Polymer light-emitting diodes are fabricated using poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene) as an emissive material, and sodium sulfonated polystyrene (SSPS) ionomers with several different neutralization levels as an electron injecting and hole blocking layer. The SSPS with higher neutralization level makes the EL device more efficient. The highest efficiency was found at 200% overneutralization of the ionomer. The main reason fur this is that the overneutralization in the ionomer helps to form a more favorable morphology to block holes better by Lightening the cluster.