The main principle of photovoltaic power generation is the photoelectric effect of semiconductor. When the photon is irradiated to the metal, its energy can be absorbed by a certain electron in the metal. The energy of the electron is large enough to overcome the work of the gravitational force inside the metal and escape out of the metal surface and become a photoelectron. The silicon atom has 4 outer electrons. If the atoms of the pure silicon are doped with 5 atoms of external electrons, such as phosphorus atoms, they will become N type semiconductors, and if the atoms of the pure silicon are doped with 3 atoms of the outer electrons, such as boron atoms, form a P type semiconductor. When P and N are combined, the potential difference between the contact surface will become a solar cell. When sunlight is irradiated to the P N junction, the hole moves from the P polar region to the N polar region, and electrons move from the N polar region to the P polar region, forming an electric current.