The degradation properties of the Organic Thin Film Electroluminescence(OTFEL) devices consisting of a Alq(as a light-emitting layer) and PVK (as a hole transporting layer) were studied under different operating conditions. Under a constant voltage driving and in an ambient temperature

it was found that the brightness

the current density and the lumen efficiency decrease very quickly at the initial step of the degradation process

then turn slow gradually. The trend of the brightness degradation is alike to that of the current density

but the degradation rate is a little larger than the later. It was also showed that when the devices were stored in the air for much longer time the degradation rate of the EL emissions will be accelerated considerably. It is concluded that the phenomenon presumably is due to the effect of the absorbed gases such as the moisture or oxygen gases in atmosphere. The experimental results indicated that the degradation rates of the EL emissions were much slower for the pulse driving than for the continuous DC driving. The degradation differences become more obvious with the fall of the duty ratio. The different degradation rates illustrate that one of the main causes of the brightness decrease is assumed to be Joule heat produced in the device operating.