Bis(1-phenyl-1H-benzo[d]imidazole)phenylphosphine oxide interlayer for effective hole blocking in efficient phosphorescent organic light emitting diodes based on widely used charge transporting layers

We have developed the efficient phosphorescent organic light emitting diodes (PHOLEDs) based on green-emitting fac-tris(2-phenylpyridine)iridium [Ir(ppy)3] dopant with widely used charge transporting layers. PHOLEDs show the electroluminescence emission from the dopant emitter at 512 nm with CIE color coordinates of (0.30, 0.59). We investigated the roll of a 10-nm-thick electron-transporting type bis(1-phenyl-1H-benzo[d]imidazole)-phenylphosphine oxide (BIPO) interlayer in the device efficiencies. BIPO with the deep HOMO energy level and higher electron transporting ability effectively blocks the holes from EML to ETL and improves the charge balance in the EML of the device, resulting in the higher device external quantum efficiency of 14.42%, current efficiency of 44.37 cd/A, and power efficiency of 14.67 lm/W with a maximum luminance of 75,080 cd/m2. The results show that the BIPO interlayer can be very much useful for the efficient low-cost device fabrication.