Low driving voltage and efficient orange-red phosphorescent organic light-emitting devices based on a benzotriazole iridium complex

Efficient orange-red phosphorescent organic light-emitting devices (PHOLED) with various doping concentrations of benzotriazole–iridium complex [(TBT)2Ir(acac)] (bis[4-(2H-benzotriazol-2-yl)-N,N-diphenyl-aniline-N1,C3] iridium acetylacetonate) in 4,4′-N,N′-di(carbazolyl) biphenyl (CBP) host were fabricated. The sterically hindered iridium ligands alleviate self-quenching of the phosphorescence at high doping levels. Under the optimal doping concentration of 20 wt.%, the maximum external quantum efficiency (EQE), luminance and power yield reach 9.06%, 15.81 cd/A and 13.8 lm/W, respectively. Increasing the doping concentration from 5% to 30 wt.% significantly decreases the driving voltage. The driving voltage of 30% (TBT)2Ir(acac) doped device is only 3.16 V at 1 mA/cm2 with power yield of 13.32 lm/W.