1.25-eV GaAsSbN/Ge Double-Junction Solar Cell Grown by Metalorganic Vapor Phase Epitaxy for High Efficiency Multijunction Solar Cell Application

Dilute-nitride-antimonide materials grown by metalorganic vapor phase epitaxy (MOVPE) with bandgap energies of 1.25 eV have been integrated into solar cell structures employing a Ge bottom cell on Ge substrate. Single homo- and heterojunction solar cells employing narrow bandgap GaAsSbN (E g ~ 1.25 eV) are grown normally lattice-matched on a GaAs substrate, using MOVPE. Homojunction solar cell structures were realized by employing GaAsSbN material with low carbon background concentration and Si doping to form a p/n junction. External quantum efficiency measurements in the range (870 nm-1000 nm) reveal that the efficiency of the homojunction solar cell is significantly improved over that of the heterojunction structure. The GaAsSbN homojunction cell was integrated with a Ge single-junction bottom cell on Ge substrate. Under AM1.5 direct illumination, the fabricated GaAsSbN (1.24 eV)/Ge double-junction solar cell with a 600-nm-thick GaAsSbN base layer exhibits J_sc, V_oc, FF, and efficiency values of 11.59 mA/cm ², 0.83 V, 72.58%, and 7% with anti-reflection coating (ARC), respectively.