NOVELTY - The solar cell (100) comprises a substrate (110), a first junction disposed over a top surface of the substrate, a second junction comprising III-V material disposed over a top surface of the first junction, a cap layer (140) disposed over the second junction in a first region, a contact disposed over the second junction in a second region adjoining the first region, a third junction disposed over a top surface of the second junction, and a template layer (120) disposed between the substrate and the first junction. The third junction comprises III-V material.    USE - The multi-junction solar cell is useful for flight applications such as satellites and solar-powered aerial vehicles.    ADVANTAGE - The multi-junction solar cell can be economically manufactured with improved power-conversion efficiency, superior electrical performance, lightweight, increased power outputs, enhanced thermal and/or electrical conductivity and high flexibility and stability and without lattice-mismatch.    DETAILED DESCRIPTION - The solar cell (100) comprises a substrate (110), a first junction disposed over a top surface of the substrate, a second junction comprising III-V material disposed over a top surface of the first junction, a cap layer (140) disposed over the second junction in a first region, a contact disposed over the second junction in a second region adjoining the first region, a third junction disposed over a top surface of the second junction, and a template layer (120) disposed between the substrate and the first junction. The third junction comprises III-V material different from the III-V material of the second junction, and has a bandgap different from the bandgaps of the first and second junctions. The first junction and the second junction have a lattice mismatch to germanium of greater than 1%. The template layer comprises a graded-composition layer. A top surface of the template layer is lattice-matched to the first junction. The solar cell has a spectral sensitivity of less than 6% for a change in spectrum from air-mass-zero to air-mass-1.5. The first junction is partitioned into two sub-cells. An interface between the first junction and the second junction comprises a tunnel junction (135). The tunnel junction comprises a first layer adjacent to the first junction and a second layer adjacent to the second junction. The first layer of the tunnel junction is doped with a first dopant species, where the second junction is free of the first dopant species. The second layer of the tunnel junction is doped with a second dopant species present in the first junction as a non-doping element. A portion of the cap layer is disposed beneath the contact in the second region. A threading dislocation density of the cap layer is higher than a threading dislocation density of the first junction by magnitude. The cap layer is partially lattice-relaxed, partially polycrystalline and amorphous, and comprises a first layer and a second layer disposed under the first layer. A density of defects in the cap layer exceeds a defect density of the second junction, where the defects comprise threading dislocations, misfit dislocations, and/or stacking faults.    DESCRIPTION OF DRAWING(S) - The diagram shows a cross-sectional view of a solar cell.    Solar cell (100)    Substrate (110)    Template layer (120)    Junctions (125, 130)    Tunnel junction (135)    Cap layer. (140)