LEDs are a ubiquitous presence in our lives. They have replaced almost all forms of lighting devices we were using earlier, replacing incandescent lamps, fluorescent lamps, compact fluorescent lamps, mercury vapor lamps, and sodium vapor lamps. This has been possible primarily because of the efficiency and long life of LED lamps. Now there is new research to suggest ways to improve their efficiency and brightness further. This could lower their cost, leading to a further lowering of the cost of scientific tools and consumer goods.
A huge team of researchers, including engineers from the Academia Sinica in Taiwan, the SLAC National Accelerator Lab, Brookhaven, National Laboratory, Los Alamos, and the Center of Nanoscale Materials, Argonne, have managed to make stabilized perovskite nanocrystals. They will use these nanocrystals in LEDs to improve their brightness and stability substantially.
Perovskite crystals have a singular crystalline structure, giving them properties for absorbing and emitting light. This characteristic is helpful in making energy-efficient devices including gamma detectors, consumer devices, and solar cells.
Although scientists have long considered perovskite nanocrystals as a prime candidate material for LEDs, the unstable nature of the perovskites prevented them from actual implementation. The research team stabilized the crystals by embedding them in a porous structure of MOF or a framework of metal and organic substances.
Such an intriguing concept of stabilization has been accomplished earlier also. But scientists could demonstrate that only in powder form. Earlier attempts to create LEDs from perovskite nanocrystals failed as the nanocrystals degraded back to their bulk phase. This led to a loss of their nanocrystal advantages in building LEDs. In the bulk form, the perovskite is in the nanophase, and it behaves differently.
The team managed to solve the problem by creating the perovskite crystals in the emission layer in an LED, for the first time. They have demonstrated that it is possible to manufacture light-emitting diodes at a low cost with perovskite nanocrystals by embedding them in a framework of metal and organic substances. Embedding the perovskite nanocrystals in a MOF framework stabilizes them for the working conditions of the LED.
For making the MOF, the team used a framework of lead nodes as the metal precursor, and for the organic material, they used halide salts. The methylammonium bromide in the halide salts reacted with the lead in the framework, forming nanocrystals around the lead core, and trapping them in the matrix.
As the matrix isolates the nanocrystals, they cannot interact and degrade. The researchers used this method as a coating, as it is substantially cheaper than vacuum processing. Almost all inorganic LEDs in wide use today require vacuum processing.
The team claims it is possible to create bright red, green, and blue LEDs with the MOF-stabilized technique. According to them, it is also possible to create them in various shades of the three colors. They have demonstrated, for the first time, that by stabilizing perovskite nanocrystals in MOF, they can create bright and stable LEDs in a full range of colors. It is possible to create LEDs of different colors, and improve their color purity while enhancing their ability to generate light.
