Zurich Federal Institute of Technology chemical engineers for the first time successfully developed a pure green light. The new light-emitting diodes will provide significant enhancements to the next generation of ultra-high-definition displays for televisions and smartphones.
Chih-Jen Shih, a chemical engineer at the Federal Institute of Technology in Zurich, is very satisfied with the breakthrough. "So far, no one has succeeded in producing green light like ours."
The ultra-thin, flexible light-emitting diode (LED) shows the three letters "ETH" in bright green tones.
Shih's research is progressing significantly, especially in the next generation of ultra-high-resolution displays for televisions and smartphones. The electronic device must first be capable of producing ultrapure red, blue and green light so that the next generation of displays can display clearer, richer details as well as images of finer color ranges. In most cases, red and blue light can already be achieved; however, the green light has reached the technical limit.
This is mainly due to differences in human perception; because compared to red and blue tones, the human eye can distinguish between more intermediate green tones. "This makes the ultra-pure green process very complex and presents us with a great challenge in developing technology and materials," said Sudhir Kumar, co-principal author of the study.
Purity up to 99% green
From the definition of ultra-high-definition norms of the ITU Rec.2020 international standard can be clearly seen, Shih research and development of ultra-green light in the next generation of the development of the display has made great progress. The international standard defines the technical requirements for ultra-high resolution (known as "Ultra HD") displays, providing a basic framework for further research and development. These requirements also include improved visual quality of the naked eye. The standard provides a color scale that the display can reproduce, thus providing a wider range of colors.
Ultra-pure green plays a key role in extending the color range or color gamut. Eventually, new colors are created by mixing the three primary colors (red, blue, and green). The more pure the color, the wider the range of colors that the screen can display. Shih developed a new LED to 97% to 99% of the Rec.2020 international standard. In contrast, the market's most pure color TV display on average only 73.11% to 77.72%, no more than 80%.
Cheap, can produce LED technology
Wendelin Stark, professor of functional materials engineering at the Federal Institute of Technology in Zurich, and researchers from South Korea and Taiwan also contributed to the project. Shih not only made breakthroughs in research results, but also made breakthroughs in materials and methods. He and his colleagues have developed a thin, flexible, light-emitting diode that emits pure green light at a simple room temperature. Shih said that this is the second aspect of the project breakthrough. Because so far, through the LED technology to produce pure light need to use high-temperature process, this breakthrough is at least the same important position. "Because we are able to achieve the whole process at room temperature, we have the opportunity for future simple, low-cost industrial production of ultra-green light-emitting diodes," said Jakub Jagielski, principal co-author of the study.
More precisely, Shih and his team have further developed the LED technology using nanomaterials. The light emitting diode typically includes a semiconductor crystal that converts the current through the diode into radiated light. The raw material is usually indium gallium nitride (InGaN); however, the material does not have the ideal properties for producing ultrapure green light. So Shih's team turned to perovskite, which could also be used for the production of solar cells and could convert electricity to light relatively efficiently. Shih pointed out that this material is very cheap, but also make the whole manufacturing process simple and fast - chemical clean perovskite only half an hour, then you can use.
Shih developed the thickness of the perovskite material in the light-emitting diodes is less than 4.8 nanometers. This is also a very important factor because the color quality depends on the thickness and form of the nanocrystals used. In order to achieve the required pure green, the thickness of the crystal should be just right, not too thick nor too thin. These flexible ultra-thin LEDs can be bent like paper. Thus, production can be carried out inexpensively and quickly using, for example, existing roll-to-roll processes. Shih said the progress will also benefit the future of industrial production.
Next goal: to improve LED efficiency
However, it takes time to realize the first industrial application of ultra-green light-emitting diodes. The next step of the Shih team is to improve efficiency first. At present, he developed the LED in the electric conversion to light when the efficiency of 3%, compared to the current market, the TV screen efficiency value of 5% to 10%. Shih hopes that the next version will increase efficiency by 6% to 7%. In addition, he also found the potential to enhance its LED life. At present, the LED light only two hours, while the market can use the display for many years.