Synthesis of a dibenzothiophene/carboline/carbazole hybrid bipolar host material for green phosphorescent OLEDs

• Bipolar host material for Ir(ppy)2(acac)-based green PHOLEDs were designed, using dibenzothiophene, α-carboline and carbazole moieties.
• The compound showed a high triplet energy (>2.67 eV) and good thermal stability.
• The host material allowed high external quantum efficiency of 18.9% in the green PHOLEDs.

A bipolar host material for green phosphorescent organic light-emitting diodes (OLEDs) was designed and synthesized through a combination of dibenzothiophene, α-carboline, and carbazole (DTCC) moieties. The synthesized host material showed a sufficient HOMO/LUMO bandgap (3.49 eV) and triplet energy (2.67 eV) for green emitting bis[2-(2-pyridinyl-N)phenyl-C] (acetylacetonato) iridium(III) [Ir(ppy)2(acac)]. From the results of a single charge device for DTCC, the hole current density of DTCC was similar to the electron current density, indicating that DTCC possesses bipolar charge transport properties, confirming its bipolar nature and thus its applicability as the host of PHOLED. Thus, the DTCC host showed efficient energy transfer to the Ir(ppy)2(acac) dopant in the device. A maximum external quantum efficiency of 18.9% was obtained using DTCC as the host material and the color coordinate of the green PHOLED was (CIEx,y = 0.34, 0.62) at 10% doping concentration.

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