The first solar cell made entirely out of carbon has been created by researchers from Stanford University. This technological breakthrough is offering the possibility of cheap, practical alternatives to the sometimes rather expensive materials used in current solar cells.
“Carbon has the potential to deliver high performance at a low cost,” said study senior author Zhenan Bao, a professor of chemical engineering at Stanford. “To the best of our knowledge, this is the first demonstration of a working solar cell that has all of the components made of carbon. This study builds on previous work done in our lab.”
In contrast to the rigid silicon solar panels that cover many rooftops, the new thin-film prototype was created entirely of carbon materials that can be coated from solution. “Perhaps in the future we can look at alternative markets where flexible carbon solar cells are coated on the surface of buildings, on windows or on cars to generate electricity,” Bao said.
The new coating technique also creates the possibility of greatly reducing current manufacturing costs, according to Stanford grad student Michael Vosgueritchian, co-lead author of the study with postdoctoral researcher Marc Ramuz.
“Processing silicon-based solar cells requires a lot of steps,” Vosgueritchian explained. “But our entire device can be built using simple coating methods that don’t require expensive tools and machines.”
The new solar cell is composed of a photoactive layer that absorbs the sunlight, which is sandwiched between two electrodes. In the common thin-film solar cells of today, the electrodes are usually made from conductive metals and indium tin oxide (ITO). “Materials like indium are scarce and becoming more expensive as the demand for solar cells, touchscreen panels and other electronic devices grows,” Bao said. “Carbon, on the other hand, is low cost and Earth-abundant.”
So, in creating the new solar cell, the researchers replaced the silver and ITO that is used in typical electrodes with graphene and carbon nanotubes. “Carbon nanotubes have extraordinary electrical conductivity and light-absorption properties,” Bao said.
And the active layer was replaced with carbon nanotubes and “buckyballs,” which are carbon molecules just one nanometer in diameter that are shaped like soccer balls. The research team has filed a patent for the new technology.
“Every component in our solar cell, from top to bottom, is made of carbon materials,” Vosgueritchian said. “Other groups have reported making all-carbon solar cells, but they were referring to just the active layer in the middle, not the electrodes.”
There is a drawback to the all-carbon prototype, though — it mostly just absorbs near-infrared wavelengths of light. This results in a laboratory efficiency of only around 1 percent. “We clearly have a long way to go on efficiency,” Bao said. “But with better materials and better processing techniques, we expect that the efficiency will go up quite dramatically.”
The researchers are currently experimenting with a wide variety of carbon nanomaterials, looking to inprove the efficiency.
But improving the efficiency may not be immediately necessary because these new solar solar cells have a significant advantage operating in extreme environments, potentially carving out a place for themselves there.
“Materials made of carbon are very robust,” Bao said. “They remain stable in air temperatures of nearly 1,100 degrees Fahrenheit.”
“We believe that all-carbon solar cells could be used in extreme environments, such as at high temperatures or at high physical stress,” Vosgueritchian said. “But obviously we want the highest efficiency possible and are working on ways to improve our device.”
The research was just published on October 31st in the online edition of the journal ACS Nano.
Source: Stanford University
Image Credits: Mark Shwartz
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