JANUARY 31, 2005
By Olga Kharif
Solar Cells: The New Light Fantastic
A novel and inexpensive material that ekes current
from even the weakest rays could someday make the
world a cleaner, greener place
day last July, Ted Sargent was typing away in his
office at the University of Toronto when a graduate
student rushed in. His excited visitor explained
that he had just shone infrared light -- invisible
to the human eye -- onto a tiny sample of a special
material Sargent and his researchers had developed,
and the sample actually converted the light into
energy. Always the skeptic, Sargent asked, "Did
you turn the
[overhead] lights off?"
Soon, however, it became clear that this research group had stumbled onto something
big. Sargent and his team describe their discovery -- the world's first plastic
solar cell able to absorb infrared light -- in the February issue of the prestigious
journal Nature Materials. Their little sample could bring about a sea
change in the energy industry, perhaps making solar energy so cheap that it becomes
alternative to fossil fuels.
Solar cells in commercial production today are expensive, around $6 per watt.
To understand what that means, consider this: If you install $600 worth of solar
cells, you can power a typical light bulb for 25 years, figures Ron Pernick,
co-founder of renewable-energy consultancy Clean Edge in San Francisco. That's
about twice the cost of
Through various technological improvements, solar-cell prices have typically
fallen by 5% to 6% a year -- but no more, because cells are manufactured through
complex processes similar to those employed for making PC processors and memory
bridge that price gap, scientists have long attempted
to develop so-called plastic solar cells. Essentially,
they're a thin film that can be manufactured through
a much cheaper process, one analogous to a newspaper
printing press. They can be flexible and light.
Plastic solar cells can also, potentially, be simply
sprayed onto any surface -- and, voila! -- that
wall, roof, or consumer electronics case becomes
a solar-energy collector. Goodbye, ugly solar-panel
roofs. Goodbye, lead storage batteries. Welcome,
walls, cars, MP3 players, even shirts doubling
A person could, potentially, unfurl a roll of such plastic solar cells in a field
and create a huge solar farm in a matter of minutes, says Sargent. The beauty
of plastic solar cells is that they do away with the costly installation required
for traditional, heavy
On the downside, today's plastic solar cells are highly inefficient. They only
convert about 6% of the sunlight that hits them into energy. Standard solar cells
can have 30%-plus efficiency. That's why no company produces plastic solar cells
today, though one, startup Konarka in Lowell, Mass., plans to begin selling its
cells for use as a supplemental energy sources for consumer electronics later
this year, says Daniel McGahn, the outfit's executive vice-president and chief
marketing officer. Konarka is mum on its product's features, but McGahn admits
that even under optimal conditions, the cells are only 7%
Plastic solar cells are also terribly expensive. They can cost 10 times more
than the traditional, semiconductor solar cells.
discovery could drastically increase plastic solar
cells' light absorption -- and tip the cost-benefit
scale in favor of the cells. A plastic solar cell
that captures both visible and infrared light might
be able to reach 30% efficiency, figures Peter
Peumans, an organic-electronics expert at Stanford
The main principle of Sargent's solar-cell operation is nothing out of the ordinary.
Light hits the cell's material, which absorbs a portion of its energy. The energy
knocks tiny electrons that are part of the material loose, and they start flowing
in a certain
direction. That creates an electrical current.
Sargent's knowhow is in the material from which electrons are generated. Semiconductor
material used in regular solar cells requires particularly intense solar power,
found in visible sunlight but not infrared light, for electrons to be knocked
out of place.
But electrons in Sargent's material "get excited" under the influence of infrared
light. The material is made with so-called quantum dots. These are particles
of semiconductor material so small they're invisible to the human eye. To those,
Sargent attaches nanosize organic molecules sometimes found in skin moisturizers.
They're about 100,00 times smaller than the diameter of a human hair. This unique
combination is super responsive to infrared light.
work is far from done, of course. Sargent's still-unnamed
material will have to be improved before it's used
in commercial products. So far, it can convert
only a very small amount of infrared light into
energy -- about 1,000 times less than what's needed
for commercial use. "We have a hint of a solution,
maybe," says Stanford's Peumans.
What's more, materials containing organic molecules decompose when heated. So,
theoretically, such organic-based plastic solar cells will have a life span that's
a lot shorter than today's mainstream solar cells, which are guaranteed to function
for more than 25 years. Still, Sargent says his material has withstood being
heated to 200 degrees Celsius (392 degrees Fahrenheit) without disintegrating.
Plus, a dirt-cheap plastic solar cell that can last for, say, three to five years,
will find its uses -- particularly in consumer-electronics devices, which typically
aren't designed to last longer, anyway.
It will probably take Sargent and the industry up to 10 years to get this technology
to become a significant commercial product. But many venture capitalists and
solar-cell companies believe it's worth
the wait. "I view this work to be groundbreaking," says Josh Wolfe, managing
partner at New York-based venture-capital firm Lux Partners. "There's an opportunity
for a disruptive breakthrough technology with
major social implications."
Indeed, with its potential to be used in power-generating garments, the day may
not be that far off when the term "power suit" takes on a whole new meaning.
Kharif is a reporter for BusinessWeek
Online in Portland, Ore.