TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Solar Cell: In the multijunction solar cell, the first graded interlayer is compositionally graded to lattice match the second subcell on one side and the third subcell on the other side. The second graded interlayer is compositionally graded to lattice match the third subcell on one side and the bottom fourth subcell on the other side. The first graded interlayer is composed of any of arsenic (As), phosphorus (P), nitrogen (N), antimony (Sb) based III-V compound semiconductors subject to the constraints of having the in-plane lattice parameter greater or equal to that of the second subcell and less than or equal to that of the third subcell, and having a band gap energy greater than that of the second subcell and of the third subcell. The second graded interlayer is composed of any of the As, P, N, Sb based III-V compound semiconductors subject to the constraints of having the in-plane lattice parameter greater or equal to that of the third subcell and less than or equal to that of the bottom fourth subcell, and having a band gap energy greater than that of the third subcell and of the fourth subcell. The first and second graded interlayers are composed of (InxGa1-x)yAl1-y with x and y selected such that the band gap of each interlayer remains constant throughout its thickness. The band gap of the first graded interlayer remains constant at 1.5 eV. The band gap of the second graded interlayer remains constant at 1.1 eV. The upper subcell is composed of an InGaP emitter layer and an indium gallium phosphide (InGaP) base layer, the second subcell is composed of InGaP emitter layer and a gallium arsenide (GaAs) base layer, the third subcell is composed of an InGaP emitter layer and an indium gallium arsenide (InGaAs) base layer, and the bottom fourth subcell is composed of an InGaAs base layer and an InGaAs emitter layer lattice matched to the base. The lower fourth subcell has a band gap in the range of approximately 0.6-0.8 eV, the third subcell has a band gap in the range of approximately 0.9-1.1 eV, the second subcell has a band gap in the range of approximately 1.35-1.45 eV and the upper subcell has a band gap in the range of 1.8-2.1 eV. Preferred Method: In manufacturing the solar cell, the lower fourth subcell has a band gap in the range of 0.6-0.8 eV; the third subcell has a band gap in the range of 0.9-1.1 eV, the second subcell has a band gap in the range of 1.35-1.45 eV, and the first subcell has a band gap in the range of 1.8-2.1 eV. The first substrate is composed of gallium arsenide or germanium, and the surrogate substrate is composed of sapphire, gallium arsenide (GaAs), germanium (Ge) or silicon (Si). The first graded interlayer is compositionally graded to lattice match the second subcell on one side and the third subcell on the other side, and the second graded interlayer is compositionally graded to lattice match the third subcell on one side and the bottom fourth subcell on the other side. The first graded interlayer is composed of any of the As, P, N, Sb based III-V compound semiconductors subject to the constraints of having the in-plane lattice parameter greater or equal to that of the second subcell and less than or equal to that of the third subcell, and having a band gap energy greater than that of the second subcell and of the third subcell. The second graded interlayer is composed of any of the As, P, N, Sb based III-V compound semiconductors subject to the constraints of having the in-plane lattice parameter greater or equal to that of the third subcell and less than or equal to that of the bottom fourth subcell, and having a band gap energy greater than that of the third subcell and of the fourth subcell. Alternatively, manufacturing the solar cell comprises: providing a first substrate; depositing on a first substrate a first sequence of layers of semiconductor material forming a first and second solar cells depositing on the first and second solar cells a first grading interlayer; depositing on the first grading interlayer a second sequence of layers of semiconductor material including a second grading interlayer and third and fourth solar cells; mounting and bonding a surrogate substrate on top of the sequence of layers; and removing the first substrate.