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

Abstract

To provide a composite film with a high coverage rate of nanocrystalline plates and a high amount of light absorption per unit thickness. [Solution] 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.

Description

Technical Field

[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.

Background Art

[0002] Nanocrystals having a perovskite crystal structure are known to be applicable to light-emitting materials such as photoluminescence (PL) type and electroluminescence (EL) type, and light-receiving materials such as solar cells and optical sensors because they have a narrow full width at half maximum in spectral sensitivity characteristics and exhibit high color purity. 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 nanocrystals having a perovskite crystal structure becomes small, the emission wavelength is shifted 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] 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 as thin a film thickness 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.

[0004] 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.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

[0006] 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. 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 is large, self-assembled aggregates are formed or the nanoplates are aligned vertically, making it impossible to obtain a dense film. This disclosure was made in view of the above-mentioned problems, and aims to provide a composite film with high coverage of the nanocrystalline plate and high light absorption per unit thickness by fabricating a dense ABX3 perovskite layer with few voids between crystals. [Means for solving the problem]

[0007] To address the above issues, this disclosure provides: A composite film comprising 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, 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. Let t be the thickness of the nanocrystalline plate, and S be the length of the minor axis intersecting the stacking direction of the nanocrystalline plate. Then, t and S satisfy S / t ≥ 3. The composite film has a dispersion σn of the number of stacked nanocrystalline plates of 0.7 or less. Furthermore, this disclosure relates to a quantum dot-containing electroluminescent device comprising the composite film described above. Furthermore, this disclosure relates to a quantum dot-containing wavelength conversion sheet comprising the composite film described above. Furthermore, this disclosure relates to a quantum dot-containing wavelength conversion layer comprising the above-described composite film. [Effects of the Invention]

[0008] According to this disclosure, by providing a dense ABX3 perovskite layer with few intercrystalline voids, it is possible to suppress charge leakage paths and improve carrier recombination probability in EL and solar cell applications. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1(a) shows a composite film comprising a plurality of nanocrystalline plates (L / S ≤ 5) according to the present disclosure. Figure 1(b) shows an image of the composite film of Figure 1(a) projected from the thickness direction D onto a plane in the thickness direction. [Figure 2] Figure 2(a) shows a composite film consisting of multiple nanocrystalline plates (L / S>5). Figure 2(b) shows a composite film using nanoparticles. [Modes for carrying out the invention]

[0010] 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. <One Embodiment> One embodiment relates to a composite film. The composite film disclosed herein is A composite film comprising 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, 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. Let t be the thickness of the nanocrystalline plate, and S be the length of the minor axis intersecting the stacking direction of the nanocrystalline plate. Then, t and S satisfy S / t ≥ 3. The dispersion σn of the number of stacked nanocrystalline plates is 0.7 or less.

[0011] (Structure of nanocrystalline plate) The composite film of this disclosure is a composite film comprising 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.

[0012] 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 nanocrystalline 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 nanocrystalline plate of this disclosure, it is preferable that the ligand coordinates to cation B.

[0013] 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.

[0014] In the composite film of the present disclosure, the rectangular shape feature (aspect ratio) preferably corresponds to two directions that define the plate size of the nanocrystalline plate, where the longer of the two axes intersecting the thickness direction of the nanocrystalline plate is the major axis and the shorter of the two axes is the minor axis, and the aspect ratio is expressed as either the average length of the major axis / the average length of the minor axis, or the aspect ratio = the average length of the minor axis / the average length of the major axis.

[0015] The composite film of this disclosure has an aspect ratio, which is a rectangular shape feature in the direction intersecting the stacking direction of the composite layer structure, that is between 0.2 and 5, and preferably between 0.2 and 3.6. In Table 1 described later, the LS aspect ratio = average length of the major axis / average length of the minor axis (= L / S).

[0016] When the longitudinal axis and the short axis are defined as the major axis among the two axes intersecting the thickness direction of the nanocrystalline 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 nm or less, even more preferably 6 or more and 20 nm or less, and particularly preferably 7 or more and 18 nm or less.

[0017] 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 nm or more and 30 nm or less, even more preferably 15 nm or more and 27 nm or less, and particularly preferably 18 nm 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.

[0018] [Perovskite-type structure A site (cation A)] Site A employs a monovalent cation. The monovalent cation (cation A) employed at site A is an ammonium cation (NH4 + ), and alkylammonium cations having 6 or fewer carbon atoms, formamidinium cation (HC(NH2)2 + ), guanidinium cation (C(NH2)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 cation (Cs+ Examples of such alkali metal cations include

[0019] In the composite membrane of the present disclosure, cation A is an ammonium cation (NH4 + ), an alkylammonium cation having 6 or less carbon atoms, a formamidinium cation (HC(NH2)2 + ), a guanidinium cation (C(NH2)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 preferably contains one or more selected from the group consisting of Since the monovalent cations employed in these A sites have a small ionic diameter and are of a size that can enter the crystal lattice, the perovskite compound can form a stable three-dimensional crystal.

[0020] Preferred examples of the alkylammonium cation having 6 or less carbon atoms include methylammonium cation (CH3NH3 + ), ethylammonium cation (C2H5NH3 + ), propylammonium cation (C3H7NH3 + ), and the like.

[0021] From the viewpoint of obtaining high luminous efficiency, it is preferable that at least one of methylammonium cation, formamidinium cation or cesium cation is used as the A site, and from the viewpoint of suppressing color change, it is more preferable that cesium cation is used as the A site. Two or more of these monovalent cations employed in these A sites may be used in combination.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] [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.

[0026] 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+Preferably, it includes one or more selected from the group consisting of ).

[0027] The composite film of this disclosure contains 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 (Cd 2+ ), 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 ).

[0028] 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.

[0029] 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.

[0030] [X-site (anion X) of perovskite crystal structure] The composite film of this disclosure preferably contains a monovalent anion, including a halide anion, as X (anion X) in the perovskite crystal structure. 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. The luminescence color is blue when chloride anions are used, green when bromide anions are used, and red when iodide anions are used.

[0031] 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.

[0032] 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.

[0033] [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.

[0034] 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.

[0035] 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.

[0036] (Method for manufacturing perovskite-type nanocrystalline plates) 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 nanoplate layers is adjusted during synthesis by controlling the reaction temperature, precursor ratio, ligand concentration, ligand acid-base balance, and ligand chain length. The number 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.

[0037] (Evaluation of the number of layers of 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 can be described as structural parameters: 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. 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.

[0038] 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).

[0039] Furthermore, the nanocrystalline plate can be evaluated by transmission electron microscopy (TEM) observation. By incidenting an electron beam from the same direction as the thickness direction of the nanocrystalline plate and performing TEM observation, the aspect ratio (L / S or S / L) of the two axes intersecting the thickness direction can be evaluated. In addition, by aligning the incident electron beam direction with a direction perpendicular to the thickness direction of the nanocrystalline plate 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 nanocrystalline plate layers n, the dispersion σn of the number of layers n, the spacing D of the nanocrystalline plates, the dispersion σD of the spacing D, and the thickness t and number of layers N of the nanocrystalline plate, as described later. It is also possible to calculate similar structural parameters from aggregate data obtained from evaluating individual nanocrystalline plates rather than the entire assembly. In evaluation using TEM, it is also possible to identify the stacked structure of the perovskite-type nanocrystalline plate of this disclosure, for example, incorporated into a device.

[0040] (Composite film using perovskite-type nanocrystalline plates) Figure 1(a) 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 possible to make the biaxial aspect ratio 0.3 or more and 3 or 0.5 or more and 2 or less. When the L / S is small in this way, when the solution containing this nanocrystalline plate 11 is applied to a substrate and left to stand and dry, a composite film 10 is obtained consisting of a plurality of self-aligned nanocrystalline plates with a thickness T = {t (thickness of individual nanocrystalline plates) + 1.1 nm (thickness of intercrystalline ligands)} × N (number of layers), as shown in Figure 1(a).

[0041] 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 2(a), 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 2(b), when using nanoparticles 14, for the same thickness T as in Figure 1(a), voids exist in the thickness direction of the layer, making it impossible to increase the coverage of the area projected onto a surface in the thickness direction.

[0042] Figure 1(b) 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.

[0043] If the coverage in the thickness direction of the layer is insufficient, these voids become leakage paths for excitation light and charge leakage. For PL and photosensor applications, it is possible to provide high-density perovskite crystal films with high coverage that can absorb light without leakage with the thinnest possible film thickness, serving as wavelength conversion layers or light absorption layers. For EL and solar cell applications, it is possible to provide dense perovskite crystal films that suppress charge leakage paths and improve carrier recombination probability. Here, the area referred to as a void means a region where no nanocrystalline plate exists, and in reality, ligands or a medium may be filled in that area.

[0044] Furthermore, the following conditions are necessary to induce self-alignment. In the composite film of this 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 that shown in Figure 2(a) will be formed.

[0045] 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.

[0046] 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 0.70. This can improve density. This is because variations in the number of stacked plates inhibit self-alignment and lead to the formation of voids.

[0047] 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. This improves density. This is because it makes it easier to create a difference between the thickness t of the nanocrystalline plate and the short-axis length S.

[0048] 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, for n=3, the coverage is approximately 80% when N=1, approximately 90% when N=2, and 95% or more when N≧3.

[0049] <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) devices.

[0050] [Quantum dot-containing electroluminescent (QD-EL) element] The quantum dot-containing electroluminescent device of this disclosure includes the composite film of this disclosure. The QD-EL element of this disclosure comprises, 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.

[0051] (electrode) 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.

[0052] 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.

[0053] (Hole injection / transport layer) Suitable materials for the hole injection / transport layer include those used in organic EL displays, for example. 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, TiO2, and MoO. x These are some examples. These can be used individually or in combination of two or more.

[0054] 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. 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.

[0055] (Emitting layer) A composite film consisting of multiple nanocrystalline plates according to this disclosure can be used as a light-emitting layer. 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.

[0056] (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). 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.

[0057] 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. 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.

[0058] In the above description, the case where the light-emitting element is a bottom emission type that extracts light from the anode side (substrate side) has been mainly shown, but it is not limited thereto. For example, the light-emitting element may be a top emission type that extracts light from the cathode side (opposite substrate side).

[0059] [Quantum dot-containing wavelength conversion layer (QD-CC)] The quantum dot-containing wavelength conversion layer of the present disclosure includes the composite film of the present disclosure. The quantum dot-containing wavelength conversion layer of the present disclosure is a member obtained by curing a photo-responsive composition containing nanocrystalline plates in a co-dispersed state and a polymerizable compound on a substrate. The quantum dot-containing wavelength conversion layer takes a layer form supported by other members. The support forms include a laminated form and a dispersed form dispersed in a matrix material. The quantum dot-containing wavelength conversion layer may be obtained by coating and curing a photo-responsive composition on a support member (substrate) to form a film or a sheet or a patterned pixel.

[0060] [Quantum dot-containing wavelength conversion sheet (QD sheet)] The quantum dot-containing wavelength conversion sheet of the present disclosure includes the composite film of the present disclosure. The quantum dot-containing wavelength conversion sheet is obtained by coating and curing a photo-responsive composition on a support member (substrate) to form a sheet form. [Examples]

[0061] Hereinafter, the display element according to the examples of the present disclosure will be described in detail, but the present disclosure is not limited to the following examples. [Example 1] [Synthesis of perovskite-type nanocrystalline plates of CsPbBr3] 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 stream 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 reaction solution 1.

[0062] Step 2: Add 14 mL of methyl acetate to reaction solution 1 and keep in a dark place at room temperature (25°C) for 10 days to obtain reaction solution 2. Hereafter, one day will be defined as 24 hours.

[0063] Step 3: Centrifugation was performed and the supernatant was removed. The resulting residue was dispersed in toluene to obtain a dispersion of CsPbBr3 perovskite-type nanocrystalline plates (nanocrystalline plates).

[0064] Step 4: The solvent was removed from the dispersion of the CsPbBr3 perovskite nanocrystalline plate by blowing a stream of dry nitrogen air onto it, and the CsPbBr3 perovskite nanocrystalline plate was dispersed in hexane solvent to a concentration of 0.1% by mass. 10 μL of this dispersion was coated onto a glass substrate and dried to obtain a composite film of the perovskite nanocrystalline plate.

[0065] (Example 2) The composite film was fabricated in the same manner as in Example 1, except that in step 4, the amount of CsPbBr3 perovskite-type nanocrystalline plate was changed from 0.1 mass% to 0.15 wt%.

[0066] (Example 3) The composite film was fabricated in the same manner as in Example 1, except that in step 4, the amount of CsPbBr3 perovskite-type nanocrystalline plate was changed from 0.1 mass% to 0.3 wt%.

[0067] (Example 4) The composite film was fabricated in the same manner as in Example 1, except that in step 4, the amount of CsPbBr3 perovskite-type nanocrystalline plate was changed from 0.1 mass% to 1.0 wt%.

[0068] (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.

[0069] (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 changed from 90°C to 95°C.

[0070] (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.

[0071] (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.

[0072] (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.

[0073] (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 changed from 90 °C to 95 °C, and in Step 2, instead of being kept in a dark environment at room temperature of 25 °C for 10 days, it was kept in a dark environment at room temperature of 25 °C for 5 days.

[0074] (Comparative Example 2) The 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 at 40°C in a dark environment for 10 days.

[0075] (Comparative Example 3) A composite film was fabricated in the same manner as in Example 1, except that in Step 1, 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, the liquid temperature was changed from 90°C to 185°C, and in Step 4, the amount of CsPbBr3 perovskite-type nanocrystalline plate was changed from 0.1 mass% to 0.5 wt%. In this case, instead of a nanocrystalline plate, granular CsPbBr3 quantum dots with a diameter of approximately 12 nm were formed.

[0076] <Evaluation of Perovskite Nanocrystalline Plates> XRD measurements were taken on samples obtained by coating a dispersion of the perovskite-type 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 (EE 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 of the nanocrystalline plate t (nm) = 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.

[0077] <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. Optical density (OD) = -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.

[0078] <Evaluation of coverage> The perovskite-type nanocrystalline plate dispersion obtained in step 3 was applied to a glass substrate and dried. TEM observation was performed on the sample from the layer thickness direction D, and the coverage rate was calculated as {1 - (area of ​​voids)} / (area of ​​crystalline portion)} × 100 (%) by image processing based on the contrast between the crystalline and void portions of the acquired image.

[0079] [Table 1]

[0080] Table 1 shows that 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 between 0.2 and 5, and the coverage can be increased by creating a composite film where the thickness t of the nanocrystalline plate and the average value S of the short axis length are S / t > 1. As a result, it was found that the absorption amount per unit thickness of the composite film (OD / T × 1000) is high, and it can be used as a high-density wavelength conversion layer or light absorption layer that can effectively absorb light even with a thin film thickness. Based on the above, we were able to provide a dense ABX3 perovskite layer with few intercrystalline voids as described in this disclosure.

[0081] This embodiment includes the following configuration. (Composition 1) A composite film comprising 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, 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. Let t be the thickness of the nanocrystalline plate, and S be the length of the minor axis intersecting the stacking direction of the nanocrystalline plate. Then, t and S satisfy S / t ≥ 3. A composite film in which the dispersion σn of the number of stacked nanocrystalline plates is 0.7 or less. (Structure 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 5 nm and 50 nm. The average length of the aforementioned major axis is between 10 nm and 50 nm. The composite film according to Structure 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. (Structure 3) The composite film according to structure 1 or 2, wherein the rectangular shape feature corresponds to two directions that define the plate size of the nanocrystalline plate. (Structure 4) The ligand coordinates to the cation B, and the composite film is according to any one of structures 1 to 3. (Structure 5) The composite film according to any one of structures 1 to 4, wherein the dispersion σn of the number of stacked nanocrystalline plates is 0.1 or greater. (Structure 6) The composite film according to any one of structures 1 to 5, wherein the number of stacked nanocrystalline plates is 3 or more and 5 or less. (Structure 7) It has a crystalline portion containing the structural units of the nanocrystalline plate and a void portion that does not contain the structural units of the nanocrystalline plate, A composite film according to any one of structures 1 to 6, wherein, when an image obtained by observing the surface of the composite film using a transmission electron microscope shows the coverage of the nanocrystalline plate as {1 - (area of ​​the void) / (area of ​​the crystalline portion)} × 100 (%), the coverage is 80% or more. (Structure 8) The nanocrystalline plate is a composite film according to any one of structures 1 to 7, having a perovskite-type crystalline structure. (Structure 9) 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 composite film according to any one of structures 1 to 8, comprising one or more selected from the group consisting of ). (Structure 10) The composite film according to any one of structures 1 to 9, wherein the cation B comprises a divalent transition metal cation or a divalent typical metal cation. (Structure 11) 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 composite film according to structure 10, comprising one or more selected from the group consisting of ). (Structure 12) 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 composite film according to structure 10 or 11, comprising one or more selected from the group consisting of ). (Structure 13) The composite film according to any one of structures 1 to 12, wherein the anion X includes a monovalent anion, including a halide anion. (Structure 14) A quantum dot-containing electroluminescent element comprising a composite film described in any one of structures 1 to 13. (Structure 15) A quantum dot-containing wavelength conversion sheet comprising a composite film described in any one of structures 1 to 13. (Structure 16) A quantum dot-containing wavelength conversion layer comprising a composite film described in any one of structures 1 to 13. [Explanation of Symbols]

[0082] 10 Composite membrane 11 Nanocrystalline plates ((L / S≦5) 12 Nanocrystalline plates (L / S>5) 13 Aggregate 15 Crystalline part 16 Cavity

Claims

1. A composite film comprising 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, 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. Let t be the thickness of the nanocrystalline plate, and S be the length of the minor axis intersecting the stacking direction of the nanocrystalline plate. Then, t and S satisfy S / t ≥ 3. A composite film in which the dispersion σn of the number of stacked nanocrystalline plates is 0.7 or less.

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 minor axis is between 5 nm and 50 nm. The average length of the major axis is between 10 nm and 50 nm. The composite film 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 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 claim 1 or 2, wherein the ligand coordinates to the cation B.

5. The composite film according to claim 1 or 2, wherein the dispersion σn of the number of stacked nanocrystalline plates is 0.1 or greater.

6. The composite film according to claim 1 or 2, wherein the number of stacked nanocrystalline plates is 3 or more and 5 or less.

7. It has a crystalline portion containing the structural units of the nanocrystalline plate and a void portion that does not contain the structural units of the nanocrystalline plate, The composite film according to claim 1 or 2, wherein, with respect to an image obtained by observing the surface of the composite film using a transmission electron microscope, the coverage rate of the nanocrystalline plate is {1 - (area of ​​the void portion) / (area of ​​the crystalline portion)} × 100 (%), and the coverage rate is 80% or more.

8. The composite film according to claim 1 or 2, 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 the composite membrane according to claim 1 or 2, comprising one or more selected from the group consisting of.

10. The composite film according to claim 1 or 2, wherein the cation B comprises a divalent transition metal cation or a divalent typical metal cation.

11. 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 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, comprising one or more selected from the group consisting of ).

13. The composite film according to claim 1 or 2, wherein the anion X includes a monovalent anion including a halide anion.

14. A quantum dot-containing electroluminescent element comprising the composite film described in claim 1 or 2.

15. A quantum dot-containing wavelength conversion sheet comprising the composite film described in claim 1 or 2.

16. A quantum dot-containing wavelength conversion layer comprising the composite film according to claim 1 or 2.

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