JPH0685295A - Organic solar cell - Google Patents

Abstract

PURPOSE:To enhance photoelectric conversion efficiency and stability at continuous use by providing a photoconductive layer containing a charge generation pigment and a charge transport pigment between two electrodes and using a compound which is expressed by a specific expression for the charge transport pigment. CONSTITUTION:A charge transport pigment is a phenylenediamine compound expressed by formula I. R<1>, R<2>, R<3>, R<4>, R<5>, R<6>, R<7>, and R<8> in the formula I may be equal or different, namely indicate a hydrogen atom, halogen atom, alkyl group or alkoxy group, and Z indicates a thio group, oxy group, seleno group, telluro group, alkylene group, or a group which is expressed by formula II or formula III. N in the formula II indicates 1 or 2. Y in the formula III indicates a sulphur atom, oxygen atom, or nitrogen atom. By allowing the phenylenediamine compound to be contained in a photoconductive layer as a charge transport material, a solar cell with an improved photoelectric conversion efficiency can be obtained. Also, an improved light stability for a long-term light exposure and a light exposure at a high temperature can be achieved.

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 dye.

[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, in JP-A 1-215070, a photoconductive layer in which an organic charge generating pigment and an organic charge transporting dye are dispersed in a binder resin is formed by disposing between two electrodes. Organic solar cells are disclosed.

In this organic solar cell, organic compounds such as pyrazoline type, hydrazone type, oxazole type, trianolmethane type and polyarylalkanes are used as the organic charge transport dye.

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 Patent Laid-Open No. 1-215070, it is said that an organic solar cell which is inexpensive, has high photoelectric conversion efficiency, and has high continuous use stability can be obtained.

[0008]

However, in the organic solar cell using the above organic charge transport dye, the carrier mobility is low and the photoelectric conversion efficiency is insufficient. Further, it has a problem that it is easily deteriorated by irradiation of ultraviolet rays and its characteristics are unstable during continuous use.

The present invention has been made to solve the above problems, and its object is to have a high photoelectric conversion rate,
An object of the present invention is to provide an organic solar cell having stable characteristics during continuous use.

[0010]

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 transporting dye is provided between two electrodes, The charge-transporting dye is an organic solar cell which is a phenylenediamine compound represented by the following general formula (1), and thereby the above object is achieved.

[0011]

[Chemical 4]

(Wherein R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ ,
R ⁷ and R ⁸ are the same or different and each represents a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group, and Z is
A thio group, an oxy group, a seleno group, a telluro group, an alkylene group, and a group represented by the following general formula (2) or the following general formula (3))

[0013]

[Chemical 5]

(In the formula, n represents 1 or 2)

[0015]

[Chemical 6]

(In the formula, Y represents a sulfur atom, an oxygen atom or a nitrogen atom)

[0017]

[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, the phenylenediamine compound used in the present invention is superior in charge transporting ability to the charge transporting dye disclosed in JP-A 1-215070. Therefore, by including this phenylenediamine compound as a charge transport material in the photoconductive layer,
An organic solar cell excellent in photoelectric conversion efficiency can be obtained.

By the way, in the phenylenediamine compounds, the cause of the deterioration of the characteristics due to photodegradation is generally as follows.
The impurities serving as traps are generated in the photoconductive layer. For example, a photooxidation reaction of the central benzene ring can be considered. It is considered that this reaction is likely to occur because the electron density of the molecule of the phenylenediamine compound is biased to the central benzene ring. In particular, the 5-position of the central benzene ring has a molecular structure that is easily attacked by an oxidizing substance such as oxygen during photoexcitation due to its steric configuration, and it is considered that photooxidation is likely to occur because electrons are extracted from this part. .
Therefore, by substituting and protecting this portion with a substituent, the reactivity of the phenylenediamine compound can be suppressed and the stability to light can be improved.

Therefore, the phenylenediamine compound represented by the above general formula (1) is less susceptible to attack from oxidizing substances and the like due to the fact that the 5-position of the central benzene ring is protected by a substituent, and the oxidation reaction Is suppressed and stability against light is improved. As a result, the holes generated by the charge generation pigment move to the negative electrode without being trapped in the middle.

Further, the phenylenediamine compound represented by the general formula (1) suffers less damage than conventional charge transport dyes when exposed to light for a long time or at high temperature, Excellent light stability.

Further, since the phenylenediamine compound represented by the above general formula (1) has excellent charge transporting ability, the sensitivity can be improved by incorporating the phenylenediamine compound as a charge transporting material into the photoconductive layer. Also, it is possible to obtain an organic solar cell having excellent chargeability and high repeating characteristics.

[0023]

[Preferable Embodiment] The organic solar cell according to the present invention can be constructed, for example, as shown in FIG.

The 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, metal such as aluminum and stainless steel, paper, plastic and the like can be used.

As the 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 SnO ₂ 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 evaporation or sputtering.

The photoconductive layer 3 generally contains a binder resin, a charge generating pigment, and a charge transport dye.

As the organic charge transport dye contained in the photoconductive layer 3, a phenylenediamine compound represented by the following general formula (1) is used.

[0031]

[Chemical 7]

(Wherein R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ ,
R ⁷ and R ⁸ represent a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group, Z is a thio group, an oxy group,
Seleno group, telluro group, alkylene group, the following general formula (2)
Or represents a group represented by the following general formula (3))

[0033]

[Chemical 8]

(In the formula, n represents 1 or 2)

[0035]

[Chemical 9]

(In the formula, Y represents a sulfur atom, an oxygen atom or a nitrogen atom.) The halogen atom is fluorine,
Examples include chlorine, bromine, and iodine.

Examples of the alkyl group include lower alkyl groups having 1 to 6 carbon atoms such as methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, t-butyl group, pentyl group and hexyl group. can give.

Examples of the alkoxy group include methoxy group, ethoxy group, isopropoxy group, butoxy group, t
-A lower alkoxy group having 1 to 6 carbon atoms in the alkyl moiety such as butoxy group, pentyloxy group and hexyloxy group.

Examples of the alkylene group include lower alkylene groups having 1 to 6 carbon atoms such as ethylene group, propylene group, butylene group, amylene group and hexylene group.

Examples of the phenylenediamine compounds represented by the above general formula (1) include those represented by the following general formula.

[0041]

[Chemical 10]

[0042]

[Chemical 11]

[0043]

[Chemical 12]

[0044]

[Chemical 13]

The above phenylenediamine compounds can be synthesized by various methods and can be obtained, for example, by the following reaction formula.

[0046]

[Chemical 14]

(In the formula, R ⁿ and R ^m represent a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group) This reaction formula is a phenyl ether substituted with two iodo groups represented by the formula (a). The compound and a secondary amine compound represented by the formula (b) having two phenyl groups bonded to each other are reacted in an organic solvent in the presence of copper or a basic substance to give a compound represented by the formula (1-1). The above obtained phenylenediamine compound is obtained.

The secondary amine compound (b) may be reacted with the phenyl ether compound (a) in a molar amount of at least 4 times. Examples of the basic substance include NaOH, K ₂ CO ₃ , and Na ₂ CO ₃ , and examples of the organic solvent include nitrobenzene, dichlorobenzene, n-methylpyrrolidone, and the like. It is also suitable to carry out this reaction at about 190 to 220 ° C.

The phenylenediamine compound can also be obtained by the following reaction formula.

[0050]

[Chemical 15]

(Wherein R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ ,
R ⁷ and R ⁸ are the same as above) This reaction formula is based on the Wittig reaction and has the formula (c)
A phosphonium salt represented by the formula (d) is added to a carbonyl compound represented by a basic substance such as C ₆ H ₅ Li or NaO.
By reacting in the presence of a catalyst such as H, the above phenylenediamine compound represented by the formula (1-2) is obtained. HI is eliminated from the phosphonium salt (d) by the action of the basic substance, and the reaction proceeds.

The carbonyl compound (c) and the phosphonium salt (d) are used in equimolar amounts and can be obtained by reacting in an organic solvent at about 10 to 50 ° C. As the organic solvent, for example, nitrobenzene, THF, dioxane or the like can be used.

The phenylenediamine compound represented by the general formula (1) can be used alone or in combination with other conventionally known charge transport materials. 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.

As the electron donating compound, 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 and condensed polycyclic compounds such as compounds, oxazole compounds, isoxazole compounds, thiazole compounds, thiadiazole compounds, imidazole compounds, pyrazole compounds and triazole 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.

The organic charge generating pigment contained in the photoconductive layer 3 preferably has a good absorption of sunlight or visible light, and functions as an electron acceptor for the organic charge transporting dye. Those are preferable. For example, selenium, selenium-tellurium, selenium-arsenic, amorphous silicon, pyrylium salts, thiopyrylium pigments, phthalocyanine compounds, ansanthuron compounds, anthanthrone pigments, perylene compounds, dibenzpyrenequinone pigments, pyratron pigments, trisazo pigments. , Bisazo pigments, azo compounds, disazo compounds, indigo compounds, thioindigo compounds, triphenylmethane compounds, slene compounds, toluidine compounds, pyrazoline compounds, quinacdrine compounds, pyrrolopyrrole compounds, asymmetric quinocyanines, Quinocyanine, polycyclic condensed dyes, porphyrin dyes and the like can be used.

These charge generating pigments may be used alone or in combination of two or more.

The charge-generating organic pigment can be formed into fine particles having a suitable crystal form by heating and stirring the milling dispersion.

Examples of the binder resin constituting the photoconductive layer 3 include styrene polymers, styrene-butadiene copolymers, styrene-acrylonitrile copolymers, styrene-maleic acid copolymers, acrylic copolymers, Styrene-acrylic acid copolymer, polyethylene, ethylene-vinyl acetate copolymer, chlorinated polyethylene, polyvinyl chloride, polypropylene, vinyl chloride-vinyl acetate copolymer, polyester, polyamide, alkyd resin, polycarbonates, polyarylate, Polysulfone, diallyl phthalate resin, ketone resin, polyvinyl butyral resin, polyether resin, polyurethane resin and other thermoplastic resins, silicone resin, epoxy resin, phenol resin, urea resin, melamine resin, other crosslinkable thermosetting resin, It 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.

A coating solution is prepared from the above organic pigment, organic dye, binder resin and the above solvent by a method such as homogenizer, ultrasonic wave, ball mill, sand mill, attritor, roll mill, paint shaker and the like, and is cast or dipping. Then, the photoconductive layer 3 is formed by laminating on the electrode 2.

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 dyeing property of the charge transport dye or the charge generating pigment.

Here, the charge generating pigment is 2 to 20 parts by weight, especially 3 to 1 with respect to 100 parts by weight of the binder resin.
5 parts by weight, 40 to 200 parts by weight, especially 50 to 150 parts by weight of the phenylenediamine compound represented by the general formula (1).
It is preferably part by weight. The thickness of the photoconductive layer is preferably 0.1 to 2 μm, and more preferably about 0.5 μm.

[0066]

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

(1) Synthesis of phenylenediamine type compound Phenyl ether compound 2.2 represented by the following formula (4)
g, N, N-di (3-methylphenyl) amine 2.6 g
And 0.01 g of copper powder in 50 ml of nitrobenzene under reflux at a temperature of 200 ° C. for 24 hours for reaction, isolation, purification by a conventional method, and phenylenediamine compound represented by the following formula (5). (Compound represented as an organic dye in Table 1 below) was obtained.

[0068]

[Chemical 16]

[0069]

[Chemical 17]

The yield of the above phenylenediamine compound was 55%, and it was a white powder having a melting point of 188 to 192 ° C. In addition, the elemental analysis of the compound gave the following results.

Elemental analysis value: Calculated value (%) as C ₆₈ H ₆₂ N ₄ C85.86 H6.57 N5.89 Actual value (%) C85.77 H6.50 N5.80 (2) Phenylenediamine compound Synthesis The same procedure as in Example 1 was repeated except that 2.48 g of the compound represented by the following formula (6) was used in place of the phenyl ether compound represented by the above formula (4), and the following formula (7) A phenylenediamine compound represented by (in Table 1 below,
A compound represented as an organic dye) was obtained.

[0072]

[Chemical 18]

[0073]

[Chemical 19]

The yield of the above phenylenediamine compound was 54%, and it was a pale yellow powder having a melting point of 185 to 188 ° C. In addition, the elemental analysis of the compound gave the following results.

Elemental analysis value: calculated value as C ₆₈ H ₆₂ N ₄ (%) C84.43 H6.46 N5.79 actual measurement value (%) C84.40 H6.41 N5.72 (Examples 1 to 5 and comparison) Examples 1 to 4) 100 mm x 10
An aluminum electrode having a thickness of 500 nm (light transmittance of 70%) was vacuum-deposited on a 0 mm glass plate.

Next, as an organic charge generating pigment and an organic charge transporting dye, 10 parts by weight of each of the compounds shown in Table 1, 10 parts by weight of polyvinyl butyral resin (S-REC BM-1, manufactured by Sekisui Chemical Co., Ltd.) and 50 parts by weight of cyclohexanone are used. The parts were mixed, and mixed and dispersed by a ball mill using glass beads having a diameter of 1 mm for 24 hours. The obtained dispersion is applied onto the aluminum electrode by spin coating,
It was dried at 0 ° C. for 30 minutes to form a photoconductive layer having a thickness of 0.5 μm.

A 20 mm × 20 mm gold electrode was vapor-deposited thereon to a thickness of 2000 Å.

An organic solar cell was obtained by the above steps.

(Evaluation Test) The open circuit voltage V _OC (V), short circuit current I _SC (mA) and maximum of 1 kΩ when the organic solar cells obtained in Examples 1 to 5 and Comparative Examples 1 to 5 were added. Photoelectric conversion efficiency E
_MAX (%) was measured under the following conditions.

The measurement conditions are as follows.

Light source: tungsten lamp Light intensity: 200 lux The test results are also shown in Table 1. The chemical structural formulas of the organic pigments and organic dyes shown in Table 1 are shown below.

[0082]

[Table 1]

[0083]

[Chemical 20]

[0084]

[Chemical 21]

[0085]

[Chemical formula 22]

[0086]

[Chemical formula 23]

[0087]

[Chemical formula 24]

[0088]

[Chemical 25]

From these test results, all of the organic solar cells of the present invention have an open circuit voltage V
_{The OC} (V), the short circuit current I _SC (mA), and the maximum photoelectric conversion efficiency E _MAX (%) when 1 kΩ are added show good values as compared with the conventional organic solar cell.

Further, as compared with the conventional organic solar cell, the stability against light is excellent, so that the characteristics during continuous use can be made stable.

[0091]

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 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 dye is provided between two electrodes, wherein the charge transporting dye is represented by the following general formula (1): An organic solar cell which is a phenylenediamine compound represented by. [Chemical 1] (Wherein, R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ and R ⁸
Are the same or different and represent a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group, and Z is a thio group, an oxy group, a seleno group, a telluro group, an alkylene group, the following general formula (2) or the following general formula (3 ) Represents a group represented by) (In the formula, n represents 1 or 2.) (In the formula, Y represents a sulfur atom, an oxygen atom or a nitrogen atom)