JP2008243618A - Photoelectric conversion element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric conversion element capable of providing high output, and hardly causing aged deterioration. <P>SOLUTION: The photoelectric conversion element includes: an electrode 1; a semiconductor layer 2 arranged in contact with one surface of the electrode 1, and having a sensitizing dye fixed thereto; a counter electrode 3 arranged to face the electrode 1 on the semiconductor layer 2 side; and a charge transport layer 4 arranged between the electrode 1 and the counter electrode 3. The charge transport layer 4 is formed of an electrolytic solution 41 containing a water-containing porous body 42. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a photoelectric conversion element.

  Most of the solar cells currently in practical use use silicon such as single crystal silicon, polycrystalline silicon, and amorphous silicon. However, since the manufacturing processes of these silicon-based solar cells are complicated and expensive, reduction of manufacturing costs has become a major issue.

  Therefore, in recent years, dye-sensitized solar cells have attracted attention as solar cells that do not require high-purity materials and high-energy processes. This dye-sensitized solar cell adsorbs a sensitizing dye that absorbs light on the surface of a semiconductor electrode, and absorbs visible light having a wavelength longer than the band gap of the semiconductor electrode with the sensitizing dye, thereby improving photoelectric conversion efficiency. The photoelectric conversion element shown in FIG.

An example of a dye-sensitized solar cell is a Gretzel cell. Its general structure is a translucent and highly conductive electrode, and a porous film using oxide semiconductor nanoparticles such as titanium dioxide is formed on one side of the electrode, and this is loaded with a sensitizing dye. And a counter electrode made of a conductive glass or the like doped with a metal such as platinum arranged to face the electrode on the semiconductor layer side, and an electric charge formed by filling an electrolyte between both electrodes And a transport layer. Here, examples of the electrolyte solution in the dye-sensitized solar cell include a solution in which tetra-n-propylammonium iodide and iodine are dissolved in a mixed organic solvent of ethylene carbonate and acetonitrile. However, due to the high vapor pressure of the organic solvent, there has been a problem that the electrolyte is gradually discharged and the predetermined performance is not obtained, or the electrolyte is deposited inside the battery due to the ingress of water and the efficiency is lowered. Thus, for example, it has been proposed to use an electrolytic solution containing water as in Patent Document 1.
JP 2002-110262 A

  High output can be obtained by using an electrolytic solution containing water as in Patent Document 1 described above. However, the actual situation is that the deterioration over time of the output has not been sufficiently improved.

  The present invention has been made in view of the circumstances as described above, and an object of the present invention is to provide a photoelectric conversion element that realizes high output and little deterioration with time.

  The present invention is characterized by the following in order to solve the above problems.

  First, the photoelectric conversion element of the present invention has an electrode, a semiconductor layer in which a sensitizing dye disposed in contact with one surface of the electrode is fixed, and the semiconductor layer side so as to face the electrode. A photoelectric conversion element comprising a counter electrode disposed and a charge transport layer disposed between the electrode and the counter electrode, wherein the charge transport layer is made of an electrolytic solution containing a hydrous porous body. Is.

  Secondly, the water-containing porous body is contained in the electrolytic solution at a ratio of 0.1 to 30 wt%.

  Third, the photoelectric conversion element has a counter electrode formed on one surface of a substrate and a heating element on the other surface.

  According to the first aspect of the invention, it is possible to achieve a high output by using the electrolytic solution containing the hydrous porous body and obtain a photoelectric conversion element with little deterioration with time.

  According to the second aspect, the effects of the first aspect can be further improved.

  According to the third aspect of the present invention, the water-containing porous body can be heated by the heating element to forcibly release moisture from the water-containing porous body, and a photoelectric conversion element with less deterioration with time can be obtained. .

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a first embodiment of the photoelectric conversion element of the present invention. In this embodiment, as shown in FIG. 1, the electrode 1 is formed on one surface of the first substrate 5, and the semiconductor layer 2 on which the sensitizing dye is fixed is formed on the surface of the electrode 1. The counter electrode 3 is disposed so as to face the electrode 1 on the semiconductor layer 2 side. The counter electrode 3 is formed on one surface of the second substrate 6. A charge transport layer 4 is formed between the electrode 1 and the counter electrode 3, and a sealing material 7 is formed around the charge transport layer 4 in order to hold the charge transport layer 4. The semiconductor layer 2 to which the sensitizing dye is fixed has a porous structure, and the charge transport layer 4 penetrates into the semiconductor layer 2. In this embodiment, light is incident from the first substrate 5 side.

  The charge transport layer 4 in the present invention is composed of an electrolytic solution 41 containing a hydrous porous body 42. When only water is added to the electrolytic solution 41 without using the hydrous porous body 42, the initial characteristics are improved and a high output is obtained, but there is a problem that deterioration with time is large, but the hydrous porous body 42 is used. Then, moisture can be gradually supplied to the electrolytic solution 41, and a photoelectric conversion element with little deterioration with time can be obtained. Here, the water-containing porous body 42 refers to a state in which water is absorbed by a porous body such as zeolite (molecular sieve), silica gel, and aluminum oxide, for example, water is present in the pores of the porous body. Adsorbed. The size and average pore diameter of the porous body are not particularly limited. For example, the pore diameter may be any of macropores larger than 50 nm, mesopores of 2 to 50 nm, and micropores smaller than 2 nm. Generally, micropores are considered for zeolite, and mesopores are considered for silica gel and aluminum oxide. The water content of water in the porous body varies depending on the pore diameter, specific surface area, etc., but is, for example, about 5 to 50%.

  It is considered that the water-containing porous body 42 is contained in the electrolytic solution 41 at a ratio of 0.1 wt% to 30 wt%. In particular, it is preferably contained in a proportion of 3 wt% to 30 wt% in order to improve output and reduce deterioration with time. If it is less than 0.1 wt%, the effect of reducing deterioration over time is small, which is not preferable. If it exceeds 30 wt%, the ratio of the organic solvent in the electrolytic solution 41 is reduced, and the power generation efficiency may be reduced. Moreover, it is considered that the ratio of the moisture contained in the hydrous porous body 42 to the electrolytic solution 41 is 0.1 wt% to 15 wt%, more preferably 3 wt% to 15 wt%. If it is less than 0.1 wt%, the effect of reducing deterioration over time is small, which is not preferable. If it exceeds 15 wt%, the ratio of the organic solvent in the electrolytic solution 41 is reduced, and power generation efficiency may be reduced.

  For example, the water-containing porous body 42 can be easily and inexpensively prepared by exposing the porous body to a high humidity atmosphere to absorb moisture.

As a method for preparing the electrolytic solution 41 in the present invention, a conventionally known method can be adopted. For example, it can be prepared by dissolving iodide and iodine (I ₂ ) in the following organic solvent or the like. Examples of iodides include tetraalkylammonium iodides such as tetrapropylammonium iodide, asymmetrical alkylammonium iodides such as methyltripropylammonium iodide and diethyldibutylammonium iodide, and quaternary ammonium iodides such as pyridinium iodide. Salt compounds, lithium iodide, 1,2-dimethyl-3-propyl-imidazolium iodide and the like are preferable.

  The organic solvent preferably contains at least N-methylformamide, and when N-methylformamide alone is not used as an organic solvent, it is preferably used in a mixed system with the following organic solvent. For example, carbonate compounds such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate and propylene carbonate, ester compounds such as methyl acetate, methyl propionate and 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, acetonitrile, methoxyacetonitrile, propionitrile, 3-methoxypropionitrile, Yoshi Examples include nitrile compounds such as valeric acid nitrile, aprotic polar compounds such as sulfolane, didimethyl sulfoxide, and dimethylformamide. Each of these may be mixed alone with N-methylformamide, or two or more may be mixed with N-methylformamide. For example, carbonate compounds such as ethylene carbonate and propylene carbonate, ester compounds such as γ-butyrolactone, heterocyclic compounds such as 3-methyl-2-oxazolidinone and 2-methylpyrrolidone, acetonitrile, methoxyacetonitrile, propionitrile, 3-methoxypropyl A mixed system with nitrile compounds such as pionitrile and valeric nitrile can be used.

  Further, an ionic liquid (also referred to as a room temperature molten salt) may be used in place of these organic solvents. The ionic liquid is preferable from the viewpoints of non-volatility and flammability. Examples of the ionic liquid include imidazolium salts, pyridine salts, ammonium salts, alicyclic amines, aliphatic amines, azonium amines, and the like. Alternatively, EP-718288, WO95 / 18456, Electrochemistry 65, 11, 923 (1997), J. Org. Electrochem. Soc. 143, No. 10, 3099 (1996), Inorg. chem. An ionic liquid described in Vol. 35, page 1168 (1996) can also be used.

  Furthermore, the electrolytic solution 41 preferably contains at least one selected from the group consisting of pyridine, pyridine derivatives, imidazoles, and imidazole derivatives. Examples of the pyridine derivative include 4-tert-butylpyridine, and examples of the imidazole derivative include N-methylbenzimidazole. These have the effect of improving the initial output by adsorbing on the surface of the semiconductor layer 2 where no sensitizing dye is adsorbed.

  The material of the first substrate 5 is not particularly limited as long as it is a material having excellent translucency, weather resistance, and gas barrier properties. For example, a transparent glass plate or resin film that is transmissive to visible light (wavelength 400 nm to 800 nm) can be used. When a resin film having flexibility is used, the semiconductor layer 2 can be formed by pressing.

  Examples of the resin film material include regenerated cellulose, diacetate cellulose, triacetate cellulose, tetraacetyl cellulose, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polyethylene terephthalate, polycarbonate, polyethylene naphthalate, and polyether. Group consisting of sulfone, polyether ether ketone, polysulfone, polyether imide, polyimide, polyarylate, cycloolefin polymer, norbornene resin, polystyrene, hydrochloric acid rubber, nylon, polyacrylate, polyvinyl fluoride, and polytetrafluoroethylene 1 type, or 2 or more types selected from can be used. In particular, it is preferable to use one or more selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, polyethersulfone, polyimide, polyarylate, cycloolefin polymer, and norbornene resin. Resin films using these resins are tough and excellent in heat resistance.

  As the material of the second substrate 6, for example, the same material as that of the first substrate 5 can be used, but a metal foil such as nickel, zinc, or titanium may be used. When a material having the same translucency as that of the first substrate 5 is used as the material of the second substrate 6, the photoelectric conversion element of the present invention is preferable because light can enter from both substrate sides.

  There are no particular restrictions on the thickness of the first substrate 5 and the second substrate 6. For example, when the material of the substrate is a glass plate, 0.1 mm to 5 mm is appropriate, and in particular, about 0.7 mm to 2 mm is considered. In the case of a resin film or metal foil, the thickness is suitably from 0.01 mm to 5 mm, and in particular, a thickness of about 0.07 mm to 1 mm is considered.

  The semiconductor layer 2 can be formed by a conventionally known method. For example, it can be formed by applying a paste containing semiconductor particles and a binder to the electrode 1 using, for example, a doctor blade or a bar coater. Further, the paste may be attached to the surface of the electrode 1 by, for example, a spray method, a dip coating method, a screen printing method, a spin coating method, an electrodeposition method or the like. When the first substrate 5 is a glass substrate, the paste on the electrode 1 is baked at around 500 ° C. to become the semiconductor layer 2. When the first substrate 5 is a resin film, the paste on the electrode 1 is pressed together with the first substrate 5 in the thickness direction by a press, or heated by microwave irradiation to become the semiconductor layer 2. The pressing method is not particularly limited and may be any of flat plate press, roll press, and the like. However, in the case of roll pressing, the semiconductor layer 2 can be continuously formed on the resin film, which is preferable.

The material of the semiconductor particles used for forming the semiconductor layer 2 includes Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr. , Ga, Si, Cr and other metal oxides, SrTiO ₃ , CaTiO _{3 and} other perovskite oxides, CdS, ZnS, In ₂ S ₃ , PbS, Mo ₂ S, WS ₂ , Sb ₂ S ₃ , Bi ₂ Sulfides such as S ₃ , ZnCdS ₂ , Cu ₂ S, metal chalcogenides such as CdSe, In ₂ Se ₃ , WSe ₂ , HgS, PbSe, CdTe, GaAs, Si, Se, Cd ₂ P ₃ , Zn ₂ P ₃ , Examples thereof include a complex containing one or more selected from the group consisting of InP, AgBr, PbI ₂ , HgI ₂ , and BiI ₃ . Among these, TiO ₂ that is difficult to be photodissolved in the electrolytic solution 41 and excellent in photoelectric conversion characteristics is preferable. Examples of the composite include CdS / TiO ₂ , CdS / AgI, Ag ₂ S / AgI, CdS / ZnO, CdS / HgS, CdS / PbS, ZnO / ZnS, ZnO / ZnSe, 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 / CdSeCd _y Zn _1-y S, CdS / HgS / CdS etc. are mentioned,
In general, the particle diameter of the semiconductor particles is preferably 5 nm to 1000 nm, and particularly preferably 10 nm to 100 nm. If the particle size is 5 nm to 1000 nm, the semiconductor layer 2 having a surface area capable of adsorbing a sufficient amount of sensitizing dye can be formed, and the light utilization efficiency can be increased. In addition, since the semiconductor layer 2 having moderately sized pores can be formed, the electrolytic solution 41 in the charge transport layer 4 can sufficiently penetrate into the semiconductor layer 2 to obtain excellent photoelectric conversion characteristics.

  The thickness of the semiconductor layer 2 is preferably 0.1 μm to 100 μm. If the thickness of the semiconductor layer 2 is 0.1 μm to 100 μm, a sufficient photoelectric conversion effect can be obtained, and transparency to visible light and near infrared light can be sufficiently secured. The thickness of the semiconductor layer 2 is more preferably 1 μm to 50 μm, further preferably 3 μm to 20 μm, and most preferably 5 μm to 10 μm. In the present embodiment, the thickness of the semiconductor layer 2 may be smaller than the optimum thickness (for example, 10 μm) of the semiconductor layer 2 of the conventional photoelectric conversion element that is assumed to be used under sunlight. Good.

  The electrode 1 functions as a negative electrode of the photoelectric conversion element. The material of the electrode 1 is preferably a material having high conductivity and high translucency, such as zinc oxide, indium-tin composite oxide, a laminate composed of an indium-tin composite oxide layer and a silver layer, and doped with antimony. Tin oxide, tin oxide doped with fluorine, or the like can be used. Among these, tin oxide doped with fluorine is particularly preferable because of its high conductivity and translucency. The higher the light transmittance of the electrode 1, the better, preferably 50% or more, more preferably 80% or more.

  The thickness of the electrode 1 is not particularly limited as long as it has sufficient translucency so that light can be sufficiently incident on the semiconductor layer 2. For example, a range of 0.1 μm to 10 μm is considered. Moreover, if the thickness of the electrode 1 is within the range, it is preferable because the electrode 1 having a uniform thickness can be produced.

  The surface resistance of the electrode 1 is preferably as low as possible, but is preferably 200Ω / □ or less, and more preferably 50Ω / □ or less. Although there is no restriction | limiting in particular about the lower limit of the surface resistance of the electrode 1, Usually, it is 0.1 ohm / square.

  The photoelectric conversion element used under sunlight often has a surface resistance of the electrode 1 of about 10Ω / mouth. However, in a photoelectric conversion element used under a fluorescent lamp or the like having a lower illuminance than sunlight, the amount of photoelectrons (photocurrent value) is small, so that it is difficult to be adversely affected by the resistance component included in the electrode 1. Therefore, in the photoelectric conversion element used in a low illumination environment, the surface resistance of the electrode 1 is 30Ω / □ to 200Ω / □ from the viewpoint of cost reduction by reducing the conductive material included in the electrode 1. preferable.

  The counter electrode 3 functions as a positive electrode of the photoelectric conversion element. As the material of the counter electrode 3, the same material as that of the electrode 1 can be used, but it is preferable to include a material having a catalytic action to give electrons to the reductant. Examples of the material having the catalytic action include metals such as platinum, gold, silver, copper, aluminum, rhodium, and indium, graphite, carbon carrying platinum, indium-tin composite oxide, and tin oxide doped with antimony. Or a metal oxide such as tin oxide doped with fluorine. Of these, platinum, graphite and the like are particularly preferable in consideration of cost, performance, and the like.

The sensitizing dye fixed to the semiconductor layer 2 may be the same as the sensitizing dye used in the conventional photoelectric conversion element, and may be either an inorganic dye or an organic dye. Examples of the inorganic dye include a ruthenium-cis-diaqua-bipyridyl complex represented by the composition formula RuL ₂ (H ₂ 0) ₂ (where L is 4,4′-dicarboxyl-2,2′-bipyridine). ), Or a transition metal complex represented by ruthenium-tris (RuL ₃ ), ruthenium-bis (RuL ₂ ), osnium-tris (OsL ₃ ), a composition formula osnium-bis (OsL ₂ ), or zinc-tetra ( 4-carboxyphenyl) porphyrin, iron-hexocyanide complex, phthalocyanine and the like. As organic dyes, 9-phenylxanthene dyes, coumarin dyes, acridine dyes, triphenylmethane dyes, tetraphenylmethane dyes, quinone dyes, azo dyes, indigo dyes, cyanine dyes, merocyanine dyes Examples thereof include dyes and xanthene dyes. Of these, a ruthenium-bis (RuL ₂ ) derivative having a broad absorption spectrum in the visible light region is particularly preferable. Examples of the method for fixing (supporting) the sensitizing dye on the semiconductor layer 2 include a method in which the sensitizing dye is adsorbed by immersing the semiconductor layer 2 in a solution in which the sensitizing dye is dissolved in a solvent. Examples of the solvent include water, alcohol, toluene, dimethylformamide and the like. While the semiconductor layer 2 is immersed in the solution, the adsorption of the sensitizing dye to the semiconductor layer 2 may be promoted by heating and refluxing the solution or applying an ultrasonic wave to the solution. After the sensitizing dye is adsorbed to the semiconductor layer 2, the sensitizing dye that is not adsorbed and remains in the semiconductor layer 2 may be removed from the semiconductor layer 2 by washing with alcohol or heating and refluxing. The adsorption amount of the sensitizing dye is preferably 1 × 10 ⁻⁸ to 1 × 10 ⁻⁶ mol / cm ² . Within this range, economical and sufficient photoelectric conversion efficiency can be realized.

  The sealing material 7 is formed between the electrode 1 and the counter electrode 3 so as to enclose the charge transport layer 4 and is sealed so that the electrolytic solution 41 does not leak to the outside. As a material of the sealing material 7, for example, a thermoplastic resin or a thermosetting resin can be used. Examples of the thermoplastic resin include ionomers, polyolefins, and fluorine resins, and examples of the thermosetting resin include epoxy resins and silicon resins.

  In the photoelectric conversion element of the present invention, for example, a transparent conductive film may be further provided between the second substrate 6 and the counter electrode 3. The transparent conductive film can be formed of the same material as the electrode 1, for example. At this time, the counter electrode 3 is also preferably transparent. If the counter electrode 3 is transparent, light can be received from the second substrate 6 side, the first substrate 5 side, or both.

  FIG. 2 shows a second embodiment of the photoelectric conversion element of the present invention. In the present embodiment, parts common to the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  In the second embodiment, the heating element 8 is provided on the other surface of the second substrate 6 on which the counter electrode 3 is formed. The heating element 8 can be a thermoelectric cooling element (Peltier module) or the like, but is not limited thereto. When such a heating element 8 is provided, the water-containing porous body 42 can be heated by the heating element 8, so that moisture can be forcibly released from the water-containing porous body 42, and water is contained. It becomes possible to maintain the effect of doing for a long time, and it becomes a photoelectric conversion element with less deterioration with time.

<Example>
TiO ₂ nanoparticles with an average primary particle size of 20 nm were dispersed in alcohol to prepare a screen printing paste. This paste is applied onto a 1 mm thick conductive glass substrate (manufactured by Asahi Glass, one surface coated with fluorine-doped tin oxide (SnO ₂ ), surface resistance 10 Ω / □) and dried. did. Subsequently, the dried product was immersed in an aqueous TiCl ₄ solution at 80 ° C. for 1 hr, washed with pure water and air-dried. This was baked in the air at 500 ° C. for 30 minutes using an electric furnace to form a semiconductor layer having a thickness of 10 μm on the conductive glass substrate. Next, a sensitizing dye [Ru (4,4′nidicarboxyl-2,2′-bipyridine) ₂ (NCS) ₂ ] bis-tetrabutylammonium (3 × 10 ⁻⁴ mol / dm ³ ) is added to ethanol. After immersing the semiconductor layer in the obtained solution, the semiconductor layer was taken out from the solution and allowed to stand in the dark at room temperature for 24 hours to adsorb the sensitizing dye to the semiconductor layer. On the other hand, a platinum layer was formed on the other surface of the conductive glass substrate by sputtering.

Subsequently, a hole was made with a diamond drill so as to penetrate the conductive glass substrate and the platinum layer. Note that the fluorine-doped SnO ₂ layer and the platinum layer coated on the glass substrate are counter electrodes.

Next, between the conductive glass substrate on which the semiconductor layer is formed and the counter electrode, a hot-melt sealing material is disposed so as to surround the semiconductor layer, and these are pressed in the thickness direction while heating, The said conductive glass substrate and the counter electrode were joined through the sealing material. Subsequently, an electrolytic solution containing 10 wt% of a molecular sieve having a particle size of 1 μm or less, which was allowed to stand in a constant temperature and humidity chamber at 25 ° C. and 85% Rh for 24 hours, was injected between the conductive glass substrate and the counter electrode. A transport layer was formed, and the hole was closed to obtain a dye-sensitized solar cell as a photoelectric conversion element having a light receiving area of 1 cm ² .
<Comparative example>
In the above example, a dye-sensitized solar cell having a light receiving area of 1 cm ² was produced in the same manner as in the example except that the molecular sieve impregnated with water was not added.

About the dye-sensitized solar cell of an Example and a comparative example, after preserve | saving in the high temperature (80 degreeC) environment of 100, 200, 300 hours, a battery output was measured and the result was shown in Table 1 as a relative value with respect to an initial stage battery output. Indicated. For the measurement, the prepared dye-sensitized solar cell was connected to an ammeter (KEYTHLEY 236 model), and a solar simulator (manufactured by Yamashita Denso) having an intensity of 100 mW / cm ² was used.

  As shown in Table 1, when an electrolytic solution containing a hydrous porous body was used (Example), the Pmax relative value with respect to the initial battery output after 80 hours at 80 ° C. was an electrolyte containing no hydrous porous body. Compared with the case of using (Comparative Example), it was confirmed that it was kept high and the rate of change was small.

It is the schematic diagram which showed 1st Embodiment of the photoelectric conversion element of this invention. It is the schematic diagram which showed 2nd Embodiment of the photoelectric conversion element of this invention.

Explanation of symbols

1 Electrode 2 Semiconductor layer 3 Counter electrode 4 Charge transport layer 41 Electrolytic solution 42 Hydrous porous material

Claims (3)

  An electrode, a semiconductor layer to which a sensitizing dye disposed in contact with one surface of the electrode is fixed, a counter electrode disposed to face the electrode on the semiconductor layer side, the electrode and the pair A photoelectric conversion device comprising a charge transport layer disposed between electrodes, wherein the charge transport layer comprises an electrolytic solution containing a hydrous porous material.   2. The photoelectric conversion element according to claim 1, wherein the hydrous porous body is contained in the electrolytic solution at a ratio of 0.1 to 30 wt%.   The photoelectric conversion element according to claim 1, wherein a counter electrode is formed on one surface of the substrate and a heating element is provided on the other surface.