"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."
Unlike silicon-based solar cells that require a lot of processing steps, the entire device can be built using simple coating methods, using a photoactive layer which absorbs sunlight sandwiched between two electrodes.
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.
For the active layer, the scientists used material made of carbon nanotubes and "buckyballs" - soccer ball-shaped carbon molecules just one nanometer in diameter. The research team recently filed a patent for the entire device
So far. 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 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."
"Roughness can short-circuit the device and make it hard to collect the current," Bao said. "We have to figure out how to make each layer very smooth by stacking the nanomaterials really well." The researchers are also experimenting with carbon nanomaterials that can absorb more light in a broader range of wavelengths, including the visible spectrum.
Due to the high stability of carbon, the ability of carbon solar cells to out-perform conventional devices under extreme conditions could overcome the need for greater efficiency, though.
The research was funded by the Global Climate and Energy Project at Stanford and the Air Force Office for Scientific Research.
Source and top image of all carbon solar cell: Stanford