JP4829046B2 - Method for producing metal sulfide nanoparticles and photoelectric conversion element - Google Patents

Description

  The present invention relates to a method for producing metal sulfide nanoparticles and a photoelectric conversion element such as a solar cell.

  In recent years, nanomaterials have been actively researched because of their unique properties different from bulk materials. When the size of a semiconductor is on the order of nanometers, a “quantum confinement effect” in which electron-hole pairs (excitons) are confined in a narrow region is observed. As an example, direct transition semiconductor nanoparticles such as CdS are called “quantum dots”, and it is well known that the emission wavelength and band gap can be controlled by the particle size. In addition, it is known that a semiconductor ultrathin film is cut in one direction by using a method such as electron beam lithography to form a linear quantum well structure, and a quantum size effect with a shape can be obtained. As described above, semiconductor nanoparticles capable of controlling an electronic state are expected to be applied to next-generation light-emitting materials, optical materials, or energy conversion materials. In recent years, nanoparticles have been put into practical use as products that replace conventional organic dyes in the biomedical field as markers for biological tissues.

  Conventional methods for producing nanoparticles are roughly divided into a breakdown method (top-down method) and a build-up method (bottom-up method). The breakdown method is a method in which a bulk material is pulverized into fine particles, but the particle size is limited to the submicron level. The build-up method is further classified into three types: a solid phase method, a gas phase method, and a liquid phase method. The solid phase method takes a long time in the production process, and particle aggregation is remarkable and size control is difficult. Therefore, the solid phase method is not suitable for practical use, and the gas phase method and the liquid phase method are mainly used. . In the vapor phase method, the particle size, crystal structure, and the like can be controlled by selecting the concentration of vapor and reaction gas and the carrier gas type, and nanoparticles with a pure composition can be obtained, but they are not suitable for mass synthesis. In addition, since the obtained nanoparticles accumulate randomly on the substrate, it is difficult to form a device by arranging the nanoparticles in an ordered manner. On the other hand, the liquid phase method is advantageous in that it can be mass-produced and a device can be created by utilizing self-assembly of nanoparticles (Non-Patent Document 1).

  In the liquid phase method, synthesis in a dilute solution has been tried for a long time (homogeneous liquid phase synthesis), and made a great contribution to the study of quantum dots in the early stage. In addition, the synthesis of nanoparticles using reverse micelles has been actively studied in recent years, and it has been shown that monodisperse nanoparticles can be synthesized in a relatively large amount (reverse micelle method). In the course of such research, the group of Bawendi and Alivissatos et al. Found a method for synthesizing highly monodisperse semiconductor nanoparticles in a high-temperature polar solvent (hot soap method). In this method, the surfactant adsorbed on the surface of the particles controls particle growth and prevents aggregation, whereby monodispersed nanoparticles can be obtained. Unlike the reverse micelle method, this hot soap method is synthesized in a non-aqueous solvent, so it is less affected by oxidation and the like, and the surfactant inactivates dangling bonds on the surface. It is characterized by extremely high quantum efficiency compared to particles.

  However, in the hot soap method, it is very difficult to scale up the production process because dangerous raw materials such as metal alkoxides are used, and TOP / TOPO used as a surface protective agent is expensive and corrosive. (Nonpatent literature 2, 3) There existed a fault.

On the other hand, the present inventors and Korgel's group obtained copper sulfide nanoparticles by reacting a copper precursor with a thiol compound (Non-Patent Documents 4 and 5), and reacting a metal precursor with a thiol compound. And a method for producing metal sulfide nanoparticles is proposed (Patent Document 1 ).

Kikuo Okumura “Forefront of Nanomaterials” Chemistry Doujin 2002 C. B. Murray et al .: J. Am. Chem. Soc 115,8706 (1993) X. Peng et al .: J. Am. Chem. Soc 119,7019 (1997) Chem. Lett.vol.33 352-353 (2004) J. Am. Chem. Soc. Vol.125,5638 (2003) JP 2005-325016 A

  However, at present, there are only a few practical examples, and the nanoparticle production itself that fully considers the size distribution, chemical composition, material purity, material type, crystal structure, etc., which greatly affects the functional expression of nanoparticles, is a technical issue. It is.

Further, the methods disclosed in Non- Patent Documents 4 and 5 have relatively high reaction conditions (300 ° C.), and a method of synthesis under milder conditions has been desired. In Patent Document 1, it is said that metal sulfide nanocrystals can be applied to inorganic-organic hybrid electroluminescent devices, but the application to photoelectric conversion devices is not described.

  The inventors have previously found that copper sulfide and zinc sulfide can be easily obtained by thermally decomposing a metal-thiol complex. This method uses a relatively harmless raw material as a raw material, but has a problem of requiring an expensive high-boiling solvent because the decomposition temperature of the complex is high.

  The present invention has been made in view of the above-described conventional circumstances, and can be expected to be applied to optical functional materials, electronic devices and the like industrially at a low cost and at a low cost compared to conventional synthesis methods. The synthesis of metal sulfide nanoparticles is an issue to be solved. Another object of the present invention is to propose a novel photoelectric conversion element using metal sulfide nanoparticles.

The method for producing metal sulfide nanoparticles of the present invention comprises a precursor metal complex (excluding a precursor metal complex prepared from copper acetate or acetylacetone copper and an amine compound) and a thiol compound solution (hereinafter referred to as “ sulfur” ). , Referred to as “sulfur / thiol solution”).

  In the production method of the present invention, metal sulfide nanoparticles can be synthesized under mild conditions and at a low cost compared to conventional synthesis methods. The obtained metal sulfide nanoparticles can be expected to be applied to photoelectric conversion elements and other electronic devices.

The method for producing metal sulfide nanoparticles will be described in detail. First, the preparation method of a precursor metal complex is demonstrated. The method for preparing the precursor metal complex is not particularly limited except that it is prepared from copper acetate or acetylacetone copper and an amine compound, but the metal salt containing the target metal and the amine compound are converted into an ether compound, toluene. It is preferable to contact them in a solvent such as hexane, or to add a metal salt directly into the amine using the amine itself as a solvent.

  A metal-amine complex (precursor metal complex) is formed by the reaction between the metal salt and the amine compound. By reacting this metal-amine complex with a sulfur / thiol solution and sulfiding, metal sulfide nanoparticles can be obtained.

  Examples of the metal salt include, but are not limited to, acetate, acetylacetonate, metal halide, sulfate, nitrate, perchlorate, hydrochloride, perchlorate, oxide, and organic acid salt. Of these, acetate and acetylacetonate are preferred.

Acetate, as the acetylacetonate, acetate, cadmium acetylacetonate, zinc acetate, zinc acetylacetonate, mercury acetate, mercury acetylacetonate, lead acetate, lead acetylacetonate, tin acetate, tin acetylacetonate, Germanium acetate, germanium acetylacetonate, gallium acetate, gallium acetylacetonate, indium acetate, indium acetylacetonate, thallium acetate, thallium acetylacetonate, titanium acetate, titanium acetylacetonate, manganese acetate, manganese acetylacetonate, nickel acetate , Nickel acetylacetonate, molybdenum acetate, molybdenum acetylacetonate, palladium acetate, palladium acetylacetonate, silver acetate, silver acetylacetonate It can be mentioned.

  Any amine compound may be used as long as it has a primary amine or secondary amine structure. For example, ethylamine, propylamine, 1-butylamine, octylamine, oleylamine, aniline and the like can be mentioned, among which octylamine and oleylamine are preferably used. The amine compound functions as a “surface protective agent” in addition to functioning as a “complexing agent”.

  The mixing ratio of the metal salt, the amine compound and the solvent is not particularly limited as long as the whole is a uniform solution, and is appropriately selected depending on the combination of the metal salt to be used and the amine compound to be used.

  The preparation temperature and contact time of the precursor metal complex are not particularly limited and can be appropriately selected depending on the combination of the metal salt and the amine compound, but the preparation temperature is usually preferably in the range of −20 ° C. to 150 ° C., The contact time is preferably in the range of 0.5 minutes to 3 hours.

  In the present invention, sulfur and a thiol compound are mixed to prepare a sulfur / thiol solution. When sulfur is dissolved in the thiol compound, it becomes hydrogen sulfide by the reducing ability of the thiol compound under the reaction formula (R is an alkyl group) of Chemical Formula 1 and becomes a sulfur source for the target metal sulfide nanoparticles.

(Chemical formula 1)
S + 2RSH → (RSH) ₂ S → H ₂ S + RSSR

The thiol compound comprises (1) an alkyl group having 3 to 20 carbon atoms, (2) an aryl group having 6 to 14 carbon atoms, (3) an aralkyl group having 7 to 20 carbon atoms , and (4) nitrogen, sulfur and oxygen. It may have a functional group selected from heterocyclic groups including one or more selected. In addition to functioning as a “reducing agent” for sulfur, the thiol compound functions as a “surface protective agent”.

  Specifically, as the thiol compound having an alkyl group, ethanethiol, 1-propanethiol, 2-propanethiol, 1-butanethiol, 2-butanethiol, 1-pentanethiol, octanethiol, decanethiol, dodecanethiol And pentadecanethiol. Moreover, dithiol, trithiol, etc. which have two or more thiol parts can also be used.

  Examples of the thiol compound having an aryl group include thiophenol, 2-naphthalenethiol, 3-naphthalenethiol, dimethylbenzenethiol, and ethylbenzenethiol. Moreover, dithiol, trithiol, etc. which have two or more thiol parts can also be used.

  Examples of the thiol compound having an aralkyl group include benzylthiol, 2-phenylethanethiol, and 3-phenylpropylthiol. Moreover, dithiol, trithiol, etc. which have two or more thiol parts can also be used.

  Examples of the thiol compound having a heterocyclic group include 2-mercaptopyridine, 4-mercaptopyridine, 2-mercaptopyrimidine, 2-mercaptoimidazole, 2-mercaptobenzimidazole, 2-mercaptobenzothiazole and the like. Moreover, dithiol, trithiol, etc. which have two or more thiol parts can also be used.

  Among the thiol compounds listed above, a thiol compound having an alkyl group is preferably used, and particularly preferably a thiol compound having an alkyl group having 6 or more carbon atoms.

  As a method for dissolving sulfur in the thiol compound, heating and stirring are performed after mixing in order to promote dissolution of sulfur. The reaction time is about 10 minutes to 1 hour, and can be arbitrarily set depending on the reaction temperature. The reaction temperature ranges from room temperature to 200 ° C, preferably 50 ° C to 150 ° C.

  In the present invention, the precursor metal complex and the sulfur / thiol solution are mixed. At this time, the mixing ratio of the precursor metal complex and the sulfur / thiol solution is not particularly limited, but the mixing is usually performed so that the atomic ratio of metal to sulfur is the target metal sulfide nanoparticles.

  Examples of the solvent that can be used include ethers, alcohols, halides, hydrocarbons, aromatics (toluene and benzene), amines, and the like. The reaction temperature is 0 ° C. or higher, preferably room temperature or higher, 300 ° C. or lower, preferably 200 ° C. or lower.

  The particle size can be controlled by the reaction temperature. Similarly, the shape of the particles can be controlled. In general, when the reaction temperature is increased, the formation of the metal-thiol complex in the initial process is accelerated and the amount of the core increases, so that the size of the finally formed nanoparticles tends to decrease. However, in the case of ZnS and PbS, the particle size tends to be smaller as the reaction temperature is lower.

Sulfurized metal nanoparticles, CdS, ZnS, HgS, PbS , SnS X (X is 1~2), GeS, GaS, InS , In 2 S 3, TlS x (X is 1~2), TiS _2, MnS _X (X is 1-2), FeS _X (X is 1-2), Fe ₂ S ₃ , NiS, Cu _X S (X is 1-2), MoS ₂ , PdS, Ag ₂ S, PtS ₂ , AuS, It may be one or more substances selected from Au ₂ S and Au ₂ S ₃ .

As for Cu, CuS and Cu ₂ S can be individually adjusted, and can also be obtained as a mixture thereof. For _{example, CuS, Cu 9 S 5,} Cu 9 S 8, Cu 2 S , and the like.

As for Sn, Mn, and Tl, SnS and SnS ₂ , MnS and MnS ₂ , and TlS and TlS ₂ can be prepared individually or as a mixture.

  The metal sulfide nanoparticles can be individually adjusted to one selected from a spherical shape, a coin shape, a film shape, a string shape and a star shape, and can also be obtained as a mixture thereof. For example, spherical nanoparticles can be prepared by carrying out at a reaction temperature of 80 to 150 ° C. from the beginning to the end. The coin-shaped nanoparticles can be prepared by setting the reaction temperature to about 30 ° C. Film-like nanoparticles can be prepared by growing into a film by continuing the reaction for a long time (2 hours or more) in an atmosphere containing oxygen.

  The photoelectric conversion element of the present invention is characterized by using the metal sulfide nanoparticles obtained above.

  The photoelectric conversion element of the present invention is characterized by using an electrode in which the metal sulfide nanoparticles obtained above are adsorbed on titanium oxide nanoparticles.

  A solar cell which is a specific example of the photoelectric conversion element of the present invention will be described. As an example of a solar cell, the element which has the cross section shown in FIG. 1 can be mentioned, for example.

  In this element, a semiconductor layer 3 in which metal sulfide nanoparticles that act as a light absorber are adsorbed is disposed on a transparent conductive substrate 1, and an electrolyte layer 4 is disposed between the semiconductor layer 3 and the counter electrode substrate 2. Is sealed with a sealing material 5. Note that the lead wire is connected to the conductive portion of the transparent conductive substrate 1 and the counter electrode substrate 2 so that electric power can be taken out.

  The transparent conductive substrate 1 is usually manufactured by laminating a transparent electrode layer on a transparent substrate. The transparent substrate is not particularly limited, and the material, thickness, dimensions, shape, and the like can be appropriately selected according to the purpose. For example, colorless or colored glass, meshed glass, glass block, etc. are used, and colorless. Alternatively, a colored transparent resin may be used. Specific examples of such resins include polyesters such as polyethylene terephthalate, polyamide, polysulfone, polyether sulfone, polyether ether ketone, polyphenylene sulfide, polycarbonate, polyimide, polymethyl methacrylate, polystyrene, cellulose triacetate, and polymethylpentene. Etc. In addition, the transparency in this invention is having the transmittance | permeability of 10 to 100%. Moreover, the board | substrate in this invention has a smooth surface at normal temperature, The surface may be a plane or a curved surface, and may deform | transform by stress.

In addition, the transparent conductive film for forming the transparent electrode layer is not particularly limited as long as it fulfills the object of the present invention, and is made of, for example, a metal thin film such as gold, silver, chromium, copper, tungsten, or a metal oxide. Examples thereof include a conductive film. Examples of the metal oxide include Indium Tin Oxide (ITO (In ₂ O ₃ : Sn)) obtained by doping a small amount of other metal elements with tin oxide or zinc oxide, or Fluorine doped Tin Oxide (FTO (SnO ₂ : F)). ), Aluminum doped Zinc Oxide (AZO (ZnO: Al)) and the like are preferably used.

  The film thickness is usually 10 nm to 10 μm, preferably 100 nm to 2 μm. The surface resistance (resistivity) is appropriately selected depending on the use of the substrate of the present invention, but is usually 0.5 to 500 Ω / sq, preferably 2 to 50 Ω / sq.

  As an electrode of the counter electrode substrate 2, platinum, a carbon electrode, etc. can be normally used. The material of the counter electrode substrate 2 is not particularly limited, and the material, thickness, dimensions, shape, and the like can be appropriately selected according to the purpose. For example, colorless or colored glass, glass with mesh, glass block, or the like is used. In addition, a resin having colorless or colored transparency may be used. Specifically, polyesters such as polyethylene terephthalate, polyamide, polysulfone, polyether sulfone, polyether ether ketone, polyphenylene sulfide, polycarbonate, polyimide, polymethyl methacrylate, polystyrene, cellulose triacetate, polymethylpentene, and the like can be given. Moreover, a metal plate etc. can also be used as a board | substrate.

As the semiconductor layer 3 used in the solar cell is not particularly limited, for example, TiO _2, ZnO, such as a layer made of SnO _2, Nb ₂ O ₅ and the like, the layer preferably consists of among others TiO _2, ZnO. The semiconductor may be single crystal or polycrystalline. As the crystal system, anatase type, rutile type, brookite type and the like are mainly used, and anatase type is preferable.

  A known method can be used to form the semiconductor layer 3. As a formation method of the semiconductor layer 3, it can obtain by apply | coating the said semiconductor nanoparticle dispersion liquid, a sol solution, etc. on a board | substrate by a well-known method. The coating method in this case is not particularly limited, and examples thereof include various printing methods including a screen printing method, in addition to a method obtained in a thin film state by a casting method, a spin coating method, a dip coating method, and a bar coating method. Can do.

  Although the thickness of the semiconductor layer 3 is arbitrary, it is 0.5 μm or more and 50 μm or less, preferably 1 μm or more and 20 μm or less.

  In the present invention, a metal sulfide nanoparticle layer is disposed on the semiconductor layer 3. A method for disposing the metal sulfide nanoparticle layer on the semiconductor layer 3 is not particularly limited, but the semiconductor layer 3 is placed on a conductive glass substrate in a suspension in which metal sulfide nanoparticles are dispersed in a solvent. It is common practice to immerse and adsorb the placed laminate. Preferably, after adsorption, drying or baking. The drying is usually performed at room temperature to about 200 ° C., and the baking is performed at 300 ° C. or more, preferably 300 to 500 ° C. in order to remove the remaining carbon source such as an alkyl group. The firing time is about 20 minutes to 2 hours.

  The electrolyte layer 4 used in the present invention is not particularly limited, and may be either a liquid system or a solid system and desirably exhibits reversible electrochemical redox characteristics. Here, showing reversible electrochemical redox characteristics means that an electrochemical redox reaction can occur reversibly in the potential region where the photoelectric conversion element acts. Typically, it is usually desirable to be reversible in the potential range of −1 to +2 V vs NHE with respect to the hydrogen reference electrode (NHE).

The ionic conductivity of the electrolyte layer 4 is usually 1 × 10 ⁻⁷ S / cm or more at room temperature, preferably 1 × 10 ⁻⁶ S / cm or more, more preferably 1 × 10 ⁻⁵ S / cm or more. Is desirable.

  The thickness of the electrolyte layer 4 is not particularly limited, but is preferably 1 μm or more, more preferably 10 μm or more, and preferably 3 mm or less, more preferably 1 mm or less.

  The electrolyte layer 4 is not particularly limited as long as the above-described conditions are satisfied, and liquid and solid systems known in the art can be used.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
(Example 1)

Lead acetate (444 mg) and oleylamine (4.8 ml) were mixed in toluene, stirred for several minutes in an argon atmosphere, and then heated to 100 ° C. Next, after dissolving sulfur (32 mg) and dodecane cantilever ol (6.2 ml), this solution was added to a solution of lead acetate and oleylamine. After stirring at 100 ° C. for 30 minutes, the mixture was cooled, and the target lead sulfide nanoparticles were obtained using a centrifuge.

  The average particle size of the lead sulfide nanoparticles was 7 nm. Moreover, the obtained lead sulfide nanoparticles were dispersed in hexane, and the absorption spectrum was measured (FIG. 2).

  When the conductive glass substrate in which the titanium oxide nanoparticles were laminated in the obtained dispersion of lead sulfide nanoparticles was immersed, the lead sulfide nanoparticles were adsorbed on the titanium oxide nanoparticle layer. Using this substrate as a photoelectric conversion layer, using conductive glass with a platinum layer formed on the counter electrode, facing the two substrates, sealing the periphery, and injecting an electrolyte for iodine redox between the substrates, A battery was produced.

When the spectral sensitivity measurement was implemented about the solar cell of Example 1, the photoelectric conversion efficiency of 0.5% was obtained at 900 nm.
(Reference example)

  Copper acetate (79 mg) and oleylamine (1.9 ml) were mixed in dioctyl ether (20 ml), stirred for several minutes under an argon atmosphere, and then heated to 100 ° C.

  Next, sulfur (13 mg) was dissolved in dodecanethiol (2.5 ml), and this solution was added to a solution of copper acetate and oleylamine. After stirring at 100 ° C. for 30 minutes, the mixture was cooled, and the target copper sulfide nanoparticles were obtained using a centrifuge.

  The average particle diameter of the copper sulfide nanoparticles was 5 nm. Further, the obtained copper sulfide nanoparticles were dispersed in hexane, and the absorption spectrum was measured (FIG. 3).

  When the conductive glass substrate in which the titanium oxide nanoparticles were laminated in the obtained dispersion liquid of copper sulfide nanoparticles was immersed, the copper sulfide nanoparticles were adsorbed on the titanium oxide nanoparticle layer. Using this substrate as a photoelectric conversion layer, using conductive glass with a platinum layer formed on the counter electrode, facing the two substrates, sealing the periphery, and injecting an electrolyte for iodine redox between the substrates, A battery was produced.

When a spectral sensitivity measurement was performed on the solar cell of the reference example, a photoelectric conversion efficiency of 0.3% was obtained at 950 nm.

  The present invention can be used for solar cells and the like.

It is an example of the cross section of a solar cell. It is an absorption spectrum figure of lead sulfide. It is an absorption spectrum figure of copper sulfide.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Transparent conductive substrate 2 ... Counter electrode substrate 3 ... Semiconductor layer which impregnated metal sulfide nanoparticle 4 ... Electrolyte layer 5 ... Sealing material

Claims (3)

  A method for producing metal sulfide nanoparticles, wherein lead acetate and oleylamine are mixed and mixed with a solution in which sulfur is dissolved in dodecanethiol to obtain lead sulfide nanoparticles. A photoelectric conversion element using metal sulfide nanoparticles obtained by the production method according to claim 1. A photoelectric conversion element using an electrode in which metal sulfide nanoparticles obtained by the production method according to claim 1 are adsorbed on titanium oxide nanoparticles.

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