Method for manufacturing solar cell, and solar cell

Abstract

The present invention addresses the problem of providing a method for manufacturing a high-productivity solar cell with which high performance is achieved in a solar cell. The aforementioned problem can be solved by a method for manufacturing a solar cell, the method comprising: 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.

Description

Solar cell manufacturing method and solar cell

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

[0002] Solar cells include silicon solar cells manufactured using materials such as monocrystalline or polycrystalline silicon. While these solar cells have excellent durability, they are expensive to manufacture and thick, making them suitable for use in large-scale power generation facilities. Thin-film solar cells are also available, in which a thin film-like light-absorbing layer is formed on a substrate such as glass or metal. Thin-film solar cells are inexpensive to manufacture and are very thin, allowing them to be used in flexible configurations. 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 preparation for their application.

[0003] For example, in Patent Document 1, metal components such as Cu, In, and Ga are deposited by sputtering, and then H ２ Se and H ２ It is described that the manufacturing cost can be reduced by using a method of forming a light absorbing layer while heating in an atmosphere of S. Furthermore, in addition to the above method, Patent Document 2 describes that 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 equipment 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 a single element or as an alloy, were simultaneously sputtered, and then annealed to crystallize, but the power generation performance was insufficient. Therefore, in Patent Document 4, CuSe, which is a group I selenium, and InGaSe, which is a group III selenium, were stacked, and Se vapor or H ２ It is described that power generation performance can be improved by carrying out crystallization in an atmosphere of Se gas.

[0005] Japanese Patent Application Laid-Open No. 10-135495 Japanese Patent Application Laid-Open No. 2012-513127 International Publication No. 2011 / 052574 International Publication No. 2011 / 090959

[0006] In the methods described in Patent Documents 1 and 2, H ２Se and H ２ When reacting under heating in an S atmosphere, 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, Se vapor and H ２ Annealing in an atmosphere of Se gas requires equipment that takes environmental and safety into consideration, which increases costs. In addition, the crystal grains are small, and power generation performance is still insufficient.

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

[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 resulting solar cells have high performance.

[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.

[0011] Fig. 1 is a schematic cross-sectional view of a precursor of a light absorbing layer according to one embodiment of the present invention. Fig. 2 is a schematic cross-sectional view of a precursor of a light absorbing layer according to one embodiment of the present invention. Fig. 3 is a schematic cross-sectional view of a precursor of a light absorbing layer according to one embodiment of the present invention. Fig. 4 is a schematic cross-sectional view of a solar cell according to one embodiment of the present invention. Fig. 5 is a view showing X-ray diffraction patterns of each layer included in a light absorbing layer according to one embodiment of the present invention. Fig. 6 is a view showing changes in X-ray diffraction patterns depending on the formation temperature of an InSe layer according to one embodiment of the present invention.

[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. 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.

[0013] 1. Light-Absorbing Layer Forming Step In the light-absorbing layer forming step of the solar cell manufacturing method of the present embodiment, the method 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, a method for manufacturing a CIGS-type chalcopyrite solar cell containing Cu, In, Ga, and Se involves separately stacking Group I CuSe and Group III InGaSe, and then oxidizing the CuSe layer with Se vapor or H ２ A method for improving power generation performance by annealing and crystallizing in a Se gas atmosphere has been developed. However, the solar cells obtained by the above 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, the above method uses Se vapor or H ２ Since annealing must be performed in a Se gas atmosphere, facilities that take environmental and safety aspects into consideration are required, which raises concerns about the enormous cost involved.

[0015] Therefore, the inventors of the present application discovered that by separately stacking an InGaSe layer, a CuSe layer, and an InSe layer as precursors for the chalcopyrite light absorption layer and then heating and crystallizing the precursors, the crystal grains of the light absorption layer can be enlarged and the crystal quality can be improved, resulting in a high-performance solar cell. Furthermore, since a heating step in an atmosphere containing Se is not necessarily required, solar cells can be manufactured with high productivity. The reasons for the superiority of this method are not entirely clear, but it is believed that by separately forming an InGaSe layer, a CuSe layer, and an InSe layer and then crystallizing them, good seed crystals are preferentially formed at the interface between the CuSe layer and the InSe layer, thereby increasing the crystal grains and improving the crystal quality. It is also believed that the relaxation of crystal strain due to the elemental profile of Se elements in the film being favorably arranged during crystallization also contributed synergistically. However, the factors are not limited to those mentioned above.

[0016] In this specification, "a 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, "a 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 Step 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 these layers, the crystal grains of the resulting light absorption layer are increased, improving the crystal quality and power generation performance.

[0018] A schematic cross-sectional view of one example of a precursor of the light absorption 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, which increases the crystal grains in the resulting light absorption layer and improves the crystal quality, tending to further improve power generation performance. In this specification, "being amorphous" is determined by the absence of peaks that exceed a region that is twice the noise width above and below the baseline in the 2θ-θ pattern of X-ray diffraction measurement.

[0020] The method for forming each layer is not particularly limited, and from the viewpoint of mass productivity and reliability, it is preferable to form them by sputtering and / or vapor deposition, or sputtering alone may be used. 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 InSe layer tend to become amorphous layers, and the resulting solar cell tends to have higher performance and higher productivity. In this specification, the sputtered substrate refers to the substrate on the stage during sputtering, on which the compound derived from the sputtering target is deposited.

[0021] The target used for sputtering is not particularly limited. For example, in the case of forming an InGaSe layer, In, In ４ Se ３ , InSe, In ２ Se ３ , GaSe, Ga ２ Se ３ , Se alone or in mixture, Cu, Cu in the case of a CuSe layer ２ Se, CuSe ２ , Se alone or in admixture, In in the case of an InSe layer, In ４ Se ３ , InSe, In ２ Se ３In the case of an InGaSe layer, In is preferably used alone or in combination with Se. ２ Se ３ , Ga ２ Se ３ and Ga ２ Se ３ In the case of a CuSe layer, CuSe is used. ２ In the case of a single layer, InSe layer ２ Se ３ The gas supplied during sputtering may be an inert gas such as Ar or He, or may be, for example, H ２ or H ２ Se, H ２ Among these, from the viewpoint of more reliably achieving the effects of the present invention, Ar is preferred as the inert gas, and other gases include H ２ is preferred.

[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 forming the InSe layer closer to the light-receiving surface than the InGaSe layer tends to further improve the power generation performance of the resulting solar cell.

[0023] In the precursor formation step, it is preferable to form the InSe layer closest to the light-receiving surface. Forming the InSe layer closest to the light-receiving surface tends to further improve the power generation performance of the resulting solar cell. From the same perspective, 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 a precursor for 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 be formed closer to the light-receiving surface 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 be formed closest to the light-receiving surface.

[0025] In the precursor formation step, preferably, two or more InGaSe layers and two or more CuSe layers are formed, and two or more InGaSe layers and two or more CuSe layers are formed, which tends to further improve the power generation performance of the obtained solar cell.

[0026] Fig. 3 shows a schematic cross-sectional view of another example of a precursor for the light absorption 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.

[0027] In the entire precursor to be formed, the ratio of the amount of substance of Ga element to the total amount of substance of In element and Ga element (Ga / (In+Ga)) is preferably 0.10 or more and 0.50 or less, 0.15 or more and 0.40 or less, or 0.20 or more and 0.40 or less. By setting the amount of substance ratio of (Ga / (In+Ga)) in the entire precursor within the above ranges, the power generation performance of the obtained solar cell tends to be further improved. Furthermore, 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 or more and 1.0 or less, 0.75 or more and 0.95 or less, or 0.80 or more and 0.90 or less. By setting the amount of substance ratio of (Cu / (In+Ga)) in the entire precursor within the above ranges, 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. Furthermore, 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, 0.3 to 0.6, or 0.4 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 total amount of substance Y (Y / X) of In and Ga elements in the InGaSe layer to the amount of substance X of In element in the InSe layer is preferably 0.5 to 2.5, 0.6 to 2.3, 0.8 to 2.0, or 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, 0.9 to 1.9, or 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 to 2.0, or 1.25 to 1.75. When a 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 to 2.0, or 1.0 to 1.5. When the (Se / (In+Ga)) value in the InGaSe layer and the InSe layer is set 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) molar ratio in the CuSe layer is preferably 0.5 to 4.0, or 0.5 to 3.0. When the CuSe layer is formed on the outermost layer of the precursor, the ratio of the amount of Se to the amount of Cu in the CuSe layer (Se / Cu) is preferably 1.5 to 5.0, or 1.5 to 4.0, or 2.0 to 3.0, or 2.2 to 2.7. When the CuSe layer is not formed on the outermost layer of the precursor, the ratio of the amount of Se to the amount of Cu in the CuSe layer (Se / Cu) is preferably 0.3 to 2.5, or 0.4 to 2.2, or 0.5 to 2.0. 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 step, examples of a method 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 vapor deposition, and a method for controlling the film formation pressure or applied power.

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

[0035] The crystallization step of the present embodiment is a step of obtaining a light-absorbing layer by heating the 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 higher and 600° C. or lower, 320° C. or higher and 600° C. or lower, 350° C. or higher and 600° C. or lower, or 400° C. or higher and 600° C. By setting the heating temperature within the above range, the crystal grains in the light absorption layer increase, improving the crystal quality, and the power generation performance of the obtained solar cell tends to be further improved.

[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 the crystallization in an inert atmosphere, the power generation performance of the solar cell can be further improved. Examples of the inert gas include nitrogen (N ２ ), argon (Ar), and preferably nitrogen.

[0038] 1.3. Surface Treatment Step The method for manufacturing a solar cell according to the present embodiment preferably further includes, 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 performing 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 performing 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 Cell The solar cell of this embodiment includes the light absorbing layer 104 manufactured by the above-described method, and has the configuration described below. A solar cell including the light absorbing layer 104 manufactured by the above-described manufacturing method has excellent conversion efficiency and high performance, and also has excellent productivity because the manufacturing process can be simplified.

[0042] An example of the cross-sectional structure of a solar cell of this embodiment is shown in Figure 4. As shown in Figure 4, the solar cell 10 includes, for example, 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 and generates 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 examples thereof include glass substrates such as soda lime glass and low-alkali glass, metal substrates such as stainless steel foil, aluminum foil, and titanium foil, and resin substrates such as polyimide resin film and epoxy resin film. The thickness of the substrate 107 is not particularly limited, and is, for example, 10 μm to 500 μm, 20 μm to 250 μm, or 30 μm to 100 μm. A thickness of the substrate 107 within the above range is preferable in that it allows for lighter and more flexible solar cells.

[0045] 2.2. First Electrode Layer The first electrode layer 106 is generally provided to extract current due to holes generated in the light absorption layer 104 described below. The first electrode layer 106 is not particularly limited as long as it is conductive. For example, a metal conductive layer made of a metal such as Mo, Cr, or Ti; a conductive inorganic compound conductive layer made of a conductive inorganic compound other than a metal; or a conductive organic compound conductive layer made of a conductive organic compound can be used. The thickness of the first electrode layer 106 is not particularly limited and is, for example, 200 nm to 800 nm, or 300 nm to 700 nm. A thickness of the first electrode layer 106 within the above range is preferable in that it allows sufficient current to be extracted without loss while enabling the solar cell to be lightweight and flexible.

[0046] 2.3 Hole Transport Layer The hole transport layer 105 has a function of, for example, efficiently extracting holes generated in the light absorption layer 104 (described later) from the light absorption layer 104 and preventing recombination of electrons and holes generated simultaneously with the electron-hole absorbing step in the light absorption layer 104 (described later). 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 organic compounds such as polythiophene derivatives such as poly(3,4-ethylene-dioxythiophene):polystyrene sulfonate (PEDOT:PSS), poly(3-hexylthiophene) (P3HT), and poly(3-octylthiophene) (P3OT); fluorene derivatives such as 2,2'-7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-MeO-TAD); carbazole derivatives such as polyvinylcarbazole; triphenylamine derivatives; diphenylamine derivatives; polysilane derivatives; and polyaniline derivatives; as well as inorganic compounds such as nickel oxide, molybdenum oxide, gallium copper oxide, aluminum copper oxide, molybdenum selenide, and molybdenum sulfide selenide. The p-type semiconductor in the hole transport layer 105 may be used alone or in combination of two or more types. In the solar cell, the formation of the hole transport layer 105 may be omitted.

[0047] 2.4. Light Absorption Layer 2.4.1. Light Absorption Layer of the Present Embodiment The light absorption layer 104 has the function of absorbing light such as near-infrared light, visible light, and ultraviolet light to generate electrons and holes. Examples of such light include sunlight. The light absorption layer 104 in the solar cell of the present embodiment contains CIGS-type chalcopyrite obtained by the precursor formation step and crystallization step described above. Note that if the obtained light absorption layer 104 is additionally subjected to the surface treatment step described above, it will further contain a sulfur component, and therefore can also be said to be a light absorption layer 104 containing 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 exhibits high performance.

[0049] The band gap can be measured by a known method, such as spectral transmittance measurement or spectral quantum efficiency measurement.

[0050] In the light absorbing layer 104 of this embodiment, the band gap in the section from the light-receiving surface side to a depth of 200 nm is preferably 1.1 eV or more and 1.4 eV or less, the band gap in the section from 200 nm to 400 nm in the depth direction is preferably 0.9 eV or more and 1.2 eV or less, and the band gap from 400 nm in the depth direction onward is preferably 1.2 eV or more and 1.7 eV or less. 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 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 light absorbing layer 104 within the above range, 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 of this embodiment is not particularly limited, and is, for example, 50% by mass or more and 100% by mass or less, 60% by mass or more and 100% by mass or less, 70% by mass or more and 100% by mass or less, 80% by mass or more and 100% by mass or less, or 90% by mass or more and 100% by mass or less, relative to the total mass of the light absorbing layer 104.

[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 formed by further providing a hole-transporting layer on the second electrode layer 102 of a solar cell that already has a light-absorbing layer, thereby providing an additional light-absorbing layer. In cases where no additional hole-transporting layer is provided, the solar cell may have an additional light-absorbing layer on the second electrode layer 102. Examples of compounds that can form the additional light-absorbing layer include compounds containing perovskite compounds, chalcopyrite compounds, and kesterite compounds. Each compound may be used alone, or two or more types 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. 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 NH ３ Pb （１－ｙ） Snｙ 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.

[0055] As the chalcopyrite compound, those different from the CIGS type chalcopyrite compound obtained by the production method of the present invention include, for example, CuAlS ２ , CuAlSe ２ , CuAlTe ２ , CuGaS ２ , CuGaSe ２ , CuGaTe ２ , CuInS ２ , CuInSe ２ , CuInTe ２ , AgAlS ２ , AgAlSe ２ , AgAlTe ２ , AgGaS ２ , AgGaSe ２ , AgGaTe ２ , AgInS ２, AgInSe ２ , AgInTe ２ and combinations thereof. The term "combinations thereof" is not particularly limited, and 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).

[0056] Examples of kesterite compounds include I ２ -II-IV-VI ４ Group kesterite compounds, more specifically Cu ２ ZnSnS ４ , Cu ２ ZnSnSe ４ , Cu ２ ZnGeS ４ , Cu ２ ZnGeSe ４ , Cu ２ MnSnS ４ , Cu ２ MnSnSe ４ , Cu ２ MnGeS ４ , Cu ２ MnGeSe ４ , Ag ２ ZnSnS ４ , Ag ２ ZnSnSe ４ , Ag ２ ZnGeS ４ , Ag ２ ZnGeSe ４ , Ag ２ MnSnS ４ , Ag ２ MnSnSe ４ , Ag ２ MnGeS ４ , Ag ２ MnGeSe ４ and combinations thereof. The "combinations thereof" are not particularly limited, and examples thereof include Cu ２ ZnSnS ４ and Ag ２ ZnSnSe ４When combined with (Cu ｘ Ag １－ｘ ) ２ ZnSn(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 absorption layer 104 from the light absorption layer 104 and preventing recombination of electrons and holes generated simultaneously in the light absorption 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 Examples of n-type semiconductors include organic compounds such as 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), n-type oxide semiconductors consisting essentially of zinc oxide, tin oxide, titanium oxide, zinc sulfide oxide, magnesium zinc oxide, zinc tin oxide, or zinc titanium oxide, and n-type semiconductors containing cadmium sulfide, indium sulfide, or indium sulfide doped with oxygen or an alkali metal element. The n-type semiconductors in the electron transport layer 103 may be used singly or in combination of two or more. 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 lighter and more flexible while retaining the above functions.

[0058] 2.6. Second Electrode Layer The second electrode layer 102 is provided, for example, to extract current due to electrons generated in the light absorbing layer 104. In solar cells, the light absorbing layer 104 typically absorbs light that passes through the second electrode layer 102. Therefore, it is preferable to form the second electrode layer 102 as a transparent electrode layer to increase the amount of light absorbed by the light absorbing layer 104. Known materials can be used for the transparent electrode, such as 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 to 1500 nm, or 200 nm to 1000 nm. Setting the thickness of the second electrode layer 102 within the above range is preferable because it allows sufficient current to be extracted without loss while also enabling the solar cell to be lightweight and flexible.

[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 materials that can be used include metals such as Mo, Cr, Ag, Cu, Ni, Al, and Ti; conductive inorganic compounds other than metals; and conductive organic compounds. The thickness of the grid electrode 101 is not particularly limited, and is, for example, 5 μm to 50 μm. Setting the thickness of the grid electrode 101 within the above range is preferable because it allows for lighter and more flexible solar cells.

[0060] 2.8. Modifications 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 needed. Specifically, the hole transport layer 105 may have two or more hole transport layers each containing a different material, and an anti-contamination layer for preventing external contamination may be provided on the grid electrode 101. Alternatively, the second electrode layer 102 may have another hole transport layer instead of the grid electrode 101, and an additional light absorbing layer may be provided thereon. 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. A grid electrode may also be provided on the uppermost second electrode layer.

[0063] When there are a plurality of layers 101 to 107, the plurality of layers may be the same or different. For example, when there are a plurality of light-absorbing layers 104, each light-absorbing layer may contain a compound with a different absorption spectrum, and the electron transport layer and hole transport layer in contact with each light-absorbing layer may be selected according to the properties of the light-absorbing layer in contact with the layer. However, at least one of the light-absorbing layers is the light-absorbing layer 104 obtained by the above-described manufacturing method.

[0064] Like conventional solar cells, the solar cell of this embodiment can be used in normal temperature environments where the temperature of the solar cell is about 45 to 85° C. 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. 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, 1.0 μm to 10.0 μm, 1.1 μm to 8.0 μm, or 1.2 μm to 6.0 μm. The solar cell of the present invention can be a thin-film solar cell by forming each layer to be sufficiently thin.

[0067] 3. Method for Manufacturing Solar Cell 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 Step First, for example, the first electrode layer 106 is formed on the substrate 107. Methods for forming the first electrode layer 106 include dry processes and wet processes, with the dry process being preferred. The dry process is not particularly limited, and an example 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, the substrate 107 may be the sputtered substrate, for example. 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 deposited.

[0069] 3.2. Hole Transport Layer Formation Step Next, for example, the 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 the 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 an example thereof is an applied power of 0.5 to 3.0 W / cm. ２ The film formation atmosphere may be an argon atmosphere or a mixed atmosphere of argon and oxygen, and the film formation pressure may be 0.5 to 3.0 Pa. When forming the light absorbing layer 104, a compound may be formed between the elements of the first electrode layer 106 and the elements contained in 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 Forming Step Next, the light-absorbing layer 104 is formed on the hole-transporting 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 Step 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 depositing an n-type oxide semiconductor by sputtering while supplying a gas containing an oxygen source and a hydrogen source, or the n-type oxide semiconductor may be deposited by sputtering while supplying a gas not containing a hydrogen source. The deposition conditions for the sputtering method are not particularly limited, and examples thereof include applied power of 0.5 to 3.0 W / cm. ２ The film formation atmosphere may be an argon atmosphere which 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 Step Next, the second electrode layer 102 is formed on the electron transport layer 103. Methods for forming the second electrode layer 102 include dry processes and wet processes, with the dry process being preferred. The dry process is not particularly limited, and an example 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 is an applied power of 0.5 to 3.0 W / cm. ２ The film formation atmosphere may be an argon atmosphere or a mixed atmosphere of argon, oxygen, and hydrogen. The film formation pressure may be 0.5 to 3.0 Pa.

[0073] 3.6 Grid Electrode Formation Step 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. Specific examples include sputtering, vapor deposition, a method of printing a paste-like conductive material on the second electrode layer 102, and a method of crimping a conductive wire.

[0074] Note that, after forming the light absorbing layer 104, an additional light absorbing layer forming step may be performed before forming the grid electrode. For example, such an additional light absorbing layer forming step may involve forming a hole transport layer on the second electrode layer 102 and then forming the additional light absorbing layer. If no hole transport layer is present, the additional light absorbing layer may be formed on the second electrode layer. Methods for forming the additional light absorbing layer include dry processes and wet processes, with dry processes being preferred. The dry process is not particularly limited, and examples include a method of forming an additional light absorbing layer containing a perovskite compound, a chalcopyrite compound, or a kesterite compound by sputtering. The film formation conditions for the sputtering method are not particularly limited, and examples include applied power of 0.5 to 3.0 W / cm. ２The film formation atmosphere may be an argon atmosphere, and the film formation 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. or higher and 200° C. or lower. Alternatively, after sputtering, the method may include a step of annealing in a nitrogen or selenium and sulfur atmosphere at 350° C. or higher and 650° C. or lower.

[0075] <Supplementary Notes> Embodiments of the present disclosure include the following aspects. [1] A method for manufacturing a solar cell, comprising: 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 obtain a crystallized light-absorbing layer. [2] The method for manufacturing a solar cell according to [1], wherein the InGaSe layer and the InSe layer are amorphous in the precursor formation step. [3] The method for manufacturing a solar cell according to [1] or [2], wherein each layer is formed at 200°C or less by sputtering and / or vapor deposition in the precursor formation step. [4] The method for manufacturing a solar cell according to any one of [1] to [3], wherein the InSe layer is formed closer to the light-receiving surface than the InGaSe layer in the precursor formation step. [5] The method for manufacturing a solar cell according to any one of [1] to [4], wherein the InSe layer is formed closest to the light-receiving surface in the precursor formation step. [6] The method for manufacturing a solar cell according to any one of [1] to [5], wherein the precursor forming step forms two or more InGaSe layers and two or more CuSe layers. [7] The method for manufacturing a solar cell according to any one of [1] to [6], wherein in the InGaSe layer, a ratio of the amount of substance of Ga elements to the total amount of substance of In elements and Ga elements (Ga / (In+Ga)) is 0.3 or more and 0.6 or less. [8] The method for manufacturing a solar cell according to any one of [1] to [7], wherein a ratio of the amount of substance X of In elements in the InSe layer to the total amount of substance Y of In elements and Ga elements in the InGaSe layer (Y / X) is 0.5 or more and 2.5 or less. [9] The method for manufacturing a solar cell according to any one of [1] to [8], wherein in the precursor, a value of a ratio of the amount of substance of Ga element to the total amount of substance of In element and Ga element (Ga / (In+Ga)) is 0.15 or more and 0.40 or less, a value of a 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 0.75 or more and 0.95 or less, and a value of a 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 1.0 or more.

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

[11] The method for manufacturing a solar cell according to any one of [1] to

[10] , wherein, when the CuSe layer is formed on the outermost layer of the precursor, 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.

[12] The method for manufacturing a solar cell according to any one of [1] to

[11] , wherein, when the CuSe layer is not formed on the outermost layer of the precursor, 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.

[13] The method for manufacturing a solar cell according to any one of [1] to

[12] , wherein the crystallization step involves heating in an inert atmosphere at 300° C. or higher and 600° C. or lower.

[14] The method for manufacturing a solar cell according to any one of [1] to

[13] , further comprising, after the crystallization step, a surface treatment step of treating the surface of the light absorbing layer in a sulfur atmosphere at 350° C. or higher and 600° C. or lower.

[15] A solar cell manufactured by the method according to any one of [1] to

[14] , wherein in the light absorbing layer, a band gap in a section from the light-receiving surface side to 200 nm in the depth direction is 1.1 eV or higher and 1.4 eV or lower, a band gap in a section from 200 nm in the depth direction from the light-receiving surface side to 400 nm in the depth direction from the light-receiving surface side is 0.9 eV or higher and 1.2 eV or lower, and a band gap in a section beyond 400 nm in the depth direction from the light-receiving surface side is 1.2 eV or higher and 1.7 eV or lower.

[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] <Method of Manufacturing Solar Cell> A solar cell having a single electron transport layer, as shown in FIG. 4, was fabricated. A 50 μm-thick titanium foil was used as the substrate. A 600 nm-thick first electrode layer containing metallic molybdenum was formed on this substrate using a sputtering method. The light-absorbing layer of this embodiment was then formed thereon under the conditions described below. When the crystals of the light-absorbing layer were formed, a 50 nm-thick MoSe layer, serving as a hole transport layer, was also formed between the light-absorbing layer and the first electrode layer. Furthermore, the resulting light-absorbing layer was subjected to surface treatment by annealing in a sulfur atmosphere at 500° C. to 600° C. for 3 minutes to 30 minutes.

[0078] Next, an n-type electron transport layer containing titanium zinc oxide doped with hydrogen and sulfur 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 formed on the n-type electron transport layer to a thickness of 300 nm, and a silver grid electrode with a width of 50 μm was 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 above except for the light absorbing layer.

[0080] 1. Introduction of InSe Layer 1.1. Formation of Light-Absorbing Layer (Example 1) Example 1 employed a precursor structure as shown in FIG. 1 . 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 in that order until the thicknesses reached 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. After the crystallization process, a surface treatment was performed on the surface of the light-absorbing layer in a sulfur atmosphere at 500°C to 600°C, thereby obtaining a light-absorbing layer. <Sputtering Film Formation Conditions> Applied power: 0.5 to 3.0 W / cm ２ Film formation atmosphere: argon Pressure during film formation: 0.2 Pa to 3.0 Pa Substrate temperature: room temperature Target species: InGaSe layer is In ２ Se ３ , Ga２ Se ３ and Ga ２ Se ３ The ratio of CuSe is 30% or more and 60% or less, and the CuSe layer is CuSe ２ The InSe layer is In ２ Se ３ Single unit

[0081] Comparative Example 1 In Comparative Example 1, sputtering was performed in the same manner as in the non-patent document (Zhu, XL, & Wang, LK (2014), 13.6%-efficient Cu(In,Ga)Se2 solar cell with absorber fabricated by RF sputtering of (In,Ga)2Se3 and CuSe targets, Solar Energy Materials and Solar Cells, 124, 21-25.), and a precursor was prepared by sequentially forming an InGaSe layer and a CuSe layer to thicknesses of 1700 nm and 400 nm, respectively. This precursor was crystallized by heating in a nitrogen atmosphere at 400°C or higher and 600°C or lower. After the crystallization step, the surface of the light-absorbing layer was further treated in a sulfur atmosphere at 500°C or higher and 600°C or lower, 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 absorption 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, higher PL intensity indicates higher crystal quality, and it is suggested that the light absorption layer of Example 1 has dramatically improved crystal quality.

[0083] 2. Aspects of Precursor 2.1. Formation of Light Absorption Layer (Examples 2 and 3) Examples 2 and 3 employed precursor structures shown in Figures 2 and 3, respectively. In Examples 2 and 3, the same sputtering conditions as in Example 1 were used, but the order of deposition 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 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 deposited to the same thickness. The precursor of each example was crystallized by heating at 400°C or higher and 600°C or lower in a nitrogen atmosphere, and after the crystallization step, a surface treatment was performed to treat the surface of the light absorbing layer in a sulfur atmosphere at 500°C or higher and 600°C or lower, thereby obtaining a light absorbing layer.

[0084] 2.2. Evaluation of Cell Characteristics (Conversion Efficiency) A solar cell was fabricated as described above, and the IV curve was measured under standard test conditions (light with a spectral spectrum of AM1.5 at an irradiance of 1 kW / m ２ The measurements were taken under test conditions where light was incident at 1000kJ / s and the solar cell temperature was 25°C. 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 in the I-V curve by the light energy E received by the solar cell, and the fill factor is the value obtained by dividing the maximum output Pmax by the product of the open circuit voltage (Voc) and the 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 x Isc)

[0085] 3. Amount of Group III Elements in InGaSe Layer and InSe Layer 3.1. Formation of Light-Absorbing Layer (Formation of Light-Absorbing Layer with Different Amounts of Group III Elements) When forming a light-absorbing layer in the same manner as in Example 1 above, the ratios of In and Ga elements were specified as shown in Table 3 to examine the contents of In and Ga elements contained in the InGaSe layer and InSe layer. Each row of Table 3 specifies the ratio of Ga element to the total amount of In and Ga element in the InGaSe layer. Each column specifies the ratio of the total amount of In and Ga element in the InGaSe layer, Y (Y / X), to the amount of In element in the InSe layer, X. As a result, the Ga / (In+Ga) value for the entire light-absorbing layer is as shown in Table 3. Light-absorbing layers were fabricated under the conditions numbered (1) to (6) among the conditions shown.

[0086] 3.2. Evaluation of Cell Characteristics (Relative Ratio of 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 using the same method 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 efficiencies measured under each condition was calculated based on these. The results are shown in Table 4.

[0087] 4. Amount of Se in Each Layer 4.1. Formation of Light-Absorbing Layer To investigate the effect of the amount of Se contained in a group I CuSe layer and a group III InGaSe layer and InSe layer, the ratio of the amount of Se to Cu in the CuSe layer (Se / Cu) was set as shown in Tables 5 and 6. Furthermore, the ratio of the amount of Se 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, light-absorbing layers with seven different compositions were fabricated (Table 5), where precursors were formed by laminating layers in the same manner as in Example 1, and where precursors were formed by laminating layers in the same manner as in Example 2 (Table 6) ((7) to (20)).

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

[0089] 5. Evaluation of Crystallinity of Each Layer In the same manner as in the precursor formation process of Example 1, an InGaSe layer, a CuSe layer, and an InSe layer were each formed on a Ti metal substrate, and X-ray diffraction measurements were performed. Measurements were performed using a Malvern Panalytical X-ray diffractometer and 2θ-θ measurements using Cu-Kα radiation. The diffraction measurement results are shown in Figure 5. For the CuSe layer, growth of the (111) and (220) planes was confirmed near 27° and 45°. Furthermore, no significant peaks indicating crystallinity were confirmed for the InGaSe and InSe layers.

[0090] 6. InSe Layer Formation Temperature An InSe layer was formed on a Ti metal substrate using the same formation method as the precursor formation process of Example 1, except that the substrate surface temperature was changed. Film formation was performed four times, with the substrate surface temperature set to room temperature (RT), 200°C, 250°C, and 300°C. X-ray diffraction measurements were performed using the X-ray diffraction apparatus and measurement conditions described above. The obtained diffraction measurement results are shown in FIG. 6. The results shown in FIG. 6 indicate that the higher the substrate surface temperature, the higher the crystallinity of the formed InSe layer. Furthermore, similar tests were performed on an InGaSe layer, and it was found that crystallization was more likely to proceed when a surface temperature higher than that of the InSe layer was set.

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

Claims

1. A method for manufacturing a solar cell, comprising: a precursor formation step of forming a precursor having an InGaSe layer, a CuSe layer, and an InSe layer; and a crystallization step of obtaining a light absorbing layer by crystallizing the precursor by heating.

2. The method for producing a solar cell according to claim 1, wherein in the precursor formation step, the InGaSe layer and the InSe layer are amorphous.

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

4. The method for manufacturing a solar cell according to claim 1, wherein in the precursor formation step, the InSe layer is formed closer to the light-receiving surface than the InGaSe layer.

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

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

7. The method for manufacturing a solar cell according to claim 1, wherein 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.

8. The method for manufacturing a solar cell according to claim 1, wherein a ratio of a total amount of In and Ga elements Y (Y / X) in said InGaSe layer to an amount of In element X in said InSe layer is 0.5 or more and 2.5 or less.

9. A method for manufacturing a solar cell as described in claim 1, wherein in the precursor, a ratio of the amount of substance of Ga element to the total amount of substance 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 substance of Cu element to the total amount of substance of In element and Ga element (Cu / (In+Ga)) is 0.75 or more and 0.95 or less, and a 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 1.0 or more.

10. The method for manufacturing a solar cell according to claim 1, wherein 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.

11. The method for manufacturing a solar cell described in claim 1, wherein, when the 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 2.0 or more and 3.0 or less.

12. The method for manufacturing a solar cell described in claim 1, wherein, 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 0.5 or more and 2.0 or less.

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

14. The method for producing a solar cell according to claim 1, further comprising 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 after the crystallization step.

15. A solar cell manufactured by the method according to any one of claims 1 to 14, wherein in the light absorption layer, the band gap in the section from the light receiving surface side to a depth of 200 nm 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 to 400 nm in the depth direction from the light receiving surface side is 0.9 eV or more and 1.2 eV or less, and the band gap in the section beyond 400 nm in the depth direction from the light receiving surface side is 1.2 eV or more and 1.7 eV or less.

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