Solar cell and method for manufacturing solar cell

Abstract

To provide a solar cell in which deterioration of a hole transport layer is suppressed even in annealing within a corrosive gas, and a method for manufacturing the solar cell.SOLUTION: This solar cell at least comprises a substrate 101, a reverse-surface electrode layer 102, a hole transport layer 103 that is a p-type oxide semiconductor to which an alkali metal element is added, and a light absorption layer 104, in the stated order.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Chalcopyrite thin-film solar cells, kesterite thin-film solar cells, perovskite thin-film solar cells, and other solar cells generally use hole transport layers and electron transport layers to efficiently extract holes and electrons generated in the light-absorbing layer. Among these, the hole transport layer must be a p-type material. Generally, inorganic materials such as MoSe or MoSeS layers, which are naturally formed on the molybdenum back electrode layer during the light-absorbing layer deposition process, are used as the hole transport layer in chalcopyrite thin-film solar cells and kesterite thin-film solar cells. Perovskite thin-film solar cells use organic materials such as Spiro-MeOTAD as the hole transport layer. In recent years, inorganic materials such as NiO, CuO, CuSCN, CuI, CuGaO, CuCrO, and CuAlO have been investigated as new hole transport layers with higher efficiency and weather resistance (e.g., Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 10,515,767 [Patent Document 2] Chinese Patent No. 109378362 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in solar cells such as those shown in Patent Documents 1 and 2, a hole transport layer is generally formed, followed by lamination of a light absorption layer, and the layer is then heat-treated, i.e., annealed, in a corrosive gas containing selenium, sulfur, or the like at a temperature of, for example, 150°C to 600°C. This makes the hole transport layer susceptible to deterioration, and there is room for improvement in this regard.

[0005] Therefore, an object of the present invention is to provide a solar cell in which deterioration of the hole transport layer is suppressed even when annealed in a corrosive gas, and a method for manufacturing the solar cell. [Means for solving the problem]

[0006] A solar cell according to one embodiment of the present invention comprises at least a substrate, a back electrode layer, a hole transport layer made of a p-type oxide semiconductor doped with an alkali metal element, and a light absorption layer, in this order.

[0007] The present inventors have found that the use of a p-type oxide semiconductor doped with an alkali metal element for a p-type hole transport layer material in a solar cell improves corrosion resistance, specifically, that deterioration of the hole transport layer is suppressed even when annealed in a corrosive gas at temperatures of 150° C. to 600° C. Furthermore, the present inventors have found that the p-type hole transport layer material suppresses the diffusion of harmful elements into the light absorption layer and / or the blocking of the diffusion of elements necessary for the light absorption layer, even after the annealing. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a solar cell in which deterioration of the hole transport layer is suppressed even when annealed in a corrosive gas, and a method for manufacturing the solar cell. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating an example of a cross-sectional structure of a solar cell. DETAILED DESCRIPTION OF THE INVENTION

[0010] 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, but the present invention is not limited to this, 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 will be 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.

[0011] 1. Solar cells 1 , the solar cell 100 of this embodiment includes a substrate 101, a back electrode layer 102 provided on the substrate 101, a hole transport layer 103 provided on the back electrode layer 102, a light absorbing layer 104 provided on the hole transport layer 103, an electron transport layer 105 provided on the light absorbing layer 104, a front electrode layer 106 provided on the electron transport layer 105, and a grid electrode 107 provided on the front electrode layer 106. The solar cell 100 receives light from the front electrode layer 106 side to generate electricity.

[0012] 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 103 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.

[0013] Although not shown, the solar cell 100 of this embodiment may have two or three sets of a hole transport layer 103, a light absorption layer 104 provided on the hole transport layer 103, an electron transport layer 105 provided on the light absorption layer 104, and a front electrode layer 106 provided on the electron transport layer 105, stacked on the back electrode layer 102. In addition, a grid electrode 107 may be provided on the uppermost front electrode layer 106.

[0014] The solar cell 100 includes, in this order, at least a substrate 101, a back electrode layer 102, a hole transport layer 103 made of a p-type oxide semiconductor doped with an alkali metal element, and a light absorption layer 104. The hole transport layer 103 made of a p-type oxide semiconductor doped with an alkali metal element is resistant to deterioration even when annealed in a corrosive gas atmosphere. The annealing temperature is preferably 50°C to 700°C, more preferably 100°C to 650°C, and even more preferably 150°C to 600°C. This is thought to be because the crystal structure of the p-type oxide semiconductor is stabilized by the addition of an alkali metal element, but the cause is not limited to this. Note that deterioration refers to the generation of impurities in the hole transport layer, a change in color, or a change in the crystal structure of the material constituting the hole transport layer, and the like. Such deterioration may degrade the performance of the solar cell 100. The corrosive gas is a gas constituting one or more atmospheres selected from the group consisting of sulfur atmosphere, selenium atmosphere, chlorine atmosphere, bromine atmosphere, and iodine atmosphere, such as sulfur dioxide, hydrogen sulfide, selenium dioxide, chlorine, hydrogen chloride, bromine, iodine, and hydrogen iodide. Furthermore, by suppressing the deterioration of the hole transport layer 103, the annealing process suppresses the diffusion of harmful elements from the hole transport layer 103 to the light absorbing layer 104 and blocks the diffusion of necessary elements to the light absorbing layer 104. Harmful elements include, for example, nickel, whose diffusion into the light absorbing layer 104 reduces the performance of the solar cell and adversely affects the photoelectric conversion efficiency of the solar cell 100. Necessary elements include alkali metal elements, particularly sodium, potassium, rubidium, and cesium. The inclusion of these alkali metal elements in the light absorbing layer 104 can improve the photoelectric conversion efficiency and thereby enhance performance, i.e., improve the conversion efficiency of the solar cell 100. By adding an alkali metal element to the hole transport layer 103, it is expected that part of the alkali metal element in the hole transport layer 103 will diffuse upward by the annealing, thereby providing the alkali element to the light absorption layer 104.

[0015] The thickness of the solar cell 100 excluding the substrate 101 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.

[0016] 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.

[0017] Each component that may be included in the solar cell 100 will be described in detail below.

[0018] In this embodiment, when a compound is expressed by its name, it includes not only the pure compound itself, but also a compound to which trace amounts of elements, etc. have been added, as long as the properties of the compound are not lost, and a compound whose composition ratio is slightly different from that of the pure compound.

[0019] 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.

[0020] 1.1.Substrate Substrate 101 is not particularly limited, but can be a glass substrate such as soda lime glass or low-alkali glass, a metal substrate such as a stainless steel plate, aluminum foil or titanium substrate, or a resin substrate such as a polyimide resin substrate or an epoxy resin substrate. The thickness of substrate 101 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 substrate 101 within the above ranges tends to enable the solar cell to be lighter and more flexible.

[0021] 1.2.Back electrode layer The back electrode layer 102 is provided, for example, to extract current due to holes generated in the light absorption layer 104 described below. The back electrode layer 102 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 back electrode layer 102 is not particularly limited, but is, for example, 200 nm to 800 nm, or 300 nm to 700 nm. Having the thickness of the back electrode layer 102 within the above range tends to enable the solar cell to be made lighter and more flexible while still extracting sufficient current without loss.

[0022] 1.3.Metal mirror layer A highly reflective metal mirror layer may be formed on the back electrode layer 102, and a transparent conductive oxide film serving both protection and conductivity may be capped on top of the metal mirror layer. This allows a portion of the sunlight that has passed through from the front electrode to the light absorbing layer to be reflected by the back surface and reabsorbed by the light absorbing layer, thereby increasing the amount of light absorbed and improving the photoelectric conversion efficiency of the solar cell. The highly reflective metal mirror layer is preferably selected to include at least one material selected from the group consisting of gold, silver, aluminum, gold alloys, silver alloys, and aluminum alloys. The thickness of the metal mirror layer is preferably 5 to 70 nm, 10 to 50 nm, or 15 to 30 nm. Having a thickness within the above range of the metal mirror layer improves light reflectivity and allows for a thin shape.

[0023] 1.4.Hole transport layer The hole transport layer 103 has the function of, for example, efficiently extracting holes generated in the light absorption layer 104 (described later) from the light absorption layer 104 and preventing recombination of electrons and holes generated simultaneously with the holes in the light absorption layer 104. The hole transport layer 103 is not particularly limited as long as it is essentially a p-type oxide semiconductor doped with an alkali metal element. The hole transport layer 103 is preferably a p-type oxide semiconductor doped with an alkali metal element source containing one or more selected from the group consisting of sodium oxide (NaO), potassium oxide (KO), rubidium oxide (RbO), and cesium oxide (CsO). That is, the alkali metal element doped to the p-type oxide semiconductor is preferably one or more selected from the group consisting of sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). The p-type oxide semiconductor may include one or more selected from the group consisting of nickel oxide (NiO), copper oxide (CuO), copper gallium oxide (CuGaO2), copper chromium oxide (CuCrO2), and copper aluminum oxide (CuAlO2). By using a p-type oxide semiconductor for the hole transport layer 103, the weather resistance of the hole transport layer 103 can be improved, resulting in a solar cell 100 with high weather resistance.

[0024] In the hole transport layer 103, the molar number of the alkali metal element is 0.1 to 0.3 times the sum of the molar number of one metal element and the alkali metal element among the constituent elements of the p-type oxide semiconductor, and the one metal element is preferably selected from the group consisting of nickel (Ni) and copper (Cu). As a specific example, the hole transport layer 103 is made of CuAlO2 doped with Na. It is believed that in the Na-doped CuAlO2, Na partially substitutes for sites where Cu would normally be located in the crystal structure of CuAlO2. Therefore, the molar ratio of Na to Cu in the Na-doped CuAlO2 is expressed as x:1-x, where x is the molar number of Na. In the hole transport layer 103, the mole number x of the alkali metal element Na is preferably 0.1 to 0.3 times the sum of the mole number 1-x of Cu, one of the constituent elements of the p-type oxide semiconductor, and the mole number x of the alkali metal element Na. In other words, the mole number x of Na in the hole transport layer 103 is preferably 0.1 to 0.3. Having the mole number x of Na of 0.1 or greater improves the corrosion resistance of the hole transport layer 103 and suppresses deterioration due to annealing in a corrosive gas atmosphere. This is thought to be due to, but not limited to, the stabilization of the crystal structure of the p-type oxide semiconductor CuAlO2 in a corrosive gas atmosphere by the addition of the alkali metal element Na. Specifically, Na partially substitutes for sites in the crystal structure of CuAlO2 where Cu would normally be located, but the reason for this is not limited to this. Furthermore, having the mole number x of Na of 0.3 or less allows the amount of alkali element supplied to the light absorption layer to be increased without destabilizing the crystal structure. In the above example, the alkali metal element to be added is Na and the p-type oxide semiconductor is CuAlO2, but the target substance is not limited to these, and other alkali metal elements may be used. As for the p-type oxide semiconductor, those containing nickel and / or copper are preferable.

[0025] The content of the p-type oxide semiconductor doped with the alkali metal element in the hole transport layer 103 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, based on the total amount of the hole transport layer 103.

[0026] The thickness of the hole transport layer 103 is preferably 5 nm to 100 nm, 7 nm to 75 nm, or 10 nm to 50 nm. When the thickness of the hole transport layer 103 is within the above range, the layer efficiently extracts holes generated in the light absorbing layer 104 (described below) from the light absorbing layer 104 and prevents recombination of electrons and holes generated simultaneously with the holes in the light absorbing layer 104 (described below), while tending to enable a lighter and more flexible solar cell.

[0027] 1.5.Light-absorbing layer The light absorbing layer 104 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 104 preferably contains a perovskite compound, a chalcopyrite compound, or a kesterite compound. One type of perovskite compound may be used alone, or two or more types may be used in combination. One type of chalcopyrite compound may be used alone, or two or more types may be used in combination. One type of kesterite compound may be used alone, or two or more types may be used in combination.

[0028] Examples of perovskite compounds include those represented by the general formula AMX3 and A2MX4, where M represents a divalent cation, A represents a monovalent cation, and X represents a monovalent anion.

[0029] The monovalent cation A is not particularly limited, and examples thereof include cations of Group 1 elements of the periodic table and organic cations. Among these, cesium ion, rubidium ion, optionally substituted ammonium ion (including amidinium ion), optionally substituted phosphonium ion, and optionally substituted amidinium ion are preferred. Examples of optionally substituted ammonium ions include primary ammonium ions and secondary ammonium ions. Specific examples of optionally substituted ammonium ions include alkylammonium ions, arylammonium ions, amidinium ions, and guanidium ions. In particular, monoalkylammonium ions are preferred to avoid steric hindrance, and alkylammonium ions substituted with one or more fluorine atoms are preferred to improve stability. Furthermore, a combination of two or more cations can be used as the cation A. Examples of the monovalent cation A include a methylammonium ion, a methylammonium monofluoride ion, a methylammonium difluoride ion, a methylammonium trifluoride ion, an ethylammonium ion, an isopropylammonium ion, an n-propylammonium ion, an isobutylammonium ion, an n-butylammonium ion, a t-butylammonium ion, a dimethylammonium ion, a diethylammonium ion, a phenylammonium ion, a benzylammonium ion, a phenethylammonium ion, a guanidium ion, a formamidinium ion, an acetamidinium ion, and an imidazolium ion.

[0030] The divalent cation M is not particularly limited, and examples thereof include divalent metal cations and semimetal cations. Specific examples include cations of elements in Group 14 of the periodic table, and more specific examples include lead cations (Pb 2+ ), tin cation (Sn 2+ ), and germanium cation (Ge 2+ ) In addition, as the cation M, a combination of two or more types of cations can be used.

[0031] The monovalent anion X is not particularly limited and may include, for example, a halide ion, acetate ion, nitrate ion, sulfate ion, borate ion, acetylacetonate ion, carbonate ion, citrate ion, sulfur ion, tellurium ion, thiocyanate ion, titanate ion, zirconate ion, 2,4-pentanedionate ion, and silicofluoride ion. X may be a single anion or a combination of two or more anions. It is preferable to use a halide ion or a combination of a halide ion and another anion as X. Examples of halide ions X include chloride ions, bromide ions, and iodide ions.

[0032] Examples of perovskite compounds include organic-inorganic perovskite compounds, particularly halide-based organic-inorganic perovskite compounds. Specific examples of perovskite compounds include CH3NH3PbI3, CH3NH3PbBr3, CH3NH3PbCl3, CH3NH3SnI3, CH3NH3SnBr3, CH3NH3SnCl3, and CH3NH3PbI (3-x) Cl x , CH3NH3PbI (3-x) Br x , CH3NH3PbBr (3-x) Cl x , CH3NH3Pb (1-y) Sn y I3, CH3NH3Pb (1-y) Sn y Br3, CH3NH3Pb (1-y) Sn y Cl3, CH3NH3Pb (1-y) Sn y I (3-x) Cl x , CH3NH3Pb (1-y) Sn y I (3-x) Br x , and CH3NH3Pb (1-y) Sn y Br (3-x) Cl xand compounds in which CFH2NH3, CF2HNH3, CF3NH3, or NH2CH=NH2 is used in place of CH3NH3 in the above compounds. In the above formula, x is an arbitrary value of 0 or more and 3 or less, and y is an arbitrary value of 0 or more and 1 or less.

[0033] The chalcopyrite compound is preferably a I-III-VI2 group chalcopyrite compound. The I-III-VI2 group chalcopyrite compound is not particularly limited, but examples thereof include CuAlS2, CuAlSe2, CuAlTe2, CuGaS2, CuGaSe2, CuGaTe2, CuInS2, CuInSe2, CuInTe2, AgAlS2, AgAlSe2, AgAlTe2, AgGaS2, AgGaSe2, AgGaTe2, AgInS2, AgInSe2, AgInTe2, and combinations thereof. The term "combinations thereof" is not particularly limited, but examples thereof include Cu(In) when CuGaS2 and CuInSe2 are combined. x Ga 1-x )(Se y S 1-y )2 (0≦x≦1, 0≦y≦1). Among these chalcopyrite compounds, CuGaS2, CuGaSe2, CuInS2, CuInSe2, 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 this 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.

[0034] The kesterite compound is preferably a Group I2-II-IV-VI4 kesterite compound. The Group I2-II-IV-VI4 kesterite compound is not particularly limited, but examples thereof include Cu2ZnSnS4, Cu2ZnSnSe4, Cu2ZnGeS4, Cu2ZnGeSe4, Cu2MnSnS4, Cu2MnSnSe4, Cu2MnGeS4, Cu2MnGeSe4, Ag2ZnSnS4, Ag2ZnSnSe4, Ag2ZnGeS4, Ag2ZnGeSe4, Ag2MnSnS4, Ag2MnSnSe4, Ag2MnGeS4, Ag2MnGeSe4, and combinations thereof. The term "combinations thereof" is not particularly limited, but examples thereof include the combination of Cu2ZnSnS4 and Ag2ZnSnSe4 (Cu x Ag 1-x )2ZnSn(S y Se 1-y )4(0≦x≦1). Cu2ZnSn(S x Se 1-x )4 (0≦x≦1, 0≦y≦1). Among these kesterite compounds, Cu2ZnSnS4, Cu2ZnSnSe4, Ag2ZnSnS4, Ag2ZnSnSe4, (Cu x Ag 1-x )2ZnSn(S y Se 1-y ) 4 (0≦x≦1, 0≦y≦1) is preferred, and (Cu x Ag 1-x )2ZnSn(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.

[0035] The content of the perovskite compound, chalcopyrite compound, or kesterite compound in the light absorbing layer 104 is not particularly limited as long as the light absorbing layer 104 has the function of absorbing light such as visible light or ultraviolet light to generate electrons and holes. More specifically, without being particularly limited, the content is 50% by mass or more and 100% by mass or less, 60% by mass or more and 100% by mass or less, 70% by mass or more and 100% by mass or less, 80% by mass or more and 100% by mass or less, or 90% by mass or more and 100% by mass or less, relative to the total mass of the light absorbing layer 104.

[0036] In addition to the above materials, the light absorbing layer 104 may contain additives such as a binder, a surfactant, etc. The content of the additives is not particularly limited, but is, for example, 0.1 to 10 mass % with respect to the total mass of the light absorbing layer 104. The light absorbing layer 104 does not necessarily need to contain the additives.

[0037] The thickness of the light absorbing layer 104 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 104 is within the above range, the solar cell tends to be lighter and more flexible while still retaining the function of absorbing light such as visible light and ultraviolet light to generate electrons and holes.

[0038] The solar cell 100 of this embodiment may have two light absorbing layers 104. In this case, the substance contained in the first light absorbing layer 104 may be different from the substance contained in the second light absorbing layer 104, but it is preferable that they are different. A solar cell in which the first and second light absorbing layers 104 contain different substances is also called a tandem solar cell. When the solar cell 100 has two light absorbing layers 104, the wavelength range of light that can be absorbed by the light absorbing layer 104 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 104.

[0039] 1.6.Electron transport layer The electron transport layer 105 is substantially made of an n-type semiconductor and has the function of preventing the alkali metal elements contained in the light absorbing layer 104 from diffusing to the surface electrode layer 106, and the function of efficiently extracting electrons generated in the light absorbing layer 104 from the light absorbing layer 104 and preventing the recombination of holes and electrons generated simultaneously with the electrons in the light absorbing layer 104. The n-type semiconductor is not particularly limited, but may be Zn(O,S,OH) x , CdS, In2S3 or ZnTiO x Preferably, the electron transport layer 105 may contain an alkali metal element. By annealing in a corrosive gas, a part of the alkali metal element contained in the electron transport layer 105 diffuses downward, and the alkali element can be provided to the light absorption layer 104.

[0040] The content of the above-mentioned n-type semiconductor in the electron transport layer 105 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 electron transport layer 105.

[0041] The thickness of the electron transport layer 105 is preferably 10 nm to 150 nm, 15 nm to 125 nm, or 20 nm to 100 nm. When the thickness of the electron transport layer 105 is within the above range, the layer has the function of preventing the alkali metal element contained in the light absorbing layer 104 from diffusing to the surface electrode layer 106, and the function of efficiently extracting electrons generated in the light absorbing layer 104 from the light absorbing layer 104 and preventing recombination of holes and electrons generated simultaneously with the electrons in the light absorbing layer 104, while tending to enable a lighter and more flexible solar cell.

[0042] 1.7.Surface electrode layer The surface electrode layer 106 is provided, for example, to extract a current due to electrons generated in the light absorbing layer 104. In the solar cell 100, the light absorbing layer 104 absorbs light that has passed through the surface electrode layer 106, and therefore, in order to increase the amount of light absorbed by the light absorbing layer 104, the surface 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. There is no particular limitation on high electrical conductivity, but it may be, for example, a material with a specific resistance of 5.0×10 -3 It means that the resistivity is Ωcm or less. High visible light transmittance is not particularly limited, but for example, it means that the average transmittance in the wavelength range of 400 to 1300 nm is 80% or more. 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).

[0043] The content of the above-mentioned materials in the surface electrode layer 106 is not particularly limited as long as the surface electrode layer 106 functions as a transparent electrode. More specifically, although not particularly limited, the content of the above-mentioned materials relative to the total mass of the surface electrode layer 106 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, 90% by mass to 100% by mass, or 95% by mass to 100% by mass.

[0044] The thickness of the front 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 front 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.

[0045] 1.8.Grid Electrode The grid electrode 107 is provided, for example, to extract electricity from the surface electrode layer 106. The material of the grid electrode 107 is not particularly limited as long as it is conductive, and examples thereof include metals such as Mo, Cr, Ag, Cu, Ni, Al, and Ti; conductive inorganic compounds other than metals; and conductive organic compounds.

[0046] The content of the above materials 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 materials 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.

[0047] The thickness of grid electrode 107 is not particularly limited, but is, for example, 5 μm to 50 μm. When the thickness of grid electrode 107 is within the above range, it tends to be possible to extract sufficient current without loss, while making the solar cell lighter and more flexible.

[0048] 2. Solar cell manufacturing method The method for manufacturing the solar cell 100 of this embodiment includes a laminate preparation step of preparing a laminate including, in this order, at least a substrate 101, a back electrode layer 102, a hole transport layer 103 which is a p-type oxide semiconductor doped with an alkali metal element, and a precursor layer of a light absorbing layer 104, and a heat treatment step of heat treating the laminate in one or more atmospheres selected from the group consisting of a sulfur atmosphere, a selenium atmosphere, a chlorine atmosphere, a bromine atmosphere, and an iodine atmosphere.

[0049] The present inventors have found that, in the method for manufacturing a solar cell according to this embodiment, by depositing a p-type oxide semiconductor doped with an alkali metal element as the hole transport layer 103 in the stack preparation step, deterioration of the hole transport layer 103 during the heat treatment step can be suppressed. Specifically, the present inventors have found that annealing in a corrosive gas atmosphere at high temperatures can suppress deterioration of the hole transport layer 103 itself, diffusion of harmful elements into the light absorbing layer 104, and conversely, blocking of the diffusion of elements necessary for the light absorbing layer 104. This is thought to be because the addition of an alkali metal element stabilizes the crystal structure of the p-type oxide semiconductor in a corrosive gas atmosphere, but the cause is not limited to this. Furthermore, suppressing deterioration of the hole transport layer 103 suppresses the diffusion of harmful elements from the hole transport layer 103 to the light absorbing layer 104 and the blocking of the diffusion of necessary elements into the light absorbing layer 104 during the annealing. The temperature at which the heat treatment step is carried out is preferably 50 to 700°C, more preferably 100 to 650°C, and even more preferably 150 to 600°C.

[0050] Each step that may be included in the method for manufacturing the solar cell 100 of this embodiment will be described in detail below. 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.

[0051] 2.1.Laminate preparation process 2.1.1. Back electrode layer formation process In the back electrode layer forming step, for example, the back electrode layer 102 may be formed on the substrate 101. Methods for forming the back electrode layer 102 include a dry process and a wet process, with the dry process being preferred. The dry process is not particularly limited, but an example is a method for forming the back electrode layer 102, 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 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 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 back electrode layer forming step, for example, the substrate 101 may be the sputtering substrate.

[0052] 2.1.2.Metal mirror layer formation process A metal mirror layer may be formed by, for example, sputtering on the back electrode layer 102. As described above, 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.

[0053] 2.1.3. Hole transport layer formation process In the hole transport layer forming step, for example, the hole transport layer 103 may be formed on the back electrode layer 102. Methods for forming the hole transport layer 103 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 103, which is a p-type oxide semiconductor doped with an alkali metal element, 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 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. Addition of an alkali metal element to a p-type oxide semiconductor can be achieved by using, as a sputtering target, a mixture of a p-type oxide semiconductor raw material and an alkali metal element source. The amount of the alkali metal element added can be changed by adjusting the amount of the alkali metal element source.

[0054] In a method for forming the hole transport layer 103, which is a p-type oxide semiconductor doped with an alkali metal element, by sputtering, it is particularly preferable to form the hole transport layer 103 on the back electrode layer 102 by sputtering in an atmosphere with an oxygen concentration of 8% or more, preferably 8% to 50%, and even more preferably 9% to 30%. Conditions other than the deposition atmosphere are not particularly limited. As described in detail below, the hole transport layer 103 formed under these conditions tends to have high corrosion resistance, and the effects of a heat treatment process performed in a corrosive gas can be suppressed.

[0055] Preferably, the method further includes a step of pre-heat-treating the hole transport layer 103 formed on the back electrode layer 102 by the above-described method in an inert atmosphere at a temperature of 525°C to 575°C, preferably 535°C to 565°C, or even 545°C to 555°C. As described in detail below, the hole transport layer 103 formed under these conditions tends to have high corrosion resistance, and the effects of the heat treatment step performed in a corrosive gas can be suppressed. Note that when the hole transport layer 103 to be pre-heat-treated is formed by sputtering, the film formation conditions may be an atmosphere with an oxygen concentration of 8% or more, as described above, or may be other conditions.

[0056] The hole transport layer 103 is not particularly limited as long as it is a p-type oxide semiconductor doped with an alkali metal element. However, a p-type oxide semiconductor doped with an alkali metal element source containing at least one selected from the group consisting of Na2O, KO, Rb2O, and Cs2O is preferred. The p-type oxide semiconductor may contain at least one selected from the group consisting of NiO, CuO, CuGaO2, CuCrO2, and CuAlO2. The amount of alkali metal element added is adjusted so that the number of moles of the alkali metal element in the hole transport layer 103 is 0.1 to 0.3 times the sum of the number of moles of one metal element and the alkali metal element among the constituent elements of the p-type oxide semiconductor, and the one metal element is preferably selected from the group consisting of Ni and Cu. The amount of alkali metal element added can be changed, for example, when the hole transport layer is formed by sputtering, by changing the amount of alkali metal element source added to the raw material of the p-type oxide semiconductor for the sputtering target.

[0057] 2.1.4. Light absorption layer precursor layer formation process The precursor layer of the light absorbing layer 104 contains a substance that will constitute the light absorbing layer 104, which is formed by a heat treatment process described below. In the precursor layer formation process for the light absorbing layer, for example, the precursor layer of the light absorbing layer 104 may be formed on the hole transport layer 103. Methods for forming the precursor layer of the light absorbing layer 104 include dry processes and wet processes, with dry processes being preferred. The dry process is not particularly limited, but examples thereof include a method for forming a precursor layer of the light absorbing layer 104 containing a perovskite compound, a chalcopyrite compound, or a kesterite compound by a sputtering method. The film formation conditions for the sputtering method are not particularly limited, but examples thereof include 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. Furthermore, the temperature of the atmosphere and the temperature of the sputtering substrate may not be controlled during sputtering. When the light absorbing layer 104 contains a perovskite compound, the precursor layer of the light absorbing layer 104 may include, but is not limited to, a laminate of PbI2, FAI, or the like. When the light absorbing layer 104 contains a chalcopyrite compound, the precursor layer of the light absorbing layer 104 may include, but is not limited to, a laminate of CuGa, In, or the like. When the light absorbing layer 104 contains a kesterite compound, the precursor layer of the light absorbing layer 104 may include, but is not limited to, a laminate of Zn, Sn, Cu, or the like.

[0058] When the light absorbing layer 104 contains an alkali metal element, the precursor layer formation step for light absorption preferably uses a sputtering target doped with an alkali metal element to form a precursor layer for the light absorbing layer 104 containing a perovskite compound, a chalcopyrite compound, or a kesterite compound by sputtering. Alternatively, an alkali metal element may be added to the hole transport layer 103, the substrate 101, or the back electrode layer 102, and the alkali metal element may be thermally diffused into the light absorbing layer 104 during the formation of the light absorbing layer 104.

[0059] 2.2.Heat treatment process A laminate prepared by the above-described method, which includes at least the substrate 101, the back electrode layer 102, the hole transport layer 103, which is a p-type oxide semiconductor doped with an alkali metal element, and a precursor layer of the light absorbing layer 104, in this order, is heat-treated in one or more atmospheres selected from the group consisting of a sulfur atmosphere, a selenium atmosphere, a chlorine atmosphere, a bromine atmosphere, and an iodine atmosphere. In the heat treatment step, the laminate is preferably heat-treated at a temperature of 50°C to 700°C, more preferably 100°C to 650°C, and even more preferably 150°C to 600°C. The preferred heat treatment temperature for the laminate varies depending on the type of compound used in the light absorbing layer 104. When a perovskite compound is used in the light absorbing layer 104, the heat treatment temperature for the laminate is preferably 50°C to 250°C, more preferably 100°C to 200°C, even more preferably 125°C to 175°C, and even more preferably 145°C to 155°C. Furthermore, when a chalcopyrite compound or a kesterite compound is used for the light-absorbing layer 104, the temperature for the heat treatment of the laminate is preferably 300°C to 700°C, more preferably 350°C to 650°C, and even more preferably 400°C to 600°C. Regarding the preferred atmosphere during the heat treatment, when a perovskite compound is used for the light-absorbing layer 104, the heat treatment step is preferably carried out in one or more atmospheres selected from the group consisting of a chlorine atmosphere, a bromine atmosphere, and an iodine atmosphere. Furthermore, when a chalcopyrite compound or a kesterite compound is used for the light-absorbing layer 104, the heat treatment step is preferably carried out in one or more atmospheres selected from the group consisting of a sulfur atmosphere and a selenium atmosphere, and more preferably, the heat treatment step is carried out in a selenium atmosphere followed by a sulfur atmosphere.

[0060] 2.3.Electron transport layer formation process In the electron transport layer forming step, the electron transport layer 105 is formed by a sputtering method on the substrate including the light absorbing layer 104. In the electron transport layer forming step, for example, the substrate has the light absorbing layer 104 on the outermost surface thereof, and the light absorbing layer 104 may contain a perovskite compound, a chalcopyrite compound, or a kesterite compound.

[0061] The film formation conditions for the sputtering method are not particularly limited. For example, when the electron transport layer 105 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. Meanwhile, during sputtering, the base material including the light absorbing layer 104 is preferably heated to 150°C or higher and 250°C or lower, more preferably 160°C or higher and 250°C or lower, more preferably 170°C or higher and 250°C or lower, more preferably 180°C or higher and 250°C or lower, more preferably 190°C or higher and 250°C or lower, and more preferably 200°C or higher and 250°C or lower. When a metal substrate is used as the substrate 101, the temperature of the base material and the heating temperature are approximately the same.

[0062] 2.4. Surface electrode layer formation process In the surface electrode layer forming step, for example, the surface electrode layer 106 may be formed on the electron transport layer 105. Methods for forming the surface electrode layer 106 include a dry process and a wet process, with the dry process being preferred. The dry process is not particularly limited, but an example is a method for forming the surface 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.

[0063] 2.5.Grid electrode formation process In the grid electrode forming step, for example, the grid electrode 107 may be formed on the surface electrode layer 106. Methods for forming the grid electrode 107 include a dry process and a wet process. Specific examples include a sputtering method, a vapor deposition method, a method of printing a paste-like conductive material on the surface electrode layer 106, and a method of crimping a conductive wire.

[0064] 3. How to use solar cells 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.).

[0065] Furthermore, the solar cell 100 of this embodiment can be used as an independent power source device for street lights, sensors, digital signage, etc. Furthermore, the solar cell 100 of this embodiment can also be used as a mobile energy device. [Example]

[0066] 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 experiments were carried out at room temperature (25°C) under 1 atmosphere.

[0067] 4.1. Comparison of resistance of various hole transport layers to high-temperature annealing in corrosive gases [Example 1] First, the conditions for fabricating the laminate including the substrate to the hole transport layer of the solar cell shown in each Example and Comparative Example are described. In Example 1, a 2 mm thick glass substrate was used as the substrate. In addition, a composite film was fabricated by laminating a 400 nm thick molybdenum back electrode layer on this substrate, followed by a 50 nm nickel and a 50 nm silver metal mirror layer in this order.

[0068] Next, a p-type oxide semiconductor CuAlO2 doped with sodium, an alkali metal element, was formed on the substrate or the metal mirror layer by sputtering to a thickness of 50 nm as a hole transport layer. That is, as Example 1, a stacked body with and without a metal mirror layer was prepared. The sputtering conditions were as follows: Sputtering target: A mixture of copper oxide (Cu2O), aluminum oxide (Al2O3) and sodium oxide, adjusted so that the molar ratio of Na, Cu and Al is 0.2:0.8:1. Film formation atmosphere: Argon / oxygen gas atmosphere (adjusted so that argon gas:oxygen gas = 90% by volume: 10% by volume) Heating temperature of the sputtered substrate during film formation: Unheated

[0069] [Comparative Example 1] The laminate of Comparative Example 1 was fabricated in the same manner as the laminate of Example 1, except that nickel oxide (NiO), a p-type oxide semiconductor doped with silver, was formed as the hole transport layer instead of the p-type oxide semiconductor CuAlO2 doped with sodium. In Comparative Example 1, the hole transport layer was formed of nickel oxide (NiO), a p-type oxide semiconductor doped with silver, with a thickness of 50 nm, and the sputtering conditions were as follows: Sputtering target: A mixture of nickel oxide and silver, adjusted so that the molar ratio of Ag to Ni is 0.01:0.99. Film formation atmosphere: Argon / oxygen gas atmosphere (adjusted so that argon gas:oxygen gas = 90% by volume: 10% by volume) Heating temperature of the sputtered substrate during film formation: Unheated

[0070] Comparative Example 2 The laminate of Comparative Example 2 was fabricated in the same manner as the solar cell of Example 1, except that a p-type oxide semiconductor, copper gallium oxide (CuGaO2), was formed as the hole transport layer instead of the p-type oxide semiconductor CuAlO2 to which sodium was added. In Comparative Example 2, the p-type oxide semiconductor, copper gallium oxide, was formed to a thickness of 50 nm as the hole transport layer, and the sputtering conditions were as follows: Sputtering target: A mixture of copper oxide (Cu2O) and gallium oxide (Ga2O3) adjusted so that the molar ratio between them is 1:1. Film formation atmosphere: Argon / oxygen gas atmosphere (adjusted so that argon gas:oxygen gas = 90% by volume: 10% by volume) Heating temperature of the sputtered substrate during film formation: Unheated

[0071] The laminates including the solar cell substrate to the hole transport layer (HTL) obtained in Example 1, Comparative Example 1, and Comparative Example 2 were annealed for 10 minutes at 500°C in a hydrogen sulfide atmosphere (hydrogen sulfide gas:nitrogen gas=5% by volume:95% by volume). The change in transmittance was measured for the laminates that did not include a metal mirror layer, and the change in reflectance was measured for the laminates that included a metal mirror layer. The transmittance of the laminates was measured by spectral transmittance measurement, and the reflectance of the laminates was measured by spectral reflectance measurement. The magnitude of the change in transmittance and reflectance serves as an indicator of the corrosion resistance of the hole transport layer in the laminate. In other words, the smaller the change in transmittance and reflectance, the higher the corrosion resistance of the hole transport layer in the laminate. The results are shown in Table 1.

[0072] [Table 1]

[0073] As shown in Table 1, the laminate of Example 1 exhibited small changes in transmittance and reflectance and high corrosion resistance compared to the other comparative examples. This means that the p-type oxide semiconductor doped with an alkali metal element is a p-type hole transport layer material that is resistant to deterioration even at high temperatures and in corrosive gases.

[0074] 4.2. Comparison of CuAlO2-based thin film deposition conditions and resistance to high-temperature annealing in corrosive gases [Example 2] In Example 2, compared to the method for producing the laminate in Example 1, only the atmospheric conditions for film formation by sputtering were changed, specifically, the oxygen concentration of the film formation atmosphere was changed to 2%. In addition, after the back electrode layer was laminated on the substrate, a metal mirror layer was provided.

[0075] [Example 3] In Example 3, compared to the method for producing a laminate in Example 2, only the atmospheric conditions for film formation by sputtering were changed, specifically, the oxygen concentration of the film formation atmosphere was changed to 5%.

[0076] [Example 4] In Example 4, compared to the method for producing a laminate in Example 2, only the atmospheric conditions for film formation by sputtering were changed, specifically, the oxygen concentration of the film formation atmosphere was changed to 7.5%.

[0077] [Example 5] In Example 5, compared to the method for producing a laminate in Example 2, only the atmospheric conditions for film formation by sputtering were changed, specifically, the oxygen concentration of the film formation atmosphere was changed to 9%.

[0078] [Example 6] In Example 6, compared to the manufacturing method of Example 1, the sputtering deposition atmosphere conditions were changed to an oxygen concentration of 5%, and then the laminate was prepared, and the laminate was pre-heat-treated in an inert atmosphere, specifically, in a nitrogen atmosphere, at 500°C for 20 minutes. In addition, after a back electrode layer was laminated on the substrate, a metal mirror layer was provided.

[0079] [Example 7] In Example 7, compared to the method for producing a laminate in Example 6, only the temperature conditions of the pre-heat treatment were changed, specifically, the temperature conditions were changed to 550°C, and production was carried out.

[0080] [Example 8] In Example 8, compared to the method for producing a laminate in Example 6, only the temperature conditions of the pre-heat treatment were changed, specifically, the temperature conditions were changed to 600°C, and production was carried out.

[0081] The laminates including the hole transport layer of the solar cells obtained in Examples 2 to 8 were annealed in a hydrogen sulfide atmosphere at 500°C for 10 minutes, and the change in reflectance of the laminate before and after annealing was examined. The reflectance of the laminate was measured by spectral reflectance measurement. As mentioned above, the smaller the change in transmittance, the higher the corrosion resistance of the hole transport layer in the laminate. The results are shown in Table 2.

[0082] [Table 2]

[0083] As shown in Table 2, the change in reflectance for the laminates of Examples 2 to 8 was suppressed to a decrease of 50% or less. Among these, the laminates of Examples 5 and 7 showed smaller change in reflectance and higher corrosion resistance compared to the other examples. Specifically, conditions for obtaining a more corrosion-resistant hole transport layer include increasing the oxygen concentration in the sputtering deposition atmosphere to more than 7.5%, and further increasing the oxygen concentration to between 8% and 50%, or even increasing the oxygen concentration to between 9% and 30%, and pre-heat-treating the laminate at a temperature greater than 500°C and less than 600°C, further increasing the temperature range from 525°C to 575°C, further increasing the temperature range from 535°C to 565°C, or further increasing the temperature range from 545°C to 555°C. Although not shown in Table 2, the conditions for obtaining a highly corrosion-resistant hole transport layer are similar even when CuO or CuCrO2 is used instead of CuAlO2 as the p-type oxide semiconductor for the hole transport layer.

[0084] 4.3. Comparison of photoluminescence intensity and element diffusion in various laminates [Example 9] Compared to the fabrication method of Example 1, the following modifications were made: after forming the hole transport layer, a precursor layer for the light absorbing layer, specifically a laminate containing Cu, Ga, and In, was formed by sputtering; the precursor layer for the light absorbing layer was heat-treated in a selenium atmosphere at 400°C to 600°C for 5 to 30 minutes, and then heat-treated in a hydrogen sulfide atmosphere at 400°C to 600°C for 5 to 30 minutes; and Cu(In,Ga)(Se,S)2 was formed as the light absorbing layer through this heat treatment process. The back electrode layer was formed to a thickness of 400 nm, and the precursor layer for the light absorbing layer was formed so that the thickness of the heat-treated light absorbing layer was 2 μm. The laminate did not include a metal mirror layer.

[0085] Comparative Example 3 Compared to the fabrication method of Example 9, the hole transport layer was fabricated by forming a p-type semiconductor, MoSeS, instead of the sodium-doped p-type oxide semiconductor CuAlO2. The MoSeS was not formed by sputtering, but by forming a precursor layer of the light absorption layer on the substrate and then performing a heat treatment process similar to that of Example 9, whereby part of the molybdenum in the back electrode layer was converted to MoSeS.

[0086] Comparative Example 4 In comparison with the fabrication method of Example 9, the hole transport layer was fabricated using nickel oxide (NiO), a p-type oxide semiconductor doped with silver, instead of the sodium-doped p-type oxide semiconductor CuAlO2. The sputtering conditions were as follows: Sputtering target: A mixture of nickel oxide and silver, adjusted so that the molar ratio of Ag to Ni is 0.01:0.99. Film formation atmosphere: Argon / oxygen gas atmosphere (adjusted so that argon gas:oxygen gas = 90% by volume: 10% by volume) Heating temperature of the sputtered substrate during film formation: Unheated

[0087] Comparative Example 5 In comparison with the fabrication method of Example 9, the hole transport layer was fabricated using a p-type oxide semiconductor, copper gallium oxide (CuGaO), instead of the sodium-doped p-type oxide semiconductor CuAlO. The sputtering conditions were as follows: Sputtering target: A mixture of copper oxide (Cu2O) and gallium oxide (Ga2O3) in a molar ratio of 1:1. Film formation atmosphere: Argon / oxygen gas atmosphere (adjusted so that argon gas:oxygen gas = 90% by volume: 10% by volume) Heating temperature of the sputtered substrate during film formation: Unheated

[0088] Comparative Example 6 Compared to the fabrication method of Example 9, the hole transport layer was fabricated by simply forming CuAlO2 instead of the sodium-doped p-type oxide semiconductor CuAlO2. The sputtering conditions were as follows: Sputtering target: A mixture of copper oxide (Cu2O) and aluminum oxide (Al2O3), adjusted so that the molar ratio of copper to aluminum is 1:1. Film formation atmosphere: Argon / oxygen gas atmosphere (adjusted so that argon gas:oxygen gas = 90% by volume: 10% by volume) Heating temperature of the sputtered substrate during film formation: Unheated

[0089] For the stacks including the light absorbing layer of the solar cells obtained in Example 9 and Comparative Examples 3 to 6, the photoluminescence intensity and element diffusion of the light absorbing layer immediately after formation were analyzed. The photoluminescence intensity was measured by a photoluminescence method, and high photoluminescence intensity indicates high quality of the measured sample. The element diffusion was also analyzed by secondary ion mass spectrometry (SIMS), which allows us to examine the diffusion of impurity elements and alkali metal elements into the light absorbing layer. The results are shown in Table 3.

[0090] [Table 3]

[0091] As shown in Table 3, the laminate of Example 9 has a higher photoluminescence intensity than the other comparative examples. Furthermore, in terms of element diffusion, there is no impurity diffusion into the light absorbing layer in Example 9, while alkali element diffusion into the light absorbing layer is confirmed. From the viewpoint of element diffusion, it can be seen that Comparative Example 3 also shows a similar tendency. However, from the viewpoint of photoluminescence intensity, it can be seen that Example 9 has a higher photoluminescence intensity than Comparative Example 3, and thus has higher quality. Therefore, in these comparisons, it can be seen that Example 9 has the highest corrosion resistance.

[0092] 4.4. Comparison of electrical properties of thin-film solar cell devices using various laminates Subsequently, the electrical properties were measured for the thin-film solar cell devices using the laminates including the layers from the substrate to the light absorbing layer obtained in Example 9 and Comparative Examples 3 to 6. Specifically, the IV curves for the thin-film solar cell devices were measured under standard test conditions for solar cells (light with a spectral spectrum of AM1.5 at an irradiance of 1 kW / m 2 The measurements were taken under test conditions where light was incident at 1000kJ / s and the solar cell temperature was 25°C, and various physical properties such as conversion efficiency (Eff) were calculated using the following formula. Conversion efficiency is the value obtained by dividing the output (maximum output: Pmax) at the optimum operating point on the IV curve by the light energy E received by the solar cell. The FF value is the output (maximum output: Pmax) at the optimum operating point on the IV curve, which is the output characteristic of the solar cell. max ) and open circuit voltage (V oc ) and short circuit current (I s ) and is an index that indicates the quality of the current-voltage characteristics of a solar cell. Conversion efficiency Eff(%)=P max ÷E×100 FF value (%) = P max ÷(V oc ×I sc ) x 100

[0093] The results are shown in Table 4.

[0094] [Table 4]

[0095] As shown in Table 4, it can be seen that the thin-film solar cell device using the laminate of Example 9 has excellent current-voltage characteristics and conversion efficiency compared to the other comparative examples.

[0096] <Additional Notes> Embodiments of the present disclosure include the following aspects. [1] A substrate; a back electrode layer; a hole transport layer that is a p-type oxide semiconductor doped with an alkali metal element; a light absorbing layer in this order. [2] The solar cell according to [1], wherein the p-type oxide semiconductor comprises one or more selected from the group consisting of NiO, CuO, CuGaO2, CuCrO2, and CuAlO2. [3] The solar cell according to [1] or [2], wherein the hole transport layer is a p-type oxide semiconductor to which an alkali metal element source containing one or more selected from the group consisting of Na2O, K2O, Rb2O, and Cs2O is added. [4] In the hole transport layer, the number of moles of the alkali metal element is 0.1 to 0.3 times the sum of the number of moles of one metal element among the constituent elements of the p-type oxide semiconductor and the alkali metal element, The solar cell according to [2], wherein the one metal element is selected from the group consisting of Ni and Cu. [5] The solar cell according to any one of [1] to [4], wherein the light absorbing layer contains one or more compounds selected from the group consisting of chalcopyrite compounds, kesterite compounds, and perovskite compounds. [6] a laminate preparation step of preparing a laminate including, in this order, at least a substrate, a back electrode layer, a hole transport layer that is a p-type oxide semiconductor to which an alkali metal element is added, and a precursor layer of a light absorption layer; a heat treatment step of heat treating the laminate in one or more atmospheres selected from the group consisting of a sulfur atmosphere, a selenium atmosphere, a chlorine atmosphere, a bromine atmosphere, and an iodine atmosphere. [7] The laminate preparation step includes: The method for producing a solar cell according to [6], further comprising a step of pre-heat-treating the hole transport layer at a temperature of 525°C to 575°C in an inert atmosphere. [8] The method for manufacturing a solar cell according to [6] or [7], wherein the laminate preparation step includes a step of forming the hole transport layer on the back electrode layer by a sputtering method performed in an atmosphere having an oxygen concentration of 8% or more. [9] The method for producing a solar cell according to any one of [6] to [8], wherein the p-type oxide semiconductor contains one or more selected from the group consisting of NiO, CuO, CuGaO2, CuCrO2, and CuAlO2.

[10] The method for producing a solar cell according to any one of [6] to [9], wherein the hole transport layer is a p-type oxide semiconductor to which an alkali metal element source containing one or more selected from the group consisting of Na2O, K2O, Rb2O, and Cs2O is added.

[11] In the hole transport layer, the number of moles of the alkali metal element is 0.1 to 0.3 times the sum of the number of moles of one metal element among the constituent elements of the p-type oxide semiconductor and the alkali metal element, The solar cell according to [9], wherein the one metal element is selected from the group consisting of Ni and Cu.

[12] The method for producing a solar cell according to any one of [6] to

[11] , wherein the light absorbing layer contains at least one compound selected from the group consisting of a chalcopyrite compound, a kesterite compound, and a perovskite compound.

[13] The method for manufacturing a solar cell according to any one of [6] to

[12] , wherein in the heat treatment step, the laminate is heat treated at a temperature of 150°C to 600°C.

[0097] The above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The elements of the embodiments, as well as their arrangement, materials, conditions, shapes, sizes, etc., are not limited to those illustrated and can be modified as appropriate. Furthermore, configurations shown in different embodiments can be partially substituted or combined with each other. [Industrial Applicability]

[0098] 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. [Explanation of symbols]

[0099] 100... solar cell, 101... substrate, 102... rear electrode layer, 103... hole transport layer, 104... light absorption layer, 105... electron transport layer, 106... front electrode layer, 107... grid electrode

Claims

1. A substrate; a back electrode layer; a hole transport layer made of a p-type oxide semiconductor doped with an alkali metal element; a light absorbing layer in this order.

2. The p-type oxide semiconductor is NiO, CuO, CuGaO 2 , CuCrO 2 and CuAlO 2 The solar cell according to claim 1 , comprising one or more selected from the group consisting of:

3. The hole transport layer is made of Na 2 O.K. 2 O, Rb 2 O and Cs 2 3. The solar cell according to claim 1, wherein the p-type oxide semiconductor is doped with an alkali metal element source containing at least one selected from the group consisting of O.

4. in the hole transport layer, the number of moles of the alkali metal element is 0.1 to 0.3 times the sum of the number of moles of one metal element among the constituent elements of the p-type oxide semiconductor and the alkali metal element, 3. The solar cell according to claim 2, wherein the one metal element is selected from the group consisting of Ni and Cu.

5. 2. The solar cell according to claim 1, wherein the light absorbing layer comprises at least one compound selected from the group consisting of a chalcopyrite compound, a kesterite compound, and a perovskite compound.

6. a laminate preparation step of preparing a laminate including, in this order, at least a substrate, a back electrode layer, a hole transport layer that is a p-type oxide semiconductor to which an alkali metal element is added, and a precursor layer of a light absorption layer; a heat treatment step of heat treating the laminate in one or more atmospheres selected from the group consisting of a sulfur atmosphere, a selenium atmosphere, a chlorine atmosphere, a bromine atmosphere, and an iodine atmosphere.

7. The laminate preparation step includes:

7. The method for producing a solar cell according to claim 6, further comprising the step of pre-heat-treating the hole transport layer at a temperature of 525° C. to 575° C. in an inert atmosphere.

8. 7. The method for manufacturing a solar cell according to claim 6, wherein the stack preparation step includes a step of forming the hole transport layer on the back electrode layer by sputtering in an atmosphere having an oxygen concentration of 8% or more.

9. The p-type oxide semiconductor is NiO, CuO, CuGaO 2 , CuCrO 2 and CuAlO 2 The method for producing a solar cell according to claim 6 , comprising one or more selected from the group consisting of:

10. The hole transport layer is made of Na 2 O.K. 2 O, Rb 2 O and Cs 2 10. The method for producing a solar cell according to claim 6, wherein the p-type oxide semiconductor is a p-type oxide semiconductor to which an alkali metal element source containing one or more selected from the group consisting of O is added.

11. in the hole transport layer, the number of moles of the alkali metal element is 0.1 to 0.3 times the sum of the number of moles of one metal element among the constituent elements of the p-type oxide semiconductor and the alkali metal element, The method for producing a solar cell according to claim 9 , wherein the one metal element is selected from the group consisting of Ni and Cu.

12. 10. The method for producing a solar cell according to claim 6, wherein the light absorbing layer comprises at least one compound selected from the group consisting of a chalcopyrite compound, a kesterite compound, and a perovskite compound.

13. 10. The method for manufacturing a solar cell according to claim 6, wherein the laminate is heat-treated at a temperature of 150°C to 600°C in the heat treatment step.

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