Multiple solar cell technologies from three different generations of photovoltaic cells were studied for space applications. The GaAsSb, crystalline first-generation solar cells were studied under low-intensity-low-temperature (LILT) space conditions. In order to examine performance of the cells in energetic irradiation environments this system was exposed to electron irradiation of 1 MeV. Improvement in the carrier extraction was observed in short wavelength regime in the external quantum efficiency (EQE) measurements after electron irradiation. Transmission electron microscope (TEM) images indicated enhanced crystallinity near the top of the cells, coinciding with the region that short wavelength incident light is absorbed. The Cu(InGa)Se2 (CIGS), thin film second generation solar cells were studied under space LILT conditions. These conditions included low Sun intensity at the outer planets in the solar system and their respective temperatures. The unencapsulated CIGS cells were irradiated with 1.5 MeV protons of varying fluence, resulting in significant damage to the performance of the cells. The damage rooted in irradiation induced defects which diffused toward the grain boundaries and resulted in reduced shunt resistance. The degradation manifested more pronounced at low temperatures of the outer planets. A Fresnel lens concentrating system was suggested for the CIGS solar cells to compensate for low light intensity of the outer planets. This concentrating system has a remarkable effect on improving the efficiency of the cells at the planets with dim conditions. Multiple structures of the perovskite solar cells, third generation photovoltaics, were studied in extreme space conditions of irradiation and temperature. Proton irradiation induced defect states inside the perovskite solar cells compromised the performance of the cells. Although, after two months of keeping samples in the dark we observed self-healing in the perovskite cells, resulting in performance of the cells to become very similar to the pre-irradiation conditions. We observed that for irradiation with 1 MeV and extreme fluence level of 4 × 1014 (1/cm2) the solar cell stopped functioning after a few months. Through modifications in architecture of the FACsPb(IBrCl)3 solar cells, very high temperature, 490 K (217 °C), performance of the perovskite solar cells was achieved with 70% of the room temperature efficiency. The modifications to the FACsPb(IBrCl)3 perovsite solar cell included: First, use of a double cation (FACs) composition which improves the stability of the perovskite absorber layer. Second, a transparent conductive back contact was used to prevent metal migration or iodine-metal corrosion. Finally, a alumina-based nanolaminate was applied on top of the cell to prevent thermal decomposition due to loss of volatile species. The investigation of these solar cell technologies under extreme space conditions resulted in finding the weak points and also hidden capacities of these systems. In the case of CIGS solar cells grain boundaries facilitate shunting after irradiation. In perovskite solar cells aside from the stability problem, samples showed very high radiation tolerance and extremely good performance at temperatures more than 200 °C.