First all-carbon solar cell
31 October 2012, by Mark Shwartz
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."
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."
This shows the new all-carbon solar cell consists of a
photoactive layer, which absorbs sunlight, sandwiched
between two electrodes. Credit: Mark Shwartz / Stanford
University
(Phys.org)—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 Oct. 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
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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."
Provided by Stanford University
More information:
pubs.acs.org/doi/full/10.1021/nn304410w
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APA citation: First all-carbon solar cell (2012, October 31) retrieved 15 October 2014 from
http://phys.org/news/2012-10-all-carbon-solar-cell.html
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