Degradation mechanisms in electrically stressed organic light-emitting devices

The effect of electrical stress on polymer degradation has been studied on the organic device structure ITO/HTL/PPV/Ca/Ag. The devices were electrically stressed for duration up to different hours in nitrogen environment. The electrically stressed polymer was characterised by X-ray diffraction (XRD), photoluminescence (PL) spectrum and photoluminescence quantum efficiency (PLQE). The measurements were conducted from the side of glass substrate. PL results show that there is a significant drop after the sample has been taken out from the nitrogen environment and the PL intensity decrease extent differently with different stressing time. PLQE decreases with prolonged stress time. XRD results showed that there was an increase in crystallinity peak with increasing driving electrical stress time. All the results compared with non-stressed polymer give us a better understanding of the polymer degradation mechanism. (C) 2002 Elsevier Science B.V. All rights reserved.