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Organic Photovoltaics Absorb From Near Infrared Frequencies
A research group has developed organic nanostructures photovoltaics
that can absorb photons near the infrared frequency.
Ewing, NJ | 4 January 2006 -- Global Photonic Energy
Corporation (GPEC), developer of organic photovoltaic
(OPVtm) technology for ultra-low cost high power solar
cells, announced that the company's research partners
at Princeton University and the University of Southern
California (USC) have achieved a new record in an organic
solar cell that is responsive to light in the near infrared
(NIR) range of the solar spectrum. NIR radiation is
invisible to the human eye.
Many so-called "night vision" devices operate by sensing
infrared light which is emitted by warm objects and makes
up a substantial portion of all energy reaching the earth
from the sun. Under only NIR radiation, the Princeton solar
cell would appear to be generating power in the dark -- as
the human eye is only sensitive to visible light.
This latest achievement is the highest level of conversion
performance yet achieved for an organic solar cell in the
IR portion of the solar spectrum. The Company's researchers
detail this latest achievement in the December 2 issue of
Applied Physics Letters.
The Global thirst for energy is continually expanding.
Renewable energy sources have experienced rapid growth
in recent years as costs have improved. Global solar cell
production has grown over 20% annually for the last 20
years, reaching sales of $6 billion in 2004. This strong
growth has resulted in a world-wide shortage of semiconductor
silicon driving 2005 solar cell prices higher. Cost is a
critical factor in the continued expansion of the solar
cell industry. Currently, solar-generated power is four
to six times more expensive to consumers than coal-generated
power.
Silicon crystals are too expensive as a starting material
for making photovoltaics cells. The development of organic
photovoltaic materials holds the potential for much cheaper
photovoltaics. These Princeton and USC researchers (see below)
are not only pursuing organically based photovoltaics but
they are also pursuing the development of much higher
efficiency photovoltaics. The odds are developing a way
to double or triple the conversion efficiency of organic
photovoltaics will not increase costs per square meter of
materials anywhere near as much. So cost per unit of energy
produced will drop.
Recent efforts have focused on the use of "organic" materials.
Organic semiconductors contain the ubiquitous element carbon
and are capable of achieving ultra-low cost solar power
generation that is competitive with traditional fossil fuel
sources. Organic materials have the potential to achieve
ultra-low cost production costs and high power output. The
materials are ultra-thin and flexible and can be applied to
large, curved or spherical surfaces. Because the layers are
so thin, transparent solar cells can be applied to windows
creating power-generating glass that retains its basic
functionality.
GPEC sponsors research by Professor Stephen R. Forrest at
Princeton and Professor Mark E. Thompson at USC. Professor
Forrest's research team has focused on organic "small-molecule"
devices that are assembled literally a molecule at a time
in highly efficient nanostructures. These devices have layers
and/or structural elements that can be extremely small --
at only 0.5 billionth of a meter thick and can be applied to
low-cost, flexible plastic surfaces.
These scientists want to boost absorption of photons near the
infrared frequency range because that is where much of the
energy in sunlight is found.
One challenge for organic solar cells has been the efficient
capture and conversion of sunlight. Sunlight consists of
photons (particles of light) that are delivered across a
spectrum that includes invisible ultraviolet (UV) light,
the visible spectrum of colors -- violet, indigo, blue,
green, yellow, orange and red -- and the invisible infrared
or IR spectrum. The amount of incoming photons across the
UV, visible and IR spectrums is about 4%, 51% and 45%,
respectively. The photons absorbed by a solar cell directly
impacts the power output. To achieve high power output,
solar devices must take advantage of as much of the solar
spectrum as possible. Typical organic solar cells absorb
only a fraction of the visible portion of the solar spectrum.
In fact, the best organic solar cells absorb and convert
only about 1/3 of the total available light utilizing
primarily the visible portion of the spectrum.
"This latest device demonstrates that significant power can
be harvested from the IR and near-IR portion of the solar
spectrum.", said Dr. Stephen R. Forrest. "In fact, this novel
approach has the potential to double the power output of
organic solar devices with power harvested from the near-IR
and IR portion of the solar spectrum. With this approach we
are well on our way to power levels exceeding 100 watts
per meter", Forrest concluded.
Imagine organic photovoltaics coating windows especially in
hot climates. Instead of letting in the infrared frequencies
the photovoltaics convert those photons to useful electricity.
So instead of heating a building and thereby increasing the
demand for air conditioning the photovoltaic coating could
keep out heat and turn it into electricity that would power
air conditioners.
In the longer run imagine nanomaterials-based photovoltaic
coatings that could adjust how much electricity they let
into a room or into a car depending on whether a human was
in the room or car. When a human was present the material
could become transparent to allow ing lighting or provide
the ability to look outside. House and car windows could
be turned dark or transparent by dynamically changing
nanostructures. When no one was in a car or house room the
windows could become dark and that would mean the nanocoatings
were absorbing the light that hit them and turning them
into electric to charge batteries (which of course will
be made from some nanomaterials as well). So on a hot summer
day your car's seats wouldn't get as hot. Also, the inside
trim wouldn't degrade as rapidly due to sun damage.
GPEC is funded by electric power industry venture capitalists
Kuhns Brothers.
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