ScienceDaily (Oct. 31, 2012) ? Stanford University scientists have built the first solar cell made entirely of carbon, a promising alternative to the expensive materials used in photovoltaic devices today. The results are published in the October 31 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 that adorn many rooftops, 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.
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."
Carbon nanomaterials
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 like 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."
The Bao group's all-carbon solar cell consists of 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 that are 10,000 times narrower than a human hair. "Carbon nanotubes have extraordinary electrical conductivity and light-absorption properties," Bao said.
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.
"Every component in our solar cell, from top to bottom, is made of carbon materials," Vosgueritchian said. "Other groups have reported making all-carbon solar cells, but they were referring to just the active layer in the middle, not the electrodes."
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 -- much lower than commercially available solar cells. "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."
Improving efficiency
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 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.
"Materials made of carbon are very robust," Bao said. "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 said. "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 said. "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."
Other authors of the study are Peng Wei of Stanford and Chenggong Wang and Yongli Gao of the University of Rochester Department of Physics and Astronomy. The research was funded by the Global Climate and Energy Project at Stanford and the Air Force Office for Scientific Research.
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The above story is reprinted from materials provided by Stanford University. The original article was written by Mark Shwartz.
Note: Materials may be edited for content and length. For further information, please contact the source cited above.
Journal Reference:
- Marc P. Ramuz, Michael Vosgueritchian, Peng Wei, Chenggong Wang, Yongli Gao, Yingpeng Wu, Yongsheng Chen, Zhenan Bao. Evaluation of Solution-Processable Carbon-Based Electrodes for All-Carbon Solar Cells. ACS Nano, 2012; : 121031083325001 DOI: 10.1021/nn304410w
Note: If no author is given, the source is cited instead.
Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.
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BETHESDA, Md., Oct. 29, 2012 (SEND2PRESS NEWSWIRE) ? ADF Solutions announced today that Triage-Examiner?, a forensic triage tool, was utilized by all five of the East Midlands police forces participating in the highly successful e-Forensics pilot program conducted by the National Policing Improvement Agency (NPIA) in the U.K. The aim of the six-month pilot was to speed up the process for all forces by providing one standardized approach to the examination of computers and mobile devices.
Jack?s Perspective
support schemes, but has received only Bt198 billion in compensation from the government so far, or less than half of the total cost. Due to rising cost, the Finance Ministry proposed to the Commerce Ministry and the National Rice Policy Committee to report the cost every quarter. To make the rice pledging scheme sustainable, the government needs to review the way it buys rice from farmers. The price should not be too much higher than the market, according to officials. The government promises to buy unlimited rice from farmers at an average price of Bt15,000 per tonne of unmilled rice. The government was also urged to limit the quantity of rice that it will buy from farmers, as the open-ended policy has led to overproduction of rice and other farm products, officials said. For example, now farmers plant seven crops in each two-year cycle, up from five previously. Since the government now has a monopoly in rice trading, it has distorted the market mechanism. Exporters and millers cannot buy rice at a reasonable price for trade. A few of them can win rice at government auctions, but that is because they have an unfair advantage over others, officials said. The price support scheme also makes Thai rice more expensive than rivals? rice in the world market, leading to shrinking market share. The scheme has also encouraged smuggling, as farmers in Asean countries can get higher prices by selling their rice to Thais. The government should also consult with other agencies on conducting a comprehensive appraisal of the price support schemes to determine if they should be continued or changed, they said.