High efficiency green phosphorescent organic light emitting diodes using an ultrathin nondoped emitting layer

The nondoped emitting layer (EML) was constructed by introducing a ultrathin layer of pure green phosphorescent dye tris(2-phenylpyridine)iridium[Ir(ppy)₃] between a hole transporting layer TCTA and an electron transporting layer TPBi. The device structure is ITO/MoO₃(2 nm)/NPB(40 nm)/TCTA(10 nm)/Ir(ppy)₃(0.1-0.5 nm)/TPBi(40 nm)/LiF(1 nm)/Al(80 nm). The thickness of EML can affect the performance of green phosphorescent organic light emitting diodes (PhOLEDs). By changing the thickness of emitting layers, the best performance of green PhOLEDs can be achieved with a 0.2 nm pure phosphorescent dye. The device exhibits highly efficient green emission with a maximum luminance of 26 350 cd·m^-2, a maximum current efficiency of 42.9 cd·A^-1 and a maximum external quantum efficiency of 12.9%. These results indicate that the high performance PhOLEDs can be realized with only ultrathin nondoped EMLs in a simple way.