Laminate, organic thin-film solar cell, method of producing laminate, and method of producing organic thin-film solar cell

Abstract

Provided is a laminate yielding a perovskite solar cell that has excellent output characteristics. Provided is an organic thin-film solar cell comprising a light-transmitting electrode layer, an electron transport layer, an organic semiconductor layer, a hole transport layer, and a collector electrode layer in the stated order. The laminate serves as the light-transmitting electrode layer and the electron transport layer and includes: an electroconductive member (8) serving as the light-transmitting electrode layer; and a tin oxide layer (9) serving as the electron transport layer and arranged on the surface of the electroconductive member (8). The film thickness of the tin oxide layer (9) is 5.0 to 80.0 nm, and a condition A is satisfied. Condition A: Current value A and potential V are a peak current and a peak potential, respectively, of an anode peak appearing in a first cyclic voltammogram obtained by performing cyclic voltammetry on an electroconductive member a surface of which has not been covered. Current value B is a current value at the potential V in a second cyclic voltammogram obtained by performing cyclic voltammetry on the laminate. Coverage, as calculated by formula (1) (coverage (%) = (1-B / A) × 100), is 90% or higher.

Description

Laminate, organic thin-film solar cell, method for manufacturing laminate, and method for manufacturing organic thin-film solar cell

[0001] The present invention relates to a laminate, an organic thin-film solar cell, a method for manufacturing a laminate, and a method for manufacturing an organic thin-film solar cell.

[0002] Conventionally, as organic thin-film solar cells, "normal type (NIP structure)" organic thin-film solar cells having a light-transmitting electrode layer, an electron transport layer, an organic semiconductor layer, a hole transport layer, and a collector electrode layer in this order have been known. Furthermore, in recent years, from the viewpoint of improving durability, etc., "inverted type (PIN structure)" organic thin-film solar cells having a light-transmitting electrode layer, a hole transport layer, an organic semiconductor layer, an electron transport layer, and a collector electrode layer in this order have been proposed. For example, Patent Document 1 describes a technology relating to an organic thin-film solar cell in which an oxide semiconductor layer, an organic semiconductor layer, a conductive polymer layer, and a collector electrode layer are formed in this order on a transparent electrode layer, and the oxide semiconductor layer, the organic semiconductor layer, the conductive polymer layer, and the collector electrode layer are each made of a specific material.

[0003] Special Publication No. 2009-146981

[0004] As described above, an organic thin-film solar cell has, for example, a light-transmitting electrode layer, an electron transport layer, an organic semiconductor layer, a hole transport layer, and a collector electrode layer in this order, and is required to exhibit excellent output characteristics.

[0005] Therefore, an object of the present invention is to provide a laminate that serves as the light-transmitting electrode layer and the electron transport layer of a forward-type 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 electrode layer in this order, and that can provide an organic thin-film solar cell with excellent output characteristics. Another object of the present invention is to provide an organic thin-film solar cell with excellent output characteristics. A further object of the present invention is to provide a novel method for producing the laminate and a novel method for producing an organic thin-film solar cell.

[0006] As a result of extensive research, the present inventors have found that the above object can be achieved by employing the following configuration, and have completed the present invention.

[0007] That is, the present invention provides the following [1] to [4]. [1] 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 electrode layer in this order, wherein the laminate serves as the light-transmitting electrode layer and the electron transport layer, the laminate comprising: a conductive member serving as the light-transmitting electrode layer; and a tin oxide layer disposed on the surface of the conductive member and serving as the electron transport layer, wherein the tin oxide layer has a film thickness of 5.0 nm to 80.0 nm, and the laminate satisfies the following condition A. Condition A: The peak current and peak potential of an anodic peak appearing in a first cyclic voltammogram obtained by performing cyclic voltammetry on the conductive member whose surface is uncoated are defined as current value A and potential V, respectively. The current value at the potential V in a second cyclic voltammogram obtained by performing cyclic voltammetry on the laminate is defined as current value B. In this case, the coverage calculated by equation (1) (coverage (%) = (1 - B / A) × 100) is 90% or more. [2] 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 electrode layer in this order, wherein the light-transmitting electrode layer and the electron transport layer are the laminate according to [1]. [3] A method for producing the laminate according to [1], comprising cathodically polarizing the conductive member in a treatment solution containing a Sn component and a nitrate ion component to form the tin oxide layer on the surface of the conductive member. [4] A method for producing an organic thin-film solar cell using the laminate according to [1], wherein the 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 electrode layer in this order.

[0008] According to the present invention, there is provided a laminate that serves as the light-transmitting electrode layer and the electron transport layer of 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 electrode layer in this order, and that can provide an organic thin-film solar cell with excellent output characteristics. Furthermore, according to the present invention, there is provided an organic thin-film solar cell with excellent output characteristics. Furthermore, according to the present invention, there are provided a novel method for producing the laminate and a novel method for producing an organic thin-film solar cell.

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

[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, the scale of components may differ from the actual scale to facilitate easier viewing and explanation. In this specification, when a range is expressed using "to", the range includes both ends of "to". For example, a range of "A to B" includes A and B. In this specification, each component may be a single substance corresponding to the component, or two or more substances may be used in combination. In this specification, when two or more types of a component are present, a description of the content of that component refers to the total content of the two or more components. In this specification, a combination of two or more preferred aspects is a more preferred aspect.

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

[0012] Suitable examples of the light-transmitting electrode layer 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 corresponds to the thickness of the conductive member 8 (see FIG. 2 ), which will be described later. The light-transmitting electrode layer 2 may 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 later, and a preferred embodiment of the electron transport layer 3 will also be described later. The electron transport layer 3 is made of, for example, tin oxide (SnO2 ２ The thickness of the electron transport layer 3 corresponds to the thickness of the tin oxide layer 9 (see FIG. 2) described later.

[0014] The organic semiconductor layer 4 may be formed of, for example, a polythiophene derivative, poly-3-hexylthiophene (P3HT), and a fullerene derivative, [6,6]-phenyl-C ６１ Examples of such a layer include a layer containing P3HT and PCBM (polybutyric acid methyl ester (PCBM). The mass ratio of P3HT to PCBM (P3HT:PCBM) is preferably 5:3 to 5:6, and more preferably 5:3 to 5:4. Such an organic semiconductor layer 4 may further contain additives such as conductive materials and dyes. Examples of conductive materials include polyacetylene-based, polypyrrole-based, polythiophene-based, polyparaphenylene-based, polyparaphenylene vinylene-based, polythienylene vinylene-based, poly(3,4-ethylenedioxythiophene)-based, polyfluorene-based, polyaniline-based, and polyacene-based conductive materials (excluding PEDOT / PSS, which will be described later). Examples of the dye include cyanine, merocyanine, phthalocyanine, naphthalocyanine, azo, quinone, quinacridone, squarylium, triphenylmethane, xanthene, porphyrin, perylene, and indigo dyes. The content of the additive is preferably 1 to 100 parts by mass, and more preferably 1 to 40 parts by mass, per 100 parts by mass of the total of P3HT and PCBM.

[0015] The material for forming the hole transport layer 5 is PEDOT / PSS, vanadium oxide (V ２ O ５ ), and molybdenum oxide (MoO ３ PEDOT / PSS is a polymer in which PEDOT (poly-3,4-ethylenedioxythiophene) and PSS (polystyrene sulfonic acid) are integrated, and is sometimes written as PEDOT:PSS.

[0016] Examples of the collector electrode layer 6 include an Au electrode layer, an Ag electrode layer, an Al electrode layer, and a Ca electrode layer, and among these, an Au electrode layer is preferred.

[0017] [Laminate] Next, the laminate 7 that will become the light-transmitting electrode layer 2 and the electron transport layer 3 of the organic thin-film solar cell 1 (see FIG. 1) will be described with reference to Fig. 2. Fig. 2 is a cross-sectional view that schematically shows an example of the configuration of the laminate 7. The laminate 7 has a conductive member 8 that will become the light-transmitting electrode layer 2 (see Fig. 1) and a tin oxide layer 9 that is disposed on the surface of the conductive member 8 and will become the electron transport layer 3 (see Fig. 1).

[0018] <Conductive Member> The conductive member 8 contains a light-transmitting conductive compound and functions as the light-transmitting electrode layer 2 (see FIG. 1 ) when used in an organic thin-film solar cell. The conductive member 8 preferably contains a conductive metal oxide, more preferably indium oxide or tin oxide. When the conductive member 8 contains indium oxide, it is more preferably a member containing indium tin oxide (ITO), and particularly preferably an ITO film. When the conductive member 8 contains tin oxide, it is more preferably a member containing fluorine-doped tin oxide (FTO), and even more preferably an FTO film. The conductive member 8 may 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 member 8 opposite the tin oxide layer 9.

[0019] The thickness of the conductive member 8, which is, for example, an ITO film or an FTO film, is set appropriately depending on the organic thin-film solar cell 1 to be obtained (see FIG. 1 ), but is 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 member 8 is a value obtained by forming a cross section of the conductive member 8 with a focused ion beam and measuring the formed cross section 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 (see FIG. 1 ). The electron transport layer 3 extracts electrons generated in the organic semiconductor layer 4 upon light absorption and suppresses the backflow of holes, thereby suppressing the recombination of electrons and holes and contributing to improved output characteristics. Conventionally, metal oxides such as titanium oxide, tin oxide, and zinc oxide have been used as materials for the electron transport layer 3, but in the present invention, tin oxide is used as the material for the electron transport layer 3. This is because tin oxide has an optimal energy level, high electron mobility, high transmittance, environmental stability, etc.

[0021] <<Film Thickness>> The film thickness of the tin oxide layer 9 is 5.0 nm or more and 80.0 nm or less. As a result, the organic thin-film solar cell 1 manufactured using the laminate 7 has excellent output characteristics. When the film thickness of the tin oxide layer 9 is 5.0 nm or more, it is unlikely that there will be any areas on the surface of the conductive member 8 that are not covered by the tin oxide layer 9. This is presumably to reduce leakage current generation and improve output characteristics. Furthermore, when the film thickness of the tin oxide layer 9 is 80.0 nm or less, it is presumed that the migration resistance of electrons generated in the organic semiconductor layer 4 adjacent to the electron transport layer 3 (tin oxide layer 9) is reduced, thereby improving output characteristics. However, even if a mechanism other than the above is used, it is considered to be within the scope of the present invention as long as the film thickness of the tin oxide layer 9 is 5.0 nm or more and 80.0 nm or less.

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

[0023] In the present disclosure, the thickness of the tin oxide layer 9 is determined as follows. First, a cross-sectional sample is prepared by processing an arbitrary portion of the tin oxide layer 9 into a thin section using a focused ion beam (FIB). The obtained cross-sectional sample is subjected to fluorescent X-ray analysis using an X-ray fluorescence analyzer (XRF device) under the following conditions to measure the fluorescent X-ray intensity of tin (Sn). The thickness (unit: nm) of the tin oxide layer 9 is determined from the obtained Sn fluorescent X-ray intensity and the film thickness measured by STEM using a calibration curve prepared in advance. The calibration curve is prepared by the following method. First, a sample having a tin oxide layer is prepared, and a cross-sectional sample is prepared by processing the sample into a thin section using a focused ion beam (FIB). The obtained cross-sectional sample is observed using a scanning transmission electron microscope (STEM) to measure the film thickness (unit: nm). Furthermore, an X-ray fluorescence analysis is performed on an arbitrary portion of the same sample used for length measurement by the STEM device using an X-ray fluorescence analyzer (XRF device) under the following conditions to measure the X-ray fluorescence intensity of tin (Sn). A calibration curve is created by linear regression from the obtained X-ray fluorescence intensity of Sn and the film thickness measured by the STEM. Hereinafter, the film thickness of the tin oxide layer measured by the above measurement method will also be referred to as the "Sn film thickness."

[0024] (Conditions for measurement using XRF device) XRF device: EDX-7000 (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 Smoothing points: 5 Number of repetitions: 1 Background calculation: Automatic Sample form: Bulk (sample size: 16 mm × 11 mm)

[0025] Condition A: Coverage of Tin Oxide Layer The laminate according to the present invention satisfies the following condition A. Condition A: The peak current and peak potential of the anodic peak in a first cyclic voltammogram obtained by performing cyclic voltammetry on a conductive member whose surface is not covered with a tin oxide layer or the like are defined as current value A and potential V, respectively. The current value at potential V in a second cyclic voltammogram obtained by performing cyclic voltammetry on a laminate in which a tin oxide layer is disposed on the surface of a conductive member is defined as current value B. In this case, the coverage calculated by the following formula (1) is 90% or more. Coverage (%)=(1-B / A)×100 (1)

[0026] The coverage derived by the above-mentioned cyclic voltammetry measurement indicates the coverage state of the tin oxide layer on the surface of the conductive member, and it is considered that the higher the coverage rate, the larger the area covered by the tin oxide layer on the surface of the conductive member and the more densely the tin oxide layer is covered. When the coverage rate is 90% or more and the laminate 7 satisfies condition A, the organic thin-film solar cell 1 manufactured using the laminate 7 will have excellent output characteristics. The measurement conditions for the above-mentioned cyclic voltammetry are shown below.

[0027] (Measurement conditions for cyclic voltammetry) Potentiostat: Multi-electrochemical measurement system (HZ-Pro S12, manufactured by Meiden Hokuto Co., Ltd.) Application: Hoktnet Client (version 1.15a, manufactured by Meiden Hokuto Co., Ltd.) Electrochemical cell: Plate electrode evaluation cell (VM2, manufactured by EC Frontier Co., Ltd.) Reference electrode: Ag / AgCl (RE-2A, manufactured by EC Frontier Co., Ltd.) Counter electrode: Platinum (CE-2, manufactured by EC Frontier Co., Ltd.) Reaction solution: 0.5 mM K ４ [Fe(CN) ６ ]・3H ２ O (Fujifilm Wako Pure Chemical Industries, Ltd.), 0.5 mM K ３ [Fe(CN) ６] (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and an aqueous solution containing 0.5 M KCl (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). Sweep rate: 50 mV / s Sweep range: -0.5 to 1.0 V

[0028] In order to obtain an organic thin-film solar cell having more excellent output characteristics, the coverage of the tin oxide layer 9 is preferably 90% or more, and more preferably 93% or more. The upper limit of the coverage of the tin oxide layer 9 is not particularly limited, and may be 100% or less.

[0029] [Method for Producing Laminate] The method for producing a laminate of the present invention is, in outline, a method for producing a laminate having a conductive member that serves as a light-transmitting electrode layer and a tin oxide layer that serves as an electron transport layer and is disposed on the surface of the conductive member. The method for producing a laminate of the present invention is not particularly limited, as long as it is a method that can produce a laminate having the above-mentioned conductive member and tin oxide layer, in which the Sn film thickness of the tin oxide layer is 5.0 to 80.0 nm and that satisfies condition A.

[0030] A more detailed example of a method for manufacturing a laminate is a method in which a conductive member 8 is cathodically polarized in a treatment solution containing a Sn component and a nitrate ion component, i.e., a current is passed through the conductive member 8 as a cathode, thereby forming a tin oxide layer 9 on the surface of the conductive member 8 (hereinafter also referred to as the "film formation method").

[0031] In this film formation method, the tin oxide layer 9 is presumed to be formed by the following mechanism. First, on the surface of the conductive member 8, a reduction reaction from nitrate ions to nitrite ions occurs, causing an increase in the pH of the treatment solution. As a result, for example, if the Sn component in the treatment solution is tin chloride, tin hydroxide is produced. This tin hydroxide adheres to the surface of the conductive member 8, and then undergoes dehydration and condensation through washing, drying, etc., to form the tin oxide layer 9. However, even if a mechanism other than the above is used, it is considered to be within the scope of the present invention 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.

[0032] The conductive member 8 used in this film formation method has been 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 (for example, a glass substrate with an ITO film) is cathodically polarized. In this case, the laminate obtained by this film formation method also has a transparent substrate.

[0033] The treatment liquid contains a Sn component (Sn compound). The Sn component supplies Sn (tin element) to the tin oxide layer 9 to be formed. The Sn component is not particularly limited as long as it is a compound that dissociates in the treatment liquid to generate Sn cations, and examples thereof include tin nitrate (Sn(NO ３ ) ２ ), tin fluoride (SnF ２ ), tin chloride (SnCl ２ ), tin bromide (SnBr ２ ), tin sulfate (SnSO ４ ) and tin acetate (Sn(CH ３ COO) ２ ) is preferably at least one selected from the group consisting of

[0034] The treatment liquid contains a nitrate ion component. The nitrate ion component is not particularly limited as long as it is a compound that dissociates in the treatment liquid to generate nitrate ions, and examples thereof include tin nitrate (Sn(NO ３ ) ２ ), nitric acid (HNO ３ ), sodium nitrate (NaNO ３ ), potassium nitrate (KNO ３ ), magnesium nitrate (Mg(NO ３ ) ２ ), calcium nitrate (Ca(NO ３ ) ２ ) and ammonium nitrate (NH ４ NO ３ ) is preferably at least one selected from the group consisting of

[0035] One of the Sn component and the nitrate ion component may also serve as the other. For example, when the Sn component is tin nitrate, the Sn component also serves as the nitrate ion component.

[0036] The content of the Sn component 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 content of the Sn component 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 is nitrate ions (NO ３ － On the other hand, the content of the nitrate ion component in the treatment solution 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, calculated as nitrate ions (NO ３ － ) 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 liquid is not particularly limited, but water is preferred. The pH of the treatment liquid is not particularly limited, but is, for example, 0.0 to 8.0, and preferably 0.1 to 6.0. A known acid component (e.g., phosphoric acid, sulfuric acid, etc.) or an alkali component (e.g., sodium hydroxide, aqueous ammonia, etc.) can be used to adjust the pH. The treatment liquid may contain a surfactant such as sodium lauryl sulfate and acetylene glycol, as necessary. From the viewpoint of stability of adhesion behavior over time, the treatment liquid may contain a condensed phosphate such as pyrophosphate.

[0039] The temperature of the treatment solution when performing this film formation method is preferably 20°C or higher, more preferably 40°C or higher, and even more preferably 50°C or higher, from the viewpoint of increasing the Sn film thickness of the resulting tin oxide layer 9. If the temperature of the treatment solution is high, the activation energy of the dehydration reaction is likely to be exceeded, and the number of hydroxy groups in the formed tin oxide layer tends to decrease. Therefore, it is thought that an increase in the temperature of the treatment solution promotes the production of tin hydroxide, resulting in a thicker Sn film thickness of the tin oxide layer. On the other hand, the upper limit of the temperature of the treatment solution is not particularly limited and is, for example, 90°C or lower, preferably 85°C or lower.

[0040] The treatment solution may further contain a conduction aid. Examples of the conduction aid 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. The above-mentioned nitrate ion component is also contained in the conduction aid. The content of the conduction aid in the treatment solution is preferably 0.001 to 3.5 mol / L, more preferably 0.005 to 3.0 mol / L, and even more preferably 0.01 to 2.0 mol / L.

[0041] The current density during cathodic polarization was 0.1 mA / cm ２ More than 1.0 mA / cm is preferred. ２ On the other hand, the current density when performing cathodic polarization is 100 mA / cm ２ Preferably, 80 mA / cm or less ２ More preferably, 50 mA / cm or less ２ The following is even more preferable. If the current density is within this range, it is easy to obtain a tin oxide layer 9 that uniformly covers the surface of the conductive member 8. The current application time is set appropriately to obtain the desired coverage and Sn film thickness of the tin oxide layer 9. As the counter electrode when performing cathodic polarization, an insoluble electrode such as a platinum electrode is preferred because it is suitable for this film formation method.

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

[0043] <Relationship between Current Flow Time and Current Density and Coverage Rate> When the current density is the same, the coverage rate can be increased by increasing the current flow time. The tin oxide layer 9 is formed by increasing the pH near the conductive member 8 due to current flow, generating tin hydroxide, which then undergoes a dehydration reaction. As the current flow time increases, there is time for the dehydration reaction to proceed sufficiently, which is thought to increase the Sn film thickness of the tin oxide layer 9 and increase the coverage rate.

[0044] <Relationship between Nitrate Ion Component Content and Coverage Rate> When the current density and current application time are the same, increasing the content of the nitrate ion component increases the Sn film thickness of the tin oxide layer 9 and can increase the coverage rate. Increasing the electrical conductivity in the treatment solution increases the reduction reaction rate, which promotes the production of tin hydroxide and increases the Sn film thickness of the tin oxide layer.

[0045] <Relationship between Temperature of Treatment Solution and Coverage Rate> When the temperature of the treatment solution is high, the activation energy of the dehydration reaction is easily exceeded, promoting the production of tin hydroxide, increasing the Sn film thickness of the tin oxide layer, and increasing the coverage rate.

[0046] <Relationship between pH of treatment solution and coverage rate> When the current density and current application time are the same, the lower the pH of the treatment solution, the more easily tin hydroxide generated by cathodic polarization redissolves in the treatment solution, resulting in a decrease in 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 current application time, thereby increasing the coverage rate.

[0047] In this film formation method, after cathodic polarization is performed by passing a current through the conductive member, the laminate 7 may be held in the treatment solution. It is believed that dissolution of the deposited tin oxide layer progresses as the holding time increases. Therefore, the holding time is not particularly limited as long as the tin oxide layer 9 does not dissolve completely, but is preferably 30 seconds or less, and more preferably 2 seconds or less.

[0048] In this film formation method, the conductive member with a tin oxide layer may be washed with water after cathodic polarization. The method of washing with water is not particularly limited, and examples include a method of immersing the conductive member with a tin oxide layer in water after cathodic polarization. The temperature (water temperature) of the water used for washing with water is preferably 10 to 90°C. The washing time is preferably more than 0.5 seconds, more preferably 1.0 to 5.0 seconds. Furthermore, instead of washing with water, or after washing with water, the conductive member with a tin oxide layer may be dried. The temperature and method of drying are not particularly limited, and for example, a drying method using a conventional dryer or electric furnace can be applied. The drying temperature is preferably 100°C or lower.

[0049] [Method for manufacturing organic thin-film solar cell] The method for manufacturing an organic thin-film solar cell of the present invention is a method for manufacturing an organic thin-film solar cell having, in this order, a light-transmitting electrode layer 2, an electron transport layer 3, an organic semiconductor layer 4, a hole transport layer 5, and a collector layer 6, using the above-mentioned laminate 7 of the present invention. Examples of the method for manufacturing an organic thin-film solar cell include a method of sequentially forming layers to become the organic semiconductor layer 4, the hole transport layer 5, and the collector layer 6 on the surface of the tin oxide layer 9 in the laminate 7.

[0050] An example of a method for forming the organic semiconductor layer 4 is to spin-coat a solution prepared by dissolving P3HT and PCBM in a solvent onto the surface of the tin oxide layer 9 that will become the electron transport layer 3, followed by drying. Examples of solvents for the solution include N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, pyridine, and γ-butyrolactone. A mixed solvent of two or more solvents may also be used as the solvent.

[0051] The hole transport layer 5 may be formed, for example, by spin-coating an aqueous dispersion of PEDOT / PSS onto the surface of the organic semiconductor layer 4 and drying it.

[0052] An example of a method for forming the collecting electrode layer 6 is a method for forming the collecting electrode layer 6 by vapor-depositing a conductive metal such as Au on the surface of the hole transport layer 5. The method for forming each layer is not limited to these methods, and any conventionally known method can be used as appropriate.

[0053] The present invention will be specifically described below with reference to examples, although the present invention is not limited to the following examples.

[0054] <Preparation of Conductive Member> An ITO (Indium Tin Oxide) film-coated glass substrate (sheet resistance: 5 Ω / sq, manufactured by Geomatec Co., Ltd.) was prepared, which had an ITO (indium tin oxide) film deposited by sputtering on one surface of a glass substrate (15 mm × 35 mm, thickness 0.7 mm, alkali-free glass). This ITO film-coated glass substrate was used as a transparent substrate with a conductive member to produce a laminate.

[0055] <Preparation of Laminate> First, tin chloride (SnCl ２ ) as a nitrate ion component, and ３ ) or potassium nitrate (KNO ３ In preparing each treatment solution, the amounts of the Sn component and the nitrate ion component were adjusted so that the contents (unit: mol / L) of the Sn component and the nitrate ion component were as shown in Tables 1 and 2 below.

[0056] Next, the prepared ITO-coated glass substrate (transparent substrate with conductive member) was immersed in a cleaning solution prepared by diluting Semiclean (registered trademark) M4 (manufactured by Yokohama Yushi Kogyo Co., Ltd.) detergent 20 times with ion-exchanged water, and ultrasonic cleaning was performed for 10 minutes. Thereafter, the ITO-coated glass substrate was removed from the cleaning solution, immersed in ion-exchanged water, and ultrasonic cleaning was performed for 10 minutes.

[0057] The cleaned ITO-coated glass substrate was immersed in each of the prepared treatment solutions. The temperature (unit: °C) of the treatment solution was set as shown in Tables 1 and 2 below. Tables 1 and 2 also show the pH of the treatment solution measured with a pH meter. The ITO-coated glass substrate was cathodically polarized in the treatment solution under the cathodic polarization conditions (current density and current application time) shown in Tables 1 and 2 below. The current application was stopped, and within 2 seconds from the end of the cathodic polarization, the ITO-coated glass substrate with the tin hydroxide attached was removed from the treatment solution. It was then immersed in water at 25°C in a water tank for 2.0 seconds to be washed, and then dried at room temperature using a blower. This formed a tin oxide layer (16 mm × 10 mm) that would serve as an electron transport layer on the surface of the ITO film of the ITO-coated glass substrate, thereby producing an ITO-coated glass substrate (a laminate that would serve as a light-transmitting electrode layer and an electron transport layer) with the tin oxide layer formed thereon.

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

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

[0060] <Fabrication of Organic Thin Film Solar Cells> Each of the fabricated laminates was used to fabricate a 4 mm x 10 mm, i.e., 0.4 cm, thin film solar cell as follows. ２ We fabricated an organic thin-film solar cell (PSC) with a photoelectric conversion area of ​​1000 nm.

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

[0062] <<Formation of Hole Transport Layer>> Polyoxyethylene tridecyl ether (PTE:C １３ H ２７ (OCH ２ CH ２ ) ６ A nonionic surfactant (manufactured by Aldrich) containing 1% by weight of ethylenediaminetetraacetic acid (E2O3) and 1% by weight of xylene, and solvents of water and isopropanol, was prepared. A PTE-containing PEDOT / PSS aqueous dispersion was prepared by mixing 0.5 parts by weight of this nonionic surfactant with 100 parts by weight of a 1.3% by weight PEDOT / PSS aqueous dispersion (manufactured by Aldrich). The PTE-containing PEDOT / PSS aqueous dispersion heated to 70°C was dropped onto the surface of the organic semiconductor layer, spin-coated at 6000 rpm for 60 seconds, and air-dried at room temperature to form a hole-transport layer with a thickness of 80 nm.

[0063] <<Formation of Collector Layer>> An Au electrode layer (collector layer) was formed on the surface of the formed hole transport layer by vacuum deposition to a thickness of approximately 100 nm. More specifically, a shadow mask corresponding to the shape of the 4 mm × 10 mm electrode and a glass substrate on which the hole transport layer had been formed were placed in a chamber. The pressure inside the chamber was reduced using a rotary pump and a turbomolecular pump, and the pressure inside the chamber was reduced to 2 × 10 －３ In this chamber, a gold wire was resistance-heated, and a 100 nm thick Au film was formed on the surface of the hole transport layer through a shadow mask. The film formation rate was 10 to 15 nm / min, and the pressure during film formation was 1×10 －２ Pa or less.

[0064] The glass substrate thus obtained, having an ITO film (light-transmitting electrode layer), a tin oxide layer (electron transport layer), an organic semiconductor layer, a hole transport layer, and a collector electrode layer formed on one surface thereof, was sealed in the atmosphere to produce an organic thin-film solar cell having the glass substrate, ITO film (light-transmitting electrode layer), a tin oxide layer (electron transport layer), an organic semiconductor layer, a hole transport layer, and a collector electrode layer in this order.

[0065] <Evaluation of Organic Thin-Film Solar Cells> The following evaluations were carried out on the fabricated organic thin-film solar cells. Using a solar simulator (XES-502S, manufactured by SAN-EI Electric Co.), a solar cell with a spectral distribution of AM1.5G (IEC standard 60904-3) and a power of 100 mW / cm ２ The organic thin-film solar cell was irradiated from the ITO film side with simulated sunlight having a light intensity of 1000 kJ / s. In this state, the photocurrent-voltage profile of the organic thin-film solar cell was measured using a linear sweep voltammetry (LSV) measuring device (HZ-5000, manufactured by Hokuto Denko Corporation). The conversion efficiency (photoelectric conversion efficiency) was determined from the obtained profile and evaluated according to the following criteria. The results are shown in Tables 1 and 2 below. The higher the conversion efficiency value, the more excellent the output characteristics can be evaluated.

[0066] (Conversion efficiency evaluation criteria) A: Conversion efficiency is 1.2 times or more that of the reference cell B: Conversion efficiency is more than 1 time but less than 1.2 times that of the reference cell C: Conversion efficiency is 1 time or less that of the reference cell

[0067] In addition, the reference cell (organic thin-film solar cell of Comparative Example 9) was produced according to the above-mentioned method for producing an organic thin-film solar cell, except that, when producing the laminate, instead of forming a tin oxide layer by cathode polarization, a dispersion of 2.5% by mass of tin oxide nanoparticles (18282-10-5, manufactured by Thermo Scientific) dispersed in 1-butanol (solvent) was spin-coated at 4000 rpm for 10 seconds to form a tin oxide layer having a Sn film thickness of 20.0 nm. The organic thin-film solar cells of Comparative Example 7 and Comparative Example 8 were produced according to the above-mentioned method for producing the reference cell, except that the spin-coating conditions were changed to form tin oxide layers having Sn film thicknesses of 300.0 nm and 100.0 nm, respectively.

[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 produced organic thin-film solar cell (OPV). In the tables, when the "Classification" column of "Film Formation Method" shows "A," it means that the tin oxide layer was formed and the laminate was produced by performing cathodic polarization using the treatment solution shown in the "Treatment Solution Composition" column under the conditions shown in the "Cathode Polarization Conditions" column. Furthermore, when the "Classification" column of "Film Formation Method" shows "B," it means that the tin oxide layer was formed by the above-mentioned spin coating and the laminate was produced.

[0069]

[0070]

[0071] <Summary of Evaluation Results> In Tables 1 and 2, underlined values ​​indicate values ​​outside the range of the present invention. As shown in Tables 1 and 2, all of Examples 1 to 19, in which the Sn film thickness of the tin oxide layer was 5.0 nm or more and 80.0 nm or less and the coverage of the tin oxide layer was 90% or more, exhibited good output characteristics. In particular, Examples 1 to 17, in which the Sn film thickness of the tin oxide layer was 10.0 nm or more and 50.0 nm or less and the coverage was 90% or more, exhibited better output characteristics. In contrast, Comparative Example 4, in which the Sn film thickness of the tin oxide layer was too thin, Comparative Examples 2 and 5, in which the Sn film thickness was too thick, and Comparative Examples 1, 3, and 6 to 9, in which the coverage was too low, exhibited insufficient output characteristics.

[0072] <<Sn Film Thickness>> The Sn film thickness increases with an increase in the charge density, which is the product of the current density and the current flow time. Comparing Examples 9 to 11 and 15 to 17, which differ only in the current flow time, the Sn film thickness increased with an increase in the current flow time. By adjusting the current flow time so that the Sn film thickness was 5.0 nm or more and 80.0 nm or less, the power generation efficiency was evaluated as B. Furthermore, by adjusting the current flow time so that the Sn film thickness was 10.0 nm or more and 50.0 nm or less, the power generation efficiency was evaluated as A. This is presumably because adjusting the Sn film thickness can suppress leakage current and reduce the migration resistance of holes generated in the organic semiconductor layer 4 adjacent to the electron transport layer 3 (tin oxide layer 9). Furthermore, when obtaining similar Sn film thicknesses at different current densities, the current flow time decreased at higher current densities and increased at lower current densities. Thus, adjusting the current flow time can obtain similar Sn film thicknesses even when the current density is changed. As the current density increases, the reduction reaction rate of nitrate ions increases, so that a desired Sn film thickness can be obtained in a short current application time.

[0073] <<Coverage>> The coverage increased with increasing Sn film thickness, reaching 90% or more when the Sn film thickness was 5.0 nm or greater, and tended to reach 95% or greater when the Sn film thickness was 10.0 nm or greater. Comparing Examples 1 to 19 and Comparative Examples 1 to 6, when the Sn film thickness was greater than a predetermined value, the coverage reached a sufficiently high value of 90% or greater. On the other hand, in Comparative Example 2, when the Sn film thickness was too thick, the coverage fell to 90% or less. This is thought to be because an excessively thick Sn film makes the tin oxide layer more susceptible to cracking, exposing part of the light-transmitting electrode and reducing the coverage. Furthermore, in Comparative Examples 1 and 3, the coverage sometimes fell to 90% or less even when the Sn film thickness was within the range of 5.0 to 80.0 nm. This is thought to be due to the fact that, under conditions that favor relatively favorable reaction, such as high reaction temperature, high current density, and long current application time, tin oxide is generated locally in a short period of time, causing unevenness in the Sn film thickness, resulting in a reduced coverage.

[0074] 1: Organic thin-film solar cell 2: Light-transmitting electrode layer 3: Electron transport layer 4: Organic semiconductor layer 5: Hole transport layer 6: Collector electrode layer 7: Laminate 8: Conductive member 9: Tin oxide layer

Claims

1. 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 electrode layer in this order, wherein the laminate that forms the light-transmitting electrode layer and the electron transport layer comprises: a conductive member that forms the light-transmitting electrode layer; and a tin oxide layer that forms the electron transport layer and is disposed on the surface of the conductive member, wherein the film thickness of the tin oxide layer is 5.0 nm or more and 80.0 nm or less, and the laminate satisfies the following condition A. Condition A: The peak current and peak potential of an anodic peak that appear in a first cyclic voltammogram obtained by performing cyclic voltammetry on the conductive member whose surface is uncoated are defined as current value A and potential V, respectively. The current value at potential V in a second cyclic voltammogram obtained by performing cyclic voltammetry on the laminate is defined as current value B. In this case, the coverage calculated by the following formula (1) is 90% or more. Coverage (%) = (1 - B / A) × 100 (1) 2. An organic thin-film solar cell having, in this order, a light-transmitting electrode layer, an electron transport layer, an organic semiconductor layer, a hole transport layer, and a collector electrode layer, wherein the light-transmitting electrode layer and the electron transport layer are the laminate according to claim 1.

3. A method for producing the laminate according to claim 1, comprising cathodically polarizing the conductive member in a treatment solution containing a Sn component and a nitrate ion component, thereby forming the tin oxide layer on the surface of the conductive member.

4. A method for producing an organic thin-film solar cell, using the laminate according to claim 1, which comprises producing 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 electrode layer in this order.

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