Improved performance of blue phosphorescent organic light-emitting diodes with a mixed host system

We have investigated a relationship between device performances and host properties in the emissive layer (EML) of iridium(III) bis(⁠$4′,6′$-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate doped blue phosphorescent organic light-emitting diodes (PHOLEDs). We found that the recombination zone as well as charge carrier injection properties of the EML could be systematically engineered through a mixed host system. Therefore, light-emitting performances of blue PHOLEDs were greatly improved with external quantum and power efficiencies of 20.5% and 43.5 lm/W at a luminance of $56cd/m2$⁠, respectively.