JP5745294B2 - Organic thin film solar cell - Google Patents

Description

  The present invention relates to an organic thin film solar cell, and more particularly to an organic thin film solar cell with improved performance of a bulk hetero type organic thin film solar cell.

Organic thin-film solar cells using organic thin-film semiconductors combined with conductive polymers and fullerenes are cheaper and easier to manufacture than conventional solar cells, and have features such as light weight and flexibility. Development is expected.
The power generation mechanism (photoelectric conversion process) of the organic thin film solar cell is as follows. First, organic molecules absorb light energy to generate excitons (a pair of excited electrons and holes). This exciton diffuses and moves while forming a pair, reaches the pn junction interface, and separates charges. Then, electrons and holes generated thereby move to each electrode interface, and current can be taken out.
Among the organic thin-film solar cells described above, various organic thin-film solar cells having a bulk heterostructure have been studied because they exhibit high conversion efficiency.

Now, the photoelectric conversion efficiency of a solar cell is represented by the product of light absorption efficiency, exciton diffusion efficiency, charge transfer efficiency, and charge injection efficiency. As one method for improving the photoelectric conversion efficiency, an attempt has been made to improve the charge injection efficiency by suppressing a reverse charge injection by providing a buffer layer between the electrode and the organic thin film semiconductor layer.
Among these, as a typical buffer layer on the anode side formed between the transparent electrode and the photoelectric conversion layer, for example, poly (3,4-ethylenedioxythiophene) / poly (styrenesulfonate) (PEDOT / PSS) is used. Such an anode buffer layer can be formed by a solution coating method having a low manufacturing cost.
On the other hand, as the buffer layer on the cathode side formed between the metal electrode and the photoelectric conversion layer, for example, metal oxide such as lithium fluoride (LiF), molybdenum oxide (MoO ₃ ), vanadium oxide (V ₂ O ₅ ), etc. Things are used.

  The above-described cathode buffer layer cannot be formed by a solution coating method applicable to the anode buffer layer, and is usually formed by a vacuum vapor deposition method, and thus has a drawback that the production cost is increased. However, there are few reports on a cathode buffer layer that can be produced by a solution coating method, and organic thin-film solar cells using a cathode buffer layer formed by coating a terphenyl derivative have been proposed ( Patent Document 1) has a problem that sufficient photoelectric conversion efficiency has not been achieved.

  The present inventors can easily form a cathode buffer layer by a solution coating method by using a polymer compound having an amino functional group or an imino functional group at the end as a buffer material on the cathode side, and also provide photoelectric conversion efficiency. The present inventors have found that a new type of organic thin-film solar cell having a high value can be obtained.

That is, as a first aspect, the present invention provides a transparent electrode on a transparent substrate, a metal electrode, a photoelectric conversion layer interposed between both electrodes, a metal electrode between the photoelectric conversion layer and the metal electrode, An organic thin film solar cell comprising a cathode buffer layer formed so as to be in contact with the cathode, wherein the cathode buffer layer is made of a polymer compound having an amino functional group or an imino functional group at its terminal. It relates to batteries.
As a second aspect, the polymer compound is a hyperbranched polymer having a weight average molecular weight of 1,000 to 2,000,000 measured in terms of polystyrene by gel permeation chromatography, The present invention relates to an organic thin film solar cell described in the viewpoint.
As a third aspect, the polymer compound comprises a monomer A having two or more radically polymerizable double bonds in the molecule, 5 mol% to 200 mol% of amino functional group or imino functional with respect to the monomer A. It is related with the organic thin-film solar cell as described in a 1st viewpoint or a 2nd viewpoint which is a hyperbranched polymer obtained by making it superpose | polymerize in presence of the polymerization initiator B which has group.
As a 4th viewpoint, the polymerization initiator B which has the said amino functional group or imino functional group is related with the organic thin-film solar cell as described in a 3rd viewpoint which is a polymerization initiator which has a heterocyclic amine structure.
As a 5th viewpoint, the polymerization initiator B which has the said amino functional group or an imino functional group is a polymerization initiator which has a functional group represented by Formula [1], The organic as described in a 3rd viewpoint or a 4th viewpoint The present invention relates to a thin film solar cell.
(In the formula [1], R ¹ , R ² and R ³ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or a hydroxyalkyl group having 1 to 6 carbon atoms, and R ¹ Any two or more of R ² and R ³ may be combined with the nitrogen atom to which they are bonded to form a ring.)
As a sixth aspect, the polymerization initiator B having the amino functional group or imino functional group is a polymerization initiator represented by the formula [2], and is described in any one of the third to fifth aspects. The present invention relates to an organic thin film solar cell.
(In the formula [2], R ¹ , R ² and R ³ each independently represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or a hydroxyalkyl group having 1 to 6 carbon atoms, and R ¹ Any two or more of R ² and R ³ may be combined with the nitrogen atom to which they are bonded to form a ring, and R ⁴ and R ⁵ each independently represent 1 to 1 carbon atoms. 6 represents an alkyl group.)
As a seventh aspect, A) a step of preparing a transparent substrate on which the transparent electrode is formed on the substrate surface, B) a step of forming a photoelectric conversion layer on or above it, and C) on the photoelectric conversion layer or A method for producing an organic thin-film solar cell, comprising: forming a cathode buffer layer above; and D) further laminating a metal electrode thereon.
Among these, the most preferred embodiment of the present invention is a transparent electrode on a transparent substrate, a metal electrode, a photoelectric conversion layer interposed between both electrodes, and a metal electrode between the photoelectric conversion layer and the metal electrode. In an organic thin film solar cell comprising a cathode buffer layer formed so as to come into contact with
The cathode buffer layer is made of a polymer compound having an amino functional group or an imino functional group at its end,
The polymer compound comprises an aromatic vinyl hydrocarbon as monomer A having two or more radically polymerizable double bonds in the molecule, 5 mol% to 200 mol% of amino functional group or The present invention relates to an organic thin film solar cell characterized by being a highly branched polymer obtained by polymerization in the presence of a polymerization initiator B having an imino functional group, and a method for producing the same.

In the organic thin film solar cell of the present invention, a cathode buffer layer can be easily formed by a solution coating method by using a polymer compound having an amino functional group or an imino functional group at the terminal as a buffer material on the cathode side.
And this invention can provide the organic thin-film solar cell which has a high photoelectric conversion efficiency comparable to the conventional solar cell using the lithium fluoride formed with the vapor deposition method used as a cathode buffer layer.

FIG. 1 is a schematic view of an organic thin film solar cell of the present invention. FIG. 2 is a ¹ H-NMR spectrum of the hyperbranched polymer used for the cathode buffer layer.

The organic thin film solar cell of the present invention comprises a transparent electrode on a transparent substrate, a metal electrode, a photoelectric conversion layer interposed between both electrodes, and a metal electrode in contact with the photoelectric conversion layer and the metal electrode. The cathode buffer layer is formed of a polymer compound having an amino functional group or an imino functional group at its terminal.
The components constituting the cathode buffer layer and the components constituting the organic thin film solar cell of the present invention will be described below.

<Cathode buffer layer>
The cathode buffer material according to the present invention is a polymer compound having an amino functional group or an imino functional group at its end, and more preferably has a weight average molecular weight of 1,000 to 2 measured in terms of polystyrene by gel permeation chromatography. It is a hyperbranched polymer that is 1,000,000.
In particular, the polymer compound suitable as a cathode buffer material according to the present invention includes a monomer A having two or more radical polymerizable double bonds in the molecule, in an amount of 5 mol% to 200 mol% with respect to the monomer A. It is a hyperbranched polymer obtained by polymerizing in the presence of a polymerization initiator B having an amino functional group or an imino functional group.

  In the present invention, the monomer A having two or more radically polymerizable double bonds in the molecule preferably has one or both of a vinyl group and a (meth) acryl group, and in particular, a divinyl compound or di (meta). ) An acrylate compound is preferred. In the present invention, the (meth) acrylate compound refers to both an acrylate compound and a methacrylate compound. For example, (meth) acrylic acid refers to acrylic acid and methacrylic acid.

Examples of such a monomer A include organic compounds shown in the following (A1) to (A7).
(A1) Vinyl hydrocarbon:
(A1-1) Aliphatic vinyl hydrocarbons; isoprene, butadiene, 3-methyl-1,2-butadiene, 2,3-dimethyl-1,3-butadiene, 1,2-polybutadiene, pentadiene, hexadiene, octadiene (A1-2) Alicyclic vinyl hydrocarbons; cyclopentadiene, cyclohexadiene, cyclooctadiene, norbornadiene, etc. (A1-3) aromatic vinyl hydrocarbons; divinylbenzene, divinyltoluene, divinylxylene, trivinylbenzene , Divinylbiphenyl, divinylnaphthalene, divinylfluorene, divinylcarbazole, divinylpyridine, etc. (A2) Vinyl esters, allyl esters, vinyl ethers, allyl ethers, vinyl ketones:
(A2-1) vinyl ester; divinyl adipate, divinyl maleate, divinyl phthalate, divinyl isophthalate, divinyl itaconate, vinyl (meth) acrylate, etc. (A2-2) allyl ester; diallyl maleate, diallyl phthalate, Diallyl isophthalate, diallyl adipate, allyl (meth) acrylate, etc. (A2-3) vinyl ether; divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, etc. (A2-4) allyl ether; diallyl ether, diallyloxyethane, tri Allyloxyethane, tetraallyloxyethane, tetraallyloxypropane, tetraallyloxybutane, tetramethallyloxyethane, etc. (A2-5) vinyl ketone; divinyl ketone, diallyl Tons, etc. (A3) (meth) acrylic acid ester:
Ethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, glycerol tri (meth) acrylate, Pentaerythritol tetra (meth) acrylate, alkoxy titanium tri (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 2-methyl-1,8-octanediol di (meth) acrylate, 1,9-nonanediol Di (meth) acrylate, 1,10-decanediol di (meth) acrylate, tricyclodecane dimethanol di (meth) acrylate, dioxane glycol di (meth) acrylate, 2-hydroxy 1-acryloyloxy-3-methacryloyloxypropane, 2-hydroxy-1,3-di (meth) acryloyloxypropane, 9,9-bis [4- (2- (meth) acryloyloxyethoxy) phenyl] fluorene, un Decylenoxyethylene glycol di (meth) acrylate, bis [4- (meth) acryloylthiophenyl] sulfide, bis [2- (meth) acryloylthioethyl] sulfide, 1,3-adamantanediol di (meth) acrylate, 1 , 3-Adamantanedimethanol di (meth) acrylate, bisphenol A diethoxydi (meth) acrylate, etc. (A4) Vinyl compounds having a polyalkylene glycol chain:
Polyethylene glycol (molecular weight 300) di (meth) acrylate, polypropylene glycol (molecular weight 500) di (meth) acrylate, etc. (A5) Nitrogen-containing vinyl compounds:
Diallylamine, diallyl isocyanurate, diallyl cyanurate, methylenebis (meth) acrylamide, bismaleimide, etc. (A6) silicon-containing vinyl compounds:
Dimethyldivinylsilane, divinylmethylphenylsilane, diphenyldivinylsilane, 1,3-divinyl-1,1,3,3-tetramethyldisilazane, 1,3-divinyl-1,1,3,3-tetraphenyldisilazane (A7) fluorine-containing vinyl compounds such as dietoxydivinylsilane:
1,4-divinylperfluorobutane, 1,6-divinylperfluorohexane, 1,8-divinylperfluorooctane, etc.

  Among these, preferred are the aromatic vinyl hydrocarbon compounds of the above group (A1-3), vinyl esters, allyl esters, vinyl ethers, allyl ethers and vinyl ketones of the group (A2), (meth) acrylic of the group (A3). An acid ester, a vinyl compound having a polyalkylene glycol chain of (A4) group, and a nitrogen-containing vinyl compound of (A5) group. Particularly preferred are divinylbenzene belonging to group (A1-3), diallyl phthalate belonging to group (A2), ethylene glycol di (meth) acrylate belonging to group (A3), 1,3-adamantane dimethanol di (meta). ) Acrylate, tricyclodecane dimethanol di (meth) acrylate, bisphenol A diethoxydi (meth) acrylate, 9,9-bis [4- (2- (meth) acryloyloxyethoxy) phenyl] fluorene and (A5) group Methylenebis (meth) acrylamide. Among these, divinylbenzene, ethylene glycol di (meth) acrylate, and bisphenol A diethoxydi (meth) acrylate are preferable, and divinylbenzene is more preferable.

In the present invention, the polymerization initiator B having an amino functional group or an imino functional group includes an amino group and an amine or imine compound in which a hydrogen atom of ammonia is substituted with a monovalent or divalent hydrocarbon residue, as well as a heterocyclic ring. A polymerization initiator containing an amine.
Examples thereof include primary to tertiary aliphatic amines such as cyclohexylamine, dimethylamine, triethylamine, phenethylamine, and dibenzylamine; primary to tertiary amines such as aniline, dimethylaminopyridine, diphenylamine, and triphenylamine. Tertiary aromatic amines; imines such as methanimine, propan-2-imine, N-methylethaneimine; pyrroline, pyrrolidine, pyrazoline, pyrazolidine, imidazoline, imidazolidine, dihydropyridine, tetrahydropyridine, piperidine, dihydropyrimidine, tetrahydropyrimidine, hexa Such as hydropyrimidine, dihydropyrazine, tetrahydropyrazine, piperazine, morpholine, thiomorpholine, quinuclidine, 1,4-diazabicyclo [2.2.2] octane Cyclic heterocyclic amines; polymerization initiators containing structures such as aromatic heterocyclic amines such as pyrrole, pyrazole, imidazole, pyridine, pyridazine, pyrimidine, pyrazine, quinoline, isoquinoline, cinnoline, phthalazine, quinazoline, quinoxaline, carbazole Is mentioned.

Therefore, the polymerization initiator B having an amino functional group or imino functional group is preferably a polymerization initiator having a heterocyclic amine structure, or a polymerization initiator having a functional group represented by the following formula [1], particularly An azo polymerization initiator can be mentioned.
In the formula [1], R ¹ , R ² and R ³ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or a hydroxyalkyl group having 1 to 6 carbon atoms. Further, any two or more of R ¹ , R ² and R ³ may be combined with the nitrogen atom to which they are bonded to form a ring, and those forming a ring are more preferred.

Examples of the functional group represented by the above formula [1] include, but are not limited to, groups represented by the following formulas [A] to [M].

Examples of the azo polymerization initiator composed of a compound having a functional group represented by the above formulas [A] to [M] include a polymerization initiator represented by the following formula [2].
In the formula [2], R ¹ , R ² and R ³ represent those defined in the formula [1], and R ⁴ and R ⁵ each independently represent an alkyl group having 1 to 6 carbon atoms. .

Examples of the azo polymerization initiator represented by the formula [2] include compounds shown in the following (1) to (2);
(1) Cyclic azoamidine compound:
2,2′-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane] disulfate dihydrate, 2,2′-azobis [2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] -propane] dihydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) ) Propane], 2,2′-azobis (1-imino-1-pyrrolidino-2-methylpropane) dihydrochloride and the like;
(2) Azoamidine compound:
2,2′-azobis (2-methylpropionamidine) dihydrochloride, 2,2′-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] tetrahydrate, and the like.

Among the azo polymerization initiators, 2,2′-azobis [2-
(2-Imidazolin-2-yl) propane] or 2,2′-azobis (1-imino-1-pyrrolidino-2-methylpropane) dihydrochloride is particularly preferred.

  The polymerization initiator B is used in an amount of 5 mol% to 200 mol%, preferably 15 mol% to 200 mol%, more preferably 15 mol% to 170 mol%, and more preferably based on the monomer A. Is used in an amount of 50 mol% to 100 mol%.

  The hyperbranched polymer used in the present invention is obtained by polymerizing the aforementioned monomer A in the presence of a predetermined amount of a polymerization initiator B. As the polymerization method, known methods such as solution polymerization, dispersion polymerization, precipitation Polymerization, bulk polymerization and the like can be mentioned, among which solution polymerization or precipitation polymerization is preferable. In particular, it is preferable to carry out the reaction by solution polymerization in an organic solvent from the viewpoint of molecular weight control.

  Examples of organic solvents used here include aromatic hydrocarbon solvents such as benzene, toluene, xylene, ethylbenzene, and tetralin; aliphatic or alicyclic hydrocarbon solvents such as n-hexane, n-heptane, mineral spirit, and cyclohexane Solvent: Halogen solvents such as methyl chloride, methyl bromide, methyl iodide, methylene dichloride, chloroform, carbon tetrachloride, trichloroethylene, perchloroethylene, orthodichlorobenzene; ethyl acetate, butyl acetate, methoxybutyl acetate, methyl cellosolve acetate , Ethyl cellosolve acetate, propylene glycol monomethyl ether acetate, etc. ester or ester ether solvents; diethyl ether, tetrahydrofuran, 1,4-dioxane, methyl cellosolve, ethyl celloso Ether solvents such as butyl, cellosolve, propylene glycol monomethyl ether; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, di-n-butyl ketone, cyclohexanone; methanol, ethanol, n-propanol, isopropanol, n-butanol, iso Alcohol solvents such as butanol, tert-butanol, 2-ethylhexyl alcohol, benzyl alcohol, ethylene glycol, propylene glycol, propylene glycol monomethyl ether, ethyl lactate; N, N′-dimethylformamide, N, N′-dimethylacetamide, N -Amide solvents such as methyl-2-pyrrolidone; Sulfoxide solvents such as dimethyl sulfoxide; Aliphatic carboxylic acid solvents such as acetic acid and propionic acid And mixed solvents of two or more thereof.

Among these, preferred are aromatic hydrocarbon solvents, halogen solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, amide solvents, aliphatic carboxylic acid solvents, and the like. Benzene, toluene, xylene, orthodichlorobenzene, ethyl acetate, butyl acetate, propylene glycol monomethyl ether acetate, tetrahydrofuran, dioxane, methyl ethyl ketone, methyl isobutyl ketone, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol , Tert-butanol, ethylene glycol, propylene glycol monomethyl ether, N, N′-dimethylformamide, N, N′-dimethylacetamide, N-methyl-2-pyrrolidone and vinegar , And the most preferred are n- propanol, n- butanol, ethylene glycol, N, N'-dimethylformamide, N, N'-dimethylacetamide, N- methyl-2-pyrrolidone and acetic acid.

  When the polymerization reaction is performed in the presence of an organic solvent, the content of the organic solvent in the entire polymerization reaction product is preferably 5 to 200 parts by weight, more preferably 10 to 150 parts by weight, with respect to 1 part by weight of the monomer A. Most preferably, it is 30 to 120 parts by mass.

The polymerization reaction is carried out under normal pressure, under pressure and under pressure, or under reduced pressure, and is preferably carried out under normal pressure in view of simplicity of the apparatus and operation. Further, preferably carried out in an atmosphere of inert gas such as N _2.
The polymerization temperature is arbitrary as long as it is not higher than the boiling point of the reaction mixture, but from the viewpoint of polymerization efficiency and molecular weight control, it is preferably 50 ° C. or higher and 200 ° C. or lower, more preferably 80 ° C. or higher and 150 ° C. or lower, more preferably 80 ° C. The temperature is 120 ° C. or lower.
Although the reaction time varies depending on the reaction temperature, the types and ratios of the monomer A and the polymerization initiator B, the organic solvent type, etc., it cannot be defined unconditionally, but preferably 30 minutes or more and 720 minutes or less, more preferably It is 40 minutes or more and 540 minutes or less.

  After completion of the polymerization reaction, the obtained hyperbranched polymer is recovered by an arbitrary method, and post-treatment such as washing is performed as necessary. Examples of a method for recovering the polymer from the reaction solution include a method such as reprecipitation.

As a specific method for forming the cathode buffer layer made of the above-mentioned highly branched polymer, it is dissolved or dispersed in an appropriate solvent to form a varnish (film forming material).
The solvent used here is not particularly limited as long as it can dissolve the hyperbranched polymer uniformly, and alcohols such as water, methanol, ethanol, n-propanol, isopropanol, benzene, toluene, xylene, ethylbenzene, Aromatic hydrocarbons such as chlorobenzene and dichlorobenzene, ether compounds such as tetrahydrofuran, methyltetrahydrofuran, 1,4-dioxane, diethyl ether, diethylene glycol dimethyl ether and propylene glycol methyl ether, ester compounds such as ethyl acetate, acetone and methyl ethyl ketone , Ketone compounds such as methyl isobutyl ketone, cyclopentanone, cyclohexanone, N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetate Amide compounds such as amides, dimethyl sulfoxide, 1,2-dichloroethane, halogenated aliphatic hydrocarbons such as chloroform, n-heptane, n-hexane, aliphatic hydrocarbons such as cyclohexane or the like can be used. These organic solvents may be used alone, or two or more kinds of solvents may be mixed.
In particular, when the buffer layer has a laminated structure by a coating method, a solvent such as water, methanol, ethanol, n-propanol, and isopropanol is preferable as a solvent that can be applied without dissolving the previously applied layer.

  The concentration of the varnish is not particularly limited as long as a coating film can be formed. The total mass of the hyperbranched polymer is preferably 0.01 to 10% by mass, more preferably 0.01 to 5% by mass with respect to the total mass of the varnish. %.

Subsequently, the varnish is applied onto a desired layer, usually a photoelectric conversion layer, by spin coating, blade coating, dip coating, roll coating, bar coating, die coating, ink jet, printing (letter plate, A liquid thin layer is formed by coating with a relief printing plate, a flat plate, screen printing, or the like, and then baked to evaporate and dry the solvent, thereby forming a cured film (cathode buffer layer).
Of these coating methods, spin coating is preferred. In the case of using the spin coating method, since it can be applied in a single time, even a highly volatile solution can be used, and there is an advantage that highly uniform application can be performed.

  The method for drying the solvent is not particularly limited. For example, the solvent may be evaporated in a suitable atmosphere, that is, in an inert gas such as air or nitrogen, in a vacuum, or the like using a hot plate or an oven. Thereby, a cathode buffer layer having a uniform film formation surface can be obtained. Although a calcination temperature will not be specifically limited if a solvent can be evaporated, It is preferable to carry out at 40-250 degreeC. In this case, two or more stages of temperature changes may be applied for the purpose of developing higher uniform film forming properties or allowing the reaction to proceed on the substrate.

<Other layers constituting the organic thin-film solar cell>
The organic thin film solar cell of the present invention includes a pair of electrodes (transparent electrode, metal electrode) and a photoelectric conversion layer interposed therebetween, and has the above-described cathode buffer layer between the photoelectric conversion layer and the metal electrode. It is.
Therefore, as a method for producing the organic thin film solar cell of the present invention, after preparing another layer, for example, an anode buffer layer, if necessary, a transparent electrode (anode) substrate, and subsequently producing a photoelectric conversion layer It is preferable to form the metal electrode (cathode) by forming the above-described cathode buffer layer.
Hereinafter, materials for the electrode material, the photoelectric conversion layer, and other layers will be described.

<Transparent electrode>
As the transparent electrode, a highly light-transmitting material that can efficiently supply light irradiated to the organic thin-film solar cell to the photoelectric conversion layer is preferable, and conductivity that can efficiently extract electric energy generated in the photoelectric conversion layer is preferable. High material is preferred.
Therefore, as a transparent electrode material, a transparent electrode using a conductive metal oxide typified by indium tin oxide (ITO) and indium zinc oxide (IZO) can be cited, and a material subjected to planarization treatment is used. preferable. Of these, ITO is particularly preferable.
The transparent electrode can improve the photoelectric conversion efficiency by washing and other treatments. For example, in the case of ITO, it is possible to remove foreign substances such as organic substances on the surface by performing washing treatment such as reverse sputtering, ozone treatment, acid treatment, etc. Used. However, when the transparent electrode material contains an organic substance as a main component, the surface treatment may not be performed.

<Photoelectric conversion layer>
The photoelectric conversion layer contains an electron accepting material and an electron donating material.
Examples of the electron-accepting material include fullerene derivatives such as [6,6] -phenyl-C ₆₁ -butyric acid methyl ester (PCBM), perylene derivatives, and the like.
Examples of the electron donating material include polythiophene derivatives such as poly-3-hexylthiophene (P3HT), poly-2-methoxy-5- (3 ′, 7′-dimethyloctyloxy) -1,4-phenylene vinylene ( Examples thereof include polymers having a light absorption region in visible light, such as phenylene vinylene derivatives such as MDMO-PPV) and polyfluorene derivatives such as poly (9,9-dioctylfluorenyl-2,7-diyl) (PFO).
The blending ratio of the electron-accepting material and the electron-donating material is not particularly limited, but the mass ratio is, for example, electron-accepting material: electron-donating material = 5: 2 to 5: 7.

The photoelectric conversion layer may be formed only from the electron-accepting material and the electron-donating material, but a conductive material or a dye having a photoelectric conversion function may be further added as appropriate.
Examples of the conductive material include polyacetylene, polypyrrole, polythiophene, polyparaphenylene, polyparaphenine vinylene, polythienylene vinylone, poly (3,4-ethylenedioxythiophene), and polyfluorene. -Based, polyaniline-based, and polyacene-based conductive materials (excluding PEDOT: PSS).
Examples of the dye include cyanine-based, merocyanine-based, phthalocyanine-based, naphthalocyanine-based, azo-based, quinone-based, quinoisin-based, quinacrine-based, squarylium-based, triphenylmethane-based, xanthene-based, porphyrin-based, perylene-based, Indigo pigments can be mentioned.
When these other additives (conductive materials and dyes) are added to the photoelectric conversion layer, the amount of these additives is not limited, but the total amount of the electron accepting material and the electron donating material is 100 mass. As a part, about 1-100 mass parts is preferable, and about 1-40 mass parts is more preferable.

A method for forming the photoelectric conversion layer is not limited. For example, the photoelectric conversion layer is formed by dissolving the electron-accepting material and the electron-donating material in a suitable solvent and spin-coating the solution on the buffer layer. When other additives are included, it is preferable to mix (dissolve) the solution in advance.
Although the thickness of a photoelectric converting layer is not limited, about 1-500 nm is preferable and about 5-100 nm is more preferable.

Examples of the metal electrode material include aluminum, magnesium-silver alloy, aluminum-lithium alloy, lithium, sodium, potassium and cesium.
The metal electrode is laminated by a vacuum deposition method, and an organic thin film solar cell can be manufactured.

In addition, poly (3,4-ethylenedioxythiophene) / poly (styrenesulfonate) is used as a buffer layer (hereinafter referred to as an anode buffer layer) to be the transparent electrode between the transparent electrode and the photoelectric conversion layer. A (PEDOT / PSS) layer, a molybdenum oxide layer, or an amorphous titanium oxide layer can be inserted.
These layers can be produced by a solution coating method using a solvent that does not erode the underlayer, a vacuum deposition method, a reduction deposition method, or the like.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limited to the following Example.
In the examples, the apparatus and conditions used for sample preparation and physical property analysis are as follows.
(1) GPC (gel permeation chromatography)
Equipment: GPC-101 manufactured by Showa Denko K.K.
Column: Showa Denko LF-804 × 4
Column temperature: 60 ° C
Solvent: NMP with 20 mM LiBr added
Detector: RI
(2) ¹ H-NMR spectrum apparatus: JNM-ECA700 manufactured by JEOL Ltd.
Solvent: CDCl ₃
Internal standard: Tetramethylsilane (3) spin coater Device: MS-A100 manufactured by Mikasa Co., Ltd.
(4) Light source Device: Solar simulator (YSS-50A: manufactured by Yamashita Denso Co., Ltd.)
Irradiation light: Standard sunlight spectrum AM 1.5G
Irradiation intensity: White light 100 mW / cm ² (1 sun)
Irradiation time: about 1 minute (5) Voltage application and current measurement Device: Source measure unit 238 (manufactured by Keithley Instruments Co., Ltd.)
Measurement conditions: Voltage range: 1.5 V to 1.5 V, sweep speed: 0.05 V / second

[Synthesis Example 1]
<Synthesis of hyperbranched polymer (HI-DVB)>
To a 2 L reaction flask, 781 g of n-propanol was charged, nitrogen was poured for 5 minutes with stirring, and the mixture was heated until n-propanol was refluxed (standard boiling point 97 ° C.).
In a separate 1 L reaction flask, 13.0 g (100 mmol) of divinylbenzene, 20.0 g of 2,2′-azobis [2- (2-imidazolin-2-yl) propane] (AIYP) (80 mmol, based on divinylbenzene) 80 mol%) and 781 g of n-propanol were charged, and nitrogen was introduced for 5 minutes while stirring to replace the nitrogen, and the mixture was cooled to 0 ° C. in an ice bath.
From the 1 L reaction flask charged with divinylbenzene, AIYP and n-propanol into the refluxed n-propanol in the 2 L reaction flask, the contents were dropped over 60 minutes using a dropping pump. . After completion of dropping, the mixture was aged for 1 hour.
Next, this reaction solution was concentrated to 260 g using a rotary evaporator, and dropped into 1,300 g of ion-exchanged water to perform reprecipitation. The obtained residue was dissolved again in 130 g of n-propanol and dropped into 1,300 g of ion-exchanged water for reprecipitation. The obtained pale yellow powder was vacuum-dried to obtain 14.6 g of a target product (HI-DVB) represented by the following formula [3]. The measurement result of the ¹ H-NMR spectrum of the obtained target product is shown in FIG. Moreover, the weight average molecular weight Mw measured by polystyrene conversion by GPC of the target object was 29,000, and dispersion degree: Mw / Mn was 2.35.

[Example 1 to Example 4: Preparation of organic thin film solar cell (ITO / PEDOT: PSS / P3HT: PCBM / HI-DVB / Cu)]
An organic thin-film solar cell (hereinafter also simply referred to as an element) as shown in FIG. 1 was prepared as the cathode-side buffer layer (hereinafter referred to as the cathode buffer layer) using the imidazoline group-containing polymer compound (HI-) produced in Synthesis Example 1 above. DVB).

<Preparation of anode buffer layer>
A transparent conductive film substrate in which an indium-tin oxide (ITO) transparent electrode is formed on a glass substrate as a transparent electrode (thickness 150 nm, surface resistance 10Ω / □: manufactured by Mitani Vacuum Co., Ltd.
Called substrate).
On the ITO substrate, a poly (ethylenedioxythiophene) (PEDOT) / polystyrene sulfonic acid (PSS) solution (manufactured by C. Starck, AI4083) was used for 2,0.
A film was formed by spin coating at 00 rpm for 30 seconds, and annealed at 130 ° C. for 20 minutes using an air hot plate to form an anode buffer layer.

<Preparation of Photoelectric Conversion Layer (P3HT: PCBM)>
Next, a 1: 1 (mass ratio) 3 wt% orthodichlorobenzene solution of poly (3-hexylthiophene-2,5-diyl) (P3HT), phenyl-C61-butyric acid methyl ester) (PCBM) was used as a glove box. Prepared in. This solution was shielded from light at 50 ° C. in a glove box and stirred for 12 hours.
Next, a 3 wt% orthodichlorobenzene solution of P3HT: PCBM (1 wt: 1 wt) was filtered through a PTFE disposable membrane filter (DISMIC series 13JP050AN: ADVANTEC) having a pore diameter of 0.20 μm, and the above-described anode buffer layer was manufactured. Two to three drops were dropped on the filmed substrate and spin-coated using a spin coater under the conditions of the first time: 500 rpm, 60 seconds, the second time: 2,000 rpm, 1 second, the third time: 500 rpm, 80 seconds.
Thereafter, the spin-coated substrate was annealed at 120 ° C. for 10 minutes using a hot plate.

<Preparation of cathode buffer layer>
HI-DVB was weighed, put into a sample bottle, carried into a glove box, and a solution was prepared using isopropanol as a solvent in the glove box. At this time, the HI-DVB concentration was 0.03 wt%, 0.05 wt%, and 0.10 wt%.
Thereafter, the HI-DVB solution is dropped onto the substrate through a syringe filter (hydrophilic) having a pore diameter of 0.45 μm on the substrate on which the anode buffer layer (PEDOT: PSS) and the photoelectric conversion layer (P3HT: PCBM) are formed. Then, spin coating was performed using a spin coater at 3,000 rpm for 30 seconds.
The spin-coated substrate was annealed at 120 ° C. for 10 minutes using a hot plate.

<Production of Metal Electrodes (Examples 1 to 3: Al, Example 4: Cu)>
Preparation of Al electrode: A small piece of aluminum (purity 99.999%: Nilaco Co., Ltd.) was filled in a tungsten basket on the substrate on which the cathode buffer layer was formed, and the deposition rate was from 0 to 20 nm. The film was vapor-deposited at a rate of 0 nm / second, and then at a deposition rate of 3.0 to 4.0 m / second.
Preparation of Cu electrode: A copper wire (0.50 mm purity 99.9%: Nilaco Co., Ltd.) was filled in a tungsten boat on the substrate on which the cathode buffer layer was formed, and the deposition rate was 1.0 to 0-20 nm. The film was vapor-deposited at 70 nm at a deposition rate of 1.0 to 2.0 kg / sec.

The element produced as described above was sealed in a glove box. That is, a UV curable epoxy resin sealant (XNR 5516Z: Nagase ChemteX Corporation) is placed on the edge of a cylindrical sealing glass, and a UV lamp (Spot Cure SP3: Ushio Electric Co., Ltd.) is used. And cured by UV to produce a sealing element.
In addition, the schematic diagram of the produced organic thin film solar cell is shown in FIG.

[Comparative Example 1 and Comparative Example 2]
A device was fabricated in the same manner as in the example except that the cathode buffer layer was not used.
In Comparative Example 1, the metal electrode was Al, and in Comparative Example 2, Cu was used.

[Measurement method of organic thin film solar cells]
For the organic thin-film solar cells produced in Examples 1 to 4 and Comparative Examples 1 and 2, the photoelectric conversion efficiency (PCE), short-circuit current density (J _SC ), and open-circuit voltage (V _OC ) in the atmosphere, respectively. ) And the durability of each element was evaluated.
〔Measurement procedure〕
A 2 mm × 2 mm square effective element surface of the substrate was surrounded by a light-shielding sheet, and measurement was performed in the atmosphere in accordance with a hole having a diameter of 3 mm.
In addition, a gold wire (purity 99.95%, diameter 0.05 mm: Nilaco Co., Ltd.) and silver paste (Dotite D-550: Fujikura Kasei Co., Ltd.) were used for connection between the element electrode and the source measure unit. .

As shown in Table 1, when the elements of Examples 1 to 3 and Comparative Example 1 in which the cathode is aluminum are compared, the elements of the Examples have higher short-circuit current densities than the elements of the Comparative Example. Open circuit voltage and conversion efficiency are shown. That is, by using HI-DVB for the cathode buffer layer, it is possible to achieve an open-circuit voltage Voc (0.58 V) comparable to that obtained when LiF (lithium fluoride) that is conventionally used as the cathode buffer layer is used. all right.
In addition, even when the cathode was copper (Example 4 and Comparative Example 2), the result was that the open-circuit voltage Voc of the element of the example exceeded 0.5V. That is, it was shown that a metal that is easily oxidized, such as copper, can be used for the electrode.

DESCRIPTION OF SYMBOLS 10 Transparent electrode 11 Anode buffer layer 12 Photoelectric conversion layer 13 Cathode buffer layer 14 Metal electrode

JP 2008-135500 A

Claims (6)

A transparent electrode on a transparent substrate, a metal electrode, a photoelectric conversion layer interposed between the two electrodes, and a cathode buffer layer formed so as to be in contact with the metal electrode between the photoelectric conversion layer and the metal electrode; In an organic thin film solar cell comprising:
The cathode buffer layer is Ri Do a polymer compound having an amino functional group or imino functional group at the terminal,
The polymer compound comprises an aromatic vinyl hydrocarbon as monomer A having two or more radically polymerizable double bonds in the molecule, 5 mol% to 200 mol% of amino functional group or An organic thin-film solar cell, which is a highly branched polymer obtained by polymerization in the presence of a polymerization initiator B having an imino functional group . The organic polymer according to claim 1, wherein the polymer compound is a hyperbranched polymer having a weight average molecular weight of 1,000 to 2,000,000 measured in terms of polystyrene by gel permeation chromatography. Thin film solar cell. The organic thin film solar cell according to claim 1 or 2 , wherein the polymerization initiator B having the amino functional group or imino functional group is a polymerization initiator having a heterocyclic amine structure. The polymerization initiator B having the amino functional group or imino functional group is a polymerization initiator having a functional group represented by the formula [1], according to any one of claims 1 to 3 . Organic thin film solar cell.
(In the formula [1], R ¹ , R ² and R ³ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or a hydroxyalkyl group having 1 to 6 carbon atoms, and R ¹ Any two or more of R ² and R ³ may be combined with the nitrogen atom to which they are bonded to form a ring.) Polymerization initiator B having an amino functional group or imino functional group, a polymerization initiator represented by the formula [2], an organic thin film solar cell according to any one of claims 1 to 4 .
(In the formula [2], R ¹ , R ² and R ³ each independently represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or a hydroxyalkyl group having 1 to 6 carbon atoms, and R ¹ Any two or more of R ² and R ³ may be combined with the nitrogen atom to which they are bonded to form a ring, and R ⁴ and R ⁵ each independently represent 1 to 1 carbon atoms. 6 represents an alkyl group.) A) preparing a transparent substrate having a transparent electrode formed on the substrate surface;
B) forming a photoelectric conversion layer thereon or above;
C) forming a cathode buffer layer on or above the photoelectric conversion layer;
D) Furthermore, the manufacturing method of the organic thin-film solar cell as described in any one of Claims 1 thru | or 5 which has a step which laminates | stacks a metal electrode on it.