JP2007087772A - Photoelectric conversion element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric conversion element which is low in cost, easy to produce, high in light conversion efficiency and usable as a dye-sensitized solar cell. <P>SOLUTION: The photoelectric conversion element comprises a laminated layer of a transparent electrode layer 1, a semiconductor layer 2, a dye adsorption layer 3 which is made by an adsorption in the semiconductor constituting the semiconductor layer 2, an electrolyte layer 4, and opposing electrode layer 5 in this order. The dye above mentioned is carbon black. In addition, carbon black having functional groups is preferred, and metal oxide semiconductor is preferred as the semiconductor layer 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a photoelectric conversion element that can be used as, for example, a solar cell or an optical sensor. Specifically, the present invention relates to a photoelectric conversion element that can be easily manufactured, and is highly efficient and inexpensive.

  Solar cells, which are clean energy sources, are attracting attention due to tight energy supply and demand and environmental pollution problems. Single crystal silicon, polycrystalline silicon, amorphous silicon, indium copper selenide, or cadmium telluride in inorganic solar cells have been put into practical use as a power source for homes for a long time. However, the manufacturing process of these inorganic solar cells has a large number of processes, requires special equipment, and has a high manufacturing cost. Therefore, development of a cheaper and higher performance next-generation solar cell has been expected.

  In recent years, dye-sensitized solar cells have attracted attention as candidates. Dye-sensitized solar cells have been studied for a long time, but there are problems of dye stability, problems of low conversion efficiency due to low dye adsorption amount, and problems of complex structure due to the use of an electrolyte solution. There were technical problems such as, and so on, and it was difficult to put it into practical use.

  However, in 1991, Gretzell et al. Announced a new type of dye-sensitized solar cell (so-called “Gretzel cell”) with a high conversion efficiency of 7.9% (see Patent Document 1). Since then, research has been conducted energetically all over the world, and some are now being put into practical use.

The Gretzel et al. Solar cell has achieved high efficiency mainly due to the following three points. The first was the development of Ru (ruthenium) complex dyes with a wide light absorption region, and then the use of fine particles of TiO ₂ (titanium oxide) as electrodes to increase the surface area by increasing the surface area of the dye. And assembled cells using them.

  However, Ru is a so-called rare metal and is expensive and resource-constrained. Therefore, organic dyes that do not contain Ru, such as polyene dyes and coumarin dyes, have been studied, and other dyes that can provide inexpensive and high-performance dye-sensitized solar cells are required. .

Japanese Patent Laid-Open No. 01-220380

  Accordingly, an object of the present invention is to provide a photoelectric conversion element that can be used as a dye-sensitized solar cell, which is inexpensive and easy to manufacture but has high light conversion efficiency.

The above object is achieved by the present invention described below. That is, the present invention is a photoelectric conversion element in which a transparent electrode layer, a semiconductor layer, a dye adsorption layer in which a dye is adsorbed on a semiconductor constituting the semiconductor layer, an electrolyte layer, and a counter electrode layer are laminated in this order. In addition, the photoelectric conversion element is characterized in that the dye is carbon black.
That is, the present invention is characterized in that carbon black is used as a dye in a so-called dye-sensitized solar cell (hereinafter referred to as “sensitizing dye”).

  The application of the carbon-based material in the dye-sensitized solar cell has been used as a sensitizing dye although there is an example in which activated carbon is used as a counter electrode from the expectation of the size of the specific surface area (see Japanese Patent Application Laid-Open No. 2003-297446). There are no examples, and there has never been such an idea. Further, since the carbon-based material is a black pigment and has excellent light resistance and chemical stability, it can be expected that the properties are reflected in the dye-sensitized solar cell. Furthermore, since the carbon-based material is black, light having a wide wavelength from a short wavelength region to a long wavelength region may be used. Among the carbon-based materials, particularly, carbon black used in the present invention has already established an inexpensive mass production technique, and can solve the problem of resource limitation of sensitizing dyes.

As a result of intensive studies to apply the carbon-based material to the sensitizing dye of the dye-sensitized solar cell, carbon black is another carbon-based material such as carbon nanotube and fullerene (C ₆₀ ) among the carbon-based materials. It has been found that it exhibits superior performance.

  In general dye-sensitized solar cells, metal oxides such as titanium oxide, zinc oxide, and tin oxide are mostly used for semiconductors that carry sensitizing dyes. In this case, the junction between the dye and the semiconductor is an important factor that determines the performance of the solar cell. That is, not only the physical contact but also the chemical bonding of both can achieve the stability of dye support and the reduction in current loss. In the case of the present invention using carbon black as a sensitizing dye, a chemical treatment is performed to add a functional group (particularly a carboxyl group), and the surface is chemically modified to facilitate loading on the semiconductor surface. Can be preferred.

  In the present invention, the semiconductor layer is preferably composed of a metal oxide semiconductor (particularly tin oxide). In addition, the semiconductor layer preferably has a porous structure so as to ensure its surface area and to adsorb more carbon black as a sensitizing dye.

  According to the present invention, it is possible to provide a photoelectric conversion element that can be used as a dye-sensitized solar cell that is inexpensive and easy to manufacture but has high light conversion efficiency.

Hereinafter, the photoelectric conversion element of the present invention will be described in detail.
In FIG. 1, the schematic cross section of the photoelectric conversion element which is an example of this invention is shown. In FIG. 1, reference numeral 1 is a transparent electrode layer, reference numeral 2 is a semiconductor layer, reference numeral 3 is a dye adsorption layer, reference numeral 4 is an electrolyte layer, and reference numeral 5 is a counter electrode layer. By connecting a negative (−) terminal to the transparent electrode layer 1 and a positive (+) terminal to the counter electrode 5, a predetermined electromotive force can be taken out between the two terminals.

In the photoelectric conversion element shown in FIG. 1, a semiconductor layer in which a dye is supported on a transparent electrode such as ITO (in the present invention, a region in which a dye is supported is separately named “dye adsorption layer”. In the present invention, the dye-adsorbing layer 3 in this dye-sensitized solar cell has the same structure as that of a general dye-sensitized solar cell having a structure in which the electrolyte layer is sealed at the counter electrode. Carbon black is used as a dye.
Hereinafter, the description will be divided into each layer.

(Transparent electrode layer 1)
As the transparent electrode layer 1, a material having high transparency at the wavelength of light to be used and good electrical conductivity is used. In general dye-sensitized solar cells, an ITO (tin-doped indium oxide) film, an FTO (fluorine-doped indium oxide) film, or a glass substrate on which a composite film thereof is formed is often used. Although it can use suitably, it is not specifically limited. Of course, the glass substrate is not an indispensable member, and the transparent electrode layer 1 may be a conductive layer such as ITO or FTO. You can also serve as

(Semiconductor layer 2)
As a material for the semiconductor layer 2, metal oxides such as tin oxide, titanium oxide, and zinc oxide can be easily formed into fine particles, and the specific surface area is increased as a porous structure by forming a layer using the fine particles. This is preferable because it can be performed at low cost. Although tin oxide is particularly suitable, it is not particularly limited. As long as fine particles are not used, a single semiconductor or a compound semiconductor other than a metal oxide may be used.

  In addition, the fine particles in the “micronization” referred to herein indicate a range of about 10 nm to 10 μm in particle size. The average particle size of the metal oxide semiconductor fine particles is preferably in the range of 10 nm to 100 nm, more preferably in the range of 10 nm to 30 nm.

  The thickness of the semiconductor layer 2 is preferably about 0.1 μm to 100 μm, more preferably about 10 μm to 20 μm, together with the dye adsorption layer 3 described later. If the thickness is less than 0.1 μm, the entire transparent electrode cannot be covered with the semiconductor layer 2 and current may leak. On the other hand, if the thickness exceeds 100 μm, the electrical resistance value of the semiconductor layer 2 becomes too high. Current may not flow, which is not preferable.

As the metal oxide semiconductor can be used as a material of the semiconductor layer 2, for _{example, Fe 2 O 3, Cu 2} O, In 2 O 3, WO 3, Fe 2 TiO 3, PbO, V 2 O 5, FeTiO 3, Bi ₂ O ₃ , Nb ₂ O ₃ , SrTiO ₃ , ZnO, BaTiO ₃ , CaTiO ₃ , KTaO ₃ , ZrO _{2 and the} like can be mentioned. Moreover, Si is mentioned as a single semiconductor, and GaAs, CdSe, GaP, CdS, ZnS etc. can be mentioned as compound semiconductors other than a metal oxide.

  The method for forming the semiconductor layer 2 is not particularly limited, and a conventionally known method may be used as it is. When forming using a metal oxide semiconductor in the form of fine particles, the fine particles are added to a solvent such as water, acetone or ethylene glycol, pasted, applied by a method such as spin coating or squeegee method, and dried. The method of forming a layer can be mentioned.

(Dye adsorption layer 3)
The dye adsorption layer 3 is a layer in which a dye (sensitizing dye) is adsorbed on the semiconductor constituting the semiconductor layer 2. The dye adsorption layer 3 is preferably formed by forming the semiconductor layer 2 and adsorbing a sensitizing dye thereto. A specific adsorption method will be described later.
In the present invention, carbon black is used as the sensitizing dye to be adsorbed. The carbon black which is a main component in the present invention will be described.

Carbon black is in the form of particles and is formed of an aggregate of carbon microcrystals. The particle size of carbon black has a distribution, and the average particle size is about 10 to 500 nm although it depends on the type. Further, several particles gather to form an aggregate called a structure.
Carbon black, on the other hand, has been studied from the viewpoint of controlling conductivity and controlling dispersibility in rubber and solvent, and is known to be capable of various surface treatments and modifications.

By the way, in general, in the dye-sensitized solar cell, the electron transfer between the sensitizing dye and the semiconductor is an important factor that determines the performance as the battery. Moreover, it can be expected that the stronger the bond between the two, the greater the amount of dye supported per unit area of the semiconductor surface. In the Gretzel cell, the carboxyl group of the Ru dye and the OH group of the TiO ₂ (semiconductor) surface have ester-like bonds, and research is also conducted from the viewpoint of modifying the surface of the TiO ₂ fine particles and strengthening the bond. (See Y. Wada, K.-i. Tomita, K. Murakoshi and S. Yanagida, J. Chem. Res. (S), 320 (1996)).

In the present invention, it is preferable to chemically modify the carbon black and introduce some functional group to the surface of the carbon black particles. Since the surface of carbon black is rich in reactivity, it is possible to add various functional groups. Adsorption to a semiconductor can be strengthened by introducing some functional group. Specific introduced functional groups, -COOH, -COX (X is a halogen atom), - OH, -CHO, -NH 2, -X (X is a halogen atom), - SH, and -NCO like Can be mentioned. It is also possible to introduce another functional functional group by reaction with these added functional groups.

  Among these functional groups, it is particularly preferable to introduce a carboxyl group (—COOH) into carbon black. By introducing a carboxyl group, for example, an ester-like bond can be formed with a semiconductor surface such as titanium oxide or tin oxide, and smooth electron transfer, stable loading, and increased loading can be realized.

  It is desirable to introduce these functional groups until the water dispersibility is sufficiently improved. Specifically, in the evaluation method by X-ray photoelectron spectroscopy described in JP-A-11-92703, the surface carboxyl group carbon concentration is preferably 0.3% or more, and 0.4% or more. More preferably.

  As described above, it is preferable to form the semiconductor layer once, and then adsorb carbon black on the semiconductor layer to make the adsorbed region the dye adsorbing layer 3. As a method for adsorbing carbon black on an already formed semiconductor layer, a method of adsorbing carbon black generated in a gaseous state directly on the semiconductor layer can be adopted, but it is more efficiently adsorbed. For this, it is preferable to use a method in which carbon black is dispersed in some dispersion medium to prepare a dispersion, and this is in contact with the semiconductor layer. According to this method, it is easy to increase the amount of adsorption, it is extremely simple, excellent in production suitability, and can greatly reduce the production cost.

For example, water, ethanol, ethylene glycol, glycerin, or the like can be used as a dispersion medium used for the preparation of the carbon black dispersion, but is not limited thereto. Moreover, you may use these multiple types together.
A known dispersion accelerator such as a surfactant can be added to the dispersion to improve the dispersibility of the carbon black. It is also possible to add various other additives.

  The concentration of carbon black in the dispersion is not particularly limited, but is generally selected from the range of 0.01 to 10 g / l, and preferably in the range of 0.1 to 1 g / l. If the concentration is too low, it is difficult to secure the amount of adsorption to the semiconductor. Conversely, if the concentration is too high, the dispersion stability of the carbon black in the dispersion is lowered, which is not preferable.

  In order to disperse the carbon black in the dispersion medium, manual stirring with a spatula or shaking may be used. However, in order to ensure stable and homogeneous dispersibility, it is preferable to apply known mechanical stirring. For mechanical stirring, a general method such as a method using a stirring blade or a method using a stirring pump may be used, but in order to further improve the dispersion stability, a powerful stirrer such as an ultrasonic stirrer, a homogenizer, or a double jet stirrer is used. Is preferably used.

  When a functional group, particularly a hydrophilic functional group such as a carboxyl group, is introduced into the carbon black and an aqueous medium such as water is used as a dispersion medium, the above-mentioned stirring and dispersion promoting means such as a dispersion accelerator are used. Even if not applied, sufficient dispersion stability may be obtained, in which case it is not necessary to employ them.

  Examples of the method for bringing the dispersion into contact with the semiconductor include a dropping method in which the dispersion is directly dropped onto a semiconductor layer formed in an excessive thickness, a spraying method in which the semiconductor layer is applied by spraying, and an immersion method in which the dispersion is immersed in the dispersion. The immersion method can be used because the dispersion liquid and the semiconductor can be kept in contact with each other for a long time, and the semiconductor layer can be penetrated deeper and more carbon black can be adsorbed. Most preferred. In the case of the immersion method, it may be left as it is during the immersion treatment, but it is preferable to stir the dispersion by the above-mentioned various methods in order to ensure the dispersion stability of the dispersion.

Although there is no restriction | limiting in particular as immersion time in the case of an immersion method, In order to make more carbon black adsorb | suck to a semiconductor more reliably, it is desired to make it some length. The immersion time depends on the concentration of carbon black in the dispersion, the stirring state during the immersion treatment, the environmental temperature, and the like. Preferably, it is more than 10 hours.
The semiconductor layer after being in contact with the dispersion liquid is washed with the dispersion liquid as necessary and then dried to form the dye adsorption layer 3 on which carbon black is adsorbed on or near the surface.

(Electrolyte layer 4)
The electrolyte layer 4 is a layer in which an electrolyte is sealed in a cell, and is generally hermetically sealed so that the sealed electrolyte does not leak (except in the case of a solid electrolyte). There is no restriction | limiting in particular in the structure of the said electrolyte layer 4, A conventionally well-known structure can be selected as it is as an electrolyte layer in a dye-sensitized solar cell conventionally.

  In the case of a conventionally known dye-sensitized solar cell, an iodine solution is often used as the electrolyte to be used, but it is not particularly limited in the present invention. Recently, not only liquid electrolytes but also solid electrolytes, room-temperature molten salts, gelling agents, etc. are used in the electrolyte layer, and solid-state (pseudo-solidification) dye-sensitized solar cells are being studied. There is no problem in applying the above configuration to the present invention.

  When the electrolyte is a liquid, a gap is provided between the electrolyte layer 4 and the counter electrode 5, and the electrolyte layer 4 is formed so as to enclose the electrolyte in the gap. At this time, a spacer is previously provided between the electrolyte layer 4 and the counter electrode 5 in order to prevent a contact between the electrolyte layer 4 and the counter electrode 5 and to secure a gap in which the electrolyte is enclosed. It is preferable to enclose the electrolyte.

(Counter electrode 5)
In the case of a conventionally known dye-sensitized solar cell, platinum is often used as the counter electrode 5, but is not particularly limited in the present invention. Since the counter electrode 5 is not required to be transparent, conventionally known various metals and other conductive materials can be used as they are. Of course, the same material as that of the transparent electrode 1 described above may be used. Recently, carbon-based materials such as activated carbon, conductive polymers, and the like have been studied as material candidates. Further, the counter electrode 5 may be used as a thick film to serve as a substrate, or a separate substrate may be provided.

  Although the photoelectric conversion element of the present invention has been described above, the configuration of the present invention is not limited to the above configuration.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limited to these Examples.
[Example 1]
<Manufacture of photoelectric conversion elements>
In Example 1, a photoelectric conversion element having a structure shown in FIG. 2 that can be used as a solar cell was manufactured. Here, FIG. 2 is a schematic cross-sectional view of the photoelectric conversion element of Example 1. In FIG. 2, the code | symbol 6 represents a glass substrate, the code | symbol 7 is a spacer, and the codes | symbols 1-5 are the same as FIG.

(1: Carbon black carboxylation: synthesis of carbon black carboxylic acid)
Add 3 g of carbon black powder (REGAL (registered trademark) 330, manufactured by Cabot Corporation, average particle size 25 nm) to 50 ml of concentrated nitric acid (60% by weight aqueous solution, manufactured by Kanto Chemical Co., Ltd.), reflux at a temperature of 120 ° C. for 50 hours, Black carboxylic acid was synthesized. The above reaction scheme is shown in FIG. In FIG. 3, the carbon black portion is represented by a hollow ellipse.

  After returning the temperature of the solution to room temperature, the mixture was centrifuged for 10 minutes under the condition of 12000 rpm, and the supernatant and the precipitate were separated. The collected precipitate was dispersed in 25 ml of pure water and centrifuged again at 12000 rpm for 10 minutes to separate the supernatant and the precipitate. About 25 ml of pure water was added to the precipitate, and the mixture was centrifuged for 6 hours under the condition of 18000 rpm, and the brown supernatant was recovered.

Among the above three centrifugation operations, when the infrared absorption spectrum of the dried solid product of the supernatant collected in the last operation was measured, the absorption at 1734 cm ⁻¹ characteristic for the carboxyl group was confirmed. From this, it was found that a carboxyl group was introduced into carbon black by reaction with nitric acid. Further, the supernatant liquid is brown, and this is considered to be a result of the addition of a sufficiently hydrophilic carboxyl group to carbon black and the good dispersibility. Hereinafter, it is referred to as carbon black carboxylic acid.

(2: Production of transparent electrode layer with semiconductor layer)
a) Preparation of tin oxide paste 1.35 g of tin oxide (diameter, average particle size 18.3 nm, specific surface area 47.2 m ² / g, manufactured by Aldrich) was suspended in 4 ml of pure water, and 1 ml of Triton X100 (30%) And mixed well in a mortar. Further, 0.1 ml of acetylacetone and 0.135 g of polyethylene glycol (number average molecular weight 20000) were added and mixed in a mortar for 2 hours to prepare a tin oxide paste.

(3: Formation of tin oxide semiconductor layer)
The obtained tin oxide paste was applied to the ITO side surface of an ITO glass substrate (a glass plate with an ITO film formed on one side; 10Ω / □) so as to have a coating film thickness of 50 μm by a squeegee method. After drying at room temperature, the film was baked for 30 minutes in an electric furnace at a temperature of 450 ° C. to obtain a tin oxide film (semiconductor layer) having a thickness of about 5 μm. The ITO in the ITO glass substrate corresponds to the transparent electrode layer 1 in FIG. 2, and the glass portion that carries the transparent electrode layer 1 corresponds to the glass substrate 6a.

(4: Formation of dye adsorption layer: support of carbon black carboxylic acid on tin oxide semiconductor layer)
A carbon black dispersion was prepared by dispersing 5 mg of carbon black carboxylic acid in 10 ml of pure water. The ITO glass substrate on which the tin oxide semiconductor layer was formed was immersed in this carbon black dispersion for about 12 hours, and carbon black carboxylic acid was adsorbed on the tin oxide semiconductor layer to form a dye adsorption layer.

  Then, the said ITO glass substrate was taken out and dried, and it used as a semiconductor part electrode (The glass substrate 6a, the transparent electrode layer 1, the semiconductor layer 2, and the pigment | dye adsorption layer 3) of the cell of a photoelectric conversion element. In the tin oxide semiconductor layer, the region where the carbon black carboxylic acid is adsorbed corresponds to the dye adsorbing layer 3 in FIG. 2, and the remaining portion corresponds to the semiconductor layer 2.

(5: Production of counter electrode)
Platinum was deposited by ion dc sputtering on the ITO side surface of an ITO glass substrate (glass plate with ITO film formed on one side; 10Ω / □), and used as a counter electrode. The layer on which platinum is deposited corresponds to the counter electrode layer 5 in FIG. 2, and the ITO glass substrate corresponds to the glass substrate 6b.

(6: Preparation of electrolyte solution)
The electrolyte solution constituting the electrolyte layer was prepared by adding acetonitrile (20 vol%) to 10 ml in total with respect to 0.78315 g of tetrapropylammonium iodide, 0.05076 g of iodine, and 10.568 g of ethylene carbonate (80 vol%). Obtained by mixing well.

(7: Cell assembly)
Using the semiconductor part electrode (glass substrate, transparent electrode layer, semiconductor layer and dye adsorption layer), the counter electrode, and the electrolyte solution of the cell of the photoelectric conversion element obtained as described above, as follows. Thus, a cell-like photoelectric conversion element was assembled.

A slight gap is provided on the surface of the semiconductor part electrode on which the dye adsorption layer 3 is formed, and the counter electrode is overlapped so that the surface on which platinum is deposited (the counter electrode layer 5) is opposed to the gap. The electrolyte solution was impregnated. At that time, as shown in FIG. 2, a sill is formed on the surface of the counter electrode layer 5 with a polykapton tape (thickness of about 50 μm) as a spacer 7 so that the two plates are not in direct contact and short-circuited. Oita. A region where the gap between the dye adsorbing layer 3 and the counter electrode layer 5 is impregnated with the electrolyte solution corresponds to the electrolyte layer 4 in FIG.
The photoelectric conversion element of Example 1 was manufactured as described above.

<Performance evaluation>
(Light response test)
The voltage and current responses of the obtained photoelectric conversion element of Example 1 to light were measured. As a light source, a halogen lamp (manufactured by Hayashi Watch Industry Co., Ltd., Lumina Ace) was used, and as a current voltage monitor, a digital multimeter (2000 manufactured by KEITHLEY) was used.

The results are shown graphically in FIG. Here, the graph of FIG. 4 shows the results of measuring the open circuit voltage generated between the transparent electrode 1 and the counter electrode 5 by turning on and off the halogen lamp in time series. The halogen lamp is turned on after 30 seconds and turned off after 70 seconds.
As can be seen from the graph of FIG. 4, by applying the halogen lamp (incident light: about 35 mW / cm ² ), the open-circuit voltage of the photoelectric conversion element of this example is output by 230 mV.

(Power generation experiment)
Further, the photoelectric conversion element of Example 1 was subjected to a power generation experiment under the following conditions. Connect this photoelectric conversion element to a resistor of 1Ω to 1MΩ, and shine light with the same light source as the optical response test (incident light: about 35mW / cm ² ), then apply the current flowing at that time and the resistor The measured voltage was measured using a digital multimeter (2000 manufactured by KEITHLEY).

The results are shown graphically in FIG. Here, the graph of FIG. 5 is a graph which shows a current-voltage characteristic about the result obtained by the power generation experiment performed on the said conditions. From the graph shown in FIG. 5, the photoelectric conversion element of this example has an open circuit voltage of 190 mV and a maximum output of 14 μW / cm ² (when the electromotive voltage is 93 mV and the current is 0.15 mA / cm ² ). confirmed.
From the above results, it was confirmed that the photoelectric conversion element of this example was generated by light irradiation.

(Measurement of photocurrent action spectrum)
About the photoelectric conversion element of Example 1, the photocurrent action spectrum at the time of monochromatic light incidence was measured. FIG. 6 is a graph showing the photoelectric conversion efficiency IPCE (incident photo to current conversion efficiency) per incident monochromatic light. At this time, the exposure intensity was 50 μW / cm ² and the measurement area was 0.25 cm ² .

Here, IPCE will be briefly described. IPCE is the percentage (%) of the number of photons converted into electrons that are incident at a certain wavelength, and the cell (photoelectric conversion element) while continuously changing the wavelength of the irradiated light. , Solar cell).
IPCE is expressed by the following equation.

Here, J _SC (mA / cm ² ) is a short-circuit current, λ (nm) is the wavelength of incident light, and Φ (W / cm ² ) is incident light flux (incident light intensity per unit area).
From the graph of FIG. 6, it can be seen that IPCE is 90% or more near λ = 400 nm, and high efficiency is exhibited under the measurement conditions.

[Reference Examples 1-3]
A photoelectric conversion element using carbon nanotubes and fullerene (C ₆₀ ), which are the same carbon-based substance, instead of carbon black carboxylic acid as a sensitizing dye, was prepared in the same manner as in Example 1. An element in which no sensitizing dye was adsorbed on the semiconductor layer was also produced in the same manner as in Example 1.

(Reference Example 1)
Fullerene (C ₆₀₎ itself would hardly adsorbed on the tin oxide semiconductor layer, a fullerene PCBM a functional group is added to the surface adsorptive (C ₆₀₎ is increasing ([6,6] -phenyl C ₆₁ butyric acid methyl ester) was used. Specifically, an ITO glass substrate with a tin oxide semiconductor layer formed in the same manner as in Example 1 was immersed in a toluene dispersion (1% by mass) of PCBM for about 12 hours, and the tin oxide semiconductor layer was immersed in the tin oxide semiconductor layer. PCBM was adsorbed. Then, this was taken out, dried, used as a semiconductor part electrode of a cell of a photoelectric conversion element, and the photoelectric conversion element of Reference Example 1 was obtained in the same manner as Example 1.

(Reference Example 2)
On the other hand, carbon nanotubes are also difficult to adsorb on the tin oxide semiconductor layer as they are. Therefore, carboxylic acid was added to the surface of the carbon nanotube to enable adsorption to the tin oxide semiconductor layer. In order to introduce a carboxyl group into the carbon nanotube, it may be refluxed with an acid having an oxidizing action. This operation is relatively easy and is preferable because a carboxyl group rich in reactivity can be added.

  Specifically, 30 mg of single-walled carbon nanotube powder (purity 90%, average diameter 1.1 nm, length 0.5 to 100 μm; manufactured by Aldrich) is added to 20 ml of concentrated nitric acid (60% by mass aqueous solution, manufactured by Kanto Chemical). The carbon nanotube carboxylic acid was synthesized by refluxing at a temperature of 120 ° C. for 1.5 hours. After returning the temperature of the solution to room temperature, centrifugation was performed at 5000 rpm for 15 minutes to separate the supernatant and the precipitate. The collected precipitate was dispersed in 10 ml of pure water, and centrifuged again at 5000 rpm for 15 minutes to separate the supernatant and the precipitate (the washing operation was performed once). This washing operation was further repeated 5 times, and finally the precipitate was collected.

An infrared absorption spectrum of the collected precipitate was measured. For comparison, the infrared absorption spectrum of the used multi-walled carbon nanotube raw material itself was also measured. When both spectra were compared, absorption of 1735 cm ⁻¹ characteristic of carboxylic acid, which was not observed in the single-walled carbon nanotube raw material itself, was observed in the precipitate. From this, it was found that a carboxyl group was introduced into the carbon nanotube by reaction with nitric acid. That is, it was confirmed that the precipitate was carbon nanotube carboxylic acid.
Further, when the collected precipitate was added to neutral pure water, it was confirmed that the dispersibility was good. This result supports the result of the infrared absorption spectrum that a hydrophilic carboxyl group was introduced into the carbon nanotube.

  Next, an ITO glass substrate with a tin oxide semiconductor layer formed in the same manner as in Example 1 was immersed in an aqueous dispersion (1% by mass) of nanotube carboxylic acid for about 24 hours, and nanotubes were immersed in the tin oxide electrode. Carboxylic acid was adsorbed. Then, this was taken out, dried and used as a semiconductor part electrode of a cell of a photoelectric conversion element, and the photoelectric conversion element of Reference Example 2 was obtained in the same manner as in Example 1.

(Reference Example 3)
Further, as Reference Example 3, an element of Reference Example 3 was obtained in the same manner as in Example 1 except that no sensitizing dye was adsorbed to the ITO glass substrate on which the tin oxide semiconductor layer was formed.

A power generation experiment was performed on the photoelectric conversion elements of Reference Examples 1 and 2 and the element of Reference Example 3 thus manufactured under the same conditions as in Example 1.
The results are shown graphically in FIG. Here, the graph of FIG. 7 is a graph showing the results of the current-voltage characteristics obtained by the power generation experiment performed under the same conditions as in Example 1 for Reference Examples 1 to 3 together with the results of Example 1. From the graph shown in FIG. 7, it can be seen that the output of the photoelectric conversion element of Example 1 using carbon black carboxylic acid as a sensitizing dye is the highest.

  On the other hand, the photoelectric conversion elements of Reference Examples 1 and 2 using PCBM or carbon nanotube carboxylic acid as a sensitizing dye have poor output, but the output of Reference Example 3 in which the sensitizing dye is not adsorbed on the semiconductor layer is almost output. As compared with the fact that is not detected, it can be seen that it works as a sensitizing dye.

  As described above, the photoelectric conversion element of the present invention can be easily manufactured, and can be used as a solar cell from the viewpoint of high light efficiency at a low cost. It is extremely useful as various photoelectric conversion elements.

It is a schematic cross section of the photoelectric conversion element which is an example of this invention. 1 is a schematic cross-sectional view of a photoelectric conversion element of Example 1. FIG. It is a scheme of a carboxyl group addition reaction to carbon black. 3 is a graph showing a result of an optical response test of the photoelectric conversion element of Example 1. 3 is a graph showing a power generation experiment result of the photoelectric conversion element of Example 1. 6 is a graph showing the measurement result of the photocurrent action spectrum of the photoelectric conversion element of Example 1. It is a graph which shows the electric power generation experiment result of the photoelectric conversion element of Example 1 and Reference Examples 1-3.

Explanation of symbols

  1: Transparent electrode layer 2: Semiconductor layer 3: Dye adsorption layer 4: Electrolyte layer 5: Counter electrode layer 6: Glass substrate 7: Spacer

Claims (6)

A photoelectric conversion element comprising a transparent electrode layer, a semiconductor layer, a dye adsorption layer formed by adsorbing a dye on a semiconductor constituting the semiconductor layer, an electrolyte layer, and a counter electrode layer in this order, wherein the dye is carbon A photoelectric conversion element characterized by being black. The photoelectric conversion element according to claim 1, wherein the carbon black is a carbon black having a functional group. The photoelectric conversion element according to claim 2, wherein the functional group is a carboxyl group. The photoelectric conversion element according to claim 1, wherein the semiconductor layer is made of a metal oxide semiconductor. The photoelectric conversion element according to claim 1, wherein the semiconductor layer is made of tin oxide. The photoelectric conversion element according to claim 1, wherein the semiconductor layer has a porous structure.

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