JP2011086481A - Photoelectric conversion element and solar cell - Google Patents

Abstract

A photoelectric conversion element with high photoelectric conversion efficiency, a method for manufacturing the photoelectric conversion element, and a solar cell using the photoelectric conversion element are provided.
Dye sensitization in which a semiconductor layer containing an n-type semiconductor carrying a dye and a solid hole transport layer are provided between a transparent conductive film formed on a substrate and a counter electrode. In the photoelectric conversion element of the type, the hole transport layer contains at least an aromatic amine derivative A having a hole transport ability and a hydrocarbon B, and the mass mole fraction of B is equal to or less than the mass mole fraction of A. Furthermore, when the molecular weights of A and B are M _W (A) and M _W (B), respectively, the following conditions are satisfied: A photoelectric conversion element and a solar cell.
400 ≦ M _W (A) ≦ 2000
2 ≦ M _W (A) / M _W (B) ≦ 10
[Selection figure] None

Description

  The present invention relates to a dye-sensitized photoelectric conversion element and a solar cell configured using the photoelectric conversion element.

  In recent years, the use of sunlight, which is infinite and does not generate harmful substances, has been energetically studied. What is currently put into practical use as solar energy, which is a clean energy source, includes residential single crystal silicon, polycrystalline silicon, amorphous silicon, and inorganic solar cells such as cadmium telluride and indium copper selenide. .

  However, the disadvantages of these inorganic solar cells include, for example, that silicon is required to have a very high purity, and naturally, the purification process is complicated, the number of processes is large, and the manufacturing cost is high.

  On the other hand, many solar cells using organic materials have been proposed. As an organic solar cell, a Schottky photoelectric conversion element that joins a p-type organic semiconductor and a metal having a low work function, a p-type organic semiconductor and an n-type inorganic semiconductor, or a p-type organic semiconductor and an electron-accepting organic compound are joined. There are heterojunction photoelectric conversion elements and the like, and organic semiconductors used are synthetic dyes and pigments such as chlorophyll and perylene, conductive polymer materials such as polyacetylene, or composite materials thereof. These are thinned by a vacuum deposition method, a casting method, a dipping method, or the like to form a battery material. Although organic materials have advantages such as low cost and easy area enlargement, there are many problems that the conversion efficiency is as low as 1% or less and the durability is poor.

  Under such circumstances, a solar cell exhibiting good characteristics has been reported by Dr. Gretzell of Switzerland (see, for example, Non-Patent Document 1). The proposed battery is a dye-sensitized solar cell, which is a wet solar cell using a titanium oxide porous thin film spectrally sensitized with a ruthenium complex as a working electrode. An advantage of this method is that an inexpensive metal semiconductor such as titanium oxide can be used without the need to purify it to high purity, and thus a solar cell can be produced at low cost. In addition, the spectral sensitization effect of the dye can effectively convert sunlight with many visible light components into electricity.

  The above dye-sensitized solar cell uses, as a charge transport layer, an electrolytic solution in which an electrolyte containing iodine is dissolved in an organic solvent, but has problems such as volatilization and leakage of the electrolytic solution or corrosion by iodine. . In order to compensate for these drawbacks, there are those using a solid hole transport agent as the charge transport layer, for example, those using an aromatic amine solid p-type semiconductor have been reported (for example, Patent Document 1, Non-patent document 2). In general, the semiconductor layer is made of a porous material consisting of nano-sized particles. In order to effectively transport the charge generated by charge separation within the dye molecule, the hole transport agent penetrates into the porous material. Need to be. The smaller the hole transport agent molecular size, the better the penetration into the porous material. However, when the solvent evaporates from the hole transport layer preparation liquid, it becomes easier to microcrystallize, and the holes caused by the grain boundaries. A decrease in transport capacity occurs. At this time, if an amorphous hole transport layer can be obtained without microcrystallization, this problem can be solved.

JP 2003-123856 A

B. O'Regan, M.M. Gratzel, Nature, 353, 737 (1991) U. Bach, M.M. Gratzel, Nature, 395, 583 (1998)

  An object of the present invention is to provide a photoelectric conversion element having high photoelectric conversion efficiency, a method for producing the photoelectric conversion element, and a solar cell using the photoelectric conversion element.

  The above object of the present invention can be achieved by the following configuration.

1. Dye-sensitized photoelectric conversion in which a semiconductor layer containing an n-type semiconductor carrying a dye and a solid hole transport layer are provided between a transparent conductive film formed on a substrate and a counter electrode In the element, the hole transport layer contains at least an aromatic amine derivative A having a hole transport ability and a hydrocarbon B, and the mass mole fraction of B is equal to or less than the mass mole fraction of A. , A and B, when the molecular weights are M _W (A) and M _W (B), respectively, the photoelectric conversion device satisfies the following conditions.

400 ≦ M _W (A) ≦ 2000
2 ≦ M _W (A) / M _W (B) ≦ 10
2. 2. The photoelectric conversion element as described in 1 above, wherein the hydrocarbon B is an aromatic hydrocarbon having a secondary alkyl group or a tertiary alkyl group.

  3. 3. The photoelectric conversion element as described in 1 or 2 above, wherein the n-type semiconductor is titanium oxide.

  4). A solar cell comprising the photoelectric conversion device according to any one of 1 to 3 above.

  According to the present invention, a photoelectric conversion element having high photoelectric conversion efficiency, a method for producing the same, and a solar cell using the photoelectric conversion element can be obtained.

It is a structure sectional view showing an example of a photoelectric conversion element of the present invention.

  Hereinafter, the best mode for carrying out the present invention will be described in detail, but the present invention is not limited thereto.

  As shown in FIG. 1, the photoelectric conversion element according to the present invention includes a substrate 1, a transparent conductive film 2, a barrier layer 3, a semiconductor layer 6, a hole transport layer 7, a counter electrode 8, and the like.

  The manufacture example of the photoelectric conversion element of this invention is shown below. An n-type semiconductor 5 having pores formed by depositing and then sintering a barrier layer 3 on a substrate 1 (also referred to as a conductive support) provided with a transparent conductive film 2 is manufactured. The semiconductor layer 6 is formed by adsorbing the sensitizing dye 4 on the surface. A hole transport layer 7 mainly composed of a p-type semiconductor is present on the semiconductor layer 6, and a counter electrode 8 is attached thereon. A terminal is attached to the transparent conductive film 2 and the counter electrode 8, and a photocurrent is taken out.

  The present invention relates to a hole transport layer used in this photoelectric conversion element.

《Hole transport layer》
The solid hole transport layer of the present invention refers to a hole transport layer that is solid at 25 ° C., and contains at least an aromatic amine derivative A having a hole transport ability and a hydrocarbon B. The hydrocarbon in the present invention refers to a compound composed of carbon and hydrogen.

In FIG. 1, the hole transport layer 7 is preferably in the form of a uniform film from the viewpoint of preventing charge leakage, and the organic compound is superior in terms of film formability compared to an inorganic compound that is easily formed into fine particles. . Among organic compounds, aromatic amine derivatives having a molecular weight of 400 or more (hereinafter abbreviated as “A”) are excellent organic compounds having a large mobility and high mobility between molecules because the π-conjugated system is spatially spread. A p-type semiconductor is provided. Examples of the structure of the aromatic amine compound A include triarylamine compounds represented by general formulas (A1) to (A8) having a triarylamine structure in the molecule. Ar _{1 to} Ar ₃₇ each represents a substituted or unsubstituted aryl group or heterocyclic group, and may be linked to each other to form a cyclic structure. n _{1, n 2} is an integer from 1 to 6.

  More specific structural examples of the aromatic amine compound A include compounds represented by the following A-1 to A-136, but the present invention is not limited thereto.

The aromatic amine derivative A is preferably also present inside the vacancies in the semiconductor layer. In general, the aromatic amine derivative A is prepared after the solution of A is applied on the semiconductor layer and penetrated into the vacancies. When the molecular weight of A exceeds 2000, the molecular size becomes large and the penetration into the porous interior is inhibited. A smaller molecular size is advantageous for permeation into the porous body, but when the solvent volatilizes, it becomes easier to crystallize, and the hole transport ability is reduced due to the crystal grain boundary. At this time, when hydrocarbon B (hereinafter abbreviated as B) is introduced into the hole transport layer, the formation of an amorphous state is promoted, so that the grain boundary disappears and the hole transport ability is improved. Examples of the structure of B include compounds of the general formulas (B1) to (B6) containing both aromatic and aliphatic hydrocarbon moieties. R _{1 to} R ₆ each represents an alkyl group, and R ₁₀ represents an alkylene group, which may be different from each other. n1 is an integer from 1 to 6, n2, n3 and n4 are from 1 to 10, n5 is from 1 to 14, and n6 is an integer from 1 to 18. When B has a bulky substituent, that is, a secondary alkyl group or a tertiary alkyl group, the above-mentioned amorphization is further promoted, which is preferable.

  In order to improve the hole transport ability, it is necessary to ensure intermolecular contact between molecules A. In order to suppress inhibition of intermolecular contact of A by B contained, the molecular size of A is larger than the molecular size of B. It must be sufficiently large. Specifically, the molecular weight of A is at least twice that of B. On the other hand, if the molecular weight of B is too small compared to A, the amorphous forming ability of B will be insufficient, so the molecular weight of A must be 10 times or less of B. Similarly, in order to ensure intermolecular contact between molecules A, the mass mole fraction of B must be equal to or less than the mass mole fraction of A. In addition, B, which is a sufficiently low molecular weight hydrocarbon, is inactive to redox and does not transfer charges with A. Therefore, the positive charge existing in A moves to B and is localized. As a result, the hole transport ability is prevented from being lowered due to the localization of electric charges to specific molecules. Specific examples of B are shown below, but the present invention is not limited thereto.

In the present invention, when the molecular weights of A and B are M _W (A) and M _W (B), respectively, the object of the present invention can be achieved by satisfying the following conditions.

400 ≦ M _W (A) ≦ 2000
2 ≦ M _W (A) / M _W (B) ≦ 10
"substrate"
The substrate 1 is provided on the light incident direction 9 side (also referred to as the light incident surface side), and preferably has a light transmittance of 10% or more from the viewpoint of improving the photoelectric conversion efficiency of the dye-sensitized photoelectric conversion element. Further, it is preferably 50% or more, and particularly preferably 80% to 100% (indicating that it is transparent).

  In order for the substrate 1 to exhibit the light transmittance as described above, it is preferable to use a material that is transparent to light, such as a glass plate or a plastic film.

<Transparent conductive film>
The transparent conductive film 2 (also referred to as a transparent conductive layer) will be described.

  The transparent conductive film 2 is provided on one surface that is opposite to the light incident direction 9 of the substrate 1.

As a material for forming the transparent conductive film 2, a transparent conductive metal oxide is preferably used. For example, SnO ₂ , CdO, ZnO, CTO-based (CdSnO ₃ , Cd ₂ SnO ₄ , CdSnO ₄ ), In ₂ O ₃ , CdIn ₂ O _{4 and the} like.

  Preferably, a composite (dope) material in which one or more selected from Sn, Sb, F and Al is added to the above metal oxide can be used.

Of these, conductive metal oxides such as In ₂ O ₃ (ITO) doped with Sn, SnO ₂ doped with Sb, and SnO ₂ (FTO) doped with F are preferably used, from the viewpoint of heat resistance. FTO is most preferred.

<Transparent conductive support>
A transparent conductive support is formed from the substrate 1 and the transparent conductive film 2.

In addition, as a film thickness of an electroconductive support body (it consists of the board | substrate 1 and the transparent conductive layer 2), the range of 0.3 mm-5 mm is preferable. The surface resistance of the conductive support is preferably 50 Ω / cm ² or less, and more preferably 10 Ω / cm ² or less.

  The preferred range of light transmittance of the transparent conductive support is synonymous with the preferred range of light transmittance of the substrate 1.

<Semiconductor layer>
The semiconductor layer 6 according to the present invention includes a sensitizing dye 4 and an n-type semiconductor 5 (also simply referred to as a semiconductor).

  When the semiconductor according to the present invention is produced by firing, it is preferable that the semiconductor sensitization treatment (adsorption, penetration into the porous body, etc.) using the sensitizing dye is performed after the semiconductor is fired. It is particularly preferable to perform the sensitizing dye adsorption treatment quickly after the firing and before the water is adsorbed to the semiconductor.

  When the semiconductor according to the present invention is in the form of particles, the semiconductor is preferably manufactured by applying or spraying the semiconductor on the conductive layer. In the case where the semiconductor is in a film form and is not held on the conductive layer, the semiconductor is preferably bonded to the conductive layer.

  In the photoelectric conversion element of the present invention, as the semiconductor, a compound having a Group 3 to Group 5, Group 13 to Group 15 element of a periodic table (also referred to as an element periodic table), a metal chalcogenide (for example, Oxides, sulfides, selenides, etc.), metal nitrides, etc. can be used.

  Preferred metal chalcogenides include titanium, tin, zinc, iron, tungsten, zirconium, hafnium, strontium, indium, cerium, yttrium, lanthanum, vanadium, niobium or tantalum oxides, cadmium, zinc, lead, silver, antimony or Bismuth sulfide, cadmium or lead selenide, cadmium telluride and the like. Examples of other semiconductors include phosphides such as zinc, gallium, indium, and cadmium, gallium-arsenic or copper-indium selenides, copper-indium sulfides, and titanium nitrides.

_{Examples, TiO 2, ZrO 2, SnO} 2, Fe 2 O 3, WO 3, ZnO, Nb 2 O 5, Ta 2 O 5, CdS, ZnS, PbS, Bi 2 S 3, CdSe, CdTe, GaP , InP, GaAs, CuInS ₂ , CuInSe ₂ , Ti ₃ N _{4 and the} like, but TiO ₂ , ZnO, SnO ₂ , Fe ₂ O ₃ , WO ₃ , Nb ₂ O ₅ , CdS, etc. are preferably used. PbS is more preferably used, and TiO ₂ or SnO ₂ is used. Of these, TiO ₂ (titanium oxide) is particularly preferably used.

As the semiconductor used for the photoelectrode, a plurality of the above-described semiconductors may be used in combination. For example, several kinds of the above-described metal oxides or metal sulfides can be used in combination, and a titanium oxide semiconductor may be used by mixing 20% by mass of titanium nitride (Ti ₃ N ₄ ). In addition, J.H. Chem. Soc. Chem. Commun. 15 (1999). At this time, when a component is added as a semiconductor in addition to the metal oxide or metal sulfide, the mass ratio of the additional component to the metal oxide or metal sulfide semiconductor is preferably 30% or less.

(Preparation of coating liquid containing semiconductor fine powder)
First, a coating solution containing fine semiconductor powder is prepared. The finer the primary particle diameter of the semiconductor fine powder, the better. The primary particle diameter is preferably 1 to 5000 nm, and more preferably 2 to 50 nm. The coating liquid containing the semiconductor fine powder can be prepared by dispersing the semiconductor fine powder in a solvent. The semiconductor fine powder dispersed in the solvent is dispersed in the form of primary particles. The solvent is not particularly limited as long as it can disperse the semiconductor fine powder.

  Examples of the solvent include water, an organic solvent, and a mixed solution of water and an organic solvent. As the organic solvent, alcohols such as methanol and ethanol, ketones such as methyl ethyl ketone, acetone and acetyl acetone, hydrocarbons such as hexane and cyclohexane, and the like are used. A surfactant and a viscosity modifier (polyhydric alcohol such as polyethylene glycol) can be added to the coating solution as necessary. The range of the semiconductor fine powder concentration in the solvent is preferably 0.1 to 70% by mass, and more preferably 0.1 to 30% by mass.

(Application of coating solution containing fine semiconductor powder and baking treatment of the formed semiconductor layer)
The semiconductor fine powder-containing coating solution obtained as described above is applied or sprayed onto a conductive support, dried, etc., and then baked in air or an inert gas to provide a conductive support. A semiconductor layer (semiconductor film) is formed thereon.

  The film obtained by applying and drying the coating liquid on the conductive support is composed of an aggregate of semiconductor fine particles, and the particle size of the fine particles corresponds to the primary particle size of the semiconductor fine powder used. is there.

  Since the semiconductor fine particle aggregate film formed on the substrate such as the conductive support in this way has a low bonding strength with the conductive support or between the fine particles and a low mechanical strength. In order to increase the mechanical strength and to obtain a fired product film firmly adhered to the substrate, the semiconductor fine particle aggregate film is preferably subjected to a firing treatment.

  In the present invention, the fired product film obtained by this firing treatment may have any structure, but is preferably a porous structure film (also referred to as a porous layer having voids).

  Here, the porosity of the semiconductor thin film according to the present invention is preferably 10% by volume or less, more preferably 8% by volume or less, and particularly preferably 0.01 to 5% by volume or less. The porosity of the semiconductor thin film means a porosity that is penetrable in the thickness direction of the dielectric, and can be measured using a commercially available apparatus such as a mercury porosimeter (Shimadzu Polarizer 9220 type).

  As for the film thickness of the semiconductor layer used as the baked material film | membrane which has a porous structure, 10 nm or more is preferable, More preferably, it is 100-10000 nm.

  From the viewpoint of appropriately preparing the actual surface area of the fired product film during the firing treatment and obtaining a fired product film having the above porosity, the firing temperature is preferably lower than 1000 ° C, more preferably in the range of 200 to 800 ° C. Especially preferably, it is the range of 300-800 degreeC.

  The ratio of the actual surface area to the apparent surface area can be controlled by the particle size, specific surface area, firing temperature, etc. of the semiconductor fine particles. In addition, for example, an aqueous titanium tetrachloride solution is used for the purpose of increasing the surface area of the semiconductor particles after the heat treatment, increasing the purity in the vicinity of the semiconductor particles, and increasing the efficiency of electron injection from the sensitizing dye to the semiconductor particles. Chemical plating or electrochemical plating using a titanium trichloride aqueous solution may be performed.

<Sensitizing dye>
In the present invention, the sensitizing dye 4 is carried on the semiconductor 5. From the viewpoint of efficient injection of electric charges into the semiconductor, the sensitizing dye preferably has a carboxyl group. Although the specific example of a sensitizing dye is shown below, this invention is not limited to these.

(Semiconductor sensitization treatment)
The semiconductor sensitization treatment is performed by dissolving the sensitizing dye in an appropriate solvent as described above, and immersing the substrate on which the semiconductor is baked and fixed in the solution. In that case, a semiconductor layer (also referred to as a semiconductor film) is formed by baking, the substrate is preliminarily decompressed or heated to remove bubbles in the film, and the sensitizing dye is deep inside the semiconductor layer (semiconductor film). It is preferable to allow entry, and it is particularly preferable when the semiconductor layer (semiconductor film) is a porous structure film.

  The solvent used for dissolving the sensitizing dye is not particularly limited as long as it can dissolve and does not dissolve the semiconductor or react with the semiconductor, but is dissolved in the solvent. In order to prevent moisture and gas from entering the semiconductor film and hindering the sensitizing treatment such as adsorption of the sensitizing dye, it is preferable to degas and purify in advance.

  Solvents preferably used include alcohol solvents such as methanol, ethanol, n-propanol, and t-butyl alcohol, ketone solvents such as acetone and methyl ethyl ketone, and ether solvents such as diethyl ether, diisopropyl ether, tetrahydrofuran, and 1,4-dioxane. Solvents, nitrile solvents such as acetonitrile and propionitrile, halogenated hydrocarbon solvents such as methylene chloride and 1,1,2-trichloroethane, and mixed solvents may be used. Particularly preferred are ethanol, t-butyl alcohol and acetonitrile.

  The time for immersing the substrate on which the semiconductor has been baked in the solution containing the sensitizing dye is sufficient to cause the sensitizing dye to enter the semiconductor layer (semiconductor film) deeply so that the adsorption proceeds sufficiently and the semiconductor is sufficiently sensitized In addition, from the viewpoint of suppressing degradation products generated by decomposition of the sensitizing dye in the solution from interfering with the adsorption of the sensitizing dye, 1 to 48 hours are preferable at 25 ° C., more preferably 3 to 24 hours. It is. This temperature and time are particularly preferred when the semiconductor film is a porous structure film. However, the immersion time is a value at 25 ° C., and this is not the case when the temperature condition is changed.

  In soaking, the solution containing the sensitizing dye may be heated to a temperature that does not boil as long as the sensitizing dye does not decompose. A preferable temperature range is 10 to 100 ° C., more preferably 25 to 80 ° C., but this is not the case when the solvent boils in the temperature range as described above.

  When the sensitizing treatment is performed using a sensitizing dye, the sensitizing dye may be used alone or a plurality thereof may be used in combination.

  Moreover, the sensitizing dye which has a carboxyl group preferable for the present invention and other sensitizing dyes can be used in combination. As the sensitizing dye that can be used in combination, any sensitizing dye that can spectrally sensitize the semiconductor layer according to the present invention can be used. It is preferable to mix two or more types of sensitizing dyes in order to make the wavelength range of photoelectric conversion as wide as possible and increase the photoelectric conversion efficiency. Further, it is possible to select the sensitizing dye to be mixed and its ratio so as to match the wavelength range and intensity distribution of the target light source.

  In particular, when the use of the photoelectric conversion element of the present invention is a solar cell to be described later, two or more types of absorption having different absorption wavelengths are used so that the wavelength range of photoelectric conversion can be made as wide as possible to effectively use sunlight. It is preferable to use a mixture of dyes.

  Among the sensitizing dyes used in combination, metal complex dyes, phthalocyanine dyes, porphyrin dyes, and polymethine dyes are preferably used from the comprehensive viewpoints such as photoelectron transfer reaction activity, light durability, and photochemical stability. It is done.

  Examples of the sensitizing dye that can be used in combination with the sensitizing dye having a carboxyl group preferable in the present invention include, for example, U.S. Pat. Nos. 4,684,537 and 4,927,721. 5,084,365, 5,350,644, 5,463,057, 5,525,440, JP-A-7-249790, JP2000 And sensitizing dyes described in JP-A-15-150007.

  In order to include a sensitizing dye in the semiconductor layer, a method in which the sensitizing dye is dissolved in an appropriate solvent (ethanol or the like) and a well-dried semiconductor is immersed in the solution for a long time is generally used.

  When a sensitizing dye is used in combination with a plurality of sensitizing dyes or in combination with a sensitizing dye other than the sensitizing dye having a carboxyl group preferable for the present invention, a mixed solution of each sensitizing dye May be prepared and used, or a solution may be prepared for each sensitizing dye and immersed in each solution in order. When preparing a separate solution for each sensitizing dye and immersing in each solution in order, the effects described in the present invention can be obtained regardless of the order in which the sensitizing dye is included in the semiconductor layer. Obtainable. Alternatively, it may be produced by mixing semiconductor fine particles on which a sensitizing dye is adsorbed alone.

  The adsorption treatment may be performed when the semiconductor layer is in the form of particles, or may be performed after the film is formed on the support. A solution in which the compound used for the adsorption treatment is dissolved may be used at room temperature, or may be used by heating in a temperature range in which the compound does not decompose and the solution does not boil. Moreover, you may implement the said sensitizing dye adsorption | suction after application | coating of semiconductor fine particle like manufacture of the photoelectric conversion element mentioned later. Alternatively, the sensitizing dye may be adsorbed by simultaneously applying the semiconductor fine particles and the sensitizing dye. Unadsorbed sensitizing dye can be removed by washing.

  Further, the sensitization treatment of the semiconductor layer according to the present invention is performed by the semiconductor containing the sensitizing dye. The details of the sensitization treatment are specifically described in the photoelectric conversion element described later. explain.

  In the case of a semiconductor layer having a semiconductor thin film with a high porosity, before the water is adsorbed on the semiconductor thin film and in the voids inside the semiconductor thin film by moisture, water vapor, etc., the sensitizing dye adsorption treatment ( It is preferable to complete the sensitization treatment of the semiconductor layer.

《Barrier layer》
In the present embodiment, as a short-circuit prevention means, a barrier layer 3 is provided which is in the form of a film (layer) and is located between the transparent conductive film 2 and the hole transport layer 7. The barrier layer 3 is formed so that the porosity is smaller than the porosity of the hole transport layer 7.

  When manufacturing a photoelectric conversion element, applying a positive hole transport layer to the upper surface of a semiconductor layer by the apply | coating method is performed. In this case, in a solar cell in which no barrier layer is provided, when the porosity of the semiconductor is increased, the hole transport layer material penetrates into the holes of the semiconductor and reaches the transparent conductive film 2. There is. That is, in a solar cell that does not have a barrier layer, a contact (short circuit) occurs between the transparent conductive film and the hole transport layer, resulting in an increase in leakage current and a decrease in power generation efficiency (photoelectric conversion efficiency). There is a case.

  On the other hand, in the photoelectric conversion element provided with the barrier layer 3, the inconvenience as described above is prevented, and a decrease in power generation efficiency is preferably prevented or suppressed.

  Further, when the porosity of the barrier layer is C [%] and the porosity of the semiconductor layer is D [%], D / C is preferably about 1.1 or more, for example, 5 or more. More preferably, it is about 10 or more. Thereby, a barrier layer and a semiconductor layer can exhibit those functions more suitably, respectively.

  More specifically, the porosity C of the barrier layer is, for example, preferably about 20% or less, more preferably about 5% or less, and further preferably about 2% or less. That is, the barrier layer is preferably a dense layer. Thereby, the said effect can be improved more.

  The average thickness (film thickness) of the barrier layer 8 is, for example, preferably about 0.01 to 10 μm, and more preferably about 0.1 to 1 μm. Thereby, the said effect can be improved more.

The constituent material of the barrier layer 8 is not particularly limited. For example, in addition to titanium oxide which is the main constituent material of the semiconductor layer, for example, SrTiO ₃ , ZnO, SiO ₂ , Al ₂ O ₃ , SnO ₂ , etc. Various metal oxides, CdS, CdSe, TiC, various kinds of metal compounds such as Si ₃ N ₄ , SiC, and BN can be used in combination of two or more, and among these, the same as the semiconductor layer Those having electrical conductivity are preferable, and those mainly composed of titanium oxide are more preferable.

《Counter electrode》
The counter electrode 8 used in the present invention will be described.

  The counter electrode only needs to have conductivity, and any conductive material can be used, but a metal thin film having good contact with the hole transport layer is preferable. A gold thin film which is a chemically stable metal having a small work function difference from the hole transport layer is particularly preferable.

《Solar cell》
The solar cell of the present invention will be described.

  The solar cell of the present invention has a structure in which the optimum design and circuit design for sunlight are performed as one aspect of the photoelectric conversion element of the present invention, and the optimum photoelectric conversion is performed when sunlight is used as a light source. Have. That is, the semiconductor is dye-sensitized and can be irradiated with sunlight. When configuring the solar cell of the present invention, it is preferable that the semiconductor layer, the charge transfer layer, and the counter electrode are housed in a case and sealed, or the whole is resin-sealed.

  When the solar cell of the present invention is irradiated with sunlight or an electromagnetic wave equivalent to sunlight, the dye according to the present invention adsorbed on the semiconductor is excited by absorbing the irradiated light or electromagnetic wave. Electrons generated by the excitation move to the semiconductor, and then move to the counter electrode via an electric circuit connected to the solar cell to reduce the redox electrolyte of the charge transfer layer. On the other hand, the dye according to the present invention in which electrons are transferred to a semiconductor is an oxidant, but is reduced and returned to its original state by supplying electrons from the counter electrode via the hole transport layer. At the same time, the redox electrolyte of the hole transport layer is oxidized and returned to a state where it can be reduced again by the electrons supplied from the counter electrode. In this way, electrons flow, and a solar cell using the photoelectric conversion element of the present invention can be configured.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these.

Example 1
[Production of Photoelectric Conversion Element 1]
A solution obtained by diluting 1.2 ml of tetrakisisoporopoxytitanium and 0.8 ml of acetylacetone in 18 ml of ethanol is dropped onto a fluorine-doped tin oxide (FTO) conductive glass substrate, and after film formation by spin coating, the film is heated at 450 ° C. for 8 hours. A barrier layer was formed on the transparent conductive film (FTO) by heating for a minute. On this barrier layer, a commercially available titanium oxide paste (particle size: 18 nm) was applied in an area of 5 × 5 mm ² by screen printing. After heating at 120 ° C. for 3 minutes to dry the paste, baking was performed at 450 ° C. for 30 minutes to obtain a 1.0 μm thick titanium oxide thin film as an n-type semiconductor. The whole substrate was immersed in a 0.02 mol / l aqueous solution of titanium tetrachloride overnight and then baked again at 450 ° C. for 10 minutes.

Exemplified compound D-12 was dissolved in a 1: 1 mixed solvent of t-butyl alcohol and acetonitrile to prepare a 5 × 10 ⁻⁴ mol / l solution. An FTO glass substrate coated with titanium oxide was immersed in this solution at room temperature for 3 hours, and a dye adsorption process was performed to obtain a semiconductor layer.

  Next, 153 mmol of aromatic amine A-134, 17 mmol of hydrocarbon B-2, 15 mmol of lithium bis (trifluoromethanesulfonyl) imide, and 50 mmol of 4-t-butylpyridine were dissolved in chlorobenzene. Then, a film was formed on the semiconductor layer by a spin coat method, followed by vacuum drying for 30 minutes to produce a hole transport layer. Furthermore, 60 nm of gold was vapor-deposited by a vacuum vapor deposition method, a counter electrode was produced, and the photoelectric conversion element 1 was produced.

[Production of photoelectric conversion elements 2 to 17]
In the production of the photoelectric conversion element 1, photoelectric conversion elements 2 to 17 were produced in the same manner except that the aromatic amine and the hydrocarbon were changed to those shown in Table 1.

The produced photoelectric conversion element was irradiated with 100 mW / cm ² pseudo sunlight from a xenon lamp that passed through an AM filter (AM-1.5) using a solar simulator (manufactured by Eihiro Seiki). That is, for the photoelectric conversion elements 1 to 17, current-voltage characteristics were measured at room temperature using an IV tester, and a short circuit current (Jsc), an open circuit voltage (Voc), and a form factor (FF) were obtained. From this, the photoelectric conversion efficiency (η (%)) was determined. The photoelectric conversion efficiency (η (%)) of the photoelectric conversion element was calculated based on the following formula (A).

η = 100 × (Voc × Jsc × FF) / P (A)
Here, P is an incident light intensity [mW · cm ⁻² ], Voc is an open circuit voltage [V], Jsc is a short circuit current density [mA · cm ⁻² ], and FF is a form factor.

  The evaluation results are shown in Table 1.

From Table 1, the hole transport layer contains the aromatic amine derivative A and the hydrocarbon B, the mass mole fraction of B is equal to or less than the mass mole fraction of A, and the molecular weights of A and B are respectively M _W (A ) And M _W (B), the photoelectric conversion element (1) that satisfies all of the following conditions: 400 ≦ M _W (A) ≦ 2000 and 2 ≦ M _W (A) / M _W (B) ≦ 10 -(11) was excellent in photoelectric conversion efficiency compared with the comparative examples (12)-(17) which do not satisfy | fill conditions. In addition, in the photoelectric conversion elements (1) to (9) in which B is an aromatic hydrocarbon having a secondary alkyl group or a tertiary alkyl group, B is an aliphatic hydrocarbon (10) or a primary alkyl group Compared with (11) which is only an aromatic hydrocarbon, the photoelectric conversion efficiency was more excellent.

  From the above results, by using the aromatic amine derivative and hydrocarbon of the present invention for the hole transport layer, the hole transport ability can be improved by promoting the amorphization, leading to the improvement of the photoelectric conversion efficiency. I understood.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Transparent conductive film 3 Barrier layer 4 Sensitizing dye 5 N-type semiconductor 6 Semiconductor layer 7 Hole transport layer 8 Counter electrode 9 Light traveling direction

Claims (4)

Dye-sensitized photoelectric conversion in which a semiconductor layer containing an n-type semiconductor carrying a dye and a solid hole transport layer are provided between a transparent conductive film formed on a substrate and a counter electrode In the element, the hole transport layer contains at least an aromatic amine derivative A having a hole transport ability and a hydrocarbon B, and the mass mole fraction of B is equal to or less than the mass mole fraction of A. , A and B, when the molecular weights are M _W (A) and M _W (B), respectively, the photoelectric conversion device satisfies the following conditions.
400 ≦ M _W (A) ≦ 2000
2 ≦ M _W (A) / M _W (B) ≦ 10   The photoelectric conversion element according to claim 1, wherein the hydrocarbon B is an aromatic hydrocarbon having a secondary alkyl group or a tertiary alkyl group.   The photoelectric conversion element according to claim 1, wherein the n-type semiconductor is titanium oxide.   It has a photoelectric conversion element of any one of Claims 1-3, The solar cell characterized by the above-mentioned.

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