JP2014003255A - Organic thin film and photoelectric conversion element using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic thin film which allows for independent photoelectric conversion while having a function as a buffer layer, and to provide a photoelectric conversion element using the same.SOLUTION: A homogeneous film soluble in an organic solvent by having an alkyl ester group in the side-chain can be produced by coating. Subsequently, the alkyl group is detached by giving an external stimulation to obtain a thiophene copolymer composing an organic thin film 3. Since the organic thin film 3 is insoluble in an organic solvent, a lamination structure can be formed by coating. Furthermore, since the thin film is capable of photoelectric conversion independently, it is useful as a buffer layer of a photoelectric conversion element 10.

Description

  The present invention relates to an organic thin film made of a thiophene copolymer that is excellent in function as a buffer layer and capable of photoelectric conversion alone, and a photoelectric conversion element having the organic thin film.

  Photovoltaic power generation is attracting attention as the leading energy alternative to oil because it has a particularly high potential use of renewable energy. Examples of elements responsible for photovoltaic power generation include silicon-based solar cells such as single crystal silicon and amorphous silicon, and inorganic compound thin-film solar cells such as GaAs, CIGS, and CdTe. These solar cells have a relatively high photoelectric conversion efficiency, but are problematic in that they are expensive compared to other power supply costs. A factor of high cost is a process in which a semiconductor thin film must be manufactured under high vacuum and high temperature. Therefore, in recent years, an organic thin film solar cell using an organic semiconductor material which is expected to simplify the manufacturing process has been studied.

  Since the organic semiconductor thin film can be formed by a coating method or a printing method, it is expected to simplify the manufacturing process and reduce the power generation cost. In addition, since lightweight and flexible elements and modules can be manufactured, it is highly portable and has the potential to easily use electrical energy even in areas where electrical infrastructure is not established. Furthermore, since the organic semiconductor can control the absorption band by molecular design, it can provide a solar cell with various colors and excellent design.

  The current mainstream element configuration of organic thin-film solar cells is that an electron-donating organic semiconductor (p-type organic semiconductor) and an electron-accepting organic semiconductor (n-type organic semiconductor) are mixed to cause charge separation. It is a bulk heterojunction type photoelectric conversion element in which the area of the pn junction interface is increased. However, the bulk heterojunction photoelectric conversion element has a problem in that both p-type and n-type semiconductor materials are in contact with the electrode, so that charge is lost due to recombination and the photoelectric conversion efficiency remains low.

  As one method for improving the photoelectric conversion efficiency of the organic thin film solar cell, insertion of a buffer layer has been devised. The buffer layer functions to improve photoelectric conversion efficiency by blocking inflow of reverse charges to the collector electrode and suppressing charge recombination.

  For example, Patent Document 1 reports that the photoelectric conversion efficiency is improved by using a buffer layer for isolating an electrode and a photoelectric conversion active layer in an organic photoelectric conversion element. Alkali metals such as lithium halides, halides of alkaline earth metals, metal oxides and the like, and organic substances such as arylamine derivatives such as CBP (4,4′-bis (9H-carbazol-9-yl) biphenyl), bathocuproine, etc. Examples of the phenanthrene derivative are as follows. However, when these materials are formed into a film, the cost becomes high when the vacuum deposition method is used. On the other hand, as a process for realizing low cost, it is possible to form the material dissolved in various solvents by a coating method, but the solvent that can be used is limited to form a laminated structure. Moreover, it cannot apply to the thing in which the solvent which melt | dissolves does not exist. For this reason, there is a demand for a material that has a function and solubility as a buffer layer and becomes insoluble after film formation by a coating method.

  Patent Document 2 describes a polymer or oligomer having one or more polymerizable substituents as a buffer layer that has solubility but becomes insoluble after film formation by a coating method. However, when a polymerization initiator is used, charge transfer is inhibited by the initiator remaining in the system, so that an element with excellent photoelectric conversion efficiency cannot be obtained, and when the initiator is not used, it becomes insoluble. It is not possible to obtain a sufficient crosslinking density.

JP 2008-109114 A JP 2010-287767 A

  The present invention has been made in order to solve the above-described problems, and an organic thin film that can be formed by a coating method, has an excellent function as a buffer layer, and can also be subjected to photoelectric conversion alone, and the same are used. It aims at providing the photoelectric conversion element which is excellent in conversion efficiency. Moreover, an object of this invention is to provide the method of manufacturing the photoelectric conversion element which has this organic thin film easily.

  As a result of intensive studies to solve the above problems, the present inventors have been able to produce a homogeneous film that is soluble in an organic solvent and has a coating method by having an alkyl ester group in the side chain. It has been found that the rectifying property of the photoelectric conversion element is improved by using an organic thin film made of a thiophene copolymer having a carboxyl group in the side chain, obtained by desorbing as a buffer layer. Furthermore, since the organic thin film has a photoelectric conversion function alone, it is possible to increase the current of the photoelectric conversion element, and when used as a buffer layer, the conversion efficiency of the photoelectric conversion element is improved by the synergistic effect. As a result, the present invention has been completed.

（式中、Ｒ^１は置換基を有してもよい炭素数１〜２０のアルキル基、置換基を有してもよい炭素数６〜２０のアリール基又は置換基を有してもよい炭素数４〜２０のヘテロアリール基であり、Ｒ^２は水素原子、フッ素原子、置換基を有してもよい炭素数１〜２０のアルキル基、置換基を有してもよい炭素数６〜２０のアリール基又は置換基を有してもよい炭素数４〜２０のヘテロアリール基であり、ｐ＋ｑ＝ｎ、０≦ｐ＜ｎ、０＜ｑ≦ｎであり、ｎは２以上の正数である。）
で表される数平均分子量が１５，０００以上１，０００，０００以下であるチオフェン共重合体からなる膜厚が１０ｎｍ以上３０ｎｍ以下である有機薄膜；
［２］前記［１］の有機薄膜及び光電変換活性層を、少なくとも一方が光透過性を有する一対の電極の間に有する光電変換素子；
［３］前記有機薄膜を正極と光電変換活性層との間に有することを特徴とする［２］に記載の光電変換素子；
［４］前記光電変換活性層が、電子供与性有機半導体と電子受容性有機半導体との混合物である［２］または［３］に記載の光電変換素子；
［５］前記電子供与性有機半導体が、化学構造の一部にチオフェン、フルオレン、カルバゾール、ジべンゾシロール、ジベンゾゲルモール、ベンゾジチオフェン及びジケトピロロピロールから選ばれる複素環骨格を少なくとも一つ有する単量体単位からなるπ電子共役系重合体である［４］に記載の光電変換素子；
［６］前記π電子共役系重合体がブロック共重合体であることを特徴とする［５］に記載の光電変換素子；
［７］電極と有機薄膜との間に正孔輸送材料からなる正孔輸送層をさらに有する［２］〜［６］のいずれかに記載の光電変換素子；
［８］下記一般式（２）

（式中、Ｒ^１は置換基を有してもよい炭素数１〜２０のアルキル基、置換基を有してもよい炭素数６〜２０のアリール基又は置換基を有してもよい炭素数４〜２０のヘテロアリール基であり、Ｒ^２は水素原子、フッ素原子、置換基を有してもよい炭素数１〜２０のアルキル基、置換基を有してもよい炭素数６〜２０のアリール基又は置換基を有してもよい炭素数４〜２０のヘテロアリール基であり、ｎは２以上の正数である。）
で表される数平均分子量が２０，０００以上１，０００，０００以下であるチオフェン共重合体を溶媒に溶解して製膜した後、熱処理することによって、下記一般式（１）

（式中、Ｒ^１は置換基を有してもよい炭素数１〜２０のアルキル基、置換基を有してもよい炭素数６〜２０のアリール基又は置換基を有してもよい炭素数４〜２０のヘテロアリール基であり、Ｒ^２は水素原子、フッ素原子、置換基を有してもよい炭素数１〜２０のアルキル基、置換基を有してもよい炭素数６〜２０のアリール基又は置換基を有してもよい炭素数４〜２０のヘテロアリール基であり、ｐ＋ｑ＝ｎ、０≦ｐ＜ｎ、０＜ｑ≦ｎであり、ｎは２以上の正数である。）
で表される数平均分子量が１５，０００以上１，０００，０００以下であるチオフェン共重合体からなる膜厚が１０ｎｍ以上３０ｎｍ以下である有機薄膜を形成することを特徴とする、［２］〜［７］のいずれかに記載の光電変換素子の製造方法；
［９］前記溶媒が、テトラヒドロフラン、１，２−ジクロロエタン、シクロヘキサン、クロロホルム、ブロモホルム、ベンゼン、トルエン、ｏ−キシレン、クロロベンゼン、ブロモベンゼン、ヨードベンゼン、ｏ−ジクロロベンゼン、アニソール、メトキシベンゼン、トリクロロベンゼン及びピリジンから選ばれる有機溶媒またはこれらの混合溶媒であることを特徴とする［８］に記載の光電変換素子の製造方法；
［１０］前記熱処理を１８０℃以上２８０℃以下で行うことを特徴とする［８］または［９］に記載の光電変換素子の製造方法；
［１１］前記有機薄膜を形成した後、前記有機薄膜の表面にさらに光電変換活性層を塗布によって形成する［８］〜［１０］のいずれかに記載の光電変換素子の製造方法；
に関する。 That is, the present invention
[1] The following general formula (1)

(Wherein R ¹ is an optionally substituted alkyl group having 1 to 20 carbon atoms, an optionally substituted aryl group having 6 to 20 carbon atoms, or an optionally substituted carbon. A heteroaryl group having 4 to 20 carbon atoms, and R ² is a hydrogen atom, a fluorine atom, an optionally substituted alkyl group having 1 to 20 carbon atoms, or an optionally substituted carbon atom having 6 to 20 carbon atoms. Or a heteroaryl group having 4 to 20 carbon atoms which may have a substituent, p + q = n, 0 ≦ p <n, 0 <q ≦ n, and n is a positive number of 2 or more. is there.)
An organic thin film having a thickness of 10 nm to 30 nm, comprising a thiophene copolymer having a number average molecular weight of 15,000 to 1,000,000;
[2] A photoelectric conversion element having the organic thin film and the photoelectric conversion active layer of [1] between a pair of electrodes, at least one of which has light transmittance;
[3] The photoelectric conversion element according to [2], which has the organic thin film between a positive electrode and a photoelectric conversion active layer;
[4] The photoelectric conversion element according to [2] or [3], wherein the photoelectric conversion active layer is a mixture of an electron donating organic semiconductor and an electron accepting organic semiconductor;
[5] The electron-donating organic semiconductor has at least one heterocyclic skeleton selected from thiophene, fluorene, carbazole, dibenzosilole, dibenzogermole, benzodithiophene and diketopyrrolopyrrole as part of the chemical structure. The photoelectric conversion device according to [4], which is a π-electron conjugated polymer composed of monomer units;
[6] The photoelectric conversion element according to [5], wherein the π-electron conjugated polymer is a block copolymer;
[7] The photoelectric conversion device according to any one of [2] to [6], further including a hole transport layer made of a hole transport material between the electrode and the organic thin film;
[8] The following general formula (2)

(Wherein R ¹ is an optionally substituted alkyl group having 1 to 20 carbon atoms, an optionally substituted aryl group having 6 to 20 carbon atoms, or an optionally substituted carbon. A heteroaryl group having 4 to 20 carbon atoms, and R ² is a hydrogen atom, a fluorine atom, an optionally substituted alkyl group having 1 to 20 carbon atoms, or an optionally substituted carbon atom having 6 to 20 carbon atoms. And a heteroaryl group having 4 to 20 carbon atoms that may have an aryl group or a substituent, and n is a positive number of 2 or more.)
A thiophene copolymer having a number average molecular weight of 20,000 or more and 1,000,000 or less represented by the following formula is dissolved in a solvent to form a film, followed by heat treatment to give the following general formula (1)

(Wherein R ¹ is an optionally substituted alkyl group having 1 to 20 carbon atoms, an optionally substituted aryl group having 6 to 20 carbon atoms, or an optionally substituted carbon. A heteroaryl group having 4 to 20 carbon atoms, and R ² is a hydrogen atom, a fluorine atom, an optionally substituted alkyl group having 1 to 20 carbon atoms, or an optionally substituted carbon atom having 6 to 20 carbon atoms. Or a heteroaryl group having 4 to 20 carbon atoms which may have a substituent, p + q = n, 0 ≦ p <n, 0 <q ≦ n, and n is a positive number of 2 or more. is there.)
An organic thin film having a film thickness of 10 nm or more and 30 nm or less is formed of a thiophene copolymer having a number average molecular weight of 15,000 or more and 1,000,000 or less [2] to [7] The method for producing a photoelectric conversion element according to any one of the above;
[9] The solvent is tetrahydrofuran, 1,2-dichloroethane, cyclohexane, chloroform, bromoform, benzene, toluene, o-xylene, chlorobenzene, bromobenzene, iodobenzene, o-dichlorobenzene, anisole, methoxybenzene, trichlorobenzene and The method for producing a photoelectric conversion element according to [8], which is an organic solvent selected from pyridine or a mixed solvent thereof;
[10] The method for producing a photoelectric conversion element according to [8] or [9], wherein the heat treatment is performed at 180 ° C. or higher and 280 ° C. or lower;
[11] The method for producing a photoelectric conversion element according to any one of [8] to [10], wherein after forming the organic thin film, a photoelectric conversion active layer is further formed on the surface of the organic thin film by coating;
About.

  ADVANTAGE OF THE INVENTION According to this invention, the organic thin film which can form the laminated structure by the apply | coating method, is excellent in the function as a buffer layer, and can also perform photoelectric conversion independently can be provided. Moreover, the photoelectric conversion element which is excellent in the photoelectric conversion efficiency which has this organic thin film, and its simple manufacturing method can be provided.

It is a schematic diagram of the photoelectric conversion element which has the organic thin film and photoelectric conversion active layer of this invention. It is a schematic diagram of the organic photoelectric conversion element which has the organic thin film of this invention, a photoelectric conversion active layer, and a positive hole transport layer. It is a schematic diagram of the photoelectric conversion element which has the organic thin film of this invention, a photoelectric conversion active layer, a positive hole transport layer, and an electron carrying layer.

The organic thin film of the present invention comprises a thiophene copolymer represented by the following general formula (1) (hereinafter sometimes referred to as thiophene copolymer (1)). In the formula, R ¹ is an optionally substituted alkyl group having 1 to 20 carbon atoms, an optionally substituted aryl group having 6 to 20 carbon atoms, or an optionally substituted carbon number. a 4-20 heteroaryl group, R ² represents a hydrogen atom, a fluorine atom, an alkyl group having 1 to 20 carbon atoms which may have a substituent, an even better C6-20 have substituent It is a C4-C20 heteroaryl group which may have an aryl group or a substituent. The substituents that R ¹ and R ² may have may be the same or different.

The alkyl group used for R ¹ in the general formula (1) may be a linear or branched alkyl group or a cyclic cycloalkyl group. For example, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group, tert-pentyl group, Linear or branched such as n-hexyl group, isohexyl group, 2-methyl-2-hexyl group, 2-ethylhexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, dodecyl group Chain alkyl group; cycloalkyl groups such as cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, cyclooctyl group, cyclononyl group, cyclodecyl group, cycloundecyl group, cyclododecyl group and the like can be mentioned.

The alkyl group of R ¹ may have a substituent. Examples of the substituent include aryl groups such as a phenyl group, a naphthyl group, an anthryl group, and a phenanthryl group; a pyridyl group, a thienyl group, a furyl group, and a pyrrolyl group. Group, imidazolyl group, pyrazinyl group, oxazolyl group, thiazolyl group, pyrazolyl group, benzothiazolyl group, benzimidazolyl group and other heteroaryl groups; methoxy group, ethoxy group, n-propyloxy group, isopropoxy group, n-butoxy group, isobutoxy group Group, sec-butoxy group, tert-butoxy group, pentyloxy group, isopentyloxy group, neopentyloxy group, n-hexyloxy group, cyclohexyloxy group, heptyloxy group, n-octyloxy group, nonyloxy group, n -Decyloxy group, n-dodecylo group Alkoxy groups such as xy group; alkylthio groups such as methylthio group, ethylthio group, propylthio group and butylthio group; arylthio groups such as phenylthio group and naphthylthio group; methoxycarbonyl group, ethoxycarbonyl group, propoxycarbonyl group, isopropoxycarbonyl group, alkoxycarbonyl groups such as n-butoxycarbonyl group, isobutoxycarbonyl group, sec-butoxycarbonyl group, tert-butoxycarbonyl group, pentyloxycarbonyl group, hexyloxycarbonyl group, heptyloxycarbonyl group, octyloxycarbonyl group; Alkyl sulfenyl groups such as foxoxide groups and ethyl sulfoxide groups; aryl sulfoxide groups such as phenyl sulfoxide groups; methyl sulfonyloxy groups; Sulphonic acid ester groups such as tilsulfonyloxy group, phenylsulfonyloxy group, methoxysulfonyl group, ethoxysulfonyl group, phenyloxysulfonyl group; dimethylamino group, diphenylamino group, methylphenylamino group, methylamino group, ethylamino group, etc. A primary or secondary amino group; methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert, substituted with acetyl, benzoyl, benzenesulfonyl, tert-butoxycarbonyl, etc. -An amino group which may be substituted with an alkyl group such as a butyl group or a phenyl group or an aryl group; a cyano group; a nitro group; a halogen atom such as a fluorine atom, a chlorine atom, a bromine atom or an iodine atom; .

Examples of the aryl group used for R ¹ in the general formula (1) include a phenyl group, a naphthyl group, an anthryl group, and a phenanthryl group. These aryl groups may have a substituent, and as such a substituent, a substituent other than the aryl group exemplified in the description of the alkyl group, the above-described alkyl group, and the like can be used.

Examples of the heteroaryl group used for R ¹ in the general formula (1) include a pyridyl group, a thienyl group, a furyl group, and a pyrrolyl group. These heteroaryl groups may have a substituent, and as such a substituent, a substituent other than the heteroaryl group exemplified in the description of the alkyl group, the above-described alkyl group, and the like can be used.

R ¹ is preferably an alkyl group which may have a substituent from the viewpoint of ease of synthesis and production cost. Among these, a branched alkyl group is preferable from the viewpoint of imparting solubility in an organic solvent and being easily removed by thermal stimulation, and a bulky alkyl such as a 2-methyl-2-hexyl group or a 2-ethylhexyl group. More preferred are groups.

Examples of the alkyl group, aryl group and heteroaryl group used for R ² in the general formula (1) include the same groups as those described above for R ¹ , and these may have a substituent. Examples of the group include the same groups as those described for R ¹ . R ² can be arbitrarily selected depending on the characteristics required for the polymer. For example, from the viewpoint of improving the main chain skeleton planarity, a hydrogen atom and a fluorine atom are used. From the viewpoint of improving the crystallinity of the polymer, an n-hexyl group, an n-heptyl group, and an n-octyl group are used to improve the polymer solubility. Is preferably a 2-ethylhexyl group.

  In the general formula (1), p + q = n, 0 ≦ p <n, and 0 <q ≦ n. n represents the degree of polymerization of the thiophene copolymer represented by the general formula (1), and may be any positive number of 2 or more, and is not particularly limited. From the viewpoint of photoelectric conversion characteristics, n is preferably 10 or more.

  The thiophene copolymer (1) is required to have a number average molecular weight of 15,000 or more converted by polystyrene standard using gel permeation chromatography. Thereby, formation of a homogeneous thin film is possible, high photoelectric conversion characteristics can be expressed, and when used as a buffer layer of a photoelectric conversion element, photoelectric conversion efficiency can be improved. The number average molecular weight is preferably 18,000 or more, and more preferably 25,000 or more. When the number average molecular weight is 18,000 or more, the obtained organic thin film has high crystallinity, and is excellent in light absorption characteristics and charge mobility, so that a photoelectric conversion element with more excellent photoelectric conversion efficiency can be obtained. The upper limit of the number average molecular weight is 1,000,000 or less and more preferably 500,000 or less from the viewpoint of solubility.

  The film thickness of the organic thin film of the present invention comprising the thiophene copolymer (1) needs to be 10 nm or more and 30 nm or less. When the film thickness is less than 10 nm, a sufficient function as a buffer layer cannot be obtained, and when the film thickness exceeds 30 nm, the resistance increases and causes a decrease in photoelectric conversion efficiency. More preferably, the film thickness is 10 nm or more and 20 nm or less.

The method for producing an organic thin film of the present invention is not particularly limited, but a thiophene copolymer represented by the following general formula (2) (hereinafter sometimes referred to as thiophene copolymer (2)) is a solvent. It can be produced by dissolving R ¹ in a film and then removing R ¹ by external stimulation to obtain a thiophene copolymer (1). In the following general formula (2), R ¹ and R ² are as defined above. R ¹ is preferably an alkyl group which may have a substituent from the viewpoint of ease of synthesis and production cost, and is branched from the viewpoint of imparting solubility in an organic solvent and being easily desorbed by heat treatment. A chain alkyl group is more preferable, and a bulky alkyl group such as a 2-methyl-2-hexyl group and a 2-ethylhexyl group is more preferable.

  The thiophene copolymer (2) can be obtained, for example, by copolymerizing a thiophene having an ester group at the 3-position and a substituted or unsubstituted thiophene by a so-called coupling reaction in the presence of a metal complex catalyst. it can. As the metal complex catalyst, a nickel complex or a palladium complex is preferably used.

  The thiophene copolymer represented by the general formula (2) preferably has a number average molecular weight of 20,000 or more converted by polystyrene standard using gel permeation chromatography. If it is less than 20,000, the number average molecular weight of the resulting thiophene copolymer (1) becomes less than 15,000, and the effects of the present invention may not be obtained. The number average molecular weight of the thiophene copolymer (2) is preferably 25,000 or more, and more preferably 35,000 or more. Although an upper limit is not specifically limited, It is preferable that it is 1,000,000 or less from a viewpoint of film forming property.

The external stimulus for detaching R ¹ in the formula (2) is not particularly limited as long as it can detach R ¹ , but is preferably a heat treatment from the viewpoint of ease of control and processing. The temperature of the heat treatment is not particularly limited as long as it is a temperature capable of desorbing R ¹ , but is preferably 180 ° C. or higher, and is 280 from the viewpoint of excessive polymer modification and suppression of deterioration of other members, process control, safety and the like. It is preferable that it is below ℃. Furthermore, it is more preferable that it is 250 degrees C or less from a viewpoint of producing the photoelectric conversion element which has high photoelectric conversion efficiency.

In the process of producing an organic thin film composed of the thiophene copolymer (1) by detaching R ¹ from the thiophene copolymer (2), the proportion of R ¹ remaining without being desorbed is the above general formula (1). P in the formula, and the ratio of desorption and replacement with hydrogen atoms is represented by q in the formula (1). The ratio of p and q is not particularly limited and depends on the ease of R ¹ desorption and the heat treatment temperature, but q / (p + q) is preferably 0.5 or more and 1 or less, and 0.8 or more and 1 The following is more preferable. The closer q / (p + q) is to 1, the more R ¹ is desorbed.

  The thiophene copolymer (2) can be dissolved in various organic solvents to form a uniform solution, and can be applied to a substrate to form a thin film. The soluble solvent is not particularly limited, and examples thereof include tetrahydrofuran, 1,2-dichloroethane, cyclohexane, chloroform, bromoform, benzene, toluene, o-xylene, chlorobenzene, bromobenzene, iodobenzene, o-di. Examples include chlorobenzene, anisole, methoxybenzene, trichlorobenzene, pyridine and the like. These solvents may be used singly or in combination of two or more, but o-dichlorobenzene, chlorobenzene, bromobenzene, iodobenzene, chloroform and mixtures thereof having particularly high solubility are preferred, and o- Particularly preferred are dichlorobenzene, chlorobenzene and mixtures thereof.

  The concentration at the time of preparing the solution of the thiophene copolymer (2) is not particularly limited as long as the organic thin film of the present invention can be obtained, but from the viewpoint of obtaining a thin film having a thickness of 10 nm or more and 30 nm or less, The concentration of the thiophene copolymer is preferably 0.5 mg / mL or more and 20 mg / mL or less. Moreover, although the heating conditions at the time of melt | dissolution are not specifically limited, It is preferable that heating temperature is 10 to 120 degreeC from a viewpoint of stability of a compound, productivity, and safety. The stirring conditions are not particularly limited, but the stirring speed is preferably 50 rpm to 1500 rpm, and more preferably 100 rpm to 700 rpm.

  The solution of the thiophene copolymer (2) may be filtered as necessary. By filtering, foreign matter can be removed and a good quality thin film with few defects can be obtained. As the filter medium used in the filtration step, various commercially available ones can be used. Although the filter medium can be selected from materials that do not dissolve in accordance with the organic solvent used, those made of polyvinylidene fluoride or polytetrafluoroethylene are preferably used from the viewpoint of solvent resistance. The pore diameter of the filter medium to be used can be arbitrarily selected according to the solubility of the thiophene copolymer (2). However, in order to obtain the homogeneous organic thin film of the present invention, the pore diameter is 0.1 μm to 5 μm. The pore diameter is preferable, and the pore diameter is more preferably 0.2 μm or 0.45 μm.

  The method for forming the organic thin film of the present invention is not particularly limited, and in the application of the thiophene copolymer solution to a substrate or a support, a conventionally known coating method using a liquid coating material is used. Either can be adopted. For example, dip coating method, spray coating method, ink jet method, aerosol jet method, spin coating method, bead coating method, wire bar coating method, blade coating method, roller coating method, curtain coating method, slit die coater method, gravure coater method , Slit reverse coater method, micro gravure method, comma coater method, etc. can be adopted, and the coating method can be selected according to the coating film properties to be obtained, such as coating thickness control and orientation control. That's fine. At this time, material denaturation can be suppressed by forming a film in an inert gas atmosphere as necessary.

  The organic thin film of the present invention is used as a buffer layer of a photoelectric conversion element, thereby blocking the inflow of reverse charges to the collector electrode to improve the rectification property of the photoelectric conversion element, and the organic thin film of the present invention itself also performs photoelectric conversion. Thus, a photoelectric conversion element having excellent photoelectric conversion efficiency can be obtained. Below, the photoelectric conversion element using the organic thin film of this invention is demonstrated.

  The photoelectric conversion element using the organic thin film of the present invention has the organic thin film and the photoelectric conversion active layer of the present invention between a pair of electrodes, at least one of which has optical transparency, that is, a positive electrode and a negative electrode.

  The operation mechanism of the photoelectric conversion element is an electron accepting compound in which light energy incident from a transparent or translucent electrode is an electron accepting component and / or an electron donating compound in the photoelectric conversion active layer. Absorbed and produces excitons that combine electrons and holes. When the generated excitons move and reach the heterojunction interface where the electron-accepting compound and the electron-donating compound are adjacent to each other, electrons and holes are separated due to the difference in HOMO energy and LUMO energy at the interface. Electric charges (electrons and holes) that can move are generated. The generated charges can be taken out as electric energy (current) by moving to the electrodes.

  The photoelectric conversion element is usually formed on a substrate. This substrate may be any substrate that does not change when an electrode is formed and an organic layer is formed. As a substrate material, for example, an inorganic material such as alkali-free glass, quartz glass, or silicon, or any organic material such as polyester, polycarbonate, polyolefin, polyamide, polyimide, polyphenylene sulfide, polyparaxylene, epoxy resin, or fluorine resin can be used. Films and plates produced by the above method can be used. In the case of an opaque substrate, the opposite electrode, that is, the electrode far from the substrate is preferably transparent or translucent. In the case of a transparent substrate, the electrode in contact with the substrate may be a light transmissive electrode.

  Examples of the transparent or translucent electrode material having optical transparency include a conductive metal oxide film and a translucent metal thin film. Specifically, indium oxide, zinc oxide, tin oxide, and their composites, indium tin oxide (ITO), fluorine tin oxide (FTO), antimony tin oxide, indium zinc oxide (IZO), gallium / zinc / oxide, aluminum / zinc / oxide, antimony / zinc / oxide conductive film, gold, platinum, silver, copper ultrathin film is used, ITO , FTO, IZO and tin oxide are preferred. Examples of the method for producing the electrode include a vacuum deposition method, a sputtering method, an ion plating method, and a plating method. Moreover, you may use organic transparent conductive films, such as polyaniline and its derivative (s), polythiophene, and its derivative (s) as a transparent electrode material.

  As the counter electrode material, a known metal, a conductive polymer, or the like can be used, and it may not have optical transparency, and may be transparent or translucent. Preferably, one of the pair of electrodes is preferably made of a material having a low work function. For example, metals such as lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium, aluminum, scandium, vanadium, zinc, yttrium, indium, cerium, samarium, europium, terbium, ytterbium, and two of them One or more alloys, or one or more of them, and an alloy of one or more of gold, silver, platinum, copper, manganese, titanium, cobalt, nickel, tungsten, tin, graphite, or a graphite intercalation compound are used. It is done. Examples of the alloy include magnesium-silver alloy, magnesium-indium alloy, magnesium-aluminum alloy, indium-silver alloy, lithium-aluminum alloy, lithium-magnesium alloy, lithium-indium alloy, calcium-aluminum alloy, and the like.

  For the electrode used in the photoelectric conversion element of the present invention, it is preferable to use a conductive material having a high work function on one side and a conductive material having a low work function on the other side. The electrode using the conductive material having a small work function becomes the negative electrode.

  The photoelectric conversion element of the present invention comprises a photoelectric conversion activity comprising an organic semiconductor composition containing an electron-donating organic semiconductor (p-type organic semiconductor) and an electron-accepting organic semiconductor (n-type organic semiconductor) between a positive electrode and a negative electrode. Has a layer.

  The p-type organic semiconductor used for the photoelectric conversion active layer of the photoelectric conversion element of the present invention may be a low molecular compound or a high molecular compound. Examples of the low molecular weight compound include phthalocyanine, metal phthalocyanine, porphyrin, metal porphyrin, oligothiophene, tetracene, pentacene, and rubrene. The polymer compound includes a monomer unit having at least one heterocyclic skeleton selected from thiophene, fluorene, carbazole, dibenzosilole, dibenzogermole, diketopyrrolopyrrole and derivatives thereof as part of the chemical structure. Among these, π electron conjugated polymers composed of monomer units having a heterocyclic skeleton containing at least one thiophene ring as part of the chemical structure are photoelectric conversion efficiencies. From the viewpoint of Examples of the heterocyclic skeleton containing at least one thiophene ring as a part of the chemical structure include cyclopentadithiophene, thienopyrrole, dithienopyrrole, dithienosilole, dithienogermol, benzodithiophene, naphthodithiophene, and derivatives thereof. It is done. These may introduce a substituent into the main chain skeleton for the purpose of controlling solubility and polarity. These polymer compounds may be either homopolymers, random or block copolymers, and the molecular chain may be linear, branched, physically or chemically cross-linked. Among these, from the viewpoint of applying to a coating process, a polymer compound is preferable, and a π-electron conjugated polymer comprising a monomer unit having a heterocyclic skeleton including at least one thiophene ring as a part of the chemical structure is provided. More preferred. Moreover, you may use the thiophene copolymer represented by the said Formula (1) as a p-type organic semiconductor.

  The degree of polymerization of the π-electron conjugated polymer is not particularly limited, but from the viewpoint of obtaining a homogeneous thin film having no defects, the number average molecular weight converted to polystyrene standard is 10,000 using gel permeation chromatography. The above is preferable. Further, from the viewpoint of obtaining an element with high photoelectric conversion efficiency, the number average molecular weight is more preferably 20,000 or more.

  The n-type organic semiconductor used for the photoelectric conversion active layer of the photoelectric conversion element of this invention will not be specifically limited if it is an organic material which has an electron-accepting property. As an n-type organic semiconductor, for example, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, N, N′-dioctyl-3,4,9 , 10-naphthyltetracarboxydiimide, 2- (4-biphenylyl) -5- (4-tert-butylphenyl) -1,3,4-oxadiazole, 2,5-di (1-naphthyl) -1, Oxazole derivatives such as 3,4-oxadiazole, triazole derivatives such as 3- (4-biphenylyl) -4-phenyl-5- (4-t-butylphenyl) -1,2,4-triazole, phenanthroline derivatives, Induction of introduction of cyano group into C60 or C70 fullerene derivative, carbon nanotube, poly-p-phenylene vinylene polymer A conductor (CN-PPV) etc. are mentioned. These may be used alone or in combination of two or more. Among these, fullerene derivatives are preferably used from the viewpoint of an n-type semiconductor that is stable and excellent in carrier mobility.

  Fullerene derivatives suitably used as the n-type organic semiconductor include unsubstituted ones such as C60, C70, C76, C78, C82, C84, C90, and C94, and [6,6] -phenyl C61 butyric acid. Methyl ester (PC61BM), [5,6] -phenyl C61 butyric acid methyl ester, [6,6] -phenyl C61 butyric acid n-butyl ester, [6,6] -phenyl C61 butyric acid i-butyl Ester, [6,6] -phenyl C61 butyric acid hexyl ester, [6,6] -phenyl C61 butyric acid dodecyl ester, [6,6] -diphenyl C62 bis (butyric acid methyl ester) (bis-PC62BM) ), [6,6] -phenyl C71 butyric Acid methyl ester (PC71BM), [6,6] -diphenyl C72 bis (butyric acid methyl ester) (bis-PC72BM), indene C60-mono adduct, indene C60-bis adduct, indene C70-mono adduct, Examples thereof include substituted derivatives including indene C70-bis adduct.

  The fullerene derivatives can be used alone or as a mixture thereof. From the viewpoint of solubility in organic solvents, PC61BM, bis-PC62BM, PC71BM, bis-PC72BM, indene C60-mono adduct, indene C60-bis adduct, indene C70-mono adduct, and indene C70-bis adduct are preferable. Used for. Further, among these, from the viewpoint of light absorption, PC71BM, bis-PC72BM, indene C70-mono adduct, and indene C70-bis adduct are preferable. From the viewpoint of production cost, PC61BM, bis-PC62BM, indene C60- Bis adducts are more preferably used.

  The contents of the p-type organic semiconductor and the n-type organic semiconductor in the organic semiconductor composition constituting the photoelectric conversion active layer are not particularly limited. The composition ratio of the p-type organic semiconductor to the n-type organic semiconductor is preferably in the range of p-type organic semiconductor: n-type organic semiconductor = 1 to 99:99 to 1, more preferably 20 to 80:80 to 20. Range. Moreover, it is preferable that the sum of the mass of a p-type organic semiconductor and an n-type organic semiconductor is 0.1-10 mass parts with respect to 100 mass parts of the sum of the mass of the dissolution solvent mentioned later, 0.5-5 More preferably, it is part by mass.

  The photoelectric conversion active layer can be produced by dissolving the organic semiconductor composition containing the p-type organic semiconductor and the n-type organic semiconductor in a solvent, coating the substrate, and forming a film. Solvent solvents include tetrahydrofuran, 1,2-dichloroethane, cyclohexane, chloroform, bromoform, benzene, toluene, o-xylene, chlorobenzene, bromobenzene, iodobenzene, o-dichlorobenzene, anisole, methoxybenzene, trichlorobenzene, pyridine, etc. Is mentioned. These solvents may be used singly or in combination of two or more, but o-dichlorobenzene, chlorobenzene, bromobenzene, iodo having high solubility especially for each of p-type organic semiconductor and n-type organic semiconductor. Benzene, chloroform and mixtures thereof are preferred. More preferably, o-dichlorobenzene, chlorobenzene, and a mixture thereof having the highest solubility for each of the p-type organic semiconductor and the n-type organic semiconductor are used.

  In the above step, the organic semiconductor composition solution may contain an additive other than the p-type organic semiconductor and the n-type organic semiconductor. In the process of forming a photoelectric conversion active layer by adding an additive, a fine and continuous phase separation structure of a p-type organic semiconductor and an n-type organic semiconductor is formed, so that the photoelectric conversion active layer is excellent in photoelectric conversion efficiency Can be obtained.

  As additives, octanedithiol (boiling point: 270 ° C.), dibromooctane (boiling point: 272 ° C.), diiodooctane (boiling point: 327 ° C.), diiodohexane (boiling point: 142 ° C. [10 mmHg]), diiodobutane (boiling point: 125 ° C. [12 mmHg]), diethylene glycol diethyl ether (boiling point: 162 ° C.), N-methyl-2-pyrrolidone (boiling point: 229 ° C.), 1- or 2-chloronaphthalene (boiling point: 256 ° C.), and the like. Among these, from the viewpoint of obtaining a photoelectric conversion element having excellent photoelectric conversion efficiency, octanedithiol, dibromooctane, diiodooctane, 1- or 2-chloronaphthalene is preferably used.

  Furthermore, the said organic-semiconductor composition may contain other additive components, such as surfactant, binder resin, and a filler, in the range which does not inhibit the effect of this invention.

  The film thickness of the photoelectric conversion active layer is usually 1 nm to 2000 nm, preferably 2 nm to 1000 nm, more preferably 5 nm to 500 nm, and further preferably 20 nm to 300 nm. If the film thickness is too thin, the light is not sufficiently absorbed. Conversely, if it is too thick, it becomes difficult for the charge to reach the electrode due to resistance loss.

  The photoelectric conversion active layer may be further subjected to heat or solvent annealing as necessary. By performing the annealing treatment, it is possible to change the crystallinity of the photoelectric conversion active layer material and the phase separation structure between the p-type organic semiconductor and the n-type organic semiconductor, thereby obtaining an element having excellent photoelectric conversion characteristics. In addition, you may perform this annealing process after formation of a negative electrode.

  The thermal annealing is performed by holding the substrate on which the photoelectric conversion active layer is formed at a desired temperature. The thermal annealing may be performed under reduced pressure or in an inert gas atmosphere, and a preferable temperature is 40 ° C to 150 ° C, more preferably 70 ° C to 150 ° C. If the temperature is low, a sufficient effect cannot be obtained. If the temperature is too high, the organic thin film is oxidized and / or decomposed, and sufficient photoelectric conversion characteristics cannot be obtained.

  The solvent annealing is performed by holding the substrate on which the photoelectric conversion active layer is formed in a solvent atmosphere for a desired time. The annealing solvent at this time is not particularly limited, but is preferably a good solvent for the photoelectric conversion active layer. Solvent annealing may be performed in a state where the organic semiconductor composition constituting the photoelectric conversion active layer is applied onto the substrate and the solvent remains in the composition.

  The photoelectric conversion element of this invention may provide a positive hole transport layer as needed. The material for forming the hole transport layer is not particularly limited as long as it has p-type semiconductor characteristics. However, polythiophene polymers, polyaniline polymers, poly-p-phenylene vinylene polymers, polyfluorene polymers are not limited. Preferred are conductive polymers such as coalescence, low molecular organic compounds exhibiting p-type semiconductor properties such as phthalocyanine derivatives (such as H2Pc, CuPc, and ZnPc), porphyrin derivatives, and metal oxides such as molybdenum oxide, zinc oxide, and vanadium oxide. Used. In particular, polyethylenedioxythiophene (PEDOT), which is a polythiophene polymer, or PEDOT to which polystyrene sulfonate (PSS) is added is preferably used. The hole transport layer preferably has a thickness of 1 nm to 600 nm, more preferably 20 nm to 300 nm.

  The photoelectric conversion element of this invention may provide an electron carrying layer as needed. The material for forming the electron transport layer is not particularly limited as long as it has n-type semiconductor characteristics, but the above-described electron-accepting organic materials (NTCDA, PTCDA, PTCDI-C8H, oxazole derivatives, triazole derivatives, phenanthroline derivatives, Fullerene derivatives, CNT, CN-PPV, etc.) are preferably used. The thickness of the electron transport layer is preferably 1 nm to 600 nm, more preferably 5 nm to 100 nm.

  In the photoelectric conversion element of the present invention, a metal fluoride may be provided as a buffer layer for facilitating charge transfer between the electrode and the organic thin film or photoelectric conversion active layer of the present invention and the electrode, if necessary. Examples of the metal fluoride include lithium fluoride, sodium fluoride, potassium fluoride, magnesium fluoride, calcium fluoride, cesium fluoride, and lithium fluoride is particularly preferably used. The buffer layer preferably has a thickness of 0.05 nm to 50 nm, more preferably 0.5 nm to 20 nm.

  A preferred embodiment of a multilayered photoelectric conversion element having an organic thin film of the present invention will be described with reference to the drawings. FIG. 1 shows a photoelectric conversion element 10 according to the first embodiment. The substrate 1, the organic thin film 3 of the present invention, the photoelectric conversion active layer 4, and a pair of electrodes 2 at least one of which has optical transparency and 5 is a photoelectric conversion element. Any of the electrode materials described above may be used for the transparent electrode 2 and the counter electrode 5, and an electrode using a conductive material having a large work function is selected as a positive electrode, and an electrode using a conductive material having a small work function. Becomes the negative electrode. The organic thin film of the present invention is preferably used as a buffer layer between the positive electrode and the photoelectric conversion active layer. Thereby, inflow of the electron which is a reverse charge to the positive electrode is shielded, the rectification property of the photoelectric conversion element can be improved, and the conversion efficiency can be improved. That is, in FIG. 1, it is preferable that the transparent electrode 2 is a positive electrode.

  FIG. 2 shows a photoelectric conversion element 10 according to the second embodiment. The substrate 1, the organic thin film 3 of the present invention, the photoelectric conversion active layer 4, at least one of which has a pair of light-transmitting electrodes 2, 2. 5 and a photoelectric conversion element having a hole transport layer 6. The hole transport layer 6 is preferably used between the positive electrode and the organic thin film of the present invention. In FIG. 2, the transparent electrode 2 is preferably the positive electrode. The hole transport layer 6 may use any of the hole transport materials described above.

  FIG. 3 shows a photoelectric conversion element 10 according to the third embodiment. The substrate 1, the organic thin film 3 of the present invention, the photoelectric conversion active layer 4, a pair of electrodes 2 and 5, at least one of which is transparent, A photoelectric conversion element having a hole transport layer 6 and an electron transport layer 7. The electron transport layer 7 is preferably used between the negative electrode and the photoelectric conversion active layer. In FIG. 3, the transparent electrode 2 is preferably the positive electrode. The electron transport layer 7 may use any of the electron transport materials described above.

  The photoelectric conversion element of the present invention may be used as a tandem photoelectric conversion element. The tandem photoelectric conversion element can be produced using a method known in the literature, for example, a method described in Science, 2007, Vol. 317, pp222. Specifically, the photoelectric conversion active layer (I) capable of absorbing and photoelectrically converting the charge recombination layer to the long wavelength side (up to 1100 nm) and the photoelectric conversion in the ultraviolet to visible light region (190 to 700 nm) are possible. A structure sandwiched between the photoelectric conversion active layer (II) may be mentioned. The order of connection between the photoelectric conversion active layer (I) and the photoelectric conversion active layer (II) may be reversed.

  The charge recombination layer functions to recombine electrons generated in the positive-electrode side photoelectric conversion active layer and holes generated in the negative-electrode side photoelectric conversion active layer. Holes and electrons generated by charge separation in each photoelectric conversion active layer move toward the positive electrode and the negative electrode, respectively, by an internal electric field in the photoelectric conversion active layer. At this time, holes generated in the photoelectric conversion active layer on the positive electrode side and electrons generated in the photoelectric conversion active layer on the negative electrode side are taken out to the positive electrode and the negative electrode, respectively, and electrons generated on the photoelectric conversion active layer on the positive electrode side and the negative electrode side When the holes generated in the photoelectric conversion active layer are recombined, each photoelectric conversion active layer functions as a battery electrically connected in series, and the open circuit voltage increases.

  The charge recombination layer preferably has optical transparency so that the plurality of photoelectric conversion active layers can absorb light. Further, the charge recombination layer need only be designed so that holes and electrons are sufficiently recombined. Therefore, the charge recombination layer does not necessarily have to be a film. For example, it is uniformly formed on the photoelectric conversion active layer. It may be a metal cluster. Therefore, the charge recombination layer includes a very thin metal film or metal cluster made of gold, platinum, chromium, nickel, lithium, magnesium, calcium, tin, silver, aluminum or the like and having a light transmittance of several nm or less. (Including alloys), ITO, IZO, AZO, GZO, FTO, highly transparent metal oxide films and clusters such as titanium oxide and molybdenum oxide, conductive organic material films such as PEDOT to which PSS is added, or These composites are used. For example, uniform silver clusters can be formed by depositing silver so as to be several nm or less on a quartz oscillator film thickness monitor using a vacuum deposition method. In addition, if a titanium oxide film is formed, for example, the sol-gel method described in Advanced Materials, 2006, Vol. 18, pp572 may be used. If it is a composite metal oxide such as ITO or IZO, the film may be formed by sputtering. The formation method and type of these charge recombination layers are appropriately determined in consideration of the non-destructive property to the photoelectric conversion active layer at the time of charge recombination layer formation, the formation method of the next photoelectric conversion active layer, etc. Just choose.

  The photoelectric conversion element provided with the organic thin film of the present invention is excellent in photoelectric conversion efficiency, and can be applied to various photosensors including solar cells.

  Moreover, since the organic thin film of the present invention can be formed by a coating method and has a photoelectric conversion function by itself, it can be applied to a switching device in addition to the organic photoelectric conversion element. The switching device is a device in which the organic thin film of the present invention is sandwiched between a pair of electrodes, at least one of which is transparent. A small current is generated by sensing light to control on / off of a circuit. Furthermore, the organic thin film of this invention can be used also as a positive electrode buffer layer of an organic electroluminescent element.

  Examples of the present invention will be described in detail below, but the scope of the present invention is not limited to these examples.

About the molecular structure of the compound obtained by the following synthesis examples, the structure was identified by < ¹ > H-NMR measurement. The apparatus used was GSX-270 (manufactured by JEOL Ltd.), the solvent was deuterated chloroform (manufactured by Wako Pure Chemical Industries, Ltd.), and the temperature was measured at 25 ° C.

The number average molecular weight (Mn) and the weight average molecular weight (Mw) of the polymer were both measured using size exclusion chromatography (SEC) and calculated as polystyrene equivalent molecular weight. Details of the measurement conditions are shown below.
<Measurement conditions>
Apparatus: High performance liquid chromatography SSC-7000 (manufactured by Senshu Kagaku Co.)
Column: HT-G and GPC HT-806M (manufactured by Showa Denko KK) are connected in two (column temperature: 135 ° C.)
Mobile phase: o-dichlorobenzene

Thermogravimetric analysis (TG-DTA) and Fourier transform infrared spectrophotometer (FT-IR) were performed in order to analyze the elimination behavior of the side chain substituents by heating the polymer. Details of the measurement conditions are shown below.
<Analysis conditions for TG-DTA>
Apparatus: Differential type differential thermal balance Thermo plus TG8120 (manufactured by Rigaku Corporation)
Measurement range: 25-250 ° C
Temperature increase rate: 10 ° C / min
<FT-IR analysis conditions>
Apparatus: Fourier transform infrared spectrophotometer JIR-5500 (manufactured by JEOL)
Mode: attenuated total reflection (ATR) method Integration count: 128 times

The production process of the thiophene copolymer used for the organic thin film of the present invention is shown in the following reaction formulas (I) and (II).

(Synthesis Example 1)
Compound 1 (2,5-dibromothiophene-3-carboxylic acid) shown in Reaction Formula (I) is described in J. Am. Am. Chem. Soc. 76, 2445, (1954).

(Synthesis Example 2)
The synthesis of compound 2 (2-methyl-2-hexyl 2,5-dibromothiophene-3-carboxylic acid) shown in reaction formula (I) is shown.
The compound 1 (12.0 g, 42 mmol), 2-methyl-2-hexanol (6.4 g, 55 mmol) and pyridine (60 mL) were added to a 250 mL three-necked flask, and the mixture was stirred under normal pressure under a nitrogen atmosphere. Chloro-3,5-dinitropyridine (8.6 g, 42 mmol) was added, and the mixture was stirred with heating at 120 ° C. for 30 min. After cooling to room temperature, the inner solution was placed in a 6% aqueous sodium hydrogen carbonate solution (720 mL) and extracted twice with 400 mL petroleum ether. The obtained organic phase was washed with 300 mL of water three times, and anhydrous sodium sulfate was added to dehydrate overnight. After removing the solvent, the residue was purified by silica gel column chromatography using methyl acetate / hexane (1/7) as a developing solvent to obtain a pale yellow oil (yield 7.5 g, 41%). .
¹ H-NMR (CDCl ₃ ): δ 7.26 (s, 1H), δ 1.84 (t, 2H), δ 1.53 (s, 6H), δ 1.31-1.36 (m, 4H), 0 .90 (t, 3H)
Mass spectrometry GC-MS (GCMS-QP2010Plus (manufactured by Shimadzu Corporation)): m / s 3844.1275 (M +)

(Synthesis Example 3)
The synthesis of Compound 3 (2,5-bis-trimethylstannylthiophene) shown in Reaction Formula (II) is shown.
Thiophene (10.0 g, 119 mmol) and tetramethylethylenediamine (35.9 mL, 238 mmol) were added to a 500 mL three-necked flask under a nitrogen atmosphere. Subsequently, butyl lithium (2.5 M hexane solution, 100 mL, 250 mmol) was gradually added dropwise, and when refluxed, a white powder precipitated in 30 minutes. The reaction solution was cooled to −70 ° C., trimethyltin chloride (1M tetrahydrofuran solution, 250 mL, 250 mmol) was gradually added while stirring, and the temperature was raised to room temperature and maintained for 12 hours. After stopping the stirring, the reaction solution was poured into 500 mL of water and extracted twice with 200 mL of diethyl ether. Magnesium sulfate was added to the obtained organic phase, dehydrated overnight, filtered to remove the solvent, and recrystallized with ethanol to obtain white needle crystals (yield 36.9 g, yield 76%). ).
¹ H-NMR (CDCl ₃ ): δ 7.37 (s, 1H), δ 0.36 (s, 9H)

(Synthesis Example 4)
It shows about the synthesis | combination of the thiophene copolymer 4 and 4 'shown in Reaction formula (II).
In a 1.0 L three-necked flask, the compound 2 obtained in Synthesis Example 2 (12.8 g, 33.3 mmol) and the compound 3 obtained in Synthesis Example 3 (13.7 g, 33.3 mmol) were placed. The nitrogen substitution was repeated 5 times or more, and palladium catalyst [Pd (PPh ₃ ) ₄ , 2.05 g, 1.76 mmol], dimethylformamide (90 mL) and toluene (385 mL) were added using a syringe. The mixture was heated and stirred at 120 ° C. for 24 hours under a nitrogen atmosphere and cooled to room temperature, and then the reaction solution was put into 3.6 L of methanol to precipitate a reaction product. The precipitate was separated by filtration, Soxhlet extracted with hexane for 12 hours, and then Soxhlet extracted with 300 mL of tetrahydrofuran (THF) for 12 hours to obtain a THF solution of the polymer. The obtained THF solution was put into 3.6 L of methanol to precipitate a polymer, and filtered to obtain a solid. Subsequently, the obtained solid was subjected to Soxhlet extraction with acetone and dried to obtain a thiophene copolymer 4 (yield 3.3 g, yield 32.3%). The number average molecular weight (Mn) measured by SEC was 25,000, and the molecular weight distribution (PDI) obtained by weight average molecular weight (Mw) / number average molecular weight (Mn) was 3.35.
¹ H-NMR (CDCl ₃ ): δ 7.35 (s, 1 H), δ 7.35 (s, 1 H), δ 7.15 (s, 1 H), δ 1.83 (t, 2 H), δ 1.54 (s , 6H), δ 1.26-1.30 (m, 4H) δ 0.91 (t, 3H)

The obtained thiophene copolymer 4 was subjected to thermogravimetric analysis at a rate of temperature increase of 10 ° C./min according to the above method. As a result, the weight loss reached 28% at 220 ° C. and remained unchanged until 250 ° C. Further, when the temperature was raised from room temperature to 200 ° C. and then held at 200 ° C., the weight reduction started after 18 minutes from the start of the holding, and the weight reduction reached 28% after 20 minutes, and then after 60 minutes. There was no change until. Further, the obtained thiophene copolymer 4 was subjected to FT-IR analysis according to the above method. The analysis was carried out on a sample immediately after polymerization and purification and a sample subjected to heat treatment at 200 ° C. for 20 minutes. As a result, only the alkyl ester-derived peak (1714 cm ⁻¹ ) was confirmed immediately after the polymerization / purification, whereas the alkyl ester-derived peak (1714 cm ⁻¹ ) decreased with heat treatment at 200 ° C. for 20 minutes. The appearance of a carboxylic acid-derived peak (1680 cm ⁻¹ ) was confirmed.
From the above results, it was revealed that the side chain alkyl group of the thiophene copolymer 4 was eliminated by heat treatment at 200 ° C. for 20 minutes, and the thiophene copolymer 4 ′ was obtained.

(Synthesis Example 5)
A thiophene copolymer was obtained in the same manner as in Synthesis Example 4 except that the solvent added during polymerization was changed to dimethylformamide (63 mL) and toluene (270 mL) (yield 3.7 g, yield 36.2%).
The number average molecular weight (Mn) measured by SEC was 51,000, and the molecular weight distribution (PDI) obtained by weight average molecular weight (Mw) / number average molecular weight (Mn) was 4.28.

(Synthesis Example 6)
A thiophene copolymer was obtained in the same manner as in Synthesis Example 4 except that the solvent added during the polymerization was changed to dimethylformamide (135 mL) and toluene (405 mL) (yield 2.8 g, yield 27.4%).
The number average molecular weight (Mn) measured by SEC was 12,000, and the molecular weight distribution (PDI) obtained by weight average molecular weight (Mw) / number average molecular weight (Mn) was 3.28.

(Synthesis Example 7)
The block copolymer 9 was synthesized according to the following reaction formula (III).

  In a eggplant flask A thoroughly dried and substituted with argon, 21 mL of THF subjected to dehydration and peroxide removal treatment and 1.53 g (4.1 mmol, 4.1 mmol, 2-bromo-5-iodo-3-hexylthiophene in formula (III) 2) and 2.1 mL of a 2.0M solution of i-propylmagnesium chloride were added, and the mixture was stirred at 0 ° C. for 30 minutes to synthesize an organomagnesium compound solution represented by compound 6 represented by formula (III). . In another eggplant flask B that had been thoroughly dried and purged with argon, 4 mL of THF subjected to dehydration and peroxide removal treatment and 0.361 g (0.9 mmol, 2,5-dibromo-3- (6-bromohexyl) thiophene) Compound 0.9) shown in (III) and 0.9 mL of a 1.0M solution of t-butylmagnesium chloride were added, stirred at 60 ° C. for 2 hours, and the organomagnesium compound shown as Compound 8 shown in Formula (III) A solution was synthesized.

To a dried eggplant flask C substituted with argon, 25 mL of THF and 27 mg (0.05 mmol) of NiCl ₂ (dppp) subjected to dehydration and peroxide removal treatment were added and heated to 35 ° C. Then, the compound 6 prepared above was heated. 70% of the solution was added and stirred with heating at 35 ° C. for 1.5 hours. Then, the remaining compound 6 solution and a separately prepared compound 8 solution were added and reacted at 35 ° C. for 2 hours. After completion of the reaction, 2 mL of 1.0 M THF solution of t-butylmagnesium chloride was added and stirred at 35 ° C. for 1 hour, and then 30 mL of 5M hydrochloric acid was added and stirred at room temperature for 1 hour. This reaction solution was extracted with 450 mL of chloroform, and the organic layer was washed with 100 mL of sodium bicarbonate water and 100 mL of distilled water in this order. The organic layer was dried over anhydrous sodium sulfate and concentrated to dryness. The obtained black purple solid was dissolved in 30 mL of chloroform, reprecipitated in 300 mL of methanol, and sufficiently dried, and purified using a preparative GPC column to block copolymer 9 (750 mg) Got. The resulting block copolymer 9 had a weight average molecular weight (Mw) of 27,400, a number average molecular weight (Mn) of 25,370, and a polydispersity of 1.08.
¹ H-NMR (CDCl ₃ ): δ = 6.97 (s, 1H), 3.41 (t, J = 6.8 Hz, 0.2H), 2.80 (t, J = 8.0 Hz, 2H) ), 1.89-1.27 (m, 9.8H), 0.91 (t, J = 6.8 Hz, 2.7H)

  Hereinafter, examples of the present invention produced using the polymer obtained in the synthesis example will be described. In addition, evaluation in an Example was performed as follows.

[Measurement of organic thin film thickness]
The film thickness of the organic thin film of the following Examples and Comparative Examples was measured using a contact-type step gauge (DEKTAK8: manufactured by Veeco) under the conditions of stylus pressure: 3 mg and measurement range: 50 kÅ.
[Spectral sensitivity measurement]
The spectral sensitivity of the photoelectric conversion elements produced in the following examples and comparative examples was measured using a spectral sensitivity measuring device (SM-250 type: manufactured by Spectrometer Co., Ltd.). Keithley 2400 (manufactured by KEITHLEY) was used as a source meter. The irradiation intensity at a specific wavelength at the time of measurement was calibrated using a photodiode (S1337-66BQ, manufactured by Hamamatsu Photonics). At the time of measurement, an irradiation light mask having the same area as the light receiving area of the photoelectric conversion element was worn to eliminate excessive light incidence.

[Measurement of photoelectric conversion efficiency]
The photoelectric conversion efficiency of the photoelectric conversion elements prepared in the following examples and comparative examples was measured using a solar simulator (PEC-L11: manufactured by Pexel Technology) and a source meter (KEITHLEY2400: manufactured by KEITHLEY). AM1.5, irradiation intensity was measured at 100 mW / cm2. The irradiation intensity at the time of measurement was adjusted to be a solar cell evaluation standard using a photodiode (BS-520, manufactured by Spectrometer Co., Ltd.). At the time of measurement, an irradiation light mask having the same area as the light receiving area of the photoelectric conversion element was worn to eliminate excessive light incidence.

Example 1
Chlorobenzene was added to the thiophene copolymer obtained in Synthesis Example 4 to prepare a concentration of 10 mg / mL, heated and stirred at 60 ° C. for 6 hours, cooled to room temperature, and 0.45 μm polytetrafluoroethylene (PTFE). ) To obtain a uniform solution.

A substrate (manufactured by Geomatech Co., Ltd.) with 150 nm indium tin oxide (ITO) formed on a 0.7 mm glass, semi-clean (Furuuchi Chemical Co., Ltd.), ultrapure water, acetone (special reagent grade: Wako Jun) Yaku Kogyo Co., Ltd.) Isopropanol (reagent grade: Wako Pure Chemical Industries, Ltd.) in the order of ultrasonic cleaning for 10 minutes, dried, and then ozone-cleaned for 20 minutes using a UV-O ₃ cleaner (manufactured by Filgen). .

  The prepared solution and the cleaned ITO substrate were introduced into a glove box filled with nitrogen, and spin-coated at 1000 rpm for 60 seconds in a nitrogen atmosphere. After film formation, the film was dried under reduced pressure for 1 hour, and heat-treated at 200 ° C. for 20 minutes in a nitrogen atmosphere to obtain the organic thin film of the present invention. The film thickness of the obtained organic thin film was 15 nm.

  When the obtained organic thin film was immersed in 50 mL of toluene, THF, chloroform (CF), chlorobenzene (CBz), dichlorobenzene (DCBz), and trichlorobenzene (TCBz) for 1 hour, it was insoluble in any organic solvent. Met.

(Example 2)
The organic thin film (film thickness of 15 nm) of the present invention formed on a 150 nm ITO substrate obtained in Example 1 was introduced into a resistance heating vacuum deposition apparatus without being exposed to the atmosphere, and 5.0 × 10 ⁻ 80 nm of aluminum (Al) (purity 99.995%) was vacuum-deposited under reduced pressure of ⁵ Pa to produce a photoelectric conversion element. The light receiving area of the produced photoelectric conversion element was 0.25 cm ² .

When the spectral sensitivity of the produced photoelectric conversion element was measured, it was revealed that photoelectric conversion was performed in a wavelength range of 400 to 620 nm. Subsequently, when the photoelectric conversion efficiency of the produced photoelectric conversion element was measured, the short-circuit current density = 0.2 mA / cm ² , the open circuit voltage = 0.61 V, the fill factor = 0.35, and the photoelectric conversion efficiency = 0.04%. Met.

  From the results of Example 1, it was revealed that the organic thin film of the present invention was insolubilized by heat treatment after being dissolved in an organic solvent to form a film. Therefore, the organic thin film of the present invention can form a photoelectric conversion active layer without elution even if a solution of the organic semiconductor composition is applied on the organic thin film after forming the film, and a laminated structure is produced by a solution process. Is possible. From the results of Example 2, the organic thin film of the present invention has a photoelectric conversion function even when the thin film is used alone.

(Example 3)
A glass substrate (ITO substrate) on which ITO of 150 nm was deposited was washed in the same manner as in Example 1. Subsequently, polyethylene dioxythiophene: polystyrene sulfonate additive (PEDOT: PSS) (CLEVIOS PH 500: manufactured by HC Starck Co., Ltd.) is dropped on the cleaned ITO substrate in the air, and is spun at 4000 rpm for 60 seconds. Coated. The substrate after film formation was baked at 140 ° C. for 10 minutes. The film thickness of PEDOT: PSS at this time was 40 nm.

A synthetic example was formed on an ITO substrate on which PEDOT: PSS was formed in the same manner as in Example 1 except that the number of revolutions when spin-coating the polymer solution described in Example 1 was changed to 1500 revolutions. The solution containing the polymer obtained in 4 was spin-coated and heat-treated at 200 ° C. for 20 minutes in a nitrogen atmosphere to form the organic thin film of the present invention. The film thickness of the organic thin film was 10 nm. Subsequently, the polymer obtained in Synthesis Example 4 and [6,6] -phenyl C ₆₁ butyric acid methyl ester (PC ₆₁ BM) (E-100H: manufactured by Frontier Carbon Co.) were used at a weight ratio of 1: 0. The chlorobenzene solution of the organic semiconductor composition mixed in step 8 is spin-coated on a substrate in a nitrogen atmosphere and heat-treated at 200 ° C. for 20 minutes to form a photoelectric conversion active layer formed on the organic thin film of the present invention. The body was made. The film thickness of the photoelectric conversion active layer was 90 nm.

Subsequently, by the same method as in Example 2, 0.5 nm of lithium fluoride (LiF) (purity 99.99%) was vacuum-deposited on the photoelectric conversion active layer film, and then 80 nm of aluminum (Al) (purity). 99.995% (manufactured by Niraco) was vacuum-deposited to produce a photoelectric conversion element. The light receiving area of the produced photoelectric conversion element was 0.25 cm ² . When the photoelectric conversion efficiency of the produced photoelectric conversion element was measured, the photoelectric conversion efficiency was 2.55%.

Example 4
A photoelectric conversion element was produced in the same manner as in Example 3 except that the number of revolutions when the organic thin film of the present invention was formed by spin coating was changed to 1000 revolutions. The film thickness of the organic thin film was 15 nm. The photoelectric conversion efficiency of the obtained photoelectric conversion element was 2.42%.

(Example 5)
A photoelectric conversion element was produced in the same manner as in Example 3 except that the number of revolutions when the organic thin film of the present invention was formed by spin coating was changed to 900 revolutions. The film thickness of the organic thin film was 22 nm. The photoelectric conversion efficiency of the obtained photoelectric conversion element was 2.31%.

(Example 6)
A photoelectric conversion element was produced in the same manner as in Example 3 except that the temperature when heat treating the organic thin film of the present invention was changed to 240 ° C. The film thickness of the organic thin film was 12 nm. The photoelectric conversion efficiency of the obtained photoelectric conversion element was 2.35%.

(Example 7)
A photoelectric conversion element was produced in the same manner as in Example 3 except that the temperature when heat treating the organic thin film of the present invention was changed to 270 ° C. The film thickness of the organic thin film was 13 nm. The photoelectric conversion efficiency of the obtained photoelectric conversion element was 2.28%.

(Example 8)
A photoelectric conversion element was produced in the same manner as in Example 3 except that the thiophene copolymer for producing the organic thin film of the present invention was changed to the polymer obtained in Synthesis Example 5 (Mn = 51,000). . The film thickness of the organic thin film was 11 nm. The photoelectric conversion efficiency of the obtained photoelectric conversion element was 2.72%.

Example 9
The photoelectric conversion active layer was obtained by combining the block polymer 9 obtained in Synthesis Example 7 with [6,6] -phenyl C ₆₁ butyric acid methyl ester (bis-PC ₆₂ BM) (E-100H: manufactured by Frontier Carbon Co.). A chlorobenzene solution of an organic semiconductor composition mixed at a weight ratio of 1: 0.8 is spin-coated on a substrate in a nitrogen atmosphere, vacuum-dried for 3 hours, and then thermally annealed at 120 ° C. for 30 minutes. Produced a photoelectric conversion element in the same manner as in Example 3. The film thickness of the organic thin film was 10 nm, and the film thickness of the photoelectric conversion active layer was 90 nm. The photoelectric conversion efficiency of the obtained photoelectric conversion element was 4.51%.

(Comparative Example 1)
An 18 nm organic thin film was obtained in the same manner as in Example 1 except that heat treatment was not performed at 200 ° C. for 20 minutes. When the obtained organic thin film was immersed in 50 mL of toluene, THF, CF, CBz, DCBz, and TCBz for 1 hour, the organic thin film was dissolved in all organic solvents.

(Comparative Example 2)
In Example 2, a photoelectric conversion element was produced in the same manner as in Example 2 except that a 40 nm PEDOT: PSS film formed by the same method as in Example 3 was used instead of the organic thin film of the present invention. Although the photoelectric conversion efficiency of the obtained photoelectric conversion element was measured, the photovoltaic force was not confirmed and the result which shows photoelectric conversion was not obtained.

(Comparative Example 3)
A photoelectric conversion element was produced in the same manner as in Example 3 except that the organic thin film of the present invention was not formed. The photoelectric conversion efficiency of the obtained photoelectric conversion element was 2.02%.

(Comparative Example 4)
A photoelectric conversion element was produced in the same manner as in Example 3 except that the number of rotations when the organic thin film of the present invention was formed by spin coating was changed to 6000. The film thickness of the organic thin film was 1 nm or less. The photoelectric conversion efficiency of the obtained photoelectric conversion element was 2.18%.

(Comparative Example 5)
A photoelectric conversion element was produced in the same manner as in Example 3 except that the number of revolutions when the organic thin film of the present invention was formed by spin coating was changed to 600 revolutions. The film thickness of the organic thin film was 40 nm. The photoelectric conversion efficiency of the obtained photoelectric conversion element was 1.41%.

(Comparative Example 6)
A photoelectric conversion element was produced in the same manner as in Example 3 except that the temperature when the organic thin film of the present invention was heat-treated was changed to 100 ° C. The film thickness of the organic thin film was 1 nm or less. The photoelectric conversion efficiency of the obtained photoelectric conversion element was 1.98%.

(Comparative Example 7)
A photoelectric conversion element was produced in the same manner as in Example 3 except that the polythiophene copolymer for producing the organic thin film of the present invention was changed to the polymer obtained in Synthesis Example 6 (Mn = 12,000). . The film thickness of the organic thin film was 5 nm. The photoelectric conversion efficiency of the obtained photoelectric conversion element was 1.87%.

Table 1 summarizes the physical properties of the organic thin films obtained in Examples 3 to 9 and Comparative Examples 3 to 7 and the conversion efficiency of the photoelectric conversion elements.

  Comparison between Example 3 and Comparative Example 3 revealed that a photoelectric conversion element having excellent photoelectric conversion efficiency can be obtained by using the thiophene copolymer organic thin film of the present invention. Moreover, when the film thickness conditions of the organic thin film of this invention are not satisfied by comparison with Examples 3-5 and Comparative Examples 4-6, the photoelectric conversion element which is excellent in photoelectric conversion efficiency cannot be obtained. Moreover, when the organic thin film which consists of a thiophene copolymer whose number average molecular weight is smaller than the prescription | regulation range of this invention is used from the comparative example 7, photoelectric conversion efficiency falls rather.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Transparent electrode 3 Organic thin film 4 Photoelectric conversion active layer 5 Counter electrode 6 Hole transport layer 7 Electron transport layer 10 Photoelectric conversion element

Claims (11)

The following general formula (1)

(Wherein R ¹ is an optionally substituted alkyl group having 1 to 20 carbon atoms, an optionally substituted aryl group having 6 to 20 carbon atoms, or an optionally substituted carbon. A heteroaryl group having 4 to 20 carbon atoms, and R ² is a hydrogen atom, a fluorine atom, an optionally substituted alkyl group having 1 to 20 carbon atoms, or an optionally substituted carbon atom having 6 to 20 carbon atoms. Or a heteroaryl group having 4 to 20 carbon atoms which may have a substituent, p + q = n, 0 ≦ p <n, 0 <q ≦ n, and n is a positive number of 2 or more. is there.)
An organic thin film having a thickness of 10 nm or more and 30 nm or less comprising a thiophene copolymer having a number average molecular weight of 15,000 or more and 1,000,000 or less.   The photoelectric conversion element which has the organic thin film and photoelectric conversion active layer of Claim 1 between a pair of electrodes in which at least one has a light transmittance.   The photoelectric conversion element according to claim 2, wherein the organic thin film is provided between a positive electrode and a photoelectric conversion active layer.   The photoelectric conversion element according to claim 2, wherein the photoelectric conversion active layer is a mixture of an electron donating organic semiconductor and an electron accepting organic semiconductor.   The electron-donating organic semiconductor has a monomer having at least one heterocyclic skeleton selected from thiophene, fluorene, carbazole, dibenzosilole, dibenzogermole, benzodithiophene and diketopyrrolopyrrole as part of the chemical structure The photoelectric conversion element according to claim 4, which is a π-electron conjugated polymer composed of units.   The photoelectric conversion element according to claim 5, wherein the π-electron conjugated polymer is a block copolymer.   The photoelectric conversion element according to claim 2, further comprising a hole transport layer made of a hole transport material between the electrode and the organic thin film. The following general formula (2)

(Wherein R ¹ is an optionally substituted alkyl group having 1 to 20 carbon atoms, an optionally substituted aryl group having 6 to 20 carbon atoms, or an optionally substituted carbon. A heteroaryl group having 4 to 20 carbon atoms, and R ² is a hydrogen atom, a fluorine atom, an optionally substituted alkyl group having 1 to 20 carbon atoms, or an optionally substituted carbon atom having 6 to 20 carbon atoms. And a heteroaryl group having 4 to 20 carbon atoms that may have an aryl group or a substituent, and n is a positive number of 2 or more.)
A thiophene copolymer having a number average molecular weight of 20,000 or more and 1,000,000 or less represented by the following formula is dissolved in a solvent to form a film, followed by heat treatment to give the following general formula (1)

(Wherein R ¹ is an optionally substituted alkyl group having 1 to 20 carbon atoms, an optionally substituted aryl group having 6 to 20 carbon atoms, or an optionally substituted carbon. A heteroaryl group having 4 to 20 carbon atoms, and R ² is a hydrogen atom, a fluorine atom, an optionally substituted alkyl group having 1 to 20 carbon atoms, or an optionally substituted carbon atom having 6 to 20 carbon atoms. Or a heteroaryl group having 4 to 20 carbon atoms which may have a substituent, p + q = n, 0 ≦ p <n, 0 <q ≦ n, and n is a positive number of 2 or more. is there.)
An organic thin film having a thickness of 10 nm or more and 30 nm or less is formed of a thiophene copolymer having a number average molecular weight of 15,000 or more and 1,000,000 or less. 8. A method for producing a photoelectric conversion element according to any one of 7 above.   The solvent is selected from tetrahydrofuran, 1,2-dichloroethane, cyclohexane, chloroform, bromoform, benzene, toluene, o-xylene, chlorobenzene, bromobenzene, iodobenzene, o-dichlorobenzene, anisole, methoxybenzene, trichlorobenzene and pyridine. The method for producing a photoelectric conversion element according to claim 8, wherein the organic solvent is a mixed solvent or a mixed solvent thereof.   The method for manufacturing a photoelectric conversion element according to claim 8 or 9, wherein the heat treatment is performed at 180 ° C or higher and 280 ° C or lower.   The method for producing a photoelectric conversion element according to claim 8, wherein after forming the organic thin film, a photoelectric conversion active layer is further formed on the surface of the organic thin film by coating.

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