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 of the present invention is a solar cell having a bulk heterojunction structure including a photoelectric conversion layer in which an electron donor and an electron acceptor that accepts an electron donated from the electron donor are mixed, wherein the photoelectric conversion layer contains 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. 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.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.

[0004] For example, organic thin-film solar cells using organic materials have attracted attention as solar cells that can be easily manufactured by low-cost processes such as a roll-to-roll process. A bulk heterojunction organic thin-film solar cell is known as one of these types of organic thin-film solar cells.

[0005] Bulk heterojunction solar cells have a photoelectric conversion layer that converts light into electricity and contains a donor domain made of a photoelectric conversion material that acts as an electron donor (donor) and an acceptor domain made of a photoelectric conversion material that acts as an electron acceptor (acceptor). Specifically, the photoelectric conversion layer is sandwiched between a positive electrode and a negative electrode, and sunlight enters the photoelectric conversion layer through the positive electrode, generating excitons.

[0006] When the exciton reaches the interface between the donor and acceptor domains, it separates into an electron and a hole. The electron then moves through the acceptor domain and reaches the negative electrode, while the hole moves through the donor domain and reaches the positive electrode. These holes and electrons become electrical energy that powers an external circuit electrically connected to the negative and positive electrodes.

[0007] As a representative example of the photoelectric conversion material in the photoelectric conversion layer, i.e., the donor and acceptor, the substance shown in Patent Document 1 is known. Specifically, Patent Document 1 describes a photoelectric conversion material in which poly(3-hexylthiophene) (P3HT, see FIG. 11) is used as the donor and phenyl C61 butyric acid methyl ester (PCBM, see FIG. 12) is used as the acceptor.

[0008] However, since the photoelectric conversion materials used in conventional solar cells are expensive, cost reduction has not been sufficiently achieved.

[0009] 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]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-273939 Summary of the Invention [Problem to be solved by the invention]

[0011] 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]

[0012] These objects can be achieved by the present invention as set forth in (1) to (8) below. (1) A solar cell having a bulk heterojunction structure, which includes a photoelectric conversion layer containing a mixture of an electron donor and an electron acceptor that accepts electrons donated by the electron donor, The solar cell, wherein the photoelectric conversion layer contains a phenolic resin.

[0013] (2) The solar cell according to (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.

[0014] (3) The solar cell according to (2) 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] (4) The solar cell according to (3) above, wherein the phenolic resin is mainly composed of a resorcinol-formaldehyde resin.

[0016] (5) The solar cell according to any one of (1) to (4) 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] (6) A solar cell according to any one of (1) to (5) above, which is configured by laminating the photoelectric conversion layer between a transparent electrode formed on a transparent substrate and a back electrode formed on a transparent or opaque substrate.

[0018] (7) The solar cell according to (6), wherein the phenolic resin is in the form of a thin film having a thickness of 10 nm or more and 10 μm or less.

[0019] (8) The solar cell according to (6) above, wherein a hole transport layer is disposed between the photoelectric conversion layer and the back electrode. [Effects of the Invention]

[0020] 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]

[0021] [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

[0022] Preferred embodiments of the present invention will now be described in detail. [1] Solar cells First, the solar cell of the present invention will be described.

[0023] 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.

[0024] The solar cell 1 is a solar cell having a bulk heterojunction structure including a photoelectric conversion layer 10 containing a mixture of an electron donor and an electron acceptor that accepts electrons donated by the electron donor. The photoelectric conversion layer 10 contains a phenolic resin.

[0025] 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, and are also less expensive than conventional organic materials used as photoelectric conversion materials.

[0026] Thus, according to the solar cell 1 of the present invention, since the photoelectric conversion layer 10 contains a phenolic resin, it can be manufactured at low cost and can generate sufficient electricity using indoor light.

[0027] The solar cell 1 shown in FIG. 1 is configured by laminating a photoelectric conversion layer 10 between a transparent electrode 20 formed on a transparent substrate 21 and a back electrode 30 formed on a transparent or opaque substrate 31.

[0028] [1-1]Transparent electrode The transparent electrode 20 is an electron collecting electrode that receives electrons 41 generated in the photoelectric conversion layer 10. In other words, the transparent electrode 20 functions as a negative electrode.

[0029] The transparent electrode 20 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 20 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 20 is formed on a transparent substrate 21 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 21 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 20 and the transparent substrate 21 are integrated together. 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 21, metal lead wires or the like may be disposed on the transparent substrate 21.

[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 21 by, for example, vapor deposition, sputtering, pressure bonding, etc., and the transparent electrode 20 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 20 and the photoelectric conversion layer 10.

[0039] The electron transport layer is a layer that assists the electrons 41 generated in the photoelectric conversion layer 10 to move to the transparent electrode 20, and is made of, for example, bathocuproine or lithium fluoride.

[0040] [1-3] Photoelectric conversion layer The photoelectric conversion layer 10 is formed as a layer in which donor domains 11 that act as electron donors (donors) and acceptor domains 12 that act as electron acceptors (acceptors) are mixed.

[0041] In the solar cell 1 of the present invention, the photoelectric conversion layer 10 contains a phenolic resin.

[0042] [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 layer 10 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] In the solar cell 1 of the present invention, the phenolic resin constituting the photoelectric conversion layer 10 preferably contains a resorcinol-formaldehyde resin as a main component. This makes the effect of the present invention particularly remarkable.

[0047] 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 total phenolic resin constituting the photoelectric conversion layer 10 is not particularly limited, but is preferably 50% by mass or more, and more preferably 80% by mass or more.

[0048] In the following description, the case where the phenolic resin constituting the photoelectric conversion layer 10 is a resorcinol-formaldehyde resin will be mainly described, but the present invention is not limited to this.

[0049] 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.

[0050] 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. In the photoelectric conversion layer 10, the benzenoid moiety of the resorcinol-formaldehyde resin becomes the donor domain 11, and the quinoid moiety becomes the acceptor domain 12.

[0051] 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.

[0052] Furthermore, resorcinol-formaldehyde resin has a layered structure, and due to stacking interactions (π-π interactions), impurities are less likely to enter between the molecules. This allows stable and suitable extraction of electricity.

[0053] 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.

[0054] The phenolic resin preferably has a granular shape with an average particle size of 1 μm or more and 100 μm or less.

[0055] This allows the incident light to be scattered more suitably, further increasing the light utilization efficiency and the photoelectric conversion efficiency.

[0056] As described above, the average particle size of the phenolic resin in granular form 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.

[0057] This reduces the rate of incident light that does not hit the particles and passes through the back surface, further increasing the light utilization efficiency and the photoelectric conversion efficiency.

[0058] 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.

[0059] 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.

[0060] Furthermore, it is preferable that the particle size distribution has two or more peaks, as this increases packing properties.

[0061] The phenolic resin may be in the form of a thin film, with a thickness of 10 nm or more and 10 μm or less.

[0062] This makes it possible to provide a compact solar cell 1, which has the effect of reducing costs and the burden on the environment.

[0063] The proportion of the phenolic resin as the photoelectric conversion material in the photoelectric conversion layer 10 is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more. This makes it possible to make the above-mentioned effects of the present invention more pronounced.

[0064] [1-3-2] Method for synthesizing phenolic resin Next, a method for synthesizing the above-mentioned phenolic resin will be described.

[0065] 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.

[0066] That is, in the process for producing this phenolic resin, a phenolic compound having one or more hydroxyl groups and substituents on an 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.

[0067] This manufacturing process does not require any expensive organic solvents, and therefore is extremely inexpensive and places little strain on the environment.

[0068] 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.

[0069] Examples of aldehydes include formaldehyde, acetaldehyde, benzaldehyde, etc., and one or more selected from these can be used in combination. Among these, formaldehyde is preferred as the aldehyde.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] [1-3-3] Other ingredients The photoelectric conversion layer 10 may contain components other than the phenolic resin as the photoelectric conversion material (hereinafter, such components will be referred to as "other components").

[0084] 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, binders, various additives, and the like.

[0085] The proportion of other components in the photoelectric conversion layer 10 is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0086] [1-3-4] Other conditions The thickness of the photoelectric conversion layer 10 is not particularly limited, but is preferably 0.01 μm to 100 μm, more preferably 0.1 μm to 50 μm, and even more preferably 1 μm to 20 μm. This makes it possible to make the above-mentioned effects of the present invention more pronounced.

[0087] [1-4] Hole transport layer In the solar cell 1, a hole transport layer (not shown) may be disposed between the photoelectric conversion layer 10 and the back electrode 30.

[0088] The hole transport layer is a layer that assists the movement of holes 42 generated in the photoelectric conversion layer 10 to the rear electrode 30.

[0089] 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.

[0090] 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 assist the movement of the holes 42.

[0091] 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).

[0092] 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.

[0093] The hole transport layer can be formed directly on the photoelectric conversion layer 10 . 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 formation method, etc. Considering production costs, etc., the wet film formation method is preferred, and a method of coating on the photoelectric conversion layer 10 is more preferred.

[0094] [1-5] Back electrode The back electrode 30 is a hole collecting electrode to which holes 42 generated in the photoelectric conversion layer 10 migrate. In other words, the back electrode 30 functions as a positive electrode.

[0095] Examples of materials constituting the back electrode 30 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 may be used in combination.

[0096] The back electrode 30 is formed on a transparent or opaque substrate 31 . The transparent substrate may be the same as the transparent substrate 21 on which the transparent electrode 20 is formed.

[0097] The thickness of the back electrode 30 is preferably 0.1 μm or more and 100 μm or less, and more preferably 1 μm or more and 50 μm or less.

[0098] 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).

[0099] 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 20, which is the electron collecting electrode. In this case, it is preferable to use a light-reflecting material for back electrode 30, which is the hole collecting electrode, and it is particularly preferable to use a metal, or glass or plastic on which a thin film of metal and / or conductive oxide is formed.

[0100] A reflective layer may be provided on the sunlight incident side of the transparent substrate or opaque substrate 31. This makes it possible to improve the light utilization efficiency.

[0101] [2] Function of solar cells The solar cell 1 according to this embodiment is configured as described above, and its operation will be described below.

[0102] When light (for example, sunlight or room light) is irradiated onto the transparent electrode 20 of the solar cell 1, the light reaches the photoelectric conversion layer 10. As a result, excitons 40 are generated in the photoelectric conversion layer 10.

[0103] The generated exciton 40 moves through the donor domain 11 and reaches the interface between the donor domain 11 and the acceptor domain 12. At this interface, the exciton 40 separates into an electron 41 and a hole 42. The hole 42 moves through the donor domain 11 and reaches the rear electrode 30, which is the positive electrode. Meanwhile, the electron 41 moves through the acceptor domain 12 and reaches the transparent electrode 20, which is the negative electrode.

[0104] These holes 42 and electrons 41 become electrical energy that energizes an external circuit electrically connected to the negative and positive electrodes.

[0105] In particular, in the solar cell 1, since the photoelectric conversion layer 10 contains a phenolic resin, it is possible to generate sufficient electricity using indoor light.

[0106] Furthermore, according to the solar cell 1, the generated charges can be extracted to the outside without recombining.

[0107] [3] Solar cell manufacturing method The method for manufacturing a solar cell will be described below.

[0108] The solar cell 1 as described above is manufactured by a manufacturing method including, for example, (1) a pretreatment step of pretreating a composition containing a phenol compound and an aldehyde, (2) an application step of applying the pretreated composition onto a transparent electrode 20 formed on a transparent substrate 21, (3) a high-temperature, high-pressure treatment step of applying a high-temperature, high-pressure treatment to the applied composition, and (4) a back electrode formation step of forming a back electrode 30 on the photoelectric conversion layer 10.

[0109] (1) Pretreatment process In the pretreatment step, the composition containing the phenol compound and the aldehyde is subjected to pretreatment such as treatment with an acid catalyst, preliminary reaction at low temperature, etc. Note that this step may be omitted.

[0110] (2) Application process In the application step, the pretreated composition is applied onto a transparent electrode 20 formed on a transparent substrate 21 .

[0111] The phenolic resin may be applied to the transparent electrode 20 by printing, for example.

[0112] (3) High-temperature and high-pressure treatment process In the high-temperature, high-pressure treatment step, the composition applied onto the transparent electrode 20 is treated at high temperature and high pressure. As a result, a phenolic resin having a photoelectric conversion function is produced, and the photoelectric conversion layer 10 is formed.

[0113] (4) Back electrode formation process In the back electrode forming step, the back electrode 30 is formed on the photoelectric conversion layer 10.

[0114] Examples of methods for forming the back electrode 30 include a method of forming it by coating, sputtering, or the like, and a method of laminating a transparent substrate or opaque substrate 31 on which the back electrode 30 has been previously formed. When the back electrode 30 is formed by sputtering, a step of forming a protective coating layer or a protective film on the back electrode 30 may be further included.

[0115] The above-described method can suitably manufacture the solar cell 1. According to such a method, the solar cell 1 containing the phenolic resin as the photoelectric conversion material can be suitably manufactured at low cost.

[0116] Furthermore, the manufacturing method of the solar cell 1 of this embodiment may include a step of forming an electron transport layer on the transparent electrode 20 before the (1) pretreatment step, or may include a step of forming a hole transport layer on the photoelectric conversion layer 10 after the (3) high-temperature, high-pressure treatment step and before the (4) back electrode formation step.

[0117] [4] Solar cell applications The uses of the solar cell of the present invention will be described below.

[0118] 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 settings, etc. In particular, it can be used as a power supply for micro-power devices used indoors and wearable devices, in environments where the amount of incident light is relatively small and the wavelength is in the visible light range. It can also be used as an auxiliary power source to extend the continuous use time of rechargeable or battery-powered electrical devices.

[0119] 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.

[0120] 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).

[0121] Examples of applications in offices include environmental sensors (temperature, humidity, illuminance), clocks, emergency power supplies, and security equipment.

[0122] Applications in logistics and retail include location sensors, temperature data loggers, refrigerator / freezer thermometers, smart tags, and electronic shelf labels.

[0123] 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.

[0124] Applications in medical and nursing care include, for example, environmental sensors (temperature, humidity, illuminance) / data loggers, wearable vital signs sensors, position sensors, beacons, etc.

[0125] In particular, the solar cell 1 of the present invention can be manufactured at low cost because the photoelectric conversion layer 10 contains a phenolic resin, and can generate sufficient electricity even with indoor light, making it suitable for use as a power supply for electrical equipment used indoors.

[0126] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above.

[0127] 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.

[0128] 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.

[0129] 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]

[0130] 1: Solar cell 10: Photoelectric conversion layer 11: Donor domain 12: Acceptor domain 20: Transparent electrode 21: Transparent substrate 30: Back electrode 31: Transparent or opaque substrate 40:Exciton 41:Electronic 42: Hole

Claims

1. A solar cell having a bulk heterojunction structure including a photoelectric conversion layer in which an electron donor and an electron acceptor that accepts electrons donated from the electron donor are mixed, The solar cell, wherein the photoelectric conversion layer contains a phenolic resin.

2. 2. 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.

3. 3. The solar cell according to claim 2, 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.

4. 4. The solar cell according to claim 3, wherein the phenolic resin is mainly composed of a resorcinol-formaldehyde resin.

5. 5. The solar cell according to claim 1, wherein the phenolic resin has a granular shape and an average particle size of 1 [mu]m or more and 100 [mu]m or less.

6. 5. The solar cell according to claim 1, wherein the photoelectric conversion layer is laminated between a transparent electrode formed on a transparent substrate and a back electrode formed on a transparent or opaque substrate.

7. The solar cell according to claim 6 , wherein the phenolic resin is in the form of a thin film having a thickness of 10 nm to 10 μm.

8. The solar cell according to claim 6 , further comprising a hole transport layer disposed between the photoelectric conversion layer and the back electrode.

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