Photovoltaic Cells: Converting Photons to Electrons

The solar cells that you see on calculators and satellites
are photovoltaic cells or modules (modules are simply a group
of cells electrically connected and packaged in one frame).
Photovoltaics, as the word implies (photo = light, voltaic =
electricity), convert sunlight directly into electricity.
Once used almost exclusively in space, photovoltaics are used
more and more in less exotic ways. They could even power your
house. How do these devices work?

Photovoltaic (PV) cells are made of special materials called
semiconductors such as silicon, which is currently the most
commonly used. Ba­sically, when light strikes the cell,
a certain portion of it is absorbed within the semiconductor
material. This means that the energy of the absorbed light is
transferred to the semiconductor. The energy knocks electrons
loose, allowing them to flow freely. PV cells also all have
one or more electric fields that act to force electrons freed
by light absorption to flow in a certain direction. This flow
of electrons i­s a current, and by placing metal contacts on
the top and bottom of the PV cell, we can draw that current
off to use externally. For example, the current can power
a calculator. This current, together with the cell's voltage
(which is a result of its built-in electric field or fields),
defines the power (or wattage) that the solar cell can
produce.

That's the basic process, but there's really much more to it.