A degradation study of poly(p-phenylene vinylene) based light emitting diodes

The degradation of poly(p-phenylene vinylene) (PPV) based light emitting diodes (LEDs) was examined by electrical measurements and by scanning electron microscopy (SEM) performed on the devices after several working cycles up to their complete destruction. It is demonstrated that the stability of the samples depends greatly on their thickness and the conduction mechanism in the polymer film is not affected by the degradation of the diodes. In the degraded samples, dark spots are formed on the surface of the electrode in circular configuration and seem to be linked to the presence of oxygen. The results are compared to those obtained in organic diodes and discussed in relation with the failure mechanism.