Enhanced charge generation in doped organic/organic p–n heterojunction for improving the performance of tandem organic light emitting diode

The doped organic/organic p–n heterojunctions have been applied as charge generation structure (CGS) in tandem organic light emitting diodes (TOLEDs). It is found that the field‐induced charge generation takes place more efficiently at the interface between Li₂CO₃ n‐doped bathocuproine (BCP:Li₂CO₃) and MoO₃ p‐doped 4,4′‐N ,N′‐dicarbazole‐biphenyl (CBP:MoO₃) than at the interface between BCP:Li₂CO₃ and MoO₃ p‐doped 4,4‐bis[N‐1‐naphthyl‐N‐phenylamino]biphenyl (NPB:MoO₃). It is because the process of electrons tunneling through the depletion zone from the highest occupied molecular orbit (HOMO) of CBP:MoO₃ to the lowest unoccupied molecular orbit (LUMO) of BCP:Li₂CO₃ is more efficient than that from the HOMO of NPB:MoO₃ to the LUMO of BCP:Li₂CO₃. Compared to the TOLED using the conventional CGS of 10‐nm BCP:Li₂CO₃/20‐nm NPB:MoO₃, the one using the CGS of 10‐nm BCP:Li₂CO₃/10‐nm CBP:MoO₃/10‐nm NPB:MoO₃ shows increased device performance. In addition, the interconnecting property of CGS of 10‐nm BCP:Li₂CO₃/x nm CBP:MoO₃/20 ? x nm NPB:MoO₃ shows a strong dependence on the thickness of CBP:MoO₃. We provide a new insight on optimizing Ohmic loss in the CGSs, useful for improving the performance of TOLEDs.