“Electrons orbit the nucleus of an atom in different “states”, which form regions that are called “bands”. These bands keep their electrons firmly in place. In between these bands are “bandgaps” – states in which no electron can be.
Conductors have no bandgaps, and so electrons flow through them. That is why a copper wire conducts electricity, for example. In insulators (like wood, glass, plastics, or ceramics), there is a very wide bandgap, which blocks the flow of electricity. Finally, in semiconductors, there’s a relatively narrow bandgap. That allows them to either act as an insulator or a conductor. Semiconductors can become conductors when they absorb a “photon” (an elementary particle of light) with an energy potential equal to or greater than the bandgap of the semiconductor material.”
kris de decker, How to Build a Low-Tech Solar Panel?
