27.6% efficiency (1 sun, air mass 1.5) monolithic Al0.37Ga0.63As/GaAs two-junction cascade solar cell with prismatic cover glass

Abstract

A 27.6% efficiency measured under 1 sun, air mass 1.5 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. The component cells were electrically connected together using a metal‐interconnect contact fabricated during post‐growth processing. Also, a prismatic cover glass was bonded to the front surface of the cascade structure 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 23.0% was obtained. Both results represent the highest 1 sun efficiencies ever reported. The implications of achieving this high efficiency in a two‐junction cascade solar cell for terrestrial and space applications are also described.