Technological developments
Technological developments
Discovery of an unexpected boost for
solar water-splitting cells
controlling the deposition high surface to volume ratio. titania nanotubes, previous
of potassium on the surface They also were interested in measurements were not
of the nanotubes, engineers how best to incorporate carbon sensitive enough to detect it.
can achieve significant energy into the nanotubes, because The result was mildly
savings in a promising new carbon helps titania absorb interesting, but became much
alternate energy system. light in the visible spectrum. more so when the research team
Titania (or titanium (Pure titania absorbs in the compared the performance
dioxide) is a versatile chemical ultraviolet region, and much of of the potassium-bearing
compound best known as a the ultraviolet is filtered by the nanotubes to similar arrays
white pigment. As such it’s atmosphere.) deliberately prepared without
Scanning electron microscope image
found in everything from paint This brought them to potassium. The former required
of typical titania nanotubes for
to toothpastes and sunscreen the NIST x-ray spectroscopy only about one-third the
a photocatalytic cell to produce
hydrogen gas from water. Nanotubes
lotions. Thirty-five years ago, beamline at the National electrical energy to produce
average roughly 90-100 nanometers
Akira Fujishima startled the Synchrotron Light Source. The the same amount of hydrogen
in diameter. (Source: Brookhaven
electrochemical world by NIST facility uses low-energy as an equivalent array of
National Lboratory) demonstrating that it also x-rays that can be precisely potassium-free nanotubes. “The
functioned as a photocatalyst, tuned to specific elements to result was so exciting,” recalls
A research team from
producing hydrogen gas from measure chemical bonds, and is Northeastern physicist Latika
Northeastern University and
water, electricity, and sunlight. at least 10 times more sensitive Menon, “that we got sidetracked
the National Institute of
In recent years, researchers have than commonly available from the carbon research.”
Standards and Technology
been exploring different ways laboratory instruments, allowing Because it has such a strong
(NIST) has discovered,
to optimize the process and researchers to detect elements at effect at nearly undetectable
serendipitously, that a residue
create a commercially viable extremely low concentrations. concentrations, Menon says,
of a process used to build arrays
technology that, essentially, While making measurements potassium probably has played
of titania nanotubes—a residue
transforms cheap sunlight into of the carbon atoms, the team an unrecognized role in many
that wasn’t even noticed before
hydrogen, a pollution-free fuel noticed spectroscopic data experimental water-splitting
this—plays an important role
that can be stored and shipped. that indicated that the titania cells that use titania nanotubes,
in improving the performance
Increasing the available nanotubes had small amounts because potassium hydroxide
of the nanotubes in solar cells
surface area is one way to boost of potassium ions strongly is commonly used in the cells.
that produce hydrogen gas from
a catalyst’s performance, so a bound to the surface, evidently By controlling it, she says,
water. Their results, published
team at Northeastern has been left by the fabrication process hydrogen solar cell designers
online on March 27, 2009
studying techniques to build that used potassium salts. This could use it to optimize
in the Journal of Materials
tightly packed arrays of titania was the first time the potassium performance.
Chemistry, indicate that by
nanotubes, which have a very has ever been observed on
Mitsubishi develops organic solar
cell, Mitsubishi Chemical utilized an “We believe we can achieve a
cells using TFT technology
organic semiconductor material that the conversion efficiency of 10% with a single-
Mitsubishi is one of the many electronics
company developed for TFTs in 2006. At junction cell through the optimization of
companies that have decided to go with the
the moment the solar cell has an energy elemental technologies,” a spokesperson
flow and turn green. The only difference
conversion efficiency of 4.9%, in the for the company said. “We will use a
is that the manufacturer did it in a rather
case of a 2 mm-square cell. Presently, the tandem solar cell when we try for a cell
unconventional way: through recycling.
cell is a single-junction cell with one p-n conversion efficiency of 15%.”
Mitsubishi Chemical, ensuring that phased-
junction. The company intends to use In addition to the development of its
out TFT technology doesn’t go to waste,
the single-junction approach until these own solar cells, Mitsubishi Chemical plans
is reusing old technology to develop the
cells reach an efficiency of at least 10% by to start designing and developing building
newest in solar cells, which it showcased at
2010. Once achieved, the company plans materials made with other manufacturers’
the PV EXPO 2009.
to use a tandem of solar cells to achieve a thin-film solar cells in the near future. But
In order to develop the new solar
conversion efficiency of 15% by 2015. in order to do that, the maker definitely
20 – Global Solar Technology – May/June 2009
www.globalsolartechnology.com
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