Solar cell, multi-junction solar cell, solar cell module, and solar power generation system

Abstract

The solar cell of the embodiment has a first transparent electrode, a p-type light absorbing layer provided on the first transparent electrode, a first n-type layer provided on the p-type light absorbing layer, a second n-type layer provided on the first n-type layer, a second transparent electrode provided on the second n-type layer, and an antireflection layer on the second transparent electrode. The refractive index of the second n-type layer is higher than the refractive index of the first n-type layer. The second n-type layer contains a metal oxide containing titanium.

Description

Citation of relevant applications

[0001] This application is based on Japanese Patent Application 2025-009581 (filed on January 23, 2025), which enjoys priority. The entire contents of that application are incorporated herein by reference. Technical Field

[0002] This invention relates to solar cells, multijunction solar cells, solar cell modules, and solar power generation systems. Background Technology

[0003] One type of new solar cell uses cuprous oxide (Cu2O) in its light-absorbing layer. Cu2O is a wide-bandgap semiconductor. Because Cu2O is a safe and inexpensive material composed of copper and oxygen, which are abundant on Earth, it is expected to enable high-efficiency and low-cost solar cells. Summary of the Invention

[0004] The implementation provides high-performance solar cells, multi-junction solar cells, solar cell modules, and solar power generation systems.

[0005] The solar cell of this embodiment includes a first transparent electrode, a p-type light-absorbing layer disposed on the first transparent electrode, a first n-type layer disposed on the p-type light-absorbing layer, a second n-type layer disposed on the first n-type layer, a second transparent electrode disposed on the second n-type layer, and an anti-reflective layer disposed on the second transparent electrode. The refractive index of the second n-type layer is higher than that of the first n-type layer. The second n-type layer contains a metal oxide comprising titanium.

[0006] Based on the above configuration, an excellent solar cell can be provided. Attached Figure Description

[0007] Figure 1 This is a schematic cross-sectional view of the solar cell according to the embodiment.

[0008] Figure 2 This is a diagram illustrating the analysis points of a solar cell in an embodiment.

[0009] Figure 3 This is a schematic cross-sectional view of a multi-junction solar cell according to an embodiment.

[0010] Figure 4 This is a three-dimensional schematic diagram of the solar cell module according to the implementation method.

[0011] Figure 5 This is a three-dimensional schematic diagram of the solar cell module according to the implementation method.

[0012] Figure 6 This is a schematic diagram of the solar power generation system according to the implementation method.

[0013] Figure 7 This is a schematic diagram of the vehicle used in the implementation method.

[0014] Figure 8 This is a schematic diagram of the drone used in the implementation method.

[0015] Figure 9 This is a table relating to the embodiments.

[0016] Figure 10 This is a table relating to the embodiments.

[0017] Figure 11 This is a table relating to the embodiments.

[0018] Figure 12 This is a table relating to the embodiments.

[0019] Figure 13 This is a table relating to the embodiments.

[0020] Figure 14 This is a table relating to the embodiments.

[0021] Explanation of symbols 1: Substrate 2: First transparent electrode 2A: First Intermediate Layer 3: p-type light absorption layer 4: Type 1n layer 5: Type 2n layer 6: Second transparent electrode 7: Anti-reflective layer 100: Solar cells 200: Multijunction Solar Cell 201: Second solar cell 300: Solar cell module 301: First Solar Cell Module 302: Second solar cell module 310: Solar cell module 400: Solar power generation system 401: Solar cell module 402: Converter 403: Storage battery 404: Overload 500: Vehicles 501: Vehicle body 502: Solar cell module 503: Power conversion device 504: Storage battery 505: Motor 506: Wheels 600: Drone 601: Solar cell module 602: Body Skeleton 603: Motor 604: Rotary Wing 605: Control Unit Detailed Implementation

[0022] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0023] Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the values ​​represent physical properties at 25°C and 1 atmosphere (atmosphere). Furthermore, "average" refers to the arithmetic mean. "Each concentration" refers to the average concentration of the target region or layer. Each layer contains specific elements, such as elements confirmed to be present by SIMS (Secondary Ion Mass Spectrometry), and does not contain specific elements, such as elements that cannot be confirmed to be present by SIMS.

[0024] In the instruction manual, " / " represents the division symbol. However, the " / " in "and / or" means "or". The instruction manual also uses "·" and "". The dot (.) indicates the multiplication symbol. In the instruction manual, the period (.) represents the decimal point.

[0025] The thickness and structure of the components described in the specification can be obtained, for example, from images of the cross-section obtained using a scanning electron microscope (SEM), a transmission electron microscope (TEM), or a high-angle annular dark field scanning transmission electron microscope (HAADF-STEM). Furthermore, the boundaries of the components described in the specification can be determined from images obtained by a scanning electron microscope or a transmission electron microscope, from measurements taken by a scanning electron microscope with energy dispersive X-ray spectroscopy (SEM-EDS) or a transmission electron microscope with energy dispersive X-ray spectroscopy (TEM-EDX), or from secondary ion mass analysis. Furthermore, the composition of the components described in the specification can be determined using secondary ion mass analysis, inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy with energy-dispersive X-ray spectrometry (EDX-SEM), or transmission electron microscopy with EDM. Additionally, the crystallinity of the components described in the specification can be evaluated, for example, by images obtained through X-ray diffraction (XRD), electron backscatter diffraction (EBSD), or high-angle annular dark-field scanning transmission electron microscopy, scanning electron microscopy, or transmission electron microscopy. The materials contained in the components described in the specification (crystal defects, bonding states, etc.) can be evaluated using high-angle annular dark-field scanning transmission electron microscopy, photoluminescence (PL), or X-ray photoelectron spectrophotometry (XPS). These analytical methods are examples and do not negate the specific analytical methods described in the specification.

[0026] (First Embodiment) The first embodiment relates to a solar cell. Figure 1 A schematic cross-sectional view of the solar cell 100 according to the first embodiment is shown. Figure 1The solar cell 100 shown has a substrate 1, a first transparent electrode 2, a p-type light-absorbing layer 3, a first n-type layer 4, a second n-type layer 5, a second transparent electrode 6, and an anti-reflection layer 7. The solar cell 100 preferably receives light from the side of the anti-reflection layer 7.

[0027] When the first transparent electrode 2 and the second transparent electrode 6 are made of transmissive electrodes, the solar cell 100 of the embodiment is a transmissive solar cell with high transmittance of light in the wavelength band of 700 nm or more and 1200 nm or less.

[0028] In the case of a transmission-type solar cell that uses transmission-type electrodes for the first transparent electrode 2 and the second transparent electrode 6, the solar cell 100 of the embodiment is preferably used on the top cell side (light incident side).

[0029] Substrate 1 is a transparent substrate. Substrate 1 can be made of light-transmitting acrylic resin, polyimide, polycarbonate, polyethylene terephthalate (PET), polypropylene (PP), fluorine-based resins (polytetrafluoroethylene (PTFE), perfluoroethylene propylene copolymer (FEP), ethylene tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), perfluoroalkoxyalkane (PFA), etc.), polyarylate, polysulfone, polyethersulfone, or polyetherimide, or other organic substrates, or inorganic substrates such as soda-lime glass, white glass, chemically strengthened glass, or quartz. Substrate 1 can also be made by stacking the substrates listed above.

[0030] As substrate 1, soda-lime glass, white glass, chemically strengthened glass or quartz are preferred, and soda-lime glass, white glass or quartz are more preferred.

[0031] A first transparent electrode 2 is disposed on a substrate 1, and the first transparent electrode 2 is a planar conductive film. The first transparent electrode 2 is a conductive layer with light transmittance. The first transparent electrode 2 preferably comprises one or more oxide transparent conductive films. As an oxide transparent conductive film, semiconductor conductive films such as 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) can be used, and there is no particular limitation. The oxide transparent conductive film can also be a stacked film having multiple films. As a dopant in films such as tin oxide, there is no particular limitation as long as it is selected from one or more elements chosen from the group consisting of In, Si, Ge, Ti, Cu, Sb, Nb, Ta, W, Mo, F, and Cl. The first transparent electrode 2 preferably comprises 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, and Cl. In the doped tin oxide film, the element selected from the group consisting of In, Si, Ge, Ti, Cu, Sb, Nb, Ta, W, Mo, F, and Cl preferably comprises 10 atomic% or less relative to the tin contained in the tin oxide film. The first transparent electrode 2 can be a laminated film obtained by stacking an oxide transparent conductive film and a metal film. The metal (including alloys) contained in the metal film is not particularly limited to Mo, Au, Cu, Ag, Al, Ta, or W. Furthermore, the first transparent electrode 2 preferably includes dot-shaped, line-shaped, or mesh-shaped electrodes (selected from one or more of the group consisting of metals, alloys, graphene, conductive nitrides, and conductive oxides) between the oxide transparent conductive film and the substrate 1. The dot-shaped, line-shaped, or mesh-shaped metal preferably has an aperture ratio of 50% or more relative to the oxide transparent conductive film. The dot-shaped, line-shaped, or mesh-shaped metal is Mo, Au, Cu, Ag, Al, Ta, or W, etc., and is not particularly limited. When a metal film is used in the first transparent electrode 2, from the viewpoint of transmissivity, a film thickness of about 5 nm or less is preferably set. When a line-shaped or mesh-shaped metal film is used, since transmissivity is ensured by the openings, the film thickness of the metal film is not limited thereto.

[0032] Specific examples of the first transparent electrode 2 include a transparent electrode made of an ITO film, and a transparent electrode of a laminate of an ITO film and a doped tin oxide film.

[0033] The thickness of the first transparent electrode 2 is preferably 50 nm or more and 500 nm or less, more preferably 50 nm or more and 300 nm or less, and even more preferably 75 nm or more and 200 nm or less.

[0034] The solar cell 100 may also include an intermediate layer containing a low-refractive-index insulating layer such as SiO2 or MgF2 between the substrate 1 and the first transparent electrode 2.

[0035] The p-type light-absorbing layer 3 is an overall p-type semiconductor layer. The p-type light-absorbing layer 3 is disposed on the first transparent electrode 2. Preferably, the p-type light-absorbing layer 3 is in direct contact with the first transparent electrode 2. The p-type light-absorbing layer 3 is disposed between the first transparent electrode 2 and the 1n-type layer 4. The p-type light-absorbing layer 3 in direct contact with the 1n-type layer 4 is preferably pn-bonded to the 1n-type layer 4. The p-type light-absorbing layer 3 is preferably a compound semiconductor layer. The p-type light-absorbing layer 3 is preferably a semiconductor layer containing a compound with a chalcopyrite structure, such as CGS or CIGS, or a semiconductor layer containing a compound with a cuprous oxide structure, such as cuprous oxide. The p-type light-absorbing layer 3 is preferably based on a cuprous oxide compound. The cuprous oxide compound preferably has a cuprous oxide structure. Hereinafter, a solar cell using a compound containing a cuprous oxide compound in the p-type light-absorbing layer 3 will be described as an example. In the case of a solar cell using other compounds in the p-type light-absorbing layer 3, it is preferable to adopt a configuration suitable for the solar cell 100 of the first embodiment and the various compounds.

[0036] The p-type light-absorbing layer 3 is preferably a semiconductor layer containing a cuprous oxide compound. The p-type light-absorbing layer 3 is preferably a polycrystalline cuprous oxide compound. In the p-type light-absorbing layer 3, as part of the impurities, one or more cuprous oxide impurities selected from the group consisting of copper (Cu), copper oxide (CuO) and copper hydroxide (Cu(OH)2) may also be included in trace amounts.

[0037] When all elements except oxygen contained in the p-type light-absorbing layer 3 are set to 100 [atomic%], the copper element contained in the p-type light-absorbing layer 3 is preferably 90 [atomic%] or more and less than 100 [atomic%], preferably 95 [atomic%] or more and less than 100 [atomic%], more preferably 98 [atomic%] or less and less than 100 [atomic%], and even more preferably 99 [atomic%] or more and less than 100 [atomic%].

[0038] When all elements except oxygen contained in the p-type light-absorbing layer 3 are set to 100 [atomic%], the copper element contained in the p-type light-absorbing layer 3 is preferably 90 [atomic%] or more and 99.9 [atomic%] or less, preferably 95.0 [atomic%] or more and 99.9 [atomic%] or less, more preferably 98 [atomic%] or less and 99.9 [atomic%] or less, and even more preferably 99.0 [atomic%] or more and 99.9 [atomic%] or less.

[0039] The cuprous oxide compound contains copper and oxygen, and optionally further contains the element represented by M1. The element represented by M1 is preferably one or more elements selected from the group consisting of Cl, F, Br, I, Sn, Sb, Ag, Li, Na, K, Cs, Rb, Al, In, Zn, Mg, Ga, Si, Ge, N, P, B, Ti, Hf, Zr and Ca.

[0040] If the number of copper atoms is set to 1, the number of oxygen atoms in the cuprous oxide compound is preferably 0.48 or more and 0.56 or less. If there is more oxygen relative to copper, the proportion of copper oxide in the cuprous oxide compound becomes higher, resulting in a narrower band gap and reduced light transmittance of the p-type light absorption layer 3, which is not preferred. If there is less oxygen relative to copper, the proportion of copper in the cuprous oxide compound becomes higher, resulting in reduced light transmittance, which is also not preferred. Furthermore, when the oxygen-to-copper ratio does not meet the above range, the cuprous oxide compound becomes difficult to have a cuprite-type structure.

[0041] Preferably, 95% to 100% of the p-type light-absorbing layer 3 is a cuprous oxide compound, more preferably 98% to 100% of the p-type light-absorbing layer 3 is a cuprous oxide compound, and even more preferably 99% to 100% of the p-type light-absorbing layer 3 is a cuprous oxide compound. 100% of the p-type light-absorbing layer 3 can be composed of a cuprous oxide compound.

[0042] If the p-type light-absorbing layer 3 contains few heterogeneous phases and has good crystallinity, the light transmittance of the p-type light-absorbing layer 3 will be higher, which is therefore preferable. The band gap of the p-type light-absorbing layer 3 can be adjusted by including elements other than Cu and O in the p-type light-absorbing layer 3. The band gap of the p-type light-absorbing layer 3 is preferably 2.0 eV or higher and 2.2 eV or lower. If the band gap is within this range, in a multi-junction solar cell where Si is used in the light-absorbing layer for the bottom unit and the solar cell of the embodiment is used in the top unit, sunlight can be efficiently utilized in both the top and bottom units. The p-type light-absorbing layer 3 preferably contains Sn and / or Sb. The Sn or Sb in the p-type light-absorbing layer 3 can be Sn or Sb added to the p-type light-absorbing layer 3, or it can originate from the first transparent electrode 2. The Ga contained in the p-type light-absorbing layer 3 is not contained in the raw material for forming the p-type light-absorbing layer 3, but is Ga diffused from the Ga contained in the first n-type layer 4 into the p-type light-absorbing layer 3. When other elements are used during the formation of the 1n-type layer 4, these elements sometimes diffuse into the p-type light-absorbing layer 3.

[0043] The composition ratio of the p-type light-absorbing layer 3 described above is the overall composition ratio of the p-type light-absorbing layer 3. Furthermore, the compound composition ratio of the p-type light-absorbing layer 3 is preferably satisfied overall within the p-type light-absorbing layer 3.

[0044] The p-type light absorption layer 3 preferably has a p+ type (p-positive type) region on the side of the first transparent electrode 2.

[0045] The p-type light absorption layer 3 preferably has a p-type (p-negative) region on the side of the n-type layer 4.

[0046] The p-type light absorption layer 3 preferably has a p-type (p-negative) region on the side of the 1n-type layer 4 and a p+ type (p-positive) region on the side of the 1st transparent electrode 2.

[0047] The thickness of the p-type light-absorbing layer 3 is preferably 500 nm or more and 10 μm or less, more preferably 750 nm or more and 7.0 μm or less. The p-type light-absorbing layer 3 is preferably the thickest layer among the layers contained between the first transparent electrode 2 and the second transparent electrode 6. The p-type light-absorbing layer 3 is preferably the thickest semiconductor layer contained in the solar cell 100.

[0048] Preferably, the surface of the p-type light-absorbing layer 3 on the side of the first n-type layer 4 has fine irregularities. The average deviation of the surface roughness on the side of the first n-type layer 4 of the p-type light-absorbing layer 3 is preferably 50 nm or more, more preferably 50 nm or more and 500 nm or less, and even more preferably 55 nm or more and 300 nm or less.

[0049] The p-type light-absorbing layer 3 is preferably formed by sputtering, for example. Specifically, it is preferable to heat the component on which the first transparent electrode 2 is formed on the substrate 1 to 300°C or higher and 1000°C or lower, and to perform the deposition at a rate of 0.02 μm / min or higher and 20 μm / min or lower, within a range where the oxygen partial pressure is 0.01 Pa or higher and 4.8 Pa or lower. From the viewpoint of forming a polycrystalline film with high transmittance and large particle size, when the deposition rate is set to d, the oxygen partial pressure is more preferably 0.20 × d Pa or higher and 1.00 × d Pa or lower (for example, in the case of high-temperature sputtering, it is preferably 0.20 × d Pa or higher and 0.50 × d Pa or lower, and in the case of low-temperature sputtering, it is preferably 0.55 × d Pa or higher and 1.00 × d Pa or lower). Furthermore, the heating temperature is more preferably higher than 550°C and lower than 850°C. The element M1 can be added to the film.

[0050] By forming a p-type light-absorbing layer 3 using the method described above, a large-particle-size cuprous oxide compound is formed. Preferably, the p-type light-absorbing layer 3 comprises crystals of a cuprous oxide compound with a particle size at least five times the thickness of the p-type light-absorbing layer 3.

[0051] The first n-type layer 4 is an n-type semiconductor layer that is transmissive to visible light. The first n-type layer 4 is disposed between the p-type light-absorbing layer 3 and the second n-type layer 5. The first n-type layer 4 is preferably disposed on the p-type light-absorbing layer 3. The first n-type layer 4 is formed, for example, by the ALD method. The first n-type layer 4 is preferably primarily amorphous, but may also contain a portion of crystals.

[0052] The first n-type layer 4 is preferably an n-type layer in which the metal oxide containing titanium is not the main component. The first n-type layer preferably contains a compound (oxide) with Ga as the main component. The first n-type layer 4 preferably contains a compound (oxide) with Ga as the main component and a compound (oxide) with Zn as the main component.

[0053] The thickness of the first n-type layer 4 is typically 3 nm or more and 100 nm or less. If the thickness of the first n-type layer 4 is less than 3 nm, leakage current will occur due to poor coverage of the first n-type layer 4, which may sometimes degrade the characteristics. The film thickness is not limited to the above when the coverage is good. If the thickness of the first n-type layer 4 exceeds 50 nm, the characteristics may be degraded due to excessive high resistivity of the first n-type layer 4, or the short-circuit current may be reduced due to reduced transmittance. Therefore, the thickness of the first n-type layer 4 is more preferably 3 nm or more and 20 nm or less, and even more preferably 5 nm or more and 20 nm or less.

[0054] Of the metal elements contained in the 1n-type layer 4, titanium is preferably 0% or more and 10% or less, more preferably 0% or more and 5% or less, and even more preferably 0% or more and 1% or less.

[0055] The first n-type layer 4 can be a single layer or multiple layers. Preferably, the first n-type layer 4 contains a first layer comprising an oxide primarily composed of Ga and, optionally, a second layer comprising an oxide primarily composed of Zn. Preferably, the first layer is disposed on the p-type light-absorbing layer 3 side, and the second layer is disposed on the second n-type layer side. Preferably, the first layer is in direct contact with the p-type light-absorbing layer 3, and the second layer is in direct contact with the second n-type layer 5. An intermediate layer may also exist between the first and second layers. Alternatively, there may be no interface between the first and second layers, and the composition may change obliquely.

[0056] The conduction band bottom is preferably continuous from the p-type light absorption layer 3 to the second layer of the n-type layer 4.

[0057] Compounds with Ga as the main component preferably contain Ga₂O₃ or oxides containing the element represented by M₂ and Ga. Oxides with Ga as the main component are preferably those with an average composition of Ga. h1 M2 i1 O j1 The oxide represented by M2. h1, i1, and j1 preferably satisfy 1.8 ≤ h1 ≤ 2.1, 0.0 ≤ i1 ≤ 0.2, and 2.9 ≤ j1 ≤ 3.1. It is an oxide containing the element represented by M2 and Ga. M2 is preferably selected from one or more elements chosen 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, Ca, Ce, La, Pr, and Nd. The first layer preferably contains an average composition of 90% to 100% Ga. h1 M2 i1 O j1 The oxide is represented.

[0058] The compound (oxide) with Zn as the main component is preferably zinc oxide doped with one or more zinc oxides selected from the group consisting of Sn, Sb, Hf, Zr, Si, Al, and Mg. The compound (oxide) with Zn as the main component is more preferably zinc oxide doped with Sn. The second layer preferably contains 90% to 100% of a compound with Zn as the main component.

[0059] From the viewpoint of improving the light transmittance between the first and second layers, the refractive index difference between the first and second layers is preferably small. The refractive index difference between the first and second layers is preferably 0.1 or less, more preferably 0.05 or less, and even more preferably 0.03 or less. The thickness and refractive index of each layer contained in the solar cell 100 can be determined, for example, by spectroscopic ellipsometric analysis. All refractive indices described in this specification are values ​​obtained from measurements taken at a wavelength of 700 nm.

[0060] The second n-type layer 5 is an n-type semiconductor layer that is transmissive to visible light. The second n-type layer 5 is disposed between the first n-type layer 4 and the second transparent electrode 6. The second n-type layer 5 is formed, for example, by the ALD method. The second n-type layer 5 is preferably primarily amorphous, but may also contain a portion of crystals. Preferably, by including the second n-type layer 5 in addition to the first n-type layer 4, the transmittance of the solar cell 100 in the wavelength band of 600 nm and above to 1100 nm and below is improved.

[0061] The thickness of the second-n type layer 5 is preferably 1 nm or more and 50 nm or less, more preferably 5 nm or more and 30 nm or less, and even more preferably 10 nm or more and 30 nm or less. If the thickness of the second-n type layer 5 is 100 nm or more, the light transmittance and short-circuit current density of the solar cell 100 may decrease. Therefore, the thickness of the second-n type layer 5 is preferably 50 nm or less.

[0062] The second-n type layer 5 preferably contains a titanium-containing metal oxide. The second-n type layer 5 preferably has a titanium-containing metal oxide as its main component. Preferably, 50% to 100% of the second-n type layer 5 is a titanium-containing metal oxide, more preferably, 80% to 100% of the second-n type layer 5 is a titanium-containing metal oxide, and even more preferably, 95% to 100% of the second-n type layer 5 is a titanium-containing metal oxide.

[0063] Of the metallic elements contained in the 2n-type layer 5, titanium is preferably 45 atomic percent or more and 100 atomic percent or less, more preferably 80 atomic percent or more and 100 atomic percent or less. Of the metallic elements contained in the 1n-type layer 4, titanium is preferably 0% or more and 10% or less, more preferably 0% or more and 5% or less, and even more preferably 0% or more and 1% or less.

[0064] Since the absorption band wavelength of the titanium-containing metal oxide is mainly below 400 nm, it is shorter than the absorption band wavelength of the power generation layer (p-type light absorption layer 3) of the solar cell 100 and shorter than the absorption band wavelength of the Si solar cell. Therefore, setting the second n-type layer 5 closer to the light incident side than the p-type light absorption layer 3 can also improve the conversion efficiency.

[0065] The titanium-containing metal oxide contained in the 2n-type layer 5 is preferably one or more selected from the group consisting of titanium dioxide, doped titanium dioxide, and doped strontium titanate. The dopant for the doped titanium dioxide and doped strontium titanate is preferably one or more selected from the group consisting of Nb, Ta, Mo, and W, more preferably Nb. The titanium dioxide is preferably anatase type. The strontium titanate is preferably cubic perovskite type.

[0066] The second-n type layer 5 can be a single layer or multiple layers. For example, a multi-layer second-n type layer 5 includes a TiO2 layer on the side of the first-n type layer 4 and a strontium titanate layer on the side of the second transparent electrode 6 with a refractive index higher than that of the TiO2 layer.

[0067] When the surface of the p-type light-absorbing layer 3 on the side of the first n-type layer 4 has fine irregularities, it is preferable that the surface of the second n-type layer 5 on the side of the second transparent electrode 6 also has fine irregularities due to the surface irregularities of the p-type light-absorbing layer 3. The average deviation of the surface roughness on the side of the second transparent electrode 6 of the second n-type layer 5 is preferably 50 nm or more, more preferably 50 nm or more and 500 nm or less, and even more preferably 55 nm or more and 300 nm or less. The fine irregularities of the second n-type layer 5 caused by the large particle size of the p-type light-absorbing layer 3 can suppress light reflection through the same function as the anti-reflection layer 7. It is preferable that the surface of the anti-reflection layer 7 also has the same fine irregularities.

[0068] From the viewpoint of suppressing reflection between the second n-type layer 5 and the second transparent electrode 6, the second n-type layer 5 is preferably in direct contact with the second transparent electrode 6.

[0069] From the viewpoint of suppressing reflection between the first n-type layer 4 and the second transparent electrode 6, the second n-type layer 5 is preferably in direct contact with the first n-type layer 4.

[0070] The conduction band bottom is preferably continuous from the p-type light absorption layer 3 to the 2n-type layer 5.

[0071] The second transparent electrode 6 is disposed between the 2n-type layer 5 and the anti-reflection layer 7. The second transparent electrode 6 is an electrode on the 2n-type layer 5 side that is transparent to visible light. The second transparent electrode 6 is preferably disposed on the 2n-type layer 5. For the second transparent electrode 6, an oxide transparent conductive film is preferably used. As the oxide transparent conductive film used in the second transparent electrode 6, it is preferably a semiconductor conductive film 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. As the dopant in the film such as tin oxide, it is not particularly limited as long as it is selected from the group consisting of In, Si, Ge, Ti, Cu, Sb, Nb, Ta, W, Mo, F, and Cl. In order to reduce the resistance of the oxide transparent conductive film, the second transparent electrode 6 may include a mesh or wire-shaped electrode. For the mesh or wire-shaped electrode, it is not particularly limited to Mo, Au, Cu, Ag, Al, Ta, or W. Graphene can also be used for the second transparent electrode 6. Graphene is preferably stacked with silver nanowires.

[0072] The thickness of the second transparent electrode 6 is determined by cross-sectional observation using an electron microscope or by a height difference measuring instrument.

[0073] The thickness of the second transparent electrode 6 is 30 nm or more and 2 μm or less, more preferably 30 nm or more and 100 nm or less, and even more preferably 30 nm or more and 70 nm or less.

[0074] The refractive index of the second transparent electrode 6 is preferably 1.6 or higher and 1.99 or lower, more preferably 1.6 or higher and 1.9 or lower, and even more preferably 1.6 or higher and 1.85 or lower.

[0075] The second transparent electrode 6 is preferably formed by, for example, ALD or sputtering.

[0076] The anti-reflective layer 7 is transparent to visible light. The anti-reflective layer 7 is disposed on the second transparent electrode 6. The anti-reflective layer 7 can be in direct contact with the second transparent electrode 6, or other layers can be sandwiched between the anti-reflective layer 7 and the second transparent electrode 6. From the viewpoint of increasing the amount of light incident on the power generation layer, i.e., the p-type light absorption layer 3, of the solar cell 100, the anti-reflective layer 7 is preferably disposed. Furthermore, by increasing the transmittance of light outside the absorption band of the p-type light absorption layer 3, when using a cell with a narrow bandgap light absorption layer, such as a Si solar cell, as the bottom unit of a multi-junction solar cell with the solar cell 100 as the top unit, the power generation of the bottom unit can be increased.

[0077] The antireflective layer 7 may comprise, for example, one or more inorganic and / or organic materials selected from the group consisting of SiO2, MgF2, MgO, Al2O3, etc. From the substrate 1 to the second transparent electrode 6, it is preferably a non-porous dense layer, but the antireflective layer 7 may be a dense layer or a porous layer. The antireflective layer 7 may also have regular or irregular protrusions.

[0078] The thickness of the anti-reflective layer 7 is not particularly limited, but typically it is above 70 nm and below 130 nm.

[0079] The refractive index of the antireflective layer 7 (the apparent refractive index of the porous antireflective layer 7 or the antireflective layer 7 with protrusions) is preferably 1.3 or more and 1.7 or less, more preferably 1.3 or more and 1.5 or less, and even more preferably 1.3 or more and 1.47 or less.

[0080] Next, the refractive index of the 2n-type layer 5, the refractive index of the 1n-type layer 4 as needed, and the refractive index of the second transparent electrode 6 will be explained. Preferably, the refractive index of the 2n-type layer 5 is higher than that of the 1n-type layer 4. The refractive index of the second transparent electrode 6 is close to that of the 1n-type layer 4, but by using the 2n-type layer 5, which has a higher refractive index than the 1n-type layer 4, light reflection between the 1n-type layer 4 and the second transparent electrode 6 is suppressed, thereby increasing light transmittance.

[0081] Therefore, based on the above viewpoint, the refractive index of the 2n-type layer 5 is preferably 2.0 or higher and 2.5 or lower, more preferably 2.1 or higher and 2.5 or lower, and even more preferably 2.2 or higher and 2.4 or lower.

[0082] Based on the above viewpoint, the refractive index (maximum and average value) of the 1n-type layer 4 is preferably 1.6 or more and 1.99 or less, more preferably 1.6 or more and 1.9 or less, and even more preferably 1.6 or more and 1.85 or less.

[0083] Based on the above viewpoint, the refractive index (refractive index of the second layer) on the side of the second type layer 5 of the first type layer 4 is preferably 1.6 or more and 1.99 or less, more preferably 1.6 or more and 1.9 or less, and even more preferably 1.6 or more and 1.85 or less.

[0084] Based on the above viewpoint, the refractive index of the 2n-type layer 5 is preferably 0.01 or more and 0.9 or less higher than the refractive index (maximum and average value) of the 1n-type layer 4, more preferably 0.2 or more and 0.9 or less higher, and even more preferably 0.35 or more and 0.8 or less higher.

[0085] Based on the above viewpoint, the refractive index of the 2n-type layer 5 is preferably 0.01 or more and 0.9 or less higher than the refractive index of the 2n-type layer 5 side of the 1n-type layer 4 (the refractive index of the second layer), more preferably 0.2 or more and 0.9 or less higher, and even more preferably 0.35 or more and 0.8 or less higher.

[0086] Furthermore, from the viewpoint of improving light transmittance, the refractive index between the first n-type layer 4 and the second transparent electrode 6 preferably satisfies a medium-large-medium relationship. That is, it is preferable that the refractive index of the second n-type layer 5 is higher than that of the second transparent electrode 6.

[0087] Furthermore, from the viewpoint of improving light transmittance, the refractive index between the 1n-type layer 4 and the anti-reflective layer 7 preferably satisfies a medium-large-medium-small relationship. That is, it is preferable that the refractive index of the 2n-type layer 5 is higher than that of the second transparent electrode 6, and the refractive index of the anti-reflective layer 7 is lower than that of the 1n-type layer 4, the 2n-type layer 5, and the second transparent electrode 6.

[0088] Based on the above viewpoint, the refractive index of the second transparent electrode 6 is preferably 1.6 or higher and 1.99 or lower, more preferably 1.6 or higher and 1.9 or lower, and even more preferably 1.6 or higher and 1.85 or lower.

[0089] Based on the above viewpoint, the refractive index of the second n-type layer 5 is preferably 0.01 or more and 0.9 or less higher than the refractive index of the second transparent electrode 6, more preferably 0.2 or more and 0.9 or less higher, and even more preferably 0.35 or more and 0.8 or less higher.

[0090] Furthermore, from the viewpoint of improving light transmittance, the refractive index and thickness of the 2n-type layer 5 preferably satisfy the following relationship. When the refractive index of the 2n-type layer 5 is set to n1 and the thickness of the 2n-type layer 5 is set to d1, n1 and d1 [nm] preferably satisfy 2 [nm]≤n1·d1 [nm]≤125 [nm], preferably satisfy 2 [nm]≤n1·d1 [nm]≤115 [nm], more preferably satisfy 20 [nm]≤n1·d1 [nm]≤100 [nm], and even more preferably satisfy 20 [nm]≤n1·d1 [nm]≤70 [nm].

[0091] From the viewpoint of improving the conversion efficiency of the solar cell 100, it is preferable to have high carrier concentrations in the 2n-type layer 5 and the 1n-type layer 4. Therefore, it is preferable to use the 1n-type layer 4 and the 2n-type layer 5 described above as the n-type layers of the solar cell 100.

[0092] Compositional analysis of the 2n-type layer 5, for example, through the analysis of... Figure 2The analysis points (A1 to A9) shown in the diagram are distributed at equal intervals as closely as possible to the point of no discrepancy. For example, they can be obtained by analysis using TEM-EDX (Transmission Electron Microscopy-Energy Dispersive X-ray Spectroscopy). Figure 2 This is a schematic diagram of the solar cell 100 as observed from the side of the second transparent electrode 6. In analyzing the composition of the solar cell 100, D1 is the length of the solar cell 100 in the width direction (long side direction), and D2 is the length of the solar cell 100 in the depth direction (short side direction). By magnifying the image at 2 million times using TEM, the composition can be determined by analyzing a 100 nm × 100 nm region encompassing the center of each analytical point. Furthermore, by using XPS to analyze the center of each analytical point along the thickness direction of the solar cell 100, the chemical bonding state can be evaluated, and the compounds of elements contained in each layer can be identified. Additionally, by observing the solar cell 100 from the side of the second transparent electrode 6 using a scanning electron microscope (SEM), the surface irregularities and the particle size of each layer can be analyzed.

[0093] (Second Implementation) The second embodiment relates to a multijunction solar cell. Figure 3 The diagram shows a cross-sectional concept of a multi-junction solar cell according to the second embodiment. Figure 3 The multi-junction solar cell 200 has a solar cell (first solar cell) 100 of the first embodiment and a second solar cell 201 on the light incident side. The band gap of the light-absorbing layer of the second solar cell 201 is smaller than the band gap of the p-type light-absorbing layer 3 of the solar cell 100 of the first embodiment. It should be noted that the multi-junction solar cell 200 of the embodiment also includes a solar cell obtained by joining three or more solar cells.

[0094] Since the band gap of the p-type light-absorbing layer (cuprous oxide) 3 of the first solar cell 100 in the second embodiment is approximately 2.0 eV or more and 2.2 eV or less, the band gap of the light-absorbing layer of the second solar cell 201 is preferably 1.0 eV or more and 1.6 eV or less. As the light-absorbing layer of the second solar cell 201, it is preferably selected from one of the following groups: compound semiconductor layers composed of CIGS and CdTe compounds with high In content, crystalline silicon, and perovskite compounds.

[0095] (Third implementation) The third embodiment relates to a solar cell module. Figure 4 The diagram shows a perspective view of the solar cell module 300 according to the third embodiment. Figure 4 The solar cell module 300 includes a first solar cell module 301 containing multiple solar cells 100 or a first solar cell module 301 containing multiple multi-junction solar cells 200. The solar cell module 300 can also be disposed on the light incident side of the solar cells that have been disposed.

[0096] Figure 5 The diagram shows a perspective view of the solar cell module 310 according to the third embodiment. The solar cell module 310 is a solar cell module (connected in series) formed by stacking a first solar cell module 301 containing a plurality of solar cells 100 and a second solar cell module 302. The first solar cell module 301 is the light incident side. For the second solar cell module 302, a second solar cell 201 is preferably used.

[0097] (Fourth implementation) The fourth embodiment relates to a solar power generation system. The solar cell module of the fourth embodiment can be used as a generator in the solar power generation system of the fourth embodiment. The solar power generation system of the embodiment is a system that uses a solar cell module to generate electricity; specifically, it includes a solar cell module for generating electricity, a mechanism for converting the generated electricity into power, and an energy storage mechanism for storing the generated electricity or a load for consuming the generated electricity. Figure 6 The diagram shows the configuration of a solar power generation system 400 according to an embodiment. Figure 6 The solar power generation system includes a solar cell module 401 (300), a converter 402, a battery 403, and a load 404. Either the battery 403 or the load 404 may be omitted. The load 404 may also be configured to utilize the electrical energy stored in the battery 403. The converter 402 is a device containing circuits or components that perform power conversion, such as voltage transformation or DC-AC conversion, including DC-DC converters, DC-AC converters, and AC-AC converters. The configuration of the converter 402 can be optimized based on the generated voltage, the configuration of the battery 403, or the load 404.

[0098] The solar cells in the solar cell module 401 generate electricity after receiving sunlight. This electrical energy is converted by the converter 402 and stored in the battery 403 or consumed by the load 404. Preferably, the solar cell module 401 is equipped with a solar tracking drive to ensure it always faces the sun, a concentrator to focus sunlight, or additional devices to improve power generation efficiency. The load 404 can be an electrolysis device used for water electrolysis, CO2 electrolysis, ammonia electrolysis, ammonia synthesis, etc.

[0099] The solar power generation system 400 is preferably used in immovable properties such as residences, commercial facilities, or factories, or in movable properties such as vehicles, aircraft, or electronic equipment. By using solar cells with excellent conversion efficiency in the implementation method in solar cell modules, an increase in power generation can be expected.

[0100] As an example of the use of the solar power generation system 400, a vehicle is shown. Figure 7 The diagram shows vehicle 500. Figure 7 The vehicle 500 includes a body 501, a solar cell module 502, a power conversion device 503, a battery 504, a motor 505, and tires (wheels) 506. The electricity generated by the solar cell module 502, located on the upper part of the body 501, is converted by the power conversion device 503, and either charged by the battery 504 or consumed by loads such as the motor 505. Using the electricity supplied by the solar cell module 502 or the battery 504, the motor 505 rotates the tires (wheels) 506, thereby enabling the vehicle 500 to operate. The solar cell module 502 may not be multi-junction type, but may consist only of a first solar cell module, such as the solar cell 100 of the first embodiment. When using a transmissive solar cell module 502, it is preferable to use the solar cell module 502 as a power generation window on the side of the body 501, in addition to the upper part of the body 501.

[0101] As an example of the use of the solar power generation system 400, a drone (quadcopter) is shown. The drone uses a solar cell module 401. The configuration of the drone according to this embodiment is described below. Figure 8 A simplified explanation of the schematic diagram of the drone 600 is provided below. The drone 600 includes a solar cell module 601, a frame 602, a motor 603, a rotor 604, and a control unit 605. The solar cell module 601, motor 603, rotor 604, and control unit 605 are disposed within the frame 602. The control unit 605 converts or adjusts the power output from the solar cell module 601. The motor 603 uses the power output from the solar cell module 601 to rotate the rotor 604. By manufacturing the drone 600 of this configuration, which includes the solar cell module 601 with this embodiment, a drone capable of flying using more electricity can be provided.

[0102] The present invention will now be described in more detail based on embodiments, but the present invention is not limited to the following embodiments.

[0103] (Example A1) The simulation was conducted under the following conditions. The simulation was not an evaluation of power generation characteristics, but rather an evaluation of the light transmittance resulting from the use of the 2n-type layer 5; therefore, calculations were performed using a portion of the solar cell 100 (without power generation). For the simulation, the configuration consisted of a substrate 1, a first transparent electrode 2, a p-type light-absorbing layer 3, a 1n-type layer 4, a 2n-type layer 5, a second transparent electrode 6, and an anti-reflection layer 7 stacked sequentially. The transmittance and reflectance of light in the 600 nm to 1000 nm wavelength band were determined through the simulation. Example A1 was simulated under the conditions described below. The simulation conditions and the transmittance and reflectance of light in the 600 nm to 1000 nm wavelength band are shown below. Figure 9 The table shows the change in short-circuit current density of the solar cell 100 (ΔJsc [mA / cm²) calculated from the change in absorptivity in the p-type light-absorbing layer 3). 2 ]) also shown in Figure 9 The table shows the change in short-circuit current density (ΔJsc [mA / cm²) of the Si solar cell that generates electricity by transmitting light through the simulated component, along with the change in transmittance. 2 ]) also shown in Figure 9 In the table.

[0104] Substrate 1: White glass (thickness 0.5 mm, refractive index 1.53) The first transparent electrode 2 is made of ITO (In:Sn=80:20, film thickness 100 [nm], refractive index 1.89) on the substrate 1 side and ATO (Sn:Sb=98:2, film thickness 50 [nm], refractive index 1.95) on the p-type light-absorbing layer 3 side. p-type light-absorbing layer 3: Cu2O layer (thickness 6.0 [μm], refractive index 2.87) Layer 4 of type 1n: Ga2O3 (film thickness 10 nm, refractive index 1.81) is placed on the side of p-type light-absorbing layer 3 (layer 1), and ZnSnO (Zn:Sn=80:20) (film thickness 14 nm, refractive index 1.83) is placed on the side of type 2n layer 5 (layer 2). Type 2n layer 5: Anatase TiO2 layer (film thickness 20 nm, refractive index 2.30) Second transparent electrode 6: AZO (Zn:Al=19:1, film thickness 40 [nm], refractive index 1.78) Anti-reflective layer: MgF2 (film thickness 90 nm, refractive index 1.38) Simulation method: The transmittance and reflectance of the aforementioned solar cells were calculated by simulating them using e-ARC (a simulation software for thin-film solar cells, developed by the National Institute of Advanced Industrial Science and Technology, an independent administrative agency). The change in short-circuit current density of the Si solar cell relative to the transmittance of the comparison object was estimated.

[0105] (Examples A1-A5, Comparative Examples A1-A3) like Figure 9 As shown in the table, simulations were performed by varying the thickness of the 2n-type layer 5. The simulation conditions and the changes in light transmittance, reflectivity, short-circuit current density of the solar cell 100 in the 600-1000 nm wavelength band, and short-circuit current density of the Si solar cell are presented in the table. Figure 9 The table shows the relationship between the refractive index and thickness of the 2n-type layer 5. Figure 9 The table shows the values ​​of n1 (refractive index of the 2n-type layer 5) × d1 (thickness of the 2n-type layer 5). Figure 10 The table shows the change in short-circuit current density (ΔJsc) of the solar cell 100 in Example A1, which is based on the Jsc of Comparative Example A1. The change in short-circuit current density (ΔJsc) of the Si solar cell in Example A1 is also based on the Jsc of Comparative Example A1.

[0106] (See Example A1) On a white glass substrate 1, ITO (In:Sn=80:20, film thickness 150 nm) and ATO (Sn:Sb=98:2, film thickness 100 nm) are deposited on the upper surface of the side in contact with the glass to serve as the first transparent electrode 2 on the back side. The thickness of the white glass substrate 1 is 0.5 mm. A Cu2O layer with a thickness of 6 μm is formed on the ATO by sputtering in an oxygen and argon atmosphere to serve as a p-type light-absorbing layer 3. After the formation of the p-type light-absorbing layer 3, a Ga2O3 film with a thickness of 10 nm is formed to serve as the first layer of the 1n-type layer 4. A ZnSnO (Zn:Sn=80:20) film with a thickness of 14 nm is formed on the Ga2O3 to serve as the second layer of the 1n-type layer 4. Then, an AZO (ZnO:Al) film with a thickness of 40 nm is formed as the second transparent electrode 6, and a MgF2 layer with a thickness of 90 nm is further formed as the anti-reflection layer 7, thereby obtaining the solar cell 100. The solar cell of Example A1 has a configuration in which the second n-type layer 5 is formed in the configuration of Reference Example A1.

[0107] A solar simulator simulating an AM1.5G light source was used. Under this light source, the light intensity was adjusted using a Si element as a reference, with the intensity adjusted to 1 sun. Measurements were performed at atmospheric pressure, with the indoor temperature set to 25°C. Voltage was scanned, and the short-circuit current density Jsc (the value obtained by dividing the current by the element area) was measured. With the horizontal axis set to voltage and the vertical axis to current density, the point where the horizontal axis intersects the short-circuit voltage Voc is defined. On the measurement curve, the point where the voltage multiplied by the short-circuit current density reaches its maximum is set as Vmpp and Jmpp (maximum power point), respectively. The formula FF = (Vmpp) / (Jmpp) is used to calculate the maximum power. Jmpp) / (Voc) The fill factor is calculated using Jsc. Additionally, Eff. = Voc. Jsc The conversion efficiency is determined by FF. The transmittance of light in the wavelength band above 600 nm and below 1000 nm in Reference Example A1 can be measured. Power generation is also achieved by placing a second n-type layer 5 between the first n-type layer 4 and the second transparent electrode 6. In the following embodiments, the preferred refractive index and thickness of the second n-type layer 5 were studied by simulation.

[0108] According to Example A, by providing a TiO2 layer as a second n-type layer between the first n-type layer 4 and the second transparent electrode 6, the transmittance of the solar cell 100, the ΔJsc of the solar cell 100, and the ΔJsc of the Si solar cell are increased, while the reflectivity is decreased. There are also examples where using a ZnO layer or a Ga2O3 layer, which function as an n-type layer, as the second n-type layer 5 results in increased transmittance and decreased reflectivity. However, since the ΔJsc of the solar cell 100 decreases, it is preferable to use a preferred n-type layer such as TiO2 as the second n-type layer 5. If the thickness of the TiO2 layer is too thick, the ΔJsc of the solar cell 100 and the ΔJsc of the Si solar cell may sometimes decrease; therefore, the thickness of the second n-type layer 5 is preferably 50 nm or less.

[0109] (Example B, Examples B1-B3, Comparative Example B1) Example B used TiO2, SrTiO3, and Nb-doped TiO2 as the 2n-type layer 5, and performed the same simulation as in Example A. The simulation conditions and results are shown below. Figure 11 In the table.

[0110] According to Example B, the same effect was also confirmed in the solar cell 100, which used SrTiO3 and Nb-doped TiO2 as the second n-type layer 5 in addition to TiO2.

[0111] (Example C, Examples C1-C5, Comparative Example C5) Example C simulated a solar cell using only Ga2O3 in the 1n-type layer 4 and in contact with Ga2O3 in the 2n-type layer. The simulation conditions and results are shown below. Figure 12 The table shows the values ​​of n1 (refractive index of the 2n-type layer 5) × d1 (thickness of the 2n-type layer 5). Figure 13 In the table.

[0112] According to Example C, the same effect was confirmed even when the structure of the 1n-type layer 4 was different from that in Example A.

[0113] (Example D, Examples D1-D4, Comparative Examples D1-D2) Example D simulated the solar cell 100 with the second transparent electrode 6 configured as a single-layer oxide transparent conductive film and the solar cell 100 configured as a two-layer oxide transparent conductive film, in the same manner as in Example A. The simulation conditions and results are shown below. Figure 14 In the table, the ITO of the second transparent electrode 6 in Examples D3-D4 and Comparative Example D2 is disposed on the side of the second n-type layer 5.

[0114] According to Example D, the same effect was confirmed even when the configuration of the second transparent electrode 6 differed from that in Example A.

[0115] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments. During implementation, the constituent elements can be modified and embodied without departing from its spirit. Furthermore, various inventions can be formed through suitable combinations of the multiple constituent elements disclosed in the above embodiments. For example, constituent elements from different embodiments can be appropriately combined as in the variations.

[0116] Some elements in the instruction manual are represented only by element symbols.

[0117] The technical solutions for the implementation methods are described below.

[0118] Technical Solution 1 A solar cell having: First transparent electrode, The p-type light-absorbing layer disposed on the first transparent electrode mentioned above, The first n-type layer disposed on the above-mentioned p-type light-absorbing layer, The 2n-type layer disposed on the aforementioned 1n-type layer, The second transparent electrode disposed on the aforementioned type 2n layer, and The anti-reflective layer on the aforementioned second transparent electrode, The refractive index of the 2n-type layer is higher than that of the 1n-type layer. The aforementioned type 2n layer contains a metal oxide comprising titanium.

[0119] Technical Solution 2 According to the solar cell of technical solution 1, 50% to 100% of the second n-type layer is a titanium-containing metal oxide.

[0120] Technical Solution 3 According to the solar cell of technical solution 1 or 2, the aforementioned titanium-containing metal oxide comprises one or more selected from the group consisting of titanium dioxide, doped titanium dioxide, and doped strontium titanate.

[0121] Technical Solution 4 According to any one of technical solutions 1 to 3, the solar cell comprising titanium includes one or more metal oxides selected from the group consisting of titanium dioxide, doped titanium dioxide, and doped strontium titanate. The dopant of the aforementioned doped titanium dioxide and doped strontium titanate is selected from one or more of the group consisting of Nb, Ta, Mo and W.

[0122] Technical Solution 5 According to the solar cell described in any of technical solutions 1 to 4, among the metal elements contained in the aforementioned type 1n layer, titanium is 0% or more and 10% or less. Of the metallic elements contained in the aforementioned type 2n layer, titanium is 45% or more and 100% or less.

[0123] Technical Solution 6 According to any one of the technical solutions 1 to 5, the thickness of the aforementioned second-n type layer is more than 1 [nm] and less than 50 [nm].

[0124] Technical Solution 7 According to any one of technical solutions 1 to 6, the refractive index of the second n-type layer is higher than the refractive index of the second transparent electrode.

[0125] Technical Solution 8 According to any one of technical solutions 1 to 7, the refractive index of the aforementioned 2n-type layer is set to n1. When the thickness of the aforementioned type 2n layer is set to d1 [nm] n1 and d1 satisfy 2[nm]≤n1·d1[nm]≤125[nm].

[0126] Technical Solution 9 According to any one of technical solutions 1 to 8, in the solar cell, the refractive index of the second n-type layer is 0.01 or higher and 0.9 or lower than the refractive index of the first n-type layer. The refractive index of the second n-type layer is 0.01 or more and 0.9 or less higher than the refractive index of the second transparent electrode.

[0127] Technical Solution 10 According to any one of the technical solutions 1 to 9, the solar cell wherein the second n-type layer is in direct contact with the first n-type layer and the second transparent electrode.

[0128] Technical Solution 11 According to any one of the technical solutions 1 to 10, the average deviation of the surface roughness of the second transparent electrode side of the second n-type layer is 50 nm or more.

[0129] Technical Solution 12 According to any one of technical solutions 1 to 11, the solar cell wherein the aforementioned 1n-type layer comprises a first layer containing an oxide primarily composed of Ga and optionally a second layer containing an oxide primarily composed of Zn. The first layer mentioned above is disposed on the p-type light-absorbing layer side. The second layer is configured on the side of the second nth type layer.

[0130] Technical Solution 13 According to any one of technical solutions 1 to 12, in the solar cell, the refractive index of the aforementioned 2n-type layer is 2.0 or higher and 2.5 or lower. The refractive index of the second transparent electrode mentioned above is 1.6 or higher and 1.99 or lower. The refractive index of the second-nth type layer side of the first-nth type layer is 1.6 or higher and 1.99 or lower. The refractive index of the aforementioned 2n-type layer is 0.01 or more but less than 0.9 higher than the refractive index of the aforementioned 1n-type layer. The refractive index of the second n-type layer is 0.01 or more and 0.9 or less higher than the refractive index of the second transparent electrode.

[0131] Technical Solution 14 The solar cell according to any one of technical solutions 1 to 13, wherein the p-type light-absorbing layer comprises a compound having a chalcopyrite structure or a cuprous oxide compound.

[0132] Technical Solution 15 According to any one of technical solutions 1 to 14, in the solar cell, the p-type light-absorbing layer comprises a compound having a chalcopyrite structure or a cuprous oxide compound. The p-type light-absorbing layer is the thickest among the semiconductor layers contained in the solar cell.

[0133] Technical Solution 16 According to any one of technical solutions 1 to 15, the solar cell wherein the p-type light-absorbing layer comprises a cuprous oxide compound. The p-type light-absorbing layer is the thickest among the semiconductor layers contained in the solar cell.

[0134] Technical Solution 17 According to any one of technical solutions 1 to 16, the solar cell wherein the p-type light-absorbing layer comprises crystals of cuprous oxide compound with a particle size more than 5 times the thickness of the p-type light-absorbing layer.

[0135] Technical Solution 18 A multi-junction solar cell uses the solar cell described in any one of technical solutions 1 to 18.

[0136] Technical Solution 19 A solar cell module that uses the solar cell described in any one of technical solutions 1 to 17.

[0137] Technical Solution 20 A solar power generation system that uses the solar cell module described in technical solution 19 to generate electricity.

Claims

1. A solar cell, comprising: First transparent electrode, The p-type light-absorbing layer disposed on the first transparent electrode The first n-type layer disposed on the p-type light-absorbing layer, The second n-type layer disposed on the first n-type layer, The second transparent electrode disposed on the secondn-type layer, and The anti-reflective layer on the second transparent electrode The refractive index of the 2n-type layer is higher than that of the 1n-type layer. The second-n type layer contains a metal oxide comprising titanium.

2. The solar cell according to claim 1, wherein, The second n-type layer comprises 50 wt% to 100 wt% of a titanium-containing metal oxide.

3. The solar cell according to claim 1, wherein, The titanium-containing metal oxide comprises one or more selected from the group consisting of titanium dioxide, doped titanium dioxide, and doped strontium titanate.

4. The solar cell according to claim 1, wherein, The titanium-containing metal oxide comprises one or more selected from the group consisting of titanium dioxide, doped titanium dioxide, and doped strontium titanate. The dopant of the doped titanium dioxide and the dopant of the doped strontium titanate are selected from one or more of the group consisting of Nb, Ta, Mo and W.

5. The solar cell according to claim 1, wherein, Of the metallic elements contained in the 1n-type layer, titanium accounts for more than 0 atomic percent and less than 10 atomic percent. Of the metallic elements contained in the second n-type layer, titanium accounts for more than 45 atomic% and less than 100 atomic% 6. The solar cell according to claim 1, wherein, The thickness of the second n-type layer is greater than 1 nm and less than 50 nm.

7. The solar cell according to claim 1, wherein, The refractive index of the second n-type layer is higher than that of the second transparent electrode.

8. The solar cell according to claim 1, wherein, When the refractive index of the 2n-type layer is set to n1 and the thickness of the 2n-type layer is set to d1, where the unit of d1 is nm, n1 and d1 satisfy 2nm≤n1·d1nm≤125nm.

9. The solar cell according to claim 1, wherein, The refractive index of the 2n-type layer is 0.01 higher and 0.9 lower than the refractive index of the 1n-type layer. The refractive index of the second n-type layer is 0.01 higher and 0.9 lower than the refractive index of the second transparent electrode.

10. The solar cell according to claim 1, wherein, The second type layer is in direct contact with the first type layer and the second transparent electrode.

11. The solar cell according to claim 1, wherein, The average deviation of the surface roughness on the second transparent electrode side of the second n-type layer is greater than 50 nm.

12. The solar cell according to claim 1, wherein, The 1n-type layer comprises a first layer containing an oxide primarily composed of Ga and a second layer optionally containing an oxide primarily composed of Zn. The first layer is disposed on the p-type light-absorbing layer side. The second layer is disposed on the side of the second n-type layer.

13. The solar cell according to claim 1, wherein, The refractive index of the second-n type layer is greater than 2.0 and less than 2.

5. The refractive index of the second transparent electrode is greater than or equal to 1.6 and less than 1.

99. The refractive index of the second-nth type layer side of the first-nth type layer is 1.6 or higher and 1.99 or lower. The refractive index of the 2n-type layer is 0.01 higher and 0.9 lower than the refractive index of the 1n-type layer. The refractive index of the second n-type layer is 0.01 higher and 0.9 lower than the refractive index of the second transparent electrode.

14. The solar cell according to claim 1, wherein, The p-type light-absorbing layer contains compounds with a chalcopyrite structure or cuprous oxide compounds.

15. The solar cell according to claim 1, wherein, The p-type light-absorbing layer contains compounds with a chalcopyrite structure or cuprous oxide compounds. The p-type light-absorbing layer is the thickest among the semiconductor layers contained in the solar cell.

16. The solar cell according to claim 1, wherein, The p-type light-absorbing layer contains a cuprous oxide compound. The p-type light-absorbing layer is the thickest among the semiconductor layers contained in the solar cell.

17. The solar cell according to claim 1, wherein, The p-type light-absorbing layer comprises crystals of cuprous oxide compounds with a particle size more than five times the thickness of the p-type light-absorbing layer.

18. A multijunction solar cell using any one of claims 1 to 17.

19. A solar cell module that uses the solar cell according to any one of claims 1 to 17.

20. A solar power generation system that generates electricity using the solar cell module of claim 19.

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