Solar cell, solar cell module, and method for producing solar cell

Abstract

The purpose of the present invention is to provide a solar cell in which the efficiency of light absorption is increased and deterioration of a conductive mirror layer is suppressed, a solar cell module, and a method for producing the solar cell. The present disclosure relates to a solar cell (100) at least comprising, in the following order, a substrate (101), a conductive mirror layer (104), a p-type oxide semiconductor that is a hole transport layer (105), and a light absorption layer (106).

Description

Solar cell, solar cell module, and method for manufacturing solar cell

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

[0002] In solar cells, there is a limit to the upper limit of the thickness of the light absorbing layer from the viewpoint of reducing mass production costs and preventing peeling of the light absorbing layer. Therefore, there is a problem that the efficiency of absorbing light such as sunlight in solar cells cannot be increased to a certain level. Therefore, attempts have been made to increase the light absorption efficiency without increasing the thickness of the light absorbing layer. For example, Non-Patent Document 1 considers improving the light absorption efficiency of solar cells by reflecting sunlight that has passed through the light absorbing layer because it cannot absorb it on the back surface and allowing the sunlight to be absorbed by the light absorbing layer.

[0003] Prog. Photovolt: Res. Appl. , 2018, 23, pp. 1-7.

[0004] In the solar cell described in Non-Patent Document 1, a metal mirror layer is formed on a back electrode, a transparent conductive oxide layer is formed on top of that for the purpose of protecting the metal mirror layer and ensuring conductivity, and an extremely thin molybdenum or molybdenum selenide layer is further formed on top of that.

[0005] However, it has been found that the oxide transparent conductive layer cannot sufficiently protect the metal mirror layer, and the conductive mirror layer is prone to deterioration.

[0006] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a solar cell, a solar cell module, and a method for manufacturing a solar cell that improves light absorption efficiency and suppresses deterioration of the conductive mirror layer.

[0007] A solar cell according to one embodiment of the present invention comprises at least a substrate, a back electrode, a conductive mirror layer, a hole transport layer which is a p-type oxide semiconductor, and a light absorption layer, in this order.

[0008] The present inventors have found that when a solar cell includes a conductive mirror layer and a hole transport layer that is a p-type oxide semiconductor is present between the conductive mirror layer and the light absorbing layer, the solar light absorption efficiency of the solar cell is improved and deterioration of the conductive mirror layer can be suppressed.

[0009] A method for manufacturing a solar cell according to one embodiment of the present invention includes a laminate preparation step of preparing a laminate including at least a substrate, a back electrode, a conductive mirror layer, a hole transport layer that is a p-type semiconductor, and a precursor layer of a light absorption layer, in this order, 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.

[0010] The present inventors have found that the solar cell manufactured by the above-described manufacturing method can have improved sunlight absorption efficiency and can suppress deterioration of the conductive mirror layer when the laminate prepared in the laminate preparation step includes a conductive mirror layer and a hole transport layer that is a p-type oxide semiconductor is present between the conductive mirror layer and the precursor layer of the light absorbing layer.

[0011] According to the present invention, it is possible to provide a solar cell, a solar cell module, and a method for manufacturing a solar cell that improves the efficiency of absorbing light such as sunlight and suppresses deterioration of the conductive mirror layer.

[0012] 1 is a schematic cross-sectional view of a solar cell according to one embodiment of the present invention. 2 is a graph showing the results of a simulation.

[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] 1. Solar Cell Fig. 1 is a schematic cross-sectional view of a solar cell according to one embodiment of the present invention. The solar cell 100 of this embodiment includes at least a substrate 101, a back electrode 102, a conductive mirror layer 104, a hole transport layer 105 which is a p-type oxide semiconductor, and a light absorbing layer 106, in this order. The back electrode 102 may be provided between the substrate 101 and the conductive mirror layer 104. An intermediate layer may be provided between each layer as needed, from the viewpoints of interlayer adhesion, bonding, conductivity, etc.

[0015] The solar cell 100 of this embodiment generates electricity by receiving light such as sunlight from the light absorbing layer 106 side when viewed from the substrate 101. Here, in the solar cell 100 of this embodiment, by providing the conductive mirror layer 104 between the back electrode 102 and the light absorbing layer 106, the light absorption efficiency of the solar cell 100 tends to improve. This is thought to be because the conductive mirror layer 104 reflects light that the light absorbing layer 106 cannot fully absorb, and the reflected light can be absorbed by the light absorbing layer 106.

[0016] The solar cell 100 of this embodiment also includes a hole transport layer 105 made of a p-type oxide semiconductor. The conductive mirror layer 104 is preferably made of a material with high light reflectivity. However, such materials are prone to a decrease in light reflectivity due to oxidation, corrosion, and the like, so a layer that can protect the conductive mirror layer 104 is generally provided. In this regard, the hole transport layer 105 made of a p-type oxide semiconductor protects the conductive mirror layer 104 and can suppress a decrease in the light reflectivity of the conductive mirror layer 104. Furthermore, from the perspective of the valence band position, a p-type oxide semiconductor has good electrical compatibility with the light absorption layer 106, so even if the hole transport layer 105 is provided between the back electrode 102 and the light absorption layer 106, a decrease in photoelectric conversion efficiency can be suppressed.

[0017] Furthermore, solar cells are generally subjected to heat treatment during the manufacturing process, and as described above, the reflectance of the conductive mirror layer 104 is easily reduced by the heat treatment. In this regard, the hole transport layer 105, which is a p-type oxide semiconductor, protects the conductive mirror layer 104 and can suppress the reduction in reflectance of the conductive mirror layer 104.

[0018] The solar cell 100 can be formed into a thin-film solar cell or a thin-film flexible solar cell by forming each layer sufficiently thin. Thin-film solar cells and thin-film flexible solar cells are lightweight and highly flexible, and can be applied to a variety of locations. Furthermore, forming the light absorbing layer 106 thin is preferable because it reduces mass production costs and prevents peeling of the light absorbing layer. Here, because the solar cell 100 includes the conductive mirror layer 104, a decrease in light absorption efficiency can be suppressed even if the light absorbing layer 106 is formed sufficiently thin.

[0019] The solar cell 100 may include at least a substrate 101, a conductive mirror underlayer 103, a conductive mirror layer 104, a hole transport layer 105 which is a p-type oxide semiconductor, and a light absorbing layer 106, in this order. Alternatively, the solar cell 100 may include at least a substrate 101, a back electrode 102, a conductive mirror underlayer 103, a conductive mirror layer 104, a hole transport layer 105 which is a p-type oxide semiconductor, and a light absorbing layer 106, in this order. Alternatively, the solar cell 100 may include a substrate 101, a back electrode 102 on the substrate 101, a conductive mirror underlayer 103 on the back electrode 102, a conductive mirror layer 104 on the conductive mirror underlayer 103, a hole transport layer 105 which is a p-type oxide semiconductor on the conductive mirror layer 104, and a light absorbing layer 106 on the hole transport layer 105. Alternatively, the solar cell 100 may include a substrate 101, a back electrode 102 on the substrate 101, a conductive mirror underlayer 103 on the back electrode 102, a conductive mirror layer 104 on the conductive mirror underlayer 103, a hole transport layer 105 which is a p-type oxide semiconductor on the conductive mirror layer 104, a light absorbing layer 106 on the hole transport layer 105, an electron transport layer 107 on the light absorbing layer 106, and an electrode 108 on the electron transport layer 107. In addition, in the solar cell 100, the conductive mirror layer 104 may be provided on the hole transport layer 105, and the conductive mirror underlayer 103 may be provided on the conductive mirror layer 104. In addition, in the solar cell 100, the light absorbing layer 106 may be provided on the hole transport layer 105 which is a p-type oxide semiconductor. In addition, in the solar cell 100, the hole transport layer 105 may be provided on the light absorption layer 106, the conductive mirror layer 104 may be provided on the hole transport layer 105, and the conductive mirror base layer 103 may be provided on the conductive mirror layer 104.

[0020] Each component that can be included in the solar cell 100 will be described in detail below.

[0021] In this embodiment, when a compound is expressed by its name, it includes not only the pure compound itself, but also the compound to which trace amounts of elements, etc. have been added, as long as the properties of the compound are not lost.

[0022] Also, in this embodiment, because elements in each layer of the solar cell module 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" refers to hydrogen atoms, hydrogen ions, hydride ions, hydrogen in compounds, and hydrogen in elemental form.

[0023] In this embodiment, the oxide is MO ｘ (where M represents a metal element) includes not only compounds in which the molar ratio of metal element to oxygen element is strictly 1:x, but also compounds in which the molar ratio is slightly different. For example, when expressed as NiO, it includes not only compounds in which the molar ratio of Ni element to O element is 1:1, but also nickel oxide in which the molar ratio of Ni element to O element is different from 1:1 due to the inclusion of a small amount of trivalent Ni or oxygen vacancies.

[0024] In addition, in this embodiment, when a numerical range is described as A to B, this means that the numerical range is A or more and B or less.

[0025] 1.1. Substrate The solar cell 100 includes a substrate 101. The substrate 101 is not particularly limited, and examples thereof include glass substrates; metal substrates such as stainless steel plates and aluminum foil; and resin substrates such as polyimide resin substrates and epoxy resin substrates. Among these, glass substrates and metal substrates are preferred. The inclusion of an alkali metal element in the light-absorbing layer 106 tends to improve the performance of the solar cell 100. Specifically, defects are passivated, and the open-circuit voltage tends to increase. In this regard, using a glass substrate as the substrate 101 allows alkali metal elements, such as sodium, contained in the glass substrate to be diffused into the light-absorbing layer 106, which will be described later. Furthermore, using a metal substrate allows the substrate 101 to be used as an electrode, eliminating the need for a separate electrode. This tends to enable the solar cell 100 to be made thinner. When a metal substrate is used as the substrate 101, using a metal substrate containing an alkali metal element as the material of the metal substrate allows the alkali metal element to be diffused into the light-absorbing layer 106, which will be described later. The substance contained in the substrate 101 may be one kind used alone or two or more kinds used in combination.

[0026] Examples of alkali metal elements include sodium, potassium, rubidium, and cesium, and among these, sodium and potassium are preferred.

[0027] The thickness of the substrate 101 is not particularly limited, but is, for example, 0.01 to 30.0 mm, 0.05 to 25.0 mm, 0.1 to 20.0 mm, 0.5 to 20.0 mm, 1.0 to 10.0 mm, or 1.5 to 5.0 mm. When the thickness of the substrate 101 is within the above range, the solar cell 100 tends to be thinner. In other words, the solar cell 100 tends to be lighter and more flexible.

[0028] 1.2. Rear Surface Electrode The solar cell 100 includes a rear surface electrode 102. The rear surface electrode 102 is not particularly limited as long as it is conductive, but examples of the rear surface electrode 102 that can be used include a metal conductive layer made of a metal such as molybdenum, chromium, tungsten, or titanium; 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 material contained in the rear surface electrode 102 may be a single material, or two or more materials may be used in combination.

[0029] When a metal is used as the substance contained in the back electrode 102, a metal that undergoes little volume change upon heating is preferred. This tends to make the back electrode 102 less likely to peel off from the substrate 101. Examples of such metals include tungsten and molybdenum. Tungsten and molybdenum are also preferred from the standpoint of cost.

[0030] The thickness of the back electrode 102 is not particularly limited, but is, for example, 100 to 800 nm, 150 to 750 nm, or 200 to 700 nm. When the thickness of the back electrode 102 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.

[0031] 1.3 Conductive Mirror Underlayer The solar cell 100 may include a conductive mirror underlayer 103 between the rear electrode 102 and the conductive mirror layer 104. By providing the conductive mirror underlayer 103, the light reflectance of the conductive mirror underlayer 103 and the conductive mirror layer 104 described below tends to be further improved, and thermal stability also tends to be improved.

[0032] The conductive mirror underlayer 103 preferably has high light reflectance. From this viewpoint, the conductive mirror underlayer 103 preferably contains a metal. Examples of metals include metals that have a face-centered cubic lattice structure at room temperature and metals that have a structure other than a face-centered cubic lattice structure at room temperature (e.g., titanium). However, from the viewpoint of improving the light reflectance of the conductive mirror layer 103, metals that have a face-centered cubic lattice structure at room temperature are more preferred. Specific examples of metals that have a face-centered cubic lattice structure at room temperature preferably include one or more metals selected from the group consisting of nickel, aluminum, calcium, copper, strontium, rhodium, palladium, silver, iridium, platinum, gold, and lead. Furthermore, it is more preferred to include one or more metals selected from the group consisting of aluminum, calcium, copper, strontium, rhodium, palladium, silver, iridium, platinum, gold, and lead. Furthermore, it is even more preferred to include one or more metals selected from the group consisting of gold, aluminum, copper, and silver. Furthermore, it is even more preferable that the conductive mirror underlayer 103 contains one or more materials selected from the group consisting of aluminum, copper, and silver. The materials contained in the conductive mirror underlayer 103 may be used alone or in combination of two or more materials.

[0033] The metal content in the conductive mirror underlayer 103 is preferably 50 to 100 mass%, 60 to 100 mass%, 70 to 100 mass%, 80 to 100 mass%, 90 to 100 mass%, or 95 to 100 mass%, relative to the total amount of the conductive mirror underlayer 103.

[0034] The thickness of the conductive mirror underlayer 103 is preferably 5 to 75 nm, 7 to 50 nm, or 10 to 30 nm. When the thickness of the conductive mirror underlayer 103 is within the above range, the light reflectance is further improved, and the thermal stability also tends to be improved.

[0035] 1.4. Conductive Mirror Layer The solar cell 100 includes a conductive mirror layer 104. The conductive mirror layer 104 is not particularly limited as long as it is capable of reflecting light such as sunlight, but it preferably contains one or more materials selected from the group consisting of gold, silver, aluminum, gold alloys, silver alloys, and aluminum alloys. It is more preferable that the conductive mirror layer 104 contains one or more materials selected from the group consisting of silver, aluminum, silver alloys, and aluminum alloys. The conductive mirror layer 104 may contain one material alone or two or more materials in combination.

[0036] It is preferable that the conductive mirror underlayer 103 and the conductive mirror layer 104 are made of different materials.

[0037] The conductive mirror layer 104 preferably has a reflectance of 60 to 98% for light having a wavelength range of 800 to 1140 nm.

[0038] The metal content in the conductive mirror layer 104 is preferably 50 to 100 mass%, 60 to 100 mass%, 70 to 100 mass%, 80 to 100 mass%, 90 to 100 mass%, or 95 to 100 mass%, relative to the total amount of the conductive mirror layer 104.

[0039] The thickness of the conductive mirror layer 104 is preferably 5 to 75 nm, 7 to 50 nm, or 10 to 30 nm. When the thickness of the conductive mirror underlayer 103 is within the above range, the light reflectance tends to be further improved.

[0040] 1.5 Hole Transport Layer The solar cell 100 includes a hole transport layer 105 made of a p-type oxide semiconductor. The hole transport layer 105 tends to efficiently extract holes generated in the light absorbing layer 106 (described later) from the light absorbing layer 106, and to suppress recombination of electrons and holes generated simultaneously with the holes in the light absorbing layer 106.

[0041] The hole transport layer 105 is not particularly limited as long as it is a p-type oxide semiconductor, but may be formed of molybdenum oxide (MoO ２ , MoO ３ ), nickel oxide (NiO), copper oxide (CuO), copper gallium oxide (CuGaO ２ ), copper chromium oxide (CuCrO ２ ), and copper aluminum oxide (CuAlO ２ ), and preferably contains at least one metal oxide selected from the group consisting of NiO, CuO, CuGaO ２ , CuCrO ２ , and CuAlO ２ Preferably, the metal oxide contains at least one selected from the group consisting of CuAlO ２ More preferably, it contains MoO ２ , MoO ３ , NiO, CuO, CuGaO ２ , and CuAlO ２ The hole transport layer 105 preferably contains one or more metal oxides selected from the group consisting of: The material contained in the hole transport layer 105 may be one material alone or two or more materials may be used in combination.

[0042] By including one or more metal oxides selected from the above-mentioned metal oxides in the hole transport layer 105, it is possible to further protect the conductive mirror layer 104 and to suppress a decrease in the photoelectric conversion efficiency of the solar cell 100. Furthermore, since the above-mentioned metal oxides have excellent heat resistance and weather resistance, solar cell 100 using the above-mentioned metal oxides also tends to have excellent heat resistance and weather resistance.

[0043] The hole transport layer 105 is also subjected to heat treatment together with the precursor layer of the light absorbing layer 106. In particular, when the heat treatment is performed at a high temperature (e.g., 500°C) in a corrosive gas atmosphere such as a sulfur atmosphere, a selenium atmosphere, a chlorine atmosphere, a bromine atmosphere, or an iodine atmosphere, the hole transport layer 105 may be at least partially denatured. For example, the hole transport layer 105 subjected to heat treatment at a high temperature (e.g., 500°C) in a sulfur atmosphere, a selenium atmosphere, a chlorine atmosphere, a bromine atmosphere, or an iodine atmosphere may be at least partially sulfurized, selenized, chlorided, brominated, or iodized. The "part of the hole transport layer 105" is not particularly limited, and may be, for example, a part of the surface of the hole transport layer 105 facing the light absorbing layer 106. Note that the hole transport layer 105 is not denatured in its entirety or in most part (e.g., the entire surface of the hole transport layer 105 facing the light absorbing layer 106) even when subjected to heat treatment. Furthermore, the at least partially modified hole transport layer 105 can further suppress a decrease in the photoelectric conversion efficiency of the solar cell 100, similar to the unmodified hole transport layer 105.

[0044] Furthermore, the hole transport layer 105 preferably contains a metal oxide to which an alkali metal element has been added. Adding an alkali metal element to the light absorption layer 106, which will be described later, tends to improve the performance of the solar cell 100. One method for adding an alkali metal element to the light absorption layer 106 is to diffuse the alkali metal element from the substrate 101 to the light absorption layer 106 by heat treatment. In this case, it is preferable that the hole transport layer 105 contains a metal compound to which an alkali metal element has been added, because this makes it easier for the alkali metal element to diffuse from the substrate 101 to the light absorption layer 106. In this embodiment, the term "metal oxide" simply refers to not only metal oxide but also metal oxide to which an alkali metal element has been added.

[0045] In this embodiment, the metal oxide to which an alkali metal element is added may be expressed using the composition formula before the alkali metal element is added. For example, in the aluminum copper oxide to which sodium element is added, the molar ratio of Cu element to Al element may not be 1:1, but the aluminum copper oxide to which sodium element is added may be referred to as CuAlO ２ It may be expressed as:

[0046] Examples of alkali metal elements include sodium, potassium, rubidium, and cesium, and among these, sodium and potassium are preferred.

[0047] The hole transport layer 105 is made of CuAlO ２ or CuAlO to which an alkali metal element is added ２ This makes it possible to better protect the conductive mirror layer 104 and tends to improve the performance of the solar cell 100.

[0048] The content of the alkali metal element in the hole transport layer 105 is preferably 5 to 30 mol %, and more preferably 10 to 25 mol %, based on the number of moles of all metal elements contained in the hole transport layer 105 .

[0049] The content of the alkali metal element in the hole transport layer 105 is not particularly limited, but can be measured using, for example, ICP, EDX, or SIMS.

[0050] The oxide content in the hole transport layer 105 is not particularly limited as long as the hole transport layer 105 has properties as a p-type semiconductor, but is, for example, 80 to 100 mass %, 90 to 100 mass %, 95 to 100 mass %, or 99 to 100 mass % relative to the total amount of the hole transport layer 105.

[0051] The thickness of the hole transport layer 105 is preferably 5 to 100 nm, 7 to 80 nm, or 10 to 60 nm. When the thickness of the hole transport layer 105 is within the above range, holes generated in the light absorbing layer 106 (described below) can be efficiently extracted from the light absorbing layer 106, and recombination of electrons and holes generated simultaneously with the holes in the light absorbing layer 106 can be suppressed, which tends to enable a lighter and more flexible solar cell.

[0052] 1.6. Light Absorption Layer The solar cell 100 includes a light absorption layer 106. The light absorption layer 106 absorbs 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 absorption layer 106 preferably contains one or more compounds selected from the group consisting of chalcopyrite compounds, kesterite compounds, and perovskite compounds. One perovskite compound may be used alone, or two or more perovskite compounds may be used in combination. One chalcopyrite compound may be used alone, or two or more perovskite compounds may be used in combination. Furthermore, one kesterite compound may be used alone, or two or more perovskite compounds may be used in combination.

[0053] When the light absorbing layer 106 contains one or more compounds selected from the group consisting of chalcopyrite compounds, kesterite compounds, and perovskite compounds, it is preferable to form the light absorbing layer 106 thin from the viewpoints of reducing mass production costs and preventing peeling of the light absorbing layer. In this case, even if the light absorbing layer 106 is formed thin, it still fully functions as a solar cell, so it is also preferable to form the light absorbing layer 106 thin from the viewpoints of making the solar cell lighter and more flexible. On the other hand, if the light absorbing layer 106 is formed thin, the light absorbing layer 106 may not be able to absorb all light such as sunlight, and the light absorption efficiency tends to decrease.

[0054] In this regard, the solar cell 100 has the conductive mirror layer 104, and therefore tends to have improved light absorption efficiency.

[0055] Furthermore, when the light absorbing layer 106 of the solar cell 100 contains one or more compounds selected from the group consisting of chalcopyrite compounds, kesterite compounds, and perovskite compounds, the light absorbing layer 106 has good electrical compatibility with the hole transport layer 105, which is a p-type oxide semiconductor, in terms of the valence band position. Therefore, even if the hole transport layer 105 is provided between the back electrode 102 and the light absorbing layer 106, a decrease in photoelectric conversion efficiency tends to be more effectively suppressed. Furthermore, even if the hole transport layer 105 is provided on the surface of the light absorbing layer 106 facing the substrate 101, an increase in electrical resistance at the interface between the hole transport layer 105 and the light absorbing layer 106 tends to be more effectively suppressed, thereby more effectively suppressing a decrease in photoelectric conversion efficiency.

[0056] Furthermore, when the light absorbing layer 106 includes one or more compounds selected from the group consisting of a chalcopyrite compound, a kesterite compound, and a perovskite compound, the solar cell 100 is fabricated by heat-treating a precursor layer of the light absorbing layer 106 in an atmosphere of selenium gas, sulfur gas, or the like. In this case, the conductive mirror layer 104 and the hole transport layer 105 present on the substrate 101 side (below) of the light absorbing layer 106, along with the precursor layer of the light absorbing layer 106, are also subjected to the heat treatment. The conductive mirror layer 104 is prone to a decrease in reflectance due to oxidation, corrosion, or the like. Therefore, in the solar cell 100, the hole transport layer 105, which is a p-type oxide semiconductor, is formed above the conductive mirror layer 104. Therefore, even when the conductive mirror layer 104 is subjected to heat treatment in an atmosphere of selenium gas, sulfur gas, or the like, the hole transport layer 105 protects the conductive mirror layer 104, and tends to suppress a decrease in the reflectance of the conductive mirror layer 104.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] The light absorbing layer 106 preferably contains a perovskite compound to which an alkali metal element has been added, a chalcopyrite compound to which an alkali metal element has been added, or a kesterite compound to which an alkali metal element has been added, which tends to improve the performance of the solar cell 100. Examples of alkali metal elements include sodium, potassium, rubidium, and cesium, and among these, sodium is preferred.

[0065] The content of the alkali metal element in the light absorbing layer 106 is preferably 0.1 to 5 mol %, and more preferably 0.5 to 2 mol %, relative to the number of moles of all metal elements contained in the light absorbing layer 106. When the content of the alkali metal element in the light absorbing layer 106 is within the above range, the performance of the solar cell 100 tends to be further improved.

[0066] The content of the alkali metal element in the light absorbing layer 106 is not particularly limited, but can be measured using, for example, ICP, EDX, or SIMS.

[0067] The contents of the perovskite compound, chalcopyrite compound, and kesterite compound in the light absorbing layer 106 are not particularly limited as long as the light absorbing layer 106 can absorb light such as visible light and ultraviolet light to generate electrons and holes. More specifically, although not particularly limited, the contents of the chalcopyrite compound and kesterite compound are 50 to 100 mass%, 60 to 100 mass%, 70 to 100 mass%, 80 to 100 mass%, or 90 to 100 mass%, relative to the total mass of the light absorbing layer 106.

[0068] In addition to the above materials, the light absorbing layer 106 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 106. The light absorbing layer 106 does not necessarily need to contain the additives.

[0069] The thickness of the light absorbing layer 106 is preferably 0.5 to 5.0 μm, 0.5 to 4.5 μm, or 0.5 to 3.0 μm. When the thickness of the light absorbing layer 106 is within the above range, it is possible to absorb light such as visible light and ultraviolet light to generate electrons and holes, while also tending to enable a lighter and more flexible solar cell. It also tends to be possible to prevent peeling of the light absorbing layer 106.

[0070] The solar cell 100 of this embodiment may have two light absorbing layers 106. In this case, the substance contained in the first light absorbing layer 106 may be different from the substance contained in the second light absorbing layer 106, but it is preferable that they are different. A solar cell in which the first and second light absorbing layers 106 contain different substances is also called a tandem solar cell. By having two light absorbing layers 106 in the solar cell 100, the wavelength range of light that can be absorbed by the light absorbing layers 106 tends to be expanded, and as a result, the performance of the solar cell 100 tends to be improved. Furthermore, the solar cell 100 of this embodiment may have three or more light absorbing layers 106.

[0071] 1.7. Electron Transport Layer The solar cell 100 may or may not include an electron transport layer 107 on the side of the light absorption layer 106 opposite the substrate 101. However, from the viewpoint of improving the photoelectric conversion efficiency of the solar cell 100, it is preferable to include the electron transport layer 107.

[0072] The electron transport layer 107 tends to efficiently extract electrons generated in the light absorption layer 106 from the light absorption layer 106 and suppress recombination of holes and electrons generated simultaneously with the electrons in the light absorption layer 106. The electron transport layer 107 is preferably an n-type semiconductor. The substance contained in the n-type semiconductor is not particularly limited, but examples thereof include metal oxides such as 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). The substance contained in the electron transport layer 107 may be used alone or in combination of two or more.

[0073] The electron transport layer 107, 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 the metal oxide, such as zinc oxide, tin oxide, titanium oxide, zinc oxide sulfide, magnesium zinc oxide, zinc tin oxide, or titanium zinc oxide, in the electron transport layer 107, which is an n-type oxide semiconductor, is preferably 80 to 100 mass%, 90 to 100 mass%, 95 to 100 mass%, or 99 to 100 mass%, relative to the total amount of the electron transport layer 107.

[0074] The thickness of the electron transport layer 107 is preferably 50 to 200 nm, 55 to 175 nm, 60 to 150 nm, or 65 to 125 nm. When the thickness of the electron transport layer 107 is within the above range, electrons generated in the light absorbing layer 106 can be efficiently extracted from the light absorbing layer 106, and recombination of holes and electrons generated simultaneously with the electrons in the light absorbing layer 106 can be suppressed, which tends to enable a lighter and more flexible solar cell.

[0075] 1.8 Front Surface Electrode The solar cell 100 has a front surface electrode 108. The front surface electrode 108 is provided to extract a current due to electrons generated in the light absorption layer 106, for example.

[0076] 1.8.1. Transparent Electrode Layer The surface electrode 108 may have a transparent electrode layer 109. 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 for example, a material with 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). The substance contained in the transparent electrode layer 109 may be used alone or in combination of two or more.

[0077] When second transparent electrode 109 is a transparent electrode, the content of the above material is not particularly limited as long as second transparent electrode 109 functions as a transparent electrode. More specifically, although not particularly limited, the content of the above material is 50 to 100 mass %, 60 to 100 mass %, 70 to 100 mass %, 80 to 100 mass %, 90 to 100 mass %, or 95 to 100 mass % relative to the total mass of second transparent electrode 109.

[0078] The thickness of the second transparent electrode 109 is not particularly limited, but is, for example, 100 to 1500 nm, or 200 to 1000 nm. When the thickness of the second transparent electrode 109 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.

[0079] 1.8.2 Grid Electrode The surface electrode 108 may have a grid electrode 110. The material of the grid electrode 110 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. The substance contained in the grid electrode 110 may be one type alone or two or more types in combination.

[0080] The content of the above-mentioned material in the grid electrode 110 is not particularly limited as long as the grid electrode 110 functions as an electrode. More specifically, although not particularly limited, the content of the above-mentioned material is 50 to 100 mass %, 60 to 100 mass %, 70 to 100 mass %, 80 to 100 mass %, or 90 to 100 mass % relative to the total mass of the grid electrode 110.

[0081] The thickness of the grid electrode 110 is not particularly limited, but is, for example, 5 to 50 μm. When the thickness of the grid electrode 110 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.

[0082] The surface electrode 108 may include only the transparent electrode 109, may include only the grid electrode 110, or may include both the transparent electrode 109 and the grid electrode 110. The electrode 110 preferably includes both the transparent electrode 109 and the grid electrode 110.

[0083] 2. Method for Manufacturing Solar Cell The method for manufacturing the solar cell 100 of this embodiment includes a laminate preparation step of preparing a laminate including at least the substrate 101, the back electrode 102, the conductive mirror layer 104, the hole transport layer 105 which is a p-type semiconductor, and a precursor layer of the light absorbing layer 106, in this order, 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.

[0084] In the solar cell 100 manufactured by the manufacturing method of this embodiment, the hole transport layer 105, which is a p-type semiconductor, is present between the conductive mirror layer 104 and the light absorption layer 106. Therefore, the conductive mirror layer 104 is not denatured, for example, by corrosion, by the heat treatment step, and a decrease in the light reflectance of the conductive mirror layer 104 can be suppressed.

[0085] Each step that may be included in the method for manufacturing the solar cell 100 of this embodiment will be described in detail below.

[0086] The method for manufacturing a solar cell of this embodiment includes a laminate preparation step of preparing a laminate including, in this order, at least the substrate 101, the back electrode 102, the conductive mirror layer 104, the hole transport layer 105 which is a p-type semiconductor, and a precursor layer of the light absorbing layer 106. A sputtering method, for example, can be used to prepare such a laminate.

[0087] Specifically, the back electrode 102 may be deposited on the substrate 101 by sputtering, the conductive mirror layer 104 may be deposited on the back electrode 102 by sputtering, the hole transport layer 105 may be deposited on the conductive mirror layer 104 by sputtering, and a precursor layer of the light absorbing layer 106 may be deposited on the hole transport layer 105 by sputtering. Alternatively, the back electrode 102 may be deposited on the substrate 101 by sputtering, the conductive mirror underlayer 103 may be deposited on the back electrode 102 by sputtering, the conductive mirror layer 104 may be deposited on the conductive mirror underlayer 103 by sputtering, the hole transport layer 105 may be deposited on the conductive mirror layer 104 by sputtering, and a precursor layer of the light absorbing layer 106 may be deposited on the hole transport layer 105 by sputtering. Furthermore, from the viewpoint of adhesion, bonding, conductivity, etc. between the layers, an intermediate layer may be provided between the layers by a sputtering method, a vapor deposition method, a spray coating method, etc., as necessary.

[0088] The sputtering method may be performed in an argon atmosphere using the material of each layer as a sputtering target. For example, when forming the conductive mirror layer 104 by sputtering, sputtering may be performed in an argon atmosphere using aluminum as a sputtering target.

[0089] If necessary, sputtering may be performed using a sputtering target containing two or more compounds. If necessary, sputtering may be performed in an atmosphere other than an argon atmosphere, such as an oxygen atmosphere. For example, CuAlO ２ When the hole transport layer 105 containing Cu is formed by a sputtering method, ２ O and Al ２ O ３ Alternatively, sputtering may be performed under an oxygen atmosphere using Cu as a sputtering target. ２ O and Al ２ O ３ and Cu ２ O and Al ２ O ３The sputtering target may contain additives such as a binder in addition to the materials of each layer. The concentration of the oxygen source in the gas supplied during sputtering is not particularly limited, but is, for example, 0.2 to 10.0 volume % in terms of oxygen molecules.

[0090] As a method for adding an alkali metal element to the hole transport layer 105, a sputtering target to which an alkali metal element has been added may be used. For example, CuAlO ２ When the hole transport layer 105 containing CuO, Al is formed by a sputtering method, the material is not particularly limited. ２ O ３ and Na ２ Three sputtering targets of O may be used, CuO and Al ２ O ３ and Na ２ Two sputtering targets of CuO and Al may be used. ２ O ３ and Na ２ One sputtering target that is a mixture of 0 may be used.

[0091] The amount of alkali metal element added to the hole transport layer 105 can be adjusted by adjusting the amount of alkali metal element in the sputtering target.

[0092] The precursor layer of the light absorbing layer 106 contains a substance that will become the light absorbing layer 106 through a heat treatment process described below. When the light absorbing layer 106 contains a perovskite compound, the precursor layer of the light absorbing layer 106 may contain, but is not limited to, PbI ２ When the light absorbing layer 106 contains a chalcopyrite compound, the precursor layer of the light absorbing layer 106 may include, but is not limited to, a laminate of CuGa, In, etc. When the light absorbing layer 106 contains a kesterite compound, the precursor layer of the light absorbing layer 106 may include, but is not limited to, a laminate of Zn, Sn, Cu, etc.

[0093] Methods for adding an alkali metal element to the light absorbing layer 106 include a method in which an alkali metal element that may be contained in the substrate 101 or the hole transport layer 105 is diffused to the light absorbing layer 106 by a heat treatment process described below, and a method in which an alkali metal element is added to a precursor layer of the light absorbing layer 106. A method for adding an alkali metal element to a precursor layer of the light absorbing layer 106 includes a technique in which a sputtering target to which an alkali metal element has been added is used.

[0094] The method for manufacturing a solar cell of this embodiment includes a heat treatment step of heat treating the stack prepared in the stack preparation step 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. This turns the precursor layer of the light absorbing layer 106 into the light absorbing layer 106.

[0095] The laminate includes a p-type semiconductor hole transport layer 105. The hole transport layer 105 can protect the conductive mirror layer 104, and therefore can prevent the conductive mirror layer 104 from being degraded, such as corroded, by the heat treatment step, and can suppress a decrease in the light reflectance of the conductive mirror layer 104.

[0096] The atmosphere in the heat treatment step is 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. Specifically, the atmosphere may include one selected from the group consisting of a sulfur atmosphere, a selenium atmosphere, a chlorine atmosphere, a bromine atmosphere, and an iodine atmosphere, or may be a mixed atmosphere including two or more selected from the group consisting of the above. Furthermore, after a heat treatment step is performed in one atmosphere, a further heat treatment step may be performed in a different atmosphere. Specifically, after a heat treatment step is performed in a selenium atmosphere, a heat treatment step may be performed in a sulfur atmosphere.

[0097] When the light absorbing layer 106 is a chalcopyrite compound or a kesterite compound, it is preferable that the heat treatment step is performed in one or more of a sulfur atmosphere and a selenium atmosphere, and it is more preferable that the heat treatment step is performed in a selenium atmosphere and then in a sulfur atmosphere.

[0098] When the light absorbing layer 106 is made of a perovskite compound, 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.

[0099] In this embodiment, the term "sulfur atmosphere" refers to an atmosphere containing a gas containing sulfur element. That is, an atmosphere containing a gas containing sulfur element and another gas not containing sulfur element (e.g., nitrogen gas, argon gas) is included in the sulfur atmosphere. The same applies to a selenium atmosphere, a chlorine atmosphere, a bromine atmosphere, and an iodine atmosphere.

[0100] In the heat treatment step, the laminate is preferably heat treated at a temperature of 60 to 600° C., more preferably 150 to 600° C. More specifically, in the case of a sulfur atmosphere and a selenium atmosphere, the heat treatment temperature is preferably 300 to 600° C., 350 to 600° C., 400 to 600° C., or 450 to 600° C. In the case of a chlorine atmosphere, a bromine atmosphere, or an iodine atmosphere, the heat treatment temperature is preferably 60 to 230° C., 70 to 200° C., or 80 to 170° C.

[0101] In the heat treatment step, the heat treatment time is preferably 1 minute or more and 30 minutes or less, 3 minutes or more and 15 minutes or less, or 5 minutes or more and 15 minutes or less.

[0102] 2.3. Electron Transport Layer Forming Step The method for manufacturing a solar cell according to this embodiment may include an electron transport layer forming step of forming the electron transport layer 107. The electron transport layer forming step may be performed using a sputtering method. Specifically, an electron transport layer that is an n-type oxide semiconductor containing zinc titanium oxide may be formed on the light absorbing layer 106 by sputtering in an argon atmosphere using zinc oxide and titanium oxide as sputtering targets. The sputtering target may be changed as appropriate depending on the substance contained in the electron transport layer 107.

[0103] 2.4 Front Surface Electrode Forming Step The method for manufacturing a solar cell of this embodiment may include a front surface electrode forming step of forming the front surface electrode 108. The front surface electrode forming step may be performed using a sputtering method.

[0104] Specifically, the transparent electrode layer 109 may be laminated by sputtering on the light absorption layer 106 or the electron transport layer 107, and the grid electrode 110 may be provided by sputtering on the transparent electrode layer 109. The sputtering may be performed in an argon atmosphere using the materials of each component as sputtering targets.

[0105] Alternatively, a method of combining sputtering with another method may be used to form the surface electrode 108. Specifically, the transparent electrode layer 109 may be laminated on the light absorption layer 106 or the electron transport layer 107 by sputtering, and the grid electrode 110 may be provided on the transparent electrode layer 109 by vapor deposition, printing a paste-like conductive material, or crimping a conductive wire.

[0106] 3. Solar Cell Module In the solar cell module of this embodiment, multiple solar cells 100 are electrically connected in series or in parallel. A method for electrically connecting multiple solar cells 100 in series includes soldering the back electrode 102 of one solar cell 100 to a metal ribbon, and soldering the metal ribbon wire to the front electrode 108 of the other solar cell 100. A method for electrically connecting multiple solar cells 100 in parallel includes preparing multiple solar cells 100 each having a metal ribbon soldered to the back electrode 102 and another metal ribbon soldered to the front electrode 108, and then electrically connecting the metal ribbons soldered to the back electrode 102 and the metal ribbons soldered to the front electrode 108.

[0107] A solar cell module in which a plurality of solar cells 100 are electrically connected in series is preferable because it can obtain a higher voltage. Also, a solar cell module in which a plurality of solar cells 100 are electrically connected in parallel is preferable because it can obtain a higher current and generate power more stably. Also, a solar cell module in which a plurality of solar cells 100 are electrically connected in a combination of series and parallel is preferable because it can adjust the voltage and current within a suitable range and generate power stably.

[0108] 4. Method of Using the Solar Cell The solar cell 100, like conventional solar cells, 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 100 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.).

[0109] Furthermore, the solar cell 100 can be thinned, allowing for lighter weight and flexibility. Therefore, the solar cell 100 can be attached to windows or walls of buildings such as buildings, or windows or roofs of vehicles such as cars, and used as a power generation device. Furthermore, the solar cell 100 can be used as an independent power source device for street lights, sensors, digital signage, etc., and in such cases, the solar cell 100 can be bent to adapt to various environments. The solar cell 100 can also be used as a mobile energy device.

[0110] 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.

[0111] 1. Simulation experiment on conductive mirror layer The effect of providing a conductive mirror layer was investigated using simulation software (thin-film solar cell characteristic simulation software (e-ARC) manufactured by the National Institute of Advanced Industrial Science and Technology, National Research and Development Agency). First, Model 1 was prepared, which had the following layers in this order: glass substrate / rear electrode / hole transport layer / light absorption layer / electron transport layer / front electrode. Also, Model 2 was prepared, which had the following layers in this order: glass substrate / rear electrode / conductive mirror layer / hole transport layer / light absorption layer / electron transport layer / front electrode. Note that in Models 1 and 2, the layers were configured as follows: Substrate: 2 mm thick glass Rear electrode: 400 nm thick layer made of metallic molybdenum Conductive mirror layer: 50 nm thick layer made of metallic silver Hole transport layer: 50 nm thick CuAlO ２Light absorbing layer: 1 to 3 μm thick layer made of a CIGSS compound. Electron transport layer: 100 nm thick layer made of titanium zinc oxide. Surface electrode: 350 nm thick layer made of ITO.

[0112] A simulation was carried out using the above-mentioned Models 1 and 2, in which light was irradiated from the front electrode side. The results are shown in Figure 2. Model 2, which includes a conductive mirror layer, has a higher short-circuit current density J at each thickness of the light absorption layer than Model 1, which does not. ＳＣ This shows that the provision of the conductive mirror layer allows the light absorption layer to absorb more light, that is, the light absorption efficiency is improved.

[0113] 2. Fabrication of a Partial Structure of a Solar Cell [Example 1] In Example 1, a 2 mm thick glass substrate was used. A back electrode containing metallic molybdenum was formed on this substrate to a thickness of 400 nm. When forming the back electrode, a sputtering method was used in an argon atmosphere using metallic molybdenum as a sputtering target.

[0114] A conductive mirror underlayer containing metallic nickel was formed on the back electrode by sputtering in an argon atmosphere using metallic nickel as a sputtering target.

[0115] A conductive mirror layer containing metallic silver was formed on the conductive mirror underlayer to a thickness of 50 nm by sputtering in an argon atmosphere using metallic silver as a sputtering target.

[0116] CuGaO is deposited on the conductive mirror layer by sputtering. ２ A hole transport layer, which is a p-type semiconductor containing Cu, was formed to a thickness of 50 nm. ２ O and Ga ２ O ３A mixture of these compounds, in which the molar ratio of Cu to Ga was 1:1, was used as a sputtering target, and sputtering was performed in an atmosphere of a mixed gas (oxygen atmosphere) of argon gas:oxygen gas=90% by volume:10% by volume. In this way, a partial structure of the solar cell of Example 1 before heat treatment was prepared.

[0117] The partial structure of the solar cell before heat treatment was placed in a sulfur atmosphere (nitrogen gas: H ２ The substrate was subjected to a heat treatment at 500° C. for 10 minutes in a mixed gas atmosphere of sulfur gas (95% by volume: 5% by volume). In this way, a partial structure of the solar cell of Example 1 after the heat treatment was produced.

[0118] Example 2 Except for using a 50 nm-thick hole transport layer that was a p-type semiconductor containing NiO, the partial structures of the solar cell of Example 2 before and after heat treatment were fabricated in the same manner as Example 1. In forming the hole transport layer, NiO was used as the sputtering target and a sputtering method was used in an atmosphere of a mixed gas (oxygen atmosphere) of argon gas:oxygen gas=90% by volume:10% by volume.

[0119] [Example 3] MoO ２ The partial structures of the solar cell of Example 3 before and after the heat treatment were fabricated in the same manner as in Example 1, except that a hole transport layer that was a p-type semiconductor containing MoO was used. ２ was used as the evaporation source and an evaporation method was used.

[0120] [Example 4] MoO ３ The partial structures of the solar cell of Example 4 before and after the heat treatment were fabricated in the same manner as in Example 1, except that a hole transport layer that was a p-type semiconductor containing MoO was used. ３ was used as the evaporation source and an evaporation method was used.

[0121] Example 5 Except for using a 50 nm-thick hole transport layer that was a p-type semiconductor containing NiO doped with elemental silver, partial structures of a solar cell of Example 5 before and after heat treatment were fabricated in the same manner as Example 1. In forming the hole transport layer, a mixture of AgO and NiO mixed at a molar ratio of Ag to Ni of 1:99 was used as a sputtering target, and sputtering was performed in a mixed gas atmosphere (oxygen atmosphere) of argon gas:oxygen gas = 90 vol%:10 vol%.

[0122] [Example 6] 50 nm thick CuAlO ２ The partial structures of the solar cell of Example 6 before and after the heat treatment were fabricated in the same manner as in Example 1, except that a hole transport layer that was a p-type semiconductor containing Cu was used. ２ O and Al ２ O ３ A mixture obtained by mixing these compounds so that the molar ratio of Cu element to Al element was 1:1 was used as a sputtering target, and sputtering was performed in a mixed gas atmosphere (oxygen atmosphere) of argon gas:oxygen gas=90% by volume:10% by volume.

[0123] Comparative Example 1 In Comparative Example 1, a 2 mm thick glass substrate was used. A 400 nm thick back electrode containing metallic molybdenum was formed on this substrate. The back electrode was formed by sputtering in an argon atmosphere using metallic molybdenum as a sputtering target. In this manner, a partial structure of the solar cell of Comparative Example 1 before heat treatment was prepared.

[0124] The partial structure of the solar cell before the heat treatment was placed in a sulfur atmosphere (nitrogen gas: H ２ The substrate was subjected to a heat treatment at 500° C. for 10 minutes in a mixed gas atmosphere of 95% by volume of sulfur gas and 5% by volume of sulfur gas. In this way, a partial structure of the solar cell of Comparative Example 1 after the heat treatment was produced.

[0125] In Comparative Example 2, a 2 mm thick glass substrate was used. A 400 nm thick back electrode containing metallic molybdenum was formed on this substrate. The back electrode was formed by sputtering in an argon atmosphere using metallic molybdenum as a sputtering target.

[0126] A conductive mirror layer containing metallic silver was formed on the back electrode by sputtering to a thickness of 50 nm. The conductive mirror layer was formed using metallic silver as a sputtering target under an argon atmosphere. In this manner, a partial structure of the solar cell of Comparative Example 2 before heat treatment was prepared.

[0127] The partial structure of the solar cell before the heat treatment was placed in a sulfur atmosphere (nitrogen gas: H ２ The substrate was subjected to a heat treatment at 500° C. for 10 minutes in a mixed gas atmosphere of 95% by volume of sulfur gas and 5% by volume of sulfur gas. In this way, a partial structure of the solar cell of Comparative Example 2 after the heat treatment was produced.

[0128] In Comparative Example 3, a 2 mm thick glass substrate was used. A 400 nm thick back electrode containing metallic molybdenum was formed on this substrate. The back electrode was formed by sputtering in an argon atmosphere using metallic molybdenum as a sputtering target.

[0129] A conductive mirror underlayer containing metallic nickel was formed on the back electrode by sputtering in an argon atmosphere using metallic nickel as a sputtering target.

[0130] A conductive mirror layer containing metallic silver was formed on the conductive mirror underlayer by sputtering to a thickness of 50 nm. The conductive mirror layer was formed using metallic silver as a sputtering target in an argon atmosphere. In this manner, a partial structure of the solar cell of Comparative Example 3 before heat treatment was prepared.

[0131] The partial structure of the solar cell before the heat treatment was placed in a sulfur atmosphere (nitrogen gas: H ２ The substrate was subjected to a heat treatment at 500° C. for 10 minutes in a mixed gas atmosphere of 95% by volume of sulfur gas and 5% by volume of sulfur gas. In this way, a partial structure of the solar cell of Comparative Example 3 after the heat treatment was produced.

[0132] For each solar cell substructure, light having a wavelength of 800 to 1140 nm was incident on the exposed surface opposite the substrate, and the reflectance of the light was measured. The reflectance of the light was measured for each of the substructures of the single battery cells before and after the heat treatment.

[0133] The results of Examples 1 to 6 and Comparative Examples 1 to 3 are shown in Table 1.

[0134]

[0135] It can be seen that the provision of a conductive mirror layer improves the light reflectance, the provision of a conductive mirror underlayer further improves the light reflectance, and the provision of a hole transport layer which is a p-type semiconductor improves the light reflectance after heat treatment.

[0136] [Example 7] A conductive mirror layer containing metallic silver with a thickness of 25 nm was used, and a CuAlO ２ The partial structures of the solar cell of Example 7 before and after the heat treatment were fabricated in the same manner as in Example 6, except that a hole transport layer that was a p-type semiconductor containing

[0137] Example 8 A partial structure of a solar cell of Example 8 before and after heat treatment was produced in the same manner as Example 7, except that a conductive mirror underlayer containing Al with a thickness of 25 nm was used. When forming the conductive mirror underlayer, a sputtering method was used in an argon atmosphere using Al as a sputtering target.

[0138] [Example 9] 10 nm thick CuAlO doped with sodium element ２ The partial structures of the solar cell of Example 9 before and after the heat treatment were fabricated in the same manner as in Example 8, except that a hole transport layer that was a p-type semiconductor containing Na ２ O and Cu ２ O and Al ２ O ３ A mixture obtained by mixing these elements so that the molar ratio of Na:Cu:Al was 1:4:5 was used as a sputtering target, and sputtering was performed in a mixed gas atmosphere (oxygen atmosphere) of argon gas:oxygen gas = 90 vol %:10 vol %.

[0139] Example 10 The partial structure of the solar cell of Example 10 before and after heat treatment was produced in the same manner as Example 9, except that a 25 nm thick conductive mirror layer containing Al and a 25 nm thick conductive mirror underlayer containing Ti were used. When forming the conductive mirror layer, Al was used as the sputtering target and a sputtering method was used in an argon atmosphere. Furthermore, when forming the conductive mirror underlayer, Ti was used as the sputtering target and a sputtering method was used in an argon atmosphere.

[0140] [Example 11] Except for using a conductive mirror underlayer containing Ag with a thickness of 25 nm, the partial structure of the solar cell of Example 11 before and after heat treatment was produced in the same manner as in Example 10. When forming the conductive mirror underlayer, Ag was used as the sputtering target and a sputtering method was used in an argon atmosphere.

[0141] For each partial structure of the solar cell after the heat treatment, light having a wavelength range of 800 to 1140 nm was incident on the exposed surface opposite the substrate, and the reflectance of the light was measured.

[0142] The results of Examples 7 to 11 are shown in Table 2.

[0143]

[0144] In Example 11, sodium was added to the hole transport layer of CuAlO ２ Instead of the p-type semiconductor containing , an ITO layer, which is an oxide transparent conductive layer, was formed, and the light reflectance after the heat treatment was measured in the same manner as in Example 11. As a result, the light reflectance was significantly reduced.

[0145] 3. Fabrication of Solar Cell [Example 12] In Example 12, a 2 mm thick glass substrate was used. A back electrode containing metallic molybdenum was formed on this substrate to a thickness of 400 nm. When forming the back electrode, a sputtering method was used in an argon atmosphere using metallic molybdenum as a sputtering target.

[0146] A conductive mirror layer containing metallic silver was formed on the back electrode by sputtering in an argon atmosphere using metallic silver as a sputtering target.

[0147] On the conductive mirror layer, sodium-doped CuAlO was deposited by sputtering. ２ A hole transport layer, which is a p-type semiconductor containing Na, was formed to a thickness of 10 nm. ２ O and Cu ２ O and Al ２ O ３ A mixture obtained by mixing these elements so that the molar ratio of Na:Cu:Al was 1:4:5 was used as a sputtering target, and sputtering was performed in a mixed gas atmosphere (oxygen atmosphere) of argon gas:oxygen gas = 90 vol %:10 vol %.

[0148] A precursor layer of the light absorbing layer containing Cu, Ga, and In was formed on the hole transport layer by sputtering. After that, heat treatment was performed in a selenium atmosphere at 400°C to 600°C for 5 to 30 minutes, and then heat treatment was performed in a hydrogen sulfide atmosphere at 400°C to 600°C for 5 to 30 minutes to form Cu(In,Ga)(Se,S). ２ A light absorbing layer containing a CIGSS compound was formed. The light absorbing layer was formed to a thickness of 2 μm.

[0149] An electron transport layer, which was an n-type oxide semiconductor containing zinc titanium oxide, was formed to a thickness of 80 nm on the light absorption layer of the heat-treated laminate by sputtering. The electron transport layer was formed by sputtering using a mixture of zinc oxide and titanium oxide as a sputtering target in an atmosphere of a mixed gas (argon gas:oxygen gas) of 90% by volume:10% by volume (oxygen atmosphere).

[0150] A transparent electrode layer containing hydrogenated indium oxide (IOH) was formed on the electron transport layer using a sputtering method to a thickness of 300 nm. A grid electrode made of metallic silver was formed on the electrode layer using a vapor deposition method to a thickness of 5 μm. In this manner, the solar cell of Example 12 was prepared.

[0151] [Comparative Example 4] 10 nm thick sodium-doped CuAlO ２ A solar cell of Comparative Example 4 was prepared in the same manner as in Example 12, except that a 110 nm thick oxide transparent conductive layer containing ITO was formed by sputtering instead of the hole transport layer which was a p-type semiconductor containing

[0152] [Measurement of Conversion Efficiency] The solar cells of Example 12 and Comparative Example 4 were subjected to standard solar cell testing conditions (light with a spectral spectrum of AM 1.5 and an irradiance of 1 kW / m ２ The IV curve was measured under test conditions where the solar cell temperature was 25°C and the incident light was 1000kJ / s. The conversion efficiency was measured from the IV curve. The conversion efficiency is the output (maximum output: P ｍａｘ ) divided by the light energy E received by the solar cell. Conversion efficiency (%) = P ｍａｘ ÷E×100

[0153] The conversion efficiency of the solar cell of Example 12 was 12.3%, while the conversion efficiency of the solar cell of Comparative Example 4 was 7.6%.

[0154] <Additional Notes> Embodiments of the present disclosure include the following aspects. [1] A solar cell comprising at least a substrate, a back electrode, a conductive mirror layer, a hole transport layer which is a p-type oxide semiconductor, and a light absorption layer, in this order. [2] The solar cell according to [1], comprising a conductive mirror underlayer between the back electrode and the conductive mirror layer. [3] The solar cell according to [2], wherein the conductive mirror underlayer contains a metal having a face-centered cubic lattice structure. [4] The solar cell according to [2] or [3], wherein the conductive mirror underlayer contains one or more selected from the group consisting of gold, aluminum, copper, and silver. [5] The solar cell according to any one of [2] to [4], wherein the conductive mirror layer is provided on the hole transport layer, and the conductive mirror underlayer is provided on the conductive mirror layer. [6] The hole transport layer is formed of a material selected from the group consisting of NiO, CuO, CuGaO, and the like. ２ , CuCrO ２ , and CuAlO ２[7] The solar cell according to any one of [1] to [5], wherein the hole transport layer comprises at least one metal oxide selected from the group consisting of CuAlO ２ or CuAlO to which an alkali metal element is added ２ [9] The solar cell according to any one of [1] to [8], wherein the conductive mirror layer comprises one or more selected from the group consisting of gold, silver, aluminum, gold alloys, silver alloys, and aluminum alloys.

[10] The solar cell according to any one of [1] to [9], wherein the light absorbing layer comprises one or more selected from the group consisting of chalcopyrite compounds, kesterite compounds, and perovskite compounds.

[11] A solar cell module, wherein a plurality of the solar cells according to any one of [1] to

[10] are electrically connected in series or in parallel.

[12] A method for manufacturing a solar cell, comprising: a laminate preparation step of preparing a laminate including at least a substrate, a back electrode, a conductive mirror layer, a hole transport layer that is a p-type semiconductor, and a precursor layer of a light absorbing layer, in this order; 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.

[13] The manufacturing method according to

[12] , wherein in the heat treatment step, the laminate is heat treated at a temperature of 60 to 600°C.

[0155] The solar cell of the present invention has improved absorption efficiency of light such as sunlight, and therefore has industrial applicability as a solar cell that can be used in a variety of environments.

[0156] 100...solar cell, 101...substrate, 102...rear electrode, 103...conductive mirror underlayer, 104...conductive mirror layer, 105...hole transport layer, 106...light absorption layer, 107...electron transport layer, 108...surface electrode, 109...transparent electrode layer, 110...grid electrode

Claims

1. A solar cell comprising at least a substrate, a back electrode, a conductive mirror layer, a hole transport layer which is a p-type oxide semiconductor, and a light absorption layer, in this order.

2. The solar cell according to claim 1, further comprising a conductive mirror underlayer between the rear electrode and the conductive mirror layer.

3. The solar cell according to claim 2, wherein the conductive mirror underlayer contains a metal having a face-centered cubic lattice structure.

4. The solar cell according to claim 3, wherein the conductive mirror underlayer contains at least one material selected from the group consisting of gold, aluminum, copper, and silver.

5. The solar cell according to claim 2, wherein the conductive mirror layer is provided on the hole transport layer, and the conductive mirror underlayer is provided on the conductive mirror layer.

6. The hole transport layer is made of NiO, CuO, or CuGaO ２ , CuCrO ２ , and CuAlO ２ The solar cell according to claim 1 , comprising at least one metal oxide selected from the group consisting of:

7. The solar cell according to claim 6, wherein the metal oxide is a metal oxide to which an alkali metal element is added.

8. The hole transport layer is CuAlO ２ or CuAlO to which an alkali metal element is added ２ The solar cell according to claim 6 , comprising:

9. The solar cell according to claim 1, wherein the conductive mirror layer comprises at least one material selected from the group consisting of gold, silver, aluminum, gold alloys, silver alloys, and aluminum alloys.

10. The solar cell according to claim 1, wherein the light absorbing layer contains at least one compound selected from the group consisting of chalcopyrite compounds, kesterite compounds, and perovskite compounds.

11. A solar cell module comprising a plurality of solar cells according to claim 1 electrically connected in series or in parallel.

12. A method for manufacturing a solar cell, comprising: a laminate preparation step of preparing a laminate having at least a substrate, a back electrode, a conductive mirror layer, a hole transport layer which is a p-type semiconductor, and a precursor layer of a light absorption layer, in this order; 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.

13. The manufacturing method according to claim 12, wherein the laminate is heat-treated at a temperature of 60 to 600°C in the heat treatment step.

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