All-carbon solar cell is 'world's first'
Stanford University scientists have built the first ever solar cell made entirely of carbon, a promising alternative to the expensive materials used in photovoltaic devices today.
"Carbon has the potential to deliver high performance at a low cost," said professor of chemical engineering, Zhenan Bao. "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."
Unlike rigid silicon solar panels that adorn many rooftops, Stanford's thin film prototype is made 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 researchers estimate that the coating technique also has the potential to reduce manufacturing costs. "Processing silicon-based solar cells requires a lot of steps," Bao added. "But our entire device can be built using simple coating methods that don't require expensive tools and machines."
The experimental solar cell consists of a photoactive layer, which absorbs sunlight, sandwiched between two electrodes. In a typical thin film solar cell, the electrodes are made of conductive metals and indium tin oxide (ITO).
For the study, Bao and her colleagues replaced the silver and ITO used in conventional electrodes with graphene – sheets of carbon that are one atom thick –and single-walled carbon nanotubes that are 10,000 times narrower than a human hair.
For the active layer, the scientists used a material made of carbon nanotubes and 'buckyballs' – football-shaped carbon molecules just one nanometre in diameter.
"Every component in our solar cell, from top to bottom, is made of carbon materials," Bao 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."
One drawback of the all-carbon prototype is that it primarily absorbs near-infrared wavelengths of light, contributing to a laboratory efficiency of less than 1% – much lower than commercially available solar cells. "We clearly have a long way to go on efficiency," Bao concluded. "But with better materials and better processing techniques, we expect that the efficiency will go up quite dramatically."
