JP7494347B2 - How solar cells are manufactured - Google Patents

Description

The present invention relates to a method for manufacturing solar cells, multi-junction solar cells, solar cell modules, and photovoltaic power generation systems.

One of the new solar cells is a solar cell that uses cuprous oxide (Cu ₂ O) in the light absorption layer. Cu ₂ O is a wide-gap semiconductor. Cu ₂ O is a safe and inexpensive material made of copper and oxygen, which are abundant on Earth, so it is expected to realize highly efficient and low-cost solar cells.

JP 2017-54917 A

The problem that this invention aims to solve is to provide a method for manufacturing solar cells with excellent open-circuit voltage, a multi-junction solar cell, a solar cell module, and a solar power generation system.

The solar cell of the embodiment includes a step of forming a p-electrode on a substrate, a step of forming a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide on the p-electrode, and a step of oxidizing the film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide. In the oxidation treatment, the oxygen partial pressure is 100 [Pa] or more and less than 5000 [Pa], the treatment temperature is 125°C or more and 250°C or less, and the treatment time is 1 second or more and 90 minutes or less. The composite oxide of cuprous oxide and/or cuprous oxide is polycrystalline. In a region 5 nm deep from the surface of the oxidized film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide, the ratio of CuO and Cu(OH) ₂ calculated from the peak area of X-ray photoelectron spectroscopy is 0.1 [%] or more and less than 10 [%].

FIG. 1 is a cross-sectional view of a solar cell according to an embodiment. FIG. 2 is a diagram for explaining analysis spots of a solar cell according to an embodiment. FIG. 3 is a flowchart of a method for manufacturing a solar cell according to an embodiment. FIG. 4 is a cross-sectional view of a multi-junction solar cell according to an embodiment. FIG. 5 is a perspective view of a solar cell module according to an embodiment. FIG. 6 is a cross-sectional view of a solar cell module according to an embodiment. FIG. 7 is a configuration diagram of a solar power generation system according to an embodiment. FIG. 8 is a conceptual diagram of a vehicle according to an embodiment. FIG. 9 is a conceptual diagram of a flying object according to an embodiment. FIG. 10 is a table relating to an embodiment. FIG. 11 is a table relating to an embodiment. FIG. 12 is a table relating to an embodiment. FIG. 13 is a table relating to an embodiment. FIG. 14 is a table relating to an embodiment. FIG. 15 is a table relating to an embodiment. FIG. 16 is a table relating to an embodiment. FIG. 17 is a table relating to an embodiment.

A preferred embodiment of the present invention will be described in detail below with reference to the drawings. Unless otherwise specified, values are shown at 25°C and 1 atmospheric pressure (atmosphere). Also, the average represents the arithmetic mean value.

In the specification, "/" represents a division symbol. However, the "/" in "or/and" means "or."

First Embodiment
The first embodiment relates to a solar cell and a method for manufacturing the solar cell. FIG. 1 shows a cross-sectional view of a solar cell 100 of the first embodiment. As shown in FIG. 1, the solar cell 100 according to this embodiment has a substrate 1, a p-electrode 2 as a first electrode, a p-type light absorbing layer 3, an n-type layer 4, and an n-electrode 5 as a second electrode. An intermediate layer (not shown) may be included between the n-type layer 4 and the n-electrode 5. Sunlight may be incident from either the n-electrode 5 side or the p-electrode 2 side, but it is more preferable that it is incident from the n-electrode 5 side. The solar cell 100 of the embodiment is a transparent solar cell, so it is preferable to use it as a top cell (light incident side) of a multi-junction solar cell. In FIG. 1, the substrate 1 is provided on the opposite side of the p-electrode 2 from the p-type light absorbing layer 3 side, but the substrate 1 may be provided on the opposite side of the n-electrode 5 from the n-type layer 4 side. The embodiment shown in FIG. 1 will be described below, but the embodiment in which the substrate 1 is provided on the n-electrode 5 side is the same except that the position of the substrate 1 is different. In the solar cell 100 of the embodiment, light is incident from the n-electrode 5 side toward the p-electrode 2 side.

In the embodiment, a solar cell having a light transmittance of 50% to 100% for light having a wavelength of 700 nm to 1000 nm and using cuprous oxide or/and a composite oxide of cuprous oxide in the p-type light absorbing layer 3 is considered to be a transparent solar cell.

When performing the oxidation treatment of the embodiment, it is preferable that the substrate 1 is provided on the p-electrode 2 side.

The substrate 1 is a transparent substrate. For the substrate 1, organic substrates such as light-transmitting acrylic, polyimide, polycarbonate, polyethylene terephthalate (PET), polypropylene (PP), fluorine-based resins (polytetrafluoroethylene (PTFE), perfluoroethylene propene copolymer (FEP), ethylene tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), perfluoroalkoxyalkane (PFA), etc.), polyarylate, polysulfone, polyethersulfone, polyetherimide, etc., or inorganic substrates such as soda-lime glass, white plate glass, chemically strengthened glass, and quartz can be used. The substrate 1 may be a laminate of the substrates listed above.

The substrate 1 is preferably one selected from the group consisting of soda lime glass, white plate glass, chemically strengthened glass, and quartz.

The p-electrode 2 is provided on the substrate 1 and is disposed between the substrate 1 and the p-type light absorbing layer 3. The p-electrode 2 is a conductive layer having optical transparency provided on the p-type light absorbing layer 3 side. The thickness of the p-electrode 2 is typically 100 nm or more and 2,000 nm or less. In FIG. 1, the p-electrode 2 is in direct contact with the p-type light absorbing layer 3. The p-electrode 2 preferably includes one or more layers of an oxide transparent conductive film. Examples of the oxide transparent conductive film include, but are not limited to, indium tin oxide (ITO), aluminum-doped zinc oxide (AZO), boron-doped zinc oxide (BZO), gallium-doped zinc oxide (GZO), doped tin oxide, titanium-doped indium oxide (ITiO), indium zinc oxide (IZO), indium gallium zinc oxide (IGZO), and hydrogen-doped indium oxide (IOH). The oxide transparent conductive film may be a laminated film having a plurality of films. The dopant for the tin oxide film is not particularly limited as long as it is one or more selected from the group consisting of In, Si, Ge, Ti, Cu, Sb, Nb, Ta, W, Mo, F, Cl, etc. The p-electrode 2 preferably includes a tin oxide film doped with one or more elements selected from the group consisting of In, Si, Ge, Ti, Cu, Sb, Nb, Ta, W, Mo, F, Cl, etc. In the doped tin oxide film, it is preferable that one or more elements selected from the group consisting of In, Si, Ge, Ti, Cu, Sb, Nb, Ta, W, Mo, F, Cl, etc. are contained in an amount of 10 atomic % or less with respect to the tin contained in the tin oxide film. A laminated film in which an oxide transparent conductive film and a metal film are laminated can be used as the p-electrode 2. The thickness of the metal film is preferably 10 nm or less, and the metal (including alloy) contained in the metal film is not particularly limited to Mo, Au, Cu, Ag, Al, Ta, W, etc. In addition, the p-electrode 2 preferably includes a dot-shaped, line-shaped or mesh-shaped electrode (one or more selected from the group consisting of metals, alloys, graphene, conductive nitrides and conductive oxides) between the oxide transparent conductive film and the substrate 1, or between the oxide transparent conductive film and the p-type light absorbing layer 3. The dot-shaped, line-shaped or mesh-shaped metal preferably has an aperture ratio of 50% or more with respect to the transparent conductive film. The dot-shaped, line-shaped or mesh-shaped metal is not particularly limited to Mo, Au, Cu, Ag, Al, Ta, W, etc. When a metal film is used for the p-electrode 2, it is preferable to set the film thickness to about 5 nm or less from the viewpoint of transparency. When a line-shaped or mesh-shaped metal film is used, transparency is ensured by the openings, so there is no restriction on the film thickness of the metal film.

The p-electrode 2 preferably includes one or more oxide transparent conductive films selected from the group consisting of oxides containing Zn, In, and Sn. The oxide transparent conductive film of the p-electrode 2 is preferably in direct contact with the crystal grains of the cuprous oxide and/or composite oxide of cuprous oxide of the p-type light absorbing layer 3. It is preferable that 80% to 100% of the area of the surface of the p-type light absorbing layer 3 facing the p-electrode 2 is in direct contact with the Cu2O crystal grains of the p-type light absorbing layer 3.

The p-type light absorbing layer 3 is a p-type semiconductor layer. The p-type light absorbing layer 3 may be in direct contact with the p-electrode 2, or other layers may be present as long as the contact with the p-electrode 2 can be ensured. The p-type light absorbing layer 3 may include a thin n-type region (for example, 1 nm to 10 nm) on the n-type layer 4 side. Except for this n-type region, the conductivity type of the p-type light absorbing layer 3 is p-type including p-type and p+ type. The p-type light absorbing layer 3 is disposed between the p-electrode 2 and the n-type layer 4. The p-type light absorbing layer 3 is in direct contact with the n-type layer 4. The p-type light absorbing layer 3 is a semiconductor layer of a metal oxide mainly composed of Cu. The metal oxide mainly composed of Cu is a complex oxide of cuprous oxide or/and cuprous oxide. The p-type light absorbing layer 3 is preferably a polycrystal of a complex oxide of cuprous oxide or/and cuprous oxide. The cuprous oxide or/and composite oxide of cuprous oxide is an oxide represented by Cu _a M1 _b O _c . M1 is preferably one or more elements selected from the group consisting of Sn, Sb, Ag, Li, Na, K, Cs, Rb, Al, In, Zn, Mg, Ca, Cl, F, Br, I, Mn, Tc and Re. a, b and c preferably satisfy 1.80≦a≦2.01, 0.00≦b≦0.20 and 0.98≦c≦1.02. It is preferable that 90 wt % or more of the p-type light absorbing layer 3 is a composite oxide of cuprous oxide or/and cuprous oxide. It is more preferable that 95 wt % or more of the p-type light absorbing layer 3 is a composite oxide of cuprous oxide or/and cuprous oxide. It is even more preferable that 98 wt % or more of the p-type light absorbing layer 3 is a composite oxide of cuprous oxide or/and cuprous oxide. It is preferable that the p-type light absorbing layer 3 contains almost no Cu or/and CuO, which are heterophases. It is preferable that the p-type light absorbing layer 3 contains few heterophases and has good crystallinity, because the light transmittance of the p-type light absorbing layer 3 is high. When the p-type light absorbing layer 3 contains an element M2, the band gap of the p-type light absorbing layer 3 can be adjusted. The band gap of the p-type light absorbing layer 3 is preferably 2.0 eV or more and 2.2 eV or less. With a band gap in this range, in a multi-junction solar cell in which a solar cell using Si as a light absorbing layer is used as a bottom cell and the solar cell of the embodiment is used as a top cell, sunlight can be efficiently used in both the top cell and the bottom cell.

Cuprous oxide and composite oxides of cuprous oxide contain carrier-doped cuprous oxide.

The composition ratio of the p-type light absorbing layer 3 is the overall composition ratio of the p-type light absorbing layer 3. It is preferable that the compound composition ratio of the p-type light absorbing layer 3 is satisfied throughout the p-type light absorbing layer 3.

The composition of the p-type light absorbing layer 3 is the average value of the composition at depths of 0.2d ₃ , 0.5d ₃ , and 0.8d ₃ from the surface of the p-type light absorbing layer 3 on the p-electrode 2 side, assuming that the thickness of the p-type light absorbing layer 3 is d ₃ . Except for the condition that the element composition ratio of the compound of the p-type light absorbing layer 3 is inclined, it is preferable that the p-type light absorbing layer 3 satisfies the above and following preferred compositions at each depth. The analysis is performed by analyzing the analysis spots (A1 to A9) distributed as equally spaced as possible at each distance from the surface of the n-type layer 4 as shown in the diagram explaining the analysis spots in FIG. 2 by, for example, secondary ion mass spectrometry (SIMS). FIG. 2 is a schematic diagram of the solar cell 100 viewed from the light incident side. When analyzing the composition of the p-type light absorbing layer 3, D1 is the length in the width direction of the p-type light absorbing layer 3, and D2 is the length in the depth direction of the p-type light absorbing layer 3.

The thickness of the p-type light absorbing layer 3 is determined by cross-sectional observation using an electron microscope or a step gauge, and is preferably 1,000 nm or more and 10,000 nm or less.

The p-type light absorbing layer 3 includes crystal grains (large grains) of the cuprous oxide and/or composite oxide of cuprous oxide, the length of which in the thickness direction of the p-type light absorbing layer 3 is 80% or more and less than 100% of the thickness of the p-type light absorbing layer 3. In a cross section including the center of the p-type light absorbing layer 3, the area occupied by the large grains is preferably 60% or more and less than 100%, and more preferably 80% or more and less than 100%.

The n-type layer 4 is an n-type semiconductor layer. The n-type layer 4 is disposed between the p-type light absorbing layer 3 and the n-electrode 5. The n-type layer 4 is in direct contact with the surface of the p-type light absorbing layer 3 opposite to the surface in contact with the p-electrode 2. The n-type layer 4 is an oxide semiconductor layer containing Ga, and preferably contains a Ga-based compound. The n-type layer 4 may be a mixture of a Ga-based oxide with other oxides, a Ga-based oxide doped with other elements, or a mixture of a Ga-based oxide doped with other elements and other oxides. The n-type layer 4 is a single layer or a multilayer. Of the metal elements contained in the n-type layer 4, Ga is preferably 50 atomic % or more. The metal elements contained in the n-type layer 4 may be inclined from the p-type light absorbing layer 3 side to the n-electrode 5 side.

The n-type layer 4 preferably contains 90 wt% or more of an oxide containing Ga and M2, which is one or more elements selected from the group consisting of H, Sn, Sb, Cu, Ag, Li, Na, K, Cs, Rb, Al, In, Zn, Mg, Si, Ge, N, B, Ti, Hf, Zr, and Ca. The n-type layer 4 may contain elements other than M2 contained in the p-type light absorbing layer 3.

It is preferable that 90 wt% or more of the n-type layer 4 is an oxide containing M2 and Ga. It is more preferable that 95 wt% or more of the n-type layer 4 is an oxide containing M2 and Ga. It is even more preferable that 98 wt% or more of the n-type layer 4 is a compound represented by an oxide containing M2 and Ga. It is more preferable that the n-type layer 4 is composed of a compound represented by an oxide containing M2 and Ga, except for the intermediate region described below.

The composition of the compound of the n-type layer 4 is the average composition of the entire n-type layer 4 unless otherwise specified. The composition of the n-type layer 4 is the average value of the composition at depths of 0.2d ₄ , 0.5d ₄ , and 0.8d ₄ from the surface of the n-type layer 4 on the p-type light absorbing layer 3 side, when the thickness of the n-type layer ₄ is d 4. Except for the condition that the element composition ratio of the compound of the n-type layer 4 is inclined, the n-type layer 4 preferably satisfies the above and following preferred compositions at each depth. When the n-type layer 4 is very thin (for example, 5 nm or less), the composition at a depth of 0.5d ₄ from the surface of the n-type layer 4 on the p-type light absorbing layer 3 side can be regarded as the composition of the entire n-type layer 4. The analysis is performed by analyzing the analysis spots (A1 to A9) distributed as closely as possible at equal intervals at each distance from the surface of the n-type layer 4 as shown in the diagram explaining the analysis spots in FIG. 2 by, for example, secondary ion mass spectrometry (SIMS). 2 is a schematic diagram of the solar cell 100 as viewed from the light incident side. When analyzing the composition of the n-type layer 4, D1 is the length of the n-type layer 4 in the width direction, and D2 is the length of the n-type layer 4 in the depth direction.

It is preferable to include an intermediate region between the p-type light absorbing layer 3 and the n-type layer 4. The intermediate region is a transition region between the p-type light absorbing layer 3 and the n-type layer 4. The intermediate region includes a heterogeneous phase of the p-type light absorbing layer 3, which is an interface defect, and a complex oxide of cuprous oxide. The heterogeneous phase included in the intermediate region includes one or more selected from the group consisting of a CuO phase, a Cu phase, and a phase containing Cu, Ga, M3, and O. In the intermediate region, the total number of one or more selected from the group consisting of Cu, Ga, M3, and O is 95 atom% or more and 100 atom% or less in the intermediate region, and preferably 98 atom% or more and 100 atom% or less. It is preferable that the intermediate region includes a CuO phase. The element represented by M3 is one or more selected from the group consisting of Sn, Sb, Ag, Li, Na, K, Cs, Rb, Al, In, Zn, Mg, Ca, Cl, F, Br, I, Mn, Tc, Re, H, Sn, Sb, Si, Ge, N, B, Ti, Hf, and Zr.

The intermediate region is a region from a depth of 2 nm from the interface between the p-type light absorbing layer 3 and the n-type layer 4 toward the n-type layer 4 (starting point) to a depth of 2 nm or less from the interface between the p-type light absorbing layer 3 and the n-type layer 4 toward the p-type light absorbing layer 3 (end point). In a solar cell using _Cu2O for the p-type light absorbing layer 3, the power generation efficiency is improved by the presence of defects in a very thin region of 4 nm width. If the region where a different phase that causes interface defects exists is thick, for example, 10 nm wide, the conversion efficiency is significantly reduced.

The interface between the p-type light absorbing layer 3 and the n-type layer 4 may be unclear. When the interface between the p-type light absorbing layer 3 and the n-type layer 4 is unclear, the center part of the unclear part between the p-type light absorbing layer 3 and the n-type layer 4 is the interface between the p-type light absorbing layer 3 and the n-type layer 4. The interface between the p-type light absorbing layer 3 and the n-type layer 4 may be uneven rather than flat. The interface between the p-type light absorbing layer 3 and the n-type layer 4 can be identified by observing the cross section of the p-type light absorbing layer 3 and the n-type layer 4. Since the unclear part between the p-type light absorbing layer 3 and the n-type layer 4 contains a different phase, the width of the unclear part between the p-type light absorbing layer 3 and the n-type layer 4 is 0 nm or more and 10 nm or less in the stacking direction of the p-type light absorbing layer 3 and the n-type layer 4, preferably 1 nm or more and 5 nm or less, and more preferably 2 nm or more and 4 nm or less.

The n-electrode 5 is an electrode on the n-type layer 4 side that has optical transparency to visible light. The n-type layer 4 is sandwiched between the n-electrode 5 and the p-type light absorbing layer 3. An intermediate layer (not shown) can be provided between the n-type layer 4 and the n-electrode 5. This intermediate layer can include a mesh or line-shaped electrode. The n-electrode 5 is preferably made of an oxide transparent conductive film. The oxide transparent conductive film used in the n-electrode 5 is preferably one or more transparent conductive films selected from the group consisting of indium tin oxide, aluminum-doped zinc oxide, boron-doped zinc oxide, gallium-doped zinc oxide, indium-doped zinc oxide, titanium-doped indium oxide, indium gallium zinc oxide, and hydrogen-doped indium oxide. The dopant for the tin oxide film is not particularly limited as long as it is one or more selected from the group consisting of In, Si, Ge, Ti, Cu, Sb, Nb, Ta, W, Mo, F, and Cl. Graphene can also be used for the n-electrode 5. It is preferable to laminate the graphene with silver nanowires.

The n-electrode 5 preferably includes one or more transparent conductive films selected from the group consisting of oxides containing Zn, In, and Sn. It is preferable that the n-electrode 5 of one or more transparent conductive films selected from the group consisting of oxides containing Zn, In, and Sn is in direct contact with the n-type layer 4.

The thickness of the n-electrode 5 is determined by cross-sectional observation using an electron microscope or a step gauge, and is not particularly limited, but is typically 1 nm or more and 2 μm or less.

The p-type light absorbing layer 3 is preferably formed by, for example, sputtering. After the p-type light absorbing layer 3 is formed, the surface of the p-type light absorbing layer 3 is oxidized. More specifically, the p-type light absorbing layer 3 is a film that is oxidized and is mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide.

More specifically, the p-type light absorbing layer 3 is a film in which an n-type layer 4 is formed by oxidizing a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide.

Both the film mainly made of cuprous oxide and/or a composite oxide of cuprous oxide and the oxidized p-type light absorbing layer 3 are polycrystalline films of cuprous oxide and/or a composite oxide of cuprous oxide.

The crystal grains of the cuprous oxide and/or cuprous oxide composite oxide of the film mainly composed of cuprous oxide and/or cuprous oxide composite oxide contain crystal grains (large grains) whose length in the thickness direction of the film mainly composed of cuprous oxide and/or cuprous oxide composite oxide is 80% or more and less than 100% of the thickness of the film mainly composed of cuprous oxide and/or cuprous oxide composite oxide. In a cross section including the center of the film mainly composed of cuprous oxide and/or cuprous oxide composite oxide, the area occupied by the large grains is preferably 60% or more and less than 100%, and more preferably 80% or more and less than 100%.

Next, a method for manufacturing the solar cell 100 will be described. A flow chart of the method for manufacturing the solar cell 100 of the embodiment is shown in FIG. 3. The method for manufacturing the solar cell 100 of the embodiment includes the steps of forming a p-electrode 2 on the substrate 1, forming a film mainly composed of cuprous oxide and/or a complex oxide of cuprous oxide on the p-electrode 2, oxidizing the film mainly composed of cuprous oxide and/or a complex oxide of cuprous oxide, forming an n-type layer 4 on the film mainly composed of cuprous oxide and/or a complex oxide of cuprous oxide that has been oxidized, and forming an n-electrode 5 on the n-type layer 4.

First, in the process of forming the p-electrode 2 on the substrate 1, the p-electrode 2 is formed on the substrate 1. The oxide transparent conductive film is formed by, for example, sputtering. If the p-electrode 2 contains a metal film, a mesh-shaped metal, or a line-shaped metal, these metals are formed and patterned as necessary.

Next, as a step of forming a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide on the p-electrode 2, a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide is formed on the p-electrode 2 of the member having the p-electrode 2 formed on the substrate 1. The film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide is preferably formed by sputtering. It is preferable to form a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide with few heterogeneous phases. The sputtering is preferably performed by heating the member having the p-electrode 2 formed on the substrate 1 to 300° C. or more and 600° C. or less, and the oxygen partial pressure is preferably within the range of 0.01 [Pa] to 4.8 [Pa] and within the range of 0.02 μm/min to 20 μm/min. From the viewpoint of forming a polycrystalline film with high permeability and large grain size, it is more preferable that the oxygen partial pressure satisfies 0.55xd [Pa] to 1.00xd [Pa] when the deposition rate is d. Moreover, the heating temperature is more preferably 350° C. or more and 500° C. or less. The element M1 can be added during the formation of a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide. When a film of a composite oxide of cuprous oxide and/or cuprous oxide is formed by this method, the ratio of crystals satisfying 0.8 μm ² or more in the area of crystal grains (area bounded by grain boundaries) on the surface of the film of the composite oxide of cuprous oxide and/or cuprous oxide (surface facing the n-type layer 4 side of the p-type light absorbing layer 3) is preferably 80% or more in total, and the ratio (number) of crystals satisfying 1.0 μm ^{2 or} more is preferably 80% or more in total.

Note that from 0.02 μm/min to 20 μm/min, the deposition rate is d [μm/min]. When the oxygen partial pressure is from 0.55 x d [Pa] to 1.00 x d [Pa], the units of the deposition rate are ignored.

In the process of oxidizing a film mainly made of cuprous oxide and/or a composite oxide of cuprous oxide, a p-electrode 2 is formed on a substrate 1, and an oxidation treatment is performed on the member on which a film mainly made of cuprous oxide and/or a composite oxide of cuprous oxide is formed on the p-electrode 2. The oxidation treatment is performed in a high-temperature, low-oxygen partial pressure atmosphere. The oxidation treatment is performed to oxidize a very thin region on the surface of the film mainly made of cuprous oxide and/or a composite oxide of cuprous oxide. If the oxidation treatment is performed under high oxygen partial pressure conditions or excessively high temperature conditions such as 500°C, the oxidation progresses deep into the film mainly made of cuprous oxide and/or a composite oxide of cuprous oxide, and excessive copper oxide and the like are generated inside the film, which causes a decrease in the transparency of the film and the open-circuit voltage of the solar cell. The oxidation treatment includes treating a member on which a p-electrode 2 is formed on a substrate 1, and a film mainly made of cuprous oxide and/or a composite oxide of cuprous oxide is formed on the p-electrode 2 in an oxygen-containing atmosphere in a vacuum chamber.

When a member on which a film mainly made of cuprous oxide and/or a composite oxide of cuprous oxide is formed is oxidized, the cuprous oxide and/or the composite oxide of cuprous oxide on the surface of the film is partially oxidized and changes to a CuO phase or the like. The presence of these different phases can be confirmed by XRD (X-ray diffraction method) or XPS (X-ray photoelectron spectroscopy). In the oxidation treatment of the embodiment, if the oxidation proceeds too much, the production ratio of the Cu(OH) ₂ phase increases. The CuO phase and Cu(OH) ₂ phase generated by the oxidation treatment are mostly eliminated in the solar cell 100 on which the n-type layer 4 and the like are formed, but the CuO phase and Cu(OH) ₂ phase are formed in a very thin region on the surface of the film mainly made of cuprous oxide and/or a composite oxide of cuprous oxide before the formation of the n-type layer 4, thereby obtaining a solar cell 100 having a high current density and a high open circuit voltage.

The presence of the CuO phase is observed even when the oxidation treatment of the embodiment is not performed, but the open circuit voltage is improved when the oxidation treatment of the embodiment is performed. Improving the open circuit voltage is important for improving the conversion efficiency. It has been confirmed that when the oxidation treatment is performed by the method of the embodiment, the CuO phase is formed in a very thin region on the surface of the p-type light absorbing layer 3. When the p-type light absorbing layer 3 is formed by epitaxial growth, the film surface of the p-type light absorbing layer 3 is flat, making it easy to quantitatively evaluate the CuO phase in the depth direction of the surface, but when the p-type light absorbing layer 3 is formed by sputtering, fine irregularities exist on the film surface. If fine irregularities (number-average irregularity height of 1 nm to 10 nm) exist, it is difficult to quantitatively evaluate the CuO phase on the surface of the p-type light absorbing layer 3 after it is made into a solar cell.

Before and after the oxidation treatment, it is preferable to store the member on which the film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide is formed on the p-electrode 2 so that unintended oxidation reactions do not occur. After the step of performing the oxidation treatment on the film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide, it is preferable to store the member after the oxidation treatment in an atmosphere with an oxygen partial pressure of 50 [Pa] or less and 80°C or less, more preferably 50°C or less, or to continue the formation of the n-type layer 4. Before the formation of the n-type layer 4, the member that has been subjected to the oxidation treatment can be stored in an atmosphere with an oxygen partial pressure of 30°C or less for 1 hour or less, preferably 30 minutes or less. Before the oxidation treatment, it can be stored in an atmosphere with an oxygen partial pressure of 50 [Pa] or less and 80°C or less, more preferably 50°C or less, or can be stored in an atmosphere with an oxygen partial pressure of 30°C or less for 1 hour or less, preferably 30 minutes or less. These storage atmospheres may contain 0.1% or less ozone relative to the oxygen partial pressure.

In these storage atmospheres, the water vapor concentration (mass/volume) is preferably 5.0×10 ⁻⁸ [g/L] or more and 5.0×10 ⁻⁵ [g/L] or less, and more preferably 5.0×10 ⁻⁸ [g/L] or more and 4.0×10 ⁻⁵ [g/L] or less.

It is preferable that the storage atmosphere does not contain plasma gas.

In the oxidation treatment, a member having a film mainly made of cuprous oxide and/or a composite oxide of cuprous oxide formed on the p-electrode 2 is placed on a stage in a vacuum chamber, and before introducing a gas containing oxygen, the pressure is reduced so that the total pressure is 2×10 ⁻⁴ [Pa] or more and 1×10 ⁻¹ [Pa] or less. Oxygen is introduced after the total pressure in the vacuum chamber has stabilized. Before introducing oxygen, the temperature of the member having a film mainly made of cuprous oxide and/or a composite oxide of cuprous oxide formed on the p-electrode 2 is heated to 100° C. or more and 300° C. or less as described below. The temperature of the member at this time is the temperature of the stage.

The atmosphere for the oxidation treatment contains oxygen. The atmosphere for the oxidation treatment may contain ozone at an oxygen partial pressure of 0.0% to 0.1% (maximum 0.5 [Pa] or less). The atmosphere for the oxidation treatment may contain unavoidable substances such as carbon monoxide, carbon dioxide, and hydrocarbons at 1 ppm or less in addition to oxygen. The atmosphere for the oxidation treatment may further contain an inert gas such as nitrogen or argon. Since the atmosphere for the oxidation treatment does not contain any reactive gases other than oxygen and ozone, no reactive gases other than oxygen and ozone are introduced into the chamber where the oxidation treatment is performed. Therefore, it is preferable to introduce only oxygen gas and an inert gas, optionally including ozone, into the chamber for the oxidation treatment.

In the oxidation treatment, the oxygen partial pressure is preferably 100 [Pa] or more and less than 5000 [Pa]. If the oxygen partial pressure is too low, the treatment time will be long, resulting in poor productivity, or the oxidation reaction will not proceed. If the oxygen partial pressure is too high, the oxidation reaction will proceed from the surface to the depths of the cuprous oxide and/or cuprous oxide composite oxide. Therefore, the oxygen partial pressure in the oxidation treatment is more preferably 300 [Pa] or more and less than 5000 [Pa], and even more preferably 500 [Pa] or more and 2000 [Pa] or less. The oxygen partial pressure and ozone partial pressure are values inside the chamber.

In the oxidation treatment, the treatment temperature is preferably 100°C or more and 300°C or less. If the treatment temperature is too low, the treatment time will be long, resulting in poor productivity or the oxidation reaction will not proceed. If the treatment temperature is too high, the oxidation reaction will proceed from the surface of the cuprous oxide and/or the composite oxide of cuprous oxide to its depths. Therefore, the treatment temperature in the oxidation treatment is preferably 125°C or more and 300°C or less, more preferably 125°C or more and 250°C or less, and even more preferably 125°C or more and 200°C or less. The treatment temperature is the surface temperature of the cuprous oxide and/or the composite oxide of cuprous oxide. The oxidation reaction proceeds slowly, so the heat generated by the oxidation reaction is small. Therefore, the surface temperature of the cuprous oxide and/or cuprous oxide composite oxide of the member on which a film mainly made of cuprous oxide and/or cuprous oxide composite oxide is formed on the p-electrode 2 is substantially the same as the temperature of the member on which a film mainly made of cuprous oxide and/or cuprous oxide composite oxide is formed on the p-electrode 2. The temperature of the member on which a film mainly made of cuprous oxide and/or cuprous oxide composite oxide is formed on the p-electrode 2 is the set temperature of the stage of the chamber used for the oxidation treatment, and is the treatment temperature.

The treatment time in the oxidation treatment is preferably 1 second (approximately 0.017 minutes) or more and 90 minutes or less. If the treatment time is too short, the oxidation reaction will not proceed. If the treatment time is too long, the oxidation reaction will proceed from the surface to the depths of the cuprous oxide and/or cuprous oxide composite oxide. Therefore, the treatment time in the oxidation treatment is more preferably 1 minute or more and 60 minutes or less, and even more preferably 1 minute or more and 30 minutes or less.

In the oxidation treatment, when the pressure is 300 [Pa] or more and 2000 [Pa] or less, the treatment temperature is preferably 180 [°C] or more and 250 [°C] or less. When the pressure is 300 [Pa] or more and 2000 [Pa] or less and the treatment temperature is 180 [°C] or more and 250 [°C] or less, the treatment time is preferably 5 seconds or more and 45 minutes or less, and more preferably 1 minute or more and 30 minutes or less. When the oxygen partial pressure is medium to high, the treatment temperature and treatment time are also medium to high, so that a very thin area on the surface of the cuprous oxide and/or cuprous oxide composite oxide can be locally oxidized.

In the oxidation treatment, when the pressure is 500 [Pa] or more and 2000 [Pa] or less, the treatment temperature is preferably 180 [°C] or more and 250 [°C] or less. When the pressure is 500 [Pa] or more and 2000 [Pa] or less and the treatment temperature is 180 [°C] or more and 250 [°C] or less, the treatment time is preferably 1 minute or more and 30 minutes or less, and more preferably 5 minutes or more and 25 minutes or less. When the oxygen partial pressure is medium to high, the treatment temperature and treatment time are also medium to high, so that a very thin area on the surface of the cuprous oxide and/or cuprous oxide composite oxide can be locally oxidized.

In the oxidation treatment, when the treatment time is less than 1 minute (preferably, 1 second or more and less than 1 minute, more preferably, 5 seconds or more and 30 seconds or less), the treatment temperature is preferably 200 [°C] or more and 300 [°C] or less. When the treatment time is long, oxidation may proceed too much under high treatment temperature conditions. When the treatment time is less than 1 minute (1 second or more and less than 1 minute, preferably, 5 seconds or more and 30 seconds or less) and the treatment temperature is 240°C or more and 300°C or less, the oxygen partial pressure is preferably 500 [Pa] or more and 2000 [Pa] or less, and more preferably 500 [Pa] or more and 1000 [Pa] or less. In the case of oxidation treatment at high temperature for a very short time, a very thin region on the surface of the cuprous oxide and/or cuprous oxide composite oxide can be locally oxidized by lowering the oxygen partial pressure.

In the oxidation treatment, when the treatment time is 1 minute or more and less than 10 minutes, the treatment temperature is preferably 200 [℃] or more and 300 [℃] or less. When the treatment time is 1 minute or more and less than 10 minutes and the treatment temperature is 250 [℃] or more and 300 [℃] or less, the oxygen partial pressure is preferably 100 [Pa] or more and 2000 [Pa] or less, more preferably 100 [Pa] or more and 1000 [Pa] or less, and even more preferably 100 [Pa] or more and 500 [Pa] or less. When the treatment time is 1 minute or more and less than 10 minutes and the treatment temperature is 200 [℃] or more and less than 250 [℃], the oxygen partial pressure is preferably 1000 [Pa] or more and less than 5000 [Pa], and more preferably 1500 [Pa] or more and 3000 [Pa] or less. In the case of high-temperature, short-time oxidation treatment, a medium to high oxygen partial pressure can be used to locally oxidize a very thin region on the surface of cuprous oxide and/or a composite oxide of cuprous oxide.

In the oxidation treatment, when the treatment time is 10 minutes or more and 60 minutes or less, the treatment temperature is preferably 100 [℃] or more and 250 [℃] or less, and more preferably 100 [℃] or more and 200 [℃] or less. When the treatment time is 10 minutes or more and 60 minutes or less and the treatment temperature is 100 [℃] or more and 150 [℃] or less, the oxygen partial pressure is preferably 1000 [Pa] or more and less than 5000 [Pa], and more preferably 3000 [Pa] or more and less than 5000 [Pa]. In the case of a relatively low-temperature oxidation treatment that requires a medium time, by increasing the oxygen partial pressure, it is possible to locally oxidize a very thin region on the surface of the cuprous oxide and/or cuprous oxide composite oxide. When the treatment time is 10 minutes or more and 60 minutes or less and the treatment temperature is higher than 150 [℃] and 250 [℃] or less, the oxygen partial pressure is preferably 300 [Pa] or more and 2500 [Pa] or less, and more preferably 500 [Pa] or more and 2000 [Pa] or less. In the case of a relatively high-temperature oxidation process that requires a medium amount of time, a very thin area on the surface of the cuprous oxide and/or cuprous oxide composite oxide can be locally oxidized by lowering the oxygen partial pressure.

In the oxidation treatment, when the treatment time is 10 minutes or more and 30 minutes or less, the treatment temperature is preferably 100 [℃] or more and 200 [℃] or less. When the treatment time is 10 minutes or more and 30 minutes or less and the treatment temperature is 100 [℃] or more and 175 [℃] or less, the oxygen partial pressure is preferably 500 [Pa] or more and less than 5000 [Pa], and more preferably 1000 [Pa] or more and 2000 [Pa] or less. When the treatment time is 10 minutes or more and 30 minutes or less and the treatment temperature is 150 [℃] or more and 200 [℃] or less, the oxygen partial pressure is preferably 300 [Pa] or more and 1500 [Pa] or less, and more preferably 400 [Pa] or more and 1000 [Pa] or less. In the case of oxidation treatment at a moderate temperature requiring a moderate time, by not increasing the oxygen partial pressure too much, it is possible to locally oxidize a very thin region on the surface of the cuprous oxide and/or the cuprous oxide composite oxide.

In the oxidation treatment, when the treatment time is 10 minutes or more and 20 minutes or less, the treatment temperature is preferably 100°C or more and 200°C or less. When the treatment time is 10 minutes or more and 20 minutes or less and the treatment temperature is 100°C or more and 200°C or less, the oxygen partial pressure is preferably 500 Pa or more and less than 5000 Pa, and more preferably 500 Pa or more and 2000 Pa or less. In the case of oxidation treatment at a medium temperature requiring a medium time, by not increasing the oxygen partial pressure too much, it is possible to locally oxidize a very thin region on the surface of the cuprous oxide and/or cuprous oxide composite oxide.

In the oxidation treatment, if the treatment time is longer than 60 minutes and shorter than 90 minutes, the treatment temperature is preferably 100°C or higher and 150°C or lower. If the treatment time is longer than 60 minutes and shorter than 90 minutes and the treatment temperature is 100°C or higher and 150°C or lower, the oxygen partial pressure is preferably 1000 Pa or higher and lower than 5000 Pa, and more preferably 1500 Pa or higher and 3000 Pa or lower. In the case of oxidation treatment at low temperature for a long time, a very thin area on the surface of the cuprous oxide and/or cuprous oxide composite oxide can be locally oxidized by slightly increasing the oxygen partial pressure.

When the oxygen partial pressure in the oxidation process is high, the progress of oxidation can be easily controlled by lowering the processing temperature and shortening the processing time.When the processing temperature in the oxidation process is high, the progress of oxidation can be easily controlled by lowering the oxygen partial pressure and shortening the processing time.

When the oxygen partial pressure in the oxidation process is low, the progress of the oxidation can be easily controlled by increasing the processing temperature or lengthening the processing time.When the oxygen partial pressure in the oxidation process is low, the progress of the oxidation can be easily controlled by increasing the processing temperature or lengthening the processing time.

The partial pressure of oxygen in a gas can be determined from the oxygen concentration in the gas, for example, using a galvanic cell sensor or a zirconia oxide sensor.

The oxidation treatment of the embodiment is easily affected by the oxygen partial pressure, treatment temperature, and treatment time. High oxygen partial pressure, high temperature, and long treatment time accelerate the oxidation reaction. By performing the oxidation treatment so that these three conditions satisfy the above ranges, it is possible to oxidize a very thin region on the surface of the film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide. If these three conditions are not met, the oxidation will proceed too far or will hardly occur at all.

The oxidation treatment is preferably performed on a film of cuprous oxide or/and cuprous oxide composite oxide formed by sputtering. The surface of the film of cuprous oxide or/and cuprous oxide composite oxide formed by sputtering has fine irregularities. It is believed that by performing the oxidation treatment on the film of cuprous oxide or/and cuprous oxide composite oxide formed by sputtering, which has fine irregularities on its surface, a favorable oxidation reaction occurs, which contributes to improving the open circuit voltage of the solar cell.

The oxygen partial pressure in the oxidation process is the partial pressure of _O2 gas in the processing atmosphere. In the oxidation process, the _O2 gas is not turned into plasma.

By subjecting the polycrystalline film to oxidation treatment, only a very thin region (e.g., a region from the surface of the film mainly made of cuprous oxide and/or a composite oxide of cuprous oxide to a depth of 1 atomic layer or more and 1 nm or less) of the surface of the film mainly made of cuprous oxide and/or a composite oxide of cuprous oxide can be oxidized. The surface of the film mainly made of cuprous oxide and/or a composite oxide of cuprous oxide is oxidized as a whole. When the oxidation conditions are different (e.g., oxidation of small grain size Cu ₂ O, single crystal Cu ₂ O film, low oxygen conditions), it is considered that Cu ₂ O is not oxidized, the surface of the film mainly made of cuprous oxide and/or a composite oxide of cuprous oxide is partially oxidized, oxidation progresses to the deeper part, and the grain size is enlarged due to recrystallization.

The crystallinity and the presence or absence of heterogeneous phases of a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide change depending on the film formation conditions. Therefore, since there is no report that CuO is formed in a thin surface region by annealing performed on a single crystal _Cu2O film, it is considered that the reaction mechanism of the oxidation treatment of a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide formed by the sputtering method of the embodiment is different from that of the same oxidation treatment on a single crystal _Cu2O film.

When an oxidation treatment is performed on a Cu ₂ O film having many OH groups (Cu(OH) ₂ ) on the surface, the OH groups promote oxidation, and the oxidation tends to progress deep into the Cu ₂ O film. When selectively oxidizing a thin region of the surface of a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide, it is preferable not to perform a treatment for increasing the amount of OH groups after the formation of the film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide.

When the oxidation treatment of the embodiment is performed, oxidation does not progress to the depths. After the oxidation treatment, the ratio of CuO to all phases in the region from the surface of the film mainly made of cuprous oxide and/or composite oxide of cuprous oxide to a depth of 5 nm is preferably 1% or more and 10% or less, more preferably 5% or more and 10% or less.

When a film mainly made of cuprous oxide and/or a composite oxide of cuprous oxide is treated under oxidizing conditions, it is expected that the increase in defects will result in a decrease in efficiency and a decrease in permeability. When considering conversion efficiency and permeability, it is generally avoided to perform an oxidation treatment after forming a film mainly made of cuprous oxide and/or a composite oxide of cuprous oxide, which has good crystallinity. If oxidation is insufficient and the film quality is poor, an oxidation treatment is required. However, it is possible to improve the conversion efficiency by controlling the oxidation conditions of a film with good quality mainly made of cuprous oxide and/or a composite oxide of cuprous oxide.

When the oxidation treatment of the embodiment is performed on a single crystal Cu ₂ O film, oxidation tends to progress deep inside.

In the oxidation treatment of the embodiment, when the water vapor concentration in the oxidation treatment atmosphere is high, the Cu(OH) ₂ phase is likely to increase. In this case, the oxidation treatment of the film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide is likely to progress to a deeper portion. Therefore, the water vapor concentration (mass/volume) in the oxidation treatment atmosphere of the embodiment is preferably 5.0×10 ⁻⁸ [g/L] or more and 5.0×10 ⁻⁵ [g/L] or less, and more preferably 5.0×10 ⁻⁸ [g/L] or more and 4.0×10 ⁻⁵ [g/L] or less.

The oxidation treatment of the embodiment is effective when applied to a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide formed by a sputtering method to realize a transparent solar cell.

In order to adjust the carrier concentration of the p-type light absorbing layer 3 before and/or after the oxidation treatment, a p-type dopant and/or an n-type dopant can be doped.

In the process of forming the n-type layer 4 on the film mainly made of cuprous oxide and/or a composite oxide of cuprous oxide that has been subjected to an oxidation treatment, the n-type layer 4 is formed on the film mainly made of cuprous oxide and/or a composite oxide of cuprous oxide by, for example, ALD (atomic layer deposition) or CVD (chemical vapor deposition).

In the process of forming the n-electrode 5 on the n-type layer 4, the n-electrode 5 is formed on the n-type layer 4 by sputtering or the like. If an intermediate layer is provided between the n-type layer 4 and the n-electrode 5, the intermediate layer is formed before the formation of the n-electrode 5. Through the above process, a solar cell 100 is manufactured, which has the substrate 1, the p-electrode 2, the p-type light absorbing layer 3 mainly made of cuprous oxide and/or a composite oxide of cuprous oxide whose surface has been oxidized, the n-type layer 4, and the n-electrode 5.

In a solar cell in which an n-type layer 4 is formed on the oxidized surface of a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide, and an n-electrode 5 is formed on the n-type layer, the conversion efficiency is improved by the oxidation treatment.

Second Embodiment
The second embodiment relates to a multi-junction solar cell. Fig. 4 shows a cross-sectional conceptual diagram of a multi-junction solar cell of the second embodiment. The multi-junction solar cell 200 of Fig. 4 has a solar cell (first solar cell) 100 of the first embodiment and a second solar cell 201 on the light incident side. The first solar cell 100 is the solar cell of the first embodiment. The band gap of the light absorption layer of the second solar cell 201 has a smaller band gap than the p-type light absorption layer 3 of the multi-junction solar cell 200 of the second embodiment. The multi-junction solar cell of the embodiment also includes a solar cell in which three or more solar cells are joined together.

Since the band gap of the p-type light absorbing layer 3 of the solar cell 100 of the first embodiment is about 2.0 eV-2.2 eV, it is preferable that the band gap of the light absorbing layer of the second solar cell 201 is 1.0 eV or more and 1.6 eV or less. The light absorbing layer of the second solar cell is preferably one or more compound semiconductor layers selected from the group consisting of CIGS and CdTe with a high In content, crystalline silicon, and one selected from the group consisting of perovskite type compounds.

Third Embodiment
The third embodiment relates to a solar cell module. Fig. 5 shows a perspective view of a solar cell module 300 of the third embodiment. The solar cell module 300 in Fig. 5 is a solar cell module in which a first solar cell module 301 and a second solar cell module 302 are stacked. The first solar cell module 301 is on the light incident side, and uses the solar cell 100 of the first embodiment. It is preferable to use the second solar cell 201 for the second solar cell module 302.

Figure 6 shows a cross-sectional view of the solar cell module 300. In Figure 6, the structure of the first solar cell module 301 is shown in detail, but the structure of the second solar cell module 302 is not shown. For the second solar cell module 302, the structure of the solar cell module is appropriately selected depending on the light absorption layer of the solar cell to be used. The solar cell module 300 in Figure 6 includes multiple submodules 303 surrounded by dashed lines in which multiple solar cells 100 (solar cells) are arranged horizontally and electrically connected in series with wiring 304, and the multiple submodules 303 are electrically connected in parallel or in series. Adjacent submodules 303 are electrically connected with bus bars 305.

Adjacent solar cells 100 have their n-electrodes 5 on the upper side and p-electrodes 2 on the lower side connected by wiring 304. Both ends of the solar cells 100 in the submodule 303 are connected to a bus bar 305, and the bus bar 305 is preferably configured to electrically connect the multiple submodules 303 in parallel or series and adjust the output voltage with the second solar cell module 302. Note that the connection form of the solar cells 100 shown in the third embodiment is one example, and solar cell modules can be configured using other connection forms.

Fourth Embodiment
The fourth embodiment relates to a solar power generation system. The solar cell module of the third embodiment can be used as a generator that generates power in the solar power generation system of the fourth embodiment. The solar power generation system of the embodiment generates power using a solar cell module, and specifically includes a solar cell module that generates power, a means for converting the generated electricity into electric power, and a storage means for storing the generated electricity or a load for consuming the generated electricity. FIG. 7 shows a configuration diagram of a solar power generation system 400 of the embodiment. The solar power generation system of FIG. 7 includes a solar cell module 401 (300), a converter 402, a storage battery 403, and a load 404. Either the storage battery 403 or the load 404 may be omitted. The load 404 may be configured to be able to utilize the electric energy stored in the storage battery 403. The converter 402 is a device including a circuit or element that performs power conversion such as voltage transformation and DC-AC conversion, such as a DC-DC converter, a DC-AC converter, or an AC-AC converter. The converter 402 may have a suitable configuration depending on the generated voltage and the configurations of the storage battery 403 and the load 404 .

The solar cell included in the solar cell module 300 generates electricity, and the electrical energy is converted by the converter 402 and stored in the storage battery 403 or consumed by the load 404. It is preferable to provide the solar cell module 401 with a solar tracking drive device to always point the solar cell module 401 toward the sun, a collector to collect sunlight, or a device to improve power generation efficiency.

The solar power generation system 400 is preferably used in real estate such as residences, commercial facilities, and factories, and in movable property such as vehicles, aircraft, and electronic devices. By using the solar cell with excellent open circuit voltage of the embodiment in a solar cell module, an increase in the amount of power generation is expected.

A vehicle is shown as an example of the use of the solar power generation system 400. FIG. 8 shows a schematic diagram of the vehicle 500. The vehicle 500 in FIG. 8 has a vehicle body 501, a solar cell module 502, a power conversion device 503, a storage battery 504, a motor 505, and tires (wheels) 506. The power generated by the solar cell module 502 provided on the upper part of the vehicle body 501 is converted by the power conversion device 503 and charged in the storage battery 504, or the power is consumed by a load such as the motor 505. The vehicle 500 can be moved by rotating the tires (wheels) 506 with the motor 505 using the power supplied from the solar cell module 502 or the storage battery 504. The solar cell module 502 may not be a multi-junction type, but may be composed of only the first solar cell module equipped with the solar cell 100 of the first embodiment. When a transparent solar cell module 502 is adopted, it is also preferable to use the solar cell module 502 as a window for generating power on the side of the vehicle body 501 in addition to the upper part of the vehicle body 501.

An air vehicle (drone) is shown as an example of the use of the solar power generation system 400. The air vehicle uses a solar cell module 300. The configuration of the air vehicle according to this embodiment will be briefly described using the schematic diagram of an air vehicle (quadcopter) 600 in FIG. 9. The air vehicle 600 has a solar cell module 300, a frame 601, a motor 602, a rotor 603, and a control unit 604. The solar cell module 300, the motor 602, the rotor 603, and the control unit 604 are arranged on the frame 601. The control unit 604 converts the power output from the solar cell module 300 and adjusts the output. The control unit 604 may further include a storage battery that stores the power generated by the solar cell module 300. The motor 602 rotates the rotor 603 using the power output from the solar cell module 300. By making the air vehicle 600 of this configuration having the solar cell module 300 of the embodiment, a air vehicle that can fly using more power is provided.
The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

(Examples A-1 to A-8, Comparative Examples A-1 to A-2)
On a glass substrate, ITO (In:Sn=80:20, 20 nm thick) and ATO (Sn:Sb=98:2, 150 nm thick) are deposited on the top surface of the glass as a p-electrode on the back side. A _Cu2O light absorbing layer is formed on the transparent p-electrode by heating at 500°C in an oxygen and argon gas atmosphere using a sputtering method. The surface of the _Cu2O light absorbing layer is then oxidized under the conditions shown in the table in Figure 10. The surface of the _Cu2O light absorbing layer oxidized by XPS is then observed by XPS. The heights of the peaks corresponding to _Cu2O , CuO, and Cu(OH) ₂ are obtained. Figure 11 shows the peak heights obtained by XPS. In addition to oxygen, the oxidation process contains less than 1 ppm of nitrogen, argon, carbon monoxide, carbon dioxide, and hydrocarbons.

XPS analysis was performed using a Quantera SXM from ULVAC-PHI, with a single crystal spectrometer Al Kα ray as the X-ray source, an X-ray output of 50 W, an X-ray irradiation area of 200 μmφ to 300 μmφ, an X-ray irradiation angle of 45 deg to the sample, an angle of 90 deg between the sample and the detector, and no charge neutralization gun. Measurement under these conditions allows the ratio of Cu ₂ O contained in the extremely thin area on the surface of the film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide to its heterophases, CuO and Cu(OH) ₂ , to be evaluated.

The proportions of _Cu2O , CuO, and Cu(OH) ₂ are determined by fitting the spectrum of Cu2p3/2 (binding energy around 932.5 eV) obtained by XPS analysis with a pseudo-Voigt function at _Cu2O (center: around 932.5 eV), CuO (center: around 933.7 eV), and Cu(OH) ₂ (center: around 935.1 eV) respectively, and fitting the XPS spectrum with a Lorentz distribution equation at a ratio of 40% and a Gauss distribution equation at a ratio of 60%. The baseline of the XPS spectrum is determined by the dynamic Shirley method. The integral area enclosed by the fitted pseudo-Voigt function and the baseline obtained above is defined as the integral intensity. The integral intensities of _Cu2O , CuO, and Cu(OH) ₂ are calculated respectively. The proportions of _Cu2O , CuO, and Cu(OH) ₂ can be expressed as _Cu2O [%] = _Cu2O integral intensity ÷ ( _Cu2O integral intensity + CuO integral intensity + Cu(OH) ₂ integral intensity) × 100, CuO [%] = CuO integral intensity ÷ ( _Cu2O integral intensity + CuO integral intensity + Cu(OH) ₂ integral intensity) × 100, and Cu(OH) ₂ [%] = Cu(OH) ₂ integral intensity ÷ ( _Cu2O integral intensity CuO integral intensity + Cu(OH) ₂ integral intensity) × 100.

In Fig. 11, the ratio of CuO and Cu(OH) ₂ was evaluated in four stages, A, B, C, and D, according to the ratio of CuO and Cu(OH)2 on the surface of the film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide. When the ratio of CuO and Cu(OH) ₂ on the surface of the film is 10% or more and 100% or less, it was evaluated as A, when it is 1% or more and less than 10%, it was evaluated as B, when it is 0.1% or more and less than 1%, it was evaluated as C, and when it is 0.0% or more and less than 0.1%, it was evaluated as D. When XPS analysis is performed under the conditions of an X-ray irradiation angle of 45deg to the sample and an angle of 90deg between the sample and the detector, intensity can be obtained up to a depth of about 5nm, so when the ratio of CuO and Cu(OH) ₂ is 10% or more and 100% or less, which is evaluated as A, it is considered that the film is too oxidized. With this analysis method, CuO and Cu(OH) ₂ between 1% and 10%, which is rated B, is considered optimal. In the case of a B rating, it is believed that only a very thin area on the surface has been oxidized, and oxidation has not progressed in deeper areas.

In a vacuum with almost no nitrogen or water vapor, oxygen gas supplied into the chamber reacts efficiently with the surface of the _Cu2O layer, so that heterogeneous phases CuO and/or Cu(OH) ₂ can be generated in an extremely thin region of 1 atomic layer to 1 nm in the low-oxygen region. The generation of heterogeneous phases CuO and/or Cu(OH) ₂ in an extremely thin region of 1 atomic layer to 1 nm increases the voltage of the _Cu2O solar cell. However, if the substrate temperature is high or the reaction is allowed to proceed for a long time, heterogeneous phases such as CuO are generated deep inside, and the generated heterogeneous phases such as CuO become impurity layers in the _Cu2O layer, lowering the current density of the _Cu2O solar cell.

(Examples B-1 to B-8, Comparative Examples B-1 to B-2)
On a glass substrate, ITO (In:Sn=80:20, film thickness 20 nm) and ATO (Sn:Sb=98:2 150 nm) are deposited on the upper surface of the glass as a p-electrode on the back side. A _Cu2O light absorbing layer is formed on the transparent p-electrode by heating at 500°C in an oxygen and argon gas atmosphere using a sputtering method. Then, the surface of the _Cu2O light absorbing layer is oxidized under the conditions shown in the table of FIG. 12. Next, _{Ga2O3 is} deposited to a thickness of 10 nm as an n-type layer by the ALD method. An AZO transparent conductive film is deposited on the n-type layer as an n-electrode. Then, a _MgF2 film is formed as an anti-reflection film to obtain a solar cell. The open circuit voltage (Voc) and current density (Jsc) of the obtained solar cell are evaluated.

A solar simulator simulating an AM1.5G light source is used, and a reference Si cell is used under that light source to adjust the amount of light to 1 sun. Measurements are taken at atmospheric pressure with the temperature in the measurement room at 25°C. The voltage is swept and the current density (current divided by the cell area) is measured. With the horizontal axis representing voltage and the vertical axis representing current density, the point at which the horizontal axis intersects the line represents the open circuit voltage Voc, and the point at which the vertical axis intersects the line represents the short circuit current density Jsc.

The table for the examples in Figure 13 shows the open circuit voltage (Voc) and current density (Jsc) for the examples and comparative examples.

If Voc is less than or equal to the Voc of the comparison example, it is evaluated as B, and if it is greater than the Voc of the comparison example, it is evaluated as A. If Jsc is less than the Jsc of the comparison example, it is evaluated as B, and if it is greater than or equal to the Jsc of the comparison example, it is evaluated as A.

As can be seen from the tables in Figures 12 and 13, by performing oxidation treatment under appropriate conditions, Voc can be improved while maintaining the same or higher Jsc.

(Example C-1)
On a glass substrate, ITO (In:Sn=80:20, film thickness 20 nm) and ATO (Sn:Sb=98:2, 150 nm) are deposited on the top surface of the glass substrate as a p-electrode on the rear side. A 5 μm-thick Cu ₂ O light absorbing layer is formed on the transparent p-electrode by sputtering in an oxygen and argon gas atmosphere at 500° C. Then, the surface of the Cu ₂ O light absorbing layer is oxidized under the conditions shown in the table of FIG. 14. The oxidized member is promptly sealed at 25° C. and analyzed after the oxidation.

(Comparative Example C-1)
A member having a 200 μm-thick single crystal Cu ₂ O layer formed on Al ₂ O ₃ is subjected to oxidation treatment under the conditions shown in the table of Fig. 14. Immediately after the oxidation treatment, the oxidized member is sealed at 25°C and analyzed.

(Comparative Example C-2)
The surface of the _Cu2O layer of a _member having a 200 μm-thick single crystal _Cu2O layer formed on _Al2O3 is treated with water vapor. The member that has been treated with water vapor is then subjected to an oxidation treatment under the conditions shown in the table of Fig. 14. Immediately after the oxidation treatment, the member that has been oxidized is sealed at 25°C and analyzed.

The table for the embodiment in Figure 15 shows the ratio of CuO to all phases in the region from the surface to a depth of 10 nm of the film mainly composed of cuprous oxide and/or composite oxide of cuprous oxide after oxidation treatment.

When the ratio of CuO to all phases in the region from the surface to a depth of 10 nm of the film mainly made of cuprous oxide and/or a composite oxide of cuprous oxide after oxidation treatment is 10% or more and 100% or less, it is evaluated as A, when it is 1% or more and 10% or less, it is evaluated as B, and when it is 0.1% or more and 10% or less, it is evaluated as C. The ratio of CuO to all phases in the region from the surface to a depth of 10 nm of the film mainly made of cuprous oxide and/or a composite oxide of cuprous oxide after oxidation treatment is determined by analysis using a method in which the analysis depth is changed from the above-mentioned XPS measurement method.

As can be seen from the tables of Figures 14 and 15, the ratio of CuO near the surface of the film mainly composed of cuprous oxide and/or composite oxide of cuprous oxide after oxidation treatment changes depending on the difference in crystallinity and the ratio of OH groups before oxidation treatment. Also, in a solar cell made using a _Cu2O layer in which oxidation has progressed deep down as in the comparative example, the transmittance of light with wavelengths from 700 nm to 1000 nm is reduced by CuO. When oxidation progresses deep down, both the transmittance and the power generation efficiency decrease.

(Examples D-1 to D-11, Comparative Examples D-1 to D-12)
On a glass substrate, ITO (In:Sn=80:20, film thickness 20 nm) and ATO (Sn:Sb=98:2 150 nm) are deposited on the upper surface of the glass as a p-electrode on the rear side. A 5.0 μm thick Cu ₂ O light absorbing layer is formed on the transparent p-electrode by heating at 500° C. in an oxygen and argon gas atmosphere by sputtering. Then, the surface of the Cu ₂ O light absorbing layer is oxidized under the conditions shown in the table of FIG. 16. Next, Ga ₂ O ₃ is deposited to a thickness of 10 nm as an n-type layer by ALD. An AZO transparent conductive film is deposited on the n-type layer as an n-electrode. Then, a MgF ₂ film is formed as an anti-reflection film to obtain a solar cell. The open circuit voltage (Voc) and current density (Jsc) of the obtained solar cell are evaluated.

A solar simulator simulating an AM1.5G light source is used, and a reference Si cell is used under that light source to adjust the amount of light to 1 sun. Measurements are taken at atmospheric pressure with the temperature in the measurement room at 25°C. The voltage is swept and the current density (current divided by the cell area) is measured. With the horizontal axis representing voltage and the vertical axis representing current density, the point at which the horizontal axis intersects the line represents the open circuit voltage Voc, and the point at which the vertical axis intersects the line represents the short circuit current density Jsc.

The table for the examples in Figure 17 shows the open circuit voltage (Voc) and current density (Jsc) for the examples and comparative examples.

If Voc is less than or equal to the Voc of the comparison example, it is evaluated as B, and if it is greater than the Voc of the comparison example, it is evaluated as A. If Jsc is less than the Jsc of the comparison example, it is evaluated as B, and if it is greater than or equal to the Jsc of the comparison example, it is evaluated as A.

As can be seen from the tables in Figures 16 and 17, by performing oxidation treatment under appropriate conditions, Voc can be improved while maintaining the same or higher Jsc.

Some elements in this specification are shown only by their element symbols.

The technical proposal of the embodiment is shown below.
Technical proposal 1
forming a p-electrode on the substrate;
forming a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide on the p-electrode;
and a step of subjecting the film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide to an oxidation treatment,
In the oxidation treatment, the oxygen partial pressure is equal to or greater than 100 [Pa] and less than 5000 [Pa];
In the oxidation treatment, the treatment temperature is 100 [°C] or more and 300 [°C] or less,
The method for manufacturing a solar cell, wherein the oxidation treatment is carried out for a treatment time of 1 second to 90 minutes.
Technical proposal 2
The method for manufacturing a solar cell described in Technical Proposal 1, wherein the treatment temperature in the oxidation treatment is 125°C or higher and 250°C or lower.
Technical proposal 3
A method for manufacturing a solar cell as described in Technical Proposal 1, wherein, in the oxidation treatment, the oxygen partial pressure is 300 [Pa] or more and 2000 [Pa] or less, the treatment temperature is 180 [°C] or more and 250 [°C] or less, and the treatment time is 5 seconds or more and 45 minutes or less.
Technical proposal 4
The method for manufacturing a solar cell described in Technical Proposal 1, wherein, in the oxidation treatment, the oxygen partial pressure is 500 [Pa] or more and 2000 [Pa] or less, the treatment temperature is 180 [°C] or more and 250 [°C] or less, and the treatment time is 1 minute or more and 30 minutes or less.
Technical proposal 5
A method for manufacturing a solar cell as described in Technical Proposal 1, wherein, in the oxidation treatment, the treatment time is 1 minute or more and less than 10 minutes, the treatment temperature is 250°C or more and 300°C or less, and the oxygen partial pressure is 100 Pa or more and 2000 Pa or less.
Technical proposal 6
The method for manufacturing a solar cell described in Technical Proposal 1, wherein, in the oxidation treatment, the treatment time is 1 minute or more and less than 10 minutes, the treatment temperature is 200 [°C] or more and less than 250 [°C], and the oxygen partial pressure is 1000 [Pa] or more and less than 5000 [Pa].
Technical proposal 7
The method for manufacturing a solar cell described in Technical Proposal 1, wherein, in the oxidation treatment, the treatment time is 10 minutes or more and 60 minutes or less, the treatment temperature is 100 [°C] or more and 250 [°C] or less, and the oxygen partial pressure is 1000 [Pa] or more and less than 5000 [Pa].
Technical proposal 8
The method for manufacturing a solar cell described in Technical Proposal 1, wherein, in the oxidation treatment, the treatment time is 10 minutes or more and 30 minutes or less, the treatment temperature is 100 [°C] or more and 175 [°C] or less, and the oxygen partial pressure is 500 [Pa] or more and less than 5000 [Pa].
Technical proposal 9
The method for manufacturing a solar cell described in Technical Proposal 1, wherein, in the oxidation treatment, the treatment time is 10 minutes or more and 30 minutes or less, the treatment temperature is 150 [°C] or more and 200 [°C] or less, and, in the oxidation treatment, the oxygen partial pressure is 300 [Pa] or more and 1500 [Pa] or less.
Technical proposal 10
The method for manufacturing a solar cell described in Technical Proposal 1, wherein, in the oxidation treatment, the treatment time is 10 minutes or more and 20 minutes or less, the treatment temperature is 150 [°C] or more and 200 [°C] or less, and, in the oxidation treatment, the oxygen partial pressure is 500 [Pa] or more and less than 5000 [Pa].
Technical proposal 11
The method for manufacturing a solar cell described in Technical Proposal 1, wherein, in the oxidation treatment, the treatment time is longer than 60 minutes and shorter than 90 minutes, the treatment temperature is 100 [°C] or higher and 150 [°C] or lower, and the oxygen partial pressure is 1000 [Pa] or higher and lower than 5000 [Pa].
Technical proposal 12
12. A method for manufacturing a solar cell according to any one of technical proposals 1 to 11, comprising a step of forming an n-type layer on the film mainly composed of the oxidized cuprous oxide and/or composite oxide of cuprous oxide.
Technical proposal 13
forming an n-type layer on the oxidized film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide;
A method for manufacturing a solar cell according to any one of technical proposals 1 to 12, comprising a step of forming an n-electrode on the n-type layer.
Technical proposal 14
The film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide is formed by sputtering,
The sputtering is performed by heating the substrate having the p-electrode 2 formed thereon to a temperature of 300° C. or higher and 600° C. or lower.
The oxygen partial pressure of the sputtering is in the range of 0.01 [Pa] to 4.8 [Pa] and in the range of 0.02 μm/min to 20 μm/min,
The method for manufacturing a solar cell according to any one of technical proposals 1 to 13, wherein when the deposition rate of the sputtering is d, the oxygen partial pressure satisfies 0.55xd [Pa] or more and 1.00xd [Pa] or less.
Technical proposal 15
The method for manufacturing a solar cell described in Technical Proposal 14, wherein the heating temperature of the sputtering is 350°C or higher and 500°C or lower.
Technical proposal 16
A multi-junction solar cell using a solar cell manufactured by the manufacturing method described in any one of Technical Solutions 1 to 15.
Technical proposal 17
A solar cell manufactured by the manufacturing method described in any one of Technical Schemes 1 to 15, or a solar cell module using the multi-junction solar cell described in Technical Scheme 16.
Technical proposal 18
A solar power generation system that generates power using the solar cell module described in Technical Proposal 17.

Although the embodiments of the present invention have been described above, the present invention should not be interpreted as being limited to the above-mentioned embodiments as they are, and the components can be modified and embodied in the implementation stage without departing from the gist of the invention. Furthermore, various inventions can be formed by appropriate combinations of the multiple components disclosed in the above-mentioned embodiments. For example, components from different embodiments may be appropriately combined as in modified examples.

100, 101... solar cell (first solar cell), 1... substrate, 2... p-electrode, 3... p-type light absorbing layer, 4... n-type layer, 5... n-electrode 200... multi-junction solar cell, 201... second solar cell,
300... solar cell module, 6... substrate, 301 first solar cell module, 302... second solar cell module, 303... submodule, 304... bus bar,
400...Solar power generation system, 401...Solar cell module, 402...Converter, 403...Storage battery, 404...Load 500...Vehicle, 501...Vehicle body, 502...Solar cell module, 503...Power conversion device, 504...Storage battery, 505...Motor, 506...Tire (wheel)
600: flying object, 601: aircraft frame, 602: motor, 603: rotor, 604: control unit

Claims (15)

forming a p-electrode on the substrate;
forming a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide on the p-electrode;
and a step of subjecting the film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide to an oxidation treatment,
In the oxidation treatment, the oxygen partial pressure is equal to or greater than 100 [Pa] and less than 5000 [Pa];
In the oxidation treatment, the treatment temperature is 125° C. or more and 250° C. or less,
In the oxidation treatment, the treatment time is from 1 second to 90 minutes,
The cuprous oxide and/or the composite oxide of cuprous oxide is polycrystalline,
In a region 5 nm deep from the surface of the film mainly composed of the oxidized cuprous oxide and/or composite oxide of cuprous oxide, the ratio of CuO and Cu(OH) ₂ determined from a peak area of X-ray photoelectron spectroscopy is 0.1% or more and less than 10% . forming a p-electrode on the substrate;
forming a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide on the p-electrode;
and a step of subjecting the film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide to an oxidation treatment,
In the oxidation treatment, the oxygen partial pressure is 300 [Pa] or more and 2000 [Pa] or less,
In the oxidation treatment, the treatment temperature is 180° C. or more and 250° C. or less,
In the oxidation treatment, the treatment time is 5 seconds or more and 45 minutes or less,
The cuprous oxide and/or the composite oxide of cuprous oxide is polycrystalline,
In a region 5 nm deep from the surface of the film mainly composed of the oxidized cuprous oxide and/or composite oxide of cuprous oxide, the ratio of CuO and Cu(OH) ₂ determined from a peak area of X-ray photoelectron spectroscopy is 0.1% or more and less than 10% . forming a p-electrode on the substrate;
forming a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide on the p-electrode;
and a step of subjecting the film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide to an oxidation treatment,
In the oxidation treatment, the oxygen partial pressure is 500 [Pa] or more and 2000 [Pa] or less,
In the oxidation treatment, the treatment temperature is 180° C. or more and 250° C. or less,
In the oxidation treatment, the treatment time is 1 minute or more and 30 minutes or less,
The cuprous oxide and/or the composite oxide of cuprous oxide is polycrystalline,
In a region 5 nm deep from the surface of the film mainly composed of the oxidized cuprous oxide and/or composite oxide of cuprous oxide, the ratio of CuO and Cu(OH) ₂ determined from a peak area of X-ray photoelectron spectroscopy is 0.1% or more and less than 10% . forming a p-electrode on the substrate;
forming a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide on the p-electrode;
and a step of subjecting the film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide to an oxidation treatment,
In the oxidation treatment, the oxygen partial pressure is 100 [Pa] or more and 2000 [Pa] or less,
In the oxidation treatment, the treatment temperature is 250° C. or more and 300° C. or less,
In the oxidation treatment, the treatment time is 1 minute or more and less than 10 minutes,
The cuprous oxide and/or the composite oxide of cuprous oxide is polycrystalline,
In a region 5 nm deep from the surface of the film mainly composed of the oxidized cuprous oxide and/or composite oxide of cuprous oxide, the ratio of CuO and Cu(OH) ₂ determined from a peak area of X-ray photoelectron spectroscopy is 0.1% or more and less than 10% . forming a p-electrode on the substrate;
forming a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide on the p-electrode;
and a step of subjecting the film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide to an oxidation treatment,
In the oxidation treatment, the oxygen partial pressure is equal to or greater than 1000 [Pa] and less than 5000 [Pa];
In the oxidation treatment, the treatment temperature is equal to or higher than 200 [°C] and lower than 250 [°C];
In the oxidation treatment, the treatment time is 1 minute or more and less than 10 minutes,
The cuprous oxide and/or the composite oxide of cuprous oxide is polycrystalline,
In a region 5 nm deep from the surface of the film mainly composed of the oxidized cuprous oxide and/or composite oxide of cuprous oxide, the ratio of CuO and Cu(OH) ₂ determined from a peak area of X-ray photoelectron spectroscopy is 0.1% or more and less than 10% . forming a p-electrode on the substrate;
forming a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide on the p-electrode;
and a step of subjecting the film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide to an oxidation treatment,
In the oxidation treatment, the oxygen partial pressure is equal to or greater than 1000 [Pa] and less than 5000 [Pa];
In the oxidation treatment, the treatment temperature is 100 [° C.] or more and 250 [° C.] or less,
In the oxidation treatment, the treatment time is 10 minutes or more and 60 minutes or less,
The cuprous oxide and/or the composite oxide of cuprous oxide is polycrystalline,
In a region 5 nm deep from the surface of the film mainly composed of the oxidized cuprous oxide and/or composite oxide of cuprous oxide, the ratio of CuO and Cu(OH) ₂ determined from a peak area of X-ray photoelectron spectroscopy is 0.1% or more and less than 10% . forming a p-electrode on the substrate;
forming a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide on the p-electrode;
and a step of subjecting the film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide to an oxidation treatment,
In the oxidation treatment, the oxygen partial pressure is equal to or greater than 500 [Pa] and less than 5000 [Pa];
In the oxidation treatment, the treatment temperature is 100 [° C.] or more and 175 [° C.] or less,
In the oxidation treatment, the treatment time is 10 minutes or more and 30 minutes or less,
The cuprous oxide and/or the composite oxide of cuprous oxide is polycrystalline,
In a region 5 nm deep from the surface of the film mainly composed of the oxidized cuprous oxide and/or composite oxide of cuprous oxide, the ratio of CuO and Cu(OH) ₂ determined from a peak area of X-ray photoelectron spectroscopy is 0.1% or more and less than 10% . forming a p-electrode on the substrate;
forming a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide on the p-electrode;
and a step of subjecting the film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide to an oxidation treatment,
In the oxidation treatment, the oxygen partial pressure is 300 [Pa] or more and 1500 [Pa] or less,
In the oxidation treatment, the treatment temperature is 150 [°C] or more and 200 [°C] or less,
In the oxidation treatment, the treatment time is 10 minutes or more and 30 minutes or less,
The cuprous oxide and/or the composite oxide of cuprous oxide is polycrystalline,
In a region 5 nm deep from the surface of the film mainly composed of the oxidized cuprous oxide and/or composite oxide of cuprous oxide, the ratio of CuO and Cu(OH) ₂ determined from a peak area of X-ray photoelectron spectroscopy is 0.1% or more and less than 10% . forming a p-electrode on the substrate;
forming a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide on the p-electrode;
and a step of subjecting the film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide to an oxidation treatment,
In the oxidation treatment, the oxygen partial pressure is equal to or greater than 500 [Pa] and less than 5000 [Pa];
In the oxidation treatment, the treatment temperature is 150 [°C] or more and 200 [°C] or less,
In the oxidation treatment, the treatment time is 10 minutes or more and 20 minutes or less,
The cuprous oxide and/or the composite oxide of cuprous oxide is polycrystalline,
In a region 5 nm deep from the surface of the film mainly composed of the oxidized cuprous oxide and/or composite oxide of cuprous oxide, the ratio of CuO and Cu(OH) ₂ determined from a peak area of X-ray photoelectron spectroscopy is 0.1% or more and less than 10% . forming a p-electrode on the substrate;
forming a film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide on the p-electrode;
and a step of subjecting the film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide to an oxidation treatment,
In the oxidation treatment, the oxygen partial pressure is equal to or greater than 1000 [Pa] and less than 5000 [Pa];
In the oxidation treatment, the treatment temperature is 100 [° C.] or more and 150 [° C.] or less,
In the oxidation treatment, the treatment time is more than 60 minutes and not more than 90 minutes,
The cuprous oxide and/or the composite oxide of cuprous oxide is polycrystalline,
In a region 5 nm deep from the surface of the film mainly composed of the oxidized cuprous oxide and/or composite oxide of cuprous oxide, the ratio of CuO and Cu(OH) ₂ determined from a peak area of X-ray photoelectron spectroscopy is 0.1% or more and less than 10% . The method for manufacturing a solar cell according to any one of claims 1 to 10, wherein the oxidation treatment oxidizes only a region from the surface of the film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide to a depth of 1 atomic layer or more and 1 nm or less. The method for manufacturing a solar cell according to any one of claims 1 to 10, further comprising a step of forming an n-type layer on the film mainly composed of the oxidized cuprous oxide and/or composite oxide of cuprous oxide. forming an n-type layer on the oxidized film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide;
The method for producing a solar cell according to claim 1 , further comprising the step of forming an n-electrode on the n-type layer. The film mainly composed of cuprous oxide and/or a composite oxide of cuprous oxide is formed by sputtering,
The sputtering is performed by heating the substrate having the p-electrode 2 thereon to a temperature of 300° C. or higher and 600° C. or lower.
The oxygen partial pressure of the sputtering is in the range of 0.01 [Pa] to 4.8 [Pa] and in the range of 0.02 μm/min to 20 μm/min,
11. The method for manufacturing a solar cell according to claim 1, wherein the oxygen partial pressure satisfies 0.55xd [Pa] or more and 1.00xd [Pa] or less, where d is a deposition rate of the sputtering. The method for manufacturing a solar cell according to claim 14, wherein the heating temperature of the sputtering is 350°C or higher and 500°C or lower.