KR101765816B1 - Fabrication method of photo electrode and dye-sensitized solar cell by low temperature atmospheric pressure plasma - Google Patents

Abstract

The present invention provides a method for producing a photoelectrode and a dye-sensitized solar cell by effectively sintering TiO ₂ at a low temperature. In the present invention, ^o C for 1 hour to solve the process limit when a low-temperature process such as a flexible substrate is required through a low-temperature atmospheric plasma, thereby proposing a new dye-sensitized solar cell process technology. In particular, the low temperature sintering process through atmospheric pressure plasma has a very high economic value because it can shorten the process time as well as the development of a thin film solar cell as compared with the conventional method.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a photo-electrode and a dye-sensitized solar cell,

The present invention relates to a photoelectrode and a dye-sensitized solar cell having the same, and more particularly, to a method for manufacturing a high-quality dye-sensitized solar cell by developing a low-temperature TiO ₂ photoelectrode sintering process and applying it to a conductive flexible substrate .

Recently, renewable energy has been attracting attention due to global environmental problems, depletion of fossil energy, disposal of nuclear power generation waste, and location of new power plants. Among them, the research and development on the photovoltaic power generation, which is pollution-free energy, is progressing actively both domestically and abroad.

The solar cell is a device that converts solar energy directly into electric energy. Depending on the constituent material, solar cell made of inorganic material using silicon, compound semiconductor, dye-sensitized solar cell in which the photosensitive dye is adsorbed on the surface of transition metal oxide particles , And solar cells composed of organic molecules.

Currently, silicon-based solar cells are the mainstream, but since monocrystalline and polycrystalline silicon are made from raw materials in bulk, the material cost is high, which limits the cost reduction. In order to solve such problems, a thin film type solar cell is manufactured on a cheap substrate such as glass, and a dye-sensitized solar cell is being studied in recent years as an inexpensive solar cell for commercialization.

The dye-sensitized solar cell is composed of three parts: a light electrode (semiconductor electrode), an electrolyte solution, and an opposite electrode. Here, the photoelectrode refers to a transition metal oxide layer formed on a substrate on which a transparent conductive oxide thin film is formed. The transition metal oxide layer adsorbs a photoactive dye that absorbs sunlight to generate photoelectrons. The photoelectrons generated in the dye are transferred to the transparent conductive oxide thin film and the substrate through the transition metal oxide layer and transferred to an external circuit, thereby generating an electromotive force. The counter electrode refers to a catalyst layer such as platinum formed on a substrate such as a conductive glass. The electrolyte solution is a portion inserted between the photoelectrode and the counter electrode.

The photoelectrode should have a suitable bandgap to receive electrons from the dye and be made of a semiconductor oxide that can easily attach the dye to the surface. In particular, TiO ₂ , which is cheap and has high chemical stability and high photoactivity, has a band gap of 3.2 eV and is used as a main material of photoelectrode. Therefore, the dye-sensitized solar cell has a structure in which n-type TiO ₂ When the nanoparticle semiconductor oxide electrode absorbs light, the dye molecules generate electron-hole pairs, and the generated electrons are injected into the conduction band of TiO ₂ , which is a semiconductor oxide. The photoelectrons injected are transferred to the photoelectrode coated with the conductive film through the interface between the nanoparticles, and the current is generated and is transferred to the opposite electrode. The electrons are transferred and the holes generated in the dye molecules are redoxed by the oxidation and reduction in the iodine-based electrolyte. In order to increase the photoelectric current production efficiency increase of solar light energy conversion efficiency, the size of the particles of the TiO ₂ sintered to the photo-electrode (size), shape (mopology), crystalline (crystallinity) and the surface state (surface state) and stacked on the TiO ₂ Thickness plays an important role. Therefore, the photoelectrode is required to transfer a large number of electrons produced from the dye to the opposite electrode without loss, and thus a semiconductor oxide having a relatively large specific surface area is required. The specific surface area of the material (Brunauer, Emmett, Teller; BET) is a numerical value indicating the surface area of particles per unit mass or volume. It is known that the anatase phase specific surface area in TiO ₂ is much larger than the rutile phase. Therefore, TiO ₂ on the anatase phase should be used in order to increase the amount of dye adsorbed on the photoelectrode and increase the photocurrent generation efficiency. In addition, in order to increase the conversion efficiency of solar cells, it is required to manufacture photoelectrode having good optical activity through optimization of size and shape surface state, and to increase the generation of photocurrent through it.

In recent years, research has been conducted focusing on the following four points for the purpose of increasing the electron transfer at each interface of the dye-sensitized solar cell and increasing the conversion efficiency thereof. First, the development of a dye capable of absorbing light at a wide wavelength with an appropriate band gap to easily transfer photoelectrons to TiO ₂ ; Second, the development of a solid electrolyte to solve the leakage problem of the liquid electrolyte, which is called a disadvantage of the dye-sensitized solar cell; Third, the development of nano-structured TiO ₂ nanostructures to enhance the reflectivity of incident light, and the effective transfer of electrons through nanoparticles and nanowires; Finally, TiO ₂ The development of conductive electrodes with nanostructures. This can reduce the loss of electrons through a transparent conductive oxide (TCO) substrate with a high conductivity, thereby maximizing the conversion efficiency and making the dye-sensitized solar cell from various surfaces.

The conventional technique sintered TiO ₂ only at a high temperature of 450 ^° C, and fabricated a dye-sensitized solar cell using the photoelectrode. However, since a dye-sensitized solar cell based on a flexible polymer substrate can not be heat-treated at a high temperature, a new low-temperature sintering process is required.

SUMMARY OF THE INVENTION The present invention provides a method of manufacturing a photoelectrode and a dye-sensitized solar cell by effectively sintering TiO ₂ at a low temperature.

According to an embodiment of the present invention, a TiO ₂ paste is coated on a substrate to form a TiO ₂ After forming the thin film, the TiO ₂ The thin film is subjected to an atmospheric plasma of 200 ^o C or less.

TiO ₂ Thin film formation and atmospheric pressure plasma treatment are repeatedly performed to form TiO ₂ The thickness of the thin film can be adjusted.

In the method of manufacturing a dye-sensitized solar cell according to the present invention, a photoelectrode is prepared using the photo-electrode manufacturing method as described above, and the dye-sensitized solar cell is prepared by combining the photo-electrode and an electrolyte.

According to the present invention, it is possible to effectively sinter TiO ₂ at a low temperature by using an atmospheric plasma, and at the same time to facilitate the decomposition of organic materials through generated active oxygen species, and to manufacture a photo electrode in a short period of time.

The TiO ₂ photoelectrode fabrication technique using the present invention can be utilized effectively in dye-sensitized solar cells and can be applied to any process requiring heat treatment based on a flexible substrate.

1 is a schematic view of a dye-sensitized solar cell manufactured by a method according to the present invention.
2 is a view illustrating a process of manufacturing a photoelectrode using a low temperature atmospheric pressure plasma according to the present invention.
3 is a gas temperature and emission light analysis chart of the atmospheric plasma.
4 is a current-voltage curve.
5 is a graph showing J _sc , V _oc , FF, and Efficiency.
6 is a graph showing the efficiency per thickness and a cross-sectional photograph of a TiO ₂ photoelectrode.
Figure 7 shows the comparison of the plasma treatment and heat treatment at an optimized thickness and efficiency at 4 um thickness.
Figure 8 is a Nyquist plot of the transmission line model and interface.
FIG. 9 shows the resistance and frequency change depending on the thickness of the TiO ₂ / electrolyte interface.
10 is a comparative graph of dye adsorption amount, wherein (a) is the adsorption amount at the maximum efficiency and (c) is the adsorption amount according to the thickness.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. It is provided to let you know.

The present invention is a new method for the fabrication of photoelectrodes through low temperature sintering of titanium dioxide (TiO ₂ ) using atmospheric plasma which is discharged in a cold open space. The TiO ₂ photoelectrode for generating a transparent and efficient photocurrent is a key component of a dye-sensitized solar cell (DSC). Recently, research is underway to develop a TiO ₂ photoelectrode with good photo-conversion efficiency. Especially, the development of a flexible solar cell having good portability and easy adhesion to all materials has been attracting attention all over the world. However, the flexible substrate made of polymer has a serious problem in that it is damaged by the high-temperature heat treatment of 500 ^° C or more used in the conventional photo-electrode sintering process. Therefore, it has been found that TiO ₂ It is required to develop a technique of photoelectrode through sintering.

SUMMARY OF THE INVENTION [ ^o C for 1 hour to solve the process limit when a low-temperature process such as a flexible substrate is required through a low-temperature atmospheric plasma, thereby characterizing the process technology of a new dye-sensitized solar cell. In particular, the low temperature sintering process through atmospheric pressure plasma has a very high economic value because it can shorten the process time as well as the development of a thin film solar cell as compared with the conventional method.

The present invention develops a low-temperature TiO ₂ photoelectrode sintering process using an atmospheric pressure plasma to replace a conventionally used high temperature heat treatment method, and can effectively apply the sintering process to a conductive flexible substrate.

To confirm the low temperature sintering process, TiO ₂ photoelectrodes were fabricated and used to fabricate dye - sensitized solar cells. A doctor-blade method was used to control the thickness. Hereinafter, the present invention will be described in detail.

[Experimental Example 1]

Through low temperature sintering Photoelectrode  Necessity of Manufacturing and Atmospheric Pressure Plasma  role

Recently, Flexible DSC has been concentrating worldwide efforts to develop solar cell flexible DSC. Flexible DSCs, however, are a very challenging technology because all work on dyes, electrolytes, TiO ₂ and flexible conductive substrates related to increased conversion efficiency must be based. Above all, the most important technology to develop flexible DSCs and to find breakthroughs is the process of making photoelectrodes by sintering TiO ₂ on a transparent conductive flexible substrate made of polymer. Conventional photo-electrode manufacturing method of DSC is to bond porous TiO ₂ of nanoparticles to a substrate coated with TCO and sinter at a high temperature of 450-500 ^° C for more than 1 hour to decompose the bonding organic material and to connect TiO ₂ To create a structure through which electrons can move. Since most of the flexible substrates are made of polymer, it is impossible to manufacture them at the high temperature of 450 ^o C as in the current heat treatment. Therefore, a method of effectively forming a photoelectrode at a low temperature is most urgent. Recently, a new process such as applying pressure has been developed to compensate for these drawbacks, but there are still problems such as complicated processes and time consuming processes. Therefore, the development of a new process that sintered to a flexible substrate at low temperature is necessary, and if it succeeds, it can give a significant industrial impact.

The low temperature sintering process can be applied not only to DSC but also to various flexible circuits and displays, which is very technically valuable. At this time, since the atmospheric plasma can control the temperature, active excited species having high energy as well as reactive oxygen species (ROS) are included in the plasma discharge, and therefore, It has a sufficient condition for decomposing organic materials for bonding as well as for producing a photoelectrode at a low temperature. Therefore, it is expected that the photoelectrode can be fabricated more simply by fabricating the optimized atmospheric plasma generator and sintering the TiO ₂ through the generated low temperature atmospheric plasma discharge. In particular, the atmospheric plasma can easily change the wettability of the TiO ₂ surface, thereby increasing the dye adsorption of TiO ₂ and controlling the band gap by changing the physical properties of the TiO ₂ , so that it can absorb not only ultraviolet rays but also visible light It has optimal conditions for making high efficiency DSC. Accordingly, the present invention aims at developing a new process for producing high-efficiency flexible DSC using the world's first atmospheric plasma by developing a series of processes of low-temperature sintering process using atmospheric plasma and applying it to a conductive flexible substrate.

Low temperature atmospheric pressure Plasma  Used Photoelectrode  Manufacture process

1 is a schematic view of a dye-sensitized solar cell manufactured by a method according to the present invention.

1, a dye-sensitized solar cell 100 according to the present invention includes a first substrate 110, a transparent conductive oxide thin film 120, a light electrode 130, a counter electrode 140, a second substrate 150 And an electrolyte 160.

The type of the first substrate 110 is not particularly limited, and glass, plastic, or the like can be used. Transparent glass can be used as the first substrate 110. The method of forming the transparent conductive oxide thin film 120 on the first substrate 110 is not particularly limited and may be deposited on the first substrate 110 through pulsed laser deposition (PLD). The light electrode 130 is formed on the transparent conductive oxide thin film 120 and is manufactured by low-temperature sintering according to the method according to the present invention. The counter electrode 140 is formed on the second substrate 150 and may be made of platinum Pt. The counter electrode 140 is arranged to face the light electrode 130.

2 is a view illustrating a process of manufacturing a photoelectrode using a low temperature atmospheric pressure plasma according to the present invention. Referring to FIG. 2, in a large-area plasma source of 13.56 MHz used for manufacturing a DSC photoelectrode using a low-temperature atmospheric plasma, a distance between the source and the sample was fixed to 2 mm to treat a uniform plasma. For low-temperature sintering, the input power was performed at a gas temperature of about 200 ^° C or less.

3 is a gas temperature and emission light analysis chart of the atmospheric plasma. The gas temperature of the plasma is 6 slpm at 120 psig when using ultra high purity argon (99.999%), 200 ^{o The} temperature could be lowered to below C, and when the oxygen was mixed with 12 sccm of 0.2% compared to argon, 150 W to 190 ^It was possible to maintain the temperature at ^o C.

The sintering process using such a low-temperature plasma has a short process time in comparison with the heat treatment at a high temperature, and is easily performed in the air since it is performed in an open space. This is a very effective method because it saves time for heating and cooling time for sintering process at high temperature. As shown in FIG. 3, various kinds of atomic and molecular beam spectra are observed in the oxygen-containing argon plasma. In particular, molecular line spectra such as N2 and N2 ⁺ and OI, including OH, which are expected to effectively affect organic decomposition from plasma emission light, are observed.

TiO ₂ used for the photoelectrode of the DSC The paste was about 20 nm TiO ₂ Nanoparticles Prepared as anatase phase by mixing 0.133 cc of Acetyl Acetone, 3.2 cc of DI water and 3.2 cc of ETOH. The anatase phase has a larger specific surface area than that of the rutile phase and has good photoactivity at low temperatures, so that it is very effectively used for photoelectrodes. The prepared TiO ₂ was screen-formed on a conductive glass substrate coated with FTO (fluorine-doped tin oxide, SnO ₂ : F) with a square size of 0.5 × 0.5 cm using a 3M tape, and then subjected to a doctor- Lt; / RTI > Coated TiO ₂ The thin film was treated with a low-temperature atmospheric plasma for 30 minutes and repeatedly performed as shown in Fig. 1 to find a suitable thickness. In order to reduce the number of repetitions, the thickness of TiO ₂ was adjusted by adding 5 minutes of drying process at 85 ^° C on a hot plate. The thickness of the TiO ₂ to be used as the photoelectrode should be appropriately adjusted by repeating several times because the thickness of the doctor blade method for manufacturing the thin film is changed by the pressure of the pressing by the human hand. Generally, in the case of 20 nm nanoparticles using heat treatment, the appropriate thickness is about 15-20 nm, and doctor - blade method and plasma treatment are repeated to build up TiO ₂ of appropriate thickness.

Atmospheric pressure plasma  Treated The  With characteristics DSC  analysis

In order to investigate the characteristics of DSCs fabricated through the photoelectrode treated with atmospheric plasma, we compared the DSCs fabricated with photoelectrodes annealed at high temperatures. The energy conversion efficiency of DSC is 100 mW / cm ² We measured the efficiency of DSC by measuring the open circuit voltage and the short circuit voltage while applying the forward bias voltage to the assembled DSC. The energy conversion efficiency? Is a value of an electric energy (P _out ) ratio generated with respect to the incident light energy P _in , and is expressed by the following equation (1.1).

(1.1)

(1.1)

Where J _sc is the current in the short circuit, V _oc is the voltage on the open circuit, and FF is the fill factor, as shown in Figure 4 (J _max × V _max ) / (J _sc × V _oc ), and the value of the fill factor increases as the current-voltage curve approaches the quadrangle. Thus, high current density, high open-circuit voltage and high photo-conversion efficiency can be obtained in FF.

The photocurrent generated in the DSC starts when the photon having energy greater than the band gap is absorbed by the dye molecule bound to TiO ₂ and electron-hole pairs are generated. The generated electrons are injected at a very high rate of picosecond to the conduction band of TiO ₂ , and are transmitted to the transparent conductive substrate along the interface of TiO ₂ to generate current. At this time, the holes formed in the oxidized dye molecules are redoxed by the electrolyte within a few nanoseconds, and then they are re-reduced by electrons. In terms of the diffusion rate of electrons, electrons are lost to the electrolyte through the surface state of TiO ₂ , and the recombination or back reaction rate is slightly slower from micro to millisecond. Therefore, most of the electrons are transmitted through the conduction band of TiO ₂ . The measured photocurrent (I _ph ) is thus determined by the difference between the currents I _r lost by surface recombination at the current (I _inj ) injected from the dye molecules and is represented by equation (1.2) I _sc .

(1.2)

(1.2)

The open-circuit voltage is expressed by equation (1.3)

(1.3)

(1.3)

Where n _so is the concentration of electrons on the TiO ₂ surface, and K _ET is the rate constant with which the electrons injected into the TiO _{2 couple} with the oxidant or I ₃ ^- of the electrolyte.

(1.4)

(1.4)

Therefore, if the recombination speed is reduced, the reduction of the voltage can be reduced, and as a result, the energy conversion efficiency can be increased. In other words, in order to slow the rate at which I3 ^- is reduced to I ^- by recombination, it is necessary to control the surface state distributed below the conduction band. In other words, it is necessary to control the size, mophology, crystallinity and surface state of nanoparticles in order to obtain high photocurrent and light voltage. If the size of the particles is too small to be several nanometers or less, the amount of dye adsorption increases with an increase in the specific surface area. However, since the surface state of the incomplete particles also increases, the number of recombined electrons increases and it is difficult to obtain a high photocurrent. On the contrary, when the particle size is too large, the diffusion coefficient of the electron increases and the recombination speed decreases. On the contrary, it is difficult to obtain a high photocurrent conversion efficiency due to the decrease of the dye adsorption amount. Therefore, the use of nanoparticles of appropriate size is required. In this experiment, spherical nanoparticles of about 20 nm in the anatase phase having a large specific surface area are used in order to increase the adsorption of dye molecules. In this case, DSC composed of spherical nanoparticles has a higher energy conversion efficiency It is difficult to expect. It is reported that when the necking length between spherical nanoparticles is too long, the transfer of electrons is limited.

FIG. 5 is a graph showing the relationship between the thickness measured by a voltage-current density curve of a DSC fabricated with a photoelectrode treated for 30 minutes by a low-temperature atmospheric plasma of 200 ^o C or less and a photoelectrode heat-treated for 60 minutes in a 450 ^° C. high- A short circuit current, a fill factor, and an energy conversion efficiency according to the open circuit voltage and the short-circuit current according to the present invention. In both cases, as the thickness increases, the open-circuit voltage decreases slightly, but the density of the short-circuit current steadily increases. In the case of the high-temperature annealing, the increase in the short-circuit current density decreases as the thickness increases. As a result, a conversion efficiency of 6.08% is measured when the thickness is 13 μm and a value of 5.84 % Conversion efficiency was measured. That is, it can be seen that a very high conversion efficiency is measured even at a low thickness. In the case of plasma treated DSC, unlike the heat treatment, the Voc size did not change much, but the Jsc and FF had a high value even at a low thickness of 9 탆 or less, and consequently, the light conversion efficiency was higher at a low thickness. Therefore, it can be seen that the high efficiency DSC can be obtained by using the photoelectrode using the sintering action of TiO _{2 at} a low temperature by using the atmospheric plasma.

Referring to FIG. 6 (a), it can be seen that the efficiency per thickness is much higher in the DSC by the atmospheric plasma. The light conversion efficiency is about 2.5% at 1.5 ㎛, 1.5% at 4 ㎛, and almost similar at 12 ㎛. 6 (b) is an SEM image of the cross section of the photoelectrode sintered by the low temperature atmospheric plasma. Of 20 nm TiO ₂ The nanoparticles were sintered well on the surface of 0.7 ㎛ FTO and measured to be about 9 ㎛ thick. The ability to produce high efficiency DSCs in these low-thickness films also means that flexible DSCs can be made at low temperatures using atmospheric plasma.

7 shows the characteristics of DSC at 4 탆 using the photoelectrode sintered by atmospheric plasma and DSC characteristics at the maximum efficiency. In both cases, it can be seen that the dye adsorption amount of TiO ₂ functionalized by plasma is increased. Especially at 4 ㎛, the photocurrent density is 1.5 times as high as the low thickness, resulting in high conversion efficiency.

Photoelectrode  Efficiency enhancement mechanism

The impedance analysis and the dye adsorption amount were investigated to investigate the cause of improvement of efficiency of DSC improved by atmospheric plasma. Impedance analysis has long been used in electrochemistry, and it has been applied to electrochemical DSC studies using electrolytes. The impedance is obtained by analyzing the AC current obtained by applying a very small alternating electric potential, which is made by dislocation perturbation, to the DC potential (or equilibrium potential) by applying a resistance to the electrode, a capacitor, and an inductor. The DSC should also consider the complex impedance since the capacitance of the capacitor together with the interfacial resistance between the material of the counter electrode, the dye and the electrolytes, as well as the TiO2 should be taken into consideration (FIG. 8). According to Ohm's law, the capacitive reactance (X _C ) is expressed by the following equation (1.5), and is in inverse proportion to the frequency and the capacitance C, and has a phase difference of -90 ^° with respect to the resistance.

(1.5)

(1.5)

The admittance of the parallel circuit composed of the polarization resistance Rp and the electric capacity Cd of the electric double layer at the electrode / electrolyte interface is expressed by Equation (1.6), and once connected to the series resistance Rs, the total impedance is expressed by Equation (1.7).

(1.6)

(1.6)

(1.7)

(1.7)

Therefore, the real number (Z ') and the imaginary number (Z ") of the complex resistance are divided by the following equations (1.8) and (1.9), and the graph of these two terms in terms of the impedance complex plane is called the Nyquist plot.

(1.8)

(1.8)

(1.9)

(1.9)

The Nyquist plot is measured in the frequency domain (10 ^-2 -10 ⁶ Hz) in an open circuit con- dition in an illumination condition and generally exhibits three characteristic semicircles. A description of the resistance at the interface represented by each characteristic semicircle by a typical transmission line model is illustrated in FIG.

According to FIG. 8, the Rs measured in the Nyquist plot is generally a value indicating the sheet resistance at the transparent electrode, which can be regarded as a value depending on the state of the transparent electrode. In the case of glass substrates with FTO-coated is measured resistance of about 10 Ω anpak, In this study, the thermal protection tape (Kepton tape) as FTO is lost, because the number of the resistance increase due to the etching action of plasma TiO ₂ sintered region To minimize loss of TCO surface. The value of R1 is a value mainly appearing at the interface between the counter electrode and the electrolyte, which is small when a redox reaction occurs well in the platinum coated counter electrode. In other words, it can be expected that electrons generated by photo-activation in the dye are collected into the photoelectrode along the TiO2 interface, and the efficiency improves as the electrolyte and oxidation / reduction are well performed at the counter electrode. The value of R2 can be considered to be that the electron transfer is good because the resistance between the resistance and the electrolyte is small when the TiO2 sintering is good due to the charge transfer at the interface between TiO2 and the electrolyte. The value R3 is a value indicating the diffusion of ion species in the electrolyte. When the ion species in the electrolyte is diffused, the recombination of electrons and holes is actively performed. Therefore, the smaller the value is, the better the efficiency is. Therefore, when the Nyquist plot is drawn after measuring the impedance, the resistance at each interface can be known, and a deeper understanding of the electron transmission in the DSC can be obtained.

FIG. 9 shows the R ₂ (TiO ₂ / electrolyte interface resistance) obtained from the Nyquist plot of DSC prepared by 450 ^° C and low temperature plasma treatment, respectively. It can be seen that the resistance at each interface is smaller in the plasma treatment than in the heat treatment. Resistance between the resistance of R2 which is related to the electronic jeoldal i.e., TiO ₂ and the electrolyte in the TiO ₂ will exhibit a tendency to decrease in thickness, the thin when pressure plasma treatment as compared to heat-treated films can be seen that especially the smaller resistance have. It can also be seen that the frequency associated with the charge transfer at the interface made by TiO2 and the electrolyte is higher due to the atmospheric plasma. This means that the inverse relationship with the impedance due to the plasma is established, that is, the impedance is smaller, which means that electrons are transmitted smoothly at the interface. 9 (a) and (b), the frequency of Z2 tends to decrease as the thickness of TiO ₂ increases. This is because the thicker the thickness, the greater the number of electrons lost to the electrolyte . It can be seen that the DSC produced by the photoelectrode functionalized by the atmospheric plasma is very active at the interface of the electron.

As shown in FIG. 10, when the dye adsorption amount is compared, TiO ₂ It can be seen that a considerable amount of dyes are adsorbed on the surface to produce many electrons and transfer them to TiO ₂ .

The dye adsorbed on the TiO ₂ sintered to the photoelectrode is a typical example of the ruthenium based dye, N719, which is red in color, and is most absorbed at 370 nm and 510 nm. Therefore, the amount of TiO ₂ adsorbed dye was measured using a UV-VIS absorbance spectrophotometer based on 0.1 mM and then converted into the amount of molar concentration. Fig. 10 (c) shows the adsorption amount in the heat-treated sample and the dye adsorption amount in the photo-electrode treated by the atmospheric plasma. It can be seen that the adsorption amount of the dye increases at all thicknesses as compared with the sample subjected to heat treatment at atmospheric pressure plasma. It can be assumed that the surface state and physical properties of TiO ₂ are changed by the atmospheric plasma. That is, the photoelectrode sintered by the low-temperature atmospheric plasma does not have much phase transition to the rutile phase unlike at high temperature, so that the reduction of the specific surface area due to the conversion to the rutile phase by heat treatment is small and the state change to the hydrophilic surface The adsorption amount of the dye is increased. Therefore, the conversion efficiency similar to that of the heat treatment can be obtained by increasing the dye adsorption amount by the atmospheric plasma and sintering the photoelectrode at a low temperature.

summary

The dye-sensitized solar cell using the dye-sensitized solar cell using the dye-sensitized solar cell can realize a very high conversion efficiency even though it has a lower thickness than the sample made by the heat treatment at a high temperature. In particular, the conversion efficiency per thickness of the photoelectrode sintered using atmospheric pressure plasma is very high when used as a thin film, and as a result, it is very likely to be used as a flexible DSC. This can be effectively used for a process for a flexible substrate requiring a low-temperature process, and can be regarded as a new process replacing heat treatment. Especially, the DSC produced by the atmospheric plasma showed that the resistance at the interface between TiO2 and electrolyte was smaller than that of the heat treatment and the adsorption amount of dye was increased by the impedance analysis. It can be seen that the TiO2 photoelectrode made by atmospheric plasma maintains the specific surface area because the phase transition to the rutile phase is small and the wettability of the surface is increased by the plasma, and the adsorption is very good with the dye molecules. This means that the increase of the dye adsorption amount facilitates the transfer of the electrons, thereby increasing the photocurrent and consequently increasing the energy conversion efficiency.

As can be seen from the experimental examples of the present invention, the present invention can replace the process of TiO ₂ sintered through heat treatment by using low temperature atmospheric plasma. Therefore, it can be considered that it is very suitable for manufacturing a photoelectrode on a flexible substrate which requires conventional low-temperature sintering.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation in the embodiment in which said invention is directed. It will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the appended claims.

Claims (3)

(a) forming a TiO ₂ thin film by coating a paste containing anatase phase TiO ₂ nanoparticles on a substrate; And
(b) processes the atmospheric pressure plasma of less than 200 ^o C with respect to the TiO ₂ thin film, and the rutile phase in the TiO ₂ thin film sintering and TiO ₂ thin film for a hydrophilic surface to the connection between the TiO ₂ nanoparticles, preventing phase change of on an anatase And changing the state of the photoelectrode. According to claim 1, by performing the step (a) the cycle consisting of step and (b) twice or more TiO ₂ And adjusting the thickness of the thin film. (a) forming a TiO ₂ thin film by coating a paste containing anatase phase TiO ₂ nanoparticles on a substrate; And
(b) processes the atmospheric pressure plasma of less than 200 ^o C with respect to the TiO ₂ thin film, and the rutile phase in the TiO ₂ thin film sintering and TiO ₂ thin film for a hydrophilic surface to the connection between the TiO ₂ nanoparticles, preventing phase change of on an anatase The method comprising: preparing a dye-sensitized solar cell comprising a photo-electrode and an electrolyte between the photo-electrode and the counter electrode.

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