Photovoltaicsare
devices and materials that convert light energy to electricity.
The term was first used in about 1890. It is derived from the Greek
words phos,
which means light, and volt,
a measurement unit named for Alessandro Volta (1745-1827), a pioneer in
the study of electricity. So, photovoltaics could literally be
translated as light-electricity.
More on Photovoltaic (PV)
Systems
How do we get electricity from the sun?
Sunlight
is made up of photons, or particles of solar energy. Photons
contain various amounts of energy, corresponding to the different
wavelengths of the solar spectrum.
When
photons strike and is absorbed by certain semiconducting materials, such
as certain kinds of silicon (in which a PV cell is usually made
of), the energy of the photon is transferred to an electron in an
atom of the semiconductor .
With its
newfound energy, the electron escapes from its normal position in an
atom of the semiconductor material and becomes part of the current in an
electrical circuit. By leaving its position, the electron causes a
hole to form. Special electrical properties of the PV cell—a
built-in electric field—provide the voltage needed to drive the current
through an external load (such as a light bulb).
This
process is known as the photoelectric effect.
NJIT Researchers Develop Inexpensive,
Easy Process To Produce Solar Panels
NEWARK, July 18, 2007
Researchers at New Jersey Institute of Technology (NJIT)
have developed an inexpensive solar cell that can be painted or printed
on flexible plastic sheets. “The process is simple,” said lead
researcher and author Somenath Mitra, PhD, professor and acting chair of
NJIT’s Department of Chemistry and Environmental Sciences. “Someday
homeowners will even be able to print sheets of these solar cells with
inexpensive home-based inkjet printers. Consumers can then slap the
finished product on a wall, roof or billboard to create their own power
stations.”
“Fullerene single wall carbon nanotube complex for
polymer bulk heterojunction photovoltaic cells,” featured as the June
21, 2007 cover story of the Journal of Materials Chemistry
published by the Royal Society of Chemistry, details the process. The
Society, based at Oxford University, is the British equivalent of the
American Chemical Society.
Harvesting energy directly from abundant solar
radiation using solar cells is increasingly emerging as a major
component of future global energy strategy, said Mitra. Yet, when it
comes to harnessing renewable energy, challenges remain. Expensive,
large-scale infrastructures such as wind mills or dams are necessary to
drive renewable energy sources, such as wind or hydroelectric power
plants. Purified silicon, also used for making computer chips, is a
core material for fabricating conventional solar cells. However, the
processing of a material such as purified silicon is beyond the reach of
most consumers.
“Developing organic solar cells from polymers,
however, is a cheap and potentially simpler alternative,” said Mitra.
“We foresee a great deal of interest in our work because solar cells can
be inexpensively printed or simply painted on exterior building walls
and/or roof tops. Imagine some day driving in your hybrid car with a
solar panel painted on the roof, which is producing electricity to drive
the engine. The opportunities are endless.”
The science goes something like this. When
sunlight falls on an organic solar cell, the energy generates positive
and negative charges. If the charges can be separated and sent to
different electrodes, then a current flows. If not, the energy is
wasted. Link cells electronically and the cells form what is called a
panel, like the ones currently seen on most rooftops. The size of both
the cell and panels vary. Cells can range from 1 millimeter to several
feet; panels have no size limits.
The solar cell developed at NJIT uses a carbon
nanotubes complex, which by the way, is a molecular configuration of
carbon in a cylindrical shape. The name is derived from the tube’s
miniscule size. Scientists estimate nanotubes to be 50,000 times smaller
than a human hair. Nevertheless, just one nanotube can conduct current
better than any conventional electrical wire. “Actually, nanotubes are
significantly better conductors than copper,” Mitra added.
Mitra and his research team took the carbon
nanotubes and combined them with tiny carbon Buckyballs (known as
fullerenes) to form snake-like structures. Buckyballs trap electrons,
although they can’t make electrons flow. Add sunlight to excite the
polymers, and the buckyballs will grab the electrons. Nanotubes,
behaving like copper wires, will then be able to make the electrons or
current flow.
“Using this unique combination in an organic solar
cell recipe can enhance the efficiency of future painted-on solar
cells,” said Mitra. “Someday, I hope to see this process become an
inexpensive energy alternative for households around the world.”
This
story has been adapted from a news release issued by New Jersey
Institute of Technology
