Are Perovskite LEDs an Up-and-Comer on the Display Scene?April 07, 2020 by Robin Mitchell
Maybe you've heard of perovskite for solar cells. But what about perovskite LEDs? Can a team of researchers make them a viable alternative to organic LEDs or quantum-dot LEDs?
Perovskite is a semiconductor material consisting of calcium and titanium that shows promise in the electronics industry because of its electrical and optical properties, according to Perovskite-Info. It is also easy and inexpensive to produce.
Although perovskites are a promising candidate for future LEDs, they currently suffer from some major issues, including low efficiency and short lifespan. One team of researchers claims to have created close-to-viable perovskite LEDs that solves this problem.
In this article, we'll discuss how perovskites LEDs have been used in the past and how a team of researchers has found a way to make them a useful alternative to organic LEDs. We'll also explore how these new LEDs may potentially affect the industry once some of their developmental kinks are worked out.
Perovskite for Solar Cells
One area of electronics that this semiconductor has gained traction is in solar cells, which I've discussed in further detail in an article exclusively on perovskite solar cells. In the article, we refer to one group of researchers who even created a paintable ink from perovskite that turns any surface into a solar cell.
Thin-film perovskite solar cell (left) and perovskite on silicon tandem solar cell (right). Image used courtesy of Solar Energy Technology Office
But generally speaking, a technology that can be used to create solar cells can also be used to create LEDs since an LED is essentially a solar panel in reverse; when you apply power to a solar cell, it emits infrared light that can be seen on a camera.
Perovskite for LEDs
While researchers have made significant progress on the solar cell front, they have faced some hiccups in creating perovskite LEDs. Researchers have been attracted to perovskites a viable LED material because it can be easily tuned to any frequency between infrared and ultraviolet, according to researchers at Linköping University studying perovskite-based light-emitting diodes.
New perovskite material for LEDs. Image used courtesy of Thor Balkhed, Linköping University
Perovskite-Info poses the possibility that perovskite light-emitting diodes (PeLEDs) may even replace organic LEDs or quantum-dot LEDs. The buzz about PeLEDs comes at an especially timely moment when previously-giant LED players like Samsung and LG are halting the production of LCDs in favor of organic LEDs and quantum-dot LEDs.
The researchers from Linköping University explain that when perovskite LEDs were been developed in the past, they typically had low efficiencies (less than commercialized LEDs) and a short lifespan. Low efficiencies in perovskite LEDs are caused by the electrons and holes weakly binding, which results in low quantum efficiency and high leakage current.
Increasing the Lifespan of PeLEDs
In an effort to continue the research into PeLEDs and to further realize their commercial potential, the team of researchers at Linköping University has developed a thin-film PeLED whose efficiency is on par with commercial devices and has an increased lifespan greater than that of others to date.
The team tests the new material at a LiU lab. Image used courtesy of Magnus Johansson, Linköping University
The perovskite thin films for efficient and stable LEDs, which is outlined in detail in a Nature article, uses formamidinium lead iodide (FAPbI3) perovskite nanocrystal islands embedded in an electron-transport molecular matrix of 4,4′-diamino diphenyl sulfone (DDS). The researchers observed that the DDS controls the nucleation process that results in a longer lifetime of the resultant LED.
Molecular structure of DDS. Image used courtesy of Heyong Wang et. al
The device is stable for up to half a year in ambient environmental conditions and has a half lifespan of 100 hours. It also has a peak efficiency of 17.3%.
One major advantage of the PeLEDs is that they are easier to manufacture than their silicon counterparts since they do not require high temperatures or vacuum conditions to grow and deposit layers. Instead, the PeLEDs are fabricated with solutions that are spin-coated onto substrates.
The Issue of Lead
One of the materials used to make the PeLEDs—lead—is a double-edged sword. This material provides high optical and electrical properties but is not environmentally-friendly. A device with lead would not pass commercial qualifications, like the RoHS, which has even stricter specifications in 2020.
"We would very much like to get rid of the lead. So far we haven’t found a good way to do this, but we are working hard on it," says Feng Gao, head of the division of biomolecular and organic electronics at Linköping University.
Potential Applications of PeLEDs
PeLEDs' success in the industry depends on how well they can size up to mature technologies. One area that these devices may thrive is in thin displays in wearable technologies, proposed in an article on flexible green perovskite LEDs, since LEDs can effectively be painted onto a surface.
PeLED on a flexible substrate. Image used courtesy of Giuseppe Cantarella, et. al
This also makes PeLEDs potentially viable in HUDs and other augmented realities technologies that require bright and lightweight displays. Because of PeLED's tune-ability, they may also replace standard LEDs when a customer requires a specific wavelength of light, like in telecommunications.
Where Do PeLEDs Go From Here?
As technology currently stands, PeLEDs will not be replacing their LED counterparts anytime soon due to their short lifespan (arguably the most important factor in a design).
Feng Gao expresses optimism in where PeLEDs may springboard with this new film: "Light-emitting diodes based on perovskites are still not sufficiently stable for practical use, but we have brought them one step closer."
The researchers say that they now plan to test different combinations of organic molecules and perovskites to delve into how crystallization and nucleation occur. "Different perovskites give light at different wavelengths, which is a requirement for the long-term goal of obtaining white light LEDs," they explain in the press release.