Photoresponsive nanocrystals, method for producing photoresponsive nanocrystals

Abstract

To provide a photoresponsive nanocrystal having a narrow FWHM blue emission wavelength or a narrow FWHM red emission wavelength in the color gamut defined by BT.2020. [Solution] A photoresponsive nanocrystal having a composite layer structure in which a first layer containing cation A and a second layer containing cation B and anion X are alternately stacked, and comprising a nanocrystalline plate having ligands that exist by substituting at least a portion of cation A, wherein the aspect ratio, which is a rectangular shape feature in a direction intersecting the stacking direction of the composite layer structure, is 0.2 or more and 5 or less, and the superlattice structure has superlattice peaks in the diffraction angle range of ±5 degrees that straddles the main diffraction peak of the X-ray diffraction profile by the 2θ method.

Description

Technical Field

[0001] The present disclosure relates to a light-responsive nanocrystal and a method for manufacturing the light-responsive nanocrystal.

Background Art

[0002] Nanocrystals having a perovskite-type crystal structure are known to be applicable to light-emitting materials and materials for solar cells because they have a narrow full width at half maximum in spectroscopic sensitivity characteristics and exhibit high color purity. Further, since the absorption and emission wavelengths can be controlled depending on the halogen composition, there is an advantage that it is easy to provide a material that responds to light in a wide wavelength range. When the structural scale of nanocrystals having a perovskite-type crystal structure becomes small, the emission wavelength shifts to the short wavelength side due to the quantum confinement effect, and thus the emission wavelength can also be adjusted to a desired wavelength.

[0003] Nanocrystals having a perovskite-type crystal structure are known to take various forms such as nanoparticles and nanoplatelets depending on the synthesis conditions. The perovskite-type crystal structure CsPbBr3 exhibits green emission at 520 nm when the diameter is 15 nm or more where the quantum size effect does not occur, but blue emission around 465 nm can be obtained by making nanoparticles with a diameter of 3 nm or less (Non-Patent Document 1).

[0004] In the case of nanoplatelets (NPL), it is known that the emission wavelength can be controlled by the layer thickness. For example, blue emission can be obtained by controlling the number of layers of NPL of the crystal structure CsPbBr3 by the precursor raw material ratio (Non-Patent Document 2). Similarly, in the case of the crystal structure CsPbI3, red emission can be obtained by controlling the number of layers of NPL (Non-Patent Document 3).

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

[0006] When using the nanoparticles described in Non-Patent Literature 1, obtaining a blue emission wavelength of 467 nm within the BT.2020 color gamut requires precise control of the size distribution with a diameter of 3 nm or less, making it difficult to obtain emission exhibiting a narrow FWHM (Full Width at Half Maximum). When using the NPL described in Non-Patent Literature 2, it was difficult to selectively obtain only three or more layers of NPL. Therefore, in both cases using nanoparticles and NPL, it was difficult to achieve both an emission peak of 467 nm and a narrow FWHM. Similarly, the red emission using the crystal structure CsPbI3 described in Non-Patent Literature 3 also faced similar challenges, making it difficult to achieve both red emission at a wavelength of 632 nm within the BT.2020 color gamut and a narrow FWHM.

[0007] This disclosure has been made in view of the above issues and aims to provide a photoresponsive nanocrystal having a narrow FWHM blue emission wavelength or a narrow FWHM red emission wavelength in the color gamut defined by BT.2020. Furthermore, this disclosure aims to provide a method for producing a photoresponsive nanocrystal having a narrow FWHM blue emission wavelength or a narrow FWHM red emission wavelength in the color gamut defined by BT.2020. [Means for solving the problem]

[0008] This disclosure is, A photoresponsive nanocrystal comprising a nanocrystalline plate having a composite layer structure in which a first layer containing cation A and a second layer containing cation B and anion X are alternately stacked, and having ligands present in which at least a portion of cation A is substituted, The aspect ratio, which is a rectangular shape feature in the direction intersecting the stacking direction of the composite layer structure, is between 0.2 and 5. This is a photoresponsive nanocrystal with a superlattice structure, in which superlattice peaks exist within a diffraction angle range of ±5 degrees surrounding the main diffraction peak of the X-ray diffraction profile, as determined by the 2θ method. Furthermore, this disclosure is, A method for producing a photoresponsive nanocrystal having a composite layer structure in which a first layer containing a ligand and cation A and a second layer containing cation B and anion X are alternately stacked, A first step involves reacting a first precursor solution containing cation A and a first organic acid with a second precursor solution containing cation B, anion X, a second organic acid, and a first organic base, under predetermined conditions: the molar ratio obtained by dividing the sum of the amounts of the first organic acid and the second organic acid by the amount of the first organic base is a predetermined value, and at a predetermined reaction temperature, to produce a first reaction solution containing nanocrystalline particles. The second step involves maintaining the first reaction solution at a predetermined growth temperature range which is lower than the reaction temperature and for a predetermined growth time, and growing crystals in a predetermined axial direction using the nanocrystalline particles as nuclei to produce a second reaction solution. This is a method for producing photoresponsive nanocrystals, which include [the specified element]. [Effects of the Invention]

[0009] According to this disclosure, a perovskite nanocrystalline composition having a nanocrystalline plate form with a small dispersion σn of the number of layers and exhibiting blue or red light emission can be provided, and a solar cell material that corresponds to light in a wide wavelength range can be provided. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 shows the XRD results for Examples 1 and 2 and Comparative Examples 1 and 2. [Figure 2] Figure 2(a) shows the TEM image of Example 1. Figure 2(b) shows the TEM image of Comparative Example 1. [Figure 3] Figure 3(a) shows the emission spectra of Example 1 and Comparative Example 1. Figure 3(b) shows the emission spectrum of Example 8. [Modes for carrying out the invention]

[0011] Preferred embodiments of the present disclosure will be described in detail below with reference to the drawings, but the present disclosure is not limited thereto. <First Embodiment> The first embodiment relates to a photoresponsive nanocrystal. The photoresponsive nanocrystals disclosed herein are A photoresponsive nanocrystal comprising a nanocrystalline plate having a composite layer structure in which a first layer containing cation A and a second layer containing cation B and anion X are alternately stacked, and having ligands present in which at least a portion of cation A is substituted, The aspect ratio, which is a rectangular shape feature in the direction intersecting the stacking direction of the composite layer structure, is between 0.2 and 5. The 2θ method indicates that the X-ray diffraction profile contains superlattice peaks within a diffraction angle range of ±5 degrees surrounding the main diffraction peak, thus possessing a superlattice structure. The explanation is as follows.

[0012] (Structure of nanocrystalline plate) The photoresponsive nanocrystals disclosed herein include a nanocrystal plate (hereinafter also referred to as a perovskite-type nanocrystal plate) having a composite layer structure in which a first layer containing cation A and a second layer containing cation B and anion X are alternately stacked, and which has ligands present in which at least a portion of cation A is substituted. The presence of the nanocrystal plate can be confirmed by TEM-EDS.

[0013] The bulk perovskite crystal structure can be described by the formula ABX3 (where A is a cation, B is a metal, and X is a halogen). In the case of perovskite nanocrystalline plates with dimensions limited to one direction, L2[ABX3] n-1 It can be described as BX4 (L: ligand, n: number of metal halide octahedral layers). Here, the n-1 term represents the thickness of the nanocrystal plate converted to a bulk unit cell, n=2 corresponds to a complete ABX3 perovskite unit cell, and when n=1, the structure does not contain a cation species (A). In the photoresponsive nanocrystals of this disclosure, it is preferable that the ligand coordinates to cation B.

[0014] The perovskite-type nanocrystal plates of this disclosure have a superlattice structure. That is, the photoresponsive nanocrystals of this disclosure have superlattice peaks within a diffraction angle range of ±5 degrees surrounding the main diffraction peak of the X-ray diffraction profile. The 2θ method is used for X-ray diffraction.

[0015] Thus, although the crystalline structure of the nanocrystalline plate is not strictly represented as ABX3, here the crystalline structure of the nanocrystalline plate will be represented as ABX3, which signifies a perovskite-type crystalline structure, and it will also be called a perovskite-type nanocrystalline plate. Hereafter, the number of layers will be represented as n. Also, the layer thickness direction will refer to the direction in which the layers are stacked.

[0016] In the photoresponsive nanocrystals of the present disclosure, it is preferable that the rectangular shape feature (aspect ratio) corresponds to two directions that define the plate size of the nanocrystal plate. Here, of the two axes that intersect the thickness direction of the nanocrystal plate, the longitudinal direction is defined as the major axis and the short direction as the minor axis, and the aspect ratio is expressed as either the average length of the major axis / the average length of the short axis, or the aspect ratio = average length of the short axis / the average length of the major axis. In the photoresponsive nanocrystals of the present disclosure, the aspect ratio, which is the rectangular shape feature in the direction intersecting the stacking direction of the composite layer structure, is between 0.2 and 5. In Table 1 described later, the aspect ratio is expressed as the average length of the major axis / the average length of the short axis.

[0017] When the photo-responsive nanocrystals of the present disclosure have a biaxial direction intersecting the layer thickness direction of the nanocrystal plate, with the axis in the longitudinal direction being the long axis and the axis in the short transverse direction being the short axis, the average value of the length of the short axis is preferably 6 nm or more and 20 nm or less, more preferably 7 nm or more and 15 nm or less, and even more preferably 7.3 nm or more and 14.5 nm or less.

[0018] When the photo-responsive nanocrystals of the present disclosure have a biaxial direction intersecting the layer thickness direction of the nanocrystal plate, with the axis in the longitudinal direction being the long axis and the axis in the short transverse direction being the short axis, the average value of the length of the long axis is preferably 10 nm or more and 45 nm or less, more preferably 7 nm or more and 15 nm or less, and even more preferably 7.3 nm or more and 14.5 nm or less. And the average value of the length of the short axis is preferably less than or equal to the average value of the length of the long axis.

[0019] [A site (cation A) of the perovskite structure] A monovalent cation is adopted for the A site. The monovalent cation (cation A) adopted for the A site includes an ammonium cation (NH4 + ), an alkylammonium cation having a carbon number of 6 or less, a formamidinium cation (HC(NH2)2 + ), a guanidinium cation (C(NH2)3 + ), a nitrogen-containing organic compound cation such as an imidazolium cation, a pyridinium cation, and a pyrrolidinium cation, and an alkali metal cation such as a lithium cation (Li + ), a sodium cation (Na + ), a potassium cation (K + ), a rubidium cation (Rb + ), and a cesium cation (Cs + ).

[0020] In the photo-responsive nanocrystals of the present disclosure, cation A is an ammonium cation (NH4 + ), an alkylammonium cation having a carbon number of 6 or less, a formamidinium cation (HC(NH2)2 +), guanidinium cation (C(NH2)3 + ), imidazolium cation, pyridinium cation, pyrrolidinium cation, lithium cation (Li + ), sodium cation (Na + ), potassium cation (K + ), rubidium cation (Rb + ), and cesium cation (Cs + Preferably, it includes one or more selected from the group consisting of ).

[0021] The monovalent cations employed at these A sites have small ionic diameters and are small enough to fit within the crystal lattice, allowing the perovskite compound to form a stable three-dimensional crystal.

[0022] A preferred example of an alkylammonium cation having 6 or fewer carbon atoms is the methylammonium cation (CH3NH3 + ), ethylammonium cation (C2H5NH3 + ), propylammonium cation (C3H7NH3 + Examples include:

[0023] From the viewpoint of obtaining high luminescence efficiency, it is preferable to use at least one of methylammonium cation, formamidinium cation, or cesium cation as the A site, and from the viewpoint of suppressing color change, it is more preferable to use cesium cation as the A site. Two or more monovalent cations may be used in combination as the A site.

[0024] When site A is a cesium cation, cesium salts can be used as raw materials for nanoparticle synthesis. Such cesium salts may include cesium chloride, cesium bromide, cesium iodide, cesium hydroxide, cesium carbonate, cesium bicarbonate, cesium bicarbonate, cesium formate, cesium acetate, cesium propionate, cesium pivalate, and cesium oxalate, as appropriate. From these candidate cesium salts, an appropriate one can be used depending on the synthesis method.

[0025] If site A is another alkali metal cation, salts of the above-mentioned cesium compound in which the cesium element is replaced with another alkali metal cation element can be used as raw materials.

[0026] If site A is a nitrogen-containing organic compound cation such as a methylammonium cation, then a neutral compound other than a salt, such as methylamine, can be used as a raw material. Two or more of these raw materials may be used in combination.

[0027] [Perovskite crystal structure B site (cation B)] The photoresponsive nanocrystals of this disclosure preferably contain a divalent transition metal cation or a divalent typical metal cation at the B site (cation B) of the perovskite-type crystal structure.

[0028] The photoresponsive nanocrystals disclosed herein contain divalent transition metal cations, and scandium cations (Sc 2+ ), titanium cation (Ti 2 +), vanadium cation (V 2+ ), chromium cation (Cr 2+ ), manganese cation (Mn 2+ ), iron cation (Fe 2+ ), cobalt cation (Co 2+ ), nickel cation (Ni 2+ ), copper cation (Cu 2+ ), palladium cation (Pd 2+ ), Europium cation (Eu 2+ ), and ytterbium cation (Yb 2+ Preferably, it includes one or more selected from the group consisting of ).

[0029] The photoresponsive nanocrystals disclosed herein contain divalent typical metal cations, and magnesium cations (Mg 2+ ), calcium cation (Ca 2+ ), strontium cation (Sr 2+ ), barium cation (Ba 2+ ), zinc cation (Zn 2+ ), cadmium cation (Cd2+ ), germanium cation (Ge 2+ ), tin cation (Sn 2+ ), and lead cations (Pb 2+ Preferably, it includes one or more selected from the group consisting of ).

[0030] Among these divalent cations, typical metal cations are preferred in terms of the growth of stable three-dimensional crystals, tin cations or lead cations are more preferred, and lead cations are particularly preferred from the viewpoint of obtaining high luminescence intensity. Two or more of these divalent cations may be used in combination, and the perovskite crystal structure may be a so-called double perovskite type.

[0031] When the B site is a lead cation, lead compounds can be used as raw materials for nanoparticle synthesis, and appropriate compounds can be used depending on the synthesis method. Examples of lead compounds include lead chloride, lead bromide, lead iodide, lead oxide, lead hydroxide, lead sulfide, lead carbonate, lead formate, lead acetate, lead 2-ethylhexanoate, lead oleate, lead stearate, lead naphthenate, lead citrate, lead maleate, and lead acetylacetonate. When the B site is another divalent metal cation, salts of the above-mentioned lead compounds in which the lead element is replaced with another divalent metal cation element can be used as raw materials. Two or more of these raw materials may be used in combination.

[0032] [X-site (anion X) of perovskite crystal structure] The photoresponsive nanocrystals disclosed herein preferably contain a monovalent anion, including a halide anion, in the perovskite-type crystal structure X (anion X). As the halide anion, a fluoride anion (F - ), chloride anion (Cl - ), bromide anion (Br - ), iodide anion (I - Examples include the following. Among these, chloride anions, bromide anions, or iodide anions are preferred from the viewpoint of forming stable three-dimensional crystals and exhibiting strong luminescence in the visible light range.

[0033] When a perovskite crystal is applied to the nanocrystalline particles constituting a photoresponsive nanocrystal, the spectral components of the emission color exhibited by the nanocrystalline particles can be enhanced as follows: blue when chloride anions are used, green when bromide anions are used, and red when iodide anions are used. When a perovskite crystal is applied to the nanocrystalline plate constituting the photoresponsive nanocrystal according to this embodiment, the emission color can be controlled by the average number of stacked nanocrystalline plates and the average aspect ratio of the main surface of the plate.

[0034] Two or more types of halide anions may be used in combination. In particular, when chloride anions, bromide anions, and iodide anions are used in combination, the emission wavelength of the nanoparticles can be set to a desired wavelength depending on the content ratio of the anion species. That is, when chloride anions, bromide anions, and iodide anions are used in combination, it is preferable because an emission spectrum covering almost the entire visible light region from blue to red can be obtained while maintaining a narrow full width at half maximum, depending on the content ratio of the anion species.

[0035] The X site (anion X) may contain a monovalent anion other than a halide anion. Such a monovalent anion other than a halide anion is a cyanide anion (CN - ), thiocyanate anion (SCN - ), isothiocyanate anion (CNS - Examples include pseudohalide anions such as ). When synthesizing nanoparticles, appropriate raw materials can be selected from salts with A-site and B-site cations, such as cesium chloride and lead bromide, or salts with other cations, depending on the synthesis method.

[0036] [Ligand] In this disclosure, the ligand is preferably selected from at least one compound or ion chosen from the group consisting of weak acids such as carboxylic acids, weak bases such as amines, and salts or ions thereof.

[0037] Examples of acids include branched or linear fatty acids having 1 to 30 carbon atoms. The alkyl chain may be saturated or unsaturated. Among these, linear fatty acids are preferred from the viewpoint of solubility and stability in solvents, and oleic acid is more preferred.

[0038] Examples of bases include branched or linear organic bases having 1 to 30 carbon atoms. The alkyl chain may be saturated or unsaturated. Among these, linear organic bases are preferred from the viewpoint of solubility and stability in solvents, and oleylamines are more preferred. Ligands may be used individually or in combination of two or more types.

[0039] [others] In the photoresponsive nanocrystals of this disclosure, the dispersion σn of the number of stacked nanocrystal plates is preferably 0.1 or more and 0.8 or less, more preferably 0.1 or more and 0.7 or less, even more preferably 0.2 or more and 0.5 or less, and particularly preferably 0.24 or more and 0.45 or less.

[0040] In the photoresponsive nanocrystals disclosed herein, the number of stacked nanocrystal plates n (indicated as the number of NPL layers n in Table 1) is preferably 3 or more and 5 or less, more preferably 3 or more and 4 or less, and even more preferably 3.

[0041] In the photoresponsive nanocrystals of the photoresponsive nanocrystals disclosed herein, when the peak intensity of the main diffraction peak (the peak with the greater peak intensity among the peaks around 15.1 degrees and the peak around 30.4 degrees) of the X-ray diffraction pattern of the photoresponsive nanocrystal is defined as I0, and the peak intensity of one or more superlattice peaks located within ±5 degrees of the main diffraction peak is defined as Ip, then Ip / I0 is preferably 0.1 or greater, and more preferably 0.3 or greater. The superlattice peak having the superlattice peak intensity Ip in this case is the superlattice peak whose superlattice peak intensity is maximized after separating the main diffraction peaks and superlattice peaks from the broad main diffraction peaks around 15.1 degrees and 30.4 degrees based on the XRD results, and removing the background from the main diffraction peaks. In this way, the present disclosure makes it possible to provide solar cell materials that correspond to light in a wider wavelength range.

[0042] <Second Embodiment> The method for producing the photoresponsive nanocrystals disclosed herein is: A method for producing a photoresponsive nanocrystal having a composite layer structure in which a first layer containing a ligand and cation A and a second layer containing cation B and anion X are alternately stacked, A first step involves reacting a first precursor solution containing cation A and a first organic acid with a second precursor solution containing cation B, anion X, a second organic acid, and a first organic base, under predetermined conditions: the molar ratio obtained by dividing the sum of the amounts of the first organic acid and the second organic acid by the amount of the first organic base is a predetermined value, and at a predetermined reaction temperature, to produce a first reaction solution containing nanocrystalline particles. The second step involves maintaining the first reaction solution at a predetermined growth temperature range which is lower than the reaction temperature and for a predetermined growth time, and growing crystals in a predetermined axial direction using the nanocrystalline particles as nuclei to produce a second reaction solution. Includes. Items that overlap with the first embodiment may be omitted from the explanation as they are the same.

[0043] Generally, perovskite nanocrystalline plates can be fabricated by hot injection or ligand-assisted reprecipitation (LARP). When fabricating nanocrystalline plates by hot injection, the number of layers of nanocrystalline plates is adjusted during synthesis by controlling the reaction temperature, precursor ratio, ligand concentration, ligand acid-base equilibrium, and ligand chain length. The number of layers of nanocrystalline plates decreases as the reaction temperature is lowered, and nanocrystalline plates are produced at reaction temperatures below approximately 130°C. By controlling the temperature, the thickness can be adjusted from a single layer to several layers. The number of layers can also be adjusted by changing the precursor ratio of the reaction solution.

[0044] Perovskite-type nanocrystalline plates fabricated by controlling the synthesis conditions in this way tend to exhibit variations in the number of layers. While it is possible to synthesize relatively well-dispersible nanocrystalline plates when n=1 or 2, obtaining monodisperse nanocrystalline plates with a uniform number of layers is difficult when n≧3. Furthermore, the aspect ratio of the two axes intersecting the thickness direction of the nanocrystalline plates also exhibits significant variation, resulting in the formation of nanocrystalline plates with different aspect ratios even with the same number of layers.

[0045] The ABX3 perovskite-type nanocrystalline plate according to this embodiment, which has a layered structure in which ABX3 perovskite structural units are connected and extended in two dimensions, and in which the layered structure is stacked in the thickness direction, can be manufactured by the following process.

[0046] The following explains each step in the process. (First step) A method for producing photoresponsive nanocrystals according to the present disclosure is a method for producing photoresponsive nanocrystals having a composite layer structure in which a first layer containing a ligand and cation A and a second layer containing cation B and anion X are alternately stacked, comprising a first step of reacting a first precursor solution containing cation A and a first organic acid with a second precursor solution containing cation B, the anion X, a second organic acid and a first organic base, under a predetermined molar ratio obtained by dividing the sum of the amounts of substance of the first organic acid and the second organic acid by the amount of substance of the first organic base, and under a predetermined reaction temperature, to produce a first reaction solution containing nanocrystal particles.

[0047] The first step is to produce a first reaction solution containing the nucleus crystals for the ABX3 perovskite nanocrystalline plate. The molar ratio obtained by dividing the sum of the amounts of the first organic acid and the second organic acid by the amount of the first organic base can also be said to be the molar ratio obtained by dividing the amount of the weak acid by the amount of the weak base, for example, the ratio (molar ratio) obtained by dividing the amount of oleic acid by the amount of oleylamine, and is controlled by the synthesis temperature, but is not limited to this.

[0048] Here, the predetermined value of the molar ratio obtained by dividing the sum of the amounts of the first organic acid and the second organic acid by the amount of the first organic base means that the ratio of the amount of the acidic ligand to the amount of the basic ligand (in Table 1, the ratio of the amount of oleic acid to the amount of oleylamine) is between 1.5 and 3.0, and is particularly preferably 2.0. If the ratio of oleic acid to oleylamine is too large or too small, the appropriate range for the holding temperature and holding time in the second step described later will be narrowed.

[0049] Furthermore, the specified reaction temperature range is 70°C to 110°C, with 90°C being particularly preferred. If the reaction temperature is too high or too low, the structural change to the ABX3 perovskite nanocrystalline plate will not be induced even after the second step. If the first reaction solution synthesized outside this range is used, the peak wavelength, FWHM, and PLQY (PhotoLuminesence Quantum Yield) values ​​of the obtained ABX3 perovskite nanocrystalline plate will be poor. In this context, good optical properties are considered to be a peak wavelength of 450 nm to 470 nm, an FWHM of 20 nm or less, and a PLQY of 50% or more.

[0050] In general synthesis methods, as described in Non-Patent Documents 1 and 2, a poor solvent is added and the mixture is centrifuged to purify and recover the synthesized nanocrystals from the synthesis solution. However, in this disclosure, the reaction solution, in which the raw material solution remains and coexists with the precursor crystals of the layered structure, is retained in the second step to induce a structural change to an ABX3 perovskite-type nanocrystal plate.

[0051] (Second step) The present disclosure provides a method for producing photoresponsive nanocrystals, which includes a second step of maintaining a first reaction solution in a predetermined growth temperature range lower than the reaction temperature and for a predetermined growth time, and growing crystals in a predetermined axial direction using nanocrystal particles as nuclei to produce a second reaction solution. The present disclosure provides a method for producing photoresponsive nanocrystals, which preferably includes a second step of growing crystals in two axial directions to produce nanocrystal plates, and more preferably a step of stacking the nanocrystal plates in the plate thickness direction of the nanocrystal plates.

[0052] The second step involves growing a precursor crystal on an ABX3 perovskite nanocrystalline plate to produce a second reaction solution, and includes a step of controlling the temperature and time at which the first reaction solution is held. The predetermined growth temperature range is lower than the reaction temperature of the first step, and is in the range of 10°C to 50°C, with a range of 20°C to 30°C being more preferable.

[0053] The predetermined growth time varies depending on the growth temperature, as follows: the growth time is longer at lower temperatures and shorter at higher temperatures. When the growth time at a growth temperature of 25°C is set to 100 (=24 hours), the relationship between the predetermined growth time and the predetermined growth temperature is roughly as follows: At a growth temperature of 10°C, the growth time is 1000; at a growth temperature of 15°C, the growth time is 500; at a growth temperature of 20°C, the growth time is 200; at a growth temperature of 30°C, the growth time is 45; at a growth temperature of 35°C, the growth time is 20; at a growth temperature of 40°C, the growth time is 10; at a growth temperature of 45°C, the growth time is 4; and at a growth temperature of 50°C, the growth time is 2.

[0054] For example, when the ratio of oleic acid to oleylamine is 2.0, holding the first reaction solution at a growth temperature of 25°C for 1 day (24 hours) or more yields an ABX3 perovskite-type nanocrystalline plate with a peak wavelength of 450 nm to 470 nm, an FWHM of 20 nm or less, and a PLQY of 50% or more. The growth time is preferably 1 day (24 hours) to 20 days or less. In the second step, the reaction can be accelerated or stopped by changing the temperature midway through the process.

[0055] The predetermined axial direction refers, for example, to two axial directions that intersect with the thickness direction of the nanocrystalline particles that form the nanocrystalline plate, specifically the longitudinal direction (long axis) and the short axis (short axis) of the two axes that intersect with the thickness direction of the nanocrystalline particles.

[0056] In the method for producing photoresponsive nanocrystals of the present disclosure, it is preferable that the second step is carried out such that at least one selected from the group consisting of vibrational energy to the reaction solution, flow rate of the reaction solution, and illuminance to the reaction solution is lower than that of the first step.

[0057] Furthermore, the second step is carried out under low vibration, low light, and environmental conditions in order to mitigate the effects of external disturbances and prevent phase separation that inhibits crystal growth. In other words, this step can be carried out in a constant temperature chamber where the effects of vibration, sound, and background light are reduced, in order to mitigate the effects of external disturbances and prevent phase separation that inhibits crystal growth.

[0058] (Third step) The method for producing photoresponsive nanocrystals according to the present disclosure preferably includes a third step of adding a poor solvent to a second reaction solution (a solution containing a nanocrystal plate) to separate the nanocrystal plate from the solvent, and the third step preferably includes applying an external force to the solution containing the poor solvent.

[0059] The third step involves adding a poor solvent such as ethyl acetate or methyl acetate to the second reaction solution, allowing it to settle by centrifugation, and then dispersing it in toluene or hexane to stop the change in crystal morphology in the second reaction solution. The second step may already contain the poor solvent ethyl acetate or methyl acetate.

[0060] (others) Through the above steps 1 to 3, a perovskite-type nanocrystalline plate is obtained with a peak wavelength of 450 nm to 470 nm, an FWHM of 20 nm or less, and a PLQY of 50% or more.

[0061] In the method for producing photoresponsive nanocrystals according to the present disclosure, it is preferable that the aspect ratio, which is a rectangular shape feature in a direction intersecting the stacking direction of the composite layer structure, is 0.2 or more and 5 or less.

[0062] In the method for producing photoresponsive nanocrystals of the present disclosure, it is preferable that the photoresponsive nanocrystal has a superlattice structure in which superlattice peaks exist in a diffraction angle range of ±5 degrees surrounding the principal diffraction peak of the X-ray diffraction profile by the 2θ method.

[0063] <Evaluation Method> This section describes the evaluation method common to both the first and second embodiments. (Evaluation of the number of layers of nanocrystalline plates) The structural parameters of nanocrystalline plates can be evaluated using X-ray diffraction (XRD). The nanocrystalline plates form a self-stacked aggregate (superlattice) via ligands. The periodicity of this superlattice can be described by structural parameters such as the interplanar spacing d of ABX3, the number of stacked nanocrystalline plates n, the dispersion σn of the number of stacked plates n, the spacing D of the nanocrystalline plates, and the dispersion σD of the spacing D. The spacing D of the nanocrystalline plates is substantially determined by the ligands on the surface of the nanocrystalline plates.

[0064] The first and second principal diffraction peaks of CsPbBr3 are 15.1° and 30.4°, respectively, and the first and second principal diffraction peaks of CsPbI3 are 13.8° and 27.2°, respectively. Here, the scattering vector coefficient is (q = 4π·sin(θ) / λ Xray If we assume that the first main diffraction peak is (q ≈ 0.9~1.1 Å), then the first main diffraction peak is (q ≈ 0.9~1.1 Å). -1 ), and the second main diffraction peak (q≒1.8~2.2Å) -1 By analyzing the superlattice peaks of ), structural parameters can be calculated, for example, by the analysis method described in non-patent literature (EE Fullerton, et al., Phys. Rev. B 45, pp. 9292-9310, 1992).

[0065] Superlattice peaks are observed when σn and σD are small and d, n, and D are uniform. If there is variation in the number of layers n or if the dispersion σn of the number of layers n is large, the superlattice peaks are lost. When n≦2, it is possible to synthesize nanocrystalline plates with relatively good dispersibility, and for example, in Non-Patent Literature 2, superlattice peaks are observed near the main diffraction peaks. However, when n≧3, it is difficult to obtain monodisperse nanocrystalline plates with a uniform number of layers, and so far, there have been no examples of superlattice peaks being observed. This is because perovskite-type nanocrystalline plates fabricated by controlling the conditions during synthesis tend to have variations in the number of layers.

[0066] Here, when d, D, and σD other than the number of stacked layers are the same, when σn < π / 2q, superlattice peaks are observed. Since other parameters are the same, this means the maximum value of the allowable dispersion σn for observing superlattice peaks. For σn < π / 2q, when the main diffraction peak of CsPbBr3 is 15.1 degrees, σn < 1.50; when it is 30.4 degrees, σn < 0.74. For CsPbI3, when the main diffraction peak is 13.8 degrees, σn < 1.65; when it is 27.2 degrees, σn < 0.83. Therefore, the second main diffraction peak with a larger scattering vector coefficient on the higher angle side corresponds to a structure with a smaller period, is more susceptible to the influence of σn, and superlattice peaks are not observed unless the number of stacked layers is the same.

[0067] Transmission electron microscopy (TEM) observation can evaluate the nanocrystal plates. By irradiating an electron beam from the same direction as the layer thickness direction of the nanocrystal plates and performing TEM observation, the biaxial aspect ratio (length of the long axis / length of the short axis in Table 1) intersecting the layer thickness direction can be evaluated. Also, by aligning the incident direction of the electron beam with the direction orthogonal to the layer thickness direction of the nanocrystal plates and measuring and analyzing the TEM observation and electron diffraction pattern, it is possible to evaluate the crystal plane spacing d of ABX3, the number of stacked layers n of the nanocrystal plates, the dispersion σn of the number of stacked layers n, the spacing D between the nanocrystal plates, and the dispersion σD of the spacing D.

[0068] Also, it is possible to calculate the same structural parameters from the aggregated data of the results of evaluating each individual nanocrystal plate rather than the aggregate. In the evaluation using TEM, for example, it is also possible to identify the stacked structure of the perovskite-type nanocrystal plates of the present disclosure incorporated in the device.

Examples

[0069] Hereinafter, the nanocrystal composition and the method for manufacturing nanocrystals according to the examples of the present disclosure will be described in detail, but the present disclosure is not limited to the following examples. [[ID=十六]] [[ID=十七]](Example 1)[[ID=十八]] [[ID=十九]][Synthesis of perovskite-type nanocrystal plates of CsPbBr3] [[ID=二十]] Step 1: 0.1 g of cesium carbonate, 0.8 mL of oleic acid, and 10 mL of 1-octadecene were placed in a flask, the solution was heated to 100°C, and degassed for 30 minutes using a vacuum pump. Further heating to 120°C under a dry nitrogen flow and holding for 20 minutes, then holding at 90°C, yielded precursor solution 1 of cation A. Separately, 0.276 g of lead(II) bromide and 20 mL of 1-octadecene were placed in a flask, the solution was heated to 100°C, and degassed for 1 hour using a vacuum pump, then heated to 120°C and degassed for 1 hour using a vacuum pump. 2.4 mL of oleic acid and 1.2 mL of oleylamine were added to the flask, and further degassed for 30 minutes using a vacuum pump. After that, the solution temperature was reduced to 90°C instead of nitrogen flow, yielding precursor solution 2 of cation B and anion X. 3.2 mL of precursor solution 1 of cation A was added to precursor solution 2 of cation B and anion X, and after 10 seconds, the mixture was cooled on ice to obtain the first reaction solution.

[0070] Step 2: 14 mL of methyl acetate was added to the first reaction solution, and the mixture was kept in a dark place at room temperature (25°C) for 10 days to obtain the second reaction solution. Hereafter, one day will be defined as 24 hours. Step 3: The supernatant was removed by centrifugation. The resulting residue was dispersed in toluene to obtain a dispersion of CsPbBr3 perovskite-type nanocrystalline plates. The perovskite-type nanocrystalline plate dispersion was coated onto a glass substrate and dried to obtain a laminated structure of perovskite-type nanocrystalline plates.

[0071] (Example 2) A laminated structure was obtained in the same manner as in Example 1, except that in the second step, instead of holding the material in a dark environment at room temperature of 25°C for 10 days, it was held in a dark environment at room temperature of 25°C for 5 days.

[0072] (Example 3) A laminated structure was obtained in the same manner as in Example 1, except that in the second step, instead of holding the material in a dark environment at room temperature of 25°C for 10 days, it was held in a dark environment at room temperature of 25°C for 1 day.

[0073] (Example 4) A laminated structure was obtained in the same manner as in Example 1, except that in the second step, instead of holding the material in a dark environment at room temperature of 25°C for 10 days, it was held in a dark environment at 40°C for 1 day.

[0074] (Example 5) A laminated structure was obtained in the same manner as in Example 1, except that in the second step, instead of holding the material in a dark environment at room temperature of 25°C for 10 days, it was held at 50°C in a dark environment for 2 hours.

[0075] (Example 6) A laminated structure was obtained in the same manner as in Example 1, except that 2.4 mL of oleic acid and 1.6 mL of oleylamine were used instead of 2.4 mL of oleic acid and 1.2 mL of oleylamine in the first step.

[0076] (Example 7) A laminated structure was obtained in the same manner as in Example 1, except that 2.4 mL of oleic acid and 0.8 mL of oleylamine were used instead of 2.4 mL of oleic acid and 1.2 mL of oleylamine in the first step.

[0077] (Example 8) A laminated structure was obtained in the same manner as in Example 1, except that 0.350 g of lead(II) iodide was used instead of 0.276 g of lead(II) bromide in the first step.

[0078] (Example 9) A laminated structure was obtained in the same manner as in Example 1, except that in the first step, 0.350 g of lead(II) iodide was used instead of 0.276 g of lead(II) bromide, and in the second step, instead of holding in a dark environment at room temperature of 25°C for 10 days, the structure was held in a dark environment at 40°C for 1 day.

[0079] (Example 10) A laminated structure was obtained in the same manner as in Example 1, except that in the second step, instead of holding the material in a dark environment at room temperature of 25°C for 10 days, it was held at 40°C in a dark environment for 3 days.

[0080] (Comparative Example 1) A laminated structure was obtained in the same manner as in Example 1, except that in the second step, instead of holding the material in a dark environment at room temperature of 25°C for 10 days, it was held for 2 hours in a dark environment at room temperature of 25°C.

[0081] (Comparative Example 2) A laminated structure was obtained in the same manner as in Example 1, except that in the second step, instead of holding the material in a dark environment at room temperature of 25°C for 10 days, it was held at 0°C in a dark environment for 5 days.

[0082] (Comparative Example 3) A laminated structure was obtained in the same manner as in Example 1, except that 2.4 mL of oleic acid and 2.4 mL of oleylamine were used instead of 2.4 mL of oleic acid and 1.2 mL of oleylamine in the first step.

[0083] (Comparative Example 4) A laminated structure was obtained in the same manner as in Example 1, except that the second step was omitted and the third step was carried out immediately on the first reaction solution.

[0084] (Comparative Example 5) A laminated structure was obtained in the same manner as in Example 1, except that in the first step, 0.350 g of lead(II) iodide was used instead of 0.276 g of lead(II) bromide, and in the second step, instead of holding in a dark environment at room temperature of 25°C for 10 days, it was held in a dark environment at 25°C for 2 hours.

[0085] <Evaluation of Perovskite Nanocrystalline Plates> The following evaluations were performed on the resulting perovskite-type nanocrystalline plate layered structures. The evaluations were conducted on samples prepared by coating a dispersion of the perovskite-type nanocrystalline plate onto a glass substrate and drying it.

[0086] An example of XRD results is shown in Figure 1. Structural parameters were calculated from the measured XRD using the analysis method described in the aforementioned non-patent literature (EEFullerton, et al., Phys. Rev. B 45, pp. 9292-9310, 1992). The number of nanocrystalline plates stacked n, the dispersion σn of stacked n, the spacing D of the nanocrystalline plates, the dispersion σD of the spacing D, and the presence or absence of superlattice peaks were evaluated. The presence or absence of superlattice peaks was determined by whether one or more superlattice peaks existed within ±5 degrees of the main diffraction peak. Here, for the first and second main diffraction peaks, Ip / I0 was calculated from the main diffraction peak intensity I0 and the superlattice peak intensity Ip, respectively. Note that "Reference) CsPbBr3 quantum dots" are the XRD results for particles with a roughly cubic shape, approximately 10-20 nm on each side.

[0087] An example of TEM results is shown in Figure 2. The aspect ratio (length of the major axis / length of the minor axis) of the two axes intersecting the thickness direction was evaluated from TEM images obtained by incidenting an electron beam from the same direction as the thickness direction of the nanocrystalline plate. Table 1 shows the results for the number of nanocrystalline plate layers n, the dispersion σn of the number of layers n, the presence or absence of superlattice peaks, Ip / I0, and aspect ratio. If one or more superlattice peaks are present within ±5 degrees of the main diffraction peak of the X-ray diffraction pattern, the superlattice peaks are indicated as "Present" in Table 1; otherwise, they are indicated as "Absent".

[0088] [Evaluation of Luminescence Characteristics] The emission peak wavelength, full width at half maximum (FWHM), and absolute emission quantum yield (PLQY) were measured. An example of the emission spectrum results is shown in Figure 3. The emission peak wavelength and full width at half maximum are values ​​of the emission spectrum used to calculate PLQY, where PLQY is the number of photons of fluorescence emission when the number of excited photons absorbed by the luminescent nanocrystal is set to 1. The measurement conditions and evaluation criteria are shown below.

[0089] <Measurement conditions> Measurement device: Absolute PL quantum yield analyzer C9920-03 (manufactured by Hamamatsu Photonics) Excitation light wavelength: 400nm Excitation light integration range: Excitation light wavelength ±10 nm Emission integration range: (excitation light wavelength + 20) nm to 770 nm

[0090] <Evaluation Criteria> PLQY was evaluated according to the following criteria. A: PLQY is 75% or higher B: PLQY is between 60% and 75% The rate of change of C:PLQY is less than 60.

[0091] [Table 1]

[0092] According to Table 1, a synthesis method comprising all three steps—the first, second, and third steps—can provide a perovskite nanocrystalline composition having the form of a nanocrystalline plate with a small dispersion σ of layer thickness and exhibiting blue or red luminescence, as well as a method for producing the same.

[0093] This embodiment includes the following configurations and methods. (Composition 1) A photoresponsive nanocrystal comprising a nanocrystalline plate having a composite layer structure in which a first layer containing cation A and a second layer containing cation B and anion X are alternately stacked, and having ligands present in which at least a portion of cation A is substituted, The aspect ratio, which is a rectangular shape feature in the direction intersecting the stacking direction of the composite layer structure, is between 0.2 and 5. A photoresponsive nanocrystal having a superlattice structure, in which superlattice peaks exist within a diffraction angle range of ±5 degrees surrounding the main diffraction peak of the X-ray diffraction profile, as determined by the 2θ method. (Configuration 2) When, of the two axes intersecting the thickness direction of the nanocrystalline plate, the axis in the longitudinal direction is defined as the major axis and the axis in the transverse direction is defined as the minor axis, The average length of the aforementioned short axis is between 6 nm and 20 nm. The average length of the major axis is between 10 nm and 45 nm. The photoresponsive nanocrystal according to configuration 1, wherein the average value of the length of the short axis is less than or equal to the average value of the length of the long axis. (Composition 3) The rectangular shape feature corresponds to two directions defining the plate size of the nanocrystal plate, as described in configuration 1 or 2, for the photoresponsive nanocrystal. (Composition 4) The ligand is a photoresponsive nanocrystal according to any one of configurations 1 to 3, which coordinates to the cation B. (Composition 5) The photoresponsive nanocrystal according to any one of configurations 1 to 4, wherein the dispersion σn of the number of stacked nanocrystal plates is 0.1 or more and 0.8 or less. (Composition 6) The photoresponsive nanocrystal according to any one of configurations 1 to 5, wherein the number of layers n of the nanocrystal plates is 3 or more and 5 or less. (Composition 7) The photoresponsive nanocrystal according to any one of configurations 1 to 6, wherein the peak intensity of the main diffraction peak (the peak with the greater peak intensity among the peak around 15.1 degrees and the peak around 30.4 degrees) of the X-ray diffraction pattern of the photoresponsive nanocrystal is defined as I0, and the peak intensity of one or more superlattice peaks located within ±5 degrees of the main diffraction peak is defined as Ip, and Ip / I0 is 0.1 or greater. (Composition 8) The aforementioned cation A is an ammonium cation (NH4 + ), alkylammonium cations with 6 or fewer carbon atoms, formamidinium cation (HC(NH2)2 + ), guanidinium cation (C(NH2)3 + ), imidazolium cation, pyridinium cation, pyrrolidinium cation, lithium cation (Li + ), sodium cation (Na + ), potassium cation (K + ), rubidium cation (Rb + ), and cesium cation (Cs + A photoresponsive nanocrystal according to any one of configurations 1 to 7, comprising one or more selected from the group consisting of ). (Composition 9) The photoresponsive nanocrystal according to any one of configurations 1 to 8, wherein the cation B comprises a divalent transition metal cation or a divalent typical metal cation. (Composition 10) The aforementioned divalent transition metal cation is a scandium cation (Sc 2+ ), titanium cation (Ti 2 +), vanadium cation (V 2+ ), chromium cation (Cr 2+ ), manganese cation (Mn 2+ ), iron cation (Fe 2+ ), cobalt cation (Co 2+ ), nickel cation (Ni 2+ ), copper cation (Cu 2+ ), palladium cation (Pd 2+ ), Europium cation (Eu 2+ ), and ytterbium cation (Yb 2+ A photoresponsive nanocrystal according to configuration 9, comprising one or more selected from the group consisting of ). (Composition 11) The aforementioned divalent typical metal cation is magnesium cation (Mg 2+ ), calcium cation (Ca 2+ ), strontium cation (Sr 2+ ), barium cation (Ba 2+ ), zinc cation (Zn 2+ ), cadmium cation (Cd 2+ ), germanium cation (Ge 2+ ), tin cation (Sn 2+ ), and lead cations (Pb 2+ A photoresponsive nanocrystal according to configuration 9 or 10, comprising one or more selected from the group consisting of ). (Composition 12) The anion X is a photoresponsive nanocrystal according to any one of configurations 1 to 11, comprising a monovalent anion including a halide anion. (Method 1) A method for producing a photoresponsive nanocrystal having a composite layer structure in which a first layer containing a ligand and cation A and a second layer containing cation B and anion X are alternately stacked, A first step involves reacting a first precursor solution containing cation A and a first organic acid with a second precursor solution containing cation B, anion X, a second organic acid, and a first organic base, under predetermined conditions: the molar ratio obtained by dividing the sum of the amounts of the first organic acid and the second organic acid by the amount of the first organic base is a predetermined value, and at a predetermined reaction temperature, to produce a first reaction solution containing nanocrystalline particles. The second step involves maintaining the first reaction solution at a predetermined growth temperature range which is lower than the reaction temperature and for a predetermined growth time, and growing crystals in a predetermined axial direction using the nanocrystalline particles as nuclei to produce a second reaction solution. A method for producing photoresponsive nanocrystals, including [the specified element]. (Method 2) A method for producing photoresponsive nanocrystals according to Method 1, wherein the second step is performed such that at least one selected from the group consisting of the vibrational energy to the first reaction solution, the flow rate of the first reaction solution, and the illuminance to the first reaction solution is lower than that of the reaction step. (Method 3) The method for producing photoresponsive nanocrystals according to Method 1 or 2, further comprising the step of growing crystals in two axial directions to produce a nanocrystal plate. (Method 4) A method for producing photoresponsive nanocrystals according to any one of methods 1 to 3, wherein the second step includes stacking nanocrystal plates in the plate thickness direction of the nanocrystal plates. (Method 5) A method for producing photoresponsive nanocrystals according to any one of methods 1 to 4, comprising a third step of adding a poor solvent to the second reaction solution to separate the nanocrystal plate from the solvent. (Method 6) The method for producing photoresponsive nanocrystals according to Method 5, wherein the third step includes applying an external force to a liquid containing the poor solvent. (Method 7) The photoresponsive nanocrystal has an aspect ratio, which is a rectangular shape feature in a direction intersecting the stacking direction of the composite layer structure, that is between 0.2 and 5. The method for producing a photoresponsive nanocrystal according to any one of methods 1 to 6, wherein the photoresponsive nanocrystal has a superlattice structure in which superlattice peaks exist in a diffraction angle range of ±5 degrees surrounding the principal diffraction peak of the X-ray diffraction profile by the 2θ method.

Claims

1. A photoresponsive nanocrystal comprising a nanocrystalline plate having a composite layer structure in which a first layer containing cation A and a second layer containing cation B and anion X are alternately stacked, and having ligands present in which at least a portion of cation A is substituted, The aspect ratio, which is a rectangular shape feature in the direction intersecting the stacking direction of the composite layer structure, is between 0.2 and 5. A photoresponsive nanocrystal having a superlattice structure, in which superlattice peaks exist within a diffraction angle range of ±5 degrees surrounding the main diffraction peak of the X-ray diffraction profile, as determined by the 2θ method.

2. When, of the two axes intersecting the thickness direction of the nanocrystalline plate, the axis in the longitudinal direction is defined as the major axis and the axis in the transverse direction is defined as the minor axis, The average length of the short axis is between 6 nm and 20 nm. The average length of the major axis is between 10 nm and 45 nm. The photoresponsive nanocrystal according to claim 1, wherein the average value of the length of the short axis is less than or equal to the average value of the length of the long axis.

3. The photoresponsive nanocrystal according to claim 1 or 2, wherein the rectangular shape feature corresponds to two directions that define the plate size of the nanocrystal plate.

4. The ligand coordinates to the cation B, the photoresponsive nanocrystal according to claim 1 or 2.

5. The photoresponsive nanocrystal according to claim 1 or 2, wherein the dispersion σn of the number of stacked nanocrystal plates is 0.1 or more and 0.8 or less.

6. The photoresponsive nanocrystal according to claim 1 or 2, wherein the number of stacked nanocrystal plates n is 3 or more and 5 or less.

7. The photoresponsive nanocrystal according to claim 1 or 2, wherein when the peak intensity of the main diffraction peak of the X-ray diffraction pattern of the photoresponsive nanocrystal (the peak with the greater peak intensity among the peak around 15.1 degrees and the peak around 30.4 degrees) is I0, and the peak intensity of one or more superlattice peaks located within ±5 degrees of the main diffraction peak is Ip, then Ip / I0 is 0.1 or greater.

8. The cation A is an ammonium cation (NH ４ ＋ ), an alkylammonium cation having 6 or fewer carbon atoms, a formamidinium cation (HC(NH ２ ), ２ ＋ ), a guanidinium cation (C(NH ２ ), ３ ＋ ), an imidazolium cation, a pyridinium cation, a pyrrolidinium cation, a lithium cation (Li ＋ ), a sodium cation (Na ＋ ), a potassium cation (K ＋ ), a rubidium cation (Rb ＋ ), and a cesium cation (Cs ＋ ), and includes one or more selected from the group consisting of, the photoreactive nanocrystal according to claim 1 or 2.

9. The photoresponsive nanocrystal according to claim 1 or 2, wherein the cation B comprises a divalent transition metal cation or a divalent typical metal cation.

10. The aforementioned divalent transition metal cation is a scandium cation (Sc ２＋ ), titanium cation (Ti ２ +), vanadium cation (V ２＋ ), chromium cation (Cr ２＋ ), manganese cation (Mn ２＋ ), iron cation (Fe ２＋ ), cobalt cation (Co ２＋ ), nickel cation (Ni ２＋ ), copper cation (Cu ２＋ ), palladium cation (Pd ２＋ ), Europium cation (Eu ２＋ ), and ytterbium cation (Yb ２＋ The photoresponsive nanocrystal according to claim 9, comprising one or more selected from the group consisting of ).

11. The aforementioned divalent typical metal cation is a magnesium cation (Mg ２＋ ), calcium cation (Ca ２＋ ), strontium cation (Sr ２＋ ), barium cation (Ba ２＋ ), zinc cation (Zn ２＋ ), cadmium cation (Cd ２＋ ), germanium cation (Ge ２＋ ), tin cation (Sn ２＋ ), and lead cations (Pb ２＋ The photoresponsive nanocrystal according to claim 9, comprising one or more selected from the group consisting of ).

12. The photoresponsive nanocrystal according to claim 1 or 2, wherein the anion X includes a monovalent anion including a halide anion.

13. A method for producing a photoresponsive nanocrystal having a composite layer structure in which a first layer containing a ligand and cation A and a second layer containing cation B and anion X are alternately stacked, A first step involves reacting a first precursor solution containing cation A and a first organic acid with a second precursor solution containing cation B, anion X, a second organic acid, and a first organic base, under a predetermined molar ratio obtained by dividing the sum of the amounts of the first organic acid and the second organic acid by the amount of the first organic base, and at a predetermined reaction temperature, to produce a first reaction solution containing nanocrystalline particles. The second step involves maintaining the first reaction solution at a predetermined growth temperature range which is lower than the reaction temperature and for a predetermined growth time, and growing crystals in a predetermined axial direction using the nanocrystalline particles as nuclei to produce a second reaction solution. A method for producing photoresponsive nanocrystals, including [the specified element].

14. The method for producing a photoresponsive nanocrystal according to claim 13, wherein the second step is performed such that at least one selected from the group consisting of vibrational energy to the reaction solution, flow rate of the reaction solution, and illuminance to the reaction solution is lower than that of the first step.

15. The method for producing a photoresponsive nanocrystal according to claim 13, wherein the second step includes a step of growing crystals in two axial directions to produce a nanocrystal plate.

16. The method for producing a photoresponsive nanocrystal according to claim 13, wherein the second step includes stacking nanocrystal plates in the plate thickness direction of the nanocrystal plates.

17. A method for producing photoresponsive nanocrystals according to claim 13, comprising a third step of adding a poor solvent to the second reaction solution to separate the nanocrystal plate from the solvent.

18. The method for producing photoresponsive nanocrystals according to claim 17, wherein the third step includes applying an external force to a liquid containing the poor solvent.

19. The photoresponsive nanocrystal has an aspect ratio, which is a rectangular shape feature in a direction intersecting the stacking direction of the composite layer structure, that is between 0.2 and 5. The method for producing a photoresponsive nanocrystal according to claim 13, wherein the photoresponsive nanocrystal has a superlattice structure in which superlattice peaks exist in a diffraction angle range of ±5 degrees that straddles the principal diffraction peak of the X-ray diffraction profile, as determined by the 2θ method.

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