Triplet energy boosting ternary exciplex host for improved efficiency in deep blue phosphorescent organic light emitting diode

A high triplet energy exciplex host derived from a ternary mixture of hosts was developed for efficient energy transfer to a deep blue phosphor by suppressing reverse energy transfer. In the thermally activated delayed fluorescent type exciplex host of 4,4′-bis(carbazol-9-yl)-2,2′-dimethylbiphenyl (CDBP) and 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T), the (oxybis(2,1-phenylene))bis(diphenylphosphine oxide) (DPEPO) was added as a third component to increase the triplet energy of the exciplex host. The addition of DPEPO in the CDBP:PO-T2T exciplex host increased the triplet energy of the exciplex from 2.88 eV to 2.97 eV, and the photoluminescence quantum yield of the deep blue phosphor doped exciplex from 0.77 to 0.86. The triplet energy boosting function of the DPEPO improved the maximum external quantum efficiency of the deep blue phosphorescent organic light-emitting diode from 12.8% to 16.6% at a DPEPO content of 70%.