Poly [2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and poly (sodium 4-styrenesulfonate) ionomer (PSS-ionomer) blends were used as emitting layers in polymer light-emitting diodes (LEDs). The polymers were blended in various ratios, and their luminescent properties were compared with those of a MEH-PPV/polystyrene (PS) blend system. The MEH-PPV/PSS-ionomer and MEH-PPV/PS devices showed a much higher luminescent efficiency when compared with pure polymer devices, due to the dilution effect. The MEH-PPV/PSS-ionomer blend device achieved a more enhanced luminescent efficiency as compared with that of the MEH-PPV/PS device, due to polar groups in the PSS-ionomer, which may enhance the electron injection from the cathode to the emitting molecules. In addition, the turn-on voltage of the MEH-PPV/PSS-ionomer based on LEDs was also dramatically decreased. (C) 2004 Elsevier Ltd. All rights reserved.