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Highly efficient ultra-lightweight doubled linear Fresnel-lens concentrators of solar light, which operate in tandem with multijunction InGaP/GaAs/Ge solar cells, have been developed and fabricated. The concentrators have a total photoactive area of (50×100) mm2, with the total thickness of ≤0.35 mm and optical focus of 32 mm. The Fresnel profile of each linear lens in the concentrator is formed from silicone rubber on ≤100 µm radiation-hard glass. The efficiency of the linear lens concentrators was 90% for the AM0 spectrum (1367 W/m2). The efficiency of the concentrators was examined before and after the irradiation and thermal-cycling tests. A 10% decrease in the efficiency of the linear lens concentrators is observed upon irradiation with 1 MeV electrons at a fluence of 3×1015 cm−2 and a

Publisher Summary This chapter presents basic concepts related to GaAs and high-efficiency space cells. GaAs has been found to have an optimal bandgap for effective sunlight conversion. In the first solar cells based on AlGaAs/GaAs heterojunctions, the basic narrow bandgap material was GaAs. A wide bandgap window was made of AlGaAs close in the composition to AlAs, which is almost completely transparent to sunlight, making solar cells very sensitive in the short wavelength range of the sun spectrum. Such a cell is illuminated through the window, and the light with photon energy exceeding the bandgap value of GaAs is absorbed in it, while the generated minority carriers are separated by the p–n junction field located in GaAs. Because of the close lattice parameters of the contacting materials, the interface in AlGaAs/GaAs heterojunctions is characterized by a low density of surface states, providing a highly effective accumulation of carriers. This chapter begins with a historical review of III–V solar cells. It then explains single-junction III–V space solar cells. Solar cells based on AlGaAs/GaAs heterostructures are then explained. The chapter also discusses solar cells with internal Bragg reflector and basic concepts related to GaAs-based cells on Ge substrates.