Online proceedings - EDA Publishing Association

11-13 May 2011, Aix-en-Provence, France
Brightness Enhancement of OLEDs by Using
Microlens Array Film with Silicon Oil and Ag
Particles
Shan-Shan Hsu 1 , Tung-Yu Chang 1 , Hsiharng Yang 1 , Jen-Sung Hsu 2
1 Institute of Precision Engineering, National Chung Hsing University, Taichung, Taiwan 402
2 Chemical Systems Research Division, Chung-Shan Institute of Science & Technology, Tao-Yuan, Taiwan 325
Abstract- This paper introduces a new method to
improve the external quantum efficiency of organic
light emitted diode (OLED) by adding Ag particle into
the silicon oil layer in OLED. By measuring the
brightness of the front luminance, when the lens is 11μm
in height and 30μm in diameter, the brightnes is
increased 45% by adding the silicon oil between OLED
module and brightness enhancement film, and the
brightness could be further improved to 61% by adding
the Ag particle into the silicon oil. In this work, the
optical waveguide was disturbed by adding Ag particle
into silicon oil and let more lights emit from the OLED
component, it results in higher external quantum
efficiency and lower energy consumption.
I. INTRODUCTION
Various light sources play important roles in recent
displays. Especially for those consumers’electronic devices,
low power consumption and light weight are required.
Conventional CRT (cathode ray tube) television has been
replaced by TFT LCD (thin film technology liquid crystal
display). Obviously, backlighting modules using LEDs
(light emitted diodes) have replaced CRT as the main stream.
However, LED is a point light source, it requires a light
guide plate and other optical films to achieve a lighting plane
for the display. The plane lighting technology may need to
develop for the displays. In 1987, Tang and VanSlyke using
vacuum deposition method to produce the organic light
emitted diode (OLED), the research of OLED grow up
rapidly since that [1]. Due to OLED fit the requirement of
energy saving, high uniformity, flatness, and large size
capability, also it has the benefits such as simple
manufacture process, self -illumination, short response time,
no perspective limit, high contrast ,and low driving voltage,
OLED draw a lot of attention for the next generation display
device. The most important reason people interest in OLED
is the capability of using flexible base plate. Therefore,
OLED not only have the potential to be the illuminate
component for next generation, it also become the major
competitor of the flat display technique in the future [2-4].
The external quantum efficiency is the ratio of the light
generated by the illuminate component and the external light.
The quantum efficiency is usually improved by disturbing
the optical waveguide. Kwon et al., 2008 [5], successfully
fabricates a high-sag microlens array film with a full fill
factor by a simple micromachining process including trench
formation and the conformal vapor phase deposition of a
polymer. According to the fabrication design process, the
lens diameter increased from 12 μm to 17.32 μm, the
required initial radius of curvature of the reflowed
photoresist pattern is 6 μm, and both the final radius
curvature and the sag height after the conformal gap-filling
proces are 8.66 μm. The normal brightnes of the ful white
light emitted from the test panel was measured by PR-650
spectra colorimeter, the result shows the luminance was
increased by up to 48%.
Wei et al., 2006 [6], study the influences of the edge
length and the gap of the microlens array on the luminance
efficiency on OLED. They use the photolithography and hot
melt process to transform these base plates into the shape of
the microlens array on substrate. The duplicated microlens
array adhering to the PMMA film was formed after
separating the mold from the film. The luminance efficiency
of OLEDs has been found to increase linearly with the
increasing area ratio of the microlens base area to the device
area and microlens number density. The luminance
efficiency measured by CS-100 spectra colorimeter was
increase by up to 55%.
Wei et al., 2006 [7], analyze the influences of the fill
factor and the sag of hexagon-based microlens on the optical
characteristics of OLED device. Compared to OLED, the
luminous current and power efficiency of the device can be
enhanced by 35% and 40%, respectively, by attaching a
microlens array having a fill factor of 0.90 and a height ratio
of 0.56. The result shows the efficiency increased as the lens
size decreased and the height ratio increased.
Möller and Forrest [8] demonstrate that ordered
microlens arays with 10μm diameter siloxane lenses
attached to glass substrates increase the light output of
OLED by a factor of 1.5 over unlensed substrates. Peng et.
al., 2004 [9], employed a simple soft-lithography approach
to fabricate the microlens array on glass substrates. With the
use of an optimized lens pattern, an increase of 70%
efficiency in the coupling efficiency is achieved. Lee et al.,
2003 [10], introduced a photonic crystal pattern into the
glass substrate of an OLED. The finite-difference
time-domain method was used to optimize the structural
parameters of the photonic crystal pattern. With the use of an
optimized photonic crystal pattern, an increase in the
extraction efficiency of over 50% was achieved
experimentally.
294