JP6568354B2 - Electrolyte, electrolyte for photoelectric conversion element, photoelectric conversion element, and dye-sensitized solar cell - Google Patents

Description

  The present invention relates to an electrolyte, a photoelectric conversion element, and a dye-sensitized solar cell.

Dye-sensitized solar cells (DSCs) are flexible and lightweight power generation elements with transparent conductive substrates, semiconductors, dyes, electrolytes, and counter electrodes, and are being actively developed because their manufacturing processes are simple. . The cause of the decrease in photoelectric conversion efficiency, which is an important characteristic of DSC, is that the recombination reaction from the semiconductor to the redox oxidation species I ₃ ^- or Co (III) complex occurs, and the open circuit voltage (Voc) decreases. Can be mentioned.

  As an attempt to suppress this recombination reaction, it has been proposed to add tert-butylpyridine to the electrolytic solution (see Non-Patent Document 1). Further, the recombination reaction can be carried out by adding 2-n-propylpyridine having a propyl group introduced into pyridine (see Patent Document 1) or by adding an aminopyridine compound having an amino group introduced into pyridine (see Patent Document 2). It is said that it is suppressed and the photoelectric conversion efficiency is improved.

Japanese Patent No. 4019139 Japanese Patent No. 4019140

“TiO2 Band Shift by Nitrogen-Containing Heterocycles in Dye-Sensitized Solar Cells: a Periodic Density Functional Theory Study” Langmuir 2008, 24, 4411-4419

  However, the degree of the recombination reaction suppressed by the addition of the pyridine compound of Patent Document 1 is not sufficient, and the addition of the pyridine compound of Patent Document 2 significantly reduces the short-circuit current (Isc) in exchange for the improvement of Voc. There was a problem to do.

  The present invention has been made in view of the above circumstances, and includes an electrolyte for a dye-sensitized solar cell that can improve open-circuit voltage and photoelectric conversion efficiency and suppress a decrease in short-circuit current, and the electrolyte. An object is to provide a photoelectric conversion element and a dye-sensitized solar cell.

  As a result of intensive studies by the present inventors, it was considered that the electron transfer from the dye to the semiconductor was hindered by the shielding effect on the semiconductor surface because the basicity of the conventional additive was excessive. As a result of further investigation, it was found that by adding an additive having an appropriate basicity to the electrolyte, the recombination reaction can be suppressed and the photoelectric conversion efficiency can be improved, and the present invention has been completed. That is, the present invention provides the following means.

（式中、R1、R2、R3、R4及びR5からなる群のうち何れか一つが下記一般式(2)又は(3)であり、その他の四つはそれぞれ独立に、水素原子、メチル基又はエチル基であり、k, l, mは整数であり、k≧4、l＋m≧2である。）

［２］R1、R2、R4及びR5はそれぞれ独立に、水素原子、メチル基又はエチル基であり、R3が前記一般式(2)又は(3)であることを特徴とする前記［１］に記載の電解質。
［３］前記複素芳香族化合物及び酸化還元反応を生じるレドックスを含有することを特徴とする前記［１］又は［２］に記載の電解質。
［４］前記レドックスがハロゲン化合物、Co錯体化合物、Fe錯体化合物及び有機ラジカル化合物から選択される１以上であることを特徴とする前記［３］に記載の電解質。
［５］前記［１］〜［４］の何れか一項に記載の電解質を備えた光電変換素子。
［６］前記［５］に記載の光電変換素子であり、透明導電層、半導体層及び色素を有する光電極と、前記電解質と、対向電極とを備えたことを特徴とする色素増感太陽電池。 [1] An electrolyte comprising a heteroaromatic compound represented by the following general formula (1).

(In the formula, any one of the group consisting of R1, R2, R3, R4 and R5 is the following general formula (2) or (3), and the other four are independently a hydrogen atom, a methyl group or An ethyl group, k, l and m are integers, and k ≧ 4 and l + m ≧ 2.)

[2] In the above [1], R1, R2, R4 and R5 are each independently a hydrogen atom, a methyl group or an ethyl group, and R3 is the general formula (2) or (3) The electrolyte described.
[3] The electrolyte according to [1] or [2] above, which contains the heteroaromatic compound and a redox that causes a redox reaction.
[4] The electrolyte according to [3], wherein the redox is at least one selected from a halogen compound, a Co complex compound, an Fe complex compound, and an organic radical compound.
[5] A photoelectric conversion element comprising the electrolyte according to any one of [1] to [4].
[6] The dye-sensitized solar cell according to [5], comprising a photoelectrode having a transparent conductive layer, a semiconductor layer, and a dye, the electrolyte, and a counter electrode. .

  According to the electrolyte of the present invention, a recombination reaction in which electrons move from a dye to a redox oxidation species in a photoelectric conversion element and a dye-sensitized solar cell provided with the same is suppressed, a decrease in short-circuit current is suppressed, an open-circuit voltage and Photoelectric conversion efficiency can be improved.

It is sectional drawing which shows an example of the photoelectric conversion element concerning this invention.

  In FIG. 1, sectional drawing of 1st embodiment of the photoelectric conversion element concerning this invention is shown. The photoelectric conversion element 10 is a dye-sensitized solar cell, and includes a photoelectrode substrate 11, a counter electrode substrate 12, and a charge transport layer 20. The photoelectrode substrate 11 includes a transparent base material 13, a transparent conductive film (transparent conductive layer) 14 formed on one plate surface of the transparent base material 13, and a semiconductor layer 15 formed on the transparent conductive film 14. And a photoelectrode composed of a semiconductor layer 15 and a sensitizing dye (not shown). The counter electrode substrate 12 includes a transparent base material 13, a counter base material 16 arranged with a certain thickness, and a counter conductive film (counter conductive layer) 17 formed on the plate surface of the counter base material 16. It is comprised by the counter electrode. The charge transport layer 20 is filled in a gap between the semiconductor layer 15 and the counter conductive film 17, and the side of the charge transport layer 20 is sealed with a sealing material 21.

If the transparent base material 13 is a member used as the base of the transparent conductive film 14, and can be applied to manufacture and utilization of a dye-sensitized solar cell and is comprised with a transparent material, a kind etc. will not be specifically limited. .
As the transparent substrate 13, for example, a film substrate made of transparent glass or a transparent resin material is suitable.

  The transparent conductive film 14 is formed on one plate surface of the transparent substrate 13 by a sputtering method or a printing method. For the transparent conductive film 14, for example, tin-doped indium oxide, fluorine-doped tin oxide, aluminum-doped zinc oxide, tin oxide, antimony-doped tin oxide, indium oxide / zinc oxide, gallium-doped zinc oxide, or the like is used.

  The semiconductor layer 15 is not particularly limited as long as it is an n-type semiconductor capable of adsorbing a sensitizing dye and receiving electrons from the photoexcited sensitizing dye and passing the electrons to the transparent conductive film 14. As a material for such a semiconductor layer, for example, fine particles made of a semiconductor such as a metal oxide semiconductor or metal chalcogenide are preferable, and fine particles of titanium oxide are more preferable.

  The form of the semiconductor layer 15 may be a dense layer or a porous layer, but is preferably a porous layer from the viewpoint of increasing photoelectric conversion efficiency, and is a porous material in which the fine particles are sintered together. More preferred are layers or porous layers joined by physical impingement of powder spraying by aerosol deposition method.

  As a kind of titanium oxide, anatase type titanium oxide is preferable from the viewpoint of improving electrical bonding between titanium oxide fine particles. The titanium oxide fine particles are preferably titanium oxide in which anatase type and rutile type are mixed, and may be only rutile type titanium oxide. In the dye-sensitized solar cell, the average particle diameter of the titanium oxide fine particles is preferably 10 nm or more and 500 nm or less from the viewpoint of increasing the specific surface area of the porous titanium oxide film and the utilization efficiency of incident light.

  The sensitizing dye adsorbed on the semiconductor layer 15 is a compound that emits electrons when excited by the light applied to the photoelectric conversion element 10. The emitted electrons are transferred to the semiconductor layer 15 having a wide band gap and no absorption band in the visible light region, and further move to the transparent conductive film 14. As such a sensitizing dye, a dye used in a conventional dye-sensitized solar cell is applicable, and examples thereof include organic dyes such as a ruthenium complex, cyanine, and chlorophyll. As the sensitizing dye, a ruthenium complex is preferable because it has a wide absorption wavelength range, has a long photoexcitation lifetime, and stabilizes electrons transferred to the semiconductor layer 15. For example, N3, N719, N749, CYC -A dye generally called B11 is mentioned. A carbazole organic dye having a carbazole skeleton such as MK2 is also suitable.

  The opposing base material 16 is a member that becomes a base of the opposing conductive film 17, and the type and the like are not particularly limited as long as the opposing base material 16 is made of a material that can be applied to manufacture and use of the dye-sensitized solar cell. As the counter substrate 16, for example, a film substrate made of glass or a resin material is suitable.

  The counter conductive film 17 is formed on the plate surface of the counter substrate 16 on the transparent substrate 13 side by a sputtering method or a printing method. As the counter conductive film 17, one having catalytic ability in the oxidation-reduction reaction of the charge transport layer 20 described later is selected. Examples of such a catalyst include metal catalysts such as gold and platinum, conductive carbon such as carbon nanotubes and graphite, and conductive polymers that function as p-type semiconductors such as polyaniline, polypyrrole, and polythiophene. The counter substrate 16 and the counter conductive film 17 may be opaque. In order to allow the light transmitted through the counter electrode substrate 12 from the outside to reach the photoelectrode substrate 11, it is preferably transparent.

  The material of the sealing material 21 is not particularly limited as long as it is a material that can seal the charge transport layer 20 between the photoelectrode substrate 11 and the counter electrode substrate 12. For example, the material of the sealing material 21 includes a photocurable resin and a thermosetting resin. A mixture etc. are mentioned.

  The charge transport layer 20 contains an electrolyte used in a known dye-sensitized solar cell. When the heteroaromatic compound represented by the following general formula (1) is contained in the electrolyte, the photoelectric conversion efficiency of the photoelectric conversion element and the dye-sensitized solar cell including the electrolyte is improved.

  In the following general formula (1), any one of the groups consisting of R1, R2, R3, R4 and R5 is the following general formula (2) or (3), and the other four, that is, the following among the above groups: The four which are not the general formula (2) or (3) are each independently a hydrogen atom, a methyl group or an ethyl group, k, l and m are integers, and k ≧ 4 and l + m ≧ 2. The left end of the following general formula (2) or (3) is bonded to the carbon atom to which R1, R2, R3, R4 and R5 are bonded.

In general formula (1), among R1, R2, R3, R4 and R5, R2, R3 or R4 is preferably general formula (2) or (3), and R3 is general formula (2) or (3 ) Is more preferable.
When these suitable heteroaromatic compounds are contained, the photoelectric conversion efficiency of the photoelectric conversion element and the dye-sensitized solar cell provided with the electrolyte can be further improved. As the mechanism, the basicity of the compound becomes even more moderate, the shielding effect that inhibits electron transfer from the dye to the semiconductor on the semiconductor surface is reduced, and recombination from the semiconductor to the redox oxidized species due to moderate steric hindrance This is presumably because the reaction is suppressed.

The integer k in the general formula (2) where k ≧ 4 is preferably 4-20, more preferably 4-15, and still more preferably 4-10.
When these suitable heteroaromatic compounds are contained, the photoelectric conversion efficiency of the photoelectric conversion element and the dye-sensitized solar cell provided with the electrolyte can be further improved. When the integer k is 4 or more, the basicity of the compound becomes moderate, the shielding effect is reduced, and the recombination reaction from the semiconductor to the redox oxidized species is suppressed by moderate steric hindrance. . When the integer is 20 or less, sufficient solubility or dispersibility of the compound in the electrolyte can be obtained.

In general formula (3), integers l and m satisfying l + m ≧ 2 are each independently preferably 0 to 20, more preferably 1 to 10, and further preferably 1 to 5. The l + m is preferably 2 to 12, more preferably 2 to 8, and still more preferably 2 to 6. Here, the absolute value of “l-m” is preferably 0 to 4, more preferably 0 to 2, and still more preferably 0 to 1.
When these suitable heteroaromatic compounds are contained, the photoelectric conversion efficiency of the photoelectric conversion element and the dye-sensitized solar cell provided with the electrolyte can be further improved. When the l + m is 2 or more, it is presumed that the basicity of the compound becomes appropriate, the shielding effect is reduced, and the recombination reaction from the semiconductor to the redox oxidized species is suppressed by appropriate steric hindrance. When the l + m is 12 or less, sufficient solubility or dispersibility in the electrolyte can be obtained. When the absolute value of l-m is 0 to 4, the solubility or dispersibility of the compound in the electrolyte is sufficiently obtained.

In general formula (1), among R1, R2, R3, R4 and R5, the four groups not in general formula (2) or (3) are each independently a hydrogen atom, a methyl group or an ethyl group, An atom or a methyl group is preferable, and a hydrogen atom is more preferable.
When these suitable heteroaromatic compounds are contained, the photoelectric conversion efficiency of the photoelectric conversion element and the dye-sensitized solar cell provided with the electrolyte can be further improved. When the four groups are each independently a hydrogen atom or a methyl group, the basicity of the compound becomes appropriate, the shielding effect is further reduced, and the solubility or dispersibility of the compound in the electrolyte is sufficiently obtained. It is done.

  Specific examples of suitable compounds represented by the general formula (1) include, for example, linear forms such as 4-heptylpyridine, 4-octylpyridine and 4- (5-nonyl) pyridine used in Examples described later. Alternatively, a pyridine compound having a branched alkyl group having 4 to 10 carbon atoms at the 4-position can be given.

  The heteroaromatic compound contained in the electrolyte constituting the charge transport layer 20 may be one type or two or more types.

The electrolyte constituting the charge transport layer 20 contains redox that causes a redox reaction.
Here, “redox” refers to a substance that can take both an oxidized state and a reduced state to reduce the sensitizing dye. Redox can be called redox couple.
The redox contained in the electrolyte may be one type or two or more types.

The type of the redox is not particularly limited, and redox used in a conventional dye-sensitized solar cell can be applied. For example, iodine redox (I ⁻ , I ₃ ⁻ ), bromine redox (Br ⁻ , Br ₃ ⁻ And the like are preferred.

As the redox, it is preferable that at least one selected from a halogen compound, a cobalt (Co) complex compound, an iron (Fe) complex compound, and an organic radical compound constitutes the electrolyte.
The halogen compound is preferably included in the charge transport layer 20 together with a halogen such as fluorine, chlorine, bromine or iodine.

  Examples of the halogen compound include halogenated inorganic halogen compounds such as lithium, magnesium, and calcium, 1-ethyl-3methylimidazolium iodide salt, 1-ethyl-3 methyl iodide salt containing the halogen as a counter anion, and the like. Organic halide salts such as methyl imidazolium bromide salt, 1,2-dimethyl-3-propyl imidazolium iodide salt (abbreviation: DMPImI), 1,2-dimethyl-3-propyl imidazolium bromide salt, etc. It is done.

  The charge transport layer 20 may contain two or more redox composed of halogen and a halogen compound. For example, the electrolyte contained in the charge transport layer 20 may be a mixture of redox pairs containing two or more redox composed of halogen and a halogen compound.

Examples of the cobalt complex compound include cobalt (II / III) tris (2,2′-bipyridine), cobalt (II / III) tris (4,4′-dimethyl-2,2-bipyridine), cobalt (II / III) tris (4,4′-ditert-butyl-2,2-bipyridine), cobalt (II / III) tris (1,10-phenanthroline), and the like.
The cobalt complex compound contained in the electrolyte may be one type or two or more types.

  Examples of the iron complex compound include ferrocyanate and ferrocene.

  Examples of the organic radical compound include TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl), benzoquinone, viologen, and the like.

  In the charge transport layer 20, an organic solvent or an ionic liquid (room temperature molten salt) may be included as a solvent for dissolving or dispersing the redox and heteroaromatic compound constituting the electrolyte. As said organic solvent, the organic solvent used for the electrolyte solution of the conventional dye-sensitized solar cell is applicable, For example, acetonitrile, propionitrile, (gamma) -butyrolactone etc. are mentioned. As the ionic liquid, an ionic liquid used in an electrolyte solution of a conventional dye-sensitized solar cell is applicable, and examples thereof include an imidazolium-based ionic liquid, a pyridinium-based ionic liquid, and an aliphatic ionic liquid. . In the charge transport layer 20, the organic solvent and the ionic liquid may be used in combination. The organic solvent constituting the charge transport layer 20 may be gelled with a gelling agent such as polyacrylonitrile.

  The concentration of the redox contained in the charge transport layer 20 is not particularly limited, and the same concentration as the redox used in the conventional dye-sensitized solar cell can be applied. For example, 0.01 to 3 M (mol / L ).

  The concentration of the heteroaromatic compound contained in the charge transport layer 20 depends on the type and solubility of the solvent, but is about the same as the redox concentration or about 0.1 to 2.0 times the redox concentration. For example, about 0.005 to 3 M (mol / L). When contained in a concentration within the above range, the solubility or dispersibility is good, the shielding effect can be reduced, and the photoelectric conversion efficiency can be sufficiently improved.

  The charge transport layer 20 is produced by the same method as the liquid, gel, and solid electrolytes used in conventional dye-sensitized solar cells. For example, the electrolyte solution as the charge transport layer 20 can be obtained by introducing the heteroaromatic compound and redox into a solvent and mixing them uniformly by a known method. Moreover, a photoelectric conversion element can be obtained by assembling a known member of a photoelectric conversion element by a conventional method and sealing the charge transport layer 20 between the photoelectrode substrate 11 and the counter electrode substrate 12 by a known method. It is used as a dye-sensitized solar cell capable of extracting current to an external circuit through an extraction wiring connected to the photoelectrode substrate 11 and the counter electrode substrate 12 by irradiating light to the photoelectrode of the photoelectric conversion element. be able to.

  Next, the present invention will be described in detail by the following examples, but the present invention is not limited only to these examples.

<Preparation of dye-sensitized solar cell>
As a transparent conductive substrate, a glass substrate (manufactured by Nippon Sheet Glass Co., Ltd.) on which an FTO film having a surface resistance of 10Ω / sq was formed. On the surface of the substrate on which the FTO film is formed, a Nanoxide paste manufactured by Solaronix is applied by screen printing and baked at 500 ° C. for 30 minutes in an air atmosphere. The film thickness is about 5 μm and the cell area is 0.16 cm ^2. A titanium oxide porous film was formed.
The titanium oxide porous membrane is immersed in dye solution A “dye: 0.3 mM N719, solvent: acetonitrile: t-butanol = 1: 1” or dye solution B “dye: 0.3 mM MK2, solvent: toluene” for 24 hours. An electrode was produced. An injection hole previously opened in a counter electrode substrate having a counter electrode in a cell sealed by placing a frame type high-Milan separator between the electrodes with the Pt foil as a counter electrode facing this photoelectrode The following electrolyte was injected.

<Preparation of electrolyte>
By dissolving basic additives, redox 1 and redox 2 in acetonitrile so as to have the compositions and concentrations shown in Table 1 as electrolytes of Examples 1 to 6 and Comparative Examples 1 to 6, an iodine redox system An electrolytic solution and a cobalt redox solution were prepared. N719 was used as the dye for the photoelectrodes of Examples 1 to 3 and Comparative Examples 1 to 3, and MK2 was used as the dye for the photoelectrodes of Examples 4 to 6 and Comparative Examples 4 to 6. The structural formula of the basic additive described in Table 1 is shown below.

  In the above table, “DMPImI” represents 1,2-dimethyl-3-propylimidazolium iodide salt, “I2” represents iodine, “TBP” represents tert-butylpyridine, and “bpy” represents tris. Represents a (2,2'-bipyridine) cobalt (II) / (III) complex.

<Evaluation of dye-sensitized solar cell>
Using a solar simulator (model number: XES-301S, manufactured by Mitsunaga Electric Manufacturing Co., Ltd.), irradiating pseudo-sunlight with a light amount of 100 mW / cm ² , Examples 1 to 6 and Comparative Examples 1 to 6 prepared above were used. The current-voltage characteristics of the dye-sensitized solar cell were evaluated. The results are shown in Table 2.

  From the above results, it is clear that the dye-sensitized solar cells of Examples 1 to 6 according to the present invention suppress the decrease in short-circuit current and improve the open-circuit voltage and photoelectric conversion efficiency.

  The configurations and combinations thereof in the embodiments described above are examples, and the addition, omission, replacement, and other modifications of the configurations can be made without departing from the spirit of the present invention. Further, the present invention is not limited by each embodiment, and is limited only by the scope of the claims.

  The present invention can be widely used in the field of dye-sensitized solar cells.

DESCRIPTION OF SYMBOLS 10 ... Photoelectric conversion element, 11 ... Photoelectrode substrate, 12 ... Counter electrode substrate, 13 ... Transparent base material (base material), 14 ... Transparent electrically conductive film, 15 ... Semiconductor layer (photoelectrode), 16 ... Counter base material, 17 ... counter conductive film (counter electrode), 20 ... charge transport layer, 21 ... sealing material

Claims (8)

An electrolyte for a photoelectric conversion element comprising a heteroaromatic compound represented by the following general formula (1).

(In the formula, any one of the group consisting of R1, R2, R3, R4 and R5 is the following general formula (2) or (3), and the other four are independently a hydrogen atom, a methyl group or An ethyl group, k, l, m are integers, k is 6-20, and l + m is 3-12.)

2. The photoelectric conversion according to claim 1, wherein R 1, R 2, R 4 and R 5 are each independently a hydrogen atom, a methyl group or an ethyl group, and R 3 is the general formula (2) or (3). Electrolyte for device . 3. The electrolyte for a photoelectric conversion element according to claim 1, comprising the heteroaromatic compound and a redox that causes a redox reaction. 4. The said redox is 1 or more selected from a halogen compound, Co complex compound, Fe complex compound, and an organic radical compound, The electrolyte for photoelectric conversion elements of Claim 3 characterized by the above-mentioned. The photoelectric conversion element provided with the electrolyte for photoelectric conversion elements as described in any one of Claims 1-4. 6. A dye-sensitized solar cell according to claim 5, comprising a photoelectrode having a transparent conductive layer, a semiconductor layer and a dye, the electrolyte for the photoelectric conversion element, and a counter electrode. . An electrolyte containing a heteroaromatic compound represented by the following general formula (1):
Furthermore, the electrolyte characterized by including the redox which produces a redox reaction.

(In the formula, any one of the group consisting of R1, R2, R3, R4 and R5 is the following general formula (2) or (3), and the other four are independently a hydrogen atom, a methyl group or An ethyl group, k, l, m are integers, k is 6-20, and l + m is 3-12.)

8. The electrolyte according to claim 7, wherein R1, R2, R4 and R5 are each independently a hydrogen atom, a methyl group or an ethyl group, and R3 is the general formula (2) or (3).

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