New low-cost, efficient LEDs in the offing

Scientists have developed an efficient alternative to materials used in traditional LEDs, an advance that would lead to low-cost lasers, lighting and display screens, reduce energy use and cut electricity bills.
Researchers from Princeton University in the US developed a technique in which nanoscale crystalline substances known as perovskite self-assemble to produce more efficient, stable and durable perovskite-based LEDs.
This may speed the use of perovskite technologies in commercial applications such as lighting, lasers and television and computer screens.
"The performance of perovskites in solar cells has really taken off in recent years and they have properties that give them a lot of promise for LEDs, but the inability to create uniform and bright nanoparticle perovskite films has limited their potential," said Barry Rand, assistant professor at Princeton.

"Our new technique allows these nanoparticles to self-assemble to create ultra-fine grained films, an advance in fabrication that makes perovskite LEDs look more like a viable alternative to existing technologies," said Rand.
LEDs emit light when voltage is applied across the it. When the light is turned on, electrical current forces electrons from the negative side of the diode to the positive side. This releases energy in the form of light.

LEDs operate best when this current can be strictly controlled. In Rand's devices, the thin nanoparticle-based films allowed just that.
LEDs have many advantages over incandescent bulbs, including durability, longer life, smaller size, energy efficiency and low-heat.

While they are still more expensive than fluorescent lights for room illumination, they are more energy efficient, light up faster and present fewer environmental concerns related to disposal.
Scientists are exploring perovskites as a potential lower-cost alternative to gallium nitride (GaN) and other materials used in LED manufacturing.
Lower-cost LEDs would speed the acceptance of the bulbs, reducing energy use and environmental impacts.
Researchers said that the use of an additional type of organic ammonium halide and in particular a long-chain ammonium halide, to the perovskite solution during production dramatically constrained the formation of crystals in the film.
The resulting crystallites were much smaller (around 5-10 nanometres across) than those generated with previous methods, and the halide perovskite films were far thinner and smoother.

This led to better external quantum efficiency, meaning the LEDs emitted more photons per number of electrons entering the device. The films were also more stable that those produced by other methods.
The study appears in the journal Nature Photonics.