JP2008034258A - Dye-sensitized photoelectric conversion element and dye-sensitized photoelectric conversion element module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dye-sensitized photoelectric conversion element capable of effectively utilizing incident light; and to restrain drop of an output current value, in a tandem type photoelectric conversion element. <P>SOLUTION: The tandem type photoelectric conversion element capable of effectively utilizing incident light is formed by combining a plurality of dyes having absorption peak wavelengths different from one another. In addition, in the tandem type photoelectric conversion element composed by stacking photoelectric conversion cells comprising photoelectrodes having a plurality of dyes having absorption peak wavelengths different from one another, a current value adjustment means restraining drop of an output current value is provided for any of the photoelectric conversion cells. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a dye-sensitized photoelectric conversion element and a dye-sensitized photoelectric conversion element module.

Solar cells have attracted attention as an energy source to replace fossil fuels, and various studies have been conducted. The mainstream of solar cells currently in practical use is silicon-based solar cells made of monocrystalline, polycrystalline, and amorphous silicon, but these materials have high material costs and high energy costs in the manufacturing process, and solar cells are widely used. It is an obstacle.
Therefore, a dye-sensitized solar cell has attracted attention as a solar cell that can be manufactured at low cost.

  A dye-sensitized solar cell is a wet solar cell using a photoelectrode in which a dye is adsorbed on a semiconductor (preferably porous), and the principle of photosensitization (in this case, a semiconductor having absorption in the ultraviolet region) On the other hand, by applying a dye having absorption in the visible light or near infrared light region to cause photoelectric conversion by light having a wavelength longer than the absorption region of the semiconductor) It is a battery.

The power generation principle of such a dye-sensitized photoelectric conversion element will be described with reference to an energy diagram shown in FIG.
In FIG. 8, 2 is a photoelectrode made of a porous semiconductor to which a dye is adsorbed, 3 is a counter electrode, 4 is an electrolyte, 801 is incident light, 802 is a HOMO level of the dye, 803 is a LUMO level of the dye, Reference numeral 804 denotes a conduction band energy level of the porous semiconductor, and 805 denotes a redox level of a redox pair (R / R-) contained in the electrolyte 4.
Hereinafter, a case where light having an energy of hν (h is Planck's constant and ν is the frequency of light) is incident on the photoelectrode 2 will be considered.

If the energy hv of the incident light 801 is equal to or greater than the HOMO-LUMO energy gap of the dye (LUMO level 803-HOMO level 802), the incident light is absorbed and the dye is excited. Electrons in the excited dye are injected into the conduction band energy level 804 of the porous semiconductor. The electrons reach the counter electrode 3 via the external circuit 806.
On the other hand, the dye that has lost the electrons receives electrons from the reduced state R− of the redox pair contained in the electrolyte 4 and returns to the ground state.
Furthermore, the oxidation state R of the oxidation-reduction pair oxidized by passing electrons to the dye receives the electron that has reached the counter electrode 3 and returns to the reduction state R-, thereby completing one cycle of electron flow.

Such dye-sensitized photoelectric conversion elements can be reduced in cost in that they do not require large-scale equipment (such as silicon melting equipment) and do not require advanced material purification compared to photoelectric conversion elements using silicon. However, since the absorption wavelength of the dye is limited compared to silicon, the utilization efficiency of incident light (for example, sunlight, the same shall apply hereinafter) is low, and the photoelectric conversion element is smaller than the silicon photoelectric conversion element. There was a problem that the exchange efficiency was low.
Therefore, for effective use of incident light (in this case, mainly using light on the long wavelength side that was not absorbed by conventional dyes for power generation), the development of dyes with longer absorption peak wavelengths was developed. (For example, Non-Patent Document 1).

Also, for effective use of incident light (mainly, light in a wavelength range that is not absorbed by a single dye is absorbed by combining multiple dyes, and light in a wider wavelength range is used for power generation). In addition, a tandem photoelectric conversion element having a structure in which dye-sensitized photoelectric conversion cells using different dyes in a photoelectrode is laminated has been proposed.
For example, Patent Document 1 discloses the use of photoelectrodes having different long wavelength side absorption wavelength ends in a tandem photoelectric conversion element. However, in Patent Document 1, the long wavelength side absorption wavelength end is defined as “a wavelength on the long wavelength side indicating an absorbance of 10% of the absorbance at the absorption peak wavelength”, but this definition is not general. In general, the long wavelength side absorption wavelength end means “the wavelength of light having the minimum energy absorbed by the dye”, and the absorption wavelength end in this sense corresponds to the band gap energy of the dye.

Hereinafter, when simply referring to the absorption wavelength end in the present specification, the long wavelength side absorption wavelength end in the general sense is shown.
In the present invention, the absorption spectrum of the photoelectrode in which the dye is adsorbed to the porous semiconductor is measured, and the wavelength having the highest absorption value within a certain wavelength range is defined as the absorption peak wavelength of the corresponding dye. .
Further, as described with reference to FIG. 8, in the dye-sensitized photoelectric conversion element, the electrons in the excited dye are injected into the conduction band of the semiconductor.

However, the conduction band energy level is a value inherent to semiconductors, and accurate measurement requires a relatively large measuring device such as a UPS measurement in a vacuum. Therefore, the flat band level of the semiconductor is considered as a factor more preferable than the conduction band energy that represents the energy state of the semiconductor in the dye-sensitized photoelectric conversion element.
The flat band level is an electrode potential when a horizontal band state is formed across the semiconductor when in contact with the electrolytic solution, and can be obtained relatively easily from impedance measurement at the electrode interface.

That is, since the equation of Mott-schottky is established between the differential capacitance C and the electrode potential E, when 1 / C ² is plotted against E, a linear relationship is obtained, and the flat band level is obtained from the intercept of the straight line. Is required. Further, it is known that the flat band level has a value almost equal to the conduction band energy level. Therefore, in the present invention, the flat band level is used instead of the conduction band energy level.
The flat band level in the present invention is a value obtained by the Mott-Schottky equation by performing impedance measurement using a 0.2 M LiClO ₄ aqueous solution as an electrolyte, a platinum wire as a counter electrode, and Ag / AgCl as a reference electrode. It is.

Chem. Commun. , P1705-1706, 1997 JP 2001-319698 A

The absorption wavelength end in Patent Document 1 and the absorption wavelength end in a general sense are dyes that can effectively use incident light in a dye-sensitized photoelectric conversion element using a photoelectrode made of a semiconductor to which a plurality of dyes are adsorbed. However, it is not always effective.
In addition, although it is a preferable technique to use a tandem photoelectric conversion element for effective use of incident light, in the simplest configuration of a tandem photoelectric conversion element (a configuration in which a plurality of photoelectric conversion cells are connected in series), When the output currents of the respective photoelectric conversion cells are greatly different, there is a problem that the output current value (generally represented by the short circuit current value Isc or the short circuit current density Jsc) of the entire tandem photoelectric conversion element is lowered.

Therefore, in view of the above problems, an object of the present invention is to provide a dye-sensitized photoelectric conversion element capable of effectively using incident light by combining a plurality of dyes having different absorption peak wavelengths.
In addition, the present invention suppresses a decrease in output current value, which is a conventional problem, in a tandem photoelectric conversion element that enables effective use of incident light by combining a plurality of dyes having different absorption peak wavelengths. It aims at providing the dye-sensitized photoelectric conversion element which shows practical photoelectric conversion efficiency by.

In the photoelectric conversion element disclosed in Patent Document 1, dyes having different absorption wavelength ends are used. However, in such a conventional example, as shown in FIG. 10, since the absorbance of the dye is low near the absorption wavelength end, the incident light may not be sufficiently utilized. FIG. 10 shows absorption spectra Sa and Sb of two types of dyes having different absorption wavelength ends and substantially the same absorption peak wavelengths.
On the other hand, in order to use incident light more effectively, it is important that the absorption peak wavelengths are different as shown in FIG. 9 (the present invention). FIG. 9 shows absorption spectra Sx and Sy of two types of dyes having different absorption peak wavelengths.

The dye-sensitized photoelectric conversion element of the present invention is a dye-sensitized photoelectric conversion element including a photoelectrode on which a plurality of dyes having different absorption peak wavelengths, which generate excited electrons by incident light, are adsorbed.
Of the absorption peak wavelengths of the respective dyes, the absorption peak wavelengths on the longest wavelength side are preferably different from each other, and the absorption wavelength end of at least one dye is particularly preferably in the near infrared region. In the present invention, “near infrared region” and “near infrared light” refer to a wavelength region or wavelength light longer than 700 nm and shorter than 2500 nm. In the present invention, the difference in absorption peak wavelength means that the difference in peak position differs by 10 nm or more in the absorption spectrum of each dye.

A preferred embodiment of the present invention is a so-called tandem in which a plurality of photoelectric conversion cells having a photoelectrode on which a plurality of dyes having different absorption peak wavelengths are adsorbed are stacked in a direction intersecting with incident light. Type photoelectric conversion elements.
As a particularly preferred embodiment of the present invention, in the tandem photoelectric conversion element, it is possible to provide a current value adjusting means for reducing a difference in output current between the photoelectric conversion cells.

Further, as a preferable current value adjusting means, the haze ratio of the photoelectrode constituting one of the photoelectric conversion cells is set to be the haze of the photoelectrode constituting the photoelectric conversion cell (hereinafter referred to as the top cell) closest to the incident light side. It can be mentioned that it is larger than the rate.
The haze ratio in the present invention is the diffuse transmittance when a light beam having a spectrum in the visible light region and / or near infrared region (for example, the standard light source D65 or the standard light source C) is incident on the measurement sample. It is the value divided by the transmittance. This is usually expressed as a value between 0 and 1 or as a percentage from 0 to 100%.

According to the present invention, a dye-sensitized photoelectric conversion element capable of effectively using incident light can be obtained by using a plurality of dyes having different absorption peak wavelengths.
Moreover, according to this invention, the tandem photoelectric conversion element which suppressed the fall of output current value can be obtained by making the difference of the electric current value between each photoelectric conversion cell small.

The dye-sensitized photoelectric conversion element of the present invention has a photoelectrode on which a plurality of dyes having different absorption peak wavelengths are adsorbed.
Such a photoelectrode is generally a plurality of photoelectrodes on which different dyes are adsorbed (see FIG. 1), but is not limited to this, and a single photoelectrode in which a plurality of dyes are mixed and adsorbed (FIG. 2). Or a multi-layer photoelectrode (see FIG. 3) in which a plurality of dyes are adsorbed for each region.
Embodiments of the present invention will be described below.

  In the dye-sensitized photoelectric conversion element 100 shown in FIG. 1, the first photoelectrode 2-1 made of the first porous semiconductor to which the first dye is adsorbed is used as the first support 110 with the first transparent conductive layer 111. A first photoelectric element formed by holding a first electrolyte 4-1 between a first counter electrode 3-1 (formed on the incident light side of the second support member 120) formed on and opposed to the first counter electrode 3-1. A conversion cell 101 and a photoelectrode 2-2 made of a second porous semiconductor to which a second dye is adsorbed are formed on a second support 120 with a second transparent conductive layer 121, and are arranged opposite to this. A second photoelectric conversion cell 102 that holds the second electrolyte 4-2 between the second counter electrode 3-2 (formed on the incident light side of the third support 130) and the incident light 140 direction. The first counter electrode 3-1 and the second transparent conductive layer are stacked in an intersecting direction by (electrical) connecting means 150. And 21 is a dye-sensitized photoelectric conversion elements connected in series.

In a so-called tandem photoelectric conversion element in which photoelectric conversion cells are stacked in this way, each photoelectric conversion cell may be connected (electrically) by any connection means.
However, in this embodiment and in the following examples, as the simplest connection method, a method of connecting the counter electrode constituting the incident light side photoelectric conversion cell and the photoelectrode constituting the non-incident light side photoelectric conversion cell in series is adopted. is doing.

Moreover, the dye-sensitized photoelectric conversion element of this invention may consist of a photoelectric conversion cell which is not a laminated structure as shown in FIG.2 and FIG.3. In this case, a plurality of dyes having different absorption peak wavelengths are mixed and adsorbed on a single-layer porous semiconductor (FIG. 2), or a porous semiconductor having adsorbed dyes having different absorption peak wavelengths is used. A multilayer structure (FIG. 3) may be used as a dye-sensitized photoelectric conversion element.
Hereafter, the component of the dye-sensitized photoelectric conversion element in this invention is demonstrated.

<Dye>
Various dyes having absorption in the visible light region and / or the near-infrared light region can be used for the dye-sensitized photoelectric conversion element.
The dye used in the present invention is a plurality of dyes having different absorption peak wavelengths, and preferably includes a combination of dyes having a difference in absorption peak wavelength of 90 nm or more.
Further, among the respective absorption peak wavelengths, it is preferable that the absorption peak wavelengths on the longest wavelength side are different from each other, particularly including a combination in which the difference between absorption peak wavelengths on the longest wavelength side is 90 nm or more. preferable. This is because a dye-sensitized photoelectric conversion element with higher utilization efficiency of incident light can be obtained by selecting a dye having an absorption wavelength edge in a longer wavelength (for example, near infrared region).

Furthermore, when a combination of dyes having different absorption peak wavelengths is selected, each dye preferably has a different LUMO-HOMO energy gap, and the difference in the LUMO-HOMO energy gap is 0.3 eV or more. It is particularly preferred.
The difference in the HOMO-LUMO energy gap means that the absorption wavelength ends are different. At this time, the magnitude relationship between the absorption peak wavelengths in each dye may be different from the magnitude relationship between the absorption wavelength ends.

  Further, it is preferable that the dye has a carboxylic acid group, carboxylic anhydride group, alkoxy group, hydroxyl group, hydroxyalkyl group, sulfonic acid group, ester group, mercapto group, phosphonyl group or the like in the molecule. . Among these interlock groups, a carboxylic acid group and a carboxylic anhydride group are more preferable. The “interlock group” here is a functional group that provides an electrical bond that facilitates electron transfer between the excited dye and the conduction band of the (porous) semiconductor.

  Examples of these dyes containing an interlock group include pyridine ruthenium complex dyes, azo dyes, quinone dyes, quinone imine dyes, quinacridone dyes, squarylium dyes, cyanine dyes, merocyanine dyes, and triphenylmethane dyes. Examples include dyes, xanthene dyes, porphyrin dyes, phthalocyanine dyes, berylene dyes, indigo dyes, naphthalocyanine dyes, and the like.

  Examples of pyridine-based ruthenium complexes include cis-dithiocyanato-bis (4,4′-dicarboxyl-2,2′-bipyridine) ruthenium (valence 2) complex (common name: N3 dye, compound E), cis-dithiocyanato- Bis (4,4′-dicarboxyl-2,2′-bipyridine) ruthenium (valence 2) bis-tetrabutylammonium complex (common name: N719 dye), trithiocyanate (4,4 ′, 4 ″ -tricarboxy- 2,2 ′: 6 ′, 2 ″ -terpyridine) ruthenium (valence 2) tri-tetrabutylammonium complex (common name: black dye, compound B), cis-dithiocyanato-bis (4,4′-dicarboxyl- Known substances such as 2,2′-biquinoline) ruthenium (valence 2) complex (compound I) can be used.

  Here, bipyridine-based ruthenium complexes are disclosed in, for example, the known literature J.P. Am. Chem. Soc. 115 (1993) 6382. It can be synthesized with reference to the method described in 1. Terpyridine-based ruthenium complexes are disclosed in known literature J. Org. Am. Chem. Soc. 123 (2001) 1613. And can be synthesized. Biquinoline-based ruthenium complexes can be obtained from Inorganica Chimica Acta. 322 (2001) 7. Etc. can be synthesized with reference to the method described in the above.

  In addition, the present invention includes JP-A-11-163378, JP-A-11-167937, JP-A-11-214731, JP-A-2000-106224, JP-A-2001-052766, JP-A-2004-235052, JP-A-2004-235052. JP 2004-234953, JP 2005-19252, JP 2005-129429, JP 2005-129430, JP 2005-209359, JP 2006-156212, JP 2006-156213, and these specifications A so-called organic dye synthesized by referring to a conventionally known method described in the literature cited in the book can be used. Specific examples of the organic dye in the present invention include, but are not limited to, the following compounds A, C, D, F, G, and H.

<Porous semiconductor>
As a material for the porous semiconductor in the present invention, a known semiconductor such as titanium oxide, zinc oxide, tungsten oxide, tin oxide, barium titanate, strontium titanate, cadmium sulfide, or the like may be used alone or in combination. it can.
As a method for forming the porous semiconductor on the support, various known methods can be used. Specifically, a method in which a paste containing semiconductor particles (hereinafter sometimes referred to as a suspension) is applied on a support by a screen printing method, an ink jet method, or the like, and baked can be preferably exemplified.
As the semiconductor particles in this case, single or compound semiconductor particles having an appropriate average particle diameter, for example, an average particle diameter of about 1 nm to 500 nm can be preferably used.

In addition, the porous semiconductor used in the present invention may be made of the same kind of semiconductor, or may be made of a different kind of semiconductor, but is preferably made of a different kind of semiconductor.
The term “heterogeneous semiconductor” as used herein includes a case where they are different compounds (for example, titanium oxide and tin oxide) and a case where the same compound has a different crystal system (for example, rutile type and anatase type in titanium oxide). . When at least one of the porous semiconductors has a core-shell structure (for example, a structure in which zinc oxide particles are coated with a thin film of titanium oxide), each surface (surface directly in contact with the dye) is different. If there is, the semiconductor constituting one core may be made of the same material as the other porous semiconductor.

As a preferred configuration in this embodiment, the LUMO-HOMO energy gap of the second dye is smaller than the LUMO-HOMO energy gap of the first dye, and the flat band level of the second porous semiconductor is the flat band level of the first porous semiconductor. It can be mentioned that it is lower than the position (in the positive direction).
Further, the flat band level of the porous semiconductor only needs to be more positive than the LUMO level of the adsorbed dye, and the value of the difference between the LUMO level of the dye and the flat band level of the porous semiconductor is 0.1 eV or more and 0.0. It is preferably 6 eV or less, more preferably 0.2 eV or more and 0.4 eV or less.
Moreover, as a preferable configuration in the present embodiment, it can be mentioned that the haze ratio of the second porous semiconductor and / or the second photoelectrode is larger than the haze ratio of the first porous semiconductor and / or the first photoelectrode. .

Here, a method for measuring the haze ratio of the porous semiconductor and / or the photoelectrode will be described.
In general, in order to obtain the haze ratio of a certain sample, the total light transmittance and diffuse transmittance when light is incident on the sample may be measured. If these devices have a light source and a light quantity measuring unit (for example, an integrating sphere closely attached to the measurement sample and a light trap (dark box) or standard plate on the opposite side of the integrating sphere from the measurement sample) It can be measured easily. That is, when the standard plate is set, the incident light amount T1 when there is no sample, and the total light transmitted light amount T2 when the sample is present are measured, and when the light trap is set and there is no sample. The amount of diffused light T3 from the apparatus and the amount of diffused transmitted light T4 when a sample is present are measured, and the total light transmittance Tt = T2 / T1, diffuse transmittance Td = [T4-T3 (T2 / T1)] / By calculating T1, the haze ratio H = Td / Tt is obtained.

<Photoelectrode>
Examples of the method for producing the photoelectrode 2, that is, a dye adsorption method on a porous semiconductor include a method in which a support on which a porous semiconductor is formed is immersed in a solution in which a dye is dissolved (dye adsorption solution).

  The solvent used in the dye adsorption solution is not particularly limited as long as it dissolves the dye. Specifically, alcohols such as ethanol, ketones such as acetone, ethers such as diethyl ether and tetrahydrofuran, nitrogen compounds such as acetonitrile, halogenated aliphatic hydrocarbons such as chloroform, and aliphatic hydrocarbons such as hexane , Aromatic hydrocarbons such as benzene, esters such as ethyl acetate, water, and the like. Two or more of these solvents can be used in combination.

The concentration of the dye in the dye adsorption solution can be adjusted as appropriate depending on the type of the dye and the solvent to be used, but it is preferably as high as possible in order to improve the adsorption function. For example, it is preferably 1 × 10 ⁻⁵ mol / liter or more, particularly preferably 5 × 10 ⁻⁵ mol / liter or more and 1 × 10 ⁻² mol / liter or less.

  In addition, the haze ratio of the photoelectrode in the present invention is a value obtained by measuring the haze ratio of the object to which the dye adsorbed on the photoelectrode is detached. Examples of the method for removing the dye include a method of immersing the photoelectrode in an alkaline aqueous solution, a method of dropping the aqueous solution onto a sample, and the like. As the alkaline aqueous solution, an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, or the like is preferably used, and an aqueous sodium hydroxide solution that is relatively easy to handle is more preferable. The concentration of the aqueous solution is not particularly limited as long as the pH (pH) is large, but pH 10 to 14 is preferable.

<Support>
The support (the first support 110, the second support 120, etc. according to the present invention increases as the number of stacked photoelectric conversion cells increases) with respect to the process temperature required for forming the porous semiconductor. A substrate or film made of a transparent material having heat resistance (for example, 120 ° C. or higher, generally 180 ° C. or higher).

  For example, a glass substrate such as soda glass or quartz glass, or a film made of an organic polymer such as polyester, polyacryl, polyimide, Teflon (registered trademark), polyethylene, polypropylene, polyethylene terephthalate, etc. Not limited).

Furthermore, since the support farthest from the incident light direction (the third support 130 in this embodiment) does not necessarily need to be transparent, in addition to the above materials, ceramics such as silica and alumina, carbon, metal, etc. You can use it. Since the third support 130 does not require the formation of a porous semiconductor, the heat resistance is lower than the organic polymer used for the first support 110 and the second support 120 (for example, about 90 ° C. or more and less than 120 ° C. () Organic polymers can also be used.
In addition, “transparent” described in the present specification means that the average of transmittance in at least a visible light region (light having a wavelength of 400 nm or more and 700 nm or less) is 10% or more, generally 50% or more, Preferably it means 70% or more.

<Transparent conductive layer>
The first transparent conductive layer 111 and the second transparent conductive layer 121 in this embodiment have a function of collecting electrons generated in the photoelectrode 2 and transporting them to an external circuit.
The transparent conductive layer is made of a conductive material. In addition, when the electrolyte 4 has a strong corrosive component such as iodine, it is preferable to use a material having strong corrosion resistance at least on the surface thereof. The term “corrosion resistance” as used herein means that the material has a property of resisting corrosion caused by electrolyte.

Therefore, transparent conductive metal such as ITO (indium-tin composite oxide), fluorine-doped tin oxide, boron or gallium or aluminum-doped zinc oxide, niobium-doped titanium oxide as the transparent conductive layer An oxide can be preferably used, and a thin film of a metal such as gold, silver, aluminum, titanium, or indium can also be used. Furthermore, these can also be used in combination.
As a method for forming the transparent conductive layer, any known method such as a vacuum deposition method, a plating method, a sputtering method, a PVD method, and a coating method can be used.

<Counter electrode>
The counter electrode 3 constitutes a pair of electrodes together with the photoelectrode 2. The counter electrode 3 functions to transport electrons taken from an external circuit and further promotes an oxidation-reduction reaction that transports the electrons to the electrolyte 4 (catalytic function). )have. Platinum or carbon (carbon black, graphite particles, etc.) is preferably used as the material having a catalytic function.
The counter electrode 3 is formed by a known method (vacuum deposition method, plating method, sputtering method, PVD method, coating method, etc.) similar to the method for forming the transparent conductive layer.

Moreover, in this invention, when installing a photoelectric conversion cell in the non-incident light side of the counter electrode 3, it is preferable that this counter electrode 3 permeate | transmits light. The transmittance at this time is preferably at least 10% or more, more preferably 65% or more. As a means for adjusting the transmittance, there are a method of forming the counter electrode 3 thin and a method of providing an opening in the counter electrode 3.
In order to form the counter electrode 3 thin, the conditions may be adjusted when the counter electrode 3 is formed (the above-mentioned known method).
As a method of providing an opening in the counter electrode 3, the counter electrode 3 may be formed in various shapes such as a stripe shape and a lattice shape. In this case, since the incident light can be taken into the cell from the opening, the counter electrode 3 itself may be opaque.

<Electrolyte>
The electrolyte 4 is disposed between the photoelectrode 2 (including the pores of the porous semiconductor constituting the electrode) and the counter electrode 3, and includes an oxidation-reduction pair and a medium capable of holding the redox pair. If a liquid (solvent) is used as a medium, an electrolytic solution is obtained, and if a polymer gel is used, a gel electrolyte is obtained.

  As the redox couple, generally, metals such as iron and cobalt, and halogen substances such as chlorine, bromine and iodine are used, and iodine is preferably used. Among these, a combination of metal iodides such as lithium iodide, sodium iodide, potassium iodide, calcium iodide and iodine is most preferable. Furthermore, an imidazole salt such as dimethylpropylimidazolium iodide may be mixed.

As the solvent, carbonate compounds such as propylene carbonate, nitrile compounds such as acetonitrile, alcohols such as ethanol, water, aprotic polar substances, and the like are used. Among them, carbonate compounds and nitrile compounds are preferably used. . Two or more of these solvents can be used in combination. On the other hand, when the volatilization of the solvent becomes a problem, a molten salt may be used instead of the solvent.
The concentration of the redox couple in the electrolyte 4 is appropriately selected according to the type of redox couple material and medium. When the medium is a liquid (solvent) or a molten salt, it is generally 0.01 mol / liter. A range of 1.5 mol / liter or less is preferable.

<Connection part>
The connection unit 150 externally connects the first counter electrode 3-1 formed in the incident light direction of the second support 120 and the second transparent conductive layer 121 formed in the non-incident light direction with a metal paste, a metal wire, or the like. A material having both conductivity and transparency is used as the second support 120 that is connected by a conductive layer formed on the side surface of the second support 120 (for example, a conductive polymer, etc. 2 transparent conductive layer 121 is not necessarily required).

<Sealing part>
The sealing portion 160 is generally formed at the peripheral portion of the photoelectric conversion element, and refers to a region and / or member that seals the inside of the element by joining a pair of supports.
As a material for the sealing portion 160, an organic polymer such as a silicone resin, an ionomer resin, an epoxy resin, or a polyisobutylene resin is generally used. These may be used alone or in combination of two or more materials.
Further, when a paste-like resin is used as the sealing portion 160, a pattern can be formed by a method such as a dispenser or screen printing. In addition, when a sheet-shaped resin is used, the sheet-shaped resin may be cut and patterned using a cutter, a laser, or the like.

<Current value adjusting means>
In the tandem photoelectric conversion element, the series connection method as shown in FIG. 1 is the most simple and preferable connection method.
However, if the output current value of each photoelectric conversion cell differs greatly, the lowest output current value among the output current values of each cell becomes the bottleneck. There was a problem of lowering.

Therefore, in order to avoid this, in the present invention, it is preferable to provide a current value adjusting means for reducing the difference between the output current values of the photoelectric conversion cells.
As specific current value adjusting means, a photoelectric conversion cell in which the optical thickness of the photoelectrode is changed is appropriately arranged, a photoelectric conversion cell in which the redox pair concentration in the electrolyte is changed is appropriately arranged, in the photoelectric conversion cell Although a method such as dividing the transparent conductive layer, the photoelectrode, and the counter electrode and changing the number of divisions between the photoelectric conversion cells can be mentioned, a preferable current value adjusting means includes photoelectrodes having different haze ratios. And a method of combining these, or a method of combining a plurality of photoelectric conversion cells having different transmittances (for example, by changing the transmittance of the counter electrode or the support) and combining them. .

  As a combination of photoelectric conversion cells including photoelectrodes having different haze ratios, an example in which a photoelectrode having a larger haze ratio than a photoelectrode constituting the top cell is used for a photoelectric conversion cell other than the top cell can be shown. . Here, the haze ratio of the photoelectrode constituting the top cell is preferably 30% or less, more preferably 10% or less, and further preferably 5% or less. When a photoelectrode with a high haze ratio is used for the top cell, light is scattered by the top cell, and the amount of light irradiated to the photoelectric conversion cell located on the non-incident light side decreases, so the photoelectric conversion efficiency in the tandem photoelectric conversion element This is because the improvement rate is not so large.

  On the other hand, the haze ratio of the photoelectrode constituting the photoelectric conversion cell located on the non-incident light side is not particularly limited, but is preferably larger than the haze ratio of the photoelectrode constituting the top cell, preferably haze. The rate is 60% or more, more preferably 80% to 95%.

An example of a photoelectrode having a haze ratio larger than that of the photoelectrode constituting the top cell is a photoelectrode having a multilayer structure composed of semiconductor fine particles having different particle diameters. An example of this is shown in FIG.
That is, the second photoelectrode 2-2 in FIG. 4 is a semiconductor (for example, rutile type titanium oxide) formed behind (on the non-incident light side) and having a larger average particle diameter than the second porous semiconductor 2-2. A multi-layer structure is formed together with a porous layer 170 formed of fine particles.
Further, as a combination of a plurality of photoelectric conversion cells having different transmittances, an example in which the transmittance of the counter electrode constituting the top cell is higher than the transmittance of the counter electrode constituting the photoelectric conversion cell on the non-incident light side is preferable. Can be mentioned. Here, the transmittance of the counter electrode constituting the top cell is more preferably 65% or more.

  Examples of a method for obtaining a counter electrode having a high transmittance include a method of reducing the thickness of the counter electrode, a method of using a counter electrode having a relatively high transmittance, and a method of providing an opening in the counter electrode. Moreover, you may use combining these methods. When platinum is used for the counter electrode of the top cell, the thickness of the platinum film is preferably 0.1 nm to 30 nm, more preferably 0.5 nm to 20 nm.

When an opening is formed in the counter electrode, incident light can be taken into the cell from the opening, so the counter electrode may be opaque. Therefore, since the counter electrode can be sufficiently thick, the electrical resistance is low, and the reduction of the form factor (FF) can be suppressed. In this case, the counter electrode preferably has an aperture ratio of 65% to 99%, preferably 75% to 97.5%.
When the aperture ratio of the counter electrode is less than 65%, it is not preferable because the transmitted light intensity per unit area cannot be significantly improved. In addition, when the aperture ratio of the counter electrode exceeds 99%, the function as an electrode is lowered, the catalytic ability of the counter electrode that can be used for the redox reaction is lowered, the redox reaction is not smoothly performed, and the high photoelectric conversion efficiency. Is not preferable because it cannot be expected.
Moreover, the output current of each photoelectric conversion cell can be adjusted by controlling the opening.

The shape of the counter electrode is not particularly limited as long as it is a shape having an opening, but is preferably a fine line shape, and particularly preferably a stripe shape and / or a lattice shape.
It is preferable that the counter electrode has a stripe shape because the moving distance of the oxidation-reduction pair with respect to the aperture ratio is shortened and the photoelectric conversion efficiency is improved.
Further, if the counter electrode has a lattice shape, a current can be taken out even if a disconnection failure occurs in part, that is, it is a preferable shape because the influence of the disconnection failure can be reduced.

The stripe shape is preferably composed of fine lines having a line width of 0.1 to 50 μm, preferably 1 to 30 μm and an interval of 1 to 200 μm, preferably 5 to 100 μm.
If the line width of the stripe is less than 0.1 μm, the resistance becomes high, which is not preferable. In addition, when the line width of the stripe exceeds 50 μm, the aperture ratio becomes too low, which is not preferable.
On the other hand, when the stripe interval is narrow, the aperture ratio decreases unless the line width is reduced, and the resistance increases when the line width is excessively reduced. Therefore, the interval is preferably 1 μm or more. Further, when the stripe interval is wide, the oxidation-reduction pair becomes difficult to move and the resistance increases. For example, from the viewpoint of the movement distance of iodine as the oxidation-reduction pair, the interval is preferably 200 μm or less.

The lattice shape is preferably composed of fine wires having an interval of 5 to 250 μm, preferably 20 to 150 μm, a line width of 0.1 to 50 μm, preferably 1 to 30 μm, and an intersection angle of 80 to 100 °, preferably 85 to 95 °.
The shape of the grid surrounded by the thin lines may be any shape such as a parallelogram, a rhombus, a rectangle, or a square.
The line width and interval of the lattice are preferably set for the same reason as the stripe.
Further, the crossing angle, that is, the angle between the two sides where the thin line contacts is preferably set in the above range in order to shorten the moving distance to the counter electrode of the redox pair and increase the aperture ratio.

  The material constituting the counter electrode may be any material that activates the redox reaction of the electrolyte described later, such as platinum, palladium, carbon (carbon black, graphite, glass carbon, amorphous carbon, hard carbon, soft carbon, Carbon whisker, carbon nanotube, fullerene) and the like. Among these, platinum is particularly preferable from the viewpoint of catalytic function and conductivity.

In addition, the method of obtaining a combination of photoelectric conversion cells having different transmittances is not limited to changing the transmittance of the counter electrode, but an intermediate layer (the counter electrode of the incident light side photoelectric conversion cell and the transparent conductive layer of the non-incident light side photoelectric conversion cell) Any one or more of the transmittances may be changed.
As a configuration example of the intermediate layer, a counter electrode (made of platinum or carbon) is formed on the incident light side of a single support, and a transparent conductive layer (fluorine-doped tin oxide or the like is formed on the non-incident light side of the same support. ) Can be given.

The transmittance of the support used for the intermediate layer is preferably higher than the transmittance of the support located on the incident light side of the top cell. For example, it is preferable that the support of the intermediate layer is thinner than the support used on the incident light side of the top cell. The preferable thickness of the support used for the intermediate layer is 0.1 μm to 5 mm, more preferably 0.2 μm to 1 mm.
When the thickness of the support used for the intermediate layer is 5 mm or more, the weight of the photoelectric conversion element increases and the portability is inferior, and the improvement rate of the photoelectric conversion efficiency may decrease due to light absorption of the support itself. This is because if the thickness of the support used for the layer is 0.1 μm or less, there is a risk of variations in photoelectric conversion efficiency due to insufficient strength or uneven support thickness.

  The transmittance of the transparent conductive layer formed on the non-incident light side of the intermediate layer support is higher than the transmittance of the transparent conductive layer formed on the support positioned on the incident light side of the top cell. Is more preferable. Specifically, the intermediate transparent layer is made of a material having a relatively high conductivity (high transmittance so that the film thickness required for obtaining the same conductivity is thin). Examples thereof include a method of relatively reducing the thickness of the conductive layer.

<Dye-sensitized photoelectric conversion element module>
In the present embodiment, an example of a tandem photoelectric conversion element composed of two photoelectric conversion cells has been shown. However, the dye-sensitized photoelectric conversion element of the present invention is a tandem photoelectric conversion element composed of three or more photoelectric conversion cells. It may be a conversion element.
As the three photoelectric conversion cells, for example, a first photoelectric conversion cell using zirconium oxide or tantalum oxide from the incident light side, a second photoelectric conversion cell using titanium oxide or the like, a first photoelectric conversion cell using tin oxide or tungsten oxide, or the like. An example of combining three photoelectric conversion cells can be given.
In addition, the dye-sensitized photoelectric conversion element of the present invention is a dye-sensitized type in which a plurality of tandem photoelectric conversion elements are connected (generally connected in series but may be connected in parallel). Includes a photoelectric conversion element module.
FIG. 5 shows a dye-sensitized photoelectric conversion element module 500 in which three tandem photoelectric conversion elements are connected in series. In FIG. 5, reference numeral 501 denotes an external circuit (load).

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

<Example 1>
1. Preparation of Support First, as shown in FIG. 6, a first support 110 and a third support 130 in which a transparent conductive layer made of tin oxide doped with fluorine is formed on one side of a transparent substrate made of glass, and The 2nd support body 120 which formed the transparent conductive layer on both surfaces was prepared.
Here, the transparent conductive layer on one side of the first support 110 is the first transparent conductive layer 111. In addition, one transparent conductive layer of the second support 120 is the second transparent conductive layer 121, and the other transparent conductive layer is the first counter electrode 3-1 together with a platinum thin film (described later). The transparent conductive layer on one side of the third support 130 becomes the second counter electrode 3-2 together with a platinum thin film to be described later.

2. Formation of Porous Semiconductor Next, the surface of the first support 110 on which the first transparent conductive layer 111 is formed and the surface of the second support 120 on which the second transparent conductive layer 121 is formed are porous. A quality semiconductor was formed by the following method.
By mixing 125 mL of titanium isopropoxide (manufactured by Kishida Chemical Co., Ltd.) and 750 mL of 0.1M nitric acid aqueous solution (manufactured by Kishida Chemical Co., Ltd.) which is a pH adjuster, and heating at 80 ° C. for 8 hours, titanium isopropoxide The hydrolysis reaction was advanced to prepare a sol solution. Next, particles were grown at 230 ° C. for 11 hours in a titanium autoclave.

Next, ultrasonic dispersion was performed for 30 minutes to prepare a solution (colloid solution I) containing titanium oxide particles having an average particle diameter of 15 nm, and titanium oxide particles were precipitated by centrifugation at 5000 rpm. . Next, this particle | grain and 1000 mL ethanol were mixed, and the operation which precipitates a titanium oxide particle by centrifugation was repeated 3 times, and the titanium oxide particle was produced. In addition, the average particle diameter of the titanium oxide particles contained in the colloidal solution was obtained by analyzing dynamic light scattering of laser light using a light scattering photometer (manufactured by Otsuka Electronics Co., Ltd.).
Next, titanium oxide particles having an average particle diameter of 400 nm (manufactured by Catalyst Kasei Co., Ltd., HPW-400C) were prepared. The colloidal solution containing the titanium oxide particles is referred to as colloidal solution II (adjusted below).

  After washing each of the above two types of titanium oxide particles, ethyl cellulose (manufactured by Kishida Chemical Co., Ltd.) and terpineol (manufactured by Kishida Chemical Co., Ltd.) dissolved in absolute ethanol are added, and the titanium oxide particles are dispersed by stirring. I let you. Thereafter, ethanol was evaporated at 50 ° C. under reduced pressure of 40 mbar, and titanium oxide pastes (suspensions I to II) were prepared from the colloidal solutions I to II. The final composition was adjusted so that the titanium oxide solid concentration was 20 wt%, ethyl cellulose 10 wt%, and terpineol 64 wt%.

  First, the suspension I is applied on the first support 110 and the second support 120 in an area of 10 mm × 10 mm by screen printing, preliminarily dried at 80 ° C. for 30 minutes, and then at 500 ° C. for 30 minutes. Baked in air. By repeating this step, a 10 μm thick porous semiconductor was formed on the first support 110 and the second support 120. A porous semiconductor α on the first support 110 is indicated by a first porous semiconductor 1-1 in FIG. Further, a porous semiconductor was formed on the porous semiconductor formed on the second support 120 by the same method using the suspension II. The obtained porous semiconductor β on the second support 120 is shown as a second porous semiconductor 1-2 in FIG. The film thickness of the porous semiconductor β was 15 μm.

Next, platinum is sputtered onto the transparent conductive layer on the surface of the second support 120 where the porous semiconductor is not formed and the transparent conductive layer of the third support 130 by 20 nm and 100 nm, respectively. -1 and a second counter electrode 3-2 were formed. Here, the transmittance of the first counter electrode 3-1 was 65%, and the transmittance of the second counter electrode 3-2 was 5%.
In addition, the porous semiconductor α and the porous semiconductor β are separately formed on a glass substrate with fluorine-doped tin oxide, and the haze ratio thereof is measured using an ultraviolet-visible spectrophotometer (manufactured by Shimadzu Corporation, UV-3150). As a result, 3.1% and 78.2% (measurement wavelength was 700 nm) were obtained, respectively.

3. Adsorption of dye Compound A and compound B were each dissolved in absolute ethanol at a concentration of 4 × 10 ⁻⁴ mol / liter to prepare dye adsorption solution A and dye adsorption solution B, respectively. The porous semiconductor α is immersed in the dye adsorbing solution A, and the porous semiconductor β is immersed in the dye adsorbing solution B, left at room temperature for 20 hours, then lifted, washed with ethanol, dried, and dried. A photoelectrode 2-1 and a second photoelectrode 2-2 were produced.

4. Injection of Electrolyte Next, as shown in FIG. 7, the first support 110 and the third support 130 are bonded to the epoxy resin (which becomes the sealing portion 160) via the second support 120. And bonded together. The first support body 110 and the third support body 130 are previously formed with injection holes for electrolyte injection (not shown).

  Next, acetonitrile (manufactured by Kishida Chemical Co., Ltd.) was mixed with 0.1 mol / liter of lithium iodide, 0.05 mol / liter of iodine, and 0.6 mol / liter of 1,2-dimethyl-3-liter. Electrolyte X in which propylimidazolium iodide and 0.5 mol / liter of 4-tert-butylpyridine are dissolved, lithium iodide at a concentration of 0.1 mol / liter and a concentration of 0 in acetonitrile (manufactured by Kishida Chemical Co., Ltd.) Electrolyte Y in which 0.03 mol / liter iodine, 0.6 mol / liter 1,2-dimethyl-3-propylimidazolium iodide and 0.5 mol / liter 4-tert-butylpyridine were dissolved Each was prepared.

Next, the electrolytic solution Y is injected into the photoelectric conversion cell composed of the first photoelectrode 2-1, and the electrolytic solution X is injected into the photoelectric conversion cell composed of the second photoelectrode 2-2. After forming the second electrolyte 4-2, the injection hole was sealed with an epoxy resin.
Both surfaces of the second support 120 were electrically connected by applying a silver paste (trade name Dotite, manufactured by Fujikura Kasei Co., Ltd.), and a dye-sensitized photoelectric conversion element 400 was produced.
The produced dye-sensitized photoelectric conversion element was irradiated with light having an intensity of 1 kW / m ² (AM1.5 solar simulator), and the photoelectric conversion efficiency was measured. This dye-sensitized photoelectric conversion element has a short-circuit current density (hereinafter referred to as Jsc) of 8.1 mA / cm ² , an open-circuit voltage (hereinafter referred to as Voc) of 1.32 V, and a form factor (hereinafter referred to as FF) of 0.75. The conversion efficiency was 8.0%.

<Example 2>
A dye-sensitized photoelectric conversion element was produced according to Example 1 except that Compound C was used instead of Compound A used in Example 1. The produced dye-sensitized photoelectric conversion element was irradiated with light having an intensity of 1 kW / m ² (AM1.5 solar simulator), and the photoelectric conversion efficiency was measured. This dye-sensitized photoelectric conversion element exhibited Jsc = 8.0 mA / cm ² , Voc = 1.31 V, FF = 0.74, and the photoelectric conversion efficiency was 7.8%.

<Example 3>
Tin oxide paste III (suspension III) was prepared according to Example 1 using tin oxide (Aldrich, particle size 18.3 nm).
A porous semiconductor γ was formed in the same manner as the porous semiconductor β except that the suspension III was used instead of the suspension I used when forming the porous semiconductor β in Example 1. As a result of measuring the haze ratio of the porous semiconductor γ in the same manner as described above, it was 75.4%.
A dye-sensitized photoelectric conversion element was produced according to Example 1 except that the porous semiconductor γ was used instead of the porous semiconductor β and the compound D was used instead of the compound B. The produced dye-sensitized photoelectric conversion element was irradiated with light having an intensity of 1 kW / m ² (AM1.5 solar simulator), and the photoelectric conversion efficiency was measured. This dye-sensitized photoelectric conversion element exhibited Jsc = 8.7 mA / cm ² , Voc = 1.20 V, FF = 0.74, and the photoelectric conversion efficiency was 7.7%.

<Example 4>
Dye-sensitized photoelectric conversion according to Example 3, except that the thickness of the porous semiconductor α in Example 3 was 7 μm, Compound E was used in place of Compound A, and the electrolyte was formed of electrolyte X. An element was produced. The produced dye-sensitized photoelectric conversion element was irradiated with light having an intensity of 1 kW / m ² (AM1.5 solar simulator), and the photoelectric conversion efficiency was measured. This dye-sensitized photoelectric conversion element exhibited Jsc = 6.8 mA / cm ² , Voc = 1.35 V, FF = 0.75, and the photoelectric conversion efficiency was 6.9%.

<Example 5>
Dye-sensitized photoelectric conversion according to Example 1 except that the thickness of the porous semiconductor α in Example 1 was 7 μm, Compound F was used instead of Compound A, and the electrolyte was formed of electrolyte X. An element was produced. The produced dye-sensitized photoelectric conversion element was irradiated with light having an intensity of 1 kW / m ² (AM1.5 solar simulator), and the photoelectric conversion efficiency was measured. This dye-sensitized photoelectric conversion element exhibited Jsc = 6.5 mA / cm ² , Voc = 1.25 V, FF = 0.74, and the photoelectric conversion efficiency was 6.0%.

<Example 6>
A dye-sensitized photoelectric conversion element was produced according to Example 3 except that Compound G was used instead of Compound D in Example 3. The produced dye-sensitized photoelectric conversion element was irradiated with light having an intensity of 1 kW / m ² (AM1.5 solar simulator), and the photoelectric conversion efficiency was measured. This dye-sensitized photoelectric conversion element exhibited Jsc = 8.1 mA / cm ² , Voc = 1.18 V, FF = 0.75, and the photoelectric conversion efficiency was 7.2%.

<Example 7>
A dye-sensitized photoelectric conversion element was produced in the same manner as in Example 1 except that the porous semiconductor β in Example 1 was changed to a porous semiconductor having the same configuration as that of the porous semiconductor α. The produced dye-sensitized photoelectric conversion element was irradiated with light having an intensity of 1 kW / m ² (AM1.5 solar simulator), and the photoelectric conversion efficiency was measured. This dye-sensitized photoelectric conversion element exhibited Jsc = 6.2 mA / cm ² , Voc = 1.34 V, FF = 0.76, and the photoelectric conversion efficiency was 6.3%.

<Example 8>
A dye-sensitized photoelectric conversion element was produced according to Example 3 except that tungsten oxide (manufactured by Aldrich, 30 to 50 nm) was used instead of tin oxide in Example 3. The produced dye-sensitized photoelectric conversion element was irradiated with light having an intensity of 1 kW / m ² (AM1.5 solar simulator), and the photoelectric conversion efficiency was measured. This dye-sensitized photoelectric conversion element exhibited Jsc = 7.2 mA / cm ² , Voc = 1.28 V, FF = 0.73, and the photoelectric conversion efficiency was 6.7%.

<Example 9>
A dye-sensitized photoelectric conversion element was produced in the same manner as in Example 1 except that Compound F was used instead of Compound B in Example 1. The prepared dye-sensitized photoelectric conversion element was irradiated with light having an intensity of 1 kW / m ² (AM1.5 solar simulator) to measure the conversion efficiency. The dye-sensitized photoelectric conversion element exhibited Jsc = 8.5 mA / cm ² , Voc = 1.08 V, FF = 0.75, and the photoelectric conversion efficiency was 6.9%.

<Example 10>
A dye-sensitized photoelectric conversion element was produced according to Example 4 except that Compound I was used instead of Compound D in Example 4. The produced dye-sensitized photoelectric conversion element was irradiated with light having an intensity of 1 kW / m ² (AM1.5 solar simulator), and the photoelectric conversion efficiency was measured. This dye-sensitized photoelectric conversion element exhibited Jsc = 8.2 mA / cm ² , Voc = 1.31 V, FF = 0.74, and the photoelectric conversion efficiency was 7.9%.

<Example 11>
To tin oxide paste III (suspension III) containing tin oxide prepared in Example 3 (manufactured by Aldrich, particle size: 18.3 nm), magnesium oxide powder (manufactured by Kishida Chemical Co., Ltd.) was added at 10 wt. %, The pH was adjusted to about 1 with hydrochloric acid, stirred for 10 minutes, and then subjected to ultrasonic dispersion for 10 minutes to obtain a suspension IV in which magnesium oxide was dispersed in a tin oxide paste. A porous semiconductor δ was formed in the same manner as the porous semiconductor β, except that the suspension IV was used instead of the suspension I used when forming the porous semiconductor β. As a result of measuring the haze ratio of the porous semiconductor δ in the same manner as described above, it was 78.1%.
A dye-sensitized photoelectric conversion element was produced according to Example 10 except that the formed porous semiconductor δ was used instead of the porous semiconductor γ. The produced dye-sensitized photoelectric conversion element was irradiated with light having an intensity of 1 kW / m ² (AM1.5 solar simulator), and the photoelectric conversion efficiency was measured. This dye-sensitized photoelectric conversion element exhibited Jsc = 7.8 mA / cm ² , Voc = 1.37 V, FF = 0.75, and the photoelectric conversion efficiency was 8.0%.

<Example 12>
A dye-sensitized photoelectric conversion element was produced in the same manner as in Example 1 except that the porous semiconductor α in Example 1 was a porous semiconductor having the same configuration as that of the porous semiconductor β. The produced dye-sensitized photoelectric conversion element was irradiated with light having an intensity of 1 kW / m ² (AM1.5 solar simulator), and the photoelectric conversion efficiency was measured. This dye-sensitized photoelectric conversion element exhibited Jsc = 5.1 mA / cm ² , Voc = 1.30 V, FF = 0.75, and the photoelectric conversion efficiency was 5.0%.

<Example 13>
A dye-sensitized photoelectric conversion element was produced according to Example 1 except that the platinum film thickness on the first counter electrode 3-1 in Example 1 was changed and the transmittance of the first counter electrode was set to 50%. The produced dye-sensitized photoelectric conversion element was irradiated with light having an intensity of 1 kW / m ² (AM1.5 solar simulator), and the photoelectric conversion efficiency was measured. This dye-sensitized photoelectric conversion element exhibited Jsc = 5.9 mA / cm ² , Voc = 1.31 V, FF = 0.75, and the photoelectric conversion efficiency was 5.8%.

<Example 14>
Dye sensitization according to Example 1 except that platinum was formed in a stripe shape in the first counter electrode 3-1 of Example 1 (the counter electrode shape had a line spacing of 76 μm and an aperture ratio of 75%). Type photoelectric conversion element was produced. The produced dye-sensitized photoelectric conversion element was irradiated with light having an intensity of 1 kW / m ² (AM1.5 solar simulator), and the photoelectric conversion efficiency was measured. This dye-sensitized photoelectric conversion element exhibited Jsc = 7.9 mA / cm ² , Voc = 1.32 V, FF = 0.76, and the photoelectric conversion efficiency was 7.9%.

<Example 15>
The first support 110 in which the photoelectrode in which the compound A and the compound B are simultaneously adsorbed on the porous semiconductor α in Example 1 and the third support 130 in which the second counter electrode 3-2 is formed are made of epoxy resin. Sealed and injected with the electrolyte solution X used in Example 1 to produce a photoelectric conversion element.
Specifically, first, Compound A and Compound B were dissolved in absolute ethanol so as to have a concentration of 4 × 10 ⁻⁴ mol / liter, respectively, to prepare a dye adsorption solution A & B. The porous semiconductor α was immersed in the dye adsorbing solution A & B and allowed to stand at room temperature for 20 hours, then pulled up, washed with ethanol, and dried to prepare a photoelectrode. Other methods are the same as those described in Example 1.
The produced photoelectric conversion element was irradiated with light having an intensity of 1 kW / m ² (AM1.5 solar simulator), and the photoelectric conversion efficiency was measured. This photoelectric conversion element showed Jsc = 12.1 mA / cm ² , Voc = 0.62 V, FF = 0.72, and the photoelectric conversion efficiency was 5.4%.

<Comparative Example 1>
The first support 110 in Example 1 (compound A was adsorbed on the porous semiconductor α) and the third support 130 (formed with the second counter electrode 3-2) were sealed with an epoxy resin, and the electrolyte solution X was injected to prepare a dye-sensitized photoelectric conversion element. The produced dye-sensitized photoelectric conversion element was irradiated with light having an intensity of 1 kW / m ² (AM1.5 solar simulator), and the photoelectric conversion efficiency was measured. This dye-sensitized photoelectric conversion element exhibited Jsc = 8.1 mA / cm ² , Voc = 0.54 V, FF = 0.72, and the photoelectric conversion efficiency was 3.2%.

<Comparative example 2>
A dye-sensitized photoelectric conversion element was produced in the same manner as in Example 1 except that Compound E was used instead of Compound A and Compound B used in Example 1. The produced dye-sensitized photoelectric conversion element was irradiated with light having an intensity of 1 kW / m ² (AM1.5 solar simulator), and the photoelectric conversion efficiency was measured. This dye-sensitized photoelectric conversion element exhibited Jsc = 3.4 mA / cm ² , Voc = 1.42 V, FF = 0.75, and the photoelectric conversion efficiency was 3.6%.

<Comparative Example 3>
A dye-sensitized photoelectric conversion element was produced in the same manner as in Example 1 except that Compound E and Compound H were used instead of Compound A and Compound B used in Example 1, respectively. The produced dye-sensitized photoelectric conversion element was irradiated with light having an intensity of 1 kW / m ² (AM1.5 solar simulator), and the photoelectric conversion efficiency was measured. This dye-sensitized photoelectric conversion element exhibited Jsc = 3.8 mA / cm ² , Voc = 1.32 V, FF = 0.74, and the photoelectric conversion efficiency was 3.7%.
The results of the above examples and comparative examples are listed in Table 1 below.

From these results, the following results became clear.
1. When a single photoelectric conversion cell is used (comparison between Example 14 and Comparative Example 1), a dye having a different absorption wavelength peak (compound) than using the dye (compound A, compound B) alone Higher photoelectric conversion efficiency can be obtained when A and compound B) are mixed (or used as a multilayer).
2. When a plurality of photoelectric conversion cells are used, it is necessary to use dyes having different absorption peak wavelengths (comparison between Examples 1 to 13 and Comparative Examples 2 and 3). Among them, the difference in absorption peak wavelength is preferably 90 nm or more (comparison between Examples 1 and 5 and Example 9). In addition, although the data of the absorption peak wavelength in a present Example and a comparative example are the absorption peak wavelengths in the longest wavelength side in each absorption spectrum, it is not restricted to this.

3. When using a plurality of photoelectric conversion cells, it is understood that it is preferable to use photoelectrodes having different haze ratios from the viewpoint of light utilization efficiency. It turns out that it is especially preferable that the haze rate of the photoelectrode which comprises a top cell is lower than the haze rate of the photoelectrode which comprises another photoelectric conversion cell (Example 1, 7, 12 comparison).
4). When a plurality of photoelectric conversion cells are used, it is understood that the transmittance of the counter electrode constituting the top cell is preferably higher than the transmittance of the counter electrode constituting the other photoelectric conversion cell from the viewpoint of light utilization efficiency ( Comparison of Examples 1 and 13).

It is a section schematic diagram of a tandem type photoelectric conversion element which is an example of a dye sensitizing type photoelectric conversion element of the present invention. It is a cross-sectional schematic diagram which shows the example which mixed and adsorb | sucked the several pigment | dye which has a different absorption peak wavelength in the single layer porous semiconductor which is an example of the dye-sensitized photoelectric conversion element of this invention. 1 is a schematic cross-sectional view showing an example in which a porous semiconductor adsorbing dyes having different absorption peak wavelengths, which is an example of the dye-sensitized photoelectric conversion element of the present invention, has a multilayer structure. It is a cross-sectional schematic diagram which shows an example of the dye-sensitized photoelectric conversion element of this invention. It is a cross-sectional schematic diagram which shows an example of the dye-sensitized photoelectric conversion element module of this invention. It is a block diagram which shows an example of the dye-sensitized photoelectric conversion element of this invention. It is a cross-sectional schematic diagram which shows an example of the dye-sensitized photoelectric conversion element of this invention. It is an energy diagram which shows the operating principle of the conventional dye-sensitized photoelectric conversion element. It is a spectrum which shows an example of the combination of the pigment | dye which has a different absorption peak used for the dye-sensitized photoelectric conversion element of this invention. It is a spectrum which shows an example of the combination of the pigment | dye which has a different absorption wavelength edge used for the conventional dye-sensitized photoelectric conversion element.

Explanation of symbols

1 Porous semiconductor (shown as 1-1, 1-2)
2 Photoelectrode 3 Counter electrode 4 Electrolyte

Claims (31)

A dye-sensitized photoelectric conversion element comprising a photoelectrode on which a plurality of dyes having different absorption peak wavelengths, which generate excited electrons by incident light, are adsorbed. The dye-sensitized photoelectric conversion element according to claim 1, comprising a combination of dyes having a difference in absorption peak wavelength of 90 nm or more. The dye-sensitized photoelectric conversion element according to claim 1 or 2, wherein, in the plurality of dyes having different absorption peak wavelengths, absorption peak wavelengths on the longest wavelength side are different from each other. The dye-sensitized photoelectric conversion device according to claim 3, comprising a combination of dyes having a difference between absorption peak wavelengths on the longest wavelength side of 90 nm or more. The dye-sensitized photoelectric conversion element according to any one of claims 1 to 4, wherein the plurality of dyes having different absorption peak wavelengths have different LUMO-HOMO energy gaps. The dye-sensitized photoelectric conversion element according to claim 5, comprising a combination of dyes having a difference between the different LUMO-HOMO energy gaps of 0.3 eV or more. The dye-sensitized photoelectric conversion element according to any one of claims 1 to 6, wherein at least one of the dyes has a long wavelength side absorption wavelength end in a near infrared region. The photoelectrode is made of a semiconductor on which a plurality of dyes having different absorption peak wavelengths are adsorbed, and the flat band level of the semiconductor is more positive than the LUMO level of the dye. The dye-sensitized photoelectric conversion element as described in any one of the above. The dye-sensitized photoelectric conversion element according to claim 8, wherein the flat band level of the semiconductor is 0.1 eV or more positive than the LUMO level of the dye. The plurality of photoelectric conversion cells each having a combination of photoelectrodes on which the plurality of dyes having different absorption peak wavelengths are adsorbed are stacked in a direction intersecting the incident light. The dye-sensitized photoelectric conversion element as described in one. In a dye-sensitized photoelectric conversion element comprising a plurality of photoelectric conversion cells having a combination of photoelectrodes on which a plurality of dyes having different absorption peak wavelengths are adsorbed,
LUMO-HOMO energy gap EgT of the dye constituting the photoelectric conversion cell on the most incident light side;
LUMO-HOMO energy gap EgB of the dye constituting the photoelectric conversion cell farthest from the incident light direction,
EgT> EgB
The dye-sensitized photoelectric conversion element according to claim 10 that satisfies the following relationship. The LUMO-HOMO energy gap EgT of the dye constituting the photoelectric conversion cell on the most incident light side, and the LUMO-HOMO energy gap EgB of the dye constituting the photoelectric conversion cell farthest from the incident light direction,
EgT-EgB> 0.3 eV
The dye-sensitized photoelectric conversion element according to claim 11, wherein the following relationship is satisfied. The dye-sensitized photoelectric conversion according to any one of claims 10 to 12, wherein a LUMO-HOMO energy gap of the dye constituting the plurality of photoelectric conversion cells is sequentially reduced from the incident light side. element. The dye-sensitized photoelectric conversion element according to any one of claims 10 to 13, wherein the LUMO level of the dye constituting the plurality of photoelectric conversion cells is sequentially in the positive direction from the incident light side. The dye-sensitized photoelectric conversion element according to any one of claims 10 to 14, wherein a flat band level of the semiconductor is sequentially in a positive direction from the incident light side. The dye-sensitized photoelectric conversion element according to any one of claims 10 to 15, wherein the semiconductor constituting at least one of the plurality of photoelectric conversion cells is tin oxide or tungsten oxide. . The dye-sensitized photoelectric conversion element according to claim 16, wherein the dye adsorbed on the photoelectric conversion cell in which the semiconductor is tin oxide or tungsten oxide is a dye having a long wavelength side absorption wavelength end in the near infrared region. The dye-sensitized photoelectric conversion element which made the photoelectric conversion cell of Claim 17 the furthest photoelectric conversion cell from the said incident light direction. The dye sensitizing method according to any one of claims 10 to 18, wherein at least one of the plurality of photoelectric conversion cells is provided with a current value adjusting means for reducing a difference in output current between the photoelectric conversion cells. Sensitive photoelectric conversion element. The dye-sensitized photoelectric conversion element according to claim 19, wherein the current value adjusting means includes a plurality of photoelectric conversion cells including photoelectrodes having different haze ratios. 21. The photoelectric conversion cell according to claim 20, wherein the current value adjusting means includes a photoelectrode having a haze ratio larger than a haze ratio of a photoelectrode constituting the photoelectric conversion cell on the most incident light side. Dye-sensitized photoelectric conversion element. The dye according to claim 21, wherein the photoelectrode having a haze ratio larger than that of the photoelectrode constituting the photoelectric conversion cell located closest to the incident light side has a multilayer structure composed of semiconductor fine particles having different particle diameters. Sensitization type photoelectric conversion element. The dye-sensitized photoelectric conversion element according to any one of claims 20 to 22, wherein a haze ratio of a photoelectrode constituting the photoelectric conversion cell closest to the incident light side is 10% or less. The photoelectric conversion cell includes an incident light side support on which a transparent conductive layer is formed and a non-incident light side support on which a counter electrode is formed, and the current value adjusting unit includes a counter electrode having different transmittance. The dye-sensitized photoelectric conversion element according to claim 19, which is provided with a plurality of photoelectric conversion cells. The transmittance of the counter electrode constituting the photoelectric conversion cell on the most incident light side is higher than the transmittance of the counter electrode constituting the photoelectric conversion cell on the non-incident light side in the current value adjusting means. 24. The dye-sensitized photoelectric conversion element according to 24. The dye-sensitized photoelectric conversion element according to claim 25, wherein a transmittance of a counter electrode constituting the photoelectric conversion cell closest to the incident light side is 65% or more. An intermediate layer serving as the counter electrode constituting the photoelectric conversion cell on the most incident light side and the transparent conductive layer of the photoelectric conversion cell located on the non-incident light side of the photoelectric conversion cell on the most incident light side is provided. The dye-sensitized photoelectric conversion element according to any one of claims 24 to 26. The intermediate layer is a support having a counter electrode formed on the incident light side and a transparent conductive layer formed on the non-incident light side, and the transmittance of the support constituting the intermediate layer is the most incident light side. 28. The dye-sensitized photoelectric conversion element according to claim 27, wherein the dye-sensitized photoelectric conversion element is higher in transmittance than a support located on the incident light side of the photoelectric conversion cell. 29. The dye-sensitized photoelectric conversion element according to claim 28, wherein a thickness of the support constituting the intermediate layer is thinner than a thickness of the support positioned on the incident light side of the photoelectric conversion cell located closest to the incident light. . The transmittance of the transparent conductive layer on the support constituting the intermediate layer is higher than the transmittance of the transparent conductive layer formed on the support located on the incident light side of the photoelectric conversion cell on the most incident light side. 30. A dye-sensitized photoelectric conversion device according to claim 28 or 29, which is high. A dye-sensitized photoelectric conversion element module in which the dye-sensitized photoelectric conversion elements according to any one of claims 1 to 30 are connected in series.

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