The present invention relates to an electrode structure of a solar cell including a chalcogen solar cell.
CIS-based solar cells using group I-III-VI2 compound semiconductors each having a chalcopyrite structure containing Cu, In, Ga, Se, and S as a photoelectric conversion layer has conventionally been proposed. The CIS-based solar cells are relatively low in manufacturing cost, and have a large absorption coefficient in a range from a visible wavelength to a near-infrared wavelength. Therefore, high photoelectric conversion efficiency is expected. In addition, the CIS-based solar cells for use in outer space applications are also studied as solar cells, which are excellent in radiation resistance, which have longer lives than those of Si-based solar cells, and which are lower in price than GaAs-based solar cells.
The CIS-based solar cells are each configured by, for example, forming a backside electrode layer of a metal on a substrate, forming a photoelectric conversion layer that 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. Regarding wiring on a backside electrode on the positive electrode side of the CIS-based solar cell, a method of using soldering as described in Patent Literature 1, an adhesion method of using a conductive paste as described in Patent Literature 2, and the like have conventionally been used.
For example, Patent Literature 1 discloses a connection method for firmly fixing an electrode film or a conductive film by use of a copper foil ribbon conductive wire coated with In-solder, with no damage.
In addition, in the configuration of Patent Literature 2, a ribbon wire adhered with the conductive paste intermittently applied on an electrode is sandwiched between a solar cell submodule and a cover glass that are adhered and held through a filler. Accordingly, the ribbon wire is attached in surface contact with the electrode of the solar cell module.
Further, as a method for bonding a backside electrode layer and a metal ribbon in a solar cell for use on the ground, for example, ultrasonic seam welding as described in Patent Literature 3 is known.
In addition, Patent Literature 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 in Patent Literature 4 includes a GaAs semiconductor layer including a contact region selectively set on a 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 on a partial or entire surface of the region located on the TiN layer on a surface of the electrode layer.
In the solar cells for outer space applications, there is a demand for a bonding technique of an interconnector with higher adhesion than that for use on the ground so as to be capable of withstanding a rapid temperature change in outer space environments and an impact at the time of launching. Further, the solar cells for outer space applications are exposed to temperatures equal to or higher than the melting point of solder, depending on the altitude or solar radiation. Furthermore, commonly used adhesives for adhering electrodes and the like are poor in UV resistance.
For this reason, when the interconnector is bonded by soldering or adhering that is common in the solar cells for use on the ground, there is a concern that adhesive force decreases under operation of the solar cells, thereby leading to an electrical connection failure. From such a viewpoint, parallel-gap resistance welding is recommended for bonding the interconnector in the solar cells for outer space applications.
On a surface of the backside electrode layer (Mo) of the CIS-based solar cell, by the way, a Mo(Se,S)2 layer having a layered structure and low adhesive strength is present. Therefore, in bonding the interconnector of the CIS-based solar cell, even though a Ti-based bonding layer is formed on the backside electrode layer as described in Patent Literature 4, it is difficult to sufficiently enhance the adhesive strength between the bonding layer and the backside electrode layer because of the presence of the Mo(Se,S)2 layer.
In addition, the phenomenon of this type may occur in a similar manner, for example, also in a case where a wiring element is welded to a conductive substrate of the CIS-based solar cell, and a Mo(Se,S)2 layer or a Ti(Se,S)2 layer is present on a substrate surface.
The present invention has been made in view of the above circumstances, and provides an electrode structure in which adhesive strength between an electric conductor on a substrate side of a chalcogen solar cell and a wiring element is enhanced, in a solar cell including a chalcogen solar cell.
One aspect of the present invention is an electrode structure of a solar cell includes an electric conductor on a substrate side of a chalcogen solar cell, and a wiring element to be electrically connected with the electric conductor. The wiring element is stacked on and bonded with the electric conductor. The wiring element and the electric conductor each contain a group VI element. In a stacked direction of the electric conductor and the wiring element, a peak of a concentration distribution of the group VI element is shifted from an interface between the electric conductor and the wiring element.
According to the present invention, in a solar cell including a chalcogen solar cell, the adhesive strength between an electric conductor on a substrate side of the chalcogen solar cell and a wiring element can be enhanced.
Hereinafter, embodiments will be described with reference to the drawings.
In the embodiments, in order to facilitate understanding, structures and elements other than the main components of the present invention will be described in a simplified or omitted manner. In addition, in the drawings, the same elements are denoted by the same reference numerals. Note that in the drawings, shapes, dimensions, and the like of each element are schematically illustrated, and do not indicate actual shapes, dimensions, or the like.
<Structure of Solar Cell>
The solar cell module 10 illustrated in
(Conductive Substrate 11)
The conductive substrate 11 is formed of, for example, titanium (Ti), stainless steel (SUS), copper, aluminum, an alloy thereof, or the like. The conductive substrate 11 may be a flexible substrate. The conductive substrate 11 may have a stacked structure in which a plurality of metal base materials are stacked. For example, stainless foil, titanium foil, or molybdenum foil may be formed on a surface of the substrate.
The shape and dimensions of the conductive substrate 11 are appropriately determined in accordance with the size or the like of the solar cell module 10. The entire shape of the conductive substrate 11 in the first embodiment is, for example, a rectangular flat plate shape, but is not limited to this.
In a case where a metal substrate or a flexible substrate is applied as the conductive substrate 11, the solar cell module 10 becomes bendable, and cracking of the substrate due to bending can also be suppressed. Furthermore, in the above case, it becomes easy to reduce the weight and thickness of the solar cell module 10, as compared with a glass substrate or a resin substrate.
Note that regarding the solar cells for outer space applications, the conductive substrate 11 is desirably formed of titanium or an alloy containing titanium from the viewpoint of suppressing the load weight at the time of launching and enhancing the strength of the solar cells.
(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 the conductive substrate 11. Light such as sunlight enters the photoelectric conversion element 12 from an opposite side (upper side of
(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. The first electrode layer 21 faces a back surface side (substrate side) of the photoelectric conversion layer 22 that is not a light-receiving surface side, and thus will also be referred to as a backside electrode. Although not particularly limited, the thickness of the first electrode layer 21 is, for example, 200 nm to 1000 nm.
In addition, in the first electrode layer 21 in the photoelectric conversion element 12, a group VI compound layer 26 made of Mo(Se,S)2 is formed in an interface with the photoelectric conversion layer 22. Mo(Se,S)2 of the group VI compound layer 26 is formed in the first electrode layer 21, when a precursor layer 22p to be described later is chalcogenized to form the photoelectric conversion layer 22. Note that 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 peeled off by cleavage between layers.
Here, in the solar cell module 10 in the first embodiment, the photoelectric conversion element 12 is stacked on the conductive substrate 11, and thus the photoelectric conversion layer 22 can be directly stacked on the conductive substrate 11 without the first electrode layer 21. In a case where the photoelectric conversion layer 22 is directly stacked on the conductive substrate 11, a group VI compound layer is formed in an interface between the conductive substrate 11 and the photoelectric conversion layer 22, when the precursor layer 22p to be described later is chalcogenized. For example, in a case where the conductive substrate 11 is Ti, a group VI compound layer made of Ti(Se,S)2 is formed in the interface between the conductive substrate 11 and the photoelectric conversion layer 22. Note that similarly to Mo(Se,S)2, Ti(Se,S)2 is also a substance having the graphite-like multilayer structure, and has a property of being easily peeled off by the cleavage between layers.
(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 a band gap is large on each the light-receiving surface side (upper side of
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 group I-III-VI2 compound semiconductor having a chalcopyrite structure containing a group I element, a group III element, and a group VI element (chalcogen element). The group I element is selectable from copper (Cu), silver (Ag), gold (Au), and the like. The group III element is selectable from indium (In), gallium (Ga), aluminum (Al), and the like. In addition, the photoelectric conversion layer 22 may contain tellurium (Te) or the like, in addition to selenium (Se) and sulfur (S) as the group VI elements. Further, the photoelectric conversion layer 22 may contain an alkali metal such as Li, Na, K, Rb, or Cs.
Note that the photoelectric conversion layer 22 as a chalcogen solar cell may be a CZTS-based photoelectric conversion element using a chalcogenide-based group I2-(II-IV)-VI4 compound semiconductor containing Cu, Zn, Sn, S, or Se. As typical examples of the CZTS-based photoelectric conversion element, a CZTS-based photoelectric conversion element using a compound such as Cu2ZnSnSe4 or Cu2ZnSn(S,Se)4 can be mentioned.
(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 an i(intrinsic)-type high-resistance conductive layer. Here, the term “high resistance” means having a resistance value higher than the resistance value of the second electrode layer 24 to be described later.
The buffer layer 23 is selectable from compounds containing zinc (Zn), cadmium (Cd), and indium (In). Examples of the compounds containing zinc include ZnO, ZnS, and Zn(OH)2, or Zn(O,S) and Zn(O,S,OH) which are their mixed crystals, and further include ZnMgO and ZnSnO. Examples of the compound containing cadmium include CdS and CdO, or Cd(O,S) and Cd(O,S,OH) which are their mixed crystals. Examples of the compound containing indium include InS and InO, or In(O,S) and In(O,S,OH) which are their mixed crystals, and In2O3, In2S3, In or the like can be used. In addition, the buffer layer 23 may have a stacked structure of these compounds.
Note that the buffer layer 23 has an effect of improving characteristics such as photoelectric conversion efficiency, but can be omitted. In a case where the buffer layer 23 is omitted, the second electrode layer 24 is formed on the photoelectric conversion layer 22.
(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 desirably includes, for example, a material having a wide forbidden band width and a sufficiently low resistance value. In addition, the second electrode layer 24 serves as a passage for light such as sunlight, and thus the second electrode layer 24 desirably has a property of transmitting light having a wavelength that can be absorbed by the photoelectric conversion layer 22. From this point of view, the second electrode layer 24 will also be referred to as a transparent electrode layer or a window layer.
The second electrode layer 24 includes, for example, a metal oxide to which a group III element (B, Al, Ga, or In) is added as a dopant. Examples of the metal oxide include ZnO and SnO2. The second electrode layer 24 is selectable from, for example, indium tin oxide (ITO), indium titanium oxide (ITiO), indium zinc oxide (IZO), zinc tin oxide (ZTO), fluorine-doped tin oxide (FTO), gallium-doped zinc oxide (GZO), boron-doped zinc oxide (BZO), and the like.
(Interconnector 13)
The interconnector 13 is a wiring member on the positive electrode side of the solar cell module 10, and two interconnectors are connected in parallel with each other respectively in end parts on a right side of the solar cell module 10 in
Although not particularly limited, regarding the dimensions of the interconnector, a strip shape with a thickness of approximately 30 μm and a width of approximately 2.5 mm can be formed.
Here, the material of the interconnector 13 is not limited to the electrically conductive metal containing Ag. For example, an iron(Fe)-nickel(Ni)-cobalt(Co) alloy (for example, Kovar (registered trademark) or the like) or Ti may be used.
In a case where the iron-nickel-cobalt alloy is used as the material of the interconnector 13, the ratios of Fe, Ni, and Co may be similar to those in Kovar (Fe: 53.5%, Ni: 29%, Co: 17%) or may be any other ratios.
For example, in reducing the difference in thermal expansion coefficient between the interconnector 13 and the conductive substrate 11, the stress acting on the connection portion 14 due to thermal expansion is reduced, and thus it becomes easy to suppress a decrease in adhesive strength of the connection portion 14. For this reason, the ratios of Fe, Ni, and Co in the iron-nickel-cobalt alloy may be adjusted to reduce the difference in thermal expansion coefficient from the conductive substrate 11.
In addition, Fe contained in the iron-nickel-cobalt alloy may be increased in order to promote diffusion of metals between the elements that face each other.
Note that in the first embodiment, the description of the wiring on the negative electrode side of the solar cell module 10 is omitted.
(Connection Portion 14)
The connection portion 14 is an element for connecting the interconnector 13 and the first electrode layer 21 of the photoelectric conversion element 12, and the connection portions 14 are respectively provided in two places in end parts on the right side of the solar cell module 10 of
As illustrated in
The first electrode layer 21a corresponding to the wiring region 10a is formed integrally with the first electrode layer 21 of the photoelectric conversion element 12.
However, in the first electrode layer 21, which faces the photoelectric conversion layer 22 of the photoelectric conversion element 12, the group VI compound layer 26 is formed in the interface with the photoelectric conversion layer 22. On the other hand, the group VI compound layer 26 is not formed in the first electrode layer 21a of the wiring region 10a. In the wiring region 10a, the group VI compound layer 26, which is easily peeled off, is not formed between the first electrode layer 21a and the bonding layer 27. Therefore, the bonding layer 27 is hardly peeled off from the first electrode layer 21a.
In addition, in the first electrode layer 21a of the wiring region 10a, a metal element (for example, Al) of the bonding layer 27, Se and S that are the group VI elements, and the like are diffused, as will be described later. The metal element of the bonding layer 27 diffuses into the first electrode layer 21a, and thus the first electrode layer 21a and the bonding layer 27 have high adhesive 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. For this reason, there is almost no diffusion of the metal element into the bonding layer 27 in the first electrode layer 21 in the photoelectric conversion element 12, unlike the first electrode layer 21a in the wiring region 10a.
(Bonding Layer 27)
The bonding layer 27 is a conductive layer for electrically connecting the first electrode layer 21a of the wiring region 10a and the interconnector 13, and is made up of a substance containing a group VI element that has diffused into a conductive metal material. As an example, the bonding layer 27 in the first embodiment is a substance containing Al and Ag, and containing Se and S that have been diffused.
As illustrated in
As the metal material of the bonding layer 27, a metal material having a melting point equal to or higher than 230° C. and higher than that of the solder alloy is used in order to ensure the use of the solar cell module 10 at high temperatures due to solar radiation or the like in outer space environments. Note that both Al and Ag described above have melting points equal to or higher than 230° C.
In addition, the material of the bonding layer 27 desirably contains at least one of Al, Pt, Zn, and Sn, which are metal elements to be easily chalcogenized. Since the bonding layer 27 contains a metal element to be easily chalcogenized, the group VI compound is likely to be distributed uniformly in the bonding layer 27. Then, when the bonding layer 27 to be described later is formed, the diffusion of the group VI element from the group VI compound layer 26 into the bonding layer 27 is promoted. By such diffusion of the group VI element, the group VI compound layer 26 can be made to disappear from between the first electrode layer 21a and the bonding layer 27.
As described above, when the bonding layer 27 is formed, the group VI element diffuses into the bonding layer 27, and the group VI compound layer 26 disappears. For this reason, 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 in the interface between the first electrode layer 21a and the bonding layer 27.
In addition, the material of the bonding layer 27 contains a metal element to be easily chalcogenized, and thus the group VI element diffuses more into the bonding layer 27 side 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 is generated in the bonding layer 27. In other words, the number of atoms of the group VI element contained in the bonding layer 27 is larger than the number of atoms of the group VI element contained in the first electrode layer 21a.
In addition, the material of the bonding layer 27 desirably contains a metal element having an alloy phase in a phase diagram with respect to the material of the first electrode layer 21a, which is a backside electrode layer. Alternatively, the material of the bonding layer 27 may include at least one of the constituent elements of the first electrode layer 21a.
In selecting the material of the bonding layer 27, it is sufficient if a metal having an alloy phase in a phase diagram with respect to the material (Mo) of the first electrode layer 21a is selected from a binary phase diagram (for example, BINARY ALLOY PHASE DIAGRAMS SECOND EDITION Vol. 1, T. B. Massalski, 1990).
The bonding layer 27 includes a metal element (for example, Al or the like) having an alloy phase in a phase diagram with respect to the material of the first electrode layer 21a or at least one of constituent elements of the first electrode layer 21a, and thus the metal element easily diffuses between the first electrode layer 21a and the bonding layer 27. Further, as described above, in accordance with the group VI element diffusing more into the bonding layer 27 side, the metal element contained in the bonding layer 27 becomes in a state of easily diffusing into the first electrode layer 21a. Accordingly, the adhesive strength between the first electrode layer 21a and the bonding layer 27 can be improved.
In addition, Ag contained in the bonding layer 27 is also contained in the interconnector 13 as described above. That is, the interface between the bonding layer 27 and the interconnector 13 has high affinity, because both materials contain Ag. Therefore, when the interconnector 13 is welded, the metal elements also diffuse in the interface between the interconnector 13 and the bonding layer 27, and the adhesive strength between the interconnector 13 and the bonding layer 27 is improved.
<Method for Manufacturing Solar Cell>
Next, an example of a manufacturing method of the solar cell module 10 will be described.
(S1: Formation of First Electrode Layer)
In S1, as illustrated in
(S2: Formation of Precursor Layer)
In S2, a precursor layer 22p in a thin film shape is formed on the first electrode layer 21, as indicated by a broken line in
As a method for forming the precursor layer 22p on the first electrode layer 21, for example, the above sputtering method, a vapor deposition method, and an ink coating method can be mentioned. The vapor deposition method is a method for making a film by heating a vapor deposition source and then using atoms or the like that have become a vapor phase. The ink coating method is a method for dispersing the powdered material of the precursor film in a solvent such as an organic solvent, applying the solvent onto the first electrode layer 21, and then evaporating the solvent to form the precursor layer 22p.
When the CIS-based photoelectric conversion layer 22 is formed, 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 to be contained in the precursor layer 22p is selectable from copper, gold, and the like. In addition, the group III element to be contained in the precursor layer 22p is selectable from indium, gallium, aluminum, and the like. Further, the precursor layer 22p may contain an alkali metal such as Li, Na, K, Rb, or Cs. Further, the precursor layer 22p may contain tellurium as a group VI element, in addition to selenium and sulfur.
On the other hand, when the CZTS-based photoelectric conversion layer 22 is formed, the precursor layer 22p is made as a thin film of Cu—Zn—Sn or Cu—Zn—Sn—Se—S.
(S3: Formation of Photoelectric Conversion Layer)
In S3, as illustrated in
In a case where the CIS-based photoelectric conversion layer 22 is formed, in a chalcogenized treatment of the precursor layer 22p, the precursor layer 22p containing a group I element and a group III element is subject to a thermal treatment in an atmosphere containing a group VI element to be chalcogenized, and the photoelectric conversion layer 22 is formed.
For example, first, selenization in a vapor phase selenization method is performed. The selenization is performed by heating the precursor layer in an atmosphere of a selenium source gas (for example, hydrogen selenide or selenium vapor) containing selenium as a group VI element source. Although not particularly limited, the selenization is, for example, desirably performed at a temperature within a range equal to or higher than 300° C. and equal to or lower than 600° C. in a heating furnace.
As a result, the precursor layer is converted into a compound containing a group I element, a group III element, and selenium (photoelectric conversion layer 22). Note that the compound containing the group I element, the group III element, and selenium (photoelectric conversion layer 22) may be formed by any other method than the vapor phase selenization method. For example, such a compound can also be formed in a solid-phase selenization method, a vapor deposition method, an ink application method, an electrodeposition method, or the like.
Next, the photoelectric conversion layer 22 containing the group I element, the group III element, and selenium is sulfurized. Sulfurization is performed by heating the photoelectric conversion layer 22 in an atmosphere of a sulfur source gas that contains 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 group VI elements. In a surface part of the photoelectric conversion layer 22, the sulfur source gas serves as substituting selenium in a crystal containing a group I element, a group III element, and selenium, such as for example selenium in a chalcopyrite crystal with sulfur.
Although not particularly limited, the sulfurization is, for example, desirably performed at a temperature within a range equal to or higher than 450° C. and equal to or lower than 650° C. in a heating furnace.
On the other hand, in a case where the CZTS-based photoelectric conversion layer 22 is formed, in the chalcogenized treatment of the precursor layer 22p, the precursor layer 22p containing Cu, Zn, and Sn is sulfurized and selenized in a hydrogen sulfide atmosphere and a hydrogen selenide atmosphere at 500° C. to 650° C. Accordingly, the CZTS-based photoelectric conversion layer 22 containing Cu2ZnSn(S,Se)4 can be formed.
In addition, in accordance with the chalcogenized treatment of the precursor layer 22p in S3, the group VI compound layer 26 containing Mo(Se,S)2 is formed in the interface in the first electrode layer 21 between the first electrode layer 21 and the photoelectric conversion layer 22.
(S4: Formation of Buffer Layer)
In S4, as illustrated in
(S5: Formation of Second Electrode Layer)
In S5, as indicated by a broken line in
In the above steps S1 to S5, the photoelectric conversion element 12 is formed on the conductive substrate 11.
(S6: Formation of Wiring Region)
In S6, a predetermined position in an end part of the light-receiving surface of the photoelectric conversion element 12 is partially cut out by, for example, mechanical patterning, and the wiring region 10a in which the first electrode layer 21 is exposed is formed on the light-receiving surface side. Note that in step S6, the group VI compound layer 26 is present on a surface of the first electrode layer 21 in the wiring region 10a, in a similar manner to the first electrode layer 21 in the photoelectric conversion element 12.
As an example,
(S7: Formation of Precursor Layer in Wiring Region)
In S7, as illustrated in
In S7, first, on the light-receiving surface of the photoelectric conversion element 12, a region other than the region where the precursor layer 27p is to be formed (inside of the groove 28 in the wiring region 10a) is appropriately masked. Thereafter, the precursor layer 27p is formed on the first electrode layer 21 in the wiring region 10a in a vapor deposition method, for example.
The precursor layer 27p in S7 is formed by sequentially stacking an Al layer 27p1 and an Ag layer 27p2 in this order from a conductive substrate 11 side. The film-making conditions for the Al layer 27p1 are, for example, an applied voltage of approximately 10 kV, an EB current of approximately 0.2 A, a film-making rate of 0.4 nm/sec, and a thickness of 0.5 μm. Similarly, the film-making conditions for the Ag layer 27p2 are, for example, an applied voltage of approximately 10 kV, an EB current of approximately 0.1 A, a film-making rate of 0.5 nm/sec, and a thickness of 2.0 μm.
In the precursor layer 27p, the Ag layer 27p2 is disposed on an upper surface side facing the interconnector 13. By disposing the Ag layer 27p2 common to a material of the interconnector 13 in a region facing the interconnector 13, diffusion easily occurs in the interface between the interconnector 13 and the precursor layer 27p at the time of welding.
In addition, in the precursor layer 27p, the Al layer 27p1 is disposed on a 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 chalcogenized, in a region facing the group VI compound layer 26, the group VI compound easily diffuses into the bonding layer 27 side at the time of welding.
(S8: Welding of Interconnector)
In S8, an end portion of the interconnector 13 made of an electrically conductive metal containing Ag is disposed on an upper surface of the precursor layer 27p, and the interconnector 13 is welded to the solar cell module 10. As an example, the interconnector 13 is welded in a parallel-gap welding method using a resistance welding machine with a transistor control method.
Specifically, as illustrated in
Note that 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.
While being welded with the interconnector 13, the precursor layer 27p receives thermal energy from the electrodes 30 through the interconnector 13. Then, diffusion occurs in an interface between the interconnector 13 and the precursor layer 27p and an interface between the precursor layer 27p and the first electrode layer 21. Diffusion also occurs between the Al layer 27p1 and the Ag layer 27p2 in the precursor layer 27p. Accordingly, as illustrated in
When the diffusion occurs in the interface between the precursor layer 27p and the first electrode layer 21 because of the thermal energy at the time of 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 from between the first electrode layer 21a and the bonding layer 27. Since the group VI compound layer 26, which is easily peeled off, is no longer present between the first electrode layer 21a and the bonding layer 27 after the welding, the first electrode layer 21a and the bonding layer 27 are hardly peeled off.
In addition, the Al layer 27p1, which is easily chalcogenized, is disposed on the first electrode layer 21 side of the precursor layer 27p. Therefore, Se that diffuses from the group VI compound layer 26 diffuses more into the bonding layer 27 side containing Al to be easily chalcogenized than into the first electrode layer 21a side containing Mo. Then, in accordance with Se diffusing more into the bonding layer 27 side, Al of the metal element contained in the precursor layer 27p easily diffuses into the first electrode layer 21a. Al, which is a metal element of the bonding layer 27, diffuses into the first electrode layer 21a, and thus the adhesive strength between the first electrode layer 21a and the bonding layer 27 after the welding is further improved.
On the other hand, the interface between the Ag layer 27p2 of the precursor layer 27p and the interconnector 13 has high affinity, because both materials contain Ag. Therefore, the metal element diffuses into the interface between the interconnector 13 and the precursor layer 27p at the time of welding, and the interconnector 13 and the bonding layer 27 are bonded together with high adhesive strength.
In steps S1 to S8 described above, the connection portion 14, in which the first electrode layer and the interconnector are bonded together through the bonding layer, is formed in the wiring region of the solar cell module 10.
Heretofore, the description with reference to
As described above, in the first embodiment, in the wiring region 10a, the precursor layer 27p containing Al is formed on the first electrode layer 21, which includes the group VI compound layer 26 (S7). Then, the precursor layer 27p and the interconnector 13 are welded together, thermal energy is applied, and then the bonding layer 27 containing the group VI element and Al of the precursor layer 27p is formed (S8).
Accordingly, 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 in the concentration distribution of the group VI element is shifted in a stacked direction from the interface between the first electrode layer 21 and the bonding layer 27. That is, in the connection portion 14 in the first embodiment, since the group VI compound layer 26 disappears from the interface between the first electrode layer 21 and the bonding layer 27, the adhesive strength between the first electrode layer 21 and the bonding layer 27 can be enhanced.
Note that in the following description of each embodiment, the same reference numerals are given to the same configurations as those of the first embodiment, and overlapping descriptions will be omitted.
As illustrated in
The conductive coating layer 31 is formed on the back surface side of the conductive substrate 11, so that warpage of the solar cell module 10 can be reduced.
In addition, a group VI compound layer 32, which is made of Mo(Se,S)2, is formed on a surface of the conductive coating layer 31, except for a region where the bonding layer 27a is stacked. Mo(Se,S)2 of the group VI compound layer 32 is formed in the conductive coating layer 31, when the precursor layer 22p is chalcogenized to form the photoelectric conversion layer 22. Note that the group VI compound layer 32 made of Mo(Se,S)2 has properties similar to those of the group VI compound layer 26 of the first electrode layer 21.
In other words, the group VI compound layer 32, which is easily peeled off, is not formed between the conductive coating layer 31 and the bonding layer 27a. Therefore, the bonding layer 27a is hardly peeled off from the conductive coating layer 31.
In addition, the bonding layer 27a in the second embodiment is a substance containing at least one of Al, Pt, Zn, and Sn and containing diffused Se and S. As the metal material of the bonding layer 27a, a metal material having a melting point equal to or higher than 230° C. and higher than that of the solder alloy is used in order to ensure the use of the solar cell module 10 at high temperatures due to solar radiation or the like in outer space environments. In addition, the material of the bonding layer 27a desirably contains a metal element having an alloy phase in a phase diagram with respect to the material of the conductive coating layer 31 and the material of the interconnector 13 in order to promote diffusion of the metal element between the members.
In addition, the material of the bonding layer 27a desirably contains at least one of Al, Pt, Zn, and Sn, which are metal elements to be easily chalcogenized. Accordingly, the group VI compound is likely to be uniformly distributed in the bonding layer 27a. When the bonding layer 27a is formed, diffusion of the group VI element from the group VI compound layer 32 into the bonding layer 27a side is promoted, so that the group VI compound layer 32 can be made to disappear from between the conductive coating layer 31 and the bonding layer 27a.
In addition, in the conductive coating layer 31, a metal element (for example, Al) of the bonding layer 27a, Se and S that are group VI elements, and the like are diffused in a region where the bonding layer 27a is stacked, as will be described later. The metal element of the bonding layer 27a diffuses into the conductive coating layer 31, and thus the conductive coating layer 31 and the bonding layer 27a have high adhesive strength.
On the other hand, in the conductive coating layer 31, in a region where the bonding layer 27a is not stacked, there is almost no diffusion of the metal element of the bonding layer 27a.
When the connection portion 14 in the second embodiment is formed, steps (S1 to S5) of forming the photoelectric conversion element 12 are substantially similar to the steps of the manufacturing method in the first embodiment. However, in the second embodiment, the conductive coating layer 31 is formed on the back surface side of the conductive substrate 11 in step S1. In addition, in step S3, the group VI compound layer 32 is formed on a surface of the conductive coating layer 31.
Thereafter, a precursor layer (not illustrated) of the bonding layer 27a is formed on the conductive coating layer 31 including 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 together, thermal energy is applied, and the bonding layer 27a is formed.
When the bonding layer 27a is formed, the group VI element diffuses into the bonding layer 27a side, and the group VI compound layer 32 disappears. For this reason, 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 in the interface between the conductive coating layer 31 and the bonding layer 27a.
In addition, the material of the bonding layer 27a contains a metal element to be easily chalcogenized, and thus the group VI element diffuses more into the bonding layer 27a side 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 in the second embodiment, a peak in the concentration of the group VI element is generated in the bonding layer 27a. In other words, the number of atoms of the group VI element contained in the bonding layer 27a is larger than the number of atoms of the group VI element contained in the conductive coating layer 31.
According to the configuration in the second embodiment described above, the adhesive strength between the conductive coating layer 31, which is formed on the substrate back surface side of the chalcogen solar cell, and the connection portion 14 can be improved.
As illustrated in
In addition, a group VI compound layer 33 made of Ti(Se,S)2 is formed on a surface of the conductive substrate 11, except for a region where the bonding layer 27b is stacked. 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 chalcogenized to form the photoelectric conversion layer 22. Note that 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 peeled off by the cleavage between layers.
In other words, the group VI compound layer 33, which is easily peeled off, is not formed between the conductive substrate 11 and the bonding layer 27b. Therefore, the bonding layer 27b is hardly peeled off from the conductive substrate 11.
In addition, the bonding layer 27b in the third embodiment is a substance containing at least one of Al, Pt, Zn, and Sn and containing diffused Se and S. As the metal material of the bonding layer 27b, a metal material having a melting point equal to or higher than 230° C. and higher than that of the solder alloy is used in order to ensure the use of the solar cell module 10 at high temperatures due to solar radiation or the like in outer space environments. Further, the material of the bonding layer 27b desirably contains a metal element having an alloy phase in a phase diagram with respect to the material of the conductive substrate 11 and the material of the interconnector 13 in order to promote diffusion of the metal element between the members.
In addition, the material of the bonding layer 27b desirably contains at least one of Al, Pt, Zn, and Sn, which are metal elements to be easily chalcogenized. Accordingly, the group VI compound is likely to be uniformly distributed in the bonding layer 27b. When the bonding layer 27b is formed, diffusion of the group VI element from the group VI compound layer 33 into the bonding layer 27b side is promoted, so that the group VI compound layer 33 can be made to disappear from between the conductive substrate 11 and the bonding layer 27b.
Further, in the conductive substrate 11, a metal element (for example, Al) of the bonding layer 27b, Se and S that are group VI elements, and the like are diffused in a region where the bonding layer 27b is stacked, as will be described later. The metal element of the bonding layer 27b diffuses into the conductive substrate 11, and thus the conductive substrate 11 and the bonding layer 27b have high adhesive strength.
On the other hand, in the conductive substrate 11, in a region where the bonding layer 27b is not stacked, there is almost no diffusion of the metal element of the bonding layer 27b.
When the connection portion 14 in the third embodiment is formed, steps (S1 to S5) of forming the photoelectric conversion element 12 are substantially similar to the steps of the manufacturing method in the first embodiment. Note that in the third embodiment, the group VI compound layer 33 is formed on a surface of the conductive substrate 11 in step S3.
Thereafter, a precursor layer (not illustrated) of the bonding layer 27b is formed on the conductive substrate 11 including 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 together, thermal energy is applied, and the bonding layer 27b is formed.
When the bonding layer 27b is formed, the group VI element diffuses into the bonding layer 27b side, and the group VI compound layer 33 disappears. For this reason, 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 in the interface between the conductive substrate 11 and the bonding layer 27b.
In addition, the material of the bonding layer 27b contains a metal element to be easily chalcogenized, and thus the group VI element diffuses more into the bonding layer 27b side 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 in the third embodiment, a peak of the concentration of the group VI element is generated in the bonding layer 27b. In other words, the number of atoms of the group VI element contained in the bonding layer 27b is larger than the number of atoms of the group VI element contained in the conductive substrate 11.
According to the configuration in the third embodiment described above, the adhesive strength between the conductive substrate 11 of the chalcogen solar cell and the connection portion 14 can be improved.
In other words, the group VI compound layer 32, which is easily peeled off, is not formed between the conductive coating layer 31 and the interconnector 13. Therefore, the interconnector 13 is hardly peeled off from the conductive coating layer 31.
In addition, a material having a melting point equal to or higher than 230° C. and higher than that of a solder alloy is used as the material of the interconnector 13 to be applied in the connection portion 14 in order to ensure the use of the solar cell module 10 at high temperatures due to solar radiation or the like in outer space environments. In addition, the material of the interconnector 13 in the fourth embodiment contains a metal element having an alloy phase in a phase diagram with respect to the material of the conductive coating layer 31 in order to promote diffusion of the metal element between the members.
In the conductive coating layer 31 in the fourth embodiment, a metal element of the interconnector 13, Se and S that are group VI elements, and the like are diffused in a region where the interconnector 13 is bonded. The metal element of the interconnector 13 diffuses into the conductive coating layer 31, and thus the conductive coating layer 31 and the interconnector 13 have high adhesive strength.
On the other hand, in the conductive coating layer 31, in a region where the interconnector 13 is not bonded, there is almost no diffusion of the metal element of the interconnector 13.
When the connection portion 14 in the fourth embodiment is formed, steps (S1 to S5) of forming the photoelectric conversion element 12 are substantially similar to the steps of the manufacturing method in the first embodiment. However, in the fourth embodiment, the conductive coating layer 31 is formed on the back surface side of the conductive substrate 11 in step S1. In addition, in step S3, the group VI compound layer 32 is formed on a surface of the conductive coating layer 31.
Thereafter, the interconnector 13 is disposed on the conductive coating layer 31 including the group VI compound layer 32, the conductive coating layer 31 and the interconnector 13 are welded together, and thermal energy is applied. Accordingly, the group VI element diffuses from the interface between the conductive coating layer 31 and the interconnector 13, and the group VI compound layer 32 disappears. For this reason, in the concentration distribution of the group VI element in the thickness direction of the connection portion 14 in the fourth embodiment, there is no peak in the concentration of the group VI element in the interface between the conductive coating layer 31 and the interconnector 13.
According to the configuration in the fourth embodiment described above, the adhesive strength between the conductive coating layer 31, which is formed on the substrate back surface side of the chalcogen solar cell, and the interconnector 13 can be improved.
In other words, the group VI compound layer 33, which is easily peeled off, is not formed between the conductive substrate 11 and the interconnector 13. Therefore, the interconnector 13 is hardly peeled off from the conductive substrate 11.
In addition, a material having a melting point equal to or higher than 230° C. and higher than that of a solder alloy is used as the material of the interconnector 13 to be applied in the connection portion 14 in order to ensure the use of the solar cell module 10 at high temperatures due to solar radiation or the like in outer space environments. Further, the material of the interconnector 13 in the fifth embodiment contains a metal element having an alloy phase in a phase diagram with respect to the material of the conductive substrate 11 in order to promote diffusion of the metal element between the members.
In the conductive substrate 11 in the fifth embodiment, a metal element of the interconnector 13, Se and S that are group VI elements, and the like are diffused in a region where the interconnector 13 is bonded. The metal element of the interconnector 13 diffuses into the conductive substrate 11, and thus the conductive substrate 11 and the interconnector 13 have high adhesive strength.
On the other hand, in the conductive substrate 11, in a region where the interconnector 13 is not bonded, there is almost no diffusion of the metal element of the interconnector 13.
When the connection portion 14 in the fifth embodiment is formed, steps (S1 to S5) of forming the photoelectric conversion element 12 are substantially similar to the steps of the manufacturing method in the first embodiment. Note that in the fifth embodiment, the group VI compound layer 33 is formed on a surface of the conductive substrate 11 in step S3.
Thereafter, the interconnector 13 is disposed on the conductive substrate 11 including the group VI compound layer 33, the conductive substrate 11 and the interconnector 13 are welded together, and thermal energy is applied. Accordingly, the group VI element diffuses from the interface between the conductive substrate 11 and the interconnector 13, and the group VI compound layer 33 disappears. For this reason, in the concentration distribution of the group VI element in the thickness direction of the connection portion 14 in the fifth embodiment, there is no peak in the concentration of the group VI element in the interface between the conductive substrate 11 and the interconnector 13.
According to the configuration in the fifth embodiment described above, the adhesive strength between the conductive substrate 11 of the chalcogen solar cell and the interconnector 13 can be improved.
Hereinafter, examples of the solar cell module in the present invention will be described.
Here, a connection portion in an example is formed in a similar manner to the configuration described in the first embodiment. That is, Ti is a material of the substrate, and the backside electrode layer before the welding is a Mo film in which a Se layer is formed on a 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 stacked. The backside electrode layer after the welding is Mo in which Al and Se are diffused, and the bonding layer after the welding is a substance containing Se diffused into Ag and Al.
(Concentration Distribution of Elements in Connection Portion)
In an example, the concentration distribution of elements in the connection portion of the solar cell module was obtained in the following method.
First, a cross-section in the thickness direction of the connection portion in an example is formed by use of a focused ion beam (FIB) device. Then, a scanning ion microscope (SIM) image of the cross-section of the connection portion was captured at an accelerating voltage of 15 kV. Thereafter, elements contained in the cross-section of the connection portion were analyzed by energy dispersive X-ray analysis (EDX).
Note that the instruments that were used in the analysis of elements in an example are listed as follows. The FIB device is SMI3200F manufactured by SII NanoTechnology Inc., the SEM is SU8240 manufactured by Hitachi High-Technologies Corporation, and the EDX is EX-370 manufactured by HORIBA, Ltd.
In each of
In addition, the contents indicated on the vertical axes in
In addition,
As illustrated in
In addition, as illustrated in
Further, as illustrated in
Further, as illustrated in
(Adhesive Strength Test of Connection Portion)
In addition, in order to evaluate the adhesive strength of the connection portion of the solar cell module, the following test was conducted. In the test, a tip end of an interconnector after the welding was clamped by a jig, and the tip end of the interconnector was pulled upward in 45-degree direction at a speed of 5 mm/min by use of an autograph device. Then, the tensile strength (maximum strength) at the time when the interconnector is detached from the connection portion is measured.
As test targets, a test piece of the above example (hereinafter, referred to as Example 1) and the following three test pieces as Comparative Examples were used.
Comparative Example 1 denotes a test piece in which an interconnector is welded with a layered body of Ti substrate/Mo(MoSeS)/Ag. Comparative Example 2 denotes a test piece in which an interconnector is welded with a layered body of Ti substrate/Mo(MoSeS)/In-solder. Note that a bonding area of Comparative Example 2 is approximately 60 times that of Example. Comparative Example 3 denotes a test piece in which an interconnector is welded with a layered body of Ti substrate/Mo(MoSeS). Note that the materials of the interconnectors of Example 1 and Comparative Examples 1 to 3 are all Ag.
In
Assuming that the maximum strength of the test piece of Comparative Example 1 was 1, the maximum strength of the test piece of Comparative Example 2 was 0.18, and the maximum strength of the test piece of Comparative Example 3 was 0.12. On the other hand, it was confirmed that the test piece of Example 1 was larger than 1, had the maximum strength higher than any of Comparative Examples 1 to 3, and had good adhesive strength of the connection portion.
In addition, as illustrated in
On the other hand, in the test piece of Comparative Example 1, neither Ag that is a material of the bonding layer nor Mo that is a material of the backside electrode layer has an alloy phase in a phase diagram. In addition, in the test piece of Comparative Example 2, neither In-solder that is a material of the bonding layer nor Mo that is a material of the backside electrode layer has an alloy phase in a phase diagram. Therefore, in Comparative Examples 1 and 2, no diffusion of metal elements occurs in the materials of the bonding layer and the backside electrode layer. Therefore, it is considered that the adhesive strength is lower than that of Example 1.
Similarly, in the test piece of Comparative Example 3, neither Ag that is a material of the interconnector nor Mo that is a material of the backside electrode layer has an alloy phase in a phase diagram. Therefore, in Comparative Example 3, no diffusion of metal elements occurs in the materials of the interconnector and the backside electrode layer. Therefore, it is considered that the adhesive strength is lower than that of Example 1.
A test piece of Example 2 has a configuration corresponding to the second embodiment described above. In Example 2, Ti is a material of the interconnector, Al is a material of the bonding layer, Mo is a material of the conductive coating layer, and Ti is a material of the substrate. In Example 2, the materials of the interconnector and the bonding layer have an alloy phase in a phase diagram, and the materials of the bonding layer and the conductive coating layer have an alloy phase in a phase diagram. Assuming that the maximum strength of the test piece of Comparative Example 1 was 1, the maximum strength of the test piece of Example 2 was 1.38, which indicated a larger value than that of Comparative Example 1.
The test piece of Example 3 has a configuration corresponding to the third embodiment described above. In Example 3, Ti is a material of the interconnector, Al is a material of the bonding layer, and Ti is a material of the substrate. In Example 3, the materials of the interconnector and the bonding layer have an alloy phase in a phase diagram, and the materials of the bonding layer and the substrate have an alloy phase in a phase diagram. Assuming that the maximum strength of the test piece of Comparative Example 1 was 1, the maximum strength of the test piece of Example 3 was 1.24, which indicated a larger value than that of Comparative Example 1.
The test piece of Example 4 has a configuration corresponding to the third embodiment described above. In Example 4, Kovar is a material of the interconnector, Sn is a material of the bonding layer, and Ti is a material of the substrate. In Example 4, the materials of the interconnector and the bonding layer have an alloy phase in a phase diagram, and the materials of the bonding layer and the substrate have an alloy phase in a phase diagram. Assuming that the maximum strength of the test piece of Comparative Example 1 was 1, the maximum strength of the test piece of Example 4 was 2.18, which indicated a larger value than that of Comparative Example 1.
The test piece of Example 5 has a configuration corresponding to the fourth embodiment described above. In Example 5, Kovar is a material of the interconnector, Mo is a material of the conductive coating layer, and Ti is a material of the substrate. In Example 5, the materials of the interconnector and the conductive film layer have an alloy phase in a phase diagram. Assuming that the maximum strength of the test piece of Comparative Example 1 was 1, the maximum strength of the test piece of Example 5 was 2.06, which indicated a larger value than that of Comparative Example 1.
The test piece of Example 6 has a configuration corresponding to the fifth embodiment described above. In Example 6, Kovar is a material of the interconnector, and Ti is a material of the substrate. In Example 6, the materials of the interconnector and the substrate have an alloy phase in a phase diagram. Assuming that the maximum strength of the test piece of Comparative Example 1 was 1, the maximum strength of the test piece of Example 6 was 2.09, which indicated a larger value than that of Comparative Example 1.
The test piece of Example 7 has a configuration corresponding to the fifth embodiment described above. In Example 7, Ti is a material of the interconnector, and Ti is a material of the substrate. In Example 6, the materials of the interconnector and the substrate are homogeneous metals. Assuming that the maximum strength of the test piece of Comparative Example 1 was 1, the maximum strength of the test piece of Example 7 was 3.15, which indicated a larger value than that of Comparative Example 1.
As described above, in Examples 2 to 7, unlike Comparative Examples 1 to 3 described above, all metal materials between the elements that face each other have an alloy phase in a phase diagram. Therefore, the metal elements diffuse between the elements that face each other at the time of welding, and it is considered that the adhesive strength between the elements is improved.
In particular, the test piece of Example 7 has high affinity, because the materials of the interconnector and the substrate are homogeneous metals. The metal elements diffuse in the interface between the interconnector and the substrate at the time of welding, and it is considered that the adhesive strength between the interconnector and the substrate is further improved.
«Supplementary Matters of Embodiments»
In the above embodiments, the configuration of the solar cell module having a single cell structure including 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 a planar direction of the light-receiving surface of the conductive substrate and these photoelectric conversion elements are connected in series. Note that in the case of the solar cell module having the integrated structure, an insulating layer is formed between the conductive substrate and the first electrode layer.
In addition, the precursor layer 27p of the bonding layer 27 is not limited to the configurations in the above embodiments, in which one Al layer 27p1 and one Ag layer 27p2 are stacked. For example, the precursor layer 27p may be made up of a single-layer film containing Al and Ag. Further, the precursor layer 27p may be made up of a stacked film of three or more layers. In a case where the precursor layer 27p is the stacked film of three or more layers, layers of the two materials may be alternately arranged in a thickness direction, and a layer of another material may be further added to the layers of the two materials. In addition, a layer containing Al and Ag may be added to the stacked film.
In addition, in the fourth embodiment described above (
Similarly, in the fifth embodiment described above (
Further, the electrode structure of the solar cell in the present invention is not limited to outer space applications. For example, the present invention may be applied to a solar cell to be installed on the ground, in forming a connection portion that is less likely to have a failure even when receiving external force of strong winds or an earthquake.
As described heretofore, the embodiments of the present invention have been described. However, the embodiments are each presented as an example, and there is no intention of limiting the scope of the present invention. The embodiments can be implemented in various forms other than the above description, and various omissions, substitutions, changes, and the like can be made without departing from the gist of the present invention. Embodiments and modifications thereof are included in the scope and gist of the present invention, and the invention described in the claims and equivalents thereof are also included in the scope and gist of the present invention.
Number | Date | Country | Kind |
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2020-211733 | Dec 2020 | JP | national |
The present application claims priority under 35 U.S.C. § 371 to International Patent Application No. PCT/JP2021/047252, filed Dec. 21, 2021, which claims priority to and the benefit of Japanese Patent Application No. 2020-211733, filed on Dec. 21, 2020. The contents of these applications are hereby incorporated by reference in their entireties.
Filing Document | Filing Date | Country | Kind |
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PCT/JP2021/047252 | 12/21/2021 | WO |