This page is under construction. Photovoltaics are solid-state semiconductor devices that convert light directly into electricity. Most of the material is silicon. A thin layer on the front of the cell is treated with phosphorous to give it a negative character. The interface between two layers contains an electric field and is called a junction.
Light consists of particles called photons.
When light hits the solar cell, some of the photons are absorbed in the region of the junction, freeing electrons in the silicon. If the photons have enough energy, the electrons will be able to overcome the electric field at the junction and are free to move through the silicon and into an external circuit. Some of the more commonly available units generate 5W or 10W per square foot of collector surface. The first one installed is located on the roof of Main Building at Penn State - Delaware Valley . The second is located on the roof of the Physical Plant Building at University Park .