Transition metals and other impurities, which are also undesirable from a point of view of photo-chemical stability, are avoided by the nature of the synthetic route. Water may also cause photo-chemical degradation of the polymer as well as corrosion of the cathode. Thus, LEP devices must be encapsulated. We typically use a glass slide which is glued over the top of the LEP device with an epoxy resin. These devices can be driven very reliably in either constant current or voltage mode.
Current densities ca.
2.5 V and efficiencies ca. The devices show an initial 'settling-in' phase, manifested by an increase of light output which is correlated with an increase in efficiency and voltage. Beyond this 'settling-in' period there are no signs of a degradation in device performance over the operating life. Figure 3 shows a photograph of the EL emission of one of the devices from Fig. 2 taken after ca.