An optimized p-doped hole injection structure to improve the performance of organic light emitting diodes

Organic light emitting diodes (OLEDs) have been fabricated using various p-doped hole injection structures based on MoO3 doped 4,4′-N,N′-dicarbazole-biphenyl (CBP:MoO3) and 2,3,5,6-Tetrafluoro-7,7,8,8,-tetracyano-quinodimethane doped 4,4-bis[N-1-naphthyl-N-phenylamino]biphenyl (NPB:F4-TCNQ). It is found that the hole injection from indium tin oxide (ITO) to CBP:MoO3 is more efficient than that from ITO to NPB:F4-TCNQ, although the CBP:MoO3 is much less conductive than the NPB:F4-TCNQ. In addition, the CBP:MoO3 is helpful to block F4-TCNQ from diffusing into the emissive zone and thereby relieve the exciton quenching induced by organic p-dopant. Thus, the improved hole injection structure of ITO/10 nm CBP:MoO3/5 nm NPB:F4-TCNQ/5 nm CBP:MoO3 is provided to diminish the hole and exciton losses, greatly increasing the device performance than the other hole injection structures. The current research is believed beneficial for the development of OLEDs based on a p-i-n junction.