The researchers of Stanford and those of Samsung Advanced Institute of Technology (SAIT) have developed a new architecture for screens OLED (organic light-emitting diode) which could allow the creation of TV, smartphone or viewer for virtual / augmented reality with a density up to 10. 00 0 pixels per inch (PPI) , an incredibly high value if we think that smartphone displays reach values ​​between 400 and 500 PPI.

The joint study – published in Science – is based on the research of Mark Brongersma, a materials scientist at Stanford University, who began work on this solution thinking about something else, that is to create an ultra-thin solar panel . “We took advantage of the fact that, at the nanoscale, light can flow around objects such as water,” Brongersma explained. “The nano-scale photonics field continues to surprise and we are now starting to have a real impact. Our designs have worked well for solar cells and now we have the option to leave the sign on the next generation of screens “. In addition to achieving record density, the new “metaphotonic” OLED screen would also be brighter and more accurate than the best existing solutions, as well as easier to produce and cheaper .

10. 00 0 PPI? How did they do it?

The heart of an OLED are organic materials that emit light, sandwiched between semi-transparent and highly reflective electrodes which allow to inject current into the device. When electricity flows into the OLED, the emitters return red, green or blue light. Each pixel in an OLED screen is made up of smaller sub-pixels that produce these primary colors. When the resolution is high enough, the pixels are perceived by the human eye as a color. OLEDs are thin, light and flexible and produce brighter and more colorful images than other types of screens, so they are finding great application.

Samsung and Stanford studio offers an alternative to the two types of OLED screens currently available on the market . There are in fact the OLED RGB (red-green-blue), where the individual sub-pixels each contain only one color to emit. These OLEDs are made by “spraying” each layer of material through a thin metal mesh to control the composition of each pixel. The problem is that at the moment can only be produced on a small scale, such as the screen size of a smartphone.

TVs use white OLED based panels . Each of these sub-pixels contains a set of all three emitters and then relies on filters to determine the final color of the sub-pixel. This is a technology that is easier to produce , however as filters reduce the overall light output, White OLEDs consume more energy and are prone to show so-called burn-in , which is a kind of effect ” ghost “on the screen.

The fundamental innovation behind the solar panel and the new OLED proposed by Stanford and Samsung is a base layer of reflective metal with nanoscale corrugations, called optical metasurfaces . Metasurfaces can manipulate the reflective properties of light and thus allow different colors to “resonate in the pixels”. These resonances are critical to facilitate effective extraction of light from OLEDs. “It is similar to the way musical instruments use acoustic resonances to produce beautiful and easily audible sounds,” Brongersma explained.

For example, red emitters have a length of d ‘wave of light longer than blue emitters, and this, in a conventional RGB OLED, results in sub-pixels of different heights. In order to create an overall flat screen, the materials deposited above the emitters must have unequal thicknesses. On the other hand, in the OLEDs proposed by this study, the corrugations of the base layer allow each pixel to have the same height and this facilitates production.

In laboratory tests the researchers successfully produced test pixels, of the so-called “proof of con