Four Junction Inverted Metamorphic Multijunction Solar Cell with Two Metamorphic Layers

1 .- 20 . (canceled)

21 . A multijunction solar cell comprising:

one or more upper solar subcells;

a first upper barrier layer below the one or more upper solar subcells, the first upper barrier layer being composed of InGa(Al)P;

a first graded interlayer composed of InGaAlAs, the first graded interlayer being below and adjacent the first upper barrier layer and having a band gap that is constant throughout the thickness of the first graded interlayer;

a first lower barrier layer below and adjacent the first graded interlayer, the first lower barrier layer being composed of InGaP and having a composition different from that of the first upper barrier layer;

at least one middle solar subcell below the first lower barrier layer;

a second graded interlayer composed of InGaAlAs and disposed below the at least one middle solar subcell and having a band gap that is constant throughout the thickness of the second graded interlayer; and

at least one lower solar subcell below the second graded interlayer.

22 . The multijunction solar cell of claim 21 wherein the first upper barrier layer and the first lower barrier layer help prevent threading dislocations from propagating, respectively, into adjacent ones of the solar subcells.

23 . The multijunction solar cell of claim 21 wherein the band gap of the first graded interlayer is 1.5 eV.

24 . The multijunction solar cell of claim 23 wherein the band gap of the second graded interlayer is 1.1 eV.

25 . The multijunction solar cell of claim 24 wherein:

the one or more upper solar subcells include a first solar subcell having a first band gap in the range of 1.8 to 2.1 eV, and a second solar subcell below the first solar subcell and having a second band gap in the range of 1.35 to 1.45 eV;

the at least one middle solar subcell includes a third solar subcell having a band gap in the range of 0.9 to 1.1 eV; and

the at least one lower solar subcell includes a fourth solar subcell having a band gap in the range of 0.6 to 0.8 eV.

26 . The multijunction solar cell of claim 21 wherein:

the one or more upper solar subcells include a first solar subcell having a first band gap, and a second solar subcell disposed below the first solar subcell and having a second band gap smaller than the first band gap;

the first graded interlayer has a third band gap greater than the second band gap;

the at least one middle solar subcell includes a third solar subcell having a fourth band gap smaller than the second band gap such that the third subcell is lattice mismatched with respect to the second subcell, and wherein the first graded interlayer provides a gradual transition in lattice constant from the second solar subcell to the third solar subcell;

the second graded interlayer has a fifth band gap greater than the fourth band gap; and

the at least one lower solar subcell includes a fourth solar subcell having a sixth band gap smaller than the fourth band gap such that the fourth solar subcell is lattice mismatched with respect to the third solar subcell, and wherein the second graded interlayer provides a gradual transition in lattice constant from the third solar subcell to the fourth solar subcell.

27 . The multijunction solar cell of claim 21 wherein the first upper barrier layer is n-type, and the first lower barrier layer is n+ type.

28 . The multijunction solar cell of claim 21 wherein the first upper barrier layer is composed of InGaP.

29 . The multijunction solar cell of claim 21 further including a second upper barrier layer disposed below the at least one middle solar subcell, and disposed above and adjacent to the second graded interlayer.

30 . The multijunction solar cell of claim 29 wherein the second upper barrier layer is composed of GaInP.

31 . A method of manufacturing a solar cell comprising:

providing a first substrate;

depositing over the first substrate a first sequence of layers of semiconductor material forming one or more first solar subcells;

depositing over the first sequence of layers a first upper barrier layer composed of InGa(Al)P;

depositing over the first upper barrier layer a first graded interlayer composed of InGaAlAs, the first graded interlayer being adjacent the first upper barrier layer and having a band gap that is constant throughout the thickness of the first graded interlayer;

depositing over the first graded interlayer a first lower barrier layer such that the first lower barrier layer is adjacent the first graded interlayer, the first lower barrier layer being composed of InGaP and having a composition different from that of the first upper barrier layer;

depositing over the first lower barrier layer at least one second solar subcell;

depositing over the at least one second solar subcell a second graded interlayer composed of InGaAlAs and having a band gap that is constant throughout the thickness of the second graded interlayer; and

depositing over the second graded interlayer at least one third solar subcell.

32 . The method of claim 31 wherein the first upper barrier layer and the first lower barrier layer help prevent threading dislocations from propagating, respectively, into adjacent ones of the solar subcells.

33 . The method of claim 31 wherein depositing a first graded interlayer includes depositing a graded interlayer having a band gap of 1.5 eV.

34 . The method of claim 33 wherein depositing a second graded interlayer included depositing a graded interlayer having a band gap of 1.1 eV.

35 . The method of claim 34 wherein:

depositing the one or more first solar subcells includes:

depositing a first solar subcell having a first band gap in the range of 1.8 to 2.1 eV; and

depositing over the first solar subcell another solar subcell having a second band gap in the range of 1.35 to 1.45 eV;

depositing the at least one second solar subcell includes depositing a solar subcell having a band gap in the range of 0.9 to 1.1 eV; and

depositing the at least one third solar subcell includes depositing a solar subcell having a band gap in the range of 0.6 to 0.8 eV.

36 . The method of claim 31 wherein:

depositing the one or more first solar subcells includes:

depositing a first solar subcell having a first band gap; and

depositing over the first solar subcell another solar subcell having a second band gap smaller than the first band gap;

depositing the first graded interlayer includes depositing a graded interlayer having a third band gap greater than the second band gap;

depositing the at least one second solar subcell includes depositing a solar subcell having a fourth band gap smaller than the second band gap, wherein the solar subcell having the fourth band gap is lattice mismatched with respect to the solar subcell having the second band gap, and wherein the first graded interlayer provides a gradual transition in lattice constant from the solar subcell having the second band gap to the solar subcell having the fourth band gap;

depositing a second graded interlayer includes depositing a graded interlayer having a fifth band gap greater than the fourth band gap; and

depositing the at least one third solar subcell includes depositing a solar subcell having a sixth band gap smaller than the fourth band gap such that the solar subcell having the sixth band gap is lattice mismatched with respect to the solar subcell having the fourth band gap, and wherein the second graded interlayer provides a gradual transition in lattice constant from the solar subcell having the fourth band gap to the solar subcell having the sixth band gap.

37 . The method of claim 31 wherein depositing a first upper barrier layer includes depositing a barrier layer composed of an n-type layer, and wherein depositing a first lower barrier layer includes depositing a barrier layer composed of an n+ type layer.

38 . The method of claim 31 wherein depositing a first upper barrier layer includes depositing a barrier layer composed of InGaP.

39 . The method of claim 31 further including depositing a second upper barrier layer over the at least one second solar subcell prior to depositing the second graded interlayer.

40 . The method of claim 39 wherein depositing a second upper barrier layer includes depositing a barrier layer composed of GaInP.