In this review paper, a detailed overview of the transflective liquid crystal display (LCD) technology is presented. We first introduce the transflector classifications based on their composition and properties. Then, in reviewing the development history, we investigate the mainstream transflective LCDs, including their operating principles, advantages, and disadvantages. Finally, the image quality issues of transflective LCDs, such as color balance, image brightness, and viewing angle, are discussed.

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Transflective Liquid Crystal Displays

The presence of ions in liquid crystals is one of the grand challenges that hinder the application of liquid crystals in various devices, which include advanced 3-D and flexible displays, tunable lenses, etc. Not only do they compromise the overall performance of liquid crystal devices, ions are also responsible for slow response, image sticking, and image flickering, as well as many other negative effects. Even highly purified liquid crystal materials can get contaminated during the manufacturing process. Moreover, liquid crystals can degrade over time and generate ions. All of these factors raise the bar for their quality control, and increase the manufacturing cost of liquid crystal products. A decade of dedicated research has paved the way to the solution of the issues mentioned above through merging liquid crystals and nanotechnology. Nano-objects (guests) that are embedded in the liquid crystals (hosts) can trap ions, which decreases the ion concentration and electrical conductivity, and improves the electro-optical response of the host. In this paper, we (i) review recently published works reporting the effects of nanoscale dopants on the electrical properties of liquid crystals; and (ii) identify the most promising inorganic and organic nanomaterials suitable to capture ions in liquid crystals.

https://www.mdpi.com/2073-4352/5/4/501/pdf

Nano-Objects and Ions in Liquid Crystals: Ion Trapping Effect and Related Phenomena

A small quantity of BaTiO3 ferroelectric nanoparticles (FNPs) of 50 nm diameter was doped in a nematic liquid crystal (LC), and the free ion concentration was found to be significantly reduced in the LC + FNP hybrid compared to that of the pure LC. The strong electric fields, due to the permanent dipole moment of the FNPs, trapped some mobile ions, reducing the free ion concentration in the LC media. The reduction of free ions was found to have coherent impacts on the LC's conductivity, rotational viscosity, and electric field-induced nematic switching.

Effects of ferroelectric nanoparticles on ion transport in a liquid crystal

A photoluminescent liquid crystal display (PL-LCD) includes: a front plate and a rear plate; liquid crystals disposed between the front and rear plates; an electrode that is disposed on an inner surface of each of the front and rear plates and forms an electric field in the liquid crystals; an emitting layer that is formed on the front plate and emits visible light by being excited by light having a wavelength of about 390 nm to about 410 nm; a light source unit that is formed on a rear side of the rear plate and includes a lamp emitting near blue-UV light having a wavelength of about 390 nm to about 410 nm toward the emitting layer; and a UV filter blocking UV rays in ambient light from entering a front side of the front plate.

Photoluminescent liquid crystal display

Displays play an extremely important role in modern information society, which creates a never-ending demand for the new and better products and technologies The latest requirements for novel display technologies focus on high resolution and high color gamut Among emerging technologies that include organic light-emitting diode (OLED), micro light-emitting diode (micro-LED), quantum dot light-emitting diode (QLED), laser display, holographic display and others, QLED is promising owing to its intrinsic high color gamut and the possibility to achieve high resolution with photolithography approach However, previously demonstrated photolithography techniques suffer from reduced device performance and color impurities in subpixels from the process In this study, we demonstrated a sacrificial layer assisted patterning (SLAP) approach, which can be applied in conjunction with photolithography to fabricate high-resolution, full-color quantum dot (QD) patterns In this approach, the negative photoresist (PR) and sacrificial layer (SL) were utilized to determine the pixels for QD deposition, while at the same time the SL helps protect the QD layer and keep it intact (named PR-SL approach) To prove this method’s viability for QLED display manufacture, a 500-ppi, full-color passive matrix (PM)-QLED prototype was fabricated via this process Results show that there were no color impurities in the subpixels, and the PM-QLED has a high color gamut of 114% National Television Standards Committee (NTSC) To the best of our knowledge, this is the first full-color QLED prototype with such a high resolution We anticipate that this innovative patterning technique will open a new horizon for future display technologies and may lead to a disruptive and innovative change in display industry

High-resolution, full-color quantum dot light-emitting diode display fabricated via photolithography approach

Leakage current measurements are performed on prototype cells revealing an S-shaped current versus voltage curve. This result indicates the presence of ion generation and recombination in the liquid crystal bulk. The compensation of the electrical field and the saturation current are related to the alignment layer thickness and to the temperature. The slope of the I–V curve corresponds with Onsager's dependency of the ion generation. The time dependency of the current is modelled by an empirical fitting of the generation constant. A complete theoretical model is thus presented. The simulation fits with the measurements and gives a profound insight in the long term ion transport in nematic liquid crystal displays.

http://iopscience.iop.org/article/10.1143/JJAP.40.3272/pdf

Long-term Ion Transport in Nematic Liquid Crystal Displays

Liquid crystal displays using a UV backlight and photoluminescent color filter have the advantages of improved light utilization efficiency and wide viewing angle. In order to fully exploit these benefits, dedicated components are developed. Furthermore, technology needed to integrate these components and to make such a display are described.

23.3: Light-Efficient Liquid Crystal Displays Using Photoluminescent Color Filters

A radiation-sensitive detector includes a first substrate 202 with first and second opposing sides. The first side detects incident radiation, and the first substrate 202 produces a signal indicative of the detected radiation. At least one electrical contact 204 is located on the first substrate 202. An electrically conductive material 214 is coupled to the at least one electrical contact 204. The electrically conductive material 214 has a melting point in a range of about seventy-two (72) degrees Celsius to about ninety-five (95) degrees Celsius.

Direct conversion detector

Nematic liquid crystal displays (LCDs) contain ions that influence the electrooptical characteristics of the display. A typical super-twisted nematic (STN) display for mobile phone applications becomes darker at a standard driving frequency if it contains many impurity ions. We have discovered that ions can travel in the plane of the glass plates in the absence of a lateral electric field, leading to lateral nonhomogeneity in transmission (dark and bright stripes). In this paper, we present our research on the lateral ion transport dependence on the driving square wave (SQW) amplitude and dc component at a wide range of ion concentrations. The existence of a dc component, a high ion concentration and high SQW amplitudes increase the lateral ion speed.

The Influence of the Driving Voltage and Ion Concentration on the Lateral Ion Transport in Nematic Liquid Crystal Displays

The ions present in liquid crystal devices modulate the applied electric field and lead to deterioration of the expected good optical response. In addition to the flicker and ghost images, a boundary image-retention effect is also possible. It occurs near the edges of a stressed pixel. We have attributed this effect to ions moving in the plane perpendicular to the applied electric field. This hypothesis has been proven using a combination of electrical and optical measurements. The observed optical non-homogeneity and its evolution with stress time were explained using the new model of lateral ion transport. The physical cause of this phenomenon is subject to further study.

/pdf/measurements-of-lateral-ion-transport-in-lcd-cells-5201h0tqq5.pdf

Rob van Asselt

Papers

Long-term Ion Transport in Nematic Liquid Crystal Displays

23.3: Light-Efficient Liquid Crystal Displays Using Photoluminescent Color Filters

Direct conversion detector

The Influence of the Driving Voltage and Ion Concentration on the Lateral Ion Transport in Nematic Liquid Crystal Displays

Measurements of Lateral Ion Transport in LCD Cells