Anode/organic interface modification by plasma polymerized fluorocarbon films

We investigated the effects of plasma polymerized fluorocarbon films (CFx) on device performance in organic light-emitting diodes (OLEDs). OLEDs with a 0.3-nm thick CFx film on an untreated indium tin oxide (ITO) anode showed identical current density–voltage characteristics and improved operational stability, as compared to the device with an ultra violet-treated ITO anode. Hole injection was virtually blocked when Au was replaced for ITO as an anode, while an ultrathin CFx film overlaid on an Au anode substantially reduced the barrier height and facilitated hole injection. The enhancement of hole injection was attributed to the manipulation of the energy level offset at the anode/organic interface by the formation of an artificial dipolar layer resulting from rich, negatively charged fluorine. The dipolar interface was fairly stable when being exposed to air, and the improved operational stability of OLEDs was ascribed to the stability of the ITO/CFx anode against atmospheric moisture.