Fuzhou University research team achieves new breakthrough in QLED quantum dot display

Will future AR glasses be able to achieve functions such as high-definition navigation, real-time translation, and seamless access to virtual meetings while still weighing about the same as ordinary glasses?

The core challenge in realizing this idea is how to integrate hundreds of millions of high-performance luminescent pixels on tiny display chips. The latest breakthrough from a Chinese scientific research team has brought new hope for solving this problem.

This achievement was led by Lin Lihua, a young teacher from the team of Professor Li Fushan of the School of Physics and Information Engineering of Fuzhou University. He drew inspiration from daily life and based on nano-transfer printing technology, successfully prepared full-color ultra-high-resolution quantum dot light-emitting diodes (QLED) with a pixel density of up to 25,400 PPI (pixels per inch).

This data far exceeds the "retina-level" display standard commonly defined in the industry (that is, a pixel density exceeding 10,000 PPI). This research result has solved the core problem of "high resolution", "full red, green and blue color" and "high performance" that has long plagued the industry. Relevant papers have been published in the top international academic journal "Nature".
Image source: Fujian University

At the technical level, the challenge in achieving "retina-level" ultra-high-definition display is that when the pixel size is reduced to the micron or even nanometer scale, it is difficult to accurately prepare patterns using traditional photolithography, inkjet printing and other methods, and the colors are prone to interfere with each other. At the same time, the luminous performance of the device will also be significantly reduced.

In the past, researchers often used methods similar to "soft seals" to transfer luminescent materials. However, this material is prone to deformation at extremely small scales, resulting in blurred edges of the pattern or incomplete transfer.

In order to solve this problem, the team designed a new "hard nanoimprinting-integral inverted transfer" solution, which uses a hard and reusable silicon template to accurately "stamp" at the nanoscale like a high-precision mold, ensuring that the pattern is not deformed from the source.

On this basis, the team proposed a "double force dynamics" strategy, which uses the subtle force changes during the imprinting and release process of the material to allow the luminescent material to automatically "crowd" and "align" in the nanoscale micropores, achieving a dense and uniform filling effect.

Through this innovative method, the researchers successfully placed the three luminescent materials of red, green, and blue at their respective positions, achieving a nearly defect-free pixel arrangement within the ultra-high resolution range of 9072 to 25400 PPI, significantly improving display accuracy.

However, accurately preparing these perfect pixels is only the first step. Studies have found that when pixels are reduced to sub-micron scale, the electric field distribution inside the device will become uneven, especially the electric field concentration effect will occur in the edge area of ​​​​the pixel, which causes charges to accumulate at the edges, forming a "current crowding" phenomenon, thereby increasing energy loss and affecting the long-term stability of the device.

In response to this long-term problem that restricts performance, the research team innovatively proposed the "titanium dioxide nanoparticle dielectric matching" strategy. By introducing an appropriate amount of titanium dioxide nanoparticles into the charge blocking layer, the dielectric properties of the material are successfully adjusted to better match the quantum dot light-emitting layer, thereby making the electric field distribution inside the device uniform, just like installing an "intelligent regulator" for the electric field.

This breakthrough has been strongly confirmed by data: at an ultra-high resolution of 12,700 PPI, the peak external quantum efficiency (EQE) of the red light device reached 26.1%, and the life span was as long as 65,190 hours. The efficiency of the green light and blue light devices also increased by 124% and 119% respectively. Many performance indicators have refreshed industry records.

It is worth mentioning that the process of this technology is also highly adaptable. It can complete high-precision pattern transfer and maintain stable performance even on flexible substrates that can be bent. At the same time, the entire process does not require high temperatures and complex photolithography processes, and is also compatible with environmentally sensitive perovskite materials. In addition, the research team has combined this technology with integrated circuits and successfully developed an integrated display prototype that can control pixels one by one and realize dynamic image display, providing a new path for the development of high-end integrated display chips.

Editor: Yan Zhixiang