Scientists create first all-carbon solar cell

Scientists at Stanford University have created the world’s first solar cell constructed entirely of carbon, which they say is a promising alternative to the expensive materials currently used in photovoltaic devices.

“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.”

Stanford’s thin film stereotype differs from rigid solar panels commonly used on rooftops in that it 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.

According to co-lead author of the study Michael Vosgueritchian, the coating technique may well reduce manufacturing costs as well.

“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 solar cell consists of a photoactive layer that absorbs sunlight sandwiched between two electrodes. A typical thin film solar cell would have electrodes made of conductive materials and indium tin oxide (ITO). Bao said the demand for solar cells and touch-screen panels is driving up the price of materials like indium, which are already scarce. “Carbon, on the other hand, is low cost and earth-abundant,” Bao said.

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. “Carbon nanotubes have extraordinary electrical conductivity and light-absorption properties,” Bao said.

For the active layer, the scientists used material made of carbon nanotubes and ‘buckyballs’ - soccer-ball-shaped carbon molecules just one nanometre in diameter. The research team recently filed a patent for the entire device.

“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.”

The research team is now investigating ways to improve efficiency and is experimenting with carbon nanomaterials that can absorb more light.

The research team published their results in the online edition of the journal ACS Nano.