Multi-junction solar cell

Abstract

The utility model provides a multi-junction solar cell. 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 utility model relates to the technical field of solar cell, especially a kind of multi-junction solar cell. BACKGROUND

[0002] Solar cell can convert solar energy directly into electrical energy, and it is the most effective clean energy form. III-V compound semiconductor solar cell has the highest conversion efficiency in the current material system, and has good high-temperature resistance and strong anti-radiation ability, and is recognized as a new generation of high-performance long-life space main power supply.

[0003] In the field of solar cell, how to realize the full absorption of solar full spectrum and improve the generation efficiency of photo-generated carriers has been the core key problem of improving the efficiency of solar cell. Most of the current solar cell structure designs choose GaInP / InGaAs / Ge lattice matched three-junction battery with mature technology, and the highest conversion efficiency of this material system under one sun is 32-33%. However, in space environment, the gallium arsenide multi-junction solar cell is damaged by a large number of high-energy particles, which affects the performance by causing current density attenuation. Specifically, in the GaInP / InGaAs / Ge three-junction solar cell structure, the irradiation damage of InGaAs sub-cell is greater than that of Ge sub-cell and GaInP sub-cell.

[0004] In order to improve the anti-radiation ability of GaInP / GaInAs / Ge solar cell, the commonly used technology at present is mainly to increase the distributed Bragg reflector (DBR) structure in the sub-cell, which reflects the primary unabsorbed photons back for secondary absorption, which is equivalent to increasing the effective absorption thickness, which can thin the cell base region thickness, reduce the minority carrier recombination, and thus improve the anti-radiation performance of the cell. Although the above structure can improve the anti-radiation ability of GaInP / GaInAs / Ge solar cell, due to the influence of the structure of the cell itself and the remaining functional layer, the remaining factor of the irradiation efficiency of GaInP / GaInAs / Ge solar cell is only about 85%, and the anti-radiation ability and the collection efficiency of photo-generated carriers of solar cell are limited.

[0005] Therefore, the present application has been designed to solve the above problems. CONTENT OF THE UTILITY MODEL

[0006] The utility model aims at providing a kind of multi-junction solar cell, effectively solve the technical problems existing in prior art, improve the anti-radiation ability and the collection efficiency of photo-generated carriers of multi-junction solar cell.

[0007] In order to achieve the above purpose, the technical scheme adopted by the utility model is as follows:

[0008] A multi-junction solar cell, comprising:

[0009] A multi-junction sub-cell and a tunnel junction between two adjacent junction sub-cells; the tunnel junction comprises an N-type layer and a P-type layer stacked in a first direction;

[0010] At least one of the sub-cells comprises a back field layer, a base region, an emitter region and a window layer arranged in the first direction; and in the sub-cell, a DBR mirror is further arranged between the back field layer and the base region; and the thickness of the back field layer is the thickness required for complete destructive interference of first reflected light and second reflected light, the first reflected light being the reflected light of sunlight normally incident from the DBR mirror to the interface between the DBR mirror and the back field layer, and the second reflected light being the reflected light of sunlight normally incident from the DBR mirror to the surface of the back field layer close to the tunnel junction.

[0011] Preferably, the DBR mirror comprises first material layers with low refractive index and second material layers with high refractive index alternately stacked. In this specification, the "first material layers with low refractive index" and the "second material layers with high refractive index" represent the difference in refractive index between the first material layers and the second material layers, and the first material layers with low refractive index have a lower refractive index than the second material layers with high refractive index.

[0012] Preferably, the first material layers and the second material layers each have an optical thickness of not less than 0.25λ; wherein λ represents the center reflection wavelength of the DBR mirror.

[0013] Preferably, the optical thickness of the first material layers and the second material layers is 0.25λ.

[0014] Preferably, when the refractive index of the material layer in contact with the back field layer of the DBR mirror 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 back field layer of the DBR mirror 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 comprises a bottom cell, a plurality of intermediate cells and a top cell which are sequentially stacked, wherein the intermediate cell comprises a back field layer, a base region, an emission region and a window layer which are sequentially arranged along the first direction; and the DBR mirror is arranged between the back field layer and the base region of at least one intermediate cell.

[0018] Preferably, the multi-junction solar cell is a three-junction solar cell, and the multi-junction sub-cell comprises a Ge bottom cell, an InGaAs intermediate cell and a GaInP top cell which are sequentially stacked.

[0019] Or the multi-junction solar cell is a four-junction solar cell, and the multi-junction sub-cell comprises a Ge bottom cell, an InGaAs intermediate cell, an AlInGaAs intermediate cell and a GaInP top cell which are sequentially stacked.

[0020] The InGaAs intermediate cell comprises a back field layer, a base region, an emission region and a window layer which are sequentially arranged along the first direction; and the DBR mirror is arranged between the back field layer and the base region of the InGaAs intermediate cell.

[0021] Preferably, in the InGaAs intermediate cell, the back field layer comprises an AlGaAs back field layer or a GaInP back field layer or an AlGaInP back field layer, the base region comprises a P-type InGaAs base region, the emission region comprises an N-type InGaAs emission region, and the window layer comprises an AlGaInP or AlInP window layer; the DBR mirror comprises alternately stacked AlGaAs layers and AlGaInP layers, wherein 0≤x<y≤1, the AlGaAs layer is taken as the first material layer, and the AlGaInP layer is taken as the second material layer. x GaAs layer and Al y GaAs layer, wherein 0≤x<y≤1, the Al x GaAs layer is taken as the first material layer, and the Al y GaAs layer is taken as the second material layer. It should be noted that for the AlGaAs material, the higher the Al component, the smaller the refractive index, and the smaller the nanohardness of the material. For the DBR mirror, it is preferred to have a material layer with larger nanohardness so as to reduce the dislocation extending upward to the emission region and reduce the influence of residual stress on the emission region of the sub-cell grown thereon. That is, the Al x GaAs layer with smaller Al component is selected as the first material layer of the DBR mirror so as to reduce the dislocation extending upward to the emission region and reduce the residual stress; at the same time, in order to ensure that the DBR mirror has good light reflection function, the DBR mirror further comprises an Al y GaAs layer as the second material layer of the DBR mirror, and the DBR mirror comprises a plurality of periods of high-refractive-index Al y GaAs layers and low-refractive-index Al xThe alternating stack of GaAs layers forms a Bragg reflector. However, the first and second material layers are not limited to Al x GaAs layers and Al y GaAs layers. The first and second material layers can also use other semiconductor layers as long as they have different refractive indexes and have light transmission. However, semiconductor layers such as Al x GaAs layers and Al y GaAs layers have high light transmission and are easy to deposit, and the difference in refractive index is relatively large, and thus are more suitable.

[0022] Preferably, when the DBR reflector contacts the back field layer is 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 DBR reflector contacts the back field layer is the first material 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] According to the technical solution, the multi-junction solar cell includes at least one sub-cell, the 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 a DBR reflector is arranged between the back field layer and the base region. 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, the DBR reflector is arranged between the back field layer and the base region, the light photons that are not absorbed initially are reflected back to be absorbed again, which is equivalent to increasing the effective absorption thickness, the thickness of the base region can be reduced, and the recombination of the minority carriers can be reduced, thereby improving the anti-radiation performance of the cell. In addition, the back field layer is arranged to realize complete destructive interference, which can ensure that the surface of the sub-cell is effectively passivated by the back field layer without affecting the reflection effect of the DBR reflector, improve the collection efficiency of the photo-generated carriers, and improve the conversion efficiency of the cell. Thus, the anti-radiation performance of the cell and the collection efficiency of the photo-generated carriers are simultaneously improved.

[0027] Further, the multi-junction sub-cell comprises a bottom cell, a plurality of intermediate cells and a top cell which are sequentially stacked, wherein the intermediate cell comprises a back field layer, a base region, an emission region and a window layer which are sequentially arranged along the first direction; and the DBR mirror is arranged between the back field layer and the base region of at least one intermediate cell. Based on this, the concentrated irradiation damage of the intermediate cell can be well avoided, and it is especially suitable for the GaInP / InGaAs / Ge three-junction cell structure, and the problem that the irradiation damage of the InGaAs sub-cell is greater than that of the Ge sub-cell and the GaInP sub-cell is well solved. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only the embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor based on the provided drawings.

[0029] Figure 1 A structure schematic diagram of a multi-junction solar cell provided by the embodiment of the present application;

[0030] Figure 2 A structure schematic diagram of a multi-junction solar cell provided by the embodiment 1 of the present application;

[0031] Figure 3 Another structure schematic diagram of a multi-junction solar cell provided by the embodiment 1 of the present application;

[0032] Figure 4 A structure schematic diagram of a multi-junction solar cell provided by the embodiment 2 of the present application;

[0033] Figure 5 Still another structure schematic diagram of a multi-junction solar cell provided by the embodiment 2 of the present application;

[0034] Symbol explanation in the figure: 11, bottom cell, 12, 16: intermediate cell, 13, top cell, 14, tunnel junction, 15, ohmic contact layer. DETAILED DESCRIPTION

[0035] In order to make the content of the present application more clear, the content of the present application will be further described below in combination with the drawings. The present application is not limited to the specific embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the protection scope of the present application.

[0036] As Figure 1As shown, a multi-junction solar cell comprises:

[0037] The multi-junction sub-cell and the tunnel junction 14 between the two adjacent junction sub-cells; the tunnel junction 14 comprises an N-type layer and a P-type layer which are stacked in the first direction in sequence;

[0038] At least one of the sub-cells comprises a back field layer, a base region, an emitter region and a window layer which are arranged in the first direction in sequence; and in the sub-cell, a DBR mirror is further arranged between the back field layer and the base region; meanwhile, the thickness of the back field layer is the thickness required for the complete destructive interference of the first reflected light and the second reflected light, the first reflected light is the reflected light of the sunlight which is normally incident to the interface between the DBR mirror and the back field layer from the DBR mirror, and the second reflected light is the reflected light of the sunlight which is normally incident to the surface of the back field layer close to the tunnel junction 14 from the DBR mirror.

[0039] Based on the above, in one embodiment of the present application, the DBR mirror comprises first material layers with low refractive index and second material layers with high refractive index which are alternately stacked, wherein the first material layers and the second material layers are alternately grown for n cycles, 3≤n≤30. In the present specification, the "first material layer with low refractive index" and the "second material layer with high refractive index" represent the difference in refractive index between the first material layer and the second material layer, and the first material layer with low refractive index has a lower refractive index than the second material layer with high refractive index.

[0040] Based on the above, in one embodiment of the present application, the first material layer and the second material layer each have an optical thickness of not less than 0.25λ; wherein λ represents the center reflection wavelength of the DBR mirror.

[0041] Based on the above, in one embodiment of the present application, the optical thickness of the first material layer and the second material layer is 0.25λ.

[0042] Based on the above, in one embodiment of the present application, when the refractive index of the material layer in contact with the back field layer of the DBR mirror 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.

[0043] Based on the above, in one embodiment of the present application, when the refractive index of the material layer in contact with the back field layer of the DBR mirror 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.

[0044] Based on the above, in one embodiment of the present application, the multi-junction sub-cell includes a bottom cell 11, a plurality of intermediate cells (12...) and a top cell 13 arranged in sequence, wherein the intermediate cells (12...) include a back field layer, a base region, an emission region and a window layer arranged in sequence along the first direction; and the DBR mirror 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 the present embodiment. The multi-junction solar cell can be a three-junction solar cell as shown in Embodiment 1 (at which time the intermediate cell is only one), or a four-junction solar cell as shown in Embodiment 2 (at which time the intermediate cell has two), and the specific number of junctions is determined according to the situation.

[0045] Based on the same utility model concept, the present embodiment of the present application further provides a manufacturing method of a multi-junction solar cell, the manufacturing method of the multi-junction solar cell comprising:

[0046] providing a substrate;

[0047] forming a multi-junction sub-cell on the substrate, and forming a tunnel junction 14 between adjacent two junction sub-cells; the tunnel junction 14 includes an N-type layer and a P-type layer stacked in sequence along the growth direction;

[0048] wherein 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 a DBR mirror is further arranged between the back field layer and the base region in the sub-cell; and the thickness of the back field layer is the thickness required for complete destructive interference of first reflected light and second reflected light, the first reflected light is reflected light when sunlight is vertically incident from the DBR mirror to the interface between the DBR mirror and the back field layer, and the second reflected light is reflected light when sunlight is vertically incident to the surface of the back field layer close to the tunnel junction 14.

[0049] Preferably, the DBR mirror includes first material layers with low refractive index and second material layers with high refractive index alternately stacked;

[0050] wherein the first material layer and the second material layer each have an optical thickness of not less than 0.25λ; wherein λ represents the center reflection wavelength of the DBR mirror.

[0051] Preferably, when the refractive index of the material layer in contact with the DBR mirror 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;

[0052] Or, when the DBR mirror and the material layer formed in contact with 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.

[0053] Through the above technical solutions, the multi-junction solar cell provided by the utility model, at least one sub-cell includes back field layer, base region, emission region and window layer arranged in the first direction in turn; and in the sub-cell, DBR mirror is further arranged 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 of the first reflected light and the second reflected light. Based on the above structure, by arranging DBR mirror between the back field layer and the base region, the primary unabsorbed photons are reflected back to be absorbed again, which is equivalent to increasing the effective absorption thickness, so that the base region thickness can be thinned, the minority carrier recombination can be reduced, and the radiation resistance of the cell can be improved. By arranging the back field layer, complete destructive interference can be realized, so that the back field layer can effectively passivate the minority carrier recombination on the surface of the sub-cell without affecting the reflection effect of the DBR mirror, the collection efficiency of the photo-generated carrier is improved, and the conversion efficiency of the cell is improved. Therefore, the radiation resistance of the cell and the collection efficiency of the photo-generated carrier are simultaneously improved.

[0054] Further, the multi-junction sub-cell includes a bottom cell 11, a plurality of intermediate cells 12 and a top cell 13 arranged in the first direction in turn, wherein the intermediate cell 12 includes a back field layer, a base region, an emission region and a window layer arranged in the first direction in turn; and the DBR mirror is arranged between the back field layer and the base region of at least one intermediate cell 12. Based on this, the damage of the intermediate cell 12 caused by concentrated radiation can be well avoided.

[0055] The utility model also provides a kind of multi-junction solar cell manufacturing method, while realizing the beneficial effects of the above solar cell, its process production is simple and convenient, and it is convenient for production.

[0056] Embodiment 1

[0057] As Figure 2 As shown in a kind of multi-junction solar cell, the multi-junction solar cell is three-junction solar cell (the intermediate cell 12 only has one at that time), then the multi-junction sub-cell includes Ge bottom cell 11, InGaAs intermediate cell 12 and GaInP top cell 13 arranged in the first direction in turn;

[0058] In this embodiment, the multi-junction solar cell includes Ge bottom cell 11, first tunnel junction 14, InGaAs intermediate cell 12, second tunnel junction 14 and GaInP top cell 13 arranged in the first direction in turn, and is specifically arranged as follows:

[0059] The Ge bottom cell 11 forms a PN junction by diffusing phosphorus on a P-type Ge substrate to obtain an N-type emitter region, and grows a (Al) GaInP nucleation layer on the P-type Ge substrate to serve as a window layer of the Ge bottom cell 11.

[0060] In the first tunnel junction 14, an N-type GaAs or an N-type GaInP is used as an N-type layer of the first tunnel junction 14, and a P-type (Al) GaAs material is used as a P-type layer of the first tunnel junction 14; wherein the N-type and P-type doping are respectively doped by Si and C.

[0061] The InGaAs middle cell 12 includes a back field layer, a base region, an emitter region, and a window layer arranged in sequence along a first direction; further, in the InGaAs middle cell 12, a DBR mirror is further arranged between the back field layer and the base region; meanwhile, the thickness of the back field layer is the thickness required for complete destructive interference of first reflected light and second reflected light, the first reflected light is reflected light when sunlight is vertically incident on the DBR mirror from the DBR mirror to the interface between the DBR mirror and the back field layer, and the second reflected light is reflected light when sunlight is vertically incident on the surface of the back field layer close to the second tunnel junction 14.

[0062] The DBR mirror includes first material layers with low refractive index and second material layers with high refractive index which are alternately stacked. In this specification, the first material layers with low refractive index and the second material layers with high refractive index represent the difference in refractive index by comparing the first material layers and the second material layers, and the first material layers with low refractive index have a lower refractive index than the second material layers with high refractive index. Meanwhile, the back field layer has a low refractive index.

[0063] Based on the above, in an embodiment of the present application, the first material layers and the second material layers both have an optical thickness of not less than 0.25λ; wherein λ represents the center reflection wavelength of the DBR mirror.

[0064] Based on the above, in an embodiment of the present application, the optical thicknesses of the first material layers and the second material layers are both 0.25λ.

[0065] Based on the above, in an embodiment of the present application, when the second material layers form a contact with the back field layer of the DBR mirror, the optical thickness of the back field layer is Kλ / 2. Preferably, the optical thickness of the back field layer is λ / 2 (i.e. k = 1).

[0066] Based on the above, in one embodiment of the present application, when the DBR mirror is in contact with the back field layer and the first material 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 (i.e. k = 1).

[0067] Specifically, in the InGaAs intermediate cell 12, the back field layer includes an AlGaAs back field layer or a GaInP back field layer or an AlGaInP back 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, wherein N-type and P-type doping are obtained by doping with Si, C, respectively; the DBR mirror includes alternately stacked Al x GaAs layers and Al y GaAs layers, wherein 0≤x<y≤1, the Al x GaAs layer as the first material layer, the Al y GaAs layer as the second material layer, and the Al x GaAs layer and the Al y GaAs layer have an optical thickness of 0.25λ, wherein the first material layer and the second material layer are alternately grown for n periods, 3≤n≤30. It should be noted that for AlGaAs material, the higher the Al component, the smaller the refractive index, and the smaller the nanohardness of the material. For the DBR mirror, it is preferred to have a material layer with a larger nanohardness so as 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 thereon. That is, the Al x GaAs layer as the first material layer of the DBR mirror so as to reduce the dislocations extending upward to the emitter region and reduce the residual stress; at the same time, in order to ensure that the DBR mirror has a good light reflection function, the DBR mirror further includes an Al y GaAs layer as the second material layer of the DBR mirror, and the Bragg reflection mirror is formed by alternately stacking a plurality of 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 Al x GaAs layers and Al y GaAs layers. The first material layer and the second material layer only need to have different refractive indexes and have light transmission, i.e. 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 yThe semiconductor layer such as GaAs layer has high light transmittance and is easy to deposit, and the difference in refractive index is relatively large, and thus is more suitable.

[0068] Based on the above, in one embodiment of the present application, the DBR mirror is in contact with the back field layer by the second material layer (Al y When the back field layer is a GaAs layer, the optical thickness of the back field layer is Kλ / 2. Preferably, the optical thickness of the back field layer is λ / 2 (i.e., k = 1).

[0069] Based on the above, in another embodiment of the present application, the DBR mirror is in contact with the back field layer by the first material layer (Al x When the back field layer is a GaAs 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 (i.e., k = 1).

[0070] 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 GaAs layer material is used as the P-type layer of the first tunnel junction 14; wherein, Si and C are used for N-type and P-type doping, respectively.

[0071] The GaInP top cell 13 includes a back field layer, a base region, an emission region and a window layer arranged in the first direction in sequence; 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 emission region includes an N-type AlGaInP emission region or an N-type GaInP emission region, and the window layer includes an AlInP window layer or an AlGaInP window layer.

[0072] In the embodiment of the utility model, the top cell 13 is further provided with an ohmic contact layer 15 on the side surface away from the middle cell 12. As a structure layer for forming ohmic contact with the electrode, the ohmic contact layer 15 further improves the performance of the multi-junction solar cell.

[0073] Based on the same utility model concept, the embodiment of the utility model further provides a manufacturing method of a multi-junction solar cell, which is used for manufacturing the three-junction solar cell described above, and the manufacturing method comprises the following steps:

[0074] S01, providing a substrate, the substrate includes a P-type Ge substrate;

[0075] 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 cell 11, and a (Al)GaInP nucleation layer which is lattice-matched with the substrate is grown on the P-type Ge substrate to serve as a window layer of the Ge bottom cell 11; finally, the Ge bottom cell 11 is formed.

[0076] Step S03, the first tunnel junction 14 is made.

[0077] 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, Si and C are used for doping to obtain N-type and P-type doping, respectively.

[0078] Step S04, the InGaAs middle cell 12 is made, which includes a back field layer, a base region, an emitter region and a window layer arranged in sequence along a first direction; further, a DBR mirror is arranged between the back field layer and the base region in the InGaAs middle cell 12; at the same time, the thickness of the back field layer is the thickness required for complete destructive interference of 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 mirror to the interface between the DBR mirror and the back field layer, and the second reflected light is the reflected light when the sunlight is vertically incident from the DBR mirror to the surface of the back field layer close to the second tunnel junction 14.

[0079] The DBR mirror includes first material layers with low refractive index and second material layers with high refractive index which are alternately stacked. In this specification, the first material layers with low refractive index and the second material layers with high refractive index represent the difference in refractive index between the first material layers and the second material layers, and the first material layers with low refractive index have a lower refractive index than the second material layers with high refractive index. At the same time, the back field layer has a low refractive index.

[0080] Based on the above, in an embodiment of the present application, the first material layers and the second material layers both have an optical thickness of not less than 0.25λ; wherein λ represents the center reflection wavelength of the DBR mirror.

[0081] Based on the above, in an embodiment of the present application, the optical thickness of the first material layers and the second material layers is 0.25λ.

[0082] Based on the above, in an embodiment of the present application, in the DBR mirror, the optical thickness of the back field layer is Kλ / 2 when the second material layer is in contact with the back field layer. Preferably, the optical thickness of the back field layer is λ / 2 (i.e. k = 1).

[0083] Based on the above, in one embodiment of the present application, in the DBR mirror, when the contact with the back field layer is the first material 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 (i.e. k = 1).

[0084] Specifically, in the InGaAs intermediate cell 12, the back field layer includes an AlGaAs back field layer or a GaInP back field layer or an AlGaInP back 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, wherein N-type and P-type doping are doped by Si, C respectively; the DBR mirror includes alternatingly stacked Al x GaAs layers and Al y GaAs layers, wherein 0≤x<y≤1, the Al x GaAs layer as the first material layer, the Al y GaAs layer as the second material layer, and the Al x GaAs layer and the Al y GaAs layer have an optical thickness of 0.25λ, wherein the first material layer and the second material layer are alternately grown for n periods, 3≤n≤30. It should be noted that for AlGaAs material, the higher the Al component, the smaller the refractive index, and the smaller the nanohardness of the material. For the DBR mirror, it is preferred to have a material layer with larger nanohardness, so as to reduce the dislocation extending upward to the emitter region, and reduce the influence of residual stress on the emitter region of the sub-cell grown thereon. That is, the Al x GaAs layer with a smaller Al component is selected as the first material layer of the DBR mirror, so as to reduce the dislocation extending upward to the emitter region and reduce the residual stress; at the same time, in order to be able to ensure that the DBR mirror has a good reflection light function, the DBR mirror in the utility model further includes an Al y GaAs layer as the second material layer of the DBR mirror, and a Bragg reflector is formed by the alternating stacking of the 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 Al x GaAs layers and Al y GaAs layers. The first material layer and the second material layer only need to have different refractive indexes and have light transmission, 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 yThe semiconductor layer such as GaAs layer has high light transmittance and is easy to deposit, and the difference of refractive index is relatively large, and thus is more suitable.

[0085] Based on the above, in one embodiment of the present application, the second material layer (Al y GaAs layer) having high refractive index contacts the back field layer.

[0086] Based on the above, in another embodiment of the present application, the first material layer (Al x GaAs layer) having low refractive index contacts the back field layer.

[0087] Step S05, manufacturing the second tunnel junction 14;

[0088] 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 GaAs layer material is used as the P-type layer of the second tunnel junction 14; wherein, Si and C are used for N-type and P-type doping respectively.

[0089] Step S06, manufacturing the GaInP top cell 13;

[0090] Specifically, the GaInP top cell 13 includes a back field layer, a base region, an emission region and a window layer arranged in the first direction in sequence; 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 emission region includes an N-type AlGaInP emission region or an N-type GaInP emission region, and the window layer includes an AlInP window layer or an AlGaInP window layer.

[0091] As Figure 3 As shown in the top cell 13 of the embodiment of the present application, an ohmic contact layer 15 is further arranged on the side surface of the top cell 13 away from the middle cell 12. The ohmic contact layer 15 is used as a structure layer for forming ohmic contact with the electrode, and further improves the performance of the multi-junction solar cell.

[0092] Via the technical scheme, the multi-junction solar cell provided by the utility model, the multi-junction sub-cell includes Ge bottom cell 11, InGaAs middle cell 12 and GaInP top cell 13 that are sequentially stacked, and a DBR reflector is further arranged between the back field layer and the base region in the InGaAs middle cell 12, and the thickness of the back field layer is the thickness required for complete destructive interference of the first reflected light and the second reflected light. Based on the above structure, the DBR reflector is arranged between the back field layer and the base region, the photons that are not absorbed initially are reflected back to be absorbed secondarily, which is equivalent to increasing the effective absorption thickness, the base region thickness can be thinned, and the minority carrier recombination can be reduced, so that the radiation resistance of the cell is improved. The back field layer is arranged to realize complete destructive interference, so that the back field layer can effectively passivate the minority carrier recombination on the surface of the sub-cell under the premise of not affecting the reflection effect of the DBR reflector, the collection efficiency of the photo-generated carrier is improved, and the conversion efficiency of the cell is improved. Therefore, the radiation resistance of the cell and the collection efficiency of the photo-generated carrier are simultaneously improved.

[0093] Further, the DBR reflector is arranged between the back field layer and the base region of the InGaAs middle cell 12. Based on this, the concentrated irradiation damage of the middle cell 12 can be well avoided, and the problem that the irradiation damage of the InGaAs middle cell 12 is greater than that of the Ge sub-cell and the GaInP sub-cell can be well solved, especially for the GaInP / InGaAs / Ge three-junction cell structure.

[0094] The utility model also provides a kind of multi-junction solar cell's manufacturing method, while realizing the beneficial effects of the above solar cell, its process production is simple and convenient, and it is convenient for production.

[0095] Example 2

[0096] As Figure 4 shown, a kind of multi-junction solar cell, the multi-junction solar cell is four-junction solar cell (there are two middle cells), specifically, the multi-junction sub-cell includes Ge bottom cell 11, InGaAs middle cell 12, AlInGaAs middle cell 16 and GaInP top cell 13 that are sequentially stacked.

[0097] In this embodiment, the multi-junction solar cell includes Ge bottom cell 11, first tunnel junction 14, InGaAs middle cell 12, second tunnel junction 14, AlInGaAs middle cell 12, third tunnel junction 14 and GaInP top cell 1313 that are sequentially stacked, and is specifically arranged as follows:

[0098] The Ge bottom cell 11 forms a PN junction by diffusing phosphorus on a P-type Ge substrate to obtain an N-type emitter region, and grows a (Al) GaInP nucleation layer on the P-type Ge substrate to serve as a window layer of the Ge bottom cell 11.

[0099] In the first tunnel junction 14, an N-type GaAs or an N-type GaInP is used as an N-type layer of the first tunnel junction 14, and a P-type (Al) GaAs material is used as a P-type layer of the first tunnel junction 14; wherein, the N-type and P-type doping are respectively doped by Si and C.

[0100] The InGaAs middle cell 12 includes a back field layer, a base region, an emitter region, and a window layer arranged in sequence along a first direction; further, in the InGaAs middle cell 12, a DBR mirror is further arranged between the back field layer and the base region; meanwhile, the thickness of the back field layer is the thickness required for complete destructive interference of first reflected light and second reflected light, the first reflected light is reflected light when sunlight is vertically incident on the DBR mirror from the DBR mirror to the interface between the DBR mirror and the back field layer, and the second reflected light is reflected light when sunlight is vertically incident on the surface of the back field layer close to the tunnel junction 14.

[0101] The DBR mirror includes first material layers with low refractive index and second material layers with high refractive index which are alternately stacked. In this specification, the first material layers with low refractive index and the second material layers with high refractive index represent the difference in refractive index by comparing the first material layers and the second material layers, and the first material layers with low refractive index have a lower refractive index than the second material layers with high refractive index. Meanwhile, the back field layer has a low refractive index.

[0102] Based on the above, in an embodiment of the present application, the first material layers and the second material layers both have an optical thickness of not less than 0.25λ; wherein, λ represents the center reflection wavelength of the DBR mirror.

[0103] Based on the above, in an embodiment of the present application, the optical thicknesses of the first material layers and the second material layers are both 0.25λ.

[0104] Based on the above, in an embodiment of the present application, when the second material layers form a contact with the back field layer of the DBR mirror, the optical thickness of the back field layer is Kλ / 2. Preferably, the optical thickness of the back field layer is λ / 2 (i.e. k = 1).

[0105] Based on the above, in one embodiment of the present application, when the DBR mirror is in contact with the back field layer and the first material 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 (i.e. k = 1).

[0106] Specifically, in the InGaAs intermediate cell 12, the back field layer includes an AlGaAs back field layer or a GaInP back field layer or an AlGaInP back 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, wherein N-type and P-type doping are obtained by doping with Si, C, respectively; the DBR mirror includes alternately stacked Al x GaAs layers and Al y GaAs layers, wherein 0≤x<y≤1, the Al x GaAs layer as the first material layer, the Al y GaAs layer as the second material layer, and the Al x GaAs layer and the Al y GaAs layer have an optical thickness of 0.25λ, wherein the first material layer and the second material layer are alternately grown for n periods, 3≤n≤30. It should be noted that for AlGaAs material, the higher the Al component, the smaller the refractive index, and the smaller the nanohardness of the material. For the DBR mirror, it is preferred to have a material layer with larger nanohardness so as 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 thereon. That is, the Al x GaAs layer with a smaller Al component is selected as the first material layer of the DBR mirror so as to reduce the dislocations extending upward to the emitter region and reduce the residual stress; at the same time, in order to ensure that the DBR mirror has a good reflection light function, the DBR mirror further includes an Al y GaAs layer as the second material layer of the DBR mirror, and the Bragg reflection mirror is formed by alternately stacking a plurality of 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 Al x GaAs layers and Al y GaAs layers. The first material layer and the second material layer only need to have different refractive indexes and have light transmission, i.e. 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 yThe semiconductor layer such as GaAs layer has high light transmittance and is easy to deposit, and the difference in refractive index is relatively large, and thus is more suitable.

[0107] Based on the above, in one embodiment of the present application, the DBR mirror contacts the back field layer by the second material layer (Al y When the back field layer is GaAs layer, the optical thickness of the back field layer is Kλ / 2. Preferably, the optical thickness of the back field layer is λ / 2 (i.e. k = 1).

[0108] Based on the above, in another embodiment of the present application, the DBR mirror contacts the back field layer by the first material layer (Al x When the back field layer is GaAs 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 (i.e. k = 1).

[0109] 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 GaAs layer material is used as the P-type layer of the first tunnel junction 14; wherein, N-type and P-type doping are respectively doped by Si and C.

[0110] The AlInGaAs intermediate cell 16 comprises a back field layer, a base region, an emission region and a window layer arranged in sequence along the first direction; further, in the AlInGaAs intermediate cell 16, the back field layer comprises a GaInP or AlGaAs back field layer, the base region comprises a P-type AlInGaAs base region, the emission region comprises an N-type AlInGaAs emission region, and the window layer comprises an AlGaInP or AlInP window layer; wherein, N-type and P-type doping are respectively doped by Si and C.

[0111] It should be noted that, as Figure 5 As shown in the AlInGaAs intermediate cell 16, the DBR mirror can also be arranged between the back field layer and the base region of the AlInGaAs intermediate cell 16, as described above for the InGaAs intermediate cell 12; 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 be completely destructively interfered, the third reflected light is the reflected light of the sunlight vertically incident to the interface between the DBR mirror and the back field layer of the AlInGaAs intermediate cell 16, and the fourth reflected light is the reflected light of the sunlight vertically incident to the surface of the back field layer of the AlInGaAs intermediate cell 16 close to the third tunnel junction 14. For details, reference can be made to the arrangement of the InGaAs intermediate cell 12, which will not be described herein again.

[0112] 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, P-type Al x GaAs layer material is used as the P-type layer of the third tunnel junction 1414; wherein, Si and C are used for N-type and P-type doping respectively.

[0113] The GaInP top cell 13 comprises a back field layer, a base region, an emission region and a window layer arranged in sequence along the first direction; further, in the GaInP top cell 13, the back field layer comprises an AlGaInP back field layer, the base region comprises a P-type AlGaInP base region or a P-type GaInP base region, the emission region comprises an N-type AlGaInP emission region or an N-type GaInP emission region, and the window layer comprises an AlInP window layer or an AlGaInP window layer.

[0114] In the embodiment of the utility model, the top cell 13 is further provided with an ohmic contact layer 15 on the side surface away from the middle cell 12. As a structure layer for forming ohmic contact with the electrode, the ohmic contact layer 15 further improves the performance of the multi-junction solar cell.

[0115] Based on the same utility model concept, the utility model embodiment further provides a manufacturing method of a multi-junction solar cell, which is used for manufacturing the four-junction solar cell described above, and the manufacturing method comprises the following steps:

[0116] Step A01, providing a substrate, wherein the substrate comprises a P-type Ge substrate;

[0117] Step A02, performing phosphorus diffusion on the P-type Ge substrate to obtain an N-type emission region, thereby forming a PN junction of the Ge bottom cell 11, and growing a (Al) GaInP nucleation layer on the P-type Ge substrate and matching the substrate lattice to serve as a window layer of the Ge bottom cell 11; finally, the Ge bottom cell 11 is formed.

[0118] Step A03, manufacturing a first tunnel junction 14;

[0119] 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, Si and C are used for N-type and P-type doping respectively.

[0120] Step A04, manufacturing an InGaAs middle cell 12, the InGaAs middle cell 12 comprising 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 middle cell 12, a DBR mirror is further arranged between the back field layer and the base region; meanwhile, the thickness of the back field layer is the thickness required for complete destructive interference of a first reflected light and a second reflected light, the first reflected light being the reflected light of the sunlight normally incident to the interface between the DBR mirror and the back field layer from the DBR mirror, and the second reflected light being the reflected light of the sunlight normally incident to the surface of the back field layer close to the second tunnel junction 14 from the DBR mirror.

[0121] The DBR mirror comprises first material layers with low refractive index and second material layers with high refractive index alternately stacked. In the present specification, the first material layers with low refractive index and the second material layers with high refractive index represent the difference in refractive index between the first material layers and the second material layers, and the first material layers with low refractive index have lower refractive index than the second material layers with high refractive index. Meanwhile, the back field layer has low refractive index.

[0122] Based on the above, in an embodiment of the present application, the first material layers and the second material layers both have an optical thickness of not less than 0.25λ; wherein λ represents the central reflection wavelength of the DBR mirror.

[0123] Based on the above, in an embodiment of the present application, the optical thickness of the first material layers and the second material layers is 0.25λ.

[0124] Based on the above, in an embodiment of the present application, in the DBR mirror, when the contact with the back field layer is 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 (i.e. k = 1).

[0125] Based on the above, in an embodiment of the present application, in the DBR mirror, when the contact with the back field layer is the first material 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 (i.e. k = 1).

[0126] Specifically, in the InGaAs middle cell 12, the back field layer comprises an AlGaAs back field layer or a GaInP back field layer or an AlGaInP back field layer, the base region comprises a P-type InGaAs base region, the emission region comprises an N-type InGaAs emission region, the window layer comprises an AlGaInP or AlInP window layer, wherein, N-type and P-type doping are respectively doped by Si and C; the DBR mirror comprises alternately stacked Al x GaAs layers and Al y GaAs layers, wherein 0≦x<y≦1, the Al x GaAs layer as the first material layer, the Al y GaAs layer as the second material layer, and the Al x GaAs layer and the Al y GaAs layer, and the optical thickness of the Al x GaAs layer as the first material layer of the DBR mirror, so as to reduce the dislocation extending upward to the emission region and reduce the residual stress; meanwhile, in order to ensure that the DBR mirror has a good reflection light function, the DBR mirror further comprises an Al y GaAs layer as the second material layer of the DBR mirror, by alternately stacking a plurality of periods of high-refractive Al y GaAs layer and low-refractive Al x GaAs layer, the Bragg reflection mirror is formed. However, the first material layer and the second material layer are not limited to Al x GaAs layer and Al y GaAs layer. The first material layer and the second material layer only need to have different refractive indexes and have light transmission, that is, other semiconductor layers can also be used as the first material layer and the second material layer. However, semiconductor layers such as Al x GaAs layer and Al y GaAs layer and the like have high light transmission and are easy to deposit, and the refractive index difference is relatively large, and thus are more suitable.

[0127] Based on the above, in an embodiment of the present application, the second material layer (Al yWhen the optical thickness of the back field layer is kλ / 2 (k is an integer, and the material of the back field layer is GaAs 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 (i.e. k = 1).

[0128] Based on the above, in another embodiment of the present application, the DBR mirror contacts the first material layer (Al x When the optical thickness of the back field layer is kλ / 2 (k is an integer, and the material of the back field layer is GaAs 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 (i.e. k = 1).

[0129] Step A05, making the second tunnel junction 14;

[0130] 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, P-type Al x GaAs layer material is used as the P-type layer of the second tunnel junction 14; wherein, N-type and P-type doping are respectively doped by Si and C.

[0131] Step S06, making the AlInGaAs intermediate cell 16;

[0132] Specifically, the AlInGaAs intermediate cell 16 includes a back field layer, a base region, an emission region and a window layer arranged in the first direction in sequence; 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 emission region includes an N-type AlInGaAs emission region, and the window layer includes an AlGaInP or AlInP window layer; wherein, N-type and P-type doping are respectively doped by Si and C.

[0133] It should be noted that, in the AlInGaAs intermediate cell 12, the DBR mirror can also be arranged between the back field layer and the base region of the AlInGaAs intermediate cell 16 according to the above arrangement of the InGaAs intermediate cell 12; 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 be completely destructive interference, the third reflected light is the reflected light of the sunlight vertically incident to the interface between the DBR mirror and the back field layer of the AlInGaAs intermediate cell 16, and the fourth reflected light is the reflected light of the sunlight vertically incident to the surface of the back field layer of the AlInGaAs intermediate cell 16 close to the third tunnel junction 14. For details, please refer to the arrangement of the InGaAs intermediate cell 12, which will not be described herein.

[0134] Step A07, making the third tunnel junction 14;

[0135] 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, P-type Al x GaAs layer material is used as the P-type layer of the third tunnel junction 1414; wherein, Si and C are used for N-type and P-type doping respectively.

[0136] Step A08, manufacturing GaInP top cell 13;

[0137] Specifically, the GaInP top cell 13 comprises a back surface 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 surface field layer comprises an AlGaInP back surface field layer, the base region comprises a P-type AlGaInP base region or a P-type GaInP base region, the emitter region comprises an N-type AlGaInP emitter region or an N-type GaInP emitter region, and the window layer comprises an AlInP window layer or an AlGaInP window layer.

[0138] In the embodiment of the utility model, ohmic contact layer 15 is further arranged on the side surface of top cell 13 away from intermediate cell 12. Wherein, as the structure layer forming ohmic contact with electrode, the performance of multi-junction solar cell is further improved.

[0139] According to the technical scheme, the multi-junction solar cell comprises Ge bottom cell 11, InGaAs intermediate cell 12, AlInGaAs intermediate cell 16 and GaInP top cell 13 arranged in sequence; and DBR reflector is further arranged between the back surface field layer and the base region of InGaAs intermediate cell 12 or AlInGaAs intermediate cell 16; and the thickness of the back surface field layer is the thickness required for complete destructive interference of the first reflected light and the second reflected light. Based on the above structure, by arranging DBR reflector between the back surface field layer and the base region, the primary unabsorbed photons are reflected back to be absorbed secondarily, which is equivalent to increasing the effective absorption thickness, and the base region thickness can be thinned and the minority carrier recombination can be reduced, thereby improving the anti-radiation performance of the cell. By arranging the back surface field layer, complete destructive interference can be realized, which can ensure effective passivation of the minority carrier recombination on the surface of the cell through the back surface field layer without affecting the reflection effect of the DBR reflector, improve the collection efficiency of the photo-generated carriers, and thereby improve the conversion efficiency of the cell. Thus, the anti-radiation performance of the cell and the collection efficiency of the photo-generated carriers are simultaneously improved.

[0140] Further, the DBR mirror is arranged between the back field layer and the base region of the InGaAs intermediate cell 12 / AlInGaAs intermediate cell 16, so that the concentrated irradiation damage of the intermediate cell 12 can be avoided, and the large irradiation damage of the InGaAs intermediate cell 12 / AlInGaAs intermediate cell 12 can be well solved.

[0141] The utility model further provides a kind of multi-junction solar cell's manufacturing method, while realizing the beneficial effect of the above-mentioned solar cell, its process production is simple and convenient, and it is convenient for production.

[0142] Each embodiment in the present specification is described in a progressive manner, and each embodiment focuses on the difference from other embodiments, and the same or similar parts between each embodiment can be referred to each other.

[0143] It should also be noted that, in this document, relational terms such as first and second and the like can only be used to distinguish one entity or action from another entity or action, and do not necessarily require or imply that there is any such actual relationship or order between these entities or actions. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that the item or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such item or device. Without more limitations, the element defined by the statement "comprising a" does not exclude the presence of additional identical elements in the item or device including the above element.

[0144] The above description of the disclosed embodiments enables a person 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 can 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 by, The application relates to a multi-junction solar cell. The multi-junction solar cell comprises a plurality of sub-cells and a tunnel junction between two adjacent sub-cells; the tunnel junction comprises an N-type layer and a P-type layer which are stacked in a first direction. At least one of the sub-cells comprises a back field layer, a base region, an emission region and a window layer which are arranged in the first direction; and a DBR mirror is arranged between the back field layer and the base region in the sub-cell; and the thickness of the back field layer is the thickness required for complete destructive interference of first reflected light and second reflected light, the first reflected light being reflected light of sunlight which is normally incident on the interface between the DBR mirror and the back field layer, and the second reflected light being reflected light of sunlight which is normally incident on the surface of the back field layer close to the tunnel junction.

2. The multi-junction solar cell of claim 1, wherein The DBR mirror comprises first material layers with low refractive index and second material layers with high refractive index which are alternately stacked.

3. The multi-junction solar cell of claim 2, wherein, The first material layers and the second material layers have an optical thickness of not less than 0.25 lambda; wherein lambda represents the central reflection wavelength of the DBR mirror.

4. The multi-junction solar cell of claim 3, wherein, The optical thickness of the first material layers and the second material layers is 0.25 lambda.

5. The multi-junction solar cell of claim 3, wherein, When the refractive index of the material layer in contact with the back field layer of the DBR mirror is greater than the refractive index of the back field layer, the optical thickness of the back field layer is K lambda / 2; wherein k is an integer not less than 0.

6. The multi-junction solar cell of claim 5, wherein, The k is 1.

7. The multi-junction solar cell of claim 3, wherein, When the refractive index of the material layer in contact with the back field layer of the DBR mirror 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) lambda / 4; wherein k is an integer not less than 0.

8. The multi-junction solar cell according to any one of claims 2 to 7, characterized in that The multi-junction solar cell comprises a plurality of sub-cells and a tunnel junction between two adjacent sub-cells; the tunnel junction comprises an N-type layer and a P-type layer which are stacked in a first direction.

9. The multi-junction solar cell of claim 8, wherein, The multi-junction solar cell is a three-junction solar cell, and the multi-junction sub-cell comprises a Ge bottom cell, an InGaAs middle cell and a GaInP top cell which are stacked in the first direction. The multi-junction solar cell is a four-junction solar cell, and the multi-junction sub-cell comprises a Ge bottom cell, an InGaAs middle cell, an Al InGaAs middle cell and a GaInP top cell which are stacked in the first direction. The InGaAs middle cell comprises a back field layer, a base region, an emission region and a window layer which are arranged in the first direction; and the DBR mirror is arranged between the back field layer and the base region of the InGaAs middle cell.

10. The multi-junction solar cell of claim 9, wherein, In the InGaAs middle cell, the back field layer comprises an AlGaAs back field layer or a GaInP back field layer or an AlGaInP back field layer, the base region comprises a P-type InGaAs base region, the emitting region comprises an N-type InGaAs emitting region, the window layer comprises an AlGaInP or AlInP window layer; the DBR mirror comprises alternately stacked Al x GaAs layers and Al y GaAs layers, wherein 0≦x<y≦1, the Al x GaAs layer as the first material layer, the Al y GaAs layer as the second material layer.

11. The multijunction solar cell of claim 9, wherein, When the second material layer of the DBR mirror is in contact with the back field layer, the optical thickness of the back field layer is K lambda / 2; wherein k is an integer not less than 0.

12. The multijunction solar cell of claim 11, wherein, The optical thickness of the back field layer is lambda / 2.

13. The multijunction solar cell of claim 9, wherein, When the first material layer of the DBR mirror is in contact with the back field layer, the optical thickness of the back field layer is (2K-1) lambda / 4; wherein k is an integer not less than 0.

14. The multi-junction solar cell of claim 13, wherein, The optical thickness of the back field layer is lambda / 4.

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