JP2018043943A - Novel squarylium derivative and organic thin film solar battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a novel squarylium derivative which enhances carrier mobility in a thin film state without changing energy level and further enhances energy conversion efficiency by improving a fill factor (FF); a donor material consisting of the novel squarylium derivative; and an organic thin film solar battery using the same.SOLUTION: There is provided a squarylium derivative represented by the following formula (1). (wherein, Rto Reach independently represent a monovalent aliphatic group or a monovalent aromatic group, when Rand Rare a monovalent aliphatic group, Rand Rmay be bonded to form a ring; when Rand Rare a monovalent aliphatic group, Rand Rmay be bonded to form a ring; X is a phenyl group or a thialilium group at the counter-position of benzothiophene; A is a divalent aromatic group.)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 the coating type organic thin film solar cell, [6,6] -phenyl C71 methyl butyrate (PC ₇₁ BM) having high solubility is usually used as an acceptor material. Since the LUMO level of PC ₇₁ BM is 4.0 eV, the donor material is required to have a LUMO level of about 3.7 eV.

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. Polymer type materials have improved energy conversion efficiency to about 12%, but polymer type materials are difficult to purify and highly purified, and the quality changes greatly between production lots to maintain quality. Is 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 mobility as low as about 10 ⁻⁵ cm ² / Vs at the present time, and the energy conversion efficiency finally exceeds 10% by using fullerene as an acceptor. 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. In a BHJ (bulk heterojunction) type element formed by coating, for example, in a mixed BHJ element using S-ASQ and PC ₇₁ BM (S-ASQ / PC ₇₁ BM (1: 7 (mass ratio)), PCE (Power conversion efficiency) is 5.52%, although the energy conversion efficiency of these derivatives is improved compared to the previous one, but still remains low. The organic thin-film solar cell using a squarylium derivative of the above has a problem that its V _OC (open circuit voltage) and J _SC (short circuit current density) are higher than other materials, but its FF (curve factor) is low. It was.

  In the S-ASQ, for example, it is considered that light in the visible to near infrared region can be absorbed by extending the π-conjugated system. Moreover, it is considered that if the hole mobility is improved by extending the π-conjugated system, various optical and electrochemical functions derived from freely moving π electrons can be improved.

  In the present invention, in order to provide a novel squarylium derivative useful for providing a high-efficiency device, focusing on the ASQ structure, the terminal substituent is improved, and without changing the energy level, in a thin film state. It is an object to improve the energy conversion efficiency by improving the FF (curve factor). Another object of the present invention is to provide an organic thin film solar cell using the obtained squarylium derivative.

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 to} R ⁶ each independently represents an aliphatic group or an aromatic group, and when R ² and R ³ are aliphatic groups, R ² and R ³ are linked to form a ring. When R ⁵ and R ⁶ are aliphatic groups, R ⁵ and R ⁶ may be linked to form a ring, and X is a phenyl group or a substituent represented by the following structural formula Represents a group, and Ar represents an aromatic group.

In the general formula (1), Ar preferably represents a thiophenylene group.
In the general formula (1), Ar represents a thiophenylene group, and R ^{1 to} R ⁶ preferably each independently represent an aliphatic group having 1 to 20 carbon atoms. The aliphatic group may be linear or branched.
The organic thin film solar cell of the present invention is characterized by using the above squarylium derivative.

  The squarylium derivative of the present invention has a bridge of benzo [1,2-b: 4,5-b ′] dithiophene (BDT), which is an aromatic condensed ring, on one of the conventionally known substituents at the end of S-ASQ. By adding a phenyl group or a squarylium derivative structure through a hanging structure, the π conjugation in the molecule is expanded, the hole mobility is improved, and the highest occupied molecular orbital (HOMO) Deepens and improves stability.

  In addition, the squarylium derivative of the present invention can expand the absorption wavelength in the solid thin film to the near-infrared region of 750 nm by extending the π conjugation, and can have appropriate electronic properties. In particular, since D-BDT-ASQ has a planar and asymmetric dimer structure, the face-on orientation during film formation is increased, hole mobility is improved, and 550 to 700 nm. Strong absorption is shown in the region.

  Therefore, according to the present invention, by using the squarylium derivative represented by the general formula (1), the resulting device has improved carrier mobility in a thin film state and improved FF value. A highly efficient organic thin-film solar cell with improved energy conversion efficiency can be provided.

FIG. 1 is a schematic cross-sectional view schematically showing the element structure of the organic thin film solar cell of the present invention. FIG. 2A is a diagram showing a ¹ H NMR spectrum of BDT-ASQ, and FIG. 2B is a diagram showing a ¹³ C NMR spectrum of BDT-ASQ. FIG. 3A is a view showing a ¹ H NMR spectrum of D-BDT-ASQ, and FIG. 3B is a view showing a ¹³ C NMR spectrum of D-BDT-ASQ. FIG. 4 is a diagram showing the results of thermogravimetry (TGA) of S-ASQ, BDT-ASQ, and D-BDT-ASQ. FIG. 5 (a) is a diagram showing a UV-Vis-NIR absorption spectrum of S-ASQ, BDT-ASQ, and D-BDT-ASQ in a chloroform solution, and FIG. 5 (b) shows S-ASQ, It is a figure showing the normalized UV-Vis-NIR absorption spectrum in the thin film of BDT-ASQ and D-BDT-ASQ. FIG. 6A is a diagram showing a voltage-current density relationship (JV characteristic) of S-ASQ, and FIG. 6B is a voltage-current density relationship of JDT-ASQ (JV characteristic). FIG. 6C is a diagram showing a voltage-current density relationship (JV characteristics) of D-BDT-ASQ, and FIG. 6D is a diagram showing S-ASQ, BDT-ASQ, and It is a figure showing the relationship of the wavelength-external quantum efficiency (EQE) of D-BDT-ASQ. 6 (a) to 6 (c), 1 represents the result measured at room temperature after thermal annealing of the active layer at 80 ° C. for 15 minutes, and 2 represents the result measured at 80 ° C. . FIG. 7A is a diagram showing a voltage-current density relationship (JV characteristics) of a mixed BHJ element using D-BDT-ASQ and PC ₇₁ BM at various mass ratios. b) is a diagram illustrating the relationship between wavelength and external quantum efficiency (EQE) of a mixed BHJ element using D-BDT-ASQ and PC ₇₁ BM at various mass ratios.

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 the general formula (1), R ^{1 to} R ⁶ are each independently a monovalent aliphatic group or a monovalent aromatic group.
The aliphatic group may widely include groups other than aromatic groups, and specifically refers to a linear or branched aliphatic group having 1 to 20 carbon atoms. Further, within a range not impairing the effects of the present invention, a part of the hydrogen atoms constituting the aliphatic group is substituted with, for example, a nitrogen atom, a sulfur atom, an oxygen atom, a phosphorus atom, a silicon atom, or a substituent containing these. May be.
Examples of the aliphatic group having 1 to 20 carbon atoms include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, and heptyl. Group, octyl group, ethylhexyl group, dodecyl group and the like. Of these, isopropyl group, butyl group, isobutyl group, sec-butyl group, hexyl group, octyl group, and ethylhexyl group are more preferable, and butyl group and ethylhexyl group are particularly preferable.
The aromatic group may be a monocyclic aryl group or heteroaryl group, or may be a polycyclic (fused ring) aryl group or heteroaryl group. Moreover, some hydrogen atoms on the aromatic ring in the aromatic group may be substituted with, for example, a methyl group, an isopropyl group, an isobutyl group, or the like.
The aromatic group is preferably an aromatic group having 6 to 50 carbon atoms.
Examples of the aromatic group having 6 to 50 carbon atoms include phenyl group, pyridyl group, thiophenyl group, biphenyl group, naphthyl group, triphenylenyl group, terphenyl group, quarterphenyl group, anthracenyl group, benzothiophenyl group, and benzofuranyl group. , Dibenzothiophenyl group, and dibenzofuranyl group. Of these, a phenyl group, a pyridyl group, a thiophenyl group, a biphenyl group, a benzothiophenyl group, a benzofuranyl group, and the like are more preferable.
When R ² and R ³ are aliphatic groups, R ² and R ³ may be linked to form a 4-membered ring, 5-membered ring or 6-membered ring, and when R ⁵ and R ⁶ are aliphatic groups , R ⁵ and R ⁶ may be linked to form a 4-membered, 5-membered or 6-membered ring.

Ａｒは２価の芳香族基を示す。芳香族基としては、例えば、フェニレン基、ピリジニレン基、チオフェニレン基（チエニレン基）、ビフェニリレン基、ナフチレン基、トリフェニレニレン基、ターフェニリレン基、クオーターフェニリレン基、アセアントリレニレン基、ベンゾチオフェニル基、ベンゾフラニル基、ジベンゾチオフェニル基、及びジベンゾフラニル基等が挙げられる。これらのうち、チオフェニレン基、ベンゾチオフェニル基、及びベンゾフラニル基等が好ましく、特に２，５−チオフェニレン基が好ましい。 X represents a phenyl group or a monovalent substituent represented by the following structural formula.

Ar represents a divalent aromatic group. Examples of the aromatic group include a phenylene group, a pyridinylene group, a thiophenylene group (thienylene group), a biphenylylene group, a naphthylene group, a triphenylenylene group, a terphenylylene group, a quarterphenylylene group, an aceanthryllenylene group, and a benzothiophenyl group. Benzofuranyl group, dibenzothiophenyl group, dibenzofuranyl group and the like. Of these, a thiophenylene group, a benzothiophenyl group, a benzofuranyl group, and the like are preferable, and a 2,5-thiophenylene group is particularly preferable.

Specifically, the compound represented by the general formula (1) is preferably a compound BDT-ASQ or D-BDT-ASQ represented by the following structural formula.

したがって、上記スクアリリウム誘導体は、ＰＣ₇₁ＢＭ等のフラーレン又はその誘導体からなるアクセプター材料に対するドナー材料として好適に用いることができる。 The squarylium derivative represented by the general formula (1) includes benzo [1,2-b: 4,5-b ′] dithiophene, which is an aromatic condensed ring, on one of the terminal substituents of the conventional S-ASQ. By having a structure in which a phenyl group or a squarylium derivative is added via a bridge structure of (BDT), it can have a wide absorption in the deep HOMO and near-infrared regions, and has a long-chain branched structure. By having an aromatic hydrocarbon group, the solubility in an organic solvent is improved. For example, when the terminal substituent of the squarylium derivative is an aromatic group, or one of the terminal substituents is an aromatic group. Compared with the case where the other is a linear aliphatic group, the molar absorption 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 BDT-ASQ is shown as an example.
3-((5-Bromo-1-butyl-3,3-dimethylindoline-2-ylidene) methyl) 4-ethoxycyclobut-3-ene-1,2-dione and 4,8-bis [5- ( 2-ethylhexyl) thiophen-2-yl] -2,6-bis (trimethylstannyl) benzo [1,2-b: 4,5-b ′] dithiophene in toluene in the presence of Pd (PPh ₃ ) ₄ After heating to reflux for 36 hours in solution, the resulting reaction mixture is purified by silica gel column chromatography to give compounds 1a and 1b in 29% and 36% yield, respectively. Of the obtained compounds 1a and 1b, compound 1a is dissolved in acetone, 8 mL of 6M hydrochloric acid is dropped, and the mixture is heated to reflux for 5 hours to obtain compound 2a in a yield of 82%. Compound 2a and 5- (1,3,3a, 8b-tetrahydrocyclopenta [b] indol-4 (2H) -yl) benzene-1,3-diol are then mixed in a 1: 1 mixture of toluene and n-butanol. BDT-ASQ, a dark red solid, is obtained by reacting in solution at 140 ° C. for 36 hours (yield 70%).
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 also referred to as “solar cell element”) has an element structure in which an active layer including an interface structure of a donor and an acceptor is laminated between a pair of electrodes (anode 2 and cathode 6). Have Charges (electrons, holes) are generated at the interface where the donor material and the acceptor material are interlaced with each other. Typically, as shown in FIG. 1, it 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, a material having a surface resistance of usually 1000Ω (ohms) or less, preferably 100Ω or less in a temperature range of −5 to 80 ° C. is used.
When extracting light from the anode side of the solar cell element (bottom emission), the anode needs to be transparent to visible light (average transmittance for light of 380 to 680 nm is 50% or more). For the material of the anode, indium tin oxide (ITO), indium-zinc oxide (IZO), or the like is used. Of these, ITO is preferable from the viewpoint of availability.

  In addition, when light is extracted from the cathode side of the device (top emission), the light transmittance of the anode is not limited. Therefore, in addition to ITO and IZO, the anode material includes stainless steel, copper, silver, gold, Platinum, tungsten, titanium, tantalum, niobium, or an alloy thereof is used.

  In the case of bottom emission, the thickness of the anode 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 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, In addition, a known coating method such as an ink jet printing method can be applied.

Further, as the material for the anode buffer layer, a material having high resistance to an organic solvent is usually used from the viewpoint of preventing the anode buffer layer from being dissolved during the formation of the active layer.
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 active layer in the solar cell element includes an active layer, a hole transport layer, and an electron transport layer.
The squarylium derivative represented by the general formula (1) is used for the active layer. 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 may be inserted between the hole transport layer and the electron transport layer as shown in FIG. 1 for the purpose of supplementing the carrier transport property of the active layer, and the acceptor material may be inserted in the active layer. In addition, a hole transporting compound or an electron transporting compound may be dispersed and used.

Examples of the hole transporting compound include metal oxides such as molybdenum oxide (VI) (MoO ₃ ), vanadium oxide (V ₂ O ₅ ), tungsten oxide (WO ₃ ), and ruthenium oxide (RuO ₂ ); Low molecular weight materials such as azatriphenylene hexacarbonyl (HATCN) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4TCNQ); and polymerizable functional groups in the low molecular weight material And the like which are polymerized by introducing.

  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) Oligopyridine derivatives such as -pyridylphenyl) -2-methylpyrimidine); low molecular materials such as [60] fullerene and nanocarbon derivatives such as [70] fullerene; and a polymerizable functional group introduced into the low molecular material. And polymerized.

<Hole blocking layer>
A hole blocking layer may be provided adjacent to the cathode side of the active layer for the purpose of suppressing the passage of holes through the active layer and efficiently recombining with electrons in the active layer. 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.

  Furthermore, an exciton block layer may be provided adjacent to the cathode side of the active layer in order to prevent excitons (excitons) 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. Specifically, a known cathode material of an alloy such as Al, MgAg, AlLi, or AlCa can be used. As a film forming method of 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 is usually 10 nm to 1 μm, preferably 50 to 500 nm.

  In addition, a metal layer having a lower work function than the cathode is inserted as a cathode buffer layer between the cathode and the layer adjacent to the cathode in order to lower the electron injection barrier from the cathode to the active layer and increase the efficiency of electron injection. May be. 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 constituting the element.
For the bottom emission type solar cell element, a substrate 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, and nylon resin. A transparent plastic such as silicon, and a substrate made of silicon can be used.

The top emission type solar cell element includes, in addition to the substrate used for the bottom emission type solar cell element, stainless steel, copper, silver, gold, platinum, tungsten, titanium, tantalum, niobium, or an alloy thereof. Can be used.
Although the thickness of a board | substrate 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 active layer is formed by, 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 method). It can be formed by wet processes such as 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. it can. 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, a metal oxide, a metal fluoride, a metal boride, or the like is used. The protective cover is made of a glass plate, a plastic plate having 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. Are 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.

[Synthesis of BDT-ASQ and D-BDT-ASQ]
BDT-ASQ and D-BDT-ASQ were synthesized according to the following scheme.

Synthesis Example 1 Synthesis of Compounds 1a and 1b 3-((5-Bromo-1-butyl-3,3-dimethylindoline-2-ylidene) methyl) 4-ethoxycyclobut-3-ene-1,2- Dione (2.40 g, 5.75 mmol) and 4,8-bis [5- (2-ethylhexyl) thiophen-2-yl] -2,6-bis (trimethylstannyl) benzo [1,2-b: 4 , 5-b ′] dithiophene (2.00 g, 2.21 mmol) was dissolved in 200 mL of toluene and degassed with nitrogen for 30 minutes. Then 660 mg of Pd (PPh ₃ ) ₄ was added under nitrogen and the mixture was heated to reflux for 36 hours. After removing the solvent, the crude product was purified by silica gel column chromatography (eluent; dichloromethane / ethyl acetate = 30: 1), 0.80 g (yield 29%) of Compound 1a as a yellow solid, and Compound 1b 1.02 g (yield 36%) was obtained.

The measurement results of ¹ H NMR of compounds 1a and 1b are shown below.
Compound 1a; 3-((5- (4,8-bis (5- (2-ethylhexyl) thiophen-2-yl) benzo [1,2-b: 4,5-b ′] dithiophen-2-yl) -1-butyl-3,3-dimethylindoline-2-ylidene) methyl) -4-ethoxyoctbut-3-ene-1,2-dione
¹ H NMR (400 MHz, THF-d8, ppm) δ: 7.86 (s, 1H, ArH), 7.81 (s, 1H, ArH), 7.73 (d, 3H, J = 8.0 HZ, ArH), 7.65 (d , 1H, J = 8.4 HZ, ArH), 7.40-7.29 (m, 5H, ArH), 7.04 (d, 1H, J = 8.4 HZ, ArH), 7.00 (d, 2H, J = 3.2 HZ, ArH), 5.46 (s, 1H, = CH-), 4.86 (q, 2H, J = 7.2 HZ, -OCH _2- ), 3.93 (t, 2H, J = 7.2 HZ, -NCH _2- ), 2.94 (d, 4H , J = 6.8 HZ, -CH _2- ), 1.78-1.72 (m, 2H, -CH _2- ), 1.66 (s, 6H, -CH ₃ ), 1.52-1.35 (m, 23H, -CH _2- , -CH ₃ ), 1.00-0.92 (m, 15H, -CH ₃ )
Compound 1b; 4,4 ′-(5,5 ′-(4,8-bis (5- (2-ethylhexyl) thiophen-2-yl) benzo [1,2-b: 4,5-b ′] dithiophene -2,6-diyl) bis (1-butyl-3,3-dimethylindoline-5-yl-2-ylidene)) bis (methanylylidene)) bis (3-ethoxycyclobut-3-ene-1,2- Zeon)
¹ H NMR (400 MHz, THF-d8, ppm) δ: 7.79 (s, 2H, ArH), 7.70 (s, 2H, ArH), 7.64 (d, 2H, J = 8.4 HZ, ArH), 7.38 (d , 2H, J = 3.2 HZ, ArH), 7.04 (d, 2H, J = 8.4 HZ, ArH), 7.00 (d, 2H, J = 3.2 HZ, ArH), 5.46 (s, 2H, = CH-), 4.87 (q, 4H, J = 7.2 HZ, -OCH _2- ), 3.93 (t, 4H, J = 7.6 HZ, -NCH _2- ), 2.94 (d, 4H, J = 6.4 HZ, -CH _2- ) , 1.76-1.67 (m, 4H, -CH _2- ), 1.66 (s, 12H, -CH ₃ ), 1.50-1.39 (m, 28H, -CH _2- , -CH ₃ ), 1.01-0.93 (m, 18H, -CH ₃ ).

[Synthesis Example 2] Synthesis of Compound 2a Compound 1a (0.80 g, 0.81 mmol) was dissolved in 80 mL of acetone and heated to reflux for 30 minutes. To this solution, 8 mL of 6M hydrochloric acid was added dropwise, and the mixture was further heated to reflux for 5 hours. Then 200 mL of deionized water was added dropwise and a yellow solid precipitated in the reaction mixture. This mixture was filtered, and the product was purified with deionized water to obtain 0.64 g (yield 82%) of compound 2a.

The measurement result of ¹ H NMR of compound 2a is shown below.
Compound 2a; 3-((5- (4,8-bis (5- (2-ethylhexyl) thiophen-2-yl) benzo [1,2-b: 4,5-b ′] dithiophen-2-yl) -1-butyl-3,3-dimethylindoline-2-ylidene) methyl) -4-hydroxycyclobut-3-ene-1,2-dione
¹ H NMR (400 MHz, THF-d8, ppm) δ: 7.86 (s, 1H, ArH), 7.80 (s, 1H, ArH), 7.73 (d, 3H, J = 8.0 HZ, ArH), 7.64 (d , 1H, J = 8.4 HZ, ArH), 7.40-7.28 (m, 5H, ArH), 7.01-6.99 (m, 3H, ArH), 5.55 (s, 1H, = CH-), 3.91 (t, 2H, J = 7.2 HZ, -NCH _2- ), 2.94 (d, 4H, J = 6.8 HZ, -CH _2- ), 1.77-1.72 (m, 2H, -CH _2- ), 1.67 (s, 6H, -CH ₃ ), 1.53-1.35 (m, 20H, -CH _2- ), 1.00-0.92 (m, 15H, -CH ₃ ).

[Synthesis Example 3] Synthesis of Compound 2b Compound 1b (0.90 g, 0.72 mmol) was dissolved in a mixed solvent of 60 mL of acetone and 110 mL of THF and heated to reflux for 30 minutes. Into this solution, 20 mL of 6M hydrochloric acid acetone solution was dropped and heated to reflux for 3 hours. Then 600 mL of deionized water was added dropwise and an orange solid precipitated in the reaction mixture. The mixture was filtered, and the product was purified with deionized water to obtain 0.78 g (yield 91%) of compound 2b.

The measurement result of ¹ H NMR of compound 2b is shown below.
Compound 2b; 4,4 ′-((5,5 ′-(4,8-bis (5- (2-ethylhexyl) thiophen-2-yl) benzo [1,2-b: 4,5-b ′] Dithiophene-2,6-diyl) bis (1-butyl-3,3-dimethylindoline-5-yl-2-ylidene)) bis (methanylylidene)) bis (3-hydroxycyclobut-3-ene-1,2 -Dione)
¹ H NMR (400 MHz, THF-d8, ppm) δ: 7.78 (s, 2H, ArH), 7.69 (s, 2H, ArH), 7.63 (d, 2H, J = 8.4 HZ, ArH), 7.38 (d , 2H, J = 3.6 HZ, ArH), 7.02-7.00 (m, 4H, ArH), 5.55 (s, 2H, = CH-), 3.92 (t, 4H, J = 6.8 HZ, -NCH _2- ), 2.94 (d, 4H, J = 6.4 HZ, -CH _2- ), 1.77-1.70 (m, 4H, -CH _2- ), 1.67 (s, 12H, -CH ₃ ), 1.55-1.35 (m, 22H, -CH _2- ), 1.01-0.93 (m, 18H, -CH ₃ ).

Example 1 Synthesis of BDT-ASQ Compound 2a (0.50 g, 0.52 mmol) and 5- (1,3,3a, 8b-tetrahydrocyclopenta [b] indole-4 (2H) -yl) benzene 1,3-diol (0.20 g, 0.73 mmol) was dissolved in a mixed solvent of 50 mL of toluene and 50 mL of n-butanol and degassed with nitrogen for 30 minutes. The solution was then heated at 140 ° C. for 36 hours. The crude product was purified by silica gel column chromatography (eluent; dichloromethane / ethyl acetate = 10: 1) to obtain a dark red solid. Recrystallization from a solvent of dichloromethane and methanol 4: 1 (volume ratio) gave 0.44 g of a dark red solid (yield 70%).

The measurement results of melting point (mp), ¹ H NMR (FIG. 2 (a)), ¹³ C NMR (FIG. 2 (b)), purity (purity) and HR-MS (high resolution mass spectrum) of BDT-ASQ are shown. .
BDT-ASQ; 4-((5- (4,8-bis (5- (2-ethylhexyl) thiophen-2-yl) benzo [1,2-b: 4,5-b ′] dithiophen-2-yl ) -1-Butyl-3,3-dimethyl-3H-indol-1-ium-2-yl) methylene) -2- (2,6-dihydroxy-4- (1,3,3a, 8b-tetrahydrocyclopenta) [B] Indol-4 (2H) -yl) phenyl) -3-oxocyclobut-1-enolate
mp: 206-207 ° C;
¹ H NMR (400 MHz, CDCl ₃ , ppm): δ: 12.40 (s, 2H, -OH), 7.84 (d, 2H, J = 1.6 HZ, ArH), 7.72-7.66 (m, 4H, ArH), 7.43-7.33 (m, 6H, ArH), 7.19-7.15 (m, 2H, ArH), 7.06 (d, 1H, J = 8.0 HZ, ArH), 6.97-6.93 (m, 3H, ArH), 6.35 (s , 2H, ArH), 5.90 (s, 1H, = CH-), 4.70 (t, 1H, J = 8.0, 2.8 HZ, -NCH-), 4.04 (t, 2H, J = 7.2 HZ, -NCH _2- ), 3.92 (t, 1H, J = 8.0 HZ, -CH-), 2.93 (d, 4H, J = 6.4 HZ, -CH _2- ), 2.09-1.91 (m, 4H, -CH _2- ), 1.84 -1.64 (m, 11H, -CH _2- , -CH ₃ ), 1.51-1.36 (m, 19H, -CH _2- ), 1.02-0.93 (m, 15H, -CH ₃ );
¹³ C NMR (100 MHz, CDCl ₃ , ppm): δ: 172.6, 170.9, 169.5, 163.1, 152.9, 146.1, 145.0, 143.9, 143.5, 143.3, 141.7, 139.0, 138.7, 137.7, 137.4, 137.0, 136.9, 134.1 , 131.7, 128.9, 128.5, 127.9, 127.8, 127.4, 126.6, 126.4, 125.6, 125.5, 124.9, 123.7, 123.6, 122.5, 120.3, 119.1, 118.9, 113.8, 110.7, 105.0, 96.7, 88.0, 68.7, 50.1, 45.5 , 44.2, 41.5, 34.6, 34.3, 33.7, 32.5, 29.4, 28.9, 26.8, 25.8, 24.3, 23.1, 20.3, 14.2, 13.8, 11.0;
purity: 100% (HPLC, eluent: THF / H ₂ O = 83: 17);
HR-MS (ESI): m / z [M + H] ⁺ calcd. For C ₇₆ H ₈₁ N ₂ O ₄ S ₄ , 1213.5079; found, 1213.5074;
Elemental analysis: calcd. For C ₇₆ H ₈₀ N ₂ O ₄ S ₄ : C75.21, H 6.64, N 2.31, S 10.57; found, C 75.28, H 6.93, N 2.26, S 10.75.
FIG. 4 shows the results of thermogravimetry (TGA) of BDT-ASQ. It can be seen that BDT-ASQ has high thermal stability.

Example 2 Synthesis of D-BDT-ASQ Compound 2b (0.51 g, 0.43 mmol) and 5- (1,3,3a, 8b-tetrahydrocyclopenta [b] indol-4 (2H) -yl) Benzene-1,3-diol (0.30 g, 1.12 mmol) was dissolved in 60 mL of toluene and 60 mL of n-butanol, degassed with nitrogen for 30 minutes, and then heated at 140 ° C. for 36 hours. After finishing the reaction and cooling, 120 mL of methanol was added dropwise to obtain a dark red solid. The dark red solid was filtered off and purified by silica gel column chromatography (eluent, dichloromethane / ethyl acetate = 100: 1). The obtained dark red solid was recrystallized with a mixed solvent of dichloromethane and hexane (dichloromethane: hexane = 10: 1) to obtain a black solid (0.54 g, yield 75%).

Measurement results of melting point (mp), ¹ H NMR (FIG. 3 (a)), ¹³ C NMR (FIG. 3 (b)), purity (purity) and HR-MS (high resolution mass spectrum) of D-BDT-ASQ Indicates.
D-BDT-ASQ; 4,4 ′-((5,5 ′-(4,8′-bis (5- (2-ethylhexyl) thiophen-2-yl) benzo [1,2-b: 4,5 -B '] dithiophene-2,6-diyl) bis (1-butyl-3,3-dimethyl-3H-indole-1-ium-5,2-diyl)) bis (methanylylidene)) bis (2- (2 , 6-Dihydroxy-4- (1,3,3a, 8b-tetrahydrocyclopenta [b] indole-4 (2H) -yl) phenyl) -3-oxocyclobut-1-enolate)
mp303-304 ℃;
¹ H NMR (400 MHz, CDCl ₃ , ppm) δ: 12.41 (s, 4H, -OH), 7.84 (s, 2H, ArH), 7.71 (d, 2H, J = 8.4 HZ, ArH), 7.66 (d , 2H, J = 1.6 HZ, ArH), 7.39 (t, 4H, J = 4.0 HZ, ArH), 7.18 (t, 4H, J = 6.0 HZ, ArH), 7.09 (d, 2H, J = 8.4 HZ, ArH), 6.99 (d, 2H, J = 3.2 HZ, ArH), 6.97 (t, 2H, J = 7.6 HZ, ArH), 6.34 (s, 4H, ArH), 5.91 (s, 2H, = CH-) , 4.70 (t, 2H, J = 8.0, 2.8 HZ, -NCH-), 4.08 (t, 4H, J = 7.2 HZ, -NCH _2- ), 3.92 (t, 2H, J = 7.6 HZ, -CH- ), 2.94 (d, 4H, J = 6.8 HZ, -CH _2- ), 2.11-1.90 (m, 10H, -CH _2- ), 1.85-1.64 (m, 20H, -CH _2- , -CH ₃ ) , 1.53-1.36 (m, 20H, -CH _2- ), 1.03-0.93 (m, 18H, -CH ₃ );
¹³ C NMR (100 MHz, CDCl ₃ , ppm) δ: 172.5, 171.1, 169.4, 163.1, 153.0, 146.2, 143.9, 143.8, 143.3, 141.8, 138.9, 137.6, 137.0, 136.8, 131.6, 127.9, 127.4, 126.7, 125.6, 124.9, 123.7, 122.6, 120.3, 119.1, 113.8, 110.7, 105.0, 96.7, 88.0, 68.7, 50.1, 45.5, 44.2, 41.5, 34.6, 34.3, 33.7, 32.5, 29.4, 28.9, 26.8, 25.8, 24.3, 23.1, 20.3, 14.2, 13.8, 11.0;
purity: 100% (HPLC, eluent: THF / H ₂ O = 83: 17);
HR-MS (ESI): m / z [M + 2H] ⁺ calcd.for C ₁₀₆ H ₁₁₂ N ₄ O ₈ S ₄ , 1697.7397; found, 1697.7400;
elemental anal.Calcd.for C ₁₀₆ H ₁₁₀ N ₄ O ₈ S ₄ : C 75.05, H 6.54, N 3.30, S 7.56; found, C 75.08, H 6.84, N 3.25, S 7.50.
FIG. 4 shows the results of thermogravimetry (TGA) of D-BDT-ASQ. It can be seen that D-BDT-ASQ has high thermal stability.

図４にＳ−ＡＳＱの熱重量測定（ＴＧＡ）の結果を示す。 [Comparative Example 1]
As a comparative example, S-ASQ having the following structural formula was used.

FIG. 4 shows the results of thermogravimetry (TGA) of S-ASQ.

Test Example 1 Optical and Electrochemical Evaluation S-ASQ of Comparative Example 1 and BDT-ASQ and D-BDT-ASQ obtained in Examples 1 and 2 were dissolved in chloroform, and 3.00 × A 10 ⁻⁶ mol / L solution was prepared.
When the chloroform solutions prepared for each of S-ASQ, BDT-ASQ, and D-BDT-ASQ are measured by placing them in quartz glass (FIG. 5 (a)), and when measured as a cast film (FIG. 5). (B)) was subjected to ultraviolet-visible-near-infrared spectroscopic analysis (UV-Vis-NIR).

In the UV-Vis-NIR absorption spectrum, in the case of a cast film (FIG. 5B), BDT-ASQ and D-BDT-ASQ were shifted by 34 nm and 47 nm longer than S-ASQ, respectively. Specifically, the wavelength was increased in the order of S-ASQ <BDT-ASQ <D-BDT-ASQ. However, the energy difference was only about 0.03 eV.
S-ASQ and BDT-ASQ, as shown in Table 1, showed high molar extinction coefficient of almost equal to ^{(~2.0M -1 cm -1), D} -BDT-ASQ in 4.0 M ^-1 cm ^It showed a high value of ^-1 .
Both BDT-ASQ and D-BDT-ASQ had a longer wavelength shift and a broader waveform when measured with a cast film than when measured with a solution. The absorption band observed at 300 to 450 nm is considered to be due to the π-π ^* transition of the BDT segment. From the onset position of the absorption spectrum, the optical band gaps (E _g ^opt ) of BDT-ASQ and D-BDT-ASQ are estimated to be 1.39 eV and 1.36 eV, respectively, and 0.02 eV from S-ASQ. And 0.05 eV lower. The optical band gap (E _g ^opt ) of 1.36 eV of D-BDT-ASQ is the lowest value among ASQ-based photovoltaic materials known so far.

  Moreover, in cyclic voltammetry (CV), as shown in Table 1, the HOMO and LUMO energies of BDT-ASQ are −5.16 eV and −3.54 eV, respectively, and the HOMO and LUMO energies of D-BDT-ASQ, respectively. Were −5.15 eV and −3.55 eV, respectively. Compared to the HOMO and LUMO energies of S-ASQ (HOMO: -5.10 eV and LUMO: -3.43 eV), BDT-ASQ reduces HOMO by 0.06 eV and LUMO decreases by 0.11 eV. In D-BDT-ASQ, HOMO decreased by 0.05 eV and LUMO decreased by 0.12 eV, suggesting that the band gap was reduced by introducing the BDT structure.

[Test Example 2] Photovoltaic evaluation of organic solar cell As an anode, an ITO substrate in which an indium tin oxide (ITO) film was coated on the entire surface of a glass substrate was prepared, and a hole transport layer was formed on the ITO electrode. A molybdenum (VI) (MoO ₃ ) layer having a thickness of 6 nm is stacked, and as an active layer thereon, BDT-ASQ, D-BDT-ASQ, or S-ASQ is used as a donor material, and an acceptor material is used. [6,6] -Phenyl C71 methyl butyrate (PC ₇₁ BM) mixed at a mass ratio of 1: 7 was applied to a thickness of 70 to 100 nm, and an electron transport layer was formed thereon with a thickness of 10 nm. Of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) and a 100 nm thick aluminum plate as a cathode, Solar cell element: to produce a _{(ITO / MoO 3 / ASQ PC} 71 BM / BCP / Al structure) was subjected to characteristic evaluation. Note that “ASQ” described in the element structure represents BDT-ASQ, D-BDT-ASQ, or S-ASQ.

Ｓ−ＡＳＱ、ＢＤＴ−ＡＳＱ、及びＤ−ＢＤＴ−ＡＳＱのそれぞれの素子特性結果を表２及び図６（ａ）〜（ｄ）に示す。

The element characteristic results of S-ASQ, BDT-ASQ, and D-BDT-ASQ are shown in Table 2 and FIGS. 6 (a) to 6 (d).

From Table 2, the element using S-ASQ had a PCE of 3.82%, V _oc of 0.87 V, J _sc of 10.71 mAcm ⁻² , and FF of 0.41, and an element using BDT-ASQ. Then, PCE is 4.11%, V _oc is 0.93 V, J _sc is 10.79 mAcm ⁻² , and FF is 0.41. In the element using D-BDT-ASQ, PCE is 5.75%. , V _oc was 0.92 V, J _sc was 12.50 mAcm ⁻² , and FF was 0.50. BDT-ASQ and D-BDT-ASQ were found to have a V _oc higher by 0.05 to 0.06 V than S-ASQ. This is consistent with the CV result that the HOMO energy levels of BDT-ASQ and D-BDT-ASQ are 0.05-0.06 eV lower than S-ASQ.
The PCE of S-ASQ was 4.31%, while the PCE of BDT-ASQ and D-BDT-ASQ were 4.77% and 6.33%, respectively.
Since the solar cell is assumed to be used outside and at a temperature higher than normal temperature, the experiment was performed under the condition of 80 ° C. In all elements of S-ASQ, BDT-ASQ and D-BDT-ASQ, V _oc decreased slightly and J _sc and FF increased slightly. Further, in the element using D-BDT-ASQ, PCE showed the highest value of 7.41%.

Next, BHJ-type solar cell devices are manufactured using D-BDT-ASQ, which is a donor material, and [6,6] -phenyl C71 methyl butyrate (PC ₇₁ BM), which is an acceptor material, in various mass ratios. FIG. 7A and FIG. 7B and Table 3 show the result of characteristic evaluation in this case.

When the mass ratio (D / A) between the donor and the acceptor was 1: 3 to 1: 9, the PCE of the device exceeded 5%. It was found that when D / A was around 1: 7, PCE was the highest value.
In D-BDT-ASQ, since it has a planar asymmetric dimer structure, BDT having a bulky condensed ring structure plays the role of a donor. Compared to S-ASQ, D-BDT-ASQ not only has a HOMO energy level lower by 0.05 eV, but also has a longer wavelength shift. More importantly, the hole mobility of D-BDT-ASQ is higher than that of S-ASQ in both single films and mixed films with acceptor materials. As a result, the element of the BHJ type solar cell using D-BDT-ASQ has a higher V _oc , J _sc , and FF and a D / A ratio of 1: 7 than when S-ASQ is used. In the vicinity, the PCE showed the excellent result of the highest value of 7.41%. This figure is the highest among the squalene-based single-junction organic solar cells known so far, and improvement of such a planar asymmetric dimer structure will lead to high-performance photovoltaics in the future. It can be said that this is an important method for obtaining electric materials.

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

Claims (4)

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

(In the general formula (1), R ^{1 to} R ⁶ each independently represents a monovalent aliphatic group or a monovalent aromatic group,
When R ² and R ³ are aliphatic groups, R ² and R ³ may be linked to form a ring,
When R ⁵ and R ⁶ are aliphatic groups, R ⁵ and R ⁶ may be linked to form a ring,
X represents a phenyl group or a monovalent substituent represented by the following structural formula;
Ar represents a divalent aromatic group. )

  The squarylium derivative according to claim 1, wherein Ar in the general formula (1) represents a thiophenylene group. In the general formula (1),
Ar represents a thiophenylene group, and
The squarylium derivative according to claim 1 or 2, wherein R ^{1 to} R ⁶ each independently represents a monovalent aliphatic group having 1 to 20 carbon atoms.   The organic thin-film solar cell using the squarylium derivative as described in any one of Claims 1-3.

Images