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Scientific Interpretation of Quantum Dot Display Technology

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Time of issue:2016-08-03
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(Summary description)"Quantum Dot TV" is a new product with a very high frequency in the color TV market in the past two years. Like other new things, quantum dot TV has been questioned since its inception, and the most common one is the "cadmium pollution" problem.

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Scientific Interpretation of Quantum Dot Display Technology

Categories:Company News
Author:
Origin:
Time of issue:2016-08-03
Views:0

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Introduction: "Quantum Dot TV" is a new product with a very high frequency in the color TV market in the past two years. Like other new things, quantum dot TV has been questioned since its inception, and the most common one is the "cadmium pollution" problem. A few days ago, Professor Xiaogang Peng, a top expert in the field of international quantum dot display and currently working in the Department of Chemistry at Zhejiang University, interpreted the quantum dot display technology.

What are quantum dots?

Quantum dots are a kind of solution semiconductor nanocrystals. The size of quantum dots ranges from 2 nanometers to 8 nanometers. Depending on the diameter of the same chemical composition, quantum dots can emit light ranging from blue, green, yellow, orange, to red.

Quantum dot technology first appeared in the late 1970s. It was discovered when Western countries wanted to find an efficient photoelectric conversion technology during the oil crisis. The scientific community believes that “quantum dots may be the most excellent luminescent material ever discovered by mankind.” Because quantum dots can achieve continuous and controllable light emission by changing the size, and light of any wavelength can be achieved. In addition, the color purity of quantum dot luminescent materials is very pure, which is hard to compare with other luminescent materials that humans have.

At present, research on quantum dots is a very popular field internationally, and the number of papers published in a year can be tens of thousands. The American scientist Brus and the former Soviet Union scientist Efros, who have made important contributions to the quantum dot display theory, are also hot spots for the Nobel Prize.

Application of quantum dots in the display field

The areas where quantum dot technology can be used mainly include LEDs, solar cells, and bio-medical markers. But I personally think that it is the LED lighting field that can enter human life relatively quickly.

The application of the first generation of quantum dot technology is the "photoluminescence" element. Adding a film with green and red quantum dots in front of the blue LED can emit the white backlight required by the liquid crystal display. Compared with the traditional white light backlight, the color purity of the three primary colors of red, green and blue is very high in the quantum dot white light backlight. There are three very obvious "peaks" in the spectrogram, instead of the ordinary LED backlight, which is flat. And continuous white light.

Photoluminescent quantum dots mainly solve the fatal problem of too small color gamut of traditional liquid crystal displays. Even with the latest BT2020 color gamut in the industry, quantum dots can theoretically achieve close to 100%. The color gamut of quantum dot TVs on the market can basically reach 65%-90% of BT2020 (ordinary LCD screens, including iPhone screens, can only cover about 50% of the BT2020 color gamut).

The second-generation quantum dot technology currently under study is an application represented by "electroluminescent" materials. The so-called "electroluminescence" means that the material can emit light directly when current is applied to it. If it is applied to a liquid crystal display device, it does not require a backlight and color filters. Since quantum dots are inorganic materials, they not only have better stability, but also can realize flexible display and even printed display, and have very broad application prospects. At present, this technology is still in the laboratory stage, and I expect to gradually get out of the laboratory and start commercial applications in 3-5 years.

About cadmium pollution in quantum dots

The first generation of quantum dots, that is, photoluminescent quantum dots, will use a certain amount of cadmium in the production process. Therefore, the most controversial point of quantum dot TV at present is its "environmental protection."

The main reason why the toxicity of cadmium gets everyone's attention is mainly due to the discharge of nickel-cadmium batteries and mines. A large nickel-cadmium battery contains up to 22g of cadmium. Taiwan and other places have produced "cadmium rice" with a cadmium content that exceeds the standard. But on a quantum dot TV, a square centimeter of quantum dot LED only needs 0.000002g of cadmium, which is one ten-millionth of a nickel-cadmium battery, roughly equivalent to the amount of cadmium in a cigarette. The current quantum dot backlight TVs on the market, take a TCL 55-inch quantum dot TV that went on the market last year as an example. The cadmium content in it is approximately equivalent to the cadmium content of one kilogram of international standard rice. In other words, if you eat one TV set, it is equivalent to eating one kilogram of international standard rice. Therefore, the content of cadmium in quantum dot TVs is not terrible from a scientific point of view, but it is rendered terrible by some people who do not know the truth.

Secondly, the TV is not for food when you buy it back. The cadmium in the quantum dot TV is encapsulated in a polymer medium. Take the quantum dot TV component that I am familiar with as an example. The quantum dot material will not leak, nor will it run out by itself, even if it is smashed, it will not run out. It is extremely difficult to be absorbed by the human body and extremely difficult to be released into the air and In the water. When producing quantum dots in the United States, in order to obtain approval from the U.S. Environmental Protection Agency, the quantum dot components were crushed and immersed in hydrochloric acid. The final result was that no cadmium was detected in the hydrochloric acid solution.

Regarding the danger of cadmium quantum dots, there are two more facts that can be shared with you:

First, the quantum dot production technology I invented in the United States is called green synthetic chemistry. Later, the American company QDvision industrialized this technology on a large scale and applied for the "Green Chemistry Presidential Award" in the United States.

Second, my students in laboratories in the United States and China, NN-Labs and Najing colleagues usually check the body's cadmium content every year. In the past ten years, no one has found detectable amounts of cadmium in their bodies.

So in comparison, the cadmium content of quantum dot TVs is not a problem from a scientific point of view.

Are quantum dots and OLED comparable?

OLED is also a popular self-luminous display technology. In the past, it was generally believed that the development roadmap of TV sets was from CRT-LCD liquid crystal-OLED, but if quantum dots can achieve electroluminescence, it will pose a challenge to the OLED technology route.

Compared with the first-generation quantum dot backlight TV based on photoluminescence technology, OLED TV does have advantages in black field, flexibility, and viewing angle. The black field is when it is completely black, LCD will never catch up with OLED; flexible, OLED can be made on a flexible substrate. But in terms of brightness and color gamut, the first-generation photoluminescent quantum dots are no longer inferior to OLEDs.

If electroluminescent quantum dots go out of the laboratory, then I believe that these last advantages of OLED will soon disappear. Electroluminescence quantum dots are used for display, the same is quantum dots, the same material, electroluminescence is not limited by the color filter, and the achievable color gamut range is larger than that of photoluminescence. Moreover, the advantages of quantum dots will be more prominent in terms of production energy consumption and end product life.

The future of quantum dot technology

In the first generation of photoluminescent quantum dot TVs, China is currently not lagging behind others. From the perspective of making quantum dot materials and backlight components, there are currently three most competitive companies: QDVision, Nanosys, and Nanojing Technology. The first two are American companies. QDVision can produce tube-type quantum dot backlights. Nansys’ quantum dots can be used to produce thin-film quantum dot backlights. Only Nanocrystalline’s quantum dots can produce two types of quantum dot backlight components at the same time.

When I came back from the United States, I thought that electroluminescence quantum dot technology was the easiest area to break through. As a result, our laboratory began to concentrate on conquering quantum dot electroluminescent materials. Under normal circumstances, the study of quantum dot luminescence is to study their photoluminescence, which is characterized by a photon that can emit light. The principle of electroluminescence is completely different. It requires an electron and a hole to reach a quantum dot at the same time. In our laboratory at Zhejiang University, the main focus of the past few years has been to understand and control the photoluminescence of quantum dots, and to improve it to an unprecedented level. On this basis, it can be realized as electroluminescent quantum dots.

The Ministry of Industry and Information Technology of our country also regards quantum dot printing and display as a key national technology and the direction of the next-generation display industry. The Ministry of Science and Technology has also released the "13th Five-Year Plan", which lists QLED printing as a key common technology. The country believes that quantum dot printing technology is promising to become the mainstream of next-generation displays. In this regard, we must maintain our current leading position. If this is achieved, it will be of great significance to the country's strategic value. China is the world's largest manufacturer of display terminals, but we basically rely on imports for our high-end LCD and OLED high-end display modules and modules, which consumes a lot of foreign exchange reserves. If the quantum dot printing and display field can maintain its leading position and take this leading position to occupy the commanding heights in the entire industrial process, it is very important to the national strategy. After all, display is a big industry related to all aspects of our production and life.

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