JP5121678B2 - Compound semiconductor thin film manufacturing method and thin film solar cell manufacturing method - Google Patents

Description

  The present invention relates to a method for producing a compound semiconductor thin film having photoelectric conversion characteristics and a method for producing a thin film solar cell.

  FIG. 1 shows a basic structure of a thin film solar cell including a compound semiconductor thin film having a general chalcopyrite structure. As shown in FIG. 1, a molybdenum (Mo) electrode layer 2 to be a back electrode is formed on the surface of a substrate 1, and a light absorption layer 3 made of a compound semiconductor thin film is formed on the molybdenum electrode layer 2. A transparent electrode layer 5 made of a composite oxide of zinc oxide and aluminum (ZnO: Al) is disposed on the light absorption layer 3 through a buffer layer 4 made of zinc sulfide (ZnS) or CdS (cadmium sulfide). Is formed.

As the light absorption layer 3 made of a compound semiconductor thin film, Cu (In, Ga) Se ₂ (hereinafter abbreviated as CIGS) has been attracting attention as a material capable of obtaining high energy conversion efficiency. Various developments aiming at cost reduction have been carried out in place of high-cost manufacturing methods using system-type devices.

For example, in Patent Document 1, a metal chalcogenide such as Cu ₂ S is dissolved in hydrazine (N ₂ H ₄ ) to form a metal hydrazinium-based precursor solution, and this solution is added to a substrate having an electrode layer. A technique is disclosed in which a metal chalcogenide film can be obtained by applying a film on the electrode to form a film and then heat-treating the film.
US Pat. No. 7,341,917

  However, in the production method of Patent Document 1, hydrazine used as a reagent for dissolving metal chalcogenide is extremely toxic to the human body, and harmful gases such as ammonia may be generated when dissolving metal chalcogenide. There was a problem that it could not be adopted in the manufacturing process.

  Accordingly, an object of the present invention is to provide a method for producing a compound semiconductor thin film and a method for producing a thin film solar cell, which are low in production cost and less dangerous to the human body.

The method for producing a compound semiconductor thin film of the present invention comprises dissolving a chalcogenide of copper, indium and gallium with a compound having an amino group and a hydroxy group as a solvent, and dissolving the copper, indium and gallium, A step of preparing a complex containing at least one of sulfur and selenium, which are constituents of the chalcogenide, a step of applying the complex to the surface of a substrate and drying to form a film of the complex, and the complex And the copper, the indium, the gallium, the sulfur, and the surface of the substrate are heat-treated in a reducing atmosphere containing hydrogen, nitrogen, or any one of these mixed gases and selenium. Forming a thin film mainly composed of at least one of selenium.

  In the method for producing a compound semiconductor thin film of the present invention, since a compound having an amino group and a hydroxy group is used as a solvent for dissolving each chalcogenide of copper, indium and gallium, the structure of copper, indium and gallium and chalcogenide At least one of sulfur and selenium as components can be easily dissolved, and in the step of dissolving these metal components, and in the compound having an amino group and a hydroxy group, copper, indium and gallium, In the process of producing a complex containing at least one of sulfur and selenium, which are constituents of chalcogenide, there is no generation of harmful gases such as ammonia, so that safe production is possible with little danger to the human body. Become.

In addition, by using a gas containing selenium as the reducing atmosphere, evaporation of highly volatile selenium can be suppressed, so that a dense compound semiconductor thin film can be obtained, and composition fluctuations and depletion defects can be prevented. Therefore, it is possible to easily manufacture a compound semiconductor thin film having a stable composition.

The method for producing a thin-film solar cell of the present invention comprises dissolving a chalcogenide of copper, indium, and gallium with a compound having an amino group and a hydroxy group as a functional group, and dissolving the copper, indium, and gallium, A step of preparing a complex containing at least one of sulfur and selenium, which are constituents of the chalcogenide, and a step of applying the complex on a pre-formed electrode layer and drying to form a film of the complex The film of the complex is heat-treated in a reducing atmosphere containing hydrogen, nitrogen, or a mixed gas thereof and selenium, and the copper, the indium, and the gallium on the electrode layer, A step of forming a light absorption layer comprising a thin film mainly comprising at least one of sulfur and selenium; and on the light absorption layer Characterized by comprising a step of forming a buffer layer, and a step of further forming a transparent electrode layer on the buffer layer.

  Also in the method of manufacturing the thin film solar cell of the present invention, as in the above-described method of manufacturing the compound semiconductor thin film, a compound having an amino group and a hydroxy group is used as a solvent for dissolving the respective chalcogenides of copper, indium and gallium. Therefore, it is possible to easily dissolve copper, indium, and gallium and at least one of sulfur and selenium, which are components of chalcogenide, and a step of dissolving these metal components, an amino group, and In the process of preparing a complex in which copper, indium, gallium and chalcogen are incorporated into a compound having a hydroxy group, there is no generation of harmful gases such as ammonia, so there is little danger to the human body and it is a safe thin film solar The battery can be manufactured.

In addition, by using a gas containing selenium as a reducing atmosphere gas, it is possible to suppress evaporation of chalcogen components such as highly volatile selenium. Therefore, an element having photoelectric conversion characteristics constituting a thin film solar cell. A certain compound semiconductor thin film can be densified, and composition fluctuations and depletion defects of the thin film can be suppressed, so that high photoelectric conversion characteristics can be obtained.

  According to the method for producing a compound semiconductor thin film and the method for producing a thin film solar cell of the present invention, there is no generation of harmful gas such as ammonia when dissolving metal chalcogenide. It becomes possible, and cost reduction can be achieved.

  The manufacturing method of the compound semiconductor thin film of this invention is demonstrated in detail.

  In the present invention, a compound having an amino group and a hydroxy group is used as a solvent, and a chalcogenide of copper (Cu), indium (In) and gallium (Ga) (hereinafter abbreviated as metal chalcogenide) is dissolved therein, and then copper, indium And a gallium and a complex containing at least one of sulfur and selenium which are constituents of chalcogenide (hereinafter abbreviated as complex), and then applying the complex on a substrate and heat-treating the compound semiconductor A thin film is formed.

As the chalcogenide of copper (Cu), Cu ₂ S or Cu ₂ Se, or a mixture thereof is used. As the chalcogenide of indium (In), In ₂ S or In ₂ Se ₃ , or a mixture thereof is used. As the chalcogenide of gallium (Ga), Ga ₂ S ₃ , Ga ₂ Se ₃ , or a mixture thereof is used.

  The composition of these copper (Cu), indium (In), gallium (Ga), Se (selenium) and sulfur (S) is 0.8 to 1.1 for copper and 0.5 to 0 for indium in a molar ratio. .9, each metal chalcogenide is blended so that the ratio of gallium is 0.1 to 0.5 and sulfur or selenium is 1.7 to 2.3.

  The purity of these metal chalcogenides is preferably 99% or more for the reason of improving the characteristics as a P-type semiconductor element. In the present invention, tellurium (Te) chalcogenide may be used instead of sulfur or selenium.

  In the method for producing a compound semiconductor of the present invention, a compound having an amino group and a hydroxy group is used as a solvent for dissolving a metal chalcogenide. In addition, about the compound which has an amino group and a hydroxy group, the identification whether it has an amino group and a hydroxy group is performed by infrared absorption spectroscopy analysis.

  As the compound having an amino group and a hydroxy group, it is desirable to use one kind selected from hydroxylamine, ethanolamine, diethanolamine, 2-dimethylaminoethanol, acetohydroxamic acid, and benzbenzhydroxamic acid.

  Of these, hydroxylamine or ethanolamine is particularly preferred because of the high solubility of metal chalcogenides.

These compounds having an amino group and a hydroxy group are less toxic than hydrazine (N ₂ H ₄ ) that has been conventionally used to dissolve metal chalcogenides, and even when reacted, hydrazine is used. Since no harmful gas such as ammonia is detected, the production process can be constructed with low impact on the human body and high safety. A compound having an amino group and a hydroxy group is preferably used with a purity of 99% or more.

  The mixing ratio of the compound having an amino group and a hydroxy group and the metal chalcogenide is desirably a ratio of 2.5 to 14 when the metal chalcogenide is 1 by mass ratio. When the mixing ratio of the compound having an amino group and a hydroxy group and the metal chalcogenide is set to the above ratio, the metal chalcogenide is easily dissolved in the compound having an amino group and a hydroxy group, and the precipitation of the metal component in the complex is suppressed. Can be kept stable for a long time.

  In addition, there is an advantage that the compound semiconductor thin film obtained after the complex is applied on the substrate, dried and heat-treated can be prevented from being distributed in an island shape.

  Here, the distribution of the compound semiconductor thin film in an island shape means a state in which the compound semiconductor thin film formed on the substrate is present in isolation on the substrate. The state in which the compound semiconductor thin film is distributed in an island shape is determined by observing the substrate on which the compound semiconductor thin film is formed with a metal microscope.

  Next, each metal chalcogenide of copper, indium and gallium is dissolved in a compound having an amino group and a hydroxy group to prepare a complex containing copper, indium and gallium and at least one of sulfur and selenium.

  In the present invention, a crystal having a chalcopyrite structure is formed by crystallization from a complex containing all components constituting the crystal, so that Se or S or the like is formed on a film containing Cu, In and Ga as main components. Compared with the conventional method of forming a CIGS film by diffusion by spraying a gas, Se or S does not have a concentration gradient in the thickness direction from the surface side of the film to the substrate side, so the composition of the film is more uniform. There is an advantage that it can be made.

  In this case, the mixing of these metal chalcogenides and the compound having an amino group and a hydroxy group may employ a method in which each metal chalcogenide is dissolved in a compound having an amino group and a hydroxy group, respectively. By using a method in which each metal chalcogenide is dissolved in a compound having an amino group and a hydroxy group, the metal chalcogenide can be dissolved in accordance with the difference in solubility of the metal chalcogenide and the dissolution time can be shortened. It becomes possible to suppress insolubilization due to.

  In the method for producing a compound semiconductor thin film of the present invention, when metal chalcogenide is dissolved in a compound having an amino group and a hydroxy group, the operation is performed in a glove box substituted with nitrogen gas. This is because the metal chalcogenide is prevented from being oxidized and a residue of oxides such as sulfur and selenium generated from the metal chalcogenide is not left.

  The metal chalcogenide is preferably used in the form of a powder for the purpose of enhancing the solubility in a compound having an amino group and a hydroxy group, and the average particle size is preferably 2 μm or less, while the rapid reaction during dissolution The average particle size is desirably 10 nm or more from the reason of suppressing the above.

  Next, a complex obtained by dissolving a metal chalcogenide in a compound having an amino group and a hydroxy group is applied to the surface of the substrate and dried to prepare a complex film. The substrate to be used is preferably a highly heat-resistant substrate such as a soda lime glass substrate, a ceramic substrate, a metal substrate such as molybdenum (Mo) and SUS, or a resin substrate such as polyimide.

  The complex is preferably coated on the substrate using a spin coater, screen printing, dipping, spraying, a die coater or the like. The drying is preferably performed in a low oxygen reducing atmosphere, and the temperature is preferably 50 to 200 ° C. for the purpose of suppressing polymerization of the compound having an amino group and a hydroxy group to prevent carbonization during heat treatment. .

  For the reason that the surface of the substrate increases the wettability of the complex, the surface roughness (Ra) is preferably 0.1 μm or less, particularly preferably 0.01 μm or less. Further, a compound having an amino group and a hydroxy group may be coated on the surface of the substrate for the purpose of increasing the wettability of the complex to the substrate surface.

  In addition, the thickness of the complex applied to the surface of the substrate is appropriately set depending on the application. For example, when used as a light absorption layer of a thin film solar cell, the output and a compound semiconductor thin film (hereinafter also referred to as a film) are necessary. In consideration of strength and the like, it is preferable that the thickness after drying is in the range of 2 to 5 μm and the variation is within 20%. If the variation in film thickness after drying is within 20%, the compound semiconductor thin film formed on the substrate can have the same level of P-type semiconductor characteristics over the entire surface, thereby providing uniform photoelectric conversion characteristics. There is an advantage that a film having the following can be obtained.

Next, the complex film is heat-treated in a reducing atmosphere containing any one of hydrogen, nitrogen, and a mixed gas thereof (forming gas (N ₂ −12.5% H ₂ )). In this case, hydrogen is preferable as the gas used because the film can be densified. The reducing atmosphere during the heat treatment is preferably a reducing atmosphere in which moisture is removed through a hygroscopic agent. The hygroscopic agent is not particularly limited as long as it can remove moisture, but a molecular sieve or the like is preferably used.

In the preparation of the compound semiconductor thin film of the present invention, as a gas for a reducing atmosphere, further Ru using a gas containing selenium. When heating is performed by further containing selenium in the reducing atmosphere, formation of voids due to evaporation of chalcogen components such as selenium generated during heating can be suppressed in the obtained compound semiconductor thin film, and composition change and depletion defects of this thin film can be suppressed. There is an advantage that can be compensated.

  Here, the compactness of the compound semiconductor thin film is obtained by polishing the cross section of the obtained compound semiconductor thin film, observing the cross section by observation with a scanning electron microscope, and visually confirming that there is no elongated void along the grain boundary in the cross section of the film. The case is a dense film. On the other hand, a non-densified film refers to a case where elongated voids along grain boundaries are clearly visible on the cross section of the film. Here, the magnification in the scanning electron microscope when observing the cross section of the film is 10000 to 20000 times. In this observation, the entire region in the direction perpendicular to the stacking direction of the compound semiconductor thin films formed on the substrate is observed with respect to the cross section of the sampled sample. The number of samples to be observed is one extracted from the obtained compound semiconductor film.

  The temperature of the heat treatment is preferably 400 to 600 ° C., although it depends on the composition of the obtained compound semiconductor thin film. When the temperature of the heat treatment is 400 to 600 ° C., a compound semiconductor thin film (CIGS thin film) having a chalcopyrite type crystal structure formed from at least one of copper, indium and gallium, sulfur and selenium is obtained. There is an advantage that crystallinity can be enhanced.

  The thickness of the thin film is 1 to 2.5 μm because it has a P-type semiconductor characteristic as a compound semiconductor thin film, and high photoelectric conversion characteristics can be obtained over the entire film and the photoelectric conversion characteristics per unit mass can be enhanced. In this case as well, it is desirable that the film thickness variation is within 20%. In order to keep the variation in film thickness within 20%, it is better to control the content of the metal component contained in the complex. In this case, the mixing ratio of the compound having an amino group and a hydroxy group and the metal chalcogenide is mass. When the ratio of the metal chalcogenide is 1, the ratio is preferably 2.5 to 14.

  Next, the manufacturing method of the thin film solar cell of this invention is demonstrated. Also in the manufacturing method of the thin film solar cell of this invention, the process of forming the compound semiconductor thin film as a light absorption layer is the same as the manufacturing method of the compound semiconductor thin film mentioned above.

First, a substrate made of soda lime glass is prepared, and an electrode layer is formed on this substrate. The electrode layer is preferably made of any electrode material such as molybdenum (Mo), tungsten (W), chromium (Cr), polysilicon (SiO ₂ ), metal silicide, or aluminum (Al). The electrode layer can be formed by a vapor deposition method, a sputtering method, a coating method, or the like. The thickness of this electrode layer is, for example, 0.5 to 1.5 μm.

  Next, a compound semiconductor thin film as a light absorption layer is formed on the electrode layer by the manufacturing method described above.

Next, after forming a compound semiconductor thin film as a light absorption layer, the high resistance layer made of Cu ₂ Se or the like on the surface is removed by etching with an aqueous KCN solution. By removing the high resistance layer made of Cu ₂ Se or the like on the surface, the adhesion with the buffer layer can be improved and the electrical resistance can be lowered.

Thereafter, an n-type buffer layer for heterojunction is formed on the light absorption layer. CdS, ZnS, ZnSe, ZnMgO, ZnS / ZnMgO, ZnO, InS, InSe, In (OH) ₃ , ZnInSe, ZnInS, ZnSSe, CuI, Mg Materials such as OH) ₂ are used. These can be produced by immersing a substrate formed up to the light absorption layer by a dip coating method, CBD method (solution growth method) or the like in an aqueous solution, depositing fine particles, and performing a heat treatment under a predetermined temperature condition. In this case, the thickness of the buffer layer is desirably 10 to 200 nm. When the thickness of the buffer layer is 10 to 200 nm, there is an advantage that the conductivity between the light absorption layer and the transparent electrode layer stacked via the buffer layer can be increased.

  Next, a transparent electrode layer made of ITO or ZnO is formed on the buffer layer by sputtering, spraying, or coating. Further, the thickness of the transparent electrode layer is desirably 0.5 to 3.0 μm. When the thickness of the transparent electrode layer is 0.5 to 3.0 μm, there is an advantage that the conductivity of the transparent electrode layer can be secured and the light transmittance can be increased.

  According to the method of manufacturing a thin film solar cell described above, a compound semiconductor thin film can be produced at low cost, and there is no danger to the human body because no harmful gas such as ammonia is generated when the compound semiconductor thin film is produced. Safe manufacturing is possible.

  The thin film solar cell thus obtained is a thin film solar cell having a light absorption layer between a pair of electrode layers. For example, as shown in FIG. 1, an electrode layer 2 serving as a back electrode is formed on a substrate 1. A light absorption layer 3 made of a compound semiconductor thin film is formed on the electrode layer 2, and a transparent electrode layer 5 is formed on the light absorption layer 3 through a buffer layer 4. In addition, although the example which laminated | stacked the board | substrate 1, the electrode layer 2, the light absorption layer 3, the buffer layer 4, and the transparent electrode layer 5 was demonstrated one by one, in this invention, the light absorption layer 3 is provided between a pair of electrode layers 2 and 5. As long as it has, you may form various intermediate | middle layers between the said layers. Further, the present invention may be of a type that does not include the substrate 1, in other words, a type in which the electrode layer 2 functions as a substrate.

  EXAMPLES Hereinafter, although the manufacturing method of the compound semiconductor thin film and thin film solar cell of this invention is demonstrated in detail, giving an Example and a comparative example, this invention is not limited only to a following example.

First, Cu ₂ Se, In ₂ Se ₃ and Ga ₂ Se ₃ which are chalcogenides of selenium and Cu ₂ S, In ₂ S ₃ and Ga ₂ S ₃ which are chalcogenides of sulfur were prepared as metal chalcogenides. The purity of these metal chalcogenides is 99.9%.

  As the compound having an amino group and a hydroxy group, hydroxylamine and ethanolamine were prepared. Metal chalcogenides have a molar ratio of Cu: In: Ga: Se (or S) of 1: 0.7: 0.3; 2 and Cu: In: Ga: Se: S of 1: 0.7: 0. The composition was adjusted to a molar ratio of 3: 1: 1.

  Next, a mixture of a metal chalcogenide and a compound having an amino group and a hydroxy group is prepared by adding a predetermined amount of a compound having an amino group and a hydroxy group to each metal chalcogenide and dissolving them, and then dissolving the solution in which each metal chalcogenide is dissolved at room temperature. In addition, by stirring for 12 hours in a nitrogen atmosphere, a complex which is a solution in which a metal chalcogenide is dissolved in a compound having an amino group and a hydroxy group was prepared.

  Note that Cu: In: Ga: Se (or S) is 1: 0.7: 0.3; 2 or Cu: In: Ga: Se: S is 1: 0.7: 0.3: 1: 1. Table 1 shows the amount of metal chalcogenide blended in a molar ratio. Table 1 shows the total amount of the compounds having amino groups and hydroxy groups used.

  A complex composed of Cu, In, Ga, Se (or S, or Se and S) when the metal chalcogenide is dissolved in a compound having an amino group and a hydroxy group, and a solution in which each metal chalcogenide is dissolved is mixed and stirred. In the process during the manufacturing process, the presence or absence of gas generation was confirmed. The generation of this gas was confirmed by collecting the gas from an exhaust pipe provided in the glove box and confirming this gas with a gas chromatography apparatus.

  Next, the prepared complex was applied on a soda lime glass substrate (hereinafter referred to as substrate) using a spin coater in a nitrogen-substituted glove box to form a complex film.

Next, the substrate on which the complex film was formed was heated in a drier to produce a complex film. At this time, the heating conditions were 150 ° C. and 1 hour. Next, the substrate on which the complex film was formed was placed in a tubular furnace and subjected to heat treatment, and the complex film was crystallized to produce a compound semiconductor thin film having an average thickness of 0.5 to 1.5 μm. The heat treatment conditions were a maximum temperature of 525 ° C., a holding time of 1 hour, and hydrogen gas, nitrogen gas, forming gas (N ₂ −12.5% H ₂ ), hydrogenated selenium gas, and nitrogen gas as carriers as a reducing atmosphere. Any one of the selenium gases was introduced.

  With respect to the obtained compound semiconductor thin film, first, it was determined whether or not the compound semiconductor thin film formed on the substrate was distributed in an island shape by observation with a metal microscope. The number of samples to be observed was one extracted from the obtained compound semiconductor film.

  Next, cross-sectional observation of the compound semiconductor thin film was performed to evaluate the denseness of the film. The cross section of the thin film was observed using a scanning electron microscope at a magnification of 15000 times, and the entire cross section of the sampled sample was observed in the direction perpendicular to the stacking direction of the compound semiconductor thin film formed on the substrate. . Also, the number of samples to be observed was one extracted from the compound semiconductor film obtained in this case.

  As is apparent from the results in Table 1, sample No. 1 was prepared by using a compound having an amino group and a hydroxy group as a solvent for dissolving the metal chalcogenide and performing heat treatment in a reducing atmosphere of hydrogen, nitrogen and forming gas. In 1-12 and 14-25, there was no generation | occurrence | production of harmful | toxic gas, such as ammonia, and the compound semiconductor thin film was able to be manufactured safely.

  In particular, when selenium hydride is used as a reducing atmosphere gas (Sample Nos. 10 and 23) and when selenium gas is used as a carrier gas (Sample Nos. 11 and 24), the obtained compound semiconductor film As for the cross-section, no voids were observed at the grain boundary, and a dense film was obtained.

  On the other hand, in samples (samples Nos. 13 and 26) using hydrazine to dissolve the metal chalcogenide, it was confirmed that ammonia gas harmful to the human body was generated when the metal chalcogenide was dissolved.

  In addition, sample No. In the case where a thin film solar cell having the structure of FIG. 1 in which a compound semiconductor thin film is used as a light absorption layer using a complex prepared under the conditions of 1 to 12 and 14 to 25 is used, a metal chalcogenide is added to a compound having an amino group and a hydroxy group. In the process of dissolving, no harmful gas was generated, and the thin film solar cell could be manufactured safely.

  According to the manufacturing method of the present invention, since a vacuum system apparatus such as a sputtering apparatus is not used for manufacturing the compound semiconductor thin film, the manufacturing cost can be reduced.

It is sectional drawing which shows an example of a general thin film solar cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Electrode layer 3 ... Light absorption layer 4 ... Buffer layer 5 ... Transparent electrode layer

Claims (2)

A compound having an amino group and a hydroxy group as a functional group is used as a solvent to dissolve each chalcogenide of copper, indium and gallium, and sulfur and selenium as constituent components of the copper, the indium and the gallium, and the chalcogenide A step of preparing a complex containing at least one of the above, a step of applying the complex to the surface of the substrate and drying to form a film of the complex, and forming a film of the complex with hydrogen, nitrogen and these Heat treatment is performed in a reducing atmosphere containing any one of the mixed gases and selenium, and the surface of the substrate is mainly composed of the copper, the indium, and the gallium, and at least one of the sulfur and the selenium. Forming a thin film comprising: a method of manufacturing a compound semiconductor thin film. A compound having an amino group and a hydroxy group as a functional group is used as a solvent to dissolve each chalcogenide of copper, indium and gallium, and sulfur and selenium as constituent components of the copper, the indium and the gallium, and the chalcogenide A step of preparing a complex containing at least one of the above, a step of applying and drying the complex on an electrode layer formed in advance, and preparing a film of the complex; And a heat treatment in a reducing atmosphere containing any of these mixed gases and selenium, and on the electrode layer, the copper, the indium and the gallium, and at least one of the sulfur and the selenium, Forming a light-absorbing layer comprising a thin film containing as a main component, forming a buffer layer on the light-absorbing layer, Preparation of thin-film solar cell, characterized by comprising a step of forming a transparent electrode layer on Rani該 buffer layer.