JPH0424970A - Organic solar cell - Google Patents

Abstract

PURPOSE:To obtain high efficiency of photoelectric conversion in a wide range of wavelength, by a method wherein, in a layer containing two or more kinds of organic pigment and organic dye having different spectral characteristics and work functions, a photoconductive layer in which the work function of the organic pigment is large as compared with that of the organic dye is used. CONSTITUTION:A glass plate is used as a substratum 4, on which a semitransparent aluminum conducting layer (500Angstrom ) is formed as a facing electrode 3 by a vacuum evaporation method. By a spin coating method, 5% methanol solution of polyamide resin is spread and an under coat layer is formed. Next, 5 pts.wt. of trisazo pigment, 5 pts.wt. of diazo pigment and 7 pts.wt. of hydrazone compound are mixed as the charge transfer dye, and applied to the under coat layer, thereby obtaining an organic photoconducting layer 2. A gold electrode 1 is subjected to vapor deposition by vacuum sputtering. In this case, it is necessary that the work function of at least out of organic pigments is larger than that of at least one organic dye by 0.3eV or more, and the work function of one organic pigment is separated from the other by 0.2V or more.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an organic solar cell, and more particularly to a functionally separated organic solar cell using a mixed system of an organic pigment and an organic dye.

[Prior Art] Due to its high conversion efficiency, solar cells are typically made of a single crystal of an inorganic semiconductor with a pn junction formed therein. These conversion efficiencies reach as high as 12 to 15% when silicon is used, for example.

However, solar cells using these inorganic semiconductor single crystals require many processes such as single crystal manufacturing and doping processes to manufacture the battery, resulting in extremely high production costs, making them unsuitable for consumer use. There wasn't. In order to reduce the production cost of such solar cells, research is being conducted on organic solar cells using organic photoconductors that can be easily formed into thin films by vapor deposition, casting, or the like.

Traditionally, known organic solar cell materials include natural dyes such as chlorophyll, synthetic dyes such as merocyanine and phthalocyanine, pigments, conductive polymer materials such as polyacetylene, and composite materials thereof. Organic solar cells have been devised that can be obtained by forming thin films using vapor deposition or casting methods.

However, the photoelectric conversion efficiency of conventional organic solar cells is extremely low, and when exposed to strong light irradiation, a large number of generated carriers fill up and cannot move smoothly. is at most 0
Examples of conventional organic solar cells in Japan include US Pat. No. 3,844,843 using crystal violet, and other US Pat. However, none of these have been put into practical use due to their low efficiency.

In addition, conventional organic solar cells have low mobility due to many carrier traps in the layer containing organic materials.
Carrier transport properties are very poor compared to inorganic crystalline semiconductors, and this is one of the causes of the poor efficiency mentioned above.In addition, carrier traps in the layer containing the above-mentioned organic material occur during continuous use. promotes the deterioration of the characteristics of
This was a major factor hindering the practical application of organic solar cells.

[Problems to be Solved by the Invention] The purpose of the present invention is to solve the problems of the prior art described above, and to provide a method that is inexpensive, has high photoelectric conversion efficiency even under strong light irradiation such as sunlight, and has a wide wavelength range. Our objective is to provide solar cells with high stability for continuous use.

[Means for Solving the Problems] The present invention provides an organic solar cell having an organic photoconductive layer and two electrodes, at least one of which is translucent, provided to sandwich the photoconductive layer, The photoconductive layer is 1
a binder resin containing at least one kind of organic dye and two or more kinds of organic pigments, wherein the work function of at least one organic pigment is 0.3 eV or more larger than the work function of at least one organic dye, and the work function of each organic pigment is are separated from each other by 0.2 eV or more.

In general, in organic photoconductive materials, the quantum efficiency during photoelectric conversion upon irradiation with light strongly depends on the arrangement of individual molecules. Therefore, when using an organic photoconductive material in a solar cell, it is very important to use a certain crystalline organic photoconductive material in order to increase the conversion efficiency of the solar cell.

Methods for obtaining a thin film of an organic photoconductive material include vacuum deposition, casting of an organic material solution, dipping, and casting and dipping of a dispersion of organic material particles.

In vacuum evaporation of organic materials, it is very difficult to selectively obtain the desired crystal form, and complex processes such as post-treatment are often required to obtain the desired crystal form. From the perspective of producing large-area organic solar cells, vacuum evaporation, which requires high equipment costs and involves a complicated process, has many disadvantages compared to casting and dipping methods.

Furthermore, in casting or dipping an organic material in a solution system, it is very difficult to obtain a thin film of an organic photoconductive material in the desired crystalline form, similar to the vacuum evaporation described above. At present, high conversion efficiency has not been achieved.

Here, for the purpose of obtaining an organic photoconductive material in a desired crystalline form, a casting method or a dipping method is used using a dispersion of organic photoconductive material particles in a desired crystalline form and a binder resin that have been previously obtained by various treatments. The method for obtaining thin films is attracting attention. However, when a film in which crystalline particles of an organic photoconductive material are simply dispersed in a binder resin is used as a solar cell, the transportability of photocarriers generated by light irradiation is very poor, resulting in poor conversion efficiency. Good stability in continuous use cannot be obtained.

Therefore, as a result of repeated studies on improving the transportability of carriers in films with this fine particle dispersion system, we found that, as in the present invention, photogenerated holes can be improved without interfering with light absorption and photocarrier generation in the crystalline particles of organic photoconductive materials. It has been found that it is an effective means to dissolve and mix an organic dye to be transported at the molecular level, and the work function of the organic pigment is 0.3 [eV] or more larger than the work function of the organic dye. This made it possible to provide an organic solar cell with high conversion efficiency and stability for long-term continuous use.

The solar cell of the present invention is formed by laminating a base 4, an electrode 3, an organic photoconductive layer 2, and an electrode 1, as shown in FIG. 1, for example. When light irradiation is performed from the electrode l side, the electrode] is made a transparent conductive layer, and when light irradiation is performed from the substrate 4 side, the substrate 4 and the electrode 3 are made transparent. The electrode (and base) on the side that is not irradiated with light does not necessarily have to be transparent.

As the organic photoconductive layer 2, a mixture of an organic dye and two types of organic pigments having different spectral characteristics mixed and dispersed in a polymer binder can be preferably used. Various conductive materials such as polymers, snow, and oxides such as ITO can be used as the electrodes. As the light-transmitting electrode, it is necessary to use a translucent material such as a semi-transparent thin film of metal or a transparent conductive oxide.

Furthermore, since the solar cell of the present invention obtains an electromotive force by the Schottky junction formed between the organic pigment and the electrode, it is possible to control the electromotive force of the solar cell by changing the material of the electrode.

Further, in the present invention, the electrode 1 and the photoconductive layer 2 or the electrode 3
In order to improve the adhesion between the photoconductive layer and the photoconductive N2, an undercoating stone can be provided between layers 1 and 2, between layers 2 and 3, etc.

A wide variety of materials can be used for the base 4 depending on the purpose, usage, and shape, such as metals such as aluminum and stainless steel, paper, and plastic, but the material is not particularly limited to these materials. However, when this organic solar cell is irradiated with light from the substrate side, the substrate needs to be translucent, and in this case, transparent glass, plastic, etc. are useful.

For the electrodes 1 and 3, it is desirable to select a material that can form a Schottky junction with the organic photoconductive layer and transfer photocarriers well.

Transport of photocarriers in the solar cell of the present invention is carried out in such a way that electrons of the photocarriers pass through an organic pigment and holes pass through an organic dye. Therefore, in order to maintain good transfer of photocarriers to and from each electrode, one electrode material has a work function smaller than all the organic pigments in the organic photoconductive layer, and the other electrode material has a work function smaller than all the organic pigments in the organic photoconductive layer. Select the one with a larger work function. Although the material for the electrode is not particularly limited, it is preferable that it satisfies this condition. Examples of the electrode material include metals such as aluminum, copper, and stainless steel, conductive polymers such as polyacetylene and polypyrrole, and layers in which quaternary ammonium salts are dissolved in polymers.

The present invention will be explained in more detail below.

The basic operating mechanism of the present invention is that a Schottky junction is formed between the electrode and the organic pigment in the organic photoconductive layer due to the difference in work functions between the two, and this barrier portion causes the organic pigment to absorb the irradiated light and emit light. Generate a carrier pair. Next, holes among the photocarrier pairs generated in the pigment are injected into the organic dye in the organic photoconductive layer, and the holes move through the dye and the electrons move through the pigment, respectively, according to the potential difference of the Schottky junction. It is something that moves.

In the present invention, a Schottky junction is created in the organic photoconductive layer, and the organic pigment is given the function of absorbing irradiated light and generating photocarriers, and the function of transporting electrons among the photocarriers. By giving organic dyes the ability to transport pores, we have made it possible to create functionally separated organic solar cells that effectively utilize the characteristics of each material.

When two or more types of organic pigments having different spectral characteristics, such as those having absorption at short wavelengths and long wavelengths, are mixed in the organic photoconductive layer, each organic pigment absorbs the irradiated light and generates photocarriers. Among the generated photocarriers, electrons move according to the potential difference of the Schottky junction formed between the electrode and the pigment, but because carrier traps exist between different organic pigments, the electron transportability is extremely poor. There were bad flaws. Therefore, by providing a work function difference of 0.2 [eV] or more between each organic pigment as in the present invention, it has become possible to improve the electron transportability within the pigment. Such an increase in electron transportability brings about a sensitizing effect, and by using the above pigments as pigments, it becomes possible to generate photocarriers over a wide range from short wavelengths to long wavelengths.

On the other hand, the work function of the pigment is 0 from the work function of the organic dye.
．． By increasing the value to 3 [eV] or more, holes among the photocarrier pairs generated within the pigment of the organic photoconductive layer are efficiently injected into the dye, and the transportability of holes is enhanced.

As described above, the organic solar cell of the present invention improves the transportability of electrons and holes by creating an energy difference between the organic pigments and between the pigment and the organic dye, thereby achieving high conversion efficiency and good continuous use. made possible.

The basic composition of the organic photoconductive layer 2 is an organic charge-generating pigment in the form of crystalline particles, an organic charge-transporting dye dissolved at the molecular level, and
A polymer that serves as a binder. These are mixed and dissolved in a solvent to form a dispersion, and a layer is formed from this dispersion by casting or dipping.

Organic charge-generating pigments include biryllium, thiopyrylium dyes, phthalocyanine pigments, anthoanthrone pigments, dibenzpyrenequinone pigments, biratron pigments, trisazo pigments, bisazo pigments, azo pigments, indigo pigments, quinactrin pigments, asymmetric quinocyanine, quinocyanine, etc. can be used.

In addition, methods such as milling and heat loss of a dispersion can be used to selectively change the charge-generating pigment into a crystalline form that provides good photoelectric properties. It is possible to obtain crystalline fine particles having the following crystalline form.

In the present invention, since light absorption and photocarrier generation are performed using this charge-generating pigment, it is preferable to use a charge-generating pigment that has good absorption of sunlight or visible light. It is desirable that near-infrared light has an absorption peak, and the charge transport dye should not interfere with light absorption in the charge-generating pigment, that is, it should be transparent to light that can be absorbed by the charge-generating pigment. It is desirable that the light absorption peak be at a wavelength of 400 nm or less, and the mixing ratio of the charge-generating pigment and the charge-transporting dye should range from 01 to SO, O in terms of molar ratio in order to achieve good generation, injection, and transport of photogenerated carriers. (dye/pigment), optimally from 1.0 to
It is in the range of 20.0.

Charge transport dyes include pyrene, N-ethylcarbazole, N-isopropylcarbazole, N-methyl-N-
Phenylhydrazino-3-methylidene-9-ethylcarbazole, N,N-diphenylhydrazino-3-methylidene-9-ethylcarbazole, N,N-diphenylhydrazino-3=methylidene-10-ethylphenothiazine, N,N -diphenylhydrazino-3-methylidene-
10-Nitylphenoxazine, p-diethylaminobenzaldehyde-N, N-diphenylhydrazone, p-diethylaminobenzaldehyde-N-α-naphthyl-N
-Phenylhydrazone, p-pyrrolidinobenzaldehyde-N,N-diphenylhydrazone, 1,3.3-trimethylindolenine-ω-aldehyde-N,N-diphenylhydrazone, p-diethylbenzaldehyde-3-
Hydrazones such as methylbenzthiazolinone-2-hydrazone, 2,5-bis(p-diethylaminophenyl)
-1,3,4-oxadiazole, 1-phenyl-3-
(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, 1-[quinolyl (2)]
-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, ]-[pyridyl(
2)]-3-(p-diethylaminostyryl)-5-(
p-diethylaminophenyl)pyrazoline, 1-[6-
Medoxybilidyl(2)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, 1-[pyridyl(3)]-3-(p-diethylaminostyryl)-5-(p -diethylaminophenyl)pyrazoline, 1-[levidyl(2)]-3-(p-
diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, 1-[pyridyl(2)]-3-
(p-diethylaminostyryl)-4-methyl-5-(
p-diethylaminophenyl)pyrazoline, 1-[pyridyl(2)]-3-(α-methyl-p-diethylaminostyryl)-5-(p-diethylaminophenyl)birazolone, ]-phenyl-3-(p- diethylaminostyryl)-4-methyl-5-(p-diethylaminophenyl)pyrazoline, 1-phenyl-3(α-benzyl-
p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, spiropyrazoline and other pyrazolines, 2-(p-diethylaminostyryl)-6
-Oxazole compounds such as dinithylaminobenzoxazole, 2-(p-diethylaminophenyl)-4-(p-dimethylaminophenyl)-5-(2-chlorophenyl)oxazole, 2-(p-diethylaminostyryl)-6 -thiazole compounds such as dinithylaminobenzothiazole, triarylmethane compounds such as bis(4-diethylamino-2-methylphenyl)-phenylmethane, 1,1-bis(4-N,N-diethylamino 2-methyl polyarylalkanes such as phenyl)hebutane, 1.1.2.2-tetrakis-(4-N,N-dimethylamino-2methylphenyl)ethane, N,N'
- benzidine compounds such as tetraethylbenzidine, a
-phenyl-4-N,N diphenylaminostilbene,
Examples include styryl compounds such as 5-(4-dimethylaminobenzylidene)-5H-dibenzo[ad]cyclohebutane, but any combination that satisfies the conditions of the present invention may be used.

The organic pigment is preferably dispersed in the form of particles in the photoconductive layer, and the organic charge transport dye is preferably uniformly dissolved throughout the layer. Therefore, it is desirable to select a solvent for the dispersion that can dissolve the organic dye.

Next, the binder resin used in the present invention is selected from acrylic resins, styrene resins, polyesters, polycarbonates, polyarylates, polysulfones, polyphenylene oxides, epoxy resins, polyurethane resins, alkyd resins, unsaturated resins, etc. Resins are preferred. Particularly suitable resins include polymethyl methacrylate, polystyrene, styrene-acrylonitrile copolymers, polycarbonates or diallyl phthalate resins, among which polymethyl methacrylate, polystyrene, styrene-acrylonitrile copolymers or diallyl phthalate resins are preferred. be.

The photoconductive layer of the present invention is formed by thoroughly dispersing the organic pigment, organic dye, and binder resin as described above together with a solvent using a method such as a homogenizer, ultrasonic wave, ball mill, sand mill, attritor, roll mill, etc., coating, and drying. be done.

Furthermore, the photoconductive layer of the present invention can contain various additives for the purpose of improving generation, injection, and transport properties of photogenerated carriers. Such additives include diphenyl, diphenyl chloride, 0-terphenyl, p-terphenyl, dibutyl phthalate, dimethyl glycol phthalate, dioctyl phthalate, triphenyl phosphoric acid, methylnaphthalene, benzophenone, chlorinated paraffin, dilaurylthiopropionate. , 3,5-dinitrosalicylic acid, and various fluorocarbons.

In the present invention, the adhesiveness of the photoconductive layer is improved between the substrate and the photoconductive layer, the coating property is improved, the substrate is protected, defects on the substrate are covered, charge injection property from the substrate is improved, and electrical breakdown of the photosensitive layer is achieved. An undercoat layer can be formed for protection against. Materials for the undercoat layer include polyvinyl alcohol and polyvinyl alcohol.
Examples include N-vinylimidazole, polyethylene oxide, ethyl cellulose, methyl cellulose, ethylene-acrylic acid copolymer, casein, polyamide, copolymerized nylon, glue, and seratin. These are each dissolved in a suitable solvent and applied onto the substrate. The film thickness is preferably about 0.001 to 5 μm.

[Example] Example 1 A glass plate of 100 mm x 100 mm was used as the substrate 4,
On top of this is a semi-transparent shape (51:1Qnm light transmittance 70%)
An aluminum conductive layer (500 people) was prepared as the counter electrode 3 by vacuum evaporation. Add to this 5% meta of polyamide resin (trade name, Amilan CM 8000, manufactured by Toshisha Co., Ltd.)
A two layer thick layer was formed by applying the solution using a subinner coating method.

Next, 5 parts (parts by weight, same applies hereinafter) of trisazo pigment (1) having the following structural formula p1 t 5 parts of a disazo pigment (1) having the following structural formula, polyvinyl butyral resin (trade name, S-LEC BXL)
(manufactured by Sekisui Chemical Co., Ltd.) and 60 parts of cyclohexanone were dispersed for 20 hours using a Santo Mill apparatus using 1 mm diameter glass beads.

To this dispersion, 7 parts of a hydrazone compound (3) having the structural formula shown was mixed as a charge transport dye, and the mixture was further dispersed in a sand mill for 20 hours until it was completely dissolved.

Fifty parts of methyl ethyl ketone was added to this dispersion and coated on the undercoat layer to obtain an organic photoconductive layer 2. At this time, the film thickness of this organic photoconductive layer was set to 05 μm. Next, a 20 mm x 20 gold electrode 1 was deposited on the organic photoconductive layer by vacuum sputtering to produce an organic solar cell.

In addition, the above organic pigments (1), (2) and organic dye (3) were made into a binderless pellet shape, and the work function was adjusted to 20° using a low energy electron spectrometer (Model AC-1, manufactured by Riken Keiki). The measurement was carried out under an environment of C45%RH. The results are in Table 1
It was shown to.

The organic solar cell produced as described above was exposed to 100 nm of light using a tungsten lamp as a light source and cutting off light of 500 nm or less using a Corning 3384 filter.
Irradiation was performed at a light intensity of mW/cm2. At this time, the open circuit voltage (Voc) is 1.2■, the short circuit current (Isc) is L 2mA, and the maximum power is lkΩ.
The conversion efficiency (E-E) was 0.70%.

Next, after continuous irradiation for 10 hours with the same amount of light and a load of 1Ω, the conversion efficiency (E + aax, .hr) was 0.65% and 7
The decrease was only about %.

Example 2 5 parts of disazo pigment (4) having the following structural formula was used instead of trisazo pigment (1), and polycarbonate resin (trade name: z-200, manufactured by Mitsubishi Gas) was used instead of butyral resin.
A sample similar to Example 1 was prepared except for using
A similar light irradiation experiment was conducted and the following results were obtained. The work function of 4) was also measured in the same manner as in Example 1, and the results are shown in Table 1.

Example 3 Type phthalocyanine (
(manufactured by Toyo Ink) (5) using 5 parts of disazo pigment (2)
Disazo pigment (6) 5 represented by the following structural formula instead of
A sample was prepared in the same manner as in Example 1, except that 20 parts of benzidine compound (7) represented by the following structural formula was used instead of the hydrazone dye, and the same light irradiation experiment was conducted. The following results were obtained. I got it.

Voc=1. lV I sc = 1.2 mA E, □ = 0.61% E□. , 1°h, = 0.60% In addition, the above τ-type phthalocyanine (5) and the disazo pigment (
6) and the work function of benzidine compound (7) in Example 1
Measurements were carried out in the same manner as above, and the results are shown in Table 1.

Example 4 As an organic photoconductive layer in the electrode configuration of Example 1, 5 parts of trisazo pigment (1), 5 parts of disazo pigment (4), 5 parts of te-type phthalocyanine ($15) 5i, and hydrazone dye (7) were used.
A sample similar to that in Example 1 was prepared except that 30 parts was used, and a similar light irradiation experiment was conducted to obtain the following results.

■. . = 1.7 [V] I sc = 0.9 [mA] E, 1lIl = 0.92 [%] E----Iohr = 0.88 [%] Also, the above trisazo pigment (1), disazo pigment The work functions of (4), τ-type phthalocyanine pigment (5), and hydrazone dye (7) were also measured in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 1 A sample similar to Example 1 was prepared, except that 7 parts of hydrazone compound (8) represented by the following structural formula was used instead of hydrazone dye (3), and a light irradiation experiment was conducted. Got the results.

■. C=0.75[V] I sc2 0.11 [mA E0. =0.07 [%co E,,, =0.02 [%co In addition, the above hydrazone dye (8) The work function of similar Measurements were carried out in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 2 Except for using 5 parts of the disazo pigment (9) shown by the following structural formula in place of the disazo pigment (1) and using 5 parts of the disazo pigment (6) I in place of the disazo pigment (2). A sample similar to that in Example 1 was prepared and a similar light irradiation experiment was conducted to obtain the following results.

V oc = 0.65 [V] I sc = 0.07 [mA] E ff111, = (1, [14 [%] E□8 +oh
-=0.01 [%] Also, the above disazo pigment (9)
The work function of was also measured in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 3 Hydrazone dye (3) instead of hydrazone dye (7)
A sample similar to that in Example 4 was prepared except that 30 parts was used, and a similar light irradiation experiment was conducted to obtain the following results.

■o. = 15 [v] I sc = 0.03 [mA = o, oB% = E-x, +ohr = 001 [%] In addition, pigments (1) and (4) used in the photoconductive layer )(5)
The work function of hydrazone dye (3) was also measured in the same manner as in Example 1, and the results are shown in Table 1.

[Effects of the Invention] As explained above, in a layer containing two or more types of organic pigments and organic dyes that have different spectral characteristics and a work function difference of 0.2 [eV] or more, the organic pigment The work function is 0.3 [eV] compared to the work function of organic dyes.
By using a solar cell having a large photoconductive layer, high photoelectric conversion efficiency was obtained over a wide wavelength range. Moreover, as can be seen from the comparison between the working example and the comparative example,
It has become possible to create a solar cell with almost no decrease in conversion efficiency even when used continuously at extremely strong light intensity of 100 mW/cm2.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing the structure of an example of the organic solar cell of the present invention. 1: Transparent electrode 2: Organic photoconductive layer 3/Counter electrode 4 2 Substrate M1 diagram

Claims (1)

[Claims] 1. An organic solar cell comprising an organic photoconductive layer and two electrodes, at least one of which is translucent, provided to sandwich the photoconductive layer, the photoconductive layer comprising: consisting of a binder resin containing one or more organic dyes and two or more organic pigments, in which the work function of at least one organic pigment is 0.3 eV or more greater than the work function of at least one organic dye, and the work function of each organic pigment is Organic solar cells whose functions are separated from each other by 0.2 eV or more. 2. The organic solar cell according to claim 1, wherein a mixing molar ratio of the total amount of the organic dye to the total amount of the organic pigment is in the range of 0.1 to 50.0.