JPH0521823A - Photovoltaic element - Google Patents

Abstract

PURPOSE:To offer an element having high conversion efficiency as an organic photovoltaic element by finding a new effective organic semiconductor material being stable and hard to generate a pin hole such as to be used for a photovoltaic element of an organic/organic pn type. CONSTITUTION:In a photovoltaic element including a part consisting of two organic semiconductor layers generating an internal electric field by junction between two electrodes of which at least one is transparent, the semiconductor layer consists of a compound shown by a formula (I), (II), (III), (IV), (V) or (VI).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic element which is also useful as an optical sensor or the like.

[0002]

2. Description of the Related Art A lot of research has been conducted on photovoltaic devices using organic materials as active materials. The purpose is difficult to achieve with single crystal, polycrystal, and amorphous Si.
This is to develop an inexpensive and non-toxic photovoltaic device.

Since a photovoltaic element is an element that converts light energy into electric energy (voltage × current), its conversion efficiency is a main evaluation target. The generation of photocurrent requires the presence of an internal electric field, but several device configurations are known as methods for generating an internal electric field.

1) Schottky junction or MIS type junction One that utilizes an internal electric field generated in a metal / semiconductor junction. As organic semiconductor materials, merocyanine dyes, phthalocyanine pigments and the like have been reported (AK Ghosh et al., J. Chem.
Appl. Phys. 49 , 5982 (1978)).
Although this element has a large open circuit voltage (V _oc ), since the metal material is used as the electrode, the light transmittance of the electrode is low. The actual light transmittance is at most 30%, usually around 10%. Also, these materials have poor oxidation resistance. Therefore, it is not possible to expect high conversion efficiency and stable characteristics with this element form.

2) Hetero pn junction using n-type inorganic semiconductor / p-type organic semiconductor junction A method utilizing an internal electric field generated when n-type inorganic semiconductor / p-type organic semiconductor is joined. CdS, Z as n-type material
nO or the like is used. Merocyanine dyes, phthalocyanines, etc. have been reported as p-type organic semiconductor materials (A.
Hor et al. Appl. Phys. Lett. , 42 . 1
5 (1983)). This device is limited in spectral sensitivity because charge generation is mainly performed in the organic layer. Normal,
This is because the organic layer is formed of a single material, but no organic semiconductor having strong light absorption from 400 to 800 nm exists at present. Therefore, with this element structure, although the problems of the light transmittance of the light incident electrode and the stability of the electrode can be solved, a high conversion efficiency cannot be expected because the spectral sensitivity region is narrow.

3) Utilizing an organic / organic hetero pn junction A technique utilizing an electric field generated when an electron-accepting organic substance and an electron-donating organic substance are bonded.

As the electron-accepting organic substance, dyes such as malachite green, methyl violet and pyrylium,
Condensed polycyclic aromatic compounds such as flavanthurone and perylene pigments have been reported, and phthalocyanine pigments, merocyanine dyes and the like have been reported as electron-donating organic substances (C. Tang Appl. Phys. Lett., 4
8 , 183 (1986)). It is currently the most desirable compared to the above two configurations. Light can be irradiated from the transparent electrode, and since photocharges can be generated with two kinds of materials, the spectral sensitivity can be expanded. But Ta
Mr. ng's technology has the following drawbacks.

The electron-donating organic substance and the electron-accepting organic substance have problems such as photocurrent, open-circuit voltage, stability and the like, and pinholes are easily generated during film formation. In addition, the materials described have electron-accepting organic substances having a spectral sensitivity in the short wavelength region, and electron-donating organic substances have a spectral sensitivity in the long wavelength region, so that the stacking combinations are limited.

[0009]

DISCLOSURE OF THE INVENTION An object of the present invention is to find a new effective organic semiconductor material which has good stability and is less likely to cause pinholes in an organic / organic pn type photovoltaic device. An organic photovoltaic element is to provide an element that provides high conversion efficiency.

[0010]

In order to achieve the above-mentioned object, as a result of intensive studies, as a result, two continuous organic semiconductor layers which generate an internal electric field by a junction between two electrodes, at least one of which is transparent. It was found that the object can be achieved by using a specific diimidazole compound as the organic semiconductor material in a photovoltaic device having the following laminated structure.

That is, according to the present invention, an organic / organic pn type photovoltaic element having two stacked organic semiconductor layers which generate an internal electric field by a junction between two electrodes, at least one of which is transparent. In the general formula (I) and (I
By using the diimidazole compounds represented by I), (III), (IV), (V), and (VI), it is possible to provide an organic photovoltaic device having high conversion efficiency. The organic / organic pn type device according to the present invention is composed of two layers, which are an electron-accepting organic semiconductor and an electron-donating organic semiconductor layer, which are stacked, and the electron-accepting property and the electron-donating property are two layers. The diimidazole compound may also be electron-donating, depending on the relative electronic states of, and thus the other layered material.

In the organic photovoltaic element of the present invention, the diimidazole compounds represented by the above general formulas (I), (II) and (III) used as a material for the organic semiconductor layer are, for example, structural formulas.

[0013]

[Chemical 10]

Biphenyl tetracarboxylic acid anhydride represented by the general formula

[0015]

[Chemical 11]

X is produced by reacting a diamine compound represented by the same X _{1 to} X ₆ of claim 1.

Specific examples of the diimidazole compounds represented by the above general formulas (I), (II) and (III) are shown below.

[0018]

[Table 1]

[0019]

[Table 2]

Next, the diimidazole compounds represented by the above general formulas (IV), (V) and (VI) used as a material for the organic semiconductor layer are, for example, structural formulas

[0021]

[Chemical 12]

Tetraaminobiphenyl represented by the general formula

[0023]

[Chemical 13]

X is produced by reacting a dicarboxylic acid anhydride represented by the same as X _{7 to} X ₁₂ of claim 1.

Specific examples of the diimidazole compound represented by the above general formulas (IV), (V) and (VI) are shown below.

[0026]

[Table 3]

[0027]

[Table 4]

[0028]

[Table 5]

The present invention uses a diimidazole compound in an electron-accepting organic material layer or an electron-donating layer in an organic / organic pn type photovoltaic device. Such a photoelectric conversion device is shown in FIG. 2, FIG. 3, FIG.
It is used in the form of FIGS.

In FIG. 1, a transparent electrode 2, an electron-accepting organic material layer 3, an electron-donating organic material layer 4 and a back electrode 5 are laminated on a transparent insulating support 1, and the transparent electrode 2 and the back electrode 5 are respectively lead. The wire 6 is attached.

Here, the support 1 may be on the back electrode side. The order of the electron-accepting organic material layer 3 and the electron-donating organic material layer 4 may be reversed.

FIG. 2 shows a transparent n-type inorganic semiconductor layer 7 between the transparent electrode 2 and the electron-accepting organic material layer 3 shown in FIG.
Is provided.

The feature of this structure is that the transparent n-type inorganic semiconductor layer 7 is inserted. The n-type inorganic semiconductor layer 7 may be on the back electrode side. In this case, the n-type inorganic semiconductor layer 7 need not be translucent, but from the transparent electrode side, the electron-donating organic compound layer 4, the electron-accepting organic compound layer 3, the n-type The inorganic semiconductor layer 7 is arranged in this order. In the case of FIG. 2 as well, the support may be on the back electrode side as in FIG.

FIG. 3 shows the electron donating organic layer 4 of the device of FIG.
Is replaced with a two-layer structure including an electron-donating organic compound layer (1) 41 and an electron-donating organic compound layer (2) 42.

Also in this case, the order of the electron accepting layer 3 and the electron donating layer (1) 41 (2) 42 may be reversed. That is, the order is the electron donating organic compound layer (2) 42, the electron donating organic compound layer (1) 41, and the electron accepting organic compound layer 3.

FIG. 4 shows the device of FIG. 3 in which a translucent n-type inorganic semiconductor layer 7 is inserted. This layer may be on the back electrode side, and in this case, it does not have to be translucent, and the order of the organic material layers is opposite as in FIG.

In FIG. 5, the electron-accepting substance layer 3 of FIG. 1 is replaced with an electron-accepting substance layer (1) 31 and an electron-accepting substance layer (2) 32. Also in this case, the support may be on the back electrode side. The order of the electron-accepting layer and the electron-donating layer may be reversed, and in that case, the electron-accepting organic compound layer (2) 32, the electron-accepting organic compound layer (1) 31, and the electron-donating organic compound layer. The order is 4.

FIG. 6 shows the electron-accepting organic compound layer (2) 3 of FIG.
The n-type inorganic semiconductor layer 8 is inserted between 2 and the back electrode 5. The n-type inorganic semiconductor layer 8 may be on the transparent electrode side, in which case it needs to be translucent.
In addition, the order of the organic layers is reversed as in FIGS. 2 and 4.

The reason why the present device of FIGS. 1 to 6 has a photovoltaic function is that the local internal electric field generated at the interface between the electron-accepting organic material layer and the electron-donating organic material layer due to the difference in Fermi level between both layers. Due to. The light is absorbed in the portion where the internal electric field is working, so that carriers are generated. This is finally taken out as a current.
Therefore, how much light reaches and is absorbed at this interface, the level of the internal electric field generated between the electron-accepting organic material layer and the electron-donating organic material layer, the carrier-generating ability and the electron-accepting organic material layer, the electron Electron and hole transferability and injectability of the donor organic material layer are major factors in the conversion efficiency of the photovoltaic device. These largely depend on the materials used for the electron-accepting organic material layer and the electron-donating organic material layer, but at present, it is completely unknown what kind of material is suitable for each layer. The conversion efficiency (η) of the photovoltaic element is expressed by the following equation.

[0040]

[Equation 1]

In the above equation, V _oc is the voltage at opening, J _sc
Is a current at the time of a short circuit, and ff is a value indicating a factor of a voltage-current curve at the time of light irradiation called a filter factor. P _in
Is the incident light energy.

The n-type inorganic semiconductor layer provided in FIGS. 2, 4 and 6 serves to eliminate the energy barrier between the electron-accepting organic compound layer and the electrode material to smooth the movement of charges, and also has an electron-accepting property. It is considered to play a role of eliminating the effect of pinholes in the organic material layer.

The electron donating organic material layer (2) shown in FIGS. 3 and 4,
It is considered that the electron-accepting organic substance layer (2) 32 shown in FIGS. 5 and 6 plays a role of effectively utilizing the absorbed light in the photoactive layer and reducing the recombination establishment of generated charges.

The present invention has found that a diimidazole compound is effective as a material for the electron-donating organic substance layer or the electron-accepting organic substance layer in FIGS. 1 to 6. The diimidazole compound is shown in FIG. It is also effective as a material for the electron-donating organic compound layer (2) 42 in FIG. 4 and the electron-accepting organic compound layer (2) 32 in FIGS. The reason why this diimidazole compound is effective as a material for an electron-accepting organic substance of an organic / organic pn type photovoltaic device is not yet known. The organic semiconductor layer of the diimidazole compound is formed by vapor deposition, spin coating or dipping. Vapor deposition is preferred for thinning and uniforming. The thin film preferably has a thickness of 50 to 3000A.

Next, various materials used for the photovoltaic element of the present invention, manufacturing methods and the like will be described.

As the transparent insulating support used in the present invention, glass, plastic film or the like is used.

As the transparent electrode used in the present invention, indium tin oxide (ITO), tin oxide, indium oxide, zinc oxide, semitransparent Au, etc. are used. The preferred thickness is 100-10,000A.

As the n-type semiconductor layer used in the present invention, zinc oxide, zinc oxide doped with a trivalent metal,
CdS, titanium oxide, amorphous silicon doped with phosphorus, n-type crystalline silicon, or the like is used. this house,
When translucency is required, zinc oxide, zinc oxide doped with a trivalent metal, CdS, titanium oxide or the like is used. The thickness is 10 to 10,000 when it is translucent.
A, otherwise thicker is possible.

The material for the electron-accepting organic material layers (1) and (2) used in the present invention is a perylene pigment Pigment Red (hereinafter PR).
179, PR190, PR149, PR189, PR1
23, Pigment Brown 26, etc. Perinone-based pigment Pigment Orange 4
3, PR 194, etc. Anthraquinone-based pigments PR168, PR177, Va
t Yellow 4, etc. Quinone-containing yellow pigments such as flavansulon, etc. Dye fluorenone such as crystal violet, methyl violet, malachite green, etc., 2,4,7 trinitrofluorenone, tetracyanoquinodimethane, acetbuta compounds such as tetracyanoethylene, etc. You can These are vapor deposition, spin coating,
It is formed by dipping. Vapor deposition is preferred for thinning and uniforming. The film thickness is preferably 100 to 3000A.

The electron-donating organic material layers (1) and (2) used in the present invention include phthalocyanine pigments (having a central metal of Cu, Zn, Co, Ni, Pb, Pt, Fe, M).
trivalent metal phthalocyanine, halogenated copper phthalocyanine, chlorinated copper phthalocyanine, etc. to which a halogen atom is coordinated such as divalent compounds such as g, metal-free phthalocyanine, aluminum chlorophthalocyanine, indium chlorophthalocyanine, indium bromophthalocyanine, gallium chlorophthalocyanine, etc. , Other phthalocyanines in which oxygen is coordinated such as vanadyl phthalocyanine and titanyl phthalocyanine) Indigo, thioindigo pigments (Pigment Bl)
ue 66, Pigment Violet 36
Etc.), quinacridone pigment (Pigment Viol)
et 19, Pigment Red 122) A dye such as a merocyanine compound, a cyanine compound, and a squarylium compound A polymer having a π-electron conjugate refers to a polymer having a π-electron conjugate including a lone electron pair (for example, Lone pair of nitrogen). For example, the following may be mentioned.

Polyacetylenes, Polydiacetylenes Heterocyclic polymers such as polythiophene, polysubstituted thioene, polypyrrole, polysubstituted pyrrole, polyfuran, polysubstituted furan, polyindole and polycarbazole.

Amine-based polymers such as polyaniline, polysubstituted aniline, polydiphenylamine, poly (N, N'-diphenylbenzidine), polydiaminonaphthalene, polytriphenylamine and polyaminopyrene.

Condensed ring and condensed polycyclic polymers such as polyparaphenylene and polyazulene.

Polyvinylcarbazole Electrolytic Oxidation Polymer These conjugated polymers are synthesized by chemical polymerization or electrolytic polymerization.

Charge transfer agents used in organic electrophotographic photoreceptors (hydrazone compounds, pyrazoline compounds, triphenylmethane compounds, triphenylamine compounds, styryl compounds, benzosidithiol compounds, oxadiazole compounds, oxazole compounds, etc.), electric conduction -Donating compounds used in basic organic charge transfer complexes (tetrathiofulvalene, tetraphenyltetrathioflavalene, etc.)
Etc. can be mentioned.

These layers are formed by vapor deposition, spin coating, dipping, electrolytic polymerization or the like. In this,
Vapor deposition is preferred for thinning and uniforming.

A suitable thin film for the electron-donating organic layers (1) and (2) is 50 to 3000 A. Further, as the back electrode used in the present invention, a metal having a high work function such as Au, Pt, Ni, Pd, Cu, Cr or Ag is used when it comes into contact with the electron donating organic material layer. In addition, when contacting with the electron-accepting organic material layer, Al, In, Pb, Zn, M
g, Ag, etc. are used. Furthermore, when contacting with the n-type inorganic semiconductor layer, these metals and the above-mentioned metals having a high work function are also used. The film thickness of the metal is preferably 50 to 3000A.

[0058]

The present invention will be described in more detail with reference to the following examples.

Example 1 Well-cleaned ITO glass (Matsuzaki Vacuum, 30Ω / □)
On top, about 400 A of perylene tetracarboxylic acid methylimide (PL-ME), which is an electron-accepting substance, is deposited by vacuum deposition.
Thickness, and then the exemplary compound No. Diimidazole of 6 was provided in a thickness of about 400 A, and gold was vacuum-deposited on it.
The area formed by ITO and gold was 0.25 cm ² . Lead wires were attached to the two electrodes with silver paste.

The conversion efficiency was measured by applying a voltage swept at 6 mV / s to the ITO side of this device while irradiating it with white light of 75 mW / cm ² , and V _oc = 0.25 V, J _sc
= 0.25 mA / cm ² , ff = 0.28, and a conversion efficiency of 0.023% was obtained. This value is large for an organic photovoltaic element.

Example 2 Well-cleaned ITO glass (Matsuzaki Vacuum, 30Ω / □)
When the substrate temperature is about 250 ° C., argon is used as an introduction gas, and the zinc oxide is about 1 by RF magnetron sputtering.
It was provided with a thickness of 500A. Then, perylene tetracarboxylic acid methylimide (PL-ME), which is an electron-accepting substance, was deposited in a thickness of about 400 A by a vacuum deposition method, and then the exemplified compound No. Diimidazole of 6 was provided in a thickness of about 400 A, and gold was vacuum-deposited on it. The area formed by ITO and gold was 0.25 cm ² . Lead wires were attached to the two electrodes with silver paste.

The conversion efficiency was measured in the same manner as in Example 1 below. As a result, V _oc = 0.40 V, J _sc = 0.30 mA
/ Cm ² , ff = 0.32, and a conversion efficiency of 0.051% was obtained. This value is large for an organic photovoltaic element.

Example 3 On zinc oxide prepared in the same manner as in Example 2, perylene tetracarboxylic acid methylimide (PL-ME), which is an electron-accepting substance, was deposited in a thickness of about 400 A by the vacuum deposition method. Compound No. The conversion efficiency was measured in the same manner as in Example 1 except that the diimidazole of 6 was provided in a thickness of about 100 A and quinacridone (QA) was provided in a thickness of about 300 A. As a result, V _oc = 0.44 V, J _sc = 0.58 mA /
cm ² , ff = 0.35, and a conversion efficiency of 0.12% was obtained. This value is large for an organic photovoltaic element.

Example 4 On zinc oxide prepared in the same manner as in Example 2, perylene tetracarboxylic acid methylimide (PL-ME), which is an electron-accepting substance, was vacuum-deposited to a thickness of about 400 A, and then aluminum. Chlorphthalocyanine (AlClPc)
With a thickness of about 100 A, and the exemplary compound No. Example 1 except that the diimidazole of 6 was provided at a thickness of about 300A.
The conversion efficiency was measured in the same manner as in. As a result, V _oc =
0.47V, J _sc = 1.39mA / cm ² , ff = 0.38
The conversion efficiency was 0.33%. This value is large for an organic photovoltaic element.

Example 5 The diimidazole of Example 3 was added to No. A device was manufactured in the same manner as in Example 3 except that the conversion efficiency was changed to 9, and the conversion efficiency was measured in the same manner as in Example 1. As a result, V _oc = 0.52V, J _sc =
0.19 mA / cm ² , ff = 0.32, and conversion efficiency was 0.
042% was obtained.

Example 6 The diimidazole of Example 3 was added to No. A device was manufactured in the same manner as in Example 3 except that the conversion efficiency was changed to 20, and the conversion efficiency was measured in the same manner as in Example 1. As a result, V _oc = 0.55V, J _sc
= 0.25 mA / cm ² , ff = 0.31, and a conversion efficiency of 0.057% was obtained.

Example 7 Well-cleaned ITO glass (Matsuzaki Vacuum, 30 Ω / □)
On the top, exemplary compound N, which is an electron-accepting substance by vacuum deposition
o. 27 with a thickness of about 400 A, and then aluminum chlorophthalocyanine (AlClP) which is an electron donating substance.
c) was provided with a thickness of about 400 A, and gold was vacuum-deposited on it. The area formed by ITO and gold was 0.25 cm 2. Two
Lead wires were attached to the two electrodes with silver paste.

The conversion efficiency was measured by applying a voltage swept at 6 mV / s to the ITO side of this device while irradiating it with white light of 75 mW / cm ² , and found that V _oc = 0.38 V, J _sc
= 0.12 mA / cm ² , ff = 0.20, and a conversion efficiency of 0.012% was obtained. This value is large for an organic photovoltaic element.

Example 8 Well-cleaned ITO glass (Matsuzaki Vacuum, 30Ω / □)
When the substrate temperature is about 250 ° C., argon is used as an introduction gas, and the zinc oxide is about 1 by RF magnetron sputtering.
It was provided with a thickness of 500A. In addition, the compound No. 27 was provided with a thickness of about 400 A, and then aluminum chlorophthalocyanine (AlClPc), which is an electron donating substance, was provided with a thickness of about 400 A, and gold was vacuum-deposited thereon. The area formed by ITO and gold was 0.25 cm ² . Lead wires were attached to the two electrodes with silver paste.

The conversion efficiency was measured in the same manner as in Example 7. As a result, V _oc = 0.51 V, J _sc = 0.23 mA
/ Cm ² , ff = 0.22, and a conversion efficiency of 0.035% was obtained. This value is large for an organic photovoltaic element.

Example 9 On the zinc oxide prepared in the same manner as in Example 8, the exemplified compound No. 27 to about 40
The conversion efficiency was measured in the same manner as in Example 7, except that aluminum chlorophthalocyanine (AlClPc) was provided at a thickness of about 100 A, and quinacridone (QA) was provided at a thickness of about 300 A. As a result, V
_{oc = 0.50V, J sc = 0.37mA} / cm 2, ff = 0.
And the conversion efficiency was 0.062%. This value is large for an organic photovoltaic element.

Example 10 The electron-accepting substance of Example 9 was prepared using the compound No. A device was prepared in the same manner as in Example 9 except that the conversion efficiency was changed to 44, and the conversion efficiency was measured in the same manner as in Example 7. As a result, V _oc = 0.5
5V, J _sc = 0.25 mA / cm ² , ff = 0.24, and a conversion efficiency of 0.044% was obtained.

Example 11 The electron accepting substance of Example 9 was prepared using the compound No. A device was prepared in the same manner as in Example 9 except that the conversion efficiency was changed to 51, and the conversion efficiency was measured in the same manner as in Example 7. As a result, V _oc = 0.4
8 V, J _sc = 4.25 mA / cm ² , ff = 0.32, and a conversion efficiency of 0.087% was obtained.

Example 12 The electron-accepting substance of Example 9 was prepared using the compound No. A device was prepared in the same manner as in Example 9 except that 54 was used, and the conversion efficiency was measured in the same manner as in Example 7. As a result, V _oc = 0.4
5 V, J _sc = 0.67 mA / cm ² , ff = 0.35, and a conversion efficiency of 0.14% was obtained.

[0075]

The effects of the photovoltaic device of the present invention described above are summarized as follows.

1. In the organic / organic pn type photovoltaic device, high conversion efficiency as an organic substance was obtained by using such a diimidazole compound as a material of the organic semiconductor layer.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a specific example of a photovoltaic element of the present invention.

FIG. 2 is a schematic cross-sectional view showing a specific example of the photovoltaic element of the present invention.

FIG. 3 is a schematic cross-sectional view showing a specific example of the photovoltaic element of the present invention.

FIG. 4 is a schematic cross-sectional view showing a specific example of the photovoltaic device of the present invention.

FIG. 5 is a schematic cross-sectional view showing a specific example of the photovoltaic element of the present invention.

FIG. 6 is a schematic cross-sectional view showing a specific example of the photovoltaic element of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent insulating support 2 Transparent electrode 3 Electron-accepting organic compound layer 31 Electron-accepting organic compound layer (1) 32 Electron-accepting organic compound layer (2) 4 Electron-donating organic compound layer 41 Electron-donating organic compound layer (1) 42 Electron-donating Organic compound layer (2) 5 back electrode 6 lead wire 7 translucent n-type inorganic semiconductor layer 8 n-type inorganic semiconductor layer

Claims (1)

Claim: What is claimed is: 1. A photovoltaic device having two stacked organic semiconductor layers, at least one of which is transparent, between which two electrodes generate an internal electric field by a junction. The organic semiconductor layer is a compound of any one of the following general formulas (I), (II) and (III), or general formulas (IV), (V) and (VI)
2. A photovoltaic element comprising a compound of [Chemical 1] [Chemical 2] [Chemical 3] However, in the above general formulas (I), (II) and (III), X ₁
~ X ₆ is as follows. [Chemical 4] It is one of the [Chemical 5] [Chemical 6] [Chemical 7] However, X _{7 in} the above general formulas (IV), (V) and (VI)
~ X ₁₂ is as follows. [Chemical 8] [Chemical 9] And any of R _{1 to} R ₁₇ in the above substituents.
Represents a halogen atom, an alkyl group, an alkoxy group, a cyano group, and a nitro group, and n _{1 to} n ₁₇ represent an integer of 0 to 4. When n is 2 or more, R _{1 to} R ₁₇ may be different from each other.