Wavelength conversion layer, display element, and method for manufacturing the wavelength conversion layer

Abstract

To provide a wavelength conversion layer with improved light extraction efficiency, a display element using the wavelength conversion layer, and a method for manufacturing the wavelength conversion layer. [Solution] A wavelength conversion layer having a perovskite-type crystal structure, 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; a medium that supports the nanocrystalline plate and propagates light from the nanocrystalline plate; a first photo-coupler that guides light from outside the layer into the layer; and a second photo-coupler positioned differently from the first photo-coupler that guides light propagating within the layer to the outside of the layer, wherein the composite layer structure has an average number of stacks of 3 to 5, and the nanocrystalline plate is oriented such that the normal to the main surface of the plate intersects with the second photo-coupler.

Description

Technical Field

[0001] The present invention relates to a wavelength conversion layer, a display element, and a method for manufacturing the wavelength conversion layer.

Background Art

[0002] In a display element for displaying an image, as a technique for realizing color reproducibility corresponding to a wide color purity and high luminous efficiency, there is a technique using quantum dots that exhibit light emission with a narrow half-value width. By performing color conversion in a wavelength conversion layer provided with quantum dots using ultraviolet light or blue light as excitation light, a display element that achieves both color reproducibility and high luminous efficiency can be realized. As a light source for the excitation light, a light-emitting diode (LED), an organic light-emitting diode (OLED), or the like can be used. In particular, a configuration has been proposed in which a wavelength conversion layer composed of quantum dots that emit red and green light is patterned in a subpixel composed of a black bank partition, and color conversion is performed for each pixel by excitation light. In this configuration, the size of the subpixel is several μm pitch in the case of a small display element used for an EVF (Electric ViewFinder) or the like, and several tens of μm pitch in a large high-resolution television. For example, in Patent Document 1, perovskite-structured quantum dots, nanocrystals, and nanosheets are used as color conversion materials.

Prior Art Documents

Patent Documents

[0003] <ov

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] For the wavelength conversion layer to absorb excitation light and perform color conversion, a thickness of several micrometers to 10 micrometers is required for the wavelength conversion layer. In order to increase the display resolution, the aspect ratio, which is the thickness / width ratio of the wavelength conversion layer formed in the subpixel, increases. When the aspect ratio is high and the radial distance surrounded by the black matrix is ​​short relative to the distance in the direction of light extraction, the light propagating through the wavelength conversion layer collides with the black matrix and is absorbed. As a result, the probability of light incident on the wavelength conversion layer that contributes to the conversion efficiency is higher than in the configuration with a low aspect ratio under constant thickness conditions, leading to a decrease in brightness. In other words, there was a trade-off relationship between the light extraction efficiency from the wavelength conversion layer and its thickness.

[0005] The present invention has been made in view of the above problems, and aims to provide a wavelength conversion layer in which the attenuation of the light extraction efficiency of the wavelength conversion layer, which is optically coupled with high-brightness light at a narrow aperture, due to incidence to the black matrix is ​​reduced. The present invention also aims to provide a display element, a display device, and a method for manufacturing a wavelength conversion layer using the wavelength conversion layer. [Means for solving the problem]

[0006] The wavelength conversion layer according to an embodiment of the present invention is a wavelength conversion layer having a perovskite-type crystal 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; a medium that supports the nanocrystal plate and propagates light from the nanocrystal plate; a first photo-coupler that guides light from outside the layer into the layer; and a second photo-coupler that is positioned differently from the first photo-coupler and guides light propagating within the layer to the outside of the layer, wherein the composite layer structure has an average number of stacks of 3 to 5, and the nanocrystal plate is oriented so that the normal of the plate intersects with the second photo-coupler. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a wavelength conversion layer with improved light extraction efficiency, a display element using the wavelength conversion layer, and a method for manufacturing the wavelength conversion layer. [Brief explanation of the drawing]

[0008] [Figure 1] (a) is a plan view of the array of display elements, (b) is a plan view of a display element, and (c) is a cross-sectional view of a display element. [Figure 2] (a) is a cross-sectional view of the green display element, (b) is a cross-sectional view of another embodiment of the green display element, and (c) is a schematic diagram of the perovskite crystal structure having a composite layer structure of the green display element. [Modes for carrying out the invention]

[0009] Preferred embodiments of the present invention will be described in detail below with reference to the drawings, but the present invention is not limited thereto. (Display this element) A display element 10 according to an embodiment of the present invention will be described with reference to Figures 1(a) to (c).

[0010] Figure 1(a) is a plan view showing a configuration in which multiple display elements (pixels) 10 according to this embodiment are arranged in a two-dimensional manner. The arrangement of the display elements (pixels) can be changed as appropriate depending on the application, in addition to the array arrangement shown in Figure 1(a). Figure 1(b) is an enlarged plan view of one of the display elements (pixels) 10 in Figure 1(a). The display element 10 has a green subpixel region 11, a red subpixel region 12, and a blue subpixel region 13. Figure 1(c) is a cross-sectional view taken along A-A' in Figure 1(b). In this embodiment, the order of each pixel region in the x-axis direction is not particularly limited. In addition to the configuration in which each subpixel region is arranged in the x-axis direction as shown in Figure 1(a), a configuration in which the three subpixel regions are arranged at the vertices of a triangle is also possible.

[0011] In this specification, green, red, and blue are treated as having maximum values ​​in the wavelength bands of at least 515 nm to 545 nm, 615 nm to 645 nm, and 445 nm to 475 nm, respectively. More preferably, green, red, and blue are selected whose wavelengths at which they obtain maximum values ​​fall within the respective bands of 528 nm to 532 nm, 628 nm to 632 nm, and 458 nm to 462 nm.

[0012] The display element 10 is constructed by laminating a light source 14 that emits light L1 of a first wavelength (excitation color, primary light) and a wavelength conversion layer 15 containing a nanocrystalline plate that receives the primary light from the light source 14 and emits light L2 of a second wavelength (green, secondary light (hereinafter also referred to as "wavelength conversion light")). The thickness of the wavelength conversion layer 15 is typically several μm to 10 μm. The wavelength conversion layer 15 contains the nanocrystalline plate at a concentration of 2 to 30 wt% in order to completely absorb the light L1 of the first wavelength in the propagation path of that thickness.

[0013] When the excitation light L1 is ultraviolet light, a wavelength conversion layer 16 containing a nanocrystalline plate that emits a third wavelength of light L3 (red, secondary light) and a wavelength conversion layer 17 containing a nanocrystalline plate that emits a fourth wavelength of light L4 (blue, secondary light) are used to form pixels that emit green, red, and blue light. The wavelength conversion layers 15, 16, and 17 each have a medium for propagating light from the nanocrystalline plate, a first optical coupling portion 20-1, and a second optical coupling portion 20-2, and are provided via a partition wall 18. <Perovskite-type crystal structure with a composite layer structure> As shown in Figure 2(c), the nanocrystalline plate 19 has a first layer 19-1 containing ligand-coordinated cation A, and a second layer 19-2 containing cation B and anion X. The nanocrystalline plate 19 exhibits a perovskite-type crystalline structure having a composite layer structure 19-C in which the first layer 19-1 and the second layer 19-2 are alternately stacked. <First photocoupler> The wavelength conversion layer 15 includes a medium 15-M that supports the nanocrystalline plate 19 and propagates light from the nanocrystalline plate 19, and a first optical coupling portion 20-1 that guides light L1 from outside the layer into the layer. <Second photocoupler> The wavelength conversion layer 15 is positioned differently from the first optical coupling portion and includes a second optical coupling portion 20-2 that guides light L1 propagating within the layer to the outside of the layer as light L2. The composite layer structure 19-C exhibits an average number of layers between 3 and 5, and the nanocrystalline plate 19 has a normal 22 (hereinafter referred to as "D NPL It is also called the second optical coupling portion 20-2, which is oriented to intersect with it.

[0014] When the excitation light L1 is blue light, the wavelength conversion layer 15 contains a nanocrystalline plate that emits light L2 of a second wavelength (green, secondary light), and the wavelength conversion layer 16 contains a nanocrystalline plate that emits light L3 of a third wavelength (red, secondary light). The excitation light L1 passes through the wavelength conversion layer 17, and blue light is emitted from the blue subpixel region 13, thus forming pixels that emit green, red, and blue light. In this case, the wavelength conversion layer 17 does not need to contain a nanocrystalline plate for wavelength conversion.

[0015] (First display element array) The wavelength conversion layer (green) 15 has a layer structure in which perovskite structural units of ABX3 are connected and extended in two dimensions, and the layer structure is stacked in the thickness direction, and includes a nanocrystalline plate in which the number of inorganic layers of the nanocrystalline plate is 3 to 5. Furthermore, the nanocrystalline plate is a wavelength conversion layer in which the normal of the plate intersects with the second photocoupler. The above nanocrystalline plate is also called a nanocrystalline plate. Perovskite-type nanocrystalline plates will be described below.

[0016] (Display this element) In the embodiment of the present invention, it is preferable that the display element has the wavelength conversion layer and a light source that is optically coupled to the first optical coupling portion. Furthermore, in the embodiment of the present invention, the display element preferably has a wavelength conversion layer that converts the light guided from the light source via the first optical coupling portion to a longer wavelength, and more preferably has a drive circuit that controls the emission of light from the light source.

[0017] (Structure of perovskite-type nanocrystalline plate) 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). Thus, although the notation for the crystal structure of the nanocrystalline plate is not strictly ABX3, the crystal structure of the nanocrystalline plate here is represented as ABX3, which means a perovskite-type crystal structure, and is called a perovskite-type nanocrystalline plate. Hereafter, the number of layers represents n. Also, the layer thickness direction means the stacking direction of the layers. Here, the nanocrystalline plate has a main surface that corresponds to one of the two opposing faces with the first and second largest areas among the six faces that make up the rectangular parallelepiped, when viewed as a reference structure. The nanocrystalline plate is oriented so that the normal to the main surface of the plate intersects with the second photocoupler. When a nanocrystalline plate is viewed as a rectangular parallelepiped, it has a layer thickness z in the direction along the normal to the main surface of the plate. Furthermore, the nanocrystalline plate has two sides intersecting the normal to the main surface, with one side having length l and the other length w. The average value of lengths l and w, y, represents the typical plate length when the nanocrystalline plate is considered as a rectangular parallelepiped. In other words, the average value y can be rephrased as the representative plate length y or average plate length y representing the plate length of the nanocrystalline plate. The aspect ratio AR of the nanocrystalline plate is obtained by dividing the average plate length by the layer thickness z. y / z It has.

[0018] [A site (cation A) of perovskite structure] The A site employs a monovalent cation. The monovalent cations employed in the A site (cation A) include ammonium cation (NH4 + ), alkylammonium cations with 6 or fewer carbon atoms, formamidinium cation (HC(NH2)2 + ), guanidinium cation (C(NH2)3 + ), nitrogen-containing organic compound cations such as imidazolium cation, pyridinium cation, pyrrolidinium cation, etc., and alkali metal cations such as lithium cation (Li + ), sodium cation (Na + ), potassium cation (K + ), rubidium cation (Rb + ), and cesium cation (Cs + ).

[0019] Since these monovalent cations employed in the A site have a small ionic radius and are of a size that can fit into the crystal lattice, the perovskite compound can form a stable three-dimensional crystal.

[0020] Preferred examples of alkylammonium cations with 6 or fewer carbon atoms include methylammonium cation (CH3NH3 + ), ethylammonium cation (C2H5NH3 + ), propylammonium cation (C3H7NH3 + ), etc.

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

[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 B site (cation B) of a perovskite crystal structure employs a divalent cation, including either a divalent transition metal cation or a divalent typical metal cation.

[0026] Divalent transition metal cations include 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+ ), ytterbium cation (Yb 2+ ) will be adopted.

[0027] A typical divalent metal cation is the 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+ ), lead cation (Pb 2+ ) may be adopted.

[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] In the perovskite crystal structure, X (anion X) is a monovalent anion, including a halide anion. Examples of halide anions include fluoride anions (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 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 ). 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 embodiment, the ligand (hereinafter also referred to as "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 using the hot injection method, the number of layers in the nanocrystalline plate is adjusted during synthesis by controlling the reaction temperature, precursor ratio, ligand concentration, ligand acid-base equilibrium, and alkylamine ligand chain length. The number of layers decreases as the reaction temperature is lowered; nanocrystalline plates are formed 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.

[0037] (Evaluation of the number of nanocrystalline plate layers) The structural parameters of nanocrystalline plates can be evaluated using X-ray diffraction (XRD). The nanocrystalline plates form a self-stacked aggregate (superlattice) via ligands. The periodicity of this superlattice can be described by structural parameters: the interplanar spacing d of ABX3, the number of layers n of the nanocrystalline plate, the dispersion σn of layer 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 plate. The first and second principal diffraction peaks of CsPbBr3 are 15.1° and 30.4°, respectively, and the first and second principal diffraction peaks of CsPbI3 are 13.8° and 27.2°, respectively. Here, the scattering vector coefficient is (q = 4π·sin(θ) / λ X-ray 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 Phys. Rev. B1992, 45, 9292-9310.

[0038] 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 average plate length y (representative plate length y), which is a representative value of the plate length when considered as a rectangular parallelepiped, can be evaluated. In addition, by aligning the incident direction of the electron beam 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 layers n of the nanocrystalline plate, the variance σn of the number of layers n, the spacing D of the nanocrystalline plate, and the variance σD of the spacing D. It is also possible to calculate similar structural parameters from aggregate data obtained from evaluating individual nanocrystalline plates rather than the entire assembly. With evaluation using TEM, it is also possible to identify the composite layer structure of the perovskite-type nanocrystalline plate of the present invention, for example, when it is incorporated into a device.

[0039] (Wavelength conversion layer using perovskite-type nanocrystalline plates) First, when a nanocrystalline plate has an internal quantum efficiency ηi as its quantum luminescence efficiency, and a pixel containing the nanocrystalline plate has an optical extraction window between it and the outside, the external quantum efficiency EQE, which is the luminescence efficiency of the pixel to the outside, is expressed as the product of (optical extraction efficiency ηg) and (internal quantum efficiency ηi). The optical extraction window may be referred to as an optical coupling, and the optical extraction efficiency may be referred to as extraction efficiency. In this embodiment, the pixel has an increased external quantum efficiency EQE by increasing the optical extraction efficiency. By using a perovskite-type nanocrystalline plate as the nanocrystalline plate and arranging it in a predetermined geometric configuration within the pixel, it is possible to improve the light extraction efficiency from pixels having a wavelength conversion layer. Figure 2(a) is a cross-sectional view taken along B-B' in Figure 1(b). As shown in Figure 2(a), the wavelength conversion layer (green) 15 includes a nanocrystalline plate 19. The nanocrystalline plate 19 is a perovskite-type nanocrystalline plate, and the plane formed by two axes intersecting its thickness direction has a substantially perpendicular axis D NPL However, the light extraction direction D of the wavelength conversion layer 15 OUT It is oriented in that direction. In the case of granular quantum dots, where the crystal form is isotropic in three dimensions, there is no directionality of emission. On the other hand, in the case of nanocrystalline plate form, the directionality of emission is along the vertical axis D NPL (Hereafter simply "D" NPL It was found that there are conditions under which the emission can be increased in the direction of ). In this case, the emission is D NPL Because radiation will be preferentially directed in the direction of D NPL Light extraction direction D OUT By matching this, the proportion of light emitted remaining inside the wavelength conversion layer 15 due to total internal reflection can be reduced, improving the efficiency of light extraction to the outside. In addition, since light absorption by the partition wall 18 can be avoided, the efficiency of light extraction can be improved, and as a result the brightness is increased.

[0040] Also, as shown in Figure 2(b), D NPL Light extraction direction D OUT By arranging the nanocrystalline plate 19 at an angle so as to face the center of the opening, the nanocrystalline plate 19 near the partition wall 18 can be extracted to the outside without being absorbed by the partition wall 18, thus resulting in a more preferable configuration from the viewpoint of improving light extraction efficiency. In this case, by arranging the curved optical member 20 at the bottom, D NPL It becomes easier to control.

[0041] Here, D NPL The light extraction efficiency in a given direction is determined by the aspect ratio AR of the nanocrystalline plate, which is the average plate length y of the nanocrystalline plate and the layer thickness z. y / zIt was found that (=y / z) is determined by the dielectric constant of the medium surrounding the nanocrystalline plate.

[0042] First, AR y / z D is derived from the contained nanocrystalline plate. NPL Light extraction efficiency in that direction is improved. AR y / z The larger D NPL Radiation in a specific direction is enhanced. In the case of granular quantum dots, AR is enhanced, which improves the efficiency of extraction in a predetermined direction from light-emitting materials such as phosphors. y / z = 1, and D at this time NPL Let the radiation amount at a solid angle of 3sr (steradians) in the direction be 100. AR y / z If =3, D NPL The radiation in the direction is approximately 125, AR y / z If = 10, D NPL The radiation in the direction was approximately 135. In the case of a 3-layer CsPbBr3 nanocrystalline plate, z = 1.8 nm, so for a nanocrystalline plate with an average plate length y of about 18 nm, AR y / z = 10. In the present invention, a rectangular parallelepiped is used as the basic structure, and the aspect ratio AR is the ratio of the layer thickness z in the direction along the normal and the average plate length y in the direction along two axes intersecting the normal. y / z It is preferable that (=y / z) is between 2.0 and 10.

[0043] The medium through which light propagates from the nanocrystalline plate has a predetermined dielectric constant. NPL The light extraction efficiency in a given direction also depends on and varies with respect to the dielectric constant of the medium. The medium through which light propagates from the nanocrystalline plate can be manufactured as an array of pixels of a predetermined size and arrangement by applying a fluid raw material containing a polymerizable compound, a wet manufacturing process, and a known patterning method. The fluid raw material containing a polymerizable compound is one that polymerizes and hardens upon application of light or heat. Polymerizable compounds are low-molecular-weight compounds that thicken and harden upon polymerization, and may be referred to as polymerizable monomers, polymerizable oligomers, etc. Therefore, the medium can include a cured product obtained by polymerizing polymerizable compounds. As polymerizable compounds, TMCHA: 3,3,5-trimethylcyclohexyl acrylate (dielectric constant 2.12), HDDA: 1,6-hexanediol diacrylate (dielectric constant 2.12), THFA: tetrahydrofurfuryl acrylate (dielectric constant 2.12), CHA: cyclohexyl acrylate (dielectric constant 2.13), IBXA: isobornyl acrylate (dielectric constant 2.09), TBA: t-butyl acrylate (dielectric constant 2.00), etc. can be used. The dielectric constant of the perovskite-type nanocrystalline plate in this embodiment varies depending on the composition, with CsPbCl3 having a dielectric constant of 3.80, CsPbBr3 having a dielectric constant of 4.93, and CsPbI3 having a dielectric constant of 6.92. The ratio of the dielectric constant of the luminescent nanocrystalline plate to the dielectric constant of the polymerizable polymer is ε NPL / Polymer Therefore, the ratio of these dielectric constants gives D NPL The light extraction efficiency in the direction is controlled, and this light extraction efficiency has a positive correlation with the ratio of dielectric constants. When the composition of the perovskite nanocrystal is fixed with CsPbBr3 and the polymerizable compound is changed, the efficiency is up to approximately 7% higher compared to the case of oleic acid (dielectric constant 2.11), which is a ligand added in the initial stage of manufacturing the perovskite nanocrystal plate. NPL The efficiency of light extraction in that direction is improved. In this embodiment, the medium preferably has a relative permittivity of 2.0 or more and 2.2 or less.

[0044] The above applies when the orientation of the nanocrystalline plate is 100%; if the orientation decreases, D NPL The light extraction efficiency in the direction decreases. The degree of orientation in this invention is D NPL Light extraction direction D OUT The proportion of nanocrystalline plates 19 whose angles are 10 degrees or less is determined.

[0045] In the present invention, it is preferable that the second photo-coupled portion has a normal to the injection surface, and the normal of the nanocrystalline plate is within 10 degrees of the normal to the injection surface, and that the proportion of the nanocrystalline plate to the total nanocrystalline plate is 20% or more.

[0046] Here, the degree of orientation in this invention can be determined by methods for evaluating crystal orientation using X-ray diffraction (XRD) or backscattered electron diffraction (EBSD), or by structural evaluation methods using TEM or SEM. The degree of orientation by X-ray diffraction is calculated using the Lotgering factor with respect to the peak intensity of the X-rays diffracted from the target crystal plane. The degree of orientation by EBSD is defined as the proportion of nanocrystalline plate 19 within 10 degrees from the main diffraction peak of the inverse polarity diagram.

[0047] Furthermore, if the shape of the nanocrystalline plate inside the wavelength conversion layer (two axes intersecting the layer thickness direction) can be determined by structural evaluation using TEM or SEM, then D NPL This is approximately equal to the perpendicular axis of the plane formed by the two axes intersecting the layer thickness direction. Therefore, by identifying the three-dimensional arrangement of nanocrystalline plates within the wavelength conversion layer, D NPL It is also possible to evaluate the following: For example, by continuously surface-leveling the wavelength conversion layer using an ion beam or FIB (Focused Ion Beam) from the top or side, and performing a slice-and-view process, it is possible to identify the three-dimensional arrangement of individual nanocrystal plates and calculate their degree of orientation. In addition, methods such as TEM and X-ray three-dimensional tomography can also be used.

[0048] Here, as shown in Figure 2(b), when the curved optical element 20 is placed at the bottom, the degree of orientation cannot be accurately evaluated by macroscopic evaluation methods using XRD. Therefore, it is more appropriate to estimate the degree of orientation from evaluations using EBSD, TEM, or SEM. In this case, the degree of orientation is D NPL Light extraction direction D OUT The proportion of the nanocrystalline plate 19 is within 10 degrees of the central direction of the opening.

[0049] This invention relates to the substantially perpendicular axis D of a surface formed by two axes intersecting the thickness direction. NPL However, it is preferable that the proportion (degree of orientation) of nanocrystalline plates that are within 10 degrees of the light extraction direction of the wavelength conversion layer is 20% or more.

[0050] (Method for manufacturing a wavelength conversion layer) The orientation of the nanocrystalline plates 19 will be described in detail in the following examples, but it can be formed with some control by the following manufacturing methods. These include a method of printing an ink composition containing perovskite-type nanocrystalline plates and a medium, and then allowing a predetermined settling time (standing time) to allow the nanocrystalline plates 19 to self-align and harden the printed material; a method of introducing a volatile solvent into the ink composition and using a drying process to align and harden the nanocrystalline plates 19; and a method of adding the above-mentioned ligands, which are additives that coordinate to the nanocrystalline plates, to the ink composition, and then using the attractive force between the ligands to align and harden the nanocrystalline plates 19. By combining these methods, nanocrystalline plates 19 arranged in the wavelength conversion layer 15 can be obtained. A method of gradually removing the solvent from the polymerizable compound by introducing several types of volatile solvents and utilizing the differences in drying time and drying temperature is effective. The drying temperature is preferably in the range of 10°C to 50°C, and more preferably in the range of 20°C to 30°C. The drying time varies depending on the drying temperature; the drying time is longer at lower temperatures and shorter at higher temperatures. When the drying time at a drying temperature of 25°C is set to 100 (=24 hours), the relationship between a given drying time and a given drying temperature is roughly as follows: at a drying temperature of 10°C, the drying time is 1000; at a drying temperature of 15°C, the drying time is 500; at a drying temperature of 20°C, the drying time is 200; at a drying temperature of 30°C, the drying time is 45; at a drying temperature of 35°C, the drying time is 20; at a drying temperature of 40°C, the drying time is 10; at a drying temperature of 45°C, the drying time is 4; and at a drying temperature of 50°C, the drying time is 2.

[0051] In other words, the method for manufacturing the wavelength conversion layer of the present invention comprises the steps of preparing an ink composition containing a perovskite-type nanocrystal, a polymerizable compound, a solvent, and an additive that coordinates to the perovskite-type nanocrystal, The process of applying the ink composition onto a substrate, The process includes a step of curing the coated ink composition, The step of preparing the ink composition is performed such that the cured ink composition exhibits a perovskite crystal structure having a composite layer structure in which a first layer containing cation A coordinated with a ligand and a second layer containing cation B and anion X are alternately laminated. The coating step is performed such that the cured ink composition has a first optical coupling portion that guides light from outside the layer into the layer and a second optical coupling portion that is disposed at a position different from the first optical coupling portion and guides light propagating in the layer to the outside of the layer.

Example

[0052] Hereinafter, the display element according to the embodiment of the present invention will be described in detail, but the present invention is not limited to the following examples. (Example 1) (Synthesis of CsPbBr3 perovskite-type nanocrystal plates) Step 1: 0.1 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 degassed with a vacuum pump for 3o minutes. Further, the liquid temperature was heated to 120 ° C under a dry nitrogen stream and held for 20 minutes, and then held at 90 ° C to obtain a precursor solution 1 of cation A. Separately, 〇.276 g of lead (II) bromide and 20 mL of 1-octadecene were placed in a flask, the liquid temperature was heated to 100 ° C, degassed with a vacuum pump for 1 hour, and further heated to 120 ° C and degassed with a vacuum pump for 1 hour. 2.4 mL of oleic acid and 1.2 mL of oleylamine were added, and further degassed with a vacuum pump for 30 minutes. Then, the liquid temperature was set to 90 ° C instead of the nitrogen flow to obtain a precursor solution 2 of cation B and halogen X. 3.2 mL of the precursor solution 1 of cation A was added to the precursor solution 2 of cation B and halogen X, and after 10 seconds, it was ice-cooled to obtain a reaction solution 1.

[0053] Step 2: To the reaction solution 1, 14 mL of methyl acetate was added and held at room temperature of 30 ° C in a dark environment for 10 days to obtain a reaction solution 2. Hereinafter, one day is assumed to be 24 hours.

[0054] 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.

[0055] Step 4: (Fabrication of display elements) The solvent was removed from the dispersion of the above-mentioned CsPbBr3 perovskite-type nanocrystalline plate by blowing a stream of dry nitrogen air onto it, and ink composition A was prepared to consist of 1 wt% CsPbBr3 nanocrystals, 94 wt% 3,3,5-trimethylcyclohexyl acrylate (TMCHA), and 5 wt% 1-hydroxycyclohexyl phenyl ketone (Omnirad 184, manufactured by IGM Resins).

[0056] Using the above ink composition A, a black bank measuring 80 μm x 80 μm x 10 μm in thickness was printed and embedded as a partition material using a material printer (Fujifilm Dimatix, DMP-2850). After standing for 1 hour, it was cured by UV irradiation in a nitrogen atmosphere to create a wavelength conversion layer that emits green light.

[0057] (Example 2) The wavelength conversion layer was fabricated in the same manner as in Example 1, except that in Step 2, instead of holding the material in a dark environment at room temperature of 30°C for 10 days, it was held in a dark environment at room temperature of 25°C for 10 days.

[0058] (Example 3) The wavelength conversion layer was fabricated in the same manner as in Example 1, except that in Step 2, instead of holding the material in a dark environment at room temperature of 30°C for 10 days, it was held in a dark environment at room temperature of 25°C for 1 day.

[0059] (Example 4) The wavelength conversion layer was fabricated in the same manner as in Example 1, except that IBXA was used instead of TMCHA in step 4.

[0060] (Example 5) The wavelength conversion layer was fabricated in the same manner as in Example 1, except that TBA was used instead of TMCHA in step 4.

[0061] (Example 6) The wavelength conversion layer was prepared in the same manner as in Example 1, except that in step 4, instead of letting it stand for 1 hour after printing, it was allowed to stand for 30 minutes after printing, and then cured by UV irradiation under a nitrogen atmosphere.

[0062] (Example 7) The wavelength conversion layer was prepared in the same manner as in Example 1, except that in step 4, instead of letting it stand for 1 hour after printing, it was allowed to stand for 10 minutes after printing, and then cured by UV irradiation under a nitrogen atmosphere.

[0063] (Example 8) A wavelength conversion layer was prepared in the same manner as in Example 1, except that ink composition A', which had the same amount of hexane added as ink composition A in step 4, was allowed to stand until the hexane dried, and then cured by UV irradiation under a nitrogen atmosphere.

[0064] (Example 9) The wavelength conversion layer was fabricated in the same manner as in Example 1, except that in step 4, instead of using a black bank measuring 80 μm in length, 80 μm in width, and 10 μm in thickness as a partition wall, a black bank with a curved optical element provided at the bottom of the partition wall was used.

[0065] (Example 10) The wavelength conversion layer was prepared in the same manner as in Example 1, except that 0.350 g of lead(II) iodide was used instead of 0.276 g of lead(II) bromide in Step 1.

[0066] (Comparative Example 1) The display element was fabricated in the same manner as in Example 1, except that 2.4 mL of oleic acid and 2.4 mL of oleylamine were used instead of 2.4 mL of oleic acid and 1.2 mL of oleylamine in Step 1, and the liquid temperature was changed from 90°C to 185°C. In this case, instead of a nanocrystalline plate, granular CsPbBr3 quantum dots with a diameter of approximately 12 nm were formed.

[0067] (Comparative Example 2) The display element was fabricated in the same manner as in Example 1, except that in Step 1, 0.350 g of lead(II) iodide was used instead of 0.276 g of lead(II) bromide, 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, and the liquid temperature was set to 185°C instead of 90°C. In this case, instead of a nanocrystalline plate, granular CsPbI3 quantum dots with a diameter of approximately 12 nm were formed.

[0068] (Comparative Example 3) The display element was fabricated in the same manner as in Example 1, except that in step 4, instead of allowing it to stand for 1 hour after printing, it was cured immediately after printing by UV irradiation in a nitrogen atmosphere. In this case, a wavelength conversion layer containing nanocrystalline plates with a small degree of orientation and oriented in random directions was formed.

[0069] <Evaluation of Perovskite Nanocrystalline Plates> The perovskite-type nanocrystalline plate was evaluated by applying the perovskite-type nanocrystalline plate dispersion obtained in step 3 onto a glass substrate and drying the sample. XRD measurements were taken, and structural parameters were calculated from the superlattice peaks using the analysis method described in the aforementioned non-patent document Phys.Rev.B1992,45,9292-9310, thereby evaluating the number of layers n of the nanocrystalline plate.

[0070] The degree of orientation was determined by continuously surface-finishing the conversion layer of the display element fabricated in step 4 using FIB, performing a slice-and-view process to identify the three-dimensional arrangement of individual nanocrystal plates, and then calculating the degree of orientation. By performing TEM observation, we evaluated the average plate length y (representative plate length y), which is a representative value of the plate length when considered as a rectangular prism.

[0071] <Brightness Evaluation> Ultraviolet light with a peak emission wavelength of 400 nm was irradiated from the back of the display element as excitation light. An integrating sphere was placed directly above the wavelength conversion layer, and the integral values ​​of the emission spectra at 460 nm ± 30 nm for blue, 530 nm ± 30 nm for green, and 630 nm ± 30 nm for red were measured as luminance using a multi-channel spectrometer C10027-01 (Hamamatsu Photonics). Examples 1-9 and Comparative Example 3 emitted blue light, Example 10 emitted red light, and Comparative Examples 1-2 emitted green light.

[0072] [Table 1]

[0073] Table 1 shows the aspect ratio AR of the average plate length y and layer thickness z of a nanocrystalline plate. y / z It can be seen that brightness can be improved by increasing the dielectric constant of the medium (polymerizable compound) surrounding the nanocrystalline plate and the degree of orientation of the nanocrystalline plate. Therefore, the present invention provides a wavelength conversion layer with improved extraction efficiency, and a display element and display device using the wavelength conversion layer.

[0074] This embodiment includes the following configurations and methods. [Configuration 1] A nanocrystalline plate exhibiting a perovskite-type crystal structure having a composite layer structure in which a first layer containing ligand-coordinated cation A and a second layer containing cation B and anion X are alternately stacked, A medium that supports the nanocrystalline plate and propagates light from the nanocrystalline plate, It has a first optical coupling portion that guides light from outside the layer into the layer, and a second optical coupling portion that is positioned differently from the first optical coupling portion and guides light propagating within the layer to the outside of the layer, The composite layer structure exhibits an average number of layers between 3 and 5, and the nanocrystalline plate is a wavelength conversion layer oriented such that the normal of the plate intersects with the second photocoupler. [Configuration 2] The main surface of the plate corresponds to either the first or second largest surface in terms of area when the nanocrystalline plate is viewed with a rectangular parallelepiped as the basic structure, The nanocrystalline plate, when viewed with a rectangular parallelepiped as the reference structure, has a layer thickness z in the direction along the normal, and a representative plate length y which is the summation average of the two representative plate lengths of the two sides intersecting the layer thickness direction, and an aspect ratio AR obtained by dividing the average plate length y by the layer thickness z. y / z The wavelength conversion layer described in Configuration 1 is between 2.0 and 10. [Configuration 3] The medium is a wavelength conversion layer according to configuration 1 or 2, having a relative permittivity of 2.0 or more and 2.2 or less. [Structure 4] The medium is a wavelength conversion layer according to configuration 1 or 2, which includes a cured product obtained by polymerizing a polymerizable compound. [Composition 5] The wavelength conversion layer according to configuration 1 or 2, wherein the second optical coupling portion has an exit plane normal, the normal of the nanocrystalline plate is within 10 degrees of the exit plane normal, and the proportion of the nanocrystalline plate to the total nanocrystalline plate is 20% or more. [Composition 6] A wavelength conversion layer as described in configuration 1 or 2, A light source that is optically coupled to the first optical coupling unit, A display element with a rounded shape. [Composition 7] The display element according to configuration 6, wherein the wavelength conversion layer converts the light guided from the light source through the first optical coupling portion to the longer wavelength side. [Structure 8] The display element according to configuration 7, further comprising a drive circuit for controlling the emission of light from the aforementioned light source. [Method 1] A step of preparing an ink composition comprising a perovskite-type nanocrystal, a polymerizable compound, a solvent, and an additive that coordinates to the perovskite-type nanocrystal, The process of applying the ink composition onto a substrate, The process includes a step of curing the coated ink composition, The process of preparing the ink composition is carried out such that the cured ink composition exhibits a perovskite-type crystalline structure having a composite layer structure in which a first layer containing ligand-coordinated cation A and a second layer containing cation B and anion X are alternately stacked. A method for manufacturing a wavelength conversion layer, characterized in that the coating step is performed such that the cured ink composition has a first photo-coating portion that guides light from outside the layer into the layer, and a second photo-coating portion that is positioned differently from the first photo-coating portion and guides light propagating within the layer to the outside of the layer. [Explanation of Symbols]

[0075] 10 display elements 11 Green subpixel region 12 Red subpixel region 13 Blue subpixel region 14 Light source 15 Wavelength conversion layer (green) 15-M medium 16. Wavelength conversion layer (red) 17 Wavelength conversion layer (blue) 18 Bulkhead 19 Nanocrystalline Plates 19-1 First Layer 19-2 Second Layer 19-C Composite layer structure 20-1 First coupling part (optical component) 20-2 Second coupling part (optical component) 21 Main surface of plate 22 Normal vector

Claims

1. A nanocrystalline plate exhibiting a perovskite-type crystalline structure having a composite layer structure in which a first layer containing ligand-coordinated cation A and a second layer containing cation B and anion X are alternately stacked, A medium that supports the nanocrystalline plate and propagates light from the nanocrystalline plate, It has a first optical coupling portion that guides light from outside the layer into the layer, and a second optical coupling portion that is positioned differently from the first optical coupling portion and guides light propagating within the layer to the outside of the layer, The composite layer structure exhibits an average number of layers between 3 and 5, and the nanocrystalline plate is a wavelength conversion layer in which the normal to the main surface of the plate intersects with the second photo-coupled portion.

2. The main surface of the plate corresponds to either the first or second largest surface in terms of area when the nanocrystalline plate is viewed with a rectangular parallelepiped as the basic structure, The nanocrystalline plate, when viewed with a rectangular parallelepiped as the reference structure, has a layer thickness z in the direction along the normal, and a representative plate length y which is the summation average of the two representative plate lengths of the two sides intersecting the layer thickness direction, and the aspect ratio AR obtained by dividing the average plate length y by the layer thickness z. ｙ／ｚ The wavelength conversion layer according to claim 1, wherein the value is 2.0 or more and 10 or less.

3. The wavelength conversion layer according to claim 1 or 2, wherein the medium has a relative permittivity of 2.0 or more and 2.2 or less.

4. The wavelength conversion layer according to claim 1 or 2, wherein the medium comprises a cured product obtained by polymerization of a polymerizable compound.

5. The wavelength conversion layer according to claim 1 or 2, wherein the second optical coupling portion has an exit plane normal, and the normal of the nanocrystalline plate is within 10 degrees of the exit plane normal, and the proportion of the nanocrystalline plate to the total nanocrystalline plate is 20% or more.

6. A wavelength conversion layer according to claim 1 or 2, A light source that is optically coupled to the first optical coupling unit, A display element with a rounded shape.

7. The display element according to claim 6, wherein the wavelength conversion layer converts the light guided from the light source through the first optical coupling portion to a longer wavelength.

8. The display element according to claim 7, further comprising a drive circuit for controlling the emission of light from the aforementioned light source.

9. A step of preparing an ink composition comprising a perovskite-type nanocrystal, a polymerizable compound, a solvent, and an additive that coordinates to the perovskite-type nanocrystal, The process of applying the ink composition onto a substrate, The process includes a step of curing the coated ink composition, The process of preparing the ink composition is carried out such that the cured ink composition exhibits a perovskite-type crystalline structure having a composite layer structure in which a first layer containing ligand-coordinated cation A and a second layer containing cation B and anion X are alternately stacked. A method for manufacturing a wavelength conversion layer, characterized in that the coating step is performed such that the cured ink composition has a first photo-coating portion that guides light from outside the layer into the layer, and a second photo-coating portion that is positioned differently from the first photo-coating portion and guides light propagating within the layer to the outside of the layer.

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