Screen technology that can do almost anything

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

The screen was 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 both absorb and emit light, which means you can use the same material to integrate touch, fingerprint and ambient light sensing capabilities, says Feng Gao of Linköping University in Sweden.

“It’s difficult, but we think it’s possible.”

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

“It’s a very nice demonstration… it’s very new,” says Daniele Braga, head of sales and marketing at Fluxim, a technology research company in Switzerland. Although he notes that optimizing all the various features promised here may make it difficult to quickly commercialize this kind of display.

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

A simple animation will play on the screen showing two stick figures fighting. A document has just been published with more details about this prototype.

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

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

“By slightly tweaking the chemistry, you can cover the entire visible spectrum,” says Dr. Braga and explains that making perovskites is a relatively simple and inexpensive process. “If you think about mass production, it’s gigantic.”

However, there are some problems.

PeLEDs are notoriously unstable – they deteriorate when exposed to moisture or oxygen, for example. Loreta Muscarella at the VU University Amsterdam is working on the development of new types of PeLED.

He says that if you leave a PeLED sitting around for 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 key hues required for full-color digital displays.

To make 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 languish for a long time.

Dr Muscarella says that traditional LEDs have a lifespan of 50,000 hours or more, while PeLEDs are still in the hundreds to thousands of hours.

It could be years before you can buy a commercial product that contains PeLED, he adds.

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

It relies on photoluminescence. It is not an LED per se, but rather a filter or film material that absorbs and re-emits light in a certain color.

In some TVs on the market today, a color filter supplies the key red, green, and blue colors used in each pixel on the screen.

By mixing these colors at different levels, you can get the range of shades needed to display a full image.

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

Photoluminescent perovskites, on the other hand, transmit almost all light, which would mean a large increase in brightness and efficiency.

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

The technology that Prof Gao and his colleagues are developing is quite different. They are experimenting with screens that emit light using LEDs that are themselves made of perovskites.

These are known as electroluminescent perovskites. They are tricky to work with because they are sensitive to electric fields and, as already mentioned, not very stable. But in the end, they could be even more efficient options for lighting up red, green, and blue pixels on a smartphone, tablet, or TV screen without the need for color filters at all.

The main benefits of switching to this technology could be to reduce the cost of these devices and reduce their energy consumption.

No one is quite sure how much less power a future PeLED display can use compared to, say, an OLED screen, but lab experiments suggest that PeLEDs are already competitive with OLEDs and could one day significantly surpass them in terms of efficiency. says Dr. Muscarella.

Professor Sir Richard Friend from the University of Cambridge is one of the co-founders of Helio along with Professor Henry Snaith at the University of Oxford. He points out that one of the problems with PeLEDs is getting them to emit light in the right direction. It really matters with displays.

“You need the light to shine forward, instead of getting stuck to the side,” he explains.

Scientists are experimenting with many different techniques to solve this problem. Dr. For example, Muscarella and colleagues tried to imprint a bumpy nanoscale pattern on the surface of a PeLED, which appears to improve light emission.

For Professor Gao, who published alongside Professor Sir Friend and received his PhD from Cambridge University in 2011, the promise of PeLED screens that can do much more than just emit light is enticing.

From fingerprint authentication to heart rate sensing and light detection, it could all one day be done using a single sheet of layered materials with the all-important light-absorbing perovskite in the middle.

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