Generating Electricity from Shadows

A new device uses the contrast between light and shade to generate power, currently enough to power small electronic devices.

“We can harvest energy anywhere on Earth, not just open spaces,” says Swee Ching Tan, a materials scientist at the National University of Singapore.

Tan and his team created the a “shadow-effect energy generator” (SEG) from a superthin coating of gold on silicon, similar to other solar cells. The light shining on the silicon excites its electrons, which transfer from the silicon to the gold. When part of the device is shaded, voltage from the illuminated side increase and flows to the darker side and creates sufficient power for a small gadget, Tan’s team reports in Energy & Environmental Science.

Thin-film optoelectronic devices like organic photovoltaics, photodetectors, polymer light-emitting diodes, and optoelectronic prosthetic skins are becoming increasingly common and have many potential applications. The successful development of modern optoelectronic materials depends on their materials, the fine adjustment of energy levels, and something called work function.

Work function (WF) the minimum energy needed to eject an electron from a solid into a vacuum. Light-intensity-independent, WF was previously observed in semiconductors coated with thin metallic films. Selective illumination creates a WF function contrast on the metal film that enables charge transport in the same plane.

The degree of contrast between light and dark determines the amount of energy produced. The team is now working to boost performance by borrowing solar cell techniques for gathering light. Increased light would allow the generator to better exploit shadows.

This SEG promises to help power electronics that generate green energy from ambient conditions. I may also work well as a component of smart sensor systems to detect when shadow-casting objects pass by.

Someday, these generators could produce energy in the shadowy spots in a solar array, between skyscrapers, or even indoors. “A lot of people think that shadows are useless,” Tan says. But “anything can be useful, even shadows.”