Thermally stable triphenylene-based hole-transporting materials for organic light-emitting devices

The thermally stable hole transport layer (HTL) materials, 1,4-bis[(N,N′-di(2-naphthyl)-N,N′-diphenyl)aminophenyl]triphenylene (NPAPT) and 1,4-bis[(N,N′-di(2-naphthyl)-N,N′-diphenyl) aminophenyl]-2,3-diphenyl triphenylene (NPAPPT), were synthesized and the device performances of the organic light-emitting diodes (OLEDs) with NPAPT and NPAPPT as a hole transport layer were investigated. The glass transition temperatures of NPAPT and NPAPPT could be enhanced to 153 °C and 157 °C by the introduction of a rigid triphenylene backbone in the main chain. The use of NPAPT and NPAPPT as a HTL for OLEDs lowered the driving voltage and enhanced the light-emitting efficiency. The power efficiencies of triphenylene-based devices with tris(8-hydroxyquinoline)aluminum as an emitting material could be improved by 20% compared with that of N,N′-di(naphthalene-1-yl)-N,N′-diphenyl benzidine based devices.