A solar cell made entirely from carbon-based materials has been developed by researchers at Stanford University, they said yesterday.
The solar cell is still at the research stage, but if successfully refined and commercialised it could mean substantially cheaper cells because they wouldn't rely on expensive materials like indium.
Details of their research were published in the online edition of the journal ACS Nano.
"It took some time to develop this," said Zhenan Bao, a professor of chemical engineering at Stanford and a senior author of the study.
Like a conventional solar cell, the Stanford prototype employs a photo-active layer that collects sunlight. That layer is sandwiched between two electrodes, and the flow of electrons from the photo-active layer to the electrodes creates the electrical current.
In today's commercial cells, those electrodes are made of conductive metals like indium tin oxide. Indium is a rare metal, making it expensive, and its price is set to rise as it becomes more difficult to mine and supply.
The Stanford cell replaces those metals with sheets of graphene that are a single atom thick and single-walled carbon nanotubes. The active layer in the centre is made of buckyballs, carbon molecules that are just 1 nanometer in diameter.
Carbon is one of the most abundant elements on the planet, so it's much cheaper than indium and similar rare metals.
But to date, the all-carbon solar cell isn't nearly as efficient as a conventional cell. In lab tests the Stanford team measured its efficiency at less than 1 percent, which is much less than commercial cells. Japan's Sharp, for example, said earlier this year it had developed a cell with 43.5% efficiency.
The low efficiency is due in part to the cell's absorption of light at near-infrared wavelengths. The researchers are working on cells that absorb a wider range of wavelengths.
"We need to make the materials better and improve the process for fabricating the cells so we get better collection of the charge and absorb sunlight," said Bao. "We've already started working on that."
The Stanford team has already applied for patents covering its work. It was funded by Stanford's Global Climate and Energy Project and the US Air Force Office for Scientific Research.