Carbon based solar cell

The Bao group’s all-carbon solar cell consists of a photoactive layer, which absorbs sunlight, sandwiched between two electrodes. (Photo: Mark Shwartz / Stanford University)

Stanford University scientists have built the first solar cell made entirely of carbon, a promising alternative to the expensive materials used in photovoltaic devices today. Zhenan Bao, a professor of chemical engineering at Stanford says,  “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.”

Carbon based solar energy

Carbon allotropes possess unique and interesting physical, chemical, and electronic properties that make them attractive for next-generation electronic devices and solar cells.

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.

Stanford graduate student Michael Vosgueritchian, co-lead author of the study with postdoctoral researcher Marc Ramuz says, “Processing silicon-based solar cells requires a lot of steps. But our entire device can be built using simple coating methods that don’t require expensive tools and machines.”

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 material made of carbon nanotubes and “buckyballs” – soccer ball-shaped carbon molecules just one nanometer in diameter. “Every component in our solar cell, from top to bottom, is made of carbon materials,” Vosgueritchian said.

The ability of carbon solar cells to out-perform conventional devices under extreme conditions could overcome the need for greater efficiency, according to Vosgueritchian. “We believe that all-carbon solar cells could be used in extreme environments, such as at high temperatures or at high physical stress,” he said. “But obviously we want the highest efficiency possible and are working on ways to improve our device.”