Stacked monolithic multijunction solar cell

Abstract

A stacked monolithic multijunction solar cell, which includes a first subcell having a p-n junction with an emitter layer and a base layer, the thickness of the emitter layer being less than the thickness of the base layer at least by a factor of ten, and the first subcell comprising a substrate having a semiconductor material from the groups III and V or a substrate from the group IV, and which further includes a second subcell arranged on the first subcell and a third subcell arranged on the second subcell, the two subcells each including an emitter layer and a base layer, and a tunnel diode and a back side field layer each being formed between the subcells, the thickness of the emitter layer being greater than the thickness of the base layer in each case between the second subcell and in the third subcell.

Claims

1. A stacked monolithic multifunction solar cell comprising: a first subcell that has a p-n junction with a first emitter layer and a first base layer, a thickness of the first emitter layer being less than a thickness of the first base layer at least by a factor of five, and the first subcell comprising a substrate having a semiconductor material from the groups III and V or the substrate from the group IV; a second subcell arranged on the first subcell, the second subcell including a second emitter layer and a second base; a third subcell arranged on the second subcell, the third subcell including a third emitter layer and a third base; a first tunnel diode and a first back side field layer formed between the first and second subcells and a second tunnel diode and a second back side field layer formed between the second and third subcells, wherein the second subcell and the third subcell comprise III-V semiconductor materials; wherein a thickness of the second emitter layer is greater than a thickness of the second base in the second subcell, and wherein a thickness of the third emitter layer is greater than a thickness of the third base in the third subcell.

2. The stacked monolithic multijunction solar cell according to claim 1, wherein the first back side field layer is designed as the second base in the second subcell and/or the second back side field layer is designed as the third base in the third subcell.

3. The stacked monolithic multijunction solar cell according to claim 1, wherein, in the second subcell, the first back side field layer comprises a different semiconductor material with respect to the second emitter layer of the second subcell, or the first back side field layer has a different stoichiometry than the second emitter layer of the second subcell, and the first back side field layer has a higher band gap than the second emitter layer of the second subcell, and/or wherein, in the third subcell, the second back side field layer comprises a different semiconductor material with respect to the third emitter layer of the third subcell, or the second back side field layer has a different stoichiometry than the third emitter layer of the third subcell, and the second back side field layer has a higher band gap than the third emitter layer of the third subcell.

4. The stacked monolithic multijunction solar cell according to claim 1, wherein, in the second subcell, the thickness of the second emitter layer is greater than the thickness of the second base and/or a thickness of the first back side field layer by a factor between five and ten, and wherein, in the third subcell, the thickness of the third emitter layer is greater than the thickness of the third base and/or a thickness of the second back side field layer by a factor between five and ten.

5. The stacked monolithic multijunction solar cell according to claim 1, wherein a thickness of the first back side field layer is in a range between 20 nm and 100 nm, and a band gap energy changes within the first back side field layer, and/or wherein a thickness of the second back side field layer is in a range between 20 nm and 100 nm, and a band gap energy changes within the second back side field layer.

6. The stacked monolithic multijunction solar cell according to claim 1, further comprising: a semiconductor mirror formed between the first subcell and the second subcell.

7. The stacked monolithic multijunction solar cell according to claim 1, wherein the second emitter layer of the second subcell comprises an (Al)InGaAs material.

8. The stacked monolithic multijunction solar cell according to claim 1, wherein the third emitter layer of the third subcell comprises an (Al)InGaP material.

9. The stacked monolithic multijunction solar cell according to claim 1, wherein the first, second, and third subcells are lattice-matched to each other.

10. The stacked monolithic multijunction solar cell according to claim 1, further comprising: a metamorphic buffer formed between the first subcell and the second subcell.

11. The stacked monolithic multijunction solar cell according to claim 1, wherein a band gap energy of the second subcell is greater than a band gap energy of the first subcell, and wherein a band gap energy of the third subcell is greater than the band gap energy of the second subcell.

12. The stacked monolithic multijunction solar cell according to claim 1, further comprising: a fourth subcell arranged beneath the second subcell or above the third subcell or between the second subcell and the third subcell.

13. The stacked monolithic multijunction solar cell according to claim 12, further comprising: a fifth subcell (T5) arranged beneath the second subcell or above the third subcell or between the fourth subcell and the third subcell.

14. The stacked monolithic multijunction solar cell according to claim 1, wherein the second emitter layer has a lower doping than a second base layer of the second base in the second subcell, and wherein the third emitter layer has a lower doping than a third base layer (BS3) of the third base in the third subcell.

15. The stacked monolithic multijunction solar cell according to claim 1, wherein a thickness of the first back side field layer is in a range between 20 nm and 100 nm, and a band gap energy is constant within the first back side field layer, and/or wherein a thickness of the second back side field layer is in a range between 20 nm and 100 nm, and a band gap energy is constant within the second back side field layer.

16. The stacked monolithic multijunction solar cell according to claim 1, wherein lattice constants are different between at least two of the first, second, and third subcells.

17. The stacked monolithic multijunction solar cell according to claim 1, wherein the first subcell is arranged such that light entering the monolithic multijunction solar cell strikes the first emitter layer before striking the first base layer, strikes the second emitter layer before striking the second base, and strikes the third emitter layer before striking the third base.

18. The stacked monolithic multijunction solar cell according to claim 12, wherein the fourth subcell comprises a fourth emitter on a fourth base, a thickness of the fourth base being greater than a thickness of the fourth emitter.

19. The stacked monolithic multijunction solar cell according to claim 13, wherein the fifth subcell comprises a fifth emitter on a fifth base, a thickness of the fifth base being greater than a thickness of the fifth emitter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

(2) FIG. 1 shows a cross-section of an example of a multijunction solar cell including three subcells;

(3) FIG. 2 shows a cross-section of a further example of a multijunction solar cell including three subcells; and

(4) FIG. 3 shows a cross-section of a further example of a multijunction solar cell including five subcells.

DETAILED DESCRIPTION

(5) The illustration in FIG. 1 shows a cross-sectional view of an example of a stacked monolithic three-junction solar cell MS, which includes a first subcell T1 and a second subcell T2 and a third subcell T3. Upon an irradiation with light L, the latter always first strikes the emitter of the topmost subcell.

(6) A tunnel diode TD is formed in each case between individual subcells T1, T2 and T3.

(7) It is understood that, for reasons of clarity, metal or connecting contact layers, in particular, as well as window layers and antireflection layers are not shown. It should also be noted that the emitter is n-doped and the base is p-doped.

(8) In the present case, the three subcells T1, T2 and T3 are designed to be lattice-matched to each other.

(9) It should be noted that, in an example which is not illustrated, a fourth subcell and/or a fifth subcell are optionally formed above first subcell T1.

(10) First subcell T1 includes an n-doped emitter layer EM1 and a p-doped base layer BS1, the thickness of emitter layer EM1 being less than the thickness of base layer BS1 at least by a factor of ten.

(11) First subcell T1 may also be referred to as a substrate cell and, in the present case, comprises Ge as the semiconductor material. It is understood that GaAs or InP, in particular, may also be used instead of Ge as the substrate material.

(12) A second subcell T2 is arranged on first subcell T1. Second subcell T2 has a larger band gap than first subcell T1. A third subcell T3 is arranged on second subcell T2. Third subcell T3 has a larger band gap than second subcell T2.

(13) A tunnel diode TD is arranged in each case between first subcell T1 and second subcell T2 and between second subcell T2 and third subcell T3.

(14) Second subcell T2 includes a back side field layer RF2 arranged above tunnel diode TD and an optional base layer BS2 arranged above back side field layer RF2 and an emitter layer EM2 arranged above the base layer BS2, emitter layer EM2 being thicker than optional base layer BS2 and/or back side field layer RF2 at least by a factor of 10.

(15) Third subcell T3 includes a back side field layer RF3 arranged above tunnel diode TD and an optional base layer BS3 arranged above back side field layer RF3 and an emitter layer EM3 arranged above the base layer BS3, emitter layer EM3 being thicker than optional base layer BS3 and/or back side field layer RF3 at least by a factor of 10.

(16) The illustration in FIG. 2 shows a cross-sectional view of a further example of a stacked monolithic three-junction solar cell MS. Only the differences from the example shown in FIG. 1 are explained below.

(17) A metamorphic buffer MM and a semiconductor mirror BR are arranged between first subcell T1 and second subcell T2.

(18) In an example, which is not illustrated, either only metamorphic buffer MM or only semiconductor mirror BR are formed.

(19) Base layers BS2 and BS3 are not formed in the case of second subcell T2 and third subcell T3. Back side field layers RF2 and RF3 each thereby form the bases of the two subcells T2 and T3. Back side field layers RF2 and RF3 preferably each have a different stoichiometry or a different semiconductor material than emitter layers EM2 and EM3 formed in each case directly on back side field layers RF2 and RF3.

(20) Subcells of this type are also referred to as heterocells.

(21) The illustration in FIG. 3 shows a cross-sectional view of a further example of a stacked monolithic five-junction solar cell MS. Only the differences from the example shown in FIG. 2 are explained below.

(22) A fourth subcell T4, which includes an emitter with an emitter layer EM4 and a base with a base layer BS4, is arranged between second subcell T2 and third subcell T3. A back side field layer RF4 is formed between base layer BS4 and second subcell T2. A tunnel diode TD is formed between back side field layer RF4 and second subcell T2. The thickness of base layer BS4 is greater than the thickness of emitter layer EM4 in keeping with the present prior art.

(23) A fifth subcell T5, which includes an emitter with an emitter layer EM5 and a base with a base layer BS5, is arranged on third subcell T3. A back side field layer RF5 is formed between base layer BS5 and third subcell T3. A tunnel diode TD is formed between back side field layer RF5 and third subcell T3. The thickness of base layer BS5 is greater than the thickness of emitter layer EM5 in keeping with the present prior art.

(24) The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.