The advance from Princeton University could hasten the use of perovskite technologies in commercial applications such as lighting, lasers and television or computer screens. The findings have been published in Nature Photonics.
"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, an assistant professor of electrical engineering at Princeton's Andlinger Centre for Energy and the Environment. "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.”
Rand's team and others researchers are exploring perovskites as a potential lower-cost alternative to gallium nitride (GaN) and other materials used in LED manufacturing. Perovskites possess a number of properties that make them promising materials for use in electrical devices. They can, for example, be superconductive or semiconductive, depending on their structure. In recent years, they have been touted as a potential replacement for silicon in solar panels because they are cheaper to manufacture and offer equal efficiency as some silicon-based solar cells.
Fabrication
Hybrid organic-inorganic perovskite layers are fabricated by dissolving perovskite precursors in a solution containing a metal halide and an organic ammonium halide. It is a relatively cheap and simple process that could offer an inexpensive alternative to LEDs based on silicon and other materials.
The resulting semiconductor films emit light in vivid colours, but the crystals forming the molecular structure of the films are too large, making them inefficient and unstable.
In their new paper, Rand and his team report that the use of an additional type of organic ammonium halide, particularly a long-chain ammonium halide, to the perovskite solution during production constrained the formation of crystals in the film. The resulting crystallites were 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 than those produced by other methods.
The paper - Efficient perovskite light-emitting diodes featuring nanometre-sized crystallites – can be found here.
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