cells or photovoltaic cells convert sunlight directly into electricity.
They are made from semiconductors, silicone is the most commonly used.
When sunlight strikes a semiconductor it is absorbed, and an electron
is knocked free. This happens naturally but the electron is not captured.
PV cells direct that free electron to a wire that directs the electron
to where it can be used. A flow of electrons is called a current, and
by drawing that current off of the PV cells it can be directed to electronic
devices, whatever they may be.
The solar cells voltage, in combination with the current determines
the amount of power in watts that can be produced. An atom of silicone
is arranged in 3 layers and contains 14 electrons. The first two layers
are completely full of electrons with 5 each, while the outer layer
has only 4 electrons. Silicone will always try to fill that outer layer,
so it shares the electrons with the inner layers forming a crystalline
structure. This is pure silicone, which is actually very poor at conducting
electricity because the electrons are not free to move.
Solar cells use a slightly modified silicone with impurities. Other
elements with more electrons are introduced into the silicone. This
allows for extra, un-bonded electrons to move freely. When photons strike
the surface they knock some of the un-bonded electrons free from their
nucleus. These are called free carriers and these are where the current
comes from. Adding other elements to silicone is called doping and it
is what makes solar cells more useful and efficient.