Abstract
Molecular dye dispersed solution processable blue emitting organic light-emitting
devices have been fabricated and the resulting devices exhibit efficiency
as high as 25 cd/A. With down-conversion phosphors, white emitting devices
have been demonstrated with peak efficiency of 38 cd/A and luminous efficiency
of 25 lm/W. The high efficiencies have been a product of proper tuning of
carrier transport, optimization of the location of the carrier recombination
zone and, hence, microcavity effect, efficient down-conversion from blue to
white light, and scattering/isotropic remission due to phosphor particles.
An optical model has been developed to investigate all these effects. In contrast
to the common misunderstanding that light out-coupling efficiency is about
22% and independent of device architecture, our device data and optical modeling
results clearly demonstrated that the light out-coupling efficiency is strongly
dependent on the exact location of the recombination zone. Estimating the
device internal quantum efficiencies based on external quantum efficiencies
without considering the device architecture could lead to erroneous conclusions.
© 2007 IEEE
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