Multi-junction solar cell and preparation method thereof
By employing a Ge substrate and a composite functional buffer layer in gallium arsenide solar cells, the problems of lattice mismatch, dislocations, and reverse current channels were solved, enabling efficient and reliable fabrication of multi-junction solar cells, simplifying the process and reducing costs.
Patent Information
- Application Number
- CN202610193119.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-02-10
- Publication Date
- 2026-05-05
AI Technical Summary
When traditional gallium arsenide solar cells are grown directly on Ge substrates using epitaxial growth of III-V semiconductor materials, there are problems such as lattice mismatch, dislocations, and reverse current channels, which lead to decreased cell performance and increased costs.
The structure employs a Ge substrate, a nucleation layer, and a composite functional buffer layer. The composite functional buffer layer includes InGaAs and GaAs or AlGaAs layers, which serve as a lattice transition layer to filter dislocations and block reverse current channels, simplifying the structure and reducing costs.
Effectively filters misalignments, eliminates reverse current paths, improves battery efficiency and reliability, simplifies the process, and reduces costs.
Smart Images
Figure CN121985591A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of solar cell technology, and in particular to a multi-junction solar cell and its fabrication method. Background Technology
[0002] Gallium arsenide (GaAs), as a III-V compound semiconductor material, has a higher bandgap matching degree with the solar spectrum, making the bandgap matching degree of GaAs solar cells superior to that of silicon solar cells. Therefore, GaAs solar cells can theoretically achieve much higher efficiency than silicon solar cells; specifically, the theoretical efficiency of GaAs solar cells is approximately twice that of crystalline silicon solar cells, and they are also more sensitive to sunlight.
[0003] Furthermore, arsenide solar cells (such as GaAs cells) have higher photoelectric conversion efficiency, excellent radiation resistance and high temperature resistance, making them irreplaceable in space aerospace, concentrated photovoltaics (CPV), and certain special ground applications. Summary of the Invention
[0004] In view of this, this application provides a multi-junction solar cell and its fabrication method, as follows:
[0005] A multi-junction solar cell, the multi-junction solar cell comprising a first junction cell and at least one second junction cell;
[0006] The first junction cell comprises, from bottom to top, a Ge substrate, a nucleation layer, and a composite functional buffer layer. The at least one second junction cell is located on the side of the composite functional buffer layer away from the nucleation layer. The composite functional buffer layer includes a first functional layer and a second functional layer arranged sequentially along the direction away from the nucleation layer. The first functional layer is an InGaAs layer, and the second functional layer is a GaAs layer or an AlGaAs layer.
[0007] Optionally, the first functional layer is In x Ga 1-x As layer, 0 <x≤0.3。
[0008] Optionally, the base region layer of the first junction cell includes the Ge substrate, the emitter region layer of the first junction cell includes the first functional layer, and the window layer of the first junction cell includes the second functional layer.
[0009] Optionally, the composite functional layer further includes a transition layer, which is located between the first functional layer and the second functional layer;
[0010] The transition layer is an InGaAs layer.
[0011] Optionally, the transition layer is In y Ga 1-y As layer, and along the direction away from the first functional layer, the content y of the In component in the transition layer gradually decreases from x to 0.
[0012] Optionally, the thickness of the first functional layer is D1, the thickness of the second functional layer is D2, and the thickness of the transition layer is D3, wherein D3 < (D1 + D2) / 2.
[0013] Optionally, the thickness of the composite functional buffer layer ranges from 50nm to 1000nm, including the endpoint values; the thickness of the first functional layer ranges from 50nm to 900nm, including the endpoint values; and the thickness of the second functional layer ranges from 5nm to 200nm, including the endpoint values.
[0014] Optionally, the Ge substrate is a p-type doped single-crystal Ge substrate, and the carrier concentration of the Ge substrate ranges from 0.1 / cm³. 3 ~5.0E18 / cm 3 .
[0015] Optionally, the composite functional buffer layer is an N-type doped composite functional buffer layer, and the N-type doping material of the composite functional buffer layer is Si.
[0016] Optionally, the nucleation layer includes one or more layers selected from GaAs, AlGaAs, InAlGaAs, AlGaInP, InAlGaAsP, AlGaAsP, and GaInP; or,
[0017] The nucleation layer includes a superlattice structure composed of one or more of the following: GaAs layer, AlGaAs layer, InAlGaAs layer, AlGaInP layer, InAlGaAsP layer, AlGaAsP layer, and GaInP layer.
[0018] Optionally, the thickness of the nucleation layer ranges from 2nm to 200nm, including the endpoint values, and the thickness of the nucleation layer is less than the thickness of the composite functional buffer layer.
[0019] Optionally, the at least one second junction cell sequentially comprises a GaAs cell and a GaInP cell along a direction away from the first junction cell.
[0020] A method for fabricating a multi-junction solar cell, used to fabricate the multi-junction solar cell described in any one of the above claims, the method comprising:
[0021] Provide a Ge substrate;
[0022] A nucleation layer, a composite functional buffer layer, and at least one second junction cell are sequentially formed on the Ge substrate; the formation of the composite functional buffer layer includes:
[0023] A first functional layer and a second functional layer are formed sequentially along a direction away from the nucleation layer. The first functional layer is an InGaAs layer, and the second functional layer is a GaAs layer or an AlGaAs layer.
[0024] Optionally, the base region layer of the first junction cell includes the Ge substrate, the emitter region layer of the first junction cell includes the first functional layer, and the window layer of the first junction cell includes the second functional layer.
[0025] Optionally, forming the composite functional layer further includes:
[0026] After the first functional layer is formed and before the second functional layer is formed, a transition layer is formed, the transition layer being located between the first functional layer and the second functional layer;
[0027] The lattice transition layer is an InGaAs layer.
[0028] Optionally, the transition layer is In y Ga 1-y As layer, and along the direction away from the first functional layer, the content y of the In component in the transition layer gradually decreases to 0.
[0029] Compared with related technologies, the beneficial effects of the technical solution of this application are as follows:
[0030] This multi-junction solar cell includes a first junction cell and at least one second junction cell. The first junction cell, from bottom to top, comprises a Ge substrate, a nucleation layer, and a composite functional buffer layer. The at least one second junction cell is located on the side of the composite functional buffer layer away from the nucleation layer. The composite functional buffer layer includes a first functional layer and a second functional layer arranged sequentially in a direction away from the nucleation layer. The first functional layer is an InGaAs layer, and the second functional layer is a GaAs layer or an AlGaAs layer. In this multi-junction solar cell, the lattice constant of the first functional layer is between that of Ge and GaAs / AlGaAs. It can serve as a lattice transition layer between the Ge substrate and the upper composite functional buffer layer. Furthermore, it allows the first junction cell to have an optimized bandgap combination, enabling good matching with the upper middle and top cells in terms of solar spectral response, contributing more photocurrent, and improving the overall short-circuit current and conversion efficiency of the multi-junction solar cell. Attached Figure Description
[0031] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.
[0032] The structures, proportions, sizes, etc., shown in the accompanying drawings are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the implementation conditions of this application. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size should still fall within the scope of the technical content disclosed in this application, provided that they do not affect the effects and purposes that this application can produce.
[0033] Figure 1 This is a schematic diagram of the structure of a multi-junction solar cell provided in this application;
[0034] Figure 2 A flowchart illustrating a method for fabricating a multi-junction solar cell provided in this application;
[0035] Figure 3 A flowchart illustrating another method for fabricating a multi-junction solar cell provided in this application. Detailed Implementation
[0036] The embodiments of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. 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.
[0037] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0038] As described in the background section, arsenide solar cells hold an important and indispensable position in the field of solar cell technology.
[0039] Traditional triple-junction solar cell structures typically consist of a Ge bottom cell, a GaAs middle cell, and a GaInP top cell grown on a Ge substrate. However, directly epitaxially growing III-V semiconductor materials on a Ge substrate faces two major challenges: 1. Lattice mismatch and dislocations: Ge and upper-layer materials such as GaAs have a lattice constant difference of approximately 0.08% and different coefficients of thermal expansion, easily introducing mismatch dislocations at the interface. These dislocations extend upwards, severely impairing the performance of the upper-layer cells, especially the middle cell, which is most sensitive to dislocations; 2. Reverse current path (reverse diode effect): An unwanted parasitic PN junction forms at the Ge-GaAs interface, whose polarity is usually opposite to that of the triple-junction cell stack above. Under non-ideal operating conditions such as shading, obstruction, or partial illumination, this parasitic PN junction will conduct, forming a reverse current path to consume the energy generated by the cell, leading to a significant decrease in cell output power (i.e., the "voltage clamping" effect), and even causing localized overheating and burnout.
[0040] The known solution to the above problem is to grow a thicker GaAs or AlGaAs buffer layer to block dislocations, but this does not effectively suppress the formation of the parasitic PN junction and adds extra epitaxial cost and time.
[0041] Based on the above, this application provides a multi-junction solar cell, such as... Figure 1 As shown, Figure 1 This is a schematic diagram of a multi-junction solar cell provided in this application. The multi-junction solar cell includes a first junction cell 100 and at least one second junction cell 200. It should be noted that the first junction cell 100 can also be referred to as the bottom cell.
[0042] Specifically, continue as Figure 1 As shown, the first junction cell, from bottom to top, includes: a Ge substrate 10, a nucleation layer 12, and a composite functional buffer layer 14. At least one second junction cell 200 is located on the side of the composite functional buffer layer 14 away from the nucleation layer 12. Specifically, the at least one second junction cell 200 is located on the side of the composite functional buffer layer 14 away from the nucleation layer 12 and is arranged sequentially along the direction away from the composite functional buffer layer 14.
[0043] The composite functional buffer layer 14 includes a first functional layer 16 and a second functional layer 18 arranged sequentially along the direction away from the nucleation layer 12. The first functional layer 16 is an InGaAs layer, and the second functional layer 18 is a GaAs layer or an AlGaAs layer. The lattice constant of the first functional layer 16 is located between the lattice constants of Ge and GaAs, so that the first functional layer 16 can serve as a lattice transition layer between the Ge substrate 10 and the upper composite functional buffer layer 14. It can effectively filter and block the upward propagation and extension of dislocations, laying the foundation for the high-quality growth of the upper film layer.
[0044] Among them, the first functional layer can be In x Ga 1-x As layer, where 0 < x ≤ 0.3. The base region layer of the first sub-cell 100 includes a Ge substrate 10, the emitter region layer of the first sub-cell 100 includes the first functional layer 16, and the window layer of the first sub-cell 100 includes the second functional layer 18. That is to say, the Ge substrate 10 can serve as the base region of the first sub-cell 100, and the In x Ga 1-x As layer with a low In composition in the first functional layer can serve as the emitter region of the first sub-cell 100, and the second functional layer 18, which is a GaAs layer or an AlGaAs layer, can serve as the window layer of the first sub-cell 100. It should be noted that the content value range of the In composition in the first functional layer can be 0.02 to 0.1, including the endpoint values. Specifically, for example, x = 0.04, that is, the first functional layer is In 0.06 Ga 0.96 As layer.
[0045] As can be seen from the above, the Ge substrate 10 and the composite functional buffer layer 14 of this multi-junction solar cell not only serve as the substrate 10 and buffer layer of this multi-junction solar cell, but the Ge substrate 10 also serves as the base region of the first sub-cell 100, that is, the bottom cell, and the first functional layer 16 and the second functional layer 18 of the composite functional buffer layer 14 also serve as the emitter region and window layer of the first sub-cell 100, that is, the bottom cell, respectively. That is to say, this multi-junction solar cell forms the base region of the first sub-cell 100 by using the Ge substrate 10, that is, the Ge substrate 10 is designed and integrated into a part of the first sub-cell 100, so that the PN junction formed based on the Ge substrate 10 is a complete, correctly polarized, and PN junction belonging to this multi-junction solar cell itself. This PN junction is the functional optoelectronic device junction required by this multi-junction solar cell, rather than a parasitic PN junction that is harmful to the battery performance and is not desired to exist. Fundamentally, it eliminates the parasitic PN junction caused by the Ge substrate 10 of the traditional solar cell, and further eliminates the generation of the reverse current channel, which can significantly improve the working stability and reliability of this multi-junction solar cell under non-uniform illumination conditions such as partial shading, and further improve the efficiency and reliability of this multi-junction solar cell.
[0046] Furthermore, the composite functional buffer layer 14 of this multi-junction solar cell not only serves as a buffer layer, but its first functional layer 16 and second functional layer 18 also serve as the emitter region and window layer of the first junction cell 100, i.e., the bottom cell, respectively. In other words, the composite functional buffer layer 14 of this multi-junction solar cell also integrates the core functional layers of the first junction cell 100. Compared to the buffer layer of a traditional solar cell, this achieves multi-functional reuse of the buffer layer, eliminating the need to form an additional emitter region and window layer for the first junction cell 100, and also eliminating the need for an additional buffer layer. This simplifies the structure of the solar cell, saves on growth processes, and reduces costs. Similarly, the Ge substrate 10 also serves as the base region of the first junction cell 100, eliminating the need to form an additional base region for the first junction cell 100, further simplifying the structure of the solar cell, saving on growth processes, and reducing costs.
[0047] In addition to the above, low In content In x Ga 1-x The lattice constant of the As layer is between that of Ge and GaAs, serving as a lattice transition layer between the Ge substrate 10 and the upper composite functional buffer layer 14. This effectively filters and blocks the upward propagation and extension of dislocations, laying the foundation for high-quality growth of the upper film layers, such as the upper GaAs middle cell 202 and the GaInP top cell 204. Simultaneously, the base region of the first junction cell 100 (bottom cell) of this multi-junction solar cell is the Ge substrate 10, and the emitter region is the InGaAs layer. The small lattice difference between the two layers results in an optimized bandgap combination for the first junction cell 100, enabling good matching with the upper middle and top cells in solar spectral response, contributing more photocurrent, and improving the overall short-circuit current and conversion efficiency of the multi-junction solar cell.
[0048] In one embodiment of this application, such as Figure 1 As shown, the composite functional layer also includes a transition layer 20, which is located between the first functional layer 16 and the second functional layer 18. The lattice transition layer 20 is an InGaAs layer, and the lattice constant of the lattice transition layer 20 is located between the first functional layer 16 and the second functional layer 18. This is used to achieve a smooth transition of the lattice constant from the first functional layer to the second functional layer, which greatly reduces the interface defect density between the first functional layer and the second functional layer 18.
[0049] Specifically, transition layer 20 is In y Ga 1-yAs layer, and along the direction away from the first functional layer 16, the In content y in the transition layer 20 gradually decreases from x to 0. That is, a transition layer 20 is inserted between the first functional layer 16 and the second functional layer 18 of the composite functional buffer layer 14, and the In content in the transition layer 20 gradually decreases from x to 0 in the direction towards the upper second functional layer 18, so that the transition layer 20 is a lattice transition layer in which the In content gradually decreases from x to 0. Therefore, the transition layer 20 can achieve a smooth transition of the lattice constant from the first functional layer 16 to the second functional layer 18, and greatly reduce the interface defect density between the first and second functional layers 18.
[0050] In one embodiment of this application, the thickness of the first functional layer 16 is D1, the thickness of the second functional layer 18 is D2, and the thickness of the transition layer 20 is D3, wherein D3 < (D1 + D2) / 2, that is, the thickness of the transition layer 20 is less than half the sum of the thicknesses of the first functional layer 16 and the second functional layer 18. Specifically, along the direction perpendicular to the plane where the multi-junction solar cell is located, the thickness of the first functional layer 16 is D1, the thickness of the second functional layer 18 is D2, and the thickness of the transition layer 20 is D3, wherein D3 < (D1 + D2) / 2.
[0051] It should be noted that since the first functional layer 16 and the second functional layer 18 also serve as the emitter region and window layer of the first junction cell 100, respectively, the aforementioned transition layer 20 is located between the emitter region and the window layer of the first junction cell 100, specifically above the emitter layer. Therefore, the thickness of the transition layer 20 is less than half the sum of the thicknesses of the first functional layer 16 and the second functional layer 18. This ensures that the thickness of the transition layer 20 is moderate, specifically avoiding an excessively thick transition layer 20 that would affect the function of the emitter region, and also avoiding an excessively thin transition layer 20 that would affect the transition effect.
[0052] In one embodiment of this application, the thickness of the composite functional buffer layer 14 ranges from 50 nm to 1000 nm, including the endpoint values. However, this application does not limit this value and it depends on the specific circumstances. It should be noted that the thickness of the composite functional buffer layer 14 mentioned above refers to the sum of the thicknesses of the first functional layer 16 and the second functional layer 18, that is, the thickness of the composite functional buffer layer 14 mentioned above refers to the thickness of the composite functional buffer layer 14 excluding the transition layer 20.
[0053] In one embodiment of this application, the thickness of the first functional layer 16 ranges from 50 nm to 900 nm, including the endpoint values; the thickness of the second functional layer 18 ranges from 5 nm to 200 nm, including the endpoint values. However, this application does not limit the thickness ranges of the first functional layer 16 and the second functional layer 18 as described above, and it depends on the specific circumstances.
[0054] In one embodiment of this application, the Ge substrate 10 is a p-type doped single-crystal Ge substrate 10. Preferably, the N-type doping material of the composite functional buffer layer 14 is Si. However, this application is not limited to this, and the N-type doping material of the composite functional buffer layer 14 can also be other suitable doping materials other than Si, depending on the specific circumstances.
[0055] In one embodiment of this application, the composite functional buffer layer 14 is an N-type doped composite functional buffer layer 14, and the carrier concentration of the Ge substrate 10 ranges from 0.1 / cm². 3 ~5.0E18 / cm 3 However, this application does not impose any limitation on the carrier concentration of the Ge substrate 10; it depends on the specific circumstances.
[0056] It should be noted that, for the multi-junction solar cell provided in this application, the Ge substrate 10 can also be an N-type doped Ge substrate 10, and the composite functional buffer layer 14 can also be a P-type doped composite functional buffer layer 14. This application does not impose any limitations on this, and it depends on the specific circumstances.
[0057] In one embodiment of this application, the nucleation layer 12 includes one or more layers selected from GaAs, AlGaAs, InAlGaAs, AlGaInP, InAlGaAsP, AlGaAsP, and GaInP. In another embodiment of this application, the nucleation layer 12 includes a superlattice structure composed of one or more layers selected from GaAs, AlGaAs, InAlGaAs, AlGaInP, InAlGaAsP, AlGaAsP, and GaInP.
[0058] In one embodiment of this application, the thickness of the nucleation layer 12 is in the range of 2nm to 200nm, including the endpoint value, and the thickness of the nucleation layer 12 is less than the thickness of the composite functional buffer layer 14, so as to avoid affecting the battery performance of the first junction cell 100, i.e., the bottom cell, due to the excessive thickness of the nucleation layer 12.
[0059] In one embodiment of this application, at least one second junction cell 200 includes, in a direction away from the first junction cell 100, a GaAs cell 202 and a GaInP cell 204 sequentially. That is, the multi-junction solar cell can be a triple-junction solar cell, with the GaAs cell 202 and GaInP cell 204 being the GaAs middle cell and GaInP top cell, respectively. However, this application is not limited to this; the multi-junction solar cell can also be a quadruple-junction solar cell, depending on the specific circumstances.
[0060] The present application also provides a method for manufacturing a multi-junction solar cell, which is used to manufacture the multi-junction solar cell described in any of the above embodiments. As Figure 2 shown, Figure 2 FIG. is a flowchart of a method for manufacturing a multi-junction solar cell provided by the present application. The manufacturing method includes:
[0061] S1: Provide a Ge substrate 10, which can be a P-type doped single crystal Ge substrate 10.
[0062] S2: Sequentially form a nucleation layer 12, a composite functional buffer layer 14, and at least one second junction sub-cell 200 on the Ge substrate 10. Forming the composite functional buffer layer 14 includes:
[0063] Successively form a first functional layer 16 and a second functional layer 18 in a direction away from the nucleation layer 12. The first functional layer 16 is an InGaAs layer, specifically an In x [[ID=1,5]]Ga 1-x As layer, where 0 < x ≤ 0.3, and the second functional layer 18 is a GaAs layer or an AlGaAs layer, where 0 < x ≤ 0.3. Specifically, as Figure 3 shown, forming the composite functional buffer layer 14 includes:
[0064] S21: Sequentially form a nucleation layer 12 on the Ge substrate 10.
[0065] After forming the nucleation layer 12, form the first functional layer 16 on a side of the nucleation layer 12 away from the Ge substrate 10. After forming the first functional layer 16, form the second functional layer 18 on a side of the first functional layer 16 away from the nucleation layer 12.
[0066] S23: After forming the composite functional layer, form at least one second junction sub-cell 200.
[0067] The base region layer of the first junction sub-cell 100 includes the Ge substrate 10, the emitter region layer of the first junction sub-cell 100 includes the first functional layer 16, and the window layer of the first junction sub-cell 100 includes the second functional layer 18.
[0068] Specifically, the manufacturing method includes: providing a Ge substrate 10, forming a nucleation layer 12 on the Ge substrate 10, and the growth temperature of the nucleation layer 12 is between 550°C and 650°C. Specifically, before forming the nucleation layer 12, a group V element source is introduced in advance, and a temperature treatment process of first heating and then cooling is performed, where the heating range is 30°C to 100°C higher than the temperature during subsequent growth of the nucleation layer 12. To more effectively remove impurities and form an interface on the Ge substrate 10 that is more likely to form growth bonds with the nucleation layer 12.
[0069] After the nucleation layer 12 is formed, a composite functional buffer layer 14 is formed on the nucleation layer 12. Specifically, before forming the composite functional buffer layer 14 on the nucleation layer 12, the structure is cooled by pausing and introducing a protective gas, and then the composite functional buffer layer 14 is grown. That is, before forming the composite functional buffer layer 14 on the nucleation layer 12, the already formed structure is cooled and a protective gas is introduced, with each cooling increment not exceeding 30°C. After reaching a suitable temperature, the composite functional buffer layer 14 is grown. It should be noted that the introduction of the aforementioned protective gas is stopped during the growth of the composite functional buffer layer 14.
[0070] After forming the composite functional buffer layer 14, at least one second junction cell 200 is formed sequentially from bottom to top. For example, after forming the composite functional buffer layer 14, a GaAs middle cell and a GaInP top cell are grown sequentially.
[0071] As described above, the Ge substrate 10 and composite functional buffer layer 14 of the multi-junction solar cell prepared by this method not only serve as the substrate 10 and buffer layer of the multi-junction solar cell, but the Ge substrate 10 also serves as the base region of the first junction cell 100, i.e., the bottom cell. The first functional layer 16 and the second functional layer 18 of the composite functional buffer layer 14 also serve as the emitter region and window layer of the first junction cell 100, i.e., the bottom cell, respectively. In other words, the multi-junction solar cell prepared by this method utilizes the Ge substrate 10 to form the base region of the first junction cell 100, making the PN junction formed based on the Ge substrate 10 a complete, correctly polarized PN junction that belongs to the multi-junction solar cell itself. This fundamentally eliminates the parasitic PN junctions caused by the Ge substrate 10 of traditional solar cells, thereby preventing the generation of reverse current channels and improving the efficiency and reliability of the multi-junction solar cell.
[0072] Furthermore, the composite functional buffer layer 14 of this multi-junction solar cell not only serves as a buffer layer, but its first functional layer 16 and second functional layer 18 also serve as the emitter region and window layer of the first junction cell 100, i.e., the bottom cell, respectively. This achieves multi-functional reuse of the buffer layer, simplifies the structure of the solar cell, saves on growth processes, and reduces costs. Similarly, the Ge substrate 10 also serves as the base region of the first junction cell 100, eliminating the need to form an additional base region for the first junction cell 100, further simplifying the structure of the solar cell, saving on growth processes, and reducing costs.
[0073] In addition to the above, the lattice constant of the first functional layer is between that of Ge and GaAs, serving as a lattice transition layer between the Ge substrate 10 and the upper composite functional buffer layer 14. This effectively filters and blocks the upward propagation and extension of dislocations, laying the foundation for the high-quality growth of the upper film layer. Simultaneously, the base region of the first junction cell 100 (the bottom cell) of this multi-junction solar cell is the Ge substrate 10, and the emitter region is an InGaAs layer. The small difference in their band gaps results in an optimized band gap combination for the first junction cell 100, enabling it to achieve good matching with the upper middle and top cells in terms of solar spectral response, contributing more photocurrent, and improving the overall short-circuit current and conversion efficiency of the multi-junction solar cell.
[0074] In one embodiment of this application, forming the composite functional layer further includes:
[0075] After the formation of the first functional layer 16 and before the formation of the second functional layer 18, a transition layer 20 is formed. This transition layer 20 is located between the first functional layer 16 and the second functional layer 18. The transition layer 20 is an InGaAs layer, which enables a smooth transition of the lattice constant between the first functional layer 16 and the second functional layer 18, significantly reducing the interface defect density between the first and second functional layers 18.
[0076] Specifically, the aforementioned transition layer can be In y Ga 1-y As layer, and along the direction away from the first functional layer 16, the In content y in the transition layer 20 gradually decreases to 0. That is, a transition layer 20 is inserted between the first functional layer 16 and the second functional layer 18 of the composite functional buffer layer 14, and the In content in the transition layer 20 gradually decreases to 0 in the direction towards the upper second functional layer 18. In other words, the transition layer 20 is a transition layer 20 in which the In content gradually decreases to 0. Therefore, the transition layer 20 can achieve a smooth transition of the lattice constant from the first functional layer 16 to the second functional layer 18, which greatly reduces the interface defect density between the first and second functional layers 18.
[0077] In summary, this application provides a multi-junction solar cell and its fabrication method. The multi-junction solar cell includes a Ge substrate, a nucleation layer, a composite functional buffer layer, and at least one second junction sub-cell located on the side of the composite functional buffer layer away from the nucleation layer. The composite functional buffer layer includes a first functional layer and a second functional layer arranged sequentially along the direction away from the nucleation layer. The first functional layer is an InGaAs layer, specifically, the first functional layer can be In... x Ga 1-xThe As layer, where 0 < x ≤ 0.3, and the second functional layer is a GaAs layer or an AlGaAs layer. Moreover, the base region layer of the first sub-cell includes a Ge substrate, the emitter region layer of the first sub-cell includes the first functional layer, and the window layer of the first sub-cell includes the second functional layer. Thus, this multi-junction solar cell forms the base region of the first sub-cell by using the Ge substrate, making the PN junction formed based on the Ge substrate the PN junction of the multi-junction solar cell itself. This PN junction is the functional optoelectronic device junction required by the multi-junction solar cell, rather than a parasitic PN junction that harms the battery performance. Fundamentally, it eliminates the parasitic PN junction caused by the Ge substrate of traditional solar cells, thereby eliminating the generation of reverse current channels and improving the efficiency and reliability of the multi-junction solar cell. At the same time, this multi-junction solar cell realizes the reuse of the Ge substrate and the buffer layer, simplifies the structure of the solar cell, saves the growth process, and also reduces the cost. In addition to the above, the lattice constant of the first functional layer is between the lattice constants of Ge and GaAs, which can serve as a lattice transition layer between the Ge substrate and the upper composite functional buffer layer, and enables the first sub-cell to have an optimized bandgap combination, capable of achieving good matching with the middle cell and the top cell above in the solar spectrum response, contributing more photocurrent, and improving the short-circuit current and conversion efficiency of the overall battery of the multi-junction solar cell.
[0078] In this specification, various embodiments are described in a progressive, or parallel, or combined progressive and parallel manner. Each embodiment focuses on the differences from other embodiments. For the same or similar parts among the embodiments, reference can be made to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple. For the relevant parts, reference can be made to the description in the method part.
[0079] It should be noted that in the description of this application, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to this application. When a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be an intermediate component present at the same time.
[0080] It should also be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or apparatus comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or apparatus that includes the aforementioned element.
[0081] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. A multi-junction solar cell, characterized in that, The multi-junction solar cell includes a first junction cell and at least one second junction cell; The first junction cell comprises, from bottom to top, a Ge substrate, a nucleation layer, and a composite functional buffer layer. The at least one second junction cell is located on the side of the composite functional buffer layer away from the nucleation layer. The composite functional buffer layer includes a first functional layer and a second functional layer arranged sequentially along the direction away from the nucleation layer. The first functional layer is an InGaAs layer, and the second functional layer is a GaAs layer or an AlGaAs layer.
2. The multi-junction solar cell according to claim 1, characterized in that, The first functional layer is In x Ga 1-x As layer, 0 <x≤0.3。 3. The multi-junction solar cell according to claim 1 or 2, characterized in that, The base region layer of the first junction cell includes the Ge substrate, the emitter region layer of the first junction cell includes the first functional layer, and the window layer of the first junction cell includes the second functional layer.
4. The multi-junction solar cell according to claim 1, characterized in that, The composite functional layer further includes a transition layer, which is located between the first functional layer and the second functional layer; The transition layer is an InGaAs layer.
5. The multi-junction solar cell according to claim 4, characterized in that, The transition layer is In y Ga 1-y As layer, and along the direction away from the first functional layer, the content y of the In component in the transition layer gradually decreases from x to 0.
6. The multi-junction solar cell according to claim 4, characterized in that, The thickness of the first functional layer is D1, the thickness of the second functional layer is D2, and the thickness of the transition layer is D3, wherein D3 < (D1 + D2) / 2.
7. The multi-junction solar cell according to claim 1, characterized in that, The thickness of the composite functional buffer layer ranges from 50nm to 1000nm, including the endpoint values; the thickness of the first functional layer ranges from 50nm to 900nm, including the endpoint values; and the thickness of the second functional layer ranges from 5nm to 200nm, including the endpoint values.
8. The multi-junction solar cell according to claim 1, characterized in that, The Ge substrate is a p-type doped single-crystal Ge substrate, and the carrier concentration of the Ge substrate ranges from 0.1 / cm³. 3 ~5.0E18 / cm 3 .
9. The multi-junction solar cell according to claim 8, characterized in that, The composite functional buffer layer is an N-type doped composite functional buffer layer, and the N-type doping material of the composite functional buffer layer is Si.
10. The multi-junction solar cell according to claim 1, characterized in that, The nucleation layer includes one or more layers selected from GaAs, AlGaAs, InAlGaAs, AlGaInP, InAlGaAsP, AlGaAsP, and GaInP; or, The nucleation layer includes a superlattice structure composed of one or more of the following: GaAs layer, AlGaAs layer, InAlGaAs layer, AlGaInP layer, InAlGaAsP layer, AlGaAsP layer, and GaInP layer.
11. The multi-junction solar cell according to claim 1, characterized in that, The thickness of the nucleation layer ranges from 2nm to 200nm, including the endpoint values, and the thickness of the nucleation layer is less than the thickness of the composite functional buffer layer.
12. The multi-junction solar cell according to claim 1, characterized in that, The at least one second junction cell sequentially comprises a GaAs cell and a GaInP cell in a direction away from the first junction cell.
13. A method for fabricating a multi-junction solar cell, characterized in that, The method for preparing the multi-junction solar cell according to any one of claims 1-12 includes: Provide a Ge substrate; A nucleation layer, a composite functional buffer layer, and at least one second junction cell are sequentially formed on the Ge substrate; the formation of the composite functional buffer layer includes: A first functional layer and a second functional layer are formed sequentially along a direction away from the nucleation layer. The first functional layer is an InGaAs layer, and the second functional layer is a GaAs layer or an AlGaAs layer.
14. The method for fabricating a multi-junction solar cell according to claim 13, characterized in that, The first functional layer is In x Ga 1-x As layer, the second functional layer is GaAs layer or AlGaAs layer, 0 <x≤0.3。 15. The method for fabricating a multi-junction solar cell according to claim 13 or 14, characterized in that, The base region layer of the first junction cell includes the Ge substrate, the emitter region layer of the first junction cell includes the first functional layer, and the window layer of the first junction cell includes the second functional layer.
16. The method for fabricating a multi-junction solar cell according to claim 13, characterized in that, The composite functional layer further includes: After the first functional layer is formed and before the second functional layer is formed, a transition layer is formed, the transition layer being located between the first functional layer and the second functional layer; The lattice transition layer is an InGaAs layer.
17. The method for fabricating a multi-junction solar cell according to claim 16, characterized in that, The transition layer is In y Ga 1-y As layer, and along the direction away from the first functional layer, the content y of the In component in the transition layer gradually decreases to 0.