The first commercial photovoltaic cells were made in the 1950s and were intensively developed for use on satelites and lunar craft in the 60s and 70s. Each cell is made of a semiconductor and when light strikes the cell, some of it is absorbed. The energy of this light is transferred to the semiconductor which knocks electrons loose, allowing them to flow freely.
PV cells also have an electric field that acts to force electrons freed by light absorption to flow in a certain direction. This flow of electrons is a current, and by placing metal contacts on the top and bottom of the PV cell, it can be drawn off and used externally. This current is DC and is passed through an inverter which changes it to AC for use in your house or feeding back into the grid.
