KR20130044967A - A method for preparing nano-tube of titanium dioxide and a photoelectrode for dye-sensitized solar cell comprising the nano-tube - Google Patents

Abstract

PURPOSE: A manufacturing method of titanium dioxide nanotubes and a photoelectrode for high efficiency dye-sensitized solar cells including the titanium dioxide nanotubes are provided to mass produce hollow rod shaped titanium dioxide nanotubes with wide surfaces and a large dye adsorption amount by using a microwave reactor. CONSTITUTION: A manufacturing method of hollow rod shaped titanium dioxide nanotubes comprises the following steps: mixing titanium precursors with base additives in an alcohol solvent with a molar ratio of 1:5-10 moles; and performing a reaction for the obtained solution from the first step in a high pressure microwave reactor. The base additive is TBAH(tetrabutylammonium hydroxide). The hollow rod shaped titanium dioxide nanotube is comprised of titanium dioxide nanoparticles with an average particle diameter of 20-35 nanometers. The hollow stick has a width of 500-1000 nanometers and a length of 10-20 micrometers. The reaction is performed at 150-250 deg. Celsius for 2-6 hours in the high pressure microwave reactor with an output of 150-500W.

Description

 A manufacturing method of titanium dioxide nanotubes and a high-efficiency dye-sensitized solar cell photoelectrode comprising the titanium dioxide nanotubes TECHNICAL FIELD

The present invention relates to a method for producing titanium dioxide nanotubes and to a photoelectrode for a high efficiency dye-sensitized solar cell comprising the titanium oxide nanotubes, and more particularly to mixing a titanium precursor and a base additive in an alcohol solvent, The present invention relates to a method for producing titanium dioxide nanotubes and to a highly efficient dye-sensitized photovoltaic photoelectrode comprising the titanium oxide nanotubes.

In recent years, countries with high energy dependence on oil imports and the Kyoto Convention on Greenhouse Gas Emissions, especially in oil producing countries, need to develop and commercialize renewable energy to overcome future energy and environmental problems.

The importance of environmentally friendly solar cells that use infinite solar light as an energy source among future renewable energy is emerging. Currently, such solar cells include silicon solar cells, dye-sensitized solar cells, and organic semiconductor solar cells.

Photoelectric chemistry dye-sensitized solar cells (DSSC) were developed in 1991 by Professor Gratzel, Switzerland, by adsorbing ruthenium (Ru (Ⅱ))-based complexes on TiO ₂ semiconductor thin films. Dye-sensitized solar cell, which is the closest to commercialization as a solar cell to replace silicon solar cell, is slightly lower than photovoltaic efficiency by about 10% compared to conventional solar cell, but due to low-cost manufacturing equipment and process technology Due to the advantages that can be lowered to 1/5 of silicon-based, and can be applied as a transparent solar cell to a flexible substrate, intensive research is being conducted worldwide.

The dye-sensitized solar cell is composed of a photoelectrode, a counter electrode and an electrolyte, and the photoelectrode is used by adsorbing a photosensitive dye on metal oxide nanoparticles (TiO ₂ ) having a wide bandgap energy on a transparent conductive substrate (FTO). The counter electrode is used by coating platinum (Pt) on a transparent conductive substrate. In general, in the dye-sensitized solar cell, the size of the metal oxide of the photoelectrode uses titanium dioxide (TiO ₂ ) having a size of 10 ~ 20nm, the coating film is formed to a thickness of about 10㎛. The operation principle of such dye-sensitized solar cell is as follows.

When a ruthenium-based dye is adsorbed onto the titanium dioxide nanoelectrode and the dye is excited by receiving light energy, electrons are injected into the titanium dioxide nanoelectrode. At this time, electrons are injected at high speed, and the oxidized dye is also regenerated at high speed.

On the other hand, since the recombination rate of electrons lost to the electrolyte through the surface state is rather slow, most photoelectrons are injected into the semiconductor conduction band and participate in electron transfer, so that the photo-electric energy conversion efficiency is excellent.

In order to manufacture high efficiency dye-sensitized solar cells, the surface area of titanium dioxide must be large and the amount of absorbed photosensitive dyes must be large. In order to increase the adsorption amount of the dye, the size of titanium dioxide should be small, but in this case, it has the disadvantage of providing a recombination site of holes and electrons generated by the adsorbed dye.

The photoelectrode includes a light absorbing layer composed of titanium dioxide nanoparticles on which dye is adsorbed, and a scattering layer for returning unabsorbed light back to the light absorbing layer.

Early dye-sensitized solar cells had no light scattering layer and had to thicken the dye absorbing light absorbing layer to absorb all the incident light. However, if the absorber layer is too thick, the resistance increases, and the energy conversion efficiency decreases when the absorber layer is above the appropriate thickness.

In order to compensate for the above disadvantage, a light scattering layer was introduced using titanium dioxide having relatively large particles. It is a method of increasing the efficiency by scattering again the light not absorbed in the absorber layer. However, titanium dioxide having a large particle used as a light scattering layer has a disadvantage of adsorbing less dye than titanium dioxide in the light absorption layer.

An object of the present invention is to produce hollow rod-type titanium dioxide nanotubes with a larger surface area and larger dye adsorption than the larger titanium dioxide particles used in the light scattering layer of the photoelectrode, and then applying the same to the photoelectrode for solar cells. At the same time, it is possible to produce photoelectrons through light absorption while acting as light scattering, thereby enabling the production of highly efficient dye-sensitized solar cells.

The method for producing the hollow rod-type titanium dioxide nanotubes of the present invention is characterized by being prepared by mixing a titanium precursor and a base additive in an alcohol solvent and reacting the solution in a high pressure microwave reactor.

 As the alcohol solvent used in the present invention, an aliphatic alcohol may be used, and preferred examples thereof include methanol, ethanol, 1-propanol, 2-propanol, butanol, and the like.

As the titanium precursor used in the present invention, an alkoxide including oxygen atoms such as ethoxide, butoxide and isopropoxide is bonded to the titanium center atom to decompose by external energy. Titanium alkoxide, which is a precursor from which titanium dioxide particles can be produced, can be used. Among them, titanium (IV) isopropoxide (TTIP, 97%, manufactured by Aldrich) is particularly preferable.

The base additive used in the present invention includes tetrabutylammonium hydroxide (TBAH: tetrabuthylammonium hydroxide). The base additive is preferably used by mixing in a molar ratio of the titanium precursor: base additive = 1: 5 to 10, preferably 1: 8.5, by adjusting the concentration of the base additive in the above range, pure anatase Titanium dioxide nanotubes having an (anatase) crystal phase and having a uniform size can be prepared.

In the production of titanium dioxide nanotubes according to the present invention, as the concentration of the titanium precursor and the base additive increases, the length of the hollow rod becomes longer.

In the present invention, the titanium precursor and the base additive is characterized in that the reaction using a high-pressure microwave, the reaction conditions are preferably reacted with an output 150 ~ 500W for 2-6 hours in the temperature range of 150 ~ 250 ℃. .

If the reaction temperature is less than 150 ℃ the size of the particles are uneven, bad agglomeration phenomenon is not preferable, if the temperature exceeds 250 ℃ high power microwave vessel is deformed due to the high temperature, can not withstand high pressure It is not preferable that the ejection occurs, and if the reaction time is less than 2 hours, the reaction time is not sufficient, so the size or shape of the titanium dioxide particles cannot be controlled as desired, and the reaction time is more than 6 hours. In the case of the experiment, it is not preferable to obtain the desired titanium dioxide particles by the reaction of 5 to 6 hours, so that the excess reaction time is not necessary.In addition, when the output is less than 150W, the desired temperature is maintained in the high-power microwave vessel in time. There is not enough to raise and is undesirable If more than 500W this is not preferable because the burden on the high-power microwave synthesizer. However, if there are two or more high-power microwave vessels, a power of 500 W or more is required.

Titanium dioxide nanotubes produced by the manufacturing method of the present invention is a cube-shaped (cube) titanium dioxide nanoparticles are formed in a hollow rod form, the hollow rod-shaped titanium dioxide nanotubes according to the present invention It is preferable that the average particle diameter of a titanium dioxide nanoparticle is 20-35 nm, the width of a hollow rod is 500-1000 nm, and it is preferable that the length is 10-20 micrometers. When the average particle diameter of the titanium dioxide nanoparticles is less than 20nm, the particles are too small to limit dye adsorption, and when the average particle diameter exceeds 35nm, the surface area becomes small and the dye adsorption rate is not preferable. If it is less than 500nm, light scattering is not preferable, and if it is more than 1000nm, it is not preferable because it is difficult to maintain a nanotube form during paste production, and if the length of the hollow rod is less than 10 μm, light scattering is reduced. In the case of exceeding 20 μm, it is difficult to maintain the shape of the nanotubes during paste production, which is not preferable.

According to the present invention, there is provided a photoelectrode for dye-sensitized solar cell comprising a titanium dioxide nanotube produced by the method of the present invention as described above.

The photoelectrode of the present invention is characterized in that it comprises a light scattering layer comprising hollow rod-shaped titanium dioxide nanotubes produced by the method of the present invention.

In the photoelectrode of the present invention, the light scattering layer is formed using a hollow rod-shaped titanium dioxide nanotube produced by the method of the present invention, a paste containing a binder polymer and a solvent.

According to one preferred embodiment of the photoelectrode of the present invention, there is provided a photoelectrode comprising a photoelectrode substrate, a light absorbing layer formed thereon and a light scattering layer formed on the light absorbing layer, wherein the light absorbing layer has a general particle shape. A paste is formed by applying a paste containing an additive such as titanium dioxide nanoparticles, a polymer for a binder and a solvent, and a dispersion stabilizer, if necessary, onto the photoelectrode substrate, and the light scattering layer is formed of the titanium dioxide nanotube and the binder polymer according to the present invention. And a paste comprising a solvent is applied onto the light absorbing layer.

The binder polymer used in the preparation of the photoelectrode of the present invention may be used in the art without particular limitation on the kind thereof, preferably ethyl cellulose, polyethylene glycol and the like, and the solvent Furnace may be those commonly used in the art, preferably water, alcohol, terpineol and the like.

In the photoelectrode of the present invention, the light absorbing layer and the light scattering layer have a thickness of 1 to 50 µm, preferably 5 to 30 µm, respectively. If the thickness is less than 1 μm, the amount of dye adsorption is small and the number of generated electrons decreases, thereby decreasing the photoelectric conversion efficiency. If the thickness exceeds 50 μm, the number of generated electrons increases in proportion to the amount of dye adsorption, but the electron transfer path Phosphorus nano TiO ₂ interface is relatively high, so it does not increase above the critical efficiency or the possibility of the reversal of the electrons directly coupled with the electrolyte and the electron is increased, which is not preferable because the efficiency tends to decrease.

According to the method for producing titanium dioxide nanotubes of the present invention, by using a microwave reactor for a long time reaction time, which is a disadvantage of the pressurized reactor, the production time can be shortened, and mass production is possible at a low cost and a simple process.

Titanium dioxide nanotubes prepared according to the method of the present invention have the advantage of improving the energy conversion efficiency because the dye adsorption can generate photoelectrons as well as light scattering effect.

In addition, the hollow rod-type titanium dioxide prepared in the present invention can contribute to improving the energy conversion efficiency of the dye-sensitized solar cell at the same time since the light absorbing and light absorption at the same time.

In addition, when manufacturing a photosensitive electrode for a dye-sensitized solar cell using the titanium dioxide nanotube prepared by the method of the present invention, high efficiency of the solar cell can be expected, and the manufacturing cost of the dye-sensitized solar cell can be lowered.

1 is a photograph showing the results of observing the size and shape of titanium dioxide nanotubes prepared according to the present invention through an electron microscope,
Figure 2 is a photograph showing the results observed by X-ray diffraction analysis (XRD) for comparing the crystal phase of the titanium dioxide nanotubes prepared according to the present invention and P25,
3 is a view schematically showing a structure of a dye-sensitized solar cell having a photoelectrode including a light scattering layer formed using titanium dioxide nanotubes prepared according to the present invention.
Figure 4 is a graph showing the change in the photocurrent density for the dye-sensitized solar cell manufactured by using each photoelectrode prepared in Examples and Comparative Examples of the present invention.

Preparation Example: Preparation of Hollow Titanium Dioxide Nanotubes

Titanium isopropoxide (TTIP, 97%, manufactured by Aldrich) was added to 24 ml of ethanol and stirred for 10 minutes, followed by TBAH (tetrabutylammonium hydroxide solution, 40 wt.% In H2O, manufactured by Aldrich) ) Was added and stirred for about 10 minutes. At this time, the molar ratio of each chemical species was Ti: TBAH: H ₂ O: EtOH = 5: 42.5: 2: 41.5, and the solution obtained here was transparent and free of precipitates.

The mixed solution is transferred to a high-pressure microwave reaction vessel (MicroSYNTH, Milestone S & T Co., Ltd) to irradiate microwaves, and after heating up to 200 ° C. for 30 minutes at a power of 500 W, up to 3 or 6 hours of hydrothermal The reaction proceeded to produce TiO ₂ nanoparticles. Most of the reaction conditions were maintained at 200 ℃, 6 hours.

The reactor for the high-pressure microwave reactor is made of Teflon material, can withstand pressure up to 100bar, temperature up to 300 ℃, and can be synthesized using 10 containers at the same time with a maximum capacity of 100ml. It is possible.

Washing with distilled water and ethanol, and repeating the process of collecting the precipitate using a centrifuge several times, and dried to obtain the final product.

All species were run at room temperature and atmospheric pressure without purification. And deionized distilled water was used as water.

After the reaction, pure white titanium dioxide anatase crystal phase was obtained, and 3.56 g of titanium dioxide nanotubes having a width of 500 to 1000 nm and a length of 10 to 20 μm composed of nanoparticles (average particle diameter of 20 to 35 nm) were obtained as shown in FIG. 1.

≪ Example 1 >

-Photoelectrode fabrication using titanium dioxide nanoparticles (P25) as light absorbing layer and hollow rod-shaped titanium dioxide nanotubes as light scattering layer

An FTO glass substrate was prepared as a photoelectrode substrate, and an adhesive tape was attached to the conductive side of the substrate to mask an area of 0.275 cm 2.

Terpineol (terpineol): ethyl cellulose: lauric acid = 0.75: 0.05: 0.02 by mixing in a weight ratio to prepare a binder. Thereafter, TiO ₂ nanoparticles (trade name P25, average particle diameter: 20 nm, manufactured by Degussa): binder = 0.18: mixed at a weight ratio of 0.82, the weight ratio of TiO ₂ / terpineol / ethylcellulose / lauric acid was 0.18 / 0.75 / 0.05 /0.02. TiO ₂ paste 1 was prepared by mixing about 30 minutes at 1000 rpm using a paste mixer.

The TiO ₂ paste 1 prepared above was coated on the transparent electrode (FTO) layer by a doctor-blade method, and the transparent electrode substrate was baked at 450 ° C. for 15 minutes to form a light absorbing layer (thickness 10). Μm) was formed.

Using the hollow rod in the form of titanium oxide nanotubes and the binder polymer (ethyl cellulose) and solvent (terpineol) for prepared in Preparative Example, a TiO ₂ paste 2 in the same manner as the TiO ₂ produced in paste 1 It was prepared and coated on the light absorbing layer in the same manner, and baked at 450 ℃ for 15 minutes to form a light scattering layer (thickness 10㎛) consisting of a porous membrane.

Then, N719 (cis-bis (isothiocyanato) bis (2,2'-bipyridyl-4,4'-dicarboxylato) -ruthenium (II)) of Dyesol was prepared by dissolving 0.5 mmol of ethanol in the light scattering layer. One dye solution was adsorbed for 24 hours to prepare a photoelectrode.

<Example 2>

-Photoelectrode fabrication using P25 as light absorbing layer, hollow rod-shaped titanium dioxide nanotube 70% by weight + P25 30% by weight as light scattering layer

To determine whether there is a difference in the light scattering effect according to the content of the hollow rod-type titanium dioxide nanotubes, 70% by weight of the hollow rod-shaped titanium dioxide nanotubes prepared in the preparation example and titanium dioxide nanoparticles (P25 A photoelectrode was prepared in the same manner as in Example 1 except that the light scattering layer was formed using a mixture composed of 30 wt%.

<Example 3>

-Photoelectrode fabrication using 30% by weight of P25 as light absorption layer and hollow rod-shaped titanium dioxide nanotube + 70% by weight of P25 as light scattering layer

In order to determine whether there is a difference in the light scattering effect according to the content of the hollow rod-type titanium dioxide nanotubes, 30% by weight of the hollow rod-shaped titanium dioxide nanotubes prepared in the preparation example and titanium dioxide nanoparticles (P25 A photoelectrode was prepared in the same manner as in Example 1 except that the light scattering layer was formed using a mixture composed of 70 wt%.

<Example 4>

-Photoelectrode fabrication using P90 as light absorption layer and hollow rod-shaped titanium dioxide nanotubes as light scattering layer

Except for using P90 (trade name, anatase: rutile = 90:10, average particle diameter 10 ~ 15nm, manufactured by Degussa) instead of P25 as the titanium dioxide nanoparticles used in the formation of the light absorption layer in Example 1 A photoelectrode was prepared.

<Example 5>

-Photoelectrode fabrication using P90 as light absorption layer, hollow rod-shaped titanium dioxide nanotube 70% by weight + P90 30% by weight as light scattering layer

To determine whether there is a difference in the light scattering effect according to the content of the hollow rod-type titanium dioxide nanotubes, 70% by weight of the hollow rod-shaped titanium dioxide nanotubes prepared in the above preparation and titanium dioxide nanoparticles (P90 A photoelectrode was prepared in the same manner as in Example 1 except that the light scattering layer was formed using a mixture composed of 30 wt%.

<Example 6>

-Photoelectrode manufacturing using P90 as light absorption layer, hollow rod-shaped titanium dioxide nanotube 30% by weight + P90 70% by weight as light scattering layer

In order to determine whether there is a difference in the light scattering effect according to the content of the hollow rod-type titanium dioxide nanotubes, 30% by weight of the hollow rod-shaped titanium dioxide nanotubes prepared in the preparation example and the titanium dioxide nanoparticles (P90 A photoelectrode was prepared in the same manner as in Example 1 except that the light scattering layer was formed using a mixture composed of 70 wt%.

&Lt; Comparative Example 1 &

-Photoelectrode manufacturing using P25 as light absorption layer without light scattering layer

A photoelectrode was manufactured in the same manner as in Example 1 except that the light scattering layer was not formed in Example 1.

Comparative Example 2

-Photoelectrode manufacturing using P90 as light absorption layer without light scattering layer

A photoelectrode was manufactured in the same manner as in Example 4 except that the light scattering layer was not formed in Example 4.

&Lt; Comparative Example 3 &

-Photoelectrode fabrication using hollow rod-shaped titanium dioxide nanotubes as light absorption layer without light scattering layer

A photoelectrode was fabricated to see if a hollow rod-type titanium dioxide nanotube could be used in the light absorption layer to generate a photocurrent.

Except for forming a light absorbing layer using a hollow rod-shaped titanium dioxide nanotubes prepared in the manufacturing example instead of P25 used in the formation of the light absorbing layer in Example 1, except that the light scattering layer is not formed, Example 1 In the same manner as in the photoelectrode was prepared.

&Lt; Comparative Example 4 &

-Photoelectrode fabrication using 70% by weight of hollow rod-type titanium dioxide nanotubes + 30% by weight of P25 as a light absorption layer without light scattering layer

A photoelectrode was fabricated to see if 70% by weight of hollow rod-type titanium dioxide nanotubes were used in the light absorption layer to generate a photocurrent.

Instead of P25 used in the formation of the light absorption layer in Example 1 to form a light absorption layer by using a mixture of 70% by weight of the hollow rod-shaped titanium dioxide nanotubes and P25 30% by weight, a light scattering layer A photoelectrode was prepared in the same manner as in Example 1, except that no was formed.

&Lt; Comparative Example 5 &

-Photoelectrode fabrication using 30% by weight of hollow rod-type titanium dioxide nanotubes + 70% by weight of P25 as light absorption layer without light scattering layer

A photoelectrode was fabricated to determine whether 30 wt% of hollow titanium dioxide nanotubes in the form of hollow rods could be used to generate a photocurrent.

Instead of P25 used in the formation of the light absorbing layer in Example 1 to form a light absorbing layer using a mixture of 30% by weight of the hollow rod-shaped titanium dioxide nanotubes and P25 70% by weight, a light scattering layer A photoelectrode was prepared in the same manner as in Example 1, except that no was formed.

&Lt; Comparative Example 6 >

-Photoelectrode fabrication using P25 for both light absorption layer and light scattering layer

To compare whether P25 can be used as a light scattering layer by using P25 as a light scattering layer, the same method as in Example 1 except that P25 was used instead of the hollow rod-shaped titanium dioxide nanotubes used in the formation of the light scattering layer. A photoelectrode was prepared.

&Lt; Comparative Example 7 &

-Photoelectrode fabrication using P90 for both light absorption layer and light scattering layer

In order to compare whether P90 can be used as a light scattering layer by using P90 as a light scattering layer, the same method as in Example 1 except that P90 was used instead of the hollow rod-shaped titanium dioxide nanotubes used in the formation of the light scattering layer. A photoelectrode was prepared.

<Experimental Example 1>

-Particle size and shape measurement

The form of the titanium dioxide nanotubes prepared in Preparation Example was observed with an electron microscope, and the results are shown in FIG. 1, and the cross section of the photoelectrode prepared in Example 1 was confirmed using SEM.

<Experimental Example 2>

-Investigate crystal type of particles

The crystallinity of titanium dioxide nanotubes (HT) and P25 prepared according to the preparation example were analyzed by an X-ray diffractometer (Rigaku Multiflex diffractometer CuKa radiation (λ) = 1.5406 A), and are shown in FIG. 2 together. When looking at the X-ray diffraction pattern of HT, it can be confirmed that it is consistent with the peak of titania dioxide, which is anatase type JCPDS 21-1272.

<Experimental Example 3>

-Solar cell manufacturing

Each photoelectrode and the counter electrode manufactured in the above Examples and Comparative Examples were bonded to each other through a polymer film (Sealing material, SX1170-60) in the form of a sandwich, and finally an electrolyte was injected to form a dye-sensitized solar cell. Produced.

Open voltage, photocurrent density, energy conversion efficiency and fill factor of each of the fabricated dye-sensitized solar cells are shown in Tables 1, 2 and 5 below.

As can be seen from the results of the above table, when the titanium dioxide nanotubes were used as the light scattering layer in the dye-sensitized solar cell, the light conversion efficiency was increased (Examples 1 and 4 and Comparative Examples 1 and 2). Efficiency difference), and also the difference in efficiency can be obtained depending on the weight percent of titanium dioxide nanotubes (results of Examples 1 to 6).

Titanium dioxide nanotubes have the optimum conditions to be used as the light scattering layer was confirmed through the comparative experiment results (results of Examples 1, 4 and Comparative Examples 6, 7).

However, when titanium dioxide nanotubes were used as the light absorption layer, respectively, it was confirmed that the change in efficiency appeared depending on the nanotube content (comparative examples 3 to 5).

Claims (8)

A hollow rod-type titanium dioxide nanotube, which is prepared by mixing a titanium precursor and a base additive in an alcohol solvent in a molar ratio of titanium precursor: base additive = 1: 5 to 10, and reacting the obtained solution in a high pressure microwave reactor. Manufacturing method. The method of claim 1, wherein the alcohol solvent is selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol and butanol. The method of claim 1, wherein the base additive is tetrabutylammonium hydroxide. The hollow rod-type titanium dioxide nanotube is made of titanium dioxide nanoparticles having an average particle diameter of 20 ~ 35nm, the width of the hollow rod is 500 ~ 1000nm, the length is 10 ~ 20㎛ Method for producing hollow rod-type titanium dioxide nanotubes characterized in that. The method of claim 1, wherein the reaction conditions of the high-pressure microwave reactor are hollow rod-type titanium dioxide nanotubes, characterized in that the reaction at 150 ~ 500W output for 2-6 hours in the temperature range of 150 ~ 250 ℃. . A photosensitive electrode for dye-sensitized solar cells comprising a light scattering layer formed by using hollow rod-type titanium dioxide nanotubes prepared by the method according to any one of claims 1 to 5. 7. The photoelectrode of claim 6, wherein the photoelectrode comprises a photoelectrode substrate, a light absorption layer formed by applying a paste containing titanium dioxide nanoparticles on the photoelectrode substrate, and the hollow rod-shaped titanium dioxide nanotube on the photoabsorption layer. Dye-sensitized solar cell photoelectrode comprising a light scattering layer formed by applying a paste containing. Dye-sensitized solar cell comprising a photoelectrode for dye-sensitized solar cell according to claim 7.

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