Confinement of triplet energy on phosphorescent molecules for highly-efficient organic blue-light-emitting devices

We have significantly improved the emission efficiency in an organic light-emitting device (OLED) based on iridium (III)bis[(4,6-di-fluoropheny)-pyridinato-N,C2′]picolinate (FIrpic). To improve the efficiency, 4,4′-bis(9-carbazolyl)-2,2′-dimethyl-biphenyl, which has a high triplet energy, was used as the carrier-transporting host for the emissive layer. The FIrpic-based OLED exhibited a maximum external quantum efficiency of 10.4%, corresponding to a current efficiency of 20.4 cd/A, and a maximum power efficiency of 10.5 lm/W. The efficiency was drastically improved compared to that of a previously reported FIrpic-based OLED. This result indicates that triplet energy is efficiently confined on FIrpic molecules, resulting in the high efficiency.