JP2007235040A - Method of forming metal copper layer on cuprous oxide film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new method of forming a metal layer on a Cu<SB>2</SB>O film by a simple processing method, without requiring a complicated processing step. <P>SOLUTION: There is provided a method of forming a metal Cu layer on a Cu<SB>2</SB>O film surface in which an object to be processed formed with the Cu<SB>2</SB>O film is brought into contact with an aqueous solution containing a reducing agent. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a method for forming a metal Cu layer on the surface of a cuprous oxide (Cu ₂ O) film.

Cuprous oxide (Cu ₂ O) is mainly used as an antifouling agent for ship bottom paints. In addition, it is a p-type semiconductor with a forbidden band around 2.1 eV, which absorbs light in the visible light region. Therefore, the use of solar cells as photoelectric conversion materials has been proposed. For example, there are research reports such as a Schottky type solar cell having a Cu / Cu ₂ O laminated structure, a heterojunction solar cell with In ₂ O ₃ which is an n-type semiconductor (see Non-Patent Documents 1 to 3 below).

Cu ₂ O can be produced by a thermal oxidation method of Cu, and in recent years, there have been several reports on Cu ₂ O film formation by an aqueous solution electrolysis method. For example, it has been reported that a Cu ₂ O film can be obtained directly from an alkaline copper sulfate aqueous solution to which lactic acid, malic acid or the like is added as a complexing agent by a cathodic electrolysis method (see Non-Patent Documents 4 to 6 below).

When forming a solar cell using a Cu ₂ O film as a photoelectric conversion material, it is necessary to form a metal thin film as an electrode so as to form an ohmic junction on the surface of the Cu ₂ O film.

In general, when a metal film is formed on an oxide thin film, the metal thin film is often formed by a dry method such as sputtering or vapor deposition. However, this method requires a large-scale apparatus and has a processing efficiency. Has the disadvantage of being low. As a method of forming a metal thin film by a wet method, after applying an electroless plating catalyst such as Pd to the oxide film surface, Cu, Au, Ag, Ni-P, Ni-B, etc. A method of forming a metal such as is known. However, this method requires a complicated operation consisting of two steps in which electroless plating is performed after applying the catalyst, and a general catalyst application solution contains noble metals such as Pd, Pt, Au, and Ag. In many cases, the aqueous solution is dissolved in an acidic region, and the Cu ₂ O layer may be dissolved.
Solar Energy Materials 4 (1980), P101-112p Appl.Phys. Lett. 34 (1), 47-49 (1979) Bulletin of Nagano National College of Technology No. 25 (1992) Chem. Mater. 8 (1996), p2499 J. Mater. Res 13 (1988). P 909 J. Appl. Electrochem. 34 (2004), p 687p

The present invention has been made in view of the current state of the prior art described above, and its main object is to form a metal layer on a Cu ₂ O film by a simple processing method without requiring a complicated processing step. It is to provide a novel method that is possible.

As a result of intensive studies to achieve the above object, the present inventor has achieved an ohmic junction on the surface of the Cu ₂ O film by a very simple method of bringing the Cu ₂ O film into contact with an aqueous solution containing a reducing agent. The present inventors have found that an Cu layer can be formed, whereby an electrode can be easily formed on the surface of the Cu ₂ O film, and the present invention has been completed here.

That is, the present invention provides a method for forming a metal Cu layer on the surface of the following Cu ₂ O film.
1. A method for forming a metal Cu layer on the surface of a Cu ₂ O film, wherein the object to be treated on which the Cu ₂ O film is formed is brought into contact with an aqueous solution containing a reducing agent.
2. Item 2. The method according to Item 1, wherein the reducing agent is at least one compound selected from the group consisting of amine borane compounds and borohydride compounds.
3. Item 3. The method according to Item 1 or 2, wherein the object to be processed is a solar cell material having a Cu ₂ O layer as a photoelectric conversion material.
4). Item 3. The method according to Item 1 or 2, wherein the workpiece is a material containing a Cu ₂ O film deposited by a photochemical reaction.

Hereinafter, a method for forming a metal Cu layer on the surface of the Cu ₂ O film of the present invention will be specifically described.
According to the method for forming the present invention a method of (I) a metal Cu layer, by contacting the Cu ₂ O film to be processed in an aqueous solution containing a reducing agent, the surface of the Cu ₂ O film is reduced, Cu ₂ An ohmic junction metal Cu layer can be formed on the surface of the O film.

The type of reducing agent is not particularly limited, but examples of reducing agents that exhibit a practical reduction rate include amine borane compounds such as dimethylamine borane (DMAB) and trimethylamine borane (TMAB); sodium borohydride (NaBH ₄ ) And borohydride compounds such as potassium borohydride (KBH ₄ ).

The concentration of the reducing agent in the aqueous solution is not particularly limited, but when the reducing agent concentration is too high, the reduction rate increases and a high-density metallic Cu layer cannot be formed. In addition, when the Cu ₂ O film is thin, the entire film is reduced and metallized in a short time, so that it is difficult to control the manufacturing conditions. Considering these points, the reducing agent concentration is preferably about 0.0001 to 1 mol / l, and more preferably about 0.01 to 0.1 mol / l.

The method of bringing the Cu ₂ O film into contact with the aqueous solution containing the reducing agent is not particularly limited, and the aqueous solution containing the reducing agent is removed from the Cu ₂ O film until a metal Cu layer having a required thickness is formed. Any method can be used as long as it can be brought into contact with the surface. Normally, efficient treatment is possible by a method of immersing an object to be treated in which a Cu ₂ O film is formed in an aqueous solution containing a reducing agent.

  The liquid temperature of the aqueous solution containing the reducing agent is not particularly limited. When the concentration of the reducing agent is high, the Cu layer can be formed at a low liquid temperature, and when the concentration of the reducing agent is low, the treatment is higher. Temperature is required. Usually, the liquid temperature may be about 10 to 70 ° C, preferably about 30 to 60 ° C.

The reduction reaction proceeds from the surface of the Cu ₂ O film, and the thickness of the metal Cu layer increases as the processing time increases. Therefore, the film thickness of the metal Cu layer can be controlled by adjusting the processing time.

(II) Application Example of the Method of the Present Invention (1) Utilization of an Oxide Thin Film Solar Cell as an Electrode Formation Method The method for forming a metal Cu layer of the present invention is, for example, in a solar cell using a Cu ₂ O film as a photoelectric conversion material. It can be applied as a method for forming electrodes on the surface of the Cu ₂ O film.

Hereinafter, a specific configuration example of an oxide thin film solar cell using a Cu ₂ O film as a photoelectric conversion material and a manufacturing method thereof will be described.

As a specific example of a solar cell to which the method for forming a metal Cu layer of the present invention can be applied, an oxide thin film having a structure in which a ZnO film, an Ag ₂ O film, and a Cu ₂ O film are sequentially laminated on a transparent electrode A solar cell can be mentioned. This solar cell has a high conversion efficiency by using Ag ₂ O, which is a p-type oxide semiconductor, as a photoelectric conversion layer and laminated with ZnO, which is an n-type semiconductor. The formation of a Cu ₂ O film with a wide forbidden band suppresses recombination of electrons and holes generated during light irradiation at the ZnO / Ag ₂ O junction interface, resulting in extremely high conversion. The efficiency can be demonstrated.

The transparent electrode is not particularly limited, and a transparent electrode conventionally used in solar cells, for example, a ZnO electrode, an ITO electrode, a SnO ₂ electrode, a NESA electrode, or the like can be used. Although there is no limitation in particular about the thickness of a transparent electrode, What is necessary is just to be about 0.1-1 micrometer, for example.

  A transparent electrode is formed on a transparent substrate as needed. There is no limitation in particular also about the kind of transparent substrate, For example, the various transparent substrates currently used in normal solar cells, such as a glass substrate and a polymer substrate, can be used. Although there is no limitation in particular about the thickness of a transparent substrate, What is necessary is just to be about 0.1-10 mm, for example.

The thicknesses of the ZnO film, the Ag ₂ O film, and the Cu ₂ O film formed on the transparent electrode are not particularly limited, but are usually about 0.01 to 20 μm.

There are no particular limitations on the method of forming the ZnO film, Ag ₂ O film, and Cu ₂ O film. CVD, vapor deposition, sputtering, laser ablation, MBE, and other dry methods, spray pyrolysis, sol-gel methods Further, it can be formed by various methods such as a wet method such as a liquid phase growth method. In particular, when a film is formed from an aqueous solution by an electrochemical method or a chemical method, since the raw materials are relatively inexpensive and the manufacturing cost is low, a solar cell having excellent conversion performance can be obtained at a low cost. Can do.

In addition, according to the formation method from an aqueous solution, a (0001) -oriented ZnO film can be formed. The formed ZnO film has a hexagonal crystal structure with a lattice constant a of about 0.325 nm and c of about 0.521 nm. On this, an AgO film is formed from an aqueous solution, whereby the ZnO (0001) plane is formed. Further, the (−111) plane of AgO having a monoclinic structure having a lattice constant a of about 0.586 nm, b of 0.324 nm, c of 0.550 nm, and β of 107.5 degrees can be preferentially grown. After the AgO film having the (−111) plane preferentially oriented is formed in this way, the (111) plane of the Ag ₂ O film is preferentially formed on the (0001) plane of the ZnO film by heat treatment. It is possible to form a heteroepitaxial structure grown on the substrate. Furthermore, a solar cell having a heteroepitaxial junction can be obtained by forming a Cu ₂ O film from an aqueous solution thereon. In this solar cell, a good junction interface is formed at the atomic level, and the solar cell has high conversion efficiency.

  Methods for forming a ZnO film from an aqueous solution are described in, for example, JP-A-8-217443, JP-A-8-260175, JP-A-9-278437, and JP-A-2005-47752. A known method can be adopted.

  Hereinafter, these methods will be specifically described.

(I) Formation method of ZnO film from aqueous solution (a) Chemical formation method
As a chemical formation method of the ZnO film, a method of immersing an object to be processed in a composition for forming a zinc oxide film made of an aqueous solution containing zinc ions, nitrate ions and an amine borane compound can be employed.

  As a compound serving as a zinc ion source, a water-soluble zinc salt may be used. Specific examples thereof include zinc nitrate, zinc sulfate, zinc chloride, zinc acetate, zinc phosphate, zinc pyrophosphate, and zinc carbonate. Can do. As the nitrate ion source, nitric acid, water-soluble nitrate and the like can be used, and specific examples of nitrate include zinc nitrate, ammonium nitrate, sodium nitrate, potassium nitrate, lithium nitrate, urea nitrate and the like. The compound serving as the zinc ion source and the compound serving as the nitrate ion source can be used singly or in combination of two or more, respectively, and zinc nitrate alone can be used as both the zinc ion and nitrate ion sources. It may be used. In particular, when zinc nitrate is used alone, there are not many unnecessary components in the bath, formation of zinc hydroxide and the like are suppressed, and a high-purity zinc oxide film is formed in a wide concentration range. It becomes possible.

  The concentration of zinc ions and nitrate ions can be adjusted over a wide range. However, if either ion concentration is too low, a zinc oxide film cannot be formed, and if either ion concentration is too high, hydroxylation can occur. A zinc film is easily formed, and the purity of the zinc oxide film is likely to be lowered. For this reason, it is preferable that each density | concentration of zinc ion and nitrate ion exists in the range of about 0.001 mol / l-0.5 mol / l (0.065-32.7 g / l in conversion of zinc content), 0 More preferably, it is in the range of about 0.01 mol / l to 0.2 mol / l (0.65 to 13 g / l in terms of zinc content).

  As the amine borane compound, any water-soluble compound can be used, and specific examples include dimethylamine borane, trimethylamine borane and the like. In particular, when trimethylamine borane is used, the stability of the bath is improved and a good zinc oxide film can be formed continuously for a long period of time.

  The compounding amount of the amine borane compound is not particularly limited. However, if the compounding amount is too small, the stability of the aqueous solution is improved, but the precipitation rate of zinc oxide is slowed, while the compounding amount is too large. In addition to difficulty in dissolution, there is a problem that when heated, the stability of the bath is lowered and precipitation is likely to occur. For this reason, the compounding amount of the amine borane compound is preferably about 0.001 mol / l to 0.5 mol / l, and more preferably about 0.005 mol / l to 0.1 mol / l.

  The liquid temperature during the treatment is preferably about 40 to 100 ° C, more preferably about 60 to 100 ° C. Further, the pH of the composition for forming a zinc oxide film is not particularly limited. However, when the pH is low, the stability of the bath is improved, but the film formation rate is lowered, while when the pH is high. However, the deposition rate is improved, but the stability of the bath is lowered and precipitation is likely to occur, making it difficult to obtain a zinc oxide film. From these points, the pH of the composition is preferably about 4 to 7.

  When the object to be treated does not have catalytic activity, a treatment for imparting a catalytic metal such as palladium, iron, cobalt, nickel, or platinum used when forming an electroless plating film before immersing in the composition. To do. As a specific method of the catalyst application treatment, any known method similar to the catalyst application method in the case of forming an electroless plating film can be applied, and generally a method of applying palladium is widely performed. The catalyst may be applied by a sensitizing-activation method, a catalyst-accelerator method, an alkaline catalyst method, or the like.

  Under the above-mentioned film forming conditions, a ZnO film with good orientation on the (0001) plane can be formed by setting the liquid temperature during film formation to a high temperature of about 75 to 100 ° C.

  In addition, when adopting the method described in Japanese Patent Application Laid-Open No. 2005-28183, a ZnO film preferentially oriented on the (0001) plane can be formed by a simple method, and the orientation and deposition state can be controlled. can do.

  That is, it contains zinc ions, nitrate ions and amine borane compounds, the zinc ion concentration is 0.06 to 0.075 mol / l, and the molar concentration of nitrate ions is within the range of 1 to 3 times the molar concentration of zinc ions. By bringing a composition for forming a zinc oxide film made of a certain aqueous solution into contact with an object to be processed, a ZnO film having a dense structure preferentially oriented on the (0001) plane can be formed. The addition amount of the amine borane compound can be adjusted in a wide range, for example, about 0.001 to 0.5 mol / l, but about 0.01 to 0.1 mol / l. It is preferable. The pH of the composition is preferably about 4 to 7, and the liquid temperature of the composition is preferably about 40 to 90 ° C, more preferably about 55 to 90 ° C.

  Moreover, it contains zinc ions, nitrate ions and amine borane compounds, the zinc ion concentration is 0.075 to 0.1 mol / l, and the molar concentration of nitrate ions is within the range of 1 to 3 times the molar concentration of zinc ions. A ZnO film having a dense structure preferentially oriented in the (0001) plane can also be formed by bringing a composition for forming a zinc oxide film made of an aqueous solution into contact with an object to be processed at a liquid temperature of 70 to 90 ° C. it can. The addition amount of the amine borane compound can be adjusted in a wide range, for example, about 0.001 to 0.5 mol / l, and about 0.01 to 0.1 mol / l. Is preferred. The pH of the composition is preferably about 4-7. In this method, the degree of orientation can be strengthened by increasing the liquid temperature, and the degree of preferential orientation can be adjusted by appropriately setting the liquid temperature of the treatment liquid.

  Furthermore, it contains zinc ions, nitrate ions and amine borane compounds, the zinc ion concentration is 0.01 to 0.05 mol / l, and the molar concentration of nitrate ions is within the range of 1 to 3 times the molar concentration of zinc ions. A composition for forming a zinc oxide film made of an aqueous solution is brought into contact with an object to be processed, and then contains zinc ions, nitrate ions and an amine borane compound, and the zinc ion concentration is 0.08 to 0.1 mol / l. By bringing the composition for forming a zinc oxide film made of an aqueous solution having a molar concentration of ions in the range of 1 to 3 times the molar concentration of zinc ions into contact with the object to be processed, a densely oriented layer preferentially oriented on the (0001) plane A ZnO film having a structure can be formed. According to this method, a porous zinc oxide film preferentially oriented in the (0001) plane is formed in the first step, and then, in the second step, the porous zinc oxide film formed in the first step is formed. Zinc oxide particles grow in the pores, and the pores between the particles disappear, and a zinc oxide film having a dense structure is formed that is preferentially oriented in the (0001) plane. In particular, according to the two-stage deposition method, a zinc oxide film having a very high (0001) plane orientation can be formed.

  Also for the zinc oxide film forming composition used in this method, the amount of amine borane compound added can be adjusted in a wide range, and the zinc oxide film forming composition used in the first step and the oxidation used in the second step. For any of the compositions for forming a zinc film, it can be about 0.001 to 0.5 mol / l, and preferably about 0.01 to 0.1 mol / l. Although it does not specifically limit about the pH of the composition for zinc oxide film formation, It is preferable to set it as about pH 4-7.

  With respect to the treatment time, the treatment in the first step may be performed until a porous zinc oxide film having a desired film thickness is formed, and then the treatment in the second step may be performed until the pores between the particles disappear. For example, when processing is performed for about 5 to 30 minutes in the first step, processing may be performed for about 10 to 60 minutes in the second step. In this method, the treatment temperature can be about 40 to 90 ° C., preferably about 55 to 90 ° C. in both the first step and the second step. In particular, this method can form a dense zinc oxide film preferentially oriented on the (0001) plane at a relatively low treatment liquid temperature of about 55 to 70 ° C., further about 55 to 65 ° C. This is advantageous in that the stability of the treatment liquid is less likely to deteriorate.

The ZnO film formed by the various methods described above is further heated at about 400 to 600 ° C. for about 10 to 300 minutes in an inert gas atmosphere such as N ₂ or Ar or an oxidizable atmosphere such as vacuum. , Electrical conductivity can be improved.

(B) Electrochemical formation method As a method of forming a ZnO film by an electrochemical method, electrolytic treatment may be performed in an aqueous solution containing zinc ions and nitrate ions. By this electrolytic reaction, a ZnO film can be formed on the cathode.

  The electrolytic solution for forming the zinc oxide film may be an aqueous solution containing zinc ions and nitrate ions. For example, an aqueous solution containing zinc nitrate serving as an ion source of both zinc ions and nitrate ions, and water-soluble as a zinc ion source An aqueous solution containing nitric acid or water-soluble nitrate as a nitrate ion source can be used.

  The water-soluble zinc salt is not particularly limited, and examples thereof include zinc nitrate, zinc sulfate, zinc chloride, zinc acetate, zinc phosphate, zinc pyrophosphate, and zinc carbonate. The water-soluble nitrate is not particularly limited, and examples thereof include zinc nitrate, ammonium nitrate, sodium nitrate, potassium nitrate, lithium nitrate, and urea nitrate.

  As the compound used as the zinc ion source and the compound used as the nitrate ion source, one type of each may be used, or a plurality of types may be used in combination.

  The concentration of zinc ions and nitrate ions can be adjusted over a wide range, but if the concentration is too low, it will be difficult to form a continuous film even if the electrolysis conditions are adjusted, and if the concentration is too high, the zinc hydroxide film Tends to be obtained. For this reason, it is appropriate that the concentrations of zinc ions and nitrate ions are usually in the range of about 0.001 mol / l to 0.5 mol / l (0.065 to 32.7 g / l in terms of zinc content). In particular, the concentration is preferably about 0.1 mol / l (6.5 g / l in terms of zinc content).

As the electrolysis method, any ordinary electrolysis method can be adopted. For example, the cathode potential may be appropriately set according to the concentration of the electrolytic solution, etc., but is usually about −0.2 V to −2.0 V on the basis of the Ag / AgCl electrode, and −0.5 V to − About 1.6 V is preferable, and about −0.7 V to −1.6 V is particularly preferable. The cathode current density in this potential range is about 0.00001 mA / cm ² to ²⁰⁰ mA / cm ² , but the cathode current density varies depending on the type of substrate used. The deposition rate of the zinc oxide film increases as the cathode potential becomes lower, in other words, as the cathode current density increases.

  The temperature of the electrolytic solution can be set in a wide range, but is usually about 20 ° C to 100 ° C. In addition, if the pH of the electrolytic solution becomes too high, precipitates are generated in the electrolytic solution, making it impossible to obtain a zinc oxide film. Therefore, it is appropriate to adjust the pH to about 1 to 7, and about pH 5.2. It is preferable that

  As an anode used for electrolysis, any anode used for normal galvanization can be used. As a specific example, insoluble anode materials such as carbon, platinum, and platinum-plated titanium can be used in addition to zinc which is a soluble anode.

  In the electrolysis method described above, in particular, the liquid temperature is set to about 60 to 100 ° C., preferably about 80 to 100 ° C., and constant potential electrolysis is performed at about −0.5 V to −0.8 V on the basis of the Ag / AgCl electrode. However, a ZnO film having a good orientation on the (0001) plane can be obtained.

Method of forming Ag _{2 O} film from (ii) an aqueous solution Next, a method for forming from an aqueous solution of Ag _{2 O} film.
As a method for forming an Ag ₂ O film from an aqueous solution, for example, a method described in “J. Electrochem. Soc., Vol. 143, No. 9, September 1996.” can be employed. Specifically, an Ag ₂ O film can be formed by forming an AgO film by an electrolytic reaction in an aqueous solution containing a water-soluble silver salt and then performing a heat treatment.

  There is no limitation in particular as water-soluble silver salt, For example, silver acetate, silver nitrate, silver lactate, silver methanesulfonate etc. can be used. The concentration of the aqueous silver salt is about 0.01 mol / l to 1 mol / l, preferably about 0.01 mol / l to 0.1 mol / l.

  Furthermore, in order to improve the electrical conductivity of an aqueous solution containing a water-soluble silver salt, sodium acetate, potassium acetate, lithium acetate, ammonium acetate, ammonium nitrate, potassium nitrate, sodium nitrate, sodium lactate, ammonium lactate, etc. may be added. Good. The concentration of these components is preferably about 0.01 mol / l to 1 mol / l, and more preferably about 0.01 mol / l to 0.1 mol / l.

  Although pH of the aqueous solution containing water-soluble silver salt is not specifically limited, It is preferable that it is about 4-9, and it is more preferable that it is about 5-9. The bath temperature is preferably about 10 to 60 ° C, and more preferably about 20 to 40 ° C.

As an electrolysis method, electrolysis may be performed by a method such as constant potential electrolysis or constant current electrolysis using the object to be processed on which the ZnO film is formed as an anode. For example, an Ag plate can be used as the cathode. In the case of galvanostatic electrolysis, the current density 0.1~100mA / cm ^2, preferably about may be set to 0.1~10mA / cm ² approximately. By performing electrolysis by such a method, an AgO film can be formed.

Next, the formed AgO film is heat-treated in an oxidizing atmosphere such as the air, whereby an Ag ₂ O film can be obtained. The heating temperature may be about 100 to 250 ° C., preferably about 130 to 200 ° C. When the heat treatment temperature is too low, it is not preferable because it is not completely Ag ₂ O and tends to have a two-phase structure of AgO + Ag ₂ O. On the other hand, when the heat treatment temperature is too high, Ag in a metallic state is precipitated, and therefore, it is easy to have a two-phase structure of Ag + Ag ₂ O, which is not preferable.

When an Ag ₂ O film is grown heteroepitaxially on a (0001) oriented ZnO film, electrolysis was performed at a current density of about 0.1 to 100 mA / cm ^{2 in} accordance with the above-described conditions to form an AgO film. After that, heat treatment may be performed.

As a method for forming a Cu _{2 O} layer from forming method an aqueous solution of Cu _{2 O} film from (iii) an aqueous solution, for example, a method of electrolytic deposition from an alkaline aqueous solution containing a water-soluble copper salt.

  The water-soluble copper salt is not particularly limited, and for example, copper sulfate, copper chloride, copper nitrate, copper acetate and the like can be used. Moreover, since the aqueous solution containing water-soluble copper salt is used in an alkaline area | region, the complexing agent for suppressing precipitation of a hydroxide is normally mix | blended.

  Usable complexing agents include hydroxycarboxylic acids such as lactic acid, tartaric acid, citric acid, glycolic acid and malic acid.

  The copper salt concentration in the aqueous solution is preferably about 0.1 to 0.5 mol / l and the complexing agent concentration is preferably about 0.5 to 5 mol / l.

  Although the pH of the aqueous solution containing water-soluble copper salt is not specifically limited, Usually, it is preferable that it is about 8-14, and it is more preferable that it is about 9-13. The bath temperature is preferably about 25 to 80 ° C.

As an electrolysis method, electrolysis may be performed by a method such as constant-potential electrolysis or constant-current electrolysis using a workpiece on which an Ag ₂ O film is formed as a cathode. In particular, constant current electrolysis is preferable. As the anode, for example, a Cu plate, a Ti-Pt plate, or the like can be used. In the case of constant current electrolysis, the current density may be in the range of about 30 to 1000 μA / cm ² .

To _{Ag 2 O (111) Cu 2} O (111) on the surface to grow the face, the liquid temperature 40 to 60 ° C. or so, as a range of preferably 45 to 55 ° C., a current density range 30～100Myuei / it is preferably in the cm ^2, and more preferably in a 30～80Myuei / cm ² or so.

According to the method described above, the Cu ₂ O film can be laminated on the Ag ₂ O film by an electrolytic reaction from an aqueous solution.

For the solar cell having a laminated structure of ZnO film / Ag ₂ O film / Cu ₂ O film obtained by the above method, an electrode composed of a metallic Cu layer is formed on the surface of the Cu ₂ O film by applying the method of the present invention. By doing, it can be set as a solar cell. The thickness of the metal Cu layer used as an electrode is not particularly limited, but is usually about 10 to 500 nm.

According to the method for forming a metal Cu layer of the present invention, an electrode can be formed by a very simple method for a solar cell using the above-described Cu ₂ O layer as a photoelectric conversion material. It is easy to control the height.

(2) Application to metallization of Cu ₂ O film formed by photochemical reaction:
By irradiating the alkaline aqueous solution containing a water-soluble copper salt with light through a light-transmitting material placed in contact with the aqueous solution, a Cu ₂ O film is formed on the light-transmissive material. Can be formed. The method for forming a metal Cu layer of the present invention can also be applied to a Cu ₂ O film deposited by such a photochemical reaction.

As a specific method for depositing a Cu ₂ O film by a photochemical reaction, for example, an alkaline aqueous solution containing a water-soluble copper salt is placed in a container at least partially formed of a light-transmitting material, and the light What is necessary is just to irradiate light through a transparent material.

  The light transmissive material is not particularly limited as long as it is a material that can transmit light of a predetermined wavelength. For example, glass materials such as quartz glass, soda glass, and NESA glass, and light transmissive resin materials such as PET, polycarbonate, and ABS can be used.

  The water-soluble copper salt is not particularly limited, and for example, copper sulfate, copper chloride, copper nitrate, copper acetate and the like can be used. Moreover, since the aqueous solution containing water-soluble copper salt is used in an alkaline area | region, the complexing agent for suppressing precipitation of a hydroxide is normally mix | blended.

  Usable complexing agents include hydroxycarboxylic acids such as lactic acid, tartaric acid, citric acid, glycolic acid and malic acid.

  The copper salt concentration in the aqueous solution is preferably about 0.1 to 0.5 mol / l and the complexing agent concentration is preferably about 0.5 to 5 mol / l.

  Although the pH of the aqueous solution containing water-soluble copper salt is not specifically limited, Usually, it is preferable that it is about 8-14, and it is more preferable that it is about 9-13. The bath temperature is preferably about 25 to 80 ° C.

  As light to irradiate, for example, light having a wavelength of about 270 nm or more can be used. As a specific example, an ultrahigh pressure mercury lamp, a high pressure mercury lamp, a low pressure mercury lamp, or the like can be used.

  For example, when using an ultra-high pressure mercury lamp with an output of about 250 to 500 W, the distance from the light source to the substrate on which the film is formed may be about 1 to 5 cm.

According to this method, a Cu ₂ O film can be formed even for various non-conductive materials.

The method for forming a metal Cu layer of the present invention can also be applied to a Cu ₂ O film deposited by the above-described photochemical reaction. For example, a photomask of an arbitrary shape is formed in advance on the surface of a light transmissive material forming a Cu ₂ O film with a light blocking material, and light is irradiated to an alkaline aqueous solution containing a water-soluble copper salt through this material. Cu _{2 O} film is formed Te, the formed Cu _{2 O} film surface by metallization by the method of the present invention, it is possible to form a conductor circuit of any shape.

According to the method for forming a metallic copper layer of the present invention, Cu can be obtained by using a very simple method of bringing a Cu ₂ O film into contact with an aqueous solution containing a reducing agent without using complicated processing steps and large-scale equipment. _A metal Cu layer can be formed on the surface of the ₂ O film.

The method of the present invention is very useful as a method of forming an ohmic junction electrode on the surface of a Cu ₂ O film of a solar cell using, for example, a Cu ₂ O film as a photoelectric conversion material. Further, it can be used for a wide range of applications as a method for metallizing the surface of various other Cu ₂ O films.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Examples 1-4 and Comparative Examples 1-4
A NESA glass substrate is immersed in an aqueous solution of pH 12.5 containing 3 mol / l of lactic acid and 0.4 mol / l of copper sulfate. Using this as a cathode, the liquid temperature is 45 ° C., the cathode current density is 1.0 mA / cm ² , and the current is applied. Electrolysis was performed at an electric amount of 1 C / cm ² to form a Cu ₂ O film having a thickness of about 1.3 μm on the NESA glass substrate.

Next, the substrate on which the Cu ₂ O film was formed by the above-described method was immersed in each aqueous solution shown in Table 1 under the conditions shown in Table 1. Each film after the treatment was measured by thin film XRD diffraction with an incident angle of 0.5 ° to evaluate the presence or absence of metallization, and the film thickness of the Cu layer was determined by cross-sectional SEM observation. The results are shown in Table 1 below.

Claims (4)

A method for forming a metal Cu layer on the surface of a Cu ₂ O film, wherein the object to be treated on which the Cu ₂ O film is formed is brought into contact with an aqueous solution containing a reducing agent. The method according to claim 1, wherein the reducing agent is at least one compound selected from the group consisting of an amine borane compound and a borohydride compound. The method according to claim 1, wherein the object to be processed is a solar cell material having a Cu ₂ O layer as a photoelectric conversion material. The method according to claim 1 or 2, wherein the workpiece is a material containing a Cu ₂ O film deposited by a photochemical reaction.