Efficiency and colour optimization of carbazole based deep blue phosphorescent organic light emitting devices

We report highly efficient deep blue phosphorescent organic light emitting devices using a silicon based carbazole host with deep highest occupied molecular orbital level and high triplet energy doped with a phosphorescent dopant, iridium(III)bis (4',6',-difluorophenylpyridineato)tetrakis(1-pyrazolyl)borate. The charge transport and emission mechanisms of the light emission layer were investigated by means of current versus voltage measurements, transient photoluminescence and photoemission spectroscopy. By utilizing both energy transfer from host to dopant and direct charge trapping in the dopant material, as well as by optimizing the emission zone, a peak external quantum efficiency of 15%, power efficiency of 19.4 lm W-1 and CIE coordinates of (0.15, 0.23) were achieved.