JP2014241370A - Photoelectric conversion element and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric conversion element which has excellent long-term stability, high photoelectric conversion efficiency, an element structure in which light energy is absorbed from a negative electrode side, and a buffer layer function for improving the efficiency of collecting current of the electrons generated in a photoelectric conversion layer on the negative electrode, and in which formation of the buffer layer is simple.SOLUTION: A photoelectric conversion element 10 comprises a photoelectric conversion layer 4 including an organic semiconductor between a positive electrode 5 and a negative electrode 2. The negative electrode 2 at least has light permeability, and a buffer layer 3 containing sodium halide between the photoelectric conversion layer 4 and the negative electrode 2. The buffer layer 3 is formed by vacuum-depositing the sodium halide on the negative electrode 2.

Description

  The present invention relates to a photoelectric conversion element in which a buffer layer made of sodium halide is formed between a photoelectric conversion layer and a light-transmissive negative electrode, and a method for manufacturing the photoelectric conversion element.

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

  Since the organic semiconductor thin film can be formed by a coating method or a printing method, it is expected that the manufacturing process can be simplified and the power generation cost can be reduced. In addition, since lightweight and flexible elements and modules can be manufactured, it has excellent portability and has the potential to be used even in areas where electrical infrastructure is not established. Furthermore, since the organic semiconductor can control the light absorption band by molecular design, it can provide a solar cell with various colors and excellent design. However, although these advantages can be expected, further long-term stability and improvement in photoelectric conversion efficiency are required for practical use of organic thin-film solar cells.

  As one method for improving the long-term stability of an organic thin-film solar cell, an element configuration that absorbs light energy from the negative electrode side (referred to herein as “reverse cell”) has been proposed. It is known that a reverse cell can obtain high long-term stability with respect to an element configuration that absorbs light energy from the positive electrode side (referred to as “forward cell” in this specification) (Non-patent Document 1).

  Further, as one method for improving the photoelectric conversion efficiency of the organic thin film solar cell, there is insertion of a buffer layer. The buffer layer blocks the charge generated in the photoelectric conversion layer from flowing into the opposite electrode, suppresses charge recombination, reduces the electron energy barrier at the interface between the photoelectric conversion layer and the electrode, and performs photoelectric conversion. It works to improve the efficiency of collecting charges generated in the layer.

  As the buffer layer, for example, a buffer layer formed from a mixture containing a polymer or oligomer having one or more polymerizable substituents is disclosed (Patent Document 1). The buffer layer is mainly useful as a buffer layer on the positive electrode side of the forward cell. As the buffer layer on the negative electrode side of the forward cell, a metal having a low work function such as calcium (Non-patent Document 2), a carbonate such as cesium carbonate (Non-patent Document 3), or an alkali metal halogen such as lithium fluoride. A chemical (Patent Document 2) is known. However, a metal having a small work function such as calcium easily reacts with oxygen and water, and cesium carbonate has deliquescence, so that it is necessary to produce an organic thin film solar cell in an inert atmosphere. In addition, lithium fluoride is stable in the atmosphere and exhibits good performance when used as a buffer layer in a forward cell, but does not exhibit sufficient performance when used in a reverse cell. (Non-Patent Document 4).

  As described above, various compounds are known as buffer layers for forward cells, but compounds that form an effective buffer layer when used in reverse cells are not yet known, and can be applied to reverse cells. Therefore, the development of a buffer layer capable of maintaining high long-term stability and photoelectric conversion efficiency has been desired.

JP 2010-287767 A Special table 2003-533034 gazette

Thin Solid Films, 2005, 476, p.340 Applied Physics Letters, 2009, Vol. 95, p.153304 Applied Physics Letters, 2008, Vol. 92, p.173303 Applied Physics Letters, 2006, Vol. 88, p.253503

  The present invention has been made in order to solve the above-described problems, and has an element structure that has excellent long-term stability, high photoelectric conversion efficiency, and absorbs light energy from the negative electrode side, and is generated by a photoelectric conversion layer. An object of the present invention is to provide a photoelectric conversion element that has a function of a buffer layer that increases the efficiency of collecting current to the negative electrode and that can be easily formed, and a method for manufacturing the photoelectric conversion element.

  As a result of diligent research to solve the above problems, the present inventors have achieved high photoelectric conversion efficiency by using sodium halide in the buffer layer between the photoelectric conversion layer and the negative electrode having optical transparency. It was found that it can be obtained.

  The photoelectric conversion element according to claim 1, which has been made to achieve the above object, is a photoelectric conversion element having a photoelectric conversion layer containing an organic semiconductor between a positive electrode and a negative electrode. In addition, at least the negative electrode has optical transparency, and a buffer layer containing sodium halide is provided between the photoelectric conversion layer and the negative electrode.

  Similarly, the photoelectric conversion element according to claim 2 is the one described in claim 1, and has a hole transport layer containing a hole transport material between the photoelectric conversion layer and the positive electrode. It is characterized by.

  A photoelectric conversion element according to a third aspect is the photoelectric conversion element according to the first or second aspect, wherein the negative electrode is indium tin oxide.

  The photoelectric conversion element according to claim 4 is the one described in any one of claims 1 to 3, wherein the photoelectric conversion layer is a mixture of an electron-donating organic semiconductor and an electron-accepting organic semiconductor. It is characterized by that.

  The photoelectric conversion device according to claim 5 is the photoelectric conversion device according to claim 4, wherein the electron-donating organic semiconductor is thiophene, fluorene, carbazole, dibenzosilole, dibenzogermole, benzodithiophene, and di It is a π-electron conjugated polymer containing a monomer unit having at least part of a heterocyclic skeleton group selected from ketopyrrolopyrrole.

  A photoelectric conversion element according to a sixth aspect is the photoelectric conversion element according to the fourth aspect, wherein the electron-accepting organic semiconductor is a fullerene derivative.

  Moreover, the manufacturing method of the photoelectric conversion element of Claim 7 made | formed in order to achieve the said objective contains an organic semiconductor between the positive electrode and the negative electrode which has a light transmittance. A photoelectric conversion layer, and a buffer layer containing sodium halide between the photoelectric conversion layer and the negative electrode, and a hole transport layer between the photoelectric conversion layer and the positive electrode A good method for producing a photoelectric conversion element, wherein the buffer layer is formed by vacuum-depositing sodium halide on the negative electrode.

  The photoelectric conversion element of the present invention has a buffer layer containing sodium halide between the photoelectric conversion layer and the light-transmitting negative electrode, and can exhibit excellent photoelectric conversion efficiency. In addition, since the photoelectric conversion element of the present invention is an “inverse cell” having an element configuration that absorbs light energy from the negative electrode side, it is possible to use a metal having a high work function and high oxidation stability on the positive electrode side. And long-term stability.

  According to the method for producing a photoelectric conversion element of the present invention, a buffer layer can be formed by vacuum-depositing sodium halide on a light-transmitting negative electrode, so that high photoelectric conversion efficiency can be achieved by a simple process. The photoelectric conversion element which has can be provided. In addition, since a metal having high oxidation stability is used on the positive electrode side, it can be handled in the atmosphere, and it is not necessary to form the positive electrode in an inert layer atmosphere, and the manufacturing process can be simplified.

It is a schematic cross section which shows one typical Example of the photoelectric conversion element to which this invention is applied. It is a schematic cross section which shows another Example of the photoelectric conversion element to which this invention is applied.

  Although embodiments of the present invention will be described, the scope of the present invention is not limited to these embodiments.

  As shown in FIG. 1, a photoelectric conversion element 10 according to an example of the present invention is formed on a substrate 1 and includes a photoelectric conversion layer 4 between a pair of positive electrodes 5 and a negative electrode 2. The negative electrode 2 is light transmissive, and the positive electrode 5 may be light transmissive or non-light transmissive. Between the photoelectric conversion layer 4 and the negative electrode 2, it has the buffer layer 3 containing a sodium halide. The substrate 1 may be on the negative electrode 2 side or on the positive electrode 5 side.

  In the operation mechanism of the photoelectric conversion element 10, light energy incident from the negative electrode 2 having optical transparency is absorbed by the photoelectric conversion layer 4 to generate excitons in which holes and electrons are combined. The photoelectric conversion layer 4 is usually composed of a mixture of an electron-donating compound and an electron-accepting compound. When excitons reach the interface, holes and electrons are caused by the difference in LUMO energy and HOMO energy at the interface. Are separated and charges (holes and electrons) that can move independently are generated. The generated holes move to the positive electrode 5, and the electrons move to the negative electrode 2, so that they can be taken out as electric energy (current). In order to efficiently extract holes from the positive electrode 5, a conductive material having a work function close to the HOMO energy of the electron donating compound is preferably used for the positive electrode 5. In order to efficiently extract electrons from the negative electrode 2, it is preferable to use a conductive material having a work function close to the LUMO energy of the electron accepting compound for the negative electrode 2.

  The photoelectric conversion element 10 is usually formed on the substrate 1. The substrate 1 may be any substrate that does not change when an electrode is formed and an organic layer is formed. Examples of the material of the substrate 1 include inorganic materials such as alkali-free glass, quartz glass, and silicon, and organic materials such as polyester, polycarbonate, polyolefin, polyamide, polyimide, polyphenylene sulfide, polyparaxylene, epoxy resin, and fluorine resin. A film or plate produced by any method can be used. In the case of the opaque substrate 1, the opposite electrode, that is, the electrode far from the substrate 1 (the positive electrode 5 in the example of FIG. 1) is preferably transparent or translucent. In the case of the transparent substrate 1, the electrode in contact with the substrate 1 (the negative electrode 2 in the example of FIG. 1) may be an electrode having optical transparency.

  The negative electrode 2 is light transmissive. Examples of the transparent or translucent electrode material having optical transparency include a conductive metal oxide film and a translucent metal thin film. Specifically, indium oxide, zinc oxide, tin oxide, and their composites, indium tin oxide (ITO), fluorine tin oxide (FTO), antimony tin oxide, indium zinc oxide (IZO), Gallium / Zinc / Oxide (GZO), Aluminum / Zinc / Oxide (AZO), Antimony / Zinc / Oxide conductive films, gold, platinum, silver, copper electrodes A thin film is used, and among them, ITO, FTO, IZO, GZO, AZO and the like are preferable. Examples of the method for producing the electrode include a vacuum deposition method, a sputtering method, an ion plating method, and a plating method. Further, as a transparent electrode, a film of a conductive polymer material such as polyaniline and derivatives thereof, polythiophene and derivatives thereof, or a film of nanocarbon materials such as carbon nanotubes and graphene may be used.

  The positive electrode 5 may or may not have optical transparency. A known metal, a conductive polymer, or the like can be used as the electrode that does not have optical transparency. For example, metals such as platinum, gold, silver, aluminum, chromium, nickel, copper, titanium, magnesium, calcium, barium, sodium, or alloys thereof can be used. As a method for producing the positive electrode 5, any of those exemplified as the film forming method for the negative electrode 2 described above can be employed.

  The buffer layer 3 is made of sodium halide and has a function of efficiently extracting electrons generated in the photoelectric conversion layer 4 to the negative electrode 2 side. By inserting the buffer layer 3, the energy barrier between the LUMO level of the electron-accepting material in the photoelectric conversion layer 4 and the Fermi level (work function) of the negative electrode 2 is reduced, so that the negative electrode 2 has the effect of reducing the electrical resistance of the electrons moving to 2. Thereby, the photoelectric conversion element 10 can exhibit the outstanding photoelectric conversion efficiency.

  The kind of halogen contained in the sodium halide used as the buffer layer 3 in the present invention is not particularly limited, and fluorine, bromine, chlorine, and iodine can be used. Among these, fluorine is preferable. As a method for forming the buffer layer 3, an existing method can be used, and examples thereof include a vacuum deposition method and a sputtering method. When sodium halide is used in the reverse cell, an effective dipole moment is formed at the interface between the negative electrode 2 and the photoactive layer 4, and the Fermi level (work function) of the negative electrode 2 and the electron-accepting material It is considered that the energy barrier between the LUMO level is reduced and the electric resistance is reduced.

  Although it does not specifically limit as a film thickness of the buffer layer 3 containing a sodium halide, 0.1-10 nm is suitable. When the film thickness is too thin, a sufficient function as the buffer layer 3 may not be obtained. If the film thickness is too thick, the resistance may increase and cause a decrease in photoelectric conversion efficiency. More preferably, it is 0.1 nm-5 nm, More preferably, it is 0.2 nm-3 nm.

  The film thickness of the buffer layer 3 can be measured by a method of observing the cross-sectional shape of the substrate 1 formed with sodium halide with an electron microscope, or by a stylus-type step gauge. When the film thickness of sodium halide is thin and it is difficult to measure by the above method, the weight of the sodium halide film formed on the substrate 1 (weight per unit area of the substrate 1) is measured. The film thickness can be determined from the specific gravity.

  The buffer layer 3 containing sodium halide may contain a small amount of a compound other than sodium halide as long as the effects of the present invention are not impaired. Examples of such a compound include an alkali metal halogen compound and an alkaline earth metal halogen compound. Examples of the alkali metal halogen compound include lithium fluoride, lithium chloride, lithium bromide, lithium iodide, potassium fluoride, potassium chloride, cesium chloride, cesium bromide and the like. Examples of the alkaline earth metal halogen compound include calcium fluoride, barium fluoride, and magnesium fluoride. The content of the compound other than sodium halide in the buffer layer 3 is preferably 0 to 20% by weight, and more preferably 0 to 10% by weight. Moreover, as a content rate of the sodium halide in the buffer layer 3, 80-100 weight% is preferable and 90-100 weight% is more preferable.

  The photoelectric conversion layer 4 is usually composed of a mixture of an electron donating compound and an electron accepting compound. In the present invention, the electron donating organic semiconductor (p-type organic semiconductor) and the electron accepting organic semiconductor (n-type organic semiconductor) are used. ) And a mixture thereof. The junction between the electron-donating organic semiconductor and the electron-accepting organic semiconductor may be a planar heterojunction or a bulk heterojunction.

  The p-type organic semiconductor used for the photoelectric conversion layer 4 may be a low molecular compound or a high molecular compound. Examples of the low molecular weight compound include phthalocyanine, metal phthalocyanine, porphyrin, metal porphyrin, oligothiophene, tetracene, pentacene, and rubrene. As a polymer compound, a monomer unit having at least one heterocyclic skeleton selected from thiophene, fluorene, carbazole, dibenzosilole, dibenzogermole, diketopyrrolopyrrole, and derivatives thereof as part of the chemical structure. And a π-electron conjugated polymer. Among these, a π-electron conjugated polymer including a monomer unit having a heterocyclic skeleton including at least one thiophene ring as a part of the chemical structure is preferable from the viewpoint of photoelectric conversion efficiency. Examples of the heterocyclic skeleton include cyclopentadithiophene, thienopyrrole, dithienopyrrole, dithienosilole, dithienogermol, benzodithiophene, naphthodithiophene, and derivatives thereof. These may have a substituent in the main chain skeleton for the purpose of controlling solubility and polarity. These polymer compounds may be either homopolymers, random or block copolymers, and their molecular chains may be linear, branched, physically or chemically cross-linked. Among these, the p-type organic semiconductor is preferably a polymer compound from the viewpoint of application to a coating process, and includes a monomer unit having a heterocyclic skeleton including at least one thiophene ring as part of the chemical structure. An electron conjugated polymer is more preferable.

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

The n-type organic semiconductor used for the photoelectric conversion layer 4 is not particularly limited as long as it is an organic material having an electron accepting property. As an n-type organic semiconductor, for example, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, N, N′-dioctyl-3,4,9 , 10-naphthyltetracarboxydiimide, 2- (4-biphenylyl) -5- (4-tert-butylphenyl) -1,3,4-oxadiazole, 2,5-di (1-naphthyl) -1, Oxazole derivatives such as 3,4-oxadiazole, triazole derivatives such as 3- (4-biphenylyl) -4-phenyl-5- (4-t-butylphenyl) -1,2,4-triazole, phenanthroline derivatives, C ₆₀ or _{C 70} fullerene derivative, introducing a carbon nanotube, poly -p- phenylene vinylene-based polymer cyano group And the like derivatives (CN-PPV). These may be used alone or in combination of two or more. Among these, fullerene derivatives are preferably used from the viewpoint of an n-type semiconductor that is stable and excellent in carrier mobility.

Fullerene derivatives suitably used as the n-type organic semiconductor include unsubstituted ones such as C ₆₀ , C ₇₀ , C ₇₆ , C ₇₈ , C ₈₂ , C ₈₄ , C ₉₀ , C ₉₄ , and [6, 6] -phenyl C ₆₁ butyric acid methyl ester (PC ₆₁ BM), [5,6] -phenyl C ₆₁ butyric acid methyl ester, [6,6] -phenyl C ₆₁ butyric acid n-butyl ester, [ 6,6] -phenyl C ₆₁ butyric acid i-butyl ester, [6,6] -phenyl C ₆₁ butyric acid hexyl ester, [6,6] -phenyl C ₆₁ butyric acid dodecyl ester, [6,6 ] - diphenyl _{C 62} bis (butyric acid methyl _{ester) (bis-PC 62 BM)} , [6,6] - Fe Le _{C 71} butyric acid methyl ester _{(PC 71 BM), [6,6} ] - diphenyl _{C 72} bis (butyric acid methyl _{ester) (bis-PC 72 BM)} , indene _{C 60} - monoadduct, indene _{C 60} - bis-adduct, indene C _{70 -} monoadduct, indene C _{70 -} and substituted derivatives including bis adduct thereof. Among _{these, C 60} or _{C 70} fullerene derivatives are particularly preferably used.

The fullerene derivatives can be used alone or as a mixture thereof. From the viewpoint of solubility in an organic solvent, PC ₆₁ BM, bis-PC ₆₂ BM, PC ₇₁ BM, bis-PC ₇₂ BM, indene C ₆₀ -mono adduct, indene C ₆₀ -bis adduct, indene C ₇₀ -mono Adducts and indene C ₇₀ -bis adducts are preferably used. Further, among these, from the viewpoint of light absorption, PC ₇₁ BM, bis-PC ₇₂ BM, indene C ₇₀ -mono adduct, and indene C ₇₀ -bis adduct are used. From the viewpoint of production cost, PC ₆₁ BM Bis-PC ₆₂ BM and indene C ₆₀ -bis adduct are more preferably used.

  The contents of the p-type organic semiconductor and the n-type organic semiconductor in the photoelectric conversion layer 4 are not particularly limited. The composition ratio of the p-type organic semiconductor to the n-type organic semiconductor is preferably in the range of p-type organic semiconductor: n-type organic semiconductor = 1 to 99:99 to 1, more preferably 20 to 80:80. It is in the range of ~ 20. Moreover, it is preferable that the sum of the masses of the p-type organic semiconductor and the n-type organic semiconductor is 0.1 to 10.0 parts by mass with respect to 100 parts by mass of the mass of the dissolving solvent described later, More preferably, it is -5.0 mass parts.

  The film thickness of the photoelectric conversion layer 4 is usually 1 nm to 2000 nm, preferably 2 nm to 1000 nm, more preferably 5 nm to 500 nm, and further preferably 20 nm to 300 nm. If the film thickness is too thin, the light is not sufficiently absorbed. Conversely, if it is too thick, it becomes difficult for the charge to reach the electrode due to resistance loss.

  As shown in FIG. 2, the photoelectric conversion element 10 of another example of the present invention has a photoelectric conversion layer 4 formed on a substrate 1 between a pair of positive electrode 5 and negative electrode 2, A buffer layer 3 containing sodium halide is provided between the photoelectric conversion layer 4 and the negative electrode 2, and a hole transport layer 6 containing a hole transport material is further provided between the photoelectric conversion layer 4 and the positive electrode 5. Have. The substrate 1 may be on the negative electrode 2 side or on the positive electrode 5 side.

The material for forming the hole transport layer 6 is not particularly limited as long as it has p-type semiconductor characteristics, but is a polythiophene polymer, a polyaniline polymer, a poly-p-phenylene vinylene polymer, a polyfluorene polymer. Conductive polymers such as polymers; low molecular organic compounds exhibiting p-type semiconductor properties such as phthalocyanine derivatives (H ₂ Pc, CuPc, ZnPc, etc.), porphyrin derivatives; transition metal oxides such as molybdenum oxide, tungsten oxide, vanadium oxide The product is preferably used. In particular, polyethylenedioxythiophene (PEDOT), which is a polythiophene polymer, or PEDOT to which polystyrene sulfonate (PSS) is added is preferably used. The thickness of the hole transport layer 6 is preferably 1 nm to 600 nm, and more preferably 20 nm to 300 nm.

  The manufacturing method of the photoelectric conversion element of this invention is demonstrated. The photoelectric conversion element 10 forms the buffer layer 3 by vacuum-depositing sodium halide on the surface of the light transmissive negative electrode 2. The method of vacuum vapor deposition is not particularly limited, and for example, a vacuum vapor deposition method such as resistance heating type or electron beam type can be adopted. A film forming method may be selected according to the film characteristics to be obtained, such as a film forming speed.

  The photoelectric conversion layer 4 can be manufactured by dissolving the p-type organic semiconductor and the n-type organic semiconductor in a solvent, forming an organic semiconductor composition solution, and applying the solution onto the buffer layer 3 to form a film. The coating method is not particularly limited. For example, dip coating method, spray coating method, ink jet method, aerosol jet method, spin coating method, bead coating method, wire bar coating method, blade coating method, roller coating method, Methods such as a curtain coating method, a slit die coater method, a gravure coater method, a slit reverse coater method, a micro gravure method, and a comma coater method can be employed.

  When the spin coating method is employed as the coating method, the photoelectric conversion layer 4 having a desired film thickness can be obtained by adjusting the spin coating rotation speed and the solution concentration. The spin coating conditions are not particularly limited, but if the rotational speed is small, film thickness unevenness is caused. Therefore, the rotational speed is preferably 1000 to 8000 rpm, and more preferably 2000 to 6000 rpm. At this time, material denaturation can be suppressed by forming a film in an inert gas atmosphere as necessary.

  Solvents for dissolving the organic semiconductor include tetrahydrofuran, 1,2-dichloroethane, cyclohexane, chloroform, bromoform, benzene, toluene, o-xylene, chlorobenzene, bromobenzene, iodobenzene, o-dichlorobenzene, anisole, methoxybenzene, Examples include chlorobenzene and pyridine. These solvents may be used singly or in combination of two or more, but o-dichlorobenzene, chlorobenzene, bromobenzene, iodo having high solubility especially for each of p-type organic semiconductor and n-type organic semiconductor. Benzene, chloroform, and mixtures thereof are preferred. More preferably, o-dichlorobenzene, chlorobenzene, and a mixture thereof having the highest solubility for each of the p-type organic semiconductor and the n-type organic semiconductor are used.

  In the above step, the organic semiconductor composition solution may contain a high-boiling compound as an additive in addition to the p-type organic semiconductor and the n-type organic semiconductor. In the process of forming the photoelectric conversion layer 4 by containing a high-boiling compound, a fine and continuous phase separation structure of a p-type organic semiconductor and an n-type organic semiconductor is formed, so that the photoelectric conversion layer is excellent in photoelectric conversion efficiency. 4 can be obtained.

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

  The amount of the high-boiling compound added is not particularly limited as long as the p-type organic semiconductor and the n-type organic semiconductor do not precipitate and give a uniform solution, but the volume fraction of the solvent is 0.1% to 20%. % Is preferable, and a range of 0.5% to 10% is more preferable. When the addition amount is in the range of 0.1% to 20%, the photoelectric conversion layer 4 having a fine and continuous phase separation structure can be formed. When there is more addition amount than 20%, there exists a tendency for the drying rate of a solvent and an additive to become slow.

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

  When the photoelectric conversion layer 4 is formed, heat or solvent annealing may be performed as necessary. By applying the annealing treatment, the crystallinity of the material of the photoelectric conversion layer 4 and the phase separation structure between the p-type organic semiconductor and the n-type organic semiconductor can be changed, and an element having excellent photoelectric conversion characteristics can be obtained.

  Thermal annealing is performed by holding the substrate 1 on which the photoelectric conversion layer 4 is formed at a desired temperature. Thermal annealing may be performed under reduced pressure or in an inert gas atmosphere, and a preferable temperature is 40 ° C to 200 ° C, more preferably 70 ° C to 150 ° C. If the temperature is low, sufficient effects cannot be obtained, and if the temperature is too high, the photoelectric conversion layer 4 is oxidized and / or decomposed, and sufficient photoelectric conversion characteristics cannot be obtained.

  The solvent annealing is performed by holding the substrate 1 on which the photoelectric conversion layer 4 is formed in a solvent atmosphere for a desired time. The solvent used for annealing at this time is not particularly limited, but is preferably a good solvent for the photoelectric conversion layer 4. The solvent annealing may be performed in a state where the organic semiconductor composition constituting the photoelectric conversion layer 4 is applied on the buffer layer 3 formed on the substrate 1 and the solvent remains in the composition.

  Here, if necessary, the hole transport layer 6 may be laminated on the photoelectric conversion layer 4. The formation method of the positive hole transport layer 6 is not specifically limited, A vacuum evaporation method, sputtering method, the apply | coating method etc. can be used. In order to manufacture the photoelectric conversion element 10 at low cost, a method suitable for a continuous process is more preferable, and a coating method is particularly preferable. Furthermore, by forming the positive electrode 5 on the photoelectric conversion layer 4 or the hole transport layer 6, the photoelectric conversion element 10 of the present invention having a laminated structure can be manufactured.

  The photoelectric conversion element of the present invention may be used as a tandem photoelectric conversion element. The tandem photoelectric conversion element can be produced by a method known in the literature, for example, the method described in Science, 2007, Vol. 317, p.222. Specifically, the charge recombination layer absorbs light up to the long wavelength side (up to 1100 nm) and can perform photoelectric conversion, and photoelectric conversion capable of photoelectric conversion in the ultraviolet to visible light region (190 to 700 nm). A structure sandwiched between the conversion layers (II) may be mentioned. The order of connection between the photoelectric conversion layer (I) and the photoelectric conversion layer (II) may be reversed.

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

  The charge recombination layer preferably has optical transparency so that the plurality of photoelectric conversion layers can absorb light. In addition, the charge recombination layer only needs to be designed so that holes and electrons are sufficiently recombined. Therefore, the charge recombination layer does not necessarily have to be a film. For example, the charge recombination layer is uniformly formed on the photoelectric conversion layer. It may be a metal cluster. Therefore, the charge recombination layer includes a very thin metal film or metal cluster made of gold, platinum, chromium, nickel, lithium, magnesium, calcium, tin, silver, aluminum or the like and having a light transmittance of several nm or less. (Including alloys), ITO, IZO, AZO, GZO, FTO, highly transparent metal oxide films and clusters such as titanium oxide and molybdenum oxide, conductive organic material films such as PEDOT to which PSS is added, or These composites are used. For example, uniform silver clusters can be formed by depositing silver so as to be several nm or less on a quartz oscillator film thickness monitor using a vacuum deposition method. In addition, if a titanium oxide film is formed, for example, the sol-gel method described in Advanced Materials, 2006, Vol. 18, p.572 may be used. If it is a composite metal oxide such as ITO or IZO, the film may be formed by sputtering. The formation method and type of these charge recombination layers should be appropriately selected in consideration of the non-destructive property to the photoelectric conversion layer when the charge recombination layer is formed, the formation method of the next photoelectric conversion layer, and the like. That's fine.

  The photoelectric conversion element of the present invention is excellent in photoelectric conversion efficiency, and can be applied to various optical sensors including solar cells.

  Examples of the present invention will be described in detail below, but the scope of the present invention is not limited to these examples. In addition, evaluation in an Example was performed as follows.

[Measurement of film thickness of photoelectric conversion layer]
The film thickness of the photoelectric conversion layer of an Example and a comparative example was measured on the conditions of a stylus pressure: 3 mg and a measurement range: 50 kÅ using a contact-type step meter (DEKTAK8: manufactured by Veeco).

[Measurement of photoelectric conversion efficiency]
Photoelectric conversion efficiencies of the photoelectric conversion elements prepared in Examples and Comparative Examples are solar simulator (OTENTO-SUNII: manufactured by Spectrometer Co., Ltd.) and source meter (KEITHLEY2400: manufactured by KEITHLEY), irradiation spectrum is AM1.5, irradiation The intensity was measured at 100 mW / cm ² . The irradiation intensity at the time of measurement was adjusted to be a solar cell evaluation standard using a photodiode (BS-520, manufactured by Spectrometer Co., Ltd.). At the time of measurement, an irradiation light mask having the same area as the light receiving area of the photoelectric conversion element was worn to eliminate excessive light incidence.

Example 1
A substrate (manufactured by Geomatech) with 155 nm indium-tin-oxide formed on 0.7 mm glass was ultrasonically cleaned with semicoclean (manufactured by Furuuchi Chemical), ultrapure water, acetone and isopropanol for 10 minutes. After drying, ozone cleaning was performed using a UV-O ₃ cleaner (manufactured by Philgen) for 20 minutes.
The ozone-cleaned substrate was introduced into a resistance heating vacuum deposition apparatus, and a commercially available sodium fluoride (99.99%) was vacuumed on the ITO substrate under a reduced pressure condition of 5.0 × 10 ⁻⁵ Pa. A buffer layer was formed by vapor deposition. The deposition rate during vacuum deposition can be monitored by a quartz oscillator, and the deposition rate is controlled to 0.2 kg / sec to obtain a buffer layer having a thickness of 2.0 nm. The ITO substrate on which the buffer layer was formed was introduced into a glove box filled with nitrogen.

Subsequently, commercially available poly (3-hexylthiophene-2,5-diyl) (P3HT, manufactured by Aldrich) as an electron-donating organic semiconductor and [6,6] -phenyl C ₆₁ butyric acid as an electron-accepting organic semiconductor. Methyl ester (manufactured by Frontier Acabon) was mixed at a weight ratio of 60:40, and a chlorobenzene solution was added under a nitrogen atmosphere to adjust the solid content concentration to 2.7% by weight. After stirring, the solution was filtered through a 0.45 μm polytetrafluoroethylene filter to obtain a uniform solution. The prepared solution was spin-coated at 2500 rpm for 30 seconds on the buffer layer on the ITO substrate under a nitrogen atmosphere. After vacuum drying for 3 hours, thermal annealing was performed at 150 ° C. for 30 minutes. The film thickness of the obtained photoelectric conversion layer was 90 nm.

Subsequently, the substrate was introduced into a resistance heating vacuum deposition apparatus, and 5 nm molybdenum trioxide (purity 99.99%) was vacuum deposited under a reduced pressure condition of 5.0 × 10 ⁻⁵ Pa to transport holes. A layer was formed. Furthermore, 80 nm of silver (Ag) (purity 99.999%) was vacuum-deposited to produce a photoelectric conversion element. The power generation area of the produced photoelectric conversion element was 0.25 cm ² . Subsequently, a UV curable resin was applied to a glass sealing cap, bonded to the produced photoelectric conversion element, and then irradiated with a UV lamp to seal the photoelectric conversion element. As a result of measuring the photoelectric conversion efficiency of the produced photoelectric conversion element, the photoelectric conversion efficiency was 3.63%.

(Example 2)
Commercially available poly (3-hexylthiophene-2,5-diyl) (manufactured by Aldrich) and [6,6] -diphenyl C ₆₂ bis (butyric acid methyl ester) (Frontier Acabon) as an electron-accepting organic semiconductor Manufactured at a weight ratio of 55:45, and a chlorobenzene solution was added under a nitrogen atmosphere to adjust the solid concentration to 2.7% by weight. After stirring at 40 ° C. for 3 hours, 0.45 μm The solution was filtered through a polytetrafluoroethylene filter to obtain a uniform solution. Subsequently, the prepared solution was spin-coated at 3500 rpm for 30 seconds on the buffer layer on the ITO substrate produced by the same method as in Example 1 in a nitrogen atmosphere. The film thickness of the obtained photoelectric conversion layer was 90 nm. A photoelectric conversion element was produced in the same manner as in Example 1 except that the material of the photoelectric conversion layer was changed. As a result of measuring the photoelectric conversion efficiency of the produced photoelectric conversion element, the photoelectric conversion efficiency was 3.68%.

Example 3
A π-electron conjugated polymer (PSiTTPD) composed of a monomer unit represented by the following chemical formula (1) as an electron-donating organic semiconductor and [6,6] -phenyl C ₇₁ butyric acid methyl as an electron-accepting organic semiconductor Ester (manufactured by Frontiacabon) was mixed at a weight ratio of 40:60, and a chlorobenzene solution was added under a nitrogen atmosphere to prepare a solid concentration of 2.2% by weight. After stirring at 0 ° C. for 3 hours, the solution was filtered through a 0.45 μm polytetrafluoroethylene filter to obtain a uniform solution. Subsequently, the prepared solution was spin-coated at 1600 rpm for 30 seconds on the buffer layer on the ITO substrate produced by the same method as in Example 1 in a nitrogen atmosphere. The film thickness of the obtained photoelectric conversion layer was 90 nm. A photoelectric conversion element was produced in the same manner as in Example 2 except that the material of the photoelectric conversion layer was changed. As a result of measuring the photoelectric conversion efficiency of the produced photoelectric conversion element, the photoelectric conversion efficiency was 6.50%.

(Comparative Example 1)
A photoelectric conversion element was produced in the same manner as in Example 1 except that the buffer layer made of lithium fluoride was not formed on the ITO substrate. As a result of measuring the photoelectric conversion efficiency of the produced photoelectric conversion element, the photoelectric conversion efficiency was 1.73%.

(Comparative Example 2)
In a nitrogen atmosphere, 2-ethoxyethanol was added to commercially available cesium carbonate to adjust the concentration to 0.2% by weight, stirred at room temperature, and then filtered through a 0.45 μm polyvinylidene fluoride filter to make it uniform. Obtained an aqueous solution. The prepared cesium carbonate solution was spin-coated at 2000 rpm for 60 seconds on an ITO substrate cleaned in the same manner as described above in a nitrogen atmosphere, and heat treatment was performed at 170 ° C. for 10 minutes using a hot plate. A photoelectric conversion element was produced in the same manner as in Example 1 except that the buffer layer was changed to cesium carbonate. As a result of measuring the photoelectric conversion efficiency of the produced photoelectric conversion element, the photoelectric conversion efficiency was 2.78%.

(Comparative Example 3)
In a nitrogen atmosphere, dehydrated ethanol was added to commercially available titanium isopropoxide to prepare a 300-fold diluted solution, stirred at room temperature, and then filtered through a 0.45 μm polyvinylidene fluoride filter to obtain a uniform aqueous solution. Got. In the air, the prepared titanium isopropoxide container was spin-coated at 2000 rpm for 60 seconds on the cleaned ITO substrate. By allowing it to stand at room temperature for 12 hours, the hydrolysis reaction was advanced to form a titanium oxide layer on the ITO substrate. A photoelectric conversion element was produced in the same manner as in Example 1 except that the buffer layer was changed to titanium oxide. As a result of measuring the photoelectric conversion efficiency of the produced photoelectric conversion element, the photoelectric conversion efficiency was 2.85%.

(Comparative Example 4)
The ITO substrate cleaned by the same method as described above was introduced into a resistance heating vacuum deposition apparatus, and calcium (99.5%) having a thickness of 2 nm was vacuum deposited under a reduced pressure condition of 5.0 × 10 ⁻⁵ Pa. . Subsequently, the solution for the photoelectric conversion layer prepared in Example 1 was spin-coated at 2500 rpm for 30 seconds in a nitrogen atmosphere, and thermal annealing was performed at 150 ° C. for 30 minutes using a hot plate. A photoelectric conversion element was produced in the same manner as in Example 1 except that the buffer layer was changed to calcium. As a result of measuring the photoelectric conversion efficiency of the produced photoelectric conversion element, the photoelectric conversion efficiency was 3.20%.

(Comparative Example 5)
On the ITO substrate cleaned in the same manner as described above, a commercially available lithium fluoride (Fluuchi 99.99%) was deposited to a thickness of 2.0 nm under the condition of a deposition rate of 0.2 Å / sec. A photoelectric conversion element was produced in the same manner as in Example 1 except that it was formed. As a result of measuring the photoelectric conversion efficiency of the produced photoelectric conversion element, the photoelectric conversion efficiency was 1.53%.

(Comparative Example 6)
A commercially available PEDOT: PSS (manufactured by Clevios) was spin-coated at 6000 rpm for 60 seconds on the ITO substrate washed in the same manner as described above. After the substrate on which PEDOT: PSS was formed was introduced into a glove box in a nitrogen atmosphere, heat treatment was performed at 150 ° C. for 10 minutes. Subsequently, the solution for the photoelectric conversion layer prepared in Example 1 was spin-coated at 2500 rpm for 30 seconds, and thermal annealing was performed at 150 ° C. for 30 minutes using a hot plate.
Subsequently, the substrate was introduced into a resistance heating vacuum deposition apparatus, and sodium fluoride having a film thickness of 0.5 nm was vacuum deposited under a reduced pressure condition of 5.0 × 10 ⁻⁵ Pa. Furthermore, 80 nm of aluminum (purity 99.999%) was vacuum-deposited to produce a photoelectric conversion element. The power generation area of the photoelectric conversion element was 0.25 cm ² . Subsequently, a UV curable resin was applied to a glass sealing cap, bonded to the produced photoelectric conversion element, and then irradiated with a UV lamp to seal the photoelectric conversion element. As a result of measuring the photoelectric conversion efficiency of the produced photoelectric conversion element, the photoelectric conversion efficiency was 0.73%.

(Comparative Example 7)
A photoelectric conversion element was produced in the same manner as in Comparative Example 6 except that the film thickness of sodium fluoride was changed to 2.0 nm. As a result of measuring the photoelectric conversion efficiency of the produced photoelectric conversion element, the photoelectric conversion efficiency was 0.01%.

  Tables 1 and 2 show the conversion efficiencies of the photoelectric conversion elements obtained in Examples 1 to 3 and Comparative Examples 1 to 7.

  From Table 1 and Table 2, it is clear that the photoelectric conversion elements of the present invention that are Examples 1 to 3 exhibit higher conversion efficiency than the photoelectric conversion elements of Comparative Examples 1 to 7 that are not applicable to the present invention. became.

  The photoelectric conversion element of the present invention having a buffer layer made of sodium halide between a light-transmissive negative electrode and a photoelectric conversion layer has excellent photoelectric conversion efficiency and can be applied to various photosensors including solar cells. It is.

  1 is a substrate, 2 is a light transmissive negative electrode, 3 is a buffer layer, 4 is a photoelectric conversion layer, 5 is a positive electrode, 6 is a hole transport layer, and 10 is a photoelectric conversion element.

Claims (7)

  A photoelectric conversion element having a photoelectric conversion layer containing an organic semiconductor between a positive electrode and a negative electrode, wherein at least the negative electrode has light transmittance, and between the photoelectric conversion layer and the negative electrode, A photoelectric conversion element having a buffer layer containing sodium halide.   The photoelectric conversion element according to claim 1, further comprising a hole transport layer including a hole transport material between the photoelectric conversion layer and the positive electrode.   The photoelectric conversion element according to claim 1, wherein the negative electrode is indium tin oxide.   The photoelectric conversion element according to claim 1, wherein the photoelectric conversion layer is a mixture of an electron donating organic semiconductor and an electron accepting organic semiconductor.   The electron-donating organic semiconductor includes a monomer unit having at least part of a heterocyclic skeleton group selected from thiophene, fluorene, carbazole, dibenzosilole, dibenzogermole, benzodithiophene, and diketopyrrolopyrrole. It is an electron conjugated polymer, The photoelectric conversion element of Claim 4 characterized by the above-mentioned.   The photoelectric conversion element according to claim 4, wherein the electron-accepting organic semiconductor is a fullerene derivative.   A photoelectric conversion layer including an organic semiconductor between a positive electrode and a negative electrode having optical transparency; and a buffer layer including sodium halide between the photoelectric conversion layer and the negative electrode. A method of manufacturing a photoelectric conversion element that may have a hole transport layer between a conversion layer and the positive electrode, wherein the buffer layer is formed by vacuum-depositing sodium halide on the negative electrode. A method for producing a photoelectric conversion element.

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