Dual-function nanorod LEDs could make multifunctional displays

February 9, 2017, University of Illinois at Urbana-Champaign
A laser stylus writes on a small array of multifunction pixels made by dual-function LEDs than can both emit and respond to light. Credit: Moonsub Shim, University of Illinois

Cellphones and other devices could soon be controlled with touchless gestures and charge themselves using ambient light, thanks to new LED arrays that can both emit and detect light.

Made of tiny nanorods arrayed in a thin film, the LEDs could enable new interactive functions and multitasking devices. Researchers at the University of Illinois at Urbana-Champaign and Dow Electronic Materials in Marlborough, Massachusetts, report the advance in the Feb. 10 issue of the journal Science.

"These LEDs are the beginning of enabling displays to do something completely different, moving well beyond just displaying information to be much more interactive devices," said Moonsub Shim, a professor of materials science and engineering at the U. of I. and the leader of the study. "That can become the basis for new and interesting designs for a lot of electronics."

The tiny nanorods, each measuring less than 5 nanometers in diameter, are made of three types of semiconductor material. One type emits and absorbs visible light. The other two semiconductors control how charge flows through the first material. The combination is what allows the LEDs to emit, sense and respond to light.

The nanorod LEDs are able to perform both functions by quickly switching back and forth from emitting to detecting. They switch so fast that, to the human eye, the display appears to stay on continuously—in fact, it's three orders of magnitude faster than standard display refresh rates. Yet the LEDs are also near-continuously detecting and absorbing light, and a display made of the LEDs can be programmed to respond to light signals in a number of ways.

Credit: Nuri Oh, Seongyong Cho and Moonsub Shim

For example, a display could automatically adjust brightness in response to conditions—on a pixel-by-pixel basis.

"You can imagine sitting outside with your tablet, reading. Your tablet will detect the brightness and adjust it for individual pixels," Shim said. "Where there's a shadow falling across the screen it will be dimmer, and where it's in the sun it will be brighter, so you can maintain steady contrast."

The researchers demonstrated pixels that automatically adjust brightness, as well as pixels that respond to an approaching finger, which could be integrated into interactive displays that respond to touchless gestures or recognize objects.

They also demonstrated arrays that respond to a laser stylus, which could be the basis of smart whiteboards, tablets or other surfaces for writing or drawing with light. And the researchers found that the LEDs not only respond to light, but can convert it to electricity as well.

A schematic of the device. Credit: Nuri Oh, Seongyong Cho and Moonsub Shim

"The way it responds to light is like a solar cell. So not only can we enhance interaction between users and devices or displays, now we can actually use the displays to harvest light," Shim said. "So imagine your cellphone just sitting there collecting the ambient light and charging. That's a possibility without having to integrate separate solar cells. We still have a lot of development to do before a display can be completely self-powered, but we think that we can boost the power-harvesting properties without compromising LED performance, so that a significant amount of the display's power is coming from the array itself."

In addition to interacting with users and their environment, nanorod LED displays can interact with each other as large parallel communication arrays. It would be slower than device-to-device technologies like Bluetooth, Shim said, but those technologies are serial—they can only send one bit at a time. Two LED arrays facing each other could communicate with as many bits as there are pixels in the screen.

"We primarily interface with our electronic devices through their displays, and a display's appeal resides in the user's experience of viewing and manipulating information," said study coauthor Peter Trefonas, a corporate fellow in Electronic Materials at the Dow Chemical Company. "The bidirectional capability of these new LED materials could enable devices to respond intelligently to external stimuli in new ways. The potential for touchless gesture control alone is intriguing, and we're only scratching the surface of what could be possible."

The researchers did all their demonstrations with arrays of red LEDs. They are now working on methods to pattern three-color displays with red, blue and green pixels, as well as working on ways to boost the -harvesting capabilities by adjusting the composition of the nanorods.

Explore further: Luminescent proteins provide colour to ecological and cheap Bio-displays

More information: "Double-heterojunction nanorod light-responsive LEDs for display applications," Science, science.sciencemag.org/cgi/doi … 1126/science.aal2038

Related Stories

Bendable electronic paper displays whole color range

October 14, 2016

Less than a micrometre thin, bendable and giving all the colours that a regular LED display does, it still needs ten times less energy than a Kindle tablet. Researchers at Chalmers University of Technology have developed ...

Aluminum nanoparticles could improve electronic displays

January 6, 2016

Whether showing off family photos on smartphones or watching TV shows on laptops, many people look at liquid crystal displays (LCDs) every day. LCDs are continually being improved, but almost all currently use color technology ...

Turning clothing into information displays

September 2, 2015

Researchers from Holst Centre (set up by TNO and imec), imec and CMST, imec's associated lab at Ghent University, have demonstrated the world's first stretchable and conformable thin-film transistor (TFT) driven LED display ...

Recommended for you

A soft solution to the hard problem of energy storage

May 18, 2018

It's great in the lab, but will it actually work? That's the million-dollar question perpetually leveled at engineering researchers. For a family of layered nanomaterials, developed and studied at Drexel University—and ...

New blood test rapidly detects signs of pancreatic cancer

May 17, 2018

Pancreatic cancer is expected to become the second deadliest cancer in the United States by 2030. It is tough to cure because it is usually not discovered until it has reached an advanced stage. But a new diagnostic test ...

Metallic drivers of Alzheimer's disease

May 17, 2018

X-ray spectromicroscopy at the Scanning X-ray Microscopy beamline (I08), here at Diamond, has been utilised to pinpoint chemically reduced iron and calcium compounds within protein plaques derived from brains of Alzheimer's ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

dirk_bruere
not rated yet Feb 10, 2017
"...and charge themselves using ambient light," Which sounds impressive until you run the numbers.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.