Germanium substrate-based three-junction gallium arsenide solar cell and preparation method thereof

Abstract

The invention provides a germanium substrate-based three-junction gallium arsenide solar cell and a preparation method thereof, and the solar cell sequentially comprises a germanium substrate, a GaInP nucleating layer, a GaInAs buffer layer, a first tunnel junction, a plurality of periodic structure lattice gradient buffer layers, a periodic structure overshoot layer, a Ga1-hInhAs sub-cell, a second tunnel junction, an (AlGa) 1-iIniP sub-cell, and a Ga1-jInjAs cap layer along the thickness direction of the solar cell. A lower metal electrode and an upper metal electrode are respectively arranged on the germanium substrate and the Ga1-jInjAs cap layer; 0 < h < = 0.5, 0.4 < = i < 1, and 0 < j < = 0.5; each periodic structure lattice gradual change buffer layer has different In components, and from the first tunnel junction to the periodic structure overshoot layer, the In component between at least one adjacent periodic structure lattice gradual change buffer layer increases, and the In component between at least one adjacent periodic structure lattice gradual change buffer layer decreases. According to the invention, a non-monotonic gradient multi-layer buffer structure is adopted, stress relaxation and broadband high-efficiency spectral reflection are cooperatively realized, and the current matching and conversion efficiency of the cell is improved.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, and in particular to a triple-junction gallium arsenide solar cell based on a germanium substrate and its fabrication method. Background Technology

[0002] The main power source for spacecraft currently widely employs GaInP / GaAs / Ge triple-junction solar cells with germanium single crystals as substrates. This technology is mature, and its typical efficiency can reach approximately 30% under AM0 spectral conditions. However, due to lattice matching limitations, the band gaps (~1.9 eV, ~1.4 eV, ~0.67 eV) of its three sub-cells do not optimally divide the solar spectrum. Specifically, a significant band gap difference exists between the 1.4 eV GaAs intermediate cell and the 0.67 eV germanium bottom cell, leading to insufficient utilization of mid-to-long wavelength photons in the 0.67 eV to 1.4 eV spectral range. This results in current mismatch among the sub-cells, severely restricting further improvements in conversion efficiency.

[0003] To optimize spectral utilization and improve current matching, the industry is committed to fabricating novel intermediate cell structures with band gaps below 1.4 eV on germanium substrates. However, achieving lower band gaps typically requires introducing material systems that are lattice mismatched with the germanium substrate. Therefore, when developing such lattice mismatched epitaxial structures, a lattice-gradient buffer layer is usually introduced to control stress and suppress defects. Traditional lattice-gradient buffer layers typically employ a single series or simple gradient composition design, which has limited stress control capabilities and easily leads to significant warping of the epitaxial wafer during growth. This warping not only affects the uniform growth of subsequent epitaxial materials and reduces structural quality, but also causes process consistency issues in subsequent device fabrication, and in severe cases, even wafer breakage.

[0004] Furthermore, traditional lattice-gradient buffer layers are often used as Bragg mirrors to improve the secondary absorption utilization rate of mid- and long-wavelength photons. However, the reflection effect depends on two key factors: the band gap width of each layer determines the reflectivity at different wavelengths, while the rationality of the structural design determines whether the reflection spectrum can cover the entire absorption range of the mesocell. Existing designs often struggle to achieve a balance between high reflectivity and broad spectral coverage, and there is insufficient research on the multi-segment, nonlinear modulation of the In composition and its synergistic effect between stress control and broadband high reflectivity. Summary of the Invention

[0005] The purpose of this invention is to provide a triple-junction gallium arsenide solar cell based on a germanium substrate and its fabrication method, so as to solve the problems in the background art.

[0006] The technical solution adopted in this invention includes: a triple-junction gallium arsenide solar cell based on a germanium substrate, comprising, along the thickness direction of the solar cell: a germanium substrate, a GaInP nucleation layer, a GaInAs buffer layer, a first tunnel junction, multiple periodic lattice gradient buffer layers, a periodic overshoot layer, and a Ga... 1-h In h As subcell, second tunnel junction, (AlGa) 1-i In i P-cells, Ga 1-j In j As cap layer, the germanium substrate and the Ga 1-j In j The As cap layer is provided with a lower metal electrode and an upper metal electrode respectively; 0 < h ≤ 0.5, 0.4 ≤ i < 1, 0 < j ≤ 0.5; each of the periodic structure lattice gradient buffer layers has a different In composition, from the first tunnel junction to the periodic structure overpass layer, there is at least one place where the In composition between adjacent periodic structure lattice gradient buffer layers increases, and there is at least one place where the In composition between adjacent periodic structure lattice gradient buffer layers decreases.

[0007] Preferably, the number of periodic structure lattice gradient buffer layers is ≥6, the lattice constant of the periodic structure lattice gradient buffer layer adjacent to the first tunnel junction is ≥ the lattice constant of the germanium substrate, and the lattice constant of the periodic structure lattice gradient buffer layer adjacent to the periodic structure overshoot layer is = the Ga 1-h In h The lattice constant of an As subcell.

[0008] Preferably, the periodic structure overpass layer extends from the first tunnel junction to the periodic structure lattice gradient buffer layer, which sequentially includes a first periodic structure lattice gradient buffer layer, a second periodic structure lattice gradient buffer layer, a third periodic structure lattice gradient buffer layer, a fourth periodic structure lattice gradient buffer layer, a fifth periodic structure lattice gradient buffer layer, and a sixth periodic structure lattice gradient buffer layer, wherein the In composition content is: first periodic structure lattice gradient buffer layer > 0, second periodic structure lattice gradient buffer layer > first periodic structure lattice gradient buffer layer, first periodic structure lattice gradient buffer layer < third periodic structure lattice gradient buffer layer < second periodic structure lattice gradient buffer layer, fourth periodic structure lattice gradient buffer layer > second periodic structure lattice gradient buffer layer, second periodic structure lattice gradient buffer layer < fifth periodic structure lattice gradient buffer layer < fourth periodic structure lattice gradient buffer layer, and sixth periodic structure lattice gradient buffer layer ≥ fourth periodic structure lattice gradient buffer layer.

[0009] Preferably, the first periodic lattice gradient buffer layer comprises multiple (AlGa) layers with an In composition of a. 1-a In a As / Ga1-a In a As a periodic structure, with 2 to 30 periods, each (AlGa) 1-a In a As / Ga 1-a In a In the periodic structure of As: (AlGa) 1- a In a The thickness of As is 2nm~300nm, Ga 1-a In a The thickness of As is 2nm~300nm;

[0010] The second-period lattice gradient buffer layer consists of multiple (AlGa) layers with an In composition of b. 1-b In b As / Ga 1-b In b As a periodic structure, with 2 to 30 periods, each (AlGa) 1-b In b As / Ga 1-b In b In the periodic structure of As: (AlGa) 1-b In b The thickness of As is 2nm~300nm, Ga 1-b In b The thickness of As is 2nm~300nm;

[0011] The third-period lattice gradient buffer layer consists of multiple (AlGa) layers with an In composition of C. 1-c In c As / Ga 1-c In c As a periodic structure, with 2 to 30 periods, each (AlGa) 1-c In c As / Ga 1-c In c In the periodic structure of As: (AlGa) 1-c In c The thickness of As is 2nm~300nm, Ga 1-c In c The thickness of As is 2nm~300nm;

[0012] The fourth-period lattice gradient buffer layer consists of multiple (AlGa) layers with an In composition of d. 1-d In d As / Ga 1-d In d As a periodic structure, with 2 to 30 periods, each (AlGa) 1-d Ind As / Ga 1-d In d In the periodic structure of As: (AlGa) 1-d In d The thickness of As is 2nm~300nm, Ga 1-d In d The thickness of As is 2nm~300nm;

[0013] The fifth-period lattice gradient buffer layer consists of multiple (AlGa) layers with an In composition of e. 1-e In e As / Ga 1-e In e As a periodic structure, with 2 to 30 periods, each (AlGa) 1-e In e As / Ga 1-e In e In the periodic structure of As: (AlGa) 1-e In e The thickness of As is 2nm~300nm, Ga 1-e In e The thickness of As is 2nm~300nm;

[0014] The sixth-period lattice gradient buffer layer consists of multiple (AlGa) layers with an In composition of f. 1-f In f As / Ga 1-f In f As a periodic structure, with 2 to 30 periods, each (AlGa) 1-f In f As / Ga 1-f In f In the periodic structure of As: (AlGa) 1-f In f The thickness of As is 2nm~300nm, Ga 1-f In f The thickness of As ranges from 2nm to 300nm.

[0015] Preferably, the lattice constant of the periodic structure lattice gradient buffer layer adjacent to the periodic structure overshoot layer is less than or equal to the lattice constant of the periodic structure overshoot layer.

[0016] Preferably, the periodic overshoot layer comprises a plurality of (AlGa) layers with an In composition of g. 1-g In g As / Ga 1-g In g As a periodic structure, with 2 to 40 periods, each (AlGa) 1-g Ing As / Ga 1-g In g In the periodic structure of As: (AlGa) 1-g In g The thickness of As ranges from 5nm to 300nm, while that of Ga... 1-g In g The thickness of As ranges from 5nm to 300nm.

[0017] Preferably, the Ga 1-h In h As sub-cells include p-type doped Ga. 1-h In h The structure consists of an As base layer, an unintentionally doped i-layer, and an n-type doped emitter layer, wherein:

[0018] Ga 1-h In h As base layer: doping concentration is 1×10 16 cm -3 ~1×10 19 cm -3 The thickness ranges from 30nm to 5000nm;

[0019] The unintentionally doped i-layer is Ga 1-h In h As material or Ga 1-x In x P material, with a thickness of 10nm~1000nm;

[0020] The emitter layer is Ga 1-h In h As material or Ga 1-x In x P material, with a doping concentration of 1×10⁻⁶ 16 cm -3 ~1×10 19 cm -3 The thickness is 30nm~5000nm, and 0.4≤x<1.

[0021] Preferably, the (AlGa) 1-i In i A p-type sub-cell consists of a p-type doped base layer, an unintentionally doped i-layer, and an n-type doped emitter layer, wherein:

[0022] Base layer: doping concentration of 1×10 16 cm -3 ~1×10 19 cm -3 The thickness ranges from 30nm to 5000nm;

[0023] The thickness of the unintentionally doped i-layer is 10 nm to 1000 nm;

[0024] Emitter layer: doping concentration of 1×10 16 cm -3 ~1×10 19 cm -3 The thickness ranges from 30nm to 5000nm.

[0025] Preferably, the Ga 1-j In j The As cap layer is n-type doped with a doping concentration of 1×10⁻⁶. 18 cm -3 ~1×10 21 cm -3 The thickness is 50nm~500nm; the first tunnel junction includes an n-type doped GaAs layer and a p-type doped AlGaAs layer, wherein the doping concentration of the GaAs layer is 1×10⁻⁶. 19 ~1×10 21 cm -3 The thickness ranges from 5 nm to 50 nm, and the doping concentration of the AlGaAs layer is 1 × 10⁻⁶. 19 ~1×10 21 cm -3 The thickness is 5nm~50nm;

[0026] The second tunnel junction comprises an n-type doped AlGaInP layer and a p-type doped AlGaInAs layer, wherein the doping concentration of the AlGaInP layer is 1 × 10⁻⁶. 19 ~1×10 21 cm -3 The thickness ranges from 5 nm to 50 nm, and the doping concentration of the AlGaInAs layer is 1 × 10⁻⁶. 19 ~1×10 21 cm -3 The thickness is 5nm~50nm.

[0027] The technical solution of the present invention also includes: a method for preparing the above-mentioned triple-junction gallium arsenide solar cell based on a germanium substrate, comprising the steps of:

[0028] An n-type doped GaInP nucleation layer was grown on a p-type germanium substrate using MOCVD technology. The n-type dopant was Si or Se, the growth temperature was 450~700℃, and the thickness was 20nm~500nm.

[0029] An n-type doped GaInAs buffer layer was grown on a GaInP nucleation layer using MOCVD technology. The n-type dopant was Si or Se, the growth temperature was 500~750℃, and the thickness was 100nm~2000nm.

[0030] The first tunnel junction was grown on the GaInAs buffer layer using MOCVD technology, with Se or Te as the n-type dopant and Zn or C as the p-type dopant, and the growth temperature was 450~700℃.

[0031] A periodic lattice gradient buffer layer is grown on the first tunnel junction using MOCVD technology, with Zn or C as the p-type dopant and a doping concentration of 1×10⁻⁶. 17 cm -3 ~1×10 19 cm -3 The growth temperature is 600~750℃;

[0032] A p-type doped periodic overshoot layer was grown on a periodic lattice gradient buffer layer using MOCVD technology. The p-type dopant was Zn or C, and the doping concentration was 1×10⁻⁶. 17 cm -3 ~1×10 19 cm -3 The growth temperature is 600~750℃;

[0033] Ga was grown on a periodic overshoot layer using MOCVD technology. 1-h In h As sub-cells, with n-type dopant Si or Se and p-type dopant Zn or C, and growth temperature of 600~750℃;

[0034] Using MOCVD technology in Ga 1-h In h The second tunnel junction is grown on the As sub-cell, with the n-type dopant being Se or Te and the p-type dopant being Zn or C, and the growth temperature being 450~700℃.

[0035] (AlGa) was grown on the second tunnel junction using MOCVD technology. 1-i In i As sub-cells, with n-type dopant Si or Se and p-type dopant Zn or C, and growth temperature of 600~700℃;

[0036] Using MOCVD technology in (AlGa) 1-i In i Ga grown on As sub-cell 1-j In j The As cap layer has an n-type dopant of Si or Se and a growth temperature of 600~700℃.

[0037] The upper metal electrode, lower metal electrode, and antireflective coating of the battery are prepared.

[0038] The beneficial effects of this invention are as follows: By adopting a periodic lattice gradient buffer layer design with non-monotonic, segmented In composition, the large lattice mismatch stress between the germanium substrate and the intermediate sub-cell is precisely controlled and efficiently relaxed. This effectively suppresses the significant epitaxial wafer warpage caused by traditional linearly gradient In composition buffer layers, thus ensuring the uniformity of the epitaxial material and the yield of subsequent device processes. In terms of optical function, the composite structure composed of multiple buffer layers works synergistically to function as a Bragg mirror. By decomposing the broad-spectrum reflection requirement into multiple independent buffer layers with different band gaps and thicknesses, each layer can achieve high reflectivity within a specific narrow band gap. The superposition effect of their reflection spectra ultimately accurately covers and matches the absorption spectrum range of the intermediate sub-cell. This design avoids the contradiction of a single reflective layer reducing reflectivity due to the pursuit of broad-spectrum coverage, and efficiently recovers the medium and long-wavelength photons transmitted due to the limited thickness of the intermediate sub-cell. This significantly improves the spectral utilization rate and the current matching between the sub-cells, thereby systematically improving the overall photoelectric conversion efficiency of the battery. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the triple-junction gallium arsenide solar cell based on a germanium substrate according to the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Reference Appendix Figure 1 This invention provides a triple-junction gallium arsenide solar cell based on a germanium substrate and its fabrication method. To concisely and clearly introduce the technical solution of this invention, the following will describe each structural layer in the solar cell in the order of design and fabrication.

[0042] In the triple-junction gallium arsenide solar cell based on a germanium substrate provided in this embodiment, the solar cell sequentially includes, along its thickness direction: a germanium substrate, a GaInP nucleation layer, a GaInAs buffer layer, a first tunnel junction, multiple periodic lattice gradient buffer layers, a periodic overshoot layer, and a Ga... 1-h In h As subcell, second tunnel junction, (AlGa) 1-i In i P-cells, Ga 1-j In j As cap layer, germanium substrate and Ga 1-j Inj The As cap layer is provided with a lower metal electrode and an upper metal electrode respectively; each periodic structure lattice gradient buffer layer has a different In composition. From the first tunnel junction to the periodic structure overpass layer, there is at least one place where the In composition between adjacent periodic structure lattice gradient buffer layers increases, and there is at least one place where the In composition between adjacent periodic structure lattice gradient buffer layers decreases.

[0043] By adopting the above technical solution, multiple periodic lattice gradient buffer layers with non-monotonic In composition changes are introduced on the germanium substrate in a specific order, which effectively controls the lattice mismatch stress. This design can disperse and relax the stress accumulated during the growth process by varying the In composition at least once and at least once, thereby significantly suppressing the warping of the epitaxial wafer and ensuring the uniformity of thickness, composition and doping of the subsequent epitaxial layer structure and the quality of the material, laying the foundation for the consistency of the final solar cell performance.

[0044] More preferably, the number of periodic lattice gradient buffer layers is ≥6, the lattice constant of the periodic lattice gradient buffer layer adjacent to the first tunnel junction is ≥ the lattice constant of the germanium substrate, and the lattice constant of the periodic lattice gradient buffer layer adjacent to the periodic overshoot layer is = Ga 1-h In h The lattice constant of the As sub-cell; in this technical solution, multiple periodic lattice-gradient buffer layers not only buffer lattice mismatch and release structural stress, but also each periodic lattice-gradient buffer layer has a different In composition and the thickness of each layer can be independently adjusted, thus jointly constituting a distributed Bragg reflector. The synergistic combination of the reflection spectra of its sub-reflectors can cover Ga 1-h In h The absorption spectrum range of As sub-cells.

[0045] This preferred scheme achieves a synergistic design for stress relaxation and optical functionality by setting at least six layers of periodically structured lattice-gradient buffer layers: structurally, the multi-level design ensures that the lattice constant changes from the germanium substrate to Ga... 1-h In h The nonlinear gradient of the As sub-cell provides a sufficient transition, achieving gradual stress release and warpage suppression. Optically, this numerical design allows multiple sub-mirror units to handle the broad-spectrum reflection task independently. Each sub-mirror unit is precisely designed to achieve high reflectivity within a narrow bandgap through its specific In composition and independently adjustable thickness. These narrow-band reflection spectra are synergistically superimposed, ultimately resulting in Ga... 1-h In h As-based cells exhibit a broadband response with high reflectivity across the entire absorption spectrum, effectively recovering unabsorbed photons and improving the cell's photoelectric conversion efficiency.

[0046] As a non-limiting example, this embodiment describes an implementation comprising six periodic structure lattice gradient buffer layers, namely: from the first tunnel junction to the periodic structure overpass layer, the periodic structure lattice gradient buffer layers sequentially include a first periodic structure lattice gradient buffer layer, a second periodic structure lattice gradient buffer layer, a third periodic structure lattice gradient buffer layer, a fourth periodic structure lattice gradient buffer layer, a fifth periodic structure lattice gradient buffer layer, and a sixth periodic structure lattice gradient buffer layer, wherein the In composition content is: first periodic structure lattice gradient buffer layer > 0, second periodic structure lattice gradient buffer layer > first periodic structure lattice gradient buffer layer, first periodic structure lattice gradient buffer layer < third periodic structure lattice gradient buffer layer < second periodic structure lattice gradient buffer layer, fourth periodic structure lattice gradient buffer layer > second periodic structure lattice gradient buffer layer, second periodic structure lattice gradient buffer layer < fifth periodic structure lattice gradient buffer layer < fourth periodic structure lattice gradient buffer layer, and sixth periodic structure lattice gradient buffer layer ≥ fourth periodic structure lattice gradient buffer layer.

[0047] When this battery is fabricated using MOCVD technology:

[0048] The germanium substrate is p-type, and the GaInP nucleation layer is n-type doped. The n-type dopant is Si or Se. The growth temperature is 450~700℃ and the thickness is 20nm~500nm. Due to their high diffusion coefficient and solubility, the phosphorus atoms in the nucleation layer diffuse significantly to the upper surface of the p-type germanium substrate, forming an n-type doped layer near the surface of the germanium substrate, thus forming a germanium sub-cell with the p-type germanium substrate.

[0049] The GaInAs buffer layer is n-type doped, with Si or Se as the n-type dopant. The growth temperature is 500~750℃ and the thickness is 100nm~2000nm.

[0050] The first tunnel junction comprises an n-type doped GaAs layer and a p-type doped AlGaAs layer, wherein the n-type dopant of the GaAs layer is Se or Te, and the doping concentration is 1 × 10⁻⁶. 19 ~1×10 21 cm -3 The thickness ranges from 5 nm to 50 nm, and the p-type dopant of the AlGaAs layer is Zn or C, with a doping concentration of 1 × 10⁻⁶. 19 ~1×10 21 cm -3 The thickness is 5nm~50nm; the growth temperature of the first tunnel junction is 450~700℃.

[0051] The first-period lattice gradient buffer layer consists of multiple (AlGa) layers with an In composition of a. 1-a In a As / Ga 1-a In aAs is a periodic structure, a > 0; (AlGa) 1-a In a As / Ga 1-a In a The periodicity of As periodic structures ranges from 2 to 30, each (AlGa) 1-a In a As / Ga 1-a In a In the periodic structure of As: (AlGa) 1-a In a The thickness of As is 2nm~300nm, Ga 1-a In a The thickness of As ranges from 2nm to 300nm.

[0052] The second-period lattice gradient buffer layer consists of multiple (AlGa) layers with an In composition of b. 1-b In b As / Ga 1-b In b As is a periodic structure, b > a; (AlGa) 1-b In b As / Ga 1-b In b The periodicity of As periodic structures ranges from 2 to 30, each (AlGa) 1-b In b As / Ga 1-b In b In the periodic structure of As: (AlGa) 1-b In b The thickness of As is 2nm~300nm, Ga 1-b In b The thickness of As ranges from 2nm to 300nm.

[0053] The third-period lattice gradient buffer layer consists of multiple (AlGa) layers with In composition of c. 1-c In c As / Ga 1-c In c As is a periodic structure, a < c < b; (AlGa) 1-c In c As / Ga 1-c In c The periodicity of As periodic structures ranges from 2 to 30, each (AlGa) 1- c In c As / Ga 1-c In c In the periodic structure of As: (AlGa) 1-c In cThe thickness of As is 2nm~300nm, Ga 1-c In c The thickness of As ranges from 2nm to 300nm.

[0054] The fourth-period lattice gradient buffer layer consists of multiple (AlGa) layers with In composition of d. 1-d In d As / Ga 1-d In d As is a periodic structure, d > b; (AlGa) 1-d In d As / Ga 1-d In d The periodicity of As periodic structures ranges from 2 to 30, each (AlGa) 1-d In d As / Ga 1-d In d In the periodic structure of As: (AlGa) 1-d In d The thickness of As is 2nm~300nm, Ga 1-d In d The thickness of As ranges from 2nm to 300nm.

[0055] The fifth-period lattice gradient buffer layer consists of multiple (AlGa) layers with In composition of e. 1-e In e As / Ga 1-e In e As is a periodic structure, b < e < d; (AlGa) 1-e In e As / Ga 1-e In e The periodicity of As periodic structures ranges from 2 to 30, each (AlGa) 1- e In e As / Ga 1-e In e In the periodic structure of As: (AlGa) 1-e In e The thickness of As is 2nm~300nm, Ga 1-e In e The thickness of As ranges from 2nm to 300nm.

[0056] The sixth-period lattice gradient buffer layer consists of multiple (AlGa) layers with an In composition of f. 1-f In f As / Ga 1-f In f As a periodic structure, f = h ≥ d; (AlGa) 1-f Inf As / Ga 1-f In f The periodicity of As periodic structures ranges from 2 to 30, each (AlGa) 1- f In f As / Ga 1-f In f In the periodic structure of As: (AlGa) 1-f In f The thickness of As is 2nm~300nm, Ga 1-f In f The thickness of As ranges from 2nm to 300nm.

[0057] In this embodiment, all of the aforementioned periodic lattice gradient buffer layers are p-type doped, with Zn or C as the p-type dopant and a doping concentration of 1×10⁻⁶. 17 cm -3 ~1×10 19 cm -3 The growth temperature is 600~750℃.

[0058] The periodic overshoot layer is composed of multiple In-part (AlGa) layers with an In composition of g. 1-g In g As / Ga 1-g In g For an As periodic structure, the In composition is greater than or equal to the In composition of the lattice-gradient buffer layer of the sixth periodic structure, i.e., g ≥ f = h, thus making the lattice constant of the overshoot layer of the periodic structure ≥ (AlGa). 1-i In i The lattice constant of the p-cell plays a role in stress regulation; (AlGa) 1-g In g As / Ga 1-g In g The periodicity of As periodic structures ranges from 2 to 40, each (AlGa) 1-g In g As / Ga 1-g In g In the periodic structure of As: (AlGa) 1-g In g The thickness of As is 5nm~300nm, Ga 1-g In g The thickness of As ranges from 5nm to 300nm.

[0059] In this embodiment, the periodic overshoot layer is p-type doped, and the p-type dopant is Zn or C with a doping concentration of 1×10⁻⁶. 17 cm -3 ~1×10 19 cm-3 The growth temperature is 600~750℃.

[0060] Ga 1-h In h As sub-cells include p-type doped Ga atoms distributed sequentially along the cell thickness direction. 1-h In h The growth process consists of an As-based layer, an unintentionally doped i-layer, and an n-type doped emitter layer, with 0 < h ≤ 0.5 and a growth temperature of 600~750℃; where:

[0061] Ga 1-h In h The p-type dopant of the As base layer is Zn or C, with a doping concentration of 1 × 10⁻⁶. 16 cm -3 ~1×10 19 cm -3 The thickness ranges from 30nm to 5000nm;

[0062] Ga 1-h In h The unintentionally doped i-layer in the As sub-cell is Ga 1-h In h As material or Ga 1-x In x P material, with a thickness of 10nm~1000nm, 0.4≤x<1;

[0063] Ga 1-h In h The emitter layer of the As sub-cell is Ga 1-h In h As material or Ga 1-x In x P material, wherein the n-type dopant is Si or Se, and the doping concentration is 1×10⁻⁶. 16 cm -3 ~1×10 19 cm -3 The thickness is 30nm~5000nm, and 0.4≤x<1.

[0064] The second tunnel junction comprises an n-type doped AlGaInP layer and a p-type doped AlGaInAs layer, wherein the n-type dopant of the AlGaInP layer is Se or Te, and the doping concentration is 1 × 10⁻⁶. 19 ~1×10 21 cm -3 The AlGaInAs layer has a thickness of 5nm to 50nm, and the p-type dopant is Zn or C with a doping concentration of 1×10⁻⁶. 19 ~1×10 21 cm -3The thickness is 5nm~50nm. The growth temperature of the second tunnel junction is 450~700℃.

[0065] (AlGa) 1-i In i A p-type solar cell consists of a p-type doped base layer, an unintentionally doped i-layer, and an n-type doped emitter layer, where 0.4 ≤ i < 1, and the growth temperature is 600~750℃; where:

[0066] (AlGa) 1-i In i The base layer of the p-type cell: the p-type dopant is Zn or C, with a doping concentration of 1×10⁻⁶. 16 cm -3 ~1×10 19 cm -3 The thickness ranges from 30nm to 5000nm;

[0067] (AlGa) 1-i In i The thickness of the unintentionally doped i-layer in a P-sub-cell is 10 nm to 1000 nm.

[0068] (AlGa) 1-i In i The emitter layer of the p-cell: the n-type dopant is Si or Se, with a doping concentration of 1×10⁻⁶. 16 cm -3 ~1×10 19 cm -3 The thickness ranges from 30nm to 5000nm.

[0069] Ga 1-j In j In the As cap layer, 0 < j ≤ 0.5, this layer is n-type doped, and its n-type dopant is Si or Se, with a doping concentration of 1 × 10⁻⁶. 18 cm -3 ~1×10 21 cm -3 The thickness ranges from 50nm to 500nm. Ga 1-j In j The growth temperature of the As cap layer is 600~750℃.

[0070] After the above epitaxial structures are prepared sequentially using MOVCD technology, the upper metal electrode, lower metal electrode, and antireflection film of the battery can be prepared according to known battery device processes.

[0071] The beneficial effects of this invention include at least the following: By employing a non-monotonic, segmented, periodic lattice-gradient buffer layer design with a non-monotonic In composition, the invention achieves precise control and efficient relaxation of the large lattice mismatch stress between the germanium substrate and the intermediate sub-cell, effectively suppressing the significant epitaxial wafer warpage caused by traditional linearly graded In composition buffer layers, thereby ensuring the uniformity of the epitaxial material and the yield of subsequent device processes. In terms of optical function, the composite structure composed of multiple buffer layers works synergistically to function as a Bragg mirror. By decomposing the broad-spectrum reflection requirement into multiple independent buffer layers with different band gaps and thicknesses, each layer can achieve high reflectivity within a specific narrow band gap. The superposition effect of their reflection spectra ultimately accurately covers and matches the absorption spectrum range of the intermediate sub-cell. This design avoids the contradiction of a single reflective layer reducing reflectivity due to the pursuit of broad-spectrum coverage, and efficiently recovers the medium- and long-wavelength photons transmitted due to the limited thickness of the intermediate sub-cell, significantly improving spectral utilization and current matching between sub-cells, thereby systematically improving the overall photoelectric conversion efficiency of the battery.

[0072] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the claims, or equivalent forms of such scope and boundaries.

Claims

1. A triple-junction gallium arsenide solar cell based on a germanium substrate, characterized in that, Along the thickness direction of the solar cell, it sequentially comprises: a germanium substrate, a GaInP nucleation layer, a GaInAs buffer layer, a first tunnel junction, multiple periodic lattice gradient buffer layers, a periodic overshoot layer, and Ga... 1-h In h As subcell, second tunnel junction, (AlGa) 1-i In i P-cells, Ga 1-j In j As cap layer, the germanium substrate and the Ga 1-j In j The As cap layer is provided with a lower metal electrode and an upper metal electrode respectively; 0 < h ≤ 0.5, 0.4 ≤ i < 1, 0 < j ≤ 0.5; each of the periodic structure lattice gradient buffer layers has a different In composition, from the first tunnel junction to the periodic structure overpass layer, there is at least one place where the In composition between adjacent periodic structure lattice gradient buffer layers increases, and there is at least one place where the In composition between adjacent periodic structure lattice gradient buffer layers decreases.

2. The triple-junction gallium arsenide solar cell based on a germanium substrate according to claim 1, characterized in that, The number of periodic structure lattice gradient buffer layers is ≥6, the lattice constant of the periodic structure lattice gradient buffer layer adjacent to the first tunnel junction is ≥ the lattice constant of the germanium substrate, and the lattice constant of the periodic structure lattice gradient buffer layer adjacent to the periodic structure overshoot layer is = the Ga 1-h In h The lattice constant of an As subcell.

3. The triple-junction gallium arsenide solar cell based on a germanium substrate according to claim 2, characterized in that, From the first tunnel junction to the periodic structure overpass layer, the periodic structure lattice gradient buffer layer sequentially includes a first periodic structure lattice gradient buffer layer, a second periodic structure lattice gradient buffer layer, a third periodic structure lattice gradient buffer layer, a fourth periodic structure lattice gradient buffer layer, a fifth periodic structure lattice gradient buffer layer, and a sixth periodic structure lattice gradient buffer layer, wherein the In composition content is: first periodic structure lattice gradient buffer layer > 0, second periodic structure lattice gradient buffer layer > first periodic structure lattice gradient buffer layer, first periodic structure lattice gradient buffer layer < third periodic structure lattice gradient buffer layer < second periodic structure lattice gradient buffer layer, fourth periodic structure lattice gradient buffer layer > second periodic structure lattice gradient buffer layer, second periodic structure lattice gradient buffer layer < fifth periodic structure lattice gradient buffer layer < fourth periodic structure lattice gradient buffer layer, and sixth periodic structure lattice gradient buffer layer ≥ fourth periodic structure lattice gradient buffer layer.

4. The triple-junction gallium arsenide solar cell based on a germanium substrate according to claim 3, characterized in that, The first-period lattice gradient buffer layer consists of multiple (AlGa) layers with an In composition of a. 1-a In a As / Ga 1-a In a As a periodic structure, with 2 to 30 periods, each (AlGa) 1-a In a As / Ga 1-a In a In the periodic structure of As: (AlGa) 1-a In a The thickness of As is 2nm~300nm, Ga 1- a In a The thickness of As is 2nm~300nm; The second-period lattice gradient buffer layer consists of multiple (AlGa) layers with an In composition of b. 1-b In b As / Ga 1-b In b As a periodic structure, with 2 to 30 periods, each (AlGa) 1-b In b As / Ga 1-b In b In the periodic structure of As: (AlGa) 1-b In b The thickness of As is 2nm~300nm, Ga 1-b In b The thickness of As is 2nm~300nm; The third-period lattice gradient buffer layer consists of multiple (AlGa) layers with an In composition of C. 1-c In c As / Ga 1-c In c As a periodic structure, with 2 to 30 periods, each (AlGa) 1-c In c As / Ga 1-c In c In the periodic structure of As: (AlGa) 1-c In c The thickness of As is 2nm~300nm, Ga 1-c In c The thickness of As is 2nm~300nm; The fourth-period lattice gradient buffer layer consists of multiple (AlGa) layers with an In composition of d. 1-d In d As / Ga 1-d In d As a periodic structure, with 2 to 30 periods, each (AlGa) 1-d In d As / Ga 1-d In d In the periodic structure of As: (AlGa) 1-d In d The thickness of As is 2nm~300nm, Ga 1-d In d The thickness of As is 2nm~300nm; The fifth-period lattice gradient buffer layer consists of multiple (AlGa) layers with an In composition of e. 1-e In e As / Ga 1-e In e As a periodic structure, with 2 to 30 periods, each (AlGa) 1-e In e As / Ga 1-e In e In the periodic structure of As: (AlGa) 1-e In e The thickness of As is 2nm~300nm, Ga 1-e In e The thickness of As is 2nm~300nm; The sixth-period lattice gradient buffer layer consists of multiple (AlGa) layers with an In composition of f. 1-f In f As / Ga 1-f In f As a periodic structure, with 2 to 30 periods, each (AlGa) 1-f In f As / Ga 1-f In f In the periodic structure of As: (AlGa) 1-f In f The thickness of As is 2nm~300nm, Ga 1-f In f The thickness of As ranges from 2nm to 300nm.

5. The triple-junction gallium arsenide solar cell based on a germanium substrate according to any one of claims 2-4, characterized in that, The lattice constant of the periodic structure lattice gradient buffer layer adjacent to the periodic structure overshoot layer is less than or equal to the lattice constant of the periodic structure overshoot layer.

6. The triple-junction gallium arsenide solar cell based on a germanium substrate according to claim 5, characterized in that, The periodic overshoot layer comprises multiple (AlGa) layers with an In composition of g. 1-g In g As / Ga 1-g In g As a periodic structure, with 2 to 40 periods, each (AlGa) 1-g In g As / Ga 1-g In g In the periodic structure of As: (AlGa) 1-g In g The thickness of As is 5nm~300nm, Ga 1-g In g The thickness of As ranges from 5nm to 300nm.

7. The triple-junction gallium arsenide solar cell based on a germanium substrate according to claim 6, characterized in that, The Ga 1- h In h As sub-cells include p-type doped Ga. 1-h In h The system consists of an As base layer, an unintentionally doped i-layer, and an n-type doped emitter layer, wherein: Ga 1-h In h As base layer: doping concentration is 1×10 16 cm -3 ~1×10 19 cm -3 The thickness ranges from 30nm to 5000nm; The unintentionally doped i-layer is Ga 1-h In h As material or Ga 1-x In x P material, with a thickness of 10nm~1000nm; The emitter layer is Ga 1-h In h As material or Ga 1-x In x P material, with a doping concentration of 1×10⁻⁶ 16 cm -3 ~1×10 19 cm -3 The thickness is 30nm~5000nm, and 0.4≤x<1.

8. The triple-junction gallium arsenide solar cell based on a germanium substrate according to any one of claims 1-4 and 6-7, characterized in that, The (AlGa) 1-i In i A p-type sub-cell consists of a p-type doped base layer, an unintentionally doped i-layer, and an n-type doped emitter layer, wherein: Base layer: doping concentration of 1×10 16 cm -3 ~1×10 19 cm -3 The thickness ranges from 30nm to 5000nm; The thickness of the unintentionally doped i-layer is 10 nm to 1000 nm; Emitter layer: doping concentration of 1×10 16 cm -3 ~1×10 19 cm -3 The thickness ranges from 30nm to 5000nm.

9. The triple-junction gallium arsenide solar cell based on a germanium substrate according to claim 8, characterized in that, The Ga 1- j In j The As cap layer is n-type doped with a doping concentration of 1×10⁻⁶. 18 cm -3 ~1×10 21 cm -3 The thickness is 50nm~500nm; the first tunnel junction includes an n-type doped GaAs layer and a p-type doped AlGaAs layer, wherein the doping concentration of the GaAs layer is 1×10⁻⁶. 19 ~1×10 21 cm -3 The thickness ranges from 5 nm to 50 nm, and the doping concentration of the AlGaAs layer is 1 × 10⁻⁶. 19 ~1×10 21 cm -3 The thickness is 5nm~50nm; The second tunnel junction comprises an n-type doped AlGaInP layer and a p-type doped AlGaInAs layer, wherein the doping concentration of the AlGaInP layer is 1 × 10⁻⁶. 19 ~1×10 21 cm -3 The thickness ranges from 5 nm to 50 nm, and the doping concentration of the AlGaInAs layer is 1 × 10⁻⁶. 19 ~1×10 21 cm -3 The thickness is 5nm~50nm.

10. A method for preparing a triple-junction gallium arsenide solar cell based on a germanium substrate as described in any one of claims 1-9, characterized in that, Including the following steps: An n-type doped GaInP nucleation layer was grown on a p-type germanium substrate using MOCVD technology. The n-type dopant was Si or Se, the growth temperature was 450~700℃, and the thickness was 20nm~500nm. An n-type doped GaInAs buffer layer was grown on a GaInP nucleation layer using MOCVD technology. The n-type dopant was Si or Se, the growth temperature was 500~750℃, and the thickness was 100nm~2000nm. The first tunnel junction was grown on the GaInAs buffer layer using MOCVD technology, with Se or Te as the n-type dopant and Zn or C as the p-type dopant, and the growth temperature was 450~700℃. A periodic lattice gradient buffer layer is grown on the first tunnel junction using MOCVD technology, with Zn or C as the p-type dopant and a doping concentration of 1×10⁻⁶. 17 cm -3 ~1×10 19 cm -3 The growth temperature is 600~750℃; A p-type doped periodic overshoot layer was grown on a periodic lattice gradient buffer layer using MOCVD technology. The p-type dopant was Zn or C, and the doping concentration was 1×10⁻⁶. 17 cm -3 ~1×10 19 cm -3 The growth temperature is 600~750℃; Ga was grown on a periodic overshoot layer using MOCVD technology. 1-h In h As sub-cells, with n-type dopant Si or Se and p-type dopant Zn or C, and growth temperature of 600~750℃; Using MOCVD technology in Ga 1-h In h The second tunnel junction is grown on the As sub-cell, with the n-type dopant being Se or Te and the p-type dopant being Zn or C, and the growth temperature being 450~700℃. (AlGa) was grown on the second tunnel junction using MOCVD technology. 1-i In i As sub-cells, with n-type dopant Si or Se and p-type dopant Zn or C, and growth temperature of 600~700℃; Using MOCVD technology in (AlGa) 1-i In i Ga grown on As sub-cell 1-j In j The As cap layer has an n-type dopant of Si or Se and a growth temperature of 600~700℃. The upper metal electrode, lower metal electrode, and antireflective coating of the battery are prepared.

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