JP2016103570A - Photovoltaic element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photovoltaic element capable of achieving both photoelectric conversion efficiency and durability at a high level by searching a novel compound suitable for an electron extraction layer and using the compound.SOLUTION: A photovoltaic element comprises at least a positive electrode 2, a photoelectric conversion layer 3, an electron extraction layer 4 and a negative electrode 5 in this order. The photovoltaic element contains, in the electron extraction layer, a compound having a structure in which three or more nitrogen atoms included in a nitrogen-containing six-membered aromatic ring can adopt a spatial arrangement capable of donating an electron pair with respect to the same negative electrode metal, that is, a metal atom of the same type of metal constituting the negative electrode, or ions thereof.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a photovoltaic device.

  Solar cells are environmentally friendly electrical energy sources and are currently attracting attention as potential energy sources for increasingly serious energy problems. Currently, inorganic materials such as single crystal silicon, polycrystalline silicon, amorphous silicon, and compound semiconductors are used as semiconductor materials for photovoltaic elements of solar cells. However, solar cells manufactured using inorganic semiconductors have not been widely used in general households because of high costs. The high cost factor is mainly in the process of manufacturing a semiconductor thin film under vacuum and high temperature. Therefore, organic solar cells using organic semiconductors and organic dyes such as conjugated polymers and organic crystals are being studied as semiconductor materials expected to simplify the manufacturing process.

  However, an organic solar cell using a conjugated polymer or the like has the biggest problem that the photoelectric conversion efficiency is lower than that of a conventional solar cell using an inorganic semiconductor, and has not yet been put into practical use. In addition, in order to put an organic solar cell into practical use, high durability that maintains high photoelectric conversion efficiency for a long time is essential.

  As one method for improving the photoelectric conversion efficiency and durability of the organic solar cell, there is a method in which an electron extraction layer is installed between the power generation layer and the negative electrode. As an electron taking-out layer, the usage example of a phenanthroline compound (patent document 1) and a phosphine oxide compound (patent document 2) is known, for example.

JP 2011-192916 A JP 2011-176305 A

  However, the effect of improving the photoelectric conversion efficiency and durability by inserting the conventional electron extraction layer has not been sufficient for the practical use. According to the knowledge of the present inventors, for example, in an element configuration using an electron extraction layer of a phenanthroline compound or a bipyridyl compound as disclosed in Patent Document 1, storage stability in the atmosphere is not a problem. Sufficient durability as an organic solar cell at the time of irradiation was not obtained.

  Further, the element configuration using the electron extraction layer of the phosphine oxide compound as disclosed in Patent Document 2 cannot provide sufficient photoelectric conversion efficiency, and further, the durability against heat is not sufficient.

  Therefore, the present invention has been made to search for a novel compound suitable for the electron extraction layer, and to provide a photovoltaic device capable of achieving both high photoelectric conversion efficiency and durability by using the compound. To do.

  Based on the above problems, the present inventors have studied the function of the electron extraction layer. As a result, by using a compound that can interact more strongly with the metal electrode used for the negative electrode in the electron extraction layer, high photoelectric conversion efficiency can be obtained. It has been found that a photovoltaic device having high durability can be obtained.

  That is, the gist of the present invention is as follows.

  A photovoltaic device having at least a positive electrode, a photoelectric conversion layer, an electron extraction layer, and a negative electrode composed of a metal in this order, and a photovoltaic device including a compound that satisfies all of (a) to (c) described later in the electron extraction layer It is a power element.

  According to the present invention, it is possible to provide a photovoltaic device that achieves both high photoelectric conversion efficiency and high durability.

The schematic diagram which shows the one aspect | mode of the photovoltaic device of this invention The schematic diagram which shows another aspect of the photovoltaic device of this invention

The photovoltaic device of the present invention is a photovoltaic device having at least a positive electrode, a photoelectric conversion layer, an electron extraction layer, and a negative electrode composed of a metal in this order, and the following (a) to (c) are included in the electron extraction layer: It is a photovoltaic device including a compound that satisfies all (hereinafter sometimes referred to as “the compound of the present invention” for convenience).
(A) a group containing a nitrogen-containing six-membered ring aromatic ring (nitrogen-containing six-membered ring aromatic group) having one or more, at least one of which is a non-condensed nitrogen-containing six-membered ring aromatic ring It is a group (non-condensed nitrogen-containing six-membered aromatic group).
(B) The one or two or more nitrogen-containing six-membered ring aromatic groups have a spatial arrangement capable of donating electron pairs to the same metal atom or ion (negative electrode metal) as the metal constituting the negative electrode. There are three or more ring nitrogen atoms (coordinating nitrogen atoms) to be obtained, and at least one of the coordinating nitrogen atoms is a nitrogen atom on the non-condensed nitrogen-containing six-membered aromatic group.
(C) The total molecular weight of all nitrogen-containing six-membered aromatic rings in the compound is 60% or more of the total molecular weight of the entire compound.

  First, (a) will be described. The nitrogen-containing 6-membered aromatic group means a group containing a nitrogen-containing 6-membered aromatic ring. The nitrogen-containing six-membered aromatic ring is an aromatic ring composed of six ring constituent atoms, and is an aromatic ring in which at least one of the six ring constituent atoms is a nitrogen atom. Specific examples of the nitrogen-containing six-membered aromatic ring include a pyridine ring, a pyrazine ring, a pyrimidine ring, a pyridazine ring, a triazine ring, and a tetrazine ring. In the present invention, a group containing a condensed nitrogen-containing six-membered aromatic ring is also included in the nitrogen-containing six-membered aromatic group. Specific examples of the condensed nitrogen-containing six-membered aromatic ring include a quinoline ring, a quinoxaline ring, and a phenanthroline ring. Among these, a nitrogen-containing six-membered aromatic group is preferable in that it can easily form a space arrangement capable of providing an electron pair to a metal atom constituting the negative electrode or an ion thereof (hereinafter collectively referred to as “negative electrode metal”). Is a group containing a non-condensed nitrogen-containing six-membered aromatic ring (hereinafter referred to as “non-condensed nitrogen-containing six-membered aromatic group”).

  In the compound of the present invention, at least one of the nitrogen-containing six-membered aromatic groups is a non-condensed nitrogen-containing six-membered aromatic group. The presence of the non-condensed nitrogen-containing six-membered aromatic group makes it easy to optimize the position of the electron pair to be donated in accordance with the size of the interacting negative electrode metal and the positional relationship therewith. Such a non-condensed nitrogen-containing six-membered aromatic group is preferably a group containing a pyridyl group, a pyrazyl group, a pyrimidyl group, a triazyl group or a tetrazyl group, and a pyrazyl group, a pyrimidyl group, a triazyl group or a tetrazyl group is preferred. More preferably, it is a group having a structure in which two or more nitrogen-containing aromatic groups selected from the group consisting of these groups and a quinolyl group, a quinoxalyl group, and a phenanthryl group are bonded via a single bond. Two or more non-condensed nitrogen-containing six-membered aromatic groups are preferably present in the compound, more preferably three or more.

  The compound of the present invention is optionally substituted as long as the above (c) is satisfied, that is, unless the total molecular weight of all the nitrogen-containing six-membered aromatic rings in the compound is less than 60% of the total molecular weight of the entire compound. However, if the ortho position of the coordinating nitrogen atom is substituted with a bulky group, the coordinating nitrogen atom is difficult to coordinate with the negative electrode metal, so the ortho position of the coordinating nitrogen atom is not substituted. Is preferred.

  Next, (b) will be described.

  In the present invention, whether or not “three or more ring-constituting nitrogen atoms (coordinating nitrogen atoms) capable of taking an electron-donating space configuration exist” is determined by the following procedure.

  1) Use the chemical structure drawing software “ChemBioDraw Ultra” (manufactured by Cambridge Soft) to draw the structure of the compound to be judged (hereinafter referred to as Compound X) and prepare the structure using the “Clean up structure” function of the software. .

  2) The above structural formula is taken into the molecular modeling / visualization software “ChemBio3D” (Cambridge Soft) and MM2 (Molecular Mechanics program 2) calculation is performed to determine the initial structure.

  3) Import the initial structure into 3D molecular structure drawing software “Material Studio” (manufactured by Accelrys).

  4) A combination of any three nitrogen atoms is selected from the nitrogen atoms contained in the nitrogen-containing six-membered aromatic ring in compound X.

  5) On the “Material Studio” screen, adjust the torsion angle of the rotatable single bond within the CPK model so that the atoms do not touch each other, and minimize the sum of the distances between the three selected nitrogen atoms. To.

  6) As an initial arrangement for performing the DFT calculation, the negative electrode metal of the electromotive element is placed at the center of gravity of a triangle having the selected three nitrogen atoms as vertices.

  7) The structure was optimized by DFT calculation, and in the resulting structure, the metal bond radius of the negative electrode metal (hereinafter referred to as the negative metal radius) and the van der Waals radius of nitrogen atoms (1 .5 angstroms), whether or not all the centers of the three nitrogen atoms exist on the surface or inside of the sphere whose radius is the sum of the distances (hereinafter referred to as coordination bond distances) and outside the radius of the negative electrode metal. Determine whether. In the present invention, the metal bond radius indicates a distance that is half the shortest interatomic distance of a single metal, and is a value described in Chemical Handbook Basic Edition II (5th revised edition), page 887.

  8) When the above 7) is satisfied, the center of atoms other than three nitrogen atoms (hereinafter, non-coordinating atoms) is the sum of the negative metal radius and the van der Waals radius of the non-coordinating atoms from the center of the sphere. It is determined whether or not an arrangement that does not exist within the range can be taken.

  Note that when four or more atoms are coordinated to the negative electrode metal, atoms other than all the atoms to be coordinated are non-coordinating atoms.

  9) For each of the three nitrogen atoms, a plane perpendicular to the straight line connecting the nitrogen atom and three adjacent atoms on the nitrogen-containing six-membered aromatic ring containing the nitrogen atom and passing through the nitrogen atom In contrast, it is determined whether the center of the negative electrode metal exists on the opposite side of the nitrogen-containing six-membered aromatic ring.

  10) If any of the above conditions 7), 8) and 9) is not satisfied, a combination of the other three nitrogen atoms in compound X is selected, and the process returns to 5) and repeats. When all the combinations of the three nitrogen atoms in the compound X do not satisfy the above condition, the compound X is determined as “cannot take a space configuration capable of donating electrons”.

  11) When there is an arrangement that satisfies any of the above conditions 7), 8), and 9), it is determined that the compound X can “take a space arrangement capable of donating electrons”.

  Next, the above (c) will be described. When the portion other than the nitrogen-containing six-membered aromatic ring is larger than the nitrogen-containing six-membered aromatic ring, the interaction with the negative electrode metal may be inhibited. Therefore, the total molecular weight of all the nitrogen-containing six-membered aromatic rings in the compound needs to be 60% or more of the total molecular weight of the whole compound. This ratio is preferably 65% or more, and more preferably 70% or more. When calculating the total molecular weight of the nitrogen-containing six-membered aromatic ring, only the six atoms constituting the six-membered ring of the nitrogen-containing six-membered aromatic ring and the hydrogen atoms directly bonded to those atoms are referred to as “ "Total molecular weight of nitrogen-containing six-membered aromatic ring". Therefore, in the case where the nitrogen-containing six-membered aromatic ring is condensed, the molecular weight of the nitrogen-containing six-membered ring other than the ring-constituting atoms and the hydrogen atoms directly bonded to them is It is not included in “total molecular weight of ring aromatic ring”.

  Moreover, since the compound of this invention needs to be able to hold | maintain a thin film structure, it is preferable that molecular weight is 500 or more, 550 or more is more preferable, 600 or more is further more preferable. Molecular weight is one of the factors that greatly affect the glass transition temperature. When the molecular weight is 500 or more, the thin film structure of the electron extraction layer is stabilized, and the durability of the photovoltaic device of the present invention can be enhanced. .

  In the present invention, the compound satisfying all of (a) to (c) is preferably a compound represented by the following general formula (1).

B- (A) n (1)
In general formula (1), A is a nitrogen-containing six-membered aromatic group containing three or more coordination nitrogen atoms. n represents an integer of 1 or more. When n is 1, A is a non-condensed nitrogen-containing six-membered aromatic group. When n is 2 or more, two or more A may be the same or different, but at least one of the two or more A is a non-condensed nitrogen-containing six-membered aromatic group. B represents an n-valent group directly bonded to any ring constituent atom of the nitrogen-containing six-membered aromatic ring of A.

  B is an n-valent group directly bonded to any of the ring-constituting atoms of the nitrogen-containing six-membered aromatic ring of A, but is preferably a divalent or higher group, and more preferably a trivalent or higher group. It is more preferable. That is, n is preferably an integer of 2 or more, and more preferably an integer of 3 or more. When n is 1, B may be a hydrogen atom.

  It is preferable that B is a group having an aryl group or an aromatic heterocyclic group as a skeleton because the photoelectric conversion efficiency of the photovoltaic device of the present invention can be increased due to the presence of the conjugated structure. Here, B is a group having an aryl group or aromatic heterocyclic group as a skeleton, which means that all A are directly bonded to the aryl group or aromatic heterocyclic group. B is more preferably an aryl group or an aromatic heterocyclic group itself, and most preferably an unsubstituted aryl group.

  Specific examples of B include the following structures.

(In each structure shown above, n hydrogens are replaced with A, resulting in a compound represented by the general formula (1). M and l are each an arbitrary natural number.)
In the compound represented by the general formula (1), A is preferably bonded to B at the meta or para position of the coordinating nitrogen atom of the nitrogen-containing six-membered aromatic ring contained in A. This is because when A is bonded to B at the ortho position of the coordinating nitrogen atom, the coordinating nitrogen atom is difficult to coordinate with the negative electrode metal due to the steric hindrance of B.

  Specific examples of A include the following structures.

As the compound represented by the general formula (1), compounds satisfying the following (i) and (ii) are particularly preferably used in the present invention.
(I) A is a group selected from the following formulas (A ₁ ) and (A ₂ ).

(A ₁ and A ₂ may each have a substituent.)
(Ii) (A) The total molecular weight of the nitrogen-containing six-membered aromatic ring contained in the n portion is 60% or more of the total molecular weight of the entire compound.

  In the compound satisfying the above (i) and (ii), B is preferably a group having a skeleton of an aryl group or an aromatic heterocyclic group. B is more preferably an aryl group or an aromatic heterocyclic group itself, and most preferably an unsubstituted aryl group.

The compound satisfying the above (i) and (ii) may have a substituent at the A ₁ , A ₂ or B portion as long as it is not contrary to the above (ii). The substituent is not particularly limited, and examples thereof include alkyl groups, alkenyl groups, alkynyl groups, alkoxy groups, aryl groups, heterocyclic groups, halogen atoms, hydroxyl groups, cyano groups, amino groups, carboxyl groups, carbonyls. And a group composed of a group, an acetyl group, a sulfonyl group, a silyl group, a boryl group, a nitrile group, and combinations thereof.

  Here, the alkyl group represents a saturated aliphatic hydrocarbon group, and examples thereof include a methyl group, an ethyl group, a propyl group, and a butyl group.

  An alkenyl group represents an unsaturated aliphatic hydrocarbon group having a carbon-carbon double bond, and examples thereof include a vinyl group, a propenyl group, and a butenyl group.

  An alkynyl group represents an unsaturated aliphatic hydrocarbon group having a carbon-carbon triple bond, and examples thereof include an ethynyl group, a propynyl group, and a butynyl group.

  The alkoxy group represents an aliphatic hydrocarbon group via an ether bond, and examples thereof include a methoxy group, an ethoxy group, a propoxy group, and a butoxy group.

  An aryl group represents an aromatic hydrocarbon group, such as a phenyl group, naphthyl group, biphenyl group, phenanthryl group, anthryl group, terphenyl group, pyrenyl group, fluorenyl group, perylenyl group, indenyl group, coronyl group, azulenyl group, etc. Is mentioned.

  The heterocyclic group represents a group having an aliphatic or aromatic cyclic structure containing an atom other than a carbon atom. For example, an epoxy group, an aziridyl group, an episulfide group, an oxolanyl group, a pyrrolidinyl group, a thiolanyl group, an oxanyl group, Piperidinyl, thianyl, pyridyl, thienyl, furyl, pyrrolyl, oxazolyl, thiazolyl, oxadiazolyl, thiadiazolyl, pyrazyl, pyrimidyl, pyrazolyl, imidazolyl, benzothienyl, benzodithienyl , Dibenzofuryl group, dibenzothienyl group, phenylcarbazolyl group, phenoxathienyl group, xanthenyl group, benzofuranyl group, thiantenyl group, indolizinyl group, phenoxazinyl group, phenothiazinyl group, acridinyl group, phenanthryl group, phenanthrene Lysinyl group, quinolyl group, isoquinolyl group, indolyl group, a quinoxalinyl group, a silole group, Benzoshiroru group, etc. dibenzosilole group.

  In the compound satisfying the above (i) and (ii), it is preferable that the ortho positions of all nitrogen atoms of the nitrogen-containing six-membered aromatic ring are not substituted or substituted with a group other than an aryl group. . The ortho-position of the coordination nitrogen atom is a group having a large steric hindrance on a carbon atom bonded to a nitrogen-containing six-membered aromatic ring such as a tertiary alkyl group or an aryl group, or an atom adjacent thereto. When the coordinate nitrogen atom tries to coordinate with the negative electrode metal, a hydrogen atom on the aryl group tends to exist at the position where the negative electrode metal should exist, and as a result, three or more nitrogen atoms can be This is because it becomes difficult to obtain a space arrangement that can be provided.

Examples of groups other than aryl groups include primary or secondary alkyl groups, alkenyl groups, alkynyl groups, alkoxy groups, heterocyclic groups, halogen atoms, hydroxyl groups, cyano groups, amino groups, carboxyl groups, carbonyl groups, and acetyl groups. , A sulfonyl group, a silyl group, a boryl group, and a nitrile group. The ortho position of the nitrogen atom of (A ₁ ) and (A ₂ ) is preferably not substituted, but when substituted, it is preferably substituted with a primary or secondary alkyl group. The primary or secondary alkyl group represents a saturated aliphatic hydrocarbon group having at least one hydrogen atom on a carbon atom bonded to a nitrogen-containing six-membered aromatic ring, such as a methyl group, an ethyl group, or n-propyl. Group, i-propyl group, n-butyl group, s-butyl group and the like.

  Next, the photovoltaic element of the present invention will be described. The photovoltaic device of the present invention has at least a positive electrode and a negative electrode, and has a photoelectric conversion layer and an electron extraction layer containing the compound of the present invention between them. FIG. 1 is a schematic view showing an example of the photovoltaic element of the present invention. In FIG. 1, reference numeral 1 is a substrate, reference numeral 2 is a positive electrode, reference numeral 3 is a photoelectric conversion layer, reference numeral 4 is an electron extraction layer, and reference numeral 5 is a negative electrode. The photovoltaic element of the present invention may be in the order of substrate 1 / negative electrode 5 / electron extraction layer 4 / photoelectric conversion layer 3 / positive electrode 2 as illustrated in FIG.

The substrate is a substrate on which an electrode material or an organic semiconductor layer can be stacked, for example, an alloy such as alkali-free glass, quartz glass, aluminum, iron, copper, and stainless steel, depending on the type and application of the material used for the photoelectric conversion layer. Films and plates made by any method from inorganic materials such as polyester, polycarbonate, polyolefin, polyamide, polyimide, polyphenylene sulfide, polyparaxylene polymethyl methacrylate, epoxy resin and fluorine resin can be used is there. In addition, in the case where light is incident from the substrate side and used, it is preferable that each substrate described above has a light transmittance of 80% or more. Here, the light transmittance is
[Transmission light intensity (W / m ² ) / incident light intensity (W / m ² )] × 100 (%)
The value given by.

  The positive electrode or the negative electrode of the photovoltaic element of the present invention has optical transparency. It is sufficient that at least one of them has optical transparency, and both of them may have optical transparency. Here, having light transparency means that incident light reaches the photoelectric conversion layer and an electromotive force is generated. That is, when the light transmittance exceeds 0%, it is said to have light transmittance. The light-transmitting electrode preferably has a light transmittance of 60 to 100% in all wavelength regions of 400 nm to 900 nm. Moreover, the thickness of the electrode which has a light transmittance should just be sufficient electroconductivity, and although it changes with materials, 20 nm-300 nm are preferable. In addition, the electrode which does not have a light transmittance should just be electroconductive, and thickness is not specifically limited, either.

  As the electrode material, it is preferable to use a conductive material having a high work function for the positive electrode and a conductive material having a low work function for the other negative electrode.

  Examples of conductive materials include metals such as gold, platinum, silver, copper, iron, zinc, tin, aluminum, indium, chromium, nickel, cobalt, scandium, vanadium, yttrium, cerium, samarium, europium, terbium, and ytterbium. In addition, metal oxides such as indium oxide, tin oxide, molybdenum oxide, nickel oxide, composite metal oxides (indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zinc oxide (AZO) ), Gallium zinc oxide (GZO) and the like. Note that an electrode containing either a metal oxide or a composite metal oxide may be referred to as a metal electrode. As metals other than the above, alkali metals and alkaline earth metals, specifically lithium, magnesium, sodium, potassium, calcium, strontium, barium, and the like are also preferably used. Furthermore, an electrode made of an alloy made of the above metal or a laminate of the above metal is also preferably used. Further, graphite, graphite intercalation compounds, carbon nanotubes, graphene, polyaniline and derivatives thereof, and electrodes containing polythiophene and derivatives thereof are also preferably used. The electrode material may be a mixed layer composed of two or more materials and a laminated structure.

In the present invention, the conductive material used for the negative electrode includes at least one of a metal, a metal oxide, and a composite metal oxide. In the present invention, the negative electrode made of metal is
An electrode containing any of metal, metal oxide, and composite metal oxide. The negative electrode composed of the metal may contain an inorganic salt, a metal oxide other than the above, or a composite metal oxide other than the above.

  In the present invention, the conductive material used for the positive electrode is preferably an ohmic junction with the photoelectric conversion layer. In the case where a hole transport layer described later is used, the conductive material used for the positive electrode is preferably an ohmic junction with the hole transport layer. In addition, the conductive material used for the negative electrode is preferably an ohmic junction with the photoelectric conversion layer or the electron extraction layer. Here, as a method for facilitating ohmic bonding on the negative electrode side, a method of introducing a metal fluoride such as lithium fluoride (LiF) or cesium fluoride as an electron extraction layer on the negative electrode side can be mentioned. By introducing the electron extraction layer, it is possible to increase the extraction current.

In the organic electromotive force element of the present invention, a hole transport layer may be provided between the positive electrode and the photoelectric conversion layer. As the material for forming the hole transport layer, a polythiophene polymer, a poly-p-phenylene vinylene polymer, a polyfluorene polymer, a polypyrrole polymer, a polyaniline polymer, a polyfuran polymer, a polypyridine polymer, a poly Low molecular organic compounds exhibiting p-type semiconductor properties such as conductive polymers such as carbazole polymers, phthalocyanine derivatives (H ₂ Pc, CuPc, ZnPc, etc.), porphyrin derivatives, acene compounds (tetracene, pentacene, etc.), graphene And carbon compounds such as graphene oxide, molybdenum oxide (MoO _x ) such as MoO ₃ , tungsten oxide (WO _x ) such as WO ₃ , nickel oxide (NiO _x ) such as NiO, and vanadium oxide (VO) such as V ₂ O _{5 x),} zirconium oxide such as ZrO ₂ (ZrO ), Copper oxide _(CuO x, such as Cu ₂ O), copper iodide, ruthenium oxide, such as RuO ₄ (RuO _x), an inorganic material such as ruthenium oxide (ReO _x), such as Re ₂ O ₇ is preferably used. Among them, polyethylenedioxythiophene (PEDOT), which is a polythiophene polymer, or PEDOT with polystyrene sulfonate (PSS) added (hereinafter sometimes referred to as PEDOT: PSS), molybdenum oxide, vanadium oxide, tungsten oxide. Is more preferably used.

  Among the materials for forming the hole transport layer, as a method for forming the hole transport layer using an inorganic material, a precursor solution such as a metal salt or a metal alkoxide is applied and then heated to form a layer. And a method of forming a layer by applying a nanoparticle dispersion on a substrate. At this time, the inorganic material is not fully reacted due to the heating temperature and time, and the synthesis conditions of the nanoparticles, partially hydrolyzed, or partially condensed, It may be an intermediate product or a mixture of a precursor, an intermediate product, a final product, and the like.

  The hole transport layer may be a layer made of a single compound, a mixed layer made of two or more compounds, or a laminated structure. The thickness of the hole transport layer is preferably 5 nm to 600 nm, and more preferably 5 nm to 200 nm.

  Next, the photoelectric conversion layer in the photovoltaic device of the present invention will be described. The photoelectric conversion layer is sandwiched between the positive electrode and the negative electrode, and includes at least an electron-donating organic material and an electron-accepting organic material described later. As the structure of the photoelectric conversion layer, for example, a structure including a layer including a mixture of an electron donating organic material and an electron accepting organic material, a layer including an electron donating organic material, and a layer including an electron accepting organic material are stacked. Examples thereof include a structure in which a layer made of a mixture of these layers is laminated between a layer made of an electron donating organic material and a layer made of an electron accepting organic material. Of these, a structure composed of a layer containing a mixture of an electron-donating organic material and an electron-accepting organic material is more preferable. The mixing method of the mixture is not particularly limited, but after adding to the solvent at a desired ratio, a method of heating, stirring, ultrasonic irradiation or the like is used in combination with one or a plurality of methods and dissolved in the solvent. Is mentioned.

  The photoelectric conversion layer may contain two or more kinds of electron donating organic materials and / or electron accepting organic materials.

  Although the content ratio of the electron donating organic material and the electron accepting organic material in the photoelectric conversion layer is not particularly limited, the electron donating organic material: electron accepting organic material (donor acceptor ratio) is 1:99 to 99: 1 is preferable, 10:90 to 90:10 is more preferable, and 20:80 to 60:40 is more preferable.

  As will be described later, when the photovoltaic element material forms a single organic semiconductor layer, the above-mentioned content ratio is the content ratio of the electron-donating organic material and the electron-accepting organic material contained in the single layer. When the photoelectric conversion layer has a laminated structure of two or more layers, it means the content ratio of the electron donating organic material and the electron accepting organic material in the whole organic semiconductor layer.

  The photoelectric conversion layer in the present invention may contain other components such as a surfactant, a binder resin, and a filler as long as the object of the present invention is not impaired.

  The thickness of the photoelectric conversion layer in the present invention may be sufficient as long as the electron-donating organic material and the electron-accepting organic material generate photovoltaic power by light absorption. Although the thickness of the said photoelectric converting layer changes with materials, 10 nm-1000 nm are preferable and 50 nm-500 nm are more preferable.

  In order to further improve the photoelectric conversion efficiency of the photoelectric conversion layer in the present invention, it is preferable to remove impurities that can trap carriers as much as possible. A method for removing impurities from the electron-donating organic material and the electron-accepting organic material is not particularly limited, but column chromatography method, recrystallization method, sublimation method, reprecipitation method, Soxhlet extraction method, molecular weight fractionation method by GPC A filtration method, an ion exchange method, a chelate method, or the like can be used. In general, a column chromatography method, a recrystallization method, and a sublimation method are preferably used for purification of a low molecular weight organic material. On the other hand, for purification of high molecular weight compounds, reprecipitation method, Soxhlet extraction method, molecular weight fractionation method by GPC is preferably used when removing low molecular weight components, and reprecipitation method or the like when removing metal components. A chelate method or an ion exchange method is preferably used. Of these methods, a plurality may be used in combination.

  The electron-donating organic material contained in the photoelectric conversion layer in the present invention is not particularly limited as long as it is an organic substance exhibiting p-type semiconductor characteristics. For example, polythiophene polymer, 2,1,3-benzothiadiazole-thiophene copolymer, quinoxaline-thiophene copolymer, thiophene-benzodithiophene copolymer, poly-p-phenylene vinylene polymer, Conjugated polymers such as poly-p-phenylene polymer, polyfluorene polymer, polypyrrole polymer, polyaniline polymer, polyacetylene polymer, polythienylene vinylene polymer, H2 phthalocyanine (H2Pc), Phthalocyanine derivatives such as copper phthalocyanine (CuPc) and zinc phthalocyanine (ZnPc), porphyrin derivatives, N, N′-diphenyl-N, N′-di (3-methylphenyl) -4,4′-diphenyl-1,1 ′ -Diamine (TPD), N, N'-dinaphthyl-N, N'-diphenyl Triarylamine derivatives such as 4,4′-diphenyl-1,1′-diamine (NPD), carbazole derivatives such as 4,4′-di (carbazol-9-yl) biphenyl (CBP), oligothiophene derivatives (ter Low molecular organic compounds such as thiophene, quarterthiophene, sexithiophene, octithiophene). Two or more of these may be used.

  Among the examples of the electron donating organic material, the polythiophene polymer refers to a conjugated polymer having a thiophene skeleton in the main chain, and includes those having a side chain. Specifically, poly-3-alkylthiophene such as poly-3-methylthiophene, poly-3-butylthiophene, poly-3-hexylthiophene, poly-3-octylthiophene, poly-3-decylthiophene, poly- Poly-3-alkoxythiophene such as 3-methoxythiophene, poly-3-ethoxythiophene, poly-3-dodecyloxythiophene, poly-3-methoxy-4-methylthiophene, poly-3-dodecyloxy-4-methylthiophene And poly-3-alkoxy-4-alkylthiophene.

  The 2,1,3-benzothiadiazole-thiophene copolymer refers to a conjugated copolymer having a thiophene skeleton and a 2,1,3-benzothiadiazole skeleton in the main chain. Specific examples of the 2,1,3-benzothiadiazole-thiophene copolymer include the following structures. In the following formula, n represents a range of 1 to 1000.

  Among the examples of the electron donating organic material, the quinoxaline-thiophene copolymer refers to a conjugated copolymer having a thiophene skeleton and a quinoxaline skeleton in the main chain. Specific examples of the quinoxaline-thiophene copolymer include the following structures. In the following formula, n represents a range of 1 to 1000.

  Among the examples of the electron donating organic material, the thiophene-benzodithiophene polymer refers to a conjugated copolymer having a thiophene skeleton and a benzodithiophene skeleton in the main chain. Specific examples of the thiophene-benzodithiophene copolymer include the following structures. In the following formula, n represents a range of 1 to 1000.

  Among the examples of the electron donating organic material, the poly-p-phenylene vinylene polymer refers to a conjugated polymer having a p-phenylene vinylene skeleton in the main chain, and includes those having a side chain. Specifically, poly [2-methoxy-5- (2-ethylhexyloxy) -1,4-phenylenevinylene], poly [2-methoxy-5- (3 ′, 7′-dimethyloctyloxy) -1, 4-phenylene vinylene] and the like.

The electron-accepting organic material contained in the photoelectric conversion layer in the present invention is not particularly limited as long as it is an organic substance exhibiting n-type semiconductor characteristics. For example, 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA), 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA), 3,4,9,10-perylenetetracarboxyl Rick bisbenzimidazole (PTCBI), N, N′-dioctyl-3,4,9,10-naphthyltetracarboxydiimide (PTCDI-C8H), 2- (4-biphenylyl) -5- (4-t-butylphenyl) ) -1,3,4-oxadiazole (PBD), 2,5-di (1-naphthyl) -1,3,4-oxadiazole (BND) and other oxazole derivatives, 3- (4-biphenylyl) Triazole derivatives such as -4-phenyl-5- (4-t-butylphenyl) -1,2,4-triazole (TAZ) Body, phenanthroline derivatives, phosphine oxide derivatives, and those of the unsubstituted to fullerene compound _{(C 60, C 70, C} 76, C 78, C 82, C 84, C 90, C 94 started, [6,6] -Phenyl C61 butyric acid methyl ester ([6,6] -PCBM), [5,6] -phenyl C61 butyric acid methyl ester ([5,6] -PCBM), [6,6] -phenyl C61 buty Rick acid hexyl ester ([6,6] -PCBH), [6,6] -phenyl C61 butyric acid dodecyl ester ([6,6] -PCBD), phenyl C71 butyric acid methyl ester (PC ₇₀ BM), phenyl C85 butyric acid methyl ester _(PC 84 BM), etc.), carbon Nanotubes (CNT), poly -p- phenylene vinylene-based polymer derivatives obtained by introducing cyano group into (CN-PPV) and the like. Among these, fullerene compounds are preferably used because of their high charge separation speed and electron transfer speed. Among fullerene compounds, C ₇₀ derivatives (such as the above PC ₇₀ BM) are more preferable because they are excellent in light absorption characteristics and can obtain higher photoelectric conversion efficiency.

  The photovoltaic device of the present invention has an electron extraction layer containing the compound of the present invention. The electron extraction layer may contain a substance other than the compound of the present invention as long as the effect of the present invention is not impaired.

  Specific examples of substances other than the compounds satisfying all of the above (a) to (c) include, for example, electron-accepting organic materials (NTCDA, PTCDA, PTCDI-C8H, oxazole derivatives, triazole derivatives, phenanthroline derivatives, phosphine oxide derivatives, phosphine Organic materials exhibiting n-type semiconductor properties such as sulfide derivatives, quinoline derivatives, fullerene compounds, CNT, CN-PPV, etc.) are preferably used for the electron extraction layer.

  Also, ionic substituted fluorene-based polymers ("Advanced Materials", 2011, 23, 4636-4463, "Organic Electronics", 2009, 10, 476-500). ) And combinations of ionic substituted fluorene polymers and substituted thiophene polymers (Journal of the American Chemical Society, 2011, 133, 8416-8419) Compound, polyethylene oxide ("Advanced Materials", 2007, 19 , Pp. 1835-1838) preferably used in the electron extraction layer is also like.

  Also, compounds having an ionic group, such as ammonium salts, amine salts, pyridinium salts, imidazolium salts, phosphonium salts, carboxylates, sulfonates, phosphates, sulfate esters, phosphate ester salts, sulfates , Nitrates, acetonate salts, oxo acid salts, halides and metal complexes can also be used as the electron extraction layer. Specifically, ammonium chloride, ammonium acetate, ammonium phosphate, hexyltrimethylammonium bromide, tetrabutylammonium bromide, octadecyltrimethylammonium bromide, hexadecylpyridinium bromide, 1-butyl-3-methylimidazolium bromide, tributylhexadecylphosphonium bromide , Zinc formate, zinc acetate, zinc propionate, zinc butyrate, zinc oxalate, sodium heptadecafluorononanoate, sodium myristate, sodium benzoate, sodium 1-hexadecanesulfonate, sodium dodecyl sulfate, sodium monododecyl phosphate, Zinc acetylacetonate, ammonium chromate, ammonium metavanadate, ammonium molybdate, hexafluorozirconium acid Monium, sodium tungstate, ammonium tetrachlorozincate, tetraisopropyl orthotitanate, lithium nickelate, potassium permanganate, silver phenanthroline complex, silver-tetracyanoquinodimethane complex (AgTCNQ) and JP2013-58714A Compounds used for the electron transport layer are also preferably used for the electron extraction layer.

Further, titanium oxide such as TiO ₂ (TiO _x ), zinc oxide such as ZnO (ZnO _x ), silicon oxide such as SiO ₂ (SiO _x ), tin oxide such as SnO ₂ (SnO _x ), oxidation such as WO ₃ Tungsten oxide (TaO _x ) such as tungsten (WO _x ), Ta ₂ O _3, barium titanate (BaTi _x O _y ) such as BaTiO ₃ , barium zirconate (BaZr _x O _y ) such as BaZrO ₃ , ZrO _2, etc. Zirconium oxide (ZrO _x ), hafnium oxide (HfO _x ) such as HfO ₂ , aluminum oxide (AlO _x ) such as Al ₂ O _3, yttrium oxide (YO _x ) such as Y ₂ O ₃ , and silicon such as ZrSiO ₄ Of metal oxides such as zirconium oxide (ZrSi _x O _y ), silicon nitride (SiN _x ) such as Si ₃ N ₄ Semiconductors such as nitrides, cadmium sulfide (CdS _x ) such as CdS, zinc selenide (ZnSe _x ) such as ZnSe, zinc sulfide (ZnS _x ) such as ZnS, cadmium telluride (CdTe _x ) such as CdTe Inorganic materials such as alkali metals such as lithium, magnesium and calcium, alkaline earth metals, and metal fluorides such as lithium fluoride and cesium fluoride are also preferably used for the electron extraction layer.

  As a method of forming the electron extraction layer with the inorganic material, after applying a precursor solution such as a metal salt or metal alkoxide, the layer is formed by heating, or a nanoparticle dispersion is applied to the substrate. There are methods for forming layers. At this time, depending on the heating temperature and time, and the synthesis conditions of the nanoparticles, the reaction does not proceed completely, and it becomes an intermediate product by partially hydrolyzing or partially condensing. Or a mixture of a precursor, an intermediate organism, and an end product.

  In addition, the phenanthroline derivative in the case where it is contained in the electron extraction layer as a substance other than the compound satisfying all of the above (a) to (c) is not particularly limited. (Bphen), 2-naphthalen-2-yl-4,7-diphenyl-1,10-phenanthroline (HNBphen), 2,9-bisnaphthalen-2-yl-4,7-diphenyl-1,10-phenanthroline ( And phenanthroline monomer compounds such as NBphen) and phenanthroline multimeric compounds described in JP2012-39097A. The phenanthroline dimer compound is a compound described in JP 2012-39097 A, and is a compound represented by the following general formula (2).

Here, R ^{54 to} R ⁶⁰ may be the same or different and are selected from hydrogen, an alkyl group, and an aryl group. X is a divalent aromatic hydrocarbon group. The substituents having two phenanthroline skeletons may be the same or different. Here, the alkyl group represents a saturated aliphatic hydrocarbon group such as a methyl group, an ethyl group, a propyl group, or a butyl group, and the aryl group represents, for example, a phenyl group, a tolyl group, a biphenyl group, a naphthyl group, a phenanthryl group, An aromatic hydrocarbon group such as an anthryl group is shown and may be unsubstituted or substituted. As for carbon number of an alkyl group or an aryl group, about 1-20 are preferable. Further, the groups having two phenanthroline skeletons may be the same or different.

Further, the phosphine oxide derivative in the case where it is contained in the electron extraction layer as a substance other than the compound satisfying all of the above (a) to (c) is not particularly limited, but for example, phenyl dipyrenyl phosphine oxide Examples include phosphine compounds such as (POPy ₂ ).

  In addition, the quinoline derivative in the case where it is contained in the electron extraction layer as a substance other than the compound satisfying all of the above (a) to (c) is not particularly limited, but, for example, 8-hydroxyquinolate lithium ( Liq) and tris (8-hydroxyquinolate) aluminum.

  The electron extraction layer in the present invention may also contain a substance that does not have an electron transporting property as long as it does not significantly hinder extraction of electrons from the photoelectric conversion layer to the negative electrode in the photovoltaic element of the present invention. . Further, the substance having no electron transporting property may form a mixed layer with a compound satisfying all of the above (a) to (c), or may have a laminated structure.

  The content ratio of the compound satisfying all of (a) to (c) in the electron extraction layer in the case of a mixed layer with a substance having no electron transporting property is not particularly limited, but is 1 by weight. It is preferably in the range of -99%, more preferably in the range of 10-99%.

  The film thickness of the electron extraction layer in the present invention may be appropriately set to an optimum film thickness depending on the desired photoelectric conversion efficiency of the photovoltaic device, but is preferably 0.1 nm to 50 nm, preferably 0.5 nm to 10 nm. More preferred.

  Although the mechanism of improving the characteristics by the electron extraction layer in the present invention is not clear, it is possible to reduce the energy barrier in the interface bonding with the negative electrode, or the negative electrode interface of excitons generated in the electron donating organic material and the electron accepting organic material. It is considered that the electron extraction efficiency and the charge generation efficiency are improved by preventing the deactivation in the substrate.

  In the photovoltaic device of the present invention, two or more photoelectric conversion layers may be stacked (tandemized) via one or more charge recombination layers to form a series junction. For example, a laminated structure of substrate / positive electrode / first photoelectric conversion layer / first electron extraction layer / charge recombination layer / second photoelectric conversion layer / second electron extraction layer / negative electrode can be given. By laminating in this way, the open circuit voltage can be further increased. Note that the above-described hole transport layer may be provided between the positive electrode and the first photoelectric conversion layer and between the charge recombination layer and the second photoelectric conversion layer. The hole transport layer described above may be provided between the bonding layers and between the second photoelectric conversion layer and the negative electrode.

  The charge recombination layer used here needs to have optical transparency so that a plurality of photoelectric conversion layers can absorb light. In addition, 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, a metal cluster uniformly formed on the photoelectric conversion layer. It doesn't matter.

  Therefore, for the charge recombination layer, a very thin metal film having a light transmittance of several angstroms to several tens of angstroms made of gold, platinum, chromium, nickel, lithium, magnesium, calcium, tin, silver, aluminum, etc. Metal clusters (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: PSS, or these Or a complex thereof.

  For example, uniform silver clusters can be formed by depositing silver so as to be several angstroms to 1 nm on a crystal oscillator film thickness monitor using a vacuum deposition method. In addition, if a titanium oxide film is formed, the sol-gel method described in Advanced Materials, 2006, Vol. 18, 572-576 may be used. If it is a composite metal oxide such as ITO or IZO, the film may be formed by sputtering. These charge recombination layer formation methods and types may be appropriately selected in consideration of the non-destructive property to the photoelectric conversion layer at the time of charge recombination layer formation, the formation method of the next photoelectric conversion layer, and the like. .

  Next, the manufacturing method of the photovoltaic device of the present invention will be described with reference to examples.

  First, a transparent electrode such as ITO (in this case, corresponding to a positive electrode) is formed on a substrate by a sputtering method or the like.

  Next, a photoelectric conversion layer is formed on the transparent electrode.

  The photoelectric conversion layer is formed, for example, by dissolving a material for a photoelectric conversion layer containing an electron-donating organic material and, if necessary, an electron-accepting organic material in a solvent, and applying the solution on a transparent electrode. Can do.

  The solvent used at this time is not particularly limited as long as the organic semiconductor can be appropriately dissolved or dispersed in the solvent, but an organic solvent is preferable, for example, hexane, heptane, octane, isooctane, nonane, decane, cyclohexane, Aliphatic hydrocarbons such as decalin and bicyclohexyl, alcohols such as methanol, ethanol, butanol, propanol, ethylene glycol, and glycerin, ketones such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, and isophorone, ethyl acetate, and butyl acetate , Methyl lactate, γ-butyrolactone, diethylene glycol monobutyl ether acetate, esters such as dimethyl carbonate, ethyl ether, methyl tertiary butyl ether, tetrahydrofuran, , 4-dioxane, tetrahydropyran, 3,4-dihydro-2H-pyran, isochroman, ethylene glycol monomethyl ether, ethers such as diglyme, amines such as ammonia and ethanolamine, N, N-dimethylformamide, dimethylacetamide, Amides such as N-methyl-2-pyrrolidone, sulfones such as sulfolane, sulfoxides such as dimethyl sulfoxide, thiols such as carbon disulfide and 1,8-octanedithiol, nitriles such as acetonitrile and acrylonitrile, acetic acid, Fatty acids such as lactic acid, heterocyclic compounds such as furan, thiophene, pyrrole, pyridine, benzene, toluene, xylene, ethylbenzene, cumene, n-butylbenzene, sec-butylbenzene, tert-butylbenzene Benzene, styrene, mesitylene, 1,2,4-trimethylbenzene, p-cymene, cyclohexylbenzene, diethylbenzene, pentylbenzene, dipentylbenzene, dodecylbenzene, ethynylbenzene, tetralin, anisole, phenetole, butylphenyl ether, pentylphenyl ether, Veratrol, 1,3-dimethoxybenzene, 1,2,4-trimethoxybenzene, 3,4,5-trimethoxytoluene, 2-methoxytoluene, 2,5-dimethylanisole, o-chlorophenol, chlorobenzene, dichlorobenzene , Trichlorobenzene, 1-chloronaphthalene, 1-bromonaphthalene, 1-methylnaphthalene, o-diiodobenzene, acetophenone, 2,3-benzofuran, 2,3-dihydrobenzofura Aromatic hydrocarbons such as 1,4-benzodioxane, phenyl acetate, methyl benzoate, cresol, aniline, nitrobenzene, dichloromethane, 1,2-dichloroethylene, trichloroethylene, tetrachloroethylene, chloroform, carbon tetrachloride, dichloroethane, trichloroethane, 1,3-dichloropropane, 1,1,1,2-tetrachloroethane, 1,1,1,3-tetrachloropropane, 1,2,2,3-tetrachloropropane, 1,1,2,3-tetrachloropropane , Pentachloropropane, hexachloropropane, heptachloropropane, 1-bromopropane, 1,2-dibromopropane, 2,2-dibromopropane, 1,3-dibromopropane, 1,2,3-tribromopropane, 1,4- Dibromobutane, 1,5 Dibromopentane, 1,6-dibromohexane, 1,7-dibromoheptane, 1,8-dibromooctane, 1-iodopropane, 1,3-diiodopropane, 1,4-diiodobutane, 1,5-diiodopentane 1,6-diiodohexane, 1,7-diiodoheptane, 1,8-diiodooctane, and other halogen hydrocarbons. Among these, toluene, xylene, mesitylene, 1,2,4-trimethylbenzene, tetralin, anisole, phenetole, veratrol, 1,3-dimethoxybenzene, 1,2,4-trimethoxybenzene, 3,4,5- Aromatic hydrocarbons such as trimethoxytoluene, 2-methoxytoluene, 2,5-dimethylanisole, chlorobenzene, dichlorobenzene, trichlorobenzene, 1-chloronaphthalene, chloroform, dichloromethane, 1,2-dibromopropane, 1, 3-dibromopropane, 1,2,3-tribromopropane, 1,4-dibromobutane, 1,6-dibromohexane, 1,8-dibromooctane, 1,3-diiodopropane, 1,4-diiodobutane, 1,5-diiodopentane, 1,6-diiodohexane Emissions, 1,7-diiodo-heptane, 1,8-halogen hydrocarbons such as diiodooctane, and the like. Two or more of these solvents may be mixed and used.

  When a photoelectric conversion layer is formed by mixing an electron-donating organic material and an electron-accepting organic material, the electron-donating organic material and the electron-accepting organic material of the present invention are added to a solvent at a desired ratio, and heated. A solution is prepared by using a method such as stirring or ultrasonic irradiation, and the solution is applied on the transparent electrode. In addition, when a photoelectric conversion layer is formed by laminating an electron-donating organic material and an electron-accepting organic material, for example, a layer having an electron-donating organic material is formed by applying a solution of the electron-donating organic material. Later, a photoelectric conversion layer can be formed by applying a solution of an electron-accepting organic material to form a layer having the electron-accepting organic material. When the electron-donating organic material and the electron-accepting organic material are low molecular weight substances having a molecular weight of about 1000 or less, the photoelectric conversion layer can be formed using a vapor deposition method.

  For the formation of the photoelectric conversion layer, any of spin coating, blade coating, slit die coating, screen printing coating, bar coater coating, mold coating, print transfer method, dip pulling method, ink jet method, spray method, vacuum deposition method, etc. This method may be used, and the formation method may be selected according to the characteristics of the photoelectric conversion layer to be obtained, such as film thickness control and orientation control.

  For example, when spin coating is performed, the electron donating organic material of the present invention and the electron accepting organic material have a concentration of 1 to 20 g / l (the electron donating organic material and the electron accepting organic material of the present invention The weight of the electron-donating organic material and the electron-accepting organic material of the present invention with respect to the volume of the solution containing the solvent is preferable, and by setting this concentration, a homogeneous photoelectric conversion layer having a thickness of 5 to 200 nm is obtained. be able to.

  In order to remove the solvent, the formed photoelectric conversion layer may be subjected to an annealing treatment under reduced pressure or under an inert atmosphere (nitrogen or argon atmosphere). A preferable temperature for the annealing treatment is 40 ° C to 300 ° C, more preferably 50 ° C to 200 ° C. This annealing treatment may be performed after the formation of the negative electrode.

  Next, an electron extraction layer containing a compound that satisfies all of the above (a) to (c) is formed on the photoelectric conversion layer. For the formation of the electron extraction layer, the same coating method or vapor deposition method as that for the photoelectric conversion layer can be used. When the coating method is used, a solution is prepared by dissolving an electron extraction layer material containing a compound satisfying all of the above (a) to (c) in a solvent.

  The solvent used at this time is preferably an organic solvent, for example, aliphatic hydrocarbons such as hexane, heptane, octane, isooctane, nonane, decane, cyclohexane, decalin, bicyclohexyl, methanol, ethanol, butanol, propanol, ethylene glycol, Alcohols such as glycerin, ketones such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, isophorone, ethyl acetate, butyl acetate, methyl lactate, γ-butyrolactone, esters such as diethylene glycol monobutyl ether acetate, dimethyl carbonate, ethyl ether, Methyl tertiary butyl ether, tetrahydrofuran, 1,4-dioxane, tetrahydropyran, 3,4-dihydro-2H-pyran, isochroma , Ethers such as ethylene glycol monomethyl ether and diglyme, amines such as ammonia and ethanolamine, amides such as N, N-dimethylformamide, dimethylacetamide and N-methyl-2-pyrrolidone, sulfones such as sulfolane, dimethyl Sulfoxides such as sulfoxide, thiols such as carbon disulfide and 1,8-octanedithiol, nitriles such as acetonitrile and acrylonitrile, fatty acids such as acetic acid and lactic acid, heterocyclic compounds such as furan, thiophene, pyrrole and pyridine Benzene, toluene, xylene, ethylbenzene, cumene, n-butylbenzene, sec-butylbenzene, tert-butylbenzene, styrene, mesitylene, 1,2,4-trimethylbenzene, p-cymene, cyclohexane Xylbenzene, diethylbenzene, pentylbenzene, dipentylbenzene, dodecylbenzene, ethynylbenzene, tetralin, anisole, phenetole, butylphenyl ether, pentylphenyl ether, veratrol, 1,3-dimethoxybenzene, 1,2,4-trimethoxybenzene, 2-methoxytoluene, 2,5-dimethylanisole, o-chlorophenol, chlorobenzene, dichlorobenzene, trichlorobenzene, 1-chloronaphthalene, 1-bromonaphthalene, 1-methylnaphthalene, o-diiodobenzene, acetophenone, 2, Aromatic hydrocarbons such as 3-benzofuran, 2,3-dihydrobenzofuran, 1,4-benzodioxane, phenyl acetate, methyl benzoate, cresol, aniline, nitrobenzene , Dichloromethane, 1,2-dichloroethylene, trichloroethylene, tetrachloroethylene, chloroform, carbon tetrachloride, dichloroethane, trichloroethane, 1,3-dichloropropane, 1,1,1,2-tetrachloroethane, 1,1,1,3-tetra Chloropropane, 1,2,2,3-tetrachloropropane, 1,1,2,3-tetrachloropropane, pentachloropropane, hexachloropropane, heptachloropropane, 1-bromopropane, 1,2-dibromopropane, 2,2-dibromo Propane, 1,3-dibromopropane, 1,2,3-tribromopropane, 1,4-dibromobutane, 1,5-dibromopentane, 1,6-dibromohexane, 1,7-dibromoheptane, 1,8 -Dibromooctane, 1-iodopropane Halogen hydrocarbons such as 1,3-diiodopropane, 1,4-diiodobutane, 1,5-diiodopentane, 1,6-diiodohexane, 1,7-diiodoheptane, 1,8-diiodooctane And the like. Of these, toluene, xylene, mesitylene, 1,2,4-trimethylbenzene, tetralin, anisole, phenetol veratrol, 1,3-dimethoxybenzene, 1,2,4-trimethoxybenzene, 2-methoxytoluene, Aromatic hydrocarbons such as 2,5-dimethylanisole, chlorobenzene, dichlorobenzene, trichlorobenzene, 1-chloronaphthalene, chloroform, dichloromethane, 1,2-dibromopropane, 1,3-dibromopropane, 1,2, 3-tribromopropane, 1,4-dibromobutane, 1,6-dibromohexane, 1,8-dibromooctane, 1,3-diiodopropane, 1,4-diiodobutane, 1,5-diiodopentane, 1 , 6-diiodohexane, 1,7-diiodoheptane, 1, - and halogen hydrocarbons such as di-iodo octane. Two or more of these may be mixed and used.

  Further, by mixing a compound satisfying all of the above (a) to (c) and a protonic acid in the same solvent, a nitrogen-containing six-membered aromatic ring in A of the compound satisfying all of the above (a) to (c) A salt of a ring and a protonic acid can be formed and used for forming the electron extraction layer.

  Specific examples of the protonic acid include carboxylic acids such as formic acid, acetic acid, trifluoroacetic acid, heptadecafluorononanoic acid, butyric acid, oxalic acid, and benzoic acid, sulfonic acids such as methanesulfonic acid, benzenesulfonic acid, and tosylic acid, and fluorine. Examples thereof include inorganic acids such as acid, hydrochloric hydrobromic acid, hydroiodic acid, sulfuric acid, nitric acid, perchloric acid, phosphoric acid, boric acid and chromic acid, and organic acids such as phenol.

  For the formation of the electron extraction layer, a film may be formed using the same coating method as that for forming the photoelectric conversion layer, and the formation method is selected according to the electron extraction layer to be obtained, such as film thickness control and orientation control. That's fine.

  For example, when spin coating is performed, 0.01 to 5 g / l of the compound satisfying all of the above (a) to (c) of the present invention and, if necessary, the compound represented by the above general formula (2). The electron extraction layer having a thickness of about 0.1 to 40 nm can be obtained by using this concentration.

  In order to remove the solvent, the formed electron extraction layer may be subjected to an annealing treatment under reduced pressure or in an inert atmosphere (nitrogen or argon atmosphere). A preferable temperature for the annealing treatment is 40 ° C to 300 ° C, and a more preferable temperature is 50 ° C to 200 ° C. This annealing treatment may be performed after the formation of the negative electrode.

  In addition, the electron extraction layer may be formed in multiple stages by a plurality of methods. First, the first layer is formed by a coating method or a vapor deposition method, and then the second layer is formed by a coating method or a vapor deposition method. Or may be further laminated. At this time, the number of layers to be formed is not limited as long as the film thickness of the entire electron extraction layer is within an appropriate range. Moreover, the compound which satisfy | fills all the said (a)-(c) should just be contained in a part in the laminated | stacked layer, and it is more preferable that it exists in the outermost layer which touches an electrode.

  Next, a metal electrode such as silver (corresponding to a negative electrode in this case) is formed on the electron extraction layer by vacuum deposition or sputtering. When the electron extraction layer is vacuum-deposited, the metal electrode is preferably formed continuously while maintaining the vacuum.

  When a hole transport layer is provided between the positive electrode and the photoelectric conversion layer, for example, a desired material (such as PEDOT: PSS) is applied on the positive electrode, and then the solvent is removed using a vacuum thermostat or a hot plate. By doing so, a hole transport layer can be formed. As the coating method, the same coating method as in the case of forming the photoelectric conversion layer described above can be used. In the case of using a low molecular organic material such as a phthalocyanine derivative or a porphyrin derivative and an inorganic material such as molybdenum oxide, a vacuum deposition method or a sputtering method can be applied.

  In the above description, the method for forming a photovoltaic element by first forming a positive electrode on a substrate and forming layers sequentially from the positive electrode side has been described. However, an electrode (negative electrode) is formed on the substrate by a sputtering method or the like. Moreover, the photovoltaic device manufacturing method which forms an electron taking-out layer, a photoelectric converting layer, a positive hole transport layer, and an electrode (positive electrode) in this order on the said electrode is also mentioned. In this case, the laminated structure of the photovoltaic elements is reversed, and the photoelectric conversion layer is formed on the electron extraction layer, but the others are the same as described above.

  The photovoltaic element of the present invention can be applied to various photoelectric conversion devices using a photoelectric conversion function, an optical rectification function, and the like. For example, it is useful for photovoltaic cells (such as solar cells), electronic devices (such as optical sensors, optical switches, and phototransistors), optical recording materials (such as optical memories), and imaging devices.

Hereinafter, the present invention will be described more specifically based on examples. In addition, this invention is not limited to the following Example. Of the compounds used in the examples and the like, those using abbreviations are shown below.
Isc: Short-circuit current density Voc: Open circuit voltage FF: Fill factor η: Photoelectric conversion efficiency ITO: Indium tin oxide PEDOT: Polyethylenedioxythiophene PSS: Polystyrene sulfonate A-1, B-1 to B-4: Scheme 1 described later To C-7: Compounds C-1 to C-2: Compounds represented by the following formulae

PC ₇₀ BM: phenyl C71 butyric acid methyl ester BCP: 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (basocuproin)
Mw (CU): Total molecular weight of all nitrogen-containing six-membered aromatic rings of A in the molecule Mw (all): Molecular weight of the whole compound The measurement in each Example and Comparative Example was performed by the following method.
(1) Measurement of photoelectric conversion efficiency The photoelectric conversion efficiency was calculated | required by following Formula.
η (%) = Isc (mA / cm ² ) × Voc (V) × FF / irradiation light intensity (mW / cm ² ) × 100
FF = JVmax / (Isc (mA / cm ² ) × Voc (V))
JVmax (mW / cm ² ) is a value of the product of the current density and the applied voltage at the point where the product of the current density and the applied voltage is maximum between the applied voltage of 0 V and the open circuit voltage.
(2) ¹ H-NMR measurement
^{For the 1} H-NMR measurement, an FT-NMR apparatus (JEOL JNM-EX270 manufactured by JEOL Ltd.) was used.
(3) Average molecular weight measurement The average molecular weight (number average molecular weight, weight average molecular weight) was calculated by an absolute calibration curve method using a GPC apparatus (manufactured by TOSOH Co., Ltd., which was supplied with chloroform, high-speed GPC apparatus HLC-8320GPC). The degree of polymerization n was calculated by the following formula.
Degree of polymerization n = [(weight average molecular weight) / (molecular weight of repeating unit)]
(4) Measurement of 90% photoelectric conversion efficiency holding time As a durability evaluation of the photovoltaic device of the present invention, 90% photoelectric conversion efficiency holding time was measured. First, the photoelectric conversion efficiency (η) of the photovoltaic element is measured by the measurement method (1) above, and the initial photoelectric conversion efficiency (initial efficiency) is obtained. Next, the photovoltaic element is heat-treated on a hot plate at 85 ° C. under nitrogen, and the photoelectric conversion efficiency (efficiency after heat treatment) of the photovoltaic element after the heat treatment is measured. The time required for (post-heat treatment efficiency) / (initial efficiency) × 100 (%) to be 90% is defined as 90% photoelectric conversion efficiency retention time.

Synthesis example 1
Compound X-1 was synthesized by the method shown in Scheme 1. The compound (1-i) described in Synthesis Example 1 is obtained by referring to the method described in Journal of the American Chemical Society, 2009, Vol. 131, pages 7792-7799. (1-p) was synthesized with reference to the method described in Angewante Chem International Edition, 2011, Vol. 50, pages 9697-9702.

38 g (0.27 mol) of methyl-2-thiophenecarboxylate (Tokyo Chemical Industry Co., Ltd.) and 108 g (1.34 mol) of chloromethyl methyl ether (Tokyo Chemical Industry Co., Ltd.) are stirred at 0 ° C. Then, 125 g (0.48 mol) of tin tetrachloride (manufactured by Wako Pure Chemical Industries, Ltd.) was added over 1 hour, and then stirred at room temperature for 8 hours. After completion of stirring, 100 ml of water was slowly added at 0 ° C., and extracted with chloroform three times. The organic layer was washed with saturated brine, the solvent was dried over anhydrous magnesium sulfate, and the solvent was removed under reduced pressure. The obtained brown solid was recrystallized from methanol to obtain compound (1-b) as a pale yellow solid (24.8 g, yield 39%). The measurement result of ¹ H-NMR of the compound (1-b) is shown below.
¹ H-NMR (270 MHz, CDCl ₃ ): 7.71 (s, 1H), 4.79 (s, 1H), 4.59 (s, 1H), 3.88 (s, 3H) ppm.

24.8 g (0.10 mmol) of the compound (1-b) was dissolved in 1.2 L of methanol (manufactured by Sasaki Chemical Co., Ltd.) and stirred at 60 ° C., and sodium sulfide (Wako Pure Chemical Industries ( 100 ml of a methanol solution of 8.9 g (0.11 mol) was added dropwise over 1 hour and further stirred at 60 ° C. for 4 hours. After completion of the reaction, the solvent was removed under reduced pressure, 200 ml of chloroform and 200 ml of water were added, and insoluble matters were filtered off. The organic layer was washed twice with water and once with saturated brine, dried over anhydrous magnesium sulfate, and the solvent was removed under reduced pressure. The product was purified by silica gel column chromatography (eluent, chloroform) to give compound (1-c) as a white solid (9.8 g, yield 48%). The measurement result of ¹ H-NMR of the compound (1-c) is shown below.
¹ H-NMR (270 MHz, CDCl ₃ ): 7.48 (s, 1H), 4.19 (t, J = 3.0 Hz, 2H), 4.05 (t, J = 3.0 Hz, 2H), 3.87 (s, 3H) ppm.

To 9.8 g (49 mmol) of the compound (1-c), 100 ml of water and 30 ml of 3M aqueous sodium hydroxide solution were added, followed by heating and stirring at 80 ° C. for 4 hours. After completion of the reaction, 15 ml of concentrated hydrochloric acid was added at 0 ° C., and the precipitated solid was collected by filtration and washed several times with water. The obtained solid was dried to obtain compound (1-d) as a white solid (8.9 g, yield 98%). The measurement result of ¹ H-NMR of the compound (1-d) is shown below.
¹ H-NMR (270 MHz, DMSO-d ₆ ): 7.46 (s, 1H), 4.18 (t, J = 3.2 Hz, 2H), 4.01 (t, J = 3.2 Hz, 2H) ) Ppm.

1.46 g (7.8 mmol) of the compound (1-d) was dissolved in 60 ml of dehydrated tetrahydrofuran (manufactured by Wako Pure Chemical Industries, Ltd.) and stirred at −78 ° C. to obtain a normal butyl lithium hexane solution ( 1.6 M, 10.7 ml (17.2 mmol) manufactured by Wako Pure Chemical Industries, Ltd. was added dropwise, and the mixture was stirred at -78 ° C for 1 hour. Subsequently, 20 ml of a dry tetrahydrofuran solution of 3.19 g (10.1 mmol) of N-fluorobenzenesulfonimide (manufactured by Tokyo Chemical Industry Co., Ltd.) was added dropwise at −78 ° C. over 10 minutes, followed by stirring at room temperature for 12 hours. After completion of the reaction, 50 ml of water was slowly added. 3M Hydrochloric acid was added to acidify the aqueous layer, and the mixture was extracted 3 times with chloroform. The organic layer was dried over anhydrous magnesium sulfate, and the solvent was distilled off under reduced pressure. By-product was removed by silica gel column chromatography (eluent, ethyl acetate) and then recrystallized from ethyl acetate to obtain compound (1-e) as a pale yellow powder (980 mg, 61% yield). The measurement result of ¹ H-NMR of the compound (1-e) is shown below.
¹ H-NMR (270 MHz, DMSO-d ₆ ): 13.31 (brs, 1H), 4.20 (t, J = 3.0 Hz, 2H), 4.03 (t, J = 3.0 Hz, 2H) ) Ppm.

  To 10 ml of a dehydrated dichloromethane (manufactured by Wako Pure Chemical Industries) solution of 800 mg (3.9 mmol) of the compound (1-e), 1 ml of oxalyl chloride (manufactured by Tokyo Chemical Industry Co., Ltd.) and then dimethylformamide (Wako Pure Chemical Industries, Ltd.) 1 drop of Kogyo Co., Ltd. was added and stirred at room temperature for 3 hours. The solvent and excess oxalyl chloride were removed under reduced pressure to obtain compound (1-f) as a yellow oil. Compound (1-f) was used in the next reaction as it was.

10 ml of a dichloromethane solution of the compound (1-f, crudely purified product) 1.3 g (10 mmol) of 1-octanol (manufactured by Wako Pure Chemical Industries, Ltd.) and 800 mg (8 mmol) of triethylamine (manufactured by Wako Pure Chemical Industries, Ltd.) ) In dichloromethane (15 ml) at room temperature and stirred for 6 hours at room temperature. The reaction solution was washed twice with 1M hydrochloric acid, once with water and once with saturated brine, dried over anhydrous magnesium sulfate, and the solvent was evaporated under reduced pressure. Purification by silica gel column chromatography (eluent, chloroform) gave compound (1-g) as a pale yellow solid (1.12 g, yield 90%). The measurement result of ¹ H-NMR of the compound (1-g) is shown below.
¹ H-NMR (270 MHz, CDCl ₃ ): 4.27 (t, J = 6.7 Hz, 2H), 4.16 (t, J = 3.0 Hz, 2H), 4.01 (t, J = 3) 0.0 Hz, 2H), 1.72 (m, 2H), 1.5-1.3 (m, 12H), 0.88 (t, J = 7.0 Hz, 3H) ppm.

10 ml of an ethyl acetate solution of 630 mg (3.6 mmol) of metachlorobenzoic acid (manufactured by Nacalai Tesque) was added to 40 ml of an ethyl acetate solution of 1.1 g (3.5 mmol) of the compound (1-g) at 0 ° C. Stir at room temperature for 5 hours. After removing the solvent under reduced pressure, 30 ml of acetic anhydride was added, and the mixture was heated to reflux for 3 hours. The solvent was removed again under reduced pressure, and the residue was purified by silica gel column chromatography (eluent, dichloromethane: hexane = 1: 1) to give compound (1-h) as a pale yellow oil (1.03 g, yield 94%). Obtained. The measurement result of ¹ H-NMR of the compound (1-h) is shown below.
¹ H-NMR (270 MHz, CDCl ₃ ): 7.65 (d, J = 2.7 Hz, 1H), 7.28 (dd, J = 2.7 Hz and 5.4 Hz, 1H), 4.31 (t , J = 6.8 Hz, 2H), 1.75 (m, 2H), 1.42-1.29 (m, 12H), 0.89 (t, J = 6.8 Hz, 3H) ppm.

To 20 ml of a dimethylformamide solution of 1.0 g (3.2 mmol) of the compound (1-h), 1.25 g (7.0 mmol) of N-bromosuccinimide (manufactured by Wako Pure Chemical Industries, Ltd.) is added at room temperature. Stir for hours at room temperature. After completion of the reaction, 80 ml of ethyl acetate was added, the organic layer was washed 5 times with water and once with saturated brine, dried over anhydrous magnesium sulfate, and the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography (eluent, chloroform: hexane = 1: 3) gave compound (1-i) as a pale yellow solid (1.2 g, yield 79%). The measurement result of ¹ H-NMR of compound (1-i) is shown below.
¹ H-NMR (270 MHz, CDCl ₃ ): 4.32 (t, J = 6.5 Hz, 2H), 1.75 (m, 2H), 1.42-1.29 (m, 12H), 0. 89 (t, J = 6.8 Hz, 3H) ppm.

To 300 ml of dichloromethane solution of 110 g (1.5 mol) of diethylamine (manufactured by Wako Pure Chemical Industries, Ltd.), 100 g (0.68 mol) of 3-thiophenecarbonyl chloride (manufactured by Wako Pure Chemical Industries, Ltd.) at 0 ° C. for 1 hour. And stirred at room temperature for 3 hours. After completion of the stirring, 200 ml of water was added, and the organic layer was washed three times with water and once with a saturated saline solution. After drying over anhydrous magnesium sulfate, the solvent was distilled off under reduced pressure. The residue was distilled under reduced pressure to obtain compound (1-k) as a pale orange liquid (102 g, yield 82%). The measurement result of ¹ H-NMR of the compound (1-k) is shown below.
¹ H-NMR (270 MHz, CDCl ₃ ): 7.47 (dd, J = 3.2 Hz and 1.0 Hz, 1H), 7.32 (dd, J = 5.0 Hz and 3.2 Hz, 1H), 7 .19 (dd, J = 5.0 Hz and 1.0 Hz, 1H), 3.43 (brs, 4H), 1.20 (t, J = 6.5 Hz, 6H) ppm.

To 400 ml of a dehydrated tetrahydrofuran (manufactured by Wako Pure Chemical Industries, Ltd.) solution of 73.3 g (0.40 mol) of the compound (1-k), a normal butyl lithium hexane solution (1.6 M, manufactured by Wako Pure Chemical Industries, Ltd.). ) 250 ml (0.40 mol) was added dropwise at 0 ° C. over 30 minutes. After completion of dropping, the mixture was stirred at room temperature for 4 hours. After stirring, 100 ml of water was slowly added and stirred for a while, and then the reaction mixture was poured into 800 ml of water. The precipitated solid was collected by filtration and washed with water, methanol, and hexane in this order to obtain compound (1-l) as a yellow solid (23.8 g, yield 27%). The measurement result of ¹ H-NMR of the compound (1-l) is shown below.
¹ H-NMR (270 MHz, CDCl ₃ ): 7.69 (d, J = 4.9 Hz, 2H), 7.64 (d, J = 4.9 Hz, 2H) ppm.

To 400 ml of dehydrated tetrahydrofuran (manufactured by Wako Pure Chemical Industries, Ltd.) solution of 42 g (0.50 mol) of thiophene, 250 ml (0.40 mol) of normal butyl lithium hexane solution (1.6 M, manufactured by Wako Pure Chemical Industries, Ltd.) was added. The solution was added dropwise at −78 ° C. over 30 minutes. The reaction mixture was stirred at -78 ° C for 1 hour, and then 76.4 g (0.40 mol) of 2-ethylhexyl bromide (manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise at -78 ° C over 15 minutes. The reaction solution was stirred at room temperature for 30 minutes and then heated and stirred at 60 ° C. for 6 hours. After completion of the stirring, the reaction solution was cooled to room temperature, and 200 ml of water and 200 ml of ether were added. The organic layer was washed twice with water and saturated brine, and then dried over anhydrous magnesium sulfate, and the solvent was evaporated under reduced pressure. The residue was distilled under reduced pressure to obtain compound (1-n) as a colorless liquid (28.3 g, 36%). The measurement result of ¹ H-NMR of the compound (1-n) is shown below.
¹ H-NMR (270 MHz, CDCl ₃ ): 7.11 (d, 4.9 Hz, 1 H), 6.92 (dd, 4.9 Hz and 3.2 Hz, 1 H), 6.76 (d, J = 3 .2 Hz, 1H), 2.76 (d, J = 6.8 Hz, 2H), 1.62 (m, 1H), 1.4-1.3 (m, 8H), 0.88 (m, 6H) ) Ppm.

In 400 ml of dehydrated tetrahydrofuran (manufactured by Wako Pure Chemical Industries, Ltd.) solution of 17.5 g (89 mmol) of the compound (1-n), 57 ml of normal butyl lithium hexane solution (1.6 M, manufactured by Wako Pure Chemical Industries, Ltd.) (89 mmol) was added dropwise at 0 ° C. over 30 minutes. The reaction solution was stirred at 50 ° C. for 1 hour, and then 4.9 g (22 mmol) of the compound (1-1) was added at 50 ° C. and stirred as it was for 1 hour. After completion of the stirring, the reaction solution was cooled to 0 ° C., and a solution of 39.2 g (175 mmol) of tin chloride dihydrate (manufactured by Wako Pure Chemical Industries, Ltd.) in 80 ml of 10% hydrochloric acid was added. Stir for hours. After completion of the stirring, 200 ml of water and 200 ml of diethyl ether were added, and the organic layer was washed twice with water and then with a saturated saline solution. After drying over anhydrous magnesium sulfate, the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography (eluent, hexane) gave compound (1-o) as a yellow oil (7.7 g, yield 59%). The measurement result of ¹ H-NMR of the compound (1-o) is shown below.
¹ H-NMR (270 MHz, CDCl ₃ ): 7.63 (d, J = 5.7 Hz, 1H), 7.45 (d, J = 5.7 Hz, 1H), 7.29 (d, J = 3 .6 Hz, 1H), 6.88 (d, J = 3.6 Hz, 1H), 2.86 (d, J = 7.0 Hz, 2H), 1.70-1.61 (m, 1H), 1 .56-1.41 (m, 8H), 0.97-0.89 (m, 6H) ppm.

Into 25 ml of dehydrated tetrahydrofuran (manufactured by Wako Pure Chemical Industries, Ltd.) solution of 870 mg (1.5 mmol) of the compound (1-o), normal butyl lithium hexane solution (1.6M, manufactured by Wako Pure Chemical Industries, Ltd.) 2 0.0 ml (3.3 mmol) was added at −78 ° C. using a syringe, and the mixture was stirred at −78 ° C. for 30 minutes and at room temperature for 30 minutes. After cooling the reaction mixture to −78 ° C., 800 mg (4.0 mmol) of trimethyltin chloride (manufactured by Wako Pure Chemical Industries, Ltd.) was added at once at −78 ° C., and the mixture was stirred at room temperature for 4 hours. After completion of the stirring, 50 ml of diethyl ether and 50 ml of water were added and stirred at room temperature for 5 minutes, and then the organic layer was washed twice with water and then with a saturated saline solution. After drying the solvent with anhydrous sodium sulfate, the solvent was distilled off under reduced pressure. The obtained orange oil was recrystallized from ethanol to obtain the compound (1-p) as a pale yellow solid (710 mg, yield 52%). The measurement result of ¹ H-NMR of the compound (1-p) is shown below.
¹ H-NMR (270 MHz, CDCl ₃ ): 7.68 (s, 2H), 7.31 (d, J = 3.2 Hz, 2H), 6.90 (d, J = 3.2 Hz, 2H), 2.87 (d, J = 6.2 Hz, 4H), 1.69 (m, 2H), 1.40-1.30 (m, 16H), 1.0-0.9 (m, 12H), 0.39 (s, 18H) ppm.

  Compound (1-i) 71 mg (0.15 mmol) and compound (1-p) 136 mg (0.15 mmol) in toluene (manufactured by Wako Pure Chemical Industries, Ltd.) 4 ml and dimethylformamide (manufactured by Wako Pure Chemical Industries, Ltd.) ) 5 mg of tetrakistriphenylphosphine palladium (manufactured by Tokyo Chemical Industry Co., Ltd.) was added to the solution dissolved in 1 ml, and the mixture was stirred at 100 ° C. for 15 hours in a nitrogen atmosphere. Next, 15 mg of bromobenzene (manufactured by Tokyo Chemical Industry Co., Ltd.) was added and stirred at 100 ° C. for 1 hour. Subsequently, 40 mg of tributyl (2-thienyl) tin (manufactured by Tokyo Chemical Industry Co., Ltd.) was added, and the mixture was further stirred at 100 ° C. for 1 hour. After completion of the stirring, the reaction mixture was cooled to room temperature and poured into 100 ml of methanol. The precipitated solid was collected by filtration and washed with methanol, water, and acetone in this order. Subsequently, it wash | cleaned in order of acetone and hexane using the Soxhlet extractor. Next, the obtained solid was dissolved in chloroform, passed through Celite (manufactured by Nacalai Tesque), and then a silica gel column (eluent, chloroform), and then the solvent was distilled off under reduced pressure. The obtained solid was dissolved again in chloroform and then reprecipitated in methanol to obtain Compound X-1 (85 mg). The weight average molecular weight was 25,000 and the number average molecular weight was 16,000.

Synthesis example 2
Compound B-1 was synthesized by the method shown in Scheme 2.

1,3,5-triformylbenzene (manufactured by Aldrich) 250 mg (1.54 mmol), 2-acetylpyridine (manufactured by Tokyo Chemical Industry Co., Ltd.) 1.2 g (10 mmol), sodium hydroxide 500 mg (12.3 mmol) Was ground with a mortar and pestle, and the resulting yellow powder was dissolved in 30 ml of ethanol (Aldrich) and stirred at room temperature for 2 hours. After stirring, 30 ml of an aqueous ammonia solution (28%, manufactured by Wako Pure Chemical Industries, Ltd.) was added and stirred at 70 ° C. for 20 hours under a nitrogen atmosphere. After completion of the stirring, the reaction mixture was cooled to room temperature, and the solid obtained by filtering the solution was purified by alumina column chromatography (eluent, chloroform) to give Compound B-1 as a white solid (366 mg, yield 31). 0.0%).
The measurement result of ¹ H-NMR of compound B-1 is shown below.
¹ H-NMR (270 MHz, CDCl ₃ ): 8.89 (s, 6H), 8.75-8.70 (m, 12H), 8.42 (s, 3H), 7.90 (t, J = 7.83 Hz, 6H), 7.38-7.34 (m, 6H) ppm.

Synthesis example 5
Compound B-2 was synthesized by the method shown in Scheme 3.

600 mg (1.38 mol) of the compound (4-a), 1,3,5-tribromobenzene (manufactured by Wako Pure Chemical Industries, Ltd.) 97.6 mg (0.31 mmol), t-butyl alcohol (Wako Pure Chemical) 7 ml of Kogyo Co., Ltd., 292 mg (2.76 mmol) of sodium carbonate (Wako Pure Chemical Industries, Ltd.) and 20 ml of water were dissolved in 25 ml of toluene (Nacalai Tesque). Thereto was added 37 mg (0.051 mmol) of [1.1′-bis (diphenylphosphino) ferrocene] dichloropalladium (manufactured by Aldrich), and the mixture was stirred at 90 ° C. for 72 hours under a nitrogen atmosphere. After completion of the stirring, the reaction mixture was cooled to room temperature, chloroform (40 ml) and water (40 ml) were added, and after stirring for a while, the organic layer was washed twice with water and then with a saturated saline solution. After drying the solvent with sodium sulfate, the solvent was distilled off under reduced pressure. A solid obtained by washing the residue in order of water and methanol was dissolved in chloroform, 100 mg of Quadrasil (manufactured by Aldrich) was added, and the mixture was stirred at 60 ° C. for 2 hours under a nitrogen atmosphere. After stirring, the solution was filtered through Celite (manufactured by Nacalai Tesque Co., Ltd.), 40 ml of a saturated aqueous EDTA solution was added to the filtrate, and after stirring for a while, the organic layer was washed with water. After drying the solvent with sodium sulfate, the solvent was distilled off under reduced pressure to obtain Compound B-2 as a white solid (178 mg, yield 57.0%).
The measurement result of ¹ H-NMR of compound B-2 is shown below.

¹ H-NMR (270 MHz, CDCl ₃ ): 8.84 (s, 6H), 8.78-8.75 (m, 6H), 8.70 (d, J = 8.4 Hz, 6H), 8. 09 (d, J = 8.64 Hz, 6H), 7.93-7.87 (m, 15H), 7.40-7.37 (m, 6H) ppm.

Synthesis Example 6
Compound B-3 was synthesized by the method shown in Scheme 4.

150 mg (0.34 mol) of the compound (4-a), 51 mg (0.22 mmol) of 4 ′-(4-bromophenyl) -4-bromobiphenyl (manufactured by Wako Pure Chemical Industries, Ltd.), t-butyl alcohol ( 1.5 ml of Wako Pure Chemical Industries, Ltd., 72 mg (0.68 mmol) of sodium carbonate (Wako Pure Chemical Industries, Ltd.) and 5 ml of water were dissolved in 6 ml of toluene (Nacalai Tesque). Thereto was added 10 mg (0.014 mmol) of [1.1′-bis (diphenylphosphino) ferrocene] dichloropalladium (manufactured by Aldrich), and the mixture was stirred at 90 ° C. for 12 hours in a nitrogen atmosphere. After completion of the stirring, the reaction mixture was cooled to room temperature, 20 ml of chloroform and 20 ml of water were added and stirred for a while, and then the organic layer was washed twice with water and then with a saturated saline solution. After drying the solvent with sodium sulfate, the solvent was distilled off under reduced pressure. The residue was washed with water and methanol in this order to obtain Compound B-5 as a white solid (60 mg, yield 59.0%).
The measurement result of ¹ H-NMR of compound B-3 is shown below.

¹ H-NMR (270 MHz, CDCl ₃ ): 8.82 (s, 2H), 8.75 (d, J = 4.6 Hz, 2H), 8.70 (d, J = 8.1 Hz, 2H), 8.03 (d, J = 6.75 Hz, 2H), 7.90-7.82 (m, 2H), 7.87-7.66 (m, 10H), 7.51-7.50 (m , 2H), 7.36-7.35 (m, 2H) ppm.

Synthesis example 7
Compound B-4 was synthesized by the method shown in Scheme 5.

150 mg (0.34 mol) of the compound (4-a), 4-bromotriphenylamine (manufactured by Wako Pure Chemical Industries, Ltd.) 71 mg (0.22 mmol), t-butyl alcohol (manufactured by Wako Pure Chemical Industries, Ltd.) 1.5 ml, 72 mg (0.68 mmol) of sodium carbonate (manufactured by Wako Pure Chemical Industries, Ltd.) and 5 ml of water were dissolved in 6 ml of toluene (manufactured by Nacalai Tesque). Thereto was added 10 mg (0.014 mmol) of [1.1′-bis (diphenylphosphino) ferrocene] dichloropalladium (manufactured by Aldrich), and the mixture was stirred at 90 ° C. for 12 hours in a nitrogen atmosphere. After completion of the stirring, the reaction mixture was cooled to room temperature, 20 ml of chloroform and 20 ml of water were added and stirred for a while, and then the organic layer was washed twice with water and then with a saturated saline solution. After drying the solvent with sodium sulfate, the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography (eluent, ethyl acetate: hexane = 2: 1) gave Compound B-6 as a white solid (60 mg, yield 59.0%).
The measurement result of ¹ H-NMR of compound B-4 is shown below.

¹ H-NMR (270 MHz, CDCl ₃ ): 8.79 (s, 2H), 8.75-8.73 (m, 2H), 8.69 (d, J = 8.1 Hz, 2H), 7. 99 (d, J = 8.37 Hz, 2H), 7.92-7.86 (m, 2H), 7.71 (d, J = 7.01 Hz, 2H), 7.56 (d, J = 8 .1 Hz, 2H), 7.36-7.28 (m, 4H), 7.18-7.15 (m, 6H), 7.05 (t, J = 7.3 Hz, 2H) ppm.

Example 1
(A-1) 0.9 mg, PC ₇₀ BM (manufactured by Solenne) 1.1 mg, 1,8-diiodooctane (manufactured by Wako Pure Chemical Industries, Ltd.) is included at a volume concentration ratio of 3%. In addition to 0.20 ml of the chloroform solution, the container containing the solution was subjected to ultrasonic irradiation for 30 minutes in an ultrasonic cleaner (US-2 (trade name) manufactured by Inoue Seieido Co., Ltd., output 120 W) for 30 minutes. (Donor acceptor weight ratio = 1: 1) was obtained.

A glass substrate having an ITO transparent conductive layer of 125 nm deposited as a positive electrode deposited by sputtering was cut into 38 mm × 46 mm, and then ITO was patterned into a 38 mm × 13 mm rectangular shape by photolithography. The obtained substrate was subjected to ultrasonic cleaning for 10 minutes with an alkali cleaning solution (“Semico Clean” EL56 (trade name), manufactured by Furuuchi Chemical Co., Ltd.), and then washed with ultrapure water. After this substrate was UV / ozone treated for 30 minutes, a PEDOT: PSS aqueous solution (0.8% by weight of PEDOT, 0.5% by weight of PPS) serving as a hole transport layer was formed on the substrate to a thickness of 60 nm by spin coating. did. After drying by heating at 200 ° C. for 5 minutes using a hot plate, the solution A was dropped onto the PEDOT: PSS layer, and a 100 nm photoelectric conversion layer having a thickness of 130 nm was formed by spin coating. The substrate and the hole extraction layer mask were placed in a vacuum deposition apparatus, and the degree of vacuum in the apparatus was evacuated to 1 × 10 ⁻³ Pa or less, and the compound (B-1) was reduced to 3 nm by resistance heating. Then, a silver layer serving as a negative electrode was deposited to a thickness of 100 nm. The extraction electrodes were taken out from the upper and lower electrodes of the manufactured element, and a photovoltaic element having an area where the band-like ITO layer and the silver layer overlap each other was 5 mm × 5 mm was manufactured.

The positive and negative electrodes of the photovoltaic device thus fabricated were connected to a Keithley 2400 series source meter and simulated sunlight (OTENTO-SUNIII, manufactured by Spectrometer Co., Ltd., spectral shape) from the ITO layer side in the atmosphere. : AM1.5, intensity: 100 mW / cm ² ), and the current value was measured when the applied voltage was changed from −1V to + 2V. As a result of calculating photoelectric conversion efficiency ((eta)) from the obtained electric current value, it was 7.92%. Further, the photovoltaic element was heat-treated on a hot plate at 85 ° C. under nitrogen, and the photoelectric conversion efficiency (η) was calculated in the same manner as described above. As a result, the photoelectric conversion efficiency retention after the heat treatment was 90. % (90% photoelectric conversion efficiency retention time) was 10 hours or more.

Example 2
A photovoltaic device was produced in the same manner as in Example 1 except that B-2 (3 nm) was used instead of B-1, and the photoelectric conversion efficiency (η) was calculated. As a result, it was 8.17%. It was. Further, the photovoltaic element was heat-treated on a hot plate at 85 ° C. under nitrogen, and the photoelectric conversion efficiency (η) was calculated in the same manner as described above. As a result, the photoelectric conversion efficiency retention after the heat treatment was 90. % (90% photoelectric conversion efficiency retention time) was about 45 hours.

Comparative Example 1
A photovoltaic device was prepared in the same manner as in Example 1 except that B-3 (4 nm) was used instead of B-1, and the photoelectric conversion efficiency (η) was calculated. As a result, it was 2.52%. It was.

Comparative Example 2
A photovoltaic device was produced in the same manner as in Example 1 except that B-4 (4 nm) was used instead of B-1, and the photoelectric conversion efficiency (η) was calculated. As a result, it was 7.04%. It was.

Comparative Example 3
A photovoltaic device was produced in the same manner as in Example 1 except that C-1 (Phenyl-diphenylphosphine oxide (PoPy2)) (4 nm) (4 nm) manufactured by Luminescence Technology was used instead of B-1. η) was calculated to be 5.16%.

Comparative Example 4
Other than using C-2 (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)) (5 nm) / LiF (0.5 nm) manufactured by Luminescence Technology instead of B-1 A photovoltaic device was produced in exactly the same manner as in Example 1, and the photoelectric conversion efficiency (η) was calculated. As a result, it was 7.93%. Further, the photovoltaic element was heat-treated on a hot plate at 85 ° C. under nitrogen, and the photoelectric conversion efficiency (η) was calculated in the same manner as described above. As a result, the photoelectric conversion efficiency retention after the heat treatment was 90. % (90% photoelectric conversion efficiency retention time) was less than 1 hour.

  The results of Examples and Comparative Examples are summarized in Table 1. From the comparison between Example 1 and Comparative Examples 1 to 3, and Example 2 and Comparative Example 4, it can be seen that the present invention can simultaneously improve the photoelectric conversion efficiency and durability of the photovoltaic element.

1 Substrate 2 Positive Electrode 3 Photoelectric Conversion Layer 4 Electron Extraction Layer 5 Negative Electrode

Claims (8)

A photovoltaic device having at least a positive electrode, a photoelectric conversion layer, an electron extraction layer, and a negative electrode composed of a metal in this order, wherein the electron extraction layer contains a compound that satisfies all of the following (a) to (c): Power element.
(A) a group containing a nitrogen-containing six-membered ring aromatic ring (nitrogen-containing six-membered ring aromatic group) having one or more, at least one of which is a non-condensed nitrogen-containing six-membered ring aromatic ring It is a group (non-condensed nitrogen-containing six-membered aromatic group).
(B) The one or two or more nitrogen-containing six-membered ring aromatic groups have a spatial arrangement capable of donating electron pairs to the same metal atom or ion (negative electrode metal) as the metal constituting the negative electrode. There are three or more ring nitrogen atoms (coordinating nitrogen atoms) to be obtained, and at least one of the coordinating nitrogen atoms is a nitrogen atom on the non-condensed nitrogen-containing six-membered aromatic group.
(C) The total molecular weight of all nitrogen-containing six-membered aromatic rings in the compound is 60% or more of the total molecular weight of the entire compound.   The light according to claim 1, wherein the non-condensed nitrogen-containing six-membered aromatic group is a group containing a group selected from the group consisting of a pyridyl group, a pyrazyl group, a pyrimidyl group, a triazyl group, and a tetrazyl group. Electromotive force element. The photovoltaic element of Claim 1 or 2 whose compound which satisfy | fills all said (a)-(c) is a compound represented by following General formula (1).
B- (A) n (1)
(In General Formula (1), A is a nitrogen-containing six-membered aromatic group containing three or more coordinate nitrogen atoms. N represents an integer of 1 or more. A condensed nitrogen-containing six-membered aromatic group, when n is 2 or more, two or more As may be the same or different, but at least one of the two or more A is non-condensed nitrogen-containing (It is a 6-membered aromatic group, and B represents an n-valent group that is directly bonded to any ring constituent atom of the nitrogen-containing 6-membered aromatic ring of A.)   In the compound represented by the general formula (1), A is bonded to B at the meta-position or para-position of the coordinating nitrogen atom of the nitrogen-containing six-membered aromatic ring contained in A. The photovoltaic element as described. The photovoltaic device according to claim 3 or 4, wherein the compound represented by the general formula (1) is a compound satisfying the following (i) and (ii).
(I) A is a group selected from the following formulas (A ₁ ) and (A ₂ ).

(A ₁ and A ₂ may each have a substituent.)
(Ii) (A) The total molecular weight of the nitrogen-containing six-membered aromatic ring contained in the n portion is 60% or more of the total molecular weight of the entire compound.   The photovoltaic device according to any one of claims 3 to 5, wherein in the compound represented by the general formula (1), B is a group having an aryl group or an aromatic heterocyclic group as a skeleton. Wherein A ₁ and all ortho positions of the ring constituting nitrogen atom of A ₂ is substituted by unsubstituted or non-aryl group group, photovoltaic element according to claim 5 or 6. The photovoltaic element in any one of Claims 1-7 whose molecular weight of the compound which satisfy | fills all said (a)-(c) is 500 or more.

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