Method for manufacturing solar cell, and solar cell

Abstract

To provide a method for manufacturing a high-productivity solar cell to realize high performance of the solar cell.SOLUTION: A method for manufacturing a solar cell comprises: a precursor formation step for forming a precursor having an InGaSe layer, a CuSe layer and an InSe layer; and a crystallization step for heating the precursor to obtain a crystallized light absorption layer.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Solar cells include silicon solar cells manufactured using materials such as single crystal or polycrystalline silicon. While they have excellent durability, they are expensive to manufacture and thick, so they are used in large-scale power generation facilities. There are also thin-film solar cells, which are solar cells formed by forming a thin film-like light absorption layer on a substrate such as glass or metal. Thin-film solar cells are inexpensive to manufacture and very thin, so they can also be used in a flexible manner. Due to these characteristics, various studies have been conducted in recent years on the conversion efficiency, durability, and other aspects of thin-film solar cells in order to apply them to other applications.

[0003] For example, Patent Document 1 describes that the manufacturing cost can be reduced by using a method in which metal components such as Cu, In, and Ga are laminated by a sputtering method, and then a light absorbing layer is formed while heating in an atmosphere of H2Se or H2S. Furthermore, Patent Document 2 describes that in addition to the above method, internal defects in the thin film can be reduced by forming a light absorbing layer while heating the substrate to a temperature equal to or higher than the crystallization temperature, but there is a concern that the cost of the device will increase because high-temperature heating and sputtering are performed simultaneously.

[0004] In Patent Document 3, a method was attempted in which Cu, In, Ga, and Se, either as simple substances or as alloys, were simultaneously sputtered, and then annealed to crystallize, but the power generation performance was insufficient. Therefore, Patent Document 4 describes that the power generation performance can be improved by laminating CuSe, which is a group I selenium, and InGaSe, which is a group III selenium, and crystallizing the layers in an atmosphere of Se vapor or H2Se gas. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-135495 [Patent Document 2] Special Publication No. 2012-513127 [Patent Document 3] International Publication No. 2011 / 052574 [Patent Document 4] International Publication No. 2011 / 090959 Summary of the Invention [Problem to be solved by the invention]

[0006] In the methods described in Patent Documents 1 and 2, when reacting while heating in an atmosphere of H2Se or H2S, there is a concern that the volume expansion of the light absorbing layer is large, many defects appear in the film, and the surface irregularities become large. Furthermore, according to the methods described in Patent Documents 3 and 4, although the defects in the film and the surface irregularities can be suppressed to some extent, the need for annealing in an atmosphere of Se vapor or H2Se gas requires equipment that takes into consideration the environment and safety, leading to high costs, and in addition, the crystal grains are small and the power generation performance is still insufficient.

[0007] The present invention has been made in view of the above problems, and an object of the present invention is to provide a solar cell manufacturing method and a solar cell that achieves both high performance and high productivity. [Means for solving the problem]

[0008] A method for manufacturing a solar cell according to one embodiment of the present invention includes a precursor formation step of forming a precursor having an InGaSe layer, a CuSe layer, and an InSe layer, and a crystallization step of heating the precursor to crystallize it to obtain a light absorbing layer.

[0009] In the production of solar cells, the precursor having an InGaSe layer, a CuSe layer, and an InSe layer improves the productivity of solar cells and the obtained solar cells have high performance. Effect of the Invention

[0010] According to the present invention, it is possible to provide a solar cell that achieves both high performance and high productivity, and a method for manufacturing the same. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a schematic cross-sectional view of a precursor of a light absorbing layer according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic cross-sectional view of a precursor of a light absorbing layer according to one embodiment of the present invention. [Diagram 3] FIG. 2 is a schematic cross-sectional view of a precursor of a light absorbing layer according to one embodiment of the present invention. [Figure 4] 1 is a schematic cross-sectional view of a solar cell according to one embodiment of the present invention. [Diagram 5] FIG. 2 is a diagram showing X-ray diffraction patterns of each layer included in a light absorbing layer according to one embodiment of the present invention. [Figure 6] FIG. 4 is a diagram showing a change in an X-ray diffraction pattern depending on the formation temperature of an InSe layer according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail with reference to the drawings as necessary, but the present invention is not limited to this, and various modifications are possible without departing from the gist of the present invention. In the drawings, the same elements are given the same reference numerals, and duplicated 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.

[0013] 1. Light absorbing layer formation process In the method for manufacturing a solar cell of the present embodiment, the light absorbing layer forming step includes a precursor forming step of forming a precursor having an InGaSe layer, a CuSe layer, and an InSe layer, and a crystallization step of heating the precursor to crystallize the precursor to obtain the light absorbing layer.

[0014] Conventionally, as a manufacturing method of CIGS-type chalcopyrite solar cells containing Cu, In, Ga, and Se, a method has been developed in which I-type CuSe and III-type InGaSe are separately laminated, and then annealed under Se vapor or H2Se gas atmosphere to crystallize, thereby improving the power generation performance. However, the solar cells obtained by the above-mentioned method have a problem that the crystal grains in the light absorption layer are small and the crystal quality is insufficient, and the power generation performance is not sufficient. Furthermore, since the above-mentioned method requires annealing under Se vapor or H2Se gas atmosphere in the manufacturing process, equipment that takes into consideration the environment and safety is required, and there is a concern that the cost will be enormous.

[0015] Therefore, the inventors of the present application have found that by laminating an InGaSe layer, a CuSe layer, and an InSe layer separately as precursors of a chalcopyrite light absorbing layer, and then heating and crystallizing the precursor, the crystal grains of the light absorbing layer can be enlarged and the crystal quality can be improved, resulting in a high-performance solar cell, and further, since a step of heating in an atmosphere containing Se element is not necessarily required, solar cells can be manufactured with high productivity. The reason why the above method is superior is not necessarily clear, but it is believed that by forming an InGaSe layer, a CuSe layer, and an InSe layer separately and then crystallizing them, good seed crystals are preferentially formed at the interface between the CuSe layer and the InSe layer, which increases the crystal grains and improves the crystal quality. It is also presumed that the element profile of the Se element in the film is favorably arranged when it crystallizes, which relaxes the distortion of the crystal, also contributed synergistically. However, the factors are not limited to those mentioned above.

[0016] In this specification, "the solar cell has high performance" means that the cell characteristics related to the power generation performance of the solar cell are excellent in at least one parameter. In addition, in this specification, "the solar cell has high productivity" means that the production cost of the solar cell is low and the manufacturing method is highly reliable. The manufacturing method of the solar cell of this embodiment will be described in detail below.

[0017] 1.1. Precursor formation process The precursor formation step of this embodiment is a step of forming a precursor having an InGaSe layer, a CuSe layer, and an InSe layer. By forming a precursor having the above layers, the crystal grains of the obtained light absorbing layer are increased, and the crystal quality is improved, thereby improving the power generation performance.

[0018] A schematic cross-sectional view of one example of a precursor of a light absorbing layer is shown in Fig. 1. As shown in Fig. 1, the precursor of this embodiment has at least one InGaSe layer, one CuSe layer, and one InSe layer.

[0019] In the precursor formation step, it is preferable to make the InGaSe layer or the InSe layer amorphous, and it is more preferable to make both the InGaSe layer and the InSe layer amorphous. By making the InGaSe layer or the InSe layer amorphous, the generation of unintended seed crystals other than at the interface with the CuSe layer is suppressed, so that the crystal grains of the obtained light absorption layer are increased, and the crystal quality is improved, which tends to further improve the power generation performance. In this specification, "amorphous" is determined by the absence of peaks in the 2θ-θ pattern of X-ray diffraction measurement that extend beyond a region that is twice the noise width above and below the baseline.

[0020] The method for forming each layer is not particularly limited, and from the viewpoints of mass productivity and reliability, it is preferable to form the layers by a sputtering method and / or a vapor deposition method, or it is also possible to use only a sputtering method. When forming the precursor, the surface temperature of the sputtered substrate is preferably 300° C. or less, 250° C. or less, 200° C. or less, or room temperature (RT). By setting the temperature of the sputtered substrate within the above range, the InGaSe layer and the InSe layer tend to become amorphous layers, and the solar cell obtained thereby tends to have higher performance and higher productivity. In this specification, the sputtered substrate refers to a substrate on a stage during sputtering, on which a compound derived from the sputtering target is laminated.

[0021] The target used for sputtering is not particularly limited, and in forming each layer, for example, a single substance or mixture of In, In4Se3, InSe, In2Se3, GaSe, Ga2Se3, and Se may be used for the InGaSe layer, a single substance or mixture of Cu, Cu2Se, CuSe2, and Se may be used for the CuSe layer, and a single substance or mixture of In, In4Se3, InSe, In2Se3, and Se may be used for the InSe layer. Among these, it is preferable to use a mixture of In2Se3 and Ga2Se3 with a Ga2Se3 ratio of 30% to 60% for the InGaSe layer, a single substance of CuSe2 for the CuSe layer, and a single substance of In2Se3 for the InSe layer. Examples of the gas supplied during sputtering include inert gases such as Ar and He, as well as H, HSe, HS, etc. Among these, from the viewpoint of more reliably achieving the effects of the present invention, Ar is preferable as the inert gas, and H is preferable as the other gas.

[0022] In the precursor formation step, it is preferable to form the InSe layer closer to the light-receiving surface than the InGaSe layer, as the power generation performance of the obtained solar cell tends to be further improved by forming the InSe layer closer to the light-receiving surface than the InGaSe layer.

[0023] In the precursor formation step, it is preferable to form the InSe layer closest to the light-receiving surface. When the InSe layer is formed closest to the light-receiving surface, the power generation performance of the obtained solar cell tends to be further improved. From the same viewpoint, it is preferable to form the InSe layer closest to the light-receiving surface and the CuSe layer as the second layer on the light-receiving surface.

[0024] Fig. 2 shows a schematic cross-sectional view of another example of the precursor of the light absorption layer. As shown in Fig. 2, the precursor of this embodiment has an InGaSe layer, a CuSe layer, and an InSe layer, and it is preferable that the InSe layer is formed closer to the light receiving surface side than the InGaSe layer. Also, as shown in Fig. 2, the precursor of this embodiment has an InGaSe layer, a CuSe layer, and an InSe layer, and it is preferable that the InSe layer is formed closest to the light receiving surface side.

[0025] In the precursor formation step, preferably, the InGaSe layer and the CuSe layer are formed in a number of 2 or more, 3 or more, or 5 or more. By forming the InGaSe layer and the CuSe layer in a number of 2 or more, the power generation performance of the obtained solar cell tends to be further improved.

[0026] Fig. 3 shows a schematic cross-sectional view of another example of the precursor of the light absorbing layer. As shown in Fig. 3, the precursor of this embodiment has an InGaSe layer, a CuSe layer, and an InSe layer, and preferably forms two or more InGaSe layers and two or more CuSe layers. Also, as shown in Fig. 3, the precursor of this embodiment has an InGaSe layer, a CuSe layer, and an InSe layer, and preferably forms the InSe layer closest to the light receiving surface side.

[0027] In the entire precursor to be formed, the ratio of the amount of Ga element to the total amount of In element and Ga element (Ga / (In+Ga)) is preferably 0.10 to 0.50, 0.15 to 0.40, or 0.20 to 0.40. By setting the amount of Ga / (In+Ga)) ratio in the entire precursor within the above range, the power generation performance of the obtained solar cell tends to be further improved. In addition, in the entire precursor to be formed, the ratio of the amount of substance of Cu element to the total amount of substance of In element and Ga element (Cu / (In+Ga)) is preferably 0.50 to 1.0, 0.75 to 0.95, or 0.80 to 0.90. By setting the amount of substance ratio (Cu / (In+Ga)) in the entire precursor within the above range, the power generation performance of the obtained solar cell tends to be further improved. In the entire precursor to be formed, the ratio of the amount of substance of Se element to the total amount of substance of Cu element, In element, and Ga element (Se / (Cu+In+Ga)) is preferably 0.5 or more, 0.8 or more, or 1.0 or more. By setting the amount of substance ratio (Se / (Cu+In+Ga)) within the above range, the amount of Se element in the precursor becomes sufficient, and the power generation performance and productivity of the obtained solar cell tend to be further improved. In addition, the upper limit of the amount of substance ratio (Se / (Cu+In+Ga)) is not particularly limited, and may be, for example, 10.0 or less, 7.5 or less, 5.0 or less, or 3.0 or less.

[0028] In the InGaSe layer, the ratio of the amount of Ga element to the total amount of In element and Ga element (Ga / (In+Ga)) is preferably 0.1 to 0.8, 0.2 to 0.7, or 0.3 to 0.6. By setting the amount of Ga / (In+Ga)) ratio in the InGaSe layer within the above range, the power generation performance of the obtained solar cell tends to be further improved.

[0029] The ratio of the amount of substance X of the In element in the InSe layer to the total amount of substance Y of the In element and the Ga element in the InGaSe layer (Y / X) is preferably 0.5 to 2.5, and more preferably 1.0 to 1.5. By setting the amount of substance ratio (Y / X) within the above range, the power generation performance of the obtained solar cell tends to be further improved.

[0030] In the InGaSe layer and the InSe layer, the ratio of the amount of Se element to the total amount of In element and Ga element (Se / (In+Ga)) is preferably 0.8 to 2.0, and more preferably 1.0 to 1.75. When a CuSe layer is formed on the outermost layer of the precursor, the value of (Se / (In+Ga)) in the InGaSe layer and the InSe layer is preferably 1.0 or more and 2.0 or less, and more preferably 1.25 or more and 1.75 or less. When the CuSe layer is not formed on the outermost layer of the precursor, the value of (Se / (In+Ga)) in the InGaSe layer and the InSe layer is preferably 1.0 or more and 2.0 or less, and more preferably 1.0 or more and 1.5 or less. When the (Se / (In+Ga)) value in the InGaSe layer and the InSe layer is within the above range, the power generation performance of the obtained solar cell tends to be further improved. In this specification, the outermost layer of the precursor means the layer closest to the light-receiving surface.

[0031] The (Se / Cu) substance amount ratio in the CuSe layer is preferably 0.5 to 4.0, more preferably 0.5 to 3.0. When a CuSe layer is formed on the outermost layer of the precursor, the ratio of the amount of substance of Se element to the amount of substance of Cu element in the CuSe layer (Se / Cu) is preferably 1.5 or more and 5.0 or less, and 2.0 or more and 3.0 or less. When the CuSe layer is not formed on the outermost layer of the precursor, the ratio of the amount of substance of Se element to the amount of substance of Cu element in the CuSe layer (Se / Cu) is preferably 0.3 or more and 2.5 or less, and more preferably 0.5 or more and 2.0 or less. In the CuSe layer, by setting the ratio of the amount of substance of Se element to the amount of substance of Cu element (Se / Cu) within the above range, the power generation performance of the obtained solar cell tends to be further improved.

[0032] The method for examining the content of elements in each layer of the precursor is not particularly limited, and for example, optical emission spectroscopy using inductively coupled plasma (ICP), energy dispersive X-ray analysis (EDX or EDS), secondary ion mass spectrometry (SIMS), etc. can be used.

[0033] In the precursor formation process, examples of methods for adjusting the content of elements in each layer include a method for adjusting the content of elements in the raw material (target) used during sputtering or deposition, a method for controlling the film formation pressure or applied power, and the like.

[0034] The thickness of the precursor to be formed may be adjusted as required depending on the configuration and purpose of the solar cell, etc. The thickness of the entire precursor is preferably 700 nm or more and 3200 nm or less, or 1500 nm or more and 2700 nm or less. The thickness of each InGaSe layer to be formed is preferably 300 nm or more and 1300 nm or less, and more preferably 600 nm or more and 1200 nm or less. The thickness of each CuSe layer is preferably 100 nm or more and 700 nm or less, and more preferably 300 nm or more and 600 nm or less. The thickness of each InSe layer is preferably 300 nm or more and 1200 nm or less, and more preferably 600 nm or more and 1100 nm or less. By setting the thickness of each layer in the precursor formation step as described above, the power generation performance of the obtained solar cell can be further improved with greater certainty.

[0035] 1.2.Crystallization process The crystallization step of the present embodiment is a step of obtaining a light absorbing layer by heating the formed precursor to crystallize it. The heating may be performed only once, or may be performed stepwise in two or more stages.

[0036] The heating temperature in the crystallization step is preferably 300° C. or more and 600° C. or less, and more preferably 400° C. or more and 600° C. or less. By setting the heating temperature within the above range, the crystal grains of the light absorbing layer are increased, and the crystal quality is improved, which tends to further improve the power generation performance of the obtained solar cell.

[0037] The crystallization step may be performed in an inert atmosphere or an atmosphere containing Se element, and is preferably performed in an inert atmosphere. By performing crystallization in an inert atmosphere, the power generation performance of the solar cell can be improved more reliably. Examples of the inert gas include nitrogen (N2) and argon (Ar), and nitrogen is preferably used.

[0038] 1.3.Surface treatment process The method for producing a solar cell according to the present embodiment preferably further comprises, after the crystallization step, a surface treatment step of treating the surface of the light absorbing layer in a sulfur atmosphere at 350° C. to 600° C. By carrying out the surface treatment step, the band gap on the light receiving surface side of the light absorbing layer can be controlled, which tends to result in a solar cell with even higher performance.

[0039] The temperature of the atmosphere during the surface treatment may be 400° C. or higher and 600° C. or lower, or 500° C. or higher and 600° C. or lower. By carrying out the surface treatment step within the above temperature range, the solar cell tends to have higher performance.

[0040] The time for the surface treatment step may be, for example, from 1 minute to 60 minutes, or from 3 minutes to 30 minutes. By setting the time for the surface treatment step within the above range, the solar cell tends to have higher performance.

[0041] 2. Solar cells The solar cell of this embodiment includes the light absorbing layer 104 manufactured by the above-mentioned method, and has a configuration described below. The solar cell including the light absorbing layer 104 manufactured by the above-mentioned manufacturing method has excellent conversion efficiency and high performance, and also has excellent productivity because the manufacturing process can be simplified.

[0042] FIG. 4 shows an example of a cross-sectional structure of the solar cell of this embodiment. 4, the solar cell 10 includes a substrate 107, a first electrode layer 106 provided on the substrate 107, a hole transport layer 105 provided on the first electrode layer 106, a light absorbing layer 104 provided on the hole transport layer 105, an electron transport layer 103 provided on the light absorbing layer 104, a second electrode layer 102 provided on the electron transport layer 103, and a grid electrode 101 provided on the second electrode layer 102. The solar cell 10 receives light from the second electrode layer 102 side to generate electricity.

[0043] Each layer constituting the solar cell 10 will be described below.

[0044] 2.1.Substrate The substrate 107 is not particularly limited, and may be, for example, a glass substrate such as soda lime glass or low alkali glass, a metal substrate such as stainless steel foil, aluminum foil or titanium foil, or a resin substrate such as a polyimide resin film or an epoxy resin film. The thickness of the substrate 107 is not particularly limited, and 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. It is preferable that the thickness of the substrate 107 is within the above range in terms of making the solar cell lighter and more flexible.

[0045] 2.2.First electrode layer The first electrode layer 106 is generally provided to extract current due to holes generated in the light absorbing layer 104 described later. The first electrode layer 106 is not particularly limited as long as it has electrical conductivity, and may be, for example, a metal conductive layer made of a metal such as Mo, Cr, or Ti; a conductive inorganic compound conductive layer made of a conductive inorganic compound other than metal; or a conductive organic compound conductive layer made of a conductive organic compound. The thickness of the first electrode layer 106 is not particularly limited, and may be, for example, 200 nm or more and 800 nm or less, or 300 nm or more and 700 nm or less. If the thickness of the first electrode layer 106 is within the above range, it is preferable in that the solar cell can be made lighter and more flexible while sufficiently extracting current without loss.

[0046] 2.3. Hole transport layer The hole transport layer 105 has a function of, for example, efficiently extracting holes generated in the light absorbing layer 104 described below from the light absorbing layer 104, and preventing recombination of electrons and holes generated simultaneously with the electron absorption in the light absorbing layer 104 described below. The hole transport layer 105 is preferably a p-type semiconductor. The substance contained in the p-type semiconductor is not particularly limited, and examples thereof include 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; organic compounds such as polyaniline derivatives; and inorganic compounds such as nickel oxide, molybdenum oxide, copper gallium oxide, copper aluminum oxide, molybdenum selenide, and molybdenum sulfide selenide. The p-type semiconductor in the hole transport layer 105 may be used alone or in combination of two or more kinds. In the solar cell, the formation of the hole transport layer 105 may be omitted.

[0047] 2.4.Light absorbing layer 2.4.1. Light-absorbing layer of this embodiment The light absorbing layer 104 has a function of absorbing light such as near infrared light, visible light, and ultraviolet light to generate electrons and holes. An example of such light is sunlight. The light absorbing layer 104 in the solar cell of this embodiment contains CIGS-type chalcopyrite obtained by the above-mentioned precursor formation step and crystallization step. When the above-mentioned surface treatment step is additionally performed on the obtained light absorbing layer 104, it further contains sulfur components, so it can also be said that the light absorbing layer 104 contains CIGSS-type (containing Cu, In, Ga, Se, and S) chalcopyrite.

[0048] The band gap of the light absorbing layer 104 of this embodiment is preferably 2.0 eV or less, 1.8 eV or less, 1.5 eV or less, 1.2 eV or less, or 1.1 eV or less, based on the minimum value in the depth direction. The lower limit of the band gap may be, for example, 0.5 eV or 0.8 eV or more. When the band gap of the light absorbing layer 104 satisfies the above range, the solar cell has high performance.

[0049] The band gap can be measured by a known method, for example, by measuring the spectral transmittance or the spectral quantum efficiency.

[0050] In the light absorbing layer 104 of this embodiment, the band gap in the section from the light receiving surface side to 200 nm in the depth direction is preferably 1.1 eV to 1.4 eV, the band gap in the section from 200 nm in the depth direction to 400 nm in the depth direction is preferably 0.9 eV to 1.2 eV, and the band gap from 400 nm in the depth direction onward is preferably 1.2 eV to 1.7 eV. By setting the band gap within the above ranges, it tends to be possible to prevent recombination of electrons and holes generated by light absorption.

[0051] The thickness of each layer of the light absorbing layer 104 in this embodiment is preferably 0.5 μm to 5 μm, 0.8 μm to 4 μm, or 1 μm to 3 μm. By setting the thickness of each layer of the light absorbing layer 104 within the above range, the productivity of the solar cell is further improved, and it tends to be easier to make the solar cell lighter and more flexible.

[0052] The ratio of the light absorbing layer 104 in this embodiment is not particularly limited, and is, for example, 50 mass% or more and 100 mass% or less, 60 mass% or more and 100 mass% or less, 70 mass% or more and 100 mass% or less, 80 mass% or more and 100 mass% or less, or 90 mass% or more and 100 mass% or less, relative to the total mass of the light absorbing layer 104.

[0053] 2.4.2. Additional Light-Absorbing Layer The solar cell may have an additional light absorbing layer different from the light absorbing layer 104. For example, such an additional light absorbing layer may be an embodiment in which a hole transport layer is further provided on the second electrode layer 102 of a solar cell that already has a light absorbing layer, and an additional light absorbing layer is provided. In the case where no additional hole transport layer is provided, the solar cell may have an additional light absorbing layer on the second electrode layer 102. Examples of compounds that can be used as the additional light absorbing layer include perovskite compounds, chalcopyrite compounds, and kesterite compounds. Each compound may be used alone, or two or more of perovskite, chalcopyrite, or kesterite may be used in combination.

[0054] Examples of perovskite compounds include organic-inorganic perovskite compounds, particularly halide-based organic-inorganic perovskite compounds. Specific examples include CH3NH3PbI3, CH3NH3PbBr3, CH3NH3PbCl3, CH3NH3SnI3, CH3NH3SnBr3, CH3NH3SnCl3, CH3NH3PbI (3-x) Cl x , CH3NH3PbI (3-x) Br x , CH3NH3PbBr (3-x) Cl x , CH3NH3Pb (1-y) Sn y I3, CH3NH3Pb (1-y) Sn y Br3, CH3NH3Pb (1-y) Sn y Cl3, CH3NH3Pb (1-y) Sn y I (3-x) Cl x , CH3NH3Pb (1-y) Sn y I (3-x) Br x , and CH3NH3Pb (1-y) Sn y Br (3-x) Cl xand the above compounds in which CFH2NH3, CF2HNH3, CF3NH3, or NH2CH=NH2 is used instead of CH3NH3. 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.

[0055] Examples of chalcopyrite compounds that are different from the CIGS-type chalcopyrite compounds obtained by the manufacturing method of the present invention include CuAlS2, CuAlSe2, CuAlTe2, CuGaS2, CuGaSe2, CuGaTe2, CuInS2, CuInSe2, CuInTe2, AgAlS2, AgAlSe2, AgAlTe2, AgGaS2, AgGaSe2, AgGaTe2, AgInS2, AgInSe2, AgInTe2, and combinations thereof. The term "combinations of these" is not particularly limited, and includes, for example, Cu(In) when CuGaS2 and CuInSe2 are combined. x Ga 1-x )(Se y S 1-y )2(0≦x≦1, 0≦y≦1).

[0056] Examples of kesterite compounds include I2-II-IV-VI4 group kesterite compounds, and more specifically, Cu2ZnSnS4, Cu2ZnSnSe4, Cu2ZnGeS4, Cu2ZnGeSe4, Cu2MnSnS4, Cu2MnSnSe4, Cu2MnGeS4, Cu2MnGeSe4, Ag2ZnSnS4, Ag2ZnSnSe4, Ag2ZnGeS4, Ag2ZnGeSe4, Ag2MnSnS4, Ag2MnSnSe4, Ag2MnGeS4, Ag2MnGeSe4, and combinations thereof. "Combinations of these" are not particularly limited, and examples include the combination of Cu2ZnSnS4 and Ag2ZnSnSe4 (Cu x Ag 1-x )2ZnSn(S y Se 1-y )4(0≦x≦1).

[0057] 2.5.Electron transport layer The electron transport layer 103 has a function of, for example, efficiently extracting electrons generated in the light absorbing layer 104 from the light absorbing layer 104 and preventing recombination of the electrons and holes generated simultaneously in the light absorbing layer 104. The electron transport layer 103 is preferably an n-type semiconductor. The material contained in the n-type semiconductor is not particularly limited, and may be, for example, C 60 phenanthroline derivatives such as 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), phenylpyridine derivatives such as 4,6-bis(3,5-di-4-pyridinylphenyl)-2-methylpyrimidine (B4PymPm) and tris(2,4,6-trimethyl-3-(pyridin-3-yl)phenyl)borane (3TPYMB), and organic compounds such as n-type oxide semiconductors essentially consisting of zinc oxide, tin oxide, titanium oxide, zinc oxide sulfide, magnesium zinc oxide, zinc tin oxide, or zinc titanium oxide, and n-type semiconductors containing cadmium sulfide, indium sulfide, or indium sulfide to which an oxygen element or an alkali metal element has been added. The n-type semiconductor in the electron transport layer 103 may be used alone or in combination of two or more kinds. The thickness of the electron transport layer 103 is, for example, 50 nm to 200 nm, 60 nm to 150 nm, or 75 nm to 135 nm. When the thickness of the electron transport layer 103 is within the above range, it is preferable in that the solar cell can be made lightweight and flexible while maintaining the above functions.

[0058] 2.6.Second electrode layer The second electrode layer 102 is provided, for example, to extract a current due to electrons generated in the light absorbing layer 104. In a solar cell, the light absorbing layer 104 typically absorbs light that has passed through the second electrode layer 102, so it is preferable to make the second electrode layer 102 a transparent electrode layer in order to increase the amount of light absorbed by the light absorbing layer 104. As a material for the transparent electrode, a known material can be used, 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 thickness of the second electrode layer 102 is not particularly limited, and is, for example, 100 nm or more and 1500 nm or less, or 200 nm or more and 1000 nm or less. When the thickness of the second electrode layer 102 is within the above range, it is preferable in that the solar cell can be made lighter and more flexible while sufficiently extracting the current without loss.

[0059] 2.7.Grid Electrode The grid electrode 101 is provided, for example, to extract electricity from the second electrode layer 102. The material of the grid electrode 101 is not particularly limited as long as it is conductive, and examples of the material that can be used include metals such as Mo, Cr, Ag, Cu, Ni, Al, and Ti; conductive inorganic compounds other than metals; and conductive organic compounds. The thickness of the grid electrode 101 is not particularly limited, and is, for example, 5 μm or more and 50 μm or less. Setting the thickness of the grid electrode 101 within the above range is preferable in terms of making the solar cell lighter and more flexible.

[0060] 2.8. Example of changes The solar cell 10 shown in FIG. 4 is an example for explaining the solar cell of the present invention, and is not intended to limit the present invention to only this embodiment. The solar cell of the present invention can be modified in various ways without departing from the gist of the invention.

[0061] For example, the solar cell 10 may have other layers between the layers, on the grid electrode 101, or under the substrate 107, as necessary. Specifically, the hole transport layer 105 may have two or more hole transport layers each containing a different material, and a contamination prevention layer for preventing contamination from the outside may be provided on the grid electrode 101. Alternatively, instead of the grid electrode 101, another hole transport layer may be provided on the second electrode layer 102, and an additional light absorbing layer may be provided thereon, and the electron transport layer 103 may have two or more electron transport layers 103 each containing a different material. However, at least one of the light absorbing layers is the light absorbing layer 104 obtained by the manufacturing method of this embodiment.

[0062] Although not shown, the solar cell 10 may have two or three sets of a hole transport layer 105, a light absorbing layer 104 provided on the hole transport layer 105, an electron transport layer 103 provided on the light absorbing layer, and a second electrode layer 102 provided on the electron transport layer 103, stacked on the first electrode layer 106. In addition, a grid electrode may be provided on the uppermost second electrode layer.

[0063] When any of the layers 101 to 107 is present in a plurality of layers, the plurality of layers may be the same as or different from each other. For example, when the light absorbing layer 104 is provided in a plurality of layers, each light absorbing layer may contain a compound having a different absorption spectrum, and the electron transport layer and the 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 each layer. However, at least one layer among the light absorbing layers is the light absorbing layer 104 obtained by the above-mentioned manufacturing method.

[0064] The solar cell of this embodiment, like a conventional solar cell, can be used in a normal temperature environment where the temperature of the solar cell is about 45 to 85° C. For example, it can be suitably used as a power generation device attached to the windows or walls of buildings or vehicles, as an independent power source device for street lights or sensors, as a mobile energy device, and as a power generation device in space or the stratosphere.

[0065] The solar cell of this embodiment has a high conversion efficiency. More specifically, the conversion efficiency of the solar cell of this embodiment is preferably 14% or more, 15% or more, or 16% or more. Having a conversion efficiency in the above range indicates that a high-performance solar cell has been obtained.

[0066] The thickness of the solar cell excluding the substrate 107 is not particularly limited and is, for example, from 1.0 μm to 10.0 μm, from 1.1 μm to 8.0 μm, or from 1.2 μm to 6.0 μm. The solar cell of the present invention can be a thin-film solar cell by forming each layer sufficiently thin.

[0067] 3. Manufacturing method of solar cells Next, a method for manufacturing the solar cell of this embodiment shown in FIG. 4 will be described.

[0068] 3.1. First electrode layer formation process First, for example, the first electrode layer 106 is formed on the substrate 107. Methods for forming the first electrode layer 106 include a dry process and a wet process, with the dry process being preferred. The dry process is not particularly limited, and an example thereof is a method for forming the first electrode layer 106, which is a metal conductive layer, by a sputtering method. The film formation conditions for the sputtering method are not particularly limited, and for example, applied power: 1.0 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. In the first electrode layer forming step, for example, the substrate 107 may be a substrate to be sputtered. In this specification, the substrate to be sputtered is a substrate on a stage during sputtering, on which a compound derived from the sputtering target is laminated.

[0069] 3.2. Hole transport layer formation process Next, for example, a hole transport layer 105 is formed on the first electrode layer 106. Methods for forming the hole transport layer 105 include a dry process and a wet process, with a dry process being preferred. The dry process is not particularly limited, and an example thereof is a method for forming the hole transport layer 105, 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, and for example, applied power: 0.5 to 3.0 W / cm 2 The deposition atmosphere may be an argon atmosphere or a mixed atmosphere of argon and oxygen, and the deposition pressure may be 0.5 to 3.0 Pa. When the light absorbing layer 104 is formed, a compound may be formed between the first electrode layer 106 and the light absorbing layer 104, and the hole transport layer 105 may be formed between the first electrode layer 106 and the light absorbing layer 104.

[0070] 3.3. Light absorbing layer formation process Next, the light absorbing layer 104 is formed on the hole transport layer 105. The method for forming the light absorbing layer 104 is as described in "1. Light absorbing layer forming step".

[0071] 3.4.Electron transport layer formation process Next, the electron transport layer 103 is formed on the light absorbing layer 104. For example, the electron transport layer 103 may be formed on the sputtered substrate including the light absorbing layer 104 by forming an n-type oxide semiconductor film by sputtering while supplying a gas containing an oxygen source and a hydrogen source, or the n-type oxide semiconductor film may be formed by sputtering while supplying a gas not containing a hydrogen source. The film formation conditions for the sputtering method are not particularly limited, and examples thereof include applied power: 0.5 to 3.0 W / cm 2 The film formation atmosphere may be an argon atmosphere that may contain oxygen, and the film formation pressure may be 0.5 to 3.0 Pa. It is also preferable to heat the substrate to be sputtered during sputtering.

[0072] 3.5. Second electrode layer formation process Next, the second electrode layer 102 is formed on the electron transport layer 103. Methods for forming the second electrode layer 102 include a dry process and a wet process, with the dry process being preferred. The dry process is not particularly limited, and an example thereof is a method for forming the second electrode layer 102, which is a transparent electrode layer, by a sputtering method. The film formation conditions for the sputtering method are not particularly limited, and an example thereof is an applied power of 0.5 to 3.0 W / cm. 2 The deposition atmosphere may be an argon atmosphere or a mixed atmosphere of argon, oxygen, and hydrogen, and the deposition pressure may be 0.5 to 3.0 Pa.

[0073] 3.6. Grid electrode formation process Next, the grid electrode 101 is formed on the second electrode layer 102. Methods for forming the grid electrode 101 include a dry process and a wet process. Specifically, for example, there are a sputtering method, a vapor deposition method, a method of printing a paste-like conductive material on the second electrode layer 102, and a method of crimping a conductive wire.

[0074] After the light absorbing layer 104 is formed, an additional light absorbing layer forming step may be performed before the grid electrode is formed. As such an additional light absorbing layer forming step, for example, a hole transport layer may be further formed on the second electrode layer 102, and then an additional light absorbing layer may be formed on the second electrode layer when there is no hole transport layer. Methods for forming the additional light absorbing layer include a dry process and a wet process, but a dry process is preferred. The dry process is not particularly limited, and examples of the dry process include a method of forming an additional light absorbing layer containing a perovskite compound, a chalcopyrite compound, and a kesterite compound by a sputtering method. The film forming conditions for the sputtering method are not particularly limited, and examples of the applied power are 0.5 to 3.0 W / cm. 2The deposition atmosphere may be an argon atmosphere, and the deposition pressure may be 0.2 to 3.0 Pa. After sputtering, the method may include a step of annealing in a nitrogen or iodine atmosphere at 80° C. to 200° C. Alternatively, after sputtering, the method may include a step of annealing in a nitrogen or selenium and sulfur atmosphere at 350° C. to 650° C.

[0075] <Additional Notes> Embodiments of the present disclosure include the following aspects. [1] a precursor forming step of forming a precursor having an InGaSe layer, a CuSe layer, and an InSe layer; A crystallization step of obtaining a crystallized light absorbing layer by heating the precursor. How solar cells are manufactured. [2] In the precursor forming step, the InGaSe layer and the InSe layer are amorphous. A method for producing the solar cell described in [1]. [3] In the precursor formation step, each layer is formed at 200° C. or less by a sputtering method and / or a deposition method. A method for producing a solar cell according to [1] or [2]. [4] In the precursor formation step, the InSe layer is formed closer to the light-receiving surface than the InGaSe layer. The method for producing a solar cell according to any one of [1] to [3]. [5] In the precursor formation step, the InSe layer is formed closest to the light-receiving surface. The method for producing a solar cell according to any one of [1] to [4]. [6] In the precursor forming step, the InGaSe layer and the CuSe layer are each formed in two or more layers. The method for producing a solar cell according to any one of [1] to [5]. [7] In the InGaSe layer, a ratio of the amount of Ga element to the total amount of In element and Ga element (Ga / (In+Ga)) is 0.3 or more and 0.6 or less. The method for producing a solar cell according to any one of [1] to [6]. [8] a ratio of a total amount Y of In and Ga in the InGaSe layer (Y / X) to an amount X of In in the InSe layer is 1.0 or more and 1.5 or less; The method for producing a solar cell according to any one of [1] to [7]. [9] In the precursor, The ratio of the amount of Ga element to the total amount of In element and Ga element (Ga / (In+Ga)) is 0.15 or more and 0.40 or less, The ratio of the amount of Cu to the total amount of In and Ga (Cu / (In+Ga)) is 0.75 or more and 0.95 or less, The ratio of the amount of Se to the total amount of Cu, In, and Ga (Se / (Cu+In+Ga)) is 1.0 or more. The method for producing a solar cell according to any one of [1] to [8].

[10] In the InGaSe layer and the InSe layer, the ratio of the amount of Se element to the total amount of In element and Ga element (Se / (In+Ga)) is 1.25 or more and 1.75 or less. The method for producing a solar cell according to any one of [1] to [9].

[11] When the CuSe layer is formed on the outermost layer of the precursor, in the CuSe layer, a ratio of the amount of substance of Se element to the amount of substance of Cu element (Se / Cu) is 2.0 or more and 3.0 or less. The method for producing a solar cell according to any one of [1] to

[10] .

[12] When the CuSe layer is not formed on the outermost layer of the precursor, in the CuSe layer, a ratio of the amount of substance of Se element to the amount of substance of Cu element (Se / Cu) is 0.5 or more and 2.0 or less. The method for producing a solar cell according to any one of [1] to

[11] .

[13] In the crystallization step, heating is performed in an inert atmosphere at 300° C. or more and 600° C. or less. The method for producing a solar cell according to any one of [1] to

[12] .

[14] After the crystallization step, a surface treatment step of treating a surface of the light absorbing layer in a sulfur atmosphere at 350° C. or higher and 600° C. or lower is further provided. The method for producing a solar cell according to any one of [1] to

[13] .

[15] [1] to

[14] , In the light absorbing layer, a band gap in a section from the light receiving surface side to 200 nm in a depth direction is 1.1 eV or more and 1.4 eV or less, the band gap in the section from 200 nm in the depth direction from the light receiving surface side to 400 nm in the depth direction is 0.9 eV or more and 1.2 eV or less; The band gap in the section from 400 nm in the depth direction from the light receiving surface side is 1.2 eV or more and 1.7 eV or less. Solar cell. EXAMPLES

[0076] The present embodiment will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0077] <How to make solar cells> A solar cell having one electron transport layer as shown in FIG. 4 was fabricated. A titanium foil having a thickness of 50 μm was used as the substrate. A first electrode layer containing metallic molybdenum was formed to a thickness of 600 nm on this substrate by sputtering. The light absorbing layer of this embodiment was formed thereon under the conditions described below. Here, when the crystals of the light absorbing layer were formed, a 50 nm MoSe layer, which is a hole transport layer, was also formed between the light absorbing layer and the first electrode layer. Furthermore, the obtained light absorbing layer was annealed in a sulfur atmosphere at 500° C. to 600° C. for 3 minutes to 30 minutes to perform a surface treatment.

[0078] Next, an n-type electron transport layer containing titanium zinc oxide doped with hydrogen and sulfur elements was formed on the light absorption layer by a sputtering method to a thickness of 70 nm to 120 nm. A second electrode layer of hydrogen-containing indium oxide was then formed to a thickness of 300 nm on the n-type electron transport layer, and a silver grid electrode with a width of 50 μm was then formed on the surface of the second electrode layer, finally obtaining a solar cell.

[0079] In the following Examples and Comparative Examples, solar cells were fabricated and evaluated in the same configuration as described above except for the light absorbing layer.

[0080] 1. Introduction of InSe layer 1.1. Formation of light absorbing layer Example 1 In Example 1, a precursor structure as shown in FIG. 1 was adopted. In Example 1, an InGaSe layer, a CuSe layer, and an InSe layer were formed by sputtering. In Example 1, an InGaSe layer, a CuSe layer, and an InSe layer were formed to have thicknesses of 900 nm, 800 nm, and 400 nm, respectively, to prepare a precursor. This precursor was crystallized by heating in a nitrogen atmosphere at 400° C. to 600° C., and after the crystallization process, a surface treatment was performed to treat the surface of the light absorbing layer in a sulfur atmosphere at 500° C. to 600° C., thereby obtaining a light absorbing layer. <Conditions for sputtering film formation> ·Applied power: 0.5~3.0W / cm 2 Deposition atmosphere: Argon Pressure during deposition: 0.2 Pa to 3.0 Pa Substrate temperature: Room temperature Target species: InGaSe layer is a mixture of In2Se3 and Ga2Se3 with Ga2Se3 content of 30% to 60%; CuSe layer is CuSe2 alone; InSe layer is In2Se3 alone

[0081] Comparative Example 1 In Comparative Example 1, sputtering was performed in the same manner as described in a non-patent document (Zhu, XL, & Wang, LK (2014), 13.6%-efficient Cu(In,Ga)Se2solar cell with absorber fabricated by RF sputtering of (In,Ga)2Se3and CuSe targets, Solar Energy Materials and Solar Cells, 124, 21-25.), and an InGaSe layer and a CuSe layer were formed in order to a thickness of 1700 nm and 400 nm, respectively, to prepare a precursor. This precursor was crystallized by heating in a nitrogen atmosphere at 400°C to 600°C, and after the crystallization process, a surface treatment was performed to treat the surface of the light absorbing layer in a sulfur atmosphere at 500°C to 600°C, thereby obtaining the light absorbing layer of Comparative Example 1.

[0082] 1.2.Evaluation The photoluminescence intensity (PL intensity) and band gap [eV] of the obtained light absorbing layer were measured using a near-infrared fluorescence lifetime estimation device manufactured by Hamamatsu Photonics KK The wavelength of incident light was 532 nm. The obtained results are shown in Table 1. Generally, it is suggested that the higher the PL intensity, the higher the crystal quality, and it is suggested that the crystal quality of the light absorbing layer of Example 1 is dramatically improved. [Table 1]

[0083] 2. Precursor Aspects 2.1. Formation of light absorbing layer (Examples 2 and 3) Examples 2 and 3 employ precursor structures as shown in Figures 2 and 3. In Examples 2 and 3, the same sputtering conditions as in Example 1 were used, but the order of lamination was changed. In Example 2, the CuSe layer was formed closer to the substrate than the InSe layer, as in Example 1, and the thicknesses of the InGaSe layer, CuSe layer, and InSe layer were 900 nm, 400 nm, and 800 nm, respectively. In Example 3, the InGaSe layer and the CuSe layer were repeatedly formed, and then the InSe layer was formed. The thicknesses of the InGaSe layer, CuSe layer, and InSe layer were 450 nm, 200 nm, and 800 nm, respectively, and layers of the same compound were laminated with the same thickness. The precursor of each example was crystallized by heating in a nitrogen atmosphere at 400°C to 600°C, and further, after the crystallization process, a surface treatment was performed to treat the surface of the light absorbing layer in a sulfur atmosphere at 500°C to 600°C, thereby obtaining a light absorbing layer.

[0084] 2.2.Evaluation of battery characteristics (Conversion efficiency) A solar cell was fabricated as described above, and the IV curve was measured under standard test conditions (light with spectrum AM1.5 and irradiance of 1kW / m 2 The measurements were taken under test conditions where light was incident at 4000K and the solar cell temperature was 25°C. The conversion efficiency and fill factor of each solar cell were calculated using the following formulas. The conversion efficiency is the value obtained by dividing the output (maximum output: Pmax) at the optimum operating point on the IV curve by the light energy E received by the solar cell, and the fill factor is the value obtained by dividing the above maximum output Pmax by the product of the open circuit voltage (Voc) and short circuit current (Isc). The values ​​obtained by the measurements are shown in Table 2. Conversion efficiency (%) = (Pmax / E) x 100 Fill factor (%)=Pmax / (Voc×Isc) [Table 2]

[0085] 3. Amount of Group III elements in InGaSe and InSe layers 3.1. Formation of light absorbing layer (Formation of light absorbing layers with different amounts of group III elements) In the case where the light absorbing layer is formed in the same manner as in Example 1, the ratio of In and Ga elements as shown in Table 3 is specified in order to examine the contents of In and Ga elements contained in the InGaSe layer and the InSe layer. In each row of Table 3, the ratio of Ga element to the total amount of substance of In and Ga elements in the InGaSe layer is specified. In each column, the ratio of the total amount of substance Y of In and Ga elements in the InGaSe layer to the amount of substance X of In element in the InSe layer (Y / X) is specified. As a result, the value of Ga / (In+Ga) in the entire light absorbing layer is as shown in Table 3. Among the conditions shown, light absorbing layers were fabricated under the conditions numbered (1) to (6). [Table 3]

[0086] 3.2.Evaluation of battery characteristics (Relative conversion efficiency) Solar cells were fabricated using light absorbing layers that satisfied the above conditions (1) to (7), and the conversion efficiency was measured. The conversion efficiency was measured in the same manner as in 2.2. above. The solar cells obtained under conditions (3) and (5) had the highest conversion efficiency, and the ratio of the conversion efficiency measured under each condition was calculated based on these. The results are shown in Table 4. [Table 4]

[0087] 4. Amount of Se in each layer 4.1. Formation of light absorbing layer In order to study the influence of the amount of Se element contained in the group I CuSe layer and the group III InGaSe layer and InSe layer, the ratio of the amount of Se element to the Cu element in the CuSe layer (Se / Cu) was set as shown in Tables 5 and 6. Furthermore, the ratio of the amount of Se element to the total amount of group III elements (In+Ga) in the InGaSe layer and InSe layer (Se / (In+Ga)) was set as shown in Tables 5 and 6. For each set ratio of the amount of S element, light absorption layers having seven different compositions were fabricated ((7) to (20)) in the case where a precursor was formed by laminating in the same manner as in Example 1 (Table 5) and the case where a precursor was formed by laminating in the same manner as in Example 2 (Table 6).

[0088] 4.2.Evaluation of Battery Characteristics (Conversion efficiency) Solar cells were fabricated using the light absorption layers of (7) to (20), and the conversion efficiency was measured. The results are shown in Tables 5 and 6. [Table 5] [Table 6]

[0089] 5. Evaluation of crystallinity of each layer In the same manner as in the formation of each layer in the precursor formation step of Example 1, an InGaSe layer, a CuSe layer, and an InSe layer were formed on a Ti metal substrate, and X-ray diffraction measurements were performed. The measurements were performed using an X-ray diffraction device manufactured by Malvern Panalytical, and were 2θ-θ measurements using Cu-Kα radiation. The results of the obtained diffraction measurements are shown in FIG. For the CuSe layer, the growth of the (111) and (220) planes was confirmed at angles of 27° and 45°, respectively. For the InGaSe and InSe layers, no significant peaks indicating crystallinity were confirmed.

[0090] 6. InSe layer formation temperature Except for changing the surface temperature of the substrate, an InSe layer was formed on a Ti metal substrate using the same formation method as the precursor formation step of the above-mentioned Example 1. The substrate surface temperature during formation was set to room temperature (RT), 200°C, 250°C, and 300°C, and film formation was performed four times. X-ray diffraction measurements were performed using the X-ray diffraction apparatus and measurement conditions described above. The results of the obtained diffraction measurements are shown in Figure 6. From the results shown in Figure 6, it was found that the higher the surface temperature of the substrate, the higher the crystallinity of the formed InSe layer. Furthermore, similar tests were performed on the InGaSe layer, and it was found that crystallization was more likely to proceed when the surface temperature was set higher than that of the InSe layer. [Explanation of symbols]

[0091] 10...solar cell, 101...grid electrode, 102...second electrode layer, 103...electron transport layer, 104...light absorbing layer, 105...hole transport layer, 106...first electrode layer, 107...substrate.

Claims

1. a precursor forming step of forming a precursor having an InGaSe layer, a CuSe layer, and an InSe layer; A crystallization step of obtaining a crystallized light absorbing layer by heating the precursor. How solar cells are manufactured.

2. In the precursor forming step, the InGaSe layer and the InSe layer are amorphous. The method for producing the solar cell according to claim 1 .

3. In the precursor formation step, each layer is formed by a sputtering method and / or a deposition method at 200° C. or less. The method for producing the solar cell according to claim 1 .

4. In the precursor formation step, the InSe layer is formed on a light receiving surface side of the InGaSe layer. The method for producing the solar cell according to claim 1 .

5. In the precursor formation step, the InSe layer is formed closest to the light-receiving surface. The method for producing the solar cell according to claim 1 .

6. In the precursor formation step, the InGaSe layer and the CuSe layer are each formed in two or more layers. The method for producing the solar cell according to claim 1 .

7. In the InGaSe layer, a ratio of the amount of Ga element to the total amount of In element and Ga element (Ga / (In+Ga)) is 0.3 or more and 0.6 or less. The method for producing the solar cell according to claim 1 .

8. a ratio of a total amount of substance Y (Y / X) of In and Ga elements in the InGaSe layer to an amount of substance X of In element in the InSe layer is 1.0 or more and 1.5 or less; The method for producing the solar cell according to claim 1 .

9. In the precursor, a ratio of the amount of Ga element to the total amount of In element and Ga element (Ga / (In+Ga)) is 0.15 or more and 0.40 or less, a ratio of the amount of Cu element to the total amount of In element and Ga element (Cu / (In+Ga)) is 0.75 or more and 0.95 or less; the ratio of the amount of Se element to the total amount of Cu element, In element, and Ga element (Se / (Cu+In+Ga)) is 1.0 or more; The method for producing the solar cell according to claim 1 .

10. In the InGaSe layer and the InSe layer, a ratio of the amount of Se element to the total amount of In element and Ga element (Se / (In+Ga)) is 1.25 or more and 1.75 or less. The method for producing the solar cell according to claim 1 .

11. When the CuSe layer is formed on the outermost layer of the precursor, in the CuSe layer, a ratio of the amount of substance of Se element to the amount of substance of Cu element (Se / Cu) is 2.0 or more and 3.0 or less. The method for producing the solar cell according to claim 1 .

12. When the CuSe layer is not formed on the outermost layer of the precursor, in the CuSe layer, a ratio of the amount of substance of Se element to the amount of substance of Cu element (Se / Cu) is 0.5 or more and 2.0 or less. The method for producing the solar cell according to claim 1 .

13. In the crystallization step, heating is performed under an inert atmosphere at 300° C. or higher and 600° C. or lower. The method for producing the solar cell according to claim 1 .

14. The crystallization step further includes a surface treatment step of treating a surface of the light absorbing layer in a sulfur atmosphere at 350° C. or higher and 600° C. or lower. The method for producing the solar cell according to claim 1 .

15. Produced by the method according to any one of claims 1 to 14, In the light absorbing layer, a band gap in a section from a light receiving surface side to a depth direction of 200 nm is 1.1 eV or more and 1.4 eV or less, a band gap in a section from 200 nm in a depth direction from the light receiving surface side to 400 nm in a depth direction is 0.9 eV or more and 1.2 eV or less; The band gap in a section from 400 nm in the depth direction from the light receiving surface side is 1.2 eV or more and 1.7 eV or less. Solar cell.

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