p-n junction refers to the boundary between two types of semiconductor material. One type is called the p-type and the other is called the n-type. In a typical solar cell, one side of the cell is doped with boron (the p-type), and the other side (n-type) is doped with phosphorus. The p-n junction generates current and voltage due to the “built-in” electric field at the junction of the p-type and n-type material.