Inspired by the existing ultra-thin solar panel electrode design technology, Stanford University, South Korea’s Samsung Advanced Technology Institute (SAIT) and South Korea’s Hanyang University have jointly developed a new architecture for OLED displays that can enable TVs, mobile phones, etc. The resolution of the device reaches 10,000 PPI, while the resolution of existing mobile phone screens is only 400-500 PPI.
Such a high pixel density display will be able to provide more realistic and stunning images, which will be more important for the design of head-mounted displays.
Mark Brongersma, a materials scientist at Stanford University, initially embarked on this research path because he wanted to create an ultra-thin solar panel design.
"We took advantage of the fact that on the nanometer scale, light can flow around objects such as water," said Brangosma. He is a professor of materials science and engineering and the senior author of a paper detailing this research published in the journal Science on October 22. "The field of nanophotonics continues to bring new surprises, and now we are beginning to influence real technology. The design is very effective for solar cells, and now we have the opportunity to influence the next generation of displays."
In addition to having a record pixel density, the new "superphotonics" OLED display will also be brighter than the current version, with better color accuracy, and easier to produce and more cost-effective.
The core of OLED is organic light-emitting material. These electrodes are sandwiched between highly reflective and semi-transparent electrodes to inject current into the device. When current passes through the OLED, the emitter emits red, green or blue light. Each pixel in an OLED display consists of smaller sub-pixels that produce these primary colors. When the resolution is high enough, the human eye will treat the pixel as a color. OLEDs are an attractive technology because they are thin, light, and flexible, and can produce brighter and more colorful images than other types of displays.
This research aims to provide an alternative to two types of OLED displays currently commercially available: one type is called red, green and blue OLED, which has separate sub-pixels, and each sub-pixel contains only one color emitter. These OLEDs are manufactured by evaporating each layer of material through a high-precision metal mask FMM to control the composition of each pixel. However, they can only be produced on a small scale.
Larger devices such as TVs use white-light OLED+CF displays, which are relatively easy to manufacture. However, because the filter reduces the total light output, the white light OLED display consumes more power, and it is easy to burn the image onto the screen, resulting in the phenomenon of flask afterimage.
The key innovation behind the ultra-thin solar panels and the new OLED display is a metal reflective substrate with nano-scale ripples, called an optical metasurface. The metasurface can control the reflection characteristics of light, so that different colors resonate in the pixels. These resonances are the key to promoting the effective extraction of light by the OLED.
In order to create an overall flat screen, the material deposited on the top must be laid with unequal thickness. In contrast, in the proposed OLED, the base layer corrugation allows each pixel to have the same height, which facilitates a simpler process for large-scale and micro-scale manufacturing.
Stanford University professor Mark Blangsma, who led the research, said: "This is similar to a musical instrument using acoustic resonance to produce beautiful and easy-to-heard sounds." For example, red light has a longer wavelength than blue light, which is in traditional RGB- In OLED, red light is transformed into sub-pixels of different heights. In order to create an overall flat screen, the material deposited above the emitter must be laid in a way of unequal thickness. In contrast, in the new OLED, the base layer corrugation makes the height of each pixel the same, which is conducive to simplifying the large-scale and micro-scale manufacturing process.
In laboratory tests, the researchers successfully produced miniature proof-of-concept pixels. Compared with color-filtered white OLEDs (used in OLED TVs), these pixels have higher color purity and twice the luminous efficiency, which is a measure of screen brightness and energy consumption. They also allow an ultra-high pixel density of 10,000 pixels per inch.
Comparison of EL performance of super surface OLED and standard color filter white OLED
The next step of integrating this work into a full-size display is what Samsung is advancing. Mark Brangosma is eagerly awaiting the result, hoping to be one of the first people to see the meta-OLED display put into use. .
The research paper was published in Science on October 23 with the title of "Metasurface-driven OLED displays beyond 10,000 pixels per inch".