Silicon is the most common conductor used in PV cells nowadays, for several reasons. The main reasons lie in the extremely low price of silicon and the fact that it’s widely available worldwide.
However, pure silicon is not an excellent conductor due to its crystalline structure. A silicon atom has 14 electrons in three different layers (or shells), with 2 electrons in the first, 8 in the second, and 4 in the third layer.
This third layer is only half full and the atoms always seek to fill up their layers with electrons by sharing them with other atoms around them.
However, because of the even number of electrons, each silicon atom will have a full share, which leaves less room for free electrons to go. When energy is added to silicon, some of these electrons break free and look for holes left by other free electrons.
This movement of electrons is what actually generates electricity. The photons strike the PV cell and ideally, each photon will knock one electron free and send it searching for a hole to fill, thus conducting electricity. Because silicon has an even number of electrons, all modern solar cells use impure silicon as a way to free up extra electrons to conduct energy better.
All solar companies have a patented crystalline structure that they use in their own panels, and these are made by adding other atoms into the silicon, although usually only a few parts per million. The two main types of atoms that are added to silicon to form solar cells are usually phosphorous and boron.