GaInNAs　materials　with　narrow　bandgaps　of　1.10　eV　have　been　grown　on　a　Ge　substrate　by　metalorganic　chemical　vapor　deposition　to　fabricate　GaInNAs/Ge　(1.10/0.67　eV)　double-junction　solar　cells.　We　have　studied　the　photovoltaic　characteristics　and　the　external　quantum　efficiencies　of　the　double-junction　cells　with　various　annealing　conditions　and　different　GaInNAs　base　layer　thicknesses.　The　best　external　quantum　efficiency　is　obtained　from　the　double-junction　cell　with　a　1170　nm　thick　GaInNAs　base　layer　annealed　at　675　degrees　C　for　30　min.　Under　AM1.5G　illumination,　the　best　double-junction　cell　has　a　short　circuit　current　density　(J(SC))　as　23.63　mA　cm(-2),　which　is　dominated　by　the　J(SC)　of　the　GaInNAs　subcell.