Researchers at North Carolina State University are looking to biomimicry to solve one of thin-film solar technology's biggest problems: light reflection between films that causes light to be lost before it can be harnessed for energy production. They found their solution in the eyes of moths.
A moth's eyes are highly non-reflective so that it can use what little light is available to see in the dark. The scientists have been able to study the moth eyes and come up with a structure that cuts down on reflection in thin-film devices, also known as thin-film interference.
North Carolina University explains, "Thin-film interference occurs when a thin film of one substance lies on top of a second substance. For example, thin-film interference is what causes the rainbow sheen we see when there is gasoline in a puddle of water.
Thin-film interference is a problem for devices that use multiple layers of thin films, like thin-film solar cells, because it means that some wavelengths of light are being reflected – or “lost” – at every film interface. The more thin films a device has, the more interfaces there are, and the more light is lost."
“We were inspired by the surface structure of a moth’s eye, which has evolved so that it doesn’t reflect light,” says Dr. Chih-Hao Chang, an assistant professor of mechanical and aerospace engineering at NC State and co-author of a paper on the research. “By mimicking that concept, we’ve developed a nanostructure that significantly minimizes thin-film interference.”
The nanostructures are arranged in thin films on top of a bottom layer (this would likely be silicon in a solar cell) and then a second layer of thin film is placed on top. The nanostructures are shaped like tiny cones that protrude into the thin film layer on top, much like the structures found in moths' eyes, and limit the light reflection at the interface of the layers by meshing the two layers together. The researchers found that the nanostructure device reflected 100 times less light than the a thin-film device without the nanostructures.
The next step is to create a solar cell using where the nanostructure layer would be added to the thin film device and test the results. If successful, then the researchers will look to scaling up the technology for commercialization.