Solar Cell Stores Energy, Too

Solar cells could soon double as rechargeable batteries, greatly enhancing their power and efficiency.

Developed by a team at The Ohio State University, a new hybrid device combines a battery with a solar cell. The researchers said the new device could reduce energy costs by at least 25 percent.

With this device, light is converted to electrons inside the battery, allowing nearly 100 percent of the electrons to be saved. It also eliminates the loss of electricity that typically occurs when electrons have to travel between a solar cell and an external battery. Typically, only 80 percent of such electrons emerging from a solar cell make it into a battery.

In the study, the researchers designed a permeable mesh solar panel from titanium gauze — a flexible fabric upon which vertical rods of titanium dioxide are grown like blades of grass — using red dye to tune the wavelength of light it captures. Air passes freely through the gauze while the rods capture sunlight.

These scanning electron microscope images show nanometer-sized rods of titanium dioxide (larger image) which cover the surface of a piece of titanium gauze (inset). Courtesy of Yiying Wu/The Ohio State University.

The mesh solar panel forms an electrode. Beneath, the researchers placed a thin sheet of porous carbon and a lithium plate. This hybrid design uses three electrodes rather than the four usually required when connecting a solar cell to a battery.

Between the electrodes, the researchers sandwiched layers of electrolyte to carry electrons back and forth.

Inside the battery, electrons are involved in the chemical decomposition of lithium peroxide into lithium ions and oxygen. The oxygen is released into the air, and the lithium ions are stored in the battery as lithium metal after capturing the electrons.

When the battery discharges, it chemically consumes oxygen from the air to re-form the lithium peroxide. An iodide additive in the electrolyte acts as a redox shuttle that carries electrons and then transports them between the battery electrode and the mesh solar panel, the researchers wrote in the study.

“Basically, it’s a breathing battery,” said professor Dr. Yiying Wu. “It breathes in air when it discharges, and breathes out when it charges.”

Based on early tests, the researchers said the new solar battery’s lifetime could be comparable to rechargeable batteries that are already on the market.

The new device is similar to a battery previously developed by Wu and Ohio State doctoral candidate Xiaodi Ren. That high-efficiency, air-powered battery that discharges by chemically reacting potassium with oxygen this year was awarded a U.S. Department of Energy clean energy prize.

The work was funded by the U.S. Department of Energy. The research was published in Nature Communications (doi: 10.1038/ncomms6111).

For more information, visit www.osu.edu.