Scientists want to improve LEDs based on firefly research

Scientists at the Pennsylvania State University think they can improve LEDs based on research on fireflies. These luminescent insects, among others, appear to have certain structures that can significantly increase the efficiency of LEDs.

The researchers describe that fireflies and LEDs face the same challenges in emitting as much of the light produced as possible. In doing so, it must be prevented as much as possible that the light is reflected and thus lost. A solution for this is the use of certain microstructures. With LEDs, symmetrical structures are often used. However, both fireflies and certain luminescent cockroaches are said to have asymmetric microstructures, yielding an extraction efficiency of 90 percent, the researchers say. That is significantly more than commercial LEDs, which, according to the researchers, amount to about fifty percent.

These microstructures can in fact be thought of as microscopic projections on the surface through which more light can escape. The symmetrical structures look more or less like upright pyramids, while the asymmetrical structures look like rows of slanting triangles. According to the researchers, there are two advantages to be gained from this. The slanted structures offer a larger surface area, allowing more interaction with the light. This leads to less light being ‘captured’. In addition, the two different angles of the pyramids’ slopes create a greater random reflective effect, giving the light a second chance, as it were, to escape and find its way out.

The asymmetric microstructures (left) and the symmetric variant

These findings have been confirmed by a computer simulation, which showed that the asymmetric surface can theoretically improve the light extraction efficiency. An experiment was then set up to test this. Tiny symmetrical and asymmetrical surfaces were made by means of a 3D printer, after which the amount of light emitted was measured. As expected, the asymmetric surface was found to ‘produce’ more light, the researchers report.

The researchers have a patent application pending for their invention. They say they are considering working with LED manufacturers once they get the patent. According to the scientists, the asymmetrical structures are quite easy to use in the commercial manufacturing process of LEDs. The textured surfaces are applied to sapphire wafers. If a sapphire block is cut at an oblique angle, the oblique pyramids are immediately created, the researchers say.

The research is published in the journal Optik under the title Ultrahigh light extraction efficiency light emitting diodes by harnessing asymmetric obtuse angle microstructured surfaces.