Metasurface-driven OLED displays promise 10,000+ PPI
The new ultra-high-resolution display, which could be especially useful for virtual and augmented reality technologies, is based on solar panel research on the design for electrodes of ultra-thin solar panels.
“We’ve taken advantage of the fact that, on the nanoscale, light can flow around objects like water,” says Mark Brongersma, a professor of materials science and engineering at Stanford and a senior author of a paper on the research. “The field of nanoscale photonics keeps bringing new surprises and now we’re starting to impact real technologies. Our designs worked really well for solar cells and now we have a chance to impact next generation displays.”
In addition to having a record-setting pixel density, say the researchers, the new “metaphotonic” OLED displays would also be brighter and have better color accuracy than existing versions, and they’d be much easier and cost-effective to produce as well. The key innovation behind both the solar panel and the new OLED is a base layer of reflective metal with nanoscale corrugations, called an optical metasurface, which can manipulate the reflective properties of light and thereby allow the different colors to resonate in the pixels.
These resonances, say the researchers, are key to facilitating effective light extraction from the OLEDs.
“This is akin to the way musical instruments use acoustic resonances to produce beautiful and easily audible tones,” says Brongersma.
For example, red emitters have a longer wavelength of light than blue emitters, which, in conventional RGB OLEDs, translates to sub-pixels of different heights. In order to create a flat screen overall, the materials deposited above the emitters have to be laid down in unequal thicknesses. By contrast, in the proposed OLEDs, the base layer corrugations allow each pixel to be the same height and this facilitates a simpler process for large-scale as well as micro-scale fabrication.
In lab tests, the researchers say they successfully produced miniature proof-of-concept pixels. Compared with color-filtered white OLEDs (which are used in OLED televisions) these pixels had a higher color purity and a twofold increase in luminescence efficiency – a measure of how bright the screen is compared to how much energy it uses. They also allow for an ultra-high pixel density of 10,000 pixels-per-inch.
The next steps for integrating this work into a full-size display, say the researchers, is being pursued by Samsung. For more, see “Metasurface-driven OLED displays beyond 10,000 pixels per inch.”