Certain materials produce an electric flow when they are struck by sufficient amounts of light. This is called the photoelectric effect. When formed into cells, they are called photovoltaic cells or PVs. Materials with photovoltaic properties include silicon and more complex composites such as copper indium diselenide, cadmium telluride, and gallium arsenide.
PV cells are made up of semiconductors, which are materials that conduct electricity under some, but not all, conditions. When light strikes the cell, it is absorbed by the semiconductor. The energy of the light is transferred to the semiconductor and knocks loose electrons.
PV cells are designed with layers of slightly different materials, which results in all the loose electrons flowing in a specific direction and thus creates an electric current. Metal contacts are placed at the edges of each cell allowing this current to be drawn off for external use.