The jagged pattern of scales on the abdomen of a firefly has inspired researchers to create a new coating for light emitting diodes (LEDs) that extracts 55 per cent more light than noncoated LEDs.
Researchers in Belgium examined fireflies and noted scales with a periodically repeating saw-tooth pattern, similar to that seen on the roofs of old factories. Although the scales were about 10 micrometres apart — much wider than nanometre scales traditionally dealt with in LED fabrication — computer modelling showed that the design minimizes internal reflection, allowing more light to be extracted.
Researchers at Université de Sherbrooke set about replicating the pattern. “In the past, other teams have tried to etch the active layer of the LED itself,” says Ali Belarouci, a senior research scientist with France’s Centre national de la recherche Fireflies inspire LED coating scientifique who is working at Sherbrooke’s Laboratoire Nanotechnologies Nanosystèmes (LN2). But etching valuable semiconductor material like gallium nitride is difficult and expensive, not to mention wasteful. Instead, Belarouci and his team coated the LEDs with an inexpensive photoresist polymer called AZ9245. This polymer can be cross-linked by laser light, allowing for very specific patterns to be developed. The work is published in Optics Express.
The results — a 55 per cent increase in light efficiency — are impressive, and Belarouci believes the team could get as high as 75 per cent with further refinement. Best of all, the process can be added on top of just about any LED. “You don’t have to re-do the design,” says Belarouci. “You just take your LED as you buy it and coat a very thin overlayer using a standard photolithography process. It’s very compatible and very cost-effective.”