Highly efficient and solution-processed iridium complex for single-layer yellow electrophosphorescent diodes

A novel electrophosphorescent material based on a biscyclometalated iridium(m) complex of the N,N-dipheny1-4 ''-(1-phenyl-1H-benzo[d]imidazol-2-yl)[1,1':4',1 ''-terphenyl]-4-amine ligand, named Ir(TPABPBI)(2)(acac), has been synthesized and its application in organic light emitting devices (OLEDs) was studied. Highly efficient, solution-processed, single-layer, electrophosphorescent diodes utilizing the complex have been prepared and characterized. In these devices, the high triplet energy poly(9-vinylcarbazole) (PVK) is used as a host polymer doped with 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) employed for electron transport. When the doping concentration of Ir(TPABPBI)(2)(acac) is up to 4%, devices with a current efficiency of 30.0 cd A(-1) corresponding to an EQE of 15% can thus be achieved, along with the Commission de l'Eclairage 1931 chromaticity coordinates of (0.507, 0.486). More importantly, the yellow phosphorescence can be achieved without the generation of excimer emission. Such devices exhibit a very broad and featureless peak at ca. 568 nm with a wide full spectral width at half maximum (FWHM) of 83 nm. These results render Ir(TPABPBI)(2)(acac) a promising organic phosphor for applications in yellow OLEDs, especially for large-area, highly efficient and cheap yellow PhOLEDs.