A dual-junction solar cell with improved photoelectric conversion efficiency and a method for manufacturing the same

Abstract

The application relates to the technical field of solar cells, in particular to a double-junction solar cell for improving photoelectric conversion efficiency and a preparation method thereof. The double-junction solar cell comprises, from bottom to top, a GaAs substrate, a GaAs buffer layer, a middle bottom tunnel junction, a DBR, a middle cell, a middle top tunnel junction, a top cell, and an ohmic contact layer. The middle cell comprises a middle cell base region, a middle cell emission region and a middle cell window layer. The materials of the middle cell base region and the middle cell emission region are different and form a heterojunction. The top cell comprises a back electric field, a top cell base region, a top cell emission region and a top cell window layer. The materials of the top cell base region and the top cell emission region are different and form a heterojunction. The solar cell has high lattice matching degree of epitaxial materials, low voltage loss, high anti-radiation performance, low cost, high power-to-mass ratio and is suitable for the field of spaceflight.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, specifically to a double-junction solar cell with improved photoelectric conversion efficiency and its fabrication method. Background Technology

[0002] Gallium arsenide (GaAs) solar cells, with their superior photoelectric conversion efficiency, excellent high-temperature resistance, and long lifespan, have demonstrated irreplaceable importance in space power applications such as satellites, spacecraft, and space laboratories. my country has already widely adopted these cells in this field. With the booming development of commercial spaceflight, more stringent requirements have been placed on the performance and cost of solar cells. The next generation of space-grade solar cells not only needs higher photoelectric conversion efficiency but also stronger resistance to radiation degradation, while simultaneously requiring lower production costs to facilitate large-scale use in commercial spaceflight.

[0003] Gallium arsenide double-junction solar cells, due to their shorter epitaxial growth time and fewer junctions, have a much lower production cost than triple-junction cells, making them advantageous for mass production in commercial spaceflight. However, the reduced number of junctions significantly lowers the photoelectric conversion efficiency of double-junction cells, failing to meet the high-efficiency requirements of space-grade solar cells. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a double-junction solar cell with improved photoelectric conversion efficiency and its fabrication method. This solar cell features high lattice matching of the epitaxial material, low voltage loss, high radiation resistance, and uses a lightweight GaAs substrate, resulting in low cost, high power-to-weight ratio, and suitability for the aerospace field.

[0005] The purpose of this invention is to provide a double-junction solar cell with improved photoelectric conversion efficiency. The double-junction solar cell, from bottom to top, consists of a GaAs substrate, a GaAs buffer layer, a middle-bottom tunnel junction, a DBR, a middle cell, a middle-top tunnel junction, a top cell, and an ohmic contact layer. The intermediate cell includes an intermediate cell base region, an intermediate cell emitter region, and an intermediate cell window layer; the intermediate cell base region and the intermediate cell emitter region are made of different materials and form a GaInP / GaAs heterojunction; The top cell includes a back electric field, a top cell base region, a top cell emitter region, and a top cell window layer; the top cell base region and the top cell emitter region are made of different materials and form an AlGaInP / GaInP heterojunction.

[0006] The inventors discovered that the emitter and base regions are composed of different lattice-matched materials. The emitter region is a high-bandgap material, while the base region is a narrow-bandgap material. This creates a bandgap difference across the np junction. Sunlight is primarily absorbed by the base region, generating a large number of electron-hole pairs. The small conduction band gap facilitates electron extraction, while the large valence band gap hinders hole diffusion, thereby suppressing nonradiative recombination of the np junction and improving the open-circuit voltage of the battery. Furthermore, the high-bandgap material exhibits superior radiation resistance. As the surface emitter region, it can weaken the impact of radiation on the battery's internal performance, further enhancing its radiation resistance. Therefore, this invention replaces the homogeneous GaAs np junction in the middle cell and the homogeneous GaInP np junction in the top cell with heterojunctions, effectively suppressing photogenerated carrier recombination and improving the open-circuit voltage and radiation resistance of the dual-junction battery. Simultaneously, by using a lighter GaAs substrate that perfectly matches the lattice of the GaAs in the middle cell and the GaInP in the top cell, the power-to-weight ratio of the battery is effectively improved, and the production cost of the dual-junction battery is significantly reduced.

[0007] Furthermore, the material of the intermediate battery base region is GaAs, with a thickness of 1.5 μm to 2.5 μm; the material of the intermediate battery emitter region is Ga... x1 In 1-x1 P has a thickness of 0.1 μm to 0.3 μm, where x1 takes the value of 0.48 ≤ x1 ≤ 0.52. In this invention, the material of the emitter region of the middle cell is changed from GaAs to GaInP to form a GaInP / GaAs heterojunction. This not only improves the voltage, but also further improves the radiation resistance of the GaAs sub-cell of the double-junction cell by replacing the GaAs in the emitter region with GaInP, which has better radiation resistance.

[0008] Furthermore, the material of the top battery base region is GaInP, with a thickness of 0.5 μm to 1.0 μm; the material of the top battery emitter region is Al. y The GaInP material has a thickness of 0.1 μm to 0.3 μm, where y is 0.30 ≤ y ≤ 0.50. In this invention, 30% to 50% Al is doped into the GaInP material in the top-mount emitter region to form an AlGaInP / GaInP heterojunction. This not only further increases the voltage, but also improves the stability of the GaInP material after Al doping, thus enhancing the radiation resistance of the dual-junction cell.

[0009] Furthermore, the middle and bottom tunnel joint adopts N ++ AlGaAs-N ++ GaAs-P ++ GaAs-P ++ AlGaAs structures with a thickness of 0.04 μm to 0.06 μm.

[0010] Furthermore, the DBR is a periodic GaAs / Al x2 GaAs material with more than 6 pairs of periods and a period thickness of 0.12μm to 0.14μm, where x2 takes the value of 0.6≤x2≤0.8.

[0011] Furthermore, the central tunnel-through structure adopts N... ++ GaInP-P ++ AlGaAs structures with a thickness of 0.04 μm to 0.06 μm.

[0012] Furthermore, both the middle battery window layer and the top battery window layer are made of AlInP, and their thicknesses are both 0.05μm to 0.2μm.

[0013] Furthermore, the material of the back electric field is Al. x3 GaInP with a thickness of 0.05μm to 0.2μm, where x3 takes the value of 0.15≤x3≤0.4.

[0014] This invention also provides a method for fabricating a double-junction solar cell with improved photoelectric conversion efficiency, the method comprising the following steps: (1) Grow a GaAs buffer layer on a GaAs substrate; (2) Growth of mid-basal tunneling knots; (3) Growth of DBR; (4) A growing battery; (5) Top tunneling knot during growth; (6) Growth of the top cell; (7) Grow GaAs ohmic contact layer.

[0015] Furthermore, the lattice constant of the top cell matches the lattice constant of the middle cell.

[0016] Compared with the prior art, the present invention has the following advantages: This invention optimizes the conventional dual-cell structure by replacing the original germanium substrate with a lighter GaAs substrate that is lattice-matched to the GaAs material of the middle cell and the GaInP material of the top cell. This not only improves the photoelectric conversion power-to-weight ratio and photoelectric conversion efficiency but also reduces production costs. At the same time, replacing the GaAs homojunction in the middle cell and the GaInP homojunction in the top cell with GaInP / GaAs and AlGaInP / GaInP heterojunctions can effectively suppress photogenerated carrier recombination and improve the open-circuit voltage and radiation resistance of the dual-junction cell.

[0017] The present invention has a simple manufacturing process, and the resulting double-junction solar cell epitaxial material has high lattice matching, low voltage loss, high radiation resistance, low cost, and high photoelectric conversion power-to-weight ratio, effectively improving photoelectric conversion efficiency. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the epitaxial structure of the double-junction solar cell of the present invention.

[0019] Explanation of the labels in the diagram: 1. GaAs substrate; 2. GaAs buffer layer; 3. Middle-bottom tunnel junction; 4. DBR; 5. Middle cell base region; 6. Middle cell emitter region; 7. Middle cell window layer; 8. Middle-top tunnel junction; 9. Back electric field; 10. Top cell base region; 11. Top cell emitter region; 12. Top cell window layer; 13. Ohmic contact layer. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0021] In the description of this application, it should be understood that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this application.

[0022] In the description of this application, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is usually based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this application and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this application; the directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0023] Please see Figure 1It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the shape, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0024] One embodiment of the present invention provides a double-junction solar cell with improved photoelectric conversion efficiency, the schematic diagram of which is shown below. Figure 1 As shown, the dual-junction solar cell consists of GaAs substrate 1, GaAs buffer layer 2, bottom-middle tunnel junction 3, DBR 4, middle cell, top-middle tunnel junction 8, top cell, and ohmic contact layer 13 from bottom to top. The middle battery includes a middle battery base region 5, a middle battery emitter region 6, and a middle battery window layer 7; the top battery includes a back electric field 9, a top battery base region 10, a top battery emitter region 11, and a top battery window layer 12.

[0025] In some embodiments, the material of the intermediate battery base region is GaAs, with a thickness of 1.5 μm to 2.5 μm; the material of the intermediate battery emitter region is Ga... x1 In 1-x1 P has a thickness of 0.1 μm to 0.3 μm, where x1 takes the value of 0.48 ≤ x1 ≤ 0.52. A GaInP / GaAs heterojunction is formed between the base region and the emitter region of the middle cell. Utilizing the high bandgap material of the emitter region and the narrow bandgap material of the base region, a bandgap difference is formed on both sides of the np junction. Sunlight is mainly absorbed by the base region, generating a large number of electron-hole pairs. The small conduction band gap facilitates electron extraction, while the large valence band gap hinders hole diffusion, thereby suppressing nonradiative recombination of the np junction, increasing the open-circuit voltage of the cell, and improving the radiation resistance of the GaAs sub-cell in the double-junction cell.

[0026] In some embodiments, the material of the back electric field is Al. x3 The material of the top-mounted battery base region is GaInP, with a thickness of 0.05 μm to 0.2 μm, where x3 is 0.15 ≤ x3 ≤ 0.4; the material of the top-mounted battery base region is GaInP, with a thickness of 0.5 μm to 1.0 μm; the material of the top-mounted battery emitter region is Al. y The GaInP material has a thickness of 0.1 μm to 0.3 μm, where y is 0.30 ≤ y ≤ 0.50. 30%–50% Al is doped into the GaInP material of the top-mount cell emitter region to form an AlGaInP / GaInP heterojunction. Similarly, by using a high bandgap material in the emitter region and a narrow bandgap material in the base region, a bandgap difference is formed on both sides of the np junction, which can further increase the voltage. Simultaneously, Al doping of GaInP material improves its stability and enhances the radiation resistance of the dual-junction cell.

[0027] In some embodiments, the thickness of the GaAs buffer layer is 0.3 μm to 0.5 μm; the mid-bottom tunnel junction uses N... ++ AlGaAs-N ++ GaAs-P ++ GaAs-P ++ AlGaAs structures with a thickness of 0.04 μm to 0.06 μm.

[0028] In some embodiments, the DBR is a periodic GaAs / Al x2 GaAs material with more than 6 pairs of periods and a period thickness of 0.12μm to 0.14μm, where x2 takes the value of 0.6≤x2≤0.8.

[0029] In some embodiments, the central tunnel connection adopts N ++ GaInP-P ++ The AlGaAs structure has a thickness of 0.04 μm to 0.06 μm; the middle battery window layer and the top battery window layer are both made of AlInP with a thickness of 0.05 μm to 0.2 μm.

[0030] Another embodiment of the present invention provides a method for fabricating a double-junction solar cell with improved photoelectric conversion efficiency, comprising the following steps: (1) A GaAs buffer layer is grown on a GaAs substrate; specifically, a GaAs buffer layer with a thickness of 0.3 μm to 0.5 μm is grown on a GaAs substrate.

[0031] (2) Growth of mid-base tunneling knots; specifically, mid-base tunneling knots are produced using N ++ AlGaAs-N ++ GaAs-P ++ GaAs-P ++ The AlGaAs structure has a thickness of 0.04 μm to 0.06 μm.

[0032] (3) Growth of DBR; specifically, DBR is a multi-period GaAs / Al x2 GaAs material with more than 6 pairs of periods and a period thickness of 0.12μm to 0.14μm, where 0.6≤x2≤0.8.

[0033] (4) Growing the cell; specifically, the cell material includes a cell base region, a cell emitter region, and a cell window layer, wherein the cell base region is made of GaAs, and the cell emitter region is made of Ga… x1 In 1-x1P, where 0.48≤x1≤0.52, the thickness of the base region of the middle cell is 1.5μm~2.5μm, the thickness of the emitter region of the middle cell is 0.1μm~0.3μm, and the material of the window layer of the middle cell is AlInP with a thickness of 0.05μm~0.2μm.

[0034] (5) Growth of the top tunnel joint; specifically, the top tunnel joint adopts N ++ GaInP-P ++ The AlGaAs structure has a thickness of 0.04 μm to 0.06 μm.

[0035] (6) Growth of the top cell; specifically, the lattice constant of the top cell matches that of the middle cell, and it consists of a back electric field, a top cell base region, a top cell emitter region, and a top cell window layer, wherein the material of the back electric field is Al. x3 The material of the top-cell base region is GaInP, and the material of the top-cell emitter region is Al. y The top cell window layer is made of GaInP, with 0.15≤x3≤0.4 and 0.30≤y≤0.50. The thickness of the back electric field is 0.05μm~0.2μm, the thickness of the top cell base region is 0.5μm~1.0μm, the thickness of the top cell emitter region is 0.1μm~0.3μm, and the thickness of the top cell window layer is 0.05μm~0.2μm.

[0036] (7) Grow a GaAs ohmic contact layer, specifically, the thickness of the GaAs ohmic contact layer is 0.4 μm to 0.6 μm.

[0037] In summary, this invention replaces the conventional dual-cell germanium substrate with a lighter GaAs substrate whose lattice is perfectly matched to the GaAs material of the middle cell and the GaInP material of the top cell. At the same time, it replaces the GaAs homojunction of the middle cell and the GaInP homojunction of the top cell with GaInP / GaAs and AlGaInP / GaInP heterojunctions, which can effectively improve the open-circuit voltage and radiation resistance of the dual-junction cell, improve the photoelectric conversion efficiency, and reduce the production cost. It can be widely used in the aerospace field.

[0038] Finally, it should be emphasized that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A double-junction solar cell with improved photoelectric conversion efficiency, characterized in that, The dual-junction solar cell consists of, from bottom to top, a GaAs substrate, a GaAs buffer layer, a middle-bottom tunnel junction, a DBR, a middle cell, a middle-top tunnel junction, a top cell, and an ohmic contact layer. The intermediate cell includes an intermediate cell base region, an intermediate cell emitter region, and an intermediate cell window layer; the intermediate cell base region and the intermediate cell emitter region are made of different materials and form a GaInP / GaAs heterojunction; The top cell includes a back electric field, a top cell base region, a top cell emitter region, and a top cell window layer; the top cell base region and the top cell emitter region are made of different materials and form an AlGaInP / GaInP heterojunction.

2. A double-junction solar cell with improved photoelectric conversion efficiency according to claim 1, characterized in that, The material of the intermediate battery base region is GaAs, with a thickness of 1.5 μm to 2.5 μm; the material of the intermediate battery emitter region is Ga... x1 In 1-x1 P has a thickness of 0.1μm to 0.3μm, where x1 has a value of 0.48≤x1≤0.

52.

3. A double-junction solar cell with improved photoelectric conversion efficiency according to claim 1, characterized in that, The material of the top battery base region is GaInP, with a thickness of 0.5 μm to 1.0 μm; the material of the top battery emitter region is Al. y GaInP with a thickness of 0.1μm to 0.3μm, where the value of y is 0.30≤y≤0.

50.

4. A double-junction solar cell with improved photoelectric conversion efficiency according to claim 1, characterized in that, The mid-bottom tunnel joint adopts N ++ AlGaAs-N ++ GaAs-P ++ GaAs-P ++ AlGaAs structures with a thickness of 0.04 μm to 0.06 μm.

5. A double-junction solar cell with improved photoelectric conversion efficiency according to claim 1, characterized in that, The DBR is a periodic GaAs / Al x2 GaAs material with more than 6 pairs of periods and a period thickness of 0.12μm to 0.14μm, where x2 takes the value of 0.6≤x2≤0.

8.

6. A double-junction solar cell for improving photoelectric conversion efficiency according to claim 1, characterized in that, The middle-top tunnel connection adopts N ++ GaInP-P ++ AlGaAs structures with a thickness of 0.04 μm to 0.06 μm.

7. A double-junction solar cell with improved photoelectric conversion efficiency according to claim 1, characterized in that, The material of both the middle battery window layer and the top battery window layer is AlInP, and the thickness of both is 0.05μm to 0.2μm.

8. A double-junction solar cell with improved photoelectric conversion efficiency according to claim 1, characterized in that, The material of the back electric field is Al. x3 GaInP with a thickness of 0.05μm to 0.2μm, where x3 takes the value of 0.15≤x3≤0.

4.

9. A method for preparing a double-junction solar cell with improved photoelectric conversion efficiency according to any one of claims 1-8, characterized in that, The preparation method includes the following steps: (1) Grow a GaAs buffer layer on a GaAs substrate; (2) Growth of mid-basal tunneling knots; (3) Growth of DBR; (4) A growing battery; (5) Tunneling and crossing during growth; (6) Growth of the top cell; (7) Grow GaAs ohmic contact layer.

10. A method for preparing a double-junction solar cell with improved photoelectric conversion efficiency according to claim 9, characterized in that, The lattice constant of the top cell matches the lattice constant of the middle cell.

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