Degradation mechanisms in organic light emitting diodes

Lifetime measurement results on organic light emitting diodes (OLEDs) are presented and analyzed. The drive voltage tends to increase and the luminance tends to decrease with operating time. Upon the reversal of the polarity of the external field, the voltage trends are reversed almost completely and the luminance trends undergo weak changes. It is suggested that mobile ions can be the cause of the observed voltage changes. Mobile ion transient equations are solved and their time-dependent distributions are obtained. The mobile ion induced voltage changes are also calculated and fitted to the experiment. The agreement between the calculation and experiment suggest that the mobile ions can indeed be the origin of the observed device degradation phenomenon. (C) 2000 Elsevier Science S.A. All rights reserved.