NOVELTY - The method involves providing a subcell layer comprising gallium arsenide-based material with a lattice and a current and voltage retention. A subcell layer material comprising an amount of group-V element e.g. nitrogen, is provided, where the subcell layer material is located proximate to the subcell layer. A gallium arsenide-based subcell (24) is doped with a group-V element dopant. An amount of the group-V element is provided for migration into the gallium arsenide-based material lattice immediately after exposure of a photovoltaic cell (20) to radiation.    USE - Method for repairing radiation-induced damage to photovoltaic cells e.g. solar cells such as multi junction solar cells, single junction solar cells and triple junction lattice-matched solar cells, of a vehicle i.e. space craft, and a laser (all claimed). Can also be used for a manned and unmanned aircraft, satellite, rocket, missile and terrestrial/non-terrestrial/surface/subsurface waterborne vehicle.    ADVANTAGE - The method allows optical reflectors to thin an active area of a radiation damage-prone region or base of p-type material to accommodate strengthening of crystal lattice gallium arsenide material, so that current retention in the gallium arsenide-based subcells after irradiation improves subcell performance at beginning-of-life and end-of-life, thus increasing performance, efficiency and useful life of metamorphic alloys utilized in manufacture of space solar cells.    DETAILED DESCRIPTION - The photovoltaic cell is made by sequentially growing semiconductor alloys selected from a group consisting of gallium arsenide, gallium indium arsenide, gallium arsenide antimony, gallium arsenide bismuth, gallium indium arsenide phosphide, aluminum gallium arsenide, gallium indium arsenide antimony, aluminum gallium indium arsenide, aluminum indium arsenide, aluminum gallium arsenide antimony, aluminum gallium indium arsenide antimony and aluminum gallium indium arsenide phosphide. The nitrogen is incorporated within the gallium arsenide-based layer from a source selected from a group consisting of symmetric or nonsymmetric dimethyl hydrazine, trimethylhydrazine and nitrogen trifluoride. INDEPENDENT CLAIMS are also included for the following:    (1) a solar cell    (2) a vehicle    (3) a laser.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of gallium indium phosphide/gallium arsenide/germanium photovoltaic cells with gallium arsenide-containing layers.    Photovoltaic cell (20)    Germanium subcell (22)    Gallium arsenide-based subcell (24)    Gallium indium phosphide subcell (26)    Cap or contact layer (28)