JP6739290B2 - Material for photoelectric conversion element for imaging device and photoelectric conversion element including the same - Google Patents

Description

The present invention relates to a novel fused polycyclic aromatic compound that can be used in photoelectric conversion devices, image pickup devices, optical sensors, organic semiconductor devices and the like.

In recent years, interest in organic electronic devices has increased. Its characteristics are that it has a flexible structure and can be made large in area, and further, it enables an inexpensive and high-speed printing method in the electronic device manufacturing process. Typical devices include organic EL elements, organic solar cell elements, organic photoelectric conversion elements, organic transistor elements, and the like. Organic EL devices are expected to serve as main targets for next-generation display applications as flat panel displays, are applied to mobile phone displays, TVs, etc., and are being further developed for higher functionality. Organic solar cell elements and the like have been researched and developed as flexible and inexpensive energy sources, and organic transistor elements and the like have been made into flexible displays and inexpensive ICs.

In the development of organic electronic devices, the development of materials that make up the devices is very important. Therefore, many materials have been studied in each field, but they cannot be said to have sufficient performance, and materials useful for various devices are still being vigorously developed. Among them, compounds having a mother skeleton of benzothienobenzothiophene or the like have also been developed as organic electronic materials (Patent Documents 1 to 3), and when an alkyl derivative of benzothienobenzothiophene is used, a semiconductor thin film is formed by a printing process. However, it has a problem that the heat resistance of the organic electronic device is inferior because a phase transition is likely to occur at a low temperature because the number of condensed rings is relatively small with respect to the alkyl chain length.

Further, in recent years in organic electronics, the organic photoelectric conversion element is expected to be developed into a next-generation image pickup element, and some groups have reported on it. For example, an example in which a quinacridone derivative or a quinazoline derivative is used for a photoelectric conversion element (Patent Document 4), an example in which a photoelectric conversion element using a quinacridone derivative is applied to an imaging element (Patent Document 5), and a diketopyrrolopyrrole derivative is used. There is an example (Patent Document 6). In general, it is considered that the performance of an image pickup device is improved by aiming to reduce dark current for the purpose of achieving high contrast and power saving. Therefore, in order to reduce the leak current from the photoelectric conversion unit in the dark, a method of inserting a hole blocking layer or an electron blocking layer between the photoelectric conversion unit and the electrode unit is used.

The hole blocking layer and the electron blocking layer are generally widely used in the field of organic electronic devices, and are arranged at the interface between an electrode or a conductive film and other films in the constituent films of the device, respectively. It is a film having a function of controlling the reverse transfer of holes or electrons, and is a film for adjusting unnecessary leakage of holes or electrons. Depending on the device application, heat resistance, transmission wavelength, film forming method, etc. It is selected and used in consideration of the characteristics of. However, the performance requirements for materials for photoelectric conversion devices are particularly high, and conventional hole blocking layers or electron blocking layers are sufficiently satisfactory in terms of leakage current prevention characteristics, heat resistance to process temperature, and visible light transparency. It cannot be said that it has excellent performance, and has not yet been used commercially.

JP, 2008-258592, A WO2008-047896 WO2010-098372 Patent 4945146 Patent No. 5022573 Japanese Patent Laid-Open No. 2008-290963

J. Am. Chem. Soc., 2006, 128(39), 12604.

The present invention has been made in view of such circumstances, and is a photoelectric conversion element having excellent hole or electron leakage prevention characteristics, hole or electron transport characteristics, heat resistance to process temperature, visible light transparency, and the like. Another object of the present invention is to provide a novel fused polycyclic aromatic compound that can be used in various electronic devices including organic transistors having excellent mobility and heat resistance.

As a result of diligent efforts to solve the above problems, the present inventor has found that the above problems can be solved by using a compound represented by the following formula (1), and has completed the present invention.
That is, the present invention is as follows.
[1] The following formula (1)

(In the formula (1), R ₁ and R ₂ each independently represent a substituted or unsubstituted heterocyclic condensed aromatic group), and a material for a photoelectric conversion element for an imaging element,
[2] The compound of formula (1) is represented by the following formula (2)

(In the formula (2), R ₁ and R ₂ have the same meanings as those in the formula (1) described in the above item [1].) For the image pickup device described in the above item [1]. Photoelectric conversion element material,
[3] The material for a photoelectric conversion element as described in the above item [1], wherein the heteroatoms contained in the heterocyclic condensed aromatic group represented by R ₁ and R ₂ are each independently a sulfur atom or an oxygen atom,
[4] R ₁ and R ₂ are each independently a substituted or unsubstituted furan-condensed aromatic group or a substituted or unsubstituted thiophene-condensed aromatic group, and the photoelectric conversion element for an imaging device according to the above [3]. Materials for
[5] R ₁ and R ₂ are substituted or unsubstituted benzo[b]furan, or substituted or unsubstituted benzo[b]thiophene, the photoelectric conversion element material for an image sensor according to the above item [4],
[6] A photoelectric conversion element for an image pickup device, comprising the material for a photoelectric conversion device for an image pickup element according to any one of [1] to [5] above.
[7] A photoelectric conversion device having a p-type organic semiconductor material and an n-type organic semiconductor material, wherein the p-type organic semiconductor material is the photoelectric conversion device for an image pickup device according to any one of items [1] to [5]. A photoelectric conversion element for an image pickup element including an element material,
[8] Photoelectric conversion having (A) first electrode film, (B) second electrode film, and (C) photoelectric conversion unit arranged between the first electrode film and the second electrode film. An element, wherein the (C) photoelectric conversion part includes at least an organic thin film layer other than the (c-1) photoelectric conversion layer and the (c-2) photoelectric conversion layer, and the (c-2) photoelectric conversion layer. A photoelectric conversion element for an imaging device, wherein the organic thin film layer other than the layer includes the material for the photoelectric conversion device for an imaging device according to any one of [1] to [5] above,
[9] The photoelectric conversion element for an image pickup device according to the above item [8], wherein the organic thin film layer other than the photoelectric conversion layer (c-2) is an electron block layer.
[10] (c-2) The photoelectric conversion element for an image sensor according to the above item [8], wherein the organic thin film layer other than the photoelectric conversion layer is a hole blocking layer,
[11] (c-2) The photoelectric conversion element for an image pickup device according to the above item [8], wherein the organic thin film layer other than the photoelectric conversion layer is an electron transport layer.
[12] (c-2) The photoelectric conversion element for an image pickup device according to the above item [8], wherein the organic thin film layer other than the photoelectric conversion layer is a hole transport layer.
[13] Any one of the above [6] to [12], further including (D) a thin film transistor having a hole accumulating portion, and (E) a signal reading portion for reading a signal corresponding to an electric charge accumulated in the thin film transistor. The photoelectric conversion element for an image sensor according to the item,
[14] (D) A thin film transistor having a hole accumulating portion further has (d) a connecting portion that electrically connects the hole accumulating portion to one of the first electrode film and the second electrode film. The photoelectric conversion device for an image pickup device according to the item [13],
[15] An image pickup device in which the photoelectric conversion elements for an image pickup device according to any one of [6] to [14] are arranged in a plurality of arrays, and [16] any of [6] to [14]. An optical sensor including the photoelectric conversion element for an image sensor according to the item 1 or the image sensor according to the item [15].

INDUSTRIAL APPLICABILITY According to the present invention, a novel imaging device using a compound represented by the formula (1), which is excellent in required properties such as hole or electron leakage prevention property, transport property, heat resistance, and visible light transparency. A photoelectric conversion element can be provided.

FIG. 1 is a cross-sectional view illustrating an embodiment of the photoelectric conversion element for an image pickup device of the present invention.

The contents of the present invention will be described in detail. The description of the constituent elements described below is based on the representative embodiments and specific examples of the present invention, but the present invention is not limited to such embodiments and specific examples.

The first feature of the photoelectric conversion element material for an image sensor of the present invention is that it contains a compound represented by the following general formula (1).

R ₁ and R ₂ in the above formula (1) each independently represent a substituted or unsubstituted heterocyclic fused aromatic group.

The heterocyclic fused aromatic group represented by R ₁ and R _{2 in} formula (1) means a residue obtained by removing one hydrogen atom from a heterocyclic fused aromatic, and specific examples thereof include a benzothienyl group, Naphthienyl group, anthrathienyl group, benzodithienyl group, dibenzothienyl group, benzotrithienyl group, thienothienyl group, benzofuranyl group, naphthofuranyl group, anthrafuranyl group, benzodifuranyl group, dibenzofuranyl group, benzotrifuranyl group, quinolyl Group, isoquinolyl group, benzopyrrolyl group, indolenyl group, benzimidazolyl group, carbazolyl group, xanthenyl group and thioxanthenyl group. Of these, a heterocyclic condensed aromatic group having a thiophene ring or a furan ring as a heterocycle is preferable, a benzothienyl group or a benzofuranyl group is more preferable, and a 2-benzo[b]thienyl group or a 2-benzo[b]furanyl group is preferable. Is more preferable. Further, it is preferable that both R ₁ and R ₂ are the same.

Here, the "substituted or unsubstituted heterocyclic condensed aromatic group" means a heterocyclic condensed aromatic group or a heterocyclic condensed aromatic group in which a hydrogen atom on the heterocyclic condensed aromatic group is substituted with a substituent. Means a heterocyclic fused aromatic group in which the hydrogen atom of is not substituted with a substituent. When the heterocyclic fused aromatic group has a substituent, it may have at least one kind of substituent, and the substitution position and the number of substituents are not particularly limited.
The heterocyclic condensed aromatic group represented by R ₁ and R _{2 in} the formula (1) has no limitation on the substituents, for example, an alkyl group, an alkoxy group, an aromatic group, a halogen atom, a hydroxyl group, a mercapto group, a nitro group. , An alkyl-substituted amino group, an aryl-substituted amino group, an unsubstituted amino group (NH ₂ group), an acyl group, an alkoxycarbonyl group, a cyano group, an isocyano group and the like.

The alkyl group as a substituent which the heterocyclic fused aromatic group represented by R ₁ and R ₂ of the formula (1) has is not limited to linear, branched or cyclic, and the number of carbon atoms is also particularly Although not limited, it is usually a linear or branched alkyl group having 1 to 4 carbon atoms, or a cyclic alkyl group having 5 to 6 carbon atoms.
Specific examples of the alkyl group as the substituent of the heterocyclic fused aromatic group represented by R ₁ and R ₂ of the formula (1) include a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, and an n- group. Examples thereof include a butyl group, an iso-butyl group, a tert-butyl group, a sec-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, a cyclopentyl group and a cyclohexyl group, each of which has a carbon number of 1 to 4 It is preferably a chain or branched alkyl group, and more preferably a linear alkyl group having 1 or 2 carbon atoms.

Specific examples of the alkoxy group as the substituent of the heterocyclic fused aromatic group represented by R ₁ and R ₂ of the formula (1) include a methoxy group, an ethoxy group, a propoxy group, an iso-propoxy group, and an n-butoxy group. , Iso-butoxy group, t-butoxy group, n-pentyloxy group, iso-pentyloxy group, t-pentyloxy group, sec-pentyloxy group, n-hexyloxy group, iso-hexyloxy group, n-heptyl Oxy group, sec-heptyloxy group, n-octyloxy group, n-nonyloxy group, sec-nonyloxy group, n-decyloxy group, n-undecyloxy group, n-dodecyloxy group, n-tridecyloxy group, n-tetradecyloxy group, n-pentadecyloxy group, n-hexadecyloxy group, n-heptadecyloxy group, n-octadecyloxy group, n-nonadecyloxy group, n-eicosyloxy group, docosyloxy group, n -Pentacosyloxy group, n-octacosyloxy group, n-tricontyloxy group, 5-(n-pentyl)decyloxy group, heneicosyloxy group, tricosyloxy group, tetracosyloxy group, hexa C1-C36 alkoxy groups such as cosyloxy group, heptacosyloxy group, nonacosyloxy group, n-triacontyloxy group, squaryloxy group, dotriacontyloxy group and hexatriacontyloxy group. And an alkoxy group having 1 to 24 carbon atoms is preferable, an alkoxy group having 1 to 20 carbon atoms is more preferable, and an alkoxy group having 1 to 12 carbon atoms is further preferable. An alkoxy group having 1 to 6 is particularly preferable, and an alkoxy group having 1 to 4 carbon atoms is most preferable.

Specific examples of the aromatic group as the substituent of the heterocyclic fused aromatic group represented by R ₁ and R ₂ of the formula (1) include not only aromatic hydrocarbon groups such as phenyl group and naphthyl group but also the above The heterocyclic condensed aromatic group described above is included, and an aromatic hydrocarbon group is preferable. The aromatic group as the substituent which the heterocyclic fused aromatic group may have may have a substituent, and the substituent which may be present is represented by R ₁ and R ₂ of the formula (1). The same thing as the substituent which a heterocyclic condensed aromatic group has is mentioned.
Specific examples of the halogen atom as the substituent of the heterocyclic fused aromatic group represented by R ₁ and R ₂ of the formula (1) include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom.
The alkyl-substituted amino group as a substituent that the heterocyclic fused aromatic group represented by R ₁ and R ₂ of the formula (1) has is not limited to either a monoalkyl-substituted amino group or a dialkyl-substituted amino group, and these alkyl groups may be used. Examples of the alkyl group in the substituted amino group include the same as the alkyl group as the substituent of the heterocyclic fused aromatic group represented by R ₁ and R ₂ in formula (1).

The aryl-substituted amino group as a substituent which the heterocyclic fused aromatic group represented by R ₁ and R ₂ of the formula (1) has is not limited to either a monoaryl-substituted amino group or a diaryl-substituted amino group, and these aryls As the aryl group in the substituted amino group, the same aromatic hydrocarbon groups as those described in the paragraph of the substituent contained in the heterocyclic condensed aromatic group represented by R ₁ and R ₂ of the formula (1) can be mentioned.
The acyl group as the substituent which the heterocyclic fused aromatic group represented by R ₁ and R ₂ of the formula (1) has is a substituent which the heterocyclic fused aromatic group represented by R ₁ and R ₂ of the formula (1) has. The alkyl group described in the item of the substituent which the aromatic hydrocarbon group described in the item of the group or the heterocyclic condensed aromatic group represented by R ₁ and R ₂ of the formula (1) has is a carbonyl group (=CO group) And a substituent bonded to.
The alkoxycarbonyl group as a substituent of the heterocyclic condensed aromatic group represented by R ₁ and R ₂ of the formula (1) has the heterocyclic condensed aromatic group represented by R ₁ and R ₂ of the formula (1). The substituent which the alkoxy group as a substituent couple|bonded with the carbonyl group is mentioned.
The substituent that the heterocyclic fused aromatic group represented by R ₁ and R _{2 in} formula (1) has is preferably an alkyl group, an aromatic group, a halogen atom or an alkoxyl group, and a halogen atom or an unsubstituted aromatic group A group hydrocarbon group is more preferable, and a phenyl group or a biphenyl group is further preferable.

As R ₁ and R ₂ in the formula (1), it is preferable that they are the same substituted or unsubstituted 2-benzo[b]thienyl group or 2-benzo[b]furanyl group, and both are the same. A benzo[b]thienyl group or a 2-benzo[b]furanyl group having one or more substituents selected from the group consisting of a halogen atom and an unsubstituted aromatic group is more preferable, and both are the same. A benzo[b]thienyl group or a 2-benzo[b]furanyl group having a phenyl group is more preferable.

The substitution position of R ₁ and R ₂ in the above formula (1) is not particularly limited, but it should be the 2,7 position in [1]benzothieno[3,2-b][1]benzothiophene in the formula (1). Is preferred. That is, as the compound represented by the formula (1), a compound represented by the following general formula (2) is preferable.

In formula (2), R ₁ and R ₂ have the same meanings as in formula (1), and preferred ones are also the same as in formula (1).
That is, as the compound represented by the formula (2), those in which both R ₁ and R ₂ in the formula (2) are preferable or most preferable in the above-mentioned formula (1) are preferable.

Specific examples of the compound represented by the formula (1) are shown below, but the present invention is not limited to these specific examples.

The compound represented by the formula (1) can be synthesized by a known method disclosed in Patent Document 1, Patent Document 6 and Non-Patent Document 1. For example, the method described in the following scheme can be mentioned. A nitrostilbene derivative (A) is used as a raw material to form a benzothienobenzothiophene skeleton (D), and this is reduced to form an amination compound (E) (R ₁ and R ₂ in the formula (1) are amino groups. Compound) is obtained. When this compound (E) is halogenated, a halide (F) (a compound in which R ₁ and R ₂ in the formula (1) are halogen, and a compound in which R ₁ and R ₂ are iodine is described in the following scheme as an example. ) Is obtained, and this compound (F) is further coupled with a boric acid derivative to obtain a compound in which R ₁ and R ₂ in the formula (1) are aromatic groups and the like. The method of Patent Document 5 is more effective because a compound in which R ₁ and R ₂ in the formula (1) are aromatic groups or the like can be produced from the corresponding benzaldehyde derivative in one step.

The method for purifying the compound represented by formula (1) is not particularly limited, and known methods such as recrystallization, column chromatography, and vacuum sublimation purification can be adopted. Moreover, these methods can be combined as needed.

The photoelectric conversion device for an image pickup device of the present invention (hereinafter, may be simply referred to as “photoelectric conversion device”) has two electrodes facing each other (A) a first electrode film and (B) a second electrode film. An element in which (C) a photoelectric conversion unit is arranged between films, and light is incident on the photoelectric conversion unit from above (A) the first electrode film or (B) the second electrode film. .. (C) The photoelectric conversion unit generates electrons and holes according to the incident light amount, and the semiconductor reads out a signal corresponding to the charge, and the incident light amount according to the absorption wavelength of the photoelectric conversion film unit. Is an element showing. A transistor for reading may be connected to the electrode film on the side where light does not enter. When a large number of photoelectric conversion elements are arranged in an array, the photoelectric conversion elements show incident position information in addition to the amount of incident light, so that the photoelectric conversion elements are image pickup elements. When the photoelectric conversion element arranged closer to the light source does not block (transmit) the absorption wavelength of the photoelectric conversion element arranged behind it when viewed from the light source side, a plurality of photoelectric conversion elements are stacked. You may use. By stacking and using a plurality of photoelectric conversion elements each having a different absorption wavelength in the visible light region, a multicolor image pickup element (full-color photodiode array) can be obtained.

The photoelectric conversion element material for an image sensor of the present invention is used as a material forming the photoelectric conversion part (C).
The (C) photoelectric conversion part is selected from the group consisting of (c-1) the photoelectric conversion layer, and an electron transport layer, a hole transport layer, an electron block layer, a hole block layer, a crystallization preventing layer, an interlayer contact improving layer, and the like. It is often composed of an organic thin film layer other than the selected (c-2) photoelectric conversion layer. The photoelectric conversion element material for an image pickup device of the present invention can be used in any of the organic thin film layers other than the (c-1) photoelectric conversion layer and the (c-2) photoelectric conversion layer. It is preferably used for an organic thin film layer other than the layer.

The (A) first electrode film and the (B) second electrode film that the photoelectric conversion element for an image sensor of the present invention has (C-1) photoelectric conversion layer included in the (C) photoelectric conversion unit to be described later. In the case of having a hole transport property, or (c-2) an organic thin film layer other than the photoelectric conversion layer (hereinafter, the organic thin film layer other than the photoelectric conversion layer is also simply referred to as “(c-2)) organic thin film layer”. Is a hole transporting layer having a hole transporting property, it plays a role of taking out holes from the (c-1) photoelectric conversion layer or (c-2) organic thin film layer and collecting the holes. When (c-1) the photoelectric conversion layer contained in the (C) photoelectric conversion part has an electron transporting property, or (c-2) the organic thin film layer is an electron transporting layer having an electron transporting property, It plays a role of taking out electrons from the (c-1) photoelectric conversion layer and the (c-2) organic thin film layer and discharging the electrons. Therefore, the materials that can be used as the (A) first electrode film and the (B) second electrode film are not particularly limited as long as they have a certain degree of conductivity, but adjacent (c-1) photoelectric conversion layers (C-2) It is preferable to select it in consideration of the adhesion to the organic thin film layer, the electron affinity, the ionization potential, the stability, and the like. Examples of materials that can be used as (A) the first electrode film and (B) the second electrode film include tin oxide (NESA), indium oxide, indium tin oxide (ITO), and zinc indium oxide (IZO). Conductive metal oxides; metals such as gold, silver, platinum, chromium, aluminum, iron, cobalt, nickel and tungsten; inorganic conductive substances such as copper iodide and copper sulfide; conductive polymers such as polythiophene, polypyrrole and polyaniline Carbon, etc. may be mentioned. If necessary, a plurality of these materials may be mixed and used, or a plurality of these materials may be stacked in two or more layers and used. The conductivity of the material used for (A) the first electrode film and (B) the second electrode film is not particularly limited as long as it does not hinder the light reception of the photoelectric conversion element more than necessary. From the viewpoint of electric power, it is preferable to be as high as possible. For example, an ITO film having a sheet resistance of 300 Ω/□ or less sufficiently functions as (A) the first electrode film and (B) the second electrode film, but has a conductivity of about several Ω/□. It is desirable to use such a substrate having high conductivity, since a commercial product of a substrate provided with an ITO film having is available. The thickness of the ITO film (electrode film) can be arbitrarily selected in consideration of conductivity, but is usually 5 to 500 nm, preferably about 10 to 300 nm. Examples of methods for forming a film of ITO or the like include conventionally known vapor deposition methods, electron beam methods, sputtering methods, chemical reaction methods, coating methods, and the like. If necessary, the ITO film provided on the substrate may be subjected to UV-ozone treatment, plasma treatment, or the like.

Among the (A) first electrode film and the (B) second electrode film, as the material of the transparent electrode film used on at least one of the light incident sides, ITO, IZO, SnO ₂ , ATO ( Examples thereof include antimony-doped tin oxide), ZnO, AZO (Al-doped zinc oxide), GZO (gallium-doped zinc oxide), TiO ₂ and FTO (fluorine-doped tin oxide). (C-1) The transmittance of light incident through the transparent electrode film at the absorption peak wavelength of the photoelectric conversion layer is preferably 60% or more, more preferably 80% or more, and 95% or more. It is particularly preferable that

Further, when a plurality of photoelectric conversion layers having different wavelengths to be detected are laminated, the electrode films used between the photoelectric conversion layers (other than (A) the first electrode film and (B) the second electrode film). It is necessary to transmit light having a wavelength other than the light detected by each photoelectric conversion layer, and it is preferable to use a material that transmits 90% or more of incident light for the electrode film. It is more preferable to use a material that transmits% or more of light.

It is preferable that the electrode film is formed without plasma. By forming these electrode films without using plasma, the influence of the plasma on the substrate on which the electrode films are provided can be reduced, and the photoelectric conversion characteristics of the photoelectric conversion element can be improved. Here, plasma-free means that plasma is not generated during the formation of the electrode film, or the distance from the plasma generation source to the substrate is 2 cm or more, preferably 10 cm or more, more preferably 20 cm or more, and reaches the substrate. It means a state in which plasma is reduced.

Examples of the apparatus that does not generate plasma during the formation of the electrode film include an electron beam evaporation apparatus (EB evaporation apparatus) and a pulse laser evaporation apparatus. Hereinafter, a method of forming a transparent electrode film using an EB evaporation device is called an EB evaporation method, and a method of forming a transparent electrode film using a pulse laser evaporation device is called a pulse laser evaporation method.

As an apparatus that can realize a state in which plasma can be reduced during film formation (hereinafter referred to as a plasma-free film formation apparatus), for example, a facing target type sputtering apparatus, an arc plasma vapor deposition apparatus, or the like can be considered.

When the transparent conductive film is used as an electrode film (for example, the first conductive film), DC short circuit or increase in leak current may occur. One of the causes of this is that minute cracks generated in the photoelectric conversion layer are covered with a dense film such as TCO (Transparent Conductive Oxide), and between the transparent conductive film and the electrode film (second conductive film) on the opposite side. It is thought that this is due to an increase in the conduction of. Therefore, when a material such as Al having a poor film quality is used for the electrode, the increase in leak current is unlikely to occur. By controlling the film thickness of the electrode film according to the film thickness of the photoelectric conversion layer (the depth of cracks), it is possible to suppress an increase in leak current.

Usually, when the conductive film is made thinner than a predetermined value, the resistance value rapidly increases. The sheet resistance of the conductive film in the photoelectric conversion element for an image sensor of the present embodiment is usually 100 to 10000 Ω/□, and the degree of freedom in film thickness is large. In addition, the thinner the transparent conductive film, the smaller the amount of light absorbed, and generally the higher the light transmittance. When the light transmittance is high, the amount of light absorbed by the photoelectric conversion layer is increased and the photoelectric conversion ability is improved, which is very preferable.

The (C) photoelectric conversion part included in the photoelectric conversion element for an image pickup device of the present invention includes at least an organic thin film layer other than the (c-1) photoelectric conversion layer and the (c-2) photoelectric conversion layer.
An organic semiconductor film is generally used for the photoelectric conversion layer (c-1) constituting the photoelectric conversion part (C), but the organic semiconductor film may be a single layer or a plurality of layers. A P-type organic semiconductor film, an N-type organic semiconductor film, or a mixed film thereof (bulk heterostructure) is used as the material. On the other hand, in the case of a plurality of layers, the number of layers is about 2 to 10 and is a structure in which any one of a P-type organic semiconductor film, an N-type organic semiconductor film, or a mixed film (bulk hetero structure) thereof is laminated. A buffer layer may be inserted in.

(C-1) The organic semiconductor film of the photoelectric conversion layer has a triarylamine compound, a benzidine compound, a pyrazoline compound, a styrylamine compound, a hydrazone compound, a triphenylmethane compound, a carbazole compound, a polysilane compound depending on the absorption wavelength band. , Thiophene compound, phthalocyanine compound, cyanine compound, merocyanine compound, oxonol compound, polyamine compound, indole compound, pyrrole compound, pyrazole compound, polyarylene compound, carbazole derivative, naphthalene derivative, anthracene derivative, chrysene derivative, phenanthrene derivative, pentacene derivative, Phenyl butadiene derivative, styryl derivative, quinoline derivative, tetracene derivative, pyrene derivative, perylene derivative, fluoranthene derivative, quinacridone derivative, coumarin derivative, porphyrin derivative, fullerene derivative and metal complex (Ir complex, Pt complex, Eu complex, etc.) are used. be able to.

In the photoelectric conversion device for an image pickup device of the present invention, the organic thin film layer other than the (c-2) photoelectric conversion layer constituting the (C) photoelectric conversion part is a layer other than the (c-1) photoelectric conversion layer, for example, an electron. It is also used as a transport layer, a hole transport layer, an electron blocking layer, a hole blocking layer, a crystallization preventing layer, an interlayer contact improving layer, or the like. In particular, by using it as one or more thin film layers selected from the group consisting of an electron transport layer, a hole transport layer, an electron block layer and a hole block layer, an element capable of efficiently converting an electrical signal even with weak light energy can be obtained. Therefore, it is preferable.

The electron transport layer plays a role of transporting the electrons generated in (c-1) the photoelectric conversion layer to (A) the first electrode film or (B) the second electrode film, and (c) from the electrode film of the electron transport destination (c). -1) It plays a role of blocking the transfer of holes to the photoelectric conversion layer.
The hole transport layer transports the generated holes from the (c-1) photoelectric conversion layer to (A) the first electrode film or (B) the second electrode film, and the hole transport destination electrode film. To (c-1), it plays a role of blocking the transfer of electrons to the photoelectric conversion layer.
The electron blocking layer prevents transfer of electrons from the (A) first electrode film or the (B) second electrode film to the (c-1) photoelectric conversion layer, and (c-1) within the photoelectric conversion layer. It plays a role of preventing recombination and reducing dark current.
The hole blocking layer prevents movement of holes from (A) the first electrode film or (B) the second electrode film to the (c-1) photoelectric conversion layer, and It has the function of preventing the recombination in and reducing the dark current.
The hole blocking layer is formed by stacking or mixing two or more kinds of hole blocking substances. The hole blocking substance is not limited as long as it is a compound capable of blocking holes from flowing out of the electrode to the outside of the device. Examples of the compound that can be used in the hole blocking layer include, in addition to the compound represented by the general formula (1), phenanthroline derivatives such as bathophenanthroline and bathocuproine, silole derivatives, quinolinol derivative metal complexes, and oxadiazole derivatives. , Oxazole derivatives, quinoline derivatives and the like, and of these, one kind or two or more kinds can be used.

The organic thin film layer other than the (c-2) photoelectric conversion layer containing the compound represented by the general formula (1) can be particularly preferably used as the hole blocking layer. From the viewpoint of preventing leakage current, the hole blocking layer should have a large film thickness, but from the viewpoint of obtaining a sufficient amount of current when reading out a signal when light is incident, it is preferable that the film thickness be as thin as possible. .. In order to make these contradictory properties compatible, it is generally preferable that the film thickness of the (C) photoelectric conversion part including (c-1) and (c-2) is about 5 to 500 nm. The function of the layer in which the compound represented by the general formula (1) is used depends on what other compound is used in the photoelectric conversion element.
In addition, the hole blocking layer and the electron blocking layer preferably have a high transmittance at the absorption wavelength of the photoelectric conversion layer in order to prevent light absorption of the photoelectric conversion layer (c-1), and are preferably used as a thin film. preferable.

The thin film transistor outputs a signal to the signal reading unit based on the charge generated by the photoelectric conversion unit. The thin film transistor has a gate electrode, a gate insulating film, an active layer, a source electrode, and a drain electrode, and the active layer is formed of a silicon semiconductor, an oxide semiconductor, or an organic semiconductor.

If the active layer used for the thin film transistor is formed of an oxide semiconductor, the mobility of charges is much higher than that of the active layer of amorphous silicon, and it can be driven at a low voltage. In addition, when an oxide semiconductor is used, it is possible to form an active layer which has higher light transmittance than silicon and which is flexible. In addition, since an oxide semiconductor, particularly an amorphous oxide semiconductor, can be uniformly formed at a low temperature (for example, room temperature), it is particularly advantageous when a flexible resin substrate such as plastic is used. Further, since a plurality of secondary light receiving pixels are stacked, the lower secondary light receiving pixels are affected when forming the upper secondary light receiving pixels. The photoelectric conversion layer is particularly susceptible to heat, but oxide semiconductors, especially amorphous oxide semiconductors, are advantageous because they can be formed at low temperatures.

As the oxide semiconductor for forming the active layer, an oxide containing at least one of In, Ga, and Zn (for example, In—O system) is preferable, and at least two of In, Ga, and Zn are included. An oxide containing (for example, In-Zn-O-based, In-Ga-O-based, Ga-Zn-O-based) is more preferable, and an oxide containing In, Ga, and Zn is further preferable. As the In-Ga-ZnO based oxide semiconductor, the composition in a crystalline state is an oxide semiconductor is preferably represented by InGaO ₃ (ZnO) m (m is a natural number less than 6), in particular, more preferably InGaZnO ₄ .. The characteristic of the amorphous oxide semiconductor of this composition is that the electron mobility tends to increase as the electrical conductivity increases.

The signal reading unit reads charges generated and accumulated in the photoelectric conversion unit or a voltage corresponding to the charges.

FIG. 1 illustrates in detail the typical device structures of the photoelectric conversion device for an image sensor of the present invention, but the present invention is not limited to these structures. In the example of the embodiment shown in FIG. 1, 1 is an insulating part, 2 is one electrode film (first electrode film or second electrode film), 3 is an electron block layer, 4 is a photoelectric conversion layer, and 5 is a hole block. A layer, 6 represents the other electrode film (second electrode film or first electrode film), and 7 represents an insulating base material or a laminated photoelectric conversion element. The readout transistor (not shown in the drawing) may be connected to either the electrode film 2 or 6 and, for example, if the photoelectric conversion layer 4 is transparent, the side opposite to the light incident side. The film may be formed on the outer side of the electrode film (above the electrode film 2 or below the electrode film 6). If the thin film layers (electron block layer, hole block layer, etc.) other than the photoelectric conversion layer constituting the photoelectric conversion element do not extremely block the absorption wavelength of the photoelectric conversion layer, the direction of light incidence is at the top (Fig. 1) or the lower part (the insulating substrate 7 side in FIG. 1).

In the method for forming the (c-1) photoelectric conversion layer and the (c-2) organic thin film layer other than the (c-2) photoelectric conversion layer in the photoelectric conversion element for an image pickup device of the present invention, generally, resistance heating vapor deposition which is a vacuum process, Coating methods such as electron beam evaporation, sputtering, molecular lamination method, solution process casting, spin coating, dip coating, blade coating, wire bar coating, spray coating, etc., inkjet printing, screen printing, offset printing, letterpress printing, etc. A soft lithography method such as a printing method or a microcontact printing method, or a method combining a plurality of these methods can be adopted. The thickness of each layer cannot be limited because it depends on the resistance value and charge mobility of each substance, but is usually in the range of 7 to 5000 nm, preferably 1 to 1000 nm, more preferably 5 to 500 nm. Is the range.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
The blocking layer described in the examples may be either a hole blocking layer or an electron blocking layer. The photoelectric conversion element is manufactured by a vapor deposition machine integrated with the glove box, and the photoelectric conversion element is installed in a closed bottle-type measurement chamber (made by ALS Technology Co., Ltd.) in a nitrogen atmosphere glove box. Then, the application of the current voltage was measured. Unless otherwise specified, the current/voltage application measurement was performed using a semiconductor parameter analyzer 4200-SCS (Keithley Instruments Inc.). Unless otherwise specified, PVL-3300 (manufactured by Asahi Bunko Co., Ltd.) was used to irradiate incident light with an irradiation light wavelength of 550 nm and an irradiation light half-value width of 20 nm. The light-dark ratio in the examples indicates the current value when light irradiation is performed divided by the current value in the dark place.

Synthesis Example 1 (Synthesis of 2,7-bis(benzo[b]furan-2-yl)-[1]benzothieno[3,2-b][1]benzothiophene)
2,7-diiodo[1]benzothieno[3,2-b][1]benzothiophene (3.8 parts) synthesized by the method described in Japanese Patent No. 4945757 in DMF (250 parts), generally available Benzo[b]furan-2-ylboronic acid (1.9 parts), tripotassium phosphate (27 parts) and tetrakis(triphenylphosphine)palladium (0.47 parts) were mixed and at 90° C. under a nitrogen atmosphere. Stir for 6 hours. The obtained reaction solution was cooled to room temperature, water (250 parts) was added, and the solid content was collected by filtration. The obtained solid content was washed with acetone, dried, and then subjected to sublimation purification to obtain No. 1 of the above specific example. A compound represented by 1 (2.6 parts, yield 73%) was obtained.

Synthesis Example 2 (Synthesis of 2,7-bis(benzo[b]thiophen-2-yl)-[1]benzothieno[3,2-b][1]benzothiophene)
Synthesis Example 1 except that a commonly available benzo[b]thiophen-2-ylboronic acid (2.1 parts) was used instead of benzo[b]furan-2-ylboronic acid (1.9 parts). No. of the above specific example according to the above. A compound represented by 5 (2.7 parts, yield 70%) was obtained.

Example 1 (Production of photoelectric conversion element and evaluation thereof)
2,7-Bis(benzo[b]furan-2-yl)-[1]benzothieno[3,2-b][1]benzo was added to ITO transparent conductive glass (manufactured by Geomatec Co., Ltd., ITO film thickness 150 nm). Thiophene (a compound represented by No. 1 obtained in Synthesis Example 1) was deposited as a block layer by resistance heating vacuum deposition to a thickness of 50 nm. Next, 100 nm of quinacridone was vacuum-deposited as a photoelectric conversion layer on the block layer. Finally, 100 nm of aluminum was vacuum-deposited as an electrode on the above-mentioned photoelectric conversion layer, and the photoelectric conversion element for imaging devices of the present invention was produced. The light/dark ratio was 2.5×10 ⁵ when a voltage of 5 V was applied using ITO and aluminum as electrodes.

Example 2 (Production of photoelectric conversion element and its evaluation)
2,7-Bis(benzo[b]furan-2-yl)-[1]benzothieno[3,2-b][1]benzothiophene (Compound represented by No. 1 obtained in Synthesis Example 1) Instead of 2,7-bis(benzo[b]thiophen-2-yl)-[1]benzothieno[3,2-b][1]benzothiophene (shown in No. 5 obtained in Synthesis Example 2). The evaluation was carried out according to Example 1 except that the compound) was used, and the light/dark ratio was 2.5×10 ⁵ when a voltage of 5 V was applied.

Comparative Example 1 (Production of photoelectric conversion element and its evaluation)
2,7-Bis(benzo[b]furan-2-yl)-[1]benzothieno[3,2-b][1]benzothiophene (Compound represented by No. 1 obtained in Synthesis Example 1) Evaluation was carried out in accordance with Example 1 except that No. was used, and the bright/dark ratio was 4.7 when a voltage of 5 V was applied.

Comparative Example 2 (Production of photoelectric conversion element and its evaluation)
2,7-Bis(benzo[b]furan-2-yl)-[1]benzothieno[3,2-b][1]benzothiophene (Compound represented by No. 1 obtained in Synthesis Example 1) According to Example 1, except that 2,7-diphenyl[1]benzothieno[3,2-b][1]benzothiophene (a compound represented by the following formula (11)) was used instead of As a result of evaluation, the light/dark ratio was 600 when a voltage of 5 V was applied.

Comparative Example 3 (Production of photoelectric conversion element and evaluation thereof)
2,7-Bis(benzo[b]furan-2-yl)-[1]benzothieno[3,2-b][1]benzothiophene (Compound represented by No. 1 obtained in Synthesis Example 1) Evaluation was carried out in accordance with Example 1 except that tris(8-quinolinolato)aluminum was used instead of, and the light/dark ratio was 31 when a voltage of 5 V was applied.

Comparative Example 4 (Production of photoelectric conversion element and evaluation thereof)
2,7-Bis(benzo[b]furan-2-yl)-[1]benzothieno[3,2-b][1]benzothiophene (Compound represented by No. 1 obtained in Synthesis Example 1) Instead of using 2,7-bis(9-phenanthrenyl)-[1]benzothieno[3,2-b][1]benzothiophene (a compound represented by the following formula (12)), When evaluated in accordance with Example 1, the light/dark ratio was 690 when a voltage of 5 V was applied.

Comparative Example 5 (Production of photoelectric conversion element and evaluation thereof)
2,7-Bis(benzo[b]furan-2-yl)-[1]benzothieno[3,2-b][1]benzothiophene (Compound represented by No. 1 obtained in Synthesis Example 1) Instead of using 2,7-bis(1-naphthyl)-[1]benzothieno[3,2-b][1]benzothiophene (compound represented by the following formula (13)), When evaluated in accordance with Example 1, the light/dark ratio was 240 when a voltage of 5 V was applied.

The brightness/darkness ratios obtained in the evaluations of Examples 1 and 2 above clearly show excellent characteristics as a photoelectric conversion element for an image sensor.

From the above evaluation results, the photoelectric conversion element for an image sensor of the example including the material for a photoelectric conversion element for an image sensor of the present invention containing the compound represented by the formula (1) is the photoelectric conversion element for the image sensor of the comparative example. It is clear that it has better properties than.

As described above, the photoelectric conversion element for an image pickup device including the material for photoelectric conversion device for an image pickup device of the present invention containing the compound represented by the formula (1) has excellent performance in organic photoelectric conversion characteristics, Not only organic imaging devices with high resolution and high response, but also organic electronic devices such as organic EL devices, organic solar cell devices and organic transistor devices, optical sensors, infrared sensors, ultraviolet sensors, devices such as X-ray sensors and photon counters. And their applications in the fields of cameras, video cameras, infrared cameras, etc. are expected.

1 Insulation Part 2 Upper Electrode 3 Electron Block Layer or Hole Transport Layer 4 Photoelectric Conversion Part 5 Hole Block Layer or Electron Transport Layer 6 Lower Electrode 7 Insulating Substrate or Other Photoelectric Conversion Element

Claims (5)

A photoelectric conversion element having (A) a first electrode film, (B) a second electrode film, and (C) a photoelectric conversion part arranged between the first electrode film and the second electrode film. The (C) photoelectric conversion part contains at least an organic thin film layer other than the (c-1) photoelectric conversion layer and the (c-2) photoelectric conversion layer, and the (c-2) photoelectric conversion layer other than The organic thin film layer is represented by the following formula (2)

(In the formula (2) , R ₁ and R _{2 each} represent an unsubstituted benzo[b]furan or an unsubstituted benzo[b]thiophene ). A photoelectric conversion element for an image pickup element, which is an electron block layer or a hole block layer containing: The photoelectric conversion element for an image sensor according to claim 1 , further comprising (D) a thin film transistor having a hole accumulating portion and (E) a signal reading portion for reading a signal corresponding to an electric charge accumulated in the thin film transistor. (D) a thin film transistor having a hole accumulation unit further (d) according to claim 2 having a connecting portion for electrically connecting the one of the positive hole accumulation portion and the first electrode film and second electrode film The photoelectric conversion element for an image sensor according to item 1. An image pickup device in which a plurality of photoelectric conversion devices for an image pickup device according to any one of claims 1 to 3 are arranged in an array. An optical sensor including the photoelectric conversion element for an image pickup device according to claim 1 or the image pickup device according to claim 4 .

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