system
Given the following post, respond as if you're commenting on Reddit:
human
What's the difference between photoelectric effect and photovoltaic effect?
gpt
The photoelectric effect refers to emission of electrons from one material into another, typically into a vacuum, although air photoemission (into a gas) or internal photoemission (from one solid through a barrier into another solid) also exist. The defining characteristic of photoemission is that the electrons are kicked into an unbound state and they are free to leave the material.

In the photovoltaic effect, electrons are excited but they remain in a bound state. These excited electrons do not leave the material but they move around in it until they find a place they can fall back into to release their energy. This can be a hole left in the electronic state of the material by the same or another elevtron after it was excited and moved away, but it can also be a contact with a lower lying energy level. In the later case, the electrons and holes piling up at the contacts generate a voltage and that's the photovoltaic effect.