Progress of dark spot and blister formation in polymeric lighting-emitting diodes

Progress of dark spot formation during the device operation in polymeric light-emitting diodes (PLEDs) with poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) layer as an emissive layer was clarified by in situ measurement with the interferomer and other various analytical instruments. According to the morphological change of the Al electrode, the dark spot in electroluminescent images was initiated by the pinhole. It is found that the pinhole in devices is one of critical factors in the formation of dark spots. Blister formation due to the detachment of ITO / polymer layers in PELDs was varied by the humidity level of environmental conditions during operation and irradiation time of the light before operation.