Reduced hole loss in organic light emitting diode incorporating two p-doped hole transport layers

摘要

The hole-injecting structure of 15 nm MoO_(3-) doped 4,4-N,N-bis [N-1-naphthyl-N-phenyl-amino]biphe-nyl (NPB:MoO_3)/5 nm MoO_3-doped 4,4'-N, N'-dicarba-zole-biphenyl (CBP:MoO_3) has been used in organic light emitting diodes (OLEDs). It was found that a device using the 15 nm NPB:MoO_3/5 nm CBP:MoO_3/NPB combination was superior to one adopting the 20 nm NPB:MoO_3/NPB combination due to two major causes: the NPB:MoO_3/ CBP:MoO_3 interface is a quasi-ohmic contact, and the hole transport barrier from CBP:MoO_3 to NPB is smaller than that from NPB:MoO_3 to NPB; moreover, it outperformed the device employing the 20 nm CBP:MoCO_3/NPB combination, mostly because of the higher conductivity of NPB:MoO_3 compared to CBP:MoO_3. We demonstrate that using a structure resulting from uniting two p-doped hole transporters is a beneficial, simple method of achieving an improved trade-off between high conductivity and small hole transport barrier, thereby leading to a significantly reduced ohmic loss in the hole current conduction in the OLEDs, relative to the single p-doped layers.