EFFECT OF OXYGEN ON THE ELECTRICAL CHARACTERISTICS OF PPV-LEDS

The presence of oxygen in the surrounding atmosphere exerts an importa nt influence on the electro-optical characteristics and the degradatio n behaviour of organic electroluminescent Al-PPV-ITO-diodes. Experimen ts in various gas atmospheres show that the devices possess gas sensin g properties. For particular gas compositions the current-voltage (IV) -characteristics feature negative resistance sections in the form of a nomalous bumps superimposed on Shockley-like diode characteristics. A new interpretation is provided for the memory switch phenomena related to these anomalous electrical characteristics. The gas sensor like be haviour and the increase in conductivity in an oxygen free ambient is believed to be related to the formation of localized Ohmic paths. The growth of these Ohmic paths is inhibited by oxidation and the paths ca n melt due to excessive joule heating. (C) 1998 Elsevier Science B.V.