Multilayer organic light-emitting devices with phosphorescent guest emitter,
tris(2-phenylpyridine) iridium doped in a host 4,4′-N,N′-dicarbazol-biphenyl layer were prepared.
The device with the 6.5 wt% guest emitter exhibited external quantum efficiency and power
luminous efficiency of 13.7% and 38.3 lm/W, respectively at the luminance of 105 cd/m2
driven at the voltage of 4.0 V and current density of 0.215 mA/cm2. The half decay lifetime
under continuous constant-current driving for the initial luminance of 500 cd/m2 was 170 h.
Using poly(9-vinylcarbazole)(PVCz) as a host material for tris(2-phenylpyridine)iridium (Ir(ppy)3) guest emitter, double-layer and triple-layer organic light-emitting devices were fabricated. Tris(8-hydroxyquinolino)aluminum (Alq3) and 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxadiazolyl]phenylene (OXD-7) were used for electron-transporting layers. The insertion of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) as a hole-blocking layer was also tested. The double-layer device composed of PVCz doped with 6.8 wt% Ir(ppy)3 and OXD-7 gave the highest external quantum efficiency of 7.5% and power luminous efficiency of 5.8 lm/W at the luminance of 106 cd/m2 (current density of 0.40 mA/cm2 and drive voltage of 14.5 V).
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