Method for manufacturing solar cell and solar cell

Abstract

Provided are a method for manufacturing a solar cell (100) and a solar cell (100) that combine high performance with high productivity. The present disclosure relates to a method for manufacturing a solar cell (100), the method including a step for forming an electron transport layer (104) on a substrate including a light absorption layer (103) by depositing an n-type oxide semiconductor (104) by sputtering while supplying a gas containing an oxygen source and a hydrogen source.

Description

Solar cell manufacturing method and solar cell

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

[0002] One type of solar cell is a compound solar cell that uses a chalcopyrite compound, a kesterite compound, a perovskite compound, or the like. Compound solar cells have a structure in which a p-type light absorption layer and an n-type heterogeneous material serving as an electron transport layer are stacked. Cadmium sulfide is generally used as the n-type layer.

[0003] Non-Patent Documents 1 and 2 discuss the use of n-type oxide semiconductors such as zinc oxide, tin oxide, titanium oxide, zinc oxide sulfide, magnesium zinc oxide, zinc tin oxide, and titanium zinc oxide in place of cadmium sulfide for the electron transport layer.

[0004] EB Yousfi et al., Cadmium-free buffer layers deposited by atomic later epitaxy for copper indium diselenide solar cells, Thin Solid Films, 361-362, 183-186 (2000)Soumyadeep Sinha et al., A review on atomic layer deposited buffer layers for Cu(In,Ga)Se2(CIGS) thin film solar cells: Past, present, and future, Solar Energy, 209, 515-537 (2020)

[0005] However, when an n-type oxide semiconductor is used instead of cadmium sulfide as the electron transport layer, the resistance tends to be higher and the performance tends to be inferior compared to solar cells using cadmium sulfide. Furthermore, when forming an n-type oxide semiconductor as the electron transport layer, it is difficult to improve performance when using a sputtering method that is easy to mass-produce, and it is difficult to improve productivity when using an atomic layer deposition method that can produce high-performance solar cells.

[0006] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a solar cell manufacturing method and a solar cell that achieve both high performance and high productivity.

[0007] A method for manufacturing a solar cell according to one embodiment of the present invention includes a step of forming an electron transport layer on a substrate including a light absorbing layer by depositing an n-type oxide semiconductor by a sputtering method while supplying a gas including an oxygen source and a hydrogen source.

[0008] The present inventors have discovered that one of the factors that causes a decrease in the performance of solar cells when an n-type oxide semiconductor film is formed by sputtering is film damage that occurs on the surface of the substrate on which the n-type oxide semiconductor film is formed. A solar cell manufacturing method according to one embodiment of the present invention can reduce or suppress damage to the substrate caused by sputtering by forming the n-type oxide semiconductor film while supplying a gas containing not only an oxygen source but also a hydrogen source. As a result, high-performance solar cells can be manufactured with high productivity.

[0009] A solar cell according to one embodiment of the present invention comprises at least a first electrode layer, a light absorption layer, an electron transport layer which is an n-type oxide semiconductor doped with hydrogen elements, and a second electrode layer, in this order.

[0010] In a solar cell, by using an n-type oxide semiconductor to which hydrogen elements are added as the electron transport layer, the electron transport layer can be formed by sputtering while reducing or suppressing film formation damage to layers below the electron transport layer. As a result, such a solar cell can achieve both high performance and high productivity.

[0011] According to the present invention, it is possible to provide a solar cell manufacturing method and a solar cell that achieve both high performance and high productivity.

[0012] 1 is a schematic cross-sectional view of a solar cell according to one embodiment of the present invention, a schematic cross-sectional view of a solar cell according to another embodiment of the present invention, and a diagram showing the relationship between atmospheric conditions in a film formation step of an n-type oxide semiconductor and film formation damage caused by sputtering.

[0013] 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.

[0014] [Solar Cell] The solar cell according to this embodiment includes at least a first electrode layer, a light absorbing layer, an electron transport layer that is an n-type oxide semiconductor doped with hydrogen, and a second electrode layer, in this order. The solar cell may include layers other than these layers, or may include a plurality of these layers.

[0015] Fig. 1 shows a schematic cross-sectional view of a solar cell according to one embodiment. The solar cell 100 of the embodiment shown in Fig. 1 includes a substrate 107, a first electrode layer 101 provided on the substrate 107, a hole transport layer 102 provided on the first electrode layer 101, a light absorbing layer 103 provided on the hole transport layer 102, an electron transport layer 104 provided on the light absorbing layer 103, a second electrode layer 105 provided on the electron transport layer 104, and a grid electrode 106 provided on the second electrode layer 105. The solar cell 100 typically receives light from the second electrode layer 105 side to generate electricity.

[0016] In the solar cell 100 of this embodiment, the electron transport layer 104 is an n-type oxide semiconductor doped with hydrogen. Therefore, as described in detail in [Method for manufacturing a solar cell], it is presumed that the electron transport layer 104 can be formed by sputtering while reducing or suppressing film formation damage that occurs on the light absorbing layer 103 when the electron transport layer 104 is formed on the light absorbing layer 103. As a result, such a solar cell can achieve both high performance and high productivity. However, the present invention is not limited to the above presumption.

[0017] The thickness of the solar cell 100 excluding the substrate 107 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. The solar cell 100 of this embodiment can be a thin-film solar cell by forming each layer to be sufficiently thin.

[0018] Each component that may be included in the solar cell 100 will be described in detail below.

[0019] In this specification, when each layer or the semiconductor contained in each layer is expressed by the name of a certain compound, this includes not only the pure compound itself, but also the compound doped with a trace amount of an element or the like to the extent that the properties of the compound are not lost.

[0020] 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 clearly stated. For example, "elemental hydrogen" can refer to hydrogen atoms, hydrogen ions, hydride ions, hydrogen in a compound state, and hydrogen in an elemental state.

[0021] (Substrate) The substrate 107 is not particularly limited, but may be, for example, a glass substrate such as soda lime glass or low-alkali glass, a metal substrate such as a stainless steel plate or aluminum foil, or a resin substrate such as a polyimide resin substrate or an epoxy resin substrate. The thickness of the substrate 107 is not particularly limited, but may be, for example, 10 μm or more and 500 μm or less, 20 μm or more and 250 μm or less, or 30 μm or more and 100 μm or less. Having the thickness of the substrate 107 within the above ranges tends to enable the solar cell to be lighter and more flexible.

[0022] (First Electrode Layer) The first electrode layer 101 is provided, for example, to extract current due to holes generated in the light absorbing layer 103 described below. The first electrode layer 101 is not particularly limited as long as it is conductive, but examples thereof include 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; and a conductive organic compound conductive layer made of a conductive organic compound. 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 allowing current to be extracted sufficiently without loss.

[0023] (Hole Transport Layer) The solar cell 100 of this embodiment includes a hole transport layer 102, but this layer may be omitted. The hole transport layer 102 has the function of, for example, efficiently extracting holes generated in the light absorbing layer 103 (described later) 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 later). 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 organic compounds such as polythiophene derivatives such as poly(3,4-ethylene-dioxythiophene):polystyrene sulfonate (PEDOT:PSS), poly(3-hexylthiophene) (P3HT), and poly(3-octylthiophene) (P3OT); fluorene derivatives such as 2,2'-7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-MeO-TAD); carbazole derivatives such as polyvinylcarbazole; triphenylamine derivatives; diphenylamine derivatives; polysilane derivatives; and polyaniline derivatives; as well as inorganic compounds such as nickel oxide, molybdenum oxide, gallium copper oxide, aluminum copper 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.

[0024] The hole transport layer 102 preferably consists essentially of the aforementioned organic compound or inorganic compound, and is preferably the aforementioned organic compound or inorganic compound. The content of the aforementioned organic compound or 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.

[0025] 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.

[0026] (Light-absorbing layer) The light-absorbing layer 103 has a function of absorbing light such as near-infrared light, visible light, ultraviolet light, etc., 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 perovskite compound, a chalcopyrite compound, or a kesterite compound. The perovskite compound may be used alone or in combination of two or more types. 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.

[0027] The perovskite compound may be a compound represented by the general formula AMX ３ and those represented by the general formula A ２ MX ４ Here, M represents a divalent cation, A represents a monovalent cation, and X represents a monovalent anion.

[0028] 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 ions, rubidium ions, optionally substituted ammonium ions (including amidinium ions), optionally substituted phosphonium ions, and optionally substituted amidinium ions 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 also 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.

[0029] 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 cations (Sn ２＋ ), and germanium cation (Ge ２＋ In addition, a combination of two or more types of cations can be used as the cation M.

[0030] The monovalent anion X is not particularly limited, and examples thereof include 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 one type of anion or a combination of two or more types of 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.

[0031] The perovskite compound includes organic-inorganic perovskite compounds, particularly halide-based organic-inorganic perovskite compounds. Specific examples of perovskite compounds include CH ３ NH ３ PbI ３ , C.H. ３ NH ３ PbBr ３ , C.H. ３ NH ３ PbCl ３ , C.H. ３ NH ３ SnI ３ , C.H. ３ NH ３ SnBr ３ , C.H. ３ NH ３ SnCl ３ , C.H. ３ NH ３ PbI （３－ｘ） Cl ｘ , C.H. ３ NH ３ PbI （３－ｘ） Br ｘ , C.H. ３ NH ３ PbBr （３－ｘ） Cl ｘ , C.H. ３ NH ３ Pb （１－ｙ） Sn ｙ I ３ , C.H. ３ NH３ Pb （１－ｙ） Sn ｙ Br ３ , C.H. ３ NH ３ Pb （１－ｙ） Sn ｙ Cl ３ , C.H. ３ NH ３ Pb （１－ｙ） Sn ｙ I （３－ｘ） Cl ｘ , C.H. ３ NH ３ Pb （１－ｙ） Sn ｙ I （３－ｘ） Br ｘ , and C.H. ３ NH ３ Pb （１－ｙ） Sn ｙ Br （３－ｘ） Cl ｘ , and CH in the above compounds ３ NH ３ Instead of CFH ２ NH ３ , C.F. ２ HNH ３ , C.F. ３ NH ３ , or NH ２ CH=NH ２ 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.

[0032] 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 , AgAlTe２ , 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.

[0033] 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 , Cu２ 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 ４ When 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(Sｙ 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.

[0034] The content of the perovskite compound, chalcopyrite compound, or kesterite compound in the light absorbing layer 103 is not particularly limited as long as the light absorbing layer 103 has the function of absorbing light such as visible light or ultraviolet light to generate electrons and holes. More specifically, although not 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 103.

[0035] In addition to the above materials, the light absorbing layer 103 may contain additives such as a binder and a surfactant. 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 103. The light absorbing layer 103 does not necessarily need to contain the additives.

[0036] 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.

[0037] 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.

[0038] (Electron Transport Layer) The electron transport layer 104 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.

[0039] 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 electron transport layer 104, 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.

[0040] 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.

[0041] 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, 1.0×10１６ 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.

[0042] 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.

[0043] The refractive index of the n-type oxide semiconductor doped with hydrogen is not particularly limited. The refractive index of the n-type oxide semiconductor is, for example, 1.8 or more, preferably 2.1 or more. The refractive index is also not particularly limited, but is, for example, 1.8 to 3.0, 2.1 to 2.8, or 2.1 to 2.6. It is preferable to appropriately adjust the refractive index of the electron transport layer 104 so that the refractive index of the electron transport layer 104 does not become too large compared with that of an adjacent layer.

[0044] The refractive index can be measured by any known method, including, but not limited to, spectral transmittance measurement, spectroscopic ellipsometry, or the like.

[0045] 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 ２Ωcm 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.

[0046] 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.

[0047] 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 to which hydrogen elements are added preferably has a band gap of 3.3 eV or more and a carrier concentration of 1.0×10 ２０ cm －３ The resistivity is 1.6×10 or less. －２ Preferably, it is Ωcm or more.

[0048] The band gap is 3.3 eV or more, and the carrier concentration is 1.0×10 ２０ cm －３ The resistivity is 1.6×10 or less. －２ Preferred examples of the substance contained in the n-type oxide semiconductor in the n-type oxide semiconductor doped with hydrogen having a resistivity of Ωcm or more include zinc oxide, tin oxide, titanium oxide, zinc oxide sulfide (zinc oxide doped with sulfur), magnesium zinc oxide (zinc oxide doped with magnesium), zinc tin oxide (zinc oxide doped with tin), and titanium zinc oxide (zinc oxide doped with titanium). Of these, titanium zinc oxide (zinc oxide doped with titanium) is preferred. One type of n-type oxide semiconductor may be used alone, or two or more types may be used in combination.

[0049] In zinc oxide to which sulfur element is added, from the viewpoint of more reliably exhibiting the function of the electron transport layer 104, 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.

[0050] In zinc oxide doped with magnesium element, from the viewpoint of more reliably exhibiting the function of the electron transport layer 104, the molar ratio of magnesium element to zinc element is preferably 0 or more and 0.4 or less, or 0.1 or more and 0.3 or less.

[0051] In zinc oxide to which tin element is added, from the viewpoint of more reliably exhibiting the function of the electron transport layer 104, the molar ratio of tin element to zinc element is preferably 0 or more and 1.0 or less, or 0.2 or more and 0.4 or less.

[0052] In zinc oxide to which titanium element is added, from the viewpoint of more reliably exhibiting the function of the electron transport layer 104, 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.

[0053] In the n-type oxide semiconductor to which hydrogen elements are added, from the viewpoint of more reliably exhibiting the functions of the electron transport layer 104, 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.

[0054] The electron transport layer 104, which is an n-type oxide semiconductor to which hydrogen elements have been added, may be an electron transport layer formed by an electron transport layer forming step to be described later.

[0055] The electron transport layer 104, which is an n-type oxide semiconductor, is preferably composed essentially of zinc oxide, tin oxide, titanium oxide, zinc oxide sulfide, magnesium zinc oxide, zinc tin oxide, or titanium zinc oxide, and is preferably zinc oxide, tin oxide, titanium oxide, zinc oxide sulfide, magnesium zinc oxide, zinc tin oxide, or titanium zinc oxide. The content of zinc oxide, tin oxide, titanium oxide, zinc oxide sulfide, magnesium zinc oxide, zinc tin oxide, or titanium zinc oxide in the electron transport layer 104, 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, based on the total amount of the electron transport layer 104.

[0056] The thickness of the electron transport layer 104 is preferably 50 nm to 150 nm, 55 nm to 140 nm, 60 nm to 135 nm, or 65 nm to 130 nm. When the thickness of the electron transport layer 104 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.

[0057] (Second Electrode Layer) The second electrode layer 105 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 typically absorbs light that has passed through the second electrode layer 105. Therefore, in order to increase the amount of light absorbed by the light absorbing layer 103, the second electrode layer 105 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. The high electrical conductivity is not particularly limited, but may be, for example, a material having a specific resistance of 5.0×10 －３ This 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).

[0058] When the second electrode layer 105 is a transparent electrode, the content of the above material is not particularly limited as long as the second electrode layer 105 functions as a transparent electrode. More specifically, although not particularly limited, the content of the above material is, relative to the total mass of the second electrode layer 105, 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.

[0059] The thickness of the second electrode layer 105 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 105 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.

[0060] (Grid Electrode) The grid electrode 106 is provided, for example, to extract electricity from the second electrode layer 105, but may be omitted. The material of the grid electrode 106 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.

[0061] The content of the above-mentioned material in the grid electrode 106 is not particularly limited as long as the grid electrode 106 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 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, or 90% by mass to 100% by mass.

[0062] The thickness of the grid electrode 106 is not particularly limited, but is, for example, 5 μm to 50 μm. When the thickness of the grid electrode 106 is within this range, the solar cell tends to be lighter and more flexible while allowing sufficient current to be extracted without loss.

[0063] [Modifications] The solar cell 100 shown in FIG. 1 above is an example for explaining the present invention, and is not intended to limit the present invention to only this embodiment. The present invention can be modified in various ways without departing from the gist of the invention.

[0064] For example, the solar cell 100 of this embodiment may have two or three or more sets of a hole transport layer 102, a light absorbing layer 103 provided on the hole transport layer 102, an electron transport layer 104 provided on the light absorbing layer 103, and a second electrode layer 105 provided on the electron transport layer 104, stacked on the first electrode layer 101. Furthermore, a grid electrode 106 may be provided on the uppermost second electrode layer 105.

[0065] When there are a plurality of layers 101 to 107, the plurality of layers may be the same or different. For example, when there are a plurality of light-absorbing layers, each light-absorbing layer may contain a compound having a different absorption spectrum, and the electron transport layer and hole transport layer in contact with each light-absorbing layer may be selected according to the properties of the light-absorbing layer in contact with it.

[0066] Furthermore, the solar cell 100 of this embodiment may have other layers between the layers, on the grid electrode 106, or under the substrate 107, as necessary. For example, the hole transport layer 102 may have two or more hole transport layers each containing a different material, and a contamination prevention layer for preventing external contamination may be provided on the grid electrode 106. Furthermore, the electron transport layer 104 may have two or more electron transport layers each containing a different material, with the proviso that at least one of the layers is an n-type oxide semiconductor doped with hydrogen.

[0067] Figure 2 shows a schematic cross-sectional view of a solar cell according to one embodiment having two electron transport layers. The solar cell 200 of the embodiment shown in Figure 2 includes a substrate 107, a first electrode layer 101 provided on the substrate 107, 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 201 provided on the light absorbing layer 103, a second electron transport layer 202 provided on the first electron transport layer 201, a second electrode layer 105 provided on the second electron transport layer 202, and a grid electrode 106 provided on the second electrode layer 105. The solar cell 200 typically receives light from the second electrode layer 105 side to generate electricity.

[0068] 2 differs from the solar cell 100 shown in Fig. 1 in that it includes a first electron transport layer 201 and a second electron transport layer 202 instead of the electron transport layer 104. The other configurations may be similar to those of the solar cell 100.

[0069] (Electron Transport Layer) The solar cell 200 includes a first electron transport layer 201 and a second electron transport layer 202. At least one of the first electron transport layer 201 and the second electron transport layer 202 is an n-type oxide semiconductor doped with hydrogen elements. Either the first electron transport layer 201 or the second electron transport layer 202 may be an n-type oxide semiconductor doped with hydrogen elements, or both may be n-type oxide semiconductors doped with hydrogen elements. When the first electron transport layer 201 or the second electron transport layer 202 is an n-type oxide semiconductor doped with hydrogen elements, examples and preferred aspects of the n-type oxide semiconductor are similar to or the same as those of the electron transport layer 104.

[0070] Either the first electron transport layer 201 or the second electron transport layer 202 may be an electron transport layer other than an n-type oxide semiconductor doped with hydrogen. Such an electron transport layer is preferably an n-type semiconductor. The substance contained in the n-type semiconductor is not particularly limited, but examples thereof include oxide semiconductors such as zinc oxide, tin oxide, titanium oxide, zinc oxide sulfide, magnesium zinc oxide, zinc tin oxide, and titanium zinc oxide; sulfide semiconductors such as cadmium sulfide, indium oxide sulfide, and indium sulfide; and organic compounds such as PEIE (ethoxylated polyethyleneimine) and PEI (polyethyleneimine). Among these, sulfide semiconductors are preferred, with cadmium sulfide and indium sulfide being more preferred. The n-type semiconductors in the first electron transport layer 201 and the second electron transport layer 202 may be used singly or in combination of two or more.

[0071] The electron transport layer other than the n-type oxide semiconductor doped with hydrogen elements preferably consists essentially of the oxide semiconductor, sulfide semiconductor, or organic compound described above, and is preferably the oxide semiconductor, sulfide semiconductor, or organic compound described above. The content of the oxide semiconductor, sulfide semiconductor, or organic compound in the electron transport layer other than the n-type oxide semiconductor doped with hydrogen elements 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, relative to the total amount of the electron transport layer.

[0072] As described in detail in [Method for Manufacturing Solar Cell], when an n-type oxide semiconductor doped with hydrogen elements is formed as the electron transport layer, it is presumed that film formation damage to layers below the n-type oxide semiconductor can be reduced or suppressed. Furthermore, an n-type oxide semiconductor doped with hydrogen elements is less likely to be damaged during film formation when another layer is formed thereon. Therefore, when the first electron transport layer 201 is an n-type oxide semiconductor doped with hydrogen elements, film formation damage to the light absorbing layer 103 can be reduced or suppressed, and the first electron transport layer 201 is resistant to film formation damage during the formation of the second electron transport layer 202. When the second electron transport layer 202 is an n-type oxide semiconductor doped with hydrogen elements, film formation damage to the first electron transport layer 201 can be reduced or suppressed, and the second electron transport layer 202 is resistant to film formation damage during the formation of the second electrode layer 105.

[0073] In one embodiment of the solar cell 200, the first electron transport layer 201 is an n-type oxide semiconductor doped with hydrogen elements. In this case, the n-type oxide semiconductor doped with hydrogen elements is provided on the light absorbing layer 103.

[0074] In one aspect of the solar cell 200, the second electron transport layer 202 is an n-type oxide semiconductor doped with hydrogen elements. In this aspect, if the first electron transport layer 201 is not an n-type oxide semiconductor doped with hydrogen elements, an electron transport layer other than the n-type oxide semiconductor doped with hydrogen elements is provided between the light absorbing layer 103 and the second electron transport layer 202 that is an n-type oxide semiconductor doped with hydrogen elements.

[0075] When the first electron transport layer 201 or the second electron transport layer 202 is an n-type oxide semiconductor to which hydrogen elements have been added, the thickness of the first electron transport layer 201 or the second electron transport layer 202 is preferably 40 nm or more and 140 nm or less, 50 nm or more and 130 nm or less, or 55 nm or more and 120 nm or less.

[0076] When the first electron transport layer 201 or the second electron transport layer 202 is not an n-type oxide semiconductor doped with hydrogen elements, the thickness of the first electron transport layer 201 or the second electron transport layer 202 may be adjusted depending on the function of the electron transport layer and the materials contained therein, and is, for example, 10 nm or more and 60 nm or less, 15 nm or more and 50 nm or less, or 20 nm or more and 40 nm or less.

[0077] [Method for Manufacturing Solar Cell] (Electron Transport Layer Forming Step) The method for manufacturing a solar cell according to this embodiment includes a step of forming an electron transport layer on a substrate including a light absorption layer by depositing an n-type oxide semiconductor by a sputtering method while supplying a gas including an oxygen source and a hydrogen source (hereinafter referred to as the "electron transport layer forming step").

[0078] The present inventors have discovered that one of the factors that reduces the performance of solar cells when an n-type oxide semiconductor is deposited by sputtering is damage to the substrate on which the n-type oxide semiconductor is deposited. The solar cell manufacturing method according to the present embodiment deposits an n-type oxide semiconductor while supplying a gas containing not only an oxygen source but also a hydrogen source, thereby reducing or suppressing film formation damage to the substrate caused by sputtering. As a result, high-performance solar cells can be manufactured with high productivity. The present inventors have hypothesized that one of the factors that contributes to the reduction or suppression of film formation damage by supplying a gas containing a hydrogen source is that the hydrogen source captures active oxygen species generated on the substrate surface during sputtering. That is, when an oxide semiconductor is deposited by sputtering, a gas containing an oxygen source is supplied. The present inventors hypothesized that one of the factors that causes film formation damage is that active species generated from the oxygen source damage the surface of the substrate on which the oxide semiconductor is to be formed. As a result of extensive research, the inventors have found that a method for forming an n-type oxide semiconductor suitable as an electron transport layer while capturing the active species involves depositing an n-type oxide semiconductor by sputtering while supplying a gas containing a hydrogen source. Note that the above predictions and hypotheses are made for the purpose of explaining the present invention, and are not intended to limit the present invention.

[0079] The solar cell manufacturing method according to the present embodiment may have the following advantages over conventional solar cell manufacturing methods. As described above, forming an electron transport layer by sputtering in conventional methods can damage layers below the electron transport layer. Therefore, conventional solar cell manufacturing methods use expensive deposition methods, such as atomic layer deposition and chemical solution deposition, to form the electron transport layer. In contrast, the solar cell manufacturing method according to the present embodiment can form the electron transport layer by sputtering, which is suitable for mass production, thereby enabling the production of high-performance solar cells with high productivity. Furthermore, while deposition methods such as chemical solution deposition are wet processes, most steps in the solar cell manufacturing method are dry processes. Therefore, compared to methods that use a wet process to form the electron transport layer, the solar cell manufacturing method according to the present embodiment can also form the electron transport layer by a dry process, further shortening the manufacturing time. Note that, in this specification, a wet process refers to a process using a solution. A dry process refers to a process that does not use a solution.

[0080] Damage to the film formation caused on the substrate by sputtering can be evaluated by measuring the open-circuit voltage retention rate as shown in Example 1. That is, damage to the film formation can be evaluated by measuring the open-circuit voltage under standard test conditions for a solar cell manufactured by the manufacturing method according to this embodiment and a solar cell (control example) in which an electron transport layer is formed using a chemical solution deposition method, and calculating the open-circuit voltage value of the solar cell manufactured by the manufacturing method according to this embodiment using the open-circuit voltage of the solar cell of the control example as a reference. The standard test conditions for solar cells are light with a spectral spectrum of AM 1.5 at an irradiance of 1 kW / m ２ The test conditions were that the incident light was incident at 1000 W and the solar cell temperature was 25° C. The electron transport layer of the solar cell (control example) in which the electron transport layer was formed using the chemical solution deposition method may be a layer of an n-type oxide semiconductor containing cadmium sulfide having the same thickness as the electron transport layer of the comparative solar cell.

[0081] In the solar cell manufacturing method and electron transport layer forming step according to this embodiment, the open-circuit voltage maintenance rate is preferably 60% or more, 70% or more, 75% or more, 80% or more, 85% or more, or 90% or more. The manufacturing method according to this embodiment forms the electron transport layer by sputtering while supplying a gas containing an oxygen source and a hydrogen source. Therefore, even though the electron transport layer is formed using sputtering, film formation damage to the substrate can be reduced or suppressed. Therefore, it is believed that a high level of open-circuit voltage can be maintained compared to solar cells in which the electron transport layer is formed using chemical solution deposition instead of sputtering.

[0082] As a standard for the open-circuit voltage maintenance rate, a solar cell in which an electron transport layer is formed by atomic layer deposition may be used instead of a solar cell in which an electron transport layer is formed by chemical solution deposition. The open-circuit voltage value of the solar cell manufactured by the manufacturing method according to this embodiment, based on a solar cell in which an electron transport layer is formed by atomic layer deposition in the manufacturing method of the solar cell according to this embodiment and the electron transport layer forming step, is preferably 60% or more, 70% or more, 75% or more, 80% or more, 85% or more, or 90% or more.

[0083] In the electron transport layer forming step, an n-type oxide semiconductor is deposited by sputtering while supplying a gas containing an oxygen source and a hydrogen source, thereby forming an electron transport layer on a substrate containing a light absorbing layer. More specifically, the substrate containing a light absorbing layer is heated, and an n-type oxide semiconductor is deposited on the substrate using an appropriate sputtering target while supplying a gas containing an oxygen source and a hydrogen source.

[0084] The substrate on which the n-type oxide semiconductor film is formed may be a substrate including a light absorbing layer, but a substrate including a light absorbing layer and a first electrode is preferred, a substrate including a laminated structure in which a light absorbing layer, a hole transport layer, and a first electrode are laminated in this order is more preferred, and a substrate including a laminated structure in which a light absorbing layer, a hole transport layer, a first electrode, and a substrate are laminated in this order is even more preferred.

[0085] In one embodiment, the substrate may have a light absorbing layer on its surface, in which case the n-type oxide semiconductor is deposited on the light absorbing layer. In one embodiment, the substrate may have an electron transport layer on its surface, in which case the n-type oxide semiconductor is deposited on the electron transport layer. The substrate may be, for example, a stack in which a light absorbing layer, a hole transport layer, a first electrode, and a substrate are stacked in this order, a stack in which an electron transport layer, a light absorbing layer, a hole transport layer, a first electrode, and a substrate are stacked in this order, or any of these stacks that does not include a hole transport layer. When the stack serving as the substrate includes an electron transport layer, the electron transport layer may be an electron transport layer that is an n-type oxide semiconductor doped with hydrogen, or may be another electron transport layer. Specifically, it may be the first electron transport layer 201 in the solar cell 200. Using such a substrate makes it possible to more easily manufacture a solar cell.

[0086] The electron transport layer, light absorption layer, hole transport layer, first electrode, and substrate that the substrate may include may be the same as or similar to the first electron transport layer 201, light absorption layer 103, hole transport layer 102, first electrode layer 101, and substrate 107, respectively.

[0087] The sputtering target in the electron transport layer formation step may contain any element 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 more preferably an oxide of a metal contained in the n-type oxide semiconductor to be formed. For example, titanium zinc oxide (zinc oxide doped with titanium element) can be formed by using a mixture of titanium oxide and zinc oxide as the sputtering target. Furthermore, an n-type oxide semiconductor containing sulfur element can be formed by using a sputtering target containing a sulfide of a metal contained in the n-type oxide semiconductor to be formed. The content of metal element and other elements including oxygen element and sulfur element in the n-type oxide semiconductor to be formed can be controlled by adjusting the elements added to the sputtering target.

[0088] In one embodiment, the sputtering target is a mixture of titanium oxide and zinc oxide. This allows for the deposition of a titanium zinc oxide film (zinc oxide doped with titanium element). The content of titanium oxide in 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. The remainder may be the content of zinc oxide.

[0089] The gas supplied in the electron transport layer forming step includes an oxygen source and a hydrogen source. The gas may be mainly composed of an inert gas, preferably argon gas. The oxygen source is not particularly limited as long as it contains oxygen element. For example, H ２ O steam, O ２ gas, and 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, and H ２ Gases include H ２ Gas is preferred.

[0090] The concentration of the oxygen source in the supply gas is preferably 0.12 vol% or more and 2.0 vol% or less, 0.40 vol% or more and 1.8 vol% or less, 0.70 vol% or more and 1.6 vol% or less, 0.80 vol% or more and 1.5 vol% or less, 0.90 vol% or more and 1.5 vol% or less, or 1.0 vol% or more and 1.5 vol% or less, in terms of oxygen molecules. The concentration of the oxygen source in terms of oxygen molecules is specifically calculated as follows. When the oxygen source is H 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.

[0091] The molar ratio of hydrogen element to oxygen element (H / O) contained in the supply gas is preferably 0.60 or more and 4.0 or less, 0.80 times or more and 3.0 times or less, 1.0 times or more and 2.5 times or less, 1.2 times or more and 2.0 times or less, or 1.3 times or more and 1.8 times or less. 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 ２ O 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. Therefore, the molar ratio of hydrogen atoms to oxygen atoms is calculated as (1.6 x 2) ÷ (1.6 + 0.8 x 2) = 1.0. ２ Gas, H as hydrogen source ２ When gas is used, O ２ Gas and H ２ The volume ratio of the gas corresponds to the molar ratio.

[0092] It is particularly preferable that the oxygen source and hydrogen source of the supply gas satisfy the following condition (1) or (2): (1) The concentration of the oxygen source is 0.80% by volume or more and 1.6% by volume or less in terms of oxygen molecules, and when the concentration of the oxygen source (volume % in terms of oxygen molecules) is y and the molar ratio of hydrogen element to oxygen element (H / O) is x, the following formula is satisfied: 0.85y + 0.1≦x≦3.0y − 0.9 (2) The concentration of the oxygen source is 0.12% by volume or more and less than 0.80% by volume, and when the concentration of the oxygen source (volume % in terms of oxygen molecules) is y and the molar ratio of hydrogen element to oxygen element (H / O) is x, the following formula is satisfied: 0.78≦x≦−2.2y + 3.3

[0093] The concentration of the inert gas (e.g., argon gas) in the supply gas is not particularly limited, but may be, for example, 90.0 vol% to 99.0 vol%, 91.0 vol% to 98.5 vol%, 92.0 vol% to 98.0 vol%, 93.0 vol% to 97.5 vol%, or 94.0 vol% to 97.0 vol%. The remainder excluding the oxygen source and the hydrogen source may be the inert gas.

[0094] In the electron transport layer forming step, it is preferable to perform the sputtering treatment while heating the base material including the light absorbing layer. The heating temperature (heat source temperature) is not particularly limited, but may be, for example, 80° C. to 230° C., preferably 100° C. to 200° C., or 120° C. to 180° C. When a metal substrate is used as the substrate, the temperature of the base material and the heating temperature are almost the same.

[0095] Other film formation conditions for the sputtering method may be adjusted depending on the type of n-type oxide semiconductor to be formed and the type of sputtering target. For example, applied power: 0.5 to 3.0 W / cm ２ The film formation pressure may be set to 0.5 to 3.0 Pa. The temperature of the atmosphere does not need to be controlled during sputtering.

[0096] The method for manufacturing a solar cell according to this embodiment may include a step of preparing a base material including a light absorbing layer, followed by the above-described step of forming an electron transport layer. The method for manufacturing a solar cell according to this embodiment may include a step of forming another layer on the electron transport layer, followed by the above-described step of forming an electron transport layer.

[0097] The step of preparing a substrate including a light absorbing layer may include at least one of forming a first electrode layer, forming a hole transport layer, forming a light absorbing layer, and forming an electron transport layer. The step of forming another layer on the electron transport layer may include at least one of forming a further electron transport layer, forming a second electrode layer, and forming a grid electrode.

[0098] The method for manufacturing a solar cell according to this embodiment may include, in this order, at least a step of forming a first electrode layer, a step of forming a light absorbing layer, the above-mentioned step of forming an electron transport layer, and a step of forming a second electrode layer.

[0099] Hereinafter, each step that can be included in the method for manufacturing a solar cell according to this embodiment will be described in detail with reference to FIGS. 1 and 2 as needed.

[0100] (First Electrode Layer Forming Step) In the first electrode layer forming step, for example, the first electrode layer 101 may be formed on the substrate 107. Methods for forming the first electrode layer 101 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 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 the substrate on the 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 107 may be the sputtering substrate.

[0101] (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 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 of forming the hole transport layer 102, which is a p-type semiconductor containing an organic compound or 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.

[0102] (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 of the dry process is a method for forming the light-absorbing layer 103 containing a perovskite compound, 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.

[0103] 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 perovskite compound, a chalcopyrite compound, or a kesterite compound by a sputtering method. Alternatively, the alkali metal element may be added to the substrate 107 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.

[0104] (Additional Electron Transport Layer Forming Step) The method for manufacturing a solar cell according to this embodiment may include an additional electron transport layer forming step in addition to the above-described electron transport layer forming step. When the additional electron transport layer forming step is included, a solar cell 200 including a first electron transport layer 201 and a second electron transport layer 202 can be formed as shown in FIG. 2 . The additional electron transport layer forming step may be a step of forming an electron transport layer on a substrate including a light absorbing layer by depositing an n-type oxide semiconductor by a sputtering method while supplying a gas including an oxygen source and a hydrogen source, similar to the above-described electron transport layer forming step, or may be a step of forming an electron transport layer by a method different from the above-described electron transport layer forming step.

[0105] In the additional electron transport layer formation step, for example, a first electron transport layer 201 may be formed on the light absorbing layer 103, or a second electron transport layer 202 may be formed on the first electron transport layer 201 formed in the above-mentioned electron transport layer formation step.

[0106] Examples of a process for forming an electron transport layer by a method different from the above-described electron transport layer formation process include a process for depositing an n-type oxide semiconductor by a sputtering method while supplying a gas not containing a hydrogen source, and a process for depositing an n-type oxide semiconductor by a method other than the sputtering method.

[0107] 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 that may contain oxygen, and the deposition pressure may be 0.5 to 3.0 Pa. The temperature of the atmosphere may not be controlled during sputtering. It is preferable to heat the substrate to be sputtered during sputtering. For other sputtering conditions, refer to the above-mentioned electron transport layer forming step.

[0108] Methods other than sputtering for forming an n-type oxide semiconductor film include chemical solution deposition and atomic layer deposition, which are well known in the art.

[0109] (Second Electrode Layer Forming Step) In the second electrode layer forming step, for example, the second electrode layer 105 may be formed on the electron transport layer 104 or the second electron transport layer 202. Methods for forming the second electrode layer 105 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 for forming the second electrode layer 105, 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.

[0110] (Grid Electrode Forming Process) In the grid electrode forming process, for example, the grid electrode 106 may be formed on the second electrode layer 105. Methods for forming the grid electrode 106 include a dry process and a wet process. Specific examples of the methods include sputtering, vapor deposition, a method of printing a paste-like conductive material on the second electrode layer 105, and a method of crimping a conductive wire.

[0111] [Method of Using Solar Cell] Like conventional solar cells, the solar cell 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, the solar cell 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, deserts, tropical zones, building rooftops, automobile roofs, the exterior walls of airplanes, etc.).

[0112] The solar cell of this embodiment can also be used as an independent power source device for street lights, sensors, digital signage, etc. The solar cell of this embodiment can also be used as a mobile energy device.

[0113] [Additional Notes] Embodiments of the present disclosure include the following aspects. [1] A method for manufacturing a solar cell, comprising the step of forming an electron transport layer on a substrate including a light absorbing layer by depositing an n-type oxide semiconductor by sputtering while supplying a gas containing an oxygen source and a hydrogen source. [2] The manufacturing method according to [1], wherein the open-circuit voltage under standard test conditions of the manufactured solar cell is 70% or more, preferably 80% or more, compared to a solar cell in which an electron transport layer made of an n-type oxide semiconductor is formed by chemical solution deposition instead of the step of forming the electron transport layer. [3] The manufacturing method according to [1] or [2], wherein the substrate has, as an outermost layer, the light absorbing layer or a second electron transport layer made of a material different from the n-type oxide semiconductor. [4] The manufacturing method according to any one of [1] to [3], wherein the substrate has, as an outermost layer, the light absorbing layer, and the light absorbing layer contains a chalcopyrite compound, a kesterite compound, or a perovskite compound. [5] The manufacturing method according to any one of [1] to [4], wherein the concentration of the oxygen source in the gas supplied in the step is 0.12 vol % or more and 2.0 vol % or less, preferably 0.8 vol % or more and 1.6 vol % or less, calculated as oxygen molecules. [6] The manufacturing method according to any one of [1] to [5], wherein the molar ratio of hydrogen elements to oxygen elements contained in the gas supplied in the step is 0.60 times or more and 4.0 times or less, preferably 1.0 times or more and 2.0 times or less. [7] 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 －３The manufacturing method according to any one of [1] to [6], wherein the n-type oxide semiconductor is one of the following oxide semiconductors: [8] The manufacturing method according to [7], wherein the n-type oxide semiconductor is zinc oxide, tin oxide, titanium oxide, zinc oxide sulfide, magnesium zinc oxide, zinc tin oxide, or titanium zinc oxide. [9] The manufacturing method according to any one of [1] to [8], wherein the n-type oxide semiconductor is titanium zinc oxide, and the film formation is performed using a mixture of zinc oxide and titanium oxide containing 4.0 mass % to 20 mass % titanium oxide as a sputtering target.

[10] The manufacturing method according to [9], wherein the film formation is performed while heating the base material to 100°C to 200°C.

[11] A solar cell comprising at least a first electrode layer, a light absorbing layer, an electron transport layer which is an n-type oxide semiconductor doped with hydrogen, and a second electrode layer, in this order.

[12] The solar cell according to

[11] , wherein the electron transport layer is provided on the light absorbing layer.

[13] The solar cell according to

[11] , further comprising a second electron transport layer between the light absorbing layer and the second electrode layer, the second electron transport layer being made of a material different from the electron transport layer which is an n-type oxide semiconductor doped with hydrogen.

[14] The solar cell according to

[13] , wherein the second electron transport layer is provided between the light absorbing layer and the electron transport layer which is an n-type oxide semiconductor doped with hydrogen.

[15] The solar cell according to any one of

[11] to

[14] , wherein the light absorbing layer contains a chalcopyrite compound, a kesterite compound, or a perovskite compound.

[16] 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 The solar cell according to any one of

[11] to

[15] , wherein the n-type oxide semiconductor is any of the following oxide semiconductors:

[17] The solar cell according to

[16] , wherein the n-type oxide semiconductor is zinc oxide, tin oxide, titanium oxide, zinc sulfide oxide, magnesium zinc oxide, zinc tin oxide, or titanium zinc oxide.

[0114] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0115] Example 1 (Method of Manufacturing Solar Cell) A solar cell having a single electron transport layer was manufactured as shown in Figure 1. A titanium foil having a thickness of 50 µm was used as the substrate 107. A first electrode layer 101 containing metallic molybdenum was formed on the substrate 107 by sputtering to a thickness of 600 nm.

[0116] 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.

[0117] Next, a sputtering method was used to form an electron transport layer 104, which was an n-type oxide semiconductor containing zinc oxide doped with hydrogen and titanium, on the light absorption layer 103 to a thickness of 100 nm. The sputtering conditions were as follows: Sputtering target: a mixture of zinc oxide and titanium oxide (titanium oxide was 14 mass %) Film formation atmosphere: argon, hydrogen gas, and oxygen gas atmosphere (sputtering was performed under multiple conditions with the volume concentration of oxygen gas in the supplied mixed gas ranging from 0.12 volume % to 1.6 volume %. Sputtering was also performed under multiple conditions with the volume ratio of hydrogen gas to oxygen gas ranging from 0.67 to 4.0). Heating temperature of the sputtering substrate during film formation: 160°C

[0118] The amount of hydrogen element in the electron transport layer 104 formed under the conditions where the volume concentration of hydrogen gas in the supplied mixed gas was 1.6 vol % and the volume concentration of oxygen gas was 1.2 vol % was measured by the RBS / HFS method. As a result, the molar ratio of hydrogen element to all metal elements was 0.011.

[0119] Next, a second electrode layer 105, which is a transparent electrode layer containing hydrogen-containing indium oxide (IOH), was formed on the electron transport layer 104 by sputtering to a thickness of 300 nm.

[0120] (Estimation of Film Formation Damage) First, a solar cell of a control example was fabricated. Similar to Example 1, a first electrode layer and a light absorbing layer were formed on a substrate. Then, a 100 nm-thick electron transport layer, which was an n-type oxide semiconductor containing cadmium sulfide, was formed on the light absorbing layer using a chemical solution deposition method. Then, a second electrode layer was formed on the electron transport layer. The second electrode layer was formed in the same manner as in Example 1.

[0121] The electron transport layer was formed by chemical solution deposition as follows: an aqueous solution containing cadmium sulfate, thiourea, and ammonia was placed in a beaker, the surface of the light absorbing layer was immersed in the solution, and the aqueous solution was gradually heated from room temperature to form an electron transport layer, which was an n-type oxide semiconductor.

[0122] Next, the open circuit voltage (V ｏｃ The open circuit voltage can be determined from the IV curve. Specifically, the intersection of the IV curve and the x-axis (voltage axis) on the graph is V ｏｃ The IV curve was measured under standard solar cell test conditions (light with spectrum AM1.5 at an irradiance of 1kW / m ２ The measurements were performed under test conditions in which the solar cell temperature was 25°C and the incident light was incident at a wavelength of 1.6 vol. The open-circuit voltage of the solar cell fabricated under each condition in Example 1 was divided by the open-circuit voltage of the solar cell in the control example to calculate the open-circuit voltage maintenance rate. Table 1 shows the relationship between the volume concentration of oxygen gas in the mixed gas supplied in the sputtering process, the volume ratio of oxygen gas to hydrogen gas, and the open-circuit voltage maintenance rate. In Table 1, values ​​highlighted in bold and underlined are actual measured values, and other values ​​are the average of at least two adjacent values. A graph created by linear interpolation based on Table 1 is shown in Figure 3. In the following Examples 2 and 3, conditions were used in which the volume concentration of hydrogen gas was 1.6 vol.% and the volume ratio of oxygen gas was 1.2 vol.% (the volume ratio of hydrogen gas to oxygen gas was 1.3).

[0123]

[0124] Example 2 (Method of Producing Solar Cells) In the method of producing solar cells of Example 1, a plurality of solar cells were produced by changing the thickness of the electron transport layer, which is an n-type oxide semiconductor containing zinc oxide doped with titanium element, the proportion of titanium oxide in the sputtering target, and the heating temperature of the sputtered substrate during film formation (see Table 2-3 below for each condition).

[0125] (Conversion Efficiency) First, a solar cell of a control example was fabricated. The solar cell of the control example was fabricated in the same manner as the solar cell of Example 1, except for the electron transport layer. In the solar cell of the control example, an n-type semiconductor containing cadmium sulfide was formed to a thickness of 70 nm on the light absorption layer using a chemical solution deposition method as the electron transport layer.

[0126] Next, the conversion efficiency was measured for the solar cell of Example 2 and the solar cell of the control example. The IV curves 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 performed under test conditions where the solar cell temperature was 25°C and the incident light was 1000kJ / s. The conversion efficiency of each solar cell was calculated using the following formula. The conversion efficiency is calculated as the output (maximum output: P ｍａｘ ) divided by the light energy E received by the solar cell. Conversion efficiency (%) = P ｍａｘ ÷E×100

[0127] The conversion efficiency ratio was calculated by dividing the conversion efficiency of the solar cell fabricated under each condition of Example 2 by the conversion efficiency of the solar cell of the Control Example. The relationship between the thickness of the electron transport layer, which is an n-type oxide semiconductor containing zinc oxide doped with titanium element, the proportion of titanium oxide in the sputtering target, or the heating temperature of the sputtered substrate during film formation and the conversion efficiency ratio is shown in Table 2-3 below. In the table, "-" indicates that no solar cell was fabricated.

[0128]

[0129]

[0130] Example 3 (Method of Producing Solar Cell) A solar cell having a two-layer electron transport layer was produced as shown in Fig. 2. The solar cell was produced in the same manner as in Example 1, except that two electron transport layers were formed.

[0131] The electron transport layer was formed as follows. First, a first electron transport layer 201, which was an n-type semiconductor containing indium sulfide or an n-type semiconductor containing cadmium sulfide, was formed to a thickness of 30 nm on the light absorption layer 103. The n-type semiconductor containing cadmium sulfide was formed using a chemical solution deposition method. The n-type semiconductor containing indium sulfide was formed using a sputtering method. The sputtering conditions were as follows: Sputtering target: indium sulfide Film formation atmosphere: argon atmosphere Heating temperature of sputtered substrate during film formation: 200°C

[0132] Next, a second electron transport layer 202, which was an n-type oxide semiconductor containing zinc oxide doped with hydrogen and titanium, was formed by sputtering on the first electron transport layer 201. The second electron transport layer 202 was formed in the same manner as the electron transport layer in Example 1, except that the thickness of the n-type oxide semiconductor (second electron transport layer 202), the proportion of titanium oxide in the sputtering target, and / or the heating temperature of the sputtered substrate during film formation were changed to the values ​​shown in Table 4-5 below.

[0133] The conversion efficiency of the solar cells fabricated under each condition was measured in the same manner as in Example 2. Similarly, the conversion efficiency ratio to that of a control solar cell having an electron transport layer that is an n-type semiconductor containing cadmium sulfide was calculated. The results are shown in Tables 4-5 below. In the tables, "-" indicates that the solar cell was not fabricated, and "RT" indicates room temperature.

[0134]

[0135]

[0136] 100, 200... solar cell, 101... first electrode layer, 102... hole transport layer, 103... light absorption layer, 104... electron transport layer, 105... second electrode layer, 106... grid electrode, 107... substrate, 201... first electron transport layer, 202... second electron transport layer.

Claims

1. A method for manufacturing a solar cell, comprising the step of forming an n-type oxide semiconductor film by a sputtering method while supplying a gas containing an oxygen source and a hydrogen source, thereby forming an electron transport layer on a substrate including a light absorbing layer.

2. The manufacturing method according to claim 1, wherein the open circuit voltage under standard test conditions of the manufactured solar cell is 70% or more compared to a solar cell in which an electron transport layer made of an n-type oxide semiconductor is formed by a chemical solution deposition method instead of the step of forming the electron transport layer.

3. The manufacturing method according to claim 1 or 2, wherein the substrate has, as an outermost layer, a second electron transport layer made of a material different from the light absorbing layer or the n-type oxide semiconductor.

4. The manufacturing method according to any one of claims 1 to 3, wherein the substrate has the light absorbing layer on an outermost surface thereof, and the light absorbing layer contains a chalcopyrite compound, a kesterite compound, or a perovskite compound.

5. The manufacturing method according to any one of claims 1 to 4, wherein the concentration of the oxygen source in the gas supplied in the step is 0.12 vol % or more and 2.0 vol % or less in terms of oxygen molecules.

6. The method according to any one of claims 1 to 5, wherein the molar ratio of hydrogen element to oxygen element contained in the gas supplied in the step is 0.60 to 4.

0.

7. 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 any one of claims 1 to 6, wherein the oxide semiconductor is one of the following:

8. The method according to claim 7, wherein the n-type oxide semiconductor is zinc oxide, tin oxide, titanium oxide, zinc sulfide oxide, zinc magnesium oxide, zinc tin oxide, or zinc titanium oxide.

9. The manufacturing method according to any one of claims 1 to 8, wherein the n-type oxide semiconductor is zinc titanium oxide, and the film formation 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.

10. The manufacturing method according to claim 9, wherein the film formation is carried out while heating the substrate to 100°C or higher and 200°C or lower.

11. A solar cell comprising at least a first electrode layer, a light absorbing layer, an electron transport layer which is an n-type oxide semiconductor doped with hydrogen elements, and a second electrode layer, in this order.

12. The solar cell according to claim 11, wherein the electron transport layer is provided on the light absorbing layer.

13. The solar cell according to claim 11 or 12, further comprising a second electron transport layer between the light absorption layer and the second electrode layer, the second electron transport layer being made of a material different from that of the electron transport layer, which is an n-type oxide semiconductor doped with hydrogen elements.

14. The solar cell according to claim 13, wherein the second electron transport layer is provided between the light absorption layer and the electron transport layer which is an n-type oxide semiconductor doped with hydrogen elements.

15. The solar cell according to any one of claims 11 to 14, wherein the light absorbing layer contains a chalcopyrite compound, a kesterite compound, or a perovskite compound.

16. 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 11 to 15, wherein the oxide semiconductor is one of the following:

17. The solar cell according to claim 16, wherein the n-type oxide semiconductor is zinc oxide, tin oxide, titanium oxide, zinc sulfide oxide, zinc magnesium oxide, zinc tin oxide, or zinc titanium oxide.

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