Method of fabricating metamorphic multijunction solar cells for space applications

Patent metadata

Field	Value
Publication number	US-12501736-B2
Application number	US-202117543937-A
Country	US
Kind code	B2
Filing date	Dec 7, 2021
Priority date	Aug 17, 2015
Publication date	Dec 16, 2025
Grant date	Dec 16, 2025

Abstract

A method of fabricating a four junction solar cell by identifying the composition and band gaps of the upper first, second and third subcells that maximizes the efficiency of the solar cell at a predetermined time after initial deployment by simulation; fabricating one or more four-junction test solar cells in accordance with the identified composition and band gaps of the upper first, second and third subcells; performing one or more optical or electrical tests on the fabricated one or more four-junction test solar cells; based on results of the tests, determining one or more properties of at least one of the upper first, second or third subcells to be modified in subsequent fabrication of four-junction solar cells, including the band gap, doping level and profile, and thickness of each of the subcell layers; and fabricating a further four-junction solar cell in accordance with the modified properties of at least one of the upper first, second or third subcells to optimize the efficiency of the solar cell at the predetermined time.

First claim

The invention claimed is:

1 . A method of fabricating a four-junction solar cell for deployment in space in an AM0 environment comprising:
simulating the effect of radiation and temperature on a plurality of upper first, second and third subcell candidates for implementation in a four-junction solar cell; identifying the composition and band gaps of the upper first, second and third subcells that maximizes the efficiency of the four-junction solar cell at a predetermined time after initial deployment based on the simulation, wherein the four-junction solar cell comprises a germanium substrate and a plurality of subcells comprising the upper first subcell, the second subcell, and the third subcell, wherein the third subcell is disposed over and lattice mis-matched to the germanium substrate, the second subcell is disposed over and lattice matched to the third subcell and having a band gap in the range of approximately 1.65 to 1.8 eV, and the upper first subcell is disposed over and lattice matched to the second subcell and having a band gap in the range of 2.0 to 2.15 eV; fabricating one or more four-junction test solar cells in accordance with the identified composition and band gaps of the upper first, second and third subcells, wherein fabricating comprises growing on a germanium substrate a lattice matched sequence of layers of semiconductor material using a metal organic chemical vapor deposition process to form the one or more four-junction test solar cells; performing one or more optical or electrical tests on the fabricated one or more four-junction test solar cells; based on the results of the test, determining one or more modified properties of at least one of the upper first, second or third subcells to be modified in subsequent fabrication of four-junction solar cells, including the band gap, doping level and profile, and thickness of each of the subcell layers; and fabricating a further four-junction solar cell in accordance with the one or more modified properties to optimize the efficiency of the four-junction solar cell at the predetermined time.

2 . A method as defined in claim 1 , wherein the step of fabricating one or more four-junction test solar cells utilizes an MOCVD reactor which accommodates five or more semiconductor wafers, which are disposed at different positions on a platter, and the step of performing one or more optical or electrical tests include making an electroluminescence measurement on each of the one or more four-junction test solar cells.

3 . A method as defined in claim 2 , wherein the electrical tests include measuring the open circuit voltage, the short circuit current, and the fill factor associated with the one or more four-junction test solar cells.

4 . A method as defined in claim 3 , wherein the characteristics to be modified in each of the subcells as a result of the electrical tests include interdependent variables including the thickness of the layers, the doping, and the doping profile of each respective layer.

5 . A method as defined in claim 1 , wherein the upper first subcell is composed of indium gallium aluminum phosphide with at least 20% aluminum by mole fraction and has a first band gap;
the second subcell is adjacent to said first subcell and includes an emitter layer composed of indium gallium phosphide or aluminum gallium arsenide, and a base layer composed of aluminum gallium arsenide, the emitter layer and the base layer forming a photovoltaic junction, wherein the second subcell has a second band gap smaller than the first band gap and is lattice matched with the upper first subcell; the third subcell is adjacent to said second subcell, is composed of indium gallium arsenide, has a third band gap smaller than the second band gap, and is lattice matched with the second subcell; and a fourth subcell is adjacent to said third subcell and is composed of germanium having a fourth band gap smaller than the third band gap.

6 . A method as defined in claim 1 , wherein the third subcell has a band gap of approximately 1.41 eV, the second subcell as a band gap in the range of approximately 1.65 to 1.8 eV and the upper first subcell has a band gap in the range of 2.0 to 2.15 eV.

7 . A method as defined in claim 6 , wherein the second subcell has a band gap of approximately 1.73 eV and the upper first subcell has a band gap of approximately 2.10 eV.

8 . A method as defined in claim 1 , wherein a determination of an amount of radiation at the predetermined time is 1 MeV electron equivalent fluence of 1×10 15 electrons/cm 2 .

9 . A method as defined in claim 1 , wherein a determination of an amount of radiation at the predetermined time is 1 MeV electron equivalent fluence of between 5×10 14 electrons/cm 2 and 5×10 15 electrons/cm 2 .

10 . A method as defined in claim 1 , wherein the identifying is performed by specifying either a low earth orbit (LEO) or a geosynchronous earth orbit (GEO).

11 . A method as defined in claim 1 , wherein the step of identifying utilizes the design rule of incorporating at least 20% aluminum by mole fraction in the composition of at least the upper first subcell.

12 . A method as defined in claim 11 , wherein the step of identifying comprises assessing an analysis of test results subsequently to independently incrementally adjust one or more interdependent variables, including composition, thickness, doping, and doping profile of the upper first, second, and third subcells, so as to determine the open circuit voltage, the short circuit density and the fill factor of each of the subcells and thereby the overall power output of the solar cell.

13 . A method as defined in claim 1 , wherein at least one of the upper first, second and third subcells includes an emitter region and a base region, with the base region having a gradation in doping that increases from the base-emitter junction to the bottom of the base region in the range of 1×10 15 to 5×10 18 per cubic centimeter.

14 . A method as defined in claim 13 , wherein the gradation in doping is exponential.

15 . A method as defined in claim 1 , wherein the efficiency of the solar cell at the predetermined time is at least 24.4%, wherein the efficiency is measured at a temperature in the range of 70 to 100 degrees C. and the predetermined time is at least fifteen years.

16 . A method as defined in claim 1 , further comprising;
providing a distributed Bragg reflector (DBR) layer adjacent to and between the third subcell and a fourth subcell, and arranged so that light can enter and pass through the second and third subcells, or the upper first subcell and at least a portion of which can be reflected back into the third subcell by the DBR layer, wherein the distributed Bragg reflector layer is composed of a plurality of alternating layers of lattice matched materials with discontinuities in their respective indices of refraction, and the difference in the refractive indices between alternating layers is maximized in order to minimize the number of periods required to achieve a given reflectivity, and the thickness and refractive index of each period determines the stop band and its limiting wavelength, and the DBR layer includes a first DBR layer composed of a plurality of p type Al x Ga 1-x As layers, and a second DBR layer disposed over the first DBR layer and composed of a plurality of n or p type Al y Ga 1-y As layers, where 0<x<1, 0<y<1, and y is greater than x.

17 . A method as defined in claim 1 , wherein one or more of the plurality of subcells have a base region having a gradation in doping that increases exp

Assignees

• Solaero Tech Corp

Inventors

• Derkacs Daniel
• Mcglynn Daniel

Classifications

• H10P74/207

  Electrical properties, e.g. testing or measuring of resistance, deep levels or capacitance-voltage characteristics · CPC title

• H10F10/161

  comprising multiple PN heterojunctions, e.g. tandem cells · CPC title

• H10F10/163

  comprising only Group III-V materials, e.g. GaAs/AlGaAs or InP/GaInAs photovoltaic cells · CPC title

• H10F77/488

  Reflecting light-concentrating means, e.g. parabolic mirrors or concentrators using total internal reflection · CPC title

• Y02E10/544

  Solar cells from Group III-V materials · CPC title