How is sunlight turned into electricity?
Solar or photovoltaic (photo = light, voltaic =
voltage or electricity) cells are created from
special materials such as Silicon (Si) mixed with
other elements, which when exposed to sunlight
will generate an electrical current. Basically
sunlight is absorbed into the photovoltaic
material, which in turn knocks electrons within
the material loose. This allows the electrons to
flow freely within the material structure,
creating an electrical current.
Why use Silicon?
Silicon is a common choice for solar cells because
of its inherent physical qualities. Silicon has 4
outer shell electrons from a possible 8 ‘holes’. It
will always try to fill the other 4 ‘holes’, and does
this by sharing electrons with neighbouring silicon
atoms. This creates a lattice type structure,
where every atom in the structure bonds with
four other atoms in the structure.
When energy is added to the silicon, in the form of
sunlight, it can knock electrons free of the lattice
structure, but this requires a lot of energy and
generates very few free electrons. With few free
electrons, there is very little current flow, so
impurities are added to the silicon to increase its
current carrying properties. This process is called
‘doping’.
The silicon is ‘doped’ with atoms which contain
more electrons to create negatively charged
silicon or with atoms which contain less electrons
to create positively charged silicon. These
compounds are referred to as n-type and p-type
respectively.
When energy is added to n-type silicon there are a
lot more free electrons present within the
structure. This n-type silicon is placed next to
the p-type silicon, causing the free electrons in
the n-type silicon to rush towards the holes in the
p-type silicon, which creates a current flow.
