WO2018155349A1 - Solar cell and method for producing same - Google Patents

Solar cell and method for producing same Download PDF

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Publication number
WO2018155349A1
WO2018155349A1 PCT/JP2018/005581 JP2018005581W WO2018155349A1 WO 2018155349 A1 WO2018155349 A1 WO 2018155349A1 JP 2018005581 W JP2018005581 W JP 2018005581W WO 2018155349 A1 WO2018155349 A1 WO 2018155349A1
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layer
solar cell
light absorption
group
absorption layer
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PCT/JP2018/005581
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French (fr)
Japanese (ja)
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尚吾 石塚
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国立研究開発法人産業技術総合研究所
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Priority to JP2019501293A priority Critical patent/JP6738078B2/en
Publication of WO2018155349A1 publication Critical patent/WO2018155349A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
    • H01L31/068—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/541—CuInSe2 material PV cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/547—Monocrystalline silicon PV cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to a solar cell and a method for manufacturing the solar cell, and more particularly to a solar cell using an I-III-VI 2 chalcopyrite material as a light absorption layer and a method for manufacturing the solar cell.
  • a solar cell using an I-III-VI 2 polycrystal chalcopyrite material composed of an element as a light absorption layer has a negative electrode transparent electrode layer such as conductive zinc oxide, an n-type buffer layer, a p-type The light absorption layer, the positive electrode back electrode layer, and the substrate are stacked in this order (for example, see Non-Patent Document 1).
  • the n-type buffer layer is made of CdS, ZnS (O, OH), In 2 S 3 or the like
  • the positive electrode back electrode layer is generally made of molybdenum (Mo)
  • the substrate is made of glass, metal foil, It is made of resin material such as polyimide, plastic, or ceramic.
  • the light absorbing layer is polycrystalline chalcopyrite materials as for example Cu (In, Ga) constructed using Se 2 (so-called CIGS).
  • the buffer layer is mainly formed by solution growth (wet process), and includes heavy metals as compared with the manufacturing process of other constituent layers such as an electrode layer and a light absorption layer formed by a dry process.
  • the problem was the generation of waste liquid. For this reason, proposals have been made to form the buffer layer by a dry process, but if a solar cell structure that does not use the buffer layer itself can be established, drastic time reduction and cost reduction in the solar cell manufacturing process can be expected.
  • Non-Patent Documents 2 to 5 After forming a Cu (In, Ga) Se 2 light absorption layer, a group II element (such as cadmium (Cd) or zinc (Zn)) is ion-implanted into the thin film surface, or a solution Methods such as water immersion are disclosed.
  • Non-Patent Documents 4 and 5 disclose configurations in which the buffer layer is not used by optimally coupling the energy band offset of the negative electrode transparent electrode layer with that of the light absorption layer.
  • Non-Patent Documents 2 and 3 cannot reduce the number of solar cell device manufacturing steps, and cannot solve the generation of heavy metal waste. Moreover, the method of a nonpatent literature 4 and 5 has the subject that the photoelectric conversion efficiency of the produced solar cell has remained as low as about 10%.
  • the present invention has been made in view of the above points, and an object of the present invention is to provide a highly efficient solar cell having a thin buffer layer or completely eliminating the buffer layer and a method for manufacturing the solar cell.
  • a solar cell of the present invention includes a first electrode layer, a second electrode layer having optical transparency, and light provided between the first and second electrode layers.
  • An absorption layer, wherein the light absorption layer is an I-III-VI 2 based polycrystalline chalcopyrite material to which Si or Ge is added.
  • the method for manufacturing a solar cell of the present invention includes a step of forming a first electrode layer on a substrate, and Si or Ge is added to the first electrode layer. Forming a light absorption layer using the I-III-VI 2- based polycrystalline chalcopyrite material, and forming a light-transmitting second electrode layer above the light absorption layer.
  • the step of forming the light absorption layer includes a step of adding Si or Ge during a period in which an excess region of the group I element is formed with respect to the group III element.
  • a highly efficient solar cell can be realized without having a thin buffer layer or completely eliminating the buffer layer.
  • FIG. 1 It is a schematic structure sectional view of one embodiment of a solar cell concerning the present invention. It is a flowchart for outline explanation of one embodiment of a manufacturing method of a solar cell concerning the present invention. It is a structure ratio vs. time characteristic figure of the light absorption layer of the principal part of one Embodiment of the manufacturing method of the solar cell which concerns on this invention. It is a film growth model figure of an element section in each step of the three-step vapor deposition method of FIG. Si is added Cu (In, Ga) Se 2 film cross-section SEM image, Cu (In, Ga) to and Si were not added is a view showing a sectional SEM image of the Se 2 film.
  • FIG. 3 is a diagram showing an example of current-voltage characteristics of a solar cell of one embodiment of the present invention and current-voltage characteristics of a solar cell of Comparative Example 1.
  • EBIC measurement image of solar absorption layer and cross section of solar cell of one embodiment of the present invention, solar cell of comparative example 2 having no buffer layer, and solar cell of comparative example 1 having a buffer layer and a high resistance layer It is a figure which shows a SEM image.
  • FIG. 1 shows a schematic cross-sectional view of one embodiment of a solar cell according to the present invention.
  • the solar cell 10 of the present embodiment includes a back electrode layer 12, which is a first electrode layer made of Mo, and the like, a light absorption layer 13, and a second electrode layer having light transmittance on a glass substrate 11.
  • the light absorption layer 13 is an I-III-VI 2 compound light absorption layer to which a group IV element such as silicon (Si) or germanium (Ge) is added, and a buffer layer.
  • a group IV element such as silicon (Si) or germanium (Ge) is added
  • the negative transparent electrode layer 14 formed immediately above the light absorption layer 13 is made of conductive zinc oxide or the like.
  • FIG. 2 is a flowchart for explaining the outline of one embodiment of the method for manufacturing a solar cell according to the present invention.
  • a back electrode layer (12 in FIG. 1) is formed on a blue glass substrate (11 in FIG. 1) by a known method by sputtering (step S1 in FIG. 2).
  • Stainless steel or metal plate can be used for the substrate.
  • the back electrode layer for example, a metal film made of Mo is used.
  • a light absorption layer (13 in FIG. 1) is formed on the back electrode layer by a three-stage vapor deposition method (step S2 in FIG. 2).
  • the present embodiment is characterized in that an I-III-VI 2- based polycrystalline chalcopyrite material is used as the light absorption layer, and the light absorption layer is formed by a three-stage vapor deposition method described in detail later.
  • a transparent electrode film (14 in FIG. 1) having a thickness of 2 to 3 ⁇ m is directly formed by sputtering, vacuum evaporation, metal organic chemical vapor deposition or the like. It forms by a well-known method (step S3 of FIG. 2).
  • ZnO: Al containing ZnO: B or alumina (Al 2 O 3 ) doped with boron (B) from diborane is necessary because it has translucency and conductivity. Is used.
  • the solar cell of this embodiment is manufactured.
  • FIG. 3 is a diagram showing the composition ratio versus time characteristic of the light absorption layer of the main part of one embodiment of the method for manufacturing a solar cell according to the present invention, and FIG. Indicates.
  • the vertical axis represents the [Cu] / ([In] + [Ga]) ratio of the Cu (In, Ga) Se 2 film constituting the light absorption layer 13, and the horizontal axis represents time.
  • group III elements In and Ga and group VI element Se are simultaneously deposited on the back electrode. Since Cu is not deposited in this first stage, the [Cu] / ([In] + [Ga]) ratio is “0” as shown in FIG. Further, the film growth model on the back electrode is as shown in FIG.
  • a Cu—Se liquid phase is formed on the surface of the deposited film due to excessive deposition of Cu.
  • Si group IV elements are simultaneously deposited.
  • the film growth model at the start of the third stage is as shown in FIG.
  • the deposition time elapses the deposition amounts of In and Ga are relatively increased as compared with the deposition amount of Cu, so that the [Cu] / ([In] + [Ga]) ratio is as shown in FIG.
  • the third stage deposition is completed.
  • the film growth model at the end of the third stage of deposition is such that Si dissolves in the CIGS film and becomes Cu (In, Ga) Se 2 : Si.
  • the formation of the Cu (In, Ga) Se 2 film to which Si is added as the light absorption layer 13 of the present embodiment is completed.
  • Si may be deposited from the point in time when the [Cu] / ([In] + [Ga]) ratio exceeds “1” in the second stage of the process.
  • FIG. 5A shows a cross-sectional SEM image of a Cu (In, Ga) Se 2 film to which Si, which is the light absorption layer 13 of this embodiment, is added.
  • FIG. 5B shows a cross-sectional SEM image of a Cu (In, Ga) Se 2 film to which Si is not added.
  • a cross-sectional SEM image of a Cu (In, Ga) Se 2 film added with Si, which is the light absorption layer 13 of this embodiment, obtained by a scanning electron microscope (SEM) is shown in FIG. ), A layer formed between CIGS polycrystalline grains (hereinafter referred to as “coating layer” in this specification) exists.
  • This coating layer is presumed to be a layer having a slightly different composition from the crystal grains, or a layer having the same composition but a different crystal orientation. It was confirmed by an experiment described later that this coating layer performs a function similar to the buffer layer of Comparative Example 1 described later. On the other hand, the cross-sectional SEM image of the Cu (In, Ga) Se 2 film to which Si is not added has no coating film as shown in FIG. 5B.
  • FIG. 6A shows an example of current-voltage characteristics of the solar cell of this embodiment
  • FIG. 6B shows an example of current-voltage characteristics of the solar cell of Comparative Example 1.
  • the current-voltage characteristics at the time of light incidence of the solar cell of the present embodiment having the light absorption layer 13 which is the Cu (In, Ga) Se 2 film added with Si and having the cross-sectional structure shown in FIG. 6 (a) is indicated by A1, and the dark current-voltage characteristic is indicated by A2 in FIG.
  • a Cu (In, Ga) Se 2 film to which Si is not added is provided as a light absorption layer, and a buffer layer, a high resistance layer, and a transparent electrode layer are stacked in this order on the light absorption layer.
  • the current-voltage characteristic at the time of light incidence of the solar cell of Comparative Example 1 having the structure is indicated by B1 in FIG. 6B
  • the current-voltage characteristic at the dark time is indicated by B2 in FIG. 6B.
  • EBIC Electron Beam Induced Current
  • an electron-hole pair excited by irradiating an electron beam to a cross section of a measurement sample is detected as an EBIC signal (current), but there is no pn junction in the measurement sample (depletion)
  • the electron-hole pair is recombined in the part where the layer is not formed) and carrier loss occurs and disappears, whereas the pn junction part (the part where the depletion layer is formed) does not recombine.
  • the magnitude of the measurement sample in which the depletion layer is not formed is relatively smaller than that of the EBIC signal in which the depletion layer is formed. Therefore, the presence or absence of a depletion layer in the measurement sample can be observed from an image in which the luminance is changed according to the magnitude of the EBIC signal.
  • a monochrome image indicated by 31 in FIG. 7A shows an EBIC measurement image of the light absorption layer of the solar cell of the present embodiment.
  • a coating layer is formed in the Cu (In, Ga) Se 2 film to which Si is added.
  • Ga) Se 2 film and the covering layer form a charge separation interface, and a depletion layer is formed. Therefore, the bright monochrome image 31 shows that the depletion layer exists uniformly in the entire light absorption layer.
  • the monochrome image 30 is an SEM image of the back electrode layer of the solar cell of this embodiment.
  • Monochrome image 32 shows an SEM image of the transparent (surface) electrode layer.
  • a monochrome image indicated by 41 in FIG. 7B shows an EBIC measurement image of the light absorption layer made of a Cu (In, Ga) Se 2 film to which Si is not added.
  • the solar cell of Comparative Example 2 having this light absorption layer is the same as the present embodiment in that the transparent electrode layer is directly laminated on the upper surface of the light absorption layer without a buffer layer. Since the layer is a Cu (In, Ga) Se 2 film to which Si is not added, the above-described coating layer is not formed as shown in FIG. For this reason, as can be seen from the monochrome image 41 in FIG.
  • 7B in the solar cell of Comparative Example 2, there are many dark portions indicating portions where there is no coating layer in the light absorption layer, and almost no depletion layer. Indicates that it does not exist.
  • 7B shows the intensity distribution of the EBIC signal image 41 of the light absorption layer
  • the monochrome image 30 is an SEM image of the back electrode layer of the solar cell
  • the monochrome image 32 is transparent ( The SEM image of the (surface) electrode layer is shown.
  • the transparent (surface) electrode layer is 2 ⁇ m thick ZnO: B.
  • FIG. 7C shows a Cu (In, Ga) Se 2 film to which Si is not added as a light absorption layer, and a buffer layer, a high resistance layer, and a transparent electrode on the light absorption layer.
  • stacked in this order are shown. That is, a monochrome image 51 shown in FIG. 7C shows an EBIC measurement image of a light absorption layer made of a Cu (In, Ga) Se 2 film to which Si is not added, and 51 ′ in FIG.
  • the image indicated by is an image showing the intensity distribution of the EBIC measurement signal of the light absorption layer.
  • an image 30 shows an SEM image of the back electrode layer
  • an image 52 shows an SEM image of the buffer layer and the high resistance layer
  • an image 53 shows an SEM image of the transparent (front) electrode layer.
  • the transparent (surface) electrode layer represented by the SEM image 53 is ZnO: Al having a thickness of 0.3 ⁇ m.
  • the buffer layer and the high resistance layer each have a thickness of only 50 nm, their SEM images 52 exist, but in FIG. However, when enlarged and looked closely, it was confirmed that the SEM images of the buffer layer and the high resistance layer were slightly whitish images.
  • the solar cell of Comparative Example 1 can confirm the region where the depletion layer hardly exists in the light absorption layer as can be seen from the EBIC measurement image 51.
  • the depletion layer uniformly spreads in the entire light absorption layer as compared with the solar cells of Comparative Examples 1 and 2, so that even if the buffer layer is not provided, the solar cell is high. Efficiency can be realized.
  • the solar cell of the present embodiment does not have a buffer layer, it is possible to omit a device manufacturing process necessary for buffer layer manufacturing and solve the problem of heavy metal waste liquid generated by buffer layer manufacturing. be able to.
  • the present invention is not limited to the above-described embodiment, and includes various other modifications.
  • Ge can be used in place of Si as a group IV element to be vapor-deposited at the same time in addition to In, Ga and Se.
  • a buffer layer was not provided in embodiment, you may provide a very thin buffer layer 30 nm or less. Also in this case, since the depletion layer spreads uniformly throughout the light absorption layer, high efficiency can be realized.
  • the buffer layer is not limited to a single buffer layer composed of CdS or the like, but also includes a broad buffer layer that is a composite layer composed of a buffer layer and a high resistance layer.
  • the I-III-VI 2 polycrystal chalcopyrite material is formed by three-stage vapor deposition, but in addition, the I-III-VI 2 polycrystal chalcopyrite material may be formed by a selenization method.
  • a selenization method for example, in order to form a Cu (Se, Ga) Se 2 film by a selenization method, a Cu—Ga / In metal precursor film is formed and then selenized using a selenium source such as solid selenium or hydrogen selenide. To do.
  • a selenium source such as solid selenium or hydrogen selenide.

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Abstract

The present invention enables the achievement of a solar cell which has high efficiency without using a buffer layer. A solar cell 10 according to the present invention has a structure wherein a backside electrode layer 12 that is formed from Mo or the like, a light absorption layer 13 and a transparent electrode layer 14 are laminated on a glass substrate 11. This solar cell 10 is configured such that the light absorption layer 13 is a I-III-VI2 compound light absorption layer into which a group IV element such as silicon (Si) and germanium (Ge) is added. The light absorption layer 13 is obtained by vapor depositing a group IV element, namely Si simultaneously with group III elements, namely In and Ga and a group VI element, namely Se in the third stage of a three-stage vapor deposition method. Consequently, a coating layer is formed within the light absorption layer 13, thereby enabling the achievement of high efficiency.

Description

太陽電池及びその製造方法Solar cell and manufacturing method thereof
　本発明は太陽電池及びその製造方法に係り、特にI-III-VI2系カルコパイライト材料を光吸収層に用いた太陽電池及びその製造方法に関する。 The present invention relates to a solar cell and a method for manufacturing the solar cell, and more particularly to a solar cell using an I-III-VI 2 chalcopyrite material as a light absorption layer and a method for manufacturing the solar cell.
　銅（Ｃｕ）や銀（Ａｇ）などのＩ族元素と、インジウム（Ｉｎ）、ガリウム（Ｇａ）あるいはアルミニウム（Ａｌ）などのＩＩＩ族元素と、セレン（Ｓｅ）や硫黄（Ｓ）などのＶＩ族元素とからなるＩ－ＩＩＩ－ＶＩ２系多結晶カルコパイライト材料を光吸収層に用いた太陽電池は、光入射側から導電性酸化亜鉛などの負極透明電極層、ｎ型バッファ層、ｐ型の上記光吸収層、正極裏面電極層及び基板の順で積層された構造である（例えば、非特許文献１参照）。上記ｎ型バッファ層は、ＣｄＳ、ＺｎＳ（Ｏ，ＯＨ）あるいはＩｎ２Ｓ３などで構成され、上記正極裏面電極層は一般的にモリブデン（Ｍｏ）で構成され、上記基板はガラス、金属箔、ポリイミドなどの樹脂材やプラスチック、あるいはセラミックで構成される。また、上記光吸収層は、多結晶カルコパイライト材料として例えばＣｕ（Ｉｎ，Ｇａ）Ｓｅ２（いわゆるＣＩＧＳ）を用いて構成される。 Group I elements such as copper (Cu) and silver (Ag); Group III elements such as indium (In), gallium (Ga) and aluminum (Al); and Group VI such as selenium (Se) and sulfur (S) A solar cell using an I-III-VI 2 polycrystal chalcopyrite material composed of an element as a light absorption layer has a negative electrode transparent electrode layer such as conductive zinc oxide, an n-type buffer layer, a p-type The light absorption layer, the positive electrode back electrode layer, and the substrate are stacked in this order (for example, see Non-Patent Document 1). The n-type buffer layer is made of CdS, ZnS (O, OH), In 2 S 3 or the like, the positive electrode back electrode layer is generally made of molybdenum (Mo), and the substrate is made of glass, metal foil, It is made of resin material such as polyimide, plastic, or ceramic. Further, the light absorbing layer is polycrystalline chalcopyrite materials as for example Cu (In, Ga) constructed using Se 2 (so-called CIGS).
　ここで、バッファ層は溶液成長（ウェットプロセス）によって形成されるのが主流であり、ドライプロセスで形成される電極層や光吸収層などの他の構成層の製造工程と比較すると、重金属を含む廃液の発生などがあることが課題であった。そのため、バッファ層をドライプロセスで形成する提案もなされてきたが、バッファ層自体を用いない太陽電池構造が確立できれば、太陽電池製造工程における抜本的な時間短縮やコスト削減が期待できる。 Here, the buffer layer is mainly formed by solution growth (wet process), and includes heavy metals as compared with the manufacturing process of other constituent layers such as an electrode layer and a light absorption layer formed by a dry process. The problem was the generation of waste liquid. For this reason, proposals have been made to form the buffer layer by a dry process, but if a solar cell structure that does not use the buffer layer itself can be established, drastic time reduction and cost reduction in the solar cell manufacturing process can be expected.
　そこで、バッファ層自体を用いない太陽電池の作製方法が提案されている（例えば、非特許文献２～５参照）。非特許文献２及び３には、Ｃｕ（Ｉｎ，Ｇａ）Ｓｅ２光吸収層を成膜後にその薄膜表面へＩＩ族元素（カドミウム（Ｃｄ）や亜鉛（Ｚｎ）等）をイオン注入したり、溶液浸水することなどの方法が開示されている。また、非特許文献４及び５には、負極透明電極層のエネルギーバンドオフセットを光吸収層のそれと最適結合を図ることでバッファ層を用いない構成が開示されている。 Therefore, a method for manufacturing a solar cell that does not use the buffer layer itself has been proposed (see, for example, Non-Patent Documents 2 to 5). In Non-Patent Documents 2 and 3, after forming a Cu (In, Ga) Se 2 light absorption layer, a group II element (such as cadmium (Cd) or zinc (Zn)) is ion-implanted into the thin film surface, or a solution Methods such as water immersion are disclosed. Non-Patent Documents 4 and 5 disclose configurations in which the buffer layer is not used by optimally coupling the energy band offset of the negative electrode transparent electrode layer with that of the light absorption layer.
　しかしながら、非特許文献２及び３記載の方法は、太陽電池デバイス作製工程数を減らすことはできず、また重金属廃棄物の発生を解決できない。また、非特許文献４及び５記載の方法は、作成された太陽電池の光電変換効率が１０％程度と低い値に留まっているという課題がある。 However, the methods described in Non-Patent Documents 2 and 3 cannot reduce the number of solar cell device manufacturing steps, and cannot solve the generation of heavy metal waste. Moreover, the method of a nonpatent literature 4 and 5 has the subject that the photoelectric conversion efficiency of the produced solar cell has remained as low as about 10%.
　本発明は以上の点に鑑みなされたもので、薄いバッファ層を有するか、完全にバッファ層をなくしても高効率な太陽電池及びその製造方法を提供することを目的とする。 The present invention has been made in view of the above points, and an object of the present invention is to provide a highly efficient solar cell having a thin buffer layer or completely eliminating the buffer layer and a method for manufacturing the solar cell.
　上記の目的を達成するため、本発明の太陽電池は、第１の電極層と、光透過性を有する第２の電極層と、前記第１及び第２の電極層の間に設けられた光吸収層と、を備え、前記光吸収層は、Ｓｉ又はＧｅが添加されたＩ－ＩＩＩ－ＶＩ２系多結晶カルコパイライト材料であることを特徴とする。 In order to achieve the above object, a solar cell of the present invention includes a first electrode layer, a second electrode layer having optical transparency, and light provided between the first and second electrode layers. An absorption layer, wherein the light absorption layer is an I-III-VI 2 based polycrystalline chalcopyrite material to which Si or Ge is added.
　また、上記の目的を達成するため、本発明の太陽電池の製造方法は、基板上に第１の電極層を形成する工程と、前記第１の電極層上に、Ｓｉ又はＧｅが添加されたＩ－ＩＩＩ－ＶＩ２系多結晶カルコパイライト材料を用いた光吸収層を製膜する工程と、前記光吸収層の上方に光透過性を有する第２の電極層を形成する工程と、を含む太陽電池の製造方法であって、前記光吸収層を製膜する工程は、ＩＩＩ族元素に対してＩ族元素の過剰域が形成される期間においてＳｉ又はＧｅを添加する工程を有することを特徴とする。 In order to achieve the above object, the method for manufacturing a solar cell of the present invention includes a step of forming a first electrode layer on a substrate, and Si or Ge is added to the first electrode layer. Forming a light absorption layer using the I-III-VI 2- based polycrystalline chalcopyrite material, and forming a light-transmitting second electrode layer above the light absorption layer. In the method for manufacturing a solar cell, the step of forming the light absorption layer includes a step of adding Si or Ge during a period in which an excess region of the group I element is formed with respect to the group III element. And
　本発明によれば、薄いバッファ層を有するか、完全にバッファ層をなくしても高効率の太陽電池を実現することができる。 According to the present invention, a highly efficient solar cell can be realized without having a thin buffer layer or completely eliminating the buffer layer.
本発明に係る太陽電池の一実施形態の概略構成断面図である。It is a schematic structure sectional view of one embodiment of a solar cell concerning the present invention. 本発明に係る太陽電池の製造方法の一実施形態の概略説明用フローチャートである。It is a flowchart for outline explanation of one embodiment of a manufacturing method of a solar cell concerning the present invention. 本発明に係る太陽電池の製造方法の一実施形態の要部の光吸収層の構成比対時間特性図である。It is a structure ratio vs. time characteristic figure of the light absorption layer of the principal part of one Embodiment of the manufacturing method of the solar cell which concerns on this invention. 図３の三段階蒸着法の各段階における素子断面の膜成長モデル図である。It is a film growth model figure of an element section in each step of the three-step vapor deposition method of FIG. Ｓｉが添加されたＣｕ（Ｉｎ，Ｇａ）Ｓｅ２膜の断面ＳＥＭ像、及びＳｉが添加されていないＣｕ（Ｉｎ，Ｇａ）Ｓｅ２膜の断面ＳＥＭ像を示す図である。Si is added Cu (In, Ga) Se 2 film cross-section SEM image, Cu (In, Ga) to and Si were not added is a view showing a sectional SEM image of the Se 2 film. 本発明の一実施形態の太陽電池の電流－電圧特性と、比較例１の太陽電池の電流－電圧特性の一例を示す図である。FIG. 3 is a diagram showing an example of current-voltage characteristics of a solar cell of one embodiment of the present invention and current-voltage characteristics of a solar cell of Comparative Example 1. 本発明の一実施形態と、バッファ層を有しない比較例２の太陽電池と、バッファ層及び高抵抗層を有する比較例１の太陽電池それぞれの、光吸収層のＥＢＩＣ測定画像及び太陽電池の断面ＳＥＭ画像を示す図である。EBIC measurement image of solar absorption layer and cross section of solar cell of one embodiment of the present invention, solar cell of comparative example 2 having no buffer layer, and solar cell of comparative example 1 having a buffer layer and a high resistance layer It is a figure which shows a SEM image.
　次に、本発明の実施形態について図面を参照して説明する。 Next, an embodiment of the present invention will be described with reference to the drawings.
　図１は、本発明に係る太陽電池の一実施形態の概略構成断面図を示す。同図において、本実施形態の太陽電池１０は、ガラス基板１１上に、Ｍｏ等からなる第１の電極層である裏面電極層１２、光吸収層１３及び光透過性を有する第２の電極層である透明電極層１４が積層された構造である。本実施形態の太陽電池１０は、光吸収層１３が、シリコン（Ｓｉ）やゲルマニウム（Ｇｅ）などのＩＶ族元素が添加されたＩ－ＩＩＩ－ＶＩ２化合物光吸収層であり、かつ、バッファ層を有していない点に特徴がある。光吸収層１３の直上に形成された負極の透明電極層１４は、導電性酸化亜鉛などで構成されている。 FIG. 1 shows a schematic cross-sectional view of one embodiment of a solar cell according to the present invention. In the figure, the solar cell 10 of the present embodiment includes a back electrode layer 12, which is a first electrode layer made of Mo, and the like, a light absorption layer 13, and a second electrode layer having light transmittance on a glass substrate 11. This is a structure in which transparent electrode layers 14 are stacked. In the solar cell 10 of the present embodiment, the light absorption layer 13 is an I-III-VI 2 compound light absorption layer to which a group IV element such as silicon (Si) or germanium (Ge) is added, and a buffer layer. There is a feature in that it does not have. The negative transparent electrode layer 14 formed immediately above the light absorption layer 13 is made of conductive zinc oxide or the like.
　次に、本発明に係る太陽電池の製造方法の一実施形態について図面を参照して説明する。 Next, an embodiment of a method for manufacturing a solar cell according to the present invention will be described with reference to the drawings.
　図２は、本発明に係る太陽電池の製造方法の一実施形態の概略説明用フローチャートを示す。本実施形態の製造方法では、まず、公知の方法で青板ガラス製の基板（図１の１１）上に裏面電極層（図１の１２）をスパッタ法などにより形成する（図２のステップＳ１）。基板にはステンレスあるいは金属板等も使用できる。裏面電極層としては例えばＭｏからなる金属膜が用いられる。 FIG. 2 is a flowchart for explaining the outline of one embodiment of the method for manufacturing a solar cell according to the present invention. In the manufacturing method of the present embodiment, first, a back electrode layer (12 in FIG. 1) is formed on a blue glass substrate (11 in FIG. 1) by a known method by sputtering (step S1 in FIG. 2). . Stainless steel or metal plate can be used for the substrate. As the back electrode layer, for example, a metal film made of Mo is used.
　続いて、裏面電極層の上に光吸収層（図１の１３）が三段階蒸着法で製膜される（図２のステップＳ２）。本実施形態は、光吸収層としてＩ－ＩＩＩ－ＶＩ２系多結晶カルコパイライト材料を用い、後に詳述する三段階蒸着法により光吸収層を製膜する点に特徴がある。最後に、光吸収層の上にバッファ層を形成することなく直接に例えば厚さ２～３μｍの透明電極膜（図１の１４）をスパッタ法、真空蒸着法あるいは有機金属気相成長法などの公知の方法で形成する（図２のステップＳ３）。透明電極層としては、透光性を有し、かつ、導電性を有する必要から、ジボランからのホウ素（Ｂ）をドーパントしたＺｎＯ：Ｂ、あるいはアルミナ（Ａｌ２Ｏ３）を含有するＺｎＯ：Ａｌが用いられる。このようにして、本実施形態の太陽電池が製造される。 Subsequently, a light absorption layer (13 in FIG. 1) is formed on the back electrode layer by a three-stage vapor deposition method (step S2 in FIG. 2). The present embodiment is characterized in that an I-III-VI 2- based polycrystalline chalcopyrite material is used as the light absorption layer, and the light absorption layer is formed by a three-stage vapor deposition method described in detail later. Finally, without forming a buffer layer on the light absorption layer, for example, a transparent electrode film (14 in FIG. 1) having a thickness of 2 to 3 μm is directly formed by sputtering, vacuum evaporation, metal organic chemical vapor deposition or the like. It forms by a well-known method (step S3 of FIG. 2). As the transparent electrode layer, ZnO: Al containing ZnO: B or alumina (Al 2 O 3 ) doped with boron (B) from diborane is necessary because it has translucency and conductivity. Is used. Thus, the solar cell of this embodiment is manufactured.
　次に、本実施形態の製造方法の要部の三段階蒸着法について更に詳細に説明する。図３は、本発明に係る太陽電池の製造方法の一実施形態の要部の光吸収層の構成比対時間特性図、図４は、三段階蒸着法の各段階における素子断面の膜成長モデルを示す。図３は、縦軸が光吸収層１３を構成するＣｕ（Ｉｎ，Ｇａ）Ｓｅ２膜の［Ｃｕ］／（［Ｉｎ］＋［Ｇａ］）比、横軸が時間を示す。三段階蒸着法の第一段階では、ＩＩＩ族元素であるＩｎ及びＧａと、ＶＩ族元素であるＳｅとを同時に裏面電極上に蒸着する。この第一段階ではＣｕは蒸着されないので、図３に示すように［Ｃｕ］／（［Ｉｎ］＋［Ｇａ］）比は「０」である。また、裏面電極上の膜成長モデルは第一段階終了時は図４（ａ）に示す如くになる。 Next, the three-stage vapor deposition method as the main part of the manufacturing method of this embodiment will be described in more detail. FIG. 3 is a diagram showing the composition ratio versus time characteristic of the light absorption layer of the main part of one embodiment of the method for manufacturing a solar cell according to the present invention, and FIG. Indicates. In FIG. 3, the vertical axis represents the [Cu] / ([In] + [Ga]) ratio of the Cu (In, Ga) Se 2 film constituting the light absorption layer 13, and the horizontal axis represents time. In the first stage of the three-stage vapor deposition method, group III elements In and Ga and group VI element Se are simultaneously deposited on the back electrode. Since Cu is not deposited in this first stage, the [Cu] / ([In] + [Ga]) ratio is “0” as shown in FIG. Further, the film growth model on the back electrode is as shown in FIG.
　次の第二段階では、第一段階で形成されたＩｎ及びＧａとＳｅとの化合物（Ｉｎ，Ｇａ）２Ｓｅ３の上にＩ族元素であるＣｕとＶＩ族元素であるＳｅとを同時に蒸着する。従って、第二段階の蒸着時間が経過するにつれて、Ｃｕの蒸着量が増え図３に実線２１で示すように、［Ｃｕ］／（［Ｉｎ］＋［Ｇａ］）比が直線的に増加していき、第二段階の終了時にはＣｕが過剰な状態（上記比が「１」より大）となる。第二段階終了時の膜成長モデルは図４（ｂ）に示す如くになる。以上の第一段階及び第二段階の動作は公知であるが、本実施形態は次の第三段階に特有の特徴がある。 In the next second stage, Cu, which is a group I element, and Se, which is a group VI element, are simultaneously deposited on the compound of In and Ga and Se (In, Ga) 2 Se 3 formed in the first stage. To do. Therefore, as the second stage deposition time elapses, the amount of Cu deposition increases, and the [Cu] / ([In] + [Ga]) ratio increases linearly as shown by the solid line 21 in FIG. At the end of the second stage, Cu is in an excessive state (the above ratio is greater than “1”). The film growth model at the end of the second stage is as shown in FIG. Although the operations of the first stage and the second stage described above are known, this embodiment has a characteristic characteristic of the following third stage.
　第二段階の終了直後の第三段階開始時には、Ｃｕの過剰蒸着により蒸着膜の表面にＣｕ－Ｓｅ液相ができている。この状態から開始する第三段階において、ＩＩＩ族元素であるＩｎ及びＧａとＶＩ族元素であるＳｅとに加えて、ＩＶ族元素であるＳｉを同時に蒸着する。第三段階開始時の膜成長モデルは図４（ｃ）に示す如くになる。第三段階では、蒸着時間が経過するにつれてＩｎ及びＧａの蒸着量がＣｕの蒸着量と比較して相対的に増加するため、［Ｃｕ］／（［Ｉｎ］＋［Ｇａ］）比が図３に実線２３で示すように直線的に減少すると共にＣｕの過剰域２２が無くなり、Ｓｉのドーパント量が所定範囲（例えば、０．０１～０．５ａｔｍ％）になった時点（上記比が１未満で０より大）で第三段階の蒸着を終了する。第三段階の蒸着終了時の膜成長モデルは図４（ｄ）に示す如くＳｉがＣＩＧＳ膜に溶け込み、Ｃｕ（Ｉｎ，Ｇａ）Ｓｅ２：Ｓｉになる。このようにして、本実施形態の光吸収層１３としてＳｉが添加されたＣｕ（Ｉｎ，Ｇａ）Ｓｅ２膜の製膜が終了する。なお、Ｓｉは第二段階の工程後期において［Ｃｕ］／（［Ｉｎ］＋［Ｇａ］）比が「１」を超えた時点より蒸着を開始してもよい。 At the start of the third stage immediately after the end of the second stage, a Cu—Se liquid phase is formed on the surface of the deposited film due to excessive deposition of Cu. In the third stage starting from this state, in addition to group III elements In and Ga and group VI element Se, Si group IV elements are simultaneously deposited. The film growth model at the start of the third stage is as shown in FIG. In the third stage, as the deposition time elapses, the deposition amounts of In and Ga are relatively increased as compared with the deposition amount of Cu, so that the [Cu] / ([In] + [Ga]) ratio is as shown in FIG. As shown by a solid line 23, the amount of Si decreases linearly and the excess Cu region 22 disappears, and the amount of Si dopant reaches a predetermined range (for example, 0.01 to 0.5 atm%) (the ratio is less than 1). And greater than 0), the third stage deposition is completed. As shown in FIG. 4D, the film growth model at the end of the third stage of deposition is such that Si dissolves in the CIGS film and becomes Cu (In, Ga) Se 2 : Si. In this manner, the formation of the Cu (In, Ga) Se 2 film to which Si is added as the light absorption layer 13 of the present embodiment is completed. Note that Si may be deposited from the point in time when the [Cu] / ([In] + [Ga]) ratio exceeds “1” in the second stage of the process.
　図５（ａ）は、本実施形態の光吸収層１３であるＳｉが添加されたＣｕ（Ｉｎ，Ｇａ）Ｓｅ２膜の断面ＳＥＭ像を示す。また、図５（ｂ）は、Ｓｉが添加されていないＣｕ（Ｉｎ，Ｇａ）Ｓｅ２膜の断面ＳＥＭ像を示す。走査電子顕微鏡（ＳＥＭ：Scanning Electron Microscope)により得られた、本実施形態の光吸収層１３であるＳｉが添加されたＣｕ（Ｉｎ，Ｇａ）Ｓｅ２膜の断面ＳＥＭ像には、図５（ａ）に示すように、ＣＩＧＳの多結晶の粒と粒との間に形成された層（以下、本明細書では、この層を「被覆層」という）が存在している。この被覆層は、結晶粒とは若干組成の異なる成分の層、又は組成は同じでも結晶方位の異なる層であると推測される。この被覆層が後述の比較例１のバッファ層に類似した機能を果たすことが後述の実験により確かめられた。これに対し、Ｓｉが添加されていないＣｕ（Ｉｎ，Ｇａ）Ｓｅ２膜の断面ＳＥＭ像は、図５（ｂ）に示すように、上記被覆膜は形成されていない。 FIG. 5A shows a cross-sectional SEM image of a Cu (In, Ga) Se 2 film to which Si, which is the light absorption layer 13 of this embodiment, is added. FIG. 5B shows a cross-sectional SEM image of a Cu (In, Ga) Se 2 film to which Si is not added. A cross-sectional SEM image of a Cu (In, Ga) Se 2 film added with Si, which is the light absorption layer 13 of this embodiment, obtained by a scanning electron microscope (SEM) is shown in FIG. ), A layer formed between CIGS polycrystalline grains (hereinafter referred to as “coating layer” in this specification) exists. This coating layer is presumed to be a layer having a slightly different composition from the crystal grains, or a layer having the same composition but a different crystal orientation. It was confirmed by an experiment described later that this coating layer performs a function similar to the buffer layer of Comparative Example 1 described later. On the other hand, the cross-sectional SEM image of the Cu (In, Ga) Se 2 film to which Si is not added has no coating film as shown in FIG. 5B.
　次に、本実施形態の太陽電池の特性と比較例１の太陽電池の特性とを対比して説明する。 Next, the characteristics of the solar cell of the present embodiment will be described in comparison with the characteristics of the solar cell of Comparative Example 1.
　図６（ａ）は、本実施形態の太陽電池の電流－電圧特性、図６（ｂ）は比較例１の太陽電池の電流－電圧特性の一例を示す。図１に示す断面構造で、かつ、Ｓｉが添加されたＣｕ（Ｉｎ，Ｇａ）Ｓｅ２膜である光吸収層１３を有する本実施形態の太陽電池の、光入射時の電流－電圧特性は図６（ａ）にＡ１で示され、暗時の電流－電圧特性は同図（ａ）にＡ２で示される。一方、Ｓｉが添加されていないＣｕ（Ｉｎ，Ｇａ）Ｓｅ２膜を光吸収層として有し、かつ、その光吸収層の上にバッファ層、高抵抗層及び透明電極層の順で積層された構造の比較例１の太陽電池の、光入射時の電流－電圧特性は図６（ｂ）にＢ１で示され、暗時の電流－電圧特性は同図（ｂ）にＢ２で示される。 FIG. 6A shows an example of current-voltage characteristics of the solar cell of this embodiment, and FIG. 6B shows an example of current-voltage characteristics of the solar cell of Comparative Example 1. The current-voltage characteristics at the time of light incidence of the solar cell of the present embodiment having the light absorption layer 13 which is the Cu (In, Ga) Se 2 film added with Si and having the cross-sectional structure shown in FIG. 6 (a) is indicated by A1, and the dark current-voltage characteristic is indicated by A2 in FIG. On the other hand, a Cu (In, Ga) Se 2 film to which Si is not added is provided as a light absorption layer, and a buffer layer, a high resistance layer, and a transparent electrode layer are stacked in this order on the light absorption layer. The current-voltage characteristic at the time of light incidence of the solar cell of Comparative Example 1 having the structure is indicated by B1 in FIG. 6B, and the current-voltage characteristic at the dark time is indicated by B2 in FIG. 6B.
　図６（ａ）に示した本実施形態の太陽電池の電流－電圧特性と、図６（ｂ）に示した比較例１の太陽電池の電流－電圧特性に基づいて得られる変換効率、開放電圧、短絡電流密度及び曲線因子をそれぞれまとめると表１に示す如くになる。 Conversion efficiency and open-circuit voltage obtained based on the current-voltage characteristics of the solar cell of the present embodiment shown in FIG. 6A and the current-voltage characteristics of the solar cell of Comparative Example 1 shown in FIG. 6B. Table 1 summarizes the short circuit current density and the fill factor.
Figure JPOXMLDOC01-appb-T000001
 　表１に示すように、本実施形態は比較例１の太陽電池に比べて光電変換効率が向上することが確かめられた。また、図６（ａ）及び（ｂ）を対比すると分かるように、本実施形態では、比較例１の太陽電池で生じていた逆バイアス印加時のブレークダウンを抑制することができた。
Figure JPOXMLDOC01-appb-T000001
 As shown in Table 1, it was confirmed that the photoelectric conversion efficiency of this embodiment was improved as compared with the solar cell of Comparative Example 1. Further, as can be seen by comparing FIGS. 6A and 6B, in this embodiment, it was possible to suppress the breakdown at the time of applying the reverse bias, which occurred in the solar cell of Comparative Example 1.
　次に、本実施形態の太陽電池の高効率化の理由について説明する。本実施形態では、太陽電池の構造を電子線誘起電流(ＥＢＩＣ:Electron Beam Induced Current)測定法を適用して観察した。ＥＢＩＣ測定では、周知のように、測定試料の断面に電子線を照射して励起させた電子-正孔対をＥＢＩＣ信号（電流）として検出するが、測定試料内のｐｎ接合が無い部分（空乏層が形成されない部分）で電子-正孔対が再結合してキャリア損失が生じて消滅するのに対し、ｐｎ接合部分（空乏層が形成されている部分）では再結合しないため、ＥＢＩＣ信号の大きさは空乏層が形成されていない測定試料では空乏層が形成されているＥＢＩＣ信号に比べて相対的に小さくなる。そこで、ＥＢＩＣ信号の大きさに応じて輝度を変化させた画像により測定試料内の空乏層の有無を観察できる。 Next, the reason for increasing the efficiency of the solar cell of this embodiment will be described. In this embodiment, the structure of the solar cell was observed by applying an electron beam induced current (EBIC: Electron Beam Induced Current) measurement method. In EBIC measurement, as is well known, an electron-hole pair excited by irradiating an electron beam to a cross section of a measurement sample is detected as an EBIC signal (current), but there is no pn junction in the measurement sample (depletion) The electron-hole pair is recombined in the part where the layer is not formed) and carrier loss occurs and disappears, whereas the pn junction part (the part where the depletion layer is formed) does not recombine. The magnitude of the measurement sample in which the depletion layer is not formed is relatively smaller than that of the EBIC signal in which the depletion layer is formed. Therefore, the presence or absence of a depletion layer in the measurement sample can be observed from an image in which the luminance is changed according to the magnitude of the EBIC signal.
　図７（ａ）に３１で示すモノクロ画像は、本実施形態の太陽電池の光吸収層のＥＢＩＣ測定画像を示す。本実施形態の太陽電池の光吸収層では、図５（ａ）に示したようにＳｉが添加されたＣｕ（Ｉｎ，Ｇａ）Ｓｅ２膜内に被覆層が形成されているため、Ｃｕ（Ｉｎ，Ｇａ）Ｓｅ２膜と被覆層とで電荷分離界面が形成され、空乏層が形成されるため、明るい輝度のモノクロ画像３１は光吸収層内全体で空乏層が均一に存在することを示している。なお、図７（ａ）に３１’で示す画像は本実施形態の太陽電池の光吸収層のＥＢＩＣ信号の強度分布を示し、モノクロ画像３０は本実施形態の太陽電池の裏面電極層のＳＥＭ画像、モノクロ画像３２は透明（表面）電極層のＳＥＭ画像を示す。 A monochrome image indicated by 31 in FIG. 7A shows an EBIC measurement image of the light absorption layer of the solar cell of the present embodiment. In the light absorption layer of the solar cell of this embodiment, as shown in FIG. 5A, a coating layer is formed in the Cu (In, Ga) Se 2 film to which Si is added. , Ga) Se 2 film and the covering layer form a charge separation interface, and a depletion layer is formed. Therefore, the bright monochrome image 31 shows that the depletion layer exists uniformly in the entire light absorption layer. Yes. 7A shows the intensity distribution of the EBIC signal of the light absorption layer of the solar cell of this embodiment, and the monochrome image 30 is an SEM image of the back electrode layer of the solar cell of this embodiment. Monochrome image 32 shows an SEM image of the transparent (surface) electrode layer.
　これに対し、図７（ｂ）に４１で示すモノクロ画像は、Ｓｉが添加されていないＣｕ（Ｉｎ，Ｇａ）Ｓｅ２膜からなる光吸収層のＥＢＩＣ測定画像を示す。この光吸収層を備える比較例２の太陽電池は光吸収層の上面にバッファ層を介さず直接に透明電極層が積層された構造である点は本実施形態と同様であるが、この光吸収層はＳｉが添加されていないＣｕ（Ｉｎ，Ｇａ）Ｓｅ２膜であるため、図５（ｂ）に示したように前述した被覆層が形成されていない。このため、図７（ｂ）のモノクロ画像４１から分かるように、比較例２の太陽電池では、光吸収層内の被覆層が無い個所の部分を示す輝度が暗い部分が多く、空乏層が殆ど存在しないことを示している。なお、図７（ｂ）に４１’で示す画像は上記の光吸収層のＥＢＩＣ信号画像４１の強度分布を示し、モノクロ画像３０は太陽電池の裏面電極層のＳＥＭ画像、モノクロ画像３２は透明（表面）電極層のＳＥＭ画像を示す。図７（ａ）及び（ｂ）では透明（表面）電極層は、厚さ２μｍのＺｎＯ：Ｂである。 On the other hand, a monochrome image indicated by 41 in FIG. 7B shows an EBIC measurement image of the light absorption layer made of a Cu (In, Ga) Se 2 film to which Si is not added. The solar cell of Comparative Example 2 having this light absorption layer is the same as the present embodiment in that the transparent electrode layer is directly laminated on the upper surface of the light absorption layer without a buffer layer. Since the layer is a Cu (In, Ga) Se 2 film to which Si is not added, the above-described coating layer is not formed as shown in FIG. For this reason, as can be seen from the monochrome image 41 in FIG. 7B, in the solar cell of Comparative Example 2, there are many dark portions indicating portions where there is no coating layer in the light absorption layer, and almost no depletion layer. Indicates that it does not exist. 7B shows the intensity distribution of the EBIC signal image 41 of the light absorption layer, the monochrome image 30 is an SEM image of the back electrode layer of the solar cell, and the monochrome image 32 is transparent ( The SEM image of the (surface) electrode layer is shown. In FIGS. 7A and 7B, the transparent (surface) electrode layer is 2 μm thick ZnO: B.
　また、図７（ｃ）は、Ｓｉが添加されていないＣｕ（Ｉｎ，Ｇａ）Ｓｅ２膜を光吸収層として有し、かつ、その光吸収層の上にバッファ層、高抵抗層及び透明電極層がこの順で積層された構造の前記比較例１の太陽電池のＥＢＩＣ測定画像及びＳＥＭ画像を示す。すなわち、図７（ｃ）に５１で示すモノクロ画像は、Ｓｉが添加されていないＣｕ（Ｉｎ，Ｇａ）Ｓｅ２膜からなる光吸収層のＥＢＩＣ測定画像を示し、同図（ｃ）に５１’で示す画像は当該光吸収層のＥＢＩＣ測定信号の強度分布を示す画像である。また、図７（ｃ）において、画像３０は裏面電極層のＳＥＭ画像、画像５２はバッファ層及び高抵抗層のＳＥＭ画像、画像５３は透明（表面）電極層のＳＥＭ画像を示す。 FIG. 7C shows a Cu (In, Ga) Se 2 film to which Si is not added as a light absorption layer, and a buffer layer, a high resistance layer, and a transparent electrode on the light absorption layer. The EBIC measurement image and SEM image of the solar cell of the said comparative example 1 of the structure where the layer was laminated | stacked in this order are shown. That is, a monochrome image 51 shown in FIG. 7C shows an EBIC measurement image of a light absorption layer made of a Cu (In, Ga) Se 2 film to which Si is not added, and 51 ′ in FIG. The image indicated by is an image showing the intensity distribution of the EBIC measurement signal of the light absorption layer. In FIG. 7C, an image 30 shows an SEM image of the back electrode layer, an image 52 shows an SEM image of the buffer layer and the high resistance layer, and an image 53 shows an SEM image of the transparent (front) electrode layer.
　なお、ＳＥＭ画像５３で表される透明（表面）電極層は、厚さ０．３μｍのＺｎＯ：Ａｌである。また、上記のバッファ層と高抵抗層はそれぞれ５０ｎｍの厚みしかないので、それらのＳＥＭ画像５２は存在するが、図７（ｃ）では倍率の関係上識別困難である。しかし、拡大してよく見ると、バッファ層と高抵抗層のＳＥＭ画像はうっすらと白っぽい画像であることが確認できた。この比較例１の太陽電池でも比較例２の太陽電池と同様に、ＥＢＩＣ測定画像５１から分かるように光吸収層には空乏層が殆ど存在しない領域が確認できる。 In addition, the transparent (surface) electrode layer represented by the SEM image 53 is ZnO: Al having a thickness of 0.3 μm. Further, since the buffer layer and the high resistance layer each have a thickness of only 50 nm, their SEM images 52 exist, but in FIG. However, when enlarged and looked closely, it was confirmed that the SEM images of the buffer layer and the high resistance layer were slightly whitish images. Similarly to the solar cell of Comparative Example 2, the solar cell of Comparative Example 1 can confirm the region where the depletion layer hardly exists in the light absorption layer as can be seen from the EBIC measurement image 51.
　このように、本実施形態の太陽電池は、比較例１及び２の太陽電池と比較して、光吸収層内全体に空乏層が均一に広がっているため、バッファ層を有しなくても高効率を実現できる。また、本実施形態の太陽電池では、バッファ層を有しないため、バッファ層作製のために必要なデバイス作製工程を省略することができるとともに、バッファ層作製に伴い発生する重金属廃液の問題を解決することができる。 Thus, in the solar cell of this embodiment, the depletion layer uniformly spreads in the entire light absorption layer as compared with the solar cells of Comparative Examples 1 and 2, so that even if the buffer layer is not provided, the solar cell is high. Efficiency can be realized. In addition, since the solar cell of the present embodiment does not have a buffer layer, it is possible to omit a device manufacturing process necessary for buffer layer manufacturing and solve the problem of heavy metal waste liquid generated by buffer layer manufacturing. be able to.
　なお、本発明は以上の実施形態に限定されるものではなく、その他種々の変形例を包含するものである。例えば、三段階蒸着法の第三段階において、Ｉｎ及びＧａとＳｅとに加えて、同時に蒸着するＩＶ族元素としてＳｉの代わりにＧｅを用いることも可能である。また、実施形態ではバッファ層を設けないように説明したが、３０ｎｍ以下の極めて薄い厚さのバッファ層を設けてもよい。この場合も光吸収層内全体に空乏層が均一に広がっているため、高効率を実現できる。なお、上記のバッファ層には、ＣｄＳなどからなるバッファ層単体の狭義のバッファ層に限らず、バッファ層と高抵抗層とからなる複合層である広義のバッファ層も含む。 Note that the present invention is not limited to the above-described embodiment, and includes various other modifications. For example, in the third stage of the three-stage vapor deposition method, Ge can be used in place of Si as a group IV element to be vapor-deposited at the same time in addition to In, Ga and Se. Moreover, although it demonstrated that a buffer layer was not provided in embodiment, you may provide a very thin buffer layer 30 nm or less. Also in this case, since the depletion layer spreads uniformly throughout the light absorption layer, high efficiency can be realized. The buffer layer is not limited to a single buffer layer composed of CdS or the like, but also includes a broad buffer layer that is a composite layer composed of a buffer layer and a high resistance layer.
　さらに上記実施形態では三段階蒸着でＩ－ＩＩＩ－ＶＩ２系多結晶カルコパイライト材料を形成したが、この他、セレン化法でＩ－ＩＩＩ－ＶＩ２系多結晶カルコパイライト材料を形成することも考えられる。例えば、セレン化法でＣｕ（Ｓｅ，Ｇａ）Ｓｅ２膜を形成するには、Ｃｕ－Ｇａ／Ｉｎ金属プリカーサ膜を形成し、それを固体セレンやセレン化水素等のセレン源を用いてセレン化することで行う。この金属プリカーサ膜にＳｉを含有させることで上記実施形態のようにＳｉが添加されたＣｕ（Ｓｅ，Ｇａ）Ｓｅ２膜を形成することが期待できる。 Furthermore, in the above embodiment, the I-III-VI 2 polycrystal chalcopyrite material is formed by three-stage vapor deposition, but in addition, the I-III-VI 2 polycrystal chalcopyrite material may be formed by a selenization method. Conceivable. For example, in order to form a Cu (Se, Ga) Se 2 film by a selenization method, a Cu—Ga / In metal precursor film is formed and then selenized using a selenium source such as solid selenium or hydrogen selenide. To do. By including Si in this metal precursor film, it can be expected to form a Cu (Se, Ga) Se 2 film to which Si is added as in the above embodiment.
１０　太陽電池
１１　ガラス基板
１２　裏面電極層
１３　光吸収層
１４　透明電極層 DESCRIPTION OF SYMBOLS 10 Solar cell 11 Glass substrate 12 Back surface electrode layer 13 Light absorption layer 14 Transparent electrode layer

Claims (10)

  1. 　第１の電極層と、
    　光透過性を有する第２の電極層と、
    　前記第１及び第２の電極層の間に設けられた光吸収層と、を備え、
    　前記光吸収層は、Ｓｉ又はＧｅが添加されたＩ－ＩＩＩ－ＶＩ２系多結晶カルコパイライト材料であることを特徴とする太陽電池。     A first electrode layer;
    A second electrode layer having optical transparency;
    A light absorption layer provided between the first and second electrode layers,
    The solar cell, wherein the light absorption layer is an I-III-VI 2- based polycrystalline chalcopyrite material to which Si or Ge is added.
  2. 　前記光吸収層は、バッファ層を介さず直接に前記第２の電極層の直下に形成されていることを特徴とする請求項１記載の太陽電池。 The solar cell according to claim 1, wherein the light absorption layer is formed directly below the second electrode layer without a buffer layer interposed therebetween.
  3. 　前記光吸収層は、厚さ３０ｎｍ以下のバッファ層を介して前記第２の電極層の直下に形成されていることを特徴とする請求項１記載の太陽電池。 The solar cell according to claim 1, wherein the light absorption layer is formed immediately below the second electrode layer through a buffer layer having a thickness of 30 nm or less.
  4. 　前記光吸収層は、層内全体で空乏層が均一に形成されていることを特徴とする請求項１乃至３のうちいずれか一項記載の太陽電池。 4. The solar cell according to claim 1, wherein a depletion layer is uniformly formed throughout the light absorption layer. 5.
  5. 　前記光吸収層は、層内全体で被覆層が形成されていることを特徴とする請求項１乃至４のうちいずれか一項記載の太陽電池。 The solar cell according to any one of claims 1 to 4, wherein a coating layer is formed in the entire light absorption layer.
  6. 　前記光吸収層は、Ｓｉが０．０１～０．５ａｔｍ％のドーパント量で添加されたＩ－ＩＩＩ－ＶＩ２系多結晶カルコパイライト材料であることを特徴とする請求項１乃至５のうちいずれか一項記載の太陽電池。 6. The light absorbing layer is an I-III-VI 2- based polycrystalline chalcopyrite material to which Si is added in an amount of 0.01 to 0.5 atm% dopant. A solar cell according to claim 1.
  7. 　基板上に第１の電極層を形成する工程と、
    　前記第１の電極層上に、Ｓｉ又はＧｅが添加されたＩ－ＩＩＩ－ＶＩ２系多結晶カルコパイライト材料を用いた光吸収層を製膜する工程と、
    　前記光吸収層の上方に光透過性を有する第２の電極層を形成する工程と、を含む太陽電池の製造方法であって、
    　前記光吸収層を製膜する工程は、ＩＩＩ族元素に対してＩ族元素の過剰域が形成される期間においてＳｉ又はＧｅを添加する工程を有することを特徴とする太陽電池の製造方法。     Forming a first electrode layer on a substrate;
    Forming a light absorption layer using an I-III-VI 2- based polycrystalline chalcopyrite material to which Si or Ge is added on the first electrode layer;
    Forming a second electrode layer having light permeability above the light absorption layer, and a method for manufacturing a solar cell,
    The method of forming a light absorption layer includes a step of adding Si or Ge during a period in which an excess region of a group I element is formed with respect to a group III element.
  8. 　前記光吸収層を製膜する工程は、
    　前記第１の電極層上に、ＩＩＩ族元素とＶＩ族元素とを同時に蒸着する第一段階の蒸着と、
    　前記第一段階の蒸着により形成された前記ＩＩＩ族元素及びＶＩ族元素の化合物の上に、Ｉ族元素の過剰域が形成されるまで前記Ｉ族元素と前記ＶＩ族元素とを同時に蒸着する第二段階の蒸着と、
    　前記第二段階の蒸着終了後、前記ＩＩＩ族元素及びＶＩ族元素と共にＩＶ族元素であるＳｉ又はＧｅを同時に蒸着する第三段階の蒸着と、
    　を有することを特徴とする請求項７記載の太陽電池の製造方法。     The step of forming the light absorption layer comprises:
    A first stage of vapor deposition of a Group III element and a Group VI element on the first electrode layer;
    First, the Group I element and the Group VI element are simultaneously deposited on the Group III element and Group VI element compounds formed by the first stage deposition until an excess region of the Group I element is formed. Two-stage deposition,
    After the completion of the second stage deposition, a third stage deposition for simultaneously depositing the group IV element and the group IV element together with the group IV element Si or Ge;
    The method for producing a solar cell according to claim 7, comprising:
  9. 　前記ＩＩＩ族元素はＩｎ及びＧａであり、前記ＶＩ族元素はＳｅであり、前記Ｉ族元素はＣｕであることを特徴とする請求項７又は８記載の太陽電池の製造方法。 9. The method for manufacturing a solar cell according to claim 7, wherein the group III element is In and Ga, the group VI element is Se, and the group I element is Cu.
  10. 　前記第２の電極層を形成する工程は、前記光吸収層を製膜する工程の後に、バッファ層を形成する工程を含まずに、実行されることを特徴とする請求項７乃至９のうちいずれか一項記載の太陽電池の製造方法。 10. The step of forming the second electrode layer is performed without including a step of forming a buffer layer after the step of forming the light absorption layer. The manufacturing method of the solar cell as described in any one.
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