JP2010278377A - Organic photoelectric conversion element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic photoelectric conversion element which has high photoelectric conversion efficiency and durability. <P>SOLUTION: The organic photoelectric conversion element having a bulk heterojunction type photoelectric conversion layer held between a first electrode and a second electrode is characterized in that the photoelectric conversion layer contains particulates bonded to at least an organic semiconductor. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a bulk heterojunction organic photoelectric conversion element.

  Organic solar cells are attracting attention as solar cells suitable for mass production because they can be formed by a coating method, and many research institutions are actively researching them. In organic solar cells, charge separation efficiency, which has been a problem, is improved by a so-called bulk heterojunction structure in which an organic donor material and an organic acceptor material are mixed. As a result, the energy conversion efficiency is improved to the 5% level, which can be said to be a field that has been developed to a practical level at once (for example, see Patent Document 1).

  In bulk heterojunction solar cells, it is generally considered advantageous that the domain size of the p-type semiconductor and the n-type semiconductor is small and the surface area of the pn interface is large, because the number of exciton generation sites increases. However, in order to carry the generated carriers to the electrode, it is necessary to form a conductive path to the electrode by the domain, and for this purpose, a domain size comparable to the film thickness is required, and both are traded. It was an off relationship. In addition, as a method for forming a conductive path by a domain, a method of performing a baking treatment after applying a mixed solution of a p-type semiconductor and an n-type semiconductor is used. In this method, a method of forming a domain is used. There is also a problem that it is difficult to control, and an electric power generation region in which electric charges cannot be taken out even if carriers are generated without being connected to an electrode is also caused.

  Furthermore, the bulk heterojunction layer can absorb sunlight efficiently by increasing the film thickness, but if it is too thick, the generated carriers are deactivated and recombined before reaching the electrode. There is.

  Currently used semiconductors have a problem that the p-type mobility is lower than the n-type mobility, and it is difficult to extract holes compared to electrons. In order to solve this problem, n-type has high mobility even in an amorphous state where no baking treatment is performed, whereas p-type semiconductor needs to be subjected to baking treatment to increase the crystallinity of p-type semiconductor and improve mobility. When the baking treatment is performed, organic substances are aggregated and the domain size is enlarged.

  In addition, there is a report of manufacturing a photoelectric conversion element having a bulk heterojunction layer using P3HT as a p-type semiconductor and CdSe nanoparticles as an n-type semiconductor (see, for example, Non-Patent Document 1). The low mobility of type semiconductors could not be improved.

US Pat. No. 5,331,183

W. U. Huynh, J .; J. et al. Dittmer, A.M. P. Alivisatos, Science, 295, 2425 (2002)

  An object of the present invention is to provide an organic photoelectric conversion element having high photoelectric conversion efficiency and durability.

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

  1. An organic photoelectric conversion element having a bulk heterojunction photoelectric conversion layer sandwiched between a first electrode and a second electrode, wherein the photoelectric conversion layer contains at least fine particles bonded to an organic semiconductor. Photoelectric conversion element.

  2. 2. The organic photoelectric conversion element as described in 1 above, wherein the fine particles are metal fine particles.

  3. 3. The organic photoelectric conversion element as described in 1 or 2 above, wherein the fine particles and the organic semiconductor are bonded via a thiol group.

  4). 4. The organic photoelectric conversion device as described in any one of 1 to 3, wherein the organic semiconductor includes either a p-type semiconductor or an n-type semiconductor.

  5. 5. The organic photoelectric conversion element according to any one of 1 to 4, wherein the photoelectric conversion layer includes p-type organic semiconductor-coated fine particles and an n-type semiconductor material.

  6). 6. The organic photoelectric conversion element according to any one of 1 to 5, wherein the fine particles are gold nanoparticles.

  According to the present invention, an organic photoelectric conversion element capable of achieving high conversion efficiency, high durability, and inexpensive production can be provided.

It is sectional drawing which shows the solar cell which consists of a bulk hetero junction type organic photoelectric conversion element. It is sectional drawing which shows the solar cell which consists of an organic photoelectric conversion element provided with a tandem-type bulk heterojunction layer. It is sectional drawing which shows the solar cell which consists of an organic photoelectric conversion element provided with a tandem-type bulk heterojunction layer. It is a figure which shows the structure of an optical sensor array.

  The present invention relates to an organic photoelectric conversion device having a bulk heterojunction photoelectric conversion layer sandwiched between a first electrode and a second electrode, wherein the photoelectric conversion layer contains at least fine particles bonded to an organic semiconductor. The present invention relates to a characteristic organic photoelectric conversion element.

  That is, the bulk heterojunction layer is formed by forming a bulk heterojunction layer containing metal fine particles adsorbed or bonded to the ends of the metal fine particles by an organic semiconductor (p-type semiconductor or n-type semiconductor) having a thiol group or the like. As a result, it was found that the light absorption efficiency was increased, and the present invention was achieved.

  Further, even when the bulk heterojunction layer is thickened by enclosing the metal fine particles having high mobility, the carriers can reach the electrode without being deactivated. In particular, when metal fine particles containing a p-type semiconductor are used in the bulk heterojunction layer, transmission of holes passing through the p-type semiconductor to the electrode is achieved by the high mobility of the metal fine particles. Furthermore, even when a baking treatment for increasing the crystallinity of the p-type semiconductor is performed, since the p-type semiconductor is fixed around the fine particles, there is an advantage that excessive enlargement is suppressed.

  Next, the best mode for carrying out the present invention will be described, but the present invention is not limited thereto.

<Fine particles>
As the fine particles, fine particles of metals, inorganic oxides, inorganic nitrides, polymers and the like are used, and metal fine particles are preferable. As the metal of the metal fine particles of the present invention, platinum, gold, silver, nickel, chromium, copper, iron, tin, tantalum, indium, cobalt, palladium, tellurium, rhenium, iridium, aluminum, ruthenium, germanium, molybdenum, tungsten, Zinc or the like can be used. In particular, platinum, gold, silver, copper, cobalt, chromium, iridium, nickel, palladium, molybdenum, and tungsten having a work function of 4.5 eV or more are preferable.

  Such metal fine particles can be produced by reducing metal ions in the liquid phase, such as physical generation methods such as gas evaporation, sputtering, and metal vapor synthesis, colloidal methods, and coprecipitation methods. The colloidal method described in JP-A-11-76800, JP-A-11-80647, JP-A-2000-239853, etc., JP-A-2001-254185, This is a gas evaporation method described in JP 2001-53028 A, JP 2001-35814 A, JP 2001-35255 A, JP 2000-124157 A, JP 2000-123634 A, or the like.

  Examples of the inorganic oxide fine particles include fine particles of silicon oxide, titanium oxide, aluminum oxide and the like. Such an inorganic oxide may be a sol. The size of the fine particles is arbitrary, but is 0.1 nm to 1 μm, preferably 1 to 100 nm. In order to function well as a semiconductor material, the surface is preferably smooth. The size of the fine particles here is the diameter of spherical fine particles, and the size of a circular image having the same area as the projected image of fine particles having a shape other than spherical. In the present invention, the semiconductor channel contains an organic semiconductor compound bonded to metal fine particles, but the content of the metal fine particles varies depending on the metal used, but is generally 30 to 5000 parts by mass with respect to 100 parts by mass of the organic semiconductor compound. It is.

<Organic semiconductor>
A known organic semiconductor can be used, but the p-type semiconductor is preferably a π-conjugated polymer or oligomer. Of these, polythiophene derivatives are particularly preferable. The polythiophene derivative is more preferably a derivative containing a regioregular poly (3-alkylthiophene) structure (hereinafter simply referred to as a regioregular poly (3-alkylthiophene) derivative). More preferably, the alkyl group of the regioregular poly (3-alkylthiophene) derivative is an alkyl group having 4 to 15 carbon atoms. The n-type semiconductor is preferably a perfluoro product in which a hydrogen atom of a p-type semiconductor is substituted with a fluorine atom, such as fullerene or octaazaporphyrin. Of these, fullerene derivatives are preferred. The fine particles are preferably metal fine particles.

  The fine particles and the organic semiconductor compound are preferably bonded via a thiol group, dithiol group, carboxyl group, sulfonic acid group, sulfinic acid group, phosphonic acid group, or phosphoric acid group, more preferably a thiol group. Are connected through.

  In the organic semiconductor composition of the present invention, the bonded fine particles and the organic semiconductor compound are preferably dispersed in a solvent. When forming the organic semiconductor layer from the dispersion of the organic semiconductor composition of the present invention, in the casting process of the dispersion, the fine particles form a self-organized arrangement structure, preferably a finely packed (hexagonal packing) structure, As a result, since the organic semiconductor compound forms an array structure in a self-organized manner, not only the domain size of the p / n semiconductor in the bulk heterojunction can be controlled, but also the carrier transport ability can be achieved by containing metal fine particles. It is possible to increase the film thickness while maintaining it. The organic semiconductor compound used in the present invention has an arbitrary linking group having binding properties to the fine particles at at least one position of the end of the molecule.

Examples of an arbitrary substituent having a binding property to the fine particles include a thiol group, a dithiol group, a carboxyl group, a sulfonic acid group, a sulfinic acid group, a phosphonic acid group, and a phosphoric acid group, and a thiol group is preferable. For example, when binding to metal fine particles such as gold, silver, platinum, etc., a thiol group, a methylthio group (—SCH ₃ ), a mercaptothio group (—S—SH), a methyl mercaptothio group (—S—SCH ₃ ), acetylthio An organic semiconductor compound having a terminal group (—SAc) or the like is used and bonded to the surface of the metal fine particle by a chemical bond or adsorption by a sulfide bond based on the compound.

As a method for synthesizing sexualciophene, which is one of the preferred organic semiconductor compounds used in the present invention, Just. Liebigs, Ann. Chem. 546; 1941; 180, 194. (Synthesized from iodothiophene), Mol. Cryst. Liq. Cryst. EN; 167; 1989; 227-232. (Synthesized from dibromobithiophene and bithiophene magnesium bromide); Org. Chem. EN; 59; 16; 1994; 4630-4636. (Using thallium catalyst by homocoupling of terthiophene), Heterocycles; EN; 26; 7; 1987; 1793-1796. (Homocoupling of bromoterthiophene with NiCl ₂ catalyst) and the like can be referred to.

  Although the structure and preparation example of the organic semiconductor which has a thiol group which can be used by this invention are shown below, this invention is not limited to this.

  A method for introducing a thiol group at the end of a fullerene derivative is described in J. Am. Mater. Chem. , 2005, 15, 5158-5163 and Chemical & Pharmaceutical Bulletin +; English; 31; 2; 1983; 454-465.

(Configuration of organic photoelectric conversion element and solar cell)
Although the preferable aspect of the organic photoelectric conversion element which concerns on this invention is demonstrated, it is not limited to this. There is no restriction | limiting in particular as an organic photoelectric conversion element, A power generation layer (a layer in which a p-type semiconductor and an n-type semiconductor are mixed, a bulk heterojunction layer, or an i layer) sandwiched between the anode and the cathode is at least one layer. Any element that generates current when irradiated with light may be used.

The preferable specific example of the layer structure of an organic photoelectric conversion element is shown below.
(I) anode / power generation layer / cathode (ii) anode / hole transport layer / power generation layer / cathode (iii) anode / hole transport layer / power generation layer / electron transport layer / cathode (iv) anode / hole transport layer / P-type semiconductor layer / power generation layer / n-type semiconductor layer / electron transport layer / cathode (v) anode / hole transport layer / first light emitting layer / electron transport layer / intermediate electrode / hole transport layer / second light emitting layer Here, the power generation layer needs to contain a p-type semiconductor material capable of transporting holes and an n-type semiconductor material capable of transporting electrons, which are substantially two layers and heterojunction. Alternatively, a bulk heterojunction that is mixed in one layer may be formed, but a bulk heterojunction configuration is preferable because of high photoelectric conversion efficiency. A p-type semiconductor material and an n-type semiconductor material used for the power generation layer will be described later.

  Like the organic EL element, the efficiency of taking out holes and electrons to the anode / cathode can be increased by sandwiching the power generation layer between the hole transport layer and the electron transport layer. Therefore, the structure having them ((ii), ( iii)) is preferred. Further, in order to improve the rectification of holes and electrons (selection of carrier extraction), the power generation layer itself is sandwiched between layers of a p-type semiconductor material and a single n-type semiconductor material as shown in (iv). It may be a configuration (also referred to as a pin configuration). Moreover, in order to improve the utilization efficiency of sunlight, the tandem configuration (configuration (v)) in which sunlight of different wavelengths is absorbed by each power generation layer may be employed.

  Instead of the sandwich structure in the organic photoelectric conversion element 10 shown in FIG. 1 for the purpose of improving the sunlight utilization rate (photoelectric conversion efficiency), a hole transport layer 14 and an electron transport layer 16 are respectively formed on a pair of comb-like electrodes. The back contact type organic photoelectric conversion element can be configured such that the photoelectric conversion unit 15 is disposed thereon.

  FIG. 1 is a cross-sectional view showing an example of a solar cell composed of a bulk heterojunction organic photoelectric conversion element. In FIG. 1, a bulk heterojunction organic photoelectric conversion element 10 has an anode 12, a hole transport layer 17, a power generation layer 14 of a bulk heterojunction layer, an electron transport layer 18, and a cathode 13 sequentially stacked on one surface of a substrate 11. Has been.

  The substrate 11 is a member that holds the anode 12, the power generation layer 14, and the cathode 13 that are sequentially stacked. In the present embodiment, since light that is photoelectrically converted enters from the substrate 11 side, the substrate 11 can transmit the light that is photoelectrically converted, that is, with respect to the wavelength of the light to be photoelectrically converted. It is a transparent member. As the substrate 11, for example, a glass substrate or a resin substrate is used. The substrate 11 is not essential. For example, the bulk heterojunction organic photoelectric conversion element 10 may be configured by forming the anode 12 and the cathode 13 on both surfaces of the power generation layer 14.

  The power generation layer 14 is a layer that converts light energy into electrical energy, and includes a bulk heterojunction layer in which a p-type semiconductor material and an n-type semiconductor material are uniformly 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).

  In FIG. 1, light incident from the anode 12 through the substrate 11 is absorbed by the electron acceptor or electron donor in the bulk heterojunction layer of the power generation layer 14, and electrons move from the electron donor to the electron acceptor. A pair of holes and electrons (charge separation state) is formed. The generated electric charge is caused by an internal electric field, for example, when the work function of the anode 12 and the cathode 13 is different, the electrons pass between the electron acceptors and the holes are electron donors due to the potential difference between the anode 12 and the cathode 13. The photocurrent is detected by passing through different electrodes to different electrodes. For example, when the work function of the anode 12 is larger than that of the cathode 13, electrons are transported to the anode 12 and holes are transported to the cathode 13. 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 anode 12 and the cathode 13.

  Although not shown in FIG. 1, other layers such as a hole blocking layer, an electron blocking layer, an electron injection layer, a hole injection layer, or a smoothing layer may be included.

  As a more preferable configuration, the power generation layer 14 has a so-called p-i-n three-layer configuration (FIG. 2). A normal bulk heterojunction layer is a single i layer in which a p-type semiconductor material and an n-type semiconductor layer are mixed, but is sandwiched between a p-layer made of a single p-type semiconductor material and an n-layer made of a single n-type semiconductor material. As a result, the rectification of holes and electrons becomes higher, loss due to recombination of charge-separated holes and electrons is reduced, and higher photoelectric conversion efficiency can be obtained.

  Furthermore, it is good also as a tandem-type structure which laminated | stacked such a photoelectric conversion element for the purpose of the improvement of sunlight utilization factor (photoelectric conversion efficiency). FIG. 3 is a cross-sectional view showing a solar cell composed of an organic photoelectric conversion element including a tandem bulk heterojunction layer. In the case of the tandem configuration, the transparent electrode 12 and the first power generation layer 14 ′ are sequentially stacked on the substrate 11, the charge recombination layer 15 is stacked, the second power generation layer 16, and then the counter electrode 13 are stacked. By stacking, a tandem structure can be obtained. The second power generation layer 16 may be a layer that absorbs the same spectrum as the absorption spectrum of the first power generation layer 14 ′ or may be a layer that absorbs a different spectrum, but is preferably a layer that absorbs a different spectrum. Further, both the first power generation layer 14 ′ and the second power generation layer 16 may have the above-described three-layer structure of pin.

  Below, the material which comprises these layers is described.

(P-type semiconductor material)
Examples of the p-type semiconductor material used for the power generation layer (bulk heterojunction layer) of the present invention include various condensed polycyclic aromatic low molecular compounds and conjugated polymers / oligomers.

  Examples of the condensed polycyclic aromatic low-molecular compound include anthracene, tetracene, pentacene, hexacene, heptacene, chrysene, picene, fluorene, pyrene, peropyrene, perylene, terylene, quaterylene, coronene, ovalene, circumanthracene, bisanthene, zeslen, Compounds such as heptazeslen, pyranthrene, violanthene, isoviolanthene, cacobiphenyl, anthradithiophene, porphyrin, copper phthalocyanine, tetrathiafulvalene (TTF) -tetracyanoquinodimethane (TCNQ) complex, bisethylenetetrathiafulvalene (BEDTTTTF ) -Perchloric acid complexes, and derivatives and precursors thereof.

  Examples of the derivative having the above-mentioned condensed polycycle include WO 03/16599 pamphlet, WO 03/28125 pamphlet, US Pat. No. 6,690,029, JP 2004-107216 A. A pentacene derivative having a substituent described in JP-A No. 2003-136964, a pentacene precursor described in US Patent Application Publication No. 2003/136964, and the like; Amer. Chem. Soc. , Vol127. No. 14.4986, J. MoI. Amer. Chem. Soc. , Vol. 123, p9482; Amer. Chem. Soc. , Vol. 130 (2008), no. 9, acene-based compounds substituted with a trialkylsilylethynyl group described in 2706 and the like.

  Examples of the conjugated polymer include a polythiophene such as poly-3-hexylthiophene (P3HT) and an oligomer thereof, or a technical group described in Technical Digest of the International PVSEC-17, Fukuoka, Japan, 2007, P1225. Polythiophene, Nature Material, (2006) vol. 5, p328, a polythiophene-thienothiophene copolymer described in WO 2008/000664, a polythiophene-diketopyrrolopyrrole copolymer described in WO 2008/000664, a polythiophene-thiazolothiazole copolymer described in Adv Mater, 2007 p4160, Nature Mat. vol. 6 (2007), p497 described in PCPDTBT, etc., polypyrrole and its oligomer, polyaniline, polyphenylene and its oligomer, polyphenylene vinylene and its oligomer, polythienylene vinylene and its oligomer, polyacetylene, polydiacetylene, Examples thereof include polymer materials such as σ-conjugated polymers such as polysilane and polygermane.

  In addition, oligomer materials, not polymer materials, include thiophene hexamer α-seccithiophene α, ω-dihexyl-α-sexualthiophene, α, ω-dihexyl-α-kinkethiophene, α, ω-bis (3 Oligomers such as -butoxypropyl) -α-sexithiophene can be preferably used.

  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.

  Further, when the electron transport layer is formed on the power generation layer by coating, there is a problem that the electron transport layer solution dissolves the power generation layer. Therefore, a material that can be insolubilized after coating by a solution process may be used. .

  Examples of such a material include materials that can be insolubilized by polymerizing and crosslinking the coating film after coating, such as polythiophene having a polymerizable group described in Technical Digest of the International PVSEC-17, Fukuoka, Japan, 2007, P1225. Alternatively, a soluble substituent reacts and becomes insoluble (pigmented) by applying energy such as heat, as described in US Patent Application Publication No. 2003/136964, and Japanese Patent Application Laid-Open No. 2008-16834. Materials etc. can be mentioned.

(N-type semiconductor material)
The n-type semiconductor material used for the bulk heterojunction layer of the present invention is not particularly limited. Perfluorophthalocyanine), naphthalenetetracarboxylic anhydride, naphthalenetetracarboxylic acid diimide, perylenetetracarboxylic acid anhydride, perylenetetracarboxylic acid diimide and other aromatic carboxylic acid anhydrides and imidized compounds thereof as a skeleton Etc.

  However, fullerene derivatives that can perform charge separation with various p-type semiconductor materials at high speed (˜50 fs) and efficiently are preferable. Fullerene derivatives 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), and the like. Partially by hydrogen atom, halogen atom, substituted or unsubstituted alkyl group, alkenyl group, alkynyl group, aryl group, heteroaryl group, cycloalkyl group, silyl group, ether group, thioether group, amino group, silyl group, etc. Examples thereof include substituted fullerene derivatives.

  Among them, [6,6] -phenyl C61-butyric acid methyl ester (abbreviation PCBM), [6,6] -phenyl C61-butyric acid-nbutyl ester (PCBnB), [6,6] -phenyl C61-buty Rick acid-isobutyl ester (PCBiB), [6,6] -phenyl C61-butyric acid-n hexyl ester (PCBH), Adv. Mater. , Vol. 20 (2008), p2116, etc., aminated fullerenes such as JP-A 2006-199674, metallocene fullerenes such as JP-A 2008-130889, and cyclics such as US Pat. No. 7,329,709. It is preferable to use a fullerene derivative having a substituent and having improved solubility, such as fullerene having an ether group.

(Hole transport layer / electron block layer)
In the organic photoelectric conversion element 10 of the present invention, the hole transport layer 17 can be taken out between the bulk heterojunction layer and the anode, and charges generated in the bulk heterojunction layer can be taken out more efficiently. It is preferable to have.

  As the material constituting these layers, for example, as the hole transport layer 17, PEDOT such as trade name BaytronP, polyaniline and its doped material, a cyanide compound described in WO2006 / 019270, etc. Etc. can be used. Note that the hole transport layer having a LUMO level shallower than the LUMO level of the n-type semiconductor material used for the bulk heterojunction layer has a rectifying effect that prevents electrons generated in the bulk heterojunction layer from flowing to the anode side. It has an electronic block function. Such a hole transport layer is also called an electron block layer, and it is preferable to use a hole transport layer having such a function. As such a material, a triarylamine compound described in JP-A-5-271166 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 may be either a vacuum deposition method or a solution coating method, but is preferably a solution coating method. Forming the coating film in the lower layer before forming the bulk heterojunction layer is preferable because it has the effect of leveling the coating surface and reduces the influence of leakage and the like.

(Electron transport layer / hole blocking layer)
In the organic photoelectric conversion element 10 of the present invention, by forming the electron transport layer 18 between the bulk heterojunction layer and the cathode, it becomes possible to more efficiently take out the charges generated in the bulk heterojunction layer. It is preferable to have these layers.

  As the electron transport layer 18, octaazaporphyrin, a p-type semiconductor perfluoro product (perfluoropentacene, perfluorophthalocyanine, etc.) can be used. Similarly, a p-type semiconductor material used for a bulk heterojunction layer is used. The electron transport layer having a HOMO level deeper than the HOMO level is given a hole blocking function having a rectifying effect so that holes generated in the bulk heterojunction layer do not flow to the cathode side. Such an electron transport layer is also called a hole blocking layer, and it is preferable to use an electron transport layer having such a function. Examples of such materials include phenanthrene compounds such as bathocuproine, n-type semiconductor materials such as naphthalenetetracarboxylic acid anhydride, naphthalenetetracarboxylic acid diimide, perylenetetracarboxylic acid anhydride, perylenetetracarboxylic acid diimide, and titanium oxide. N-type inorganic oxides such as zinc oxide and gallium oxide, and alkali metal compounds such as lithium fluoride, sodium fluoride, and cesium fluoride 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.

Other Layers For the purpose of improving energy conversion efficiency and device life, various intermediate layers may be included in the device. Examples of the intermediate layer include a hole block layer, an electron block layer, a hole injection layer, an electron injection layer, an exciton block layer, a UV absorption layer, a light reflection layer, and a wavelength conversion layer.

Transparent electrode (first electrode)
In the transparent electrode of the present invention, the cathode and the anode are not particularly limited and can be selected depending on the element structure, but preferably the transparent electrode is used as the anode. For example, when used as an anode, it is preferably an electrode that transmits light of 380 to 800 nm. As the material, for example, indium tin oxide _(ITO), SnO 2, transparent conductive metal oxides such as ZnO, gold, silver, a metal thin film of platinum or the like, metal nanowires, it is possible to use carbon nanotubes.

  Also, a conductive material selected from the group consisting of polypyrrole, polyaniline, polythiophene, polythienylene vinylene, polyazulene, polyisothianaphthene, polycarbazole, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, polyphenylacetylene, polydiacetylene and polynaphthalene. A functional polymer can also be used. A plurality of these conductive compounds can be combined to form a transparent electrode.

Counter electrode (second electrode)
The counter electrode may be a single layer of a conductive material, but in addition to a conductive material, a resin that holds these may be used in combination. As the conductive material for the counter electrode, a material having a small work function (4 eV or less) metal, alloy, 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₎ mixture, indium, a lithium / aluminum mixture, and rare earth metals. Among these, in view of electron extraction performance and durability against oxidation, etc., a mixture of these metals and a second metal which is a stable metal having a larger work function value 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 counter electrode can be produced by forming a thin film of these electrode materials by a method such as vapor deposition or sputtering. 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 counter electrode, the light coming to the counter electrode side is reflected and reflected to the first electrode side, and this light can be reused and is absorbed again by the photoelectric conversion layer, and more photoelectric conversion efficiency Is preferable.

  Further, the counter electrode 13 may be a metal (for example, gold, silver, copper, platinum, rhodium, ruthenium, aluminum, magnesium, indium, etc.), carbon nanoparticle, nanowire, or nanostructure. If it is a thing, a transparent and highly conductive counter electrode can be formed by the apply | coating method, and it is preferable.

  Moreover, when making the counter electrode side light-transmitting, for example, after forming a conductive material suitable for the counter electrode such as aluminum and aluminum alloy, silver and silver compound in a thin film thickness of about 1 to 20 nm, By providing a film of the conductive light transmissive material mentioned in the description of the transparent electrode, a light transmissive counter electrode can be obtained.

Intermediate electrode Further, the material of the intermediate electrode required in the case of the tandem configuration as in (v) (or FIG. 3) is preferably a layer using a compound having both transparency and conductivity. Materials used for transparent electrodes (transparent metal oxides such as ITO, AZO, FTO and titanium oxide, very thin metal layers such as Ag, Al and Au, or layers containing nanoparticles / nanowires, PEDOT: PSS, For example, a conductive polymer material such as polyaniline) can be used.

  In addition, in the hole transport layer and the electron transport layer described above, there is also a combination that works as an intermediate electrode (charge recombination layer) by appropriately combining and laminating, and with such a configuration, the process of forming one layer This is preferable because it can be omitted.

(Metal nanowires)
As the conductive fibers of the present invention, organic fibers or inorganic fibers coated with metal, conductive metal oxide nanowires, carbon fibers, carbon nanotubes, and the like can be used. Metal nanowires are preferred.

  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 of nm size.

  The metal nanowire according to the present invention preferably has an average length of 3 μm or more in order to form a long conductive path with a single metal nanowire and to exhibit appropriate light scattering properties. 3-500 micrometers is preferable and it is especially preferable that it is 3-300 micrometers. 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. In order to achieve both conductivity and stability (sulfurization and oxidation resistance of metal nanowires and migration resistance), it is also preferable to include silver and at least one metal belonging to a noble metal other than silver. 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 inside and the surface of the metal nanowire, or the entire metal nanowire has the same metal composition. May be.

  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. For example, as a method for producing Ag nanowires, Adv. Mater. , 2002, 14, 833-837; Chem. Mater. , 2002, 14, 4736-4745, etc. As a method for producing Co nanowires, a method for producing Au nanowires is disclosed in JP 2006-233252A, and a method for producing Cu nanowires is disclosed in JP 2002-266007 A, etc. Reference can be made to Japanese Unexamined Patent Publication No. 2004-149871. In particular, Adv. Mater. And Chem. Mater. The method for producing Ag nanowires reported in (1) can be easily produced in an aqueous system, and since the conductivity of silver is the highest among metals, it is preferable as the method for producing metal nanowires according to the present invention. Can be applied.

  In the present invention, the metal nanowires come into contact with each other to form a three-dimensional conductive network, exhibiting high conductivity, and allowing light to pass through the window of the conductive network where no metal nanowire exists. In addition, the power generation from the organic power generation layer can be efficiently performed by the scattering effect of the metal nanowires. If a metal nanowire is installed in the 1st electrode at the side close | similar to an organic electric power generation layer part, since this scattering effect can be utilized more effectively, it is more preferable embodiment.

Substrate When light that is photoelectrically converted enters from the substrate side, the substrate is preferably a member that can transmit the photoelectrically converted light, that is, a member that is transparent to the wavelength of the light to be photoelectrically converted. . 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 lightness 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), 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 ~800nm), 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. A polyethylene terephthalate film and a biaxially stretched polyethylene naphthalate film are more preferable.

  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.

  Further, for the purpose of suppressing the permeation of oxygen and water vapor, 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. Good.

(Optical function layer)
The organic photoelectric conversion element of the present invention may have various optical functional layers for the purpose of more efficient reception of sunlight. As the optical functional layer, for example, a light condensing layer such as an antireflection film or a microlens array, or a light diffusion layer that can scatter light reflected by the cathode and enter the power generation layer again may be provided. .

  Various known antireflection layers can be provided as the antireflection layer. For example, when the transparent resin film is a biaxially stretched polyethylene terephthalate film, the refractive index of the easy adhesion layer adjacent to the film is 1.57. It is more preferable to set it to ˜1.63 because the interface reflection between the film substrate and the easy adhesion layer can be reduced and the transmittance can be improved. 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.

  As the condensing layer, for example, it is processed so as to provide a structure on the microlens array on the sunlight receiving side of the support substrate, or the amount of light received from a specific direction is increased by combining with a so-called condensing sheet. Conversely, the incident angle dependency of sunlight can be reduced.

  As an example of the microlens array, quadrangular pyramids having a side of 30 μm and an apex angle of 90 degrees are two-dimensionally arranged on the light extraction side of the substrate. One side is preferably 10 to 100 μm. If it is smaller than this, the effect of diffraction is generated and colored.

  Examples of the light scattering layer include various antiglare layers, layers in which nanoparticles or nanowires such as metals or various inorganic oxides are dispersed in a colorless and transparent polymer, and the like.

Film-forming method / Surface treatment method (Formation method of various layers)
Examples of a method for forming a bulk heterojunction layer in which an electron acceptor and an electron donor are mixed, and a transport layer / electrode include a vapor deposition method and a coating method (including a casting method and a spin coating method). Among these, examples of the method for forming the bulk heterojunction layer 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. The coating method is also excellent in production speed.

  Although there is no restriction | limiting in the coating method used in this case, For example, a spin coat method, the casting method from a solution, a dip coat method, a blade coat method, a wire bar coat method, a gravure coat method, a spray coat method etc. are mentioned. Furthermore, patterning can also be performed by a printing method such as an ink jet method, a screen printing method, a relief printing method, an intaglio printing method, an offset printing method, or a flexographic printing method.

  After coating, it is preferable to perform heating in order to cause removal of residual solvent, moisture and gas, and improvement of mobility and absorption longwave due to crystallization of the semiconductor material. When annealing is performed at a predetermined temperature during the manufacturing process, a part of the particles is microscopically aggregated or crystallized, and the bulk heterojunction layer can have an appropriate phase separation structure. As a result, the carrier mobility of the bulk heterojunction layer is improved and high efficiency can be obtained.

  The power generation layer (bulk heterojunction layer) 14 may be composed of a single layer in which an electron acceptor and an electron donor are uniformly mixed, but a plurality of layers in which the mixing ratio of the electron acceptor and the electron donor is changed. You may comprise. In this case, it can be formed by using a material that can be insolubilized after coating as described above.

Patterning There is no restriction | limiting in particular in the method and process of patterning the electrode, electric power generation layer, positive hole transport layer, electron transport layer, etc. which concern on this invention, A well-known method can be applied suitably.

  If it is a soluble material such as a bulk heterojunction layer and a transport layer, only unnecessary portions may be wiped after the entire surface of die coating, dip coating, etc., or direct patterning at the time of coating using a method such as an ink jet method or screen printing. May be.

  In the case of an insoluble material such as an electrode material, the electrode can be patterned by a known method such as mask vapor deposition during vacuum deposition or etching or lift-off. Alternatively, the pattern may be formed by transferring a pattern formed on another substrate.

(Optical sensor array)
Next, an optical sensor array to which the bulk heterojunction type organic photoelectric conversion element 10 described above is applied will be described in detail. The optical sensor array is produced by arranging the photoelectric conversion elements in a fine pixel form by utilizing the fact that the bulk heterojunction type organic photoelectric conversion elements generate a current upon receiving light, and projected onto the optical sensor array. It is a sensor having a function of converting an image into an electrical signal.

  FIG. 4 is a diagram showing the configuration of the photosensor array. 4A is a top view, and FIG. 4B is a cross-sectional view taken along the line A-A ′ of FIG.

  In FIG. 4, the optical sensor array 20 is paired with a transparent electrode 22 as a lower electrode, a power generation layer 24 for converting light energy into electric energy, and a transparent electrode 22 on a substrate 21 as a holding member, and as an upper electrode. The counter electrodes 23 are sequentially stacked. The power generation layer 24 includes two layers, a photoelectric conversion layer 24b having a bulk heterojunction layer in which a p-type semiconductor material and an n-type semiconductor material are uniformly mixed, and a buffer layer 24a. In the example shown in FIG. 4, six bulk heterojunction type organic photoelectric conversion elements are formed.

  The substrate 21, the transparent electrode 22, the photoelectric conversion layer 24 b, and the counter electrode 23 have the same configuration and role as the transparent electrode 12, the power generation layer 14, and the counter electrode 13 in the bulk heterojunction photoelectric conversion element 10 described above. is there.

  For example, glass is used for the substrate 21, ITO is used for the transparent electrode 22, and aluminum is used for the counter electrode 23, for example. For example, the BP-1 precursor is used for the p-type semiconductor material of the photoelectric conversion layer 24b, and for example, the exemplified compound is used for the n-type semiconductor material.

  The buffer layer 24a is made of PEDOT (poly-3,4-ethylenedioxythiophene) -PSS (polystyrene sulfonic acid) conductive polymer (trade name BaytronP, manufactured by Stark Vitec). Such an optical sensor array 20 was manufactured as follows.

  An ITO film was formed on the glass substrate by sputtering and processed into a predetermined pattern shape by photolithography. The thickness of the glass substrate was 0.7 mm, the thickness of the ITO film was 200 nm, and the measurement area (light receiving area) of the ITO film after photolithography was 1 mm × 1 mm. Next, a PEDOT-PSS film was formed on the glass substrate 21 by spin coating (conditions: rotational speed = 1000 rpm, filter diameter = 1.2 μm). Thereafter, the substrate was heated in an oven at 140 ° C. for 10 minutes and dried. The thickness of the PEDOT-PSS film after drying was 30 nm.

  Next, a 1: 1 mixed film of P3HT and PCBM was formed on the PEDOT-PSS film by a spin coating method (conditions: rotational speed = 3300 rpm, filter diameter = 0.8 μm). After forming the mixed film of P3HT and PCBM, annealing was performed by heating in an oven at 180 ° C. for 30 minutes in a nitrogen gas atmosphere. The thickness of the bulk heterojunction layer after the annealing treatment was 70 nm.

  Thereafter, an aluminum layer as an upper electrode was formed on the bulk heterojunction layer by a vapor deposition method (thickness = 10 nm) using a metal mask having a predetermined pattern opening. Thereafter, 1 μm of PVA (polyvinyl alcohol) was formed by spin coating and baked at 150 ° C. to prepare a passivation layer (not shown). The optical sensor array 20 was produced as described above.

  The manufactured photosensor array 20 having 2 rows × 3 columns of pixels is irradiated with light so that only the two pixels in the center column are exposed to light, and the 6 pixels are sequentially set to −0. When the current value was read by applying a voltage of 5 V, the current was observed only in the pixels that were exposed to light, and no current flowed in the pixels that were not exposed to light. Therefore, it was confirmed that the optical sensor array 20 operates as an optical sensor.

(Preparation of sample 1)
J. et al. Amer. Chem. Soc. , Vol127. A dichloroethane solution of 2.0 nm triphenylphosphine protected gold nanoparticles was obtained with reference to No. 7.2172. A chloroform solution of thiophene (compound 1) having a thiol group at the end was added and stirred, and then the chloroform phase was thoroughly purified to obtain Sample 1 which is the chloroform dispersion of the present invention. By TEM observation, it was confirmed that gold particles having a diameter of about 2.0 nm were well dispersed.

(Preparation of sample 2)
A composition was prepared in the same manner as in Sample 1 except that the organic compound semiconductor was changed to a fullerene derivative having a thiol group at the end (Compound 2), and Sample 2 was obtained as a chloroform dispersion.

(Preparation of organic photoelectric conversion element SC-101)
The transparent electrode patterned on the glass substrate was cleaned in the order of ultrasonic cleaning with surfactant and ultrapure water, followed by ultrasonic cleaning with ultrapure water, dried with nitrogen blow, and finally UV ozone cleaning. .

  On this transparent substrate, Baytron P4083 (manufactured by Starck Vitec), which is a conductive polymer, was spin-coated with a film thickness of 30 nm, and then dried by heating at 140 ° C. in the air for 10 minutes.

  After this, the substrate was brought into the glove box and worked under a nitrogen atmosphere. First, the substrate was heat-treated at 140 ° C. for 3 minutes in a nitrogen atmosphere. A solution was prepared by dissolving 1.5% by mass of sample 1 as a p-type semiconductor material and 1.5% by mass of sample 2 as an n-type semiconductor material in chloroform and filtered at 500 rpm while filtering through a 0.45 μm filter. Second, followed by spin coating at 2200 rpm for 1 second and left at room temperature for 30 minutes to form a bulk heterojunction layer.

  Next, a solution in which Ti-isopropoxide is dissolved in ethanol to a concentration of 25 mmol / l is prepared, and after the take-out electrode portion is masked and spin-coated at 2000 rpm, it is taken out into the atmosphere and left for 60 minutes to leave Ti- By hydrolyzing isopropoxide, a 10 nm thick TiOx layer was formed, and an electron transport layer was formed.

Next, the substrate on which the series of organic layers was formed was placed in a vacuum deposition apparatus without being exposed to the atmosphere. The element was set so that the shadow mask with a width of 2 mm was orthogonal to the transparent electrode, and the inside of the vacuum deposition apparatus was depressurized to 10 ⁻³ Pa or less, and then 100 nm of Al was deposited. Finally, heating was performed at 120 ° C. for 30 minutes to obtain SC-101 which is an organic photoelectric conversion element of the present invention. The vapor deposition rate was 2 nm / second, and the size was 2 mm square.

  The obtained organic photoelectric conversion element SC-101 was sealed in the atmosphere after sealing with an aluminum cap and a UV curable resin (manufactured by Nagase ChemteX Corporation, UV RESIN XNR5570-B1) in a nitrogen atmosphere. I took it out.

(Preparation of organic photoelectric conversion element SC-102)
In production of the organic photoelectric conversion element SC-101, a bulk heterojunction layer was formed using a solution in which 1.5% by mass of Sample 1 as a p-type semiconductor and 1.5% by mass of PCBM as an n-type semiconductor were dissolved in chloroform. Except that, an organic photoelectric conversion element SC-102 was obtained in the same manner.

(Preparation of organic photoelectric conversion element SC-103)
In production of the organic photoelectric conversion element SC-101, a bulk heterojunction layer was formed using a solution in which 1.5% by mass of P3HT as a p-type semiconductor and 1.5% by mass of a sample 2 as an n-type semiconductor were dissolved in chloroform. Except that, an organic photoelectric conversion element SC-103 was obtained in the same manner.

(Preparation of organic photoelectric conversion element SC-104)
In the production of the organic photoelectric conversion element SC-101, a bulk heterojunction layer was formed using a solution obtained by dissolving 1.5% by mass of P3HT as a p-type semiconductor and 1.5% by mass of PCBM as an n-type semiconductor in chloroform. In the same manner, an organic photoelectric conversion element SC-104 was obtained.

(Evaluation of conversion efficiency)
Photoelectric conversion elements prepared above, was irradiated with light having an intensity of 100 mW / cm ² solar simulator (AM1.5G filter), a superposed mask in which the effective area 4.0 mm ² on the light receiving portion, the short circuit current density Jsc ( The four light-receiving portions formed on the same element were measured for mA / cm ² ), open-circuit voltage Voc (V), and fill factor (fill factor) FF, and the average value was obtained. Further, energy conversion efficiency η (%) was obtained from Jsc, Voc, and FF according to Equation 1. The results are shown in Table 1.

Formula 1 Jsc (mA / cm ² ) × Voc (V) × FF = η (%)

  As shown in Table 1, it can be seen that SC-101, 102 and 103 of the present invention are superior in conversion efficiency compared to SC-104 which is a comparative example.

DESCRIPTION OF SYMBOLS 10 Bulk heterojunction type organic photoelectric conversion element 11 Substrate 12 Anode 13 Cathode 14 Power generation layer (bulk heterojunction layer)
14p p layer 14n n layer 14 'first power generation layer 15 charge recombination layer 16 second power generation layer 17 hole transport layer 18 electron transport layer 20 photosensor array 21 substrate 22 transparent electrode 23 counter electrode 24 power generation layer 24a buffer Layer 24b Photoelectric conversion layer

Claims (6)

  An organic photoelectric conversion element having a bulk heterojunction photoelectric conversion layer sandwiched between a first electrode and a second electrode, wherein the photoelectric conversion layer contains at least fine particles bonded to an organic semiconductor. Photoelectric conversion element.   The organic photoelectric conversion element according to claim 1, wherein the fine particles are metal fine particles.   The organic photoelectric conversion element according to claim 1, wherein the fine particles and the organic semiconductor are bonded via a thiol group.   The organic photoelectric conversion element according to claim 1, wherein the organic semiconductor includes a p-type semiconductor or an n-type semiconductor.   The organic photoelectric conversion element according to any one of claims 1 to 4, wherein the photoelectric conversion layer includes p-type organic semiconductor-coated fine particles and an n-type semiconductor material.   The organic photoelectric conversion element according to claim 1, wherein the fine particles are gold nanoparticles.

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