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To explore energy loss by diffusive triplet excitons in single emissive white phosphorescent organic light-emitting devices, the authors investigated collisional quenching between the electron transport materials 4,7-diphenyl-1,10-phenanthroline (Bphen), 2′,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi), or 1,3,5-tri(3-pyrid-3-yl-phenyl)benzene (TmPyPB) and the blue phosphorescent material, 3,5-difluoro-2-(2-pyridyl)-phenyl-(2-carboxypyridyl) Iridium III (FIrpic) spectroscopically in solution. The luminous efficiency and the external quantum efficiency (EQE) of an emissive white phosphorescent organic light-emitting device, in which TmPyPB acted as the electron transport material, was found to be greater than those of devices prepared using Bphen or TPBi due to the lack of collisional quenching. In addition, it was found that to prevent triplet exciton loss, an ETL material should have a low bimolecular quenching rate constant k q of less than 1.458 × 10 7 s −1 M −1 , which is the k q of TmPyPB. [ABSTRACT FROM AUTHOR]

Blue phosphorescent organic light-emitting diodes (PHOLEDs) were fabricated using double dopants FIrpic and FIr6 in emissive layer (EML) with structure of ITO/NPB (700 Å)/mCP:FIrpic-8%:FIr6- x % (300 Å)/TPBi (300 Å)/Liq (20 Å)/Al (1200 Å). We optimized concentration of the second dopant FIr6 in the presence of a fixed FIrpic to observe its effect on electrical performance of PHOLED device. 24.8 cd/A of luminous efficiency was achieved by the device with dopant ratio of 8%FIrpic:4%FIr6 in EML. Efficiency roll-off was also improved 20% compared to the PHOLED device singly dopped with FIrpic or FIr6 only. Second doping proved its effect in stabilizing charge balance in EML and enhancing energy transfer of triplet excitons between two dopants. [ABSTRACT FROM AUTHOR]

The performance of three color single emissive layer white phosphorescent organic light-emitting diodes (PHOLEDs), with different hole transporting materials of N,N′-diphenyl-N,N′-bis(l-naphthyl-phenyl)-(l,l′-biphenyl)-4,4′-diamine (NPB), 4,4_,4_-tris_N-carbazolyl_tri-Phenylamine (TCTA) and 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC), was analyzed. It is found that the luminous efficiency of white PHOLEDs is closely related to the triplet exciton energy level in the hole transporting layer (HTL). White PHOLEDs with a TAPC as HTL, having the highest triplet exciton energy level amongst the three different hole transporting materials, yielded external quantum efficiency of 25.5% at 4.5 V and a high luminous efficiency of 51 cd/A at 4.5 V with CIE color coordinates of (0.34, 0.39) at 10 V. The results reveal that the effective confinement of triplet excitons in white PHOLEDs with a high triplet exciton energy level HTL (TAPC) allows improving the luminous efficiency, as compared to the devices made with NPB and TCTA. Additionally, we demonstrated possibility for the loss of intensity in EL spectra of the white PHOLED devices with NPB and TCTA as HTL compared to that of the device with TAPC as HTL. [ABSTRACT FROM AUTHOR]