Method for producing cuprous oxide and cuprous oxide

Abstract

To obtain cuprous oxide with appropriate performance. [Solution] The method for producing cuprous oxide includes the steps of: obtaining copper ink, which is a liquid composition containing copper particles (S10); forming a film on a substrate by coating or printing the copper ink (S12); producing cuprous oxide on a substrate by drying the film formed on the substrate with copper ink, and then heating it by irradiating it with light in the visible to infrared wavelength range in an atmosphere with an oxygen concentration of 10% to 21% (S16); and heating the cuprous oxide in an atmosphere with an oxygen concentration lower than the oxygen concentration at which the copper particles were oxidized and sintered (S18).

Description

Technical Field

[0001] The present invention relates to a method for producing cuprous oxide and cuprous oxide.

Background Art

[0002] Since cuprous oxide (Cu2O) is a p-type semiconductor, its application to various uses such as solar cells, thin film transistors, sensors, varistors, catalysts, etc. has been studied. Patent Document 1 describes that copper ink is formed on a substrate and irradiated with light in the visible to infrared region in an atmosphere with an oxygen concentration of 10% or more and 21% or less to produce cuprous oxide on the substrate.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, further performance improvement of cuprous oxide is required.

[0005] An object of the present invention is to provide a method for producing cuprous oxide capable of obtaining cuprous oxide having appropriate performance and cuprous oxide having appropriate performance.

Means for Solving the Problems

[0006] The method for producing cuprous oxide according to the present disclosure includes the steps of: obtaining a copper ink which is a liquid composition containing copper particles; forming a film by coating or printing the copper ink onto a substrate; producing cuprous oxide on the substrate by drying the film formed on the substrate with the copper ink and then heating it by irradiating it with light in the visible to infrared region in an atmosphere with an oxygen concentration of 10% to 21%; and heating the cuprous oxide in an atmosphere with an oxygen concentration lower than the oxygen concentration at which the copper particles were oxidized and sintered.

[0007] In the step of heating the cuprous oxide, it is preferable to heat the cuprous oxide in an atmosphere of inert gas with an oxygen concentration of 0.01 ppm or more and 100 ppm or less.

[0008] In the step of heating the cuprous oxide, it is preferable to heat the cuprous oxide at a heating temperature of 400°C or more and 800°C or less, and for a holding time of 1 second or more and 60 minutes or less.

[0009] The inert gas is preferably a noble gas or nitrogen gas.

[0010] In the step of heating the cuprous oxide, it is preferable to heat the cuprous oxide in an atmosphere of superheated steam with a steam volume of 10 kg / h to 60 kg / h.

[0011] In the step of heating the cuprous oxide, it is preferable to heat the cuprous oxide at a heating temperature of 300°C or more and 800°C or less, and for a holding time of 1 second or more and 60 minutes or less.

[0012] The cuprous oxide of this disclosure has an average transmittance of light with wavelengths of 600 nm to 1200 nm of 40% to 100% when the film thickness is 0.5 μm, and a hole concentration of 1 × 10⁻¹⁶ 12 (1 / cm 3 ) 1 x 10 20 (1 / cm 3 ) or less, and the hole mobility is 1 (cm 2 / V s) or more 100(cm) 2 / V·s) is less than or equal to the above.

[0013] The cuprous oxide of this disclosure has an average transmittance of light with wavelengths of 600 nm to 1200 nm of 40% or more and 100% or less when the film thickness is 0.5 μm, and satisfies at least one of the following conditions in the CMKY color notation: K is less than 60% and M is 30% or more, and the value obtained by dividing K by M is less than 1.40. [Effects of the Invention]

[0014] According to the present invention, it is possible to obtain cuprous oxide with appropriate performance. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a schematic diagram of the cuprous oxide film produced in the embodiment. [Figure 2] Figure 2 is a flowchart illustrating the method for producing cuprous oxide according to the embodiment. [Figure 3] Figure 3 is a schematic diagram of the copper ink according to the embodiment. [Figure 4] Figure 4 is a flowchart illustrating the method for manufacturing copper ink according to the embodiment. [Figure 5A] Figure 5A is a table showing each example. [Figure 5B] Figure 5B is a table showing each example. [Figure 5C] Figure 5C is a table showing each example. [Figure 5D] Figure 5D is a table showing each example. [Figure 6] Figure 6 is a table showing the inks used in each example. [Figure 7] Figure 7 is a table showing the evaluation of the options. [Modes for carrying out the invention]

[0016] The present invention will now be described in detail with reference to the drawings. However, the present invention is not limited to the embodiments described below. Furthermore, the components in the embodiments below include those easily conceivable by those skilled in the art, those substantially identical, and those within the so-called equivalent range. Moreover, the components disclosed in the embodiments below can be combined as appropriate. Numerical values ​​are rounded to the nearest whole number.

[0017] (Method for producing cuprous oxide) Figure 1 is a schematic diagram of the cuprous oxide film produced in this embodiment, and Figure 2 is a flowchart illustrating the method for producing cuprous oxide according to this embodiment. In this embodiment, cuprous oxide 100 is manufactured on a substrate 110 as shown in the laminate 1 in Figure 1. Cuprous oxide 100 is a film made of Cu2O (also written as copper(I) oxide, cuprous oxide, or copper(I) oxide). In this embodiment, cuprous oxide 100 is in the form of a film, but is not limited to that, and cuprous oxide 100 may be in any shape, not just a film. Furthermore, in this embodiment, cuprous oxide 100 is formed on a substrate 110, but is not limited to forming cuprous oxide 100 on a substrate 110.

[0018] (Steps to obtain copper ink) As shown in Figure 2, in this manufacturing method, copper ink 10 is first obtained (step S10). Copper ink 10 is a liquid composition containing copper particles. Details of copper ink 10 will be described later.

[0019] (Application step) Next, the obtained copper ink 10 is applied or printed onto the substrate 110 (step S12) to form a film of copper ink 10 on the substrate 110. The material, size, thickness, etc., of the substrate 110 to which the copper ink 10 is applied or printed may be arbitrary. For example, the specific heat [kJ / (kg·K)] of the substrate 110 is preferably 0.1 or more and 3 or less, more preferably 0.1 or more and 2 or less, and even more preferably 0.1 or more and 1.5 or less. The specific heat of the substrate 110 is measured by the laser flash method using a flash analyzer LFA 467 HyperFlash (manufactured by NETZSCH) under the conditions of JIS standard JIS R 1611. Furthermore, for example, the material of the base material 110 is preferably glass, ceramic, or metal. For example, the thickness of the base material 110 is preferably 0.01 mm or more and 10 mm or less, more preferably 0.05 mm or more and 5 mm or less, and even more preferably 0.05 mm or more and 1 mm or less. By ensuring that the heat capacity, material, and thickness of the substrate 110 fall within this range, the copper ink 10 can be appropriately oxidized and sintered to suitably produce a cuprous oxide film 100. Furthermore, the method of applying or printing the copper ink 10 onto the substrate 110 is arbitrary. Moreover, the step of applying or printing the copper ink 10 onto the substrate 110 is not essential; for example, the copper ink 10 placed at any location may be heated in a later step.

[0020] (Drying step) Next, the copper ink 10 (the film of copper ink 10 formed on the substrate in this embodiment) is dried (step S14). The conditions for drying the copper ink 10 may be arbitrary. For example, the temperature at which the copper ink 10 is dried is preferably 30°C to 150°C, more preferably 30°C to 120°C, and even more preferably 30°C to 100°C. For example, the drying time for the copper ink 10 is preferably 0.1 minutes or more and 60 minutes or less, more preferably 0.5 minutes or more and 60 minutes or less, and even more preferably 0.5 minutes or more and 30 minutes or less. For example, while any atmosphere, such as air or an inert atmosphere, is acceptable for drying the copper ink 10, an air atmosphere is preferable considering workability and other factors. By setting the drying conditions as described above, the liquid component in the copper ink 10 can be properly removed, and the copper particles can be properly oxidized and sintered. However, the drying step of the copper ink 10 is not essential.

[0021] (Sintering step) Next, the copper ink 10 (in this embodiment, the film of copper ink 10 formed on the substrate) is heated in a predetermined atmosphere with light having a spectral distribution with a peak at a predetermined wavelength to oxidize and sinter the copper particles in the copper ink 10 and produce cuprous oxide 100 (step S16).

[0022] The predetermined atmosphere under which the copper ink 10 is heated refers to an atmosphere with an oxygen concentration of 10% to 21%, preferably 15% to 21%, and more preferably 18% to 21%. By heating the copper ink 10 under such an atmosphere, the copper particles can be appropriately oxidized, and cuprous oxide 100 can be appropriately produced. The oxygen concentration is measured using a zirconia-type oxygen concentration meter LC-860 (manufactured by Toray Engineering Co., Ltd.).

[0023] The light with a spectral distribution having a peak at a predetermined wavelength used to heat the copper ink 10 refers to light with a spectral distribution having a peak at a wavelength in the visible to infrared region (light with a spectral distribution having a peak at a wavelength within the wavelength range from the visible light band to the infrared light band), and it is more preferable that the light has a spectral distribution with a wavelength (the wavelength at which the intensity of the irradiated light peaks) of 0.6 μm to 10 μm, and even more preferable that it is light with a wavelength of 0.6 μm to 5 μm. By heating the copper ink 10 with light with a spectral distribution having such a peak at a specific wavelength, it becomes possible to effectively heat the copper ink 10 rather than the substrate, thereby appropriately oxidizing the copper particles and appropriately, or more appropriately, producing cuprous oxide 100.

[0024] The heating temperature for heating the copper ink 10 is preferably 180°C to 500°C, more preferably 300°C to 500°C, and even more preferably 300°C to 450°C. By setting the heating temperature within this range, the copper particles can be appropriately oxidized and sintered, allowing for more appropriate production of cuprous oxide 100.

[0025] The holding time, which is the time the copper ink 10 is held at the heating temperature, is preferably 1 second or more and 600 seconds or less, more preferably 10 seconds or more and 600 seconds or less, and even more preferably 10 seconds or more and 300 seconds or less. By setting the holding time within this range, the copper particles can be appropriately oxidized and sintered, and cuprous oxide 100 can be produced more appropriately.

[0026] The heating rate, which is the rate at which the copper ink 10 is heated to the heating temperature, is preferably 0.1°C / second or more and 50°C / second or less, more preferably 0.1°C / second or more and 10°C / second or less, and even more preferably 0.5°C / second or more and 10°C / second or less. By setting the heating rate within this range, the copper particles can be appropriately oxidized and sintered, and cuprous oxide 100 can be produced more appropriately.

[0027] In this embodiment, it is preferable to heat the copper ink 10 by irradiating it with light from a light irradiation unit that emits light with a spectral distribution peaking in the visible to infrared wavelength range. Any light irradiation unit that emits light with a spectral distribution peaking in the visible to infrared wavelength range may be used, for example, a light source that emits light in a predetermined wavelength band. By irradiating with light from such a light source, the copper ink 10 can be appropriately heated, and cuprous oxide 100 can be produced appropriately, or more appropriately. However, the method for heating the copper ink 10 is not limited to irradiation from a light source; for example, any method or apparatus capable of heating the copper ink 10 within the range of light with a spectral distribution having the wavelength specified above as a peak may be used.

[0028] (Heating step) Next, the cuprous oxide 100 obtained in step S16 is heated in an atmosphere with an oxygen concentration lower than that at the time of oxidation and sintering of the copper particles, i.e., in an atmosphere with an oxygen concentration lower than that at the time of step S16 (step S18). This promotes the crystal growth of the cuprous oxide 100, and cuprous oxide 100 with appropriate properties can be obtained. These properties include, for example, the transmittance to visible light, the hole concentration, and the hole mobility.

[0029] Furthermore, when heating cuprous oxide 100 in this step, the oxygen concentration is preferably 0.01 ppm to 500 ppm, more preferably 0.01 ppm to 200 ppm, and even more preferably 0.01 ppm to 100 ppm. Having the lower limit of the oxygen concentration within this range suppresses the reduction of cuprous oxide 100, and having the upper limit of the oxygen concentration within this range suppresses the oxidation of cuprous oxide 100, thereby enabling proper crystal growth of cuprous oxide 100.

[0030] In this step, the cuprous oxide 100 may be heated while it is still formed on the substrate 110, or the cuprous oxide 100 may be heated after being separated from the substrate 110. Furthermore, in this step, the cuprous oxide 100 may be heated by any method; for example, the cuprous oxide 100 may be heated by placing it in a furnace and heating the furnace, or the cuprous oxide 100 may be heated by irradiating it with light, similar to step S16.

[0031] In this step, it is preferable to heat the cuprous oxide 100 under either the following first heating conditions or second heating conditions. However, the heating conditions for cuprous oxide 100 are not limited to these first or second heating conditions. That is, by heating the cuprous oxide 100 under any conditions lower than the oxygen concentration in step S16, the crystal growth of cuprous oxide 100 can be promoted.

[0032] (1st heating condition) Under the first heating conditions, cuprous oxide 100 is heated in an atmosphere of inert gas with an oxygen concentration of 0.001 ppm to 100 ppm. The oxygen concentration under the first heating conditions is more preferably 0.01 ppm to 500 ppm, and even more preferably 0.01 ppm to 100 ppm. By heating cuprous oxide 100 in an inert gas atmosphere and at such an oxygen concentration, the oxidation and reduction of cuprous oxide 100 can be suppressed while the crystal growth of cuprous oxide 100 can be more appropriately promoted, resulting in cuprous oxide 100 with appropriate performance.

[0033] The inert gas used when heating cuprous oxide 100 under the first heating conditions can be any gas that does not react easily with other substances, but in this embodiment, a noble gas or nitrogen gas is preferred. As a noble gas, argon is more preferred, for example.

[0034] The first heating temperature, which is the temperature at which cuprous oxide 100 is heated under the first heating conditions, is preferably 300°C to 800°C, more preferably 400°C to 800°C, and even more preferably 500°C to 800°C. By setting the heating temperature within this range, the crystal growth of cuprous oxide 100 can be more appropriately promoted.

[0035] The holding time, which is the time for holding cuprous oxide 100 at the first heating temperature, is preferably 1 second or more and 60 minutes or less, more preferably 30 seconds or more and 60 minutes or less, and even more preferably 60 seconds or more and 60 minutes or less. By setting the holding time within this range, the crystal growth of cuprous oxide 100 can be promoted more appropriately.

[0036] The heating rate, which is the rate at which cuprous oxide 100 is heated to the first heating temperature, is preferably 0.1°C / second or more and 10°C / second or less, more preferably 0.1°C / second or more and 5°C / second or less, and even more preferably 1°C / second or more and 5°C / second or less. By setting the heating rate within this range, the crystal growth of cuprous oxide 100 can be more appropriately promoted.

[0037] (Second heating condition) Under the second heating condition, cuprous oxide 100 is heated in an atmosphere of superheated steam with a steam vapor concentration of 10 kg / h to 60 kg / h. The steam vapor concentration under the second heating condition is more preferably 20 kg / h to 60 kg / h, and even more preferably 30 kg / h to 60 kg / h. By heating cuprous oxide 100 in a superheated steam atmosphere with such an oxygen concentration, the oxidation and reduction of cuprous oxide 100 can be suppressed while the crystal growth of cuprous oxide 100 can be more appropriately promoted, resulting in cuprous oxide 100 with appropriate performance. The amount of water vapor is measured using a mass flow meter (flow meter).

[0038] The second heating temperature, which is the temperature at which cuprous oxide 100 is heated under the second heating conditions, is preferably 300°C to 800°C, more preferably 400°C to 800°C, and even more preferably 500°C to 800°C. By setting the heating temperature within this range, the crystal growth of cuprous oxide 100 can be more appropriately promoted.

[0039] The holding time, which is the time for holding cuprous oxide 100 at the second heating temperature, is preferably 1 second to 60 minutes, more preferably 30 seconds to 60 minutes, and even more preferably 60 seconds to 60 minutes. By setting the holding time within this range, the crystal growth of cuprous oxide 100 can be more appropriately promoted.

[0040] The heating rate, which is the rate at which cuprous oxide 100 is heated to the second heating temperature, is preferably 0.01°C / second or more and 10°C / second or less, more preferably 0.01°C / second or more and 5°C / second or less, and even more preferably 0.1°C / second or more and 5°C / second or less. By setting the heating rate within this range, the crystal growth of cuprous oxide 100 can be more appropriately promoted.

[0041] In this embodiment, steps S12, S14, S16, and S18 may be performed only once to produce cuprous oxide 100. That is, cuprous oxide 100 may be produced by heating once after one coating and drying process, and then the crystal growth of cuprous oxide 100 may be promoted by heating once more. Alternatively, for example, steps S12 and S14 may be repeated multiple times before step S16 is performed. That is, after repeating the coating and drying process multiple times, cuprous oxide 100 may be produced by heating as in steps S16 and S18. Alternatively, for example, steps S12, S14, S16, and S18 may be treated as a series of processes, and this series of processes may be repeated multiple times to produce cuprous oxide 100. That is, the process of heating twice after one coating and drying process may be repeated multiple times.

[0042] (cuprous oxide) The properties of cuprous oxide 100 (cuprous oxide film) of this embodiment will be described below. While the properties of cuprous oxide 100 produced by the manufacturing method of this embodiment are described below, the cuprous oxide 100 of this embodiment is not limited to being produced by this method. Any cuprous oxide 100 that satisfies at least one of the properties described below may be produced by any manufacturing method.

[0043] (Crystal peak) In this embodiment, it is preferable that when measured by X-ray diffraction (XRD), at least one crystal peak of Cu2O with a plane index, as shown in the following equations (1) to (12), is detected in the cuprous oxide 100. Here, a crystal peak refers to a peak whose intensity is above a threshold, and the threshold here is, for example, a relative intensity of 5 when the maximum peak intensity of the measurement result is set to 100.

[0044] 2θ=33.35°±1.0°

[0110] ···(1) 2θ=36.37°±1.0°

[0002] ···(2) 2θ=36.48°±1.0°[11-1] ···(3) 2θ=39.72°±1.0°

[0111] ···(4) 2θ=39.97°±1.0°

[0200] ···(5) 2θ=47.51°±1.0°[11-2] ···(6) 2θ=50.10°±1.0°[20-2] ···(7) 2θ=52.73°±1.0°

[0112] ···(8) 2θ=54.91°±1.0°

[0020] ···(9) 2θ=58.25°±1.0°

[0020] ···(10) 2θ=59.88°±1.0°

[0202] ···(11) 2θ=63.30°±1.0°[11-3] ···(12)

[0045] Furthermore, when quantitative analysis of cuprous oxide 100 using the RIR (Reference Intensity Ratio) from a PDF database on XRD measurement data using the integrated X-ray analysis software PDXL2 (Rigaku), it is preferable that the weight ratio of Cu2O (the ratio of the weight of Cu2O to the total weight) is 80% or more, more preferably 90% or more, and even more preferably 95% or more. For the PDF database used, 01-071-3645 was used for Cu2O, 01-070-6828 for CuO, and 01-071-4610 for Cu.

[0046] Cuprous oxide 100, as shown in the XRD measurement results above, contains an appropriate amount of Cu2O and can provide the appropriate performance. The X-ray diffractometer used for XRD measurements will be Rigaku's fully automated multi-purpose X-ray diffractometer (SmartLab). The conditions for the X-ray diffraction method will be as follows: ·X-ray output: 45kV, 200mA • Scan mode: Continuous • Scan speed: 10° / min Step width: 0.05° • Scan axis: 2θ • Scan range: 10-100°

[0047] (transmittance) The cuprous oxide 100 of this embodiment can be applied to at least one of the following applications: solar cells, thin-film transistors, sensors, varistors, and catalysts. For example, when the film thickness of the cuprous oxide 100 of this embodiment is 0.5 μm, the average transmittance of light with wavelengths from 600 nm to 1200 nm (visible light to infrared) is preferably 40% to 100%, more preferably 50% to 100%, and even more preferably 60% to 100%. The visible light transmittance falls within this range, making it suitable for use as a top cell (solar cell) in a tandem solar cell system, for example, using a see-through type solar cell or a crystalline silicon solar cell as the bottom cell (solar cell). The transmittance here was measured using a UH-4150 ultraviolet-visible-near-infrared spectrophotometer (standard integrating sphere) (manufactured by Hitachi High-Tech Corporation) under the following conditions. • Measurement mode: Wavelength scan • Data mode: %T ·Starting wavelength: 1200.00nm Termination wavelength: 300.00 nm • Scan speed: 300nm / min • Sampling interval: 1.00 nm • Initial waiting time: 0 sec • Repeat cycle: 0.0 min • Number of measurements: 1 • Auto-zero before measurement: Off Slit: 5.00nm • Photomal voltage: Automatic 1 • Light source switching mode: Automatic switching ·Light source switching wavelength: 340.00nm • Baseline setting: User 1 ·High resolution measurement: Off D2 lamp: On • WI lamp: On • R / S inversion: Off • Dimming plate attenuation rate: 'Dimming plate not used' • Detector zero correction: 'No correction' --- Near infrared --- • Scan speed: 750nm / min • Slit: Automatic control · PbS sensitivity: 2 · Detector switching correction: With correction · Detector switching wavelength: 850.0 nm · Light quantity control mode: Fixed

[0048] For the copper oxide (copper oxide film) of this embodiment, when the film thickness is 0.5 μm, the ratio (transmittance ratio: T2 / T1) of the average transmittance (T2) of light with wavelengths of 600 nm to 1200 nm to the average transmittance (T1) of light with wavelengths of 300 nm to 600 nm is preferably 3.5 or more, more preferably 4.0 or more and 20.0 or less, and even more preferably 4.5 or more and 15.0 or less. When the transmittance ratio is within this range, light in the infrared region can be appropriately transmitted with respect to short-wavelength light, and a copper oxide film having appropriate performance can be obtained. For example, it can be suitably used as the top cell (solar cell) of a tandem-type solar cell with a through-type solar cell or a crystalline silicon solar cell as the bottom cell (solar cell).

[0049] (Hole concentration) The hole concentration of copper oxide 100 is 1×10 12 (1 / cm 3 ) or more and 1×10 20 (1 / cm 3 ) or less is preferable, 1×10 13 (1 / cm 3 ) or more and 1×10 19 (1 / cm 3 ) or less is more preferable, and 1×10 14 (1 / cm 3 ) or more and 1×10 19 (1 / cm 3 ) or less is even more preferable. When the hole concentration is within this range, it can be suitably applied to solar cells and the like. The hole concentration is measured under the following conditions. As the measuring device, it is measured using the Resi Test8400 series (Tokuyo Technica). The measurement conditions are as follows. · Hole measurement method: AC magnetic field Hall measurement · Resistance measurement method: Medium resistance · AC magnetic field frequency: 100 mHz · Filter constant: Medium Voltage range (AD conversion range): 10mV to 200μV • AC Gain: 36~48dB ·Measurement temperature: room temperature (300K)

[0050] (Hole mobility) The hole mobility of cuprous oxide 100 is 1 cm 2 / V s) or more 100(cm) 2 / V·s) or less is preferable, and 5(cm 2 / V s) or more 100(cm) 2 / V·s) or less is more preferable, 10(cm 2 / V s) or more 100(cm) 2 A value of less than or equal to / V·s is even more preferable. When the hole mobility falls within this range, it can be suitably applied to solar cells and the like. The hole mobility is measured under the same conditions as those used to measure the hole concentration described above.

[0051] (Thickness) Cuprous oxide 100 preferably has a thickness of 0.1 μm to 1000 μm, more preferably 0.3 μm to 1000 μm, and even more preferably 0.3 μm to 500 μm. By setting the thickness within this range, it can be appropriately applied to various applications such as solar cells, thin-film transistors, sensors, varistors, and catalysts.

[0052] (Sintering density) Cuprous oxide 100 is preferably a sintered body. For example, cuprous oxide 100 preferably has a sintering density of 70% or more, more preferably 80% or more, and even more preferably 85% or more. By having a sintering density within this range, cuprous oxide 100 can adequately ensure the characteristics of solar cells. Note that sintering density refers to the ratio of the volume of cuprous oxide excluding open and closed pores to the total volume of cuprous oxide including open and closed pores. The sintering density is calculated by randomly acquiring images of a cross-section of cuprous oxide 100 at a magnification of 50,000x using an SEM (Scanning Electron Microscope), binarizing them using image processing software (ImageJ from the National Institutes of Health, USA), separating them into particle and pore portions, and calculating them using the following formula. Sintered density (%) = (Total area of ​​particles / (Total area of ​​particles + Total area of ​​voids)) × 100

[0053] However, as described above, the method for producing cuprous oxide 100 in this embodiment is arbitrary and is not limited to a sintered body.

[0054] (Color tone) Cuprous oxide 100 preferably satisfies (D) below and at least one of (B) and (C) below in the CMKY color notation. Furthermore, it is more preferable that cuprous oxide 100 satisfies (D) below and at least one of (B) and (C) below, as well as (A) below. Furthermore, cuprous oxide 100 may satisfy only one of (B) and (C), but it is preferable that it satisfies both (B) and (C). (A): C (Cyan) is 0% or less (B): M (Magenta) is 30% or more (C): K / M (the value obtained by dividing K (keyplate) by M (magenta)) is less than 1.40 (D): K (key plate) is less than 60%

[0055] By satisfying the above requirements regarding the color of cuprous oxide 100, the crystallite size can be increased, thereby improving hole mobility. This allows for the development of appropriate properties for cuprous oxide 100, making it suitable for applications such as solar cells.

[0056] Furthermore, in the CMKY color notation, it is more preferable that the M (magenta) of cuprous oxide 100 is 30% or more and 100%, and even more preferable that it is 40% or more and 100%. Furthermore, in the CMKY color notation, it is more preferable that the K (key plate) of cuprous oxide 100 is 0% or more and less than 60%, and even more preferable that it is 0% or more and 50%. Furthermore, in the CMKY color notation, it is more preferable that the K / M ratio of cuprous oxide 100 is 0 or more and less than 1.40, and even more preferable that it is 0 or more and 1.0. Furthermore, in the CMKY color notation, it is preferable that the Y (yellow) of cuprous oxide 100 is 20% or more and 90%, more preferable that it is 30% or more and 80%, and even more preferable that it is 40% or more and 80%. Cuprous oxide 100 can provide more appropriate performance by satisfying the above requirements regarding color.

[0057] Each color (C, M, K, Y) in the CMKY color notation is measured as follows:

[0058] First, using a one-shot 3D shape measuring machine VR-5000 (manufactured by Keyence Corporation), place cuprous oxide 100 with the glass substrate side up on a sheet of paper printed entirely in black on the stage. Set the camera to a low-magnification camera, set the magnification to 12x, and after AF autofocus, capture an image and save it as a JPEG image file. The camera settings during shooting are as follows. Display switching: Color Camera brightness: Manual, 18.0ms • Improved image quality Edge enhancement: 1.0 Offset: 0.0 Gamma correction: 2.00 White balance R:1.11 G:1.20 B:1.00

[0059] Next, the obtained JPEG image file is opened using image editing software (such as Windows Paint or Microsoft PowerPoint). The color information of the image in RGB, HSV, or hexadecimal (Hex) notation (color code) is then obtained using the color picker function in Windows Paint or the eyedropper function in Microsoft PowerPoint. By using software that can convert the aforementioned color notation (color code) to another color notation (such as Color Picker & Converter or a color code conversion tool), the color information in RGB, HSV, or hexadecimal (Hex) notation (color code) is converted to color information in CYMK notation, thereby obtaining the color information in CYMK notation from the location of cuprous oxide 100 in the image file.

[0060] (Copper ink) The copper ink 10 according to this embodiment may be any liquid composition containing copper particles as described above, but preferred embodiments of the copper ink 10 used in this embodiment will be described below.

[0061] Figure 3 is a schematic diagram of the copper ink according to this embodiment. As shown in Figure 3, the copper ink 10 according to this embodiment preferably contains copper particles 12, a polyhydric alcohol 14, a solvent 16, and an organic solvent 18. The copper ink 10 refers to an ink-like substance in which solid copper particles 12 are present in the solvent 16 without being dissolved in the liquid solvent 16. In the copper ink 10, the copper particles 12 may be settled in the solvent 16 or dispersed.

[0062] (Copper particles) Copper particles 12 are copper particles. Preferably, the particle size (Peak value of particle size distribution (number of particles)) of the copper particles 12 is between 10 nm and 1000 nm. The particle size of the copper particles 12 in the copper ink 10 is determined using a particle size analyzer (Malvern Zetasizer Nano Series ZSP), by setting the refractive index of the copper particles and the refractive index and viscosity of the solvent in the ink, and measuring at 20°C or 25°C, matching the temperature conditions of the physical properties, to obtain the Peak value of the particle size distribution (number of particles) of the copper particles 12. If sufficient measurement quality cannot be obtained in the measurement of the particle size distribution due to the high concentration of copper particles 12 in the copper ink 10, the copper particles 12 may be diluted and dispersed 10 to 1000 times with the main solvent in the copper ink 10 (water, ethanol, or high-boiling point solvent) before measurement.

[0063] If the particle size is 10 nm or less, the specific surface area increases inversely proportional to the particle size, which can lead to a greater effect of surface oxidation and a decrease in the sinterability of the coating film obtained using the copper particles 12. On the other hand, if the particle size of the copper particles 12 is 1000 nm or more, the particle size becomes too large, which can lead to the copper particles 12 being more likely to settle and separate in the ink dispersed in the solvent. The particle size of the copper particles 12 is preferably in the range of 30 nm to 500 nm, and particularly preferably in the range of 30 nm to 300 nm.

[0064] The BET specific surface area of ​​copper particles 12 is determined by measuring the amount of gas adsorbed by the copper particles 12 using a specific surface area measuring device (QUANTACHROME AUTOSORB-iQ2, manufactured by Quantachrome Instruments) with nitrogen or krypton gas as the measuring gas. The BET specific surface area of ​​copper particles 12 is 2.0 m². 2 / g or more 8.0m 2 It is preferable that the range be less than or equal to / g, and 3.5m 2 / g or more 8.0m 2 It is more preferable that the range be less than or equal to / g, and 4.0m 2 / g or more 8.0m 2 It is particularly preferable that the amount is within the range of / g or less. Furthermore, the shape of the copper particles 12 is not limited to spherical, but may also be needle-shaped or flattened plate-shaped.

[0065] Preferably, the surface of the copper particles 12 is partially or entirely coated with an organic substance. This coating suppresses oxidation of the copper particles 12, further reducing the likelihood of a decrease in sinterability due to oxidation. Furthermore, the organic substance coating the copper particles 12 is not formed by or derived from the polyhydric alcohol 14 or solvent 16. Also, the organic substance coating the copper particles 12 is not a metal oxide (copper oxide) formed by the oxidation of metal.

[0066] The fact that copper particles 12 are coated with organic matter is confirmed by analyzing the surface of copper particles 12 using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The copper particles 12 are detected by analyzing the surface using a time-of-flight secondary ion mass spectrometer PHI nanoTOF2 (ULVAC PHI). + C3H3O3 relative to the amount of ions detected - Ratio of detected ions (C3H3O3) - / Cu + The ratio is preferably 0.001 or higher. C3H3O3 - / Cu + The ratio is more preferably within the range of 0.05 to 0.2. Note that in this analysis, the surface of the copper particles 12 refers not to the surface of the copper particles 12 after organic matter has been removed, but to the surface of the copper particles 12 containing the covering organic matter (i.e., the surface of the organic matter).

[0067] The copper particle 12 was analyzed on its surface using time-of-flight secondary ion mass spectrometry to determine the presence of C3H4O2. - Ions and ions of C5 or higher may be detected. + C3H4O2 relative to the amount of ions detected - Ratio of detected ions (C3H4O2) - / Cu + The ratio is preferably 0.001 or higher. Also, Cu + Ratio of the amount of C5 or greater ions detected to the amount of ions detected (C5 or greater ions / Cu +The ratio is preferably less than 0.005.

[0068] C3H3O3 detected by time-of-flight secondary ion mass spectrometry - Ions and C3H4O2 - The ions and ions with C5 or more originate from the organic material covering the surface of the copper particles 12. Therefore, C3H3O3 - / Cu + Ratio and C3H4O2 - / Cu + When each of the ratios is 0.001 or higher, the surface of the copper particles 12 becomes less susceptible to oxidation, and the copper particles 12 become less susceptible to aggregation. Also, C3H3O3 - / Cu + Ratio and C3H4O2 - / Cu + When the ratio is 0.2 or less, oxidation and aggregation of copper particles 12 can be suppressed without excessively reducing the sinterability of copper particles 12, and the generation of organic decomposition gases during heating can be suppressed, so that cuprous oxide with fewer voids can be formed. To further improve the oxidation resistance of copper particles 12 during storage and to further improve sinterability at low temperatures, C3H3O3 - / Cu + Ratio and C3H4O2 - / Cu + The ratio is preferably within the range of 0.08 to 0.16. Also, C5 or higher ions / Cu + If the ratio is 0.005 or higher, a large amount of organic matter with a relatively high desorption temperature is present on the particle surface, resulting in insufficient sinterability and making it difficult to obtain strong cuprous oxide. C5 or higher ions / Cu + The ratio is preferably less than 0.003 times.

[0069] The organic material coating the copper particles 12 is preferably a carboxylic acid derived from a carboxylic acid metal used in the production of the copper particles 12. The method for producing copper particles 12 coated with a carboxylic acid-derived organic material will be described later. The amount of organic material coating the copper particles 12 is preferably in the range of 0.5% to 2.0% by mass, more preferably in the range of 0.8% to 1.8% by mass, and even more preferably in the range of 0.8% to 1.5% by mass, based on 100% by mass of copper particles. By having an organic material coating amount of 0.5% by mass or more, the copper particles 12 can be uniformly coated with the organic material, and the oxidation of the copper particles 12 can be more reliably suppressed. Furthermore, by having an organic material coating amount of 2.0% by mass or less, the generation of voids in the sintered body (bonding layer) of copper particles due to gases generated by the decomposition of the organic material by heating can be suppressed. The amount of organic material coating can be measured using commercially available equipment. For example, the amount of coating can be measured using a differential thermal balance TG8120-SL (manufactured by RIGAKU Corporation). In this case, for example, copper particles from which moisture has been removed by freeze-drying are used as the sample. To suppress oxidation of the copper particles, the measurement is performed in nitrogen (G2 grade) gas, the heating rate is set to 10°C / min, and the weight loss rate when heated from 250°C to 300°C is defined as the amount of organic coating. That is, coating amount = (weight of sample after measurement) / (weight of sample before measurement) × 100 (wt%). The measurement is performed three times for each batch of copper particles from the same lot, and the arithmetic mean may be used as the coating amount.

[0070] When copper particles 12 are heated at 300°C for 30 minutes under an inert gas atmosphere such as argon gas, it is preferable that 50% or more by mass of organic matter decomposes. Organic matter derived from carboxylic acid generates carbon dioxide gas, nitrogen gas, acetone vapor, and water vapor during decomposition.

[0071] (Polyhydric alcohol) The polyhydric alcohol 14 is preferably an alcohol containing two or more OH groups and soluble in water and ethanol. Furthermore, the polyhydric alcohol 14 is preferably melted at 30°C or higher.

[0072] The polyhydric alcohol 14 may be at least one of the following, for example: 2,2-dimethyl-1,3-propanediol, 2,5-dimethyl-2,5-hexanediol, 2-hydroxymethyl-2-methyl-1,3-propanediol, 1-phenyl-1,2-ethanediol, 1,1,1-tris(hydroxymethyl)propane, erythritol, pentaerythritol, ribitol, resorcinol, (pyro)catechol, 5-methylresorcinol, pyrogallol, 1,2,3-cyclohexanetriol, and 1,3,5-cyclohexanetriol.

[0073] The polyhydric alcohol 14 is a non-electrolyte and is present in the copper ink 10 dissolved in the solvent 16 (with the molecules of the polyhydric alcohol 14 dispersed in the solvent 16). However, the form in which the polyhydric alcohol 14 exists in the copper ink 10 is arbitrary, and it may also be in an insoluble state in the solvent 16.

[0074] The inclusion of polyhydric alcohol 14 in the copper ink 10 allows the polyhydric alcohol 14 to coordinate around the copper particles 12, thereby effectively suppressing the aggregation of the copper particles 12. In other words, in this embodiment, it is preferable that the polyhydric alcohol 14 is coordinated around the copper particles 12.

[0075] (solvent) Solvent 16 is a liquid (medium) for dispersing the copper particles 12. Details of solvent 16 will be described later.

[0076] (organic solvent) The organic solvent 18 is an organic solvent with components different from the polyhydric alcohol 14 and the solvent 16. The organic solvent 18 has a boiling point of 150°C or higher at atmospheric pressure and is miscible with water. It is more preferable that the organic solvent 18 has a boiling point of 200°C or higher. Here, miscible means that the organic solvent 18 can be mixed with water in any ratio (i.e., they can completely dissolve each other at any concentration). In this embodiment, it is preferable that the organic solvent 18 is miscible with the solvent 16.

[0077] The organic solvent 18 is preferably a glycol ether or an aprotic polar solvent. More specifically, the organic solvent 18 may contain both a glycol ether and an aprotic polar solvent; in other words, it is preferable that it contains at least one of a glycol ether and an aprotic polar solvent. Examples of glycol ethers contained in the organic solvent 18 include diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, polyethylene glycol monomethyl ether, diethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, ethylene glycol isobutyl ether, diethylene glycol monoisobutyl ether, ethylene glycol monoallyl ether, diethylene glycol monobenzyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, propylene glycol monopropyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethylene glycol methyl ethyl ether, and diethylene glycol diethyl ether. If the organic solvent 18 contains glycol ethers, it may contain at least one selected from the enumerated list. Examples of aprotic polar solvents included in organic solvent 18 include N-methylpyrrolidone, dimethylformamide, 2-pyrrolidone, and propylene carbonate. If organic solvent 18 contains aprotic polar solvents, it may contain at least one selected from the enumerated list.

[0078] (Copper ink) Preferably, the copper ink 10 contains polyhydric alcohol 14 in a mass ratio of 0.01% to 20% of the total copper ink 10. This range of polyhydric alcohol 14 content allows for proper dispersion of copper particles 12 while preventing the concentration of copper particles 12 from becoming too low.

[0079] The copper ink 10 preferably contains copper particles 12 in a mass ratio of 1% to 50% of the total copper ink 10, more preferably 5% to 50%, and even more preferably 5% to 30%. Having the copper particles 12 within this range allows for sufficient concentration of copper particles 12 while suppressing a decrease in the fluidity of the copper ink 10, thus offering advantages in manufacturing, such as improved nozzle ejection performance.

[0080] The copper ink 10 preferably contains solvent 16 at a mass ratio of 50% to 99% of the total copper ink 10, more preferably 50% to 95%, and even more preferably 60% to 95%. Having solvent 16 within this range allows for sufficient concentration of copper particles 12 while suppressing a decrease in the fluidity of the copper ink 10, thus offering advantages in manufacturing, such as improved nozzle ejection performance.

[0081] The copper ink 10 preferably contains organic solvent 18 in a mass ratio of 0.01% to 20% of the total copper ink 10, and more preferably 0.1% to 20%. This range of organic solvent 18 content ensures sufficient mold resistance even when the copper ink 10 is left unattended for extended periods, allowing for proper long-term storage.

[0082] The copper ink 10 may contain ionized copper particles 12 (ions of the metal that make up the copper particles 12). That is, the liquid component of the copper ink 10 may contain ionized copper particles 12. The ionized copper particles 12 may be copper ions.

[0083] The copper ink 10 described above can have variations in the components of the solvent 16. Below, we will describe each copper ink 10 with different solvent components.

[0084] (First copper ink) Let us designate one of the copper inks 10, each with a different solvent 16 component, as the first copper ink 10A. In the first copper ink 10A, the solvent 16 is water. The first copper ink 10A is formed by dissolving a polyhydric alcohol 14 and an organic solvent 18 in water (solvent 16) while mixing in copper particles 12. In other words, the first copper ink 10A is an aqueous solution of polyhydric alcohol 14 and organic solvent 18 containing copper particles 12.

[0085] The first copper ink 10A preferably contains polyhydric alcohol 14 in a mass ratio of 0.1% to 20% of the total first copper ink 10A, more preferably 0.5% to 20%, and even more preferably 1% to 20%. By having the polyhydric alcohol 14 content within this range, it is possible to appropriately disperse the copper particles 12 while preventing the concentration of copper particles 12 from becoming too low.

[0086] The first copper ink 10A preferably contains copper particles 12 in a mass ratio of 1% to 50% of the total first copper ink 10A, more preferably 5% to 50%, and even more preferably 5% to 30%. Having the copper particle 12 content within this range allows for sufficient concentration of copper particles 12 while suppressing a decrease in the fluidity of the first copper ink 10A, thus offering advantages in manufacturing, such as improved nozzle ejection performance.

[0087] The first copper ink 10A preferably contains organic solvent 18 in a mass ratio of 0.5% to 20% of the total first copper ink 10A, more preferably 1% to 20%, and even more preferably 2% to 20%. This range of organic solvent 18 content allows for proper storage over a long period.

[0088] In this embodiment, it is preferable that the first copper ink 10A does not contain any substances other than copper particles 12, polyhydric alcohol 14, solvent 16 which is water, and organic solvent 18, excluding unavoidable impurities. However, it is not limited to this, and the first copper ink 10A may contain additives other than copper particles 12, polyhydric alcohol 14, solvent 16 which is water, and organic solvent 18 (dispersants, adhesion modifiers, rheology modifiers, rust inhibitors, etc.).

[0089] (Second copper ink) One of the copper inks 10, each with a different solvent 16 component, is designated as the second copper ink 10B. The second copper ink 10B contains ethanol as the solvent 16, and more specifically, the main solvent, which is the primary component of the solvent 16, is ethanol. Here, the main solvent refers to the component that accounts for more than 50% by mass of the total solvent 16. The second copper ink 10B may contain other solvents as the solvent 16 besides the main solvent ethanol, and in this embodiment, it may contain water. The second copper ink 10B is obtained by dissolving a polyhydric alcohol 14 and an organic solvent 18 in the solvent 16 and mixing in copper particles 12. That is, for example, the second copper ink 10B is obtained by adding copper particles 12 to an aqueous solution of polyhydric alcohol 14, organic solvent 18, and ethanol.

[0090] The second copper ink 10B preferably contains polyhydric alcohol 14 in a mass ratio of 0.01% to 10% of the total second copper ink 10B, more preferably 0.1% to 10%, and even more preferably 0.1% to 5%. By having a polyhydric alcohol 14 content within this range, it is possible to appropriately disperse the copper particles 12 while preventing the concentration of copper particles 12 from becoming too low.

[0091] The content of copper particles 12 in the second copper ink 10B is preferably 1% to 50% by mass, more preferably 5% to 50%, and even more preferably 5% to 30%. Having the copper particle 12 content within this range allows for sufficient concentration of copper particles 12 while suppressing a decrease in the fluidity of the second copper ink 10B, thus offering advantages in manufacturing, such as improved nozzle ejection performance.

[0092] The second copper ink 10B preferably contains ethanol at a mass ratio of 50% to 99% of the total second copper ink 10B, more preferably 50% to 95%, and even more preferably 60% to 95%. Having the ethanol content within this range allows for sufficient concentration of copper particles 12 while suppressing a decrease in the fluidity of the second copper ink 10B, thus offering advantages in manufacturing, such as improved nozzle ejection performance.

[0093] The second copper ink 10B preferably contains organic solvent 18 in a mass ratio of 0.01% to 20% of the total second copper ink 10B, more preferably 0.1% to 20%, and even more preferably 0.5% to 20%. This range of organic solvent 18 content allows for proper storage over a long period.

[0094] In this embodiment, it is preferable that the second copper ink 10B contains no substances other than copper particles 12, polyhydric alcohol 14, solvent 16 (in this case, water and ethanol), and organic solvent 18, excluding unavoidable impurities. However, it is not limited to this, and the second copper ink 10B may contain additives other than copper particles 12, polyhydric alcohol 14, solvent 16, and organic solvent 18 (dispersants, adhesion modifiers, rheology modifiers, rust inhibitors, etc.).

[0095] Copper inks that use ethanol as the main solvent may cause copper particles to aggregate due to the ethanol. In contrast, the second copper ink 10B contains a polyhydric alcohol 14, which, for example, coordinates around the copper particles 12, thereby suppressing aggregation of the copper particles 12 themselves.

[0096] (Third copper ink) One of the copper inks 10, each with a different solvent 16 component, is designated as the third copper ink 10C. The third copper ink 10C contains a high-boiling point solvent as the solvent 16, and more specifically, the main solvent, which is the primary component of the solvent 16, is a high-boiling point solvent. For example, the third copper ink 10C contains copper particles 12 while a polyhydric alcohol 14 and an organic solvent 18 are dissolved in the solvent 16. Note that the third copper ink 10C may contain a solvent other than the main high-boiling point solvent as the solvent 16. The third copper ink 10C may contain at least one of water and ethanol as the solvent 16, and in this embodiment, it contains both water and ethanol.

[0097] A high-boiling point solvent is a liquid containing one or more OH groups, with a boiling point of 150°C or higher, and sparingly soluble or insoluble in water. A high-boiling point solvent that is sparingly soluble or insoluble in water is preferably a solvent classified as a non-water-soluble liquid in Appendix 3 of the Cabinet Order Concerning the Regulation of Hazardous Materials under the Fire Service Act. The high-boiling point solvent is preferably a so-called organic solvent, and may be, for example, at least one of α-terpineol and 2-ethyl-1,3-hexanediol. Note that any of these solvents may contain isomers.

[0098] The third copper ink 10C preferably contains polyhydric alcohol 14 in a mass ratio of 0.01% to 5% of the total third copper ink 10C, more preferably 0.01% to 5%, and even more preferably 0.01% to 3%. By having a polyhydric alcohol 14 content within this range, it is possible to appropriately disperse the copper particles 12 while preventing the concentration of copper particles 12 from becoming too low.

[0099] The third copper ink 10C preferably contains copper particles 12 in a mass ratio of 1% to 50% of the total third copper ink 10C, more preferably 5% to 50%, and even more preferably 5% to 30%. Having the copper particle 12 content within this range allows for sufficient concentration of copper particles 12 while suppressing a decrease in the fluidity of the second copper ink 10B, thus offering advantages in manufacturing, such as improved nozzle ejection performance.

[0100] The third copper ink 10C preferably contains a high-boiling-point solvent in a mass ratio of 50% to 99% of the total third copper ink 10C, more preferably 50% to 95%, and even more preferably 60% to 95%. Having the high-boiling-point solvent content within this range allows for sufficient concentration of copper particles 12 while suppressing a decrease in the fluidity of the third copper ink 10C, thus offering advantages in manufacturing, such as improved nozzle ejection performance.

[0101] The third copper ink 10C preferably contains organic solvent 18 in a mass ratio of 0.01% to 20% of the total third copper ink 10C, more preferably 0.01% to 10%, and even more preferably 0.1% to 10%. This range of organic solvent 18 content allows for proper storage over a long period.

[0102] The third copper ink 10C preferably contains a dispersant, which is a component other than copper particles 12, polyhydric alcohol 14, solvent 16, and organic solvent 18. Examples of dispersants include cationic dispersants, anionic dispersants, nonionic dispersants, and amphoteric dispersants. Among these, carboxylic acid dispersants, sulfonic acid dispersants, and phosphoric acid dispersants are examples of anionic dispersants, and phosphoric acid ester compounds are particularly preferred as phosphoric acid dispersants. The molecular weight of the phosphoric acid ester compound used as a dispersant is preferably 200 to 2000, more preferably 200 to 1500, and even more preferably 200 to 1000. A molecular weight of 200 or more provides sufficient hydrophobicity, resulting in good dispersibility of copper particles in a high-boiling point solvent. A molecular weight of 2000 or less allows for decomposition and reaction at the target heating temperature (approximately 200 to 350°C), thus avoiding interference with sintering of copper particles. The phosphate ester compound used as a dispersant can be any type, but examples include polyoxyethylene alkyl ether phosphate esters such as laureth-n phosphate, oleth-n phosphate, steareth-n phosphate (n=2-10), and alkyl phosphate esters. One of these may be used as the dispersant, or two or more may be used.

[0103] The third copper ink 10C preferably contains a dispersant in a mass ratio of 0.01% to 5% of the total third copper ink 10C, more preferably 0.1% to 5%, and even more preferably 0.1% to 3%. This range of dispersant content effectively suppresses the aggregation of copper particles 12.

[0104] In this embodiment, it is preferable that the third copper ink 10C, excluding unavoidable impurities, does not contain any substances other than copper particles 12, polyhydric alcohol 14, solvent 16 (here, water, ethanol, and high-boiling point solvent), organic solvent 18, and dispersant. However, it is not limited to this, and the third copper ink 10C may not contain a dispersant, or it may contain additives other than copper particles 12, polyhydric alcohol 14, solvent 16, organic solvent 18, and dispersant (adhesion enhancers, rheology modifiers, rust inhibitors, etc.).

[0105] Copper inks that use a high-boiling point solvent as the main solvent may cause the copper particles 12 to aggregate due to the high-boiling point solvent. In contrast, the third copper ink 10C has a polyhydric alcohol 14 mixed in, which allows the polyhydric alcohol 14 to coordinate around the copper particles 12, for example, thereby suppressing the aggregation of the copper particles 12 together.

[0106] (Method of manufacturing copper ink) Next, an example of a method for manufacturing the copper ink 10 described above will be explained. Figure 4 is a flowchart illustrating the method for manufacturing the copper ink according to this embodiment.

[0107] (Manufacturing of copper particles) As shown in Figure 4, in this manufacturing method, copper particles 12 are produced by mixing a copper carboxylate aqueous dispersion with a reducing agent (step S20). Specifically, first, an aqueous dispersion of copper carboxylate is prepared, and a pH adjusting agent is added to this aqueous dispersion to adjust the pH to between 2.0 and 7.5. Next, under an inert gas atmosphere, a hydrazine compound in an amount of 1.0 to 1.2 equivalents, which can reduce copper ions, is added to this pH-adjusted aqueous dispersion of copper carboxylate and mixed as a reducing agent. The resulting mixture is heated to a temperature of 60°C to 80°C under an inert gas atmosphere and held for 1.5 to 2.5 hours. This reduces the copper ions eluted from the copper carboxylate to produce copper particles 12, and also causes organic matter derived from copper carboxylate to form on the surface of these copper particles 12. The carboxylic acids used here include glycolic acid, citric acid, malic acid, maleic acid, malonic acid, fumaric acid, succinic acid, tartaric acid, oxalic acid, phthalic acid, benzoic acid, and their salts. While hydrazine compounds were used as reducing agents, the formula is not limited to these; hydrazine, ascorbic acid, oxalic acid, formic acid, and their salts may also be used.

[0108] Aqueous dispersions of copper carboxylate can be prepared by adding powdered metal carboxylate to pure water such as distilled water or deionized water at a concentration of 25% to 40% by mass, stirring with a stirring blade, and dispersing it uniformly. Examples of pH adjusting agents include triammonium citrate, ammonium hydrogen citrate, and citric acid. Among these, triammonium citrate is preferred because it allows for mild pH adjustment. The pH of the aqueous copper carboxylate dispersion is set to 2.0 or higher to increase the elution rate of copper ions eluted from copper carboxylate, thereby accelerating the formation of copper particles and obtaining the target fine copper particles. The pH is set to 7.5 or lower to suppress the formation of copper(II) hydroxide from the eluted metal ions, thereby increasing the yield of copper particles. Furthermore, by setting the pH to 7.5 or lower, the reducing power of the hydrazine compound can be suppressed from becoming excessively high, making it easier to obtain the target copper particles. It is preferable to adjust the pH of the aqueous copper carboxylate dispersion within the range of 4 to 6.

[0109] The reduction of copper carboxylate with hydrazine compounds is carried out under an inert gas atmosphere. This is to prevent the oxidation of copper ions dissolved in the solution. Examples of inert gases include nitrogen gas and argon gas. Hydrazine compounds have advantages such as not producing residue after the reduction reaction when reducing copper carboxylate under acidic conditions, being relatively safe, and being easy to handle. Examples of hydrazine compounds include hydrazine monohydrate, anhydrous hydrazine, hydrazine hydrochloride, and hydrazine sulfate. Among these hydrazine compounds, hydrazine monohydrate and anhydrous hydrazine, which do not contain components that can become impurities such as sulfur and chlorine, are preferred.

[0110] Generally, copper generated in acidic solutions with a pH below 7 dissolves. However, in this embodiment, a hydrazine compound, which is a reducing agent, is added to an acidic solution with a pH below 7 and mixed, generating copper particles in the resulting mixture. As a result, the carboxylic acid-derived components generated from copper carboxylate quickly coat the surface of the copper particles, suppressing the dissolution of the copper particles. It is preferable to raise the aqueous dispersion of copper carboxylate, after adjusting the pH, to a temperature of 50°C to 70°C to facilitate the reduction reaction.

[0111] The mixture of copper particles and hydrazine compounds, heated to a temperature of 60°C to 80°C under an inert gas atmosphere and held for 1.5 hours to 2.5 hours, is intended to generate copper particles and to form and coat the surface of the generated copper particles with organic matter. The heating and holding under an inert gas atmosphere is intended to prevent oxidation of the generated copper particles. The starting material, copper carboxylate, typically contains about 35% by mass of copper. By adding a hydrazine compound, which is a reducing agent, to an aqueous dispersion of carboxylic acid containing this amount of copper, heating it to the above temperature, and holding it for the above time, the generation of copper particles and the generation of organic matter on the surface of the copper particles proceed in a balanced manner, so that copper particles can be obtained in which the amount of organic matter coating is in the range of 0.5% by mass to 2.0% by mass per 100% by mass of copper particles. If the heating temperature is below 60°C and the holding time is less than 1.5 hours, the carboxylic acid metal may not be completely reduced, the rate of copper particle generation may become too slow, and there is a risk that the amount of organic matter coating the copper particles will be excessive. Furthermore, if the heating temperature exceeds 80°C and the holding time exceeds 2.5 hours, the rate of copper particle formation may become too fast, potentially resulting in insufficient organic matter coating the copper particles. The preferred heating temperature is 65°C to 75°C, and the preferred holding time is 2 hours to 2.5 hours.

[0112] The copper particles generated in the mixture can be separated from the mixture under an inert gas atmosphere, for example, using a centrifuge, to obtain a water slurry containing copper particles 12 with a fixed solid-liquid ratio (e.g., solid-liquid ratio: 50 / 50 [mass%]). In some cases, solid-liquid separation can be performed, and copper particles coated with organic matter can be obtained by freeze-drying or vacuum drying. Because these copper particles are coated with organic matter, they are less susceptible to oxidation even when stored in the atmosphere.

[0113] (Manufacturing of the first copper ink) Next, copper particles 12, polyhydric alcohol 14, organic solvent 18, and water are mixed to produce the first copper ink 10A (step S22). Here, it is preferable to produce the first copper ink 10A by mixing copper particles 12, polyhydric alcohol 14, organic solvent 18, and water so that the content of copper particles 12, polyhydric alcohol 14, and organic solvent 18 falls within the numerical range described above. The method of mixing copper particles 12, polyhydric alcohol 14, organic solvent 18, and water is arbitrary. For example, an aqueous solution of polyhydric alcohol 14 and organic solvent 18 containing water may be mixed with a metal slurry containing copper particles 12, or an aqueous solution of polyhydric alcohol 14 and organic solvent 18 may be mixed with copper particles 12 that do not contain water.

[0114] (Manufacturing of second copper ink) Next, the first copper ink 10A and ethanol are mixed to produce the second copper ink 10B (step S24). Here, it is preferable to produce the second copper ink 10B by mixing the first copper ink 10A and ethanol such that the content of copper particles 12, polyhydric alcohol 14, ethanol, and organic solvent 18 falls within the numerical range described above. The method of mixing the first copper ink 10A and ethanol is arbitrary. For example, the first copper ink 10A obtained in step S22 may be left to stand for a predetermined time (e.g., about one day) or centrifuged under predetermined conditions, a portion of the supernatant may be removed, and ethanol may be added to the first copper ink 10A from which the supernatant has been removed.

[0115] (Manufacturing of third-copper ink) Next, the second copper ink 10B, a high-boiling solvent, and a dispersant are mixed to produce the third copper ink 10C (step S26). Here, it is preferable to produce the third copper ink 10C by mixing the second copper ink 10B, a high-boiling solvent, and a dispersant so that the content of copper particles 12, polyhydric alcohol 14, high-boiling solvent, dispersant, and organic solvent 18 is within the numerical range described above. The method of mixing the second copper ink 10B, the high-boiling solvent, and the dispersant is optional. For example, the second copper ink 10B obtained in step S24 may be left to stand for a predetermined time (e.g., about one day) or centrifuged under predetermined conditions, and then a portion of the supernatant may be removed, and the high-boiling solvent may be added to the second copper ink 10B from which the supernatant has been removed. Furthermore, the addition of a dispersant is not essential. Furthermore, solvents (water, ethanol, high-boiling point solvents, etc.) may be removed from or added to the third copper ink 10C so that the numerical range described above is maintained.

[0116] The third copper ink 10C produced in this manner is used as copper ink 10. In the above explanation, the second copper ink 10B was produced using the first copper ink 10A, and the third copper ink 10C was produced using the second copper ink 10B. In other words, the first copper ink 10A and the second copper ink 10B were intermediate materials for producing the third copper ink 10C. However, the first copper ink 10A and the second copper ink 10B are not limited to being intermediate materials, and the first copper ink 10A and the second copper ink 10B themselves may be used as copper ink 10.

[0117] The method for manufacturing the copper particles 12 and copper ink 10 described above is merely an example, and the copper particles 12 and copper ink 10 may be manufactured by any method.

[0118] (effect) The method for producing cuprous oxide 100 according to this disclosure includes the steps of: obtaining a copper ink 10 which is a liquid composition containing copper particles 12; forming a film by coating or printing the copper ink 10 onto a substrate 110; producing cuprous oxide 100 on the substrate 110 by drying the film formed by the copper ink 10 on the substrate 110, and then heating it by irradiating it with light in the visible to infrared wavelength range in an atmosphere with an oxygen concentration of 10% to 21%; and heating the cuprous oxide 100 in an atmosphere with an oxygen concentration lower than the oxygen concentration at which the copper particles 12 were oxidized and sintered. According to this disclosure, by further heating the cuprous oxide 100 obtained by sintering in a low-oxygen atmosphere, crystal growth can be promoted to obtain cuprous oxide 100 with appropriate performance.

[0119] In the step of heating cuprous oxide 100, it is preferable to heat the cuprous oxide 100 in an atmosphere of inert gas with an oxygen concentration of 0.01 ppm to 100 ppm. This allows for appropriate promotion of crystal growth of cuprous oxide 100.

[0120] In the step of heating cuprous oxide 100, it is preferable to heat the cuprous oxide 100 at a heating temperature of 400°C to 800°C (first heating time) and for a holding time of 1 second to 60 minutes. This allows for appropriate promotion of crystal growth of cuprous oxide 100.

[0121] The inert gas is preferably a noble gas or nitrogen gas. This allows for appropriate promotion of cuprous oxide 100 crystal growth.

[0122] In the step of heating cuprous oxide 100, it is preferable to heat the cuprous oxide 100 in an atmosphere of superheated steam with a water vapor concentration of 10 kg / h to 60 kg / h. This allows for appropriate promotion of crystal growth of cuprous oxide 100.

[0123] In the step of heating cuprous oxide 100, it is preferable to heat the cuprous oxide 100 at a heating temperature of 300°C to 800°C (second heating temperature) and for a holding time of 1 second to 60 minutes. This allows for appropriate promotion of crystal growth of cuprous oxide 100.

[0124] The cuprous oxide 100 of this disclosure has an average transmittance of light with wavelengths of 600 nm to 1200 nm of 40% to 100% when the film thickness is 0.5 μm, and a hole concentration of 1 × 10⁻¹⁶ 12 (1 / cm 3 ) 1 x 10 20 (1 / cm 3 ) or less, and the hole mobility is 1 (cm 2 / V s) or more 100(cm) 2 The value is less than or equal to / V·s). According to this disclosure, cuprous oxide 100 with appropriate performance can be obtained.

[0125] The cuprous oxide 100 of this disclosure has an average transmittance of light with wavelengths of 600 nm to 1200 nm of 40% or more and 100% or less when the film thickness is 0.5 μm, and satisfies at least one of the following conditions in the CMKY color notation: K is less than 60%, M is 30% or more, and the value obtained by dividing K by M is less than 1.40. According to this disclosure, cuprous oxide 100 with appropriate performance can be obtained.

[0126] (Examples) Next, we will describe the examples. Figures 5A to 5D are tables showing each example, and Figure 6 is a table showing the inks used in each example.

[0127] (Copper ink) The method for manufacturing copper ink is described below. In the production of copper ink, copper phthalate was prepared as the copper carboxylate, which is the starting material. Copper phthalate was placed in deionized water at room temperature and stirred with a stirring blade to prepare an aqueous dispersion of copper phthalate with a concentration of 30% by mass. Next, an aqueous solution of ammonium phthalate was added to this aqueous dispersion of copper phthalate as a pH adjusting agent to adjust the pH of the aqueous dispersion to 3. Then, the pH-adjusted solution was heated to 50°C and, under a nitrogen gas atmosphere, an aqueous solution of hydrazine monohydrate with an oxidation-reduction potential of -0.5V (diluted twice) was added all at once as a reducing agent, in an amount equivalent to 1.2 times that can reduce copper ions, and the mixture was uniformly mixed using a stirring blade. Furthermore, in order to synthesize the target copper particles, the mixture of the aqueous dispersion and the reducing agent was heated to the holding temperature of 70°C under a nitrogen gas atmosphere and held at 70°C for 2 hours. Finally, an aqueous slurry of copper particles (copper powder concentration: 50% by mass) was obtained by dehydrating and desalting using a centrifuge.

[0128] From the obtained aqueous slurry of copper particles (copper powder concentration: 50% by mass), copper inks 1, 2, and 3 were prepared with the compositions shown in Figure 6.

[0129] (Example 1) In Example 1, ink 1 was applied to a 50mm x 50mm, 0.7mm thick glass substrate using a dispenser, covering a 30mm x 30mm area in the center of the substrate. The ink film was then dried in air at 80°C for 15 minutes to form an ink film with a thickness of 1μm. The ink film formed on the glass substrate was then heated in an atmosphere with an oxygen concentration of 20.4% (the oxygen concentration in the atmosphere was measured using a zirconia-type oxygen concentration meter LC-860 manufactured by Toray Engineering Co., Ltd.) using a high-temperature observation microscope SMT Scope SK-8000 (manufactured by Sanyo Seikou Co., Ltd.). The heating temperature was 300°C, the heating rate to the heating temperature was 3°C / second, and the holding time at the heating temperature was 30 seconds. A sintered body was then produced on the glass substrate. The obtained sintered body was then heated using a high-temperature observation microscope, SMT Scope SK-8000 (manufactured by Sanyo Seikou Co., Ltd.), under the following conditions: nitrogen atmosphere, oxygen concentration of 1000 ppm, heating temperature of 300°C, heating rate to heating temperature of 3°C / second, and holding time at heating temperature of 60 seconds.

[0130] (Examples 2-57, Comparative Examples 1-3) In Examples 2-57 and Comparative Examples 1-3, sintered bodies were obtained using the same method as in Example 1, except for the conditions shown in Figures 5A-5D. In Examples 37-57, a superheated steam batch furnace (furnace dimensions: W400 x D400 x H400, Aqua Steam Heater: 4.5kW x 2 units, manufactured by Shinetsu Kogyo Co., Ltd.) was used for heating in a superheated steam atmosphere, and the sintered bodies were obtained using the same method as in Example 1, except for the conditions shown in Figures 5C-5D.

[0131] (evaluation) For the evaluation, XRD measurement data was prepared for each sintered body using the method described in this embodiment, and quantitative analysis was performed. Based on the results of the quantitative analysis, Cu2O weight ratios of 99% or more were classified as "A: excellent," 95% or more and less than 99% as "B: good," 90% or more and less than 95% as "C: fair," and less than 90% as "D: poor." Furthermore, the average transmittance of light with wavelengths of 600 nm to 1200 nm was measured for each example of the sintered body using the method described in this embodiment. An average transmittance of 40% or more was considered acceptable, and an average transmittance of less than 40% was considered unacceptable. Furthermore, for each example of sintered body, the hole concentration and hole mobility were measured using the method described in this embodiment. 12 The above 1 x 10 20 The following case is "A: excellent", 1 × 10 12 Less than, or 1 × 10 20 If the value exceeds a certain threshold, it is classified as "D: poor". Additionally, hole mobility of 30 or more and 100 or less is classified as "A: excellent", 10 or more and less than 30 as "B: good", 1 or more and less than 10 as "C: fair", and less than 1 as "D: poor". The measurement results for each example are shown in Figures 5A to 5D.

[0132] As shown in Figures 5A to 5D, the sintered bodies of Examples 1 to 57, obtained by heating copper ink, a liquid composition containing copper particles, under conditions of an oxygen concentration of 10% to 21%, irradiated with light in the visible to infrared wavelength range, and heated in an atmosphere with a lower oxygen concentration, showed that cuprous oxide was properly produced (i.e., XRD evaluation was A to C), the average transmittance was between 40% and 100%, and the hole concentration was 1 × 10⁻⁶. 12 The above 1 x 10 20 The results are as follows, and since the hole mobility is between 1 and 100, it can be seen that cuprous oxide with appropriate performance has been obtained. On the other hand, the sintered bodies of Comparative Examples 1 to 3, which were manufactured under conditions different from those of the Examples, showed that cuprous oxide was properly produced, the average transmittance was between 40% and 100%, and the hole concentration was 1 × 10⁻⁶. 12 The above 1 x 10 20 It is clear that cuprous oxide with appropriate performance cannot be obtained because at least one of the following conditions is not met: the material is as described below and the hole mobility is between 1 and 100.

[0133] (Evaluation of options) Figure 7 is a table showing the evaluation of options. For the sintered bodies of Examples 18, 27, 33, 51 and Comparative Example 3, the color in the CMKY color notation was measured as an evaluation of the options. Figure 7 shows the measurement results of the color values ​​in the CMKY color notation for each example. The measurement method used was the one described in the embodiments above. In Figure 7, a result of "pass" was given if at least one of the following conditions was met: K is less than 60% and M is 30% or more, and K / M is less than 1.40. A result of "fail" was given if these conditions were not met. As shown in Figure 7, Examples 18, 27, 33, and 51 satisfy at least one of the following conditions: K is less than 60%, M is 30% or more, and K / M is less than 1.40, indicating that they have appropriate performance. On the other hand, in Comparative Example 3, M is not 30% or more, and K / M is not less than 1.40, and the hole mobility is D, indicating that they do not have appropriate performance.

[0134] Although embodiments of the present invention have been described above, the embodiments are not limited to those described herein. Furthermore, the aforementioned components include those that can be easily conceived by those skilled in the art, those that are substantially the same, and those that fall within the so-called equivalent range. Moreover, the aforementioned components can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the embodiments described above. [Explanation of symbols]

[0135] 10 Copper Ink 12 copper particles 100 Cuprous oxide 110 Base material

Claims

1. A step of obtaining copper ink, which is a liquid composition containing copper particles, The steps include forming a film by applying or printing the copper ink onto a substrate, The steps include: drying the film formed on the substrate with the copper ink, then heating it by irradiating it with light in the visible to infrared wavelength range in an atmosphere with an oxygen concentration of 10% to 21%, thereby oxidizing and sintering the copper particles in the copper ink to produce cuprous oxide on the substrate; The steps include heating the cuprous oxide in an atmosphere with an oxygen concentration lower than that at the time the copper particles were oxidized and sintered, including, A method for producing cuprous oxide.

2. In the step of heating the cuprous oxide, the cuprous oxide is heated in an atmosphere of inert gas with an oxygen concentration of 0.01 ppm or more and 100 ppm or less. A method for producing cuprous oxide according to claim 1.

3. In the step of heating the cuprous oxide, the cuprous oxide is heated at a heating temperature of 400°C or more and 800°C or less, and for a holding time of 1 second or more and 60 minutes or less. The method for producing cuprous oxide according to claim 2.

4. The inert gas is a noble gas or nitrogen gas. A method for producing cuprous oxide according to claim 2 or claim 3.

5. In the step of heating the cuprous oxide, the cuprous oxide is heated in an atmosphere of superheated steam with a steam vapor concentration of 10 kg / h or more and 60 kg / h or less. A method for producing cuprous oxide according to claim 1.

6. In the step of heating the cuprous oxide, the cuprous oxide is heated at a heating temperature of 300°C or more and 800°C or less, and for a holding time of 1 second or more and 60 minutes or less. The method for producing cuprous oxide according to claim 5.

7. When the film thickness is 0.5 μm, the average transmittance of light with wavelengths of 600 nm to 1200 nm is between 40% and 100%. The hole concentration is 1 × 10⁻⁶ １２ (1 / cm ３ ) 1 x 10 ２０ (1 / cm ３ ) and below, The hole mobility is 1 (cm ２ / V・s) or more 100 (cm ２ / V・s) is less than or equal to Cuprous oxide.

8. When the film thickness is 0.5 μm, the average transmittance of light with wavelengths of 600 nm to 1200 nm is between 40% and 100%. In the CMKY color notation, K is less than 60%, At least one of the following conditions is met: M is 30% or more, and the value obtained by dividing K by M is less than 1.

40. Cuprous oxide.

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