Display technology contrast, LCD / quantum dot / OLED have flaws

Recently, the display industry, quantum dot display technology, the major manufacturers are rushing to produce quantum dot displays, but the display industry can not be completed overnight, the quantum dot display turned out, whether it is good or not, it is not very powerful, today is a simple Take everyone to see what is a quantum dot and what is a quantum dot display.

What is a quantum dot?

First, we need to understand what quantum dots (QDs) are. Quantum dots are very small semiconductor particles, only a few nanometers in size, so small that their optoelectronic properties differ from the optoelectronic properties of larger particles.

The principle of luminescence is to apply stimulation to the quantum dot material by electricity or light. The material of the quantum dot will emit light of a specific frequency, and these frequencies can be changed by changing the size and shape of the quantum dot to achieve precise tuning.

Simply speaking, the photoelectric properties of quantum dots are quite different from those of conventional luminescent display particles. Because quantum particles are very small, in nanometers, the display color of quantum dots is changed by changing the size and shape of the particles. Because of this, in theory, quantum dots show more continuity and lower cost.

In fact, it is a nano-scale particle. We know that many materials have different physicochemical properties at the nanometer level, but quantum dots are better to call.

Quantum dots of different sizes emit different colors. When stimulated by light or electricity, quantum dots emit colored light. The color of the light is determined by the material and size of the quantum dots. Generally, the smaller the particles, the longer the wave will be absorbed. The larger the particle, the shorter the wave will be absorbed.

The 2 nm-sized quantum dot absorbs the long-wave red and shows blue; the 8 nm-sized quantum dot absorbs the short-wave blue and appears red. This feature allows quantum dots to change the color of the light emitted by the source. Compared to the original display technology, the RGB three primary colors displayed by quantum dots will be more pure.

Current application of quantum dots on displays

In fact, quantum dot technology is not an emerging technology. As early as 1983, scientists at Bell Labs in the United States have studied it.

Only a few years later, Marc Reid, a physicist at Yale University in the United States, officially named this semiconductor micro-block as a "quantum dot" and used it to this day. So strictly speaking, this is not a new technology, only recently. In the past few years, the display giant led by Samsung has developed a strong interest in quantum dot technology.

Well, after understanding the origin and characteristics of quantum dots, let's take a look at the current application of quantum dots on displays, and what is the difference between traditional LCD displays and OLEDs that are currently very hot.

LCD panel

Let's take a look at the long-standing LCD display technology. The LCD display structure is very complicated. The LCD is constructed by placing a liquid crystal cell in two parallel glass substrates, and a TFT (thin film transistor) and an upper substrate glass on the lower substrate glass. A color filter is disposed on the TFT to control the rotation direction of the liquid crystal molecules by changing the signal and voltage on the TFT, so as to control whether the polarized light of each pixel is emitted or not to achieve the display purpose.

According to the backlight source, the LCD display is divided into CCFL (Cold Cathode Fluorescent Tube) and LED (Light Emitting Diode). We generally think that the LCD and LED are the two types of display is wrong, it is completely the majority of manufacturers. Misleading, the two are just different backlight sources.

Of course, the different panels for LCD alignment are not going deeper here.

OLED panel

The OLED panel is quite different from the LCD panel. In comparison, the OLED panel structure is simpler. The OLED is called an organic light emitting diode. That is, the luminescent material of the OLED panel is an organic material, compared to an inorganic material. Organic materials have a natural shortcoming in terms of life.

OLED display technology has self-luminous properties, using a very thin coating of organic materials and a glass substrate. When there is current, these organic materials will emit light, and the OLED display screen has a large viewing angle and can save power.

Because of the self-illuminating properties, OLEDs are more pure in black, because the material is black as long as it does not emit light, while the viewing angle is wide, the contrast is high, the power consumption is low, and the reaction rate is high.

Quantum dot panel

Quantum dot technology, which we have already said, will not go into details any more. Now, what are the differences between quantum dot displays?

In fact, as far as the current quantum dot screen is concerned, the traditional LCD panel is only a backlight change, and it is an extension of the LCD panel, and there is no fundamental change.

Popularly speaking, the current quantum dot display is to add a film in the VA panel, which is the QDEF film in the above figure.

We all know that in the current LED backlight mode, in order to show the three primary colors, there are two backlight methods:

One is to directly backlight through RGBLED lighting, so the cost is very high, basically no display is used; the second is the common backlight mode of commercial display: pseudo white LED backlight, using pixel color phosphor color, what is pseudo white LED Backlighting is to emit a white backlight by adding a yellow phosphor to the blue LED (the position of the blueLEDs in the figure above).

This is also the source of the Internet's wide-ranging "screen with blue-light eyes", but there is a saying that "aside from the dose, the toxicity is a rogue", as long as it is a display that meets the safety standards, and reasonable use of the eye, it will not The rumors that caused a major network to spread, so don't worry too much.

Quantum dot panel display principle

However, if color is developed by quantum dots, there is no need to perform white backlighting. There are two reasons (in fact, it should be counted as one): the reason for photoluminescence, blue quantum dots cannot be debuted, so blue must be added in the backlight. The color light source, secondly, is because the current quantum dot is only responsible for generating green light and red light, so the white LED in the original backlight module must be replaced with a blue LED.

At the same time, the placement of the QDEF layer is very important. In order to allow the light to travel through the QDEF when traveling in the layered optical film, the QDEF has to be placed closest to the light source, once in order. Shifting, the conversion of red and green light is insufficient, which will cause a blue phenomenon.

At the same time, the application of QDEF film and blue LED light source is also one of the reasons why the quantum dot display color display is more pure than the ordinary display.

So here will be said, in terms of the current quantum dot display technology, only the backlight of the screen has been changed, and a film has been added.

What is the actual experience of quantum dot technology?

In fact, the technical prospects of quantum dots are very broad, and it is not just a change in backlighting. Quantum dot technology is advancing toward LED packaging (encapsulating quantum dot materials into LEDs).

The current QDEF film is not cheap. For a 55-inch TV, a QDEF offer is about $100.

A large part of the source is because the material needs water-blocking oxygen. Because the quantum dots are inorganic, they claim to be more stable than OLEDs in propaganda, but in fact nano-sized quantum dots are sensitive, not only as hot as phosphors, but also Like OLEDs, they are afraid of water and oxygen, and they are more stable than OLEDs. There is really no such capital.

In the process of commercialization, much energy and cost are consumed in water-blocking oxygen. Taking QDF from 3M and Nanosys as an example, QDEF is about 210μm thick, and the upper and lower barrierFilm (water-blocking oxygen layer) accounts for 110μm, and the cost also accounts for half of the whole film.

What is the actual experience brought by such a expensive film?

As we said before, because of the special properties of quantum dot materials, it can emit light close to continuous spectrum, that is, the color of quantum dots can be more delicate and the color gamut can be wider, which is also strongly claimed by many quantum dot display manufacturers. In fact, our evaluation room also measured the corresponding quantum dot display, which is much better than the non-quantum dot display in the color gamut. This is also determined by the material properties of the quantum dots.

User comments on a brand 27-inch 2K resolution quantum dot display grainy serious

Our website has also been authorized to reprint a user's quantum dot display experience.

But we see the advantages, we must also see the shortcomings of the current quantum dot display.

In an e-commerce platform, many netizens found that the quantum dot display has a very heavy graininess after buying a monitor. Even if the resolution of the display reaches 2K (27 inch), there is still a very heavy graininess. The reason is unknown.

At the same time, because the current quantum dot technology is still an extension on the VA screen (LCD) panel, the leakage and color cast of the LCD panel are also present on the quantum dot display. This is the current quantum dot backlight technology without circumvention. Can only say that the quality control of each manufacturer.

DIY old driver summary

So is it a good technique to talk about quantum dots? Xiao Bian seems to be a good technology. There has always been a comparison between quantum dot technology and OLED technology on the Internet. The future is definitely the PK of these two technologies. But in terms of the current actual experience, it is not necessarily better than the mature traditional LCD panel, let alone the OLED panel.

The future development direction of quantum dot technology

Of course, the current quantum dots are not particularly satisfactory, but if you see the future of quantum dots and the direction of development, there must be a very broad space.

It can be roughly divided into three stages: one, replacing the traditional luminescent phosphor; the second, removing the color filter; the third is officially becoming the luminescent layer (that is, the current OLED pixel self-luminous form)

Future quantum dot technology will inevitably bring fundamental changes to the display industry, even revolutions, but there is still a long way to go.