Polymer light-emitting diodes were fabricated using poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] as an emissive material. Sodium ionic polyurethane (NaPU), a single-ion conductor (SIC), was employed as an electron-injecting material and compared with the case of sodium sulfonated polystyrene (SSPS). The quantum efficiency was greatly enhanced, compared with the SSPS-based device. The electron injection in the NaPU-based device is more favorable, compared with the SSPS-based device because of a larger ionic space charge accumulation near the cathode by the good chain segmental motion of the soft block in the polymer chains of the SIC. Thus, a balanced injection of an electron–hole pair can be achieved to greatly improve the quantum efficiency. © 2000 American Institute of Physics.