Spiro-fused N-phenylcarbazole-based host materials for blue phosphorescent organic light-emitting diodes

• Two spiro-fused host materials can achieve high triplet energies for blue electroluminescence.
• Both materials showed high glass transition temperatures over 130 °C.
• A blue PHOLED device based on SPCC host exhibited a maximum EQE of 19.0%.

Two host materials, SFCA and SFCC, consist of a diphenylamine or carbazole unit linking to spiro-fused phenyl carbazole (SFC) backbone, were designed and synthesized. By choosing the meta linkage way between diphenylamine/carbazole units and SFC ring, higher triplet energies could be easily achieved for the two new materials, which mean that they could be used as effective host material for popular blue phosphorescent material Iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C2′] picolinate (FIrpic, ET = 2.65). Besides that, the steric SFC structure could guarantee their good thermal stabilities. Their thermal, photophysical and electroluminescent properties were systematically investigated. The blue phosphorescent OLEDs with the two materials as hosts and FIrpic as a dopant exhibited excellent performance with maximum current efficiencies of 33.9 and 40.8 cd/A, respectively.

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