Quantum dot layer, light-emitting element, display device, and method for manufacturing light-emitting element

Abstract

A quantum dot layer (Em) according to the present disclosure comprises: a first quantum dot (QD1) and a second quantum dot (QD2), which are composed of an equivalent crystal plane and have a region having a first lattice constant accounting for 80% or more of the surface; and a matrix material (Mx) filled between the first quantum dots (QD1) and the second quantum dots (QD2) and having a second lattice constant that is 95-105% of the first lattice constant.

Description

Technical Field

[0001] The present disclosure relates to a quantum dot layer, a light-emitting element, a display device, and a method for manufacturing a light-emitting element. Background Art

[0002] Patent Document 1 discloses a light-emitting device in which a perovskite crystal is encapsulated by an insulating layer. Prior Art Documents Patent Documents

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 2018-525776 (published on September 6, 2018) Summary of the Invention Technical Problem to be Solved by the Invention

[0004] In a light-emitting element including quantum dots, there is a problem that dangling bonds (unbonded bonds) generated around the quantum dots reduce the light-emitting efficiency. Solution to the Problem

[0005] According to one aspect of the present disclosure, a quantum dot layer includes: a first quantum dot and a second quantum dot, a region composed of one equivalent crystal plane and having a first lattice constant occupies more than 80% of the surface; and a matrix material that fills between the first quantum dot and the second quantum dot and has a second lattice constant of 95% to 105% of the first lattice constant.

[0006] According to one aspect of the present disclosure, a quantum dot layer includes: a first quantum dot and a second quantum dot, a region composed of one equivalent crystal plane occupies more than 80% of the surface; and a matrix material that fills between the first quantum dot and the second quantum dot and is lattice-matched at the interface with the region.

[0007] According to one aspect of the present disclosure, a method for manufacturing a light-emitting element includes: a step of coating a quantum dot solution on a base layer, the quantum dot solution containing quantum dots in which a region composed of one equivalent crystal plane and having a first lattice constant occupies more than 80% of the surface, a precursor, and a solvent; and a step of epitaxially growing a matrix material having a second lattice constant of 95% to 105% of the first lattice constant on the region by denaturing the precursor. Advantageous Effects of the Invention

[0008] According to one aspect of the present disclosure, the light-emitting efficiency can be improved. Brief Description of the Drawings

[0009] Figure 1 It is a cross-sectional view showing a structural example of a light-emitting element according to an embodiment of the present disclosure. Figure 2 It shows Figure 1Schematic diagram of an example of the region between the quantum dots shown. Figure 3 is a diagram showing Figure 1 Schematic diagram of another example of the region between the quantum dots shown. Figure 4 is a diagram showing an example of the appearance of a quantum dot having a zinc blende crystal structure and with (100) equivalent planes accounting for more than 80% of the surface. Figure 5 is a diagram showing an example of the appearance of a quantum dot having a zinc blende crystal structure and with (111) equivalent planes accounting for more than 80% of the surface. Figure 6 is a diagram showing an example of the appearance of a quantum dot having a zinc blende crystal structure and with (110) equivalent planes accounting for more than 80% of the surface. Figure 7 is a diagram showing an example of the appearance of a quantum dot having a wurtzite crystal structure and with (11-20) equivalent planes accounting for more than 80% of the surface. Figure 8 is a diagram showing Figure 1 Cross-sectional view of a constitutional example of the quantum dot layer shown. Figure 9 is a diagram showing Figure 1 Cross-sectional view of another constitutional example of the quantum dot layer shown. Figure 10 is a diagram showing Figure 1 Cross-sectional view of another structural example of the quantum dot layer shown. Figure 11 is a diagram showing Figure 1 Cross-sectional view of another constitutional example of the quantum dot layer shown. Figure 12 is a diagram showing the production of the coating liquid related to Example 1. Figure 13 is a diagram showing the production of the light-emitting element related to Example 1. Figure 14 is a top view showing a constitutional example of the display device related to one embodiment of the present disclosure. Detailed implementation mode

[0010] 〔Embodiment 1〕 (Constitution of the light-emitting element) Figure 1 is a cross-sectional view showing a structural example of the light-emitting element related to one embodiment of the present disclosure. As Figure 1As shown, the light-emitting element 3 includes a first electrode E1 and a second electrode E2 facing each other, and a quantum dot layer Em located between the first electrode E1 and the second electrode E2. The quantum dot layer Em can be an electroluminescent light-emitting layer. The light-emitting element 3 may include one or both of a charge function layer F1 located between the first electrode E1 and the quantum dot layer Em and a charge function layer F2 located between the second electrode E2 and the quantum dot layer Em.

[0011] The quantum dot layer Em includes: a plurality of quantum dots QD, which include a first quantum dot QD1 and a second quantum dot QD2; and a matrix material Mx, which is filled between the first quantum dot QD1 and the second quantum dot QD2. A region k composed of an equivalent crystal plane and having a first lattice constant occupies more than 80% of the respective surfaces of the first quantum dot QD1 and the second quantum dot QD2. The matrix material Mx has a second lattice constant, and the second lattice constant is 95% to 105% of the first lattice constant.

[0012] In addition, "an equivalent crystal plane" is the same in the first quantum dot QD1 and the second quantum dot QD2. Hereinafter, the "region k composed of an equivalent crystal plane and having a first lattice constant" will be referred to as the "equivalent region k". Figure 1 and as described later Figures 2 to 12 The shape of the quantum dot QD is not limited. The three-dimensional shape of the quantum dot QD can be any shape, for example, it can also be a substantially spherical shape, a substantially rotational ellipsoid shape, a substantially cylindrical shape, a substantially prismatic shape, or a substantially polyhedral shape. The cross-sectional shape of the quantum dot QD can be any shape, for example, it can also be a substantially circular shape, a substantially elliptical shape, a substantially triangular shape, a substantially rectangular shape, a substantially hexagonal shape, or a substantially octagonal shape.

[0013] At least one of the first electrode E1 and the second electrode E2 is a transparent electrode. One of the first electrode E1 and the second electrode E2 is an anode, and the other is a cathode. The charge function layers F1 and F2 may each include any one or more of a charge injection layer, a charge transport layer, and a charge shielding layer.

[0014] The matrix material Mx refers to a component that contains and holds other objects. In other words, it can be said to be a base material, a mother material, or a filling material. The matrix material Mx can be a solid at normal temperature. The matrix material Mx can be a component that contains and holds the first quantum dot QD1 and the second quantum dot QD2. The matrix material Mx can be a constituent element of the quantum dot layer Em that contains the first quantum dot QD1 and the second quantum dot QD2.

[0015] Figure 2 and Figure 3 respectively show Figure 1 As shown, it is a schematic diagram showing an example of the region between the quantum dots. The matrix material Mx can be filled in the quantum dot layer Em. As Figure 1As shown, the matrix material Mx can fill the region L (space) between the first and second quantum dots QD1 and QD2. As Figure 2 and Figure 3 shown, the region L is a region surrounded in a cross-sectional view by two straight lines (common external tangents) circumscribing the outer perimeters of the first and second quantum dots QD1 and QD2 and the outer perimeter (opposing outer perimeter) on the side where the first and second quantum dots QD1 and QD2 face each other. As Figure 3 shown, even if the first quantum dot QD1 approaches the second quantum dot QD2, the region L may exist.

[0016] The matrix material Mx can also fill the region (space) in the quantum dot layer Em other than the quantum dot group including the first and second quantum dots QD1 and QD2. In addition, three or more quantum dots are collectively referred to as a quantum dot group. The matrix material Mx can also fill the region (space) in the quantum dot layer Em other than the quantum dot group including the first and second quantum dots QD1 and QD2. The first and second quantum dots QD1 and QD2 can be buried in the matrix material Mx with a gap therebetween.

[0017] The outer edges (upper and lower surfaces) of the quantum dot layer Em can be covered by the matrix material Mx. Alternatively, it can be configured such that a part of the matrix material Mx extends from the outer edge of the quantum dot layer Em and the quantum dots QD are located at positions away from the outer edge. The outer edge of the quantum dot layer Em may not be formed only by the matrix material Mx, and a part of the quantum dot group may protrude from the matrix material Mx. The matrix material Mx can also represent the part in the quantum dot layer Em other than the quantum dot group including the first and second quantum dots QD1 and QD2.

[0018] The matrix material Mx can contain the first and second quantum dots QD1 and QD2. The matrix material Mx can contain the quantum dot group including the first and second quantum dots QD1 and QD2. The matrix material Mx can be formed to fill the space formed between the first and second quantum dots QD1 and QD2. The matrix material Mx can partially or completely fill between the quantum dot groups.

[0019] The matrix material Mx can include a continuous film having an area of 1000 nm 2 or more along a plane direction orthogonal to the layer thickness direction of the quantum dot layer Em. The continuous film means a film that is not interrupted by materials other than the material constituting the continuous film in one plane. The continuous film can also be an integral film-like structure that is continuously connected by chemical bonds of the material constituting the matrix material Mx.

[0020] The matrix material Mx can be the same material as the shell of the first quantum dot QD1. In this case, the average distance between adjacent nuclei (inter-nuclear distance) can be 3 nm or more, or can be 5 nm or more. Alternatively, the average distance between the above-mentioned adjacent nuclei can be 0.5 times or more of the average nuclear diameter. The inter-nuclear distance is obtained by averaging the distances between adjacent cores in a space containing 20 nuclei. The inter-nuclear distance can be maintained wider than the distance when the shells are in contact with each other. The average nuclear diameter is obtained by averaging the nuclear diameters of 20 nuclei in a cross-sectional observation of a space containing 20 nuclei. The nuclear diameter can be the diameter of a circle with the same area as the nuclear area in cross-sectional observation.

[0021] The concentration of the matrix material Mx in the quantum dot layer Em is, for example, the area ratio occupied by the matrix material Mx in the cross-section of the quantum dot layer Em. Under cross-sectional observation, this concentration can be 10% or more and 90% or less, or can be 30% or more and 70% or less. This concentration can be measured, for example, according to the area ratio in image processing under cross-sectional observation. When the first quantum dot QD1 is a core-shell structure, the concentration of the shell can be 1% or more and 50% or less. In the case where the shell material and the matrix material are the same material (same composition) and the shell and the matrix material Mx cannot be distinguished, as the concentration of the region where the matrix material Mx and the shell are combined, it is only necessary to add the numerical range of the concentration of the shell to the numerical range of the concentration of the matrix material Mx. The ratios of the core and shell of the quantum dot QD and the matrix material Mx can be appropriately adjusted so that the total ratio is 100% or less. Thus, even in the case where the shell and the matrix material Mx cannot be distinguished, the shell can also be regarded as a part of the matrix material Mx.

[0022] The quantum dot layer Em can be composed of a quantum dot group including the first and second quantum dots QD1, QD2 and the matrix material Mx. When analyzing the quantum dot layer Em, the intensity of carbon detected by a chain structure can also be below the noise.

[0023] The constituent material of the matrix material Mx is an inorganic material, and it is desired that the band gap is wider than the constituent materials of the first and second quantum dots QD1, QD2. As the material for constituting the matrix material Mx, a semiconductor or an insulator can be used. As an example of the constituent material of the matrix material Mx, it includes metal sulfides and / or metal oxides. The metal sulfide can be, for example, zinc sulfide (ZnS), zinc magnesium sulfide (ZnMgS, ZnMgS 2 ), gallium sulfide (GaS, Ga 2 S 3 ), zinc tellurium sulfide (ZnTeS), magnesium sulfide (MgS), zinc gallium sulfide (ZnGa 2 S 4 ), magnesium gallium sulfide (MgGa 2 S 4)). The metal oxide may be zinc oxide (ZnO), titanium oxide (TiO 2 ), tin oxide (SnO 2 ), tungsten oxide (WO 3 ), zirconium oxide (ZrO 2 ). In addition, the chemical formula described in parentheses after the compound name is a representative example. Also, the composition ratio described in the chemical formula is preferably the stoichiometry as shown in the chemical formula of the actual compound, but it does not necessarily have to be stoichiometry.

[0024] Regarding the structure of the matrix material Mx, it is sufficient to observe it with a width of about 100 nm in the cross-section observation of the quantum dot layer Em and know that it is the above-mentioned structure, without observing the above-mentioned structure throughout the quantum dot layer Em. The matrix material Mx may contain, for example, a substance different from the main material (e.g., an inorganic substance such as an inorganic semiconductor) as an additive.

[0025] In the quantum dot layer where the surface of the quantum dot is protected by the organic ligand, there are many voids in the quantum dot layer. Therefore, when the organic ligand loses its binding to the quantum dot, it is easy to move, and the probability of not binding again is high. In addition, the organic ligand itself is easily deteriorated or decomposed by light, heat, and current injection. Therefore, the light-emitting layer that protects the surface of the quantum dot with the organic ligand has problems in terms of durability and reliability. In contrast, in the quantum dot layer Em according to the present disclosure, the matrix material Mx protects the surface of the quantum dot QD, and has excellent durability and reliability. This is because the matrix material Mx is formed as a dense continuous film without voids. Due to its density, even if the binding to the quantum dot QD is lost, the constituent elements of the matrix material Mx are difficult to move, and the probability of recombination is high. In addition, since the matrix material Mx is composed of an inorganic material. Compared with organic materials, inorganic materials are not easily deteriorated.

[0026] Moreover, through the matrix material Mx, the resistance to exposure to oxygen and water possessed by the quantum dot layer, and the resistance to coating liquids and developing liquids, etc. in the process of forming and patterning the layer above the quantum dot layer can be improved.

[0027] The matrix material Mx has a second lattice constant that is the same as or close to the first lattice constant. Therefore, the matrix material Mx is lattice-matched with the first quantum dot QD1 and the second quantum dot QD2 at the interface with the equivalent region k. As described above, the second lattice constant may be 95% to 105% of the first lattice constant, more preferably 98% to 102% of the first lattice constant. The band gap of the matrix material Mx is preferably greater than the band gap of the core of the first quantum dot QD1. The band gap of the matrix material Mx is preferably greater than the band gap of the core of the second quantum dot QD2.

[0028] One of the equivalent crystal planes constituting the equivalent region k is preferably a polar plane. A polar plane refers to a crystal plane where there is a deviation in the valence of the cations and anions exposed on the surface. Specifically, a polar plane refers to a crystal plane where the valence of the exposed cations is different from that of the anions, and it is a plane that can carry a positive charge and strongly attract anions, or a plane that can carry a negative charge and strongly attract cations. In contrast, a non-polar plane refers to a crystal plane where the valence of the exposed cations and anions is balanced. Therefore, compared with the case where the equivalent region k is composed of non-polar planes, when it is composed of polar planes, the constituent elements of the matrix material Mx are strongly attracted to the equivalent region k. The more the constituent elements of the matrix material Mx are attracted to the equivalent region k, the easier it is for the matrix material Mx to grow crystals, making the crystal lattice of the matrix material Mx match the crystal lattice of the equivalent region k. At least a part of the matrix material Mx can use the equivalent region k as the starting point for crystal growth and epitaxially grow on the equivalent region k.

[0029] The first quantum dot QD1 can be a core-shell structure, a shell-less structure, or a multi-shell structure. In the cross-sectional view of the core of the first quantum dot QD1, the boundary surface between the core or shell of the first quantum dot QD1 and the material occupying the outside of the first quantum dot QD1 can be regarded as the surface of the first quantum dot QD1. For example, in the case where the first quantum dot QD1 has a core-shell structure in which the shell is partially formed on the surface of the core, the surface of the first quantum dot QD1 can include the boundary between the core and the material and the boundary between the shell and the material. In this case, it is possible that only the boundary surface between the core and the material appears in the cross-section, only the boundary surface between the shell and the material appears in the cross-section, or both appear in the cross-section. For example, in the case where the first quantum dot QD1 has a core-shell structure in which the shell completely covers the core, the surface of the first quantum dot QD1 can only include the boundary between the shell and the material. For example, in the case where the first quantum dot QD1 has a shell-less structure, the surface of the first quantum dot QD1 can only include the boundary surface between the core and the material. The material occupying the outside of the first quantum dot QD1 includes the matrix material Mx. The material occupying the outside of the first quantum dot QD1 can also include the material constituting any one of the charge functional layers F1, F2, the first electrode E1, and the second electrode E2. Similarly to the first quantum dot QD1, the second quantum dot QD2 can also be a core-shell structure, a shell-less structure, or a multi-shell structure.

[0030] The crystal structure of the core and the crystal structure of the shell can be the same as or different from each other. It is known that in the case of stacking multiple layers, if a certain layer is thin (typically less than 3 atomic layers), the crystal structure of this layer usually follows the crystal structure of the lower layer of this layer. On the other hand, it is known that if a certain layer is thick, the crystal structure of this layer usually follows one of the crystal structures that can be spontaneously obtained by the material forming this layer in the bulk.

[0031] The crystal plane of the first quantum dot QD1 can be determined by the following method. By observing the first quantum dot QD1 using an X-ray diffraction (XRD) measurement device, an energy dispersive X-ray spectroscopy (EDS) measurement device, an X-ray photoelectron spectroscopy (XPS) measurement device, an electron energy loss spectroscopy (EELS) measurement device, a transmission electron microscopy (TEM), etc., the constituent elements and crystal planes of the first quantum dot QD1 can be analyzed.

[0032] The crystal structure of the first quantum dot QD1 can be measured by TEM and the electron diffraction pattern using TEM. Based on the atomic arrangement and diffraction pattern observed by high-resolution TEM, the crystal structure can be identified. The composition analysis of the first quantum dot QD1 can be discriminated by EDS or EELS attached to TEM. This is because the peaks unique to the constituent elements of the first quantum dot QD1 appear in the spectroscopic results at intensity ratios corresponding to the composition ratios.

[0033] Therefore, the composition and the interplanar spacing of each crystal plane of the first quantum dot QD1 can be determined. Then, by comparing specific values with the interplanar spacing obtained from TEM observation, the Miller indices, lattice constants, and area ratios of the regions occupying the surface of the first quantum dot QD1 can be calculated.

[0034] The second quantum dot QD2 and the matrix material Mx can also be analyzed by the same method as the first quantum dot QD1. Additionally, the first quantum dot QD1, the second quantum dot QD2, and the matrix material Mx can be analyzed by other methods.

[0035] Generally, the composition of the quantum dot layer Em is random and uniform regardless of position. More specifically, with respect to the composition, shape, crystal structure, Miller indices, and the ratio of the surface occupied by the equivalent region k of the quantum dot QD, and the composition and crystal structure of the matrix material Mx, the quantum dot layer Em is uniform and independent of position. Therefore, the analysis results for a part of the quantum dot layer Em can be applied to the entire quantum dot layer Em.

[0036] Generally, when analyzing the first quantum dot QD1 in the matrix material Mx, even when a quantum dot QD in which the equivalent region k occupies approximately 100% of the surface is used, there is a tendency for the calculated value of the area ratio occupied by the equivalent region K to be greater than 80% and less than 100% due to the analysis accuracy, measurement limit, and blurring caused by the presence of the matrix material Mx. Therefore, if the calculated area ratio of the equivalent region k is greater than 80%, it is considered that there is a high possibility that the equivalent region k occupies approximately 100% of the surface of the first quantum dot QD1. In addition, if the calculated area ratio of the equivalent region k is greater than 60%, it is considered that there is a high possibility that the equivalent region k occupies 80% of the surface of the first quantum dot QD1.

[0037] (Miller Index) In this disclosure, Miller indices are used to identify crystal planes. That is, for crystals other than the hexagonal system, the unit lattice vector a is used. 1 、a 2 、a 3 and integers h, k, l, will be passed through the vector a by 1 / h* 1 , 1 / k*vector a 2 , 1 / l×vector a 3 The crystal plane with three specified points is called (hkl) plane. 4 :=-a 1 -a 2 The unit lattice vector a is defined 4 And the integer i defined by i:=-hk, and the crystal plane passing through the above three points is called the (hkil) plane.

[0038] In this specification, for crystals other than the hexagonal system, the (hkl) plane and the plane equivalent to the (hkl) plane are collectively referred to as the (hkl) equivalent plane. In addition, for crystals of the hexagonal system, the (hkil) plane and the plane equivalent to the (hkil) plane are collectively referred to as the (hkil) equivalent plane.

[0039] (Combination of quantum dots and base materials 1) Figure 4 : is a diagram showing an example of the appearance of a quantum dot having a zinc-blende crystal structure and having a (100) equivalent plane occupying 80% or more of the surface. Figure 4 As shown, the quantum dot QD with a zinc blende-type crystal structure includes a (100) plane, a (-100) plane, a (010) plane, a (0-10) plane, a (001) plane, and a (00-1) plane, and these six planes are equivalent to each other. In the present disclosure, these six planes are referred to as (100) equivalent planes. In the zinc blende-type crystal structure, the (100) equivalent plane is a polar plane. The typical shape of a quantum dot QD with a zinc blende-type crystal structure in which the (100) equivalent plane occupies 100% of the surface is a rectangular parallelepiped.

[0040] As an example, ZnS having a zinc blende crystal structure is included in the equivalent region k, and the equivalent crystal plane constituting the equivalent region k may be a (100) equivalent plane. In this example, the matrix material Mx may include ZnS, Y 2 O 3 , Si, Zn 3 P 2 , GaAs, GaP, SiC, Cu 2 ZnSnS 4 , CuInS 2 , GaN and ZnMgSe or more than one of them. The matrix material may include a mixed crystal containing two or more of them.

[0041] As another example, ZnSe having a zinc blende crystal structure is included in the equivalent region k, and the equivalent crystal plane constituting the equivalent region k may be a (100) equivalent plane. In this example, the matrix material Mx may include ZnSe, GaAs and Al 2 O 3 or more than one of them. The matrix material may include a mixed crystal containing two or more of them.

[0042] (Quantum dot and base material combination 2) Figure 5 is a diagram showing an external appearance example of a quantum dot having a zinc blende crystal structure and having a (111) equivalent plane occupying 80% or more of the surface. As Figure 5 shown, the zinc blende crystal structure quantum dot QD includes (111) plane, (-111) plane, (1-11) plane, (-1-11) plane, (11-1) plane, (-11-1) plane, (1-1-1) plane and (-1-1-1) plane, and these 8 planes are equivalent to each other. In the present disclosure, these 8 planes are referred to as (111) equivalent planes. In the zinc blende crystal structure, the (111) equivalent plane is a polar plane. Typical shapes of quantum dots QD having a zinc blende crystal structure with a (111) equivalent plane occupying 100% of the surface are octahedron and tetrahedron.

[0043] As an example, ZnS having a zinc blende crystal structure is included in the equivalent region k, and the equivalent crystal plane constituting the equivalent region k may be a (111) equivalent plane. In this example, the matrix material Mx may include Si, SiC and CeO 2 or more than one of them. The matrix material may include a mixed crystal containing two or more of them.

[0044] (Quantum dot and base material combination 3) Figure 6 is a diagram showing an external appearance example of a quantum dot having a zinc blende crystal structure and having a (110) equivalent plane occupying 80% or more of the surface. As Figure 6As shown, the quantum dot QD with a zinc blende crystal structure includes (110) plane, (011) plane, (101) plane, (1-10) plane, (01-1) plane, (-101) plane, (-110) plane, (0-11) plane, (10-1) plane, (-1-10) plane, (0-1-1) plane, (-10-1) plane, and these 12 planes are equivalent to each other. In the present disclosure, these 12 planes are referred to as (110) equivalent planes. In the zinc blende crystal structure, the (110) equivalent plane is a non-polar plane. The typical shape of the quantum dot QD with a zinc blende crystal structure having 100% (110) equivalent planes on the surface is a dodecahedron.

[0045] As an example, the equivalent region k contains ZnS with a zinc blende crystal structure, and the equivalent crystal planes constituting the equivalent region k can be (110) equivalent planes. In this example, the matrix material Mx can include one or more of Si and CeO2. The matrix material can include a mixed crystal containing both of them.

[0046] (Quantum dot and base material combination 4) The appearance of the quantum dot QD having a sodium chloride crystal structure and with more than 80% (111) equivalent planes on the surface is the same as that of the quantum dot having a zinc blende crystal structure and with more than 80% (111) equivalent planes on the surface. Refer to Figure 5 and the quantum dot QD having a sodium chloride crystal structure includes (111) equivalent planes. In the sodium chloride crystal structure, the (111) equivalent plane is a polar plane.

[0047] As an example, the equivalent region k contains PdS with a sodium chloride crystal structure, and the equivalent crystal planes constituting the equivalent region k can be (111) equivalent planes. In this example, the matrix material Mx can include one or more of InP and CsPdBr 3 and the matrix material can include a mixed crystal containing both of them.

[0048] (Quantum dot and base material combination 5) Figure 7 is a diagram showing an example of the appearance of a quantum dot having a wurtzite crystal structure and with more than 80% (11-20) equivalent planes on the surface. As Figure 7 shown, the quantum dot QD with a wurtzite crystal structure includes (11-20) plane, (-1-120) plane, (1-210) plane, (-12-10) plane, (2-1-10) plane, and (-210) plane, and these 6 planes are equivalent to each other. In the present disclosure, these 6 planes are referred to as (11-20) equivalent planes. In the wurtzite crystal structure, the (11-20) equivalent plane is a polar plane. The typical shape of the quantum dot QD with a wurtzite crystal structure having more than 80% (11-20) equivalent planes on the surface is a hexagonal prism.

[0049] As an example, the equivalent region k contains ZnS having a wurtzite-type crystal structure, and the equivalent crystal plane constituting the equivalent region k may be a (11-20) equivalent plane. In this example, the matrix material Mx may include one or more of ZnS, ZnO, ZnSe, and ZnTe. The matrix material may include a mixed crystal containing two or more of them.

[0050] (Constitution Example 1 of Quantum Dot Layer) Figure 8 shows Figure 1 a cross-sectional view of the structural example of the quantum dot layer shown, which is a partial enlarged cross-sectional view obtained by enlarging and showing the portion shown by the range A of Figure 1 . As shown in Figure 8 , the matrix material Mx may include a first single crystal portion CG1 and a second single crystal portion CG2. The first single crystal portion CG1 is a single crystal in contact with the first quantum dot QD1, and the second single crystal portion CG2 is a single crystal in contact with the second quantum dot QD2. The matrix material Mx protects the surfaces of the first quantum dot QD1 and the second quantum dot QD2. In addition, Figure 8 the shape of the quantum dot QD is not limited as described above. The cross-sectional shape of the quantum dot QD may be any shape, for example, it may also be a substantially circular shape, a substantially elliptical shape, a substantially triangular shape, a substantially rectangular shape, a substantially hexagonal shape, or a substantially octagonal shape. In addition, Figure 8 the shapes of the single crystal portions such as the first single crystal portion CG1 and the second single crystal portion CG2 are not limited.

[0051] The first single crystal portion CG1 is a single crystal epitaxially grown from the surface of the first quantum dot QD1 and is substantially lattice-matched with the first quantum dot QD1. Therefore, compared with a configuration in which the single crystal portion is not lattice-matched with the quantum dot lattice, according to the configuration of the present disclosure, there are fewer lattice defects or dangling bonds between the first quantum dot QD1 and the first single crystal portion CG1. The second single crystal portion CG2 is a single crystal epitaxially grown from the surface of the second quantum dot QD2. Therefore, similarly, there are few lattice defects between the second quantum dot QD2 and the second single crystal portion CG2. Since there are few lattice defects, non-radiative recombination of defect levels is reduced, and the light emission efficiency of the quantum dot layer Em is improved. In addition, since charge trapping due to lattice defects is reduced, the resistivity of the quantum dot layer Em is reduced, and the driving voltage and heat generation of the light emitting element 3 can be reduced. A mismatch plane B1 is generated between the first single crystal portion CG1 and the second single crystal portion CG2. In the mismatch plane B1, at least one of the lattice and the crystal orientation is mismatched, and there are many lattice defects or dangling bonds. Generally, the mismatch plane B1 is at a position far from the surface of the first quantum dot QD1 and has little influence on the excitons of the nucleus. Therefore, the defect levels of the mismatch plane B1 between the first single crystal portion CG1 and the second single crystal portion CG2 do not have a great adverse effect on the improvement of the light emission efficiency of the quantum dot layer Em. Therefore, the driving voltage and heat generation of the light emitting element 3 can be reduced.

[0052] (Constitution Example 2 of Quantum Dot Layer) Figure 9 It shows Figure 1 A cross-sectional view of another structural example of the quantum dot layer shown, which is a partial enlarged cross-sectional view obtained by enlarging and showing the portion shown by the range A in Figure 1 As shown in Figure 9 The matrix material Mx may include a third single crystal part CG3. The third single crystal part CG3 is in contact with the first quantum dot QD1. The third single crystal part CG3 is a single crystal epitaxially grown from the surface of the first quantum dot QD1 and is substantially lattice-matched with the first quantum dot QD1. The surface on which the third single crystal part CG3 grows is different from the surface on which the first single crystal part CG1 grows, and the third single crystal part CG3 and the first single crystal part CG1 are lattice mismatched. In addition Figure 9 The shape of the quantum dot QD is not limited as described above. The cross-sectional shape of the quantum dot QD can be any shape, for example, it can also be substantially circular, substantially elliptical, substantially triangular, substantially rectangular, substantially hexagonal, or substantially octagonal. In addition Figure 9 The shapes of the single crystal parts such as the first single crystal part CG1, the second single crystal part CG2, and the third single crystal part CG3 are not defined

[0053] When the crystal structure on the surface of the first quantum dot QD1 is different from the crystal structure of the matrix material Mx, even for a combination in which the matrix material Mx can be epitaxially grown, lattice matching does not hold at the corners of the first quantum dot QD1. And a mismatch plane B2 extending from the corners of the first quantum dot QD1 is generated. Generally, the corners of the first quantum dot QD1 are positions on the surface of the first quantum dot QD1 that are farthest from the core and have little influence on the excitons of the core. Therefore, the defect energy levels caused by the lattice mismatch of the mismatch plane B2 between the first single crystal part CG1 and the third single crystal part CG3 do not have much adverse effect on the improvement of the light emission efficiency of the quantum dot layer Em. Therefore, similar to the above Constitution Example 1, according to this Constitution Example, it is also possible to improve the light emission efficiency of the quantum dot layer Em, reduce the driving voltage and heat generation of the light emitting element 3

[0054] (Constitution Example 3 of Quantum Dot Layer) Figure 10 It shows Figure 1 A cross-sectional view of another structural example of the quantum dot layer shown, which is a partial enlarged cross-sectional view obtained by enlarging and showing the portion shown by the range A in Figure 1 As shown in Figure 10 The matrix material Mx may include a non-crystal Ap. At least a part of the non-crystal Ap is located between the first single crystal part CG1 and the second single crystal part CG2. In addition Figure 10The shape of the quantum dots QD as described above is not limited. The cross-sectional shape of the quantum dots QD can be any shape, for example, it can also be substantially circular, substantially elliptical, substantially triangular, substantially rectangular, substantially hexagonal, or substantially octagonal. In addition, Figure 10 The shapes of single crystal portions such as the first single crystal portion CG1 and the second single crystal portion CG2 are not limited.

[0055] The heat treatment for forming the matrix material Mx can also be adjusted in consideration of the thermal degradation of layers other than the quantum dots QD and the quantum dot layer Em. For example, the temperature of the heat treatment can be lowered, or the time of the heat treatment can be shortened. As a result, in the matrix material Mx, sometimes only the portion near the surface of the quantum dots QD grows epitaxially, and other portions become amorphous Ap. Even under heat treatment conditions where it is difficult for the matrix material Mx to grow crystals, it is considered that precursors are preferentially decomposed on the surface of the quantum dots QD where the matrix material Mx can grow epitaxially, and the matrix material Mx can grow epitaxially. The surface of the first quantum dot QD1 is protected by the first single crystal portion CG1, and the surface of the second quantum dot QD2 is protected by the second single crystal portion CG2. Therefore, similarly to the above-described Configuration Examples 1 and 2, according to this configuration example, the light emission efficiency of the quantum dot layer Em can also be improved, and the driving voltage and heat generation of the light emitting element 3 can be reduced.

[0056] As Figure 8 、 Figure 9 、 Figure 10 and Figure 11 As indicated by the dashed arrows in

[0057] When the light emitting element 3 emits light, there may sometimes be a leakage current that does not inject charges into the quantum dots QD but only passes through the matrix material Mx. This leakage current does not contribute to light emission. The density of lattice defects in the amorphous Ap is larger than the density of lattice defects in the single crystal portion of the matrix material. Due to charge trapping caused by lattice defects, the resistivity of the amorphous Ap is sometimes larger than the resistivity of the single crystal portion of the matrix material. Therefore, compared with the above-described Configuration Examples 1 and 2 and Configuration Example 4 described later, in this configuration example, the resistance value of the path through which the leakage current flows can be increased. By this increase in resistance, the leakage current can be reduced. In addition, since the temperature of the heat treatment is low or the time of the heat treatment is short, the thermal degradation of the quantum dots QD is small.

[0058] (Configuration Example 4 of Quantum Dot Layer) Figure 11 is a cross-sectional view showing another configuration example of the quantum dot layer shown in Figure 1 , and is a partial enlarged cross-sectional view showing an enlarged view of the portion shown by the range A in Figure 1 . As Figure 11As shown, the matrix material Mx may include a fourth single crystal part CG4. The fourth single crystal part CG4 is not in contact with any of the plurality of quantum dots QD, but is located between the first single crystal part CG1 and the second single crystal part CG2. The fourth single crystal part CG4 has a lattice mismatch with the first single crystal part CG1 and the second single crystal part CG2.

[0059] In addition, Figure 11 The shape of the quantum dots QD as described above is not limited. The cross-sectional shape of the quantum dots QD can be any shape, for example, it can also be substantially circular, substantially elliptical, substantially triangular, substantially rectangular, substantially hexagonal, substantially octagonal. In addition, Figure 11 The shape of the single crystal parts such as the first single crystal part CG1, the second single crystal part CG2, and the fourth single crystal part CG4 is not limited.

[0060] (Method for manufacturing quantum dots) As a method for manufacturing the quantum dots QD, for example, there are a heating method, a thermal injection method, a microwave-assisted method, and a continuous flow method. Each of these manufacturing methods will be described.

[0061] (Heating method) The heating method refers to a method of synthesizing each layer of the quantum dots QD by mixing materials in an organic solvent and heating to cause thermal decomposition of the materials and thus cause a reaction. In the heating method, TOP (trioctylphosphine) or TOP (trioctylphosphine oxide) is used as the organic solvent, dimethylcadmium is used as the Group II raw material, and a desired element such as S, Se, Te, etc., or an organometallic compound combined with methyl or ethyl, etc., is used as the Group VI raw material. The Group II and Group VI raw materials are mixed in the organic solvent and heated to about 300 °C to cause thermal decomposition of the raw materials, maintaining a high saturation of the Group II and Group VI elements in the organic solvent, promoting the reaction to a Group II-VI compound, and each layer of the quantum dots QD can be synthesized.

[0062] (Thermal injection) The thermal injection method refers to a method of rapidly injecting raw materials into a heated organic solvent and using the supersaturation near the injection region to generate uniform crystal growth nuclei at a high density. In the thermal injection method, the raw materials used are TOP or T-TOPO as the organic solvent, and by heating to about 300 °C, the Group II and Group VI raw materials are rapidly injected into the organic solvent, locally and sharply increasing the supersaturation with the injection region as the center, and generating uniform crystal growth nuclei at a high density. Since the high supersaturation is near the injection region, the raw materials consumed for the growth of the growth nuclei are continuously supplied by diffusion from the surrounding low supersaturation region through the concentration gradient, and the quantum dots continue to grow. In this method, since the nucleation is at a high density, alkylphosphines, alkylphosphine oxides such as trioctylphosphine or trioctylphosphine oxide, long-chain carboxylic acids such as oleic acid, and long-chain amines such as oleylamine are added as surfactants or ligands to prevent the aggregation of the quantum dots.

[0063] (Microwave-assisted method) The microwave-assisted method refers to: a method of selectively heating the growth raw materials by using microwaves. The heating of this method is selective, so the reaction can be well controlled, and the temperature can be raised to the required reaction temperature range in a short time. In addition, compared with the injection method, quantum dots can be synthesized simply and under atmospheric conditions. Since microwaves are selectively resonantly absorbed by polarized molecules, for example, if a chalcogenide suitable for the microwave wavelength is used as the raw material, the raw material can be selectively heated, and the growth of quantum dots can be controlled. According to this characteristic, the raw material needs to be polarized, and raw materials different from the above first and second methods are used. As an example of the raw material, a mixed solution of cadmium stearate, an alkane solvent, and a Group VI powder can be cited.

[0064] (Continuous flow method) The continuous flow method refers to: a method in which while flowing an organic solvent mixed with raw materials, the reaction of the raw materials is carried out, so that the nucleation reaction and the growth reaction occur in mutually different reactors. Since the nucleation reaction and the growth reaction occur in different reactors, an appropriate temperature gradient can be precisely set, and each reaction can be precisely controlled. This method is suitable for mass production in that the control of crystal growth is relatively easy. In the continuous flow method, as also described in the above three manufacturing methods, quantum dot type QD can be grown either in an organic solution or in a gas phase containing a vapor of an organic solution. In the continuous flow method, by mixing an organic solvent with Group II and Group VI raw materials, the raw materials are moved along the flow of the liquid phase or the gas phase, and a temperature gradient suitable for the nucleation stage and the crystal growth stage, which are the starting points for the growth of quantum dot QD, is set, so that the nucleation and growth reactions can be precisely controlled in different reactors. By separating nucleation and crystal growth into separate containers and transporting them through the flow of the liquid phase or the gas phase between the containers, the conditions suitable for each stage can be precisely and independently controlled.

[0065] In crystal growth, it is important to maintain a high saturation of the raw materials, which is the driving force for nucleation and crystal growth. Depending on the means of achieving and maintaining this condition, for example, the above 4 manufacturing methods have been developed.

[0066] To synthesize quantum dot QD, it is necessary to control the synthesis conditions when synthesizing each layer of quantum dot QD. As a method of selectively making a specific crystal plane appear, for example, in the process of synthesizing each layer, the pH (hydrogen ion concentration) of the solvent mixed with the material is controlled within a specific range. For example, through experiments, it has been obtained that: in order for the surface of quantum dot QD to have a zinc blende-type crystal structure and have a shape terminated only at the (111) equivalent plane and / or the (100) equivalent plane, which are polar planes, it is only necessary to maintain the pH of the solvent in the range of 9 to 11. At the pH within this range, since H+ The concentration ratio is higher than the neutral condition of pH = 7, so it is considered that H + The intermediate reaction with the raw material type is related to the mechanism of preferentially forming a specific crystal plane.

[0067] In addition, as another method, for example, when using group II-VI crystals such as ZnS and CdS, or using group III-V crystals such as InN and InP, the (111) equivalent plane appears by relatively reducing the group VI or group V raw materials. This is because, due to the reduction of the group V or group VI raw materials, the unbonded orbitals of the (111) equivalent plane with a high surface density of bonding orbitals relatively increase.

[0068] In addition, as another method, it is known that by adding an organic ligand that strongly binds to the crystal plane where appearance is desired to an organic solvent mixed with raw materials, the crystal plane where appearance is desired is stabilized, and crystal growth preferentially occurs on other crystal planes. As a result, the crystal plane where appearance is desired can account for more than 80% of the surface of the quantum dot QD. For example, when the surface of the quantum dot QD has a zinc blende crystal structure, by adding a neutral ligand that strongly binds to the non-polar plane, crystal growth preferentially occurs on the (111) equivalent plane and the (100) equivalent plane, which are polar planes, and the (110) equivalent plane, which is a non-polar plane, appears.

[0069] The binding between the surface of the growing quantum dot QD and the organic ligand is considered to be temporary. In the organic solvent, the ligand is in an equilibrium state of repeated detachment and binding. Therefore, by increasing the solution temperature, the detachment and binding rates increase, and the raw materials can easily access the entire surface of the quantum dot QD. As a result, atoms are preferentially deposited on the crystal plane with more dangling bonds and higher surface energy. For example, when synthesizing the CdS shell of the quantum dot QD at 275 degrees Celsius or higher, atoms are preferentially deposited on the (111) equivalent plane with a high dangling bond density, and the (100) equivalent plane appears on the surface of the quantum dot QD. Example 1

[0070] Figure 12 It is a diagram showing the manufacture of the coating liquid related to Example 1. As Figure 12As shown, the ligands bound to the quantum dots QD are replaced. Generally, when synthesizing the quantum dots QD, organic ligands bind to the quantum dots QD, and the quantum dots QD are dispersed in a non-polar solvent. The quantum dot dispersion contains 10 mg of quantum dots QD and 1 mL of hexane. The concentration of the quantum dots QD in the quantum dot dispersion is 10 mg / mL. The quantum dots QD contain ZnS with a zinc blende crystal structure in the equivalent region k, and the equivalent crystal plane constituting the equivalent region k is the (100) equivalent plane. The exchange solution is a solution formed by mixing 7.5 mL of ZnCl solution and 2.5 mL of EtXanK solution. The solvents of the two solutions are NMF. The concentration of the ZnCl solution is 0.2 M, i.e., 27.2 mg / mL. The concentration of the EtXanK solution is 0.2 M, i.e., 32 mg / mL. Here, "NMF" is the abbreviation of N-methylformaldehyde, "EtXanK" is the abbreviation of ethyl xanthate, and "M" is the abbreviation of mol / L.

[0071] The quantum dot dispersion and the exchange solution are placed in a container V. The two liquids do not mix, the quantum dot dispersion is in the upper layer L1, and the exchange solution is in the lower layer L2. The two solutions are continuously and strongly stirred overnight. As a result of the stirring, the quantum dots QD move from the upper layer L1 to the lower layer L2. The stirred liquid is centrifuged at 2000 rpm for 3 minutes, and the lower layer L2 is extracted. In the extracted lower layer L2, chloride ions as inorganic ligands bind to the quantum dots QD.

[0072] Next, ethyl acetate is added to the extracted lower layer L2 to precipitate the quantum dots QD, the solvent is removed, and the quantum dots QD are taken out. Then, the taken-out quantum dots QD are dispersed in a solution in which the precursor My of the matrix material Mx is dissolved. The matrix material Mx is Y 2 O 3 . The precursor My is Y(NO 3 ) 3 . The solvent of the solution in which the precursor My is dissolved is a polar solvent, which is DMF. The solution in which the precursor My is dissolved contains ZnCl at a concentration of 0.05 M. Here, "DMF" is the abbreviation of dimethylformaldehyde.

[0073] As described above, a quantum dot solution L3 for forming the quantum dot layer Em is manufactured (step S1). The quantum dot solution L3 contains Y(NO 3 ) 3 as the precursor My of the matrix material Mx and contains DMF as the solvent.

[0074] Figure 13 is a diagram showing the manufacture of the light-emitting element of Example 1. As Figure 13As shown, a first electrode E1 and a charge functional layer F1 are formed (step S2). A quantum dot solution L3 is coated on the charge functional layer F1 (base layer) (step S3). Heat treatment or light irradiation treatment is performed on the coating film of the quantum dot solution L3 to decompose and denature the precursor My (step S4). In the coating film, Y(NO 3 ) 3 is decomposed and denatured, and Y 2 O 3 epitaxially grows on the (100) equivalent plane of the quantum dot QD. Then, a charge functional layer F2 and a second electrode E2 are formed (step S5).

[0075] 〔Embodiment 2〕 Another embodiment of the present disclosure will be described below. In addition, for ease of explanation, components having the same functions as those described in the above embodiments are denoted by the same reference numerals, and their descriptions will not be repeated.

[0076] Regardless of the relationship between the first lattice constant of the equivalent region K and the second lattice constant of the matrix material Mx, the matrix material Mx is lattice-matched with the first quantum dot QD1 and the second quantum dot QD2 at the interface with the equivalent region K. That is, the quantum dot layer Em includes the first quantum dot QD1, the second quantum dot QD2, and the matrix material Mx. The region composed of one kind of equivalent crystal plane occupies more than half, more than 80%, more than 90%, and more preferably more than 95% of the surfaces of the first quantum dot QD1 and the second quantum dot QD2 respectively, and the matrix material Mx is lattice-matched at the interface with the above region.

[0077] 〔Embodiment 3〕 Another embodiment of the present disclosure will be described below.

[0078] Figure 14 is a top view showing a configuration example of a display device according to an embodiment of the present disclosure. As Figure 14 shown, the display device 100 includes a display unit 15 including a plurality of sub-pixels X and a driving circuit 25 for driving the display unit 15. For example, the sub-pixel X includes the light-emitting element 3 and the pixel circuit 5 described in the first or second embodiment above.

[0079] The present disclosure is not limited to the above embodiments, and various modifications can be made within the scope shown in the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure. Further, new technical features can be formed by combining the technical solutions disclosed in each embodiment. Description of Reference Numerals

[0080] 3 Light-emitting element 100 Display device Amorphous CG1 First single crystal part CG2 Second single crystal part K region, equivalent region L3 Quantum dot solution Mx Matrix material My Precursor QD1 First quantum dot QD2 Second quantum dot

Claims

1. A quantum dot layer, characterized in that, it comprises: a first quantum dot and a second quantum dot, and the region composed of an equivalent crystal plane and having a first lattice constant occupies more than 80% of the surface; and a matrix material, which is filled between the first quantum dot and the second quantum dot and has a second lattice constant that is 95% to 105% of the first lattice constant.

2. The quantum dot layer according to claim 1, characterized in that, the second lattice constant is 98% to 102% of the first lattice constant.

3. The quantum dot layer according to claim 1 or 2, characterized in that, the band gap of the matrix material is greater than the band gap of the core of the first quantum dot.

4. The quantum dot layer according to any one of claims 1 to 3, characterized in that, the equivalent crystal plane is a polar plane.

5. The quantum dot layer according to any one of claims 1 to 4, characterized in that, the first quantum dot has a core-shell structure.

6. The quantum dot layer according to any one of claims 1 to 5, characterized in that, the surface of the first quantum dot includes one or both of the interface between the core of the first quantum dot and the substance occupying the outside of the first quantum dot, and the interface between the shell of the first quantum dot and the substance.

7. The quantum dot layer according to any one of claims 1 to 6, characterized in that, a part of the matrix material grows epitaxially on the region.

8. The quantum dot layer according to any one of claims 1 to 7, characterized in that, ZnS is contained in the region, and the ZnS has a zinc blende crystal structure, the equivalent crystal plane is the (100) equivalent plane, The matrix material contains ZnS, Y 2 O 3 , Si, Zn 3 P 2 , GaAs, GaP, SiC, Cu 2 ZnSnS 4 , CuInS 2 , more than one of GaN and ZnMgSe.

9. The quantum dot layer according to any one of claims 1 to 8, characterized in that, ZnSe is contained in the region, and the ZnSe has a zinc blende crystal structure, the equivalent crystal plane is the (100) equivalent plane, The matrix material contains one or more of ZnSe, GaAs, and Al 2 O 3 above.

10. The quantum dot layer according to any one of claims 1 to 7, characterized in that, ZnS having a zinc blende crystal structure is contained in the region, the equivalent crystal plane is the (111) equivalent plane, The matrix material contains one or more of Si, SiC, and CeO 2 above.

11. The quantum dot layer according to any one of claims 1 to 7, characterized in that, ZnS is contained in the region, and the ZnS has a zinc blende crystal structure, the equivalent crystal plane is the (110) equivalent plane, The matrix material contains one or more of Si and CeO 2 above.

12. The quantum dot layer according to any one of claims 1 to 7, characterized in that, PdS is contained in the region, and the PdS has a sodium chloride crystal structure, the equivalent crystal plane is the (111) equivalent plane, The matrix material contains one or more of InP and CsPdBr 3 above.

13. The quantum dot layer according to any one of claims 1 to 7, characterized in that, the region contains ZnS, and the ZnS has a wurtzite crystal structure, the equivalent crystal plane is the (11-20) equivalent plane, the matrix material contains one or more of ZnS, ZnO, ZnSe and ZnTe.

14. The quantum dot layer according to any one of claims 1 to 13, characterized in that, the matrix material includes a first single crystal part in contact with the first quantum dot and a second single crystal part in contact with the second quantum dot.

15. The quantum dot layer according to claim 14, wherein, the matrix material includes an amorphous body located between the first single crystal part and the second single crystal part.

16. A quantum dot layer, wherein, it includes: a first quantum dot and a second quantum dot, and the area formed by an equivalent crystal plane accounts for more than 80% of the surface; and a matrix material, which is filled between the first quantum dot and the second quantum dot and is lattice-matched at the interface with the area.

17. A light-emitting element, wherein, it includes the quantum dot layer according to any one of claims 1 to 16.

18. A display device, wherein, it includes the light-emitting element according to claim 17.

19. A method for manufacturing a light-emitting element, wherein, it includes: a step of coating a quantum dot solution on a base layer, the quantum dot solution containing quantum dots, a precursor and a solvent, in which the area formed by an equivalent crystal plane and having a first lattice constant accounts for more than 80% of the surface; and a step of epitaxially growing a matrix material having a second lattice constant of 95% to 105% of the first lattice constant on the area by denaturing the precursor.

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