Research On Key Technologies Of Epitaxial Devices For Three-junction Solar Cells In Space

With the continuous improvement of production and living standards,the demand for space vehicles such as satellites and near space vehicles such as solar powered UAVs is increasing.With its special advantages,such as high photoelectric conversion efficiency,good temperature characteristics,superior radiation resistance and long service life,GaAs-based multijunction solar cell has attracted increasing attention as the key component of space vehicles and near space vehicles power systems.High efficiency and lightweight are the two main directions for the development of solar cells in the future.In this paper,the key technologies of epitaxial growth and device fabrication are demonstrated for lattice-match triple junction solar cell and inverted metamorphic solar cell,and the main achievements are summarized as follows:1.By combining theory and experiment,the subcell structures and epitaxial growth process are optimized,and the high-efficient GaInP/InGaAs/Ge triple-junction solar cell for space applications was obtained,showing a high conversion efficiency of 31%with 30.15 cm2 area under the AMO spectrum at 25 ?.By further optimizing the middle subcell structure,the remaining factor of conversion efficiency for triple-junction solar cells was 85.5%under 1MeV electrons and 1×1015/cm2 radiation conditions.Moreover,the ultra-thin GaInP/InGaAs/Ge triple-junction solar cell is also obtained with total thickness of 40 ?m by thinning the Ge substrate,and the power-to-weight ratio is increased from 480W/Kg to 1400W/Kg.2.The inverted metamorphic Ga0.51In0.49P/GaAs/In0.3Ga0.7As triple-junction solar cells are grown on 4-inch GaAs substrates via metal organic chemical vapor deposition.Optimizing the epitaxial structure and epitaxy process,AlInGaAs graded buffer shows nearly 100%relaxation by the reciprocal space mapping of the high-resolution X-ray diffraction and low average threading dislocation density?5.4×106/cm2 evaluated from the cathodoluminescence image.Using Au-Au bonding and chemical mechanical polishing,the inverted metamorphic Ga0.51In0.49P/GaAs/In0.3Ga0.7As triple-junction solar cell for space applications with 24 cm2 area is fabricated and shows a conversion efficiency of 32%under AMO spectrum,25? conditions.Under 1MeV electron irradiation test,the degradations of the external quantum efficiency and I-V characteristics of inverted metamorphic triple-junction solar cell are exhibited each as a function of fluence,and finally the end-of-life efficiency is 27.2%with a degradation of 15%under 1×1015/cm2 fluence.On the basis of inverted metamorphic solar cell process,a flexible Ga0.51In0.49P/GaAs/In0.5Ga0.7As inverted metamorphic triple-junction solar cell is fabricated and shows a conversion efficiency of 31.7%under AMO spectrum,25 ?conditions and a power-to-weight ratio of 1085W/Kg.