SolarSystem

Solar cells today ar nighly made of silicon, mavin 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 impart 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 staple fibre atomic

concepts. In the simplest model of the atom, electrons orbit a central nucleus, composed

of

protons and neutrons. for each one electron carries one negative charge and each proton one

positive

charge. Neutrons play no charge. Every atom has the same number of electrons as there

are

protons, so, on the whole, it is electrically neutral. The electrons have discrete kinetic

energy

levels, which increase with the orbital radius. When atoms bond together to form a solid,

the

electron energy levels mix into dress circles.



In electrical conductors, these bands are

continuous 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 butt to the nucleii, are free to move in response to an apply 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...

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