Philips Research Laboratories engineers have taken inspiration from moth eyes to develop a coating for solar cells that increases their efficiency. Nanostructures, comparable to the tapered structures on the insects' eyes, reduce the amount of light that's reflected off the photovoltaic material. From Physics World:
To maximize the amount of light entering (moths') eyes, to help them see at night, the insects' eyes are covered in tapered nanostructures. This creates an "effective medium" where the refractive index gradually increases as light travels from air through to the insects' optical nerve. The resulting effective index is close to one, which means that very little light is reflected out of the eye.
Inspired by these biostructures, Gomez Rivas and colleagues have mimicked the effect by growing nanowires of different lengths – creating a metamaterial with optical properties that change gradually as a function of distance.