Photocell is photoelectric cells and is used in many applications to act as a switch getting on and off by the action of light. They are also used to produce electricity (solar cells are photovoltaic cells).

If u mean a photo electric cell or a solar cell............? then its a semiconductor which produces a small amount of current when light falls on its surface or in other words photons strike the atoms of semiconductor to produce an electron flow

Photocells are sensors that allow you to detect light. They are small, inexpensive, low-power, easy to use and don't wear out. For that reason they often appear in toys, gadgets and appliances. Theys are are often referred to as CdS cells (they are made of Cadmium-Sulfide), light-dependent resistors (LDR), and photoresistors.

Photocells are basically a resistor that changes its resistive value (in ohms ) depending on how much light is shining onto the squiggly face. They are very low cost, easy to get in many sizes and specifications, but are very innacurate. Each photocell sensor will act a little differently than the other, even if they are from the same batch. The variations can be really large, 50% or higher! For this reason, they shouldn't be used to try to determine precise light levels in lux or millicandela. Instead, you can expect to only be able to determine basic light changes

The y convert solar radiation into direct current electricity. Materials presently used for photovoltaics include monocrystalline silicon, polycrystalline silicon, microcrystalline silicon, cadmium telluride, and copper indium selenide/sulfide

It is a type of resistor ,its'resistance drops when light falls on it ,
it can be used in automation of street lighting for making on /off automatically .