Multi-junction solar cell structure and preparation method thereof

Abstract

The invention discloses a multi-junction solar cell structure and a preparation method thereof, relates to the technical field of solar cells, and is characterized in that two groups of metamorphic buffer layers are arranged between a first sub-cell and a second sub-cell with lattice mismatch to play a role in lattice transition; residual stress generated by lattice mismatch between the first sub-cell and the second sub-cell is effectively released, and dislocation generated by lattice mismatch between the first sub-cell and the second sub-cell is effectively prevented from extending to an active region (namely a pn junction of the second sub-cell) of the second sub-cell; moreover, the first group of metamorphic buffer layers is made of an AlGaInAs material, the second group of metamorphic buffer layers is made of an (Al) GaInP material, and the hardness of the (Al) GaInP material is higher than that of the AlGaInAs material, so that the second group of metamorphic buffer layers is less prone to dislocation and defects, the dislocation of the metamorphic buffer layers is further prevented from extending to the active region of the second sub-cell, and the performance of the multi-junction solar cell structure is improved.

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 electrical energy and are an effective form of clean energy. Traditional solar cells are usually silicon solar cells, but the absorption band of silicon solar cells to the solar spectrum is relatively single, so multi-junction solar cells came into being. Multi-junction solar cells are composed of sub-cells with different bandgap widths connected in series through tunnel junctions. Each sub-cell absorbs a different band of the solar spectrum, thereby greatly improving the conversion efficiency of solar cells.

[0003] III-V compound semiconductor solar cells have the highest conversion efficiency in the current material system, and have the advantages of good high temperature resistance and strong radiation resistance, and are recognized as a new generation of high-performance and long-life space main power. For example, GaInP / InGaAs / Ge lattice-matched triple-junction solar cells 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 smaller than the current density of the Ge bottom cell, which cannot fully utilize the solar spectrum and limits the improvement of the photoelectric conversion efficiency of solar cells.

[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 a sub-cell often leads to lattice mismatch between 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] In order 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 groups of metamorphic buffer layers between two adjacent sub-cells with lattice mismatch in the multi-junction solar cell structure, play the role of lattice transition between two adjacent sub-cells with lattice mismatch, effectively release the residual stress generated during the epitaxial expansion of the lattice mismatch material, and effectively block 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 application provides the following technical solutions:

[0007] In a first aspect, an embodiment of the present application provides 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 composed of a material having a first lattice constant, the second sub-cell comprising a pn junction composed 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] Wherein, two groups of metamorphic buffer layers are arranged 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 the first group of metamorphic buffer layers includes m-layer sequences stacked in a direction from the first subcell to the second subcell, where 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; 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 n-layer sequences stacked along 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 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.

[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] A plurality of stacked subcells are formed 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 comprises a pn junction formed of a material having a first lattice constant, the second subcell comprises a pn junction formed of a material having a second lattice constant, and the first lattice constant is at least 0.002 nm smaller than the second lattice constant;

[0022] Wherein, two groups of metamorphic buffer layers are arranged 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 the first group of metamorphic buffer layers includes m-layer sequences stacked in a direction from the first subcell to the second subcell, where 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; 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 n-layer sequences stacked along 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 plurality of 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 composed of the first ohmic contact layer to the second ohmic contact layer is peeled off from the GaAs substrate, and the battery structure composed 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 plurality of sub-cells stacked on one side of the substrate include:

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

[0030] Compared with the prior art, the above technical solution has the following advantages:

[0031] The multi-junction solar cell structure provided in 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 played between the first sub-cell and the second sub-cell, the residual stress generated by the lattice mismatch between the first sub-cell and the second sub-cell is effectively released, and the dislocation generated by the lattice mismatch between the first sub-cell and the second sub-cell is effectively blocked from extending to 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 subcell and the second subcell, the second group of metamorphic buffer layers is located on a side of the first group of metamorphic buffer layers close to the second subcell, wherein the first group of metamorphic buffer layers is made of AlGaInAs material, and the first group of metamorphic buffer layers includes an m-layer sequence stacked in a direction from the first subcell to the second subcell, 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 n-layer sequences 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 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.

[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 of 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 are composed of AlGaInAs material, and the second group of metamorphic buffer layers are composed of GaInP material or AlGaInP material, and the hardness of the (Al)GaInP material is higher than that of the 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, and can further prevent the dislocations of the metamorphic buffer layers from extending to the active region 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 in conjunction with 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 drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 paying creative work.

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

[0039] Figure 2 A cross-sectional schematic diagram 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 the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work 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 need not be 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, which is only to describe the distinction mode adopted by the objects of the same attributes when describing 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, the present application is described in detail with reference to the schematic diagram. When describing the embodiments of the present application in detail, for the sake of convenience, the drawings showing the device structure will not be partially enlarged according to the general scale, and the schematic diagram is only an example, which should not limit the scope of protection of the present application. In addition, 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 a sub-cell often leads to lattice mismatch between 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 present application provides a multi-junction solar cell structure. Figure 1 A cross-sectional schematic diagram of a multi-junction solar cell structure provided in an embodiment of the present application is shown. 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 include a first sub-cell 210 and a second sub-cell 220 arranged adjacent to each other, the first sub-cell 210 includes a pn junction formed of a material having a first lattice constant a1, the second sub-cell 220 includes a pn junction formed of a material having a second lattice constant a2, the first lattice constant a1 is at least 0.002nm smaller than the second lattice constant a2, that is, a1≤a2-0.002nm, or a2≥a1+0.002nm; in this way, if the first sub-cell 210 and the second sub-cell 220 are connected only by a tunneling 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, and 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, and the second group of metamorphic buffer layers 320 are 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 played between the first sub-cell 210 and the second sub-cell 220, and the residual stress generated by the lattice mismatch between the first sub-cell 210 and the second sub-cell 220 is effectively released, and the dislocation generated by the lattice mismatch between the first sub-cell 210 and the second sub-cell 220 is effectively blocked from extending to the active area 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, 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 m-layer sequences stacked in the 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 the 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. Thus, 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 m-th layer sequence is smaller than the lattice constant of the m-1-th layer sequence, so that the m-1-th layer sequence serves as an overshoot layer; then, when the m-th layer sequence with a relatively small lattice constant is grown on the m-1-th 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 as a whole from the first lattice constant a1 to the second lattice constant a2.

[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, on the basis of the first group of metamorphic buffer layers 310, further transitions to the second lattice constant a2; 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-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 n-th layer sequence 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 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. Thus, 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] Furthermore, in the second group of metamorphic buffer layers 320, the lattice constant of the nth layer sequence is smaller than the lattice constant of the n-1th layer sequence, so that the n-1th layer sequence serves as an overshoot layer; then, when the nth layer sequence with a relatively small lattice constant is grown on the n-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 (including the first group of metamorphic buffer layers 310 and the previous sequence in the second group of metamorphic buffer layers 320). On the one hand, it can compensate for the residual stress generated by 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 (that is, the pn junction of the second sub-battery 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, and 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 nth layer sequence in the second group of metamorphic buffer layers 320 and the second lattice constant a2 is less than a preset threshold, and the nth 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 option is that the lattice constant of the 1st layer sequence of the second group of metamorphic buffer layers 320 is less than the mth layer sequence of the first group of metamorphic buffer layers 310.

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

[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-th layer sequence, and the m-1-th 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 the dislocation from extending to the subsequent sequence; 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-th layer sequence, and the n-1-th 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 the dislocation 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 the dislocation from extending to the subsequent sequence; the lattice constant of the first layer sequence in the second group of metamorphic buffer layers 320 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 the dislocation from extending to the subsequent sequence; 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 the dislocation from extending to the active area of ​​the second sub-battery 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 the dislocation from extending to the subsequent sequence; in the second group of metamorphic buffer layers 320, the lattice constant of the first n-1 layer sequence gradually increases, and the lattice constant of the n-th layer sequence is smaller than the lattice constant of the n-1-th layer sequence, and the n-1-th 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 the dislocation 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, there is at least one overshoot layer at the junction of the first group of metamorphic buffer layers 310 and the second group of metamorphic buffer layers 320, and there is one overshoot layer at the junction of the second group of metamorphic buffer layers 320 and the second sub-cell 220, so that the two groups of metamorphic buffer layers 300 can effectively release the residual stress generated by the lattice mismatch between the first sub-cell 210 and the second sub-cell 220 while realizing the lattice transition between the first sub-cell 210 and the second sub-cell 220, and effectively block the dislocation generated by the lattice mismatch between the first sub-cell 210 and the second sub-cell 220 from extending to the active area 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 group of metamorphic buffer layers 310 and the second group of metamorphic buffer layers 320 , which can also relieve the pressure of the overshoot layer provided at the interface between the second group of metamorphic buffer layers 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 sequence 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, there is an overshoot layer mainly 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 to the active area of ​​the second sub-cell (i.e., the pn junction of the second sub-cell).

[0070] On the basis of the above-mentioned several 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 of the second group of metamorphic buffer layers 320 and the second sub-battery 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 of the second group of metamorphic buffer layers 320 and the second sub-battery 220 can also be lattice matched, and the n-th layer sequence of the second group of metamorphic buffer layers 320 can also serve as 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 (i.e., the pn junction of the second sub-battery 220).

[0071] In summary, the multi-junction solar cell structure provided in 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 composed of AlGaInAs material, and the second group of metamorphic buffer layers 320 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 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 produce dislocations and defects, and the dislocations of the metamorphic buffer layers can be further prevented from extending to the active region of the second sub-battery 220 (i.e., the pn junction of the second sub-battery 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 can be a GaAs substrate. In this case, the multi-junction solar cell structure can 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 stacked in sequence 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 subcell 230 may be an AlGaInP subcell, which may specifically include an n-type AlInP 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, 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), 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.

[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, 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), 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.

[0083] The second ohmic contact layer 14 may be a p-type ohmic contact layer, and specifically may be 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 sequentially formed on the GaAs substrate (i.e., substrate 100) along the direction away from the GaAs substrate (i.e., substrate 100), the sacrificial layer 10 can be corroded by HF etching solution. Since the etching selectivity of the HF etching solution to the sacrificial layer 10 (AlAs layer) and the GaAs substrate (i.e., substrate 100) is greatly different, the battery 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 battery structure composed of the first ohmic contact layer 11 to the second ohmic contact layer 14 can be transferred to other substrates such as flexible substrates, so as to prepare a flexible thin-film solar cell structure with a very high weight-to-power 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-growing 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-1th layer sequence, the w-1th 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, it is necessary to increase the lattice constant of the corresponding sequence by increasing the In component. That is, in the metamorphic buffer layer composed of AlGaInAs material, along the direction from the first subcell 210 to the second subcell 220, the In component of the first w-1 layer sequence gradually increases, so that the lattice constant of the first w-1 layer sequence gradually increases, but it will also cause the band gap of the first w-1 layer sequence to gradually decrease. The smaller the band gap, the easier it is to absorb light. In particular, the w-1 layer sequence as the overshoot layer has a relatively high In component, a large lattice constant, but a small band gap, which is likely to absorb light. In order to prevent the sequence with a higher In component and a smaller band gap in the metamorphic buffer layer from absorbing light, it is necessary to set a higher Al component in these sequences to increase the band gap and prevent light absorption. For example, in the metamorphic buffer layer composed of AlGaInAs material, along the direction from the first subcell 210 to the second subcell 220, the Al component of the first w-1 layer sequence also gradually increases. In this way, the Al component of the w-1 layer sequence is relatively high, usually needs to be higher than 50%. However, the sequence with too high Al content in the metamorphic buffer layer, especially the w-1th layer sequence as the overshoot layer, is easy 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 arranged 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 material and AlGaInAs material, although the lattice constant of both is increased by increasing the In component, when the lattice constants of (Al)GaInP material and AlGaInAs material are equivalent, the band gap of (Al)GaInP material is significantly larger than the band gap of AlGaInAs material. Even for GaInP material, when the lattice constant of GaInP material is equivalent to that of AlGaInAs material, the band gap of GaInP material is large enough and there will be no light absorption problem. In this way, the Al component of each layer sequence in the second group of metamorphic buffer layers 320 does not need to be set high to increase the band gap and prevent light absorption, or in other words, the Al component of each layer sequence in the second group of metamorphic buffer layers 320 can be low, and the Al component of each layer sequence in the first group of metamorphic buffer layers 310 does not need to be high. Therefore, both the first group of metamorphic buffer layers 310 and the second group of metamorphic buffer layers 320 do not need to be set with a high Al component, and thus will not react with the HF etching solution in the process of stripping the GaAs substrate to affect 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, Figure 2 As shown, Figure 2 A cross-sectional schematic diagram of another multi-junction solar cell structure provided in 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, which 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 to form a pn junction of the first subcell 210 (i.e., Ge subcell). 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 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, 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 reflection 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 sublayer and the second sublayer are grown alternately for s periods, 3≤s≤30;

[0094] The second subcell 220 may be an InGaAs subcell, which 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, 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 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., the 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., the substrate 100);

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

[0098] Based on the same inventive concept, the present application also provides a method for preparing a multi-junction solar cell structure, referring to 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, wherein the plurality of sub-cells 200 include a first sub-cell 210 and a second sub-cell 220 disposed adjacent to each other; the first sub-cell 210 includes a pn junction formed of a material having a first lattice constant a1, and the second sub-cell 220 includes 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] Wherein, two groups of metamorphic buffer layers 300 are arranged between the first sub-battery 210 and the second sub-battery 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-battery 220;

[0102] The first group of metamorphic buffer layers 310 is made of AlGaInAs material, and the first group of metamorphic buffer layers 310 includes m-layer sequences 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 layer sequences 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, and 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, 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 sequence 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 may be greater than the lattice constant of the mth layer sequence of the first group of metamorphic buffer layers 310, or may be less than the lattice constant of the mth layer sequence of the first group of metamorphic buffer layers 310, or may even be 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 away from the GaAs substrate (ie, the substrate 100 ) as an n-type ohmic contact layer, namely, the first ohmic contact layer 11 ;

[0111] Thirdly, on the side of the first ohmic contact layer 11 away from the GaAs substrate (i.e., the 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 field layer are sequentially formed in a direction away from the GaAs substrate (i.e., the substrate 100), forming a third subcell 230, which is an AlGaInP subcell;

[0112] Fourth, on the side of the third subcell 230 away from the GaAs substrate (i.e., the 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 may be doped with Si or Te, and the p-type layer may 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 away from the GaAs substrate (i.e., the 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 the side of the second group of metamorphic buffer layers 320 away from the GaAs substrate (i.e., the 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., the substrate 100) to form a second subcell 220, the second subcell 220 being an InGaAs subcell, 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 that forms an ohmic contact with the electrode, that is, the second ohmic contact layer 14 .

[0118] S220: using HF etching solution to corrode the sacrificial layer 10, peeling off the battery structure composed of the first ohmic contact layer 11 to the second ohmic contact layer 14 from the GaAs substrate (ie, the substrate 100), and transferring the battery structure composed of the first ohmic contact layer 11 to the second ohmic contact layer 14 to another substrate.

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

[0120] Optionally, in some 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: A first subcell 210, a third tunnel junction 20, two groups of metamorphic buffer layers 300, a Bragg reflection layer 21, a second subcell 220, a fourth tunnel junction 22, a fourth subcell 240 and a third ohmic contact layer 23 are sequentially formed on one side of the Ge substrate (ie, the substrate 100).

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

[0123] Second, on the side of the first subcell 210 away from the Ge substrate (i.e., the 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, wherein the n-type layer may be doped with Si, and the p-type layer may 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 reflection layer 21 is grown on the side of the second group of metamorphic buffer layers 320 away from the Ge substrate (ie, the substrate 100). The Bragg reflection 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 sublayer and the second sublayer are grown alternately for s periods, 3≤s≤30;

[0126] Fifth, on the side of the Bragg reflector 21 away from the Ge substrate (i.e., the 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 along a direction away from the Ge substrate (i.e., the substrate 100) to form a second subcell 220, wherein the second subcell 220 is an InGaAs subcell, 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 subcell 220 away from the Ge substrate (i.e., the 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 may be doped with Si, and the p-type layer may be doped with C;

[0128] Seventh, a fourth subcell 240 is formed on the side of the fourth tunnel junction 22 away from the Ge substrate (i.e., the 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., the 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., the 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, that is, 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 ways. 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 embodiments in this specification may be replaced or combined with each other, so that professionals in the field can implement or use the present application. Various modifications to these embodiments will be apparent to professionals in the field, 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 will not be limited to the embodiments shown herein, but will 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 method for manufacturing a semiconductor device comprising a substrate and a plurality of subcells stacked on one side of the substrate, wherein the plurality of subcells include a first subcell and a second subcell disposed adjacent to each other; the first subcell includes a pn junction formed of a material having a first lattice constant, the second subcell includes a pn junction formed of a material having a second lattice constant, and the first lattice constant is at least 0.002 nm smaller than the second lattice constant; Wherein, two groups of metamorphic buffer layers are arranged 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 the first group of metamorphic buffer layers includes m-layer sequences stacked in a direction from the first subcell to the second subcell, where 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; 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 n-layer sequences stacked along 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, characterized in that: 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 nth 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 not greater than 30%.

8. The multi-junction solar cell structure according to claim 1, characterized in that: 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.

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 which are sequentially stacked in 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; A plurality of stacked subcells are formed 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 comprises a pn junction formed of a material having a first lattice constant, the second subcell comprises a pn junction formed of a material having a second lattice constant, and the first lattice constant is at least 0.002 nm smaller than the second lattice constant; Wherein, two groups of metamorphic buffer layers are arranged 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 the first group of metamorphic buffer layers includes m-layer sequences stacked in a direction from the first subcell to the second subcell, where 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; 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 n-layer sequences stacked along 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, characterized in that: 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 composed of the first ohmic contact layer to the second ohmic contact layer is peeled off from the GaAs substrate, and the battery structure composed 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, characterized in that: The substrate is a Ge substrate, and a plurality of sub-cells stacked on one side of the substrate include: The first subcell, the third tunnel junction, the two groups of metamorphic buffer layers, the Bragg reflection layer, the second subcell, the fourth tunnel junction, the fourth subcell and the third ohmic contact layer are sequentially formed on one side of the Ge substrate, wherein the first subcell is a Ge cell, the second subcell is an InGaAs subcell, and the fourth subcell is an AlGaInP subcell or a GaInP subcell.

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