JP2018127425A - New squarylium derivative and organic thin film solar cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a new squarylium derivative capable of improving carrier mobility in a thin film state without changing an energy level and further improving a curve factor (FF) to enhance energy conversion efficiency; a donor material consisting of the new squarylium derivative; and an organic thin film solar cell using the donor material.SOLUTION: The squarylium derivative is represented by the following general formula (1), (where, in the general formula (1), Rand Rindependently represents a branched aliphatic substituent having a carbon atom number of 4 or more; R-Rindependently represents a hydrogen atom, an aliphatic substituent or an aromatic substituent; Rand R, or Rand Rmay connect with each other to form a ring; and Xand Xindependently represent -S- or -O-.).SELECTED DRAWING: None

Description

  The present invention relates to a novel squarylium derivative and an organic thin film solar cell element using the same.

  In recent years, organic thin film solar cells are lightweight and can be bent freely, and are advantageous in terms of manufacturing cost. Therefore, instead of silicon-based inorganic solar cells, they are entering the stage of commercialization and market introduction. Organic thin film solar cells include a vapor deposition type and a coating type. Particularly, a coating type organic thin film solar cell has a lower manufacturing cost and is suitable for mass production than a vapor deposition type organic thin film solar cell. However, organic thin-film solar cells have a photoelectric energy conversion efficiency of about 10%, and there is still room for improvement in terms of efficiency and reliability compared to silicon-based inorganic solar cells. It has been broken.

Sunlight has 50% or more of its energy in the near infrared / infrared region having a wavelength longer than 650 nm. Therefore, to dramatically improve the photoelectric conversion efficiency, it is essential to efficiently absorb this wavelength region and take it out as electric energy. The organic thin film solar cell element is manufactured using a donor material and an acceptor material. In general, fullerene derivatives used in acceptor materials have the advantage of slow reverse electron transfer and high symmetry, but they do not have strong absorption near the near infrared region, so the efficiency of organic thin-film solar cells is improved. For this purpose, it is very important to develop a donor material having absorption in the long wavelength region. In addition, the relationship between the energy levels of the donor material and the acceptor material is important for increasing the efficiency of the organic thin film solar cell. In general, the lowest unoccupied molecular orbital (LUMO) level of the donor material is the LUMO of the acceptor material in order to transfer charge from the exciton (exciton) generated by absorbing sunlight in the donor material to the acceptor material. It is preferable that the depth is shallower by 0.3 eV or more than the level. In a coating type organic thin film solar cell, phenyl C71 methyl butyrate (PC ₇₀ BM) having high solubility is usually used as an acceptor material. Since the LUMO level of PC ₇₀ BM is 4.0 eV, a LUMO level of about 3.7 eV is required for the donor material.

Needless to say, the donor material used in the coating type organic thin film solar cell needs to be well dissolved in a solvent. Donor materials are roughly classified into two types, a high molecular type and a low molecular type. The conversion efficiency of polymer materials has improved to about 8%. However, polymer materials are difficult to purify and highly purified, and the quality changes greatly between production lots. difficult. On the other hand, the low molecular weight material has characteristics such as no molecular weight distribution, easy purification and high reliability, or quality between production lots does not change, and energy conversion efficiency is not affected by lots. However, the low molecular weight material has a low mobility of about 10 ⁻⁴ cm ² / Vs at the present time, and the energy conversion efficiency remains at 8% or less. Further, among the low molecular weight materials, materials that have achieved high efficiency are generally low in solubility, and halogen-based materials such as orthodichlorobenzene (ODCB), chloroform, etc. are used in the production of coated organic thin film solar cells. Solvents must be used and are environmentally problematic. Therefore, a new low molecular weight material that has high absorption capability and high mobility for near-infrared light, and high solubility in non-halogen solvents, etc., to improve the performance and practicality of coated organic thin-film solar cells. Development is required.

  As a donor material, squarylium derivatives are highly soluble in non-halogen solvents, have strong absorption in the near infrared region, have slow reverse electron transfer, and high symmetry. Research and development has been conducted, and many reports have already been reported (Non-Patent Documents 1 to 3).

G. Chen, H. Sasabe, Y. Sasaki, H. Katagiri, X.F.Wang, T. Sano, Z. Hong, Y. Yang, and J. Kido, “Chem. Mater.” 2014, 26, 1356-1364. Sasaki, Isobe, Hong, Hou, and Kido "The 62nd Annual Meeting of the Society of Polymer Science", 1J28 (2013) H. Sasabe, T. Igarashi, Y. Sasaki. G. Chen, Z. Hong, and J. Kido, “RSC Advances” 2014,4, 42804-42807.

The squarylium derivative can be synthesized relatively easily in a high yield by a dehydration condensation reaction, is environmentally friendly, and can introduce various substituents. Among the squarylium derivatives, SQ-1, YSQ-8, and SQ-BP are BHJ (bulk heterojunction) type devices formed by coating, and have a PCE (power conversion efficiency) of 4.0%, 3.8%, 4.8% has been achieved. The energy conversion efficiencies of these derivatives are improved compared to previous ones, but are still low. In addition, organic thin-film solar cells using these squarylium derivatives have lower _VFF (open circuit voltage) and _JSC (short circuit current density) values than other materials, but low FF (curve factor). There was a problem.

前記誘導体のうち、ＹＳＱ−８、ＳＱ−ＢＰは、アクセプター材料としてＰＣ₇₀ＢＭを組み合わせるのに適したエネルギー準位になるように設計した分子である。なかでもＳＱ−ＢＰはその分子構造が左右対称であり、合成の収率が８０％以上であり、ＰＣＥも４．８％と比較的高い。

Among the derivatives, YSQ-8 and SQ-BP are molecules designed to have an energy level suitable for combining PC ₇₀ BM as an acceptor material. Among them, SQ-BP has a symmetrical molecular structure, a synthesis yield of 80% or more, and PCE is relatively high at 4.8%.

  Therefore, in the present invention, in order to provide a novel squarylium derivative useful for providing a highly efficient device, focusing on SQ-BP, improving the terminal substituent, without changing the energy level, It is an object to improve mobility in a thin film state and further improve FF to improve energy conversion efficiency. Another object of the present invention is to provide a donor material comprising the obtained squarylium derivative and an organic thin film solar cell using the donor material.

The present invention comprises the following items.
The squarylium derivative of the present invention is represented by the following general formula (1).

In general formula (1), R ₁ and R ₂ each independently represents a branched aliphatic substituent having 4 or more carbon atoms, and R _{3 to} R ₆ each independently represent a hydrogen atom or an aliphatic group. Represents a substituent or an aromatic substituent, and R ₃ and R ₄ , or R ₅ and R ₆ may be linked to each other to form a ring, and X ¹ and X ² are each independently —S -Or -O- is represented.
In the general formula (1), R _{3 to} R ₆ preferably represent a hydrogen atom.
The organic thin film solar cell of the present invention uses the above-mentioned squarylium derivative.

By introducing a polycyclic aromatic amino group, the squarylium derivative of the present invention has a deepest occupied molecular orbital (HOMO) and can absorb light having a long wavelength. Furthermore, strong absorption is shown in the region of 550 to 700 nm. Therefore, the use of the squarylium derivative can be expected to increase the efficiency of the organic thin film solar cell.
Further, since the squarylium derivative is soluble in a non-halogen solvent, it can be expected to solve environmental problems and improve device performance.

FIG. 1 is a schematic cross-sectional view showing the element structure of the organic thin film solar cell of the present invention. FIG. 2 represents the ¹ HNMR spectrum of SQ-EDT. FIG. 3 represents the ¹ HNMR spectrum of SQ-EDF. FIG. 4 represents the ¹ HNMR spectrum of SQ-EBT. FIG. 5 represents the ¹ HNMR spectrum of SQ-EBF. FIG. 6 shows UV-vis absorption spectra of a 3 mg / ml chloroform solution of SQ-EDT, SQ-EDF, SQ-EBT, and SQ-EBF. FIG. 7 shows UV-vis absorption spectra of cast films of SQ-EDT, SQ-EDF, SQ-EBT, and SQ-EBF. FIG. 8 is a schematic cross-sectional view showing an element structure of a BHJ type solar cell using SQ-EBT as a donor material and PC ₇₁ BM as an acceptor material. FIG. 9 shows the case of SQ-EBT when film cast (-●-), (-■-) and (-▲-), after film cast and after thermal annealing treatment (70 ° C, 10 minutes) (-X -) About SQ-EP, the JV curve of the reference | standard device of the organic thin-film solar cell when film-casting (-+-) is represented. FIG. 10 represents an external quantum yield (EQE) spectrum of an organic thin film solar cell.

Hereinafter, the present invention will be described in detail.
[Squarylium derivatives]
The squarylium derivative of the present invention is represented by the following general formula (1).

In general formula (1), R ₁ and R ₂ each independently represents a branched aliphatic substituent having 4 or more carbon atoms, and R _{3 to} R ₆ each independently represent a hydrogen atom or an aliphatic group. Represents a substituent or an aromatic substituent, and R ₃ and R ₄ , or R ₅ and R ₆ may be linked to each other to form a ring, and X ¹ and X ² are each independently —S -Or -O- is represented.
Examples of the branched aliphatic substituent having 4 or more carbon atoms include, for example, t-butyl group, s-butyl group, isobutyl group, t-amyl group, s-amyl group, isoamyl group, 1-methylbutyl group, 3 -Methylbutyl group, 1,1-dimethylpropyl group, 2-ethylhexyl group, 2-ethyloctyl group and the like. Of these, 2-ethylhexyl group, isobutyl group, 2-ethyloctyl group and the like are more preferable, and 2-ethylhexyl group is particularly preferable.
R _{3 to} R ₆ each independently represent a hydrogen atom, an aliphatic substituent or an aromatic substituent.

The aliphatic substituents of R _{3 to} R ₆ are widely groups other than aromatic substituents, and may be chain (acyclic) or cyclic. Further, the aliphatic substituent has a hydrogen atom part of an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, or a nitrogen atom, a sulfur atom, an oxygen within a range not impairing the effects of the present invention. It may be substituted with an atom, phosphorus atom, silicon atom or a substituent containing these atoms. The aliphatic substituent is specifically an alkyl group having 1 to 20 carbon atoms, specifically a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a cyclopentyl group, or a cyclohexyl group. In view of solubility, a butyl group, a pentyl group, a hexyl group, a cyclopentyl group, a cyclohexyl group, and the like are more preferable.

The aromatic substituents of R _{3 to} R ₆ may be monocyclic or polycyclic (fused ring), and may be monocyclic or heterocyclic. For example, phenyl group, thienyl group, furyl group, pyrrolyl group, pyridyl Group, quinolyl group, quinoxalyl group, imidazopyridyl group, benzothiazole group and the like. Of these, a phenyl group, a pyridyl group, and the like are preferable. Moreover, a part of hydrogen atoms constituting the aromatic substituent may be substituted with, for example, a methyl group, an isopropyl group, an isobutyl group, or the like.
R ₃ and R ₄ , or R ₅ and R ₆ may be connected to each other to form a 5- to 7-membered ring, specifically a 6-membered ring.

Specifically, the compound represented by the general formula (1) is preferably a compound SQ-EDT, SQ-EDF, SQ-EBT, or SQ-EBF represented by the following structural formula.

The squarylium derivative represented by the general formula (1) can have deep HOMO and broad absorption in the near infrared region by having a condensed ring at the terminal substituent, and branched aliphatic carbonization on the other side. By having a hydrogen group, the solubility in an organic solvent is improved. For example, when the terminal substituents of the squarylium derivative are all aromatic groups, one of the terminal substituents is an aromatic group, and the other Compared with the case where is a linear aliphatic group, the molar extinction coefficient in the near infrared region and the solubility in an organic solvent are improved.
Therefore, the squarylium derivative can be suitably used as a donor material for an acceptor material made of fullerene such as PC ₇₁ BM or a derivative thereof.

[Method for producing squarylium derivative]
The squarylium derivative of the present invention can be produced, for example, by the method shown below. A method for producing SQ-EDT is shown as an example.

2-Ethylhexane-1-amine and 4-bromodibenzothiophene are stirred in DMSO in the presence of CuI / L-proline catalyst and potassium carbonate to give an amine derivative that is a yellow viscous (step 1). Next, the amine derivative and 1-bromo-3,5-dimethoxybenzene are heated and stirred in toluene in the presence of a Pd (0) catalyst, a phosphine ligand, and sodium t-butoxide base, and the dimethoxybenzene derivative is then obtained. (Step 3). Further, the dimethoxybenzene derivative is demethylated with boron tribromide (step 3), and the obtained dihydroxybenzene derivative and squaric acid are reacted in a mixed solution of toluene and butanol to obtain SQ-EDT.
However, the squarylium derivative represented by the general formula (1) is not limited to the above-described method, and can be produced by various known methods.

[Organic thin film solar cell and manufacturing method thereof]
The organic thin film solar cell element of the present invention (hereinafter referred to as “solar cell element”) has an element structure in which at least one organic power generation layer is laminated between a pair of electrodes (anode 2 and cathode 6). 1 has an element structure in which a substrate 1, an anode 2, a hole transport layer 3, an active layer 4, an electron transport layer 5 and a cathode 6 are sequentially laminated.
Hereinafter, the configuration of the solar cell element of the present invention will be described.

<Configuration of solar cell element>
The configuration of the solar cell element of the present invention is not limited to the example shown in FIG. 1, and 1) an anode buffer layer (not shown) / hole transport layer / active layer, and 2) an anode sequentially between the anode and the cathode. Buffer layer (not shown) / active layer / electron transport layer, 3) anode buffer layer (not shown) / hole transport layer / active layer / electron transport layer, 4) anode buffer layer (not shown) / positive Layer containing hole transporting compound, active compound and electron transporting compound, 5) Anode buffer layer (not shown) / Layer containing hole transporting compound and active compound, 6) Anode buffer layer (not shown) / Layer containing active compound and electron transporting compound, 7) Anode buffer layer (not shown) / layer containing hole electron transporting compound and active compound, 8) Anode buffer layer (not shown) / active layer / positive The structure etc. which provided the hole block layer (not shown) / electron carrying layer are mentioned. Further, the active layer shown in FIG. 1 is a single layer, but may be two or more layers.

<Anode>
For the anode 2, a material having a surface resistance of usually 1000 Ω (ohms) or less, preferably 100 Ω or less in a temperature range of −5 to 80 ° C. is used.
When light is extracted from the anode 2 side of the solar cell element (bottom emission), the anode 2 needs to be transparent to visible light (average transmittance for light of 380 to 680 nm is 50% or more). Therefore, indium tin oxide (ITO), indium-zinc oxide (IZO), or the like is used as the material of the anode 2. Of these, ITO is preferable from the viewpoint of availability.
Further, when light is extracted from the cathode 6 side of the device (top emission), the light transmittance of the anode 2 is not limited. Therefore, in addition to ITO and IZO, materials for the anode 2 include stainless steel, copper, silver , Gold, platinum, tungsten, titanium, tantalum, niobium, or an alloy thereof.
In the case of bottom emission, the thickness of the anode 2 is usually 2 to 300 nm in order to realize high light transmittance, and in the case of top emission, it is usually 2 nm to 2 mm.

<Anode buffer layer>
The anode buffer layer is formed by applying an anode buffer layer material on the anode 2 and further heating.
In this coating operation, spin coating method, casting method, micro gravure coating method, gravure coating method, bar coating method, roll coating method, dip coating method, spray coating method, screen printing method, flexographic printing method, offset printing method, A known coating method such as an inkjet printing method can be applied.
Moreover, from the viewpoint of preventing the anode buffer layer from being dissolved when the active layer 4 is formed, a material having high resistance to an organic solvent is usually used as the anode buffer layer material.
The thickness of the anode buffer layer is usually 5 to 50 nm, preferably 10 to 30 nm, from the viewpoint of sufficiently exhibiting the effect as the buffer layer and preventing an increase in the driving voltage of the solar cell element.

<Active layer, hole transport layer, electron transport layer>
The organic power generation layer in the solar cell element includes a hole transport layer 3, an active layer 4, and an electron transport layer 5.
For the active layer 4, the squarylium derivative represented by the general formula (1) is used. The squarylium derivative is usually used in combination with an acceptor material. By using the squarylium derivative as a donor material and forming the active layer 4 together with an acceptor material, a highly efficient organic thin-film solar cell can be provided.
As the acceptor material, a known material is appropriately selected and used, but a compound having an electron transporting property and a deep HOMO energy level is preferable. Specifically, fullerene (C60, C70, etc.) or a derivative thereof. (PC ₇₁ BM etc.) is preferably used.

The active layer 4 may be inserted between the hole transport layer 3 and the electron transport layer 5 as shown in FIG. 1 for the purpose of supplementing the carrier transport property of the active layer 4. In addition, a hole transporting compound or an electron transporting compound may be dispersed together with the acceptor material.
Examples of the hole transporting compound include molybdenum oxide (VI) (MoO ₃ ), vanadium oxide (V ₂ O ₅ ), tungsten oxide (WO ₃ ), ruthenium oxide (RuO ₂ ), and other metal oxides, hexaaza Low molecular materials such as triphenylenehexacarbonyl (HATCN), 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4TCNQ), and polymerizable functional groups introduced into the low molecular materials And polymerized.
Examples of the electron transporting compound include phenanthroline derivatives such as BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline), B4PyMPM (bis-3,6- (3,5-di-4), and the like. Low molecular materials such as oligopyridine derivatives such as -pyridylphenyl) -2-methylpyrimidine) and nanocarbon derivatives such as [60] fullerene and [70] fullerene, and polymerizable functional groups are introduced into the low molecular material. Polymerized ones can be mentioned.

<Hole blocking layer>
A hole blocking layer may be provided adjacent to the cathode 6 side of the active layer 4 for the purpose of suppressing passage of holes through the active layer and efficiently recombining with electrons in the active layer 4. For the hole blocking layer, a compound having a deeper HOMO level than the active compound is used. For example, a triazole derivative, an oxadiazole derivative, a phenanthroline derivative, an aluminum complex, or the like is used.
Further, an exciton block layer may be provided adjacent to the active layer 4 on the cathode 6 side in order to prevent the exciton (exciton) from being deactivated by the cathode metal. In this exciton block layer, a compound having a triplet excitation energy larger than that of the active compound is used. As the compound, a triazole derivative, a phenanthroline derivative, an aluminum complex, or the like is used.

<Cathode>
As the cathode material, a material having a low work function (4 eV or less) and chemically stable is used. Specific examples include known cathode materials such as Al, MgAg alloys, alloys of Al and alkali metals such as AlLi and AlCa. As a film forming method for these cathode materials, a resistance heating vapor deposition method, an electron beam vapor deposition method, a sputtering method, an ion plating method, or the like is used. The thickness of the cathode 6 is usually 10 nm to 1 μm, preferably 50 to 500 nm.

  For the purpose of lowering the electron injection barrier from the cathode 6 to the organic power generation layer and increasing the electron injection efficiency, a metal layer having a work function lower than that of the cathode 6 is used as a cathode buffer layer and is adjacent to the cathode 6 and the cathode 6. It may be inserted between the layers. Examples of low work function metals that can be used for such purposes include alkali metals, alkaline earth metals, and rare earth metals. Moreover, an alloy or a metal compound can also be used if it has a work function lower than that of the cathode. As a method for forming these cathode buffer layers, vapor deposition, sputtering, or the like can be used. The thickness of the cathode buffer layer is usually 0.05 to 50 nm, preferably 0.1 to 20 nm.

  Further, the cathode buffer layer can be formed as a mixture of the above-described low work function metal or the like and an electron transporting compound. In this case, a co-evaporation method can be used as a film forming method. In addition, in the case where coating film formation using a solution is possible, film formation methods such as a spin coating method, a spray coating method, a dip coating method, and a printing method (inkjet printing method, dispenser coating method) can be used. In this case, the thickness of the cathode buffer layer is usually 0.1 to 100 nm, preferably 0.5 to 50 nm. A layer made of a conductive polymer or a layer made of a metal oxide, a metal fluoride, an organic insulating material, or the like with an average film thickness of 2 nm or less may be provided between the cathode and the organic material layer.

<Board>
A material that satisfies the mechanical strength required for the solar cell element is used for the substrate 1 constituting the element.
For the bottom emission type solar cell element, a substrate 1 transparent to visible light is used. For example, glass such as soda glass and non-alkali glass; acrylic resin, methacrylic resin, polycarbonate resin, polyester resin, nylon resin, etc. A transparent plastic; a substrate 1 made of silicon can be used.
The top emission type solar cell element includes, in addition to the substrate 1 used for the bottom emission type solar cell element, a simple substance of stainless steel, copper, silver, gold, platinum, tungsten, titanium, tantalum or niobium, or an alloy thereof. A substrate 1 made of or the like can be used.
Although the thickness of the board | substrate 1 is based also on the mechanical strength requested | required, it is 0.1-10 mm normally, Preferably it is 0.25-2 mm.
In addition, the film thickness of each layer is in the range of approximately 5 nm to 5 μm.

(Method for forming solar cell element)
The organic power generation layer is, for example, a vapor deposition method (resistance heating vapor deposition method, electron beam vapor deposition method, etc.), a dry process such as a sputtering method, or a coating method (spin coating method, casting method, die coating method, micro gravure coating method, Gravure coating method, bar coating method, roll coating method, wire bar coating method, dip coating method, spray coating method, screen printing method, flexographic printing method, offset printing method, inkjet printing method, etc.) Can do. Of these methods, spin coating, die coating, and spray coating are preferably used.

  In addition, in order to use a solar cell element stably for a long period of time, it is preferable to attach a protective layer and / or a protective cover around it. For the protective layer, a polymer compound, metal oxide, metal fluoride, metal boride and the like are used. The protective cover is made of a glass plate, a plastic plate with a low water permeability treatment on the surface, a metal, or the like, and the cover is bonded to the element substrate with a thermosetting resin or a photocurable resin and sealed. Preferably used. Furthermore, if an inert gas such as nitrogen or argon is sealed in the space, oxidation of the cathode can be prevented, and if a desiccant such as barium oxide is placed in the space, moisture adsorbed in the manufacturing process is absorbed by the sun. The battery element can be prevented from being damaged.

[Usage]
The organic thin film solar cell of the present invention is suitably used for an image display device as a pixel by a matrix method or a segment method. Moreover, the said organic thin film solar cell is used suitably also as a surface emitting light source, without forming a pixel.
Specifically, the organic thin film solar cell of the present invention includes a display device, backlight, electrophotography, illumination, resist, etc. for computers, televisions, portable terminals, cellular phones, car navigation systems, signs, signboards, video camera viewfinders, etc. It is suitably used for a light irradiation device in exposure, reading device, interior lighting, optical communication system and the like.

  EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not restrict | limited by the following Example.

[Example 1] Synthesis of SQ-EDT

(I) Step 1
2-ethylhexane-1-amine 16.3 mL (100 mmol), 4-bromodibenzothiophene 5.26 mg (20 mmol), K ₂ CO ₃ 1.11 g (8 mmol), L-proline 0.691 g (6 mmol) ), 5 mL of dimethyl sulfoxide (DMSO) was added, and N ₂ bubbling was performed for 60 minutes. The jelly-like mixture was heated to 40 ° C. in an oil bath, and another 5 mL of DMSO was added. After N ₂ bubbling for another 60 minutes, 0.761 g (4 mmol) of CuI was added. Thereafter, the oil bath was heated to 120 ° C. and stirred for 86 hours. The change in the color of the solution during that period was blue → purple → maroon → dark blue. The heating and stirring were stopped, 100 mL of ethyl acetate was added to the reaction mixture, and the mixture was separated 11 times with 100 mL of saturated brine with a separatory funnel, and then the organic layer was dehydrated with magnesium sulfate and filtered. The solvent was removed under reduced pressure using an evaporator to obtain a viscous body (13.6 g). Further, column chromatography without the origin was performed on the viscous body to obtain 5.4 g of a yellowish brown viscous body. Then, 350 mL of silica gel was used, the developing solvent was hexane, and purification by column chromatography was performed to obtain 3.8 g of a yellow viscous body. Yield 3.8g (Yield 61%)

(Ii) Step 2
In a 50 mL three-necked flask, put 2.6 g (8.3 mmol) of the compound obtained in Step 1, 2.2 g (10 mmol) of 1-bromo-3,5-dimethoxybenzene and 10 mL of dehydrated toluene, and perform N ₂ bubbling. I went for 60 minutes. Pd ₂ (dba) ₃ 375 mg (0.41 mmol), tBu ₃ PHBF ₄ 240 mg (0.83 mmol) and tBuONa 1.9 g (20 mmol) were added, and the mixture was heated and stirred at 100 ° C. in an oil bath. The reaction was completed in 20 hours after the reaction.
The reaction mixture was poured into a separatory funnel with 100 mL of ethyl acetate, and the liquid separation was performed by 2 sets of 100 mL of saturated brine, and then ethyl acetate was again added to the aqueous layer and separated 4 times with 100 mL of saturated brine. . The organic layers were combined, dehydrated with magnesium sulfate, and the solvent was removed under reduced pressure with an evaporator to obtain 4.6 g of a viscous body. Purification by column chromatography using 400 mL of silica gel and hexane as the developing solvent gave 3.2 g of a viscous body. Yield 3.2g (86% yield)

(Iii) Step 3
First, 3.2 g (7.2 mmol) of the dimethoxybenzene derivative obtained in Step 2 was pumped up while warming with a dryer, and the remaining solvent was removed under reduced pressure. This dimethoxybenzene derivative was dissolved in 15 mL of dehydrated CH ₂ Cl _{2 in a} 50 mL four-necked flask and cooled in an ice bath for 30 minutes while performing N ₂ flow. BBr ₃ 16 mL (16 mmol) was added to the well cooled in an ice bath using a dropping funnel over about 30 minutes. After completion of dropping, the ice bath was stopped and the mixture was stirred at room temperature for 42 hours.
Using a dropping funnel, 20 mL of pure water was slowly added to terminate the reaction. At this time, after dropping 10 drops at a rate of 1 drop every 3 minutes, the first 5 mL was dropped at a rate of 1 drop every 30 seconds. After the addition of pure water, the reaction solution was transferred to a separatory funnel and washed and separated once with 100 mL of pure water and twice with 100 mL of saturated saline. Then, it was dried with magnesium sulfate. Purification was performed by column chromatography using silica gel and methylene chloride: ethyl acetate = 20: 1 as a developing solvent. The isolation of the target product was confirmed by TLC (methylene chloride: ethyl acetate = 20: 1) (Rf value 0.25), and the solvent was removed under reduced pressure using an evaporator. Yield 1.5g (Yield 50%)

(Iv) Step 4
To a 100 mL three-necked flask equipped with a Dean-Stark tube, 2.3 g (5.5 mmol) of the dihydroxybenzene derivative obtained in Step 3, 285 mg of 3,4-dihydroxycyclobut-3-ene-1,2-dione ( 2.5 mmol), butanol: toluene = 1: 3 mixed solvent 60 mL was added, and the oil bath was heated to 130 ° C. and heated under reflux in a nitrogen atmosphere. Since 2.5 hours after the reaction, almost no material was left from TLC, the reaction was terminated.
The reaction solution was concentrated to about 20 mL using a Dean-Stark tube, and the oil bath was turned off. Thereafter, 20 mL of cyclohexane was added and the mixture was sufficiently cooled to room temperature. As a result, the target product precipitated, and was collected by suction filtration.
After filtration, the filtrate was dispersed and washed with 50 mL of methanol and 50 mL of hexane and dried under reduced pressure. Yield 2.3g (Yield 100%)
The synthesized product was identified by mass spectrum, ¹ HNMR (FIG. 2), and elemental analysis.
Elemental analysis: Theoretical value C, 73.25%; H, 6.26%; N, 3.05%, S, 6.98%, O, 10.45%
Found C, 73.28%; H, 6.51%; 3,10.01%, S, 6.99%

[Example 2] Synthesis of SQ-EDF

(I) Step 1
In a 25 mL three-necked flask, 0.98 mL (6 mmol) of 2-ethylhexane-1-amine, 0.99 mg (4 mmol) of 4-bromodibenzofuran, 0.221 g (1.6 mmol) of K ₂ CO ₃ , 0.14 g (1.2 mmol) of L-proline mmol) and 5 mL of DMSO was added. In order to prevent solidification at this time, it heated at 40 degreeC with the oil bath. After N ₂ bubbling was performed for 60 minutes, 0.153 g (0.8 mmol) of CuI was added, and then the oil bath was heated at 120 ° C. and stirred. During that time, the color change of the solution was blue → purple → amber. After 43 hours, heating and stirring were stopped, 100 mL of ethyl acetate was added to the reaction mixture, and 100 mL of saturated brine was separated and washed 6 times with a separatory funnel, and the organic layer was dried over magnesium sulfate. The solvent was removed under reduced pressure using an evaporator to obtain a viscous body (1.5 g).
Purification was performed with silica gel column chromatography with hexane (Rf = 1.7), and the solvent was removed under reduced pressure with an evaporator to obtain 0.7 g of the desired product. Yield 0.7g (59% yield)

(Ii) Step 2
Three-neck flask 25 mL, amine derivative 0.7 g (2.4 mmol) obtained in Step 1, 1-bromo-3,5-dimethoxybenzene 0.61 g (2.8 mmol), dehydrated xylene 5 mL put N ₂ bubbling For 120 minutes. Pd ₂ (dba) ₃ 110 mg (0.12 mmol), tBu ₃ PHBF ₄ 70 mg (0.24 mmol), and tBuOK 0.66 g (5.9 mmol) were added, and the mixture was heated and stirred at 130 ° C. in an oil bath. At 49 hours after the reaction, the reaction was stopped after confirming that the reaction had progressed from TLC.
The liquid separation was poured into 100 mL of ethyl acetate, and washed 5 times with 100 mL of saturated saline. The organic layer was dehydrated with magnesium sulfate, and the solvent was removed under reduced pressure with an evaporator to obtain 1.9 g of a viscous body.
Purification was performed by column chromatography using 200 mL of silica gel and hexane: toluene = 1: 1 as a developing solvent, and the solvent was removed under reduced pressure using an evaporator to obtain 0.6 g of a viscous body.

(Iii) Step 3
In a 50 mL four-necked flask, 2.9 g (6.7 mmol) of the dimethoxy derivative obtained in Step 2 was dissolved in 10 mL of dehydrated CH ₂ Cl _{2 and} cooled in an ice bath for 30 minutes while performing N ₂ flow. 14.6 mL (14.6 mmol) of BBr ₃ was slowly added with a dropping funnel while the mixture was sufficiently cooled in an ice bath. After completion of the dropwise addition, the ice bath was stopped and the mixture was stirred at room temperature for 20 hours.
After dropping 10 mL of pure water at a rate of 1 drop every 3 minutes, the reaction was terminated slowly by adding a dropping funnel at a rate of 1 drop every 30 seconds.
The reaction solution was transferred to a separatory funnel and washed and separated once with 100 mL of pure water and twice with 100 mL of saturated saline. Then, it was dried with magnesium sulfate. Purification was performed by column chromatography using 300 mL of silica gel and methylene chloride: ethyl acetate = 20: 1 as a developing solvent. Isolation of the target product (Rf value 0.25) was confirmed with TLC (methylene chloride: ethyl acetate = 20: 1), and the solvent was removed under reduced pressure with an evaporator to obtain 1.6 g of a viscous body. Yield 1.6g (Yield 59%)

(Iv) Step 4
In a 100 mL three-necked flask equipped with a Dean-Stark tube, 2.0 g (4.95 mmol) of a dihydroxybenzene derivative obtained by repeating Steps 1 to 3 and 3,4-dihydroxycyclobut-3-ene-1 , 2-dione (squaric acid) 257 mg (2.25 mmol), butanol: toluene = 1: 3 mixed solvent 60 mL was added, the oil bath was heated to 130 ° C., and heated under reflux in a nitrogen atmosphere. The reaction was completed because the starting material was almost free from TLC in 1.5 hours.
The reaction solution was concentrated to about 20 mL using a Dean-Stark tube, and the oil bath was turned off. Thereafter, 20 mL of cyclohexane was added, and the product was sufficiently cooled to room temperature. As a result, the target product precipitated, and was collected by suction filtration.
After filtration, the filtrate was dispersed and washed with 50 mL of methanol and 50 mL of hexane and dried under reduced pressure to recover 2.3 g of the desired product. Yield after purification 1.43 g (72% yield)
^The synthesized product was identified by ¹ HNMR (FIG. 3).

[Example 3] Synthesis of SQ-EBT

(I) Step 1
In a 50 mL three-necked flask, 5.17 mL (32 mmol) 2-ethylhexane-1-amine, 4.50 mg (21 mmol) 5-bromobenzo [b] thiophene, 1.17 g (8.5 mmol) K ₂ CO _3, 0.730 L-proline g (6.4 mmol) was added, 10 mL of DMSO was added, and the oil bath was set to 40 ° C. After carrying out N ₂ bubbling for 60 minutes, Cu07 (0.807 g, 4.3 mmol) was added, and then the oil bath was heated at 130 ° C. and stirred. During that time, the color change of the solution was blue → purple → amber. After 68 hours, pour into a separating funnel with 100 mL of ethyl acetate, separate and wash 5 times with 100 mL of saturated brine, remove the origin with 100 mL of silica gel, dry the organic layer with magnesium sulfate, and remove the solvent under reduced pressure to remove yellow A viscous body was obtained.
Thereafter, purification was performed by column chromatography using 350 mL of silica gel with hexane: toluene = 1: 1 as a developing solvent (Rf = 2.8) to obtain 3.0 g of the desired product. Yield 3.0g (55% yield)

(Ii) Step 2
Placed in a three necked flask 50 mL, amine derivative obtained in Step 1 3.0g (11.4mmol), 1- bromo-3,5-dimethoxybenzene 2.95 g (13.6 mmol), dehydrated xylene 15 mL, N ₂ Bubbling was performed for 60 minutes. Pd ₂ (dba) ₃ 110 mg (0.114 mmol), tBu ₃ PHBF ₄ 134 mg (0.456 mmol), and tBuOK 3.02 g (28.5 mmol) were added, and the mixture was stirred in an oil bath at 140 ° C. for 18 hours.
The reaction mixture was poured into a separatory funnel with 100 mL of ethyl acetate, washed with 100 mL of saturated brine five times, dried over magnesium sulfate and concentrated to obtain 6.7 g of a black viscous body.
Thereafter, 350 mL of silica gel was used, and purification was performed by column chromatography using hexane: toluene = 2: 1 as a developing solvent to obtain 2.9 g of a viscous body. Yield 2.9g (64% yield)

(Iii) Step 3
In a 50 mL four-necked flask, dissolve 2.9 g (7.3 mmol) of the dimethoxybenzene derivative obtained in Step 2 with 20 mL of dehydrated CH ₂ Cl _{2 and} cool in an ice bath for 30 minutes with N ₂ flow. ₃ 26 mL (26 mmol) was slowly added with a dropping funnel. After completion of the dropwise addition, the temperature was returned to room temperature, and 10 mL of dehydrated CH ₂ Cl ₂ was further added along the way, and 10 mL of BBr ₃ was added in an ice bath and stirred for 6 hours.
20 mL of pure water was added dropwise at a rate of 10 drops per 3 minutes with a dropping funnel, and then added at a rate of 1 drop per 30 seconds to complete the reaction. The reaction mixture was transferred to a separatory funnel and washed and separated three times with 100 mL of saturated brine. Then, it was dried with magnesium sulfate. Column chromatography was performed using 300 mL of silica gel and methylene chloride: ethyl acetate = 20: 1 as a developing solvent (Rf value 0.25) to obtain 1.6 g of a viscous body. Yield 1.6g (Yield 59%)

(Iv) Step 4
To a 100 mL three-necked flask equipped with a Dean-Stark tube, 1.6 g (4.3 mmol) of the dihydroxybenzene derivative obtained in Step 3, 228 mg of 3,4-dihydroxycyclobut-3-ene-1,2-dione (2.0 mmol), butanol: toluene = 1: 3 mixed solvent was added, heated to 130 ° C. in an oil bath, and heated to reflux in a nitrogen atmosphere. The reaction was completed because the starting material was almost free from TLC after a reaction time of 9.5 hours.
The reaction solution was concentrated to about 20-25 mL using a Dean-Stark tube, and the oil bath was turned off. Thereafter, the reaction mixture was cooled to 80 ° C., 20 mL of cyclohexane was added, and the mixture was sufficiently cooled to room temperature. After filtration, the residue was dispersed and washed with 40 mL of methanol and 40 mL of hexane and dried under reduced pressure for 3.5 hours to recover 1.6 g. Yield 1.6g (98% yield)
^The synthesized product was identified by ¹ HNMR (FIG. 4).

[Example 4] Synthesis of SQ-EBF

(I) Step 1
In a 50 mL three-necked flask, 4-ethylhexane-1-amine 4.91 mL (30 mmol), 5-bromobenzofuran 2.55 mL (20 mmol), K ₂ CO ₃ 1.1 g (8.0 mmol), L-proline 690 mg (6.0 mmol) ), DMSO was added, and the oil bath was set to 40 ° C. After bubbling for 60 minutes, 760 mg (4.0 mmol) of CuI was added, and then the oil bath was heated at 130 ° C. and stirred. During that time, the color change of the solution was blue → purple → amber. After 69 hours, the reaction solution was poured into a separatory funnel with 100 mL of ethyl acetate, separated and washed 9 times with 100 mL of saturated brine, the origin was removed with 100 mL of silica gel, and the organic layer was dried over magnesium sulfate. The solvent was removed under reduced pressure with an evaporator to obtain a yellow viscous body.
Thereafter, purification was performed by column chromatography using hexane: toluene = 1: 1 as a developing solvent (Rf = 2.8) to obtain 2.6 g of the desired product. Yield 2.6g (53% yield)

(Ii) Step 2
Placed in a three necked flask 50 mL, amine derivative obtained in Step 1 2.6g (10.6mmol), 1- bromo-3,5-dimethoxybenzene 2.76 g (12.7 mmol), dehydrated xylene 15 mL, N ₂ Bubbling was performed for 60 minutes. Add Pd ₂ (dba) ₃ 100 mg (0.11 mmol), tBu ₃ PHBF ₄ , 122 mg (0.42 mmol), tBuOK 2.96 g (26.5 mmol), set the oil bath at 140 ° C., and heat and stir. 18 hours later The reaction was stopped. The reaction solution was poured into a separatory funnel with 100 mL of ethyl acetate, and washed with 100 mL of saturated brine five times. Thereafter, the mixture was dehydrated with magnesium sulfate, and the solvent was removed under reduced pressure using an evaporator to obtain 6.4 g of a black viscous body.
Purification was performed by column chromatography using hexane: toluene = 1: 2 as a developing solvent to obtain 2.5 g of a viscous body. Yield 2.5g (62% yield)

(Iii) Step 3
In a 50 mL four-necked flask, 3.0 g (7.8 mmol) of the dimethoxybenzene derivative obtained in Step 2 was dissolved in 11 mL of dehydrated CH ₂ Cl _{2 and} cooled in an ice bath for 30 minutes while performing N ₂ flow. BBr ₃ 17 mL (17.3 mmol) was slowly added with a dropping funnel to a place sufficiently cooled in an ice bath.
After confirming that the reaction had progressed with TLC, 20 mL of pure water was slowly added with a dropping funnel (1 drop / 3 minutes up to the first 10 drops, then 1 drop / 30 seconds) to complete the reaction. The reaction solution was transferred to a separatory funnel, washed and separated three times with 100 mL of saturated brine, and then dried over magnesium sulfate.
Purification was performed by silica gel column chromatography (Rf value 0.22) using methylene chloride: ethyl acetate = 20: 1 as a developing solvent. After confirming that the desired product was isolated, the solvent was removed under reduced pressure with an evaporator to obtain 1.4 g of a viscous body. Yield 1.4g (51% yield)

(Iv) Step 4
In a 100 mL three-necked flask equipped with a Dean-Stark tube, 1.4 g (3.7 mmol) of a dihydroxybenzene derivative, 190 mg (1.67 mmol) of 3,4-dihydroxycyclobut-3-ene-1,2-dione, butanol: 60 mL of a mixed solvent of toluene = 1: 3 was added, the oil bath was heated to 130 ° C., and heated under reflux in a nitrogen atmosphere. The reaction was completed because the starting material was almost free from TLC in 1.5 hours.
The reaction solution was concentrated to about 20 mL using a Dean-Stark tube, and the oil bath was turned off. Thereafter, 20 mL of cyclohexane was added and the mixture was sufficiently cooled to room temperature. As a result, the target product precipitated, and was collected by suction filtration.
After filtration, the target product was dispersed and washed with 50 mL of methanol and 50 mL of hexane, dried under reduced pressure, and 1.0 g was collected and stored. Yield 1.0g (76% yield)
^The synthesized product was identified by ¹ HNMR (FIG. 5).

[Test Example 1] Evaluation of thermal and optical characteristics The main equipment and measurement conditions used for optical characteristics evaluation are as follows.
(1) Ultraviolet / visible (UV-vis) spectrophotometer UV-3150 manufactured by Shimadzu Corporation
Measurement conditions: medium scan speed, measurement range 200 to 800 nm, sampling pitch 0.5 nm, slit width 0.5 nm
(2) Cyclic voltammetry (CV) measuring device
ALS 660B Model Electrochemical Analyzer (BS Corporation)
Measurement conditions: Measurement was performed by adjusting the sample concentration to 0.5 mM in the presence of dichloromethane (6 mL), ferrocene (1.0 mg), and tetrabutylammonium tetrafluoroborate (170 mg) as a solvent. The measurement environment was performed in a glove box under nitrogen.
(3) Photoelectron Yield Spectroscopy (PYS) Device Ionization Potential Measurement Device manufactured by Sumitomo Heavy Industries, Ltd. Ionization potential (Ip) was measured in vacuum using an ionization potential measurement device.
The electron affinity (E _a ) was calculated by estimating the energy gap (E _g ) from the absorption edge of the UV-vis absorption spectrum.
(4) Thermal analyzer TGA diamond and DSCDTA manufactured by PerkinElmer Japan Co., Ltd.

In comparison between the compounds synthesized in Examples 1 to 4 and the conventional examples SQ-EP and SQ-EB, thermal and optical properties were evaluated.

FIGS. 56 and 67 show UV-vis absorption spectra of a 1.0 × 10 ⁻⁵ M solution obtained by dissolving the compounds of Examples 1 to 4 in chloroform and a thin film obtained by film-casting the solution.
Table 1 shows the results of thermal properties and optical properties of SQ-EDT, SQ-EDF, SQ-EBT and SQ-EBF.

Compared to SQ-EP, all of the compounds of Examples 1 to 4 were improved in rigidity and greatly improved heat resistance by introducing a condensed ring. In SQ-EBT and SQ-EBF, the absorption wavelength is slightly longer, and the conjugate length has been extended as intended (FIGS. 56 and 67). On the other hand, in SQ-EDT and SQ-EDF, the conjugation length is considered shorter than SQ-EBT and SQ-EBF because the dibenzothiophene and dibenzofuran sites are twisted from the absorption wavelength. It is done. It can also be seen that the band gap is slightly larger and the HOMO is deeper in SQ-EDT and SQ-EDF due to the twist of the donor site and the shortening of the conjugate length. Regarding the molar extinction coefficient, there was almost no difference because the basic skeleton of SQ was the same.
In addition, the following formula was used for calculation of HOMO / LUMO.
E _HOMO (eV) =-[E _ox ^onset -E1 / 2 (Fc / Fc ⁺ ) +4.8]
E _LUMO (eV) =-[E _red ^onset -E1 / 2 (Fc / Fc ⁺ ) +4.8]

[Test Example 2] Solubility Evaluation In comparison between SQ-EDF and SQ-EDT synthesized in Examples 1 and 2 and the conventional example SQ-EB, thermal and optical characteristics were evaluated.

Weigh each 6.7 mg of the above compound into a sample tube, add 1 mL of chloroform, chlorobenzene, o-dichlorobenzene, cyclopentanone, and cyclohexanone (6.7 mg / 1 mL), and finally add the solvent to 4 mL. The solubility was confirmed.
SQ-EDT did not dissolve in any of these solvents, but SQ-EDF dissolved in chloroform at a concentration capable of forming an element (6.7 mg / mL).

The results are shown in Table 2. ○ represents complete dissolution, and x represents that some or all did not dissolve.

[Test Example 3] Evaluation of solar cell characteristics The element structure, film formation method and conditions are as follows.
Device structure: [ITO / MoO ₃ (8 nm) / SQ-EBT: PC ₇₁ BM = 1: 2 / BCP (5 nm) / Al (100 nm)]
Deposition method and conditions:
Glass ITO substrate is cleaned with UV-ozone treatment for 20 minutes
MoO ₃ , BCP and Al are vacuum-deposited (3.0 × 10 ^-4 Pa or less)
Deposition rate: MoO ₃ = 0.2 to 0.3 Å / s, BCP = 0.2 to 0.3 Å / s, Al = 5.0 Å / s
SQ-EBT: PC ₇₁ BM 20 mg / mL CHCl ₃ solution as cast at 3000 rpm

That is, an ITO substrate in which an indium tin oxide (ITO) film is coated on the entire surface of a glass substrate is prepared as an anode, and 8 nm-thick molybdenum oxide (VI) (MoO ₃ ) is formed as a hole transport layer on the ITO electrode. ) Layer, and as an active layer thereon, SQ-EBT obtained in Example 3 was used as the donor material, and [6,6] -phenyl C71 methyl butyrate (PC ₇₁ BM) was used as the acceptor material. : A mixture with a mass ratio of 2 was applied so as to be 70 to 100 nm thick, and an electron transporting layer was applied thereon as a 5 nm thick 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline ( BCP) was laminated, and an aluminum plate with a thickness of 100 nm was laminated as a cathode to produce a BHJ type solar cell element (FIG. 78), and the characteristics were evaluated.
As element characteristics, measurement was performed under irradiation of 100 mW / cm ^{2 of} pseudo sunlight, and short circuit current density (J _sc) , open circuit voltage (V _oc) , _fill factor (FF), and photoelectric conversion efficiency (PCE) were obtained. External quantum yield (EQE) spectra were measured at room temperature.

物性評価の結果を表３に示す。比較のため、ＳＱ−ＥＰの評価結果も合わせて示す。 The structural formulas of PC ₇₁ BM and BCP are as follows.

The results of physical property evaluation are shown in Table 3. For comparison, the evaluation results of SQ-EP are also shown.

In the element structure used this time, in the element using SQ-EBT, V _OC (open circuit voltage) does not change much compared to the element using SQ-EP, and J _SC (short circuit current density) tends to be small. is there. In addition, an element using SQ-EBT has a larger R _S (series resistance), smaller R _Sh (parallel resistance), and lower FF (curve factor) than an element using SQ-EP. PCE (photoelectric conversion efficiency) also becomes low, and there is room for improvement in device performance.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Anode 3 Hole transport layer 4 Active layer 5 Electron transport layer 6 Cathode

Claims (3)

A squarylium derivative represented by the following general formula (1).

(In General Formula (1), R ₁ and R ₂ each independently represents a branched aliphatic substituent having 4 or more carbon atoms, and R _{3 to} R ₆ each independently represents a hydrogen atom, Represents a group substituent or an aromatic substituent, and R ₃ and R ₄ , or R ₅ and R ₆ may be linked to each other to form a ring, and X ¹ and X ² are each independently- Represents S- or -O-.) The squarylium derivative according to claim 1, wherein R _{3 to} R ₆ represent a hydrogen atom in the general formula (1).   The organic thin-film solar cell using the squarylium derivative | guide_body of Claim 1 or 2.

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