The energy of electrons extracted from a photocathode

[azy]

Hi
How much is the energy of electrons extracted from a photocathode (radiated for example by green light)? I've read that a negative potential is applied to the photocathode to accelerate the electrons extracted (in photomultipliers), what happens if we do not apply such a potential to the photocathode? Does the energy of electrons differ in this case?

Thanks