Improved hole injection and transport of organic light-emitting devices with an efficient p-doped hole-injection layer

A 4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine thin film doped with Fe3O4 has been demonstrated an efficient p-type hole-injection layer (HIL) in organic light-emitting devices (OLEDs). The tris-(8-hydroxyquinoline) aluminum-based OLEDs with the p-type HIL exhibit a very low turn-on voltage of 2.4 V and a high luminance of 29 360 cd/m2 at 8 V, while it is 3 V and 6005 cd/m2, respectively, for the nondoped devices. The improvement in the device performance is clarified as arising from the improved hole injection and transport by the results of ultraviolet/visible/near-infrared absorption, x-ray photoelectron spectra and current density-voltage characteristics of hole-only devices.