Luminance Decay Mechanisms in Organic Light-Emitting Diodes

Influence of several operating conditions on luminance decay in a green organic light-emitting diode with tris (8-hydrooxyquinoline) aluminum (Alq3) has been investigated by the analysis of its luminance decay curves. The conditions varied were operating current mode (DC or pulse) and environmental temperature (25–120 oC). The decay curves measured were analyzed by fitting the curves to stretched exponential ones. The analysis results showed that the curves measured under both operation modes well fit to the stretched exponential ones, and that the curves measured under the pulse mode were closer to simple exponential curves than those measured under the DC mode. A rapid decline in the initial stages of operation appeared in the DC mode, though it was not clearly observed in the pulse mode. Thus, the luminance decay was divided into two major components: a simple exponential during operation and a rapid decline in the initial stages of operation. The simple exponential decline was due to a chemical degradation of Alq3, while the rapid decline is probably due to the generation of an internal electric field. The results also showed that the environmental temperature has little effect on the shape of the decay curves, suggesting that the relative contributions of the two decay components are independent of temperature.