Progress of dark spot formation during the. device operation in polymeric l
ight-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 inst
ruments. According to the morphological change of the Al electrode, the dar
k spot in electroluminescent images was initiated by the pinhole. It is fou
nd 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 lay
ers in PELDs was varied by the humidity level of environmental conditions d
uring operation and irradiation time of the light before operation.