JP4942013B2 - Titanium oxide paste for screen printing, porous titanium oxide thin film electrode and photoelectric conversion element using the paste, and method for producing titanium oxide paste - Google Patents

Description

  The present invention relates to an oxide photo semiconductor paste for screen printing, an oxide photo semiconductor porous thin film electrode and a photoelectric conversion element using the paste, and a method for producing an oxide photo semiconductor paste for screen printing.

  Solar cells are highly expected as clean, regenerative energy sources. Single-crystal silicon-based, polycrystalline silicon-based, amorphous silicon-based solar cells, and solar cells made of compound semiconductors such as cadmium telluride and indium copper selenide However, in order to spread it as a household power source, all the solar cells have many problems such as high cost and problems of securing raw materials.

  Under such circumstances, it is said that the dye-sensitized solar cell is very advantageous in terms of cost, large area, and raw materials. The dye-sensitized solar cell includes a dye-sensitized photoelectric conversion element, and the photoelectric conversion element includes a photoelectrode composed of a semiconductor fine particle-containing layer adsorbing a dye formed on a conductive support, a charge transfer layer, and Consists of a counter electrode. In particular, Nature (Vol. 353, 737-740, 1991) and US Pat. No. 4,927,721 disclose a photoelectric conversion element and a solar cell using semiconductor fine particles sensitized with a dye, and a material for producing the same. And manufacturing techniques are disclosed.

  The photoelectric conversion element and solar cell described above are used as a charge transfer layer containing a photoelectrode composed of a porous semiconductor film spectrally sensitized with a light-absorbing dye and a redox species of halogens such as iodine and bromine. An electrolyte and a counter electrode on which a catalyst for facilitating electron transfer to the redox electrolyte is fixed on a conductive substrate as necessary. In particular, the porous semiconductor film is composed of titanium oxide, the sensitizing dye is composed of a ruthenium metal complex, the electrolyte is composed of an electrolytic solution obtained by dissolving iodine redox in an organic solvent, and the counter electrode is composed of platinum metal. It is known that high photoelectric conversion efficiency can be obtained when it is made of a material fixed to tin oxide transparent conductive glass.

  Thus, at present, studies on modularization of dye-sensitized solar cells are actively conducted. However, in the modularization, a method for producing a porous semiconductor film which is a photoelectric conversion element becomes important. There are various methods such as spin coating method, die coater method, screen printing method and spraying method for producing porous semiconductor film, but in order to make complex electrode shape for modularization, screen printing method is used. Is desirable.

  A general paste for screen printing is composed of an inorganic powder filler, a resin, and a solvent. Here, as an oxide optical semiconductor paste for a dye-sensitized solar cell, titanium oxide is used as an inorganic powder filler, ethyl cellulose is used as a resin, and α-terpineol, butyl carbitol, etc. are used as a solvent (for example, Japanese Patent Application Laid-Open No. 2004-2004). -153030), these compositions require a solvent replacement operation from an aqueous system to a solvent system, and the above-mentioned α-terpineol and butyl carbitol are not soluble in water, and therefore have a low boiling point intermediate solvent. There was a problem that it had to be replaced with a high cost. Furthermore, the performance of the obtained paste itself is not excellent, and when the paste is applied on a substrate (electrode) by screen printing or the like, anyone is generated, and when trying to suppress this, the leveling property becomes very poor. A uniform coating could not be performed.

Nature (Vol. 353, 737-740, 1991) U.S. Pat. No. 4,927,721 JP 2004-153030 A

  The present invention provides a paste containing an oxide optical semiconductor, which has a very small dripping when applied, enables thick film printing and automatic printing, and has a uniform thickness using the paste. It aims at providing the photoelectric conversion element which has a porous thin film electrode, and this oxide optical semiconductor porous thin film electrode.

In order to achieve the above object, the present invention
The present invention relates to an oxide photo-semiconductor paste for screen printing, comprising a diol-based solvent which is an amphiphilic solvent and an oxide photo-semiconductor.

The present invention also provides:
Using an aqueous dispersion in which oxide photo-semiconductor fine particles are dispersed as a starting material, a diol-based solvent that is an amphiphilic solvent is mixed into the aqueous dispersion, and only water is evaporated to replace the solvent. Producing an oxide photo semiconductor fine particle dispersion in which semiconductor fine particles are dispersed in the diol-based solvent;
Adding a cellulose-based thickener to the oxide photo-semiconductor fine particle dispersion;
The manufacturing method of the oxide optical semiconductor paste characterized by comprising.

  As a result of diligent investigations to achieve the above object, the present inventors have found that when producing a porous semiconductor film by screen printing, the cause of the above is a solvent such as α-terpineol or butyl carbitol used in the paste. It was found to be due to the characteristics of From this point of view, the present inventors conducted further diligent studies to find a novel solvent that can replace the conventional α-terpineol and the like in order to suppress the above-described problem.

  As a result, the diol-based solvent that is an amphiphilic solvent has good compatibility with the oxide optical semiconductor. In the oxide optical semiconductor paste for screen printing obtained by dispersing the oxide optical semiconductor in the solvent, Even when the film is applied on a predetermined substrate (electrode) by screen printing, the thick film printing and the automatic printing can be easily performed with almost no dripping. As a result, an oxide photo semiconductor porous thin film electrode having a uniform thickness can be formed, and a photoelectric conversion element having good characteristics, a dye-sensitized solar cell, and a dye-sensitized solar cell module are obtained. Can be produced.

  In the above method for producing an oxide optical semiconductor paste of the present invention, the solvent can be quickly replaced from the aqueous dispersion to the diol solvent. It can be easily dissolved in the oxide semiconductor paste obtained after solvent replacement.

  In a preferred embodiment of the present invention, the oxide optical semiconductor paste for screen printing contains a liquid having no solubility in a resin as an additive. In this case, the additive functions as a leveling agent for the paste, and suppresses the unevenness when the oxide photo semiconductor porous thin film electrode is produced by applying the paste on a substrate (electrode). And a uniform surface. Therefore, it is possible to impart a sagging suppressing effect and a leveling effect to the paste, and the obtained oxide photo semiconductor porous thin film electrode can have a very uniform thickness and can be used for a long time. The electrode characteristics can be stably obtained, and thick film printing and automatic printing can be made easier.

  In another preferred embodiment of the present invention, the oxide optical semiconductor paste for screen printing contains at least one additional additive selected from the group consisting of a chelating agent, a surfactant, and a titanium coupling agent. Including. In this case, the additional additive functions as an excellent leveling agent in the same manner as the additive when added to the dispersion solution composed of the above-described oxide optical semiconductor and the amphiphilic diol solvent. become.

  Therefore, in the oxide semiconductor paste for screen printing according to the present invention, by adding the additional additive in addition to the additive or separately from the additive, a drool suppression effect on the paste. And the obtained oxide photo semiconductor porous thin film electrode can have a very uniform thickness, and can stably obtain desired electrode characteristics over a long period of time. In addition, thick film printing and automatic printing can be realized more easily.

  As described above, according to the present invention, in the paste containing the oxide optical semiconductor, the dripping at the time of application is very small, thick film printing and automatic printing can be performed, and uniform using the paste. It is possible to provide an oxide photo semiconductor porous thin film electrode having a sufficient thickness, a photoelectric conversion element having the oxide photo semiconductor porous thin film electrode, a dye-sensitized solar cell, and a dye-sensitized solar cell module.

  Hereinafter, other features and advantages of the present invention will be described in detail based on the best mode for carrying out the invention.

(Oxide optical semiconductor paste for screen printing)
The oxide photo-semiconductor paste for screen printing of this invention contains the oxide photo-semiconductor which is the main raw material for forming the target oxide photo-semiconductor porous thin film electrode. As the oxide optical semiconductor, a single metal oxide, a compound having a perovskite structure, or the like can be used. The single metal oxide is preferably an oxide of titanium, tin, zinc, iron, tungsten, zirconium, hafnium, strontium, indium, cerium, yttrium, lanthanum, vanadium, niobium, or tantalum. Preferred examples of the compound having a perovskite structure include strontium titanate, calcium titanate, sodium titanate, barium titanate, and potassium niobate.

  Among these, it is preferable to use titanium oxide and zinc oxide from the viewpoint of facilitating electron transfer with a dye or the like to be adsorbed later, and improving power generation efficiency when configured as a photoelectric conversion element. It is preferable to use titanium oxide.

  With regard to the titanium oxide, particularly high characteristics are obtained by using titanium oxide fine particles prepared by a wet synthesis method from the viewpoints of particle size control, crystallinity, and particle dispersibility. Wet synthesis methods include titanium alkoxide and titanium metal salts and other precursors obtained by hydrolyzing titanium precursors to crystallize into oxides under hydrothermal conditions. A method of making oxides fine particles using a sol-gel method in which hydrolysis polymerization is performed in the presence of an acid-base catalyst and an acid-base catalyst is preferably used. Titanium oxide produced by the wet synthesis method exemplified above necessarily shows a state of being dispersed in a solvent containing water by obtaining a hydrolysis step and a hydrothermal synthesis step.

  The oxide optical semiconductor is present in the form of fine particles in the paste. Therefore, the short metal oxide, the compound having a perovskite structure, etc. are present as fine particles and dispersed in the solvent shown below to obtain the paste.

  The particle diameter of the oxide photo semiconductor fine particles is preferably 5 to 500 nm, more preferably 10 in consideration of the simplicity of the production process, the production cost associated therewith, and the adsorption ratio (adsorption amount) of the dye. It is -300 nm, Most preferably, it is 15-200 nm.

  Moreover, the oxide optical semiconductor paste for screen printing of this invention contains the solvent for disperse | distributing the oxide optical semiconductor (fine particle) mentioned above to make a paste. As the solvent, a diol-based solvent that is amphiphilic, strongly polar, and highly soluble in a resin is used. Examples of such solvents include hexylene glycol, propylene glycol, trimethylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, tetramethylene glycol, pentamethylene glycol, and 2-butene-1,4-diol. It can be illustrated. Among these, hexylene glycol, propylene glycol, and trimethylene glycol are preferable, and hexylene glycol is particularly preferable. These solvents can be used alone or in combination of two or more.

  Note that the oxide optical semiconductor paste for screen printing can contain a liquid that is not soluble in a resin as an additive. As described above, an oxide photo-semiconductor paste composed only of an oxide photo-semiconductor (fine particles) and a diol-based solvent is prepared, and this is applied to the substrate (electrode) by screen printing. Can be suppressed.

  However, depending on the type and blending amount of the oxide semiconductor (fine particles) and the compatibility with the selected diol solvent, many irregularities occur on the applied film surface, and the surface smoothness of the obtained coating film is reduced. You may not get enough. Therefore, when the target oxide photo semiconductor porous thin film electrode is formed using such a coating film, it is difficult to increase the thickness sufficiently, and the electrode characteristics are sufficiently stabilized due to the unevenness. In other words, the electrode characteristics deteriorate over time.

  Therefore, as described above, by including the additive in the oxide photo semiconductor paste, the additive functions as a leveling agent, and the oxide photo semiconductor porous thin film electrode obtained by screen printing is It is possible to have a very uniform thickness, to stably obtain desired electrode characteristics over a long period of time, and to enable thick film printing and automatic printing more easily.

  Examples of the additive include water, ethylene glycol, polyethylene glycol, and glycerin. These can be used alone or in a mixture of two or more.

  Further, in the oxide photo semiconductor paste for screen printing, a chelating agent such as acetylacetone, a surfactant such as polyethylene glycol, a titanium coupling agent and the like can be added as additional additives. In this case, the additional additive functions as an excellent leveling agent in the same manner as the additive when added to the dispersion solution composed of the above-described oxide optical semiconductor and the amphiphilic diol solvent. become.

  Therefore, in the oxide semiconductor paste for screen printing according to the present invention, by adding the additional additive in addition to the additive or separately from the additive, a drool suppression effect on the paste. And the obtained oxide photo semiconductor porous thin film electrode can have a very uniform thickness, and can stably obtain desired electrode characteristics over a long period of time. In addition, thick film printing and automatic printing can be realized more easily.

  In addition, a general purpose thing can be used as the said chelating agent, the said surfactant, and the said titanium coupling agent. For example, as the chelating agent, benzylacetone and acetic acid can be used in addition to acetylacetone described above.

  In addition, the chelating agent, the surfactant, and the titanium coupling agent can be used alone or in combination of two or more. In this case, for example, only two or more titanium coupling agents can be mixed and used, or a surfactant and a titanium coupling agent can be used in combination.

  In addition, the oxide semiconductor paste for screen printing has a certain degree of viscosity by including the oxide photo semiconductor (fine particles), an additive as a leveling agent, and an additional additive. If it becomes suitable, but the viscosity is not sufficient depending on the content thereof, and it is difficult to carry out film formation by screen printing, a cellulose-based thickener is added to the oxide semiconductor paste. Added. This thickener reduces the viscosity of the oxide photo-semiconductor paste without deteriorating the sagging suppression effect due to the diol solvent described above and the leveling property due to an additive such as water or an additional additive such as a chelating agent. It can be increased effectively.

  The above-mentioned oxide photo-semiconductor paste for screen printing is prepared by preparing an aqueous dispersion in which oxide photo-semiconductor fine particles used as a raw material for the target oxide photo-semiconductor porous thin film electrode are dispersed, and then evaporating only water. Thus, the aqueous dispersion is obtained by solvent substitution with a diol solvent that is an amphiphilic solvent. Therefore, when the additive, the additional additive, and the thickener are added to the aqueous dispersion, they may not be uniformly dissolved and dispersed, and solvent replacement may not be easily performed. Therefore, it is preferable to add the additive etc. into the final oxide optical semiconductor paste after solvent substitution.

  An example of the oxide photo-semiconductor paste is obtained by preparing an aqueous dispersion in which oxide photo-semiconductor fine particles are dispersed, and then substituting the aqueous dispersion with a diol solvent that is an amphiphilic solvent. 2 to 3 times the amount of ethanol is added to the solution to facilitate the dissolution of the thickener. Then, after the said thickener is dissolved and ethanol is evaporated, the said oxide optical semiconductor paste is produced by adding shear by adding a shear with a 3 roll mill. The above-mentioned additives and additional additives may be added after the three-roll mill and stirred and defoamed, or may be added before the three-roll mill.

  In addition, as an example of a preferable composition of the oxide optical conductor paste for screen printing of the present invention, the ratio of the oxide photo semiconductor fine particles is obtained when the paste composition is printed by a printing method such as screen printing. This is the main factor that affects the film thickness. Here, the higher the ratio of the oxide photo-semiconductor fine particles, the thicker the film thickness obtained by one printing, the more preferable from the viewpoint of reducing the number of steps, at least the ratio of the oxide photo-semiconductor fine particles in the paste composition Needs to be 20% by weight or more. Although there is no upper limit in particular, it is restrict | limited by the mixing ratio with the solvent normally used for a paste, and is about 50 weight%. The proportion of the additive is 1-14% by weight, preferably 4-10% by weight, the proportion of the additional additive is 2% by weight or less, the proportion of the thickener is 2-10% by weight, The proportion of the diol solvent is 50-80% by weight, preferably 60-73% by weight.

(Photoelectric conversion element)
Next, a photoelectric conversion element using the above-described oxide optical semiconductor paste for screen printing will be described. FIG. 1 is a schematic configuration diagram showing an example of a photoelectric conversion element, and FIG. 2 is an enlarged view showing the vicinity of a photoelectrode of the photoelectric conversion element shown in FIG.

  As shown in FIGS. 1 and 2, a photoelectric conversion element 100 includes an oxide photo semiconductor porous thin film electrode 101 that functions as a photo electrode, and a counter electrode 109 provided so as to face the oxide photo semiconductor porous thin film electrode 101. An electrolyte 108 is interposed therebetween. The porous thin film electrode 101 includes a transparent conductive substrate 102 on which a transparent conductive layer 105 is formed on a transparent substrate 104, and an oxide semiconductor electrode 103 formed on the substrate. The oxide semiconductor electrode 103 is configured by carrying a sensitizing dye 107 on the surface of an oxide semiconductor fine particle 106.

  The oxide semiconductor electrode 103 is obtained by applying and baking the above-described oxide optical semiconductor paste for screen printing, and the oxide semiconductor fine particles 106 are caused by the oxide photo semiconductor fine particles contained in the paste. To do.

  Next, a method for manufacturing the photoelectric conversion element shown in FIGS. 1 and 2 will be described. First, the transparent substrate 104 is prepared, the transparent conductive layer 105 is formed thereon, and the transparent conductive substrate 102 is manufactured. The transparent conductive layer 105 can be formed using a known film formation technique such as a sputtering method, a CVD method, or a coating method. A transparent substrate 104 on which a commercially available transparent conductive layer 105 is formed can also be used directly as the transparent conductive substrate 102.

  Next, the oxide photo-semiconductor paste is prepared, screen-printed on the transparent conductive substrate 102, and baked to remove components other than the oxide photo-semiconductor fine particles, whereby an oxide is formed on the transparent conductive substrate 102. A film made of the optical semiconductor fine particles 106 is formed.

  As said baking temperature, 250-600 degreeC is used, Preferably 400-550 degreeC is used. If the firing temperature is lower than the above range, a good crystal state cannot be obtained, so the produced oxide photo semiconductor fine particle film is not preferable because it becomes a high resistance film, and if it is higher than the above range, crystallite growth occurs. Becomes noticeable and the specific surface area decreases, which is not preferable.

  Next, the sensitizing dye 107 is dissolved in a predetermined solvent to prepare a sensitizing dye solution, and the electrode 101 including the oxide semiconductor fine particles 106 is immersed in the solution to thereby make the sensitizing dye 107 an oxide semiconductor. The oxide photo semiconductor fine particles 106 adsorbed and supported on the fine particles 106 and the sensitizing dye 107 adsorbed, that is, the photoelectric conversion element 101 including the oxide photo semiconductor electrode 103 are obtained.

  The solvent for preparing the sensitizing dye solution includes alcohols such as methanol, ethanol, 2 propanol, 1 butanol and t-butanol, acetonitrile, methoxyacetonitrile, propionitrile, 3 methoxypropionitrile and the like. Nitriles or a mixed solvent thereof can be used. As the sensitizing dye 107, N3, N719, Black Dye, and coumarin dyes are used.

  Next, a partition 110 is provided between a porous thin film electrode 101 as a photoelectrode and a counter electrode 109, and an electrolyte 108 is injected into a space formed by these to obtain a target photoelectric conversion element 100. Examples of the electrolyte 108 include a known electrochemically inert solvent such as 3-methoxypropionitrile, acetonitrile, propylene carbonate, ethylene carbonate, lithium iodide, iodine, t-butylpyridine, 1,2-dimethyl- What melt | dissolved 3-propyl imidazolium iodide etc. can be used.

  Note that a catalyst layer made of platinum, carbon, or the like may be provided on the surface of the counter electrode 109 in order to facilitate electron exchange with the electrolyte 108. This catalyst layer can be formed by sputtering or CVD.

  The photoelectric conversion element 100 shown in FIGS. 1 and 2 can be used as a dye-sensitized solar cell module by forming a module, and can also be used as a dye-sensitized solar cell by being incorporated in a predetermined circuit. can do.

EXAMPLES Hereinafter, although this invention is demonstrated concretely according to an Example, this invention is not limited to the content of an Example.

( Reference Example 1)
<Preparation of oxide photo semiconductor paste>
Titanium oxide fine particle aqueous dispersion (manufactured by Sumitomo Osaka Cement Co., Ltd., average particle size 20 nm, solid content concentration 4 wt%) is used as oxide photo semiconductor fine particles, and 2,4-pentanediol (hexylene glycol: manufactured by Kanto Chemical Co., Inc.) is used for this. The solvent was replaced by removing water with a rotary evaporator. Ethanol and ethyl cellulose (Ethoseru (trade name): manufactured by Nisshin Kasei Co., Ltd.) were mixed here, subjected to ultrasonic dispersion, ethanol was removed with a rotary evaporator, and titanium oxide was applied by applying three rolls (EXAKT). A containing paste was prepared.

The composition ratio of this paste was TiO ₂ ultrafine particles 35 wt%, hexylene glycol 62 wt%, and ethyl cellulose 3 wt%. The viscosity was 5.42 × 10 ² Pa · s (VAR-50 (manufactured by Jusco International Co., Ltd.), measurement mode: viscosity at a constant speed and shear rate of 1 / s). Note that automatic screen printing was not possible due to the viscosity being too high at low shear rates.

(Example 1 )
<Preparation of oxide photo semiconductor paste>
Titanium oxide fine particle aqueous dispersion (manufactured by Sumitomo Osaka Cement Co., Ltd., average particle size 20 nm, solid content concentration 4 wt%) is used as oxide photo semiconductor fine particles, and 2,4-pentanediol (hexylene glycol: manufactured by Kanto Chemical Co., Inc.) is used for this. The solvent was replaced by removing water with a rotary evaporator. Ethanol and ethyl cellulose (Ethoseru (trade name): manufactured by Nisshin Kasei Co., Ltd.) are mixed here, subjected to ultrasonic dispersion, ethanol is removed with a rotary evaporator, and a three-roll roll (manufactured by EXAKT) is applied to form a titanium oxide-containing paste. Prepared. Ethylene glycol (manufactured by Kanto Chemical Co., Inc.) was added thereto and mixed with Mazerustar (manufactured by Co., Ltd.).

The composition ratio of this paste was TiO ₂ ultrafine particles 32 wt%, hexylene glycol 56 wt%, ethyl cellulose 3 wt%, and ethylene glycol 9 wt%. The viscosity was 5.36 × 10 ² Pa · s (VAR-50 (manufactured by Jusco International), measurement mode: viscosity at a constant speed and shear rate of 1 / s). It has been found that automatic screen printing is also possible.

(Example 2 )
<Preparation of oxide photo semiconductor paste>
Titanium oxide fine particle aqueous dispersion (manufactured by Sumitomo Osaka Cement Co., Ltd., average particle size 20 nm, solid content concentration 4 wt%) was used as oxide photo semiconductor fine particles, and this was used as 2,4-pentanediol (hexylene glycol: manufactured by Kanto Chemical Co., Inc.). The solvent was replaced by removing water with a rotary evaporator. Ethanol and ethyl cellulose (Ethoseru (trade name): manufactured by Nisshin Kasei Co., Ltd.) are mixed here, subjected to ultrasonic dispersion, ethanol is removed with a rotary evaporator, and a three-roll roll (manufactured by EXAKT) is applied to form a titanium oxide-containing paste. Prepared. Ethylene glycol (manufactured by Kanto Chemical Co., Inc.) and acetylacetone (manufactured by Kanto Chemical Co., Ltd.) were added thereto and mixed with Mazerustar (manufactured by Kanto Chemical Co., Ltd.).

The composition ratio of this paste was TiO ₂ ultrafine particles 34 wt%, hexylene glycol 59 wt%, ethyl cellulose 3 wt%, ethylene glycol 3 wt%, and acetylacetone 1 wt%. The viscosity was 5.56 × 10 ² Pa · s (VAR-50 (manufactured by Jusco International Co., Ltd.), measurement mode: viscosity at a constant speed and shear rate 1 / s). It has been found that automatic screen printing is also possible.

(Example 3 )
<Preparation of oxide photo semiconductor paste>
Titanium oxide fine particle aqueous dispersion (manufactured by Sumitomo Osaka Cement Co., Ltd., average particle size 20 nm, solid content concentration 4 wt%) was used as oxide photo semiconductor fine particles, and this was used as 2,4-pentanediol (hexylene glycol: manufactured by Kanto Chemical Co., Inc.). The solvent was replaced by removing water with a rotary evaporator. Ethanol and ethyl cellulose (Ethoseru (trade name): manufactured by Nisshin Kasei Co., Ltd.) are mixed here, subjected to ultrasonic dispersion, ethanol is removed with a rotary evaporator, and a three-roll roll (manufactured by EXAKT) is applied to form a titanium oxide-containing paste. Prepared. Ethylene glycol (Kanto Chemical) was added here and mixed with Mazerustar (made by company).

The composition ratio of this paste is TiO ₂ ultrafine particles 32 wt%, hexylene glycol 60 wt%, ethyl cellulose 4 wt%, and ethylene glycol 4 wt%. Viscosity: 5.36 × 10 ² Pa · s (VAR-50 (manufactured by Jusco International), measurement mode: viscosity at a constant speed and a shear rate of 1 / s). It has been found that automatic screen printing is also possible.

(Comparative Example 1)
<Preparation of oxide photo semiconductor paste>
Titanium oxide fine particle aqueous dispersion (manufactured by Sumitomo Osaka Cement Co., Ltd., average particle size 20 nm, solid content concentration 4 wt%) was used as the oxide photo-semiconductor fine particle with ethanol substitution (solid content concentration 8 wt%). -Menten-8-ol (α-terpineol (trade name): manufactured by Kanto Chemical Co., Inc.) and ethyl cellulose (Ethocel (trade name): manufactured by Nisshin Kasei Co., Ltd.) are mixed and applied to a mechanical homogenizer (manufactured by IKA). After that, the mixture was mixed well with an ultrasonic homogenizer. Thereafter, ethanol was removed with a rotary evaporator, and a three-roll roll (manufactured by EXAKT) was applied to prepare a titanium oxide-containing paste.

The composition ratio of this paste was TiO ₂ ultrafine particles 26 wt%, α-terpineol 66 wt%, and ethyl cellulose 8 wt%. The viscosity was 6.92 × 10 ² Pa · s (VAR-50 (manufactured by Jusco International), measurement mode: viscosity at a constant speed and shear rate of 1 / s). Note that automatic screen printing could not be performed due to the high viscosity.

(Comparative Example 2)
<Preparation of oxide photo semiconductor paste>
A titanium oxide paste was prepared in the same manner as in Comparative Example 1. The composition ratio of the paste is TiO ₂ ultrafine particles 20 wt%, α-terpineol 75 wt%, ethyl cellulose 5 wt%, and the viscosity is 5.29 × 10 ² Pa · s (VAR-50 (manufactured by Jusco International Co., Ltd.)). , Measurement mode: viscosity at a constant speed and shear rate of 1 / s). Automatic screen printing was also possible.

(Comparative Example 3)
<Preparation of oxide photo semiconductor paste>
In this comparative example, a titanium oxide paste was prepared according to the conditions disclosed in JP-A No. 2004-153030. Specifically, in the titanium oxide paste described in Reference Example 1, ethyl cellulose is not added, and propylene glycol (manufactured by Kanto Chemical Co.) is used instead of 2,4-pentanediol (hexylene glycol: manufactured by Kanto Chemical Co., Inc.). A titanium oxide paste was prepared in the same manner except that it was used. The composition ratio of this paste was TiO ₂ ultrafine particles 25 wt% and propylene glycol 75 wt%. The viscosity was 5.44 × 10 ⁻² Pa · s (VAR-50 (manufactured by Jusco International), measurement mode: viscosity at a constant speed and shear rate 1 / s).

  In addition, since the titanium oxide paste thus obtained had a low viscosity, a coating film could not be obtained even when screen printing was performed.

(Evaluation of porous titanium oxide thin film electrode)
The pastes of Examples 1 to 3 and the pastes of Comparative Examples 1 and 2 were screen-printed on a transparent conductive substrate, and the entire transparent conductive substrate was placed in an electric furnace (Yamato Scientific Muffle Furnace FP-32 type). The porous thin film electrode which consists of titanium oxide microparticles | fine-particles was produced by baking off components other than titanium oxide by baking for 2 hours.

  The characteristics of the porous thin-film electrode were measured with Tencor (manufactured by company). As shown in FIG. 3, the characteristics are better as the values of the parameters b and d represent a sag index and are smaller. The leveling property can also be expressed from the difference between the parameters a and c, or the difference between e and c, but is more preferably judged from the sectional view of the film. The values of the above parameters are shown in Table 1.

Moreover, the film | membrane sectional drawing of the titanium oxide porous thin film electrode by the measurement result of the reference example 1, Example 1 , Example 3 , and the tencor of the comparative example 1 is shown to FIGS.

In Table 1, when the values of parameters b and d in Reference Example 1 , Example 1-3 and Comparative Examples 1 and 2 are compared, the values of b and d in Reference Example 1 and Example 1-3 are Comparative Example 1. It can be seen that the values of b and d at −2 are reduced to about ½ to ６. Therefore, it can be seen that the titanium oxide paste obtained according to the present invention is significantly improved when applied.

Moreover, when FIG. 4 regarding Reference Example 1 and FIGS. 5 and 6 regarding Examples 1 and 3 are compared, leveling of the titanium oxide porous thin film electrode can be achieved by including ethylene glycol as a leveling agent in the titanium oxide paste. It can be seen that it has improved. Further, as is clear from FIG. 7 relating to Comparative Example 1, in the conventional titanium oxide paste using α-terpineol as the solvent, the leveling is not so bad, but it can be seen that who is large as shown in Table 1 as well. .

(Example 4 )
<Production of photoelectric conversion element>
The titanium oxide porous membrane electrode produced according to Example 1 was immersed in 0.3 mmol of N719 dye solution and allowed to stand at 20 ° C. for 3 days to adsorb and carry the dye, and the titanium oxide photo semiconductor porous as a photoelectrode A thin film electrode was formed. Next, platinum is deposited on the transparent conductive film by sputtering to form a counter electrode, and an electrolytic solution (1-2 dimethyl-3-propylimidazolium as a supporting electrolyte in acetonitrile is formed in the space formed by these electrodes and partition walls. Iodine salt 0.6 mol / liter, lithium iodide 0.1 mol / liter, iodine 0.05 mol / liter, tertiary-butylpyridine 0.5 mol / liter) was injected, and FIG. A photoelectric conversion element as shown in FIG.

(Comparative Example 4)
<Production of photoelectric conversion element>
The titanium oxide porous membrane electrode produced in Comparative Example 1 was subjected to the same operation as in Example 4 to form a titanium oxide photo semiconductor porous thin film electrode as a photoelectrode, and the formation of the counter electrode and electrolyte injection were the same. The photoelectric conversion element as shown in FIG. 1 was obtained.

(Evaluation of photoelectric conversion characteristics)
AM ₁ . 5. By passing solar simulator (YSS80A made by Yamashita Denso Co., Ltd.) and sharp cut filter (HOYA L-42) with spectral emission characteristics of JIS-Class A Generated. The intensity of this light was 86 mW / cm ² . And the conversion efficiency was calculated | required by irradiating the said simulated sunlight continuously with respect to the obtained photoelectric conversion element, and measuring an IV characteristic with a current-voltage measuring apparatus (Caseley 2400).

As a result of calculating | requiring the said conversion efficiency about the photoelectric conversion element obtained in Example 4 and Comparative Example 4, the result as shown in Table 2 and FIG. 8 was obtained. As is apparent from Table 2 and FIG. 8, the photoelectric conversion element of the present invention configured using hexylene glycol as the main solvent of the oxide optical semiconductor paste is the same as the conventional photoelectric conversion element configured from the conventional paste. It has been found that a high conversion efficiency can be obtained.

  As described above, the present invention has been described in detail based on the embodiments of the present invention with specific examples. However, the present invention is not limited to the above contents, and all modifications and changes are made without departing from the scope of the present invention. It can be changed.

It is a block diagram which shows roughly an example of the photoelectric conversion element of this invention. It is a figure which expands and shows the photoelectrode vicinity of the photoelectric conversion element shown in FIG. It is a figure which shows the film | membrane shape measurement point corresponding to Table 1. FIG. 4 is a cross-sectional view of a titanium oxide porous thin film electrode produced from the titanium oxide paste obtained in Reference Example 1. FIG. 1 is a cross-sectional view of a titanium oxide porous thin film electrode produced from the titanium oxide paste obtained in Example 1. FIG. 3 is a cross-sectional view of a titanium oxide porous thin film electrode produced from the titanium oxide paste obtained in Example 3. FIG. 4 is a cross-sectional view of a titanium oxide porous thin film electrode produced from the titanium oxide paste obtained in Comparative Example 1. FIG. It is a photoelectric conversion characteristic graph containing the titanium oxide porous thin film electrode produced from the titanium oxide paste obtained in Example 1 and Comparative Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Photoelectric conversion element 101 Photoelectrode 102 Transparent conductive substrate 103 Oxide semiconductor electrode 104 Transparent substrate 105 Transparent conductive layer 106 Oxide semiconductor fine particle 107 Sensitizing dye 108 Electrolyte 109 Counter electrode 110 Partition

Claims (4)

Titanium oxide dispersed in hexylene glycol prepared by mixing an aqueous dispersion in which fine titanium oxide particles are dispersed, mixing hexylene glycol with the aqueous dispersion, evaporating only water and replacing the solvent, and cellulose during the titanium oxide paste containing a thickener system, e Ji glycol, polyethylene glycol, and is characterized in that it is contains at least one liquid as an additive selected from the group consisting of glycerol, for screen printing Titanium oxide paste.   A titanium oxide porous thin-film electrode produced using the titanium oxide paste for screen printing according to claim 1. According to claim 2, the oxidation of titanium porous thin film electrode, characterized in that a sensitizing dye adsorbed thereon, a photoelectric conversion element. Starting with an aqueous dispersion in which titanium oxide fine particles are dispersed, hexylene glycol is mixed with the aqueous dispersion, and only water is evaporated to replace the solvent, and the titanium oxide fine particles are dispersed in the hexylene glycol. Producing a titanium fine particle dispersion;
Adding a cellulose-based thickener to the titanium oxide fine particle dispersion;
During the titanium oxide paste, et Ji glycol, a step of incorporating polyethylene glycol, and at least one liquid selected from the group consisting of glycerine as an additive,
A method for producing a titanium oxide paste, comprising:

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