Photovoltaics, abbreviated as PV, is a technology to convert light into electrical power. A solar cell is a kind of semiconductor device that takes advantage of photovoltaic effect, from which electricity is produced when the semiconductor's PN junction is irradiated. The electrons are set free and pulled through the electric field and move into the N-area and the holes produced move to the P-area, of which process is called photovoltaic effect. When an outside circuit is closed, the electricity flows naturally.