Space solar power systems require photovoltaic materials that can withstand extreme conditions while delivering high efficiency and reliability. The harsh environment of space, including ionizing radiation, thermal cycling, and micrometeoroid impacts, demands advanced semiconductor technologies with superior performance. Multi-junction solar cells, perovskite photovoltaics, and III-V compound semiconductors are among the most promising candidates for space applications, each offering distinct advantages and challenges.

Multi-junction solar cells, typically based on III-V materials like GaInP/GaAs/Ge, dominate space photovoltaics due to their unmatched efficiency. These cells achieve conversion efficiencies exceeding 30% under AM0 (air mass zero) conditions, with laboratory demonstrations reaching beyond 47% under concentrated sunlight. Their layered structure allows absorption across multiple wavelengths, maximizing energy harvest from the solar spectrum. However, radiation-induced degradation remains a critical concern. Displacement damage from high-energy protons and electrons creates defects in the crystal lattice, reducing minority carrier lifetime and increasing recombination losses. Radiation hardening techniques, such as epitaxial designs with wider bandgap subcells and thinner active regions, mitigate these effects. In low Earth orbit (LEO), where atomic oxygen erosion is an additional factor, protective coatings like SiO2 or Al2O3 are essential. In geostationary orbit (GEO) and deep space, where radiation fluxes are higher, shielding and cell architecture optimization become even more critical.

Perovskite solar cells have emerged as a disruptive technology due to their high efficiency potential, tunable bandgap, and low-cost processing. Recent advancements have pushed their AM0 efficiency above 25%, with theoretical limits suggesting further improvements. Their lightweight and flexible nature make them attractive for deployable solar arrays, reducing launch mass and volume. However, perovskite stability under space conditions remains a major hurdle. Ultraviolet radiation, vacuum-induced degradation, and thermal cycling can accelerate ion migration and phase segregation, leading to rapid performance loss. Encapsulation strategies using atomic layer deposition (ALD) and radiation-resistant buffer layers are under investigation to enhance durability. Additionally, all-perovskite multi-junction designs are being explored to combine high efficiency with mechanical flexibility.

III-V semiconductors, particularly GaAs and InP-based cells, offer excellent radiation resistance compared to silicon, owing to their direct bandgap and high carrier mobility. Single-junction GaAs cells exhibit lower initial degradation rates in proton-rich environments, making them suitable for long-duration missions. Further improvements involve heterostructure engineering, such as incorporating AlGaAs window layers to reduce surface recombination. For deep space missions, where solar intensity diminishes, III-V cells with optical concentrators can maintain sufficient power output. However, the high manufacturing cost of III-V materials limits their widespread adoption outside of high-value missions.

Lightweight and flexible solar array designs are critical for next-generation space power systems. Thin-film photovoltaics, including CIGS and organic-inorganic hybrids, enable roll-out or foldable arrays that minimize stowage volume. Advances in substrate materials, such as polyimide and carbon fiber composites, enhance mechanical resilience while reducing mass. Beamed power concepts, where solar energy is converted to microwaves or lasers for transmission, are also gaining traction. These systems could enable continuous power delivery to spacecraft or lunar bases without reliance on onboard storage. Key challenges include achieving high conversion efficiency and precise beam steering over astronomical distances.

Degradation mechanisms vary significantly across orbital regimes. In LEO, atomic oxygen reacts with cell surfaces, eroding contacts and coatings. GEO environments expose cells to higher radiation doses, requiring robust shielding. Deep space missions face extreme temperature fluctuations and cumulative radiation damage, necessitating materials with superior thermal conductivity and defect tolerance. Accelerated lifetime testing under simulated space conditions is essential for validating new photovoltaic technologies.

Innovations in radiation-hardened materials, such as wide bandgap semiconductors like GaN and SiC, are being explored for their inherent resistance to displacement damage. Hybrid systems combining perovskite top cells with silicon or III-V bottom cells aim to balance efficiency, cost, and durability. Furthermore, self-healing materials that autonomously repair radiation-induced defects could revolutionize long-duration mission capabilities.

The future of space photovoltaics lies in optimizing the trade-offs between efficiency, mass, and reliability. Multi-junction III-V cells will continue leading high-performance applications, while perovskite and flexible technologies may enable new mission architectures. Continued research into degradation mechanisms and protective strategies will be crucial for extending operational lifetimes in the increasingly demanding space environment.