We have studied the use of a thin copper iodide (Cul) film as an efficient injection layer of holes from tin oxide (ITO) anode in a light-emitting diode structure based on tris-8-hydroxyquinoline (Alq3). The results of impedance analysis of two types of diode structures, glycol) dimethyl ether/Aland ITO/A1q3/poly(ethylene glycol) dimethyl ether/Al, are presented. analysis of their current density-voltage, luminance-voltage and impedance characteristics shows presence of CuI layer facilitates injection of holes from ITO anode into the light-emitting layer Alq3 increases electroluminescence efficiency of the organic light emitting diodes. (C) 2010 Elsevier BM. All rights reserved