A Photo cell is a device which converts light energy into electrical energy.

Working:

The working of photocell depends upon the photo electric effect.It consist of an evacuated  glass tube in which anode cell and cathode cell are sealed.the cathode is of usually sodium or potassium.which emits electrons by visible light.

but in the case of silver oxidize cathode the photo electrons emits by using infra red light...

this photo cell is connected in the circuit to operate for a particular use. when the light of frequency greater than the threshold  frequency falls on the cathode.it emits photo electrons.

Uses:

It is use to operate the burglar alarms

it is use to open door automatically.

it is used as the detector in the light meter of camera.