WO2015050083A1 - Photovoltaic element - Google Patents

Photovoltaic element Download PDF

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Publication number
WO2015050083A1
WO2015050083A1 PCT/JP2014/075889 JP2014075889W WO2015050083A1 WO 2015050083 A1 WO2015050083 A1 WO 2015050083A1 JP 2014075889 W JP2014075889 W JP 2014075889W WO 2015050083 A1 WO2015050083 A1 WO 2015050083A1
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transparent conductive
conductive film
photovoltaic device
mass
film
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PCT/JP2014/075889
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French (fr)
Japanese (ja)
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小林　英治
宣孝 中村
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長州産業株式会社
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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
    • H01L31/02—Details
    • H01L31/0224—Electrodes
    • H01L31/022466—Electrodes made of transparent conductive layers, e.g. TCO, ITO layers
    • H01L31/022475—Electrodes made of transparent conductive layers, e.g. TCO, ITO layers composed of indium tin oxide [ITO]
    • 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 at least one potential-jump barrier or surface barrier
    • 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 at least one potential-jump barrier or surface barrier the potential barriers being only of the PN heterojunction type
    • H01L31/0745—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 at least one potential-jump barrier or surface barrier the potential barriers being only of the PN heterojunction type comprising a AIVBIV heterojunction, e.g. Si/Ge, SiGe/Si or Si/SiC solar cells
    • H01L31/0747—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 at least one potential-jump barrier or surface barrier the potential barriers being only of the PN heterojunction type comprising a AIVBIV heterojunction, e.g. Si/Ge, SiGe/Si or Si/SiC solar cells comprising a heterojunction of crystalline and amorphous materials, e.g. heterojunction with intrinsic thin layer or HIT® solar cells; solar cells
    • 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
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/1884—Manufacture of transparent electrodes, e.g. TCO, ITO
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy

Definitions

  • the present invention relates to a photovoltaic device (solar cell) having a heterojunction.
  • Photovoltaic elements are attracting attention as clean power generation means that does not generate greenhouse gases such as CO 2 and as power generation means with high operational safety in place of nuclear power generation.
  • a photovoltaic element having a heterojunction with high power generation efficiency (heterojunction photovoltaic element).
  • the heterojunction refers to, for example, a junction between a single crystal semiconductor and an amorphous semiconductor, and a diffusion potential is formed by this junction.
  • an n-type amorphous semiconductor thin film and a first transparent conductive film are laminated in this order on the light incident surface side of the n-type crystal semiconductor substrate, and the n-type crystal semiconductor substrate
  • a rear emitter type structure in which a p-type amorphous semiconductor thin film and a second transparent conductive film are laminated in this order on the side opposite to the light incident surface has been developed (see Patent Document 1).
  • ITO indium tin oxide
  • a crystalline silicon solar cell including a transparent conductive film whose average major axis crystal grain size (in-plane major axis average crystal grain size) is controlled to 300 to 2000 nm using ITO or the like is disclosed. It has been developed (see Patent Document 2).
  • a film made of ITO or the like is required to be formed at a relatively high temperature (for example, higher than 200 ° C.) or to be heat-treated after the film formation in order to crystallize and lower the resistance.
  • the present invention has been made in view of such circumstances, and an object thereof is to provide a heterojunction photovoltaic device having high power generation efficiency by forming a transparent conductive film using a material that can be crystallized even at a relatively low temperature.
  • the inventors have made use of the fact that a transparent conductive film having a small crystal grain size and a high mobility is formed at a relatively low temperature by doping indium oxide with a specific dopant, and this transparent conductive film has a rear emitter structure.
  • the present invention was found to be suitable for the heterojunction photovoltaic device.
  • the photovoltaic device according to the present invention that meets the above object includes an n-type crystal semiconductor substrate, an n-type amorphous semiconductor thin film laminated in this order on one side of the n-type crystal semiconductor substrate, and the first transparent In a photovoltaic device comprising a conductive film, a p-type amorphous semiconductor thin film and a second transparent conductive film stacked in this order on the other side of the n-type crystal semiconductor substrate, and one side used as a light incident surface , Either one or both of the first and second transparent conductive films is crystalline indium oxide doped with one or more elements (x) belonging to Groups 4, 5, and 6 of the periodic table.
  • a transparent conductive film ( ⁇ ) having an average major axis crystal grain size of 10 nm or more and less than 300 nm.
  • the photovoltaic device according to the present invention since a specific dopant is used, crystal nuclei are likely to be formed during film formation. Therefore, the photovoltaic device is crystallized even at a relatively low temperature, and has a small crystal grain size and high mobility A conductive film is formed. Therefore, the photovoltaic device according to the present invention has high power generation efficiency.
  • the element (x) includes one or more elements (x1) selected from the group consisting of tungsten and tantalum.
  • elements (x1) selected from the group consisting of tungsten and tantalum.
  • the content of the element (x1) in the transparent conductive film ( ⁇ ) is preferably 0.1% by mass or more and 10% by mass or less in terms of oxide.
  • the element (x) further includes one or more elements (x2) selected from the group consisting of titanium, vanadium, and niobium.
  • elements (x2) selected from the group consisting of titanium, vanadium, and niobium.
  • the content of the element (x2) in the transparent conductive film ( ⁇ ) is preferably 0.1% by mass or more and 5% by mass or less in terms of oxide.
  • the content of the element (x) in the transparent conductive film ( ⁇ ) is preferably 0.1% by mass or more and 10% by mass or less in terms of oxide.
  • the second transparent conductive film is the transparent conductive film ( ⁇ ).
  • ⁇ transparent conductive film
  • the reason for this is as follows. According to the knowledge of the inventors, in the heterojunction photovoltaic device having a rear emitter structure, the lateral direction of the second transparent conductive film laminated on the back side, that is, on the p-type amorphous semiconductor thin film The current collecting property in the (planar direction) becomes low. Therefore, it is particularly preferable to increase the low resistance of the second transparent conductive film.
  • the light transmittance (particularly, (Transmission of light having a wavelength of 900 to 1200 nm) is lowered, and output characteristics are lowered.
  • the 2nd transparent conductive film provided in the back side also has a high transmittance
  • the power generation efficiency can be increased by providing the second transparent conductive film with the transparent conductive film ( ⁇ ) that can achieve crystallization at a low temperature and has low resistance without increasing the amount of dopant. .
  • the first transparent conductive film is also the transparent conductive film ( ⁇ ).
  • productivity and the like can be further increased in addition to power generation efficiency.
  • the transparent conductive film ( ⁇ ) is preferably formed at a forming temperature of 200 ° C. or less.
  • a transparent conductive film ( ⁇ ) is preferably formed at a formation temperature of 200 ° C. or less.
  • amorphous means not only amorphous but also microcrystals.
  • Morocrystal means a crystal peak observed by Raman spectroscopy.
  • the “forming temperature” refers to a substrate temperature when a sputtering method, an ion plating method, or the like is used, and a heat treatment temperature after film deposition performed as necessary.
  • the transparent conductive film is formed using a material that is crystallized even at a relatively low temperature, and has high power generation efficiency.
  • the photovoltaic device 10 which concerns on one Example of this invention is a plate-shaped multilayered structure.
  • the photovoltaic element 10 includes an n-type crystal semiconductor substrate 11, a first intrinsic amorphous semiconductor thin film 12 stacked in this order on one side (the upper side in FIG. 1) of the n-type crystal semiconductor substrate 11, an n-type A second intrinsic amorphous semiconductor thin film laminated in this order on the other side (lower side in FIG. 1) of the amorphous semiconductor thin film 13 and the first transparent conductive film 14 and the n-type crystal semiconductor substrate 11 15, a p-type amorphous semiconductor thin film 16 and a second transparent conductive film 17.
  • the photovoltaic element 10 is a collector electrode 18 disposed on the surface (one side) of the first transparent conductive film 14 and a collector electrode disposed on the surface (other side) of the second transparent conductive film 17.
  • an electrode 19 is a collector electrode 18 disposed on the surface (one side) of the first transparent conductive film 14 and a collector electrode
  • the n-type crystal semiconductor substrate 11 is not particularly limited as long as it is a crystalline substrate having n-type semiconductor characteristics, and a known substrate can be used.
  • Examples of the crystal semiconductor constituting the n-type crystal semiconductor substrate 11 include SiC (SiGe), SiN, etc. in addition to silicon (Si), but silicon is preferable from the viewpoint of productivity.
  • the n-type crystal semiconductor substrate 11 may be a single crystal or a polycrystal.
  • a texture structure is formed on one surface of the n-type crystal semiconductor substrate 11.
  • This texture structure may also be formed on the other surface.
  • This texture structure enables light confinement due to diffuse reflection of light.
  • a concavo-convex structure having a large number of pyramid shapes is irregularly arranged so as to cover substantially the entire upper and lower surfaces (one side and the other side) of the n-type crystal semiconductor substrate 11.
  • the height (size) of the concavo-convex structure (texture structure) may be uneven, and adjacent concavo-convex portions may overlap.
  • a vertex and a trough part may be roundish.
  • the height of the unevenness is about several ⁇ m to several tens of ⁇ m.
  • Such a texture structure can be obtained, for example, by immersing the substrate material in an etching solution containing about 1 to 5% by mass of sodium hydroxide and anisotropically etching the (100) plane of the substrate material.
  • the first intrinsic amorphous semiconductor thin film 12 is stacked on one side of the n-type crystal semiconductor substrate 11.
  • the semiconductor constituting the first intrinsic amorphous semiconductor thin film 12 include silicon (Si), SiC, SiGe, SiN, etc., but silicon is preferable from the viewpoint of productivity.
  • the thickness of the intrinsic amorphous semiconductor thin film 12 is not particularly limited, but can be, for example, 1 nm or more and 10 nm or less, and preferably 8 nm or less. When the film thickness is less than 1 nm, recombination of carriers is likely to occur due to defects easily occurring. Moreover, when this film thickness exceeds 10 nm, it becomes easy to produce the fall of a short circuit current and the increase in light absorption.
  • the n-type amorphous semiconductor thin film 13 is laminated on one side of the first intrinsic amorphous semiconductor thin film 12.
  • Examples of the semiconductor constituting the n-type amorphous semiconductor thin film 13 include n-type amorphous silicon, n-type amorphous SiC, SiGe, SiN, etc. From this point, n-type amorphous silicon is preferable.
  • the thickness of the n-type amorphous semiconductor thin film 13 is not particularly limited, but is preferably 1 nm to 15 nm, for example, and more preferably 2 nm to 10 nm. By setting the film thickness within such a range, occurrence of carrier recombination and series resistance can be reduced in a balanced manner.
  • the first transparent conductive film 14 (transparent conductive film ( ⁇ )) is stacked on one side of the n-type amorphous semiconductor thin film 13.
  • the first transparent conductive film 14 is made of crystalline indium oxide doped with one or more elements (x) belonging to Groups 4, 5 and 6 of the periodic table.
  • the element (x) is not particularly limited as long as it is an element belonging to Group 4, Group 5, and Group 6 of the periodic table, but preferably includes elements of the sixth period (hafnium, tungsten, and tantalum). And one or more elements (x1) selected from the group consisting of tantalum and tantalum.
  • the content of the element (x1) in the first transparent conductive film 14 is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.3% by mass or more in terms of oxide (WO 3 , Ta 2 O 5 ). 5 mass% or less is more preferable, and 0.5 mass% or more and 3 mass% or less are still more preferable.
  • the element (x) preferably contains at least one element (x2) selected from the group consisting of titanium, vanadium and niobium in addition to the element (x1). Of the elements (x2), titanium is more preferable.
  • the content of the element (x2) in the first transparent conductive film 14 is preferably 0.1% by mass or more and 5% by mass or less in terms of oxides (TiO 2 , V 2 O 5 and Nb 2 O 5 ), and 0 More preferably, the content is 5% by mass or more and 3% by mass or less.
  • the total content of the element (x) in the first transparent conductive film 14 is preferably 0.1% by mass or more and 10% by mass or less, and 0.5% by mass or more and 5% by mass or less in terms of oxide. More preferred is 3% by mass or less.
  • the first transparent conductive film 14 may further contain other elements (for example, tin or the like) as long as the effects of the present invention are not impaired.
  • content of indium oxide in the 1st transparent conductive film 14 90 mass% or more is preferable, 95 mass% or more is more preferable, 97 mass% or more and 99.9 mass% or less are further more preferable.
  • the average major axis crystal grain size of crystalline indium oxide in the first transparent conductive film 14 is 10 nm or more and less than 300 nm, and preferably 40 nm or more and 250 nm or less.
  • the average long-axis crystal grain size is measured by measuring the longest diameter of each crystal grain existing in the plane in an image obtained from a scanning electron microscope (SEM). The average value of the measured values of the top 20 particles with the largest value. Since the first transparent conductive film 14 is mainly composed of crystalline indium oxide having such a small particle diameter, even if the formation temperature is 200 ° C. or less, the film has high crystallinity and high mobility. It becomes. In addition, it is thought that the formation of a crystal having such a small particle diameter is derived from the element (x) to be doped.
  • the specific resistance value of the first transparent conductive film 14 is preferably 5 ⁇ 10 ⁇ 5 ⁇ ⁇ cm to 1 ⁇ 10 ⁇ 3 ⁇ ⁇ cm, and more preferably 5 ⁇ 10 ⁇ 4 ⁇ ⁇ cm.
  • the carrier density has an upper limit of 3 ⁇ 10 20 cm ⁇ 3 and the mobility has a lower limit of 40 cm 2 V ⁇ 1 s ⁇ 1. .
  • the second intrinsic amorphous semiconductor thin film 15 is stacked on the other side of the n-type crystal semiconductor substrate 11.
  • the semiconductor constituting the second intrinsic amorphous semiconductor thin film 15 can be the same as the first intrinsic amorphous semiconductor thin film 12.
  • the film thickness of the second intrinsic amorphous semiconductor thin film 15 can be, for example, 1 nm or more and 10 nm or less.
  • the p-type amorphous semiconductor thin film 16 is laminated on the other side of the second intrinsic amorphous semiconductor thin film 15.
  • Examples of the semiconductor composing the p-type amorphous semiconductor thin film 16 include p-type amorphous silicon, p-type amorphous SiC, SiGe, SiN and the like. From this point, p-type amorphous silicon is preferable.
  • the thickness of the p-type amorphous semiconductor thin film 16 is not particularly limited, but is preferably 1 nm or more and less than 6 nm, for example, and more preferably 2 nm or more and 5 nm or less. By setting the film thickness within such a range, occurrence of carrier recombination and series resistance can be reduced in a balanced manner.
  • the second transparent conductive film 17 (transparent conductive film ( ⁇ )) is laminated on the other side of the p-type amorphous semiconductor thin film 16.
  • the material (composition), characteristics, crystal grain size, film thickness, and the like that form the second transparent conductive film 17 are the same as those of the first transparent conductive film 14.
  • the first transparent conductive film 14 and the second transparent conductive film 17 may be different in composition, film thickness, specific resistance, and the like.
  • the second transparent conductive layer laminated on the back side that is, on the p-type amorphous semiconductor thin film 16.
  • the second transparent conductive film 17 Since the current collecting property in the lateral direction (planar direction) of the film 17 becomes low, it is preferable that the second transparent conductive film 17 has a lower resistance than the first transparent conductive film 14. As the carrier density increases, the absorption in the near-infrared wavelength region of 900 nm or more in the transparent conductive film increases remarkably. However, when the n-type crystal semiconductor substrate 11 is silicon (Si), the wavelength is 900 nm to 1200 nm. Since the light absorptance is low, light with a wavelength of 900 nm to 1200 nm tends to reach the second transparent conductive film 17 laminated on the back side.
  • Si silicon
  • the upper limit of the carrier density in the second transparent conductive film 17 is 3 ⁇ 10 20 cm ⁇ 3 and the lower limit of the mobility is 40 cm 2 V ⁇ 1 s ⁇ 1 .
  • the collector electrodes 18 and 19 have a plurality of bus bar electrodes formed in parallel with each other at equal intervals, and a plurality of finger electrodes orthogonal to these bus bar electrodes and formed in parallel with each other at equal intervals.
  • the bus bar electrode and the finger electrode each have a linear shape or a strip shape, and are formed of a conductive material.
  • a conductive adhesive such as a silver paste or a metal conductive wire such as a copper wire can be used.
  • the width of each bus bar electrode is, for example, about 0.5 mm to 2 mm, and the width of each finger electrode is, for example, about 10 ⁇ m to 300 ⁇ m.
  • interval between each finger electrode it is about 0.5 mm or more and 4 mm or less, for example.
  • the collector electrode 19 on the other side may be a structure in which a conductive material is laminated on the entire surface, instead of a structure including a bus bar electrode and a finger electrode.
  • the collector electrode having such a structure can be formed by plating, metal foil lamination, or the like.
  • the photovoltaic elements 10 having such a structure are usually used by connecting a plurality of photovoltaic elements 10 in series. By using a plurality of photovoltaic power generation devices 10 connected in series, the generated voltage can be increased.
  • the light incident surface of the photovoltaic element 10 is on one side (the upper side in FIG. 1). That is, the photovoltaic device 10 has a rear emitter structure in which a p-type amorphous semiconductor thin film 16 is provided on the side opposite to the light incident surface with respect to the n-type crystal semiconductor substrate 11.
  • the transparent conductive films 14 and 17 made of crystals with a small particle diameter are formed of indium oxide doped with a specific dopant (element (x)). Low resistance and excellent power generation efficiency.
  • the second transparent conductive film 17 on the back side that can reduce the lateral current collecting property usually has the specific dopant and crystallinity.
  • the photovoltaic element 10 includes a step of laminating a first intrinsic amorphous semiconductor thin film 12 on one side of an n-type crystal semiconductor substrate 11, a step of laminating an n-type amorphous semiconductor thin film 13, and a first step.
  • a step of laminating the transparent conductive film 14 a step of laminating the second intrinsic amorphous semiconductor thin film 15 on the other side of the n-type crystal semiconductor substrate 11, and a step of laminating the p-type amorphous semiconductor thin film 16.
  • the order of each process will not be specifically limited as long as it is the order which can obtain the layer structure of the photovoltaic device 10.
  • a method of laminating the first and second intrinsic amorphous semiconductor thin films 12 and 15 for example, chemical vapor deposition (for example, plasma CVD method or catalytic CVD method (also called hot wire CVD method)) or the like is used.
  • chemical vapor deposition for example, plasma CVD method or catalytic CVD method (also called hot wire CVD method)
  • a well-known method is mentioned.
  • the plasma CVD method for example, a mixed gas of SiH 4 and H 2 can be used as the source gas.
  • a chemical vapor deposition method for example, a plasma CVD method or a catalytic CVD method (also called hot wire CVD method)
  • the film can be formed by a known method such as If by plasma CVD method, a mixed gas of SiH 4, H 2, and PH 3 for example in the n-type amorphous-based semiconductor 13 as a source gas, the p-type amorphous-based semiconductor thin film 16 is for example a SiH 4 A mixed gas of H 2 and B 2 H 6 can be used.
  • Examples of the method of laminating the first and second transparent conductive films 14 and 17 include a sputtering method, a vacuum deposition method, and an ion plating method (reactive plasma deposition method). It is preferable to use a plating method.
  • the sputtering method is excellent in film thickness controllability and the like, and can be performed at a lower cost than the ion plating method.
  • the ion plating method it is possible to perform film formation while suppressing generation of defects.
  • a main component is indium oxide, and an oxide of the element (x) is included. Is used.
  • the component ratio of each component in the vapor deposition material can be appropriately adjusted according to the desired component ratio of the first and second transparent conductive films 14 and 17.
  • the vapor deposition material may further contain other components (for example, tin oxide).
  • content (content ratio) of the metal component in each transparent conductive films 14 and 17 is the vapor deposition material used.
  • the vapor deposition material when the element (x) is tungsten or the like (in the case of so-called IWO), a known vapor deposition material can be used. Further, when the element (x) is tantalum, the vapor deposition material is prepared, for example, by a step (a) of preparing a solution containing a precursor of indium oxide and a precursor of tantalum oxide, and an alkali compound in the solution. To obtain a metal hydroxide precipitate (b), washing and drying the obtained metal hydroxide precipitate to obtain a metal oxide powder (c), and The metal oxide powder can be obtained by a method including a step (d) of sintering after pulverization.
  • the indium oxide precursor examples include indium nitrate and indium chloride
  • examples of the tantalum oxide precursor include tantalum chloride.
  • the pH of the solution obtained in step (a) is preferably 1 to 4. Moreover, you may add other components (For example, metal components other than element (x), a pH adjuster, etc.) to this solution.
  • the pH of the solution after adding the alkali compound in the step (b) is preferably 7 to 10.
  • the sintering temperature in step (d) can be about 1250 to 1600 ° C., and the sintering time can be about 10 to 20 hours.
  • the sputtering method can be performed using a known sputtering apparatus.
  • the initial degree of vacuum in the chamber of the sputtering apparatus can be about 1 ⁇ 10 ⁇ 7 to 1 ⁇ 10 ⁇ 5 Torr.
  • the ion plating method can also be performed using a commonly used known apparatus.
  • the substrate temperature during lamination (vapor deposition) by sputtering or ion plating is not particularly limited, but is preferably 200 ° C. or lower, more preferably 0 ° C. or higher and 80 ° C. or lower, and may be room temperature.
  • the formation pressure can be about 7.5 ⁇ 10 ⁇ 4 to 7.5 ⁇ 10 ⁇ 3 Torr, and preferably 2 ⁇ 10 ⁇ 3 Torr to 7 ⁇ 10 ⁇ 3 Torr.
  • the formation temperature (the substrate temperature during sputtering and ion plating, and the heat treatment temperature performed thereafter if necessary) is 200 ° C. or less (more preferably 150 ° C. or less).
  • the transparent conductive films 14 and 17 have the above-described composition, so that the formation of fine crystal grains proceeds even in the formation at such a relatively low temperature, A low resistance film can be obtained.
  • the formation temperature is 200 ° C. or lower, the influence on other amorphous semiconductor thin films and the like can be suppressed, and a heterojunction photovoltaic device having high power generation efficiency can be obtained.
  • the collector electrodes 18 and 19 can be disposed by a known method.
  • a conductive adhesive is used as a material for the collector electrodes 18 and 19, it can be formed by a printing method such as screen printing or gravure offset printing.
  • a metal conducting wire for the collector electrodes 18 and 19 it can fix on the transparent conductive films 14 and 17 with a conductive adhesive or a low melting point metal (solder etc.).
  • the present invention is not limited to the above-described embodiments, and the configuration thereof can be changed without changing the gist of the present invention.
  • the first intrinsic amorphous semiconductor thin film 12 and the second intrinsic amorphous semiconductor thin film 15 included in the photovoltaic device 10 are not essential components.
  • the maximum output can be further increased in order to improve translucency by adopting a configuration in which the first intrinsic amorphous semiconductor thin film 12 on the light incident side is not laminated.
  • the first transparent conductive film 14 or the second transparent conductive film 17 may be formed by another transparent conductive material or a different film formation method, and the crystallinity is not particularly limited. Examples of other transparent conductive materials include ITO.
  • the first transparent conductive film 14 is a film formed by ion plating using, for example, IWO
  • the second transparent conductive film 17 is formed by sputtering using indium oxide doped with at least tantalum. Film.
  • a hydroxide precipitate was obtained by adding an alkali to an aqueous solution in which indium nitrate (In (NO 3 ) 3 ), tantalum chloride and tetraisopropyl orthotitanate were dissolved.
  • the hydroxide precipitate was dried and pulverized and then sintered to obtain a sintered body (sputtering target).
  • the amounts of tantalum chloride and tetraisopropyl orthotitanate were adjusted so that the contents of tantalum oxide and titanium oxide in the sputtering target were 0.5% by mass, respectively.
  • the obtained sputtering target was attached to a DC magnetron sputter, an initial vacuum degree in the chamber was set to 1 ⁇ 10 ⁇ 6 Torr or less, and an In—Ta—Ti—O-based thin film was deposited on a glass substrate with a thickness of 100 nm at room temperature. It was. Thereafter, the In—Ta—Ti—O-based thin film was heat-treated at 150 ° C. for 2 hours in an air atmosphere to obtain a transparent conductive film. The surface of the obtained transparent conductive film was confirmed to have crystallinity by SEM observation, and the specific resistance was 3.78 ⁇ 10 ⁇ 4 ⁇ ⁇ cm. The average major axis crystal grain size based on the SEM image was 100 nm. Moreover, as a result of measuring the resistance change after storing the obtained transparent conductive film at 80 ° C. under a room temperature of 85% for 5 days, the resistance change was within 3.2%.
  • a transparent conductive film was obtained in the same manner as in Production Example 1 using an indium tin oxide sputtering target having an indium oxide content of 90% by mass and a tin oxide content of 10% by mass.
  • the surface of the obtained transparent conductive film could not be confirmed by SEM observation, and the specific resistance was 7.19 ⁇ 10 ⁇ 4 ⁇ ⁇ cm.
  • the resistance change was within 12.9%.
  • n-type single crystal silicon substrate On one side of the n-type single crystal silicon substrate, a first intrinsic amorphous silicon thin film (film thickness 6 nm), an n-type amorphous silicon thin film (film thickness 8 nm), and a first transparent conductive film (film thickness) 65 nm) was laminated in this order.
  • the n-type single crystal silicon substrate used what formed the fine uneven structure (texture structure) which has innumerable pyramid shape on both surfaces. This concavo-convex structure was formed by immersing the substrate material in an etching solution containing about 3% by mass of sodium hydroxide and anisotropically etching the (100) plane of the substrate material.
  • a second intrinsic amorphous silicon thin film (film thickness 6 nm), a p-type amorphous silicon thin film (film thickness 4 nm), and a second transparent conductive film ( A film thickness of 65 nm) was laminated in this order.
  • Each silicon thin film was laminated by a plasma CVD method.
  • n-type amorphous silicon thin film (film thickness: 8 nm) and a first transparent conductive film (film thickness: 65 nm) were laminated in this order on one side of an n-type single crystal silicon substrate (first intrinsic amorphous system) Except that the silicon thin film was not laminated), it was performed in the same manner as in Experimental Example 1 and the like.
  • the first and second transparent conductive films in each experimental example and comparative example were laminated by the following materials and methods.
  • Experimental Example 2 and Experimental Example 4 In—Ta—Ti—O material (sputtering target of Production Example 1), sputtering method (deposition conditions of Production Example 1)
  • the maximum output (Pmax) of each obtained photovoltaic device was measured. As measurement results, values based on Comparative Example 1 are shown in FIG. In addition, each was measured by using one side as a light incident surface, that is, a heterojunction structure (Rear emitter) in which the p layer was laminated on the opposite side to the light incident side.
  • a heterojunction structure Rear emitter
  • the photovoltaic elements of Experimental Examples 1 to 4 have a maximum output that is higher than those of Comparative Examples 1 and 2 in which a transparent conductive film is formed of ITO and crystallization is not sufficiently advanced. .
  • a transparent conductive film is formed using a material that can be crystallized even at a relatively low temperature, so that high power generation efficiency can be obtained, and a photovoltaic device that has attracted attention in recent years can be provided.
  • 10 photovoltaic device
  • 11 n-type crystal semiconductor substrate
  • 12 first intrinsic amorphous semiconductor thin film
  • 13 n-type amorphous semiconductor thin film
  • 14 first transparent conductive film
  • 15 first 2 intrinsic amorphous semiconductor thin film
  • 16 p-type amorphous semiconductor thin film
  • 17 second transparent conductive film
  • 18, 19 collector electrode

Abstract

This photovoltaic element (10), of which one side is used as a light entrance surface, is provided with: an n-type crystalline semiconductor substrate (11); an n-type amorphous semiconductor thin film (13) and a first transparent conductive film (14) laminated in the given sequence to one side of the n-type crystalline semiconductor substrate (11); and a p-type amorphous semiconductor thin film (16) and a second transparent conductive film (17) laminated in the given sequence to the other side of the n-type crystalline semiconductor substrate (11). The first and/or second transparent conductive film (14, 17) is a transparent conductive film (α) formed from crystalline indium oxide doped with at least one element (x) belonging to groups 4, 5, and 6 of the periodic table, the average major-axis crystal grain size of the crystalline indium oxide being at least 10 nm and less than 300 nm.

Description

光発電素子Photovoltaic element
本発明は、ヘテロ接合を有する光発電素子（太陽電池）に関する。 The present invention relates to a photovoltaic device (solar cell) having a heterojunction.
ＣＯ２等の温室効果ガスを発生しないクリーンな発電手段として、また、原子力発電に代わる操業安全性の高い発電手段として、光発電素子（太陽電池）が注目されている。光発電素子の一つとして、発電効率の高いヘテロ接合を有する光発電素子（ヘテロ接合型の光発電素子）がある。ヘテロ接合とは、例えば単結晶半導体と非晶質半導体との接合をいい、この接合により拡散電位が形成される。 Photovoltaic elements (solar cells) are attracting attention as clean power generation means that does not generate greenhouse gases such as CO 2 and as power generation means with high operational safety in place of nuclear power generation. As one of the photovoltaic elements, there is a photovoltaic element having a heterojunction with high power generation efficiency (heterojunction photovoltaic element). The heterojunction refers to, for example, a junction between a single crystal semiconductor and an amorphous semiconductor, and a diffusion potential is formed by this junction.
ヘテロ接合型の光発電素子として、ｎ型結晶半導体基板に対して光入射面側にｎ型非晶質系半導体薄膜及び第１の透明導電膜がこの順に積層され、ｎ型結晶半導体基板に対して光入射面と反対側にｐ型非晶質系半導体薄膜及び第２の透明導電膜がこの順に積層されたリアエミッター型構造を有するものが開発されている（特許文献１参照）。これらの光発電素子に備わる透明導電膜を形成する材料としては、低抵抗性（導電性）を有するインジウム錫酸化物（Ｉｎｄｉｕｍ　Ｔｉｎ　Ｏｘｉｄｅ：ＩＴＯ）が広く使用されている。このような中、光電変換効率を高めるべく、ＩＴＯ等を用い平均長軸結晶粒径（面内長軸平均結晶粒径）を３００～２０００ｎｍに制御した透明導電膜を備える結晶シリコン系太陽電池が開発されている（特許文献２参照）。ここで、ＩＴＯ等からなる膜は、結晶化させて抵抗を下げるために比較的高温（例えば２００℃超）で成膜することや、成膜後熱処理することが必要とされる。しかし、ヘテロ接合型の光発電素子においては、２００℃超といった高温で透明導電膜を積層又は処理すると、非晶質半導体の結晶化や水素の拡散が生じることなどにより性能が劣化する傾向にある。 As a heterojunction photovoltaic device, an n-type amorphous semiconductor thin film and a first transparent conductive film are laminated in this order on the light incident surface side of the n-type crystal semiconductor substrate, and the n-type crystal semiconductor substrate A rear emitter type structure in which a p-type amorphous semiconductor thin film and a second transparent conductive film are laminated in this order on the side opposite to the light incident surface has been developed (see Patent Document 1). As a material for forming the transparent conductive film provided in these photovoltaic elements, indium tin oxide (ITO) having low resistance (conductivity) is widely used. Under such circumstances, in order to increase the photoelectric conversion efficiency, a crystalline silicon solar cell including a transparent conductive film whose average major axis crystal grain size (in-plane major axis average crystal grain size) is controlled to 300 to 2000 nm using ITO or the like is disclosed. It has been developed (see Patent Document 2). Here, a film made of ITO or the like is required to be formed at a relatively high temperature (for example, higher than 200 ° C.) or to be heat-treated after the film formation in order to crystallize and lower the resistance. However, in a heterojunction photovoltaic device, when a transparent conductive film is laminated or processed at a high temperature of over 200 ° C., performance tends to deteriorate due to crystallization of an amorphous semiconductor or hydrogen diffusion. .
特許第５０３１００７号公報Japanese Patent No. 5031007 特開２０１２－９５９８号公報JP 2012-9598 A
本発明はかかる事情に鑑みてなされたもので、比較的低温でも結晶化される材料を用いて透明導電膜を形成し、高い発電効率を有するヘテロ接合型の光発電素子を提供することを目的とする。 The present invention has been made in view of such circumstances, and an object thereof is to provide a heterojunction photovoltaic device having high power generation efficiency by forming a transparent conductive film using a material that can be crystallized even at a relatively low temperature. And
発明者らは、酸化インジウムに特定のドーパントをドープさせることで、比較的低温でも結晶粒径が小さく移動度の高い透明導電膜が形成されることを利用し、この透明導電膜がリアエミッター構造のヘテロ接合型光発電素子に好適であることを見出し、本発明に至った。 The inventors have made use of the fact that a transparent conductive film having a small crystal grain size and a high mobility is formed at a relatively low temperature by doping indium oxide with a specific dopant, and this transparent conductive film has a rear emitter structure. The present invention was found to be suitable for the heterojunction photovoltaic device.
すなわち、前記目的に沿う本発明に係る光発電素子は、ｎ型結晶半導体基板と、該ｎ型結晶半導体基板の一側にこの順に積層されるｎ型非晶質系半導体薄膜及び第１の透明導電膜と、前記ｎ型結晶半導体基板の他側にこの順に積層されるｐ型非晶質系半導体薄膜及び第２の透明導電膜とを備え、一側が光入射面として用いられる光発電素子において、
前記第１及び第２の透明導電膜のいずれか一方又は双方は、周期表第４族、第５族及び第６族に属する１種以上の元素（ｘ）がドープされた結晶性の酸化インジウムから形成され、該結晶性の酸化インジウムの平均長軸結晶粒径が１０ｎｍ以上３００ｎｍ未満の透明導電膜（α）である。 That is, the photovoltaic device according to the present invention that meets the above object includes an n-type crystal semiconductor substrate, an n-type amorphous semiconductor thin film laminated in this order on one side of the n-type crystal semiconductor substrate, and the first transparent In a photovoltaic device comprising a conductive film, a p-type amorphous semiconductor thin film and a second transparent conductive film stacked in this order on the other side of the n-type crystal semiconductor substrate, and one side used as a light incident surface ,
Either one or both of the first and second transparent conductive films is crystalline indium oxide doped with one or more elements (x) belonging to Groups 4, 5, and 6 of the periodic table. A transparent conductive film (α) having an average major axis crystal grain size of 10 nm or more and less than 300 nm.
本発明に係る光発電素子においては、特定のドーパントを用いているため成膜の際に結晶核の形成が起こりやすく、そのため比較的低温でも結晶化され、結晶粒径が小さく移動度の高い透明導電膜が形成されている。従って、本発明に係る光発電素子は高い発電効率を有する。 In the photovoltaic device according to the present invention, since a specific dopant is used, crystal nuclei are likely to be formed during film formation. Therefore, the photovoltaic device is crystallized even at a relatively low temperature, and has a small crystal grain size and high mobility A conductive film is formed. Therefore, the photovoltaic device according to the present invention has high power generation efficiency.
本発明に係る光発電素子において、前記元素（ｘ）がタングステン及びタンタルからなる群より選ばれる１種以上の元素（ｘ１）を含むことが好ましい。元素（ｘ）としてタングステン又はタンタルを用いることで、低温結晶性等がより効果的に発現され、発電効率を高めることができる。 In the photovoltaic device according to the present invention, it is preferable that the element (x) includes one or more elements (x1) selected from the group consisting of tungsten and tantalum. By using tungsten or tantalum as the element (x), low-temperature crystallinity and the like can be expressed more effectively, and power generation efficiency can be increased.
本発明に係る光発電素子において、前記透明導電膜（α）における前記元素（ｘ１）の含有量が酸化物換算で０．１質量％以上１０質量％以下であることが好ましい。元素（ｘ１）の含有量を上記範囲とすることで、低温結晶性、結晶粒径の制御性等を高めることができる。 In the photovoltaic device according to the present invention, the content of the element (x1) in the transparent conductive film (α) is preferably 0.1% by mass or more and 10% by mass or less in terms of oxide. By setting the content of the element (x1) in the above range, low temperature crystallinity, crystal grain size controllability, and the like can be improved.
本発明に係る光発電素子において、前記元素（ｘ）が、チタン、バナジウム及びニオブからなる群より選ばれる１種以上の元素（ｘ２）をさらに含むことが好ましい。元素（ｘ）としてさらにこれらの元素（ｘ２）を用いることで、低温結晶性、低抵抗性等を高めることができる。 In the photovoltaic device according to the present invention, it is preferable that the element (x) further includes one or more elements (x2) selected from the group consisting of titanium, vanadium, and niobium. By further using these elements (x2) as the element (x), low-temperature crystallinity, low resistance, and the like can be improved.
本発明に係る光発電素子において、前記透明導電膜（α）における前記元素（ｘ２）の含有量が酸化物換算で０．１質量％以上５質量％以下であることが好ましい。元素（ｘ２）の含有量を上記範囲とすることで、低温結晶性、低抵抗性等をより高めることができる。 In the photovoltaic device according to the present invention, the content of the element (x2) in the transparent conductive film (α) is preferably 0.1% by mass or more and 5% by mass or less in terms of oxide. By setting the content of the element (x2) in the above range, low-temperature crystallinity, low resistance, and the like can be further increased.
本発明に係る光発電素子において、前記透明導電膜（α）における前記元素（ｘ）の含有量が酸化物換算で０．１質量％以上１０質量％以下であることが好ましい。元素（ｘ）の総含有量を上記範囲とすることで、低温結晶性、結晶粒径の制御性等を高めることができる。 In the photovoltaic device according to the present invention, the content of the element (x) in the transparent conductive film (α) is preferably 0.1% by mass or more and 10% by mass or less in terms of oxide. By setting the total content of the element (x) within the above range, low temperature crystallinity, crystal grain size controllability, and the like can be improved.
本発明に係る光発電素子において、前記第２の透明導電膜が前記透明導電膜（α）であることが好ましい。この理由は以下のとおりである。発明者らの知見によれば、リアエミッター構造を有するヘテロ接合型の光発電素子においては、裏面側、すなわちｐ型非晶質系半導体薄膜上に積層される第２の透明導電膜の横方向（平面方向）の集電性が低くなる。そこで、特に第２の透明導電膜の低抵抗性を高めることが好ましいが、例えばＩＴＯにおいて単にドーパントの量を増やしキャリア密度を高めるとＩＴＯの吸収損失が増大し、その結果として光透過性（特に波長９００～１２００ｎｍの光の透過性）が低下し、出力特性が低下する。なお、光発電素子においては、通常、光電変換されずｐｎ接合部分を通過した光を反射させて再度利用する。このため、裏面側に設けられる第２の透明導電膜も、透過率が高いことが好ましい。このようなことから、ドーパント量を増やさなくとも、低温で結晶化が達成でき低抵抗性を有する透明導電膜（α）を第２の透明導電膜に設けることにより、発電効率を高めることができる。 In the photovoltaic device according to the present invention, it is preferable that the second transparent conductive film is the transparent conductive film (α). The reason for this is as follows. According to the knowledge of the inventors, in the heterojunction photovoltaic device having a rear emitter structure, the lateral direction of the second transparent conductive film laminated on the back side, that is, on the p-type amorphous semiconductor thin film The current collecting property in the (planar direction) becomes low. Therefore, it is particularly preferable to increase the low resistance of the second transparent conductive film. However, for example, simply increasing the amount of dopant and increasing the carrier density in ITO increases the absorption loss of ITO, and as a result, the light transmittance (particularly, (Transmission of light having a wavelength of 900 to 1200 nm) is lowered, and output characteristics are lowered. In a photovoltaic device, light that has not been photoelectrically converted and has passed through a pn junction is reflected and reused. For this reason, it is preferable that the 2nd transparent conductive film provided in the back side also has a high transmittance | permeability. For this reason, the power generation efficiency can be increased by providing the second transparent conductive film with the transparent conductive film (α) that can achieve crystallization at a low temperature and has low resistance without increasing the amount of dopant. .
本発明に係る光発電素子において、前記第１の透明導電膜も前記透明導電膜（α）であることが好ましい。両面に透明導電膜（α）を用いることで、発電効率に加え、生産性等もより高めることができる。 In the photovoltaic device according to the present invention, it is preferable that the first transparent conductive film is also the transparent conductive film (α). By using the transparent conductive film (α) on both sides, productivity and the like can be further increased in addition to power generation efficiency.
本発明に係る光発電素子において、前記透明導電膜（α）が形成温度２００℃以下で成膜されていることが好ましい。このように形成温度２００℃以下で透明導電膜（α）を成膜することにより、高い発電効率を有するヘテロ接合型光発電素子とすることができる。 In the photovoltaic device according to the present invention, the transparent conductive film (α) is preferably formed at a forming temperature of 200 ° C. or less. Thus, by forming a transparent conductive film (α) at a formation temperature of 200 ° C. or less, a heterojunction photovoltaic device having high power generation efficiency can be obtained.
ここで、「非晶質系」とは、非晶質のみならず、微結晶を含む意味である。「微結晶」とは、ラマン分光法により結晶ピークが観察されるものを意味する。また、「形成温度」とは、スパッタリング法やイオンプレーティング法等を用いた際の基板温度、及び必要に応じて行われる膜積層後の熱処理温度をいう。 Here, “amorphous” means not only amorphous but also microcrystals. “Microcrystal” means a crystal peak observed by Raman spectroscopy. The “forming temperature” refers to a substrate temperature when a sputtering method, an ion plating method, or the like is used, and a heat treatment temperature after film deposition performed as necessary.
本発明に係る光発電素子は、比較的低温でも結晶化される材料を用いて透明導電膜が形成されており、高い発電効率を有する。 In the photovoltaic device according to the present invention, the transparent conductive film is formed using a material that is crystallized even at a relatively low temperature, and has high power generation efficiency.
本発明の一実施例に係る光発電素子を示す断面図である。It is sectional drawing which shows the photovoltaic device which concerns on one Example of this invention. 比較例１、２及び実験例１～４の測定結果を示すグラフである。6 is a graph showing measurement results of Comparative Examples 1 and 2 and Experimental Examples 1 to 4.
続いて、添付した図面を参照しながら本発明を具体化した実施例について説明する。
図１に示すように、本発明の一実施例に係る光発電素子１０は、板状の多層構造体である。光発電素子１０は、ｎ型結晶半導体基板１１と、ｎ型結晶半導体基板１１の一側（図１における上側）にこの順で積層される第１の真性非晶質系半導体薄膜１２、ｎ型非晶質系半導体薄膜１３及び第１の透明導電膜１４と、ｎ型結晶半導体基板１１の他側（図１における下側）にこの順で積層される第２の真性非晶質系半導体薄膜１５、ｐ型非晶質系半導体薄膜１６及び第２の透明導電膜１７とを有する。さらに、光発電素子１０は、第１の透明導電膜１４の表面（一側）に配設される集電極１８と、第２の透明導電膜１７の表面（他側）に配設される集電極１９とを有する。 Next, embodiments of the present invention will be described with reference to the accompanying drawings.
As shown in FIG. 1, the photovoltaic device 10 which concerns on one Example of this invention is a plate-shaped multilayered structure. The photovoltaic element 10 includes an n-type crystal semiconductor substrate 11, a first intrinsic amorphous semiconductor thin film 12 stacked in this order on one side (the upper side in FIG. 1) of the n-type crystal semiconductor substrate 11, an n-type A second intrinsic amorphous semiconductor thin film laminated in this order on the other side (lower side in FIG. 1) of the amorphous semiconductor thin film 13 and the first transparent conductive film 14 and the n-type crystal semiconductor substrate 11 15, a p-type amorphous semiconductor thin film 16 and a second transparent conductive film 17. Further, the photovoltaic element 10 is a collector electrode 18 disposed on the surface (one side) of the first transparent conductive film 14 and a collector electrode disposed on the surface (other side) of the second transparent conductive film 17. And an electrode 19.
ｎ型結晶半導体基板１１としては、ｎ型の半導体特性を有する結晶体の基板であれば特に限定されず公知のものを用いることができる。ｎ型結晶半導体基板１１を構成する結晶半導体としては、シリコン（Ｓｉ）の他、ＳｉＣ、ＳｉＧｅ、ＳｉＮ等を挙げることができるが、生産性等の点からシリコンが好ましい。ｎ型結晶半導体基板１１は、単結晶体であってもよいし、多結晶体であってもよい。 The n-type crystal semiconductor substrate 11 is not particularly limited as long as it is a crystalline substrate having n-type semiconductor characteristics, and a known substrate can be used. Examples of the crystal semiconductor constituting the n-type crystal semiconductor substrate 11 include SiC (SiGe), SiN, etc. in addition to silicon (Si), but silicon is preferable from the viewpoint of productivity. The n-type crystal semiconductor substrate 11 may be a single crystal or a polycrystal.
ｎ型結晶半導体基板１１の一側の面には、テクスチャー構造が形成されている。このテクスチャー構造は他側の面にも形成されていてもよい。このテクスチャー構造は、光の乱反射による光閉じ込めを有効にする。このテクスチャー構造としては、具体的にはｎ型結晶半導体基板１１の上下（一側及び他側）の面の略全面を覆うように多数のピラミッド形状を有する凹凸構造が不規則に配置されている。前記凹凸構造（テクスチャー構造）の高さ（大きさ）は不揃いであって、隣り合う凹凸の一部が重なっていてもよい。また、頂点や谷部が丸みを帯びていてもよい。この凹凸の高さとしては、数μｍ～数十μｍ程度である。このようなテクスチャー構造は、例えば、約１～５質量％の水酸化ナトリウムを含むエッチング液に基板材料を浸漬し、基板材料の（１００）面を異方性エッチングすることにより得ることが出来る。 A texture structure is formed on one surface of the n-type crystal semiconductor substrate 11. This texture structure may also be formed on the other surface. This texture structure enables light confinement due to diffuse reflection of light. Specifically, as this texture structure, a concavo-convex structure having a large number of pyramid shapes is irregularly arranged so as to cover substantially the entire upper and lower surfaces (one side and the other side) of the n-type crystal semiconductor substrate 11. . The height (size) of the concavo-convex structure (texture structure) may be uneven, and adjacent concavo-convex portions may overlap. Moreover, a vertex and a trough part may be roundish. The height of the unevenness is about several μm to several tens of μm. Such a texture structure can be obtained, for example, by immersing the substrate material in an etching solution containing about 1 to 5% by mass of sodium hydroxide and anisotropically etching the (100) plane of the substrate material.
第１の真性非晶質系半導体薄膜１２は、ｎ型結晶半導体基板１１の一側に積層されている。第１の真性非晶質系半導体薄膜１２を構成する半導体としては、シリコン（Ｓｉ）の他、ＳｉＣ、ＳｉＧｅ、ＳｉＮ等を挙げることができるが、生産性等の点からシリコンが好ましい。真性非晶質系半導体薄膜１２の膜厚としては特に限定されないが、例えば１ｎｍ以上１０ｎｍ以下とすることができ、８ｎｍ以下が好ましい。この膜厚が１ｎｍ未満の場合は、欠陥が発生しやすくなることなどにより、キャリアの再結合が生じやすくなる。また、この膜厚が１０ｎｍを超える場合は、短絡電流の低下や、光吸収量の増加が生じやすくなる。 The first intrinsic amorphous semiconductor thin film 12 is stacked on one side of the n-type crystal semiconductor substrate 11. Examples of the semiconductor constituting the first intrinsic amorphous semiconductor thin film 12 include silicon (Si), SiC, SiGe, SiN, etc., but silicon is preferable from the viewpoint of productivity. The thickness of the intrinsic amorphous semiconductor thin film 12 is not particularly limited, but can be, for example, 1 nm or more and 10 nm or less, and preferably 8 nm or less. When the film thickness is less than 1 nm, recombination of carriers is likely to occur due to defects easily occurring. Moreover, when this film thickness exceeds 10 nm, it becomes easy to produce the fall of a short circuit current and the increase in light absorption.
ｎ型非晶質系半導体薄膜１３は、第１の真性非晶質系半導体薄膜１２の一側に積層されている。ｎ型非晶質系半導体薄膜１３を構成する半導体としては、ｎ型非晶質系シリコンのほか、それぞれｎ型非晶質系のＳｉＣ、ＳｉＧｅ、ＳｉＮ等を挙げることができるが、生産性等の点からｎ型非晶質系シリコンが好ましい。ｎ型非晶質系半導体薄膜１３の膜厚としては特に限定されないが、例えば１ｎｍ以上１５ｎｍ以下が好ましく、２ｎｍ以上１０ｎｍ以下がさらに好ましい。このような範囲の膜厚とすることで、キャリアの再結合の発生と直列抵抗とをバランスよく低減することができる。 The n-type amorphous semiconductor thin film 13 is laminated on one side of the first intrinsic amorphous semiconductor thin film 12. Examples of the semiconductor constituting the n-type amorphous semiconductor thin film 13 include n-type amorphous silicon, n-type amorphous SiC, SiGe, SiN, etc. From this point, n-type amorphous silicon is preferable. The thickness of the n-type amorphous semiconductor thin film 13 is not particularly limited, but is preferably 1 nm to 15 nm, for example, and more preferably 2 nm to 10 nm. By setting the film thickness within such a range, occurrence of carrier recombination and series resistance can be reduced in a balanced manner.
第１の透明導電膜１４（透明導電膜（α））は、ｎ型非晶質系半導体薄膜１３の一側に積層されている。第１の透明導電膜１４は、周期表第４族、第５族及び第６族に属する１種以上の元素（ｘ）がドープされた結晶性の酸化インジウムから形成されている。 The first transparent conductive film 14 (transparent conductive film (α)) is stacked on one side of the n-type amorphous semiconductor thin film 13. The first transparent conductive film 14 is made of crystalline indium oxide doped with one or more elements (x) belonging to Groups 4, 5 and 6 of the periodic table.
元素（ｘ）としては、周期表第４族、第５族及び第６族に属する元素であれば特に限定されないが、第６周期の元素（ハフニウム、タングステン及びタンタル）を含むことが好ましく、タングステン及びタンタルからなる群より選ばれる１種以上の元素（ｘ１）を含むことがさらに好ましい。第１の透明導電膜１４における元素（ｘ１）の含有量としては、酸化物換算（ＷＯ３、Ｔａ２Ｏ５）で０．１質量％以上１０質量％以下が好ましく、０．３質量％以上５質量％以下がより好ましく、０．５質量％以上３質量％以下がさらに好ましい。元素（ｘ１）の含有量を上記範囲とすることで、低温結晶性、結晶粒径の制御性等を高めることができる。 The element (x) is not particularly limited as long as it is an element belonging to Group 4, Group 5, and Group 6 of the periodic table, but preferably includes elements of the sixth period (hafnium, tungsten, and tantalum). And one or more elements (x1) selected from the group consisting of tantalum and tantalum. The content of the element (x1) in the first transparent conductive film 14 is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.3% by mass or more in terms of oxide (WO 3 , Ta 2 O 5 ). 5 mass% or less is more preferable, and 0.5 mass% or more and 3 mass% or less are still more preferable. By setting the content of the element (x1) in the above range, low temperature crystallinity, crystal grain size controllability, and the like can be improved.
元素（ｘ）としては、元素（ｘ１）に加えて、チタン、バナジウム及びニオブからなる群より選ばれる少なくとも１種の元素（ｘ２）を含むことが好ましい。元素（ｘ２）の中では、チタンがより好ましい。第１の透明導電膜１４における元素（ｘ２）の含有量としては、酸化物（ＴｉＯ２、Ｖ２Ｏ５及びＮｂ２Ｏ５）換算で０．１質量％以上５質量％以下が好ましく、０．５質量％以上３質量％以下がより好ましい。 The element (x) preferably contains at least one element (x2) selected from the group consisting of titanium, vanadium and niobium in addition to the element (x1). Of the elements (x2), titanium is more preferable. The content of the element (x2) in the first transparent conductive film 14 is preferably 0.1% by mass or more and 5% by mass or less in terms of oxides (TiO 2 , V 2 O 5 and Nb 2 O 5 ), and 0 More preferably, the content is 5% by mass or more and 3% by mass or less.
第１の透明導電膜１４における元素（ｘ）の総含有量としては、酸化物換算で０．１質量％以上１０質量％以下であることが好ましく、０．５質量％以上５質量％以下がより好ましく、３質量％以下がさらに好ましい。元素（ｘ）の総含有量を上記範囲とすることで、低温結晶性、結晶粒径の制御性等を高めることができる。なお、第１の透明導電膜１４には、本発明の効果を阻害しない範囲で他の元素（例えば、錫等）がさらに含まれていてもよい。また、第１の透明導電膜１４における酸化インジウムの含有量としては、９０質量％以上が好ましく、９５質量％以上がより好ましく、９７質量％以上９９．９質量％以下がさらに好ましい。 The total content of the element (x) in the first transparent conductive film 14 is preferably 0.1% by mass or more and 10% by mass or less, and 0.5% by mass or more and 5% by mass or less in terms of oxide. More preferred is 3% by mass or less. By setting the total content of the element (x) within the above range, low temperature crystallinity, crystal grain size controllability, and the like can be improved. Note that the first transparent conductive film 14 may further contain other elements (for example, tin or the like) as long as the effects of the present invention are not impaired. Moreover, as content of indium oxide in the 1st transparent conductive film 14, 90 mass% or more is preferable, 95 mass% or more is more preferable, 97 mass% or more and 99.9 mass% or less are further more preferable.
第１の透明導電膜１４中の結晶性の酸化インジウムの平均長軸結晶粒径としては、１０ｎｍ以上３００ｎｍ未満であり、４０ｎｍ以上２５０ｎｍ以下が好ましい。平均長軸結晶粒径（面内長軸平均結晶粒径）とは、走査型電子顕微鏡（ＳＥＭ）から得られる像において、面内に存在する各結晶粒子の最も長い径を測定し、この測定値が大きい上位２０粒子の測定値を数平均したものをいう。第１の透明導電膜１４が、このように小さい粒径の結晶性酸化インジウムから主に構成されることで、形成温度が２００℃以下であっても、結晶性の高く、移動度の高い膜となる。なお、このように粒径の小さい結晶が形成されることは、ドープされる元素（ｘ）に由来すると考えられる。 The average major axis crystal grain size of crystalline indium oxide in the first transparent conductive film 14 is 10 nm or more and less than 300 nm, and preferably 40 nm or more and 250 nm or less. The average long-axis crystal grain size (in-plane long-axis average crystal grain size) is measured by measuring the longest diameter of each crystal grain existing in the plane in an image obtained from a scanning electron microscope (SEM). The average value of the measured values of the top 20 particles with the largest value. Since the first transparent conductive film 14 is mainly composed of crystalline indium oxide having such a small particle diameter, even if the formation temperature is 200 ° C. or less, the film has high crystallinity and high mobility. It becomes. In addition, it is thought that the formation of a crystal having such a small particle diameter is derived from the element (x) to be doped.
第１の透明導電膜１４の膜厚としては、特に限定されないが、透光性と集電性とを両立させることができるなどの点から４０ｎｍ以上１００ｎｍ以下が好ましい。また、第１の透明導電膜１４の比抵抗値としては、５×１０－５Ω・ｃｍ以上１×１０－３Ω・ｃｍ以下が好ましく、５×１０－４Ω・ｃｍ以下がより好ましい。さらに、透光性と集電性とを両立させるために、キャリア密度としては３×１０２０ｃｍ－３を上限とし、移動度としては４０ｃｍ２Ｖ－１ｓ－１を下限とするのが好ましい。 Although it does not specifically limit as a film thickness of the 1st transparent conductive film 14, 40 nm or more and 100 nm or less are preferable from the point of being able to make translucency and current collection compatible. Further, the specific resistance value of the first transparent conductive film 14 is preferably 5 × 10 −5 Ω · cm to 1 × 10 −3 Ω · cm, and more preferably 5 × 10 −4 Ω · cm. Further, in order to achieve both the light transmitting property and the current collecting property, it is preferable that the carrier density has an upper limit of 3 × 10 20 cm −3 and the mobility has a lower limit of 40 cm 2 V −1 s −1. .
第２の真性非晶質系半導体薄膜１５は、ｎ型結晶半導体基板１１の他側に積層されている。第２の真性非晶質系半導体薄膜１５を構成する半導体は、第１の真性非晶質系半導体薄膜１２と同様とすることができる。第２の真性非晶質系半導体薄膜１５の膜厚としては、例えば１ｎｍ以上１０ｎｍ以下とすることができる。 The second intrinsic amorphous semiconductor thin film 15 is stacked on the other side of the n-type crystal semiconductor substrate 11. The semiconductor constituting the second intrinsic amorphous semiconductor thin film 15 can be the same as the first intrinsic amorphous semiconductor thin film 12. The film thickness of the second intrinsic amorphous semiconductor thin film 15 can be, for example, 1 nm or more and 10 nm or less.
ｐ型非晶質系半導体薄膜１６は、第２の真性非晶質系半導体薄膜１５の他側に積層されている。ｐ型非晶質系半導体薄膜１６を構成する半導体としては、ｐ型非晶質系シリコンのほか、それぞれｐ型非晶質系のＳｉＣ、ＳｉＧｅ、ＳｉＮ等を挙げることができるが、生産性等の点からｐ型非晶質系シリコンが好ましい。ｐ型非晶質系半導体薄膜１６の膜厚としては特に限定されないが、例えば１ｎｍ以上６ｎｍ未満が好ましく、２ｎｍ以上５ｎｍ以下がさらに好ましい。このような範囲の膜厚とすることで、キャリアの再結合の発生と直列抵抗とをバランスよく低減することができる。 The p-type amorphous semiconductor thin film 16 is laminated on the other side of the second intrinsic amorphous semiconductor thin film 15. Examples of the semiconductor composing the p-type amorphous semiconductor thin film 16 include p-type amorphous silicon, p-type amorphous SiC, SiGe, SiN and the like. From this point, p-type amorphous silicon is preferable. The thickness of the p-type amorphous semiconductor thin film 16 is not particularly limited, but is preferably 1 nm or more and less than 6 nm, for example, and more preferably 2 nm or more and 5 nm or less. By setting the film thickness within such a range, occurrence of carrier recombination and series resistance can be reduced in a balanced manner.
第２の透明導電膜１７（透明導電膜（α））は、ｐ型非晶質系半導体薄膜１６の他側に積層されている。第２の透明導電膜１７を形成する材料（組成）、特性、結晶粒径、膜厚等は、第１の透明導電膜１４と同様である。但し、第１の透明導電膜１４と第２の透明導電膜１７とは、組成、膜厚、比抵抗等が異なっていてもよい。例えば、発明者らの知見によれば、リアエミッター構造を有するヘテロ接合型の光発電素子１０においては、裏面側、すなわちｐ型非晶質系半導体薄膜１６上に積層される第２の透明導電膜１７の横方向（平面方向）の集電性が低くなるので、第1の透明導電膜１４に比べて第２の透明導電膜１７は低抵抗とすることが好ましい。また、キャリア密度の増大に伴い、透明導電膜における９００ｎｍ以上の近赤外波長域の吸収は顕著に増大するが、ｎ型結晶半導体基板１１がシリコン（Ｓｉ）である場合、波長９００ｎｍ～１２００ｎｍの光に対する吸収率は低くなるため、波長９００ｎｍ～１２００ｎｍの光は裏面側に積層される第２の透明導電膜１７に到達しやすくなる。従って、波長９００ｎｍ～１２００ｎｍの光を有効に用いるためには、第２の透明導電膜１７のキャリア密度を低くしつつ、移動度を高めなければならない。具体的には、第２の透明導電膜１７におけるキャリア密度の上限を３×１０２０ｃｍ－３とし、移動度の下限を４０ｃｍ２Ｖ－１ｓ－１とするのが好ましい。 The second transparent conductive film 17 (transparent conductive film (α)) is laminated on the other side of the p-type amorphous semiconductor thin film 16. The material (composition), characteristics, crystal grain size, film thickness, and the like that form the second transparent conductive film 17 are the same as those of the first transparent conductive film 14. However, the first transparent conductive film 14 and the second transparent conductive film 17 may be different in composition, film thickness, specific resistance, and the like. For example, according to the knowledge of the inventors, in the heterojunction photovoltaic device 10 having a rear emitter structure, the second transparent conductive layer laminated on the back side, that is, on the p-type amorphous semiconductor thin film 16. Since the current collecting property in the lateral direction (planar direction) of the film 17 becomes low, it is preferable that the second transparent conductive film 17 has a lower resistance than the first transparent conductive film 14. As the carrier density increases, the absorption in the near-infrared wavelength region of 900 nm or more in the transparent conductive film increases remarkably. However, when the n-type crystal semiconductor substrate 11 is silicon (Si), the wavelength is 900 nm to 1200 nm. Since the light absorptance is low, light with a wavelength of 900 nm to 1200 nm tends to reach the second transparent conductive film 17 laminated on the back side. Therefore, in order to effectively use light with a wavelength of 900 nm to 1200 nm, it is necessary to increase the mobility while lowering the carrier density of the second transparent conductive film 17. Specifically, it is preferable that the upper limit of the carrier density in the second transparent conductive film 17 is 3 × 10 20 cm −3 and the lower limit of the mobility is 40 cm 2 V −1 s −1 .
集電極１８、１９は、互いに平行かつ等間隔に形成される複数のバスバー電極、及びこれらのバスバー電極に直交し、互いに平行かつ等間隔に形成される複数のフィンガー電極を有する。 The collector electrodes 18 and 19 have a plurality of bus bar electrodes formed in parallel with each other at equal intervals, and a plurality of finger electrodes orthogonal to these bus bar electrodes and formed in parallel with each other at equal intervals.
バスバー電極及びフィンガー電極は、それぞれ線状又は帯状であり、導電性材料から形成されている。この導電性材料としては、銀ペースト等の導電性接着剤や、銅線等の金属導線を用いることができる。各バスバー電極の幅としては、例えば０．５ｍｍ以上２ｍｍ以下程度であり、各フィンガー電極の幅としては、例えば１０μｍ以上３００μｍ以下程度である。また、各フィンガー電極間の間隔としては、例えば０．５ｍｍ以上４ｍｍ以下程度である。 The bus bar electrode and the finger electrode each have a linear shape or a strip shape, and are formed of a conductive material. As this conductive material, a conductive adhesive such as a silver paste or a metal conductive wire such as a copper wire can be used. The width of each bus bar electrode is, for example, about 0.5 mm to 2 mm, and the width of each finger electrode is, for example, about 10 μm to 300 μm. Moreover, as a space | interval between each finger electrode, it is about 0.5 mm or more and 4 mm or less, for example.
なお、他側（光入射面と反対側）の集電極１９は、バスバー電極とフィンガー電極とからなる構造ではなく、全面に導電性材料が積層された構造とすることもできる。このような構造の集電極はめっきや金属箔の積層等により形成することができる。他側の集電極１９をこのような構造にすることで、他側の集電効率を高めることができる。また、一側からの入射光のうち、ｐｎ接合部分を透過した入射光が、全面積層された集電極全面により反射するため発電効率を高めることができる。 In addition, the collector electrode 19 on the other side (opposite to the light incident surface) may be a structure in which a conductive material is laminated on the entire surface, instead of a structure including a bus bar electrode and a finger electrode. The collector electrode having such a structure can be formed by plating, metal foil lamination, or the like. By making the collector electrode 19 on the other side in such a structure, the current collection efficiency on the other side can be increased. In addition, among incident light from one side, incident light transmitted through the pn junction portion is reflected by the entire surface of the collector electrode laminated on the entire surface, so that power generation efficiency can be improved.
このような構造を有する光発電素子１０は、通常、複数を直列に接続して使用される。複数の光発電装置１０を直列接続して使用することで、発電電圧を高めることができる。 The photovoltaic elements 10 having such a structure are usually used by connecting a plurality of photovoltaic elements 10 in series. By using a plurality of photovoltaic power generation devices 10 connected in series, the generated voltage can be increased.
光発電素子１０における光入射面は一側（図１における上側）である。すなわち、光発電素子１０は、ｎ型結晶半導体基板１１に対して光入射面と反対側にｐ型非晶質系半導体薄膜１６を設けたリアエミッター構造である。光発電素子１０においては、特定のドーパント（元素（ｘ））をドープした酸化インジウムにより、粒径の小さい結晶からなる透明導電膜１４、１７が形成されているため、透明導電膜１４、１７が低抵抗となっており発電効率が優れる。特に、光発電素子１０においては、通常、横方向の集電性が低下しうる裏面側の第２の透明導電膜１７が上記特定のドーパント及び結晶性を有している。このため、第２の透明導電膜１７のキャリア密度を高めることなく移動度を上げることで低抵抗性を達成することができるため、透光性（特に波長９００ｎｍ～１２００ｎｍの光の透過性）の低下を抑えつつ、低抵抗性を達成できる。 The light incident surface of the photovoltaic element 10 is on one side (the upper side in FIG. 1). That is, the photovoltaic device 10 has a rear emitter structure in which a p-type amorphous semiconductor thin film 16 is provided on the side opposite to the light incident surface with respect to the n-type crystal semiconductor substrate 11. In the photovoltaic element 10, the transparent conductive films 14 and 17 made of crystals with a small particle diameter are formed of indium oxide doped with a specific dopant (element (x)). Low resistance and excellent power generation efficiency. In particular, in the photovoltaic device 10, the second transparent conductive film 17 on the back side that can reduce the lateral current collecting property usually has the specific dopant and crystallinity. For this reason, since low resistance can be achieved by increasing mobility without increasing the carrier density of the second transparent conductive film 17, it is light transmissive (especially, light transmissive with a wavelength of 900 nm to 1200 nm). Low resistance can be achieved while suppressing the decrease.
次いで、光発電素子１０の製造方法について説明する。光発電素子１０は、ｎ型結晶半導体基板１１の一側に第１の真性非晶質系半導体薄膜１２を積層する工程、さらにｎ型非晶質系半導体薄膜１３を積層する工程、さらに第１の透明導電膜１４を積層する工程、ｎ型結晶半導体基板１１の他側に第２の真性非晶質系半導体薄膜１５を積層する工程、さらにｐ型非晶質系半導体薄膜１６を積層する工程、さらに第２の透明導電膜１７を積層する工程、及び第１の透明導電膜１４の一側表面及び第２の透明導電膜１７の他側表面に集電極１８、１９を配設する工程を有する。なお、各工程の順は、光発電素子１０の層構造を得ることができる順である限り特に限定されるものではない。 Next, a method for manufacturing the photovoltaic element 10 will be described. The photovoltaic element 10 includes a step of laminating a first intrinsic amorphous semiconductor thin film 12 on one side of an n-type crystal semiconductor substrate 11, a step of laminating an n-type amorphous semiconductor thin film 13, and a first step. A step of laminating the transparent conductive film 14, a step of laminating the second intrinsic amorphous semiconductor thin film 15 on the other side of the n-type crystal semiconductor substrate 11, and a step of laminating the p-type amorphous semiconductor thin film 16. Further, a step of laminating the second transparent conductive film 17 and a step of disposing the collector electrodes 18 and 19 on the one side surface of the first transparent conductive film 14 and the other side surface of the second transparent conductive film 17. Have. In addition, the order of each process will not be specifically limited as long as it is the order which can obtain the layer structure of the photovoltaic device 10. FIG.
第１及び第２の真性非晶質系半導体薄膜１２、１５を積層する方法としては、例えば、化学気相成長法（例えばプラズマＣＶＤ法や触媒ＣＶＤ法（別名ホットワイヤＣＶＤ法）等）などの公知の方法が挙げられる。プラズマＣＶＤ法による場合、原料ガスとしては例えばＳｉＨ４とＨ２との混合ガスを用いることができる。 As a method of laminating the first and second intrinsic amorphous semiconductor thin films 12 and 15, for example, chemical vapor deposition (for example, plasma CVD method or catalytic CVD method (also called hot wire CVD method)) or the like is used. A well-known method is mentioned. In the case of the plasma CVD method, for example, a mixed gas of SiH 4 and H 2 can be used as the source gas.
ｎ型非晶質系半導体薄膜１３及びｐ型非晶質系半導体薄膜１６を積層する方法としても、例えば、化学気相成長法（例えばプラズマＣＶＤ法や触媒ＣＶＤ法（別名ホットワイヤＣＶＤ法）等）などの公知の方法により成膜することができる。プラズマＣＶＤ法による場合、原料ガスとしてはｎ型非晶質系半導体１３においては例えばＳｉＨ４とＨ２とＰＨ３との混合ガスを、ｐ型非晶質系半導体薄膜１６においては例えばＳｉＨ４とＨ２とＢ２Ｈ６との混合ガスを用いることができる。 As a method of laminating the n-type amorphous semiconductor thin film 13 and the p-type amorphous semiconductor thin film 16, for example, a chemical vapor deposition method (for example, a plasma CVD method or a catalytic CVD method (also called hot wire CVD method)) The film can be formed by a known method such as If by plasma CVD method, a mixed gas of SiH 4, H 2, and PH 3 for example in the n-type amorphous-based semiconductor 13 as a source gas, the p-type amorphous-based semiconductor thin film 16 is for example a SiH 4 A mixed gas of H 2 and B 2 H 6 can be used.
第１及び第２の透明導電膜１４、１７を積層する方法としては、例えばスパッタリング法、真空蒸着法、イオンプレーティング法（反応性プラズマ蒸着法）等を挙げることができるが、スパッタリング法又はイオンプレーティング法によることが好ましい。スパッタリング法は、膜厚制御性等に優れ、また、イオンプレーティング法等に比べて低コストで行うことができる。一方、イオンプレーティング法によれば、欠陥の発生を抑制した成膜を行うことができる。 Examples of the method of laminating the first and second transparent conductive films 14 and 17 include a sputtering method, a vacuum deposition method, and an ion plating method (reactive plasma deposition method). It is preferable to use a plating method. The sputtering method is excellent in film thickness controllability and the like, and can be performed at a lower cost than the ion plating method. On the other hand, according to the ion plating method, it is possible to perform film formation while suppressing generation of defects.
第１及び第２の透明導電膜１４、１７をスパッタリング法又はイオンプレーティング法により形成する際に用いられる蒸着材としては、主成分が酸化インジウムであり、元素（ｘ）の酸化物を含むものが用いられる。蒸着材における各成分の成分比は、所望する第１及び第２の透明導電膜１４、１７の成分比に応じて適宜調整することができる。また、蒸着材には、さらに他の成分（例えば酸化錫等）が含まれていてもよい。なお、スパッタリング法又はイオンプレーティング法により第１又は第２の透明導電膜１４、１７を形成した場合、各透明導電膜１４、１７における金属成分の含有量（含有比）は、用いた蒸着材と実質的に同一であるとみなす。 As a vapor deposition material used when the first and second transparent conductive films 14 and 17 are formed by a sputtering method or an ion plating method, a main component is indium oxide, and an oxide of the element (x) is included. Is used. The component ratio of each component in the vapor deposition material can be appropriately adjusted according to the desired component ratio of the first and second transparent conductive films 14 and 17. The vapor deposition material may further contain other components (for example, tin oxide). In addition, when the 1st or 2nd transparent conductive films 14 and 17 are formed by sputtering method or ion plating method, content (content ratio) of the metal component in each transparent conductive films 14 and 17 is the vapor deposition material used. Are considered to be substantially the same.
前記蒸着材は、元素（ｘ）がタングステン等である場合（いわゆるＩＷＯの場合）、公知の蒸着材を用いることができる。また、元素（ｘ）がタンタルである場合、前記蒸着材は、例えば、インジウム酸化物の前駆体と、タンタル酸化物の前駆体とを含む溶液を調製する工程（ａ）、前記溶液にアルカリ化合物を添加して、金属水酸化物の沈殿物を得る工程（ｂ）、得られた金属水酸化物の沈殿物を洗浄及び乾燥し、金属酸化物の粉末を得る工程（ｃ）、及び得られた金属酸化物の粉末を粉砕後焼結する工程（ｄ）を含む方法により得ることができる。前記インジウム酸化物の前駆体としては硝酸インジウム、塩化インジウム等を挙げることができ、前記タンタル酸化物の前駆体としては塩化タンタル等を挙げることができる。工程（ａ）で得られた溶液のｐＨとしては、１～４が好ましい。また、この溶液には、他の成分（例えば、元素（ｘ）以外の金属成分、ｐＨ調整剤等）を添加してもよい。工程（ｂ）においてアルカリ化合物を添加した後の溶液のｐＨとしては、７～１０が好ましい。また、工程（ｄ）における焼結温度は１２５０～１６００℃程度、焼結時間は１０～２０時間程度とすることができる。 As the vapor deposition material, when the element (x) is tungsten or the like (in the case of so-called IWO), a known vapor deposition material can be used. Further, when the element (x) is tantalum, the vapor deposition material is prepared, for example, by a step (a) of preparing a solution containing a precursor of indium oxide and a precursor of tantalum oxide, and an alkali compound in the solution. To obtain a metal hydroxide precipitate (b), washing and drying the obtained metal hydroxide precipitate to obtain a metal oxide powder (c), and The metal oxide powder can be obtained by a method including a step (d) of sintering after pulverization. Examples of the indium oxide precursor include indium nitrate and indium chloride, and examples of the tantalum oxide precursor include tantalum chloride. The pH of the solution obtained in step (a) is preferably 1 to 4. Moreover, you may add other components (For example, metal components other than element (x), a pH adjuster, etc.) to this solution. The pH of the solution after adding the alkali compound in the step (b) is preferably 7 to 10. The sintering temperature in step (d) can be about 1250 to 1600 ° C., and the sintering time can be about 10 to 20 hours.
スパッタリング法は、公知のスパッタリング装置を用いて行うことができる。スパッタリング装置のチャンバー内の初期真空度としては、１×１０－７～１×１０－５Ｔｏｒｒ程度とすることができる。イオンプレーティング法も、通常用いられる公知の装置を用いて行うことができる。スパッタリング法やイオンプレーティング法による積層（蒸着）の際の基板温度としては、特に限定されないが、２００℃以下が好ましく、０℃以上８０℃以下がより好ましく、室温でよい。形成圧力としては、７．５×１０－４～７．５×１０－３Ｔｏｒｒ程度とすることができ、２×１０－３Ｔｏｒｒ以上７×１０－３Ｔｏｒｒ以下が好ましい。 The sputtering method can be performed using a known sputtering apparatus. The initial degree of vacuum in the chamber of the sputtering apparatus can be about 1 × 10 −7 to 1 × 10 −5 Torr. The ion plating method can also be performed using a commonly used known apparatus. The substrate temperature during lamination (vapor deposition) by sputtering or ion plating is not particularly limited, but is preferably 200 ° C. or lower, more preferably 0 ° C. or higher and 80 ° C. or lower, and may be room temperature. The formation pressure can be about 7.5 × 10 −4 to 7.5 × 10 −3 Torr, and preferably 2 × 10 −3 Torr to 7 × 10 −3 Torr.
スパッタリング法やイオンプレーティング法等により膜を積層後、必要に応じて、熱処理を行うことができる。この熱処理温度としては、５０℃以上２００℃以下が好ましく、１８０℃以下がより好ましい。ここで、透明導電膜１４、１７の形成においては、形成温度（スパッタリングやイオンプレーティングの際の基板温度、及びその後必要に応じて行われる熱処理温度）２００℃以下（より好ましくは、１５０℃以下。下限としては、例えば２０℃）で行うことができ、透明導電膜１４、１７は前記組成からなるため、このような比較的低温での形成においても、微細な結晶粒子の形成が進行し、低抵抗の膜を得ることができる。また、形成温度が２００℃以下であるため、他の非晶質系半導体薄膜等に与える影響が抑えられ、高い発電効率を有するヘテロ接合型光発電素子を得ることができる。 After the films are stacked by a sputtering method, an ion plating method, or the like, heat treatment can be performed as necessary. As this heat processing temperature, 50 to 200 degreeC is preferable and 180 degreeC or less is more preferable. Here, in the formation of the transparent conductive films 14 and 17, the formation temperature (the substrate temperature during sputtering and ion plating, and the heat treatment temperature performed thereafter if necessary) is 200 ° C. or less (more preferably 150 ° C. or less). As the lower limit, for example, 20 ° C.), the transparent conductive films 14 and 17 have the above-described composition, so that the formation of fine crystal grains proceeds even in the formation at such a relatively low temperature, A low resistance film can be obtained. In addition, since the formation temperature is 200 ° C. or lower, the influence on other amorphous semiconductor thin films and the like can be suppressed, and a heterojunction photovoltaic device having high power generation efficiency can be obtained.
集電極１８、１９の配設は公知の方法で行うことができる。集電極１８、１９の材料として導電性接着剤が用いられている場合、スクリーン印刷やグラビアオフセット印刷等の印刷法により形成することができる。また、集電極１８、１９に金属導線を用いる場合、導電性接着剤や低融点金属（半田等）によりの透明導電膜１４、１７上に固定することができる。 The collector electrodes 18 and 19 can be disposed by a known method. When a conductive adhesive is used as a material for the collector electrodes 18 and 19, it can be formed by a printing method such as screen printing or gravure offset printing. Moreover, when using a metal conducting wire for the collector electrodes 18 and 19, it can fix on the transparent conductive films 14 and 17 with a conductive adhesive or a low melting point metal (solder etc.).
本発明は前記した実施例に限定されるものではなく、本発明の要旨を変更しない範囲でその構成を変更することもできる。例えば、光発電素子１０が有する第１の真性非晶質系半導体薄膜１２及び第２の真性非晶質系半導体薄膜１５は必須の構成要件ではない。特に、光入射側の第１の真性非晶質系半導体薄膜１２を積層しない構成とすることにより、透光性の向上等のため最大出力をさらに高めることもできる。また、第１の透明導電膜１４又は第２の透明導電膜１７は、他の透明導電材料又は異なる成膜法により形成されていてもよく、結晶性も特に限定されない。他の透明導電材料としては、ＩＴＯ等を挙げることができる。 The present invention is not limited to the above-described embodiments, and the configuration thereof can be changed without changing the gist of the present invention. For example, the first intrinsic amorphous semiconductor thin film 12 and the second intrinsic amorphous semiconductor thin film 15 included in the photovoltaic device 10 are not essential components. In particular, the maximum output can be further increased in order to improve translucency by adopting a configuration in which the first intrinsic amorphous semiconductor thin film 12 on the light incident side is not laminated. The first transparent conductive film 14 or the second transparent conductive film 17 may be formed by another transparent conductive material or a different film formation method, and the crystallinity is not particularly limited. Examples of other transparent conductive materials include ITO.
具体的には、第１の透明導電膜１４を例えばＩＷＯを用いてイオンプレーティング法により形成した膜とし、第２の透明導電膜１７を少なくともタンタルがドープされた酸化インジウムによりスパッタリング法にて形成した膜とすることができる。光入射面側に位置する第１の透明導電膜１４をイオンプレーティング法により形成することで、ｎ型非晶質系半導体薄膜１３の劣化が抑制され、発電効率を高めることができる。 Specifically, the first transparent conductive film 14 is a film formed by ion plating using, for example, IWO, and the second transparent conductive film 17 is formed by sputtering using indium oxide doped with at least tantalum. Film. By forming the first transparent conductive film 14 positioned on the light incident surface side by an ion plating method, deterioration of the n-type amorphous semiconductor thin film 13 is suppressed, and power generation efficiency can be increased.
実験例Experimental example
以下、実験例及び比較例を挙げて、本発明の内容をより具体的に説明する。なお、本発明は以下の実験例に限定されるものではない。 Hereinafter, the contents of the present invention will be described more specifically with reference to experimental examples and comparative examples. Note that the present invention is not limited to the following experimental examples.
＜製造例１＞
硝酸インジウム（Ｉｎ（ＮＯ３）３）、塩化タンタル及びオルトチタン酸テトライソプロピルが溶解された水溶液に対し、アルカリ添加して水酸化物沈殿物を得た。この水酸化物沈殿物を乾燥及び粉砕後、焼結させて焼結体（スパッタリングターゲット）を得た。なお、このスパッタリングターゲットの酸化タンタル及び酸化チタンの含有量がそれぞれ０．５質量％となるように塩化タンタル及びオルトチタン酸テトライソプロピルの量を調製した。得られたスパッタリングターゲットをＤＣマグネトロンスパッタに装着させ、チャンバー内の初期真空度を１×１０－６Ｔｏｒｒ以下とし室温で１００ｎｍの厚みでガラス基板上にＩｎ－Ｔａ－Ｔｉ－Ｏ系薄膜を蒸着させた。その後、Ｉｎ－Ｔａ－Ｔｉ－Ｏ系薄膜を大気雰囲気下で１５０℃、２時間熱処理し、透明導電膜を得た。得られた透明導電膜の表面はＳＥＭ観察により結晶性が確認でき、比抵抗は３．７８×１０－４Ω・ｃｍであった。ＳＥＭ画像を元にした平均長軸結晶粒径は１００ｎｍであった。また、得られた透明導電膜を８０℃、８５％の室度下で５日間保管した後の抵抗変化を測定した結果、３．２％以内の抵抗変化であった。 <Production Example 1>
A hydroxide precipitate was obtained by adding an alkali to an aqueous solution in which indium nitrate (In (NO 3 ) 3 ), tantalum chloride and tetraisopropyl orthotitanate were dissolved. The hydroxide precipitate was dried and pulverized and then sintered to obtain a sintered body (sputtering target). The amounts of tantalum chloride and tetraisopropyl orthotitanate were adjusted so that the contents of tantalum oxide and titanium oxide in the sputtering target were 0.5% by mass, respectively. The obtained sputtering target was attached to a DC magnetron sputter, an initial vacuum degree in the chamber was set to 1 × 10 −6 Torr or less, and an In—Ta—Ti—O-based thin film was deposited on a glass substrate with a thickness of 100 nm at room temperature. It was. Thereafter, the In—Ta—Ti—O-based thin film was heat-treated at 150 ° C. for 2 hours in an air atmosphere to obtain a transparent conductive film. The surface of the obtained transparent conductive film was confirmed to have crystallinity by SEM observation, and the specific resistance was 3.78 × 10 −4 Ω · cm. The average major axis crystal grain size based on the SEM image was 100 nm. Moreover, as a result of measuring the resistance change after storing the obtained transparent conductive film at 80 ° C. under a room temperature of 85% for 5 days, the resistance change was within 3.2%.
＜製造例２＞
ＩＷＯ蒸着材（Ｗ＝１質量％）を用いイオンプレーティング法により成膜した。具体的には、室温で１００ｎｍの厚みでガラス基板上にＩｎ－Ｗ－Ｏ系薄膜を蒸着させた。その後、Ｉｎ－Ｗ－Ｏ系薄膜を大気雰囲気下で２００℃、３０分熱処理し、透明導電膜を得た。得られた透明導電膜の表面はＳＥＭ観察により結晶性が確認できた。ＳＥＭ画像を元にした平均長軸結晶粒径は２００ｎｍであった。 <Production Example 2>
A film was formed by an ion plating method using an IWO vapor deposition material (W = 1 mass%). Specifically, an In—W—O-based thin film was deposited on a glass substrate with a thickness of 100 nm at room temperature. Thereafter, the In—W—O-based thin film was heat-treated at 200 ° C. for 30 minutes in an air atmosphere to obtain a transparent conductive film. The crystallinity of the surface of the obtained transparent conductive film could be confirmed by SEM observation. The average major axis crystal grain size based on the SEM image was 200 nm.
＜比較製造例１＞
酸化インジウムの含有量が９０質量％、酸化錫の含有量が１０質量％のインジウム錫酸化物スパッタリングターゲットを用い、製造例１と同様の方法により透明導電膜を得た。得られた透明導電膜の表面はＳＥＭ観察により結晶性が確認できず、比抵抗は７．１９×１０－４Ω・ｃｍであった。また、得られた透明導電膜を８０℃、８５％の室度下で５日間保管した後の抵抗変化を測定した結果、１２．９％以内の抵抗変化であった。 <Comparative Production Example 1>
A transparent conductive film was obtained in the same manner as in Production Example 1 using an indium tin oxide sputtering target having an indium oxide content of 90% by mass and a tin oxide content of 10% by mass. The surface of the obtained transparent conductive film could not be confirmed by SEM observation, and the specific resistance was 7.19 × 10 −4 Ω · cm. Moreover, as a result of measuring the resistance change after storing the obtained transparent conductive film at 80 ° C. under a room temperature of 85% for 5 days, the resistance change was within 12.9%.
＜比較例１、２、実験例１、２＞
ｎ型単結晶シリコン基板の一側に、第１の真性非晶質系シリコン薄膜（膜厚６ｎｍ）、ｎ型非晶質系シリコン薄膜（膜厚８ｎｍ）及び第１の透明導電膜（膜厚６５ｎｍ）をこの順に積層した。なお、ｎ型単結晶シリコン基板は、両面に無数のピラミッド形状を有する微細な凹凸構造（テクスチャー構造）が形成されたものを用いた。この凹凸構造は、約３質量％の水酸化ナトリウムを含むエッチング液に基板材料を浸漬し、基板材料の（１００）面を異方性エッチングすることにより形成した。
ついで、ｎ型単結晶シリコン基板の他側に、第２の真性非晶質系シリコン薄膜（膜厚６ｎｍ）、ｐ型非晶質系シリコン薄膜（膜厚４ｎｍ）及び第２の透明導電膜（膜厚６５ｎｍ）をこの順に積層した。各シリコン薄膜は、プラズマＣＶＤ法により積層した。 <Comparative Examples 1 and 2, Experimental Examples 1 and 2>
On one side of the n-type single crystal silicon substrate, a first intrinsic amorphous silicon thin film (film thickness 6 nm), an n-type amorphous silicon thin film (film thickness 8 nm), and a first transparent conductive film (film thickness) 65 nm) was laminated in this order. In addition, the n-type single crystal silicon substrate used what formed the fine uneven structure (texture structure) which has innumerable pyramid shape on both surfaces. This concavo-convex structure was formed by immersing the substrate material in an etching solution containing about 3% by mass of sodium hydroxide and anisotropically etching the (100) plane of the substrate material.
Next, on the other side of the n-type single crystal silicon substrate, a second intrinsic amorphous silicon thin film (film thickness 6 nm), a p-type amorphous silicon thin film (film thickness 4 nm), and a second transparent conductive film ( A film thickness of 65 nm) was laminated in this order. Each silicon thin film was laminated by a plasma CVD method.
＜実験例３、４＞
ｎ型単結晶シリコン基板の一側に、ｎ型非晶質系シリコン薄膜（膜厚８ｎｍ）及び第１の透明導電膜（膜厚６５ｎｍ）をこの順に積層した（第１の真性非晶質系シリコン薄膜を積層しなかった）こと以外は実験例１等と同様に行った。 <Experimental Examples 3 and 4>
An n-type amorphous silicon thin film (film thickness: 8 nm) and a first transparent conductive film (film thickness: 65 nm) were laminated in this order on one side of an n-type single crystal silicon substrate (first intrinsic amorphous system) Except that the silicon thin film was not laminated), it was performed in the same manner as in Experimental Example 1 and the like.
各実験例及び比較例における第１及び第２の透明導電膜は、以下の材料及び方法により積層した。
比較例１：ＩＴＯ（Ｓｎ＝１０質量％）、スパッタリング法
比較例２：ＩＴＯ（Ｓｎ＝５質量％）、イオンプレーティング法
実験例１、実験例３：ＩＷＯ（Ｗ＝１質量％）、イオンプレーティング法（製造例２の条件）
実験例２、実験例４：Ｉｎ－Ｔａ－Ｔｉ－Ｏ材料（製造例１のスパッタリングターゲット）、スパッタリング法（製造例１の成膜条件） The first and second transparent conductive films in each experimental example and comparative example were laminated by the following materials and methods.
Comparative example 1: ITO (Sn = 10 mass%), sputtering method comparative example 2: ITO (Sn = 5 mass%), ion plating method experimental example 1, experimental example 3: IWO (W = 1 mass%), ion Plating method (conditions of production example 2)
Experimental Example 2 and Experimental Example 4: In—Ta—Ti—O material (sputtering target of Production Example 1), sputtering method (deposition conditions of Production Example 1)
次いで、第１及び第２の透明導電膜の表面（外側の面）にそれぞれ、集電極として、平行な複数のバスバー電極と、このバスバー電極にそれぞれ直交する複数のフィンガー電極を形成した。この集電極は、銀ペーストを用いてスクリーン印刷により形成した。このようにして、比較例１、２、及び実験例１～４の光発電素子を得た。 Next, a plurality of parallel bus bar electrodes and a plurality of finger electrodes respectively orthogonal to the bus bar electrodes were formed as collector electrodes on the surfaces (outer surfaces) of the first and second transparent conductive films. This collector electrode was formed by screen printing using a silver paste. Thus, the photovoltaic elements of Comparative Examples 1 and 2 and Experimental Examples 1 to 4 were obtained.
得られた各光発電素子の最大出力（Ｐｍａｘ）を測定した。測定結果として、比較例１を基準とした値を図２に示す。なお、一側を光入射面として、すなわちｐ層が光入射側とは反対側に積層されているヘテロ接合構造（Ｒｅａｒ　ｅｍｉｔｔｅｒ）となるようにして、それぞれを測定した。 The maximum output (Pmax) of each obtained photovoltaic device was measured. As measurement results, values based on Comparative Example 1 are shown in FIG. In addition, each was measured by using one side as a light incident surface, that is, a heterojunction structure (Rear emitter) in which the p layer was laminated on the opposite side to the light incident side.
図２に示されるように、実験例１～４の光発電素子は、ＩＴＯで透明導電膜を形成し、結晶化が十分に進行していない比較例１、２と比べて高い最大出力を有する。 As shown in FIG. 2, the photovoltaic elements of Experimental Examples 1 to 4 have a maximum output that is higher than those of Comparative Examples 1 and 2 in which a transparent conductive film is formed of ITO and crystallization is not sufficiently advanced. .
比較的低温でも結晶化される材料を用いて透明導電膜が形成されており、高い発電効率得ることができ、近年注目されている光発電素子を提供できる。 A transparent conductive film is formed using a material that can be crystallized even at a relatively low temperature, so that high power generation efficiency can be obtained, and a photovoltaic device that has attracted attention in recent years can be provided.
１０：光発電素子、１１：ｎ型結晶半導体基板、１２：第１の真性非晶質系半導体薄膜、１３：ｎ型非晶質系半導体薄膜、１４：第１の透明導電膜、１５：第２の真性非晶質系半導体薄膜、１６：ｐ型非晶質系半導体薄膜、１７：第２の透明導電膜、１８、１９：集電極 10: photovoltaic device, 11: n-type crystal semiconductor substrate, 12: first intrinsic amorphous semiconductor thin film, 13: n-type amorphous semiconductor thin film, 14: first transparent conductive film, 15: first 2 intrinsic amorphous semiconductor thin film, 16: p-type amorphous semiconductor thin film, 17: second transparent conductive film, 18, 19: collector electrode

Claims (9)

  1. ｎ型結晶半導体基板と、該ｎ型結晶半導体基板の一側にこの順に積層されるｎ型非晶質系半導体薄膜及び第１の透明導電膜と、前記ｎ型結晶半導体基板の他側にこの順に積層されるｐ型非晶質系半導体薄膜及び第２の透明導電膜とを備え、一側が光入射面として用いられる光発電素子において、
    前記第１及び第２の透明導電膜のいずれか一方又は双方は、周期表第４族、第５族及び第６族に属する１種以上の元素（ｘ）がドープされた結晶性の酸化インジウムから形成され、該結晶性の酸化インジウムの平均長軸結晶粒径が１０ｎｍ以上３００ｎｍ未満の透明導電膜（α）であることを特徴とする光発電素子。     An n-type crystal semiconductor substrate, an n-type amorphous semiconductor thin film and a first transparent conductive film stacked in this order on one side of the n-type crystal semiconductor substrate, and this on the other side of the n-type crystal semiconductor substrate In a photovoltaic device comprising a p-type amorphous semiconductor thin film and a second transparent conductive film, which are sequentially stacked, and one side used as a light incident surface,
    Either one or both of the first and second transparent conductive films is crystalline indium oxide doped with one or more elements (x) belonging to Groups 4, 5, and 6 of the periodic table. A photovoltaic device, wherein the crystalline indium oxide is a transparent conductive film (α) having an average major axis crystal grain size of 10 nm or more and less than 300 nm.
  2. 請求項１記載の光発電素子において、前記元素（ｘ）がタングステン及びタンタルからなる群より選ばれる１種以上の元素（ｘ１）を含むことを特徴とする光発電素子。 2. The photovoltaic device according to claim 1, wherein the element (x) includes one or more elements (x1) selected from the group consisting of tungsten and tantalum.
  3. 請求項２記載の光発電素子において、前記透明導電膜（α）における前記元素（ｘ１）の含有量が酸化物換算で０．１質量％以上１０質量％以下であることを特徴とする光発電素子。 The photovoltaic device according to claim 2, wherein the content of the element (x1) in the transparent conductive film (α) is 0.1% by mass or more and 10% by mass or less in terms of oxide. element.
  4. 請求項２又は３記載の光発電素子において、前記元素（ｘ）が、チタン、バナジウム及びニオブからなる群より選ばれる１種以上の元素（ｘ２）をさらに含むことを特徴とする光発電素子。 4. The photovoltaic element according to claim 2, wherein the element (x) further includes one or more elements (x2) selected from the group consisting of titanium, vanadium and niobium.
  5. 請求項４記載の光発電素子において、前記透明導電膜（α）における前記元素（ｘ２）の含有量が酸化物換算で０．１質量％以上５質量％以下であることを特徴とする光発電素子。 5. The photovoltaic device according to claim 4, wherein the content of the element (x2) in the transparent conductive film (α) is 0.1% by mass or more and 5% by mass or less in terms of oxide. element.
  6. 請求項１～５のいずれか１項に記載の光発電素子において、前記透明導電膜（α）における前記元素（ｘ）の含有量が酸化物換算で０．１質量％以上１０質量％以下であることを特徴とする光発電素子。 6. The photovoltaic device according to claim 1, wherein the content of the element (x) in the transparent conductive film (α) is 0.1% by mass or more and 10% by mass or less in terms of oxide. A photovoltaic device characterized by being.
  7. 請求項１～６のいずれか１項に記載の光発電素子において、前記第２の透明導電膜が前記透明導電膜（α）であることを特徴とする光発電素子。 The photovoltaic element according to any one of claims 1 to 6, wherein the second transparent conductive film is the transparent conductive film (α).
  8. 請求項７記載の光発電素子において、前記第１の透明導電膜も前記透明導電膜（α）であることを特徴とする光発電素子。 The photovoltaic device according to claim 7, wherein the first transparent conductive film is also the transparent conductive film (α).
  9. 請求項１～８のいずれか1項に記載の光発電素子において、前記透明導電膜（α）が形成温度２００℃以下で成膜されていることを特徴とする光発電素子。 The photovoltaic element according to any one of claims 1 to 8, wherein the transparent conductive film (α) is formed at a formation temperature of 200 ° C or lower.
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