Efficiency improvement of solution processed red phosphorescent organic light-emitting diodes using optimized hole transport material

We fabricated highly efficient solution processed red phosphorescent organic light-emitting diodes (PhOLEDs) composed of bis[9-ethyl-3-(4-phenylquinolin-2-yl)-9H-carbazolato-N,C2′]iridium picolinate N-oxide (Et-CVz-PhQ)2Ir(pic-N-O) and bis[9-(2-(2-methoxyethoxy)ethyl)-3-(4-phenylquinolin-2-yl)-9H-carbazolato-N,C2′]iridium picolinate N-oxide (EO-CVz-PhQ)2Ir(pic-N-O) as an emitter, which were doped into poly(N-vinylcarbazole) (PVK), electron transport material, 1,3-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazo-5-yl]benzene (OXD-7) and optimized concentration of hole transport material, N,N′-diphenyl-N,N′-(bis(3-methylphenyl)-[1,1-biphenyl]-4,4′-diamine (TPD). The optimized PhOLEDs doped with 16 wt% of TPD shows a maximum external quantum efficiency of 9.21% and a luminance efficiency of 15.24 cd/A with a CIE coordinate of (0.62, 0.38).

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► We synthesized the new red iridium complexes for solution processable PhOLEDs.
► Emitting layer was composed with PVK, TPD, OXD-7, and iridium dopant.
► PhOLEDs performance was dependent on the concentration of TPD in emitting layer.
► New red iridium dopant in PhOLEDs is finely investigated using current density–voltage-brightness-efficiency.