KR101143474B1 - Methods for manufacturing titanium dioxide and dye-sensitized solar cell using the same - Google Patents

Abstract

A method for producing titanium dioxide and a method for producing a dye-sensitized solar cell using the method. Titanium dioxide (TiO ₂ ) manufacturing method according to the present invention comprises the steps of providing a mixed aqueous solution containing titanium alkoxide and ethanolamine; Adjusting the pH of the aqueous solution to 4-12; Applying heat to the aqueous solution to form a TiO ₂ precipitate; And drying the precipitate. According to the invention, possible to manufacture the particle shape and the control of TiO ₂ in size depending on the pH adjustment, and in particular the production of TiO ₂ for the high efficiency dye-sensitized solar cell, when to adjust the pH of the aqueous solution to 5.8 ~ 8.5 have.

Description

Method for manufacturing titanium dioxide and method for producing dye-sensitized solar cell using this method {Methods for manufacturing titanium dioxide and dye-sensitized solar cell using the same}

The present invention relates to a method for producing titanium dioxide (TiO ₂ ) and a dye-sensitized solar cell, and more particularly, to a method for producing TiO ₂ having controlled particle shape and size and a high efficiency dye-sensitized solar cell using the method. It relates to a method of manufacturing.

Recently, interest in renewable energy is increasing due to global environmental problems, exhaustion of fossil energy, waste disposal of nuclear power generation, and location selection due to the construction of new power plants. Among them, research and development on solar power generation, which is a pollution-free energy source, is being actively conducted at home and abroad.

A solar cell is a device that directly converts solar energy into electrical energy. The solar cell is made of an inorganic material using silicon or a compound semiconductor, or a dye-sensitized solar cell in which a photosensitive dye is adsorbed on the surface of a transition metal oxide particle depending on the material of the solar cell. And solar cells composed of organic molecules.

Currently, silicon-based solar cells are the mainstream, but since monocrystalline and polycrystalline silicon are made from bulk raw materials, the material cost is high, and thus there is a limit in terms of cost reduction. In order to solve this problem, a solution derived from manufacturing a thin film solar cell on an inexpensive substrate such as glass is a dye-sensitized solar cell, which is being researched recently as an inexpensive solar cell for commercialization.

Dye-sensitized solar cells consist of three parts: a semiconductor electrode, an electrolyte solution and an opposite electrode. Here, the semiconductor electrode refers to a transition metal oxide layer formed on a substrate such as conductive glass, and a photosensitive dye that absorbs sunlight and generates photoelectrons is adsorbed on the transition metal oxide layer. The counter electrode refers to a catalyst layer such as platinum formed on a substrate such as conductive glass. The electrolyte solution is the portion inserted between the semiconductor electrode and the counter electrode.

Since the energy conversion efficiency of solar cells is proportional to the amount of electrons generated by light absorption, the amount of dye adsorption must be increased to generate a large amount of electrons. Therefore, in order to increase the concentration of the adsorbed dye per unit area, it is required to prepare the transition metal oxide particles constituting the transition metal oxide layer to a nano size.

Nanocrystalline TiO ₂ is a material that is attracting attention as a transition metal oxide layer material for semiconductor electrodes of dye-sensitized solar cells because of its unique optical and electrical properties suitable for solar energy conversion, such as photocatalysts, photoelectric conversion devices. Extensive studies on the effect of the shape of TiO ₂ nanomaterials show that the energy conversion efficiency of photovoltaic devices using nanocrystalline TiO ₂ is dependent on the morphology of the nanomaterials. The use in the dye-sensitized solar cell of one-dimensional nanowires TiO ₂ or only dispersed (monodispersed) TiO ₂ is known to increase the energy conversion efficiency by improving charge transport ability. Accordingly, researches for synthesizing monodisperse TiO ₂ nanomaterials having various shapes have been actively conducted.

Traditional methods such as hydrothermal, flame, sol-gel and precipitate methods are available for mass production, but achieve shape control and monodispersity of TiO ₂ . Not suitable for Advanced methods using reverse micelles, polyol reactions, and sonochemical reactions can achieve shape control and monodispersity of TiO ₂ but are not applicable to mass production. In addition, the proposed methods have problems such as residues on the TiO ₂ surface or low crystallinity, which is an obstacle to using solar energy.

SUMMARY OF THE INVENTION The present invention has been made to solve the conventional problems, and the problem to be solved by the present invention is to provide a method of manufacturing a modified TiO ₂ in a shape-controlled, high crystallinity and monodisperse in a manner suitable for mass production It is.

Another object of the present invention is to provide a method of manufacturing a dye-sensitized solar cell having increased energy conversion efficiency by including an improved TiO ₂ layer in a semiconductor electrode.

Titanium dioxide (TiO ₂ ) manufacturing method according to the present invention for solving the above technical problem, providing a mixed aqueous solution containing titanium alkoxide and ethanolamine; Adjusting the pH of the aqueous solution to 4-12; Applying heat to the aqueous solution to form a TiO ₂ precipitate; And drying the precipitate.

According to the pH control, the TiO ₂ may have any one of a spherical shape and a rod shape. When ethylenediamine is added to the mixed aqueous solution, the TiO ₂ may have a wire shape according to the pH control. Can be.

In particular, since the pH of the mixed aqueous solution is adjusted to 5.8 to 8.5, TiO ₂ having an average particle size of 18 to 24 nm can be produced, and such pH adjustment is useful for obtaining TiO ₂ for dye-sensitized solar cells.

In the method of manufacturing a dye-sensitized solar cell according to the present invention, TiO ₂ paste is prepared by mixing TiO ₂ and a binder thus prepared, and then the TiO ₂ paste is coated on a substrate. Thereafter, the substrate coated with the TiO ₂ paste is fired to form a semiconductor electrode. A sandwich type dye-sensitized solar cell can be manufactured by assembling this semiconductor electrode with a counter electrode and filling it with an electrolyte solution.

In the binder, terpineol and ethylcellulose are preferably mixed in a mass ratio of 7: 1, wherein the TiO ₂ and the binder are mixed in a mass ratio of 1: 3 to 1: 3.5. The TiO ₂ paste may be applied to the substrate by a doctor blade method or a screen printing method, and may be applied such that the coating thickness of the TiO ₂ paste reaches 12 to 15 μm.

According to the present invention, the shape-controlled and monodispersed anatase TiO ₂ nanoparticles can be prepared by adjusting the pH of the sol-gel reaction. The nanoparticles have a uniform particle size distribution, high crystallinity, and a clean surface free from residual organics and defects. Mesoporous (mesoporous), so a uniform particle size distribution is essential for the nanoparticles in to improve the catalytic performance of material, forming a TiO ₂ layer with a TiO ₂ prepared according to the present invention is to have a high porosity and a specific surface area . By using this, the performance of the photocatalyst and the photoelectric conversion element can be improved. This method is also suitable for mass production.

In particular, according to the present invention, TiO ₂ having suitable physical properties for dye-sensitized solar cells can be produced. In the method for producing a dye-sensitized solar cell according to the present invention, a semiconductor electrode is formed by mixing and baking a binder on a substrate. . Since the semiconductor electrode includes a TiO ₂ layer having a high porosity and a specific surface area, transport of the photosensitive dye and the electrolyte in the dye-sensitized solar cell including the semiconductor electrode can be promoted to increase energy conversion efficiency. By optimizing the type of binder, the mixing ratio of TiO ₂ and the binder, and the like, the semiconductor electrode can be formed by preventing the TiO ₂ layer from breaking during firing.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, embodiments of the present invention may be modified in many different forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

(Example 1 _ TiO ₂ Preparation)

1 is a flow chart of a TiO ₂ manufacturing method according to the present invention.

Referring to Figure 1, in the first step (S1) of the present invention provides a mixed aqueous solution containing titanium alkoxide and ethanolamine. As the titanium alkoxide, at least one selected from titanium methoxide, titanium ethoxide, titanium butoxide, titanium n-butoxide, titanium tert-butoxide and titanium isopropoxide may be used. At least one selected from monoethanolamine, diethanolamine and triethanolamine can be used. The mixed aqueous solution may adjust the concentration of Ti ions using distilled water. Here, when the distilled water is small, the reaction does not occur completely, and the structure of the Ti (OH) ₄ gel is weak. When the distilled water is large, the reaction rate is too fast, and the viscosity increases too quickly. Ethylenediamine can also be added to a mixed aqueous solution as a shape control agent. As detailed in the Experimental Example 1, unless the addition of ethylene diamine or spherical with a large film of TiO _2, the addition of ethylene diamine is of the wire-like TiO ₂ can be obtained.

Next, the second step (S2) in the present invention various types? The pH of the mixed aqueous solution is adjusted to 4-12 using an inorganic acid and a base. At this time, an inorganic acid such as hydrochloric acid, sulfuric acid, nitric acid, perchloric acid (HClO ₄ ), a base such as sodium hydroxide (NaOH) solution, and an organic acid such as citric acid may be used. As described in detail in Experimental Example 1, since the TiO ₂ shape is determined to be spherical or rod-shaped according to pH, and its size also varies, pH control is an important factor for determining the shape and particle size of the finally produced TiO ₂ .

When the pH is lower than 4, the average particle size of TiO ₂ obtained is small, so that when the dye-sensitized solar cell is manufactured using this, smooth electron transfer may not be achieved. If the pH is greater than 12, the specific surface area of the resulting TiO ₂ is small, and when the dye-sensitized solar cell is manufactured using this, the amount of dye adsorbed may be insufficient, which may affect the efficiency. PH range which can exhibit excellent efficiency compared to the efficiency of the dye-sensitized solar cell using a commercially available powder of TiO ₂ is 4.7 ~ 10.5, particularly 5.8 ~ 8.5 is preferable.

In the third step (S3) in the present invention by applying heat to the mixed aqueous solution, to produce a TiO ₂ precipitate. If necessary, the mixed aqueous solution may be stirred. Alternatively, the mixed aqueous solution may be selectively stirred only in some sections of the reaction process (initial reaction). For example, a mixed aqueous solution is placed in an autoclave and heated. Here, the temperature and the reaction time may be adjusted according to the concentration of Ti ions. In this step the Ti (OH) ₄ gel matrix is crystallized and precipitated with TiO ₂ . If the reaction time is too short, it is difficult to obtain pure TiO ₂ , and if it is too long, the efficiency of the process is disadvantageous.

In the last step S4, the precipitate produced in the step S3 is filtered and dried to obtain TiO ₂ in powder form. In this step (S4) may be performed in the order of filtration, drying after performing an appropriate washing process to remove the residual organic matter on the surface.

As confirmed in Experimental Example 1 to be described later, TiO ₂ prepared according to the present invention is pure under all pH conditions. It has an anatase phase and is excellent in crystallinity. In addition, when the pH is less than 10.5, spherical particles having an aspect ratio of 1, the rod-shaped particles having an aspect ratio of 5 at a pH of 10.5 or more, and the wire-shaped particles having an aspect ratio of 10 are added when the pH is at least 10.5 and ethylenediamine is added. Can be diversified In addition, as revealed in Experimental Example 3 to be described later, TiO ₂ prepared according to the present invention has monodispersity having a uniform particle size distribution around the average particle size.

As described above, according to the present invention, TiO ₂ may be manufactured to have a spherical shape, a rod shape, and a wire shape according to pH adjustment and ethylenediamine addition, and the control of the shape is comprehensive compared to the existing methods. . In other words, instead of using a separate process depending on the shape, the pH control and the addition of the shape control agent in one process to obtain various forms of TiO ₂ .

As described above, according to the present invention, since the monodisperse TiO ₂ having excellent crystallinity can be manufactured in various forms by a relatively simple process, the manufacturing process is simplified, cost reduction is possible, and more advantageous for mass production.

In particular, by controlling the pH of the mixed aqueous solution containing the titanium alkoxide, and ethanol amine, as shown in Experiment 2 5.8 ~ 8.5 can be prepared a rectangle of TiO ₂ having an average particle size of 18 ~ 24nm, these TiO ₂ After forming a TiO ₂ layer using a dye-sensitized solar cell efficiency is more than 5.5%. Therefore, the TiO ₂ manufacturing method of the present invention can be used to manufacture TiO ₂ for high efficiency dye-sensitized solar cells.

(Example 2 _ dye-sensitized solar cell production)

2 is a view schematically showing the configuration of a dye-sensitized solar cell to be manufactured according to an embodiment of the present invention.

Referring to FIG. 2, the dye-sensitized solar cell 100 manufactured according to the embodiment of the present invention includes a semiconductor electrode 10 and a counter electrode 30, and an electrolyte solution 50 is injected therebetween to seal it. One sandwich structure. The electrolyte solution 50 may be sealed with a thermoplastic polymer material 60 such as surlyn (DuPont 1702) to prevent leakage.

The semiconductor electrode 10 includes a TiO ₂ layer 14 formed on the conductive first substrate 12, and a photosensitive dye is chemically adsorbed on the TiO ₂ layer 14. The TiO ₂ layer 14 is formed using TiO ₂ prepared by the TiO ₂ manufacturing method according to the present invention. The counter electrode 30 includes a catalyst layer (for example, platinum and graphite) 34 formed on the conductive second substrate 32, and the catalyst layer 34 faces the TiO ₂ layer 14. The electrolyte solution 50 is an iodine-based redox liquid electrolyte, for example, a redox electrolyte composed of iodine / iodide ions using a nitrile solvent.

The principle of the dye-sensitized solar cell 100 is as follows. When sunlight is incident on the dye-sensitized solar cell 100, photons are first absorbed by the dye chemically adsorbed to the TiO ₂ layer 14 of the semiconductor electrode 10. The dye electrons transfer from the ground state to the excited state to form an electron-hole pair, and the electrons in the excited state are injected into the conduction band of the TiO ₂ layer 14. The injected with TiO ₂ layer 14, electrons (not shown) outside of the wire transmitted to the first conducting substrate (12) in contact with the TiO ₂ layer 14 is connected to the first conducting substrate 12 through an interface between particles It is moved to the counter electrode 30 through.

Oxidized as a result of electron transfer dye oxidation of iodide ions in the electrolyte solution ^{(50) (3I - ->} I 3 - + 2e -) of iodine ions oxidation is reduced again accept electrons provided by (I ₃ ^-) The silver is reduced again by the electrons reaching the counter electrode 30 to complete the operation of the dye-sensitized solar cell 100. The photocurrent is obtained as a result of the diffusion of electrons injected into the TiO ₂ layer 14 and the open-circuit voltage ( V _oc ) is the Fermi energy of the TiO ₂ layer 14 and the oxidation of the electrolyte solution 50. It is determined by the reduction potential difference.

As mentioned above, the energy conversion efficiency of dye-sensitized solar cells is proportional to the amount of electrons generated by light absorption, so the amount of dye adsorption must be increased to generate a large amount of electrons. Therefore, particles of the transition metal oxide layer of the semiconductor electrode are generally formed in nano size and possibly thick film.

The TiO ₂ layer 14 is formed using TiO ₂ prepared by the manufacturing method according to the present invention, and thus made of monodisperse TiO ₂ . Therefore, since the TiO ₂ layer 14 has mesoporous properties, has a large number of pores and a structure in which the pores are connected to each other, and has a large specific surface area, the concentration of dye adsorbed per unit area is greatly increased. In addition, since the TiO ₂ layer 14 can be formed sufficiently thick using the coating method proposed in the present invention without losing transparency due to the properties of the TiO ₂ prepared according to the present invention, sufficient dye adsorption can be induced. In addition, since the TiO ₂ layer 14 has a mesoporous structure into which an electrolyte can be injected, the TiO ₂ layer 14 has a smooth electron transport capability. Therefore, the dye-sensitized solar cell 100 including the TiO ₂ layer 14 exhibits high photoelectric conversion efficiency due to effects of a large amount of dye adsorption, smooth electron transport, and the like.

Now, the dye-sensitized solar cell manufacturing method according to the present invention will be described in detail.

In order to manufacture the semiconductor electrode 10, TiO ₂ and a binder are mixed to prepare a TiO ₂ paste. This paste may contain other additives and solvents to aid in dispersion.

TiO ₂ is prepared by using the TiO ₂ production method according to the present invention, in particular by adjusting the pH of the mixed aqueous solution containing titanium alkoxide and ethanolamine to 5.8 ~ 8.5, spherical having an average particle size of 18 ~ 24nm TiO ₂ to be prepared and used. The pH range and particle size are not merely numerical limitations, and are optimized in terms of efficiency of the dye-sensitized solar cell, as shown in Experimental Example 2 described later.

The binder refers to a material having a function of preventing the crack generated at the time of applying the TiO ₂ and the film forming substrate or the like, or prevent peeling from the substrate. The binder can be polyethylene glycol, polyvinyl alcohol, poly-N-vinylacetamide, polyacrylamide, polyacrylate, N-vinylacetamide-sodium acrylate copolymer, acrylamide-sodium acrylic lake copolymer or polytetrafluoro Although ethylene can be used, it is preferable to use a mixture of terpineol and ethyl cellulose in a mass ratio of 7: 1.

Next, the TiO ₂ paste prepared above is applied to the conductive first substrate 12. Examples of the method of applying the TiO ₂ paste include a squeegee method, a doctor blade method, a screen printing method, a spray method and a spin coating method. As long as the film thickness can be adjusted, other methods can be used without particular limitation.

Here, the conductive first substrate 12 is coated with a transparent conductive oxide film (TCO) such as FTO, ITO and dried electrode substrate (eg, polyolefins such as glass or polyethylene, polypropylene and polystyrene, nylon 6, nylon 66). And polyamides such as aramid, polyesters such as polyethylene terephthalate, polyethylene naphthalate and unsaturated polyester, polyvinyl chloride, polyvinylidene chloride, polyethylene oxide, polyethylene glycol, silicon resin, polyvinyl alcohol, vinyl acetal resin , Polyacetates, ABS resins, epoxy resins, vinylacetate resins, cellulose and cellulose derivatives (e.g. rayon), urethane resins, polyurethane resins, polycarbonate resins, urea resins, pullulo resins, polyvinylidene fluorides, phenols Resin, Celluloid, Chitin, Starch Sheet, Acrylic Resin, Mela It may be an organic polymer) such as a resin, an alkyd resin.

In the experiment, when TiO ₂ and the binder were mixed in a 1: 2.5 mass ratio, the viscosity was very high and could not be applied by the doctor blade method or the screen printing method. When TiO ₂ and the binder were mixed in a mass ratio of 1: 3 to 1: 3.5, very good results were obtained in viscosity and film state after firing when applied by the doctor blade method or the screen printing method. When TiO ₂ and the binder were mixed in a 1: 4 mass ratio, coating was possible by the doctor blade method or the screen printing method, but a film cracking phenomenon occurred after firing. Therefore, TiO ₂ and the binder are preferably used by mixing in a mass ratio of 1: 3 to 1: 3.5.

If the thickness of the TiO ₂ layer 14 is too thin, light scattering or absorption is insufficient to reduce the photoelectric conversion efficiency, while too thick the thickness of the TiO ₂ layer 14 increases the dispersion resistance of the electrolyte or extends the electron travel distance, thereby necessarily improving performance. In addition, the film forming operation is complicated. Therefore, the coating thickness of the TiO ₂ paste is appropriately determined and formed by repeatedly applying the final TiO ₂ layer 14 to reach a thickness of 12 to 15 μm, or by applying it in one step. In the case of coating by the screen printing method, when TiO ₂ and the binder were mixed in a 1: 3 mass ratio, a coating thickness of 12 to 13 μm was obtained in three coatings, and TiO ₂ and the binder were mixed in a mass ratio of 1: 3.5. In the case of coating three times, a coating thickness of 15 μm was obtained.

Next, the conductive first substrate 12 coated with the TiO ₂ paste is fired to form the TiO ₂ layer 14. Drying the applied TiO ₂ paste may further comprise before firing. Examples of the drying method include a method in which hot air is blown into the coated TiO ₂ paste by a dryer or the like, a method of irradiating infrared rays, a heating method, or the like. In addition, if the drying temperature is a temperature at which the deformation or modification of the conductive first substrate 12 does not occur, a method of evaporating the solvent from the TiO ₂ paste applied on the conductive first substrate 12 without particular limitation may be used. It may be. For example, a treatment such as drying for 10 minutes in an electric oven maintained at a temperature of 100 ° C may be performed.

Firing may be heat treatment at 450 ° C. for 1 hour in an air atmosphere. The purpose of heating is to improve the photoelectric conversion properties by increasing the electrical contact of TiO ₂ particles and removing the polymer added during the preparation of the paste. Since TiO ₂ prepared according to the present invention has a very uniform particle size distribution, there is almost no film shrinkage during firing, and as shown in Experimental Example 5 (Fig. 14 (a)), the morphology and size uniformity of TiO ₂ after the firing process are observed. There is no noticeable change, and the coating thickness of 12 to 15 mu m is maintained almost as it is to obtain a thick film TiO ₂ layer 14.

Next, the semiconductor electrode 10 is formed by impregnating the TiO ₂ layer 14 in a solution in which ruthenium (Ru) dye is dissolved for 24 hours or more to adsorb the dye.

Then, the counter electrode 30 which is an anode is formed. To this end, the catalyst layer 34 is formed on the conductive second substrate 32. Here, the conductive second substrate 32 may be an electrode substrate coated and dried with FTO, ITO, etc. similarly to the conductive first substrate 12. Platinum may be used as the catalyst layer 34. For example, a conductive glass substrate may be prepared, and a 5 mM hexachloroplatinic acid (H ₂ PtCl ₆占 xH ₂ O) aqueous solution may be dispersed thereon, followed by drying. The coated substrate was treated with 60 mM sodium borohydride (NaBH ₄ ) aqueous solution to reduce platinum ions to platinum, washed with distilled water, and dried. Instead, the catalyst layer 34 may be formed using an electron beam deposition technique.

Next, the counter electrode 30 and the semiconductor electrode 10 face the catalyst layer 34 and the TiO ₂ layer 14 coated with a dye with the conductive surface inward. When assembling the counter electrode 30 and the semiconductor electrode 10, a thermoplastic polymer material 60 having a thickness of 30 to 50 μm is placed on the edge between the two electrodes, and then pressed to closely adhere the three surfaces between the two electrodes.

Next, the electrolyte solution 50 is injected and filled through the remaining non-sealed surface. In addition to the electrolyte solution described above, the electrolyte solution 50 is 0.8M 1,2-dimethyl-3-hexyl-imidazolium iodide (1,2-dimethyl-3-hexyl-imidazolium iodide) and 40 mM I. ₂ dissolved in acetonitrile or 0.8 M LiI and 40 mM I ₂ and 0.2 M TBP (4-tert-butylpyridine) dissolved in acetonitrile can be used. After filling the electrolyte solution 50, the thermoplastic polymer material 60 is placed on an unsealed surface, and then sealed by heating and pressing.

As described above, the production method according to the present invention forms a mesoporous TiO ₂ layer 14 composed of monodisperse TiO ₂ , so that the concentration of dye adsorbed per unit area is greatly increased. However dispersibility of TiO ₂ TiO ₂ the nature layer 14 does not affect the transparency of the thickening is formed by also dye-sensitized solar cell 100 is transparent. In particular, the TiO ₂ paste application conditions of the production method according to the present invention enable formation of the TiO ₂ layer 14 of the thick film without cracking, thereby inducing sufficient dye adsorption. In addition, since the TiO ₂ layer 14 has a structure in which the electrolyte solution 50 can be added well, the TiO ₂ layer 14 has a smooth electron transport capability. Therefore, the dye-sensitized solar cell 100 manufactured according to the present invention shows high photoelectric conversion efficiency.

Hereinafter, various aspects of the present invention described above will be described in more detail through specific experimental examples. The following experimental examples do not limit the scope of the present invention, but are merely exemplary for implementing the present invention.

In all the following experimental examples, the TiO ₂ nanoparticles prepared according to the present invention were observed in shape by high resolution transmission electron microscopy (HR-TEM, JEM 3000F, Japan). The crystal structure was confirmed by X-ray diffractometer (X-ray diffractometer: XRD, M18XHF-SRA, MAC-Science Instruments, Japan). Absorption isotherm of the specific surface area of TiO ₂ and TiO ₂ layer was measured by the BET analyzer (BELSORP-mini II, BEL, Japan). The electron binding energy of TiO ₂ nanoparticles was analyzed using X-ray photoelectron spectroscopy (XPS, SIGMA PROBE, ThermoVG, UK). The XPS spectrum is obtained using a monochromatic Al-K source (100 W), and the binding energy of the Ti (2p) peak is 284.6 eV from TiO ₂ . Corrected for C (1s) peaks. The IR transmittance spectrum of the prepared TiO ₂ nanoparticles was measured using an FT-IR spectrometer (Nicolet6700, ThermoScientific, USA) in the range of 600 ~ 4000cm ^-1 at room temperature. After the TiO ₂ layer was formed on the FTO-coated conductive substrate, the reflectance and transmittance of the TiO ₂ layer without dye were measured by UV-Vis spectroscopy.

Dye-sensitized solar cells were prepared in the sandwich type as in Example 2. The thickness of the TiO ₂ layer in the semiconductor electrode was measured by FE-SEM (JSM-6330F, Japan). The amount of dye adsorbed on the TiO ₂ layer was checked by measuring the UV-Vis spectrum of the desorbed dye solution. Photoelectric conversion characteristics of the solar cell were measured under an air weight of 1.5 (with Solar simulator; Peccell Technologies, Japan; intensity: 100 mW cm ⁻² ) using a potentiometer (potentiostat, CHI 608C, CH Instruments, USA).

Light intensity was calibrated using standard solar cells (PV Measurements, USA). All photoelectric conversion characteristics were evaluated using a mask (active layer area 0.25 cm ² ). The electrochemical impedance of the solar cell was measured by irradiating 100 mW cm ⁻² using a constant ^{potentiometer} and applying an open circuit voltage ( V _oc ) as a bias. The response time (electron lifetime) obtained from V _oc reduction was measured by open circuit voltage reduction (OCVD) method as a function of time. For the measurement of V _oc reduction, the flow decay curve of V _oc was monitored during relaxation from the quasi- equilibrium state to the dark equilibrium state where the incident light was temporarily blocked and then started to be irradiated. Data was collected every 50 ms using a constant potentiometer. Electron diffusion coefficients were obtained by stepwise light-induced fluidity measurements using the photocurrent (SLIM-PC) method and laser diode (660 nm).

Experimental Example 1 _ TiO of Various Shapes ₂  Nanoparticle manufacturing)

TiO ₂ nanocrystals having various aspect ratios were synthesized according to pH adjustment and ethylenediamine (ED) addition.

Titanium isopropoxide (TTIP) and triethanolamine (TEOA) were mixed at a molar ratio of 1: 2, and then diluted with distilled water to prepare a stock solution of Ti ⁴⁺ (0.5 M). The pH of the mixed aqueous solution was adjusted to 8.5-10.5 by adding HClO ₄ and / or NaOH solution to the solution. The case where 0.4 M ED was added as a shape control agent was also performed. The mixed aqueous solution was placed in an autoclave and primary aged at 100 ° C. for 24 hours, followed by secondary aging at 140 ° C. for 72 hours to facilitate nucleation and growth of TiO ₂ seeds. The synthesized TiO ₂ nanoparticles were washed with NaOH (No. 6), HNO ₃ (No. 2), and distilled water (No. 4) to remove residual organic matter on the surface, and dried by centrifugation.

(A) to (d) of Figure 3 deulyigo TEM photograph of the synthesized nanocrystalline TiO _2, (e) is a XRD pattern of the as-synthesized nanocrystalline TiO _2. In FIG. 3 (d), the arrow indicates the crystal lattice direction. In FIG. 3E, the x-axis is 2θ value and the y-axis is intensity of diffraction peak.

First, FIG. 3 (a) shows a TEM image of spherical TiO ₂ nanocrystals (GSS) having an average particle size of 20 nm. It was synthesized at pH 8.5 conditions without ED. As revealed in Experimental Example 3 described later, this is monodisperse particles having a uniform particle size distribution around the average particle size.

When the pH was increased to 10.5, rod-shaped TiO ₂ nanocrystals (GSR) were obtained as shown in FIG. 3 (b), and the average size thereof was 20 nm (width) × 100 nm (length). When ED is added under these pH conditions, wire-type TiO ₂ nanocrystals (GSW) are obtained at 20 nm (width) × 200 nm (length), and the aspect ratio is rod-shaped (as shown in Fig. 3 (c)). Double the GSR). When the amino acid group is adsorbed on the plane parallel to the c-axis of the anatase structure, anisotropic anatase TiO ₂ is formed. As such, the Ti (OH) ₄ gel matrix is anisotropically crystallized. In high pH (10.5 and above) solutions, the amine groups form strong bonds to the TiO ₂ side and are therefore anisotropic. It can be seen that ED is an effective shape modifier to obtain GSW with high aspect ratio as primary amine. Figure 3 (d) is a HR-TEM picture of GSW, showing that the nanocrystals are grown along the [001] direction because the individual nanowires are single crystals and ED adsorption on the crystal plane parallel to the c-axis.

In addition, as shown in FIG. 3 (e), the XRD pattern of the synthesized TiO ₂ shows that all the shape controlled monodisperse particles have a pure TiO ₂ anatase phase without any secondary phase. The anatase phase is known to be the most effective phase as an electron carrier in dye-sensitized solar cells.

In summary, when the TiO ₂ production method according to the present invention was carried out, TiO ₂ having excellent crystallinity was obtained, and spherical particles below pH 10.5, rod-shaped particles above pH 10.5, and when pH 10.5 and ED were added. It was possible to obtain wire-shaped particles. As such, according to the present invention, various types of TiO ₂ may be manufactured by a relatively simple process, thereby simplifying the manufacturing process, enabling cost reduction, and being more advantageous for mass production.

Experimental Example 2 _ GSS of Various Average Particle Sizes  Produce)

TTIP and TEOA were mixed at a molar ratio of 1: 2 and diluted with distilled water to prepare a stock solution of Ti ⁴⁺ (0.5 M), and the pH of the prepared stock solution was 10.0. HClO ₄ was added thereto to adjust the pH of the mixed aqueous solution to 4.7 to 10.0. Then, the mixed aqueous solution was placed in an autoclave and primary aged at 100 ° C. for 24 hours, followed by secondary aging at 140 ° C. for 72 hours. The synthesized TiO ₂ nanoparticles were washed with NaOH (No. 6), HNO ₃ (No. 2), and distilled water (No. 4) to remove residual organic matter on the surface, and then centrifuged and dried.

Figure 4 is a TEM picture of the TiO ₂ nanocrystals prepared according to the above method, it is possible to determine the shape and particle size of each nanocrystals at pH 4.7, 5.8, 8.0, 8.5, 9.0 and 10.0 conditions. The average particle size was calculated using the Scherrer equation after measuring the diameter of 300 particles in each sample. It can be seen that at pH 4.7, 5.8, 8.0, 8.5, 9.0 and 10.0, each nanocrystal was formed into a spherical shape, GSS, and the average particle size was 14 nm, 18 nm, 22 nm, 24 nm, 31 nm and Calculated at 38 nm.

The TiO ₂ layer was formed using GSSs having various average particle sizes thus obtained. After forming the semiconductor electrode, the efficiency of the dye-sensitized solar cell was measured and summarized in FIG. 5. At this time, the thickness of the TiO ₂ layer was 10 μm, and a dense TiO ₂ layer of 80 nm was also formed as an undercoat layer or a blocking layer commonly employed between the transition metal oxide layer and the TCO of the dye-sensitized solar cell (transition metal). The presence of microcracks, etc., in the oxide layer can cause the substrate to come into direct contact with the electrolyte, resulting in reverse electron transfer (leakage current), in order to prevent cracking, an undercoat or barrier layer is often formed between the transition metal oxide layer and the TCO. Forms). Referring to FIG. 5, in all cases obtained under pH 4.7, 5.8, 8.0, 8.5, 9.0 and 10.0 conditions, the efficiency of dye-sensitized solar cells using it is greater than 4.7.

On the other hand, Table 1 below shows the specific surface area when the TiO ₂ layer was formed using the GSS, GSR, GSW and the commercial TiO ₂ powder Degussa P25 of Experimental Example 1 to form a semiconductor electrode, and a dye-sensitized solar cell using the same. The amount of adsorption dye, short-circuit current density (J _sc ), V _oc , fill factor ( ff ), and photoelectric conversion efficiency (η) are summarized.

Where η (%) = J _sc × V _oc × ff / incident light energy × 100

The thickness of the TiO ₂ layer was 10 μm, and a dense TiO ₂ layer of 80 nm was also formed as an undercoat or barrier layer commonly employed between the transition metal oxide layer and the TCO of the dye-sensitized solar cell.

As shown in Table 1 above, considering that the efficiency when manufactured using a commercial TiO ₂ powder Degussa P25 is 4, the result according to Figure 5 is a very good result. If the size of the TiO ₂ nanocrystals is too small, smooth electron transfer may not be achieved. If the TiO ₂ nanocrystals are too large, the specific surface area may be small, resulting in insufficient amount of dye absorbed, which may affect efficiency. According to the present invention, the GSS obtained at pH 4.7 to 10.0 is an ideal case in which the average particle size is neither too small nor large, and thus all are suitable for dye-sensitized solar cells.

In particular, if the efficiency is defined as higher than 5.5%, the dye-sensitized solar cell using the same when the average particle size of GSS is 18 nm, 22 nm, and 24 nm is shown from FIG. To be used, TiO ₂ is preferably prepared in a spherical shape with an average particle size in the range of 18 nm to ₂₄ nm. Thus, pH conditions for the production of TiO ₂ it can be seen that it is most desirable to 5.8 ~ 8.5.

In summary, the efficiency of the dye-sensitized solar cell using GSS obtained at pH 4.7 to 10.0 is 4.7 or more, and as summarized in Table 1, GSR and GSW prepared according to Experimental Example 1 of the present invention were used for semiconductor electrodes. In addition, since the efficiency of the dye-sensitized solar cell can be increased compared to the case of using Degussa P25, which is a commercial TiO ₂ powder, a pH higher than 10.0 and a pH of 10.5 or less are also suitable conditions for efficiency of the dye-sensitized solar cell. Therefore, a useful pH range in consideration of the efficiency of the dye-sensitized solar cell is 4.7 to 10.5, and is particularly preferable since a high efficiency dye-sensitized solar cell can be produced at pH 5.8 to 8.5 of 5.5% or more.

Experimental Example 3 Evaluation of Monodispersed GSS 1

Monodisperse GSS prepared according to the present invention was analyzed in comparison with P25. As monodispersed GSS prepared according to the present invention was synthesized at pH 8.5 in Experimental Example 1.

First, the crystallinity of GSS was compared with P25. 6 is an XRD pattern of GSS and P25 and also shows the XRD pattern of anatase (SG) synthesized by the conventional method. In Fig. 6, (●) indicates anatase, and ★ indicates (110) plane, that is, rutile. SG was synthesized by hydrolysis of TTIP and distilled water at 80 ° C. for 48 hours and then calcined at 450 ° C. for 1 hour in air. As shown in Figure 6, GSS anatase is very good crystallinity compared to P25, which is much higher than SG.

Next, particle size, defects, and residual organic matter were evaluated. The average particle size was calculated using the Scherer equation after measuring the diameter of 300 particles in P25 and GSS TEM images, 21.5 nm and 18.6 nm, respectively.

FIG. 7A is a particle size distribution obtained from P25 and GSS TEM images, (b) is a Ti 2p XP spectrum of P25 and GSS, and (c) is an FT-IR spectrum.

As shown in Figure 7 (a), GSS was shown to have a monodispersity having a uniform particle size distribution around the average particle size while the particle size of P25 has a widely distributed polydispersity.

Surface defect states and residual organic compounds were analyzed using XPS and FT-IR.

First, as shown in FIG. 7B, the peak binding energies of Ti 2p _3/2 and 2p _1/2 were the same at 458.40 eV and 464.16 eV in GSS and P25. Therefore, it can be seen that the concentration of nonstoichiometric defects such as Ti ³⁺ ions in the GSS is negligible.

Looking at the FT-IR spectrum of each sample shown in Fig. 7 (c), the upper part is before firing after application of TiO ₂ paste and the lower part is after firing at 450 ° C. for 1 hour in air. Viewed as missing the NH (~ 1405 cm ^-1) and NO (~ 1340cm ^-1) absorption peaks after firing, it can be seen that the amino acid residue on the GSS group being easily removed in 1 hours heat treatment conditions, 450 ℃, in the air.

Removing surface defects and residual organics from TiO ₂ is a prerequisite for obtaining high efficiency in dye-sensitized solar cells. This is because if the crystallinity is low or there is a lattice defect, the conduction band energy level of TiO ₂ is reduced and the solar cell is manufactured so that the open circuit voltage is lowered and the photoelectric conversion efficiency is reduced. The GSS prepared according to the present invention is suitable for dye-sensitized solar cells because it has excellent crystallinity and no defects and residual organic matter as described above.

Experimental Example 4 Evaluation of Monodispersed GSS 2

The effect of GSS on the performance of dye-sensitized solar cells was analyzed in comparison with the case of using P25, especially in terms of optical reflectance and carrier transport.

A TiO ₂ layer was formed using GSS and P25 to form a semiconductor electrode, and a dye-sensitized solar cell was manufactured using the same. As seen in Experimental Example 3, since GSS and P25 have similar average particle size and crystallinity except for particle size distribution, the IV curve of FIG. 8 shows the effect of particle uniformity on the operating performance of dye-sensitized solar cells. do.

As summarized in Table 1 above, the total conversion efficiency of the dye-sensitized solar cell (hereinafter referred to as GSS solar cell) using GSS is 32.5% higher than that of the dye-sensitized solar cell (hereinafter referred to as P25 solar cell) using P25. The high conversion efficiency of GSS solar cells is due to the significant improvement in J _sc . The J _sc of the GSS solar cell is 9.9 mA cm ^−2, which is higher than the 8.3 mA cm ⁻² , which is the J _sc of the P25 solar cell.

First, the reason why the J _sc of the GSS solar cell is large is due to the high surface area. Figure 9 is a cross-sectional FE-SEM photograph of TiO ₂ layer made of TiO ₂ layer and the GSS made with P25. TiO ₂ layer is also made of TiO ₂ layer and the GSS made with P25, as shown at 9, is only gajyeotji substantially the same thickness of about 10 ㎛, the specific surface area of the TiO ₂ layer made of GSS 80 than the TiO ₂ layer made of P25 % Higher (Table 1). The larger specific surface area increases the amount of dye adsorbed on the surface, thus improving the ability to harvest photons. If GSS particles and P25 particles are piled regularly, the surface area of the TiO ₂ layer made of GSS and TiO ₂ layer made of P25 is 80.0 m ² g ^-1 and 71.7m ² g ^-1, respectively. However, the surface area of the TiO ₂ layer made of P25 is only 41.5 m ² g ⁻¹ , which is much smaller than the calculated value. This suggests that only monodisperse GSS particles pile up regularly, creating a very mesoporous structure. In TiO ₂ layers made of P25, the small particles fill the voids between the large particles, causing the surface area to decrease during the subsequent firing process. When preparing a dye-sensitized solar cell with a small pore state and a lack of the electrolyte inside the TiO ₂ layer occurs because the electrolyte is not substantially dispersed in TiO ₂ layer, the lack of the electrolyte is brought to failure in smooth movement of the charge performance of the solar cell Decreases.

In FIG. 10, (a) is a schematic diagram of a TiO ₂ layer made of P25. Since polydispersity has small surface area with small particles filling pores between large particles, (b) shows a TiO ₂ layer made of GSS. As a schematic diagram, since it has monodispersity, particles are piled up regularly and have a mesoporous structure. Thus, that there is a porosity of the TiO ₂ layer made of the TiO ₂ produced by the present invention higher, the film thickness can adsorb a larger amount of light-sensitive dyestuff case, and the electrolyte is dispersed in TiO ₂ layer It can be seen that this can help move the charge smoothly and increase the performance of the solar cell.

Of Figure 11 (a) is N ₂ absorption isotherm and pore determined from the TiO ₂ layer with TiO ₂ layer made of GSS made with P25 - a particle size distribution (not the box). (b) the green electron diffusion coefficient as a function of J _sc in the TiO ₂ layer made of TiO ₂ layer and the GSS made with P25: shows the (electron diffusion coefficients D). (c) and (d) shows a relative light reflectance and transmittance of the TiO ₂ layer made from 550nm to the TiO ₂ layer and the GSS made from P25 to the film thickness. (e) shows the total energy conversion efficiency of dye-sensitized solar cells as a function of film thickness. At this time, in order to exclude the influence on the reflectance, transmittance and operation performance in all cases, it was prepared without the dense TiO ₂ layer commonly employed between the transition metal oxide layer and TCO of the dye-sensitized solar cell.

First, in FIG. 11 (a) is N ₂ adsorption in the TiO ₂ layer made of TiO ₂ layer and the GSS made with P25 - shows the particle size distribution-desorption isotherm and pore. The isotherm of the TiO ₂ layer made of GSS shows a typical isotherm of mesoporous material containing uniform spherical particles. This mesoporous material with a periodic particle arrangement has a narrow pore-particle size distribution, which is the pore-particle size of the TiO ₂ layer made of GSS and the TiO ₂ layer made of P25 as shown in the box of FIG. 11 (a). It can be confirmed from the distribution. 11 (a) shows that the pores of the TiO ₂ layer made of GSS have an average pore size of 16.3 nm and have a more uniform distribution. The mesopore volume fraction (mesopore / pores) was 99.3% in the TiO ₂ layer made of GSS and 93.7% in the TiO ₂ layer made of P25. This confirms that the TiO ₂ layer made of GSS has more connected pores than the TiO ₂ layer made of P25.

Thus, the dye is more actively transported through the interconnected mesopores so that the amount of adsorbed dye in the TiO ₂ layer made of GSS is higher than that in the TiO ₂ layer made of P25 (see Table 1 and FIG. 12). 12 shows the dye adsorption amount in the TiO ₂ layer made of GSS and the TiO ₂ layer made of P25 as a function of film thickness. The homogeneously connected nanoparticle network of TiO ₂ layers made of GSS also contributes to improving the solar cell's operational performance by improving electrical charge transport, which is critical for determining the energy conversion efficiency of dye-sensitized solar cells.

13 is flowable photocurrent data. From this, D was calculated to investigate the transport of photogenerated charges. Figure 11 (b) shows a D-drawn as a function of J _sc in the TiO ₂ layer made of TiO ₂ layer and the GSS made with P25.

It is well known that D increases with the size and crystallinity of TiO ₂ and the ratio of the rutile and anatase phases. However, the TiO ₂ layer made of P25 has a small D compared to the TiO ₂ layer made of GSS despite having larger particles and more rutile phase. In Experimental Example 3, the difference in surface defects was negligible from the FT-IR and XPS data, so the difference in D cannot be explained by surface trapping.

The inventors believe that the large D in the GSS solar cell is due to the fast extraction of holes. Connected mesopores in the TiO ₂ layer made of GSS facilitate access to most dyes coated on the TiO ₂ surface. Therefore, the holes generated by the decomposition of the exciton can react quickly with the electrolyte before the electrons recombine with the surrounding holes. Reduction of electron-hole recombination potential contributes to increasing D and increasing J _sc .

The third mechanism by which the mesoporous structure increases J _sc is through a change in light transmittance. Figure 11 (c) shows a light reflection factor at 550 nm of TiO ₂ layer made of TiO ₂ layer and the P25 made by GSS in the absence of the dye adsorption state to the TiO ₂ layer thickness functions. The reflectance of the TiO ₂ layer made of GSS bit lower than the TiO ₂ layer made with P25, this is true because the TiO ₂ layer is a film of only the dispersed nanoparticles made by GSS. In the case of the anti-reflective coating film (ARC), mono-dispersed silica is used, since the mono-dispersed particles have a more porous structure than the poly-dispersed particles as shown in FIG.

Figure 11 (d) it shows a light transmittance at 550 nm of TiO ₂ layer made of TiO ₂ layer and the P25 made by GSS a TiO ₂ layer thickness functions. Within the film thickness range, the TiO ₂ layer made of GSS showed higher transmittance than the TiO ₂ layer made of P25. The change in reflectance and transmittance suggests that the scattering of light in the TiO ₂ layer made of GSS is significantly reduced, so that solar light can penetrate deeper than that of P25 solar cells. Thus, if the dye is adsorbed on the surface, the specific gravity of the dye, which contributes to the retrieval of light from the GSS solar cell, will be greater. The total energy conversion efficiency of dye-sensitized solar cells as a function of film thickness shows that GSS solar cells are more efficient than P25 solar cells. It should be noted that while the efficiency of GSS solar cells increases steadily in the range of irradiated thicknesses (˜40 μm), the efficiency of P25 solar cells is saturated at about 30 μm thickness.

As such, the good operating performance of GSS solar cells is due to dye adsorption, electron transport and increased light transmittance derived from the mesoporous properties of monodisperse GSS particles. Using monodisperse GSS particles allows the formation of many pores of uniform size, allowing the electrolyte to enter well and the high specific surface area greatly increases the amount of photosensitive dyes that react directly with sunlight, increasing the efficiency of the solar cell. It also increases necking of the particles to achieve smooth electron transfer. In addition, the distribution of pore sizes is narrowed, making the TiO ₂ layer made of GSS transparent. Even though the thickness of the TiO ₂ layer is increased, the transparency of the TiO ₂ layer is superior to that of the conventional film, and thus a high photocatalytic effect and a photoelectric effect can be expected. Therefore, the dye-sensitized solar cell manufactured using this can be applied to various applications in life such as glass windows and sunroofs.

Experimental Example 5 _ TiO ₂  Evaluation of the Effect of Geometry on Dye-Sensitized Solar Cells)

The morphology of TiO ₂ affects the energy conversion efficiency of dye-sensitized solar cells by altering electron transport performance. Came the study on the TiO ₂ Morphology on the photoelectric conversion operation in the performance of dye-sensitized solar cells is often performed bar TiO ₂ has had the amount is less than the result of the spherical TiO ₂ it is not a single dispersion is guaranteed. The spherical, rod-shaped, and wire-shaped TiO ₂ synthesized according to the present invention showed high crystallinity without surface defects as seen in Experimental Example 1, and had various aspect ratios (1, 5, and 10) at the same diameter of 20 nm. Therefore, it is well suited to investigate the effect of TiO ₂ morphology on the charge transport in the electrode and consequently on the energy conversion efficiency of dye-sensitized solar cells. The effect of the aspect ratio of the nanomaterial synthesized according to the present invention on the performance of the dye-sensitized solar cell was investigated in terms of the lifetime of the former.

(A), (b) and (c) of FIG. 14 are FE-SEM plane photographs of TiO ₂ layers made of GSS, GSR and GSW, respectively, (d) is an XRD pattern of each TiO ₂ layer, and (e) For dye-sensitized solar cells using GSS solar cells and GSW (hereafter GSW solar cells), the Nyquist plot (top figure) and the imaginary part of impedance as a function of frequency (bottom figure). (f) shows the dark current characteristics of the GSS solar cell and the GSW solar cell, and (g) shows the response time (electron lifetime) as a function of time.

Referring first to (a), (b) and (c) of FIG. 14, there is no noticeable change in morphology and size uniformity of TiO ₂ after the firing process.

Figure 14 (d) shows the XRD pattern of each TiO ₂ layer, it can be seen that no phase conversion from anatase to rutile during the firing process. It should be noted here that the peak intensity ratio of the (200) plane to the (004) plane changes as a function of the particle aspect ratio. I ₍₂₀₀₎ / I ₍₀₀₄₎ is 1.0, 2.0, 2.2 for GSS (aspect ratio, AR = 1), GSR (AR = 5), and GSW (AR = 10), respectively.

The change in I ₍₂₀₀₎ / I ₍₀₀₄₎ in each TiO ₂ layer is shown in each of the TiO ₂ , as can be seen in the SEM photographs (FIGS. 14B and 14C) and the TEM photographs (FIG. 3D). This is due to the ordered structure of rod and wire particles in the layer.

To understand the difference in charge recombination and electron lifetime in each TiO ₂ layer, electrochemical impedance spectrum (EIS) analysis was performed.

The upper figure of FIG. 14 (e) shows Nyquist plots of GSS solar cells and GSW solar cells. The impedance components of the interface in the dye-sensitized solar cell were observed from the left to the right in the frequency ranges 10 ³ -10 ⁵ (ω ₁ orω ₂ ), 1-10 ³ (ω ₃ ), and 0.1-1 Hz (ω ₄ ). These arcs form the TCO / TiO ₂ (ω ₁ ) of the semiconductor electrode, the Pt / electrolyte (ω ₂ ) of the opposite electrode, or the TiO ₂ / dye / electrolyte (ω ₃ ) interface, and the diffusion of the I ³ / I ^- electrolyte ( ω ₄ ) is assigned to the impedance. The ω ₃ component ( R ₃ ) of the GSW solar cell increased significantly compared to the GSS solar cell due to the following causes.

i) Reduction of adsorbed dye decreases the injected electron density in the TiO ₂ conduction band, thus increasing the impedance at the TiO ₂ / dye / electrolyte (ω ₃ ) interface (see Table 1).

ii) Because of the anisotropic and one-dimensional nanoparticles, the grain boundary density is reduced, thus facilitating the collection of photogenerated electrons from the TiO ₂ surface into TCO. This slows the recombination of the injected electrons and the electrolyte, increasing the impedance ( R ₃ ) at the TiO ₂ / dye / electrolyte (ω ₃ ) interface.

iii) The lower figure of FIG. 14 (e) shows the imaginary part of impedance as a function of frequency in GSS solar cells and GSW solar cells. The maximum frequency ω _max in the ω ₃ region is defined as ω _max = ( RC ) ^-1 ∝ 1 / τ, where R , C , and τ represent the resistance, the capacitance at the electrochemical interface, and the electron lifetime, respectively. The ω _max of the GSW solar cell is shifted toward lower frequencies than the GSS solar cell, indicating that the electron lifetime is longer for the wire-like particles than for the spherical particles. In addition, as shown in Figs. 14 (f) and 14 (g), the electron lifetime and dark current characteristics obtained from the reduction of V _oc as a function of time confirm that the charge recombination in GSW is slowed down. For GSW solar cells, dark current initiation shifts to a high potential range and the electron lifetime is noticeably increased. These results show that the use of one-dimensional TiO ₂ inhibits recombination of electrolyte and photogenerated electrons, which is consistent with the previous EIS analysis.

Although GSW has the advantage of reducing charge recombination, the photoelectric conversion efficiency of GSW solar cells is low compared to GSS solar cells. As summarized in Table 1, GSW solar cells have a lower photocurrent density than GSS solar cells. Thus, although the V _oc and ff of each dye-sensitized solar cell comprising anisotropic GSR and GSW TiO ₂ layers are slightly higher, the total conversion efficiency is reduced to 4.7% and 4.2%, respectively, compared to 5.3% for GSS solar cells. This low efficiency is due to the small specific surface area of GSR and GSW, which reduces dye adsorption and thus light absorption.

To summarize the results of the above experiments, the sol-gel method was used to synthesize various monodisperse TiO ₂ shapes such as spherical with aspect ratio 1, rod with aspect ratio 5, and wire with aspect ratio 10 and dye them. The possibility of using it as an electrode of a sensitized solar cell was investigated. The anatase obtained by the sol-gel method is characterized by high crystallinity, size uniformity, negligible surface defects, and almost no residual organic compounds, which is advantageous for improving photoelectric conversion device operation performance. In particular, the monodisperse GSS showed much higher efficiency in solar cell fabrication than polydispersed TiO ₂ (P25, commercial) because of increased dye adsorption, charge transport and improved light reflectance and transmittance. It is explained that the TiO ₂ layer made of monodispersed GSS has mesoporous properties.

Furthermore, the TiO ₂ layer made of GSW has a longer electron lifetime compared to the TiO ₂ layer made of GSS because the increase in the extraction of the photogenerated charges by inhibiting the photogenerated charges from recombining at the grain boundaries. do. However, GSW solar cells show lower efficiency than GSS solar cells due to their small specific surface area. As shown in FIG. 15, the total efficiency is 6.72% when the optimal thickness of the undercoat layer or the barrier layer is applied in the GSS solar cell ( J _sc : 14.38 mA cm ⁻² , V _oc : 687 mV, ff: 0.680). Thus, it is shown that the anatase obtained by the sol-gel method according to the present invention is very suitable for producing high efficiency dye-sensitized solar cells.

In the above, the present invention has been described in detail with reference to preferred embodiments and experimental examples, but the present invention is not limited to the above examples, and various modifications made by those skilled in the art within the technical spirit of the present invention. This is possible. To the present invention, the TiO ₂ production process, and this method a dye-sensitized solar but cell described with respect to the production method, a composition comprising a TiO ₂ obtained by the TiO ₂ production process (e.g., slurry, paste or the like), TiO ₂ production process using the The present invention can be applied to a film containing TiO ₂ obtained by the present invention, and any dye-sensitized solar cell manufacturing method can be used as long as it includes a step of containing TiO ₂ obtained by the TiO ₂ production method as an electrode of a dye-sensitized solar cell. The present invention can be applied. Examples of the invention have been considered by way of example and not limitation, all of which are intended to include the scope of the invention as indicated by the appended claims, their equivalents, and all modifications within the means rather than by the detailed description therein. will be.

1 is a flow chart of a TiO ₂ manufacturing method according to the present invention.

2 is a view schematically showing the configuration of a dye-sensitized solar cell to be manufactured according to an embodiment of the present invention.

3 is TEM photographs and XRD patterns of TiO ₂ nanocrystals prepared according to the present invention.

4 is TEM photographs of spherical TiO ₂ nanocrystals (GSS) prepared according to the present invention.

5 is a graph of efficiency of dye-sensitized solar cells according to GSS average particle size.

Figure 6 shows the XRD pattern of GSS and commercial powder P25, and anatase (SG) synthesized by the conventional method.

FIG. 7A is a particle size distribution obtained from P25 and GSS TEM images, (b) is a Ti 2p XP spectrum of P25 and GSS, and (c) is an FT-IR spectrum.

8 is an I-V curve of a dye-sensitized solar cell prepared using GSS and P25.

Figure 9 is a cross-sectional FE-SEM photograph of TiO ₂ layer made of TiO ₂ layer and the GSS made with P25.

10 is a schematic view of the TiO ₂ layer made of TiO ₂ layer and the GSS made with P25.

Figure 11 (a) N ₂ absorption isotherm and pore in the TiO ₂ layer made of TiO ₂ layer and the GSS made of P25 - The particle size distribution, (b) J _sc function green electron diffusion coefficient, (c) back to the light reflection factor, ( d) the total energy conversion efficiency of the dye-sensitized solar cell as a function of light transmittance and (e) film thickness.

12 illustrates a function of the dye adsorption amount of the thickness of the TiO ₂ layer with TiO ₂ layer made from P25 made by GSS.

13 is flowable photocurrent data.

(A), (b) and (c) of FIG. 14 are FE-SEM plane photographs of TiO ₂ layers made of GSS, GSR and GSW, respectively, (d) is an XRD pattern of each TiO ₂ layer, and (e) In the dye-sensitized solar cell comprising the TiO ₂ layer made of GSS and the dye-sensitized solar cell comprising the TiO ₂ layer made of GSW, the imaginary part of the impedance expressed as a function of the Nyquist plot and frequency, (f) is the respective dye-sensitized solar cell Represents a dark current characteristic, and (g) represents a response time (electron lifetime) as a function of time.

FIG. 15 shows the efficiency when a blocking layer of optimal thickness is applied in a dye-sensitized solar cell including a TiO ₂ layer made of GSS.

<Explanation of symbols for the main parts of the drawings>

10 ... semiconductor electrode 12 ... conductive first substrate

14 ... TiO ₂ layer 30 ... counter electrode

32 ... conductive second substrate 34 ... catalyst layer

50 electrolyte solution 60 polymer material

Dye-sensitized solar cell

Claims (6)

delete Providing a mixed aqueous solution comprising titanium alkoxide, ethylenediamine and ethanolamine; Adjusting the pH of the aqueous solution to 4-12; Heating the aqueous solution to produce a wire-type TiO ₂ precipitate; And Titanium dioxide production method comprising the step of drying the precipitate. Providing a mixed aqueous solution comprising titanium alkoxide and ethanolamine; Adjusting the pH of the aqueous solution to 5.8 to 8.5; Applying heat to the aqueous solution to produce spherical TiO ₂ precipitates having an average particle size of 18-24 nm; And Titanium dioxide production method comprising the step of drying the precipitate. Preparing a TiO ₂ paste by mixing TiO ₂ and the binder prepared by the method of claim 2 or 3; Applying the TiO ₂ paste to a substrate; And And baking the substrate coated with the TiO ₂ paste to form a semiconductor electrode. The method of claim 4, wherein the binder is terpineol and ethyl cellulose in a mass ratio of 7: 1. The method of claim 5, wherein the TiO ₂ and the binder are mixed in a mass ratio of 1: 3 to 1: 3.5.

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