MoO3 doped 4,4′-N,N′-dicarbazole-biphenyl for low voltage organic light emitting diodes

MoO3 doped 4,4′-N,N′-dicarbazole-biphenyl (CBP) was found to provide significantly reduced driving voltage when used as a hole transport layer (HTL) in organic light emitting diodes (OLEDs). Up to 70% improvement in power efficiency was realized in a fluorescent green OLED when MoO3 doped CBP was used in place of the traditional N,N′-diphenyl-N,N′-bis-(1-naphthyl)-1-1′-biphenyl-4,4′-diamine (α-NPD) HTL. It is also found that the hole injection across the CBP:MoO3/CBP interface is dependent on the CBP:MoO3 layer thickness. Therefore, the hole injection can be engineered by tuning the doping thickness which is useful for optimizing the electron-hole balance.