Triphenylsilyl- and trityl-substituted carbazole-based host materials for blue electrophosphorescence.
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.
Tsai
Ming-Han
MH
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.
Ke
Tung-Huei
TH
Lin
Hao-Wu
HW
Wu
Chung-Chih
CC
Chiu
Shih-Feng
SF
Fang
Fu-Chuan
FC
Liao
Yuan-Li
YL
Wong
Ken-Tsung
KT
Chen
Yu-Hung
YH
Wu
Chih-I
CI