NOVELTY - Multijunction solar cell array comprises many solar cells mounted on a carrier, each solar cell comprising: a top contact; an upper first solar subcell having a first band gap disposed over the top contact; a middle second solar subcell having a second band gap smaller than the first band gap; a graded interlayer (116) composed of indium gallium aluminum arsenide and having a third band gap greater than the second band gap; a lower third solar subcell having a fourth band gap smaller than the second band gap; a bottom metal contact layer (123); and a bond layer.    USE - The multijunction solar cell array is useful in concentrator terrestrial power systems and satellites used in data communications.    ADVANTAGE - The multijunction solar cell array: exhibits improved power and energy conversion characteristics and short wavelength response for both subcells; more effectively absorbs and collects the bulk of the radiation in the narrower band gap base; is prepared by the method that minimizes the effect of recombination loss; and is economical.    DETAILED DESCRIPTION - Multijunction solar cell array comprises many solar cells mounted on a carrier, each solar cell comprising: a top contact; an upper first solar subcell having a first band gap disposed over the top contact; a middle second solar subcell having a second band gap smaller than the first band gap, disposed over the upper first solar subcell; a graded interlayer (116) composed of indium gallium aluminum arsenide and having a third band gap greater than the second band gap, disposed over the middle second solar subcell; a lower third solar subcell having a fourth band gap smaller than the second band gap (so that the lower third solar subcell is lattice mismatched with respect to the middle second solar subcell), disposed over the graded interlayer; a bottom metal contact layer (123) disposed over the lower third solar subcell; and a bond layer disposed over the bottom metal contact layer that mounts the solar cell to the carrier, where the graded interlayer is compositionally graded to lattice match the middle second solar subcell on one side and the lower third solar subcell on the other side, and each pair of solar cells is electrically interconnected by a discrete conductor from the top contact of one solar cell to the bottom contact of the other solar cell for each pair of solar cells. An INDEPENDENT CLAIM is also included for preparing the multijunction solar cell array, comprising: providing a first semiconductor substrate; depositing a sequence of layers of semiconductor material on the first semiconductor substrate to form a solar cell; mounting the carrier on top of the sequence of layers; forming many discrete solar cells from the sequence of layers; and electrically interconnecting the solar cells, where depositing the sequence of layers comprises forming the upper first solar subcell on the first substrate, forming the middle second solar subcell over the upper first solar subcell, forming the graded interlayer over the middle second solar subcell, and forming the lower third solar subcell over the graded interlayer.    DESCRIPTION OF DRAWING(S) - The figure shows a cross-sectional view of the solar cell.    Window layer (110)    Barrier layer (115)    Graded interlayer (116)    Metal contact layer (123)    Adhesive layer (124)