Chemical engineers from Eidgenössische Technische Hochschule Zürich, (ETH Zurich) which translates to Swiss Federal Institute of Technology Zurich, have developed an ultra-pure green LED light for the first time. The new LED is expected to lead to visibly improved color quality for a new crop of ultra-high definition displays for TVs and smartphones.
Chih-Jen Shih, professor of Chemical Engineering at the Hönggerberg campus said, “To date, no one has succeeded in producing green light as pure as we have.” He pointed to an ultra-slim, bendable light-emitting diode (LED), which shows the three letters “ETH” in a distinct hue of bright green.
The new LED is reportedly up to 99% green. According to the researchers, even the best displays available on the market use green that is no more than 80% pure.
This green purity is in line with the Rec.2020 international standard which requires prescribes 97-99 % pure green for next generation displays. The international standard specifies the technical requirements for ultra-high resolution (known as “Ultra HD”) displays and gives a framework for further research and development. The purer the green and other colors, the wider the color gamut that mixtures of the color LEDs can produce.
Green is especially difficult to make pure because human perception of green light is exceptionally precise. Humans can perceive a much broader range of intermediary green light than they can of red and blue.
“This makes the technical production of ultra-pure green very complex, which creates challenges for us when it comes to developing technology and materials,” said Sudhir Kumar, co-lead author of the paper detailing the development.
The LED they produced uses perovskite material that is very inexpensive to produce in a roll-to-roll process. According to the researchers, the new green LED is as flexible and bendable as a sheet of paper, and it even allows room temperature fabrication.
However, the researchers still must overcome major problems of inefficiency and lifetime before the development can be made practical. The green and bendable LED is only 3 percent efficient and lasts merely two hours. The researchers contend that the best TV screens available on the market are just 5-10 percent efficient. Screens available on the market currently work for many years with regular use.
The researchers published the details about the development in the journal Nano Letters.
In addition to Sudhir Kumar, Wendelin Stark, ETH Professor of Functional Materials Engineering, and researchers from Taiwan and South Korea contributed to the project results.
Reference
Kumar S, et al. Ultrapure Green Light-Emitting Diodes Using Two-Dimensional Formamidinium Perovskites: Achieving Recommendation 2020 Color Coordinates. Nano Letters, 3 August 2017 (web), doi: 10.1021/acs.nanolett.7b01544
