All-carbon solar cell could be used in photovoltaic devices

Stanford University scientists have built the first solar cell made entirely of carbon — a development claimed to be a promising alternative to the expensive materials used in photovoltaic devices today.

The results are published in the 31 October online edition of the journal ACS Nano.

‘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.’

Unlike rigid silicon solar panels, 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 in a statement.

The coating technique also has the potential to reduce manufacturing costs, said Stanford graduate student Michael Vosgueritchian, co-lead author of the study with postdoctoral researcher Marc Ramuz.

‘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 Bao group’s experimental solar cell consists of a photoactive layer, which absorbs sunlight, sandwiched between two electrodes. In a typical thin-film solar cell, the electrodes are made of conductive metals and indium tin oxide (ITO).

‘Materials such as indium are scarce and becoming more expensive as the demand for solar cells, touchscreen panels and other electronic devices grows,’ Bao said. ‘Carbon, on the other hand, is low cost and Earth abundant.’

For the study, Bao and her colleagues replaced the silver and ITO used in conventional electrodes with graphene 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. The research team recently filed a patent for the entire device.

‘Other groups have reported making all-carbon solar cells, but they were referring to just the active layer in the middle, not the electrodes,’ Vosgueritchian said.

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 one per cent.

‘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.’