Organic light-emitting diodes (OLEDs) are of considerable interest in flat panel displays and ligh-ting applications due to their many advantages
however
only about 20% light generated from the organic layer in the devices can escape to external forward space due to total internal reflection effect. Therefore
many methods have been used to increase the outcoupling efficiency of the devices. In this article
a monolayer of polyethylene (PS) microspheres (MS) with diameter of around 3 μm was prepared by self-assembly method on microscope cover glass. The microlens-like structure was obtained by annealing the PS MS monolayer at 120 ℃ for around 20 min. The annealed PS MS monolayer was then optically coupled (by refractive-index-matched material) on the outside of an OLED
with structure of Glass/ITO(40 nm)/NPB(40 nm)/Alq
3
(60 nm)/LiF (1 nm)/Al (100 nm) as a light scattering layer. The OLEDs with the annealed monolayer of PS MS exhibit improved normal direction luminance and efficiency (about 9% at the current density of 50 mA/cm
2
and the luminance round 1 250 cd/m
2
) compared to the control devices
which indicated that part of the light confined within the glass substrates can be extracted to the external forward space through scattering effects of the annealed monolayer of PS MS.
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references
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