WH Smith high power solar cell calculator, c 1990s.

Solar cells work as a result of the photoelectric effect. Instead of pushing electrons out of metal, light falling on a solar cell is used to loosen electrons within a semiconductor, usually silicon. The light energy arrives at the cell in packets, or photons, and these dislodge electrons within the silicon to create the current. The amount of electricity produced by an individual solar cell is relatively small, but sufficient to power a small device such as this pocket calculator.