The core of this cell is a thin layer of a solid semiconductor material. Older devices typically used plain selenium or copper oxide, written as Cu2O. This semiconductor layer presses tightly against a conductive metal base plate to work.
A microscopic boundary called a potential barrier forms exactly where the two materials touch. This built-in barrier acts exactly like a one-way street for moving electric charges. When particles of light strike the cell, they transfer their energy to resting electrons.
These energized electrons suddenly gain enough power to jump firmly across the boundary layer. This continuous jumping motion creates a steady flow of useful electric current. The total strength of the resulting current directly matches the incoming light intensity.
Unlike many modern sensors, these older cells operate entirely on their own power. They never require an external battery voltage to push the electrons along. Students often confuse these unique cells with standard chemical storage batteries.
Standard batteries rely on internal chemical reactions to store energy for later use. A barrier-layer cell only generates its current while a light source actively shines. These simple cells are the direct ancestors of today’s silicon solar panels.