Zhenyue Luo

Emerging Quantum-Dots-Enhanced LCDs

Quantum dots (QDs)-based backlight greatly enhances the color performance for liquid crystal displays (LCDs). In this review paper, we start with a brief introduction of QD backlight, and then present a systematic photometric approach to reveal the remarkable advantages of QD backlight over white LED, such as much wider color gamut, higher optical efficiency, enhanced ambient contrast ratio, and smaller color shift. Some popular LC modes are investigated, including twisted nematic, fringing field switching (FFS) for touch panels, multi-domain vertical alignment (MVA) for TVs, and blue phase liquid crystal (BPLC) for next-generation displays. Especially, QD-enhanced BPLC combines the major advantages of FFS and submillisecond response time. It has potential to become a unified display solution.

High performance liquid crystal displays with a low dielectric constant material

We report high performance liquid crystal displays (LCDs), including fringe field switching (p-FFS) and in-plane switching (p-IPS), with a small average dielectric constant (e) but positive dielectric anisotropy material. Our low e based p-FFS and p-IPS LCDs offer several attractive properties, such as high transmittance, low operation voltage, fast response time (even at −20°C), which is particularly desirable for outdoor applications of mobile or wearable display devices, and suppressed flexoelectric effect. Combining these advantages with the inherent outstanding features, such as wide viewing angle, no grayscale inversion, negligible color shift, and pressure resistance, the low e LC based p-FFS and p-IPS are strong contenders for next-generation mobile displays, and high resolution and high frame rate TVs.

Fringe-Field Switching with a Negative Dielectric Anisotropy Liquid Crystal

We report a high performance negative dielectric anisotropy (Δε) liquid crystal for fringing field switching (n-FFS) display. We compare the electro-optic characteristics of FFS cells using positive and negative Δε LCs. With comparable driving voltage and response time, the n-FFS cell has advantages in higher transmittance, single gamma curve, less cell gap sensitivity and slightly wider viewing angle. LC director deformation distribution is analyzed to explain these performance differences.

Realizing Rec. 2020 color gamut with quantum dot displays

We analyze how to realize Rec. 2020 wide color gamut with quantum dots. For photoluminescence, our simulation indicates that we are able to achieve over 97% of the Rec. 2020 standard with quantum dots by optimizing the emission spectra and redesigning the color filters. For electroluminescence, by optimizing the emission spectra of quantum dots is adequate to render over 97% of the Rec. 2020 standard. We also analyze the efficiency and angular performance of these devices, and then compare results with LCDs using green and red phosphors-based LED backlight. Our results indicate that quantum dot display is an outstanding candidate for achieving wide color gamut and high optical efficiency.

Low voltage and high contrast blue phase liquid crystal with red-shifted Bragg reflection

We demonstrated a low voltage and high contrast polymer-stabilized blue phase liquid crystal (BPLC) by shifting the Bragg reflection to a red wavelength. To retain high contrast ratio, a left-handed BPLC is sandwiched between a right-handed circular polarizer and a left-handed circular analyzer. The driving voltage is reduced by 35% as compared to that of a transparent BPLC, while keeping submillisecond response time. The proposed approach would accelerate the emergence of BPLC for next-generation display and photonic applications.

A High Performance Single-Domain LCD With Wide Luminance Distribution

In this paper, we review the device structures and present the simulation results of four single-domain LCDs with a quasi-collimated backlight and a free-form optics-engineered diffuser. Such a non-emissive LCD exhibits similar luminance distribution to an emissive OLED, while keeping high transmittance, high contrast ratio over a large (80 °) viewing cone, with low ambient reflection, indistinguishable color shift, and negligible off-axis grayscale distortion.

Quantum Dots Enhanced Liquid Displays

Two types of dielectrophoretic liquid displays with patterned quantum dots (QDs) array for enhancing the color performance are demonstrated. QDs not only provide vivid color (~136% AdobeRGB in CIE1976 color space) but also greatly improve light efficiency by reducing the optical loss from color filters. These polarizer-free liquid displays offer vivid colors, high transmittance, wide viewing angle, and modest response time and contrast ratio. They are promising candidates for E-book and mobile display applications.

Fast-response liquid crystals for high image quality wearable displays

We demonstrate two ultra-low viscosity liquid crystal mixtures to enable field-sequential-color wearable displays for low temperature operation, while keeping a wide color gamut. Our mixtures offer ~4X faster response time than a commercial material at 20°C and ~8X faster at −20°C. Other major attractive features include: (1) submillisecond response time at room temperature and vivid color even at −20°C without a heating device, (2) high brightness and excellent ambient contrast ratio, and (3) suppressed color breakup with 360Hz frame rate.

A Spatiotemporal Four-Primary Color LCD With Quantum Dots

A four-primary liquid crystal display (LCD) by hybrid color processing in spatial and temporal domains is presented. By integrating with quantum dots, the number of LED can be reduced and the emission spectrum optimized. This approach exhibits following advantages over conventional three-primary LCDs: 1) it has 1.5X higher spatial resolution and 2X higher light efficiency; 2) it can achieve 130% color gamut in CIE 1931 and 155% in CIE 1976 color space; and 3) it has a more relaxed LC response time requirement and can be readily integrated into commercial LCD products.

A fast-response A-film-enhanced fringe field switching liquid crystal display

We propose a new A-film-enhanced fringe field switching (A-FFS) liquid crystal display whose required dΔn value is only λ/4, which is one-half of a conventional FFS. Fast response time can be achieved by either decreasing the cell gap (d) or choosing a low birefringence (Δn) and low-viscosity liquid crystal. The effect of dΔn mismatch between A-film and FFS cell on contrast ratio is analysed. By choosing a dispersion-matched A-film, we can obtain a reasonably high contrast ratio in the entire visible region.