JP5561641B2 - Dye-sensitized solar cell - Google Patents

Description

  The present invention relates to a dye-sensitized solar cell, and more specifically to a dye-sensitized solar cell that utilizes a surface plasmon resonance electric field enhancement phenomenon that occurs by changing the wavelength of light or the incident angle of light.

  Solar cells are classified into silicon-based, compound semiconductor-based, organic semiconductor-based, metal oxide semiconductor-based, etc., depending on the semiconductor material used. Here, a metal oxide semiconductor solar cell is also called a dye-sensitized solar cell. For example, a photosensitizer (dye) is bonded onto the surface of titanium oxide fine particles coated and sintered on conductive glass. Then, a photoelectrode is formed, the inside of the porous titanium oxide of the photoelectrode is filled with an electrolyte, and then the counter electrode is bonded together.

  In recent years, in the development of solar cells, which are photoelectric conversion technologies using sunlight, various studies have been conducted on optimizing electrode interfaces and performing light control as one of the key points for higher efficiency. In particular, the application of solar cells using dye-sensitized electric field enhancement by the surface plasmon resonance effect excited on the electrode surface has attracted attention.

  As a prior art relating to a dye-sensitized solar cell using a surface plasmon resonance electric field enhancement phenomenon, Patent Document 1 discloses a light response in which a glass prism having a triangular cross section is in contact with a metal film on which a photoresponsive molecule is fixed. A wet solar cell with an electrode is disclosed. Surface plasmon resonance using such a glass prism is called the total reflection attenuation (ATR) method, and the arrangement of such a prism is called a Kretschmann arrangement.

  In Non-Patent Document 1, a photoelectrode having an irregular fine particle aggregation structure in which metal fine particles supporting a photosensitizer are aggregated is prepared, and surface plasmon resonance due to the interaction between the photosensitizer and the metal fine particles is performed. It is used to increase the absorption coefficient (and hence energy conversion efficiency) of the photosensitizer. In Patent Document 2, a metal modifying compound is further arranged on the surface of the metal fine particles to increase energy conversion efficiency.

  Further, in Patent Document 3, in a photoelectrode having a laminated structure of metal fine particles and semiconductor fine particles, localized surface plasmon resonance is enhanced by the interaction between regularly arranged metal fine particles and absorption of the photosensitizer is performed. The coefficient is improved.

  However, the dye-sensitized solar cell disclosed in Patent Document 1 has a problem that the size of the device is increased and the degree of design freedom is limited due to the presence of a prism that generates surface plasmon resonance.

  Moreover, the excitation wavelength range of surface plasmon with respect to light in the visible range is limited to one wavelength range. In addition, the resonance incident angle θ and the like were also limited to a predetermined angle range (for example, as described in Patent Document 1, page 3, column 4, lines 48 to 50, when the electrolyte is aqueous, θ was 70 to 85 degrees). Therefore, the wavelength range and incident angle of sunlight that can be incident on a solar cell and effectively convert energy by exciting surface plasmons are extremely limited. In other words, even if the solar cell disclosed in Patent Document 1 is exposed to sunlight all day, it can be said that the time zone in which the electric field is enhanced by the surface plasmon resonance and the wavelength of light are limited. Furthermore, in the case of the total reflection attenuation method, since sunlight is irradiated from the back side of the metal electrode, there is a problem that all the rays except the angle at which the surface plasmon is excited are totally reflected and the sunlight does not reach the pigment.

  In addition, the dye-sensitized solar cells disclosed in Patent Document 2, Patent Document 3, and Non-Patent Document 1 use localized plasmons of metal fine particles, and the problem of enlargement of the device as in Patent Document 1 does not occur. However, the problem of limiting the excitation wavelength range of surface plasmons remained and remained unresolved.

Japanese Patent Laid-Open No. 10-340742 JP 2007-265694 A JP 2007-335222 A

Manabu Ihara et al., Journal of Physical Chemistry Part B (J. Phys. Chem. Part B), 1997, Vol. 101, p. 5153

  The present invention has been proposed in view of the above circumstances, and an object thereof is to provide a dye-sensitized solar cell having a simple configuration. Furthermore, the present invention provides a dye-sensitized solar capable of simultaneously enhancing the electric field of sunlight over a wide range from the visible range to the infrared range by simultaneously resonantly exciting surface plasmons over a plurality of wavelength ranges with a simple configuration. An object is to provide a battery.

  The present inventor paid attention to a grating coupling method as one of surface plasmon excitation methods, applied this grating coupling method to a dye-sensitized solar cell, and applied this grating structure and a thin film layer adjacent thereto. The inventors have found that the above problems can be solved by setting the appropriate configuration and dimensions, and have completed the present invention.

That is, the present invention employs the following configurations and features.
1. A dye-sensitized type comprising a porous film containing a metal oxide, a photoelectrode having a dye supported on one surface of the porous film, a counter electrode, and an electrolyte layer interposed between the photoelectrode and the counter electrode A solar cell,
The photoelectrode further includes a substrate having a structure with a period of 300 nm to 2 μm formed on the surface, and a metal thin film formed between the other surface of the porous film and the surface of the substrate ,
The dye-sensitized solar cell , wherein the structure is a grating structure capable of exciting surface plasmon resonance over a plurality of wavelengths .
2. 2. The dye-sensitized solar cell according to 1, wherein the cycle is 1 μm to 2 μm.
3. The dye-sensitized solar cell according to 1 or 2, wherein the metal oxide is titanium oxide, and the thickness of the porous film is 2 nm to 50 nm.
4). The dye-sensitized solar cell according to any one of claims 1 to 3, wherein the dye is layered along the one surface of the porous film, and the thickness of the layer is 5 nm to 50 nm.
5. The dye-sensitized solar cell according to any one of claims 1 to 4, wherein the dye contains two or more kinds of dye compounds.

  According to the dye-sensitized solar cell of the present invention, the prism is not required as compared with the conventional dye-sensitized solar cell using the total reflection attenuation (ATR) method, so that the entire device can be simplified, downsized and designed freely. It is possible to improve the degree. For example, since a grating structure can be manufactured on a plastic substrate, a solar cell having a flexible structure can be provided.

  According to the dye-sensitized solar cell of the present invention, since a grating structure having a period of a predetermined dimension is formed on the photoelectrode, the surface plasmon is simultaneously resonance-excited over a plurality of wavelength regions, so that the visible region to the infrared region. Thus, it is possible to simultaneously increase the electric field of solar light over a wide range, and thus dramatically increase the energy conversion efficiency.

It is the figure which showed the outline of the dye-sensitized solar cell of this invention. It is the figure which showed the relationship between the period (pitch) of a lattice structure (grating), and surface plasmon excitation. It is the figure which showed the surface plasmon excitation characteristic in the dye-sensitized solar cell of this invention, and the light absorption characteristic of a pigment | dye. It is the figure which showed the short circuit photocurrent characteristic of the dye-sensitized solar cell with and without surface plasmon excitation.

  Hereinafter, although the present invention is explained based on an embodiment shown in a drawing, the present invention is not limited to the following concrete embodiment at all.

  As schematically shown in FIG. 1, the dye-sensitized solar cell 10 of the present invention includes a porous film 4 containing a metal oxide and a photoelectrode 1 having a dye 5 supported on one surface 4 a of the porous film 4. And a counter electrode 7 and an electrolyte layer 6 interposed between the photoelectrode 1 and the counter electrode 7.

Here, as a metal oxide which comprises the porous film 4, titanium oxide (TiO2) is preferable, and the film thickness of this porous film 4 has preferable ₂ nm-50 nm. Examples of the dye 5 include ruthenium (Ru), which is a metal complex, and porphyrin, which is an organic dye. In particular, as shown in FIG. 1, the dye 5 is formed along one surface 4a of a porous film 4 containing titanium oxide or the like. It is layered, and the thickness of this layer 5 is preferably 5 nm to 50 nm, and more preferably contains two or more dye compounds 5a and 5b.

  In the conventional dye-sensitized solar cell, the thickness of the layer containing the dye is usually 100 nm or more. In the present invention, the light I incident from the counter electrode 7 and passed through the electrolyte 6 and the dye layer 5 is applied to the photoelectrode 1. In order to excite the surface plasmon, the thickness of the dye layer 5 needs to be extremely reduced to about 1 to 50 nm.

  Further, by including two or more dye compounds 5a and 5b, the light absorption characteristics (light absorption peak and profile thereof) of the dye layer 5 can be adjusted as described later. The absorption peak can be broadened gently, or the peak can be matched with the surface plasmon excitation wavelength, and the electric field of sunlight can be enhanced more effectively.

  As a method for forming the dye layer 5 including two or more kinds of dyes 5a and 5b, an alternate adsorption (LbL) method is preferable. Here, the alternate adsorption method is a method for producing a laminated thin film by alternately adsorbing polymer electrolytes having opposite charges to a solid surface such as a glass substrate. The advantage of this method is that the one type of dye compound 5a having a positive charge and the other type of dye compound 5b having a negative charge are alternately adsorbed to form a layer of the dye compounds 5a and 5b. Can be formed, and the thickness of each layer 5a, 5b can also be made very thin to about 1 nm. Therefore, the thickness of the dye layer 5 can be set to a desired dimension in the nano order by adjusting the number and time of the alternate adsorption.

  In the dye-sensitized solar cell 10 of the present invention, the photoelectrode 1 includes a substrate 2 having a structure with a period of 300 nm to 2 μm formed on the surface 2 a, the other surface 5 b of the porous film 5, and the surface 2 a of the substrate 2. It is an important feature that the metal thin film 3 formed between the two is provided. By configuring the photoelectrode 1 as described above, a surface lattice structure (grating structure) capable of exciting surface plasmon resonance is formed in the photoelectrode 1.

  Here, as the substrate 2 constituting a part of the photoelectrode 1, polyolefin such as polyethylene, polypropylene, polymethylpentene, polystyrene, polyester such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, acrylic resin such as polymethyl methacrylate, ABS Resin, epoxy resin, polyarylate, polysulfone, polyethersulfone, nylon resin, fluororesin, phenoxy resin, polyimide resin, resin material such as polycarbonate, inorganic material such as quartz, glass, etc. It is not limited. The counter electrode 7 is preferably a transparent material such as an ITO glass substrate in order to transmit the incident light I to the photoelectrode 1 side.

  The material of the metal thin film 3 is preferably gold, silver, copper or aluminum. By using these materials, the photoelectrode 1 itself including the metal thin film 3 can be stably operated without a chemical reaction. Of these materials, gold is particularly preferable from the viewpoint of electrochemical stability, and silver is particularly preferable from the viewpoint of plasmon excitation intensity. The metal thin film 3 can be deposited on the surface 2a of the substrate 2 by a technique such as vacuum deposition, sputtering, or CVD. In addition, since the thin film deposited by vacuum vapor deposition has a weak adhesive force and may be easily peeled off, another metal such as chromium may be deposited on the surface 2a of the substrate 2 in advance.

  More preferably, the grating period Λ on the surface 2 a of the substrate 2 is in the range of 1 μm to 2 μm. Thereby, resonance excitation of surface plasmons can be performed in two or three wavelength ranges with respect to incident light in the visible range to infrared range, and as a result, the electric field of incident light can be enhanced in a wide range of wavelengths. It should be noted that if the grating period Λ is less than 300 nm, the plasmon excitation angle is limited (that is, plasmon excitation does not occur on the low angle side and the high angle side). It is not preferable.

  FIG. 2 is a diagram showing the relationship between the grating period and surface plasmon excitation. When the grating period Λ is less than 1 μm (for example, when Λ = 320 nm shown in FIG. 2B), resonance excitation of surface plasmons can be observed only in one wavelength region in the visible region. This is the same tendency even if the incident angle of light is changed variously. Specifically, it is in the vicinity of the wavelength of 420 nm at 20 degrees, in the vicinity of the wavelength of 540 nm at 40 degrees, and in the vicinity of the wavelength of 630 nm at 70 degrees. Each is resonantly excited.

  On the other hand, when the grating period Λ is 1 μm or more (for example, when Λ = 1, 6 μm shown in FIG. 2A), the incident angle θ is 40 degrees, 44 degrees, or 54 degrees. Resonant excitation of surface plasmons can be confirmed in two or three wavelength regions in visible light. In addition, in the case of Λ = 1, 6 μm shown in FIG. 2A, the resonance excitation wavelength region is greatly changed by slightly changing the incident angle θ, compared to the case of Λ = 320 nm shown in FIG. Can be made.

(Method for producing dye-sensitized solar cell)
The features and performance of the dye-sensitized solar cell 10 of the present invention will be described with reference to examples produced by the following method. As the substrate 2, a polycarbonate substrate having a grating structure with a period Λ of 1.6 μm formed on the surface 2 a was prepared. A gold thin film 3 was deposited on the surface 2a of the substrate 2 by a vacuum deposition method so that the film thickness was about 130 nm. A thin film of titanium oxide (TiO ₂ ) having an average particle size on the order of several tens of nm was further deposited on the gold thin film 2 by electrophoresis.

The photoelectrode 1 composed of this grating / Au / TiO ₂ is used as an ultrathin film by alternating adsorption method using two types of dye compounds 5a and 5b of TMPyP which is a kind of porphyrin and copper chlorophyllin sodium (SCC). Each dye layer was formed into 20 dye layers, each having a layer thickness of about 20 nm. The electrolyte 6 was an aqueous solution in which sodium sulfate (Na ₂ SO ₄ ) and ferrous sulfate heptahydrate (FeSO ₄ · 7H ₂ O) were mixed. The counter electrode 7 was an ITO substrate.

The official name of TMPyP is 5,10,15,20-Tetrakis (1-methyl-4-pyridineio) porphyrinTetra (p-toluenesulfonate), and its chemical formula is C ₇₂ H ₆₆ N ₈ O ₁₂ S ₄ . This TMPyP is a water-soluble red pigment. In Example 1, what was melt | dissolved in the pure water was used as a cation. Adsorbed by anions and N +.

The chemical formula of sodium copper chlorophyllin is _{C 34 H 31 CuN 4 Na 3} O 6. Copper chlorophyllin sodium replaces magnesium in a mixture of chlorophyll a (—CH 3) and chlorophyll b (—CHO) with copper to form an extremely stable water-soluble green pigment. In Example 1, what was melt | dissolved in the pure water was used as an anionic polymer. Adsorption by cations and COO-.

  Various characteristics of the dye-sensitized solar cell 10 produced as described above will be described below with reference to the drawings.

(Surface plasmon excitation characteristics)
FIG. 3A shows surface plasmon excitation characteristics when the incident angle θ is changed to 20 degrees, 36 degrees, and 40 degrees. As shown in FIG. 3A, even in a solar cell actually manufactured, the surface in a plurality of wavelength regions confirmed in an experiment using only the grating structure (Λ = 1.6 μm, see FIG. 2A). A phenomenon similar to the plasmon resonance excitation phenomenon was observed.

  Specifically, in the wavelength region 600 nm to 770 nm, when the incident angle θ is 20 degrees, resonance dip was observed at two locations near 670 nm and 760 nm. When the incident angle θ was 36 degrees, resonance dip was observed at two locations near 640 nm and 740 nm. When the incident angle θ was 40 degrees, resonance dip was observed at two locations near 630 nm and 725 nm.

(Light absorption characteristics of dyes)
FIG. 3B shows the light absorption characteristics of the dye layer 5 employed in Example 1. From FIG. 3A and FIG. 3B described above, it can be seen that when the incident angle θ is 36 degrees, the wavelength at which the resonance dip occurs coincides with the wavelength at which the light absorption of the dye layer 5 is maximized. Therefore, the surface plasmon resonance excitation wavelength and the light absorption peak of the dye layer 5 can be matched by changing the incident angle θ of light.

  The dye layer 5 of Example 1 is produced by an alternate adsorption method, and two kinds of dye molecules are alternately stacked for a total of 40 layers. The advantage of producing the dye layer 5 by the alternate adsorption method is that the desired film thickness for allowing the incident light to pass through the photoelectrode 1 can be obtained accurately, and the light absorption profile possessed by each of the dye compounds 5a and 5b It becomes possible to change the peak.

  For example, FIG. 3C shows the light absorption characteristics of TMPyP, which is one of the dye compounds employed in the dye layer 5, and the light absorption characteristics of copper chlorophyllin sodium (SCC), which is the other dye compound. It can be seen that the result of superimposing the respective light absorption profiles of the respective dyes shown in FIG. 3C substantially coincides with the light absorption characteristics of the dye layer 5 of Example 1 shown in FIG. Therefore, the light absorption peak can be arbitrarily changed by preparing the dye layer 5 containing two or more kinds (for example, two kinds, four kinds, six kinds) of dye compounds by the alternate adsorption method, and the vicinity of the light absorption peak. It is also possible to smooth the slope of the curve. Thereby, the surface plasmon resonance excitation wavelength and the dye peak wavelength coincide with each other over a wide range.

(Electrochemical characteristics)
In order to verify the electrochemical characteristics of the dye-sensitized solar cell 10 of the present invention, the short-circuit photocurrent-time characteristics were measured. Specifically, the short-circuit photocurrent characteristics were examined with a potentiostat at an applied voltage of 0 V. First, the measurement was started with the light blocked, and the change in the current value was measured by repeating the light irradiation and blocking every 60 seconds. Then, the white light was irradiated and the short circuit photocurrent when the incident angle θ was changed to 20 degrees, 36 degrees, and 40 degrees was measured. The results are shown in FIGS. 4 (a), (b), and (c). The difference in the magnitude of the photocurrent was also compared between P-polarized light that excites surface plasmons and S-polarized light that does not excite surface plasmons.

  In any of the cases of FIGS. 4A, 4B, and 4C, a larger photocurrent is generated when P-polarized light that excites surface plasmons is irradiated than S-polarized light that does not excite surface plasmons. You can see that In particular, when the incident angle θ is 36 degrees (see FIG. 4B), it can be seen that about twice as much photocurrent is generated. Since the surface plasmon resonance excitation wavelength at the incident angle θ matches the light absorption peak wavelength of the dye layer 5 as shown in FIG. 3, it can be said that the electric field enhancement was promoted.

(Effect of porous membrane / dye layer thickness on electric field enhancement)
Next, by changing the thickness of the porous film 4 containing titanium oxide and the thickness of the dye layer 5, the short-circuit photocurrent characteristic test and the theoretical calculation related thereto were performed. Table 1 shows the effect of these parameters on the surface plasmon resonance electric field enhancement.

As shown in Table 1, in order to transmit incident light I and obtain a suitable surface plasmon resonance electric field enhancement in the photoelectrode 1, the porous film 4 (TiO ₂ film in the figure) has a thickness of 5 nm to 30 nm. The pigment layer 5 preferably has a thickness of 10 nm to 50 nm. More preferably, the combination of the thickness of the porous film 4 and the layer thickness of the dye layer 5 is 5 nm to 15 nm and 10 nm to 15 nm.

  In theoretical calculation, if the layer thickness of the dye layer 5 is set to about 10 nm, a suitable surface plasmon resonance electric field enhancement can be obtained when the thickness of the porous film 4 is in the range of 2 nm to 50 nm. It was found that if the thickness of the material film 4 is set to about 5 nm, a suitable surface plasmon resonance electric field enhancement can be obtained when the layer thickness of the dye layer 5 is in the range of 5 nm to 50 nm.

  The dye-sensitized solar cell of the present invention is provided with a simple grating structure on the photoelectrode in order to obtain an electric field enhancement by surface plasmon resonance excitation. Thereby, since the dye-sensitized solar cell of this invention can simplify the whole apparatus and can improve a design freedom, it is industrially very useful.

  Furthermore, if the dye-sensitized solar cell of the present invention adopts a grating structure with a predetermined period, it is possible to convert the energy of sunlight at various incident angles or over a wide wavelength range during the daylight hours of the day. It is.

1 Photoelectrode 2 Substrate 2a Substrate surface 3 Metal thin film 4 Porous film 4a, 4b Porous film surface 5 Dye (dye layer)
5a, 5b Dye compound 6 Electrolyte 7 Counter electrode 10 Dye-sensitized solar cell Λ Period (or pitch) of grating structure
θ Incident angle

Claims (5)

A dye-sensitized type comprising a porous film containing a metal oxide, a photoelectrode having a dye supported on one surface of the porous film, a counter electrode, and an electrolyte layer interposed between the photoelectrode and the counter electrode A solar cell,
The photoelectrode further includes a substrate having a structure with a period of 300 nm to 2 μm formed on the surface, and a metal thin film formed between the other surface of the porous film and the surface of the substrate ,
The dye-sensitized solar cell , wherein the structure is a grating structure capable of exciting surface plasmon resonance over a plurality of wavelengths .   The dye-sensitized solar cell according to claim 1, wherein the period is 1 μm to 2 μm.   The dye-sensitized solar cell according to claim 1 or 2, wherein the metal oxide is titanium oxide, and the thickness of the porous film is 2 nm to 50 nm.   The dye-sensitized solar cell according to any one of claims 1 to 3, wherein the dye is layered along the one surface of the porous film, and the thickness of the layer is 5 nm to 50 nm. .   The dye-sensitized solar cell according to any one of claims 1 to 4, wherein the dye contains two or more kinds of dye compounds.