title: Cyclohexane-Coupled Bipolar Host Materials with High Triplet Energies for Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence.
abstract: Thermally activated delayed fluorescence-based organic light-emitting diodes (TADF-OLEDs) have recently attracted tremendous research interest as next-generation optoelectronic devices. However, there are a limited number of host materials with an appropriately high lowest-excited triplet energy (ET) and bipolar charge transport properties for high-efficiency TADF-OLEDs. Moreover, these host materials should have high thermal and morphological stabilities. In this study, we develop novel bipolar host materials consisting of an electron-donating 9-phenylcarbazole unit and an electron-accepting triphenylphosphine oxide, triphenylphosphine sulfide, or 2,4,6-triphenyl-1,3,5-triazine unit linked by a nonconjugated cyclohexane core. These bipolar host materials possess high glass-transition temperatures of over 100 °C and high ETvalues of approximately 3.0 eV. TADF-OLEDs employing these bipolar host materials could achieve high external electroluminescence quantum efficiencies of up to 21.7% together with reduced efficiency roll-off characteristics, because of expansion of the charge-recombination zone within the emission layer arising from the bipolar charge transport ability of these host materials.
authors.forename: In Seob
authors.initials: IS
authors.lastname: Park
authors.affiliation: Department of Graphic Arts and Information Engineering, Pukyong National University , #100, Yong Dang-dong, Nam-gu, Busan 608-020, Korea.
authors.forename: Hongwook
authors.initials: H
authors.lastname: Seo
authors.forename: Hiroki
authors.initials: H
authors.lastname: Tachibana
authors.affiliation: Department of Graphic Arts and Information Engineering, Pukyong National University , #100, Yong Dang-dong, Nam-gu, Busan 608-020, Korea.
authors.forename: Joung Uk
authors.initials: JU
authors.lastname: Kim
authors.affiliation: Department of Graphic Arts and Information Engineering, Pukyong National University , #100, Yong Dang-dong, Nam-gu, Busan 608-020, Korea.
authors.forename: Jinbo
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Department of Graphic Arts and Information Engineering, Pukyong National University , #100, Yong Dang-dong, Nam-gu, Busan 608-020, Korea.
authors.forename: Se Mo
authors.initials: SM
authors.lastname: Son
authors.forename: Takuma
authors.identifier: http://orcid.org/0000-0003-1586-4701
authors.initials: T
authors.lastname: Yasuda
keywords: bipolar hosts; high triplet energy; organic light-emitting diodes; phosphine sulfide; thermally activated delayed fluorescence