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

We demonstrate the thermally activated degradation pathways of the ITO-coated -lass/CuPc (copper phthalocyanine)/NPB (N, N'-di(naphthalene-1-yl)-N,N'-diphthalbenzidine)/Alq(3) (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 Alq(3) surface occurred at about 75degreesC. NPB gradually erupted from the Alq(3) capping layer at 120degreesC. The NPB layer and the Alq(3) layer were gradually mixed with increase in temperature from 130degreesC. 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/Alq(3) device. The results should shed light on the thermally activated degradation mechanisms of organic light-emitting diodes.