InGaAsNSb/Ge double-junction solar cells grown by metalorganic chemical vapor deposition

InGaAsNSb/Ge (1.14/0.67 eV) double-junction solar cells have been grown by metalorganic chemical vapor deposition (MOCVD). Ge p-n junction structures are realized by phosphorous diffusion on p-type Ge substrates. GaAs/InGaAsNSb heterojunction structures are grown on the Ge solar cells. The single-junction InGaAsNSb and Ge subcells are electrically connected by a GaAs tunnel junction. The fabricated solar cell exhibits an efficiency of 9.05% under AM 1.5G illumination with an open circuit voltage of 0.92 V. The InGaAsNSb subcell possessed a low external quantum efficiency over the sub-GaAs bandgap spectral range, reflecting the short minority carrier diffusion length of the dilute-nitride-antimonide material.