Abstract
We investigate the electrical properties of three different trilayer
organic light-emitting diodes (OLEDs), one of which is based on a conventional
layered structure and the others on a blended structure where an emitting
layer (EML) is uniformly or stepwise mixed with an electron transport layer
(ETL), Tris-(8-hydroxyquinoline) aluminum (
${\rm Alq}_{3}$
). By way of simulations,
we visualize the electrical behaviors that provide a clear understanding on
why the uniformly mixed structure enhances further the longevity of OLEDs,
compared to the other configurations. Namely, the uniformly mixed structure
has the lowest concentration of positive charges in the ETL (thereby reducing
oxidative degradation of
${\rm
Alq}_{3}$
) and weakest electric field (decreasing the probability
of Joule heating), followed by the stepwise mixed one and then the layered
one. However, such blended structures show lower recombination efficiency
due to the delocalization of carriers (recombination), which has been demonstrated
by simulations of the current balance.
© 2009 IEEE
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