JP2011150881A - Photoelectric transfer element, optical sensor, and solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric transfer element of high transfer efficiency. <P>SOLUTION: The photoelectric transfer element includes a semiconductor electrode 9 having a semiconductor layer 6 having a pigment adsorbed, a counter electrode 3 provided opposedly to the semiconductor electrode 9, and an electrolyte layer 4 containing an ionic solution, nitroxyl radical and an oxoammonium salt, and provided to contact respectively with the semiconductor layer 6 of the semiconductor electrode 9 and the counter electrode 3, in a position sandwiched by the semiconductor electrode 9 and the counter electrode 3. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a photoelectric conversion element, an optical sensor, and a solar cell.

  Conventionally, various structures have been proposed as photoelectric conversion elements that convert light energy into electrical energy. Among them, the dye-sensitized solar cell (Gretzel type) proposed by Gretzer et al. Of Lausanne Institute of Technology in Switzerland in 1991 can achieve conversion efficiency equivalent to amorphous silicon by a relatively inexpensive material and a simple manufacturing process. It was. For this reason, the Gretzel type dye-sensitized solar cell is expected to be put to practical use as a next-generation solar cell.

  The Gretzel type dye-sensitized solar cell includes a semiconductor electrode in which a semiconductor layer adsorbing an absorbing dye is formed on a conductive substrate, a counter electrode made of a conductive substrate opposite to the electrode, and both electrodes And an electrolyte layer (charge transporter) held therebetween. In this battery, the dye adsorbed on the semiconductor layer absorbs light and enters an excited state, and electrons are injected from the excited dye into the semiconductor layer. The dye that is in an oxidized state due to the emission of electrons returns to the original state when electrons move to the dye due to the oxidation reaction of the redox agent in the electrolyte layer. Then, the redox agent that has donated electrons to the dye is reduced again on the counter electrode side. This series of reactions functions as a battery.

  Photochemical reaction cells with such a dye sensitizing action have been known for a long time, but Gretzel type dye-sensitized solar cells are effective by using porous titania in which fine particles are sintered in a semiconductor layer. The reaction surface area has increased by a factor of 1000, and it is a great feature that a larger photocurrent can be obtained than before.

  As an example of the dye used in the Gretzel type dye-sensitized solar cell, there is a spectral sensitizing dye composed of a transition metal complex described in Patent Document 1. More specifically, as a spectral sensitizing dye, cis-bis (isothiocyanato) -bis- (2,2′-bipyridyl-4,4′-dicarboxylic acid) ruthenium (II) ditetra, which is a kind of bipyridine complex. There is a butylammonium complex (commonly known as N719), which is excellent in performance as a sensitizing dye and is generally used. In addition, cis-bis (isothiocyanato) -bis- (2,2′-bipyridyl-4,4′-dicarboxylic acid) ruthenium (II) (common name: N3), which is a kind of bipyridine complex, and a kind of terpyridine complex Tris (isothiocyanato) (2,2 ′: 6 ′, 2 ″ -terpyridyl-4,4 ′, 4 ″ -tricarboxylic acid) ruthenium (II) tritetrabutylammonium complex (commonly known as black dye) is common. Used for. In recent years, organic materials containing no metal complex such as derivatives of coumarin-based materials have been reported.

  Here, as a method of forming an electrolyte layer used in a Gretzel type dye-sensitized solar cell, an electrolytic solution in which a redox agent composed of iodine / iodide ions is dissolved in a nitrile organic solvent or an ionic liquid having low volatility Is generally injected between the semiconductor electrode and the counter electrode. In this method, since highly corrosive iodine is used, Patent Document 2 describes that the solidification is performed by gelation in order to prevent leakage of liquid to the outside. Patent Document 3 reports an example using a nitroxyl radical as a redox material that does not use iodine. Patent Document 4 proposes that in a photoelectric conversion element using a nitroxyl radical as a redox material, an electron-transmitting insulator layer is used at the interface between the semiconductor electrode and the electrolyte layer containing the nitroxyl radical. .

JP-A-11-345991 JP 2002-289271 A JP 2003-100360 A JP 2009-021212 A

  However, all of the photoelectric conversion elements of Patent Documents 1 to 4 have a problem of low conversion efficiency.

  In addition, although the above demonstrated the Gretzel type | mold dye-sensitized solar cell as an example, when using in another use, sufficient change efficiency is not obtained similarly.

  Then, the objective of this invention is providing the photoelectric conversion element excellent in practicality which is the subject mentioned above.

  According to the present invention, the semiconductor electrode includes a semiconductor electrode having a semiconductor layer on which a dye is adsorbed, a counter electrode provided opposite to the semiconductor electrode, an ionic liquid, a nitroxyl radical, and an oxoammonium salt. There is also provided a photoelectric conversion element having an electrolyte layer provided in contact with each of the semiconductor layer and the counter electrode of the semiconductor electrode at a position sandwiched between the counter electrodes.

  Moreover, according to this invention, the optical sensor characterized by including the said photoelectric conversion element is provided.

  Moreover, according to this invention, the solar cell characterized by including the said photoelectric conversion element is provided.

  According to the present invention, a photoelectric conversion element having a sufficiently high conversion efficiency can be realized.

It is the structure figure which showed typically an example of the photoelectric conversion element of this embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

<< Embodiment >>
FIG. 1 is a cross-sectional view showing an example of the configuration of the photoelectric conversion element in the present embodiment. The photoelectric conversion element shown in FIG. 1 includes a semiconductor electrode 9, a counter electrode 3, and an electrolyte layer 4 held between both electrodes facing each other with a spacer 5 interposed therebetween. The photoelectric conversion element of the present embodiment is an element that receives light energy with a dye adsorbed on the semiconductor layer 6 and extracts the energy via the transparent conductive film 7. Hereinafter, each component will be described in detail by taking the photoelectric conversion element shown in FIG. 1 as an example.

(I) Semiconductor electrode The semiconductor electrode 9 has a semiconductor layer 6 and a dye (not shown) adsorbed on the semiconductor layer 6. In FIG. 1, the semiconductor electrode 9 has a configuration in which a conductive substrate (transparent substrate 8, transparent conductive film 7) and a semiconductor layer 6 are laminated in this order from the outside to the inside of the element.

(I-1) Conductive Substrate The conductive substrate may be one that has conductivity, or a substrate that is made conductive by forming a conductive layer on the substrate. It may be. For example, as shown in FIG. 1, a transparent conductive film 7 may be formed on a transparent substrate 8. The substrate and the conductive layer are preferably transparent as described above, but are not necessarily limited thereto.

Here, as a board | substrate, a glass substrate, a plastic substrate, a metal plate etc. are mentioned, for example, A board | substrate with high transparency is especially preferable especially. The type of the conductive layer formed on the substrate is not particularly limited. For example, indium tin oxide (ITO), fluorine doped tin oxide (FTO), A conductive layer made of a transparent material such as indium zinc oxide (IZO) or tin oxide (SnO ₂ ) is preferable. The conductive layer may be formed in a film shape on the entire surface or a part of the surface of the substrate. A method for manufacturing the conductive layer, a film thickness, and the like can be selected as appropriate. For example, a conductive layer having a thickness of about 0.1 μm to 5 μm can be used.

(I-2) Semiconductor layer (i-2-1) Material and structure of semiconductor layer As materials constituting the semiconductor layer 6, titanium oxide, zinc oxide, tungsten oxide, barium titanate, strontium titanate, cadmium sulfide, etc. And known semiconductor materials. These semiconductor materials can be used alone or in combination of two or more. Among these, it is preferable that the semiconductor layer 6 is comprised with the semiconductor material containing a titanium oxide from a viewpoint of conversion efficiency, stability, and safety. More specifically, examples of titanium oxide include anatase-type titanium oxide, rutile-type titanium oxide, amorphous titanium oxide, various titanium oxides such as metatitanic acid and orthotitanic acid, and titanium oxide-containing composites. Among these, anatase type titanium oxide is preferable from the viewpoint of further improving the stability of photoelectric conversion.

  Examples of the shape of the semiconductor layer 6 include a porous semiconductor layer obtained by sintering semiconductor fine particles, a thin film semiconductor layer obtained by a sol-gel method, a sputtering method, a spray pyrolysis method, and the like. In addition, it is good also as the semiconductor layer 6 which consists of a fibrous semiconductor layer and an acicular crystal | crystallization. The shape of the semiconductor layer 6 can be appropriately selected according to the purpose of use of the photoelectric conversion element.

  Among these, a semiconductor layer having a large specific surface area such as a porous semiconductor layer and a semiconductor layer made of needle crystals is preferable from the viewpoint of the amount of dye adsorbed. Furthermore, it is preferable to use a porous semiconductor layer formed of semiconductor fine particles as the semiconductor layer 6 from the viewpoint of adjusting the utilization rate of incident light and the like by the particle size of the semiconductor fine particles.

  The semiconductor layer 6 may be a single layer or a multilayer. By forming a multilayer, the semiconductor layer 6 having a sufficient thickness can be formed more easily. The porous multilayer semiconductor layer formed from semiconductor fine particles may be composed of a plurality of semiconductor layers having different average particle diameters of the semiconductor fine particles. For example, the average particle diameter of the semiconductor fine particles of the semiconductor layer closer to the light incident side (first semiconductor layer) may be smaller than that of the semiconductor layer farther from the light incident side (second semiconductor layer). With this configuration, the first semiconductor layer absorbs a large amount of light, and the light that has passed through the first semiconductor layer is efficiently scattered by the second semiconductor layer and returned to the first semiconductor layer. By making it absorb in, the whole light absorption rate can be improved further.

The film thickness of the semiconductor layer 6 is not particularly limited, but can be set to, for example, 0.5 μm or more and 45 μm or less from the viewpoint of permeability, conversion efficiency, and the like. The specific surface area of the semiconductor layer 6 can be set to, for example, 10 m ² / g or more and 200 m ² / g or less from the viewpoint of adsorbing a large amount of dye.

  In addition, in the structure in which the dye is adsorbed on the porous semiconductor layer 6, in order for the ions in the electrolyte to be more sufficiently diffused and charge transport be performed, the porosity of the porous semiconductor layer 6 is set to 40%, for example. It is desirable to set it to 80% or less. The porosity is a percentage of the volume of the semiconductor layer 6 occupied by pores in the semiconductor layer 6.

(I-2-2) Method for Forming Semiconductor Layer Next, a method for forming the semiconductor layer 6 will be described taking a porous semiconductor layer as an example. The porous semiconductor layer includes, for example, the above-described fine particles of the semiconductor material (hereinafter referred to as “semiconductor fine particles”) exemplified as the material constituting the semiconductor layer 6 together with an organic compound such as a polymer and a dispersant, an organic solvent, and water. A suspension is prepared in addition to an equal dispersion medium. Then, this suspension is formed on a conductive substrate (transparent conductive film 7 in FIG. 1), dried and baked. In addition, in this embodiment, it can also be set as the semiconductor layer 6 which consists of several layers obtained by repeating the process of application | coating of the said suspension, drying, and baking several times.

  When an organic compound is added to the dispersion medium together with the semiconductor fine particles, the organic compound is combusted at the time of firing, and a sufficient gap can be secured in the porous semiconductor layer. Moreover, the porosity can be changed by controlling the molecular weight and the addition amount of the organic compound combusted during firing. The type and amount of the organic compound can be appropriately selected and adjusted depending on the state of the fine particles used, the total weight of the entire suspension, and the like. However, when the ratio of the semiconductor fine particles is 10 wt% or more with respect to the total weight of the whole suspension, the strength of the produced film can be further sufficiently increased. For this reason, the ratio of the semiconductor fine particles is preferably 10 wt% or more with respect to the total weight of the entire suspension. Moreover, if the ratio of the semiconductor fine particles is 40 wt% or less with respect to the total weight of the whole suspension, a porous semiconductor layer having a large porosity can be obtained more stably. For this reason, the ratio of the semiconductor fine particles is preferably 40 wt% or less with respect to the total weight of the entire suspension. From the above, the ratio of the semiconductor fine particles may be 10 wt% or more and 40 wt% or less with respect to the total weight of the entire suspension.

  As the semiconductor fine particles, single or compound semiconductor particles having an appropriate average particle diameter, for example, an average particle diameter of about 1 nm to 500 nm are used. Among these, from the viewpoint of increasing the specific surface area, those having an average particle diameter of about 1 nm to 50 nm are desirable. In order to increase the utilization factor of incident light, semiconductor particles having a relatively large average particle diameter of about 200 nm to 400 nm may be added.

  Here, examples of the method for producing the semiconductor fine particles include a sol-gel method such as a hydrothermal synthesis method, a sulfuric acid method, a chlorine method and the like, and any method can be used as long as it can produce the desired fine particles. From the viewpoint of property, it is preferable to synthesize by a hydrothermal synthesis method. As the organic compound added to the dispersion medium together with the semiconductor fine particles, any organic compound can be used as long as it dissolves in the suspension and can be removed by burning when baked. Examples thereof include polymers such as polyethylene glycol and ethyl cellulose. Examples of the dispersion medium for the suspension include glyme solvents such as ethylene glycol monomethyl ether; alcohols such as isopropyl alcohol; and mixed solvents such as isopropyl alcohol / toluene; and water.

  Examples of the suspension application method include a doctor blade method, a squeegee method, a spin coating method, and a screen printing method. The conditions for drying and baking performed after the application can be, for example, about 10 seconds to 12 hours in the range of about 50 ° C. to 800 ° C. in the air or an inert gas atmosphere. This drying and baking may be performed once at a single temperature or twice or more by changing the temperature.

  In addition, although the formation method of the porous semiconductor layer was explained in full detail here, the other kind of semiconductor layer 6 can also be formed using various well-known methods.

(I-3) Dye In the present embodiment, any known material that functions as a photosensitizer can be used as the dye. For example, it may be an inorganic material such as semiconductor ultrafine particles, a so-called functional dye that exhibits a special function when subjected to external stimuli such as light, electric field, and heat, or an organic material such as a pigment. However, a functional dye is particularly preferable from the viewpoint of efficiently absorbing light and separating charges.

  As an example of the dye used in the Gretzel type dye-sensitized solar cell, there is a spectral sensitizing dye composed of a transition metal complex. More specifically, as a spectral sensitizing dye, cis-bis (isothiocyanato) -bis- (2,2′-bipyridyl-4,4′-dicarboxylic acid) ruthenium (II) ditetra, which is a kind of bipyridine complex. There is a butylammonium complex (commonly known as N719), which is excellent in performance as a sensitizing dye and is generally used. In addition, cis-bis (isothiocyanato) -bis- (2,2′-bipyridyl-4,4′-dicarboxylic acid) ruthenium (II) (common name: N3), which is a kind of bipyridine complex, and a kind of terpyridine complex Tris (isothiocyanato) (2,2 ′: 6 ′, 2 ″ -terpyridyl-4,4 ′, 4 ″ -tricarboxylic acid) ruthenium (II) tritetrabutylammonium complex (commonly known as black dye) is common. Used for. In recent years, organic materials containing no metal complex such as derivatives of coumarin-based materials have been reported. As other dyes, for example, the dyes described in “FPD / DSSC / Optical memory and functional dye latest technology and material development” (NTS Corp.) can be applied. Indoline dye D149 can also be used. In particular, a dye having associative properties on the semiconductor layer 6 is preferable from the viewpoint of stability. Examples of the dye having an effect of forming an aggregate include those having a carboxyl group, a sulfonyl group, and a phosphonyl group. Among these, a dye having a carboxyl group is preferable because it forms a strong aggregate.

  Next, as the semiconductor ultrafine particles, sulfide semiconductors such as cadmium sulfide, lead sulfide, and silver sulfide can be used. The particle diameter is not particularly limited as long as it has a photosensitizing effect on the semiconductor layer 6 of the present embodiment, but a range of 1 nm to 10 nm is desirable.

  Examples of the method of supporting the photosensitizer (dye) on the semiconductor layer 6 include a method of immersing the semiconductor substrate provided with the semiconductor layer 6 in a solution in which the photosensitizer is dissolved. The solvent of this solution is not particularly limited as long as it can dissolve the photosensitizer, such as water, alcohol, toluene, dimethylformamide, t-butyl alcohol / acetonitrile mixed solvent. In addition, when immersed in the photosensitizer solution for a certain period of time, it can be heated to reflux or an ultrasonic wave can be applied. In addition, after carrying | supporting a photosensitizer, in order to remove the photosensitizer which was not carry | supported, it is desirable to wash | clean with alcohol or to heat-reflux.

The amount of the photosensitizer supported may be in the range of 1 × 10 ⁻¹⁰ mol / cm ² or more and 1 × 10 ⁻⁴ mol / cm ² or less, particularly 1 × 10 ⁻⁹ mol / cm ² or more. A range of 0 × 10 ⁻⁶ mol / cm ² or less is preferable. This is because within this range, the effect of improving the photoelectric conversion efficiency can be obtained economically and sufficiently.

(Ii) Counter Electrode The counter electrode 3 of the present embodiment can have a structure in which the substrate 1 and the catalyst layer 2 are laminated. The photoelectric conversion element having such a counter electrode 3 is disposed so that the catalyst layer 2 is in contact with the electrolyte layer 4 described below.

  Examples of the substrate 1 include transparent substrates such as glass and polymer films, metal plates (foil), and the like. In particular, in order to reduce the resistance value of the counter electrode 3, a conductive substrate is desirable.

  The catalyst layer 2 can be, for example, a layer containing a metal catalyst such as platinum or a carbon material. The carbon material is not particularly limited, and examples thereof include activated carbon, graphite, carbon black, acetylene black, ketjen black, carbon nanofiber, vapor grown carbon fiber, carbon nanotube, and various fullerenes. The catalyst layer 2 may be formed in a film shape on the entire surface or a part of the substrate 1. The thickness of the catalyst layer 2 should just be the thickness which can express a catalyst function, and can specifically be about 1 nm or more and 20 micrometers or less.

  The counter electrode 3 may be formed on the same substrate as the semiconductor electrode 9. In this case, two or more electrodes can be formed on the same substrate by cutting the conductive layer between the counter electrode 3 and the semiconductor electrode 9 by laser scribing or the like.

(Iii) Electrolyte layer <ionic liquid>
The electrolyte layer 4 in this embodiment contains an ionic liquid. An ionic liquid is an ionic compound that is liquid at room temperature, and consists of a cation component and an anion component.

  The cation component of the ionic liquid is not particularly limited. Examples thereof include nitrogen-containing compound cations such as a lithium cation, phosphorus-containing compound cations such as a tetraalkylphosphonium cation, and sulfur-containing compound cations such as a trialkylsulfonium cation. Of these, dialkylimidazolium cations are preferred from the viewpoint of relatively low viscosity and excellent ion conductivity.

While anion component of the ionic liquid is not particularly limited, for example, _{^{- N (FSO 2) 2,}} - N (CF 3 SO 2) 2, - N (C 2 F 5 SO 2) 2, - N (CF 3 SO 2) _(C 4 _F 9 SO ₂₎ imide such as _{^{anionic, - C (CF 3 SO 2}} ) 3, - C (C 2 F 5 SO 2) _3, etc. methide _{^{anion, ClO 4 -, PF 6 -}} , BF 4 -, AsF ₆ ⁻ , B (C ₂ O ₄ ) ₂ ⁻ , CF ₃ SO ₃ ⁻ , Cl ⁻ , Br ⁻ , I ^{− and the} like can be mentioned. Among these, bis (trifluoromethylsulfonyl) imide anion is preferable from the viewpoint of stability.

  The kind of the ionic liquid is not particularly limited, but is preferably a hydrophobic ionic liquid from the viewpoint of low hygroscopicity and high stability. The structure of the hydrophobic ionic liquid is not particularly limited. For example, 1-ethyl-3-methylimidazolium bis (trifluoromethyl sulfonyl) imide salt or 1-methyl-3-propylimidazolium bis (trifluoromethyl fluoride) is used. Phonyl) imide salt, 1-methyl-3-butylimidazolium bis (trifluoromethylsulfonyl) imide salt, tetrabutylammonium tetrafluoroborate salt and the like.

<Nitroxyl radical>
The electrolyte layer 4 in the present embodiment contains nitroxyl radical as one of the redox species. The structure of the nitroxyl radical is not particularly limited. For example, 2,2,6,6-tetramethylpiperidinoxyl, 2,2,5,5-tetramethylpyrrolidinoxyl, 2,2,5,5-tetra And cyclic nitroxyl radicals such as methylpyrrolinoxyl. Of these, 2,2,6,6-tetramethylpiperidinoxyl represented by the following general formula (2) is preferable from the viewpoint of stability. Specifically, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), 2,2,5,5-tetramethylpyrrolidinoxyl (PROXYL) and the like are applicable.

  The nitroxyl radical in the present embodiment may be substituted or unsubstituted, and may be bonded as a side chain of the polymer compound. Examples of the polymer compound include poly (2,2,6,6-tetramethylpiperidinoxyl) in which 2,2,6,6-tetramethylpiperidinoxyl is bonded as a side chain of the methacrylate polymer. ) Methacrylate, polyvinyloxy (2,2,6,6-tetramethylpiperidinoxyl) in which 2,2,6,6-tetramethylpiperidinoxyl is bonded as a side chain of a vinyl ether polymer It is done.

<Oxoammonium salt>
In the present embodiment, the electrolyte layer 4 contains an oxoammonium salt as one of the redox species. The oxoammonium salt is a salt composed of an oxoammonium cation which is a one-electron oxidant of a nitroxyl radical and a monovalent anion.

  The structure of the oxoammonium cation is not particularly limited. For example, 1-oxo-2,2,6,6-tetramethylpiperidinium, 1-oxo-2,2,5,5-tetramethylpyrrolidinium, And cyclic oxoammonium cations such as oxo-2,2,5,5-tetramethylpyrrolinium. Among these, from the viewpoint of stability, 1-oxo-2,2,6,6 corresponding to a one-electron oxidant of 2,2,6,6-tetramethylpiperidinoxyl represented by the following general formula (3) -Tetramethylpiperidinium is preferred. Specifically, 2,2,6,6-tetramethylpiperidine-1-oxoammonium bistrifluoromethylsulfonylimide salt (TEMPO · TFSI), 1-oxo-2,2,5,5-tetramethylpyrrolidinium Bis (trifluoromethylsulfonyl) imide salt (PROXYL · TFSI) and the like are applicable.

  The oxoammonium cation in this embodiment may be substituted or unsubstituted, and may be bonded as a side chain of the polymer compound. Examples of the polymer compound include poly (1-oxo-2,2,6,6) in which 1-oxo-2,2,6,6-tetramethylpiperidinium is bonded as a side chain of a methacrylate polymer. -Tetramethylpiperidinium) methacrylate or 1-oxo-2,2,6,6-tetramethylpiperidinoxyl bonded as a side chain of a vinyl ether polymer, polyvinyloxy (1-oxo-2,2, 6,6-tetramethylpiperidinium) and the like.

Examples of the anion of the oxoammonium salt in the present embodiment is not particularly limited, for example, _{^{- N (FSO 2) 2,}} - N (CF 3 SO 2) 2, - N (C 2 F 5 SO 2) 2, - N _{(CF 3 SO 2) (C} 4 F 9 SO 2) imide anion, such _{^{as, - C (CF 3 SO 2}} ) 3, - C (C 2 F 5 SO 2) _3, etc. methide _anion, ^ClO 4 _-, PF _{6 ^{-, BF 4 -, AsF 6}} -, B (C 2 O 4) 2 -, CF 3 SO 3 -, Cl -, Br -, I - , and the like. Among these, bis (trifluoromethylsulfonyl) imide anion is preferable from the viewpoint of stability.

<Concentration of redox species>
The electrolyte layer in this embodiment uses a combination of nitroxyl radical-oxoammonium salt as a redox species. The nitroxyl radical-oxoammonium salt combination has a relatively slow diffusion as a redox species, and in some cases, the desired conversion efficiency may not be obtained. However, when the total concentration of the nitroxyl radical-oxoammonium salt is 1.5 mol / L or more, preferably 2 mol / L or more, more preferably 2.5 mol / L or more, a sufficient diffusion current can be obtained, The conversion efficiency of the photoelectric conversion element is improved. However, when the total concentration of the nitroxyl radical-oxoammonium salt is 5 mol / L or more, there is a possibility that the viscosity increases so much that a sufficient diffusion current cannot be obtained.

  Therefore, the total concentration of the nitroxyl radical-oxoammonium salt in this embodiment is 1.5 mol / L or more and 5 mol / L or less, preferably 2 mol / L or more and 5 mol / L or less, more preferably 2.5 mol / L or more and 4 mol or less. / L or less may be sufficient.

<Mixture>
The electrolyte layer 4 in this embodiment contains an ionic liquid, a nitroxyl radical, and an oxoammonium salt. In order to increase the conversion efficiency of the photoelectric conversion element, other organic solvents, electrolytes, basic additives, and the like are added. May be included.

  The organic solvent contained in the electrolyte layer is preferably a compound that has low viscosity, improves ion mobility, has a high dielectric constant, and exhibits excellent ion conductivity that improves effective carrier concentration. Examples of such solvents include carbonate compounds such as ethylene carbonate and propylene carbonate, heterocyclic compounds such as 3-methyl-2-oxazolidinone, ether compounds such as dioxane and diethyl ether, ethylene glycol dialkyl ether, propylene glycol dialkyl ether, and polyethylene. Chain ethers such as glycol dialkyl ether and polypropylene glycol dialkyl ether, methanol, ethanol, ethylene glycol monoalkyl ether, alcohols such as propylene glycol monoalkyl ether, polyethylene glycol monoalkyl ether, polypropylene glycol monoalkyl ether, ethylene glycol, Propylene glycol, polyethylene glycol, polypropylene Call, polyhydric alcohols such as glycerin, acetonitrile, glutarodinitrile, methoxy acetonitrile, propionitrile, nitrile compounds such as benzonitrile, dimethyl sulfoxide, sulfolane and the like, aprotic solvents.

As the electrolyte contained in the electrolyte layer, e.g. LiI, NaI, KI, CsI, and combinations of metal iodide salt and iodine _{I 2,} such as CaI _2, tetraalkylammonium iodide, pyridinium iodide, imidazolium iodide, etc. A combination of a quaternary ammonium iodide salt and iodine I ₂ , a combination of a metal bromide salt such as LiBr, NaBr, KBr, CsBr, CaBr ₂ and bromine Br ₂ , a quaternary ammonium bromide such as tetraalkylammonium bromide, pyridinium bromide A combination of a salt and bromine Br ₂ , a combination of ferrocyanate-ferricyanate, a combination of metal complexes such as ferrocene-ferricinium ion, a combination of hydroquinone-quinone, and the like.

  Examples of the basic additive contained in the electrolyte layer include t-butylpyridine, such as 4-t-butylpyridine, 2-picoline, 2,6-lutidine and the like. The addition concentration in the case of adding a basic compound can be, for example, about 0.05 mol / L or more and 2 mol / L or less.

<< Example >>
Hereinafter, the present invention will be described more specifically with reference to examples, but the scope of the present invention is not limited thereto. In the following examples, solar cells composed of the photoelectric conversion elements (FIG. 1) described in the above embodiment were created.

Example 1
1. Production of Semiconductor Electrode The semiconductor layer 6 was produced by the following procedure. A paste containing high-purity titanium oxide powder (manufactured by JGC Catalysts & Chemicals Co., Ltd.) having an average primary particle size of 20 nm is screen-printed on a fluorine-doped SnO ₂ electrode, dried at 110 ° C. for 1 hour, and then in air at 450 ° C. For 1 hour. Further, a paste containing a high-purity titanium oxide powder (manufactured by JGC Catalysts & Chemicals Co., Ltd.) having an average primary particle diameter of 400 nm is stacked on the electrode, screen-printed, dried at 110 ° C. for 1 hour, and then 450 in air. Sintered at 1 ° C. for 1 hour. Then, the semiconductor layer 6 was obtained by being immersed in titanium tetrachloride aqueous solution (made by Wako Pure Chemical Industries, Ltd.) for 40 minutes at 70 degreeC, and sintering at 450 degreeC in the air for 1 hour. The thickness of the semiconductor layer was about 6 μm.

2. Next, indoline dye D149 (manufactured by Mitsubishi Paper Industries) represented by the following formula (4) is mixed in a mixed solvent of t-butyl alcohol (manufactured by Sigma Aldrich) / acetonitrile (manufactured by Wako Pure Chemical Industries, Ltd.). It was dissolved at a concentration of 0.5 mmol / L to obtain an adsorption dye solution. The semiconductor electrode 9 obtained above was immersed in this dye solution for adsorption, and allowed to stand at room temperature for 4 hours to adsorb the dye. Thereafter, the mixture was washed several times with a t-butyl alcohol / acetonitrile mixed solvent to wash away excess dye.

3. Production of Photoelectric Conversion Element As a solvent, 1-ethyl-3-methylimidazolium bistrifluoromethylsulfonylimide salt (EMI • TFSI) (manufactured by Toyo Gosei Co., Ltd.), which is a hydrophobic ionic liquid, is used as a redox species and 2.5 mol / L 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) (manufactured by Wako Pure Chemical Industries, Ltd.) and 0.05 mol / L 2,2,6,6-tetramethylpiperidine-1- An electrolytic solution containing oxoammonium bistrifluoromethylsulfonylimide salt (TEMPO · TFSI) was prepared. The semiconductor electrode 9 obtained above was immersed in this electrolytic solution, and was evacuated with a rotary pump for about 2 minutes so that it was sufficiently impregnated. Next, the counter electrode 3 which has the catalyst layer 2 which consists of platinum was made to face, and the spacer 5 was pinched | interposed and it fixed with the jig | tool, and the photoelectric conversion element was produced.

(Example 2)
A photoelectric conversion element was produced in the same manner as in Example 1 except that the concentration of TEMPO as a redox species was 3.0 mol / L and the concentration of TEMPO · TFSI was 0.05 mol / L.

(Example 3)
A photoelectric conversion element was produced by the same method as in Example 1 except that the concentration of TEMPO as a redox species was 3.5 mol / L and the concentration of TEMPO · TFSI was 0.05 mol / L.

Example 4
A photoelectric conversion element was produced in the same manner as in Example 1 except that the concentration of TEMPO as redox species was 4.0 mol / L and the concentration of TEMPO · TFSI was 0.05 mol / L.

(Example 5)
A photoelectric conversion element was produced in the same manner as in Example 1 except that the concentration of TEMPO as a redox species was 4.5 mol / L and the concentration of TEMPO · TFSI was 0.05 mol / L.

(Example 6)
A photoelectric conversion element was produced in the same manner as in Example 1 except that the concentration of TEMPO as a redox species was 2.0 mol / L and the concentration of TEMPO · TFSI was 0.05 mol / L.

(Example 7)
A photoelectric conversion element was produced in the same manner as in Example 1 except that the concentration of TEMPO as a redox species was 2.5 mol / L and the concentration of TEMPO · TFSI was 0.02 mol / L.

(Example 8)
A photoelectric conversion element was produced in the same manner as in Example 1 except that the concentration of TEMPO as a redox species was 2.5 mol / L and the concentration of TEMPO · TFSI was 0.1 mol / L.

Example 9
As the redox species, 2.5 mol / L 2,2,5,5-tetramethylpyrrolidinoxyl (PROXYL) (manufactured by Wako Pure Chemical Industries, Ltd.), 0.05 mol / L 1-oxo-2,2,5,5 A photoelectric conversion element was produced in the same manner as in Example 1 except that 5-tetramethylpyrrolidinium bis (trifluoromethylsulfonyl) imide salt (PROXYL · TFSI) was used.

(Example 10)
As a dye, cis-bis (isothiocyanato) -bis- (2,2′-bipyridyl-4,4′-dicarboxylic acid) ruthenium (II) ditetrabutylammonium complex (N719) (manufactured by Solaronics) instead of D149 A photoelectric conversion element was produced in the same manner as in Example 1 except that 1.5 mol / L of 4-t-butylpyridine was added to the electrolyte layer.

(Example 11)
A photoelectric conversion element was produced in the same manner as in Example 1 except that the concentration of TEMPO as a redox species was 1.5 mol / L and the concentration of TEMPO · TFSI was 0.05 mol / L.

(Example 12)
A photoelectric conversion element was produced in the same manner as in Example 1 except that the concentration of TEMPO as a redox species was 5.0 mol / L and the concentration of TEMPO · TFSI was 0.05 mol / L.

(Example 13)
As redox species, 1.5 mol / L 2,2,5,5-tetramethylpyrrolidinoxyl (PROXYL), 0.05 mol / L 1-oxo-2,2,5,5-tetramethylpyrrolidinium bis A photoelectric conversion element was produced in the same manner as in Example 1 except that (trifluoromethylsulfonyl) imide salt (PROXYL · TFSI) was used.

(Example 14)
As the dye, cis-bis (isothiocyanato) -bis- (2,2′-bipyridyl-4,4′-dicarboxylic acid) ruthenium (II) ditetrabutylammonium complex (N719) is used instead of D149, and the electrolyte layer is used. Example 1 except that 1.5 mol / L of 4-t-butylpyridine was added and the concentration of TEMPO, which is a redox species, was 1.5 mol / L and the concentration of TEMPO · TFSI was 0.05 mol / L. The photoelectric conversion element was produced by the same method.

(Comparative Example 1)
A photoelectric conversion element was produced in the same manner as in Example 1 except that only TEMPO having a concentration of 1.5 mol / L was used as the redox species.

(Comparative Example 2)
A photoelectric conversion element was produced in the same manner as in Example 1 except that only TEMPO having a concentration of 2.0 mol / L was used as the redox species.

(Comparative Example 3)
A photoelectric conversion element was produced in the same manner as in Example 1 except that only TEMPO having a concentration of 2.5 mol / L was used as the redox species.

(Comparative Example 4)
A photoelectric conversion element was produced in the same manner as in Example 1 except that only TEMPO having a concentration of 3.0 mol / L was used as the redox species.

(Comparative Example 5)
A photoelectric conversion element was produced in the same manner as in Example 1 except that only TEMPO having a concentration of 3.5 mol / L was used as the redox species.

(Comparative Example 6)
A photoelectric conversion element was produced in the same manner as in Example 1 except that only TEMPO having a concentration of 4.0 mol / L was used as the redox species.

(Comparative Example 7)
A photoelectric conversion element was produced in the same manner as in Example 1 except that only TEMPO having a concentration of 4.5 mol / L was used as the redox species.

(Comparative Example 8)
A photoelectric conversion element was produced in the same manner as in Example 1 except that only TEMPO having a concentration of 5.0 mol / L was used as the redox species.

As evaluation of each photoelectric conversion element manufactured in Examples 1 to 14 and Comparative Examples 1 to 8 were subjected to I-V measurement at AM 1.5, 100 mW / cm ² irradiation conditions by using a solar simulator. Here, both ends of the photoelectric conversion element were connected to an electronic load device, and potential scanning at a step of 5 mV / sec was repeated until the voltage taken out from the open circuit voltage became zero.

  Assuming that the conversion efficiency of Example 1 is 100%, Example 2 is 98%, Example 3 is 95%, Example 4 is 90%, Example 5 is 83%, Example 6 is 92%, Example 7 is 96%, Example 8 is 93%, Example 9 is 82%, Example 10 is 91%, Example 11 is 76%, Example 12 is 69%, Example 13 is 74%, Example 14 Was 70%, and Comparative Examples 1 to 8 were less than 1%.

  From these results, it was found that when the electrolyte layer contains an ionic liquid, a nitroxyl radical, and an oxoammonium salt, the conversion efficiency is greatly improved as compared with the case where no oxoammonium salt is contained.

  Comparing Examples 1 to 8 and Examples 11 and 12, from the viewpoint of conversion efficiency, the total concentration of redox species TEMPO and TEMPO · TFSI is preferably 2 mol / L or more and 5 mol / L or less. It turned out that it is preferable that they are 2.5 mol / L or more and 4 mol / L or less. Comparing Example 9 and Example 13, even if the redox species is not a combination of TEMPO and TEMPO · TFSI, but a combination of PROXYL and PROXYL · TFSI, the total concentration of the redox species may be 2 mol / L or more. It turned out to be preferable. Similarly, when Example 10 and Example 14 are compared, even when the dye is N719 and 1.5 mol / L of 4-t-butylpyridine is added to the electrolyte layer, redox species TEMPO and TEMPO · It was found that the total concentration of TFSI is preferably 2 mol / L or more.

  In addition, the optical sensor and solar cell excellent in practical use can be provided by utilizing such a photoelectric conversion element with high conversion efficiency for an optical sensor and a solar cell according to a prior art.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Catalyst layer 3 Counter electrode 4 Electrolyte layer 5 Spacer 6 Semiconductor layer 7 Transparent conductive film 8 Transparent substrate 9 Semiconductor electrode

Claims (8)

A semiconductor electrode having a semiconductor layer adsorbed with a dye;
A counter electrode provided opposite to the semiconductor electrode;
An electrolyte layer that includes an ionic liquid, a nitroxyl radical, and an oxoammonium salt, and is provided in contact with each of the semiconductor layer and the counter electrode of the semiconductor electrode at a position sandwiched between the semiconductor electrode and the counter electrode;
A photoelectric conversion element having The photoelectric conversion element according to claim 1,
A photoelectric conversion element in which a total molar concentration of the nitroxy radical and the oxoammonium salt is 2 mol / L or more and 5 mol / L or less. In the photoelectric conversion element according to claim 1 or 2,
The photoelectric conversion element in which the nitroxyl radical is 2,2,6,6-tetramethylpiperidinoxyl represented by the general formula (1).

In the photoelectric conversion element according to any one of claims 1 to 3,
The photoelectric conversion element whose said ionic liquid is hydrophobic ionic liquid. The photoelectric conversion element according to claim 4,
The photoelectric conversion element in which the hydrophobic ionic liquid is a hydrophobic ionic liquid composed of an imidazolium cation and a bis (trifluoromethylsulfonyl) imide anion. In the photoelectric conversion element according to any one of claims 1 to 5,
The said semiconductor layer is comprised with the semiconductor material containing a titanium oxide, The photoelectric conversion element characterized by the above-mentioned.   An optical sensor comprising the photoelectric conversion element according to claim 1.   A solar cell comprising the photoelectric conversion element according to claim 1.

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