title: Triphenylsilyl- and trityl-substituted carbazole-based host materials for blue electrophosphorescence.
abstract: Carbazole-based materials adopting the nonconjugated substitution of triphenylsilyl (-SiPh(3)) and trityl (-CPh(3)) side groups are studied as high-triplet-energy, morphologically, and electrochemically stable host materials with tunable carrier-transport properties for organic blue electrophosphorescence. The developed host materials 9-(4-tert-butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole (CzSi), 9-(4-tert-butylphenyl)-3,6-ditrityl-9H-carbazole (CzC), and 9-(4-tert-butylphenyl)-3-(triphenylsilyl)-6-trityl-9H-carbazole (CzCSi) all show high triplet energies of 2.97-3.02 eV, along with high glass transition temperatures of 131-163 degrees C and superior electrochemical stability. Nevertheless, the carrier-transport properties show rather significant dependence on different substitutions. Although three different host materials give similar peak electroluminescence efficiencies at low driving currents, the CzSi host, which has more suitable carrier-transport properties, renders broadened distributions of the triplet excitons in phosphorescent devices, reducing the quenching associated with triplet-triplet annihilation and giving larger resistance against efficiency roll-off at higher brightnesses.
authors.affiliation: Department of Electrical Engineering, Graduate Institute of Electro-optical Engineering and Graduate Institute of Electronics Engineering, and Department of Chemistry, National Taiwan University, Taipei, Taiwan 106.
authors.forename: Ming-Han
authors.initials: MH
authors.lastname: Tsai
authors.forename: Tung-Huei
authors.initials: TH
authors.lastname: Ke
authors.forename: Hao-Wu
authors.initials: HW
authors.lastname: Lin
authors.forename: Chung-Chih
authors.initials: CC
authors.lastname: Wu
authors.forename: Shih-Feng
authors.initials: SF
authors.lastname: Chiu
authors.forename: Fu-Chuan
authors.initials: FC
authors.lastname: Fang
authors.forename: Yuan-Li
authors.initials: YL
authors.lastname: Liao
authors.forename: Ken-Tsung
authors.initials: KT
authors.lastname: Wong
authors.forename: Yu-Hung
authors.initials: YH
authors.lastname: Chen
authors.forename: Chih-I
authors.initials: CI
authors.lastname: Wu