Lifetime and electric characteristics of encapsulated organic light-emitting devices

Abstract

Organic light-emitting devices (OLEDs) with tris-(8-hydroxyquinoline)aluminum (Alq(3)) which is typically a green emitter, have been studied by many researchers because of their potential for facilitating the development of flexible electronics. In this paper, the luminance characteristics, current, capacitance, and dispersion factor for degraded OLEDs, which were obtained by applying various bias currents (0.5 <= I-Bias <= 9 mA), are studied. The current dependences of lifetime were divided at approximately 2 mA, and they represented nearly linear behaviors but had different slopes in a logarithmic plot of lifetime versus ubias current. With OLEDs emitting, the anomaly of capacitance, as shown in the capacitance-voltage curve, occurred because of two factors, polarization in the bulk of organic materials and the interface between the metal and organic layers. In decayed OLEDs that had lower bias currents of less than 2 mA, it was found that the degradation of luminance was related to both the decrease in polarization and to the lowering of the injection barrier.