Heat control opens the door to next-generation lighting and displays in perovskite LEDs

Light Emitting Diodes, or LEDs, are almost ubiquitous in modern life, providing brightness for phone screens, televisions, and lights. A new form of LED, made from a class of materials called halide perovskites, promises better color quality and ease of manufacture, but is known to fail when subjected to the type of electric current typically required for practical uses. Now Barry Rand, associate professor of electrical engineering and the Andlinger Center for Energy and the Environment, and a team of researchers have dramatically improved the stability and performance of the material by better handling the heat generated by LEDs.

The research, published in Advanced materials, identifies several techniques that reduce heat build-up in the material, which has increased its lifespan tenfold. When the researchers kept the device from overheating, they were able to pump enough current into it to produce a light hundreds of times brighter than a typical cell phone screen. Intensity, measured in watts per square meter, reflects the actual amount of light coming from a device, not influenced by human eyes or the color of the light. Previously, such a level of current would have caused the LED to fail.

This breakthrough sets a new brightness record and expands the limits of what is possible for the material by improving the well-established properties of perovskite LEDs and allowing these characteristics to be practically exploited.

“This is the first time that we have shown that heat appears to be the main bottleneck for these materials operating at high currents,” said Rand. “This means that the material could be used for bright lights and screens, which was never thought possible.”

Rand, who is also associate director for external partnerships at the Andlinger Center, said clear avenues are now open for further development, but warned the technology is still 10 to 20 years of large-scale commercial use.

To contain the Joule heat buildup in the device, or the type of heat that results from electric current, the researchers methodically addressed key things. They engineered the composition of the material in the device to make it more electrically conductive and therefore generate less heat during operation. They made the devices narrower than usual, about a tenth of the end of a strand of human hair, to allow for better heat distribution. And, they added heat sinks or components that conduct heat away from sensitive electrical components, which helped disperse the heat.

With those key pieces in place, they used a tactic to continually “pulse” the device, or turn it on and off quickly, so quickly that a human eye couldn’t see the flicker, but long enough. for the device to recover and cool down. For this part of the work, they drew on the expertise of co-author Claire Gmachl, Eugene Higgins Professor of Electrical Engineering. By reducing the runtime of the device, the researchers improved efficiency and were able to keep the device running longer than ever before. Rand describes the work as a practical guide to operating perovskite LEDs at the high power densities required for lighting and light displays.

Lianfeng Zhao, first author of the article and associate postdoctoral researcher in the Department of Electrical Engineering, said the research contradicts prevailing thinking in the field that perovskites inherently could not function efficiently at high power densities.

This work is an “important step forward” for the field, said Feng Gao, professor in the Department of Physics, Chemistry and Biology at Linköping University in Sweden, and an expert in organic semiconductors and perovskites for energy technologies.

“Reducing Joule heating is a major challenge for perovskite LEDs towards high brightness and long term stability,” said Gao. “The results are really encouraging for the future commercialization of perovskite-based lighting and displays.”

Until now, researchers believed that perovskite LEDs would be useful for producing only moderate brightness levels, but not for lighting or ultra-bright displays on cellphones and laptop screens.

“We have broadened the scope of possible applications,” Zhao said.

One of the most attractive parts of perovskite LEDs is the way they are made, which requires much less energy than the production of conventional inorganic LEDs used today for lighting. Conventional LEDs are made from a piece of a single crystal, which is very difficult and expensive to produce and often requires ultra-vacuum systems and temperatures of over 1000 degrees Celsius. Perovskite materials are typically made at temperatures below 100 degrees Celsius and formed from solutions in a process similar to inkjet printing. If the technology were to be commercialized, it would likely result in a significant reduction in the energy required and carbon footprint of these electronic devices, both in their manufacture and in their operation.

Perovskite LEDs produce pure, concentrated color, and the researchers also hope to use this material to make lasers that are cheap and easy to make. And more generally, Rand and Zhao said they will continue to study how the material works to better understand its properties in order to make devices that are better, more durable and more efficient.

“It’s a pretty big milestone,” Rand said. “This is not only important for our research, but also for technologists, designers and the electronics industry. We believe the material has a bright future.”