JP7746715B2 - Organic semiconductor ink, photoelectric conversion layer, and organic photoelectric conversion element - Google Patents

Description

The present invention relates to an organic semiconductor ink, a photoelectric conversion layer formed using this organic semiconductor ink, and an organic photoelectric conversion element having this photoelectric conversion layer.

Photoelectric conversion elements such as organic solar cells and organic photodetectors require heat resistance to withstand the heating environment that occurs during the reflow process during element manufacturing. However, these elements generally do not have sufficient heat resistance to withstand the heating environment expected during manufacturing, and this insufficient heat resistance may lead to a deterioration in photoelectric conversion characteristics.
One of the reasons for the deterioration of the photoelectric conversion characteristics is thought to be as follows.
That is, the phase-separated structure (compatibility between the p-type organic semiconductor and the n-type organic semiconductor) of a bulk heterojunction (BHJ) type photoelectric conversion layer composed of a p-type organic semiconductor and an n-type organic semiconductor plays an important role in the photoelectric conversion characteristics, but this phase-separated structure does not have sufficient stability against heat. Therefore, the phase-separated structure changes in a high-temperature environment. This is because the p-type organic semiconductor and the n-type organic semiconductor in the photoelectric conversion layer flow under high-temperature conditions, causing partial aggregation between the p-type organic semiconductors and between the n-type organic semiconductors, which damages the bulk heterojunction between the p-type organic semiconductor and the n-type organic semiconductor.
Therefore, various studies have been conducted to improve the heat resistance of the photoelectric conversion layer and the heat resistance stability of the phase-separated structure.

For example, Non-Patent Document 1 discloses that the heat resistance of a photoelectric conversion element can be improved by introducing a crosslinked structure into a photoelectric conversion layer using a p-type semiconductor into which a crosslinking group has been introduced.
Non-Patent Document 2 shows that the heat resistance of the photoelectric conversion layer can be improved by adding a thermally crosslinkable monomer, OBOCO (octane-1,8-diylbis(1,4-dihydrobenzo[d][1,2]oxathiine- ₆ -carboxylate-3-oxide)), to an active layer consisting of P3HT (poly(3-hexylthiophene)) and PC ₆₁ BM ([6,6]-phenyl-C 61 butyric acid methyl ester) and thermally curing the photoelectric conversion layer.
Non-Patent Document 3 shows that the heat resistance of a photoelectric conversion layer made of PM6 and BTTT-2Cl is improved by adding an n-type semiconductor PZ1 to the photoelectric conversion layer, as follows.

In Patent Document 1, by using a specific semiconductor material, a photoelectric conversion element was successfully developed that maintained good photoelectric conversion characteristics even after a heat resistance test at 150 to 220°C for 50 minutes.

Materials. Today. 2015, 18, 425-435 J. Mater. Chem. A, 2013, 1, 4589-4594 Nat. Commun. 2020, 11, 1218

Japanese Patent Application Laid-Open No. 2021-057573

However, the techniques of the above Non-Patent Documents 1 to 3 all have the following problems.
The methods described in Non-Patent Documents 1 and 3 require the development of a new organic semiconductor having a crosslinking group.
Furthermore, a fullerene derivative is essential for the curing reaction of the thermosetting monomer OBOCO in Non-Patent Document 2, and when this method is used, there are limitations on the selection of semiconductor materials for the photoelectric conversion layer.
The method described in Patent Document 1 requires the use of a predetermined semiconductor material that is highly heat-resistant, and is therefore not very versatile in that there are limitations on the selection of semiconductor materials.

In view of these problems of the prior art, a general-purpose system that can impart heat resistance by post-addition of additives, etc., regardless of the semiconductor material selected, is ideal. Furthermore, when considering the imparting of heat resistance by stabilizing the phase-separated structure of the photoelectric conversion layer, a system that forms a crosslinked structure within the photoelectric conversion layer is effective. Furthermore, considering the impact on the semiconductor material responsible for photoelectric conversion, it is desirable that the curing reaction proceed with heat rather than light.
However, the reality is that no technology that meets these requirements has been reported.

The present invention therefore aims to provide an organic semiconductor ink that can improve heat resistance by forming a crosslinked structure within the photoelectric conversion layer using the additives incorporated therein, thereby allowing for greater freedom in the selection of semiconductor materials and making it easily applicable to existing combinations of p-type and n-type organic semiconductors; a photoelectric conversion layer using this organic semiconductor ink; and an organic photoelectric conversion element that includes this photoelectric conversion layer.

As a result of extensive research to solve the above-mentioned problems, the inventors discovered that by incorporating a thermosetting component capable of forming a crosslinked structure into an organic semiconductor ink and then thermally curing the ink, the heat resistance of the resulting photoelectric conversion layer can be improved, and that existing combinations of p-type and n-type organic semiconductors can be used without the need for special functional or molecular design.

The present invention was achieved based on these findings and is summarized as follows:

[1] An organic semiconductor ink comprising a non-crosslinkable p-type organic semiconductor, a non-crosslinkable n-type organic semiconductor, a thermosetting component, and a solvent.

[2] The organic semiconductor ink described in [1], wherein the thermosetting component contains an epoxy resin as a main component.

[3] The organic semiconductor ink described in [2], wherein the thermosetting component further contains a curing agent.

[4] The organic semiconductor ink according to [2] or [3], wherein the epoxy resin has an epoxy equivalent of 50 to 1000 g/eq.

[5] The organic semiconductor ink according to any one of [2] to [4], wherein the content of the epoxy resin in the thermosetting component is 38 to 100 mass%.

[6] An organic semiconductor ink according to any one of [1] to [5], wherein the curing temperature of the thermosetting component is within the range of 100 to 220°C.

[7] The organic semiconductor ink according to any one of [1] to [6], wherein the content of the thermosetting component is 1 to 100 parts by mass per 100 parts by mass of the non-crosslinkable p-type organic semiconductor and the non-crosslinkable n-type organic semiconductor combined.

[8] The organic semiconductor ink according to any one of [1] to [7], having a solids concentration of 10 to 30 mg/mL.

[9] The organic semiconductor ink according to any one of [1] to [8], wherein the solvent includes an aromatic solvent.

[10] The organic semiconductor ink according to any one of [1] to [9], wherein the non-crosslinkable p-type organic semiconductor is a conjugated polymer, and the non-crosslinkable n-type organic semiconductor is a semiconductor not containing a fullerene skeleton.

[11] The organic semiconductor ink according to [10], wherein the non-crosslinkable n-type organic semiconductor comprises a compound represented by the following formula (I) and/or a polymer of two or more compounds represented by the following formula (I):

(In the above formula (I), A represents an atom selected from Group 14 of the periodic table; X ¹ to X ⁴ each independently represent a hydrogen atom or a halogen atom; R ^1a and R ^1b each independently represent a linear or branched alkyl group; and R ² to R ⁵ each independently represent a linear or branched alkyl group, a linear or branched alkoxy group, a linear or branched thioalkyl group, or a hydrogen atom.)

[12] A photoelectric conversion layer obtained by heat-curing a coating film of the organic semiconductor ink described in any one of [1] to [11].

[13] An organic photoelectric conversion element comprising the photoelectric conversion layer described in [12].

The organic semiconductor ink of the present invention contains a thermosetting component, and by thermally curing this thermosetting component, a crosslinked structure can be formed in the photoelectric conversion layer. Therefore, the network of crosslinks in this crosslinked structure suppresses the flow of the p-type organic semiconductor and the n-type organic semiconductor in a high-temperature environment, and stabilizes the phase-separated structure of the p-type organic semiconductor and the n-type organic semiconductor, thereby improving heat resistance.
In this way, in the present invention, the thermosetting component in the organic semiconductor ink itself can form a crosslinked structure, so there is no need to introduce functional groups for crosslinking reactions into the p-type organic semiconductor or n-type organic semiconductor, or to design the molecules for crosslinking reactions.
Therefore, there is a high degree of freedom in the selection of semiconductor materials, and the present invention can be easily applied to combinations of existing p-type organic semiconductors and n-type organic semiconductors. Furthermore, the present invention can provide a photoelectric conversion layer with excellent heat resistance and little deterioration in photoelectric conversion properties even in high-temperature environments, as well as an organic photoelectric conversion element having this photoelectric conversion layer.

1A and 1B are schematic diagrams illustrating the mechanism by which the heat resistance of a photoelectric conversion layer is improved by the organic semiconductor ink of the present invention, in which (a) shows a conventional method and (b) shows the present invention. 1 is a cross-sectional view schematically illustrating an example of an embodiment of an organic photoelectric conversion element of the present invention.

The following describes in detail the modes for implementing the present invention. However, the following explanations of the constituent elements are representative examples of embodiments of the present invention, and the present invention is not limited to these details.

[Organic semiconductor ink]
The organic semiconductor ink of the present invention is characterized by containing a non-crosslinkable p-type organic semiconductor, a non-crosslinkable n-type organic semiconductor, a thermosetting component, and a solvent.

In the present invention, the "non-crosslinkable" in "non-crosslinkable p-type organic semiconductor" means that the p-type organic semiconductor and the thermosetting component do not undergo a crosslinking reaction, and does not exclude crosslinking, polymerization, or condensation reactions between p-type organic semiconductors. Similarly, the "non-crosslinkable" in "non-crosslinkable n-type organic semiconductor" means that the n-type organic semiconductor and the thermosetting component do not undergo a crosslinking reaction, and does not exclude crosslinking, polymerization, or condensation reactions between n-type organic semiconductors. Furthermore, the "non-crosslinkable" of these organic semiconductors does not exclude crosslinking, polymerization, or condensation reactions between the "p-type organic semiconductor" and the "n-type organic semiconductor".
Furthermore, the term "thermosetting component" refers to a component that itself crosslinks and hardens when exposed to heat to form a crosslinked structure.

<Mechanism>
The mechanism of the effect of improving the heat resistance of the photoelectric conversion layer by the organic semiconductor ink of the present invention will be explained with reference to FIG.
As shown in Figure 1(a), conventional organic semiconductor inks consist of a p-type organic semiconductor (a p-type polymer in Figure 1) and an n-type organic semiconductor (an n-type molecule in Figure 1) dissolved in a solvent. The p-type polymer and n-type molecule are compatible with each other in the photoelectric conversion layer formed by depositing this organic semiconductor ink, resulting in high photoelectric conversion efficiency.
However, in conventional methods, when exposed to a high-temperature environment (for example, a heat resistance test at 150 to 220°C for 50 minutes), the p-type polymer and n-type molecules flow and aggregate, significantly impairing their compatibility, and the resulting partial localization of these molecules reduces the photoelectric conversion efficiency.
In terms of heat resistance to prevent deterioration of photoelectric conversion characteristics due to the heating environment expected in the device manufacturing process, it is preferable that the heat resistance be 140°C or higher, more preferably 180°C or higher, and particularly preferably 200°C or higher.

In contrast, the organic semiconductor ink of the present invention contains a thermosetting component, and when this organic semiconductor ink is formed into a film and thermally cured, the thermosetting component forms a crosslinked structure within the resulting photoelectric conversion layer. In a photoelectric conversion layer in which a crosslinked structure of the thermosetting component has been formed in this way, even when exposed to a high-temperature environment (e.g., a heat resistance test at 150-220°C for 50 minutes), the flow of the p-type polymer and n-type molecules is prevented by the network of the crosslinked structure of the thermosetting component, and the compatibility of the two is hardly impaired, thereby suppressing a decrease in photoelectric conversion efficiency.

<Thermosetting component>
The thermosetting component used in the present invention is not particularly limited as long as it can be cured by heating to form a network-like crosslinked structure in the photoelectric conversion layer.

The thermosetting component is preferably one that contains one or more of the following resins as its main component, such as epoxy resin, phenolic resin, melamine resin, urethane resin, or silicone resin, as these resins are more likely to form crosslinked structures that effectively improve heat resistance. Epoxy resin is particularly preferred. Note that "main component" here refers to the component contained in the thermosetting component with the largest content. The main component content in the thermosetting component is preferably 38% by mass or more, and particularly preferably 49 to 100% by mass.

When using epoxy resin as the thermosetting component, it is preferable to use a curing agent for the epoxy resin in combination, as the use of a curing agent in combination allows the thermosetting process to proceed more quickly.

(epoxy resin)
The epoxy resin is not particularly limited, and any epoxy resin generally known as an epoxy resin can be used.

Examples of epoxy resins that can be used include phenol novolac epoxy resins, orthocresol novolac epoxy resins, epoxy resins having a triphenylmethane skeleton, and other novolac resins obtained by condensing or co-condensing phenols such as phenols, cresol, xylenol, resorcinol, catechol, bisphenol A, bisphenol F, etc. and/or naphthols such as α-naphthol, β-naphthol, dihydroxynaphthalene, etc. with compounds having an aldehyde group such as formaldehyde, acetaldehyde, propionaldehyde, benzaldehyde, salicylaldehyde, etc. under an acidic catalyst; diglycidyl ethers of bisphenol A, bisphenol F, bisphenol S, alkyl-substituted or unsubstituted biphenols, etc.; stilbene epoxy resins. Examples of epoxy resins include epoxidized epoxy resins, hydroquinone-type epoxy resins, glycidyl ester-type epoxy resins obtained by reacting epichlorohydrin with polybasic acids such as phthalic acid or dimer acid, glycidylamine-type epoxy resins obtained by reacting epichlorohydrin with polyamines such as diaminodiphenylmethane or isocyanuric acid, epoxidized products of co-condensation resins of dicyclopentadiene and phenols, epoxidized products of aralkyl-type phenol resins such as naphthalene ring-containing epoxy resins, phenol aralkyl resins containing a xylylene skeleton or a biphenylene skeleton, and naphthol aralkyl resins, trimethylolpropane-type epoxy resins, terpene-modified epoxy resins, linear aliphatic epoxy resins or alicyclic epoxy resins obtained by oxidizing olefin bonds with a peracid such as peracetic acid, and sulfur-containing epoxy resins. These epoxy resins may be used alone or in combination of two or more.

Among these, novolac-type epoxy resins are preferred from the viewpoint of curability, dicyclopentadiene-type epoxy resins are preferred from the viewpoint of low moisture absorption, naphthalene-type epoxy resins and triphenylmethane-type epoxy resins are preferred from the viewpoint of heat resistance and low warpage, and biphenylene-type epoxy resins and naphthol aralkyl-type epoxy resins are preferred from the viewpoint of flame retardancy.

As the epoxy resin, it is preferable to use one with a small epoxy equivalent because this easily forms a crosslinked structure in the photoelectric conversion layer that is effective in improving heat resistance by forming many crosslinking points in a network structure that can prevent the flow of p-type organic semiconductors and n-type organic semiconductors by heat curing, while it is preferable to use one with a large epoxy equivalent in terms of handleability of the epoxy resin. From this perspective, the epoxy equivalent of the epoxy resin is preferably 50 to 1000 g/eq., more preferably 70 to 500 g/eq., and particularly preferably 90 to 300 g/eq.
In the present invention, the term "epoxy equivalent" is defined as "the mass of an epoxy compound containing one equivalent of an epoxy group" and can be measured in accordance with JIS K7236.

These epoxy resins can be commercially available products. Examples of commercially available epoxy resins that can be used include jER825 (epoxy equivalent weight 175 g/eq), jER827 (epoxy equivalent weight 185 g/eq), jER828 (epoxy equivalent weight 189 g/eq), jER834 (epoxy equivalent weight 250 g/eq), jER806 (epoxy equivalent weight 165 g/eq), jER807 (epoxy equivalent weight 170 g/eq), jER604 (epoxy equivalent weight 120 g/eq), jER630 (epoxy equivalent weight 98 g/eq), jER1032H60 (epoxy equivalent weight 169 g/eq), jER152 (epoxy equivalent weight 175 g/eq), and jER154 (epoxy equivalent weight 17 8g/eq), jER157S70 (epoxy equivalent 210g/eq), YX-7700 (epoxy equivalent 273g/eq), YX-8000 (epoxy equivalent 205g/eq), YX-8800 (epoxy equivalent 179g/eq), YX-4000 (epoxy equivalent 186g/eq), YX-7105 (epoxy equivalent 480g/eq), YX-7400 (epoxy equivalent 440g/eq) (all trade names, manufactured by Mitsubishi Chemical Corporation), YD-127 (epoxy equivalent 185g/eq), YD-128 (epoxy equivalent 189g/eq), YDF-170 (epoxy equivalent 170g/eq), YDPN-638 (epoxy equivalent 180g/eq), TX-0 911 (epoxy equivalent weight 172 g/eq) (all trade names, manufactured by Nippon Steel & Sumikin Chemical & Material Co., Ltd.), EPICLON 840 (epoxy equivalent weight 185 g/eq), EPICLON 850 (epoxy equivalent weight 189 g/eq), EPICLON 830 (epoxy equivalent weight 170 g/eq), EPICLON 835 (epoxy equivalent weight 172 g/eq), HP-4032 (epoxy equivalent weight 150 g/eq), HP-4700 (epoxy equivalent weight 162 g/eq), HP-4770 (epoxy equivalent weight 204 g/eq), HP-4750 (epoxy equivalent weight 185 g/eq), HP-7200 (epoxy equivalent weight 265 g/eq), N-730A (epoxy equivalent weight 174 g/eq) eq), N-740 (epoxy equivalent 181 g/eq), N-770 (epoxy equivalent 187 g/eq), TSR-400 (epoxy equivalent 338 g/eq) (all trade names, manufactured by DIC Corporation), GAN (epoxy equivalent 125 g/eq), GOT (epoxy equivalent 135 g/eq), NC-2000 (epoxy equivalent 241 g/eq), NC-3000 (epoxy equivalent 275 g/eq) (all trade names, manufactured by Nippon Kayaku Co., Ltd.), MY-0500 (epoxy equivalent 110 g/eq), MY-0600 (epoxy equivalent 106 g/eq), ECN-1299 (epoxy equivalent 230 g/eq) (all trade names, manufactured by Huntsman Japan Co., Ltd.), D.E. R331, D.E. Examples include, but are not limited to, D.E. R354 (epoxy equivalent weight 170 g/eq) (epoxy equivalent weight 187/eq), D.E. R332 (epoxy equivalent weight 173 g/eq) (all trade names, manufactured by The Dow Chemical Company).

The content of such epoxy resin in the thermosetting component is preferably 38 to 100% by mass, more preferably 49 to 99.5% by mass, and particularly preferably 75 to 99.5% by mass. If the content of epoxy resin in the thermosetting component is above the above-mentioned lower limit, the epoxy resin can efficiently form a crosslinked structure that is effective in improving heat resistance. If the content of epoxy resin in the thermosetting component is below the above-mentioned upper limit, the content of co-component components such as the curing agent shown below can be ensured, and the curing reaction can be smoothly promoted.

(hardening agent)
In the present invention, a curing agent refers to a substance that contributes to the crosslinking reaction and/or chain extension reaction between epoxy groups of an epoxy resin. In the present invention, even substances that are usually called "curing accelerators" or "curing catalysts" are considered to be curing agents as long as they contribute to the crosslinking reaction and/or chain extension reaction between epoxy groups of an epoxy resin.

There are no particular restrictions on the curing agent, and any commonly known epoxy resin curing agent can be used. Examples include phenol-based curing agents, amine-based curing agents such as aliphatic amines, polyether amines, alicyclic amines, and aromatic amines, acid anhydride-based curing agents, amide-based curing agents, tertiary amines, and imidazoles.

Among these, it is preferable to use a phenol-based curing agent, an acid anhydride-based curing agent, or an amide-based curing agent from the viewpoint of heat resistance, etc. It is also preferable to use an imidazole compound from the viewpoint of sufficiently progressing the curing reaction and improving heat resistance.
The curing agent may be used alone or in combination of two or more.

<Phenol-based hardener>
Specific examples of phenolic curing agents include various polyhydric phenols such as bisphenol A, bisphenol F, bisphenol S, bisphenol AD, hydroquinone, resorcinol, methylresorcinol, biphenol, tetramethylbiphenol, dihydroxynaphthalene, dihydroxydiphenyl ether, thiodiphenols, phenol novolac resin, cresol novolac resin, phenol aralkyl resin, biphenyl aralkyl resin, naphthol aralkyl resin, terpene phenol resin, dicyclopentadiene phenol resin, bisphenol A novolac resin, trisphenolmethane type resin, naphthol novolac resin, brominated bisphenol A, and brominated phenol novolac resin. Examples of the polyhydric phenol resin include polyhydric phenol resins obtained by the condensation reaction of phenols with various aldehydes such as benzaldehyde, hydroxybenzaldehyde, crotonaldehyde, and glyoxal, polyhydric phenol resins obtained by the condensation reaction of xylene resin and phenols, co-condensation resins of heavy oils or pitches with phenols and formaldehydes, and various phenol resins such as phenol-benzaldehyde-xylylene dimethoxide polycondensates, phenol-benzaldehyde-xylylene dihalide polycondensates, phenol-benzaldehyde-4,4'-dimethoxide biphenyl polycondensates, and phenol-benzaldehyde-4,4'-dihalide biphenyl polycondensates.

These phenolic curing agents may be used alone or in any combination of two or more in any ratio.

The amount of phenolic curing agent added is preferably 0.1 to 1,000 parts by mass per 100 parts by mass of epoxy resin, more preferably 500 parts by mass or less, even more preferably 300 parts by mass or less, and particularly preferably 100 parts by mass or less.

<Amine-based curing agent>
Examples of the amine-based curing agent (excluding tertiary amines) include aliphatic amines, polyether amines, alicyclic amines, and aromatic amines.

Examples of aliphatic amines include ethylenediamine, 1,3-diaminopropane, 1,4-diaminopropane, hexamethylenediamine, 2,5-dimethylhexamethylenediamine, trimethylhexamethylenediamine, diethylenetriamine, iminobispropylamine, bis(hexamethylene)triamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, N-hydroxyethylethylenediamine, and tetra(hydroxyethyl)ethylenediamine.

Examples of polyetheramines include triethylene glycol diamine, tetraethylene glycol diamine, diethylene glycol bis(propylamine), polyoxypropylene diamine, and polyoxypropylene triamines.

Examples of alicyclic amines include isophoronediamine, methacenediamine, N-aminoethylpiperazine, bis(4-amino-3-methyldicyclohexyl)methane, bis(aminomethyl)cyclohexane, 3,9-bis(3-aminopropyl)-2,4,8,10-tetraoxaspiro(5,5)undecane, and norbornenediamine.

Examples of aromatic amines include tetrachloro-p-xylylenediamine, m-xylylenediamine, p-xylylenediamine, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, 2,4-diaminoanisole, 2,4-toluenediamine, 2,4-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 4,4'-diamino-1,2-diphenylethane, 2,4-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, m-aminophenol, m-aminobenzylamine, benzyldimethylamine, 2-(dimethylaminomethyl)phenol, triethanolamine, methylbenzylamine, α-(m-aminophenyl)ethylamine, α-(p-aminophenyl)ethylamine, diaminodiethyldimethyldiphenylmethane, and α,α'-bis(4-aminophenyl)-p-diisopropylbenzene.

The above-listed amine-based curing agents may be used alone or in any combination of two or more in any ratio.

Amine-based curing agents are preferably used so that the equivalent ratio of functional groups in the curing agent to epoxy groups in the epoxy resin is in the range of 0.8 to 1.5. This range is preferable because it reduces the likelihood of unreacted epoxy groups or functional groups from the curing agent remaining.

Examples of tertiary amines include 1,8-diazabicyclo(5,4,0)undecene-7, triethylenediamine, benzyldimethylamine, triethanolamine, dimethylaminoethanol, and tris(dimethylaminomethyl)phenol.

The tertiary amines listed above may be used alone or in any combination of two or more in any ratio.

The above tertiary amines are preferably used so that the equivalent ratio of the functional groups in the curing agent to the epoxy groups in the epoxy resin is in the range of 0.8 to 1.5. This range is preferable because it reduces the likelihood of unreacted epoxy groups or functional groups from the curing agent remaining.

<Acid anhydride curing agent>
Examples of the acid anhydride curing agent include acid anhydrides and modified acid anhydrides.
Examples of acid anhydrides include phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, benzophenonetetracarboxylic anhydride, dodecenylsuccinic anhydride, polyadipic anhydride, polyazelaic anhydride, polysebacic anhydride, poly(ethyloctadecanedioic) anhydride, poly(phenylhexadecanedioic) anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, hexahydrophthalic anhydride, methylhimic anhydride, trialkyltetrahydrophthalic anhydride, Examples of such an anhydride include methylcyclohexene dicarboxylic acid anhydride, methylcyclohexene tetracarboxylic acid anhydride, ethylene glycol bistrimellitate dianhydride, HET anhydride, Nadic anhydride, methylnadic anhydride, 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexane-1,2-dicarboxylic acid anhydride, 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalene succinic acid dianhydride, and 1-methyl-dicarboxy-1,2,3,4-tetrahydro-1-naphthalene succinic acid dianhydride.

Examples of modified acid anhydrides include those obtained by modifying the above-mentioned acid anhydrides with glycols. Examples of glycols that can be used for modification include alkylene glycols such as ethylene glycol, propylene glycol, and neopentyl glycol, and polyether glycols such as polyethylene glycol, polypropylene glycol, and polytetramethylene ether glycol. Furthermore, copolymer polyether glycols of two or more of these glycols and/or polyether glycols can also be used.

When modifying an acid anhydride, it is preferable to modify it with 0.4 moles or less of glycol per mole of acid anhydride. When the modification amount is below the above upper limit, the viscosity of the epoxy resin composition does not become too high, which tends to improve workability and also tends to improve the rate of the curing reaction with the epoxy resin.

The above-listed acid anhydride curing agents may be used alone or in any combination of two or more in any amount.

When using an acid anhydride curing agent, it is preferable to use it so that the equivalent ratio of functional groups in the curing agent to epoxy groups in the epoxy resin is in the range of 0.8 to 1.5. This range is preferable because it is less likely that unreacted epoxy groups or functional groups from the curing agent will remain.

<Amide-based curing agent>
Examples of the amide-based curing agent include dicyandiamide and its derivatives, polyamide resins, and the like.
The amide curing agent may be used alone or in any combination and ratio of two or more kinds.
When an amide-based curing agent is used, it is preferable to use the amide-based curing agent in an amount of 0.1 to 20% by mass based on the total amount of the epoxy resin and the amide-based curing agent.

<Imidazoles>
Examples of imidazoles include 2-phenylimidazole, 2-ethyl-4(5)-methylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyano-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl- Examples of the imidazoles include 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, and adducts of epoxy resins with the above imidazoles. Note that, since imidazoles have catalytic activity, they can generally be classified as curing accelerators, but in the present invention they are classified as curing agents.

The above-listed imidazoles may be used alone or in any combination and ratio of two or more.

When using imidazoles, it is preferable to use them in an amount of 0.1 to 20% by mass based on the total amount of epoxy resin and imidazoles.

(Curing accelerator)
The thermosetting component according to the present invention may contain a curing accelerator, which can shorten the curing time and lower the curing temperature.
The curing accelerator is not particularly limited, but specific examples include organic phosphines, phosphorus compounds such as phosphonium salts, tetraphenylboron salts, organic acid dihydrazides, boron halide amine complexes, and the like.

Phosphorus compounds that can be used as curing accelerators include triphenylphosphine, diphenyl(p-tolyl)phosphine, tris(alkylphenyl)phosphine, tris(alkoxyphenyl)phosphine, tris(alkyl/alkoxyphenyl)phosphine, tris(dialkylphenyl)phosphine, tris(trialkylphenyl)phosphine, tris(tetraalkylphenyl)phosphine, tris(dialkoxyphenyl)phosphine, tris(trialkoxyphenyl)phosphine, tris(tetraalkoxyphenyl)phosphine, trialkylphosphine Examples include organic phosphines such as phosphines, dialkylarylphosphines, and alkyldiarylphosphines; complexes of these organic phosphines with organoborons; and compounds obtained by adding these organic phosphines to quinone compounds such as maleic anhydride, 1,4-benzoquinone, 2,5-toluquinone, 1,4-naphthoquinone, 2,3-dimethylbenzoquinone, 2,6-dimethylbenzoquinone, 2,3-dimethoxy-5-methyl-1,4-benzoquinone, 2,3-dimethoxy-1,4-benzoquinone, and phenyl-1,4-benzoquinone; and compounds such as diazophenylmethane.

Among the curing accelerators listed above, organic phosphines and phosphonium salts are preferred, and organic phosphines are most preferred.
The curing accelerator may be used alone or in any combination and ratio of two or more of the above-listed accelerators.

The curing accelerator is preferably used in an amount ranging from 0.1 to 20 parts by mass per 100 parts by mass of epoxy resin. It is more preferably 0.5 parts by mass or more, and even more preferably 1 part by mass or more, while it is more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less. A content of the curing accelerator above the lower limit mentioned above provides a good curing acceleration effect, while a content below the upper limit mentioned above is preferred because it makes it easier to achieve the desired cured physical properties.

(Curing temperature)
The thermosetting component used in the present invention preferably has a curing temperature in the range of 100 to 220°C.
If the curing temperature is 100°C or higher, it is possible to prevent the thermosetting component from reacting in the ink during preparation of the organic semiconductor ink. When the thermosetting component is cured by heating to form a crosslinked structure in the photoelectric conversion layer, a higher curing temperature is preferable. On the other hand, if the curing temperature is 220°C or lower, it is possible to prevent the p-type organic semiconductor and n-type organic semiconductor from flowing before the crosslinked structure is formed by curing due to excessively high heating, which changes the phase separation structure and reduces the photoelectric conversion characteristics when the thermosetting component is cured by heating to form a crosslinked structure during formation of the photoelectric conversion layer.
From this viewpoint, the curing temperature of the thermosetting component is more preferably 120 to 220°C, and particularly preferably 140 to 220°C.

To achieve the curing temperature of the thermosetting component within the above range, techniques such as selecting an epoxy resin with an appropriate curing temperature, selecting appropriate curing agents and curing accelerators, and adjusting their blending ratios can be used.

(Thermosetting component content)
The content of the thermosetting component in the organic semiconductor ink of the present invention is preferably 1 to 100 parts by mass, more preferably 1 to 40 parts by mass, and particularly preferably 1 to 10 parts by mass, per 100 parts by mass of the non-crosslinkable p-type organic semiconductor and the non-crosslinkable n-type organic semiconductor combined. Furthermore, when an epoxy resin is used as the thermosetting component, the content of the epoxy resin in the organic semiconductor ink of the present invention is preferably 1 to 100 parts by mass, more preferably 1 to 40 parts by mass, and particularly preferably 1 to 10 parts by mass, per 100 parts by mass of the non-crosslinkable p-type organic semiconductor and the non-crosslinkable n-type organic semiconductor combined.

If the content ratio of the thermosetting component and epoxy resin in the organic semiconductor ink is above the above-mentioned lower limit, a sufficient amount of crosslinked structure effective in improving heat resistance can be formed in the photoelectric conversion layer. If the content ratio of the thermosetting component in the organic semiconductor ink is below the above-mentioned upper limit, the content of the non-crosslinkable p-type organic semiconductor and non-crosslinkable n-type organic semiconductor can be ensured, allowing the formation of a photoelectric conversion layer with excellent photoelectric conversion efficiency.

<Non-crosslinkable p-type organic semiconductor>
The non-crosslinkable p-type organic semiconductor is not particularly limited and may be any known compound, but is preferably a donor semiconductor, typically an organic semiconductor (compound). For example, a hole-transporting organic compound that is a p-type conjugated polymer may be mentioned, and a compound that has a tendency to easily donate electrons may be used.
Specific examples of skeletons having excellent hole transport properties include a carbazole structure, a thiophene structure, a benzodithiophene structure, a thienothiophene structure, a dibenzofuran structure, a triarylamine structure, a naphthalene structure, a phenanthrene structure, and a pyrene structure.
Among these, it is particularly preferable to use a material that can be mixed with a non-crosslinkable n-type organic semiconductor described below to form a film by coating.

Specific examples include those represented by the following formula (II). In formula (II), n is a positive number.

In order to improve the properties of the non-crosslinkable p-type organic semiconductor used in the present invention as a p-type semiconductor, the weight-average molecular weight is preferably 100,000 or more, more preferably 150,000 or more. From the viewpoint of solubility in solvents, the upper limit is preferably 400,000 or less, more preferably 300,000 or less.
Here, the weight average molecular weight of the non-crosslinkable p-type organic semiconductor is a value determined by size exclusion chromatography.

<Non-crosslinkable n-type organic semiconductor>
An n-type semiconductor is an acceptor semiconductor, and is mainly represented by an electron transport compound, which refers to a compound that has the property of readily accepting electrons. More specifically, when two compounds are used in contact with each other, the n-type semiconductor refers to the compound with the larger electron affinity. Therefore, any compound with electron-accepting properties can be used as the acceptor compound.
For example, fused aromatic carbocyclic compounds (naphthalene derivatives, anthracene derivatives, phenanthrene derivatives, tetracene derivatives, pyrene derivatives, perylene derivatives, fluoranthene derivatives), 5- to 7-membered heterocyclic compounds containing a nitrogen atom, an oxygen atom, or a sulfur atom (e.g., pyridine, pyrazine, pyrimidine, pyridazine, triazine, quinoline, quinoxaline, quinazoline, phthalazine, cinnoline, isoquinoline, pteridine, acridine, phenazine, phenanthroline, tetrazole, pyrazole, imidazole, thiazoline, Examples of suitable metal complexes include those having, as a ligand, a tetraazoindazole, oxazole, indazole, benzimidazole, benzotriazole, benzoxazole, benzothiazole, carbazole, purine, triazolopyridazine, triazolopyrimidine, tetrazaindene, oxadiazole, imidazopyridine, pyrazine, pyrrolopyridine, thiadiazolopyridine, dibenzazepine, tribenzazepine, etc.), a polyarylene compound, a fluorene compound, a cyclopentadiene compound, a silyl compound, or a nitrogen-containing heterocyclic compound.
However, as described above, any compound having a larger electron affinity than the compound used as the donor semiconductor may be used as the acceptor semiconductor.

When a fullerene skeleton is used as an n-type semiconductor, even if a bulk heterojunction structure is used to increase photoelectric conversion efficiency, the presence of the bulky fullerene skeleton increases the distance between the n-type and p-type semiconductors, resulting in a decrease in photoelectric conversion efficiency.

Therefore, in the non-crosslinkable p-type organic semiconductor of the present invention, the ratio of the n-type semiconductor having a fullerene skeleton to the n-type semiconductor not having a fullerene skeleton is preferably 10 mass % or less, and it is more preferable that the n-type semiconductor is a fullerene skeleton-free semiconductor in which substantially no n-type semiconductor having a fullerene skeleton is contained.
Here, "substantially free of a fullerene skeleton" means that the non-fullerene n-type semiconductor is responsible for transporting electrons among the charges generated in the photoelectric conversion layer, and a small amount may be contained to improve the morphology of the photoelectric conversion layer. For such a purpose, the n-type semiconductor containing a fullerene skeleton is usually contained in an amount of 5 mass % or less relative to the non-fullerene n-type semiconductor not having a fullerene skeleton, and this proportion is preferably 2 mass % or less.

The non-crosslinkable n-type organic semiconductor used in the present invention preferably contains a compound represented by the following formula (I) and/or a polymer of two or more compounds represented by the following formula (I), particularly from the viewpoints of compatibility with the non-crosslinkable p-type organic semiconductor and the ability to form a (BHJ)-type photoelectric conversion layer.

(In the above formula (I), A represents an atom selected from Group 14 of the periodic table; X ¹ to X ⁴ each independently represent a hydrogen atom or a halogen atom; R ^1a and R ^1b each independently represent a linear or branched alkyl group; and R ² to R ⁵ each independently represent a linear or branched alkyl group, a linear or branched alkoxy group, a linear or branched thioalkyl group, or a hydrogen atom.)

In the above formula (I), A is preferably a carbon atom or a silicon atom.
X ¹ to X ⁴ are each independently a hydrogen atom or a halogen atom, and the halogen atom is preferably a fluorine atom or a chlorine atom.
R ^1a and R ^1b each independently represent a linear or branched alkyl group, and the alkyl group preferably has 8 to 24 carbon atoms, particularly 10 to 20 carbon atoms, and especially 12 to 18 carbon atoms.

Examples of linear or branched alkyl groups having 8 to 24 carbon atoms include linear alkyl groups such as n-octyl, n-decyl, lauryl, myristyl, palmityl, and stearyl; branched primary alkyl groups such as 2-ethylhexyl and 2-butyloctyl; and secondary alkyl groups such as 2-octyl, 2-nonyl, and 2-decyl. Of these, linear or branched primary alkyl groups are preferred, with 2-ethylhexyl or 2-butyloctyl being particularly preferred.

R ² to R ⁵ are each independently a linear or branched alkyl group, a linear or branched alkoxy group, a linear or branched thioalkyl group, or a hydrogen atom, and the alkyl group, alkoxy group, or thioalkyl group preferably has 8 to 24 carbon atoms, particularly 10 to 20 carbon atoms, and especially 12 to 18 carbon atoms.
R ² to R ⁵ are preferably each independently an alkoxy group having 8 to 24 carbon atoms, and specific examples thereof include a 2-ethylhexyloxy group and a palmityloxy group.

From the viewpoint of compatibility with the non-crosslinkable p-type organic semiconductor and ability to form a BHJ type photoelectric conversion layer, it is preferable that R ^1a and R ^1b are the same group, and it is preferable that R ² to R ⁵ are composed of two or more different groups.

<Contents of non-crosslinkable p-type organic semiconductor and non-crosslinkable n-type organic semiconductor>
The ratio of the non-crosslinkable p-type organic semiconductor to the non-crosslinkable n-type organic semiconductor contained in the organic semiconductor ink of the present invention is preferably 0.5 to 2.5 times, particularly 1.0 to 2.0 times, in terms of the mass ratio of the non-crosslinkable n-type organic semiconductor to the non-crosslinkable p-type organic semiconductor (n-type organic semiconductor/p-type organic semiconductor mass ratio). If the amount of non-crosslinkable n-type organic semiconductor is higher than the above range and the amount of non-crosslinkable p-type organic semiconductor is lower than the above range, sensitivity in the near-infrared region tends to decrease. Conversely, if the amount of non-crosslinkable p-type organic semiconductor is higher than the above range and the amount of non-crosslinkable n-type organic semiconductor is lower than the above range, dark current tends to be more likely to occur.

<Solvent>
The solvent contained in the organic semiconductor ink of the present invention may be any solvent capable of dissolving the non-crosslinkable p-type organic semiconductor, the non-crosslinkable n-type organic semiconductor, and the thermosetting component, and examples thereof include aromatic hydrocarbon solvents such as toluene, xylene, mesitylene, and cyclohexylbenzene, and aromatic halogen-containing solvents such as chlorobenzene and o-dichlorobenzene; aliphatic halogen-containing solvents such as 1,2-dichloroethane; and aliphatic ethers such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and propylene glycol-1-monomethyl ether acetate (PGMEA). ether-based solvents such as aromatic ethers such as phenyl acetate, 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, anisole, phenetole, 2-methoxytoluene, 3-methoxytoluene, 4-methoxytoluene, 2,3-dimethylanisole, and 2,4-dimethylanisole; aliphatic ester-based solvents such as ethyl acetate, n-butyl acetate, ethyl lactate, and n-butyl lactate; and ester-based solvents such as aromatic esters such as phenyl acetate, phenyl propionate, methyl benzoate, ethyl benzoate, isopropyl benzoate, propyl benzoate, and n-butyl benzoate.
These may be used alone or in combination of two or more.

Of these solvents, aromatic solvents are preferred from the viewpoint of the solubility of non-crosslinked p-type organic semiconductors and non-crosslinked p-type organic semiconductors, and aromatic halogen-containing solvents are particularly preferred.

<Other ingredients>
The organic semiconductor ink of the present invention may contain, in addition to the above-mentioned thermosetting component, non-crosslinkable p-type organic semiconductor, non-crosslinkable n-type organic semiconductor and solvent, a stabilizer, a thickener, etc., as necessary.
However, when the organic semiconductor ink of the present invention contains these other components, in order to fully obtain the inherent effects of the organic semiconductor ink, it is preferable that the content of the other components in the organic semiconductor ink is 10 mass % or less relative to the total of the thermosetting component, non-crosslinkable p-type organic semiconductor, non-crosslinkable n-type organic semiconductor, and other components.

<Solid content concentration>
The solids concentration of the organic semiconductor ink of the present invention, i.e., the total content of the thermosetting component, non-crosslinkable p-type organic semiconductor, non-crosslinkable n-type organic semiconductor, and other components contained as necessary, excluding the solvent in the organic semiconductor ink, is preferably 10 to 30 mg/mL, and more preferably 12 to 24 mg/mL.
If the solids concentration of the organic semiconductor ink is equal to or higher than the lower limit, the efficiency of forming the photoelectric conversion layer is excellent, while if it is equal to or lower than the upper limit, the organic semiconductor ink can be easily prepared and is easy to handle.

<Method of manufacturing organic semiconductor ink>
The organic semiconductor ink of the present invention can be produced by adding and mixing the above-mentioned thermosetting component, non-crosslinkable p-type organic semiconductor, non-crosslinkable n-type organic semiconductor, and other components, if necessary, to a solvent so as to achieve a predetermined concentration.
In this case, there is no particular restriction on the order in which the components are added.

<Applications of organic semiconductor ink>
The organic semiconductor ink of the present invention contains a thermosetting component, and thus can form a photoelectric conversion layer with excellent heat resistance, and can be effectively used to form a photoelectric conversion layer of an organic photoelectric conversion element.

[Photoelectric conversion layer]
The photoelectric conversion layer of the present invention is formed by heat-curing a coating of the organic semiconductor ink of the present invention.

The photoelectric conversion layer of the present invention can be produced by forming a film of the organic semiconductor ink of the present invention by a wet film formation method on a surface on which the photoelectric conversion layer will be formed (usually on the electrode surface of the organic photoelectric conversion element of the present invention described below, or on another layer such as a hole transport layer formed on the electrode), and then heat-curing the formed coating.

While there are no particular limitations on the wet film-forming method, examples include spin coating. In this case, the spin-coating conditions can be determined appropriately according to standard methods, taking into account factors such as the viscosity of the organic semiconductor ink. The temperature during film formation is also not particularly limited, but should be a temperature at which the thermosetting component does not harden, and is usually below 100°C, for example, around 20 to 80°C.

The heating conditions for heat-curing the formed coating film are those at which the thermosetting component can be cured to form a crosslinked structure, and although these vary depending on the type of thermosetting component, the aforementioned preferred curing temperature conditions, i.e., 100 to 220°C, more preferably 120 to 220°C, and particularly preferably 140 to 220°C, are preferred.
The heating time may be any time long enough to cure the thermosetting component and form a crosslinked structure, and varies depending on the type of thermosetting component and the heating temperature, but is usually about 1 to 60 minutes.

The film thickness of the photoelectric conversion layer of the present invention formed in this manner can be designed as desired depending on the configuration of the photoelectric conversion layer and the application of the organic photoelectric conversion element. However, if it is too thin, light absorption will be insufficient and efficiency will decrease, and if it is too thick, internal resistance will increase and loss will become significant; therefore, it is usually set to about 10 nm to 1 μm.

[Organic photoelectric conversion element]
The organic photoelectric conversion element of the present invention has the above-described photoelectric conversion layer of the present invention.

The structure of the organic photoelectric conversion element of the present invention can be determined, for example, from the description in JP 2007-324587 A, and is not particularly limited. For example, the organic photoelectric conversion element may have a structure in which a transparent electrode, an electron transport layer, a photoelectric conversion layer, a hole transport layer, and a metal electrode are stacked in this order on a transparent substrate, or a structure in which a transparent electrode, a hole transport layer, a photoelectric conversion layer, an electron transport layer, and a metal electrode are stacked in this order on a transparent substrate.

Figure 1 is a schematic cross-sectional view showing an example of an organic photoelectric conversion element of the present invention. This organic photoelectric conversion element 10 has a first electrode 11, a hole transport layer 12, a photoelectric conversion layer 13, an electron transport layer 14, and a second electrode 15 as a lower electrode stacked in this order. The hole transport layer 12, the photoelectric conversion layer 13, and the electron transport layer 14 form an organic photoelectric film 20. Typically, a substrate is provided on the side of the first electrode 11 opposite the hole transport layer 12.

<Substrate>
The organic photoelectric conversion element may include a substrate for supporting the first electrode, the hole transport layer, the photoelectric conversion layer, the electron transport layer, the second electrode, etc. The substrate may be provided on either the first electrode side or the second electrode side, or on both sides, but is preferably provided at least on the first electrode side.
The substrate can be made of any material, but if light is incident from the substrate side, it must be made of a highly transparent material.

Examples of substrate materials include inorganic materials such as glass, sapphire, and titania; organic materials such as polyethylene terephthalate, polyethylene naphthalate, polyethersulfone, polyimide, nylon, polystyrene, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, fluororesin, vinyl chloride, polyethylene, cellulose, polyvinylidene chloride, aramid, polyphenylene sulfide, polyurethane, polycarbonate, polyarylate, and polynorbornene; paper materials such as paper and synthetic paper; and composite materials such as metals such as stainless steel, titanium, and aluminum whose surfaces are coated or laminated to provide insulation. The substrate materials may be used alone, or two or more may be used in any combination and ratio.

Furthermore, there is no limitation on the shape and dimensions of the substrate, and they can be set arbitrarily.
Furthermore, another layer may be laminated on the substrate in order to impart gas barrier properties or control the surface condition.

The thickness of the substrate can be freely designed depending on the application and constituent materials of the organic photovoltaic conversion element, but if it is too thin, it will not have enough strength and will not function as a support member, and if it is too thick, costs will increase, so it is usually made into a film or plate shape of about 10 μm to 50 mm.

<Electrode>
The electrodes (first electrode, second electrode) can be made of any material that is electrically conductive.

Examples of materials for the electrodes include metals such as platinum, gold, silver, aluminum, chromium, nickel, copper, titanium, magnesium, calcium, barium, and sodium, or alloys thereof; metal oxides such as indium oxide and tin oxide, or composite oxides thereof (e.g., ITO and IZO); conductive polymers such as polyaniline, polypyrrole, polythiophene, and polyacetylene; conductive polymers to which dopants such as acids such as hydrochloric acid, sulfuric acid, and sulfonic acid, Lewis acids such as _FeCl3 , halogen atoms such as iodine, and metal atoms such as sodium and potassium have been added; and conductive composite materials in which conductive particles such as metal particles, carbon black, fullerenes, and carbon nanotubes are dispersed in a matrix such as a polymer binder. Note that the electrode materials may be used singly or in any combination and ratio of two or more.

In an organic photoelectric conversion element, at least one pair (two electrodes) of electrodes is provided, with a photoelectric conversion layer disposed between the pair of electrodes. Preferably, at least one of the pair of electrodes is transparent (i.e., it transmits light absorbed by the photoelectric conversion layer for power generation). Examples of transparent electrode materials include composite oxides such as indium tin oxide (ITO) and indium zinc oxide (IZO); thin metal films, etc. There are no specific restrictions on the range of light transmittance, but considering the photoelectric conversion efficiency of the organic photoelectric conversion element, a value of 80% or higher is preferred. Light transmittance can be measured using a standard spectrophotometer.

The electrode has the function of collecting holes and electrons generated in the photoelectric conversion layer. Therefore, it is preferable to use, as the electrode's constituent material, a constituent material suitable for collecting holes and electrons from among the materials listed above. Examples of electrode materials suitable for collecting holes include materials with a high work function, such as Au and ITO. On the other hand, examples of electrode materials suitable for collecting electrons include materials with a low work function, such as Al.

There are no particular restrictions on the thickness of the electrodes; it is determined appropriately taking into account the material used and the required conductivity, transparency, etc., but it is usually around 10 nm to 100 μm.

The electrodes can be formed by any method, including dry processes such as vacuum deposition and sputtering. They can also be formed by wet processes using conductive ink. Any conductive ink can be used, including conductive polymers and metal particle dispersions. The electrodes can also be stacked in two or more layers, and can be surface-treated to improve their properties (electrical properties, wetting properties, etc.).

<Hole transport layer>
Known hole transport materials can be used for the hole transport layer. Specific examples of hole transport polymers that can be used include polytriarylamine compounds such as those exemplified below. Other examples include 2,7-bis(4-bromophenyl)-9,9-dihexylfluorene, 2-amino-9,9-dihexylfluorene, and polytolylarylamine compounds synthesized from 4-(4-(1,1-bis(4'-bromo-[1,1'-biphenyl]-4-yl)ethyl)phenyl)-1,2-dihydrocyclobuta[a]naphthalene, as described in JP-A-2019-173032, 4,4'-dibromobiphenyl, and 2-amino-9 ,9-dihexylfluorene, polytriarylamine compounds synthesized from 3-(1,2-dihydroxycyclobuta[a]naphthalen-4-yl)aniline, 4,4'-dibromobiphenyl, 4-(3,5-dibromophenyl)-1,2-dihydrocyclobuta[a]naphthalene, and 2-amino-9,9-dihexylfluorene, and the like can be used, but are not limited to these.

The method for forming the hole transport layer is not particularly limited, but it is preferably formed by a wet film formation method using a hole transporting polymer.
To form the hole transport layer by the wet film formation method, a composition for forming the hole transport layer containing a hole transporting polymer and a solvent is used.

The solvent is sufficient as long as it dissolves the hole-transporting polymer, and typically dissolves at room temperature 0.05% by mass or more of the hole-transporting polymer, preferably 0.5% by mass or more, and more preferably 1% by mass or more. There are no particular limitations on the solvent, but preferred examples include ether-based solvents, ester-based solvents, aromatic hydrocarbon-based solvents, and amide-based solvents.

Examples of ether-based solvents include aliphatic ethers such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and propylene glycol-1-monomethyl ether acetate (PGMEA), and aromatic ethers such as 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, anisole, phenetole, 2-methoxytoluene, 3-methoxytoluene, 4-methoxytoluene, 2,3-dimethylanisole, and 2,4-dimethylanisole.

Examples of the ester solvent include aromatic esters such as phenyl acetate, phenyl propionate, methyl benzoate, ethyl benzoate, propyl benzoate, and n-butyl benzoate.
Examples of aromatic hydrocarbon solvents include toluene, xylene, cyclohexylbenzene, 3-isopropylbiphenyl, 1,2,3,4-tetramethylbenzene, 1,4-diisopropylbenzene, cyclohexylbenzene, and methylnaphthalene.
Examples of amide solvents include N,N-dimethylformamide, N,N-dimethylacetamide, etc. In addition to these, dimethyl sulfoxide, etc. can also be used.

The concentration of the hole transport polymer in the hole transport layer-forming composition may be any concentration as long as it does not significantly impair the effects of the present invention. A lower concentration is preferable in terms of film thickness uniformity, while a higher concentration is preferable in terms of reducing the likelihood of defects in the hole transport layer. Specifically, the concentration is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and particularly preferably 0.5% by mass or more. On the other hand, the concentration is preferably 70% by mass or less, more preferably 60% by mass or less, and particularly preferably 50% by mass or less.

The concentration of the solvent in the composition for forming the hole transport layer is typically 10% by mass or more, preferably 30% by mass or more, and more preferably 50% by mass or more.

When forming a hole transport layer using the composition for forming a hole transport layer, heating is usually performed after applying the composition for forming a hole transport layer. The heating method is not particularly limited, but in the case of heat drying, the layer formed using the composition for forming a hole transport layer is heated to a temperature of usually 100°C or higher, preferably 120°C or higher, more preferably 150°C or higher, and usually 400°C or lower, preferably 350°C or lower, more preferably 300°C or lower.
The heating time is usually 1 minute or more, preferably 24 hours or less. The heating method is not particularly limited, but may be, for example, placing the laminate having the formed layer on a hot plate or heating in an oven. For example, heating conditions such as heating on a hot plate at 120°C or higher for 1 minute or more may be used.

The thickness of the hole transport layer is in one embodiment 50 nm or more and 100 nm or less, and in another embodiment, more than 100 nm and 400 nm or less, preferably 350 nm or less, i.e., 50 nm or more and 400 nm or less, preferably 350 nm or less.
When the thickness of the hole transport layer is equal to or greater than the lower limit, the dark current reduction effect due to the provision of the hole transport layer as a blocking layer can be effectively obtained. When the thickness of the hole transport layer is equal to or less than the upper limit, the incident angle of light can be widened in a CMOS image sensor using an organic photoelectric conversion element, and the organic photoelectric conversion element can be made thinner.

To effectively reduce dark current, the hole transport layer preferably has a LUMO shallower by 0.3 eV or more than the n-type organic semiconductor of the photoelectric conversion layer, preferably a LUMO shallower by 0.5 eV or more, and more preferably a LUMO shallower by 1.0 eV or more. Furthermore, because the hole transport layer plays a role in efficiently transporting holes generated in the photoelectric conversion layer to the first electrode, the difference in HOMO with the p-type organic semiconductor of the photoelectric conversion layer is preferably within 0.5 eV, and more preferably within 0.3 eV.

<Photoelectric conversion layer>
The photoelectric conversion layer is a layer that absorbs light and separates charges, and the photoelectric conversion layer of the organic photoelectric conversion element of the present invention is the photoelectric conversion layer of the present invention described above, formed from the organic semiconductor ink of the present invention described above.

<Electron transport layer>
Although the electron transport layer is not necessarily required for an organic photoelectric conversion element, providing the electron transport layer between the photoelectric conversion layer and the second electrode can improve the photoelectric conversion efficiency and reduce the dark current.

The electron transport layer is formed from a compound capable of efficiently transporting electrons generated in the photoelectric conversion layer to the second electrode. The electron transporting compound used in the electron transport layer is required to have a high electron injection efficiency from the photoelectric conversion layer and a high electron mobility, so that the injected electrons can be efficiently transported.
For this reason, the difference in LUMO between the electron transport layer and the n-type semiconductor of the photoelectric conversion layer is preferably 1.5 eV or less, and more preferably 1.0 eV. Furthermore, when dark current is reduced by the electron transport layer, the electron transport layer preferably has a HOMO that is 0.3 eV or more deeper than the HOMO of the p-type semiconductor of the photoelectric conversion layer, preferably a HOMO that is 0.5 eV or more deeper, and more preferably a HOMO that is 1.0 eV or more deeper.

Examples of electron transport compounds used in the electron transport layer include metal complexes such as aluminum complexes of 8-hydroxyquinoline (Japanese Patent Laid-Open No. 59-194393), metal complexes of 10-hydroxybenzo[h]quinoline, oxadiazole derivatives, distyrylbiphenyl derivatives, silole derivatives, 3-hydroxyflavone metal complexes, 5-hydroxyflavone metal complexes, benzoxazole metal complexes, benzothiazole metal complexes, trisbenzimidazolylbenzene (U.S. Patent No. 5,645,948), quinoxaline compounds (Japanese Patent Laid-Open No. 6-207169), phenanthroline derivatives (Japanese Patent Laid-Open No. 5-331459), 2-t-butyl-9,10-N,N'-dicyanoanthraquinone diimine, n-type hydrogenated amorphous silicon carbide, n-type zinc sulfide, and n-type zinc selenide.

Metal oxides such as titanium oxide, zinc oxide, tin oxide, and cerium oxide can also be used as materials for forming the electron transport layer. In this case, the electron transport layer can be formed by wet-forming metal oxide nanoparticles and drying them to form a metal oxide layer, or by wet-forming a precursor and then converting it by heating.

The film thickness of the electron transport layer is typically 1 nm or more, preferably 5 nm or more, and typically 300 nm or less, preferably 100 nm or less.

The electron transport layer can be formed by a wet film-forming method or a vacuum deposition method, but the vacuum deposition method is usually used.

<Other constituent layers>
The organic photoelectric conversion element may include other constituent layers in addition to the substrate, first and second electrodes, hole transport layer, photoelectric conversion layer, and electron transport layer as long as the effects of the present invention are not significantly impaired.
For example, the organic photoelectric conversion element may be provided with a protective film that covers the photoelectric conversion layer portion and further the electrode portion in order to minimize the influence of the outside air. The protective layer may be composed of, for example, a polymer film such as a styrene resin, an epoxy resin, an acrylic resin, a polyurethane, a polyimide, a polyvinyl alcohol, a polyvinylidene fluoride, or a polyethylene-polyvinyl alcohol copolymer; an inorganic oxide film or nitride film such as silicon oxide, silicon nitride, or aluminum oxide; or a laminate film thereof.

There are no limitations on the method for forming the protective film. For example, if the protective film is a polymer film, examples include a method of coating and drying a polymer solution, or a method of coating or vapor-depositing a monomer and polymerizing it. When forming a polymer film, it is also possible to further perform a crosslinking process or form a multilayer film. On the other hand, if the protective film is an inorganic film such as an inorganic oxide film or nitride film, it is possible to use a vacuum process such as sputtering or vapor deposition, or a solution process such as the sol-gel method.

In order to allow the electrode to efficiently collect the charges generated in the photoelectric conversion layer, a charge injection layer may be provided between the first electrode and the hole transport layer or between the electron transport layer and the second electrode.
Furthermore, the organic photoelectric conversion element may be provided with an optical filter that blocks ultraviolet light, for example, on the light incident side. Since ultraviolet light generally accelerates the deterioration of organic photoelectric conversion elements, blocking this ultraviolet light can extend the life of the organic photoelectric conversion element.

<Method of manufacturing organic photoelectric conversion element>
An organic photoelectric conversion element is usually produced by laminating a first electrode, a hole transport layer, a photoelectric conversion layer, and a second electrode on a substrate in this order by the methods described above, with a step of forming an electron transport layer or the like between these layers as needed.

<Applications of organic photoelectric conversion elements>
The photoelectric conversion element of this embodiment is used in an optical sensor, an image sensor, etc. In this case, the optical sensor and the image sensor may have known configurations.

The present invention will be explained in more detail below using examples, but the scope of the present invention is not limited to the following examples.

<Measurement method>
Film Thickness Measurement Method The film thickness can be measured using, for example, a contact-type stylus surface profile evaluation device Dektak 150 (manufactured by ULVAC, Inc.), or, for example, a non-contact-type profile measurement laser microscope VK-X200 (manufactured by Keyence Corporation).
・Method for measuring external quantum efficiency:
The external quantum efficiency value was obtained by measuring the spectral sensitivity using a solar simulator/electrical property measuring device (manufactured by Bunkoukeiki Co., Ltd.) when a voltage of -5 V was applied to the element for light with a wavelength of 940 nm.

Example 1
A surface of an ITO substrate, on which a transparent conductive film of indium tin oxide (ITO) was patterned as an electrode, was treated with an ultraviolet ozone cleaner (NL-UV253, manufactured by Nippon Laser Electronics Co., Ltd.) for 10 minutes, and then a hole transport layer was formed as follows.

A composition for forming a hole transport layer was prepared by dissolving 60 mg of a polytriarylamine compound (hole transport polymer) represented by the following formula (1) in 1 mL of anisole. This composition was spin-coated onto the electrode surface of an ITO substrate at 1,000 rpm for 60 seconds, and then heated and dried at 240°C for 30 minutes to form a hole transport layer with a thickness of 300 nm.

An organic semiconductor ink was prepared by dissolving the following materials in a solvent: a non-crosslinkable p-type organic semiconductor, a non-crosslinkable n-type organic semiconductor, an epoxy resin, and a curing agent.
Non-crosslinkable p-type organic semiconductor: p-type organic semiconductor represented by the above formula (II) (weight average molecular weight: 240,000)
Non-crosslinkable n-type organic semiconductor: In the above formula (I),
A = carbon atom
X ¹ to X ⁴ = chlorine atoms
R ^1a and R ^1b are 2-ethylhexyl groups.
R ² = 2-ethylhexyl group
R ³ = 2-ethylhexyloxy group
n-type organic semiconductor compound in which R ⁴ and R ⁵ are hydrogen atoms Epoxy resin : epoxy resin (manufactured by Mitsubishi Chemical Corporation)
jER828 (epoxy equivalent weight 189 g/eq)

Hardener: 2-ethyl-4-methylimidazole Solvent: chlorobenzene

The mass ratio of the non-crosslinkable p-type organic semiconductor to the non-crosslinkable n-type organic semiconductor in the organic semiconductor ink (n-type organic semiconductor/p-type organic semiconductor) is 1.2, the content of the thermosetting component per 100 parts by mass of the non-crosslinkable p-type organic semiconductor and the non-crosslinkable n-type organic semiconductor combined is 5.25 parts by mass (epoxy resin content: 5 parts by mass, curing agent content: 0.25 parts by mass), and the solids concentration of the organic semiconductor ink is 16.5 mg/mL.

This organic semiconductor ink was spin-coated onto the hole transport layer at 1,000 revolutions per minute, and then heated at 120°C for 30 minutes to harden the epoxy resin, forming a photoelectric conversion layer with a thickness of 150 nm.

Next, a 40 nm thick film of C60 fullerene (manufactured by Frontier Carbon) was formed as an electron transport material, and a 100 nm thick film of aluminum was formed as a metal electrode in vacuum, to obtain an organic photoelectric conversion element.

Example 2
An organic photoelectric conversion element was produced in the same manner as in Example 1, except that the heating temperature for heat curing during the formation of the photoelectric conversion layer was set to 160°C.

Example 3
An organic photoelectric conversion element was produced in the same manner as in Example 1, except that the heating temperature for heat curing during the formation of the photoelectric conversion layer was set to 200°C.

<Reference example 1>
An organic photoelectric conversion element was produced in the same manner as in Example 1, except that heat curing was not carried out when the photoelectric conversion layer was formed.

<Heat resistance test>
The organic photoelectric conversion elements obtained in Examples 1 to 3 and Reference Example 1 were subjected to a heat resistance test in which they were kept at a temperature of 200°C for 50 minutes, and the external quantum efficiency of each organic photoelectric conversion element after the heat resistance test was measured. The results are shown in Table 1.

From Table 1, it can be seen that by using the organic semiconductor ink of the present invention and introducing a crosslinked structure due to a thermosetting component, it is possible to obtain an organic photoelectric conversion element with high external quantum efficiency after a heat resistance test, i.e., a photoelectric conversion layer and an organic photoelectric conversion element with excellent heat resistance.
It is also clear that the degree of heat resistance tends to be higher as the heating temperature during heat curing increases to a certain extent. This is thought to be because the higher the heating temperature, the more the curing reaction of the epoxy resin progresses, and the higher the degree of crosslinking, the more effectively the change in compatibility due to flow between the p-type organic semiconductor and the n-type organic semiconductor is suppressed, thereby suppressing the decrease in photoelectric conversion efficiency.
Although Reference Example 1 uses the organic semiconductor ink of the present invention, it does not undergo heat curing, thereby simulating a photoelectric conversion layer made of a conventional organic semiconductor ink, and is therefore inferior in heat resistance.

REFERENCE SIGNS LIST 10 Organic photoelectric conversion element 11 First electrode 12 Hole transport layer 13 Photoelectric conversion layer 14 Electron transport layer 15 Second electrode 20 Organic photoelectric film

Claims (11)

The composition contains a non-crosslinkable p-type organic semiconductor, a non-crosslinkable n-type organic semiconductor, a thermosetting component, and a solvent,
the non-crosslinkable p-type organic semiconductor is a conjugated polymer containing a benzodithiophene structure and a thienothiophene structure,
The non-crosslinkable n-type organic semiconductor is a compound represented by the following formula (I):
An organic semiconductor ink characterized in that the thermosetting component is bisphenol A diglycidyl ether .
(In the above formula (I), A represents an atom selected from Group 14 of the periodic table; X ¹ to X ⁴ each independently represent a hydrogen atom or a halogen atom; R ^1a and R ^1b each independently represent a linear or branched alkyl group; and R ² to R ⁵ each independently represent a linear or branched alkyl group, a linear or branched alkoxy group, a linear or branched thioalkyl group, or a hydrogen atom.) The organic semiconductor ink according to claim 1, wherein the thermally curable component further comprises a curing agent. 3. The organic semiconductor ink according to claim 1, wherein the epoxy equivalent of the bisphenol A diglycidyl ether is 50 to 1000 g/eq. 4. The organic semiconductor ink according to claim 2, wherein the content of the bisphenol A diglycidyl ether in the thermosetting component is 38 to 100% by mass. The organic semiconductor ink according to any one of claims 1 to 4, wherein the curing temperature of the thermosetting component is in the range of 100 to 220°C. The organic semiconductor ink according to any one of claims 1 to 5, wherein the content of the thermosetting component is 1 to 100 parts by mass per 100 parts by mass of the non-crosslinkable p-type organic semiconductor and the non-crosslinkable n-type organic semiconductor combined. The organic semiconductor ink according to any one of claims 1 to 6, having a solids concentration of 10 to 30 mg/mL. The organic semiconductor ink according to any one of claims 1 to 7, wherein the solvent includes an aromatic solvent. 9. The organic semiconductor ink according to claim 1, wherein the non-crosslinkable p-type organic semiconductor is a compound represented by the following formula (II):
(In the above formula (II), n is a positive number.) A photoelectric conversion layer obtained by heat-curing a coating of the organic semiconductor ink according to any one of claims 1 to 9 . An organic photoelectric conversion element comprising the photoelectric conversion layer according to claim 10 .