I'm Jake ONeal, creator of Animagraffs.
And this is how Solar Power works. Let's start in the heart of a single solar cell. Particles of light, which we call photons,
enter the solar cell and are absorbed by available electrons, exciting the
electrons to a higher energy level. Excited electrons travel out of
the cell and through an external circuit where they exchange this
newly gained energy to do work. The spent electrons return to the
cell, ready to absorb more photons. The supply of extra electrons, and the
force that turns a solar cell into a sort of "electron pump or motor", comes from
joining two special types of silicon material together to generate a reaction where
they meet. This is called a P-N junction. Making a P-N Junction
A silicon atom has 14 total electrons at various energy levels,
or shells, with 4 in its outermost shell. Electrons in the outer shell are
used for bonding with other atoms. Stable atoms generally favor eight
electrons in the outer shell, so silicon atoms share electrons
when bonding to meet that number. We need extra, free electrons to do work. It's
possible to add small amounts of impurities to silicon that change its molecular
structure. This is called "doping". N-type silicon ("n" meaning "negative") is doped with phosphorus. Phosphorus
has five electrons in its outer shell where four are used to bond with neighboring
silicon atoms, leaving an extra free electron. P-type silicon ("p" for "positive") is doped
with boron which has just three electrons in its outer shell, leaving an extra open
space or hole when bonding with silicon. When an electron leaves an open spot other
electrons naturally fill it in sequence. For our purposes, it’s convenient to track
the open space or "hole" as it moves. In the standard atom model, electrons
are represented as having a negative charge. For convenience, in our model, we can
think of holes as having a positive charge, and track that empty space
as it moves through the cell. The Space Charge Region The space charge region forms at the
junction where p and n type silicon meet. When these doped silicon types are layered,
unequal electrons and available spaces or holes naturally seek to recombine across
the junction, attempting to equalize. However, just because doped silicon creates
this intentional electron imbalance, doesn't mean the full atoms can
simply merge across the gap. Natural forces keep the rest of the atom's
structure rigidly in place and intact. Atoms generally have the same
number of orbiting electrons as protons in the nucleus, as well as
neutrons. And doped silicon does as well. P-type silicon has an extra
electron, but also, an extra proton. Electrons just naturally move
around a lot easier than protons. When these electrons wiggle free and try
to equalize, the imbalance creates special, electrically charged atoms with unequal
electrons to protons, called ions. Again, even though these atoms
are now in the ion state, they are fixed in the silicon
structure, and won't move. These opposing positively and negatively
charged ions eventually prevent further electron and hole diffusion, giving the space charge region
a precisely designed width, strength, and so on. An electrical field exists in the space
charge region. Excited electrons are attracted and swept in the positive direction,
and holes in the negative direction. As such, electrons can't go backwards, and must travel an
external circuit to recombine with an open space instead of simply doing so inside of the cell and
wasting their newly gained photon energy as heat. Supporting structures Let's look at other parts of a solar
cell that support the core process. Anti-reflective material Polished silicon alone wastes a lot of
light by reflection, so an anti-reflective coating is added for improved efficiency.
There are many types of anti-reflective material. In this example, a grid of microscopic inverted
pyramids directs and captures light at many different angles, giving it maximum opportunity
to enter the cell and remain longer inside. Photons can be absorbed at any point throughout
the cell. For example, short wavelength, high energy blue light is absorbed readily
near the surface while long wavelength, lower energy red light can require more
depth or time inside the cell to be absorbed. Front contact
Metallic fingers are screen printed and bonded to the top of the cell. They're designed
for optimal charge collection but minimal shading. Passivation layer
A special coating over the rear surface helps prevent early
recombination of electrons and holes, and gives light another chance to
bounce through the cell and be absorbed. Aluminum rear contact
A rear aluminum layer completes the electrical circuit. Electrical
contacts protrude through the passivation layer. Encapsulant
The encapsulant is an adhesive that seals around the solar cells, protecting them from harmful
outside elements and keeping them firmly in place. A common encapsulant material
called EVA (ethyl-vinyl acetate) is stable under high temperatures and UV exposure, and is also transparent.
Glass top layer A thick layer of low iron glass protects
the cell from outside conditions and provides structural strength while
also allowing maximum light passage. Low iron reduces the reflective impurities that
give normal glass a faint greenish-blue tint. Back sheet Polyvinyl fluoride film (tedlar) forms a
thin, near impenetrable protective back layer to prevent damage to sensitive internal parts
during installation and day-to-day function.
