JP2011187183A - Dye-sensitized solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dye-sensitized solar cell with low internal resistance and high power generation efficiency. <P>SOLUTION: Electron emitted from dye 38 by photoexcitation is transferred to a transparent conductive film 20 via electron collection particles for dye absorption 36 with a small particle size consisting of titanium oxide or the like, and electron collection particles for electron transfer 34 with a large particle size. As the electron is transferred to the transparent conductive film 20 via a small number of the electron collection particles for electron transfer 34, joint parts among the electron collection particles for electron transfer 34 that the electron is to go through are small in number. Also, since many electron collection particles for dye absorption 36 exist, a surface area is big and the enough number of dye 38 for power generation is absorbed in the electron collection particles for dye absorption 36. This shows that the electron emitted from the enough number of dye 38 is smoothly transferred to the transparent conductive film 20. As a result, the dye-sensitized solar cell has the low internal resistance and the high power generation efficiency. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a dye-sensitized solar cell.

  In recent years, solar power generation using natural energy that is in harmony with the environment and is inexpensive and clean has attracted attention. At present, solar cells using silicon crystals have been put into practical use, but the energy cost for production is high. In such a situation, compared with a solar cell using a silicon crystal, there is a feature that a large-area element can be manufactured at a low cost, and a flexible cell can be realized. The practical application of such dye-sensitized solar cells is expected. The power generation principle of such a dye-sensitized solar cell will be briefly described as follows. The dye molecules that have absorbed the irradiated light are excited, and the electrons of the dye molecules are injected into, for example, titanium oxide, which is a semiconductor. On the other hand, the dye molecules are supplied with the lost amount of electrons from the electrolyte. Accordingly, a potential difference is generated between the titanium oxide and the electrolyte. This potential difference is used as a battery.

JP 2008-41258 A

  For example, in a dye-sensitized solar cell as disclosed in Patent Document 1, an aggregate of titanium oxide particles having a small particle size of, for example, about 20 nm is used to receive electrons emitted by excitation of the dye. Yes. The reason why the particle size of the titanium oxide is small is that, in order to utilize the photoexcited electrons of the dye molecule, the particle needs to come into contact with many dye molecules. Generally, the roughness factor (R F = actual surface area / projected area) of the titanium oxide film composed of the particles is required to be 1000 or more. In addition, it is said that in order to obtain a sufficient output, the thickness of the film composed of the particles and the pigment needs to be 10 μm or more.

  Thus, since a thick film is formed with very small particles, for example, the bonding state of particles made of titanium oxide tends to deteriorate, and the associated dye tends to enter between the particles. For this reason, the resistance of the electrical connection path formed by the particles for transmitting the electrons emitted from the dye molecules by photoexcitation, that is, the internal resistance increases. As a result, there exists a subject that the electric power generation efficiency of the said dye-sensitized solar cell falls.

  Therefore, an object of the present invention is to provide a dye-sensitized solar cell with low internal resistance and high power generation efficiency.

  In order to achieve the above object, one aspect of the dye-sensitized solar cell of the present invention includes a pair of electrodes arranged to face each other, and one electrode of the pair of electrodes on a surface facing the other electrode. An electron scavenger disposed on, an electron supply agent disposed between the pair of electrodes, and an electron collector disposed on the electron scavenger, in an excited state, higher than the energy level of the electron scavenger, In a dye-sensitized solar cell comprising a dye having an energy level lower than the energy level of the electron supply agent in the ground state, the electron scavenger is composed of particles having different particle sizes, It is characterized by.

  According to the present invention, a dye-sensitized solar cell with low internal resistance and high power generation efficiency can be provided.

Sectional drawing which shows the structural example of the dye-sensitized solar cell which concerns on one Embodiment of this invention. The schematic diagram which shows the structural example of the part of the electrode of the dye-sensitized solar cell which concerns on one Embodiment of this invention, an electron scavenger, and a pigment | dye. The energy diagram explaining the electric power generation principle of the dye-sensitized solar cell which concerns on one Embodiment of this invention. The figure for demonstrating the electron transfer efficiency of the dye-sensitized solar cell which concerns on one Embodiment of this invention.

[Embodiment]
First, an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the dye-sensitized solar cell according to the present embodiment has, as shown in FIG. 1, an indium tin oxide (ITO) or fluorine-doped tin oxide (FTO) on a transparent substrate 10 made of, for example, glass or film. A transparent conductive film 20 is formed as an electrode made of the like. The transparent conductive film 20 may be patterned, and a current collecting pattern such as silver may be provided on the upper layer or the lower layer of the transparent conductive film 20. On the transparent conductive film 20, an electron collection-dye layer 30 is formed. The electron collection-dye layer 30 will be described in detail later.

  On the other hand, a conductive film 50 as an electrode is formed on a counter substrate 40 made of, for example, glass or a film that faces the transparent substrate 10. Further, a catalyst layer 60 made of platinum, carbon or the like is formed on the conductive film 50.

  In the transparent substrate 10 and the counter substrate 40, the surface of the transparent substrate 10 on which the electron collection-dye layer 30 is formed and the surface of the counter substrate 40 on which the catalyst layer 60 is formed face each other and face each other. For example, the peripheral portions of the opposing surfaces are bonded together by the sealing material 70 so as to have a gap of, for example, about 10 to 50 μm. An electron supply agent 80 that is an electrolyte is sealed in the gap.

As a solvent for the electron supply agent 80, for example, acetonitrile, methoxyacetonitrile, ethylene carbonate, or the like can be used. Examples of the solute of the electron supply agent 80 include 1,2-dimethyl-3-n-propylimidazolium iodide (DMPImI), lithium iodide (LiI), iodine (I ₂ ), 4-tert-butylpyridine (TBP). ) Etc. can be used.

  Here, the electron collection-dye layer 30 will be described in detail. As shown in FIG. 2, the electron collection-dye layer 30 is composed of, for example, an anatase-type titanium oxide or the like and has a large particle diameter for collecting electron transfer particles 34 and a small particle diameter for dye adsorption. It consists of collecting particles 36 and a dye 38 made of a ruthenium dye (N719 dye or the like). Here, the electron collection particles 34 for electron transfer and the electron collection particles 36 for dye adsorption are collectively referred to as an electron collection agent 32.

The electron scavenger 32 is not limited to titanium oxide, and for example, zinc oxide, tin oxide, tungsten oxide, niobium oxide, indium oxide, and a composite thereof can be used. In the present embodiment, it will be described that titanium oxide (TiO ₂ ), which is particularly excellent as a material for a dye-sensitized solar cell, is used.

  The dye 38 is not limited to the N719 dye, and for example, N3 dye, BlackDye as a ruthenium dye, D149, xanthene, PVK, merocyanine, oxazine, or the like as a pure organic dye can be used.

  As shown in FIG. 2, the electron collection particles 34 for electron transfer are in contact with each other, and some of them are in contact with the transparent conductive film 20. The dye-adsorbing electron-collecting particles 36 are in contact with the electron-transmitting electron-collecting particles 34. The dye 38 is adsorbed on the electron collecting electron collecting particles 34 and the dye adsorbing electron collecting particles 36. With such a configuration, the electron collection particle 34 for electron transmission plays a role of transmitting mainly electrons emitted from the pigment 38 to the transparent conductive film 20. Further, the dye-adsorbing electron collection particles 36 have a role of increasing the surface area of the electron collection agent 32 in order to adsorb more dye 38.

  Here, the diameter of the dye-adsorbing electron collection particles 36 is, for example, 5 nm or more and 25 nm or less, and the diameter of the electron transfer electron collection particles 34 is, for example, 100 nm or more and 400 nm or less. The ratio of the dye-adsorbing electron-collecting particles 36 and the electron-transmitting electron-collecting particles 34 is, for example, 20 to 25% of the dye-adsorbing electron-collecting particles 36 by weight, and the electron-transmitting electron-collecting particles 34. Is, for example, 75 to 80%. The thickness of the electron collection-dye layer 30 composed of the electron collection particles 34 for electron transfer, the electron collection particles 36 for dye adsorption and the dye 38 is, for example, about 10 μm.

  The electron collection-dye layer 30 is produced as follows, for example. After mixing titanium oxide particles having two kinds of particle sizes of anatase type as the electron collection particles 34 for electron transfer and the electron collection particles 36 for dye adsorption into a paste, the paste is applied to the transparent substrate 10. Printing or coating is performed, followed by baking to form a titanium oxide film. After the formation of the titanium oxide film, the titanium oxide film is immersed in a liquid of a dye 38 dissolved in an organic solvent, and the dye 38 is adsorbed on the titanium oxide.

  Thus, for example, the electron collection particles 34 for electron transfer function as particles constituting the electron collection agent having a larger particle size, and for example, the dye adsorption electron collection particles 36 have a smaller particle size. Functions as particles constituting the electron scavenger.

Next, the power generation principle of the dye-sensitized solar cell according to this embodiment will be described with reference to FIG. First, when light enters the dye-sensitized solar cell, the light is absorbed by the dye 38. The light absorbed by the dye 38 excites the dye 38 (broken line arrow in FIG. 3). The excited electrons of the dye 38 are transferred to an electron collecting agent 32 made of, for example, titanium oxide which is a wide gap semiconductor. That is, the pigment 38 is oxidized. The electrons received by the electron scavenger 32 move to the transparent conductive film 20. On the other hand, the dye 38 that has lost electrons is supplied with electrons from, for example, I ⁻ of the electron supply agent 80 in contact with the conductive film 50 having the catalyst layer 60. That is, the dye 38 is reduced by the electron supply agent 80. 3I ⁻ becomes I ₃ ⁻ when electrons are supplied to the dye 38. Therefore, for example, I ₃ ⁻ of the electron supply agent 80 tries to receive electrons from the conductive film 50. At this time, a potential difference is generated between the transparent conductive film 20 and the conductive film 50. If an external circuit is connected between the transparent conductive film 20 and the conductive film 50, the electrons that have moved to the transparent conductive film 20 move to the conductive film 50 through the external circuit. Then, the electrons move to, for example, I ₃ ⁻ of the electron supply agent 80, and I ₃ ⁻ becomes 3I ⁻ . The dye 38 that has lost electrons is supplied with electrons from, for example, I ⁻ of the electron supply agent 80. In this way, by connecting an external circuit to the transparent conductive film 20 and the conductive film 50, the external circuit can extract current from the dye-sensitized solar cell according to the present embodiment that has absorbed light. That is, this dye-sensitized solar cell functions as a battery.

  Since the power generation principle of this dye-sensitized solar cell is as described above, the energy level of the dye 38 in the excited state is higher than the energy level of the electron scavenger 32, and the energy level of the dye 38 in the ground state is the electron level. The relationship that it is lower than the energy level of the supply agent 80 is required.

[Example]
Next, examples of the dye-sensitized solar cell according to the embodiment will be described. Here, the dye-sensitized solar cell of this example using titanium oxide as two types of electron-trapping agents 32 having different diameters as the electron-collecting particles 34 for electron transfer and the electron-trapping particles 36 for dye adsorption The performance of the conventional dye-sensitized solar cell using titanium oxide as the electron scavenger 32 having one diameter was compared. What is compared is the value of the fill factor (FF), which is the ratio of the actual power to the apparent maximum power.

  In this example, the diameter of titanium oxide as the electron collection particle 34 for electron transfer was set to 100 nm, and the diameter of titanium oxide as the electron collection particle 36 for dye adsorption was set to 10 nm. The mixing ratio of the electron transfer electron collection particles 34 and the dye adsorption electron collection particles 36 is 75% by weight, the electron transfer electron collection particles 34 are 75%, and the dye adsorption electron collection particles 36 are 25%. It was. The average thickness of the electron collection-dye layer 30 containing the electron collection particles 34 for electron transfer, the electron collection particles 36 for dye adsorption and the dye 38 was 5 μm. On the other hand, in the dye-sensitized solar cell as a conventional example for reference, the diameter of titanium oxide constituting the electron scavenger 32 was all 10 nm, and other conditions were the same as in the case of the present example. Note that when the diameter of the titanium oxide constituting the electron scavenger 32 is simply increased, the roughness factor is simply reduced, and the amount of the electron trapping-dye layer 30 corresponding to the reduced roughness factor is reduced. It is known that increasing the average thickness increases the absorption of visible light and is not practical.

The FF values of the dye-sensitized solar cell according to this example and the dye-sensitized solar cell according to the conventional example were measured in accordance with JIS C 8914 “Method for measuring output of crystalline solar cell module” of JIS standard. Briefly, in the measurement, light having a wavelength of 400 to 1100 nm and an illuminance of 1000 W / m ² was irradiated to obtain a current I-voltage V curve. And FF which is the value which remove | divided the maximum output by the product of the open circuit voltage and the short circuit current was calculated | required from the acquired IV curve. The larger this value, the smaller the internal loss of the solar cell and the higher the performance.

  As a result of measuring three times for each of this example and the conventional example, the FF value is 25.6 ± 0.3 (average ± standard deviation) in the dye-sensitized solar cell according to this example, and the dye sensitization according to the conventional example. In the solar cell, the value was 44.4 ± 1.3 (average ± standard deviation). That is, the FF value of this example increased by 74% compared to the conventional example.

Possible reasons for this difference are as follows. As shown in the schematic diagram of the electron collecting-dye layer 30 of the conventional example in FIG. 4A, in the conventional example, as indicated by the white arrowhead A in FIG. ⁻ Is transmitted to the transparent conductive film 20 through many particles having a small diameter constituting the electron scavenger 32. Therefore, it is necessary for the electron e ⁻ to greatly exceed the junction of the particles in the electron scavenger 32. For this reason, the resistance of the electrical connection path formed in the electron scavenger 32 becomes high and electrons are not easily transmitted. Further, as indicated by the white arrowhead B in FIG. 4A, the dyes 38 are associated with each other and enter between the particles constituting the electron scavenger 32, so that the particles constituting the electron scavenger 32 are There may be a part that does not touch. And in the part which the particles which comprise the electron scavenger 32 do not contact in this way, an electron e < ^- > will not be transmitted.

On the other hand, as shown in the schematic diagram of the electron collection-dye layer 30 of this example in FIG. 4B, in this example, the electrons e ⁻ emitted from the dye 38 have a small number of large diameters. It is transmitted to the transparent conductive film 20 through the electron collecting particles 34 for electron transmission. Therefore, there are few junction parts of the electron collection particle | grains 34 for electron transmission which the electron e < ^- > needs to exceed. In addition, since the electron-collecting particles 34 for electron transfer have a large diameter and a large surface area per one, the bonding between the electron-collecting particles 34 for electron transfer is excellent. For this reason, the resistance of the electrical connection path formed in the electron scavenger 32 is lower than in the case of FIG. 4B, and electrons are easily transmitted. Further, since there are many dye-adsorbing electron-collecting particles 36, the surface area is large, and the roughness factor (RF = actual surface area / projected area) is 1000 or more, which is said to be necessary in dye-sensitized solar cells. It is more than a certain value. For this reason, a sufficient number of dyes 38 are adsorbed by the electron scavenger 32.

From the above, in this embodiment, electrons e ⁻ emitted from a sufficient number of dyes 38 are smoothly transmitted to the transparent conductive film 20. As a result, in this example, it is considered that the FF value increased compared to the conventional example.

  As described above, in the dye-sensitized solar cell according to the present embodiment, the electron collection particles 34 and the dye adsorption electron collection particles 36 having different particle diameters are used as the electron collection agent 32. As a result, obstacles related to the electron transfer from the dye 38 to the transparent conductive film 20 are reduced, the electron transfer is performed smoothly and has a sufficient surface area. 32 can be adsorbed. As a result, the FF value can be increased. That is, the internal loss of the dye-sensitized solar cell can be reduced and the performance can be improved.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, even if some constituent elements are deleted from all the constituent elements shown in the embodiment, the problem described in the column of problems to be solved by the invention can be solved and the effect of the invention can be obtained. The configuration in which this component is deleted can also be extracted as an invention.

  DESCRIPTION OF SYMBOLS 10 ... Transparent substrate, 20 ... Transparent electrically conductive film, 30 ... Electron collection-dye layer, 32 ... Electron collection agent, 34 ... Electron collection particle | grains for electron transfer, 36 ... Electron collection particle | grains for dye adsorption, 38 ... Dye 40 ... counter substrate, 50 ... conductive film, 60 ... catalyst layer, 70 ... sealing material, 80 ... electron supply agent.

Claims (10)

A pair of electrodes disposed opposite each other;
An electron scavenger disposed on a surface of one of the pair of electrodes facing the other electrode;
An electron supply agent disposed between the pair of electrodes;
A dye disposed on the electron scavenger, having an energy level higher than the energy level of the electron scavenger in the excited state and lower than the energy level of the electron supplier in the ground state;
In a dye-sensitized solar cell comprising:
The electron scavenger is composed of particles having different particle sizes,
The dye-sensitized solar cell characterized by the above-mentioned. The electron scavenger is
Electron collecting particles for dye adsorption having a predetermined particle size;
An electron collecting particle for electron transfer having a particle size larger than the particle size of the electron collecting particle for dye adsorption;
The dye-sensitized solar cell according to claim 1, comprising: The electron collection particles for electron transfer are in contact with each other,
A part of the electron collection particles for electron transfer is in contact with the one electrode,
The dye-adsorbing electron-collecting particles are in contact with the electron-transmitting electron-collecting particles,
The dye-sensitized solar cell according to claim 2. The dye-adsorbing electron-collecting particles play a role of increasing the surface area as the electron-trapping agent,
The electron-collecting particles for electron transfer play a role of transmitting electrons emitted from the dye to the one electrode.
The dye-sensitized solar cell according to claim 3. Since the dye-adsorbing electron-collecting particles have a large surface area, a large number of the dyes can be adsorbed on the electron-collecting agent.
The electron collection particles for electron transfer can reduce internal loss by reducing the resistance related to electron transfer from the dye to the one electrode and facilitating electron transfer.
The dye-sensitized solar cell according to claim 4. The diameter of the electron collecting particles for dye adsorption is 5 nm or more and 25 nm or less,
The diameter of the electron collection particles for electron transfer is 100 nm or more and 400 nm or less,
The dye-sensitized solar cell according to claim 2.   7. The dye-sensitized solar cell according to claim 6, wherein a weight ratio of the electron-collecting particles for dye adsorption in the electron-collecting agent is 20% or more and 25% or less. The diameter of the electron collecting particles for dye adsorption is 10 nm,
The diameter of the electron collecting particles for electron transfer is 100 nm,
Of the electron collector, the weight ratio of the dye-adsorbing electron-collecting particles is 25%.
The dye-sensitized solar cell according to claim 2.   The dye-sensitized solar cell according to any one of claims 1 to 8, wherein the particles are titanium oxide. The electron scavenger is
Mixing titanium oxide particles with different particle sizes into a paste,
Applying the paste-like titanium oxide particles on the one electrode,
Firing the pasty titanium oxide particles,
The dye-sensitized solar cell according to any one of claims 1 to 8, wherein the dye-sensitized solar cell is formed.

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