Researchers at the Center for Biomedical Engineering at MIT hold a spinach solution that makes up the active ingredient in a biologic solar cell.

Researchers at the Center for Biomedical Engineering at MIT hold a spinach solution that makes up the active ingredient in a biologic solar cell.
Photo:Donna Coveney/ MIT

The device is based on a protein complex, dubbed Photosystem I, which is derived from spinach cells. The challenge was to keep the complex functioning without water or salt, two necessities for plant life. The answer was found in a peptide, or protein fragment, that acts like a surfactant in detergents. It keeps the complex working despite being deposited on cold, hard surfaces of silicon-based ICy. The peptide also stabilizes the complex and helps it self-assemble while the circuit is being fabricated.

The lab-based device consists of a transparent layer of glass coated with a conductive material and a thin layer of gold over it to facilitate the chemical reactions that self-assemble Photosystem I. Next comes the complex itself covered with a soft organic layer that prevents electrical shorts and protects the complex from the final metallic layer. Researchers shone a laser into the device, then measured the resulting current. 'We got very little current out, mostly because we had just a thin layer of the complex," says Marc Baldy, an assistant professor at MIT. "Most optical excitation passed straight through without being absorbed. Of the light that was absorbed, we estimate 12% was converted to charge."

The team hopes to create similar devices with power conversion efficiencies of about 20% by creating several layers of Photosystem I or increasing the surface area by adding three-dimensional features. The work is supported by MIT., the University of Tennessee, the U.S. Naval Research Lab, Darpa, National Science Foundation, and the Air Force Office of Scientific Research.

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