field that act to force electrons freed by light absorption to flow in a certain direction . This flow of electrons is a current , and by placing metal contacts on the top and bottom of the PV cell , we can draw that current off to use externally . That 's the basic process , but there's really much more to it . Let 's take a deeper look in to the physics of the single crystal silicon cell . Recall that the current and voltage through a p-n junction diode can be written