KR20120119073A - Manufacturing method of dye sensitized solar cell - Google Patents

Abstract

PURPOSE: A manufacturing method of a dye sensitized solar cell is provided to form two metal oxide micro particulate layers by paste coating and to reduce material costs. CONSTITUTION: A paste including metal oxide particles is spread on one first electrode(11). A pair of first electrodes faces the paste after drying the paste. A first substrate(10) which is formed on the other first electrode is applied on the paste. A pair of the first substrate is separated after pressing the paste. A metal oxide particle layer(13) is formed on the first electrode. A light absorbing layer(15) is formed.

Description

Manufacturing method of dye-sensitized solar cell {MANUFACTURING METHOD OF DYE SENSITIZED SOLAR CELL}

The present invention relates to a method for manufacturing a dye-sensitized solar cell, and more particularly, to a method for manufacturing a dye-sensitized solar cell, which simplifies the process of forming a light absorbing layer.

Solar cells are devices that generate electrical energy using solar energy, which are environmentally friendly, have unlimited energy sources, and have a long lifespan. Dye-sensitized solar cells are solar cells in which dye molecules disposed between a pair of electrodes absorb sunlight and convert them into electrons. In a dye-sensitized solar cell, the light absorbing layer is composed of a metal oxide fine particle layer and a dye adsorbed thereto.

In the manufacture of conventional dye-sensitized solar cells, it takes about two days to form a metal oxide fine particle layer and adsorb dye thereon. In the conventional method, since a high temperature treatment of 500 ° C. or more is required to form the metal oxide fine particle layer, a heat-sensitive substrate such as plastic cannot be used. Therefore, there is a demand for a technology that can simplify a process, reduce process time, and enable a low temperature process of 100 ° C. or lower.

The present invention is to provide a method for manufacturing a dye-sensitized solar cell that can shorten the time required to form a light absorbing layer, simplify the process, and can apply plastic as a substrate.

A method of manufacturing a dye-sensitized solar cell according to an embodiment of the present invention includes preparing a plurality of first substrates each having a first electrode formed thereon, and applying a paste including metal oxide fine particles on any one first electrode. After the drying step, laminating a first substrate on which the other first electrode is formed so that the pair of first electrodes face each other with the paste interposed therebetween, and after pressing the paste, the pair of first substrates are separated Forming a metal oxide fine particle layer on each of the pair of first electrodes, and adsorbing a dye to the metal oxide fine particle layer to form a light absorbing layer.

Metal oxide fine particles consist of titanium oxide (TiO ₂ ), zinc oxide (ZnO), magnesium oxide (MgO), aluminum oxide (Al ₂ O ₃ ), tin oxide (SnO ₂ ), and niobium oxide (Nb ₂ O ₅ ). It may include at least one selected from the group.

The paste may include at least one selected from the group consisting of ethanol, methanol, propanol, butanol, 4-tertiary-butanol, water, and acetic acid as a solvent.

When compressing the paste, a pressure in the range of 1 MPa to 10 GPa may be applied for 1 second to 30 minutes. When the paste is pressed, the paste can be heated to a temperature in the range of 30 ° C to 150 ° C.

In the step of forming the light absorbing layer, the metal oxide fine particle layer may be heated, and the dye solution may be sprayed or sprayed onto the surface of the heated metal oxide fine particle layer to adsorb the dye. The heating temperature of the metal oxide fine particle layer may be in the range of 80 ° C to 90 ° C.

The dye solution may include at least one material selected from the group consisting of carboxylic acid series, phosphoric acid series, boric acid series, hexalic acid series, hydrokisanoic acid series, silane series, amide series, and ether series as dyes.

The dye solution is selected from the group consisting of ethanol, water, toluene, tetrahydrofuran, dimethylformamide, trimethylsilyl bromide, bromic acid, propanol, 4-tert-butanol, sulfuric acid, phenol, carbon dichloride, and carbon trichloride as solvents. It may include at least one.

According to the present embodiment, since two metal oxide fine particle layers can be simultaneously formed by one paste coating, it is possible to reduce material waste and simplify the process to increase productivity. In addition, since the manufacturing method of the present embodiment is a low temperature process that does not limit the material of the first substrate, a flexible solar cell can be easily manufactured by applying a plastic substrate.

1 and 2a to 2e and 3 are cross-sectional views showing the manufacturing process of the dye-sensitized solar cell according to an embodiment of the present invention.
4A is a scanning electron micrograph of the metal oxide fine particle layer prepared by the method of this embodiment.
FIG. 4B is a scanning electron micrograph of a light absorbing layer in which a dye is adsorbed using a metal oxide fine particle layer by immersion.
4C is a scanning electron micrograph of a light absorbing layer in which a dye solution is adsorbed by heating a metal oxide fine particle layer and then spraying a dye solution.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

1 and 2a to 2e and 3 are cross-sectional views showing the manufacturing process of the dye-sensitized solar cell according to an embodiment of the present invention.

The manufacturing process of the dye-sensitized solar cell according to the present embodiment includes a first step (see FIG. 1) of preparing a plurality of first substrates 10 on which first electrodes 11 are formed, and a first electrode 11. A second step (see FIGS. 2A to 2E) of forming the light absorbing layer 15 on the surface of the light absorbing layer 15 and preparing the second substrate 20 on which the second electrode 21 is formed, and then preparing the first substrate 10 and the second substrate. A third step of assembling 20 (see FIG. 3).

Referring to FIG. 1, a plurality of first substrates 10 on which first electrodes 11 are formed are prepared in a first step. In FIG. 1, two first substrates 10 are illustrated.

The first substrate 10 is made of glass or plastic as a transparent substrate. In the case of plastic, the first substrate 10 is made of polyimide (PI), polyethylene naphthalate (PEN), polyacrylate (PA), polyethylene terephthalate (PET), polystyrene (PS), polyethylene, and polypropylene. It may include at least one of (polypropylene). The first substrate 10 made of plastic may have a bending property.

The first electrode 11 is made of a transparent conductive metal oxide film. The first electrode 11 may include at least one of indium tin oxide (ITO), fluorine doped tin oxide (FTO), zinc oxide (ZnO), and aluminum doped zinc oxide (AZO). The first electrode 11 transmits light to the light absorbing layer 15 to be described later, and functions as a conducting wire for transferring electrons generated in the light absorbing layer 15 to an external circuit.

The first substrate 10 may undergo a cleaning process before being introduced into the second step. The cleaning process may include an ultrasonic cleaning step using a glass cleaner, a cleaning step using distilled water, and a cleaning step using ethanol. Through this cleaning process, organic contaminants on the surface of the first electrode 11 may be removed.

Referring to FIG. 2A, a paste 12 including metal oxide fine particles is applied on one of the first electrodes 11 in a second step. The paste 12 includes metal oxide fine particles and a solvent, and is dried in air after application to a predetermined thickness.

The metal oxide fine particles include at least one of titanium oxide (TiO ₂ ), zinc oxide (ZnO), magnesium oxide (MgO), aluminum oxide (Al ₂ O ₃ ), tin oxide (SnO ₂ ), and niobium oxide (Nb ₂ O ₅ ). It may include one. The solvent may comprise at least one of ethanol, methanol, propanol, butanol, 4-tertiary-butanol, water, and acetic acid. The kinds of the metal oxide fine particles and the solvent are not limited to the examples described above and may be variously changed.

Referring to FIG. 2B, the other first substrate 10 and the first electrode 11 are stacked on the paste 12 so that the pair of first electrodes 11 face up and down with the paste 12 interposed therebetween. . As a result, the two first substrates 10 are stacked up and down while the two first electrodes 11 are in contact with the paste 12. The two first substrates 10 and the two first electrodes 11 stacked on each other are the same product manufactured in the same process.

Referring to FIGS. 2C and 2D, the first substrate 10 is pressed to compress the paste 12, and then the two first substrates 10 are separated to form a metal oxide on the two first electrodes 11. The fine particle layer 13 is formed, respectively. As a result, since the two metal oxide fine particle layers 13 can be simultaneously formed by one coating process, the process can be simplified and the process time of the metal oxide fine particle layers 13 can be shortened effectively.

Through the pressing process, the metal oxide fine particle layer 13 having a very dense internal structure and excellent adhesion to the first electrode 11 can be formed. In the pressing process, a press apparatus not shown is used, and heat may be applied to the paste 12 to promote drying of the paste 12. At this time, the heat applied to the paste 12 is 150 degrees C or less, and the low temperature heat processing method other than the high temperature heat processing more than 500 degreeC conventionally is applied.

In the pressing process of the paste 12, the heating temperature may be in the range of 30 ° C. to 150 ° C. If the heating temperature is less than 30 ℃ may be ineffective solvent removal effect by heating, if it exceeds 150 ℃ because it belongs to a high temperature heat treatment process rather than a low temperature process, it is difficult to use a flexible substrate such as plastic as the first substrate 10 This can happen.

The pressure applied to the paste 12 in the pressing process may be in the range of 1 MPa to 10 GPa. When the first substrate 10 is made of a fragile material such as glass, or the metal oxide fine particles included in the paste 12 have good reactivity with the first electrode 11 and belong to the soft side, even when the pressure is about 1 MPa, Work is possible. On the other hand, when the first substrate 10 is made of a material resistant to pressure and the metal oxide fine particles included in the paste 12 have low reactivity with the first electrode 11 and the particles belong to a hard side, a large pressure of about 10 GPa is achieved. This is necessary.

The time for which the pressure in the above-described range is applied may be in the range of 1 second to 30 minutes. As the metal oxide fine particles included in the paste 12 have good reactivity with the first electrode 11 and belong to a soft side, coating can be performed with a short pressing time, and have low reactivity with the first electrode 11 and hard particles. The longer you go, the longer the compression time, which is about 30 minutes.

After the compression of the paste 12 described above, the metal oxide fine particle layer 13 is simultaneously formed on the two first electrodes 11. This process enables the formation of the metal oxide fine particle layer 13 in a short time within several tens of minutes and is a low temperature process that does not limit the material of the first substrate 10. In addition, since the material is wasteful and a simplified process, productivity can be increased.

If it is assumed that after applying the paste on the first electrode to form a metal oxide fine particle layer by pressing the paste with a conventional press apparatus, part of the paste is buried in the press apparatus. Therefore, the waste of the paste increases the material cost, and the process is complicated because the paste applied to the press apparatus can be removed and the press apparatus can be reused. However, in the method of this embodiment, since the paste does not adhere to the press apparatus, all the above-mentioned problems can be solved.

In the second step, the paste 12 is coated on the first electrode 11 while the first substrate 10 is continuously moved by a conveying means such as a conveyor belt, and the other first substrate 10 is pasted. (12) The process of laminating and then crimping can be carried out continuously.

Referring to FIG. 2E, the light absorbing layer 15 is formed by adsorbing the dye 14 to the metal oxide fine particle layer 13. The light absorbing layer 15 is composed of the metal oxide fine particle layer 13 and the dye 14 adsorbed thereto. Adsorption of the dye 14 may be performed by dipping the metal oxide fine particle layer 13 in the dye solution, or by heating or spraying the dye solution after heating the metal oxide fine particle layer 13 to a high temperature.

The first method for adsorption of the dye 14 is to immerse the first substrate 10 having the metal oxide fine particle layer 13 in a dye solution including a dye and a solvent to adsorb the dye onto the metal oxide fine particle layer 13. Is done. After the adsorption of the dye 14 is completed, the first substrate 10 is separated from the dye solution, washed with ethanol, and dried.

The second method for adsorbing the dye 14 is heating the metal oxide fine particle layer 13 to a constant temperature, and spraying or spraying a dye solution onto the heated metal oxide fine particle layer 13 to the metal oxide fine particle layer 13. The dye 14 is adsorbed. In this method, the dye solution impinges on the heated metal oxide fine particle layer 13 while the solvent evaporates rapidly, while the dye molecules are adsorbed directly on the surface of the metal oxide fine particles.

In the second method, even when a low concentration of the dye solution is used, the time required for the adsorption of the dye 14 can be shortened, and since the dye is not adsorbed to the portions other than the metal oxide fine particle layer 13, the material loss is small. In this case, the process of removing the dye from other parts can be omitted, thereby simplifying the process.

In the second method, the heating temperature of the metal oxide fine particle layer 13 may be in the range of 80 ° C to 90 ° C. If the heating temperature is less than 80 ° C, the evaporation time of the solvent may be long, and if it exceeds 90 ° C, the dye 14 may not be adsorbed smoothly because the solvent is evaporated before the dye solution sufficiently wets the metal oxide fine particle layer 13. have. In addition, in the case of highly flammable organic solvents, a risk may occur that the solvent vapor may catch fire.

In both the first and second methods, the dyes included in the dye solution are carboxylic acid series (including carboxylate or ruthenium series), phosphoric acid series (including phosphate), boric acid series, hexalic acid series, hydrokisamic acid series and silane series , Amide based, and ether based materials.

And the solvent included in the dye solution is at least one of ethanol, water, toluene, tetrahydrofuran, dimethylformamide, trimethylsilyl bromide, bromic acid, propanol, 4-tert-butanol, sulfuric acid, phenol, carbon dichloride, and carbon trichloride. It may include one.

Referring to FIG. 3, the first substrate 10 having the first electrode 11 and the light absorbing layer 15 and the second substrate 20 having the second electrode 21 are prepared, and the sealing material 30 is prepared. The first substrate 10 and the second substrate 20 are bonded to each other. Thereafter, the electrolyte 31 is injected between the light absorbing layer 15 and the second electrode 21 to complete the dye-sensitized solar cell 100.

Electrolyte 31 is an oxidation-reduction couple (redux couple) halogen reduction based electrolyte oxide consisting of halogen, halogen compound and a halogen molecule as an electrolyte consisting of _{^{(Br 3 - / Br -,}} I 3 - / I -), selenium redox electrolyte ((SeCN) ₂ / SeCN ⁻ ), cyanosulfur redox electrolyte ((SCN) ₂ / SCN ⁻ ), cobalt redox electrolyte (Co (II) / Co (III)), and the like. The solvent of the electrolyte 31 may include at least one of acetonitrile, methoxypropionitrile, butyronitrile, and methoxyacetonitrile.

The second electrode 21 serves as a catalyst electrode to activate the redox pair. The second electrode 21 may include at least one of platinum, gold, ruthenium, palladium, rhodium, iridium, and carbon. In the dye-sensitized solar cell 100, the first substrate 10 having the light absorbing layer 15 is disposed on the side where the sunlight is incident, and the second substrate 20 is disposed on the opposite side thereof.

When sunlight enters the dye-sensitized solar cell 100, the dye 14 of the light absorbing layer 15 is transferred from the ground state to the excited state by photons to form an electron-hole pair, and the electrons in the excited state are metal It is injected into the conduction band of the oxide fine particle interface and moves to the second electrode 21 via the first electrode 11 and the external circuit. The dye oxidized as a result of the electron transfer is reduced by the ions of the redox couple in the electrolyte 31, and the oxidized ions cause a reduction reaction with the electrons reaching the interface of the second electrode 21 to achieve charge neutrality. . In this process, the dye-sensitized solar cell 100 operates.

Hereinafter, the manufacturing process and the efficiency measurement result of the dye-sensitized solar cell of a comparative example and the dye-sensitized solar cell of an Example are demonstrated.

(Comparative Example 1)

A glass substrate (first substrate) on which fluorine-doped tin oxide (FTO) was formed as a first electrode was subjected to ultrasonic decomposition cleaning for 10 minutes in a glass cleaner, 10 minutes in distilled water, and 10 minutes in ethanol, and then a substrate was blown through nitrogen blowing. The wash solution on the surface was removed.

Using a screen printer, a titanium oxide paste from SOLARONIX was coated on the center of the cleaned fluorine-doped tin oxide (FTO) glass substrate. Immediately after coating, the mixture was left in air for 3 minutes to remove air in the titanium oxide paste, and then heat-treated in an oven at 120 ° C. for 7 minutes. The process was repeated three times and then heat-treated in an oven at 500 ° C. for 30 minutes to form a titanium oxide fine particle layer. .

Soaking the substrate coated with titanium oxide fine particle layer for 24 hours in 0.3mM dye solution prepared by using Solarium's ruthenium dye N-719 and acetonitrile 4-tert-butanol solvent to form a light absorbing layer It was. After dye adsorption, the substrate was washed with ethanol and dried in air.

Two holes for the electrolyte solution were formed in the glass substrate (second substrate) on which fluorine-doped tin oxide (FTO) was formed, and were washed in the same manner as the first substrate. The Platisol solution of Solaronics Co. was coated on fluorine-doped tin oxide (FTO), the solvent was dried in air, and then heat-treated in an oven at 400 ° C. for 5 minutes to form a second electrode made of platinum.

Sullyn from Solaron Corporation was placed between the first and second substrates, placed on a hot plate heated to 130 ° C, and heated to form a sealing material. A mixed solvent electrolyte solution of 0.6M BMII, 0.03M iodide, 0.1M guanidinium thiocyanate, 0.5M tertiary-butylpyridine, acetonitrile and valenitrile was prepared, and two holes formed in the second electrode An electrolyte solution was injected through to prepare a dye-sensitized solar cell.

(Comparative Example 2)

A dye-sensitized solar cell was manufactured in the same manner as in Comparative Example 1 except that the dye adsorption method was changed.

A 0.3 mM dye solution was prepared using acetonitrile and 4-tertary-butanol solvent in N-719, a ruthenium dye made by Solaronics, and a mask was attached on the titanium oxide fine particle layer so that only the titanium oxide fine particle layer could come into contact with the dye solution. And then placed the first substrate on a hot plate heated to 100 ° C. After the titanium oxide fine particle layer was heated to 80 ° C., the dye solution was wetted on the surface of the titanium oxide fine particle layer in an amount of 200 μl to 350 μl using a micro pipette for 4 to 7 minutes.

(Example 1)

A dye-sensitized solar cell was manufactured in the same manner as in Comparative Example 1 except that the titanium oxide fine particle layer formation and dye adsorption were changed.

A 5.8 mm diameter round mask is attached to the cleaned fluorine-doped tin oxide (FTO) glass substrate, and a titanium oxide paste made from a mixture of "P25" titanium oxide nanoparticles and ethanol purchased from Degussa is coated in the mask. It was. Immediately after coating, the mask was removed, dried in air for about 10 seconds, and another glass substrate on which the fluorine-doped tin oxide (FTO) was formed was laminated on the paste, and pressed and separated by pressing without applying heat to the two fluorine-doped tin oxides ( Titanium oxide fine particle layers were formed on FTO). The pressing pressure of the press is 600 MPa.

A 0.3 mM dye solution was prepared using acetonitrile and 4-tertary-butanol solvent in N-719, a ruthenium dye made by Solaronics, and a mask was attached on the titanium oxide fine particle layer so that only the titanium oxide fine particle layer could come into contact with the dye solution. And then placed the first substrate on a hot plate heated to 100 ° C. The titanium oxide fine particle layer was heated to 80 ° C., and then the dye solution was wetted for 6 minutes in an amount of up to 300 μl on the surface of the titanium oxide fine particle layer using a micro pipette.

(Example 2)

A titanium oxide fine particle layer was formed in the same manner as in Example 1 except that heat was applied at 50 ° C. in the titanium paste pressing process, and a dye absorbed into the titanium oxide fine particle layer in the same manner as in Comparative Example 1 to form a light absorbing layer. . Except for the light absorbing layer, the same members as in Comparative Example 1 were applied.

(Example 3)

Heat was applied at 50 ° C. in the titanium paste pressing process for forming the titanium oxide semiconductor layer, and the pressing time was controlled from 1 minute to 10 minutes. In the dye adsorption process, the dye solution was 200 μl to 50 μl on the surface of the titanium oxide semiconductor layer. A dye-sensitized solar cell was prepared in the same manner as in Example 1 except that the amount was soaked in an amount of 350 μl for 4 to 7 minutes, respectively.

In order to measure the efficiency of dye-sensitized solar cells, the dye-sensitized solar cells of the comparative examples and examples were obtained with a current-voltage curve using a Newport solar simulator and a Keithley Model 2400 source meter. , The area was set to 25 mm 2, and the light intensity was set to 100 mW / cm 2. Short-circuit photocurrent density (Jsc), open circuit volate (Voc), fill factor (FF), and incident photon-to-current conversion efficiency (IPCE) The values are shown in Table 1 below.

Referring to Table 1, Comparative Example 2 shows the highest photoelectric conversion efficiency, but Comparative Examples 1 and 2 form a metal oxide fine particle layer using a conventional screen printer, which has a high temperature treatment process and a complicated process. . The solar cells according to Examples 1, 2, and 3, which solves this problem, realize a similar photoelectric conversion efficiency compared to Comparative Examples 1 and 2 while reducing material waste and increasing productivity.

In addition, when the dye adsorption method of heating the metal oxide fine particle layer and spraying or spraying the dye solution is applied, the light absorbing layer manufacturing time is shortened from 24 hours to 7 minutes. Therefore, it is possible to effectively reduce the process time and to manufacture a dye-sensitized solar cell with higher photoelectric conversion efficiency.

FIG. 4A is a scanning electron micrograph of a metal oxide fine particle layer prepared by the method of this embodiment, FIG. 4B is a scanning electron micrograph of a light absorbing layer adsorbed dye using a immersion method on the metal oxide fine particle layer, and FIG. 4C is a metal It is a scanning electron micrograph of the light absorption layer in which the dye fine particle is adsorbed by heating the oxide fine particle layer and then spraying the dye solution.

4A to 4C, the metal oxide fine particle layer may be compressed to have a rigid cross-sectional structure. However, since the dye solution is immersed in the dye solution for 24 hours in FIG. 4B, the dye solution may penetrate into the weak contact portion of the metal oxide fine particle layer, thereby lowering the electrical conductivity between the fine particles. Since the adsorption takes place in 6 minutes, there is no such concern, and it is more advantageous for increasing the electrical conductivity and robustness of the light absorbing layer.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Of course.

100: dye-sensitized solar cell 10: first substrate
11: first electrode 12: paste
13: metal oxide fine particle layer 14: dye
15: light absorbing layer 20: second substrate
21: second electrode 30: sealing material
31: electrolyte

Claims (9)

Preparing a plurality of first substrates on which first electrodes are formed;
Applying and drying a paste including metal oxide fine particles on any one first electrode;
Stacking a first substrate on which the other first electrode is formed so that a pair of first electrodes face each other with the paste interposed therebetween;
Pressing the paste to separate the pair of first substrates to form metal oxide fine particle layers on each of the pair of first electrodes; And
Adsorbing a dye to the metal oxide fine particle layer to form a light absorbing layer
Method for producing a dye-sensitized solar cell comprising a. The method of claim 1,
The metal oxide fine particles include titanium oxide (TiO ₂ ), zinc oxide (ZnO), magnesium oxide (MgO), aluminum oxide (Al ₂ O ₃ ), tin oxide (SnO ₂ ), and niobium oxide (Nb ₂ O ₅ ). Method for producing a dye-sensitized solar cell comprising at least one selected from the group consisting of. The method of claim 2,
And the paste comprises at least one selected from the group consisting of ethanol, methanol, propanol, butanol, 4-tertiary-butanol, water, and acetic acid as a solvent. The method of claim 1,
When the paste is pressed, a pressure in the range of 1 MPa to 10 GPa is applied for 1 second to 30 minutes. The method of claim 4, wherein
A method for producing a dye-sensitized solar cell, wherein the paste is heated to a temperature in the range of 30 ° C. to 150 ° C. when the paste is pressed. The method according to any one of claims 1 to 5,
In the step of forming the light absorbing layer, the method of manufacturing a dye-sensitized solar cell by heating the metal oxide fine particle layer and adsorbing the dye by spraying or spraying a dye solution on the surface of the heated metal oxide fine particle layer. The method of claim 6,
The heating temperature of the said metal oxide fine particle layer is a manufacturing method of the dye-sensitized solar cell which belongs to the range of 80 degreeC-90 degreeC. The method of claim 6,
The dye solution is a dye-sensitized type comprising at least one material selected from the group consisting of carboxylic acid series, phosphoric acid series, boric acid series, hexalic acid series, hydrokisamic acid series, silane series, amide series, and ether series as dyes. Method for manufacturing a solar cell. 9. The method of claim 8,
The dye solution is selected from the group consisting of ethanol, water, toluene, tetrahydrofuran, dimethylformamide, trimethylsilyl bromide, bromic acid, propanol, 4-tert-butanol, sulfuric acid, phenol, carbon dichloride, and carbon trichloride as solvents. A method of manufacturing a dye-sensitized solar cell comprising at least one selected.

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