Nah they aren't.. JayWalker's right with solar cells.. photocells consist of an anode and cathode (a target metal with a certain threshold frequency)... an example is a burgular alarm which goes off when a burglar switches on the light. The photons from the light bulb hits the cathode, which emits photoelectrons to the anode and completes the circuit, switching the alarm on. A breatheliser is also an example of a photocell.