Process in which two dissimilar materials in close contact act as an electric cell when struck by light or other radiant energy.
In silicon and germanium , the electrons are usually not free to move from atom to atom. Light striking the crystal provides the energy needed to free electrons from their bound condition. These electrons can cross the junction between two dissimilar crystals more easily in one direction than another, so one side of the junction acquires a negative voltage with respect to the other. As long as light falls on the two materials, the photovoltaic {{link=battery">battery can continue to provide voltage and current. The current can be used to measure the brightness of the light or as a source of power, as in a solar cell .