INVERTED METAMORPHIC MULTIJUNCTION SOLAR CELL WITH SURFACE PASSIVATION OF THE CONTACT LAYER

1 . A method of manufacturing a solar cell comprising:

providing a first substrate;

forming a contact layer on said first substrate;

forming an upper first solar subcell having a first band gap on said contact layer;

forming a second solar subcell adjacent to said first solar subcell and having a second band gap smaller than said first band gap;

forming a first graded interlayer adjacent to said second solar subcell; said first graded interlayer having a third band gap greater than said second band gap;

forming a third solar subcell adjacent to said first graded interlayer, said third subcell having a fourth band gap smaller than said second band gap such that said third subcell is lattice mismatched with respect to said second subcell;

forming a second graded interlayer adjacent to said third solar subcell; said second graded interlayer having a fifth band gap greater than said fourth band gap;

forming a lower fourth solar subcell adjacent to said second graded interlayer, said lower subcell having a sixth band gap smaller than said fourth band gap such that said fourth subcell is lattice mismatched with respect to said third subcell;

mounting a surrogate substrate on top of fourth solar subcell;

removing the first substrate; and

passivating the exposed surface of the contact layer of the solar cell with a passivating material.

2 . The method as defined in claim 1 , wherein the passivating step is performed by application of ammonium sulphide.

3 . The method as defined in claim wherein the encapsulating layer is composed of silicon nitride or titanium oxide.

4 . The method as defined in claim 1 , wherein the encapsulating layer is deposited by plasma enhanced chemical vapor deposition.

5 . The method as defined in claim 1 , wherein there is a window layer directly adjacent to the contact layer, and further comprising passivating the window layer.

6 . The method as defined in claim 1 , wherein the solar cell is implemented on a wafer, and the passivating step is performed by dipping the wafer in a solution of ammonium sulphide.

7 . A method as defined in claim 1 , wherein the lower fourth subcell has a band gap in the range of 0.6 to 0.8 eV; the third subcell has a band gap in the range of 0.9 to 1.1 eV, the second subcell has a band gap in the range of 1.35 to 1.45 eV, and the first subcell has a band gap in the range of 1.8 to 2.1 eV.

8 . A method as defined in claim 1 , wherein the first substrate is composed of gallium arsenide or germanium, and the surrogate substrate is composed of sapphire, glass, GaAs, Ge or Si.

9 . A method as defined in claim 1 , wherein 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 it e second graded interlayer is compositionally graded to lattice match the third subcell on one side and the bottom fourth subcell on the other side.

10 . A method as defined in claim 1 , wherein said 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.

11 . A method as defined in claim 1 , wherein said 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.

12 . A method as defined in claim 1 , wherein the first and second graded interlayers are composed of (In x Ga 1-x ) y Al 1-y As with x and y selected such that the band gap of each interlayer remains constant throughout its thickness.

13 . A method as defined in claim 1 , wherein the band gap of the first graded interlayer remains constant at 1.5 eV, and the band gap of the second graded interlayer remains constant at 1.1 eV.

14 . A method as defined in claim 11 , wherein the first subcell is composed of and InGaP emitter layer and an InGaP base layer, the second subcell is composed of InGaP emitter layer and a GaAs base layer, the third subcell is composed of an InGaP emitter layer and an 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 layer.

15 . A multijunction solar cell comprising:

a contact layer having a passivated surface;

a top first solar subcell having a first band gap disposed adjacent to the contact layer;

a middle second solar subcell disposed directly adjacent to said first subcell and having a second band gap smaller than said first band gap;

a grading interlayer disposed directly adjacent to said second subcell and having a third band gap greater than second band gap, said grading interlayer being deposited using an MOCVD process;

a bottom third solar subcell disposed and directly adjacent to said grading interlayer and being lattice mismatched with respect to said middle second subcell, and having a fourth band gap smaller than said second band gap;

an encapsulating layer composed of silicon nitride or titanium oxide disposed on the top surface of the solar cell; and

an antireflection coating layer disposed over the encapsulating layer.

16 . A method of forming a multijunction solar cell comprising an upper subcell, a middle subcell, and a lower subcell from a semiconductor substrate, the method comprising:

providing a substrate for the epitaxial growth of semiconductor material;

forming a contact layer on the substrate using an MOCVD process;

forming an upper first solar subcell having a first band gap on the contact layer using an MOCVD process;

forming a middle second solar subcell over said first solar subcell having a second band gap greater than said first band gap;

forming a lower third solar subcell over said second subcell having a third greater than said second band gap;

passivating the exposed surface of the contact layer of solar cell with a passivating material; and

depositing an encapsulating layer over the passivated surface of the window layer.

17 . A method as defined in claim 16 , wherein the passivating step is performed by application of ammonium sulphide.

18 . The method as defined in claim 16 , wherein the encapsulating layer is composed of silicon nitride or titanium oxide.

19 . The method as defined in claim 16 , wherein the encapsulating layer is deposited by plasma enhanced chemical vapor deposition.

20 . The method as defined in claim 16 , wherein the contact layer is composed of GaAs.