Perovskite Nanoplatelets Yield Bright LEDs

Simple production method also creates a moisture-resistant barrier on water-sensitive perovskites

2 min read
Perovskite Nanoplatelets Yield Bright LEDs
Transmission electron microscopy image and diffraction pattern of methyl ammonium lead bromide perovskite nanoplatelets
Photo: Florida State University/Advanced Materials

Perovskites have become the hottest material for solar cells because they are cheap and very easy to process. They’ve also been tapped for use in light-emitting diodes and lasers, but LEDs incorporating materials with the perovskite crystal structure have not been very bright.

But researchers at Florida State University (FSU) now report that they have made perovskite LEDs that are more than four times as bright as earlier versions. They have a brightness of over 10,000 candelas per square meter, comparable to that of organic LEDs and quantum dot LEDs.

Instead of the perovskite thin films that others have used to make LEDs, the FSU team used flat perovskite nanoparticles, or nanoplatelets. Nanoparticles deliver a big efficiency advantage, says Hanwei Gao, a professor of physics at FSU. The small, single-crystal pieces have very few defects at which electrons and positively charged holes can recombine without producing a photon.

The researchers used common precursor materials and a simple chemical solution process to produce the highly crystalline nanoplatelets of the perovskite methyl ammonium lead bromide. They used the nanoparticles as the light emitting material in a conventional stacked architecture to make a bright green LED. Gao, professor of chemical engineering Biwu Ma, and their colleagues outlined the details in a paper in the journal Advanced Materials.

The new device also overcomes a common problem with perovskites: their penchant to quickly degrade when exposed to moisture. Because of this sensitivity to water, perovskite devices have to be made in glove boxes and also require expensive packaging. But the process that the FSU team uses to make the nanoplatelets leaves a layer of a water-repelling organic compound on their surfaces. Gao says that he and his colleagues made the new LEDs without a glove box and that the devices retained their brightness for more than a week when when exposed to humid Florida air.

But these LEDs are still a pretty early prototype. Right now, they need several volts to glow bright because the efficiency with which they convert electricity to light is low. In a practical LED, Gao says, “you need to inject charges, make sure they are confined in a small space so they can meet and recombine.” But the principal limiting factor for an efficient, bright LED is the emitter itself.

So, says Ma, “we’re making sure we have good emitters first. Now we need to do device engineering to make a practical device. It took a long time for other kinds of LEDs to reach a high efficiency level.”

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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
Green

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.

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