Effects of electron irradiation-induced deep level defects have been studied on both n/p and p/n Indium Phosphide (InP) solar cells with very thin emitters. The simulation results reveal that the n/p structure offers a somewhat better short-circuit current and that the p/n structure renders an improved open-circuit voltage, not only before electron irradiation but also after 1 MeV electron irradiation with 5×1015 electrons per cm2 fluence. Further, the calculated findings highlight that the n/p solar cell structure is more resistant than that of a p/n structure.