A solar cell, most commonly made of silicon, has an electron-rich (n) layer and an electron-poor (p, or hole) layer. A photon (light energy) is absorbed by the silicon semiconductor, and if it has sufficient energy, it forms an electron/hole pair — also known as an exciton. Under the right conditions, the charges are separated and the free electron flows through the circuit, creating a potential. Meanwhile, another electron flows from the circuit back into the hole layer where it recombines with the original hole that was created.
