KR20160010720A - Resonant Multiple Light Scattering for Photon Harvest Enhancement in Dye-Sensitized Solar Cells - Google Patents

Abstract

The present invention relates to a dye exhibiting multiple resonance light scattering in photoelectrode at electrode and high light collection efficiency at light scattering wavelength range. The present invention further relates to a dye-sensitized solar cell with increased efficiency. The organic dyes of the present invention exhibits more enhanced mole absorption coefficient, short-circuit current, and photoelectricity conversion efficiency in comparison with an existing organic dye used in the dye-sensitized solar cell, thereby remarkably increasing efficiency of the solar cell. In addition, it is possible to produced dye-sensitized solar cell with excellent long-term stability owing to the organic dyes of the present invention. It is also possible to produce a solar cell with high photoelectricity conversion efficiency by using titanium dioxide produced by electrostatic spraying technology using the organic dyes.

Description

TECHNICAL FIELD The present invention relates to a dye-sensitized solar cell, and more particularly, to a dye-sensitized solar cell having a high efficiency of light collection at a light scattering wavelength band and multiple resonance light scattering of a photo-

The present invention relates to a method of synthesizing an organic dye used in a dye-sensitized solar cell and a method of fabricating the same, and more particularly, to a dye-sensitized solar cell comprising an organic dye having a high molecular extinction coefficient and a multi- A dye-sensitized solar cell capable of exhibiting conversion efficiency and lifetime characteristics, and a method for producing the same.

In order to solve the energy problems facing the world in recent years, inventors have been working on developing various natural energy (wind, hydro, geothermal, solar energy, etc.) that can replace existing fossil fuels. In particular, solar energy is an infinite resource and environmentally friendly, so energy production technology is one of the most important and key challenges of 21st century science technology. Currently, commercial solar cells are technologies based on inorganic silicon semiconductors. However, due to the explosive increase in demand for silicon, the current price is very high. Therefore, organic solar cells are importantly invented in the photoelectric conversion element part. Among them, the dye-sensitized solar cell was developed by the Gratel Invention Team in 1991. Since the dye-sensitized nanoparticle titanium oxide solar cell was developed, it is possible to manufacture a device with a significantly lower manufacturing cost, Dye-sensitized solar cells are composed of five components in most cases. 1) photocathode, 2) porous metal oxide film, 3) dye, 4) electrolyte / hole transfer material, and 5) 1 is a schematic diagram showing the structure and operation principle of a dye-sensitized solar cell.

1

Referring to FIG. 1, the operation principle of the dye-sensitized solar cell will be described. When solar light is incident on an n-type nanoparticle semiconductor oxide electrode having a dye adsorbed on a surface thereof, the dye generates electron-hole pairs. And is injected into the conduction band of the semiconductor oxide. The injected electrons are transferred to the transparent conductor and moved to the counter electrode through the excitation circuit. On the other hand, the oxidized dye receives electrons by the oxidation-reduction electrolyte and is reduced again. The oxidized electrolyte receives electrons reaching the interface of the counter electrode and is reduced again to complete the operation. Ruthenium complexes have been the most widely used dyes for dye-sensitized solar cells, and some ruthenium complexes show a photoelectric conversion efficiency of more than 11%. However, dye-sensitized solar cells using ruthenium complexes have many limitations due to the difficulty of synthesis and purification with expensive ruthenium metals. In general, dyes generally have a wide range of light absorption, high molecular extinction coefficient, Stability, and set resistance. In particular, organic dyes composed of the basic structure of electron donor, Π bonding unit and electron acceptor have advantages such as diversity of chemical structure, high molecular extinction coefficient, ease of absorption wavelength control, and simple synthesis process. As a result, many inventors have become interested in organic dyes lacking the above-mentioned metals, and inventors have been focusing on them. However, most of the organic dyes known so far have lower conversion efficiency than ruthenium metal complex dyes, and thus the development of new dyes exhibiting high photoelectric conversion efficiency with an improved molecular extinction coefficient by changing the structures of electron donors, Π bond units and electron acceptors This is a desperate need. In general, photocathodes of dye-sensitized solar cells are mostly coated with titanium dioxide having a nanocrystal structure on an FTO substrate. These nanocrystalline titanium dioxide have to meet several conditions. First, it must have a large surface area for dye adsorption, and second, it should be able to transfer electrons quickly by reducing the number of grain boundaries. Third, it must be able to induce light scattering through the proper size and structure, and finally, it must have pores that allow the electrolyte to penetrate properly. At present, there is much interest in a structure in which a TiO ₂ (HS-TiO ₂ ) having a polydisperse size structure satisfies all of the above conditions. The titanium dioxide structure can be prepared by sol-gel method, solvent thermal reaction, hydrolysis reaction, electrostatic spraying, etc. Particularly, titanium dioxide manufacturing method by electrostatic spraying is advantageous in that it is cheap and simple process, Therefore, many inventions are progressing recently.

This patent is directed to devising electron donors of various structures to meet the requirements of organic dyes and to provide a significantly improved photoelectric conversion efficiency by applying suitable? Coupling units. It is another object of the present invention to provide an organic dye and a method for producing the same that maintain long-term stability of a solar cell. It is still another object of the present invention to provide a method of manufacturing a solar cell to which the titanium dioxide electrode fabricated through the electrostatic spraying with the organic dye is applied.

Korean Patent Publication No. 10-2013-0062234 Korean Patent Publication No. 10-2012-0088963

"Dye-sensitized Solar Cells (Fundamental Sciences. Chemistry)" (2010, K. Kalyanasundram EPFL press)

In conventional dye-sensitized solar cells, the efficiency of dye absorption and photoelectric conversion is low, and a high efficiency can not be expected for a tube P which only absorbs unevenness of penetrated light. In the present invention, a new dye capable of efficiently photoelectrically converting the HOP light with a high HSP and a very wide range of the absorption spectrum can be produced, and at the same time, the size of the titanium oxide particle can be controlled at the electrode, A process for manufacturing a dye-sensitized solar cell with high efficiency using a process for increasing the light absorption is developed and at the same time, an efficient solar cell is manufactured.

The present invention relates to a novel organic dye, a process for producing the same, and a process for producing a dye-sensitized solar cell, wherein the organic dye comprises a triphenylamine derivative as an electron donor, a thiophene- Were synthesized. The dye-sensitized solar cell according to the present invention exhibits enhanced light-collecting efficiency and charge collecting ability as compared with the conventional dye-sensitized solar cell manufactured through the organic dye through the visible light region absorption of the novel organic dye and the multiple resonance light scattering of the photo- Thereby greatly increasing the short-circuit current (J _sc ) and increasing the photoelectric conversion efficiency. INDUSTRIAL APPLICABILITY The organic dyes of the present invention exhibit an improved molar extinction coefficient, short circuit current and photoelectric conversion efficiency compared with the conventional organic dyes used in dye-sensitized solar cells, thereby remarkably improving the efficiency of a solar cell. A dye-sensitized solar cell having excellent long-term stability can be manufactured, and a method for manufacturing a solar cell having high photoelectric conversion efficiency by using organic dyes and titanium dioxide produced by electrostatic spraying technology.

The solar cell and the dye synthesized through the present invention can greatly improve the photoelectric conversion efficiency of the dye-sensitized solar cell and can maintain the long-term stability of the solar cell, and thus excellent organic dyes usable in flexible (solar) And can be widely used in solar cells for energy harvesting.

1 is a schematic diagram of a dye-sensitized solar cell principle
FIG. 2 is a graph showing the correlation between the photocurrent and the voltage of the dye-sensitized solar cell using the dye-sensitized solar cell and the N719 dye prepared according to the present invention
3 is a graph showing the time-dependent efficiency conversion of the dye-sensitized solar cell using the dye solar-sensitive cell and the N719 dye produced by the present invention

In order to solve the energy problems facing the world in recent years, inventors have been working on developing various natural energy (wind, hydro, geothermal, solar energy, etc.) that can replace existing fossil fuels. In particular, solar energy is an infinite resource and environmentally friendly, so energy production technology is one of the most important and key challenges of 21st century science technology. Currently, commercial solar cells are technologies based on inorganic silicon semiconductors. However, due to the explosive increase in demand for silicon, the current price is very high. Therefore, organic solar cells are importantly invented in the photoelectric conversion element part. Among them, the dye-sensitized solar cell was developed by the Gratel Invention Team in 1991. Since the dye-sensitized nanoparticle titanium oxide solar cell was developed, it is possible to manufacture a device with a significantly lower manufacturing cost, Dye-sensitized solar cells are composed of five components in most cases. 1) photocathode, 2) porous metal oxide film, 3) dye, 4) electrolyte / hole transfer material, and 5) 1 is a schematic diagram showing the structure and operation principle of a dye-sensitized solar cell. Other objects of the present invention will be more clearly understood from the following examples. However, the following embodiments are only examples of the present invention, and the present invention is not limited thereto.

In order to achieve the above object, the present invention provides a novel organic dye represented by the general formula (1).

Wherein R < 1 &

,

,

, 또는 이들의 조합이다. 상기 화학식에서 R2는

,

,

, Or a combination thereof. In the above formula, R2 is

,

,

, 또는 이들의 조합이다. 상기화학식에서 R₃는

,

,

, Or a combination thereof. In the above formula, R < _{3 &}

-H , -F, or a combination thereof.

The present invention provides a photoelectric conversion element comprising the organic dye of Formula 1 and titanium dioxide (HS-TiO ₂ ) having a polydisperse size structure to which the electrostatic spraying technique is applied, wherein the photoelectric conversion element And a dye-sensitized solar cell.

In order to achieve the above object, a triphenylamine derivative having a non-planar molecular structure is used as an electron donor, which prevents strong electron donating property and dye aggregation property. Also, a methoxy group and an ethylhexyloxy group were introduced into the above triphenylamine in order to invent an electron donating property and an aggregation property. The present invention introduces a thiophene-condensed thiophene bonding unit for a high molecular extinction coefficient and a broad absorption wavelength. In particular, condensed thiophenes can increase the? -Conjugation length of organic dyes due to their planar structure, and alkyl groups linked to thiophene units can block the aggregation characteristics of dyes and maintain long-term stability of the solar cells. A butyl group, a hexyl group, and an octyl group were introduced into the thiophene unit, respectively, in order to invent the solubility and aggregation characteristics of the dye. The present invention uses cyanoacetic acid as an electron acceptor for adsorbing on titanium dioxide and accelerating electron transfer. (1) reacting a compound of the formula (2) with a compound of the formula (3) to give a compound of the formula (4), (2) reacting the compound of the formula (4) in dimethylformamide (3) reacting the compound of formula (5) with cyanoacetic acid in the presence of piperidine in acetonitrile, by reaction with phosphorous oxychloride (POCl ₃ ). A specific example thereof can be shown as Reaction 1.

Scheme 1

The detailed conditions of synthesis are as follows. 2- (5-bromo-4- hexylthiophen-2-yl) -5- (4-hexylthiophen-2-yl) thieno [3,2-b] thiophene and 4- (diphenylamino) phenyl boronic acid, Pd (pph 3 ) ₄ and 2N K ₂ CO ₃ were mixed in anhydrous tetrahydrofuran (THF) and refluxed under an argon atmosphere for 24 hours. The resulting reaction mixture is stirred in water for 1 hour and extracted with dichloromethane. The extracted organic layer is washed with brine solution and water and stirred with magnesium sulfate. The resulting solution was purified by silica gel chromatography to give the following compound 1. As a result of mass spectrometry on compound 1 obtained, it was confirmed that m / z = 715.

Compound 1

The compound 1 is reacted with phosphorus oxychloride (POCl ₃ ) in dimethylformamide (DMF). The reaction is stirred at 60 < 0 > C for 12 hours. The resulting reaction mixture is poured into a 1M aqueous solution of sodium acetate and reacted for 1 hour and then extracted with dichloromethane. The extracted organic layer is washed with brine solution and water and stirred with sodium sulfate. The resulting residue was purified by silica gel chromatography to give the following compound 2. Mass spectrometry of the obtained compound 2 confirmed that m / z = 743.

Compound 2

Compound 2 was mixed with cyanoacetic acid and piperidine in acetonitrile and refluxed for 12 hours. After the completion of the reaction, the obtained reaction product was washed several times with petroleum ether and acetonitrile to obtain the following compound 3. Mass spectrometry of the obtained compound 3 confirmed that m / z = 810.

Compound 3

(4-hexylthiophen-2-yl) thieno [3,2-b] thiophene and 4- (bis (4- methoxyphenyl) amino) phenylboronic acid , Pd (pph ₃ ) ₄ and 2N K ₂ CO ₃ were mixed in anhydrous tetrahydrofuran (THF) and refluxed under an argon atmosphere for 24 hours. The resulting reaction mixture is stirred in water for 1 hour and extracted with dichloromethane. The extracted organic layer is washed with brine solution and water and stirred with magnesium sulfate. The resulting solution was purified by silica gel chromatography to give the following compound 1. The obtained compound 1 was subjected to mass spectrometry and it was confirmed that m / z = 775.

Compound 4

The compound is reacted with phosphorous oxychloride (POCl ₃ ) in dimethylformamide (DMF). The reaction is stirred at 65 < 0 > C for 24 hours. The resulting reaction mixture is poured into a 1M aqueous solution of sodium acetate and reacted for 1 hour and then extracted with dichloromethane. The extracted organic layer is washed with brine solution and water and stirred with sodium sulfate. The resulting residue was purified by silica gel chromatography to give the following compound 5. The resultant compound 5 was analyzed by mass spectrometry to find that m / z = 803.

Compound 5

The compound was mixed with cyanoacetic acid and piperidine in acetonitrile and refluxed for 12 hours. After the completion of the reaction, the obtained reaction product was washed several times with petroleum ether and acetonitrile to obtain the following compound 6. The obtained compound 6 was subjected to mass spectrometry and it was confirmed that m / z = 870.

Compound 6

In addition to using the dye of Formula 1, the present invention can also be applied to methods for preparing dye-sensitized solar cells using conventional dyes. The fabricated dye-sensitized solar cell device was prepared by preparing a transparent electrode using titanium dioxide (HS-TiO ₂ ) having a polydisperse size structure manufactured by an electrostatic spraying technique and then adsorbing the organic dye of the present invention on the electrode good. We have fabricated a device that exhibits better efficiency than conventional dye-sensitized solar cells by adsorbing a compound represented by Formula 1 having a novel organic dye structure onto a (HS-TiO ₂ ) electrode having a polydisperse size structure formed by an electrostatic spraying technique. Thereby completing the invention. In order to evaluate the photoelectric characteristics of the organic dye according to the present invention, a dye-sensitized solar cell was prepared using a (HS-TiO ₂ ) transparent layer made of titanium particles having a 13 μm polydispersity size structure. Specifically, 10 wt% P-25 (Degussa) nanocrystalline titanium dioxide was dispersed in ethanol and milled. The dispersed titanium dioxide solution is filled into a syringe infusion pump connected to a high-voltage power source. FTO glass substrate is coated with titanium dioxide through electrostatic spraying technique. The electric field is fixed at 1.5 kV cm ^-1 and the solution injection rate is set at 40 μL min ^-1 . It is then sintered in air at 500 ° C for 30 minutes and squeezed at 80 ° C for 10 minutes. For the post-treatment of the photocathode made by the electrostatic spraying technique, the titanium dioxide transparent layer was impregnated in an aqueous solution of 0.1 molar titanium tetrachloride (TiCl ₄ ) at 80 ° C for 20 minutes, rinsed with water, and sintered at 450 ° C for 30 minutes. The resulting titanium dioxide electrode was placed in a solution of compound 3 and compound 6 (0.3 mM in ethanol containing 1.5 mM DCA), respectively, and maintained for 4 hours. Titanium dioxide electrodes with organic dye adsorption were washed with ethanol and dried in a nitrogen stream. The dye-adsorbed titanium dioxide electrode and the platinum counter electrode were sandwich-typed using a thermal adhesive film (Surlyn, Dupont 1702, 25 μm-thick) as an adhesive between the electrodes. Subsequently, 0.65 mM 1-butyl-3-methylimidazolium iodide, 0.1M lithium iodide, 0.03M iodine, 0.5M iodine, and 0.5M iodine were added to a mixed solution of acetonitrile and valeronitrile (85/15 v / v) The dye-sensitized solar cell was prepared by injecting an electrolyte prepared by adding tert-butylpyridine into a cell. In order to compare the photoelectric characteristics of the novel organic dyes, a device was fabricated using N719 (Solaronix), which is the most widely used ruthenium complex dye of the following formula (6).

The dye-sensitized solar cell using the N719 dye was fabricated in the same manner as the device made from the organic dye described above. The photoelectric conversion efficiency of a dye-sensitized solar cell is represented by the generated electric energy with respect to the total energy reaching the solar cell from the sun, and is expressed by the following equation.

η = P _max / P _in = (J _sc * V _oc * FF) / P _in

The short-circuit current (J _sc ) is the current density that appears when the circuit receives light in the short-circuited state. This value depends on the intensity of the light, the wavelength region of the light, and whether electrons and holes excited by the incident light are not lost and sent toward the external circuit inside the cell. The open-circuit voltage (V _oc ) is a potential difference formed at both ends of the solar cell when light is received when the circuit is opened. The dye-sensitized solar cell is usually determined by the difference between the Fermi level of titanium dioxide and the redox energy level of the electrolyte A high open-circuit voltage is obtained when an electrolyte having a large difference is used. The filling rate (FF) is calculated by multiplying the product of the current density at the maximum power point and the voltage value (J _max x V _max ) by the short-circuit current and the open-circuit voltage J _sc x V _oc ).

The photocell performance of the dye-sensitized solar cell was measured using a 450 W xenon light source, and the results are shown in Table 1 and FIG.

Sensitizer
V _OC  (V)
J _SC  ( mA cm ^-2 )
FF
η ( efficiency ) (%)
N719

0.767
19.5
0.654
9.77
Compound 3

0.687
20.9
0.639
9.18
Compound 6

0.691
21.62
0.631
9.42

2

As shown in Table 1 and FIG. 2, the solar cell fabricated with Compound 3 under the standard AM 1.5 conditions showed a short circuit current of 20.9 mA cm ^-2 , an open circuit voltage of 0.687 V, a filling ratio of 0.639, and a photoelectric conversion efficiency of 9.18% 6 was 21.62 mA cm ^-2 , the open circuit voltage was 0.691 V, the filling rate was 0.631, and the photoelectric conversion efficiency was 9.42%. In particular, the short circuit current showed the highest value among all dyes presently announced. Also, the methoxy group of Compound 6 showed a higher short circuit current value than Compound 3 because of its excellent ability to donate electrons. As shown above, the very high short-circuit currents of Compound 3 and Compound 6 are due to the broad wavelength of light of the novel organic dye, the high molecular absorption coefficient, the harmonization of the light scattering of the titanium dioxide electrode having the appropriate energy level and the polydisperse size structure The long term stability test of the dye-sensitized solar cell was carried out at 50 DEG C for 800 hours under standard AM 1.5 conditions, and the results are shown in FIG.

3

As shown in FIG. 3, the solar cell made of the compound 3 and the compound 6 has a very excellent long-term stability compared to the solar cell made of the N719 dye. As shown in FIG. 3, the solar cell produced with N719 after 800 hours had an initial efficiency of 54%, the solar cell made with compound 3 had 81% of the initial efficiency, the solar cell made with compound 6 had 82% Value. Therefore, the novel dyes of the present invention can greatly improve the photoelectric conversion efficiency of the dye-sensitized solar cell, maintain long-term stability of the solar cell, and become excellent organic dyes usable in flexible solar cells.

Claims (4)

An organic dye for a dye-sensitized solar cell, which is represented by the following formula:

Wherein R < 1 &

,

,

, Or a combination thereof. In the above formula, R2 is

,

,

, Or a combination thereof. In the above formula, R ₃ is -H , -F or a combination thereof.
A method of controlling the size of electrode particles by radiating titanium dioxide solution by electrostatic spraying so as to cause light scattering in visible and far infrared rays.
The organic photovoltaic cell according to claim 1, wherein the organic dye of claim 1 is adsorbed on the surface of the electrode of claim 2 so that the scattered light of the transparent electrode of claim 2 coincides with the absorption wavelength band of the dye to increase the light absorption efficiency by using multiple light scattering.
A process for producing the organic dye according to claim 1 and a method for producing a solar cell having high efficiency for a long time using the dye

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