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

Abstract

Provided is a laminate that can provide a perovskite solar cell with excellent output characteristics. [Solution] 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 electrode layer in this order, the laminate that forms the light-transmitting electrode layer and the electron transport layer includes 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, and the film thickness of the tin oxide layer is 5.0 nm or more and 80.0 nm or less.

Description

[Technical Field]

[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. [Background technology]

[0002] Conventionally, organic thin-film solar cells known are those with a "forward-linked (NIP structure)" having a light-transmitting electrode layer, an electron transport layer, an organic semiconductor layer, a hole transport layer, and an electrode collector layer in that order. Furthermore, in recent years, from the perspective of improving durability and other factors, an "inverted (PIN structure)" organic thin-film solar cell has been proposed, which has a light-transmitting electrode layer, a hole transport layer, an organic semiconductor layer, an electron transport layer, and an electrode collector layer in that order. 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 an electrode collector layer are formed in order on a transparent electrode layer, and each of the oxide semiconductor layer, organic semiconductor layer, conductive polymer layer, and electrode collector layer is composed of a specific material. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Special Publication No. 2009-146981 [Overview of the project] [Problems that the invention aims to solve]

[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 an electrode collecting layer in this order. Such organic thin-film solar cells are required to exhibit excellent power output characteristics.

[0005] Therefore, the present invention aims to provide a laminate that serves as the light-transmitting electrode layer and electron transport layer for a sequential organic thin-film solar cell having a light-transmitting electrode layer, an electron transport layer, an organic semiconductor layer, a hole transport layer, and an electrode collector layer in that order, and that yields an organic thin-film solar cell with excellent output characteristics. Furthermore, the present invention aims to provide an organic thin-film solar cell having excellent output characteristics. Furthermore, the present invention aims to provide a novel method for manufacturing the above-mentioned laminate, and a novel method for manufacturing an organic thin-film solar cell. [Means for solving the problem]

[0006] As a result of diligent research, the inventors of this invention discovered that the above objective can be achieved by adopting the following configuration, and thus completed the present invention.

[0007] In other words, 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 an electrode collector layer in this order, wherein the laminate comprising 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 disposed on the surface of the conductive member, the thickness of the tin oxide layer being 5.0 nm or more and 80.0 nm or less, and satisfying the following condition A. Condition A: The peak current and peak potential of the anode peak appearing in the first cyclic voltammogram obtained by performing cyclic voltammetry on the conductive member whose surface is not coated are defined as current value A and potential V, respectively. The current value at potential V in the second cyclic voltammogram obtained by performing cyclic voltammetry on the laminate is defined as current value B. At this time, the coverage rate calculated from formula (1) (coverage rate (%) = (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 an electrode collector layer in this order, wherein the light-transmitting electrode layer and the electron transport layer are the laminate described in [1]. A method for manufacturing a laminate described in [3][1], comprising forming the tin oxide layer on the surface of the conductive member by cathode polarization of the conductive member in a treatment solution containing a Sn component and a nitrate ion component. A method for manufacturing an organic thin-film solar cell, comprising using the laminate described in [4][1] to produce 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 an electrode collector layer in that order. [Effects of the Invention]

[0008] According to the present invention, a laminate comprising a light-transmitting electrode layer, an electron transport layer, an organic semiconductor layer, a hole transport layer, and an electrode collector layer in that order can be provided as the light-transmitting electrode layer and electron transport layer of an organic thin-film solar cell, and an organic thin-film solar cell having excellent output characteristics can be obtained. Furthermore, according to the present invention, an organic thin-film solar cell with excellent output characteristics can be provided. Furthermore, the present invention provides a novel method for manufacturing the above-mentioned laminate, and a novel method for manufacturing an organic thin-film solar cell. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional view showing an example of the configuration of an organic thin-film solar cell. [Figure 2] This is a schematic cross-sectional view showing an example of the structure of a laminate. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described in detail below with reference to the drawings. However, the embodiments described below are examples only, and the present invention is not limited to the embodiments described below. In the drawings, for the sake of easier visual recognition and description, the scales of the components may be different from the actual ones. In this specification, when a range is expressed using "~", 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 kind of substance corresponding to the component, or two or more kinds may be used in combination. In this specification, when there are two or more kinds of a certain component, the description regarding the content of the component intends the total content of two or more kinds of components. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment.

[0011] [Organic thin-film solar cell] First, based on FIG. 1, the organic thin-film solar cell 1 will be described. FIG. 1 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 FIG. 1 has a light-transmissive electrode layer 2, an electron transport layer 3, an organic semiconductor layer 4, a hole transport layer 5, and a current collection electrode layer 6 in this order. The thicknesses of the organic semiconductor layer 4, the hole transport layer 5, and the current collection electrode layer 6 are appropriately set.

[0012] As the light-transmissive electrode layer 2, for example, films of conductive metal oxides such as indium tin oxide (ITO) film and fluorine-doped tin oxide (FTO) film are preferably cited. The thickness of the light-transmissive electrode layer 2 conforms to the thickness of the conductive member 8 (see FIG. 2) described later. The light-transmissive electrode layer 2 may be disposed on the surface of a transparent substrate such as a glass substrate and a resin film. In that case, the transparent substrate is disposed on the surface of the light-transmissive 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 the preferred embodiment 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 (SnO22) which is an n-type semiconductor. The thickness of the electron transport layer 3 is equivalent to the thickness of the tin oxide layer 9 (see Figure 2), which will be described later.

[0014] Examples of organic semiconductor layer 4 include poly-3-hexylthiophene (P3HT), a polythiophene derivative, and [6,6]-phenyl-C, a fullerene derivative. 61 -Examples include layers containing methyl butyrate (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, polyp-phenylene-based, polyp-phenylene-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 discussed later). Examples of pigments include cyanine, merocyanine, phthalocyanine, naphthalocyanine, azo, quinone, quinacridone, squarylium, triphenylmethane, xanthene, porphyrin, perylene, and indigo pigments. The additive content is preferably 1 to 100 parts by mass, and more preferably 1 to 40 parts by mass, based on 100 parts by mass of the total of P3HT and PCBM.

[0015] Examples of materials constituting the hole transport layer 5 include PEDOT / PSS, vanadium oxide (V2O5), and molybdenum oxide (MoO3), with PEDOT / PSS being preferred. PEDOT / PSS is a polymer formed by the integration of PEDOT (poly-3,4-ethylenedioxythiophene) and PSS (polystyrene sulfonic acid), and is sometimes written as PEDOT:PSS.

[0016] Examples of the electrode collecting layer 6 include an Au electrode layer, an Ag electrode layer, an Al electrode layer, and a Ca electrode layer, with the Au electrode layer being preferred.

[0017] [Laminated structure] Next, based on Figure 2, we will describe the laminate 7 which will form the light-transmitting electrode layer 2 and electron transport layer 3 of the organic thin-film solar cell 1 (see Figure 1). Figure 2 is a schematic cross-sectional view showing an example of the configuration of the laminate 7. The laminate 7 has a conductive member 8 which serves as a light-transmitting electrode layer 2 (see Figure 1), and a tin oxide layer 9 which serves as an electron transport layer 3 (see Figure 1) arranged on the surface of the conductive member 8.

[0018] <Conductive materials> The conductive member 8 contains a light-transmitting conductive compound and functions as a light-transmitting electrode layer 2 (see Figure 1) when used in an organic thin-film solar cell. The conductive member 8 preferably contains a conductive metal oxide, and more preferably contains indium oxide or tin oxide. If the conductive member 8 is a member containing indium oxide, it is more preferably a member containing indium tin oxide (ITO), and particularly preferably an ITO film. If the conductive member 8 is a member containing 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 placed on the surface of a transparent substrate such as a glass substrate or a resin film. In that case, the transparent substrate is placed on the surface of the conductive member 8 opposite to the tin oxide layer 9.

[0019] For example, the thickness of the conductive member 8, which is an ITO film or an FTO film, is appropriately set according to the resulting organic thin-film solar cell 1 (see Figure 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 obtained by forming a cross-section of the conductive member 8 using 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. The tin oxide layer 9 functions as the electron transport layer 3 (see Figure 1) in the organic thin-film solar cell 1. The electron transport layer 3 extracts electrons generated in the organic semiconductor layer 4 during light absorption, suppressing the backflow of holes, thereby inhibiting electron-hole recombination 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. However, in this invention, tin oxide is used as the material for the electron transport layer 3. This is because tin oxide possesses optimal energy levels, high electron mobility, high transmittance, and environmental stability.

[0021] 《Film Thickness》 The thickness of the tin oxide layer 9 is between 5.0 nm and 80.0 nm. As a result, the organic thin-film solar cell 1 manufactured using the laminate 7 exhibits excellent power output characteristics. When the thickness of the tin oxide layer 9 is 5.0 nm or more, areas not covered by the tin oxide layer 9 are less likely to exist on the surface of the conductive member 8. This is expected to reduce leakage current and improve output characteristics. Furthermore, it is presumed that if the thickness of the tin oxide layer 9 is 80.0 nm or less, the resistance to electron transfer generated in the organic semiconductor layer 4 adjacent to the electron transport layer 3 (tin oxide layer 9) will be reduced, thereby improving the output characteristics. However, even if the mechanism is different from the one described above, as long as the thickness of the tin oxide layer 9 is between 5.0 nm and 80.0 nm, it is considered to be within the scope of the present invention.

[0022] For the reason that it provides superior 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 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 then subjected to X-ray fluorescence analysis using an XRF spectrometer under the following conditions, and the X-ray fluorescence intensity of tin (Sn) is measured. The thickness of the tin oxide layer 9 (in nm) is determined from the obtained Sn X-ray fluorescence intensity and the film thickness measured by STEM, using a pre-prepared calibration curve. The calibration curve is created using the following method. First, a sample containing a tin oxide layer is prepared, and a cross-sectional sample is prepared by processing it into a thin section using a focused ion beam (FIB). The obtained cross-sectional sample is observed using a scanning transmission electron microscope (STEM), and the film thickness (in nm) is measured. In addition, X-ray fluorescence analysis is performed on any part of the same sample used for length measurement with the STEM, using an X-ray fluorescence analyzer (XRF) under the following conditions, and the X-ray fluorescence intensity of tin (Sn) is measured. A calibration curve is created using a linear regression method from the obtained Sn X-ray fluorescence intensity and the film thickness measurement obtained by STEM. Hereafter, the thickness of the tin oxide layer measured by the above measurement method will also be referred to as "Sn thickness."

[0024] (Measurement conditions using XRF equipment) • XRF device: EDX-7000 (manufactured by Shimadzu Corporation) • X-ray tube: Rhodium (Rh) target (voltage: 50kV, current: 88μA) • Primary filter: OPEN • Detector: Silicon drift semiconductor detector ·Analysis area: φ5mm ·Analysis time: 100 seconds • Dead time: 30% • Smoothing calculation method: Savitzky-Gloay Smoothing score: 5 • Number of repetitions: 1 • Background calculation: Automatic • Sample form: Bulk (Sample size: 16mm x 11mm)

[0025] Condition A: Coverage rate of the 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 anode peak in the first cyclic voltammogram obtained by performing cyclic voltammetry on a conductive member whose surface is not coated with a tin oxide layer, etc., are defined as current value A and potential V, respectively. The current value at potential V in the second cyclic voltammogram obtained by performing cyclic voltammetry on a laminate in which a tin oxide layer is arranged on the surface of the conductive member is defined as current value B. At this time, the coverage rate calculated from the following formula (1) is 90% or more. Coverage rate (%) = (1 - B / A) × 100 (1)

[0026] The coverage ratio derived from the cyclic voltammetry measurement described above indicates the state of coverage of the tin oxide layer on the surface of the conductive material. A higher coverage ratio suggests that the area covered by the tin oxide layer on the surface of the conductive material is larger, and that the tin oxide layer is more densely covering the material. As long as 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 cyclic voltammetry described above 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: An aqueous solution containing 0.5 mM K4[Fe(CN)6]·3H2O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 0.5 mM K3[Fe(CN)6] (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 0.5 M KCl (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). ·Sweep speed: 50mV / s • Sweep range: -0.5~1.0V

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

[0029] [Method for manufacturing laminates] The present invention relates to a method for manufacturing a laminate, which is generally a method for manufacturing 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 disposed on the surface of the conductive member. The method for manufacturing the laminate of the present invention is not particularly limited as long as it is a method that can obtain a laminate having the above-mentioned conductive member and tin oxide layer, wherein the Sn film thickness of the tin oxide layer is 5.0 to 80.0 nm and satisfies condition A.

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

[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, the pH of the treatment solution increases due to the reduction reaction from nitrate ions to nitrite ions. 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 after subsequent dehydration condensation through washing, drying, etc., a tin oxide layer 9 is formed. However, even if the mechanism is different from the one described above, 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, it is considered to be within the scope of the present invention.

[0032] The conductive member 8 used in this film formation method has already been described. When the conductive member 8 is placed 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 cathode-polarized. In this case, the laminate obtained by this film formation method also has a transparent substrate.

[0033] The processing solution contains a Sn component (Sn compound). The Sn component supplies Sn (elemental tin) to the tin oxide layer 9 that is formed. The Sn component is not particularly limited as long as it is a compound that dissociates in the treatment solution to produce a Sn cation, but 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) is preferred.

[0034] The treatment solution contains nitrate ions. The nitrate ion component is not particularly limited as long as it is a compound that dissociates in the treatment solution to produce nitrate ions, but at least one selected from the group consisting of 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) is preferred.

[0035] The Sn component and the nitrate ion component may each serve the same purpose as the other. For example, if the Sn component is tin nitrate, then the Sn component also functions as a nitrate ion component.

[0036] The Sn component content in the processing 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 component content in the processing 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 (NO3 - Converted to 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 is nitrate ions (NO3 - Converted to 0.001 mol / L or higher, more preferably 0.005 mol / L or higher, and even more preferably 0.01 mol / L or higher.

[0038] The solvent included in the processing solution is not particularly limited, but water is preferred. The pH of the treatment solution is not particularly limited, but is, for example, 0.0 to 8.0, and preferably 0.1 to 6.0. Known acidic components (e.g., phosphoric acid and sulfuric acid) or alkaline components (e.g., sodium hydroxide and ammonia water) can be used to adjust the pH. The treatment solution may contain surfactants such as sodium lauryl sulfate and acetylene glycol, as needed. From the viewpoint of the stability of adhesion behavior over time, the treatment solution may also contain condensed phosphates such as pyrophosphates.

[0039] When performing this film formation method, the temperature of the processing solution 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 thickness of the resulting tin oxide layer 9. When the temperature of the processing solution is high, the activation energy of the dehydration reaction is easily exceeded, so the number of hydroxyl groups in the formed tin oxide layer tends to decrease. Therefore, it is thought that increasing the temperature of the processing solution promotes the formation of tin hydroxide, and thus the thickness of the tin oxide layer increases. On the other hand, the upper limit of the liquid temperature of the processing solution is not particularly limited, but is, for example, 90°C or lower, and preferably 85°C or lower.

[0040] The processing solution may further contain a conduction aid. Examples of conduction 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 nitrate ion component mentioned above is contained in the conduction aid. The content of the conductive additive in the processing 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 when applying cathode polarization is 0.1 mA / cm². 2 The above is preferable, and 1.0 mA / cm 2 The above is preferable. On the other hand, the current density when applying cathode polarization is 100 mA / cm². 2 The following is preferable: 80 mA / cm 2 The following is more preferable: 50 mA / cm 2 The following is even more preferable: If the current density is within this range, a tin oxide layer 9 that uniformly covers the surface of the conductive member 8 is easily obtained. The energizing time is set appropriately to obtain the desired coverage and Sn thickness of the tin oxide layer 9. As the counter electrode for cathode polarization, an insoluble electrode such as a platinum electrode is preferred because it is suitable for this film deposition method.

[0042] Next, we will discuss methods for increasing coverage under various cathode polarization conditions.

[0043] Relationship between energizing time, current density, and coverage ratio When the current density is the same, the coverage can be increased by increasing the energizing time. The tin oxide layer 9 is formed when the pH near the conductive member 8 rises due to the energizing, generating tin hydroxide, which then undergoes a dehydration reaction. As the energizing time increases, there is sufficient time for the dehydration reaction to proceed, so the Sn film thickness of the tin oxide layer 9 increases, and the coverage is expected to increase.

[0044] Relationship between nitrate ion content and coverage rate When the current density and energizing time are the same, increasing the content of nitrate ions increases the Sn film thickness of the tin oxide layer 9, thereby increasing the coverage. The increased electrical conductivity in the treatment solution leads to a higher reduction reaction rate, which in turn promotes the formation of tin hydroxide and increases the Sn film thickness of the tin oxide layer.

[0045] Relationship between the temperature of the processing solution and the coverage rate. When the temperature of the processing solution is high, the activation energy of the dehydration reaction is more likely to be exceeded, which promotes the formation of tin hydroxide, increases the Sn film thickness of the tin oxide layer, and increases the coverage rate.

[0046] Relationship between pH of the treatment solution and coverage 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 cathode 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, increasing the energizing time can increase the Sn film thickness and thus increase the coverage rate.

[0047] In this film formation method, after applying current to a conductive member to perform cathode polarization, the laminate 7 may be held in the processing solution. It is thought that the dissolution of the deposited tin oxide layer progresses as the holding time increases. Therefore, the holding time is not particularly limited as long as it is not enough time for the tin oxide layer 9 to dissolve completely, but it is preferably 30 seconds or less, and more preferably 2 seconds or less.

[0048] In this film formation method, the conductive member with the tin oxide layer may be washed with water after cathode polarization. The method of washing is not particularly limited, and examples include immersing the conductive member with the tin oxide layer in water after cathode polarization. The water temperature used for washing is preferably 10 to 90°C. The rinsing time is preferably more than 0.5 seconds, and more preferably between 1.0 and 5.0 seconds. Furthermore, the conductive member with the tin oxide layer may be dried instead of, or after, rinsing with water. The temperature and method of drying are not particularly limited; 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] [Manufacturing method for organic thin-film solar cells] The present invention provides a method for manufacturing an organic thin-film solar cell, which uses the laminated structure 7 described above to produce an organic thin-film solar cell having a light-transmitting electrode layer 2, an electron transport layer 3, an organic semiconductor layer 4, a hole transport layer 5, and an electrode collector layer 6 in that order. One example of a method for manufacturing an organic thin-film solar cell is to sequentially form layers that will become an organic semiconductor layer 4, a hole transport layer 5, and an electrode collecting layer 6 on the surface of a tin oxide layer 9 in a laminate 7.

[0050] One method for forming the organic semiconductor layer 4 is to spin-coat a solution of P3HT and PCBM dissolved in a solvent onto the surface of a tin oxide layer 9 which will become the electron transport layer 3, and then dry it. 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.

[0051] One method for forming the hole transport layer 5 is to spin-coat an aqueous dispersion of PEDOT / PSS onto the surface of the organic semiconductor layer 4 and then dry it.

[0052] One method for forming the electrode collecting layer 6 is to deposit a conductive metal such as Au onto the surface of the hole transport layer 5. The method for forming each layer is not limited to these methods, and conventionally known methods can be used as appropriate. [Examples]

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

[0054] <Preparation of conductive materials> A glass substrate with an ITO (Indium Tin Oxide) film, laminated by sputtering on one surface of a glass substrate (15mm x 35mm, 0.7mm thick, alkali-free glass), was prepared (sheet resistance: 5Ω / sq, manufactured by Geomatec). This ITO-coated glass substrate was used as a transparent substrate with conductive material to fabricate a laminate.

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

[0056] Next, the prepared glass substrate with an ITO film (transparent substrate with a conductive member) was immersed in a cleaning solution in which semiclean (registered trademark) M4 (manufactured by Yokohama Oil & Fat Co., Ltd.), a detergent, was diluted 20 times with ion-exchanged water, and ultrasonic cleaning was performed for 10 minutes. Thereafter, the glass substrate with an ITO film was taken out of the cleaning solution, immersed in ion-exchanged water, and ultrasonic cleaning was performed for 10 minutes.

[0057] The cleaned glass substrate with an ITO film was immersed in each of the prepared treatment solutions. The temperature of the treatment solution (liquid temperature) was set to the temperatures (unit: °C) shown in Tables 1 and 2 below. Also, the pH of the treatment solution measured with a pH meter is shown in Tables 1 and 2 below. In the treatment solution, the glass substrate with an ITO film was cathodically polarized under the cathodic polarization conditions (current density and energization time) shown in Tables 1 and 2 below. When the energization was stopped and within 2 seconds from the end of the cathodic polarization, the glass substrate with an ITO film having tin hydroxide adhered thereto was taken out of the treatment solution, immersed in water at 25 °C in a water tank for 2.0 seconds for water washing, and then dried at room temperature using a blower. Thereby, a tin oxide layer (16 mm × 10 mm) serving as an electron transport layer was formed on the surface of the ITO film of the glass substrate with an ITO film, and a glass substrate with an ITO film (a laminate serving as a light-transmissive electrode layer and an electron transport layer) having the tin oxide layer formed thereon was produced.

[0058] 《Measurement of Sn film thickness》 For the produced laminate, the Sn film thickness of the tin oxide layer was determined according to the method described above. The results are shown in Tables 1 and 2 below.

[0059] 《Measurement of coverage rate (Condition A)》 For the produced laminate, the coverage rate of the tin oxide layer 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 cell〉 Using each of the produced laminates, as follows, 4 mm × 10 mm, that is, 0.4 cm 2We fabricated an organic thin-film solar cell (PSC) with a photoelectric conversion area.

[0061] Formation of an organic semiconductor layer A mixed solution was obtained by mixing 2,6-dichlorotoluene and chloroform in a volume ratio of 1:1. In this mixed solution, P3HT (manufactured by Aldrich) and PCBM (manufactured by Frontier Carbon Co., Ltd.) were dissolved in a mass ratio of 5:4, so that the total content of each compound relative to the total mass of the mixed solution was 3.9% by mass. The 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. The layers were then 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 the hole transport layer Polyoxyethylene tridecyl ether (PTE:C 13 H 27 A nonionic surfactant (manufactured by Aldrich) containing 1% by mass of (OCH2CH2)6OH) and 1% by mass of xylene, with water and isopropanol as solvents, was prepared. A PTE-containing PEDOT / PSS aqueous dispersion was prepared by mixing 0.5 parts by mass of this nonionic surfactant with 100 parts by mass of 1.3% by mass PEDOT / PSS aqueous dispersion (manufactured by Aldrich). A PTE-containing PEDOT / PSS aqueous dispersion heated to 70°C was dropped onto the surface of an organic semiconductor layer, spin-coated at 6000 rpm for 60 seconds, and then air-dried at room temperature to form a hole transport layer with a thickness of 80 nm.

[0063] Formation of the electrode collecting 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 glass substrate with a shadow mask and hole transport layer formed to match the electrode shape of 4 mm × 10 mm was placed inside the chamber. The pressure inside the chamber was reduced using a rotary pump and a turbomolecular pump, and the chamber pressure was set to 2 × 10⁻⁶ -3The pressure was kept below Pa. A gold wire was resistively heated in this chamber, and a 100 nm layer of Au was deposited on the surface of the hole transport layer via a shadow mask. The deposition rate was 10-15 nm / min, and the deposition pressure was 1 × 10⁻⁶. -2 It was below Pa.

[0064] The glass substrate obtained in this manner, on which an ITO film (light-transmitting electrode layer), a tin oxide layer (electron transport layer), an organic semiconductor layer, a hole transport layer, and an electrode collector layer were formed on one surface, was sealed in air. In this way, an organic thin-film solar cell having the glass substrate, ITO film (light-transmitting electrode layer), tin oxide layer (electron transport layer), organic semiconductor layer, hole transport layer, and electrode collector layer in this order was fabricated.

[0065] <Evaluation of organic thin-film solar cells> The following evaluations were performed on the fabricated organic thin-film solar cells. Using a solar-like light source device (SAN-EI Electric, XES-502S), it has a spectral distribution of AM1.5G (IEC standard 60904-3) and a power output of 100mW / cm². 2 Simulated sunlight with a light intensity of [specified intensity] was irradiated onto the organic thin-film solar cell from the ITO film side. Under these conditions, the photocurrent-voltage profile of the organic thin-film solar cell was measured using a linear sweep voltammetry (LSV) measuring device (Hokuto Denko, HZ-5000). 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. A higher conversion efficiency value indicates superior output characteristics.

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

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

[0068] Tables 1 and 2 show the film deposition method for the tin oxide layer, the measurement results for the laminate, and the evaluation results for the conversion efficiency of the fabricated organic thin-film solar cells (OPVs). In the table, if the "Classification" column for "Film Formation Method" shows "A," it means that a tin oxide layer was formed and a laminate was fabricated by performing cathode polarization under the conditions described in the "Cathode Polarization Conditions" column using the processing solution described in the "Processing Solution Composition" column. If the "Classification" column for "Film Formation Method" shows "B," it means that a tin oxide layer was formed and a laminate was fabricated by the spin coating method described above.

[0069] [Table 1]

[0070] [Table 2]

[0071] <Summary of Evaluation Results> In Tables 1 and 2 above, the underlined values ​​indicate that the present invention is outside its scope. As shown in Tables 1 and 2 above, all of the Invention Examples 1 to 19, in which the Sn film thickness of the tin oxide layer was 5.0 nm or more and the coverage rate of the tin oxide layer was 90% or more, showed good output characteristics. In particular, Invention Examples 1-2, 4-5, 7-8, 10-11, and 15-17, in which the Sn film thickness of the tin oxide layer was 10.0 nm or more and the coverage rate was 90% or more, showed better output characteristics. In contrast, Comparative Examples 4 (where the tin oxide layer was too thin), Comparative Examples 2 and 5 (where the tin oxide layer was too thick), and Comparative Examples 1, 3, and 6-9 (where the coverage was too low) exhibited insufficient output characteristics.

[0072] Sn film thickness The thickness of Sn film increases with increasing electrical density, which is the product of current density and energizing time. Comparing invention examples 9-11 and 15-17, which differ only in the energizing time, it was found that the Sn film thickness increased with increasing energizing time. By adjusting the energizing time so that the Sn film thickness was between 5.0 nm and 80.0 nm, the power generation efficiency was evaluated as B. Furthermore, by adjusting the energizing time so that the Sn film thickness was between 10.0 nm and 50.0 nm, the power generation efficiency improved to A. This is presumed to be because adjusting the Sn film thickness allows for the suppression of leakage current and the suppression of the resistance to hole movement generated in the organic semiconductor layer 4 adjacent to the electron transport layer 3 (tin oxide layer 9). Furthermore, when obtaining a similar Sn film thickness at different current densities, the energizing time decreased at higher current densities and increased at lower current densities. Thus, even when changing the current density, a similar Sn film thickness can be obtained by adjusting the energizing time. As the current density increases, the rate of the nitrate ion reduction reaction increases, allowing the desired Sn film thickness to be obtained with a shorter energizing time.

[0073] Coverage rate The coverage rate increased with increasing Sn film thickness, tending to reach over 90% when the film thickness was 5.0 nm or more, and over 95% when it was 10.0 nm or more. Comparing Invention Examples 1-19 and Comparative Examples 1-6, a sufficiently high coverage rate of over 90% was achieved when the Sn film thickness was above a predetermined value. On the other hand, in Comparative Example 2, when the Sn film thickness became too thick, the coverage rate fell below 90%. This is thought to be because excessively thick Sn film thickness makes it easier for cracks to occur in the tin oxide layer, exposing part of the light-transmitting electrode and reducing the coverage rate. Furthermore, in Comparative Examples 1 and 3, the coverage rate was sometimes 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 because, under conditions where the reaction proceeds relatively easily, such as high reaction temperature, high current density, and long current application time, tin oxide is generated locally in a short time, causing unevenness in the Sn film thickness and thus reducing the coverage rate. [Explanation of symbols]

[0074] 1:Organic thin film solar cell 2: Light-transparent electrode layer 3: Electron transport layer 4: Organic semiconductor layer 5: Hole transport layer 6:Collector electrode layer 7: Laminate 8: Conductive material 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 an electrode collector layer in this order, The light-transmitting electrode layer and the electron transport layer are The conductive member that forms the light-transmitting electrode layer, The conductive member has a tin oxide layer which serves as the electron transport layer, disposed on its surface. The thickness of the tin oxide layer is 10.0 nm or more and 80.0 nm or less. The laminate satisfies the following condition A: An organic thin-film solar cell in which the hole transport layer is composed of at least one material selected from the group consisting of a polymer in which poly-3,4-ethylenedioxythiophene and polystyrene sulfonic acid are integrated, vanadium oxide, and molybdenum oxide. Condition A: The peak current and peak potential of the anode peak appearing in the first cyclic voltammogram obtained by performing cyclic voltammetry on the conductive member whose surface is not coated are defined as current value A and potential V, respectively. The current value B is defined as the current value at potential V in the second cyclic voltammogram obtained by performing cyclic voltammetry on the laminate. At this time, the coverage rate calculated from the following formula (1) is 95% or more. Coverage rate (%) = (1 - B / A) × 100 (1)

2. 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 an electrode collector layer in this order, the laminate comprising the light-transmitting electrode layer and the electron transport layer, The conductive member that forms the light-transmitting electrode layer, The conductive member has a tin oxide layer which serves as the electron transport layer, disposed on its surface. The thickness of the tin oxide layer is 5.0 nm or more and 80.0 nm or less. A method for manufacturing a laminate that satisfies the following condition A, A method for manufacturing a laminate, comprising forming the tin oxide layer on the surface of a conductive member by cathode polarization of the conductive member in a treatment solution containing a tin component and a nitrate ion component. Condition A: The peak current and peak potential of the anode peak appearing in the first cyclic voltammogram obtained by performing cyclic voltammetry on the conductive member whose surface is not coated are defined as current value A and potential V, respectively. The current value B in the second cyclic voltammogram obtained by performing cyclic voltammetry on the laminate is defined as the current value B at the potential V. At this time, the coverage rate calculated from the following formula (1) is 90% or more. Coverage rate (%) = (1 - B / A) × 100 (1)

3. A method for manufacturing an organic thin-film solar cell, comprising using a laminate to produce 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 an electrode collector layer in that order, The aforementioned laminate, The conductive member that forms the light-transmitting electrode layer, The conductive member has a tin oxide layer which serves as the electron transport layer, disposed on its surface. The thickness of the tin oxide layer is 10.0 nm or more and 80.0 nm or less. The laminate satisfies the following condition A: A method for manufacturing an organic thin-film solar cell, wherein the hole transport layer is composed of at least one material selected from the group consisting of a polymer in which poly-3,4-ethylenedioxythiophene and polystyrene sulfonic acid are integrated, vanadium oxide, and molybdenum oxide. Condition A: The peak current and peak potential of the anode peak appearing in the first cyclic voltammogram obtained by performing cyclic voltammetry on the conductive member whose surface is not coated are defined as current value A and potential V, respectively. The current value B is defined as the current value at potential V in the second cyclic voltammogram obtained by performing cyclic voltammetry on the laminate. At this time, the coverage rate calculated from the following formula (1) is 95% or more. Coverage rate (%) = (1 - B / A) × 100 (1)

4. A method for manufacturing an organic thin-film solar cell, comprising using a laminate manufactured by the method for manufacturing a laminate described in claim 2, 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 an electrode collector layer in that order.

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