Enhanced hole injection in organic light-emitting devices by using $Fe3O4$ as an anodic buffer layer

Hole injection improvement in organic light-emitting devices with $Fe3O4$ as a buffer layer on indium tin oxide (ITO) has been demonstrated. The luminance and the current density are significantly enhanced by using the $Fe3O4/ITO$ anode, as well as the turn-on voltage is reduced by 1.5 V compared to the devices without the buffer. Results of atom force microscopy, x ray, and UV photoelectron spectroscopy studies reveal that the enhanced hole injection is attributed to the modification of the ITO surface and the reduced hole-injection barrier by the insertion of the $Fe3O4$ thin film between the ITO and hole-transporting layer.