The Stanford team is looking at a variety of ways to improve efficiency. "Roughness can short-circuit the device and make it hard to collect the current," Bao says. "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.
"Materials made of carbon are very robust," Bao says. "They remain stable in air temperatures of nearly 1,100 degrees Fahrenheit."
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 says. "But obviously we want the highest efficiency possible and are working on ways to improve our device."
"Photovoltaics will definitely be a very important source of power that we will tap into in the future," Bao says. "We have a lot of available sunlight. We've got to figure out some way to use this natural resource that is given to us."