Fullerene derivative composition and photoelectric conversion element

Abstract

A composition in which a fullerene derivative is used, the composition having a partial structure represented by general formula (1), containing stereoisomers in mirror-image relationship caused by asymmetric carbon atoms represented by C * in general formula (1), and "1" # imgabs0 # (in formula (1), each CF represents a carbon atom that forms a fullerene skeleton and is adjacent to each other, and C * represents an asymmetric carbon atom).

Description

Technical Field

[0001] The present invention relates to a composition of fullerene derivatives and an organic optoelectronic conversion element. Background Art

[0002] An organic thin-film solar cell in which an organic semiconductor film having electron-donating and electron-accepting properties is disposed between two different electrodes has the following advantages compared to an inorganic solar cell represented by silicon, etc., the manufacturing process is easy, the cost is low, and it can be made large-area. However, compared to an inorganic solar cell, an organic thin-film solar cell is difficult to be provided for practical use due to low photoelectric conversion efficiency, especially poor durability, etc.

[0003] The structures of organic thin-film solar cells are various, and Schottky type, heterojunction Pn junction type, bulk heterojunction type, etc. have been proposed. In particular, since phenyl-C 61 -butyric acid methyl ester (

[60] PCBM) (Non-Patent Document 1) which has improved compatibility with a polymer as an electron donor has been developed, there have been a large number of studies on bulk heterojunction type organic thin-film solar cells.

[0004] For example, analogs of

[60] PCBM in which the methyl group of

[60] PCBM is changed to other alkyl groups have been synthesized in large quantities. In Non-Patent Document 2, it was changed to a straight-chain or branched alkyl group of C4, C8, C 12 , C 16 , and in Non-Patent Document 3,

[60] PCBM analogs having a straight-chain alkyl group of C6, C 12 were used for organic thin-film solar cells. It is known that although these analogs have almost the same reduction potential and ultraviolet / visible absorption characteristics, they still have a great influence on the photoelectric conversion efficiency of an organic thin-film solar cell using the same polymer.

[0005] For example, in Non-Patent Document 2, in the case of butyl (C4) and in Non-Patent Document 3, in the case of hexyl (C6), compared with

[60] PCBM (ester is methyl) as a raw material, good results of organic thin-film solar cell characteristics were obtained. It is considered that these results are related to the following matters, the influence on the interaction between the fullerene derivative and the polymer caused by different alkyl groups, the change in the crystallinity of the fullerene derivatives with each other, etc.

[0006] In addition, Patent Document 1 proposed a

[60] PCBM analog having an optically active center, and reported that the photoelectric conversion efficiency and durability of an organic thin-film solar cell using it are higher than those of

[60] PCBM not having an optically active center.

[0007] However, the durability of an organic thin-film solar cell using these

[60] PCBM analogs is not sufficient for practical use.

[0008]

Prior Art Documents

[0009]

Patent Documents

[0010]

Patent Document 1

[0011]

Patent Document 2

[0012]

Patent Document 3

[0013]

Patent Document 4

[0014]

Non-Patent Documents

[0015]

Non-Patent Document 1

[0016]

Non-Patent Document 2

[0017]

Non-Patent Document 3

[0018]

Problems to be Solved by the Invention

[0019] An object of the present invention is to provide an organic optoelectronic conversion element with improved durability and a composition of a fullerene derivative for constituting the same.

[0020]

Means for Solving the Problems

[0021] To solve the above problems, the present invention provides the following means.

[0022] [1] A composition of a fullerene derivative, which has a partial structure represented by the following general formula (1) and contains stereoisomers having a mirror image relationship caused by the asymmetric carbon atom represented by C in the general formula (1) * in the formula (1), C

[0023]

Chemical Formula 1

[0024]

[0025] (In formula (1), C F respectively represent adjacent carbon atoms forming a fullerene skeleton, and C * represents an asymmetric carbon atom).

[0026] [2] In the composition according to item [1] above, with respect to one fullerene skeleton, the partial structure represented by the formula (1) is one.

[0027] [3] In the composition according to item [1] or [2] above, the molar ratio of the stereoisomers having a mirror image relationship is in the range of 40:60 to 60:40.

[0028] [4] In the composition according to any one of items [1] to [3] above, the fullerene skeleton is C 60 , C 70 , C 74 , C 76 or C 78 .

[0029] [5] A photoelectric conversion element having a first electrode and a second electrode facing each other, and an organic layer provided between the two electrodes, wherein the organic layer contains the composition according to any one of items [1] to [4] above.

[0030]

Effects of the Invention

[0031] By using the composition of the fullerene derivative of the present invention, a photoelectric conversion element with high durability can be obtained. Detailed Embodiments

[0032] Hereinafter, the structure of the embodiments of the present invention will be described. The present invention can be appropriately modified within the scope of not changing its gist.

[0033] [Composition of Fullerene Derivative]

[0034] The composition of the fullerene derivative of this embodiment has a partial structure represented by the following general formula (1), and contains stereoisomers having a mirror image relationship caused by the asymmetric carbon atom represented by C * in the general formula (1).

[0035]

Chemical Formula 2

[0036]

[0037] (In the formula (1), C F respectively represent adjacent carbon atoms forming the fullerene skeleton, and C * represents an asymmetric carbon atom)

[0038] In addition, in this embodiment, "fullerene derivative" means a compound having a structure in which a specific group is attached to the fullerene skeleton, and "fullerene skeleton" means a carbon skeleton constituting a closed shell structure derived from fullerene.

[0039] The fullerene derivative in the composition has 2-methyl-1-butyl having an asymmetric carbon atom in its side chain. Therefore, due to the steric structure of 2-methyl-1-butyl, there are isomers that are mirror images of each other. At this time, when composed of only one of the isomers that are mirror images of each other, the molecules are likely to stack, and when used in an organic thin-film solar cell, the fullerene derivative is likely to crystallize, and the durability of the organic thin-film solar cell is reduced. Therefore, the composition of the fullerene derivative of the present embodiment is a mixture containing stereoisomers that are mirror images of each other derived from the asymmetric carbon atoms on 2-methyl-1-butyl. Thereby, when the composition is used in an organic optoelectronic conversion element, the fullerene derivative is less likely to crystallize, and the durability of the organic optoelectronic conversion element is improved.

[0040] The composition ratio (molar ratio) of the stereoisomers in the composition of the fullerene derivative of the present embodiment is not particularly limited. From the viewpoint of easy availability of raw materials, a range of 40:60 to 60:40 is preferred, and more preferably closer to 50:50. In addition, the composition ratio of the stereoisomers can be measured by high-performance liquid chromatography (chiral HPLC) using a usual chiral separation column.

[0041] In the fullerene skeleton of the fullerene derivative, the number of carbon atoms is preferably 60 to 200. As specific examples, C 60 , C 70 , C 76 , C 78 , C 82 , C 84 , C 90 , C 94 , C 96 , C 120 , C 200 etc. In addition, among them, C 60 , C 70 , C 74 , C 76 or C 78 are more preferred, C 60 or C 70 are further preferred, and C 60 is particularly preferred. This is because, as the raw material fullerene, those with a smaller number of carbon atoms are more likely to obtain high purity. In particular, C 60 is more likely to obtain high purity compared to other fullerenes.

[0042] Regarding the number of the partial structures represented by the formula (1) with respect to one fullerene skeleton, from the viewpoint of improving solubility, a larger number is preferred, and from the viewpoint of avoiding complexity in synthesis and purification, a smaller number is preferred. That is, when the number of the partial structures is 1, if a solubility level that does not hinder the production of the desired photoelectric conversion element can be obtained, the number of the partial structures is most preferably 1. As shown in the following examples, generally, when the number of the partial structures is 1, a photoelectric conversion element can also be manufactured.

[0043] [Method for manufacturing a composition of fullerene derivatives]

[0044] The method for manufacturing the fullerene derivative is not particularly limited. For example, the method described in Patent Document 2 can be used. That is, phenyl-C 61 -butyric acid methyl ester (

[60] PCBM) is used as the starting fullerene derivative, and transesterification is carried out with 2-methyl-1-butanol in the presence of a base catalyst.

[0045] In this method, a mixture of optical isomers of 2-methyl-1-butanol can be used to obtain the composition of the fullerene derivative of the present embodiment, or the optical isomers of 2-methyl-1-butanol can be used separately to prepare isomers of the fullerene derivative that are mirror images of each other, and these fullerene derivatives are mixed to obtain the composition of the fullerene derivative of the present embodiment. In addition, from the viewpoint of reducing the number of steps, the former method is preferred.

[0046] [Photoelectric conversion element]

[0047] The photoelectric conversion element of the present embodiment has a first electrode and a second electrode facing each other, and an organic layer provided between the two electrodes. The organic layer contains the composition of the fullerene derivative of the present embodiment. In addition, the organic layer may contain other compounds in addition to the composition of the fullerene derivative. The first electrode and the second electrode are not particularly limited, and known materials and the like can be used. In addition, if the photoelectric conversion element of the present embodiment has the above characteristics, its structure is not particularly limited. As the structure of the photoelectric conversion element, for example, the element structure described in Patent Document 3 and the like can be cited.

[0048] As described above, the embodiments have been described, but the above embodiments are given as examples and do not limit the present invention by the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, changes, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and at the same time are included in the invention described in the patent claims and its equivalent scope.

[0049]

Examples

[0050] Examples are given below to specifically illustrate this embodiment, but this embodiment is not limited thereto.

[0051] (Synthesis Example) Synthesis of Compound 1

[0052] Dissolve 2.0 g of

[60] PCBM (nanom spectra E100 manufactured by Frontier Carbon), a fullerene derivative as a raw material, in 50 mL of ortho-dichlorobenzene (ODCB). Add 2.32 g (12 equivalents) of DL-2-methyl-1-butanol manufactured by Tokyo Chemical Industry Co., Ltd. as a raw material alcohol, 0.05 g (0.2 equivalents) of potassium tert-butoxide as a base catalyst, and 10 g (5 times the mass) of MS-4A (molecular sieve 4A) as a porous adsorbent material, and carry out the reaction at room temperature for 2 hours. When the progress of the reaction was confirmed by HPLC (high performance liquid chromatography), the transesterification rate of

[60] PCBM was 99.3%. After removing solids such as MS-4A by vacuum filtration using quantitative filter paper, purification was carried out using a silica gel column with ODCB as the developing solvent. After concentrating the fraction of the purified product to 36 mL, 150 mL of methanol was added, and the precipitate was recovered by vacuum filtration using quantitative filter paper. The filtered wet cake was dried at 150 °C for about 15 hours using a vacuum dryer, whereby 1.51 g of the following compound 1 was obtained as a black solid with a purity of 99.2% and a yield of 71%.

[0053] [Chemical Formula 3]

[0054]

[0055] In addition, when Compound 1 was measured by chiral HPLC, it was a mixture (racemic mixture) in which the molar ratio of stereoisomers that were mirror images of each other was 50:50. That is, this mixture (Compound 1) is the composition of the fullerene derivative in this embodiment.

[0056] (Comparative Synthesis Example) Synthesis of Compound 2

[0057] Using (S)-(-)-2-methyl-1-butanol manufactured by Tokyo Chemical Industry Co., Ltd. as the raw material alcohol, synthesis was carried out in the same manner as in Synthesis Example 1, and 1.60 g of Compound 2 was obtained as a black solid with a purity of 99.0% and a yield of 75%. In addition, when measured by chiral HPLC, Compound 2 was a single stereoisomer.

[0058] (Example 1)

[0059] (Fabrication of Organic Optoelectronic Conversion Element 1)

[0060] An indium-tin oxide (ITO) transparent conductive film with a thickness of 110 nm (sheet resistance of 13 Ω / square) is deposited on a glass substrate, and it is patterned with a width of 2 mm by using a conventional photolithography technique and hydrochloric acid etching to form a transparent electrode (anode).

[0061] After patterning the transparent electrode, it is cleaned in the following order: ultrasonically cleaned with a surfactant and ultrapure water, ultrasonically cleaned with ultrapure water, then dried with a nitrogen gas flow, and finally subjected to ultraviolet ozone cleaning.

[0062] On this transparent substrate, Baytron P4083 (manufactured by Starck-Vtech) as a conductive polymer is spin-coated with a film thickness of 40 nm, and then heated and dried in the atmosphere at 140 °C for 10 minutes.

[0063] After forming the layer of Baytron P4083 and transferring it under nitrogen, first, the above substrate is heat-treated at 180 °C for 3 minutes in a nitrogen atmosphere. Next, 1.2% by mass of the BP-1 precursor synthesized by the method described in Patent Document 4 as the bulk heterojunction layer, and 1.0% by mass of Compound 1 (molar ratio of stereoisomers 50:50) as an n-type semiconductor material are dissolved to make a liquid, filtered through a 0.45-μm filter, and then spin-coated with a thickness of 70 nm and heated at 180 °C for 20 minutes to obtain the i layer. In addition, when the BP-1 precursor is converted to BP-1, the molecular weight becomes about 5 / 6, so the p-type semiconductor material:n-type semiconductor material = 1:1.

[0064]

Chemical formula 4

[0065]

[0066] The substrate provided with the bulk heterojunction layer is not exposed to the atmosphere, moved to an evaporation apparatus, and set in a manner such that a 2-mm-wide shadow mask is perpendicular to the transparent electrode, and the pressure is reduced to 4×10 -4 Pa. In addition, bathocuproine and aluminum manufactured by Aldrich are added to a tantalum resistance heating boat and a tungsten resistance heating boat, and they are installed in the evaporation apparatus.

[0067] Next, the tantalum resistance heating boat is energized and heated to deposit an electron transport layer of bathocuproine (BCP) with a thickness of 6 nm on the substrate. Then, the tungsten tantalum heating boat is energized and heated, and a cathode with a film thickness of 100 nm is deposited at a deposition rate of 1 - 2 nm / second in a direction perpendicular to the transparent conductive film to obtain an organic optoelectronic conversion element 1 with a size of 2 mm square.

[0068] The obtained organic optoelectronic conversion element 1 was encapsulated under a nitrogen atmosphere using an aluminum lid and a UV-curing resin (manufactured by Nagase ChemteX Corporation, UV RESIN XNR5570-B1), taken out under the atmosphere, and irradiated with light from a solar simulator at an irradiation intensity of 100 mW / cm 2 (AM1.5G), and the voltage-current characteristics were measured to determine the initial conversion efficiency. Further, with the initial conversion efficiency at this time taken as 100, a resistor was connected between the anode and the cathode, and under this state, irradiation was continued at an irradiation intensity of 100 mW / cm 2 for 100 h, after which the conversion efficiency was evaluated and the relative reduction efficiency was calculated. The results are shown in Table 1.

[0069] (Comparative Examples 1 to 5)

[0070] <Fabrication of Organic Optoelectronic Conversion Elements 2 to 6>

[0071] In the fabrication of the organic optoelectronic conversion element 1, the n-type semiconductor material was changed to the compounds described in Table 1. Otherwise, the organic optoelectronic conversion elements 2 to 6 were obtained in the same manner as the organic optoelectronic conversion element 1. Here,

[60] PCBM in Comparative Example 2 was nanom spectra E100 manufactured by Frontier Carbon Corporation. In addition, Compounds 3 to 5 shown below used in Comparative Examples 3 to 5 were synthesized according to the method described in Patent Document 2. Here, the raw material alcohols used were compounds corresponding to the following chemical formulas of Compounds 3 to 5, respectively. In addition, the raw material alcohols used in the synthesis of Compounds 3 and 4 were both straight-chain.

[0072]

Chemical Formula 5

[0073]

[0074]

Chemical Formula 6

[0075]

[0076]

Chemical Formula 7

[0077]

[0078] The obtained organic optoelectronic conversion elements 2 to 5 were encapsulated under a nitrogen atmosphere using an aluminum can and a UV-curing resin, taken out under the atmosphere, and irradiated with light from a solar simulator (AM1.5G) at an irradiation intensity of 100 mW / cm 2 , and the voltage-current characteristics were measured to determine the initial conversion efficiency. Further, with the initial conversion efficiency at this time taken as 100%, a resistor was connected between the transparent electrode and the counter electrode, and under this state, irradiation was continued at an irradiation intensity of 100 mW / cm 2 for 100 h, after which the conversion efficiency was evaluated. The results are shown in Table 1.

[0079]

Table 1

[0080]

[0081] As can be seen from Table 1, the organic optoelectronic conversion element of this embodiment has high durability without impairing the initial conversion efficiency.

[0082]

Industrial Applicability

[0083] The present invention can be preferably used for organic optoelectronic conversion elements.

[0084] This application claims the priority based on Japanese Patent Application No. 2022-183843 filed with the Japan Patent Office on November 17, 2022, and the entire contents described in the said application are incorporated herein by reference.

Claims

1. A composition of a fullerene derivative, wherein, It has a partial structure represented by the following general formula (1) and contains C in the general formula (1). * Stereoisomers that are mirror images of each other due to the asymmetric carbon atom represented by In formula (1), C F respectively represent adjacent carbon atoms to form a fullerene skeleton, and C * represents an asymmetric carbon atom.

2. The composition according to claim 1, wherein the partial structure represented by the formula (1) is one relative to one fullerene skeleton.

3. The composition according to claim 1 or 2, wherein the molar ratio of the stereoisomers having a mirror-image relationship is in the range of 40:60 to 60:

40.

4. The composition according to claim 1 or 2, wherein the fullerene backbone is C 60 , C 70 , C 74 , C 76 or C 78 .

5. A photoelectric conversion element, wherein, A device having a first electrode and a second electrode facing each other, and an organic layer disposed between the two electrodes, wherein the organic layer contains the composition according to claim 1 or 2.

Images