JP2008153105A - Dye-sensitized solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain high open-circuit voltage by restraining occurrence of dark current in a dye-sensitized solar cell. <P>SOLUTION: The dye-sensitized solar cell is provided with an electrode layer 1 formed on a substrate, a counter electrode 5 placed in opposition to the electrode layer 1, a photoelectric conversion layer made of a porous semiconductor layer 2 with sensitizing dye adsorbed to be contacted with the electrode layer 1 provided between the electrode layer 1 and the counter electrode 5, and an electrolyte layer 4 containing electrolyte and a solvent to be contacted with the counter electrode 5 between the electrode layer 1 and the counter electrode 5. The electrolyte layer 4 has an alkaline metal compound 3 showing difficult solubility added to the solvent. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a dye-sensitized solar cell.

  As a new energy source that replaces fossil fuels, solar cells that use solar light that is sustainable and have no environmental impact have attracted attention, and various studies have been conducted. As a solar cell currently in practical use, a solar cell using single crystal silicon, polycrystalline silicon, or amorphous silicon is known. However, these solar cells have problems such as the cost of silicon as a raw material and the high energy cost in the manufacturing process.

  On the other hand, as a new type of solar cell, a dye-sensitized solar cell, which is a wet solar cell to which photoinduced electron transfer of an organic dye is applied, has been proposed (Patent Document 1, etc.). These dye-sensitized solar cells include an electrode layer formed on a substrate, a counter electrode provided to face the electrode layer, a photoelectric conversion layer provided between the electrode layer and the counter electrode, and a photoelectric conversion layer and a counter electrode. It is comprised from the electrolyte layer provided in between. The photoelectric conversion layer is configured by adsorbing a photosensitizing dye having an absorption spectrum in the visible light region on the surface of the porous semiconductor layer.

  When light is irradiated to the porous semiconductor layer of such a solar cell, electrons are generated in the porous semiconductor layer, the electrons move to the counter electrode through the electric circuit, and the electrons moved to the counter electrode are in the electrolytic layer. Electric energy is taken out by being carried by ions or returning to the porous semiconductor layer through the P-type semiconductor and repeating such a process.

  However, in such a solar cell, a counter electromotive force is generated when a reverse current (dark current) flows from the porous semiconductor layer to the charge transport material regardless of light irradiation, and a sufficient open-circuit voltage is obtained. There was no problem. When a solar cell is actually used as a device, a method of connecting a plurality of cells in series and obtaining a module in order to obtain a high voltage is used. Therefore, increasing the open circuit voltage of one cell can reduce the number of cells connected in series to obtain the same predetermined voltage, leading to cost reduction. In addition, when a solar cell is incorporated in a power storage system such as a capacitor, the maximum energy density of the capacitor is proportional to the square of the charging voltage, and thus improving the open circuit voltage is a very important factor.

  In patent document 2, generation | occurrence | production of the above dark currents is suppressed by pre-processing a photoelectric converting layer with 4-tert- butyl pyridine, or by making 4-tert- butyl pyridine contain in an electrolyte. It is disclosed that an open circuit voltage can be obtained.

  Patent Document 3 discloses a dye-sensitized solar cell in which a high open-circuit voltage can be obtained by using an electrolyte solution containing a urea derivative instead of 4-tert-butylpyridine.

  Patent Document 4 discloses a dye-sensitized solar cell in which a high open-circuit voltage can be obtained by using an electrolyte solution containing pyridine or a pyridine-based compound other than 4-tert-butylpyridine.

  Moreover, in patent document 5, the dye-sensitized solar cell from which a high open circuit voltage is obtained is disclosed by using the electrolyte solution containing a non-cyclic saccharide.

However, even in the above conventional dye-sensitized solar cells, the open-circuit voltage is not sufficiently improved, and a dye-sensitized solar cell capable of obtaining a higher open-circuit voltage is demanded.
Japanese Patent No. 2664194 Japanese Patent Laid-Open No. 11-67285 JP 2003-168493 A JP 2003-331936 A JP 2005-93313 A

  An object of the present invention is to provide a dye-sensitized solar cell capable of suppressing generation of dark current and obtaining a high open-circuit voltage.

  The present invention relates to an electrode layer formed on a substrate, a counter electrode provided opposite to the electrode layer, and a porous layer adsorbed with a sensitizing dye provided to be in contact with the electrode layer between the electrode layer and the counter electrode A dye-sensitized solar cell comprising a photoelectric conversion layer composed of a semiconductor layer, and an electrolyte layer containing an electrolyte and a solvent, which is provided so as to be in contact with the counter electrode between the electrode layer and the counter electrode. In contrast, an alkali metal compound exhibiting poor solubility is added.

  In the present invention, an alkali metal compound that is hardly soluble in the solvent of the electrolyte layer is added to the electrolyte layer. By adding an alkali metal compound that is hardly soluble in the solvent of the electrolyte layer, generation of dark current can be suppressed and a high open-circuit voltage can be obtained.

  In the present invention, the reason why the generation of dark current can be suppressed and a high open-circuit voltage can be obtained by adding an alkali metal compound that is hardly soluble in the solvent of the electrolyte layer to the electrolyte layer is considered as follows. .

  When an alkali metal compound that is sparingly soluble in the electrolyte layer solvent is added to the electrolyte layer, the alkali metal compound is dispersed in the electrolyte solution. It is considered that the dispersed alkali metal compound is adsorbed on the surface of the porous semiconductor layer to which the sensitizing dye is not adsorbed to form a very thin energy barrier film.

  FIG. 2 is a diagram schematically showing the energy band level of each layer in the solar cell in order to explain the function and effect of the present invention. An electrode layer 1 is formed on the substrate, and a porous semiconductor layer 2 is provided in contact with the electrode layer 1. A counter electrode 5 is provided so as to face the electrode layer 1, and an electrolyte layer 4 is provided so as to be in contact with the counter electrode 5.

Electrons e ⁻ excited and excited by the sensitizing dye adsorbed on the porous semiconductor layer 2 move to the Fermi level E _f of the porous semiconductor layer 2 and move to the electrode layer 1, so that a solar cell is obtained. Fulfills the function. However, in the case where the alkali metal compound layer 3 is not provided, when the electron e ⁻ moves to the _redox level E _redox of the electrolyte layer 4, a counter electromotive force, that is, a dark current is generated, resulting in a decrease in the open-circuit voltage. To do. In FIG. 2, CB of the porous semiconductor layer 2 indicates a conduction band, and VB indicates a valence band.

When an alkali metal compound is added to the electrolyte layer 4 according to the present invention, as described above, the alkali metal compound is adsorbed on the surface of the porous semiconductor layer 2 on which the sensitizing dye is not adsorbed. Form. Due to the presence of the alkali metal compound layer 3 between the porous semiconductor layer 2 and the electrolyte layer 4, the electron e ^{− that} has moved to the Fermi level E _f of the porous semiconductor layer becomes a potential barrier of the alkali metal compound layer 3. It is difficult to move directly to the _redox level E _redox of the electrolyte layer 4. Thus, it is thought that the generation of dark current can be suppressed and the open circuit voltage can be improved by the alkali metal compound layer 3 acting as an electron blocking layer.

The alkali metal compound in the present invention is hardly soluble in the solvent of the electrolyte layer. It is preferable that the alkali metal compound exhibiting poor solubility exhibits a solubility of 1 × 10 ⁻⁴ mol / l or less with respect to the solvent.

In the present invention, the amount of the alkali metal compound added to the solvent of the electrolyte layer is appropriately selected depending on the solubility of the alkali metal compound in the solvent, etc., but generally 1 × 10 ⁻⁴ to 1 × 10 ⁻² mol. / L is preferable, and 1 × 10 ^{−3 to} 5 × 10 ⁻³ mol / l is more preferable. If the amount of the alkali metal compound to be added is too small, the effect of the present invention that the generation of dark current can be suppressed and a high open-circuit voltage can be obtained may not be sufficiently obtained. Moreover, even if the addition amount of the alkali metal compound is excessively increased, the effect corresponding to the addition amount may not be sufficiently obtained.

  Examples of the alkali metal compound used in the present invention include alkali metal oxides, carbonates, and acetylacetonates. Examples of the alkali metal include lithium, cesium, potassium, sodium and the like, and the alkali metal compound of the present invention is particularly preferably a lithium compound.

  The form of the alkali metal compound is not particularly limited, but it is preferably added in the form of a fine powder.

The electrolyte layer in the present invention contains an electrolyte and a solvent. The electrolyte is preferably a redox electrolyte, for example, LiI, NaI, KI, CsI, metal iodide such as CaI _2, and tetraalkylammonium iodide, pyridinium iodide, imidazolium iodide and quaternary ammonium Combinations of iodides such as iodine salts of compounds and I ₂ ; metal bromides such as LiBr, NaBr, KBr, CsBr, CaBr ₂ , and bromides such as bromine salts of quaternary ammonium compounds such as tetraalkylammonium bromide and pyridinium bromide In combination with Br ₂ ; metal complexes such as ferrocyanate-ferricyanate and ferrocene-ferricinium ions; sulfur compounds such as sodium polysulfide and alkylthiol-alkyl disulfides; viologen dyes, Examples include droquinone-quinone. Among these, LiI, pyridinium iodide, and a combination of imidazolium iodide and I ₂ are preferable. Two or more of the above electrolytes may be mixed and used.

  The solvent for the electrolyte layer is preferably a solvent that dissolves the electrolyte and has excellent ion conductivity. As the solvent, an organic solvent is particularly preferable in order to stabilize the electrolyte. Examples of such solvents include carbonate compounds such as ethylene carbonate and propylene carbonate; heterocyclic compounds such as 3-methyl-2-oxazolidinone; ether compounds such as dioxane and diethyl ether; ethylene glycol dialkyl ether and propylene glycol dialkyl ether. Chain ethers such as polyethylene glycol dialkyl ether and polypropylene glycol dialkyl ether; alcohols such as methanol, ethanol, ethylene glycol monoalkyl ether, propylene glycol monoalkyl ether, polyethylene glycol monoalkyl ether and polypropylene glycol monoalkyl ether; ethylene Glycol, propylene glycol, polyethylene glycol Polyhydric alcohols such as polypropylene glycol and glycerol; Nitrile compounds such as acetonitrile, glutarodinitrile, methoxyacetonitrile, propionitrile, and benzonitrile; Lactone compounds such as γ-butyrolactone and valerolactone; Dimethyl sulfoxide, sulfolane, etc. Examples include organic solvents such as aprotic polar substances. Of these, carbonate compounds such as ethylene carbonate and propylene carbonate; nitrile compounds such as acetonitrile, glutarodinitrile, methoxyacetonitrile, propionitrile, and benzonitrile; and lactone compounds such as γ-butyrolactone and valerolactone are particularly preferable. These can be used alone or in combination of two or more.

  Examples of the material for the porous semiconductor layer in the present invention include inorganic semiconductors and organic semiconductors. Examples of the inorganic semiconductor include titanium oxide, zinc oxide, tungsten oxide, barium titanate, strontium titanate, cadmium sulfide, etc. Among these, titanium oxide is particularly preferable from the viewpoint of stability and safety. . Titanium oxide means anatase-type titanium oxide, rutile-type titanium oxide, amorphous titanium oxide, various titanium oxides such as metatitanic acid and orthotitanic acid, or titanium hydroxide and hydrous titanium oxide. These inorganic semiconductors can be used alone or in combination of two or more. Examples of organic semiconductors include porphine derivatives, phthalocyanine derivatives, and cyanine derivatives.

  As a method for forming a porous semiconductor layer, a conventionally known method can be used, a method of applying a suspension containing semiconductor particles and heating, a CVD method, a PVD method, a vapor deposition method, You may form by sputtering method etc. Further, it may be formed by a sol-gel method.

  The sensitizing dye in the present invention is a compound having an absorption spectrum in the visible light region and / or the infrared light region, and in order to strongly adsorb the dye to the porous semiconductor layer, a carboxyl group in the dye molecule, Those having an interlock group such as an alkoxy group, a hydroxyl group, a sulfonic acid group, an ester group, a mercapto group, and a phosphonyl group are preferred. The interlock group provides an electrical bond that facilitates electron transfer between the excited dye and the conductive band of the porous semiconductor.

  Examples of the above dyes include ruthenium bipyridine dyes, azo dyes, quinone dyes, quinone imine dyes, quinacridone dyes, squarylium dyes, cyanine dyes, merocyanine dyes, triphenylmethane dyes, xanthene dyes. Porphyrin dyes, phthalocyanine dyes, perylene dyes, indigo dyes, naphthalocyanine dyes, and the like.

  Examples of the dye include Cu, Ni, Fe, Co, V, Sn, Si, Ti, Ge, Cr, Zn, Ru, Mg, Al, Pb, Mn, In, Mo, Y, Zr, Nb, Sb, Metals such as La, W, Pt, Ta, Ir, Pd, Os, Ga, Tb, Eu, Rb, Bi, Se, As, Sc, Ag, Cd, Hf, Re, Au, Ac, Tc, Te, Rh And metal complex dyes.

  Examples of the method for adsorbing the dye on the porous semiconductor layer include a method of immersing the porous semiconductor layer in a solution containing the dye.

  The electrode layer in the present invention is formed, for example, by depositing gold, silver, aluminum, indium, tin oxide, indium tin oxide (ITO), fluorine-doped tin oxide (FTO) or the like on the substrate. can do. Similarly, the counter electrode can be formed by depositing the conductive thin film on a substrate. At least one of the electrode layer and the counter electrode is preferably transparent. In this case, it is preferable to use a transparent substrate as the substrate. As the substrate, a glass substrate, a plastic substrate, a film sheet, a metal substrate, or the like can be used. When a metal substrate is used, this metal substrate can be used as an electrode layer or a counter electrode.

  According to the present invention, generation of dark current can be suppressed and a high open circuit voltage can be obtained.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to a following example.

(Example 1)
A glass substrate (trade name “A11DU80” manufactured by Asahi Glass Co., Ltd., product name) on which an FTO film (fluorine-doped tin oxide film) as an electrode layer has been ultrasonically cleaned with 2-propanol (IPA) for 5 minutes, then UV ozone For 5 minutes.

A 125 μm spacer is attached to the surface-treated FTO substrate, and a titanium oxide (TiO ₂ ) paste (manufactured by Solaronix: Ti-Nanoxide T / SP) is applied on the FTO substrate by the doctor blade method at 500 ° C. in the atmosphere. Annealing was performed for 30 minutes to form a porous semiconductor layer.

Thereafter, the substrate on which the porous semiconductor layer was formed was immersed in the dye adsorption solution. By immersing in a constant temperature bath at 40 ° C. for 40 minutes, a Ru complex dye (N719 dye) (Peccell: PECC-D07) was adsorbed on the TiO ₂ surface of the porous semiconductor layer to form a photoelectric conversion layer. The Ru complex dye has the following structure.

The dye adsorbing solution was prepared by dissolving the Ru complex dye in a solvent in which acetonitrile and t-butyl alcohol were mixed at a volume ratio of 1: 1 so as to have a concentration of 3 × 10 ⁻⁴ mol / l.

  After adsorbing the dye, a spacer was placed on the substrate, and an iodine redox electrolyte was injected between them to form an electrolyte layer. On top of that, a counter electrode was bonded to complete a dye-sensitized solar cell. The counter electrode used was a platinum surface (Pt) deposited on the surface of the same FTO substrate as described above to have a catalytic function.

  The above iodine redox electrolyte is an acetonitrile solution containing 0.05 mol / l iodine, 0.1 mol / l lithium iodide, 0.5 mol / l 4-tert-butylpyridine, 1,2-dimethyl-3- Propyl imidazolium iodide was prepared by dissolving at 0.6 mol / l.

  4-tert-butylpyridine has the structure shown below.

  1,2-dimethyl-3-propylimidazolium iodide has the structure shown below.

In this example, lithium (I) (Li ₂ O) was added to the iodine redox electrolyte solution produced as described above so as to be 0.005 mol / l.

  FIG. 1 is a schematic cross-sectional view showing the dye-sensitized solar cell produced as described above. Referring to FIG. 1, electrode layer 1 is formed on substrate 8. A porous semiconductor layer 2 is formed on the electrode layer 1, and a sensitizing dye 6 is adsorbed on the surface of the porous semiconductor layer 2. A photoelectric conversion layer 7 is composed of the porous semiconductor layer 2 and the sensitizing dye 6. The counter electrode 5 is provided so as to face the electrode layer 1. An electrolyte layer 4 is provided between the electrode layer 1 and the counter electrode 5 so as to be in contact with the counter electrode 5.

Although not shown in FIG. 1, lithium (I) (Li ₂ O) as an alkali metal compound of the present invention is added to the electrolyte layer 4, so that the increase on the surface of the porous semiconductor layer 2 is increased. It is considered that a part of the added lithium oxide is adsorbed on the surface where the dye 6 is not adsorbed.

(Comparative Example 1)
A dye-sensitized solar cell was produced in the same manner as in Example 1 except that Li ₂ O was not added to the iodine redox electrolyte.

[Evaluation of battery characteristics]
About the solar cell of Example 1 and Comparative Example 1, the solar simulator was used to irradiate pseudo-sunlight with an intensity of 100 mW / cm ² with an air mass (AM) of 1.5, and the battery characteristics were evaluated. FIG. 3 is a graph showing voltage-current characteristics of Example 1 and Comparative Example 1.

  As shown in FIG. 3, the open circuit voltage of Comparative Example 1 was 0.707V, whereas the open circuit voltage of Example 1 was 0.75V, and it was confirmed that the open circuit voltage was significantly increased. .

(Example 2)
Except that the lithium oxide in place of _{Li 2 O (II) (Li} 2 O 2) was added 0.005 mol / l was prepared a solar cell in the same manner as in Example 1.

(Example 3)
A solar cell was fabricated in the same manner as in Example 1 except that 0.003 mol / l of lithium acetylacetonate (Li (acac)) was added instead of Li ₂ O.

Example 4
A solar cell was produced in the same manner as in Example 1 except that 0.003 mol / l of lithium carbonate (Li ₂ CO ₃ ) was added instead of Li ₂ O.

(Comparative Example 2)
A solar cell was produced in the same manner as in Example 1 except that 0.05 mol / l of lithium fluoride (LiF), which was soluble in acetonitrile as the solvent of the electrolyte layer, was added instead of Li ₂ O.

(Example 5)
A solar cell was produced in the same manner as in Example 1 except that 0.002 mol / l of cesium carbonate (Ce ₂ CO ₃ ) was added instead of Li ₂ O.

(Example 6)
A solar cell was produced in the same manner as in Example 1 except that potassium carbonate (K ₂ CO ₃ ) was added in an amount of 0.003 mol / l instead of Li ₂ O.

(Example 7)
A solar cell was produced in the same manner as in Example 1 except that 0.004 mol / l of sodium oxide (Na ₂ O) was added instead of Li ₂ O.

(Comparative Example 3)
A solar cell was produced in the same manner as in Example 1 except that 0.003 mol / l of molybdenum oxide (MoO ₃ ) was added instead of Li ₂ O.

(Example 8)
A solar cell was produced in the same manner as in Example 1 except that γ-butyllactone was used instead of acetonitrile as the solvent for the electrolyte layer.

(Comparative Example 4)
A solar cell was produced in the same manner as in Example 8 except that Li ₂ O was not added.

[Evaluation of battery characteristics]
In the same manner as in Example 1, the open-circuit voltage was measured for the solar cells of Examples 2 to 8 and Comparative Examples 2 to 4, and Table 1 shows the measurement results. Moreover, the short circuit current density, the fill factor, and the photoelectric conversion efficiency were measured, and the results are shown in Table 1. Table 1 also shows the results of Example 1 and Comparative Example 1.

  As is clear from the results shown in Table 1, Examples 1 to 8 according to the present invention show higher open-circuit voltages than Comparative Examples 1 to 4, and high photoelectric conversion efficiency is obtained.

The typical sectional view showing the dye-sensitized solar cell of one example according to the present invention. The energy band figure for demonstrating the effect of the alkali metal compound layer in this invention. The figure which shows the voltage-current characteristic of the dye-sensitized solar cell of Example 1 and Comparative Example 1 according to this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrode layer 2 ... Porous semiconductor layer 3 ... Alkali metal compound layer 4 ... Electrolyte layer 5 ... Counter electrode 6 ... Sensitizing dye 7 ... Photoelectric conversion layer 8 ... Substrate

Claims (3)

An electrode layer formed on the substrate;
A counter electrode provided facing the electrode layer;
A photoelectric conversion layer comprising a porous semiconductor layer adsorbed with a sensitizing dye, provided so as to be in contact with the electrode layer between the electrode layer and the counter electrode;
A dye-sensitized solar cell provided with an electrolyte and a solvent-containing electrolyte layer provided so as to be in contact with the counter electrode between the electrode layer and the counter electrode;
A dye-sensitized solar cell, wherein an alkali metal compound that is hardly soluble in the solvent is added to the electrolyte layer.   The dye-sensitized solar cell according to claim 1, wherein the alkali metal compound is an oxide or carbonate of an alkali metal.   The dye-sensitized solar cell according to claim 1 or 2, wherein the alkali metal compound is a lithium compound.

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