JP2003168493A - Dye sensitizing solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dye sensitizing solar cell that has high open-voltage without spoiling light fastness. <P>SOLUTION: The dye sensitizing solar cell, has a dye coupling electrode with a dye adsorbed on its surface, a counter electrode forming a pair with the dye coupling electrode, and an electrolyte containing body which makes contact with these electrodes. The dye sensitizing solar cell includes an urea derivative shown by formula I in the electrolyte containing body. In the formula R<SB>1</SB>to R<SB>4</SB>are a hydrogen atom, a halogen atom, or an alkyl group, alkoxyl group, acyl group, carbamoyl group, nytril group, amino group, amide group, phospholyl group, phosphinoyl group, thiophospholyl group, phosphanyl group, thiocarbamoyl group, thioalkyl group, thioamino group, silyl group, silanol group, sulfonyl group, germyl group, or stannyl group which may have the substitution group, respectively. R<SB>2</SB>and R<SB>3</SB>may be connected and they may form an annular structure. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dye-sensitized solar cell including a dye-bonded electrode having a dye bonded thereto, and more particularly to improvement of an electrolyte-containing material used therein.

[0002]

2. Description of the Related Art Wet solar cells including dye-sensitized oxide semiconductor electrodes have been conventionally known. Nature,
261 (1976) p.402, an oxide obtained by adsorbing rose bengal as a sensitizing dye on the surface of a sintered body disk formed by compression molding zinc oxide powder and sintering at 1300 ° C. for 1 hour. A solar cell using a semiconductor electrode has been proposed.

However, according to the current / voltage curve of the solar cell in the proposal, the current value when the electromotive voltage is 0.2 V is about 25 μA, which is very small.

By the way, researches on solar cells have been further advanced in recent years, and a porous titanium dioxide film is formed on a transparent conductive film, Ru dipyridyl complex is adsorbed on this surface as a sensitizing dye, and iodine is used as an electron mediator. A dye-sensitized wet type solar cell has been reported by Gretzell et al. (Japanese Patent Application Laid-Open No. 01-220380).

In the solar cell proposed by Gretzell et al., The dye excited by absorbing light supplies electrons to titanium oxide, the electrons move from the counter electrode to iodine, and the reduced iodide ion becomes dye. It gives electrons back to the original and completes the cycle. Such a dye-sensitized solar cell can theoretically be expected to have high efficiency.
It has been reported that an efficiency of about% has been obtained. Further, such a solar cell is considered to be very advantageous in terms of cost, as compared with a solar cell using a silicon semiconductor, because the oxide semiconductor and the dye used therein are both inexpensive. There is.

[0006]

However, the above-described conventionally known dye-sensitized solar cells have an open circuit voltage of about 0.4 to 0.5 V when an actual cell is manufactured. Therefore, as one of means for improving the open-circuit voltage, it has been proposed to include 4-tert-butylpyridine as a voltage improver in the electrolytic solution (Japanese Patent Application Laid-Open No. 2 (1999) -211 (1999)).
001-76772).

However, 4-tert-butylpyridine has poor stability itself and may weaken the bond between the dye and titanium oxide, so that the light resistance of the solar cell with time deteriorates. . Also, 4-
tert-Butylpyridine requires distillation for purification and tends to be expensive.

The present invention was devised under these circumstances, and an object thereof is to provide a dye-sensitized solar cell having a high open circuit voltage without impairing light resistance.

[0009]

In order to solve such a problem, the present invention provides a dye-bonding electrode having a dye adsorbed on the surface thereof, a counter electrode paired with the dye-bonding electrode, and contacting these electrodes. A dye-sensitized solar cell having an electrolyte-containing body, wherein the electrolyte-containing body is configured to include a urea derivative that acts to improve voltage.

In a preferred embodiment of the present invention, the urea derivative is composed of a compound represented by the following structural formula (I).

[Chemical 2] In the structural formula (I), R ₁ , R ₂ , R ₃ , and R ₄ are each a hydrogen atom, a halogen atom, or an alkyl group, an alkoxyl group, an acyl group, or carbamoyl, each of which may have a substituent. Group, nitrile group, amino group, amide group, phosphoryl group, phosphinoyl group, thiophosphoryl group, phosphanyl group, thiocarbamoyl group, thioalkyl group, thioamino group, silyl group, silanol group, sulfonyl group, germyl group, stannyl group, R ₁ , R
₂ , R ₃ and R ₄ may be the same or different. Further, R ₂ and R ₃ may be connected to each other to form a ring structure.

In the present invention, by incorporating the urea derivative into the electrolyte-containing body, although the specific mechanism has not been theoretically understood, the open circuit voltage of the dye-sensitized solar cell is 0.1 to 0. It can be increased by about 2V.
Also, when these are mixed, the light resistance of the battery is not impaired. This makes it possible to provide a dye-sensitized solar cell capable of maintaining a high conversion efficiency for a long period of time.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the dye-sensitized solar cell of the present invention will be described in detail below.

FIG. 1 shows a typical constitutional example of the dye-sensitized solar cell of the present invention. As shown in FIG. 1, the dye-sensitized solar cell 1 of the present invention has a structure in which two electrodes 10 and 30 are opposed to each other with an electrolyte-containing body 5 interposed therebetween. One of the two electrodes 10 is a dye-bonding electrode 10 provided with a dye, which is, for example,
A substrate 20 and a transparent conductive layer 22 formed thereon,
The oxide semiconductor film 4 formed on the surface of the conductive layer 22.
And the dye film 7 bonded to the surface of the oxide semiconductor film.

The essential part of the present invention is that the electrolyte-containing body 5 contains a urea derivative having a function of improving the voltage. Whether or not it corresponds to the configuration of “having the function of improving the voltage” of the present invention here is judged by whether or not the voltage improving effect can be confirmed by the presence or absence of the addition of the urea derivative. As the urea derivative used in the present invention, a compound represented by the following structural formula (I) is particularly preferable.

[0015]

[Chemical 3] In the above structural formula (I), R ₁ , R ₂ , R ₃ , and R ₄ are each a hydrogen atom, a halogen atom, or an alkyl group, an alkoxyl group, an acyl group, which may have a substituent, respectively. Carbamoyl group, nitrile group, amino group, amide group, phosphoryl group, phosphinoyl group, thiophosphoryl group, phosphanyl group, thiocarbamoyl group, thioalkyl group, thioamino group, silyl group, silanol group, sulfonyl group, germyl group, stannyl group , R ₁ , R
₂ , R ₃ and R ₄ may be the same or different. Further, R ₂ and R ₃ may be connected to each other to form a ring structure.

Further preferred examples [1] to [30] of the compound structure of the urea derivative are shown in Table 1 below as R ₁ , R ₂ , R ₃ and
And R ₄ are shown explicitly.

[0017]

[Table 1] In addition, the compound No. shown in Table 1 was used. Each of [8] to [10] is one in which R ₂ and R ₃ in the structural formula (I) are linked to form a cyclic structure. That is, compound No. [8] is represented by the following structural formula * 1).

[Chemical 4]

Further, the compound No.

[9] is represented by the following structural formula * 2).

[Chemical 5]

Further, the compound No. [10] is represented by the following structural formula * 3).

[Chemical 6]

The urea derivative preferably used in the present invention includes urea, methylurea, 1,3-dimethylurea, 1,
1-dimethylurea, butylurea, phenylurea, biuret, barbituric acid, uric acid, 1,3-dimethyl-2-
Imidazolidinone, allylurea, N-benzylurea, N, N
&#0; -bishydroxymethylurea, 1,3-bistrimethylsilylurea, 1,3-dibutylurea, formylurea,
Preferred examples include 1,1,3,3-tetramethylurea and o-tolylurea. Among these, biuret, barbituric acid, uric acid, and 1,3-dimethyl-2-imidazolidinone are particularly preferable.

The content of such a urea derivative in the electrolyte-containing body is adjusted to achieve the effect of the present invention.
It is preferably 0.001 to 1 mol / L, and particularly preferably 0.01 to 0.5 mol / L.

The above-mentioned urea derivatives may be used not only in one kind but in combination of plural kinds.

The electrolyte-containing body 5 containing such a urea derivative has a function of transferring and receiving electrons to exert the function of the battery, and the state thereof is so-called liquid state, solid state, molten salt state. (Molten salt such as imidazolium salt: 100% electrolyte), pseudo-solid state (gelled with a gelling agent, etc.), or the like.

Used in electrolyte-containing body 5 in liquid state
A so-called redox electrolyte is used as the electrolyte.
And are preferred. As a redox electrolyte, I^-/ I₃ ^-
System, Br^-/ Br₃ ^-System, quinone / hydroquinone system, etc.
Is mentioned. Such redox electrolytes have traditionally been
It can be obtained by known methods, for example I^-/ I₃ ^-
The system electrolyte is a mixture of iodine ammonium salt and iodine.
Can be obtained by doing. Also, contains electrolyte
As a solvent used for producing the body 5, an electrification
Biologically inert substances such as acetonitrile, propylene
Organic solvents such as ren carbonate and ethylene carbonate
It may be an agent.

Next, the dye-bonding electrode 10 including a dye will be described. This is, for example, as described above, the substrate 20, the transparent conductive layer 22 formed thereon, and the oxide semiconductor film 4 formed on the surface of the conductive layer 22.
And the dye film 7 bonded to the surface of the oxide semiconductor film.

The substrate 20 is not particularly limited as long as it is a light transmissive substrate, and for example, a glass substrate, a transparent resin substrate, an inorganic transparent crystal body or the like is used.

As the transparent conductive layer 22, for example, In
A metal oxide conductor such as ₂ O ₃ or SnO ₂ is preferably used.

As the oxide semiconductor material forming the oxide semiconductor film 4, various known materials are used. Specifically, Ti, Nb, Zn, Sn, Zr, Y, La, Ta
In addition to transition metal oxides such as SrTiO ₃ , CaTiO ₃
And other perovskite-based oxides. The oxide semiconductor material forming the oxide semiconductor film 4 is preferably as fine particles as possible, and its average particle diameter is 200 nm.
It is preferably 30 nm or less. For preferred specific manufacturing examples, refer to Examples below.

A dye film 7 is formed on the oxide semiconductor film 4. The dye film 7 is preferably formed on the oxide semiconductor film 4 so as to chemically bond the dye as a monomolecular film. For this purpose, the entire substrate having the oxide semiconductor film 4 on the surface is immersed in a dye solution formed by dissolving the dye in an organic solvent, and the dye is reacted with the hydroxyl group of titanium, for example, of the oxide semiconductor film 4. Alternatively, the remaining alkoxide group may be substituted.

The dye used in the present invention is preferably a dye which can be chemically bonded to the metal oxide constituting the oxide semiconductor film 4 (particularly titanium oxide film), and has a carboxyl group or a sulfonic acid group in the molecule. Those having a phosphoric acid group or a hydroxyl group are preferable. Specifically, bipyridyl R
u complex, ta-pyridyl Ru complex, phenanthroline Ru
Complex, Ru complex such as Ru complex of bicinchoninic acid, Eosin Y, dibromofluorescein, fluorescein, lo-
Examples thereof include dyes such as damine B, pyrogallol, dichlorofluorescein, erythrosin B, fluorescin, and marcrochrome.

In order to adsorb the dye as a single molecule on the surface of the titanium oxide film, which is a preferred embodiment of the oxide semiconductor film 4, the titanium oxide film is formed together with the substrate in a dye solution formed by dissolving the dye in an organic solvent. Just soak. In this case, the dye solution is subjected to decompression treatment or heat treatment prior to immersion in the dye so that the titanium oxide film, which is the porous structure film, penetrates deeply into the film, and bubbles contained in the film Is preferably removed in advance. Immersion time
30 minutes to 24 hours. A reflux treatment may be performed in order to efficiently adsorb the dye. Further, the immersion treatment can be repeated a plurality of times if necessary. After the immersion treatment, the titanium oxide film having the dye adsorbed thereon is dried at room temperature to 80 ° C.

In the present invention, the dye to be adsorbed on the titanium oxide film does not have to be one kind, and a plurality of dyes having different light absorption regions can be adsorbed if necessary. As a result, light can be used efficiently. In order to adsorb a plurality of dyes to the film, a method of immersing the film in a solution containing a plurality of dyes, a method of preparing a plurality of dye solutions, and sequentially immersing the film in these solutions can be mentioned. In the solution in which the dye is dissolved in the organic solvent, any organic solvent can be used as long as it can dissolve the dye. Examples of such substances include methanol, ethanol, acetonitrile, dimethylformamide, dioxane, dichloromethane, toluene and the like. The concentration of the dye in the solution is 100
1 to 200 mg, preferably 10 to 100 mg in ml
It is a degree.

[0033] As the counter electrode 30 paired with the dye coupling electrode 10, as long as it has conductivity, but any conductive material is used, I ₃ ^- redox ions oxidized such as ion It is preferable to use a substance having a catalytic ability to carry out the reduction reaction of (1) at a sufficient speed. Examples of such a material include a platinum electrode, a material obtained by subjecting a conductive material surface to platinum plating or platinum vapor deposition, rhodium metal, ruthenium metal, ruthenium oxide, carbon and the like.

The solar cell 1 of the present invention is generally formed in a state in which the dye-bonded electrode 10, the electrolyte-containing body 5 and the counter electrode 30 are housed in a case and sealed, or all of them are resin-sealed. It In this case, the electrode (dye binding electrode) 10 to which the dye is bound is exposed to light. In the battery having such a structure, when sunlight or visible light equivalent to sunlight is applied to the dye-bonding electrode 10, a potential difference is generated between the dye-bonding electrode 10 and the electrode 30 facing the dye-bonding electrode 10, and both electrodes 1
An electric current flows between 0 and 30.

[0035]

EXAMPLES Next, the present invention will be described in more detail with reference to specific examples of the present invention.

Experimental Example I (Preparation of Samples of Examples 1 to 10) Preparation of Titanium Oxide Sol Solution A titanium oxide sol solution was prepared by hydrolyzing titanium isopropoxide as follows.

125 ml of titanium isopropoxide,
It was added to 750 ml of 0.1 M nitric acid aqueous solution with stirring. This was vigorously stirred at 80 ° C. for 8 hours. The obtained liquid is heated at 230 ° C. in a pressure vessel made of Teflon (registered trademark),
It was autoclaved for 16 hours. The sol liquid containing the precipitate was resuspended by stirring. The precipitate that was not resuspended was removed by suction filtration, and the sol solution was concentrated with an evaporator until the titanium oxide concentration reached 11 wt%. One drop of Triton X-100 was added to improve the wettability on the substrate.

Next, titanium alkoxide was added to the sol solution as described below in order to prevent the occurrence of cracks during the firing of the titanium oxide film and the peeling of the film from the conductive surface. That is, while stirring the sol solution, di-iso-
An 80:20 mixture of propoxy bis (acetylacetonato) titanium and acetylacetone was added in small portions.
After the addition was completed, the mixture was stirred for 1 hour.

Samples were prepared with the addition amount of di-iso-propoxy bis (acetylacetonato) titanium being 3.4 g (10% by weight based on the weight of titanium oxide fine particles).

Preparation of Dye-Binding Electrode (Titanium Oxide Electrode) Using the titanium alkoxide-added sol liquid prepared as described above, a titanium oxide electrode was prepared in the following manner.

Length 2.0 cm, width 1.5 cm, thickness 1 mm
Conductive glass substrate (F-SnO ₂ , sheet resistance 10Ω
/ □), a 70 μm thick masking tape having a rectangular hole of 0.5 cm in length and 0.5 cm in width is attached to the conductive film surface side, and the titanium alkoxide-added sol liquid of 3 μm is attached to the end of the hole.
1 (microliter) was added with a pipette.

This sol solution was spread on a substrate by stretching it using a glass plate having a flat edge. The film thus spread was dried in air for 30 minutes, and after drying, a masking tape was used.
Peeled off.

Next, it was baked for 30 minutes at 500 ° C. using an electric furnace. The heating rate was 2 ° C./min.

After firing, when the substrate temperature dropped to 80 ° C., (4,4′-dicarboxylic acid-
2,2′-Bipyridine) ruthenium (II) diisothianate was immersed in 20 ml of an anhydrous ethanol solution added at a concentration of 3 × 10 ⁻⁴ M and left for 12 hours.

After standing, the titanium oxide electrode was taken out and washed with anhydrous acetonitrile. The titanium oxide film on the substrate became crimson due to the adsorbed ruthenium dye (preparation of dye-bonded electrode sample).

Preparation of Counter Electrode A counter electrode was prepared by sputtering platinum with a thickness of 100 nm on the conductive film surface side of a conductive glass substrate having two 1 mmφ holes.

Preparation of Electrolyte-Containing Body (Electrolyte Solution) 3-Methoxypropionitrile containing tetrapropylammonium iodide (0.45M) and iodine (0.06M) was used. Various electrolyte derivatives shown in each Example of Table 2 below were added to this electrolyte solution at 0.5 mol for liquid and at a saturated concentration for solid to prepare various electrolyte-containing bodies.

Preparation of Solar Cell Using the above both electrodes and the electrolyte-containing body, a solar cell sample was prepared and evaluated in the following manner.

As a spacer for bonding the dye-bonding electrode (titanium oxide electrode), which is the working electrode, and the counter electrode to each other, as a spacer, Mitsui DuPont Polychemical Co., Ltd.
m) was used. When the spacer is attached to the working electrode, the central portion of the spacer overlapping the titanium oxide film on which the dye is adsorbed is hollowed out. ) Can be stored. With this,
The dye-adsorbed titanium oxide film side of the working electrode was bonded to the platinum-sputtered side of the counter electrode.

Then, an electrolyte-containing body (electrolyte solution) containing a urea derivative was introduced from one of the two holes previously formed in the counter electrode. It was left for a sufficient time so that the electrolyte-containing body (electrolyte solution) was introduced into the battery. After that, one sheet of high milan and one sheet of cover glass were sequentially laminated as a sealing plate from the back surface side of the counter electrode to close the two holes, and the electrolyte containing body (electrolyte solution) was sealed.
In this way, various example samples shown in Table 2 were prepared.

(Preparation of Sample of Comparative Example 1) Example 1 above
In the sample, urea was not used as a urea derivative when preparing the electrolyte solution. A comparative example 1 sample was prepared in the same manner as the example 1 sample except for the above.

(Preparation of Sample of Comparative Example 2) Example 1 above
In the sample, a dye-sensitized solar cell of Comparative Example 2 sample containing 4-tert-butylpyridine in place of urea of the urea derivative at the time of preparing the electrolyte solution was prepared.

In the above Examples and Comparative Examples,
The electrolyte solution was prepared in a glove box with a dew point of −90 ° C. or less, and the electrolyte solution was sealed inside the cell in the glove box.

Evaluation of Battery Characteristics Using a metal halide of 100 mW / cm ² as a light source, an open circuit voltage (Vo
c) and the photocurrent density (Jsc) were measured, and these values were used as initial battery characteristics. The open circuit voltage (Voc) represents the voltage between both terminals when the output terminal of the solar cell module is opened. The photocurrent density (Jsc) represents a current (per 1 cm ² ) flowing between both terminals when the output terminals of the solar cell module are short-circuited.

Then, each sample was heated at a temperature of 30 ° C. and a humidity of 5
In the atmosphere of 0% RH, 100mW / cm ² (metal halide) was continuously irradiated, and the photocurrent density (Js
The change with time in c) was measured, and the time when the photocurrent density (Jsc) reached −10% of the initial battery characteristics was obtained. This time was defined as long-term battery characteristics. The larger this value, the better the durability against water and oxygen after the battery is manufactured. During the experiment, the UV light was UV
It cut using the cut filter GG435.

The results are shown in Table 2 below.

[0057]

[Table 2]

From the results of Table 2, in the sample of this example,
It can be seen that the Voc of the initial characteristics is greatly improved without deteriorating the long-term battery characteristics and Jsc, and the effect of adding the urea derivative is extremely remarkable.

[Experimental Example II] In the production of each Example sample in Experimental Example I, 3-methoxypropionitrile used as the solvent for the electrolyte-containing body was changed to propylene carbonate. Other than that was carried out similarly to the above-mentioned Experimental example I, and each Example sample of Experimental example II was produced. When the battery characteristics of the samples of Examples in Experimental Example II were evaluated in the same manner as above, it was confirmed that substantially the same effects as those of Experimental Example I were obtained.

[0060]

The effects of the present invention are clear from the above results. That is, the present invention is a dye-sensitized solar cell having a dye-bonded electrode having a dye adsorbed on the surface, a counter electrode paired with the dye-bonded electrode, and an electrolyte-containing body in contact with these electrodes, Since the electrolyte containing body is configured to contain the urea derivative, the open-circuit voltage can be improved and the long-term stability of the battery characteristics can be excellent. That is, it is possible to provide a dye-sensitized solar cell that can maintain a high conversion efficiency for a long time.

[Brief description of drawings]

FIG. 1 is a drawing showing a schematic configuration example of a dye-sensitized solar cell of the present invention.

[Explanation of symbols]

1 ... Dye-sensitized solar cell 4 ... Oxide semiconductor film 5 ... Electrolyte 7 ... Dye film 10 ... Dye binding electrode 20 ... substrate 22 ... Transparent conductive layer 30 ... Electrode

Claims (2)

[Claims] 1. A dye-sensitized solar cell comprising a dye-bonded electrode having a dye adsorbed on the surface thereof, a counter electrode paired with the dye-bonded electrode, and an electrolyte-containing body in contact with these electrodes, the electrolyte comprising: A dye-sensitized solar cell, wherein the inclusion body contains a urea derivative that acts to improve voltage. 2. The dye-sensitized solar cell according to claim 1, wherein the urea derivative comprises a compound represented by the following structural formula (I). [Chemical 1] In the structural formula (I), R ₁ , R ₂ , R ₃ , and R ₄ are each a hydrogen atom, a halogen atom, or an alkyl group, an alkoxyl group, an acyl group, or carbamoyl, each of which may have a substituent. Group, nitrile group, amino group, amide group, phosphoryl group, phosphinoyl group, thiophosphoryl group, phosphanyl group, thiocarbamoyl group, thioalkyl group, thioamino group, silyl group, silanol group, sulfonyl group, germyl group, stannyl group, R ₁ , R
₂ , R ₃ and R ₄ may be the same or different. Further, R ₂ and R ₃ may be connected to each other to form a ring structure.