Effect of various host characteristics on blue thermally activated delayed fluorescent devices

Two bipolar hosts consisting of phosphine oxide and carbazole, (9-phenyl-9H-carbazole-3,6-diyl)bis (diphenylphosphine oxide) (PPO2) and phenylbis (9-phenyl-9H-carbazol-3-yl)phosphine oxide (3DCPO) generally used as blue phosphorescence hosts are successively applied to blue thermally activated delayed fluorescence (TADF) organic light emitting diodes (OLEDs). These hosts have suitable high triplet energy (T-1) and bipolar characteristics expecting increase in TADF characteristics of dopant. The exciton decay rate and photoluminance quantum yield (PLQY) of the dopant according to the polarity of host are analyzed. It is shown that the host, PPO2, with appropriate polarity increased the TADF characteristics of the dopant and efficiency of OLED. The PPO2 based blue TADF OLED shows a high external quantum efficiency of 27.8% achieving enhanced efficiency roll-off characteristic.