Effective hole injection of organic light-emitting diodes by introducing buckminsterfullerene on the indium tin oxide anode

We demonstrate that dramatically improved hole injection can be achieved by inserting a very thin C-60 film between the indium tin oxide (ITO) electrode and N,N-'-diphenyl-N,N-'-bis(1,1'-biphenyl)-4,4'-diamine (NPB) layer. This result is ascribed to the formation of an interfacial dipole layer of buckminsterfullerene (C-60) on the ITO electrode. The dipole layer induces the surface potential shift that contributes to improve the charge injection efficiency. The chemical shift was downward to help lower the hole injection energy barrier from the ITO electrode to the NPB layer, consistent with the moderately strong electron accepting nature of C-60. The enhanced-charge injection provides a simple way of reducing the power consumption of organic electronic devices for real applications. (c) 2005 American Institute of Physics.