Solar cells are composed of an electron deficient p-type material and an electron rich n-type material which meet at a junction. At the junction, electrons from the n-type material combine with absences of electrons in the p-type material, called holes. As electrons leave the n-type material, it becomes positively charged; likewise, holes leaving the p-type material cause it to become negatively charged.

 

A charge imbalance caused by the movement of electrons through the junction creates an electric field from the positively charged n-type material to the negatively charged p-type material. As light strikes the solar cell, electrons are excited and break away from atoms in the cell, leaving holes in their place. The electric field exerts a force driving loose electrons in the n-type material and loose holes in the p-type material away from the junction and towards an external load, generating electricity.