EP3571725A1 - Multiple solar cell comprising rear-side germanium subcell and use thereof - Google Patents

Multiple solar cell comprising rear-side germanium subcell and use thereof

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Publication number
EP3571725A1
EP3571725A1 EP17826491.7A EP17826491A EP3571725A1 EP 3571725 A1 EP3571725 A1 EP 3571725A1 EP 17826491 A EP17826491 A EP 17826491A EP 3571725 A1 EP3571725 A1 EP 3571725A1
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EP
European Patent Office
Prior art keywords
subcell
solar cell
multiple solar
germanium
cell according
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP17826491.7A
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German (de)
French (fr)
Inventor
Frank Dimroth
David LACKNER
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Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
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Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
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Publication of EP3571725A1 publication Critical patent/EP3571725A1/en
Withdrawn legal-status Critical Current

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    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
    • H01L31/068—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells
    • H01L31/0687—Multiple junction or tandem solar cells
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    • H01L31/02—Details
    • H01L31/02002—Arrangements for conducting electric current to or from the device in operations
    • H01L31/02005—Arrangements for conducting electric current to or from the device in operations for device characterised by at least one potential jump barrier or surface barrier
    • H01L31/02008—Arrangements for conducting electric current to or from the device in operations for device characterised by at least one potential jump barrier or surface barrier for solar cells or solar cell modules
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    • H01L31/02—Details
    • H01L31/02016—Circuit arrangements of general character for the devices
    • H01L31/02019—Circuit arrangements of general character for the devices for devices characterised by at least one potential jump barrier or surface barrier
    • H01L31/02021—Circuit arrangements of general character for the devices for devices characterised by at least one potential jump barrier or surface barrier for solar cells
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    • H01L31/0256—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by the material
    • H01L31/0264—Inorganic materials
    • H01L31/0304—Inorganic materials including, apart from doping materials or other impurities, only AIIIBV compounds
    • H01L31/03046—Inorganic materials including, apart from doping materials or other impurities, only AIIIBV compounds including ternary or quaternary compounds, e.g. GaAlAs, InGaAs, InGaAsP
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    • H01L31/042—PV modules or arrays of single PV cells
    • H01L31/043—Mechanically stacked PV cells
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    • H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
    • H01L31/068—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells
    • H01L31/0687—Multiple junction or tandem solar cells
    • H01L31/06875—Multiple junction or tandem solar cells inverted grown metamorphic [IMM] multiple junction solar cells, e.g. III-V compounds inverted metamorphic multi-junction cells
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    • H01L31/072—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN heterojunction type
    • H01L31/0725—Multiple junction or tandem solar cells
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    • H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
    • H01L31/078—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers including different types of potential barriers provided for in two or more of groups H01L31/062 - H01L31/075
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    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/184—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof the active layers comprising only AIIIBV compounds, e.g. GaAs, InP
    • H01L31/1844—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof the active layers comprising only AIIIBV compounds, e.g. GaAs, InP comprising ternary or quaternary compounds, e.g. Ga Al As, In Ga As P
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    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/184—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof the active layers comprising only AIIIBV compounds, e.g. GaAs, InP
    • H01L31/1852—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof the active layers comprising only AIIIBV compounds, e.g. GaAs, InP comprising a growth substrate not being an AIIIBV compound
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    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/1892—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof methods involving the use of temporary, removable substrates
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/544—Solar cells from Group III-V materials
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to multiple solar cells having at least four pn junctions with a light-remote back germanium subcell and at least three above the germanium subcell arranged sub-cells of III-V compound semiconductors, wherein the multiple solar cells have at least one metamorphic buffer layer and at least one wafer bonding compound and all Layers disposed above the germanium subcell each contain a light absorbing emitter and / or base layer containing at least 20% indium, based on the sum of all Group III atoms. Furthermore, the present invention relates to the use of these multiple solar cells in space.
  • Solar cells are used in space to power satellites. Due to their high efficiency and high radiation stability compared to silicon, mainly multiple solar cells made of III-V Semiconductors used.
  • GalnP / GalnAs / Ge triple-junction solar cells are used which achieve efficiencies of about 30% under AMO conditions (ie in space) (see G. Strobl, D. Fuhrmann, W. Guter, V. Khorenko, W. Köstler and M. Meusel: About Azur's "3G30 Advanced" space solar cell and next generation product with 35% efficiency in 27th European
  • the solar cells are exposed to high-energy electrons, protons and other charged particles in space, resulting in damage to the crystals and a gradual reduction in performance. After irradiation with IMeV electrons at a flux of 10 15 cm “2 , the solar cells typically still show 85% to 90% of their original power, as well as the end-of-life efficiency (EOL).
  • EOL end-of-life efficiency
  • multiple solar cells with 4, 5 or even 6 pn junctions have been developed, for example those from PR Sharps, D. Aiken, A. Boca, B. Cho, D. Chummney, A. Cornfeld S. S., Y. Lin, C. Mackos, F. Newman, P.
  • a bonded 5-cell solar cell was presented by Boeing (P. T. Chiu, D. C. Law, R. L. Woo, S. B. Singer, D. Bhusari, W. D. Hong, A. Zakaria, J. Boisvert, S.
  • Solaero inverted metamorphic solar cells degrade faster than conventional triple-junction solar cells and, upon irradiation with 1 MeV electrons, achieve EOL efficiencies similar to the germanium-based triple solar cells at a flux of 10 15 cm "3 .
  • EP 3 012 874 A1 relates to a stacked multi-junction integrated solar cell consisting of GalnP / InP / GalnAsP / GalnAs.
  • the GaAs subcell in the inverted metamorphic structure is replaced by a very radiation-stable InP Partial cell and one of the GalnAs sub-cells replaced by a more radiation-hardy GalnAsP subcell.
  • This quadruple solar cell thus has a higher radiation stability with simultaneously higher EOL efficiency.
  • the lowest GalnAs subcell is still made of a material that has a high degradation under irradiation with high energy particles.
  • the fabrication of this multi-junction solar cell is costly because the lower layers are typically fabricated on an InP-based substrate.
  • DE 10 2012 004 734 A1 describes a multiple solar cell with at least four pn junctions, in which a lower germanium subcell is connected via a metamorphic buffer to a GalnAs subcell.
  • the GalnAs subcell is in turn connected via a wafer bond to a GaAs and a GalnP subcell.
  • the top two sub-cells of GalnP and GaAs are hereby grown lattice-matched to GaAs and transferred by wafer bonding to the lower structure.
  • the individual subcells point in the process
  • a multi-junction solar cell with at least four pn junctions which has a light-remote back germanium partial cell and at least three partial cells of II lV compound semiconductors arranged above the germanium partial cell, at least one metamorphic buffer layer and a wafer bonding compound for connecting partial cells with different Lattice constant, wherein all arranged above the germanium subcell sub-cells each contain a light-absorbing emitter and / or base layer containing at least 20% indium based on the sum of all the atoms of the group I II.
  • a subcell of I ll-V compound semiconductors in the context of the present application means that the subcell consists essentially of III-V compound semiconductors, whereby other atoms up to a
  • Dopants such as Zn, Se, Mg, C, Si.
  • the subcells arranged above the germanium subcell are abbreviated below to the indices 2, 2 ' , 2 " , 2 "', etc., the subcell being provided directly above the germanium subcell with the index 2 and those above this subcell arranged subcell receives the index 2 ' , etc. This numbering is also maintained when intermediate layers, such as metamorphic buffer layers, wafer bond or tunnel diodes are arranged between the sub-cells.
  • the percentage of indium, based on the sum of all the atoms of group II I (Group II I means the 3rd main group of the Periodic Table of the Elements, ie B, Al, Ga, I n and Tl) in the emitter and / or base layer of the subcell 2 arranged above the germanium subcell, at least 30% and preferably at least 40%.
  • the percentage of indium, based on the sum of all atoms of group II I, in the emitter and / or base layer of the subcell 2 ' and all above the subcell 2 ' arranged sub-cells 2 " , 2 "' at least 40% and preferably at least 45%.
  • the percentage of indium, based on the sum of all atoms of the group II I, in the emitter and / or base layer of the subcell 2 ' is at least 60% and preferably at least 70%.
  • the percentage of phosphorus, based on the sum of all atoms of the group V (group V means the 5th main group of the Periodic Table of the Elements, ie, N, P, As, Sb and Bi) in the emitter and / or base layer of the sub-cells 2 and 2 'arranged above the germanium subcell, at least 5%, preferably at least 15%.
  • the percentage of phosphorus, based on the sum of all the atoms of the group V, in the emitter and / or base layers of the arranged above the subcell 2 sub-cells 2 ', 2 " , 2 "' at least 50%, preferably at least 80%.
  • the thickness of the ll-V sub-cells is 400 to 4000 nm.
  • the germanium subcell has a p-doped base layer of germanium with a bandgap of 0.67 eV at 300K.
  • Another preferred embodiment of the present invention provides that the lattice constant of the germanium subcell is 5.658 angstroms.
  • the germanium partial cell has a thickness of more than 4 ⁇ m, preferably more than 60 ⁇ m.
  • Germanium is very well suited as a material for the backside subcell as it is lower cost compared to other substrates such as I nP. and pn junction can be produced by diffusion, which makes it possible to absorb photons in the infrared range with an energy greater than the band gap of 0.67 eV and convert it into electrical current.
  • germanium solar cells have a very high radiation stability in space.
  • the germanium partial cell has a metal contact on the side facing away from the light.
  • a metamorphic buffer layer is arranged between the germanium subcell and the subcell 2. This converts the lattice constant of the germanium subcell to the lattice constant of the subcell 2, the lattice constancy of the subcell 2 preferably being 5.75 to 5.90 angstroms and more preferably 5.77 to 5.85 angstroms.
  • the metamorphic buffer layer may have a steady gradient in the lattice constant, or the lattice constant may be increased in steps within the metamorphic buffer layer, with this in mind
  • the gradient in the lattice constant is achieved by a gradual change in the composition in layers of III-V compound semiconductors such as AIGalnAsP, AIGalnP, GalnP, AIGalnAs, GaAsSb or GalnAs or GalnAsN, which may be n- or p-doped, and the other elements such as N or B may contain to increase the crystal hardness.
  • the lattice constant within the layer may also be increased beyond the target lattice constant. The goal is to set the lattice constant of the subsequent subcell 2 'at the end of the metamorphic buffer layer 3 in the plane and to ensure a low density of thread or puncture dislocations.
  • Germanium be epitaxed.
  • the subcell 2 and the subcell 2 ' are lattice matched to each other.
  • the subcells 2, 2 ' preferably have a lattice constant of 5.75 to 5.90 angstroms and more preferably of 5.77 to 5.85 angstroms.
  • the wafer bond forms a flush electrically conductive, optically transparent and mechanically stable connection between the sub-cells 2 'and 2 ", which can be effected by a direct wafer bond with covalent bonds between the semiconductor surfaces or by suitable intermediate layers such as transparent, conductive oxides, amorphous semiconductors or suitable conductive adhesives
  • the emitter and / or base layer of the light-facing front-side subcell consists of AIGalnP and has a bandgap energy of preferably 1.8 to 2.1 eV, more preferably 1.85 to 2.0 eV
  • the front-side part cell is preferably lattice-matched to GaAs or germanium.
  • a preferred multiple solar cell consists of four sub-cells 1, 2, 2 ' , 2 " , wherein the emitter and / or base layer of the subcell 2 of Gal nAsP, the emitter and / or base layer of the subcell 2 ' of Gal nP and the emitter and / or base layer of the subcell 2 " consists of AIGal nP.
  • Another multiple solar cell consists of five sub-cells 1, 2, 2 ' , 2 " , 2 “' , wherein the emitter and / or base layers of the sub-cells 2, 2 ' of Gal nAsP, the emitter and / or base layer of the subcell 2 " AIGalnAsP and the emitter and / or base layer of the subcell 2 "' consists of AIGal nP.
  • the metamorphic buffer layer between the germanium subcell 1 and the subcell 2 reflects at least 30%, in particular 70%, of the radiation in the absorption region of the subcell 2.
  • tunnel diodes are arranged between the subcells 1, 2, 2 ' , 2 " , 2 "' , ..., which connect the subcells in series.
  • a further preferred embodiment of the invention provides that the power of the multiple solar cell after irradiation with 1 MeV electrons at a flow of 10 16 cm "2 degrades by less than 35%, preferably by less than 20%.
  • the multiple solar cells according to the invention are preferably used in space and find particular use for satellites.
  • Fig. 1 shows four different embodiments of the invention
  • Fig. 2 shows graphs for the bandgap and lattice constant for the Embodiments according to Fig. La and lb
  • Fig. 3 shows a detailed layer structure of an inventive
  • Fig. 4 shows a detailed layer structure of an inventive
  • FIG. 1 a shows a preferred structure of a multiple-solar cell according to the invention with 4 sub-cells, each having an emitter and base layer and a pn junction. This includes, in addition to the anti-reflection coating 5, a front side contact 6 and a rear contact 7 from bottom to top a germanium subcell 1, a metamorphic buffer layer 3, a GalnAsP subcell 2, an InP subcell 2 ' , a
  • Waferbond compound 4 and a GalnP subcell 2 " Waferbond compound 4 and a GalnP subcell 2 " .
  • the lattice constant is increased from 5.658 angstroms to 5.869 angstroms with the aid of the metamorphic buffer layer 3 located on the germanium subcell 1 (see left part of FIG. 2, the lattice constants are taken from the database of loffe: "http://www.ioffe.ru / SVA / NSM / Semicond ").
  • a second GalnAsP subcell 2 having a bandgap energy of about 1.03 eV and then a third InP subcell 2 ' having a bandgap energy of 1.35 eV is grown lattice-matched.
  • All subcells 2, 2 ', 2 each have an emitter and a base layer, a pn junction being formed between the emitter and the base layer. If the emitter layer has an n-doping, then the base layer is p-doped and vice versa.
  • Typical n-type dopants include Si, Se, Te, and p-type dopants Zn, Mg, and C. If the emitter and base layer share the same bandgap energy, this is called a homo-solar cell, but the emitter has a lower or higher bandgap compared to the base, this is called a hetero-solar cell.
  • the sub-cells 2, 2 ', 2 can be designed both as a homo and also as a hetero solar cell.
  • the resulting multiple solar cell structure comprises four sub-cells 1, 2, 2 ', 2 "each having a pn junction, wherein the materials for the emitter and / or base layer of the sub-cells (GalnP, InP, GalnAsP and Ge) a high
  • Fig. Lb shows another preferred structure of a multi-junction solar cell according to the invention.
  • This comprises, in addition to the anti-reflection coating 5, a front-side contact 6 and a rear contact 7 from bottom to top, a germanium subcell 1, a metamorphic buffer layer 3, a GalnAsP subcell 2, a GalnP subcell 2 ' , a wafer bonding compound 4 and an AlGaInP subcell 2 ".
  • This is built on the first germanium partial cell of the metamorphic buffer 3 of a lattice constant of 5.658 angstroms to a lattice constant from 5.75 to 5.90, especially 5.80 to
  • the desired band gaps for the second and third subcell can also be achieved by means of compositions of GalnAsP 2 and / or GalnP 2 ' with high radiation stability Furthermore, it is possible to reduce the mismatch between the germanium subcell 1 and the GalnAsP subcell 2, thereby possibly achieving even lower dislocation densities and substrate curvatures, and also reduces the thickness of the metamorphic buffer layers 3 when a lesser difference in lattice constant must be overcome , which brings economic advantages. "Further, for the bottom third GalnP subcell 2 ', higher barriers at the interface to the wafer bonding of the topmost AIGalnP subcell 2 " result . Due to the higher band gaps of the lower three sub-cells, it is advantageous to add the upper part of the cell by adding Al in AIGalnP 2 " in the band gap between 1.88 and 1.30
  • a front-side contact 6 and a rear-side contact 7 comprises, from bottom to top, a germanium partial cell 1, a metamorphic one
  • Buffer layer 3 two GalnAsP sub-cells 2, 2 ' , a wafer bonding compound 4, a fourth AIGalnAsP subcell 2 " and a fifth AIGalnP subcell 2 "' .
  • the first two subcells 2, 2 ' are produced on the metamorphic buffer layer 3 and the top two subcells are lattice-matched to a GaAs or Ge substrate.
  • the top two sub-cells are in turn transferred to the lower part of the solar cell structure by wafer bonding and substrate removal.
  • FIG. 1d Another preferred structure of a multiple solar cell according to the present invention is shown in FIG. 1d. This includes not only the anti-
  • Reflective coating 5 a front side contact 6 and a back contact 7 from bottom to top a germanium subcell 1, a metamorphic buffer layer 3, two GalnAsP sub-cells 2, 2 ' , an AIGal nAsP subcell 2 ", a wafer bonding compound 4 and a fifth AIGal nP subcell 2 "' .
  • the first three subcells 2, 2 ' , 2 " are thereby produced on the metamorphic buffer layer 3 and the uppermost subcell is grown lattice-matched on GaAs or Ge substrate and subsequently removed by wafer bonding and substrate removal to the lower subcells 1, 2, 2', 2". transfer.
  • a pn for the production of the multiple solar cell (according to FIGS. 1a and 1b), a pn
  • an N-doped layer of n-doped GaAs or GalnP is deposited in a lattice-matched manner. This layer serves as a front passivation for the first germanium subcell.
  • a metamorphic buffer layer of Gal nP or AIGalnAsP is deposited, in which the lattice constant of 5.658 Angstrom for Ge is converted to a lattice constant of 5.75 to 5.90, in particular 5.80 to 5.87 angstroms.
  • the lattice constant is increased continuously (eg, linearly) or in steps, forming misfit shifts and relaxing the crystal.
  • the metamorphic buffer is designed in such a way that at the end there is a relaxed crystal lattice with the target lattice constant and the lowest possible puncture dislocation density.
  • the buffer can optionally be formed as a Bragg mirror to unabsorbed photons in the above to reflect the lying subcell.
  • a tunnel diode is grown, which serves to connect the subcells serially.
  • the tunnel diode consists of degenerate n- and p-doped semiconductor layers such as p-AIGaAs and n-GalnAs and may optionally be surrounded by higher-band-gap barrier layers.
  • n- and p-doped semiconductor layers such as p-AIGaAs and n-GalnAs and may optionally be surrounded by higher-band-gap barrier layers.
  • a second In-type partial cell of GalnAsP having a bandgap energy of about 1.03 eV is deposited.
  • One possible composition of the structure to the left of Figure 1 is Gao.21rio.79Asc5Po.55 lattice-matched to InP with a bandgap energy of 1.03 eV.
  • the GalnAsP absorber layer can in this case form the n-doped or the p-doped or both regions of the subcell, wherein the doping is achieved by addition of typical doping atoms such as Si, Se, Te, C, Mg, Zn in a concentration range of 1E16-3E18 cm " 3.
  • the solar cell also has barrier layers on the front and back
  • a p-AIGalnAs backside barrier and an n-allnP frontal barrier are used.
  • another tunnel diode connects, which is formed, for example, from p-AIGaAsSb and n-GalnP.
  • Semiconductor layers are either lattice-matched to the underlying second subcell or the compressive strain of one layer is compensated by the tensile strain of an adjacent layer.
  • This "strain balancing" works for layers which do not relax due to insufficient thickness, the essential feature being that the mean lattice constant corresponds to that of the 1st subcell, a third content partial cell of GalnP with a bandgap energy of 1.35 eV is deposited on the tunnel diode in which the GalnP layer in turn forms the n-doped emitter, the p-doped base or both, and dopants such as Si, Se, Te, C, Mg, Zn are used in a concentration range of 1E16-3E18 cm -3 .
  • the third subcell is lattice matched to the second subcell.
  • an AIGalnAsP bonding layer preferably with a high n-type doping in the range of 1E19-5E19 cm -3, is applied This layer serves as the front barrier for the 3rd subcell and as the connection to the 4th subcell.
  • n-AIGalnAsP is used and machined prior to wafer bonding by chemical mechanical polishing to ensure low surface roughness a 4th upper cell of (AI) GalnP bonded with a band back energy between 1.8 to 2.1 eV, which was epitaxially grown separately and lattice matched to GaAs or Ge.
  • the wafer bond bridges the difference in lattice constant of the third (5.75 to 5.90, especially 5.80 to 5.87 angstroms) and fourth subcell (GaAs 5.653 angstroms or germanium 5.658 angstroms).
  • the epitaxial structure of the uppermost subcell again has a highly doped n-AIGalnP low roughness bonding layer, which is connected to the n-AIGalnAsP bonding layer of the lower cell structure via, for example, a direct surface-activated wafer bond.
  • the surface activation can be carried out, for example, by bombardment with argon atoms in a high vacuum, whereby a few nm thin amorphous bonding layer is formed at the interface.
  • the bond between the topmost GalnP subcell and the third subunit cell may be by transparent conductive oxides or by other conductive adhesive bonds having the required property of mechanical stability, optical transparency, and electrical conductivity.
  • the bond is followed by another tunnel diode made of degenerate n- and p-doped semiconductor layers such as p-AIGaAs and n-GalnP.
  • the mean lattice constant corresponds to that of the 4th partial cell, which consists of AIGalnP with a bandgap energy of 1.88 eV.
  • the AIGalnP absorber layer can in turn form the n-doped or the p-doped or both regions of the subcell, wherein the doping by addition of typical doping atoms such as Si, Se, Te, C, Mg, Zn in a concentration range of 1E16-3E18 cm " 3.
  • the semiconductor structure ends on the light-facing side with an AllnP window layer as a barrier and a GalnAs contact layer.
  • the production of the multiple solar cell takes place by means of epitaxial growth (preferably metal organic vapor phase epitaxy) of two separate structures.
  • epitaxial growth preferably metal organic vapor phase epitaxy
  • the lower part of the multiple solar cell up to the n-AIGalnAsP bonding layer is epitaxied on a Ge substrate, the lattice constant through the metamorphic buffer of 5.658 Angstroms to 5.75 to 5.90, especially 5.80 to 5.87 Angstrom, for the 2nd and 3rd subcell is increased.
  • the upper 4th AIGalnP subcell is epitaxially grown in a separate epitaxy process, for example, in an inverted layer order lattice-matched to GaAs 5,653 anxiety or germanium 5.658 angstroms.
  • the two layer sequences of the sub-cells 1 to 3 are connected to that of the 4th sub-cell by means of wafer bonding and the growth substrate of GaAs or Ge is removed on the 4th subcell.
  • This can be done, for example, via a lift-off process (chemically, via a laser process or by mechanical stress). conditions, via mechanical grinding, or via wet-chemical etching processes.
  • the processing of the multi-junction solar cell involves further steps to fabricate metal contacts on the front and back sides as well as removing the GaAs contact layer between the metal fingers on the front side.
  • an antireflection layer is also applied, which consists for example of two layers of titanium oxide and aluminum oxide.
  • the multiple solar cell structure according to FIG. 1b is formed just like the structure according to FIG. 1a, only a higher bandgap energy is set for the uppermost AIGalnP subcell and the lattice constants of the 2nd and 3rd subcell are adjusted by compositional changes in GalnAsP and GalnP such that the thinnest possible metamorphic Buffer with the lowest possible gradient in the lattice constant can be used. This reduces damaging puncture dislocations and is economically attractive because less semiconductor material has to be deposited. It is furthermore advantageous not to completely transfer the structure up to the lattice constant of InP since higher barriers for minority charge carriers at the front and back of the 3rd subcell are then possible.
  • AIGalnP / AIGalnAsP / GalnAsP / GalnAsP / Ge are used. As a result, the theoretical efficiency can be further increased.
  • the first three or four sub-cells are in turn epitaxied on germanium and contain a metamorphic buffer between the Ge subcell and the GalnAsP subcell.
  • the bandgaps of the materials are chosen to be close to the theoretical optimum of 2.15, 1.6, 1.21, 0.9, 0.64 eV.
  • the uppermost and the uppermost two sub-cells of AIGalnP and AIGalnAsP are epitaxially latticed to GaAs or Ge and then bonded to the lower cell structure. The result is a multiple solar cell, which can achieve even higher efficiency in space under AM0 conditions and which at the same time uses only partial cells containing ln with a high radiation hardness.
  • the examples shown here can also be extended by a further sixth subcell, which theoretically even higher AMO efficiencies are possible.
  • the band gaps and layer thicknesses of the sub-cells are adjusted so that the highest possible conversion efficiency the multiple solar cell is reached after irradiation in outer space.

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Abstract

The present invention relates to multiple solar cells comprising at least four pn junctions comprising a light-remote rear-side germanium subcell (1) and, arranged above the germanium subcell, at least three subcells (2, 2', 2'', 2''',...) composed of III-V compound semiconductors, wherein the multiple solar cells comprise at least one metamorphic buffer layer (3) and at least one wafer bond connection (4), and all layers arranged above the germanium subcell each contain a light-absorbing emitter and/or base layer containing at least 20% indium, relative to the sum of all group III atoms. Furthermore, the present invention relates to the use of said multiple solar cells in space.

Description

Mehrfachsolarzelle mit rückseitiger Germanium-Teilzelle und deren Multiple solar cell with back Germanium subcell and their
Verwendung use
Die vorliegende Erfindung betrifft Mehrfachsolarzellen mit mindestens vier pn-Übergängen mit einer lichtabgewandten rückseitigen Germanium-Teilzelle und mindestens drei oberhalb der Germanium-Teilzelle angeordneten Teilzellen aus lll-V Verbindungshalbleitern, wobei die Mehrfachsolarzellen mindestens eine metamorphe Pufferschicht und mindestens eine Waferbond- Verbindung aufweisen und alle Schichten, die oberhalb der Germanium- Teilzelle angeordnet sind, jeweils eine lichtabsorbierende Emitter- und/oder Basisschicht enthalten, die mindestens 20 % Indium, bezogen auf die Summe aller Atome der Gruppe III, enthalten. Weiterhin betrifft die vorliegende Erfindung die Verwendung dieser Mehrfachsolarzellen im Weltraum. The present invention relates to multiple solar cells having at least four pn junctions with a light-remote back germanium subcell and at least three above the germanium subcell arranged sub-cells of III-V compound semiconductors, wherein the multiple solar cells have at least one metamorphic buffer layer and at least one wafer bonding compound and all Layers disposed above the germanium subcell each contain a light absorbing emitter and / or base layer containing at least 20% indium, based on the sum of all Group III atoms. Furthermore, the present invention relates to the use of these multiple solar cells in space.
Solarzellen werden im Weltraum zur Stromversorgung von Satelliten eingesetzt. Hierbei werden aufgrund ihrer hohen Effizienz und der im Vergleich zu Silicium hohen Strahlungsstabilität vorwiegend Mehrfachsolarzellen aus lll-V- Halbleitern verwendet. Standardmäßig werden GalnP/GalnAs/Ge Dreifachsolarzellen eingesetzt, die Wirkungsgrade von etwa 30 % unter AMO Bedingungen (d.h. im Weltraum) erreichen (s. G. Strobl, D. Fuhrmann, W. Guter, V. Khorenko, W. Köstler und M. Meusel. About Azur's "3G30-Advanced" space solar cell and next generation product with 35% efficiency in 27th EuropeanSolar cells are used in space to power satellites. Due to their high efficiency and high radiation stability compared to silicon, mainly multiple solar cells made of III-V Semiconductors used. By default, GalnP / GalnAs / Ge triple-junction solar cells are used which achieve efficiencies of about 30% under AMO conditions (ie in space) (see G. Strobl, D. Fuhrmann, W. Guter, V. Khorenko, W. Köstler and M. Meusel: About Azur's "3G30 Advanced" space solar cell and next generation product with 35% efficiency in 27th European
Photovoltaic Solar Energy Conference and Exhibition 2012. Frankfurt, Photovoltaic Solar Energy Conference and Exhibition 2012. Frankfurt,
Germany. S. 104-108). Die Solarzellen sind im Weltraum hochenergetischen Elektronen, Protonen und anderen geladene Teilchen ausgesetzt, was zu einer Schädigung der Kristalle und einer allmählichen Reduktion der Leistung führt. Nach der Bestrahlung mit IMeV Elektronen bei einem Fluss von 1015 cm"2 weisen die Solarzellen typischerweise noch 85 bis 90 % ihrer ursprünglichen Leistung auf. Man spricht auch von dem Wirkungsgrad am Ende der Mission (End- of-Life oder abgekürzt EOL). Um die Wirkungsgrade und damit die Leistung der Solarzellen zu steigern wurden Mehrfachsolarzellen mit 4, 5 oder sogar 6 pn-Übergängen entwickelt, beispielsweise die von P.R. Sharps, D. Aiken, A. Boca, B. Cho, D. Chummney, A. Cornfeld, S.-S. Je, Y. Lin, C. Mackos, F. Newman, P. Patel, J. Spann, M. Stan und J. Steinfeldt in„Advances in the Performance of inverted metamorphic multi- junction solar cells in 27th European Photovoltaic Solar Energy Conference and Exhibition" 2012 in Frankfurt (S. 95-98) beschriebene invertierte metamorphe 4-fach Solarzelle von Solaero. Germany. Pp. 104-108). The solar cells are exposed to high-energy electrons, protons and other charged particles in space, resulting in damage to the crystals and a gradual reduction in performance. After irradiation with IMeV electrons at a flux of 10 15 cm "2 , the solar cells typically still show 85% to 90% of their original power, as well as the end-of-life efficiency (EOL). In order to increase the efficiencies and thus the performance of the solar cells, multiple solar cells with 4, 5 or even 6 pn junctions have been developed, for example those from PR Sharps, D. Aiken, A. Boca, B. Cho, D. Chummney, A. Cornfeld S. S., Y. Lin, C. Mackos, F. Newman, P. Patel, J. Spann, M. Stan and J. Steinfeldt in Advances in the Performance of inverted metamorphic multinucleation solar cells in 27th European Photovoltaic Solar Energy Conference and Exhibition "2012 in Frankfurt (pp. 95-98) describes Solaero's inverted metamorphic 4-fold solar cell.
Eine gebondete 5-fach Solarzelle wurde von Boeing vorgestellt (P.T. Chiu, D.C. Law, R.L. Woo, S.B. Singer, D. Bhusari, W.D. Hong, A. Zakaria, J. Boisvert, S.A bonded 5-cell solar cell was presented by Boeing (P. T. Chiu, D. C. Law, R. L. Woo, S. B. Singer, D. Bhusari, W. D. Hong, A. Zakaria, J. Boisvert, S.
Mesropian, R.R. King and N.H. Karam, 35.8 % space and 38.8 % terrestrial 5J direct bonded cells, 2014 IEEE 40th Photovoltaic Specialists Conference (PVSC), S. 11-13.). Diese Solarzellen erreichen höhere Wirkungsgrade von 33 bis 35 % unter AMO-Bedingungen. Die hohen Wirkungsgrade lassen sich aber nicht unbedingt nach der Bestrahlung mit hochenergetischen Teilchen imMesropian, R.R. King and N.H. Karam, 35.8% space and 38.8% terrestrial 5J direct bonded cells, 2014 IEEE 40th Photovoltaic Specialists Conference (PVSC), pp. 11-13.). These solar cells achieve higher efficiencies of 33 to 35% under AMO conditions. However, the high efficiencies can not be necessarily after the irradiation with high energy particles in the
Weltraum erhalten. So degradieren die invertiert metamorphen Solarzellen von Solaero schneller als herkömmliche Dreifachsolarzellen und erreichen nach der Bestrahlung mit 1 MeV Elektronen bei einem Fluss von 1015 cm"3 ähnliche EOL-Wirkungsgrade wie die Dreifachsolarzellen auf Germanium- Basis. Preserved space. For example, Solaero inverted metamorphic solar cells degrade faster than conventional triple-junction solar cells and, upon irradiation with 1 MeV electrons, achieve EOL efficiencies similar to the germanium-based triple solar cells at a flux of 10 15 cm "3 .
EP 3 012 874 AI betrifft eine stapeiförmige integrierte Mehrfachsolarzelle, die aus GalnP/lnP/GalnAsP/GalnAs besteht. Hierbei wird die GaAs-Teilzelle in der invertiert metamorphen Struktur durch eine sehr strahlungsstabile InP- Teilzelle und eine der GalnAs-Teilzellen durch eine strahlungshärtere GalnAsP- Teilzelle ersetzt. Diese Vierfachsolarzelle weist somit eine höhere Strahlungsstabilität bei gleichzeitig höherer EOL-Effizienz auf. Allerdings ist die unterste GalnAs-Teilzelle noch immer aus einem Material, das eine hohe Degradation unter Bestrahlung mit hochenergetischen Teilchen aufweist. Gleichzeitig ist die Herstellung dieser Mehrfachsolarzelle kostspielig, da die unteren Schichten typischerweise auf einem InP basierten Substrat hergestellt werden. EP 3 012 874 A1 relates to a stacked multi-junction integrated solar cell consisting of GalnP / InP / GalnAsP / GalnAs. In this case, the GaAs subcell in the inverted metamorphic structure is replaced by a very radiation-stable InP Partial cell and one of the GalnAs sub-cells replaced by a more radiation-hardy GalnAsP subcell. This quadruple solar cell thus has a higher radiation stability with simultaneously higher EOL efficiency. However, the lowest GalnAs subcell is still made of a material that has a high degradation under irradiation with high energy particles. At the same time, the fabrication of this multi-junction solar cell is costly because the lower layers are typically fabricated on an InP-based substrate.
DE 10 2012 004 734 AI beschreibt eine Mehrfachsolarzelle mit mindestens vier pn-Übergängen, in der eine untere Germanium-Teilzelle über einen metamorphen Puffer mit einer GalnAs-Teilzelle verbunden ist. Die GalnAs- Teilzelle ist wiederum über einen Waferbond mit einer GaAs- und einer GalnP-Teilzelle verbunden. Die obersten beiden Teilzellen aus GalnP und GaAs werden hierbei gitterangepasst zu GaAs gewachsen und per Waferbonding auf die untere Struktur übertragen. Die einzelnen Teilzellen weisen dabeiDE 10 2012 004 734 A1 describes a multiple solar cell with at least four pn junctions, in which a lower germanium subcell is connected via a metamorphic buffer to a GalnAs subcell. The GalnAs subcell is in turn connected via a wafer bond to a GaAs and a GalnP subcell. The top two sub-cells of GalnP and GaAs are hereby grown lattice-matched to GaAs and transferred by wafer bonding to the lower structure. The individual subcells point in the process
Bandlücken von 1,9 eV, 1,4 eV, 1,0 eV und 0,7 eV auf. Diese Mehrfachzelle zeichnet sich durch hohe Wirkungsgrade aus, hat aber unter Weltraumbedingungen den Nachteil einer geringeren Strahlungsstabilität der GalnAs- und GaAs-Teilzellen. Band gaps of 1.9 eV, 1.4 eV, 1.0 eV and 0.7 eV. This multiple cell is characterized by high efficiencies, but has the disadvantage of lower radiation stability of the GalnAs and GaAs sub-cells under space conditions.
Gegenwärtig wird geplant geostationäre Satelliten erst in einen niedrigen Erdorbit zu bringen und dann mittels lonenantrieb in den GEO Orbit zu befördern. Dabei werden die Solarzellen einer sehr hohen Strahlungsdosis ausgesetzt und für diese Anwendung geeignete Solarzellen müssen daher für Strah- lungsdosen von > 1E16 cm"2 ausgelegt werden. Die aus dem Stand der Technik bekannten Zellen würden unter diesen Bedingungen bis auf etwa 60 % ihrer anfänglichen Leistung degradieren. Currently, it is planned to bring geostationary satellites into low Earth orbit and then propel them by ion propulsion into GEO orbit. The solar cells are exposed to a very high radiation dose and therefore suitable solar cells for this application must be designed for radiation doses of> 1E16 cm "2. The cells known from the prior art would be up to about 60% of their initial power under these conditions degrade.
Ausgehend hiervon war es eine Aufgabe der vorliegenden Erfindung Mehr- fachsolarzellenstrukturen bereitzustellen, die auch, nachdem sie den beiBased on this, it was an object of the present invention to provide Mehrfachfachsolarzellenstrukturen, which also after having the
Weltraummissionen üblichen hohen Strahlungsdosen von > 1015 cm"2 1 MeV Elektronen ausgesetzt waren, noch ansprechende AM0 Wirkungsgrade, bevorzugt mehr als 30 %, erreichen. Neben der Steigerung der Effizienz und der Strahlungsstabilität sollen diese Mehrfachsolarzellen auch möglichst kosten- günstig herstellbar sein. Space missions were exposed to usual high radiation doses of> 10 15 cm "2 1 MeV electrons, and still achieve appealing AM0 efficiencies, preferably more than 30% In addition to the increase in efficiency and radiation stability, these multiple solar cells should also be producible as cost-effectively as possible.
Diese Aufgabe wird durch die Mehrfachsolarzellen mit den Merkmalen des Anspruchs 1 gelöst. Die weiteren abhängigen Ansprüche zeigen vorteilhafte Weiterbildungen auf. In Anspruch 19 sind erfindungsgemäße Verwendungen angegeben. This object is achieved by the multiple solar cells with the features of claim 1. The other dependent claims show advantageous developments. In claim 19 are uses of the invention specified.
Erfindungsgemäß wird eine Mehrfachsolarzelle mit mindestens vier pn- Übergängen bereitgestellt, die eine lichtabgewandte rückseitige Germanium- Teilzelle und mindestens drei oberhalb von der Germanium-Teilzelle angeordnete Teilzellen aus ll l-V Verbindungshalbleitern, mindestens eine metamorphe Pufferschicht sowie einer Waferbond-Verbindung zur Verbindung von Teilzellen mit unterschiedlicher Gitterkonstante aufweist, wobei alle oberhalb der Germanium-Teilzelle angeordneten Teilzellen jeweils eine lichtabsorbierende Emitter- und/oder Basisschicht enthalten, die mindestens 20 % Indium bezogen auf die Summe aller Atome der Gruppe I II enthalten. According to the invention, a multi-junction solar cell with at least four pn junctions is provided which has a light-remote back germanium partial cell and at least three partial cells of II lV compound semiconductors arranged above the germanium partial cell, at least one metamorphic buffer layer and a wafer bonding compound for connecting partial cells with different Lattice constant, wherein all arranged above the germanium subcell sub-cells each contain a light-absorbing emitter and / or base layer containing at least 20% indium based on the sum of all the atoms of the group I II.
Eine Teilzelle aus I ll-V-Verbindungshalbleitern im Rahmen der vorliegenden Anmeldung bedeutet, dass die Teilzelle im Wesentlichen aus l ll-V- Verbindungshalbleitern besteht, wobei auch andere Atome bis zum einemA subcell of I ll-V compound semiconductors in the context of the present application means that the subcell consists essentially of III-V compound semiconductors, whereby other atoms up to a
Anteil von 1 % enthalten sein können. Hierzu zählen z.B. Dotierstoffe wie Zn, Se, Mg, C, Si. 1% share. These include e.g. Dopants such as Zn, Se, Mg, C, Si.
Die oberhalb der Germanium-Teilzelle angeordneten Teilzellen werden im Folgenden mit den I ndizes 2, 2', 2", 2" ' etc. abgekürzt, dabei wird die Teilzelle direkt oberhalb der Germanium-Teilzelle mit dem Index 2 versehen und die oberhalb dieser Teilzelle angeordnete Teilzelle erhält den I ndex 2' usw. Diese Nummerierung wird auch beibehalten wenn Zwischenschichten, wie metamorphe Pufferschichten, Waferbond-Verbindung oder Tunneldioden zwischen den Teilzellen angeordnet sind. The subcells arranged above the germanium subcell are abbreviated below to the indices 2, 2 ' , 2 " , 2 "', etc., the subcell being provided directly above the germanium subcell with the index 2 and those above this subcell arranged subcell receives the index 2 ' , etc. This numbering is also maintained when intermediate layers, such as metamorphic buffer layers, wafer bond or tunnel diodes are arranged between the sub-cells.
Gemäß einer bevorzugten Ausführungsform der vorliegenden Erfindung beträgt der prozentuale Anteil von Indium, bezogen auf die Summe aller Atome der Gruppe II I (Gruppe II I meint die 3. Hauptgruppe des Periodensystems der Elemente, d.h. B, AI, Ga, I n und Tl), in der Emitter- und/oder Basisschicht der oberhalb der Germanium-Teilzelle angeordneten Teilzelle 2 mindestens 30 % und bevorzugt mindestens 40 %. According to a preferred embodiment of the present invention, the percentage of indium, based on the sum of all the atoms of group II I (Group II I means the 3rd main group of the Periodic Table of the Elements, ie B, Al, Ga, I n and Tl) in the emitter and / or base layer of the subcell 2 arranged above the germanium subcell, at least 30% and preferably at least 40%.
Gemäß einer weiteren bevorzugten Ausführungsform der vorliegenden Erfindung beträgt der prozentuale Anteil von Indium, bezogen auf die Summe aller Atome der Gruppe II I, in der Emitter- und/oder Basisschicht der Teilzelle 2' und aller oberhalb der Teilzelle 2' angeordneten Teilzellen 2" ,2" ' mindestens 40 % und bevorzugt mindestens 45 %. Gemäß einer weiteren bevorzugten Ausführungsform der vorliegenden Erfindung beträgt der prozentuale Anteil von Indium, bezogen auf die Summe aller Atome der Gruppe II I, in der Emitter- und/oder Basisschicht der Teilzelle 2' mindestens 60 % und bevorzugt mindestens 70 %. According to a further preferred embodiment of the present invention, the percentage of indium, based on the sum of all atoms of group II I, in the emitter and / or base layer of the subcell 2 ' and all above the subcell 2 ' arranged sub-cells 2 " , 2 "' at least 40% and preferably at least 45%. According to a further preferred embodiment of the present invention, the percentage of indium, based on the sum of all atoms of the group II I, in the emitter and / or base layer of the subcell 2 'is at least 60% and preferably at least 70%.
Gemäß einer weiteren bevorzugten Ausführungsform der vorliegenden Erfin dung beträgt der prozentuale Anteil von Phosphor, bezogen auf die Summe aller Atome der Gruppe V (Gruppe V meint die 5. Hauptgruppe des Perioden Systems der Elemente, d.h. N, P, As, Sb und Bi), in der Emitter- und/oder Basisschicht der oberhalb der Germanium-Teilzelle angeordneten Teilzellen 2 und 2' mindestens 5 %, bevorzugt mindestens 15 %. According to a further preferred embodiment of the present inven tion, the percentage of phosphorus, based on the sum of all atoms of the group V (group V means the 5th main group of the Periodic Table of the Elements, ie, N, P, As, Sb and Bi) in the emitter and / or base layer of the sub-cells 2 and 2 'arranged above the germanium subcell, at least 5%, preferably at least 15%.
Gemäß einer weiteren bevorzugten Ausführungsform der vorliegenden Erfin- dung beträgt der prozentuale Anteil von Phosphor, bezogen auf die Summe aller Atome der Gruppe V, in den Emitter- und/oder Basisschichten der oberhalb der Teilzelle 2 angeordneten Teilzellen 2', 2" ,2"' mindestens 50 %, bevorzugt mindestens 80 %. Nach einer anderen bevorzugten Ausführungsform der vorliegenden Erfindung beträgt die Dicke der l ll-V Teilzellen 400 bis 4000 nm. According to a further preferred embodiment of the present invention, the percentage of phosphorus, based on the sum of all the atoms of the group V, in the emitter and / or base layers of the arranged above the subcell 2 sub-cells 2 ', 2 " , 2 "' at least 50%, preferably at least 80%. According to another preferred embodiment of the present invention, the thickness of the ll-V sub-cells is 400 to 4000 nm.
Gemäß einer weiteren bevorzugten Ausführungsform der vorliegenden Erfindung weist die Germanium-Teilzelle eine p-dotierte Basisschicht aus Germanium mit einer Bandlücke von 0,67 eV bei 300 K auf. According to a further preferred embodiment of the present invention, the germanium subcell has a p-doped base layer of germanium with a bandgap of 0.67 eV at 300K.
Eine andere bevorzugte Ausführungsform der vorliegenden Erfindung sieht vor, dass die Gitterkonstante der Germanium-Teilzelle 5,658 Angström beträgt. Another preferred embodiment of the present invention provides that the lattice constant of the germanium subcell is 5.658 angstroms.
Gemäß einer weiteren bevorzugten erfindungsgemäßen Ausführungsform der vorliegenden Erfindung weist die Germanium-Teilzelle eine Dicke von mehr als 4 μιη, bevorzugt mehr als 60 μιη auf. According to a further preferred embodiment of the present invention, the germanium partial cell has a thickness of more than 4 μm, preferably more than 60 μm.
Germanium ist sehr gut als Material für die rückseitige Teilzelle geeignet, da es im Vergleich zu anderen Substraten, wie z.B. I nP, geringere Kosten verur- sacht und durch Diffusion ein pn-Übergang hergestellt werden kann, der es ermöglicht Photonen im Infrarotbereich mit einer Energie größer als der Bandlücke von 0.67 eV zu absorbieren und in elektrischen Strom zu wandeln. Zudem weisen Germanium Solarzellen eine sehr hohe Strahlungsstabilität im Weltraum auf. Germanium is very well suited as a material for the backside subcell as it is lower cost compared to other substrates such as I nP. and pn junction can be produced by diffusion, which makes it possible to absorb photons in the infrared range with an energy greater than the band gap of 0.67 eV and convert it into electrical current. In addition, germanium solar cells have a very high radiation stability in space.
Gemäß einer weiteren bevorzugten Ausführungsform der vorliegenden Erfindung besitzt die Germanium-Teilzelle auf der dem Licht abgewandten Seite einen Metal Ikontakt. According to a further preferred embodiment of the present invention, the germanium partial cell has a metal contact on the side facing away from the light.
Eine andere bevorzugte Ausführungsform vorliegender Erfindung sieht vor, dass zwischen der Germanium-Teilzelle und der Teilzelle 2 eine metamorphe Pufferschicht angeordnet ist. Diese überführt die Gitterkonstante der Germanium-Teilzelle zu der Gitterkonstante der Teilzelle 2, wobei die Gitterkonstan- te der Teilzelle 2 bevorzugt 5,75 bis 5,90 Angström und besonders bevorzugt von 5,77 bis 5,85 Angström beträgt. Another preferred embodiment of the present invention provides that a metamorphic buffer layer is arranged between the germanium subcell and the subcell 2. This converts the lattice constant of the germanium subcell to the lattice constant of the subcell 2, the lattice constancy of the subcell 2 preferably being 5.75 to 5.90 angstroms and more preferably 5.77 to 5.85 angstroms.
Die metamorphe Pufferschicht kann einen stetigen Gradienten in der Gitterkonstante aufweisen, oder die Gitterkonstante kann innerhalb der metamor- phen Pufferschicht in Stufen sprunghaft erhöht werden, wobei sich in diesemThe metamorphic buffer layer may have a steady gradient in the lattice constant, or the lattice constant may be increased in steps within the metamorphic buffer layer, with this in mind
Falle Fehlanpassungsversetzungen vorzugsweise an den Stellen bilden, in welchen die Gitterkonstante stufenweise erhöht wird. Der Gradient in der Gitterkonstante wird erreicht durch eine allmähliche Veränderung der Zusammensetzung in Schichten aus lll-V Verbindungshalbleitern wie AIGalnAsP, AIGalnP, GalnP, AIGalnAs, GaAsSb oder GalnAs oder GalnAsN, welche n- oder p-dotiert sein können und die weitere Elemente wie N oder B zur Erhöhung der Kristallhärte enthalten können. Um eine vollständige Relaxation der metamorphen Pufferschicht zu erreichen, kann auch die Gitterkonstante innerhalb der Schicht über die Zielgitterkonstante hinaus erhöht werden. Ziel ist es am Ende der metamorphen Pufferschicht 3 in der Ebene die Gitterkonstante der darauffolgenden Teilzelle 2' einzustellen und eine geringe Dichte an Faden- oder Durchstoßversetzungen zu gewährleisten. Trap mismatch preferably at the locations where the lattice constant is increased in steps. The gradient in the lattice constant is achieved by a gradual change in the composition in layers of III-V compound semiconductors such as AIGalnAsP, AIGalnP, GalnP, AIGalnAs, GaAsSb or GalnAs or GalnAsN, which may be n- or p-doped, and the other elements such as N or B may contain to increase the crystal hardness. To achieve complete relaxation of the metamorphic buffer layer, the lattice constant within the layer may also be increased beyond the target lattice constant. The goal is to set the lattice constant of the subsequent subcell 2 'at the end of the metamorphic buffer layer 3 in the plane and to ensure a low density of thread or puncture dislocations.
Es wurde in der Vergangenheit davon ausgegangen, dass metamorphe Puffer, welchen einen weiten Bereich der Gitterkonstante von mehreren Prozent überbrücken, zu hohen Versetzungsdichten > 2E6 cm"2 führen und damit zu schlechten Solarzellenergebnissen. Überraschenderweise sind aber nach neuesten Erkenntnissen Versetzungsdichten von 106 cm"2 selbst bei einem Gradienten von Germanium (5,658 Angström) bis zu InP (5,869 Angström) erreichbar. Damit lässt sich eine hohe Effizienz für Mehrfachsolarzellen erreichen, in denen Teilzellen beispielsweise aus InP oder GalnAsP direkt auf Teilzellen ausIt was thought in the past that metamorphic buffer, which span a wide range of the lattice constant of several percent, result in high dislocation densities> 2E6 cm "2 and thus bad solar cell results. Surprisingly, according to the latest findings, dislocation densities of 10 6 cm "2 can be achieved even with a gradient of germanium (5.658 angstroms) to InP (5.869 angstroms), thus achieving high efficiency for multiple solar cells, in which subcells are made, for example, of InP or GalnAsP directly on sub-cells
Germanium epitaxiert werden. Germanium be epitaxed.
Nach einer weiteren bevorzugten erfindungsgemäßen Ausführungsform sind die Teilzelle 2 und die Teilzelle 2' zueinander gitterangepasst. Bevorzugt wei- sen die Teilzellen 2,2' eine Gitterkonstante von 5,75 bis 5,90 Angström und besonders bevorzugt von 5,77 bis 5,85 Angström auf. According to a further preferred embodiment of the invention, the subcell 2 and the subcell 2 ' are lattice matched to each other. The subcells 2, 2 ' preferably have a lattice constant of 5.75 to 5.90 angstroms and more preferably of 5.77 to 5.85 angstroms.
Gemäß einer anderen bevorzugten Ausführungsform vorliegender Erfindung besteht zwischen der Teilzelle 2' und der Teilzelle 2" oder zwischen der Teil- zelle 2" und der Teilzelle 2"' eine elektrisch leitfähige Wafer-According to another preferred embodiment of the present invention, there is an electrically conductive wafer layer between the subcell 2 ' and the subcell 2 " or between the subcell 2 " and the subcell 2 "'.
Bondverbindung, die bevorzugt einen Widerstand von maximal 5 Ohm cm2, besonders bevorzugt von maximal 500 mOhm cm2 aufweisen. Der Wafer- Bond bildet eine flächenbündige elektrisch leitfähige, optisch transparente und mechanisch stabile Verbindung zwischen den Teilzellen 2' und 2". Dieser kann durch einen direkten Wafer-Bond mit kovalenten Bindungen zwischen den Halbleiteroberflächen erfolgen oder durch geeignete Zwischenschichten wie transparente, leitfähige Oxide, amorphe Halbleiter oder geeignete leitfähige Klebstoffe. Eine weitere bevorzugte erfindungsgemäße Ausführungsform sieht vor, dass die Emitter- und/oder Basisschicht der lichtzugewandten frontseitigen Teilzelle aus AIGalnP besteht und eine Bandlückenenergie von bevorzugt 1,8 bis 2,1 eV, besonders bevorzugt 1,85 bis 2,0 eV aufweist. Die frontseitige Teilzelle ist vorzugsweise gitterangepasst zu GaAs oder Germanium. Bond compound, which preferably have a maximum resistance of 5 ohm cm 2 , more preferably of at most 500 mOhm cm 2 . The wafer bond forms a flush electrically conductive, optically transparent and mechanically stable connection between the sub-cells 2 'and 2 ", which can be effected by a direct wafer bond with covalent bonds between the semiconductor surfaces or by suitable intermediate layers such as transparent, conductive oxides, amorphous semiconductors or suitable conductive adhesives Another preferred embodiment according to the invention provides that the emitter and / or base layer of the light-facing front-side subcell consists of AIGalnP and has a bandgap energy of preferably 1.8 to 2.1 eV, more preferably 1.85 to 2.0 eV The front-side part cell is preferably lattice-matched to GaAs or germanium.
Erst durch die Kombination von Wafer-Bondverbindung und metamorpher Pufferschicht wird es möglich eine besonders strahlungsstabile frontseitige AIGalnP Teilzelle mit optimaler Bandlückenenergie für die Mehrfachsolarzelle mit besonders strahlungsstabilen ln-haltigen Teilzellen mit einer Gitterkon- stante von 5,75 bis 5,90 Angström und einer besonders strahlungsharten und kostengünstigen Germanium Unterzelle zu verbinden. Eine bevorzugte Mehrfachsolarzelle besteht aus vier Teilzellen 1, 2, 2', 2", wobei die Emitter- und/oder Basisschicht der Teilzelle 2 aus Gal nAsP, die Emitter- und/oder Basisschicht der Teilzelle 2' aus Gal nP und die Emitter- und/oder Basisschicht der Teilzelle 2" aus AIGal nP besteht. Only through the combination of wafer bond connection and metamorphic buffer layer is it possible to have a particularly radiation-stable frontal AIGalnP subcell with optimum band gap energy for the multiple solar cell with particularly radiation-stable In-containing sub-cells with a lattice constant of 5.75 to 5.90 angstroms and a particularly radiation-hard and inexpensive germanium subcell to connect. A preferred multiple solar cell consists of four sub-cells 1, 2, 2 ' , 2 " , wherein the emitter and / or base layer of the subcell 2 of Gal nAsP, the emitter and / or base layer of the subcell 2 ' of Gal nP and the emitter and / or base layer of the subcell 2 " consists of AIGal nP.
Eine andere Mehrfachsolarzelle besteht aus fünf Teilzellen 1, 2, 2', 2", 2" ', wobei die Emitter- und/oder Basisschichten der Teilzellen 2, 2' aus Gal nAsP, die Emitter- und/oder Basisschicht der Teilzelle 2" aus AIGalnAsP und die Emitter- und/oder Basisschicht der Teilzelle 2"' aus AIGal nP besteht. Another multiple solar cell consists of five sub-cells 1, 2, 2 ' , 2 " , 2 "' , wherein the emitter and / or base layers of the sub-cells 2, 2 ' of Gal nAsP, the emitter and / or base layer of the subcell 2 " AIGalnAsP and the emitter and / or base layer of the subcell 2 "' consists of AIGal nP.
Gemäß einer weiteren erfindungsgemäßen Ausführungsform vorliegender Erfindung reflektiert die metamorphe Pufferschicht zwischen der Germanium- Teilzelle 1 und der Teilzelle 2 mindestens 30 %, insbesondere 70 % der Strahlung im Absorptionsbereich der Teilzelle 2. According to a further embodiment of the present invention, the metamorphic buffer layer between the germanium subcell 1 and the subcell 2 reflects at least 30%, in particular 70%, of the radiation in the absorption region of the subcell 2.
Nach einer anderen Ausführungsform vorliegender Erfindung sind zwischen den Teilzellen 1, 2, 2', 2", 2"',... Tunneldioden angeordnet, welche die Teilzellen seriell verschalten. According to another embodiment of the present invention, tunnel diodes are arranged between the subcells 1, 2, 2 ' , 2 " , 2 "' , ..., which connect the subcells in series.
Eine weitere bevorzugte erfindungsgemäße Ausführungsform sieht vor, dass die Leistung der Mehrfachsolarzelle nach Bestrahlung mit 1 MeV Elektronen bei einem Fluss von 1016 cm"2 um weniger als 35 %, bevorzugt um weniger als 20 % degradiert. A further preferred embodiment of the invention provides that the power of the multiple solar cell after irradiation with 1 MeV electrons at a flow of 10 16 cm "2 degrades by less than 35%, preferably by less than 20%.
Die erfindungsgemäßen Mehrfachsolarzellen werden bevorzugt im Weltraum verwendet und finden insbesondere Verwendung für Satelliten. The multiple solar cells according to the invention are preferably used in space and find particular use for satellites.
Anhand der nachfolgenden Figuren soll der erfindungsgemäße Gegenstand näher erläutert werden, ohne diesen auf die hier gezeigten spezifischen Ausführungsformen einschränken zu wollen. The object according to the invention is intended to be explained in more detail with reference to the following figures, without wishing to restrict it to the specific embodiments shown here.
Fig. 1 zeigt vier verschiedene erfindungsgemäße Ausführungsformen der Fig. 1 shows four different embodiments of the invention
Mehrfachsolarzelle (a, b, c, d)  Multiple solar cell (a, b, c, d)
Fig. 2 zeigt Diagramme für die Bandlücke und Gitterkonstante für die Ausführungsformen gemäß Fig. la und lb Fig. 2 shows graphs for the bandgap and lattice constant for the Embodiments according to Fig. La and lb
Fig. 3 zeigt eine detaillierte Schichtstruktur einer erfindungsgemäßen Fig. 3 shows a detailed layer structure of an inventive
Ausführungsform  embodiment
Fig. 4 zeigt eine detaillierte Schichtstruktur einer erfindungsgemäßen Fig. 4 shows a detailed layer structure of an inventive
Ausführungsform  embodiment
Fig. la zeigt eine bevorzugte Struktur einer erfindungsgemäßen Mehrfachso- larzelle mit 4 Teilzellen, welche jeweils eine Emitter und Basisschicht sowie einen pn-Übergang besitzen. Diese umfasst neben der Anti- Reflexbeschichtung 5, einem Vorderseitenkontakt 6 und einem Rückseitenkontakt 7 von unten nach oben eine Germanium-Teilzelle 1, eine metamorphe Pufferschicht 3, eine GalnAsP-Teilzelle 2, eine InP-Teilzelle 2', eine FIG. 1 a shows a preferred structure of a multiple-solar cell according to the invention with 4 sub-cells, each having an emitter and base layer and a pn junction. This includes, in addition to the anti-reflection coating 5, a front side contact 6 and a rear contact 7 from bottom to top a germanium subcell 1, a metamorphic buffer layer 3, a GalnAsP subcell 2, an InP subcell 2 ' , a
Waferbond-Verbindung 4 sowie eine GalnP-Teilzelle 2". Waferbond compound 4 and a GalnP subcell 2 " .
Mit Hilfe der auf der Germanium Teilzelle 1 befindlichen metamorphen Pufferschicht 3 wird die Gitterkonstante von 5,658 Angström auf 5,869 Angström erhöht (s. linker Teil von Figur 2, die Gitterkonstanten sind der Datenbank von loffe entnommen:„http://www.ioffe.ru/SVA/NSM/Semicond"). Auf der Gitterkonstante von 5,869 Angström wird zunächst eine zweite GalnAsP Teilzelle 2 mit einer Bandlückenenergie von etwa 1,03 eV und dann eine dritte InP Teilzelle 2' mit einer Bandlückenenergie von 1,35 eV gitterangepasst aufgewachsen. Das Wachstum der Teilzellen 2 und 2' kann im gleichen Epitaxieprozess erfolgen, in welchem auch die metamorphe Pufferschicht 3 abgeschieden wird. Alternativ wird zunächst nur die metamorphe Pufferschicht 3 abgeschieden und die Oberfläche dann in einem separaten Prozess poliert, um die Rauheit zu verringern, bevor in einem weiteren Epitaxieprozess die Teilzellen 2 und 2' abgeschieden werden. Eine vierte GalnP-Teilzelle 2" mit einer Band- lückenenergie von 1,88 eV wird gitterangepasst auf GaAs (5,653 Angström) oder Germanium (5,658 Angström) gewachsen und anschließend über Waferbonden und Substratentfernen auf die untere Struktur übertragen. The lattice constant is increased from 5.658 angstroms to 5.869 angstroms with the aid of the metamorphic buffer layer 3 located on the germanium subcell 1 (see left part of FIG. 2, the lattice constants are taken from the database of loffe: "http://www.ioffe.ru / SVA / NSM / Semicond "). At the lattice constant of 5.869 Angstroms, a second GalnAsP subcell 2 having a bandgap energy of about 1.03 eV and then a third InP subcell 2 ' having a bandgap energy of 1.35 eV is grown lattice-matched. The growth of the sub-cells 2 and 2 'can take place in the same epitaxy process in which the metamorphic buffer layer 3 is deposited Alternatively, initially only the metamorphic buffer layer 3 is deposited and the surface is then polished in a separate process to reduce the roughness before In a further epitaxy process, the sub-cells 2 and 2 'are deposited, a fourth GalnP sub-cell 2 " with a bandgap energy of 1.88 eV is grown lattice-matched on GaAs (5.653 angstroms) or germanium (5.658 angstroms) and then transferred to the bottom structure via wafer bonding and substrate removal.
Alle Teilzellen 2, 2', 2" weisen jeweils eine Emitter und eine Basisschicht auf, wobei zwischen der Emitter und der Basisschicht ein pn-Übergang ausgebildet ist. Wenn die Emitterschicht eine n-Dotierung aufweist, so ist die Basisschicht p-dotiert und umgekehrt. Typische n-Dotierstoffe umfassen Si, Se, Te und p- Dotierstoffe Zn, Mg und C. Besitzen Emitter und Basisschicht die gleiche Bandlückenenergie so spricht man von einer Homo-Solarzelle, besitzt der Emitter hingegen eine niedrigere oder höhere Bandlücke im Vergleich zur Basis, so spricht man von einer Heterosolarzelle. Die Teilzellen 2, 2', 2" können sowohl als Homo-, also auch als Heterosolarzelle ausgebildet sein. All subcells 2, 2 ', 2 "each have an emitter and a base layer, a pn junction being formed between the emitter and the base layer. If the emitter layer has an n-doping, then the base layer is p-doped and vice versa. Typical n-type dopants include Si, Se, Te, and p-type dopants Zn, Mg, and C. If the emitter and base layer share the same bandgap energy, this is called a homo-solar cell, but the emitter has a lower or higher bandgap compared to the base, this is called a hetero-solar cell. The sub-cells 2, 2 ', 2 "can be designed both as a homo and also as a hetero solar cell.
Die entstandene Mehrfachsolarzellenstruktur umfasst vier Teilzellen 1, 2, 2', 2" mit jeweils einem pn-Übergang, wobei die Materialien für die Emitter und/oder Basisschicht der Teilzellen (GalnP, InP, GalnAsP und Ge) eine hoheThe resulting multiple solar cell structure comprises four sub-cells 1, 2, 2 ', 2 "each having a pn junction, wherein the materials for the emitter and / or base layer of the sub-cells (GalnP, InP, GalnAsP and Ge) a high
Beständigkeit gegenüber Teilchenbestrahlung im Weltraum aufweisen. Resistant to particle irradiation in space.
Fig. lb zeigt eine weitere bevorzugte Struktur einer erfindungsgemäßen Mehrfachsolarzelle. Diese umfasst neben der Anti-Reflexbeschichtung 5, ei- nem Vorderseitenkontakt 6 und einem Rückseitenkontakt 7 von unten nach oben eine Germanium-Teilzelle 1, eine metamorphe Pufferschicht 3, eine GalnAsP-Teilzelle 2, eine GalnP-Teilzelle 2', eine Waferbond-Verbindung 4 sowie eine AIGalnP Teilzelle 2". Hier wird aufbauend auf der ersten Germanium Teilzelle der metamorphe Puffer 3 von einer Gitterkonstante von 5,658 Angström zu einer Gitterkonstante von 5,75 bis 5,90, insbesondere 5,80 bisFig. Lb shows another preferred structure of a multi-junction solar cell according to the invention. This comprises, in addition to the anti-reflection coating 5, a front-side contact 6 and a rear contact 7 from bottom to top, a germanium subcell 1, a metamorphic buffer layer 3, a GalnAsP subcell 2, a GalnP subcell 2 ' , a wafer bonding compound 4 and an AlGaInP subcell 2 ". This is built on the first germanium partial cell of the metamorphic buffer 3 of a lattice constant of 5.658 angstroms to a lattice constant from 5.75 to 5.90, especially 5.80 to
5,87 Angström (siehe rechter Teil von Figur 2, die Gitterkonstanten sind der Datenbank von loffe entnommen: 5.87 angstroms (see right part of Figure 2, the lattice constants are taken from the database of loffe:
„http://www.ioffe.ru/SVA/NSM/Semicond") überführt. Hierdurch können die gewünschten Bandlücken für die zweite und dritte Teilzelle ebenfalls durch Kompositionen von GalnAsP 2 bzw. GalnP 2' mit hoher Strahlungsstabilität erreicht werden. Es ist weiterhin möglich, die Fehlanpassung zwischen der Germanium-Teilzelle 1 und der GalnAsP-Teilzelle 2 zu verringern und hierdurch evtl. noch geringere Versetzungsdichten und Substratkrümmungen zu erreichen. Zudem sinkt die Dicke der metamorphen Pufferschichten 3, wenn ein geringerer Unterschied in der Gitterkonstante überwunden werden muss, was wirtschaftliche Vorteile mit sich bringt. Es ergeben sich weiterhin für die von unten aus dritte GalnP-Teilzelle 2' höhere Barrieren an der Grenzfläche zur Waferbondverbindung der obersten AIGalnP-Teilzelle 2". Durch die höheren Bandlücken der unteren drei Teilzellen ist es vorteilhaft die oberste Teil- zelle durch Zugabe von AI in AIGalnP 2" in der Bandlücke zwischen 1,88 undIn this way, the desired band gaps for the second and third subcell can also be achieved by means of compositions of GalnAsP 2 and / or GalnP 2 ' with high radiation stability Furthermore, it is possible to reduce the mismatch between the germanium subcell 1 and the GalnAsP subcell 2, thereby possibly achieving even lower dislocation densities and substrate curvatures, and also reduces the thickness of the metamorphic buffer layers 3 when a lesser difference in lattice constant must be overcome , which brings economic advantages. "Further, for the bottom third GalnP subcell 2 ', higher barriers at the interface to the wafer bonding of the topmost AIGalnP subcell 2 " result . Due to the higher band gaps of the lower three sub-cells, it is advantageous to add the upper part of the cell by adding Al in AIGalnP 2 " in the band gap between 1.88 and 1.30
2,1 eV einzustellen. Eine andere bevorzugte Struktur einer Mehrfachsolarzelle gemäß der vorliegenden Erfindung wird in Fig. lc gezeigt. Diese umfasst neben der Anti- Reflexbeschichtung 5, einem Vorderseitenkontakt 6 und einem Rückseiten- kontakt 7 von unten nach oben eine Germanium-Teilzelle 1, eine metamorpheSet 2.1 eV. Another preferred structure of a multiple solar cell according to the present invention is shown in Fig. 1c. In addition to the anti-reflection coating 5, a front-side contact 6 and a rear-side contact 7, this comprises, from bottom to top, a germanium partial cell 1, a metamorphic one
Pufferschicht 3, zwei GalnAsP-Teilzellen 2, 2', eine Waferbond-Verbindung 4, eine vierte AIGalnAsP-Teilzelle 2" sowie eine fünfte AIGalnP Teilzelle 2"' . Die ersten beiden Teilzellen 2, 2' werden dabei auf der metamorphen Pufferschicht 3 hergestellt und die obersten beiden Teilzellen werden zu einem GaAs oder Ge Substrat gitterangepasst. Die obersten beiden Teilzellen werden wiederum mittels Waferbonden und Substratentfernen auf den unteren Teil der Solarzellenstruktur übertragen. Buffer layer 3, two GalnAsP sub-cells 2, 2 ' , a wafer bonding compound 4, a fourth AIGalnAsP subcell 2 " and a fifth AIGalnP subcell 2 "' . The first two subcells 2, 2 ' are produced on the metamorphic buffer layer 3 and the top two subcells are lattice-matched to a GaAs or Ge substrate. The top two sub-cells are in turn transferred to the lower part of the solar cell structure by wafer bonding and substrate removal.
Eine weitere bevorzugte Struktur einer Mehrfachsolarzelle gemäß der vorlie- genden Erfindung wird in Fig. ld gezeigt. Diese umfasst neben der Anti-Another preferred structure of a multiple solar cell according to the present invention is shown in FIG. 1d. This includes not only the anti-
Reflexbeschichtung 5, einem Vorderseitenkontakt 6 und einem Rückseitenkontakt 7 von unten nach oben eine Germanium-Teilzelle 1, eine metamorphe Pufferschicht 3, zwei GalnAsP-Teilzellen 2, 2', eine AIGal nAsP Teilzelle 2", eine Waferbond-Verbindung 4 sowie eine fünfte AIGal nP Teilzelle 2" ' . Die ersten drei Teilzellen 2, 2', 2" werden dabei auf der metamorphen Pufferschicht 3 hergestellt und die oberste Teilzelle wird auf GaAs oder Ge Substrat gitterangepasst gewachsen und anschließend mittels Waferbonden und Substratentfernen auf die unteren Teilzellen 1, 2, 2', 2" übertragen. Zur Herstellung der Mehrfachsolarzelle (gemäß Figur la und lb) wird ein pn-Reflective coating 5, a front side contact 6 and a back contact 7 from bottom to top a germanium subcell 1, a metamorphic buffer layer 3, two GalnAsP sub-cells 2, 2 ' , an AIGal nAsP subcell 2 ", a wafer bonding compound 4 and a fifth AIGal nP subcell 2 "' . The first three subcells 2, 2 ' , 2 "are thereby produced on the metamorphic buffer layer 3 and the uppermost subcell is grown lattice-matched on GaAs or Ge substrate and subsequently removed by wafer bonding and substrate removal to the lower subcells 1, 2, 2', 2". transfer. For the production of the multiple solar cell (according to FIGS. 1a and 1b), a pn
Übergang in p-Germanium durch Diffusion von Arsen oder Phosphor aus der Gasphase erzeugt. Zudem wird eine N ukleationsschicht aus n-dotiertem GaAs oder GalnP gitterangepasst abgeschieden. Diese Schicht dient als Vordersei- tenpassivierung für die erste Germanium Teilzelle. Auf die Germanium Unter- zelle wird eine metamorphe Pufferschicht aus Gal nP oder AIGalnAsP abgeschieden, in welcher die Gitterkonstante von 5,658 Angström für Ge zu einer Gitterkonstante von 5,75 bis 5,90, insbesondere 5,80 bis 5,87 Angström überführt wird. In der metamorphen Pufferschicht wird die Gitterkonstante kontinuierlich (z.b. linear) oder in Stufen erhöht, wobei sich Fehlanpassungsverset- zungen bilden und den Kristall relaxieren. Der metamorphe Puffer ist so ausgebildet, dass am Ende ein relaxiertes Kristallgitter mit der Ziel- Gitterkonstante und einer möglichst geringen Durchstoßversetzungsdichte vorliegt. Durch Sprünge im Brechungsindex kann der Puffer optional als Bragg- Spiegel ausgebildet werden, um nicht absorbierte Photonen in die darüber liegende Teilzelle zu reflektieren. Zwischen der Germanium Teilzelle und der metamorphen Pufferschicht, bzw. zwischen der metamorphen Pufferschicht und der zweiten Teilzelle wird eine Tunneldiode gewachsen, welche dazu dient die Teilzellen seriell zu verschalten. Die Tunneldiode besteht aus entar- teten n- und p-dotierten Halbleiterschichten wie z.B. p-AIGaAs und n-GalnAs und kann optional von höherbandlückigen Barriereschichten umgeben sein. Oberhalb der Tunneldiode und der metamorphen Pufferschicht wird eine zweite ln-haltige Teilzelle aus GalnAsP mit einer Bandlückenenergie von etwa 1,03 eV abgeschieden. Eine mögliche Komposition der Struktur gemäß der linken Seite von Figur 1 ist Gao.21 l rio.79Asc 5 Po.55 gitterangepasst zu InP mit einer Bandlückenenergie von 1,03 eV. Die GalnAsP Absorberschicht kann hierbei den n-dotierten oder den p-dotierten oder beide Bereiche der Teilzelle bilden, wobei die Dotierung durch Zugabe von typischen Dotieratomen wie Si, Se, Te, C, Mg, Zn in einem Konzentrationsbereich von 1E16-3E18 cm"3 erreicht wird. Die Solarzelle weist weiterhin Barriereschichten an der Vorder- undTransition into p-germanium produced by diffusion of arsenic or phosphorus from the gas phase. In addition, an N-doped layer of n-doped GaAs or GalnP is deposited in a lattice-matched manner. This layer serves as a front passivation for the first germanium subcell. On the germanium subcell a metamorphic buffer layer of Gal nP or AIGalnAsP is deposited, in which the lattice constant of 5.658 Angstrom for Ge is converted to a lattice constant of 5.75 to 5.90, in particular 5.80 to 5.87 angstroms. In the metamorphic buffer layer, the lattice constant is increased continuously (eg, linearly) or in steps, forming misfit shifts and relaxing the crystal. The metamorphic buffer is designed in such a way that at the end there is a relaxed crystal lattice with the target lattice constant and the lowest possible puncture dislocation density. By leaps in the refractive index, the buffer can optionally be formed as a Bragg mirror to unabsorbed photons in the above to reflect the lying subcell. Between the germanium subcell and the metamorphic buffer layer, or between the metamorphic buffer layer and the second subcell, a tunnel diode is grown, which serves to connect the subcells serially. The tunnel diode consists of degenerate n- and p-doped semiconductor layers such as p-AIGaAs and n-GalnAs and may optionally be surrounded by higher-band-gap barrier layers. Above the tunnel diode and the metamorphic buffer layer, a second In-type partial cell of GalnAsP having a bandgap energy of about 1.03 eV is deposited. One possible composition of the structure to the left of Figure 1 is Gao.21rio.79Asc5Po.55 lattice-matched to InP with a bandgap energy of 1.03 eV. The GalnAsP absorber layer can in this case form the n-doped or the p-doped or both regions of the subcell, wherein the doping is achieved by addition of typical doping atoms such as Si, Se, Te, C, Mg, Zn in a concentration range of 1E16-3E18 cm " 3. The solar cell also has barrier layers on the front and back
Rückseite mit einer höheren Bandlückenenergie auf, um Minoritätsladungsträger zum pn-Übergang hin zu leiten. Beispielsweise wird eine p-AIGalnAs Rückseitenbarriere und eine n-AllnP Vorderseitenbarriere eingesetzt. Oberhalb der 2. Teilzelle schließt sich eine weitere Tunneldiode an, welche bei- spielsweise aus p-AIGaAsSb und n-GalnP gebildet wird. Die Komposition derReverse with a higher bandgap energy to conduct minority carriers to the pn junction. For example, a p-AIGalnAs backside barrier and an n-allnP frontal barrier are used. Above the second subcell, another tunnel diode connects, which is formed, for example, from p-AIGaAsSb and n-GalnP. The composition of
Halbleiterschichten wird entweder gitterangepasst zu der darunter liegenden 2. Teilzelle gewählt oder es wird die kompressive Verspannung einer Schicht durch die tensile Verspannung einer benachbarten Schicht kompensiert. Dieses„strain balancing" funktioniert bei Schichten, welche aufgrund zu geringer Dicke nicht relaxieren. Wesentlich ist, dass die mittlere Gitterkonstante derjenigen der 1. Teilzelle entspricht. Auf die Tunneldiode wird eine dritte Inhaltige Teilzelle aus GalnP mit einer Bandlückenenergie von 1,35 eV abgeschieden, wobei die GalnP Schicht wiederum den n-dotierten Emitter, die p- dotierte Basis oder beides bildet und Dotierstoffe wie Si, Se, Te, C, Mg, Zn in einem Konzentrationsbereich von 1E16-3E18 cm"3 eingesetzt werden. Eine mögliche Komposition der Struktur gemäß dem linken Teil von Figur 1 ist InP. Die dritte Teilzelle ist gitterangepasst zu der zweiten Teilzelle. Oberhalb der dritten Teilzelle ist eine AIGalnAsP Bondschicht, vorzugsweise mit einer hohen n-Dotierung im Bereich von 1E19-5E19 cm"3 aufgebracht. Diese Schicht dient als Vorderseitenbarriere für die 3. Teilzelle und als Verbindung zu der 4. Teilzelle. Die Bondschicht soll eine möglichst geringe Absorption aufweisen. Beispielsweise wird n-AIGalnAsP eingesetzt und vor dem Wafer-Bonden mittels chemisch-mechanischem Polieren bearbeitet, um eine geringe Oberflächenrauheit zu garantieren. Auf diese untere Struktur der Vierfachsolarzelle wird eine 4. Oberzelle aus (AI)GalnP mit einer Bandückenenergie zwischen 1,8 bis 2,1 eV gebondet, welche separat und gitterangepasst auf GaAs oder Ge epitaxiert wurde. Der Waferbond überbrückt den Unterschied in der Gitterkonstante der dritten (5,75 bis 5,90, insbesondere 5,80 bis 5,87 Angström) und vierten Teilzelle (GaAs 5,653 Angström oder Germanium 5,658 Angström). Die Epitaxiestruktur der obersten Teilzelle weist wiederum eine hochdotierte n-AIGalnP Bondschicht mit geringer Rauheit auf, welche zum Beispiel über einen direkten oberflächenaktivierten Wafer Bond mit der n-AIGalnAsP Bondschicht der unteren Zellstruktur verbunden wird. Die Oberflächenaktivie- rung kann zum Beispiel durch Beschuss mit Argon Atomen im Hochvakuum erfolgen, wodurch sich eine wenige nm dünne amorphe Bondschicht an der Grenzfläche ausbildet. Weiterhin kann der Bond zwischen der obersten GalnP Teilzelle und der dritten ln-haltigen Teilzelle durch transparent leitfähige Oxide erfolgen oder durch andere leitfähige Klebeverbindungen, welche die not- wendigen Eigenschaft von mechanischer Stabilität, optischer Transparenz und elektrischer Leitfähigkeit aufweisen. An die Bondverbindung schließt sich eine weitere Tunneldiode aus entarteten n- und p-dotierten Halbleiterschichten wie z.B. p-AIGaAs und n-GalnP an. Die mittlere Gitterkonstante entspricht derjenigen der 4. Teilzelle, welche aus AIGalnP mit einer Bandlückenenergie von 1,88 eV besteht. Die AIGalnP Absorberschicht kann wiederum den n- dotierten oder den p-dotierten oder beide Bereiche der Teilzelle bilden, wobei die Dotierung durch Zugabe von typischen Dotieratomen wie Si, Se, Te, C, Mg, Zn in einem Konzentrationsbereich von 1E16-3E18 cm"3 erreicht wird. Die Halbleiterstruktur endet auf der lichtzugewandten Seite mit einer AllnP Fens- terschicht als Barriere und einer GalnAs Kontaktschicht. Semiconductor layers are either lattice-matched to the underlying second subcell or the compressive strain of one layer is compensated by the tensile strain of an adjacent layer. This "strain balancing" works for layers which do not relax due to insufficient thickness, the essential feature being that the mean lattice constant corresponds to that of the 1st subcell, a third content partial cell of GalnP with a bandgap energy of 1.35 eV is deposited on the tunnel diode in which the GalnP layer in turn forms the n-doped emitter, the p-doped base or both, and dopants such as Si, Se, Te, C, Mg, Zn are used in a concentration range of 1E16-3E18 cm -3 . One possible composition of the structure according to the left part of FIG. 1 is InP. The third subcell is lattice matched to the second subcell. Above the third subcell, an AIGalnAsP bonding layer, preferably with a high n-type doping in the range of 1E19-5E19 cm -3, is applied This layer serves as the front barrier for the 3rd subcell and as the connection to the 4th subcell For example, n-AIGalnAsP is used and machined prior to wafer bonding by chemical mechanical polishing to ensure low surface roughness a 4th upper cell of (AI) GalnP bonded with a band back energy between 1.8 to 2.1 eV, which was epitaxially grown separately and lattice matched to GaAs or Ge. The wafer bond bridges the difference in lattice constant of the third (5.75 to 5.90, especially 5.80 to 5.87 angstroms) and fourth subcell (GaAs 5.653 angstroms or germanium 5.658 angstroms). The epitaxial structure of the uppermost subcell again has a highly doped n-AIGalnP low roughness bonding layer, which is connected to the n-AIGalnAsP bonding layer of the lower cell structure via, for example, a direct surface-activated wafer bond. The surface activation can be carried out, for example, by bombardment with argon atoms in a high vacuum, whereby a few nm thin amorphous bonding layer is formed at the interface. Furthermore, the bond between the topmost GalnP subcell and the third subunit cell may be by transparent conductive oxides or by other conductive adhesive bonds having the required property of mechanical stability, optical transparency, and electrical conductivity. The bond is followed by another tunnel diode made of degenerate n- and p-doped semiconductor layers such as p-AIGaAs and n-GalnP. The mean lattice constant corresponds to that of the 4th partial cell, which consists of AIGalnP with a bandgap energy of 1.88 eV. The AIGalnP absorber layer can in turn form the n-doped or the p-doped or both regions of the subcell, wherein the doping by addition of typical doping atoms such as Si, Se, Te, C, Mg, Zn in a concentration range of 1E16-3E18 cm " 3. The semiconductor structure ends on the light-facing side with an AllnP window layer as a barrier and a GalnAs contact layer.
Die Herstellung der Mehrfachsolarzelle erfolgt mittels epitaktischem Wachstum (vorzugsweise Metallorganische Gasphasenepitaxie) von zwei separaten Strukturen. Der untere Teil der Mehrfachsolarzelle bis zu der n-AIGalnAsP Bondschicht wird auf einem Ge-Substrat epitaxiert, wobei die Gitterkonstante durch den metamorphen Puffer von 5,658 Angström zu 5,75 bis 5,90, insbesondere 5,80 bis 5,87 Angström, für die 2. und 3. Teilzelle erhöht wird. Die oberste 4. AIGalnP Teilzelle wird in einem separaten Epitaxieprozess zum Beispiel in invertierter Schichtreihenfolge gitterangepasst auf GaAs 5,653 Angst- röm oder Germanium 5,658 Angström epitaxiert. Anschließend werden die beiden Schichtfolgen der Teilzellen 1 bis 3 mit derjenigen der 4. Teilzelle mittels Waferbonden verbunden und das Wachstumssubstrat aus GaAs oder Ge auf der 4. Teilzelle entfernt. Dies kann zum Beispiel über einen Lift-off Prozess (chemisch, über einen Laserprozess oder durch mechanische Spannung) erfol- gen, über mechanisches Schleifen, oder über nasschemische Ätzprozesse. Die Prozessierung der Mehrfachsolarzelle umfasst weitere Schritte zur Herstellung von Metallkontakten auf der Vorder- und Rückseite sowie dem Entfernen der GaAs Kontaktschicht zwischen den Metallfingern auf der Vorderseite. Hier wird auch noch eine Antireflexschicht aufgebracht, welche zum Beispiel aus zwei Schichten aus Titanoxid und Aluminiumoxid besteht. Andere Materialien für die Antireflexschicht umfassen beispielsweise Tantaloxid, Siliciumnitrid oder Magnesiumfluorid. Die Mehrfachsolarzellenstruktur gemäß Figur lb ist ebenso wie die Struktur gemäß Figur la ausgebildet, nur wird eine höhere Bandlückenenergie für die oberste AIGalnP Teilzelle eingestellt und die Gitterkonstante der 2. und 3. Teilzelle durch Kompositionsänderungen in GalnAsP und GalnP so angepasst, dass ein möglichst dünner metamorpher Puffer mit möglichst geringem Gra- dienten in der Gitterkonstante verwendet werden kann. Dies reduziert schädliche Durchstoßversetzungen und ist wirtschaftlich attraktiv, da weniger Halbleitermaterial abgeschieden werden muss. Es ist weiterhin vorteilhaft, die Struktur nicht ganz bis zu der Gitterkonstante von InP zu überführen, da dann höhere Barrieren für Minoritätsladungsträger an der Vorder- und Rückseite der 3. Teilzelle möglich werden. The production of the multiple solar cell takes place by means of epitaxial growth (preferably metal organic vapor phase epitaxy) of two separate structures. The lower part of the multiple solar cell up to the n-AIGalnAsP bonding layer is epitaxied on a Ge substrate, the lattice constant through the metamorphic buffer of 5.658 Angstroms to 5.75 to 5.90, especially 5.80 to 5.87 Angstrom, for the 2nd and 3rd subcell is increased. The upper 4th AIGalnP subcell is epitaxially grown in a separate epitaxy process, for example, in an inverted layer order lattice-matched to GaAs 5,653 anxiety or germanium 5.658 angstroms. Subsequently, the two layer sequences of the sub-cells 1 to 3 are connected to that of the 4th sub-cell by means of wafer bonding and the growth substrate of GaAs or Ge is removed on the 4th subcell. This can be done, for example, via a lift-off process (chemically, via a laser process or by mechanical stress). conditions, via mechanical grinding, or via wet-chemical etching processes. The processing of the multi-junction solar cell involves further steps to fabricate metal contacts on the front and back sides as well as removing the GaAs contact layer between the metal fingers on the front side. Here, an antireflection layer is also applied, which consists for example of two layers of titanium oxide and aluminum oxide. Other materials for the antireflective layer include, for example, tantalum oxide, silicon nitride or magnesium fluoride. The multiple solar cell structure according to FIG. 1b is formed just like the structure according to FIG. 1a, only a higher bandgap energy is set for the uppermost AIGalnP subcell and the lattice constants of the 2nd and 3rd subcell are adjusted by compositional changes in GalnAsP and GalnP such that the thinnest possible metamorphic Buffer with the lowest possible gradient in the lattice constant can be used. This reduces damaging puncture dislocations and is economically attractive because less semiconductor material has to be deposited. It is furthermore advantageous not to completely transfer the structure up to the lattice constant of InP since higher barriers for minority charge carriers at the front and back of the 3rd subcell are then possible.
Die Mehrfachsolarzellenstruktur gemäß Figur lc und d ist eine Weiterentwicklung der Strukturen in Fugur la und b, wobei hier 5 Teilzellen aus The multiple solar cell structure according to Figure lc and d is a further development of the structures in Fugur la and b, in which case 5 sub-cells
AIGalnP/AIGalnAsP/GalnAsP/ GalnAsP/Ge eingesetzt werden. Hierdurch kann der theoretische Wirkungsgrad weiter gesteigert werden. Die ersten drei bzw. vier Teilzellen werden wiederum auf Germanium epitaxiert und enthalten einen metamorphen Puffer zwischen der Ge Unterzelle und der GalnAsP Teilzelle. Die Bandlücken der Materialien werden so gewählt, dass sie nahe des theoretischen Optimums von 2,15, 1,6, 1,21, 0,9, 0,64 eV liegen. Die oberste bzw. die obersten beiden Teilzellen aus AIGalnP und AIGalnAsP werden gitter- angepasst auf GaAs oder Ge epitaxiert und dann auf die untere Zellstruktur gebondet. So entsteht eine Mehrfachsolarzelle, welche im Weltraum unter AM0 Bedingungen eine noch höhere Effizienz erreichen kann und die gleichzeitig nur ln-haltige Teilzellen mit einer hohen Strahlungshärte verwendet. AIGalnP / AIGalnAsP / GalnAsP / GalnAsP / Ge are used. As a result, the theoretical efficiency can be further increased. The first three or four sub-cells are in turn epitaxied on germanium and contain a metamorphic buffer between the Ge subcell and the GalnAsP subcell. The bandgaps of the materials are chosen to be close to the theoretical optimum of 2.15, 1.6, 1.21, 0.9, 0.64 eV. The uppermost and the uppermost two sub-cells of AIGalnP and AIGalnAsP are epitaxially latticed to GaAs or Ge and then bonded to the lower cell structure. The result is a multiple solar cell, which can achieve even higher efficiency in space under AM0 conditions and which at the same time uses only partial cells containing ln with a high radiation hardness.
Die hier gezeigten Beispiele lassen sich auch noch um eine weitere sechste Teilzellen erweitern, wodurch theoretisch noch höhere AM0 Wirkungsgrade möglich werden. In diesem Falle werden die Bandlücken und Schichtdicken der Teilzellen so angepasst, dass eine möglichst hohe Umwandlungseffizienz der Mehrfachsolarzelle nach Bestrahlung im Weltraum erreicht wird. The examples shown here can also be extended by a further sixth subcell, which theoretically even higher AMO efficiencies are possible. In this case, the band gaps and layer thicknesses of the sub-cells are adjusted so that the highest possible conversion efficiency the multiple solar cell is reached after irradiation in outer space.
Bezugszeichenliste: LIST OF REFERENCE NUMBERS
1 Germanium-Teilzelle 1 germanium subcell
2, 2', 2", 2"' weitere Teilzellen 2, 2 ' , 2 " , 2 "' further sub-cells
3 Metamorphe Pufferschicht zur Veränderung der Gitterkonstante 3 Metamorphic buffer layer for changing the lattice constant
4 Waferbond-Verbindung 4 wafer bonding connection
5 Anti-Reflexbeschichtung  5 anti-reflective coating
6 Vorderseitenkontakt  6 front side contact
7 Rückseitenkontakt  7 back contact

Claims

Patentansprüche claims
1. Mehrfachsolarzelle mit mindestens vier pn-Übergängen mit einer lichtabgewandten rückseitigen Germanium-Teilzelle (1) und mindestens drei oberhalb von der Germanium-Teilzelle angeordneten Teilzellen (2,2' ,2" ,2"' ,...) aus ll l-V Verbindungshalbleitern, mindestens einer metamorphen Pufferschicht (3) sowie einer Waferbond-Verbindung (4), um Teilzellen mit unterschiedlicher Gitterkonstante zu verbinden, wobei alle oberhalb der Germanium-Teilzelle angeordneten Teilzellen (2,2',2",2"',...) jeweils eine lichtabsorbierende Emitter- und/oder Basisschicht enthalten, welche jeweils mindestens 20 % Indium, bezogen auf die Summe aller Atome der Gruppe II I, enthalten. 1. Multiple solar cell with at least four pn junctions with a light-remote back germanium subcell (1) and at least three above the germanium subcell arranged sub-cells (2,2 ' , 2 " , 2 "' , ...) from ll lV Compound semiconductors, at least one metamorphic buffer layer (3) and a wafer bonding compound (4) to connect sub-cells with different lattice constants, all arranged above the germanium subcell sub-cells (2,2 ' , 2 " , 2 "' , .. .) Each containing a light-absorbing emitter and / or base layer, each containing at least 20% indium, based on the sum of all the atoms of group II I included.
2. Mehrfachsolarzelle nach Anspruch 1, 2. Multiple solar cell according to claim 1,
dadurch gekennzeichnet, dass der prozentuale Anteil von Indium, bezogen auf die Summe aller Atome der Gruppe I II, in der Emitter- und/oder Basisschicht der oberhalb der Germanium-Teilzelle angeordneten Teilzelle (2) mindestens 30 % und bevorzugt mindestens 40 % beträgt.  characterized in that the percentage of indium, based on the sum of all atoms of the group I II, in the emitter and / or base layer of the arranged above the germanium subcell subcell (2) is at least 30% and preferably at least 40%.
3. Mehrfachsolarzelle nach einem der vorhergehenden Ansprüche, 3. Multiple solar cell according to one of the preceding claims,
dadurch gekennzeichnet, dass der prozentuale Anteil von Indium, bezogen auf die Summe aller Atome der Gruppe II I, in der Emitter- und/oder Basisschicht der Teilzelle (2') und aller oberhalb der Teilzelle (2') angeordneten Teilzellen (2", 2"',...) mindestens 40 % und bevor- zugt mindestens 45 % beträgt. characterized in that the percentage of indium, based on the sum of all atoms of group II I, in the emitter and / or base layer of the subcell (2 ' ) and all above the subcell (2 ' ) arranged sub-cells (2 " , 2 "' , ...) at least 40% and at least 45%.
4. Mehrfachsolarzelle nach einem der vorhergehenden Ansprüche, 4. Multiple solar cell according to one of the preceding claims,
dadurch gekennzeichnet, dass der prozentuale Anteil von Indium, bezogen auf die Summe aller Atome der Gruppe III, in der Emitter- und/oder Basisschicht der Teilzelle (2') mindestens 60 % und bevorzugt mindestens 70 % beträgt. characterized in that the percentage of indium, based on the sum of all Group III atoms, in the emitter and / or base layer of the subcell (2 ' ) is at least 60% and preferably at least 70%.
5. Mehrfachsolarzelle nach einem der vorhergehenden Ansprüche, 5. Multiple solar cell according to one of the preceding claims,
dadurch gekennzeichnet, dass der prozentuale Anteil von Phosphor, bezogen auf die Summe aller Atome der Gruppe V, in der Emitter- und/oder Basisschicht der oberhalb der Germanium-Teilzelle angeordneten Teilzelle (2) mindestens 5 %, bevorzugt mindestens 15 % beträgt.  characterized in that the percentage of phosphorus, based on the sum of all atoms of the group V, in the emitter and / or base layer of the arranged above the germanium subcell subcell (2) is at least 5%, preferably at least 15%.
6. Mehrfachsolarzelle nach einem der vorhergehenden Ansprüche, 6. Multiple solar cell according to one of the preceding claims,
dadurch gekennzeichnet, dass der prozentuale Anteil von Phosphor, bezogen auf die Summe aller Atome der Gruppe V, in den Emitter- und/oder Basisschichten der oberhalb der Teilzelle (2) angeordneten Teilzellen (2', 2",2"',...) mindestens 50 %, bevorzugt mindestens 80 % beträgt. characterized in that the percentage of phosphorus, based on the sum of all atoms of the group V, in the emitter and / or base layers of above the subcell (2) arranged sub-cells (2 ', 2 " , 2 "' , .. .) Is at least 50%, preferably at least 80%.
7. Mehrfachsolarzelle nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Germanium-Teilzelle (1) eine p- dotierte Basisschicht aus Germanium mit eine Bandlücke von 0,67 eV bei 300 K und/oder eine Gitterkonstante von 5,658 Angström und/oder eine Dicke von mindestens 4 μιη, bevorzugt mehr als 60 μιη, aufweist. 7. Multiple solar cell according to one of the preceding claims, characterized in that the germanium subcell (1) has a p-doped base layer of germanium with a band gap of 0.67 eV at 300 K and / or a lattice constant of 5.658 Angstrom and / or a Thickness of at least 4 μιη, preferably more than 60 μιη, having.
8. Mehrfachsolarzelle nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Germanium-Teilzelle (1) auf der dem Licht abgewandten Seite einen Metal Ikontakt besitzt. 8. Multiple solar cell according to one of the preceding claims, characterized in that the germanium partial cell (1) on the side remote from the light has a metal contact I.
9. Mehrfachsolarzelle nach einem der vorhergehenden Ansprüche, 9. Multiple solar cell according to one of the preceding claims,
dadurch gekennzeichnet, dass zwischen der Germanium-Teilzelle (1) und der Teilzelle (2) eine metamorphe Pufferschicht (3) angeordnet ist, welche die Gitterkonstante der Germanium-Teilzelle (1) zu der Gitterkonstante der Teilzelle (2) überführt, wobei die Gitterkonstante der Teilzelle (2) bevorzugt 5,75 bis 5,90 Angström und besonders bevorzugt 5,77 bis 5,85 Angström beträgt.  characterized in that between the germanium subcell (1) and the subcell (2) a metamorphic buffer layer (3) is arranged, which converts the lattice constant of the germanium subcell (1) to the lattice constant of the subcell (2), wherein the lattice constant the subcell (2) is preferably from 5.75 to 5.90 angstroms and more preferably from 5.77 to 5.85 angstroms.
10. Mehrfachsolarzelle nach einem der vorhergehenden Ansprüche, 10. Multiple solar cell according to one of the preceding claims,
dadurch gekennzeichnet, dass die metamorphe Pufferschicht (3) aus n- oder p-dotierten lll-V Verbindungshalbleiterschichten aus AIGalnAsP, AIGalnP, GalnP, AIGalnAs, GaAsSb, GalnAs oder GalnAsN besteht.  characterized in that the metamorphic buffer layer (3) consists of n- or p-doped III-V compound semiconductor layers of AIGalnAsP, AIGalnP, GalnP, AIGalnAs, GaAsSb, GalnAs or GalnAsN.
11. Mehrfachsolarzelle nach einem der vorhergehenden Ansprüche, 11. Multiple solar cell according to one of the preceding claims,
dadurch gekennzeichnet, dass die Teilzelle (2) und die Teilzelle (2') zueinander gitterangepasst sind, wobei die Teilzellen (2,2') bevorzugt eine Gitterkonstante von 5,75 bis 5,90 Angström und besonders bevorzugt von 5,77 bis 5,85 Angström aufweisen. Mehrfachsolarzelle nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass zwischen der Teilzelle (2') und der Teilzelle (2") oder zwischen der Teilzelle (2") und der Teilzelle (2"') eine elektrisch leitfähige Waferbond-Verbindung besteht, bevorzugt mit einem Widerstand von maximal 5 Ohm cm2, besonders bevorzugt von maximal 500 mOhm cm2. characterized in that the subcell (2) and the subcell (2 ' ) are lattice matched to one another, the subcells (2, 2 ' ) preferably having a lattice constant of 5.75 to 5.90 angstroms and more preferably of 5.77 to 5 , 85 angstroms. Multiple solar cell according to one of the preceding claims, characterized in that between the subcell (2 ' ) and the subcell (2 " ) or between the subcell (2") and the subcell (2 "') an electrically conductive wafer bonding compound is preferred with a maximum resistance of 5 ohm cm 2 , more preferably of a maximum of 500 m ohm cm 2 .
Mehrfachsolarzelle nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Emitter- und/oder Basisschicht der lichtzugewandten frontseitige Teilzelle (2",2"',...) aus AIGalnP besteht und eine Bandlückenenergie von bevorzugt 1,8 bis 2,1 eV, besonders bevorzugt 1,85 bis 2,0 eV aufweist, wobei die frontseitige Teilzelle (2",2"',...) vorzugsweise gitterangepasst zu GaAs oder Germanium ist. Multiple solar cell according to one of the preceding claims, characterized in that the emitter and / or base layer of the light-facing front-side part cell (2 " , 2 "' , ...) consists of AIGalnP and a bandgap energy of preferably 1.8 to 2.1 eV , particularly preferably 1.85 to 2.0 eV, wherein the front-side part cell (2 " , 2 "' , ...) is preferably lattice-matched to GaAs or germanium.
14. Mehrfachsolarzelle nach einem der vorhergehenden Ansprüche, 14. Multiple solar cell according to one of the preceding claims,
dadurch gekennzeichnet, dass die Mehrfachsolarzelle aus mindestens vier Teilzellen (1,2,2', 2") besteht, wobei die Emitter- und/oder Basisschicht der Teilzelle (2) aus GalnAsP, die Emitter- und/oder Basisschicht der Teilzelle (2') aus GalnP oder InP und die Emitter- und/oder Basisschicht der Teilzelle (2") aus AIGalnP besteht. characterized in that the multiple solar cell consists of at least four sub-cells (1,2,2 ' , 2 " ), wherein the emitter and / or base layer of the subcell (2) of GalnAsP, the emitter and / or base layer of the subcell (2 ' ) consists of GalnP or InP and the emitter and / or base layer of the subcell (2 " ) consists of AIGalnP.
Mehrfachsolarzelle nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Mehrfachsolarzelle aus mindestens fünf Teilzellen (1,2,2',2",2"') besteht, wobei die Emitter- und/oder Basisschicht der Teilzellen (2,2') aus GalnAsP, die Emitter- und/oder Basisschicht der Teilzelle (2") aus AIGalnAsP und die Emitter- und/oder Basisschicht der Teilzelle (2"') aus AIGalnP besteht. Multiple solar cell according to one of the preceding claims, characterized in that the multiple solar cell consists of at least five sub-cells (1,2,2 ' , 2 " , 2 "' ), wherein the emitter and / or base layer of the sub-cells (2,2 ' ) of GalnAsP, the emitter and / or base layer of the subcell (2 " ) consists of AIGalnAsP and the emitter and / or base layer of the subcell (2 "' ) of AIGalnP.
16. Mehrfachsolarzelle nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die metamorphe Pufferschicht zwischen der Germanium-Teilzelle (1) und der Teilzelle (2) mindestens 30 %, insbesondere 70 % der Strahlung im Absorptionsbereich der Teilzelle (2) reflektiert. 16. Multiple solar cell according to one of the preceding claims, characterized in that the metamorphic buffer layer between the germanium subcell (1) and the subcell (2) at least 30%, in particular 70% of the radiation in the absorption region of the subcell (2) reflected.
17. Mehrfachsolarzelle nach einem der vorhergehenden Ansprüche, 17. Multiple solar cell according to one of the preceding claims,
dadurch gekennzeichnet, dass zwischen den Teilzellen  characterized in that between the sub-cells
(1,2,2',2",2"',...) Tunneldioden angeordnet sind, welche die Teilzellen seriell verschalten. (1,2,2 ' , 2 " , 2 "' , ...) tunnel diodes are arranged, which interconnect the sub-cells serially.
18. Mehrfachsolarzelle nach einem der vorhergehenden Ansprüche, 18. Multiple solar cell according to one of the preceding claims,
dadurch gekennzeichnet, dass die Leistung der Mehrfachsolarzelle nach Bestrahlung mit 1 MeV Elektronen bei einem Fluss von 1016 cm"2 um weniger als 35 %, bevorzugt um weniger als 20 % degradiert. characterized in that the power of the multi-junction solar cell after irradiation with 1 MeV electrons at a flow of 10 16 cm "2 degrades by less than 35%, preferably by less than 20%.
19. Verwendung einer Mehrfachsolarzelle gemäß einem der vorhergehenden Ansprüche im Weltraum, insbesondere für Satelliten. 19. Use of a multiple solar cell according to one of the preceding claims in space, in particular for satellites.
EP17826491.7A 2017-01-18 2017-12-19 Multiple solar cell comprising rear-side germanium subcell and use thereof Withdrawn EP3571725A1 (en)

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