JP5098957B2 - Organic photoelectric conversion element - Google Patents

Description

  The present invention relates to an organic photoelectric conversion element, and more particularly to a tandem organic photoelectric conversion element including a conductive fiber in a recombination layer.

  The organic photoelectric conversion element has a structure in which a photoelectric conversion layer made of an organic substance and a charge transport layer are laminated on a transparent electrode, and is further sandwiched between electrodes, and the generated free carriers are collected at each electrode and an external circuit is collected. It is a device that drives Furthermore, by using a highly flexible transparent resin substrate, not only can a flexible organic photoelectric conversion element be realized, but the organic layer can be formed by roll-to-roll coating using a production facility such as a die coater. A low-cost and highly productive process can be expected.

  In such an organic photoelectric conversion element, it is possible to efficiently absorb the solar spectrum by making a tandem when producing a solar battery cell, so that an improvement in conversion efficiency can be expected (for example, patents) Reference 1).

  The tandem organic photoelectric conversion element introduced in Patent Document 1 is a tandem element having a recombination layer containing metal nanoparticles. This enhances the absorption of incident light by using metal nanoparticles in the recombination layer, and further improves the photoelectric conversion efficiency by improving the recombination property of electrons and holes. However, this method forms a metal nanoparticle layer by vapor deposition and has a problem in terms of productivity, and the advantages of the organic photoelectric conversion element are lost. In addition, by forming a highly transparent ITO in the recombination layer and forming a surface electrode, the functional layer can be formed on the recombination layer by a coating method (for example, see Patent Document 2). The productivity was low because of the vacuum film-forming method as with the metal nanoparticles.

Further, in the configuration including the recombination layer described above, a large number of dark spots (power generation defect portions) are generated, and the behavior that the durability of the device is remarkably deteriorated is a problem in practical use.
European Patent No. 1782471B1 specification JP 2006-279111 A

  An object of the present invention is to provide an organic photoelectric conversion element with good productivity, improved energy conversion efficiency, and suppressed generation of dark spots.

  The above object of the present invention can be achieved by the following configuration.

1. A tandem organic material having at least two photoelectric conversion layers and including at least a recombination layer between at least one pair of adjacent photoelectric conversion layers among the two or more photoelectric conversion layers. It is a photoelectric conversion element, Comprising: At least 1 layer of this recombination layer contains a conductive fiber and a transparent conductive material , The organic photoelectric conversion element characterized by the above-mentioned.

2 . 2. The organic photoelectric conversion element according to item 1, wherein the conductive fiber is at least one selected from the group consisting of metal nanowires or carbon nanotubes.

  According to the present invention, an organic photoelectric conversion element with good productivity, improved energy conversion efficiency, and suppressed dark spots can be provided.

The present invention will be described in more detail. In the present invention, the recombination layer is characterized by containing conductive fibers and a transparent conductive material , and since a recombination layer having both high conductivity and transmittance can be formed, an improvement in energy conversion efficiency can be achieved. Moreover, since the recombination layer can be formed by a coating process, an organic photoelectric conversion element excellent in productivity can be provided.

In addition to the conductive fibers by combining a transparent conductive material, the conductive fiber on not only uniform conductivity throughout the surface, can be called, the surface electrodes of the improvement of energy conversion efficiency, Generation of dark spots can be suppressed. This is because the uniform recombination sites are formed in the surface direction than the recombination layers using nanoparticles.

  The organic photoelectric conversion element of this invention is demonstrated using FIG.

  In FIG. 1, the organic photoelectric conversion element 21 is characterized in that the recombination layer 6 includes conductive fibers and a transparent conductive material. In the recombination layer 6, the holes or electrons generated in the first power generation block 22 and the electrons or holes generated in the second power generation block 23 are recombined to form the first power generation block 22 and the first power generation block 22. The two power generation blocks 23 play a role of connecting two elements connected in series. The recombination layer 6 also preferably plays a role such that light transmitted through the first power generation block 22 is preferably transmitted and the transmitted light is used for power generation of the second power generation block 23. Therefore, the material used for the recombination layer 6 is preferably a layer using a material having both conductivity and transparency.

  In FIG. 1, at least one of the first photoelectric conversion layer 4 and the second photoelectric conversion layer 8 is a layer of a bulk heterojunction structure (hereinafter referred to as a bulk heterojunction layer) which is a mixture of a p-type semiconductor layer and an n-type semiconductor. Also called). For the purpose of improving the sunlight utilization rate (photoelectric conversion efficiency), the second photoelectric conversion layer 8 may be a layer that absorbs the same spectrum as the absorption spectrum of the first photoelectric conversion layer 4 or absorbs a different spectrum. Although it may be a layer, it is preferably a layer that absorbs different spectra.

  Between the first electrode 2 and the first photoelectric conversion layer 4 stacked on the first substrate 1 and / or between the first photoelectric conversion layer 4 and the recombination layer 6, and between the recombination layer 6 and the first An intermediate layer may be provided between the two photoelectric conversion layers 8 and / or between the second photoelectric conversion layer 8 and the second electrode 10. As a preferable form of the intermediate layer, there is a first hole transport layer 3 between the first electrode 2 and the first photoelectric conversion layer 4, and a recombination layer 6 and the second photoelectric conversion layer 8. The second hole transport layer 7 is laminated, and the first electron transport layer 5, the second photoelectric conversion layer 8, and the second layer are interposed between the first photoelectric conversion layer 4 and the recombination layer 6. The second electron transport layers 9 are preferably laminated as intermediate layers between the electrodes 10.

[Conductive fiber]
The conductive fiber according to the present invention is conductive and has a shape whose length is sufficiently longer than its diameter (thickness). The conductive fiber according to the present invention is considered to function as an auxiliary electrode by forming a three-dimensional conductive network when the conductive fibers contact each other in the transparent conductive layer. Accordingly, a longer conductive fiber is preferable because it is advantageous for forming a conductive network. On the other hand, when the conductive fibers are long, the conductive fibers are entangled to form aggregates, which may deteriorate the optical characteristics. Since the conductive fiber formation and aggregate formation are also affected by the stiffness and diameter of the conductive fibers, use the one with the optimum average aspect ratio (aspect = length / diameter) according to the conductive fibers used. Is preferred. As a rough guide, the average aspect ratio is preferably 10 to 10,000.

  Examples of the shape include a hollow tube shape, a wire shape, and a fiber shape, such as organic fibers and inorganic fibers coated with metal, conductive metal oxide fibers, metal nanowires, carbon fibers, and carbon nanotubes. In the present invention, from the viewpoint of transparency, it is preferable that the conductive fiber has a thickness of 300 nm or less, and in order to satisfy the conductivity, the conductive fiber is at least selected from the group of metal nanowires and carbon nanotubes. One type is preferable. Furthermore, silver nanowires are particularly preferable from the viewpoints of cost (raw material costs, manufacturing costs) and performance (conductivity, transparency, flexibility).

[Metal nanowires]
In general, the metal nanowire refers to a linear structure having a metal element as a main component. In particular, the metal nanowire in the present invention means a linear structure having a diameter from the atomic scale to the nm scale.

  As the metal nanowire applied to the conductive fiber according to the present invention, in order to form a long conductive path with one metal nanowire, the average length is preferably 3 μm or more, more preferably 3 to 500 μm, In particular, the thickness is preferably 3 to 300 μm. In addition, the relative standard deviation of the length is preferably 40% or less. Moreover, it is preferable that an average diameter is small from a transparency viewpoint, On the other hand, the larger one is preferable from an electroconductive viewpoint. In this invention, 10-300 nm is preferable as an average diameter of metal nanowire, and it is more preferable that it is 30-200 nm. In addition, the relative standard deviation of the diameter is preferably 20% or less.

  There is no restriction | limiting in particular as a metal composition of the metal nanowire which concerns on this invention, Although it can comprise from the 1 type or several metal of a noble metal element and a base metal element, noble metals (for example, gold, platinum, silver, palladium, rhodium, (Iridium, ruthenium, osmium, etc.) and at least one metal belonging to the group consisting of iron, cobalt, copper, and tin is preferable, and at least silver is more preferable from the viewpoint of conductivity. Further, in order to achieve both conductivity and stability (sulfurization and oxidation resistance of metal nanowires and resistance to magnation), silver and at least one metal belonging to a noble metal other than silver can be included. When the metal nanowire according to the present invention includes two or more kinds of metal elements, for example, the metal composition may be different between the surface and the inside of the metal nanowire, and the entire metal nanowire has the same metal composition. Also good.

  In the present invention, the means for producing the metal nanowire is not particularly limited, and for example, known means such as a liquid phase method and a gas phase method can be used. Moreover, there is no restriction | limiting in particular in a specific manufacturing method, A well-known manufacturing method can be used. In particular, Adv. Mater. , 2002, 14, 833-837 and Chem. Mater. 2002, 14, 4736-4745, the method for producing Ag nanowires can easily produce Ag nanowires in an aqueous system. Since the electrical conductivity of silver is the largest among metals, it can be preferably applied as the metal nanowire according to the present invention.

〔carbon nanotube〕
A carbon nanotube is a carbon-based fiber material having a shape in which a graphite-like carbon atomic plane (graphene sheet) having a thickness of several atomic layers is wound in a cylindrical shape. Single-walled nanotubes (SWCNT) and multi-layers are formed from the number of peripheral walls. They are roughly classified into nanotubes (MWCNT), and are divided into chiral (helical), zigzag and armchair types according to the difference in the structure of the graphene sheet, and various types are known.

  As the carbon nanotube applied to the conductive fiber according to the present invention, any type of carbon nanotube can be used, and a mixture of these various carbon nanotubes may be used. An excellent single-walled carbon nanotube is preferable, and a metallic armchair-type single-walled carbon nanotube is more preferable.

  The shape of the carbon nanotube according to the present invention is preferably a single-walled carbon nanotube having a large aspect ratio (= length / diameter), that is, a thin and long carbon nanotube, in order to form a long conductive path with one carbon nanotube. . For example, carbon nanotubes having an aspect ratio of 102 or more, preferably 103 or more can be mentioned. The average length of the carbon nanotubes is preferably 3 μm or more, more preferably 3 to 500 μm, and particularly preferably 3 to 300 μm. In addition, the relative standard deviation of the length is preferably 40% or less. Moreover, it is preferable that an average diameter is smaller than 100 nm, 1-50 nm is preferable and it is more preferable that it is 1-30 nm. In addition, the relative standard deviation of the diameter is preferably 20% or less.

  The production method of the carbon nanotube used in the present invention is not particularly limited, and catalytic hydrogen reduction of carbon dioxide, arc discharge method, laser evaporation method, CVD method, vapor phase growth method, high temperature and high pressure of carbon monoxide. Well-known means such as HiPco method in which the reaction is carried out together with an iron catalyst and grown in the gas phase can be used. Moreover, in order to remove residues such as by-products and catalytic metals, carbon nanotubes that have been further purified by various purification methods such as washing methods, centrifugal separation methods, filtration methods, oxidation methods, chromatographic methods, etc. Is more preferable because various functions can be sufficiently expressed.

  As a preferable method for forming a transparent conductive layer containing conductive fibers and a conductive material, a conductive fiber dispersion is applied or printed on the element and dried to form a conductive network structure made of conductive fibers. Next, a method is preferred in which a transparent conductive material is impregnated in the gaps on the network structure of the conductive fibers to form a transparent conductive layer containing the conductive fibers and the transparent conductive material.

[Transparent conductive material]
The transparent conductive material according to the present invention is a material that can form a film having transparency and uniform conductivity in a film-formed state. Examples of such transparent conductive materials include conductive polymers, conductive metal oxide fine particles, metal fine particles, organic fine particles coated with metal, and inorganic fine particles. In the present invention, from the viewpoint of transparency and conductivity, the conductive material is preferably at least one selected from the group of conductive polymers and conductive metal oxide nanoparticles. preferable.

[Conductive polymer]
Examples of the conductive polymer applied to the transparent conductive material according to the present invention include polypyrrole, polyaniline, polythiophene, polythienylene vinylene, polyazulene, polyisothianaphthene, polycarbazole, polyacetylene, polyphenylene, polyphenylene vinylene, and polyacene. And compounds selected from the group consisting of derivatives of polyphenylacetylene, polydiacetylene and polynaphthalene.

  The transparent conductive material according to the present invention may contain one kind of conductive polymer alone, or may contain two or more kinds of conductive polymers in combination, but the conductivity and transparency. In view of the above, polyaniline having a repeating unit represented by the following general formula (I) or general formula (II) or a derivative thereof, a polypyrrole derivative having a repeating unit represented by the following general formula (III), or the following general formula ( More preferably, it contains at least one compound selected from the group consisting of polythiophene derivatives having a repeating unit represented by IV).

  In the above general formula (III) and general formula (IV), R is mainly a linear organic substituent, preferably an alkyl group, an alkoxy group, an allyl group, or a combination of these groups. As long as it does not lose its properties, a sulfonate group, an ester group, an amide group, or the like may be bonded to or combined with these. Note that n is an integer.

The transparent conductive polymer according to the present invention can be subjected to a doping treatment in order to further increase the conductivity. As a dopant for the conductive polymer, for example, a sulfonic acid having a hydrocarbon group having 6 to 30 carbon atoms (hereinafter also referred to as a long-chain sulfonic acid) or a polymer thereof (for example, polystyrene sulfonic acid), a halogen atom , Lewis acid, proton acid, transition metal halide, transition metal compound, alkali metal, alkaline earth metal, MClO ₄ (M = Li ⁺ , Na ⁺ ), R ₄ N ⁺ (R═CH ₃ , C ₄ H ₉ , C ₆ H ₅ ), or R ₄ P ⁺ (R═CH ₃ , C ₄ H ₉ , C ₆ H ₅ ). Of these, the long-chain sulfonic acid is preferable.

  The dopant for the conductive polymer may be introduced into fullerenes such as hydrogenated fullerene, hydroxylated fullerene, and sulfonated fullerene. In the transparent conductive film, the dopant is preferably contained in an amount of 0.001 part by mass or more with respect to 100 parts by mass of the conductive polymer. Furthermore, it is more preferable that 0.5 mass part or more is contained.

The transparent conductive material of the present invention includes a long-chain sulfonic acid, a long-chain sulfonic acid polymer (for example, polystyrene sulfonic acid), a halogen, a Lewis acid, a proton acid, a transition metal halide, a transition metal compound, and an alkali metal. , Alkaline earth metal, MClO ₄ , R ₄ N ⁺ , and R ₄ P ⁺ , and at least one dopant selected from the group consisting of R ₄ P ⁺ and fullerenes may be included.

  As the conductive polymer according to the present invention, a conductive polymer modified with a metal disclosed in JP-T-2001-511581, JP-A-2004-99640, JP-A-2007-165199, or the like is used. You can also.

  The transparent conductive material containing the conductive polymer according to the present invention may contain a water-soluble organic compound. Among water-soluble organic compounds, compounds having an effect of improving conductivity by adding to a conductive polymer material are known, and 2nd. Sometimes called a dopant (or sensitizer). 2nd. Which can be used in the transparent conductive material of the present invention. There is no restriction | limiting in particular in a dopant, It can select suitably from well-known things, For example, a dimethyl sulfoxide (DMSO), diethylene glycol, and another oxygen containing compound are mentioned suitably.

  In the transparent conductive material containing the conductive polymer according to the present invention, the 2nd. 0.001 mass part or more is preferable, as for content of a dopant, 0.01-50 mass parts is more preferable, and 0.01-10 mass parts is especially preferable.

  The transparent conductive material containing the conductive polymer according to the present invention may contain a transparent resin component or additive in addition to the conductive polymer in order to ensure film formability and film strength. The transparent resin component is not particularly limited as long as it is compatible or mixed and dispersed with the conductive polymer, and may be a thermosetting resin or a thermoplastic resin. For example, polyester resins such as polyethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate, polyimide resins such as polyimide and polyamideimide, polyamide resins such as polyamide 6, polyamide 6,6, polyamide 12 and polyamide 11, polyvinylidene fluoride, Fluorine resin such as polyvinyl fluoride, polytetrafluoroethylene, ethylene tetrafluoroethylene copolymer, polychlorotrifluoroethylene, etc., vinyl resin such as polyvinyl alcohol, polyvinyl ether, polyvinyl butyral, polyvinyl acetate, polyvinyl chloride, epoxy resin, xylene Resin, aramid resin, polyurethane resin, polyurea resin, melamine resin, phenol resin, polyether, acrylic resin and their co-polymer Body, and the like.

[Conductive metal oxide]
As a conductive metal oxide applied to the transparent conductive material according to the present invention, a known transparent metal oxide conductive material can be used. For example, tin, tellurium, cadmium, molybdenum, tungsten, fluorine, zinc, germanium, antimony, etc. added indium oxide, tin oxide and cadmium oxide, aluminum, germanium, etc. added as dopants such as zinc oxide, titanium oxide, etc. A metal oxide is mentioned.

  The conductive metal oxide according to the present invention preferably contains an oxide of a metal selected from indium, zinc, and tin. Specifically, ITO in which indium oxide is doped with tin, zinc oxide with aluminum or It is preferable to contain a metal oxide selected from AZO or GZO doped with gallium, ATO or FTO doped with tin oxide and antimony or fluorine.

  Moreover, as a shape of the electroconductive metal oxide which concerns on this invention, it is preferable that it is a nanoparticle with an average particle diameter of 1-100 nm, and it is especially preferable that it is a nanoparticle with 3-50 nm.

  The transparent conductive material containing the conductive metal oxide according to the present invention may contain a transparent binder material or additive in addition to the conductive metal oxide nanoparticles. The transparent binder material can be selected from a wide range of natural polymer resins or synthetic polymer resins. For example, transparent thermoplastic resin (eg, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polymethyl methacrylate, nitrocellulose, chlorinated polyethylene, chlorinated polypropylene, vinylidene fluoride), heat, light, electron beam A transparent curable resin that is cured by radiation (for example, melamine acrylate, urethane acrylate, epoxy resin, polyimide resin, silicone resin such as acrylic-modified silicate) can be used. Examples of the additive include plasticizers, stabilizers such as antioxidants and sulfurization inhibitors, surfactants, dissolution accelerators, polymerization inhibitors, and colorants such as dyes and pigments. Furthermore, from the viewpoint of improving workability such as coating properties, solvents (for example, water, organic solvents such as alcohols, glycols, cellosolves, ketones, esters, ethers, amides, hydrocarbons, etc.) are used. May be included.

  In the present invention, the transparent conductive material is preferably a conductive polymer.

〔substrate〕
The substrate is a member that holds the first electrode, the photoelectric conversion layer, the recombination layer, the second electrode, and the like that are sequentially stacked. In the present embodiment, a substrate that is transparent to the wavelength of light to be photoelectrically converted so that light that is photoelectrically converted from at least the first electrode or the second electrode, or both electrodes can enter. It is desirable that As the substrate, for example, a glass substrate, a resin substrate and the like are preferably mentioned, but it is desirable to use a transparent resin film from the viewpoint of light weight and flexibility. There is no restriction | limiting in particular in the transparent resin film which can be preferably used as a transparent substrate by this invention, The material, a shape, a structure, thickness, etc. can be suitably selected from well-known things. For example, polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) modified polyester, polyethylene (PE) resin film, polypropylene (PP) resin film, polystyrene resin film, polyolefin resins such as cyclic olefin resin Film, vinyl resin film such as polyvinyl chloride, polyvinylidene chloride, polyether ether ketone (PEEK) resin film, polysulfone (PSF) resin film, polyether sulfone (PES) resin film, polycarbonate (PC) resin film, A polyamide resin film, a polyimide resin film, an acrylic resin film, a triacetyl cellulose (TAC) resin film, and the like can be given. If the resin film transmittance of 80% or more at ~780nm), can be preferably applied to a transparent resin film according to the present invention. Among these, from the viewpoint of transparency, heat resistance, ease of handling, strength and cost, it is preferably a biaxially stretched polyethylene terephthalate film, a biaxially stretched polyethylene naphthalate film, a polyethersulfone film, or a polycarbonate film, and biaxially stretched. More preferred are polyethylene terephthalate films and biaxially stretched polyethylene naphthalate films.

  The transparent substrate used in the present invention can be subjected to a surface treatment or an easy adhesion layer in order to ensure the wettability and adhesiveness of the coating solution. A conventionally well-known technique can be used about a surface treatment or an easily bonding layer. For example, the surface treatment includes surface activation treatment such as corona discharge treatment, flame treatment, ultraviolet treatment, high frequency treatment, glow discharge treatment, active plasma treatment, and laser treatment. Examples of the easy adhesion layer include polyester, polyamide, polyurethane, vinyl copolymer, butadiene copolymer, acrylic copolymer, vinylidene copolymer, and epoxy copolymer. When the transparent resin film is a biaxially stretched polyethylene terephthalate film, the interface reflection between the film substrate and the easy adhesion layer is reduced by setting the refractive index of the easy adhesion layer adjacent to the film to 1.57 to 1.63. Thus, the transmittance can be improved, which is more preferable. The method for adjusting the refractive index can be carried out by appropriately adjusting the ratio of the oxide sol having a relatively high refractive index such as tin oxide sol or cerium oxide sol and the binder resin. The easy adhesion layer may be a single layer, but may be composed of two or more layers in order to improve adhesion. In addition, a barrier coat layer may be formed in advance on the transparent substrate, or a hard coat layer may be formed in advance on the opposite side to which the transparent conductive layer is transferred.

[First electrode]
The cathode and anode of the first electrode of the present invention are not particularly limited and can be selected depending on the element configuration. For example, when used as an anode, the electrode preferably transmits light of 300 to 800 nm. As the material, for example, transparent conductive metal oxides such as indium tin oxide (ITO), SnO ₂ , ZnO, metal thin films such as gold, silver, and platinum, metal nanowires, carbon nanotubes, and conductive polymers are used. it can.

[Photoelectric conversion layer]
The photoelectric conversion layer 4 or 8 is a layer that converts light energy into electric energy, and includes a bulk heterojunction layer in which a p-type semiconductor material and an n-type semiconductor material are mixed. The p-type semiconductor material functions relatively as an electron donor (donor), and the n-type semiconductor material functions relatively as an electron acceptor (acceptor). Here, the electron donor and the electron acceptor are “an electron donor in which, when light is absorbed, electrons move from the electron donor to the electron acceptor to form a hole-electron pair (charge separation state)”. And an electron acceptor ”, which does not simply donate or accept electrons like an electrode, but donates or accepts electrons by a photoreaction.

  Examples of the p-type semiconductor material used in the present invention include various condensed polycyclic aromatic compounds and conjugated compounds.

  As the condensed polycyclic aromatic compound, for example, anthracene, tetracene, pentacene, hexacene, heptacene, chrysene, picene, fluorene, pyrene, peropyrene, perylene, terylene, quaterylene, coronene, ovalene, sarkham anthracene, bisanthene, zestrene, heptazelene, Examples thereof include compounds such as pyranthrene, violanthene, isoviolanthene, cacobiphenyl, anthradithiophene, and derivatives and precursors thereof.

  Examples of the conjugated compound include polythiophene and its oligomer, polypyrrole and its oligomer, polyaniline, polyphenylene and its oligomer, polyphenylene vinylene and its oligomer, polythienylene vinylene and its oligomer, polyacetylene, polydiacetylene, tetrathiafulvalene compound, quinone Compounds, cyano compounds such as tetracyanoquinodimethane, fullerenes and derivatives or mixtures thereof.

  In particular, among polythiophene and oligomers thereof, thiophene hexamer, α-seccithiophene α, ω-dihexyl-α-sexualthiophene, α, ω-dihexyl-α-kinkethiophene, α, ω-bis (3- An oligomer such as butoxypropyl) -α-sexithiophene can be preferably used.

  Other examples of the polymer p-type semiconductor include polyacetylene, polyparaphenylene, polypyrrole, polyparaphenylene sulfide, polythiophene, polyphenylene vinylene, polycarbazole, polyisothianaphthene, polyheptadiyne, polyquinoline, polyaniline, and the like. Substituted-unsubstituted alternating copolymer polythiophenes such as JP-A-2006-36755, JP-A-2007-51289, JP-A-2005-76030, J. Org. Amer. Chem. Soc. , 2007, p4112, J.A. Amer. Chem. Soc. , 2007, p7246, etc., polymers having a condensed ring thiophene structure, WO2008 / 000664, Adv. Mater. , 2007, p4160, Macromolecules, 2007, Vol. Examples thereof include thiophene copolymers such as 40 and p1981.

  Furthermore, porphyrin, copper phthalocyanine, tetrathiafulvalene (TTF) -tetracyanoquinodimethane (TCNQ) complex, bisethylenetetrathiafulvalene (BEDTTTTF) -perchloric acid complex, BEDTTTF-iodine complex, TCNQ-iodine complex, etc. Organic molecular complexes, fullerenes such as C60, C70, C76, C78 and C84, carbon nanotubes such as SWNT, dyes such as merocyanine dyes and hemicyanine dyes, σ-conjugated polymers such as polysilane and polygerman, and Organic / inorganic hybrid materials described in 2000-260999 can also be used.

  Among these π-conjugated materials, at least one selected from the group consisting of condensed polycyclic aromatic compounds such as pentacene, fullerenes, condensed ring tetracarboxylic acid diimides, metal phthalocyanines, and metal porphyrins is preferable. Further, pentacenes are more preferable.

  Examples of pentacenes include substituents described in International Publication No. 03/16599, International Publication No. 03/28125, US Pat. No. 6,690,029, Japanese Patent Application Laid-Open No. 2004-107216, and the like. A pentacene derivative described in U.S. Patent Application Publication No. 2003/136964 and the like; Amer. Chem. Soc. , Vol. 127. No. And substituted acenes described in 14.4986 and the like and derivatives thereof.

  Among these compounds, compounds that have high solubility in organic solvents to the extent that solution processing is possible, can form a crystalline thin film after drying, and can achieve high mobility are preferable. Such compounds include those described in J. Org. Amer. Chem. Soc. , Vol. 123, p9482; Amer. Chem. Soc. , Vol. 130 (2008), no. No. 9, 2706 and the like, acene-based compounds substituted with a trialkylsilylethynyl group, a pentacene precursor described in U.S. Patent Application Publication No. 2003/136964, etc., and Japanese Patent Application Laid-Open No. 2007-224019 Examples include precursor type compounds (precursors) such as porphyrin precursors. Among these, the latter precursor type can be preferably used. This is because the precursor type is insolubilized after conversion, so when forming the hole transport layer, electron transport layer, hole block layer, electron block layer, etc. on the bulk hetero junction layer by solution process, bulk hetero junction This is because the layer does not dissolve and the material constituting the layer and the material forming the bulk heterojunction layer are not mixed, and further improvement in efficiency and life can be achieved. .

  As a p-type semiconductor material of the organic photoelectric conversion element of the present invention, a chemical structure change is caused by a method such as exposing a precursor of a p-type semiconductor material to a vapor of a compound that causes heat, light, radiation, or a chemical reaction. A compound converted into a semiconductor material is preferred. Among them, compounds that cause a scientific structural change by heat are preferred.

  Examples of n-type semiconductor materials include fullerene, octaazaporphyrin, p-type semiconductor perfluoro compounds (perfluoropentacene, perfluorophthalocyanine, etc.), naphthalenetetracarboxylic anhydride, naphthalenetetracarboxylic diimide, perylenetetracarboxylic acid Examples thereof include polymer compounds containing an anhydride, an aromatic carboxylic acid anhydride such as perylenetetracarboxylic acid diimide, or an imidized product thereof as a skeleton.

  Among these, fullerene-containing polymer compounds are preferable. Fullerene-containing polymer compounds include fullerene C60, fullerene C70, fullerene C76, fullerene C78, fullerene C84, fullerene C240, fullerene C540, mixed fullerene, fullerene nanotubes, multi-walled nanotubes, single-walled nanotubes, nanohorns (conical), etc. Examples thereof include a polymer compound having a skeleton. As the fullerene-containing polymer compound, a polymer compound (derivative) having fullerene C60 as a skeleton is preferable.

  The fullerene-containing polymers are roughly classified into polymers in which fullerene is pendant from a polymer main chain and polymers in which fullerene is contained in the polymer main chain. Fullerene is contained in the polymer main chain. Are preferred. This is not because fullerene is contained in the main chain because the polymer does not have a branched structure, so that it can be packed with high density when solidified, resulting in high mobility. It is estimated that.

  Examples of a method for forming a bulk heterojunction layer in which an electron acceptor and an electron donor are mixed include a vapor deposition method and a coating method (including a casting method and a spin coating method). Among these, a coating method is particularly preferable.

  Then, the bulk heterojunction layer of the photoelectric conversion part is annealed at a predetermined temperature during the manufacturing process in order to improve the photoelectric conversion rate, and is partially crystallized microscopically.

  In the photoelectric conversion element, light incident from the transparent electrode through the substrate is absorbed by the electron acceptor or electron donor in the bulk heterojunction layer of the photoelectric conversion unit, and electrons move from the electron donor to the electron acceptor. A pair of holes and electrons (charge separation state) is formed. The generated charge is caused by an internal electric field, for example, when the work function of the transparent electrode and the counter electrode is different, due to the potential difference between the transparent electrode and the counter electrode, electrons pass between the electron acceptors and holes are electron donors. The photocurrent is detected by passing through different electrodes to different electrodes. For example, when the work function of the transparent electrode is larger than that of the counter electrode, electrons are transported to the transparent electrode and holes are transported to the counter electrode. If the magnitude of the work function is reversed, electrons and holes are transported in the opposite direction. In addition, the transport direction of electrons and holes can be controlled by applying a potential between the transparent electrode and the counter electrode.

  The photoelectric conversion unit may be composed of a single layer in which an electron acceptor and an electron donor are uniformly mixed, or may be composed of a plurality of layers in which the mixing ratio of the electron acceptor and the electron donor is changed. Good.

  Examples of a method for forming a bulk heterojunction layer in which an electron acceptor and an electron donor are mixed include a vapor deposition method and a coating method (including a casting method and a spin coating method). Among these, the coating method is preferable in order to increase the area of the interface where charges and electrons are separated from each other as described above and to produce a device having high photoelectric conversion efficiency. After application, it is preferable to perform heating in order to cause removal of residual solvent, moisture and gas, and chemical reaction of the semiconductor material as described above.

[Middle layer]
Further, the above-described bulk heterojunction type organic photoelectric conversion element is composed of a transparent electrode, a photoelectric conversion part of a bulk heterojunction layer, and a counter electrode that are sequentially stacked on a substrate. A bulk heterojunction type organic photoelectric conversion element having another layer such as a hole transport layer, an electron transport layer, a hole block layer, an electron block layer, or a smoothing layer between the counter electrode and the photoelectric conversion unit It may be configured. Among these, a hole transport layer or an electron blocking layer is placed between the bulk heterojunction layer and the anode (usually the transparent electrode side), and an electron transport layer or hole is placed between the cathode (usually the counter electrode side). By forming the block layer, charges generated in the bulk heterojunction layer can be taken out more efficiently. Therefore, these layers are preferably included.

(Hole transport layer)
Examples of the material preferably used as the hole transport layer (electron block layer) include PEDOT such as trade name BaytronP, polyaniline and its doped material, triarylamine described in JP-A-5-271166, etc. Further, a cyanide compound described in WO2006019270 pamphlet, or a metal oxide such as molybdenum oxide, nickel oxide, or tungsten oxide can be used. A layer made of a single p-type semiconductor material used for the bulk heterojunction layer can also be used. The means for forming these layers is preferably formed by a solution coating method.

(Electron transport layer)
As the electron transport layer (hole blocking layer), octaazaporphyrin, p-type semiconductor perfluoro (perfluoropentacene, perfluorophthalocyanine, etc.), naphthalenetetracarboxylic anhydride, naphthalenetetracarboxylic diimide, perylenetetra N-type semiconductor materials such as carboxylic acid anhydrides and perylenetetracarboxylic acid diimides, and n-type inorganic oxides such as titanium oxide, zinc oxide and gallium oxide, and alkali metal compounds such as lithium fluoride, sodium fluoride and cesium fluoride Etc. can be used. A layer made of a single n-type semiconductor material used for the bulk heterojunction layer can also be used. The means for forming these layers may be either a vacuum deposition method or a solution coating method, but is preferably a solution coating method.

[Second electrode]
The second electrode may be a single conductive material layer, or in addition to a conductive material, a resin that holds these may be used in combination. As the conductive material of the second electrode portion, a material having a work function (4 eV or less) metal (referred to as an electron injecting metal), an alloy, an electrically conductive compound, and a mixture thereof as an electrode material is used. Specific examples of such electrode materials include sodium, sodium-potassium alloy, magnesium, lithium, magnesium / copper mixture, magnesium / silver mixture, magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al ₂ O ₃ ) Mixtures, indium, lithium / aluminum mixtures, rare earth metals and the like. Among these, from the point of durability against electron injection and oxidation, etc., a mixture of an electron injecting metal and a second metal which is a stable metal having a larger work function than this, for example, a magnesium / silver mixture, Magnesium / aluminum mixtures, magnesium / indium mixtures, aluminum / aluminum oxide (Al ₂ O ₃ ) mixtures, lithium / aluminum mixtures, aluminum and the like are preferred. The cathode can be produced by forming a thin film of these electrode materials by a method such as vapor deposition or sputtering. The sheet resistance as the cathode is preferably several hundred Ω / □ or less, and the film thickness is usually selected in the range of 10 nm to 5 μm, preferably 50 to 200 nm.

  If a metal material is used as the conductive material of the second electrode, the light coming to the second electrode side is reflected and returns to the first electrode side. The metal nanowire of the first electrode scatters or reflects a part of the light backward, but by using a metal material as the conductive material of the second electrode, this light can be reused and the photoelectric conversion efficiency is further improved. To do.

[Sealing]
Moreover, it is preferable to seal by the well-known method so that the produced organic photoelectric conversion element may not deteriorate with oxygen, moisture, etc. in the environment. For example, a method of sealing a cap made of aluminum or glass by bonding with an adhesive, a plastic film on which a gas barrier layer such as aluminum, silicon oxide, or aluminum oxide is formed and the organic photoelectric conversion element top 10 with an adhesive A method of bonding, a method of spin-coating an organic polymer material with high gas barrier properties (polyvinyl alcohol, etc.), a method of directly depositing an inorganic thin film with high gas barrier properties (silicon oxide, aluminum oxide, etc.), and a combination of these The method of laminating can be mentioned.

Example 1
[Production of Organic Photoelectric Conversion Element SC-101]
An indium tin oxide (ITO) transparent conductive film deposited to a thickness of 110 nm on a PEN film substrate with a barrier layer (sheet resistance 13 Ω / □) is patterned to a width of 1 cm using ordinary photolithography and hydrochloric acid etching. Thus, a flexible transparent electrode was formed.

  The patterned transparent electrode was cleaned in the order of ultrasonic cleaning with a surfactant and ultrapure water, followed by ultrasonic cleaning with ultrapure water, dried with nitrogen, and finally with ultraviolet ozone cleaning.

  On this transparent substrate, Baytron PH4083 (made by Starck Vitec), which is a conductive polymer, was applied to a film thickness of 50 nm and then dried at 140 ° C. for 10 minutes to form a hole transport layer. .

  After this, the substrate was brought into the glove box and worked under a nitrogen atmosphere.

Next, P3HT (manufactured by Prectronics: regioregular poly-3-hexylthiophene) (Mw = 52000, high molecular p-type semiconductor material) and PCBM (frontier carbon: 6,6-phenyl-C ₆₁ -butylic) were added to chlorobenzene. (Acid methyl ester) (Mw = 911, low molecular weight n-type semiconductor material) prepared at a ratio of 1: 1 so as to be 3.0% by mass, and filtered through a filter so that the film thickness becomes 100 nm. Coating was performed, and the film was allowed to stand at room temperature to form a photoelectric conversion layer.

  Next, a solution in which Ti-isopropoxide is dissolved in ethanol so as to have a concentration of 0.05 mol / L is prepared, masked, and spin-coated so as to have a film thickness of 20 nm. An electron transport layer was formed by standing in the middle.

Subsequently, the silver nanowires prepared as a dispersion were applied at a basis weight of 80 mg / m ² and dried to form a silver nanowire layer (recombination layer).

  Silver nanowires are described in Adv. Mater. , 2002, 14, 833 to 837, silver nanowires having an average diameter of 75 nm and an average length of 35 μm are prepared, and the silver nanowires are filtered and washed with an ultrafiltration membrane, followed by ethanol. The resulting solution was redispersed into a silver nanowire dispersion (silver nanowire content: 5% by mass).

  Furthermore, a conductive ultraviolet curable resin (Shin-Etsu polymer: OC-X109) is applied, patterned to a predetermined size, the solvent component is vaporized, and the surface is smoothed by applying a calendar treatment, and then irradiated with ultraviolet rays. Cured.

  Further, a solution obtained by dissolving the TBP precursor so as to be 0.25% by mass of a 1: 1 mixed solvent of chloroform: chlorobenzene was applied to a dry film thickness of 25 nm, followed by heat treatment at 150 ° C. for 20 minutes to form holes. A transport layer was formed.

  A solution obtained by dissolving TBP precursor and PCBNB in a 1: 1 mixed solvent of chloroform: chlorobenzene so as to have a mass ratio of 1.2: 0.8 is applied to 70 nm, and heat treatment is performed at 150 ° C. for 20 minutes. Thus, a photoelectric conversion layer was formed.

  Next, a solution in which Ti-isopropoxide is dissolved in ethanol so as to have a concentration of 0.05 mol / L is prepared, masked, and spin-coated so as to have a film thickness of 20 nm. An electron transport layer was formed by standing in the middle.

Furthermore, the fabricated element is placed in a vacuum deposition apparatus, a 1 cm wide shadow mask is set, the inside of the vacuum deposition apparatus is depressurized to 1 × 10 ⁻³ Pa or less, and then the Al film thickness is 80 nm. A laminated electrode was formed. The obtained organic photoelectric conversion element SC-101 was sealed using a PEN film with a barrier and a UV curable resin in a nitrogen atmosphere.

[Production of Organic Photoelectric Conversion Element SC-102]
In the production of the organic photoelectric conversion element SC-101, after the conductive fiber was changed to a dispersion of SWCNT (manufactured by Unidym, HiPcoR single-walled carbon nanotube) and applied so that the basis weight of SWCNT was 10 mg / m ^2. Organic photoelectric conversion element SC-102 was obtained in the same manner as organic photoelectric conversion element SC-101, except that conductive ultraviolet curable resin (Shin-Etsu polymer: OC-X109) was applied. Similarly, obtained organic photoelectric conversion element SC-102 was sealed using a PEN film with a barrier and a UV curable resin in a nitrogen atmosphere.

[Production of Organic Photoelectric Conversion Element SC-103]
In the production of the organic photoelectric conversion element SC-101, after forming the silver nanowire layer, an epoxy adhesive (Nogawa Chemical: No. 2410) was applied instead of the conductive ultraviolet curable resin to form a recombination layer. Organic photoelectric conversion element SC-103 was obtained in the same manner as organic photoelectric conversion element SC-101 except that it was formed. Similarly, the obtained organic photoelectric conversion element SC-103 was sealed using a PEN film with a barrier and a UV curable resin in a nitrogen atmosphere.

[Production of Organic Photoelectric Conversion Element SC-104]
In production of the organic photoelectric conversion element SC-101, instead of forming the silver nanowire layer, a DC sputtering apparatus (manufactured by Anelva Co., Ltd.) is used, and an ITO ceramic target (Tosoh Corporation) is used to form an ITO thin film. Organic photoelectric conversion element SC-104 was obtained in the same manner as organic photoelectric conversion element SC-101 except that the film was formed in a vacuum so that the film thickness was 20 nm to form a recombination layer. Similarly, the obtained organic photoelectric conversion element SC-104 was sealed using a PEN film with a barrier and a UV curable resin in a nitrogen atmosphere.

[Production of Organic Photoelectric Conversion Element SC-105]
In the production of the organic photoelectric conversion element SC-101, instead of forming the silver nanowire layer, using a vacuum vapor deposition apparatus (manufactured by ULVAC, Inc.), the inside of the vacuum vapor deposition machine was depressurized to 1 × 10 ⁻³ Pa or less, Organic photoelectric conversion element SC-105 was obtained in the same manner as organic photoelectric conversion element SC-101 except that a recombination layer was formed so that the film thickness of Ag was 0.5 nm. Similarly, the obtained organic photoelectric conversion element SC-105 was sealed using a PEN film with a barrier and a UV curable resin in a nitrogen atmosphere.

[Evaluation of energy conversion characteristics of photoelectric conversion elements]
About the produced organic photoelectric conversion element, an AM1.5G filter using a solar simulator, light having an intensity of 100 mW / cm ² is irradiated, a mask having an effective area of 1 cm × 10 cm is overlaid on the light receiving portion, and a short circuit current density Jsc The energy conversion efficiency η (%) was obtained from (mA / cm ² ), the open circuit voltage Voc (V), and the fill factor ff using Formula 1, and the relative value is shown when the energy conversion efficiency of SC-105 is 100. It was shown in 1.

(Formula 1) Jsc (mA / cm ² ) × Voc (V) × ff = η (%)
[Dark spot evaluation]
The fabricated device was exposed to light from a 100 W halogen lamp for 1000 hours. Subsequently, with respect to the exposed element, a region where power was not generated in the element surface was measured by an LBIC (laser beam electromotive current) measurement method, and the appearance rate of dark spots was determined according to Equation 2, and is shown in Table 1.

  (Expression 2) Appearance rate = area of a region not generating power / effective area of an element × 100 (%)

As is clear from Table 1, the organic photoelectric conversion element of the present invention was found to improve energy conversion efficiency by including conductive fibers and a transparent conductive material in the tandem recombination layer. . In addition, in the production of a tandem organic photoelectric conversion element, it should be noted in the present invention that the first electrode to the second electrode can be performed in a consistent coating process, and high productivity is compatible. It is an effect. For example , by using a conductive fiber and a transparent conductive material in combination, as can be seen from SC-101 and SC-102, not only higher energy conversion efficiency can be obtained, but also higher than conventional techniques. It was found that the organic photoelectric conversion element was excellent in durability, with the appearance of productivity and power generation defects (dark spots) suppressed.

It is a schematic sectional drawing which shows the basic structure of the organic photoelectric conversion element of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st board | substrate 2 1st electrode 3 1st positive hole transport layer 4 1st photoelectric conversion layer 5 1st electron transport layer 6 Recombination layer 7 2nd positive hole transport layer 8 2nd photoelectric conversion Layer 9 Second electron transport layer 10 Second electrode 11 Second substrate 21 Organic photoelectric conversion element 22 First power generation block 23 Second power generation block

Claims (2)

A tandem organic material having at least two photoelectric conversion layers and including at least a recombination layer between at least one pair of adjacent photoelectric conversion layers among the two or more photoelectric conversion layers. It is a photoelectric conversion element, Comprising: At least 1 layer of this recombination layer contains a conductive fiber and a transparent conductive material , The organic photoelectric conversion element characterized by the above-mentioned. 2. The organic photoelectric conversion element according to claim 1, wherein the conductive fiber is at least one selected from the group consisting of metal nanowires or carbon nanotubes .

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