GaInNAs with bandgap 1.0eV is a promising material for multi-junction solar cell applications.However,the poor quality of GaInNAs grown by metalorganic chemical vapor deposition hinders its device performance.Here to reap the benefits of 1.0-eV sub-cell,we focus on the optimization of annealing temperature and growth ambient of GaInNAs.The GaInNAs sub-cell exhibits a concentration reduction of shallow level defects when it is annealed at 700 ℃ for 20min.As compared with the growth case using a hydrogen ambient,the N incorporation efficiency of GaInNAs can be enhanced during the growth in an N2 ambient.Furthermore,background carbon concentration is observed to reduce in the as-grown GaInNAs epilayer.A GaInNAs sub-cell with 82％ peak exteal quantum efficiency is obtained in a dual-junction GaInNAs/Ge solar cell.Finally,a monolithic AlGaInP/AlGaInAs/GaInAs/GaInNAs/Ge five-junction solar cell is grown for space application.The fabricated device shows a conversion efficiency of 31.09％ and a short-circuit current density of 11.81 mA/cm2 under 1 sun AM 0 illumination.