Real-time visualization of thermally activated degradation of the ITO/CuPC/NPB/Alq3 stack used in one of the organic light-emitting diodes

Abstract

We demonstrate the thermally activated degradation pathways of the ITO-coated glass/CuPc (copper phthalocyanine)/NPB (N, N′-di(naphthalene-1-yl)-N, N′-diphthalbenzidine)/Alq3 (tris(8-hydroxyquinoline aluminium) device by using variable temperature tapping mode atomic force microscopy. It is observed that the initially morphological change of the top Alq3 surface occurred at about 75°C. NPB gradually erupted from the Alq3 capping layer at 120°C. The NPB layer and the Alq3 layer were gradually mixed with increase in temperature from 130°C. Simultaneously, de-wetting took place at the interface of CuPc/NPB. Using conducting atomic force microscopy we see that morphological change in the device leads to a variation in current–voltage characteristics of the degraded ITO/CuPc/NPB/Alq3 device. The results should shed light on the thermally activated degradation mechanisms of organic light-emitting diodes.