LEDs have transformed the way we light our world. Far more energy efficient than fluorescents or incandescent bulbs, LED lighting has made keeping the lights on less impactful on the environment. But making LEDs is a costly endeavor. Researchers from Stanford are hoping to solve this problem with modified perovskite LEDs (or PeLEDs), which are cheaper and easier to make.
The team recently tested new additives in the PeLED manufacturing process and significantly enhanced the brightness and efficiency of the lights—but there’s a catch. The lights burnt out after just a few minutes. This is clearly a fatal flaw for any commercial application. However, the team remains optimistic their breakthrough could revolutionize LED production in the future.
LEDs work by sending an electrical current through a semiconductor material that emits light when exposed to the current. This material is often grown on a sapphire substrate, which means making it is costly. Four-inch chunks of the substrate alone can cost hundreds of dollars.
PeLEDs are cheaper to make since perovskite crystals can be grown on glass substrates. Perovskites can also dissolve in fluid, allowing engineers to “paint” it onto a surface to simplify the production process.
Unfortunately, today’s PeLED technology is limited to lights that last a few hours at most. They’re also less energy efficient than traditional LEDs due to atom-level defects in the perovskite’s structure. Dan Congreve, an assistant professor of electrical engineering at Stanford led the research team who sought to solve this problem. They published their findings in the journal Device last month.
In an interview, Congreve said of perovskite’s defects, “There should be an atom here, but there’s not. Energy goes in there, but you don’t get light out, so it harms the overall efficiency of the device.”
Part of that issue is due to gaps created by lead—an important component in LED lights. So the team turned to manganese, replacing 30% of the lead content. The result? Filled gaps and double the brightness of their PeLED lights. More importantly, the lights were three times more efficient and lasted for 37 minutes compared to just over a minute.
“We took some big steps towards understanding why it’s degrading,” Congreve said, “The question is, can we find a way to mitigate that while keeping the efficiency? If we can do that, I think we can really start to work towards a viable commercial solution.”
Following their success, the Stanford team introduced one more element to PeLED production, a phosphine oxide called TFPPO. This additive made the lights five times more efficient than those boosted with manganese alone and brighter than any PeLED ever recorded. However, that brightness lasted just two and a half minutes before starting to fade.
The team hypothesizes that TFPPO helps fill some of the defects in perovskite’s atomic structure temporarily, accounting for the increased brightness and efficiency. Those benefits are short-lived as the defects reappear soon after the oxide is introduced.
Study lead author and PhD Student Sebastian Fernandez said, “Clearly, this additive is incredible in terms of efficiency. However, its effects on stability need to be suppressed to have any hope to commercialize this material.”
Just as LEDs changed the way we view lighting, PeLEDs could highlight a revolutionary new generation of lights. While there are several issues to address, the promise of increased energy efficiency and cheaper production means this technology is one to watch in the years to come.
Moving forward, the team is exploring the potential for PeLEDs to produce violet and ultraviolet light. This could have important applications, such as water purification, medical equipment sterilization, and indoor crop farming. With lights that are cheaper to produce and more efficient to operate, these applications suddenly become more realistic.