Laminated structures, organic thin-film solar cells, manufacturing methods of laminated structures and organic thin-film solar cells

Abstract

This invention provides a stacked structure for an organic thin-film solar cell that exhibits excellent output characteristics. The stacked structure of this invention comprises a transparent electrode layer, an electron transport layer, an organic semiconductor layer, a hole transport layer, and a collector layer in sequence within an organic thin-film solar cell, forming a stacked structure of a transparent electrode layer and an electron transport layer. The stacked structure includes: a conductive member serving as the transparent electrode layer; and a tin oxide layer disposed on the surface of the conductive member to serve as the electron transport layer. The thickness of the tin oxide layer is 5.0 nm or more and 80.0 nm or less, and the stacked structure satisfies the following condition a: Condition a: A first cyclic voltammogram is obtained by performing cyclic voltammetry on the uncoated conductive member, and the peak current and peak potential of the anodic peak appearing in the first cyclic voltammogram are respectively designated as current value A and potential V. A second cyclic voltammogram is obtained by performing cyclic voltammetry on the stacked structure, and the current value below potential V in the second cyclic voltammogram is designated as current value B. At this point, the coverage rate calculated according to formula (1) (coverage rate (%) = (1-B / A) × 100) is over 90%.

Description

[Technical Field]

[0001] This invention relates to a laminate, an organic thin-film solar cell, a method for manufacturing the laminate, and a method for manufacturing the organic thin-film solar cell. [Previous Technology]

[0002] Conventionally, organic thin-film solar cells are known to have a "positive (NIP structure)" organic thin-film solar cell having a transparent electrode layer, an electron transport layer, an organic semiconductor layer, a hole transport layer, and a current collector layer in sequence. Furthermore, in recent years, from the perspective of improving durability, an "inverted (PIN structure)" organic thin-film solar cell having a transparent electrode layer, a hole transport layer, an organic semiconductor layer, an electron transport layer, and a current collector layer in sequence has been proposed. For example, Patent Document 1 describes a technology related to an organic thin-film solar cell in which an oxide semiconductor layer, an organic semiconductor layer, a conductive polymer layer, and a current collector layer are sequentially formed on a transparent electrode layer, wherein the oxide semiconductor layer, the organic semiconductor layer, the conductive polymer layer, and the current collector layer are each composed of specific materials. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2009-146981 [Summary of the Invention]

[0004] (Problem to be Solved by the Invention) As described above, an organic thin-film solar cell, for example, sequentially comprises a transparent electrode layer, an electron transport layer, an organic semiconductor layer, a hole transport layer, and a current collector layer. Such an organic thin-film solar cell is required to exhibit excellent output characteristics.

[0005] Therefore, the object of the present invention is to provide a laminate that is a laminate containing a transparent electrode layer, an electron transport layer, an organic semiconductor layer, a hole transport layer, and a current collector layer in sequence, forming a positive organic thin-film solar cell. The laminate can yield an organic thin-film solar cell with excellent output characteristics. Furthermore, the object of the present invention is to provide an organic thin-film solar cell with excellent output characteristics. Moreover, the object of the present invention is to provide a novel method for manufacturing the above-mentioned laminate and a novel method for manufacturing an organic thin-film solar cell. (Technical means to solve the problem)

[0006] The inventors have conducted intensive research and found that the above-mentioned objective can be achieved by adopting the following configuration, thereby completing the present invention.

[0007] That is, the present invention provides the following [1] to [4]. [1] A stack body, which is a stack body that forms the light-transmitting electrode layer and the electron transport layer in an organic thin-film solar cell having a light-transmitting electrode layer, an electron transport layer, an organic semiconductor layer, a hole transport layer and a collector layer in sequence; wherein the stack body has: a conductive member that forms the light-transmitting electrode layer; and a tin oxide layer disposed on the surface of the conductive member to form the electron transport layer; the thickness of the tin oxide layer is 5.0 nm or more and 80.0 nm or less, and the stack body satisfies the following condition A. Condition A: A first cyclic voltammetry diagram is obtained by performing cyclic voltammetry on the conductive member whose surface is not covered, and the peak current and peak potential of the anode peak appearing in the first cyclic voltammetry diagram are respectively set as the current value A and the potential V. A second cyclic voltammetry diagram is obtained by performing cyclic voltammetry on the above-mentioned stacked body, and the current value at the potential V in the second cyclic voltammetry diagram is set as the current value B. At this time, the coverage calculated according to formula (1) (coverage rate (%) = (1 - B / A) × 100) is 90% or more. [2] An organic thin film solar cell has a light-transmitting electrode layer, an electron transport layer, an organic semiconductor layer, a hole transport layer and a collector layer in sequence, wherein the light-transmitting electrode layer and the electron transport layer are the stacked body described in [1]. [3] A manufacturing method for the stacked body described in [1] wherein the manufacturing method involves cathode polarizing the above-mentioned conductive member in a processing solution containing Sn component and nitrate ion component, thereby forming the above-mentioned tin oxide layer on the surface of the above-mentioned conductive member. [4] A method for manufacturing an organic thin-film solar cell, which uses the laminate described in [1] to manufacture an organic thin-film solar cell having, in sequence, a transparent electrode layer, an electron transport layer, an organic semiconductor layer, a hole transport layer and a collector layer. (Comparison with prior art)

[0008] According to the present invention, a laminate is provided, which is a laminate of a transparent electrode layer and an electron transport layer of an organic thin-film solar cell having a transparent electrode layer, an electron transport layer, an organic semiconductor layer, a hole transport layer and a current collector layer in sequence; wherein the above-mentioned laminate can obtain an organic thin-film solar cell with excellent output characteristics. Furthermore, according to the present invention, an organic thin-film solar cell with excellent output characteristics is provided. Moreover, according to the present invention, a novel method for manufacturing the above-mentioned laminate and a novel method for manufacturing an organic thin-film solar cell are provided.

Implementation Method

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the embodiments described below are merely examples, and the present invention is not limited to the embodiments described below. In the drawings, for easier visual identification and explanation, there are cases where the scale of the constituent elements differs from the actual scale. In this specification, when "~" is used to indicate a range, the range includes both ends of "~". For example, the range "A~B" includes A and B. In this specification, each component may be used alone as one substance equivalent to each component, or two or more substances equivalent to each component may be used together. In this specification, when there are two or more of a certain component, the description of the content of that component is intended to indicate the total content of the two or more components. In this specification, combining two or more preferred states is a more preferred state.

[0011] [Organic Thin-Film Solar Cell] First, the organic thin-film solar cell 1 will be described with reference to FIG1. ​​FIG1 is a cross-sectional view schematically showing an example of the structure of the organic thin-film solar cell 1. The organic thin-film solar cell 1 shown in FIG1 has, in sequence, a light-transmitting electrode layer 2, an electron transport layer 3, an organic semiconductor layer 4, a hole transport layer 5, and a current collector layer 6. The thicknesses of the organic semiconductor layer 4, the hole transport layer 5, and the current collector layer 6 can be appropriately set.

[0012] Examples of suitable light-transmitting electrode layers 2 include conductive metal oxide films such as indium tin oxide (ITO) films and fluorine-doped tin oxide (FTO) films. The thickness of the light-transmitting electrode layer 2 is based on the thickness of the conductive member 8 (refer to FIG. 2). The light-transmitting electrode layer 2 can also be disposed on the surface of a transparent substrate such as a glass substrate or a resin film. In this case, the transparent substrate is disposed on the surface of the light-transmitting electrode layer 2 opposite to the electron transport layer 3.

[0013] The electron transport layer 3 is the same as the tin oxide layer 9 described below. A preferred configuration of the electron transport layer 3 will also be described later. The electron transport layer 3 may be, for example, a tin oxide layer containing tin oxide (SnO2) as an n-type semiconductor. The thickness of the electron transport layer 3 is based on the film thickness of the tin oxide layer 9 described below (refer to FIG. 2).

[0014] The organic semiconductor layer 4 may include, for example, a layer containing poly-3-hexylthiophene (P3HT) as a polythiophene derivative and methyl [6,6]-phenyl-C61-butyrate (PCBM) as a fullerene derivative. The mass ratio of P3HT to PCBM (P3HT:PCBM) is preferably 5:3 to 5:6, more preferably 5:3 to 5:4. This organic semiconductor layer 4 may further contain conductive materials, pigments, and other additives. Examples of conductive materials include: polyacetylene-based, polypyrrole-based, polythiophene-based, poly(p-phenylene)-based, poly(p-phenylene)-based, polythiophene-based, poly(3,4-ethylenedioxythiophene)-based, poly(phenylene)-based, polyaniline-based, and poly(phenylene)-based conductive materials (however, PEDOT / PSS described below is excluded). Examples of pigments include: anthocyanin, phthalocyanine, phthalocyanine, naphthalenephthalocyanine, azo, quinone, quinacrine, squaric acid, triphenylmethane, porphyrin, perylene, and indigo pigments. The additive content is preferably 1 to 100 parts by weight, more preferably 1 to 40 parts by weight, relative to 100 parts by weight of the total P3HT and PCBM.

[0015] As a material constituting the hole transport layer 5, examples include: PEDOT / PSS, vanadium oxide (V2O5), and molybdenum oxide (MoO3), with PEDOT / PSS being preferred. PEDOT / PSS is a polymer formed by integrating PEDOT (poly-3,4-ethylenedioxythiophene) and PSS (polystyrene sulfonic acid), and is sometimes referred to as PEDOT:PSS.

[0016] As the collector layer 6, examples include Au electrode layer, Ag electrode layer, Al electrode layer and Ca electrode layer, etc., with Au electrode layer being preferred.

[0017] [Laminated Structure] Next, referring to FIG2, the laminated structure 7, which serves as the light-transmitting electrode layer 2 and the electron transport layer 3 of the organic thin-film solar cell 1 (refer to FIG1), will be described. FIG2 is a cross-sectional view schematically showing an example of the structure of the laminated structure 7. The laminated structure 7 has a conductive member 8 that serves as the light-transmitting electrode layer 2 (refer to FIG1), and a tin oxide layer 9 disposed on the surface of the conductive member 8 that serves as the electron transport layer 3 (refer to FIG1).

[0018] <Conductive Component> The conductive component 8 contains a light-transmitting conductive compound. When the conductive component 8 is used in an organic thin-film solar cell, it functions as a light-transmitting electrode layer 2 (refer to FIG. 1). The conductive component 8 preferably contains a conductive metal oxide, and more preferably contains indium oxide or tin oxide. When the conductive component 8 is a component containing indium oxide, it is more preferably a component containing indium tin oxide (ITO), and especially an ITO film. When the conductive component 8 is a component containing tin oxide, it is more preferably a component containing fluorine-doped tin oxide (FTO), and even more preferably an FTO film. The conductive component 8 can be disposed on the surface of a transparent substrate such as a glass substrate or a resin film. In this case, the transparent substrate is disposed on the surface of the conductive component 8 opposite to the tin oxide layer 9.

[0019] For example, the thickness of the conductive component 8 of the ITO film or FTO film is appropriately set according to the obtained organic thin-film solar cell 1 (refer to FIG. 1), preferably 100 nm or more, more preferably 200 nm or more, and even more preferably 300 nm or more. On the other hand, it is preferably 1000 nm or less, more preferably 800 nm or less, and even more preferably 500 nm or less. The thickness of the conductive component 8 is a value obtained by measuring the cross-section of the conductive component 8 formed by focusing an ion beam using a scanning electron microscope.

[0020] <Tin Oxide Layer> The tin oxide layer 9 is a layer containing tin oxide. In the organic thin-film solar cell 1, the tin oxide layer 9 functions as the electron transport layer 3 (refer to FIG. 1). During light absorption, the electron transport layer 3 extracts electrons generated by the organic semiconductor layer 4 and suppresses hole backflow, thereby inhibiting the recombination of electrons and holes and helping to improve output characteristics. It is known that the electron transport layer 3 is made of metal oxides such as titanium oxide, tin oxide, and zinc oxide, but in this invention, tin oxide is used as the material of the electron transport layer 3. The reason is that tin oxide has the best energy level, high electron mobility, high transmittance, and environmental stability.

[0021] <<Film Thickness>> The thickness of the tin oxide layer 9 is 5.0 nm or more and 80.0 nm or less. This results in excellent output characteristics for the organic thin-film solar cell 1 manufactured using the laminate 7. If the thickness of the tin oxide layer 9 is 5.0 nm or more, there are less likely to be areas on the surface of the conductive member 8 that are not covered by the tin oxide layer 9. This reduces the likelihood of leakage current, and it is presumed that the output characteristics are improved. Furthermore, if the thickness of the tin oxide layer 9 is 80.0 nm or less, the resistance to electron movement generated in the organic semiconductor layer 4 adjacent to the electron transport layer 3 (tin oxide layer 9) decreases, thereby presumably improving the output characteristics. However, as long as the thickness of the tin oxide layer 9 is 5.0 nm or more and 80.0 nm or less, mechanisms other than those described above are also considered within the scope of this invention.

[0022] For the purpose of improving output characteristics, the thickness of the tin oxide layer 9 is preferably 10.0 nm or more, and more preferably 15.0 nm or more. For the same reason, the thickness of the tin oxide layer 9 is preferably 100.0 nm or less, and more preferably 50.0 nm or less.

[0023] In this invention, the film thickness of the tin oxide layer 9 is determined as follows: First, a cross-sectional sample, processed into a sheet shape using a focused ion beam (FIB), is prepared for any portion of the tin oxide layer 9. The obtained cross-sectional sample is subjected to X-ray fluorescence analysis (XRF) under the following conditions to determine the X-ray fluorescence intensity of tin (Sn). Based on the obtained X-ray fluorescence intensity of Sn and the film thickness measured by scanning transmission electron microscopy (STEM), a calibration curve is pre-prepared, and the film thickness (in nm) of the tin oxide layer 9 is determined using this calibration curve. The calibration curve is prepared using the following method: First, a sample having a tin oxide layer is prepared, and a cross-sectional sample, processed into a sheet shape using a focused ion beam (FIB), is prepared. The obtained cross-sectional sample is observed using a scanning transmission electron microscope (STEM) to determine the film thickness (in nm). Furthermore, for any part of the same sample used for length measurement by STEM, X-ray fluorescence (XRF) analysis was performed under the following conditions to determine the X-ray fluorescence intensity of tin (Sn). A calibration curve was constructed using linear regression based on the obtained X-ray fluorescence intensity of Sn and the film thickness measured by STEM. Hereinafter, the film thickness of the tin oxide layer measured using the above method will also be referred to as "Sn film thickness".

[0024] (Measurement conditions using XRF apparatus) • XRF apparatus: EDX-7000 (manufactured by Shimadzu Corporation) • X-ray tube: Rhodium (Rh) target (voltage: 50 kV, current: 88 μA) • Primary filter: OPEN • Detector: Silicon drift semiconductor detector • Analysis area: ϕ5 mm • Analysis time: 100 seconds • Dead time: 30% • Smoothing calculation method: Savitzky-Gloay • Number of smoothing points: 5 • Number of repetitions: 1 • Background calculation: Automatic • Sample shape: Block (sample size: 16 mm × 11 mm)

[0025] <<Condition A: Coverage of Tin Oxide Layer>> The laminated system of the present invention satisfies the following condition A. Condition A: A first cyclic voltammogram is obtained by performing cyclic voltammetry on a conductive component whose surface is not coated with a tin oxide layer or the like, and the peak current and peak potential of the anodic peak in the first cyclic voltammogram are respectively set as current value A and potential V. A second cyclic voltammogram is obtained by performing cyclic voltammetry on a laminated body formed by distributing a tin oxide layer on the surface of the conductive component, and the current value under potential V in the second cyclic voltammogram is set as current value B. At this time, the coverage calculated according to the following formula (1) is 90% or more. Coverage (%)=(1-B / A)×100 (1)

[0026] The coating ratio derived by the above-described cyclic voltammetry method represents the coating state of the tin oxide layer on the surface of the conductive component. The higher the coating ratio, the wider the area of ​​the tin oxide layer covering the surface of the conductive component, and it is considered that the tin oxide layer is coated more densely. With a coating ratio of 90% or more, the laminate 7 satisfies condition A, and thus the organic thin-film solar cell 1 made using the laminate 7 becomes one with excellent output characteristics. The measurement conditions of the above-described cyclic voltammetry method are as follows.

[0027] (Determination conditions for cyclic voltammetry) • Potentiostat: Multifunctional electrochemical measurement system (HZ-Pro S12, manufactured by Meiden Hokuto Co., Ltd.) • Application software: Hoktnet Client (version 1.15a, manufactured by Meiden Hokuto Co., Ltd.) • Electrochemical unit: Plate electrode evaluation unit (VM2, manufactured by EC FRONTIER Co., Ltd.) • Reference electrode: Ag / AgCl (RE-2A, manufactured by EC FRONTIER Co., Ltd.) • Relative electrode: Platinum (CE-2, manufactured by EC FRONTIER Co., Ltd.) • Reaction solution: Aqueous solution containing 0.5 mM K₄[Fe(CN)₆]・3H₂O (manufactured by Fujifilm and Kohden Pure Chemical Co., Ltd.), 0.5 mM K₃[Fe(CN)₆] (manufactured by Fujifilm and Kohden Pure Chemical Co., Ltd.), and 0.5 M KCl (manufactured by Fujifilm and Kohden Pure Chemical Co., Ltd.) • Scan rate: 50 mV / s • Scan range: -0.5~1.0 V

[0028] In terms of obtaining organic thin-film solar cells with superior output characteristics, the coverage of the tin oxide layer 9 is preferably 90% or more, and more preferably 93% or more. There is no particular upper limit to the coverage of the tin oxide layer 9, and it can be 100% or less.

[0029] [Method for Manufacturing a Multilayer] In general, the method for manufacturing a multilayer of the present invention is a method for manufacturing a multilayer having a conductive member that serves as a transparent electrode layer and a tin oxide layer disposed on the surface of the conductive member that serves as an electron transport layer. The method for manufacturing a multilayer of the present invention is not particularly limited, as long as it is a method that can obtain a multilayer having the aforementioned conductive member and tin oxide layer, with a Sn film thickness of 5.0 to 80.0 nm, and satisfies condition A.

[0030] As a more detailed example of the method for manufacturing the laminate, the following method (hereinafter also referred to as "this film-forming method") can be used: the conductive member 8 is cathodically polarized in a processing solution containing Sn and nitrate ions, that is, the conductive member 8 is used as a cathode to pass current through, thereby forming a tin oxide layer 9 on the surface of the conductive member 8.

[0031] In this film-forming method, it is presumed that the tin oxide layer 9 is formed according to the following mechanism. First, on the surface of the conductive member 8, the pH of the treatment solution increases due to the reduction reaction of nitrate ions to nitrite ions. As a result, for example, when the Sn component in the treatment solution is tin chloride, tin hydroxide is generated. This tin hydroxide adheres to the surface of the conductive member 8 and undergoes subsequent dehydration condensation through washing, drying, etc., thereby forming the tin oxide layer 9. However, as long as the Sn film thickness of the formed tin oxide layer 9 is 5.0 to 80.0 nm and the laminate satisfies condition A, mechanisms other than those described above are also considered within the scope of the present invention.

[0032] The conductive member 8 used in this film-forming method is as described above. When the conductive member 8 is disposed on the surface of a transparent substrate such as a glass substrate or a resin film, the transparent substrate with the conductive member 8 attached (e.g., a glass substrate with an ITO film attached) is cathodically polarized. In this case, the laminate obtained by this film-forming method also has a transparent substrate.

[0033] The treatment solution contains a Sn component (Sn compound). The Sn component supplies Sn (tin element) to the formed tin oxide layer 9. The Sn component is not particularly limited, as long as it is a compound that can dissociate in the treatment solution to generate Sn cations, preferably at least one selected from the group consisting of tin nitrate (Sn(NO3)2), tin fluoride (SnF2), tin chloride (SnCl2), tin bromide (SnBr2), tin sulfate (SnSO4), and tin acetate (Sn(CH3COO)2).

[0034] The treatment solution contains nitrate ions. There is no particular limitation on the nitrate ion component, as long as it is a compound that can dissociate in the treatment solution to generate nitrate ions. Preferably, it is selected from at least one of the following groups: tin nitrate (Sn(NO3)2), nitric acid (HNO3), sodium nitrate (NaNO3), potassium nitrate (KNO3), magnesium nitrate (Mg(NO3)2), calcium nitrate (Ca(NO3)2), and ammonium nitrate (NH4NO3).

[0035] The Sn component and the nitrate ion component can also be one of the two. For example, when the Sn component is tin nitrate, the Sn component also has the nitrate ion component.

[0036] The Sn content in the treatment solution is preferably 1.500 mol / L or less, more preferably 1.000 mol / L or less, even more preferably 0.500 mol / L or less, particularly preferably 0.400 mol / L or less, and most preferably 0.300 mol / L or less. On the other hand, the Sn content in the treatment solution is preferably 0.001 mol / L or more, more preferably 0.005 mol / L or more, and even more preferably 0.010 mol / L or more.

[0037] The content of nitrate ions in the treatment solution, converted to nitrate ions (NO3-), is preferably 3.5 mol / L or less, more preferably 3.0 mol / L or less, and even more preferably 2.0 mol / L or less. On the other hand, the content of nitrate ions in the treatment solution, converted to nitrate ions (NO3-), is preferably 0.001 mol / L or more, more preferably 0.005 mol / L or more, and even more preferably 0.01 mol / L or more.

[0038] The solvent contained in the treatment solution is not particularly limited, but water is preferred. The pH of the treatment solution is not particularly limited, for example, 0.0 to 8.0, preferably 0.1 to 6.0. The pH can be adjusted using known acidic components (e.g., phosphoric acid and sulfuric acid) or alkaline components (e.g., sodium hydroxide and ammonia). The treatment solution may also contain surfactants such as sodium lauryl sulfate and acetylenol, as needed. From the viewpoint of the long-term stability of the adhesion behavior, the treatment solution may also contain condensed phosphates such as pyrophosphate.

[0039] From the viewpoint of increasing the thickness of the Sn film in the obtained tin oxide layer 9, the liquid temperature of the processing solution during this film formation method is preferably 20°C or higher, more preferably 40°C or higher, and even more preferably 50°C or higher. When the liquid temperature of the processing solution is higher, the activation energy of the dehydration reaction is easily exceeded, and there is a tendency for the number of hydroxyl groups in the formed tin oxide layer to decrease. Therefore, by increasing the liquid temperature of the processing solution, the formation of tin hydroxide is promoted, and it is considered that the Sn film thickness of the tin oxide layer increases. On the other hand, there is no particular upper limit to the liquid temperature of the processing solution, for example, it is 90°C or lower, preferably 85°C or lower.

[0040] The treatment solution may further contain a conductivity aid. Examples of conductivity aids include sulfates such as potassium sulfate, sodium sulfate, magnesium sulfate, and calcium sulfate; and chlorides such as potassium chloride, sodium chloride, magnesium chloride, and calcium chloride. Furthermore, the aforementioned nitrate ion component is included in the conductivity aid. The concentration of the conductivity aid in the treatment solution is preferably 0.001–3.5 mol / L, more preferably 0.005–3.0 mol / L, and even more preferably 0.01–2.0 mol / L.

[0041] The current density during cathodic polarization is preferably 0.1 mA / cm² or higher, more preferably 1.0 mA / cm² or higher. On the other hand, the current density during cathodic polarization is preferably 100 mA / cm² or lower, more preferably 80 mA / cm² or lower, and even more preferably 50 mA / cm² or lower. If the current density is within this range, a uniform tin oxide layer 9 covering the surface of the conductive member 8 can be easily obtained. The energizing time can be appropriately set to obtain the desired coverage rate and Sn film thickness of the tin oxide layer 9. As the opposite electrode during cathodic polarization, an insoluble electrode such as a platinum electrode is preferred for suitability to this film formation method.

[0042] Next, the methods for increasing the coverage under various cathode polarization conditions will be explained.

[0043] <<Relationship between energizing time, current density, and coverage>> When the current density is the same, the coverage can be increased by increasing the energizing time. The tin oxide layer 9 is formed by increasing the pH near the conductive component 8 through energizing to generate tin hydroxide, which is then subjected to a dehydration reaction. As the energizing time increases, the Sn film thickness of the tin oxide layer 9 is considered to increase, and the coverage is considered to increase, because the dehydration reaction has sufficient time to proceed.

[0044] <<Relationship between nitrate ion content and coating rate>> When the current density and energizing time are the same, increasing the nitrate ion content increases the Sn film thickness of the tin oxide layer 9, thereby increasing the coating rate. By increasing the conductivity in the treatment solution, the reduction reaction rate is accelerated, thus promoting the production of tin hydroxide and increasing the Sn film thickness of the tin oxide layer.

[0045] <<Relationship between the temperature of the treatment solution and the coating rate>> When the temperature of the treatment solution is high, it is easy to exceed the activation energy of the dehydration reaction, thus promoting the production of tin hydroxide, and the Sn film thickness of the tin oxide layer increases, and the coating rate also increases.

[0046] <<Relationship between pH of the treatment solution and coating rate>> When the current density and energizing time are the same, the lower the pH of the treatment solution, the easier it is for the tin hydroxide generated by cathodic polarization to redissolve in the treatment solution, thus reducing the Sn film thickness of the tin oxide layer. Therefore, when the pH of the treatment solution is low, the Sn film thickness can be increased by extending the energizing time, thereby increasing the coating rate.

[0047] In this film formation method, after applying cathodic polarization to the conductive component by energizing it, the deposited body 7 can also be held in the processing solution. As the holding time increases, it is believed that the precipitated tin oxide layer dissolves. Therefore, there is no particular limitation on the holding time, as long as it is a time that does not cause the tin oxide layer 9 to completely dissolve, preferably within 30 seconds, more preferably within 2 seconds.

[0048] In this film-forming method, after cathodic polarization, the conductive component with the tin oxide layer can also be washed with water. The washing method is not particularly limited; for example, the conductive component with the tin oxide layer can be immersed in water after cathodic polarization. The temperature of the water used for washing is preferably 10–90°C. The washing time is preferably more than 0.5 seconds, more preferably 1.0–5.0 seconds. Alternatively, the conductive component with the tin oxide layer can be dried after washing, instead of washing. The drying temperature and method are not particularly limited; for example, a common dryer or electric furnace drying method can be used. The drying temperature is preferably below 100°C.

[0049] [Manufacturing Method of Organic Thin-Film Solar Cell] The manufacturing method of the organic thin-film solar cell of the present invention is a method of manufacturing an organic thin-film solar cell having a transparent electrode layer 2, an electron transport layer 3, an organic semiconductor layer 4, a hole transport layer 5, and a current collector layer 6 in sequence using the stacked body 7 of the present invention described above. As a manufacturing method of organic thin-film solar cell, for example, the following method can be used: forming layers serving as the organic semiconductor layer 4, the hole transport layer 5, and the current collector layer 6 in sequence on the surface of the tin oxide layer 9 in the stacked body 7.

[0050] As a method for forming the organic semiconductor layer 4, an example is the following method: a solution obtained by dissolving P3HT and PCBM in a solvent is spin-coated onto the surface of the tin oxide layer 9, which becomes the electron transport layer 3, and then dried to form the organic semiconductor layer 4. Examples of solvents for the above solution include: N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, pyridine, and γ-butyrolactone. A mixture of two or more solvents may also be used as the solvent.

[0051] As a method for forming the hole transport layer 5, for example, the following method can be used: spin-coating an aqueous dispersion of PEDOT / PSS onto the surface of the organic semiconductor layer 4 and drying it, thereby forming the hole transport layer 5.

[0052] As a method for forming the collector layer 6, an example can be given as follows: a conductive metal such as Au is vapor-deposited onto the surface of the hole transport layer 5, thereby forming the collector layer 6. The method for forming each layer is not limited to these methods, and conventionally known methods may be appropriately used. [Example]

[0053] Hereinafter, embodiments are listed to specifically illustrate the present invention. However, the present invention is not limited to the following embodiments.

[0054] <Preparation of Conductive Components> A glass substrate (film resistance: 5 Ω / sq, manufactured by GEOMATEC) with an ITO film is prepared, wherein an ITO (Indium Tin Oxide) film deposited by sputtering is disposed on one surface of the glass substrate (15 mm × 35 mm, thickness 0.7 mm, alkali-free glass). This glass substrate with the ITO film is used as a transparent substrate for fabricating a laminate containing conductive components.

[0055] <Preparation of the Lamination> First, a treatment solution (hereinafter referred to as "treatment solution") containing tin chloride (SnCl2) as the Sn component and nitric acid (HNO3) or potassium nitrate (KNO3) as the nitrate ion component is prepared. When preparing each treatment solution, the amount of each component is adjusted so that the content of the Sn component and the nitrate ion component is as shown in Tables 1 and 2 below (unit: mol / L).

[0056] Next, the prepared glass substrate with the ITO film (a transparent substrate with conductive components) is immersed in a cleaning solution and ultrasonically cleaned for 10 minutes. The cleaning solution is prepared by diluting Semi Clean (registered trademark) M4 (manufactured by Yokohama Yushi Kogyo Co., Ltd.) as a cleaning agent by 20 times with deionized water. Afterward, the glass substrate with the ITO film is removed from the cleaning solution and immersed in deionized water for ultrasonic cleaning for 10 minutes.

[0057] The cleaned glass substrate with the ITO film was immersed in the prepared processing solutions. The temperature of the processing solutions (liquid temperature) was set as shown in Tables 1 and 2 below (unit: °C). Tables 1 and 2 below show the pH of the processing solutions as measured by a pH meter. The glass substrate with the ITO film was cathodically polarized in the processing solutions under the cathodic polarization conditions (current density and energizing time) shown in Tables 1 and 2 below. The energizing was stopped, and within 2 seconds from the end of the cathodic polarization, the glass substrate with the ITO film and the attached tin hydroxide was removed from the processing solution, immersed in 25°C water in a water bath for 2.0 seconds for rinsing, and then dried at room temperature using a blower. In this way, a tin oxide layer (16 mm × 10 mm) is formed on the surface of the ITO film of the glass substrate with the ITO film to form an electron transport layer, thereby creating a glass substrate with the ITO film having the tin oxide layer formed (a laminate that forms a light-transmitting electrode layer and an electron transport layer).

[0058] <<Determination of Sn Film Thickness>> The Sn film thickness of the tin oxide layer was determined for the prepared laminate according to the method described above. The results are shown in Tables 1 and 2 below.

[0059] <<Determination of Coverage (Condition A)>> The coverage of the tin oxide layer was determined for the prepared laminate according to the method described above. The results are shown in Tables 1 and 2 below.

[0060] <Fabrication of Organic Thin Film Solar Cell> Using the prepared stacks, an organic thin film solar cell (PSC) with a photoelectric conversion area of ​​4 mm × 10 mm, or 0.4 cm2, is fabricated in the following manner.

[0061] <<Formation of Organic Semiconductor Layer>> 2,6-Dichlorotoluene and chloroform were mixed in a 1:1 volume ratio to obtain a mixed solution. P3HT (manufactured by Aldrich) and PCBM (manufactured by Frontier Carbon Corporation) were dissolved in the mixed solution in a 5:4 mass ratio, with a total content of 3.9% by mass relative to the total mass of the mixed solution. The above mixed solution was dropped onto the surface of the tin oxide layer of the laminate prepared in each example, and spin-coated at 1500 rpm for 60 seconds, and dried at room temperature (25°C) for about 10 minutes to form an organic semiconductor layer with a thickness of 250 nm.

[0062] <<Formation of the Hole Transport Layer>> A nonionic surfactant (manufactured by Aldrich) containing 1% by mass polyoxyethylene tridecyl ether (PTE: C13H27(OCH2CH2)6OH) and 1% by mass xylene, with water and isopropanol as solvents, was prepared. The nonionic surfactant was mixed with 0.5 parts by mass relative to 1.3% by mass PEDOT / PSS aqueous dispersion (manufactured by Aldrich) for 100 parts by mass to prepare a PTE-containing PEDOT / PSS aqueous dispersion. The PTE-containing PEDOT / PSS aqueous dispersion, heated to 70°C, was dropped onto the surface of an organic semiconductor layer and spin-coated at 6000 rpm for 60 seconds. The layer was then allowed to air dry at room temperature to form a hole transport layer with a thickness of 80 nm.

[0063] <<Formation of the Collector Layer>> An Au electrode layer (collector layer) with a thickness of approximately 100 nm is formed on the surface of the hole transport layer by vacuum evaporation. Specifically, a glass substrate with a light shield corresponding to the shape of the electrodes (4 mm × 10 mm) and the hole transport layer is placed in a chamber. The chamber is depressurized using a rotary pump and a turbomolecular pump to a pressure of 2 × 10⁻³ Pa or less. Gold wires are resistively heated within this chamber, and Au is deposited at a thickness of 100 nm on the surface of the hole transport layer through the light shield. The deposition rate is set to 10–15 nm / min, and the deposition pressure is 1 × 10⁻² Pa or less.

[0064] The glass substrate, which has an ITO film (transparent electrode layer), a tin oxide layer (electron transport layer), an organic semiconductor layer, a hole transport layer, and a collector layer formed on one side surface as obtained by the above method, is sealed in the atmosphere. In this way, an organic thin-film solar cell having a glass substrate, an ITO film (transparent electrode layer), a tin oxide layer (electron transport layer), an organic semiconductor layer, a hole transport layer, and a collector layer in sequence is manufactured.

[0065] <Evaluation of Organic Thin-Film Solar Cells> The organic thin-film solar cells were evaluated as follows. Using a simulated solar light source (SAN-EI Electric, XES-502S), the organic thin-film solar cells were irradiated from the ITO film side with simulated sunlight having a spectral distribution of AM1.5G (IEC standard 60904-3) and a light intensity of 100 mW / cm². Under these conditions, the photocurrent-voltage curves of the organic thin-film solar cells were measured using a linear sweep voltammetry (LSV) measuring device (Hokuto Denko, HZ-5000). The conversion efficiency (photoelectric conversion efficiency) was determined from the obtained curves and evaluated according to the following criteria. The results are shown in Tables 1 and 2 below. A higher conversion efficiency value indicates better output characteristics.

[0066] (Conversion Efficiency Evaluation Criteria) A: Conversion efficiency is 1.2 times or more of the benchmark unit. B: Conversion efficiency is more than 1 time but less than 1.2 times that of the benchmark unit. C: Conversion efficiency is less than 1 time that of the benchmark unit.

[0067] Furthermore, regarding the reference unit (the organic thin-film solar cell of Comparative Example 9), in addition to using the stack obtained by the following method, it can also be manufactured according to the above-described method for manufacturing organic thin-film solar cells. In the above-described stack, a tin oxide layer with a Sn film thickness of 20.0 nm is formed by spin-coating a dispersion of 2.5% by mass of tin oxide nanoparticles (18282-10-5, manufactured by Thermo Scientific) in 1-butanol (solvent) at 4000 rpm for 10 seconds, replacing the tin oxide layer formed by cathode polarization. Also, in addition to using stacks obtained by changing the spin-coating conditions to form tin oxide layers with Sn film thicknesses of 300.0 nm and 100.0 nm respectively, the organic thin-film solar cells of Comparative Examples 7 and 8 can also be manufactured according to the above-described method for manufacturing the reference unit.

[0068] Tables 1 and 2 show the film formation method of the tin oxide layer, the measurement results of the laminate, and the evaluation results of the conversion efficiency of the organic thin-film solar cell (OPV) obtained. In the tables, when the "Classification" column of "Film Formation Method" is marked as "A", it means that the tin oxide layer is formed and the laminate is made by using the processing solution described in the "Processing Solution Composition" column and performing cathodic polarization under the conditions described in the "Cathode Polarization Conditions" column. When the "Classification" column of "Film Formation Method" is marked as "B", it means that the tin oxide layer is formed by the above-mentioned spin coating and the laminate is made.

[0069] [Table 1] Table 1 Film formation method Tin oxide layer OPV Classification Treatment fluid composition Cathode polarization conditions Sn film thickness [nm] coverage rate [%] Conversion efficiency [%] SnCl2 [mol / L] HNO3 [mol / L] KNO3 [mol / L] temperature [℃] pH Current density [mA / cm 2 ] Power-on time [s] Energy density [mC / cm 2 ] Invention Example 1 A 0.1 2 0 80 0.33 50 100 5000 26.9 95 A Invention Example 2 A 0.1 2 0 60 0.33 50 150 7500 21.2 96 A Invention Example 3 A 0.05 1 0 80 0.74 50 9.5 475 7.5 92 B Invention Example 4 A 0.05 1 0 80 0.74 10 65 650 25.6 96 A Invention Example 5 A 0.05 1 0 60 0.74 10 90 900 31.6 99 A Comparative Example 1 A 0.02 0.4 0 80 1.3 50 10 500 13.7 50 C Invention Example 6 A 0.02 0.4 0 80 1.3 10 30 300 7.8 94 B Invention Example 7 A 0.02 0.4 0 60 1.3 50 twenty three 1150 17.2 99 A Comparative Example 2 A 0.02 0.4 0 60 1.3 10 90 900 96.5 50 C Invention Example 8 A 0.02 0.1 0 80 1.25 10 50 500 15.0 95 A Invention Example 9 A 0.02 0.1 0 60 1.25 10 70 700 67.8 99 B Invention Example 10 A 0.02 0.1 0 60 1.25 10 60 600 45.0 99 A Invention Example 11 A 0.02 0.1 0 60 1.25 10 50 500 28.4 96 A Invention Example 12 A 0.02 0.1 0 40 1.25 10 85 850 59.6 97 B

[0070] [Table 2] Table 2 Film formation method Tin oxide layer OPV Classification Treatment fluid composition Cathode polarization conditions Sn film thickness [nm] coverage rate [%] Conversion efficiency [%] SnCl2 [mol / L] HNO3 [mol / L] KNO3 [mol / L] temperature [℃] pH Current density [mA / cm 2 ] Power-on time [s] Energy density [mC / cm 2 ] Comparative Example 3 A 0.005 0.1 0 80 1.3 10 150 1500 30.5 50 C Comparative Example 4 A 0.005 0.1 0 60 1.3 10 150 1500 4.2 50 C Comparative Example 5 A 0.05 0 1 50 2.8 50 20 1000 150.0 99 C Invention Example 13 A 0.05 0 1 50 2.8 50 4 200 68.1 99 B Invention Example 14 A 0.05 0 1 50 2.8 25 8 200 59.8 99 B Invention Example 15 A 0.05 0 1 50 2.8 10 10 100 36.4 99 A Invention Example 16 A 0.05 0 1 50 2.8 10 5 50 17.2 99 A Invention Example 17 A 0.05 0 1 50 2.8 10 2.5 25 10.8 96 A Comparative Example 6 A 0.05 0 1 50 2.8 10 1 10 4.5 50 C Invention Example 18 A 0.1 0 1.4 50 2.4 10 10 100 53.0 99 B Invention Example 19 A 0.1 0 1.4 50 2.4 10 5 50 7.5 93 B Comparative Example 7 B - - - - - - - - 300 80 C Comparative Example 8 B - - - - - - - - 100 20 C Comparative Example 9 B - - - - - - - - 20 5 benchmark

[0071] <Summary of Evaluation Results> In Tables 1 and 2 above, the values ​​marked with a lower bound are outside the scope of this invention. As shown in Tables 1 and 2 above, the output characteristics of Invention Examples 1 to 19, where the Sn film thickness of the tin oxide layer is 5.0 nm or more and 80.0 nm or less, and the coverage of the tin oxide layer is 90% or more, are all good. In particular, the output characteristics of Invention Examples 1 to 2, 4 to 5, 7 to 8, 10 to 11, and 15 to 17, where the Sn film thickness of the tin oxide layer is 10.0 nm or more and 50.0 nm or less, and the coverage is 90% or more, are even better. In contrast, the output characteristics of Comparative Example 4, where the Sn film thickness of the tin oxide layer is too thin, Comparative Examples 2 and 5, where the Sn film thickness is too thick, and Comparative Examples 1, 3, and 6 to 9, where the coverage is too low, are insufficient.

[0072] <<Sn Film Thickness>> The Sn film thickness increases with the increase of the charge density, which is the product of the current density and the energizing time. Comparing Invention Examples 9-11 and 15-17, which differ only in energizing time, it was found that the Sn film thickness also increases with the increase of energizing time. By adjusting the energizing time to a Sn film thickness of 5.0 nm or more and 80.0 nm or less, the power generation efficiency evaluation was improved to B. Furthermore, by adjusting the energizing time to a Sn film thickness of 10.0 nm or more and 50.0 nm or less, the power generation efficiency evaluation was improved to A. It is speculated that this is because, with the adjustment of the Sn film thickness, leakage current can be suppressed, as well as the resistance to hole movement generated in the organic semiconductor layer 4 adjacent to the electron transport layer 3 (tin oxide layer 9) can be suppressed. Furthermore, when the same Sn film thickness is obtained at different current densities, the energizing time decreases at higher current densities and increases at lower current densities. Thus, even if the current density is changed, the same Sn film thickness can be obtained by adjusting the energizing time. As the current density increases, the reduction reaction rate of nitrate ions increases, so the desired Sn film thickness can be obtained in a shorter energizing time.

[0073] <<Coverage Rate>> The coverage rate increases with the increase of the Sn film thickness, and tends to be as follows: if the Sn film thickness is 5.0 nm or more, the coverage rate is 90% or more; if the Sn film thickness is 10.0 nm or more, the coverage rate is 95% or more. Comparing Invention Examples 1-19 and Comparative Examples 1-6, by making the Sn film thickness above a predetermined value, the coverage rate becomes a sufficiently high value of 90% or more. On the other hand, according to Comparative Example 2, if the Sn film thickness becomes too thick, the coverage rate becomes 90% or less. It is believed that the reason is that by making the Sn film thickness too thick, the tin oxide layer is prone to cracking, thus exposing part of the light-transmitting electrode, and the coverage rate decreases. Also, according to Comparative Examples 1 and 3, there are also cases where the Sn film thickness is in the range of 5.0 to 80.0 nm, but the coverage rate is 90% or less. The reason is believed to be that when the reaction is carried out under conditions that make the reaction relatively easy, such as higher reaction temperature, higher current density, and longer energizing time, tin oxide is generated locally in a short period of time, which can cause uneven Sn film thickness and thus reduce the coverage rate. [Simplified Explanation of the Diagram]

[0009] Figure 1 is a cross-sectional view schematically showing an example of the structure of an organic thin-film solar cell. Figure 2 is a cross-sectional view schematically showing an example of the structure of a laminate.

Claims

1. A stacked body comprising, in an organic thin-film solar cell having, in sequence, a transparent electrode layer, an electron transport layer, an organic semiconductor layer, a hole transport layer and a collector layer, the transparent electrode layer and the electron transport layer being a stacked body; the stacked body comprising: a conductive member serving as the transparent electrode layer; and a tin oxide layer disposed on the surface of the conductive member serving as the electron transport layer; the tin oxide layer having a film thickness of 5.0 nm or more and 80.0 nm or less, and the stacked body satisfying the following condition a: condition a: a first cyclic voltammogram is obtained by performing cyclic voltammetry on the conductive member whose surface is not covered, and the peak current and peak potential of the anode peak appearing in the first cyclic voltammogram are respectively set as current value A and potential V; a second cyclic voltammogram is obtained by performing cyclic voltammetry on the stacked body, and the current value at potential V in the second cyclic voltammogram is set as current value B; at this time, the coverage rate calculated according to the following formula (1) is 90% or more. Coverage rate (%) = (1-B / A)×100 (1).

2. An organic thin-film solar cell, comprising, in sequence, a light-transmitting electrode layer, an electron transport layer, an organic semiconductor layer, a hole transport layer, and a current collector layer, wherein the light-transmitting electrode layer and the electron transport layer are laminates of claim 1.

3. A method for manufacturing a multilayer, wherein the multilayer of claim 1 is manufactured, wherein the manufacturing method involves cathodically polarizing the conductive component in a processing solution containing Sn and nitrate ions, thereby forming the tin oxide layer on the surface of the conductive component.

4. A method for manufacturing an organic thin-film solar cell, wherein the laminate of claim 1 is used to manufacture an organic thin-film solar cell having, in sequence, a transparent electrode layer, an electron transport layer, an organic semiconductor layer, a hole transport layer and a current collector layer.

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