Eye Of Moth, Toe Of Tungsten: A Witch’s Brew Improves Solar Cells

Much recent solar energy research has been on how plants use photosynthesis to convert sunlight into energy in extremely low-light environments. Now EMPA, the Swiss Federal Laboratories for Materials Science and Technology, has turned to the eye of the moth.

EMPA reports that its researchers have come up with what they call a “photoelectrochemical” solar cell modeled after a moth’s eye to ramp up its light-gathering efficiency. And it’s made of inexpensive materials, tungsten oxide and iron oxide -- better known as rust.

EMPA says rust could be the key to the future of solar energy. Rust can be a component of photoelectrodes that split the hydrogen and oxygen atoms within water molecules, thus isolating pure hydrogen. Even better, this directly converts sunlight into useable fuel and avoids the intermediate step of generating electricity.

Rust is dirt-cheap and absorbs light in the same wavelength region in which the sun beams most of its energy. Yet it’s a poor conductor of electricity and so must be formed into an extremely thin film to achieve the splitting of water molecules. But in a thin film, rust can’t absorb much light.

Enter Florent Boudoire and Artur Braun, EMPA researchers. They solved the problem by including particles of tungsten oxide in a special microstructure laid on the surface of the photoelectrode. Tungsten oxide is yellow in color, and so is suitable for creating electrodes, which conduct electrons either from or to a non-metallic material.

Related Article: Buffett Says He Will Double Investment In Renewables

This tungsten oxide microstructure not only gathers light but also holds on to it. So when light is captured by the microstructure, it is reflected internally back and forth until the structure absorbs all the light, and its energy, that it can hold, making that energy available to split water molecules.

Boudoire says this is exactly how a moth’s eye works. It has to collect as much ambient light as possible at night, but also must not reflect light, which would betray its location to potential predators.

So, like the rust/tungsten oxide microstructure, a moth’s eye internally reflects the light and doesn’t let it go.

By Andy Tully of Oilprice.com