Solar Cell Developed from Carbon-Based Nanotech Materials

All-carbon solar cell (Mark Shwartz, Stanford University)

Researchers at Stanford University in California developed a solar cell made entirely of carbon, instead of silicon and more expensive materials found in current solar cells. The team that included contributors from University of Rochester in New York and Nankai University in China published their findings today in the online issue of the journal ACS Nano (paid subscription required).

The researchers, led by Stanford chemical engineering professor Zhenan Bao, created the new panels with a simple design, consisting of a light-responsive layer placed between two electrodes. The carbon materials in the new solar cell can be dissolved into a liquid solution, making it feasible to apply the cells as a power-generating coating on buildings, windows, and cars. “To the best of our knowledge,” says Bao, “this is the first demonstration of a working solar cell that has all of the components made of carbon.”

Today’s familiar solar cells found in panels on rooftops and electric road signs have electrodes made of conductive metals, such as silver and indium tin oxide. “Materials like indium are scarce,” notes Bao, “and becoming more expensive as the demand for solar cells, touchscreen panels and other electronic devices grows.” Materials made from carbon, on the other hand, are abundant and inexpensive.

In their solar cells, the Stanford team replaced the indium tin oxide and silver used in conventional electrodes with graphene — a single-atom thick film of carbon — and single-walled carbon nanotubes some 10,000 times narrower than a human hair. Carbon nanotubes and graphene have high conductivity. The active layer has carbon nanotubes, which also have the ability to absorb light, and soccer ball-shaped carbon molecules called “buckyballs,” about 1 nanometer in diameter (1 nanometer equals 1 billionth of a meter).

While the research team has filed a patent for the all-carbon solar cell, the technology still needs refinement before it is ready for the marketplace. The prototype cell absorbs light in near-infrared wavelengths, working at an efficiency of less than 1 percent, much lower than current solar cells. The researchers are experimenting with carbon nanomaterials that can absorb more light in a broader range of wavelengths, including the visible spectrum.

Bao says the cells can also be made more efficient by literally smoothing out their roughness. “Roughness can short-circuit the device and make it hard to collect the current,” says Bao. Some of the efficiency deficit can be offset, says graduate student and co-author Michael Vosgueritchian, by the toughness of carbon. Noting the robustness of carbon materials and their ability to withstand high temperatures, says Vosgueritchian, “We believe that all-carbon solar cells could be used in extreme environments, such as at high temperatures or at high physical stress.”

“We clearly have a long way to go on efficiency,” says Bao. “But with better materials and better processing techniques, we expect that the efficiency will go up quite dramatically.”

In the following video, Bao tells more about the all-carbon solar cell.

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