Highly Efficient Electrophosphorescence from a Grafted Biscyclometalated Iridium Complex with Triarylamine Unit in Polymer Light-Emitting Devices

The electroluminescence performance from a novel grafted cyclometalated iridium complex (BuPhNPPy)_2Ir(acac) with triarylmine unit, where BuPhNPPy is N,N-di(4-tert-butylphenyl)-4-(2-pyridyl) phenylamine and Hacac is acetylacetone, is demonstrated in the double-layered polymer light-emitting devices (PLEDs). The PLEDs emit intense green phosphorescence at 533nm with a shoulder peak of 566nm employing 4wt.% (BuPhNPPy)₂Ir(acac) doped a blend of poly(vinylcarbazole) (PVK) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD) as the emitting layer. A maximum luminance of 14610cd/m² at voltage of 24V and a maximum external quantum efficiency E_ext of 10.4% photons per electron (ph/el) at current density of 32mA/cm² are achieved. When the current density is raised to 100mA/cm², E_ext of the device still remained to 8.3% ph/el. This indicates that the triplet--triplet annihilation is restrained more effectively at high current density. The improvement of electrophosphorescence performances of the iridium complex may be contributed to an ortho-substituent effect of grafted triarylmine unit.