Composite film, quantum dot-containing electroluminescent element, quantum dot-containing wavelength conversion sheet, and quantum dot-containing wavelength conversion layer

Abstract

The purpose of the present invention is to provide a composite film having a high coverage of a nanocrystalline plate and a high amount of light absorption per unit thickness. A composite film (10) including a nanocrystalline plate (11) having a composite layer structure in which a first layer containing a cation A to which ligands coordinate and a second layer containing a cation B and an anion X are alternately stacked, wherein the aspect ratio (L / S or S / L) that is a rectangular shape feature amount in a direction intersecting the stacking direction of the composite layer structure is 0.2-5, when the thickness of the nanocrystalline plate is denoted by t and the length of the short axis intersecting the stacking direction of the nanocrystalline plate is denoted by S, t and S satisfies S / t ≥ 3, and a variance σn of the number of stacked layers in the nanocrystalline plate is 0.7 or less.

Description

Composite film, quantum dot-containing electroluminescence device, quantum dot-containing wavelength conversion sheet, and quantum dot-containing wavelength conversion layer

[0001] The present disclosure relates to a composite film, a quantum dot-containing electroluminescence device, a quantum dot-containing wavelength conversion sheet, and a quantum dot-containing wavelength conversion layer.

[0002] Nanocrystals having a perovskite crystal structure have a narrow full width at half maximum in spectral sensitivity characteristics and exhibit high color purity, so they are known to be applicable to luminescent materials such as photoluminescence (PL) type and electroluminescence (EL) type, and light receiving materials such as solar cells and optical sensors.

[0003] Further, since the absorption and emission wavelengths can be controlled by 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 the nanocrystal having a perovskite 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.

[0004] In PL applications and optical sensor applications, a perovskite layer as a high-density wavelength conversion layer or light absorption layer that can absorb light with a film thickness as thin as possible without leakage is required. In EL applications and solar cell applications, a dense perovskite layer is required to suppress the charge leakage path and improve the carrier recombination probability.

[0005] Nanocrystals having a perovskite crystal structure are known to take various forms such as nanoparticles and nanoplatelets depending on the synthesis conditions. Non-Patent Document 1 arranges using nanoparticles. Non-Patent Document 2 forms an aggregate using nanoplates.

[0006] Y. Kim, et al., Nature Nanotechnology, vol. 17, no. 6, p.590-597 (2022) H. Liu, et al., Adv. Energy Mater., p.2201605 (2022)

[0007] As mentioned above, there is a need for a high-density wavelength conversion layer or perovskite layer that can absorb light without leakage and with the thinnest possible film thickness. When using nanoparticles, it is difficult to achieve close packing of particles, making it difficult to obtain a dense film with few voids between crystals.

[0008] On the other hand, when using nanoplates, if the aspect ratio (long axis / short axis) of the two axes intersecting the thickness direction of the nanoplate layer was large, self-assembled aggregates were formed or the nanoplates were aligned vertically, preventing the formation of a dense film.

[0009] This disclosure addresses the above issues and describes a dense ABX with few intercrystalline voids. ３ The objective is to provide a composite film with high coverage of the nanocrystalline plate and high light absorption per unit thickness by fabricating a perovskite layer.

[0010] To solve the above problems, the present disclosure provides a composite film comprising a nanocrystalline plate having a composite layer structure in which a first layer containing a ligand-coordinated cation A and a second layer containing a cation B and anion X are alternately stacked, 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 when the thickness of the nanocrystalline plate is t and the length of the short axis intersecting the stacking direction of the nanocrystalline plate is S, then t and S satisfy S / t ≥ 3, and the dispersion σn of the number of stacked nanocrystalline plates is 0.7 or less. The present disclosure also provides a quantum dot-containing electroluminescent element comprising the above composite film. The present disclosure also provides a quantum dot-containing wavelength conversion sheet comprising the above composite film. The present disclosure also provides a quantum dot-containing wavelength conversion layer comprising the above composite film.

[0011] According to this disclosure, dense ABX with few intercrystalline voids ３ By providing a perovskite layer, it is possible to suppress charge leakage paths and improve carrier recombination probability in EL and solar cell applications.

[0012] This figure shows a composite film comprising multiple nanocrystalline plates (L / S ≤ 5) according to the present disclosure. This figure shows an image projected from the layer thickness direction D of the composite film in Figure 1A onto a plane in the layer thickness direction. This figure shows a composite film comprising multiple nanocrystalline plates (L / S > 5). This figure shows a composite film using nanoparticles.

[0013] 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.

[0014] <One Embodiment> One embodiment relates to a composite film. The composite film of the present disclosure is a composite film having a nanocrystalline plate having a composite layer structure in which a first layer containing a ligand-coordinated cation A and a second layer containing a cation B and anion X are alternately stacked, 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 when the thickness of the nanocrystalline plate is t and the length of the short axis intersecting the stacking direction of the nanocrystalline plate is S, then t and S satisfy S / t ≥ 3, and the variance σn of the number of stacked nanocrystalline plates is 0.7 or less.

[0015] (Structure of the nanocrystalline plate) The composite film of the present disclosure is a composite film having a nanocrystalline plate having a composite layer structure in which a first layer containing cation A to which a ligand is coordinated and a second layer containing cation B and anion X are alternately stacked.

[0016] The bulk perovskite crystal structure is given by formula ABX ３ It can be described as (A is a cation, B is a metal, X is a halogen). In the case of a perovskite-type nanocrystalline plate whose dimensions are limited to one direction, L ２ [ABX ３ ] ｎ－１ BX ４ It can be described as follows: (L: ligand, n: number of metal halide octahedron layers).

[0017] Here, the n-1 term represents the thickness of the nanocrystalline plate converted to bulk unit cells, and n=2 represents a complete ABX ３Corresponding to the perovskite unit cell, when n = 1, the cation species (A) is not included in the structure. In the nanocrystal plates of the present disclosure, it is preferable that the ligand coordinates to the cation B.

[0018] Thus, the notation of the crystal structure of the nanocrystal plate is not strictly ABX ３ However, the crystal structure of the nanocrystal plate here means ABX of the perovskite-type crystal structure ３ and is represented as such, and is also referred to as a perovskite-type nanocrystal plate. Hereinafter, the number of stacked layers represents n. Also, the layer thickness direction means the stacking direction of the layers.

[0019] In the composite film of the present disclosure, it is preferable that the rectangular shape feature amount (aspect ratio) corresponds to the two directions defining the plate size of the nanocrystal plate. Here, for the two axes intersecting the layer thickness direction of the nanocrystal plate, the longer one is the long axis and the shorter one is the short axis, and the aspect ratio = the average value of the length of the long axis / the average value of the length of the short axis, or the aspect ratio = the average value of the length of the short axis / the average value of the length of the long axis.

[0020] In the composite film of the present disclosure, the aspect ratio, which is the rectangular shape feature amount in the direction intersecting the stacking direction of the composite layer structure, is 0.2 or more and 5 or less, and preferably 0.2 or more and 3.6 or less. In Table 1 described later, the LS aspect ratio = the average value of the length of the long axis / the average value of the length of the short axis (= L / S).

[0021] When the axis in the longitudinal direction is the long axis and the axis in the short transverse direction is the short axis among the two axes intersecting the layer thickness direction of the nanocrystal plate, the average value of the length of the short axis (S in Table 1) is preferably 5 nm or more and 50 nm or less, more preferably 5 or more and 20 or less, still more preferably 6 or more and 20 or less, and particularly preferably 7 or more and 18 or less.

[0022] When the longitudinal axis and the transverse axis are defined as the major axis and the transverse axis, respectively, of the two axes intersecting the thickness direction of the nanocrystalline plate, the average length of the major axis (L in Table 1) is preferably 10 nm or more and 50 nm or less, more preferably 15 or more and 30 nm or less, even more preferably 15 or more and 27 nm or less, and particularly preferably 18 or more and 25 nm or less. Furthermore, the average length of the transverse axis is preferably less than or equal to the average length of the major axis.

[0023] [Perovskite-type structure A site (cation A)] The A site employs a monovalent cation. The monovalent cation (cation A) employed at the A site is an ammonium cation (NH ４ ＋ ), and alkylammonium cations having 6 or fewer carbon atoms, formamidinium cations (HC(NH ２ ) ２ ＋ ), guanidinium cation (C(NH ２ ) ３ ＋ Examples include nitrogen-containing organic compound cations such as imidazolium cation, pyridinium cation, and pyrrolidinium cation, and lithium cation (Li ＋ ), sodium cation (Na ＋ ), potassium cation (K ＋ ), rubidium cation (Rb ＋ ), and cesium cations (Cs ＋ Examples include alkali metal cations such as ).

[0024] The composite film disclosed herein comprises cation A and ammonium cation (NH ４ ＋ ), alkylammonium cations with 6 or fewer carbon atoms, formamidinium cations (HC(NH ２ ) ２ ＋ ), guanidinium cation (C(NH ２ ) ３ ＋ ), imidazolium cation, pyridinium cation, pyrrolidinium cation, lithium cation (Li ＋ ), sodium cation (Na ＋), potassium cation (K ＋ ), rubidium cation (Rb ＋ ), and cesium cations (Cs ＋ It is preferable to include one or more selected from the group consisting of ).

[0025] Because the monovalent cations employed at these A-sites have small ionic diameters and are small enough to fit within the crystal lattice, the perovskite compound can form a stable three-dimensional crystal.

[0026] A preferred example of an alkylammonium cation having 6 or fewer carbon atoms is the methylammonium cation (CH4). ３ NH ３ ＋ ), ethylammonium cation (C ２ H ５ NH ３ ＋ ), propylammonium cation (C ３ H ７ NH ３ ＋ Examples include:

[0027] 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.

[0028] When the A site 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.

[0029] 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.

[0030] 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.

[0031] [Perovskite crystal structure B site (cation B)] The composite film of the present disclosure preferably contains a divalent transition metal cation or a divalent typical metal cation at the B site (cation B) of the perovskite crystal structure.

[0032] The composite film disclosed herein contains 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＋ It is preferable to include one or more selected from the group consisting of ).

[0033] The composite film of this disclosure comprises a divalent typical metal cation and 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 (Pb２＋ It is preferable to include one or more selected from the group consisting of ).

[0034] 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.

[0035] When the B site is a lead cation, lead compounds can be used as raw materials for nanoparticle synthesis, and an appropriate one 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.

[0036] If the B site is another divalent metal cation, salts obtained by replacing the lead element of the above-mentioned lead compound with another divalent metal cation element can be used as raw materials. Two or more of these raw materials may be used in combination.

[0037] [X site (anion X) of the perovskite crystal structure] The composite film of the present disclosure preferably contains a monovalent anion, including a halide anion, at site X (anion X) of the perovskite crystal structure. As the halide anion, a fluoride anion (F － ), chloride anion (Cl － ), bromide anion (Br － ), iodide anion (I － Examples include:

[0038] 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. The luminescence color is blue when chloride anions are used, green when bromide anions are used, and red when iodide anions are used.

[0039] 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.

[0040] In other words, when chloride anions, bromide anions, and iodide anions are used in combination, it is preferable because, depending on the content ratio of the anion species, an emission spectrum covering almost the entire visible light range from blue to red can be obtained while maintaining a narrow full width at half maximum.

[0041] The X site (anion X) may contain monovalent anions other than halide anions. Such monovalent anions other than halide anions include cyanide anions (CN － ), thiocyanate anion (SCN － ), isothiocyanate anion (CNS － Examples include pseudohalide anions such as ).

[0042] As raw materials for nanoparticle synthesis, appropriate materials can be selected depending on the synthesis method from salts with A-site and B-site cations, such as cesium chloride and lead bromide, or salts with other cations.

[0043] [Ligand] In this disclosure, the ligand is preferably selected from at least one compound or ion selected from the group consisting of weak acids such as carboxylic acids, weak bases such as amines, and salts or ions thereof.

[0044] 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.

[0045] 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.

[0046] (Method for manufacturing perovskite nanocrystalline plates) Generally, perovskite nanocrystalline plates can be manufactured by hot injection or ligand-assisted reprecipitation (LARP). When manufacturing nanocrystalline plates by hot injection, the number of nanoplate layers is adjusted during synthesis by controlling the reaction temperature, precursor ratio, ligand concentration, ligand acid-base equilibrium, ligand chain length, etc.

[0047] The number of layers of nanocrystalline plates decreases as the reaction temperature is lowered. Nanocrystalline plates are produced at reaction temperatures below approximately 130°C, and their thickness can be adjusted from a single layer to several layers by controlling the temperature. The number of layers can also be adjusted by changing the precursor ratio in the reaction solution.

[0048] (Evaluation of the number of stacked nanocrystalline plates) The structural parameters of nanocrystalline plates can be evaluated using X-ray diffraction (XRD). Nanocrystalline plates form a self-stacked aggregate (superlattice) via ligands. The periodicity of this superlattice is expressed as a structural parameter, ABX ３ It can be described by the interplanar spacing d, 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.

[0049] The spacing D between nanocrystalline plates is substantially determined by the ligands on the surface of the nanocrystalline plates. CsPbBr ３ The first and second main diffraction peaks are 15.1 degrees and 30.4 degrees, respectively, and CsPbI ３ The first and second principal diffraction peaks are 13.8 degrees and 27.2 degrees, respectively.

[0050] Here, the scattering vector coefficient is (q = 4π sin(θ) / λ ＸｒａｙIf we assume that, then the first main diffraction peak is (q ≈ 0.9–1.1 Å). －１ ), and the second main diffraction peak (q ≈ 1.8–2.2 Å) －１ By analyzing the superlattice peaks of the material, structural parameters can be calculated, for example, by the analysis method described in Non-Patent Literature (E.E. Fullerton, et al., Phys. Rev. B 45, pp. 9292-9310, 1992).

[0051] Furthermore, nanocrystalline plates can be evaluated by transmission electron microscopy (TEM) observation. By irradiating the nanocrystalline plate with an electron beam from the same direction as the thickness direction and performing TEM observation, the aspect ratio (L / S or S / L) of the two axes intersecting the thickness direction can be evaluated.

[0052] Furthermore, by aligning the electron beam incidence direction with a direction perpendicular to the thickness direction of the nanocrystalline plate, and measuring and analyzing TEM observations and electron diffraction patterns, ABX can be achieved. ３ It is possible to evaluate the interplanar spacing d, the number of stacked nanocrystalline plates n, the dispersion σn of the number of stacked plates n, the spacing D of the nanocrystalline plates, the dispersion σD of the spacing D, the thickness t of the nanocrystalline plate (described later), and the number of layers N.

[0053] Furthermore, it is possible to calculate similar structural parameters from aggregate data obtained by evaluating each individual nanocrystal plate, rather than the entire assembly. Using TEM evaluation, it is also possible to identify, for example, the stacked structure of the perovskite-type nanocrystal plates of this disclosure incorporated within a device.

[0054] (Composite film using perovskite-type nanocrystalline plate) Figure 1A shows a schematic diagram of the composite film of the present disclosure. The perovskite-type nanocrystalline plate, which is the nanocrystalline plate 11 of the present disclosure, has a biaxial aspect ratio (L / S or S / L) of 0.2 or more and 5 or less. Furthermore, by changing the synthesis method described above, it is also possible to make the biaxial aspect ratio 0.3 or more and 3 or 0.5 or more and 2 or less.

[0055] When the L / S ratio becomes small in this way, if the solution containing the nanocrystalline plate 11 is applied to a substrate and left to stand and dry, a composite film 10 is obtained consisting of multiple self-aligned nanocrystalline plates with a thickness T = {t (thickness of each nanocrystalline plate) + 1.1 nm (thickness of the intercrystalline ligand)} × N (number of layers), as shown in Figure 1A.

[0056] On the other hand, when using a nanocrystalline plate 12 with a biaxial aspect ratio less than 0.2 or greater than 5, as shown in Figure 2A, self-assembled aggregates 13 are formed or arranged vertically, resulting in a composite film that is not dense as a whole. Also, as shown in Figure 2B, when using nanoparticles 14, if the thickness T is the same as in Figure 1A, voids exist in the thickness direction of the layer, so it is not possible to increase the coverage rate of the area projected onto a surface in the thickness direction.

[0057] Figure 1B shows an image projected from the thickness direction D of the composite film onto a plane in the thickness direction. The composite film of this disclosure has a crystalline portion 15 containing structural units of the nanocrystalline plate 11 and a void portion 16 that does not contain structural units of the nanocrystalline plate 11. When the coverage rate of the nanocrystalline plate is defined as {1 - (area of ​​the void portion) / (area of ​​the crystalline portion)} × 100 (%) for an image obtained by observing the surface of the composite film with a transmission electron microscope, the coverage rate is preferably 80% or more, more preferably 86% or more, even more preferably 90% or more, and particularly preferably 95% or more.

[0058] If the coverage in the thickness direction of the layer is insufficient, these voids become leakage paths for excitation light and charge. For PL applications and photosensor applications, it is possible to provide a high-density wavelength conversion layer or a highly covering perovskite crystal film that can absorb light without leakage with the thinnest possible film thickness.

[0059] For electroluminescent (EL) and solar cell applications, a dense perovskite crystal film can be provided to suppress charge leakage paths and improve carrier recombination probability. Here, the term "void" refers to a region where no nanocrystalline plate exists, and in reality, ligands or a medium may be filled in that region.

[0060] Furthermore, the following conditions are necessary to induce self-alignment. In the composite film of the present disclosure, when the thickness of the nanocrystalline plate is t and the length of the short axis intersecting the stacking direction of the nanocrystalline plate is S, it is preferable that t and S satisfy the relationship S / t ≥ 3, 3 ≤ S / t ≤ 6, and more preferably 3.8 ≤ S / t ≤ 5.6. This is because if S / t is not large enough, there will be no difference between the thickness t of the nanocrystalline plate and the short axis S, and an aggregate like the one shown in Figure 2A will be formed.

[0061] Furthermore, the composite film of this disclosure preferably has a number of stacked nanocrystalline plates of 3 to 5, and more preferably 3. In this case, both the stability and density of the composite film can be achieved. When the number of stacked plates is 1 to 2, the proportion of the ligand thickness relative to the nanocrystalline plate 11 becomes large, making it difficult to improve density. When the number of stacked plates is 6 or more, the number of stacked plates becomes uniform, making it difficult to reduce the dispersion σn of the number of stacked plates, but this does not exclude the case where the number of stacked plates is 6 or more.

[0062] Furthermore, the composite film of this disclosure has a dispersion σn of the number of stacked nanocrystalline plates of 0.7 or less, preferably 0.1 or more, more preferably 0.1 to 0.7, even more preferably 0.2 to 0.7, and particularly preferably 0.24 to 0.7. This can improve density. This is because variations in the number of stacked plates inhibit self-alignment and lead to the formation of voids.

[0063] Furthermore, the composite film of this disclosure preferably has a short-axis length S of 5 nm or more and 50 nm or less, more preferably 5 nm or more and 25 nm or less, and even more preferably 7 nm or more and 22 nm or less. By doing so, the density can be improved. This is because the difference between the thickness t of the nanocrystalline plate and the short-axis length S becomes easier to achieve.

[0064] As described above, the composite film of this disclosure provides a composite film in which the coverage of the area projected onto a certain surface in the thickness direction of the nanocrystalline plate is 80% or more. The coverage depends on t and N. When t is the same as n and σn, when n=3, the coverage is approximately 80% when N=1, approximately 90% when N=2, and when N≧3, the coverage is 95% or more.

[0065] <Application Examples> The composite film comprising multiple nanocrystalline plates of this disclosure can be applied to quantum dot-containing wavelength conversion sheets (QD sheets), quantum dot-containing wavelength conversion layers (QD-CCs), and quantum dot-containing electroluminescent (QD-EL) elements.

[0066] [Quantum Dot-Containing Electroluminescent (QD-EL) Devices] The quantum dot-containing electroluminescent devices of the present disclosure include the composite films of the present disclosure. The QD-EL devices of the present disclosure include, for example, electrodes (cathode and anode), an electron injection / transport layer, an emissive layer, and a hole injection / transport layer. A surface treatment layer may be provided on any surface of the emissive layer.

[0067] (Electrodes) The electrode material is not particularly limited, and materials used in organic electroluminescent (EL) elements, for example, can be suitably used. Examples include transparent conductive oxides such as indium tin oxide (ITO), metals such as Al, alloys of Ag, Pd and Cu (APC electrodes), alloys of Mg and Ag, and laminates in which a metal layer and a transparent conductive oxide layer such as ITO are laminated (laminated electrodes). Of the anode and cathode, the electrode on the side from which light is extracted from the light-emitting layer is preferably transparent.

[0068] The thickness of the anode is not particularly limited and may be, for example, 10 nm or more, 30 nm or more, or 50 nm or more, or 1000 nm or less, 500 nm or less, or 200 nm or less. The thickness of the cathode is not particularly limited and may be, for example, 10 nm or more, 30 nm or more, or 50 nm or more, or 1000 nm or less, 500 nm or less, or 200 nm or less.

[0069] (Hole Injection / Transport Layer) Suitable materials for the hole injection / transport layer include those used in organic EL displays. Examples of organic materials include polyvinylcarbazole (PVK), poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)-diphenylamine) (TFB), poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) (PTAA), poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (poly-TPD), and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). Examples of inorganic materials include NiO and TiO. ２ MoO ｘ These are some examples. These can be used individually or in combination of two or more.

[0070] The hole injection / transport layer may be a single-layer or multi-layer structure. In the case of a multi-layer structure, it may include a hole injection layer located on the anode side and a hole transport layer located on the light-emitting layer side.

[0071] In the case of a single-layer structure, the thickness of the hole injection / transport layer is not particularly limited and can be appropriately designed considering the impact on hole injection, transport, and optical properties. For example, the total thickness of the hole injection layer and the hole transport layer may be 10 nm or more, 20 nm or more, or 50 nm or more, and may also be 1000 nm or less, 500 nm or less, or 200 nm or less.

[0072] (Light-emitting layer) A composite film consisting of multiple nanocrystalline plates according to this disclosure can be used as a light-emitting layer.

[0073] The thickness of the light-emitting layer is not particularly limited and may be, for example, 10 nm or more, 50 nm or more, or 75 nm or more, or it may be 1000 nm or less, 500 nm or less, or 250 nm or less.

[0074] (Electron injection / transport layer) Suitable materials for the electron injection / transport layer include those used in organic EL displays. Examples of organic materials include LiF, 1,3,5-tris(1-phenyl-1H-benzimidazole-2-yl)benzene (TPBi), N,N'-di-1-naphthyl-N,N'-diphenylbenzidine (NPD), 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP), and 4,6-bis(3,5-di(pyridine-3-yl)phenyl)-2-methylpyrimidine (B3PyMPM).

[0075] Examples of inorganic materials include a-ZSO (amorphous zinc silicate; Zn-Si-O), ZnO, and SnO. These can be used individually or in combination of two or more.

[0076] The electron injection / transport layer may be a single-layer or multilayer structure. In the case of a multilayer structure, it may include an electron injection layer located on the cathode side and an electron transport layer located on the light-emitting layer side.

[0077] In the case of a single-layer structure, the thickness of the electron injection / transport layer is not particularly limited and can be appropriately designed considering the impact on electron injection, transport, and optical properties. For example, the total thickness of the electron injection layer and the electron transport layer may be 1 nm or more, 5 nm or more, or 10 nm or more, and may also be 1000 nm or less, 500 nm or less, or 200 nm or less.

[0078] The above explanation mainly describes the case where the light-emitting element is a bottom-emission type that extracts light from the anode side (substrate side), but it is not limited to this. For example, the light-emitting element may be a top-emission type that extracts light from the cathode side (opposite substrate side).

[0079] [Quantum Dot-Containing Wavelength Conversion Layer (QD-CC)] The quantum dot-containing wavelength conversion layer of this disclosure includes the composite film of this disclosure. The quantum dot-containing wavelength conversion layer of this disclosure is a component obtained by curing a photoresponsive composition containing a codispersed nanocrystalline plate and a polymerizable compound on a substrate.

[0080] The quantum dot-containing wavelength conversion layer takes the form of a layer supported by other components. Support configurations include a laminated configuration and a dispersed configuration in a matrix material. The quantum dot-containing wavelength conversion layer can be obtained by coating a photoresponsive composition onto a support component (substrate) and curing it to form a film, sheet, or patterned pixels.

[0081] [Quantum Dot-Containing Wavelength Conversion Sheet (QD Sheet)] The quantum dot-containing wavelength conversion sheet of this disclosure includes the composite film of this disclosure. The quantum dot-containing wavelength conversion sheet is formed in sheet form by coating a photoresponsive composition onto a support member (substrate) and curing it.

[0082] The following describes in detail the display elements according to the embodiments of this disclosure, but this disclosure is not limited to the following embodiments.

[0083] (Example 1) <CsPbBr ３ Synthesis of Perovskite Nanocrystalline Plates > 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 liquid temperature was heated to 100°C, and the mixture was degassed for 30 minutes using a vacuum pump. The mixture was then heated to 120°C under a stream of dry nitrogen and held for 20 minutes, and then held at 90°C to obtain cation A precursor solution 1.

[0084] 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, it was heated again to 120°C and degassed for another hour using a vacuum pump. 2.4 mL of oleic acid and 1.2 mL of oleylamine were added to the flask, and degassed for another 30 minutes using a vacuum pump. After that, the solution temperature was reduced to 90°C using a nitrogen flow to obtain precursor solution 2 of cation B and anion X.

[0085] 3.2 mL of cation A precursor solution 1 was added to cation B and anion X precursor solution 2, and after 10 seconds, the mixture was cooled on ice to obtain reaction solution 1.

[0086] Step 2: 14 mL of methyl acetate was added to reaction solution 1, and the mixture was kept in a dark place at room temperature of 25°C for 10 days to obtain reaction solution 2. Hereafter, one day will be defined as 24 hours.

[0087] Step 3: Centrifugation was performed to remove the supernatant. The obtained residue was dispersed in toluene to obtain a dispersion of perovskite nanocrystal plates (nanocrystal plates) of CsPbBr ３ .

[0088] Step 4: A dry nitrogen stream was blown onto the dispersion of the perovskite nanocrystal plates of CsPbBr ３ to remove the solvent, and it was dispersed in a hexane solvent so that the perovskite nanocrystal plates of CsPbBr ３ became 0.1% by mass. 10 μL of this dispersion was applied onto a glass substrate and dried to obtain a composite film of perovskite nanocrystal plates.

[0089] (Example 2) A composite film was prepared in the same manner as in Example 1, except that the perovskite nanocrystal plates of CsPbBr ３ in Step 4 were 0.15 wt% instead of 0.1% by mass.

[0090] (Example 3) A composite film was prepared in the same manner as in Example 1, except that the perovskite nanocrystal plates of CsPbBr ３ in Step 4 were 0.3 wt% instead of 0.1% by mass.

[0091] (Example 4) A composite film was prepared in the same manner as in Example 1, except that the perovskite nanocrystal plates of CsPbBr ３ in Step 4 were 1.0 wt% instead of 0.1% by mass.

[0092] (Example 5) A composite film was prepared in the same manner as in Example 1, except that 2.4 mL of oleic acid and 1.8 mL of oleylamine were used instead of 2.4 mL of oleic acid and 1.2 mL of oleylamine in Step 1.

[0093] (Example 6) A composite film was prepared in the same manner as in Example 1, except that 2.4 mL of oleic acid and 1.8 mL of oleylamine were used instead of 2.4 mL of oleic acid and 1.2 mL of oleylamine in Step 1, and the liquid temperature was 95°C instead of 90°C.

[0094] (Example 7) A composite film was prepared in the same manner as in Example 1, except that 2.4 mL of oleic acid and 1.8 mL of oleylamine were used instead of 2.4 mL of oleic acid and 1.2 mL of oleylamine in Step 1, and the liquid temperature was changed from 90°C to 100°C.

[0095] (Example 8) A composite film was prepared in the same manner as in Example 1, except that 2.4 mL of oleic acid and 1.8 mL of oleylamine were used instead of 2.4 mL of oleic acid and 1.2 mL of oleylamine in Step 1, and the liquid temperature was changed from 90°C to 110°C.

[0096] (Example 9) A composite film was prepared in the same manner as in Example 1, except that 2.4 mL of oleic acid and 1.8 mL of oleylamine were used instead of 2.4 mL of oleic acid and 1.2 mL of oleylamine in Step 1, and the liquid temperature was changed from 90°C to 92.5°C.

[0097] (Comparative Example 1) A composite film was prepared in the same manner as in Example 1, except that in Step 1, 2.4 mL of oleic acid and 1.8 mL of oleylamine were used instead of 2.4 mL of oleic acid and 1.2 mL of oleylamine, the liquid temperature was set to 95°C instead of 90°C, and in Step 2, instead of being kept at room temperature of 25°C in the dark for 10 days, it was kept at room temperature of 25°C in the dark for 5 days.

[0098] (Comparative Example 2) A composite film was prepared in the same manner as in Example 1, except that in step 2, instead of holding the film in a dark environment at room temperature of 25°C for 10 days, it was held in a dark environment at room temperature of 40°C for 10 days.

[0099] (Comparative Example 3) In step 1, instead of 2.4 mL of oleic acid and 1.2 mL of oleylamine, use 2.4 mL of oleic acid and 2.4 mL of oleylamine, change the liquid temperature from 90°C to 185°C, and in step 4, CsPbBr ３ A composite film was prepared in the same manner as in Example 1, except that the amount of perovskite-type nanocrystalline plate was changed from 0.1 mass% to 0.5 wt%. In this case, instead of a nanocrystalline plate, granular CsPbBr with a diameter of approximately 12 nm was used. ３ Quantum dots are formed.

[0100] <Evaluation of Perovskite Nanocrystalline Plates> XRD was measured on samples obtained by coating a dispersion of the perovskite nanocrystalline plate obtained in step 3 onto a glass substrate and drying it. Structural parameters were calculated from the superlattice peaks using the analysis method described in the aforementioned non-patent document (E. E. Fullerton, et al., Phys. Rev. B 45, pp. 9292-9310, 1992), and the number of layers n of the nanocrystalline plate and the dispersion σn of the number of layers n were evaluated. The thickness t (nm) of the nanocrystalline plate is n × 0.60. TEM observation was performed to evaluate the two axes (long axis L, short axis S) intersecting the layer thickness direction, and L / S, S / t, and T were evaluated.

[0101] <Evaluation of Absorption Rate> The absorption rate at 400 nm was measured for a sample obtained by coating a dispersion of the perovskite-type nanocrystalline plate obtained in step 3 onto a glass substrate and drying it. Ultraviolet light with a peak emission wavelength of 400 nm was irradiated from the back surface of the composite film as excitation light, and the absorption rate % = (1 - I / I0) × 100 was calculated from the light intensity I0 without the sample and the light intensity I with the sample. OD (optical density) = -Log(I / I0) was calculated. The value of OD / T × 1000 was calculated as an evaluation value representing the amount of absorption per unit thickness of the composite film.

[0102] <Evaluation of Coverage Rate> A sample obtained by coating a dispersion of the perovskite-type nanocrystalline plate obtained in step 3 onto a glass substrate and drying it was observed using TEM from the layer thickness direction D. Image processing was performed on the contrast between the crystalline and void portions of the acquired image to calculate the coverage rate = {1 - (area of ​​void portion)} / (area of ​​crystalline portion)} × 100 (%).

[0103]

[0104] Table 1 shows that the coverage can be increased by creating a composite film in which the aspect ratio of the two axes intersecting the thickness direction of the nanocrystalline plate (long axis L / short axis S or short axis S / long axis L) is 0.2 or more and 5 or less, and the average value S of the length of the short axis of the nanocrystalline plate is S / t > 1.

[0105] As a result, it was found that the composite film had a high absorption rate per unit thickness (OD / T × 1000), and could be used as a high-density wavelength conversion layer or light absorption layer that can effectively absorb light even with a thin film thickness.

[0106] Based on the above, the dense ABX with few intercrystalline voids described herein ３ We were able to provide a perovskite layer.

[0107] This disclosure is not limited to the embodiments described above, and various modifications and alterations are possible without departing from the spirit and scope of this disclosure. Accordingly, the following claims are attached to make the scope of this disclosure public.

[0108] This application claims priority based on Japanese Patent Application No. 2024-187556, filed on October 24, 2024, and all of its contents are incorporated herein by reference.

[0109] 10 Composite film 11 Nanocrystalline plate (L / S ≤ 5) 12 Nanocrystalline plate (L / S > 5) 13 Assembly 15 Crystal portion 16 Void portion

Claims

1. A composite film comprising a nanocrystalline plate having a composite layer structure in which a first layer containing a ligand-coordinated cation A and a second layer containing a cation B and anion X are alternately stacked, 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 when the thickness of the nanocrystalline plate is t and the length of the minor axis intersecting the stacking direction of the nanocrystalline plate is S, then t and S satisfy S / t ≥ 3, and the dispersion σn of the number of stacked nanocrystalline plates is 0.7 or less.

2. The composite film according to claim 1, wherein, of the two axes intersecting the thickness direction of the nanocrystalline plate, the longitudinal axis is defined as the major axis and the transverse axis as the minor axis, the average length of the minor axis is 5 nm or more and 50 nm or less, the average length of the major axis is 10 nm or more and 50 nm or less, and the average length of the minor axis is less than or equal to the average length of the major axis.

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

4. The composite film according to any one of claims 1 to 3, wherein the ligand coordinates to the cation B.

5. The composite film according to any one of claims 1 to 4, wherein the dispersion σn of the number of stacked nanocrystalline plates is 0.1 or greater.

6. The composite film according to any one of claims 1 to 5, wherein the number of stacked nanocrystalline plates is 3 or more and 5 or less.

7. The composite film according to any one of claims 1 to 6, having a crystalline portion containing the structural units of the nanocrystalline plate and a void portion not containing the structural units of the nanocrystalline plate, wherein, when the coverage rate of the nanocrystalline plate is defined as {1 - (area of ​​the void portion) / (area of ​​the crystalline portion)} × 100 (%) in an image obtained by observing the surface of the composite film with a transmission electron microscope, the coverage rate is 80% or more.

8. The composite film according to any one of claims 1 to 7, wherein the nanocrystalline plate has a perovskite-type crystalline structure.

9. The cation A is an ammonium cation (NH ４ ＋ ), an alkylammonium cation having 6 or less 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 composite membrane according to any one of claims 1 to 8.

10. The composite film according to any one of claims 1 to 9, wherein the cation B comprises a divalent transition metal cation or a divalent typical metal cation.

11. The 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 composite film according to claim 10, comprising one or more selected from the group consisting of ).

12. 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 composite film according to claim 10 or 11, comprising one or more selected from the group consisting of ).

13. The composite film according to any one of claims 1 to 12, wherein the anion X includes a monovalent anion including a halide anion.

14. A quantum dot-containing electroluminescent element comprising a composite film according to any one of claims 1 to 13.

15. A quantum dot-containing wavelength conversion sheet comprising the composite film according to any one of claims 1 to 13.

16. A quantum dot-containing wavelength conversion layer comprising the composite film according to any one of claims 1 to 13.

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