Admittance spectroscopic analysis was used to examine the effect of a CFX plasma surface treatment on indium tin oxide (ITO) anodes using CF4 gas and model the equivalent circuit for organic light emitting diodes (OLEDs) with the of ITO anode surface treated with CFX plasma. This device with the ITO/N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-diphenyl-4,4'-diamine/tr is-(8-hydroxyquinoline) aluminum/lithium fluoride/Al structure was modeled as a simple combination of two resistors and a capacitor. The ITO anode surface treated with the CFX plasma showed a shift in the vacuum level of the ITO, which resulted in a decrease in the barrier height for hole injection at the ITO/organic interface. Admittance spectroscopy measurements of the devices with the CFX plasma treatment on the surface of the ITO anodes showed a change in the contact resistance, bulk resistance and bulk capacitance. (c) 2007 Elsevier B.V. All rights reserved.