27.6% (1-sun, air mass 1.5 G) monolithic two-junction AlGaAs/GaAs solar cell and 25% (1-sun, air mass 0) three-junction AlGaAs/GaAs/InGaAs cascade solar cell

A 27.6% efficiency measured under 1-sun, air mass 1.5-global illumination has been achieved in a two-terminal monolithic two-junction cascade solar cell consisting of an Al_0.37Ga_0.63As (E_g=1.93 eV) upper cell and a GaAs lower cell. This result represents the highest 1-sun efficiency to date. The component cells were electrically connected using a metal interconnect contact fabricated during postgrowth processing. A prismatic cover glass was bonded to the cascade cell to minimize the obscuration effect introduced by the grid lines and metal interconnect contacts. As the cascade cell was operated under air mass 0 illumination, an efficiency of 23% was obtained. A 24.9% efficiency under 1-sun, air mass 0 condition has been achieved in a monolithic two-junction Al_0.37Ga_0.63As/Ga solar cell mechanically stacked on an InGaAs (E_g=1.0 eV) solar cell. This is the first demonstration of the high-efficiency GaAs-based three-junction solar cell. The implications of these high efficiencies, in either two-junction or three-junction cascade solar cells for terrestrial and space applications, are discussed