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GENERAL DESCRIPTION OF PV / SOLAR SYSTEM
When light enters the PV / Solar Cell, some of the "Photons" (packets of electro-
magnetic wave energy) from the light energy are absorbed by the semiconductor
atoms. The energy of the absorbed light is transferred to the negatively charged
electrons in the atoms of the solar cell. With their newfound energy, these electrons
escape from their normal positions in the atoms of the semiconductor photovoltaic
material and become part of the electrical flow, or current, in an electrical circuit. A
special electrical property of the PV / Solar Cell – a built-in electric field – provides the
force, or voltage, needed to drive the current through an external load, such as a
light bulb.
To induce the built-in electric field within a PV / Solar Cell, two layers of somewhat
differing semiconductor materials are placed in contact with one another (See Fig. 2.4).
One layer is an N-type semiconductor (e.g. Phosphorus doped Silicon) with an abundance
of "Electrons", which have a Negative electrical charge. The other layer is a P-type
semiconductor (e.g. Boron doped Silicon) with an abundance of "Holes", which have a
Positive electrical charge.
Although both materials are electrically neutral, N-type silicon has excess Electrons and
P-type silicon has excess Holes. Sandwiching these together creates a P-N Junction at their
interface, thereby creating an electric field.
When N-type and P-type silicon come into contact, excess electrons move from the
N-type side to the P-type side. The result is a buildup of Positive charge along the
N-type side of the interface and a buildup of Negative charge along the P-type side.
Because of the flow of electrons and holes, the two semiconductors behave like a battery,
creating an electric field at the surface where they meet – the P/N Junction. The electrical
field causes the electrons to move from the semiconductor toward the Negative surface,
where they become available to the electrical circuit. At the same time, the Holes move in
the opposite direction, toward the positive surface, where they await incoming electrons.
The electrical current is fed to the external load through the top electrical contact surface
(normally in the form of a grid) and the bottom base contact.
The Open Circuit Voltage V
Factors Affecting Voltage and Current Output of the PV / Solar Cell
The amount of electric current generated by photon excitation in a PV / Solar Cell at
a given temperature is affected by the incident light in two ways:
• By the intensity of the incident light.
• By the wavelength of the incident rays.
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of a PV /Solar Cell is just under 0.6 V
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