THESIS
2017
xx, 128 pages : illustrations (some color) ; 30 cm
Abstract
Nowadays, flat panel displays (FPDs), such as computer monitors, mobile phones and televisions,
are ubiquitous in our daily lives, presenting us information and entertainment. The liquid crystal
display (LCD) and organic light-emitting diode (OLED) display are the mainstream display
technologies due to their high-quality performance. The polarizer is an indispensable element in
LCDs, and has a great influence on their light efficiency and contrast ratio. The employment of a
polarizer is also necessary in OLED displays to improve the contrast ratio and readability under
sunlight. Conventional thin film polarizers have a thickness of around 25 μm and are based on
stretched polyvinyl alcohol (PVA) doped with iodine. The shrinkage force resulting from the
stretching process is a se...[
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Nowadays, flat panel displays (FPDs), such as computer monitors, mobile phones and televisions,
are ubiquitous in our daily lives, presenting us information and entertainment. The liquid crystal
display (LCD) and organic light-emitting diode (OLED) display are the mainstream display
technologies due to their high-quality performance. The polarizer is an indispensable element in
LCDs, and has a great influence on their light efficiency and contrast ratio. The employment of a
polarizer is also necessary in OLED displays to improve the contrast ratio and readability under
sunlight. Conventional thin film polarizers have a thickness of around 25 μm and are based on
stretched polyvinyl alcohol (PVA) doped with iodine. The shrinkage force resulting from the
stretching process is a serious concern for their application in flexible displays. For the
development of ultra-thin and flexible displays, polarizers with an ultra-thin profile and
compatibility with flexible displays are demanded.
Firstly, broadband reflective polarizers with a thickness less than one micrometer are
designed to improve the light efficiency of LCDs. We propose to generate giant form
birefringence based on a subwavelength silicon grating. The optical characteristics of the
proposed polarizer are investigated by the finite-difference time-domain (FDTD) method, and
show high transmission, a large extinction ratio and a wide acceptable angle. The proposed
polarizer can not only reduce the thickness of LCDs, but also improves the efficiency by 50% via
incorporating a backlight recycling technique.
What’s more, dichroic polarizers based on photoalignment methods are demonstrated.
Photoalignment is a simple and low-cost way to produce dichroic polarizers, and it shows
advantages for flexible displays because the produced polarizers are ultra-thin, are able to be
integrated inside LC cells and are free from the shrinkage issue. The main problem that has
hindered the practical application of dichroic polarizers produced by photoalignment is the
insufficient dichroic ratio. We propose two approaches to realize high-performance dichroic
polarizers based on photoalignment methods. Firstly, the photoalignment kinetics of AD-1 thin
films deposited by spin coating are studied, and the effect of relative humidity on the
photoalignment process and final achieved dichroic ratio is investigated on a hydrophobic
azobenzene molecule (AD-1) for the first time. An average dichroic ratio of up to 100 from 450
nm to 550 nm is realized after optimization, which is the highest value achieved among all
photoaligment-based approaches. Secondly, a novel photoalignment method is proposed, and
polarizers with a high average dichroic ratio of 55 from 400 nm to 500 nm are fabricated by
vacuum evaporation. Moreover, the energy consumed by this method is low, which is more
economical for practical manufacturing. Furthermore, the polarizers produced by both methods
are only several hundreds of nanometers thick, which are urgently demanded for ultra-thin and
flexible displays.
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