Solar Energy: The Physics And Engineering Of Ph... May 2026

To make these electrons move in a specific direction (creating a current), engineers create a P-N junction. By "doping" silicon with elements like phosphorus (yielding an n-type layer with extra electrons) and boron (yielding a p-type layer with "holes"), an internal electric field is established. This field pushes the excited electrons toward the front of the cell and the holes toward the back. The Engineering: Building an Efficient Cell

In a semiconductor, electrons exist in a "valence band" where they are bound to atoms. Above this is the "conduction band." The energy difference between these two is the band gap. Solar Energy: The Physics and Engineering of Ph...

When a photon (a particle of light) hits the solar cell with energy equal to or greater than the band gap, it knocks an electron loose. This creates an electron-hole pair . To make these electrons move in a specific