Improvement of current-voltage characteristics in organic light emitting diodes by application of reversed-bias voltage

The effects of reversed-bias application on current-voltage and luminance-v oltage characteristics of standard-type double-layer organic light emitting diodes [OLEDs], ITO/TPD(50 nm)/Alq(3)(50 nm)/Mg:Ag, were investigated. Bot h the magnitude of reversed-bias and the duration of reversed-bias applicat ion were systematically changed. Evident voltage shifts towards the lower v oltage side in current-voltage and luminance-voltage characteristics were o bserved in the diodes which were treated under various reversed-bias condit ion. The longer the duration of reversed-bias application, the larger the v oltage shift was. A maximum voltage shift of 0.7 V was observed in the diod e treated under a -10 V bias for 3 h. Little change in luminance-current de nsity relationships was observed for diodes which were treated under variou s reversed-bias conditions. The results were interpreted in terms of the mo vement of ionic impurities and orientational rearrangements of permanent di poles in organic layers.