Increased brightness and lifetime of polymer light-emitting diodes with polyaniline anodes

The properties of light-emitting diodes based on poly(2-methoxy,5-(2′-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) with indium-tin oxide (ITO) anodes are compared with those in which a layer of polyaniline (PAni) is coated between the ITO and the emissive polymer. It is found that the PAni injection layer yields higher current, brighter emission and a lower rate of degradation than ITO. The electrical behavior is discussed in terms of bulk and contact current limitation. The improvement in degradation is attributed to reduced oxidation as the PAni layer provides a barrier for the passage of oxygen out of the oxide. In addition, improvement in microscopic short formation indicates planarization of the anode interface by the PAni film.