Photoelectric conversion layer, photoelectric conversion element and dispersion

Abstract

To provide a photoelectric conversion layer that has photoelectric conversion capability for light in the SWIR region and enables film formation through techniques like coating.SOLUTION: The present invention provides: a photoelectric conversion layer which includes metal silicide particles with a particle diameter within a range of 50 nm or more and 300 nm or less and a dispersant; a photoelectric conversion element that includes the photoelectric conversion layer; and a dispersion element for forming the photoelectric conversion layer, wherein the dispersion element includes metal silicide particles with a particle diameter within a range of 50 nm or more and 300 nm or less, a dispersant, and a disperse medium.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a photoelectric conversion layer, a photoelectric conversion element, and a dispersion. [Background technology]

[0002] Photoelectric conversion elements are elements that convert optical signals into electrical signals and are used in a variety of applications, including imaging and sensing. In recent years, attempts have been made to use light in the short-wavelength infrared region (sometimes abbreviated as "SWIR"; in this specification, this refers to the wavelength region between 0.9 μm and 2.5 μm) to adapt it to applications that were difficult to achieve with visible light, such as nighttime surveillance, distance measurement sensors, and agricultural product inspection. This has led to a growing demand for SWIR photoelectric conversion elements that can detect light in the SWIR wavelength region with high sensitivity. Silicon and semiconductor materials have long been used as materials for photoelectric conversion elements, and research and development into these materials is still being actively conducted. However, silicon can only absorb light wavelengths up to around 1 μm, making it unsuitable for detecting light in the SWIR region. Meanwhile, semiconductor materials can detect light in the SWIR region by controlling their band gap, but known narrow-gap semiconductors such as InGaAs, InSb, and PbSe are expensive and have not yet become widespread.

[0003] In recent years, metal silicides, which are compound semiconductors composed of metal and silicon, have been proposed as materials sensitive to light in the SWIR region, and Mg2Si and the like have been reported so far (Patent Documents 1 and 2). Metal silicides are known to contain alkaline earth metals such as Mg, Ca, and Ba, and transition metals such as Mn and Fe, and have the advantage of being highly adaptable for various material designs. As mentioned above, metal silicides are excellent SWIR photoelectric conversion materials, but they can only be synthesized by limited methods, such as melt chemical reactions, crystal growth in metal solvents, and epitaxial growth on silicon substrates. Therefore, film fabrication methods are limited. While sputtering, a widely used thin-film deposition method, can deposit films on glass substrates, the silicides become amorphous, resulting in reduced charge mobility. However, to use metal silicides as photoelectric conversion materials in various industrial fields, they must be processed into various shapes while maintaining their crystalline structure. For flexible photoelectric conversion devices in particular, thin films that can conform to various shapes are useful. Therefore, there is a need for photoelectric conversion materials containing metal silicides that can be processed into various shapes and deposited on substrates by coating or other methods. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2022 / 064735 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-154005 Summary of the Invention [Problem to be solved by the invention]

[0005] The problem to be solved by the present invention is to provide a photoelectric conversion layer that has photoelectric conversion ability for light in the SWIR region and that can be formed into a film by coating or the like. [Means for solving the problem]

[0006] The present inventors have conducted extensive research to solve the above-mentioned problems and have arrived at the present invention. Specifically, the present invention relates to a photoelectric conversion layer comprising metal silicide particles having a particle diameter in the range of 50 nm to 300 nm and a dispersant.

[0007] The present invention also relates to a photoelectric conversion element having the above photoelectric conversion layer.

[0008] The present invention also relates to a dispersion for forming the photoelectric conversion layer, which contains metal silicide particles having a particle size in the range of 50 nm to 300 nm, a dispersant, and a dispersion medium. [Effects of the Invention]

[0009] The present invention provides a photoelectric conversion layer that has photoelectric conversion ability for light in the SWIR region and can be formed into a film by coating. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in detail below, but first, the terms and abbreviations used in this specification will be explained. In this specification, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0011] <Photoelectric conversion layer> The photoelectric conversion layer of the present invention is characterized by containing metal silicide particles and a dispersant, as described below. The content of the metal silicide particles in the photoelectric conversion layer is preferably at least 90%, more preferably at least 95%. The upper limit of the content of the metal silicide particles is not particularly limited, but is preferably less than 100%. The thickness of the photoelectric conversion layer is preferably in the range of 50 nm to 2 μm depending on the desired absorption rate, and more preferably in the range of 50 nm to 500 nm.

[0012] <Metal silicide particles> First, we will explain the metal silicide in the metal silicide particles used in the present invention. Metal silicides are compound semiconductors composed of metal and silicon. Representative examples include Mg2Si and β-FeSi2, and the metal can be selected from alkali metals, alkaline earth metals, transition metals, etc. The energy band of a metal silicide varies depending on the metal element, composition, and crystal structure, and it exhibits semiconductivity when the Fermi level is within the band gap. Examples of metal silicides that exhibit semiconductivity include Mg2Si, Ca2Si, β-FeSi2, Mn4Si7, CoSi, and MoSi2. Methods for synthesizing metal silicides include melt chemical reactions, crystal growth in metal solvents, and epitaxial growth on silicon substrates.

[0013] The particle diameter of the metal silicide particles contained in the photoelectric conversion layer of the present invention is 50 nm or more and 300 nm or less, and preferably 50 nm or more and 100 nm or less. In the specification, the particle diameter is the average particle diameter based on the number of particles, and represents a value measured by dynamic light scattering.

[0014] Methods for producing or synthesizing metal silicide particles include pulverizing single-crystal or polycrystalline metal silicide, and spraying molten metal and silicon liquids into a plasma torch, evaporating them, and then rapidly cooling them.

[0015] <Dispersant> Next, the dispersant will be described. A dispersant promotes and stabilizes the dispersion of metal silicide particles when dispersing the metal silicide particles in a dispersion medium. Most dispersants are composed of a moiety that adsorbs to the metal silicide particles and a moiety that stabilizes the dispersion. The dispersant used in the present invention preferably has an alkylene oxide chain (oxyalkylene group) and / or a polar group. When the dispersant has a polar group, the polar group preferably has an amino group, a quaternary ammonium base, or an acidic group, and more preferably has both an amino group or a quaternary ammonium base and an acidic group. When the dispersant has an alkylene oxide chain, the viscosity of the dispersion increases compared to when it does not have an alkylene oxide chain, thereby improving the dispersion stability of metal silicide particles with a high specific gravity. When the dispersant has a polar group, the adsorption to the metal silicide particles is improved, thereby improving the dispersion stability of the dispersion and the smoothness of the photoelectric conversion film.

[0016] When the dispersant has an amino group, the amine value is preferably 20 to 200 mgKOH / g, more preferably 25 to 150 mgKOH / g. The amine value in this specification is a value obtained by determining the total amine value by potentiometric titration using a 0.1 N aqueous hydrochloric acid solution and then converting it into an equivalent amount of potassium hydroxide, and is the value (mgKOH / g) obtained by converting the measured total amine value into the solid content of the dispersant.

[0017] When the dispersant has a quaternary ammonium base, the quaternary ammonium salt value is preferably 20 to 200 mgKOH / g, more preferably 25 to 150 mgKOH / g. The quaternary ammonium salt value in this specification is a value obtained by titrating with a 0.1 N silver nitrate aqueous solution using a 5% potassium chromate aqueous solution as an indicator, and then converting it into an equivalent amount of potassium hydroxide, and is the value (mgKOH / g) obtained by converting the measured total ammonium salt value into the solid content of the dispersant.

[0018] When the dispersant has acidic groups, the acid value is preferably 200 mgKOH / g or less, and more preferably 20 to 150 mgKOH / g. The acid value in this specification is a value determined by potentiometric titration using a 0.1 N potassium hydroxide-ethanol solution, and is the measured total acid value converted into the solid content of the dispersant (mgKOH / g).

[0019] When the dispersant has an amine value, a quaternary ammonium salt value, and an acid value within the above ranges, pulverization and dispersion during the dispersion operation are promoted, the particle size of the metal silicide particles in the dispersion can be made smaller, and the dispersion stability of the dispersion and the smoothness of the photoelectric conversion layer are improved.

[0020] The number average molecular weight (sometimes abbreviated as Mn) of the dispersant can be measured by gel permeation chromatography (GPC), and is preferably 1,000 to 10,000, more preferably 1,500 to 8,000, in terms of standard polystyrene. Known dispersants can be used, and examples of preferred embodiments include those disclosed in JP-A-2019-089954 and JP-A-2014-520127.

[0021] <Dispersion> The metal silicide particles and the dispersant can be mixed with a dispersion medium described below to form a dispersion for forming a photoelectric conversion layer.

[0022] <Dispersion medium> As the dispersion medium, known organic solvents can be used, but those capable of uniformly dispersing the metal silicide are preferred in order to form a uniform photoelectric conversion layer. Specific examples include hydrocarbon solvents such as hexane, octane, toluene, and xylene; halogenated hydrocarbon solvents such as chloroform, chlorobenzene, and o-bromotoluene; alcohol solvents such as n-butanol and ethylene glycol; ketone solvents such as methyl isobutyl ketone and cyclohexanone; and ester solvents such as ethyl acetate, isoamyl acetate, and propylene glycol monomethyl ether acetate. Among these, ethyl acetate, propylene glycol monomethyl ether acetate, and cyclohexanone are preferred, and butanol, propanol, and ethylene glycol are more preferred.

[0023] <Other additives> The photoelectric conversion layer of the present invention may contain additives other than the above-mentioned metal silicide particles and dispersant, such as a binder.

[0024] <Photoelectric conversion element> The photoelectric conversion layer of the present invention can be provided between a pair of electrodes to produce a photoelectric conversion element. The photoelectric conversion element can be produced by a known production method, for example, the production method described in JP 2015-065267 A. Examples of materials for the electrodes constituting the photoelectric conversion element include known materials such as conductive metal oxides such as tin oxide, zinc oxide, indium oxide, and indium tin oxide (ITO), and metals such as gold, silver, platinum, chromium, nickel, lithium, indium, aluminum, calcium, and magnesium. [Example]

[0025] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these examples as long as it does not deviate from the gist of the present invention. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass." Unless otherwise specified, all measurements were performed at 25°C.

[0026] <Preparation of metal silicide particles (A)> [Synthesis and preparation of metal silicide particles (A-1)] First, referring to J. Materials Sci. 16 (1981) 355, Mn and Si were mixed in a stoichiometric ratio, sealed in a quartz tube, heated to 1200°C, and crystals were grown from the melt to synthesize Mn4Si7 crystals. The Mn4Si7 crystals were then crushed in an agate mortar and subsequently crushed in a ball mill using 10 mm diameter zirconia beads, 3 mm diameter zirconia beads, and 1 mm diameter zirconia beads to produce metal silicide particles (A-1). The particle diameter of the resulting metal silicide particles (A-1) was confirmed to be 2-3 μm. Furthermore, powder X-ray diffraction confirmed that the metal silicide particles (A-1) were Mn4Si7.

[0027] [Preparation of metal silicide particles (A-2)] Metal silicide particles (A-2) were prepared in the same manner as metal silicide particles (A-1), except that CoSi crystals were synthesized by mixing Co and Si in a stoichiometric ratio, sealing the mixture in a quartz tube, heating it to 1000°C, and growing the crystals from the resulting melt. The particle diameter of the prepared metal silicide particles (A-1) was confirmed to be 2-3 μm. Furthermore, powder X-ray diffraction confirmed that the metal silicide particles (A-2) were CoSi.

[0028] [Preparation of metal silicide particles (A-3)] Metal silicide particles (A-3) were prepared in the same manner as metal silicide particles (A-1), except that stoichiometrically mixed Cr and Si were enclosed in a quartz tube, heated to 1000°C, and crystals were grown from the resulting melt to synthesize CrSi crystals. The particle diameter of the prepared metal silicide particles (A-1) was confirmed to be 2-3 μm. Powder X-ray diffraction confirmed that these metal silicide particles (A-3) were CrSi.

[0029] <Dispersant (C)> The dispersants (C-1) and (C-2) used were as follows: Dispersant (C-1): Sannol LMT-1430 (polyoxyethylene (3) lauryl ether sodium sulfate, manufactured by Lion Specialty Chemicals Co., Ltd.) Dispersant (C-2): Polyethylene (23) glycol monocetyl ether (Tokyo Chemical Industry Co., Ltd.)

[0030] <Synthesis of dispersants (C-3 to C-13)> Dispersants (C-3 to C-13) were synthesized by the following methods. The abbreviations in Table 1 are as follows. MMA: Methyl methacrylate BA: butyl acrylate BMA: butyl methacrylate BzMA: benzyl methacrylate EHMA: 2-ethylhexyl methacrylate Et-3EO-MA: Triethylene glycol monoethyl ether methacrylate DMAE-MA: N,N-dimethylaminoethyl methacrylate MPA: Methoxypropyl acetate

[0031] [Synthesis of dispersants (C-3 to C-5)] 75 g of MPA was placed in an anhydrous reaction vessel. The monomer mixture shown in Table 1 was metered in at a rate of 1.2 g / min. Immediately after the start of metering, 1-methoxy-1-(trimethylsiloxy)-2-methylpropene was added as an initiator and a 10% acetonitrile solution of tetrabutylammonium 3-chlorobenzoate (50% concentration in acetonitrile, see U.S. Pat. No. 4,588,795) was added as a catalyst to the reaction vessel. The reaction temperature was maintained at 20°C throughout the reaction. After the metering of the monomer mixture was completed, amine monomer was metered in at a rate of 1.3 g / min. After the amine monomer in the amount shown in Table 1 was metered in at a rate of 1.2 g / min, the reaction was allowed to proceed for 60 minutes. 3.3 g of 2-methoxypropanol was then added to terminate the reaction, and dispersants (C-3 to C-5) were synthesized. The numerical values ​​of the monomer mixture and amine monomer shown in Table 1 are in grams.

[0032] [Synthesis of dispersants (C-6 to C-8, C-12)] Polymers were synthesized in the same manner as for dispersants C-3 to C-5, except that the compositions of the monomer mixture and amine monomer were changed as shown in Table 1. Dispersants (C-6 to C-8, C-12) were synthesized by mixing this polymer with the amount of benzyl chloride shown in Table 1 and reacting at 110°C for 3 hours. The numerical values ​​for the monomer mixture, amine monomer, and benzyl chloride shown in Table 1 are in grams.

[0033] [Synthesis of dispersants (C-9 to C-11)] In a four-neck flask equipped with a stirrer, thermometer, dropping funnel, reflux condenser, and nitrogen inlet tube, 430 g of Desmodur T100 (approximately 100% 2,4-toluylene diisocyanate, NCO content = 48.8, hereinafter abbreviated as "TDI") and 7 g of benzoyl chloride were mixed. A PO polyether (addition polymer of butanol and propylene oxide) shown in Table 2 was slowly metered in so as not to exceed a temperature of 55°C. After metering, the mixture was stirred at 55°C for an additional 3 hours. Excess TDI was removed from the reaction mixture using a thin-film evaporator at 150°C to synthesize polymer (P1). The residual TDI content was less than 1%.

[0034] Next, a four-neck flask equipped with a stirrer, thermometer, dropping funnel, reflux condenser, and nitrogen inlet tube was first charged with the amount of polymer (P1) shown in Table 2, and then the amount of ethanolamine shown in Table 2 was slowly added dropwise while stirring. The reaction temperature was controlled so as not to exceed 50°C. After 1 hour, the temperature was raised to 80°C, and the amount of polyphosphoric acid shown in Table 2 was added. The reaction was continued for 3 hours while maintaining the temperature at 80°C, and dispersants (C-9 to C-11) were synthesized. The values ​​for PO polyether, ethanolamine, and polyphosphoric acid shown in Table 2 are in grams.

[0035] [Synthesis of dispersant (C-13)] A three-neck flask equipped with a stirrer, reflux condenser, and gas inlet was charged with 47.2 g of MPA, 2-[Nt-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)]nitroxy]-2-methylpropanoic acid, and 46.00 g of butyl acrylate under a nitrogen stream and stirred at 120 °C for 2.5 hours. Subsequently, 21.00 g of N,N-dimethylaminoethyl methacrylate was metered in at a rate of 2 ml / min. The reaction was then continued for an additional 6 hours at 120 °C to synthesize polymer (P2). After the reaction was completed, the residual monomer content was measured by liquid chromatography, and the conversion rate was found to be 98% or higher.

[0036] Next, 1280 g of dispersant (C-10) dissolved in 40 g of MPA and 40 g of butyl glycol and 1600 g of polymer (P2) were added to a four-neck flask equipped with a stirrer, thermometer, dropping funnel, reflux condenser, and nitrogen inlet tube, and the mixture was stirred at 60°C for 1 hour to synthesize dispersant (C-13). The number average molecular weight (Mn) of dispersant (C-13) was measured by GPC and found to be 1700. The acid value was 72 mg KOH / g, and the amine value was 78 mg KOH / g.

[0037] <Preparation of Dispersion (D)> Dispersion (D) was prepared by placing metal silicide particles milled to a particle size of 2-3 μm, a dispersant, a dispersion medium, and zirconia beads in a zirconia pot and dispersing them in a planetary ball mill. The particle size of the metal silicide particles in the dispersion can be controlled by changing the diameter of the zirconia beads and the dispersion time. The volume of the materials and zirconia beads to be filled was 30% of the volume of the zirconia pot.

[0038] Example 1 [Dispersion (D-1)] First, the following materials and 1 mm diameter zirconia beads were placed in a zirconia pot and dispersed for 30 minutes using a planetary ball mill. The zirconia beads were then removed. Next, 0.5 mm diameter zirconia beads were added to the zirconia pot, and the dispersion was again conducted for 30 minutes to produce a dispersion. After removing the zirconia beads, the mixture was passed through a 1 μm pore diameter polytetrafluoroethylene (PTFE) filter to remove coarse particles, producing Dispersion (D-1). The particle size and particle size distribution of Dispersion (D-1) were measured using a Zetasizer (Zetasizer Nano ZSP, manufactured by Malvern Panalytical). The measurement temperature was 25°C, and the solution was diluted with butanol as necessary. Metal silicide particles (A-1): 23.75 parts Dispersant (C-13): 1.25 parts Butanol: 75 parts

[0039] Examples 2 to 4, 7 to 26, Comparative Example 1 [Dispersion (D-2~4, D-7~26, DR-1)] Dispersions (D-2 to 4, D-7 to 26, DR-1) were prepared in the same manner as dispersion (D-1), except that the metal silicide particles, dispersant, dispersion medium, and dispersion time were changed to have the compositions and conditions shown in Table 3. In Table 3, the abbreviations BuOH, PrOH, and PGMAc represent butanol, propanol, and propylene glycol monomethyl acetate, respectively.

[0040] Example 5 [Dispersion (D-5)] The following materials and 1 mm diameter zirconia beads were placed in a zirconia pot and dispersed for 30 minutes using a planetary ball mill to prepare a dispersion. After removing the zirconia beads, the mixture was passed through a PTFE filter with a pore size of 1 μm to remove coarse particles, producing dispersion (D-5). Metal silicide particles (A-1): 23.75 parts Dispersant (C-13): 1.25 parts Butanol: 75 parts

[0041] Example 6, Comparative Example 2 [Dispersion (D-6, DR-2)] Dispersions (D-6, DR-2) were prepared in the same manner as dispersion (D-5), except that the diameters of the metal silicide particles, dispersant, dispersion medium, and zirconia beads and the dispersion time were changed to the compositions and conditions shown in Table 3.

[0042] Comparative Example 3 [Dispersion (DR-3)] First, the following materials and 1 mm diameter zirconia beads were placed in a zirconia pot, and the mixture was dispersed in a planetary ball mill for 30 minutes, after which the beads were removed. Next, 0.5 mm diameter zirconia beads were added to the zirconia pot, and the mixture was dispersed again for 30 minutes to produce a dispersion. After removing the zirconia beads, the mixture was passed through a 1 μm pore diameter PTFE filter to remove coarse particles, producing dispersion (DR-3). Metal silicide particles (A-1): 25 parts Butanol: 75 parts

[0043] <Fabrication of photoelectric conversion layer (E) and photoelectric conversion element (F)> Examples 101 and 201 [Photoelectric conversion layer (E-1) · Photoelectric conversion element (F-1)] In a glove box with a moisture and oxygen concentration of 1 ppm or less, the dispersion (D-1) was spin-coated onto a cleaned glass substrate with an ITO electrode to form a photoelectric conversion layer (E-1) with a film thickness of 250 nm after drying. A 100 nm thick Au electrode was then formed on top of the dispersion (D-1) by vapor deposition, yielding a photoelectric conversion element (F-1). The fabricated photoelectric conversion element (F-1) was then sealed in the glove box.

[0044] Examples 102 to 128, 201 to 228, Comparative Examples 4 to 9 [Photoelectric conversion layer (E-2 to 28, ER-1 to 3) · Photoelectric conversion element (F-2 to 28, FR-1 to 3)] Photoelectric conversion layers (E-2 to 28, ER-1 to 3) and photoelectric conversion elements (F-2 to 28, FR-1 to 3) were fabricated in the same manner as the photoelectric conversion layer (E-1) and photoelectric conversion element (F-1), except that the film thickness of the metal silicide particle dispersion (D) used for coating and the photoelectric conversion layer (E) were changed as shown in Tables 4 and 5. X-ray diffraction measurements were performed on the photoelectric conversion layers, and it was confirmed that the metal silicide particles in the photoelectric conversion layer had the same crystalline structure as before the dispersion process. It was not possible to obtain a uniform photoelectric conversion layer for the photoelectric conversion layers (ER-1 and 3), and photoelectric conversion elements (FR-1 and 3) could not be fabricated.

[0045] <Photoelectric conversion performance evaluation> The fabricated photoelectric conversion element was taken out of the glove box, and the voltage-current curves when irradiated with SWIR light and in the dark were measured in the range of -2 V to 2 V using a KEITHLEY MODEL 2400 source meter. The measurements were performed using an LED (light-emitting diode) with an emission wavelength of 940 nm, which is the source of SWIR light, at 5 mW / cm. 2 The exposure was adjusted to 0.04cm. 2 The light was irradiated through a photomask so that the light-dark current ratio was 1.0. The current value at a voltage of -1V was read and the light-dark current ratio was calculated. The light-dark current ratio was judged according to the following criteria. The results are shown in the table. The higher the light-dark current ratio, the better it is. A rating of 2 or higher is within the practical range. (Judgment criteria) 5: Bright / dark current ratio is 2 or more 4: Bright / dark current ratio is 1.8 or more and less than 2 3: Bright / dark current ratio is 1.5 or more and less than 1.8 2: Bright / dark current ratio is 1 or more and less than 1.5 1: Bright / dark current ratio is less than 1

[0046] As is clear from the table, the photoelectric conversion layer of the present invention was shown to respond to irradiation with SWIR light as a photodiode.

[0047] [Table 1]

[0048] Table 2

[0049] Table 3

[0050] Table 4

[0051] Table 5

Claims

1. A photoelectric conversion layer comprising metal silicide particles having a particle diameter in the range of 50 nm to 300 nm and a dispersant.

2. A photoelectric conversion element comprising the photoelectric conversion layer according to claim 1 .

3. 2. A dispersion for forming the photoelectric conversion layer according to claim 1, comprising metal silicide particles having a particle diameter in the range of 50 nm to 300 nm, a dispersant, and a dispersion medium.

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