Highly efficient soluble materials for blue phosphorescent organic light–emitting diode

A series of new carbazole derivatives with good solubility and electronic properties for use as host materials for blue phosphorescent organic light-emitting diodes is reported. A twisted biphenyl moiety at the center of the host materials was applied to enhance the solubility as well as triplet energies. Hence all the molecules showed good solubility as well as a fairly large triplet energy up to 3.01 eV. Blue phosphorescent devices employing bis(4,6-difluorophenylpyridinato-N,C2)picolinatoiridium (III) as the guest and the three new twisted carbazole derivatives as co-hosts with an electron type host material exhibited high efficiencies, up to 20.7 cd/A as a maximum current efficiency and 12.5% of external quantum efficiency. This performance was much improved by ∼27.6%, compared to that measured for the 1,3-di(9H-carbazol-9-yl)benzene: 2,6-bis(3-(9H-carbozol-9-yl)phenyl)pyridine reference system.

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