What causes the photoelectric vs photovoltaic effect? In the photoelectric effect, electrons are physically ejected from the material. In the photovoltaic effect, electrons are knocked out of their atomic orbitals but remain within the material.
What causes either the photoelectric or photovoltaic effect to take place upon photon absorption? Is it material dependent - i.e. metals follow the photoelectric effect whereas semiconductors follow the photovoltaic effect? If so, what is it about the materials that create such a difference in effects?
 A: It mainly depends on the material type due to the bonds that are formed in each material.
The photoelectric effect where a photon excites an electron out of a metal, usually the electron is not hardly bounded within the material due to the nature of electrons in metal of being free electrons in metallic bonds. It means that in the case of excitement most of the electrons are not attracted by a strong force of bonding and will leave the metal easily. The only obstacle that electron face in metals to be released is having a photon with enough energy (equal to or greater than the threshold).
In semiconductors which are always related to the photovoltaic effect. The electron is trapped in the valence band due to the covalent bond (one of the strongest bonds between elements) which creats the bandgap (or discrete "quantized" energy levels) that requires higher energy for the electron to overcome and goes to the next level. Therefore, the electron in semiconductors is facing a harder problem for the electron to be released from the covalent bond that forms the bandgap to reach the next level, let alone leave the whole material.
A: The photovoltaic effect requires a junction between different materials to convert light to electrical power.
Common PV cells use a $pn$ diode junction between a $p$-doped and an $n$-doped semiconductor. When light is absorbed, pair of electrons and "holes" are created, that are pulled to different sides by the electrical field in the junction. There are other PV systems, for example Grätzel cells.
In photoemission, electrons acquire enough energy to go to leave the material. It is like ionization, but from a surface.
