WO2020250521A1 - Solar cell, multi-junction solar cell, solar cell module, and solar power generation system - Google Patents

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

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WO2020250521A1
WO2020250521A1 PCT/JP2020/011291 JP2020011291W WO2020250521A1 WO 2020250521 A1 WO2020250521 A1 WO 2020250521A1 JP 2020011291 W JP2020011291 W JP 2020011291W WO 2020250521 A1 WO2020250521 A1 WO 2020250521A1
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concentration
solar cell
electrode
layer
photoelectric conversion
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PCT/JP2020/011291
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French (fr)
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Soichiro SHIBASAKI
Yuya HONISHI
Naoyuki Nakagawa
Mutsuki Yamazaki
Yoshiko Hiraoka
Kazushige Yamamoto
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Kabushiki Kaisha Toshiba
Toshiba Energy Systems & Solutions Corporation
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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
    • Y02E10/52—PV systems with concentrators

Definitions

  • Embodiments described herein relate generally to a solar cell, a multi-junction solar cell, a solar cell module, and a solar power generation system.
  • Tandem solar cells can be more efficient than single junction solar cells because cells having high spectral sensitivity for each wavelength band can be used in the tandem solar cells.
  • cuprous oxide compounds or the like being inexpensive, the cuprous oxide compounds or the like having a wide band gap are expected.
  • Embodiments described herein provide a solar cell, a multi-junction solar cell, a solar cell module, and a solar power generation system with improved characteristics.
  • the solar cell according to an embodiment includes a first electrode being transparent, a photoelectric conversion layer mainly including cuprous oxide on the first electrode, an n-type layer being a metal oxide layer containing Zn and Si on the photoelectric conversion layer, and a second electrode being transparent on the n-type layer.
  • FIG. 1 is a conceptual sectional view of a solar cell according to an embodiment.
  • FIG. 2 is a view illustrating analysis spots of the solar cell according to the embodiment.
  • FIG. 3 is a conceptual sectional view of a multi-junction solar cell according to the embodiment.
  • FIG. 4 is a conceptual view of a solar cell module according to the embodiment.
  • FIG. 5 is a conceptual sectional view of the solar cell module according to the embodiment.
  • FIG. 6 is a conceptual diagram of a solar power generation system according to the embodiment.
  • FIG. 7 is a conceptual diagram of a vehicle according to the embodiment.
  • FIG. 1 is a conceptual view of a solar cell 100 according to the first embodiment.
  • the solar cell 100 according to the embodiment includes a first electrode 1, a photoelectric conversion layer 2 on the first electrode 1, an n-type layer 3 on the photoelectric conversion layer 2, and a second electrode 4 on the n-type layer 3.
  • An intermediate layer (not shown) may be included between the first electrode 1 and the photoelectric conversion layer 2 or between the n-type layer 3 and the second electrode 4.
  • Light may be incident from the first electrode 1 side or from the second electrode 4 side. When the light is incident on the solar cell 100, the solar cell 100 can generate power.
  • the first electrode 1 is a transparent conductive layer 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.
  • the first electrode 1 is preferably a transparent conductive film, or a stack of a metal film, a transparent conductive film, and a metal film.
  • the transparent conductive film examples include indium tin oxide (Indium Tin Oxide; ITO), aluminum-doped zinc oxide (Al-doped Zinc Oxide; AZO), boron-doped zinc oxide (Boron-doped Zinc Oxide; BZO), gallium-doped zinc oxide (Gallium-doped Zinc Oxide; GZO), fluorine-doped tin oxide (Fluorine-doped Tin Oxide; FTO), antimony-doped tin oxide (Antimony-doped Tin Oxide; ATO), titanium-doped indium oxide (Titanium-doped Indium Oxide; ITiO), indium zinc oxide (Indium Zinc Oxide; IZO), indium gallium zinc oxide (Indium Gallium Zinc Oxide; IGZO), tantalum-doped tin oxide (Ta-doped Tin Oxide; SnO 2 : Ta), niobium-doped tin
  • the transparent conductive film may be a stacked film having a plurality of films, and the stacked film may include a film such as tin oxide in addition to the above-mentioned oxides.
  • the dopant for the film such as tin oxide include In, Si, Ge, Ti, Cu, Sb, Nb, F, Ta, W, Mo, F, and Cl, and are not particularly limited thereto.
  • the metal film include a film such as Mo, Au, Cu, Ag, Al, Ta, or W, and are not particularly limited thereto.
  • the first electrode 1 may be an electrode in which a dot-shaped, line-shaped, or mesh-shaped metal is provided on the transparent conductive film.
  • the dot-shaped, line-shaped, or mesh-shaped metal is disposed between the transparent conductive film and the photoelectric conversion layer 2 or on the opposite side of the transparent conductive film from the photoelectric conversion layer 2.
  • the dot-shaped, line-shaped, or mesh-shaped metal preferably has a numerical aperture of 50% or more based on the transparent conductive film.
  • Examples of the dot-shaped, line-shaped or mesh-shaped metal include Mo, Au, Cu, Ag, Al, Ta, and W, and are not particularly limited thereto.
  • the metal film preferably has a thickness of about 5 nm or less from the viewpoint of transparency. When the line-shaped or mesh-shaped metal film is used, the transparency is ensured at the aperture, so that the thickness of the metal film is not limited to the above-mentioned thickness.
  • the photoelectric conversion layer 2 is a semiconductor layer disposed between the first electrode 1 and the n-type layer 3.
  • the photoelectric conversion layer 2 is preferably a compound semiconductor layer.
  • Examples of the photoelectric conversion layer 2 include a semiconductor layer mainly including cuprous oxide (90% by weight or more).
  • the photoelectric conversion layer 2 is more specifically a p-type compound semiconductor layer.
  • the compound semiconductor layer is preferably a semiconductor layer mainly including cuprous oxide.
  • the photoelectric conversion layer 2 preferably has a thickness of 800 nm or more and 10 micro meter or less.
  • the semiconductor layer mainly including cuprous oxide and the like may contain an additive.
  • the photoelectric conversion layer 2 is p-type (including p + type) as a whole.
  • the n-type layer 3 side of the photoelectric conversion layer 2 may partially include an n-type region.
  • the photoelectric conversion layer 2 is produced by sputtering.
  • the atmosphere during the sputtering is preferably an atmosphere of a mixed gas of an inert gas such as Ar and an oxygen gas.
  • the substrate is heated to a temperature of 100°C or more and 600°C or less, and the sputtering is performed using a target containing Cu.
  • a thin film of cuprous oxide having a large particle size can be formed on the first electrode 1 by adjusting the temperature and the oxygen partial pressure during the sputtering.
  • Examples of the substrate used to produce the solar cell 100 include organic substrates such as acrylics, polyimides, polycarbonate, polyethylene terephthalate (PET), polypropylene (PP), fluorine-based resins (polytetrafluoroethylene (PTFE), perfluoroethylene propene copolymers (FEP), ethylene tetrafluoroethylene copolymers (ETFE), polychlorotrifluoroethylene (PCTFE), perfluoroalkoxyalkane (PFA), and the like), polyarylate, polysulfone, polyether sulfone, and polyether imide, and inorganic substrates such as soda-lime glass, white plate glass, chemically strengthened glass, and quartz.
  • organic substrates such as acrylics, polyimides, polycarbonate, polyethylene terephthalate (PET), polypropylene (PP), fluorine-based resins (polytetrafluoroethylene (PTFE), perfluoroethylene propene copolymers (FE
  • the photoelectric conversion layer 2 preferably includes 95% or more of cuprous oxide.
  • the photoelectric conversion layer 2 more preferably includes 98% or more of cuprous oxide. That is, the photoelectric conversion layer 2 preferably contains few (substantially no) different phases such as CuO and Cu.
  • the photoelectric conversion layer 2 preferably contains no different phases such as CuO and Cu and is preferably a thin film of substantially a single phase of Cu 2 O, because such a photoelectric conversion layer 2 has a very high light-transmitting property.
  • the fact that the photoelectric conversion layer 2 is substantially a single phase of Cu 2 O can be confirmed by measurement by a photoluminescence method (Photo Luminescence; PL method).
  • the n-type layer 3 is an n-type semiconductor layer disposed between the photoelectric conversion layer 2 and the second electrode 4. It is preferable that the surface of the n-type layer 3 facing the photoelectric conversion layer 2 be in direct contact with the surface of the photoelectric conversion layer 2 facing the n-type layer 3.
  • the n-type layer 3 is preferably an amorphous thin film.
  • the n-type layer 3 is preferably a metal oxide layer containing Zn and Si.
  • the metal oxide layer (the n-type layer 3) is preferably a layer including a compound represented by Zn x Si y M z O w wherein x and y satisfy 0.90 ⁇ x + y ⁇ 1.00, z satisfies 0.00 ⁇ z ⁇ 0.30, w satisfies 0.90 ⁇ w ⁇ 1.10, and M is at least one element selected from the group consisting of B, Al, Ga, In, and Ge.
  • the metal oxide layer is preferably substantially made of Zn x Si y M z O w except for an inevitable impurity.
  • n-type layer When x, y, z, and w are within the above-mentioned ranges, a good n-type layer is formed, and the position of the conduction band of the Cu 2 O film and the n-type layer can be kept within a preferable range.
  • ZnGeO being a mixture of Zn and Ge oxides
  • ZnGeO containing a high concentration of Ge for example, ZnGeO having a Ge content higher than a Zn content, more specifically ZnGeO containing Ge in the range of about 0.6 ⁇ (Ge [atom%])/(Zn [atom%] + Ge [atom%]) ⁇ 0.7 has a small difference in the conduction band minimum (Conduction Band Minimum: CBM) from cuprous oxide, and is expected to provide a high fill factor (Fill Factor: FF) and a high Voc.
  • CBM Conduction Band Minimum
  • FF Fill Factor
  • the solar cell in which a film of ZnGeO is formed on the photoelectric conversion layer 2 mainly including cuprous oxide has a Voc and an FF lower than the theoretical values, so that the conversion efficiency is not improved to the extent expected even when the high-quality photoelectric conversion layer 2 is used.
  • the n-type layer 3 preferably contains Zn at a ratio higher than that of Si. It is preferable that y being the Si content satisfy 0.10 ⁇ y ⁇ 0.50. It is not preferable that the Si content is less than 0.10, because when the Si content is less than 0.10, the increase in the conversion efficiency is small, that is, the difference in the conduction band (the conduction band offset) between the Cu 2 O layer 2 and the n-type layer 3 is large.
  • the Si content is larger than 0.5, it is considered that Si diffuses to the Cu 2 O side more than Zn does, and quality of the pn junction with the n-type layer 3 is easily affected.
  • y is larger than 0.50, because when y is larger than 0.50, the electrical conductivity of the n-type layer 3 tends to be lost, and the n-type layer 3 becomes an insulator.
  • the photoelectric conversion layer 2 contains trace amounts of Zn and Si.
  • the concentration of Zn contained in the photoelectric conversion layer 2 is preferably higher than the concentration of Si contained in the photoelectric conversion layer 2. This is because the pn junction between the region on the n-type layer side of Cu 2 O and the n-type layer 3 can be improved.
  • the concentration of Zn contained in the photoelectric conversion layer 2 is more preferably three times or more higher than the concentration of Si. It is more preferable that the concentration of Zn be higher than the concentration of Si, because when the concentration of Zn is higher than the concentration of Si, the FF and the Voc are increased and the above-mentioned relationships can be satisfied.
  • Zn be present in the deeper portion (the first electrode 1 side) of the photoelectric conversion layer 2 in a larger amount than Si. It is possible that in a region from the surface on the n-type layer 3 side of the photoelectric conversion layer 2 to the depth of, for example, 6 nm toward the first electrode 1, trace amounts of Zn and Si present in the interface side of the photoelectric conversion layer 2 on the n-type layer 3 contribute to the property of the photoelectric conversion layer 2 to form a good pn junction with the n-type layer 3.
  • the Zn and Si may be diffused from the n-type layer 3 or may be intentionally added in trace amounts during the formation of the photoelectric conversion layer 2.
  • the average concentration of Zn in the region from the interface between the photoelectric conversion layer 2 and the n-type layer 3 (the starting point) to the depth of 3 nm in the direction toward the first electrode 1 (the end point) is referred to as the first Zn concentration
  • the average concentration of Zn in the region from the depth of 3 nm from the interface between the photoelectric conversion layer 2 and the n-type layer 3 in the direction toward the first electrode 1 (the starting point) to the depth 3 nm deeper in the direction toward the first electrode 1 (the end point) is referred to as the second Zn concentration
  • the average concentration of Si in the region from the interface between the photoelectric conversion layer 2 and the n-type layer 3 (the starting point) to the depth of 3 nm in the direction toward the first electrode 1 (the end point) is referred to as the first Si concentration
  • the relationships [the first Zn concentration] > [the first Si concentration], [the second Zn concentration] > [the second Si concentration], [the first Zn concentration] > [the second Zn concentration], and [the first Si concentration] > [the second Si concentration] are satisfied. It is more preferable that the relationship 3([the first Zn concentration]/[the first Si concentration]) ⁇ ([the second Zn concentration]/[the second Si concentration]) be satisfied.
  • the comparison between the interface side and the deep portion side indicates that the ratio of the Zn concentration to the Si concentration in the deep portion side is three times or more (greater) than the ratio of the Zn concentration to the Si concentration in the interface side.
  • the above-mentioned concentrations are determined by energy dispersive X-ray spectroscopy (Energy Dispersive X-ray Spectroscopy; EDX) by cutting out a cross section in the direction of the conceptual view in FIG. 1 and scanning from the n-type layer 3 side to the photoelectric conversion layer 2.
  • EDX Energy Dispersive X-ray Spectroscopy
  • the boundary (interface) between the photoelectric conversion layer 2 and the n-type layer 3 is also determined by EDX.
  • the boundary between the photoelectric conversion layer 2 and the n-type layer 3 is determined as described below.
  • the Cu concentration and the Zn concentration are measured by EDX, and the closest position to the second electrode 4 in the n-type layer 3 at which the Cu concentration is equal to or higher than the Zn concentration is set as a boundary.
  • each spot is square and has a region of at least 5 mm 2 . As shown in FIG.
  • the cross section observed by SEM or TEM is perpendicular to the plane shown in FIG. 2.
  • the concentration is the average value of the seven analysis results excluding the maximum and minimum values of the nine analysis spots.
  • the thickness of the n-type layer 3 is typically 3 nm or more and 100 nm or less. When the thickness of the n-type layer 3 is less than 3 nm and the coverage of the n-type layer 3 is poor, a leak current may be generated and the characteristics may be deteriorated. When the coverage is good, the thickness is not limited to the above-mentioned thickness. When the thickness of the n-type layer 3 exceeds 50 nm, the characteristics may be deteriorated due to an excessive increase in the resistance of the n-type layer 3, or the short-circuit current may be reduced due to a decrease in the transmittance.
  • the thickness of the n-type layer 3 is more preferably 3 nm or more and 50 nm or less, and still more preferably 5 nm or more and 20 nm or less.
  • the transmittance of the top cell mainly depends on the quality of the photoelectric conversion layer, for example, the quality of the Cu 2 O film.
  • the n-type layer 3 can be formed by, for example, an atomic layer deposition (Atomic Layer Deposition; ALD) method or a sputtering method.
  • ALD atomic layer deposition
  • the conduction band offset is more than 0, the conduction band at the pn junction interface is discontinuous and a spike is caused.
  • the conduction band offset is less than 0, the conduction band at the pn junction interface is discontinuous and a cliff is caused.
  • 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).
  • the position of the CBM can be estimated using the following method.
  • the valence band maximum (Valence Band Maximum: VBM) is actually measured by photoelectron spectroscopy being a method for evaluating an electron occupation level, and then the band gap of the material to be measured is assumed to calculate the CBM.
  • the CBM is also evaluated by inverse photoelectron spectroscopy that directly uses the reverse process of photoelectron emission.
  • the electronic state of the pn junction interface can be evaluated by repeating low-energy ion etching and forward/inverse photoelectron spectroscopy of the solar cell surface.
  • the ratio between Zn and Si in the n-type layer 3 can be appropriately selected within the above-mentioned preferred range in consideration of the difference in the CBM.
  • the same transparent electrode as the electrode described for the first electrode 1 is preferably used.
  • another transparent electrode such as a multilayer graphene provided with an extraction electrode including a metal wire can also be used.
  • a metal auxiliary electrode may be deposited on the second electrode 4 if necessary.
  • the antireflection film according to the embodiment is a film for facilitating the introduction of light to the photoelectric conversion layer 2, and is preferably formed on the opposite side from the photoelectric conversion layer 2 side on the first electrode 1 or the second electrode 4.
  • the antireflection film for example, MgF 2 or SiO 2 is desirably used.
  • the antireflection film can be omitted.
  • it is necessary to adjust the film thickness depending on the refractive index of each layer it is preferable to deposit a thin film having a thickness of about 70 to 130 nm (preferably, 80 to 120 nm).
  • FIG. 3 shows a conceptual sectional view of a multi-junction solar cell 200 according to the second embodiment.
  • the multi-junction solar cell 200 shown in FIG. 3 includes the solar cell according to the first embodiment (first solar cell) 100 in the light incidence side and a second solar cell 201.
  • the band gap of the 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 according to the first embodiment.
  • Examples of the multi-junction solar cell according to the embodiment include a solar cell in which three or more solar cells are joined.
  • the band gap of the photoelectric conversion layer 2 of the solar cell 100 according to the first embodiment is about 2.0 eV
  • the band gap of the photoelectric conversion layer of the second solar cell 201 is preferably 1.0 eV or more and 1.4 eV or less.
  • a compound semiconductor layer including one or more of CIGS-based and CIT-based compound semiconductor layers containing a high content ratio of In, CdTe-based compound semiconductor layers, and copper oxide-based compound semiconductor layers, or crystalline silicon is preferable.
  • the solar cell 100 according to the first embodiment As the first solar cell, it is possible to prevent the reduction in the conversion efficiency of the bottom cell (the second solar cell) due to a first solar cell absorbing light in an unintended wavelength range, so that an efficient multi-junction solar cell can be obtained.
  • FIG. 4 shows a conceptual perspective view of a solar cell module 300 according to the third embodiment.
  • the solar cell module 300 shown in FIG. 4 is a solar cell module in which a first solar cell module 301 and a second solar cell module 302 are stacked.
  • the first solar cell module 301 is in the light incidence side, and the solar cell 100 according to the first embodiment is used in the first solar cell module 301. It is preferable to use the second solar cell 201 in the second solar cell module 302.
  • FIG. 5 shows a conceptual sectional view of the solar cell module 300.
  • the structure of the first solar cell module 301 is shown in detail, and the structure of the second solar cell module 302 is not shown.
  • the structure of the solar cell module is appropriately selected depending on the photoelectric conversion layer of the used solar cell, and the like.
  • the solar cell module shown in FIG. 5 includes a plurality of sub-modules 303 surrounded by a dashed line in which a plurality of solar cells 100 (photovoltaic cells) are arranged in a horizontal direction and electrically connected in series, and the plurality of sub-modules 303 are electrically connected in parallel or in series.
  • the solar cell 100 is scribed, and the upper second electrode 4 of the solar cell 100 is connected to the lower first electrode 1 of the adjacent solar cell 100.
  • the solar cell 100 according to the third embodiment also includes a substrate 10, a first electrode 1, a photoelectric conversion layer 2, an n-type layer 3, and a second electrode 4 in the same manner as the solar cell 100 according to the first embodiment.
  • the current may flow backward to a low voltage portion or extra heat may be generated, so that the output of the module is reduced.
  • the use of the solar cell makes it possible to use a solar cell suitable for each wavelength band, so that it is possible to generate power more efficiently than when the solar cell of the top cell or the bottom cell is used alone, and the output of the whole module is increased.
  • the conversion efficiency of the whole module is high, the rate of the applied light energy converted to heat can be reduced. Therefore, a reduction in the efficiency due to a rise in the temperature of the whole module can be suppressed.
  • the fourth embodiment relates to a solar power generation system.
  • the solar cell module 300 according to the third embodiment can be used as a generator for generating power in the solar power generation system according to the fourth embodiment.
  • the solar power generation system according to the embodiment generates power using a solar cell module, and specifically includes a solar cell module that generates power, a means with which the power conversion of the generated electricity is performed, and a power storage means with which the generated electricity is stored or a load that consumes generated electricity.
  • FIG. 6 shows a conceptual configuration diagram of a solar power generation system 400 according to the embodiment.
  • the solar power generation system shown in FIG. 6 includes a solar cell module 401 (300), a power conversion device 402, a battery 403, and a load 404.
  • the power conversion device 402 is a device including a circuit or an element that performs power conversion such as voltage transformation or DC/AC conversion. A suitable configuration of the power conversion device 402 is required to be employed depending on the configuration of the generated voltage, the battery 403, and the load 404.
  • the photovoltaic cell included in the sub-module 301 that is included in the solar cell module 300 and receives light generates power, and the electric energy is converted by the converter 402, and stored in the battery 403 or consumed by the load 404.
  • the solar cell module 401 is preferably provided with a solar tracking driving device for constantly directing the solar cell module 401 toward the sun and a light collector for condensing sunlight, and it is preferable to add a device for improving the power generation efficiency, and the like to the solar cell module 401.
  • the solar power generation system 400 is preferably used for real estate such as dwellings, commercial facilities, and factories, or for movable property such as vehicles, aircraft, and electronic devices.
  • real estate such as dwellings, commercial facilities, and factories
  • movable property such as vehicles, aircraft, and electronic devices.
  • FIG. 7 shows a conceptual configuration diagram of a vehicle 500.
  • the vehicle 500 shown in FIG. 7 includes a vehicle body 501, a solar cell module 502, a power conversion device 503, a battery 504, a motor 505, and a tire (wheel) 506.
  • the power generated by the solar cell module 501 provided on the upper part of the vehicle body 501 is converted by the power conversion device 503, and charged in the battery 504 or consumed by the load such as the motor 505.
  • the vehicle 500 can be moved by rotating the tire (wheel) 506 with the motor 505 using the electric power supplied from the solar cell module 501 or the battery 504.
  • the solar cell module 501 may be not a multi-junction solar cell module, and may include only the first solar cell module including the solar cell 100 according to the first embodiment.
  • the transparent solar cell module 501 it is also preferable to use the solar cell module 501 as a window that generates power on the side surface of the vehicle body 501 in addition to the upper part of the vehicle body 501.
  • Example 1 On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO 2 transparent conductive film is deposited on the ITO transparent conductive film.
  • a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C.
  • n-type Zn 0.9 Si 0.1 O is deposited on the p-cuprous oxide layer by an atomic layer deposition method.
  • an AZO transparent conductive film is deposited.
  • a metal auxiliary electrode is deposited.
  • MgF 2 is deposited as an antireflection film to obtain a solar cell.
  • a solar simulator simulating an AM1.5G light source is used, and the light amount is adjusted to 1 sun using a reference Si cell under the light source.
  • the temperature is 25°C.
  • the voltage is swept and the current density (the current divided by the cell area) is measured.
  • the abscissa axis shows the voltage scale and the ordinate axis shows the current density scale
  • the point crossing the abscissa axis shows the open circuit voltage Voc
  • the point crossing the ordinate axis shows the short-circuit current density Jsc.
  • Example 2 On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO 2 transparent conductive film is deposited on the ITO transparent conductive film.
  • a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C.
  • n-type Zn 0.7 Si 0.3 O is deposited on the p-cuprous oxide layer by an atomic layer deposition method.
  • an AZO transparent conductive film is deposited.
  • a metal auxiliary electrode is deposited on the AZO transparent conductive film. Furthermore, MgF 2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
  • Example 3 On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO 2 transparent conductive film is deposited on the ITO transparent conductive film.
  • a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C.
  • n-type Zn 0.59 Si 0.41 O is deposited on the p-cuprous oxide layer by an atomic layer deposition method.
  • an AZO transparent conductive film is deposited.
  • a metal auxiliary electrode is deposited on the AZO transparent conductive film. Furthermore, MgF 2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
  • Example 4 On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO 2 transparent conductive film is deposited on the ITO transparent conductive film. On the transparent first electrode, a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C. Next, n-type Zn 0.7 Si 0.25 B 0.05 O is deposited on the p-cuprous oxide layer by an atomic layer deposition method. Next, as a second electrode on the front surface side, an AZO transparent conductive film is deposited.
  • a metal auxiliary electrode is deposited on the AZO transparent conductive film. Furthermore, MgF 2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
  • Example 5 On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO 2 transparent conductive film is deposited on the ITO transparent conductive film. On the transparent first electrode, a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C. Next, n-type Zn 0.7 Si 0.25 Al 0.05 O is deposited on the p-cuprous oxide layer by an atomic layer deposition method. Next, as a second electrode on the front surface side, an AZO transparent conductive film is deposited.
  • a metal auxiliary electrode is deposited on the AZO transparent conductive film. Furthermore, MgF 2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
  • Example 6 On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO 2 transparent conductive film is deposited on the ITO transparent conductive film. On the transparent first electrode, a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C. Next, n-type Zn 0.7 Si 0.25 Ga 0.05 O is deposited on the p-cuprous oxide layer by an atomic layer deposition method. Next, as a second electrode on the front surface side, an AZO transparent conductive film is deposited.
  • a metal auxiliary electrode is deposited on the AZO transparent conductive film. Furthermore, MgF 2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
  • Example 7 On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO 2 transparent conductive film is deposited on the ITO transparent conductive film.
  • a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C.
  • n-type Zn 0.7 Si 0.20 In 0.10 O is deposited on the p-cuprous oxide layer by an atomic layer deposition method.
  • an AZO transparent conductive film is deposited.
  • a metal auxiliary electrode is deposited on the AZO transparent conductive film. Furthermore, MgF 2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
  • Example 8 On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO 2 transparent conductive film is deposited on the ITO transparent conductive film.
  • a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C. In the latter half of the film formation of the cuprous oxide compound, Zn and Si are sputtered together.
  • n-type Zn 0.6 Si 0.4 O is deposited on the p-cuprous oxide layer by an atomic layer deposition method.
  • an AZO transparent conductive film is deposited.
  • a metal auxiliary electrode is deposited.
  • MgF 2 is deposited as an antireflection film to obtain a solar cell.
  • Example 9 On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO 2 transparent conductive film is deposited on the ITO transparent conductive film.
  • a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C.
  • n-type Zn 0.95 Si 0.05 O is deposited on the p-cuprous oxide layer by an atomic layer deposition method.
  • an AZO transparent conductive film is deposited.
  • a metal auxiliary electrode is deposited on the AZO transparent conductive film. Furthermore, MgF 2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
  • Example 10 On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO 2 transparent conductive film is deposited on the ITO transparent conductive film.
  • a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C.
  • n-type Zn 0.5 Si 0.5 O is deposited on the p-cuprous oxide layer by an atomic layer deposition method.
  • an AZO transparent conductive film is deposited.
  • a metal auxiliary electrode is deposited on the AZO transparent conductive film. Furthermore, MgF 2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
  • Example 11 On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO 2 transparent conductive film is deposited on the ITO transparent conductive film.
  • a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C.
  • n-type Zn 0.5 Ge 0.3 Si 0.2 O is deposited on the p-cuprous oxide layer by an atomic layer deposition method.
  • an AZO transparent conductive film is deposited.
  • a metal auxiliary electrode is deposited on the AZO transparent conductive film. Furthermore, MgF 2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
  • Example 12 On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO 2 transparent conductive film is deposited on the ITO transparent conductive film.
  • a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C.
  • n-type Zn 0.7 Si 0.1 Al 0.2 O is deposited on the p-cuprous oxide layer by an atomic layer deposition method.
  • an AZO transparent conductive film is deposited.
  • a metal auxiliary electrode is deposited on the AZO transparent conductive film. Furthermore, MgF 2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
  • an ITO transparent conductive film is deposited and an Sb-doped SnO 2 transparent conductive film is deposited on the ITO transparent conductive film.
  • a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C.
  • n-type Zn 0.95 Ge 0.05 O is deposited on the p-cuprous oxide layer by an atomic layer deposition method.
  • an AZO transparent conductive film is deposited.
  • a metal auxiliary electrode is deposited on the AZO transparent conductive film. Furthermore, MgF 2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
  • an ITO transparent conductive film is deposited and an Sb-doped SnO 2 transparent conductive film is deposited on the ITO transparent conductive film.
  • a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C.
  • n-type Zn 0.5 Ge 0.5 O is deposited on the p-cuprous oxide layer by an atomic layer deposition method.
  • an AZO transparent conductive film is deposited.
  • a metal auxiliary electrode is deposited on the AZO transparent conductive film. Furthermore, MgF 2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
  • a metal auxiliary electrode is deposited on the AZO transparent conductive film. Furthermore, MgF 2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
  • a metal auxiliary electrode is deposited on the AZO transparent conductive film. Furthermore, MgF 2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
  • an ITO transparent conductive film is deposited and an Sb-doped SnO 2 transparent conductive film is deposited on the ITO transparent conductive film.
  • a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C.
  • n-type Zn 0.7 Ge 0.20 In 0.10 O is deposited on the p-cuprous oxide layer by an atomic layer deposition method.
  • an AZO transparent conductive film is deposited.
  • a metal auxiliary electrode is deposited on the AZO transparent conductive film. Furthermore, MgF 2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
  • Table 1 summarizes the Voc, the FF, and the conversion efficiency in Examples and Comparative Examples.
  • the Voc is evaluated as A when +0.1 V or more based on the Voc in Comparative Example 1, evaluated as B when +0 V or more and less than +0.1 V based on the Voc in Comparative Example 1, and evaluated as C when less than +0 V based on the Voc in Comparative Example 1.
  • the FF is evaluated as A when 1.03 times or more based on the FF in Comparative Example 1, evaluated as B when 1.00 times or more and less than 1.03 times based on the FF in Comparative Example 1, and evaluated as C when less than 1.00 times based on the FF in Comparative Example 1.
  • the conversion efficiency is evaluated as A when 1.1 times or more based on the conversion efficiency in Comparative Example 1, evaluated as B when 1.0 times or more and less than 1.1 times based on the conversion efficiency in Comparative Example 1, and evaluated as C when less than 1.0 times based on the conversion efficiency in Comparative Example 1.
  • Example 7 From Example 7, it is found that In has the effect of increasing the Voc, although the effect is not as high as those of Al and Ga. From Example 11, it is found that although the increase in the Voc is small when the amount of Ge is small, Voc tends to increase when the amount of Ge exceeds a certain value. In Examples 10 to 12, the difference in the conduction band offset was reduced as compared with that in Comparative Example, so that the increase in the Voc was further increased. Therefore, it is found that the efficiency is improved as compared with that in Comparative Example. In the specification, some elements are represented only by element symbols.
  • a solar cell including: a first electrode being transparent; a photoelectric conversion layer mainly including cuprous oxide on the first electrode; an n-type layer being a metal oxide layer containing Zn and Si on the photoelectric conversion layer; and a second electrode being transparent on the n-type layer.
  • Clause 2 The solar cell according to Clause 1, wherein the metal oxide layer is a layer including a compound represented by Zn x Si y M z O w wherein x and y satisfy 0.90 ⁇ x + y ⁇ 1.00, z satisfies 0.00 ⁇ z ⁇ 0.30, w satisfies 0.90 ⁇ w ⁇ 1.10, and M is at least one element selected from the group consisting of B, Al, Ga, In, and Ge.
  • the metal oxide layer is a layer including a compound represented by Zn x Si y M z O w wherein x and y satisfy 0.90 ⁇ x + y ⁇ 1.00, z satisfies 0.00 ⁇ z ⁇ 0.30, w satisfies 0.90 ⁇ w ⁇ 1.10, and M is at least one element selected from the group consisting of B, Al, Ga, In, and Ge.
  • Clause 3 The solar cell according to clause 1 or 2, wherein the metal oxide layer is a layer including a compound represented by Zn x Si y M z O w wherein x and y satisfy 0.90 ⁇ x + y ⁇ 1.00, y satisfies 0.10 ⁇ y ⁇ 0.50, z satisfies 0.00 ⁇ z ⁇ 0.30, w satisfies 0.90 ⁇ w ⁇ 1.10, and M is at least one element selected from the group consisting of B, Al, Ga, In, and Ge.
  • Clause 4 The solar cell according to any one of clauses 1 to 3, wherein a concentration of Zn contained in the photoelectric conversion layer is higher than a concentration of Si contained in the photoelectric conversion layer.
  • Clause 5 The solar cell according to any one of clause 1 to 4, wherein a first Zn concentration, a second Zn concentration, a first Si concentration, and a second Si concentration satisfy [the first Zn concentration] > [the first Si concentration], [the second Zn concentration] > [the second Si concentration], [the first Zn concentration] > [the second Zn concentration], and [the first Si concentration] > [the second Si concentration] wherein the first Zn concentration is an average concentration of Zn in a region from an interface between the photoelectric conversion layer and the n-type layer to a depth of 3 nm in a direction toward the first electrode 1, the second Zn concentration is an average concentration of Zn in a region from the depth of 3 nm from the interface between the photoelectric conversion layer and the n-type layer in the direction toward the first electrode 1 to a depth 3 nm deeper in the direction toward the first electrode, the first Si concentration is an average concentration of Si in the region from the interface between the photoelectric conversion layer and the n-type layer to the depth of 3 n
  • Clause 6 The solar cell according to any one of clause 1 to 5, wherein a first Zn concentration, a second Zn concentration, a first Si concentration, and a second Si concentration satisfy 3([the first Zn concentration]/[the first Si concentration]) ⁇ ([the second Zn concentration]/[the second Si concentration]) wherein the first Zn concentration is an average concentration of Zn in the region from the interface between the photoelectric conversion layer and the n-type layer to the depth of 3 nm in the direction toward the first electrode, the second Zn concentration is an average concentration of Zn in the region from the depth of 3 nm from the interface between the photoelectric conversion layer and the n-type layer in the direction toward the first electrode to the depth 3 nm deeper in the direction toward the first electrode, the first Si concentration is an average concentration of Si in the region from the interface between the photoelectric conversion layer and the n-type layer to the depth of 3 nm in the direction toward the first electrode, and the second Si concentration is an average concentration of Si in the region from the depth of 3
  • Clause 7 The solar cell according to any one of clauses 1 to 6, wherein the photoelectric conversion layer includes 90% by weight or more of cuprous oxide.
  • Clause 8 A multi-junction solar cell including the solar cell according to any one of clauses 1 to 7.
  • Clause 9 A solar cell module including the solar cell according to any one of clauses 1 to 7.
  • Clause 10 A solar power generation system configured to generate power using the solar cell module according to Clause 9.

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Abstract

Embodiments described herein provide a solar cell, a multi-junction solar cell, a solar cell module, and a solar power generation system with improved characteristics. The solar cell according to an embodiment includes a first electrode being transparent, a photoelectric conversion layer mainly including cuprous oxide on the first electrode, an n-type layer being a metal oxide layer containing Zn and Si on the photoelectric conversion layer, and a second electrode being transparent on the n-type layer.

Description

SOLAR CELL, MULTI-JUNCTION SOLAR CELL, SOLAR CELL MODULE, AND SOLAR POWER GENERATION SYSTEM
Embodiments described herein relate generally to a solar cell, a multi-junction solar cell, a solar cell module, and a solar power generation system.
Examples of a high-efficient solar cell include multi-junction (tandem) solar cells. Tandem solar cells can be more efficient than single junction solar cells because cells having high spectral sensitivity for each wavelength band can be used in the tandem solar cells. As a top cell of tandem solar cells, cuprous oxide compounds or the like being inexpensive, the cuprous oxide compounds or the like having a wide band gap are expected.
Hideo Hosono et al. PNAS., 14 (2017) 223
Embodiments described herein provide a solar cell, a multi-junction solar cell, a solar cell module, and a solar power generation system with improved characteristics.
The solar cell according to an embodiment includes a first electrode being transparent, a photoelectric conversion layer mainly including cuprous oxide on the first electrode, an n-type layer being a metal oxide layer containing Zn and Si on the photoelectric conversion layer, and a second electrode being transparent on the n-type layer.
FIG. 1 is a conceptual sectional view of a solar cell according to an embodiment. FIG. 2 is a view illustrating analysis spots of the solar cell according to the embodiment. FIG. 3 is a conceptual sectional view of a multi-junction solar cell according to the embodiment. FIG. 4 is a conceptual view of a solar cell module according to the embodiment. FIG. 5 is a conceptual sectional view of the solar cell module according to the embodiment. FIG. 6 is a conceptual diagram of a solar power generation system according to the embodiment. FIG. 7 is a conceptual diagram of a vehicle according to the embodiment.
(First Embodiment)
The first embodiment relates to a solar cell. FIG. 1 is a conceptual view of a solar cell 100 according to the first embodiment. As shown in FIG. 1, the solar cell 100 according to the embodiment includes a first electrode 1, a photoelectric conversion layer 2 on the first electrode 1, an n-type layer 3 on the photoelectric conversion layer 2, and a second electrode 4 on the n-type layer 3. An intermediate layer (not shown) may be included between the first electrode 1 and the photoelectric conversion layer 2 or between the n-type layer 3 and the second electrode 4. Light may be incident from the first electrode 1 side or from the second electrode 4 side. When the light is incident on the solar cell 100, the solar cell 100 can generate power.
(First Electrode)
The first electrode 1 according to the embodiment is a transparent conductive layer 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. The first electrode 1 is preferably a transparent conductive film, or a stack of a metal film, a transparent conductive film, and a metal film. Examples of the transparent conductive film include indium tin oxide (Indium Tin Oxide; ITO), aluminum-doped zinc oxide (Al-doped Zinc Oxide; AZO), boron-doped zinc oxide (Boron-doped Zinc Oxide; BZO), gallium-doped zinc oxide (Gallium-doped Zinc Oxide; GZO), fluorine-doped tin oxide (Fluorine-doped Tin Oxide; FTO), antimony-doped tin oxide (Antimony-doped Tin Oxide; ATO), titanium-doped indium oxide (Titanium-doped Indium Oxide; ITiO), indium zinc oxide (Indium Zinc Oxide; IZO), indium gallium zinc oxide (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 (Hydrogen-doped Indium Oxide; IOH), and are not particularly limited to the above-mentioned oxides. The transparent conductive film may be a stacked film having a plurality of films, and the stacked film may include a film such as tin oxide in addition to the above-mentioned oxides. Examples of the dopant for the film such as tin oxide include In, Si, Ge, Ti, Cu, Sb, Nb, F, Ta, W, Mo, F, and Cl, and are not particularly limited thereto. Examples of the metal film include a film such as Mo, Au, Cu, Ag, Al, Ta, or W, and are not particularly limited thereto. Furthermore, the first electrode 1 may be an electrode in which a dot-shaped, line-shaped, or mesh-shaped metal is provided on the transparent conductive film. Here, the dot-shaped, line-shaped, or mesh-shaped metal is disposed between the transparent conductive film and the photoelectric conversion layer 2 or on the opposite side of the transparent conductive film from the photoelectric conversion layer 2. The dot-shaped, line-shaped, or mesh-shaped metal preferably has a numerical aperture of 50% or more based on the transparent conductive film. Examples of the dot-shaped, line-shaped or mesh-shaped metal include Mo, Au, Cu, Ag, Al, Ta, and W, and are not particularly limited thereto. When used in the first electrode 1, the metal film preferably has a thickness of about 5 nm or less from the viewpoint of transparency. When the line-shaped or mesh-shaped metal film is used, the transparency is ensured at the aperture, so that the thickness of the metal film is not limited to the above-mentioned thickness.
(Photoelectric Conversion Layer)
The photoelectric conversion layer 2 according to the embodiment is a semiconductor layer disposed between the first electrode 1 and the n-type layer 3. The photoelectric conversion layer 2 is preferably a compound semiconductor layer. Examples of the photoelectric conversion layer 2 include a semiconductor layer mainly including cuprous oxide (90% by weight or more). The photoelectric conversion layer 2 is more specifically a p-type compound semiconductor layer. When the thickness of the photoelectric conversion layer 2 is increased, the transmittance is reduced. When the film formation by sputtering is taken into consideration, the thickness is practically 10 micro meter or less. The compound semiconductor layer is preferably a semiconductor layer mainly including cuprous oxide. 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 mainly including cuprous oxide and the like may contain an additive. The photoelectric conversion layer 2 is p-type (including p＋type) as a whole. The n-type layer 3 side of the photoelectric conversion layer 2 may partially include an n-type region.
The photoelectric conversion layer 2 is produced by sputtering. The atmosphere during the sputtering is preferably an atmosphere of a mixed gas of an inert gas such as Ar and an oxygen gas. Depending on the type of the substrate holding the solar cell 100, the substrate is heated to a temperature of 100°C or more and 600°C or less, and the sputtering is performed using a target containing Cu. For example, a thin film of cuprous oxide having a large particle size can be formed on the first electrode 1 by adjusting the temperature and the oxygen partial pressure during the sputtering. Examples of the substrate used to produce the solar cell 100 (the substrate holding the first electrode 1) include organic substrates such as acrylics, polyimides, polycarbonate, polyethylene terephthalate (PET), polypropylene (PP), fluorine-based resins (polytetrafluoroethylene (PTFE), perfluoroethylene propene copolymers (FEP), ethylene tetrafluoroethylene copolymers (ETFE), polychlorotrifluoroethylene (PCTFE), perfluoroalkoxyalkane (PFA), and the like), polyarylate, polysulfone, polyether sulfone, and polyether imide, and inorganic substrates such as soda-lime glass, white plate glass, chemically strengthened glass, and quartz.
The photoelectric conversion layer 2 preferably includes 95% or more of cuprous oxide. The photoelectric conversion layer 2 more preferably includes 98% or more of cuprous oxide. That is, the photoelectric conversion layer 2 preferably contains few (substantially no) different phases such as CuO and Cu. The photoelectric conversion layer 2 preferably contains no different phases such as CuO and Cu and is preferably a thin film of substantially a single phase of Cu2O, because such a photoelectric conversion layer 2 has a very high light-transmitting property. The fact that the photoelectric conversion layer 2 is substantially a single phase of Cu2O can be confirmed by measurement by a photoluminescence method (Photo Luminescence; PL method).
(n-Type Layer)
The n-type layer 3 is an n-type semiconductor layer disposed between the photoelectric conversion layer 2 and the second electrode 4. It is preferable that the surface of the n-type layer 3 facing the photoelectric conversion layer 2 be in direct contact with the surface of the photoelectric conversion layer 2 facing the n-type layer 3. The n-type layer 3 is preferably an amorphous thin film. The n-type layer 3 is preferably a metal oxide layer containing Zn and Si. The metal oxide layer (the n-type layer 3) is preferably a layer including a compound represented by ZnxSiyMzOw wherein x and y satisfy 0.90 ≦ x + y ≦ 1.00, z satisfies 0.00 ≦ z ≦ 0.30, w satisfies 0.90 ≦ w ≦ 1.10, and M is at least one element selected from the group consisting of B, Al, Ga, In, and Ge. The metal oxide layer is preferably substantially made of ZnxSiyMzOw except for an inevitable impurity. When x, y, z, and w are within the above-mentioned ranges, a good n-type layer is formed, and the position of the conduction band of the Cu2O film and the n-type layer can be kept within a preferable range.
As the n-type layer 3 provided on the photoelectric conversion layer 2 mainly including cuprous oxide, ZnGeO being a mixture of Zn and Ge oxides is typically used. ZnGeO containing a high concentration of Ge, for example, ZnGeO having a Ge content higher than a Zn content, more specifically ZnGeO containing Ge in the range of about 0.6 ≦ (Ge [atom%])/(Zn [atom%] + Ge [atom%]) ≦ 0.7 has a small difference in the conduction band minimum (Conduction Band Minimum: CBM) from cuprous oxide, and is expected to provide a high fill factor (Fill Factor: FF) and a high Voc. However, the solar cell in which a film of ZnGeO is formed on the photoelectric conversion layer 2 mainly including cuprous oxide has a Voc and an FF lower than the theoretical values, so that the conversion efficiency is not improved to the extent expected even when the high-quality photoelectric conversion layer 2 is used.
By using the metal oxide layer containing Zn and Si as the n-type layer 3 provided on the photoelectric conversion layer 2 mainly including cuprous oxide, the FF and the Voc are improved, and the solar cell 100 with the high conversion efficiency can be obtained. The n-type layer 3 preferably contains Zn at a ratio higher than that of Si. It is preferable that y being the Si content satisfy 0.10 ≦ y ≦ 0.50. It is not preferable that the Si content is less than 0.10, because when the Si content is less than 0.10, the increase in the conversion efficiency is small, that is, the difference in the conduction band (the conduction band offset) between the Cu2O layer 2 and the n-type layer 3 is large. When the Si content is larger than 0.5, it is considered that Si diffuses to the Cu2O side more than Zn does, and quality of the pn junction with the n-type layer 3 is easily affected. In addition, it is not preferable that y is larger than 0.50, because when y is larger than 0.50, the electrical conductivity of the n-type layer 3 tends to be lost, and the n-type layer 3 becomes an insulator.
The photoelectric conversion layer 2 contains trace amounts of Zn and Si. The concentration of Zn contained in the photoelectric conversion layer 2 is preferably higher than the concentration of Si contained in the photoelectric conversion layer 2. This is because the pn junction between the region on the n-type layer side of Cu2O and the n-type layer 3 can be improved. The concentration of Zn contained in the photoelectric conversion layer 2 is more preferably three times or more higher than the concentration of Si. It is more preferable that the concentration of Zn be higher than the concentration of Si, because when the concentration of Zn is higher than the concentration of Si, the FF and the Voc are increased and the above-mentioned relationships can be satisfied.
In the photoelectric conversion layer 2, it is preferable that Zn be present in the deeper portion (the first electrode 1 side) of the photoelectric conversion layer 2 in a larger amount than Si. It is possible that in a region from the surface on the n-type layer 3 side of the photoelectric conversion layer 2 to the depth of, for example, 6 nm toward the first electrode 1, trace amounts of Zn and Si present in the interface side of the photoelectric conversion layer 2 on the n-type layer 3 contribute to the property of the photoelectric conversion layer 2 to form a good pn junction with the n-type layer 3. The Zn and Si may be diffused from the n-type layer 3 or may be intentionally added in trace amounts during the formation of the photoelectric conversion layer 2. More specifically, the average concentration of Zn in the region from the interface between the photoelectric conversion layer 2 and the n-type layer 3 (the starting point) to the depth of 3 nm in the direction toward the first electrode 1 (the end point) is referred to as the first Zn concentration, the average concentration of Zn in the region from the depth of 3 nm from the interface between the photoelectric conversion layer 2 and the n-type layer 3 in the direction toward the first electrode 1 (the starting point) to the depth 3 nm deeper in the direction toward the first electrode 1 (the end point) is referred to as the second Zn concentration, the average concentration of Si in the region from the interface between the photoelectric conversion layer 2 and the n-type layer 3 (the starting point) to the depth of 3 nm in the direction toward the first electrode 1 (the end point) is referred to as the first Si concentration, and the average concentration of Si in the region from the depth of 3 nm from the interface between the photoelectric conversion layer 2 and the n-type layer 3 in the direction toward the first electrode 1 (the starting point) to the depth 3 nm deeper in the direction toward the first electrode 1 (the end point) is referred to as the second Si concentration. Here, the relationships [the first Zn concentration] > [the first Si concentration], [the second Zn concentration] > [the second Si concentration], [the first Zn concentration] > [the second Zn concentration], and [the first Si concentration] > [the second Si concentration] are satisfied. It is more preferable that the relationship 3([the first Zn concentration]/[the first Si concentration]) ≦ ([the second Zn concentration]/[the second Si concentration]) be satisfied. The comparison between the interface side and the deep portion side indicates that the ratio of the Zn concentration to the Si concentration in the deep portion side is three times or more (greater) than the ratio of the Zn concentration to the Si concentration in the interface side. Because Zn is diffused into the photoelectric conversion layer 2 deeper than Si, there is an advantage that the recombination at the pn interface can be suppressed. It is more preferable that the relationship 3([the first Zn concentration]/[the first Si concentration]) ≦ ([the second Zn concentration]/[the second Si concentration]) be satisfied, because when the relationship is satisfied, the recombination at the pn interface can be further suppressed.
The above-mentioned concentrations are determined by energy dispersive X-ray spectroscopy (Energy Dispersive X-ray Spectroscopy; EDX) by cutting out a cross section in the direction of the conceptual view in FIG. 1 and scanning from the n-type layer 3 side to the photoelectric conversion layer 2. The boundary (interface) between the photoelectric conversion layer 2 and the n-type layer 3 is also determined by EDX. The boundary between the photoelectric conversion layer 2 and the n-type layer 3 is determined as described below. The Cu concentration and the Zn concentration are measured by EDX, and the closest position to the second electrode 4 in the n-type layer 3 at which the Cu concentration is equal to or higher than the Zn concentration is set as a boundary. As the measurement positions, nine spots A1 to A9 on the surface of the solar cell 100 as viewed from the second electrode 4 side are determined as shown in the view illustrating analysis spots in FIG. 2. Each spot is square and has a region of at least 5 mm2. As shown in FIG. 2, when the length is D1 and the width is D2 (D1 ≧ D2), a virtual line is drawn at a distance of D3 (= D1/10) inward from each of the facing two sides in the width direction of the solar cell 100, a virtual line is drawn at a distance of D4 (= D2/10) inward from each of the facing two sides in the length direction of the solar cell 100, a virtual line passing through the center of the solar cell 100, the virtual line parallel to the width direction is further drawn, a virtual line passing through the center of the solar cell 100, the virtual line parallel to the length direction is drawn, and regions having the nine intersections of the virtual lines as a center are referred to as observation spots A1 to A9. The cross section observed by SEM or TEM is perpendicular to the plane shown in FIG. 2. When the shape of the solar cell 100 as viewed from the second electrode 4 side is not rectangular, it is preferable to determine the analysis spots based on the inscribed rectangle. The concentration is the average value of the seven analysis results excluding the maximum and minimum values of the nine analysis spots.
The thickness of the n-type layer 3 is typically 3 nm or more and 100 nm or less. When the thickness of the n-type layer 3 is less than 3 nm and the coverage of the n-type layer 3 is poor, a leak current may be generated and the characteristics may be deteriorated. When the coverage is good, the thickness is not limited to the above-mentioned thickness. When the thickness of the n-type layer 3 exceeds 50 nm, the characteristics may be deteriorated due to an excessive increase in the resistance of the n-type layer 3, or the short-circuit current may be reduced due to a decrease in the transmittance. Therefore, the thickness of the n-type layer 3 is more preferably 3 nm or more and 50 nm or less, and still more preferably 5 nm or more and 20 nm or less.
As described above, since the n-type layer is thin, even when the element is substituted, the optical effect is small. The transmittance of the top cell mainly depends on the quality of the photoelectric conversion layer, for example, the quality of the Cu2O film. By applying the n-type layer to a good Cu2O layer, high transmittance can be maintained, and the power generation amount of the bottom cell can be improved. As a result, it can be confirmed that the tandem efficiency is increased in which the top cell efficiency and the bottom cell efficiency are combined.
The n-type layer 3 can be formed by, for example, an atomic layer deposition (Atomic Layer Deposition; ALD) method or a sputtering method.
The conduction band offset being a difference between the position of the conduction band minimum (Conduction Band Minimum: CBM) of the photoelectric conversion layer 2 (Ecp (eV)) and the position below the conduction band of the n-type layer 3 (Ecn (eV)) (ΔE = Ecp - Ecn) 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 more than 0, the conduction band at the pn junction interface is discontinuous and a spike is caused. When the conduction band offset is less than 0, the conduction band at the pn junction interface is discontinuous and a cliff is caused. Both the spike and the cliff are preferably small because the spike and the cliff act as barriers for photogenerated electrons. Therefore, 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). However, the above-mentioned conduction band offset is not applied to the case where the conduction is performed using the level in the gap. The position of the CBM can be estimated using the following method. The valence band maximum (Valence Band Maximum: VBM) is actually measured by photoelectron spectroscopy being a method for evaluating an electron occupation level, and then the band gap of the material to be measured is assumed to calculate the CBM. However, at an actual pn junction interface, an ideal interface in which interdiffusion, generation of a cation vacancy, and the like occur is not maintained, so that there is a high possibility that the band gap changes. For this reason, it is preferable that the CBM is also evaluated by inverse photoelectron spectroscopy that directly uses the reverse process of photoelectron emission. Specifically, the electronic state of the pn junction interface can be evaluated by repeating low-energy ion etching and forward/inverse photoelectron spectroscopy of the solar cell surface. The ratio between Zn and Si in the n-type layer 3 can be appropriately selected within the above-mentioned preferred range in consideration of the difference in the CBM.
As the second electrode 4, the same transparent electrode as the electrode described for the first electrode 1 is preferably used. As the second electrode 4, another transparent electrode such as a multilayer graphene provided with an extraction electrode including a metal wire can also be used. A metal auxiliary electrode may be deposited on the second electrode 4 if necessary.
(Antireflection Film)
The antireflection film according to the embodiment is a film for facilitating the introduction of light to the photoelectric conversion layer 2, and is preferably formed on the opposite side from the photoelectric conversion layer 2 side on the first electrode 1 or the second electrode 4. As the antireflection film, for example, MgF2 or SiO2 is desirably used. In the embodiment, the antireflection film can be omitted. Although it is necessary to adjust the film thickness depending on the refractive index of each layer, it is preferable to deposit a thin film having a thickness of about 70 to 130 nm (preferably, 80 to 120 nm).
(Second Embodiment)
The second embodiment relates to a multi-junction solar cell. FIG. 3 shows a conceptual sectional view of a multi-junction solar cell 200 according to the second embodiment. The multi-junction solar cell 200 shown in FIG. 3 includes the solar cell according to the first embodiment (first solar cell) 100 in the light incidence side and a second solar cell 201. The band gap of the 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 according to the first embodiment. Examples of the multi-junction solar cell according to the embodiment include a solar cell in which three or more solar cells are joined.
Since the band gap of the photoelectric conversion layer 2 of the solar cell 100 according to the first embodiment is about 2.0 eV, the band gap of the photoelectric conversion layer of the second solar cell 201 is preferably 1.0 eV or more and 1.4 eV or less. As the photoelectric conversion layer of the second solar cell 201, a compound semiconductor layer including one or more of CIGS-based and CIT-based compound semiconductor layers containing a high content ratio of In, CdTe-based compound semiconductor layers, and copper oxide-based compound semiconductor layers, or crystalline silicon is preferable.
By using the solar cell 100 according to the first embodiment as the first solar cell, it is possible to prevent the reduction in the conversion efficiency of the bottom cell (the second solar cell) due to a first solar cell absorbing light in an unintended wavelength range, so that an efficient multi-junction solar cell can be obtained.
(Third Embodiment)
The third embodiment relates to a solar cell module. FIG. 4 shows a conceptual perspective view of a solar cell module 300 according to the third embodiment. The solar cell module 300 shown in FIG. 4 is a solar cell module in which a first solar cell module 301 and a second solar cell module 302 are stacked. The first solar cell module 301 is in the light incidence side, and the solar cell 100 according to the first embodiment is used in the first solar cell module 301. It is preferable to use the second solar cell 201 in the second solar cell module 302.
FIG. 5 shows a conceptual sectional view of the solar cell module 300. In FIG. 5, the structure of the first solar cell module 301 is shown in detail, and the structure of the second solar cell module 302 is not shown. In the second solar cell module 302, the structure of the solar cell module is appropriately selected depending on the photoelectric conversion layer of the used solar cell, and the like. The solar cell module shown in FIG. 5 includes a plurality of sub-modules 303 surrounded by a dashed line in which a plurality of solar cells 100 (photovoltaic cells) are arranged in a horizontal direction and electrically connected in series, and the plurality of sub-modules 303 are electrically connected in parallel or in series.
The solar cell 100 is scribed, and the upper second electrode 4 of the solar cell 100 is connected to the lower first electrode 1 of the adjacent solar cell 100. The solar cell 100 according to the third embodiment also includes a substrate 10, a first electrode 1, a photoelectric conversion layer 2, an n-type layer 3, and a second electrode 4 in the same manner as the solar cell 100 according to the first embodiment.
When the output voltage is different for each module, the current may flow backward to a low voltage portion or extra heat may be generated, so that the output of the module is reduced.
It is desirable to use the solar cell according to the present application, because the use of the solar cell makes it possible to use a solar cell suitable for each wavelength band, so that it is possible to generate power more efficiently than when the solar cell of the top cell or the bottom cell is used alone, and the output of the whole module is increased.
If the conversion efficiency of the whole module is high, the rate of the applied light energy converted to heat can be reduced. Therefore, a reduction in the efficiency due to a rise in the temperature of the whole module can be suppressed.
(Fourth Embodiment)
The fourth embodiment relates to a solar power generation system. The solar cell module 300 according to the third embodiment can be used as a generator for generating power in the solar power generation system according to the fourth embodiment. The solar power generation system according to the embodiment generates power using a solar cell module, and specifically includes a solar cell module that generates power, a means with which the power conversion of the generated electricity is performed, and a power storage means with which the generated electricity is stored or a load that consumes generated electricity. FIG. 6 shows a conceptual configuration diagram of a solar power generation system 400 according to the embodiment. The solar power generation system shown in FIG. 6 includes a solar cell module 401 (300), a power conversion device 402, a battery 403, and a load 404. Either the battery 403 or the load 404 may be omitted. The load 404 may be configured to be capable of also using the electric energy stored in the battery 403. The power conversion device 402 is a device including a circuit or an element that performs power conversion such as voltage transformation or DC/AC conversion. A suitable configuration of the power conversion device 402 is required to be employed depending on the configuration of the generated voltage, the battery 403, and the load 404.
The photovoltaic cell included in the sub-module 301 that is included in the solar cell module 300 and receives light generates power, and the electric energy is converted by the converter 402, and stored in the battery 403 or consumed by the load 404. The solar cell module 401 is preferably provided with a solar tracking driving device for constantly directing the solar cell module 401 toward the sun and a light collector for condensing sunlight, and it is preferable to add a device for improving the power generation efficiency, and the like to the solar cell module 401.
The solar power generation system 400 is preferably used for real estate such as dwellings, commercial facilities, and factories, or for movable property such as vehicles, aircraft, and electronic devices. By using the solar cell excellent in the conversion efficiency according to the embodiment in the solar cell module 401, an increase in the power generation amount is expected.
A vehicle is shown as an example in which the solar power generation system 400 is used. FIG. 7 shows a conceptual configuration diagram of a vehicle 500. The vehicle 500 shown in FIG. 7 includes a vehicle body 501, a solar cell module 502, a power conversion device 503, a battery 504, a motor 505, and a tire (wheel) 506. The power generated by the solar cell module 501 provided on the upper part of the vehicle body 501 is converted by the power conversion device 503, and charged in the battery 504 or consumed by the load such as the motor 505. The vehicle 500 can be moved by rotating the tire (wheel) 506 with the motor 505 using the electric power supplied from the solar cell module 501 or the battery 504. The solar cell module 501 may be not a multi-junction solar cell module, and may include only the first solar cell module including the solar cell 100 according to the first embodiment. When the transparent solar cell module 501 is employed, it is also preferable to use the solar cell module 501 as a window that generates power on the side surface of the vehicle body 501 in addition to the upper part of the vehicle body 501.
Hereinafter, the present disclosure will be described more specifically based on Examples, but the present disclosure is not limited to Examples described below.
(Example 1)
On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO2 transparent conductive film is deposited on the ITO transparent conductive film. On the transparent first electrode, a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C. Next, n-type Zn0.9Si0.1O is deposited on the p-cuprous oxide layer by an atomic layer deposition method. Next, as a second electrode on the front surface side, an AZO transparent conductive film is deposited. On the AZO transparent conductive film, a metal auxiliary electrode is deposited. Furthermore, MgF2 is deposited as an antireflection film to obtain a solar cell.
A solar simulator simulating an AM1.5G light source is used, and the light amount is adjusted to 1 sun using a reference Si cell under the light source. The temperature is 25°C. The voltage is swept and the current density (the current divided by the cell area) is measured. When the abscissa axis shows the voltage scale and the ordinate axis shows the current density scale, the point crossing the abscissa axis shows the open circuit voltage Voc, and the point crossing the ordinate axis shows the short-circuit current density Jsc. The voltage and the current density on the measurement curve are multiplied, and when the voltage and the current density of the point at which the resulting product is maximum (maximum power point) are Vmpp and Jmpp respectively, FF = (Vmpp * Jmpp)/(Voc * Jsc), and
Efficiency Eff. = Voc * Jsc * FF.
(Example 2)
On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO2 transparent conductive film is deposited on the ITO transparent conductive film. On the transparent first electrode, a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C. Next, n-type Zn0.7Si0.3O is deposited on the p-cuprous oxide layer by an atomic layer deposition method. Next, as a second electrode on the front surface side, an AZO transparent conductive film is deposited. On the AZO transparent conductive film, a metal auxiliary electrode is deposited. Furthermore, MgF2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
(Example 3)
On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO2 transparent conductive film is deposited on the ITO transparent conductive film. On the transparent first electrode, a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C. Next, n-type Zn0.59Si0.41O is deposited on the p-cuprous oxide layer by an atomic layer deposition method. Next, as a second electrode on the front surface side, an AZO transparent conductive film is deposited. On the AZO transparent conductive film, a metal auxiliary electrode is deposited. Furthermore, MgF2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
(Example 4)
On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO2 transparent conductive film is deposited on the ITO transparent conductive film. On the transparent first electrode, a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C. Next, n-type Zn0.7Si0.25B0.05O is deposited on the p-cuprous oxide layer by an atomic layer deposition method. Next, as a second electrode on the front surface side, an AZO transparent conductive film is deposited. On the AZO transparent conductive film, a metal auxiliary electrode is deposited. Furthermore, MgF2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
(Example 5)
On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO2 transparent conductive film is deposited on the ITO transparent conductive film. On the transparent first electrode, a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C. Next, n-type Zn0.7Si0.25Al0.05O is deposited on the p-cuprous oxide layer by an atomic layer deposition method. Next, as a second electrode on the front surface side, an AZO transparent conductive film is deposited. On the AZO transparent conductive film, a metal auxiliary electrode is deposited. Furthermore, MgF2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
(Example 6)
On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO2 transparent conductive film is deposited on the ITO transparent conductive film. On the transparent first electrode, a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C. Next, n-type Zn0.7Si0.25Ga0.05O is deposited on the p-cuprous oxide layer by an atomic layer deposition method. Next, as a second electrode on the front surface side, an AZO transparent conductive film is deposited. On the AZO transparent conductive film, a metal auxiliary electrode is deposited. Furthermore, MgF2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
(Example 7)
On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO2 transparent conductive film is deposited on the ITO transparent conductive film. On the transparent first electrode, a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C. Next, n-type Zn0.7Si0.20In0.10O is deposited on the p-cuprous oxide layer by an atomic layer deposition method. Next, as a second electrode on the front surface side, an AZO transparent conductive film is deposited. On the AZO transparent conductive film, a metal auxiliary electrode is deposited. Furthermore, MgF2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
(Example 8)
On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO2 transparent conductive film is deposited on the ITO transparent conductive film. On the transparent first electrode, a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C. In the latter half of the film formation of the cuprous oxide compound, Zn and Si are sputtered together. Next, n-type Zn0.6Si0.4O is deposited on the p-cuprous oxide layer by an atomic layer deposition method. Next, as a second electrode on the front surface side, an AZO transparent conductive film is deposited. On the AZO transparent conductive film, a metal auxiliary electrode is deposited. Furthermore, MgF2 is deposited as an antireflection film to obtain a solar cell.
(Example 9)
On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO2 transparent conductive film is deposited on the ITO transparent conductive film. On the transparent first electrode, a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C. Next, n-type Zn0.95Si0.05O is deposited on the p-cuprous oxide layer by an atomic layer deposition method. Next, as a second electrode on the front surface side, an AZO transparent conductive film is deposited. On the AZO transparent conductive film, a metal auxiliary electrode is deposited. Furthermore, MgF2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
(Example 10)
On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO2 transparent conductive film is deposited on the ITO transparent conductive film. On the transparent first electrode, a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C. Next, n-type Zn0.5Si0.5O is deposited on the p-cuprous oxide layer by an atomic layer deposition method. Next, as a second electrode on the front surface side, an AZO transparent conductive film is deposited. On the AZO transparent conductive film, a metal auxiliary electrode is deposited. Furthermore, MgF2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
(Example 11)
On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO2 transparent conductive film is deposited on the ITO transparent conductive film. On the transparent first electrode, a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C. Next, n-type Zn0.5Ge0.3Si0.2O is deposited on the p-cuprous oxide layer by an atomic layer deposition method. Next, as a second electrode on the front surface side, an AZO transparent conductive film is deposited. On the AZO transparent conductive film, a metal auxiliary electrode is deposited. Furthermore, MgF2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
(Example 12)
On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO2 transparent conductive film is deposited on the ITO transparent conductive film. On the transparent first electrode, a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C. Next, n-type Zn0.7Si0.1Al0.2O is deposited on the p-cuprous oxide layer by an atomic layer deposition method. Next, as a second electrode on the front surface side, an AZO transparent conductive film is deposited. On the AZO transparent conductive film, a metal auxiliary electrode is deposited. Furthermore, MgF2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
(Comparative Example 1)
On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO2 transparent conductive film is deposited on the ITO transparent conductive film. On the transparent first electrode, a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C. Next, n-type Zn0.95Ge0.05O is deposited on the p-cuprous oxide layer by an atomic layer deposition method. Next, as a second electrode on the front surface side, an AZO transparent conductive film is deposited. On the AZO transparent conductive film, a metal auxiliary electrode is deposited. Furthermore, MgF2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
(Comparative Example 2)
On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO2 transparent conductive film is deposited on the ITO transparent conductive film. On the transparent first electrode, a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C. Next, n-type Zn0.5Ge0.5O is deposited on the p-cuprous oxide layer by an atomic layer deposition method. Next, as a second electrode on the front surface side, an AZO transparent conductive film is deposited. On the AZO transparent conductive film, a metal auxiliary electrode is deposited. Furthermore, MgF2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
(Comparative Example 3)
On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO2 transparent conductive film is deposited on the ITO transparent conductive film. On the transparent first electrode, a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C. Next, n-type Zn0.5Ge0.3B0.2O is deposited on the p-cuprous oxide layer by an atomic layer deposition method. Next, as a second electrode on the front surface side, an AZO transparent conductive film is deposited. On the AZO transparent conductive film, a metal auxiliary electrode is deposited. Furthermore, MgF2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
(Comparative Example 4)
On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO2 transparent conductive film is deposited on the ITO transparent conductive film. On the transparent first electrode, a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C. Next, n-type Zn0.3Ge0.7O is deposited on the p-cuprous oxide layer by an atomic layer deposition method. Next, as a second electrode on the front surface side, an AZO transparent conductive film is deposited. On the AZO transparent conductive film, a metal auxiliary electrode is deposited. Furthermore, MgF2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
(Comparative Example 5)
On a white plate glass substrate, as a first electrode on the back-surface side, an ITO transparent conductive film is deposited and an Sb-doped SnO2 transparent conductive film is deposited on the ITO transparent conductive film. On the transparent first electrode, a film of a cuprous oxide compound is formed by a sputtering method in an atmosphere of a mixed gas of oxygen and argon gas with the substrate heated at 450°C. Next, n-type Zn0.7Ge0.20In0.10O is deposited on the p-cuprous oxide layer by an atomic layer deposition method. Next, as a second electrode on the front surface side, an AZO transparent conductive film is deposited. On the AZO transparent conductive film, a metal auxiliary electrode is deposited. Furthermore, MgF2 is deposited as an antireflection film to obtain a solar cell. In the same manner as in the first embodiment, the conversion efficiency, the Voc, and the FF are determined.
Table 1 summarizes the Voc, the FF, and the conversion efficiency in Examples and Comparative Examples. The Voc is evaluated as A when +0.1 V or more based on the Voc in Comparative Example 1, evaluated as B when +0 V or more and less than +0.1 V based on the Voc in Comparative Example 1, and evaluated as C when less than +0 V based on the Voc in Comparative Example 1. The FF is evaluated as A when 1.03 times or more based on the FF in Comparative Example 1, evaluated as B when 1.00 times or more and less than 1.03 times based on the FF in Comparative Example 1, and evaluated as C when less than 1.00 times based on the FF in Comparative Example 1. The conversion efficiency is evaluated as A when 1.1 times or more based on the conversion efficiency in Comparative Example 1, evaluated as B when 1.0 times or more and less than 1.1 times based on the conversion efficiency in Comparative Example 1, and evaluated as C when less than 1.0 times based on the conversion efficiency in Comparative Example 1.
Figure JPOXMLDOC01-appb-T000001
From Examples 1 to 11 and Comparative Examples 1 to 5, it is found that when the ratio of Si is too small, the difference in the conduction band position is large and the Voc is low, and when the ratio of Si is too large, the electrical conductivity of the n-type layer is easily lost and the FF decreases. From the above-mentioned result, it is found that a high Voc and a high FF can be obtained by applying an n-type layer having an appropriate Si ratio. From Examples 5, 6, and 12, although Al and Ga have the effect of increasing the Voc, the FF tends to decrease when Al and Ga are introduced in large amounts. Therefore, it is desirable to introduce Al and Ga in appropriate amounts. From Example 7, it is found that In has the effect of increasing the Voc, although the effect is not as high as those of Al and Ga. From Example 11, it is found that although the increase in the Voc is small when the amount of Ge is small, Voc tends to increase when the amount of Ge exceeds a certain value. In Examples 10 to 12, the difference in the conduction band offset was reduced as compared with that in Comparative Example, so that the increase in the Voc was further increased. Therefore, it is found that the efficiency is improved as compared with that in Comparative Example.
In the specification, some elements are represented only by element symbols.
Hereinafter, clauses according to the embodiments will be additionally described.
Clause 1
A solar cell including:
a first electrode being transparent;
a photoelectric conversion layer mainly including cuprous oxide on the first electrode;
an n-type layer being a metal oxide layer containing Zn and Si on the photoelectric conversion layer; and
a second electrode being transparent on the n-type layer.
Clause 2
The solar cell according to Clause 1, wherein the metal oxide layer is a layer including a compound represented by ZnxSiyMzOw wherein
x and y satisfy 0.90 ≦ x + y ≦ 1.00,
z satisfies 0.00 ≦ z ≦ 0.30,
w satisfies 0.90 ≦ w ≦ 1.10, and
M is at least one element selected from the group consisting of B, Al, Ga, In, and Ge.
Clause 3
The solar cell according to clause 1 or 2, wherein the metal oxide layer is a layer including a compound represented by ZnxSiyMzOw wherein
x and y satisfy 0.90 ≦ x + y ≦ 1.00,
y satisfies 0.10 ≦ y ≦ 0.50,
z satisfies 0.00 ≦ z ≦ 0.30,
w satisfies 0.90 ≦ w ≦ 1.10, and
M is at least one element selected from the group consisting of B, Al, Ga, In, and Ge.
Clause 4
The solar cell according to any one of clauses 1 to 3, wherein a concentration of Zn contained in the photoelectric conversion layer is higher than a concentration of Si contained in the photoelectric conversion layer.
Clause 5
The solar cell according to any one of clause 1 to 4, wherein a first Zn concentration, a second Zn concentration, a first Si concentration, and a second Si concentration satisfy [the first Zn concentration] > [the first Si concentration], [the second Zn concentration] > [the second Si concentration], [the first Zn concentration] > [the second Zn concentration], and [the first Si concentration] > [the second Si concentration] wherein
the first Zn concentration is an average concentration of Zn in a region from an interface between the photoelectric conversion layer and the n-type layer to a depth of 3 nm in a direction toward the first electrode 1,
the second Zn concentration is an average concentration of Zn in a region from the depth of 3 nm from the interface between the photoelectric conversion layer and the n-type layer in the direction toward the first electrode 1 to a depth 3 nm deeper in the direction toward the first electrode,
the first Si concentration is an average concentration of Si in the region from the interface between the photoelectric conversion layer and the n-type layer to the depth of 3 nm in the direction toward the first electrode, and
the second Si concentration is an average concentration of Si in the region from the depth of 3 nm from the interface between the photoelectric conversion layer and the n-type layer in the direction toward the first electrode to the depth 3 nm deeper in the direction toward the first electrode.
Clause 6
The solar cell according to any one of clause 1 to 5, wherein a first Zn concentration, a second Zn concentration, a first Si concentration, and a second Si concentration satisfy 3([the first Zn concentration]/[the first Si concentration]) ≦ ([the second Zn concentration]/[the second Si concentration]) wherein
the first Zn concentration is an average concentration of Zn in the region from the interface between the photoelectric conversion layer and the n-type layer to the depth of 3 nm in the direction toward the first electrode,
the second Zn concentration is an average concentration of Zn in the region from the depth of 3 nm from the interface between the photoelectric conversion layer and the n-type layer in the direction toward the first electrode to the depth 3 nm deeper in the direction toward the first electrode,
the first Si concentration is an average concentration of Si in the region from the interface between the photoelectric conversion layer and the n-type layer to the depth of 3 nm in the direction toward the first electrode, and
the second Si concentration is an average concentration of Si in the region from the depth of 3 nm from the interface between the photoelectric conversion layer and the n-type layer in the direction toward the first electrode 1 to the depth 3 nm deeper in the direction toward the first electrode.
Clause 7
The solar cell according to any one of clauses 1 to 6, wherein the photoelectric conversion layer includes 90% by weight or more of cuprous oxide.
Clause 8
A multi-junction solar cell including the solar cell according to any one of clauses 1 to 7.
Clause 9
A solar cell module including the solar cell according to any one of clauses 1 to 7.
Clause 10
A solar power generation system configured to generate power using the solar cell module according to Clause 9.
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 First semiconductor layer
3 Second semiconductor layer
4 Second electrode
5 Groove
102 Stacked body
200 Multi-junction 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 Sub-module
400 Solar power generation system
401 Solar cell module
402 Power conversion device
403 Battery
404 Load
500 Vehicle
501 Vehicle body
502 Solar cell module
503 Power conversion device
504 Battery
505 Motor
506 Tire (wheel)

Claims (10)

  1. A solar cell comprising:
    a first electrode being transparent;
    a photoelectric conversion layer mainly including cuprous oxide on the first electrode;
    an n-type layer being a metal oxide layer containing Zn and Si on the photoelectric conversion layer; and
    a second electrode being transparent on the n-type layer.
  2. The solar cell according to claim 1, wherein the metal oxide layer is a layer including a compound represented by ZnxSiyMzOw where
    x and y satisfy 0.90 ≦ x + y ≦ 1.00,
    z satisfies 0.00 ≦ z ≦ 0.30,
    w satisfies 0.90 ≦ w ≦ 1.10, and
    M is at least one element selected from the group consisting of B, Al, Ga, In, and Ge.
  3. The solar cell according to claim 1 or 2, wherein the metal oxide layer is a layer including a compound represented by ZnxSiyMzOw where
    x and y satisfy 0.90 ≦ x + y ≦ 1.00,
    y satisfies 0.10 ≦ y ≦ 0.50,
    z satisfies 0.00 ≦ z ≦ 0.30,
    w satisfies 0.90 ≦ w ≦ 1.10, and
    M is at least one element selected from the group consisting of B, Al, Ga, In, and Ge.
  4. The solar cell according to any one of claims 1 to 3, wherein a concentration of Zn contained in the photoelectric conversion layer is higher than a concentration of Si contained in the photoelectric conversion layer.
  5. The solar cell according to any one of claims 1 to 4, wherein
    a first Zn concentration, a second Zn concentration, a first Si concentration, and a second Si concentration satisfy [the first Zn concentration] > [the first Si concentration], [the second Zn concentration] > [the second Si concentration], [the first Zn concentration] > [the second Zn concentration], and [the first Si concentration] > [the second Si concentration] where
    the first Zn concentration is an average concentration of Zn in a region from an interface between the photoelectric conversion layer and the n-type layer to a depth of 3 nm in a direction toward the first electrode,
    the second Zn concentration is an average concentration of Zn in a region from the depth of 3 nm from the interface between the photoelectric conversion layer and the n-type layer in the direction toward the first electrode to a depth 3 nm deeper in the direction toward the first electrode,
    the first Si concentration is an average concentration of Si in the region from the interface between the photoelectric conversion layer and the n-type layer to the depth of 3 nm in the direction toward the first electrode, and
    the second Si concentration is an average concentration of Si in the region from the depth of 3 nm from the interface between the photoelectric conversion layer and the n-type layer in the direction toward the first electrode to the depth 3 nm deeper in the direction toward the first electrode.
  6. The solar cell according to any one of claims 1 to 5, wherein
    a first Zn concentration, a second Zn concentration, a first Si concentration, and a second Si concentration satisfy 3([the first Zn concentration]/[the first Si concentration]) ≦ ([the second Zn concentration]/[the second Si concentration]) where
    the first Zn concentration is an average concentration of Zn in the region from the interface between the photoelectric conversion layer and the n-type layer to the depth of 3 nm in the direction toward the first electrode,
    the second Zn concentration is an average concentration of Zn in the region from the depth of 3 nm from the interface between the photoelectric conversion layer and the n-type layer in the direction toward the first electrode to the depth 3 nm deeper in the direction toward the first electrode,
    the first Si concentration is an average concentration of Si in the region from the interface between the photoelectric conversion layer and the n-type layer to the depth of 3 nm in the direction toward the first electrode, and
    the second Si concentration is an average concentration of Si in the region from the depth of 3 nm from the interface between the photoelectric conversion layer and the n-type layer in the direction toward the first electrode to the depth 3 nm deeper in the direction toward the first electrode.
  7. The solar cell according to any one of claims 1 to 6, wherein the photoelectric conversion layer includes 90% by weight or more of cuprous oxide.
  8. A multi-junction solar cell comprising the solar cell according to any one of claims 1 to 7.
  9. A solar cell module comprising the solar cell according to any one of claims 1 to 7.
  10. A solar power generation system configured to generate power using the solar cell module according to claim 9.
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