WO2020250513A1 - Solar cell, multijunction solar cell, solar cell module, and solar power generation system - Google Patents

Solar cell, multijunction solar cell, solar cell module, and solar power generation system Download PDF

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WO2020250513A1
WO2020250513A1 PCT/JP2020/010298 JP2020010298W WO2020250513A1 WO 2020250513 A1 WO2020250513 A1 WO 2020250513A1 JP 2020010298 W JP2020010298 W JP 2020010298W WO 2020250513 A1 WO2020250513 A1 WO 2020250513A1
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Prior art keywords
solar cell
type layer
layer
photoelectric conversion
group
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PCT/JP2020/010298
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French (fr)
Inventor
Kazushige Yamamoto
Naoyuki Nakagawa
Soichiro SHIBASAKI
Yuya HONISHI
Mutsuki Yamazaki
Yoshiko Hiraoka
Original Assignee
Kabushiki Kaisha Toshiba
Toshiba Energy Systems & Solutions Corporation
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Priority claimed from JP2019148178A external-priority patent/JP7330015B2/en
Application filed by Kabushiki Kaisha Toshiba, Toshiba Energy Systems & Solutions Corporation filed Critical Kabushiki Kaisha Toshiba
Publication of WO2020250513A1 publication Critical patent/WO2020250513A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/0256—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by the material
    • H01L31/0264—Inorganic materials
    • H01L31/0328—Inorganic materials including, apart from doping materials or other impurities, semiconductor materials provided for in two or more of groups H01L31/0272 - H01L31/032
    • H01L31/0336—Inorganic materials including, apart from doping materials or other impurities, semiconductor materials provided for in two or more of groups H01L31/0272 - H01L31/032 in different semiconductor regions, e.g. Cu2X/CdX hetero- junctions, X being an element of Group VI of the Periodic Table
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/0256—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by the material
    • H01L31/0264—Inorganic materials
    • H01L31/032—Inorganic materials including, apart from doping materials or other impurities, only compounds not provided for in groups H01L31/0272 - H01L31/0312
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
    • H01L31/072—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN heterojunction type
    • H01L31/0725—Multiple junction or tandem solar cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy

Definitions

  • Embodiments described herein relate generally to a solar cell, a multijunction solar cell, a solar cell module, and a solar power generation system.
  • tandem solar cells There are multijunction (tandem) solar cells as highly efficient solar cells.
  • a cell with high spectral sensitivity for each wavelength band can be used, and thus the tandem solar cells can be more efficient than single junction solar cells.
  • a cuprous oxide compound or the like which is an inexpensive material and has a wide band gap, has been expected as a top cell of the tandem solar cell.
  • Embodiments provide a solar cell, a multijunction solar cell, a solar cell module, and a solar power generation system each having improved properties.
  • a solar cell of an embodiment has a first transparent electrode; a photoelectric conversion layer containing cuprous oxide as a main component on the first electrode; an n-type layer being a metal oxide layer containing Zn, Sn, and element M which is one or more elements selected from the group consisting of Al, Ga, In, and B and/or one or more elements selected from the group consisting of Si, Ge, Zr, and Hf, on the photoelectric conversion layer; and a second transparent electrode on the n-type layer.
  • FIG. 1 is a sectional conceptual diagram of a solar cell according to an embodiment
  • FIG. 2 is a diagram illustrating analysis spots of a solar cell according to an embodiment
  • FIG. 3 is a sectional conceptual diagram of a multijunction solar cell according to an embodiment
  • FIG. 4 is a conceptual diagram of a solar cell module according to an embodiment
  • FIG. 5 is a sectional conceptual diagram of a solar cell module according to an embodiment
  • FIG. 6 is a conceptual diagram of a solar power generation system according to an embodiment
  • FIG. 7 is a conceptual diagram of a vehicle according to an embodiment.
  • FIG. 1 shows a conceptual diagram of a solar cell 100 of the first embodiment.
  • the solar cell 100 according to the present embodiment includes a first electrode 1, a photoelectric conversion layer 2 on the first electrode 1, an n-type layer 3 (3A) on the photoelectric conversion layer 2, and a second electrode 4 on the n-type layer 3 (3A).
  • An intermediate layer (not shown) may be disposed between the first electrode 1 and the photoelectric conversion layer 2 or between the n-type layer 3 (3A) and the second electrode 4.
  • Light may enter the solar cell from the first electrode 1 side or from the second electrode 4 side. When light enters the solar cell 100, the solar cell 100 can generate electricity.
  • the first electrode (first transparent electrod) 1 of the embodiment is a transparent conductive film provided on the photoelectric conversion layer 2 side. In FIG. 1, the first electrode 1 is in direct contact with the photoelectric conversion layer 2.
  • a transparent conductive film, a metal film, and a laminate of the transparent conductive film and the metal film are preferred.
  • the transparent conductive film examples include, but are not limited to, indium tin oxide (ITO), aluminum-doped zinc oxide (Al-doped zinc oxide, AZO), boron-doped zinc oxide (BZO), gallium-doped zinc oxide (GZO), fluorine -doped tin oxide (FTO), antimony-doped tin oxide (ATO), titanium-doped indium oxide (ITiO), indium zinc oxide (IZO), indium gallium zinc oxide (IGZO), tantalum-doped tin oxide (Ta-doped tin oxide, SnO 2 :Ta), niobium-doped tin oxide (Nb-doped tin oxide, SnO 2 :Nb), tungsten-doped tin oxide (W-doped tin oxide, SnO 2 :W), molybdenum-doped tin oxide (Mo-doped tin oxide
  • the transparent conductive film may be a laminated film having a plurality of films, and the laminated film may contain a film of tin oxide or the like in addition to the above-described oxides.
  • a dopant for a film of tin oxide or the like include, but are not limited to, In, Si, Ge, Ti, Cu, Sb, Nb, F, Ta, W, Mo, F, and Cl.
  • the metal film include, but are not limited to, films of Mo, Au, Cu, Ag, Al, Ta, and W.
  • the first electrode 1 may be an electrode formed by providing a metal in the form of dots, lines, or meshes on the transparent conductive film.
  • the metal in the form of dots, lines, or meshes is disposed between the transparent conductive film and the photoelectric conversion layer 2, or on the transparent conductive film on a side opposite to the photoelectric conversion layer 2. It is preferred that the metal in the form of dots, lines, or meshes has an aperture ratio of not lower than 50% with respect to the transparent conductive film. Examples of the metal in the form of dots, lines, or meshes include, but are not limited to, Mo, Au, Cu, Ag, Al, Ta, and W. When a metal film is used for the first electrode 1, the metal film preferably has a film thickness of not larger than about 5 nm from the viewpoint of transparency.
  • the photoelectric conversion layer 2 of the embodiment is a semiconductor layer disposed between the first electrode 1 and the n-type layer 3.
  • a compound semiconductor layer is preferred.
  • the photoelectric conversion layer 2 include a semiconductor layer containing cuprous oxide as a main component (at least 90 wt%). More specifically, the photoelectric conversion layer 2 is a p-type compound semiconductor layer. Since the transmittance decreases as the thickness of the photoelectric conversion layer 2 increases, and from the viewpoint of forming a film by sputtering, a practical thickness of the photoelectric conversion layer 2 is not more than 10 micro meter.
  • the compound semiconductor layer a semiconductor layer containing cuprous oxide or the like as a main component.
  • the photoelectric conversion layer 2 preferably has a thickness of 800 nm or more and 10 micro meter or less.
  • the compound semiconductor layer the semiconductor layer containing cuprous oxide or the like as a main component may contain additives.
  • the photoelectric conversion layer 2 as a whole is p-type (including p- type and p+ type). In a part of the n-type layer 3 side of the photoelectric conversion layer 2, an n-type region may be included.
  • the photoelectric conversion layer 2 is formed by sputtering.
  • An atmosphere during sputtering is preferably a mixed gas atmosphere containing an inert gas such as Ar and oxygen gas.
  • Sputtering can be performed by heating a substrate to a temperature of 100°C or more and 600°C or less and using a target containing Cu, but the sputtering conditions depend on the type of the substrate supporting the solar cell 100. For example, by controlling the temperature and the oxygen partial pressure of sputtering, a cuprous oxide film having a large particle size can be formed on the first electrode 1.
  • Examples of the substrate used for manufacturing the solar cell 100 include organic substrates such as acryl, polyimide, a polycarbonate, polyethylene terephthalate (PET), polypropylene (PP), fluorocarbon resins (e.g., polytetrafluoroethylene (PTFE), a fluorinated ethylene propene copolymer (FEP), an ethylene tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), and perfluoroalkoxy alkane (PFA)), polyalylate, polysulfone, polyether sulfone, and polyetherimide; and inorganic substrates such as soda-lime glass, white sheet glass, chemically strengthened glass, and quartz.
  • organic substrates such as acryl, polyimide, a polycarbonate, polyethylene terephthalate (PET), polypropylene (PP), fluorocarbon resins (e.g., polytetrafluoroethylene (PTFE),
  • Cuprous oxide preferably accounts for at least 95% of the photoelectric conversion layer 2. Cuprous oxide more preferably accounts for at least 98% of the photoelectric conversion layer 2. That is, it is preferred that the photoelectric conversion layer 2 contains almost (substantially) no other phases such as CuO and Cu. When the photoelectric conversion layer 2 contains no other phases such as CuO and Cu, that is, when the photoelectric conversion layer 2 is a substantially single-phase thin film of Cu 2 O, the photoelectric conversion layer 2 has an extremely high transparency, which is preferred. Whether the photoelectric conversion layer 2 is a substantially single phase of Cu 2 O can be determined by an analysis using a photo luminescence (PL) technique.
  • PL photo luminescence
  • the n-type layer 3A is an n-type semiconductor layer disposed between the photoelectric conversion layer 2 and the second electrode 4.
  • the surface of the n-type layer 3A facing the photoelectric conversion layer 2 is preferably in direct contact with the surface of the photoelectric conversion layer 2 facing the n-type layer 3A.
  • the n-type layer 3A is preferably an amorphous thin film.
  • the n-type layer 3A is preferably a metal oxide layer containing Zn, Sn, and one or more elements M selected from the group consisting of Al, Ga, In, and B.
  • the element M is a Group III element.
  • the metal oxide layer (n-type layer 3A) is preferably a layer including a compound represented by Zn x Sn y M z O w , wherein x, y, and z preferably satisfy the following formula: 0.001 ⁇ (z/(x + y)) ⁇ 1.00.
  • the metal oxide layer has physical properties widely different from those of Zn x Sn y O w comprising the main constituent elements, which is not preferable.
  • x, y, and z more preferably satisfy 0.001 ⁇ (z/(x + y)) ⁇ 0.5, still more preferably satisfy 0.001 ⁇ (z/(x + y)) ⁇ 0.25 or 0.001 ⁇ (z/(x + y)) ⁇ 0.1.
  • the metal oxide layer preferably consists essentially of Zn x Sn y M z O w except for inevitable impurities.
  • Zn x Sn y M z O w does not experience phase separation into Zn x Sn y O w and M z O w
  • Zn x Sn y M z O w has a wide gap.
  • x, y, and z more preferably satisfy 0.6 ⁇ (x + y + z)/w ⁇ 1.4.
  • the element M is more preferably at least one element selected from the group consisting of Al, Ga, and In.
  • composition ratio is found by obtaining a section by energy dispersive X-ray spectroscopy (EDX) in a direction of the diagram in FIG. 1, and scanning the section from the n-type layer 3 side toward the photoelectric conversion layer 2 side.
  • the boundary (interface) between the photoelectric conversion layer 2 and the n-type layer 3 also can be obtained by EDX.
  • the boundary between the photoelectric conversion layer 2 and the n-type layer 3 is obtained as follows. Cu concentration and Zn concentration are measured by EDX, and a position, which is measured from the n-type layer 3, at which Cu concentration is larger then Zn concentration and which is nearest to the second electrode 4 side is designated as a boundary.
  • Each spot is a regular square and has an area of at least 5 mm 2 .
  • D1 the length of the n-type layer 3
  • D2 the width of D2 (D1 ⁇ D2).
  • analysis spots are preferably determined on the basis of an inscribed rectangle.
  • the concentration is an average of seven values obtained from seven analysis points among nine values obtained from the nine analysis spots excluding the maximum and the minimum values.
  • ZnSnO which is an oxide of Zn and Sn and does not contain one or more elements M selected from the group consisting of Al, Ga, In, and B
  • ZnSnO which does not contain one or more elements M selected from the group consisting of Al, Ga, In, and B, absorbs a relatively large amount of light within an wavelength band including 350 nm which is to be absorbed by a photoelectric conversion layer 2 with a wide band gap, and thus causes decrease in conversion efficiency of the solar cell 100.
  • a short wavelength band does not in part fall within a wavelength range of visible light in, for example, a display device such as a monitor.
  • an n-type layer 3A which does not disturb absorption of light by the photoelectric conversion layer 2 is obtained by adding one or more elements M selected from the group consisting of Al, Ga, In, and B to the n-type layer 3A, and thus transmittance of the n-type layer 3A and the solar cell 100 is improved.
  • an n-type layer 3A including a compound represented by Zn x Sn y M z O w which contains one or more elements M selected from the group consisting of Al, Ga, In, and B preferably has a transmittance of light having a wavelength of 350 nm of 90% or more.
  • the n-type layer 3A including a compound represented by Zn x Sn y M z O w which contains one or more elements M selected from the group consisting of Al, Ga, In, and B has a superior transmittance of light within a wavelength band which is to be absorbed by the photoelectric conversion layer 2. That is, the n-type layer 3A of the embodiment can increase the amount of light arriving at the photoelectric conversion layer 2 as compared to an n-type layer 3A of ZnSnO, and can increase both the amount of electricity production of the solar cell 100 and the transparency of the solar cell 100.
  • the n-type layer 3 typically, preferably has a film thickness of 3 nm or more and 50 nm or less.
  • a leakage current occurs when coverage of the n-type layer 3 is poor, which may result in decrease in properties.
  • the thickness is not limited to the above-described film thickness.
  • the thickness of the n-type layer 3 exceeds 50 nm, decrease in properties by excessive increase in the resistance of the n-type layer 3 and decrease in short-circuit current by decrease in the transmittance may occur.
  • the n-type layer 3 more preferably has a thickness of 5 nm or more and 50 nm or less, and still more preferably has a thickness of 5 nm or more and 10 nm or less. In order to achieve a layer with good coverage, the n-type layer 3 preferably has a surface roughness of not larger than 5 nm.
  • the n-type layer 3 can be formed by, for example, atomic layer deposition (ALD) or sputtering.
  • a conduction band offset ( ⁇ E Ecp - Ecn), which is a difference between a position (Ecp(eV)) of a conduction band minimum (CBM) of the photoelectric conversion layer 2 and a positon (Ecn(eV)) below a conduction band of the n-type layer 3, is preferably -0.2 eV or more and 0.6 eV or less (-0.2 eV ⁇ ⁇ E ⁇ +0.6 eV).
  • the conduction band offset is larger than 0, the conduction band at a pn junction interface becomes discontinuous, which leads to spikes.
  • the conduction band offset is more preferably 0.0 eV or more and 0.4 eV or less (0.0 eV ⁇ ⁇ E ⁇ +0.4 eV). This does not apply to a case where conduction occurs using a gap state.
  • the position of CBM can also be estimated by the following method.
  • the valence band maximum (VBM) is actually measured by photoemission spectroscopy, which is a method for evaluating an electron occupancy level, and then assuming a band gap of a target material for measurement to calculate CBM.
  • CBM is also evaluated by inverse photoemission spectroscopy which directly utilizes the inverse process of photoemission.
  • the electronic state of the pn junction interface can be evaluated by repeating low energy ion etching of the surface of a solar cell and positive/inverse photoemission spectroscopy. Since the n-type layer 3 contains at least one element M selected from B, Al, In, and Ga in addition to Zn and Sn, electron affinity becomes small, and difference between CBM of the photoelectric conversion layer 2 and CBM of the n-type layer 3 becomes small.
  • the second electrode (second transparent electrode) 4 a transparent electrode which is the same as that described as the first electrode 1 is preferably used.
  • the second electrode 4 other transparent electrode such as multilayer graphene provided with an output electrode including a metal wire can also be adopted.
  • An antireflective film of the embodiment is a film for enhancing introduction of light into the photoelectric conversion layer 2, and is preferably formed on the first electrode 1 or on the second electrode 4 on a side opposite to the photoelectric conversion layer 2 side.
  • the antireflective film MgF 2 or SiO 2 is preferably used, for example.
  • the antireflective film may be omitted. Adjustment of the film thickness depending on the refractive index of each layer is required. However, it is preferred that a thin film having a thickness of about 70 to 130 nm (preferably 80 to 120 nm) is deposited.
  • FIG. 1 shows a conceptual diagram of a solar cell 101 of the second embodiment.
  • the solar cell 101 according to the present embodiment includes a first electrode 1, a photoelectric conversion layer 2 on the first electrode 1, an n-type layer 3 (3B) on the photoelectric conversion layer 2, and a second electrode 4 on the n-type layer 3 (3B).
  • An intermediate layer (not shown) may be disposed between the first electrode 1 and the photoelectric conversion layer 2 or between the n-type layer 3 (3B) and the second electrode 4.
  • Light may enter the solar cell from the first electrode 1 side or from the second electrode 4 side.
  • the solar cell of the second embodiment is the same as the solar cell 101 of the first embodiment except for element M of the n-type layer 3B of the second embodiment.
  • the description provided in the first embodiment also applies to the second embodiment except for matters separately described in the second embodiment.
  • n-type layer 3B a metal oxide layer containing Zn, Sn, and one or more elements M selected from the group consisting of Si, Ge, Zr, and Hf is preferred.
  • the element M of the second embodiment includes a Group IVA element (Group 4 element) and a Group IVB element (Group 14 element).
  • Group IV elements Group 4 element
  • Group IVB element Group 14 element
  • the element M can further include at least one Group III element selected from the group consisting of Al, Ga, In, and B, and preferably includes at least one Group III an element selected from the group consisting of Al, Ga, In, and B.
  • the metal oxide layer (n-type layer 3B) is preferably a layer including a compound represented by Zn x Sn y M z O w , wherein x, y, and z preferably satisfy the following formula: 0.001 ⁇ (z/(x + y)) ⁇ 1.00.
  • the metal oxide layer has physical properties widely different from those of Zn x Sn y O w comprising the main constituent elements, which is not preferable.
  • x, y, and z more preferably satisfy 0.001 ⁇ (z/(x + y)) ⁇ 0.5, still more preferably satisfy 0.001 ⁇ (z/(x + y)) ⁇ 0.25 or 0.001 ⁇ (z/(x + y)) ⁇ 0.1.
  • the metal oxide layer preferably consists essentially of Zn x Sn y M z O w except for inevitable impurities. This is because when (z/(x + y)) is small, Zn x Sn y M z O w does not experience phase separation into Zn x Sn y O w and M z O w , and Zn x Sn y M z O w has a wide gap.
  • x, y, and z more preferably satisfy 0.6 ⁇ (x + y + z)/w ⁇ 1.4.
  • both a group of Group III elements consisting of Al, Ga, In, and B and a group of Group IVA and Group IVB elements consisting of Si, Ge, Zr, and Hf are preferred.
  • the latter group of Group IV elements tends to have improved properties, and is more preferred.
  • any of the group of Group IV and Group III elements can reduce electron affinity of the n-type layer 3, and Voc can be improved by almost the same degree.
  • FF Filill Factor
  • a reason for the difference in FF between Group IV and Group III is assumed as follows.
  • the n-type layer 3B when a Group IV element is added, the transmittance at wavelengths of an absorption band of the photoelectric conversion layer 2 is improved. From the viewpoint of improving FF, when the element M includes both a Group IV element and a Group III element, the concentration of the Group IV element is preferably higher than the concentration of the Group III element.
  • FIG. 3 shows a sectional conceptual diagram of a multijunction solar cell 200 of the third embodiment.
  • the multijunction solar cell 200 shown in FIG. 3 has a solar cell (first solar cell) 100 (101) of the first embodiment or the second embodiment on the light incident side, and a second solar cell 201.
  • the band gap of a photoelectric conversion layer of the second solar cell 201 is smaller than the band gap of the photoelectric conversion layer 2 of the solar cell 100 (101) of the first embodiment or the second embodiment.
  • the multijunction solar cell of the embodiment also includes a solar cell in which three or more solar cells are laminated.
  • the photoelectric conversion layer 2 of the solar cell 100 (101) of the first embodiment or the second embodiment has a band gap of about 2 eV, and thus the photoelectric conversion layer of the second solar cell 201 preferably has a band gap of 1.0 eV or more and 1.4 eV or less.
  • the photoelectric conversion layer of the second solar cell 201 is preferably at least one compound semiconductor layer of a CIGS type and a CIT type having a high In content, a CdTe type, and a tin oxide type semiconductor layers, or crystalline silicon.
  • the solar cell 100 (101) according to the first embodiment or the second embodiment is used as a first solar cell, absorption of light having unintended wavelengths by the first solar cell can be prevented, and thus decrease in conversion efficiency of a bottom cell (second solar cell) can be prevented. Accordingly, a high-efficiency multijunction solar cell can be achieved.
  • FIG. 4 shows a perspective conceptual diagram of a solar cell module 300 of the fourth embodiment.
  • the solar cell module 300 in FIG. 4 is a solar cell module in which a first solar cell module 301 and a second solar cell module 302 are laminated.
  • the first solar cell module 301 exists on the light incident side.
  • the solar cell 100 of the first embodiment is used.
  • the second solar cell 201 is preferably used.
  • FIG. 5 shows a sectional conceptual diagram of the solar cell module 300.
  • the structure of the first solar cell module 301 is illustrated in detail, and the structure of the second solar cell module 302 is omitted.
  • the structure of the solar cell module is appropriately selected depending on a photoelectric conversion layer and the like of the solar cell to be used.
  • the solar cell module in FIG. 5 includes a plurality of submodules 303 surrounded by dashed line, in which each of the submodules 303 contains a plurality of solar cells 100 (photovoltaic cells) arranged laterally and electrically connected in series.
  • the submodules 303 are electrically connected in parallel or serial.
  • the solar cell 100 has been scribed. In adjacent solar cells 100, a second electrode 4 on the upper side of a solar cell 100 is connected with a first electrode 1 on the lower side of a different solar cell 100.
  • the solar cell 100 of the fourth embodiment has, as in the solar cell 100 (101) of the first embodiment or the second embodiment, a substrate 10, a first electrode 1, a photoelectric conversion layer 2, an n-type layer 3, and a second electrode 4.
  • embodiments of the present application can provide solar cells suitable for different wavelength bands.
  • efficient generation of electricity becomes possible as compared to when a solar cell of the top cell or the bottom cell is used alone, and the total output of modules can be increased, which is preferred.
  • a fifth embodiment relates to a solar power generation system.
  • a solar cell module 300 of the fourth embodiment can be used as a power generator for generating electricity in the solar power generation system of the fifth embodiment.
  • the solar power generation system of the embodiment generates electricity using a solar cell module, and specifically has a solar cell module configured to generate electricity, a unit configured to perform electric power conversion of the generated electricity, and an electricity accumulator configured to store the generated electricity or a load configured to consume the generated electricity.
  • FIG. 6 shows a structural conceptual diagram of a solar power generation system 400 of the embodiment.
  • the solar power generation system in FIG. 6 has a solar cell module 401 (300), an electric power conversion device 402, a storage battery 403, and a load 404.
  • the load 404 can have a configuration capable of using the electric energy stored in the storage battery 403.
  • the electric power conversion device 402 is a device including a circuit or an element configured to perform electric power conversion such as transformation or DC-AC conversion.
  • the electric power conversion device 402 may have a suitable configuration depending on the generated voltage, and the configurations of the storage battery 403 and the load 404.
  • a photovoltaic cell included in the submodules 303 which is included in the solar cell module 300 and has received light, generates electricity.
  • the electric energy of the generated electricity is converted by the converter 402, and stored in the storage battery 403 or consumed by the load 404.
  • the solar cell module 401 is provided with a solar tracking actuator for constantly directing the solar cell module 401 to the sun, a light collector for collecting sunlight, or a device for improving electricity generation efficiency.
  • the solar power generation system 400 is preferably used for immovables such as residences, commercial facilities, and factories, or used for movables such as vehicles, aircrafts, and electronic equipment.
  • immovables such as residences, commercial facilities, and factories
  • movables such as vehicles, aircrafts, and electronic equipment.
  • FIG. 7 shows a structural conceptual diagram of the vehicle 500.
  • the vehicle 500 in FIG. 7 has a car body 501, a solar cell module 502, an electric power conversion device 503, a storage battery 504, a motor 505, and a tire (wheel) 506.
  • Electricity generated by the solar cell module 502 provided on the car body 501 is converted by the electric power conversion device 503, and stored in the storage battery 504, or the electric power is consumed by a load such as the motor 505.
  • the tire (wheel) 506 can be rotated by the motor 505 using electric power supplied from the solar cell module 502 or the storage battery 504, and the vehicle 500 can be moved.
  • the solar cell module 502 is not limited to a multijunction solar cell, but may consists only of a first solar cell module having the solar cell 100 of the first embodiment. When a transparent solar cell module 502 is used, it is also preferred that the solar cell module 502 is used as an electricity-generating side window of the car body 501 in addition to providing the solar cell module 502 on the top of the car body 501.
  • compositions of n-type layers in Examples and Comparative Example are compositions calculated from conditions for forming the layers.
  • FF is higher than in Examples 1 to 26. It is assumed that this is due to the influence of superior physical properties of electrons (electron concentration and electron mobility) of n-type layers containing a Group IV element and smaller electrical resistance of the n layer.
  • the solar cells in Examples have excellent transmittance of light having long wavelengths, in addition to excellent transmittance of light having short wavelengths.
  • the solar cell of the embodiment contributes to improvement in total amount of electricity production.
  • some elements are expressed only by element symbols of the elements.
  • a solar cell comprising: a first transparent electrode; a photoelectric conversion layer containing cuprous oxide as a main component on the first electrode; an n-type layer being a metal oxide layer containing Zn, Sn, and one or more elements selected from the group consisting of Al, Ga, In, and B and/or one or more elements M selected from the group consisting of Si, Ge, Zr, and Hf, on the photoelectric conversion layer; and a second transparent electrode on the n-type layer.
  • n-type layer is a layer including a compound represented by Zn x Sn y M z O w , and x, y, and z satisfy 0.001 ⁇ (z/(x + y)) ⁇ 1.00.
  • Clause 3 The solar cell according to clause 1 or 2, wherein the n-type layer is a layer including a compound represented by Zn x Sn y M z O w , and x, y, and z satisfy 0.001 ⁇ (z/(x + y)) ⁇ 0.5.
  • n-type layer is a layer including a compound represented by Zn x Sn y M z O w , x, y, and z satisfy 0.001 ⁇ (z/(x + y)) ⁇ 1.00, and x, y, z, and w satisfy 0.6 ⁇ (x + y + z)/w ⁇ 1.4.
  • Clause 5 The solar cell according to any one of clauses 1 to 4, wherein the n-type layer has a thickness of 3 nm or more and 50 nm or less.
  • Clause 6 The solar cell according to any one of clauses 1 to 5, wherein the element M is one or more elements selected from the group consisting of Al, Ga, In, and B.
  • Clause 7 The solar cell according to any one of clauses 1 to 5, wherein the element M is one or more elements selected from the group consisting of Si, Ge, Zr, and Hf.
  • Clause 8 The solar cell according to any one of clauses 1 to 5, wherein the element M is one or more elements selected from the group consisting of Al, Ga, In, and B, and one or more elements selected from the group consisting of Si, Ge, Zr, and Hf.
  • Clause 9 The solar cell according to any one of clauses 1 to 8, wherein the n-type layer has a transmittance of light having a wavelength of 350 nm of 90% or more.
  • Clause 10 The solar cell according to any one of clauses 1 to 9, wherein cuprous oxide accounts for at least 90 wt% of the photoelectric conversion layer.
  • Clause 11 The solar cell according to any one of clauses 1 to 10, wherein the n-type layer has a thickness of 5 nm or more and 50 nm or less.
  • Clause 12 A multijunction solar cell including the solar cell according to any one of clauses 1 to 11.
  • Clause 13 A solar cell module including the solar cell according to any one of clauses 1 to 11.
  • Clause 14 A solar power generation system configured to generate electricity using the solar cell module according to clause 13.

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Abstract

Embodiments provide a solar cell, a multijunction solar cell, a solar cell module, and a solar power generation system each having improved properties. A solar cell 100 of an embodiment has a first transparent electrode 1; a photoelectric conversion layer 2 including cuprous oxide as a main component on the first electrode 1; an n-type layer 3 being a metal oxide layer containing Zn, Sn, and element M which is one or more elements selected from the group consisting of Al, Ga, In, and B and/or one or more elements selected from the group consisting of Si, Ge, Zr, and Hf, on the photoelectric conversion layer 2; and a second transparent electrode 4 on the n-type layer 3.

Description

SOLAR CELL, MULTIJUNCTION SOLAR CELL, SOLAR CELL MODULE, AND SOLAR POWER GENERATION SYSTEM
Embodiments described herein relate generally to a solar cell, a multijunction solar cell, a solar cell module, and a solar power generation system.
There are multijunction (tandem) solar cells as highly efficient solar cells. In the tandem solar cells, a cell with high spectral sensitivity for each wavelength band can be used, and thus the tandem solar cells can be more efficient than single junction solar cells. Further, a cuprous oxide compound or the like, which is an inexpensive material and has a wide band gap, has been expected as a top cell of the tandem solar cell.
JP 2018-46196A
Embodiments provide a solar cell, a multijunction solar cell, a solar cell module, and a solar power generation system each having improved properties.
A solar cell of an embodiment has a first transparent electrode; a photoelectric conversion layer containing cuprous oxide as a main component on the first electrode; an n-type layer being a metal oxide layer containing Zn, Sn, and element M which is one or more elements selected from the group consisting of Al, Ga, In, and B and/or one or more elements selected from the group consisting of Si, Ge, Zr, and Hf, on the photoelectric conversion layer; and a second transparent electrode on the n-type layer.
FIG. 1 is a sectional conceptual diagram of a solar cell according to an embodiment; FIG. 2 is a diagram illustrating analysis spots of a solar cell according to an embodiment; FIG. 3 is a sectional conceptual diagram of a multijunction solar cell according to an embodiment; FIG. 4 is a conceptual diagram of a solar cell module according to an embodiment; FIG. 5 is a sectional conceptual diagram of a solar cell module according to an embodiment; FIG. 6 is a conceptual diagram of a solar power generation system according to an embodiment; and FIG. 7 is a conceptual diagram of a vehicle according to an embodiment.
(First Embodiment)
A first embodiment relates to a solar cell. FIG. 1 shows a conceptual diagram of a solar cell 100 of the first embodiment. As shown in FIG. 1, the solar cell 100 according to the present embodiment includes a first electrode 1, a photoelectric conversion layer 2 on the first electrode 1, an n-type layer 3 (3A) on the photoelectric conversion layer 2, and a second electrode 4 on the n-type layer 3 (3A). An intermediate layer (not shown) may be disposed between the first electrode 1 and the photoelectric conversion layer 2 or between the n-type layer 3 (3A) and the second electrode 4. Light may enter the solar cell from the first electrode 1 side or from the second electrode 4 side. When light enters the solar cell 100, the solar cell 100 can generate electricity.
(First Electrode)
The first electrode (first transparent electrod) 1 of the embodiment is a transparent conductive film provided on the photoelectric conversion layer 2 side. In FIG. 1, the first electrode 1 is in direct contact with the photoelectric conversion layer 2. As the first electrode 1, a transparent conductive film, a metal film, and a laminate of the transparent conductive film and the metal film are preferred. Examples of the transparent conductive film include, but are not limited to, indium tin oxide (ITO), aluminum-doped zinc oxide (Al-doped zinc oxide, AZO), boron-doped zinc oxide (BZO), gallium-doped zinc oxide (GZO), fluorine -doped tin oxide (FTO), antimony-doped tin oxide (ATO), titanium-doped indium oxide (ITiO), indium zinc oxide (IZO), indium gallium zinc oxide (IGZO), tantalum-doped tin oxide (Ta-doped tin oxide, SnO2:Ta), niobium-doped tin oxide (Nb-doped tin oxide, SnO2:Nb), tungsten-doped tin oxide (W-doped tin oxide, SnO2:W), molybdenum-doped tin oxide (Mo-doped tin oxide, SnO2:Mo), fluorine -doped tin oxide (F-doped tin oxide, SnO2:F), and hydrogen-doped indium oxide (IOH). The transparent conductive film may be a laminated film having a plurality of films, and the laminated film may contain a film of tin oxide or the like in addition to the above-described oxides. Examples of a dopant for a film of tin oxide or the like include, but are not limited to, In, Si, Ge, Ti, Cu, Sb, Nb, F, Ta, W, Mo, F, and Cl. Examples of the metal film include, but are not limited to, films of Mo, Au, Cu, Ag, Al, Ta, and W. The first electrode 1 may be an electrode formed by providing a metal in the form of dots, lines, or meshes on the transparent conductive film. At this time, the metal in the form of dots, lines, or meshes is disposed between the transparent conductive film and the photoelectric conversion layer 2, or on the transparent conductive film on a side opposite to the photoelectric conversion layer 2. It is preferred that the metal in the form of dots, lines, or meshes has an aperture ratio of not lower than 50% with respect to the transparent conductive film. Examples of the metal in the form of dots, lines, or meshes include, but are not limited to, Mo, Au, Cu, Ag, Al, Ta, and W. When a metal film is used for the first electrode 1, the metal film preferably has a film thickness of not larger than about 5 nm from the viewpoint of transparency.
(Photoelectric Conversion Layer)
The photoelectric conversion layer 2 of the embodiment is a semiconductor layer disposed between the first electrode 1 and the n-type layer 3. As the photoelectric conversion layer 2, a compound semiconductor layer is preferred. Examples of the photoelectric conversion layer 2 include a semiconductor layer containing cuprous oxide as a main component (at least 90 wt%). More specifically, the photoelectric conversion layer 2 is a p-type compound semiconductor layer. Since the transmittance decreases as the thickness of the photoelectric conversion layer 2 increases, and from the viewpoint of forming a film by sputtering, a practical thickness of the photoelectric conversion layer 2 is not more than 10 micro meter. As the compound semiconductor layer, a semiconductor layer containing cuprous oxide or the like as a main component. The photoelectric conversion layer 2 preferably has a thickness of 800 nm or more and 10 micro meter or less. As the compound semiconductor layer, the semiconductor layer containing cuprous oxide or the like as a main component may contain additives. The photoelectric conversion layer 2 as a whole is p-type (including p- type and p+ type). In a part of the n-type layer 3 side of the photoelectric conversion layer 2, an n-type region may be included.
The photoelectric conversion layer 2 is formed by sputtering. An atmosphere during sputtering is preferably a mixed gas atmosphere containing an inert gas such as Ar and oxygen gas. Sputtering can be performed by heating a substrate to a temperature of 100°C or more and 600°C or less and using a target containing Cu, but the sputtering conditions depend on the type of the substrate supporting the solar cell 100. For example, by controlling the temperature and the oxygen partial pressure of sputtering, a cuprous oxide film having a large particle size can be formed on the first electrode 1. Examples of the substrate used for manufacturing the solar cell 100 (substrate supporting the first electrode 1) include organic substrates such as acryl, polyimide, a polycarbonate, polyethylene terephthalate (PET), polypropylene (PP), fluorocarbon resins (e.g., polytetrafluoroethylene (PTFE), a fluorinated ethylene propene copolymer (FEP), an ethylene tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), and perfluoroalkoxy alkane (PFA)), polyalylate, polysulfone, polyether sulfone, and polyetherimide; and inorganic substrates such as soda-lime glass, white sheet glass, chemically strengthened glass, and quartz.
Cuprous oxide preferably accounts for at least 95% of the photoelectric conversion layer 2. Cuprous oxide more preferably accounts for at least 98% of the photoelectric conversion layer 2. That is, it is preferred that the photoelectric conversion layer 2 contains almost (substantially) no other phases such as CuO and Cu. When the photoelectric conversion layer 2 contains no other phases such as CuO and Cu, that is, when the photoelectric conversion layer 2 is a substantially single-phase thin film of Cu2O, the photoelectric conversion layer 2 has an extremely high transparency, which is preferred. Whether the photoelectric conversion layer 2 is a substantially single phase of Cu2O can be determined by an analysis using a photo luminescence (PL) technique.
(n-type Layer)
The n-type layer 3A is an n-type semiconductor layer disposed between the photoelectric conversion layer 2 and the second electrode 4. The surface of the n-type layer 3A facing the photoelectric conversion layer 2 is preferably in direct contact with the surface of the photoelectric conversion layer 2 facing the n-type layer 3A. The n-type layer 3A is preferably an amorphous thin film. The n-type layer 3A is preferably a metal oxide layer containing Zn, Sn, and one or more elements M selected from the group consisting of Al, Ga, In, and B. The element M is a Group III element. When the n-type layer 3A contains a Group III element, the n-type layer 3A can have a wide gap, and electron affinity of the n-type layer 3A can be small, and therefore the conduction band offset against the photoelectric conversion layer 2 can be small. The metal oxide layer (n-type layer 3A) is preferably a layer including a compound represented by ZnxSnyMzOw, wherein x, y, and z preferably satisfy the following formula: 0.001 ≦ (z/(x + y)) < 1.00. When x, y, and z do not satisfy the formula, the metal oxide layer has physical properties widely different from those of ZnxSnyOw comprising the main constituent elements, which is not preferable. x, y, and z more preferably satisfy 0.001 ≦ (z/(x + y)) < 0.5, still more preferably satisfy 0.001 ≦ (z/(x + y)) < 0.25 or 0.001 ≦ (z/(x + y)) < 0.1. The metal oxide layer preferably consists essentially of ZnxSnyMzOw except for inevitable impurities. This is because when (z/(x + y)) is small, ZnxSnyMzOw does not experience phase separation into ZnxSnyOw and MzOw, and ZnxSnyMzOw has a wide gap. Furthermore, x, y, and z more preferably satisfy 0.6 ≦ (x + y + z)/w ≦ 1.4. The element M is more preferably at least one element selected from the group consisting of Al, Ga, and In.
The above-described composition ratio is found by obtaining a section by energy dispersive X-ray spectroscopy (EDX) in a direction of the diagram in FIG. 1, and scanning the section from the n-type layer 3 side toward the photoelectric conversion layer 2 side. The boundary (interface) between the photoelectric conversion layer 2 and the n-type layer 3 also can be obtained by EDX. The boundary between the photoelectric conversion layer 2 and the n-type layer 3 is obtained as follows. Cu concentration and Zn concentration are measured by EDX, and a position, which is measured from the n-type layer 3, at which Cu concentration is larger then Zn concentration and which is nearest to the second electrode 4 side is designated as a boundary. As locations of the measurement, nine spots A1 to A9 on the surface of the solar cell 100 observed from the second electrode 4 side as shown in a diagram illustrating analysis spots in FIG. 2 are selected. Each spot is a regular square and has an area of at least 5 mm2. As shown in FIG. 2, the length of the n-type layer 3 is denoted by D1 and the width is denoted by D2 (D1 ≧ D2). Nine intersection points of virtual straight lines are found by drawing two virtual straight lines between two opposite sides parallel to the width direction of the solar cell 100 so that each of the virtual straight lines is apart by a distance of D3 (= D1/10) from each of the opposite sides, drawing two virtual straight lines between two opposite sides parallel to the length direction of the solar cell 100 so that each of the virtual straight lines is apart by a distance of D4 (= D2/10) from each of the opposite sides, then drawing a virtual straight line parallel to the width direction through the center of the solar cell 100, and drawing a virtual straight line parallel to the length direction through the center of the solar cell 100, and nine regions centered around the nine intersection points are designated as observation spots A1 to A9. The sections observed by SEM or TEM are perpendicular to the surface in FIG. 2. When the shape of the solar cell 100 viewed from the second electrode 4 side is not rectangular, analysis spots are preferably determined on the basis of an inscribed rectangle. The concentration is an average of seven values obtained from seven analysis points among nine values obtained from the nine analysis spots excluding the maximum and the minimum values.
As an n-type layer 3A provided on the photoelectric conversion layer 2 containing cuprous oxide as a main component, ZnSnO, which is an oxide of Zn and Sn and does not contain one or more elements M selected from the group consisting of Al, Ga, In, and B, can be used. ZnSnO, which does not contain one or more elements M selected from the group consisting of Al, Ga, In, and B, absorbs a relatively large amount of light within an wavelength band including 350 nm which is to be absorbed by a photoelectric conversion layer 2 with a wide band gap, and thus causes decrease in conversion efficiency of the solar cell 100. A short wavelength band does not in part fall within a wavelength range of visible light in, for example, a display device such as a monitor. Thus, in a transparent electrode or a transparent semiconductor layer used for these applications, transmittance in the short wavelength band is not important. On the other hand, in a solar cell 100 using the photoelectric conversion layer 2 with a wide band gap, since ZnSnO absorbs a relatively large amount of light within a short wavelength band, which is to be used by the solar cell 100 which convert energy of light having wavelengths including the short wavelength band to electricity, ZnSnO is an obstacle to improvement in conversion efficiency.
In the embodiment, an n-type layer 3A which does not disturb absorption of light by the photoelectric conversion layer 2 is obtained by adding one or more elements M selected from the group consisting of Al, Ga, In, and B to the n-type layer 3A, and thus transmittance of the n-type layer 3A and the solar cell 100 is improved. Further, by adding one or more elements M selected from the group consisting of Al, Ga, In, and B, the difference between a conduction band minimum of the photoelectric conversion layer 2 and a conduction band minimum of the n-type layer 3A becomes smaller than the difference when ZnSnO is used as the n-type layer 3, and thus Voc is improved, the transmittance is improved, and discontinuous conduction band is dissolved, resulting in improvement in conversion efficiency. An n-type layer 3A including a compound represented by ZnxSnyMzOw which contains one or more elements M selected from the group consisting of Al, Ga, In, and B preferably has a transmittance of light having a wavelength of 350 nm of 90% or more. The n-type layer 3A including a compound represented by ZnxSnyMzOw which contains one or more elements M selected from the group consisting of Al, Ga, In, and B has a superior transmittance of light within a wavelength band which is to be absorbed by the photoelectric conversion layer 2. That is, the n-type layer 3A of the embodiment can increase the amount of light arriving at the photoelectric conversion layer 2 as compared to an n-type layer 3A of ZnSnO, and can increase both the amount of electricity production of the solar cell 100 and the transparency of the solar cell 100.
The n-type layer 3, typically, preferably has a film thickness of 3 nm or more and 50 nm or less. When the thickness of n-type layer 3 is less than 3 nm, a leakage current occurs when coverage of the n-type layer 3 is poor, which may result in decrease in properties. When the coverage is good, the thickness is not limited to the above-described film thickness. When the thickness of the n-type layer 3 exceeds 50 nm, decrease in properties by excessive increase in the resistance of the n-type layer 3 and decrease in short-circuit current by decrease in the transmittance may occur. Thus, the n-type layer 3 more preferably has a thickness of 5 nm or more and 50 nm or less, and still more preferably has a thickness of 5 nm or more and 10 nm or less. In order to achieve a layer with good coverage, the n-type layer 3 preferably has a surface roughness of not larger than 5 nm.
The n-type layer 3 can be formed by, for example, atomic layer deposition (ALD) or sputtering.
[0018] A conduction band offset (ΔE = Ecp - Ecn), which is a difference between a position (Ecp(eV)) of a conduction band minimum (CBM) of the photoelectric conversion layer 2 and a positon (Ecn(eV)) below a conduction band of the n-type layer 3, is preferably -0.2 eV or more and 0.6 eV or less (-0.2 eV ≦ ΔE ≦ +0.6 eV). When the conduction band offset is larger than 0, the conduction band at a pn junction interface becomes discontinuous, which leads to spikes. When the conduction band offset is smaller than 0, the conduction band at a pn junction interface becomes discontinuous, which leads to cliffs. Both spikes and cliffs are barriers to photogenerated electrons, and thus are preferably small. Thus, the conduction band offset is more preferably 0.0 eV or more and 0.4 eV or less (0.0 eV ≦ ΔE ≦ +0.4 eV). This does not apply to a case where conduction occurs using a gap state. The position of CBM can also be estimated by the following method. The valence band maximum (VBM) is actually measured by photoemission spectroscopy, which is a method for evaluating an electron occupancy level, and then assuming a band gap of a target material for measurement to calculate CBM. However, at an actual pn junction interface, an ideal interface is not maintained because of interdiffusion or cation hole production, and thus the band gap probably changes. Thus, it is preferred that CBM is also evaluated by inverse photoemission spectroscopy which directly utilizes the inverse process of photoemission. Specifically, the electronic state of the pn junction interface can be evaluated by repeating low energy ion etching of the surface of a solar cell and positive/inverse photoemission spectroscopy. Since the n-type layer 3 contains at least one element M selected from B, Al, In, and Ga in addition to Zn and Sn, electron affinity becomes small, and difference between CBM of the photoelectric conversion layer 2 and CBM of the n-type layer 3 becomes small.
As the second electrode (second transparent electrode) 4, a transparent electrode which is the same as that described as the first electrode 1 is preferably used. As the second electrode 4, other transparent electrode such as multilayer graphene provided with an output electrode including a metal wire can also be adopted.
(Antireflective Film)
An antireflective film of the embodiment is a film for enhancing introduction of light into the photoelectric conversion layer 2, and is preferably formed on the first electrode 1 or on the second electrode 4 on a side opposite to the photoelectric conversion layer 2 side. As the antireflective film, MgF2 or SiO2 is preferably used, for example. In this embodiment, the antireflective film may be omitted. Adjustment of the film thickness depending on the refractive index of each layer is required. However, it is preferred that a thin film having a thickness of about 70 to 130 nm (preferably 80 to 120 nm) is deposited.
(Second Embodiment)
A second embodiment relates to a solar cell. FIG. 1 shows a conceptual diagram of a solar cell 101 of the second embodiment. As shown in FIG. 1, the solar cell 101 according to the present embodiment includes a first electrode 1, a photoelectric conversion layer 2 on the first electrode 1, an n-type layer 3 (3B) on the photoelectric conversion layer 2, and a second electrode 4 on the n-type layer 3 (3B). An intermediate layer (not shown) may be disposed between the first electrode 1 and the photoelectric conversion layer 2 or between the n-type layer 3 (3B) and the second electrode 4. Light may enter the solar cell from the first electrode 1 side or from the second electrode 4 side. When light enters the solar cell 101, and the solar cell 101 can generate electricity. The solar cell of the second embodiment is the same as the solar cell 101 of the first embodiment except for element M of the n-type layer 3B of the second embodiment. The description provided in the first embodiment also applies to the second embodiment except for matters separately described in the second embodiment.
As the n-type layer 3B, a metal oxide layer containing Zn, Sn, and one or more elements M selected from the group consisting of Si, Ge, Zr, and Hf is preferred. The element M of the second embodiment includes a Group IVA element (Group 4 element) and a Group IVB element (Group 14 element). When the n-type layer 3B contains these Group IV elements, as in the first embodiment in which a Group III (Group 13 element) element is contained, the n-type layer 3B can have a wide gap, and electron affinity of the n-type layer 3B can be small, and therefore the conduction band offset against the photoelectric conversion layer 2 can be small. Further, the element M can further include at least one Group III element selected from the group consisting of Al, Ga, In, and B, and preferably includes at least one Group III an element selected from the group consisting of Al, Ga, In, and B. The metal oxide layer (n-type layer 3B) is preferably a layer including a compound represented by ZnxSnyMzOw, wherein x, y, and z preferably satisfy the following formula: 0.001 ≦ (z/(x + y)) < 1.00. When x, y, and z do not satisfy the formula, the metal oxide layer has physical properties widely different from those of ZnxSnyOw comprising the main constituent elements, which is not preferable. x, y, and z more preferably satisfy 0.001 ≦ (z/(x + y)) < 0.5, still more preferably satisfy 0.001 ≦ (z/(x + y)) < 0.25 or 0.001 ≦ (z/(x + y)) < 0.1. The metal oxide layer preferably consists essentially of ZnxSnyMzOw except for inevitable impurities. This is because when (z/(x + y)) is small, ZnxSnyMzOw does not experience phase separation into ZnxSnyOw and MzOw, and ZnxSnyMzOw has a wide gap. Furthermore, x, y, and z more preferably satisfy 0.6 ≦ (x + y + z)/w ≦ 1.4.
It is found that as element M of the n-type layer 3B, both a group of Group III elements consisting of Al, Ga, In, and B and a group of Group IVA and Group IVB elements consisting of Si, Ge, Zr, and Hf are preferred. When the groups are compared with respect to solar cell properties, the latter group of Group IV elements tends to have improved properties, and is more preferred. Specifically, any of the group of Group IV and Group III elements can reduce electron affinity of the n-type layer 3, and Voc can be improved by almost the same degree. Further, when an element in the group of Group IV elements is used, FF (Fill Factor) is also improved in addition to Voc. A reason for the difference in FF between Group IV and Group III is assumed as follows. When any of Group IV elements or Group III elements are added, electron affinity of the n-type layer 3 is almost the same, but physical properties of electrons (electron concentration and electron mobility) of the n-type layer 3 vary between in the case of Group IV elements and in the case of Group III elements, which results in the difference in FF. In the n-type layer 3B, when a Group IV element is added, the transmittance at wavelengths of an absorption band of the photoelectric conversion layer 2 is improved. From the viewpoint of improving FF, when the element M includes both a Group IV element and a Group III element, the concentration of the Group IV element is preferably higher than the concentration of the Group III element.
(Third Embodiment)
A third embodiment relates to a multijunction solar cell. FIG. 3 shows a sectional conceptual diagram of a multijunction solar cell 200 of the third embodiment. The multijunction solar cell 200 shown in FIG. 3 has a solar cell (first solar cell) 100 (101) of the first embodiment or the second embodiment on the light incident side, and a second solar cell 201. The band gap of a photoelectric conversion layer of the second solar cell 201 is smaller than the band gap of the photoelectric conversion layer 2 of the solar cell 100 (101) of the first embodiment or the second embodiment. The multijunction solar cell of the embodiment also includes a solar cell in which three or more solar cells are laminated.
The photoelectric conversion layer 2 of the solar cell 100 (101) of the first embodiment or the second embodiment has a band gap of about 2 eV, and thus the photoelectric conversion layer of the second solar cell 201 preferably has a band gap of 1.0 eV or more and 1.4 eV or less. The photoelectric conversion layer of the second solar cell 201 is preferably at least one compound semiconductor layer of a CIGS type and a CIT type having a high In content, a CdTe type, and a tin oxide type semiconductor layers, or crystalline silicon.
When the solar cell 100 (101) according to the first embodiment or the second embodiment is used as a first solar cell, absorption of light having unintended wavelengths by the first solar cell can be prevented, and thus decrease in conversion efficiency of a bottom cell (second solar cell) can be prevented. Accordingly, a high-efficiency multijunction solar cell can be achieved.
(Fourth Embodiment)
A fourth embodiment relates to a solar cell module. FIG. 4 shows a perspective conceptual diagram of a solar cell module 300 of the fourth embodiment. The solar cell module 300 in FIG. 4 is a solar cell module in which a first solar cell module 301 and a second solar cell module 302 are laminated. The first solar cell module 301 exists on the light incident side. As the first solar cell module 301, the solar cell 100 of the first embodiment is used. For the second solar cell module 302, the second solar cell 201 is preferably used.
FIG. 5 shows a sectional conceptual diagram of the solar cell module 300. In FIG. 5, the structure of the first solar cell module 301 is illustrated in detail, and the structure of the second solar cell module 302 is omitted. In the second solar cell module 302, the structure of the solar cell module is appropriately selected depending on a photoelectric conversion layer and the like of the solar cell to be used. The solar cell module in FIG. 5 includes a plurality of submodules 303 surrounded by dashed line, in which each of the submodules 303 contains a plurality of solar cells 100 (photovoltaic cells) arranged laterally and electrically connected in series. The submodules 303 are electrically connected in parallel or serial.
The solar cell 100 has been scribed. In adjacent solar cells 100, a second electrode 4 on the upper side of a solar cell 100 is connected with a first electrode 1 on the lower side of a different solar cell 100. The solar cell 100 of the fourth embodiment has, as in the solar cell 100 (101) of the first embodiment or the second embodiment, a substrate 10, a first electrode 1, a photoelectric conversion layer 2, an n-type layer 3, and a second electrode 4.
When output voltages of the modules are different from each other, reverse flow of electric current to a low voltage module may occur, or unnecessary heat may be produced, which may results in decrease in output of the modules.
Further, embodiments of the present application can provide solar cells suitable for different wavelength bands. Thus, when the solar cells of the embodiments are used, efficient generation of electricity becomes possible as compared to when a solar cell of the top cell or the bottom cell is used alone, and the total output of modules can be increased, which is preferred.
When total conversion efficiency of modules is increased, the proportion of energy converted to heat in the energy of irradiated light can be decreased. Thus, decrease in efficiency due to increase in temperature of the modules as a whole can be prevented.
(Fifth Embodiment)
A fifth embodiment relates to a solar power generation system. A solar cell module 300 of the fourth embodiment can be used as a power generator for generating electricity in the solar power generation system of the fifth embodiment. The solar power generation system of the embodiment generates electricity using a solar cell module, and specifically has a solar cell module configured to generate electricity, a unit configured to perform electric power conversion of the generated electricity, and an electricity accumulator configured to store the generated electricity or a load configured to consume the generated electricity. FIG. 6 shows a structural conceptual diagram of a solar power generation system 400 of the embodiment. The solar power generation system in FIG. 6 has a solar cell module 401 (300), an electric power conversion device 402, a storage battery 403, and a load 404. Any one of the storage battery 403 and the load 404 may be omitted. The load 404 can have a configuration capable of using the electric energy stored in the storage battery 403. The electric power conversion device 402 is a device including a circuit or an element configured to perform electric power conversion such as transformation or DC-AC conversion. The electric power conversion device 402 may have a suitable configuration depending on the generated voltage, and the configurations of the storage battery 403 and the load 404.
A photovoltaic cell included in the submodules 303, which is included in the solar cell module 300 and has received light, generates electricity. The electric energy of the generated electricity is converted by the converter 402, and stored in the storage battery 403 or consumed by the load 404. It is preferred that the solar cell module 401 is provided with a solar tracking actuator for constantly directing the solar cell module 401 to the sun, a light collector for collecting sunlight, or a device for improving electricity generation efficiency.
The solar power generation system 400 is preferably used for immovables such as residences, commercial facilities, and factories, or used for movables such as vehicles, aircrafts, and electronic equipment. When the solar cell having excellent conversion efficiency of the embodiment is used for the solar cell module 401, an increase in the amount of electricity generation is expected.
A vehicle is provided as an example of the application of the solar power generation system 400. FIG. 7 shows a structural conceptual diagram of the vehicle 500. The vehicle 500 in FIG. 7 has a car body 501, a solar cell module 502, an electric power conversion device 503, a storage battery 504, a motor 505, and a tire (wheel) 506. Electricity generated by the solar cell module 502 provided on the car body 501 is converted by the electric power conversion device 503, and stored in the storage battery 504, or the electric power is consumed by a load such as the motor 505. The tire (wheel) 506 can be rotated by the motor 505 using electric power supplied from the solar cell module 502 or the storage battery 504, and the vehicle 500 can be moved. The solar cell module 502 is not limited to a multijunction solar cell, but may consists only of a first solar cell module having the solar cell 100 of the first embodiment. When a transparent solar cell module 502 is used, it is also preferred that the solar cell module 502 is used as an electricity-generating side window of the car body 501 in addition to providing the solar cell module 502 on the top of the car body 501.
The present disclosure will be described in more detail below with reference to Examples, but the present disclosure is not limited to the following Examples.
(EXAMPLE 1)
On a white sheet glass substrate, an ITO transparent conductive film as a first electrode on a rear surface side is deposited, and a Sb doped SnO2 transparent conductive film is deposited on the ITO transparent conductive film. A film of a cuprous oxide compound is formed on the first transparent electrode by sputtering in a mixed gas atmosphere containing oxygen and argon gases and heating the substrate at 450°C. Then, 10 nm of an n-type Zn0.78Sn0.21Al0.02O1 (z/(x + y) = 0.02, (x + y + z)/w = 1.01) is deposited on the p-cuprous oxide layer by atomic layer deposition. Thereafter, an AZO transparent conductive film as a second electrode on a front surface side is deposited. On the AZO transparent conductive film, MgF2 as an antireflective film is deposited to obtain a solar cell.
Using a solar simulator simulating a light source of AM 1.5G, and using a Si cell as a reference under the light source, the amount of light is adjusted to be 1 sun. The ambient temperature is 25°C. Voltage sweeping is performed to measure current density (current/area of the cell). When the horizontal axis is voltage and the vertical axis is the current density, the point that intersects the horizontal axis is open voltage Voc and the point that intersects the vertical axis is short-circuit current density Jsc. On the curve obtained by the measurement, the voltage is multiplied by the current density, and a maximum point of voltage and a maximum point of current density are denoted by Vmpp and Jmpp (maximum power points), respectively. Then, FF (= (Vmpp * Jmpp) /(Voc * Jsc)) and efficiency Eff. (= Voc * Jsc * FF) are determined.
(Example 2)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Ga0.05O1 (z/(x + y) = 0.05, (x + y + z)/w = 1.04) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 3)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21In0.10O1 (z/(x + y) = 0.1, (x + y + z)/w = 1.09) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 4)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21B0.05O1 (z/(x + y) = 0.051, (x + y + z)/w = 1.04) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 5)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Al0.001O1 (z/(x + y) = 0.001, (x + y + z)/w = 0.99) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 6)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Al0.98O2 (z/(x + y) = 0.99, (x + y + z)/w = 0.99) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 7)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Al0.01O1 (z/(x + y) = 0.01, (x + y + z)/w = 1.00) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 8)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Al0.1O1 (z/(x + y) = 0.1, (x + y + z)/w = 1.09) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 9)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.20Al0.02O1 (z/(x + y) = 0.02, (x + y + z)/w = 1.00) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 10)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.22Al0.03O1 (z/(x + y) = 0.03, (x + y + z)/w = 1.03) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 11)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Al0.015Ga0.015O1 (z/(x + y) = 0.03, (x + y + z)/w = 1.02) is deposited as an n-type layer, and the properties of the cell are evaluated.
(Example 12)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.77Sn0.19Al0.02O0.8 (z/(x + y) = 0.02, (x + y + z)/w = 1.23) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 13)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.77Sn0.19Al0.02O1.3 (z/(x + y) = 0.02, (x + y + z)/w = 0.75) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 14)
A solar cell is manufactured as in Example 1, except that 3 nm of Zn0.8Sn0.21Al0.02O1 (z/(x + y) = 0.02, (x + y + z)/w = 1.03) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 15)
A solar cell is manufactured as in Example 1, except that 50 nm of Zn0.78Sn0.21Al0.02O1.6 (z/(x + y) = 0.02, (x + y + z)/w = 0.63) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 16)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Al0.0008O1 (z/(x + y) = 0.0008, (x + y + z)/w = 0.99) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 17)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Al1.1O2 (z/(x + y) = 1.1, (x + y + z)/w = 1.05) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 18)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Al0.6O1 (z/(x + y) = 0.6, (x + y + z)/w = 1.59) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 19)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Al0.49O1 (z/(x + y) = 0.50, (x + y + z)/w = 1.48) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 20)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Al0.40O1 (z/(x + y) = 0.40, (x + y + z)/w = 1.39) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 21)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Al0.25O1 (z/(x + y) = 0.25, (x + y + z)/w = 1.24) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 22)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Al0.20O1 (z/(x + y) = 0.20, (x + y + z)/w = 1.19) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 23)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Al0.0004O1 (z/(x + y) = 0.0004, (x + y + z)/w = 0.99) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 24)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Al1.5O2 (z/(x + y) = 1.52, (x + y + z)/w = 1.25) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 25)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Al0.016In0.016Ga0.016O2 (z/(x + y) = 0.048, (x + y + z)/w = 1.04) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 26)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Al0.002O2.5 (z/(x + y) = 0.002, (x + y + z)/w = 0.40) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 27)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Si0.01O1 (z/(x + y) = 0.01, (x + y + z)/w = 1.00) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 28)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Ge0.04O1 (z/(x + y) = 0.04, (x + y + z)/w = 1.03) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 29)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Zr0.08O1 (z/(x + y) = 0.08, (x + y + z)/w = 1.07) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 30)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Hf0.08O1 (z/(x + y) = 0.08, (x + y + z)/w = 1.07) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 31)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Si0.002O1 (z/(x + y) = 0.002, (x + y + z)/w = 0.99) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 32)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Si0.77O2 (z/(x + y) = 0.78, (x + y + z)/w = 0.88) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 33)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Si0.02O1 (z/(x + y) = 0.02, (x + y + z)/w = 1.01) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 34)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Si0.17O1 (z/(x + y) = 0.17, (x + y + z)/w = 1.16) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 35)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.20Si0.04O1 (z/(x + y) = 0.04, (x + y + z)/w = 1.02) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 36)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.22Si0.05O1 (z/(x + y) = 0.05, (x + y + z)/w = 1.05) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 37)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Si0.025Hf0.025O1 (z/(x + y) = 0.05, (x + y + z)/w = 1.04) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 38)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.77Sn0.19Si0.01O0.8 (z/(x + y) = 0.01, (x + y + z)/w = 1.23) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 39)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.77Sn0.19Si0.01O1.3 (z/(x + y) = 0.01, (x + y + z)/w = 0.75) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 40)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Si0.008O1 (z/(x + y) = 0.008, (x + y + z)/w = 1.00) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 41)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Si0.01O1.6 (z/(x + y) = 0.01, (x + y + z)/w = 0.63) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 42)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Si0.002O0.7 (z/(x + y) = 0.002, (x + y + z)/w = 1.42) is deposited as an n-type layer and the properties of the solar cell are evaluated.
(Example 43)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Si1.2O2 (z/(x + y) = 1.21, (x + y + z)/w = 1.10) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 44)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Si0.032Al0.016O1 (z/(x + y) = 0.048, (x + y + z)/w = 1.04) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 45)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Si0.5O1 (z/(x + y) = 0.51, (x + y + z)/w = 1.49) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 46)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Si0.6O1 (z/(x + y) = 0.61, (x + y + z)/w = 1.59) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 47)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Si0.4O1 (z/(x + y) = 0.40, (x + y + z)/w = 1.39) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 48)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Si0.3O1 (z/(x + y) = 0.30, (x + y + z)/w = 1.29) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 49)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Si0.00002O1 (z/(x + y) = 0.00002, (x + y + z)/w = 0.99) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 50)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Si0.0002O1 (z/(x + y) = 0.0002, (x + y + z)/w = 0.99) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 51)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Si1.5O2 (z/(x + y) = 1.52, (x + y + z)/w = 1.25) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 52)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Si0.024Ge0.012Zr0.012O2 (z/(x + y) = 0.048, (x + y + z)/w = 1.04) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Example 53)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21Si0.002O2.5 (z/(x + y) = 0.002, (x + y + z)/w = 0.40) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
(Comparative Example 1)
A solar cell is manufactured as in Example 1, except that 10 nm of Zn0.78Sn0.21O1 (z/(x + y) = 0, (x + y + z)/w = 0.99) is deposited as an n-type layer, and the properties of the solar cell are evaluated.
The results of evaluations in Examples and Comparative Example are shown in Tables 1 and 2. When Voc is improved by 0.2 V or more as compared to the Voc in Comparative Example 1, the result is evaluated as grade "A". When Voc is the same as the Voc in Comparative Example 1, or improved by less than 0.2 V (including the case in which Voc is decreased) as compared to the Voc in Comparative Example 1, the result is evaluated as grade "B". When Voc is decreased as compared to the Voc in Comparative Example 1, the result is evaluated as grade "C". When transmittance at 350 nm is 50% or more and is higher than the transmittance in Comparative Example 1, the result is evaluated as grade "A", and other results are evaluated as grade "B". When FF in Example is higher than the FF in Comparative Example 1 by 10% or more, the result is evaluated as grade "A+". When FF in Example is higher than the FF in Comparative Example 1 by 5% or more and less than 10%, the result is evaluated as grade "A". Other results (e.g., FF is comparable with the FF in Comparative Example 1) are evaluated as grade "B". The compositions of n-type layers in Examples and Comparative Example are compositions calculated from conditions for forming the layers.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
All the solar cells in Examples have superior transmittance and improved Voc as compared to the solar cell in Comparative Example 1 which does not contain a Group III element. When Voc is increased by 0.2 V, Voc is increased by about at least 20%, which largely contributes to improvement in conversion efficiency. In Example using a different Group III element, a solar cell having high transmittance and Voc is also obtained. Although the amount of Group III element added may be large to some extent, when the amount added is too large, the properties tend to be decreased. When the amount of Group III elements added is small, properties are close to the properties in Comparative Example 1, but the properties are still superior to the properties without Group III element. In any one of the solar cells in Examples, FF is higher than the FF in Comparative Example. It is assumed that the higher Voc in Example than in Comparative Example exerts an influence on the FF. Further, in Examples 27 to 53, FF is higher than in Examples 1 to 26. It is assumed that this is due to the influence of superior physical properties of electrons (electron concentration and electron mobility) of n-type layers containing a Group IV element and smaller electrical resistance of the n layer. The solar cells in Examples have excellent transmittance of light having long wavelengths, in addition to excellent transmittance of light having short wavelengths. Thus, in a multijunction solar cell in which a solar cell of the embodiment or the like is used as a top cell and, for example, Si is used as a bottom cell, the solar cell of the embodiment contributes to improvement in total amount of electricity production.
Herein, some elements are expressed only by element symbols of the elements.
Clauses of the embodiments are additionally provided below.
Clause 1
A solar cell comprising:
a first transparent electrode;
a photoelectric conversion layer containing cuprous oxide as a main component on the first electrode;
an n-type layer being a metal oxide layer containing Zn, Sn, and one or more elements selected from the group consisting of Al, Ga, In, and B and/or one or more elements M selected from the group consisting of Si, Ge, Zr, and Hf, on the photoelectric conversion layer; and
a second transparent electrode on the n-type layer.
Clause 2
The solar cell according to clause 1, wherein
the n-type layer is a layer including a compound represented by ZnxSnyMzOw, and
x, y, and z satisfy 0.001 ≦ (z/(x + y)) < 1.00.
Clause 3
The solar cell according to clause 1 or 2, wherein
the n-type layer is a layer including a compound represented by ZnxSnyMzOw, and
x, y, and z satisfy 0.001 ≦ (z/(x + y)) < 0.5.
Clause 4
The solar cell according to any one of clauses 1 to 3, wherein
the n-type layer is a layer including a compound represented by ZnxSnyMzOw,
x, y, and z satisfy 0.001 ≦ (z/(x + y)) < 1.00, and
x, y, z, and w satisfy 0.6 ≦ (x + y + z)/w ≦ 1.4.
Clause 5
The solar cell according to any one of clauses 1 to 4, wherein
the n-type layer has a thickness of 3 nm or more and 50 nm or less.
Clause 6
The solar cell according to any one of clauses 1 to 5, wherein
the element M is one or more elements selected from the group consisting of Al, Ga, In, and B.
Clause 7
The solar cell according to any one of clauses 1 to 5, wherein
the element M is one or more elements selected from the group consisting of Si, Ge, Zr, and Hf.
Clause 8
The solar cell according to any one of clauses 1 to 5, wherein
the element M is one or more elements selected from the group consisting of Al, Ga, In, and B, and one or more elements selected from the group consisting of Si, Ge, Zr, and Hf.
Clause 9
The solar cell according to any one of clauses 1 to 8, wherein
the n-type layer has a transmittance of light having a wavelength of 350 nm of 90% or more.
Clause 10
The solar cell according to any one of clauses 1 to 9, wherein
cuprous oxide accounts for at least 90 wt% of the photoelectric conversion layer.
Clause 11
The solar cell according to any one of clauses 1 to 10, wherein
the n-type layer has a thickness of 5 nm or more and 50 nm or less.
Clause 12
A multijunction solar cell including the solar cell according to any one of clauses 1 to 11.
Clause 13
A solar cell module including the solar cell according to any one of clauses 1 to 11.
Clause 14
A solar power generation system configured to generate electricity using the solar cell module according to clause 13.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
100, 101 Solar cell (first solar cell, top cell)
1 First electrode
2 Photoelectric conversion layer
3(3A, 3B) n-type layer
4 Second electrode
200 Multijunction solar cell
201 Second solar cell (Bottom cell)
300 Solar cell module
301 First solar cell module
302 Second solar cell module
10 Substrate
303 Submodules
400 Solar power generation system
401 Solar cell module
402 Electric power conversion device
403 Storage battery
404 Load
500 Vehicle
501 Car body
502 Solar cell module
503 Electric power conversion device
504 Storage battery
505 Motor
506 Tire (wheel)

Claims (14)

  1. A solar cell comprising:
    a first transparent electrode;
    a photoelectric conversion layer including cuprous oxide as a main component on the first electrode;
    an n-type layer being a metal oxide layer containing Zn, Sn, and element M which is one or more elements selected from the group consisting of Al, Ga, In, and B and/or one or more elements selected from the group consisting of Si, Ge, Zr, and Hf, on the photoelectric conversion layer; and
    a second transparent electrode on the n-type layer.
  2. The solar cell according to claim 1, wherein
    the n-type layer is a layer including a compound represented by ZnxSnyMzOw, and
    x, y, and z satisfy 0.001 ≦ (z/(x + y)) < 1.00.
  3. The solar cell according to claim 1 or 2, wherein
    the n-type layer is a layer including a compound represented by ZnxSnyMzOw, and
    x, y, and z satisfy 0.001 ≦ (z/(x + y)) < 0.5.
  4. The solar cell according to any one of claims 1 to 3, wherein
    the n-type layer is a layer including a compound represented by ZnxSnyMzOw,
    x, y, and z satisfy 0.001 ≦ (z/(x + y)) < 1.00, and
    x, y, z, and w satisfy 0.6 ≦ (x + y + z)/w ≦ 1.4.
  5. The solar cell according to any one of claims 1 to 4, wherein
    the n-type layer has a thickness of 3 nm or more and 50 nm or less.
  6. The solar cell according to any one of claims 1 to 5, wherein
    the element M is one or more elements selected from the group consisting of Al, Ga, In, and B.
  7. The solar cell according to any one of claims 1 to 5, wherein
    the element M is one or more elements selected from the group consisting of Si, Ge, Zr, and Hf.
  8. The solar cell according to any one of claims 1 to 5, wherein
    the element M is one or more elements selected from the group consisting of Al, Ga, In, and B, and one or more elements selected from the group consisting of Si, Ge, Zr, and Hf.
  9. The solar cell according to any one of claims 1 to 8, wherein
    the n-type layer has a transmittance of light having a wavelength of 350 nm of 90% or more.
  10. The solar cell according to any one of claims 1 to 9, wherein
    cuprous oxide accounts for at least 90 wt% of the photoelectric conversion layer.
  11. The solar cell according to any one of claims 1 to 10, wherein
    the n-type layer has a thickness of 5 nm or more and 50 nm or less.
  12. A multijunction solar cell comprising the solar cell according to any one of claims 1 to 11.
  13. A solar cell module comprising the solar cell according to any one of claims 1 to 11.
  14. A solar power generation system configured to generate electricity using the solar cell module according to claim 13.

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