Butterfly wings inspire a better way to absorb light in solar panels

Scientists from KIT and Caltech utilize the disordered nanoholes of the black butterfly to improve solar cell performance.

 Image: Radwanul Hasan Siddique, KIT/Caltech

The wings of a butterfly have inspired a new type of solar cell that can harvest light twice as efficiently as before and could one day improve our solar panels.

Solar panels are usually made of thick solar cells, and are positioned at an angle to get the most amount of light from the sun as it moves throughout the day. Thin film solar cells, which can be only nanometers thick, have a lot of potential. These are cheaper and lighter, but because they’re less efficient, we usually use them only in watches and calculators, instead of solar panels. Scientists studied the black wings of the rose butterfly, and copied the structure to create thin solar cells that are more efficient. Unlike other types of cells, these can absorb a lot of light regardless of the angle, and are also easy to make. The results were published in the journal Science Advances.

The rose butterfly is native to Southeast Asia. Because it is cold-blooded and needs sunlight to fly, its black wings have evolved to be very good at absorbing energy. “The really interesting thing is that the butterflies, which have evolved these complex structures as a result of selection over millions of years, are still way outperforming our engineering,” YaleNUS College biology professor Vinod Saranathan told The Verge in an email. (Saranathan was not involved in the study.)

To figure out why these butterflies are so efficient, scientists led by Radwanul Siddique, a bioengineer at the California Institute of Technology, looked at wings under an electron microscope and created a 3D model of the wings’ nanostructures. The wings are built from tiny scales that are covered in randomly spaced holes. The holes are less than a millionth of a meter wide, and they help scatter the light and help the butterfly absorb heat.

Image: Radwanul Hasan Siddique, KIT/Caltech

The holes are random in size, distribution, and shape, says Siddique. Using computer models, the team figured out that the position and order are important for absorbing light, but the shape doesn’t matter. Next, they created a similar structure using extremely thin sheets of hydrogenated amorphous silicon that have the same type of holes.

“I think what’s interesting is the excellent approach of looking at the underlying physiological concepts and then taking these concepts and emulating them in a structure that doesn’t look quite look like how a butterfly looks but does the same physics,” says Mathias Kolle, a professor of engineering at the Massachusetts Institute of Technology who was not involved with the study. He added that the design will need to be scaled, but the fabrication techniques discussed in the paper were relatively simple. (Siddique says it took only about 10 minutes to make these sheets.)

Image: Radwanul Hasan Siddique, KIT/Caltech

Most solar panels are positioned at an angle, which means they generate lots of power for a few hours and then not much the rest of the time. Solar panels using Siddique’s technique could produce more power throughout the day. Though Siddique is now at CalTech, he did this research as part of his doctoral work in Germany, and some members of his old lab have already received funding from the German Research Foundation to work on solar cells and LEDs.