  A film-coupled metamaterial structure is numerically investigated for
enhancing the light absorption in an ultrathin photovoltaic layer of
crystalline gallium arsenide (GaAs). The top subwavelength concave grating and
the bottom metallic film could not only effectively trap light with the help of
wave interference and magnetic resonance effects excited above the bandgap, but
also practically serve as electrical contacts for photon-generated charge
collection. The energy absorbed by the active layer is greatly enhanced in the
film-coupled metamaterial structure, resulting in significant enhancement on
the short-circuit current density by three times over a free-standing GaAs
layer at the same thickness. The results would facilitate the development of
next-generation ultrathin solar cells with lower cost and higher efficiency.
