First low-cost, all-carbon solar cell developed

Researchers from Stanford University have built the first solar cell made entirely of carbon —in stead of silver and indium— which could drive down the cost of producing electrical energy from sunlight.

 

The scientists said flexible solar cells may soon be coated on building surfaces or on windows and cars to generate electricity, Phys.org reported.

 

"Carbon has the potential to deliver high performance at a low cost," said Zhenan Bao, a professor of chemical engineering at Stanford and the study's senior author.

 

Even better yet, Phys.org said the thin film prototype is flexible, unlike the rigid silicon solar panels that presently adorn many rooftops.

 

Bao added this could be the first demonstration of a working solar cell whose components are all made of carbon.

 

"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.

 

She added photovoltaics will be a very important source of power that people will tap into in the future.

 

"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," she said.

 

For his part, Stanford graduate student Michael Vosgueritchian, co-lead author of the study with postdoctoral researcher Marc Ramuz, said the coating technique can reduce manufacturing costs.

 

He said that while processing silicon-based solar cells requires a lot of steps, "our entire device can be built using simple coating methods that don't require expensive tools and machines."

 

Extreme environments

 

Vosgueritchian also said the ability of carbon solar cells to out-perform conventional devices under extreme conditions could overcome the need for greater efficiency.

 

"We believe that all-carbon solar cells could be used in extreme environments, such as at high temperatures or at high physical stress. But obviously we want the highest efficiency possible and are working on ways to improve our device," he said.

 

In the study, Bao and her colleagues replaced the silver and indium tin oxide (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.

 

On the other hand, Bao said carbon nanotubes have extraordinary electrical conductivity and light-absorption properties.

 

The scientists also used material made of carbon nanotubes and "buckyballs," or soccer ball-shaped carbon molecules just one nanometer in diameter.

 

The research team has filed a patent for the entire device. Low-cost substitutions

 

"Every component in our solar cell, from top to bottom, is made of carbon materials. 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.

 

The group's experimental solar cell has a photoactive layer that absorbs sunlight, sandwiched between two electrodes.

 

It then uses carbon in place of ITO. which is scarce and thus expensive.

 

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

 

Main drawback

 

But a drawback of the all-carbon prototype is that it primarily absorbs near-infrared wavelengths of light, and has a laboratory efficiency of less than 1 percent.

 

This is much lower than commercially available solar cells, Phys.org said.

 

"We clearly have a long way to go on efficiency. But with better materials and better processing techniques, we expect that the efficiency will go up quite dramatically," Bao said.

 

Improving efficiency

 

The team is now considering ways to improve efficiency.

 

Bao said that since roughness can short-circuit the device and make it hard to collect the current, "we have to figure out how to make each layer very smooth by stacking the nanomaterials really well."

 

Also, the researchers are 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. They remain stable in air temperatures of nearly 1,100 degrees Fahrenheit," Bao said. — TJD, GMA News