The addition of viologen in luminescent polymers for polymer light-emitting diodes

Polymer-typed viologen has been blended into the luminescent polymer, poly( 2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV), in fabric ating the polymer light-emitting diode (LED) in order to overcome the photo -oxidation problem of the LED. The addition of viologen improved the device performance: the stability of the luminescent polymers can be enhanced; th e rum-on voltage of the LED with viologen is decreased and the external qua ntum efficiency of its electroluminescence is increased compared with the L ED without viologen. The preliminary result of the a.c. impedance measureme nts indicate that the addition of viologen can improve the stability of the LED against the UV radiation. (C) 2000 Published by Elsevier Science S.A. All rights reserved.