Method for producing fullerene derivative solutions and coated films

Abstract

To provide industrially useful fullerene derivative solutions, etc. [Solution] The fullerene derivative solution comprises a fullerene derivative, one or more first solvents, and one or more second solvents, wherein the boiling point of the first solvent is 200°C or lower. The boiling point of the second solvent is 100°C or lower. Among the Hansen solubility parameters of the first solvent, when the dispersion force term is δD1, the polarity term is δP1, and the hydrogen bonding term is δH1, the following conditions are satisfied: 17.8 ≤ δD1 ≤ 18.9, 4.4 ≤ δP1 ≤ 4.7, and 4.8 ≤ δH1 ≤ 6.9. The volume ratio of one or more first solvents to the total volume of one or more first solvents and one or more second solvents is greater than the volume ratio of one or more second solvents to the total volume.

Description

Technical Field

[0001] The present disclosure relates to a fullerene derivative solution and a method for producing a coating film using the fullerene derivative solution.

Background Art

[0002] Organic semiconductor materials have physical properties and functions that are not possessed by conventional inorganic semiconductor materials such as silicon. Therefore, in recent years, organic semiconductor materials have been actively studied as semiconductor materials that can realize new semiconductor devices and electronic devices.

[0003] For example, it has been studied to realize a photoelectric conversion element by thinning an organic semiconductor material and using it as a photoelectric conversion material. A photoelectric conversion element using an organic material thin film can be used as an image sensor such as a solid-state imaging device by extracting charges generated by light as electrical signals (see, for example, Patent Document 1).

[0004] Also, in a photoelectric conversion element using an organic semiconductor material, fullerene derivatives represented by phenyl C 61 methyl ester (

[60] PCBM) are widely used as acceptor materials. Fullerene derivatives have the property of being easily aggregated and difficult to dissolve in solvents, and research reports on the solubility of fullerene derivatives are also known (see, for example, Non-Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Non-Patent Documents

[0006]

Non-Patent Document 1

[0007] As mentioned above, fullerene derivatives are poorly soluble in solvents. On the other hand, in the industrial manufacturing process of devices, there is a need for industrially useful fullerene derivative solutions that can ensure sufficient film thickness when forming coated films containing fullerene derivatives using coating processes.

[0008] Therefore, this disclosure provides industrially useful fullerene derivative solutions and methods for producing coated films. [Means for solving the problem]

[0009] A fullerene derivative solution according to one aspect of the present disclosure comprises a fullerene derivative, one or more first solvents, and one or more second solvents, wherein the boiling point of the first solvent is 200°C or less, the boiling point of the second solvent is 100°C or less, and the Hansen solubility parameter of the first solvent is such that the dispersion force term is δD1, the polarity term is δP1, and the hydrogen bonding term is δH1, 17.8 ≤ δD1 ≤ 18.9, 4.4 ≤ δP1 ≤ 4.7, 4.8 ≤ δH1 ≤ 6.9 The following conditions are met: the volume ratio of one or more of the first solvents to the total volume of one or more of the first solvents and one or more of the second solvents is greater than the volume ratio of one or more of the second solvents to the total volume.

[0010] Furthermore, a method for manufacturing a coating film according to one aspect of the present disclosure includes the steps of preparing the fullerene derivative solution and forming a coating film by applying the fullerene derivative solution onto a substrate. [Effects of the Invention]

[0011] According to this disclosure, it is possible to provide industrially useful fullerene derivative solutions and methods for producing coated films. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic cross-sectional view showing a photoelectric conversion element according to Embodiment 2. [Figure 2] Figure 2 is a flowchart showing a method for manufacturing a coated film used in a photoelectric conversion element according to Embodiment 2. [Modes for carrying out the invention]

[0013] (Summary of this disclosure) As an overview of one aspect of this disclosure, an example of a method for producing a fullerene derivative solution and a coated film related to this disclosure is shown below.

[0014] A fullerene derivative solution according to a first aspect of this disclosure comprises a fullerene derivative, one or more first solvents, and one or more second solvents, wherein the boiling point of the first solvent is 200°C or less, the boiling point of the second solvent is 100°C or less, and the Hansen solubility parameter of the first solvent is such that the dispersion force term is δD1, the polarity term is δP1, and the hydrogen bonding term is δH1, 17.8 ≤ δD1 ≤ 18.9, 4.4 ≤ δP1 ≤ 4.7, 4.8 ≤ δH1 ≤ 6.9 is satisfied, and the volume ratio of one or more of the first solvents to the total volume of one or more of the first solvents and one or more of the second solvents is greater than the volume ratio of one or more of the second solvents to the total volume.

[0015] Thereby, while maintaining the solubility of the fullerene derivative, the drying rate during coating can be increased, so that it is possible to ensure the film thickness when forming a coating film using the fullerene derivative solution. Therefore, an industrially useful fullerene derivative solution can be realized.

[0016] Further, for example, the fullerene derivative solution according to the second aspect of the present disclosure is the fullerene derivative solution according to the first aspect, and when the dispersion force term is δD2 among the Hansen solubility parameters of the second solvent, δD1 > δD2 is satisfied.

[0017] Thereby, the first solvent can easily cover the periphery of the fullerene derivative, and the solubility of the fullerene derivative can be maintained even when the second solvent is included in the fullerene derivative solution.

[0018] Further, for example, the fullerene derivative solution according to the third aspect of the present disclosure is the fullerene derivative solution according to the first aspect or the second aspect, and when the hydrogen bond term is δH2 among the Hansen solubility parameters of the second solvent, δH1 > δH2 is satisfied.

[0019] Thereby, the second solvent is less likely to form a hydrogen bond with the fullerene derivative than the first solvent, and the solubility of the fullerene derivative in the fullerene derivative solution can be maintained even when the second solvent is included in the fullerene derivative solution.

[0020] Further, for example, the fullerene derivative solution according to the fourth aspect of the present disclosure is the fullerene derivative solution according to any one of the first aspect to the third aspect, and when the dispersion force term is δD2, the polar term is δP2, and the hydrogen bond term is δH2 among the Hansen solubility parameters of the second solvent, 15.5 ≦ δD2 ≦ 17.5, 4.0 ≤ δP2 ≤ 6.0, 3.0 ≤ δH2 ≤ 6.0 The condition is met.

[0021] This allows the solubility of the fullerene derivative to be maintained even when a second solvent is present in the fullerene derivative solution.

[0022] Furthermore, for example, the fullerene derivative solution according to the fifth aspect of this disclosure is a fullerene derivative solution according to any one of the first to fourth aspects, wherein the first solvent is an oxygen-containing aromatic compound.

[0023] This is an example of an implementation.

[0024] Furthermore, for example, the fullerene derivative solution according to the sixth aspect of this disclosure is a fullerene derivative solution according to any one of the first to fifth aspects, wherein the first solvent is anisole, 2,3-dihydrobenzofuran, or 2-methoxytoluene.

[0025] This makes it possible to create a fullerene derivative solution with high solubility and low toxicity.

[0026] Furthermore, for example, the fullerene derivative solution according to the seventh aspect of this disclosure is a fullerene derivative solution according to any one of the first to sixth aspects, wherein the second solvent is an oxygen-containing aliphatic compound.

[0027] This is an example of an implementation.

[0028] Furthermore, for example, the fullerene derivative solution according to the eighth aspect of this disclosure is a fullerene derivative solution according to any one of the first to seventh aspects, wherein the second solvent is 2-methyltetrahydrofuran.

[0029] This makes it possible to create a fullerene derivative solution that has high solubility and low toxicity.

[0030] Furthermore, for example, the fullerene derivative solution according to the ninth aspect of this disclosure is a fullerene derivative solution according to any one of the first to eighth aspects, wherein the concentration of the fullerene derivative is 20 mg / ml or more.

[0031] This makes it possible to form thicker coating films using fullerene derivative solutions.

[0032] Furthermore, a method for manufacturing a coating film according to the tenth aspect of this disclosure includes the steps of preparing a fullerene derivative solution according to any one of the first to ninth aspects, and forming a coating film by applying the fullerene derivative solution onto a substrate.

[0033] As a result, since the coating film is formed using the fullerene derivative solution described above, the film thickness of the coating film can be ensured.

[0034] Furthermore, the method for manufacturing a coated film according to the 11th aspect of this disclosure is a method for manufacturing a coated film according to the 10th aspect, wherein the coated film is formed as a photoelectric conversion layer of a photoelectric conversion element.

[0035] This ensures sufficient film thickness in the photoelectric conversion layer, thereby improving the device characteristics of the photoelectric conversion element.

[0036] Furthermore, the method for manufacturing a coated film according to the twelfth aspect of this disclosure is a method for manufacturing a coated film according to the tenth aspect, wherein the coated film is formed as a charge blocking layer for a photoelectric conversion element.

[0037] This ensures sufficient thickness of the charge blocking layer, thereby improving the device characteristics of the photoelectric conversion element.

[0038] The embodiments of this disclosure will be described in detail below with reference to the drawings.

[0039] The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, components, arrangement and connection configurations of components, steps, and the order of steps shown in the following embodiments are examples only and are not intended to limit this disclosure. Furthermore, components in the following embodiments that are not described in an independent claim are described as optional components, and the figures are not necessarily strictly illustrative. In each figure, substantially identical components are denoted by the same reference numerals, and redundant explanations may be omitted or simplified.

[0040] Furthermore, in this specification, terms indicating relationships between elements, terms indicating the shape of elements, and numerical ranges do not represent only strict meanings, but also include substantially equivalent ranges, such as differences of a few percent.

[0041] Furthermore, the Hansen solubility parameter is known as an indicator of the solubility of substances, and is described, for example, in Non-Patent Document 2. The Hansen solubility parameter consists of three values: a dispersion force term (δD), a polarity term (δP), and a hydrogen bonding term (δH). These three parameters are expressed as the coordinates of a point in a three-dimensional space called Hansen space.

[0042] (Embodiment 1) The fullerene derivative solution according to this embodiment will be described below.

[0043] [Solubility of fullerene derivatives] First, before describing the fullerene derivative solution according to this embodiment, we will explain the results of the inventors' investigation into the solubility of fullerene derivatives in various solvents.

[0044] Specifically, the inventors attempted to dissolve

[60] PCBM as a fullerene derivative in various solvents. First, 24 mg of

[60] PCBM was weighed into a sealable glass container, then 1 ml of solvent was added, the container was sealed, and stirred at room temperature. After stirring the solvent containing

[60] PCBM for 16 hours, stirring was stopped and the container was allowed to stand for 1 hour. The solubility of

[60] PCBM was determined by visually checking for the presence or absence of precipitate at the bottom of the glass container. In determining solubility, if there was no precipitate, it was judged to be "soluble"; if there was a precipitate and the solvent was colored, it was judged to be "partially soluble"; and if there was a precipitate and the solvent was not colored, it was judged to be "insoluble".

[0045] The solvents used were anisole, 2-methoxytoluene, 3-methoxytoluene, 4-methoxytoluene, 2,3-dihydrobenzofuran, methylphenyl ether, limonene, methanol, ethanol, isopropanol, acetone, cyclohexane, cyclohexanone, propylene glycol monomethyl ether acetate, butyl acetate, tetrahydrofuran, 2-methyltetrahydrofuran, dihydropyran, 2-methyl-1,3-dioxane, and N-methyl-2-pyrrolidone. These solvents were selected because they have lower toxicity and are easier to use industrially compared to chlorobenzene and chloroform, as used in Non-Patent Document 1.

[0046] Table 1 shows the type of solvent, the Hansen solubility parameter of the solvent, the boiling point of the solvent, and the results of the solubility assessment for each of the solvents listed above.

[0047] [Table 1]

[0048] As shown in Table 1, anisole, 2-methoxytoluene, and 2,3-dihydrobenzofuran were able to dissolve

[60] PCBM.

[0049] Furthermore, limonene, 3-methoxytoluene, 4-methoxytoluene, and ethylphenyl ether were able to partially dissolve PCBM.

[60]

[0050] Methanol, ethanol, isopropanol, acetone, cyclohexane, cyclohexanone, propylene glycol monomethyl ether acetate, butyl acetate, tetrahydrofuran, 2-methyltetrahydrofuran, dihydropyran, 2-methyl-1,3-dioxane, and N-methyl-2-pyrrolidone failed to dissolve PCBM.

[60]

[0051] From the results in Table 1, the Hansen solubility parameter is 17.8 ≦ Dispersion force term (δD) ≦ 18.9, 4.4 ≦ polarity term (δP) ≦ 4.7, 4.8 ≤ Hydrogen bond term (δH) ≤ 6.9 Solvents that satisfy this condition are found to have high solubility for fullerene derivatives.

[0052] [Fullerene derivative solution] Next, we will describe the details of the fullerene derivative solution according to this embodiment.

[0053] The fullerene derivative solution according to this embodiment comprises a fullerene derivative, one or more first solvents, and one or more second solvents. In the fullerene derivative solution, the fullerene derivative is dissolved in a mixed solvent containing one or more first solvents and one or more second solvents. The main component of the solvent in the fullerene derivative solution consists, for example, one or more first solvents and one or more second solvents. Here, "main component" means that the content is greater than 50 vol%. The content of the main component of the solvent in the fullerene derivative solution may be 80 vol% or more, or 90 vol% or more. For example, the first solvent and the second solvent used in the fullerene derivative solution are each of one type, but at least one of them may be of two or more types.

[0054] Fullerene derivative solutions are used, for example, to form coating films containing fullerene derivatives. By applying the fullerene derivative solution and removing the solvent, a coating film containing the fullerene derivative can be formed.

[0055] Examples of fullerene derivatives include

[60] PCBM and phenyl C 71 Methyl butyrate (

[70] PCBM), phenyl C 61 Butyl butyrate (

[60] PCBB), phenyl C 61 Octyl butyrate (

[60] PCBO), phenyl C 61 Dodecyl butyrate (

[60] PCBD), bis-adducted phenyl C 61 Methyl butyrate (Bis-PCBM) and indene C 60 Examples include bis-adducts (ICBAs). Fullerene derivatives, for example, contain ester structures and have higher solubility in solvents compared to fullerenes. A fullerene derivative solution may contain two or more types of fullerene derivatives.

[0056] The concentration of the fullerene derivative in the fullerene derivative solution is, for example, 20 mg / ml or higher. This makes it easier to form thicker films using the fullerene derivative solution.

[0057] The first solvent is one in which the fullerene derivative has high solubility. Specifically, the first solvent is one in which, when the Hansen solubility parameters of the first solvent are defined as δD1 for the dispersion force term, δP1 for the polarity term, and δH1 for the hydrogen bonding term, δD1, δP1, and δH1 satisfy predetermined conditions.

[0058] In the fullerene derivative solution according to this embodiment, the following conditions are satisfied: 17.8 ≤ δD1 ≤ 18.9, 4.4 ≤ δP1 ≤ 4.7, and 4.8 ≤ δH1 ≤ 6.9. As a result, as can be seen from the above-mentioned solubility study of the fullerene derivative, the solubility of the fullerene derivative in the first solvent is increased, and therefore the solubility of the fullerene derivative in the fullerene derivative solution can be improved.

[0059] The first solvent, for example, does not contain halogen elements. Alternatively, the first solvent may be, for example, an oxygen-containing aromatic compound. An oxygen-containing aromatic compound is a compound in which at least some of the hydrogen atoms in an aromatic hydrocarbon are replaced by substituents containing oxygen atoms. An aromatic hydrocarbon is, for example, benzene. The substituent containing oxygen atoms is, for example, an -OR group (alkoxy group, where R represents an aliphatic hydrocarbon group). The oxygen-containing aromatic compound may also have a phenoxy structure. Furthermore, in an oxygen-containing aromatic compound, some of the hydrogen atoms in the aromatic hydrocarbon may be replaced by substituents that do not contain oxygen atoms, such as hydrocarbon groups.

[0060] From the viewpoint of low toxicity and high solubility of fullerene derivatives, the first solvent may be anisole, 2,3-dihydrobenzofuran, or 2-methoxytoluene.

[0061] The second solvent used has a lower boiling point than the first solvent. The boiling point of the first solvent is 200°C or lower. The boiling point of the second solvent is 100°C or lower. This increases the drying rate of the fullerene derivative solution, making it possible to form a thicker coating film. Furthermore, from the viewpoint of ease of handling, the boiling points of both the first and second solvents may be 50°C or higher.

[0062] Furthermore, when the Hansen solubility parameters of the second solvent are defined as follows, with the dispersion force term being δD2, the polarity term being δP2, and the hydrogen bonding term being δH2, a solvent that satisfies the specified conditions for δD2, δP2, and δH2 may be used as the second solvent.

[0063] For example, in the fullerene derivative solution according to this embodiment, δD1 > δD2 is satisfied. This makes it easier for the first solvent to cover the fullerene derivative, and thus the solubility of the fullerene derivative in the fullerene derivative solution can be maintained.

[0064] Furthermore, for example, in the fullerene derivative solution according to this embodiment, the condition δH1 > δH2 is satisfied. As a result, the second solvent is less likely to form hydrogen bonds with the fullerene derivative compared to the first solvent, and the solubility of the fullerene derivative in the fullerene derivative solution can be maintained.

[0065] Furthermore, for example, in the fullerene derivative solution according to this embodiment, the following conditions are satisfied: 15.5 ≤ δD2 ≤ 17.5, 4.0 ≤ δP2 ≤ 6.0, and 3.0 ≤ δH2 ≤ 6.0. This also allows the solubility of the fullerene derivative in the fullerene derivative solution to be maintained.

[0066] The second solvent is, for example, one that does not contain halogen elements. Alternatively, the second solvent may be, for example, an oxygen-containing aliphatic compound. An oxygen-containing aliphatic compound is a compound that contains oxygen atoms and aliphatic hydrocarbon structures, but does not contain aromatic ring structures. Examples of oxygen-containing aliphatic compounds include ethers, ketones, esters, and alcohols. Among these, the oxygen-containing aliphatic compound may be an ether. Furthermore, the ether may be a cyclic ether. In addition, some of the hydrogen atoms in the ether may be substituted with aliphatic hydrocarbon groups such as methyl groups. This can lower δD2 and δH2.

[0067] From the viewpoint of low toxicity, a low boiling point, and ease of maintaining the solubility of the fullerene derivative in the solution, the second solvent may be 2-methyltetrahydrofuran.

[0068] In the fullerene derivative solution according to this embodiment, the volume ratio of one or more first solvents to the total volume of one or more first solvents and one or more second solvents is greater than the volume ratio of one or more second solvents to the total volume. This increases the solubility of the fullerene derivative. Furthermore, the volume ratio of one or more first solvents to the total volume of one or more first solvents and one or more second solvents may be 60% or more. Also, from the viewpoint of ensuring the film thickness of the film formed using the fullerene derivative, the volume ratio of one or more first solvents to the total volume of one or more first solvents and one or more second solvents may be 90% or less, or 80% or less. Note that when multiple types of first solvents are used in the fullerene derivative solution, the volume of one or more first solvents is the sum of the volumes of the multiple types of first solvents. Similarly, when multiple types of second solvents are used in the fullerene derivative solution, the volume of one or more second solvents is the sum of the volumes of the multiple types of second solvents.

[0069] Furthermore, the volume ratio of one or more first solvents to the total volume of all solvents in the fullerene derivative solution may be, for example, greater than 50% and 60% or more. Also, the volume ratio of one or more first solvents to the total volume of all solvents in the fullerene derivative solution may be 90% or less and 80% or less.

[0070] Furthermore, the fullerene derivative solution according to this embodiment may contain components other than the fullerene derivative, the first solvent, and the second solvent. The fullerene derivative solution according to this embodiment may contain, for example, a donor material such as a donor organic semiconductor material. As a result, the fullerene derivative acts as an acceptor material, and a mixed film of bulk heterostructure can be easily formed using the fullerene derivative solution.

[0071] Fullerene derivative solutions can be prepared, for example, as follows:

[0072] First, weigh the fullerene derivative and place it in a container. If necessary, weigh other solute materials, such as donor material, and place them in the container as well. Next, add one or more first solvents and one or more second solvents to the container in a predetermined volume ratio, seal the container, and stir the mixture at room temperature. This will yield a fullerene derivative solution. The container may be heated during stirring. Alternatively, only the one or more first solvents may be added to the container and stirred before adding the one or more second solvents.

[0073] (Embodiment 2) Next, Embodiment 2 will be described. Embodiment 2 describes a photoelectric conversion element using a coated film formed from the fullerene derivative solution according to Embodiment 1. In the following description of Embodiment 2, the differences from Embodiment 1 will be the main focus, and the explanation of the common points will be omitted or simplified.

[0074] The photoelectric conversion element according to this embodiment is, for example, a charge readout type photoelectric conversion element. Figure 1 is a schematic cross-sectional view showing the photoelectric conversion element 10 according to this embodiment.

[0075] As shown in Figure 1, the photoelectric conversion element 10 is supported on a support substrate 1. The photoelectric conversion element 10 comprises a pair of electrodes, a first electrode 2 and a second electrode 6 positioned opposite the first electrode 2, and a photoelectric conversion layer 4 located between the first electrode 2 and the second electrode 6. The photoelectric conversion element 10 further comprises a charge blocking layer 3 located between the first electrode 2 and the photoelectric conversion layer 4, and a charge blocking layer 5 located between the second electrode 6 and the photoelectric conversion layer 4. Of the charge blocking layer 3 and the charge blocking layer 5, one is an electron blocking layer and the other is a hole blocking layer. Note that the photoelectric conversion element 10 only needs to include the first electrode 2, the second electrode 6 and the photoelectric conversion layer 4, and does not need to include at least one of the charge blocking layer 3 and the charge blocking layer 5.

[0076] The photoelectric conversion element 10 is used, for example, in an imaging device. An imaging device using the photoelectric conversion element 10 has, for example, a photoelectric conversion unit in which each of the multiple pixels of the imaging device is composed of the photoelectric conversion element 10. The application of the photoelectric conversion element 10 is not particularly limited, and it may be used in a light sensor or a solar cell.

[0077] The following describes each component of the photoelectric conversion element 10 according to this embodiment.

[0078] The support substrate 1 can be any substrate commonly used in photoelectric conversion elements, such as a glass substrate, semiconductor substrate, or plastic substrate.

[0079] The first electrode 2 is formed from a metal, metal nitride, metal oxide, or conductive polysilicon. Examples of metals include aluminum, copper, titanium, and tungsten. An example of a method for imparting conductivity to polysilicon is doping it with impurities.

[0080] The second electrode 6 is a transparent electrode formed from, for example, a transparent conductive material. Examples of materials for the second electrode 6 include transparent conductive oxide (TCO), ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), AZO (Aluminum-doped Zinc Oxide), FTO (Florine-doped Tin Oxide), SnO2, and TiO2. The second electrode 6 may be fabricated by combining TCO and metallic materials such as aluminum (Al) and gold (Au), either individually or in combination, depending on the desired transmittance. In the photoelectric conversion element 10, for example, light transmitted through the second electrode 6 is incident on the photoelectric conversion layer 4. In this specification, the term "transparent" means that at least a portion of the wavelengths of light that the photoelectric conversion layer 4 can absorb are transmitted, and it is not essential that light is transmitted across the entire wavelength range. Furthermore, in this specification, electromagnetic waves in general, including visible light, infrared rays, and ultraviolet rays, will be referred to as "light" for convenience.

[0081] Furthermore, the materials of the first electrode 2 and the second electrode 6 are not limited to the conductive materials described above, and other materials may be used. For example, the first electrode 2 may be a transparent electrode. In this case, light transmitted through the first electrode 2 may be incident on the photoelectric conversion layer 4.

[0082] Various methods can be used to fabricate the first electrode 2 and the second electrode 6, depending on the materials used. For example, when using ITO, chemical reaction methods such as electron beam method, sputtering method, resistance heating deposition method, sol-gel method, or coating of indium tin oxide dispersion may be used. In this case, after forming the ITO film, the first electrode 2 and the second electrode 6 may be subjected to further treatments such as UV-ozone treatment or plasma treatment.

[0083] A bias voltage is applied to the first electrode 2 and the second electrode 6, for example, by wiring (not shown). For example, the polarity of the bias voltage is determined so that electrons from the charge generated in the photoelectric conversion layer 4 move to the second electrode 6 and holes move to the first electrode 2. Below, an example in which electrons move to the second electrode 6 and holes move to the first electrode 2 will be described. Alternatively, the bias voltage may be set so that holes from the charge generated in the photoelectric conversion layer 4 move to the second electrode 6 and electrons move to the first electrode 2.

[0084] The photoelectric conversion layer 4 includes a donor material and an acceptor material. The photoelectric conversion layer 4 is fabricated using, for example, organic semiconductor materials as the donor material and acceptor material. The photoelectric conversion layer 4 can be fabricated using wet methods such as coating methods such as spin coating, or dry methods such as vacuum deposition. Vacuum deposition is a method in which the layer material is vaporized by heating under vacuum and deposited on the substrate. The charge blocking layer 3 and the charge blocking layer 5 can also be fabricated using the same method as the photoelectric conversion layer 4.

[0085] Furthermore, the photoelectric conversion layer 4 is a mixed film of a bulk heterostructure containing, for example, a donor material such as a donor organic semiconductor material and an acceptor material such as an acceptor organic semiconductor material. The photoelectric conversion layer 4 may also have a laminated structure in which layers of donor material and acceptor material are stacked.

[0086] The photoelectric conversion layer 4 generates electron-hole pairs internally upon irradiation with light. These generated electron-hole pairs are separated into electrons and holes by the electric field applied to the photoelectric conversion layer 4, and each moves towards either the first electrode 2 or the second electrode 6 according to the electric field. Here, of the electron-hole pairs generated by absorbing light, the material that donates electrons to the other material is the donor material, and the material that accepts electrons is the acceptor material. When two different types of organic semiconductors are used, which becomes the donor material and which becomes the acceptor material is generally determined by the relative positions of the HOMO (Highest-Occupied-Molecular-Orbital) and LUMO (Lowest-Unoccupied-Molecular-Orbital) energy levels of the two organic semiconductors at the contact interface. Specifically, the material with a shallower LUMO energy level that accepts electrons becomes the donor material, and the material with a deeper LUMO becomes the acceptor material.

[0087] The photoelectric conversion layer 4 is easily formed as a thin film by including a donor organic semiconductor material and an acceptor organic semiconductor material. Specific examples of the donor organic semiconductor material and the acceptor organic semiconductor material are given below.

[0088] Examples of donor organic semiconductor materials include triarylamine compounds, benzidine compounds, pyrazoline compounds, styrylamine compounds, hydrazone compounds, triphenylmethane compounds, carbazole compounds, polysilane compounds, thiophene compounds, phthalocyanine compounds, naphthalocyanine compounds, subphthalocyanine compounds, cyanine compounds, merocyanine compounds, oxonol compounds, polyamine compounds, indole compounds, pyrrole compounds, pyrazole compounds, polyarylene compounds, condensed aromatic carbocyclic compounds (e.g., naphthalene derivatives, anthracene derivatives, phenanthrene derivatives, tetracene derivatives, pyrene derivatives, perylene derivatives, and fluorantene derivatives, etc.) and metal complexes having nitrogen-containing heterocyclic compounds as ligands. However, the list is not limited to these; any organic compound with a lower ionization potential than the organic compound used as the acceptor organic semiconductor material may be used as the donor organic semiconductor material.

[0089] Examples of acceptor organic semiconductor materials include fullerene derivatives, fullerenes (e.g., C60 fullerene and C70 fullerene), condensed aromatic carbocyclic compounds (e.g., naphthalene derivatives, anthracene derivatives, phenanthrene derivatives, tetracene derivatives, pyrene derivatives, perylene derivatives and fluorantene derivatives), and 5- to 7-membered heterocyclic compounds containing nitrogen, oxygen, and sulfur atoms (e.g., pyridine, pyrazine, pyrimidine, pyridazine, triazine, quinoline, quinoxaline, quinazoline, phthalazine, cinnoline, isoquinoline, pteridine, acridine, phenazine, Examples include phenanthroline, tetrazole, pyrazole, imidazole, thiazole, oxazole, indazole, benzimidazole, benzodoriazole, benzoxazole, benzothiazole, carbazole, purine, triazolopyridazine, triazolopyrimidine, tetrazaidene, oxadiazole, imidazopyridine, pyrrolidine, pyrrolopyridine, thiadiazolopyridine, dibenzazepine and tripenzazepine, etc., polyarylene compounds, fluorene compounds, cyclopentadiene compounds, silyl compounds, and metal complexes having nitrogen-containing heterocyclic compounds as ligands. However, the materials are not limited to these; any organic compound with a greater electron affinity than the organic compound used as the donor organic semiconductor material may be used as the acceptor organic semiconductor material.

[0090] The photoelectric conversion layer 4 can be formed using the fullerene derivative solution according to Embodiment 1. In this case, the acceptor organic semiconductor material is a fullerene derivative.

[0091] The donor organic semiconductor material and acceptor organic semiconductor material are not limited to the examples above. Any organic compound that can be formed as a photoelectric conversion layer by either a dry or wet method, including low-molecular-weight organic compounds and high-molecular-weight organic compounds, may be used as the donor organic semiconductor material and acceptor organic semiconductor material constituting the photoelectric conversion layer 4.

[0092] The charge blocking layer 3 and the charge blocking layer 5 suppress the injection of charge from the electrodes into the photoelectric conversion layer 4. By providing the charge blocking layer 3 and the charge blocking layer 5, the injection of charge from the electrodes into the photoelectric conversion layer 4 can be suppressed, thereby reducing unwanted signals that adversely affect the signal-to-noise ratio (SNR).

[0093] Specifically, the charge blocking layer 3 is an electron blocking layer provided to reduce dark current caused by electron injection from the first electrode 2. The charge blocking layer 3 suppresses the injection of electrons from the first electrode 2 into the photoelectric conversion layer 4. In addition, the charge blocking layer 3 also has the function of transporting holes generated in the photoelectric conversion layer 4 to the first electrode 2.

[0094] Furthermore, the charge blocking layer 5 is a hole blocking layer provided to reduce dark current caused by the injection of holes from the second electrode 6. The charge blocking layer 5 suppresses the injection of holes from the second electrode 6 into the photoelectric conversion layer 4. The charge blocking layer 5 also has the function of transporting electrons generated in the photoelectric conversion layer 4 to the second electrode 6.

[0095] The charge blocking layers 3 and 5 are formed from, for example, an organic semiconductor material having HOMO and LUMO energy levels that act as barriers to the transfer of charge from the electrodes to the photoelectric conversion layer 4.

[0096] The charge blocking layer 3 and the charge blocking layer 5 can be formed using the fullerene derivative solution according to Embodiment 1. In this case, the organic semiconductor material is a fullerene derivative.

[0097] The materials of charge blocking layer 3 and charge blocking layer 5 are not limited to organic semiconductor materials, but may also be inorganic semiconductor materials such as oxide semiconductors and nitride semiconductors, or composite materials thereof.

[0098] In the photoelectric conversion element 10, when holes from the charge generated in the photoelectric conversion layer 4 move to the second electrode 6 and electrons move to the first electrode 2, the charge blocking layer 3 becomes a hole blocking layer and the charge blocking layer 5 becomes an electron blocking layer.

[0099] In the photoelectric conversion element 10, at least one of the photoelectric conversion layer 4, charge blocking layer 3, and charge blocking layer 5 is a coated film formed using the fullerene derivative solution according to Embodiment 1.

[0100] Figure 2 is a flowchart of a method for manufacturing a coating film used in the photoelectric conversion element 10 according to this embodiment. As shown in Figure 2, first, a fullerene derivative solution is prepared containing a fullerene derivative, one or more first solvents, and one or more second solvents (step S11). As described in Embodiment 1, the fullerene derivative solution can be obtained, for example, by adding one or more first solvents and one or more second solvents to a fullerene derivative and stirring. When the coating film is formed as a photoelectric conversion layer 4, the fullerene derivative solution may further contain a donor material.

[0101] Next, the fullerene derivative solution prepared in step S11 is applied to the substrate to form a coating film (step S12). In this embodiment, the substrate is the layer directly below the layer to be formed as the coating film of the fullerene derivative solution in the photoelectric conversion element 10. Specifically, the substrate is the first electrode 2, the charge blocking layer 3, or the photoelectric conversion layer 4. The method of applying the fullerene derivative solution is not particularly limited, but spin coating, inkjet, and coater can be used. In this embodiment, for example, the fullerene derivative solution is applied by spin coating. For example, the support substrate 1 on which the substrate is formed is placed on the stage of a spin coater, and an amount of fullerene derivative solution corresponding to the size of the substrate is dropped onto the center of the substrate. After dropping is complete, the substrate is rotated at a set rotation speed to obtain a coating film containing the fullerene derivative on the substrate. If the coating film does not dry completely during spin coating, a solvent removal step such as heating the coating film may be performed.

[0102] The film thickness of the coating can be controlled by the number of rotations per unit time in spin coating. Specifically, a lower number of rotations per unit time in spin coating results in a thicker film, while a higher number of rotations per unit time in spin coating results in a thinner film. There are no particular restrictions on the number of rotations per unit time in spin coating, but from the viewpoint of ensuring the desired film thickness and forming a coating with a uniform thickness, it may be between 300 rpm and 3000 rpm.

[0103] Furthermore, increasing the concentration of the fullerene derivative in the fullerene derivative solution can also increase the thickness of the coated film. Additionally, if the solvent in the fullerene derivative solution does not evaporate easily, the solution tends to spread during coating, resulting in a thinner coated film. Moreover, it is difficult to control the film thickness by adjusting the rotation speed per unit time in spin coating. On the other hand, if the solvent in the fullerene derivative solution evaporates easily, the solution dries before it can spread widely, making it possible to increase the thickness of the coated film.

[0104] The fullerene derivative solution according to Embodiment 1 allows for a higher concentration of the fullerene derivative by including a first solvent, and the drying rate is increased by including a second solvent, making it easy to adjust the film thickness of the coating film. For example, it is possible to form a coating film with a large film thickness.

[0105] Furthermore, the coating film formed by the above manufacturing method does not have to be used in the photoelectric conversion layer 4, charge blocking layer 3, and charge blocking layer 5 of the photoelectric conversion element 10, and can be used as various semiconductor films. The coating film may also be formed on a substrate. For example, a glass substrate using quartz glass or alkali-free glass, or a semiconductor substrate using a silicon wafer, can be used as the substrate. The substrate may be cleaned with water or an organic solvent as needed. In addition, organic matter adhering to the surface may be removed using a UV ozone cleaning device before coating. These measures improve the wettability of the fullerene derivative solution to the substrate. [Examples]

[0106] The fullerene derivative solutions according to this disclosure will be specifically described below in the examples, but this disclosure is not limited in any way to the following examples. In detail, fullerene derivative solutions for evaluation were prepared, and the solubility of the fullerene derivative in the fullerene derivative solution and the film thickness of the coating film formed using the fullerene derivative solution were evaluated.

[0107] (Preparation of fullerene derivative solution) Fullerene derivative solutions were prepared in the examples and comparative examples. In the fullerene derivative solutions in the examples and comparative examples,

[60] PCBM was used as the fullerene derivative, and the naphthalocyanine compound shown in the following structural formula (1) was used as the donor material.

[0108] [ka]

[0109] [Example 1] 24 mg of

[60] PCBM was placed in a resealable glass container, and 1 ml each of anisole as the first solvent and 2-methyltetrahydrofuran as the second solvent were added to the glass container in a volume ratio of 80:20. The container was then sealed and stirred at room temperature for 16 hours. This yielded the fullerene derivative solution of Example 1.

[0110] [Example 2] The same procedure as in Example 1 was followed to obtain the fullerene derivative solution in Example 2, except that the volume ratio of anisole to 2-methyltetrahydrofuran was changed to 60:40.

[0111] [Example 3] The same procedure as in Example 2 was followed, except that 6 mg of donor material was added to the glass container along with

[60] PCBM, to obtain the fullerene derivative solution of Example 3.

[0112] [Example 4] The same procedure as in Example 1 was followed, except that the weight of

[60] PCBM placed in the glass container was changed to 48 mg and 2,3-dihydrobenzofuran was used as the first solvent, to obtain the fullerene derivative solution of Example 4.

[0113] [Example 5] The same procedure as in Example 2 was followed to obtain the fullerene derivative solution of Example 5, except that the weight of

[60] PCBM placed in the glass container was changed to 48 mg and 2,3-dihydrobenzofuran was used as the first solvent.

[0114] [Comparative Example 1] The same procedure as in Example 1 was followed, except that 2-methyltetrahydrofuran was not added to the glass container and 1 ml of anisole was used as the first solvent, to obtain the fullerene derivative solution in Comparative Example 1.

[0115] [Comparative Example 2] The same procedure as in Example 4 was followed, except that 2-methyltetrahydrofuran was not added to the glass container, and 1 ml of 2,3-dihydrobenzofuran was used as the first solvent, to obtain the fullerene derivative solution in Comparative Example 2.

[0116] [Example 6] Except for using tetrahydrofuran as the second solvent, the same procedure as in Example 1 was followed to obtain the fullerene derivative solution in Example 6.

[0117] [Example 7] The same procedure as in Example 4 was followed to obtain the fullerene derivative solution of Example 7, except that the weight of

[60] PCBM placed in the glass container was changed to 24 mg and tetrahydrofuran was used as the second solvent.

[0118] [Example 8] The same procedure as in Example 1 was followed, except that isopropanol was used as the second solvent, to obtain the fullerene derivative solution in Example 8.

[0119] (Evaluation of solubility of fullerene derivatives and film thickness of coated films) The solubility of the obtained fullerene derivative solution was evaluated, and the film thickness of the coating film formed from the fullerene derivative solution was measured.

[0120] [Evaluation of solubility] For the fullerene derivative solutions in Examples 1 to 8 and Comparative Examples 1 and 2, the solubility of

[60] PCBM was determined by visually checking for the presence or absence of precipitate at the bottom of the glass container. In determining solubility, if there was no precipitate, it was judged as "soluble"; if there was a precipitate and the solvent was colored, it was judged as "partially soluble"; and if there was a precipitate and the solvent was not colored, it was judged as "insoluble". The evaluation results of the solubility of the fullerene derivatives are shown in Table 2.

[0121] [Measurement of coating film thickness] Coating films were formed using the fullerene derivative solutions from Examples 1 to 5 and Comparative Examples 1 and 2, and the film thickness of the coating films was measured. To form the coating films, first, a 25 mm square quartz glass substrate was placed on the stage of a spin coater, and 100 μl of the fullerene derivative solution was dropped onto the center of the quartz glass substrate. After dropping was complete, the substrate was rotated at 500 rpm for 60 seconds to form a coating film containing the fullerene derivative on the quartz glass substrate. A portion of the formed coating film was scraped off, and the film thickness of the coating film was measured by measuring the step height in that portion using a stylus-type step meter (DEKTAK® stylus-type profiling system). The measurement results of the coating film thickness are shown in Table 2.

[0122] [Table 2]

[0123] Table 2 shows the evaluation results of the solubility of the fullerene derivative and the measurement results of the film thickness of the coated film, as well as the composition of the fullerene derivative solution.

[0124] As can be seen from Table 2, in the evaluation of the solubility of the fullerene derivatives, the fullerene derivative solutions in Examples 1 to 5 and Comparative Examples 1 and 2 yielded fullerene derivative solutions in which

[60] PCBM was completely dissolved. Furthermore, in the fullerene derivative solutions in Examples 6 to 8, although some

[60] PCBM remained undissolved, more than 90% of the

[60] PCBM was dissolved. Thus, in the fullerene derivative solutions in Examples 1 to 8, the solubility of

[60] PCBM was ensured using solvents that are less toxic and more readily available industrially compared to chlorobenzene and chloroform.

[0125] Furthermore, as can be seen from Table 2, in the measurement of the coating film thickness, the fullerene derivative solutions in Comparative Examples 1 and 2 were thin, ranging from 55 nm to 60 nm, because a second solvent with a lower boiling point was not added. In contrast, the fullerene derivative solutions in Examples 1 to 5 were thicker than those in Comparative Examples 1 and 2 due to the effect of adding a second solvent, indicating that a thicker coating film can be achieved by increasing the amount of the second solvent in the fullerene derivative solution. In addition, the fullerene derivative solution in Example 3 was thicker than the solution without donor material, even with the addition of donor material. Furthermore, the fullerene derivative solutions in Examples 4 and 5 had a higher concentration of

[60] PCBM than those in Examples 1 and 2, which allowed for an even thicker coating film.

[0126] While reducing the rotation speed per unit time in spin coating can increase the thickness of the coated film, if the rotation speed per unit time becomes too low, the uniformity of the coated film thickness decreases. Therefore, there are practical limitations to increasing the film thickness by reducing the rotation speed per unit time. In the fullerene derivative solutions of Examples 1 to 5, even when spin coating was performed at the same rotation speed per unit time, a thicker coated film was obtained than that of the fullerene derivative solutions of Comparative Examples 1 and 2, thus ensuring sufficient film thickness. In other words, the fullerene derivative solutions of Examples 1 to 5 can achieve a thicker film than those of the fullerene derivative solutions of Comparative Examples 1 and 2, demonstrating a wider range of film thickness adjustment.

[0127] As described above, it can be seen that by mixing the first solvent and the second solvent and using them in the fullerene derivative solution, an industrially useful fullerene derivative solution can be realized.

[0128] The fullerene derivative solutions and photoelectric conversion elements relating to this disclosure have been described above based on embodiments and examples, but this disclosure is not limited to these embodiments and examples. Within the scope of this disclosure, various modifications to the embodiments and examples that a person skilled in the art could conceive of, as long as they do not depart from the spirit of this disclosure, as well as other forms constructed by combining some of the components of the embodiments and examples, are also included. [Industrial applicability]

[0129] The fullerene derivative solution according to this disclosure can be used to form a coating film containing the fullerene derivative. Furthermore, the coating film formed using the fullerene derivative solution according to this disclosure can be used in photoelectric conversion elements and imaging devices using photoelectric conversion elements. [Explanation of Symbols]

[0130] 1. Support substrate 2 First electrode 3, 5 Charge blocking layer 4. Photoelectric conversion layer 6 Second electrode 10 Photoelectric conversion element

Claims

1. Fullerene derivatives and One or more first solvents, It comprises one or more second solvents, The boiling point of the first solvent is 200°C or lower. The boiling point of the second solvent is 100°C or lower. In the Hansen solubility parameters of the first solvent, when the dispersion force term is δD1, the polarity term is δP1, and the hydrogen bonding term is δH1, 17.8≦δD1≦18.9, 4.4 ≦ δP1 ≦ 4.7, 4.8 ≦ δH1 ≦ 6.9 The conditions are met. The volume ratio of one or more of the first solvents to the total volume of one or more of the first solvents and one or more of the second solvents is greater than the volume ratio of one or more of the second solvents to the total volume. Fullerene derivative solution.

2. When the dispersion force term of the Hansen solubility parameter of the second solvent is defined as δD2, δD1 > δD2 The condition is met. The fullerene derivative solution according to claim 1.

3. When the hydrogen bonding term in the Hansen solubility parameters of the second solvent is defined as δH2, δH1 > δH2 The condition is met. The fullerene derivative solution according to claim 1.

4. In the Hansen solubility parameters of the second solvent, when the dispersion force term is δD2, the polarity term is δP2, and the hydrogen bonding term is δH2, 15.5 ≦ δD2 ≦ 17.5, 4.0≦δP2≦6.0, 3.0 ≦ δH2 ≦ 6.0 The condition is met. The fullerene derivative solution according to claim 1.

5. The first solvent is an oxygen-containing aromatic compound. The fullerene derivative solution according to claim 1.

6. The first solvent is anisole, 2,3-dihydrobenzofuran, or 2-methoxytoluene. The fullerene derivative solution according to claim 1.

7. The second solvent is an oxygen-containing aliphatic compound. The fullerene derivative solution according to claim 1.

8. The second solvent is 2-methyltetrahydrofuran. The fullerene derivative solution according to claim 1.

9. The concentration of the fullerene derivative is 20 mg / ml or more. The fullerene derivative solution according to claim 1.

10. A step of preparing a fullerene derivative solution according to any one of claims 1 to 9, The process includes a step of forming a coating film by applying the fullerene derivative solution onto a substrate. A method for manufacturing a coated film.

11. The aforementioned coated film is formed as the photoelectric conversion layer of a photoelectric conversion element. A method for producing a coated film according to claim 10.

12. The aforementioned coated film is formed as a charge blocking layer for a photoelectric conversion element. A method for producing a coated film according to claim 10.

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