The Role of Quantum Dot Technology in LCD Displays

By Cici Wang

Display Quantum dot technology, abbreviated as QLED, is a trademark created by Samsung. It is a backlight technology used in liquid crystal displays (LCDs). It can provide a wider color gamut, higher contrast and more vivid color performance. QLED uses a nanoscale semiconductor material called quantum dots to improve the light emission and filtering process. Thus resulting in more accurate and saturated colors. In this article, we will give a brief introduction to The Role of Quantum Dot Technology in LCD Displays.

TV with Quantum Dot Technology

Features of quantum dot technology for displays include:

a. Wider color gamut: Quantum dots can provide a wider color gamut. That is, by displaying more colors, the image seems more vivid, delicate and realistic.

b. Higher contrast ratio: The high light purity and color saturation of quantum dots can improve the contrast ratio of the display. Thus making blacks deeper and whites brighter.

Quantum dot technology is often used in the backlighting of liquid crystal displays, so-called quantum dot light-emitting diodes (QLEDs). This is different from organic light-emitting diode (OLED) technology. Because OLED technology uses light-emitting materials directly for pixels and does not require a backlight. Each technology has its characteristics and application fields.

Quantum dot technology builds on traditional LCDs. By placing the quantum dot layer between the backlight and the LCD, the quantum dot layer can precisely adjust the color and make the image more colorful.

Quantum dot technology

Quantum dot display technology mainly has two technical routes: photoluminescence and electroluminescence.

a. Photoluminescent quantum dot display technology (QD-LCD)

The current commercialized quantum dot display products are mainly based on the principle of photoluminescence. It is the product of the combination of quantum dot backlight technology and liquid crystal display. In the early days, glass sealing protect QD materials to manufacture QD-glass tubes with high stability. In the display field, they utilized quantum dots to achieve high color gamut display effects.

However, the shape of quantum dot tubes is solidified, and the requirements for specifications often require custom development. But it is weak in versatility, so it is quickly eliminated by the market. In order to realize the characteristics of light and thin, portable, and narrow frame of display equipment, the technology has gradually developed into quantum dot film. It uses expensive barrier film for upper and lower protection. And it forms a sandwich structure with QD glue to improve its reliability.

Applying the quantum dot film form to the backlight part of the liquid crystal display can significantly improve the color saturation, three-dimensionality and clarity of the screen image, and greatly improve the image quality. People widely use it in TVs, monitors, laptops, tablets, vehicles, and VR. It is the most mature and mainstream solution in quantum dot photoluminescence display technology in the market.

In addition to films, other display components such as diffusion plates and light guide plates can also utilize QD. At present, the quantum dot diffusion plate adopts melt co-extrusion technology, which has high production efficiency and low cost, and has great market potential in low-end and medium-end products.
In addition, directly in-situ packaging QDs on LEDs can maximize the efficiency of quantum dots. However, this method requires quantum dot materials to remain stable in a high-temperature environment, which is difficult to realize. If commercialized, it will become a super-scale application.

b. Electroluminescence quantum dot display technology (QLED)

Quantum dot light-emitting diodes consist of five parts: anode, hole injection/transport layer, quantum dot light-emitting layer, electron injection/transport layer and cathode. The working principle of QLED involves injecting holes from the anode and electrons from the cathode under the drive of an external voltage. The working principle of QLED involves injecting holes from the anode and electrons from the cathode under the drive of an external voltage. These holes and electrons are then transported through their respective transport layers to the quantum dots, resulting in exciton recombination and light emission.

As a next-generation new display technology, QLED has significant advantages. From the perspective of color gamut, due to the extremely narrow half-peak width and adjustable luminous wavelength with size, QLED theory can reach 140% NTSC color gamut, which is much higher than OLED‘s 100% NTSC and LCD‘s 72% NTSC. It can produce natural colors and provide strong technical support for ultra-high-definition display fields such as the future Metaverse.

In terms of contrast, since both QLED and OLED are based on self-luminous technology, they will be significantly better than traditional liquid crystal display technology based on passive luminescence in terms of contrast, and can provide more pure black field display effects for display devices. In terms of product form, QLED technology and OLED have similar device structures, and both can achieve ultra-thin and flexible features. From the perspective of energy consumption, according to the arrangement from low to high, the energy consumption levels of several technologies are QLED (low) < OLED (medium) < LCD (high); Compared with OLED, QLED requires lower driving voltage at the same brightness, so it requires lower energy consumption; Because LCD is a backlight technology, the conversion of white light into a single color light requires filtering a large amount of other light energy, so the energy consumption is relatively high.

QLED has many advantages in brightness, size and service life. The latest technology makes its display black level and viewing Angle improved. QLED TV can provide better display effect in the day, cost-effective is also higher.

However, in terms of image quality, OLED is the winner. OLED TV provide better viewing angles, purer black display, better contrast, while being lighter and thinner, using less energy, and having better display at night.

Q&A:

  1. What is Quantum dot?

It is a nanoscale semiconductor material.

  • The difference between QLED and OLED.

OLED uses light-emitting materials directly for pixels and does not require a backlight.

  • Two technical routes of Quantum dot display technology.

Photoluminescence and electroluminescence.

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