Voc, Jsc and diode ideality factor n

In general, the open circuit voltage V_oc is affected by the band gap of the absorber material, the amount of doping in the doped layers, the material quality, the current density generated by light, and the temperature.

In general, the short circuit current density J_sc is affected by the number of photons in the incident light intensity, the incident light spectrum, the absorption coefficient or optical properties of the material, and the collection probability.

Previously, when J = 0:
V_oc = (kT/q) ln (J_PH/J₀ + 1)

However, a more precise equation is:

V_oc = (nkT/q) ln (J_PH/J₀ + 1)

where n is the diode ideality factor.  

For current usage, n is equals to 1, because it is assumed that there is only or mostly SRH recombination, and this recombination is limited by minority charge carriers.  If the SRH recombination occurs at interfaces (the depletion zone), or limited by both charge carriers, or determined by Auger recombination, n will not be 1.  

Reference:
3.2.1 External Parameters of an Ideal Solar Cell, Delft University of Technology, https://www.youtube.com/watch?v=ZyedIjJ6frI