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Phosphorescent organic light emitting diodes (PHOLEDs) have been fabricated with structure of indium tin oxide/MoO3 doped 4,4′-N,N'-dicarbazole-biphenyl (CBP) 30 nm/tris(4-carbazoyl-9-ylphenyl)amine 10 nm/CBP doped with tris(2-phenylpyridine)iridium(III) (CBP:Ir(ppy)3) x/bathocuproine 50 nm/LiF 1 nm/Al, where x = 2.5, 5, 10, and 20 nm, respectively. The current efficiency (CE) of device with x = 10 nm is higher than those with x = 2.5 and 5 nm, mostly because the width of exciton formation zone (5.7 nm) with x = 10 nm is larger than those (2.5 and 5 nm) with x = 2.5 and 5 nm. However, the current density with x = 10 nm decreases than those with x = 2.5 and 5 nm at a certain driving voltage, since the ~ 4.3 nm CBP:Ir(ppy)3 accommodating no exciton formation with x = 10 nm plays a role of transporting holes, raising ohmic loss of hole and thereby increasing driving voltage. When x increases from 10 to 20 nm, the width of exciton formation zone rises from 5.7 to 6.8 nm with CE almost unchanged, and the current density decreases as a result of increased ohmic loss of hole. The current research is useful to develop high-efficiency and low-driving voltage PHOLEDs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The MoO 3 doped N,N′-bis-(1-naphthyl)-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB:MoO 3 in 2:1 mass ratio) and 4,4′-N,N′-dicarbazole-biphenyl (CBP:MoO 3 in 2:1 mass ratio) as p -doped hole transport layers have been used in inverted organic light emitting diodes (IOLEDs). Compared to the NPB/20 nm NPB:MoO 3 structure, the NPB/10 nm CBP:MoO 3 /10 nm NPB:MoO 3 structure showed increased device performance, mostly because the hole transport barrier from CBP:MoO 3 to NPB was smaller than that from NPB:MoO 3 to NPB; it also presented improved device performance than the NPB/20 nm CBP:MoO 3 structure, ascribed to the higher conductivity of NPB:MoO 3 than that of CBP:MoO 3 . We provide a manageable way to unlock the merits of p -doped hole transport layers for markedly increasing the performance of IOLEDs. [ABSTRACT FROM AUTHOR]