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Fe3O4 has been demonstrated to be an efficient p-dopant in improving the performance of organic light-emitting devices. This paper investigates in detail the role of Fe3O4 in improving the hole injection and the hole transport by the ultraviolet/visible/near-infrared absorption, x-ray, and ultraviolet photoelectron spectroscopy. The results demonstrated that Fe3O4 as a p-dopant has different effectiveness when it is doped into different host materials. The improved properties of the OLEDs with the p-doped N, N'-diphenyl-N,N'-bis (1,1'-biphenyl)-4,4'-diamine layer is mainly due to the enhanced hole injection through the lowering of the hole injection barrier, while the enhanced hole transport plays a more important role for the OLEDs with the p-doped 4,4',4”-tris (3-methylphenylphenylamino) triphenylamine due to their higher ability in the formation of charge transfer complex.

Magnetic field effects on tris-(8-hydroxyquinoline) aluminum-based organic light-emitting devices (OLEDs) by employing Fe3O4 as a magnetic dopant in the hole-transport layer (HTL) have been studied. The magnetic doped OLEDs exhibit efficient injection and transport of holes, and its performances are further enhanced after a magnetic field is applied. The enhancement of luminance and current efficiency of 20% and 24% has been obtained from the magnetic doped devices, while they are only 8% and 9%, respectively, for the nondoped devices under an applied magnetic field of 500 mT. Organic magnetoresistance induced by the magnetic doped HTL is the main origin of increased electroluminescence for the magnetic doped OLEDs.

Highly efficient top-emitting organic light-emitting devices (TOLEDs) using a Fe3O4 modified Ag anode have been demonstrated. The tris-(8-hydroxyquinoline) aluminum-based TOLEDs exhibit a very low turn-on voltage of 2.5 V and a high current efficiency of 8.1 cd/A. The improved properties for the TOLEDs is mainly due to the enhanced hole injection by introducing the anodic buffer. The mechanism of this enhanced hole injection is studied by the X-ray and ultra-violet photoemission spectroscopy, which demonstrated that the dipole layer is formed at the anode/organic interface and the hole-injection barrier is therefore reduced after introducing the thin Fe3O4 film between the Ag anode and the hole-transport layer.