Multi-junction solar cell and manufacturing method thereof

Abstract

The invention provides a multi-junction solar cell and a manufacturing method thereof. A distributed bragg reflector (DBR) is arranged between a back field layer and a base region of at least one sub-cell. Meanwhile, the thickness of the back surface field layer is the thickness required by complete destructive interference between the first reflected light and the second reflected light. Based on the structure, photons which are not absorbed for the first time are reflected back to be absorbed for the second time through the DBR reflector, which is equivalent to increasing the effective absorption thickness in a disguised manner, reducing the thickness of a base region and reducing minority carrier recombination, so that the anti-radiation performance of the cell is improved. Besides, complete destructive interference can be realized by arranging the back field layer, so that minority carrier recombination on the surface of the sub-cell can be effectively passivated through the back field layer and the collection efficiency of photon-generated carriers can be improved on the premise of not influencing the reflection effect of the DBR reflector, thereby improving the conversion efficiency of the cell. Therefore, the anti-radiation performance of the cell and the collection efficiency of the photon-generated carriers are synchronously improved.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and in particular to a multi-junction solar cell and a manufacturing method thereof. Background Art

[0002] Solar cells can directly convert solar energy into electrical energy and are the most efficient form of clean energy. III-V compound semiconductor solar cells have the highest conversion efficiency in the current material system. They also have the advantages of good high temperature resistance and strong radiation resistance. They are recognized as a new generation of high-performance and long-life space main power sources.

[0003] In the field of solar cells, how to fully absorb the full spectrum of the sun and improve the efficiency of photogenerated carriers has always been the core key issue in improving the efficiency of solar cells. Most of the current solar cell structure designs use the more mature GaInP / InGaAs / Ge lattice-matched triple-junction cells. The highest conversion efficiency currently achieved by this material system under one sun is 32-33%. However, in the space environment, after being irradiated by a large number of high-energy particles, gallium arsenide multi-junction solar cells are damaged, resulting in current density decay and affecting performance; specifically, in the GaInP / InGaAs / Ge triple-junction solar cell structure, the irradiation damage of the InGaAs subcell is greater than that of the Ge subcell and the GaInP subcell.

[0004] In order to improve the radiation resistance of GaInP / GaInAs / Ge solar cells, the commonly used technology is mainly to add a distributed Bragg reflector (DBR) structure in the sub-cell to reflect the photons that were not absorbed initially back for secondary absorption, which is equivalent to increasing the effective absorption thickness in disguise, which can reduce the thickness of the cell base region and reduce minority carrier recombination, thereby improving the radiation resistance of the cell. Although the above structure can improve the radiation resistance of GaInP / GaInAs / Ge solar cells, due to the influence of the cell's own structure and the other functional layers, the residual factor of the radiation efficiency of GaInP / GaInAs / Ge solar cells is currently only about 85%, and the improvement of the radiation resistance of solar cells and the collection efficiency of photogenerated carriers is limited.

[0005] In view of this, the inventor specially designed a multi-junction solar cell and a method for manufacturing the same, which resulted in the present case. Summary of the invention

[0006] The purpose of the present invention is to provide a multi-junction solar cell and a method for manufacturing the same, which effectively solves the technical problems existing in the prior art and improves the radiation resistance and photogenerated carrier collection efficiency of the multi-junction solar cell.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A multi-junction solar cell comprising:

[0009] A multi-junction sub-battery and a tunnel junction between two adjacent junction sub-batteries; the tunnel junction comprises an N-type layer and a P-type layer sequentially stacked along a first direction;

[0010] Among them, at least one sub-cell includes a back field layer, a base region, an emission region and a window layer arranged in sequence along a first direction; and in the sub-cell, a DBR reflector is also provided between the back field layer and the base region; at the same time, the thickness of the back field layer is the thickness required for the first reflected light and the second reflected light to completely destructively interfere, the first reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector to the interface between the DBR reflector and the back field layer, and the second reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector to the surface of the back field layer close to the tunnel junction.

[0011] Preferably, the DBR reflector includes alternately stacked first material layers with a low refractive index and second material layers with a high refractive index. In this specification, "a first material layer with a low refractive index" and "a second material layer with a high refractive index" mean that the first material layer and the second material layer are compared to reflect the difference in refractive index, and the first material layer with a low refractive index has a lower refractive index than the second material layer with a high refractive index.

[0012] Preferably, the first material layer and the second material layer both have an optical thickness of not less than 0.25λ; wherein λ represents the central reflection wavelength of the DBR reflector.

[0013] Preferably, the optical thickness of the first material layer and the second material layer are both 0.25λ.

[0014] Preferably, when the refractive index of the material layer in contact with the DBR reflector and the back field layer is greater than the refractive index of the back field layer, the optical thickness of the back field layer is Kλ / 2; wherein k is an integer not less than 0.

[0015] Preferably, k=1.

[0016] Preferably, when the refractive index of the material layer in contact with the DBR reflector and the back field layer is less than or equal to the refractive index of the back field layer, the optical thickness of the back field layer is (2K-1)λ / 4; wherein k is an integer not less than 0.

[0017] Preferably, the multi-junction sub-cell includes a bottom cell, a plurality of intermediate cells, and a top cell that are sequentially stacked, wherein the intermediate cell includes a back surface field layer, a base region, an emitter region, and a window layer that are sequentially arranged along the first direction; and the DBR mirror is disposed between the back surface field layer and the base region of at least one intermediate cell.

[0018] Preferably, the multi-junction solar cell is a triple-junction solar cell, and the multi-junction sub-cell includes a Ge bottom cell, an InGaAs intermediate cell, and a GaInP top cell that are sequentially stacked;

[0019] Or the multi-junction solar cell is a quadruple-junction solar cell, and the multi-junction sub-cell includes a Ge bottom cell, an InGaAs intermediate cell, an AlInGaAs intermediate cell, and a GaInP top cell that are sequentially stacked;

[0020] Wherein, the InGaAs intermediate cell includes a back surface field layer, a base region, an emitter region, and a window layer that are sequentially arranged along the first direction; and the DBR mirror is disposed between the back surface field layer and the base region of the InGaAs intermediate cell.

[0021] Preferably, in the InGaAs intermediate cell, the back surface field layer includes an AlGaAs back surface field layer or a GaInP back surface field layer or an AlGaInP back surface field layer, the base region includes a P-type InGaAs base region, the emitter region includes an N-type InGaAs emitter region, and the window layer includes an AlGaInP or AlInP window layer; the DBR mirror includes alternately stacked Al x GaAs layers and Al y GaAs layers, where 0 ≦ x < y ≦ 1, the Al x GaAs layer serves as the first material layer, and the Al y GaAs layer serves as the second material layer. It should be noted that for the AlGaAs material, the higher the Al composition, the smaller the refractive index, and the smaller the nano-hardness of the material. For the DBR mirror, it is preferable to use a material layer with a larger nano-hardness in order to reduce the dislocations extending upward to the emitter region and reduce the influence of residual stress on the emitter region of the sub-cell grown above it. That is, an Al x GaAs layer with a smaller Al composition is selected as the first material layer of the DBR mirror to facilitate reducing the dislocations extending upward to the emitter region and reducing the residual stress; at the same time, in order to ensure that the DBR mirror has a good light reflection function, the DBR mirror in the present invention further includes an Al y GaAs layer as the second material layer of the DBR mirror. Through multiple periods of high-refractive-index Al y GaAs layers and low-refractive-index Al xThe alternating stacking of GaAs layers forms a Bragg reflector. However, the first material layer and the second material layer are not limited to Al x GaAs layer and Al y GaAs layer. As long as the first material layer and the second material layer have different refractive indices and are light-transmissive, other semiconductor layers can also be used as the first material layer and the second material layer. x GaAs layer and Al y Semiconductor layers such as GaAs layers have high light transmittance and are easy to deposit, and have a relatively large refractive index difference, so they are more suitable.

[0022] Preferably, when the DBR reflector is in contact with the back field layer through the second material layer, the optical thickness of the back field layer is Kλ / 2.

[0023] Preferably, the optical thickness of the back field layer is λ / 2.

[0024] Preferably, when the first material layer forms contact between the DBR reflector and the back field layer, the optical thickness of the back field layer is (2K-1)λ / 4.

[0025] Preferably, the optical thickness of the back field layer is λ / 4.

[0026] The present invention also provides a method for manufacturing a multi-junction solar cell, the method comprising:

[0027] providing a substrate;

[0028] A multi-junction sub-battery is formed on the substrate, and a tunnel junction is formed between two adjacent junction sub-batteries; the tunnel junction includes an N-type layer and a P-type layer stacked in sequence along a growth direction;

[0029] Among them, at least one sub-cell includes a back field layer, a base region, an emission region and a window layer arranged in sequence along a first direction; and in the sub-cell, a DBR reflector is also provided between the back field layer and the base region; at the same time, the thickness of the back field layer is the thickness required for the first reflected light and the second reflected light to completely destructively interfere, the first reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector to the interface between the DBR reflector and the back field layer, and the second reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector to the surface of the back field layer close to the tunnel junction.

[0030] Preferably, the DBR reflector comprises alternately stacked first material layers with a low refractive index and second material layers with a high refractive index;

[0031] The first material layer and the second material layer both have an optical thickness of not less than 0.25λ; wherein λ represents the central reflection wavelength of the DBR reflector.

[0032] Preferably, when the refractive index of the material layer in contact with the DBR reflector and the back field layer is greater than the refractive index of the back field layer, the optical thickness of the back field layer is Kλ / 2; wherein k is an integer not less than 0;

[0033] Alternatively, when the refractive index of the material layer in contact with the DBR reflector and the back field layer is less than or equal to the refractive index of the back field layer, the optical thickness of the back field layer is (2K-1)λ / 4.

[0034] Through the above technical solution, it can be known that the multi-junction solar cell provided by the present invention, at least one sub-cell includes a back field layer, a base region, an emission region and a window layer arranged in sequence along the first direction; and in the sub-cell, a DBR reflector is also provided between the back field layer and the base region; at the same time, the thickness of the back field layer is the thickness required for the first reflected light and the second reflected light to completely destructively interfere. Based on the above structure, by providing a DBR reflector between the back field layer and the base region, the photons that are not absorbed initially are reflected back and absorbed twice, which is equivalent to increasing the effective absorption thickness in a disguised manner, which can reduce the thickness of the base region and reduce the recombination of minority carriers, thereby improving the radiation resistance of the battery. In addition, by providing the back field layer, complete destructive interference can be achieved, so that it can be ensured that the minority carrier recombination on the surface of the sub-cell is effectively passivated by the back field layer without affecting the reflection effect of the DBR reflector, thereby improving the collection efficiency of photogenerated carriers and improving the conversion efficiency of the battery. Thereby, the radiation resistance of the battery and the collection efficiency of photogenerated carriers are simultaneously improved.

[0035] Furthermore, the multi-junction subcell includes a bottom cell, a plurality of middle cells and a top cell stacked in sequence, wherein the middle cell includes a back field layer, a base region, an emitter region and a window layer arranged in sequence along the first direction; and the DBR reflector is arranged between the back field layer and the base region of at least one middle cell. Based on this, concentrated radiation damage to the middle cell can be well avoided, and it is particularly suitable for the GaInP / InGaAs / Ge triple junction cell structure, which well solves the problem that the radiation damage to the InGaAs subcell is greater than that to the Ge subcell and the GaInP subcell.

[0036] The present invention also provides a method for manufacturing a multi-junction solar cell, which achieves the beneficial effects of the above-mentioned solar cell while having a simple and convenient manufacturing process and is easy to produce. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention 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 embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0038] Figure 1 A schematic diagram of the structure of a multi-junction solar cell provided by an embodiment of the present invention;

[0039] Figure 2 A schematic diagram of the structure of a multi-junction solar cell provided in Example 1 of the present invention;

[0040] Figure 3 A schematic diagram of the structure of another multi-junction solar cell provided in Example 1 of the present invention;

[0041] Figure 4 A schematic diagram of the structure of a multi-junction solar cell provided in Example 2 of the present invention;

[0042] Figure 5 A schematic diagram of the structure of another multi-junction solar cell provided in Example 2 of the present invention;

[0043] Explanation of symbols in the figure: 11, bottom battery, 12, 16: middle battery, 13, top battery, 14, tunnel junction, 15, ohmic contact layer. DETAILED DESCRIPTION

[0044] To make the content of the present invention clearer, the content of the present invention is further described below in conjunction with the accompanying drawings. The present invention is not limited to this specific embodiment. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0045] like Figure 1 As shown, a multi-junction solar cell comprises:

[0046] A multi-junction sub-battery and a tunnel junction 14 located between two adjacent junction sub-batteries; the tunnel junction 14 comprises an N-type layer and a P-type layer sequentially stacked along a first direction;

[0047] Among them, at least one sub-cell includes a back field layer, a base region, an emission region and a window layer arranged in sequence along a first direction; and in the sub-cell, a DBR reflector is also provided between the back field layer and the base region; at the same time, the thickness of the back field layer is the thickness required for the first reflected light and the second reflected light to completely destructively interfere, the first reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector to the interface between the DBR reflector and the back field layer, and the second reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector to the surface of the back field layer close to the tunnel junction 14.

[0048] Based on the above, in one embodiment of the present application, the DBR reflector includes alternately stacked first material layers with a low refractive index and second material layers with a high refractive index, wherein the first material layers and the second material layers are alternately grown for n periods, 3≤n≤30. In this specification, "a first material layer with a low refractive index" and "a second material layer with a high refractive index" mean that the first material layer and the second material layer are compared to reflect the refractive index difference, and the first material layer with a low refractive index has a lower refractive index than the second material layer with a high refractive index.

[0049] Based on the above, in one embodiment of the present application, the first material layer and the second material layer both have an optical thickness of not less than 0.25λ; wherein λ represents the central reflection wavelength of the DBR reflector.

[0050] Based on the above content, in one embodiment of the present application, the optical thickness of the first material layer and the second material layer are both 0.25λ.

[0051] Based on the above, in one embodiment of the present application, when the refractive index of the material layer in contact with the DBR reflector and the back field layer is greater than the refractive index of the back field layer, the optical thickness of the back field layer is Kλ / 2, wherein k is an integer not less than 0. Preferably, k=1.

[0052] Based on the above content, in one embodiment of the present application, when the refractive index of the material layer forming contact between the DBR reflector and the back field layer is less than or equal to the refractive index of the back field layer, the optical thickness of the back field layer is (2K-1)λ / 4; wherein k is an integer not less than 0.

[0053] Based on the above, in one embodiment of the present application, the multi-junction subcell includes a bottom cell 11, a plurality of intermediate cells (12...) and a top cell 13 stacked in sequence, wherein the intermediate cell (12...) includes a back field layer, a base region, an emission region and a window layer sequentially arranged along the first direction; and the DBR reflector is arranged between the back field layer and the base region of at least one intermediate cell 12. It should be noted that the specific number of junctions of the multi-junction solar cell is not limited in this embodiment, and the multi-junction solar cell can be a three-junction solar cell as shown in Example 1 (when the intermediate cell is only one), or a four-junction solar cell as shown in Example 2 (when the intermediate cells are two), depending on the specific circumstances.

[0054] Based on the same inventive concept, the embodiment of the present invention further provides a method for manufacturing a multi-junction solar cell, the method for manufacturing a multi-junction solar cell comprising:

[0055] providing a substrate;

[0056] A multi-junction sub-battery is formed on the substrate, and a tunnel junction 14 is formed between two adjacent junction sub-batteries; the tunnel junction 14 includes an N-type layer and a P-type layer stacked in sequence along a growth direction;

[0057] Among them, at least one sub-cell includes a back field layer, a base region, an emission region and a window layer arranged in sequence along a first direction; and in the sub-cell, a DBR reflector is also provided between the back field layer and the base region; at the same time, the thickness of the back field layer is the thickness required for the first reflected light and the second reflected light to completely destructively interfere, the first reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector to the interface between the DBR reflector and the back field layer, and the second reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector to the surface of the back field layer close to the tunnel junction 14.

[0058] Preferably, the DBR reflector comprises alternately stacked first material layers with a low refractive index and second material layers with a high refractive index;

[0059] The first material layer and the second material layer both have an optical thickness of not less than 0.25λ; wherein λ represents the central reflection wavelength of the DBR reflector.

[0060] Preferably, when the refractive index of the material layer in contact with the DBR reflector and the back field layer is greater than the refractive index of the back field layer, the optical thickness of the back field layer is Kλ / 2; wherein k is an integer not less than 0;

[0061] Alternatively, when the refractive index of the material layer in contact with the DBR reflector and the back field layer is less than or equal to the refractive index of the back field layer, the optical thickness of the back field layer is (2K-1)λ / 4.

[0062] Through the above technical solutions, it can be known that the multi-junction solar cell provided by the present invention, at least one sub-cell includes a back field layer, a base region, an emission region and a window layer arranged in sequence along the first direction; and in the sub-cell, a DBR reflector is also provided between the back field layer and the base region; at the same time, the thickness of the back field layer is the thickness required for the first reflected light and the second reflected light to completely destructively interfere. Based on the above structure, by providing a DBR reflector between the back field layer and the base region, the photons that are not absorbed initially are reflected back and absorbed twice, which is equivalent to increasing the effective absorption thickness in a disguised manner, which can reduce the thickness of the base region and reduce the recombination of minority carriers, thereby improving the radiation resistance of the battery. By providing the back field layer, complete destructive interference can be achieved, so that it can be ensured that the minority carrier recombination on the surface of the sub-cell is effectively passivated by the back field layer without affecting the reflection effect of the DBR reflector, thereby improving the collection efficiency of photogenerated carriers and improving the conversion efficiency of the battery. Thereby, the radiation resistance of the battery and the collection efficiency of photogenerated carriers are simultaneously improved.

[0063] Furthermore, the multi-junction cell comprises a bottom cell 11, a plurality of middle cells 12 and a top cell 13 which are stacked in sequence, wherein the middle cell 12 comprises a back field layer, a base region, an emitter region and a window layer which are sequentially arranged along the first direction; and the DBR reflector is arranged between the back field layer and the base region of at least one middle cell 12. Based on this, concentrated radiation damage to the middle cell 12 can be well avoided.

[0064] The present invention also provides a method for manufacturing a multi-junction solar cell, which achieves the beneficial effects of the above-mentioned solar cell while having a simple and convenient manufacturing process and is easy to produce.

[0065] Example 1

[0066] like Figure 2 As shown, a multi-junction solar cell, the multi-junction solar cell is a three-junction solar cell (the middle cell 12 is then only one), and the multi-junction subcell comprises a Ge bottom cell 11, an InGaAs middle cell 12 and a GaInP top cell 13 which are stacked in sequence;

[0067] In this embodiment, the multi-junction solar cell includes a Ge bottom cell 11, a first tunnel junction 14, an InGaAs middle cell 12, a second tunnel junction 14 and a GaInP top cell 13 which are stacked in sequence, and the specific configuration is as follows:

[0068] The Ge bottom cell 11 obtains an N-type emitter region by phosphorus diffusion on a P-type Ge substrate, thereby forming a PN junction of the Ge bottom cell 11, and grows an (Al)GaInP nucleation layer that matches the substrate lattice on the P-type Ge substrate to serve as a window layer of the Ge bottom cell 11.

[0069] In the first tunnel junction 14, N-type GaAs or N-type GaInP is used as the N-type layer of the first tunnel junction 14, and P-type (Al)GaAs material is used as the P-type layer of the first tunnel junction 14; wherein the N-type and P-type doping are obtained by doping with Si and C respectively.

[0070] The InGaAs intermediate cell 12 includes a back field layer, a base region, an emission region and a window layer arranged in sequence along a first direction; further, in the InGaAs intermediate cell 12, a DBR reflector is also provided between the back field layer and the base region; at the same time, the thickness of the back field layer is the thickness required for the first reflected light and the second reflected light to completely destructively interfere with each other, the first reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector to the interface between the DBR reflector and the back field layer, and the second reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector to the surface of the back field layer close to the second tunnel junction 14.

[0071] The DBR reflector includes alternately stacked first material layers with a low refractive index and second material layers with a high refractive index. In this specification, "first material layers with a low refractive index" and "second material layers with a high refractive index" mean that the first material layer and the second material layer are compared to reflect the difference in refractive index, and the first material layer with a low refractive index has a lower refractive index than the second material layer with a high refractive index. At the same time, the back field layer has a low refractive index.

[0072] Based on the above, in one embodiment of the present application, the first material layer and the second material layer both have an optical thickness of not less than 0.25λ; wherein λ represents the central reflection wavelength of the DBR reflector.

[0073] Based on the above content, in one embodiment of the present application, the optical thickness of the first material layer and the second material layer are both 0.25λ.

[0074] Based on the above, in one embodiment of the present application, when the DBR reflector is in contact with the back field layer through the second material layer, the optical thickness of the back field layer is Kλ / 2. Preferably, the optical thickness of the back field layer is λ / 2 (ie, k=1).

[0075] Based on the above, in an embodiment of the present application, when the first material layer in contact with the back surface field layer is the DBR mirror, the optical thickness of the back surface field layer is (2K - 1)λ / 4. Preferably, the optical thickness of the back surface field layer is λ / 4 (i.e., k = 1).

[0076] Specifically, in the InGaAs intermediate cell 12, the back surface field layer includes an AlGaAs back surface field layer or a GaInP back surface field layer or an AlGaInP back surface field layer, the base region includes a P-type InGaAs base region, the emitter region includes an N-type InGaAs emitter region, and the window layer includes an AlGaInP or AlInP window layer, where N-type and P-type doping are respectively obtained by doping with Si and C; the DBR mirror includes alternately stacked Al x GaAs layers and Al y GaAs layers, where 0 ≤ x < y ≤ 1, and the Al x GaAs layer serves as the first material layer, and the Al y GaAs layer serves as the second material layer, and the optical thicknesses of both the Al x GaAs layer and the Al y GaAs layer are 0.25λ, where the first material layer and the second material layer are alternately grown for n periods, 3 ≤ n ≤ 30. It should be noted that for the AlGaAs material, the higher the Al component, the smaller the refractive index and the smaller the nano-hardness of the material. For the DBR mirror, it is preferred to have a material layer with a larger nano-hardness to reduce the dislocations extending upward to the emitter region and reduce the influence of residual stress on the emitter region of the sub-cell grown above it. That is, an Al x GaAs layer with a smaller Al component is selected as the first material layer of the DBR mirror to facilitate reducing the dislocations extending upward to the emitter region and reducing the residual stress; at the same time, in order to ensure better reflection light function of the DBR mirror, the DBR mirror in the present invention also includes an Al y GaAs layer as the second material layer of the DBR mirror, and a Bragg mirror is formed by alternately stacking multiple periods of high refractive index Al y GaAs layers and low refractive index Al x GaAs layers. However, the first material layer and the second material layer are not limited to the Al x GaAs layer and the Al y GaAs layer. As long as the first material layer and the second material layer have different refractive indices and light transmissivity, other semiconductor layers can also be used as the first material layer and the second material layer. However, such as the Al x GaAs layer and the Al ySemiconductor layers such as GaAs layers have high light transmittance and are easy to deposit, and have a relatively large refractive index difference, so they are more suitable.

[0077] Based on the above, in one embodiment of the present application, the DBR reflector is in contact with the back field layer through the second material layer (Al y When the GaAs layer is used, the optical thickness of the back field layer is Kλ / 2. Preferably, the optical thickness of the back field layer is λ / 2 (ie, k=1).

[0078] Based on the above, in another embodiment of the present application, the DBR reflector is in contact with the back field layer through the first material layer (Al x When the GaAs layer is used, the optical thickness of the back field layer is (2K-1)λ / 4. Preferably, the optical thickness of the back field layer is λ / 4 (ie k=1).

[0079] In the second tunnel junction 14, N-type GaAs or N-type GaInP is used as the N-type layer of the first tunnel junction 14, and P-type Al x The GaAs layer material is used as the P-type layer of the first tunnel junction 14; wherein the N-type and P-type doping are obtained by doping with Si and C respectively.

[0080] The GaInP top cell 13 includes a back field layer, a base region, an emitter region and a window layer arranged in sequence along the first direction; further, in the GaInP top cell 13, the back field layer includes an AlGaInP back field layer, the base region includes a P-type AlGaInP base region or a P-type GaInP base region, the emitter region includes an N-type AlGaInP emitter region or an N-type GaInP emitter region, and the window layer includes an AlInP window layer or an AlGaInP window layer.

[0081] In the embodiment of the present invention, an ohmic contact layer 15 is further provided on the surface of the top cell 13 facing away from the middle cell 12. As a structural layer forming an ohmic contact with the electrode, the ohmic contact layer 15 further improves the performance of the multi-junction solar cell.

[0082] Based on the same inventive concept, an embodiment of the present invention further provides a method for manufacturing a multi-junction solar cell, which is used to manufacture the above-mentioned triple-junction solar cell. The manufacturing method comprises:

[0083] Step S01, providing a substrate, wherein the substrate comprises a P-type Ge substrate;

[0084] Step S02, phosphorus diffusion is performed on the P-type Ge substrate to obtain an N-type emitter region, thereby forming a PN junction of the Ge bottom battery 11, and a (Al)GaInP nucleation layer that matches the substrate lattice is grown on the P-type Ge substrate to serve as a window layer of the Ge bottom battery 11; finally, the Ge bottom battery 11 is formed.

[0085] Step S03, manufacturing a first tunnel junction 14;

[0086] Specifically, N-type GaAs or N-type GaInP is used as the N-type layer of the first tunnel junction 14, and P-type (Al)GaAs material is used as the P-type layer of the first tunnel junction 14; wherein the N-type and P-type doping are obtained by doping with Si and C respectively.

[0087] Step S04, manufacturing an InGaAs intermediate cell 12, wherein the InGaAs intermediate cell 12 comprises a back field layer, a base region, an emission region and a window layer arranged in sequence along a first direction; further, in the InGaAs intermediate cell 12, a DBR reflector is also provided between the back field layer and the base region; at the same time, the thickness of the back field layer is the thickness required for complete destructive interference between the first reflected light and the second reflected light, the first reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector to the interface between the DBR reflector and the back field layer, and the second reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector to the surface of the back field layer close to the second tunnel junction 14.

[0088] The DBR reflector includes alternately stacked first material layers with a low refractive index and second material layers with a high refractive index. In this specification, "first material layers with a low refractive index" and "second material layers with a high refractive index" mean that the first material layer and the second material layer are compared to reflect the difference in refractive index, and the first material layer with a low refractive index has a lower refractive index than the second material layer with a high refractive index. At the same time, the back field layer has a low refractive index.

[0089] Based on the above, in one embodiment of the present application, the first material layer and the second material layer both have an optical thickness of not less than 0.25λ; wherein λ represents the central reflection wavelength of the DBR reflector.

[0090] Based on the above content, in one embodiment of the present application, the optical thickness of the first material layer and the second material layer are both 0.25λ.

[0091] Based on the above, in one embodiment of the present application, in the DBR reflector, when the second material layer forms contact with the back field layer, the optical thickness of the back field layer is Kλ / 2. Preferably, the optical thickness of the back field layer is λ / 2 (ie, k=1).

[0092] Based on the above, in an embodiment of the present application, in the DBR mirror, when it forms contact with the back surface field layer as the first material layer, the optical thickness of the back surface field layer is (2K - 1)λ / 4. Preferably, the optical thickness of the back surface field layer is λ / 4 (i.e., k = 1).

[0093] Specifically, in the InGaAs intermediate cell 12, the back surface field layer includes an AlGaAs back surface field layer or a GaInP back surface field layer or an AlGaInP back surface field layer, the base region includes a P-type InGaAs base region, the emitter region includes an N-type InGaAs emitter region, the window layer includes an AlGaInP or AlInP window layer, where N-type and P-type doping are respectively doped with Si and C to obtain; the DBR mirror includes alternately stacked Al x GaAs layers and Al y GaAs layers, where 0 ≤ x < y ≤ 1, the Al x GaAs layer serves as the first material layer, the Al y GaAs layer serves as the second material layer, and the optical thicknesses of both the Al x GaAs layer and the Al y GaAs layer are 0.25λ. Among them, the first material layer and the second material layer are alternately grown for n cycles, 3 ≤ n ≤ 30. It should be noted that for the AlGaAs material, the higher the Al component, the smaller the refractive index and the smaller the nano-hardness of the material. For the DBR mirror, it is preferable to have a material layer with a larger nano-hardness in order to reduce the dislocations extending upward to the emitter region and reduce the influence of residual stress on the emitter region of the sub-cell grown above it. That is, select an Al x GaAs layer with a smaller Al component as the first material layer of the DBR mirror to facilitate reducing the dislocations extending upward to the emitter region and reducing the residual stress; at the same time, in order to ensure better reflection light function of the DBR mirror, the DBR mirror in the present invention further includes an Al y GaAs layer as the second material layer of the DBR mirror. The Bragg mirror is formed by alternately stacking multiple cycles of high refractive index Al y GaAs layers and low refractive index Al x GaAs layers. However, the first material layer and the second material layer are not limited to Al x GaAs layers and Al y GaAs layers. As long as the first material layer and the second material layer have different refractive indices and have light transmissivity, that is, other semiconductor layers can also be used as the first material layer and the second material layer. However, such as Al x GaAs layers and Al ySemiconductor layers such as GaAs layers have high light transmittance and are easy to deposit, and have a relatively large refractive index difference, so they are more suitable.

[0094] Based on the above, in one embodiment of the present application, the DBR reflector is in contact with the back field layer through the second material layer (Al2O3) with a high refractive index. y When the GaAs layer is used, the optical thickness of the back field layer is Kλ / 2. Preferably, the optical thickness of the back field layer is λ / 2 (ie, k=1).

[0095] Based on the above, in another embodiment of the present application, the DBR reflector is in contact with the back field layer through the first material layer (Al2O3) with a low refractive index. x When the GaAs layer is used, the optical thickness of the back field layer is (2K-1)λ / 4. Preferably, the optical thickness of the back field layer is λ / 4 (ie k=1).

[0096] Step S05, manufacturing a second tunnel junction 14;

[0097] Specifically, in the second tunnel junction 14, N-type GaAs or N-type GaInP is used as the N-type layer of the second tunnel junction 14, and P-type Al x The GaAs layer material is used as the P-type layer of the second tunnel junction 14; wherein the N-type and P-type doping are obtained by doping with Si and C respectively.

[0098] Step S06, making GaInP top cell 13;

[0099] Specifically, the GaInP top cell 13 includes a back field layer, a base region, an emitter region and a window layer arranged in sequence along the first direction; further, in the GaInP top cell 13, the back field layer includes an AlGaInP back field layer, the base region includes a P-type AlGaInP base region or a P-type GaInP base region, the emitter region includes an N-type AlGaInP emitter region or an N-type GaInP emitter region, and the window layer includes an AlInP window layer or an AlGaInP window layer.

[0100] like Figure 3 As shown, in the embodiment of the present invention, an ohmic contact layer 15 is further provided on the surface of the top cell 13 facing away from the middle cell 12. As a structural layer forming an ohmic contact with the electrode, the performance of the multi-junction solar cell is further improved.

[0101] Through the above technical solution, it can be known that the multi-junction solar cell provided by the present invention comprises a Ge bottom cell 11, an InGaAs middle cell 12 and a GaInP top cell 13 which are stacked in sequence; and in the InGaAs middle cell 12, a DBR reflector is also provided between the back field layer and the base region; at the same time, the thickness of the back field layer is the thickness required for the first reflected light and the second reflected light to completely destructively interfere. Based on the above structure, by providing a DBR reflector between the back field layer and the base region, the photons that are not absorbed initially are reflected back and absorbed twice, which is equivalent to increasing the effective absorption thickness in a disguised manner, which can reduce the thickness of the base region and reduce the recombination of minority carriers, thereby improving the radiation resistance of the battery. By providing the back field layer, complete destructive interference can be achieved, so that it can be ensured that the minority carrier recombination on the surface of the sub-cell is effectively passivated by the back field layer without affecting the reflection effect of the DBR reflector, thereby improving the collection efficiency of photogenerated carriers and improving the battery conversion efficiency. Thus, the radiation resistance of the battery and the collection efficiency of photogenerated carriers are simultaneously improved.

[0102] Furthermore, the DBR reflector is arranged between the back field layer and the base region of the InGaAs intermediate cell 12. Based on this, concentrated radiation damage to the intermediate cell 12 can be well avoided; it is particularly suitable for the GaInP / InGaAs / Ge triple junction cell structure, and well solves the problem that the radiation damage to the InGaAs intermediate cell 12 is greater than that of the Ge subcell and the GaInP subcell.

[0103] The present invention also provides a method for manufacturing a multi-junction solar cell, which achieves the beneficial effects of the above-mentioned solar cell while having a simple and convenient manufacturing process and is easy to produce.

[0104] Example 2

[0105] like Figure 4 As shown, a multi-junction solar cell is a four-junction solar cell (there are two intermediate cells at that time). Specifically, the multi-junction subcell includes a Ge bottom cell 11, an InGaAs intermediate cell 12, an AlInGaAs intermediate cell 16 and a GaInP top cell 13 which are stacked in sequence.

[0106] In this embodiment, the multi-junction solar cell includes a Ge bottom cell 11, a first tunnel junction 14, an InGaAs middle cell 12, a second tunnel junction 14, an AlInGaAs middle cell 12, a third tunnel junction 14 and a GaInP top cell 1313 which are stacked in sequence, and the specific configuration is as follows:

[0107] The Ge bottom cell 11 obtains an N-type emitter region by phosphorus diffusion on a P-type Ge substrate, thereby forming a PN junction of the Ge bottom cell 11, and grows an (Al)GaInP nucleation layer that matches the substrate lattice on the P-type Ge substrate to serve as a window layer of the Ge bottom cell 11.

[0108] In the first tunnel junction 14, N-type GaAs or N-type GaInP is used as the N-type layer of the first tunnel junction 14, and P-type (Al)GaAs material is used as the P-type layer of the first tunnel junction 14; wherein the N-type and P-type doping are obtained by doping with Si and C respectively.

[0109] The InGaAs intermediate cell 12 includes a back field layer, a base region, an emission region and a window layer arranged in sequence along a first direction; further, in the InGaAs intermediate cell 12, a DBR reflector is also provided between the back field layer and the base region; at the same time, the thickness of the back field layer is the thickness required for the first reflected light and the second reflected light to completely destructively interfere with each other, the first reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector to the interface between the DBR reflector and the back field layer, and the second reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector to the surface of the back field layer close to the tunnel junction 14.

[0110] The DBR reflector includes alternately stacked first material layers with a low refractive index and second material layers with a high refractive index. In this specification, "first material layers with a low refractive index" and "second material layers with a high refractive index" mean that the first material layer and the second material layer are compared to reflect the difference in refractive index, and the first material layer with a low refractive index has a lower refractive index than the second material layer with a high refractive index. At the same time, the back field layer has a low refractive index.

[0111] Based on the above, in one embodiment of the present application, the first material layer and the second material layer both have an optical thickness of not less than 0.25λ; wherein λ represents the central reflection wavelength of the DBR reflector.

[0112] Based on the above content, in one embodiment of the present application, the optical thickness of the first material layer and the second material layer are both 0.25λ.

[0113] Based on the above, in one embodiment of the present application, when the DBR reflector is in contact with the back field layer through the second material layer, the optical thickness of the back field layer is Kλ / 2. Preferably, the optical thickness of the back field layer is λ / 2 (ie, k=1).

[0114] Based on the above, in an embodiment of the present application, when the first material layer in contact with the back surface field layer is the DBR mirror, the optical thickness of the back surface field layer is (2K - 1)λ / 4. Preferably, the optical thickness of the back surface field layer is λ / 4 (i.e., k = 1).

[0115] Specifically, in the InGaAs intermediate cell 12, the back surface field layer includes an AlGaAs back surface field layer or a GaInP back surface field layer or an AlGaInP back surface field layer, the base region includes a P-type InGaAs base region, the emitter region includes an N-type InGaAs emitter region, and the window layer includes an AlGaInP or AlInP window layer, where N-type and P-type doping are respectively obtained by doping with Si and C; the DBR mirror includes alternately stacked Al x GaAs layers and Al y GaAs layers, where 0 ≦ x < y ≦ 1, the Al x GaAs layer serves as the first material layer, the Al y GaAs layer serves as the second material layer, and the optical thicknesses of both the Al x GaAs layer and the Al y GaAs layer are 0.25λ. Among them, the first material layer and the second material layer are alternately grown for n cycles, 3 ≤ n ≤ 30. It should be noted that for the AlGaAs material, the higher the Al component, the smaller the refractive index and the smaller the nano-hardness of the material. For the DBR mirror, it is preferred to use a material layer with a larger nano-hardness to reduce the dislocations extending upward to the emitter region and reduce the influence of residual stress on the emitter region of the sub-cell grown above it. That is, an Al x GaAs layer with a smaller Al component is selected as the first material layer of the DBR mirror to facilitate reducing the dislocations extending upward to the emitter region and reducing the residual stress; at the same time, in order to ensure better reflection light function of the DBR mirror, the DBR mirror in the present invention also includes an Al y GaAs layer as the second material layer of the DBR mirror. The Bragg mirror is formed by alternately stacking multiple cycles of high refractive index Al y GaAs layers and low refractive index Al x GaAs layers. However, the first material layer and the second material layer are not limited to Al x GaAs layers and Al y GaAs layers. As long as the first material layer and the second material layer have different refractive indices and light transmissivity, other semiconductor layers can also be used as the first material layer and the second material layer. However, such as Al x GaAs layers and Al ySemiconductor layers such as GaAs layers have high light transmittance and are easy to deposit, and have a relatively large refractive index difference, so they are more suitable.

[0116] Based on the above, in one embodiment of the present application, the DBR reflector is in contact with the back field layer through the second material layer (Al y When the GaAs layer is used, the optical thickness of the back field layer is Kλ / 2. Preferably, the optical thickness of the back field layer is λ / 2 (ie, k=1).

[0117] Based on the above, in another embodiment of the present application, the DBR reflector is in contact with the back field layer through the first material layer (Al x When the GaAs layer is used, the optical thickness of the back field layer is (2K-1)λ / 4. Preferably, the optical thickness of the back field layer is λ / 4 (ie k=1).

[0118] In the second tunnel junction 14, N-type GaAs or N-type GaInP is used as the N-type layer of the first tunnel junction 14, and P-type Al x The GaAs layer material is used as the P-type layer of the first tunnel junction 14; wherein the N-type and P-type doping are obtained by doping with Si and C respectively.

[0119] The AlInGaAs intermediate cell 16 includes a back field layer, a base region, an emitter region and a window layer arranged in sequence along the first direction; further, in the AlInGaAs intermediate cell 16, the back field layer includes a GaInP or AlGaAs back field layer, the base region includes a P-type AlInGaAs base region, the emitter region includes an N-type AlInGaAs emitter region, and the window layer includes an AlGaInP or AlInP window layer; wherein the N-type and P-type doping are obtained by doping with Si and C respectively.

[0120] It should be noted that if Figure 5 As shown, in the AlInGaAs intermediate cell 16, the setting of the InGaAs intermediate cell 12 as described above can also be referred to, and a DBR reflector is also set between the back field layer and the base region of the AlInGaAs intermediate cell 16; at the same time, the thickness of the back field layer is the thickness required for the third reflected light and the fourth reflected light to completely destructively interfere, the third reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector of the AlInGaAs intermediate cell 16 to the interface between the DBR reflector and the back field layer, and the fourth reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector of the AlInGaAs intermediate cell 16 to the surface of the back field layer close to the third tunnel junction 14. For details, please refer to the setting of the InGaAs intermediate cell 12, which will not be described in detail in this embodiment.

[0121] In the third tunnel junction 14, N-type GaAs or N-type GaInP is used as the N-type layer of the third tunnel junction 14, and P-type Al x The GaAs layer material is used as the P-type layer of the third tunnel junction 1414; wherein the N-type and P-type doping are obtained by doping with Si and C respectively.

[0122] The GaInP top cell 13 includes a back field layer, a base region, an emitter region and a window layer arranged in sequence along the first direction; further, in the GaInP top cell 13, the back field layer includes an AlGaInP back field layer, the base region includes a P-type AlGaInP base region or a P-type GaInP base region, the emitter region includes an N-type AlGaInP emitter region or an N-type GaInP emitter region, and the window layer includes an AlInP window layer or an AlGaInP window layer.

[0123] In the embodiment of the present invention, an ohmic contact layer 15 is further provided on the surface of the top cell 13 facing away from the middle cell 12. As a structural layer forming an ohmic contact with the electrode, the ohmic contact layer 15 further improves the performance of the multi-junction solar cell.

[0124] Based on the same inventive concept, an embodiment of the present invention further provides a method for manufacturing a multi-junction solar cell, which is used to manufacture the above-mentioned four-junction solar cell. The manufacturing method includes:

[0125] Step A01, providing a substrate, wherein the substrate comprises a P-type Ge substrate;

[0126] Step A02, phosphorus diffusion is performed on the P-type Ge substrate to obtain an N-type emitter region, thereby forming a PN junction of the Ge bottom battery 11, and a (Al)GaInP nucleation layer that matches the substrate lattice is grown on the P-type Ge substrate to serve as a window layer of the Ge bottom battery 11; finally, the Ge bottom battery 11 is formed.

[0127] Step A03, manufacturing a first tunnel junction 14;

[0128] Specifically, N-type GaAs or N-type GaInP is used as the N-type layer of the first tunnel junction 14, and P-type (Al)GaAs material is used as the P-type layer of the first tunnel junction 14; wherein the N-type and P-type doping are obtained by doping with Si and C respectively.

[0129] Step A04, making an InGaAs intermediate cell 12, the InGaAs intermediate cell 12 includes a back field layer, a base region, an emission region and a window layer arranged in sequence along a first direction; further, in the InGaAs intermediate cell 12, a DBR reflector is also provided between the back field layer and the base region; at the same time, the thickness of the back field layer is the thickness required for the first reflected light and the second reflected light to completely destructively interfere, the first reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector to the interface between the DBR reflector and the back field layer, and the second reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector to the surface of the back field layer close to the second tunnel junction 14.

[0130] The DBR reflector includes alternately stacked first material layers with a low refractive index and second material layers with a high refractive index. In this specification, "first material layers with a low refractive index" and "second material layers with a high refractive index" mean that the first material layer and the second material layer are compared to reflect the difference in refractive index, and the first material layer with a low refractive index has a lower refractive index than the second material layer with a high refractive index. At the same time, the back field layer has a low refractive index.

[0131] Based on the above, in one embodiment of the present application, the first material layer and the second material layer both have an optical thickness of not less than 0.25λ; wherein λ represents the central reflection wavelength of the DBR reflector.

[0132] Based on the above content, in one embodiment of the present application, the optical thickness of the first material layer and the second material layer are both 0.25λ.

[0133] Based on the above, in one embodiment of the present application, in the DBR reflector, when the second material layer forms contact with the back field layer, the optical thickness of the back field layer is Kλ / 2. Preferably, the optical thickness of the back field layer is λ / 2 (ie, k=1).

[0134] Based on the above, in one embodiment of the present application, in the DBR reflector, when the first material layer is in contact with the back field layer, the optical thickness of the back field layer is (2K-1)λ / 4. Preferably, the optical thickness of the back field layer is λ / 4 (ie, k=1).

[0135] Specifically, in the InGaAs intermediate cell 12, the back surface field layer includes an AlGaAs back surface field layer, or a GaInP back surface field layer, or an AlGaInP back surface field layer, the base region includes a P-type InGaAs base region, the emitter region includes an N-type InGaAs emitter region, the window layer includes an AlGaInP or AlInP window layer, where N-type and P-type doping are respectively obtained by doping with Si and C; the DBR mirror includes alternately stacked Al x GaAs layers and Al y GaAs layers, where 0 ≦ x < y ≦ 1, the Al x GaAs layer serves as the first material layer, the Al y GaAs layer serves as the second material layer, and the optical thicknesses of both the Al x GaAs layer and the Al y GaAs layer are 0.25λ. Among them, the first material layer and the second material layer are alternately grown for n cycles, 3 ≤ n ≤ 30. It should be noted that for the AlGaAs material, the higher the Al component, the smaller the refractive index, and the smaller the nano-hardness of the material. For the DBR mirror, it is preferable to use a material layer with a relatively large nano-hardness to reduce the dislocations extending upward to the emitter region and reduce the influence of residual stress on the emitter region of the sub-cell grown above it. That is, the Al x GaAs layer with a smaller Al component is selected as the first material layer of the DBR mirror to facilitate reducing the dislocations extending upward to the emitter region and reducing the residual stress; at the same time, in order to ensure better reflection light function of the DBR mirror, the DBR mirror in the present invention further includes an Al y GaAs layer as the second material layer of the DBR mirror. A Bragg mirror is formed by alternately stacking multiple cycles of high refractive index Al y GaAs layers and low refractive index Al x GaAs layers. However, the first material layer and the second material layer are not limited to the Al x GaAs layer and the Al y GaAs layer. As long as the first material layer and the second material layer have different refractive indices and are optically transmissive, that is, other semiconductor layers can also be used as the first material layer and the second material layer. However, semiconductor layers such as the Al x GaAs layer and the Al y GaAs layer have high light transmittance and are easy to deposit, and the refractive index difference is relatively large, so they are more suitable.

[0136] Based on the above content, in an embodiment of the present application, the second material layer (Al yWhen the GaAs layer is used, the optical thickness of the back field layer is Kλ / 2. Preferably, the optical thickness of the back field layer is λ / 2 (ie, k=1).

[0137] Based on the above, in another embodiment of the present application, the DBR reflector is in contact with the back field layer through the first material layer (Al2O3) with a low refractive index. x When the GaAs layer is used, the optical thickness of the back field layer is (2K-1)λ / 4. Preferably, the optical thickness of the back field layer is λ / 4 (ie k=1).

[0138] Step A05, manufacturing a second tunnel junction 14;

[0139] Specifically, in the second tunnel junction 14, N-type GaAs or N-type GaInP is used as the N-type layer of the second tunnel junction 14, and P-type Al x The GaAs layer material is used as the P-type layer of the second tunnel junction 14; wherein the N-type and P-type doping are obtained by doping with Si and C respectively.

[0140] Step S06, making an AlInGaAs intermediate cell 16;

[0141] Specifically, the AlInGaAs intermediate cell 16 includes a back field layer, a base region, an emitter region and a window layer arranged in sequence along the first direction; further, in the AlInGaAs intermediate cell 16, the back field layer includes a GaInP or AlGaAs back field layer, the base region includes a P-type AlInGaAs base region, the emitter region includes an N-type AlInGaAs emitter region, and the window layer includes an AlGaInP or AlInP window layer; wherein the N-type and P-type doping are obtained by doping with Si and C, respectively.

[0142] It should be noted that, in the AlInGaAs intermediate cell 12, the above-mentioned setting of the InGaAs intermediate cell 12 can also be referred to, and a DBR reflector is also arranged between the back field layer and the base region of the AlInGaAs intermediate cell 16; at the same time, the thickness of the back field layer is the thickness required for the third reflected light and the fourth reflected light to completely destructively interfere, the third reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector of the AlInGaAs intermediate cell 16 to the interface between the DBR reflector and the back field layer, and the fourth reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector of the AlInGaAs intermediate cell 16 to the surface of the back field layer close to the third tunnel junction 14. For details, please refer to the setting of the InGaAs intermediate cell 12, which will not be described in detail in this embodiment.

[0143] Step A07, manufacturing a third tunnel junction 14;

[0144] In the third tunnel junction 14, N-type GaAs or N-type GaInP is used as the N-type layer of the third tunnel junction 14, and P-type Al x The GaAs layer material is used as the P-type layer of the third tunnel junction 1414; wherein the N-type and P-type doping are obtained by doping with Si and C respectively.

[0145] Step A08, making GaInP top cell 13;

[0146] Specifically, the GaInP top cell 13 includes a back field layer, a base region, an emitter region and a window layer arranged in sequence along the first direction; further, in the GaInP top cell 13, the back field layer includes an AlGaInP back field layer, the base region includes a P-type AlGaInP base region or a P-type GaInP base region, the emitter region includes an N-type AlGaInP emitter region or an N-type GaInP emitter region, and the window layer includes an AlInP window layer or an AlGaInP window layer.

[0147] In the embodiment of the present invention, an ohmic contact layer 15 is further provided on the surface of the top cell 13 facing away from the middle cell 12. As a structural layer forming an ohmic contact with the electrode, the ohmic contact layer 15 further improves the performance of the multi-junction solar cell.

[0148] Through the above technical solution, it can be known that the multi-junction solar cell provided by the present invention comprises a Ge bottom cell 11, an InGaAs intermediate cell 12, an AlInGaAs intermediate cell 16 and a GaInP top cell 13 which are stacked in sequence; and in the InGaAs intermediate cell 12 or the AlInGaAs intermediate cell 16, a DBR reflector is also provided between its back field layer and the base region; at the same time, the thickness of the back field layer is the thickness required for the first reflected light and the second reflected light to completely destructively interfere. Based on the above structure, by providing a DBR reflector between the back field layer and the base region, the photons that are not absorbed initially are reflected back and absorbed twice, which is equivalent to increasing the effective absorption thickness in a disguised manner, and the thickness of the base region can be reduced, and the recombination of minority carriers can be reduced, thereby improving the radiation resistance of the cell. By providing the back field layer, complete destructive interference can be achieved, so that it can be ensured that the minority carrier recombination on the surface of the sub-cell is effectively passivated by the back field layer without affecting the reflection effect of the DBR reflector, thereby improving the collection efficiency of photogenerated carriers and improving the cell conversion efficiency. Thereby, the radiation resistance of the battery and the collection efficiency of photogenerated carriers are improved simultaneously.

[0149] Furthermore, the DBR reflector is disposed between the back field layer and the base region of the InGaAs intermediate cell 12 / AlInGaAs intermediate cell 16. Based on this, concentrated radiation damage to the intermediate cell 12 can be well avoided; it is particularly suitable for the GaInP / AlInGaAs / InGaAs / Ge four-junction cell structure, and well solves the problem of large radiation damage to the InGaAs intermediate cell 12 / AlInGaAs intermediate cell 12.

[0150] The present invention also provides a method for manufacturing a multi-junction solar cell, which achieves the beneficial effects of the above-mentioned solar cell while having a simple and convenient manufacturing process and is easy to produce.

[0151] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0152] It should also be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that an article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such article or device. In the absence of further restrictions, the elements defined by the sentence "comprising a ..." do not exclude the existence of other identical elements in the article or device including the above elements.

[0153] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be 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 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, characterized in that: include: A multi-junction sub-battery and a tunnel junction between two adjacent junction sub-batteries; the tunnel junction comprises an N-type layer and a P-type layer sequentially stacked along a first direction; Among them, at least one sub-cell includes a back field layer, a base region, an emission region and a window layer arranged in sequence along a first direction; and in the sub-cell, a DBR reflector is also provided between the back field layer and the base region; at the same time, the thickness of the back field layer is the thickness required for the first reflected light and the second reflected light to completely destructively interfere, the first reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector to the interface between the DBR reflector and the back field layer, and the second reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector to the surface of the back field layer close to the tunnel junction.

2. The multi-junction solar cell according to claim 1, characterized in that: The DBR reflector includes alternately stacked first material layers with a low refractive index and second material layers with a high refractive index.

3. The multi-junction solar cell according to claim 2, characterized in that: The first material layer and the second material layer both have an optical thickness of not less than 0.25λ, wherein λ represents the central reflection wavelength of the DBR reflector.

4. The multi-junction solar cell according to claim 3, characterized in that: The optical thickness of the first material layer and the second material layer are both 0.25λ.

5. The multi-junction solar cell according to claim 3, characterized in that: When the refractive index of the material layer in contact with the DBR reflector and the back field layer is greater than the refractive index of the back field layer, the optical thickness of the back field layer is Kλ / 2; wherein k is an integer not less than 0.

6. The multi-junction solar cell according to claim 3, characterized in that: The k=1.

7. The multi-junction solar cell according to claim 3, characterized in that: When the refractive index of the material layer in contact with the DBR reflector and the back field layer is less than or equal to the refractive index of the back field layer, the optical thickness of the back field layer is (2K-1)λ / 4; wherein k is an integer not less than 0.

8. The multi-junction solar cell according to any one of claims 1 to 7, characterized in that: The multi-junction cell includes a bottom cell, a plurality of middle cells and a top cell stacked in sequence, wherein the middle cell includes a back field layer, a base region, an emission region and a window layer arranged in sequence along the first direction; and the DBR reflector is arranged between the back field layer and the base region of at least one middle cell.

9. The multi-junction solar cell according to claim 8, characterized in that: The multi-junction solar cell is a triple-junction solar cell, and the multi-junction subcell comprises a Ge bottom cell, an InGaAs middle cell and a GaInP top cell which are stacked in sequence; Or the multi-junction solar cell is a four-junction solar cell, and the multi-junction subcell comprises a Ge bottom cell, an InGaAs middle cell, an AlInGaAs middle cell and a Ga InP top cell stacked in sequence; The InGaAs intermediate cell comprises a back field layer, a base region, an emission region and a window layer sequentially arranged along the first direction; and the DBR reflector is arranged between the back field layer and the base region of the InGaAs intermediate cell.

10. The multi-junction solar cell according to claim 9, characterized in that: In the InGaAs intermediate cell, the back surface field layer includes an AlGaAs back surface field layer, a GaInP back surface field layer, or an AlGaInP back surface field layer, the base region includes a P-type InGaAs base region, the emitter region includes an N-type InGaAs emitter region, and the window layer includes an AlGaInP or AlInP window layer; the DBR mirror includes alternately stacked Al x GaAs layers and Al y GaAs layers, where 0 ≦ x < y ≦ 1, the Al x GaAs layer serves as the first material layer, and the Al y GaAs layer serves as the second material layer.

11. The multi-junction solar cell according to claim 9, characterized in that: When the second material layer is in contact with the back field layer in the DBR reflector, the optical thickness of the back field layer is Kλ / 2.

12. The multi-junction solar cell according to claim 11, characterized in that: The optical thickness of the back field layer is λ / 2.

13. The multi-junction solar cell according to claim 9, characterized in that: When the first material layer forms contact between the DBR reflector and the back field layer, the optical thickness of the back field layer is (2K-1)λ / 4.

14. The multi-junction solar cell according to claim 13, characterized in that: The optical thickness of the back field layer is λ / 4.

15. A method for manufacturing a multi-junction solar cell, characterized in that: The multi-junction solar cell manufacturing method comprises: providing a substrate; A multi-junction sub-battery is formed on the substrate, and a tunnel junction is formed between two adjacent junction sub-batteries; the tunnel junction includes an N-type layer and a P-type layer stacked in sequence along a growth direction; Among them, at least one sub-cell includes a back field layer, a base region, an emission region and a window layer arranged in sequence along a first direction; and in the sub-cell, a DBR reflector is also provided between the back field layer and the base region; at the same time, the thickness of the back field layer is the thickness required for the first reflected light and the second reflected light to completely destructively interfere, the first reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector to the interface between the DBR reflector and the back field layer, and the second reflected light is the reflected light when the sunlight is vertically incident from the DBR reflector to the surface of the back field layer close to the tunnel junction.

16. The method for manufacturing a multi-junction solar cell according to claim 15, characterized in that: The DBR reflector includes alternately stacked first material layers with a low refractive index and second material layers with a high refractive index; The first material layer and the second material layer both have an optical thickness of not less than 0.25λ; wherein λ represents the central reflection wavelength of the DBR reflector.

17. The method for manufacturing a multi-junction solar cell according to claim 16, characterized in that: When the refractive index of the material layer in contact with the DBR reflector and the back field layer is greater than the refractive index of the back field layer, the optical thickness of the back field layer is Kλ / 2; wherein k is an integer not less than 0; Alternatively, when the refractive index of the material layer in contact with the DBR reflector and the back field layer is less than or equal to the refractive index of the back field layer, the optical thickness of the back field layer is (2K-1)λ / 4.

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