text: The standard photovoltaic effect, as operating in standard photovoltaic cells, involves the excitation of negative charge carriers (electrons) within a semiconductor medium, and it is negative charge carriers (free electrons) which are ultimately extracted to produce power.  The classification of photoelectrochemical cells which includes Grätzel cells meets this narrow definition, albeit the charge carriers are often excitonic.
  The situation within a photoelectrolytic cell, on the other hand, is quite different.  For example, in a water-splitting photoelectrochemical cell, the excitation, by light, of an electron in a semiconductor leaves a hole which "draws" an electron from a neighboring water molecule:
  This leaves positive charge carriers (protons, that is, H+ ions) in solution, which must then bond with one other proton and combine with two electrons in order to form hydrogen gas, according to:
  A photosynthetic cell is another form of photoelectrolytic cell, with the output in that case being carbohydrates instead of molecular hydrogen.