The Swiss Army Knife of Displays

Modern displays are a great example of a technology that does one thing and does it well. They are designed specifically to display information, and through a series of technological advancements have been refined over the years to provide high-resolution visuals, vibrant colors, and sharp contrasts. However, as demand for multifunctional devices grows, there is a need to integrate additional capabilities such as touch sensing, stylus support, and even biometric recognition like fingerprint sensors into displays.

These additional layers of sensors that are required to enhance the functionality of displays bring about some challenges. Incorporating touch-sensitive layers, for instance, enables users to interact directly with the screen, adding convenience and interactivity to the user experience. Yet, the inclusion of these layers also results in increased complexity, cost, and thickness of the display. This can make devices bulkier and potentially reduce their flexibility, which limits the applications they are useful for.

Recently, researchers have been exploring the possibility of incorporating photo-responsive LEDs into displays. This would allow each pixel to serve not only as a part of the display, but also as an input that could provide functions like touch sensing and fingerprint recognition, all without any additional layers of sensors. However, existing photo-responsive LEDs exhibit a very weak photo-response, which severely limits their utility in practical applications.

Conventional technologies are clearly not meeting our needs, so a team led by researchers at Sweden's Linköping University took a completely different approach. They have developed a multifunctional display based on perovskite LEDs. This choice has some important implications, because perovskite LEDs are not only very bright, but are also highly photo-responsive. Interestingly, when the display is not in use, the perovskite LEDs can also be used as solar cells, converting light into electricity to charge a device’s battery. That capability could be very useful for smartphones, smartwatches, and other wearable electronics.

The researchers created a small 1,024 pixel proof-of-concept display to test their approach, and it was found that the perovskite LEDs could produce red, green, and blue light at a brightness level of 4,700 candelas per square meter, which is far brighter than a traditional smartphone display. The photosensitivity of the LEDs was demonstrated by detecting touches on the screen, and also by capturing an image of a fingerprint. Even this tiny display was sufficient to generate some electricity through the photovoltaic effect. Within about 25 minutes, it was able to charge a 0.5 farad supercapacitor.

There is a major drawback to using perovskite materials, however. Their operational lifetime is measured in just hours. After about 18.5 hours, the team noted that the devices degraded to the point that they were no longer fully functional — now you see it, now you don’t. There is hope that this problem can be overcome though, as other research groups have developed much longer-lasting perovskite materials.

With some additional work, this line of research could eventually lead to the development of a new class of ultra-thin, multifunctional displays. And their unique properties could even help solve some of the battery-related issues that modern wearable devices experience.