I have in general a doubth about different surface related effects: photoelectric, thermal radiation and charge density in capacitors (and perhaps some others): all are proportional to surface area, but there are several surface increasing methods asanodizing or grow nanotubes that does not increases the effect directly proportional to new surface that can be dozens times, but perhaps reduces a few the emission coefficient.
The photoelectric effect is very interesting, because if you place 2 pallalel graphene plates and heat one using sun energy and mirrors to high temperatures you could have a low cost photoelectric cell using almost all the sun spectrum :)
J.L.