A solar panel, such as the one shown here on the roof of a building, consists of a series of arrays that are aligned next to each other.
Solar panels are “first cousins” to the chips inside computers or cell phones. The technology used to make solar panels is similar to making computer chips. Both use a class of material called semiconductors — materials that have a limited ability to conduct an electric current.
Most semiconductors are made from crystalline silicon. In a pure silicon crystal, each silicon atom is bonded to four other silicon atoms, and each bond consists of a pair of shared electrons. This is a stable configuration. Electrons involved in these bonds move very little and are restricted to the bonds.
Silicon does not conduct electricity because its electrons do not move easily. Think about a theater filled with people. If every seat is taken, nobody can move or shift for a better seat. This changes if silicon is “doped.” Doping means intentionally adding a small amount of another element, called a dopant, to silicon.
The first kind of doped silicon is called p-type (p is for “positive”). It is produced by introducing atoms — such as boron or gallium — that have one less electron in their outer level than does silicon (Fig. 2a). This means that instead of making four bonds of shared pairs of electrons with other silicon atoms, there is one open “hole.” This is similar to having a few empty seats in a theater; it makes shifting from one seat to another much easier.
The second type of doped silicon is called n-type (n is for “negative”). It is made by including atoms that have one more electron in their outer level than does silicon (Fig. 2b). This additional electron is free to move. In our theater analogy, it is like having one seat occupied by two people. Because this is uncomfortable, one of them would hop to another seat.
(a) A gallium-doped p-type silicon semiconductor; (b) an arsenic-doped n-type silicon semiconductor.