The October 2022 issue of IEEE Spectrum is here!

Close bar

LED Displays Get 400 Percent Clearer With Nanomaterial

Nanostructured material extracts more light out LEDs without the use of mirrors or lenses

2 min read
LED Displays Get 400 Percent Clearer With Nanomaterial
Photo: Stephen Chou/Princeton University

Back in 2012, Stephen Chou of Princeton University developed a nanostructure that, if incorporated in solar cells, would let them absorb 96 percent of the light that hit them and increase their efficiency by 175 percent. The nanostructure, which was a sandwich of metal and plastic configured to behave as a subwavelength plasmonic cavity, simultaneously dampened the reflection of light and trapped it.

Chou and his Princeton colleagues were eventually struck by another possibility: If the material could absorb light, they thought, maybe it could radiate light as well. With that in mind, the team has used this same configuration of materials to improve light emitting diodes (LEDs) so that they can achieve greater brightness and better efficiency. This, they say, is true for both organic and inorganic LEDs. This advance could lead to LED displays in whose picture clarity is five times better than that provided by conventional approaches.

"From a view point of physics, a good light absorber, which we had for the solar cells, should also be a good light radiator," Chou said in a press release. "We wanted to experimentally demonstrate this is true in visible light range, and then use it to solve the key challenges in LEDs and displays."

In research published in the journal Advanced Functional Materials, the nanostructured material exploited the phenomenon known as plasmonics, which involves oscillations in the density of electrons that are generated when photons hit a metal surface, to pump more light out of the LEDs.

While LEDs are much more efficient than incandescent light, a lot of light is still trapped inside the structure. In the case of cheap LEDs, only about 2 to 4 percent of the light the device generates is actually emitted.

"It is exactly the same reason that lighting installed inside a swimming pool seems dim from outside – because the water traps the light," said Chou in the release. "The solid structure of an LED traps far more light than the pool's water."

Current methods for extracting more light from LEDs involve the use of mirrors or lenses. While these methods can increase the amount of light put to good use to around 38 percent, they come at a cost of reducing the contrast, resulting in hazy images.

To overcome the limitations of these light extraction techniques, the researchers employed their nanostructure, called a plasmonic cavity with subwavelength hole-array (PlaCSH). The device comprises a layer of light-emitting material, about 100 nanometers thick, that is sandwiched between a cavity whose surface is made from a thin-metal film and another cavity that has a metal-mesh surface made from wires that are 15 nanometers thick, 20 nanometers wide, and spaced 200 nanometers apart on center.

This design essentially guides the light out of the LED and focuses it towards the viewer.  An added benefit to the design is that it replaces the brittle transparent indium tin oxide electrodes that are used as a transparent conductor to control display pixels.

The PlaCSH organic LEDs can be produced very cheaply using a nanoimprint technology invented by Chou himself back in 1995.

Princeton has applied for patents for both organic and inorganic LEDs using the PlaCSH design. With a cheap and simple manufacturing process and a 400 percent improvement in picture clarity, it’s clear why the university was quick to file patents.

The Conversation (0)

3D-Stacked CMOS Takes Moore’s Law to New Heights

When transistors can’t get any smaller, the only direction is up

10 min read
An image of stacked squares with yellow flat bars through them.
Emily Cooper

Perhaps the most far-reaching technological achievement over the last 50 years has been the steady march toward ever smaller transistors, fitting them more tightly together, and reducing their power consumption. And yet, ever since the two of us started our careers at Intel more than 20 years ago, we’ve been hearing the alarms that the descent into the infinitesimal was about to end. Yet year after year, brilliant new innovations continue to propel the semiconductor industry further.

Along this journey, we engineers had to change the transistor’s architecture as we continued to scale down area and power consumption while boosting performance. The “planar” transistor designs that took us through the last half of the 20th century gave way to 3D fin-shaped devices by the first half of the 2010s. Now, these too have an end date in sight, with a new gate-all-around (GAA) structure rolling into production soon. But we have to look even further ahead because our ability to scale down even this new transistor architecture, which we call RibbonFET, has its limits.

Keep Reading ↓Show less