NOVELTY - A solar device (600) comprises a multijunction solar cell structure (200) having at least first subcell and a second subcell; and a notch filter (602) comprising a repeating pattern of layers of materials disposed over the multijunction solar cell structure. The repeating pattern comprises repeating pattern of three different materials having high, low and medium indices of refraction, respectively, in which two layers of high indices refraction materials are surrounded on either side by medium indices of refraction materials followed by low indices of refraction materials.    USE - As a solar cell for generating electricity from solar radiation useful in e.g. spacecraft.    ADVANTAGE - The solar device has notch filter that notch reflects the first wavelength band of incident photons to reduce a current output of the first junction to an unfiltered current output of the second junction. By reflecting unused solar energy, the notch filter allows the solar cell to run cooler yet it still allows all junctions to fully realize their electrical current production capability. The notch filter provides an optimal amount of solar energy from the Ge junction wavelength band without impacting the GaInP or GaAs junctions for all ranges of incidence angles. The depth and/or the width of the reflecting notch can also be reduced or increased by altering the number, composition, and thicknesses of the notch filter layers. The notch filter reduces heating within the cell and achieves near current matching between the junctions, thus improving the performance of multi-junction solar cell.    DETAILED DESCRIPTION - A solar device (600) comprises a multijunction solar cell structure (200) having at least first subcell and a second subcell; and a notch filter (602) comprising a repeating pattern of layers of materials disposed over the multijunction solar cell structure. The repeating pattern comprises repeating pattern of three different materials having high, low and medium indices of refraction, respectively, in which two layers of high indices refraction materials are surrounded on either side by medium indices of refraction materials followed by low indices of refraction materials. The solar cell further comprises a third subcell. The first, second, and third subcells are germanium (Ge), gallium arsenide (GaAs) and gallium-indium-phosphide (GaInP) subcells. The low refraction index material is silicon dioxide (SiO2), high refractive index material is hafnium dioxide (HfO2) and the medium refractive index material is a mixture of SiO2 (60%) and HfO2 (40%). INDEPENDENT CLAIMS are included for the following:    (1) making a solar device involving depositing a multijunction solar cell structure having at least first subcell and a second subcell on a substrate; and depositing a notch filter comprising a repeating pattern of layers of materials formed of three different materials on the multijunction solar cell structure; and    (2) improving the performance of a GaAs/photoactive junction/Ge triple junction solar cell involving filtering out incident light photoactive in the Ge junction to achieve essentially current matching between the junctions, where photoactive junction is compatible with GaAs and Ge and functional within the triple junction to capture energy in the band passed by GaAs but outside the conversion band for Ge.    DESCRIPTION OF DRAWING(S) - The figure shows a solar device having a solar device.    solar cell structure (200)    solar device (600)    notch filter (602)    first period of materials (602A)    second period of materials (602B)    third period of materials. (602C)