Electrode Structure and Manufacturing Method of Solar Cell

Abstract

This electrode structure for a solar cell comprises an electrical conductor (21) disposed on a side of a substrate (11) of a chalcogen solar cell, and a wiring element (13, 27) electrically connected to the electrical conductor (21). The wiring element (13, 27) is stacked on and bonded to the electrical conductor (21). The wiring element (13, 27) and the electrical conductor (21) include a Group VI element. In a direction in which the electrical conductor (21) and the wiring element (13, 27) are stacked, a peak of a concentration distribution of the Group VI element is deviated from an interface between the electrical conductor and the wiring element (13, 27).

Description

Technical Field

[0001] The present invention relates to an electrode structure of a solar cell including a chalcogen solar cell.

Background Art

[0002] Conventionally, CIS-based solar cells using a chalcopyrite-structured group I-III-VI2 compound semiconductor containing Cu, In, Ga, Se, and S as a photoelectric conversion layer have been proposed. CIS-based solar cells have a relatively low manufacturing cost and a high absorption coefficient in the wavelength range from visible to near-infrared, so high photoelectric conversion efficiency is expected. In addition, CIS-based solar cells have excellent radiation resistance, a longer lifespan than Si-based solar cells, and a lower price than GaAs-based solar cells, and are also being considered for use in space applications.

[0003] A CIS-based solar cell is configured, for example, by forming a metal back electrode layer on a substrate, forming a photoelectric conversion layer, which is a group I-III-VI2 compound, thereon, and further sequentially forming a buffer layer and a window layer formed of a transparent conductive film. For wiring on the back electrode on the + electrode side of a CIS-based solar cell, methods using soldering as in Patent Document 1 and adhesive methods using a conductive paste as in Patent Document 2 have been conventionally used.

[0004] For example, Patent Document 1 discloses a connection method that uses an In-solder-coated copper foil ribbon wire to fix both an electrode film and a conductive film without damaging them. Also, in the configuration of Patent Document 2, a ribbon wire adhered with a conductive paste intermittently applied on an electrode is sandwiched between a solar cell submodule adhesively held via a filler and a cover glass. Thereby, the ribbon wire is attached in surface contact with the electrode of the solar cell module.

[0005] In addition, as one of the joining methods between the back electrode layer and a metal ribbon in a terrestrial solar cell, for example, ultrasonic seam welding as in Patent Document 3 is known. In addition, Patent Document 4 discloses a technique for enhancing the bonding strength between a connection electrode and an electrode layer in a GaAs-based solar cell. The configuration of Patent Document 4 includes a GaAs semiconductor layer having a contact region selectively set on the surface, a TiN layer formed on a part of the contact region, and an electrode layer formed on the entire surface of the TiN layer and the contact region. Then, the connection electrode and the electrode layer are welded at a part or the entire surface of the region located on the TiN layer on the surface of the electrode layer.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the case of a solar cell for space use, a joining technique for an interconnector with higher adhesion than that for terrestrial use, which can withstand rapid temperature changes in the space environment and impacts during launch, is required. In addition, solar cells for space use are exposed to temperatures above the melting point of solder depending on altitude and solar radiation. Furthermore, general adhesives used for bonding electrodes and the like have poor UV resistance.

[0008] Therefore, in the case of joining an interconnector by soldering or adhesion, which is common in terrestrial solar cells, there is a concern that the adhesive strength may decrease during the operation of the solar cell, resulting in poor electrical connection. From such a perspective, parallel gap type resistance welding is recommended for joining interconnectors in solar cells for space use.

[0009] Incidentally, on the surface of the back electrode layer (Mo) of the CIS-based solar cell, there exists a Mo(Se,S)2 layer with a layered structure and weak adhesion strength. Therefore, in the joining of the interconnector of the CIS-based solar cell, even when a Ti-based joining layer is formed on the back electrode layer as in Patent Document 4, it has been difficult to sufficiently increase the adhesion strength between the joining layer and the back electrode layer due to the presence of the Mo(Se,S)2 layer.

[0010] Also, this type of phenomenon can similarly occur, for example, in the case of welding a wiring element to a conductive substrate of a CIS-based solar cell when a Mo(Se,S)2 layer or a Ti(Se,S)2 layer exists on the substrate surface.

[0011] The present invention has been made in view of the above situation, and provides an electrode structure in a solar cell including a chalcogen solar cell that enhances the adhesion strength between a conductor on the substrate side of the chalcogen solar cell and a wiring element.

Means for Solving the Problems

[0012] One aspect of the present invention is an electrode structure of a solar cell having a conductor on the substrate side of a chalcogen solar cell and a wiring element electrically connected to the conductor. The wiring element is laminated and joined to the conductor. The wiring element and the conductor contain a Group VI element. In the lamination direction of the conductor and the wiring element, the peak of the concentration distribution of the Group VI element is shifted from the interface between the conductor and the wiring element.

Effects of the Invention

[0013] According to the present invention, in a solar cell including a chalcogen solar cell, the adhesion strength between a conductor on the substrate side of the chalcogen solar cell and a wiring element can be enhanced.

Brief Description of the Drawings

[0014]

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Mode for Carrying Out the Invention

[0015] Hereinafter, embodiments will be described with reference to the drawings. In the embodiments, for the sake of easy understanding of the description, structures or elements other than the main part of the present invention will be described in a simplified or omitted manner. Also, in the drawings, the same elements are denoted by the same reference numerals. Note that in the drawings, the shapes, dimensions, etc. of each element are schematically shown and do not indicate actual shapes, dimensions, etc.

[0016] <<Description of the First Embodiment>> <Structure of Solar Cell> FIG. 1(a) is a plan view showing a configuration example of a solar cell in the first embodiment. FIG. 1(b) is an enlarged view of the vicinity of the connection portion surrounded by the broken line in FIG. 1(a). FIG. 2 is a cross-sectional view taken along the thickness direction of FIG. 1(b). In the first embodiment, as an example of a solar cell including a chalcogen solar cell, a configuration example of a CIS-based solar cell module 10 will be described.

[0017] The solar cell module 10 shown in FIGS. 1 and 2 has a conductive substrate 11 on which a photoelectric conversion element 12 is formed on the light-receiving surface side, an interconnector 13, and a connection portion 14 that electrically connects the photoelectric conversion element 12 and the interconnector 13.

[0018] (Conductive Substrate 11) The conductive substrate 11 is formed of, for example, titanium (Ti), stainless steel (SUS), copper, aluminum, or an alloy thereof. The conductive substrate 11 may be a flexible substrate. The conductive substrate 11 may have a laminated structure in which a plurality of metal substrates are laminated. For example, a stainless steel foil, a titanium foil, or a molybdenum foil may be formed on the surface of the substrate.

[0019] The shape and dimensions of the conductive substrate 11 are appropriately determined according to the size of the solar cell module 10 and the like. The overall shape of the conductive substrate 11 in the first embodiment is, for example, a rectangular flat plate shape, but is not limited thereto. When a metal substrate or a flexible substrate is applied as the conductive substrate 11, the solar cell module 10 can be bent, and cracking of the substrate due to bending can be suppressed. Further, in the above case, it is easy to reduce the weight and thickness of the solar cell module 10 compared with a glass substrate or a resin substrate.

[0020] In the case of a solar cell for space use, from the viewpoint of suppressing the loading weight at the time of launch and enhancing the strength of the solar cell, it is preferable to form the conductive substrate 11 of titanium or an alloy containing titanium.

[0021] (Photoelectric Conversion Element 12) The photoelectric conversion element 12 is an example of a chalcogen solar cell, and has a stacked structure in which a first electrode layer 21, a photoelectric conversion layer 22, a buffer layer 23, and a second electrode layer 24 are sequentially stacked on a conductive substrate 11. Light such as sunlight enters the photoelectric conversion element 12 from the side opposite to the conductive substrate 11 side (the upper side in FIG. 2).

[0022] (The first electrode layer 21) The first electrode layer 21 is, for example, a metal electrode layer of molybdenum (Mo) and is formed on the conductive substrate 11. Since the first electrode layer 21 faces the back side (substrate side) rather than the light-receiving surface side of the photoelectric conversion layer 22, it is also referred to as a back electrode. Although not particularly limited, the thickness of the first electrode layer 21 is, for example, 200 nm to 1000 nm.

[0023] In addition, a group VI compound layer 26 made of Mo(Se,S)2 is formed at the interface between the first electrode layer 21 and the photoelectric conversion layer 22 in the photoelectric conversion element 12. The Mo(Se,S)2 of the group VI compound layer 26 is formed on the first electrode layer 21 when the precursor layer 22p described later is chalcogenated to form the photoelectric conversion layer 22. Note that the Mo(Se,S)2 of the group VI compound layer 26 is a substance having a graphite-like multilayer structure and has a property of being easily exfoliated by cleavage between layers.

[0024] Here, in the solar cell module 10 of the first embodiment, since the photoelectric conversion element 12 is stacked on the conductive substrate 11, the first electrode layer 21 can be omitted and the photoelectric conversion layer 22 can be directly stacked on the conductive substrate 11. When the photoelectric conversion layer 22 is directly stacked on the conductive substrate 11, a group VI compound layer is formed at the interface between the conductive substrate 11 and the photoelectric conversion layer 22 during the chalcogenation of the precursor layer 22p described later. For example, when the conductive substrate 11 is Ti, a group VI compound layer made of Ti(Se,S)2 is formed at the interface between the conductive substrate 11 and the photoelectric conversion layer 22. Note that Ti(Se,S)2 is also a substance having a graphite-like multilayer structure and has a property of being easily exfoliated by cleavage between layers, similar to Mo(Se,S)2.

[0025] (Photoelectric conversion layer 22) The photoelectric conversion layer 22 is formed on the first electrode layer 21. The photoelectric conversion layer 22 may have a double graded structure in which the band gap is large on the light-receiving surface side (the upper side in FIG. 2) and the conductive substrate 11 side (the lower side in FIG. 2), and the band gap is small inside the thickness direction of the photoelectric conversion layer 22. Although not particularly limited, the thickness of the photoelectric conversion layer 22 is, for example, 1.0 μm to 3.0 μm.

[0026] The photoelectric conversion layer 22 functions as a polycrystalline or microcrystalline p-type compound semiconductor layer. The photoelectric conversion layer 22 is a CIS-based photoelectric conversion element using a chalcopyrite-structured I-III-VI2 group compound semiconductor containing a group I element, a group III element, and a group VI element (chalcogen element). The group I element can be selected from copper (Cu), silver (Ag), gold (Au), etc. The group III element can be selected from indium (In), gallium (Ga), aluminum (Al), etc. Further, the photoelectric conversion layer 22 may contain tellurium (Te) etc. in addition to selenium (Se) and sulfur (S) as the group VI element. Further, the photoelectric conversion layer 22 may contain an alkali metal such as Li, Na, K, Rb, Cs, etc.

[0027] Note that the photoelectric conversion layer 22 as a chalcogen solar cell may be a CZTS-based photoelectric conversion element using a chalcogenide-based I2-(II-IV)-VI4 group compound semiconductor containing Cu, Zn, Sn, S or Se. Representative examples of the CZTS-based photoelectric conversion element include those using compounds such as Cu2ZnSnSe4, Cu2ZnSn(S,Se)4, etc.

[0028] (Buffer layer 23) The buffer layer 23 is formed on the photoelectric conversion layer 22. Although not particularly limited, the thickness of the buffer layer 23 is, for example, 10 nm to 100 nm. The buffer layer 23 is, for example, an n-type or i (intrinsic) type high-resistance conductive layer. Here, "high resistance" means having a resistance value higher than the resistance value of the second electrode layer 24 described later.

[0029] The buffer layer 23 can be selected from compounds containing zinc (Zn), cadmium (Cd), and indium (In). Examples of the compound containing zinc include ZnO, ZnS, Zn(OH)2, or mixed crystals thereof such as Zn(O,S), Zn(O,S,OH), and also include ZnMgO, ZnSnO, etc. Examples of the compound containing cadmium include CdS, CdO, or mixed crystals thereof such as Cd(O,S), Cd(O,S,OH). Examples of the compound containing indium include InS, InO, or mixed crystals thereof such as In(O,S), In(O,S,OH), and In2O3, In2S3, In(OH) x etc. can be used. Further, the buffer layer 23 may have a laminated structure of these compounds. It may have.

[0030] Note that the buffer layer 23 has the effect of improving characteristics such as the photoelectric conversion efficiency, but it is also possible to omit it. When the buffer layer 23 is omitted, the second electrode layer 24 is formed on the photoelectric conversion layer 22.

[0031] (Second Electrode Layer 24) The second electrode layer 24 is formed on the buffer layer 23. The second electrode layer 24 is, for example, an n-type conductive layer. Although not particularly limited, the thickness of the second electrode layer 24 is, for example, 0.5 μm to 2.5 μm. The second electrode layer 24 preferably includes a material having a wide bandgap and a sufficiently low resistance value. Further, since the second electrode layer 24 serves as a path for light such as sunlight, it preferably has the property of transmitting light with wavelengths that can be absorbed by the photoelectric conversion layer 22. In this sense, the second electrode layer 24 is also referred to as a transparent electrode layer or a window layer.

[0032] The second electrode layer 24 includes, for example, a metal oxide doped with a group III element (B, Al, Ga, or In) as a dopant. Examples of the metal oxide include ZnO or SnO2. The second electrode layer 24 is, for example, ITO (indium tin oxide), ITiO( It can be selected from indium titanium oxide, IZO (indium zinc oxide), ZTO (zinc tin oxide), FTO (fluorine-doped tin oxide), GZO (gallium-doped zinc oxide), BZO (boron-doped zinc oxide), etc.

[0033] (Interconnector 13) The interconnector 13 is a wiring member on the +-pole side of the solar cell module 10 and is connected in parallel in two at the right end of the solar cell module 10 in FIG. 1. The interconnector 13 is, for example, a ribbon wire of a conductive metal containing Ag. Although not particularly limited, the dimensions of the interconnector can be in the shape of a strip with a thickness of 30 μm and a width of about 2.5 mm.

[0034] Here, the material of the interconnector 13 is not limited to a conductive metal containing Ag, and for example, an iron (Fe) - nickel (Ni) - cobalt (Co) alloy (such as Kovar (registered trademark), etc.) or Ti may be used.

[0035] When an iron - nickel - cobalt alloy is used as the material of the interconnector 13, the ratios of Fe, Ni, and Co may be the same as those of Kovar (Fe: 53.5%, Ni: 29%, Co: 17%), or other ratios may also be used. For example, if the difference in the thermal expansion coefficients between the interconnector 13 and the conductive substrate 11 is reduced, the stress acting on the connection part 14 due to thermal expansion is reduced, so it becomes easier to suppress the decrease in the adhesion strength of the connection part 14. Therefore, the ratios of Fe, Ni, and Co in the iron - nickel - cobalt alloy may be adjusted so that the difference from the thermal expansion coefficient of the conductive substrate 11 is reduced. Also, in order to promote the diffusion of metals between opposing elements, the Fe contained in the iron - nickel - cobalt alloy may be increased.

[0036] In addition, in the first embodiment, the description of the wiring on the - -pole side of the solar cell module 10 is omitted.

[0037] (Connection part 14) The connection part 14 is an element that connects the interconnector 13 and the first electrode layer 21 of the photoelectric conversion element 12, and is provided at two locations at the right end of FIG. 1 of the solar cell module 10. Each connection part 14 is formed in a wiring region 10a in which the photoelectric conversion element 12 is partially cut out to expose the first electrode layer 21 on the light-receiving surface side. Although not particularly limited, the planar dimension of the wiring region 10a is, for example, a rectangular shape of about 5 mm × 5 mm.

[0038] As shown in FIG. 2, the connection part 14 has a laminated structure in which a first electrode layer 21a corresponding to the wiring region 10a and a bonding layer 27 are sequentially laminated on the conductive substrate 11. Further, an end portion of the interconnector 13 is attached to the upper surface of the bonding layer 27 by welding. The welding of the bonding layer 27 and the interconnector 13 is performed by, for example, parallel gap type resistance welding.

[0039] The first electrode layer 21a corresponding to the wiring region 10a is integrally formed with the first electrode layer 21 of the photoelectric conversion element 12. However, a group VI compound layer 26 is formed at the interface with the photoelectric conversion layer 22 in the first electrode layer 21 facing the photoelectric conversion layer 22 of the photoelectric conversion element 12. On the other hand, the group VI compound layer 26 is not formed in the first electrode layer 21a of the wiring region 10a. Since an easily peelable group VI compound layer 26 is not formed between the first electrode layer 21a and the bonding layer 27 in the wiring region 10a, the bonding layer 27 is not easily peeled from the first electrode layer 21a.

[0040] In addition, metal elements (for example, Al) of the bonding layer 27 and group VI elements such as Se and S are diffused in the first electrode layer 21a of the wiring region 10a as will be described later. By the diffusion of the metal element of the bonding layer 27 into the first electrode layer 21a, the first electrode layer 21a and the bonding layer 27 have a high adhesion strength. On the other hand, the first electrode layer 21 in the photoelectric conversion element 12 is not in contact with the bonding layer 27. Therefore, in the first electrode layer 21 in the photoelectric conversion element 12, unlike the first electrode layer 21a in the wiring region 10a, there is almost no diffusion of the metal element of the bonding layer 27.

[0041] (Bonding layer 27) The bonding layer 27 is a conductive layer for electrically connecting the first electrode layer 21a in the wiring region 10a and the interconnector 13, and is composed of a substance containing a Group VI element diffused in a conductive metal material. As an example, the bonding layer 27 of the first embodiment is a substance containing Al, Ag, and diffused Se, S.

[0042] As shown in FIGS. 1 and 2, a groove 28 is formed between the bonding layer 27 and the photoelectric conversion layer 22, the buffer layer 23, and the second electrode layer 24 in the plane direction of the light-receiving surface. Therefore, the bonding layer 27 is insulated from the photoelectric conversion layer 22, the buffer layer 23, and the second electrode layer 24 by the groove 28. Although not particularly limited, the thickness of the bonding layer 27 is about 2.0 μm to 3.0 μm.

[0043] The metal material of the bonding layer 27 has a melting point of 230° C. or higher and a higher melting point than the solder alloy in order to ensure the use of the solar cell module 10 under high temperatures due to solar radiation or the like in the space environment. Note that both of the above Al and Ag have a melting point of 230° C. or higher.

[0044] Further, the material of the bonding layer 27 preferably contains at least one of Al, Pt, Zn, and Sn, which are metal elements that are easily chalcogenated. By including a metal element that is easily chalcogenated in the bonding layer 27, a Group VI compound is likely to be uniformly distributed in the bonding layer 27. Then, when the bonding layer 27 is formed, which will be described later, the diffusion of the Group VI element from the Group VI compound layer 26 to the bonding layer 27 side is promoted. Due to the diffusion of such a Group VI element, the Group VI compound layer 26 can be disappeared from between the first electrode layer 21a and the bonding layer 27.

[0045] As described above, when the bonding layer 27 is formed, the Group VI element diffuses to the bonding layer 27 side and the Group VI compound layer 26 disappears. Therefore, in the concentration distribution of the Group VI element in the thickness direction of the connection portion 14, there is no peak in the concentration of the Group VI element at the interface between the first electrode layer 21a and the bonding layer 27. In addition, since the material of the bonding layer 27 contains a metal element that is easily chalcogenated, the Group VI element diffuses more toward the bonding layer 27 in the thickness direction of the connection portion 14. Therefore, in the concentration distribution of the Group VI element in the thickness direction of the connection portion 14, a peak in the concentration of the Group VI element occurs in the bonding layer 27. In other words, the number of atoms of the Group VI element contained in the bonding layer 27 becomes larger than the number of atoms of the Group VI element contained in the first electrode layer 21a.

[0046] Further, the material of the bonding layer 27 preferably contains a metal element having an alloy phase in the phase diagram with respect to the material of the first electrode layer 21a which is the back electrode layer. Alternatively, the material of the bonding layer 27 may contain at least one of the constituent elements of the first electrode layer 21a. In the selection of the material of the bonding layer 27, a metal having an alloy phase in the phase diagram with respect to the material (Mo) of the first electrode layer 21a may be selected from a binary phase diagram (for example, BINARY ALLOY PHASE DIAGRAMS SECOND EDITION Vol.1, T.B.Massalski, 1990).

[0047] By the bonding layer 27 containing a metal element having an alloy phase in the phase diagram with respect to the material of the first electrode layer 21a (for example, Al, etc.), or at least one of the constituent elements of the first electrode layer 21a, diffusion of the metal element easily occurs between the first electrode layer 21a and the bonding layer 27. Further, as described above, as the Group VI element diffuses more toward the bonding layer 27, the metal element contained in the bonding layer 27 is in a state where it easily diffuses into the first electrode layer 21a. Thereby, the adhesion strength between the first electrode layer 21a and the bonding layer 27 can be improved.

[0048] In addition, Ag contained in the bonding layer 27 is also contained in the interconnector 13 as described above. That is, regarding the interface between the bonding layer 27 and the interconnector 13, since both of their materials contain Ag, they have a high affinity. Therefore, during the welding of the interconnector 13, diffusion of the metal element also occurs at the interface between the interconnector 13 and the bonding layer 27, and the adhesion strength between the interconnector 13 and the bonding layer 27 is improved.

[0049] <Method for manufacturing solar cell> Next, an example of the method for manufacturing the solar cell module 10 will be described. FIG. 3 is a flowchart showing the method for manufacturing the solar cell module 10. FIGS. 4 and 5 are diagrams schematically showing each step of the manufacturing method.

[0050] (S1: Formation of first electrode layer) In S1, as shown in FIG. 4(a), a thin film such as molybdenum (Mo) is formed on the surface of the conductive substrate 11 such as titanium by, for example, sputtering method, whereby the first electrode layer 21 is formed. The sputtering method may be a direct current (DC) sputtering method or a radio frequency (RF) sputtering method. Further, instead of the sputtering method, the first electrode layer 21 may be formed using a CVD (chemical vapor deposition) method, an ALD (atomic layer deposition) method, or the like.

[0051] (S2: Formation of precursor layer) In S2, as indicated by the broken line in FIG. 4(a), a thin film-like precursor layer 22p is formed on the first electrode layer 21.

[0052] Examples of the method for forming the precursor layer 22p on the first electrode layer 21 include the above-described sputtering method, evaporation method, or ink coating method. The evaporation method is a method of forming a film using atoms or the like that have become a gas phase by heating an evaporation source. The ink coating method is a method of dispersing a material of the precursor film in powder form in a solvent such as an organic solvent, coating it on the first electrode layer 21, and then evaporating the solvent to form the precursor layer 22p.

[0053] When forming the CIS-based photoelectric conversion layer 22, the precursor layer 22p contains a Group I element and a Group III element. For example, the precursor layer 22p may contain Ag as the Group I element. The Group I element other than Ag included in the precursor layer 22p can be selected from copper, gold, etc. Also, the Group III element included in the precursor layer 22p can be selected from indium, gallium, aluminum, etc. Further, the precursor layer 22p may contain an alkali metal such as Li, Na, K, Rb, Cs. Also, the precursor layer 22p may contain tellurium in addition to selenium and sulfur as the Group VI element. On the other hand, when forming the CZTS-based photoelectric conversion layer 22, the precursor layer 22p is formed as a thin film of Cu-Zn-Sn or Cu-Zn-Sn-Se-S.

[0054] (S3: Formation of the photoelectric conversion layer) In S3, as shown in Fig. 4(b), the photoelectric conversion layer 22 is formed by chalcogenating the precursor layer 22p.

[0055] When forming the CIS-based photoelectric conversion layer 22, in the chalcogenation treatment of the precursor layer 22p, the precursor layer 22p containing a Group I element and a Group III element is heat-treated in an atmosphere containing a Group VI element to perform chalcogenation and form the photoelectric conversion layer 22.

[0056] For example, first, selenization by the vapor-phase selenization method is performed. Selenization is carried out by heating the precursor layer in an atmosphere of a selenium source gas containing selenium as the Group VI element source (for example, hydrogen selenide or selenium vapor). Although not particularly limited, selenization is preferably carried out at a temperature in the range of 300°C or higher and 600°C or lower in a heating furnace, for example.

[0057] As a result, the precursor layer is converted into a compound (photoelectric conversion layer 22) containing a Group I element, a Group III element, and selenium. Note that the compound (photoelectric conversion layer 22) containing a Group I element, a Group III element, and selenium may be formed by a method other than the vapor-phase selenization method. For example, such a compound can also be formed by a solid-phase selenization method, a vapor deposition method, an ink coating method, an electrodeposition method, or the like.

[0058] Next, sulfurization of the photoelectric conversion layer 22 containing a Group I element, a Group III element, and selenium is performed. Sulfurization is carried out by heating the photoelectric conversion layer 22 in an atmosphere of a sulfur source gas having sulfur (for example, hydrogen sulfide or sulfur vapor). As a result, the photoelectric conversion layer 22 is converted into a compound containing a Group I element, a Group III element, and selenium and sulfur as a Group VI element. The sulfur source gas plays a role of substituting selenium in a crystal composed of a Group I element, a Group III element, and selenium, for example, chalcopyrite crystal, on the surface portion of the photoelectric conversion layer 22 with sulfur. Although not particularly limited, sulfurization is preferably carried out, for example, at a temperature in the range of 450°C or higher and 650°C or lower in a heating furnace.

[0059] On the other hand, when forming the CZTS-based photoelectric conversion layer 22, in the chalcogenization treatment of the precursor layer 22p, the precursor layer 22p containing Cu, Zn, and Sn is sulfurized and selenized in an atmosphere of hydrogen sulfide and an atmosphere of hydrogen selenide at 500°C to 650°C. Thereby, a CZTS-based photoelectric conversion layer 22 having Cu2ZnSn(S,Se)4 can be formed.

[0060] Further, with the chalcogenization treatment of the precursor layer 22p at S3, a Group VI compound layer 26 composed of Mo(Se,S)2 is formed at the interface between the first electrode layer 21 and the photoelectric conversion layer 22.

[0061] (S4: Formation of buffer layer) In S4, as shown in Fig. 4(c), a buffer layer 23 is formed by depositing a thin film such as Zn(O,S) on the photoelectric conversion layer 22 by a method such as chemical bath deposition (CBD) method or sputtering method. Note that the formation of the buffer layer 23 may be omitted.

[0062] (S5: Formation of the second electrode layer) In S5, as shown by the dashed line in Fig. 4(c), a second electrode layer 24 is formed on the buffer layer 23 by a method such as sputtering method, CVD method, or ALD method. The second electrode layer 24 is a transparent electrode made of a thin film such as ZnO doped with B, Al, or In as a dopant, for example. Through the steps of S1 to S5 above, a photoelectric conversion element 12 is formed on the conductive substrate 11.

[0063] (S6: Formation of the wiring region) In S6, a wiring region 10a is formed by partially notching a predetermined position at the light-receiving surface end of the photoelectric conversion element 12, for example, by mechanical patterning, to expose the first electrode layer 21 on the light-receiving surface side. Note that at the stage of S6, a Group VI compound layer 26 exists on the surface of the first electrode layer 21 in the wiring region 10a, similar to the first electrode layer 21 in the photoelectric conversion element 12.

[0064] As an example, Fig. 5(a) shows a state where the photoelectric conversion layer 22, buffer layer 23, and second electrode layer 24 corresponding to the wiring region 10a of the photoelectric conversion element 12 are removed. Note that in Fig. 5(a), the region removed in S6 is indicated by a dashed line.

[0065] (S7: Formation of the precursor layer in the wiring region) In S7, as shown in Fig. 5(b), a precursor layer 27p corresponding to the bonding layer 27 is formed on the first electrode layer 21 in the wiring region 10a.

[0066] In S7, first, except for the region where the precursor layer 27p is to be formed (inside the groove 28 in the wiring region 10a), the light-receiving surface of the photoelectric conversion element 12 is appropriately masked. Then, the precursor layer 27p is formed on the first electrode layer 21 in the wiring region 10a, for example, by vapor deposition.

[0067] The precursor layer 27p in S7 is formed by sequentially laminating an Al layer 27p1 and an Ag layer 27p2 in this order from the side of the conductive substrate 11. The film formation conditions for the Al layer 27p1 are, for example, an applied voltage of about 10 kV, an EB current of about 0.2 A, a film formation rate of 0.4 nm / sec, and a film thickness of 0.5 μm. Similarly, the film formation conditions for the Ag layer 27p2 are, for example, an applied voltage of about 10 kV, an EB current of about 0.1 A, a film formation rate of 0.5 nm / sec, and a film thickness of 2.0 μm.

[0068] In the precursor layer 27p, the Ag layer 27p2 is disposed on the upper surface side facing the interconnector 13. By disposing the Ag layer 27p2, which is common to the material of the interconnector 13, in the region facing the interconnector 13, diffusion is likely to occur at the interface between the interconnector 13 and the precursor layer 27p during welding.

[0069] Also, in the precursor layer 27p, the Al layer 27p1 is disposed on the lower surface side facing the group VI compound layer 26 of the first electrode layer 21. By disposing the Al layer 27p1, which is easily chalcogenated, in the region facing the group VI compound layer 26, diffusion of the group VI compound to the bonding layer 27 side is likely to occur during welding.

[0070] (S8: Welding of Interconnector) In S8, the end portion of the interconnector 13 made of a conductive metal containing Ag is disposed on the upper surface of the precursor layer 27p, and welding of the interconnector 13 to the solar cell module 10 is performed. As an example, the welding of the interconnector 13 is carried out by a parallel gap welding method using a resistance welder with a transistor control system.

[0071] Specifically, as shown in FIG. 5(c), the end portion of the interconnector 13 is disposed at the center of the upper surface of the precursor layer 27p so as not to protrude outward from the peripheral portion of the precursor layer 27p. Then, for example, using a pair of electrodes 30 separated by a narrow gap, the interconnector 13 is welded to the precursor layer 27p. The welding conditions in S8 are, for example, a welding current of 50 to 200 A and a welding time of 5 to 900 msec.

[0072] When welding with the interconnector 13, the precursor layer 27p receives thermal energy from the electrode 30 through the interconnector 13. Then, diffusion occurs at the interface between the interconnector 13 and the precursor layer 27p and at the interface between the precursor layer 27p and the first electrode layer 21. Also, diffusion occurs between the Al layer 27p1 and the Ag layer 27p2 in the precursor layer 27p. As a result, as shown in FIG. 5(d), the precursor layer 27p having a laminated structure of the Al layer 27p1 and the Ag layer 27p2 changes into a bonding layer 27 in which Ag, Al, and the Group VI element Se are diffused.

[0073] When diffusion occurs at the interface between the precursor layer 27p and the first electrode layer 21 due to the thermal energy during welding, Se in the Group VI compound layer 26 in the first electrode layer 21 diffuses into the first electrode layer 21a and the bonding layer 27. Due to such diffusion of Se, the Group VI compound layer 26 disappears between the first electrode layer 21a and the bonding layer 27. Since there is no easily peelable Group VI compound layer 26 between the first electrode layer 21a and the bonding layer 27 after welding, the first electrode layer 21a and the bonding layer 27 are not easily peeled.

[0074] On the other hand, an Al layer 27p1 that is easily chalcogenated is disposed on the first electrode layer 21 side of the precursor layer 27p. Therefore, Se diffusing from the Group VI compound layer 26 diffuses more into the bonding layer 27 containing Al that is more easily chalcogenated than into the first electrode layer 21a containing Mo. As Se diffuses more into the bonding layer 27 side, Al, which is a metal element contained in the precursor layer 27p, becomes more likely to diffuse into the first electrode layer 21a. When Al, which is a metal element of the bonding layer 27, diffuses into the first electrode layer 21a, the adhesion strength between the first electrode layer 21a and the bonding layer 27 after welding is further improved.

[0075] On the other hand, regarding the interface between the Ag layer 27p2 of the precursor layer 27p and the interconnector 13, since both of their materials contain Ag, they have a high affinity. Therefore, during welding, diffusion of metal elements occurs at the interface between the interconnector 13 and the precursor layer 27p, and the interconnector 13 and the bonding layer 27 are joined with high adhesion strength.

[0076] By the above-described steps S1 to S8, a connection portion 14 in which the first electrode layer and the interconnector are joined via a bonding layer is formed in the wiring region of the solar cell module 10. This concludes the description of FIG. 3.

[0077] As described above, in the first embodiment, in the wiring region 10a, a precursor layer 27p containing Al is formed on the first electrode layer 21 having a Group VI compound layer 26 (S7). Then, the precursor layer 27p and the interconnector 13 are welded to apply thermal energy, and a bonding layer 27 containing a Group VI element and Al of the precursor layer 27p is formed (S8). Thereby, in the connection portion 14 between the photoelectric conversion element 12 and the interconnector 13, the Group VI element diffuses into the bonding layer 27, and the peak of the concentration distribution of the Group VI element in the stacking direction is shifted from the interface between the first electrode layer 21 and the bonding layer 27. That is, in the connection portion 14 of the first embodiment, the Group VI compound layer 26 disappears from the interface between the first electrode layer 21 and the bonding layer 27, so that the adhesion strength between the first electrode layer 21 and the bonding layer 27 can be increased.

[0078] <<Second Embodiment>> FIG. 6 is a cross-sectional view taken along the thickness direction showing a configuration example of the solar cell according to the second embodiment. The second embodiment is a modification of the first embodiment, and a connection portion 14 is formed on the back surface side (the surface opposite to the light-receiving surface) of the conductive substrate 11 of the solar cell module 10. In the description of each of the following embodiments, the same components as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted.

[0079] As shown in FIG. 6, on the conductive substrate 11 of the second embodiment, a conductive coating layer 31 of molybdenum (Mo) is formed on the back surface side, and a bonding layer 27a is laminated on the conductive coating layer 31. And, an end portion of the interconnector 13 is attached by welding to the lower side in the drawing of the bonding layer 27a. The interconnector 13 of the second embodiment is, for example, a ribbon wire made of a conductive metal containing Ag, Ti, or an iron-nickel-cobalt alloy. By forming the conductive coating layer 31 on the back surface side of the conductive substrate 11, the warpage of the solar cell module 10 can be reduced.

[0080] Further, on the surface of the conductive coating layer 31, a Group VI compound layer 32 made of Mo(Se,S)2 is formed except for the region where the bonding layer 27a is laminated. The Mo(Se,S)2 of the Group VI compound layer 32 is formed on the conductive coating layer 31 when the precursor layer 22p is chalcogenated to form the photoelectric conversion layer 22. Note that the Group VI compound layer 32 made of Mo(Se,S)2 has the same properties as the Group VI compound layer 26 of the first electrode layer 21. In other words, a Group VI compound layer 32 that is easily peeled off is not formed between the conductive coating layer 31 and the bonding layer 27a. Therefore, the bonding layer 27a is difficult to peel off from the conductive coating layer 31.

[0081] Further, the bonding layer 27a of the second embodiment contains at least one of Al, Pt, Zn, and Sn, and is a substance containing diffused Se and S. The metal material of the bonding layer 27a has a melting point of 230°C or higher and a higher melting point than the solder alloy in order to ensure the use of the solar cell module 10 under high temperatures due to solar radiation or the like in the space environment. Further, the material of the bonding layer 27a preferably contains a metal element having an alloy phase in the phase diagram with respect to the material of the conductive film layer 31 and the material of the interconnector 13 in order to promote the diffusion of metal elements between members.

[0082] Further, the material of the bonding layer 27a preferably contains at least one of Al, Pt, Zn, and Sn, which are metal elements that are easily chalcogenated. Thereby, the group VI compound is likely to be uniformly distributed in the bonding layer 27a. When the bonding layer 27a is formed, the diffusion of the group VI element from the group VI compound layer 32 to the bonding layer 27a side is promoted, and the group VI compound layer 32 can be eliminated between the conductive film layer 31 and the bonding layer 27a.

[0083] Further, in the conductive film layer 31, in the region where the bonding layer 27a is laminated, metal elements (for example, Al) of the bonding layer 27a and Se, S, etc., which are group VI elements, are diffused as described later. When the metal element of the bonding layer 27a diffuses into the conductive film layer 31, the conductive film layer 31 and the bonding layer 27a have high adhesion strength. On the other hand, in the region of the conductive film layer 31 where the bonding layer 27a is not laminated, there is almost no diffusion of the metal element of the bonding layer 27a.

[0084] When forming the connection portion 14 of the second embodiment, the steps up to the step of forming the photoelectric conversion element 12 (S1 to S5) are almost the same as the steps of the manufacturing method of the first embodiment. However, in the case of the second embodiment, in the step of S1, the conductive film layer 31 is formed on the back surface side of the conductive substrate 11. Further, in the step of S3, the group VI compound layer 32 is formed on the surface of the conductive film layer 31.

[0085] Thereafter, a precursor layer (not shown) of the bonding layer 27a is formed on the conductive film layer 31 having the group VI compound layer 32, and the interconnector 13 is disposed on the precursor layer of the bonding layer 27a. Then, the precursor layer of the bonding layer 27a and the interconnector 13 are welded to apply thermal energy, and the bonding layer 27a is formed.

[0086] When the bonding layer 27a is formed, group VI elements diffuse to the bonding layer 27a side and the group VI compound layer 32 disappears. Therefore, in the concentration distribution of group VI elements in the thickness direction of the connection portion 14, there is no peak in the concentration of group VI elements at the interface between the conductive film layer 31 and the bonding layer 27a. Further, since the material of the bonding layer 27a contains a metal element that is easily chalcogenated, more group VI elements diffuse to the bonding layer 27a side in the thickness direction of the connection portion 14. Therefore, in the concentration distribution of group VI elements in the thickness direction of the connection portion 14 of the second embodiment, a peak in the concentration of group VI elements occurs in the bonding layer 27a. In other words, the number of atoms of group VI elements contained in the bonding layer 27a becomes larger than the number of atoms of group VI elements contained in the conductive film layer 31.

[0087] According to the configuration of the second embodiment described above, the adhesion strength between the conductive film layer 31 formed on the back surface side of the substrate of the chalcogen solar cell and the connection portion 14 can be improved.

[0088] <<Third Embodiment>> FIG. 7 is a cross-sectional view taken in the thickness direction showing a configuration example of a solar cell according to the third embodiment. The third embodiment is a modification of the second embodiment, and is different from the second embodiment in that the conductive film layer 31 is not formed on the back surface side of the conductive substrate 11.

[0089] As shown in FIG. 7, a bonding layer 27b is laminated on the conductive substrate 11 of the third embodiment. And the end part of the interconnector 13 is attached by welding to the lower side in the figure of the bonding layer 27b. The interconnector 13 of the third embodiment is also, for example, a ribbon wire made of a conductive metal containing Ag, Ti, or an iron-nickel-cobalt alloy as a material.

[0090] In addition, a Group VI compound layer 33 made of Ti(Se,S)2 is formed on the surface of the conductive substrate 11, excluding the region where the bonding layer 27b is laminated. The Ti(Se,S)2 of the Group VI compound layer 33 is formed on the surface of the conductive substrate 11 when the precursor layer 22p is chalcogenated to form the photoelectric conversion layer 22. The Group VI compound layer 33 made of Ti(Se,S)2 is a substance having a graphite-like multilayer structure and has a property of being easily exfoliated due to cleavage between layers. In other words, an easily exfoliated Group VI compound layer 33 is not formed between the conductive substrate 11 and the bonding layer 27b. Therefore, the bonding layer 27b is difficult to peel off from the conductive substrate 11.

[0091] In addition, the bonding layer 27b of the third embodiment contains at least one of Al, Pt, Zn, and Sn and is a substance containing diffused Se and S. The metal material of the bonding layer 27b has a melting point of 230°C or higher and a higher melting point than the solder alloy in order to ensure the use of the solar cell module 10 under high temperatures due to solar radiation or the like in the space environment. In addition, the material of the bonding layer 27b preferably contains a metal element having an alloy phase in the phase diagram with respect to the material of the conductive substrate 11 and the material of the interconnector 13 in order to promote the diffusion of metal elements between members.

[0092] In addition, the material of the bonding layer 27b preferably contains at least one of Al, Pt, Zn, and Sn, which are metal elements that are easily chalcogenated. Thereby, it becomes easier for the Group VI compound to be uniformly distributed in the bonding layer 27b. When the bonding layer 27b is formed, the diffusion of Group VI elements from the Group VI compound layer 33 to the bonding layer 27b side is promoted, and the Group VI compound layer 33 can be disappeared from between the conductive substrate 11 and the bonding layer 27b.

[0093] In the conductive substrate 11, in the region where the bonding layer 27b is laminated, metal elements (for example, Al) of the bonding layer 27b and Se and S, which are Group VI elements, are diffused as described later. By the diffusion of the metal elements of the bonding layer 27b into the conductive substrate 11, the conductive substrate 11 and the bonding layer 27b have high adhesion strength. On the other hand, in the region of the conductive substrate 11 where the bonding layer 27b is not laminated, there is almost no diffusion of the metal element of the bonding layer 27b.

[0094] When forming the connection part 14 of the third embodiment, the steps from the step of forming the photoelectric conversion element 12 (S1 to S5) are almost the same as the steps of the manufacturing method of the first embodiment. In the third embodiment, a group VI compound layer 33 is formed on the surface of the conductive substrate 11 in the step S3.

[0095] Thereafter, a precursor layer (not shown) of the bonding layer 27b is formed on the conductive substrate 11 having the group VI compound layer 33, and the interconnector 13 is disposed on the precursor layer of the bonding layer 27b. Thereafter, the precursor layer of the bonding layer 27b and the interconnector 13 are welded to apply thermal energy, and the bonding layer 27b is formed.

[0096] When the bonding layer 27b is formed, group VI elements diffuse to the bonding layer 27b side and the group VI compound layer 33 disappears. Therefore, in the concentration distribution of group VI elements in the thickness direction of the connection part 14, there is no peak in the concentration of group VI elements at the interface between the conductive substrate 11 and the bonding layer 27b. Further, since the material of the bonding layer 27b contains a metal element that is easily chalcogenated, more group VI elements diffuse to the bonding layer 27b side in the thickness direction of the connection part 14. Therefore, in the concentration distribution of group VI elements in the thickness direction of the connection part 14 of the third embodiment, a peak in the concentration of group VI elements occurs in the bonding layer 27b. In other words, the number of atoms of group VI elements contained in the bonding layer 27b becomes larger than the number of atoms of group VI elements contained in the conductive substrate 11.

[0097] According to the configuration of the third embodiment described above, the adhesion strength between the conductive substrate 11 and the connection part 14 of the chalcogen solar cell can be improved.

[0098] <<Fourth Embodiment>> FIG. 8 is a cross-sectional view taken along the thickness direction showing a configuration example of the solar cell according to the fourth embodiment. The fourth embodiment is a modification of the second embodiment, and is different from the configuration of the second embodiment in that the interconnector 13 is directly welded to the conductive coating layer 31 without passing through the bonding layer 27a. In the fourth embodiment as well, a group VI compound layer 32 made of Mo(Se,S)2 is formed on the surface of the conductive coating layer 31 except for the region where the interconnector 13 is welded. In other words, a group VI compound layer 32 that is easily peeled off is not formed between the conductive coating layer 31 and the interconnector 13. Therefore, the interconnector 13 is less likely to peel off from the conductive coating layer 31.

[0099] In addition, in order to ensure the use of the solar cell module 10 under high temperatures due to solar radiation or the like in the space environment, the material of the interconnector 13 applied to the connection portion 14 has a melting point of 230° C. or higher and a melting point higher than that of the solder alloy is used. Further, the material of the interconnector 13 in the fourth embodiment contains a metal element having an alloy phase in the phase diagram with respect to the material of the conductive coating layer 31 in order to promote the diffusion of metal elements between members.

[0100] In the conductive coating layer 31 of the fourth embodiment, metal elements of the interconnector 13 and Se, S, etc. which are group VI elements are diffused in the region joined to the interconnector 13. By the diffusion of the metal elements of the interconnector 13 into the conductive coating layer 31, the conductive coating layer 31 and the interconnector 13 have high adhesion strength. On the other hand, in the region of the conductive coating layer 31 that is not joined to the interconnector 13, there is almost no diffusion of the metal elements of the interconnector 13.

[0101] When forming the connection portion 14 of the fourth embodiment, the steps up to the step of forming the photoelectric conversion element 12 (steps S1 to S5) are almost the same as the steps of the manufacturing method of the first embodiment. However, in the case of the fourth embodiment, in the step of S1, the conductive coating layer 31 is formed on the back surface side of the conductive substrate 11. Further, in the step of S3, the group VI compound layer 32 is formed on the surface of the conductive coating layer 31.

[0102] Thereafter, the interconnector 13 is disposed on the conductive film layer 31 having the group-VI compound layer 32, and the conductive film layer 31 and the interconnector 13 are welded to apply thermal energy. As a result, group-VI elements diffuse from the interface between the conductive film layer 31 and the interconnector 13, and the group-VI compound layer 32 disappears. Therefore, in the concentration distribution of group-VI elements in the thickness direction of the connection portion 14 of the fourth embodiment, there is no peak in the concentration of group-VI elements at the interface between the conductive film layer 31 and the interconnector 13.

[0103] According to the configuration of the fourth embodiment described above, the adhesion strength between the conductive film layer 31 formed on the back surface side of the substrate of the chalcogen solar cell and the interconnector 13 can be improved.

[0104] <<Fifth Embodiment>> FIG. 9 is a cross-sectional view taken along the thickness direction showing a configuration example of the solar cell according to the fifth embodiment. The fifth embodiment is a modification of the third embodiment, and is different from the configuration of the third embodiment in that the interconnector 13 is directly welded to the conductive substrate 11 without passing through the bonding layer 27b. Also in the fifth embodiment, a group-VI compound layer 33 made of Ti(Se,S)2 is formed on the surface of the conductive substrate 11 except for the region where the interconnector 13 is welded. In other words, an easily-peeling group-VI compound layer 33 is not formed between the conductive substrate 11 and the interconnector 13. Therefore, the interconnector 13 is difficult to peel off from the conductive substrate 11.

[0105] In addition, in order to ensure the use of the solar cell module 10 under high temperatures due to solar radiation or the like in the space environment, the material of the interconnector 13 applied to the connection portion 14 has a melting point of 230° C. or higher and a melting point higher than that of the solder alloy. Further, the material of the interconnector 13 of the fifth embodiment contains a metal element having an alloy phase in the phase diagram with respect to the material of the conductive substrate 11 in order to promote the diffusion of metal elements between members.

[0106] In the conductive substrate 11 of the fifth embodiment, metal elements of the interconnector 13 and VI group elements such as Se and S are diffused in the region joined to the interconnector 13. When the metal elements of the interconnector 13 are diffused into the conductive substrate 11, the conductive substrate 11 and the interconnector 13 have high adhesion strength. On the other hand, in the region of the conductive substrate 11 that is not joined to the interconnector 13, there is almost no diffusion of the metal elements of the interconnector 13.

[0107] When forming the connection portion 14 of the fifth embodiment, the steps from the step of forming the photoelectric conversion element 12 (S1 to S5) are almost the same as the steps of the manufacturing method of the first embodiment. In the fifth embodiment, a VI group compound layer 33 is formed on the surface of the conductive substrate 11 in the step S3.

[0108] Thereafter, the interconnector 13 is disposed on the conductive substrate 11 having the VI group compound layer 33, and the conductive substrate 11 and the interconnector 13 are welded to apply thermal energy. As a result, the VI group elements are diffused from the interface between the conductive substrate 11 and the interconnector 13, and the VI group compound layer 33 disappears. Therefore, in the concentration distribution of the VI group elements in the thickness direction of the connection portion 14 of the fifth embodiment, there is no peak in the concentration of the VI group elements at the interface between the conductive substrate 11 and the interconnector 13.

[0109] According to the configuration of the fifth embodiment described above, the adhesion strength between the conductive substrate 11 and the interconnector 13 of the chalcogen solar cell can be improved.

[0110] <<Examples>> Hereinafter, examples of the solar cell module of the present invention will be described. Here, the connection part of the embodiment is formed in the same manner as the configuration described in the first embodiment. That is, the material of the substrate is Ti, and the back electrode layer before welding is a Mo film with a Se layer formed on the surface. The bonding layer is formed by applying thermal energy of welding to a precursor in which an Al layer and an Ag layer are laminated. The back electrode layer after welding is Mo in which Al and Se have diffused, and the bonding layer after welding is a substance containing Se diffused into Ag and Al.

[0111] (Concentration distribution of elements in the connection part) In the embodiment, the concentration distribution of elements in the connection part of the solar cell module was obtained by the following method. First, a cross-section in the thickness direction of the connection part of the embodiment was formed using a focused ion beam (FIB) apparatus. Then, a scanning ion microscope (SIM) image of the cross-section of the connection part was taken at an acceleration voltage of 15 kV. After that, the elements contained in the cross-section of the connection part were analyzed by energy dispersive X-ray analysis (EDX).

[0112] The equipment used for the element analysis in the embodiment is as follows. The FIB apparatus is SMI3200F manufactured by SII NanoTechnology, the SEM is SU8240 manufactured by Hitachi High-Technologies, and the EDX is EX-370 manufactured by Horiba, Ltd.

[0113] Figs. 10 and 11 are diagrams showing the concentration distribution of each element in the thickness direction of the connection part of the embodiment. In each of Figs. 10 and 11, the vertical axis indicates the content of the element, and the horizontal axis indicates the position in the thickness direction t of the connection part. On the horizontal axis of Figs. 10 and 11, the left end corresponds to the back side of the light-receiving surface, and the right end corresponds to the light-receiving surface side.

[0114] Also, the content shown on the vertical axis of Figs. 10 and 11 is shown after normalizing the maximum value of the content for each element to 1. Each point shown in Figs. 10 and 11 is plotted when 30% or more after normalization is detected as a threshold value.

[0115] FIG. 10(a) shows an example of the concentration distribution of Mo, Ti, Ag, Al, and Se in the connection part, superimposed. FIG. 10(b) shows an example of the concentration distribution of Mo in the connection part, and FIG. 10(c) shows an example of the concentration distribution of Ti in the connection part. Also, FIG. 11(a) shows an example of the concentration distribution of Ag in the connection part, FIG. 11(b) shows an example of the concentration distribution of Al in the connection part, and FIG. 11(c) shows an example of the concentration distribution of Se in the connection part.

[0116] As shown in FIGS. 10 and 11, the back electrode layer (indicated by Mo + Al + Se in the figure) of the connection part contains Mo, Al, and Se, and the bonding layer (indicated by Ag + Al + Se in the figure) contains Ag, Al, and Se. It can be seen from FIGS. 10(a), 11(b), and (c) that Al and Se are diffused across the back electrode layer and the bonding layer.

[0117] Also, as shown in FIG. 11(c), Se is widely distributed across the back electrode layer and the bonding layer, and the concentration distribution of Se does not have a peak at the boundary between the back electrode layer and the bonding layer. Therefore, it can be seen that there is no group VI compound layer at the boundary between the back electrode layer and the bonding layer of the connection part.

[0118] Also, as shown in FIG. 11(c), more Se is detected in the bonding layer than in the back electrode layer. Therefore, it can be seen that the number of Se atoms contained in the bonding layer is larger than the number of Se atoms contained in the back electrode layer.

[0119] Furthermore, as shown in FIG. 11(c), when comparing the maximum value of Se in the back electrode layer with the maximum value of Se in the bonding layer, the maximum value of Se in the bonding layer is larger. Therefore, it can be seen that the peak of the Se concentration is at the site of the bonding layer.

[0120] (Adhesion strength test of the connection part) In addition, in order to evaluate the adhesion strength of the connection part of the solar cell module, the following tests were conducted. In the test, the tip of the interconnector after welding was clamped with a jig, and the tip of the interconnector was pulled upward at a speed of 5 mm / min in the 45-degree direction using an autograph device. Then, the tensile strength (maximum strength) at the time when the interconnector is detached from the connection part is measured.

[0121] As test subjects, test pieces of the above-described example (hereinafter referred to as Example 1) and the following three test pieces were used as comparative examples. Comparative Example 1 is a test piece in which an interconnector is welded to a laminate of a Ti substrate / Mo (MoSeS) / Ag. Comparative Example 2 is a test piece in which an interconnector is welded to a laminate of a Ti substrate / Mo (MoSeS) / In solder. Note that the bonding area of Comparative Example 2 is about 60 times that of the example. Comparative Example 3 is a test piece in which an interconnector is welded to a laminate of a Ti substrate / Mo (MoSeS). Note that the material of the interconnector in Example 1 and Comparative Examples 1 to 3 is Ag in all cases.

[0122] FIG. 12 is a table showing the results of the adhesion strength tests of Example 1 and Comparative Examples 1 to 3, and FIG. 13 is a table showing the presence or absence of alloy phases in the phase diagrams of Example 1 and Comparative Examples 1 to 3. In the table of FIG. 13, the case where there is an alloy phase in the phase diagram between the opposing members is indicated by "〇", and the case where there is no alloy phase in the phase diagram between the opposing members is indicated by "×". In addition, in FIGS. 12 and 13, the case where there is no corresponding configuration is indicated by "-".

[0123] In FIG. 12, the values of the maximum strength normalized with respect to Comparative Example 1 are shown respectively. Assuming that the maximum strength of the test piece of Comparative Example 1 is 1, the maximum strength of the test piece of Comparative Example 2 is 0.18, and the maximum strength of the test piece of Comparative Example 3 is 0.12. On the other hand, the test piece of Example 1 was larger than 1, and it was confirmed that the maximum strength was higher than that of any of Comparative Examples 1 to 3, and the adhesion strength of the connection part was good.

[0124] Also, as shown in FIG. 13, in the test piece of Example 1, both the interconnector and the bonding layer contain Ag (the same metal) in the material, and the Ag in the material of the interconnector and the Al contained in the material of the bonding layer have an alloy phase in the phase diagram. Further, in the test piece of Example 1, the Al contained in the material of the bonding layer and the Mo in the material of the back electrode layer have an alloy phase in the phase diagram. Therefore, in the test piece of Example 1, diffusion occurs between the same metal or metals having an alloy phase in the phase diagram during welding, and it is considered that the adhesion strength between the respective elements is improved.

[0125] On the other hand, in the test piece of Comparative Example 1, the Ag in the material of the bonding layer and the Mo in the material of the back electrode layer do not have an alloy phase in the phase diagram. Also, in the test piece of Comparative Example 2, the In solder in the material of the bonding layer and the Mo in the material of the back electrode layer do not have an alloy phase in the phase diagram. Therefore, in Comparative Examples 1 and 2, since no diffusion of metal elements occurs in the materials of the bonding layer and the back electrode layer, it is considered that the adhesion strength is lower than that of Example 1. Similarly, in the test piece of Comparative Example 3, the Ag in the material of the interconnector and the Mo in the material of the back electrode layer do not have an alloy phase in the phase diagram. Therefore, in Comparative Example 3, since no diffusion of metal elements occurs in the materials of the interconnector and the back electrode layer, it is considered that the adhesion strength is lower than that of Example 1.

[0126] Also, FIG. 14 is a table showing the results of the adhesion strength test of Examples 2-7, and FIG. 15 is a table showing the presence or absence of the alloy phase in the phase diagram of Examples 2-7. The way to read the tables in FIGS. 14 and 15 is the same as in FIGS. 12 and 13.

[0127] The test piece of Example 2 has a configuration corresponding to the above-described second embodiment. The material of the interconnector of Example 2 is Ti, the material of the bonding layer is Al, the material of the conductive film layer is Mo, and the material of the substrate is Ti. In Example 2, the materials of the interconnector and the bonding layer have an alloy phase in the phase diagram, and also, the materials of the bonding layer and the conductive film layer have an alloy phase in the phase diagram. Assuming that the maximum strength in the test piece of Comparative Example 1 is 1, the maximum strength of the test piece of Example 2 is 1.38, showing a value larger than that of Comparative Example 1.

[0128] The test piece of Example 3 has a configuration corresponding to the above-described third embodiment. The material of the interconnector in Example 3 is Ti, the material of the bonding layer is Al, and the material of the substrate is Ti. In Example 3, the materials of the interconnector and the bonding layer have an alloy phase in the phase diagram, and also, the materials of the bonding layer and the substrate have an alloy phase in the phase diagram. When the maximum strength in the test piece of Comparative Example 1 is set to 1, the maximum strength of the test piece of Example 3 is 1.24, indicating a value larger than that of Comparative Example 1.

[0129] The test piece of Example 4 has a configuration corresponding to the above-described third embodiment. The material of the interconnector in Example 4 is Kovar, the material of the bonding layer is Sn, and the material of the substrate is Ti. In Example 4, the materials of the interconnector and the bonding layer have an alloy phase in the phase diagram, and also, the materials of the bonding layer and the substrate have an alloy phase in the phase diagram. When the maximum strength in the test piece of Comparative Example 1 is set to 1, the maximum strength of the test piece of Example 4 is 2.18, indicating a value larger than that of Comparative Example 1.

[0130] The test piece of Example 5 has a configuration corresponding to the above-described fourth embodiment. The material of the interconnector in Example 5 is Kovar, the material of the conductive coating layer is Mo, and the material of the substrate is Ti. In Example 5, the materials of the interconnector and the conductive coating layer have an alloy phase in the phase diagram. When the maximum strength in the test piece of Comparative Example 1 is set to 1, the maximum strength of the test piece of Example 5 is 2.06, indicating a value larger than that of Comparative Example 1.

[0131] The test piece of Example 6 has a configuration corresponding to the above-described fifth embodiment. The material of the interconnector in Example 6 is Kovar, and the material of the substrate is Ti. In Example 6, the materials of the interconnector and the substrate have an alloy phase in the phase diagram. When the maximum strength in the test piece of Comparative Example 1 is set to 1, the maximum strength of the test piece of Example 6 is 2.09, indicating a value larger than that of Comparative Example 1.

[0132] The test piece of Example 7 has a configuration corresponding to the above-described fifth embodiment. The material of the interconnector in Example 7 is Ti, and the material of the substrate is Ti. In Example 6, the materials of the interconnector and the substrate are the same type of metal. Assuming that the maximum strength of the test piece in Comparative Example 1 is 1, the maximum strength of the test piece in Example 7 is 3.15, indicating a value larger than that of Comparative Example 1.

[0133] As described above, in Examples 2-7, different from Comparative Examples 1-3 above, the metal materials between the opposing elements all have alloy phases in the phase diagram. Therefore, it is considered that during welding, diffusion of metal elements occurs between the opposing elements, improving the adhesion strength between the elements. Moreover, particularly for the test piece of Example 7, since the materials of the interconnector and the substrate are the same type of metal, they have high affinity, and it is considered that during welding, diffusion of metal elements occurs at the interface between the interconnector and the substrate, further improving the adhesion strength between the interconnector and the substrate.

[0134] <<Supplementary Matters of the Embodiment>> In the above embodiment, the configuration of a solar cell module with a single-cell structure composed of one photoelectric conversion element has been described. However, the solar cell module may have an integrated structure in which a plurality of photoelectric conversion elements are arranged in the plane direction of the light-receiving surface of the conductive substrate and these photoelectric conversion elements are connected in series. In the case of a solar cell module with an integrated structure, an insulating layer is formed between the conductive substrate and the first electrode layer.

[0135] Also, the precursor layer 27p of the bonding layer 27 is not limited to the configuration of the above embodiment in which an Al layer 27p1 and an Ag layer 27p2 are laminated one by one. For example, the precursor layer 27p may be composed of a single-layer film containing Al and Ag. Further, the precursor layer 27p may be composed of a laminated film of three or more layers. When the precursor layer 27p is a laminated film of three or more layers, the layers of the two materials may be alternately arranged in the thickness direction, or other material layers may be added to the layers of the two materials. Also, a layer containing Al and Ag may be added to the laminated film.

[0136] In addition, the above-described fourth embodiment (FIG. 8) described a configuration example in which the interconnector 13 is joined to the conductive film layer 31 formed on the back surface side of the conductive substrate 11. However, the present invention can also be applied to a configuration in which the interconnector 13 is joined to the first electrode layer 21 (back surface electrode) having the group VI compound layer 26 on the light-receiving surface side of the conductive substrate 11. Similarly, the above-described fifth embodiment (FIG. 9) described a configuration example in which the interconnector 13 is joined to the back surface side of the conductive substrate 11. However, the present invention can also be applied to a configuration in which the interconnector 13 is joined to the conductive substrate 11 having the group VI compound layer 33 formed on the surface on the light-receiving surface side of the conductive substrate 11.

[0137] In addition, the electrode structure of the solar cell of the present invention is not limited to space applications. For example, in a solar cell installed on the ground, the present invention may be applied when forming a connection portion that is less likely to fail even when subjected to external forces such as strong winds and earthquakes.

[0138] As described above, the embodiments of the present invention have been described. However, the embodiments are presented as examples and are not intended to limit the scope of the present invention. The embodiments can be implemented in various forms other than the above, and various omissions, substitutions, changes, etc. can be made without departing from the gist of the present invention. The embodiments and their modifications are included in the scope and gist of the present invention, and the invention described in the claims and its equivalents are also included in the scope and gist of the present invention.

[0139] In addition, this application claims priority based on Japanese Patent Application No. 2020-211733 filed on December 21, 2020, and incorporates the entire contents of Japanese Patent Application No. 2020-211733 into this application.

Explanation of Reference Numerals

[0140] 10…Solar cell module, 10a…Wiring area, 11…Conductive substrate, 12…Photovoltaic conversion element, 13…Interconnector, 14…Connection part, 21, 21a…First electrode layer, 22…Photovoltaic conversion layer, 22p…Precursor layer, 26, 32, 33…Group VI compound layer, 27, 27a, 27b…Junction layer, 27p…Precursor layer, 27p1…Al layer, 27p2…Ag layer, 31…Conductive coating layer

Claims

1. An electrode structure in a solar cell including a chalcogen solar cell having a photoelectric conversion layer laminated on a substrate, the electrode structure having a conductor on the substrate side of the chalcogen solar cell and a wiring element electrically connected to the conductor, the wiring element including a wiring member and a bonding layer disposed between the conductor and the wiring member, the wiring element having the bonding layer laminated and bonded to the conductor, the wiring element and the conductor containing a Group VI element, in the lamination direction of the conductor and the wiring element, a peak of the concentration distribution of the Group VI element being in the bonding layer, the bonding layer containing at least one of Al, Pt, Zn, and Sn An electrode structure of a solar cell.

2. The conductor is exposed at a position not overlapping with the photoelectric conversion layer on the light-receiving surface side of the chalcogen solar cell, the wiring element being laminated on the conductor exposed on the light-receiving surface side. The electrode structure of the solar cell according to Claim 1.

3. The conductor is a back electrode layer formed on the substrate of the chalcogen solar cell, in the lamination direction of the back electrode layer and the bonding layer, a peak of the concentration distribution of the Group VI element being in the bonding layer. The electrode structure of the solar cell according to Claim 2.

4. The material of the back electrode layer and the material of the bonding layer have an alloy phase in the phase diagram, the material of the bonding layer and the material of the wiring member having an alloy phase in the phase diagram. The electrode structure of the solar cell according to Claim 3.

5. The melting point of the bonding layer is 230 °C or higher. The electrode structure of the solar cell according to Claim 3 or Claim 4.

6. The number of atoms of the Group VI element contained in the bonding layer is larger than the number of atoms of the Group VI element contained in the back electrode layer in a region corresponding to the bonding layer. The electrode structure of the solar cell according to any one of Claims 3 to 5.

7. The back electrode layer in the region corresponding to the bonding layer contains a part of the metal element of the bonding layer. The electrode structure of the solar cell according to any one of Claims 3 to 6.

8. The wiring member contains a part of the metal element of the bonding layer. The electrode structure of the solar cell according to any one of Claims 3 to 7.

9. The wiring member contains Ag, the bonding layer containing Al and Ag. The electrode structure of the solar cell according to Claim 8.

10. The material of the wiring member contains Ti or an iron-nickel-cobalt alloy. The electrode structure of the solar cell according to any one of claims 3 to 9.

11. The conductor is exposed on the back surface side of the substrate, which is opposite to the light receiving surface of the chalcogen solar cell, The wiring element is laminated on the conductor exposed on the back surface side of the substrate The electrode structure of the solar cell according to claim 1.

12. The conductor is a conductive layer formed on the substrate of the chalcogen solar cell or the substrate of the chalcogen solar cell which is a conductive substrate The electrode structure of the solar cell according to claim 11.

13. The material of the conductor and the material of the bonding layer have an alloy phase in the phase diagram, The material of the bonding layer and the material of the wiring member have an alloy phase in the phase diagram The electrode structure of the solar cell according to claim 12.

14. The material of the wiring member includes Ti or an iron-nickel-cobalt alloy The electrode structure of the solar cell according to claim 12 or claim 13.

15. A method for manufacturing an electrode structure in a solar cell including a chalcogen solar cell having a photoelectric conversion layer laminated on a substrate, The electrode structure has a conductor on the substrate side of the chalcogen solar cell and a wiring element electrically connected to the conductor, The wiring element includes a wiring member and a bonding layer disposed between the conductor and the wiring member, A step of disposing the wiring element or a precursor layer of the wiring element on the conductor having a compound of a group VI element on its surface, A step of applying thermal energy by welding to the wiring element or the precursor layer of the wiring element to bond the wiring element to the conductor, In the stacking direction of the conductor and the wiring element, the peak of the concentration distribution of the group VI element is in the bonding layer, The bonding layer contains at least one of Al, Pt, Zn, and Sn A method for manufacturing an electrode structure of a solar cell.

16. The conductor is exposed at a position where it does not overlap the photoelectric conversion layer on the light receiving surface side of the chalcogen solar cell, The wiring element is laminated on the conductor exposed on the light receiving surface side The method for manufacturing an electrode structure of the solar cell according to claim 15.

17. The conductor is a back electrode layer formed on the substrate of the chalcogen solar cell, The wiring element includes the wiring member and the bonding layer disposed between the back electrode layer and the wiring member The method for manufacturing an electrode structure of the solar cell according to claim 16.

18. On the back electrode layer having the compound of the Group VI element on the surface, a precursor layer containing at least one of the constituent elements of the back electrode layer or any one of Al, Pt, Zn, and Sn is formed. The wiring member is disposed on the precursor layer. The precursor layer and the wiring member are welded to apply thermal energy to the precursor layer, and a bonding layer containing the elements contained in the precursor layer and the Group VI element is formed to bond the back electrode layer and the wiring member. The method for manufacturing an electrode structure of a solar cell according to claim 17.

19. The Group VI element contained in the bonding layer diffuses from the compound on the surface of the back electrode layer before welding. The method for manufacturing an electrode structure of a solar cell according to claim 18.

20. The precursor layer contains at least one of the constituent elements of the wiring member. The method for manufacturing an electrode structure of a solar cell according to claim 18 or claim 19.

21. The wiring member contains Ag. The precursor layer contains Al and Ag. The method for manufacturing an electrode structure of a solar cell according to claim 20.

22. The precursor layer has a structure in which a first layer containing any one of Al, Pt, Zn, and Sn and a second layer containing at least one of the constituent elements of the wiring member are laminated. The second layer is disposed on the surface of the precursor layer facing the wiring member. The method for manufacturing an electrode structure of a solar cell according to claim 20 or claim 21.

23. The first layer contains Al. The second layer contains Ag. The method for manufacturing an electrode structure of a solar cell according to claim 22.

24. The conductor is exposed on the back surface side of the substrate, which is opposite to the light receiving surface of the chalcogen solar cell. The wiring element is laminated on the conductor exposed on the back surface side of the substrate. The method for manufacturing an electrode structure of a solar cell according to claim 15.

25. The conductor is a conductive layer formed on the substrate of the chalcogen solar cell or the substrate of the chalcogen solar cell which is a conductive substrate. The method for manufacturing an electrode structure of a solar cell according to claim 24.

26. The material of the conductor and the material of the bonding layer have an alloy phase in the phase diagram. The material of the bonding layer and the material of the wiring member have an alloy phase in the phase diagram. The method for manufacturing an electrode structure of a solar cell according to claim 25.

27. The material of the wiring member includes Ti or an iron / nickel / cobalt alloy. A method for manufacturing an electrode structure of a solar cell according to claim 25 or claim 26.

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