The charge generation layer incorporating two p-doped hole transport layers for improving the performance of tandem organic light emitting diodes

We report the charge generation layer (CGL) structure comprising of Li 2 CO 3 doped bathocuproine (BCP:Li 2 CO 3 )/MoO 3 doped 4,4- N , N -bis [ N -1-naphthyl- N -phenyl-amino]biphenyl (NPB:MoO 3 )/MoO 3 doped 4,4′- N , N ′-dicarbazole-biphenyl (CBP:MoO 3 ) for tandem organic light emitting diodes (TOLEDs). Compared to the TOLED using the conventional CGL structure of BCP:Li 2 CO 3 /20 nm CBP:MoO 3 , the one using the CGL structure of BCP:Li 2 CO 3 /5 nm NPB:MoO 3 /15 nm CBP:MoO 3 showed increased electrical and luminous properties, mostly because the introduction of the higher-conductivity NPB:MoO 3 relative to CBP:MoO 3 could improve the current conduction in the CGL structure. Whereas, the performance of the CGL structure of BCP:Li 2 CO 3 / x nm NPB:MoO 3 /20- x nm CBP:MoO 3 decreased with x increasing, mostly due to the fact that the CBP:MoO 3 became depleted of mobile holes upon contacting p-doped NPB: the smaller thickness of CBP:MoO 3 , the worse conductivity for it. We provide some in-depth insights on designing the high-performance CGLs for TOLEDs.