A multi-junction solar cell structure and preparation method thereof

Abstract

The present application discloses a multi-junction solar cell structure and a preparation method thereof, relating to the technical field of solar cell technology. Two groups of metamorphic buffer layers are provided between a first sub-cell and a second sub-cell having a lattice mismatch, thereby serving as a lattice transition, effectively releasing residual stress generated by the lattice mismatch between the first sub-cell and the second sub-cell, and effectively blocking dislocations generated by the lattice mismatch between the first sub-cell and the second sub-cell from extending toward the active region of the second sub-cell (i.e., the pn junction of the second sub-cell). Furthermore, the first group of metamorphic buffer layers is composed of AlGaInAs material, and the second group of metamorphic buffer layers is composed of (Al)GaInP material. The hardness of (Al)GaInP material is higher than that of AlGaInAs material, making the second group of metamorphic buffer layers less susceptible to dislocations and defects, further preventing dislocations in the metamorphic buffer layers from extending to the active region of the second sub-cell, thereby improving the performance of the multi-junction solar cell structure.

Description

Technical Field

[0001] The present application relates to the technical field of solar cells, and in particular to a solar cell structure and a preparation method thereof. Background Art

[0002] Solar cells can directly convert solar energy into electricity and are an efficient form of clean energy. Traditional solar cells are typically silicon solar cells, but silicon solar cells absorb a relatively narrow band of the solar spectrum. This has led to the development of multi-junction solar cells. Multi-junction solar cells are constructed by connecting sub-cells of varying bandgap widths in series through tunnel junctions. Each sub-cell absorbs a different band of the solar spectrum, significantly improving the solar cell's conversion efficiency.

[0003] III-V compound semiconductor solar cells offer the highest conversion efficiency among current material systems, along with advantages such as excellent high-temperature resistance and strong radiation tolerance. They are widely recognized as a new generation of high-performance, long-life space primary power sources. For example, triple-junction solar cells with a lattice-matched GaInP / InGaAs / Ge structure have been widely used in the aerospace field. However, in traditional lattice-matched triple-junction solar cells, the current density of the GaInP top cell and the InGaAs middle cell is much lower than that of the Ge bottom cell. This prevents full utilization of the solar spectrum and limits improvements in the solar cell's photoelectric conversion efficiency.

[0004] The most effective way to improve the conversion efficiency of solar cells is to improve the band gap matching of each sub-cell, thereby more reasonably distributing the solar spectrum. Changing the band gap of each sub-cell in a solar cell requires changing the composition ratio of ternary or even quaternary materials in the sub-cell. However, changing the composition ratio of multi-component materials in the sub-cell often leads to lattice mismatch between the sub-cells, which in turn generates residual stress and dislocations between the sub-cells, affecting the performance of the solar cell. Summary of the Invention

[0005] To solve the above technical problems, the embodiments of the present application provide a multi-junction solar cell structure and a preparation method thereof, so as to introduce two sets of metamorphic buffer layers between two adjacent sub-cells with lattice mismatch in the multi-junction solar cell structure, thereby playing the role of lattice transition between the two adjacent sub-cells with lattice mismatch, effectively releasing the residual stress generated during the epitaxial extension of the lattice mismatch material, and effectively blocking the extension of dislocations to the active area of ​​the sub-cell, thereby improving the performance of the multi-junction solar cell structure.

[0006] To achieve the above objectives, the present invention provides the following technical solutions:

[0007] In a first aspect, embodiments of the present application provide a multi-junction solar cell structure, comprising a substrate and a plurality of sub-cells stacked on one side of the substrate, the plurality of sub-cells comprising a first sub-cell and a second sub-cell disposed adjacent to each other; the first sub-cell comprising a pn junction formed of a material having a first lattice constant, the second sub-cell comprising a pn junction formed of a material having a second lattice constant, the first lattice constant being at least 0.002 nm smaller than the second lattice constant;

[0008] Two groups of metamorphic buffer layers are provided between the first sub-cell and the second sub-cell, and the second group of metamorphic buffer layers is located on a side of the first group of metamorphic buffer layers close to the second sub-cell;

[0009] The first group of metamorphic buffer layers is made of AlGaInAs material, and includes a sequence of m layers stacked in a direction from the first sub-cell to the second sub-cell, where m is ≥ 3 and m is an integer; the lattice constant of each layer sequence in the first group of metamorphic buffer layers is greater than the first lattice constant and less than the second lattice constant; and the lattice constant of at least the first m-1 layer sequences in the first group of metamorphic buffer layers gradually increases;

[0010] The second group of metamorphic buffer layers is composed of GaInP material or AlGaInP material, and the second group of metamorphic buffer layers includes an n-layer sequence stacked in the direction from the first sub-cell to the second sub-cell, n≥2, and n is an integer; the lattice constant of each layer sequence in the second group of metamorphic buffer layers is greater than the average lattice constant of each layer sequence in the first group of metamorphic buffer layers; in the second group of metamorphic buffer layers, the lattice constant of the first n-1 layer sequences gradually increases, the lattice constant of the n-1 layer sequence is greater than the lattice constant of the n layer sequence, and the difference between the lattice constant of the n layer sequence and the second lattice constant is less than a preset threshold.

[0011] Optionally, in the first group of metamorphic buffer layers, the lattice constant of the m-th layer sequence is smaller than the lattice constant of the m-1-th layer sequence.

[0012] Optionally, in the first group of metamorphic buffer layers, the lattice constant of the m-th layer sequence is greater than the lattice constant of the m-1-th layer sequence.

[0013] Optionally, the lattice constant of the first layer sequence of the second group of metamorphic buffer layers is greater than the lattice constant of the mth layer sequence of the first group of metamorphic buffer layers.

[0014] Optionally, the lattice constant of the first layer sequence of the second group of metamorphic buffer layers is smaller than the lattice constant of the mth layer sequence of the first group of metamorphic buffer layers.

[0015] Optionally, the lattice constant of the nth layer sequence in the second group of metamorphic buffer layers is not less than the second lattice constant.

[0016] Optionally, the second group of metamorphic buffer layers is made of AlGaInP material, and the Al component of each layer sequence in the second group of metamorphic buffer layers is not greater than 30%.

[0017] Optionally, the substrate is a GaAs substrate, and the multi-junction solar cell structure includes a sacrificial layer, a first ohmic contact layer, a third sub-cell, a first tunnel junction, the first sub-cell, a second tunnel junction, the two groups of metamorphic buffer layers, the second sub-cell and a second ohmic contact layer stacked in sequence along a direction away from the GaAs substrate, wherein the sacrificial layer is an AlAs layer, the first sub-cell is a GaAs sub-cell, the second sub-cell is an InGaAs sub-cell, and the third sub-cell is an AlGaInP sub-cell.

[0018] Optionally, the substrate is a Ge substrate, and the multi-junction solar cell structure includes the first sub-cell, the third tunnel junction, the two groups of metamorphic buffer layers, the Bragg reflection layer, the second sub-cell, the fourth tunnel junction, the fourth sub-cell and the third ohmic contact layer stacked in sequence along the direction away from the Ge substrate, wherein the first sub-cell is a Ge sub-cell, the second sub-cell is an InGaAs sub-cell, and the fourth sub-cell is an AlGaInP sub-cell or a GaInP sub-cell.

[0019] In a second aspect, an embodiment of the present application provides a method for preparing a multi-junction solar cell structure, comprising:

[0020] providing a substrate;

[0021] forming a plurality of stacked subcells on one side of the substrate, the plurality of subcells including a first subcell and a second subcell disposed adjacent to each other; the first subcell including a pn junction formed of a material having a first lattice constant, the second subcell including a pn junction formed of a material having a second lattice constant, the first lattice constant being at least 0.002 nm smaller than the second lattice constant;

[0022] Two groups of metamorphic buffer layers are provided between the first sub-cell and the second sub-cell, and the second group of metamorphic buffer layers is located on a side of the first group of metamorphic buffer layers close to the second sub-cell;

[0023] The first group of metamorphic buffer layers is made of AlGaInAs material, and includes a sequence of m layers stacked in a direction from the first sub-cell to the second sub-cell, where m is ≥ 3 and m is an integer; the lattice constant of each layer sequence in the first group of metamorphic buffer layers is greater than the first lattice constant and less than the second lattice constant; and the lattice constant of at least the first m-1 layer sequences in the first group of metamorphic buffer layers gradually increases;

[0024] The second group of metamorphic buffer layers is composed of GaInP material or AlGaInP material, and the second group of metamorphic buffer layers includes an n-layer sequence stacked in the direction from the first sub-cell to the second sub-cell, n≥2, and n is an integer; the lattice constant of each layer sequence in the second group of metamorphic buffer layers is greater than the average lattice constant of each layer sequence in the first group of metamorphic buffer layers; in the second group of metamorphic buffer layers, the lattice constant of the first n-1 layer sequences gradually increases, the lattice constant of the n-1 layer sequence is greater than the lattice constant of the n layer sequence, and the difference between the lattice constant of the n layer sequence and the second lattice constant is less than a preset threshold.

[0025] Optionally, the substrate is a GaAs substrate, and the multiple sub-cells stacked on one side of the substrate include:

[0026] A sacrificial layer, a first ohmic contact layer, a third sub-cell, a first tunnel junction, the first sub-cell, a second tunnel junction, the two groups of metamorphic buffer layers, the second sub-cell, and a second ohmic contact layer are sequentially formed on one side of the GaAs substrate, wherein the sacrificial layer is an AlAs layer, the first sub-cell is a GaAs sub-cell, the second sub-cell is an InGaAs sub-cell, and the third sub-cell is an AlGaInP sub-cell;

[0027] The sacrificial layer is corroded by HF etching solution, the battery structure consisting of the first ohmic contact layer to the second ohmic contact layer is peeled off from the GaAs substrate, and the battery structure consisting of the first ohmic contact layer to the second ohmic contact layer is transferred to another substrate.

[0028] Optionally, the substrate is a Ge substrate, and the multiple sub-cells stacked on one side of the substrate include:

[0029] The first sub-cell, the third tunnel junction, the two groups of metamorphic buffer layers, the Bragg reflection layer, the second sub-cell, the fourth tunnel junction, the fourth sub-cell and the third ohmic contact layer are formed in sequence on one side of the Ge substrate, wherein the first sub-cell is a Ge cell, the second sub-cell is an InGaAs sub-cell, and the fourth sub-cell is an AlGaInP sub-cell or a GaInP sub-cell.

[0030] Compared with the existing technology, the above technical solution has the following advantages:

[0031] The multi-junction solar cell structure provided by the embodiment of the present application includes a substrate and a plurality of sub-cells stacked on one side of the substrate, the plurality of sub-cells including a first sub-cell and a second sub-cell arranged adjacent to each other, the first sub-cell including a pn junction formed of a material having a first lattice constant, the second sub-cell including a pn junction formed of a material having a second lattice constant, the first lattice constant being at least 0.002 nm smaller than the second lattice constant, that is, there is a lattice mismatch problem between the first sub-cell and the second sub-cell; by arranging two groups of metamorphic buffer layers between the first sub-cell and the second sub-cell, a lattice transition is performed between the first sub-cell and the second sub-cell, thereby effectively releasing the residual stress generated by the lattice mismatch between the first sub-cell and the second sub-cell, and effectively blocking the dislocations generated by the lattice mismatch between the first sub-cell and the second sub-cell from extending toward the active area of ​​the second sub-cell (that is, the pn junction of the second sub-cell), thereby improving the performance of the multi-junction solar cell structure.

[0032] Specifically, in the two groups of metamorphic buffer layers between the first sub-cell and the second sub-cell, the second group of metamorphic buffer layers is located on the side of the first group of metamorphic buffer layers close to the second sub-cell, wherein the first group of metamorphic buffer layers is composed of AlGaInAs material, and the first group of metamorphic buffer layers includes an m-layer sequence stacked in a direction from the first sub-cell to the second sub-cell, m ≥ 3, and m is an integer; the lattice constant of each layer sequence in the first group of metamorphic buffer layers is greater than the first lattice constant and less than the second lattice constant, and the lattice constant of at least the first m-1 layer sequences in the first group of metamorphic buffer layers gradually increases; the second group The metamorphic buffer layer is composed of GaInP material or AlGaInP material, and the second group of metamorphic buffer layers includes an n-layer sequence stacked in a direction from the first sub-cell to the second sub-cell, where n≥2 and n is an integer; the lattice constant of each layer sequence in the second group of metamorphic buffer layers is greater than the average lattice constant of each layer sequence in the first group of metamorphic buffer layers; in the second group of metamorphic buffer layers, the lattice constant of the first n-1 layer sequences gradually increases, the lattice constant of the n-1 layer sequence is greater than the lattice constant of the n layer sequence, and the difference between the lattice constant of the n layer sequence and the second lattice constant is less than a preset threshold.

[0033] That is to say, in the two groups of metamorphic buffer layers between the first sub-cell and the second sub-cell, the lattice constants of at least the first m-1 layer sequences of the first group of metamorphic buffer layers and the first n-1 layer sequences of the second group of metamorphic buffer layers gradually increase as a whole, and the lattice constant of the n-1 layer sequence in the second group of metamorphic buffer layers is greater than the lattice constant of the n layer sequence, that is, the n-1 layer sequence of the second group of metamorphic buffer layers is an overshoot layer, so that the n layer sequence is subjected to tensile stress, which is different from the compressive stress generated by the gradual increase in the lattice constant of the previous sequence. On the one hand, it can compensate for the residual stress of the previous sequence, and on the other hand, it can effectively prevent the dislocation of the metamorphic buffer layer from extending to the active area of ​​the second sub-cell. Finally, the difference between the lattice constant of the n layer sequence in the second group of metamorphic buffer layers and the second lattice constant is less than the preset threshold, and the n layer sequence of the second group of metamorphic buffer layers and the second sub-cell are lattice matched.

[0034] Furthermore, the first group of metamorphic buffer layers is composed of AlGaInAs material, and the second group of metamorphic buffer layers is composed of GaInP material or AlGaInP material, and the hardness of (Al)GaInP material is higher than that of AlGaInAs material. That is, the hardness of the second group of metamorphic buffer layers is higher than that of the first group of metamorphic buffer layers, so that the second group of metamorphic buffer layers is less likely to produce dislocations and defects, which can further prevent the dislocations of the metamorphic buffer layers from extending to the active area of ​​the second sub-cell.

[0035] In the multi-junction solar cell structure provided in the embodiment of the present application, the problem of lattice mismatch between the first sub-cell and the second sub-cell is solved by designing two sets of metamorphic buffer layers between the first sub-cell and the second sub-cell, thereby improving the performance of the multi-junction solar cell structure.

[0036] Other objects and advantages of the present application will be described in detail in the following embodiments with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0038] Figure 1 A schematic cross-sectional view of a multi-junction solar cell structure provided in an embodiment of the present application;

[0039] Figure 2 A schematic cross-sectional view of another multi-junction solar cell structure provided in an embodiment of the present application.

[0040] Reference numerals:

[0041] 100-substrate; 200-subcell; 210-first subcell; 220-second subcell; 230-third subcell; 240-fourth subcell; 300-metamorphic buffer layer; 310-first group of metamorphic buffer layers; 320-second group of metamorphic buffer layers; 10-sacrificial layer; 11-first ohmic contact layer; 12-first tunnel junction; 13-second tunnel junction; 14-second ohmic contact layer; 20-third tunnel junction; 21-Bragg reflection layer; 22-fourth tunnel junction; 23-third ohmic contact layer. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0043] The terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the terms used in this way can be interchangeable under appropriate circumstances, and this is merely a way of distinguishing the objects of the same attributes when describing them in the embodiments of the present application. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, so that the process, method, system, product or equipment comprising a series of units need not be limited to those units, but may include other units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0044] Secondly, this application is described in detail with reference to schematic diagrams. When describing the embodiments of this application, for ease of illustration, the drawings depicting device structures may be partially enlarged and not to scale. Furthermore, the schematic diagrams are merely illustrative and should not limit the scope of protection of this application. Furthermore, in actual production, the three-dimensional dimensions of length, width, and depth should be included.

[0045] As described in the background technology section, the most effective way to improve the conversion efficiency of solar cells is to improve the band gap matching of each sub-cell, thereby more reasonably distributing the solar spectrum. Changing the band gap of each sub-cell in a solar cell requires changing the composition ratio of ternary or even quaternary materials in the sub-cell. However, changing the composition ratio of multi-component materials in the sub-cell often leads to lattice mismatch between the sub-cells, which in turn generates residual stress and dislocations between the sub-cells, affecting the performance of the solar cell.

[0046] In view of this, the embodiment of the present application provides a multi-junction solar cell structure. Figure 1 A cross-sectional schematic diagram of a multi-junction solar cell structure provided by an embodiment of the present application is shown in FIG. Figure 1 As shown, the multi-junction solar cell structure includes a substrate 100 and a plurality of sub-cells 200 stacked on one side of the substrate 100, the plurality of sub-cells 200 including a first sub-cell 210 and a second sub-cell 220 arranged adjacent to each other, the first sub-cell 210 including a pn junction formed of a material having a first lattice constant a1, the second sub-cell 220 including a pn junction formed of a material having a second lattice constant a2, the first lattice constant a1 being at least 0.002 nm smaller than the second lattice constant a2, that is, a1≤a2-0.002 nm, or a2≥a1+0.002 nm; in this way, if the first sub-cell 210 and the second sub-cell 220 are connected only by a tunnel junction, there is a lattice mismatch problem between the first sub-cell 210 and the second sub-cell 220.

[0047] like Figure 1 As shown, in the multi-junction solar cell structure provided in the embodiment of the present application, two groups of metamorphic buffer layers 300 are arranged between the first sub-cell 210 and the second sub-cell 220. The two groups of metamorphic buffer layers 300 include a first group of metamorphic buffer layers 310 and a second group of metamorphic buffer layers 320. The second group of metamorphic buffer layers 320 is located on a side of the first group of metamorphic buffer layers 310 close to the second sub-cell 220. That is, by arranging two groups of metamorphic buffer layers 300 between the first sub-cell 210 and the second sub-cell 220, a lattice transition is performed between the first sub-cell 210 and the second sub-cell 220, thereby effectively releasing the residual stress generated by the lattice mismatch between the first sub-cell 210 and the second sub-cell 220, and effectively blocking the dislocations generated by the lattice mismatch between the first sub-cell 210 and the second sub-cell 220 from extending toward the active region of the second sub-cell 220 (i.e., the pn junction of the second sub-cell 220), thereby improving the performance of the multi-junction solar cell structure.

[0048] Specifically, such as Figure 1 As shown, the first group of metamorphic buffer layers 310 is composed of AlGaInAs material, and the first group of metamorphic buffer layers 310 includes an m-layer sequence stacked in a direction from the first sub-cell 210 to the second sub-cell 220, m≥3, and m is an integer, that is, the first group of metamorphic buffer layers 310 includes at least 3-layer sequences stacked in a direction from the first sub-cell 210 to the second sub-cell 220; the lattice constant of each layer sequence in the first group of metamorphic buffer layers 310 is greater than the first lattice constant a1 and less than the second lattice constant a2; the lattice constant of at least the first m-1 layer sequences in the first group of metamorphic buffer layers 310 gradually increases; that is, the lattice constant of at least the first m-1 layer sequences in the first group of metamorphic buffer layers 310 transitions from the first lattice constant a1 to the second lattice constant a2.

[0049] It can be understood that in the first m-1 layer sequence of the first group of metamorphic buffer layers 310, the lattice constant of the i+1 layer sequence is greater than the lattice constant of the i layer sequence. In this way, when the i+1 layer sequence with a relatively large lattice constant is grown on the i layer sequence with a relatively small lattice constant, compressive stress will be generated, where 1≤i≤m-1.

[0050] Optionally, in the first group of metamorphic buffer layers 310, the lattice constant of the mth layer sequence is smaller than the lattice constant of the m-1th layer sequence, so that the m-1th layer sequence serves as an overshoot layer; then, when the mth layer sequence with a relatively small lattice constant is grown on the m-1th layer sequence with a relatively large lattice constant, tensile stress will be generated, which is different from the compressive stress generated by the gradual increase in the lattice constant of the previous sequence in the first group of metamorphic buffer layers 310. On the one hand, it can compensate for the residual stress generated by the previous sequence in the first group of metamorphic buffer layers 310, and on the other hand, it can prevent the dislocations of the first group of metamorphic buffer layers 310 from extending to the second group of metamorphic buffer layers 320.

[0051] Alternatively, in the first group of metamorphic buffer layers 310 , the lattice constant of the m-th layer sequence is greater than the lattice constant of the m-1-th layer sequence; thus, the lattice constant of the m-th layer sequence in the first group of metamorphic buffer layers 310 transitions from the first lattice constant a1 to the second lattice constant a2 as a whole.

[0052] like Figure 1 As shown, the second group of metamorphic buffer layers 320 is composed of GaInP material or AlGaInP material, and the second group of metamorphic buffer layers 320 includes n-layer sequences stacked in the direction from the first sub-cell 210 to the second sub-cell 220, n≥2, and n is an integer, that is, the second group of metamorphic buffer layers 320 includes at least 2 layer sequences stacked in the direction from the first sub-cell 210 to the second sub-cell 220; the lattice constant of each layer sequence in the second group of metamorphic buffer layers 320 is greater than the average lattice constant of each layer sequence in the first group of metamorphic buffer layers 310, that is, the second group of metamorphic buffer layers 320 further transitions to the second lattice constant a2 on the basis of the first group of metamorphic buffer layers 310; in the second group of metamorphic buffer layers 320, the lattice constants of the first n-1 layer sequences gradually increase, the lattice constant of the n-1 layer sequence is greater than the lattice constant of the n layer sequence, and the difference between the lattice constant of the n layer sequence and the second lattice constant is less than a preset threshold.

[0053] It can be understood that the lattice constant of the n-th layer sequence in the second group of metamorphic buffer layers 320 can be equal to the second lattice constant a2, or can be greater than the second lattice constant a2, or can be less than the second lattice constant a2, but the lattice constant of the n-th layer sequence in the second group of metamorphic buffer layers 320 is close to the second lattice constant a2, and the difference between the lattice constant and the second lattice constant a2 is less than a preset threshold value. The preset threshold value can be determined according to actual conditions so that when the second sub-battery 220 is grown on the n-th layer sequence of the second group of metamorphic buffer layers 320, there is no longer a lattice mismatch problem.

[0054] It can also be understood that in the first n-1 layer sequence of the second group of metamorphic buffer layers 320, the lattice constant of the j+1 layer sequence is greater than the lattice constant of the j layer sequence. In this way, when the j+1 layer sequence with a relatively large lattice constant is grown on the j layer sequence with a relatively small lattice constant, compressive stress will be generated, where 1≤j≤n-1.

[0055] Moreover, in the second group of metamorphic buffer layers 320, the lattice constant of the n-th layer sequence is smaller than the lattice constant of the n-1-th layer sequence. Thus, the n-1-th layer sequence serves as an overshoot layer. Then, when the n-th layer sequence with a relatively small lattice constant is grown on the n-1-th layer sequence with a relatively large lattice constant, tensile stress is generated. This is different from the compressive stress generated by the gradual increase in the lattice constant of the previous sequences (including the first group of metamorphic buffer layers 310 and the previous sequences in the second group of metamorphic buffer layers 320). On the one hand, this can compensate for the residual stress generated by the previous sequences, and on the other hand, it can effectively prevent the dislocations of the metamorphic buffer layer from extending to the active region of the second sub-cell 220 (i.e., the pn junction of the second sub-cell 220).

[0056] From the above analysis, it can be seen that the lattice constant of at least the first m-1 layer sequence in the first group of metamorphic buffer layers 310 transitions from the first lattice constant a1 to the second lattice constant a2, and the second group of metamorphic buffer layers 320 further transitions to the second lattice constant a2 on the basis of the first group of metamorphic buffer layers 310. The lattice constant of the first n-1 layer sequence in the second group of metamorphic buffer layers 320 gradually increases. Finally, the difference between the lattice constant of the n-th layer sequence in the second group of metamorphic buffer layers 320 and the second lattice constant a2 is less than the preset threshold, and the n-th layer sequence of the second group of metamorphic buffer layers 320 is lattice matched with the second sub-battery 220.

[0057] Regarding the mth layer sequence of the first group of metamorphic buffer layers 310 and the 1st layer sequence of the second group of metamorphic buffer layers 320, optionally, the lattice constant of the 1st layer sequence of the second group of metamorphic buffer layers 320 is greater than the mth layer sequence of the first group of metamorphic buffer layers 310; another optional method is to have a smaller lattice constant than the mth layer sequence of the first group of metamorphic buffer layers 310.

[0058] That is, in the multi-junction solar cell structure provided in the embodiment of the present application, the two sets of metamorphic buffer layers 300 between the first sub-cell 210 and the second sub-cell 220 include at least the following embodiments:

[0059] The first implementation method:

[0060] In the first group of metamorphic buffer layers 310, the lattice constant of the first m-1 layer sequence gradually increases, the lattice constant of the m-th layer sequence is smaller than the lattice constant of the m-1 layer sequence, and the m-1 layer sequence is an overshoot layer, which on the one hand compensates for the residual stress of the previous sequence and on the other hand prevents dislocations from extending to subsequent sequences; the lattice constant of the first layer sequence in the second group of metamorphic buffer layers 320 is greater than the lattice constant of the m-th layer sequence in the first group of metamorphic buffer layers 310; in the second group of metamorphic buffer layers 320, the lattice constant of the first n-1 layer sequence gradually increases, the lattice constant of the n-th layer sequence is smaller than the lattice constant of the n-1 layer sequence, and the n-1 layer sequence is also an overshoot layer, which on the one hand compensates for the residual stress of the previous sequence and on the other hand prevents dislocations from extending to the active area of ​​the second sub-battery 220.

[0061] The second implementation method:

[0062] In the first group of metamorphic buffer layers 310, the lattice constant of the first m-1 layer sequence gradually increases, the lattice constant of the m-th layer sequence is smaller than the lattice constant of the m-1 layer sequence, and the m-1 layer sequence is an overshoot layer, which, on the one hand, compensates for the residual stress of the previous sequence, and on the other hand, prevents dislocations from extending to subsequent sequences; in the second group of metamorphic buffer layers 320, the lattice constant of the first layer sequence is smaller than the lattice constant of the m-th layer sequence in the first group of metamorphic buffer layers 310, and the m-th layer sequence in the first group of metamorphic buffer layers 310 is also an overshoot layer, which, on the one hand, compensates for the residual stress of the previous sequence, and on the other hand, prevents dislocations from extending to subsequent sequences; in the second group of metamorphic buffer layers 320, the lattice constant of the first n-1 layer sequence gradually increases, the lattice constant of the n-th layer sequence is smaller than the lattice constant of the n-1 layer sequence, and the n-1 layer sequence is also an overshoot layer, which, on the one hand, compensates for the residual stress of the previous sequence, and on the other hand, prevents dislocations from extending to the active area of ​​the second sub-cell 220.

[0063] The third implementation method:

[0064] In the first group of metamorphic buffer layers 310, the lattice constant of the m-layer sequence gradually increases; in the second group of metamorphic buffer layers 320, the lattice constant of the 1st layer sequence is smaller than the lattice constant of the m-th layer sequence in the first group of metamorphic buffer layers 310, and the m-th layer sequence in the first group of metamorphic buffer layers 310 is an overshoot layer, which on the one hand compensates for the residual stress of the previous sequence and on the other hand prevents dislocations from extending to the subsequent sequences; in the second group of metamorphic buffer layers 320, the lattice constant of the first n-1 layer sequences gradually increases, and the lattice constant of the n-th layer sequence is smaller than the lattice constant of the n-1th layer sequence, and the n-1th layer sequence is also an overshoot layer, which on the one hand compensates for the residual stress of the previous sequence and on the other hand prevents dislocations from extending to the active area of ​​the second sub-battery 220.

[0065] In the above three embodiments, in the two groups of metamorphic buffer layers 300 between the first sub-cell 210 and the second sub-cell 220, at least one overshoot layer is provided at the interface between the first group of metamorphic buffer layers 310 and the second group of metamorphic buffer layers 320, and one overshoot layer is provided at the interface between the second group of metamorphic buffer layers 320 and the second sub-cell 220. Thus, the two groups of metamorphic buffer layers 300 achieve lattice transition between the first sub-cell 210 and the second sub-cell 220 while effectively releasing residual stress generated by lattice mismatch between the first sub-cell 210 and the second sub-cell 220, and effectively blocking dislocations generated by lattice mismatch between the first sub-cell 210 and the second sub-cell 220 from extending toward the active region of the second sub-cell (i.e., the pn junction of the second sub-cell).

[0066] Furthermore, at least one overshoot layer is provided at the interface between the first and second metamorphic buffer layers 310 and 320 , which can also relieve the pressure of the overshoot layer provided at the interface between the second metamorphic buffer layer 320 and the second sub-cell 220 .

[0067] In other optional embodiments, the lattice constants of the m-layer sequence in the first group of metamorphic buffer layers 310 and the first n-1-layer sequence in the second group of metamorphic buffer layers 320 gradually increase, and the lattice constant of the n-th layer sequence in the second group of metamorphic buffer layers 320 is smaller than the lattice constant of its n-1-th layer sequence.

[0068] Furthermore, the lattice constant of the m-layer sequence in the first group of metamorphic buffer layers 310 gradually increases, the lattice constant of the 1st layer sequence in the second group of metamorphic buffer layers 320 is equal to the lattice constant of the m-th layer sequence in the first group of metamorphic buffer layers 310, the lattice constant of the first n-1 layer sequences in the second group of metamorphic buffer layers 320 gradually increases, and the lattice constant of the n-th layer sequence in the second group of metamorphic buffer layers 320 is smaller than the lattice constant of its n-1-th layer sequence.

[0069] In both embodiments, an overshoot layer is mainly provided at the junction of the second group of metamorphic buffer layers 320 and the second sub-cell 220, which releases the residual stress generated by the lattice mismatch between the first sub-cell 210 and the second sub-cell 220, and effectively blocks the dislocations generated by the lattice mismatch between the first sub-cell 210 and the second sub-cell 220 from extending toward the active area of ​​the second sub-cell (i.e., the pn junction of the second sub-cell).

[0070] Based on the above-mentioned embodiments, preferably, the lattice constant of the n-th layer sequence in the second group of metamorphic buffer layers 320 is not less than the second lattice constant a2, wherein when the lattice constant of the n-th layer sequence in the second group of metamorphic buffer layers 320 is equal to the second lattice constant a2, the n-th layer sequence in the second group of metamorphic buffer layers 320 and the second sub-cell 220 are completely lattice matched; when the lattice constant of the n-th layer sequence in the second group of metamorphic buffer layers 320 is greater than the second lattice constant a2, and the difference between the two is less than a preset threshold, the n-th layer sequence in the second group of metamorphic buffer layers 320 and the second sub-cell 220 can also be lattice matched, and the n-th layer sequence in the second group of metamorphic buffer layers 320 can also serve as an overshoot layer, on the one hand compensating for the residual stress of the previous sequence, and on the other hand preventing dislocations from extending to the active area of ​​the second sub-cell 220 (i.e., the pn junction of the second sub-cell 220).

[0071] In summary, the multi-junction solar cell structure provided by the embodiment of the present application plays a role of lattice transition between the first sub-cell 210 and the second sub-cell 220 by setting two groups of metamorphic buffer layers 300 between the first sub-cell 210 and the second sub-cell 220, wherein the lattice constants of at least the first m-1 layer sequence of the first group of metamorphic buffer layers 310 and the first n-1 layer sequence of the second group of metamorphic buffer layers 320 gradually increase as a whole, and the lattice constant of the n-1 layer sequence in the second group of metamorphic buffer layers 320 is greater than the lattice constant of the n layer sequence, that is, the second The n-1th layer sequence in the group of metamorphic buffer layers 320 is an overshoot layer, so that the nth layer sequence is subjected to tensile stress, which is different from the compressive stress generated by the gradual increase in the lattice constant of the previous sequence. On the one hand, it can compensate for the residual stress of the previous sequence, and on the other hand, it can effectively prevent the dislocation of the metamorphic buffer layer from extending to the active area of ​​the second sub-battery 220. Finally, the difference between the lattice constant of the nth layer sequence in the second group of metamorphic buffer layers 320 and the second lattice constant a2 is less than the preset threshold, and the nth layer sequence of the second group of metamorphic buffer layers 320 and the second sub-battery 220 are lattice matched.

[0072] Furthermore, the first group of metamorphic buffer layers 310 is made of AlGaInAs material, and the second group of metamorphic buffer layers 320 is made of GaInP material or AlGaInP material, and the hardness of (Al)GaInP material is higher than that of AlGaInAs material. That is, the hardness of the second group of metamorphic buffer layers 320 is higher than that of the first group of metamorphic buffer layers 310, so that the second group of metamorphic buffer layers 320 is less likely to generate dislocations and defects, which can further prevent the dislocations of the metamorphic buffer layer from extending to the active region of the second sub-cell 220 (i.e., the pn junction of the second sub-cell 220).

[0073] In the multi-junction solar cell structure provided in the embodiment of the present application, the problem of lattice mismatch between the first sub-cell 210 and the second sub-cell 220 is solved by designing two sets of metamorphic buffer layers between the first sub-cell 210 and the second sub-cell 220, thereby improving the performance of the multi-junction solar cell structure.

[0074] Optionally, in some embodiments of the present application, such as Figure 1 As shown, the substrate 100 may be a GaAs substrate. In this case, the multi-junction solar cell structure may be a reverse-grown GaInP / GaAs / InGaAs inverted triple-junction solar cell structure. The reverse-grown triple-junction solar cell structure includes a sacrificial layer 10, a first ohmic contact layer 11, a third sub-cell 230, a first tunnel junction 12, a first sub-cell 210, a second tunnel junction 13, two groups of metamorphic buffer layers 300, a second sub-cell 220, and a second ohmic contact layer 14, which are sequentially stacked in a direction away from the GaAs substrate (i.e., the substrate 100).

[0075] Wherein, the sacrificial layer 10 may be an AlAs layer;

[0076] The first ohmic contact layer 11 may be an n-type ohmic contact layer, specifically an n-type GaAs layer;

[0077] The third sub-cell 230 may be an AlGaInP sub-cell, and specifically may include an n-type AlGaInP window layer, an n-type AlGaInP emitter region, a p-type AlGaInP base region, and a p-type AlGaInP back field layer stacked in sequence in a direction away from the GaAs substrate (i.e., the substrate 100 );

[0078] The first tunnel junction 12 may include an n-type layer and a p-type layer, the n-type layer may be an n-type GaAs layer or an n-type GaInP layer, the n-type layer may be doped with Si or Te, and the p-type layer may be a p-type AlGaAs layer, the p-type layer may be doped with C;

[0079] The first sub-cell 210 may be a GaAs sub-cell, which may specifically include a window layer, an n-type GaAs emitter region (or an n-type GaInP emitter region), a p-type GaAs base region, and a back field layer stacked in sequence in a direction away from the GaAs substrate (i.e., the substrate 100). The window layer may be a GaInP layer, an AlGaInP layer, or an AlInP layer, and the back field layer may be a GaInP layer or an AlGaAs layer.

[0080] The second tunnel junction 13 may include an n-type layer and a p-type layer, the n-type layer may be an n-type GaAs layer or an n-type GaInP layer, the n-type layer may be doped with Si or Te, and the p-type layer may be a p-type AlGaAs layer, the p-type layer may be doped with C;

[0081] The two groups of metamorphic buffer layers 300 are as described above and will not be described in detail again;

[0082] The second sub-cell 220 may be an InGaAs sub-cell, which may specifically include a window layer, an n-type InGaAs emitter region (or an n-type GaInP emitter region), a p-type InGaAs base region, and a back field layer stacked in sequence in a direction away from the GaAs substrate (i.e., the substrate 100). The window layer may be a GaInP layer or an AlInGaAs layer, and the back field layer may be a GaInP layer or an AlInGaAs layer.

[0083] The second ohmic contact layer 14 may be a p-type ohmic contact layer, specifically a p-type AlInGaAs layer or a p-type InGaAs layer.

[0084] It can be understood that after the sacrificial layer 10, the first ohmic contact layer 11, the third sub-cell 230, the first tunnel junction 12, the first sub-cell 210, the second tunnel junction 13, the two groups of metamorphic buffer layers 300, the second sub-cell 220 and the second ohmic contact layer 14 are formed in sequence on the GaAs substrate (i.e., substrate 100) in a direction away from the GaAs substrate (i.e., substrate 100), the sacrificial layer 10 can be etched using an HF etching solution. Since the etching selectivity of the HF etching solution for the sacrificial layer 10 (AlAs layer) and the GaAs substrate (i.e., substrate 100) is significantly different, the cell structure composed of the first ohmic contact layer 11 to the second ohmic contact layer 14 can be peeled off from the GaAs substrate (i.e., substrate 100), and the cell structure composed of the first ohmic contact layer 11 to the second ohmic contact layer 14 can be transferred to another substrate, such as a flexible substrate, to prepare a flexible thin-film solar cell structure with a very high power-to-weight ratio. In addition, the stripped GaAs substrate (ie, substrate 100 ) can be reused after processing, which greatly reduces the cost of manufacturing solar cells.

[0085] The inventors have found that for a reverse-grown multi-junction solar cell structure, if only a metamorphic buffer layer composed of AlGaInAs material is used between the first sub-cell 210 and the second sub-cell 220, in order to achieve a lattice transition between the first sub-cell 210 and the second sub-cell 220, the metamorphic buffer layer is provided to include a w-layer sequence along the direction from the first sub-cell 210 to the second sub-cell 220, w ≥ 3, and w is an integer, and the lattice constant of the first w-1 layer sequence in the metamorphic buffer layer gradually increases, the lattice constant of the w-th layer sequence is smaller than the lattice constant of the w-1 layer sequence, the w-1 layer sequence serves as an overshoot layer, and the difference between the lattice constant of the w-th layer sequence and the second lattice constant a2 is smaller than a preset threshold.

[0086] For each layer sequence composed of AlGaInAs material in the metamorphic buffer layer, the lattice constant of the corresponding sequence needs to be increased by increasing the In composition. That is, in the metamorphic buffer layer composed of AlGaInAs material, the In composition of the first w-1 layer sequence gradually increases along the direction from the first sub-cell 210 to the second sub-cell 220, resulting in a gradually increasing lattice constant of the first w-1 layer sequence. However, this also causes the band gap of the first w-1 layer sequence to gradually decrease. A smaller band gap is more susceptible to light absorption. In particular, the w-1 layer sequence, which serves as the overshoot layer, has a relatively high In composition and a large lattice constant, but a small band gap, making it likely to absorb light. To prevent light absorption by sequences with high In composition and small band gaps in the metamorphic buffer layer, a higher Al composition needs to be set in these sequences to increase the band gap and prevent light absorption. For example, in the metamorphic buffer layer composed of AlGaInAs material, the Al composition of the first w-1 layer sequence also gradually increases along the direction from the first sub-cell 210 to the second sub-cell 220. As a result, the Al composition of the w-1 layer sequence is relatively high, typically requiring it to be greater than 50%. However, the sequence with too high Al content in the metamorphic buffer layer, especially the w-1 layer sequence as the overshoot layer, is prone to react with the HF etching solution during the process of stripping the GaAs substrate, affecting the stripping effect of the solar cell structure and even damaging the solar cell structure.

[0087] In the embodiment of the present application, the metamorphic buffer layer 300 located between the first sub-cell 210 and the second sub-cell 220 includes two parts. A first group of metamorphic buffer layers 310 composed of AlGaInAs material is provided in the part close to the first sub-cell 210. In the first group of metamorphic buffer layers 310, the In component of at least the first m-1 layer sequence gradually increases, so that the lattice constant of at least the first m-1 layer sequence gradually increases; in the part close to the second sub-cell 220, the sequence of higher In component and higher Al component originally required to be composed of AlGaInAs material is replaced by the second group of metamorphic buffer layers 320, and the second group of metamorphic buffer layers 320 is composed of (Al)GaInP material. For (Al)GaInP and AlGaInAs materials, although both increase their lattice constants by increasing the In content, the band gap of (Al)GaInP is significantly larger than that of AlGaInAs when their lattice constants are comparable. Even for GaInP, when the lattice constant of GaInP is comparable to that of AlGaInAs, the band gap of GaInP is sufficiently large to avoid light absorption. Therefore, the Al content of each layer sequence in the second set of metamorphic buffer layers 320 does not need to be high to increase the band gap and prevent light absorption. In other words, the Al content of each layer sequence in the second set of metamorphic buffer layers 320 can be relatively low. Furthermore, the Al content of each layer sequence in the first set of metamorphic buffer layers 310 does not need to be relatively high. Consequently, neither the first set of metamorphic buffer layers 310 nor the second set of metamorphic buffer layers 320 need to have a high Al content, thereby preventing them from reacting with the HF etching solution during the GaAs substrate stripping process and affecting the stripping effect of the solar cell structure.

[0088] Specifically, when the second group of metamorphic buffer layers 320 is made of AlGaInP material, the Al component of each layer sequence in the second group of metamorphic buffer layers 320 may be no greater than 30%, that is, may be less than or equal to 30%.

[0089] Optionally, in other embodiments of the present application, such as Figure 2 As shown, Figure 2 A cross-sectional schematic diagram of another multi-junction solar cell structure provided by an embodiment of the present application is shown. Figure 2 It can be seen that the substrate 100 can be a Ge substrate. In this case, the multi-junction solar cell structure can be a forward-grown GaInP / InGaAs / Ge triple-junction solar cell structure. The forward-grown triple-junction solar cell structure includes a first sub-cell 210, a third tunnel junction 20, two groups of metamorphic buffer layers 300, a Bragg reflection layer 21, a second sub-cell 220, a fourth tunnel junction 22, a fourth sub-cell 240 and a third ohmic contact layer 23 stacked in sequence along a direction away from the Ge substrate (i.e., the substrate 100).

[0090] The first subcell 210 may be a Ge subcell. Specifically, phosphorus diffusion may be performed on a p-type Ge substrate (i.e., substrate 100) to obtain an n-type emitter region, thereby forming a pn junction of the first subcell 210 (i.e., Ge subcell). Furthermore, an (Al)GaInP layer lattice-matched to the p-type Ge substrate (i.e., substrate 100) is grown on the p-type Ge substrate as a nucleation layer, which also serves as a window layer of the first subcell 210 (i.e., Ge subcell).

[0091] The third tunnel junction 20 may include an n-type layer and a p-type layer, the n-type layer may be an n-type GaAs layer or an n-type GaInP layer, the n-type layer may be doped with Si, and the p-type layer may be a p-type (Al) GaAs layer, the p-type layer may be doped with C;

[0092] The two groups of metamorphic buffer layers 300 are as described above and will not be described in detail again;

[0093] The Bragg reflective layer 21 may include a first sub-layer and a second sub-layer arranged alternately. The first sub-layer may be Al x In z GaAs layer, the second sublayer can be Al y In z GaAs, 0≤x<y≤1, 0.01≤z≤0.03. The first and second sublayers are grown alternately for s periods, 3≤s≤30;

[0094] The second sub-cell 220 may be an InGaAs sub-cell, and may specifically include a back field layer, a p-type InGaAs base region, an n-type InGaAs emitter region, and a window layer stacked in sequence in a direction away from the Ge substrate (i.e., the substrate 100). The back field layer may be a GaInP layer or an AlGaAs layer, and the window layer may be an AlGaInP layer or an AlInP layer.

[0095] The fourth tunnel junction 22 may include an n-type layer and a p-type layer, the n-type layer may be an n-type InGaAs layer or an n-type GaInP layer, the n-type layer may be doped with Si, and the p-type layer may be a p-type (Al)InGaAs layer, the p-type layer may be doped with C;

[0096] The fourth subcell 240 may be an AlGaInP subcell or a GaInP subcell. When the fourth subcell 240 is an AlGaInP subcell, the fourth subcell 240 may specifically include an AlGaInP back surface field layer, a p-type AlGaInP base region, an n-type AlGaInP emitter region, and an AlInP window layer stacked in sequence in a direction away from the Ge substrate (i.e., substrate 100). When the fourth subcell 240 is a GaInP subcell, the fourth subcell 240 may specifically include an AlGaInP back surface field layer, a p-type GaInP base region, an n-type GaInP emitter region, and an AlInP window layer stacked in sequence in a direction away from the Ge substrate (i.e., substrate 100).

[0097] The third ohmic contact layer 23 may be an n-type ohmic contact layer, specifically an n-type InGaAs layer.

[0098] Based on the same inventive concept, the present invention also provides a method for preparing a multi-junction solar cell structure. Figure 1 and Figure 2 As shown, the preparation method comprises:

[0099] S100: providing a substrate 100.

[0100] S200: forming a plurality of stacked sub-cells 200 on one side of the substrate 100, the plurality of sub-cells 200 including a first sub-cell 210 and a second sub-cell 220 adjacently disposed; the first sub-cell 210 including a pn junction formed of a material having a first lattice constant a1, and the second sub-cell 220 including a pn junction formed of a material having a second lattice constant a2, wherein the first lattice constant a1 is at least 0.002 nm smaller than the second lattice constant a2;

[0101] Two groups of metamorphic buffer layers 300 are provided between the first sub-cell 210 and the second sub-cell 220 , and the second group of metamorphic buffer layers 310 is located on a side of the first group of metamorphic buffer layers 320 close to the second sub-cell 220 ;

[0102] The first group of metamorphic buffer layers 310 is made of AlGaInAs material. The first group of metamorphic buffer layers 310 includes a sequence of m layers stacked in a direction from the first sub-cell 210 to the second sub-cell 220, where m ≥ 3 and m is an integer. The lattice constant of each layer sequence in the first group of metamorphic buffer layers 310 is greater than the first lattice constant a1 and less than the second lattice constant a2. The lattice constant of at least the first m-1 layers in the first group of metamorphic buffer layers 310 gradually increases.

[0103] The second group of metamorphic buffer layers 320 is composed of GaInP material or AlGaInP material. The second group of metamorphic buffer layers 320 includes an n-layer sequence stacked in a direction from the first sub-cell 210 to the second sub-cell 220, where n≥2 and n is an integer; the lattice constant of each layer sequence in the second group of metamorphic buffer layers 320 is greater than the average lattice constant of each layer sequence in the first group of metamorphic buffer layers 310; in the second group of metamorphic buffer layers 320, the lattice constant of the first n-1 layer sequences gradually increases, the lattice constant of the n-1 layer sequence is greater than the lattice constant of the n layer sequence, and the difference between the lattice constant of the n layer sequence and the second lattice constant is less than a preset threshold.

[0104] Furthermore, in the first group of metamorphic buffer layers 310 , the lattice constant of the m-th layer sequence may be smaller than the lattice constant of the m-1-th layer sequence, or may be larger than the lattice constant of the m-1-th layer sequence.

[0105] The lattice constant of the first layer sequence of the second group of metamorphic buffer layers 320 can be greater than the lattice constant of the mth layer sequence of the first group of metamorphic buffer layers 310, or less than the lattice constant of the mth layer sequence of the first group of metamorphic buffer layers 310, or even equal to the lattice constant of the mth layer sequence of the first group of metamorphic buffer layers 310.

[0106] The lattice constant of the nth layer sequence in the second group of metamorphic buffer layers 320 can be equal to the second lattice constant a2, or can be greater than the second lattice constant a2, or can be less than the second lattice constant a2, but the lattice constant of the nth layer sequence in the second group of metamorphic buffer layers 320 is close to the second lattice constant a2, and the difference between the lattice constant and the second lattice constant a2 is less than a preset threshold.

[0107] Optionally, in some embodiments of the present application, reference Figure 1 As shown, the substrate 100 may be a GaAs substrate. In this case, step S200 of forming a plurality of stacked sub-cells 200 on one side of the substrate 100 may include:

[0108] S210: A sacrificial layer 10, a first ohmic contact layer 11, a third sub-cell 230, a first tunnel junction 12, a first sub-cell 210, a second tunnel junction 13, two groups of metamorphic buffer layers 300, a second sub-cell 220 and a second ohmic contact layer 14 are sequentially formed on one side of the GaAs substrate (i.e., the substrate 100).

[0109] Specifically, first, an AlAs layer is grown on a GaAs substrate (i.e., substrate 100 ) as a sacrificial layer 10 ;

[0110] Second, an n-type GaAs layer is grown on the side of the sacrificial layer 10 facing away from the GaAs substrate (ie, the substrate 100 ) as an n-type ohmic contact layer, namely, the first ohmic contact layer 11 ;

[0111] Third, on the side of the first ohmic contact layer 11 away from the GaAs substrate (i.e., substrate 100), an n-type AlInP window layer, an n-type AlGaInP emitter region, a p-type AlGaInP base region, and a p-type AlGaInP back surface field layer are sequentially formed in a direction away from the GaAs substrate (i.e., substrate 100), forming a third sub-cell 230. The third sub-cell 230 is an AlGaInP sub-cell.

[0112] Fourth, on the side of the third subcell 230 facing away from the GaAs substrate (i.e., substrate 100), an n-type GaAs layer or an n-type GaInP layer is grown as the n-type layer of the first tunnel junction 12, and a p-type AlGaAs layer is grown as the p-type layer of the first tunnel junction 12, wherein the n-type layer can be doped with Si or Te, and the p-type layer can be doped with C;

[0113] Fifth, on the side of the first tunnel junction 12 away from the GaAs substrate (i.e., substrate 100), a window layer, an n-type GaAs emitter region (or n-type GaInP emitter region), a p-type GaAs base region, and a back field layer are sequentially formed in a direction away from the GaAs substrate (i.e., substrate 100) to constitute a first sub-cell 210. The first sub-cell 210 is a GaAs sub-cell, wherein the window layer may be a GaInP layer, an AlGaInP layer, or an AlInP layer, and the back field layer may be a GaInP layer or an AlGaAs layer.

[0114] Sixth, on the side of the first subcell 210 facing away from the GaAs substrate (i.e., substrate 100), an n-type GaAs layer or an n-type GaInP layer is grown as the n-type layer of the second tunnel junction 13, and a p-type AlGaAs layer is grown as the p-type layer of the second tunnel junction 13. The n-type layer can be doped with Si or Te, and the p-type layer can be doped with C.

[0115] Seventh, a first group of metamorphic buffer layers 310 and a second group of metamorphic buffer layers 320 are formed in sequence. The two groups of metamorphic buffer layers 300 are as described above and will not be described in detail again.

[0116] Eighth, on a side of the second group of metamorphic buffer layers 320 away from the GaAs substrate (i.e., substrate 100), a window layer, an n-type InGaAs emitter region (or an n-type GaInP emitter region), a p-type InGaAs base region, and a back field layer are sequentially formed in a direction away from the GaAs substrate (i.e., substrate 100), forming a second sub-cell 220. The second sub-cell 220 is an InGaAs sub-cell, wherein the window layer may be a GaInP layer or an AlInGaAs layer, and the back field layer may be a GaInP layer or an AlInGaAs layer;

[0117] Ninth, the p-type AlInGaAs layer or the p-type InGaAs layer serves as a p-type ohmic contact layer forming an ohmic contact with the electrode, ie, the second ohmic contact layer 14 .

[0118] S220: The sacrificial layer 10 is corroded by using HF etching solution to peel off the battery structure composed of the first ohmic contact layer 11 to the second ohmic contact layer 14 from the GaAs substrate (i.e., substrate 100), and the battery structure composed of the first ohmic contact layer 11 to the second ohmic contact layer 14 is transferred to another substrate.

[0119] In this way, a GaInP / GaAs / InGaAs inverted triple junction solar cell structure is obtained.

[0120] Optionally, in other embodiments of the present application, refer to Figure 2 As shown, the substrate 100 may be a Ge substrate. In this case, step S200 of forming a plurality of stacked sub-cells 200 on one side of the substrate 100 may include:

[0121] S230: On one side of the Ge substrate (i.e., substrate 100), a first sub-cell 210, a third tunnel junction 20, two groups of metamorphic buffer layers 300, a Bragg reflection layer 21, a second sub-cell 220, a fourth tunnel junction 22, a fourth sub-cell 240 and a third ohmic contact layer 23 are sequentially formed.

[0122] Specifically, first, phosphorus diffusion can be performed on the p-type Ge substrate (i.e., substrate 100) to obtain an n-type emitter region, forming a pn junction of the first sub-cell 210 (i.e., Ge sub-cell). Furthermore, an (Al)GaInP layer lattice-matched to the substrate is grown on the p-type Ge substrate (i.e., substrate 100) as a nucleation layer and a window layer of the first sub-cell 210 (i.e., Ge sub-cell).

[0123] Second, on the side of the first subcell 210 facing away from the Ge substrate (i.e., substrate 100), an n-type GaAs layer or an n-type GaInP layer is grown as the n-type layer of the third tunnel junction 20, and a p-type (Al) GaAs layer is grown as the p-type layer of the third tunnel junction 20. The n-type layer can be doped with Si, and the p-type layer can be doped with C.

[0124] Third, a first group of metamorphic buffer layers 310 and a second group of metamorphic buffer layers 320 are formed in sequence. The two groups of metamorphic buffer layers 300 are as described above and will not be described in detail again.

[0125] Fourth, a Bragg reflector layer 21 is grown on the side of the second group of metamorphic buffer layers 320 away from the Ge substrate (ie, substrate 100). The Bragg reflector layer 21 may include a first sublayer and a second sublayer arranged alternately. The first sublayer may be Al x In z GaAs layer, the second sublayer can be Al y In zGaAs, 0≤x<y≤1, 0.01≤z≤0.03. The first and second sublayers are grown alternately for s periods, 3≤s≤30;

[0126] Fifth, on the side of the Bragg reflector 21 facing away from the Ge substrate (i.e., substrate 100), a back field layer, a p-type InGaAs base region, an n-type InGaAs emitter region, and a window layer are sequentially formed in a direction away from the Ge substrate (i.e., substrate 100) to form a second sub-cell 220. The second sub-cell 220 is an InGaAs sub-cell, wherein the back field layer may be a GaInP layer or an AlGaAs layer, and the window layer may be an AlGaInP layer or an AlInP layer;

[0127] Sixth, on the side of the second sub-cell 220 facing away from the Ge substrate (i.e., substrate 100), an n-type InGaAs layer or an n-type GaInP layer is grown as the n-type layer of the fourth tunnel junction 22, and a p-type (Al) InGaAs layer is grown as the p-type layer of the fourth tunnel junction 22. The n-type layer can be doped with Si, and the p-type layer can be doped with C.

[0128] Seventh, a fourth subcell 240 is formed on the side of the fourth tunnel junction 22 facing away from the Ge substrate (i.e., substrate 100). The fourth subcell 240 may be an AlGaInP subcell or a GaInP subcell. When the fourth subcell 240 is an AlGaInP subcell, the fourth subcell 240 may specifically include an AlGaInP back field layer, a p-type AlGaInP base region, an n-type AlGaInP emitter region, and an AlInP window layer stacked in sequence in a direction away from the Ge substrate (i.e., substrate 100). When the fourth subcell 240 is a GaInP subcell, the fourth subcell 240 may specifically include an AlGaInP back field layer, a p-type GaInP base region, an n-type GaInP emitter region, and an AlInP window layer stacked in sequence in a direction away from the Ge substrate (i.e., substrate 100).

[0129] Eighth, an n-type InGaAs layer is grown as an n-type ohmic contact layer forming an ohmic contact with the electrode, ie, the third ohmic contact layer 23 .

[0130] In this way, a forward-grown GaInP / InGaAs / Ge triple-junction solar cell structure is obtained.

[0131] The advantages of the multi-junction solar cell structure prepared by the method provided in the embodiments of the present application have been described in detail in the aforementioned embodiments and will not be repeated here.

[0132] The various parts in this manual are described in a combination of parallel and progressive manners. Each part focuses on the differences from other parts, and the same or similar parts between the various parts can be referenced to each other.

[0133] With respect to the above description of the disclosed embodiments, the features described in the various embodiments in this specification may be interchanged or combined with one another to enable those skilled in the art to implement or use the present 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 the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A multi-junction solar cell structure, characterized in that: A device comprising a substrate and a plurality of subcells stacked on one side of the substrate, the plurality of subcells comprising a first subcell and a second subcell disposed adjacent to each other; the first subcell comprising a pn junction formed of a material having a first lattice constant, the second subcell comprising a pn junction formed of a material having a second lattice constant, the first lattice constant being at least 0.002 nm smaller than the second lattice constant; Two groups of metamorphic buffer layers are provided between the first sub-cell and the second sub-cell, and the second group of metamorphic buffer layers is located on a side of the first group of metamorphic buffer layers close to the second sub-cell; The first group of metamorphic buffer layers is made of AlGaInAs material, and includes a sequence of m layers stacked in a direction from the first sub-cell to the second sub-cell, where m is ≥ 3 and m is an integer; the lattice constant of each layer sequence in the first group of metamorphic buffer layers is greater than the first lattice constant and less than the second lattice constant; and the lattice constant of at least the first m-1 layer sequences in the first group of metamorphic buffer layers gradually increases; The second group of metamorphic buffer layers is composed of GaInP material or AlGaInP material, and the second group of metamorphic buffer layers includes an n-layer sequence stacked in the direction from the first sub-cell to the second sub-cell, n≥2, and n is an integer; the lattice constant of each layer sequence in the second group of metamorphic buffer layers is greater than the average lattice constant of each layer sequence in the first group of metamorphic buffer layers; in the second group of metamorphic buffer layers, the lattice constant of the first n-1 layer sequences gradually increases, the lattice constant of the n-1 layer sequence is greater than the lattice constant of the n layer sequence, and the difference between the lattice constant of the n layer sequence and the second lattice constant is less than a preset threshold.

2. The multi-junction solar cell structure according to claim 1, characterized in that In the first group of metamorphic buffer layers, the lattice constant of the m-th layer sequence is smaller than the lattice constant of the m-1-th layer sequence.

3. The multi-junction solar cell structure according to claim 1, wherein: In the first group of metamorphic buffer layers, the lattice constant of the m-th layer sequence is greater than the lattice constant of the m-1-th layer sequence.

4. The multi-junction solar cell structure according to any one of claims 1 to 3, characterized in that: The lattice constant of the first layer sequence of the second group of metamorphic buffer layers is greater than the lattice constant of the mth layer sequence of the first group of metamorphic buffer layers.

5. The multi-junction solar cell structure according to any one of claims 1 to 3, characterized in that: The lattice constant of the first layer sequence of the second group of metamorphic buffer layers is smaller than the lattice constant of the mth layer sequence of the first group of metamorphic buffer layers.

6. The multi-junction solar cell structure according to claim 1, characterized in that: The lattice constant of the n-th layer sequence in the second group of metamorphic buffer layers is not less than the second lattice constant.

7. The multi-junction solar cell structure according to claim 1, characterized in that: The second group of metamorphic buffer layers is made of AlGaInP material, and the Al component of each layer sequence in the second group of metamorphic buffer layers is no more than 30%.

8. The multi-junction solar cell structure according to claim 1, wherein: The substrate is a GaAs substrate, and the multi-junction solar cell structure includes a sacrificial layer, a first ohmic contact layer, a third sub-cell, a first tunnel junction, the first sub-cell, a second tunnel junction, the two groups of metamorphic buffer layers, the second sub-cell, and a second ohmic contact layer, which are stacked in sequence along a direction away from the GaAs substrate. The sacrificial layer is an AlAs layer, the first sub-cell is a GaAs sub-cell, the second sub-cell is an InGaAs sub-cell, and the third sub-cell is an AlGaInP sub-cell.

9. The multi-junction solar cell structure according to claim 1, characterized in that: The substrate is a Ge substrate, and the multi-junction solar cell structure includes the first sub-cell, the third tunnel junction, the two groups of metamorphic buffer layers, the Bragg reflection layer, the second sub-cell, the fourth tunnel junction, the fourth sub-cell and the third ohmic contact layer stacked in sequence along a direction away from the Ge substrate, wherein the first sub-cell is a Ge sub-cell, the second sub-cell is an InGaAs sub-cell, and the fourth sub-cell is an AlGaInP sub-cell or a GaInP sub-cell.

10. A method for preparing a multi-junction solar cell structure, characterized in that: include: providing a substrate; forming a plurality of stacked subcells on one side of the substrate, the plurality of subcells including a first subcell and a second subcell disposed adjacent to each other; the first subcell including a pn junction formed of a material having a first lattice constant, the second subcell including a pn junction formed of a material having a second lattice constant, the first lattice constant being at least 0.002 nm smaller than the second lattice constant; Two groups of metamorphic buffer layers are provided between the first sub-cell and the second sub-cell, and the second group of metamorphic buffer layers is located on a side of the first group of metamorphic buffer layers close to the second sub-cell; The first group of metamorphic buffer layers is made of AlGaInAs material, and includes a sequence of m layers stacked in a direction from the first sub-cell to the second sub-cell, where m is ≥ 3 and m is an integer; the lattice constant of each layer sequence in the first group of metamorphic buffer layers is greater than the first lattice constant and less than the second lattice constant; and the lattice constant of at least the first m-1 layer sequences in the first group of metamorphic buffer layers gradually increases; The second group of metamorphic buffer layers is composed of GaInP material or AlGaInP material, and the second group of metamorphic buffer layers includes an n-layer sequence stacked in the direction from the first sub-cell to the second sub-cell, n≥2, and n is an integer; the lattice constant of each layer sequence in the second group of metamorphic buffer layers is greater than the average lattice constant of each layer sequence in the first group of metamorphic buffer layers; in the second group of metamorphic buffer layers, the lattice constant of the first n-1 layer sequences gradually increases, the lattice constant of the n-1 layer sequence is greater than the lattice constant of the n layer sequence, and the difference between the lattice constant of the n layer sequence and the second lattice constant is less than a preset threshold.

11. The method for preparing a multi-junction solar cell structure according to claim 10, wherein: The substrate is a GaAs substrate, and a plurality of sub-cells stacked on one side of the substrate include: A sacrificial layer, a first ohmic contact layer, a third sub-cell, a first tunnel junction, the first sub-cell, a second tunnel junction, the two groups of metamorphic buffer layers, the second sub-cell, and a second ohmic contact layer are sequentially formed on one side of the GaAs substrate, wherein the sacrificial layer is an AlAs layer, the first sub-cell is a GaAs sub-cell, the second sub-cell is an InGaAs sub-cell, and the third sub-cell is an AlGaInP sub-cell; The sacrificial layer is corroded by HF etching solution, the battery structure consisting of the first ohmic contact layer to the second ohmic contact layer is peeled off from the GaAs substrate, and the battery structure consisting of the first ohmic contact layer to the second ohmic contact layer is transferred to another substrate.

12. The method for preparing a multi-junction solar cell structure according to claim 10, wherein: The substrate is a Ge substrate, and a plurality of sub-cells stacked on one side of the substrate include: The first sub-cell, the third tunnel junction, the two groups of metamorphic buffer layers, the Bragg reflection layer, the second sub-cell, the fourth tunnel junction, the fourth sub-cell and the third ohmic contact layer are formed in sequence on one side of the Ge substrate, wherein the first sub-cell is a Ge cell, the second sub-cell is an InGaAs sub-cell, and the fourth sub-cell is an AlGaInP sub-cell or a GaInP sub-cell.

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