Fullerene derivatives, films, electron acceptors, electron transport materials, and electronic devices

Abstract

To provide fullerene derivatives having superior properties.SOLUTION: A fullerene derivative has any one of following structures (where, Ar is any aromatic ring, for example, a benzene ring, a fused ring such as naphthalene, anthracene, phenanthrene, pyrene, pyrrole, pyrazole, or a heterocyclic ring such as furan, thiophene, X is O, S, Se, or Te, and * is a carbon atom at a point of attachment to a fullerene core).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to fullerene derivatives, films, electron acceptors, electron transport materials, and electronic devices. [Background technology]

[0002] Organic electronic devices using organic materials are in use. For electronic devices such as semiconductors, it is almost essential to make materials into thin films. Methods for making organic materials into thin films include vacuum deposition and solution coating. While solution coating is low cost, it generally produces products with lower reliability than vacuum deposition. Therefore, vacuum deposition is generally used at present because it can more reliably produce highly reliable products.

[0003] Fullerene (C 60 ) has attracted attention as one of the few organic substances that can be used as an electron acceptor or electron transport material (see, for example, Patent Document 1). It is expected that by introducing various substituents into fullerene, it will be possible to develop fullerene derivatives with suitable properties suited to purposes, specifications, etc. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-99570 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, although fullerene itself can be formed into a film by either vacuum deposition or solution coating, fullerene derivatives are generally mostly thermally decomposed by vacuum deposition, and therefore films can only be formed by solution coating.

[0006] The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide a fullerene derivative having excellent properties. [Means for solving the problem]

[0007] In order to solve the above problems, one aspect of the present disclosure is a fullerene derivative. [ka] (Here, * is the carbon atom at the point of attachment to the fullerene core.) The compound has any one of the following structures:

[0008] Another aspect of the present disclosure is a film comprising the fullerene derivative described above.

[0009] Yet another aspect of the present disclosure is an electron acceptor, which comprises a fullerene derivative as described above.

[0010] Yet another aspect of the present disclosure is an electron transport material, which comprises the fullerene derivative described above.

[0011] Yet another aspect of the present disclosure is an electronic device comprising the film, the electron acceptor, or the electron transport material described above. Effect of the Invention

[0012] According to the present disclosure, a fullerene derivative having excellent properties can be provided. [Brief description of the drawings]

[0013] [Figure 1] 1 is a diagram illustrating a schematic configuration of an organic solar cell according to an embodiment. [Diagram 2] FIG. 2 is a diagram showing the results of vacuum deposition of a fullerene derivative according to an embodiment. [Diagram 3] 3(a) and (b) are diagrams showing the results of thermogravimetric analysis of the fullerene derivatives of formula (1a) and formula (2a), respectively. [Figure 4]4(a) and (b) are electron microscope photographs of thin films of the fullerene derivative of formula (2a) formed by spin coating and vacuum deposition, respectively. [Diagram 5] 5(a) and (b) are diagrams showing the current-voltage characteristics of the fullerene derivative of formula (2a) formed into films by spin coating and vacuum deposition, respectively. [Figure 6] 6(a) and (b) are diagrams showing the electron mobility of vacuum-deposited films of C60 and the fullerene derivative of formula (2a), respectively. [Figure 7] 7(a), (b), and (c) are diagrams showing an embodiment of an organic solar cell. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] As an embodiment of the present disclosure, a vapor-depositable fullerene derivative and its precursor fullerene derivative are disclosed. For details of the synthesis method and electrical properties of the precursor fullerene derivative, please refer to the paper published by the present inventors ("Highly Selective and Scalable Fullerene-Cation-Mediated Synthesis Accessing Cyclo

[60] fullerenes with Five-Membered Carbon Ring and Their Application to Perovskite Solar Cells", Hao-Sheng Lin, Il Jeon, Yingqian Chen, Xiao-Yu Yang, Takafumi Nakagawa, Shigeo Maruyama, Sergei Manzhos, Yutaka Matsuo, Chemistry of Materials, 2019,31,20,8432-8439, published on September 11, 2019).

[0015] The fullerene derivative of the present disclosure has a structure represented by formula (1). The fullerene derivative having the structure represented by formula (1) is a precursor of a fullerene derivative having the structure represented by formula (2) described below, but the fullerene derivative having the structure represented by formula (1) itself has excellent properties and can be used as an electron acceptor or electron transport material for an organic semiconductor. [ka]

[0016] Here, Ar is any aromatic ring. Ar may be, for example, a benzene ring, a condensed ring such as naphthalene, anthracene, phenanthrene, or pyrene, or a heterocyclic ring such as furan, thiophene, pyrrole, pyrazole, imidazole, pyridine, pyridazine, pyrimidine, or pyrazine. Ar may have any substituent such as an alkyl group, a heteroalkyl group, an alkenyl group, a heteroalkenyl group, an alkynyl group, a heteroalkynyl group, a cycloalkyl group, a heterocycloalkyl group, an aryl group, a heteroaryl group, an alkoxy group, a carbonyl group, a carboxy group, a cyano group, a hydroxyl group, a thiol group, an amino group, an imino group, a nitro group, or a halogen, or may have no substituent.

[0017] * is the carbon atom at the connection point to the fullerene core. The fullerene core is, for example, C 60 , C 70 , C 72 , C 74 , C 76 , C 78 , C 80 , C 82 , C 84 , C 86 , C 88 , C 90 etc. may be used.

[0018] X is O, S, Se, or Te. X can also be C, N, P, etc.

[0019] R is any organic group. R can be, for example, an alkyl group, a heteroalkyl group, an alkenyl group, a heteroalkenyl group, an alkynyl group, a heteroalkynyl group, a cycloalkyl group, a heterocycloalkyl group, an aryl group, a heteroaryl group, an alkoxy group, a carbonyl group, an imino group, a combination thereof, and the like.

[0020] The method for producing a fullerene derivative having the structure of formula (1) includes a first step of preparing a Grignard reagent by reacting an aryl halide with magnesium, a second step of synthesizing an arylhydrofullerene by reacting the Grignard reagent with fullerene, a third step of synthesizing an arylfullerene dimer by oxidizing the arylhydrofullerene in the presence of a base, and a fourth step of synthesizing a fullerene derivative having the structure of formula (1) by oxidizing the arylfullerene dimer.

[0021] In the second step, a solvent containing an organic substance having a planar structure such as 1,3-dimethyl-2-imidazolidinone (DMI) as a co-solvent may be used, which can produce arylhydrofullerenes with high selectivity.

[0022] In the third step, a strong base with low nucleophilicity may be used as the base, such as a metal alkoxide such as potassium tert-butoxide (t-BuOK), or a metal amide such as lithium diisopropylamide (LDA), potassium hexamethyldisilazide (KHMDS), or lithium-2,2,6,6-tetramethylpiperidide (LiTMP), etc. Also, N-bromosuccinimide (NBS) may be used as the oxidizing agent.

[0023] In the fourth step, CuBr 2 In the fourth step, the aryl fullerene dimer may be heated in the presence of an oxidizing agent. The heating temperature may be, for example, 100° C., and the heating time may be, for example, 3 hours.

[0024] In each step, the product may be isolated and purified before proceeding to the next step, or the product may be without being isolated or purified before proceeding to the next step. For example, the aryl fullerene dimer produced in the third step may be directly added to an oxidizing agent and heated to synthesize a fullerene derivative having the structure of formula (1).

[0025] The vapor-depositable fullerene derivatives of the present disclosure have the structure of formula (2). [ka]

[0026] Here, Ar is any aromatic ring. Ar may be, for example, a benzene ring, a condensed ring such as naphthalene, anthracene, phenanthrene, or pyrene, or a heterocyclic ring such as furan, thiophene, pyrrole, pyrazole, imidazole, pyridine, pyridazine, pyrimidine, or pyrazine. Ar may have any substituent such as an alkyl group, a heteroalkyl group, an alkenyl group, a heteroalkenyl group, an alkynyl group, a heteroalkynyl group, a cycloalkyl group, a heterocycloalkyl group, an aryl group, a heteroaryl group, an alkoxy group, a carbonyl group, a carboxy group, a cyano group, a hydroxyl group, a thiol group, an amino group, an imino group, a nitro group, or a halogen, or may have no substituent.

[0027] * is the carbon atom at the connection point to the fullerene core. The fullerene core is C 60 , C 70 , C 72 , C 74 , C 76 , C 78 , C 80 , C 82 , C 84 , C 86 , C 88 , C 90 etc. may be used.

[0028] X is O, S, Se, or Te. X can also be C, N, P, etc.

[0029] The method for producing a fullerene derivative having a structure of formula (2) includes a step of oxidizing a fullerene derivative of formula (1). In the oxidation step, CuBr 2 may be used. In the oxidation step, the fullerene derivative of formula (1) may be heated in the presence or absence of an oxidizing agent. The heating temperature may be, for example, 80 to 130°C, and the heating time may be, for example, 1 to 6 hours. The heating temperature may be a temperature equal to or higher than the sublimation temperature of the fullerene derivative of formula (1). [ka]

[0030] Since the fourth step of the method for producing the fullerene derivative of formula (1) and the step of the method for producing the fullerene derivative of formula (2) are both oxidation reactions, these steps may be carried out consecutively. For example, the aryl fullerene dimer may be treated with CuBr as an oxidizing agent. 2 and heating at 100°C for 3 hours to synthesize a fullerene derivative of formula (1), and then further heating at 130°C for 6 hours to synthesize a fullerene derivative of formula (2) without isolating the fullerene derivative of formula (1). The heating temperature in the step of synthesizing the fullerene derivative of formula (2) may be higher than the heating temperature in the step of synthesizing the fullerene derivative of formula (1). The heating time in the step of synthesizing the fullerene derivative of formula (2) may be longer than the heating time in the step of synthesizing the fullerene derivative of formula (1). The heating temperature in the case of synthesizing the fullerene derivative of formula (2) after isolating and purifying the fullerene derivative of formula (1) may be lower than the heating temperature in the case of synthesizing the fullerene derivative of formula (2) without isolating and purifying the fullerene derivative of formula (1), and may be, for example, 100°C. The heating time in the case where the fullerene derivative of formula (2) is synthesized after isolating and purifying the fullerene derivative of formula (1) may be shorter than the heating time in the case where the fullerene derivative of formula (2) is synthesized without isolating and purifying the fullerene derivative of formula (1), and may be, for example, 3 hours.

[0031] As shown in the examples below, fullerene derivatives having the structure of formula (2) can be deposited with almost no decomposition. In general, when fullerene derivatives are deposited, many fullerene derivatives are thermally decomposed, and decomposition products such as fullerene cores are deposited. The fullerene derivatives of formula (2) have a structure in which a stable five-membered carbon ring is bonded to the fullerene core, and C-H bonds, which are relatively weak and easily decomposed bonds, do not exist in the five-membered carbon ring, so it is believed that they can be deposited without thermal decomposition even when heated to a temperature above the sublimation temperature.

[0032] As shown in the examples below, when a fullerene derivative having the structure of formula (1) is vapor-deposited, a part of it is thermally decomposed into a fullerene core, etc., but a part of it is converted into a fullerene derivative having the structure of formula (2) and vapor-deposited. Therefore, a vapor deposition material containing a fullerene derivative having the structure of formula (2) can be produced by vapor-depositing a fullerene derivative having the structure of formula (1).

[0033] The method for producing a deposition material containing a fullerene derivative according to the present disclosure includes a step of depositing a fullerene derivative having a structure of formula (2) by heating it to a sublimation temperature or higher, thereby making it possible to efficiently produce a high-purity deposition material of the fullerene derivative having excellent properties.

[0034] The method for producing a deposition material containing a fullerene derivative according to the present disclosure includes a step of heating a fullerene derivative having a structure of formula (1) to a sublimation temperature or higher to deposit the fullerene derivative. This makes it possible to efficiently produce a deposition material containing a fullerene derivative having excellent properties.

[0035] The film of the present disclosure includes a fullerene derivative having the structure of formula (1) or formula (2). The film may be produced by any film-forming technique, such as vacuum deposition or solution coating, which can provide a thin film with excellent properties.

[0036] The electron transport material of the present disclosure includes a fullerene derivative having a structure represented by formula (1) or (2), which makes it possible to provide an electron transport material with excellent properties.

[0037] The electronic device of the present disclosure includes a film or an electron transport material containing a fullerene derivative having a structure of formula (1) or formula (2). The electronic device may be, for example, an organic semiconductor, an organic solar cell, or the like. This allows the electronic device with excellent characteristics to be manufactured with a high yield.

[0038] FIG. 1 shows a schematic configuration of an organic solar cell according to an embodiment. The organic solar cell 1 includes a cathode 2, an electron transport material layer 3, an electron acceptor / electron donor layer 4, a hole transport material layer 5, an anode 6, a cathode terminal 7, and an anode terminal 8. The cathode 2 and the anode 6 are formed of metals, alloys, inorganic substances, organic substances, etc. having electrical conductivity. The electron transport material layer 3 is a thin film containing a fullerene derivative having a structure of formula (1) or formula (2). The electron acceptor / electron donor layer 4 is a layer of a mixture of an electron acceptor and an electron donor. The hole transport material layer 5 is a thin film containing any hole transport material. These thin films may be formed by solution coating or deposition. In the case of solution coating, a solution in which a fullerene derivative having a structure of formula (1) or formula (2) functioning as an electron acceptor molecule and an electron donor molecule are mixed may be applied to a transparent electrode substrate such as indium tin oxide (ITO) to form a film. In the case of vapor deposition, the fullerene derivative having the structure of formula (1) or (2) and the electron donor molecule may be separately vapor-deposited on a transparent electrode substrate to form a film, or may be co-vapor-deposited. The organic solar cell 1 is manufactured by forming the cathode 2 on the substrate thus prepared by vapor deposition or the like, and connecting the cathode terminal 7 to the cathode 2 and the anode terminal 8 to the anode 6.

[0039] When light such as sunlight strikes the organic solar cell 1, mainly the electron donor molecules absorb the light and become excited, generating excitons. The generated excitons move to the electron acceptor / electron donor layer 4, where electrons flow from the electron donor molecules to the electron acceptor molecules, forming a charge-separated state. That is, the electron donor molecules hand over electrons to the electron acceptor molecules and become cations (holes), while the electron acceptor molecules receive electrons and become anions. As holes flow to the anode 6 in the hole transport material layer 5 and electrons flow to the cathode 2 in the electron transport material layer 3, a current flows in an external circuit via the cathode terminal 7 and the anode terminal 8.

[0040] [Example] As examples of the present disclosure, fullerene derivatives (1a) to (1e) having the structure of formula (1) and fullerene derivatives (2a) to (2e) having the structure of formula (2) were synthesized. Unless otherwise indicated, all reactions were carried out by standard vacuum line techniques under an argon atmosphere in heat-dried glassware using dry solvents. [ka] [ka]

[0041] [Synthesis of aryl bromides] Methanol (20.0 mL) was slowly added to sodium (517.5 mg, 22.5 mmol) at 0 °C. After sodium reacted completely with methanol, various functionalized benzyl bromides (15 mmol) were added to the reaction solution and left at room temperature for 5 h. The reaction suspension was then quenched with 10 mL of water and extracted with dichloromethane (10 × 3 mL). The organic layer was dried over magnesium sulfate and the solvent was removed under reduced pressure to give the crude product. The product was purified on a silica gel column using n-hexane / ethyl acetate (10 / 1, v / v) as the eluent to give the product as a colorless oil.

[0042] [Step 1: Synthesis of Grignard Reagent] A solution of aryl bromide (10 mmol) in anhydrous tetrahydrofuran (THF) (10.0 mL) was slowly added dropwise to polished magnesium powder (360.0 mg, 15 mmol) at 0°C under an argon atmosphere, with a trace amount of iodine as the initiator. After vigorous stirring for 1 h, the prepared Grignard solution was transferred to a Schlenk bottle by Schlenk manipulation and stored. Prior to use, the concentration was confirmed by anhydrous titration under an argon atmosphere using a trace amount of 1,10-phenanthroline as indicator and menthol as titrant.

[0043] [Second step: Arylhydrofullerene (ArC 60 Synthesis of H) C 60 (300.0 mg, 0.417 mmol) was dissolved in anhydrous o-dichlorobenzene (o-DCB) (50.0 mL) containing 1,3-dimethyl-2-imidazolidinone (DMI) (1.4 mL, 12.5 mmol) as a co-solvent. The Grignard reagent synthesized above was then added to the solution at 25 °C under an argon atmosphere. After stirring for 15 min, the reaction was quenched by the addition of acetic acid (0.1 mL, 1.75 mmol) and the solvent was evaporated in vacuum. The residue was purified as CS 2 Dissolved in CS 2 The product was obtained by purification on a silica gel column using dichloromethane as the eluent.

[0044] [Third step: Aryl fullerene dimer (ArC 60 -C 60 Synthesis of Ar The monoadduct (0.048 mmol) synthesized in the second step was dissolved in 5.0 mL of anhydrous o-DCB solution. Then, a solution of t-BuOK in THF (58 μL, 0.058 mmol, 1 M) was added and stirred vigorously at room temperature under argon atmosphere for 15 min. Then, N-bromosuccinimide (NBS) (34.2 mg, 0.192 mmol) was added. The reaction mixture was stirred vigorously at room temperature under argon atmosphere for 12 h. The resulting brown suspension was then quenched with 1.0 mL of water, and an excess amount of methanol was added to precipitate the product. Finally, the aryl

[60] fullerene dimer was collected as a residue by filtration without the need for further purification.

[0045] [Fourth step: synthesis of fullerene derivative of formula (1)] 0.030 mmol of aryl

[60] fullerene dimer was oxidized with CuBr 2 (26.8 mg, 0.120 mmol) in 10.0 mL of anhydrous o-DCB. After vigorously stirring at 100 °C for 3 h, the resulting mixture was directly filtered through a silica gel plug to remove insoluble salts, followed by removal of the solvent by evaporation in vacuum. Then, CS 2 The residue was purified on a silica gel column using as an eluent to obtain the product. The yields of fullerene derivatives (1a) to (1d) were 93%, 90%, 86%, and 73%, respectively.

[0046] [Synthesis of fullerene derivative of formula (2)] The fullerene derivative of formula (1) is oxidized with CuBr 2 (4.0 eq.) was dissolved in 5.0 mL of anhydrous o-DCB solution. After vigorously stirring at 130 °C for 6 h, the resulting mixture was purified to obtain the products. The yields of fullerene derivatives (2a)-(2d) were 94%, 92%, 90%, and 82%, respectively.

[0047] [Characteristics of fullerene derivatives] FIG. 2 shows the results of vacuum deposition of the fullerene derivatives of formula (1) and formula (2). FIG. 2(a) is a High Performance Liquid Chromatography (HPLC) chart of the deposition source before deposition. FIG. 2(b) is an HPLC chart of the deposition product and residue after deposition. The deposition product on which the fullerene derivative of formula (2) was deposited exhibits the same peak as the fullerene derivative of formula (2) before deposition, and peaks derived from other substances are hardly observed. This shows that the fullerene derivative of formula (2) can be deposited at almost 100% without thermal decomposition.

[0048] The deposit obtained by evaporating the fullerene derivative of formula (1) shows many peaks, but also has a large peak at the same position as the fullerene derivative of formula (2). In addition, the residue after evaporating the fullerene derivative of formula (1) also shows a large peak at the same position as the fullerene derivative of formula (2). Therefore, it was shown that the fullerene derivative of formula (2) is produced by heating the fullerene derivative of formula (1) to a temperature equal to or higher than the sublimation temperature, and that a deposit containing the fullerene derivative of formula (2) is produced by evaporating the fullerene derivative of formula (1).

[0049] Figures 3(a) and (b) show the results of thermogravimetric analysis of the fullerene derivatives of formula (1a) and formula (2a), respectively. The samples were heated under a nitrogen stream and the change in mass was measured. It was found that the fullerene derivative of formula (1a) begins to decompose at around 250°C, whereas the fullerene derivative of formula (2a) is stable up to around 400°C.

[0050] Figures 4(a) and (b) show electron microscope photographs of thin films of the fullerene derivative of formula (2a) formed by spin coating and vacuum deposition, respectively. The thin film formed by vacuum deposition was a homogeneous amorphous thin film. The thin film formed by spin coating was a crystalline thin film. Figures 5(a) and (b) show the current-voltage characteristics of the fullerene derivative of formula (2a) formed by spin coating and vacuum deposition, respectively. The thin film formed by vacuum deposition had a smaller amount of charge traps than the thin film formed by spin coating. From the above, an organic thin film with better characteristics can be produced by forming a film of the fullerene derivative of formula (2a) by vacuum deposition.

[0051] Figure 6(a) and (b) show the C 60 The electron mobility of the vacuum-deposited film of the fullerene derivative of formula (2a) is shown in FIG. 1. The electron mobility of each vacuum-deposited film was measured by the Space Charge Limited Current (SCLC) method. The electron mobility of the vacuum-deposited film of the fullerene derivative of formula (2a) is C 60 The electron mobility was equivalent to that of the vacuum-deposited film.

[0052] 7(a), (b), and (c) show examples of organic solar cells. FIG. 7(a) shows the structure of an organic solar cell according to the example. On an ITO electrode, a fullerene derivative of formula (2a) is vacuum-deposited as an electron transport layer, and a perovskite compound, methylammonium lead iodide (MAPbI 3 ) was formed. Furthermore, spiro-OMeTAD was formed as a hole transport layer, and an Au electrode was formed to fabricate an organic solar cell. 60 FIG. 7(b) shows the output characteristics of the organic solar cell of the example, and FIG. 7(c) shows the output characteristics of the organic solar cell of the comparative example. Table 1 shows the open circuit voltage V OC , short circuit current density J SCThe energy conversion efficiency of the organic solar cell of the example was 13.5%, which was higher than the 10.5% of the comparative example. [Table 1]

[0053] The present disclosure has been described above based on examples. These examples are merely illustrative, and it will be understood by those skilled in the art that various modifications are possible in the combination of each component and each treatment process, and that such modifications are also within the scope of the present disclosure. [Industrial Applicability]

[0054] The present disclosure is applicable to fullerene derivatives, methods for producing fullerene derivatives, and deposition products, films, and electronic devices that include fullerene derivatives. [Explanation of symbols]

[0055] 1 organic solar cell, 2 cathode, 3 electron transport material layer, 4 electron acceptor / electron donor layer, 5 hole transport material layer, 6 anode, 7 cathode terminal, 8 anode terminal.

Claims

【Request 1】 【Chemistry 1】 (Here, * is the carbon atom at the connection point to the fullerene core.) A fullerene derivative having any one of the following structures:

2. A film comprising the fullerene derivative according to claim 1.

3. An electron acceptor comprising the fullerene derivative of claim 1.

4. An electron transport material comprising the fullerene derivative according to claim 1.

5. An electronic device comprising the film of claim 2, the electron acceptor of claim 3, or the electron transport material of claim 4.

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