JP2010016212A - Organic thin-film photoelectric conversion element and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-efficiency organic thin-film photoelectric conversion element using a low-molecular compound. <P>SOLUTION: In manufacturing an organic thin-film photoelectric conversion element, a π-conjugated low-molecular compound is formed into a film by a coating method, some or all of substituent groups are detached from the π-conjugated low-molecular compound to turn the film into an organic semiconductor thin film, and then another semiconductor material is formed into a film on the organic semiconductor thin film to fabricate a photoelectric conversion layer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a highly efficient organic thin film photoelectric conversion element and a method for producing the same.

  In the ubiquitous information society, there is a need for information terminals that can be used anytime and anywhere. For this reason, flexible, lightweight, and inexpensive electronic devices are desired, but conventional electronic devices using inorganic semiconductor materials such as silicon cannot sufficiently meet these demands. Therefore, in recent years, research on electronic devices using organic semiconductor materials that can meet these demands has been actively conducted (Non-patent Documents 1 and 2).

  By using an organic semiconductor material as a photoelectric conversion material, an organic photoelectric conversion element such as an optical sensor (Patent Documents 1 to 3) or an organic thin film solar cell (Non-Patent Documents 3 and 4) can be obtained. These devices are easier to manufacture than devices using inorganic semiconductor materials such as silicon. Especially when organic semiconductor materials that can be deposited by wet processes are used, large-area devices can be fabricated at low temperature and low cost. I have the potential to do it. The organic thin film photoelectric conversion element reported to date has the highest efficiency, and is a blend of P3HT (poly (3-hexylthiophene)) and PCBM ([6,6] -phenyl-C61-butyric acid methyl ester). It is an element using a film as a photoelectric conversion layer (Non-patent Documents 3 and 4). In this blend film, there are many contact interfaces between P3HT, which is a p-type material, and PCBM, which is an n-type material, so that charge separation occurs with high efficiency. In addition, they are phase-separated to form minute domains, and the generated charges are taken out from the respective electrodes through the domains connected in a daisy chain. However, charge transport depends on the charge transport path formed by chance, and there is a problem in reproducibility and durability. Therefore, there is a need for a method for forming a composite structure of a p-type material and an n-type material that can achieve both charge separation and charge transport at a high level.

  In addition, high molecular organic semiconductor materials represented by P3HT are highly reproducible because of the distribution of molecular weight, which is difficult to purify and cannot be purified by sublimation or recrystallization compared to low molecular organic semiconductor materials. On the other hand, materials such as pentacene and phthalocyanine, which are low molecular organic semiconductor materials and have high charge transporting ability, generally have low solubility and high crystallinity. There was a problem of being low. There have been reports of examples of devices fabricated by applying low molecular weight organic semiconductor materials by introducing appropriate substituents, but photoelectric conversion can be achieved by applying a mixed solution of p-type materials and n-type materials consisting of low molecules. When a layer is manufactured, a film in which a p-type material and an n-type material are generally mixed at a molecular level is formed, and a charge transport path is not formed well. Therefore, it is difficult to obtain a high-performance element (Non-patent Document 5). ). On the other hand, it is difficult to apply the upper layer without damaging the lower layer, and it is necessary to prepare either the upper layer or the lower layer by a vacuum deposition method. (Non-Patent Document 6). Therefore, development of an organic thin film photoelectric conversion element that can be produced by a solution coating method using a low molecular weight compound and exhibits high efficiency is demanded.

Chemical Reviews, 2007, 107, 1296-1323. “Organic Field-Effect Transistors” (2007, CRC Press), pages 159-228. "Organic Photovoltaics" (2005, Taylor & Francis) 49-104 Chemical Reviews, 2007, 107, 1324-1338. Materials Today, 2007, 10, 34-41. The latest collection of latest functional pigments (2007, Technical Information Association) pages 320-328. JP 2003-234460 A JP 2003-332551 A JP-A-2005-268609

  This invention is made | formed in view of the said background, The objective is to obtain a highly efficient organic thin film photoelectric conversion element using a low molecular weight compound.

As a result of intensive studies, the inventors have found the following organic thin film photoelectric conversion element and a method for producing the same as means for solving the above problems.
(1) After coating and film-forming a π-conjugated low molecular weight compound, an organic semiconductor thin film is formed by removing at least a part of substituents from the π-conjugated low molecular weight compound, and another semiconductor is formed on the film. An organic thin film photoelectric conversion element, wherein a photoelectric conversion layer is formed by depositing a material.
(2) The organic thin film photoelectric conversion device according to (1), wherein the π-conjugated low molecular weight compound is a phthalocyanine compound.
(3) The organic thin film photoelectric conversion element according to (1) or (2), wherein the substituent is a substituent containing a sulfonyl group as a partial structure.
(4) The organic thin film according to any one of (1) to (3), wherein the total formula weight of the detached substituents is 30% to 70% of the molecular weight of the π-conjugated low molecular compound. Photoelectric conversion element.
(5) The organic thin film photoelectric conversion device according to any one of (1) to (4), wherein the elimination reaction of the substituent is caused by heating at 250 ° C. or higher.
(6) The organic thin film photoelectric conversion element according to any one of (1) to (5), wherein one of the organic semiconductor film and another semiconductor material is a p-type semiconductor and the other is an n-type semiconductor.
(7) The organic thin film photoelectric conversion element according to any one of (1) to (6), wherein the film formation method of the other semiconductor material is a coating method.
(8) The organic thin film photoelectric conversion element according to any one of (1) to (7), wherein the another semiconductor material is an organic semiconductor material.
(9) The organic thin film photoelectric conversion element according to (8), wherein the organic semiconductor material is an n-type organic semiconductor material.
(10) The organic thin film photoelectric conversion element according to (9), wherein the n-type organic semiconductor material contains a fullerene compound.
(11) The organic thin film photoelectric conversion element according to any one of (1) to (10), which is sealed in an inert gas atmosphere.
(12) A step of forming a π-conjugated low-molecular compound on a substrate, a step of removing a part or all of substituents from the compound to convert it into an organic semiconductor film, and another semiconductor on the film The method for producing an organic thin film photoelectric conversion element according to any one of (1) to (11), comprising a step of coating and forming a material.

  The “low molecular weight compound” in the present invention means a compound having a molecular weight of preferably 10,000 or less, more preferably 5000 or less, and still more preferably 2000 or less.

  According to the present invention, it is possible to obtain a highly efficient organic thin film photoelectric conversion element by a coating film forming method using a low molecular compound.

  Hereinafter, the present invention will be described with reference to embodiments and examples, but the present invention is not limited to the following embodiments and examples, and may be arbitrarily modified and implemented without departing from the gist of the present invention. can do.

  The method for producing an organic thin film photoelectric conversion element of the present invention comprises a step of forming a film of a π-conjugated low molecular compound (hereinafter also referred to as “compound used in the present invention”) on a substrate (film formation step), and It consists of a step of removing some or all of the substituents from the compound to convert them into an organic semiconductor film (substituent elimination step), and a step of depositing another semiconductor material on the film (overcoating step). . In the substituent elimination step, volume contraction of the film and formation of voids occur by the volume of the substituent to be eliminated. By overcoating another semiconductor material here, another semiconductor material enters the gap, and the contact interface area of each semiconductor component is large as shown schematically in FIG. 1, and each semiconductor component extends to each electrode. A continuous composite structure is obtained. Here, by selecting a p-type semiconductor and an n-type semiconductor as each semiconductor component, an ideal composite structure can be formed as a photoelectric conversion layer that can achieve both high-efficiency charge separation and high charge transport capability. It is possible to obtain a highly efficient photoelectric conversion element.

The organic semiconductor in the present invention is an organic material exhibiting semiconductor characteristics. As in the case of a semiconductor made of an inorganic material, a p-type organic semiconductor that conducts holes as a main carrier (also simply referred to as a p-type material) and an n-type organic semiconductor that conducts electrons as a main carrier (also referred to simply as an n-type material). Say). The ease of carrier flow in the organic semiconductor is represented by carrier mobility μ. Although it depends on the application, in general, the mobility should be higher, preferably 10 ⁻⁷ cm ² / Vs or more, more preferably 10 ⁻⁶ cm ² / Vs or more, more preferably 10 ⁻⁵ cm ² / Vs. More preferably, it is Vs or higher. The carrier mobility μ is measured using a field effect transistor (FET), Time-of-Flight (TOF) method, space charge limited current (SCLC) method, time-resolved microwave conductivity measurement (TRMC) method, etc. It can be measured by the method.

[Π-conjugated low-molecular compounds]
The π-conjugated low-molecular compound used in the present invention may be any compound as long as it has a wide π-conjugated plane and a skeleton exhibiting carrier transport ability, but preferably a benzene ring, a pyridine ring, a pyrazine ring , Pyrimidine ring, triazine ring, pyrrole ring, pyrazole ring, imidazole ring, triazole ring, oxazole ring, thiazole ring, furan ring, thiophene ring, more preferably benzene ring, pyridine ring, pyrazine ring, pyrrole ring, pyrazole ring, Two or more aromatic hydrocarbon rings or aromatic hetero rings such as imidazole ring, oxazole ring, thiazole ring, thiophene ring, etc., which are condensed and / or covalently linked, Π-electron possessed by each aromatic hydrocarbon ring or aromatic heterocycle causes interaction by condensation and / or linking It is the case in condensed ring and / or coupling ring which is delocalized structure I. Examples of such chemical structures include “Organic Field-Effect Transistors” (2007, CRC Press), pages 159-228, and Chem. Soc. Rev. 2008, 37, 827-838. The thing of description is mentioned. The number of condensed aromatic rings and / or covalently linked aromatic hydrocarbon rings or aromatic heterocycles is preferably 1-20, more preferably 2-12.

  The molecular weight of the π-conjugated low molecular compound used in the present invention is preferably 100 or more and 10,000 or less, more preferably 200 or more and 5,000 or less, and further preferably 300 or more and 2,000 or less.

  As the π-conjugated low-molecular compound in the present invention, condensed polycyclic compounds (such as anthracene, tetracene, pentacene, anthradithiophene, hexabenzocoronene), triarylamine (triphenylamine) from the viewpoint of carrier transport ability and chemical stability Compound), hetero 5-membered ring compounds (oligothiophene compounds, TTF analogs, etc.), phthalocyanine compounds, and porphyrin compounds, and condensed polycyclic compounds (anthracene, tetracene, pentacene, anthradithiophene, hexa) Benzocoronene etc.), hetero 5-membered ring compounds (oligothiophene, TTF analogs etc.), phthalocyanine compounds are more preferred, and phthalocyanine compounds are most preferred.

The phthalocyanine compound refers to a substituted, metal-free or various metal phthalocyanine, tetrapyrazinoporphyrazine, naphthalocyanine, anthracocyanine, and the like.
The π-conjugated low molecular weight compound has one or more substituents and may be any substituent. Examples thereof include halogen atoms, alkyl groups (including cyclic structures such as cycloalkyl groups and bicycloalkyl groups), and alkenyls. Groups (including cyclic structures such as cycloalkenyl groups and bicycloalkenyl groups), alkynyl groups, aryl groups, heterocyclic groups, cyano groups, hydroxy groups, nitro groups, carboxy groups, alkoxy groups, aryloxy groups, silyloxy groups, Heterocyclic oxy group, acyloxy group, carbamoyloxy group, alkoxycarbonyloxy group, aryloxycarbonyloxy group, amino group (including anilino group), acylamino group, aminocarbonylamino group, alkoxycarbonylamino group, aryloxycarbonylamino Group, sulfamoylamino group, Alkyl or arylsulfonylamino group, mercapto group, alkylthio group, arylthio group, heterocyclic thio group, sulfamoyl group, sulfo group, alkyl or arylsulfinyl group, alkyl or arylsulfonyl group, acyl group, aryloxycarbonyl group, alkoxycarbonyl group , A carbamoyl group, an aryl or heterocyclic azo group, an imide group, a phosphino group, a phosphinyl group, a phosphinyloxy group, a phosphinylamino group, and a silyl group as partial structures. In the present invention, at least one of the substituents possessed by the π-conjugated low molecular weight compound is a leaving group described below.

  Any substituent may be used, such as a Boc (t-butoxycarbonyl) group, an ester group, a sulfonyl group, a residue of an ethylene compound, a quinone compound, or a benzene compound that is eliminated by a reverse Diels-Alder reaction. preferable. From the viewpoint of the chemical stability of the π-conjugated low molecular weight compound, a sulfonyl group is most preferable.

  The number of substituents leaving the π-conjugated low-molecular compound may be any number as long as the π-conjugated low-molecular compound exhibits solubility suitable for coating film formation, but it should be 1 to 8. The number is preferably 1 to 6, more preferably 1 to 4. The total formula weight of the leaving substituents is preferably in the range of 5% to 90% with respect to the molecular weight of the π-conjugated low molecular weight compound, more preferably in the range of 15% to 80%. More preferably, it is in the range of 30% to 70%.

  In the present invention, the term “soluble in a solvent” is defined as a compound having a solubility of 0.1% by weight or more with respect to the solvent when the solvent is heated to reflux and then cooled to room temperature. Preferably it is 0.5 weight% or more, More preferably, it is 1 weight% or more. Solvent insolubility is defined as having a solubility of less than 0.1% by weight in the solvent when the solvent is heated to reflux and then cooled to room temperature. Preferably it is less than 0.05 weight%, More preferably, it is less than 0.01 weight%.

  For examples of compounds from which substituents are eliminated by external stimuli and the mechanism by which substituents are eliminated, see Adv. Mater. 1999, 11, 480-483. (Mullen pentacene) and J.M. Am. Chem. Soc. 2002, 124, 8812-8813. (Afzali pentacene), a pentacene compound, Appl. Phys. Lett. , 2004, 84, 2085-2087. (Benzoporphyrin), a benzoporphyrin compound described in J. Porphyrins Phthalocyanines, 2006, 10, 1197-1201. A tetrapyrazinoporphyrazine compound described in J. Am. Am. Chem. Soc. 2004, 126, 1596-1597. A sexithiophene compound described in Int. Conf. on Digital Printing Technologies, 2007, 696-699. The diketopyrrolopyrrole compounds and quinacridone compounds described in 1) are known, and any of these compounds can be preferably used in the present invention.

Preferred specific examples of the π-conjugated low molecular weight compound used in the present invention are shown below, but the present invention is not limited thereto. Exemplary compounds 1 to 12 and 14 to 19 form a p-type organic semiconductor film after elimination of substituents, and exemplary compound 13 is a material that forms an n-type organic semiconductor film after elimination of substituents.
The compounds shown below have one R for each benzene ring and a total of 4 compounds as the same substituent, but 0 to 4 per benzene ring may be substituted for 1 to 16 in total. That's fine. Among them, preferred are those in which one benzene ring is substituted in total, or four in one compound.
Bu in the chemical formula of Exemplary Compound 6 represents a butyl group.

(Synthesis method)
Phthalocyanine ring-forming reaction of phthalocyanine compounds is described by Shigeyoshi Shirai, Nagao Kobayashi, edited by "Phthalocyanine-Chemistry and Function" (IPC, 1997), pages 1-62, Ryo Takahashi, Keiichi Sakamoto, and Eiko Okumura. It can be carried out according to pages 29 to 77 of “Phthalocyanine as a functional dye” (IPC, 2004).

  Typical methods for synthesizing phthalocyanine compounds include the Weiler method, phthalonitrile method, lithium method, subphthalocyanine method, and chlorinated phthalocyanine method described in these documents. Specifically, it is preferable to carry out a phthalocyanine ring formation reaction using a compound having the substituent such as t-butylsulfonylphthalonitrile as a raw material. In the present invention, any reaction conditions may be used in the phthalocyanine ring formation reaction. In the ring formation reaction, it is preferable to add various metals to be the central metal of phthalocyanine, but a desired metal may be introduced after the synthesis of a phthalocyanine compound having no central metal. Any solvent may be used as the reaction solvent, but a solvent having a high boiling point is preferable. Further, an acid or a base may be used for promoting the ring formation reaction. Optimum reaction conditions vary depending on the structure of the target phthalocyanine compound, but can be set with reference to specific reaction conditions described in the above-mentioned documents.

  As raw materials used for the synthesis of the phthalocyanine compound, derivatives such as phthalic anhydride, phthalimide, phthalic acid and salts thereof, phthalic acid diamide, phthalonitrile, 1,3-diiminoisoindoline can be used. These raw materials may be synthesized by any known method.

  Further, π-conjugated low molecular compounds other than phthalocyanine compounds used in the present invention are described in “Organic Field-Effect Transistors” (CRC Press, 2007), pages 159 to 228, Chem. Soc. Rev. 2008, 37, 827-838. The compounds can be synthesized with reference to the literature cited as known examples of π-conjugated low molecular compounds from which substituents are eliminated, and the literature cited therein.

[Film formation process]
In the production of the organic thin film photoelectric conversion element of the present invention, first, the π-conjugated low molecular compound is formed on a substrate described later.

(Film formation method)
In the present invention, any method may be used to form the π-conjugated low molecular compound on the substrate, but it is particularly preferable to form the film by a solution coating method from the viewpoint of manufacturing cost. Here, the solution coating method refers to a method in which a material is dissolved or dispersed in a solvent capable of dissolving, and the solution is coated on a substrate and dried to form a film. Specifically, casting method, blade coating method, wire bar coating method, spray coating method, dipping (dipping) coating method, bead coating method, air knife coating method, curtain coating method, ink jet method, spin coating method, Langmuir- A usual method such as a blow jet (LB) method can be used. In the present invention, it is more preferable to use a casting method, a spin coating method, and an ink jet method. By such a solution coating method, an organic film having a smooth surface and a large area can be produced at a low cost.

(Application conditions)
When a film is formed on a substrate by a solution process, carbonization of a material for forming the layer with an appropriate organic solvent (for example, hexane, octane, decane, toluene, xylene, ethylbenzene, 1-methylnaphthalene, 1,2-dichlorobenzene, etc.) Hydrogen solvents; for example, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone; halogenated carbonization such as dichloromethane, chloroform, tetrachloromethane, dichloroethane, trichloroethane, tetrachloroethane, chlorobenzene, dichlorobenzene, chlorotoluene Hydrogen solvents; for example, ester solvents such as ethyl acetate, butyl acetate, and amyl acetate; for example, methanol, propanol, butanol, pentanol, hexanol, cyclohexanol, methyl celloso Alcohol solvents such as butyl, ethyl cellosolve and ethylene glycol; for example, ether solvents such as dibutyl ether, tetrahydrofuran, dioxane and anisole; for example, N, N-dimethylformamide, N, N-dimethylacetamide, 1-methyl-2 A polar solvent such as -pyrrolidone, 1-methyl-2-imidazolidinone, dimethyl sulfoxide, etc.) and / or water to form a coating solution, and a thin film can be formed by various coating methods. . In order to improve the solubility, the coating solution may be used by heating. As temperature in the case of heating, it is preferable that it is 30-300 degreeC, It is more preferable that it is 40-250 degreeC, It is further more preferable that it is 50-200 degreeC. The concentration of the compound used in the present invention in the coating solution is preferably 0.01 to 80% by mass, more preferably 0.05 to 30% by mass, and still more preferably 0.1 to 10% by mass. A film having an arbitrary thickness can be formed.

It is also possible to use a resin binder during film formation. In this case, the material for forming the layer and the resin binder can be dissolved or dispersed in the above-mentioned appropriate solvent to form a coating solution, and a thin film can be formed by various coating methods. Resin binders include polystyrene, polycarbonate, polyarylate, polyester, polyamide, polyimide, polyurethane, polysiloxane, polysulfone, polymethyl methacrylate, polymethyl acrylate, cellulose, polyethylene, polypropylene, and other insulating polymers, and their co-polymers. Examples thereof include photoconductive polymers such as coalescence, polyvinyl carbazole and polysilane, and conductive polymers such as polythiophene, polypyrrole, polyaniline and polyparaphenylene vinylene. The resin binder may be used alone or in combination. Considering the mechanical strength of the thin film, a resin binder having a high glass transition temperature is preferable, and considering the charge mobility, a resin binder, a photoconductive polymer, or a conductive polymer having a structure that does not contain a polar group is preferable.
It is preferable not to use a resin binder in terms of the characteristics of the organic semiconductor, but it may be used depending on the purpose. The amount of the resin binder used in this case is not particularly limited, but is preferably 0.1 to 30% by mass in the organic semiconductor film of the present invention.

  In the film formation, the substrate may be heated or cooled, and the film quality and packing of molecules in the film can be controlled by changing the temperature of the substrate. Although there is no restriction | limiting in particular as temperature of a board | substrate, it is preferable that it is -200 degreeC-300 degreeC, it is more preferable that it is -150 degreeC-250 degreeC, and it is more preferable that it is -100 degreeC-200 degreeC.

  The above-mentioned π-conjugated low molecular compound used in the present invention is particularly suitable for film formation by a solution process. In the present invention, it is formed by a vacuum process such as a physical vapor deposition method such as a vacuum deposition method, a sputtering method, an ion plating method, a molecular beam epitaxy (MBE) method, or a chemical vapor deposition (CVD) method such as plasma polymerization. Although it is possible to form a film, they are expensive to manufacture and may be inferior in the smoothness of the film surface. In addition, in order to form a film by a solution process, it is necessary that the material is dissolved in the above-described solvent or the like, but it is not sufficient to simply dissolve the material. Usually, even a material for forming a film by a vacuum process can be dissolved in a solvent to some extent. However, in the solution process, there is a process in which after the material is dissolved in a solvent and applied, the solvent evaporates to form a thin film. Here, since many materials not suitable for the solution process have high crystallinity, they are crystallized in this process, and it is difficult to form a good thin film. On the other hand, the π-conjugated low-molecular compound used in the present invention is excellent in that such crystallization hardly occurs.

  The coating amount of the solution containing the compound varies depending on the type of solvent, the concentration of the solution, and the like, but is appropriately determined so that the thickness of the formed organic semiconductor film falls within the range described later.

[Substituent elimination process]
After coating the π-conjugated low molecular weight compound on a substrate, the substituent is eliminated from the compound. By removing a part or all of the substituents, a solvent-insoluble organic semiconductor film (hereinafter also referred to as “organic semiconductor film used in the present invention”) is converted. As the external stimulus that causes the elimination reaction, any material such as heat, light, chemical reaction, etc. may be used, but heat is preferably used. Heat can be caused by heating to 100 ° C. or higher, more preferably 200 ° C. or higher, and even more preferably 250 ° C. or higher. The upper limit of the heating temperature is preferably 500 ° C. or less, more preferably 450 ° C. or less, and further preferably 400 ° C. or less. The higher the temperature, the shorter the time required for the elimination reaction, and the lower the temperature, the longer the required time. The heating time is preferably 1 second to 5 hours, more preferably 10 seconds to 3 hours, and even more preferably 30 seconds to 1 hour. When the heating temperature and the heating time are insufficient, a part of the substituent is eliminated. It is also possible to adjust the characteristics (for example, mobility and redox potential) of the organic semiconductor film by intentionally removing only some of the substituents. In addition to heating by heat transfer using a heater, heating may be performed by irradiating with an infrared lamp or light having a wavelength absorbed by the compound. In addition, a layer that absorbs light may be provided in the vicinity of the film of the π-conjugated low molecular compound, and heating may be performed by absorbing light in this layer. Such heating is preferably performed in an inert atmosphere such as nitrogen, argon, or vacuum. Substantial elimination of the substituent may be accompanied by a change in film quality (for example, crystallization from amorphous to change in crystal polymorphism). The method of changing the film quality depends on the temperature of heating, the rate of temperature rise, the holding time, the cooling rate after heating, the atmosphere during heating, and the like.

(Post-processing of organic semiconductor film)
The characteristics of the manufactured organic semiconductor film can be adjusted by post-processing. For example, characteristics can be improved by changing the film morphology and molecular packing in the film by heat treatment or exposure to solvent vapor. Further, by exposing to an oxidizing or reducing gas, solvent, substance, or the like, or mixing them, an oxidation or reduction reaction is caused, and the carrier density in the film can be adjusted.

(Film thickness)
The thickness of the organic semiconductor film is not particularly limited, but is preferably 1 nm to 10 μm, more preferably 5 nm to 5 μm, and still more preferably 10 nm to 1 μm.

[Overcoating process]
Since the organic semiconductor film used in the present invention becomes insoluble in the solvent due to elimination of substituents, it becomes possible to produce a laminated film by a solution coating method, which has been difficult in the past. Further, volume shrinkage and void formation occur by the volume of the displaced substituent. By depositing another semiconductor material from above, another semiconductor material enters the gap, and the contact interface area between the two is large, and both of them can form a continuous interpenetrating structure up to each electrode. it can.
This structure is schematically shown in FIG. In FIG. 1, 1 and 4 are electrodes, 2 is an organic semiconductor film, and 3 is a film formed of another semiconductor material. As described above, when the organic semiconductor film is separated from the substituent, voids are formed in the portion where the substituent is present, and irregularities are formed on the surface. It does not have to be). When another semiconductor material is laminated on the uneven surface, the above interpenetrating structure is formed.
Here, regarding one of the organic semiconductor film and another semiconductor material, if one is a p-type material and the other is an n-type material, for example, the p-type material 2 and the n-type material 3 in FIG. Thus, an ideal structure for photoelectric conversion (a structure capable of achieving both high-efficiency charge separation and high charge transporting capability) is obtained.

When the organic semiconductor film is p-type, another semiconductor material is preferably an n-type semiconductor material. As an n-type semiconductor material to be used, any organic semiconductor material or inorganic semiconductor material may be used as long as it has an electron transporting property. Preferably, a fullerene compound, an electron-deficient phthalocyanine compound, a naphthalenetetracarboxylic acid compound, A perylene tetracarboxylic acid compound, a TCNQ analog, and an inorganic semiconductor, more preferably a fullerene compound, a phthalocyanine compound, a naphthalene tetracarboxylic acid compound, and a perylene tetracarboxylic acid compound, and particularly preferably a fullerene compound. In the present invention, the fullerene compound refers to a substituted or unsubstituted fullerene, and the fullerene is C ₆₀ , C ₇₀ , C ₇₆ , C ₇₈ , C ₈₀ , C ₈₂ , C ₈₄ , C ₈₆ , C ₈₈ , C _90. , C ₉₆ , C ₁₁₆ , C ₁₈₀ , C ₂₄₀ , C _{540 and the} like may be used, but substituted or unsubstituted C ₆₀ , C ₇₀ , C ₈₆ are preferable, and PCBM ([6, 6] is particularly preferable. - phenyl -C 61 _- those butyric acid methyl ester) and its analogs and (C ₆₀ moiety is substituted with C _70, C _86, etc., those with substitution of the benzene ring substituent in other aromatic ring or heterocyclic ring, methyl ester Are substituted with n-butyl ester, i-butyl ester and the like. The electron-deficient phthalocyanine compound refers to phthalocyanine and its analogs having four or more electron-attracting groups bonded thereto, or an electron-deficient phthalocyanine analog. The phthalocyanine analog is a tetrapyrazine other than phthalocyanines of various metals. It also includes dinoporphyrazine, naphthalocyanine, anthracyanine, etc. (F ₁₆ MPc, FPc-S8, etc.). Any naphthalene tetracarboxylic acid compound may be used, but naphthalene tetracarboxylic acid anhydride (NTCDA), naphthalene bisimide compound (NTCDI), and perinone pigment (Pigment) are preferred.
Orange 43, Pigment Red 194, etc.). Any perylene tetracarboxylic acid compound may be used, but perylene tetracarboxylic acid anhydride (PTCDA), perylene bisimide compound (PTCDI), and benzimidazole condensed ring (PV) are preferable. The TCNQ analog is obtained by replacing the benzene ring portion of TCNQ and TCNQ with another aromatic ring or heterocycle, and examples thereof include TCNQ, TCAQ, TCN3T, and the like. The inorganic semiconductor may be any material as long as it has an electron transporting property. For example, TiO ₂ , TiSrO ₃ , ZnO, Nb ₂ O ₃ , SnO ₂ , WO ₃ , Si, CdS, CdSe, V ₂ O ₅ ZnS, ZnSe, SnSe, KTaO ₃ , FeS ₂ , PbS, InP, GaAs, CuInS ₂ , CuInSe ₂ and the like. Preferred specific examples of the n-type organic semiconductor material are shown below.
R in the formula may be any, but it is a hydrogen atom, a substituent or an unsubstituted branched or straight chain alkyl group (preferably having 1 to 18 carbon atoms, more preferably 1 to 12, more preferably 1). -8) or a substituted or unsubstituted benzene ring (preferably having 6 to 30 carbon atoms, more preferably 6 to 20 and more preferably 6 to 14).

When the organic semiconductor film is n-type, another semiconductor material is preferably a p-type semiconductor material. As the p-type semiconductor material to be used, any organic semiconductor material or inorganic semiconductor material may be used as long as it has hole transport properties, but preferably a p-type π-conjugated polymer (for example, substituted or unsubstituted polythiophene). , Polyselenophene, polypyrrole, polyparaphenylene, polyparaphenylene vinylene, polythiophene vinylene, polyaniline, etc.), condensed polycyclic compounds (eg, substituted or unsubstituted anthracene, tetracene, pentacene, anthradithiophene, hexabenzocoronene, etc.) , Triarylamine compounds (eg, m-MTDATA, 2-TNATA, NPD, TPD, mCP, CBP, etc.), hetero 5-membered ring compounds (eg, substituted or unsubstituted oligothiophene, TTF, etc.), phthalocyanine compounds (substituted) Or nothing Conversion of various central metals of the phthalocyanine, naphthalocyanine, anthracyanine, tetra pyrazinoporphyrazine), porphyrin compounds (a substituted or unsubstituted various central metal of the porphyrin), p-type inorganic semiconductor (e.g., Si _1-X C _X ( 0 ≦ X ≦ 1), CuI, CuS, GaAs, ZnTe, Cu ₂ O, Cu ₂ S, CuSCN, CuF, CuCl, CuBr, CuInSe ₂ , CuInS ₂ , CuAlSe ₂ , CuGaSe ₂ , CuGaS ₂ , GaP, NiO, Inorganic oxides such as CoO, FeO, Bi ₂ O ₃ , MoO ₂ , and Cr ₂ O ₃ ), and more preferably a p-type π-conjugated polymer, a condensed polycyclic compound, a triarylamine compound, and hetero-5 A member ring compound, a phthalocyanine compound, or a porphyrin compound, Preferably the al is a p-type π-conjugated polymers.

  Any method may be used to form these different semiconductor materials, but a solution coating method is preferably used from the viewpoint of manufacturing cost. The details of the solution coating method are the same as those described in the section of the film formation step of the π-conjugated compound.

(Film thickness)
The total thickness of the two-layered film in which another semiconductor material is formed on the organic semiconductor film is preferably 10 nm to 10 μm, more preferably 30 nm to 3 μm, and more preferably 50 nm to 1 μm. Further preferred.

[Organic thin film photoelectric conversion element]
FIG. 2 is a cross-sectional view schematically showing the structure of a typical organic thin film photoelectric conversion element using the organic semiconductor material of the present invention. The element shown in FIG. 2 has a laminated structure. A substrate 21 is arranged in the lowermost layer, an electrode layer 22 is provided on the upper surface thereof, and a photoelectric conversion layer 23 (FIG. 1 shown in FIG. 2 and 3), and an electrode layer 24 is provided on the upper surface thereof. Although not shown in FIG. 2 between the electrode layers 22 and 24 and the photoelectric conversion layer 23, a buffer layer that improves surface smoothness, a carrier injection layer that promotes injection of holes or electrons from the electrode In addition, a carrier transport layer that transports holes or electrons, a carrier block layer that blocks holes or electrons, or the like (one layer may also serve as the plurality of roles) may be included. In the present invention, these layers used between the electrode layer and the photoelectric conversion layer are all expressed as a buffer layer regardless of their roles. Note that the electrode layer and each layer are not necessarily flat, and may have large unevenness or a three-dimensional shape (for example, a comb shape).

  The material used for the substrate 11 is not particularly limited as long as it transmits visible light or infrared light. The transmittance of visible light or infrared light is preferably 60% or more, more preferably 70% or more, and most preferably 80% or more. Examples of such materials include polyester films such as polyethylene naphthoate (PEN) and polyethylene terephthalate (PET), polyimide films, ceramics, silicon, quartz, and glass. The thickness is not particularly limited.

The material used for the electrode layer 12 is not particularly limited as long as it transmits visible light or infrared light and exhibits conductivity. The transmittance of visible light or infrared light is preferably 60% or more, more preferably 70% or more, and most preferably 80% or more. Such _{materials, ITO, IZO, SnO 2,} ATO ( antimony-doped tin oxide), ZnO, AZO (Al-doped zinc oxide), GZO (gallium-doped zinc _oxide), TiO _2, FTO (fluorine-doped tin oxide) A transparent conductive oxide such as ITO is preferred, and ITO or IZO is particularly preferred from the viewpoint of process suitability and smoothness. Although there is no restriction | limiting in a film thickness, it is preferable that they are 1 nm-200 nm, and it is more preferable that they are 5 nm-100 nm. When the electrode 12 has structural self-supporting properties, the substrate 11 is not necessarily required. When the electrode 12 also serves as the substrate 11, the film thickness may be larger than the above-described thickness.

The material used for the buffer layer may be any organic material or inorganic material as long as it is a material capable of transporting carriers, but is preferably amorphous. Any hole transporting buffer material may be used, but preferably a conductive polymer (for example, PEDOT: PSS), a triarylamine compound (for example, m-MTDATA), an inorganic semiconductor material (for example, Si _1-X C _X (0 ≦ X ≦ 1), CuI, CuS, GaAs, ZnTe, Cu ₂ O, Cu ₂ S, CuSCN, CuF, CuCl, CuBr, CuInSe ₂ , CuInS ₂ , CuAlSe ₂ , CuGaSe ₂ , CuGaS ₂ , GaP, NiO, CoO , FeO, Bi ₂ O ₃ , MoO ₂ , Cr ₂ O ₃ and other inorganic oxides). Any material may be used as the electron transporting buffer material. Preferably, in addition to the aforementioned n-type semiconductor material, a metal complex compound (for example, Alq), bathocuproine, inorganic fluoride (for example, LiF, CaF), inorganic oxidation an object (e.g. _{SiO X, TiO X, ZnO)} , conductive polymers (e.g. polyparaphenylene vinylene having a cyano group (CN-PPV), perinone polymer (BBL)), more preferably, naphthalene compounds, bathocuproine, Inorganic fluorides and inorganic oxides.

  The material used for the electrode layer 14 is not particularly limited as long as it exhibits conductivity. However, from the viewpoint of improving light utilization efficiency, a material having high light reflectivity is preferable, and Al, Pt, W, Au, Ag, Ta, Cu, Cr, Mo, Ti, Ni, Pd, and Zn are preferable, and Al, Pt, Au, and Ag are more preferable. The film thickness of the electrode layer 14 is not particularly limited, but is preferably 1 nm to 1 μm, and more preferably 5 nm to 500 nm.

  In order to improve the storage stability of the element, it is preferable to seal the element so that an inert atmosphere can be maintained. Preferred sealing materials include inorganic materials such as metal, glass, silicon nitride, and alumina, and high amounts of parylene and the like. Examples include molecular materials. You may enclose a desiccant etc. in the case of sealing.

The organic thin film photoelectric conversion element of the present invention may be used for energy conversion (organic thin film solar cell), or may be used as an optical sensor (solid-state imaging element or the like). When used for energy conversion, the organic thin film photoelectric conversion element of the present invention may be used alone or may be laminated (tandem) with other organic thin film photoelectric conversion elements. For the tandem method, see Applied Physics Letters, 2004, 85, 5757-5759. Is described in detail and can be used as a reference. When used as an optical sensor, it is preferable to read a signal by applying a bias between the electrode 12 and the electrode 14 in order to improve the S / N ratio. In this case, the bias applied to the photoelectric conversion layer is 1.0. It is preferable that it is x10 < ⁵ > V / cm or more and 1.0 * 10 < ⁷ > V / cm or less. Solid-state imaging devices using organic thin film photoelectric conversion devices are described in detail in JP-A Nos. 2003-234460, 2003-332551, and 2005-268609, and can be referred to.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to these.

Exemplified Compound 1 was synthesized according to the method of synthesizing the dye compound (I-1) described in JP-A-2005-119165. The purity of the synthesized exemplary compound 1 was measured by liquid chromatography (HPLC, manufactured by Tosoh Corporation, trade name, TSK-gel ODS-80Ts 4.6 × 150 mm, eluent: THF / H ₂ O = 47/53 (AcOH, NEt ₃ It was 99% or more when measured by 0.1% each) and detection wavelengths of 254 nm and 675 nm).

(TG / DTA measurement)
The synthesized exemplary compound 1 was subjected to thermal analysis (TG / DTA measurement). TG / DTA measurement was performed by Seiko Instruments Inc. Using EXSTAR6000 (trade name), the temperature was increased at a rate of 10 ° C./min in a range of 30 ° C. to 550 ° C. under a nitrogen stream (flow rate 200 mL / min) to determine the mass reduction rate. As shown in FIG. 3, a mass decrease corresponding to the mass of four substituents (—SO ₂ C (CH ₃ ) ₃ groups) was observed at about 350 ° C. From this result, it was found that the substituent was eliminated from the exemplified compound 1 by heating.

(MALDI-TOF-MS measurement)
Matrix-assisted ionization-time-of-flight mass spectrometry (MALDI-TOF-MS) measurement was performed on Exemplified Compound 1 before and after being heated to 400 ° C. at a temperature increase rate of 10 ° C./min in a nitrogen stream. MALDI-TOF-MS measurement was performed using Voyager-DE PRO (trade name) manufactured by Applied Biosystems and using α-cyano-4-hydroxycinnamic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) as a matrix. As shown in FIG. 4, in FIG. 3A showing the state before the heat treatment, a peak of 1056 ([M ⁺ ] +1) corresponding to the molecular weight of Compound 1 was observed. In FIG. 4 (b), this peak disappears and a peak of 575 ([M ⁺ ]) corresponding to the molecular weight of unsubstituted copper phthalocyanine (CuPc: C ₃₂ H ₁₆ CuN ₈ ) appears. It was. From this result, it was found that Exemplified Compound 1 was converted to unsubstituted copper phthalocyanine by heating.

(X-ray diffraction measurement)
X-ray diffraction measurement was performed on Exemplified Compound 1 before and after being heated to 400 ° C. at a rate of temperature increase of 10 ° C./min in a nitrogen stream. X-ray DIFFRACTOMETER RINT-2500 (manufactured by Rigaku, trade name) was used for X-ray diffraction measurement. As shown in FIG. 5, it was found that Exemplified Compound 1 which was an amorphous solid before heating was crystallized after heating.

(FET characteristics)
Exemplary compound 1 (20 mg) was dissolved in chloroform (1 mL) and spin-coated at 1000 rpm on the FET characteristic measurement substrate to obtain a FET characteristic measurement sample having a uniform thickness of 200 nm or less. The film thickness was measured with a stylus type film thickness meter (trade name DEKTAK 6M, manufactured by ULVAC) (hereinafter the same). This FET characteristic measurement sample was heated to 400 ° C. at 10 ° C./min in a nitrogen atmosphere and held at 400 ° C. for 5 minutes, and then the FET characteristics were examined. As the substrate for measuring the FET characteristics, the bottom contact type substrate schematically shown in FIG. 6 was used (the source and drain electrodes were arranged in a comb-shape (gate width W = 100000 μm, gate length L = 100 μm). ), The insulating film is SiO ₂ (film thickness 200 nm), and the substrate is silicon). The FET characteristics were measured under a normal pressure and nitrogen atmosphere (in a glove box) using a semiconductor parameter analyzer (manufactured by Agilent, trade name: 4156C) connected to a semi-auto prober (manufactured by Vector Semicon, AX-2000). As shown in FIG. 7, it was confirmed that the thin film of Exemplary Compound 1 that did not show any semiconductor characteristics before the heat treatment was converted into a p-type organic semiconductor film by the heat treatment.

  From the above measurement results, the thin film of exemplary compound 1 that was in an amorphous state after coating film formation is converted to a p-type organic semiconductor film made of crystalline unsubstituted copper phthalocyanine, with the substituents removed by heating. I understood that.

[Example 1]
A glass substrate (2.5 cm × 2.5 cm) on which the ITO electrode was patterned was subjected to ultrasonic cleaning in isopropyl alcohol for 10 minutes and then dried. Further, UV ozone treatment was performed for 30 minutes in order to remove organic contaminants on the surface of the ITO electrode. Next, a 20 mg / mL chloroform solution of Exemplified Compound 1 was spin coated at 1000 rpm to form a p-type organic semiconductor precursor film having a thickness of approximately 200 nm or less and a substantially uniform thickness. The film was heated to 400 ° C. at 10 ° C./min in a nitrogen atmosphere, and held at 400 ° C. for 5 minutes to convert to a p-type organic semiconductor film. After cooling to room temperature, a 20 mg / mL chloroform solution of PCBM ([6,6] -phenyl-C ₆₁ -butyric acid methyl ester), which is an n-type organic semiconductor material, is spin-coated at 1000 rpm, so that the thickness is 200 nm or less. A photoelectric conversion layer having a substantially uniform thickness was produced. On this photoelectric conversion layer, aluminum is vacuum-deposited to a thickness of about 80 nm with a vacuum degree of 2 × 10 ⁻⁴ or less using a vacuum vapor deposition apparatus (EBX-8C manufactured by ULVAC). Thus, an organic thin film photoelectric conversion element having an effective area of 0.04 cm ² was obtained by forming a metal electrode.

This element was irradiated with artificial sunlight of AM1.5 and 100 mW / cm ² using a solar simulator (Oriel, 150W simple type), and an electrochemical analyzer (trade name ALS model 660B, manufactured by BAS). When the current-voltage characteristics were measured, as shown in FIG. 8, the photoelectric conversion ability with a short-circuit current density J _SC = 0.15 mA / cm ² and an open circuit voltage V _OC = 0.43 V was shown.

[Comparative Example 1]
An organic thin film photoelectric conversion element was prepared in the same manner as in Example 1 except that a photoelectric conversion layer was prepared by spin-coating a chloroform mixed solution of Exemplified Compound 1 and PCBM (20 mg + 20 mg / mL) at 1000 rpm and heating to 400 ° C. Produced. The organic thin-film photoelectric conversion element, _{J SC} is 1/20 or less as compared with Example _{1, V OC} seemed less than 1/2.

[Comparative Example 2]
A photoelectric conversion layer by spin-coating a mixed solution (20 mg + 20 mg / mL) of Comparative Compound 1 (Chemical X) and PCBM described in the latest collection of latest functional dyes (2007, Technical Information Association) pages 320-328 at 1000 rpm. An organic thin film photoelectric conversion element was produced in the same manner as in Example 1 except that was produced. The organic thin-film photoelectric conversion element, _{J SC} is 1/10 or less as compared with Example _{1, V OC} seemed less than 1/3.

  From the above, it was found that the organic thin film photoelectric conversion element of the present invention can be produced by coating film formation of a low molecular compound, and exhibits high photoelectric conversion performance.

It is sectional drawing which shows roughly the structure of the organic thin film photoelectric conversion element of this invention. It is sectional drawing which shows roughly the structure of the organic thin film photoelectric conversion element of this invention. It is a figure which shows the TG / DTA measurement result of the exemplary compound 1. It is a figure which shows the MALDI-TOF-MS spectrum measurement result of the example compound 1 before (a) heat processing and after (b) heat processing. It is a figure which shows the X-ray-diffraction measurement result before heat processing of the example compound 1, and after heat processing. It is sectional drawing which shows the organic thin-film transistor characteristic-measurement board | substrate roughly. It is a figure which shows the FET characteristic of the film | membrane which consists of the exemplary compound 1 before (a) heat processing and after (b) heat processing. It is a figure which shows the photoelectric conversion characteristic of the organic thin film photoelectric conversion element of this invention using the exemplary compound 1.

Explanation of symbols

1, 4 Electrode 2 Organic semiconductor film 3 Another semiconductor material 11 Substrate 12 Electrode 13 Insulator layer 14 Organic layer (semiconductor organic layer)
15a, 15b Electrode 21 Substrate 22 Electrode 23 Photoelectric conversion layer 24 Electrode

Claims (12)

  After coating and film-forming a π-conjugated low molecular weight compound, an organic semiconductor thin film is formed by removing at least part of the substituents from the π-conjugated low molecular weight compound, and another semiconductor material is formed on the film. An organic thin film photoelectric conversion element characterized by producing a photoelectric conversion layer by forming a film.   The organic thin film photoelectric conversion element according to claim 1, wherein the π-conjugated low molecular weight compound is a phthalocyanine compound.   The organic thin film photoelectric conversion element according to claim 1, wherein the substituent is a substituent containing a sulfonyl group as a partial structure.   4. The organic thin film photoelectric conversion element according to claim 1, wherein the total formula weight of the detached substituents is 30% or more and 70% or less of the molecular weight of the π-conjugated low molecular compound.   The organic thin film photoelectric conversion element according to claim 1, wherein the elimination reaction of the substituent is caused by heating at 250 ° C. or higher.   6. The organic thin film photoelectric conversion element according to claim 1, wherein one of the organic semiconductor film and another semiconductor material is a p-type semiconductor and the other is an n-type semiconductor.   The organic thin-film photoelectric conversion element according to claim 1, wherein the another semiconductor material film forming method is a coating method.   The organic thin film photoelectric conversion element according to claim 1, wherein the another semiconductor material is an organic semiconductor material.   The organic thin film photoelectric conversion element according to claim 8, wherein the organic semiconductor material is an n-type organic semiconductor material.   The organic thin film photoelectric conversion element according to claim 9, wherein the n-type organic semiconductor material contains a fullerene compound.   The organic thin film photoelectric conversion element according to claim 1, wherein the organic thin film photoelectric conversion element is sealed in an inert gas atmosphere.   Forming a π-conjugated low-molecular compound on a substrate, removing some or all of the substituents from the compound to convert it into an organic semiconductor film, and applying another semiconductor material on the film The method for producing an organic thin film photoelectric conversion element according to claim 1, comprising a step of forming a film.

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