HIGH-EFFICIENCY GAAS-BASED MULTIJUNCTION SOLAR-CELLS GROWN BY METALORGANIC VAPOR-PHASE EPITAXY

A 25.2% efficiency measured under 1-sun, air mass 0 (AM0) illumination has been achieved in a three-junction AlGaAs(E(g) = 1.93 eV)/GaAs/InGaAsP(E(g) = 0.95 eV) cascade solar cell. The cascade structure grown by atmospheric pressure metalorganic vapor phase epitaxy (MOVPE) consists of a monolithic, series-connected AlGaAs/GaAs cell mechanically stacked on an InGaAsP single junction cell. The efficiency obtained in this cascade structure represents the highest 1-sun AM0 efficiency achieved in any solar cell operating in a two-terminal configuration. The performance of this triple-junction cell indicates that the GaAs component cell is the current-limiting cell in the cascade structure. To evaluate the monolithic AlGaAs/GaAs two-junction cells for space applications, radiation experiments were conducted. The cells were exposed to 1 MeV electron radiation at progressively higher fluences. Results of these experiments indicate that the two-junction cells degrade to about 70% of their initial efficiencies after exposure of a total fluence of 10(16) electrons/cm2. Quantitative results of electron radiation effects on the cell performance are addressed and discussed in this paper.