Photovoltaic effect: physical principle

The photovoltaic effect is a consequence of the light-matter interaction in which photons (from the sun or any other artificial source) cause the excitation of electrical charges which can then be collected in the form of a direct current.

The atoms of semiconductor materials used for this purpose have the particularity of having a valence band separate from the conduction band, in which charges can move freely. In the case of silicon, 4 electrons are present in the valence band, and they need to be supplied with 1.1 eV (1.76e-18 J) of energy to promote their injection into the conduction band, where they can participate in an electric current. This amount of energy is called the gap energy (or bandgap) and varies from one material to another. Since the photons making up the sun's rays have energies ranging from 0 to 4 eV, only photons with energies greater than...