The current density and the luminance efficiency of the organic light-emitting devices (OLEDs) with a cesium nitrate (CsNO3)/lithium quinolate (Liq) electron injection layer (EIL) were larger than those of the OLEDs with a Liq EIL. Residual Cs ions or cesium oxides in the OLEDs decreased the electron affinity of the cathode electrode, resulting in an improvement of the electron injection efficiency and the luminance efficiency. Electron only devices, which are elements being able to flow only electrons, showed that the electron injection magnitude was increased due to the insertion of the CsNO3 EIL into OLEDs.