Solar cell

Abstract

To provide a solar cell which can be manufactured at a low cost and can sufficiently generate power with indoor light.SOLUTION: The solar cell comprises at least a layer containing a photoelectric conversion material and a layer for transporting a positive charge, wherein the photoelectric conversion material is a phenolic resin. The phenolic resin has one or more hydroxyl groups and a substituent on an aromatic ring, and the substituent is preferably a hydrogen atom or an electron-donating group. In particular, the phenol-based resin preferably contains a resorcinol-formaldehyde resin as a main component. The phenolic resin preferably has a granular shape and an average particle diameter of 1 μm or more and 100 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a solar cell. [Background technology]

[0002] Micro-power equipment and wearable devices used indoors often use lithium primary batteries such as coin batteries and button batteries, as well as secondary batteries as power sources. When a primary battery runs out, it must be replaced with a new one. Secondary batteries usually need to be recharged every one or several days, necessitating the collection of the battery or device.

[0003] As a result, there is a growing demand for solar cells that can generate electricity using indoor light without the need for battery replacement or charging, and research and development of various low-cost solar cells is underway.

[0004] Among these, the dye-sensitized solar cell announced by Graetzel et al. of the École Polytechnique Fédérale de Lausanne, Switzerland, is attracting increasing attention for its practical application (see, for example, Patent Document 1 and Non-Patent Documents 1 and 2). The structure of this solar cell consists of a porous metal oxide semiconductor provided on a transparent conductive glass substrate, a dye adsorbed on its surface, an electrolyte having a redox pair, and a counter electrode. Graetzel et al. significantly improved the photoelectric conversion efficiency by increasing the surface area of ​​the metal oxide semiconductor electrode, such as titanium oxide, by making it porous, and by adsorbing a monomolecule of a ruthenium complex as the dye.

[0005] However, this solar cell requires a dye in addition to the metal oxide semiconductor such as titanium oxide that generates electric charges, which increases the material cost and makes the manufacturing process complicated. Also, depending on the stability of the dye, sufficient battery life may not be obtained.

[0006] Therefore, there is a demand for solar cells that can be manufactured at low cost and can generate sufficient electricity using indoor light. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 2664194 [Non-patent literature]

[0008] [Non-Patent Document 1] Nature,353(1991)737 [Non-patent document 2] J. Am. Chem. Soc., 115 (1993) 6382 Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a solar cell that can be manufactured at low cost and is capable of generating sufficient electricity using indoor light. [Means for solving the problem]

[0010] These objects can be achieved by the present invention as set forth in (1) to (9) below. (1) A solar cell comprising at least a layer containing a photoelectric conversion material and a layer that transports positive charges, wherein the photoelectric conversion material is a phenolic resin.

[0011] (2) The solar cell according to (1) above, comprising a layer containing the photoelectric conversion material and a solid hole transport layer serving as the layer for transporting positive charges, between a transparent electrode formed on a transparent substrate and an electrode formed on a transparent or opaque substrate.

[0012] (3) The solar cell according to (1) above, comprising a layer containing the photoelectric conversion material and a layer made of a liquid or gel containing a substance that can be oxidized or reduced, as the layer that transports positive charges, between a transparent electrode formed on a transparent substrate and an electrode formed on a transparent or opaque substrate.

[0013] (4) The solar cell according to any one of (1) to (3) above, wherein the phenolic resin has one or more hydroxyl groups and substituents on an aromatic ring, and the substituents are hydrogen atoms or electron-donating groups.

[0014] (5) The solar cell according to (4) above, wherein the electron-donating group is at least one selected from the group consisting of a hydroxyl group, an alkyl group, an alkyl alcohol group, an alkoxy group, and an alkoxyalkyl group.

[0015] (6) The solar cell according to (5) above, wherein the phenolic resin is mainly composed of a resorcinol-formaldehyde resin.

[0016] (7) The solar cell according to any one of (1) to (6) above, wherein the phenolic resin has a granular shape and an average particle size of 1 μm or more and 100 μm or less.

[0017] (8) The solar cell according to (2) or (3) above, wherein the layer containing the photoelectric conversion material has particles of the photoelectric conversion material fixed on the transparent electrode by a binder.

[0018] (9) The solar cell according to (8) above, wherein the binder contains a substance having electronic conductivity. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a solar cell that can be manufactured at low cost and is capable of generating sufficient power using indoor light. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a cross-sectional view schematically showing one example of the configuration of a solar cell of the present invention. [Figure 2] FIG. 1(a) is a diagram showing an example of the basic skeleton structure of a resorcinol-formaldehyde resin, and FIG. 1(b) is a diagram showing an outline of an example of the laminated structure of a resorcinol-formaldehyde resin. [Figure 3]FIG. 1 is a diagram showing an example of the absorption spectrum of a resorcinol-formaldehyde resin. DETAILED DESCRIPTION OF THE INVENTION

[0021] Preferred embodiments of the present invention will be described in detail below. [1] Solar cells First, the solar cell of the present invention will be described.

[0022] Fig. 1 is a cross-sectional view schematically showing an example of the configuration of a solar cell of the present invention. Fig. 2(a) is a diagram showing an example of the basic skeleton structure of a resorcinol-formaldehyde resin, and Fig. 2(b) is a diagram showing an example of the laminate structure of a resorcinol-formaldehyde resin. Fig. 3 is a diagram showing an example of the absorption spectrum of a resorcinol-formaldehyde resin.

[0023] The solar cell 1 of the present invention is a solar cell comprising at least a layer 10 containing a photoelectric conversion material and a layer 20 that transports positive charges. The photoelectric conversion material is a phenolic resin.

[0024] Phenolic resins as photoelectric conversion materials have a band gap corresponding to the visible light region and can generate charges in the visible light region. In addition, phenolic resins can generate charges without pigments and are less expensive than materials used in conventional solar cells.

[0025] Thus, the solar cell 1 of the present invention, which is configured such that the photoelectric conversion material contains a phenolic resin, can be manufactured at low cost and can generate sufficient electricity using indoor light.

[0026] First Embodiment The solar cell according to the first embodiment will be described below.

[0027] The solar cell 1 according to the first embodiment shown in FIG. 1 comprises a layer 10 containing a photoelectric conversion material and a solid hole transport layer 20 that transports positive charges, between a transparent electrode 30 formed on a transparent substrate 31 and an electrode 40 formed on a transparent or opaque substrate 41.

[0028] [1-1]Transparent electrode The transparent electrode 30 is an electron collecting electrode that receives electrons generated in the layer 10 containing a photoelectric conversion material. In other words, the transparent electrode 30 functions as a negative electrode.

[0029] The transparent electrode 30 is, for example, one that is generally used in solar cells and is made of a material that is conductive and translucent.

[0030] Examples of such materials include indium-tin oxide (ITO), indium-zinc oxide (IZO), fluorine-doped tin oxide (FTO), antimony-doped tin oxide (ATO), indium-zinc oxide, niobium-titanium oxide, SnO2, ZnO, and graphene.

[0031] The thickness of the transparent electrode 30 is preferably 10 nm or more and 10 μm or less, and more preferably 50 nm or more and 1 μm or less.

[0032] The transparent electrode 30 is formed on a transparent substrate 31 made of a material that is transparent to visible light, in order to maintain a predetermined mechanical strength and flexibility.

[0033] Examples of such a transparent substrate 31 include a glass plate, a transparent plastic sheet, a transparent plastic film, and a transparent inorganic crystal.

[0034] It is also possible to use a transparent electrode substrate in which the transparent electrode 30 is integrated with the transparent substrate 31. Examples of such transparent electrode substrates include an FTO-coated glass plate, an ITO-coated glass plate, a zinc oxide:aluminum-coated glass plate, an FTO-coated transparent plastic film, and an ITO-coated transparent plastic film.

[0035] The transparent electrode substrate may be a transparent electrode made of tin oxide or indium oxide doped with cations or anions having different valences, or a metal electrode having a light-transmitting structure such as a mesh or stripe pattern provided on a substrate such as a glass substrate. These may be used alone or in combination or stacked of two or more types.

[0036] Furthermore, in order to reduce the electrical resistance of the transparent substrate 31, metal lead wires or the like may be disposed on the transparent substrate 31.

[0037] Examples of materials for the metal lead wire include metals such as aluminum, copper, silver, gold, platinum, nickel, etc. The metal lead wire is formed on the transparent substrate 31 by, for example, vapor deposition, sputtering, pressure bonding, etc., and the transparent electrode 30 is formed thereon.

[0038] [1-2]Electron transport layer In the solar cell 1, an electron transport layer (not shown) may be disposed between the transparent electrode 30 and the layer 10 containing a photoelectric conversion material.

[0039] The electron transport layer is formed for the purpose of preventing electronic contact between the transparent electrode 30 and the layer 20 that transports positive charges. Therefore, as long as there is no physical contact between the transparent electrode 30 and the layer 20 that transports positive charges, it does not matter if pinholes, cracks, etc. are formed.

[0040] [1-3] Layer containing a photoelectric conversion material The solar cell 1 includes a layer 10 containing a photoelectric conversion material on a transparent electrode 30 .

[0041] In the present invention, the layer 10 containing a photoelectric conversion material is only required to contain a phenolic resin as the photoelectric conversion material, and the shape of the contained photoelectric conversion material is not particularly limited, and examples thereof include particles, flakes, and the like.

[0042] The following description will mainly focus on the case where the photoelectric conversion material is in particulate form, in other words, the case where the layer 10 containing the photoelectric conversion material is a layer containing particles of the photoelectric conversion material.

[0043] In the solar cell 1 shown in FIG. 1, in a layer 10 containing a photoelectric conversion material, phenolic resin particles 11 as particles of the photoelectric conversion material are fixed on a transparent electrode 30 by a binder 12.

[0044] This effectively prevents the generation of phenolic resin particles 11 that are free to move electrons to the transparent electrode 30 when the layer 20 that transports positive charges is liquid.

[0045] [1-3-1] Phenolic resin In the solar cell 1 of the present invention, the structure of the phenolic resin is not particularly limited as long as the charge-generating portion of the photoelectric conversion material is made of a phenolic resin. However, it is preferable that the phenolic resin has one or more hydroxyl groups and substituents on the aromatic ring, and the substituents are hydrogen atoms or electron-donating groups. This makes it possible to make the effects of the present invention more pronounced.

[0046] As described above, the phenolic resin has one or more hydroxyl groups and substituents on the aromatic ring, and the substituents are preferably hydrogen atoms or electron-donating groups, and more preferably electron-donating groups. This makes it possible to further enhance the effects of the present invention.

[0047] The electron-donating group is preferably at least one selected from the group consisting of a hydroxyl group, an alkyl group, an alkyl alcohol group, an alkoxy group, and an alkoxyalkyl group, and more preferably a hydroxyl group. In other words, the phenolic resin more preferably has two or more hydroxyl groups on the same aromatic ring. This makes it possible to further enhance the effects of the present invention.

[0048] Examples of such phenolic resins include resorcinol-formaldehyde resins, cresol-formaldehyde resins, naphthol-formaldehyde resins, and biphenylaralkyl-formaldehyde resins, with resorcinol-formaldehyde resins being preferred.

[0049] In the solar cell 1 of the present invention, the phenolic resin as the photoelectric conversion material preferably contains a resorcinol-formaldehyde resin as its main component. This makes the effect of the present invention particularly remarkable.

[0050] In this specification, the term "main component" refers to the component with the highest content in a target region. The proportion of the resorcinol-formaldehyde resin in the entire phenolic resin as a photoelectric conversion material is not particularly limited, but is preferably 50% by mass or more, and more preferably 80% by mass or more.

[0051] In the following description, the case where the phenolic resin used as the photoelectric conversion material is a resorcinol-formaldehyde resin will be mainly described, but the present invention is not limited to this.

[0052] As shown in Figure 2, in resorcinol-formaldehyde resin, the benzenoid and quinoid forms of resorcinol are linked and cross-linked, forming a structure in which they are stacked vertically.

[0053] Of these, the benzenoid moiety acts as an electron donor (D: donor), and the quinoid moiety acts as an electron acceptor (A: acceptor) (see Figure 2(a)). A donor-acceptor (DA) pair is formed by linking a benzenoid moiety with a quinoid moiety, and these pairs are stacked to form a semiconductor band structure (see Figure 2(b)). In other words, a resorcinol-formaldehyde resin has a structure in which an electron donor and an electron acceptor are mixed together. In the layer 10 containing the photoelectric conversion material, the benzenoid moiety of the resorcinol-formaldehyde resin becomes a donor domain, and the quinoid moiety becomes an acceptor domain.

[0054] As shown in Figure 3, such a resorcinol-formaldehyde resin has an absorption peak at around 500 nm in the visible light region and a band gap of approximately 2.0 eV, making it suitable for use as a photoelectric conversion material, as it can generate charges when exposed to visible light.

[0055] Furthermore, resorcinol-formaldehyde resin has a layered structure, which makes it difficult for impurities to enter between molecules due to stacking interactions (π-π interactions). This allows stable and suitable extraction of electricity.

[0056] The proportion of impurities in the phenolic resin is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less. This makes it possible to make the above-mentioned effects more pronounced.

[0057] In the solar cell 1 of the present invention, by using such a phenolic resin as a photoelectric conversion material, charges can be generated in the visible light region without the need for a dye, and the generated charges can be extracted to the outside without recombining.

[0058] When the phenolic resin used as the photoelectric conversion material has a granular shape, the average particle size is preferably 1 μm or more and 100 μm or less, more preferably 3 μm or more and 80 μm or less, and even more preferably 5 μm or more and 50 μm or less.

[0059] This reduces the rate of incident light that does not hit the particles and passes through the back surface, thereby improving the light utilization efficiency and the photoelectric conversion efficiency.

[0060] The particle size of the phenolic resin can be determined by measuring the diameter of the resin particles in a photograph taken using a scanning electron microscope (SEM). The particle size distribution can be determined using various particle size distribution meters.

[0061] In this specification, the average particle size refers to the particle size at which the integrated value is 50% in the particle size distribution based on volume.

[0062] Furthermore, it is preferable that the particle size distribution has two or more peaks, as this increases packing properties.

[0063] [1-3-2] Method for synthesizing phenolic resin Next, a method for synthesizing the above-mentioned phenolic resin will be described.

[0064] The phenolic resin used as the photoelectric conversion material in solar cell 1 (phenolic resin having photoelectric conversion function) can be obtained, for example, by reacting a phenolic compound having one or more hydroxyl groups and substituents on an aromatic ring with aldehydes at high temperature and pressure in the presence of water.

[0065] That is, in the process for producing this phenolic resin, a phenolic compound having one or more hydroxyl groups and substituents on the aromatic ring is mixed with an aldehyde, and the mixture is reacted at high temperature and pressure using water as a reaction solvent without adding a surfactant or suspending agent.

[0066] This manufacturing process does not require any expensive organic solvents, and therefore is extremely inexpensive and places little strain on the environment.

[0067] Examples of phenolic compounds having one or more hydroxyl groups and substituents on an aromatic ring include catechol, resorcinol, hydroquinone, phloroglucinol, pyrogallol, dihydroxynaphthalene, etc., and one or more selected from these can be used in combination. Among these, resorcinol is preferred as a phenolic compound having one or more hydroxyl groups and substituents on an aromatic ring.

[0068] Examples of aldehydes include formaldehyde, acetaldehyde, benzaldehyde, trioxane, etc., and one or more selected from these can be used in combination. Among these, formaldehyde is preferred as the aldehyde.

[0069] Next, the reaction between a phenol compound having one or more hydroxyl groups and substituents on the aromatic ring and an aldehyde will be described below.

[0070] The reaction temperature in the reaction between a phenol compound having one or more hydroxyl groups and substituents on an aromatic ring and an aldehyde is preferably 100°C or higher and 350°C or lower, more preferably 200°C or higher and 300°C or lower. This makes it possible to more suitably obtain a phenolic resin having a photoelectric conversion function.

[0071] The pressure during the reaction between the phenol compound having one or more hydroxyl groups and substituents on the aromatic ring and the aldehydes is preferably 1 MPa or more and 20 MPa or less, more preferably 2 MPa or more and 10 MPa or less. This makes it possible to more suitably obtain a phenolic resin having a photoelectric conversion function.

[0072] The reaction between a phenolic compound having one or more hydroxyl groups and substituents on an aromatic ring and an aldehyde in the presence of water proceeds without a catalyst, but an alkali metal catalyst such as sodium carbonate or an amine catalyst may be used.

[0073] Furthermore, the use of an acid catalyst broadens the absorption spectrum of the resulting phenolic resin to the long wavelength side, allowing it to absorb light with wavelengths longer than 600 nm, broadening the light absorption range and improving the overall power generation efficiency.

[0074] Furthermore, the use of an acid catalyst slows down the crosslinking reaction, lowering the crosslink density of the resulting phenolic resin, resulting in fewer structural constraints and stronger DA stacking, which allows for more stable and efficient extraction of electricity.

[0075] The amount of the catalyst is preferably 0.01% by mass or more and 5% by mass or less based on the monomer. This makes it possible to prevent gelation and to more suitably proceed with the target reaction.

[0076] For example, the reaction of a phenolic compound having two hydroxyl groups per aromatic ring with an aldehyde in the presence of water can be suitably carried out under the conditions of a reaction temperature of 100°C or higher and 350°C or lower, a reaction pressure of 1 MPa or higher and 20 MPa or lower, and a reaction time of 5 hours or higher and 30 hours or lower.

[0077] The molar ratio of aldehydes to phenolic compounds in the mixture subjected to the reaction (amount of aldehydes / amount of phenolic compounds) is not particularly limited, but is preferably 1.1 or more and 3.0 or less. This allows the phenolic resin to be synthesized more suitably.

[0078] On the other hand, if the reaction molar ratio is too small, the reaction rate will be slow, whereas if the reaction molar ratio is too large, the odor will be strong and the concentration of unreacted aldehydes will be high.

[0079] In the method of the present embodiment, the polymerization reaction proceeds simply by mixing, but the phenolic resin may be synthesized while mixing by stirring, etc. The mixing method is not particularly limited.

[0080] By carrying out the reaction under the above conditions, it is possible to suitably obtain a phenolic resin in a granular form that satisfies the above-mentioned condition of the average particle size.

[0081] The most preferred method for extracting resin particles from an aqueous slurry of resin particles is a slurry dryer. Methods using a fluidized bed are not preferred because of the high water content, and drying in a fixed bed is not preferred because the particles tend to aggregate.

[0082] [1-3-3] Binder As described above, in the layer 10 containing the photoelectric conversion material, the phenolic resin particles 11 are fixed on the transparent electrode by the binder 12 .

[0083] Examples of the binder 12 include water-insoluble partially esterified polyacrylic acid, norbornene-maleic acid copolymer, cellulose monoacetate, cellulose diacetate, polyvinylpyrrolidone (made insoluble in water by acrylate copolymerization or divinylbenzene copolymerization), cross-linked polyvinyl alcohol (PVA), polyacetal, styrene-butadiene copolymer, carboxymethyl cellulose, hydroxymethyl cellulose, monomethyl cellulose, triacetyl cellulose, etc. These may be used alone or in combination of two or more.

[0084] The binder 12 may contain, for example, an electron-conductive substance as a conductive aid.

[0085] This allows the phenolic resin particles 11 to transport electrons well even when they are not in sufficient contact with the transparent electrode 30 .

[0086] Examples of electron-conductive substances include carbon nanotubes, silver nanowires, Ni nanowires, and acetylene black, and one or more selected from these may be used in combination.

[0087] In the layer 10 containing the photoelectric conversion material, the ratio of the binder 12 to 100 parts by mass of the phenolic resin particles 11 is preferably 0.01 parts by mass or more and 200 parts by mass or less, more preferably 0.1 parts by mass or more and 100 parts by mass or less, and even more preferably 0.5 parts by mass or more and 50 parts by mass or less.

[0088] This allows the layer 10 containing the photoelectric conversion material to be suitably formed, and the mechanical strength of the layer 10 containing the photoelectric conversion material to be improved, while also allowing the light absorption efficiency and photoelectric conversion efficiency of the layer 10 containing the photoelectric conversion material to be improved.

[0089] The proportion of the phenolic resin particles 11 in the entire layer 10 containing the photoelectric conversion material is preferably 0.01% by mass or more and 99% by mass or less, more preferably 0.1% by mass or more and 90% by mass or less, and even more preferably 0.5% by mass or more and 60% by mass or less.

[0090] This allows the layer 10 containing the photoelectric conversion material to be suitably formed, and the mechanical strength of the layer 10 containing the photoelectric conversion material to be improved, while also allowing the light absorption efficiency and photoelectric conversion efficiency of the layer 10 containing the photoelectric conversion material to be improved.

[0091] When a plurality of phenolic resin particles 11 are present along the thickness direction of the layer 10 containing the photoelectric conversion material, and gaps or portions made of a light-transmitting material (for example, portions where a light-transmitting binder 12 is present) are provided between these phenolic resin particles 11, the following effect can be obtained. That is, with the above-mentioned configuration, light components that cannot be absorbed by the phenolic resin particles 11 upon which light is incident and are reflected can be incident on other phenolic resin particles 11. This improves the utilization efficiency (light capture rate) of light irradiated on the solar cell 1.

[0092] [1-3-4] Photosensitizing Compounds As described above, in the solar cell 1, by using a phenolic resin as a photoelectric conversion material, charges can be generated in the visible light region without the need for a dye, but the phenolic resin particles 11 may also be supported with a photosensitizing compound (sensitizing dye).

[0093] Although the phenolic resin has sufficient light absorption efficiency even without carrying a photosensitizing compound, carrying a photosensitizing compound can further increase the absorption efficiency in the longer wavelength region, for example, wavelength region longer than 500 nm, thereby making it possible to improve the overall absorption efficiency and light utilization efficiency.

[0094] The photosensitizing compound is not particularly limited as long as it is a compound that can be photoexcited by the excitation light used, and specific examples thereof include the following compounds.

[0095] That is, examples of the photosensitizing compound include metal complex compounds described in JP-A-7-500630, JP-A-10-233238, JP-A-2000-26487, JP-A-2000-323191, JP-A-2001-59062, etc.; coumarin compounds described in JP-A-10-93118, JP-A-2002-164089, JP-A-2004-95450, J. Phys. Chem. C, 7224, Vol. 111 (2007), etc.; the polyene compounds described in JP-A Nos. 2003-264010, 2004-63274, 2004-115636, 2004-200068, 2004-235052, J.Am.Chem.Soc., 12218, Vol. 126 (2004), Chem.Commun., 3036 (2003), Angew.Chem.Int.Ed., 1923, Vol. 47 (2008), and the like; ... .Soc., 14256, Vol. 128 (2006), etc.; cyanine dyes described in JP-A-11-86916, JP-A-11-214730, JP-A-2000-106224, JP-A-2001-76773, JP-A-2003-7359, etc.; merocyanine dyes described in JP-A-11-214731, JP-A-11-238905, JP-A-2001-52766, JP-A-2001-76775, JP-A-2003-7360, etc.; 91(1987), J.Phys.Chem.B,6272,Vol.97(1993), Electroanal.Chem.,31,Vol.537 (2002), JP-A 2006-032260, J. Porphyrins Phthalocyanines, 230, Vol. 3 (1999), Angew. Chem. Int. Ed., 373, Vol. 46 (2007), Langmuir, 5436, Vol. 24 (2008), etc., and one or more compounds selected from these may be used in combination. Among these, metal complex compounds, indoline compounds, thiophene compounds, and porphyrin compounds are preferred as photosensitizing compounds.

[0096] The method for supporting the photosensitizing compound on the phenolic resin particles 11 is not particularly limited, but examples thereof include a method of immersing a transparent electrode substrate on which a layer 10 containing a photoelectric conversion material has been formed in a solution or dispersion containing the photosensitizing compound, and a method of applying a solution or dispersion containing the photosensitizing compound to the layer 10 containing the photoelectric conversion material to support the photosensitizing compound.

[0097] In the former case, for example, an immersion method, a dip method, a roller method, an air knife method, etc. can be used, and in the latter case, for example, a wire bar method, a slide hopper method, an extrusion method, a curtain method, a spin method, a spray method, etc. can be used.

[0098] [1-3-5] Other ingredients The layer 10 containing the photoelectric conversion material may contain components other than those mentioned above (hereinafter, such components will be referred to as "other components").

[0099] The other component may be contained in any part of the layer 10 containing the photoelectric conversion material. More specifically, the other component may be contained in the phenolic resin particles 11 or the binder 12 in the layer 10 containing the photoelectric conversion material, or may be contained in the layer 10 containing the photoelectric conversion material as a phase different from the phenolic resin particles 11 and the binder 12.

[0100] Examples of other components include phenolic resins that do not have a photoelectric conversion function, resins other than phenolic resins that have a photoelectric conversion function, and various additives.

[0101] The proportion of other components in layer 10 containing a photoelectric conversion material is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0102] [1-3-6] Other conditions The thickness of the layer 10 containing the photoelectric conversion material is preferably 0.1 μm or more and 100 μm or less, and more preferably 0.2 μm or more and 50 μm or less.

[0103] This makes it possible to improve the light utilization efficiency in the layer 10 containing the photoelectric conversion material.

[0104] [1-4] Layer that transports positive charges The solar cell 1 of this embodiment includes a solid hole transport layer as the layer 20 that transports positive charges.

[0105] In this way, since the layer 20 that transports positive charges is a solid hole transport layer, the entire structure is solid, which has the effect of preventing liquid leakage in principle and allowing for a thinner structure.

[0106] The hole transport layer is a layer that helps holes generated in the layer 10 containing the photoelectric conversion material to move to the electrode 40 .

[0107] The material for the hole transport layer can be a known hole transport polymer material. Specific examples include hole transporting compounds such as low- to medium-molecular-weight compounds such as polythiophene compounds, metallocene compounds having cyclopentadiene as a ligand, triphenylamine derivatives, pyrazoline derivatives, hydrazone derivatives, oxadiazole derivatives, and indoline derivatives, as well as vinyl or aromatic polymers to which these compounds are covalently bonded as side chain structures. Other examples include conductive compounds such as polyvinylcarbazole and polyacetylene, polymer compounds such as derivatives thereof, and composites thereof. One or more of these compounds can be used in combination.

[0108] Among these, polythiophene compounds and metallocene compounds are preferred from the viewpoints of carrier mobility, ionization potential, and the like. This makes it possible to more suitably support the movement of positive charges.

[0109] Examples of polythiophene compounds include poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid (PEDOT:PSS), poly(3-n-hexylthiophene) (P3HT), poly(3-n-octyloxythiophene), poly(9,9'-dioctyl-fluorene-co-bithiophene), poly(3,3'''-didodecyl-quaterthiophene), poly(3,6-dioctylthieno[3,2-b]thiophene), poly(2, 5-bis(3-decylthiophen-2-yl)thieno[3,2-b]thiophene), poly(3,4-didecylthiophene-co-thieno[3,2-b]thiophene), poly(3,6-dioctylthieno[3,2-b]thiophene-co-thieno[3,2-b]thiophene), poly(3,6-dioctylthieno[3,2-b]thiophene-co-thiophene), poly(3,6-dioctylthieno[3,2-b]thiophene-co-bithiophene), and the like. One or more selected from these can be used in combination. Among these, preferred polythiophene compounds are poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid (PEDOT:PSS), and poly(3-n-hexylthiophene) (P3HT).

[0110] Examples of metallocene compounds include ferrocene, zirconocene, titanocene, etc., and one or more selected from these can be used in combination. Among these, ferrocene is preferred as the metallocene compound.

[0111] The hole transport layer can be formed directly on the layer 10 comprising the photoelectric conversion material. The method for forming the hole transport layer is not particularly limited, and examples thereof include a method for forming a thin film in a vacuum such as vacuum deposition, a wet film-forming method, etc. In consideration of production costs, etc., the wet film-forming method is preferred, and a method of coating on the layer 10 containing the photoelectric conversion material is more preferred.

[0112] In the solar cell 1 of the present invention, various additives may be added to the hole transporting compound shown above.

[0113] Examples of additives include metal iodides such as iodine, lithium iodide, sodium iodide, potassium iodide, cesium iodide, calcium iodide, copper iodide, iron iodide, and silver iodide; quaternary ammonium salts such as tetraalkylammonium iodide and pyridinium iodide; metal bromides such as lithium bromide, sodium bromide, potassium bromide, cesium bromide, and calcium bromide; bromine salts of quaternary ammonium compounds such as tetraalkylammonium bromide and pyridinium bromide; metal chlorides such as copper chloride and silver chloride; metal acetates such as copper acetate, silver acetate, and palladium acetate; metal sulfates such as copper sulfate and zinc sulfate; metal complexes such as ferrocyanide-ferricyanide and ferrocene-ferricinium ion; sulfur compounds such as sodium polysulfide and alkylthiol-alkyldisulfide; viologen dyes, hydroquinone, and the like; 1,2-iodide Examples of suitable additives include dimethyl-3-n-propylimidazoinium salt, 1-methyl-3-n-hexylimidazolinium iodide salt, 1,2-dimethyl-3-ethylimidazolium trifluoromethanesulfonate, 1-methyl-3-butylimidazolium nonafluorobutylsulfonate, 1-methyl-3-ethylimidazolium bis(trifluoromethyl)sulfonylimide, 1-methyl-3-n-hexylimidazolium bis(trifluoromethyl)sulfonylimide, 1-methyl-3-n-hexylimidazolium dicyanamide, and other ionic liquids; basic compounds such as pyridine, 4-t-butylpyridine, and benzimidazole; and lithium compounds such as lithium trifluoromethanesulfonylimide and lithium diisopropylimide. These may be used alone or in combination. Among these, additives having an imidazolinium compound as the cation and a bis(trifluoromethyl)sulfonylimide anion as the anion are preferred.

[0114] In the solar cell 1, an oxidizing agent may be added to convert part of the hole transport compound into a radical cation in order to improve the electrical conductivity.

[0115] Examples of such oxidizing agents include tris(4-bromophenyl)aminium hexachloroantimonate, silver hexafluoroantimonate, nitrosonium tetrafluoroborate, and silver nitrate.

[0116] The addition of such an oxidizing agent does not necessarily oxidize the entire hole transport compound, but only a portion of the compound may be oxidized. Furthermore, the added oxidizing agent may or may not be removed from the system after addition.

[0117] [1-5] Electrode The electrode (rear electrode) 40 is a hole collecting electrode to which positive charges (holes) generated in the layer 10 containing the photoelectric conversion material migrate. In other words, the electrode 40 functions as a positive electrode.

[0118] Examples of materials constituting the electrode 40 include metals such as platinum, gold, silver, copper, and aluminum; carbon-based materials such as carbon, graphite, fullerene, carbon nanotubes, and graphene; conductive metal oxides such as indium-tin composite oxide (ITO), indium-zinc composite oxide (IZO), SnO2, ZnO, fluorine-doped tin oxide (FTO), and antimony-doped tin oxide (ATO); and conductive polymers such as polythiophene and polyaniline. One or more of these materials can be used in combination. If necessary, a layer for protecting the electrode surface can be provided by plating or the like.

[0119] The electrode 40 is formed on a transparent or opaque substrate 41 . The transparent substrate may be the same as the transparent substrate 31 on which the transparent electrode 30 is formed.

[0120] The thickness of the electrode 40 is preferably 0.1 μm or more and 100 μm or less, and more preferably 1 μm or more and 50 μm or less.

[0121] In order for the solar cell 1 to function as a photoelectric conversion element, at least one of the electron collecting electrode and the hole collecting electrode must be transparent (light transmissive).

[0122] In solar cell 1 of this embodiment, it is preferable that the electron collecting electrode is transparent and that light is incident from the side of transparent electrode 30, which is the electron collecting electrode. In this case, it is preferable to use a light-reflecting material for electrode 40, which is the hole collecting electrode, and it is particularly preferable to use glass or plastic vapor-deposited with a metal or conductive oxide, or a thin metal film.

[0123] An anti-reflection layer may also be provided on the sunlight incident side of the electrode 40. This makes it possible to improve the light utilization efficiency.

[0124] In the solar cell 1 of Figure 1, a layer 10 containing a photoelectric conversion material and a hole transport layer as a layer 20 that transports positive charges are arranged in the space between the transparent electrode 30 and the electrode 40, and the space is sealed with a sealing material 50.

[0125] Examples of the sealant 50 include an ultraviolet curing sealant for a liquid crystal display (LCD), a sheet-like photosensitive adhesive, and the like.

[0126] Second Embodiment The solar cell according to the second embodiment will be described below, focusing on the differences from the previous embodiment, and omitting a description of the same points.

[0127] The solar cell 1 of this embodiment comprises a layer 10 containing a photoelectric conversion material and a layer 20 that transports positive charges and is made of a liquid or gel containing a substance that can be oxidized and reduced, between a transparent electrode 30 formed on a transparent substrate 31 and an electrode 40 formed on a transparent or opaque substrate 41.

[0128] In the solar cell of the second embodiment, the layer 20 that transports positive charges is provided with a layer made of a liquid or gel containing a substance that can be oxidized or reduced, and the configuration of the layer 20 that transports positive charges is different from the above-mentioned form.

[0129] Therefore, in the following, a layer made of a liquid or gel containing a substance that can be oxidized or reduced will be described as the layer 20 that transports positive charges in the solar cell of the second embodiment.

[0130] Examples of substances that can be oxidized and reduced include iodine (lithium iodide + iodine), oxygen (H2O2 or 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) is added during cell formation), iron (II, III), Ni (II, III), Co (I, II), Ce (I, II), and other ionizable substances, and one or more selected from these can be used in combination. An example of the liquid is water.

[0131] Examples of polymers for hydrogels include cross-linked polyvinyl alcohol (PVA), cross-linked polyethylene oxide (PEO), partially esterified polyacrylic acid, norbornene-maleic acid copolymer, cellulose monoacetate, cellulose diacetate, cross-linked polyvinylpyrrolidone, polyacetal, cross-linked polystyrene derivatives, etc., and one or more selected from these can be used in combination. The cross-linked structure can be a covalent cross-link or an ionic cross-link.

[0132] In this embodiment, the layer 20 that transports positive charges is a layer made of a liquid or gel containing a substance that can be oxidized or reduced, so that a layer that can perform charge transfer stably can be manufactured inexpensively.

[0133] In the solar cell 1, the space between the transparent electrode 30 and the electrode 40 is filled with a layer 10 containing a photoelectric conversion material and a liquid or gel containing an oxidized / reduced substance as a layer 20 that transports positive charges, and is sealed with a sealing material 50.

[0134] [2] Solar cell manufacturing method The method for manufacturing a solar cell will be described below.

[0135] The solar cell 1 as described above is manufactured by a manufacturing method including, for example, (1) a phenolic resin application step of applying a phenolic resin onto a transparent electrode 30 formed on a transparent substrate 31, (2) a positive charge transporting layer formation step of forming a layer 20 that transports positive charges on the layer containing the phenolic resin, (3) a step of performing an annealing treatment step (annealing treatment step), and (4) an electrode formation step of forming an electrode 40 on the layer 20 that transports positive charges.

[0136] (1) Phenolic resin application process In the phenolic resin application step, the phenolic resin is applied onto the transparent electrode 30 formed on the transparent substrate 31 .

[0137] As a method for applying the phenolic resin onto the transparent electrode 30, for example, when the phenolic resin has a particulate shape, a dispersion liquid in which phenolic resin particles 11 are dispersed in a binder 12 may be applied onto the transparent electrode 30. The application method is not particularly limited, and can be performed according to a known method.

[0138] (2) Formation of a layer that transports positive charges In the step of forming a layer that transports positive charges, a layer 20 that transports positive charges is formed on a layer containing a phenolic resin.

[0139] The method for forming the layer 20 that transports positive charges is not particularly limited, but for example, when the layer 20 that transports positive charges is a hole transport layer, examples include a method for forming a thin film in a vacuum such as vacuum deposition, a wet film formation method, etc. In consideration of production costs, etc., the wet film formation method is preferred, and a method of coating on a layer containing a phenolic resin is more preferred.

[0140] Furthermore, for example, when the layer 20 that transports positive charges is a layer made of a liquid or gel containing a substance that can be oxidized or reduced, a method of coating it onto a layer containing a phenolic resin can be used.

[0141] After forming the positive charge transporting layer 20, for example, a pressing process may be performed. By performing this pressing process, the positive charge transporting layer 20 and the layer containing the phenolic resin are more closely adhered to each other, thereby further improving the power generation efficiency.

[0142] (3) Annealing process In the annealing step, the layer containing the phenolic resin and the layer 20 that transports positive charges, which are applied onto the transparent electrode, may also be annealed. The annealing treatment is preferably carried out at a temperature equal to or higher than the softening point of the binder.

[0143] (4) Electrode formation process In the electrode formation step, the electrode 40 is formed on the layer 20 that transports positive charges. The method for forming the electrode 40 is not particularly limited, but examples thereof include a method of forming the electrode 40 by coating, sputtering, or the like, and a method of laminating a transparent or opaque substrate 41 on which the electrode 40 has been previously formed. When the electrode 40 is formed by sputtering, the method may further include a step of forming a protective coating layer or a protective film on the electrode 40.

[0144] The above-described method can suitably manufacture the solar cell 1. According to such a method, the solar cell 1, in which the photoelectric conversion material is made of a phenolic resin, can be suitably manufactured at low cost.

[0145] Furthermore, the method for manufacturing the solar cell 1 of this embodiment may include a step of forming an electron transport layer on the transparent electrode 30 before the (1) phenolic resin application step.

[0146] [3] Solar cell applications The uses of the solar cell of the present invention will be described below.

[0147] The solar cell 1 can be used as a power supply for various electrical devices, and is suitable for use in, for example, agriculture, forestry, and fisheries, construction and building sites, factories, offices, logistics and retail, personal use, medical and nursing care facilities, etc. In particular, it can be suitable for use in environments with relatively low incident light, such as for micro-power devices used indoors or wearable devices. It can also be used as an auxiliary power source to extend the continuous use time of rechargeable or battery-powered electrical devices.

[0148] Applications in agriculture, forestry, and fisheries, and construction, architecture, and building sites include, for example, work environment sensors (temperature, humidity, illuminance) / data loggers, wearable vital signs sensors, position sensors, beacons, etc.

[0149] In addition, applications in factories include, for example, electronic signs, ID tags, position sensors (for objects and people), and environmental sensors (for temperature, humidity, and illuminance).

[0150] Examples of applications in offices include environmental sensors (temperature, humidity, illuminance), clocks, emergency power supplies, and security equipment.

[0151] Applications in logistics and retail include, for example, position sensors, temperature data loggers, refrigerator / freezer thermometers, smart tags, and electronic shelf labels.

[0152] Examples of personal uses include remote controllers, kitchen timers, health meters, thermo-hygrometers, clocks, emergency power supplies, security equipment, wearable vital sensors (healthcare, fitness, pet monitoring), wireless headphones, toys, and charging spare batteries for mobile devices.

[0153] Applications in medical and nursing care include, for example, environmental sensors (temperature, humidity, illuminance) / data loggers, wearable vital signs sensors, position sensors, beacons, etc.

[0154] In particular, the solar cell 1 of the present invention contains a phenolic resin as a photoelectric conversion material, which allows it to be manufactured at low cost and is capable of generating sufficient electricity even with indoor light, making it suitable for use as a power source for electrical equipment used indoors.

[0155] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above.

[0156] For example, in the solar cell of the present invention, each component can be replaced with any component that can exert a similar function, or any component can be added.

[0157] In addition, in the above embodiment, the solar cell of the present invention has been described as being configured so that light is incident from the transparent electrode side, but this is not limited thereto, and the solar cell may be configured so that light is incident from the back electrode side.

[0158] Furthermore, the solar cell of the present invention is not limited to one produced by the above-mentioned method, and may be one produced by any method. [Explanation of symbols]

[0159] 1: Solar cell 10: Layer containing a photoelectric conversion material 11: Phenolic resin particles 12: Binder 20: Layer that transports positive charges 30: Transparent electrode 31: Transparent substrate 40: Electrode 41: Transparent or opaque substrate 50: Sealing material

Claims

1. A solar cell comprising at least a layer containing a photoelectric conversion material and a layer that transports positive charges, wherein the photoelectric conversion material is a phenolic resin.

2. 2. The solar cell according to claim 1, further comprising: a layer containing the photoelectric conversion material; and a solid hole transport layer serving as a layer for transporting positive charges, the layer being disposed between a transparent electrode formed on a transparent substrate and an electrode formed on a transparent or opaque substrate.

3. 2. The solar cell according to claim 1, comprising: a layer containing the photoelectric conversion material; and a layer made of a liquid or gel containing an oxidized / reduced substance as the layer that transports positive charges, between a transparent electrode formed on a transparent substrate and an electrode formed on a transparent or opaque substrate.

4. 4. The solar cell according to claim 1, wherein the phenolic resin has one or more hydroxyl groups and substituents on an aromatic ring, and the substituents are hydrogen atoms or electron-donating groups.

5. 5. The solar cell according to claim 4, wherein the electron-donating group is at least one selected from the group consisting of a hydroxyl group, an alkyl group, an alkyl alcohol group, an alkoxy group, and an alkoxyalkyl group.

6. 6. The solar cell according to claim 5, wherein the phenolic resin is mainly composed of a resorcinol-formaldehyde resin.

7. 4. The solar cell according to claim 1, wherein the phenolic resin has a granular shape and an average particle size of 1 μm or more and 100 μm or less.

8. 4. The solar cell according to claim 2, wherein the layer containing the photoelectric conversion material has particles of the photoelectric conversion material fixed on the transparent electrode by a binder.

9. The solar cell according to claim 8 , wherein the binder contains a substance having electronic conductivity.

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