Solar battery and solar battery module

Abstract

To provide a solar battery capable of increasing a photoelectric conversion efficiency.SOLUTION: A solar battery includes a photoelectric conversion layer, an electron transport layer or a hole transport layer laminated on the photoelectric conversion layer, and a first electrode and a second electrode sandwiching the photoelectric conversion layer and the electron transport layer or the hole transport layer in a direction perpendicular to each layer. The second electrode includes an intermediate carbon layer and a carbon electrode, the intermediate carbon layer includes graphite and acetylene black, and the carbon electrode includes carbon nanotubes.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to solar cells and solar cell modules. [Background technology]

[0002] In recent years, solar cells have attracted attention as a photoelectric conversion element that converts light energy into electricity. Solar cells have a structure in which a hole transport layer or an electron transport layer is in contact with a photoelectric conversion layer, and extract or supply only holes or electrons in one direction.

[0003] Dye-sensitized solar cells have attracted attention because they can generate electricity stably over a wide irradiation range and can be manufactured using relatively inexpensive materials without requiring large-scale equipment. For example, Patent Document 1 proposes a catalytic electrode that can be manufactured using inexpensive materials and a simple manufacturing method and that can quickly reduce the oxidant of a redox pair contained in an electrolyte, as well as a dye-sensitized solar cell equipped with the same. It states that the conversion efficiency of solar cells can be improved by including an organometallic complex, carbon nanotubes, and a conductive carbon material other than carbon nanotubes in the catalytic electrode.

[0004] On the other hand, perovskite solar cells use perovskite-type crystals represented by the chemical formula ABX3 (A is a monovalent cation, B is a divalent cation, and X is a halogen anion) or similar structures as photoelectric conversion materials (see, for example, Patent Document 2). A feature of perovskite solar cells is that the photoelectric conversion layer and intermediate layer containing organic materials can be formed by a coating method. In the examples of Patent Document 2, the second electrode is formed by vacuum deposition of a metal. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-117263 [Patent Document 2] WO2022 / 176335 publication Summary of the Invention [Problem to be solved by the invention]

[0006] However, in Patent Document 1, the catalyst layer is formed by coating a dispersion containing carbon nanotubes. It has become clear that this method results in insufficient packing of conductive particles at the interface between the catalyst layer and the electrolyte layer, resulting in insufficient conversion efficiency.

[0007] In Patent Document 2, electrodes are formed by vacuum deposition, and when forming electrodes over a large area, for example, a rectangular shape with one side exceeding 1 m or more, it takes a long time to form the electrodes, so there is room for improvement in terms of improving productivity.

[0008] Therefore, an object of the present disclosure is to provide a solar cell and a solar cell module that can form electrodes at normal pressure in a short time and can increase photoelectric conversion efficiency. [Means for solving the problem]

[0009] In order to achieve the above object, the solar cell according to the present disclosure comprises a photoelectric conversion layer, an electron transport layer or a hole transport layer stacked on the photoelectric conversion layer, and a first electrode and a second electrode sandwiching the photoelectric conversion layer and the electron transport layer or the hole transport layer in a direction perpendicular to each layer, wherein the second electrode includes an intermediate carbon layer and a carbon electrode, the intermediate carbon layer includes graphite and acetylene black, and the carbon electrode layer includes carbon nanotubes. [Effects of the Invention]

[0010] According to the solar cell of the present disclosure, electrodes can be formed under normal pressure in a short time, and a solar cell and solar cell module can be provided that can increase photoelectric conversion efficiency. [Brief explanation of the drawings]

[0011] [Figure 1]1 is a schematic cross-sectional view showing the cross-sectional structure of a solar cell according to a first embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view showing the cross-sectional structure of an intermediate carbon layer of the solar cell of FIG. [Figure 3] 1 is Table 1 showing the initial efficiencies of solar cells according to Examples 1 and 2 and Comparative Examples 1 to 7. DETAILED DESCRIPTION OF THE INVENTION

[0012] A solar cell according to a first aspect comprises a photoelectric conversion layer, an electron transport layer or a hole transport layer stacked on the photoelectric conversion layer, and a first electrode and a second electrode sandwiching the photoelectric conversion layer and the electron transport layer or the hole transport layer in a direction perpendicular to each layer, wherein the second electrode includes an intermediate carbon layer and a carbon electrode layer, the intermediate carbon layer includes graphite and acetylene black, and the carbon electrode layer includes carbon nanotubes.

[0013] The solar cell according to the second aspect may be the same as that of the first aspect, and may include a hole transport layer disposed between the photoelectric conversion layer and the second electrode, wherein the average porosity at the interface between the intermediate carbon layer and the hole transport layer is 10% or less, the thickness of the intermediate carbon layer is 0.05 μm or more and 5.0 μm or less, and the thickness of the carbon electrode layer is 0.1 μm or more and 20.0 μm or less.

[0014] A solar cell according to a third aspect is the solar cell of the first aspect, wherein the content ratio of graphite to acetylene black is 40 / 60 to 80 / 20 in mass ratio (graphite / acetylene black).

[0015] A solar cell according to a fourth aspect is the solar cell of the first aspect, wherein the average particle size of the graphite is not less than 5 μm and not more than 30 μm.

[0016] A solar cell according to a fifth aspect is the solar cell of the first aspect, wherein the average particle size of the secondary particles of the acetylene black is 30 nm or more.

[0017] The solar cell according to a sixth aspect may be the solar cell of the first aspect, further comprising a substrate, the first electrode, an electron transport layer, the photoelectric conversion layer, a hole transport layer, and the second electrode in this order.

[0018] A solar cell module according to a seventh aspect is formed by connecting a plurality of solar cells according to the first aspect in series and / or in parallel.

[0019] Solar cells and solar cell modules according to embodiments of the present disclosure will be described below with reference to the accompanying drawings.

[0020] (Embodiment 1) FIG. 1 is a schematic cross-sectional view showing the cross-sectional structure of a solar cell 100 according to the first embodiment. As shown in Fig. 1, solar cell 100 according to embodiment 1 includes, in order from the light-receiving surface side, a substrate 1, a first electrode 2, an electron transport layer 3, a photoelectric conversion layer 4, a hole transport layer 5, and a second electrode 6. Note that solar cell 100 does not need to include all of the layers shown in Fig. 1, as long as it includes first electrode 2, photoelectric conversion layer 4, electron transport layer 3 and / or hole transport layer 5, and second electrode 6; for example, substrate 1 is not essential. Here, second electrode 6 corresponds to intermediate carbon layer 7 and carbon electrode 8 of the present disclosure.

[0021] Each component will be specifically described below.

[0022] <Substrate> The substrate 1 is an additional component. The substrate serves to hold the layers of the solar cell. The substrate 1 can be made of a transparent material. For example, a glass substrate or a plastic substrate can be used as the substrate 1. The plastic substrate can be, for example, a plastic film. Note that the substrate 1 is not essential; if the first electrode 2 has sufficient strength, the first electrode 2 can hold the layers, so the substrate 1 does not need to be provided.

[0023] <1st electrode> The first electrode 2 is electrically conductive. When the solar cell does not include the electron transport layer 3, the first electrode 2 is made of a material that does not form ohmic contact with the photoelectric conversion layer 4. Furthermore, the first electrode 2 has a blocking property against holes from the photoelectric conversion layer 4. The blocking property against holes from the photoelectric conversion layer 4 means that only electrons generated in the photoelectric conversion layer 4 pass through, but do not allow holes to pass through. A material having such properties is a material whose Fermi energy is higher than the energy of the top of the valence band of the photoelectric conversion layer 4. The above-mentioned material may also be a material whose Fermi energy is higher than the Fermi energy of the photoelectric conversion layer 4. A specific example of such a material is aluminum. When the solar cell includes an electron transport layer 3 between the first electrode 2 and the photoelectric conversion layer 4, the first electrode 2 does not need to have the property of blocking holes migrating from the photoelectric conversion layer 4. The first electrode 2 may be made of a material capable of forming an ohmic contact with the photoelectric conversion layer 4.

[0024] The first electrode 2 is translucent. For example, it transmits light from the visible region to the near-infrared region. The first electrode 2 can be formed using, for example, a transparent and conductive metal oxide and / or metal nitride. Examples of such materials include titanium oxide doped with at least one element selected from the group consisting of lithium, magnesium, niobium, and fluorine; gallium oxide doped with at least one element selected from the group consisting of tin and silicon; gallium nitride doped with at least one element selected from the group consisting of silicon and oxygen; tin oxide doped with at least one element selected from the group consisting of antimony and fluorine; zinc oxide doped with at least one element selected from the group consisting of boron, aluminum, gallium, and indium; indium-tin composite oxide; and composites thereof.

[0025] The first electrode 2 can be formed using a non-transparent material and provided with a light-transmitting pattern. Examples of light-transmitting patterns include linear, wavy, lattice, and punched metal patterns with numerous fine through-holes arranged regularly or irregularly. When the first electrode has such a pattern, light can transmit through areas where no electrode material is present. Examples of non-transparent electrode materials include platinum, gold, silver, copper, aluminum, rhodium, indium, titanium, iron, nickel, tin, zinc, and alloys containing any of these. Alternatively, a conductive carbon material can be used.

[0026] The light transmittance of the first electrode 2 may be, for example, 50% or more, or 80% or more. The wavelength of light to be transmitted depends on the absorption wavelength of the photoelectric conversion layer 4. The thickness of the first electrode 2 is, for example, 1 nm or more and 1000 nm or less.

[0027] <Electron transport layer> The electron transport layer 3 includes a semiconductor. The electron transport layer 3 may be a semiconductor with a band gap of 3.0 eV or more. By forming the electron transport layer 3 from a semiconductor with a band gap of 3.0 eV or more, visible light and infrared light can be transmitted to the photoelectric conversion layer 3. Examples of semiconductors include inorganic n-type semiconductors.

[0028] Examples of inorganic n-type semiconductors that can be used include oxides of metal elements, nitrides of metal elements, and perovskite oxides. Examples of oxides of metal elements that can be used include oxides of Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, Si, and Cr. More specific examples include TiO2 or SnO2. Examples of nitrides of metal elements include GaN. Examples of perovskite oxides include SrTiO3 or CaTiO3.

[0029] The electron transport layer 3 may be formed of a substance having a band gap greater than 6.0 eV. Examples of substances having a band gap greater than 6.0 eV include alkali metal or alkaline earth metal halides such as lithium fluoride and calcium fluoride, alkali metal oxides such as magnesium oxide, and silicon dioxide. In this case, to ensure the electron transport properties of the electron transport layer 3, the electron transport layer 3 is configured to have a thickness of, for example, 10 nm or less.

[0030] The electron transport layer 3 may include multiple layers made of different materials. For example, the electron transport layer 3 may include a porous layer. The porous layer includes a porous body. Examples of the porous body include a porous body consisting of interconnected insulating or semiconducting particles. Examples of insulating particles include aluminum oxide or silicon oxide particles. Examples of semiconducting particles include inorganic semiconductor particles. Examples of inorganic semiconductors include oxides of metal elements, perovskite oxides of metal elements, sulfides of metal elements, and metal chalcogenides. Examples of oxides of metal elements include oxides of Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, Si, or Cr. A more specific example is TiO2. Examples of perovskite oxides of metal elements include SrTiO3 or CaTiO3. Examples of sulfides of metal elements include CdS, ZnS, In2S3, PbS, Mo2S, WS2, Sb2S3, Bi2S3, ZnCdS2, or Cu2S. Examples of metal chalcogenides include CsSe, In2Se3, WSe2, HgS, PbSe, or CdTe.

[0031] <Photoelectric conversion layer> The photoelectric conversion layer 4 includes a perovskite compound. The perovskite compound can be represented by the chemical formula ABX3, where A is a monovalent cation. Examples of the monovalent cation include monovalent cations such as alkali metal cations and organic cations. More specifically, a methylammonium cation (CH3NH3 +), formamidinium cation (HC(NH2) 2+ ), ethylammonium cation (CH3CH2NH3 + ), guanidinium cation (CH6N3 + ), potassium cation (K + ), cesium cation (Cs + ), and rubidium cation (Rb + ) and B is a divalent lead cation (Pb 2+ ) and tin cations (Sn 2+ ) X is a monovalent anion such as a halogen anion. Each of the A, B, and X sites may be occupied by multiple types of ions.

[0032] The thickness of the photoelectric conversion layer 4 is, for example, 50 nm or more and 10 μm or less. The photoelectric conversion layer 4 can be formed by using a solution coating method, a printing method, a vapor deposition method, or the like. The photoelectric conversion layer 4 may also be formed by cutting out a perovskite compound.

[0033] The photoelectric conversion layer 4 may primarily contain a perovskite compound represented by the chemical formula ABX3. Here, "the photoelectric conversion layer primarily contains a perovskite compound represented by the chemical formula ABX3" means that the photoelectric conversion layer 4 contains 90 mass% or more of a perovskite compound represented by the chemical formula ABX3. The photoelectric conversion layer 4 may also contain 95 mass% or more of a perovskite compound represented by the chemical formula ABX3. The photoelectric conversion layer 4 may consist of a perovskite compound represented by the chemical formula ABX3. The photoelectric conversion layer 4 may contain a perovskite compound represented by the chemical formula ABX3, and may contain defects or impurities.

[0034] The photoelectric conversion layer 4 may further contain another compound different from the perovskite compound represented by the chemical formula ABX3. Examples of the other compound include a compound having a Ruddlesden-Popper type layered perovskite structure.

[0035] <Hole transport layer> The hole transport layer 5 contains a hole transport material, which is a material that transports holes. The hole transport layer 5 is made of a hole transport material such as an organic material or an inorganic semiconductor.

[0036] Typical examples of organic materials used as hole transport materials include 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)9,9'-spirobifluorene, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (hereinafter sometimes abbreviated as "PTAA"), poly(3-hexylthiophene-2,5-diyl), poly(3,4-ethylenedioxythiophene), and copper phthalocyanine. Inorganic semiconductors used as hole transport materials are p-type semiconductors. Examples of inorganic semiconductors are Cu2O, CuGaO2, CuSCN, CuI, NiOx, MoOx, VO5, or carbon materials such as graphene oxide.

[0037] The hole transport layer 5 may include multiple layers made of different materials. For example, multiple layers may be stacked so that the ionization potentials of the hole transport layers 5 are successively smaller than that of the photoelectric conversion layer 4, thereby improving the hole transport properties.

[0038] The thickness of the hole transport layer 5 may be 1 nm or more and 1000 nm or less, or 10 nm or more and 50 nm or less. Within this range, sufficient hole transport properties can be exhibited and low resistance can be maintained, allowing for highly efficient photovoltaic power generation.

[0039] The hole transport layer 5 can be formed by a coating method, a printing method, a vapor deposition method, or the like, similar to the method for forming the photoelectric conversion layer 5. Examples of coating methods include doctor blade, bar coating, spraying, dip coating, and spin coating. Examples of printing methods include screen printing. If necessary, the hole transport layer 5 may be formed by mixing multiple materials, followed by pressing or baking. When the material for the hole transport layer 6 is an organic low-molecular-weight compound or an inorganic semiconductor, the hole transport layer 5 can also be formed by a vacuum vapor deposition method.

[0040] The hole transport layer 5 contains a dopant (supporting electrolyte). The dopant has the effect of stabilizing holes in the hole transport layer 5.

[0041] The dopant may be, for example, an ammonium salt or an alkali metal salt. Examples of the ammonium salt include tetrabutylammonium perchlorate, tetraethylammonium hexafluorophosphate, imidazolium salt, or pyridinium salt. Examples of the alkali metal salt include lithium perchlorate or potassium tetrafluoride.

[0042] <Second electrode> The second electrode 6 is made up of two layers, an intermediate carbon layer 7 and a carbon electrode 8, and is electrically conductive.

[0043] <Intermediate carbon layer> Fig. 2 is a schematic cross-sectional view showing the cross-sectional structure of the intermediate carbon layer 7 of the solar cell of Fig. 1. The intermediate carbon layer 7 contains graphite 12, acetylene black 11, and a dispersant 13. <Graphite> The graphite 12 in the intermediate carbon layer 7 has, for example, a flat plate shape and an average particle size of preferably 5 μm to 30 μm, and more preferably 10 μm to 20 μm. If the average particle size of the graphite 12 in the intermediate carbon layer 7 is within the above range, dispersibility with the acetylene black 11 is improved, the conductive particle network is improved, and high conductivity within the layer can be ensured.

[0044] <Acetylene black> The average particle size of the acetylene black 11 in the intermediate carbon layer 7 is preferably 30 nm or more, more preferably 50 nm or more, and preferably 150 nm or less. When the average particle size of the acetylene black 11 in the intermediate carbon layer 7 is within the above range, the intermediate carbon layer can be easily molded, and high conductivity within the layer can be ensured. The average particle size of acetylene black referred to here refers to the aggregation of fine particles (called primary particles) (secondary particles, aggregates, and the aggregated state is called structure). The average particle size of graphite and acetylene black can be determined, for example, by observing with a scanning electron microscope (hereinafter referred to as SEM), measuring the particle sizes based on images of 100 randomly selected graphite and acetylene black particles, and averaging the measured values. The content ratio of graphite to acetylene black is preferably 40 / 60 to 80 / 20 in terms of mass ratio (graphite / acetylene black). When the content ratio of graphite to acetylene black is within the above range, the interface resistance between the intermediate carbon layer 7 and the hole transport layer 5 is reduced, and holes and electrons are efficiently exchanged at the interface.

[0045] <Dispersant> The dispersant 13 is not particularly limited as long as it has insulating properties and functions as a self-supporting film. Cellulose-based (hydroxyethyl cellulose, carboxymethyl cellulose, etc.), polyvinyl-based, polyacrylic-based, and polyurethane-based polymer materials can be used.

[0046] The intermediate carbon layer 7 may optionally further contain an ammonium salt or alkali metal salt dopant. The ammonium salt or alkali metal salt dopant of the intermediate carbon layer 7 is the same as the dopant (indicator electrolyte) described above for the hole transport layer 5, and examples of such dopant include ammonium salts or alkali metal salts. Examples of ammonium salts include tetrabutylammonium perchlorate, tetraethylammonium hexafluorophosphate, imidazolium salts, and pyridinium salts. Examples of alkali metal salts include lithium perchlorate, potassium boron tetrafluoride, or a lithium bis(trifluoromethanesulfonyl)imide complex. The dopant used in the intermediate carbon layer 7 is preferably the same material as the dopant used in the hole transport layer 5.

[0047] <Carbon electrode> The carbon electrode 8 of the second electrode 6 contains carbon nanotubes (hereinafter also referred to as "CNTs"). While single-walled CNTs and / or multi-walled CNTs can be used without any particular limitation, the CNTs are preferably single-walled to five-walled CNTs, and more preferably single-walled CNTs. The use of single-walled CNTs can further improve conductivity compared to the use of multi-walled CNTs.

[0048] Other components that may be optionally contained in the carbon electrode 8 are not particularly limited, and examples thereof include a conductive filler, a dispersant, and a thickener. As the conductive filler, for example, a metal or metal oxide can be used, such as a metal nanowire of Ag or indium tin oxide (ITO).

[0049] <Dispersant> Examples of dispersants include copolymers of styrene and methoxypolyethylene glycol methacrylate, copolymers of styrene, acrylonitrile, methoxyethyl acrylate, and methacrylic acid, polyvinylpyrrolidone, polyoxyethylene alkyl ether (the number of carbon atoms in the alkyl group is preferably 8 to 20), and polyoxyethylene alkylphenyl ether (the number of carbon atoms in the alkyl group is preferably 8 to 9). One type of dispersant may be used alone, or two or more types may be used in combination.

[0050] <Film thickness> The thickness of the intermediate carbon layer 7 is preferably 0.05 μm to 5 μm, and more preferably 0.07 μm to 1 μm. The thickness of the carbon electrode 8 is preferably 0.1 μm to 20 μm, and more preferably 0.7 μm to 10 μm. If the thicknesses of the intermediate carbon layer 7 and the carbon electrode 8 are within the above ranges, the conductivity and film condition of the second electrode 6 are maintained favorably.

[0051] <Porosity> The average porosity at the interface between the intermediate carbon layer 7 and the hole transport layer 5 is preferably 10% or less. Here, porosity is an index that indicates the percentage (%) of the area of ​​the bonded surface area at the interface between the intermediate carbon layer and the hole transport layer that is not bonded to the hole transport layer due to voids or other gaps at the interface, relative to the bonded surface area when the intermediate carbon layer and the hole transport layer are completely bonded. The intermediate carbon layer 7 is formed on the hole transport layer 5, and the cross section of the formed layer is observed with a scanning electron microscope (hereinafter referred to as SEM). The porosity is measured based on images of 10 randomly selected cross sections, and the average value can be calculated. In the schematic cross-sectional view of Figure 2, voids 14 at the interface between the intermediate carbon layer 7 and the hole transport layer 5 are indicated by hatching. Note that Figure 2 only shows the voids 14 at the interface between the intermediate carbon layer 7 and the hole transport layer 5. Each cross section is a line segment, and in a virtual plane formed by, for example, arranging 10 cross sections at a predetermined interval, the average porosity is an area ratio that indicates the proportion of the area where the intermediate carbon layer 7 and the hole transport layer 5 are not bonded within the plane that is the interface between the intermediate carbon layer 7 and the hole transport layer 5. If the average porosity at the interface between the intermediate carbon layer 7 and the hole transport layer 5 is within the above range, it is believed that holes and electrons are efficiently exchanged at the interface.

[0052] <Method for forming intermediate carbon layer and carbon electrode> The intermediate carbon layer 7 and the carbon electrode layer 8 can be formed by, for example, a coating method or a printing method, similar to the photoelectric conversion layer 4 and the hole transport layer 5. Examples of the coating method include a doctor blade method, a bar coating method, a spray method, a dip coating method, and a spin coating method. Examples of the printing method include a screen printing method. If necessary, pressure application or baking may be performed.

[0053] <Solar cell module> The solar cell module according to the present disclosure is configured by connecting a plurality of solar cells according to the present disclosure in series and / or parallel. Here, the solar cell module can be obtained, for example, by arranging a plurality of solar cells according to the present disclosure in a planar or curved shape, providing non-conductive partition walls between each solar cell, and electrically connecting the photoelectrodes and counter electrodes of each solar cell using conductive members. The number of solar cells used to form the solar cell module is not particularly limited and can be determined appropriately depending on the target voltage.

[0054] (Example) Hereinafter, the present disclosure will be described in more detail with reference to examples. The solar cells of Examples 1 and 2 and Comparative Examples 1 to 7 have the following configurations. Substrate 1: Glass substrate First electrode 2: Indium-tin composite oxide layer · Electron transport layer 3: tin oxide layer · Photoelectric conversion layer 4: layer mainly containing CH(NH2)2PbI3 Hole transport layer 5: a layer mainly containing PTAA (but containing lithium bis(trifluoromethanesulfonyl)imide as an additive) ·Second electrode 6: Intermediate carbon layer 7: Composite of graphite, acetylene black, cellulose, and lithium bis(trifluoromethanesulfonyl)imide Carbon electrode 8: CNT and polyacrylic acid composite

[0055] <Fabrication of solar cells> Example 1 (1) First, a substrate was prepared having a transparent conductive layer on its surface that would function as the first electrode 2. In this example, a glass substrate having a thickness of 0.7 mm was used as the substrate 1. As the first electrode 2, an indium-tin composite oxide layer was formed on the substrate by sputtering. (2) Next, as the electron transport layer 3, a tin oxide layer was formed by applying a SnO2 colloidal dispersion liquid by spin coating.

[0056] (3) Next, a raw material solution of the photoelectric conversion material was applied by spin coating to form a photoelectric conversion layer 4 containing a perovskite compound. The raw material solution contained 0.92 mol / L lead(II) iodide (Tokyo Chemical Industry Co., Ltd.), 0.17 mol / L lead(II) bromide (Tokyo Chemical Industry Co., Ltd.), 0.83 mol / L formamidinium iodide (GreatCell Solar Co., Ltd.), 0.17 mol / L methylammonium bromide (GreatCell Solar Co., Ltd.), 0.05 mol / L cesium iodide (Iwatani Corporation), and 0.05 mol / L rubidium iodide (Iwatani Corporation). The solvent for the solution was a mixture of dimethyl sulfoxide (Acros Co., Ltd.) and N,N-dimethylformamide (Acros Co., Ltd.). The mixture ratio (DMSO:DMF) of dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF) in the raw material solution was 1:4 by volume.

[0057] (4) Next, a raw material solution of a hole transport material was applied by spin coating onto the photoelectric conversion layer 4 to form a hole transport layer 5 containing PTAA. The solvent for the raw material solution was toluene (manufactured by Acros), and the solution contained 10 g / L of PTAA.

[0058] (5) Next, the intermediate carbon layer 7 of the second electrode was formed on the hole transport layer 5 as follows. The raw material solution for the intermediate carbon layer 7 was prepared by mixing 5.0 g of graphite (UP-15N, manufactured by Nippon Graphite Industries Co., Ltd.), 4.4 g of acetylene black (Denka Black granules, manufactured by Denka), 1 g of cellulose (ETHOCEL STD4, manufactured by DuPont), 10 g of lithium bis(trifluoromethanesulfonyl)imide (manufactured by Tokyo Chemical Industry Co., Ltd.), and 100 g of 2-propanol, followed by dispersion treatment in an ultrasonic bath for 10 minutes. This raw material solution was applied to the hole transport layer 5 by spin coating and then annealed on a hot plate at 100°C for 5 minutes to form the intermediate carbon layer 7 of the second electrode 6.

[0059] (6) Furthermore, a carbon electrode 8 was formed on the intermediate carbon layer 7 as follows. The raw material solution for the carbon electrode 8 was prepared by mixing 1 g of carbon nanotubes (CNT) (NC-7000L, manufactured by Nanosil), 1 g of cellulose (Kimica CMC, manufactured by Kimica), and 100 g of 2-propanol, and irradiating the mixture with an ultrasonic homogenizer for 2 hours. This raw material solution was applied to the intermediate carbon layer 7 by spin coating, and then annealed on a hot plate at 100°C for 5 minutes to form the carbon electrode 8 of the second electrode 6. In this way, there was obtained the solar cell of Example 1. All of the above-mentioned steps were carried out in a dry room with a dew point of −40° C. or less.

[0060] The configuration of the second electrode 6 in each example and each comparative example is shown in Table 1 in FIG.

[0061] <Porosity measurement> The porosity was measured at the interface between the intermediate carbon layer 7 and the hole transport layer 5 of the obtained Examples 1 and 2 and Comparative Examples 1 to 7. The cross-section of the interface between the intermediate carbon layer and the hole transport layer was observed using a scanning electron microscope (JEOL Ltd., JSM-IT200).

[0062] SEM images with a horizontal dimension of approximately 1 μm were obtained using a scanning electron microscope. The porosity (%) was calculated by defining an arbitrary length at the interface between the intermediate carbon layer and the hole transport layer as 100 and the length where there was no adhesion to the hole transport layer due to voids occurring at the interface as X. The porosity was measured based on images of 10 randomly selected locations, and the average value was calculated. The average porosity values ​​measured as described above for Examples 1 and 2 and Comparative Examples 1 to 7 are shown in Table 1 of Figure 3. Average porosity values ​​of less than 10% were evaluated as "pass" (◯), and average porosity values ​​of 10% or more were evaluated as "fail" (×).

[0063] <Photoelectric conversion efficiency measurement> The photoelectric conversion efficiencies of the obtained solar cells of Examples 1 and 2 and Comparative Examples 1 to 7 were measured. The photoelectric conversion efficiency of the solar cell was measured using an electrochemical analyzer (ALS440B, manufactured by BAS) and a xenon light source (BPS X300BA, manufactured by Bunkoukeiki). Before the measurement, the light intensity was adjusted to 1 Sun (100 mW / cm) using a silicon photodiode. 2 The voltage sweep rate was 100 mV / s. No preconditioning such as light irradiation or prolonged forward bias application was performed before the start of the measurement. To fix the effective area and reduce the influence of scattered light, an aperture of 0.1 cm was used. 2 With the solar cell masked with a black mask, light was irradiated from the mask / substrate side. The photoelectric conversion efficiency was measured at room temperature in dry air (<2% RH). The initial efficiencies of the solar cells of Examples 1 and 2 and Comparative Examples 1 to 7 measured as described above are shown in Table 1 of FIG. 3. Photoelectric conversion efficiencies of 10% or more were evaluated as "pass" (◯), and those less than 10% were evaluated as "fail" (×).

[0064] <Overall Judgment> A sample that was rated as "pass" (good) for both the average porosity and the photoelectric conversion efficiency was rated as "good", and a sample that was rated as "bad" for either was rated as "bad".

[0065] Comparing Examples 1 and 2 with Comparative Examples 1 and 2, it can be seen that excellent photoelectric conversion efficiency is achieved when the graphite to acetylene black content ratio (graphite / acetylene black) is 40 / 60 to 80 / 20 by mass. This is because, in the graphite / acetylene black content ratio, the total is 100, and the graphite mass ratio is less than 40, the conductivity of the intermediate carbon layer decreases. If the graphite mass ratio exceeds 80, the number of point contacts between particles increases, increasing the interfacial resistance between the hole transport layer 5 and the intermediate carbon layer 8 and deteriorating the formability of the intermediate carbon layer.

[0066] Comparing Examples 1 and 2 with Comparative Examples 3 and 4, it can be seen that excellent photoelectric conversion efficiency is achieved when the graphite in the intermediate carbon layer 7 has a flat plate shape and an average particle size of 5 μm to 30 μm. If the average particle size is less than 5 μm, the particles come into contact with each other more frequently, reducing the conductivity of the intermediate carbon layer. If the average particle size is greater than 30 μm, the dispersibility with acetylene black decreases, reducing the conductivity of the intermediate carbon layer.

[0067] Comparing Examples 1 and 2 with Comparative Example 5, it can be seen that excellent photoelectric conversion efficiency is achieved when the average particle size of the acetylene black in the intermediate carbon layer 7 is less than 30 nm. This is because when the average particle size is less than 30 nm, the particles come into contact with each other more frequently, reducing the conductivity of the intermediate carbon layer.

[0068] Comparing Examples 1 and 2 with Comparative Examples 4 to 7, it can be seen that excellent photoelectric conversion efficiency is achieved when the thickness of the intermediate carbon layer 7 is 0.05 μm or more and 5 μm or less, and the thickness of the carbon electrode 9 is 0.1 μm or more and 20 μm or less. By forming the layers within the above ranges, the conductivity and film state of the second electrode 6 are maintained good. [Industrial Applicability]

[0069] The solar cell according to the present disclosure has excellent photoelectric conversion efficiency, and a solar cell module using this solar cell can be provided. [Explanation of symbols]

[0070] 1 board 2 1st electrode 3 Electron transport layer 4 Photoelectric conversion layer 5. Hole transport layer 6 Second electrode 7. Middle carbon layer 8 Carbon electrodes 11 Acetylene Black 12 Graphite 13 Dispersant / dopant complex 14 void 100 solar cells

Claims

1. a photoelectric conversion layer; an electron transport layer or a hole transport layer laminated on the photoelectric conversion layer; a first electrode and a second electrode sandwiching the photoelectric conversion layer and the electron transport layer or the hole transport layer in a direction perpendicular to the layers; Equipped with the second electrode includes an intermediate carbon layer and a carbon electrode layer; the intermediate carbon layer contains graphite and acetylene black, The carbon electrode layer comprises carbon nanotubes.

2. a hole transport layer disposed between the photoelectric conversion layer and the second electrode; the average porosity at the interface between the intermediate carbon layer and the hole transport layer is 10% or less, the thickness of the intermediate carbon layer is 0.05 μm or more and 5.0 μm or less, The thickness of the carbon electrode layer is 0.1 μm or more and 20.0 μm or less. The solar cell according to claim 1 .

3. 2. The solar cell according to claim 1, wherein a content ratio of the graphite to the acetylene black is 40 / 60 to 80 / 20 in terms of a mass ratio (graphite / acetylene black).

4. 2. The solar cell according to claim 1, wherein the graphite has an average particle size of 5 μm or more and 30 μm or less.

5. 2. The solar cell according to claim 1, wherein the average particle size of the secondary particles of the acetylene black is 30 nm or more.

6. The solar cell according to claim 1 , comprising a substrate, the first electrode, an electron transport layer, the photoelectric conversion layer, a hole transport layer, and the second electrode in this order.

7. A solar cell module comprising a plurality of solar cells according to claim 1 connected in series and / or in parallel.

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