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

Light emitting diodes, like LEDs, are almost exclusively present in modern life, and provide the brightness in telephone screens, televisions and lights. A new form of LEDs, made from a class of materials called halide perovskites, promises higher color quality and ease of manufacture, but is known to fail when subjected to the type of electric current typically required for practical use. Now Barry Rand, associate professor of electrical engineering and the Andlinger Center for Energy and Environment, and a team of researchers have significantly improved the stability and performance of the material by better managing the heat generated by the LEDs.

The study, published in Advanced materials, identifies various techniques that reduce the accumulation of heat in the material, which prolongs its life ten times. When the researchers prevented the device from overheating, they were able to pump enough power into it to produce hundreds of times lighter than a typical phone display. The intensity, measured in watts per square meter, reflects the actual amount of light from a device, not affected by human eyes or the color of the light. Previously, such a level of current would have failed the LED.

It sets a new brightness record and expands the boundaries of what is possible for the material by improving the well-established properties of perovskite LEDs and making practical use of these properties.

“It’s the first time we’re shown that heat seems to be the major bottleneck for these materials that work with high currents,” Rand said. “This means that the material could be used for bright lights and displays, which was never thought possible.”

Rand, who is also associate director for external partnerships at the Andlinger Center, said clear paths are now open for further development, but warned that the technology is still 10 to 20 years from wide commercial use.

To contain the accumulation of Joule heat in the device, as the type of heat resulting from electric current, the researchers methodically treated important elements. They have designed the composition of the material in the device to make it more electrically conductive and, therefore, to generate less heat during operation. They make the devices narrower than normal, about a tenth as thin as a strand of human hair, to allow better heat distribution. And they added heat sink, as components that conduct heat away from sensitive electrical components, which helped to dissipate the heat.

Once these key elements were in place, they used a tactic to continuously “pulse” the device, or to turn it on and off quickly, so fast that a human eye could not see the flicker, but enough time for it device to repair and cool. For this part of the work, she used the expertise of co-author Claire Gmachl, the professor of electrical engineering Eugene Higgins. By reducing the time that the device was actually, the researchers achieved efficiency improvements, and were able to operate the device longer than ever reported. Rand describes the work as a “how-to” manual for operating perovskite LEDs at the high power density required for lighting and bright displays.

Lianfeng Zhao, first author on paper and a postdoctoral fellow in the electrical engineering department, said the researchers believe the prevailing thought in the field is that perovskites could not operate intrinsically efficiently at high power densities.

The work is a “major breakthrough” for the field, said Feng Gao, a professor in the Department of Physics, Chemistry and Biology at Linköping University in Sweden, and an expert in organic and perovskite semiconductors for energy technologies.

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

Until now, researchers thought that perovskite LEDs would be useful for producing only moderate levels of brightness, but not for lighting like ultra-bright displays on mobile phones and laptops.

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

One of the most appealing parts of perovskite LEDs is the way they are produced, which requires much less energy than producing conventional inorganic LEDs used today for lighting. Conventional LEDs are made from a single crystal piece, which is very difficult and expensive to produce and often requires ultra-high vacuum systems and temperatures of more than 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 commercialized, it would probably result in a significant reduction in the required energy and carbon footprint of these electronics, both in their manufacture and operation.

Perovskite LEDs produce a pure, concentrated color, and the researchers also hope to use the material to build inexpensive, easy-to-build lasers. And more generally, Rand and Zhao said they will continue to study how the material works to better understand their properties to create higher quality, durable and efficient devices.

“This is a pretty big milestone,” Rand said. “It is important not only for our research, but also for technologies, designers and the electronics sector. We think there is a bright future for the material.”