Direct observation of structural changes in organic light emitting devices during degradation

Publication Type:

Journal Article

Source:

J. Appl. Phys., AIP Publishing, Volume 90, Issue 7, p.3242-3247 (2001)

ISBN:

0021-8979

Keywords:

2001, 2013 and earlier

Abstract:

A method for studying the degradation of organic light emitting devices(OLEDs) in real time is described. Transparent OLEDs allow for the
spatial correlation of cathode topographic images with optical images
(transmission, photoluminescence, and electroluminescence) of the devices
throughout the degradation process. In this study we focused on the
evolution of nonemissive, “dark” spots during device operation. We
conclude that the electroluminescent dark spots originate as nonconductive
regions at the cathode/organic interface and expand or grow as a result of
exposure to atmosphere. We propose a mechanism of dark spot growth
involving aerobic oxidation of the cathode/organic interfacial region,
leading to a highly resistive, carrier blocking interface at the dark spot
locations. No initial defects on the cathode surface, which might be
responsible for the formation of dark spots, were detected by atomic force
microscopy. Structural changes, such as degradation of organic materials
and the cathode surface, occur well after the formation and growth of the
dark spots.