JP2005243379A - Photoelectric conversion device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric conversion device with high efficiency having an improved etching workability while maintaining optical and electro-optical characteristics, and especially, easy to apply an integrated patterning. <P>SOLUTION: The photoelectric conversion device has a transparent electrode 2 made of tin oxide including zinc, indium oxide, or complex oxide composed of the above oxides; an electron transport layer 3 containing dye-stuff 4, formed on the transparent electrode 2; and a hole transport layer 6, arranged one on the other in this sequence. With this, the transparent electrode 2 with excellent etching workability can be formed while maintaining low resistance characteristics and high heat resistance, and patterning at the time of integration can be easily carried out. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a highly reliable photoelectric conversion device that can be suitably used particularly for solar cells, optical sensors, and the like.

  In recent years, dye-sensitized solar cells are a mainstream of low-cost solar cells that have been actively developed. This type of solar cell is characterized by low manufacturing costs because it does not use a vacuum device, is a low-temperature process, and has low material costs.

  Dye-sensitized solar cells often use a translucent substrate in order to utilize the high degree of freedom of cell configuration and color for product functionality. In this case, in order to maintain the function as an electrode, it is common to form a transparent conductive film on glass or a resin substrate, and the material configuration of the transparent conductive film is variously selected according to the purpose. .

  Conventionally, indium tin oxide (ITO), fluorine-doped tin oxide (FTO), indium oxide (IO), or tin oxide (SnO2) is used as the material for the transparent conductive film formed on the light-transmitting substrate. (For example, see Patent Document 1).

  Further, as a low-resistance transparent conductive film excellent in heat resistance, a two-layer structure in which FTO is formed on ITO has been proposed (see, for example, Patent Document 2).

Furthermore, as an attempt to change the film quality by adding impurities to the transparent conductive film, the chlorine concentration in the transparent conductive film mainly composed of tin oxide is 0.11% by mass, and the fluorine concentration in the transparent conductive film is the chlorine concentration The above proposal has been made (see, for example, Patent Document 3).
JP 2002-100787 A JP 2003-323818 JP 2001-36107 A

  However, the transparent conductive film composed of metal oxide cannot obtain the same electrical resistance value as a low-resistance metal. Therefore, when increasing the area, it is necessary to connect in series or in parallel after patterning. However, each of the above-described examples has the following problems at least in either the process aspect or the quality aspect.

That is, the photovoltaic device disclosed in Patent Document 1 has a pair of electrodes via a semiconductor mainly composed of titanium oxide, and at least one of the electrodes is substantially transparent. It is said. Among these, metal oxides listed as transparent electrode materials are indium tin oxide (ITO), fluorine-doped tin oxide (FTO), non-doped indium oxide (IO), or tin oxide (SnO ₂ ). However, when ITO is used, since the heat resistance is poor, the specific resistance value increases during the heating process such as when the titanium oxide layer is formed, and the device characteristics are greatly deteriorated. In addition, since an aqua regia type etchant is used at the time of etching, a material such as Al of the collecting electrode to be formed is corroded, and there is a problem in terms of workability. Further, when FTO is used, although there is no problem in heat resistance and resistance value, there is a problem that patterning processing required at the time of integration is difficult due to extremely poor etching processability. Moreover, since IO or SnO ₂ not doped with impurities has a low carrier concentration, it has a high resistance value and is not suitable as a transparent conductive film material for solar cells.

  In the technique disclosed in Patent Document 2, a low-resistance transparent conductive film excellent in heat resistance is realized by adopting a two-layer structure in which FTO is formed on ITO. The improvement in heat resistance is interpreted to be due to the suppression of oxidation during heating of the oxygen deficient portion of ITO. However, since the FTO is coated on the upper portion, the etching processability is poor, and there is a problem that the patterning process required at the time of integration becomes difficult.

  Furthermore, in the substrate for a photoelectric conversion device disclosed in Patent Document 3, the light transmittance is improved and the haze rate is controlled by controlling the chlorine and fluorine concentrations, but depending on the addition of impurities, the etching processability is improved. However, as in the case of Patent Document 2, there is a problem that the patterning process required for integration is difficult.

  Accordingly, the present invention has been made in view of the above-described problems, and a photoelectric conversion device that improves etching processability while maintaining the optical and electrical characteristics of the transparent electrode, and that is particularly easy to perform integrated patterning. The purpose is to provide.

  The photoelectric conversion device of the present invention includes a transparent electrode made of tin oxide containing zinc, indium oxide containing zinc, or a composite oxide thereof, and an electron transporter having a dye formed on the transparent electrode It is characterized by comprising.

  In addition, the photoelectric conversion device of the present invention includes a large amount of zinc particularly on the electron transporter side of the transparent electrode.

  Since the photoelectric conversion device of the present invention comprises a transparent electrode made of tin oxide or indium oxide containing zinc or a composite oxide thereof, and an electron transporter formed on the transparent electrode and having a dye. In addition, the presence of zinc makes it possible to maintain the low resistance characteristics and high heat resistance of the transparent electrode, and contribute to the formation of an amorphous material. When the transparent electrode is amorphous, the etching processability is improved. In particular, since a large amount of zinc element is contained on the electron transporter side, the initial etching rate can be increased and the subsequent stable etching can be realized.

  As described above, it is possible to form a transparent electrode excellent in etching processability while maintaining low resistance characteristics and high heat resistance, thereby providing a photoelectric conversion device that can be easily patterned during integration. .

  Hereinafter, the photoelectric conversion device of the present invention will be described in detail. FIG. 1 is a cross-sectional view showing an embodiment of the photoelectric conversion device of the present invention, wherein 1 is a translucent substrate, 2 is a transparent electrode to be one electrode, 3 is a dye 4 and an electron generated by the dye 4 is shown. An electron transport layer which is an electron transporter to be transported, 5 is a counter electrode which is the other electrode, 6 is a hole transporter which transports holes generated by the dye 3, and 7 is a sealing material , 8 are conductive connection portions for connecting adjacent photoelectric conversion regions, and 9 is a counter substrate.

First, as long as the translucent substrate 1 has a function as a support, a resin material such as glass or PET (polyethylene terephthalate) can be used. The transparent electrode 2 is a low-resistance material, and in particular, tin oxide, indium oxide, or a composite oxide thereof containing a small amount of zinc (0.1 ppm to 0.1 atomic%). Specifically, SnO ₂ doped with fluorine (F) or antimony (Sb), In ₂ O ₃ doped with SnO ₂ or manganese (Mn), In ₂ O ₃ —SnO ₂ such as In ₄ Sn ₃ O _12. Examples include complex oxides. Tin oxide, indium oxide or a composite oxide thereof has a high transmittance in the visible light region and can easily obtain a low resistance among transparent conductive materials. It is particularly suitable as a material.

  Here, a very small amount of zinc atoms contained in the transparent electrode 2 greatly contributes to improving the etching processability of the film by lowering the crystallinity (amorphizing) by causing lattice distortion. . This effect is more pronounced as the concentration of zinc atoms contained in the transparent electrode 2 is higher. However, when zinc atoms are contained in the transparent electrode 2 at a high concentration, the optical properties of the transparent electrode 2 are increased. The transmittance is lowered and the resistivity is increased, so that the short circuit current value and the fill factor of the element are not preferable. Therefore, in order to effectively improve the etching processability while maintaining the optical characteristics and electrical characteristics of the transparent electrode 2, the zinc atoms in the transparent electrode 2 are the most at the interface with the layer in contact therewith. It is preferable to be included. In particular, by containing a large amount of zinc atoms in the initial layer in etching, that is, on the electron transport layer 3 side, the etchant effectively penetrates into the film, and rapid etching becomes possible.

  The transparent electrode 2 can be easily formed by a film forming method such as a spray pyrolysis method, a paste method, or a dip coating method in addition to a vacuum film forming technique such as a sputtering method, a vapor deposition method, an ion plating method, or a CVD method. Can be formed.

  When forming by vacuum film formation, for example, when forming a fluorine-doped tin oxide layer containing zinc atoms by using a sputtering method, fluorine-doped tin oxide containing zinc atoms in advance is used as a sputtering target. A method of sputtering, a method of sputtering using pure zinc or a zinc oxide target and a fluorine-doped tin oxide target, a method of reactive sputtering of a fluorine-doped tin oxide target in a gas atmosphere containing zinc atoms, etc. Use.

On the other hand, when forming under atmospheric pressure, for example, when forming a fluorine-doped tin oxide layer containing zinc atoms using spray pyrolysis, DBTDA [(C ₄ H ₉ ) ₂ Sn (OCOCH ₃ ) ₂ ] A solvent containing zinc atoms, such as an ethanol solution containing zinc acetylacetonate monohydrate, in a solvent containing tin atoms and fluorine atoms, such as a mixed solution of an ethanol solution and an aqueous ammonium fluoride solution. It is formed by intermittent spraying on a heating substrate using a small amount of added material. As a raw material containing a tin atom, tin chloride (anhydrous), tin chloride pentahydrate, tetrabutyltin or the like may be used.

The electron transport layer 3 is made of In ₂ O ₃ , SnO ₂ , WO ₃ , ZnO, TiO ₂ , Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ , Ag ₂ O, MnO ₂ , Cu ₂ O ₃ , Fe ₂ O _3. , V ₂ O ₅ , Cr ₂ O ₃ , NiO, SrTiO _3, K ₄ NbO ₁₇ or a combination thereof is used. In addition, a band gap adjusting material or a material doped with a small amount of impurities may be used for the purpose of improving charge transport characteristics. Furthermore, the above materials may be used in combination. In particular, among the above materials, it is preferable to use titanium oxide typified by TiO ₂ or zinc oxide typified by ZnO. This is because, among metal oxides used as the electron transport layer 3, the carrier transport property is particularly excellent, the manufacturing process is simple, and the large-area film formation is easy. It is.

In addition, as long as the electron transport characteristics do not extremely decrease, a single semiconductor such as Si or Ge, a compound semiconductor such as CdSe, CdS, InP, Bi ₂ S ₃ , PbS, or ZnS, or those appropriately doped with impurities May be used as the electron transport layer 3.

  A layered oxide semiconductor layer may be inserted between the transparent electrode 2 and the electron transport layer 3. Thereby, the leakage current of the element is reduced and the open circuit voltage value is improved.

Dye 4 is ruthenium complex, phthalocyanine dye, cyanine dye, merocyanine dye, porphyrin dye, perylene dye, anthraquinone dye, azo dye, quinophthalone dye, naphthoquinone dye, quinacridone dye, triphenylmethane dye, xanthene dye, berylene dye, indigo dye, etc. It is preferable that the organic dye or inorganic dye is used. Further, considering the adsorptivity to the metal oxide semiconductor 3 and the charge transport property, the interlocking of carboxyl group, hydroxyl group, alkoxy group, sulfonic acid group, ester group, phosphonyl group, hydroxyalkyl, etc. in the molecule of the dye 4 It is preferable to have a group. In addition, the colorant here refers to a material that at least absorbs light in the visible light region and excites carriers, and may be any material that does not significantly impair the effects of the present invention. For example, a single semiconductor such as Si or Ge, a compound semiconductor such as CdSe, CdS, InP, Bi ₂ S ₃ , PbS, ZnS, or InN, or those in which impurities are appropriately doped may be used. Furthermore, organic-inorganic hybrid materials can be similarly applied.

  The counter electrode 5 is preferably made of a material having translucency and conductivity, and a transparent conductive layer formed on a support substrate is suitably used. Specifically, glass, transparent plastic, transparent resin, or the like is used for the support base. In addition, tin oxide, indium oxide, zinc oxide, or a composite oxide thereof is used for the transparent conductive layer. Furthermore, on the transparent conductive layer, a catalyst layer of platinum (Pt), carbon (C), rhodium (Rh), ruthenium (Ru), etc., in order to cause the reduction reaction of redox ions in the electrolytic solution at a sufficient rate. Is preferably formed.

  The sheet resistance of the counter electrode 5 is 20 Ω / □ or less, preferably 10 Ω / □ or less, and in order to achieve this, an extraction electrode made of a mesh metal or the like may be additionally formed. As a material for the extraction electrode, Ag, Al, Cu, Ti, Ni, Fe, Zn, Mo, W, or a compound thereof can be used. At this time, when a material having low corrosion resistance to the electrolytic solution is used, it is desirable to further provide a barrier layer having excellent corrosion resistance.

  The hole transport layer 6 uses a quaternary ammonium salt, a Li salt, or the like. As the composition of the electrolyte solution, for example, a solution prepared by mixing ethylene carbonate, acetonitrile, methoxypropionitrile, or the like with tetrapropylammonium iodide, lithium iodide, iodine, or the like can be used.

  As a material for the hole transport layer 6 instead of the above, a transparent conductive oxide, an electrolyte such as a gel electrolyte or a solid electrolyte, an organic hole transport agent, an ultrathin metal, and the like are preferable.

As the transparent conductive oxide, CuI, Cu ₂ O, CuS, CuInSe, CuInS, CuSCN, CoO, NiO, FeO, MoO _2, Cr ₂ O ₃ or the like is preferable.

  Gel electrolytes are roughly classified into chemical gels and physical gels. A chemical gel is a gel formed by chemical bonding by a cross-linking reaction or the like, and a physical gel is gelled near room temperature due to physical interaction. As a gel electrolyte, acetonitrile, ethylene carbonate, propylene carbonate, or a mixture thereof was polymerized by mixing a host polymer such as polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, polyacrylic acid, or polyacrylamide. A gel electrolyte is preferred. When using a gel electrolyte or solid electrolyte, a low-viscosity precursor is included in the oxide semiconductor layer, and a two-dimensional or three-dimensional crosslinking reaction is caused by means such as heating, ultraviolet irradiation, or electron beam irradiation. Can be gelled or solidified.

  As the ion conductive solid electrolyte, a solid electrolyte having a polymer chain such as polyethylene oxide, polyethylene oxide or polyethylene and a salt such as sulfonimidazolium salt, tetracyanoquinodimethane salt, dicyanoquinodiimine salt is preferable. As the molten salt of iodide, iodides such as imidazolium salt, quaternary ammonium salt, isoxazolidinium salt, isothiazolidinium salt, pyrazolidium salt, pyrrolidinium salt, pyridinium salt can be used.

  Examples of the molten salt of 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 and pyrrolidinium iodide.

Examples of the organic hole transporting agent include triphenyldiamine and OMeTAD. Imidazolium salt, triazolium salts and molten salt electrolyte and LiI such pyridinium salt, NaI, the mixture of KI and CaI ₂ and _{I 2,} or LiBr, NaBr, alcohols mixture of KBr and CaBr2 as Br2, nitrile compounds, carbonate compounds An electrolytic solution dissolved in is preferably used.

  The sealing material 7 preferably has a corrosion resistance against chemicals, a moisture absorption preventing function, and a sufficient adhesive strength, such as EVA (ethylene vinyl acetate copolymer resin), EEA (ethylene-ethyl acrylate copolymer), fluorine. Resins, epoxy resins, acrylic resins, saturated polyester resins, amino resins, phenol resins, polyamideimide resins, UV curable resins, silicone resins, fluororesins, urethane resins, or composites thereof can be used.

  The conductive connection portion 8 is an electrical connection portion of an adjacent cell, and a low resistance material such as a metal is used. Specifically, Ag, Al, Cu, Ti, Ni, Fe, Zn, Mo, W, or an alloy thereof or a compound containing these is preferable. The conductive connection portion 8 can be formed by using a vacuum film forming technique such as a vapor deposition method, a sputtering method, or a CVD method, or by a paste method, a dip coating method, a spray pyrolysis method, a dispenser method, or the like. Although FIG. 1 shows an example of series connection, it is possible to use any connection method in which parallel connection or a combination of both is used.

  As long as the counter substrate 9 has a function as a support, for example, a metal substrate, a resin material such as glass or PET can be used. However, when a conductive material is used, it is preferable to use the conductive material separately or to insulate the surface so that leakage does not occur during integration.

  According to the photoelectric conversion device of the present invention thus configured, the transparent electrode 2 made of tin oxide or indium oxide containing zinc or a composite oxide thereof, and the dye 4 formed on the transparent electrode 2 are provided. And an electron transport layer 3 that is an electron transporter that transports electrons generated by the dye 4 and a hole transport layer 6 that is a hole transporter that transports holes generated by the dye 4 in this order. Therefore, the presence of zinc makes it possible to maintain the low resistance characteristics and high heat resistance of the transparent electrode 2 and contribute to the amorphization. When the transparent electrode 2 is amorphous, the etching processability is improved. In particular, by containing a large amount of zinc on the electron transport layer 3 side, the initial etching rate can be increased, and stable etching thereafter can be realized.

  As described above, it is possible to form a transparent electrode excellent in etching processability while maintaining low resistance characteristics and high heat resistance, thereby providing a photoelectric conversion device that can be easily patterned during integration. .

First, a fluorine-doped tin oxide containing zinc atoms, which becomes the transparent electrode 2, was formed by sputtering on a glass substrate having a thickness of 1.1 mm that becomes the translucent substrate 1. For sputtering, a bias sputtering apparatus (manufactured by ULVAC, SBH-2306RE special type) was used, and binary sputtering with a 15 cmφ zinc oxide target and a fluorine-doped tin oxide target was performed. A shutter was provided on the substrate side of each target, and the film formation contribution rate from both targets was controlled by adjusting the opening. At this time, DC voltages of 400 to 490 V and 450 to 570 V were applied to the zinc oxide target and the fluorine-doped tin oxide target, respectively, and the sputtering current was set to 0.08 to 0.12 A and 0.55 to 0.7 A, respectively. Ar and O ₂ (however, 20% Ar dilution) were introduced as process gases at 35 sccm and 1 sccm, and the pressure in the film forming chamber was controlled to 0.5 to 0.7 Pa.

  Next, the acid resistant resist was screen-printed on the portion excluding the etching region, and then immersed in a 5 mol / l HCl solution at 25 ° C., and etching was performed while appropriately putting Mg pieces. Next, the substrate was immersed in an acetone solution to remove the acid resistant resist, and then the surface of the glass substrate was cleaned in ethanol.

Next, the TiO ₂ layer serving as the electron transport layer 3 in the same glass substrate formed partially. Specifically, a TiO ₂ paste with an average particle diameter of about 10 nm prepared from the sol-gel method is applied by screen printing, pre-dried at room temperature, and then subjected to sintering heat treatment in a muffle furnace at 450 ° C. for 30 minutes. I did it. Further, a TiO ₂ paste having an average particle size of about 50 to 100 nm was applied by screen printing in an amount of about 30% of the amount of the previous paste, and preliminarily dried at room temperature, followed by 450 ° C. × 30 in a muffle furnace. For 2 minutes. At this time, the thickness of the sintered TiO ₂ layer was about 9 μm, and was a porous shape. Thereafter, acidic TiO ₂ sol was added, and heat treatment was performed at 150 ° C. for 5 minutes.

Next, the substrate on which the TiO ₂ layer was formed was dissolved for about 15 hours in a ruthenium-tris transition metal complex dye dissolved in acetonitrile and t-butanol solvent to form the dye on the TiO ₂ layer. . During this time, the temperature of the solution was maintained at 60 ° C to 80 ° C.

  Next, a substrate in which a fluorine-doped tin oxide containing a zinc element to be the counter electrode 5 and a Pt layer are patterned on the glass substrate to be the counter substrate 9 is formed up to the dye layer, and becomes a sealing material. They were placed opposite each other through a thermoplastic epoxy resin, and the periphery was sealed by local heating, leaving an electrolyte injection hole (not shown). At this time, the transparent electrode 2 of one element and the counter electrode 5 of the adjacent element were connected via an Ag paste in order to make electrical contact between the adjacent elements.

  Subsequently, from an injection hole provided in the counter substrate 9, 0.1M iodine, 0.1M lithium iodide, 0.7M 1,2-dimethyl-3-propylimidazolium iodide to become the hole transport layer 6, 4- A solution prepared by mixing 8M of tertbutylpyridine and using methoxyacetonitrile as a solvent was used. Finally, the electrolyte injection hole was sealed with an epoxy resin.

In the above process, by adjusting the shutter opening at the time of sputtering, an element having a different content and profile of the zinc element to the transparent electrode 2 was produced, and the difference in the etching rate at the time of patterning was examined (see Table 1). reference).

Moreover, about the element produced by performing the etching process for a fixed time about each transparent electrode, the pseudo-sunlight with which incident light intensity was adjusted to 100 mW / cm < ² > was irradiated, and the characteristic evaluation was performed (refer Table 2). In the evaluation, the comparative example shows a case where fluorine-doped tin oxide not containing zinc is used for the transparent electrode 2. In Table 1, the zinc concentration was analyzed using an XRF (fluorescence X-ray analysis) apparatus (manufactured by Rigaku Corporation, model number RIX-2100) while etching in the depth direction. The measurement location is a 0.1 μm depth position from the substrate of the transparent electrode 2 (referred to as the substrate side in Table 1), a 0.5 μm depth position from the substrate (referred to as the center in Table 1), and the electron transport layer side. The measurement was carried out at a depth position of 0.1 μm from the surface (referred to as the electron transport layer side in Table 1).

As shown in Table 1, the fluorine-doped tin oxide film containing zinc atoms according to the present invention has an etching rate higher than that of the comparative example, and the effect becomes remarkable as the content of zinc atoms increases. I understand. This is considered to be caused by the fact that the crystallinity of the fluorine-doped tin oxide film was lowered by introducing zinc atoms as described above.

  Furthermore, as shown in Table 2, the element is reliably separated under the condition where the etching rate is high, thereby suppressing the leakage current and improving the open-circuit voltage and the fill factor as compared with the comparative example. I understand. However, when zinc atoms are contained at a high concentration throughout the film as in Example 1 of the present invention, the deterioration of the transmittance due to the decrease in crystallinity and the increase in the specific resistance value become remarkable, and the short circuit current value And the fill factor will decrease. On the other hand, when the zinc content is not uniform in the depth direction, particularly when it is contained at a high concentration in the vicinity of the interface with the other layer in contact with the transparent electrode (Examples 4 and 5), etching is performed. It is possible to suppress a decrease in the transmittance of the transparent electrode and an increase in the specific resistance value while maintaining the advantages due to the improved rate. Therefore, under these conditions, a significant decrease in the short circuit current value and the fill factor of the element was suppressed, and a conversion efficiency sufficiently higher than that of the comparative example could be realized.

  As described above, by including zinc atoms in the transparent electrode portion, the etching processability is improved, and the patterning process required for integration is facilitated. At the same time, characteristic deterioration due to patterning failure or the like is suppressed, and a highly efficient device can be manufactured.

  In the present invention, it is not limited to the application relating to the dye-sensitized solar cell as in the above example, but the thin film solar cell represented by the thin film silicon solar cell and the compound thin film solar cell, and the organic solar cell. It can also be used for transparent electrodes. Various adjustments and changes may be made without departing from the scope of the present invention.

It is sectional drawing which illustrates typically the photoelectric conversion apparatus of this invention.

Explanation of symbols

1: Translucent substrate 2: Transparent electrode 3: Electron transport layer 4: Dye 5: Counter electrode 6: Hole transport layer 7: Sealing material 8: Conductive connection portion 9: Counter substrate

Claims (2)

A transparent electrode comprising zinc-containing tin oxide, zinc-containing indium oxide or a composite oxide thereof, and an electron transporter having a dye formed on the transparent electrode A photoelectric conversion device. The photoelectric conversion device according to claim 1, wherein a large amount of zinc is contained on the electron transporter side of the transparent electrode.

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