Low voltage top-emitting organic light emitting devices by using 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile

Two different types of hole transport layers are applied to the standard top-emitting green organic light emitting diodes (OLEDs) with relatively thick microcavity structure for a low voltage operation. An 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN), a well-known electron accepting material, was utilized as an interlayer which induces an interfacial charge transfer. The position of an interlayer was determined by investigation of device characteristics of four different types of hole only devices. The optimized device with very thin HAT-CN layer (∼5 nm) sandwiched between N,N′-diphenyl-N,N′-bis-[4-(phenyl-m-tolylamino)-phenyl]-biphenyl-4,4′-diamine (DNTPD) layers showed very stable current efficiency and power efficiency behavior with low roll-off characteristic. The performances of the device with interlayer were compared to those of p-doped device (3%). Very interestingly, the device with HAT-CN interlayer showed very similar operating voltage behavior as well as current/power efficiency behavior compared to that prepared with p-doped hole transport layer (HTL).