What is the physical difference between a solar cell and a photo-diode?

Question

I am aware that they are different in their application (Obviously) and their area for capturing light, however from an initial reading of their working they seem to be the same thing at a fundamental level, A p-n junction excited by light.

Answer 1

Principally size.

Photodiodes may be used with reverse bias, to observe how the leakage current varies with illumination - this is more sensitive than photovoltaic mode because the reverse bias ensures the current leaves the diode rather than internally recombining. That doesn't affect the basic design but it may affect details of the process.

Beyond that, it will depend on the individual devices.

for example, a photodiode may be made in a process allowing high speed, or minimum dark current (leakage curent in the absence of light), or high avalanche voltage, or it may be coated with an IR or visible spectrum optical filter. None of these are useful for a solar cell.

Answer 2

They are both semiconductor PN junctions and they both exhibit the photovoltaic effect so, principally they are the same at a fundamental level.

See also this article that gives more detail. Another article (here) contains this information: -