Display technology that can do almost anything

At first glance, it looks like a relic from the 1980s. A small computer screen with flickering, low-resolution text scrolling across it. But this could be the future.

The display is made using perovskite light emitting diode (PeLED) technology. It’s radically different from the LED technology used in your smartphone display today and could lead to devices that are thinner, cheaper and have longer battery life.

Not only that, PeLEDs are very unusual in that they can absorb light as well as emit it, meaning you can use the same material to integrate touch, fingerprint and ambient light capabilities. , says Feng Gao at Linköping University in Sweden.

“This is difficult, but we think it is possible.”

In today’s smartphones, such functions are performed by electronic components separate from the phone screen itself.

In a paper published in AprilProf Gao and colleagues demonstrated their prototype with sensitivity to touch and ambient light already working.

“It’s a very nice demo… it’s very new,” says Daniele Braga, head of sales and marketing for Fluxim, a technology research firm in Switzerland. Although he notes that optimizing all the various functions promised here could make it difficult to quickly commercialize this type of display.

Through the video call, Prof Gao shows the latest version of the technology. It’s another small screen, but this time the pixels per inch (ppi), a measure of screen sharpness, has almost doubled – to 90 ppi.

A simple animation plays on the screen, showing two stick figures fighting. A document with further details about this prototype it has just been published.

The mineral perovskite contains calcium, titanium and oxygen arranged in a crystalline structure. It was discovered in the 1800s, but people later realized that they could make other types of perovskite that had the same structure while having different elements or molecules as ingredients.

Depending on the materials chosen, perovskites can be really good at, for example, conducting electricity or emitting light.

“By slightly tuning the chemical composition, you can cover the entire visible spectrum,” says Dr Braga, explaining that making perovskites is a relatively simple and inexpensive process. “If you think about mass production, this is gigantic.”

However, there are some problems.

PeLEDs are highly unstable – for example, they go bad when exposed to moisture or oxygen. Loreta Muscarella at VU Amsterdam, a university, is working to develop new types of PeLEDs.

She says that if you leave a PeLED lying around for a few hours or days, the color of the light it emits will gradually degrade or shift to a less pure version of, say, green, than the green you want.

And that undermines the whole point of perovskites. They are desirable in part because they can be tuned to emit a very specific, very pure form of red, green, or blue—the primary hues required for full-color digital displays.

To keep them stable, PeLEDs can be encapsulated in glue or resin, says Prof Gao. But researchers are still working to make sure the technology doesn’t falter for a long time.

Dr Muscarella says traditional LEDs have lifespans of 50,000 hours or more, while PeLED lifespans are still in the hundreds to thousands of hours range.

It could be years before you can buy a commercial product containing a PeLED, she adds.

But there is another type of light-emitting perovskite that you may see on the market first.

It relies on photoluminescence. This is not an LED as such, but a filter or film-like material that absorbs and re-emits light in a certain color.

In some televisions on the market today, a color filter provides the primary red, green, and blue colors used in each pixel on the screen.

It is by mixing those colors at different levels that you can get the range of shades needed to display a complete picture.

The red, green and blue filters are illuminated by an LED backlight. But today’s filters actually block a lot of that light.

Photoluminescent perovskites, in contrast, let almost all light through, which would mean a huge increase in brightness and efficiency.

Helio, a British company, is working on this. A video on their website shows how a red or green perovskite film can re-emit blue light as red or green almost perfectly.

The technology that Prof Gao and his colleagues are developing is quite different. They are experimenting with light-emitting displays using self-made perovskite LEDs.

These are known as electroluminescent perovskites. Working with them is complicated because they are sensitive to electric fields and, as mentioned, are not very stable. But eventually they could be even more efficient options for lighting red, green and blue pixels on a smart screen, tablet or TV without the need for color filters at all.

The main advantages of switching to this technology can be in reducing the cost of these devices and reducing their energy consumption.

No one is quite sure how much less power a future PeLED display could consume versus, say, an OLED display, but lab experiments suggest that PeLEDs are already competitive with OLEDs and may one day significantly outperform them those in terms of efficacy, says Dr Muscarella. .

Prof Sir Richard Friend, at the University of Cambridge, is one of the co-founders of Helio, along with Prof Henry Snaith at the University of Oxford. He points out that one of the challenges with PeLEDs is getting them to emit light in the right direction. This really matters for screens.

“You have to shine light in the forward direction instead of getting stuck going sideways,” he explains.

Researchers are experimenting with many different techniques to solve this problem. Dr. Muscarella and colleagues have tried typing a nanoscale bump pattern on the surface of PeLEDs, for example, which appears to improve light emission.

However, for Prof Gao, who has co-published with Prof Sir Friend and received his PhD from the University of Cambridge in 2011, the promise of PeLED displays that do much more than emit light is rediculous.

From fingerprint verification to heartbeat sensing and light detection, everything could one day be done using a single slab of layered materials with the all-important light-absorbing perovskite in between.

“It’s really quite unique,” he enthuses. “This is not possible with other LED technologies.”