Red electrophosphorescence from polymer doped with iridium complex
We demonstrate efficient, bright red electrophosphorescent light emitting diodes(LEDs) employing tris (2,5-bis-2′-(9′,9′-dihexylfluorene) pyridine) iridium (III), [Ir(HFP)3],doped into a blend of poly(vinylcarbazole) (PVK) with 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazol (PBD). At a current density of 2.35 mA/cm2(brightness of 169 cd/m2), the external quantum efficiency(QEext) and luminous efficiency (LE) were 5% ph/el and 7.2 cd/A, respectively. Even at 50 mA/cm2, QEext=3.4% ph/el and LE=5.2cd/A. The electroluminescent emission is characteristic of Ir(HFP)3, with maximum at 600 nm. The devices exhibited no emission from either PVK or PBD, even at the lowest concentration of Ir(HFP)3 (0.05 wt %). The results demonstrate that electrophosphorescence with high brightness and efficiency can be achieved from polymer-based LEDsfabricated by processing the active materials from solution.