Gallium arsenide solar cell with germanium substrate

Abstract

The gallium arsenide solar cell sequentially comprises the germanium substrate, a GaInP nucleating layer, a GaInAs buffer layer, a first tunnel junction, a (AlGa) 1-a InaAs / Ga1-a InaAs periodic structure lattice gradient buffer layer, a (AlGa) 1-b InbAs / Ga1-b InbAs periodic structure overshoot layer, a Ga1-cIncAs sub-cell, a second tunnel junction, a (AlGa) 1-d IndP sub-cell and a Ga1-eIneAs cap layer from bottom to top. And a lower electrode and an upper electrode are respectively arranged on the germanium substrate and the Ga1-eIneAs cap layer. By adopting the technical scheme, the gallium arsenide solar cell based on the germanium substrate can utilize the solar spectrum more efficiently, the photoelectric conversion efficiency is improved, and the gallium arsenide solar cell has better anti-radiation performance.

Description

Technical Field

[0001] The invention belongs to the field of solar cells, and in particular relates to a gallium arsenide solar cell with a germanium substrate. Background Art

[0002] Compared with traditional single-crystal silicon solar cells for space use, gallium arsenide solar cells based on germanium substrates have the advantages of high conversion efficiency, high temperature resistance, radiation resistance, and strong reliability. They have been widely used in primary power supplies for spacecraft, greatly improving the payload capacity and on-orbit life of spacecraft. At present, the most mature space solar cell products are germanium-based triple-junction solar cells, with a band gap distribution of 1.9 / 1.4 / 0.67eV. Due to the large band gap difference between the 1.4eV middle cell and the 0.67eV germanium sub-cell, the output current of each sub-cell does not match, limiting the further improvement of the cell conversion efficiency. In order to obtain higher conversion efficiency, the design of solar cells needs to further consider spectral matching.

[0003] By lowering the band gap of the 1.4eV middle cell and minimizing the large band gap difference between the middle cell and the 0.67eV germanium sub-cell, a 1.8 / 1.2 / 0.67eV triple-junction solar cell with a more reasonable band gap distribution is formed. This can more efficiently utilize the medium and long wavelength photons originally absorbed by the Ge sub-cell, improve the solar cell's utilization of the AM0 spectrum, and thus improve the solar cell's photoelectric conversion efficiency. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a gallium arsenide solar cell with a germanium substrate, which has the advantages of high photoelectric conversion efficiency and good radiation resistance.

[0005] The present invention is implemented as follows: a gallium arsenide solar cell with a germanium substrate comprises, from bottom to top, a germanium substrate, a GaInP nucleation layer, a GaInAs buffer layer, a first tunneling junction, and an (AlGa) 1-a In a As / Ga 1-a In a As periodic structure lattice gradient buffer layer, (AlGa) 1-b In b As / Ga 1-b In b As periodic structure overshoot layer, Ga 1-c In c As subcell, second tunnel junction, (AlGa) 1-d In d P sub-cell, Ga 1-e In e As cap layer. The germanium substrate and Ga 1-e In eA lower electrode and an upper electrode are respectively arranged on the As cap layer.

[0006] The (AlGa) 1-a In a As / Ga 1-a In a The In component of the As periodic structure lattice gradient buffer layer changes gradually from 0 to c, that is, its lattice constant changes from matching the germanium substrate to matching the Ga 1-c In c As subcells match, and the number of cycles of the structure ranges from 2 to 60, which plays a role in reflecting and transmitting Ga 1-c In c The role of photons in the As subcell, in each cycle (AlGa) 1-a In a The thickness of As is 5nm-300nm, Ga 1-a In a The thickness of As is 5nm-300nm.

[0007] The (AlGa) 1-b In b As / Ga 1-b In b The In content of the overshoot layer of the As periodic structure is greater than that of the Ga 1-c In c The In component of the As subcell, i.e. b ≥ c, plays a role in stress regulation. At the same time, the number of cycles of the structure ranges from 2 to 40, which plays a role in reflecting and transmitting Ga 1-c In c The role of photons in the As subcell, in each cycle (AlGa) 1-b In b The thickness of As is 5nm-300nm, Ga 1-b In b The thickness of As is 5nm-300nm.

[0008] The Ga 1-c In c The As subcell includes p-type doped Ga 1-c In c As base layer, unintentionally doped i layer and n-type doped emitter layer, of which Ga 1-c In c As base layer: 0<c≤0.5, doping concentration 1×10 16 cm -3 -1×10 19 cm -3 , thickness 30nm-5000nm; the unintentionally doped i layer can be Ga 1-c In cAs or Ga 1-x In x P material, 0.4≤x<1, thickness 10nm-1000nm; the emission layer can be Ga 1-c In c As or Ga 1-x In x P material, 0.4≤x<1, doping concentration 1×10 16 cm -3 -1×10 19 cm -3 , thickness 30nm-5000nm.

[0009] The (AlGa) 1-d In d The P subcell includes a p-type doped base layer, an unintentionally doped i layer, and an n-type doped emitter layer, where 0.4≤d<1, and the base layer doping concentration is 1×10 16 cm -3 -1×10 19 cm -3 , thickness 30nm-5000nm; thickness of the unintentionally doped i layer 10nm-1000nm; doping concentration of the emitter layer 1×10 16 cm -3 -1×10 19 cm -3 , thickness 30nm-5000nm.

[0010] The cap layer is n-type doped Ga 1-e In e As, where 0<e≤0.5, the doping concentration is 1×10 18 -1×10 21 cm -3 , thickness range is 50nm-500nm.

[0011] Compared with the prior art, the present invention has the following advantages and beneficial effects: the gallium arsenide solar cell on the germanium substrate of the present invention uses a periodic structure lattice gradient buffer layer to achieve a gradual enlargement of the lattice constant, and then prepares a periodic structure overshoot layer to play a role in stress regulation. At the same time, the periodic structure lattice gradient buffer layer and the periodic structure overshoot layer together play the role of a distributed Bragg reflector. On this basis, the GaInAs subcell and (AlGa) 1-h In h P-cells enable the growth of high-quality epitaxial materials and improve the conversion efficiency of solar cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a schematic diagram of a gallium arsenide solar cell with a germanium substrate according to the present invention. DETAILED DESCRIPTION

[0013] In order to further understand the content, features and effects of the present invention, the following examples are given, but the implementation of the present invention is not limited thereto, and the details are as follows:

[0014] This embodiment is a gallium arsenide solar cell with a germanium substrate, comprising the following steps:

[0015] like Figure 1 The schematic diagram of the GaAs solar cell on the germanium substrate of the present invention is shown. The GaInP nucleation layer, GaInAs buffer layer, first tunnel junction,

[0016] (AlGa) 1-a In a As / Ga 1-a In a As periodic structure lattice gradient buffer layer, (AlGa) 1-b In b As / Ga 1-b In b As periodic structure overshoot layer, Ga 1-c In c As subcell, second tunnel junction, (AlGa) 1-d In d P sub-cell, Ga 1-e In e As cap layer.

[0017] GaInP nucleation layer, whose n-type dopant is Si or Se, has a growth temperature of 450–700°C and a thickness range of 20-500nm. The n-type Ge layer is formed by the diffusion of phosphorus atoms in the nucleation layer, and forms a germanium subcell with the p-type germanium substrate;

[0018] GaInAs buffer layer, whose n-type dopant is Si or Se, grown at 500–750°C and with a thickness range of 100–2000 nm;

[0019] The first tunnel junction includes an n-type doped GaAs layer and a p-type doped AlGaAs layer, wherein the dopant of the GaAs layer is Se or Te with a doping concentration of 1×10 19 -1×10 21 cm -3 , with a thickness range of 5nm-50nm and a growth temperature of 450–700°C; the dopant of the AlGaAs layer is Zn or C with a doping concentration of 1×10 19 -1×10 21 cm -3 , thickness range is 5nm-50nm, and growth temperature is 450–700℃;

[0020] (AlGa) 1-a In a As / Ga 1-a In a The In component of the As periodic structure lattice gradient buffer layer changes gradually from 0 to c, p-type doping, and the doping concentration is 1×10 17 cm -3 -1×10 19 cm -3 The growth temperature is 600–750°C, and the lattice constant changes from matching the germanium substrate to matching the Ga 1-c In c As subcells match. At the same time, the number of cycles of the structure ranges from 2 to 60, and in each cycle (AlGa) 1-a In a The thickness of As is 5nm-300nm, Ga 1-a In a As has a thickness of 5nm-300nm and can reflect and transmit Ga 1-c In c The photons of the As sub-cell are reabsorbed by the junction sub-cell, thereby improving the quantum efficiency and radiation resistance of the sub-cell.

[0021] (AlGa) 1-b In b As / Ga 1-b In b As first periodic structure overshoot layer, doping concentration is 1×10 17 -1×10 19 cm -3 , the growth temperature is 600–750°C, and its In component is greater than Ga 1-c In c The In component of the As subcell, i.e. b ≥ c, plays a role in stress regulation. At the same time, the number of cycles of the structure ranges from 2 to 40, and in each cycle (AlGa) 1-b In b The thickness of As is 5nm-300nm, Ga 1-b In b As has a thickness of 5nm-300nm and can reflect and transmit Ga 1-c In c The photons of the As sub-cell are reabsorbed by the junction sub-cell, thereby improving the quantum efficiency and radiation resistance of the sub-cell.

[0022] Ga 1-c In c The As subcell includes p-type doped Ga 1-c In cAs base layer, unintentionally doped i layer and n-type doped emitter layer, of which Ga 1-c In c As base layer: 0<c≤0.5, doping concentration 1×10 16 cm -3 -1×10 19 cm -3 , thickness 30nm-5000nm; the unintentionally doped i layer can be Ga 1-c In c As or Ga 1-x In x P material, 0.4≤x<1, thickness 10nm-1000nm; the emission layer can be Ga 1-c In c As or Ga 1-x In x P material, 0.4≤x<1, doping concentration 1×10 16 cm -3 -1×10 19 cm -3 , thickness 30nm-5000nm.

[0023] The second tunnel junction includes an n-type doped AlGaInP layer and a p-type doped AlGaInAs layer, wherein the dopant of the AlGaInP layer is Se or Te, and the doping concentration is 1×10 19 -1×10 21 cm -3 , with a thickness range of 5nm-50nm and a growth temperature of 450–700°C; the dopant of the AlGaInAs layer is Zn or C with a doping concentration of 1×10 19 -1×10 21 cm -3 , thickness range is 5nm-50nm, and growth temperature is 450–700℃.

[0024] (AlGa) 1-d In d The P subcell includes a p-type doped base layer, an unintentionally doped i layer, and an n-type doped emitter layer, where 0.4≤d<1, and the base layer doping concentration is 1×10 16 cm -3 -1×10 19 cm -3 , thickness 30nm-5000nm; thickness of the unintentionally doped i layer 10nm-1000nm; doping concentration of the emitter layer 1×10 16 cm -3 -1×10 19 cm -3 , thickness 30nm-5000nm.

[0025] Ga 1-e In e The As cap layer is n-type doped, where 0<e≤0.5 and the doping concentration is 1×10 18 -1×10 21 cm -3 , thickness range is 50nm-500nm.

[0026] After the above structure is prepared by epitaxy, the upper and lower metal electrodes and the anti-reflection film of the battery are prepared according to the known battery device process.

[0027] By implementing the above steps, the preparation process of the gallium arsenide solar cell on the germanium substrate of the present invention is completed.

[0028] The solar cell prepared above can play a role in regulating stress under large lattice mismatch conditions through the periodic structure lattice gradient buffer layer and overshoot layer, which helps to reduce epitaxial warping, improve the relaxation degree of epitaxial materials, reduce the mismatch defect density, and improve the crystal quality of epitaxial materials. The improvement of the crystal quality of epitaxial materials has achieved an increase in the photoelectric conversion efficiency of solar cells, from the current typical efficiency of triple-junction solar cells of 32% to 34%. The following table is a comparison table of solar cell epitaxial materials and conversion efficiency before and after implementation.

[0029] Table 1 Comparison of solar cell epitaxial materials and conversion efficiency before and after implementation

[0030] Indicator parameter items Current typical product parameters Battery parameters of this patented structure Lattice mismatch 0.25％ 1.00％ Maximum epitaxial curvature <![CDATA[120km -1 ]]> <![CDATA[95km -1 ]]> Relaxation 95％ 99％ Conversion efficiency 32％ 34％

[0031] The above embodiment is one implementation mode of the present invention, but the implementation mode of the present invention is not limited to the said embodiment. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and shall be included in the protection scope of the present invention.

Claims

1. A gallium arsenide solar cell with a germanium substrate, characterized in that: From bottom to top, it includes: germanium substrate, GaInP nucleation layer, GaInAs buffer layer, first tunneling junction, (AlGa) 1-a In a As / Ga 1-a In a As periodic structure lattice gradient buffer layer, (AlGa) 1-b In b As / Ga 1-b In b As periodic structure overshoot layer, Ga 1-c In c As subcell, second tunnel junction, (AlGa) 1-d In d P sub-cell, Ga 1-e In e As cap layer, the Ge substrate and Ga 1-e In e The As cap layer is provided with a lower electrode and an upper electrode respectively.

2. The gallium arsenide solar cell with germanium substrate according to claim 1, characterized in that: The (AlGa) 1-a In a As / Ga 1-a In a The In component of the As periodic structure lattice gradient buffer layer changes gradually from 0 to c, that is, its lattice constant changes from matching the germanium substrate to matching the Ga 1-c In c As subcells are matched, and each gradient is composed of (AlGa) 1-a In a As / Ga 1-a In a As periodic structure, the number of periods ranges from 2 to 60, which plays a role in reflecting and transmitting Ga 1- c In c The role of photons in the As subcell, in each cycle (AlGa) 1-a In a The thickness of As is 5nm-300nm, Ga 1-a In a The thickness of As is 5nm-300nm.

3. The gallium arsenide solar cell with germanium substrate according to claim 1, characterized in that: The (AlGa) 1-b In b As / Ga 1-b In b The In content of the overshoot layer of the As periodic structure is greater than that of the Ga 1-c In c The In component of the As subcell, i.e., b ≥ c, plays a role in stress regulation. The number of cycles of the structure ranges from 2 to 40, which plays a role in reflecting and transmitting Ga 1-c In c The role of photons in the As subcell, in each cycle (AlGa) 1-b In b The thickness of As is 5nm-300nm, Ga 1-b In b The thickness of As is 5nm-300nm.

4. The gallium arsenide solar cell with germanium substrate according to claim 1, characterized in that: The Ga 1-c In c The As subcell includes p-type doped Ga 1-c In c As base layer, unintentionally doped i layer and n-type doped emitter layer, of which Ga 1-c In c As base layer: 0<c≤0.5, doping concentration 1×10 16 cm -3 -1×10 19 cm -3 , thickness 30nm-5000nm; the unintentionally doped i layer is Ga 1-c In c As or Ga 1-x In x P material, 0.4≤x<1, thickness 10nm-1000nm; the emission layer is Ga 1-c In c As or Ga 1- x In x P material, 0.4≤x<1, doping concentration 1×10 16 cm -3 -1×10 19 cm -3 , thickness 30nm-5000nm.

5. The gallium arsenide solar cell with germanium substrate according to claim 1, characterized in that: The (AlGa) 1-d In d The P subcell includes a p-type doped base layer, an unintentionally doped i layer, and an n-type doped emitter layer, where 0.4≤d<1, and the base layer doping concentration is 1×10 16 cm -3 -1×10 19 cm -3 , thickness 30nm-5000nm; thickness of the unintentionally doped i layer 10nm-1000nm; doping concentration of the emitter layer 1×10 16 cm -3 -1×10 19 cm -3 , thickness 30nm-5000nm.

6. The gallium arsenide solar cell with germanium substrate according to claim 1, characterized in that: The cap layer is n-type doped Ga 1-e In e As, where 0<e≤0.5, the doping concentration is 1×10 18 -1×10 21 cm -3 , thickness range is 50nm-500nm.

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