JP4791743B2 - Dye-sensitized solar cell - Google Patents

Description

  The present invention relates to a dye-sensitized solar cell having an improved photoelectric conversion rate by effectively using sunlight.

  Inorganic solar cells using single crystal silicon, amorphous silicon, and the like are mainstream as semiconductor solar cells that photoelectrically convert sunlight to extract electric energy, and the photoelectric conversion efficiency is increased to about 30%.

  In such an inorganic solar cell, the absorption peak wavelength of amorphous silicon is around 600 nm, and the single crystal silicon is around 800 nm. Therefore, light that is effectively used for photoelectric conversion is limited to light in the long wavelength region of 600 nm or more. ing.

  Therefore, in order to effectively use light in the short wavelength region in sunlight, light that can be photoelectrically converted by converting short wavelength light into long wavelength light using fluorescent materials such as rare earth metal ions, rare earth metal complexes, and fluorescent dyes. (Patent Documents 1 to 12). Such a fluorescent substance is intended to achieve its effect by being disposed as a wavelength conversion film, or dispersed in an existing transparent electrode or antireflection film, and further disposed as a cover sheet or the like.

  In addition to inorganic solar cells, semiconductor solar cells include dye-sensitized solar cells that use the sensitizing action of organic dyes such as rhodamine B and transition metal complexes such as ruthenium (Patent Documents 13 to 16). .

  Such a dye-sensitized solar cell is superior to an inorganic solar cell in that the light absorption peak wavelength position can be controlled to some extent by the selection of a sensitizing dye, and in terms of cost and ease of manufacture. There are still problems inherent in dye-sensitized solar cells that are not present, and the photoelectric conversion efficiency is limited to about 5%.

  Therefore, recently, even in dye-sensitized solar cells, an attempt is made to provide a phosphor fine particle layer on the light receiving surface side that can be converted into light having a wavelength of around 550 nm using light in the near infrared region of 700 nm or more (Patent Document). 17) and attempts to apply a phosphor layer capable of converting light of 500 nm or less into light having a wavelength of 500 to 600 nm on the light receiving surface side (Patent Document 18).

In the technique disclosed in Patent Document 17, light in the near-infrared light region of 700 nm or more is used after being converted to light having a wavelength of around 550 nm. Therefore, iodine used for redox in a dye-sensitized solar cell system Since the ions (I ⁻ , I ₃ ⁻ ) have absorption around 450 nm, the light in the vicinity of the wavelength contained in sunlight cannot be effectively used for photoelectric conversion, and the wavelength conversion efficiency is inferior.

  On the other hand, in the technique disclosed in Patent Document 18, although light having a wavelength of about 500 nm or less contained in sunlight can be effectively used for photoelectric conversion, inorganic phosphors and organic phosphors such as polystyrene and cellulose are used. Only a wavelength conversion layer dispersed in an inorganic matrix such as an organic resin or silica is suggested, and the wavelength conversion efficiency is not sufficient.

JP 58-106877 A JP-A 63-6881 JP-A-8-204222 Japanese Patent Laid-Open No. 9-230396 Japanese Patent Laid-Open No. 10-247739 JP 11-345993 A JP 2000-313877 A JP 2001-308365 A JP 2001-352091 A JP 2003-218367 A JP 2003-218379 A JP 2003-243682 A JP-A-10-255863 JP 2002-363418 A JP 2003-338326 A JP 2003-317814 A JP 2004-31050 A JP 2004-171815 A

  An object of this invention is to aim at the effective utilization of sunlight, and to improve the photoelectric conversion efficiency of a dye-sensitized solar cell.

  Another object of the present invention is to solve the problem of a decrease in photoelectric conversion efficiency due to light absorption of the redox electrolyte, which is a problem inherent to the dye-sensitized solar cell possessed by the dye-sensitized solar cell.

  That is, in the present invention, the wavelength conversion in which the phosphor (B) that converts the wavelength of light in the short wavelength region of sunlight into light in the long wavelength region of 500 nm to 650 nm that can be photoelectrically converted by the dye-sensitized semiconductor layer is dispersed. The film is disposed as the outermost layer on the sunlight side, and the wavelength conversion film has an amorphous fluorine-containing polymer (A) as a matrix polymer, and the fluorescent material (B) is dispersed in the matrix polymer. It is related with the dye-sensitized solar cell characterized by being a film which is.

  By using a film in which the amorphous fluorine-containing polymer (A) is a matrix polymer and the fluorescent material is dispersed in the matrix polymer as the wavelength conversion film, light emission of the fluorescent material (B), particularly a rare earth metal complex, is achieved. Efficiency is further improved and photoelectric conversion efficiency is also improved.

  When the redox electrolyte in the dye-sensitized solar cell is iodide ion or triiodide ion and the fluorescent substance contained in the wavelength conversion film is composed of a rare earth metal complex, not only light in the ultraviolet region Further, light having a wavelength absorbed by iodide ions or triiodide ions can be effectively used in the rare earth metal complex, and the photoelectric conversion efficiency is further improved.

  As the fluorescent substance (B) contained in the wavelength conversion film, a Tb complex or Eu complex is preferable, and the Tb complex or Eu complex has a maximum absorption peak wavelength of an absorption spectrum in a wavelength region of 400 nm or less. And when it is a complex whose absorption coefficient of the maximum absorption peak wavelength is 1000 or more, the improvement of photoelectric conversion efficiency can be achieved more.

  According to the dye-sensitized solar cell of the present invention, it is possible to effectively use sunlight and improve the photoelectric conversion efficiency.

  Moreover, the fall of the photoelectric conversion rate by the light absorption of the oxidation reduction type | system | group electrolyte which is the intrinsic problem which a dye-sensitized solar cell has can be suppressed.

  The basic structure of the dye-sensitized solar cell of the present invention will be described with reference to FIG.

  In FIG. 1, reference numeral 1 denotes a wavelength conversion film, a transparent substrate 2, a transparent electrode 3, a dye-sensitized semiconductor layer 4 composed of semiconductor particles 5 on which a sensitizing dye is adsorbed, an electrolyte solution layer (carrier transport layer) 6, (Hall current collector) It is composed of an electrode 7 and a support substrate 8, and sunlight 9 enters from the wavelength conversion film 1 side. Among these structures, other than the wavelength conversion film 1 is a basic structure that a conventional dye-sensitized solar cell has, and each of the structures, production methods, components, and the like are described in Patent Documents 13 to 18, These descriptions are also cited in the present invention. In the conventional dye-sensitized solar cell, the basic structure from the transparent electrode 2 to the support substrate 8 has been subjected to various changes such as the arrangement of a transparent electrode protective layer, an antireflection film, an ultraviolet blocking film, etc. However, such a modified structure is also applicable to the dye-sensitized solar cell of the present invention.

  In the present invention, the fluorescent material (B) is dispersed in the wavelength conversion film using the amorphous fluorine-containing polymer (A) as a matrix polymer. The fluorescent substance (B) has a function of wavelength-converting light in a short wavelength region in sunlight into light in a long wavelength region of 500 nm to 650 nm that can be photoelectrically converted by the dye-sensitized semiconductor layer, Fluorescent materials that are also used in inorganic solar cells can be used.

  However, in the present invention, the mechanism responsible for photoelectric conversion is dye sensitization, and the wavelength region of light that can be efficiently photoelectrically converted is 500 nm to 650 nm. It is necessary to select in consideration of the type of pigment (Ru pigment, coumarin pigment, etc.).

  In addition, as a factor for selecting the fluorescent substance (B), it is important to consider the action of a redox electrolyte solution (electrolyte + solvent) that is unique to the dye-sensitized solar cell. That is, each of the redox electrolyte and solvent used has a specific absorption wavelength, and the light absorbed by them does not contribute to energy conversion.

  Specific examples and combinations of the fluorescent substance, the sensitizing dye, and the redox electrolyte will be described later.

  The light absorbed by the fluorescent material is light in a short wavelength region that cannot be effectively photoelectrically converted by the dye-sensitized semiconductor layer, and is light having an absorption spectrum peak wavelength of less than 500 nm, preferably 400 nm or less. The lower limit of the absorption peak wavelength is usually about 200 nm.

  In addition, a fluorescent material having a sharp absorption spectrum peak may be used, but a material having a wide absorption wavelength range that can cover a short wavelength range widely is preferable in that sunlight can be used more effectively.

  Furthermore, a substance that also includes the above-described absorption wavelengths specific to the redox electrolyte and solvent in the absorption wavelength region is preferable in that it can suppress a decrease in photoelectric conversion efficiency.

  The conversion wavelength of the fluorescent material is in the range of 500 nm to 650 nm, and within this range, photoelectric conversion is effectively performed by the dye-sensitized semiconductor.

  Specific examples of the fluorescent substance (B) include rare earth metal complexes, rare earth metal ions, and organic fluorescent dyes.

  As the rare earth metal complex, a rare earth metal complex of Tb and Eu and having an organic compound as a ligand is preferable from the viewpoint that the absorption peak wavelength position and the absorption wavelength region width can be controlled.

  The absorption peak wavelength and the absorption wavelength width can be controlled by selecting the ligand as described above. In addition, as a ligand, specifically, a ligand having a β-diketone structure, a ligand having a β-disulfonyl structure, a ligand having a carbonylimide structure, and a coordination having a sulfonimide structure These are preferable in that the luminous efficiency of the formed complex is good.

  In particular,

Can be illustrated, among others

Are preferable in terms of a high absorption coefficient in the ultraviolet region and a high luminous efficiency of the complex formed.

  A particularly effective fluorescent substance (B) is a Tb complex or an Eu complex, which has a maximum absorption peak wavelength of an absorption spectrum in a wavelength region of 400 nm or less, and an extinction coefficient of the maximum absorption peak wavelength is 1000. More preferably, the complex is 10,000 or more. When the extinction coefficient is larger, the intensity of light having a wavelength to be converted is increased, and the photoelectric conversion efficiency is improved.

  Specific examples of these complexes include Tb complexes and Eu complexes having the above-mentioned ligands, which absorb not only light in the ultraviolet region but also light having a wavelength that is absorbed by iodide ions or triiodide ions. However, it is preferable because it can be converted into light in the visible light region with high efficiency.

  The following can be illustrated as a particularly preferable complex.

Maximum absorption peak wavelength: 390 nm
Absorption coefficient of maximum absorption peak wavelength: 12000
Absorption wavelength width: 300 to 480 nm
Conversion wavelength: 615 nm

Maximum absorption peak wavelength: 350 nm
Absorption coefficient of maximum absorption peak wavelength: 1500
Absorption wavelength width: 300 to 390 nm
Conversion wavelength: 615 nm

Maximum absorption peak wavelength: 360 nm
Absorption coefficient of maximum absorption peak wavelength: 2300
Absorption wavelength width: 300 to 380 nm
Conversion wavelength: 550 nm

As other fluorescent substances, rare earth metal ions such as Tb ³⁺ and Eu ³⁺ and fluorescent dyes such as rhodamine and coumarin can be used.

  One of the characteristics of the present invention is that the amorphous fluorine-containing polymer (A) is used as the matrix polymer of the wavelength conversion film. By using the amorphous fluorine-containing polymer (A), it is possible to form a film excellent in transparency, weather resistance, solvent resistance, heat resistance, etc., and further improve the luminous efficiency of fluorescent substances, particularly rare earth metal complexes. Thus, the photoelectric conversion efficiency can be improved.

  The amorphous fluorine-containing polymer (A) used as the matrix polymer of the wavelength conversion film in the present invention desirably has as high a fluorine content as possible. A preferable fluorine content is 20% by mass or more, preferably 30% by mass or more, more preferably 40% by mass or more, and particularly 50% by mass or more.

  The upper limit is a polymer in which all of the hydrogen atoms are replaced with fluorine atoms, but depending on the structure of the polymer, if the fluorine content becomes too high, the compatibility and dispersibility with the fluorescent material tend to decrease. .

  The preferred first polymer as the amorphous fluorine-containing polymer (A) is derived from fluorine-containing acrylates having a fluorine atom in at least one of a part capable of forming a polymer side chain or a part capable of forming a polymer main chain. It is a fluorine-containing acrylate-type polymer (A1) which has the following structural unit.

  As a specific example, the formula (1):

(In the formula, X ¹ is H, F, Cl, CH ₃ or CF ₃ ; R ¹ has a C 1-50 monovalent hydrocarbon group which may have an ether bond and an ether bond. A fluorine-containing acrylate represented by a group selected from monovalent fluorine-containing hydrocarbon groups having 1 to 50 carbon atoms, wherein at least ^one of X ¹ and R ¹ contains a fluorine atom) Those having a structural unit derived from at least one monomer selected from a1-1) are preferred.

As a specific structure excluding R ¹ ,

That have a structure such as

Those having the following structure are preferred in terms of polymerizability,

When the composition having the following structure is used as a composition with the fluorescent substance (B), it is preferable in that the light emission intensity and the light emission efficiency can be improved, and in addition, transparency and heat resistance can be imparted to the obtained polymer. It is preferable at the point which can provide mechanical strength.

When X in the fluorine-containing acrylate (a1-1) is F or CF ₃ , R ^{1 in} the side chain may not contain a fluorine atom, but is usually carbon that may have an ether bond. It is at least one selected from a monovalent fluorine-containing alkyl group having 1 to 50 carbon atoms and a monovalent fluorine-containing aryl group having 2 to 50 carbon atoms including an aromatic cyclic structure which may have an ether bond. Is preferred.

  Thereby, the fluorine content of the fluorine-containing acrylate polymer (A1) can be significantly improved, and the composition with the fluorescent material (B) is preferable in that the emission intensity and the emission efficiency can be improved.

  Among these, it is at least one selected from monovalent fluorine-containing alkyl groups having 1 to 50 carbon atoms which may have an ether bond, and further in terms of light emission intensity and light emission efficiency in terms of transparency. Improved and preferred.

  In the present invention, specific examples of the fluorine-containing acrylate (a1-1) that gives the structural unit constituting the fluorine-containing acrylate polymer (A1) include the following monomers.

(A1-i) Monomer having a linear fluorine-containing alkyl group

Are preferred, and among them, CH ₂ ═CF—COO—CH ₂ CF ₂ CF ₂ H,
_{CH 2 = CF-COO-CH} 2 (CF 2 CF 2) 2 H
Is particularly preferred.

Also,
(A1-ii) Monomer having a branched fluorine-containing alkyl group

Is particularly preferred.

(A1-iii) A monomer having a fluorine-containing alkyl group having an ether bond in the side chain

Is particularly preferred.

  The weight average molecular weight of the fluorinated acrylate polymer (A1) is preferably 500 to 1,000,000, more preferably 5,000 to 800,000, and particularly preferably 10,000 to 500,000.

  Next, the fluorinated acrylate polymer (A1) will be described and exemplified from the viewpoint of the glass transition temperature (Tg) and the fluorine content (specific examples may overlap with the above examples).

  From this viewpoint, the first of the preferred fluorine-containing acrylate polymer (A1) is (A1-I) a fluorine-containing acrylic polymer having a glass transition temperature of 40 ° C. or higher and a fluorine content of 50% by mass or higher.

  If the glass transition temperature is lower than 40 ° C., there is a problem in shape stability due to deformation at room temperature, and rare earth metal ions may move and redistribute to cause phase separation. The glass transition temperature is preferably 65 ° C. or higher, more preferably 100 ° C. or higher from the viewpoint of heat resistance, because the matrix polymer itself is heated by self-heating when a light emitting device or the like is formed. Although an upper limit is not specifically limited, In a fluorine-containing acrylic polymer, it is about 200 degreeC normally.

  Of course, a higher fluorine content is preferable, and it is 52% by mass or more, particularly 55% by mass or more. The upper limit of the fluorine content is not particularly limited, but is usually about 76% by mass from the viewpoint that the compatibility with the fluorescent material is not deteriorated and the chemical structure is limited.

  Among the fluorine-containing acrylate polymers (A1-I), the formula (2):

(Wherein Rf ¹ is a fluorine-containing hydrocarbon group having 1 to 40 carbon atoms which may contain an ether bond), the fluorine-containing acrylic polymer may be a homopolymer or a copolymer. A polymer having a glass transition temperature of 40 ° C. or more and a fluorine content of 50% by mass or more is easily obtained, and the light emission (amplification) intensity is sufficiently high. Rf ¹ is preferably a fluorine-containing alkyl group having 1 to 40 carbon atoms which may have an ether bond or a fluorine-containing aryl group having 3 to 40 carbon atoms which may have an ether bond.

  As the acrylate (hereinafter referred to as “αF acrylate”) in which the α-position is a fluorine atom, which can form the fluorine-containing acrylic polymer of the above formula (2), for example, the following can be preferably exemplified. The description after each monomer is (abbreviation) and (glass transition temperature and fluorine content (% by mass) of homopolymer) (hereinafter the same).

CH ₂ = CFCOOCH ₂ C ₂ F ₅ (5FF) (101 ° C., 51%),
CH ₂ = CFCOOCH ₂ CF ₂ CFHCF ₃ (6FF) (70 ° C., 52%),
CH ₂ = CFCOOCH ₂ C ₄ F ₈ H (8FF) (65 ° C., 56%),
CH ₂ = CFCOOC ₂ H ₄ C ₈ F ₁₇ (17FF) (66 ° C., 64%),
_{CH 2 = CFCOOC (CF 3)} 2 H (HFIP-F) (104 ℃, 55%),
CH ₂ = CFCOOC (CF ₃ ) ₂ C ₆ F ₅ (147 ° C., 56%),

  Of these, HFIP-F and 8FF are preferred because of their high affinity with the complex. Further, αF acrylate having a branched structure in the side chain is preferable in that the glass transition temperature can be increased.

  The fluorine-containing acrylate polymer (A1-I) is represented by the formula (3):

(Wherein Rf ³ is a fluorine-containing hydrocarbon group having 1 to 40 carbon atoms which may have an ether bond and having 7 or more fluorine atoms), Even a coalescence is preferable because it has a glass transition temperature of 40 ° C. or more, a fluorine content of 50% by mass or more, and a sufficiently high emission intensity. Rf ³ is preferably a fluorine-containing alkyl group having 1 to 40 carbon atoms which may have an ether bond or a fluorine-containing aryl group having 3 to 40 carbon atoms which may have an ether bond.

As the monomer giving the structure represented by the formula (3), for example, the following can be preferably exemplified.
CH ₂ ═C (CH ₃ ) COOCH ₂ C ₄ F ₈ H (8FM) (47 ° C., 51%),
_{CH 2 = C (CH 3)} COOC 2 H 4 C 8 F 17 (17FM) (40 ℃, 61%),
_{CH 2 = C (CH 3)} COOC (CF 3) 3 (9FtBuM) (156 ℃, 56%),
_{CH 2 = C (CH 3)} COOC (CF 3) 2 C 6 F 5 (132 ℃, 52%)

  Of these, 8FM is preferable because of its good affinity with the complex. Further, as the fluorine-containing methacrylate, those having a branched structure in the side chain are preferable because the glass transition temperature becomes high.

  Furthermore, the fluorine-containing acrylate polymer (A1-I) may be a copolymer of the αF acrylate and the fluorine-containing methacrylate, and the composition and copolymerization ratio of the copolymer have a glass transition temperature of 40. The composition and the copolymerization ratio are selected so as to be a copolymer having a fluorine content of 50% by mass or more at a temperature of 0 ° C. or higher.

  In this case, as a preferable combination of copolymers, a combination of HFIP-F and 8FM copolymer, 6FON0 and 8FM copolymer, 17FF and 8FM copolymer, or the like is used. It is preferable from the viewpoint of excellent mechanical strength.

  In addition to the αF acrylate and / or the fluorine-containing methacrylate exemplified above, other copolymerizable monomers may be introduced into the fluorine-containing acrylate polymer (A1-I).

  As the other monomer, a composition and a copolymerization ratio are selected so that the resulting copolymer has a glass transition temperature of 40 ° C. or more and a fluorine content of 50% by mass or more.

Examples of other monomers include the following.
CH ₂ ═C (CH ₃ ) COOCH ₃ (MMA) (120 ° C., 0%),
_{CH 2 = C (CH 3)} COOCH 2 C (CF 3) 2 H (6FiP-M) (72 ℃, 48%),
CH ₂ ═C (CH ₃ ) COOCH ₂ C (CF ₃ ) ₂ CH ₃ (6FNPM) (120 ° C., 43%),
CH ₂ = CFCOOCH ₂ CF ₃ (3FF) (125 ° C., 44%),
CH ₂ = CFCOOCH ₂ C (CF ₃ ) ₂ CH ₃ (6FNPF) (135 ° C., 49%),
_{CH 2 = CFCOOC (CH 3)} 2 H (IP-F) (93 ℃, 14%),
CH ₂ = CFCOOC ₆ F ₅ (PFPh-F) (160 ° C., 45%)

  Among other monomers, MMA is preferable because mechanical strength is improved and improved. Further, 6FNPM, 6FNPF, and PFPh-F are preferable in that the glass transition point can be raised without substantially reducing the fluorine content.

  Preferred copolymer combinations include HFIP-F and MMA binary copolymer, HFIP-F, MMA and 6FNPF terpolymer, and 5FF and 6FNPF binary copolymer. From the viewpoint of good balance between mechanical strength and light emission (amplification) strength.

  A preferred second of the fluorine-containing acrylate polymer (A1) of the present invention is (A1-II) a fluorine-containing acrylic polymer having a glass transition temperature of 100 ° C. or higher and a fluorine content of 30% by mass or more and less than 50% by mass. It is a coalescence.

  When the glass transition temperature is higher than 100 ° C., sufficient emission intensity can be obtained even if the fluorine content is relatively small. Of course, a higher fluorine content is preferable, and it is 35% by mass or more, particularly 40% by mass or more.

  The upper limit of the glass transition temperature is not particularly limited, but is usually about 200 ° C. for a fluorine-containing acrylic polymer.

  Specific examples of the fluorine-containing acrylic polymer (A1-II) include the following.

(A1-IIa) Homopolymer of fluorine-containing acrylic monomer:
Among the monomers that give the structure represented by the formula (1), a homopolymer satisfying a fluorine content of 30% by mass or more and less than 50% by mass at 100 ° C. or higher is, for example, the above (A1-I) Examples include 3FF (125 ° C, 44%), 6FNPF (135 ° C, 49%), PFPh-F (160 ° C, 45%), 6FNPM (120 ° C, 43%), and the like.

  Of these, 6FNPF and 6FNPM are preferred because of their high affinity with fluorescent materials, particularly rare earth metal complexes. Further, the obtained fluorine-containing acrylic polymer is preferably one having a branched structure in the side chain because the glass transition temperature becomes high.

(A1-IIb) Copolymers of fluorine-containing acrylic monomers represented by the above (A1-IIa) or other fluorine-containing acrylic monomers:
The composition and copolymerization ratio of the copolymer are selected such that the glass transition temperature is 100 ° C. or higher and the fluorine content is 30% by mass or more and less than 50% by mass.

  Examples of other fluorine-containing acrylic monomers include 6FiP-M and IP-F.

  Further, as a preferable combination of copolymers, a combination of a copolymer of 3FF and 6FNPM, a copolymer of PFPh-F and 6FNPM, a copolymer of 6FNPF and 6FNPM, and the like, the light emission (amplification) intensity and mechanical strength are used. Is preferable from the viewpoint of good. Further, when 6FiP-M or IP-F is used as the other fluorine-containing acrylic monomer, it is preferable because mechanical strength can be imparted without lowering the glass transition temperature.

(A1-IIc) Copolymer of fluorine-containing acrylic monomer and non-fluorine acrylic monomer represented by (A1-IIa):
As the non-fluorine-based acrylic monomer, a composition and a copolymerization ratio are selected so that the resulting copolymer has a glass transition temperature of 100 ° C. or higher and a fluorine content of 30% by mass or more and less than 50% by mass. .

  As the non-fluorinated acrylic monomer, for example, MMA (120 ° C., 0%) is particularly preferable because it can improve the mechanical strength.

  Preferable copolymers include, for example, a binary copolymer of 6FNPM and MMA, a binary copolymer of 6FNPF and MMA, a terpolymer of 6FNPM, MMA, and IP-F, and a copolymer of 6FNPF, MMA, and IP-F. A ternary copolymer and a binary copolymer of MMA and 5FF can be preferably exemplified from the viewpoint of good balance between mechanical strength and light emission (amplification) strength.

  A preferred third of the fluorinated acrylic polymer (A1) has (A1-III) a structural unit derived from the polyfunctional acrylate (a1-2) in addition to the structural unit derived from the fluorinated acrylate (a1-1). It is a polymer characterized by this.

  By introducing structural units derived from polyfunctional acrylate (a1-2), the optical functionality (emission (amplification) intensity and emission (amplification) efficiency) of the wavelength conversion film composed of the composition with the fluorescent substance is greatly improved. Can be made.

  In the present invention, the second preferred amorphous fluoropolymer (A) in the wavelength conversion film is a fluoropolymer (A2) having a curable site at the side chain or main chain terminal.

  Specific examples of the fluorine-containing polymer (A2) having a curable site are preferably the same as those described in the pamphlet of WO02 / 72706 and pamphlet of WO2004 / 016689.

  Further, the third preferable example of the amorphous fluorine-containing polymer (A) in the wavelength conversion film is a functional group capable of coordinating with a rare earth metal ion in the fluorescent substance (B) to be used or a functional group capable of forming a complex. Is a fluorine-containing polymer (A3) having a side chain or main chain terminal.

  Specific examples of the fluorine-containing polymer (A3) having a functional group capable of forming a complex are the same as those described in the pamphlets of WO02 / 72696 and WO03 / 91343.

  As a method of forming a wavelength conversion film in which a fluorescent substance (B) is dispersed in an amorphous fluorine-containing polymer (A) forming a matrix polymer, a fluorescent substance-dispersed polymer in which a fluorescent substance is added after dissolving the polymer in a solvent For example, there is a method of preparing a wavelength conversion film by applying the solution on a transparent substrate of an existing dye-sensitized solar cell and drying it. Examples of the coating method include spin coating, spin coating, roll coating, and gravure coating.

  In addition, after the film of the wavelength conversion layer is formed by melt extrusion molding or the like, the wavelength conversion layer can be formed on the transparent substrate by thermocompression bonding or the like.

  The amount of the fluorescent substance in the wavelength conversion film varies depending on compatibility with the matrix polymer in which the fluorescent substance is dispersed, but is usually 1% by mass or more, preferably 5% by mass or more of the total mass of the wavelength conversion film. . A preferable upper limit is 30 mass%. If the amount of the fluorescent substance is too large, the transmittance of the wavelength conversion film is lowered, and if it is too small, the wavelength conversion effect tends to be lowered.

  The film thickness of the wavelength conversion film may be determined in consideration of the amount of fluorescent material to be dispersed, light transmittance, film strength, and the like, but is usually 1 nm or more and 1 mm or less.

  Next, the dye-sensitized semiconductor and the oxidation-reduction system electrolyte that are the components of the existing dye-sensitized solar cell will be described particularly preferable in relation to the present invention. It is not limited.

  The dye-sensitized semiconductor (5 in FIG. 1) is described in detail and specifically in Patent Documents 13 to 18, and representative examples include sensitizing dyes on oxide semiconductor particles such as titanium oxide and zinc oxide. Is adsorbed. In the present invention, the fluorescent material may be selected according to the absorption wavelength of the dye-sensitized semiconductor used in the existing dye-sensitized solar cell, or the dye-sensitized semiconductor may be selected according to the fluorescent material. Good.

  Conventionally known substances can be used as the sensitizing dye, and typical examples thereof include those described in Patent Documents 13 to 18, particularly JP-A-2003-338326 (Patent Document 15). Among them, Ru dyes such as Ru bipyridine dyes and Ru terpyridine dyes having a strong absorption wavelength (peak wavelength) in the range of 500 to 650 nm, and coumarin dyes are preferable.

  The redox electrolyte is a liquid consisting of a redox electrolyte and a solvent, or a composition consisting of a redox electrolyte and a polymer, and fills the gap between the dye-sensitized semiconductor layer and the counter electrode. .

  Conventionally known substances can be used as the oxidation-reduction electrolyte. In addition to those described in detail in JP-A-2002-363418 (Patent Document 14), substances described in Patent Documents 13, 15-16 and 18 are used. Etc.

  Among them, iodide ions and triiodide ions can be preferably used from the viewpoint of particularly good transport efficiency.

  In addition, carbonates, nitrile compounds, alcohols, etc. are used as solvents. Among them, carbonates such as propylene carbonate and nitrile compounds such as acetonitrile and methoxyacetonitrile have an absorption wavelength range for photoelectric conversion. It is preferably used because it is out of the area used.

  As described above, these redox electrolytes have a specific absorption wavelength band, and when this band overlaps with the absorption wavelength of the dye-sensitized semiconductor, the photoelectric conversion efficiency decreases. For example, iodide ion or triiodide ion has characteristic absorption at 300 to 500 nm, so that the use of light in this portion is limited.

  In a preferred embodiment of the present invention, light having an absorption wavelength of such a redox electrolyte is previously absorbed by the fluorescent material in the wavelength conversion film, and can be used after wavelength conversion to the longer wavelength side. For example, when iodide ion or triiodide ion is used as the redox electrolyte, it is preferable to use a rare earth metal complex, particularly a Tb complex or Eu complex, as the fluorescent substance.

  The dye-sensitized solar cell of the present invention can increase the photoelectric conversion efficiency of a conventional dye-sensitized solar cell not provided with a wavelength conversion film by 1% or more.

  EXAMPLES Next, the present invention will be specifically described with reference to examples. However, the present invention is not limited only to these examples.

  First, measurement methods used in the following examples will be described.

(Measurement of fluorine content)
Burn 10 mg of sample by the oxygen flask combustion method, absorb the decomposition gas in 20 ml of deionized water, and measure the fluorine ion concentration in the absorption liquid by the fluorine selective electrode method (fluorine ion meter, model 901 manufactured by Orion). (Mass%).

(TG-DTA)
Using a differential scanning calorimeter (manufactured by SEIKO, RTG220), the temperature range from 30 ° C. to 200 ° C. under the condition of 10 ° C./min. Temperature rise / fall temperature-temperature rise (the second temperature rise is called a second run) ) Is the intermediate point of the endothermic curve in the second run obtained as Tg (° C.).

(Thickness of wavelength conversion film)
The thickness is calculated by subtracting the thickness of the solar cell before the wavelength conversion film measured in advance in the same manner from the film thickness of the entire solar cell after the wavelength conversion film is measured using the micrometer.

Synthesis Example 1 (Eu Complex, Eu (CF ₃ COCHCOCF ₃ ) ₃ · 2 (Preparation of (C ₆ H ₅ ) ₃ P═O))
Europium acetate tetrahydrate (2.0 g, 5 mmol) and hexafluoroacetylacetone (3.0 g, 20 mmol) were added to water (50 ml), and the mixture was stirred at room temperature for 3 days. The precipitated solid was filtered, washed with water, and recrystallized with a water / methanol mixed solvent to obtain a complex (Eu (CF ₃ COCHCOCF ₃ ) ₃ ) (yield 60%). From the result of TG-DTA measurement, the obtained crystal was confirmed to be dihydrate.

1.0 g of the obtained complex (Eu (CF ₃ COCHCOCF ₃ ) ₃ ) and 0.5 g of triphenylphosphine oxide were dissolved in methanol and stirred at 60 ° C. for 5 hours. The precipitated solid was filtered and recrystallized from a toluene / cyclohexane mixed solvent to obtain a complex (Eu (CF ₃ COCHCOCF ₃ ) ₃ · 2 ((C ₆ H ₅ ) ₃ P═O) (yield 50%). .

Synthesis example 2 (bulk polymerization)
In a three-necked flask, ₂ g of CH ₂ ═CFCOOCH ₂ (CF ₂ ) ₄ H (8FF) as a monomer and AIBN as an initiator were substituted with nitrogen. The reaction temperature was set to 60 ° C., and the mixture was stirred for 10 hours for bulk polymerization. The obtained transparent liquid was dissolved in 5 ml of acetone, dropped into hexane and reprecipitated. The obtained amorphous fluorine-containing polymer was 1.8 g. Table 1 shows the fluorine content of this amorphous fluorine-containing polymer.

Synthesis example 3 (bulk polymerization)
An amorphous fluorine-containing polymer was obtained in the same manner as in Synthesis Example 2 except that CH ₂ ═CFCOOCH ₂ CF ₂ CF ₃ (5FF) was used as the monomer. Table 1 shows the fluorine content of this amorphous fluorine-containing polymer.

Synthesis Example 4 (bulk polymerization)
An amorphous fluorine-containing polymer was obtained in the same manner as in Synthesis Example 2 except that CH ₂ ═CFCOOCH (CF ₃ ) ₂ H (HFIP-F) was used as the monomer. Table 1 shows the fluorine content of this amorphous fluorine-containing polymer.

Synthesis Example 5 (bulk polymerization)
An amorphous fluoropolymer for comparison was obtained in the same manner as in Synthesis Example 2 except that CH ₂ ═CFCOOCH ₂ CF ₃ (3FF) was used as the monomer. Table 1 shows the fluorine content of this amorphous fluorine-containing polymer.

Comparative Synthesis Example 1
A comparative non-fluorinated polymer (PMMA) was obtained in the same manner as in Synthesis Example 2 except that methyl methacrylate (MMA) was used as a monomer.

Example 1
(1) Production of anode electrode A commercially available fluorine-doped SnO ₂ glass (manufactured by Nippon Sheet Glass Co., Ltd., conductive layer thickness 450 nm) was used as a transparent substrate on which a transparent conductive film was formed.

A titanium oxide paste was applied to the transparent conductive film on the fluorine-doped SnO ₂ glass, naturally dried, and then baked in an electric furnace at 500 ° C. for 30 minutes. As the titanium oxide paste, a TiO ₂ paste (manufactured by Solaronix) having an average particle diameter of 15 nm was used. A single titanium oxide porous film having a thickness of about 2 μm was formed by one application, drying and baking. By repeating this operation a plurality of times, the thickness was about 10 μm.

  The titanium oxide porous membrane was immersed in a Ru dye solution, and refluxed at 80 ° C. for 2 hours, whereby the Ru dye was supported on the titanium oxide porous membrane to produce an anode electrode.

The Ru dye solution was prepared by dissolving 3 × 10 ⁻⁴ mol / L of Ru dye (Solaronix, Ruthenium 535) in ethanol.

(2) Production of cathode electrode The cathode electrode was produced by depositing platinum by sputtering on the surface of the transparent conductive film on the same fluorine-doped SnO ₂ glass used in the production of the anode electrode.

(3) Production of dye-sensitized solar cell A battery structure was formed by facing the cathode electrode and anode electrode produced in (1) and (2) above, and a redox electrolyte was injected between both electrodes. The injected redox electrolyte was an iodine-based electrolyte, and was prepared by adding iodine and lithium iodide to a mixed solvent of acetonitrile (90% by volume) and 3-methyl-2-oxazolidinone (10% by volume).

(4) Preparation of wavelength conversion film composition and formation of wavelength conversion film 3 g of the fluorinated acrylate polymer obtained in Synthesis Example 2 and 30 mg of the Eu complex obtained in Synthesis Example 1 were dissolved in 50 ml of methyl isobutyl ketone, A composition for a wavelength conversion layer was prepared.

  The obtained composition for wavelength conversion film was applied to the opposite side of the transparent conductive film on the anode electrode side of the dye-sensitized solar cell, that is, on the sunlight irradiation side using an applicator to form a wavelength conversion film. The film thickness of the wavelength conversion film was 70 μm.

(5) Measurement of photoelectric conversion rate The solar cell obtained in (4) is irradiated with 1000 W / m ² of artificial sunlight with a solar simulator of AM1.5, the spectral sensitivity characteristics are evaluated, and photoelectric conversion is performed. Efficiency was calculated. The results are shown in Table 2.

Example 2
A dye-sensitized solar cell provided with a wavelength conversion film was prepared in the same manner as in Example 1 except that the polymer obtained in Synthesis Example 3 was used as the polymer for the wavelength conversion film, and simulated sunlight was emitted. Irradiated, spectral sensitivity characteristics were evaluated, and photoelectric conversion efficiency was calculated. The results are shown in Table 2.

Example 3
A dye-sensitized solar cell provided with a wavelength conversion film was prepared in the same manner as in Example 1 except that the polymer obtained in Synthesis Example 4 was used as the polymer for the wavelength conversion film, and simulated sunlight was emitted. Irradiated, spectral sensitivity characteristics were evaluated, and photoelectric conversion efficiency was calculated. The results are shown in Table 2.

Example 4
A dye-sensitized solar cell provided with a wavelength conversion film was prepared in the same manner as in Example 1 except that the polymer obtained in Synthesis Example 5 was used as the polymer used for the wavelength conversion film, and simulated sunlight was emitted. Irradiated, spectral sensitivity characteristics were evaluated, and photoelectric conversion efficiency was calculated. The results are shown in Table 2.

Comparative Example 1
A dye-sensitized solar cell was produced in the same manner as in Example 1 except that the wavelength conversion film was not provided, irradiated with pseudo-sunlight, evaluated for spectral sensitivity characteristics, and calculated photoelectric conversion efficiency. The results are shown in Table 2.

Comparative Example 2
A dye-sensitized solar cell provided with a wavelength conversion film was prepared in the same manner as in Example 1 except that the non-fluoropolymer (PMMA) obtained in Comparative Synthesis Example 1 was used as the polymer using the wavelength conversion film. Then, simulated sunlight was irradiated, the spectral sensitivity characteristics were evaluated, and the photoelectric conversion efficiency was calculated. The results are shown in Table 2.

It is a schematic sectional drawing which shows the basic structure of the dye-sensitized solar cell of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wavelength conversion film 2 Transparent substrate 3 Transparent electrode 4 Dye sensitized semiconductor layer 5 Dye sensitized semiconductor layer 6 Electrolyte layer 7 Counter electrode 8 Support substrate 9 Sunlight

Claims (5)

A wavelength conversion film in which a fluorescent substance (B) that converts the wavelength of light in the short wavelength region of sunlight into light in the long wavelength region of 500 nm to 650 nm that can be photoelectrically converted by the dye-sensitized semiconductor layer is dispersed in sunlight. Is arranged as the outermost layer on the side,
Wherein the wavelength conversion film, the non-crystalline fluorine-containing polymer (A) as a matrix polymer, Ri film der fluorescent substance (B) is dispersed in the matrix polymer,
The amorphous fluorine-containing polymer (A) has the formula (2):

(Wherein Rf ¹ is a fluorine-containing acrylic polymer having a structure of a fluorine-containing hydrocarbon group having 1 to 40 carbon atoms which may contain an ether bond),
The fluorescent substance (B) is a Tb complex or Eu complex,
Fluorescent substances (B) a dye-sensitized solar cell amount and wherein 30 wt% or less der Rukoto at least 1% by mass of the total mass of the wavelength conversion film of in a wavelength conversion film. The dye according to claim 1, wherein the redox electrolyte in the dye-sensitized solar cell is iodide ion or triiodide ion, and the fluorescent substance contained in the wavelength conversion film is made of a rare earth metal complex. Sensitized solar cell. The dye-sensitized solar cell according to claim 1 or 2, wherein the amorphous fluorine-containing polymer (A) has a fluorine content of 40% by mass or more . The Tb complex or Eu complex is a complex having a maximum absorption peak wavelength of an absorption spectrum in a wavelength region of 400 nm or less and an extinction coefficient of the maximum absorption peak wavelength of 1000 or more . The dye-sensitized solar cell of any one of Claims 1 . The Tb complex or Eu complex is a complex having a ligand having a β-diketone structure, a ligand having a β-disulfonyl structure, a ligand having a carbonylimide structure, or a ligand having a sulfonimide structure. The dye-sensitized solar cell according to any one of claims 1 to 4.

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