JPH07142751A - Organic solar cell - Google Patents

Abstract

PURPOSE:To obtain an organic solar cell having an excellent photoelectric conversion efficiency and stable characteristics during continuous use. CONSTITUTION:This is an organic solar cell having a photoconductive layer 3 containing an electric charge generating pigment and an electric charge transport material between two electrodes 2 and 4, the electric charge generating pigment comprises a combination of a P-type electric charge generating pigment and an N-type electric charge generating pigment, and part of the P-type and N-type electric charge generating pigments are present in the form of their aggregate within the photoconductive layer of the solar cell.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an organic solar cell,
More specifically, the present invention relates to a function-separated type organic solar cell using an organic pigment and an organic material.

[0002]

2. Description of the Related Art In an organic solar cell, a pn junction is formed between an inorganic semiconductor such as silicon or germanium and a photoconductive layer made of an organic dye, or a metal and an organic dye are combined to emit light energy. It is converted into electric energy. The photoconductive layer is, for example, an organic photoconductor made of a synthetic dye or pigment such as chlorophyll, a conductive polymer material such as polyacetylene, or a composite material thereof, by a vacuum deposition method, a casting method, a dipping method, or the like. It is formed of a thin film.

The organic solar cell using the organic photoconductor or the organic semiconductor as described above is more economical than the conventional inorganic solar cell in which a pn junction is formed in a single crystal of an inorganic semiconductor such as silicon or germanium. In recent years, it has attracted attention as a solar cell for consumer use because it has advantages such as excellent heat resistance and easy manufacture. For example, JP-A 1-21
No. 5070 discloses a photoconductive layer in which an organic charge generating pigment and an organic charge transporting dye are dispersed in a binder resin,
An organic solar cell formed by being arranged between two electrodes is disclosed.

In this organic solar cell, a bisazo pigment or a phthalocyanine pigment is used as the charge generating pigment. As the charge transport dye, organic compounds such as pyrazoline-based, hydrazone-based, oxazole-based, trianolmethane-based, and polyarylalkanes are used. In this organic solar cell, a Schottky junction is formed between the electrode and the photoconductive layer containing the organic charge generating pigment. Therefore, when the organic charge generating pigment is irradiated with light, carrier pairs are generated in the Schottky barrier portion. Among the carrier pairs, holes are injected into the organic charge transport dye in the photoconductive layer, holes move in the dye, and electrons move in the pigment according to the potential difference of the Schottky junction.

Therefore, according to the organic solar cell disclosed in Japanese Unexamined Patent Publication No. 1-215070, it is said that an inexpensive organic solar cell having high photoelectric conversion efficiency and high continuous use stability can be obtained.

[0006]

However, in the organic solar cell using the pigment as described above, the amount of generated carriers cannot be said to be sufficient and the photoelectric conversion efficiency is insufficient. The present invention has been made to solve the above problems,
Its purpose is to provide an organic solar cell having a high photoelectric conversion rate.

[0007]

The organic solar cell of the present invention is an organic solar cell in which a photoconductive layer containing a charge generating pigment and a charge transport material is provided between two electrodes, The charge generating pigment comprises a combination of a P-type charge generating pigment and an N-type charge generating pigment, at least some of which are present in the photoconductive layer in the form of their aggregates. By doing so, the above object is achieved. Aggregates of P-type and N-type charge generating pigments present in the photoconductive layer of the present invention include a plurality of particles of P-type (or N-type) charge generating pigments which are N-type (or P-type) charge generating pigments. It is desirable that the particles have an agglomerated structure in which they are agglomerated through particles, and that the agglomerates generally have a particle diameter of 0.2 to 2 μm. The presence and the agglomeration structure of the agglomerates of the fine pigment particles in the photoconductive layer of the present invention are confirmed by the combined use of a transmission electron micrograph and energy dispersive X-ray spectroscopy, as will be described later. The particle size in the specification is defined as a value of 1/2 of the sum of the major axis of particles and the minor axis of particles.

[0008]

[Function] When the photoconductive layer of the organic solar cell is irradiated with light,
A charge is generated in the charge generation pigment in the photoconductive layer, electrons move to the positive electrode, and holes are injected into the charge transport dye, and move to the negative electrode via the charge transport dye. Here, FIG. 1 of the accompanying drawings is a drawing of a transmission electron micrograph of the photoconductive layer of the present invention, in which the hatched particles represent P-type charge generating pigments (phthalocyanine) and the dots are applied. The formed particles represent an N-type charge generating pigment (perylene). Referring to this figure, in the photoconductive layer of the present invention, the P-type charge-generating pigment particles and the N-type charge-generating pigment particles are in the form of an aggregate, and in particular, a plurality of P-type (N-type) charge-generating pigment particles are present. N
It becomes clear that the particles have an agglomerated structure in which they are agglomerated via the P-type (P-type) charge generating pigment particles, and the agglomeration growth of the particles occurs. In addition, in the specific example shown in FIG. 1, a part of the N-type generating pigment having a large amount ratio is present in the form of an individual particle dispersion other than the agglomerate, but the P-type charge generating pigment having a small amount ratio is used. It is also understood that most are present in the form of the aggregates. According to the present invention, at least a part of the P-type charge-generating pigment and the N-type charge-generating pigment are in the form of the above-mentioned aggregate, so that they can be used independently or in combination. Dispersion (dispersion that does not form aggregates)
Compared with the above case, the carrier generation efficiency is remarkably improved, and significant advantages are brought about in terms of an increase in sensitivity on the long wavelength side and a balance in spectral sensitivity of the photoconductive layer. In the photoconductive layer according to the present invention, the above-described improvements are caused by a large number of experimental results by the present inventors, which have been found as a phenomenon, and the reason is beyond speculation. The inventors consider the following. That is, in the photoconductive layer according to the present invention, the P-type charge-generating pigment particles or the N-type charge-generating pigment particles have an agglomerated structure in which they are agglomerated via the counterpart pigment particles. Micro P-N junction at the interface between P-N junctions
Are formed in large numbers. It is believed that in the photoconductive layer according to the present invention, the formation of the P—N junction improves the carrier generation efficiency in a wide wavelength range including the long wavelength side and increases the sensitivity. Therefore, by including at least a part of the P-type and N-type charge generating pigments in the form of their aggregates in the photoconductive layer as the charge generating material, the amount of photocarriers generated increases, so that the photoelectric conversion efficiency is improved. An excellent organic solar cell can be obtained.

[Preferable Embodiment] <Structure of Solar Cell> The organic solar cell according to the present invention may have a structure as shown in FIG. 1, for example. This organic solar cell A has a substrate 1, an electrode 2, a photoconductive layer 3 and a transparent counter electrode 4 which are sequentially laminated on the substrate 1.

In this structure, light is emitted from the transparent electrode 4 side, but when the substrate 1 and the electrode 2 are translucent, the light may be emitted from the substrate 1 side. In that case, the transparent electrode 4 may be non-translucent. In this structure, an undercoat layer may be provided on the substrate 1 in order to improve the adhesion between the electrode 2 and the substrate 1. As the material of the substrate 1, a metal such as aluminum or stainless steel,
Paper, plastic, etc. can be used.

As a material for the electrode 2 and the transparent electrode 4, any material can be used as long as it forms a Schottky junction with the photoconductive layer 3. For example, metals such as aluminum, copper, stainless steel; polyacetylene,
A conductive polymer such as polypyrrole; a quaternary ammonium salt dissolved in the polymer; an oxide such as SnO2 or ITO can be used. However, when translucency is required, it is necessary to use a semitransparent thin film of metal, a transparent conductive oxide, or the like.

The electrodes 2 and 4 are formed, for example, by vacuum vapor deposition or sputtering. The photoconductive layer 3 generally contains a binder resin, a charge generating pigment, and a charge transport dye. << Charge Generating Pigment >> In the present invention, as the charge generating pigment, P
A combination of a type charge generating pigment and an N type charge generating pigment is used and at least some of them are present in the photoconductive layer in the form of agglomerates. In this agglomerate, a plurality of particles of a P-type (or N-type) charge generating pigment are composed of agglomerates agglomerated via particles of an N-type (or P-type) charge generating pigment to be contrasted with. However, many P-N junctions are present in this aggregate. As the P-type charge generating pigment constituting the aggregate of the present invention, a P-type charge generating pigment known per se is used, and a phthalocyanine pigment,
Mention may be made of naphthalocyanine pigments and other porphyrin pigments. These porphyrin-based pigments have a skeleton represented by the following formula.

[Chemical 1] In the above formula, Z is a nitrogen atom or a CH group, R ¹ and R ² are substituted or unsubstituted monovalent hydrocarbon groups having 12 or less carbon atoms, and these groups R ¹ and R ² are linked to each other. May form a substituted or unsubstituted benzene ring or naphthalene ring with the bonding carbon atom. The following are exemplified as particularly preferable ones. Oxotitanyl phthalocyanine, metal-free phthalocyanine. It is generally desirable that the P-type charge generating pigment has a particle size of 0.1 to 1 μm.

As the N-type charge generating pigment constituting the aggregate, a known N-type charge generating pigment is used, and in particular, perylene pigments, azo pigments, squarylium salt pigments or polycyclic quinone pigments are used. used.

The perylene pigments are represented by the following formula

[Chemical 2] In the formula, each of R ³ and R ⁴ is a substituted or unsubstituted alkyl group having 18 or less carbon atoms, a cycloalkyl group, an aryl group, an aralkyl group or an alkaryl group. , An alkyl group, an alkoxy group, a halogen atom and the like.

As the azo pigment, any of monoazo pigments, disazo pigments, trisazo pigments and the like which have been conventionally used as charge generating pigments can be used.

The squarylium salt-based pigment is represented by the following formula

[Chemical 3] In the formula, each of R ⁵ and R ⁶ includes an alkyl group, an alkoxy group, a halogen atom, and R ⁷ , R ⁸ , R ⁹ and R
Each of ¹⁰ includes those which are an alkyl group, a cycloalkyl group, an alkoxy group, a halogen atom, an aryl group, an aralkyl group or an alkaryl group, and each group has an alkyl group, an alkoxy group, a halogen atom or the like as a substituent. You may have.

The polycyclic quinone pigments include anthanthrone pigments, quinacridone pigments, perinone pigments, quinophthalone pigments, flavantron pigments, pyranthrone pigments, violanthrone pigments, anthroton pigments,
Examples thereof include indanthrone pigments.

The N-type charge generating pigment used in the present invention generally preferably has a particle size of 0.1 to 1 μm. Aggregates of the P-type charge generating pigment and the N-type charge generating pigment cannot be formed by simply co-dispersing the P-type charge generating pigment and the N-type charge generating pigment in the resin solution. It is important to perform the treatment to form aggregates.

The pretreatment for producing the aggregates includes a wet method and a dry method. In the wet method, a specific polar solvent, for example, a solvent such as tetrahydrofuran or dichloromethane is used.
The P-type charge generating pigment and the N-type charge generating pigment are finely dispersed to form an aggregate. By finely dispersing both pigments in these solvents, the P-type charge-generating pigment particles are positively charged, while the N-type charge-generating pigment is negatively charged, and the formation of aggregates is effectively performed. According to the experiments conducted by the present inventors, even if both pigments are mixed in an organic solvent, alcohols, cyclohexane, toluene, dioxane, etc. do not have stable dispersibility of the individual pigments, resulting in extremely high aggregate formation efficiency. It was confirmed to decrease. For the formation of agglomerates by the wet method, a method of wet pulverization using a ball mill, colloid mill, dispers mill, homomixer or the like is effective. In the dry method, a P-type charge generating pigment and an N-type charge generating pigment are mixed and this mixture is co-ground. Also by this mechanochemical method, the crushing of each pigment into primary particles and the agglomeration of the crushed primary particles with each other occur, and the aggregates grow. Dry method pulverization can be performed using a ball mill or a vibration mill.

In the present invention, the amount ratio of the P-type charge generating pigment and the N-type charge generating pigment is generally 10: 0.1 to 0.
1:10 weight ratio, especially 10: 0.5 to 0.5: 10
Is appropriately selected from the weight ratio of. When the amount ratio of the P-type charge-generating pigment and the N-type charge-generating pigment is biased to either side, the larger pigment particles are present in the form of single particles released from the aggregates, as shown in FIG. However, even if such free particles are present, there is no particular adverse effect in terms of sensitivity. The aggregate used in the present invention is composed of a plurality of particles of the P-type (N-type) charge generating pigment aggregated through the particles of the N-type (P-type) charge generating pigment. ．
It should have a particle size of 2 to 2 μm. << Charge Transport Material >> As the charge transport material used in the present invention, a material known per se can be used. As the conventionally known charge transport material, various electron-withdrawing compounds and electron-donating compounds can be used.

Examples of the electron-withdrawing compound include:
Diphenoquinone derivatives such as 2,6-dimethyl-2 ′, 6′-ditert-dibutyldiphenoquinone, malononitrile, thiopyran compounds, tetracyanoethylene,
2,4,8-trinitrothioxanthone, 3,4,5,
Examples thereof include 7-tetranitro-9-fluorenone, dinitrobenzene, dinitroanthracene, dinitroacridine, nitroanthraquinone, dinitroanthraquinone, succinic anhydride, maleic anhydride and dibromomaleic anhydride.

The electron donating compound is 2,5
-Oxadiazole compounds such as di (4-methylaminophenyl) and 1,3,4-oxadiazole, 9- (4
-Styryl compounds such as diethylaminostyryl) anthracene, carbazole compounds such as polyvinylcarbazole, pyrazoline compounds such as 1-phenyl-3- (p-dimethylaminophenyl) pyrazoline, hydrazone compounds, triphenylamine compounds, indole compounds Examples thereof include nitrogen-containing cyclic compounds such as compounds, oxazole compounds, isoxazole compounds, thiazole compounds, thiadiazole compounds, imidazole compounds, pyrazole compounds, and triazole compounds, and condensed polycyclic compounds.

These charge transport materials may be used alone or in combination of two or more. When a charge transporting material having film-forming property such as polyvinylcarbazole is used,
The binder resin is not always necessary. Among these charge transport materials, it is particularly preferable to use hydrazone compounds, triphenylamine compounds, stilbene compounds and the like. << Binder Resin >> Examples of the binder resin forming the photoconductive layer 3 include styrene-based polymers, styrene-butadiene copolymers, styrene-acrylonitrile copolymers, styrene-maleic acid copolymers, and acrylic copolymers. , Styrene-acrylic acid copolymer, polyethylene,
Ethylene-vinyl acetate copolymer, chlorinated polyethylene,
Heat of polyvinyl chloride, polypropylene, vinyl chloride-vinyl acetate copolymer, polyester, polyamide, alkyd resin, polycarbonate, polyarylate, polysulfone, diallyl phthalate resin, ketone resin, polyvinyl butyral resin, polyether resin, polyurethane resin, etc. Plastic resin, silicone resin, epoxy resin, phenol resin, urea resin, melamine resin, other cross-linkable thermosetting resin, and epoxy acrylate,
Examples thereof include photo-curable resins such as urethane-acrylate. These binder resins can be used alone or in combination of two or more.

A solvent is used in the binder resin to disperse the organic charge generating pigment in the form of particles to uniformly dissolve the organic charge transporting dye. Various organic solvents can be used as the solvent. For example, alcohols such as methanol, ethanol, isopropanol and butanol, aliphatic hydrocarbons such as n-hexane, octane and cyclohexane, aromatic hydrocarbons such as benzene, toluene and xylene, dichloromethane, dichloroethane, carbon tetrachloride and chlorobenzene. Halogenated hydrocarbons such as dimethyl ether, diethyl ether, tetrahydrofuran,
Examples thereof include ethers such as ethylene glycol dimethyl ether and diethylene glycol dimethyl ether, ketones such as acetone, methyl ethyl ketone and cyclohexanone, esters such as ethyl acetate and methyl acetate, dimethylformaldehyde, dimethylformamide and dimethyl sulfoxide. These solvents may be used alone or in combination of two or more. << Preparation of Organic Solar Cell >> The above organic pigment, organic dye, binder resin and above solvent are used to prepare a coating solution using a method such as homogenizer, ultrasonic wave, ball mill, sand mill, attritor, roll mill, paint shaker, and casting. The photoconductive layer 3 is formed on the electrode 2 by laminating or dipping.

The photoconductive layer 3 may contain various additives in order to improve carrier generation, injection and transport properties. For example, diphenyl, diphenyl chloride, terphenyl, halonaphthoquinones, dibutyl phthalate, dimethyl glycol phthalate, dioctyl phthalate, triphenyl phosphoric acid, methyl naphthalene,
Acetylnaphthalene, benzophenone, chlorinated paraffin, dilauryl thiopropionate, 3,5-dinitrosalicylic acid, various fluorocarbons and the like can be mentioned.

Further, a surfactant, a leveling agent or the like may be used in order to improve the dispersibility and coatability of the charge transport dye or charge generating pigment. Here, the charge generating pigment is 2 to 20 parts by weight, particularly 3 to 15 parts by weight, and the phenylenediamine compound represented by the general formula (1) is 40 to 200 parts by weight with respect to 100 parts by weight of the binder resin. And particularly preferably 50 to 150 parts by weight. The thickness of the photoconductive layer is preferably 0.1 to 2 μm, and more preferably about 0.5 μm.

[0026]

The present invention will be described in detail below with reference to examples and comparative examples.

(Examples 1 to 12 and Comparative Examples 1 to 7) 1
500 nm thick on a glass plate of 00 mm x 100 mm
Of aluminum electrode (light transmittance 70%) was vacuum-deposited. next,
10 parts by weight of an organic charge generating pigment and 10 parts by weight of an organic charge transporting dye, polyvinyl butyral resin (S-REC BM-
10 parts by weight (manufactured by Sekisui Chemical Co., Ltd.) and 50 parts by weight of cyclohexanone were mixed and dispersed in a ball mill using glass beads having a diameter of 1 mm for 24 hours. The obtained dispersion was applied onto the aluminum electrode by spin coating and dried at 100 ° C. for 30 minutes to form a photoconductive layer having a thickness of 0.5 μm. The organic charge generating pigments and organic charge transporting dyes used are the compounds shown below.
The details are shown in. When two kinds of organic charge generating pigments were used, they were mixed in a ratio of 1: 1 to make the total amount 10 parts by weight. Organic charge generating pigment β-type metal-free phthalocyanine; AX-type metal-free phthalocyanine; B oxotitanyl phthalocyanine; C

[Chemical 4] Organic charge transport dye

[Chemical 5]

On the photoconductive layer, a 20 mm × 20 mm gold electrode was vapor-deposited to a thickness of 2000 Å. An organic solar cell was obtained by the above steps. (Evaluation test) Open circuit voltage VOC of the organic solar cells obtained in Examples 1 to 12 and Comparative Examples 1 to 7
(V), short circuit current ISC (mA) and maximum photoelectric conversion efficiency EMAX (%) when 1 kΩ is added
Was measured under the following conditions.

Light source: Tungsten lamp Light intensity: 50 mW / cm 2 Test results are also shown in Table 1.

[Table 1] From these test results, the organic solar cells of the present invention were found to have an open circuit voltage VOC (V), a short circuit current ISC (mA) and a maximum photoelectric conversion efficiency EMAX (%) of 1 kΩ at the time of addition of conventional organic solar cells. The value is better than that of the solar cell.

Further, since it is superior in stability to light as compared with the conventional organic solar cell, stable characteristics can be obtained during continuous use.

[0031]

As is apparent from the above description, according to the present invention, an organic solar cell having excellent photoelectric conversion efficiency and stable characteristics during continuous use can be obtained.

[Brief description of drawings]

FIG. 1 is a drawing of a transmission electrophotographic microscope of the photoconductive layer of the present invention.

FIG. 2 is a cross-sectional view of an organic solar cell that is an embodiment of the present invention.

[Explanation of symbols]

 1 substrate 2 electrode 3 photoconductive layer 4 transparent electrode

Claims (1)

[Claims] 1. An organic solar cell in which a photoconductive layer containing a charge generating pigment and a charge transporting material is provided between two electrodes, wherein the charge generating pigment is a P-type charge generating pigment and an N-type charge generating pigment. An organic solar cell, characterized in that it comprises a combination with a type charge generating pigment, wherein at least part of the P-type and N-type charge generating pigments are present in the photoconductive layer in the form of their aggregates.