WO2019058603A1 - Solar cell, multijunction solar cell, solar cell module and solar power generation system - Google Patents

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

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WO2019058603A1
WO2019058603A1 PCT/JP2018/010652 JP2018010652W WO2019058603A1 WO 2019058603 A1 WO2019058603 A1 WO 2019058603A1 JP 2018010652 W JP2018010652 W JP 2018010652W WO 2019058603 A1 WO2019058603 A1 WO 2019058603A1
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solar cell
light absorbing
absorbing layer
group
electrode
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PCT/JP2018/010652
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French (fr)
Inventor
Sara Yoshio
Miyuki Shiokawa
Soichiro SHIBASAKI
Naoyuki Nakagawa
Yukitami Mizuno
Kohei Nakayama
Mutsuki Yamazaki
Yoshiko Hiraoka
Kazushige Yamamoto
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Kabushiki Kaisha Toshiba
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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
    • H01L31/032—Inorganic materials including, apart from doping materials or other impurities, only compounds not provided for in groups H01L31/0272 - H01L31/0312
    • H01L31/0322—Inorganic materials including, apart from doping materials or other impurities, only compounds not provided for in groups H01L31/0272 - H01L31/0312 comprising only AIBIIICVI chalcopyrite compounds, e.g. Cu In Se2, Cu Ga Se2, Cu In Ga Se2
    • 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
    • H01L31/0749—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 including a AIBIIICVI compound, e.g. CdS/CulnSe2 [CIS] heterojunction 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
    • Y02E10/541—CuInSe2 material PV cells

Definitions

  • Embodiments described herein relate to a solar cell, a multijunction solar cell, a solar cell module and a solar power generation system.
  • a photoelectric conversion element in which a compound with a semiconductor thin-film used as a light absorbing layer is used has been advanced.
  • a thin-film photoelectric conversion element in which Cu(In, Ga)Se 2 or CuGaSe 2 being a group Ib-IIIb-VIb compound having a chalcopyrite structure is used as light absorbing layer (CIGS, CGS) exhibits high conversion efficiency.
  • solar cell modules and solar power generation systems using the above-mentioned photoelectric conversion element are available. In the CIGS-based photoelectric conversion element, further improvement of conversion efficiency is desired.
  • Cu(In, Ga)Se2 is hardly influenced by crystal grain boundaries because the distribution of Ga/(In + Ga) in a film thickness direction has a V shape structure, so that a double-slope forbidden band can be obtained, and therefore crystal grain boundaries do not cause a reduction in conversion efficiency, but in a CIGS thin-film having a high Ga concentration, influences of crystal grain boundaries cannot be ignored, and therefore it is desired to increase the grain size of CIGS crystals.
  • Embodiments provide a solar cell having improved efficiency, a multijunction solar cell, a solar cell module, and a photovoltaic power generation system whose solar cells have improved efficiency.
  • a solar cell of an embodiment includes a first electrode, a light absorbing layer containing Sn, an n-type layer, and a second electrode.
  • the light absorbing layer being present between the first electrode and the n-type layer.
  • the n-type layer being present between the light absorbing layer and the second electrode.
  • the light absorbing layer having a Sn concentration of 1 ⁇ 10 14 (atoms/cm 3 ) or more.
  • Fig. 1 is a conceptual sectional view of a solar cell according to an embodiment.
  • Fig. 2 is a conceptual sectional view of a solar cell according to an embodiment.
  • Fig. 3 is a conceptual perspective view of a part of a solar cell according to an embodiment.
  • Fig. 4 is a sectional conceptual view of a multijunction solar cell according to an embodiment.
  • Fig. 5 is a conceptual view of a solar cell module according to an embodiment.
  • Fig. 6 is a conceptual sectional view of a solar cell module according to an embodiment.
  • Fig. 7 is a conceptual view of a solar power generation system according to an embodiment.
  • Fig. 8 shows a SIMS measurement result in Example 2.
  • Fig. 9 shows a scanning electron microscope image in Example 2.
  • Fig. 10 shows a scanning electron microscope image in Comparative Example 1.
  • FIG. 1 is a conceptual view showing a solar cell 100 of the first embodiment.
  • the solar cell 100 includes a substrate 1, a first electrode 2 on the substrate 1, a light absorbing layer 3 on the first electrode 2, an n-type layer 4 on the light absorbing layer 3, and a second electrode 5 on the n-type layer 4.
  • An intermediate layer (not shown) may be present, for example, between the first electrode 2 and the light absorbing layer 3 or between the n-type layer 4 and the second electrode 5.
  • a soda lime glass As the substrate 1 in the embodiment, and a general glass such as quartz, white sheet glass or chemically reinforced glass, a metal plate of stainless steel, Ti (titanium) or Cr (chromium), or a resin such as polyimide or acrylic can also be used.
  • a general glass such as quartz, white sheet glass or chemically reinforced glass, a metal plate of stainless steel, Ti (titanium) or Cr (chromium), or a resin such as polyimide or acrylic can also be used.
  • the first electrode 2 in the embodiment is a layer present between the substrate 1 and the light absorbing layer 3.
  • the first electrode 2 is in direct contact with the substrate 1 and the light absorbing layer 3.
  • a transparent conductive film, or a laminate of a metal film, a transparent conductive film and a metal film is preferable.
  • the transparent conductive film is not particularly limited, and examples thereof include films of indium tin oxide (ITO), aluminum-doped zinc oxide (AZO), boron-doped zinc oxide (BZO), gallium-doped zinc oxide, fluorine-doped tin oxide (FTO), titanium-doped indium oxide (ITiO), indium zinc oxide (IZO) and indium gallium zinc oxide (IGZO).
  • the transparent conductive film may be a laminated film.
  • the metal film is not particularly limited, and examples thereof include films of Mo, Au and W.
  • the first electrode 2 may be an electrode in which a dot-shaped, line-shaped or mesh-shaped metal is provided on a transparent conductive film.
  • the dot-shaped, line-shaped or mesh-shaped metal is disposed between the transparent conductive film and the light absorbing layer 3.
  • the dot-shaped, line-shaped or mesh-shaped metal has an aperture ratio of 50% or more to the transparent conductive film.
  • the dot-shaped, line-shaped or mesh-shaped metal is not particularly limited, and examples thereof include Mo, Au and W.
  • a tin oxide film 6 that is in direct contact with the light absorbing layer 3 may be present between the second electrode 2 and the light absorbing layer 3 as shown in Fig. 2 that is a conceptual sectional view of the solar cell 101.
  • Sn diffuses into the light absorbing layer 3, so that the concentration of Sn in the light absorbing layer 3 can be partially increased.
  • the thickness of the tin oxide film 6 is preferably 10 nm or more and 200 m or less. This is because durability is markedly deteriorated when the thickness of the tin oxide film 6 is less than 10 nm, while the transmittance decreases when the thickness of the tin oxide film 6 is excessively large.
  • the thickness of the tin oxide film 6 is more preferably 20 nm or more and 150 m or less.
  • the first electrode 2 may be an electrode in which a dot-shaped, line-shaped or mesh-shaped metal is provided on a transparent conductive film
  • the tin oxide film 6 may be present either between the transparent conductive film and the dot-shaped, line-shaped or mesh-shaped metal, or between the dot-shaped, line-shaped or mesh-shaped metals and between the dot-shaped, line-shaped or mesh-shaped metal and the light absorbing layer 3.
  • the light absorbing layer 3 in the embodiment is a p-type layer present between the first electrode 2 and the n-type layer 4.
  • the light absorbing layer 3 is in direct contact with the first electrode 1 and the n-type layer 4.
  • the light absorbing layer 3 is present between the tin oxide film 6 and the n-type layer 4.
  • the light absorbing layer 3 is a layer containing a compound containing a group Ib element (group IB element, group 11 element), a group IIIb element (group IIIA element, group 13 element) and a group VIb element (group VIA element, group 16 element), and an n-type dopant.
  • the compound containing a group Ib element, a group IIIb element and a group VIb element has a chalcopyrite structure.
  • the group Ib element is Cu, or Cu and Ag
  • the group IIIb element is at least one element selected from the group consisting of Ga, Al and In
  • the group VIb element is at least one element selected from the group consisting of Se, S and Te.
  • the group Ib element is Cu
  • the group IIIb element is Ga, In, or Ga and In
  • the group VIb element is Se, S, or Se and S.
  • a compound semiconductor layer having a chalcopyrite structure such as Cu(In, Ga)Se 2 , CuInTe 2 , CuGaSe 2 , Cu(In, Ga)(S, Se) 2 , CuGa(S, Se) 2 can be used as the light absorbing layer 3.
  • the group Ib element is Cu
  • the group IIIb element is at least one selected from the group consisting of Ga and In
  • the group VIb element is at least one selected from the group consisting of Se and S.
  • the group IIIb element is Ga.
  • the amount of In in the group IIIb element is small because the band gap of the light absorbing layer 3 is easily adjusted to a suitable value as a top cell of a multijunction solar cell.
  • the film thickness of the light absorbing layer 3 is, for example, 800 nm or more and 3000 nm or less.
  • the band gap size of the light absorbing layer 3 can be easily adjusted to an intended value by combination of elements.
  • the band gap of the light absorbing layer 3 is 1.3 eV or more and 2.4 eV or less.
  • the ratio of Ga/(In + Ga) is preferably 0.5 or more.
  • the ratio of Ga/(In + Ga) is low, the grain size of the light absorbing layer 3 is not increased by Sn, and thus the effect of improving conversion efficiency due to the presence of Sn cannot be expected.
  • the light absorbing layer 3 contains Sn as an n-type dopant, a reduction in interfacial/bulk defects and an increase in grain size of the light absorbing layer 3 are promoted to increase the mobility.
  • An effect can be obtained when the concentration of Sn contained in the light absorbing layer 3 is about 1 ⁇ 10 12 (atoms/cm 3 ) or more.
  • Sn acts as an n-type dopant, and therefore when the Sn concentration is excessively large, the layer does not function as a p-type semiconductor. Therefore, the Sn concentration is preferably 1 ⁇ 10 14 (atoms/cm 3 ) or more and 1 ⁇ 10 18 (atoms/cm 3 ) or less.
  • the Sn concentration is more preferably 1 ⁇ 10 15 (atoms/cm 3 ) or more and 1 ⁇ 10 18 (atoms/cm 3 ) or less.
  • the Sn concentration is still more preferably 1 ⁇ 10 16 (atoms/cm 3 ) or more and 1 ⁇ 10 17 (atoms/cm 3 ) or less because a high-quality p-type semiconductor having high Jsc can be obtained.
  • the light absorbing layer 3 may further contain a p-type dopant.
  • the p-type dopant is preferably at least one selected from the group consisting of N, P, As, Bi, Sb and the like.
  • the concentration of the p-type dopant in the light absorbing layer 3 is lower than the concentration of the n-type dopant in the light absorbing layer 3.
  • Sb is contained as a p-type dopant because crystals of the light absorbing layer 3 have an increased grain size.
  • the light absorbing layer 3 of the solar cell 100 of the embodiment is a p-type layer
  • the light absorbing layer 3 contains an n-type dopant, and even when the light absorbing layer 3 contains a p-type dopant, the concentration of Sn is higher than that of the p-type dopant.
  • the light absorbing layer 3 in the embodiment has high crystallinity, and forms a favorable p-n junction with the n-type layer 4 to contribute to improvement of the efficiency of the solar cell 100.
  • the light absorbing layer 3 contains Sn and a p-type dopant.
  • the analysis is performed by SIMS in a depth direction from the n-type layer 4 to the light absorbing layer 3.
  • elements contained in the n-type layer 4 and the light absorbing layer 3 are measured beforehand by observing a cross-section of the solar cell with a transmission electron microscope-energy dispersive X-ray spectrometry (TEM EDX).
  • TEM EDX transmission electron microscope-energy dispersive X-ray spectrometry
  • the analysis site is a region of 78 micrometre ⁇ 78 micrometre at the center of eight regions generated by dividing the n-type layer 4 into four equal parts in a long direction and two equal parts in a short direction as shown in Fig.
  • the depth over which measurement is performed ranges from 300 nm from a surface of the light absorbing layer 3 on the n-type layer 4 side in the direction of the first electrode 2 to at least a surface of the light absorbing layer 3 on the first electrode side.
  • the point at which the concentration of an element having the maximum concentration in the n-type layer 4 crosses the concentration of a group VI element (the total concentration if there are two group VI elements) in the light absorbing layer is set to a surface of the light absorbing layer 3 on the n-type layer 4 side.
  • D is a thickness of the light absorbing layer 3
  • the average value over a depth ranging from a depth of 300 nm (start point) from a surface of the light absorbing layer 3 on the n-type layer 4 side in a first direction to a depth of D - 300 nm (end point) is defined as a concentration of Sn in the light absorbing layer 3.
  • PHI ADEPT 1010 is used, the primary ion species is Cs + , and the primary accelerating voltage is 5.0 kV.
  • the concentration of Sn in the light absorbing layer 3 influences the quality of crystals of the light absorbing layer 3, it is preferable that variations are not large.
  • the minimum value of the Sn concentration is preferably not less than 1/100, more preferably not less than 1/50, still more preferably not less than 1/10 of the maximum value of the Sn concentration.
  • Sn is diffused throughout the light absorbing layer 3.
  • the light absorbing layer 3 in the embodiment contains Sn, so that crystals have a large grain size.
  • the average crystal grain size of the light absorbing layer 3 (excluding a grain size of 50 nm or less) is 0.5 micrometre or more and 2.0 micrometre or less.
  • the diameter of the crystal of the light absorbing layer 3 is determined by observing a cross-section of the light absorbing layer 3 with a scanning electron microscope at a magnification of 20,000.
  • Sn may be added during deposition of the light absorbing layer 3.
  • a method for depositing the light absorbing layer 3 in the embodiment a method in which the light absorbing layer is deposited by a three-step method will be shown. The three-step method is changed according to the distribution of elements in the light absorbing layer 3.
  • Examples of the method for depositing the light absorbing layer 3, other than the three-step method include a sputtering method and a molecular beam epitaxy method.
  • a group IIIb element such as In or Ga and a group VIb element such as Se are first deposited on a substrate (a member with the first electrode 2 formed on the substrate 1) (first step).
  • Cu as a group Ib element, a group VIb element such as Se, and Sn are deposited (second step).
  • a group IIIb element such as In or Ga and a group VIb element such as Se are then deposited again (third step). After the process in the third step, heating is further performed to increase the grain size of crystals of the light absorbing layer 3.
  • the n-type layer 4 in the embodiment is an n-type semiconductor layer, which is present between the light absorbing layer 3 and the second electrode 5.
  • the n-type layer 4 is in direct contact with the light absorbing layer 3 and the second electrode 5.
  • the n-type layer 4 is a layer joined to the light absorbing layer 3 through heterojunction.
  • the n-type layer 4 is preferably an n-type semiconductor, the Fermi level of which is controlled so that a photoelectric conversion element with a high open circuit voltage can be obtained.
  • Zn 1-y M y O 1-x S x , Zn 1-y-z Mg z M y O, ZnO 1-x S x or Zn 1-z Mg z O can be used for the n-type layer 5.
  • the thickness of the n-type layer 4 is preferably 2 nm or more and 800 nm or less.
  • the second electrode 5 in the embodiment is an electrode present on the n-type layer 4.
  • the second electrode 5 is in direct contact with the n-type layer 4.
  • a transparent conductive film is preferable. It is preferable to use the same material as that of the first electrode 2 for the transparent conductive film.
  • the second electrode 5 may be provided with an extraction electrode.
  • a high-resistance layer of ZnMgO, ZnOS or the like, or a semi-insulating layer of i-ZnO or the like may be provided between the n-type layer 4 and the second electrode 5.
  • FIG. 4 is a conceptual sectional view of a multijunction solar cell 200 of the second embodiment.
  • the multijunction solar cell 200 in Fig. 4 has the solar cells (first solar cells) 100 and 101 of the first embodiment and a second solar cell 201 on the light incident side.
  • the band gap of a light absorbing layer of the second solar cell 201 has a band gap smaller than that of the light absorbing layer 3 of the solar cell 100 of the first embodiment.
  • the multijunction solar cell 200 of the embodiment also includes a solar cell obtained by joining three or more solar cells.
  • the band gap of the light absorbing layer 3 of the solar cell 100 of the first embodiment is 1.3 eV or more and 2.4 eV or less
  • the band gap of the light absorbing layer of the second solar cell 101 is preferably 1.0 eV or more and 1.4 eV or less.
  • the light absorbing layer of the second solar cell 101 is preferably at least one compound semiconductor layer selected from the group consisting of a CIGS-based layer with a high In content, a CIT-based layer and CdTe-based layer, or a layer including one selected from the group consisting of crystalline silicon and a perovskite-type compound.
  • the third embodiment relates to a solar cell module.
  • Fig. 5 is a conceptual perspective view of a solar cell module 300 of the third embodiment.
  • the solar cell module 300 in Fig. 5 is a solar cell module obtained by laminating a first solar cell module 301 and a second solar cell module 302.
  • the first solar cell module 301 is on a light incident side, and includes the solar cells 100 and 101 of the first embodiment.
  • the second solar cell module 302 includes the second solar cell 201 of the second embodiment.
  • Fig. 6 is a conceptual sectional view of the solar cell module 300.
  • Fig. 6 shows a structure of the first solar cell module 301 in detail.
  • a structure of the second solar cell module 302 is not shown.
  • the structure of the solar cell module is appropriately selected according to the light absorbing layer and the like of a solar cell to be used.
  • the solar cell module in Fig. 6 includes a plurality of sub-modules 303 surrounded by a broken line in which a plurality of solar cells 100 are arranged in a lateral direction and electrically connected in series, and a plurality of sub-modules 303 are electrically connected in parallel or in series. Adjacent sub-modules 303 are electrically connected to each other by a bus bar 304.
  • the solar cells 100 were scribed (P1), (P2) and (P3), and adjacent solar cells 100 are connected to each other at the second electrode 5 on the upper side and at the first electrode 2 on the lower side.
  • the solar cell 100 of the third embodiment includes a substrate 1, a first electrode 2, a light absorbing layer 3, an n-type layer 4 and a second electrode 5.
  • both ends of the solar cell 100 in the sub-module 303 are connected to the bus bar 304, and the bus bar 304 electrically connects a plurality of sub-modules 303 in parallel or in series to adjust the power voltage with the second solar cell module 302.
  • a fourth embodiment relates to a solar power generation system.
  • the solar cell module 300 of the third embodiment can be used as a power generator that generates power in the solar power generation system of the fourth embodiment.
  • the solar power generation system of the embodiment generates power using a solar cell module, and specifically, the solar power generation system includes a solar cell module that generates power, a unit that converts generated electricity to power, and an electricity accumulation unit that accumulates generated electricity or a load that consumes generated electricity.
  • Fig. 7 shows a conceptual view of the solar power generation system 400 of the embodiment.
  • the solar power generation system in Fig. 7 includes a solar cell module 401 (300), a converter 402, a storage battery 403 and a load 404.
  • the storage battery 403 and the load 404 may be omitted.
  • the load 404 may be configured such that electric energy accumulated in the storage battery 403 can also be utilized.
  • the converter 402 is an apparatus including a circuit or an element which performs power conversion, e.g. voltage transformation or direct current-alternating current conversion, such as a DC-DC converter, a DC-AC converter or an AC-AC converter.
  • a suitable configuration may be employed according to the generated voltage, or the configuration of the storage battery 403 or the load 404.
  • the solar cell module 401 is provided with a sunlight tracking drive device for causing the solar cell module 401 to constantly face the sun, a light collector for collecting sunlight, a device for improving power generation efficiency, or the like.
  • the solar power generation system 400 is used in immovable properties such as residences, commercial facilities and factories, or used in movable properties such as vehicles, aircrafts and electronic devices.
  • the photoelectric conversion element in the embodiment is excellent in conversion efficiency, and the power generation amount is expected to be increased by using the photoelectric conversion element for the solar cell module 401.
  • the embodiments will be more specifically described on the basis of examples, the embodiments are not limited to the following examples.
  • Example 1 A film-shaped first electrode composed of Mo alone is formed on a blue glass plate by sputtering in an Ar gas flow.
  • the film thickness of the first electrode is 500 nm.
  • Cu, Ga and Se are deposited as a light absorbing layer in such a manner that the film thickness is about 1.5 micrometre by the vapor deposition method.
  • the vapor deposition rate was adjusted so as to decrease the Cu concentration on the surface.
  • an extremely small amount of Sn is vapor-deposited during deposition, and annealing is performed to diffuse Sn. Thereafter, CdS is deposited as an n-type layer by a CBD method.
  • Example 1 After the n-layer is formed, ZnO : Al is deposited on the film in a thickness of about 200 nm by sputtering. Accordingly, a solar cell of Example 1 can be obtained. The resulting solar cell is irradiated with 1 Sun of simulated sunlight, and the conversion efficiency (%) and the short-circuit current (mA) are measured.
  • Table 1 the conversion efficiency in each of Examples 1 and 7 and Comparative Examples 1 and 2 is expressed as a ratio to the conversion efficiency in Comparative Example 1.
  • the conversion efficiency in each of Examples 2 to 6 and Comparative Example 5 to 7 is expressed as a ratio to the conversion efficiency in Comparative Example 6.
  • the conversion efficiency in Comparative Example 4 is expressed as a ratio to the conversion efficiency in Comparative Example 3.
  • Example 2 A solar cell of Example 2 can be obtained by the same method as in Example 1 except that in the preparation procedure in Example 1, ITO is deposited as a first electrode on a blue glass plate in a thickness of 150 nm, and SnO 2 is deposited on the top of the ITO in a thickness of 100 nm.
  • Fig. 8 shows a SIMS measurement result in Example 2.
  • Fig. 9 shows a transmission electron microscopic image (magnification: 20,000) after deposition of the light absorbing layer in Example 2. In the SIMS measurement result in Fig.
  • Fig. 8 also shows background levels of Na, Sn and K, peaks that may originate from interfering ions, and influences of charge-up.
  • Example 3 A solar cell of Example 3 can be obtained by the same method as in Example 1 except that in the preparation procedure in Example 2, ITO is deposited as a first electrode on a blue glass plate in a thickness of 150 nm.
  • Example 4 A solar cell of Example 4 can be obtained by the same method as in Example 1 except that in the preparation procedure in Example 2, ITO is deposited as a first electrode on a blue glass plate in a thickness of 150 nm, and the vapor deposition amount of Sn is increased.
  • Example 5 A solar cell of Example 5 can be obtained by the same method as in Example 1 except that in the preparation procedure in Example 2, Cu, In, Ga and Se are vapor-deposited as a light absorbing layer.
  • the Ga/(In + Ga) in Example 5 is adjusted to be 0.5.
  • Example 6 A solar cell of Example 6 can be obtained by the same method as in Example 1 except that in the preparation procedure in Example 2, Cu, In, Ga, Se and S are vapor-deposited as a light absorbing layer.
  • the Ga/(In + Ga) in Example 6 is adjusted to be 0.7.
  • Example 7 A solar cell of Example 7 can be obtained by the same method as in Example 1 except that in the preparation procedure in Example 1, a 2 nm-thick Sb film is deposited on a Mo electrode on a blue glass plate.
  • Example 1 In the preparation procedure in Example 1, the process of vapor deposition of Sn is not carried out during deposition, and other processes are carried out in the same manner as in Example 1 to obtain a solar cell of Comparative Example 1.
  • Fig. 10 shows a transmission electron microscopic image (magnification: 20,000) after deposition of the light absorbing layer in Comparative Example 1.
  • Comparative Example 2 In the preparation procedure in Example 1, Sn is vapor-deposited in an amount equivalent to 0.1% based on the amount of Cu, In, Ga and Se during deposition, and other processes are carried out in the same manner as in Example 1 to obtain a solar cell of Comparative Example 2.
  • Example 5 In the preparation procedure in Example 2, deposition is performed in such a manner that the highest temperature of a substrate during deposition of a light absorbing layer is 520°C, and other processes are carried out in the same manner as in Example 2 to obtain a solar cell of Comparative Example 5.
  • Example 1 shows that addition of Sn considerably improves the current value.
  • the amount of Sn was excessively large as in Comparative Example 2, the light absorbing layer was progressively turned to an n-type, so that a function as a solar cell was not obtained.
  • CIGSe is used for the light absorbing layer as in Examples 5 and 6
  • addition of Sn increased the grain size of CIGS grains to improve cell characteristics to some degree when the ratio of In/(In + Ga) was small, but when the ratio of In/(In + Ga) was large, conversion efficiency as a base characteristic was originally high, and as is apparent from comparison between Comparative Example 3 and Comparative Example 4, addition of Sn neither increased the grain size of CIGS grains nor improved cell characteristics.
  • Example 2 and Comparative Example 5 shows that when the deposition temperature was raised, a reaction took place at the SnO 2 /CGS interface, so that the Sn concentration on the back side increased, leading to deterioration of cell characteristics.
  • Comparison between Examples 1 and 7 shows that addition of Sb did not cause a difference in effect. On the other hand, the effect was not obtained when the amount of Sn was small as in Comparative Example 6 and Comparative Example 7.
  • the concentration of Sn in the light absorbing layer 3 was equivalent to a background level in SIMS measurement.
  • Example 8 The solar cell (top cell) of Example 2 is disposed on the light incident side, and laminated to a crystalline Si solar cell (bottom cell) with a band gap of 1.1 eV to prepare a multijunction solar cell. The resulting solar cell is irradiated with 1 Sun of simulated sunlight, and the conversion efficiency (%) is determined.
  • Comparative Example 8 The solar cell of Comparative Example 6 is disposed on the light incident side, and laminated to a crystalline Si solar cell with a band gap of 1.1 eV to prepare a multijunction solar cell. The resulting solar cell is irradiated with 1 Sun of simulated sunlight, and the conversion efficiency (%) is determined.
  • the solar cell of Example 2 For the multijunction solar cell, use of the solar cell of Example 2 with the light absorbing layer containing Sn in a suitable concentration increases conversion efficiency as compared to the multijunction solar cell of the comparative example.
  • the solar cell of the example in which a light-transmissive electrode is used is also suitable in a multijunction solar cell.
  • some elements are expressed only by element symbols thereof.
  • a solar cell comprising: a first electrode; a light absorbing layer containing Sn; an n-type layer; and a second electrode, wherein the light absorbing layer being present between the first electrode and the n-type layer, the n-type layer is present between the light absorbing layer and the second electrode, and the light absorbing layer has a Sn concentration of 1 ⁇ 10 14 (atoms/cm 3 ) or more.
  • Clause 2 The solar cell according to clause 1, wherein the Sn concentration is 1 ⁇ 10 14 (atoms/cm 3 ) or more and 1 ⁇ 10 18 (atoms/cm 3 ) or less.
  • Clause 3 The solar cell according to clause 1 or 2, wherein the light absorbing layer contains a compound containing a group I element, a group III element and a group VI element, and the Sn.
  • Clause 4 The solar cell according to any one of clauses 1 to 3, wherein the group Ib element in the light absorbing layer is Cu, or Cu and Ag, the group IIIb element in the light absorbing layer is at least one element selected from the group consisting of Ga, Al and In, and the group VIb element in the light absorbing layer is at least one element selected from the group consisting of Se, S and Te.
  • Clause 5 The solar cell according to any one of clauses 1 to 4, wherein the group Ib element in the light absorbing layer is Cu, the group IIIb element in the light absorbing layer is Ga and In, the group VIb element in the light absorbing layer is at least one element selected from the group consisting of Se and S, and the element ratio of the Ga and In satisfies the ratio of Ga/(Ga + In) being 0.5 or more.
  • Clause 6 The solar cell according to any one of clauses 1 to 5, wherein the light absorbing layer contains at least one p-type dopant selected from the group consisting of N, P, As, Bi and Sb, and the concentration of the p-type dopant is lower than the Sn concentration.
  • Clause 7 The solar cell according to any one of clauses 1 to 6, wherein the band gap of the light absorbing layer is 1.3 eV or more and 2.4 eV or less.
  • Clause 8 The solar cell according to any one of clauses 1 to 7, wherein the Sn concentration is 1 ⁇ 10 16 (atoms/cm 3 ) or more and 1 ⁇ 10 17 (atoms/cm 3 ) or less.
  • Clause 9] The solar cell according to any one of clauses 1 to 8, wherein in a region at a depth of 300 nm to 500 nm from a surface of the light absorbing layer on the n-type layer side in the direction of the first electrode, the minimum value of the Sn concentration is not less than 1/100 of the Sn concentration.
  • a multijunction solar cell comprising: the solar cell according to any one of clauses 1 to 9; and a second solar cell including a light absorbing layer having a band gap smaller than that of the light absorbing layer of the solar cell according to any one of clauses 1 to 9.
  • Clause 11 The multijunction solar cell according to clause 10, wherein the light absorbing layer of the second solar cell is a compound semiconductor or crystalline silicon.
  • Clause 12 A solar cell module comprising the solar cell according to any one of clauses 1 to 9.
  • Clause 13 A solar cell module comprising: the solar cell according to any one of clauses 1 to 9; and a second solar cell including a light absorbing layer having a band gap smaller than that of the light absorbing layer of the solar cell according to any one of clauses 1 to 9.
  • Clause 14 A solar power generation system which performs solar power generation using the solar cell module according to clause 12 or 13.

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Abstract

Embodiments provide a solar cell having improved efficiency, a multijunction solar cell, a solar cell module, a photovoltaic power generation system, and a method for producing solar cell whose solar cells have improved efficiency. A solar cell of an embodiment includes a first electrode, a light absorbing layer containing Sn, an n-type layer, and a second electrode. The light absorbing layer being present between the first electrode and the n-type layer. The n-type layer being present between the light absorbing layer and the second electrode. The light absorbing layer having a Sn concentration of 1 × 1014 (atoms/cm3) or more.

Description

SOLAR CELL, MULTIJUNCTION SOLAR CELL, SOLAR CELL MODULE AND SOLAR POWER GENERATION SYSTEM
Embodiments described herein relate to a solar cell, a multijunction solar cell, a solar cell module and a solar power generation system.
Development of a photoelectric conversion element in which a compound with a semiconductor thin-film used as a light absorbing layer is used has been advanced. In particular, a thin-film photoelectric conversion element in which Cu(In, Ga)Se2 or CuGaSe2 being a group Ib-IIIb-VIb compound having a chalcopyrite structure is used as light absorbing layer (CIGS, CGS) exhibits high conversion efficiency. In addition, solar cell modules and solar power generation systems using the above-mentioned photoelectric conversion element are available. In the CIGS-based photoelectric conversion element, further improvement of conversion efficiency is desired.
Among group I-III-VI compounds having a chalcopyrite structure, Cu(In, Ga)Se2 is hardly influenced by crystal grain boundaries because the distribution of Ga/(In + Ga) in a film thickness direction has a V shape structure, so that a double-slope forbidden band can be obtained, and therefore crystal grain boundaries do not cause a reduction in conversion efficiency, but in a CIGS thin-film having a high Ga concentration, influences of crystal grain boundaries cannot be ignored, and therefore it is desired to increase the grain size of CIGS crystals.
[PTL 1] Japanese Patent Number 6099435
Embodiments provide a solar cell having improved efficiency, a multijunction solar cell, a solar cell module, and a photovoltaic power generation system whose solar cells have improved efficiency.
A solar cell of an embodiment includes a first electrode, a light absorbing layer containing Sn, an n-type layer, and a second electrode. The light absorbing layer being present between the first electrode and the n-type layer. The n-type layer being present between the light absorbing layer and the second electrode. The light absorbing layer having a Sn concentration of 1 × 1014 (atoms/cm3) or more.
Fig. 1 is a conceptual sectional view of a solar cell according to an embodiment. Fig. 2 is a conceptual sectional view of a solar cell according to an embodiment. Fig. 3 is a conceptual perspective view of a part of a solar cell according to an embodiment. Fig. 4 is a sectional conceptual view of a multijunction solar cell according to an embodiment. Fig. 5 is a conceptual view of a solar cell module according to an embodiment. Fig. 6 is a conceptual sectional view of a solar cell module according to an embodiment. Fig. 7 is a conceptual view of a solar power generation system according to an embodiment. Fig. 8 shows a SIMS measurement result in Example 2. Fig. 9 shows a scanning electron microscope image in Example 2. Fig. 10 shows a scanning electron microscope image in Comparative Example 1.
A first embodiment relates to a solar cell. Fig. 1 is a conceptual view showing a solar cell 100 of the first embodiment. As shown in Fig. 1, the solar cell 100 according to this embodiment includes a substrate 1, a first electrode 2 on the substrate 1, a light absorbing layer 3 on the first electrode 2, an n-type layer 4 on the light absorbing layer 3, and a second electrode 5 on the n-type layer 4. An intermediate layer (not shown) may be present, for example, between the first electrode 2 and the light absorbing layer 3 or between the n-type layer 4 and the second electrode 5.
(Substrate)
It is desirable to use a soda lime glass as the substrate 1 in the embodiment, and a general glass such as quartz, white sheet glass or chemically reinforced glass, a metal plate of stainless steel, Ti (titanium) or Cr (chromium), or a resin such as polyimide or acrylic can also be used.
(First electrode)
The first electrode 2 in the embodiment is a layer present between the substrate 1 and the light absorbing layer 3. In Fig. 1, the first electrode 2 is in direct contact with the substrate 1 and the light absorbing layer 3. As the first electrode 2, a transparent conductive film, or a laminate of a metal film, a transparent conductive film and a metal film is preferable. The transparent conductive film is not particularly limited, and examples thereof include films of indium tin oxide (ITO), aluminum-doped zinc oxide (AZO), boron-doped zinc oxide (BZO), gallium-doped zinc oxide, fluorine-doped tin oxide (FTO), titanium-doped indium oxide (ITiO), indium zinc oxide (IZO) and indium gallium zinc oxide (IGZO). The transparent conductive film may be a laminated film. The metal film is not particularly limited, and examples thereof include films of Mo, Au and W. In addition, the first electrode 2 may be an electrode in which a dot-shaped, line-shaped or mesh-shaped metal is provided on a transparent conductive film. Here, the dot-shaped, line-shaped or mesh-shaped metal is disposed between the transparent conductive film and the light absorbing layer 3. Preferably, the dot-shaped, line-shaped or mesh-shaped metal has an aperture ratio of 50% or more to the transparent conductive film. The dot-shaped, line-shaped or mesh-shaped metal is not particularly limited, and examples thereof include Mo, Au and W.
In addition, a tin oxide film 6 that is in direct contact with the light absorbing layer 3 may be present between the second electrode 2 and the light absorbing layer 3 as shown in Fig. 2 that is a conceptual sectional view of the solar cell 101. By providing the tin oxide film 6, Sn diffuses into the light absorbing layer 3, so that the concentration of Sn in the light absorbing layer 3 can be partially increased. The thickness of the tin oxide film 6 is preferably 10 nm or more and 200 m or less. This is because durability is markedly deteriorated when the thickness of the tin oxide film 6 is less than 10 nm, while the transmittance decreases when the thickness of the tin oxide film 6 is excessively large. The thickness of the tin oxide film 6 is more preferably 20 nm or more and 150 m or less. When the first electrode 2 may be an electrode in which a dot-shaped, line-shaped or mesh-shaped metal is provided on a transparent conductive film, the tin oxide film 6 may be present either between the transparent conductive film and the dot-shaped, line-shaped or mesh-shaped metal, or between the dot-shaped, line-shaped or mesh-shaped metals and between the dot-shaped, line-shaped or mesh-shaped metal and the light absorbing layer 3.
(Light absorbing layer)
The light absorbing layer 3 in the embodiment is a p-type layer present between the first electrode 2 and the n-type layer 4. In Fig. 1, the light absorbing layer 3 is in direct contact with the first electrode 1 and the n-type layer 4. In Fig. 2, the light absorbing layer 3 is present between the tin oxide film 6 and the n-type layer 4.
The light absorbing layer 3 is a layer containing a compound containing a group Ib element (group IB element, group 11 element), a group IIIb element (group IIIA element, group 13 element) and a group VIb element (group VIA element, group 16 element), and an n-type dopant. The compound containing a group Ib element, a group IIIb element and a group VIb element has a chalcopyrite structure. Preferably, the group Ib element is Cu, or Cu and Ag, the group IIIb element is at least one element selected from the group consisting of Ga, Al and In, and the group VIb element is at least one element selected from the group consisting of Se, S and Te. In particular, it is more preferable that the group Ib element is Cu, the group IIIb element is Ga, In, or Ga and In, the group VIb element is Se, S, or Se and S. For example, a compound semiconductor layer having a chalcopyrite structure, such as Cu(In, Ga)Se2, CuInTe2, CuGaSe2, Cu(In, Ga)(S, Se)2, CuGa(S, Se)2 can be used as the light absorbing layer 3.
It is preferable that in the light absorbing layer 3, the group Ib element is Cu, the group IIIb element is at least one selected from the group consisting of Ga and In, and the group VIb element is at least one selected from the group consisting of Se and S. It is also preferable that the group IIIb element is Ga. It is preferable that the amount of In in the group IIIb element is small because the band gap of the light absorbing layer 3 is easily adjusted to a suitable value as a top cell of a multijunction solar cell. The film thickness of the light absorbing layer 3 is, for example, 800 nm or more and 3000 nm or less.
The band gap size of the light absorbing layer 3 can be easily adjusted to an intended value by combination of elements. The band gap of the light absorbing layer 3 is 1.3 eV or more and 2.4 eV or less.
For Cu(In, Ga)(Se, S)2 among group I-III-VI compounds having a chalcopyrite structure, the ratio of Ga/(In + Ga) is preferably 0.5 or more. When the ratio of Ga/(In + Ga) is low, the grain size of the light absorbing layer 3 is not increased by Sn, and thus the effect of improving conversion efficiency due to the presence of Sn cannot be expected.
When the light absorbing layer 3 contains Sn as an n-type dopant, a reduction in interfacial/bulk defects and an increase in grain size of the light absorbing layer 3 are promoted to increase the mobility. An effect can be obtained when the concentration of Sn contained in the light absorbing layer 3 is about 1 × 1012 (atoms/cm3) or more. However, Sn acts as an n-type dopant, and therefore when the Sn concentration is excessively large, the layer does not function as a p-type semiconductor. Therefore, the Sn concentration is preferably 1 × 1014 (atoms/cm3) or more and 1 × 1018 (atoms/cm3) or less. The Sn concentration is more preferably 1 × 1015 (atoms/cm3) or more and 1 × 1018 (atoms/cm3) or less. The Sn concentration is still more preferably 1 × 1016 (atoms/cm3) or more and 1 × 1017 (atoms/cm3) or less because a high-quality p-type semiconductor having high Jsc can be obtained.
In addition, the light absorbing layer 3 may further contain a p-type dopant. In the light absorbing layer 3, for example, the p-type dopant is preferably at least one selected from the group consisting of N, P, As, Bi, Sb and the like. The concentration of the p-type dopant in the light absorbing layer 3 is lower than the concentration of the n-type dopant in the light absorbing layer 3. For example, it is preferable that Sb is contained as a p-type dopant because crystals of the light absorbing layer 3 have an increased grain size.
Although the light absorbing layer 3 of the solar cell 100 of the embodiment is a p-type layer, the light absorbing layer 3 contains an n-type dopant, and even when the light absorbing layer 3 contains a p-type dopant, the concentration of Sn is higher than that of the p-type dopant. The light absorbing layer 3 in the embodiment has high crystallinity, and forms a favorable p-n junction with the n-type layer 4 to contribute to improvement of the efficiency of the solar cell 100.
By performing analysis by secondary ion mass spectrometry (SIMS), it can be confirmed that the light absorbing layer 3 contains Sn and a p-type dopant. The analysis is performed by SIMS in a depth direction from the n-type layer 4 to the light absorbing layer 3. Preferably, elements contained in the n-type layer 4 and the light absorbing layer 3 are measured beforehand by observing a cross-section of the solar cell with a transmission electron microscope-energy dispersive X-ray spectrometry (TEM EDX). The analysis site is a region of 78 micrometre × 78 micrometre at the center of eight regions generated by dividing the n-type layer 4 into four equal parts in a long direction and two equal parts in a short direction as shown in Fig. 3 that is a conceptual perspective view of a part of the solar cell 100. The depth over which measurement is performed ranges from 300 nm from a surface of the light absorbing layer 3 on the n-type layer 4 side in the direction of the first electrode 2 to at least a surface of the light absorbing layer 3 on the first electrode side. The point at which the concentration of an element having the maximum concentration in the n-type layer 4 crosses the concentration of a group VI element (the total concentration if there are two group VI elements) in the light absorbing layer is set to a surface of the light absorbing layer 3 on the n-type layer 4 side. Where D is a thickness of the light absorbing layer 3, the average value over a depth ranging from a depth of 300 nm (start point) from a surface of the light absorbing layer 3 on the n-type layer 4 side in a first direction to a depth of D - 300 nm (end point) is defined as a concentration of Sn in the light absorbing layer 3. As a SIMS measurement apparatus, PHI ADEPT 1010 is used, the primary ion species is Cs+, and the primary accelerating voltage is 5.0 kV.
Even when the Sn concentration is 1 × 1016 (atoms/cm3) or more only in the vicinity of the first electrode 2 of the light absorbing layer 3, crystallinity is not as high as that of the light absorbing layer 3 in the embodiment, and therefore conversion efficiency is not so high. For example, when the tin oxide film 6 is provided, and Sn is not added during deposition of the light absorbing layer 3, the Sn concentration is high only in the vicinity of the first electrode 2. Similarly, only diffusion of Sn from the n-type layer 4 side does not give a suitable Sn concentration as in the light absorbing layer 3 in the embodiment.
Since the concentration of Sn in the light absorbing layer 3 influences the quality of crystals of the light absorbing layer 3, it is preferable that variations are not large. Thus, in a region at a depth of 300 nm to 500 nm from a surface of the light absorbing layer 3 on the n-type layer 4 side in the direction of the first electrode 2, the minimum value of the Sn concentration is preferably not less than 1/100, more preferably not less than 1/50, still more preferably not less than 1/10 of the maximum value of the Sn concentration.
By adding a small amount of Sn during deposition of the light absorbing layer 3 in the embodiment, Sn is diffused throughout the light absorbing layer 3.
The light absorbing layer 3 in the embodiment contains Sn, so that crystals have a large grain size. The average crystal grain size of the light absorbing layer 3 (excluding a grain size of 50 nm or less) is 0.5 micrometre or more and 2.0 micrometre or less. The diameter of the crystal of the light absorbing layer 3 is determined by observing a cross-section of the light absorbing layer 3 with a scanning electron microscope at a magnification of 20,000. The diameter R of the crystal is determined from the equation: R = (R1 + R2)/2 where R1 is an inscribed circle diameter and R2 is a circumscribed circle diameter of each crystal.
Next, in the method for producing the light absorbing layer 3 in the embodiment, Sn may be added during deposition of the light absorbing layer 3. As an example of a method for depositing the light absorbing layer 3 in the embodiment, a method in which the light absorbing layer is deposited by a three-step method will be shown. The three-step method is changed according to the distribution of elements in the light absorbing layer 3. Examples of the method for depositing the light absorbing layer 3, other than the three-step method, include a sputtering method and a molecular beam epitaxy method.
In the vapor deposition method (three-step method), a group IIIb element such as In or Ga and a group VIb element such as Se are first deposited on a substrate (a member with the first electrode 2 formed on the substrate 1) (first step). Cu as a group Ib element, a group VIb element such as Se, and Sn are deposited (second step). A group IIIb element such as In or Ga and a group VIb element such as Se are then deposited again (third step). After the process in the third step, heating is further performed to increase the grain size of crystals of the light absorbing layer 3.
(n-type layer)
The n-type layer 4 in the embodiment is an n-type semiconductor layer, which is present between the light absorbing layer 3 and the second electrode 5. In Fig. 1, the n-type layer 4 is in direct contact with the light absorbing layer 3 and the second electrode 5. The n-type layer 4 is a layer joined to the light absorbing layer 3 through heterojunction. The n-type layer 4 is preferably an n-type semiconductor, the Fermi level of which is controlled so that a photoelectric conversion element with a high open circuit voltage can be obtained. For example, Zn1-yMyO1-xSx, Zn1-y-zMgzMyO, ZnO1-xSx or Zn1-zMgzO (M is at least one element selected from the group consisting of B, Al, In and Ga), CdS or the like can be used for the n-type layer 5. The thickness of the n-type layer 4 is preferably 2 nm or more and 800 nm or less.
(Second electrode)
The second electrode 5 in the embodiment is an electrode present on the n-type layer 4. In Fig. 1, the second electrode 5 is in direct contact with the n-type layer 4. As the second electrode 5, a transparent conductive film is preferable. It is preferable to use the same material as that of the first electrode 2 for the transparent conductive film. The second electrode 5 may be provided with an extraction electrode. A high-resistance layer of ZnMgO, ZnOS or the like, or a semi-insulating layer of i-ZnO or the like may be provided between the n-type layer 4 and the second electrode 5.
(Second embodiment)
A second embodiment relates to a multijunction solar cell. Fig. 4 is a conceptual sectional view of a multijunction solar cell 200 of the second embodiment. The multijunction solar cell 200 in Fig. 4 has the solar cells (first solar cells) 100 and 101 of the first embodiment and a second solar cell 201 on the light incident side. The band gap of a light absorbing layer of the second solar cell 201 has a band gap smaller than that of the light absorbing layer 3 of the solar cell 100 of the first embodiment. The multijunction solar cell 200 of the embodiment also includes a solar cell obtained by joining three or more solar cells.
Since the band gap of the light absorbing layer 3 of the solar cell 100 of the first embodiment is 1.3 eV or more and 2.4 eV or less, the band gap of the light absorbing layer of the second solar cell 101 is preferably 1.0 eV or more and 1.4 eV or less. The light absorbing layer of the second solar cell 101 is preferably at least one compound semiconductor layer selected from the group consisting of a CIGS-based layer with a high In content, a CIT-based layer and CdTe-based layer, or a layer including one selected from the group consisting of crystalline silicon and a perovskite-type compound.
(Third embodiment)
The third embodiment relates to a solar cell module. Fig. 5 is a conceptual perspective view of a solar cell module 300 of the third embodiment. The solar cell module 300 in Fig. 5 is a solar cell module obtained by laminating a first solar cell module 301 and a second solar cell module 302. The first solar cell module 301 is on a light incident side, and includes the solar cells 100 and 101 of the first embodiment. The second solar cell module 302 includes the second solar cell 201 of the second embodiment.
Fig. 6 is a conceptual sectional view of the solar cell module 300. Fig. 6 shows a structure of the first solar cell module 301 in detail. A structure of the second solar cell module 302 is not shown. In the second solar cell module 301, the structure of the solar cell module is appropriately selected according to the light absorbing layer and the like of a solar cell to be used. The solar cell module in Fig. 6 includes a plurality of sub-modules 303 surrounded by a broken line in which a plurality of solar cells 100 are arranged in a lateral direction and electrically connected in series, and a plurality of sub-modules 303 are electrically connected in parallel or in series. Adjacent sub-modules 303 are electrically connected to each other by a bus bar 304.
The solar cells 100 were scribed (P1), (P2) and (P3), and adjacent solar cells 100 are connected to each other at the second electrode 5 on the upper side and at the first electrode 2 on the lower side. Like the solar cell 100 of the first embodiment, the solar cell 100 of the third embodiment includes a substrate 1, a first electrode 2, a light absorbing layer 3, an n-type layer 4 and a second electrode 5. Preferably, both ends of the solar cell 100 in the sub-module 303 are connected to the bus bar 304, and the bus bar 304 electrically connects a plurality of sub-modules 303 in parallel or in series to adjust the power voltage with the second solar cell module 302.
(Fourth embodiment)
A fourth embodiment relates to a solar power generation system. The solar cell module 300 of the third embodiment can be used as a power generator that generates power in the solar power generation system of the fourth embodiment. The solar power generation system of the embodiment generates power using a solar cell module, and specifically, the solar power generation system includes a solar cell module that generates power, a unit that converts generated electricity to power, and an electricity accumulation unit that accumulates generated electricity or a load that consumes generated electricity. Fig. 7 shows a conceptual view of the solar power generation system 400 of the embodiment. The solar power generation system in Fig. 7 includes a solar cell module 401 (300), a converter 402, a storage battery 403 and a load 404. Any one of the storage battery 403 and the load 404 may be omitted. The load 404 may be configured such that electric energy accumulated in the storage battery 403 can also be utilized. The converter 402 is an apparatus including a circuit or an element which performs power conversion, e.g. voltage transformation or direct current-alternating current conversion, such as a DC-DC converter, a DC-AC converter or an AC-AC converter. As the configuration of the converter 402, a suitable configuration may be employed according to the generated voltage, or the configuration of the storage battery 403 or the load 404.
Solar cells included in the sub-module 301 included in the solar cell module 300 and receiving light generate power, and the resulting electric energy is converted by the converter 402, and stored in the storage battery 403, or consumed by the load 404. Preferably, the solar cell module 401 is provided with a sunlight tracking drive device for causing the solar cell module 401 to constantly face the sun, a light collector for collecting sunlight, a device for improving power generation efficiency, or the like.
Preferably, the solar power generation system 400 is used in immovable properties such as residences, commercial facilities and factories, or used in movable properties such as vehicles, aircrafts and electronic devices. The photoelectric conversion element in the embodiment is excellent in conversion efficiency, and the power generation amount is expected to be increased by using the photoelectric conversion element for the solar cell module 401.
Hereinafter, although the embodiments will be more specifically described on the basis of examples, the embodiments are not limited to the following examples.
(Example 1)
A film-shaped first electrode composed of Mo alone is formed on a blue glass plate by sputtering in an Ar gas flow. The film thickness of the first electrode is 500 nm. On the Mo electrode on the blue glass plate, Cu, Ga and Se are deposited as a light absorbing layer in such a manner that the film thickness is about 1.5 micrometre by the vapor deposition method. Here, the vapor deposition rate was adjusted so as to decrease the Cu concentration on the surface. In addition, an extremely small amount of Sn is vapor-deposited during deposition, and annealing is performed to diffuse Sn. Thereafter, CdS is deposited as an n-type layer by a CBD method. After the n-layer is formed, ZnO : Al is deposited on the film in a thickness of about 200 nm by sputtering. Accordingly, a solar cell of Example 1 can be obtained. The resulting solar cell is irradiated with 1 Sun of simulated sunlight, and the conversion efficiency (%) and the short-circuit current (mA) are measured. The results in examples and comparative examples are collectively shown in Table 1. In Table 1, the conversion efficiency in each of Examples 1 and 7 and Comparative Examples 1 and 2 is expressed as a ratio to the conversion efficiency in Comparative Example 1. In Table 1, the conversion efficiency in each of Examples 2 to 6 and Comparative Example 5 to 7 is expressed as a ratio to the conversion efficiency in Comparative Example 6. In Table 1, the conversion efficiency in Comparative Example 4 is expressed as a ratio to the conversion efficiency in Comparative Example 3.
(Example 2)
A solar cell of Example 2 can be obtained by the same method as in Example 1 except that in the preparation procedure in Example 1, ITO is deposited as a first electrode on a blue glass plate in a thickness of 150 nm, and SnO2 is deposited on the top of the ITO in a thickness of 100 nm. Fig. 8 shows a SIMS measurement result in Example 2. In addition, Fig. 9 shows a transmission electron microscopic image (magnification: 20,000) after deposition of the light absorbing layer in Example 2. In the SIMS measurement result in Fig. 8, the concentrations or ion intensities of Sn (thick line), Cd (thin line), K (thick broken line), Na (broken line), Se (long dashed single-dotted line) and Zn (long dashed double-dotted line). In addition, Fig. 8 also shows background levels of Na, Sn and K, peaks that may originate from interfering ions, and influences of charge-up.
(Example 3)
A solar cell of Example 3 can be obtained by the same method as in Example 1 except that in the preparation procedure in Example 2, ITO is deposited as a first electrode on a blue glass plate in a thickness of 150 nm.
(Example 4)
A solar cell of Example 4 can be obtained by the same method as in Example 1 except that in the preparation procedure in Example 2, ITO is deposited as a first electrode on a blue glass plate in a thickness of 150 nm, and the vapor deposition amount of Sn is increased.
(Example 5)
A solar cell of Example 5 can be obtained by the same method as in Example 1 except that in the preparation procedure in Example 2, Cu, In, Ga and Se are vapor-deposited as a light absorbing layer. The Ga/(In + Ga) in Example 5 is adjusted to be 0.5.
(Example 6)
A solar cell of Example 6 can be obtained by the same method as in Example 1 except that in the preparation procedure in Example 2, Cu, In, Ga, Se and S are vapor-deposited as a light absorbing layer. The Ga/(In + Ga) in Example 6 is adjusted to be 0.7.
(Example 7)
A solar cell of Example 7 can be obtained by the same method as in Example 1 except that in the preparation procedure in Example 1, a 2 nm-thick Sb film is deposited on a Mo electrode on a blue glass plate.
(Comparative Example 1)
In the preparation procedure in Example 1, the process of vapor deposition of Sn is not carried out during deposition, and other processes are carried out in the same manner as in Example 1 to obtain a solar cell of Comparative Example 1. Fig. 10 shows a transmission electron microscopic image (magnification: 20,000) after deposition of the light absorbing layer in Comparative Example 1.
(Comparative Example 2)
In the preparation procedure in Example 1, Sn is vapor-deposited in an amount equivalent to 0.1% based on the amount of Cu, In, Ga and Se during deposition, and other processes are carried out in the same manner as in Example 1 to obtain a solar cell of Comparative Example 2.
(Comparative Example 3)
In the preparation procedure in Example 1, the process of vapor deposition of Sn is not carried out during deposition of a light absorbing layer, the flux of In and Ga is adjusted to satisfy the relationship of Ga/(In + Ga) = 0.2, and other processes are carried out in the same manner as in Example 1 to obtain a solar cell of Comparative Example 3.
(Comparative Example 4)
In the preparation procedure in Example 1, the flux of In and Ga is adjusted to satisfy the relationship of Ga/(In + Ga) = 0.2, and other processes are carried out in the same manner as in Example 1 to obtain a solar cell of Comparative Example 4.
(Comparative Example 5)
In the preparation procedure in Example 2, deposition is performed in such a manner that the highest temperature of a substrate during deposition of a light absorbing layer is 520°C, and other processes are carried out in the same manner as in Example 2 to obtain a solar cell of Comparative Example 5.
(Comparative Example 6)
In the preparation procedure in Example 2, the process of vapor deposition of Sn is not carried out during deposition of a light absorbing layer, and other processes are carried out in the same manner as in Example 2 to obtain a solar cell of Comparative Example 6.
(Comparative Example 7)
In the preparation procedure in Example 3, the process of vapor deposition of Sn is not carried out during deposition of a light absorbing layer, and other processes are carried out in the same manner as in Example 3 to obtain a solar cell of Comparative Example 7.
Figure JPOXMLDOC01-appb-T000001
Comparison between Example 1 and Comparative Example 1 shows that addition of Sn considerably improves the current value. In addition, when the amount of Sn was excessively large as in Comparative Example 2, the light absorbing layer was progressively turned to an n-type, so that a function as a solar cell was not obtained. When CIGSe is used for the light absorbing layer as in Examples 5 and 6, addition of Sn increased the grain size of CIGS grains to improve cell characteristics to some degree when the ratio of In/(In + Ga) was small, but when the ratio of In/(In + Ga) was large, conversion efficiency as a base characteristic was originally high, and as is apparent from comparison between Comparative Example 3 and Comparative Example 4, addition of Sn neither increased the grain size of CIGS grains nor improved cell characteristics. Comparison between Example 2 and Comparative Example 5 shows that when the deposition temperature was raised, a reaction took place at the SnO2/CGS interface, so that the Sn concentration on the back side increased, leading to deterioration of cell characteristics. Comparison between Examples 1 and 7 shows that addition of Sb did not cause a difference in effect. On the other hand, the effect was not obtained when the amount of Sn was small as in Comparative Example 6 and Comparative Example 7. In Comparative Examples 1, 3 and 7, the concentration of Sn in the light absorbing layer 3 was equivalent to a background level in SIMS measurement.
(Example 8)
The solar cell (top cell) of Example 2 is disposed on the light incident side, and laminated to a crystalline Si solar cell (bottom cell) with a band gap of 1.1 eV to prepare a multijunction solar cell. The resulting solar cell is irradiated with 1 Sun of simulated sunlight, and the conversion efficiency (%) is determined.
(Comparative Example 8)
The solar cell of Comparative Example 6 is disposed on the light incident side, and laminated to a crystalline Si solar cell with a band gap of 1.1 eV to prepare a multijunction solar cell. The resulting solar cell is irradiated with 1 Sun of simulated sunlight, and the conversion efficiency (%) is determined.
For the multijunction solar cell, use of the solar cell of Example 2 with the light absorbing layer containing Sn in a suitable concentration increases conversion efficiency as compared to the multijunction solar cell of the comparative example. The solar cell of the example in which a light-transmissive electrode is used is also suitable in a multijunction solar cell.
Here, some elements are expressed only by element symbols thereof.
Clauses
Clause 1
A solar cell comprising:
a first electrode;
a light absorbing layer containing Sn;
an n-type layer; and
a second electrode, wherein
the light absorbing layer being present between the first electrode and the n-type layer,
the n-type layer is present between the light absorbing layer and the second electrode, and
the light absorbing layer has a Sn concentration of 1 × 1014 (atoms/cm3) or more.
Clause 2
The solar cell according to clause 1, wherein the Sn concentration is 1 × 1014 (atoms/cm3) or more and 1 × 1018 (atoms/cm3) or less.
Clause 3
The solar cell according to clause 1 or 2, wherein the light absorbing layer contains a compound containing a group I element, a group III element and a group VI element, and the Sn.
Clause 4
The solar cell according to any one of clauses 1 to 3, wherein
the group Ib element in the light absorbing layer is Cu, or Cu and Ag,
the group IIIb element in the light absorbing layer is at least one element selected from the group consisting of Ga, Al and In, and
the group VIb element in the light absorbing layer is at least one element selected from the group consisting of Se, S and Te.
Clause 5
The solar cell according to any one of clauses 1 to 4, wherein
the group Ib element in the light absorbing layer is Cu,
the group IIIb element in the light absorbing layer is Ga and In,
the group VIb element in the light absorbing layer is at least one element selected from the group consisting of Se and S, and
the element ratio of the Ga and In satisfies the ratio of Ga/(Ga + In) being 0.5 or more.
Clause 6
The solar cell according to any one of clauses 1 to 5, wherein
the light absorbing layer contains at least one p-type dopant selected from the group consisting of N, P, As, Bi and Sb, and
the concentration of the p-type dopant is lower than the Sn concentration.
Clause 7
The solar cell according to any one of clauses 1 to 6, wherein the band gap of the light absorbing layer is 1.3 eV or more and 2.4 eV or less.
Clause 8
The solar cell according to any one of clauses 1 to 7, wherein the Sn concentration is 1 × 1016 (atoms/cm3) or more and 1 × 1017 (atoms/cm3) or less.
Clause 9]
The solar cell according to any one of clauses 1 to 8, wherein in a region at a depth of 300 nm to 500 nm from a surface of the light absorbing layer on the n-type layer side in the direction of the first electrode, the minimum value of the Sn concentration is not less than 1/100 of the Sn concentration.
Clause 10
A multijunction solar cell comprising:
the solar cell according to any one of clauses 1 to 9; and
a second solar cell including a light absorbing layer having a band gap smaller than that of the light absorbing layer of the solar cell according to any one of clauses 1 to 9.
Clause 11
The multijunction solar cell according to clause 10, wherein the light absorbing layer of the second solar cell is a compound semiconductor or crystalline silicon.
Clause 12
A solar cell module comprising the solar cell according to any one of clauses 1 to 9.
Clause 13
A solar cell module comprising: the solar cell according to any one of clauses 1 to 9; and a second solar cell including a light absorbing layer having a band gap smaller than that of the light absorbing layer of the solar cell according to any one of clauses 1 to 9.
Clause 14
A solar power generation system which performs solar power generation using the solar cell module according to clause 12 or 13.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
100, 101: Solar cell(First solar cell), 1: Substrate, 2: First Electrode, 3: Light absorbing layer, 4: n-type layer, 5: Second electrode, 6: Tin oxide film,
200: Multi junction solar cell, 201: Second solar cell,
300: Solar cell module, 301: First solar cell module, 302: Second solar cell module, 303: Submodule, 304: Bus bar,
400: Photovoltaic power generation system, 401: Solar cell module, 402: Converter, 403: Storage battery, 404: Load

Claims (14)

  1. A solar cell comprising:
    a first electrode;
    a light absorbing layer containing Sn;
    an n-type layer; and
    a second electrode, wherein
    the light absorbing layer being present between the first electrode and the n-type layer,
    the n-type layer is present between the light absorbing layer and the second electrode, and
    the light absorbing layer has a Sn concentration of 1 × 1014 (atoms/cm3) or more.
  2. The solar cell according to claim 1, wherein the Sn concentration is 1 × 1014 (atoms/cm3) or more and 1 × 1018 (atoms/cm3) or less.
  3. The solar cell according to claim 1 or 2, wherein the light absorbing layer contains a compound containing a group I element, a group III element and a group VI element, and the Sn.
  4. The solar cell according to any one of claims 1 to 3, wherein
    the group Ib element in the light absorbing layer is Cu, or Cu and Ag,
    the group IIIb element in the light absorbing layer is at least one element selected from the group consisting of Ga, Al and In, and
    the group VIb element in the light absorbing layer is at least one element selected from the group consisting of Se, S and Te.
  5. The solar cell according to any one of claims 1 to 4, wherein
    the group Ib element in the light absorbing layer is Cu,
    the group IIIb element in the light absorbing layer is Ga and In,
    the group VIb element in the light absorbing layer is at least one element selected from the group consisting of Se and S, and
    the element ratio of the Ga and In satisfies the ratio of Ga/(Ga + In) being 0.5 or more.
  6. The solar cell according to any one of claims 1 to 5, wherein
    the light absorbing layer contains at least one p-type dopant selected from the group consisting of N, P, As, Bi and Sb, and
    the concentration of the p-type dopant is lower than the Sn concentration.
  7. The solar cell according to any one of claims 1 to 6, wherein the band gap of the light absorbing layer is 1.3 eV or more and 2.4 eV or less.
  8. The solar cell according to any one of claims 1 to 7, wherein the Sn concentration is 1 × 1016 (atoms/cm3) or more and 1 × 1017 (atoms/cm3) or less.
  9. The solar cell according to any one of claims 1 to 8, wherein in a region at a depth of 300 nm to 500 nm from a surface of the light absorbing layer on the n-type layer side in the direction of the first electrode, the minimum value of the Sn concentration is not less than 1/100 of the Sn concentration.
  10. A multijunction solar cell comprising:
    the solar cell according to any one of claims 1 to 9; and
    a second solar cell including a light absorbing layer having a band gap smaller than that of the light absorbing layer of the solar cell according to any one of claims 1 to 9.
  11. The multijunction solar cell according to claim 10, wherein the light absorbing layer of the second solar cell is a compound semiconductor or crystalline silicon.
  12. A solar cell module comprising the solar cell according to any one of claims 1 to 9.
  13. A solar cell module comprising: the solar cell according to any one of claims 1 to 9; and a second solar cell including a light absorbing layer having a band gap smaller than that of the light absorbing layer of the solar cell according to any one of claims 1 to 9.
  14. A solar power generation system which performs solar power generation using the solar cell module according to claim 12 or 13.
PCT/JP2018/010652 2017-09-21 2018-03-16 Solar cell, multijunction solar cell, solar cell module and solar power generation system WO2019058603A1 (en)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6153895A (en) * 1997-01-24 2000-11-28 Asahi Kasei Kogyo Kabushiki Kaisha p-type semiconductor, method for manufacturing the p-type semiconductor, semiconductor device, photovoltaic element, and method for manufacturing semiconductor device
US20140020736A1 (en) * 2012-07-17 2014-01-23 Korea Institute Of Science And Technology Method for producing cis-based thin film, cis-based thin film produced by the method and thin-film solar cell including the thin film
JP2014170889A (en) * 2013-03-05 2014-09-18 Sharp Corp Core shell particle, photoelectric conversion layer and photoelectric conversion element

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6153895A (en) * 1997-01-24 2000-11-28 Asahi Kasei Kogyo Kabushiki Kaisha p-type semiconductor, method for manufacturing the p-type semiconductor, semiconductor device, photovoltaic element, and method for manufacturing semiconductor device
US20140020736A1 (en) * 2012-07-17 2014-01-23 Korea Institute Of Science And Technology Method for producing cis-based thin film, cis-based thin film produced by the method and thin-film solar cell including the thin film
JP2014170889A (en) * 2013-03-05 2014-09-18 Sharp Corp Core shell particle, photoelectric conversion layer and photoelectric conversion element
JP6099435B2 (en) 2013-03-05 2017-03-22 シャープ株式会社 Core-shell particle, photoelectric conversion layer, and photoelectric conversion element

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