We report the charge generation layer (CGL) structure comprising of Li2CO3 doped bathocuproine (BCP:Li2CO3)/MoO3 doped 4,4-N,N-bis [N-1-naphthyl-N-phenyl-amino]biphenyl (NPB:MoO3)/MoO3 doped 4,4′-N,N′-dicarbazole-biphenyl (CBP:MoO3) for tandem organic light emitting diodes (TOLEDs). Compared to the TOLED using the conventional CGL structure of BCP:Li2CO3/20 nm CBP:MoO3, the one using the CGL structure of BCP:Li2CO3/5 nm NPB:MoO3/15 nm CBP:MoO3 showed increased electrical and luminous properties, mostly because the introduction of the higher-conductivity NPB:MoO3 relative to CBP:MoO3 could improve the current conduction in the CGL structure. Whereas, the performance of the CGL structure of BCP:Li2CO3/x nm NPB:MoO3/20- x nm CBP:MoO3 decreased with x increasing, mostly due to the fact that the CBP:MoO3 became depleted of mobile holes upon contacting p-doped NPB: the smaller thickness of CBP:MoO3, the worse conductivity for it. We provide some in-depth insights on designing the high-performance CGLs for TOLEDs.