JP5153215B2 - Photoelectric conversion device - Google Patents

Description

  The present invention relates to a photoelectric conversion device excellent in photoelectric conversion efficiency.

  Conventionally, a dye-sensitized solar cell, which is a type of photoelectric conversion device, does not require a vacuum device for its production, so it is considered to be a low-cost, low-environmental load-type solar cell, and is actively researched and developed. Has been done.

As shown in FIG. 4, a photoelectric conversion device 31 that shows a normal dye-sensitized solar cell includes a transparent conductive layer 27 such as conductive glass, and porous titanium oxide formed on the transparent conductive layer 27. Oxide semiconductor 22, a photoexciter 23 such as a dye attached to the surface of the oxide semiconductor 22, a conductive substrate 21 arranged to face the oxide semiconductor 22 with a gap, and a transparent conductive layer 27. an electrolyte 24 injected between the conductive substrate 21 (e.g., iodine redox _{^{(I - / I 3 -.}} . redox couple) and is formed from the photoelectric conversion device 31, the oxide semiconductor 22 The photoexcited body 23 adsorbed on the substrate absorbs light, and the electrons generated by the light absorption move to the oxide semiconductor 22 and pass through an external load circuit to be a conductive substrate 21 that is a counter electrode layer of the transparent conductive layer 27. More electrolytes as ions Electric energy can be taken out by moving and returning to the pigment.

  The normal dye-sensitized solar cell 31 described above includes the transparent conductive layer 27 on which the oxide semiconductor 22 is formed and the conductive substrate 21, and light is irradiated from the transparent conductive layer 27 to the oxide semiconductor 22. (Hereinafter referred to as a normal incidence type).

As shown in FIG. 5, the photoelectric conversion device 51 includes a transparent conductive layer 47 and a conductive substrate 41 on which the oxide semiconductor 42 is formed, and from the transparent conductive layer 47 to the oxide semiconductor 42. A configuration in which light is irradiated (hereinafter referred to as back-incident type) has been studied (for example, see Patent Document 1). In the back-thinned photoelectric conversion device 51, light is incident from the transparent conductive layer 47 where the oxide semiconductor 42 is not formed, and thus the substrate on which the oxide semiconductor 42 is formed does not require transparency. Therefore, as the substrate, for example, a low resistance material such as a metal substrate can be used. Therefore, it is possible to increase the area of the substrate and consequently the area of the photoelectric conversion device, and to maintain a large light receiving surface.
JP 2005-285472 A

  However, in the case of the back-thinned photoelectric conversion device 1, it is necessary for light to pass through the electrolyte 14 before reaching the photoexcited body 13 of the oxide semiconductor 12. Since the electrolyte 14 contains a material that absorbs light of a short wavelength, such as iodine, the light exciter 13 tends to be difficult to reach the short wavelength component (about 400 nm) of the light.

  Therefore, the present invention has been completed in view of the above-described problems in the prior art, and an object thereof is to provide an excellent photoelectric conversion device capable of increasing long wavelength sensitivity and further improving photoelectric conversion efficiency. There is.

The photoelectric conversion device of the present invention includes a conductive substrate, an oxide semiconductor formed on the conductive substrate, a photoexciter containing a carboxyl group attached to a surface of the oxide semiconductor, and the oxide semiconductor. And a transparent conductive layer disposed so as to face each other with a gap, and one kind selected from the group consisting of HCl, HNO ₃ and H ₂ SO ₄ provided between the oxide semiconductor and the transparent conductive layer And an electrolyte having a pH of 2.4 to 6 containing the above inorganic acid .

  The pH of the electrolyte is preferably 3 to 5.5.

  The electrolyte preferably contains iodide.

  The iodide is preferably at least one selected from the group consisting of alkali metal iodides, alkaline earth metal iodides, alkylammonium iodides, and imidazolium iodides.

  The transparent conductive layer preferably has irregularities on the surface.

  It is preferable that a translucent amorphous semiconductor layer is further included between the translucent substrate and the transparent conductive layer.

  In the photoelectric conversion device of the present invention, a conductive substrate, an oxide semiconductor formed on the conductive substrate, a photoexciter attached to the surface of the oxide semiconductor, and the oxide semiconductor are spaced apart from each other. By providing the transparent conductive layer disposed so as to face each other, the oxide semiconductor and the electrolyte having a pH of 2.4 to 6 provided between the oxide semiconductor and the transparent conductive layer, the following effects Is seen.

Conventionally, it has been thought that conversion efficiency decreases when the electrolyte is made acidic, but by setting the pH of the electrolyte within the range of 2.4 to 6, the flat band potential of the oxide semiconductor that is the electron transport layer is positive. By shifting to the side, electrons can be easily injected from the photoexciter, and the current value can be increased. When the photoexciter has a carboxyl group or the like that is an adsorbing group with the oxide semiconductor, the carboxylate group (COO ⁻ ) is protonated to become a carboxyl group (COOH) due to the acidity of the electrolyte. Thereby, the electron donating property to a ligand falls, the energy level of LUMO falls, and an absorption peak shifts to the long wavelength side. Therefore, the long wavelength sensitivity is increased, and the current value can be increased to facilitate injection of electrons from the photoexciter.

  In the photoelectric conversion device of the present invention, preferably, by adjusting the pH of the electrolyte to 3 to 5.5, the conversion efficiency is particularly improved within the pH range, so that a sufficiently high efficiency can be achieved.

Preferably, in the photoelectric conversion device of the present invention, since the surface of the transparent conductive layer has irregularities, a confinement function of incident light can be obtained. Efficiency can be improved.

  Preferably, in the photoelectric conversion device of the present invention, the oxide semiconductor further includes a long wavelength component of light by further including a translucent amorphous semiconductor layer between the translucent substrate and the transparent conductive layer. Since the absorbing and translucent amorphous semiconductor layer absorbs the short wavelength component of light, complementary light can be absorbed. In this case, it is also possible to match currents required because the amorphous semiconductor layer and the oxide semiconductor are connected in series.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the photoelectric conversion devices described in these drawings.

  1 and 2 are cross-sectional views of the photoelectric conversion device of the present invention. In addition, the arrow in a figure shows the light which injects into a photoelectric conversion apparatus.

  1 includes a conductive substrate 11, an oxide semiconductor 12 formed on the conductive substrate 11, a photoexciter 13 attached to the surface of the oxide semiconductor 12, and an oxide semiconductor. 12, a transparent conductive layer 17 disposed so as to face the electrode 12 with a gap, and an electrolyte 14. The pH of the electrolyte 14 is in the range of 2.4-6. Then, light enters the photoelectric conversion device 1 of the present invention from the transparent conductive layer 17 side, and the light that has passed through the electrolyte 14 is absorbed from the photoexciter 13 and transmitted to the oxide semiconductor 12 (hereinafter referred to as the oxide semiconductor 12). (Reverse conductivity type).

  Further, the photoelectric conversion device 1 of the present invention in FIG. 2 includes a dye-sensitized photoelectric conversion body 3 including an electrolyte 14 as a bottom cell on the main surface of a conductive substrate 11, a catalyst layer 15 for reducing overvoltage, and a top cell. The thin film photoelectric conversion body 2 including the amorphous semiconductor layer 16 and having light transparency is sequentially stacked. The thin film photoelectric converter 2 includes an amorphous semiconductor layer 16, a transparent conductive layer 17, and a translucent covering 18. The dye-sensitized photoelectric conversion body 3 includes a conductive substrate 11, an oxide semiconductor 12, a photoexciter 13, and an electrolyte 14. As in the case of FIG. 1, the pH of the electrolyte 14 is in the range of 2.4-6.

  Here, the dye-sensitized photoelectric conversion body 3 preferably has a peak sensitivity on the longer wavelength side than the thin film photoelectric conversion body 2 and exhibits a function of absorbing light transmitted through the thin film photoelectric conversion body 2.

  The dye-sensitized photoelectric conversion body 3 includes, for example, a porous oxide semiconductor 12 formed on a conductive substrate 11 and a permeable electrolyte 14 formed so as to fill the pores of the porous oxide semiconductor 12. In addition, the photoexciter 13 is disposed at the interface between the oxide semiconductor 12 and the electrolyte 14.

  The photoelectric conversion device 1 of the present invention in FIG. 2 is configured so that the current of the first output of the thin film photoelectric converter 2 is the same as the current of the second output of the dye-sensitized photoelectric converter 3 (current). It is better to match the performance of both photoelectric converters so that they match. In this case, there is no need to extract the output from the interface between the thin film photoelectric converter 2 and the dye-sensitized photoelectric converter 3, and the electrode wiring structure such as integration is simplified. In order to match the output currents of both photoelectric converters, the film thickness, sensitivity, and the like of each may be adjusted.

  Hereinafter, the photoelectric conversion device of the present invention will be described for each configuration.

<Conductive substrate>
The conductive substrate 11 is made of a metal sheet made of titanium, stainless steel, aluminum, silver, copper, nickel, etc., a resin sheet impregnated with fine wires made of carbon, metal fine particles, metal, etc., conductive resin, ITO, SnO ₂ : F Examples thereof include an oxide conductive film made of (fluorine-doped SnO ₂ ), ZnO: Al (Al-doped ZnO), and the like. In particular, since the resistance is low, the conductive substrate 11 is preferably a metal sheet because of its excellent resistance.

  When the conductive substrate 11 is made of a metal having light reflectivity such as silver or aluminum, the conductive substrate 11 is provided with excellent light reflectivity, so that the transmitted light is reflected and the light is reused. be able to.

Further, even when the conductive substrate 11 is a light-transmitting material (SnO ₂ : F (F-doped SnO ₂ ) blue plate glass with a film, etc.), light-reflective aluminum or the like is formed on the back surface of the conductive substrate 11. A sheet or film made of silver or the like may be formed to impart light reflectivity.

  The thickness of the conductive substrate 11 is preferably 0.01 mm to 5 mm, and more preferably 0.02 mm to 3.0 mm.

  The conductive substrate 11 may be composed of an insulating substrate 11a and a conductive film 11b.

  As the insulating substrate 11a, for example, a resin material such as PET (polyethylene terephthalate), PEN (polyethylene naphthalate), polyimide, polycarbonate, an inorganic material such as blue plate glass, soda glass, borosilicate glass, ceramics, or a conductive resin Examples include materials and organic-inorganic hybrid materials.

  Examples of the conductive film 11b include a laminated structure such as a titanium layer / ITO layer / titanium layer, a laminated structure such as a Ti layer / Ag layer / Ti layer with an adhesion layer, and a silver film. The conductive film 11b is formed by vacuum deposition, ion plating, sputtering, electrolytic deposition, or the like.

  The thickness of the conductive film 11b is preferably 0.001 μm to 10 μm, and more preferably 0.05 μm to 2.0 μm.

<Oxide semiconductor>
The oxide semiconductor 12 in the present invention is formed on the conductive substrate 11.

  As the oxide semiconductor 12, a porous n-type oxide semiconductor made of titanium dioxide or the like is preferably used.

  The oxide semiconductor (for example, electron transporter) 12 is usually made of titanium dioxide or the like (n-type metal oxide semiconductor), and preferably a granular body or a linear body (acicular body, tubular body). , Columnar bodies, etc.) are preferred. At this time, it is preferable that an average particle diameter or an average wire diameter is 5-500 nm, and it is more preferable that it is 10-200 nm. There is a tendency that miniaturization of the material with an average particle diameter or an average wire diameter of less than 5 nm tends to be difficult, and when the average particle diameter exceeds 500 nm, the junction area becomes small and the photocurrent tends to become extremely small.

As the oxide semiconductor 12, titanium oxide (TiO ₂ ) is optimal, and as other materials, titanium (Ti), zinc (Zn), tin (Sn), niobium (Nb), indium (In), yttrium (Y), lanthanum (La), zirconium (Zr), tantalum (Ta), hafnium (Hf), strontium (Sr), barium (Ba), calcium (Ca), vanadium (V), tungsten (W), etc. Non-metallic elements such as nitrogen (N), carbon (C), fluorine (F), sulfur (S), chlorine (Cl), phosphorus (P), etc. One or more of these may be contained. Titanium oxide or the like is preferable because it has an electron energy band gap in the range of 2 to 5 eV, which is larger than the energy of visible light. The oxide semiconductor 12 is preferably an n-type semiconductor whose conduction band is lower than the conduction band of the dye at the electron energy level.

  The porosity of the oxide semiconductor 12 is preferably 20 to 80%, and more preferably 40 to 60%. When the oxide semiconductor 12 has such a porosity, the surface area of the light working electrode can be increased by 1000 times or more, and light absorption, power generation, and electron conduction can be performed efficiently.

  The thickness of the oxide semiconductor 12 is preferably 0.1 to 50 μm, and more preferably 1 to 20 μm. If the thickness is less than 0.1 μm, the photoelectric conversion action is remarkably reduced and is not suitable for practical use. If the thickness exceeds 50 μm, light transmission becomes difficult.

  When the oxide semiconductor 12 is made of titanium dioxide, the manufacturing method is as follows.

First, acetylacetone is added to TiO ₂ anatase powder, and then kneaded with deionized water to prepare a titanium dioxide paste stabilized with a surfactant. Next, the prepared paste is applied at a constant speed onto the conductive film 11b of the conductive substrate 11 by a doctor blade method, and is 300 ° C to 600 ° C in air, preferably 400 ° C to 500 ° C, preferably 10 minutes to The porous oxide semiconductor 12 is formed by processing for 60 minutes, preferably 20 to 40 minutes.

<Photoexciter>
Photoexcitation body 13 in the present invention is state, and are not attached to the surface of the oxide semiconductor 12, that contain a carboxyl group.

  As the photoexciter 13, the photocurrent efficiency (incident photon to current efficiency; IPCE) with respect to incident light has a so-called sensitivity, such as the absorption wavelength of the electrolyte 14 in FIGS. 1 and 2, and the absorption of the amorphous semiconductor layer 16 in FIG. What has the characteristic extended to the long wavelength side rather than the wavelength is preferable. In particular, since it is rarely absorbed by the electrolyte 14 or the like, it is particularly effective that the absorption peak has a peak sensitivity at a wavelength longer than about 700 nm.

  As such a photoexciter 13, a bis-type squarylium cyanine dye is effective because the peak wavelength of IPCE is close to 800 nm. Azurenium salt compounds, squalinic acid derivatives, triallylpyrazoline, hydrazone derivatives, biphenyldiamine derivatives, tri-p-tolylamine (TPTA), trisazo pigments, τ-type non-metals with high sensitivity (IPCE) at wavelengths of 700 nm or more Photoexciters 13 such as phthalocyanine, titanyl phthalocyanine, squarylium cyanine, black dye, coumarin, β-diketonate, Re complex, Os complex, Ni complex, Pd complex, Pt complex, phthalocyanine derivative and porphyrin derivative are preferred.

Among the photoexciters 13, when used together with an electrolyte 14 having a pH of 2.4 to 6 described later, the light absorption peak is greatly shifted to the long wavelength side, and the long wavelength component of light is sufficiently absorbed. Since the effect that it can be obtained is obtained, a black die is preferably used as a photoexciter .

  Examples of the method for adsorbing the photoexciter 13 on the porous oxide semiconductor 12 include a method in which the conductive substrate 11 on which the oxide semiconductor 12 is formed is immersed in a solution in which the photoexciter 13 is dissolved. In this case, the temperature of the solution and the atmosphere is not particularly limited, and may be room temperature under atmospheric pressure, for example. Further, the immersion time can be appropriately adjusted depending on the photoexciter 13, the type of solvent, the concentration of the solution, and the like. Thereby, the photoexciter 13 can be adsorbed to the porous oxide semiconductor 12.

Examples of the solvent used for dissolving the photoexciter 13 include one or a mixture of two or more alcohols such as ethanol, ketones such as acetone, ethers such as diethyl ether, nitrogen compounds such as acetonitrile, and the like. . In this case, the concentration of the photoexciter 13 in the solution is preferably about 5 × 10 ⁻⁵ to 2 × 10 ⁻³ mol / l (l: liter (1000 cm ³ )).

<Transparent conductive layer>
The transparent conductive layer 17 in the present invention is disposed so as to face the oxide semiconductor 12 with a space therebetween, and is used as a counter electrode of the conductive substrate 11. An interval between the transparent conductive layer 17 and the oxide semiconductor 12 is set so that an amount of an electrolyte 14 (described later) sufficiently acts in the photoelectric conversion device.

The transparent conductive layer 17 is preferably a tin-doped indium oxide layer (ITO layer) or an impurity-doped indium oxide layer (In ₂ O ₃ layer) formed by a low-temperature growth sputtering method or a low-temperature spray pyrolysis method. In addition, an impurity-doped zinc oxide layer (ZnO layer) formed by a solution growth method may be used, and an ITO layer, an In ₂ O ₃ layer, or a ZnO layer may be stacked.

Furthermore, tin dioxide layer forming the fluorine doped by thermal CVD: may be used _(SnO 2 F layer) or the like. In addition, an impurity-doped indium oxide layer (In ₂ O ₃ layer) or the like can be used.

  Other film forming methods include vacuum deposition, ion plating, dip coating, and sol / gel.

  The translucent conductive layer 17 preferably has irregularities on the surface. The irregularities are preferably of the order of the wavelength of the incident light, so that a sufficient light confinement effect can be obtained.

  The transparent conductive layer 17 may be a thin metal layer that can transmit light and is made of Au, Pd, Al, or the like formed by a vacuum deposition method, a sputtering method, or the like.

<Electrolyte>
The electrolyte 14 in the present invention is provided between the oxide semiconductor 12 and the transparent conductive layer 17 and has a pH of 2.4 to 6. When the pH exceeds 6, the light absorption peak shifts to the short wavelength side, and the long wavelength sensitivity decreases, so that it is difficult to achieve high efficiency. If the pH is less than 2.4, the dye skeleton of the photoexciter 13 tends to be broken. In particular, the electrolyte 14 preferably has a pH of 3 to 5.5. When the pH is within this range, the long wavelength sensitivity can be sufficiently increased, and the efficiency of the photoelectric conversion device can be increased. Become. In the present invention, the pH of the electrolyte 14 is a pH meter to which the glass electrode method defined in JIS Z 8802 is applied (for example, a handy type pH meter manufactured by Sato Keiki Seisakusho Co., Ltd .: SK-620PH, etc.). PH value measured at 25 ° C. In addition, since the pH value is calculated by measuring the potential difference between the electrodes in the pH meter, the measured pH value can be represented by a potential. For example, pH 6 can be converted to 39 mV, and pH 3 to 5 can be converted to 88 to 187 mV.

  The electrolyte used in the conventional dye-sensitized solar cell was considered to be reduced in conversion efficiency by making the electrolyte acidic, so that an almost neutral one was used. By controlling the pH of 14 within the range of 2.4 to 6 and weak acidity, the conversion efficiency is improved more than that of the neutral electrolyte.

  As the electrolyte 14, an electrolytic solution is preferable because it exhibits the best carrier movement, and a gel electrolyte to which a gelling agent is added is preferable because liquid leakage can be prevented.

Iodides and acids (inorganic acids) are preferably used as those contained in the electrolyte having an acidity of pH 2.4 to 6. These are used as an acidity adjusting material for adjusting the acidity by being contained in the electrolyte.

Iodides include alkali metal iodides such as Li, Na, and K, alkaline earth metal iodides such as Mg and Ca, and alkylammonium and imidazolium salt iodides in combination with I ₂ to adjust the pH. It is possible to adjust. Among these, the combination of LiI, an imidazolium salt iodide and I ₂ is preferable in that the open circuit voltage can be improved. Two or more kinds of the electrolytes 14 may be mixed and used.

  In addition to iodide, bromide and cobalt complexes can be used to cause a redox reaction. In the present invention, the redox level (redox level) is compatible with titanium oxide and photoexciters. Iodide is preferred because a high voltage (Voc) is expected.

Inorganic acid used as the acid, HCl, Ru consists of at least one kind of HNO ₃ or _H 2 SO _4.

  Solvents used for the electrolyte 14 include carbonate compounds such as ethylene carbonate and propylene carbonate; heterocyclic compounds such as 3-methyl-2-oxazolidinone; ether compounds such as dioxane and diethyl ether; ethylene glycol dialkyl ether and propylene glycol dialkyl ether. , Polyethylene glycol dialkyl ether, polypropylene glycol dialkyl ether, ethylene glycol monoalkyl ether, propylene glycol monoalkyl ether, ethers such as polyethylene glycol monoalkyl ether, polypropylene glycol monoalkyl ether; alcohols such as methanol and ethanol; ethylene glycol, Propylene glycol, polyethylene glycol Polypropylene glycol, polyhydric alcohols such as glycerin; acetonitrile, glutarodinitrile, methoxy acetonitrile, propionitrile, nitrile compounds such as benzonitrile; dimethyl sulfoxide, aprotic polar substances such as sulfolane, and water. Of these, carbonate compounds and nitrile compounds are preferred. These solvents can be used alone or in admixture of two or more.

  In addition, a room temperature molten salt (ionic liquid) that is non-volatile and is a salt at room temperature can be used instead of the solvent or the like. For example, as the molten salt, an iodide such as an imidazolium salt, a quaternary ammonium salt, an isoxazolidinium salt, an isothiazolidinium salt, a pyrazolidium salt, a pyrrolidinium salt, or a pyridinium salt can be used.

  Examples of the molten salt iodide include 1,1-dimethylimidazolium iodide, 1, methyl-3-ethylimidazolium iodide, 1-methyl-3-pentylimidazolium iodide, 1-methyl- 3-isopentylimidazolium iodide, 1-methyl-3-hexylimidazolium iodide, 1-methyl-3-ethylimidazolium iodide, 1,2-dimethyl-3-propylimidazole iodide, 1-ethyl- Examples thereof include 3-isopropylimidazolium iodide, 1-n-hexyl-3-methylimidazolium iodide, and pyrrolidinium iodide.

  The gel electrolyte 14 is roughly divided into a chemical gel and a physical gel. A chemical gel forms a gel by a chemical bond by a cross-linking reaction or the like, and a physical gel is gelled near room temperature by a physical interaction. In order to sufficiently penetrate the oxide semiconductor 12, an electrolyte 14 made of a chemical gel having a low viscosity at room temperature is preferable.

  As a gelling agent constituting an electrolyte composed of a chemical gel, generally reported gelling agents can be used. For example, a compound having two or more nitrogen-containing heterocycles and a compound containing two or more halogen-containing groups capable of forming an onium salt can be used.

  Examples of the compound having two or more nitrogen-containing heterocycles described above include polyvinylimidazole, poly (4-vinylpyridine), polybenzimidazole, bipyridyl, terpyridyl, polyvinylpyrrole, 1,4-di (4-pyridyl). Examples include butane and 2- (4-pyridyl) ethyl ether.

  Examples of the compound containing two or more halogen-containing groups include dibromomethane, dibromoethane, dibromopropane, dibromobutane, dibromopentane, dibromohexane, dibromoheptane, dibromooctane, dibromononane, dibromodecane, and dibromoundecane. , Dibromododecane, dibromotridecane, dichloromethane, dichloroethane, dichloropropane, dichlorobutane, dichloropentane, dichlorohexane, dichloroheptane, dichlorooctane, dichlorononane, dichlorodecane, dichloroundecane, dichlorododecane, dichlorotridecane, diiodomethane, diiodoethane, Diiodopropane, diiodobutane, diiodopentane, diiodohexane, diiodoheptane, diiodooctane, diiodo Nan, diiododecane, diiodoundecane, diiodododecane, diiodotridecane, 1,2,4,5-tetrakisbromomethylbenzene, epichlorohydrin oligomer, epibromohydrin oligomer, hexabromocyclododecane, tris (3 , 3-dibromo-2-bromopropyl) isocyanuric acid, 1,2,3-tribromopropane, diiodoperfluoroethane, diiodoperfluoropropane, diiodoperfluorohexane, polyepichlorohydrin, polyepichlorohydrin and polyethylene ether And polyfunctional halides such as polyepibromohydrin and polyvinyl chloride. These halides can be used alone or in combination of two or more.

  Gel electrolytes contain a low-viscosity precursor (liquid phase) in which a gelling agent is mixed in an electrolyte solution in a porous oxide semiconductor, and are used for heating, ultraviolet irradiation, electron beam irradiation, natural standing, etc. It can be gelled by causing a two-dimensional or three-dimensional crosslinking reaction.

  Examples of the polymerization method in the gelation include photopolymerization, thermal polymerization, and natural standing, and can be appropriately selected depending on the constituent material used. As the porous oxide semiconductor of the dye-sensitized solar cell, titanium oxide that causes a catalytic reaction with light in the ultraviolet region is often used. When photopolymerization is performed in such a case, problems such as decomposition of the dye adsorbed on the porous oxide semiconductor can be considered. Therefore, the polymerization is preferably performed by thermal polymerization or natural standing.

  In the gelation of the electrolyte precursor by the thermal polymerization, it is preferable to heat the photoelectric conversion device 1 (battery unit). It is preferable that the temperature of heat processing shall be in the range of 50-200 degreeC. This is due to the following reason. That is, when the temperature of the heat treatment is less than 50 ° C., the degree of polymerization of the gel is lowered, and it may be difficult to form a gel. On the other hand, when heat treatment is performed at a high temperature exceeding 200 ° C., the dye is likely to be decomposed. More preferably, the temperature of heat processing is 70-150 degreeC.

<Catalyst layer>
The catalyst layer 15 is a layer for lowering the overvoltage and securing an ohmic junction between the electrolyte 14 and the thin film photoelectric converter 2. The overvoltage refers to a large voltage that is first applied to operate the photoelectric conversion device 1.

  For example, FIG. 2 shows a function of facilitating transfer of charges between the electrolyte 14 and the amorphous semiconductor layer 16.

  Examples of the catalyst layer 15 include Pt, Pd formed by vacuum deposition, sputtering, thermal decomposition of a coated complex, or polyethylenedioxythiophene (PEDOT; polystyrene sulfonate) formed by spin coating. In addition, an organic semiconductor material such as polyvinyl carbazole formed by an electrodeposition method, carbon, or the like is used. Moreover, what laminated | stacked these can also be used.

<Translucent covering>
As a material for the translucent covering 18, a fluororesin, a silicone polyester resin, a high weather resistance polyester resin, a polyvinyl chloride resin, or the like may be used, or an acrylic, urethane, silicone, Resins such as silane coupling agents or mixtures thereof are particularly preferred because of excellent weather resistance. Other materials include resin sheets such as PET (polyethylene terephthalate), PEN (polyethylene naphthalate), polyimide, and polycarbonate, inorganic sheets such as white plate glass, soda glass, borosilicate glass, and ceramics, and organic-inorganic hybrid sheets.

  The thickness of the translucent covering 18 is 0.1 μm to 6 mm, preferably 1 μm to 4 mm. In addition, antiglare, heat shield, heat resistance, low contamination, antibacterial, antifungal, design, high workability, scratch resistance / wear resistance, snow sliding, antistatic, far infrared radiation, acid resistance By providing the light-transmitting covering 18 with properties, corrosion resistance, environmental compatibility, and the like, reliability and merchantability can be further improved.

  In the case of the configuration of FIG. 2, the thin film photoelectric conversion body 2 may be formed in advance as long as the translucent covering 18 has a thickness having sufficient mechanical strength and can be used as a support. In this case, the thickness of the translucent covering 18 is preferably 0.05 mm to 2 mm, and more preferably 0.1 mm to 1 mm.

  Further, the surface on the light incident side of the translucent covering 18 may be flat, but may be a surface having irregularities in the order of the wavelength of incident light, in which case there is a light confinement effect.

<Underlayer>
Although the base layer is not shown, in the structure of FIGS. 1 and 2, the oxide semiconductor as a base layer is thin (thickness 0.05 μm to 2 μm) and dense between the conductive substrate 11 and the oxide semiconductor 12. A layer can be inserted, which makes it possible to suppress the occurrence of reverse current.

<Amorphous semiconductor layer>
The photoelectric conversion device of the present invention can include an amorphous semiconductor layer 16 between the oxide semiconductor 12 and the transparent conductive layer 17 (see FIG. 2). The amorphous semiconductor layer 16 is located closer to the light irradiation side than the oxide semiconductor 12 and absorbs a short wavelength component (about 300 to 700 nm) of light. Since the oxide semiconductor 12 absorbs a long-wavelength component of light, the provision of the amorphous semiconductor layer 16 and the oxide semiconductor 12 enables absorption of light complementary to each other.

  When the photoelectric conversion device of the present invention includes the amorphous semiconductor layer 16, since the amorphous semiconductor layer 16 and the oxide semiconductor 12 are connected in series, it is necessary that the current values of each other are matched. . For this purpose, a current equivalent to the current generated in the amorphous semiconductor layer 16 must be generated from the oxide semiconductor 12. In order to generate a current equivalent to that of the amorphous semiconductor layer 16 located on the light incident side from the oxide semiconductor 12, the long wavelength component of the light that is transmitted without being absorbed by the amorphous semiconductor 16 is changed to the oxide. It is necessary to use it for generating current in the semiconductor 12. In the present invention, by setting the pH of the photoelectrolyte to 2.4 to 6, a current equivalent to that of the amorphous semiconductor layer 12 can be generated from the oxide semiconductor 16 due to its high conversion efficiency.

  The amorphous semiconductor layer 16 may be an amorphous silicon thin film pin junction layer or a compound semiconductor thin film junction layer such as CIGS (CuInGaSe). These junction layers are preferably those that generate an internal electric field such as a pin junction type, a pn junction type, a Schottky junction type, and a hetero junction type.

  The amorphous semiconductor layer 16 has translucency in order to allow incident light to reach the oxide semiconductor 12 located below the amorphous semiconductor layer 16.

  The amorphous semiconductor layer 16 is preferably a pin junction hydrogenated amorphous silicon semiconductor layer continuously deposited by plasma CVD. Although the pin junction is provided with a p-type semiconductor layer on the catalyst layer 15 side, a nip junction that is a reverse junction may be used.

  Here, when the i-type semiconductor layer constituting the amorphous semiconductor layer 16 is amorphous, at least one of the p-type semiconductor layer and the n-type semiconductor layer has microcrystals, or a hydrogenated amorphous silicon alloy A system layer may be used. For example, the p-type semiconductor layer on the light incident side is more preferably made of hydrogenated amorphous silicon carbide because it can improve translucency and reduce light loss.

  Another deposition method for forming the amorphous semiconductor layer 16 may be a catalytic CVD method or the like. When the plasma CVD method and the catalytic CVD method are combined, the hydrogen content can be increased, and photodegradation of the amorphous semiconductor layer 16 can be suppressed, and the reliability is improved.

In addition, the amorphous semiconductor layer 16 is preferable because it can be continuously deposited under the respective film forming conditions by chemical vapor deposition. More specifically, for example, it is a p-type a-Si: H (H-doped amorphous silicon) layer, and in the case of film formation, SiH ₄ gas, H ₂ gas, B ₂ H ₆ gas (500 ppm for H ₂ ) are used as source gases. The flow rates of these gases are each optimized. The thickness of the p-type a-Si: H layer is preferably in the range of 50 to 200 mm, more preferably 80 to 120 mm. If it is thinner than 50 mm, an internal electric field cannot be formed, and if it is thicker than 200 mm, light loss increases.

Further, for example, the intrinsic amorphous amorphous semiconductor layer is an i-type a-Si: H layer, and when forming a film, SiH ₄ gas and H ₂ gas are used as source gases, and the flow rates of these gases are optimized. Turn into. The thickness of the i-type a-Si: H layer is preferably in the range of 500 to 5000 mm (0.05 μm to 0.5 μm), more preferably 1500 to 2500 mm (0.15 μm to 0.25 μm). If the thickness is less than 500 mm, sufficient photocurrent cannot be obtained. If the thickness is more than 5000 mm, light cannot be transmitted to the dye-sensitized photoelectric conversion body 3 on the rear side.

Further, for example, when forming an n-type a-Si: H layer, a raw material gas (diluted to 1000 ppm with H ₂ ) is used, and the flow rates of these gases are optimized. The thickness of the n-type a-Si: H layer is preferably in the range of 50 to 200 mm, more preferably 80 to 120 mm. If it is thinner than 50 mm, an internal electric field cannot be formed, and if it is thicker than 200 mm, light loss increases.

  The temperature of the conductive substrate 11 when forming the silicon-based semiconductor layer 16 is preferably in the range of 150 ° C. to 300 ° C., and more preferably in the range of 180 ° C. to 240 ° C. in any layer. Even if the temperature is lower than 150 ° C. or higher than 300 ° C., a suitable optical semiconductor cannot be obtained.

  Hereinafter, manufacturing methods and characteristic values of photoelectric conversion devices having different manufacturing conditions and the like will be described.

Example 1
As a conductive substrate, porous titanium dioxide as an electron transporter was formed on a titanium sheet having a thickness of 0.3 mm (size 2 cm × 2 cm). A method for producing the porous titanium dioxide will be described below.

First, acetylacetone was added to a TiO ₂ anatase powder, and then kneaded with deionized water and stabilized with a surfactant to prepare a titanium oxide paste. The prepared paste is applied by a doctor blade method onto the surface of the titanium layer on which the transparent conductive film is formed at a constant rate and baked in the atmosphere at 450 ° C. for 30 minutes to thereby form the porous dioxide. Titanium was produced.

  Using a black dye (manufactured by Solaronics) as a dye, and using acetonitrile and t-butanol (1: 1 by volume) as a solvent for dissolving the dye, a titanium sheet having a titanium dioxide layer formed thereon The pigment was supported on the titanium dioxide layer. The immersion time was 24 hours, and the temperature of the conductive substrate at that time was 24 ° C.

  Next, the sheet obtained by coating platinum on a PET film with an ITO film by a sputtering apparatus and the titanium sheet with titanium dioxide supporting the dye are faced together, and the following electrolyte is added between them and lightly bonded together. A photoelectric conversion device was prepared and used for characteristic evaluation.

Here, I ₂ (0.05 mol / l), LiI (1.0 mol / l), and HCl (0.06 mol / l), which are liquid electrolytes, are mixed with a solvent acetonitrile as an electrolyte, and measured by a pH measuring device. The pH value was adjusted to 4.0 (138 mV).

(Comparative example)
In the same manner as in Example 1 except that 0.1 mol / l LiI is contained in the electrolyte, HCl is not contained, and the pH value measured by the pH meter is 6.4 (19 mV). A photoelectric conversion device of a comparative example was produced.

(Example 2)
A photoelectric conversion device of Example 2 was produced in the same manner as Example 1 except that the electrolyte did not contain HCl and the pH value measured by the pH meter was 5.0 (88 mV).

(Example 3)
Example 3 was the same as Example 1 except that 0.13 mol / l HNO ₃ was contained in the electrolyte instead of HCl, and the pH value measured by the pH meter was 3.1 (182 mV). A photoelectric conversion device was manufactured.

Example 4
The photoelectric conversion device of Example 4 was produced in the same manner as in Example 1 except that 0.2 mol / l HCl was contained in the electrolyte and the pH value measured by the pH meter was 1.6 (256 mV). did.

(Example 5)
The electrolyte contains 0.1 mol / l of LiI, and further contains a pyridine-based additive (0.2 mol / l) instead of HCl. The pH value measured by the pH meter is 5.6 (59 mV). The photoelectric conversion device of Example 5 was produced in the same manner as in Example 1 except that.

(Example 6)
The electrolyte contains 0.1 mol / l LiI, and further contains a pyridine-based additive (0.3 mol / l) instead of HCl, and the pH value measured by the pH meter is 6.0 (39 mV). The photoelectric conversion device of Example 6 was produced in the same manner as in Example 1 except that.

(Example 7)
The electrolyte contains 0.05 mol / l of LiI, and further contains a pyridine-based additive (0.5 mol / l) instead of HCl. The pH value measured by the pH meter is 6.9 (− A photoelectric conversion device of Example 7 was produced in the same manner as Example 1 except that the voltage was 5 mV).

(Example 8)
The photoelectric conversion device of Example 8 is the same as Example 1 except that 0.03 mol / l HCl is contained in the electrolyte and the pH value measured by the pH meter is pH = 4.6 (108 mV). Was made.

Example 9
Example 3 was the same as Example 1 except that 0.07 mol / l of HNO ₃ was contained in the electrolyte instead of HCl, and the pH value measured by the pH meter was 3.6 (157 mV). A photoelectric conversion device was manufactured.

(Example 10)
Example 1 was carried out in the same manner as Example 1 except that 0.2 mol / l CH ₃ COOH was contained in the electrolyte instead of HCl, and the pH value measured by the pH meter was 2.4 (216 mV). 3 photoelectric conversion devices were produced.

The photoelectric conversion efficiencies of the dye-sensitized solar cells of Examples 1 to 10 and Comparative Example 1 obtained as described above under the conditions of 25 mC, AM1.5, and 100 mW / cm ² were obtained. It was measured. In addition, as pH measurement, the handy type pH meter SK-620PH manufactured by Sato Keiki Seisakusyo Co., Ltd., to which the glass electrode method defined in JIS Z 8802 was applied was used.

  For each measured photoelectric conversion efficiency, the photoelectric conversion efficiency of Comparative Examples was used as a reference (100), and the photoelectric conversion efficiencies of Examples 1 to 10 were displayed as indices (photoelectric conversion efficiency index). Example 1 is 130, Example 2 is 120, Example 3 is 115, Example 4 is 93, Example 5 is 110, Example 6 is 105, Example 7 is 90, Example 8 is 125, Example 9 was 127, and Example 10 was 105.

  The plotted data is shown in FIG. 3 with pH on the horizontal axis and the above-mentioned index on the vertical axis.

  From the results of FIG. 3, it can be seen that the inflection points are present particularly at pH values of 3 and 5.5, and that the photoelectric conversion efficiency index is greatly improved within the range of 3 to 5.5.

  Next, a manufacturing method and characteristic values of a photoelectric conversion device (a stacked photoelectric conversion device) including an amorphous semiconductor layer will be described.

(Example 11)
On a glass substrate (size 1 cm × 2 cm) with a transparent conductive layer (SnO ₂ : F film (FTO film), sheet resistance 10Ω / □), first, as a second conductivity type silicon-based semiconductor layer, using a plasma CVD apparatus. A p-type a-Si: H layer, an i-type a-Si: H layer as an intrinsic amorphous silicon-based semiconductor layer, and an n-type a-Si: H layer as a first conductivity-type silicon-based semiconductor layer are successively formed. And it was made to deposit in a vacuum and the thin film photoelectric conversion body was produced.

At this time, SiH ₄ gas and B ₂ H ₆ gas (diluted with H ₂ ) were used as source gases for forming the p-type a-Si: H layer, and the flow rates of these gases were 2.7 sccm, respectively. , 9 sccm, and deposited with a thickness of 100 mm (0.010 μm).

Further, SiH ₄ gas and H ₂ gas were used as source gases for forming the i-type a-Si: H layer, and the flow rates of these gases were 5 sccm and 20 sccm, respectively, and were deposited with a thickness of 1500 Å.

Further, SiH ₄ gas, H ₂ gas, and PH ₃ gas (diluted with H ₂ ) are used as source gases for forming the n-type a-Si: H layer, and the flow rates of these gases are set to 2. 7 sccm, 37 sccm, and 2.8 sccm were deposited to a thickness of 200 mm.

  Note that the temperature of the glass substrate was 200 ° C. in any of the formation of the p-type a-Si: H layer, the i-type a-Si: H layer, and the n-type a-Si: H layer.

  Next, a Pt layer as a catalyst layer was deposited to a thickness of 0.01 μm on the n-type a-Si: H layer using a sputtering apparatus. At this time, since the Pt layer was thin, the resistance was high and the sheet resistance could not be measured.

Next, as a conductive film, a porous titanium dioxide layer was formed on a glass substrate (size 1 cm × 2 cm) with a transparent conductive film (SnO ₂ : F (FTO film), sheet resistance 10Ω / □).

  The titanium dioxide layer which is an oxide semiconductor (electron transporter) was formed as follows.

First, acetylacetone was added to TiO ₂ anatase powder, and then kneaded with deionized water to prepare a titanium dioxide paste stabilized with a surfactant. Next, the prepared paste was applied onto the transparent conductive film at a constant speed by a doctor blade method, and baked at 450 ° C. for 20 minutes in the air to form a porous titanium dioxide layer.

  Next, using a black die (manufactured by Solaronics) as a dye, acetonitrile and t-butanol (1: 1 by volume) as a solvent used for dissolving the dye, and a conductive substrate having a titanium dioxide layer formed thereon The dye was immersed in a solution in which the dye was dissolved, and the dye was supported on the titanium dioxide layer. The immersion time was 24 hours, and the temperature of the conductive substrate at that time was 24 ° C.

Next, a thin film photoelectric conversion body in which a catalyst layer is laminated and a glass substrate with a transparent conductive film on which a porous titanium dioxide layer carrying a dye is formed, and the titanium dioxide layer contains the following liquid electrolyte: By laminating lightly, a stacked photoelectric conversion device was manufactured. As the hole transporter (electrolyte), in the same manner as in Example 1, an acetonitrile solution containing liquid electrolytes I ₂ , LiI, and HCl was prepared, and the pH value measured by the pH meter was 4. Was used.

The obtained stacked photoelectric conversion device exhibited a relatively high short-circuit current density of 10.00 mA / cm ² and a high open-circuit voltage of 1.435 V at 100 mW / cm ² under AM 1.5.

As described above, in Example 11, the stacked photoelectric conversion device of the present invention could be easily manufactured, and high photoelectric conversion efficiency could be realized. In addition, the leakage current characteristic of the stacked photoelectric conversion device when no voltage was applied was good, and the current density at −1.6 V in the dark was 0.075 mA / cm ² .

It is sectional drawing which shows an example of the photoelectric conversion apparatus of this invention. It is sectional drawing which shows an example of the photoelectric conversion apparatus of this invention. It is a graph which shows the relationship between pH and a photoelectric conversion efficiency index | exponent. It is sectional drawing which shows an example of the conventional photoelectric conversion apparatus (normal incidence type). It is sectional drawing which shows an example of the conventional photoelectric conversion apparatus (back-incident type).

Explanation of symbols

1, 31, 51: Photoelectric conversion device 2: Thin film photoelectric conversion body (top cell)
3: Dye-sensitized photoelectric converter (bottom cell)
11, 21, 41: conductive substrates 12, 22, 42: oxide semiconductors 13, 23, 43: photoexciters 14, 24, 44: electrolytes 15, 25, 45: catalyst layer 16: amorphous semiconductor layer 17, 27, 47: Transparent conductive layers 18, 28, 48: Translucent covering

Claims (6)

A conductive substrate;
An oxide semiconductor formed on the conductive substrate;
A photoexciter containing a carboxyl group attached to the surface of the oxide semiconductor;
A transparent conductive layer disposed to face the oxide semiconductor with a gap therebetween;
An electrolyte having a pH of 2.4 to 6 and comprising at least one inorganic acid selected from the group consisting of HCl, HNO ₃ and H ₂ SO ₄ provided between the oxide semiconductor and the transparent conductive layer; ,
A photoelectric conversion device comprising:   The photoelectric conversion device according to claim 1, wherein the electrolyte has a pH of 3 to 5.5.   The photoelectric conversion device according to claim 1, wherein the electrolyte includes an iodide.   The photoelectric conversion device according to claim 3, wherein the iodide is at least one selected from the group consisting of alkali metal iodides, alkaline earth metal iodides, alkylammonium iodides, and imidazolium iodides. The photoelectric conversion device according to claim 1, wherein the transparent conductive layer has irregularities on a surface thereof. The photoelectric conversion device according to claim 1, further comprising an amorphous semiconductor layer having a light-transmitting property between the oxide semiconductor and the transparent conductive layer.

Images