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The Research on Molecular Orientation and Characterization of the OLED Emitters

Title
The Research on Molecular Orientation and Characterization of the OLED Emitters
Authors
SOHN, SUN YOUNGPARK, KWANG HUNAHN, HYUNGJUJUNG, SUNGJUNEKWON, SOON-KIKIM, YUN-HI
POSTECH Authors
JUNG, SUNGJUNE
Date Issued
29-Nov-2018
Publisher
Material Research Society
Abstract
We analyzed the scattered X-ray intensities of the host and host:dopant emitters, which have the spectra of in-plane and out-of-plane scattering to the plane and azimuthal intensity profiles for a plot of orientation distribution using grazing incidence wide-angle X-ray diffraction (GI-WAXD) measurement for high-efficiency organic light-emitting diodes (OLEDs). In blue fluorescent emitters, we found that a non-doped anthracene derivatives have the highly rigid structure and thermal stability because pnaphthylxylene groups in 9,10-positions were highly twisted to anthracene core with steric hindrance of xylene groups. The OLEDs with non-doped emitter with 2,3-diphenyl groups showed high-efficiency of 5.21 cd/A due to enhanced carrier mobility with well-aligned π-stacking structure toward outof- plane by the face-on orientation by GI-WAXD analysis. In phosphorescent emitters, we have used the tetrahedral silicon-based host materials with electron transporting (ET) property and investigated on the preferential host orientation. The ET hosts had good morphological stability as well as balanced charge-carrier transport by pyridyl-substituted linker in the devices. The Ir(ppy)3-doped or Firpic-doped devices showed high-efficiency of 53.54 cd/A or 11.08 cd/A, respectively. In thermally activated delayed fluorescence emitters, we found that the molecular orientation of emitting materials with diphenylamine derivative containing malononitrile had different horizontal and/or random orientations as a function of para or meta linker position. It showed 12.5 times difference of the device efficiency. These improved device efficiency was confirmed by the enhanced out-coupling efficiency with wellaligned stacking structure in the emitters with horizontal molecular orientation to in-plane and out-of-plane analysis using GI-WAXD analysis. A study on the relationship between device characteristics and molecular orientation using GI-WAXD analysis for the emitting materials will contribute to basic research on molecular design for high efficiency OLEDs.
URI
http://oasis.postech.ac.kr/handle/2014.oak/94546
Article Type
Conference
Citation
2018 MRS Fall Meeting, page. 810 - 811, 2018-11-29
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Dept. of Creative IT Engin.
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