Effects of Mg:Ag interlayer between LiF and Al on electron injection and device performances of organic light-emitting diodes (OLEDs) were investigated. Thickness of Mg:Ag layer was changed from 0 to 10 nm and the relationship between interlayer thickness and device performances was studied. Current density of OLEDs was increased due to efficient electron injection from cathode to organic layer by Mg:Ag interlayer. In addition, power efficiency of OLEDs was improved by more than 50% due to low driving voltage and high recombination efficiency and it showed a maximum value at a Mg: Ag thickness of 1.0 nm. (c) 2007 The Electrochemical Society.