JP7628068B2 - Organic compound, thin film, material for blue organic photoelectric conversion element, organic photoelectric conversion element, and organic imaging element using the same - Google Patents

Description

The present invention relates to an organic compound that is substituted benzothieno[2,3-d]naphtho[2,3-b]thiophene (hereinafter referred to as "BTNT"), a material for an organic photoelectric conversion element, an organic photoelectric conversion element, and an organic imaging element using the same.

Organic electronics devices have been the subject of research and development in recent years because they do not contain rare metals as raw materials and can be supplied steadily, and because they have flexibility not found in inorganic materials and can be manufactured using wet film formation methods. Specific examples of organic electronics devices include organic electroluminescence (EL) elements, organic solar cell elements, organic photoelectric conversion elements, and organic transistor elements, and various other applications that take advantage of the characteristics of organic compounds as well as their performance as devices are being considered.

Of the above devices, organic photoelectric conversion elements are used in light sensors, etc., and their use as image sensors, for example, is being considered. Currently, three-plate and single-plate image sensors using existing inorganic materials are known. Of these, the three-plate type has excellent sensitivity because light is separated into the three primary colors of red, green, and blue using a prism, and photoelectric conversion is performed for each light in the image sensor. However, it is difficult to miniaturize the device. On the other hand, the single-plate type has a structure in which a color filter is provided on the image sensor, which allows for miniaturization, but the resolution is inferior to that of the three-plate type. Against this background, organic image sensors with a photoelectric conversion film made of organic compounds stacked on top of each other are being considered today (Patent Document 1, Patent Document 2). Such organic imaging elements are made of a laminated structure of organic thin films made of organic materials that selectively absorb light in the red, green, and blue wavelength regions, respectively, and transmit light in other wavelength regions, that is, a laminated structure in which the absorption band of the organic material when formed into a thin film is in the range of 600 nm to 700 nm, a green photoelectric conversion layer in the range of 500 nm to 600 nm, and a blue photoelectric conversion layer in the range of 400 nm to 500 nm. Organic imaging elements with a laminated structure are attractive because they can be expected to be made smaller and have higher resolution, and are expected to be used in next-generation imaging devices.

In an organic imaging element having the above-mentioned layered structure, incident light passes through the blue photoelectric conversion layer, the green photoelectric conversion layer, and the red photoelectric conversion layer in that order. This means that the higher the wavelength selectivity of light absorption in the blue photoelectric conversion layer, the more the light transmittance to the green photoelectric conversion layer and the red photoelectric conversion layer improves, which is expected to increase the light utilization efficiency and realize a high-definition imaging element.

As materials for use in the blue photoelectric conversion layer of an organic imaging element having a laminated structure, coumarin 30 (Non-Patent Document 1), porphyrin derivatives (Non-Patent Document 2), anthraquinone derivatives (Patent Document 3), dinaphthothienothiophene derivatives (Patent Documents 4, 5, Non-Patent Document 3), and the like have been considered.
However, for example, Coumarin 30 described in Non-Patent Document 1 has a peak top at 410 nm in a thin film, and absorption at wavelengths from 450 to 500 nm is not efficient. The porphyrin derivative described in Non-Patent Document 2 shows specific photoelectric conversion performance, but has problems such as absorbing light with a wavelength of 500 nm or more and not having selectivity for blue light. The dinaphthothienothiophene derivative described in Patent Document 5 is also shown to have photoelectric properties, but when a film was actually formed, it was sensitive to light with a wavelength of 500 nm or more, and there was a problem with the selectivity for blue light. Due to these problems, a material that satisfies market demands for selectivity of absorption wavelength, photoelectric conversion properties, etc. has not yet been found.

JP 2003-158254 A JP 2005-303266 A JP 2011-238781 A JP 2011-192966 A JP 2018-26559 A

Jpn. J. Appl. Phys, 2010, 49, 111601.1-11160.4 Jpn. J. Appl. Phys. , 2005, 44(6A), 3743-3747 Org. Electron. ,2015,20,63-68

In view of the above circumstances, the present invention aims to provide a compound having a specific structure that efficiently absorbs light having a wavelength of 400 nm or more and 500 nm or less and has excellent light transmittance at wavelengths exceeding 500 nm, a material for a blue photoelectric conversion element for an imaging element that contains the compound, and an organic photoelectric conversion element obtained by using the photoelectric conversion material.

In order to overcome such problems, the inventors conducted extensive research and discovered that a BTNT derivative having a specific structure has a selective absorption band in the blue wavelength region, and that when the derivative is used in the photoelectric conversion portion of a photoelectric conversion element, it exhibits an excellent photoresponse current, thereby completing the present invention.
That is, the present invention
[1] The following formula (1)

(In formula (1), R ₁ to R ₄ each independently represent a hydrogen atom or an aromatic group which may have a substituent, and X represents an oxygen atom or a sulfur atom.)
A compound represented by the formula:
[2] A material for a blue photoelectric conversion element, comprising the compound represented by formula (1) according to the preceding item [1].
[3] An organic thin film made of the material for a blue photoelectric conversion element according to the preceding item [2].
[4] An organic photoelectric conversion element comprising the material for a blue photoelectric conversion element according to the above item [2] or the organic thin film according to the above item [3].
[5] A photosensor having the organic photoelectric conversion element according to the above item [4], and [6] an organic imaging element having the organic photoelectric conversion element according to the above item [4];
Regarding.

The organic photoelectric conversion element using the organic compound represented by formula (1) of the present invention selectively absorbs blue light with a maximum absorption in the light absorption band of 400 nm to 500 nm, and has excellent transmittance for light with wavelengths of 500 nm or more. In addition, since it shows an excellent photoresponsive current, it can be used in organic photoelectric conversion elements for blue light, organic imaging elements, and materials thereof.

FIG. 1 is a cross-sectional view illustrating an embodiment of the organic photoelectric conversion element of the present invention.

The present invention will now be described in detail. The components described herein are based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples.

The compound of the present invention is represented by the following formula (1).
In formula (1), R ₁ to _{R 4} each independently represent a hydrogen atom or an aromatic group which may have a substituent, and X represents an oxygen atom or a sulfur atom.

The aromatic group represented by _R1 to _R4 in formula (1) is a residue obtained by removing one hydrogen atom from an aromatic ring of an aromatic compound, and specific examples thereof include aromatic hydrocarbon groups such as a phenyl group, a biphenyl group, an indenyl group, a naphthyl group, an anthryl group, a fluorenyl group, and a pyrenyl group.
The aromatic group represented by R ₁ to R ₄ in formula (1) may have a substituent. In the present invention, the aromatic group having a substituent means an aromatic group in which one or more hydrogen atoms of the aromatic group are substituted with a substituent, and the substitution position and the substitution position are not particularly limited. In addition, the unsubstituted aromatic group means an aromatic group in which the hydrogen atoms of the aromatic group are not substituted with a substituent.
The aromatic group represented by R ₁ to R ₄ in formula (1) is not particularly limited, and examples thereof include a phenyl group, a biphenyl group, a naphthyl group, an anthryl group, and a pyrenyl group.

In formula (1), it is preferable that _R1 and _{R2 are} different, or _R3 and _R4 are different, it is more preferable that _R1 and _R2 are _different and _R3 and _R4 are different, it is further preferable that _R1 and _R3 are aromatic groups and _R2 and _R4 are hydrogen atoms.
It should be noted that formula (1) merely shows one resonance structure, and the resonance structure is not limited to the one shown.

Specific examples of compounds represented by formula (1) are shown below as compounds (A-1) to (A-14), but the compounds of the present invention are not limited to these. Note that the structural formulas shown as specific examples merely represent one of the resonance structures, and are not limited to the resonance structures shown.

The compound represented by formula (1) can be synthesized by the same reaction steps as in known methods (e.g., Japanese Patent No. 6161168). The purification method of these compounds is not particularly limited, and for example, washing, recrystallization, column chromatography, vacuum sublimation, etc. can be adopted, and these methods can be combined as necessary.
An example of a synthesis flow of the compound represented by formula (1) is described below. In the following flow, _R1 to _R4 and X have the same meanings as _R1 to _R4 and X in formula (1), Me represents a methyl group, and TMS represents a trimethylsilyl group.

The material for a blue photoelectric conversion device of the present invention contains the compound represented by formula (1) of the present invention.
The material for photoelectric conversion elements of the present invention may contain components other than the compound represented by formula (1) within a range that does not impair the effects of the present invention. However, since it is preferable that the material for blue photoelectric conversion elements of the present invention absorbs light in the blue wavelength region of 400 nm or more and 500 nm or less and absorbs little light with wavelengths exceeding 500 nm, it is preferable to use a component having similar light absorption properties as the above in combination.
The content of the compound represented by formula (1) in the material for blue photoelectric conversion element is usually 80 mass% or more, preferably 90 mass% or more, more preferably 95 mass% or more, even more preferably 98 mass% or more, and particularly preferably 99 mass% or more.
In addition, in the material for a blue photoelectric conversion element, a plurality of compounds included in the formula (1) may be used in combination.

The organic thin film of the present invention is made of the material for a blue photoelectric conversion element of the present invention. The thickness of the organic thin film may be set to an optimum value depending on the application, but is usually 1 nm to 1 μm, preferably 5 nm to 500 nm, and more preferably 10 nm to 300 nm.
The organic thin film can be formed by a dry process such as a vapor deposition method (a method using the material for blue photoelectric conversion element as it is) or various solution processes (a method using a solution in which the material for blue photoelectric conversion element is dissolved in an organic solvent or the like), but it is preferable to form the thin film by a solution process. Examples of the solution process include letterpress printing methods such as spin coating, drop casting, dip coating, spraying, flexographic printing, and resin letterpress printing, offset printing, dry offset printing, and pad printing, intaglio printing methods such as gravure printing, screen printing, mimeograph printing, and ring graph printing, as well as a method combining a plurality of these methods. When forming a film by a solution process, it is preferable to evaporate the solvent after the above-mentioned coating and printing to form a thin film.

The organic photoelectric conversion element of the present invention includes the material for a blue organic photoelectric conversion element of the present invention or the organic thin film of the present invention. The material for a blue organic photoelectric conversion element and the organic thin film can be used in the photoelectric conversion layer of a blue light photoelectric conversion element.
In the case of a photoelectric conversion element for blue light, in an organic thin film formed by a general dry film formation method or wet film formation method, which is the above-mentioned method for forming an organic thin film, a band that absorbs light in the visible light region (380 nm to 780 nm) observed when wavelength-absorbance measurement is performed with a spectrophotometer, i.e., a light absorption band, generally referred to as λmax, has a maximum absorption that means a wavelength position of the highest absorbance in the main light absorption band, of 400 nm or more and 500 nm or less, preferably 420 nm or more and 490 nm or less, and more preferably 450 nm or more and 480 nm or less.

An organic photoelectric conversion element is an element in which a photoelectric conversion section (film) is arranged between a pair of opposing electrode films, and light is incident on the photoelectric conversion section from above the electrode film. The photoelectric conversion section generates electrons and holes in response to the incident light, and a signal corresponding to the charge is read out by a semiconductor, indicating the amount of incident light corresponding to the absorption wavelength of the photoelectric conversion film section. A transistor for reading may be connected to the electrode film on the side where light is not incident. When multiple photoelectric conversion elements are arranged in an array, they indicate not only the amount of incident light but also the incident position information, and therefore become an imaging element. In addition, if a photoelectric conversion element arranged closer to the light source does not block (transmits) the absorption wavelength of a photoelectric conversion element arranged behind it when viewed from the light source side, multiple photoelectric conversion elements may be stacked and used.

The electrode film of the organic photoelectric conversion element plays a role of extracting holes from the photoelectric conversion layer and other organic thin film layers and collecting them when the photoelectric conversion layer included in the photoelectric conversion unit described later has hole transport properties or when an organic thin film layer other than the photoelectric conversion layer is a hole transport layer having hole transport properties, and plays a role of extracting electrons from the photoelectric conversion layer and other organic thin film layers and discharging them when the photoelectric conversion layer included in the photoelectric conversion unit has electron transport properties or when the organic thin film layer is an electron transport layer having electron transport properties. Therefore, the material that can be used as the electrode film is not particularly limited as long as it has a certain degree of conductivity, but it is preferable to select it in consideration of the adhesion to the adjacent photoelectric conversion layer and other organic thin film layers, electron affinity, ionization potential, stability, etc. Examples of materials that can be used as the electrode film include conductive metal oxides such as tin oxide (NESA), indium oxide, indium tin oxide (ITO) and indium zinc oxide (IZO); 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; and carbon. These materials may be used in combination as necessary, or may be used in two or more layers. The conductivity of the material used for the electrode film is not particularly limited as long as it does not unnecessarily hinder the light reception of the photoelectric conversion element, but it is preferable that it is as high as possible from the viewpoint of the signal strength and power consumption of the photoelectric conversion element. For example, an ITO film having a sheet resistance value of 300 Ω/□ or less functions sufficiently as an electrode film, but since commercially available products with an ITO film having a conductivity of about several Ω/□ are also available, it is desirable to use a substrate having such a high conductivity. The thickness of the ITO film (electrode film) can be selected as desired, taking into account electrical conductivity, but is usually about 5 to 500 nm, and preferably about 10 to 300 nm. Methods for forming films such as ITO include conventionally known deposition methods, electron beam methods, sputtering methods, chemical reaction methods, and coating methods. The ITO film provided on the substrate may be subjected to UV-ozone treatment, plasma treatment, etc., as necessary.

In addition, when multiple photoelectric conversion layers with different wavelengths to be detected are stacked, the electrode film (which is an electrode film other than the pair of electrode films described above) used between each photoelectric conversion layer must transmit light of wavelengths other than the light detected by each photoelectric conversion layer, and it is preferable to use a material for the electrode film that transmits 90% or more of the incident light, and it is even more preferable to use a material that transmits 95% or more of the light.

The electrode film is preferably produced in a plasma-free state. By producing these electrode films in a plasma-free state, the effect of plasma on the substrate on which the electrode film is provided is reduced, and the photoelectric conversion characteristics of the photoelectric conversion element can be improved. Here, plasma-free means a state in which no plasma is generated during deposition 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, and more preferably 20 cm or more, and the plasma reaching the substrate is reduced.

Examples of devices that do not generate plasma when forming an electrode film include electron beam deposition devices (EB deposition devices) and pulsed laser deposition devices. The method of forming a transparent electrode film using an EB deposition device is called the EB deposition method, and the method of forming a transparent electrode film using a pulsed laser deposition device is called the pulsed laser deposition method.

Examples of devices that can achieve a state in which plasma can be reduced during film formation (hereafter referred to as plasma-free film formation devices) include facing target sputtering devices and arc plasma deposition devices.

When a transparent conductive film is used as an electrode film (e.g., a first conductive film), DC shorts or an increase in leakage current may occur. One of the reasons for this is thought to be that fine cracks that occur in the photoelectric conversion layer are covered by a dense film such as TCO (Transparent Conductive Oxide), which increases the conductivity between the transparent conductive film and the electrode film on the opposite side. Therefore, when a material with a comparatively inferior film quality such as Al is used for the electrode, an increase in leakage current is unlikely to occur. By controlling the film thickness of the electrode film according to the film thickness of the photoelectric conversion layer (depth of the cracks), the increase in leakage current can be suppressed.

Normally, when the conductive film is made thinner than a certain value, a sudden increase in resistance occurs. The sheet resistance of the conductive film in the photoelectric conversion element for photosensors of this embodiment is usually 100 to 10,000 Ω/□, and there is a large degree of freedom in the film thickness. Furthermore, the thinner the transparent conductive film, the less light it absorbs, and generally the higher the light transmittance. Higher light transmittance is highly preferable because it increases the amount of light absorbed by the photoelectric conversion layer and improves the photoelectric conversion ability.

The photoelectric conversion section of the organic photoelectric conversion element of the present invention may include a photoelectric conversion layer and an organic thin film layer other than the photoelectric conversion layer. An organic semiconductor film is generally used for the photoelectric conversion layer constituting the photoelectric conversion section, but the organic semiconductor film may be one layer or multiple layers. In the case of a single layer, a P-type organic semiconductor film, an N-type organic semiconductor film, or a mixed film thereof (bulk heterostructure) is used. On the other hand, in the case of multiple layers, it is about 2 to 10 layers, and has a structure in which either a P-type organic semiconductor film, an N-type organic semiconductor film, or a mixed film thereof (bulk heterostructure) is stacked, and a buffer layer may be inserted between the layers.

In the organic photoelectric conversion element of the present invention, the organic thin film layer other than the photoelectric conversion layer constituting the photoelectric conversion part is also used as a layer other than the photoelectric conversion layer, for example, an electron transport layer, a hole transport layer, an electron blocking layer, a hole blocking layer, a crystallization prevention layer, or an interlayer contact improvement layer. 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 blocking layer, and a hole blocking layer, it is preferable to obtain an element that efficiently converts even weak light energy into an electrical signal.

In addition, organic imaging elements are generally thought to aim for improved performance by reducing dark current in order to achieve high contrast and power saving. For this reason, a method of inserting a carrier block layer into the layer structure is used, resulting in a multi-layer structure for the element. For this reason, it is desirable for the material for the photoelectric conversion element to be capable of forming a thin film using a method such as resistance heating deposition. The above-mentioned carrier block layer is commonly used in the field of organic electronics devices, and has the function of controlling the reverse movement of holes or electrons in the constituent films of the device, respectively.

The electron transport layer transports electrons generated in the photoelectric conversion layer to the electrode film and blocks the movement of holes from the electrode film to which the electrons are transported to the photoelectric conversion layer. The hole transport layer transports generated holes from the photoelectric conversion layer to the electrode film and blocks the movement of electrons from the electrode film to which the holes are transported to the photoelectric conversion layer. The electron blocking layer prevents the movement of electrons from the electrode film to the photoelectric conversion layer, prevents recombination within the photoelectric conversion layer, and reduces dark current. The hole blocking layer prevents the movement of holes from the electrode film to the photoelectric conversion layer, prevents recombination within the photoelectric conversion layer, and reduces dark current.

Figure 1 shows a typical element structure of the organic photoelectric conversion element of the present invention, but the present invention is not limited to this structure. In the embodiment example of Figure 1, 1 represents an insulating part, 2 represents one electrode film, 3 represents an electron blocking layer, 4 represents a photoelectric conversion layer, 5 represents a hole blocking layer, 6 represents the other electrode film, and 7 represents an insulating substrate or another organic photoelectric conversion element. Although a readout transistor is not shown in the figure, it is sufficient that it is connected to the electrode film of 2 or 6, and further, if the photoelectric conversion layer 4 is transparent, it may be formed on the outside of the electrode film on the side opposite to the side where light is incident. Light may be incident on the organic photoelectric conversion element from either the top or bottom, as long as the components other than the photoelectric conversion layer 4 do not excessively inhibit the incidence of light of the main absorption wavelength of the photoelectric conversion layer.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The structures of the compounds described in the synthesis examples were determined by mass spectrometry and nuclear magnetic resonance spectrometry (NMR) as necessary. The ¹ H NMR measurements in the examples were performed using a JNM-ECS400 (manufactured by JEOL), the molecular weight measurements were performed using an ISQ LT GC-MS (manufactured by Thermo Fisher Scientific), and the λmax value of the absorption spectrum was measured using a UV-1700 (manufactured by Shimadzu Corporation). The application of current and voltage to the organic photoelectric conversion element was performed using a PVL-3300 (manufactured by Asahi Spectroscopy) under irradiation conditions of an irradiation light intensity of 130 μW and a half-width of 20 nm, in the range of 350 to 1100 nm using a semiconductor parameter analyzer 4200-SCS (manufactured by Keithley Instruments).

Example 1 (Synthesis of compound (A-8) of the present invention)
In a nitrogen atmosphere, PdCl ₂ (PPh ₃ ) ₂ (14 mg, 0.02 mmol) was added to a degassed solution of intermediate (1-6) (0.4 mmol) and NaOAc (67 mg, 0.8 mmol) in DMAc (14 ml), and the mixture was stirred at 140° C. for 15 hours. The reaction solution obtained above was cooled to room temperature, and the solid was filtered and washed with water and acetone. The crude product obtained above was purified by sublimation to obtain a yellow solid of compound (A-8). (Yield 20%)
The molecular weight of the compound (A-8) obtained above was measured, and the results were as follows.
EI-MS (m/z): 624 [M] ⁺

Comparative Example 1 (Synthesis of Comparative Compound)
According to the method described in Japanese Patent No. 6739290, a comparative compound represented by the following formula (B-1) was obtained.

Example 2 (Preparation of organic thin film of the present invention and confirmation of λmax)
Using the compound (A-8) obtained in Example 1, which had been previously purified by sublimation, an organic thin film of the present invention having a thickness of 100 nm was obtained on a glass substrate by a resistance heating vacuum deposition method. The absorption spectrum of the obtained organic thin film was measured to confirm the value of λmax in the long wavelength absorption band. The results are shown in Table 1.

Comparative Example 2 (Preparation of Comparative Organic Thin Film and Confirmation of λmax) A comparative organic thin film was prepared and its λmax was confirmed in a manner similar to that of Example 2, except that the compound represented by formula (B-1) obtained in Comparative Example 1 was used instead of compound (A-8). The results are shown in Table 1.

Example 3 (Preparation of organic photoelectric conversion element using compound (A-8))
A film of the compound (A-8) shown in the specific example was formed to a thickness of 100 nm on an ITO transparent conductive glass (manufactured by Geomatec Co., Ltd., ITO film thickness 150 nm) by resistance heating vacuum deposition. Next, a film of aluminum was formed to a thickness of 100 nm in a vacuum to prepare an organic photoelectric conversion element of the present invention.

Comparative Example 3 (Preparation of an organic photoelectric conversion element using a compound represented by formula (B-1))
A comparative organic photoelectric conversion element was prepared in the same manner as in Example 3, except that the compound represented by formula (B-1) obtained in Comparative Example 1 was used instead of compound (A-8).

(Evaluation of Wavelength Selectivity of Organic Photoelectric Conversion Element)
The photocurrent density was measured when a voltage of 5 V was applied while irradiating the organic photoelectric conversion elements of the present invention and the comparative organic photoelectric conversion elements obtained in Example 3 and Comparative Example 3 with light of 300 nm to 1100 nm. From the photocurrent density measurement results obtained above, the retention rates of the photocurrent density at 420 nm, 440 nm, 460 nm, 480 nm, 500 nm, and 520 nm were calculated when the photocurrent density at 400 nm was taken as 100%, and the results are shown in Table 2.

The results in Table 2 show that the organic photoelectric conversion element of the present invention has a higher current density in the wavelength region of 420 to 500 nm, particularly in the wavelength region of 460 to 500 nm, than the comparative organic photoelectric conversion element, but does not show a photoelectric effect at 520 nm in the green light region. This clearly shows that the organic photoelectric conversion element containing the organic thin film of the present invention is excellent in selective photoelectric conversion for blue light.

The organic photoelectric conversion element using the organic compound represented by formula (1) of the present invention selectively absorbs blue light with a maximum absorption in the light absorption band of 400 nm to 500 nm, and has excellent transmittance for light with wavelengths of 500 nm or more. In addition, since it shows an excellent photoresponsive current, it can be used in organic photoelectric conversion elements for blue light, organic imaging elements, and materials thereof.

(Figure 1)
1 Insulating portion 2 Upper electrode 3 Electron blocking layer 4 Photoelectric conversion layer 5 Hole blocking layer 6 Lower electrode 7 Insulating substrate or other photoelectric conversion element

Claims (6)

The following formula (1)

(In formula (1), R ₁ to R ₄ each independently represent a hydrogen atom or an aromatic group which may have a substituent, and X represents an oxygen atom or a sulfur atom.)
A compound represented by the formula: A material for a blue photoelectric conversion element containing a compound represented by formula (1) according to claim 1. An organic thin film made of the material for blue photoelectric conversion elements according to claim 2. An organic photoelectric conversion element comprising the material for blue photoelectric conversion elements according to claim 2 or the organic thin film according to claim 3. An optical sensor comprising the organic photoelectric conversion element according to claim 4. An organic imaging element comprising the organic photoelectric conversion element according to claim 4.

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