NOVELTY - The metamorphic multijunction solar cell comprises an upper first solar subcell having a first band gap of 1.8-2.1 eV, a middle second solar subcell adjacent to the first solar subcell, a graded interlayer adjacent to the second solar subcell, a lower solar subcell adjacent to the interlayer, and a tunnel diode (109). The middle second solar subcell has a second band gap of 1.2-1.6 eV, a base layer (107), an emitter layer (106), and a window layer, which is directly adjacent to the emitter layer with a refraction index equal to the emitter layer. The graded interlayer has a third band gap.    USE - The metamorphic multijunction solar cell is useful in space applications and terrestrial solar power applications.    ADVANTAGE - The metamorphic multijunction solar cell has greater energy conversion efficiencies and improved radiation resistance, and can be economically and energy efficiently manufactured in a simple manner.    DETAILED DESCRIPTION - The metamorphic multijunction solar cell comprises an upper first solar subcell having a first band gap of 1.8-2.1 eV, a middle second solar subcell adjacent to the first solar subcell, a graded interlayer adjacent to the second solar subcell, a lower solar subcell adjacent to the interlayer, and a tunnel diode (109). The middle second solar subcell has a second band gap of 1.2-1.6 eV, a base layer (107), an emitter layer (106), and a window layer, which is directly adjacent to the emitter layer with a refraction index equal to the emitter layer. The graded interlayer has a third band gap greater than the second band gap, where the layer is graded to lattice match the middle subcell on one side and the bottom subcell on the other side. The lower subcell has a fourth band gap of 0.8-1.2 eV such that the third subcell is lattice mismatched with respect to the second subcell. The graded interlayer has a band gap energy of greater than that of the middle subcell, and composed of (InxGa1-x)yAl1-yAs, where the x and y are selected such that the band gap of the interlayer material remains constant throughout its thickness. The lower solar subcell is composed an indium gallium arsenide base layer and an indium gallium phosphide emitter layer that is lattice matched to the base layer. The middle subcell is composed of indium gallium phosphide emitter layer, and gallium arsenide or indium gallium arsenide base layer. The upper subcell is disposed over and is lattice matched to the middle subcell. The tunnel diode is composed of aluminum gallium arsenide layer and indium gallium phosphide layer. The tunnel diode is disposed between the middle solar cell and the graded interlayer, and composed of an indium gallium phosphide layer having similar indices of refraction. An INDEPENDENT CLAIM is included for a method of manufacturing a multijunction solar cell.    DESCRIPTION OF DRAWING(S) - The diagram shows a cross-sectional view of the multijunction solar cell.    Substrate (101)    Emitter layer (106)    Base layer (107)    Back surface field (108)    Tunnel diode layers (109)    Barrier layer. (115)