikoga ,
Shintaro Enomoto ,
Tomoaki Sawabe ,
Akio Amano ,
Atsushi Wada ,
Jiro Yoshida  and
Tomio Ono
Yukitami Mizuno
Affiliation:
[email protected], Toshiba corp., Corporate Research & Development Center, Kawasaki, Japan
Isao Takasu
Affiliation:
[email protected], Toshiba corp., Corporate Research & Development Center, Kawasaki, Japan
Shuichi Uchikoga
Affiliation:
[email protected], Toshiba corp., Toshiba Research Europe, Ltd, Kawasaki, Japan
Shintaro Enomoto
Affiliation:
[email protected], Toshiba corp., Corporate Research & Development Center, Kawasaki, Japan
Tomoaki Sawabe
Affiliation:
[email protected], Toshiba corp., Corporate Research & Development Center, Kawasaki, Japan
Akio Amano
Affiliation:
[email protected], Toshiba corp., Corporate Research & Development Center, Kawasaki, Japan
Atsushi Wada
Affiliation:
[email protected], Toshiba corp., Corporate Research & Development Center, Kawasaki, Japan
Jiro Yoshida
Affiliation:
[email protected], Toshiba corp., Corporate Research & Development Center, Kawasaki, Japan
Tomio Ono
Affiliation:
[email protected], Toshiba corp., Corporate Research & Development Center, Kawasaki, Japan
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Abstract

Fluorinated carbazoles as host materials have been investigated for highly efficient organic light emitting diodes (OLEDs). By molecular orbital calculations, we found that fluorinations at position 2, 4, 5 and 7 of carbazole ring were effective for widening HOMO-LUMO energy gap. The energy gaps of our synthesized 2,7-difluorocarbazole (F2-Cz) and 2,4,5,7-tetrafluorocarbazole (F4-Cz), were estimated to be 3.71 eV and 3.87 eV by the absorption spectra, respectively. These energy gaps were higher than that of the non-substituted carbazole (Cz, 3.59 eV). We synthesized poly(N-vinyl-2,7-difluorocarbazole) (F2-PVK) and poly(N-vinyl-2,4,5,7-tetrafluorocarbazole) (F4-PVK) as solution processable polymer host materials. However, the F4-PVK was found to be an unsolved polymer. The F2-PVK could be compared with non substituted poly(N-vinylcarbazole) (PVK) in OLEDs. The emission layer (EML) contained iridium(III) bis [(4,6-di-fluorophenyl)-pyridinato-N,C2′] picolinate (FIrpic) as a blue phosphorescent dopant, and iridium(III) bis [2-(9,9-dihexylfluorenyl)-1-pyridine] acetylacetonate as a yellow dopant. The white OLED with the F2-PVK showed 1.4 times higher luminous current efficiency (24 cd/A) than the PVK (17 cd/A). These data show that the excitation energy is confined on dopants by using fluorinated polymer host material with higher T1 corresponding to wider HOMO-LUMO energy gap.

Keywords

luminescencepolymersolution deposition
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1197: Symposium D – Organic Materials for Printable Thin-Film Electronic Devices , 2009 , 1197-D02-08
Copyright
Copyright © Materials Research Society 2010

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