JP2008052936A - Photoelectric conversion element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric conversion element capable of enhancing light absorption efficiency and light energy conversion efficiency per area. <P>SOLUTION: The photoelectric conversion element has a first electrode 1 which is a working electrode to which a sensitized dye-carried semiconductor layer 2 is attached, a second electrode 3 facing the semiconductor layer 2, and a charge transfer layer 4 containing iodine and interposed between the first electrode 1 and the second electrode 3, and light is incident from the first electrode 1 side, and the second electrode 3 reflects incident light 5 to the semiconductor layer 2. A recessed part 8 extending to almost the whole surface where light is irradiated is installed on the surface of the second electrode 3 facing the semiconductor layer 2, and the inner peripheral shape of the recessed part 8 is made smaller with approaching the bottom. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a photoelectric conversion element comprising two electrodes, a working electrode and a counter electrode.

  A photoelectric conversion element typified by a solar cell is expected as a clean energy source, and a silicon-based pn junction solar cell has already been put into practical use. However, silicon-based solar cells use high-purity materials as raw materials or require high-energy processes such as a high-temperature process of about 1000 [° C.] or a vacuum process during manufacturing, thereby reducing manufacturing costs. This is a big issue.

Against this background, in recent years, wet solar cells, which do not require high-purity materials or high-energy processes and perform charge separation using a potential gradient generated at a solid-liquid interface, have attracted attention. In particular, a so-called dye that aims to improve conversion efficiency by adsorbing a sensitizing dye that absorbs light on the surface of the semiconductor electrode and absorbing visible light having a wavelength longer than the band gap width of the semiconductor electrode with the sensitizing dye. Research on sensitized photoelectric conversion elements has been actively conducted (see Patent Document 1).
Japanese Patent No. 2664194

  However, in the conventional photoelectric conversion element disclosed in Japanese Patent No. 2664194, the conversion efficiency of the conventional dye-sensitized photoelectric conversion element is about 1%, which is lower than that of a silicon solar cell. It is. One reason for this is that in the existing structure as shown in FIG. 5, the incident light 100 is reflected at an acute angle on the outer peripheral portion of the reflecting surface of the counter electrode 101, and as a result, light components leak outside the working electrode 102. The light energy conversion efficiency per area may be deteriorated.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a photoelectric conversion element capable of improving the light absorption efficiency and improving the light energy conversion efficiency per area. .

  In order to solve the above problems, in the invention according to claim 1 of the present application, a first electrode which is a working electrode to which a semiconductor layer carrying a sensitizing dye is attached, and a second electrode which is disposed to face the semiconductor layer. And a charge transport layer containing iodine sandwiched between the first electrode and the second electrode, light is incident from the first electrode side, and the second electrode reflects the incident light to the semiconductor layer A photoelectric conversion element, characterized in that a concave portion is provided over substantially the entire surface irradiated with light on the surface of the second electrode facing the semiconductor layer, and the inner peripheral shape of the concave portion becomes smaller as it approaches the bottom portion. It is said.

  The invention according to claim 2 is characterized in that, in the photoelectric conversion element according to claim 1, the cross-sectional shape of the concave portion in the direction perpendicular to the second electrode is substantially trapezoidal.

  The invention according to claim 3 is characterized in that, in the photoelectric conversion element according to claim 1, the cross-sectional shape of the recess in the direction perpendicular to the second electrode is substantially arc-shaped.

  Further, in the invention according to claim 4 of the present application, in the photoelectric conversion element according to any one of claims 1 to 3, the semiconductor layer protrudes toward the second electrode, and the outer peripheral shape of the semiconductor layer is the second electrode. It is characterized by becoming smaller as it approaches the side direction.

  In the photoelectric conversion element according to the first aspect of the present invention, a recess is provided on the surface of the second electrode facing the semiconductor layer over substantially the entire surface irradiated with light, and the inner peripheral shape of the recess approaches the bottom. Since it is small, when the light transmitted through the first electrode is reflected by the surface of the second electrode, it is collected at the center of the semiconductor layer. Therefore, it is possible to prevent light components from leaking or being absorbed outside the semiconductor layer, to increase the energy conversion contribution rate of incident light, and to improve the light energy conversion efficiency as a solar cell.

  In the photoelectric conversion element according to the second aspect of the present invention, in particular, since the cross-sectional shape of the recess in the direction orthogonal to the second electrode is substantially trapezoidal, the light transmitted through the first electrode is the second Even if it is incident at an acute angle with respect to the outer peripheral portion of the electrode surface, it can be reflected to the central portion of the semiconductor layer. Therefore, it is possible to prevent light components from leaking or being absorbed outside the semiconductor layer, to increase the energy conversion contribution rate of incident light, and to improve the light energy conversion efficiency as a solar cell.

  In the photoelectric conversion element of the invention according to claim 3 of the present application, in particular, since the cross-sectional shape of the concave portion in the direction orthogonal to the second electrode is substantially arc-shaped, the light transmitted through the first electrode is transmitted from the semiconductor layer. The light can be condensed at the central portion, so that the light absorption efficiency can be improved and the light energy conversion efficiency per area can be improved. Furthermore, since the light transmitted through the first electrode is collected at the center, there is no functional problem even if the area of the semiconductor layer is small, and the size of the semiconductor layer can be arbitrarily changed according to the application, A configuration according to the conditions for mounting the photoelectric conversion element can be designed.

  In the photoelectric conversion element of the invention according to claim 4 of the present application, in particular, the semiconductor layer protrudes toward the second electrode, and the outer peripheral shape of the semiconductor layer becomes smaller as it approaches the second electrode side. When the first electrode tries to absorb again the light transmitted through one electrode and reflected by the surface of the second electrode, the light can be absorbed substantially at a right angle compared to the case where the semiconductor layer is planar. Therefore, it is possible to suppress as much as possible that the light transmitted through the first electrode and reflected by the surface of the second electrode is irregularly reflected to the first electrode, contributing to the improvement of light absorption efficiency, Light energy conversion efficiency can be improved.

  Hereinafter, the present invention will be described based on embodiments shown in the accompanying drawings.

  FIG. 1 shows a photoelectric conversion element according to a first embodiment corresponding to claims 1 and 2 of the present application.

  This photoelectric conversion element includes a first electrode 1 that is a working electrode to which a semiconductor layer 2 carrying a sensitizing dye is attached, a second electrode 3 that is disposed opposite to the semiconductor layer 2, and a first electrode 1. And the charge transport layer 4 containing iodine sandwiched between the second electrodes 3, light is incident from the first electrode 1 side, and the second electrode 3 reflects the incident light 5 to the semiconductor layer 2. In the photoelectric conversion element, a concave portion 8 is provided on the surface of the second electrode 3 facing the semiconductor layer 2 over almost the entire surface, and the inner peripheral shape of the concave portion 8 becomes smaller as it approaches the bottom portion. Yes. The cross-sectional shape of the recess 8 in the direction perpendicular to the second electrode 3 is substantially trapezoidal.

  Hereinafter, the photoelectric conversion element of this embodiment will be described in more detail.

  As shown in FIG. 1, the photoelectric conversion element according to this embodiment has a configuration in which a charge transport layer 4 is sandwiched between a first substrate (not shown) and a second substrate (not shown). The outer peripheral portion of the transport layer 4 is sealed with a sealing material 7. The first substrate includes a base material (not shown), a first electrode 1 formed on the surface of the base material, and a porous semiconductor layer 2 formed on the surface of the first electrode 1. And faces the second substrate on the semiconductor layer 2 side. The second substrate has a base material and a second electrode 3 formed on the surface of the base material, and faces the first substrate on the second electrode 3 side.

  The charge transport layer 4 is formed of a solid electrolyte, a hole transport organic compound, or an electrolyte solution. When the charge transport layer 4 is formed of an electrolyte solution, the electrolyte solution is effective because it reliably contacts the surface of the porous semiconductor layer 2. The solvent used for dissolving the electrolyte is preferably a compound that dissolves the redox constituent and is excellent in ion conductivity. In this case, any of an aqueous solvent and an organic solvent can be used as the solvent, but it is desirable to use an organic solvent in order to further stabilize the redox constituent.

  For example, carbonate compounds such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, ester compounds such as methyl acetate, methyl propionate, γ-butyrolactone, diethyl ether, 1,2-dimethoxyethane, 1,3 -Ether compounds such as dioxosilane, tetrahydrofuran, 2-methyl-tetrahydrofuran, heterocyclic compounds such as 3-methyl-2-oxazodilinone, 2-methylpyrrolidone, nitrile compounds such as acetonitrile, methoxyacetonitrile, propionitrile, sulfolane, dimethylsulfone Examples include aprotic polar compounds such as foxoxide and dimethylformamide. These can be used alone or in combination of two or more. Among them, carbonate compounds such as ethylene carbonate and propylene carbonate, heterocyclic compounds such as γ-butyrolactone, 3-methyl-2-oxazodilinone and 2-methylpyrrolidone, acetonitrile, methoxyacetonitrile, propionitrile, 3-methoxypropionitrile, Nitrile compounds such as valeric nitrile are preferred.

  It is also effective to use an ionic liquid as the charge transport layer 4 from the viewpoints of non-volatility and flame retardancy. In this case, known ionic liquids in general can be used, but imidazolium-based, pyridine-based, alicyclic amine-based, aliphatic amine-based, and azonium amine-based ionic liquids, literature (European patents) No. 718288, International Patent Application No. 95/18456, Electrochemical Vol. 65, No. 11, 923 (1997), J. Electrochem. Soc. 143, 10, 3099 (1996), Inorg. Chem. .35, 1168 (1996)) is preferably used.

  A gelled electrolyte or a polymer electrolyte can also be used as the charge transport layer 4. Examples of the gelling agent include a gelling agent using a technique such as a polymer and a polymer crosslinking reaction, a gelling agent based on a polymerizable polyfunctional polymer, and an oil gelling agent. As the gelled electrolyte and the polymer electrolyte, commonly used ones can be used, such as polyvinylidene fluoride polymers such as polyvinylidene fluoride, acrylic acid polymers such as polyacrylic acid, polyacrylonitrile, etc. It is preferable to use an acrylonitrile polymer, a polyether polymer such as polyethylene oxide, or a compound having an amide structure in the structure.

  The sealing material 7 is made of a thermoplastic resin. By using a thermoplastic resin as the sealing material 7, the electrode portion and the sealing portion can be brought close to each other, which is effective for an element for consumer use that needs to increase the mounting density. Note that the distance between the electrode portion and the sealing material 7 may be 0 [mm], or in some cases, a part of the sealing material 7 may overlap the electrode portion.

  The thermoplastic resin is synonymous with so-called hot melt resin, and includes ethylene-vinyl acetate copolymer, ethylene / α-olefin copolymer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, Ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, linear low density polyethylene, acrylic resin, silicone resin, ionomer resin, polystyrene, polyolefin, porodiene, polyester, polyurethane , Fluororesin-based, polyamide-based elastomers and the like can be appropriately selected according to the material of the adherend surface. The thickness of the thermoplastic resin is not particularly limited, but is desirably in the range of 10 to 100 [μm].

  The base material of the first substrate is formed of glass, film, ceramic, metal or the like. When the base material of the first substrate is caused to function as a light incident substrate, the base material of the first substrate needs to be transparent or translucent. In addition, it is preferable to form the base material of the first substrate with a flexible film since flexibility can be imparted to the element. If the base material of the first substrate is to function as a light incident substrate, a metal foil such as nickel, zinc, titanium, or the like can be used as the base material film of the first substrate. When a flexible film is used as the base material of the first substrate, the semiconductor layer 2 can be formed by applying pressure. The type of press used at the time of pressurization is not particularly limited, such as a flat plate press or a roll press, but when the conductive film is used as the base material of the first substrate, the roll press is a roll- It is preferable because it can be continuously produced by to-roll.

  The surface resistance of the first electrode 1 is preferably as low as possible, preferably 200 [Ω / □] or less, more preferably 50 [Ω / □] or less. The lower limit is not particularly limited, but is usually 0.1 [Ω / □]. The light transmittance of the first electrode 1 is preferably as high as possible, preferably 50 [%] or more, more preferably 80 [%] or more. The film thickness of the first electrode 1 is preferably in the range of 0.1 to 10 [μm]. Within this range, an electrode film having a uniform thickness can be formed, and light transmittance is not lowered, and sufficient light can be incident on the semiconductor layer 2.

  The semiconductor layer 2 is formed of semiconductor particles having a particle size in the range of 5 to 1000 [nm]. By using semiconductor particles having a particle size in the range of 5 to 1000 [nm], the pore size of the semiconductor layer 2 becomes an appropriate pore size, and the electrolyte sufficiently penetrates into the semiconductor layer 2 and has excellent photoelectric properties. Conversion characteristics can be obtained. The film thickness of the semiconductor layer 2 is preferably in the range of 0.1 to 100 [μm]. Within this range, a sufficient photoelectric conversion effect can be obtained, and the transmittance for visible light and near-infrared light does not deteriorate. The semiconductor layer 2 is prepared by applying a mixed solution of semiconductor particles and a binder to the first electrode 1 using a known method such as a coating method using a doctor blade or a bar coater, a spray method, a dip coating method, a screen printing method, or a spin coating method. If the base material of the first substrate is a glass substrate, it is heated and fired at around 500 [° C.], and if the base material of the first substrate is a film substrate, pressure is applied with a press. Can be formed.

Examples of the semiconductor material include metals such as Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, Si, and Cr. Elemental oxides, perovskites such as SrTiO ₃ , CaTiO ₃ , CdS, ZnS, In ₂ S ₃ , PbS, Mo ₂ S, WS ₂ , Sb ₂ S ₃ , Bi ₂ S ₃ , ZnCdS ₂ , Cu ₂ S, etc. Metal chalcogenides such as sulfides, CdSe, In ₂ Se ₃ , WSe ₂ , HgS, PbSe, CdTe, GaAs, Si, Se, Cd ₂ P ₃ , Zn ₂ P ₃ , InP, AgBr, PbI ₂ , HgI ₂ , BiI ₃ can be exemplified. Further, a composite containing at least one or more kinds obtained from the semiconductor material, for example, CdS / TiO ₂ , CdS / AgI, Ag ₂ S / AgI, CdS / ZnO, CdS / HgS, CdS / PbS, ZnO / ZnS, _{CdS / HgS, CdS x / CdSe} 1-x, CdS x / Te 1-x, CdSe x / Te 1-x, ZnS / CdSe, ZnSe / CdSe, CdS / ZnS, TiO 2 / Cd 3 P 2, CdS / Examples thereof include CdSe / Cd _y Zn _1-y S, CdS / HgS / Cds, and the like. Among these, TiO ₂ is preferable in terms of avoiding photodissolution in the electrolytic solution and high photoelectric conversion characteristics.

As the sensitizing dye carried by the semiconductor layer 2, any dye that is commonly used in conventional dye-sensitized photoelectric conversion elements can be used. Specifically, RuL ₂ (H ₂ O) 2 type ruthenium-cis-diaqua-bipyridyl complex, ruthenium-tris (RuL ₃ ), ruthenium-bis (RuL ₂ ), osnium-tris (OsL ₃ ), osnium- Examples include bis (OsL ₂ ) type transition metal complexes, zinc-tetra (4-carboxyphenyl) porphyrin, iron-exocyanide complexes, phthalocyanines, and the like. Organic dyes include 9-phenylxanthene dyes, coumarin dyes, acridine dyes, triphenylmethane dyes, tetraphenylmethane dyes, quinone dyes, azo dyes, indigo dyes, cyanine dyes, merocyanine Examples thereof include system dyes and xanthene dyes. Among these, a ruthenium-bis (RuL ₂ ) derivative is particularly preferable because it has a wide absorption spectrum in the visible light region.

Examples of the method of supporting the sensitizing dye on the semiconductor layer 2 include a method of immersing the first substrate in a solution in which the sensitizing dye is dissolved. As the solvent of this solution, any solvent that can dissolve the sensitizing dye, such as water, alcohol, toluene, dimethylformamide, and the like can be used. As the immersion method, heating and refluxing or applying ultrasonic waves can be performed while the first substrate is immersed in the sensitizing dye solution for a certain period of time. In order to remove the sensitizing dye remaining on the semiconductor layer 2 without being supported after the dye is supported on the semiconductor layer 2, it is desirable to wash with alcohol or reflux with heating. The amount of the sensitizing dye supported on the semiconductor layer 2 is 1 × 10 ⁻⁸ to 1 × 10 ⁻⁶ [mol / cm ² ], more preferably 0.1 × 10 ^{−7 to} 9.0 × 10 ⁻⁷ [ mol / cm ² ] is desirable. If it is within this range, it is possible to expect a sufficient improvement in photoelectric conversion efficiency economically.

  The base material of the second substrate can use the same material as the base material of the first substrate. The first electrode 1 formed on one surface of the base material of the first substrate functions as a negative electrode of the photoelectric conversion element and is formed of metal or by laminating a conductive material layer on the film. It is formed. Conductive metal oxides such as metals such as platinum, gold, silver, copper, aluminum, rhodium, and indium, carbon, indium-tin composite oxide, tin oxide doped with antimony, tin oxide doped with fluorine, etc. And composites of these oxides, and materials obtained by coating these oxides with silicon oxide, tin oxide, titanium oxide, zirconium oxide, aluminum oxide or the like.

  The second electrode 3 functions as a positive electrode of the photoelectric conversion element and can be formed in the same manner as the first electrode 1 on the side where the semiconductor layer 2 carrying the sensitizing dye is deposited. As the second electrode 3, it is desirable to use a material having a catalytic action to give electrons to the electrolyte reductant in order to efficiently act as the positive electrode of the photoelectric conversion element. As such materials, metals such as platinum, gold, silver, copper, aluminum, rhodium and indium, graphite, carbon nanotubes, carbon materials such as carbon carrying platinum, indium-tin composite oxide, antimony doped Examples include conductive metal oxides such as tin oxide and fluorine-doped tin oxide, and conductive polymers such as polyethylenedioxythiophene, polypyrrole, and polyaniline. Among them, platinum, graphite, polyethylenedioxythiophene, etc. Particularly preferred.

  The surface of the second electrode 3 facing the semiconductor layer 2 is provided with a recess 8 over the entire surface, and the inner peripheral shape of the recess 8 becomes smaller as it approaches the bottom. The cross-sectional shape of the recess 8 in the direction perpendicular to the second electrode 3 is substantially trapezoidal.

  Therefore, in the photoelectric conversion element of this embodiment, since the cross-sectional shape of the recess 8 in the direction orthogonal to the second electrode 3 is substantially trapezoidal, the light transmitted through the first electrode 1 is the second electrode. Even if it is incident at an acute angle with respect to the outer peripheral portion of the surface 3, it can be reflected to the central portion of the semiconductor layer 2. Therefore, it is possible to prevent light components from leaking or being absorbed outside the semiconductor layer 2 (for example, leaking from a portion between the semiconductor layer 2 and the sealing material 7), and to convert the energy of the incident light 5 The contribution rate is increased, and the light energy conversion efficiency as a solar cell can be improved.

  2 and 3 show a photoelectric conversion element which is a second embodiment corresponding to claims 1 and 3 of the present application.

  Here, only matters different from those in the first embodiment will be described, and other matters (configuration, operational effects, and the like) are the same as those in the first embodiment, and the description thereof will be omitted.

  In this photoelectric conversion element, the cross-sectional shape of the recess 8 in the direction orthogonal to the second electrode 3 is substantially arc-shaped.

Therefore, in the photoelectric conversion element of this embodiment, since the cross-sectional shape of the recess 8 in the direction orthogonal to the second electrode 3 is substantially arc-shaped, the light transmitted through the first electrode 1 The light can be condensed at the central portion, so that the light absorption efficiency can be improved and the light energy conversion efficiency per area can be improved. Furthermore, since the light transmitted through the first electrode 1 is collected at the center, there is no functional problem even if the area of the semiconductor layer 2 is small, and the area of the semiconductor layer 2 can be arbitrarily changed according to the application. Thus, it is possible to design a configuration according to the conditions for mounting the photoelectric conversion element. (See Figure 3)
FIG. 4 shows a photoelectric conversion element according to a third embodiment corresponding to claims 1, 3, and 4 of the present application.

  Here, only matters different from those in the second embodiment will be described, and other matters (configuration, operational effects, and the like) are the same as those in the first embodiment, and thus description thereof will be omitted.

  This photoelectric conversion element becomes smaller as the outer peripheral shape of the semiconductor layer 2 protruding to the second electrode 3 side approaches the protruding direction.

  Therefore, in the photoelectric conversion element of this embodiment, when the first electrode 1 tries to absorb again the light 6 that has been transmitted through the first electrode 1 and reflected by the surface of the second electrode 3, the semiconductor layer 2 Can absorb light at a substantially right angle as compared with the case where is flat. Therefore, it is possible to suppress as much as possible the light 6 transmitted through the first electrode 1 and reflected from the surface of the second electrode 3 from being diffusely reflected to the first electrode 1, thereby contributing to an improvement in light absorption efficiency. In addition, the light energy conversion efficiency can be improved.

  As mentioned above, although the embodiment to which the invention made by the inventors of the present application is applied has been described, the present invention is not limited by the description and the drawings that constitute a part of the disclosure of the present invention according to this embodiment. That is, it should be added that other embodiments, examples, operation techniques, and the like made by those skilled in the art based on the above embodiments are all included in the category of the present invention.

Sectional drawing which shows the structure of the photoelectric conversion element used as 1st embodiment of this invention. Sectional drawing which shows the structure of the photoelectric conversion element used as 2nd embodiment of this invention. Sectional drawing which shows a structure when the area of the semiconductor layer of the photoelectric conversion element is smaller. Sectional drawing which shows the structure of the photoelectric conversion element used as 3rd embodiment of this invention. Sectional drawing which shows the structure of the photoelectric conversion element which is a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st electrode 2 Semiconductor layer 3 2nd electrode 4 Charge transport layer 5 Incident light 6 Reflected light 7 Sealing material 8 Recessed part

Claims (4)

  A first electrode which is a working electrode to which a semiconductor layer carrying a sensitizing dye is attached; a second electrode which is disposed opposite to the semiconductor layer; and iodine which is sandwiched between the first electrode and the second electrode. And a charge transport layer including light incident from the first electrode side, and the second electrode is a photoelectric conversion element that reflects incident light to the semiconductor layer, the second electrode facing the semiconductor layer A photoelectric conversion element characterized in that a concave portion covering substantially the entire surface irradiated with light is provided on the surface, and the inner peripheral shape of the concave portion becomes smaller as approaching the bottom portion.   The photoelectric conversion element according to claim 1, wherein a cross-sectional shape of the concave portion in a direction orthogonal to the second electrode is substantially trapezoidal.   The photoelectric conversion element according to claim 1, wherein a cross-sectional shape of the concave portion in a direction orthogonal to the second electrode is a substantially arc shape.   The photoelectric conversion according to any one of claims 1 to 3, wherein the semiconductor layer protrudes toward the second electrode, and the outer peripheral shape of the semiconductor layer decreases as the direction approaches the second electrode. element.

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