The EL properties of organic light-emitting devices using phosphorescent dyes as a guest material are described. Poly(9-vinylcarbazole) (PVCz) in the polymer system and 4,4'-N,N'-dicarbazolbiphenyl (CBP) in the low molecular system are used as a matrix. Perylene, 4-dicyano-methylene-2-methyl-6-4-dimethylami-nostyryl-4H-piran (DCM1), bis (4-phenylimidazopyridine)beryllium (Be(PIP)_2) and etc. are used as a fluorescent dopant and/or iridium-complexes: (tris-(2-phenyl-pyridine)iridium) (Ir(ppy)_3), iridium(III)bis[(4,6-di-fluorophenyl) pyridinato-N,C~(2') ] picolinate (FIrpic) and bis(2-(2'-benzo[4,5-a]thienyl)pyridinato-N,C~(3') )iridium(acetylacetonate) (btp_2Ir(acac)) are used as a phosphorescent dopant. In the ITO/PVCz:DCM1, Be(PIP)_2/Alq_3/Al devices with DCM1(0.5mol% constant) and Be(PIP)_2(variable), the peak wavelength does not change by the doping of Be(PIP)_2 and the EL intensity becomes maximum at 0.5mol% doping and increases in comparison with the case with non-doped at 2 digits. These results indicate that Be (PIP)_2 does not emit itself and roles to transfer the excited energy to the emitting centers (emitting assist). The EL properties of organic light-emitting diodes (OLEDs) using PVK as a matrix (host) and phosphorescent materials (btp_2Ir(acac) and Ir(ppy)_3) as a guest material are remarkably improved in comparison with OLEDs doped btp_2Ir(acac) (guest) into PVK (host).
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