How a Photovoltic Cell Works

Of course, n-type silicon cannot form the electric field by itself; it's also necessary to have some silicon altered to have the opposite electrical properties. So, boron, which has three valence electrons, is used for doping p-type silicon. Boron is introduced during silicon processing, where silicon is purified for use in PV devices. When a boron atom assumes a position in the crystal lattice formerly occupied by a silicon atom, there is a bond missing an electron (in other words, an extra hole).

Substituting a boron atom (with three valence electrons) for a silicon atom in a silicon crystal leaves a hole (a bond missing an electron) that is relatively free to move around the crystal.