Someday, shadows and light could team up to provide power. A new device uses the contrast between bright spots and shade to create an electric current. That current can power small electronics, such as a watch or LED lights.
Swee Ching Tan and his team call their new device a shadow-effect energy generator. They made it by coating silicon(硅) with a thin layer of gold. Silicon is often used in solar cells that produce electricity from sunlight.
As in a solar cell, light shining on this generator energizes electrons(电子)in the silicon. Those electrons then jump into the gold. The difference in light levels creates an electric current. Sending electrons makes a flow of current that can power small electronics.
Tan's team described the new device in Energy &Environmental Science. Each device measures 4 cm long and 2 cm wide. That makes its area slightly larger than a stamp. In low light, eight generators power an electronic watch. These devices can also serve as self-powered motion sensors. For instance, when a toy car passed by, its shadow fell on a generator. That created enough electricity to light an LED.
The team compared its generators to commercial solar cells that are typically used under full sunlight. With half of each device in shadow, the generators produced roughly twice as much power per surface area as the solar cells. "But it would be better to compare them to solar cells meant to work in low light, such as the silicon solar cells in classroom calculators. These are designed to use indoor light," said Emily Warren, a chemical engineer at the National Renewable Energy Laboratory. Warren also would like to see the team measure the power the devices make over a longer time, such as a whole day.
Increasing how much light the generators can absorb would allow them to make better use of shadows.
So the team is working to improve the device's performance with strategies that solar cells use to gather light.
