To improve luminance efficiency of con ventional and inverted light emitting devices,we implement an ethoxylated polyet hylenimine (PEIE) layer between light emitting polymer and cathode. Studies on c haracterizations of light emitting devices with various PEIE layer thicknesses reveal that ethoxylated pol yethylenimine layer mainly works as an electron injection/hole blocking layer.Conventional and inverted light emitting devices using a PEIE electron injection layer show comparable luminance efficiency to the analogous devices with a CsF o r with a ZnO/PEIE electron injection layer.Analyses of current density-voltage characteristics of single-electron devices manifest that PEIE layer enhances electron injection efficiency by a fac tor of 5-10.Results of X-ray ph otoelectron-spectroscopy (XPS) meas urements indicate that PEIE layer reduces the work function of Al by ca. 1eV,thus significantly decreasing the e lectron injection barrier,which can be attributed to the intrinsic dipole moment of PEIE or the formation of interfacia l dipoles. Apart from excellent electron injection/hole blocking properties,PEIE is air-stable and more compatible with the neighboring organic layer than metal fluorides,which can be processed from aqueous or alcohol solution under a mbient conditions.Thus,PEIE serves as a promising electron injector in organic electron devices and is parti cularly suitable for construction of multilayer devices with versatile and enhan ced properties.