Solar Cells


today are mostly made of silicon, one of the most common
elements on Earth. The crystalline silicon solar cell was one of the first types
to be developed and it is still the most common type in use today. They do not
pollute the atmosphere and they leave behind no harmful waste products.
Photovoltaic cells work effectively even in cloudy weather and unlike solar
heaters, are more efficient at low temperatures. They do their job silently and
there are no moving parts to wear out. It is no wonder that one marvels on how
such a device would function.
To understand how a solar cell works, it is necessary to go back to some
basic atomic concepts. In the simplest model of the atom, ...

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but in insulators and semiconductors there is an
"energy gap", in which no electron orbits can exist, between the inner valence
band and outer conduction band [Book 1]. Valence electrons help to bind together
the atoms in a solid by orbiting 2 adjacent nucleii, while conduction electrons,
being less closely bound to the nucleii, are free to move in response to an
applied voltage or electric field. The fewer conduction electrons there are, the
higher the electrical resistivity of the material.
In semiconductors, the materials from which solar sells are made, the
energy gap Eg is fairly small. Because of this, electrons in the valence band
can easily be made to jump to the conduction band by the injection of energy,
either in the form of heat or light [Book 4]. This explains why the high
resistivity of semiconductors decreases as the temperature is raised or the
material illuminated. The excitation of valence electrons to the conduction band
is best accomplished when the ...

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PAPER DETAILS
Added: 12/26/2005 02:06:24 PM
Category: Science & Nature
Type: Premium Paper
Words: 1104
Pages: 5

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