WO2013129557A1 - 化合物半導体太陽電池及び化合物半導体太陽電池の光吸収層の製造方法 - Google Patents
化合物半導体太陽電池及び化合物半導体太陽電池の光吸収層の製造方法 Download PDFInfo
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- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
- H01L31/0256—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by the material
- H01L31/0264—Inorganic materials
- H01L31/032—Inorganic materials including, apart from doping materials or other impurities, only compounds not provided for in groups H01L31/0272 - H01L31/0312
- H01L31/0322—Inorganic materials including, apart from doping materials or other impurities, only compounds not provided for in groups H01L31/0272 - H01L31/0312 comprising only AIBIIICVI chalcopyrite compounds, e.g. Cu In Se2, Cu Ga Se2, Cu In Ga Se2
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
- H01L31/036—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by their crystalline structure or particular orientation of the crystalline planes
- H01L31/0368—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by their crystalline structure or particular orientation of the crystalline planes including polycrystalline semiconductors
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
- H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
- H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
- H01L31/072—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN heterojunction type
- H01L31/0749—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN heterojunction type including a AIBIIICVI compound, e.g. CdS/CulnSe2 [CIS] heterojunction solar cells
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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
- H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/541—CuInSe2 material PV cells
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Definitions
- the present invention relates to a compound semiconductor solar cell and a method for producing a light absorption layer of the compound semiconductor solar cell.
- Non-Patent Document 1 Non-Patent Document 1
- Cu (at%) / IIIb group (at%) ⁇ 1.0 is referred to as a Cu-poor composition
- Cu (at%) / IIIb group (at%)> 1.0 is referred to as a Cu-rich composition.
- a general solar cell using a Cu-containing chalcopyrite p-type light absorption layer is used with the light absorption layer adjusted to a Cu-poor composition.
- Cu x VIb is a highly conductive material, and if this heterogeneous phase is present in the light absorption layer, the back electrode layer and the buffer layer or window layer are short-circuited, and the solar cell characteristics are greatly deteriorated. For this reason, a chalcopyrite p-type semiconductor film having a Cu-rich composition has not been generally used as a light absorption layer.
- Non-patent Document 2 a report that a chalcopyrite p-type semiconductor film having a Cu-rich composition has a smaller defect density than a film having a Cu-poor composition.
- a p-type semiconductor film having a low defect density is used for the light absorption layer of a solar cell, it is considered that high conversion efficiency can be obtained because the transport characteristics of photogenerated carriers are high.
- the chalcopyrite p-type semiconductor film having the Cu-rich composition has Cu x VIb which is a different phase at the same time, thereby making use of the good carrier transport characteristics of the original Cu-rich composition film. I can't.
- Non-patent Document 3 a p-type semiconductor film having a different phase is immersed in a potassium cyanide (KCN) aqueous solution to selectively remove only the different phase (hereinafter, this process is referred to as KCN etching).
- KCN potassium cyanide
- the solar cell using the KCN-etched light absorption layer that is, the light absorption layer from which the conductive Cu x VIb which is a different phase is removed, is improved in characteristics as compared with that before the etching, but the original Cu-rich The sufficient conversion efficiency expected from the good carrier transport property of the composition film is not obtained.
- an object of the present invention is to provide a compound semiconductor solar cell with high photoelectric conversion efficiency.
- a compound semiconductor solar battery is a compound semiconductor solar battery comprising a back electrode layer, a light absorption layer, and a transparent electrode layer,
- the light absorption layer is a p-type semiconductor layer having an element selected from Cu, Ga, and a VIb group element.
- the half-value width of the emission spectrum includes a peak of 1 meV or more and 15 meV or less, and The ratio of particles having a particle size of 2 ⁇ m or more and 8 ⁇ m or less on the surface of the light absorption layer to the surface of the light absorption layer is 90% or more.
- the compound semiconductor solar battery of the present invention it is possible to obtain higher photoelectric conversion efficiency than the conventional compound semiconductor solar battery.
- a light absorption layer having excellent carrier transport characteristics can be obtained by having a p-type semiconductor layer having a half-value width of emission peak of 1 meV or more and 15 meV or less.
- the photoluminescence spectrum and cathodoluminescence spectrum strongly depend on the energy level of the semiconductor material. Therefore, when a p-type semiconductor film that can observe photoluminescence and cathodoluminescence with a narrow half-value width is used for the light absorption layer, light absorption It is assumed that the fluctuation of the energy level in the layer is small, so that the carrier recombination probability decreases.
- the proportion of the particles having a particle diameter of 2 ⁇ m or more and 8 ⁇ m or less on the surface of the light absorption layer is 90% or more, thereby reducing the recombination of photogenerated carriers at the grain boundary. It is assumed that high photoelectric conversion efficiency can be obtained.
- the particle size when the particle size is 2 ⁇ m or more, the grain boundary can be reduced, the amount of heterogeneous phase present along the grain boundary can be reduced, and the shunt resistance can be increased. Moreover, when the particle size is 8 ⁇ m or less, it is considered that an appropriate amount of the grain boundary amount can be ensured and deterioration of carrier transport characteristics can be prevented.
- the light absorption layer is preferably a p-type semiconductor layer further containing In.
- the band gap energy of the light absorption layer can be changed between 1.0 eV and 2.5 eV.
- the spectral sensitivity characteristic of the p-type semiconductor layer can be appropriately adjusted to the spectrum of the incident light source such as sunlight.
- the cross-sectional structure of the light absorption layer it is preferable that a portion having a columnar shape in which only a single particle exists in the film thickness direction is included, and the ratio of the cross-sectional area of the portion to the cross-sectional area of the entire film is 90% or more. Thereby, it is possible to prevent deterioration of carrier transport characteristics due to an excessive amount of grain boundary in the film thickness direction and to obtain higher photoelectric conversion efficiency.
- the composition ratio of Cu and the group IIIb element contained in the light absorption layer is 0.99 or more and 1.01 or less.
- membrane excellent in the carrier transport characteristic can be obtained, and higher conversion efficiency can be obtained.
- the amount of Cu x VIb which is a different phase is an amount that does not affect the shunt resistance of the solar cell, higher conversion efficiency can be obtained.
- the carrier density of the light absorption layer is more preferably 1 ⁇ 10 16 cm ⁇ 3 or more and 5 ⁇ 10 16 cm ⁇ 3 or less.
- the diffusion potential is increased, and as a result, a high open-circuit voltage can be obtained and higher conversion efficiency can be obtained.
- the width of the depletion layer can be set to an appropriate width, a decrease in short-circuit current can be prevented, and higher conversion efficiency can be obtained.
- a compound semiconductor solar cell with high conversion efficiency can be provided.
- FIG. 10 is a cross-sectional SEM image of a light absorption layer used in the solar cell of Example 21.
- FIG. 1 shows a compound semiconductor solar cell 2 according to this embodiment.
- the compound semiconductor solar battery 2 includes a substrate 6, a back electrode layer 8 provided on the substrate 6, a light absorption layer 10 as a p-type semiconductor layer formed on the back electrode layer 8, and the light absorption layer 10.
- the compound semiconductor solar battery may be referred to as a solar battery.
- a glass substrate such as soda lime glass (blue plate glass), white glass (white plate glass), or non-alkali glass is used.
- metal foils such as stainless steel, aluminum, and titanium, and a metal plate.
- plastic films such as a PET film, a PEN film, and a polyimide film.
- the back electrode layer 8 is made of a metal such as Mo, W, Ti, Cr, Nb, V, or Mn.
- the light absorption layer 10 is a p-type compound semiconductor layer containing Cu, Ga, and at least one element selected from Group VIb elements. In may be added to the Ga position.
- the photoluminescence spectrum or cathodoluminescence spectrum of the light absorption layer 10 includes an emission peak whose half-value width of the emission peak is 1 meV or more and 15 meV or less. This emission spectrum is observed at a low temperature of 10K (Kelvin) or less.
- the carrier transport property of the p-type light absorption layer is deteriorated and high conversion efficiency tends not to be obtained.
- the proportion of particles having a particle diameter of 2 ⁇ m or more and 8 ⁇ m or less in the surface of the light absorption layer 10 (hereinafter referred to as “particle shape parameter A”) is 90% or more. is there.
- particle shape parameter A is 90% or more, recombination of photogenerated carriers at the grain boundary is reduced, and high conversion efficiency is obtained.
- the particle size is 2 ⁇ m or more, the grain boundary is reduced, and the residual amount of Cu x VIb, which is a heterogeneous phase present along the grain boundary, is reduced, thereby increasing the shunt resistance and obtaining high conversion efficiency.
- the surface is a surface of the light absorption layer 10 opposite to the surface in contact with the back electrode layer 8, that is, a side on which light is incident on the light absorption layer 10.
- the surface on the side in contact with the buffer layer 14 corresponds.
- the cross-sectional structure of the light-absorbing layer 10 includes a column-shaped portion in which only a single particle exists in the film thickness direction, and the cross-sectional area of the portion accounts for the ratio of the cross-sectional area of the entire film (hereinafter, “particle shape parameter B”) Is preferably 90% or more.
- particle shape parameter B the ratio of the cross-sectional area of the entire film
- the cross-sectional area is a surface obtained by mechanically cutting the light absorption layer 10 and then polishing and flattening, or a surface in which the cross section of the light absorption layer 10 is exposed in the film thickness direction by processing using FIB (Focused Ion Beam). Area.
- FIG. 2 shows a schematic diagram of the particle shape (particle shape parameter B) of the light absorption layer cross section.
- FIG. 2 is a cross section of the light absorption layer 10 exposed by flat processing.
- 202 represents a columnar portion where only a single particle exists in the film thickness direction
- 203 represents a portion where a plurality of particles exist in the film thickness direction.
- the particle shape parameter B is calculated by the equation (1).
- Particle shape parameter B 202 area / (202 area + 203 area) ⁇ 100 ... (1)
- the composition ratio (Cu / IIIb group composition ratio) between Cu and the group IIIb element in the light absorption layer 10 is preferably 0.99 or more and 1.01 or less. If the Cu / IIIb group composition ratio is smaller than 1.01, the amount of deposited conductive Cu x VIb, which is a different phase, is not an amount that affects the shunt resistance of the solar cell, and the conversion efficiency tends to increase. If it is larger than 0.99, the fluctuation of the energy level described above becomes small, and high conversion efficiency tends to be obtained.
- the carrier density of the light absorption layer 10 is preferably 1 ⁇ 10 16 cm ⁇ 3 or more and 5 ⁇ 10 16 cm ⁇ 3 or less.
- the carrier density of the light absorption layer 10 is preferably 1 ⁇ 10 16 cm ⁇ 3 or more and 5 ⁇ 10 16 cm ⁇ 3 or less.
- the diffusion potential increases, and as a result, a high open-circuit voltage can be obtained and conversion efficiency tends to be higher.
- the width of the depletion layer can be set to an appropriate width, a decrease in short-circuit current can be prevented, and conversion efficiency tends to increase.
- the film thickness of the light absorption layer 10 is preferably between 1 ⁇ m and 5 ⁇ m.
- the thickness is 1 ⁇ m or more, incident light can be effectively absorbed, and conversion efficiency tends to increase.
- the adhesiveness of the light absorption layer 10 and another layer increases, film peeling does not occur easily, and the yield at the time of manufacture can be improved.
- the series resistance can be reduced, and the conversion efficiency tends to increase.
- the buffer layer 14 is made of a material such as CdS, ZnS, ZnSe, InS, InSe, ZnSSe, Zn (S, OH), ZnSO, ZnSeO, or ZnSSeO.
- the thickness of the buffer layer 14 is preferably in the range of 0.01 ⁇ m to 0.1 ⁇ m. By setting it as 0.01 micrometer or more, the shunt resistance of the compound semiconductor solar cell 2 can be raised, and there exists a tendency for conversion efficiency to become high. By setting the thickness to 0.1 ⁇ m or less, loss of light absorption in the buffer layer 14 can be suppressed, and conversion efficiency tends to increase.
- the buffer layer 14 is not necessarily provided, but the conversion efficiency tends to be obtained when it is provided.
- the semi-insulating layer 16 i-ZnO (undoped ZnO), ZnMgO, or the like is used.
- the thickness of the semi-insulating layer 16 is preferably in the range of 0.01 ⁇ m to 0.1 ⁇ m. By setting it as 0.01 micrometer or more, the shunt resistance of a solar cell can be raised and there exists a tendency for conversion efficiency to become high. When the thickness is 0.1 ⁇ m or less, an increase in the series resistance of the solar cell can be suppressed, and the conversion efficiency tends to increase.
- the semi-insulating layer 16 is not necessarily provided, but the conversion efficiency tends to be obtained when it is provided.
- a transparent conductive film such as ZnO, ITO, SnO 2, or ZnInO to which a group IIIb element such as Al, B, or Ga is added is used.
- materials such as Al, Cu, Au, Ag, C, Pt, and Ni are used for current collection.
- the back electrode layer 8 is formed on the substrate 6 by, for example, a sputtering method, an electron beam evaporation method, a printing method, or the like.
- the back electrode layer 8 having a low resistance When formed by sputtering, the back electrode layer 8 having a low resistance can be uniformly formed in a relatively large area, and in-plane variation in solar cell characteristics can be reduced and high conversion efficiency tends to be obtained. .
- the light absorption layer 10 is formed after the back electrode layer 8 is formed.
- a two-stage vapor deposition method including a step of simultaneous vacuum vapor deposition of a group IIIb element and a group of VIb elements containing Ga and a step of simultaneous vacuum vapor deposition of a group element of Cu and VIb is used.
- the order of the two steps can start from either. Further, the above steps may be repeated as long as they are two or more stages.
- the multi-stage vapor deposition method local excessive precipitation of Cu x VIb, which is a different phase, can be suppressed, and Cu x VIb can be deposited relatively uniformly on the surface of the light absorption layer 10. Thereby, it becomes easy to control a particle size to the said range, and there exists a tendency for high conversion efficiency to be obtained.
- an alloy or sintered body target made of a group IIIb element and a VIb group element containing Ga and an alloy or sintered body target made of a Cu and VIb group element are sputtered in sequence.
- the two precursor layers obtained by heat treatment are heat-treated in a mixed gas in which H 2 Se or H 2 S is added to Ar (“two-layer sputtering + selenization heat treatment” or “two-layer sputtering + sulfurization heat treatment)”
- a Cu metal target may be used instead of an alloy or sintered body target made of Cu and VIb group elements, and the formation of the two precursor layers is not limited to the sputtering method.
- the total number of each precursor layer may be more than two layers. Thereby, local excessive precipitation of Cu x VIb, which is a different phase, can be suppressed, Cu x VIb can be deposited relatively uniformly on the surface of the light absorption layer 10, and the particle size can be easily controlled within the above range. High conversion efficiency can be obtained.
- the Cu / IIIb group composition ratio immediately after the formation of the light absorption layer 10 reaches a range of 1.05 to 1.80.
- high conversion efficiency tends to be obtained.
- the Cu / IIIb group composition ratio is larger than 1.05, the film has a relatively large carrier transport property, and the conversion efficiency tends to be relatively large.
- the Cu / IIIb group composition ratio smaller than 1.80, it is possible to suppress the precipitation of the conductive Cu x VIb on the grain boundary in the film, and it is possible to mainly deposit on the film surface. Thereby, Cu x VIb can be easily removed in a later step, the shunt resistance of the compound semiconductor solar cell 2 can be increased, and conversion efficiency tends to increase.
- the method for removing the Cu x VIb compound which is a different phase include an etching treatment by immersion in an aqueous potassium cyanide solution (KCN etching), a method by electrochemical etching or a heat treatment in a forming gas atmosphere, and the like.
- KCN etching aqueous potassium cyanide solution
- a method of forming a Cu-IIIb group-VIb group compound by reacting and consuming with an excess of Cu x VIb compound by co-depositing IIIb group and VIb group may be used.
- the conductive Cu x VIb compound can be removed from the light absorption layer 10, and conversion efficiency tends to increase.
- a chemical solution deposition method (Chemical Bath Deposition: CBD method), a vacuum deposition method, a sputtering method, a chemical vapor deposition method (Chemical Vapor Deposition: CVD method), or the like is used.
- CBD method Chemical Bath Deposition: CBD method
- a vacuum deposition method a vacuum deposition method
- a sputtering method a chemical vapor deposition method
- CVD method chemical Vapor Deposition: CVD method
- the semi-insulating layer 16 is formed by a sputtering method, a chemical vapor deposition method (CVD method), or the like.
- the window layer 18 is formed by a sputtering method, a chemical vapor deposition method (CVD method), or the like.
- the upper electrode 20 is formed by a sputtering method, a vacuum evaporation method, a printing method, or the like.
- the current collection efficiency is calculated from the area of the opening and the resistivity of the window layer 18 and formed into an appropriate shape pattern.
- the compound semiconductor solar cell 2 of this embodiment is formed by the above procedure.
- a film-like back electrode layer composed of Mo alone was formed on the soda lime glass 6 by a DC sputtering method.
- the film thickness of the back electrode layer was 1 ⁇ m.
- substrate means a film formation target or a measurement target in each step.
- the light absorption layer was formed using a Physical Vapor deposition (physical vapor deposition, hereinafter referred to as PVD) apparatus.
- PVD Physical vapor deposition
- the film composition was adjusted by measuring the relationship between the flux ratio of each raw material element and the composition contained in the obtained film in advance. The flux of each element was appropriately changed by adjusting the temperature of each K cell.
- Example 1 The formation of the light absorption layer in Example 1 was performed by a two-stage vapor deposition method. The procedure of the two-stage vapor deposition method will be described below.
- the substrate was placed in the chamber of the PVD apparatus, and the inside of the chamber was evacuated.
- the ultimate pressure in the vacuum apparatus was 1.0 ⁇ 10 ⁇ 8 torr.
- the shutter of each K cell of In, Ga, and Se was opened, and In, Ga, and Se were deposited on the substrate.
- the In and Ga fluxes were adjusted in advance before the film formation so that the Ga / (In + Ga) ratio of the film composition after the film formation was approximately 0.5.
- the shutters of the In and Ga K cells were closed. Se continued to supply.
- the substrate was heated to 540 ° C. and the temperature was stabilized, and then the Cu K cell shutter was opened to deposit Cu and Se.
- the power for heating the substrate was kept constant, and the temperature value was not fed back with respect to the power.
- the surface temperature of the substrate is monitored by a radiation thermometer, and the temperature rise of the substrate stops, 3 minutes after the start of the temperature decrease (hereinafter, from when the temperature decrease starts until the Cu K cell is closed)
- the time was referred to as “second stage Cu holding time”), and the shutter of the Cu K cell was closed to complete the deposition of Cu.
- the substrate was cooled to 200 ° C., and then the shutter of the Se K cell was closed to complete the formation of the light absorption layer.
- the substrate was immersed in a potassium cyanide aqueous solution (10 wt%) for 3 minutes (KCN etching) to remove Cu x Se, which is a different phase contained in the light absorption layer.
- the surface was observed to determine the particle size and distribution of the surface of the light absorption layer.
- the surface of the light absorption layer is photographed at 16 locations within the substrate surface (see FIG. 3) under the condition of an image magnification of 5000 times, and the SEM image is subjected to image analysis using ImageJ (National Institute of Health), which is free software.
- ImageJ National Institute of Health
- the cross-sectional structure of the light absorption layer processed by FIB was observed, and the particle size in the film thickness direction was evaluated.
- a cross-section of the light absorption layer was photographed at the same 16 locations (see FIG. 3) as the surface observation under the condition of an image magnification of 10000 times, and the SEM image was subjected to image analysis to obtain a single columnar particle in the film thickness direction.
- the ratio (particle shape parameter B) of the cross-sectional area occupied by only the columnar-shaped portion was obtained, and the average value of the analysis results of each measurement location was calculated. The result was 84.5%.
- the respective composition amounts of Cu, In, Ga, and Se were measured with an energy dispersive X-ray spectroscopy (EDX) attached to the same apparatus.
- EDX energy dispersive X-ray spectroscopy
- a CdS film was formed on the light absorption layer as a buffer layer having a thickness of 50 nm by a chemical solution deposition (CBD) method.
- CBD chemical solution deposition
- an i-ZnO layer (semi-insulating layer) having a thickness of 50 nm was formed on the buffer layer. Subsequently, a ZnO layer (window layer) to which Al having a thickness of 0.5 ⁇ m was added was formed on the i-ZnO layer in the same chamber.
- the i-ZnO layer (semi-insulating layer) and the ZnO layer to which Al was added were formed by RF sputtering.
- photoluminescence measurement of the light absorption layer was performed.
- An Ar ion laser having a wavelength of 514.5 nm was used as an excitation light source used for measurement, and the substrate was cooled to 10 K (Kelvin) by a cryostat during measurement.
- the excitation light intensity was changed from 1 mW / cm 2 to 100 mW / cm 2 and the dependence of the photoluminescence intensity on the excitation light intensity was measured.
- the half width of the emission peak with the narrowest half width was 9 meV.
- the substrate was cut, and cathodoluminescence measurement of the light absorption layer was performed from the fracture surface.
- the measurement was performed at 10 K (Kelvin) as in the case of photoluminescence.
- the half-value width of light emission with the narrowest half-value width was 9 meV.
- an upper electrode composed of Ni having a thickness of 50 nm and Al having a thickness of 1 ⁇ m thereon was formed on the ZnO layer to which Al was added.
- the upper electrode was formed by DC sputtering. Thereby, the compound semiconductor solar battery of Example 1 was obtained.
- Examples 2 to 5 The solar cells of Examples 2 to 5 were obtained in the same manner as in Example 1 except that the second-stage Cu holding time was set to the time shown in Table 1 in the formation of the light absorption layer.
- the film composition was adjusted by measuring the relationship between the flux ratio of each raw material element and the composition contained in the obtained film in advance.
- the flux ratio of each element was appropriately changed by adjusting the temperature of each K cell.
- the flux of each element was set so that the Cu / (In + Ga) composition ratio immediately after film formation was 1.05 and the Ga / (In + Ga) composition ratio was 0.50.
- the flux of each element was set so that the Cu / (In + Ga) composition ratio immediately after film formation was 1.35 and the Ga / (In + Ga) composition ratio was 0.50.
- the substrate was placed in the chamber of the PVD apparatus, and the inside of the chamber was evacuated.
- the ultimate pressure in the vacuum apparatus was 1.0 ⁇ 10 ⁇ 8 torr.
- the shutter of each K cell of Cu, In, Ga, and Se was opened, and Cu, In, Ga, and Se were deposited on the substrate.
- the shutters of the Cu, In, and Ga K cells were closed.
- the substrate was cooled to 200 ° C., and then the shutter of the Se K cell was closed to complete the formation of the light absorption layer.
- Table 1 shows the solar cell production conditions and various measurement results of Examples 2 to 5 and Comparative Examples 1 and 2.
- Example 6 In the solar cells of Examples 6 to 8, in the formation of the light absorption layer, the Ga / (In + Ga) ratio after the film formation is adjusted in advance so that the Ga / (In + Ga) ratio is approximately 0.51, and the second-stage Cu is retained. It was produced in the same manner as in Example 1 except that the time was set to the time shown in Table 2.
- Comparative Examples 6 and 7 The solar cells of Comparative Examples 6 and 7 were produced in the same manner as in Example 1 except that the light absorption layer was formed by a three-stage vapor deposition method and the heterophasic removal treatment was not performed. The three-stage vapor deposition method will be described below.
- the flux ratio of Ga and In was adjusted in advance so that the Ga / (In + Ga) ratio in the film composition after film formation was 0.51.
- the substrate was heated to 350 ° C., the shutter of each K cell of In, Ga, and Se was opened, and In, Ga, and Se were deposited on the substrate.
- the shutters of the In and Ga K cells were closed, and the deposition of In and Ga was completed. Se continued to supply.
- the shutter of the Cu K cell was opened, and Cu was deposited on the substrate together with Se.
- the electric power for heating the substrate was made constant, and the temperature value was not fed back with respect to the electric power.
- the surface temperature of the substrate is monitored by a radiation thermometer, and in the case of Comparative Example 6, after confirming that the temperature increase of the substrate has stopped and the temperature starts to decrease, the comparative example is In the case of 7, the Cu K cell shutter was closed after 10 minutes to complete the Cu deposition. Se continued to supply.
- the shutters of the K cells of In and Ga were opened again, and In, Ga and Se were deposited on the substrate in the same way as in the first stage.
- Comparative Example 6 15 minutes after the start of the third stage of vapor deposition, and in the case of Comparative Example 7, after 20 minutes, the shutters of the K cells of In and Ga were closed to complete the third stage of vapor deposition. did. Thereafter, the substrate was cooled to 200 degrees, and then the shutter of the Se K cell was closed to complete the formation of the light absorption layer.
- Table 2 shows the solar cell production conditions and various measurement results of Examples 6 to 8 and Comparative Examples 3 to 7.
- Table 3 shows the solar cell production conditions and measurement results of Comparative Example 8 and Examples 9 to 18.
- Example 19 to 23 In the solar cells of Examples 19 to 23, the flux ratio of Ga and In was adjusted in advance so that the Ga / (In + Ga) ratio immediately after the formation of the light absorption layer became the value shown in Table 4, and the foreign phase removal treatment was performed in Table 4. This was prepared in the same manner as in Example 1 except that the method shown in FIG.
- FIG. 4 and 5 show the SEM surface image and SEM cross-sectional image of the light absorption layer 10 of Example 21 used for the calculation of the particle shape parameter A and the particle shape parameter B.
- FIG. 4 and 5 show the SEM surface image and SEM cross-sectional image of the light absorption layer 10 of Example 21 used for the calculation of the particle shape parameter A and the particle shape parameter B.
- Table 4 shows the production conditions of the solar cells of Examples 19 to 23 and the results of various measurements.
- Example 24 Using sulfur as the VIb group element, the Ga / In flux ratio was adjusted in advance so that the Ga / (In + Ga) ratio immediately after the formation of the semiconductor layer was the value shown in Table 5, and the second stage Cu retention time was set in Table 5.
- the solar cell of Example 24 was obtained in the same manner as in Example 1 except that the time shown in FIG.
- Comparative Example 9 The light absorption layer was formed by a one-step vapor deposition method. Comparative example except that sulfur was used as the VIb group element and the flux ratio of each element was adjusted in advance so that the Cu / (In + Ga) and Ga / (In + Ga) ratio immediately after the formation of the semiconductor layer became the values shown in Table 5. The solar cell of Comparative Example 9 was obtained.
- Table 5 shows the solar cell production conditions and various measurement results of Example 24 and Comparative Example 9.
- the substrate on which the back electrode layer was formed was placed in a DC sputtering apparatus, and a precursor layer was formed by a DC sputtering method. Thereafter, the substrate was placed in an annealing furnace, and heat treatment was performed to form a light absorption layer. Details of the light absorption layer formation by the sputtering process and subsequent heat treatment will be described below.
- a target composed of a Cu—Ga alloy (Cu 50 at%, Ga 50 at%) and a target composed of In metal are sputtered simultaneously in the chamber.
- a precursor layer composed of one In alloy layer was formed on the substrate. Further, in the sputtering process, the substrate temperature was set to 200 ° C., and the flow rate of Ar gas was set so that the atmospheric pressure in the chamber was 1 Pa.
- the substrate temperature is set to 550 ° C., and the precursor layer is heated in a mixed atmosphere of Ar and H 2 Se for 1 hour, whereby the precursor layer is selenized, and the thickness is increased.
- a light absorption layer having a thickness of 2 ⁇ m was formed.
- the KCN etching for the time shown in Table 6 was performed as the foreign phase removal treatment performed after the film formation.
- Example 25 The light absorbing layer was formed by sputtering and subsequent heat treatment. Details are shown below.
- the substrate on which the back electrode layer was formed was placed in a sputtering apparatus, and a precursor layer was formed by a sputtering method. Thereafter, the substrate was placed in an annealing furnace, and heat treatment was performed to form a light absorption layer. Details of the formation of the light absorption layer by the sputtering method and the subsequent heat treatment will be described below.
- the substrate temperature is set to 550 ° C., and the precursor layer is heated in a mixed atmosphere of Ar and H 2 Se for 1 hour, whereby the precursor layer is selenized, and the thickness is increased.
- a light absorption layer having a thickness of 2 ⁇ m was formed.
- Table 6 shows the solar cell production conditions and various measurement results of Example 25 and Comparative Example 10.
- Proportion of particles having a full width at half maximum of the photoluminescence spectrum or cathodoluminescence spectrum of 1 meV or more and 15 meV or less and having a particle size of 2 ⁇ m or more and 8 ⁇ m or less on the surface of the light absorption layer particle shape parameter A
- the half width of the photoluminescence spectrum or cathodoluminescence spectrum is 1 meV or more and 15 meV or less, but the particle shape parameter A is It was confirmed that the solar cells of Comparative Examples 1 and 2 having a light absorption layer of less than 90% had a lower conversion efficiency than Examples 1-5. This tendency was also confirmed from Example 25 and Comparative Example 10 in which the light absorption layer was formed by sputtering and heat treatment. Further, when compared with Cu (In, Ga) S 2 , the same was confirmed from Example 24 and Comparative Example 9.
- a solar cell in which the half width of the photoluminescence spectrum or cathodoluminescence spectrum is 1 meV or more and 15 meV or less and the particle shape parameter A is 90% or more, it includes a columnar shape portion in which only a single particle exists in the film thickness direction,
- the solar cells of Examples 9 to 14 in which the ratio of the cross-sectional area of the portion to the cross-sectional area of the entire film (particle shape parameter B) is 90% or more are the same as in Examples 15 to It was confirmed that the conversion efficiency was higher than that of 18 solar cells.
- the conversion efficiencies of the solar cells of Examples 21 and 22 including the light absorption layer having a Cu / (In + Ga) ratio of 0.99 or more and 1.01 or less have the same composition and requirements as those of Examples 21 and 22, and Cu It was confirmed that the / (In + Ga) ratio was larger than the conversion efficiency of the solar cells of Examples 19, 20, and 23, which were outside the range of 0.99 or more and 1.01 or less, respectively.
- Cu (In, Ga) Se 2 formed by subjecting a two-layer precursor formed by sputtering to a selenization heat treatment, and its half-value width is 1 meV or more and 15 meV or less in the photoluminescence spectrum or cathodoluminescence spectrum.
- the conversion efficiency of the solar cell of Example 25 having a light absorption layer having a particle shape parameter A of 90% or more is obtained by subjecting a single layer precursor formed by sputtering to a selenization heat treatment.
- the comparative example 10 is provided with a light absorption layer having a particle shape parameter A of less than 90%. It is confirmed that it is larger than the conversion efficiency of solar cells. .
- SYMBOLS 2 Solar cell which concerns on one Embodiment of this invention, 6 ... Soda lime glass, 8 ... Back electrode layer, 10 ... Light absorption layer, 14 ... Buffer layer, 16 ... Semi-insulating layer, 18 ... window layer (transparent conductive layer), 20 ... upper electrode, 24 ... cross-sectional SEM observation location in solar cell, 202 ... only single particles exist in the film thickness direction Column-shaped portion, 203... Where a plurality of particles exist in the film thickness direction
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Abstract
Description
一般的なCu含有カルコパイライト型p型光吸収層を用いた太陽電池は、光吸収層がCu-poor組成に調整されて用いられる。これは、光吸収層のCu/IIIb元素比が化学量論組成比を超えてCu-rich組成になると、異相であるCuとVIb族元素間の化合物(CuxVIb)が析出するためである。CuxVIbは導電性の高い材料であり、光吸収層中にこの異相が存在すると裏面電極層とバッファ層または窓層とが短絡してしまい、太陽電池特性が大きく劣化してしまう。そのため、これまでCu-rich組成のカルコパイライト型p型半導体膜は光吸収層として一般的には用いられてこなかった。
光吸収層は、Cuと、Gaと、VIb族元素から選ばれる元素とを有するp型半導体層であり、
光吸収層に対するフォトルミネセンススペクトル測定またはカソードルミネセンススペクトル測定において、発光スペクトルの半値幅が1meV以上15meV以下のピークを含み、かつ、
前記光吸収層の表面において、粒径が2μm以上8μm以下である粒子が、前記光吸収層の表面に占める割合が90%以上であることを特徴とする。
図1に本実施形態に係る化合物半導体太陽電池2を示す。
化合物半導体太陽電池2は、基板6と、基板6上に設けられた裏面電極層8と、裏面電極層8上に形成されたp型半導体層として光吸収層10と、光吸収層10上に形成されたバッファ層14と、バッファ層14上に形成された半絶縁層16と、半絶縁層16上に形成された窓層18(透明導電層)と、窓層18上に形成された上部電極20(取り出し電極)と、を備える薄膜型太陽電池である。以下、化合物半導体太陽電池について、太陽電池ということがある。
ここで表面とは、光吸収層10において裏面電極層8と接する面と反対側の面、すなわち、光吸収層10に光が入射する側である。図1では、バッファ層14と接している側の面が該当する。
ここで、断面積とは、光吸収層10を機械的に切断した後研磨し平坦加工した面、またはFIB(Focused Ion Beam)による加工により光吸収層10の断面を膜厚方向に露出した面の面積である。
粒子形状パラメータB=202の面積/(202の面積+203の面積)×100
・・・(1)
IPL∝Iex k ・・・(2)
で表したとき1<k<2であることが好ましい。これにより高い変換効率が得られる傾向がある。
半絶縁層16の厚みは0.01μm以上0.1μm以下の範囲にすることが好ましい。0.01μm以上とすることで、太陽電池のシャント抵抗を高めることができ変換効率が高くなる傾向がある。0.1μm以下とすることで太陽電池の直列抵抗の増加を抑えることができ、変換効率が高くなる傾向がある。
本実施形態では、基板6の上に例えば、スパッタリング法、電子ビーム蒸着法、印刷法などの方法により裏面電極層8を形成する。
(実施例1)
光吸収層の形成において、第二段階Cu保持時間を表1に示した時間に設定した以外は、実施例1と同様に作製し、実施例2~5の太陽電池を得た。
光吸収層の形成を一段階真空蒸着法により成膜した以外は、実施例1と同様にして比較例1及び2の太陽電池を得た。以下、一段階真空蒸着法について説明する。
実施例6~8の太陽電池は、光吸収層の形成を成膜後のGa/(In+Ga)比がおよそ0.51となるようあらかじめGaとInのフラックス比を調整し、第二段階Cu保持時間を表2の時間に設定したこと以外は、実施例1と同様に作製した。
比較例3~5の太陽電池は、成膜後の光吸収層のGa/(In+Ga)比が0.51となるようあらかじめGaとInのフラックス比を調整し、また、Cu-poor組成になるように第二段階Cu保持時間を調整し、異相除去処理を行わなかったこと以外は、実施例1と同様に作製した。
比較例6、7の太陽電池は、光吸収層の形成は三段階蒸着法により行い、異相除去処理を行わなかったこと以外は実施例1と同様に作製した。以下三段階蒸着法について説明する。
比較例8、実施例9~18の太陽電池は、光吸収層の成膜直後のGa/(In+Ga)比が表3に示す値になるようあらかじめGaとInのフラックス比を調整し、第二段階Cu保持時間を表3に示した時間に設定したこと以外は実施例1と同様に作製した。
実施例19~23の太陽電池は、光吸収層の成膜直後のGa/(In+Ga)比が表4に示す値になるようあらかじめGaとInのフラックス比を調整し、異相除去処理を表4に示す方法で行ったこと以外は、実施例1と同様に作製した。
VIb族元素として硫黄を用い、半導体層の成膜直後のGa/(In+Ga)比が表5に示す値になるようあらかじめGaとInのフラックス比を調整し、第二段階Cu保持時間を表5に示す時間に設定したこと以外は実施例1と同様に作製し、実施例24の太陽電池を得た。
光吸収層の形成を一段階蒸着法により行った。VIb族元素として硫黄を用い、半導体層の成膜直後のCu/(In+Ga)とGa/(In+Ga)比が表5に示す値になるようあらかじめ各元素のフラックス比を調整したこと以外は比較例1と同様に作製し、比較例9の太陽電池を得た。
光吸収層をDCスパッタリング法およびそれに引き続く熱処理により形成した。以下に詳細を示す。
光吸収層をスパッタリング法およびそれに引き続く熱処理により形成した。以下に詳細を示す。
また、Cu(In,Ga)S2で比較すると、実施例24及び比較例9からも同様のことが確認された。
Claims (9)
- 裏面電極層と、光吸収層と、透明電極層と、を備える化合物半導体太陽電池であって、
前記光吸収層は、Cuと、Gaと、VIb族元素から選ばれる元素とを有するp型半導体層であり、
前記光吸収層に対するフォトルミネセンススペクトル測定またはカソードルミネセンススペクトル測定において、発光スペクトルの半値幅が1meV以上15meV以下のピークを含み、
かつ、
前記光吸収層の表面において、粒径が2μm以上8μm以内である粒子が、前記光吸収層の表面に占める割合が90%以上であることを特徴とする化合物半導体太陽電池。 - 前記光吸収層は、さらにInを有するp型半導体層であることを特徴とする請求項1に記載の化合物半導体太陽電池。
- 前記光吸収層の断面構造において、膜厚方向に単一の粒子のみ存在する柱状形状の部分を含み、その部分の断面積は膜全体の断面積に占める割合が90%以上であることを特徴とする請求項1または2に記載の化合物半導体太陽電池。
- 前記光吸収層に含まれるCuとIIIb族元素の組成比が0.99以上1.01以下であることを特徴とする請求項1から3に記載の化合物半導体太陽電池。
- 前記光吸収層のフォトルミネッセンスの半値幅が、514.5nmの波長を持つArイオンレーザを励起光源とし、10K(ケルビン)の温度下で測定したフォトルミネッセンスの半値幅であることを特徴とする請求項1から4に記載の化合物半導体太陽電池。
- 前記光吸収層のキャリア密度が1×1016cm-3以上 5×1016cm-3以下であることを特徴とする請求項1から5に記載の化合物半導体太陽電池
- 少なくともGaを含むIIIb族元素とVIb族元素とを同時に真空蒸着する第1のステップと、
CuとVIb族元素とを同時に真空蒸着する第2のステップと、
を有することを特徴とする化合物半導体太陽電池の光吸収層の製造方法。 - 少なくともGaを含むIIIb族元素及びVIb族元素からなる合金又は焼結体ターゲットを用いてスパッタリングする第3のステップと、
前記第3のステップに続いて、Cu及びVIb族元素からなる合金または焼結体ターゲットを用いてスパッタリングする第4のステップと、
前記第3のステップと前記第4のステップで形成された前駆体層にArと、H2SeまたはH2Sとの混合ガス中で熱処理する第5のステップと、
を有することを特徴とする化合物半導体太陽電池の光吸収層の製造方法。 - 前記化合物半導体太陽電池の光吸収層の製造方法において、
製膜直後のCu/IIIb族組成比が1.05から1.80であることを特徴とする
請求項7または8に記載の化合物半導体太陽電池の光吸収層の製造方法。
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JP2018181936A (ja) * | 2017-04-05 | 2018-11-15 | ソーラーフロンティア株式会社 | 光電変換素子 |
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