Bright idea: fireflies inspire better OLEDs

A bio-inspired prototype is 61% brighter for the same energy and casts light at a wider angle – all thanks to the humble firefly. Belinda Smith reports.

A firefly's 'lantern' is extremely good at transmitting light. Scientists have copied their structure to try to reduce reflections in OLEDs. – Dale Darwin / Getty Images

Organic light-emitting diodes (OLEDs) modelled on a firefly's backside are 61% brighter than conventional OLEDs, Korean scientists claim.

Jae-Jun Kim from the Korea Advanced Institute of Science and Technology and colleagues copied the triple-layered structure of the firefly lantern to produce their powerful prototype.

The bio-inspired OLED also emits light at a broader angle, so could be used in energy-efficient televisions and computer screens with larger viewing angles.

Fireflies have long been the subject of photonics researchers. Their glowing rears are the product of a chemical reaction within special cells called photocytes. A cuticle, or skin, lies atop the photogenic layer, and the light shines through it, signalling to other fireflies that they're ready to mate.

To minimise the amount of light reflected back into the body, firefly lanterns have a layer below the photocytes which bounces light back up and out of the insect (the dorsal layer in the diagram below).

But more importantly, the cuticle isn't smooth. Some fireflies sport a tile-like configuration, with overlapping scales made of a tough compound found in insect exoskeletons called chitin.

Kim and colleagues, in 2012, made an anti-reflective light-emitting diode (LED) lens based on the Korean firefly Luciola lateralis Motschulsky's cuticle. But its cuticle lacked the tiled geometry. Rather, it was covered in rounded bumps.

To best boost the efficiency of OLEDs, where the light-emitting layer is a film of organic compound that shines when an electric current is passed through, they took inspiration from the Pyrocoelia rufa firefly's tiled lantern.

OLEDs were modelled on the firefly's cuticle structure to minimise light reflected back into the body (or diode).

So they mimicked the layers of the P. rufa lantern: a polymer resin patterned with the same tiled geometry and dimensions of the firefly cuticle, sitting atop a layer of light-emitting organic material used in conventional OLEDs and finally, a reflective aluminium layer on the bottom.

And the bio-inspired OLED was 61% brighter than a standard OLED, using the same amount of power, and shone that light 15% wider too.

They've only made a green bio-inspired OLED so far, which also happens to be the same wavelength their P. rufa models emit. But, they write, "its engineering replication paves a new direction in biologically inspired photonics for advanced display or lighting applications".

The work was published in Nano Letters.

Further reading:
10 technologies inspired by nature

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