KR100819025B1 - Compound of polymer electrolyte, dye sensitized solar cell comprising the composition, and preparation method of the dye sensitized - Google Patents

Abstract

The present invention discloses a polymer electrolyte composition comprising a polyol and an organic polyisocyanate, a dye-sensitized solar cell comprising the same, and a method of manufacturing the dye-sensitized solar cell. The disclosed polymer electrolyte compositions are chemically crosslinked and gelled with polyols and organic polyisocyanates to improve long term storage and utility.

Crosslinking, polyols, organic polyisocyanates, polymer electrolytes, dye-sensitized solar cells

Description

Polymer electrolyte composition, dye-sensitized solar cell comprising the same, and a method for producing the dye-sensitized solar cell {Compound of polymer electrolyte, dye sensitized solar cell comprising the composition, and preparation method of the dye sensitized}

1 is a graph showing the current-voltage characteristics of a dye-sensitized solar cell including a polymer electrolyte composition according to an embodiment of the present invention.

2 is a graph showing the current-voltage characteristics of a dye-sensitized solar cell including a polymer electrolyte composition according to an embodiment of the present invention.

The present invention relates to a polymer electrolyte composition and a dye-sensitized solar cell comprising the same.

The dye-sensitized solar cell, developed by Gratzel et al., 1991, is a wet solar cell consisting of nanoporous TiO ₂ semiconductor electrodes, ruthenium metal complex dyes, and liquid electrolytes (Nature 353 (1991) 737). . Dye-sensitized solar cell having the configuration as described above has the advantage that the manufacturing cost is low, but high energy conversion rate.

However, the dye-sensitized solar cell has problems such that the solvent contained in the liquid electrolyte may leak or volatilize due to an increase in external temperature and sealing of the solar cell. Therefore, the dye-sensitized solar cell is very disadvantageous for long term stability and practical use.

Recently, in order to overcome the disadvantages of the liquid electrolyte, research has been conducted to gel the liquid electrolyte by adding a low molecular or polymer gelling agent capable of hydrogen bonding or hydrophobic bonding. Gel electrolytes using a low molecular weight gelling agent capable of hydrogen bonding or hydrophobic bonding have a problem in that the crosslinking point is lost at high temperature and liquefied again. In addition, when the polymer gelling agent is used, since the viscosity of the electrolyte is relatively high even at high temperatures, it is difficult to impregnate the gel electrolyte between the TiO ₂ particles, causing a decrease in energy conversion efficiency in the dye-sensitized solar cell.

Accordingly, the present inventors have completed the present invention by preparing a polymer electrolyte composition using a compound having a functional group capable of chemical crosslinking with a nonvolatile solvent as a result of research efforts to solve the conventional problems as described above.

Accordingly, an object of the present invention is to provide a polymer electrolyte composition of a dye-sensitized solar cell that does not volatilize or leak and has long-term stability and may be usefully used in dye-sensitized solar cells.

In addition, another object of the present invention is to provide a dye-sensitized solar cell having practical and excellent electrical properties using the polymer electrolyte composition.

Another object of the present invention is to provide a method for easily manufacturing a dye-sensitized solar cell including the polymer electrolyte composition.

The present invention provides a polymer electrolyte composition of a dye-sensitized solar cell.

The polymer electrolyte composition includes a nonvolatile solvent, a polyol, and an organic polyisocyanate.

It is preferable that the said nonvolatile solvent contains an ionic liquid or polyalkylene glycol dialkyl ether.

Specifically, the ionic liquid is a cation selected from the group consisting of quaternary ammonium salt, imidazolium salt, and pyridinium salt and Br-, Cl-, BF _4- , PF _6- , SbF _6- , CF ₃ SO _3- It may be a room temperature molten ionic liquid containing an anion selected from the group consisting of, and (CF ₃ SO ₂ ) ₂ N-.

In addition, the polyalkylene glycol dialkyl ether is polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, polyethylene glycol dipropyl ether, polyethylene glycol dibutyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol dimethyl ether, polypropylene Glycol diglycidyl ether, dibutyl ether-terminated polypropylene glycol / polyethylene glycol copolymer, dibutyl ether-terminated polyethylene glycol / polypropylene glycol / polyethylene glycol block copolymer, or a mixture thereof.

The polyol preferably comprises at least two hydroxy functional groups per polyol molecule.

Specifically, the polyol may be a polyether polyol, a polyester polyol, a polyhydric alcohol, a diethylene polymer having a hydroxy functional group, or a mixture thereof.

The polyether polyol is selected from any one selected from the group consisting of polyhydric alcohols, sugars, alkylamines, and alkanolamines, and alkylene oxides of propylene oxide, ethylene oxide, butylene oxide, and tetrahydrofuran. It may include those produced by reacting any one.

In addition, the polyester-based polyol may include polyols, polyols of polyhydric carboxylic acid condensation systems, polyols of cyclic ester ring-opening polymers, or mixtures thereof.

The polyol may include 0.1 to 45 wt% based on the polymer electrolyte composition, preferably 0.5 to 45 wt%, more preferably 1 to 45 wt%.

The organic polyisocyanate preferably includes two or more isocyanate functional groups per organic polyisocyanate molecule.

Specifically, the organic polyisocyanate may include polyfunctional aliphatic, cycloaliphatic and aromatic isocyanates, or mixtures thereof.

In addition, the organic polyisocyanate is hexamethylene diisocyanet (HDI), isopron diisocyanate (IPDI), 4,4-dicyclohexyl methane diisocyanate (H12MDI), toluene diisocyanate (TDI), 4,4 '-Diphenylmethane diisocyanate (4,4'-MDI), orthotoluidine diisocyanate (TODI), naphthylene diisocyanate (NDI), xylene diisocyanate (XDI), lysine diisocyanate (LDI), and triphenylmethyl Triisocyanate (TPTI), or mixtures thereof.

In addition, the organic polyisocyanate may include a urethane prepolymer having an isocyanate function. The urethane prepolymer is produced by reacting the polyol with the organic polyisocyanate in an isocyanate / hydroxy functional group equivalent ratio of 1.1 to 2.5.

The organic polyisocyanate may be included in an amount of 0.1 to 45% by weight, preferably 0.5 to 45% by weight, and more preferably 1 to 45% by weight, based on the polymer electrolyte composition.

The polymer electrolyte composition may further include a compound that provides an oxidation-reduction pair. For example, as the compound, iodine (I ₂ ) and iodide (I-), bromine (Br ₂ ) and bromide (Br-), TCNQ complex, hydroquinone, and the like can be used, and iodine (I ₂ ) and iodine I- / I ₃ -generated from cargo I- may be most usefully used. However, it is not limited to the compounds exemplified above.

As iodide, iodide of molten metal, iodide molten salt, etc. can be used. LiI, NaI, KI, etc. may be used as the iodide of the alkali metal, and quaternary ammonium salts, imidazolium salts, pyridinium salts, and the like may be used as iodide molten salt iodides or iodides.

Iodine (I ₂ ) and iodide (I-), which provide I- / I ₃ -redox pairs, can be dissolved and used in such nonvolatile solvents as ionic liquids or low molecular weight polyalkylene oxide oligomers. .

 The non-volatile solvent containing the compound providing the redox-pair may include 10 to 98% by weight, preferably 30 to 98% by weight, more preferably 50 to 98% by weight, based on the polymer electrolyte composition. It can be included as a range.

In addition, the polymer electrolyte composition may further include a curing catalyst.

As the curing catalyst, an organometallic compound such as dibutyl tin dilaurate, stannous oleate, cobalt naphthenate and naphthenic zinc can be used. The curing catalyst is preferably included 0.4 wt% based on the polyester polyol, more preferably contained 1.2 wt%.

The present invention also includes a dye-sensitized solar cell.

Specifically, the dye-sensitized solar cell is a semiconductor electrode including a first substrate, a metal oxide layer formed on the first substrate and a dye layer coated on the metal oxide layer, a second substrate and a metal layer formed on the second substrate It includes a counter electrode, and a polymer electrolyte composition injected between the semiconductor electrode and the counter electrode, and comprises a nonvolatile solvent, a polyol and an organic polyisocyanate.

In addition, the present invention includes a method for producing a dye-sensitized solar cell.

Specifically, the manufacturing method prepares a semiconductor electrode and a counter electrode, respectively. The polyol and the organic polyisocyanate are added to a nonvolatile solvent to form a polymer electrolyte composition, and the polymer electrolyte composition is injected between the semiconductor electrode and the counter electrode. The polymer electrolyte composition is cured by gelation by heat treatment.

The polyol and the organic polyisocyanate are crosslinked by the urethane reaction of Scheme 1 to form a polymer electrolyte capable of impregnating a nonvolatile solvent.

In the polymer electrolyte composition, a nonvolatile solvent including a redox pair, a polyol, and an organic polyisocyanate are put in a container and stirred with a stirrer to prepare a polymer electrolyte composition in a solution state. If necessary, the polymer electrolyte composition may be prepared by adding a curing catalyst and stirring the composition.

The semiconductor electrode coats a colloidal solution containing nanoparticles of metal oxide on a conductive transparent glass substrate coated with ITO or SnO ₂ to a certain thickness, and is heated to a high temperature to remove impurities and the metal oxides are in close contact with each other. To be. The substrate coated with the metal oxide is impregnated with a dye solution composed of a ruthenium complex. Therefore, the dye may be adsorbed onto the metal oxide to prepare a semiconductor electrode.

The counter electrode is prepared by coating with platinum (Pt) on the surface of the conductive transparent glass substrate to form a platinum layer.

After fixing the semiconductor electrode and the counter electrode to have a space of a predetermined interval, the polymer electrolyte composition is injected between the electrodes.

The injection method coats the polymer electrolyte composition in a solution state on the semiconductor electrode or the counter electrode. And the coated result is cured by heat treatment. It is preferable to perform the said heat processing at 30-150 degreeC.

Alternatively, the polymer electrolyte composition is coated on the semiconductor electrode or the counter electrode. Then, the thickness adjusting spacers are fixed to both ends of the coated electrode, and the remaining electrodes are covered thereon. And a solid polymer electrolyte composition is prepared by curing the polymer electrolyte composition using a heat source. At this time, the temperature of the heat source is maintained at 30 to 150 ℃.

The gelation reaction may be performed for 1 minute to 24 hours depending on the temperature condition of the heat source. Therefore, the polymer electrolyte composition of the present invention can be formed.

The dye-sensitized solar cell manufacturing method can be prepared by any method commonly used in the field to which the present invention belongs, in addition to the above-described method.

The present invention will be described in more detail based on the following production examples, but the present invention is not limited thereto.

Production Example  1: urethane prepolymer DEG -1.5 TDI Synthesis of

Diethylene glycol (DEG, Mw = 106.12) was added to 200 ml of tetrahydrofuran (THF) dried in a nitrogen atmosphere using a 1000 ml three-necked flask equipped with a stirrer, thermometer, dropping device, condenser and nitrogen injection tube. g (0.47 mol) and 124 g (0.71 mol) of toluene diisocyanate (TDI) were added dropwise at 85 ° C for 2 hours. After removal of THF under reduced pressure, the remaining reaction was vacuum dried at 50 ° C. for at least 24 hours to synthesize 162 g of urethane prepolymer DEG-1.5TDI (yield 91%).

Production Example  2: urethane prepolymer TEG -1.5 TDI Synthesis of

In the same manner as in Preparation Example 1, 60 g of urethane prepolymer TEG-1.5TDI was synthesized by reacting 70 g of tetraethylene glycol (TEG, Mw = 194.17) with 94.18 g of toluene diisocyanate (TDI) (yield 95%). .

Production Example  3: urethane prepolymer GETO -2 TDI Synthesis of

70 g of glycerol ethoxylate (EO / OH = 6.8 / 1) (GETO, Mw = 1000) and 24.4 g of toluene diisocyanate (TDI) were reacted in the same manner as in Preparation Example 1 to 60 g of prepolymer GETO-2TDI. Was synthesized (yield 97%).

Production Example  4: urethane prepolymer PAETO -2 TDI Synthesis of

In the same manner as in Preparation Example 1, 60 g of prepolymer PAETO was reacted with 70 g of pentaaritroethoxylate (EO / OH = 3/4) (PAETO, Mw = 194.17) and 90.3 g of toluene diisocyanate (TDI). -2 TDI was synthesized (yield 94%).

Next, experiments were conducted to find out the characteristics of the dye-sensitized solar cell manufactured by the above example. The experiments carried out below are exemplary and are not intended to limit the invention.

Experimental Example  One: Lithium salt  Ion Conductivity Test According to Content

Urethane prepolymer GETO-2TDI prepared in Preparation Example 1, 80% pentaerythritol ethoxylate (EO / OH = 3/4) (PAETO), polyethylene glycol dimethyl ether (PEGDME, molecular weight 250), LiI and I ₂ was mixed as shown in Table 1 to prepare a polymer electrolyte composition.

The polymer electrolyte composition was injected into a band-shaped conductive glass substrate or nickel foil, and then polymerized by thermosetting in an oven at 80 ° C. for 20 minutes. In addition, the AC impedance between the band-type or sandwich-type electrodes was measured under an argon atmosphere, and the measured value was analyzed by a frequency response analyzer to obtain the ion conductivity by analyzing the complex impedance. The band-shaped electrode was used by attaching a masking tape having a width of about 1 mm to the center of the conductive glass (ITO) at intervals of about 2 cm, placing it in an etching solution, etching, and then washing and drying.

Ionic conductivity at room temperature was measured for the polymer electrolyte compositions, and the results are shown in Table 1 below.

Experimental Example  2: Ion Conductivity Test by Nonvolatile Electrolyte Type

PAETO, GETO-2TDI and LiI are used as in Experimental Example 1, and the nonvolatile solvent is 80% polyethylene glycol dimethyl ether (PEGDME (250)) having a molecular weight of 250, polyethylene glycol dimethyl ether having a molecular weight of 500 (PEGDME ( 500)), 1-methyl-3-propylimidazolium iodide (1-methy-3-propylimidazolium iodide (MPII)) by using one selected from one by one as shown in Table 2 to prepare a polymer electrolyte compositions . Specific manufacturing method was the same as in Experimental Example 1.

The polymer electrolyte compositions were measured for ionic conductivity at room temperature, and the results are shown in Table 2 below.

Experimental Example  3: Crosslinker  Ion Conductivity Test by Type

As the lithium salt and the nonvolatile solvent, 80% polyethylene glycol dimethyl ether (PEGDME, molecular weight 250) and LiI were used as in Experimental Example 1, and the polyethylene oxide and LiI molar ratio were set to 15. Using a polyol and DEG-1.5TDI, TEG-1.5DI, PEATO-2TDI prepared in Preparation Examples 1, 2, 4 as a crosslinking agent to prepare a polymer electrolyte composition as shown in Table 3. In addition, the polymer electrolyte composition was prepared as shown in Table 3 using TDI and HDI. Specific manufacturing method was the same as in Experimental Example 1.

Ionic conductivity at room temperature was measured for the polymer electrolyte composition, and the results are shown in Table 3 below.

Experimental Example  4: of dye-sensitized solar cell Light conversion  Efficiency measurement

A conductive transparent glass substrate coated with ITO or SnO ₂ was prepared. A colloidal solution containing titanium dioxide having a size of about 15 to 30 nm was prepared. The colloidal solution was coated on the conductive transparent glass substrate to a thickness of about 10 to 15 μm, and then heated to a temperature of about 450 ° C. to remove organic substances in the colloidal solution, and titanium dioxides were contacted and filled with each other. At this time, the coating was performed on the remaining area leaving about 1 cm of the conductive transparent glass substrate in all directions. The conductive transparent glass substrate coated with titanium dioxide is left in a dye solution composed of ruthenium complex for 24 hours. Thus, the ruthenium complex was adsorbed onto the titanium dioxide by reaction with titanium dioxide to complete the semiconductor electrode.

The counter electrode was completed by preparing a conductive transparent glass substrate similar to the conductive transparent glass substrate of the semiconductor electrode and coating the conductive transparent glass substrate with platinum to form a platinum layer. Platinum coating of the counter electrode was also performed on the remaining regions of the conductive transparent glass substrate except for about 1 cm.

The semiconductor electrode and the counter electrode were disposed to face each other. A polymer film SURLYN (trade name, Du Pont Co., Ltd.) having a thickness of about 30 to 50 μm between the conductive transparent glass substrate region not coated with titanium dioxide on the semiconductor electrode and the conductive transparent glass substrate region not coated with platinum on the counter electrode. Connected to each other). In order to strongly adhere the polymer film to each of the conductive transparent glass substrate of the semiconductor electrode and the conductive transparent glass substrate of the counter electrode, the polymer film was strongly adhered to about 1 to 2 atmospheres on a heating plate of about 100 to 140 ° C. Thus, the semiconductor electrode and the counter electrode were connected by the polymer film to form a cylinder formed on a hexahedron.

The polyelectrolyte composition was one of the urethane prepolymers GETO-2TDI, PAETO-2TDI, and TDI prepared in Preparation Examples 3 and 4, and pentaerythritol ethoxylate (EO / OH = 3/4) (PAETO), 80%. Polyethylene glycol dimethyl ether (PEGDME, molecular weight 250), LiI and I ₂ were prepared by mixing as shown in Table 4 below. As a salt, [EO] / [LiI] was mixed at 15 molar ratio and [I ₂ ] / [LiI] at 1/20 molar ratio.

In order to fill the inside of the barrel with the polymer electrolyte composition, a minute hole was drilled in an area where the platinum layer of the counter electrode was not coated, and the polymer electrolyte composition was introduced.

After the inside of the barrel was filled with the polymer electrolyte composition, the micropores were blocked by instantaneous heating using a glass product made by SURLYN (trade name, manufactured by Du Pont) to prepare a dye-sensitized solar cell.

The dye-sensitized solar cell was thermoset in an oven at 80 ° C. for 60 minutes to complete the dye-sensitized solar cell of the present invention including the polymer electrolyte composition.

Calibrate solar conditions (AM 1.5) with standard solar cells (Frunhofer Institute Solare Engeriessysteme, Certificate No. C-ISE369, Type of material: Mono-Si + filter) using a xenon lamp (Oriel, 91193) as the light source Observed while.

FIG. 1 is a graph showing current-voltage characteristics of a dye-sensitized solar cell including a polymer electrolyte composition prepared using PAETO and PAETO-2TDI as polyols and polyisocyanates, respectively.

As shown in FIG. 1, the maximum possible current Is, the maximum possible voltage Voc, and the fill factor were measured at 5.58 mA / cm 3, 0.63 V, and 0.6, respectively. The light conversion efficiency is an efficiency of converting solar energy into electrical energy and is calculated as a ratio of generated electric energy (current × voltage × fill factor) to incident energy (100 mA / cm 2) per unit area, and according to the result of FIG. 1. The calculated photoelectric conversion efficiency of the solar cell of the present invention was 2.09%.

2 is used for each PAETO with TDI as rheology and a polyisocyanate as crosslinking agent, and uses 80% of the nonvolatile solvent MPII, I ₂ is comprising the polymer electrolyte composition was prepared by mixing with 1/20 molar ratio with respect to MPII A graph showing current-voltage characteristics of dye-sensitized solar cells.

Referring to FIG. 2, the current Is, the maximum possible voltage Voc, and the fill factor were measured at 5.58 mA / cm 3, 0.63 V, and 0.6, respectively, and the efficiency calculated therefrom was 3.1%.

As described above, the polymer electrolyte composition of the dye-sensitized solar cell according to the present invention significantly reduced the leakage and volatilization of the solvent and can improve long-term stability.

In addition, the present invention can provide a dye-sensitized solar cell excellent in practical and electrical properties by improving the long-term stability of the polymer electrolyte composition.

In addition, the present invention, the viscosity of the polymer electrolyte composition is very low before crosslinking can be easily injected into the dye-sensitized solar cell, and can be easily crosslinked using a heat source to obtain a gel polymer electrolyte dye-sensitized solar cell comprising a polymer electrolyte composition The manufacturing process of can be improved very simply.

In the above, the present invention has been described in detail with reference to preferred embodiments, but the present invention is not limited to the above embodiments, and various modifications and changes by those skilled in the art within the spirit and scope of the present invention. This is possible.

Claims (15)

Non-volatile solvents, polyols, and organic polyisocyanates, The nonvolatile solvent is polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, polyethylene glycol dipropyl ether, polyethylene glycol dibutyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol dimethyl ether, polypropylene glycol diglycidyl ether At least one polyalkylene glycol dialkyl ether selected from the group consisting of a dibutyl ether terminal polypropylene glycol / polyethylene glycol copolymer and a dibutyl ether terminal polyethylene glycol / polypropylene glycol / polyethylene glycol block copolymer Polymer electrolyte composition of a dye-sensitized solar cell, characterized in that. delete delete delete The polymer electrolyte composition of claim 1, wherein the polyol has at least two hydroxy functional groups per molecule of polyol. The dye-sensitized solar cell of claim 1, wherein the polyol is at least one selected from the group consisting of polyether polyols, polyester polyols, polyhydric alcohols, and diethylene polymers having hydroxy functional groups. Polymer electrolyte composition. According to claim 6, The polyether polyol is any one selected from the group consisting of polyhydric alcohols, sugars, alkylamines, and alkanolamines and alkylene of propylene oxide, ethylene oxide, butylene oxide, and tetrahydrofuran A polymer electrolyte composition of a dye-sensitized solar cell, characterized in that produced by reacting any one selected from the group consisting of oxides. The polymer of a dye-sensitized solar cell according to claim 6, wherein the polyester-based polyol is at least one selected from the group consisting of polyhydric alcohols, polyols of polyhydric carboxylic acid condensation systems, and polyols of cyclic ester ring-opening polymers. Electrolyte composition. The polymer electrolyte composition of a dye-sensitized solar cell of claim 1, wherein the organic polyisocyanate has two or more isocyanate functional groups per organic polyisocyanate molecule. The polymer electrolyte composition of claim 1, wherein the organic polyisocyanate is at least one selected from the group consisting of polyfunctional aliphatic, alicyclic and aromatic isocyanates. The organic polyisocyanate of claim 1, wherein the organic polyisocyanate is hexamethylene diisocyanate (HDI), isopron diisocyanate (IPDI), 4,4-dicyclohexyl methane diisocyanate (H12MDI), toluene diisocyanate (TDI). ), 4,4'-diphenylmethane diisocyanate (4,4'-MDI), orthotoluidine diisocyanate (TODI), naphthylene diisocyanate (NDI), xylene diisocyanate (XDI), lysine diisocyanate (LDI) And at least one selected from the group consisting of triphenylmethyl triisocyanate (TPTI). The polymer electrolyte composition of a dye-sensitized solar cell of claim 1, wherein the organic polyisocyanate is a urethane prepolymer having an isocyanate functional group. A semiconductor electrode comprising a first substrate, a metal oxide layer formed on the first substrate, and a dye layer coated on the metal oxide layer, A counter electrode comprising a second substrate and a metal layer formed on the second substrate, and A polymer electrolyte composition injected between the semiconductor electrode and the counter electrode and comprising a nonvolatile solvent, a polyol and an organic polyisocyanate, The nonvolatile solvent is polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, polyethylene glycol dipropyl ether, polyethylene glycol dibutyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol dimethyl ether, polypropylene glycol diglycidyl ether At least one polyalkylene glycol dialkyl ether selected from the group consisting of a dibutyl ether terminal polypropylene glycol / polyethylene glycol copolymer and a dibutyl ether terminal polyethylene glycol / polypropylene glycol / polyethylene glycol block copolymer Dye-sensitized solar cell characterized by the above-mentioned. Preparing a semiconductor electrode, Preparing a counter electrode, Adding a polyol and an organic polyisocyanate to a nonvolatile solvent to form a polymer electrolyte composition, Injecting the polymer electrolyte composition between the semiconductor electrode and the counter electrode, and And curing the polymer electrolyte composition by applying heat at 30 to 150 ° C., The nonvolatile solvent is polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, polyethylene glycol dipropyl ether, polyethylene glycol dibutyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol dimethyl ether, polypropylene glycol diglycidyl ether At least one polyalkylene glycol dialkyl ether selected from the group consisting of a dibutyl ether terminal polypropylene glycol / polyethylene glycol copolymer and a dibutyl ether terminal polyethylene glycol / polypropylene glycol / polyethylene glycol block copolymer The manufacturing method of the dye-sensitized solar cell characterized by the above-mentioned. delete

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