Mixing effect of hole-injecting and hole-transporting materials on the performance and lifetime of organic light-emitting devices

A hole-injecting-transporting layer (HITL), which was prepared by in situ mixing hole-injecting and hole-transporting (HTM) materials upon evaporating in vacuum, has been attempted to reduce the number of organic layers in organic light-emitting devices (OLEDs). OLEDs with HITLs showed lower current density and luminance than those with hole-injecting layer only or hole-transporting layer only, which is attributed to the charge transport change controlled by the HITL nanomorphology made upon mixing. The highest efficiency and the longest lifetime were achieved for the OLED having the HITL with 25% HTM content, while the OLED with HTM only exhibited very poor device lifetime despite the highest efficiency.