WO2010090101A1 - Thin film photoelectric conversion device and manufacturing method therefor - Google Patents

Thin film photoelectric conversion device and manufacturing method therefor Download PDF

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WO2010090101A1
WO2010090101A1 PCT/JP2010/050976 JP2010050976W WO2010090101A1 WO 2010090101 A1 WO2010090101 A1 WO 2010090101A1 JP 2010050976 W JP2010050976 W JP 2010050976W WO 2010090101 A1 WO2010090101 A1 WO 2010090101A1
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photoelectric conversion
conductive oxide
transparent conductive
thin film
oxide layer
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PCT/JP2010/050976
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French (fr)
Japanese (ja)
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崇 口山
山本　憲治
智巳 目黒
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株式会社カネカ
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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
    • 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
    • H01L31/022483—Electrodes made of transparent conductive layers, e.g. TCO, ITO layers composed of zinc oxide [ZnO]
    • 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
    • H01L31/075—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 PIN type
    • H01L31/076—Multiple junction or tandem solar cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/548—Amorphous silicon PV cells

Definitions

  • the present invention uses a suitable transparent conductive oxide layer between the photoelectric conversion unit and the back electrode of the thin film photoelectric conversion device, thereby improving the light capturing efficiency in the photoelectric conversion unit and increasing the amount of generated current.
  • the present invention relates to a thin film photoelectric conversion device and a manufacturing method thereof.
  • a thin film photoelectric conversion device typified by a thin film solar cell has a pi- structure in which an intrinsic silicon (i-type) semiconductor is sandwiched between silicon semiconductors doped in p-type or n-type, such as amorphous or thin-film polycrystalline silicon.
  • i-type intrinsic silicon
  • n-type silicon semiconductors doped in p-type or n-type
  • amorphous or thin-film polycrystalline silicon such as amorphous or thin-film polycrystalline silicon.
  • CIS type copper-indium-selenium
  • CGS type copper-indium-gallium-selenium
  • there are numerous types such as a solar cell using a wide gap semiconductor and a thin film solar cell such as an organic thin film solar cell.
  • a back electrode layer made of a metal material having a high light reflectance is formed. Most of the light transmitted without being absorbed by the photoelectric conversion unit is reflected by the back electrode layer, reenters the photoelectric conversion unit, and photoelectric conversion is performed again.
  • the back electrode is made of a metal material having a high light reflectance such as silver or aluminum, so that the amount of light taken into the photoelectric conversion unit can be improved. Even if the back electrode such as silver or aluminum is directly formed on the conversion unit, it is difficult to improve the power generation characteristics. This is considered to be due to parasitic absorption derived from the fine structure of the back electrode.
  • Non-Patent Document 1 below describes that conversion efficiency decreases due to parasitic absorption in a back electrode formed on a photoelectric conversion unit.
  • Patent Document 1 proposes a technique in which two transparent conductive oxide layers, that is, an upper transparent layer and a low refractive index layer made of silicon oxide or the like for further improving optical characteristics are arranged. Yes.
  • transparent conductive oxide material for the upper transparent layer examples include indium tin composite oxide (ITO) and zinc oxide (ZnO).
  • Patent Document 2 describes a technique in which silicon or the like is doped into ZnO as a transparent electrode on the light incident side.
  • the present invention provides a technique that can suppress parasitic absorption caused by the back electrode, increase the amount of light taken into the photoelectric conversion layer as a result, and improve the amount of generated current. It is a problem to be solved.
  • the present invention has the following configuration.
  • the thin film photoelectric conversion device in which a transparent electrode layer made of a transparent conductive oxide, at least one thin film photoelectric conversion unit, and a back electrode are arranged in this order from the light incident side, zinc oxide is interposed between the thin film photoelectric conversion unit and the back electrode.
  • a transparent conductive oxide layer containing as a main component, a conductive additive is added to the transparent conductive oxide layer, and 85 atom% or more of the conductive additive consists of silicon atoms,
  • the transparent conductive oxide layer contains 2.0 to 8.0 atom% of silicon atoms with respect to zinc atoms, and is further seen from the X-ray photoelectron spectroscopy Si2P 1/2 peak of the transparent conductive oxide.
  • a thin film photoelectric conversion device in which silicon is substantially tetravalent.
  • the transparent conductive oxide layer preferably has a thickness of 100 to 1200 mm.
  • the thickness of the transparent conductive oxide layer is 100 to 800 mm and a wet heat durability test is performed in an environment of 85 ° C. and 85% relative humidity
  • a transparent conductive oxide layer having a sheet resistance change of 1.0 to 3.0 times after 500 hours is disposed between the photoelectric conversion unit and the back electrode.
  • the thin film photoelectric conversion device of the present invention is a device having a thin film photoelectric conversion unit mainly composed of amorphous silicon and a thin film photoelectric conversion unit mainly composed of crystalline silicon (so-called multi-junction type). Good.
  • a transparent conductive oxide layer is formed by magnetron sputtering, and the power density at the time of film formation is 1.5 to 15.0 W / cm 2. It is preferable that the pressure at the time is 0.5 Pa or less.
  • the transparent conductive oxide layer according to the present invention can balance high transparency and conductivity at a high level, and as a result, power generation characteristics can be improved. Furthermore, it is possible to provide a thin film photoelectric conversion device that can improve wet heat durability and is excellent in both conversion efficiency and durability.
  • the present invention provides a "thin film photoelectric conversion device in which a transparent electrode layer made of a transparent conductive oxide, at least one thin film photoelectric conversion unit, and a back electrode are arranged in this order from the light incident side.
  • a transparent conductive oxide layer mainly composed of zinc oxide is formed between them, a conductive additive is added to the transparent conductive oxide layer, and 85 atom% or more of the conductive additive is silicon.
  • the transparent conductive oxide layer contains 2.0 to 8.0 atom% of silicon atoms with respect to zinc atoms, and X2 photoelectron spectroscopy Si2P 1 / This is related to a thin film photoelectric conversion device in which silicon is substantially tetravalent as seen from the two peaks.
  • a transparent conductive oxide layer is formed by magnetron sputtering, and the power density at the time of film formation is 1.5 to 15.0 W / cm 2 .
  • This relates to a manufacturing method in which the pressure is 0.5 Pa or less.
  • FIG. 1 is a schematic cross-sectional view of a thin film photoelectric conversion device according to the present invention.
  • a transparent electrode layer 2 and a pin junction thin film silicon photoelectric conversion layer 3 are sequentially formed on a transparent insulating substrate 1, and a transparent conductive oxide layer 4 and a back electrode 5 are formed thereon.
  • the photoelectric conversion layer 3 includes a first photoelectric conversion unit 31 (front photoelectric conversion unit, top cell), a conductive oxygenated silicon layer (transparent conductive intermediate layer) 32, and a second photoelectric conversion unit 33 (rear photoelectric conversion unit). , Bottom cell).
  • the substrate 1 a known transparent material can be used. Of these, glass and sapphire are preferably used. Specific examples of the glass include alkali glass, borosilicate glass, and non-alkali glass.
  • the thickness of the substrate using glass or sapphire can be arbitrarily selected according to the purpose of use, but 0.5 to 10.0 mm can be exemplified as a preferable range in consideration of the balance between handling and weight. If it is too thin, the strength will be insufficient and it will be easily broken by impact. On the other hand, if the thickness is too large, the weight becomes heavy and the thickness of the device is affected. Therefore, it is difficult to use the portable device, and it is not preferable in terms of transparency and cost.
  • a known transparent electrode material can be used for the transparent electrode layer 2.
  • indium oxide, tin oxide, a composite oxide thereof, zinc oxide, and the like can be given.
  • fluorinated tin oxide and zinc oxide are particularly preferably used among the above because of their resistance to hydrogen plasma.
  • the transparent electrode layer 2 is transparent and has high conductivity. In order to achieve both of these, the crystallinity of the transparent electrode material is preferably high.
  • the sheet resistance in the transparent electrode layer 2 is preferably as low as possible, but is preferably from 5 to 30 ⁇ / ⁇ from the viewpoint of balancing with transparency and as a result capable of producing a photoelectric conversion device with good performance.
  • the manufacturing method of the transparent electrode layer 2 may be any method as long as it can achieve transparency and conductivity, but a method such as a wet process or a dry process can be preferably employed.
  • a method such as a wet process or a dry process can be preferably employed.
  • MOCVD metal organic chemical vapor deposition
  • a reaction between an organometallic compound and water is preferable because a transparent electrode layer with good crystallinity can be formed.
  • the light confinement efficiency in the photoelectric conversion layer can be increased, resulting in improved power generation characteristics. Is preferable.
  • the thin-film silicon photoelectric conversion layer 3 can be configured by arranging, for example, at least one silicon semiconductor laminated structure in which one unit is a pin junction.
  • the silicon structure used may be a polycrystalline structure or an amorphous structure, and the crystal structure may be different depending on p / i / n.
  • the amorphous or crystalline silicon-based material is not only a case where only silicon is used as a main element constituting a semiconductor, but also an alloy material including elements such as carbon, oxygen, nitrogen, and germanium. Good.
  • Each semiconductor layer can be suitably manufactured by a plasma CVD method.
  • the plasma CVD method is a method in which silane gas is used as a silicon material and silicon is formed by using plasma energy, and a p-type layer or an n-type layer is formed by adding an appropriate amount of gas such as diborane or phosphine. This is possible.
  • power generation performance can be improved by stacking a plurality of the photoelectric conversion units.
  • a photoelectric conversion unit having a wide band gap in order from the light incident side is provided, incident light in each wavelength region can be used efficiently, so that an improvement in performance can be expected.
  • a wide-bandgap first photoelectric conversion unit may be disposed on the light incident side, and a narrow-bandgap second photoelectric conversion unit may be disposed thereon.
  • a photoelectric conversion unit 31 mainly composed of amorphous silicon may be disposed as the first photoelectric conversion unit, and a photoelectric conversion unit 33 primarily composed of crystalline silicon may be disposed as the second photoelectric conversion unit. Further, three or more photoelectric conversion units may be arranged.
  • a transparent conductive intermediate layer can be formed between the plurality of photoelectric conversion units, and a layer that selectively reflects and transmits light can be provided. Thereby, in the above example, more light can be taken into the first photoelectric conversion unit, and the transmitted light can contribute to the power generation of the second photoelectric conversion unit.
  • a layer for the purpose of improving electrical contact can be provided between the transparent electrode layer 2 and the photoelectric conversion layer 3.
  • a semiconductor layer having a wider band gap than the photoelectric conversion unit is used as this layer, the electron-hole recombination in the vicinity of the interface between the transparent electrode layer and the photoelectric conversion layer is suppressed.
  • -It is preferable that holes can be efficiently extracted to the electrode, and as a result, conversion efficiency can be improved.
  • An example of such a semiconductor is p-type silicon carbide.
  • a conductive additive is added to the transparent conductive oxide layer 4 in addition to atoms having a minimum impurity concentration.
  • the minimum impurity concentration atom means an atom that is unintentionally contained in the target manufacturing process, an impurity atom derived from an apparatus in the sputtering film forming process, a photoelectric conversion unit or a back surface of a thin film photoelectric conversion apparatus. Atoms by atomic diffusion from an electrode and having a concentration of 0.1 atom% or less.
  • the conductive additive is an additive capable of imparting conductivity by being ionized in the transparent conductive oxide, and examples thereof include silicon, aluminum, and gallium. Further, it is preferable that 85 atom% or more of the conductive additive is made of silicon. By containing silicon within this range, a transparent conductive oxide layer excellent in conductivity and transparency and a thin film photoelectric conversion device excellent in wet heat durability can be produced.
  • the transparent conductive oxide layer 4 in the present invention zinc oxide containing 2.0 to 8.0 atom% of silicon atoms with respect to zinc atoms is used. Further, 1.0 to 7.0 atom%, preferably 1.0 to 6.0 atom%, more preferably 1.0 to 4.5 atom% of silicon atoms are contained. By introducing silicon atoms, it is possible to improve wet heat durability during practical use.
  • atom% is the ratio of the number of silicon atoms to the number of zinc atoms in the layer or target.
  • the doping amount of silicon atoms When the doping amount of silicon atoms is less than any of the above lower limits, the effect of improving wet heat durability is reduced, whereas when the doping amount of silicon atoms is larger than any of the above upper limits, the conductivity is remarkably high. Since it decreases and increases resistance, it is not preferable because it causes a decrease in power generation efficiency.
  • the doping amount of silicon atoms can be controlled by the atomic composition ratio of the sputtering target.
  • the doping amount of silicon can be detected by various elemental analysis methods. For example, the number of atoms can be accurately counted by secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS), or the like.
  • SIMS secondary ion mass spectrometry
  • XPS X-ray photoelectron spectroscopy
  • the transparent conductive oxide layer in the present invention has the same atomic composition of the sputter target and that of the transparent conductive oxide layer 4. .
  • the atomic composition ratio of the sputter target can be controlled by kneading and sintering zinc oxide and silicon or silicon oxide in accordance with the composition ratio when creating the sintered body.
  • the silicon in the transparent conductive oxide layer 4 is preferably substantially tetravalent.
  • the details of the effects of silicon being tetravalent are unknown, but the fact that silicon becomes tetravalent provides a stable conductive carrier, and that silicon has a stable oxidation number. Is estimated to be the cause of durability improvement. In addition, it is presumed that the tetravalent is excellent in transparency because all valence electrons are supplied as carriers.
  • Such an oxidation number of silicon can be detected by X-ray photoelectron spectroscopy (XPS).
  • XPS X-ray photoelectron spectroscopy
  • the X-ray source a general source can be arbitrarily used, but AlK ⁇ or MgK ⁇ is preferably used because a wide energy range can be measured with high resolution.
  • the kinetic energy of photoelectrons generated by incident X-rays is detected, but it is preferable to evaluate the difference from the incident X-ray energy, for example, about 1254 eV for MgK ⁇ , and evaluate it by the binding energy. Focusing on the Si2P1 / 2 peak, it is expected that the Si0-valent peak is detected at a binding energy of about 100 eV. In this case, the Si trivalent peak is detected at about 103 eV, and the Si tetravalent peak is detected at about 104 eV.
  • substantially tetravalent means that the ratio of Si2P 1/2 tetravalent to trivalent (Si 4+ / Si 3+ ) measured by XPS is 0.5 or more. By taking this value, silicon becomes a stable oxidation number, and a transparent conductive oxide excellent in transparency and durability, particularly wet heat durability, can be obtained. Such a ratio can be obtained by drawing a baseline when the binding energy of the spectrum measured by XPS is around 98 to 108 eV, and taking the peak heights of 103 eV and 104 eV from the baseline (see the figure below). 2).
  • the transparent conductive oxide layer 4 can be easily formed by a magnetron sputtering method.
  • a target used for magnetron sputtering a material having the same composition as that of the transparent conductive oxide layer 4 is used. This target is ionized using a carrier gas such as argon gas, and film formation is performed by sputtering.
  • a carrier gas such as argon gas
  • an inert gas such as nitrogen can be used in addition to the argon gas.
  • a high frequency power source can be used in addition to a direct current (DC) power source and a low frequency (AC) power source.
  • the high frequency power source has a frequency such as RF or VHF, and the transparent conductive oxide layer of the present invention can be suitably formed at any frequency.
  • the power density during film formation is preferably 1.5 to 15.0 W / cm 2 , more preferably 3.5 to 12.0 W / cm 2 , and particularly preferably 7.0 to 12.0 W / cm 2 .
  • the film forming speed is not improved, and it is considered to be a problem of crystallinity, but the wet heat durability may not be good.
  • the power density is higher than these upper limits, the transparent conductive oxide layer is re-sputtered by oxygen ions generated in the plasma, resulting in a substrate with a transparent electrode having poor transparency and conductivity. This is not preferable because there is a possibility.
  • the power application method may be a continuous wave or a pulse wave, and can be arbitrarily determined according to the optimum conditions of the film forming apparatus.
  • the pressure in the film forming chamber during sputtering is preferably 0.5 Pa or less.
  • the pressure in the film forming chamber corresponds to the number of carrier gas atoms (including atomic groups and ion states) existing in the film forming chamber, and these atoms are configured in the transparent conductive oxide layer 4 flying from the target. It becomes a scattering source of atoms (including atomic groups and ion states).
  • the pressure in the film forming chamber by setting the pressure in the film forming chamber to 0.5 Pa or less, atoms flying from the target are attached to the substrate with sufficient kinetic energy, and the effective transparent conductive oxide layer 4 is formed. It becomes possible to form.
  • the substrate temperature during sputtering can be any temperature as long as it is equal to or lower than the softening temperature of the substrate, but is particularly preferably 25 ° C. or lower.
  • the kinetic energy of the sputtered particles can be drastically reduced, the crystal grains can be made dense, and depending on the composition, it can be brought into a state close to amorphous. This makes it possible to improve wet heat durability.
  • the film thickness of the transparent conductive oxide layer 4 used on the back electrode side of the solar cell is designed by optical calculation, but is 100 to 1200 mm, more preferably 250 to 1100 mm, more preferably 300 to 1100 mm, and particularly Is preferably 400 to 1100 mm.
  • the film thickness is thinner than any of the above lower limit values, not only the optical characteristics are deteriorated, but also diffusion of the metal material of the back electrode to the photoelectric conversion unit is likely to occur, resulting in deterioration of power generation characteristics. It can be.
  • the transparent conductive oxide made of zinc oxide is characterized by high transparency compared to other transparent conductive oxides. However, it is not less than the band gap (around 3.3 eV) or free electron reflection / absorption region. The light is absorbed below 1 eV, and the amount of absorption increases as the film thickness increases.
  • the optical characteristics referred to here are characteristics related to interference of light reflected at the interface of the photoelectric conversion unit / transparent conductive oxide layer and the interface of the transparent conductive oxide layer / back electrode, and have a necessary wavelength. This is a characteristic necessary for taking light into the photoelectric conversion unit.
  • a thick film is not preferable because not only the optical characteristics but also the effect of light absorption by the transparent conductive oxide layer itself is increased.
  • the film thickness is preferably 100 to 800 mm in view of the reliability of the transparent conductive oxide layer single film.
  • the transparent conductive oxide layer 4 of the present invention is characterized by high wet heat durability. Evaluation of wet heat durability is performed in an environment of 85 ° C. and 85% RH (relative humidity). This is implemented as an acceleration test for severe conditions even in the assumed use environment of the photoelectric conversion device. Taking a thin-film silicon solar cell as an example, the biggest cause of performance degradation in the wet heat durability test is the transparent conductive oxide layer provided between the photoelectric conversion unit and the back electrode. In the case where the layer is made of zinc oxide, hitherto, the performance degradation was particularly remarkable.
  • the change in sheet resistance between immediately after film formation and after 500 hours of wet heat durability test can be 1.0 to 3.0 times, preferably An effect of 1.01 to 2.0 times, further 1.02 to 1.8 times, particularly 1.03 to 1.40 can be expected.
  • the transparent conductive oxide layer becomes resistance, and carriers generated in the photoelectric conversion unit are consumed by generating heat in the transparent conductive oxide layer, and do not contribute to power generation.
  • the transparent conductive oxide layer of the present invention suppresses this and enables stable power generation over a long period of time.
  • the wet heat durability test can be carried out by removing only the back electrode after the photoelectric conversion device is made up to the back electrode, or can be carried out in a state before the back electrode is produced, but the transparent conductive material is formed on a substrate such as glass. It can also be carried out in a so-called single film state formed under the same conditions as the conductive oxide layer 4.
  • the back electrode 5 it is preferable to form at least one metal layer made of at least one material selected from Al, Ag, Au, Cu, Pt and Cr by sputtering or vapor deposition.
  • the back electrode 5 The thicker the back electrode 5 is, the better, but if it is 2000 mm or more, a good back electrode is obtained. If the thickness is smaller than this, the conductivity may not be sufficient, and the function as a light reflecting material important as the back electrode may not be sufficiently achieved. On the other hand, when it is too thick, for example, 10,000 mm, it is not preferable from the viewpoint of cost.
  • a scanning electron microscope JSM-6390-LA manufactured by JEOL Ltd.
  • a spectroscopic ellipsometer VASE manufactured by JA Woollam Co., Ltd.
  • X-ray photoelectron spectroscopy was calculated using MgK ⁇ (1254 eV) as the X-ray source and the binding energy of the Si 2 P 1/2 peak at a zero valence of about 100 eV. Fitting was carried out by calculating the transparent conductive oxide layer using the Cauchy model.
  • Photoelectric conversion characteristics were measured by irradiating simulated sunlight with an energy density of 100 mW / cm 2 at 25 ° C. using a solar simulator having a spectral distribution of AM (air mass) 1.5, and opening the circuit.
  • the voltage (Voc), short circuit current density (Jsc), fill factor (FF), power generation efficiency (Eff), and voltage-current characteristics were evaluated.
  • the open circuit voltage (Voc) is a voltage generated when light is irradiated when a very high resistance voltmeter is attached between the anode and the cathode of the solar cell (which can be considered that the actual current is zero). is there.
  • the short-circuit current is a current generated when light is irradiated without applying a potential, and the short-circuit current density (Jsc) is obtained by converting the short-circuit current per unit area.
  • the fill factor (FF) is calculated by (the output at the optimum operating point (the point at which the output is the highest)) / (short circuit current ⁇ open circuit voltage).
  • the power generation efficiency (Eff) is the ratio of the maximum output to the incident energy. In any case, a larger numerical value is preferable.
  • Example 1 A thin film photoelectric conversion device shown in FIG. 1 was manufactured.
  • a non-alkali glass substrate (thickness: 1.1 mm) was used as the translucent substrate 1.
  • the transparent electrode layer 2 was made of fluorinated tin oxide (F: SnO 2 ) produced by a thermal CVD method. At this time, the film thickness of the transparent electrode layer 2 was 800 nm, the sheet resistance was 10 ohm / ⁇ , and the haze value was 15 to 20%.
  • F fluorinated tin oxide
  • a boron-doped p-type silicon carbide (SiC) layer is 10 nm
  • a non-doped amorphous silicon photoelectric conversion layer is 200 nm
  • a phosphorus-doped n-type ⁇ c-Si layer is formed.
  • the film was formed with a film thickness of 20 nanometers.
  • the first photoelectric conversion unit 31 (top cell) made of amorphous silicon having a pin junction was formed.
  • the conductive oxygenated silicon layer 32 was formed by a plasma CVD apparatus without taking the substrate on which the first photoelectric conversion unit 31 was formed into the atmosphere.
  • the film-forming conditions at this time were such that the plasma excitation frequency was 13.56 MHz, the substrate temperature was 150 ° C., and the reaction chamber pressure was 666 Pa.
  • SiH 4 , PH 3 , CO 2 , and H 2 were used as source gases introduced into the plasma CVD reaction chamber. Under the above conditions, a conductive oxygenated silicon layer 32 having a thickness of 600 mm was formed.
  • the boron-doped p-type microcrystalline silicon layer has a thickness of 15 nm
  • the non-doped crystalline silicon photoelectric conversion layer has a thickness of 1500 nm
  • the phosphorus-doped n-type microcrystalline silicon layer has a thickness of 20 nm.
  • the in-process product in which the crystalline silicon photoelectric conversion unit has been formed is taken out from the high-frequency plasma CVD apparatus to the atmosphere, and then introduced into the film forming chamber of the high-frequency magnetron sputtering apparatus.
  • the conductive oxide layer 4 was formed.
  • the transparent conductive oxide layer 4 was formed under the conditions shown in Table 1 for the sputtering target material and film forming power density.
  • the film forming pressure was set to 0.2 Pa
  • the substrate temperature was set to 150 ° C.
  • the substrate / target distance was set to 60 mm
  • Table 1 Film formation was carried out to the film thickness shown.
  • a silicon oxide kneaded with zinc oxide so as to have a doping amount shown in Table 1 and sintered at a high temperature was bonded to a backing plate made of oxygen-free copper by hot pressing.
  • an Ag film having a thickness of 250 nanometers was formed as a back metal electrode layer using a vacuum deposition apparatus.
  • the degree of vacuum during film formation was 1 ⁇ 10 ⁇ 4 Pa or less, and the film formation rate was 0.2 ⁇ 0.02 nanometer / second.
  • Table 2 shows the photoelectric conversion characteristics of the thin film photoelectric conversion device thus formed, specifically, the short circuit current density (Jsc), the open circuit voltage (Voc), the fill factor (FF), and the power generation efficiency (Eff). .
  • Comparative Example 3 did not show a function as a thin film photoelectric conversion device. This is presumably because the current did not flow because the resistance of the transparent conductive oxide layer was very large.
  • FIG. 2 shows X-ray photoelectron spectroscopy (XPS) spectra of the transparent conductive oxides of Examples and Comparative Examples of the present invention.
  • the horizontal axis represents the binding energy, which indicates the binding energy related to the 2P orbit of silicon.
  • the vertical axis indicates the X-ray detection intensity (arbitrary).
  • the broken line graph (a) in the figure shows the binding energy of Si 2 P 1/2 of the transparent conductive oxide layer 4 of Comparative Example 5, and the solid line graph (b) shows the transparent conductive oxide layer 4 of Example 5. This shows the binding energy of Si2P1 / 2 .
  • These are representative examples of Examples and Comparative Examples.
  • the peak of 103 eV is very large, and it can be estimated that trivalent silicon is dominant.
  • the solid line graph (b) the peak intensity at 103 eV decreases, and the peak at 104 eV has become apparent, so that it can be determined that the valence of silicon has become predominant.
  • Table 4 shows the results of X-ray photoelectron spectroscopy.
  • the transparent conductive oxide layer formed under the conditions of the example has a relatively large binding energy peak of about 104 eV indicating tetravalent silicon, and the ratio of the tetravalent to trivalent peak ratio of Si 2 P 1/2 (Si 4 + / Si 3+ ) was 0.5 or more.
  • the peak of about 103 eV indicating trivalent silicon is preferential, and the ratio of the tetravalent to trivalent peak of Si2P1 / 2 (Si 4+ / Si 3+ ) was less than 0.5.
  • any peak ratio (Si 4+ / Si 3+) is a comparative example 2,3,5,6,7,10 less than 0.5, peak ratio (Si 4+ / Si 3+) 0.
  • the performance is lower than the example of 5 or more.
  • Comparative Example 1 does not contain silicon in the conductive additive
  • Comparative Example 4 is considered to have low performance because the ratio of silicon atoms in the conductive additive is low.
  • Comparative Examples 8 and 9 it is considered that the performance is lowered due to the influence of the film thickness of the transparent conductive oxide layer being too large or too small.
  • Comparative Example 8 due to the influence of absorption loss in the transparent conductive oxide layer 4 and low interference effect due to the film thickness being too thick, in Comparative Example 9 due to the influence of low interference effect and parasitic absorption of the silver back electrode. It is considered.
  • Comparative Example 6 the short-circuit current is particularly inferior among the solar cell characteristics as compared with the Example. This is presumed to be due to the effect of absorption loss due to the transparent conductive oxide layer 4, and this may be due to the fact that the Si 4+ / Si 3+ ratio is small and the absorption loss due to trivalent silicon is large.
  • a thin film photoelectric conversion device having excellent power generation efficiency can be produced by forming a zinc oxide transparent conductive oxide layer containing silicon between the photoelectric conversion unit and the back electrode. This is considered to be because the amount of light taken into the photoelectric conversion unit is increased by improving the light transmittance of the transparent conductive oxide layer. The reason why the light transmittance is improved is considered to be that the carrier concentration in the transparent conductive oxide is lowered. Furthermore, when a wet heat durability test was performed in an environment of 85 ° C. and 85% RH, it was found that the transparent conductive oxide layers of the examples had small changes in sheet resistance and excellent wet heat durability.

Abstract

Disclosed is a thin film photoelectric conversion device wherein a highly transparent and highly durable transparent electrically conductive oxide layer is formed between the photoelectric conversion unit and the back surface electrode to improve photoelectric efficiency. A silicon-containing layer that has zinc oxide as the main component is introduced as the transparent electrically conductive oxide layer between the photoelectric conversion layer and the back surface electrode. With respect to zinc atoms, 2.0‑8.0 atom% of silicon atoms is included. A highly transparent and highly durable transparent electrically conductive oxide layer can be formed, since the silicon is essentially tetravalent when seen in the Si2P½ peak in X-ray photoelectron spectroscopy of the transparent electrically conductive oxide.

Description

薄膜光電変換装置およびその製造方法Thin film photoelectric conversion device and manufacturing method thereof
　本発明は、薄膜光電変換装置の光電変換ユニットと裏面電極の間に好適な透明導電酸化物層を用いることで、光電変換ユニット内の光の取り込み効率を向上し、発生電流量向上を可能とする薄膜光電変換装置およびその製造方法に関するものである。 The present invention uses a suitable transparent conductive oxide layer between the photoelectric conversion unit and the back electrode of the thin film photoelectric conversion device, thereby improving the light capturing efficiency in the photoelectric conversion unit and increasing the amount of generated current. The present invention relates to a thin film photoelectric conversion device and a manufacturing method thereof.
　薄膜太陽電池に代表される薄膜光電変換装置には、非晶質や薄膜多結晶シリコンのようにｐ型またはｎ型にドーピングしたシリコン半導体で真性シリコン（ｉ型）半導体を挟んだｐ－ｉ－ｎ構造に形成された薄膜シリコン太陽電池や、銅－インジウム－セレン（ＣＩＳ型）や銅－インジウム－ガリウム－セレン（ＣＩＧＳ型）のような化合物半導体を用いたカルコパライト型薄膜太陽電池が広く研究開発が行われている他に、ワイドギャップ半導体を用いた太陽電池や有機薄膜太陽電池のような薄膜太陽電池など、非常に多くの種類が挙げられる。 A thin film photoelectric conversion device typified by a thin film solar cell has a pi- structure in which an intrinsic silicon (i-type) semiconductor is sandwiched between silicon semiconductors doped in p-type or n-type, such as amorphous or thin-film polycrystalline silicon. Widely researched and developed thin-film silicon solar cells with n-structures and chalcopyrite thin-film solar cells using compound semiconductors such as copper-indium-selenium (CIS type) and copper-indium-gallium-selenium (CIGS type) In addition, there are numerous types such as a solar cell using a wide gap semiconductor and a thin film solar cell such as an organic thin film solar cell.
　このような薄膜光電変換装置においては、光電変換ユニットに入射した光をより有効に利用するため、光反射率の高い金属材料により構成される裏面電極層が形成される。光電変換ユニットに吸収されずに透過した光の大部分は、裏面電極層により反射され光電変換ユニットに再入射して、再び光電変換が行われる。 In such a thin film photoelectric conversion device, in order to more effectively use the light incident on the photoelectric conversion unit, a back electrode layer made of a metal material having a high light reflectance is formed. Most of the light transmitted without being absorbed by the photoelectric conversion unit is reflected by the back electrode layer, reenters the photoelectric conversion unit, and photoelectric conversion is performed again.
　裏面電極は、銀やアルミニウムなどの光反射率の高い金属材料により形成されることで、光電変換ユニットへの光の取り込み量を向上することが可能となるが、主にシリコン系半導体からなる光電変換ユニット上に銀やアルミニウムなどの裏面電極を直接形成しても、発電特性が向上しにくい。これは、裏面電極の微細構造に由来する寄生吸収によると考えられる。下記非特許文献１には、光電変換ユニット上に形成された裏面電極における寄生吸収により変換効率が低下することが記載されている。 The back electrode is made of a metal material having a high light reflectance such as silver or aluminum, so that the amount of light taken into the photoelectric conversion unit can be improved. Even if the back electrode such as silver or aluminum is directly formed on the conversion unit, it is difficult to improve the power generation characteristics. This is considered to be due to parasitic absorption derived from the fine structure of the back electrode. Non-Patent Document 1 below describes that conversion efficiency decreases due to parasitic absorption in a back electrode formed on a photoelectric conversion unit.
　また、裏面電極材料を構成する原子が光電変換ユニットに拡散することに起因する性能低下の可能性もある。このような問題点を解消するために、光電変換ユニットと裏面電極との間に透明導電性酸化物層を設けることが提案されている。例えば下記特許文献１には、二層の透明導電性酸化物層、すなわち、上部透明層と、さらに光学特性を向上させるための酸化珪素などからなる低屈折率層を配置する技術が提案されている。 Also, there is a possibility of performance degradation due to diffusion of atoms constituting the back electrode material into the photoelectric conversion unit. In order to solve such problems, it has been proposed to provide a transparent conductive oxide layer between the photoelectric conversion unit and the back electrode. For example, Patent Document 1 below proposes a technique in which two transparent conductive oxide layers, that is, an upper transparent layer and a low refractive index layer made of silicon oxide or the like for further improving optical characteristics are arranged. Yes.
　上部透明層用の透明導電性酸化物材料として、インジウム錫複合酸化物（ＩＴＯ）や酸化亜鉛（ＺｎＯ）などが挙げられる。 Examples of the transparent conductive oxide material for the upper transparent layer include indium tin composite oxide (ITO) and zinc oxide (ZnO).
　このような透明導電性酸化物層は、二重層であるため、製造設備が煩雑になりやすく、生産性とコストに課題がある。さらに、湿熱耐久性が悪いという課題がある。 Since such a transparent conductive oxide layer is a double layer, the manufacturing equipment tends to be complicated, and there are problems in productivity and cost. Furthermore, there exists a subject that wet heat durability is bad.
　なお、裏面電極の寄生吸収を抑制するものではないが、下記特許文献２には、光入射側の透明電極としてＺｎＯに珪素等がドーピングされる技術が記載されている。 In addition, although it does not suppress the parasitic absorption of the back electrode, the following Patent Document 2 describes a technique in which silicon or the like is doped into ZnO as a transparent electrode on the light incident side.
特開２００７－２６６０９５号公報JP 2007-266095 A 特開２００２－２１７４２９号公報JP 2002-217429 A
　本発明は、薄膜光電変換装置において、裏面電極に起因する寄生吸収を抑制し、その結果として光電変換層に取り込まれる光の量を増加し、発生電流量を向上できる技術を提供することを、解決すべき課題とする。 In the thin film photoelectric conversion device, the present invention provides a technique that can suppress parasitic absorption caused by the back electrode, increase the amount of light taken into the photoelectric conversion layer as a result, and improve the amount of generated current. It is a problem to be solved.
　上記課題を解決する為に、本発明者らは鋭意検討を重ねた結果、本発明に至った。すなわち本発明は、以下の構成を有するものである。 In order to solve the above-mentioned problems, the present inventors have intensively studied to arrive at the present invention. That is, the present invention has the following configuration.
　光入射側より透明導電性酸化物からなる透明電極層、少なくとも１つの薄膜光電変換ユニット、及び裏面電極が順に配置された薄膜光電変換装置において、上記薄膜光電変換ユニットと裏面電極の間に酸化亜鉛を主成分とする透明導電性酸化物層が形成されており、該透明導電性酸化物層には導電性添加物が添加され、且つ該導電性添加物の８５ａｔｏｍ％以上が珪素原子からなり、且つ該透明導電性酸化物層中に亜鉛原子に対して２．０～８．０ａｔｏｍ％の珪素原子が含まれており、さらに透明導電性酸化物のＸ線光電子分光Ｓｉ２Ｐ1/2ピークから見て、珪素が実質４価である薄膜光電変換装置。 In the thin film photoelectric conversion device in which a transparent electrode layer made of a transparent conductive oxide, at least one thin film photoelectric conversion unit, and a back electrode are arranged in this order from the light incident side, zinc oxide is interposed between the thin film photoelectric conversion unit and the back electrode. A transparent conductive oxide layer containing as a main component, a conductive additive is added to the transparent conductive oxide layer, and 85 atom% or more of the conductive additive consists of silicon atoms, In addition, the transparent conductive oxide layer contains 2.0 to 8.0 atom% of silicon atoms with respect to zinc atoms, and is further seen from the X-ray photoelectron spectroscopy Si2P 1/2 peak of the transparent conductive oxide. A thin film photoelectric conversion device in which silicon is substantially tetravalent.
　本発明の薄膜光電変換装置において、透明導電性酸化物層の膜厚が１００～１２００Åであることが好ましい。 In the thin film photoelectric conversion device of the present invention, the transparent conductive oxide layer preferably has a thickness of 100 to 1200 mm.
　本発明の薄膜光電変換装置において、透明導電性酸化物層の膜厚が１００～８００Åであって、且つ８５℃・８５％相対湿度環境下における湿熱耐久性試験を実施した場合において、製膜直後と５００時間経過後のシート抵抗変化が１．０～３．０倍である透明導電性酸化物層が光電変換ユニットと裏面電極間に配置されていることが好ましい。 In the thin film photoelectric conversion device of the present invention, when the thickness of the transparent conductive oxide layer is 100 to 800 mm and a wet heat durability test is performed in an environment of 85 ° C. and 85% relative humidity, It is preferable that a transparent conductive oxide layer having a sheet resistance change of 1.0 to 3.0 times after 500 hours is disposed between the photoelectric conversion unit and the back electrode.
　本発明の薄膜光電変換装置は、非晶質シリコンを主成分とする薄膜光電変換ユニットと、結晶質シリコンを主成分とする薄膜光電変換ユニットとを有するもの（いわゆる多接合型）であってもよい。 The thin film photoelectric conversion device of the present invention is a device having a thin film photoelectric conversion unit mainly composed of amorphous silicon and a thin film photoelectric conversion unit mainly composed of crystalline silicon (so-called multi-junction type). Good.
　本発明の薄膜光電変換装置の製造方法として、透明導電性酸化物層がマグネトロンスパッタリング法により製膜され、製膜時のパワー密度が１．５～１５．０Ｗ／ｃｍ2であり、さらに製膜時の圧力が０．５Ｐａ以下であることが好ましい。 As a method for producing a thin film photoelectric conversion device of the present invention, a transparent conductive oxide layer is formed by magnetron sputtering, and the power density at the time of film formation is 1.5 to 15.0 W / cm 2. It is preferable that the pressure at the time is 0.5 Pa or less.
　本発明により、裏面電極の寄生吸収を抑制し、光電変換層への光の取り込み量を向上させることができる。本発明に係る透明導電性酸化物層は、高い透明性と導電性を高いレベルでバランスさせることが可能となるものであり、結果として発電特性の向上が可能である。さらに、湿熱耐久性を向上させることが可能であり、変換効率・耐久性の両方に優れる薄膜光電変換装置を提供することができる。 According to the present invention, parasitic absorption of the back electrode can be suppressed, and the amount of light taken into the photoelectric conversion layer can be improved. The transparent conductive oxide layer according to the present invention can balance high transparency and conductivity at a high level, and as a result, power generation characteristics can be improved. Furthermore, it is possible to provide a thin film photoelectric conversion device that can improve wet heat durability and is excellent in both conversion efficiency and durability.
本願発明に係る薄膜光電変換装置の模式的断面図である。It is typical sectional drawing of the thin film photoelectric conversion apparatus which concerns on this invention. 本願発明の実施例及び比較例の透明導電性酸化物のＸ線光電子分光スペクトルである。It is an X-ray photoelectron spectroscopy spectrum of the transparent conductive oxide of the Example of this invention, and a comparative example.
　本発明は「光入射側より透明導電性酸化物からなる透明電極層、少なくとも１つの薄膜光電変換ユニット、及び裏面電極が順に配置された薄膜光電変換装置において、上記薄膜光電変換ユニットと裏面電極の間に酸化亜鉛を主成分とする透明導電性酸化物層が形成されており、該透明導電性酸化物層には導電性添加物が添加され、且つ該導電性添加物の８５ａｔｏｍ％以上が珪素原子からなり、且つ該透明導電性酸化物層中に亜鉛原子に対して２．０～８．０ａｔｏｍ％の珪素原子が含まれており、さらに透明導電性酸化物のＸ線光電子分光Ｓｉ２Ｐ1/2ピークから見て、珪素が実質４価である薄膜光電変換装置」に関するものである。 The present invention provides a "thin film photoelectric conversion device in which a transparent electrode layer made of a transparent conductive oxide, at least one thin film photoelectric conversion unit, and a back electrode are arranged in this order from the light incident side. A transparent conductive oxide layer mainly composed of zinc oxide is formed between them, a conductive additive is added to the transparent conductive oxide layer, and 85 atom% or more of the conductive additive is silicon. The transparent conductive oxide layer contains 2.0 to 8.0 atom% of silicon atoms with respect to zinc atoms, and X2 photoelectron spectroscopy Si2P 1 / This is related to a thin film photoelectric conversion device in which silicon is substantially tetravalent as seen from the two peaks.
　さらに当該変換装置の製造方法として、「透明導電性酸化物層がマグネトロンスパッタリング法により製膜され、製膜時のパワー密度が１．５～１５．０Ｗ／ｃｍ2であり、さらに製膜時の圧力が０．５Ｐａ以下である製造方法」に関するものである。 Further, as a manufacturing method of the conversion device, “a transparent conductive oxide layer is formed by magnetron sputtering, and the power density at the time of film formation is 1.5 to 15.0 W / cm 2 . This relates to a manufacturing method in which the pressure is 0.5 Pa or less.
　以下、本発明に係る透明電極付き基板の代表的な態様を説明する。図１は本発明に係る薄膜光電変換装置の模式的断面図である。透明絶縁性基板上１に透明電極層２、ｐ－ｉ－ｎ接合した薄膜シリコン光電変換層３が順に形成され、その上に透明導電性酸化物層４および裏面電極５が形成されている。光電変換層３は、第１の光電変換ユニット３１（前方光電変換ユニット、トップセル）、導電性酸素化シリコン層（透明導電性中間層）３２、第２の光電変換ユニット３３（後方光電変換ユニット、ボトムセル）からなる。 Hereinafter, typical aspects of the substrate with a transparent electrode according to the present invention will be described. FIG. 1 is a schematic cross-sectional view of a thin film photoelectric conversion device according to the present invention. A transparent electrode layer 2 and a pin junction thin film silicon photoelectric conversion layer 3 are sequentially formed on a transparent insulating substrate 1, and a transparent conductive oxide layer 4 and a back electrode 5 are formed thereon. The photoelectric conversion layer 3 includes a first photoelectric conversion unit 31 (front photoelectric conversion unit, top cell), a conductive oxygenated silicon layer (transparent conductive intermediate layer) 32, and a second photoelectric conversion unit 33 (rear photoelectric conversion unit). , Bottom cell).
　上記基材１については、公知の透明材料を用いることができる。その中でもガラス、サファイヤを用いることが好ましい。ガラスの具体例としては、アルカリガラスやホウ珪酸ガラス、無アルカリガラスなどがあげられる。 For the substrate 1, a known transparent material can be used. Of these, glass and sapphire are preferably used. Specific examples of the glass include alkali glass, borosilicate glass, and non-alkali glass.
　ガラスあるいはサファイヤを用いた基板の厚みは使用目的により任意に選択することができるが、取り扱いと重量のバランスを加味して、０．５ｍｍ～１０．０ｍｍが好ましい範囲として例示できる。薄すぎると強度が不足するために、衝撃により割れやすい。また厚すぎると重量が重くなることと、機器の厚みに影響を及ぼすことから、ポータブル機器への利用は困難となる上、透明性とコストの面からも好ましくない。 The thickness of the substrate using glass or sapphire can be arbitrarily selected according to the purpose of use, but 0.5 to 10.0 mm can be exemplified as a preferable range in consideration of the balance between handling and weight. If it is too thin, the strength will be insufficient and it will be easily broken by impact. On the other hand, if the thickness is too large, the weight becomes heavy and the thickness of the device is affected. Therefore, it is difficult to use the portable device, and it is not preferable in terms of transparency and cost.
　透明電極層２には公知の透明電極材料を用いることができる。例えば、酸化インジウムや酸化錫およびその複合酸化物、酸化亜鉛などが挙げられる。薄膜シリコン太陽電池用の透明電極として使用する場合には、水素プラズマに対する耐性から、上記の中でも特にフッ素化酸化錫や酸化亜鉛が良好に使用される。 A known transparent electrode material can be used for the transparent electrode layer 2. For example, indium oxide, tin oxide, a composite oxide thereof, zinc oxide, and the like can be given. When used as a transparent electrode for a thin-film silicon solar cell, fluorinated tin oxide and zinc oxide are particularly preferably used among the above because of their resistance to hydrogen plasma.
　透明電極層２には、透明であることと高い導電性を有することが特に重要である。これらを両立する為に、透明電極材料の結晶性が高いことが好ましい。透明電極層２におけるシート抵抗は低いほど好ましいが、透明性とのバランス、その結果として性能の良い光電変換装置を製造できるという面から５～３０Ω／□が好ましい。 It is particularly important that the transparent electrode layer 2 is transparent and has high conductivity. In order to achieve both of these, the crystallinity of the transparent electrode material is preferably high. The sheet resistance in the transparent electrode layer 2 is preferably as low as possible, but is preferably from 5 to 30 Ω / □ from the viewpoint of balancing with transparency and as a result capable of producing a photoelectric conversion device with good performance.
　透明電極層２の製造方法は、透明性と導電性を達成可能な方法であればどのような手法でも構わないが、好ましくはウェットプロセスやドライプロセスなどの手法を採用することが出来る。例えば有機金属化合物と水との反応を利用した有機金属化学的気相堆積（ＭＯＣＶＤ）などが、結晶性の良い透明電極層が形成できるので好ましい。 The manufacturing method of the transparent electrode layer 2 may be any method as long as it can achieve transparency and conductivity, but a method such as a wet process or a dry process can be preferably employed. For example, metal organic chemical vapor deposition (MOCVD) using a reaction between an organometallic compound and water is preferable because a transparent electrode layer with good crystallinity can be formed.
　さらに、透明導電性酸化物の結晶方位を制御して透明電極層２表面にテクスチャ形状を形成すると、光電変換層内での光閉じ込め効率を上げることができて、結果として発電特性を向上することが可能となるので好ましい。 Furthermore, by controlling the crystal orientation of the transparent conductive oxide to form a textured shape on the surface of the transparent electrode layer 2, the light confinement efficiency in the photoelectric conversion layer can be increased, resulting in improved power generation characteristics. Is preferable.
　薄膜シリコン光電変換層３としては例えば１ユニットがｐ－ｉ－ｎ接合からなるシリコン半導体積層構造体を少なくとも１つ配置して構成することができる。用いられるシリコンの構造としては多結晶構造や非晶質構造のものを用いることができ、ｐ／ｉ／ｎで結晶構造が異なっても構わない。なお、非晶質あるいは結晶質のシリコン系材料としては、半導体を構成する主要元素としてシリコンのみを用いる場合だけでなく、炭素、酸素、窒素、ゲルマニウムなどの元素をも含む合金材料であってもよい。 The thin-film silicon photoelectric conversion layer 3 can be configured by arranging, for example, at least one silicon semiconductor laminated structure in which one unit is a pin junction. The silicon structure used may be a polycrystalline structure or an amorphous structure, and the crystal structure may be different depending on p / i / n. Note that the amorphous or crystalline silicon-based material is not only a case where only silicon is used as a main element constituting a semiconductor, but also an alloy material including elements such as carbon, oxygen, nitrogen, and germanium. Good.
　各々の半導体層は、プラズマＣＶＤ法により好適に作製することができる。プラズマＣＶＤ法とは、シランガスをシリコン材料として用い、プラズマエネルギーを利用してシリコンを形成する方法であり、ｐ型層やｎ型層の製膜は、それぞれジボランやホスフィンなどのガスを適量添加することで可能となる。 Each semiconductor layer can be suitably manufactured by a plasma CVD method. The plasma CVD method is a method in which silane gas is used as a silicon material and silicon is formed by using plasma energy, and a p-type layer or an n-type layer is formed by adding an appropriate amount of gas such as diborane or phosphine. This is possible.
　さらに、上記光電変換ユニットを複数積み重ねることで発電性能を向上させることができる。光電変換ユニットを複数ユニット積層する場合、光入射側から順にバンドギャップが広い光電変換ユニットを設けると、各波長域の入射光を効率良く利用できるので、性能向上が期待できる。 Furthermore, power generation performance can be improved by stacking a plurality of the photoelectric conversion units. When a plurality of photoelectric conversion units are stacked, if a photoelectric conversion unit having a wide band gap in order from the light incident side is provided, incident light in each wavelength region can be used efficiently, so that an improvement in performance can be expected.
　例えば薄膜シリコン太陽電池の場合には、ワイドバンドギャップの第１の光電変換ユニットを光入射側に配置し、その上にナローバンドギャップの第２の光電変換ユニットを配置すればよい。この場合、第１の光電変換ユニットとして非晶質シリコンを主成分とする光電変換ユニット３１を、第２の光電変換ユニットとして結晶質シリコンを主成分とする光電変換ユニット３３を配置すればよい。さらに３つ以上の光電変換ユニットを配置してもかまわない。 For example, in the case of a thin-film silicon solar cell, a wide-bandgap first photoelectric conversion unit may be disposed on the light incident side, and a narrow-bandgap second photoelectric conversion unit may be disposed thereon. In this case, a photoelectric conversion unit 31 mainly composed of amorphous silicon may be disposed as the first photoelectric conversion unit, and a photoelectric conversion unit 33 primarily composed of crystalline silicon may be disposed as the second photoelectric conversion unit. Further, three or more photoelectric conversion units may be arranged.
　これら複数の光電変換ユニット間には、透明導電性中間層を形成し、光の反射と透過を選択的に行う層を設けることができる。これにより、上記の例では第１の光電変換ユニットに取り込まれる光をより多くすることができ、さらに透過した光で第２の光電変換ユニットの発電に寄与することができる。 A transparent conductive intermediate layer can be formed between the plurality of photoelectric conversion units, and a layer that selectively reflects and transmits light can be provided. Thereby, in the above example, more light can be taken into the first photoelectric conversion unit, and the transmitted light can contribute to the power generation of the second photoelectric conversion unit.
　透明電極層２と光電変換層３の間には電気的なコンタクトの改善を目的とした層を設けることができる。この層としては、光電変換ユニットよりもバンドギャップの広い半導体層を用いると、透明電極層と光電変換層の界面付近での電子－正孔の再結合を抑制するので光電変換層で生成した電子－正孔を電極に効率よく取り出すことが可能となり、結果として変換効率を向上することが可能となり好ましい。この様な半導体としては例えばｐ型シリコンカーバイドなどが挙げられる。 Between the transparent electrode layer 2 and the photoelectric conversion layer 3, a layer for the purpose of improving electrical contact can be provided. When a semiconductor layer having a wider band gap than the photoelectric conversion unit is used as this layer, the electron-hole recombination in the vicinity of the interface between the transparent electrode layer and the photoelectric conversion layer is suppressed. -It is preferable that holes can be efficiently extracted to the electrode, and as a result, conversion efficiency can be improved. An example of such a semiconductor is p-type silicon carbide.
　透明導電性酸化物層４に、最低限の不純物濃度の原子以外に導電性添加物が添加される。ここで最低限の不純物濃度の原子とは、ターゲットの製造過程で意図せずに含有される原子や、スパッタリング製膜過程での装置由来による不純物原子や、薄膜光電変換装置の光電変換ユニットや裏面電極からの微量の原子拡散による原子であって、濃度として０．１ａｔｏｍ％以下のものをいう。導電性添加物は、透明導電性酸化物内でイオン化することで導電性を付与することができる添加物であり、例えば、珪素、アルミニウム、ガリウム等である。さらに、導電性添加物のうち８５ａｔｏｍ％以上が珪素からなることが好ましい。この範囲で珪素を含有することで、導電性と透明性に優れる透明導電性酸化物層および湿熱耐久性に優れた薄膜光電変換装置を作製することができる。 A conductive additive is added to the transparent conductive oxide layer 4 in addition to atoms having a minimum impurity concentration. Here, the minimum impurity concentration atom means an atom that is unintentionally contained in the target manufacturing process, an impurity atom derived from an apparatus in the sputtering film forming process, a photoelectric conversion unit or a back surface of a thin film photoelectric conversion apparatus. Atoms by atomic diffusion from an electrode and having a concentration of 0.1 atom% or less. The conductive additive is an additive capable of imparting conductivity by being ionized in the transparent conductive oxide, and examples thereof include silicon, aluminum, and gallium. Further, it is preferable that 85 atom% or more of the conductive additive is made of silicon. By containing silicon within this range, a transparent conductive oxide layer excellent in conductivity and transparency and a thin film photoelectric conversion device excellent in wet heat durability can be produced.
　本発明における透明導電性酸化物層４には、珪素原子が亜鉛原子に対して２．０～８．０ａｔｏｍ％含有される酸化亜鉛を用いる。さらに、珪素原子が１．０～７．０ａｔｏｍ％、好ましくは１．０～６．０ａｔｏｍ％、さらに好ましくは１．０～４．５ａｔｏｍ％含有されている。珪素原子を導入することで実用時の湿熱耐久性を向上することが可能である。ここでいうａｔｏｍ％とは、層あるいはターゲット中の亜鉛原子数に対する珪素原子数の割合のことである。 For the transparent conductive oxide layer 4 in the present invention, zinc oxide containing 2.0 to 8.0 atom% of silicon atoms with respect to zinc atoms is used. Further, 1.0 to 7.0 atom%, preferably 1.0 to 6.0 atom%, more preferably 1.0 to 4.5 atom% of silicon atoms are contained. By introducing silicon atoms, it is possible to improve wet heat durability during practical use. Here, atom% is the ratio of the number of silicon atoms to the number of zinc atoms in the layer or target.
　珪素原子を導入することで、結晶構造に適度な歪みを与え、残留応力のバランスをとることで、薄膜光電変換装置の湿熱耐久性を向上することが可能となると考えられる。 It is considered that by introducing silicon atoms, it is possible to improve the wet heat durability of the thin film photoelectric conversion device by giving an appropriate strain to the crystal structure and balancing the residual stress.
　珪素原子のドーピング量が上記下限値のいずれかより少ない場合は、湿熱耐久性向上の効果が低下し、一方、上記上限値のいずれかより珪素原子のドーピング量が多い場合は、導電性が著しく低下し抵抗が増すため、発電効率の低下の原因となるため好ましくない。珪素原子のドーピング量は、スパッタターゲットの原子組成比により制御することができる。 When the doping amount of silicon atoms is less than any of the above lower limits, the effect of improving wet heat durability is reduced, whereas when the doping amount of silicon atoms is larger than any of the above upper limits, the conductivity is remarkably high. Since it decreases and increases resistance, it is not preferable because it causes a decrease in power generation efficiency. The doping amount of silicon atoms can be controlled by the atomic composition ratio of the sputtering target.
　珪素のドーピング量は各種元素分析法で検出することが可能であるが、例えば、二次イオン質量分析（ＳＩＭＳ）やＸ線光電子分光（ＸＰＳ）などにより精度よく原子数をカウントすることができる。 The doping amount of silicon can be detected by various elemental analysis methods. For example, the number of atoms can be accurately counted by secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS), or the like.
　本発明における透明導電性酸化物層は、スパッタターゲットの原子組成と透明導電性酸化物層４の原子組成が等しくなることが、ＥＤＳ（エネルギー分散型Ｘ線分析）などの元素分析からわかっている。スパッタターゲットの原子組成比の制御は、焼結体作成時に酸化亜鉛と珪素または酸化珪素を組成比に従って混錬し、焼結することで実施可能である。 It is known from elemental analysis such as EDS (energy dispersive X-ray analysis) that the transparent conductive oxide layer in the present invention has the same atomic composition of the sputter target and that of the transparent conductive oxide layer 4. . The atomic composition ratio of the sputter target can be controlled by kneading and sintering zinc oxide and silicon or silicon oxide in accordance with the composition ratio when creating the sintered body.
　透明導電性酸化物層４中の珪素は実質４価であることが好ましい。珪素が４価であることが及ぼす影響についての詳細は不明であるが、珪素が４価となることで安定な導電性キャリアが供給されることと、珪素の４価が安定酸化数であることが耐久性向上の原因となっていると推定される。また４価の方が、価電子がキャリアとしてすべて供給されている事から透明性にも優れていることが推定される。 The silicon in the transparent conductive oxide layer 4 is preferably substantially tetravalent. The details of the effects of silicon being tetravalent are unknown, but the fact that silicon becomes tetravalent provides a stable conductive carrier, and that silicon has a stable oxidation number. Is estimated to be the cause of durability improvement. In addition, it is presumed that the tetravalent is excellent in transparency because all valence electrons are supplied as carriers.
　このような珪素の酸化数はＸ線光電子分光（ＸＰＳ）により検出可能である。Ｘ線源としては、一般的なものを任意に使用することができるが、広いエネルギー範囲を高分解能で測定可能であることからＡｌＫαやＭｇＫαを用いることが好ましい。ＸＰＳの通常の測定では入射Ｘ線により発生する光電子の運動エネルギーを検出するが、入射Ｘ線のエネルギー、例えばＭｇＫαでは約１２５４ｅＶ、からの差をとり結合エネルギーで評価することが好ましい。Ｓｉ２Ｐ1/2のピークに注目すると、Ｓｉ０価のピークは結合エネルギーが約１００ｅＶに検出されることが予想される。この場合Ｓｉ３価のピークは約１０３ｅＶに、Ｓｉ４価のピークは約１０４ｅＶに検出される。 Such an oxidation number of silicon can be detected by X-ray photoelectron spectroscopy (XPS). As the X-ray source, a general source can be arbitrarily used, but AlKα or MgKα is preferably used because a wide energy range can be measured with high resolution. In the normal measurement of XPS, the kinetic energy of photoelectrons generated by incident X-rays is detected, but it is preferable to evaluate the difference from the incident X-ray energy, for example, about 1254 eV for MgKα, and evaluate it by the binding energy. Focusing on the Si2P1 / 2 peak, it is expected that the Si0-valent peak is detected at a binding energy of about 100 eV. In this case, the Si trivalent peak is detected at about 103 eV, and the Si tetravalent peak is detected at about 104 eV.
　ここでの「実質４価」とは、ＸＰＳで測定されるＳｉ２Ｐ1/2の４価と３価のピーク比（Ｓｉ4+／Ｓｉ3+）が０．５以上であることをいう。この値をとることで珪素が安定酸化数となり、透明性と耐久性、特に湿熱耐久性に優れた透明導電性酸化物が得られる。このような比は、ＸＰＳで測定されるスペクトルの結合エネルギーが９８～１０８ｅＶ付近においてベースラインを引き、そのベースラインから１０３ｅＶ、１０４ｅＶのピークの高さをとることで求めることができる（後記の図２参照）。 Here, “substantially tetravalent” means that the ratio of Si2P 1/2 tetravalent to trivalent (Si 4+ / Si 3+ ) measured by XPS is 0.5 or more. By taking this value, silicon becomes a stable oxidation number, and a transparent conductive oxide excellent in transparency and durability, particularly wet heat durability, can be obtained. Such a ratio can be obtained by drawing a baseline when the binding energy of the spectrum measured by XPS is around 98 to 108 eV, and taking the peak heights of 103 eV and 104 eV from the baseline (see the figure below). 2).
　透明導電性酸化物層４は、マグネトロンスパッタリング法により容易に製膜可能である。マグネトロンスパッタリングに用いるターゲットとして、透明導電性酸化物層４と同組成の材料を用いる。アルゴンガスなどのキャリアガスを用いてこのターゲットをイオン化し、スパッタすることにより製膜を行う。キャリアガスには、アルゴンガスの他にも窒素などの不活性ガスを使用することができる。 The transparent conductive oxide layer 4 can be easily formed by a magnetron sputtering method. As a target used for magnetron sputtering, a material having the same composition as that of the transparent conductive oxide layer 4 is used. This target is ionized using a carrier gas such as argon gas, and film formation is performed by sputtering. As the carrier gas, an inert gas such as nitrogen can be used in addition to the argon gas.
　スパッタリングに用いる電源として、直流（ＤＣ）電源や低周波（ＡＣ）電源の他に、高周波電源を用いることができる。高周波電源にはＲＦやＶＨＦなどの周波数があるが、どの周波数においても本発明の透明導電性酸化物層を好適に製膜することができる。製膜時のパワー密度は１．５～１５．０Ｗ／ｃｍ2が好ましく、さらには３．５～１２．０Ｗ／ｃｍ2、その中でも特に７．０～１２．０Ｗ／ｃｍ2が好ましい。 As a power source used for sputtering, a high frequency power source can be used in addition to a direct current (DC) power source and a low frequency (AC) power source. The high frequency power source has a frequency such as RF or VHF, and the transparent conductive oxide layer of the present invention can be suitably formed at any frequency. The power density during film formation is preferably 1.5 to 15.0 W / cm 2 , more preferably 3.5 to 12.0 W / cm 2 , and particularly preferably 7.0 to 12.0 W / cm 2 .
　これらの下限値よりパワー密度が低い場合は製膜速度が向上せず、また、結晶性の問題であると考えられるが、湿熱耐久性が良くないことがある。一方パワー密度がこれらの上限値より高い場合には、プラズマ中で生成する酸素イオンにより透明導電性酸化物層が再スパッタされるために、透明性・導電性の良くない透明電極付き基板が生じる可能性があるため好ましくない。さらに、電源の印加方式は、連続波でもパルス波でもよく、製膜装置による最適条件に応じて任意に決定できる。 When the power density is lower than these lower limit values, the film forming speed is not improved, and it is considered to be a problem of crystallinity, but the wet heat durability may not be good. On the other hand, when the power density is higher than these upper limits, the transparent conductive oxide layer is re-sputtered by oxygen ions generated in the plasma, resulting in a substrate with a transparent electrode having poor transparency and conductivity. This is not preferable because there is a possibility. Furthermore, the power application method may be a continuous wave or a pulse wave, and can be arbitrarily determined according to the optimum conditions of the film forming apparatus.
　スパッタリング時の製膜室内の圧力は０．５Ｐａ以下であることが好ましい。製膜室内の圧力は、製膜室内に存在するキャリアガス原子（原子団・イオン状態を含む）の数に対応しており、これら原子は、ターゲットから飛来する透明導電性酸化物層４の構成原子（原子団・イオン状態を含む）の散乱源となる。本発明においては、製膜室内の圧力を０．５Ｐａ以下とすることで、ターゲットから飛来する原子を、十分な運動エネルギーを持ったまま基板に付着させ、有効な透明導電性酸化物層４を形成することが可能となる。 The pressure in the film forming chamber during sputtering is preferably 0.5 Pa or less. The pressure in the film forming chamber corresponds to the number of carrier gas atoms (including atomic groups and ion states) existing in the film forming chamber, and these atoms are configured in the transparent conductive oxide layer 4 flying from the target. It becomes a scattering source of atoms (including atomic groups and ion states). In the present invention, by setting the pressure in the film forming chamber to 0.5 Pa or less, atoms flying from the target are attached to the substrate with sufficient kinetic energy, and the effective transparent conductive oxide layer 4 is formed. It becomes possible to form.
　スパッタリング時の基板の温度は、基板の軟化温度以下であればどのような温度でも可能であるが、特に、２５℃以下であることが好ましい。基板温度を２５℃以下とすることで、スパッタ粒子の運動エネルギーを急激に低下させ、結晶粒を密にすること、組成によっては非晶質に近い状態にすることが可能となる。これにより湿熱耐久性の向上が可能となる。 The substrate temperature during sputtering can be any temperature as long as it is equal to or lower than the softening temperature of the substrate, but is particularly preferably 25 ° C. or lower. By setting the substrate temperature to 25 ° C. or lower, the kinetic energy of the sputtered particles can be drastically reduced, the crystal grains can be made dense, and depending on the composition, it can be brought into a state close to amorphous. This makes it possible to improve wet heat durability.
　太陽電池の裏面電極側に用いられる透明導電性酸化物層４の膜厚は、光学計算により設計されるが、１００～１２００Å、さらには２５０～１１００Åが、より好ましくは３００～１１００Åが好ましく、特には４００～１１００Åが好ましい。膜厚が上記下限値のいずれかより薄い場合には、光学特性が悪くなるだけでなく、裏面電極の金属材料の光電変換ユニットへの拡散などが起こりやすくなり、結果として発電特性を悪くする原因となりうる。 The film thickness of the transparent conductive oxide layer 4 used on the back electrode side of the solar cell is designed by optical calculation, but is 100 to 1200 mm, more preferably 250 to 1100 mm, more preferably 300 to 1100 mm, and particularly Is preferably 400 to 1100 mm. When the film thickness is thinner than any of the above lower limit values, not only the optical characteristics are deteriorated, but also diffusion of the metal material of the back electrode to the photoelectric conversion unit is likely to occur, resulting in deterioration of power generation characteristics. It can be.
　一方、膜厚が上記上限値のいずれかよりも厚い場合には、透明導電性酸化物層４の吸収ロスによる光学特性および性能の悪化が生じ得る。酸化亜鉛からなる透明導電性酸化物は、他の透明導電性酸化物に比べて透明性が高いことが特徴であるが、バンドギャップ付近（３．３ｅＶ付近）以上や自由電子反射・吸収の領域である１ｅＶ以下は光が吸収され、膜厚が厚くなるほど吸収量は大きくなる。 On the other hand, when the film thickness is thicker than any of the above upper limit values, optical characteristics and performance may be deteriorated due to absorption loss of the transparent conductive oxide layer 4. The transparent conductive oxide made of zinc oxide is characterized by high transparency compared to other transparent conductive oxides. However, it is not less than the band gap (around 3.3 eV) or free electron reflection / absorption region. The light is absorbed below 1 eV, and the amount of absorption increases as the film thickness increases.
　ここでいう光学特性とは、光電変換ユニット／透明導電性酸化物層の界面と透明導電性酸化物層／裏面電極の界面でそれぞれ反射される光の干渉に係る特性であり、必要な波長の光を光電変換ユニットに取り入れるために必要な特性である。なお、膜厚が厚い場合には、光学特性だけでなく、透明導電性酸化物層自体による光の吸収の影響が大きくなるため好ましくない。 The optical characteristics referred to here are characteristics related to interference of light reflected at the interface of the photoelectric conversion unit / transparent conductive oxide layer and the interface of the transparent conductive oxide layer / back electrode, and have a necessary wavelength. This is a characteristic necessary for taking light into the photoelectric conversion unit. A thick film is not preferable because not only the optical characteristics but also the effect of light absorption by the transparent conductive oxide layer itself is increased.
　なお、透明導電性酸化物層単膜の信頼性からは、膜厚は、１００～８００Åが好ましい。 Note that the film thickness is preferably 100 to 800 mm in view of the reliability of the transparent conductive oxide layer single film.
　本発明の透明導電性酸化物層４は湿熱耐久性の高さに特徴がある。湿熱耐久性の評価は８５℃・８５％ＲＨ（相対湿度）の環境で行われる。これは、光電変換装置の想定される使用環境の中でも過酷な条件に対する加速試験として実施されるものである。薄膜シリコン系太陽電池を例にとると、湿熱耐久性試験で性能が低下する最も大きな原因は、光電変換ユニットと裏面電極間に設けられた透明導電性酸化物層にある。該層が酸化亜鉛からなる場合には、従来は、性能低下が特に顕著であった。 The transparent conductive oxide layer 4 of the present invention is characterized by high wet heat durability. Evaluation of wet heat durability is performed in an environment of 85 ° C. and 85% RH (relative humidity). This is implemented as an acceleration test for severe conditions even in the assumed use environment of the photoelectric conversion device. Taking a thin-film silicon solar cell as an example, the biggest cause of performance degradation in the wet heat durability test is the transparent conductive oxide layer provided between the photoelectric conversion unit and the back electrode. In the case where the layer is made of zinc oxide, hitherto, the performance degradation was particularly remarkable.
　しかし、本発明の透明導電性酸化物層４では、製膜直後と湿熱耐久性試験５００時間後とのシート抵抗の変化が１．０～３．０倍であることが可能であり、好ましくは１．０１～２．０倍、さらには１．０２～１．８倍、特には１．０３～１．４０となる効果も期待できる。シート抵抗変化が大きくなると、透明導電性酸化物層が抵抗となり、光電変換ユニットで生成されたキャリアが透明導電性酸化物層で熱を発生して消費されてしまい、発電に寄与しない。本発明の透明導電性酸化物層は、これを抑制し、長時間にわたり安定して発電することを可能にしたものである。 However, in the transparent conductive oxide layer 4 of the present invention, the change in sheet resistance between immediately after film formation and after 500 hours of wet heat durability test can be 1.0 to 3.0 times, preferably An effect of 1.01 to 2.0 times, further 1.02 to 1.8 times, particularly 1.03 to 1.40 can be expected. When the change in sheet resistance increases, the transparent conductive oxide layer becomes resistance, and carriers generated in the photoelectric conversion unit are consumed by generating heat in the transparent conductive oxide layer, and do not contribute to power generation. The transparent conductive oxide layer of the present invention suppresses this and enables stable power generation over a long period of time.
　湿熱耐久性の試験は、光電変換装置を裏面電極まで作製後に裏面電極のみ除去して実施したり、裏面電極作製前の状態で実施することも可能であるが、ガラスなどの基板上に透明導電性酸化物層４と同条件で製膜した、いわゆる単膜の状態でも実施可能である。 The wet heat durability test can be carried out by removing only the back electrode after the photoelectric conversion device is made up to the back electrode, or can be carried out in a state before the back electrode is produced, but the transparent conductive material is formed on a substrate such as glass. It can also be carried out in a so-called single film state formed under the same conditions as the conductive oxide layer 4.
　裏面電極５としては、Ａｌ、Ａｇ、Ａｕ、Ｃｕ、ＰｔおよびＣｒから選ばれる少なくとも一つの材料からなる少なくとも一層の金属層をスパッタ法または蒸着法により形成することが好ましい。 As the back electrode 5, it is preferable to form at least one metal layer made of at least one material selected from Al, Ag, Au, Cu, Pt and Cr by sputtering or vapor deposition.
　裏面電極５の膜厚は厚いほど良いが、２０００Å以上あれば、良好な裏面電極となる。これより薄い場合には導電性が十分でなくなる可能性がある他、裏面電極として重要な光反射材料としての機能を十分に果たせなくなる可能性がある。一方、例えば１００００Åと厚過ぎる場合には、コストの観点から好ましくない。 The thicker the back electrode 5 is, the better, but if it is 2000 mm or more, a good back electrode is obtained. If the thickness is smaller than this, the conductivity may not be sufficient, and the function as a light reflecting material important as the back electrode may not be sufficiently achieved. On the other hand, when it is too thick, for example, 10,000 mm, it is not preferable from the viewpoint of cost.
　本発明において、ドーピング量測定には走査電子顕微鏡ＪＳＭ－６３９０－ＬＡ（日本電子社製）を用いた。透明導電性酸化物層の膜厚の測定には分光エリプソメーターＶＡＳＥ（Ｊ．Ａウーラム社製）を使用した。Ｘ線光電子分光（ＸＰＳ）は、Ｘ線源としてＭｇＫα（１２５４ｅＶ）を用いて、Ｓｉ２Ｐ1/2ピークの結合エネルギーを、０価を約１００ｅＶとして算出した。フィッティングは透明導電性酸化物層をＣａｕｃｈｙモデルで計算により実施した。光電変換特性は、ＡＭ（エアマス）１．５のスペクトル分布を有するソーラシミュレータを用いて、擬似太陽光を２５℃の下で１００ｍＷ／ｃｍ2のエネルギー密度で照射して出力特性を測定し、開放電圧（Ｖｏｃ）、短絡電流密度（Ｊｓｃ）、曲線因子（ＦＦ）、発電効率（Ｅｆｆ）、電圧－電流特性により評価した。 In the present invention, a scanning electron microscope JSM-6390-LA (manufactured by JEOL Ltd.) was used for the doping amount measurement. A spectroscopic ellipsometer VASE (manufactured by JA Woollam Co., Ltd.) was used to measure the film thickness of the transparent conductive oxide layer. X-ray photoelectron spectroscopy (XPS) was calculated using MgKα (1254 eV) as the X-ray source and the binding energy of the Si 2 P 1/2 peak at a zero valence of about 100 eV. Fitting was carried out by calculating the transparent conductive oxide layer using the Cauchy model. Photoelectric conversion characteristics were measured by irradiating simulated sunlight with an energy density of 100 mW / cm 2 at 25 ° C. using a solar simulator having a spectral distribution of AM (air mass) 1.5, and opening the circuit. The voltage (Voc), short circuit current density (Jsc), fill factor (FF), power generation efficiency (Eff), and voltage-current characteristics were evaluated.
　ここで、開放電圧（Ｖｏｃ）とは、太陽電池の陽極・陰極間にきわめて高抵抗の電圧計を取り付けた（実質電流が０となるとみなすことができる）場合、光を照射した時に生じる電圧である。短絡電流とは、電位をかけていない状態で光を照射した時に発生する電流であり、この短絡電流を単位面積あたりに換算したものが短絡電流密度（Ｊｓｃ）である。曲線因子（ＦＦ）は、（最適動作点（出力が最高となる点）の出力）÷（短絡電流×開放電圧）により算出される。発電効率（Ｅｆｆ）は、入射エネルギーに対する最大出力の割合である。いずれも、数値が大きいほうが好ましい。 Here, the open circuit voltage (Voc) is a voltage generated when light is irradiated when a very high resistance voltmeter is attached between the anode and the cathode of the solar cell (which can be considered that the actual current is zero). is there. The short-circuit current is a current generated when light is irradiated without applying a potential, and the short-circuit current density (Jsc) is obtained by converting the short-circuit current per unit area. The fill factor (FF) is calculated by (the output at the optimum operating point (the point at which the output is the highest)) / (short circuit current × open circuit voltage). The power generation efficiency (Eff) is the ratio of the maximum output to the incident energy. In any case, a larger numerical value is preferable.
　以下に、実施例をもって本発明を具体的に説明するが、本発明はこれらの実施例に限定されるものではない。 Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to these examples.
　（実施例１～１２、比較例１～１０）
　図１に示す薄膜光電変換装置を製作した。全ての実施例及び比較例において、透光性の基板１には、無アルカリガラス基板（厚み１．１ｍｍ）を使用した。透明電極層２には熱ＣＶＤ法により作製したフッ素化酸化錫（Ｆ：ＳｎＯ2）を用いた。この際の透明電極層２の膜厚は８００ｎｍ、シート抵抗は１０オーム／□、ヘイズ値は１５～２０％とした。 (Examples 1 to 12, Comparative Examples 1 to 10)
A thin film photoelectric conversion device shown in FIG. 1 was manufactured. In all Examples and Comparative Examples, a non-alkali glass substrate (thickness: 1.1 mm) was used as the translucent substrate 1. The transparent electrode layer 2 was made of fluorinated tin oxide (F: SnO 2 ) produced by a thermal CVD method. At this time, the film thickness of the transparent electrode layer 2 was 800 nm, the sheet resistance was 10 ohm / □, and the haze value was 15 to 20%.
　この上に、高周波プラズマＣＶＤ装置を用いて、ボロンドープのｐ型シリコンカーバイド（ＳｉＣ）層を１０ナノメートル、ノンドープの非晶質シリコン光電変換層を２００ナノメートル、リンドープのｎ型μｃ－Ｓｉ層を２０ナノメートルの膜厚で製膜した。これにより、ｐ－ｉ－ｎ接合の非晶質シリコンからなる第１の光電変換ユニット３１（トップセル）を形成した。 On top of this, using a high-frequency plasma CVD apparatus, a boron-doped p-type silicon carbide (SiC) layer is 10 nm, a non-doped amorphous silicon photoelectric conversion layer is 200 nm, and a phosphorus-doped n-type μc-Si layer is formed. The film was formed with a film thickness of 20 nanometers. As a result, the first photoelectric conversion unit 31 (top cell) made of amorphous silicon having a pin junction was formed.
　第１の光電変換ユニット３１を形成した基板を大気中に取り出すことなく、プラズマＣＶＤ装置にて導電性酸素化シリコン層３２を形成した。このときの製膜条件は、プラズマの励起周波数を１３．５６ＭＨｚ、基板温度を１５０℃、反応室内圧力を６６６Ｐａとした。プラズマＣＶＤ反応室内に導入される原料ガスとしてＳｉＨ4、ＰＨ3、ＣＯ2、およびＨ2を用いた。以上の条件で６００Åの導電性酸素化シリコン層３２を製膜した。 The conductive oxygenated silicon layer 32 was formed by a plasma CVD apparatus without taking the substrate on which the first photoelectric conversion unit 31 was formed into the atmosphere. The film-forming conditions at this time were such that the plasma excitation frequency was 13.56 MHz, the substrate temperature was 150 ° C., and the reaction chamber pressure was 666 Pa. SiH 4 , PH 3 , CO 2 , and H 2 were used as source gases introduced into the plasma CVD reaction chamber. Under the above conditions, a conductive oxygenated silicon layer 32 having a thickness of 600 mm was formed.
　更に、ボロンドープのｐ型微結晶シリコン層を１５ナノメートル、ノンドープの結晶質シリコン光電変換層を１５００ナノメートル、リンドープのｎ型微結晶シリコン層を２０ナノメートルの膜厚で、それぞれプラズマＣＶＤ法により製膜した。これにより、ｐ－ｉ－ｎ接合の結晶質シリコンからなる第２の光電変換ユニット３３（ボトムセル）を形成した。 Further, the boron-doped p-type microcrystalline silicon layer has a thickness of 15 nm, the non-doped crystalline silicon photoelectric conversion layer has a thickness of 1500 nm, and the phosphorus-doped n-type microcrystalline silicon layer has a thickness of 20 nm. A film was formed. As a result, a second photoelectric conversion unit 33 (bottom cell) made of crystalline silicon having a pin junction was formed.
　結晶質シリコン光電変換ユニット形成済みの仕掛品を、高周波プラズマＣＶＤ装置から大気中に取り出した後、高周波マグネトロンスパッタリング装置の製膜室に導入し、第２の光電変換ユニット３３の上に、透明導電性酸化物層４を製膜した。 The in-process product in which the crystalline silicon photoelectric conversion unit has been formed is taken out from the high-frequency plasma CVD apparatus to the atmosphere, and then introduced into the film forming chamber of the high-frequency magnetron sputtering apparatus. The conductive oxide layer 4 was formed.
　透明導電性酸化物層４は、スパッタターゲット材料・製膜パワー密度を表１に示した条件で実施した。比較例５，６以外の比較例及び実施例７，８以外の実施例において、製膜圧力を０．２Ｐａ、基板温度を１５０℃として、基板／ターゲット距離を６０ｍｍに設定して、表１に示す膜厚まで、製膜を実施した。スパッタターゲットには、酸化亜鉛に表１に示すドーピング量になるように二酸化珪素を混練し、高温焼結したものを、無酸素銅からなるバッキングプレートにホットプレスにより接着したものを用いた。 The transparent conductive oxide layer 4 was formed under the conditions shown in Table 1 for the sputtering target material and film forming power density. In Comparative Examples other than Comparative Examples 5 and 6 and Examples other than Examples 7 and 8, the film forming pressure was set to 0.2 Pa, the substrate temperature was set to 150 ° C., the substrate / target distance was set to 60 mm, and Table 1 Film formation was carried out to the film thickness shown. As the sputtering target, a silicon oxide kneaded with zinc oxide so as to have a doping amount shown in Table 1 and sintered at a high temperature was bonded to a backing plate made of oxygen-free copper by hot pressing.
　引き続き、真空蒸着装置を用いて、裏面金属電極層としてＡｇ膜を２５０ナノメートルの膜厚で製膜した。製膜中の真空度は１×１０-4Ｐａ以下、製膜速度は０．２±０．０２ナノメートル／秒とした。 Subsequently, an Ag film having a thickness of 250 nanometers was formed as a back metal electrode layer using a vacuum deposition apparatus. The degree of vacuum during film formation was 1 × 10 −4 Pa or less, and the film formation rate was 0.2 ± 0.02 nanometer / second.
　このようにして形成された薄膜光電変換装置の光電変換特性、具体的には、短絡電流密度（Ｊｓｃ）、開放電圧（Ｖｏｃ）、曲線因子（ＦＦ）、発電効率（Ｅｆｆ）を表２に示す。比較例３は薄膜光電変換装置としての機能を示さなかった。これは、透明導電性酸化物層の抵抗が非常に大きいために電流が流れなかったためだと考えられる。 Table 2 shows the photoelectric conversion characteristics of the thin film photoelectric conversion device thus formed, specifically, the short circuit current density (Jsc), the open circuit voltage (Voc), the fill factor (FF), and the power generation efficiency (Eff). . Comparative Example 3 did not show a function as a thin film photoelectric conversion device. This is presumably because the current did not flow because the resistance of the transparent conductive oxide layer was very large.
　図２は、本願発明の実施例及び比較例の透明導電性酸化物のＸ線光電子分光（ＸＰＳ）スペクトルを示す。横軸は結合エネルギーであり、シリコンの２Ｐ軌道に関する結合エネルギーを示す。縦軸はＸ線の検出強度（任意）を示す。図中の破線のグラフ（ａ）は比較例５の透明導電性酸化物層４のＳｉ２Ｐ1/2の結合エネルギーを示し、実線のグラフ（ｂ）は実施例５の透明導電性酸化物層４のＳｉ２Ｐ1/2の結合エネルギーを示す。これらは、実施例と比較例の代表例である。破線のグラフ（ａ）では１０３ｅＶのピークが非常に大きく、３価の珪素が優勢であると推定できる。一方実線のグラフ（ｂ）では１０３ｅＶのピーク強度が減少し、１０４ｅＶのピークが顕在化してきていることから、珪素の価数は４価が優勢となってきていると判断できる。 FIG. 2 shows X-ray photoelectron spectroscopy (XPS) spectra of the transparent conductive oxides of Examples and Comparative Examples of the present invention. The horizontal axis represents the binding energy, which indicates the binding energy related to the 2P orbit of silicon. The vertical axis indicates the X-ray detection intensity (arbitrary). The broken line graph (a) in the figure shows the binding energy of Si 2 P 1/2 of the transparent conductive oxide layer 4 of Comparative Example 5, and the solid line graph (b) shows the transparent conductive oxide layer 4 of Example 5. This shows the binding energy of Si2P1 / 2 . These are representative examples of Examples and Comparative Examples. In the broken line graph (a), the peak of 103 eV is very large, and it can be estimated that trivalent silicon is dominant. On the other hand, in the solid line graph (b), the peak intensity at 103 eV decreases, and the peak at 104 eV has become apparent, so that it can be determined that the valence of silicon has become predominant.
　Ｘ線光電子分光測定の結果を表４に示す。実施例の条件で製膜した透明導電性酸化物層は、４価の珪素を示す約１０４ｅＶの結合エネルギーのピークが比較的大きく、Ｓｉ２Ｐ1/2の４価と３価のピーク比（Ｓｉ4+／Ｓｉ3+）が０．５以上となった。一方比較例２，３，５，６，７，１０の透明導電性酸化物層は、３価の珪素を示す約１０３ｅＶのピークが優先し、Ｓｉ２Ｐ1/2の４価と３価のピーク比（Ｓｉ4+／Ｓｉ3+）が０．５未満となった。これらの結果より、珪素が４価になる製膜条件は、いくぶん不明確なところもあるが、「透明導電性酸化物層中に亜鉛原子に対して２.０～８.０ａｔｏｍ％の珪素原子が含まれていること」（各実施例と比較例２，７との比較）と「製膜時の圧力が０.５Pa以下であること」（実施例７，８と比較例６との比較）であると考察される。 Table 4 shows the results of X-ray photoelectron spectroscopy. The transparent conductive oxide layer formed under the conditions of the example has a relatively large binding energy peak of about 104 eV indicating tetravalent silicon, and the ratio of the tetravalent to trivalent peak ratio of Si 2 P 1/2 (Si 4 + / Si 3+ ) was 0.5 or more. On the other hand, in the transparent conductive oxide layers of Comparative Examples 2, 3, 5, 6, 7, and 10, the peak of about 103 eV indicating trivalent silicon is preferential, and the ratio of the tetravalent to trivalent peak of Si2P1 / 2 (Si 4+ / Si 3+ ) was less than 0.5. From these results, the film forming conditions for silicon to be tetravalent are somewhat unclear, but “2.0 to 8.0 atom% silicon atoms in the transparent conductive oxide layer with respect to zinc atoms”. "(Comparison between Examples and Comparative Examples 2 and 7)" and "Pressure during film formation is 0.5 Pa or less" (Comparison between Examples 7 and 8 and Comparative Example 6) ).
　表２に示すように、実施例の透明導電性酸化物層では、短絡電流密度（Ｊｓｃ）、曲線因子（ＦＦ）、発電効率（Ｅｆｆ）は、いずれも比較例のものより高くなっており、性能が向上している。なお、開放電圧（Ｖｏｃ）については、実施例と比較例の間に有意な差がみられなかった。 As shown in Table 2, in the transparent conductive oxide layer of the example, the short circuit current density (Jsc), the fill factor (FF), and the power generation efficiency (Eff) are all higher than those of the comparative example, Performance has improved. In addition, about the open circuit voltage (Voc), the significant difference was not seen between the Example and the comparative example.
　ピーク比（Ｓｉ4+／Ｓｉ3+）が０．５未満である比較例２，３，５，６，７，１０のいずれにおいても、ピーク比（Ｓｉ4+／Ｓｉ3+）が０．５以上である実施例より性能が低下している。 In any peak ratio (Si 4+ / Si 3+) is a comparative example 2,3,5,6,7,10 less than 0.5, peak ratio (Si 4+ / Si 3+) 0. The performance is lower than the example of 5 or more.
　なお、比較例１は導電性添加物に珪素を含まないため、比較例４は導電性添加物における珪素原子の比率が低いため、性能が低くなっていると考えられる。 Since Comparative Example 1 does not contain silicon in the conductive additive, Comparative Example 4 is considered to have low performance because the ratio of silicon atoms in the conductive additive is low.
　また、比較例８，９は、透明導電性酸化物層の膜厚が大きすぎ又は小さすぎることが影響して、性能が低くなっていると考察される。比較例８では膜厚が厚すぎることによる、透明導電性酸化物層４での吸収ロスと低い干渉効果の影響により、比較例９では低い干渉効果の影響と銀裏面電極の寄生吸収の影響によると考察される。 In Comparative Examples 8 and 9, it is considered that the performance is lowered due to the influence of the film thickness of the transparent conductive oxide layer being too large or too small. In Comparative Example 8, due to the influence of absorption loss in the transparent conductive oxide layer 4 and low interference effect due to the film thickness being too thick, in Comparative Example 9 due to the influence of low interference effect and parasitic absorption of the silver back electrode. It is considered.
　透明導電性酸化物層の湿熱耐久性試験は、各実施例における透明導電性酸化物層４と同条件の層を無アルカリガラス（商品名ＯＡ－１０、日本電気硝子製）上に製膜し、８５℃・８５％ＲＨの環境で５００時間放置し、その前後のシート抵抗を比較することで実施した。その結果を表３に示す。比較例３の透明導電性酸化物層は、絶縁体となった為、シート抵抗の測定ができなかった。 In the wet heat durability test of the transparent conductive oxide layer, a layer having the same conditions as the transparent conductive oxide layer 4 in each example was formed on an alkali-free glass (trade name OA-10, manufactured by Nippon Electric Glass). The sheet resistance was measured for 500 hours in an environment of 85 ° C. and 85% RH, and the sheet resistance before and after the comparison was compared. The results are shown in Table 3. Since the transparent conductive oxide layer of Comparative Example 3 became an insulator, the sheet resistance could not be measured.
　表３に示すように、実施例と比較例を比較すると、比較例６，８等の例外はあるが、一般に実施例の条件で製膜した透明導電性酸化物層は、比較例のものよりもシート抵抗の変化が小さく、耐久性に優れている。 As shown in Table 3, when Examples and Comparative Examples are compared, there are exceptions such as Comparative Examples 6 and 8, etc., but the transparent conductive oxide layer generally formed under the conditions of Examples is more than that of Comparative Examples. The sheet resistance change is small and the durability is excellent.
　比較例６では、実施例と比較して、太陽電池特性のうち、特に短絡電流が劣る結果となっている。これは透明導電性酸化物層４による吸収ロスの影響であると推測され、この原因として、Ｓｉ4+／Ｓｉ3+比が小さく、３価のシリコンによる吸収ロスが大きいことが考えられる。 In Comparative Example 6, the short-circuit current is particularly inferior among the solar cell characteristics as compared with the Example. This is presumed to be due to the effect of absorption loss due to the transparent conductive oxide layer 4, and this may be due to the fact that the Si 4+ / Si 3+ ratio is small and the absorption loss due to trivalent silicon is large.
　比較例８および９では、上記のように、透明導電性酸化物層４の膜厚によって太陽電池特性が低下している。 In Comparative Examples 8 and 9, as described above, the solar cell characteristics are degraded by the film thickness of the transparent conductive oxide layer 4.
　表１～４から、４価の珪素を含有する透明導電性酸化物層を用いることにより、特性が良く、耐久性に優れた薄膜光電変換装置が作製できることがわかった。 From Tables 1 to 4, it was found that by using a transparent conductive oxide layer containing tetravalent silicon, a thin film photoelectric conversion device having good characteristics and excellent durability can be produced.
　以上の結果、光電変換ユニットと裏面電極間に珪素を含む酸化亜鉛透明導電性酸化物層を製膜することで、発電効率に優れる薄膜光電変換装置を作製できることがわかった。これは、透明導電性酸化物層の光透過率が向上することにより、光電変換ユニット内に取り込まれる光の量が多くなるためだと考えられる。光透過率が向上した理由は、透明導電性酸化物中のキャリア濃度が低下したためであると考えられる。さらに、８５℃・８５％ＲＨ環境下で湿熱耐久性試験を実施したところ、実施例の透明導電性酸化物層はシート抵抗の変化が小さく湿熱耐久性に優れることがわかった。 As a result, it was found that a thin film photoelectric conversion device having excellent power generation efficiency can be produced by forming a zinc oxide transparent conductive oxide layer containing silicon between the photoelectric conversion unit and the back electrode. This is considered to be because the amount of light taken into the photoelectric conversion unit is increased by improving the light transmittance of the transparent conductive oxide layer. The reason why the light transmittance is improved is considered to be that the carrier concentration in the transparent conductive oxide is lowered. Furthermore, when a wet heat durability test was performed in an environment of 85 ° C. and 85% RH, it was found that the transparent conductive oxide layers of the examples had small changes in sheet resistance and excellent wet heat durability.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
　１　　基板
　２　　透明電極層
　３　　光電変換層
３１　　第１の光電変換ユニット
３２　　導電性酸素化シリコン層
３３　　第２の光電変換ユニット
　４　　透明導電性酸化物層
　５　　裏面電極 DESCRIPTION OF SYMBOLS 1 Substrate 2 Transparent electrode layer 3 Photoelectric conversion layer 31 First photoelectric conversion unit 32 Conductive oxygenated silicon layer 33 Second photoelectric conversion unit 4 Transparent conductive oxide layer 5 Back electrode

Claims (5)

  1. 光入射側より透明導電性酸化物からなる透明電極層、少なくとも１つの薄膜光電変換ユニット、及び裏面電極が順に配置された薄膜光電変換装置において、上記薄膜光電変換ユニットと裏面電極の間に酸化亜鉛を主成分とする透明導電性酸化物層が形成されており、該透明導電性酸化物層には導電性添加物が添加され、且つ該導電性添加物の８５ａｔｏｍ％以上が珪素原子からなり、且つ該透明導電性酸化物層中に亜鉛原子に対して２．０～８．０ａｔｏｍ％の珪素原子が含まれており、さらに透明導電性酸化物のＸ線光電子分光Ｓｉ２Ｐ1/2ピークから見て、珪素が実質４価である薄膜光電変換装置。 In the thin film photoelectric conversion device in which a transparent electrode layer made of a transparent conductive oxide, at least one thin film photoelectric conversion unit, and a back electrode are arranged in this order from the light incident side, zinc oxide is interposed between the thin film photoelectric conversion unit and the back electrode. And a conductive additive is added to the transparent conductive oxide layer, and 85 atom% or more of the conductive additive is composed of silicon atoms, In addition, the transparent conductive oxide layer contains 2.0 to 8.0 atom% of silicon atoms with respect to zinc atoms, and is further seen from the X-ray photoelectron spectroscopy Si2P 1/2 peak of the transparent conductive oxide. A thin film photoelectric conversion device in which silicon is substantially tetravalent.
  2. 請求項１に記載の透明導電性酸化物層の膜厚が１００～１２００Åである請求項１に記載の薄膜光電変換装置。 The thin film photoelectric conversion device according to claim 1, wherein the transparent conductive oxide layer according to claim 1 has a thickness of 100 to 1200 mm.
  3. 透明導電性酸化物層の膜厚が１００～８００Åであって、且つ８５℃・８５％相対湿度環境下における湿熱耐久性試験を実施した場合において、製膜直後と５００時間経過後のシート抵抗変化が１．０～３．０倍である透明導電性酸化物層が光電変換ユニットと裏面電極間に配置されている請求項１に記載の薄膜光電変換装置。 When the film thickness of the transparent conductive oxide layer is 100 to 800 mm and the wet heat durability test is performed in an environment of 85 ° C. and 85% relative humidity, the sheet resistance change immediately after film formation and after 500 hours has elapsed. The thin film photoelectric conversion device according to claim 1, wherein a transparent conductive oxide layer having a ratio of 1.0 to 3.0 is disposed between the photoelectric conversion unit and the back electrode.
  4. 非晶質シリコンを主成分とする薄膜光電変換ユニットと、結晶質シリコンを主成分とする薄膜光電変換ユニットとを有する請求項１～３のいずれかに記載の薄膜光電変換装置。 4. The thin film photoelectric conversion device according to claim 1, comprising a thin film photoelectric conversion unit mainly composed of amorphous silicon and a thin film photoelectric conversion unit mainly composed of crystalline silicon.
  5. 透明導電性酸化物層がマグネトロンスパッタリング法により製膜され、製膜時のパワー密度が１．５～１５．０Ｗ／ｃｍ2であり、さらに製膜時の圧力が０．５Ｐａ以下である請求項１～４のいずれかに記載の薄膜光電変換装置の製造方法。 The transparent conductive oxide layer is formed by a magnetron sputtering method, the power density during film formation is 1.5 to 15.0 W / cm 2 , and the pressure during film formation is 0.5 Pa or less. 5. A method for producing a thin film photoelectric conversion device according to any one of 1 to 4.
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