Solar cell and manufacturing method for solar cell

Abstract

The purpose of the present invention is to provide a solar cell having high heat resistance and low production costs, and to provide a manufacturing method for the solar cell. The present invention pertains to a solar cell (100) comprising at least, in order: a first electrode layer (101); a light absorption layer (103); a first electron transport layer (104) which is an n-type semiconductor containing indium sulfide or indium sulfide to which another element has been added; a second electron transport layer (105) which is an n-type oxide semiconductor to which hydrogen has been added; and a second electrode layer (106).

Description

Solar cell and method for manufacturing solar cell

[0001] The present invention relates to a solar cell and a method for manufacturing a solar cell.

[0002] Solar cells include chalcopyrite solar cells using chalcopyrite compounds and kesterite solar cells using kesterite compounds. Various studies have been conducted to improve various physical properties of chalcopyrite solar cells and kesterite solar cells, as shown in Non-Patent Documents 1 and 2 and Patent Documents 1 and 2.

[0003] In chalcopyrite solar cells and kesterite solar cells, various physical properties are improved and higher performance is expected by including alkali metal elements such as Na and K in the light-absorbing layer. However, since alkali metal elements are easily diffused by heat and electric fields, as described in Non-Patent Document 1, when the solar cell having a light-absorbing layer containing alkali metal elements is exposed to high temperatures, the alkali metal elements diffuse from the light-absorbing layer to the transparent conductive film on the light-receiving surface side, resulting in a deterioration in the performance of the solar cell. Therefore, it is difficult to use the solar cell having a light-absorbing layer containing alkali metal elements in a high-temperature environment exceeding the normal operating temperature range of solar cells, which is 45 to 85°C.

[0004] In Non-Patent Document 2, an InP film is used as an n-type electron transport layer that is usually laminated on a p-type chalcopyrite light absorption layer or a p-type kesterite light absorption layer. ２ S ３ However, it has been suggested that it acts as a diffusion barrier layer for alkali metal elements, and it is expected to be a material for an electron transport layer with heat resistance.

[0005] Therefore, In was added to the light absorption layer. ２ S ３ Patent Documents 1 and 2 disclose solar cells in which a first electron transport layer using the above compound is formed, and a second electron transport layer is formed on the first electron transport layer.

[0006] Chinese Patent No. 1820358 Specification Patent No. 5635497

[0007] Prog. Photovolt: Res. Appl. , 2015, 23, pp. 537-545Appl. Sci. , 2020, 10, pp. 1052

[0008] However, In ２ S ３ is easily damaged by the sputtering method, so when the solar cells disclosed in Patent Documents 1 and 2 are fabricated, In is sputtered. ２ S ３ It has been found that forming a second electron transport layer on a first electron transport layer using a sputtering method damages the first electron transport layer, resulting in a deterioration in the performance of the solar cell or a failure to function as a solar cell. On the other hand, it has been found that forming a second electron transport layer on a first electron transport layer using a method such as atomic layer deposition, which is less likely to cause the above-mentioned damage, in order to avoid damage to the first electron transport layer by the sputtering method, results in problems such as poor mass productivity and high production costs for solar cells.

[0009] An object of the present invention is to provide a solar cell having high heat resistance and low production costs, and a method for manufacturing the solar cell.

[0010] A solar cell according to one embodiment of the present invention comprises at least a first electrode layer, a light absorption layer, a first electron transport layer which is an n-type semiconductor containing indium sulfide or indium sulfide doped with other elements, a second electron transport layer which is an n-type oxide semiconductor doped with hydrogen elements, and a second electrode layer, in this order.

[0011] The present inventors have found that a solar cell including a first electron transport layer that is an n-type semiconductor containing indium sulfide or indium sulfide doped with other elements, and a second electron transport layer that is an n-type oxide semiconductor doped with hydrogen, tends to have improved heat resistance. In addition, the present inventors have found that the second electron transport layer can be formed by a sputtering method, which tends to reduce production costs.

[0012] In a method for manufacturing a solar cell according to one embodiment of the present invention, the solar cell comprises at least a first electrode layer, a light absorbing layer, a first electron transport layer that is an n-type semiconductor containing indium sulfide or indium sulfide doped with another element, a second electron transport layer that is an n-type oxide semiconductor doped with elemental hydrogen, and a second electrode layer, in this order, and the manufacturing method includes a first electron transport layer forming step of forming the first electron transport layer on a base material including the light absorbing layer by a sputtering method, and a second electron transport layer forming step of forming the second electron transport layer on the first electron transport layer by a sputtering method while supplying a gas containing an oxygen source and a hydrogen source.

[0013] The present inventors have found that in a method for manufacturing a solar cell, the heat resistance of a solar cell tends to be improved by including a first electron transport layer that is an n-type semiconductor containing indium sulfide or indium sulfide doped with another element, and a second electron transport layer that is an n-type oxide semiconductor doped with hydrogen. Furthermore, the present inventors have found that the second electron transport layer can be formed by a sputtering method, which tends to reduce production costs. Furthermore, the present inventors have found that in a method for manufacturing a solar cell, the second electron transport layer can be formed on the first electron transport layer without damaging the first electron transport layer by performing a sputtering method while supplying a gas containing an oxygen source and a hydrogen source, which tends to reduce production costs.

[0014] According to the present invention, it is possible to provide a solar cell having high heat resistance and low production costs, and a method for manufacturing the solar cell.

[0015] 1 is a diagram showing an example of a cross-sectional structure of a solar cell, and FIG. 2 is a diagram showing evaluation results of FF values.

[0016] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail with reference to the drawings as necessary. However, the present invention is not limited to this embodiment, and various modifications are possible without departing from the spirit of the present invention. In the drawings, the same elements are given the same reference numerals, and redundant explanations will be omitted. Furthermore, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[0017] 1. Solar Cell Fig. 1 is a diagram showing an example of a cross-sectional structure of a solar cell according to one embodiment of the present invention.

[0018] 1 , the solar cell 100 of this embodiment includes a substrate 108, a first electrode layer 101 provided on the substrate 108, a hole transport layer 102 provided on the first electrode layer 101, a light absorbing layer 103 provided on the hole transport layer 102, a first electron transport layer 104 provided on the light absorbing layer 103, a second electron transport layer 105 provided on the first electron transport layer 104, a second electrode layer 106 provided on the second electron transport layer 105, and a grid electrode 107 provided on the second electrode layer 106. The solar cell 100 receives light from the second electrode layer 106 side to generate electricity.

[0019] Although not shown, the solar cell 100 of this embodiment may have other layers between, above, or below each layer as needed. For example, the hole transport layer 102 may have a first hole transport layer and a second hole transport layer, and the grid electrode 107 may have an anti-contamination layer on it to prevent external contamination.

[0020] Although not shown, the solar cell 100 of this embodiment may have two or three sets of a hole transport layer 102, a light absorption layer 103 provided on the hole transport layer 102, a first electron transport layer 104 provided on the light absorption layer 103, a second electron transport layer 105 provided on the first electron transport layer 104, and a second electrode layer 106 provided on the second electron transport layer 105, each set being stacked on the first electrode layer 101. Furthermore, a grid electrode 107 may be provided on the uppermost second electrode layer 106.

[0021] The solar cell 100 of this embodiment includes, in this order, at least a first electrode layer 101, a light absorbing layer 103, a first electron transport layer 104 which is an n-type semiconductor containing indium sulfide or indium sulfide doped with other elements, a second electron transport layer 105 which is an n-type oxide semiconductor doped with hydrogen elements, and a second electrode layer 106. The solar cell 100 of this embodiment has the first electron transport layer 104 which is an n-type semiconductor containing indium sulfide or indium sulfide doped with other elements between the light absorbing layer 103 and the second electron transport layer 105. This makes it possible to prevent the alkali metal element contained in the light absorbing layer 103 from diffusing to the second electrode layer 106 even when the solar cell 100 is exposed to a high-temperature environment, and as a result, the solar cell 100 tends to have excellent heat resistance. This is thought to be due to the fact that the first electron transport layer 104, which is an n-type semiconductor containing indium sulfide or indium sulfide doped with other elements, functions as a diffusion prevention layer for preventing the diffusion of alkali metal elements in the light absorption layer 103, but the cause is not limited to this.

[0022] Furthermore, in conventional solar cells, in order to improve heat resistance, the electron transport layer in the solar cell has a two-layer structure, and the electron transport layer on the light absorption layer side contains indium sulfide. However, when the other electron transport layer is deposited on the electron transport layer containing indium sulfide by a sputtering method, the electron transport layer containing indium sulfide is easily damaged, so the other electron transport layer could not be formed by a sputtering method. Therefore, in conventional solar cells, it was necessary to form the other electron transport layer using a high-cost deposition method such as atomic layer deposition or chemical solution deposition while minimizing damage to the electron transport layer containing indium sulfide. Furthermore, while deposition methods such as chemical solution deposition are wet processes, most steps in the solar cell manufacturing process are dry processes. Therefore, using a wet process only when depositing the other electron transport layer not only increases costs but also takes a long time to manufacture.

[0023] On the other hand, in the solar cell 100 of this embodiment, by using an n-type oxide semiconductor doped with hydrogen as the second electron transport layer 105, the second electron transport layer 105 can be formed on the first electron transport layer 104 by sputtering, eliminating the need for costly film formation methods such as atomic layer deposition and chemical solution deposition. This is thought to be because, compared to forming an n-type oxide semiconductor without hydrogen by sputtering, the formation of an n-type oxide semiconductor doped with hydrogen by sputtering can be performed in an environment that reduces damage to the n-type semiconductor containing indium sulfide or indium sulfide doped with other elements. However, this is not the only possible reason. Furthermore, the sputtering method is a dry process, similar to the steps other than the formation of the electron transport layer in the solar cell manufacturing method. Therefore, the solar cell 100 can be manufactured by preparing only a dry process environment, without preparing both a wet process environment and a dry process environment. This also tends to reduce production costs and the manufacturing time.

[0024] Therefore, it is believed that the solar cell 100 of this embodiment has high heat resistance and low production costs, although the reasons for this are not limited to those mentioned above.

[0025] The thickness of the solar cell 100 excluding the substrate 108 is not particularly limited, but is, for example, 1.0 μm to 10.0 μm, 1.1 μm to 8.0 μm, or 1.2 μm to 6.0 μm.

[0026] The solar cell 100 of the present invention can be configured as a thin-film solar cell by forming each layer to be sufficiently thin.

[0027] Each component that may be included in the solar cell 100 will be described in detail below.

[0028] In this embodiment, when a compound is expressed by its name, it includes not only the pure compound itself, but also the compound to which trace amounts of elements, etc. have been added, as long as the properties of the compound are not lost.

[0029] Also, in this embodiment, because elements in each layer of the solar cell can exist in different oxidation states, all oxidation states are referred to by the name of the element unless otherwise expressly stated. For example, "elemental hydrogen" refers to hydrogen atoms, hydrogen ions, hydride ions, hydrogen in compounds, and hydrogen in elemental form.

[0030] 1.1. Substrate The substrate 108 is not particularly limited, but examples thereof include glass substrates such as soda lime glass and low-alkali glass, metal substrates such as stainless steel plates and aluminum foil, and resin substrates such as polyimide resin substrates and epoxy resin substrates. The thickness of the substrate 108 is not particularly limited, but is, for example, 10 μm to 500 μm, 20 μm to 250 μm, or 30 μm to 100 μm. Having the thickness of the substrate 108 within the above ranges tends to enable the solar cell to be lighter and more flexible.

[0031] 1.2. First Electrode Layer The first electrode layer 101 is provided, for example, to extract current due to holes generated in the light absorption layer 103 described below. The first electrode layer 101 is not particularly limited as long as it is conductive. For example, a metal conductive layer made of a metal such as Mo, Cr, or Ti; a conductive inorganic compound conductive layer made of a conductive inorganic compound other than a metal; or a conductive organic compound conductive layer made of a conductive organic compound can be used. The thickness of the first electrode layer 101 is not particularly limited, but is, for example, 200 nm to 800 nm, or 300 nm to 700 nm. Having the thickness of the first electrode layer 101 within the above range tends to enable the solar cell to be made lighter and more flexible while still extracting sufficient current without loss.

[0032] 1.3. Hole Transport Layer The solar cell 100 of this embodiment may have a hole transport layer 102. The hole transport layer 102 has the function of, for example, efficiently extracting holes generated in the light absorption layer 103 (described below) from the light absorption layer 103 and preventing recombination of electrons and holes generated simultaneously with the holes in the light absorption layer 103 (described below). The hole transport layer 102 is preferably a p-type semiconductor. The substance contained in the p-type semiconductor is not particularly limited, but examples thereof include inorganic compounds such as nickel oxide, molybdenum oxide, copper gallium oxide, copper aluminum oxide, molybdenum selenide, and molybdenum sulfide selenide. The p-type semiconductor in the hole transport layer 102 may be used alone or in combination of two or more types.

[0033] The hole transport layer 102 preferably consists essentially of the inorganic compound described above, and is preferably the inorganic compound described above. The content of the inorganic compound in the hole transport layer 102 is preferably 80% by mass to 100% by mass, 90% by mass to 100% by mass, 95% by mass to 100% by mass, or 99% by mass to 100% by mass, based on the total amount of the hole transport layer 102.

[0034] The thickness of the hole transport layer 102 is preferably 10 nm to 100 nm, 15 nm to 80 nm, or 20 nm to 60 nm. When the thickness of the hole transport layer 102 is within the above range, the layer has the function of efficiently extracting holes generated in the light absorbing layer 103 described below from the light absorbing layer 103 and preventing recombination of electrons and holes generated simultaneously with the holes in the light absorbing layer 103 described below, and tends to enable a lighter and more flexible solar cell.

[0035] 1.4. Light-Absorbing Layer The light-absorbing layer 103 has a function of absorbing light such as near-infrared light, visible light, and ultraviolet light to generate electrons and holes. Examples of light such as near-infrared light, visible light, and ultraviolet light include sunlight. The light-absorbing layer 103 preferably contains a chalcopyrite compound or a kesterite compound. The chalcopyrite compound may be used alone or in combination of two or more types. The kesterite compound may be used alone or in combination of two or more types.

[0036] The chalcopyrite compound is preferably I-III-VI ２ Group I-III-VI chalcopyrite compounds are also included. ２ The group chalcopyrite compound is not particularly limited, but for example, CuAlS ２ , CuAlSe ２ , CuAlTe ２ , CuGaS ２ , CuGaSe ２ , CuGaTe ２ , CuInS ２ , CuInSe ２ , CuInTe ２ , AgAlS ２ , AgAlSe ２ , AgAlTe ２ , AgGaS ２ , AgGaSe ２ , AgGaTe ２ , AgInS ２ , AgInSe ２ , AgInTe ２ The "combination of these" is not particularly limited, but examples thereof include CuGaS ２ and CuInSe ２ When combined with Cu(In ｘ Ga １－ｘ ) (Se ｙ S １－ｙ ) ２ (0≦x≦1, 0≦y≦1). Among these chalcopyrite compounds, CuGaS ２ , CuGaSe ２ , CuInS ２ , CuInSe ２ , Cu(In ｘ Ga １－ｘ ) (Se ｙ S １－ｙ ) ２ (0≦x≦1, 0≦y≦1) is preferred, and Cu(In ｘ Ga １－ｘ ) (Se ｙ S １－ｙ ) ２(0≦x≦1, 0≦y≦1) is more preferable. In the present embodiment, the term "CIS compound" refers to a chalcopyrite compound containing Cu, In, and Se, the term "CIGS compound" refers to a chalcopyrite compound containing Cu, In, Ga, and Se, and the term "CIGSS compound" refers to a chalcopyrite compound containing Cu, In, Ga, Se, and S.

[0037] The kesterite compound is preferably I ２ -II-IV-VI ４ Group I kesterite compounds are exemplified. ２ -II-IV-VI ４ The group kesterite compound is not particularly limited, but for example, Cu ２ ZnSnS ４ , Cu ２ ZnSnSe ４ , Cu ２ ZnGeS ４ , Cu ２ ZnGeSe ４ , Cu ２ MnSnS ４ , Cu ２ MnSnSe ４ , Cu ２ MnGeS ４ , Cu ２ MnGeSe ４ , Ag ２ ZnSnS ４ , Ag ２ ZnSnSe ４ , Ag ２ ZnGeS ４ , Ag ２ ZnGeSe ４ , Ag ２ MnSnS ４ , Ag ２ MnSnSe ４ , Ag ２ MnGeS ４ , Ag ２ MnGeSe ４ and combinations thereof. The "combinations thereof" are not particularly limited, but include, for example, Cu ２ ZnSnS ４ and Ag ２ ZnSnSe ４When combined with ｘ Ag １－ｘ ) ２ ZnSn(S ｙ Se １－ｙ ) ４ (0≦x≦1). ２ ZnSn(S ｘ Se １－ｘ ) ４ (0≦x≦1, 0≦y≦1). Among these kesterite compounds, Cu ２ ZnSnS ４ , Cu ２ ZnSnSe ４ , Ag ２ ZnSnS ４ , Ag ２ ZnSnSe ４ , (Cu ｘ Ag １－ｘ ) ２ ZnSn(S ｙ Se １－ｙ ) ４ (0≦x≦1, 0≦y≦1) is preferred, and (Cu ｘ Ag １－ｘ ) ２ ZnSn(S ｙ Se １－ｙ ) ４ (0≦x≦1, 0≦y≦1) is more preferable. In this embodiment, the term CZTS compound refers to a kesterite compound containing Cu, Zn, Sn, and S, the term ACZTS compound refers to a kesterite compound containing Ag, Cu, Zn, Sn, and S, and the term ACZTSS compound refers to a kesterite compound containing Ag, Cu, Zn, Sn, S, and Se.

[0038] The contents of the chalcopyrite compound and the kesterite compound in the light-absorbing layer 103 are not particularly limited as long as the light-absorbing layer 103 has the function of absorbing light such as visible light and ultraviolet light to generate electrons and holes. More specifically, although not particularly limited, the contents of the chalcopyrite compound and the kesterite compound are, relative to the total mass of the light-absorbing layer 103, 50% by mass to 100% by mass, 60% by mass to 100% by mass, 70% by mass to 100% by mass, 80% by mass to 100% by mass, or 90% by mass to 100% by mass.

[0039] The light absorbing layer 103 preferably contains an alkali metal element. Among the alkali metal elements, sodium, potassium, rubidium, and cesium are more preferably contained. When the light absorbing layer 103 contains an alkali metal element, the conversion efficiency of the solar cell tends to be improved.

[0040] The content of alkali metal elements in the light absorbing layer 103 is preferably 0% by mass or more and 2.0% by mass or less, 0% by mass or more and 1.0% by mass or less, or 0% by mass or more and 0.5% by mass or less.

[0041] The content of the alkali metal element in the light absorbing layer 103 is not particularly limited, but can be measured using, for example, ICP, EDX, or SIMS.

[0042] The thickness of the light absorbing layer 103 is preferably 0.5 μm to 10.0 μm, 0.5 μm to 7.5 μm, 0.5 μm to 5.0 μm, or 0.5 μm to 3.0 μm. When the thickness of the light absorbing layer 103 is within the above range, the solar cell tends to be lighter and more flexible while still having the function of absorbing light such as visible light and ultraviolet light to generate electrons and holes.

[0043] The solar cell 100 of this embodiment may have two light absorbing layers 103. In this case, the substance contained in the first light absorbing layer 103 and the substance contained in the second light absorbing layer 103 may be different or the same, but it is preferable that they are different. When the solar cell 100 has two light absorbing layers 103, the wavelength range of light that can be absorbed by the light absorbing layer 103 tends to be expanded, and as a result, the performance of the solar cell tends to be improved. Furthermore, the solar cell 100 of this embodiment may have three or more light absorbing layers 103.

[0044] 1.5. First Electron Transport Layer The first electron transport layer 104 is an n-type semiconductor containing indium sulfide or indium sulfide doped with other elements, and has the functions of preventing alkali metal elements contained in the light absorbing layer 103 from diffusing to the second electrode layer 106, efficiently extracting electrons generated in the light absorbing layer 103 from the light absorbing layer 103, and preventing recombination of holes and electrons generated simultaneously with the electrons in the light absorbing layer 103. Here, the other elements refer to elements other than sulfur and indium. Preferred examples of the other elements include oxygen and alkali metal elements. The other elements may be used alone or in combination of two or more. The alkali metal elements are preferably sodium and potassium, and the alkali metal elements may be used alone or in combination of two or more.

[0045] In indium sulfide to which other elements have been added, from the viewpoint of more reliably exhibiting the function of the first electron transport layer 104, the molar ratio of the other elements to the total moles of sulfur element and indium element is preferably more than 0 and 2.0 or less, 0.1 or more and 1.8 or less, 0.2 or more and 1.6 or less, or 0.3 or more and 1.4 or less.

[0046] In indium sulfide to which oxygen element has been added, from the viewpoint of more reliably exhibiting the function of the first electron transport layer 104, the molar ratio α of oxygen element to sulfur element is preferably more than 0 and 2.4 or less, 0.1 or more and 2.2 or less, 0.2 or more and 2.0 or less, 0.3 or more and 1.9 or less, 0.4 or more and 1.8 or less, or 0.5 or more and 1.7 or less.

[0047] In indium sulfide to which an alkali metal element is added, from the viewpoint of more reliably exhibiting the function of the first electron transport layer 104, the molar ratio β of the alkali metal element to the indium element is preferably more than 0 and 1.3 or less, 0.1 or more and 1.2 or less, 0.2 or more and 1.1 or less, 0.3 or more and 1.0 or less, 0.4 or more and 0.9 or less, or 0.5 or more and 0.8 or less.

[0048] In indium sulfide to which oxygen and alkali metal elements are added, from the viewpoint of more reliably exhibiting the functions of the first electron transport layer 104, the molar ratio α of oxygen element to sulfur element and the molar ratio β of alkali metal element to indium element are preferably 0 < α ≦ 2.4 and greater than 0 < β ≦ 1.3, 0.1 ≦ α ≦ 2.2 and 0.1 ≦ β ≦ 1.2, 0.2 ≦ α ≦ 2.0 and 0.2 ≦ β ≦ 1.1, 0.3 ≦ α ≦ 1.9 and 0.3 ≦ β ≦ 1.0, 0.4 ≦ α ≦ 1.8 and 0.4 ≦ β ≦ 0.9, or 0.5 ≦ α ≦ 1.7 and 0.5 ≦ β ≦ 0.8.

[0049] The first electron transport layer 104, which is an n-type semiconductor, is preferably composed essentially of indium sulfide or indium sulfide doped with other elements, and is preferably indium sulfide or indium sulfide doped with other elements. The content of indium sulfide or indium sulfide doped with other elements in the first electron transport layer 104, which is an n-type semiconductor, is preferably 80% by mass or more and 100% by mass or less, 90% by mass or more and 100% by mass or less, 95% by mass or more and 100% by mass or less, or 99% by mass or more and 100% by mass or less, relative to the total amount of the first electron transport layer 104.

[0050] The thickness of the first electron transport layer 104 is preferably 10 nm or more and 40 nm or less, 15 nm or more and 35 nm or less, or 17 nm or more and 30 nm or less. Having the thickness of the first electron transport layer 104 within the above ranges prevents the alkali metal element contained in the light absorbing layer 103 from diffusing to the second electrode layer 106, efficiently extracts electrons generated in the light absorbing layer 103 from the light absorbing layer 103, and prevents recombination of holes and electrons generated simultaneously with the electrons in the light absorbing layer 103. This tends to enable a lighter and more flexible solar cell. Furthermore, indium sulfide has a band gap of about 2.1 eV and is not highly transparent to sunlight. However, having the thickness of the first electron transport layer 104 within the above ranges tends to improve the sunlight transmittance of the first electron transport layer 104, thereby improving the performance of the solar cell. Furthermore, although indium sulfide has high resistance, by setting the thickness of the first electron transport layer 104 within the above range, the high resistance is prevented from adversely affecting the performance of the solar cell, and the performance of the solar cell tends to improve.

[0051] 1.6. Second Electron Transport Layer The second electron transport layer 105 is an n-type oxide semiconductor doped with hydrogen elements, and has the function of efficiently extracting electrons generated in the light absorbing layer 103 from the light absorbing layer 103 and preventing recombination of holes and electrons generated simultaneously with the electrons in the light absorbing layer 103.

[0052] The band gap of the n-type oxide semiconductor doped with hydrogen elements is preferably 3.3 eV or more, 3.4 eV or more, 3.5 eV or more, or 3.6 eV or more. The band gap of the n-type oxide semiconductor doped with hydrogen elements is not particularly limited, but is, for example, 3.3 eV or more and 5.0 eV or less, 3.4 eV or more and 4.5 eV or less, or 3.5 eV or more and 4.0 eV or less. Having the band gap within the above range improves the transparency of the second electron transport layer 105, thereby increasing the amount of light absorbed by the light absorption layer 103, and as a result, the conversion efficiency of the solar cell tends to improve.

[0053] The band gap can be measured by any known method, including, but not limited to, spectral transmittance measurement, spectral quantum efficiency measurement, or the like.

[0054] The carrier concentration of the n-type oxide semiconductor to which hydrogen elements have been added is preferably 1.0×10 ２０ cm －３ is less than or equal to 5.0 × 10 １９ cm －３ is less than or equal to 2.5 × 10 １９ cm －３ The carrier concentration of the n-type oxide semiconductor doped with hydrogen is not particularly limited, but is, for example, 1.0×10 １６ cm －３ Above 1.0 x 10 ２０ cm －３ is less than or equal to 1.0 × 10 １７ cm －３ Above 5.0 x 10 １９ cm －３ is less than or equal to 1.0 × 10 １８ cm －３ 2.5 x 10 or more １９ cm －３ When the carrier concentration is within the above range, electrons generated in the light absorbing layer 103 can be efficiently extracted from the light absorbing layer 103, and it becomes possible to prevent recombination of holes and electrons generated simultaneously with the electrons in the light absorbing layer 103, and as a result, the conversion efficiency of the solar cell tends to improve.

[0055] The carrier concentration can be measured by a known method, and more specifically, although not particularly limited, for example, the carrier concentration can be measured by Hall measurement.

[0056] The refractive index of the n-type oxide semiconductor doped with hydrogen is preferably 2.1 or higher. The refractive index of the n-type oxide semiconductor doped with hydrogen is not particularly limited, but is, for example, 2.1 or higher and 2.8 or lower, such as 2.1 or higher and 2.6 or lower. The first electron transport layer 104 is an n-type semiconductor containing indium sulfide or indium sulfide doped with other elements. Since the refractive index of indium sulfide is as high as approximately 2.8, the refractive index of the first electron transport layer 104 is also high. Therefore, using a semiconductor with a low refractive index as the second electron transport layer 105 tends to increase light reflection at the interface between the electron transport layers, resulting in reduced solar cell performance. On the other hand, using an n-type oxide semiconductor doped with hydrogen and having a refractive index within the above range as the second electron transport layer 105 can suppress light reflection at the interface between the first electron transport layer 104 and the second electron transport layer 105, resulting in improved solar cell conversion efficiency.

[0057] The refractive index can be measured by any known method, including, but not limited to, spectral transmittance measurement, spectroscopic ellipsometry, or the like.

[0058] The specific resistance of the n-type oxide semiconductor to which hydrogen elements are added is preferably 1.6×10 －２ Ωcm or more, and 1.8×10 －２ Ωcm or more, and 2.0×10 －２ The resistivity of the n-type oxide semiconductor doped with hydrogen is not particularly limited, but is, for example, 1.6×10 －２ Ωcm or more 1.0 x 10 ２ Ωcm or less, and is 1.8×10 －２ Ωcm or more and 10.0 Ωcm or less, and 2.0×10 －２ When the resistivity is in the above range, the conversion efficiency of the solar cell tends to be improved.

[0059] The resistivity can be measured by a known method. More specifically, although not particularly limited, the resistivity can be measured by a four-probe method, for example.

[0060] The n-type oxide semiconductor to which hydrogen elements are added has a band gap of 3.3 eV or more and a carrier concentration of 1.0×10 ２０ cm －３ Furthermore, the n-type oxide semiconductor doped with hydrogen preferably has a band gap of 3.3 eV or more and a carrier concentration of 1.0×10 ２０ cm －３ The refractive index is 2.1 or more, and the resistivity is 1.6×10 －２ Preferably, it is Ωcm or more.

[0061] The band gap is 3.3 eV or more, and the carrier concentration is 1.0×10 ２０ cm －３ The refractive index is 2.1 or more, and the resistivity is 1.6×10 －２ In the n-type oxide semiconductor doped with hydrogen having a resistivity of Ωcm or more, the substance contained in the n-type oxide semiconductor is preferably titanium oxide, zinc oxide doped with sulfur, or zinc oxide doped with titanium. Among these, zinc oxide doped with titanium is preferred. The n-type oxide semiconductor may be used alone or in combination of two or more.

[0062] In zinc oxide to which sulfur element has been added, from the viewpoint of more reliably exhibiting the function of the second electron transport layer 105, the molar ratio of sulfur element to oxygen element is preferably 0 or more and 0.7 or less, or 0.1 or more and 0.4 or less.

[0063] In zinc oxide to which titanium element has been added, from the viewpoint of more reliably exhibiting the function of the second electron transport layer 105, the molar ratio of titanium element to zinc element is preferably 0 or more and 0.3 or less, or 0.05 or more and 0.2 or less.

[0064] In the n-type oxide semiconductor to which hydrogen elements have been added, from the viewpoint of more reliably exhibiting the functions of the second electron transport layer 105, the molar ratio of hydrogen elements to all metal elements is preferably 0.001 or more and 0.030 or less, 0.005 or more and 0.020 or less, 0.007 or more and 0.015 or less, or 0.009 or more and 0.013 or less.

[0065] The second electron transport layer 105, which is an n-type oxide semiconductor to which hydrogen elements have been added, may be an electron transport layer formed by a method in a second electron transport layer forming step, which will be described later.

[0066] The second electron transport layer 105, which is an n-type oxide semiconductor, preferably consists essentially of titanium oxide, zinc oxide doped with elemental sulfur, or zinc oxide doped with elemental titanium, and is preferably titanium oxide, zinc oxide doped with elemental sulfur, or zinc oxide doped with elemental titanium. The content of titanium oxide, zinc oxide doped with elemental sulfur, or zinc oxide doped with elemental titanium in the second electron transport layer 105, which is an n-type oxide semiconductor, is preferably 80% by mass or more and 100% by mass or less, 90% by mass or more and 100% by mass or less, 95% by mass or more and 100% by mass or less, or 99% by mass or more and 100% by mass or less, relative to the total amount of the second electron transport layer 105.

[0067] The thickness of the second electron transport layer 105 is preferably 50 nm to 120 nm, 55 nm to 110 nm, or 60 nm to 100 nm. When the thickness of the second electron transport layer 105 is within the above range, the layer has the function of efficiently extracting electrons generated in the light absorbing layer 103 from the light absorbing layer 103 and preventing recombination of holes and electrons generated simultaneously with the electrons in the light absorbing layer 103, and tends to enable a lighter and more flexible solar cell.

[0068] 1.7. Second Electrode Layer The second electrode layer 106 is provided, for example, to extract a current due to electrons generated in the light absorbing layer 103. In the solar cell 100, the light absorbing layer 103 absorbs light that has passed through the second electrode layer 106. Therefore, in order to increase the amount of light absorbed by the light absorbing layer 103, the second electrode layer 106 is preferably a transparent electrode layer. A transparent electrode is an electrode made of a material that has both high electrical conductivity and high visible light transmittance. High electrical conductivity is not particularly limited, but may be, for example, a material having a specific resistance of 5.0×10 －３This means that the transmittance is Ωcm or less. High visible light transmittance is not particularly limited, but means, for example, an average transmittance of 80% or more in the wavelength region of 400 to 1300 nm. Known materials can be used as the material for the transparent electrode, and examples thereof include indium tin oxide (ITO), hydrogen-containing indium oxide (IOH), fluorine-containing tin oxide (FTO), boron-containing zinc oxide (ZnO:B), and aluminum-containing zinc oxide (ZnO:Al).

[0069] The content of the above-mentioned material in the second electrode layer 106 is not particularly limited as long as the second electrode layer 106 functions as a transparent electrode. More specifically, although not particularly limited, the content of the above-mentioned material is, relative to the total mass of the second electrode layer 106, 50% by mass to 100% by mass, 60% by mass to 100% by mass, 70% by mass to 100% by mass, 80% by mass to 100% by mass, 90% by mass to 100% by mass, or 95% by mass to 100% by mass.

[0070] The thickness of the second electrode layer 106 is not particularly limited, but is, for example, 100 nm to 1500 nm, or 200 nm to 1000 nm. When the thickness of the second electrode layer 106 is within the above range, it tends to be possible to make the solar cell lighter and more flexible while sufficiently extracting current without loss.

[0071] 1.8 Grid Electrode The grid electrode 107 is provided, for example, to extract electricity from the second electrode layer 106. The material of the grid electrode 107 is not particularly limited as long as it is conductive, and examples of materials that can be used include metals such as Mo, Cr, Ag, Cu, Ni, Al, and Ti; conductive inorganic compounds other than metals; and conductive organic compounds.

[0072] The content of the above-mentioned material in the grid electrode 107 is not particularly limited as long as the grid electrode 107 functions as an electrode. More specifically, although not particularly limited, the content of the above-mentioned material relative to the total mass of the grid electrode 107 is 50% by mass to 100% by mass, 60% by mass to 100% by mass, 70% by mass to 100% by mass, 80% by mass to 100% by mass, or 90% by mass to 100% by mass.

[0073] The thickness of the grid electrode 107 is not particularly limited, but is, for example, 5 μm to 50 μm. When the thickness of the grid electrode 107 is within the above range, the solar cell tends to be lighter and more flexible while allowing sufficient current to be extracted without loss.

[0074] 2. Manufacturing Method of Solar Cell In a manufacturing method of a solar cell 100 of this embodiment, the solar cell 100 includes, in this order, at least a first electrode layer 101, a light absorbing layer 103, a first electron transport layer 104 which is an n-type semiconductor containing indium sulfide or indium sulfide doped with another element, a second electron transport layer 105 which is an n-type oxide semiconductor doped with a hydrogen element, and a second electrode layer 106, and the manufacturing method includes a first electron transport layer forming step of forming the first electron transport layer 104 on a base material including the light absorbing layer 103 by a sputtering method, and a second electron transport layer forming step of forming the second electron transport layer 105 on the first electron transport layer 104 by a sputtering method while supplying a gas containing an oxygen source and a hydrogen source.

[0075] The solar cell 100 manufactured by the manufacturing method of this embodiment has the first electron transport layer 104, which is an n-type semiconductor containing indium sulfide or indium sulfide doped with other elements, between the light absorbing layer 103 and the second electron transport layer 105. This prevents the alkali metal element contained in the light absorbing layer 103 from diffusing to the second electrode layer 106, even when the solar cell 100 is exposed to a high-temperature environment. As a result, the solar cell 100 tends to have excellent heat resistance. This is thought to be due to the first electron transport layer 104, which is an n-type semiconductor containing indium sulfide or indium sulfide doped with other elements, functioning as a diffusion prevention layer for preventing the diffusion of the alkali metal element in the light absorbing layer 103, but the reason for this is not limited to this.

[0076] In conventional solar cell manufacturing methods, in order to improve the heat resistance of solar cells, the electron transport layer in a solar cell has a two-layer structure, and the electron transport layer on the light-absorbing layer side contains indium sulfide. However, when the other electron transport layer is deposited by sputtering on the electron transport layer containing indium sulfide, the electron transport layer containing indium sulfide is easily damaged, so it is not possible to form the other electron transport layer by sputtering. Therefore, in conventional solar cells, it is necessary to form the other electron transport layer by a high-cost deposition method such as atomic layer deposition or chemical solution deposition while minimizing damage to the electron transport layer containing indium sulfide. Furthermore, while deposition methods such as chemical solution deposition are wet processes, most steps in the solar cell manufacturing method are dry processes. Therefore, using a wet process only when depositing the other electron transport layer not only increases costs but also takes a long time to manufacture.

[0077] On the other hand, in the manufacturing method of the solar cell 100 of this embodiment, sputtering is performed while supplying a gas containing an oxygen source and a hydrogen source. This allows the second electron transport layer 105, which is an n-type oxide semiconductor, to be formed on the first electron transport layer 104 by sputtering while suppressing damage to the first electron transport layer 104, which is an n-type semiconductor containing indium sulfide or indium sulfide doped with other elements. This eliminates the need for costly film formation methods such as atomic layer deposition and chemical solution deposition. Sputtering in an environment containing an oxygen source generates active species, such as oxygen plasma, generated from the oxygen source. It is believed that excessive generation of these active species, such as oxygen plasma, can damage the first electron transport layer 104, which is an n-type semiconductor containing indium sulfide or indium sulfide doped with other elements. On the other hand, in the manufacturing method of this embodiment, the gas supplied during sputtering contains a hydrogen source. Therefore, the oxygen source concentration in the supply gas is kept within an appropriate range. Furthermore, hydrogen interacts with oxygen, thereby appropriately suppressing the generation of active species, such as oxygen plasma. As a result, it is considered that damage caused by active species such as oxygen plasma to the first electron transport layer 104, which is an n-type semiconductor containing indium sulfide or indium sulfide doped with other elements, is reduced, and therefore it is possible to form the second electron transport layer 105, which is an n-type oxide semiconductor, on the first electron transport layer 104 by a sputtering method while suppressing damage to the first electron transport layer 104. However, the factors behind this are not limited to those mentioned above.

[0078] Furthermore, since the sputtering method is a dry process similar to the steps other than the deposition of the electron transport layer in the manufacturing method of a solar cell, when manufacturing the solar cell 100, it is possible to manufacture the solar cell 100 by preparing only an environment for the dry process, without having to prepare both an environment for the wet process and an environment for the dry process. This also tends to reduce production costs and the time required for manufacturing.

[0079] Therefore, it is believed that the solar cell 100 manufactured by the manufacturing method of this embodiment has high heat resistance and low production costs, although the reasons for this are not limited to those mentioned above.

[0080] Hereinafter, each step that may be included in the method for manufacturing the solar cell 100 of this embodiment will be described in detail. In this embodiment, a wet process refers to a step that uses a solution, and a dry process refers to a step that does not use a solution.

[0081] 2.1. First Electrode Layer Formation Step In the first electrode layer formation step, for example, the first electrode layer 101 may be formed on the substrate 108. Methods for forming the first electrode layer 101 include dry processes and wet processes, with the dry process being preferred. The dry process is not particularly limited, but an example is a method for forming the first electrode layer 101, which is a metal conductive layer, by a sputtering method. The film formation conditions for the sputtering method are not particularly limited, but for example, applied power: 1.0 to 3.0 W / cm ２ The film formation atmosphere may be an argon atmosphere, and the film formation pressure may be 0.5 to 3.0 Pa. The temperature of the atmosphere and the temperature of the sputtering substrate may not be controlled during sputtering. The sputtering substrate refers to a substrate on a stage during sputtering, on which a compound derived from the sputtering target is deposited. In the first electrode layer formation step, for example, the substrate 108 may be the sputtering substrate.

[0082] 2.2. Hole Transport Layer Forming Step In the hole transport layer forming step, for example, the hole transport layer 102 may be formed on the first electrode layer 101. Methods for forming the hole transport layer 102 include dry processes and wet processes, with the dry process being preferred. The dry process is not particularly limited, but an example is a method for forming the hole transport layer 102, which is a p-type semiconductor containing an inorganic compound, by a sputtering method. The film formation conditions for the sputtering method are not particularly limited, but for example, applied power: 0.5 to 3.0 W / cm ２The film formation atmosphere may be an argon atmosphere, and the film formation pressure may be 0.5 to 3.0 Pa. The temperature of the atmosphere and the temperature of the substrate to be sputtered may not be controlled during sputtering. When forming the light absorbing layer 103, a compound may be formed between the elements of the first electrode layer 101 and the elements contained in the light absorbing layer 103, and the hole transport layer 102 may be formed between the first electrode layer 101 and the light absorbing layer 103.

[0083] 2.3. Light-Absorbing Layer Forming Step In the light-absorbing layer forming step, for example, the light-absorbing layer 103 may be formed on the hole-transporting layer 102. When the hole-transporting layer 102 is not provided, the light-absorbing layer 103 may be formed on the first electrode layer 101. Methods for forming the light-absorbing layer 103 include a dry process and a wet process, with a dry process being preferred. The dry process is not particularly limited, but an example is a method of forming the light-absorbing layer 103 containing a chalcopyrite compound or a kesterite compound by a sputtering method. The film-forming conditions for the sputtering method are not particularly limited, but for example, applied power: 0.5 to 3.0 W / cm ２ The deposition atmosphere may be an argon atmosphere, and the deposition pressure may be 0.5 to 3.0 Pa. The temperature of the atmosphere and the temperature of the substrate to be sputtered may not be controlled during sputtering. After sputtering, annealing may be performed at 350° C. or higher and 650° C. or lower in a nitrogen or selenium and sulfur atmosphere.

[0084] When the light absorbing layer 103 contains an alkali metal element, the light absorbing layer forming step preferably uses a sputtering target doped with an alkali metal element to form the light absorbing layer 103 containing a chalcopyrite compound or a kesterite compound by a sputtering method. Alternatively, the alkali metal element may be added to the substrate 108 or the first electrode layer 101, and the alkali metal element may be thermally diffused into the light absorbing layer 103 during the formation of the light absorbing layer 103.

[0085] 2.4. First Electron Transport Layer Forming Step In the first electron transport layer forming step, the first electron transport layer 104 is formed by a sputtering method on the substrate including the light absorbing layer 103. In the first electron transport layer forming step, for example, the substrate has the light absorbing layer 103 as the outermost layer, and the light absorbing layer 103 may contain a chalcopyrite compound or a kesterite compound.

[0086] The film formation conditions for the sputtering method are not particularly limited. For example, when the first electron transport layer 104 is an n-type semiconductor containing indium sulfide, the applied power is 0.5 to 3.0 W / cm. ２ The film formation atmosphere may be an argon atmosphere, and the film formation pressure may be 0.5 to 3.0 Pa. The temperature of the atmosphere does not need to be controlled during sputtering. On the other hand, during sputtering, the base material including the light absorbing layer 103 is preferably heated to 150°C or higher and 250°C or lower, preferably 160°C or higher and 250°C or lower, preferably 170°C or higher and 250°C or lower, preferably 180°C or higher and 250°C or lower, preferably 190°C or higher and 250°C or lower, and preferably 200°C or higher and 250°C or lower. When a metal substrate is used as the substrate 108, the temperature of the base material and the heating temperature are approximately the same.

[0087] When the first electron transport layer 104 is an n-type semiconductor containing indium sulfide doped with oxygen element, the first electron transport layer 104, which is an n-type semiconductor containing indium sulfide doped with oxygen element, can be formed, for example, by performing sputtering under an argon-oxygen mixed gas atmosphere as the film formation atmosphere and other film formation conditions similar to those in the case where the n-type semiconductor contains indium sulfide, without any particular limitation.

[0088] When the first electron transport layer 104 is an n-type semiconductor containing indium sulfide doped with an alkali metal element, the first electron transport layer 104, which is an n-type semiconductor containing indium sulfide doped with an alkali metal element, can be formed, for example, by performing sputtering using a sputtering target doped with an alkali metal element under other film formation conditions similar to those in the case where the n-type semiconductor contains indium sulfide, although this is not particularly limited.

[0089] When the first electron transport layer 104 is an n-type semiconductor containing indium sulfide doped with oxygen element and alkali metal element, the first electron transport layer 104, which is an n-type semiconductor containing indium sulfide doped with oxygen element and alkali metal element, can be formed, for example, by performing sputtering under an argon-oxygen mixed gas atmosphere as the film formation atmosphere, using a sputtering target doped with an alkali metal element, and other film formation conditions similar to those in the case where the n-type semiconductor contains indium sulfide, without any particular limitation.

[0090] 2.5. Second Electron Transport Layer Forming Step In the second electron transport layer forming step, the second electron transport layer 105 is formed on the first electron transport layer 104 by sputtering while supplying a gas containing an oxygen source and a hydrogen source.

[0091] The sputtering target need only contain elements contained in the n-type oxide semiconductor to be formed, preferably a metal element contained in the n-type oxide semiconductor to be formed, and preferably an oxide of the metal contained in the n-type oxide semiconductor to be formed. The contents of metal elements and other elements including oxygen and sulfur in the n-type oxide semiconductor to be formed are not particularly limited, but can be controlled, for example, by adjusting the elements added to the sputtering target. The sputtering target is preferably titanium oxide, a mixture of zinc oxide and zinc sulfide, or a mixture of zinc oxide and titanium oxide, and more preferably a mixture of zinc oxide and titanium oxide. When the n-type oxide semiconductor contains titanium oxide, it is preferable to use titanium oxide as the sputtering target. When the n-type oxide semiconductor contains zinc oxide doped with sulfur, it is preferable to use a mixture of zinc oxide and zinc sulfide as the sputtering target. When the n-type oxide semiconductor contains zinc oxide doped with titanium, it is preferable to use a mixture of zinc oxide and titanium oxide as the sputtering target. The content of titanium oxide in the mixture of zinc oxide and titanium oxide that is the sputtering target is preferably 4.0 mass% or more and 20 mass% or less, 5.0 mass% or more and 19 mass% or less, or 6.0 mass% or more and 18 mass% or less, relative to the total mass of the mixture.

[0092] The gas supplied during sputtering includes an oxygen source and a hydrogen source. The gas preferably contains argon gas as a main component. The oxygen source is not particularly limited as long as it contains oxygen element. For example, H ２ O steam, O ２ Gas, O ３ Gases include O ２ The hydrogen source is not particularly limited as long as it is a gas containing hydrogen element, but for example, H ２ O vapor, H ２ Gases include H ２ Gas is preferred.

[0093] The concentration of the oxygen source in the gas supplied during sputtering is preferably 0.8% by volume or more and 1.6% by volume or less, 0.9% by volume or more and 1.5% by volume or less, or 1.0% by volume or more and 1.5% by volume or less, in terms of oxygen molecules. The concentration of the oxygen source in terms of oxygen molecules is specifically calculated as follows. ２ When O vapor, H ２ Since O vapor contains one oxygen element, H ２ When the concentration of O vapor is 1.0% by volume, the concentration of the oxygen source in terms of oxygen molecules is 0.5% by volume, which is half of 1.0% by volume. ２ When gas, O ２ Since the gas contains two oxygen elements, the O ２ When the gas concentration is 1.0% by volume, the concentration of the oxygen source in terms of oxygen molecules is 1.0% by volume.

[0094] The molar ratio of hydrogen element to oxygen element contained in the gas supplied during sputtering is preferably 1.0 to 2.0 times, 1.2 to 2.0 times, or 1.4 to 2.0 times. The molar ratio of hydrogen element to oxygen element is specifically calculated as follows. ２ Gas, H as hydrogen source ２ When the concentration of the oxygen source in the gas is 0.8% by volume and the concentration of the hydrogen source in the gas is 1.6% by volume, the hydrogen source H ２O vapor has two hydrogen atoms and one oxygen atom per molecule, and the oxygen source O ２ The gas has two oxygen atoms per molecule, so the molar ratio of hydrogen atoms to oxygen atoms is calculated as (1.6 x 2) / (1.6 + 0.8 x 2) = 1.0.

[0095] The concentration of argon gas in the gas supplied during sputtering is not particularly limited, but is, for example, 90.0 vol.% or more and 99.0 vol.% or less, 91.0 vol.% or more and 98.5 vol.% or less, 92.0 vol.% or more and 98.0 vol.% or less, 93.0 vol.% or more and 97.5 vol.% or less, or 94.0 vol.% or more and 97.0 vol.% or less.

[0096] During sputtering, the laminate including the substrate including the light absorbing layer 103 and the first electron transport layer 104 formed on the substrate is preferably heated at a temperature of 100° C. or higher and 200° C. or lower, and more preferably at a temperature of 125° C. or higher and 175° C. When a metal substrate is used as the substrate 108, the temperature of the laminate and the heating temperature are approximately the same.

[0097] Other film formation conditions for the sputtering method are not particularly limited, but for example, applied power: 0.5 to 3.0 W / cm ２ The deposition pressure may be 0.5 to 3.0 Pa. The temperature of the atmosphere does not need to be controlled during sputtering.

[0098] 2.6. Second Electrode Layer Forming Step In the second electrode layer forming step, for example, the second electrode layer 106 may be formed on the second electron transport layer 105. Methods for forming the second electrode layer 106 include dry processes and wet processes, with the dry process being preferred. The dry process is not particularly limited, but an example is a method for forming the second electrode layer 106, which is a transparent electrode layer, by a sputtering method. The film formation conditions for the sputtering method are not particularly limited, but for example, applied power: 0.5 to 3.0 W / cm ２ The film formation atmosphere may be an argon atmosphere, and the film formation pressure may be 0.5 to 3.0 Pa. During sputtering, the temperature of the atmosphere and the temperature of the substrate to be sputtered do not need to be controlled.

[0099] 2.7 Grid Electrode Forming Process In the grid electrode forming process, for example, a grid electrode 107 may be formed on the second electrode layer 106. Methods for forming the grid electrode 107 include a dry process and a wet process. Specific examples include sputtering, vapor deposition, a method of printing a paste-like conductive material on the second electrode layer 106, and a method of crimping a conductive wire.

[0100] 3. Method of Using Solar Cell Like conventional solar cells, solar cell 100 of this embodiment can be used in normal temperature environments where the temperature of the solar cell is about 45 to 85° C. Furthermore, unlike conventional solar cells, solar cell 100 of this embodiment can be suitably used in high-temperature environments where the temperature of the solar cell exceeds 85° C. (for example, space, the stratosphere, the desert, the tropics, the rooftop of a building, the roof of a car, the exterior wall of an airplane, etc.).

[0101] The solar cell 100 of this embodiment can also be used as an independent power source device for street lights, sensors, digital signage, etc. The solar cell 100 of this embodiment can also be used as a mobile energy device.

[0102] <Additional Notes> Embodiments of the present disclosure include the following aspects. [1] A solar cell comprising, in this order, at least a first electrode layer, a light absorbing layer, a first electron transport layer that is an n-type semiconductor containing indium sulfide or indium sulfide doped with another element, a second electron transport layer that is an n-type oxide semiconductor doped with elemental hydrogen, and a second electrode layer. [2] The solar cell according to [1], wherein the first electron transport layer is provided on the light absorbing layer, and the second electron transport layer is provided on the first electron transport layer. [3] The solar cell according to [1] or [2], wherein the first electron transport layer has a thickness of 10 nm or more and 40 nm or less, and the second electron transport layer has a thickness of 50 nm or more and 120 nm or less. [4] The solar cell according to any one of [1] to [3], wherein the light absorbing layer contains a chalcopyrite compound or a kesterite compound. [5] The n-type oxide semiconductor has a band gap of 3.3 eV or more and a carrier concentration of 1.0×10 ２０ cm －３

[0013] The solar cell according to any one of [1] to [4], wherein the n-type oxide semiconductor is an oxide semiconductor having a refractive index of 2.1 or more and a refractive index of 2.1 or more. [6] The solar cell according to [5], wherein the n-type oxide semiconductor comprises titanium oxide, zinc oxide doped with elemental sulfur, or zinc oxide doped with elemental titanium. [7] A method for manufacturing a solar cell, wherein the solar cell comprises, in this order, at least: a first electrode layer, a light absorbing layer, a first electron transport layer which is an n-type semiconductor containing indium sulfide or indium sulfide doped with other elements, a second electron transport layer which is an n-type oxide semiconductor doped with elemental hydrogen, and a second electrode layer, the manufacturing method comprising: a first electron transport layer forming step of forming the first electron transport layer on a base material including the light absorbing layer by a sputtering method; and a second electron transport layer forming step of forming the second electron transport layer on the first electron transport layer by a sputtering method while supplying a gas including an oxygen source and a hydrogen source. [8] The manufacturing method according to [7], wherein the base material has the light absorbing layer on an outermost surface layer, and the light absorbing layer contains a chalcopyrite compound or a kesterite compound. [9] The manufacturing method according to [7] or [8], wherein the concentration of the oxygen source in the gas supplied in the second electron transport layer forming step is 0.8 volume % or more and 1.6 volume % or less in terms of oxygen molecules.

[10] The manufacturing method according to any one of [7] to [9], wherein the molar ratio of hydrogen elements to oxygen elements contained in the gas supplied in the second electron transport layer forming step is 1.0 times or more and 2.0 times or less.

[11] The n-type oxide semiconductor has a band gap of 3.3 eV or more and a carrier concentration of 1.0 x 10 ２０ cm －３

[12] The manufacturing method according to any one of

[11] to

[12] , wherein the n-type oxide semiconductor comprises titanium oxide, zinc oxide doped with elemental sulfur, or zinc oxide doped with elemental titanium.

[13] The manufacturing method according to any one of

[11] to

[12] , wherein the n-type oxide semiconductor is zinc oxide doped with elemental titanium, and the second electron transport layer forming step is performed using a mixture of zinc oxide and titanium oxide containing 4.0 mass % to 20 mass % titanium oxide as a sputtering target.

[14] The manufacturing method according to

[13] , wherein the first electron transport layer forming step is performed while heating the substrate at 150° C. to 250° C., and the second electron transport layer forming step is performed while heating a stack including the substrate and the first electron transport layer formed on the substrate at 100° C. to 200° C.

[0103] The present invention will be described in more detail below using examples and comparative examples. The present invention is not limited to the following examples. Unless otherwise specified, the examples were carried out at room temperature (25°C) and under 1 atmosphere.

[0104] 1. Fabrication of Solar Cell In Example 1, a titanium foil having a thickness of 50 μm was used as the substrate 108. A first electrode layer 101 containing metallic molybdenum was formed on the substrate 108 by sputtering to a thickness of 600 nm.

[0105] Next, a light absorbing layer 103 containing alkali metal elements sodium and potassium and a CIGSS compound was formed to a thickness of 2 μm by sputtering on the first electrode layer 101. When forming the light absorbing layer 103, a hole transport layer 102 containing molybdenum selenide was formed to a thickness of 50 nm between the first electrode layer 101 and the light absorbing layer 103.

[0106] Next, a first electron transport layer 104, which is an n-type semiconductor containing indium sulfide, was formed to a thickness of 30 nm on the light absorption layer 103 by sputtering under the following conditions: sputtering target: indium sulfide, film formation atmosphere: argon atmosphere, heating temperature of the sputtered substrate during film formation: 200° C.

[0107] Next, a second electron transport layer 105, which is an n-type oxide semiconductor containing zinc oxide doped with hydrogen and titanium, was formed on the first electron transport layer 104 by sputtering to a thickness of 70 nm. The amount of hydrogen in the second electron transport layer 105 was measured by RBS / HFS, and the molar ratio of hydrogen to all metal elements was found to be 0.011. The sputtering conditions were as follows: Sputtering target: a mixture of zinc oxide and titanium oxide (the mixture ratio is shown in Tables 1 to 3); Film formation atmosphere: an argon / hydrogen gas / oxygen gas atmosphere (proportion of hydrogen gas in the supplied mixed gas: 1.6% by volume, proportion of oxygen gas in the mixed gas: 1.2% by volume); Heating temperature of the sputtered substrate during film formation: 160° C.

[0108] Next, a second electrode layer 106, which is a transparent electrode layer containing hydrogen-containing indium oxide (IOH), was formed on the second electron transport layer 105 by sputtering to a thickness of 300 nm.

[0109] The solar cell of Example 1 was fabricated as described above. The solar cells of Examples 2 to 11 were fabricated in the same manner as Example 1, except that the parameters shown in Tables 1 to 3 were used. In Tables 1 to 3, "First electron transport layer deposition temperature (°C)" and "Second electron transport layer deposition temperature (°C)" indicate the heating temperature of the sputtered substrate during deposition. ２ The "ratio (%)" indicates the ratio of TiO ２ Indicates the percentage of.

[0110] Except for the first electron transport layer, the solar cell of Comparative Example 1 was fabricated in the same manner as the solar cell of Example 1. In the solar cell of Comparative Example 1, a first electron transport layer, which was an n-type semiconductor containing cadmium sulfide, was formed to a thickness of 30 nm on the light absorbing layer using a chemical solution deposition method.

[0111] The solar cell of Comparative Example 2 was fabricated in the same manner as the solar cell of Example 1, except that the step of forming the first electron transport layer was not performed and the conditions for the step of forming the second electron transport layer were changed. In the solar cell of Comparative Example 2, a second electron transport layer, which was an n-type oxide semiconductor containing zinc oxide doped with hydrogen and titanium, was formed to a thickness of 100 nm on the light absorption layer using a sputtering method. The conditions for the sputtering method were as follows: Sputtering target: a mixture of zinc oxide and titanium oxide (mixing ratio shown in Tables 1 to 3); Film formation atmosphere: an argon / hydrogen gas / oxygen gas atmosphere (proportion of hydrogen gas in the supplied mixed gas: 1.6 vol %, proportion of oxygen gas in the mixed gas: 1.2 vol %); Heating temperature of the sputtered substrate during film formation: 160°C

[0112] The solar cell of Comparative Example 3 was fabricated in the same manner as the solar cell of Example 1, except that the step of forming the second electron transport layer was not performed and the second electrode layer was formed on the first electron transport layer.

[0113] 2. Evaluation Method 2.1. Heat Resistance (FF Value) The solar cells obtained in Example 1, Comparative Example 1, and Comparative Example 2 were subjected to light with a spectrum of AM 1.5 at an irradiance of 1 kW / m ２ The solar cells were then heated at 200°C for 30 minutes while being irradiated with light of spectrum AM1.5 at an irradiance of 1 kW / m² for initial stabilization. After that, the FF values ​​were measured. ２ The sample was heated at 150°C for 208 hours while being irradiated with light. The FF value was then measured. The FF value is the output (maximum output: P ｍａｘ ) and the open circuit voltage (V ｏｃ ) and short circuit current (I ｓｃ ) and is an index that indicates the quality of the current-voltage characteristics of a solar cell. ｍａｘ ÷(V ｏｃ ×I ｓｃ ) x 100

[0114] The IV curve was measured under standard solar cell test conditions (light with a spectral spectrum of AM1.5 and an irradiance of 1kW / m ２The measurements were taken under test conditions where the solar cell temperature was 25°C and the incident light was 1000kJ / s.

[0115] 2.2. Conversion Efficiency The conversion efficiency was measured for the solar cells obtained in Examples 2 to 11 and Comparative Example 3. The conversion efficiency is the output (maximum output: P ｍａｘ ) divided by the light energy E received by the solar cell. Conversion efficiency (%) = P ｍａｘ ÷E×100

[0116] The IV curve was measured under the same conditions as when the FF value was measured.

[0117]

[0118]

[0119]

[0120] 3. Evaluation Results Figure 2 shows the IV curves of the solar cells obtained in Example 1, Comparative Example 1, and Comparative Example 2. In Figure 2, A corresponds to Comparative Example 1, B corresponds to Comparative Example 2, and C corresponds to Example 1. Table 1 also shows the FF values ​​of the solar cells obtained in Example 1, Comparative Example 1, and Comparative Example 2. From these, it can be seen that the solar cell of Example 1 shows less deterioration in current-voltage characteristics due to heating compared to the solar cells of Comparative Examples 1 and 2, and has excellent current-voltage characteristics both before and after heating. Note that at C in Figure 2, the IV curve after heating overlaps the IV curve before heating.

[0121] Tables 2 and 3 show the conversion efficiencies of the solar cells obtained in Examples 2 to 11 and Comparative Example 3. These show that the solar cells of Examples 2 to 11 have superior conversion efficiencies compared to the solar cell of Comparative Example 3.

[0122] The solar cell of the present invention has excellent heat resistance and is therefore industrially applicable as a solar cell that can be used in various environments, including high-temperature environments.

[0123] REFERENCE SIGNS LIST 100... solar cell, 101... first electrode layer, 102... hole transport layer, 103... light absorption layer, 104... first electron transport layer, 105... second electron transport layer, 106... second electrode layer, 107... grid electrode, 108... substrate

Claims

1. A solar cell comprising at least a first electrode layer, a light absorption layer, a first electron transport layer which is an n-type semiconductor containing indium sulfide or indium sulfide doped with another element, a second electron transport layer which is an n-type oxide semiconductor doped with a hydrogen element, and a second electrode layer, in this order.

2. The solar cell according to claim 1, wherein the first electron transport layer is provided on the light absorbing layer, and the second electron transport layer is provided on the first electron transport layer.

3. The solar cell according to claim 1, wherein the first electron transport layer has a thickness of 10 nm or more and 40 nm or less, and the second electron transport layer has a thickness of 50 nm or more and 120 nm or less.

4. The solar cell according to any one of claims 1 to 3, wherein the light absorbing layer contains a chalcopyrite compound or a kesterite compound.

5. The n-type oxide semiconductor has a band gap of 3.3 eV or more and a carrier concentration of 1.0×10 ２０ cm －３ The solar cell according to any one of claims 1 to 3, wherein the oxide semiconductor has a refractive index of 2.1 or more and a refractive index of 2.1 or more.

6. The solar cell according to claim 5, wherein the n-type oxide semiconductor contains titanium oxide, zinc oxide doped with elemental sulfur, or zinc oxide doped with elemental titanium.

7. A method for manufacturing a solar cell, the solar cell comprising at least a first electrode layer, a light absorbing layer, a first electron transport layer which is an n-type semiconductor containing indium sulfide or indium sulfide doped with another element, a second electron transport layer which is an n-type oxide semiconductor doped with a hydrogen element, and a second electrode layer, in this order, the method comprising: a first electron transport layer formation step of forming the first electron transport layer on a substrate including the light absorbing layer by a sputtering method; and a second electron transport layer formation step of forming the second electron transport layer on the first electron transport layer by a sputtering method while supplying a gas including an oxygen source and a hydrogen source.

8. The manufacturing method according to claim 7, wherein the substrate has the light absorbing layer on an outermost surface thereof, and the light absorbing layer contains a chalcopyrite compound or a kesterite compound.

9. The manufacturing method according to claim 7 or 8, wherein the concentration of the oxygen source in the gas supplied in the second electron transport layer formation step is 0.8 volume % or more and 1.6 volume % or less in terms of oxygen molecules.

10. The manufacturing method according to claim 7 or 8, wherein the molar ratio of hydrogen element to oxygen element contained in the gas supplied in the second electron transport layer forming step is 1.0 to 2.0 times.

11. The n-type oxide semiconductor has a band gap of 3.3 eV or more and a carrier concentration of 1.0×10 ２０ cm －３ The method according to claim 7 or 8, wherein the oxide semiconductor has a refractive index of 2.1 or more and a viscosity of 1000 saturation temperature ...

12. The method according to claim 11, wherein the n-type oxide semiconductor comprises titanium oxide, zinc oxide doped with elemental sulfur, or zinc oxide doped with elemental titanium.

13. The manufacturing method described in claim 7 or 8, wherein the n-type oxide semiconductor is zinc oxide doped with titanium element, and the second electron transport layer formation process is carried out using a mixture of zinc oxide and titanium oxide containing 4.0 mass % or more and 20 mass % or less of titanium oxide as a sputtering target.

14. The manufacturing method described in claim 13, wherein the first electron transport layer forming step is performed while heating the substrate at 150°C or more and 250°C or less, and the second electron transport layer forming step is performed while heating the substrate and a laminate including the first electron transport layer formed on the substrate at 100°C or more and 200°C or less.

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