Nanotechnology could finally make solar power a widely used electricity alternative.
A billboard on a bus or paint on a roof may be the next examples of cost effective solar
collectors
THE PAST - Harvesting solar power required getting the energy where and when it was
available, converting it to electrical energy, usually storing it and raising it to a
useful level when needed. Solar power was available at a specific, modest rate of about
one kilowatt-hour per daylight hour and was converted to electrical energy with only about
25% efficiency. An analysis of any application must compare needs to
reasonable available solar power for that purpose. However, the main reason solar power IN
THE PAST ....was not widely exploited was COMPLETELY ECONOMIC. It has been estimated that
running a household using current solar power technology would require a base equipment
cost of about $9 per watt, which was quite costly in comparison to fossil fuel power.
Traditional semiconductor-technology-based solar panels were expensive to produce and they
were rigid and so didn't conform well to many surfaces to harvest power from sunlight.
Silicon crystals had to be grown in batches, which limits production and size, thus
raising costs. Nanotechnology may come to the rescue here.
Painting the Solar Cells on
Materials - the nano cell solution
The sun may be the only energy source big enough to wean us off fossil fuels. But
harnessing its energy depends on silicon wafers that must be produced by the same exacting
process used to make computer chips. The expense of the silicon wafers raises solar-power
costs to as much as 10 times the price of fossil fuel generation, thus keeping it an
energy source best suited for satellites and other niche applications.
Paul Alivisatos, a chemist at the University of California, Berkeley, has been testing
nanotechnology to produce a photovoltaic material that can be spread like plastic wrap or
paint. Not only could the nano solar cell be integrated with other building materials, it
also offers the promise of cheap production costs that could finally make solar
power a widely used electricity alternative.
Alivisatos’s approach begins with electrically conductive polymers. Other researchers
have attempted to concoct solar cells from these plastic materials, but even the best of
these devices aren’t nearly efficient enough at converting solar energy into
electricity. To improve the efficiency, Alivisatos and his coworkers are
adding a new ingredient to the polymer: nanorods, bar-shaped semiconducting
inorganic crystals measuring just seven nanometers by 60 nanometers. The result
is a cheap and flexible material that could provide the same kind of efficiency achieved
with silicon solar cells. Indeed, Alivisatos hopes that within three years,
Nanosys, a Palo Alto, CA, startup he cofounded will roll out a nanorod solar cell that can
produce energy with the efficiency of silicon-based systems.
The prototype solar cells he has made so far consist of sheets of a nanorod-polymer
composite just 200 nanometers thick. Thin layers of an electrode sandwich the composite
sheets. When sunlight hits the sheets, they absorb photons, exciting electrons in the
polymer and the nanorods, which make up 90 percent of the composite. The result is a
useful current that is carried away by the electrodes.
Early results have been encouraging. But several tricks now in the works could further
boost performance. First, Alivisatos and his collaborators have switched to a new nanorod
material, cadmium telluride, which absorbs more sunlight than cadmium selenide, the
material they used initially. The scientists are also aligning the nanorods in branching
assemblages that conduct electrons more efficiently than do randomly mixed nanorods.
“It’s all a matter of processing,” Alivisatos explains, adding that he sees
“no inherent reason” why the nano solar cells couldn’t eventually match the
performance of top-end, expensive silicon solar cells.
The nanorod solar cells could be rolled out, ink-jet printed, or even painted onto
surfaces, so “a billboard on a bus could be a solar collector,” says
Nanosys’s director of business development, Stephen Empedocles. He predicts that
cheaper materials could create a $10 billion annual market for solar cells, dwarfing the
growing market for conventional silicon cells.
Alivisatos’s nanorods aren’t the only technology entrants chasing cheaper solar
power. But whether or not his approach eventually revolutionizes solar power, he is
bringing novel nanotechnology strategies to bear on the problem. And that alone could be a
major contribution to the search for a better solar cell. “There will be other
research groups with clever ideas and processes—maybe something we haven’t even
thought of yet,” says Alivisatos. “New ideas and new materials have opened up a
period of change. It’s a good idea to try many approaches and see what emerges.”
Thanks to nanotechnology, those new ideas and new materials could transform the solar cell
market from a boutique source to the Wal-Mart of electricity production.
Others in NANO SOLAR CELLS, RESEARCHER, PROJECT
Richard Friend , U. Cambridge, Fullerene-polymer composite solar cells
Michael Grätzel, Swiss Federal Institute ofTechnology, Nanocrystalline dye-sensitized
solar cells
Alan Heeger, U. California,Santa Barbara, Fullerene-polymer composite solar cells
N. Serdar Sariciftci, Johannes Kepler U, Polymer and fullerene-polymer composite
solarcells |
