photovoltaic cell..

A solar cell, or photovoltaic cell, is an electronic device that converts light energy into electrical energy, with the help of photovoltaic effect. Its electrical characteristics like current and voltage vary with light.
What is photovoltaic effect? Photovoltaic effect is the creation of voltage and electric current in a material upon exposure to light.
Light travels in packets of energy called photons. The generation of electric current happens inside the depletion region of the PN junction.
The depletion region is the area around the PN junction where the electrons from the N-type material diffused into the holes of the P-type material. When a photon of light is absorbed by one of these atoms in the N-Type material electrons gain sufficient energy and leave the valance band, creating free electrons and a holes. These free electrons and holes have sufficient energy to jump out of the depletion zone, and conduct electricity.