Light-emitting element and display device

Abstract

A green light-emitting element (10G) includes an anode (2), a cathode (5), and a green light-emitting layer (GEM) provided between the anode (2) and the cathode (5). The green light-emitting layer (GEM) includes a plurality of green light-emitting quantum dots (GQDs) the surfaces of which are at least partly protected by an inorganic additive 11. The plurality of green light-emitting quantum dots (GQDs) are laminated in the thickness direction of the green light-emitting layer (GEM). When the average particle diameter of the plurality of green light-emitting quantum dots (GQDs) is denoted as D, the thickness of the green light-emitting layer (GEM) is greater than 1.6 × D and less than or equal to 3.2 × D + 4 nm.

Description

Light-emitting element and display device

[0001] The present disclosure relates to a light-emitting element and a display device.

[0002] In recent years, display devices equipped with quantum dot light-emitting diodes (QLEDs), which are light-emitting elements containing quantum dots, have attracted considerable attention because of their ability to achieve low power consumption, thinness, and high image quality.

[0003] In order to improve the durability of quantum dots, research is being conducted into covering quantum dots with silica (silicon oxide). Non-Patent Document 1 discloses a structure in which quantum dots are covered with silica having an organic ring structure introduced therein.

[0004] "Blue-Emitting InP / GaP / ZnS Quantum Dots with Enhanced Stability by Siloxane Capping: Implication for Electroluminescent Devices" (ACS Appl. Nano Mater. 2022, 5, 2801-2811)

[0005] In the case of the structure in which quantum dots are covered with silica into which an organic ring structure has been introduced, as described in Non-Patent Document 1, attempts have been made to improve the carrier injection efficiency by π electrons by introducing an organic ring structure into silica, but the problem of insufficient carrier injection remains.

[0006] An object of one aspect of the present disclosure is to provide a light-emitting element and a display device that achieve good reliability and improved external quantum efficiency (EQE).

[0007] In order to solve the above-mentioned problems, the light-emitting element of the present disclosure includes an anode, a cathode, and a light-emitting layer provided between the anode and the cathode, wherein the light-emitting layer includes a plurality of quantum dots having at least a portion of a surface protected with an inorganic additive, and the quantum dots are stacked in a thickness direction of the light-emitting layer, and when the average particle size of the quantum dots is D, the thickness of the light-emitting layer is greater than 1.6 × D and not greater than 3.2 × D + 4 nm.

[0008] In order to solve the above-mentioned problems, the light-emitting element of the present disclosure includes an anode, a cathode, and a light-emitting layer provided between the anode and the cathode, wherein the light-emitting layer includes a plurality of quantum dots, at least a portion of whose surface is protected with an inorganic additive, and the quantum dots are stacked in a thickness direction of the light-emitting layer, and in a cross section cut along the thickness direction of the light-emitting layer, the shortest distance between a first quantum dot, which is one of the plurality of quantum dots, and a second quantum dot located closest to the first quantum dot, is greater than 0 nm and equal to or less than 2 nm.

[0009] In order to solve the above-mentioned problems, the light-emitting device of the present disclosure includes an anode, a cathode, and a light-emitting layer provided between the anode and the cathode, wherein the light-emitting layer includes a plurality of quantum dots, at least a portion of whose surface is protected by an inorganic additive, and the quantum dots are stacked in a thickness direction of the light-emitting layer, and in a cross section cut along the thickness direction of the light-emitting layer, (total area of ​​each of the plurality of quantum dots / area of ​​the cross section) x 100% is 50% or more.

[0010] In order to solve the above-mentioned problems, the display device of the present disclosure includes the light-emitting element.

[0011] According to one aspect of the present disclosure, it is possible to provide a light-emitting device and a display device that achieve good reliability and improved external quantum efficiency (EQE).

[0012] 1 is a plan view showing a schematic configuration of a display device of Embodiment 1; FIG. 2 is a cross-sectional view showing a schematic configuration of a green light-emitting device provided in the display device of Embodiment 1; FIG. 3 is a diagram showing the relationship between the film thickness and current density of a green light-emitting layer including a plurality of green-light-emitting quantum dots protected with an inorganic additive; FIG. 4 is a diagram showing the relationship between the film thickness and external quantum efficiency (EQE) of a green light-emitting layer including a plurality of green-light-emitting quantum dots protected with an inorganic additive; FIG. 5 is a schematic diagram showing a cross section cut along the thickness direction of the green light-emitting layer of a green light-emitting device provided in the display device of Embodiment 1; FIG. 6 is a diagram showing a plurality of green-light-emitting quantum dots included in the green light-emitting layer of a green light-emitting device provided in the display device of Embodiment 1, and inorganic additives protecting each of the plurality of green-light-emitting quantum dots; FIG. 7 is a diagram showing a plurality of green-light-emitting quantum dots included in the green light-emitting layer of a green light-emitting device provided in the display device of Embodiment 1, inorganic additives protecting each of the plurality of green-light-emitting quantum dots, and an inorganic matrix; FIG. 8 is a schematic diagram showing a cross section cut along the thickness direction of a red light-emitting layer of a red light-emitting device provided in the display device of Embodiment 1; FIG. 9 is a diagram showing a plurality of red-light-emitting quantum dots included in the red light-emitting layer of a red light-emitting device provided in the display device of Embodiment 1, and inorganic additives protecting each of the plurality of red-light-emitting quantum dots. 1 is a diagram showing a plurality of red-light-emitting quantum dots included in a red light-emitting layer of a red light-emitting element provided in the display device of embodiment 1, an inorganic additive protecting each of the plurality of red-light-emitting quantum dots, and an inorganic matrix. FIG. 2 is a diagram for explaining a method for producing a dispersion of quantum dots protected by an inorganic additive, which is used in the process of forming each of the light-emitting layers of the red light-emitting element, the green light-emitting element, and the blue light-emitting element provided in the display device of embodiment 1.

[0013] The following describes an embodiment of the present disclosure with reference to Figures 1 to 11. For the sake of convenience, components having the same functions as those described in a specific embodiment will be denoted by the same reference numerals, and their description may be omitted.

[0014] First Embodiment FIG. 1 is a plan view showing a schematic configuration of a display device 1 according to a first embodiment.

[0015] As shown in Fig. 1, the display device 1 includes a frame area NDA and a display area DA. The display area DA of the display device 1 includes a plurality of pixels PIX, each of which includes a red subpixel RSP, a green subpixel GSP, and a blue subpixel BSP. In this embodiment, a case in which one pixel PIX is configured with a red subpixel RSP, a green subpixel GSP, and a blue subpixel BSP will be described as an example, but this is not limiting. For example, one pixel PIX may include subpixels of other colors in addition to the red subpixel RSP, the green subpixel GSP, and the blue subpixel BSP.

[0016] FIG. 2 is a cross-sectional view showing a schematic configuration of a green light emitting element 10G provided in the display device 1 of the first embodiment.

[0017] The red sub-pixel RSP provided in the display area DA of the display device 1 includes a red light-emitting element not shown, the green sub-pixel GSP provided in the display area DA of the display device 1 includes a green light-emitting element 10G shown in Figure 2, and the blue sub-pixel BSP provided in the display area DA of the display device 1 includes a blue light-emitting element not shown.

[0018] 2 , the green light-emitting element 10G included in the green sub-pixel GSP includes an anode 2, a green light-emitting layer GEM, and a cathode 5. In this embodiment, an example will be described in which the green light-emitting element 10G includes a first charge transport layer 3 between the anode 2 and the green light-emitting layer GEM, and a second charge transport layer 4 between the green light-emitting layer GEM and the cathode 5. However, the present invention is not limited to this, and the green light-emitting element 10G may not include the first charge transport layer 3 and the second charge transport layer 4, or may include only one of the first charge transport layer 3 and the second charge transport layer 4.

[0019] The first charge transport layer 3 can be composed of at least one of a hole injection layer (HIL) and a hole transport layer (HTL). In this embodiment, a laminate in which a hole injection layer (HIL) and a hole transport layer (HTL) are laminated in this order from the anode 2 side is used as the first charge transport layer 3.

[0020] The second charge transport layer 4 can be configured of at least one of an electron transport layer (ETL) and an electron injection layer (EIL). In this embodiment, a laminate in which an electron transport layer (ETL) and an electron injection layer (EIL) are laminated in this order from the green light-emitting layer GEM side is used as the second charge transport layer 4.

[0021] The hole injection layer (HIL) can be formed using, for example, a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT:PSS).

[0022] The hole transport layer (HTL) may be formed using an organic material such as poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl))diphenylamine)] (TFB), N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)-benzidine (poly-TPD) or polyvinylcarbazole (PVK), or may be formed using an inorganic material such as NiO particles.

[0023] The electron transport layer (ETL) may be formed using an organic material such as 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi), or an inorganic material such as ZnO particles or particles of an oxide containing Zn and Mg.

[0024] The electron injection layer (EIL) can be formed using, for example, an alkali metal or alkaline earth metal such as aluminum, strontium, calcium, lithium, cesium, magnesium oxide, aluminum oxide, strontium oxide, lithium oxide, lithium fluoride, magnesium fluoride, strontium fluoride, calcium fluoride, barium fluoride, cesium fluoride, polymethyl methacrylate polystyrene sodium sulfonate, or the like; an oxide of an alkali metal or alkaline earth metal; a fluoride of an alkali metal or alkaline earth metal; or an organic complex of an alkali metal.

[0025] The green light-emitting element 10G shown in FIG. 2 may be a top-emission type or a bottom-emission type. In this embodiment, the green light-emitting element 10G shown in FIG. 2 is described as an example of a light-emitting element having a forward stack structure in which the cathode 5 is disposed as an upper layer than the anode 2. However, the present invention is not limited to this, and although not shown, the green light-emitting element may also be a light-emitting element having an inverted stack structure in which the anode 2 is disposed as an upper layer than the cathode 5. To make a light-emitting element with a forward stack structure a top-emission type, the anode 2 may be formed from an electrode material that reflects visible light, and the cathode 5 may be formed from an electrode material that transmits visible light. To make a light-emitting element with a forward stack structure a bottom-emission type, the anode 2 may be formed from an electrode material that transmits visible light, and the cathode 5 may be formed from an electrode material that reflects visible light. On the other hand, in order to make a light-emitting element with an inverted stack structure a top-emission type, the cathode 5 may be formed from an electrode material that reflects visible light, and the anode 2 may be formed from an electrode material that transmits visible light. In order to make a light-emitting element with an inverted stack structure a bottom-emission type, the cathode 5 may be formed from an electrode material that transmits visible light, and the anode 2 may be formed from an electrode material that reflects visible light.

[0026] The electrode material that reflects visible light is not particularly limited as long as it can reflect visible light and has electrical conductivity. Examples of the electrode material that reflects visible light include metal materials such as Al, Mg, Li, and Ag, alloys of the metal materials, laminates of the metal materials and transparent metal oxides (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.), and laminates of the alloys and the transparent metal oxides.

[0027] On the other hand, the electrode material that transmits visible light is not particularly limited as long as it can transmit visible light and has conductivity, and examples thereof include transparent metal oxides (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.), thin films made of metal materials such as Al and Ag, and nanowires made of metal materials such as Al and Ag.

[0028] The red light emitting element and blue light emitting element (not shown) provided in the display device 1 have the same configuration as the above-mentioned green light emitting element 10G except for the light emitting layer, and therefore description thereof will be omitted here.

[0029] 2 includes a green light-emitting layer GEM provided between the anode 2 and the cathode 5, and the green light-emitting layer GEM includes a plurality of green light-emitting quantum dots, at least a portion of whose surface is protected with an inorganic additive. Although not shown, the red light-emitting element includes a red light-emitting layer provided between the anode 2 and the cathode 5, and the red light-emitting layer includes a plurality of red light-emitting quantum dots, at least a portion of whose surface is protected with an inorganic additive. Although not shown, the blue light-emitting element includes a blue light-emitting layer provided between the anode 2 and the cathode 5, and the blue light-emitting layer includes a plurality of blue light-emitting quantum dots, at least a portion of whose surface is protected with an inorganic additive.

[0030] The quantum dots, such as the red-emitting quantum dots, green-emitting quantum dots, and blue-emitting quantum dots, may have, for example, a core structure, a core / shell structure, a core / shell / shell structure, or a shell structure with a continuously varying core / shell ratio. The shell may partially cover the core, but more preferably completely cover the core. The core of the quantum dot may include, for example, one or more selected from Si, Ge, CdSe, CdS, CdTe, InP, GaP, InN, ZnSe, ZnS, ZnTe, CdSeTe, GaInP, and ZnSeTe. The shell of the quantum dot may include, for example, one or more selected from CdS, ZnS, CdSSe, CdTeSe, CdSTe, ZnSSe, ZnSTe, ZnTeSe, and AgInP (AIP), and may have a lattice constant close to that of the core and a larger band gap than the core.

[0031] In this embodiment, the red-emitting quantum dots will be described by way of example, in which quantum dots with a core / shell structure having an average particle diameter of 8 nm and consisting of a core portion made of InP and having an average core diameter of 5 nm and a shell portion made of ZnS and having an average shell thickness of 1.5 nm are used; however, the materials constituting the core portion and the shell portion and the sizes of the core portion and the shell portion are not limited to these.

[0032] In this embodiment, the case will be described as an example in which green-emitting quantum dots are used, each having a core / shell structure with an average particle diameter of 5 nm, and each consisting of a core portion made of InP and having an average core diameter of 2 nm and a shell portion made of ZnS and having an average shell thickness of 1.5 nm. However, the materials constituting the core portion and the shell portion and the sizes of the core portion and the shell portion are not limited to this.

[0033] In this embodiment, the blue-emitting quantum dots are described as an example of quantum dots with a core / shell structure having an average particle diameter of 8 nm, which is composed of a core portion made of ZnSe or ZnSeTe and having an average core diameter of 5 nm, and a shell portion made of ZnS and having an average shell thickness of 1.5 nm. However, the materials constituting the core portion and the shell portion and the sizes of the core portion and the shell portion are not limited to these.

[0034] The inorganic additive that protects at least a portion of the surface of the quantum dots, such as the red-emitting quantum dots, green-emitting quantum dots, and blue-emitting quantum dots, or the inorganic additive contained in the light-emitting layer may include, for example, one selected from silicon oxide, boron oxide, phosphorus oxide, germanium oxide, beryllium fluoride, arsenic sulfide, silicon selenide, germanium sulfide, titanium oxide, tellurium oxide, aluminum oxide, bismuth oxide, vanadium oxide, antimony oxide, lead oxide, copper oxide, zirconium fluoride, aluminum fluoride, indium fluoride, zinc chloride, zinc bromide, and silicon nitride. In this embodiment, a case in which the inorganic additive is composed of silicon oxide will be described as an example, but the present invention is not limited thereto.

[0035] For example, the red-light-emitting layer may have an inorganic matrix filling the region between two adjacent red-light-emitting quantum dots, the green-light-emitting layer may have an inorganic matrix filling the region between two adjacent green-light-emitting quantum dots, and the blue-light-emitting layer may have an inorganic matrix filling the region between two adjacent blue-light-emitting quantum dots. The inorganic matrix may be an inorganic matrix containing an inorganic oxide containing a metal element or a metalloid element, an inorganic matrix containing a metal sulfide, or an inorganic matrix containing the inorganic oxide and a metal sulfide. Note that the term "fill" as used herein refers not only to completely filling a target region, but also to partially filling a target region.

[0036] 3 and 4 are graphs showing the relationship between the film thickness and current density of a green light-emitting layer containing a plurality of green light-emitting quantum dots protected with the inorganic additive described above, and the relationship between the film thickness and external quantum efficiency (EQE) of a green light-emitting layer containing a plurality of green light-emitting quantum dots protected with the inorganic additive described above.

[0037] The inventors of the present disclosure have found that, as shown in FIGS. 3 and 4 , the thicker the green light-emitting layer containing the plurality of green light-emitting quantum dots with an average particle size of 5 nm protected by the above-described inorganic additive is formed, the lower the current density when the same voltage is applied, and the lower the external quantum efficiency (EQE) at the same current density.

[0038] Between adjacent quantum dots protected by organic ligands, which are organic additives, the space charge limited current (SCLC) model equation J∝(1 / d ３ It is known that the amount of current that flows is determined by the distance J, where J is the amount of current and d is the distance between adjacent quantum dots. Therefore, when multiple adjacent quantum dots protected by organic ligands, which are organic additives, have a relatively large distance d between adjacent quantum dots, for example, when an organic ring structure with a large molecular size is introduced as in the above-mentioned Non-Patent Document 1, a satisfactory amount of current does not flow.

[0039] On the other hand, in quantum dots protected with the inorganic additives described above, as in this embodiment, carriers (electrons or holes) move by the tunneling effect and are injected into the quantum dots. That is, the carriers (electrons or holes) are injected into the quantum dots by hopping. It has been found that in parts of the light-emitting layer where this hopping is required four or more times, it becomes extremely difficult to inject carriers (electrons or holes).

[0040] Furthermore, as in this embodiment, between the multiple quantum dots protected by the inorganic additives described above, the amount of tunnel current between adjacent quantum dots is (1 / e ｄ ), where d is the distance between adjacent quantum dots, i.e., the thickness of the inorganic additive, which is an insulating material in the layer direction, along the current path. Therefore, the amount of tunneling current between adjacent quantum dots is limited by the thickness of the inorganic additive.

[0041] From the above, in a light-emitting layer containing quantum dots protected by the above-mentioned inorganic additive, the number of hopping of carriers (electrons or holes) is prevented from exceeding four, and by setting the distance between adjacent quantum dots, i.e., the thickness of the inorganic additive, to 2 nm or less, a light-emitting layer can be realized in which the quantum dots are protected by the inorganic additive and in which carriers can be efficiently injected. Furthermore, a light-emitting device including such a light-emitting layer can achieve good reliability and good external quantum efficiency (EQE).

[0042] Assuming that multiple quantum dots are stacked vertically in the thickness direction in the light-emitting layer, where the average particle size of the multiple quantum dots is D, the preferred thickness of the light-emitting layer is 3×D+4 nm or less, which is the sum of the thickness of three quantum dots with an average particle size D and the distance between the three quantum dots stacked vertically in the thickness direction (2×2 nm=4 nm). For example, when three quantum dots are stacked in the thickness direction, carriers (electrons or holes) supplied from the anode or cathode make a first hop to the quantum dots in the first layer, a second hop from the quantum dots in the first layer to the quantum dots in the second layer, and a third hop from the quantum dots in the second layer to the quantum dots in the third layer, thereby preventing the number of hops of carriers (electrons or holes) from exceeding four. In the light-emitting layer, multiple quantum dots are not necessarily stacked vertically in the thickness direction. In such a case, assuming three quantum dots are stacked in the thickness direction, a positional shift of approximately 10% of the average particle diameter D of the quantum dots occurs in each of the first and third quantum dot layers, so that the thickness of the light-emitting layer is increased or decreased. Therefore, a correction value must be added to the value of 3×D. The maximum correction value for increasing the thickness of the light-emitting layer is 2×(+0.1)×D, and the maximum correction value for decreasing the thickness of the light-emitting layer is 2×(−0.1)×D. Therefore, considering that multiple quantum dots are not necessarily stacked perpendicularly in the thickness direction, the preferred upper limit of the thickness of the light-emitting layer is 3×D+2×(+0.1)×D+4 nm. On the other hand, the lower limit of the thickness of the light-emitting layer, when two layers of quantum dots are closely packed, can be calculated from {1+√2}×(2 / 3)×D, and is approximately 1.6D. From the above, the preferred thickness of the light-emitting layer is greater than 1.6D and less than or equal to 3.2D+4 nm.

[0043] The green light-emitting layer having a thickness of approximately 12 nm, the green light-emitting layer having a thickness of approximately 24 nm, and the green light-emitting layer having a thickness of approximately 36 nm shown in FIGS. 3 and 4 each have approximately the same number of green light-emitting quantum dots per unit volume, and were formed using a quantum dot dispersion liquid in which a plurality of green light-emitting quantum dots having an average particle diameter of 5 nm and protected by the above-mentioned inorganic additive were dispersed, with only the thickness being different.

[0044] In the case of the green light-emitting layer having a film thickness of approximately 24 nm shown in FIGS. 3 and 4 , green light-emitting quantum dots having an average particle diameter of 5 nm are stacked on average in the thickness direction, with approximately four or more of them. This means that the number of hopping of carriers (electrons or holes) cannot be prevented from exceeding four, and therefore carriers cannot be injected efficiently, resulting in only a low current density and a low external quantum efficiency (EQE).

[0045] Furthermore, in the case of the green light-emitting layer having a film thickness of approximately 36 nm shown in FIGS. 3 and 4, approximately five or more green light-emitting quantum dots having an average particle diameter of 5 nm are stacked on average in the thickness direction, and the number of hopping of carriers (electrons or holes) cannot be prevented from exceeding four. Therefore, carriers cannot be injected efficiently, and only a low current density and a low external quantum efficiency (EQE) can be obtained.

[0046] In the case of the green light-emitting layer having a film thickness of approximately 12 nm shown in FIGS. 3 and 4 , green light-emitting quantum dots having an average particle diameter of 5 nm are stacked in an average number of approximately three or less in the thickness direction, i.e., an average number of approximately two, and the number of hopping of carriers (electrons or holes) can be prevented from exceeding four times. This allows carriers to be injected efficiently, resulting in a high current density and a high external quantum efficiency (EQE).

[0047] FIG. 5 is a schematic diagram showing a cross section taken along the thickness direction of the green light-emitting layer GEM of the green light-emitting element 10G provided in the display device 1 of the first embodiment.

[0048] As shown in FIG. 5 , in this embodiment, the green-emitting quantum dots GQDs included in the green-emitting layer GEM were quantum dots with a core / shell structure having an average particle diameter of 5 nm, each composed of a core portion GQDC made of InP with an average core diameter of 2 nm and a shell portion GQDS made of ZnS with an average shell thickness of 1.5 nm. Furthermore, silicon oxide was used as the inorganic additive 11 protecting the green-emitting quantum dots GQDs included in the green-emitting layer GEM. That is, the inorganic additive 11 contains an insulating material. In this embodiment, the inorganic additive 11 is bonded to the green-emitting quantum dots GQDs via an organic conjugate OL made of an organic material. However, this is not limiting. The inorganic additive 11 may be bonded to the green-emitting quantum dots GQDs via a conjugate other than an organic material, and the inorganic additive 11 may not be bonded to the green-emitting quantum dots GQDs.

[0049] In this embodiment, the green light-emitting layer GEM shown in FIG. 5 has a thickness of 18 nm, which is equal to or less than 20 nm (3.2 × 5 nm + 4 nm), because the average particle diameter D of the green light-emitting quantum dots GQD is 5 nm. However, the present invention is not limited to this example.

[0050] 5 is composed of three green-emitting quantum dots GQDs each having a thickness of approximately 5 nm, an inorganic additive 11 having a thickness of approximately 1 nm formed between the green-emitting quantum dots GQDs in the bottom layer and the green-emitting quantum dots GQDs in the middle layer, an inorganic additive 11 having a thickness of approximately 1 nm formed between the green-emitting quantum dots GQDs in the middle layer and the green-emitting quantum dots GQDs in the top layer, an inorganic additive 11 having a thickness of approximately 0.5 nm formed below the green-emitting quantum dots GQDs in the bottom layer, and an inorganic additive 11 having a thickness of approximately 0.5 nm formed above the green-emitting quantum dots GQDs. The thickness of the inorganic additive 11 can be adjusted, for example, by appropriately changing the amount of green-emitting quantum dots GQDs and the amount of the precursor of the inorganic additive 11 contained in the dispersion of green-emitting quantum dots GQDs used in the process of forming the green-emitting layer GEM. In this embodiment, a precursor of an adduct containing an organic conjugate OL capable of forming bonds with both the inorganic additive 11 and the green-emitting quantum dots GQDs is used together with the precursor of the inorganic additive 11. However, this is not limited thereto, and a precursor of an adduct containing another conjugate capable of forming bonds with both the inorganic additive 11 and the green-emitting quantum dots GQDs may also be used, or a precursor of an adduct containing a conjugate may not be used. Note that the inorganic additive 11 can be formed by subjecting the precursor of the inorganic additive 11 to at least one of light irradiation and heat treatment.

[0051] Such a green light-emitting layer GEM can prevent the number of hopping times of carriers (electrons or holes) from exceeding four, and the distance between adjacent green light-emitting quantum dots GQDs, i.e., the thickness of the inorganic additive 11, is set to 2 nm or less, thereby realizing a green light-emitting layer GEM that protects the green light-emitting quantum dots GQDs with the inorganic additive 11 and allows efficient carrier injection. Furthermore, a green light-emitting device 10G including such a green light-emitting layer GEM can achieve good reliability and good external quantum efficiency (EQE).

[0052] So far, a case has been described in which the optimal thickness of the light-emitting layer is derived by taking into consideration both the need to prevent the number of hopping times of carriers (electrons or holes) from exceeding four and the need to keep the distance between adjacent quantum dots, i.e., the thickness of the inorganic additive, at 2 nm or less. However, the present invention is not limited to this, and the distance between some of the quantum dots in the light-emitting layer, i.e., the thickness of the inorganic additive formed between some of the quantum dots in the light-emitting layer, may be set to 2 nm or less, regardless of the film thickness of the light-emitting layer.

[0053] Fig. 6 is a diagram showing a plurality of green-emitting quantum dots GQD1 and GQD2 included in the green-emitting layer GEM' of the green light-emitting element 10G provided in the display device 1 of embodiment 1, and an inorganic additive 11 that protects each of the green-emitting quantum dots GQD1 and GQD2. Fig. 7 is a diagram showing a plurality of green-emitting quantum dots GQD1 and GQD2 included in the green-emitting layer GEM'' of the green light-emitting element 10G provided in the display device 1 of embodiment 1, and an inorganic additive 11 that protects each of the green-emitting quantum dots GQD1 and GQD2, and an inorganic matrix MR.

[0054] As shown in FIG. 6 , when the shortest distance D1 between a first green-emitting quantum dot GQD1, which is one of the multiple green-emitting quantum dots GQDs, and a second green-emitting quantum dot GQD2 located closest to the first green-emitting quantum dot GQD1, is greater than 0 nm and less than or equal to 2 nm (0 < D1 ≦ 2), the distance between some of the green-emitting quantum dots GQDs in the green-emitting layer GEM′ can be shortened, facilitating carrier movement between some of the green-emitting quantum dots GQDs. This allows the green-emitting quantum dots GQDs to be protected by the inorganic additive 11, and a green-emitting layer GEM′ with improved carrier injection efficiency can be realized. Furthermore, a green light-emitting device 10G including such a green-emitting layer GEM′ can achieve good reliability and improved external quantum efficiency (EQE). Note that in this embodiment, the shortest distances D1 to D4 between quantum dots refer to the shortest distances from the outermost surface of the shell of the first quantum dot to the outermost surface of the shell of the second quantum dot located closest to the first quantum dot.

[0055] It is preferable to increase the area of ​​the inorganic additives formed between the quantum dots in the light-emitting layer where the thickness is 2 nm or less to a certain extent, thereby shortening the distance between the quantum dots in the light-emitting layer. For example, in a cross section of the green-emitting layer GEM cut along the thickness direction as shown in FIG. 5, the value of (total area of ​​each of the green-emitting quantum dots GQDs / area of ​​the cross section) × 100% is set to 50% or more. This allows the green-emitting quantum dots GQDs to be protected by the inorganic additives 11 and allows for efficient carrier injection, thereby realizing a green light-emitting layer GEM. Furthermore, a green light-emitting device 10G including such a green-emitting layer GEM can achieve good reliability and good external quantum efficiency (EQE). The cross section of the green-emitting layer GEM cut along the thickness direction as shown in FIG. 5 may be, for example, a STEM image taken using an STEM. Furthermore, the cross-sectional area is the cross-sectional area of ​​the light-emitting layer, and therefore includes, for example, the area of ​​each of the green-emitting quantum dots GQDs, the area of ​​the inorganic additive, the area of ​​any voids present between the first charge transport layer 3 and the second charge transport layer 4 shown in Figure 2, the area of ​​the organic ligand, the area of ​​the halogen element, etc. For example, the area of ​​the cross section present between the cross section of the first charge transport layer 3 and the cross section of the second charge transport layer 4 shown in Figure 2 may be the area of ​​a cross section cut along the thickness direction of the light-emitting layer.

[0056] As described above, when the distance between some of the quantum dots in the light-emitting layer, i.e., the thickness of the inorganic additive formed between some of the quantum dots in the light-emitting layer, is set to 2 nm or less, or when the value of (total area of ​​each of the quantum dots / area of ​​the cross section) × 100% in a cross section cut along the thickness direction of the light-emitting layer is set to 50% or more, for example, when green-emitting quantum dots GQD with an average particle diameter of 5 nm are used, it is preferable that the thickness of the green-emitting layer GEM be 20 nm or less.

[0057] 6, the inorganic additive 11 protects the green-emitting quantum dots GQD1 and GQD2, thereby improving the reliability of the green-emitting quantum dots GQD1 and GQD2. The small size of the inorganic additive 11 (thickness ≦1 nm) further shortens the shortest distance D1 between the green-emitting quantum dots GQD1 and GQD2 included in the green-emitting layer GEM′.

[0058] In this embodiment, the green-emitting layer GEM shown in FIG. 5 , the green-emitting layer GEM′ shown in FIG. 6 , and the green-emitting layer GEM″ shown in FIG. 7 may contain at least one of a halogen element and an organic ligand. The halogen element and the organic ligand suppress surface defects of the green-emitting quantum dots GQD1 and GQD2 to improve luminous efficiency, and can minimize the distance between the green-emitting quantum dots GQD1 and GQD2 to the extent that the green-emitting quantum dots GQD1 and GQD2 do not come into contact with each other.

[0059] 6 , when the green-emitting layer GEM′ contains a halogen element and an organic ligand, the ratio (number of halogen elements / number of elements contained in the green-emitting layer GEM′)×100% is preferably 1% or greater in the green-emitting layer GEM′. In such a case, a halogen element with a short chain length is bonded or coordinated to the green-emitting quantum dots GQD1 and GQD2, thereby shortening the distance between the green-emitting quantum dots GQD1 and GQD2 and facilitating carrier movement.

[0060] In this embodiment, for example, the content of the organic material, such as the organic material constituting the organic conjugate OL and the organic ligand, is preferably 10 wt % or less with respect to the weight of the green-emitting layer GEM / GEM' / GEM". The greater the content of the organic material, the greater the distance between the green-emitting quantum dots. Therefore, in order to facilitate carrier movement, it is necessary to keep the content of the organic material to 10 wt % or less. On the other hand, if the content of the organic material is too small, such as 0.1 wt % or less, the green-emitting quantum dots may come into contact with each other, and excitons injected into one of the two contacting green-emitting quantum dots may migrate to the other and be deactivated. In this way, when the organic material is contained in an amount of 0.1 wt % or more and 10 wt % or less with respect to the weight of the green-emitting layer GEM / GEM' / GEM"., the distance between the green-emitting quantum dots can be reduced to the extent that the green-emitting quantum dots do not come into contact with each other, thereby facilitating carrier movement.

[0061] The organic ligand preferably contains 10 or less carbon atoms. In this case, the chain length of the organic ligand bonded to or coordinated with the green-emitting quantum dots can be shortened, thereby reducing the distance between the green-emitting quantum dots and facilitating carrier movement.

[0062] For example, when the shortest distance D2 between a first green-emitting quantum dot GQD1, which is one of the multiple green-emitting quantum dots GQDs shown in FIG. 7, and a second green-emitting quantum dot GQD2, which is located closest to the first green-emitting quantum dot GQD1, is greater than 0 nm and less than or equal to 2 nm (0 < D2 ≦ 2), the distance between some of the green-emitting quantum dots GQDs in the green-emitting layer GEM″ can be shortened, facilitating carrier movement between some of the green-emitting quantum dots GQDs. This allows the green-emitting quantum dots GQDs to be protected by the inorganic additive 11, and a green-emitting layer GEM″ with improved carrier injection efficiency can be realized. Furthermore, a green light-emitting device 10G including such a green-emitting layer GEM″ can achieve good reliability and improved external quantum efficiency (EQE). The inorganic matrix MR contains an inorganic material (inorganic substance) as a main component. The inorganic material may be any inorganic semiconductor. The inorganic matrix MR may contain and support other components of the green-emitting layer GEM″. For this reason, the inorganic matrix MR can be referred to as a base material, a base material, or a filler. The inorganic matrix MR may be solid at room temperature. It is sufficient that the inorganic matrix MR has a configuration according to one aspect of the present disclosure over a width of about 100 nm in a cross-sectional observation image of the green light-emitting layer GEM". Therefore, the configuration does not have to be observed over the entire green light-emitting layer GEM". As an example, the inorganic matrix MR may be formed over a width of 1000 nm along a plane direction perpendicular to the Z direction, which is the film thickness direction of the green light-emitting layer GEM". ２The inorganic matrix MR may be formed as a continuous film having an area of ​​1000 nm or more. In this specification, a continuous film refers to a film that is not interrupted by materials other than the material constituting the continuous film in one plane. The continuous film may be an integrated film-like component that is seamlessly connected by chemical bonds in the inorganic matrix MR. The band gap of the inorganic matrix MR may be larger than the band gap of the quantum dot core. The inorganic matrix MR may be composed of an inorganic oxide containing a metal element or a metalloid element, or a metal sulfide, or may contain the inorganic oxide or metal sulfide as a main component, or a mixture of the inorganic oxide and a metal sulfide. Examples of the metalloid element include B, Si, Ge, As, Sb, and Te. The metal sulfide may contain one or more metal elements selected from Zn, Mg, and Ga, and may be any of zinc sulfide, magnesium zinc sulfide, gallium sulfide, tellurium zinc sulfide, magnesium sulfide, and gallium zinc sulfide.

[0063] The inorganic matrix MR shown in FIG. 7 is a continuous film that fills the green-emitting quantum dots GQD1 and GQD2 and is composed of, for example, ZnS or MgS. The inorganic matrix MR physically fixes the inorganic additives 11, halogens, and organic ligands around the green-emitting quantum dots GQD1 and GQD2. This further improves the reliability of the green-emitting layer GEM″.

[0064] FIG. 8 is a schematic diagram showing a cross section taken along the thickness direction of the red light-emitting layer REM of the red light-emitting element provided in the display device 1 of the first embodiment.

[0065] 8, in this embodiment, the red-emitting quantum dots RQD contained in the red-emitting layer REM were quantum dots with a core / shell structure having an average particle diameter of 8 nm, which consisted of a core portion RQDC made of InP and having an average core diameter of 5 nm and a shell portion RQDS made of ZnS and having an average shell thickness of 1.5 nm. Silicon oxide was used as the inorganic additive 11 that protects the red-emitting quantum dots RQD contained in the red-emitting layer REM.

[0066] In this embodiment, the thickness of the red light-emitting layer REM shown in FIG. 8 is described as 26.6 nm, which is equal to or less than 29.6 nm (3.2×8 nm+4 nm), because the average particle diameter D of the red light-emitting quantum dots RQD is 8 nm, but the present invention is not limited to this.

[0067] The red-light-emitting layer REM having a film thickness of 26.6 nm in the J direction shown in FIG. 8 is composed of three red-light-emitting quantum dots RQD having a thickness of approximately 8 nm, an inorganic additive 11 having a thickness of approximately 1 nm formed between the red-light-emitting quantum dots RQD in the bottom layer and the red-light-emitting quantum dots RQD in the middle layer, an inorganic additive 11 having a thickness of approximately 1 nm formed between the red-light-emitting quantum dots RQD in the middle layer and the red-light-emitting quantum dots RQD in the top layer, an inorganic additive 11 having a thickness of approximately 0.5 nm formed below the red-light-emitting quantum dots RQD in the bottom layer, and an inorganic additive 11 having a thickness of approximately 0.5 nm formed above the red-light-emitting quantum dots RQD in the top layer.

[0068] Such a red-light-emitting layer REM can prevent the number of hopping times of carriers (electrons or holes) from exceeding four, and the distance between adjacent red-light-emitting quantum dots RQD, i.e., the thickness of the inorganic additive 11, is set to 2 nm or less, thereby realizing a red-light-emitting layer REM that can protect the red-light-emitting quantum dots RQD with the inorganic additive 11 and efficiently inject carriers. Furthermore, a red light-emitting device including such a red-light-emitting layer REM can achieve good reliability and good external quantum efficiency (EQE).

[0069] Although not shown, in this embodiment, the blue light-emitting quantum dots contained in the blue light-emitting layer were quantum dots with a core / shell structure having an average particle diameter of 8 nm, each of which was composed of a core portion made of ZnSe or ZnSeTe and having an average core diameter of 5 nm, and a shell portion made of ZnS and having an average shell thickness of 1.5 nm. Furthermore, silicon oxide was used as the inorganic additive 11 that protects the blue light-emitting quantum dots contained in the blue light-emitting layer.

[0070] In this embodiment, the thickness of the blue light-emitting layer is described as 26.6 nm, which is equal to or less than 29.6 nm (3.2 × 8 nm + 4 nm) because the average particle diameter D of the blue light-emitting quantum dots is 8 nm, but the present invention is not limited to this.

[0071] Such a blue light-emitting layer can prevent the number of hopping times of carriers (electrons or holes) from exceeding four, and the distance between adjacent blue-light-emitting quantum dots, i.e., the thickness of inorganic additive 11, is set to 2 nm or less, thereby realizing a blue light-emitting layer that can protect the blue-light-emitting quantum dots with inorganic additive 11 and efficiently inject carriers. Furthermore, a blue light-emitting device including such a blue light-emitting layer can achieve good reliability and good external quantum efficiency (EQE).

[0072] Similarly to the above-described green-light-emitting layer GEM, in the above-described red-light-emitting layer REM and blue-light-emitting layer, when the distance between some of the quantum dots in the light-emitting layer, i.e., the thickness of the inorganic additive formed between some of the quantum dots in the light-emitting layer, is set to 2 nm or less, or when the value of (total area of ​​each of the multiple quantum dots / area of ​​the cross section) × 100% in a cross section cut along the thickness direction of the light-emitting layer is set to 50% or more, for example, when red-light-emitting quantum dots RQD or blue-light-emitting quantum dots having an average particle diameter of 8 nm are used, it is preferable that the thickness of each of the red-light-emitting layer REM and the blue-light-emitting layer be 29.6 nm (= 3.2 × 8 + 4) or less.

[0073] Figure 9 is a diagram showing multiple red-emitting quantum dots RQD1 and RQD2 contained in the red-emitting layer REM' of the red light-emitting element provided in the display device 1 of embodiment 1, and inorganic additives 11 that protect each of the multiple red-emitting quantum dots RQD1 and RQD2.

[0074] 9 protects the red-emitting quantum dots RQD1 and RQD2, thereby improving the reliability of the red-emitting quantum dots RQD1 and RQD2. The small size of the inorganic additive 11 (thickness ≦ 1 nm) further shortens the shortest distance D3 between the red-emitting quantum dots RQD1 and RQD2 included in the red-emitting layer REM′. Although not shown, each of the blue-emitting quantum dots included in the blue-emitting layer of the blue light-emitting element provided in the display device 1 of embodiment 1 can also be protected by the inorganic additive 11.

[0075] Figure 10 is a diagram showing a plurality of red-light-emitting quantum dots RQD1 and RQD2 contained in the red light-emitting layer REM'' of the red light-emitting element provided in the display device 1 of embodiment 1, an inorganic additive 11 that protects each of the red-light-emitting quantum dots RQD1 and RQD2, and an inorganic matrix MR.

[0076] The inorganic matrix MR shown in FIG. 10 is a continuous film that fills the red-emitting quantum dots RQD1 and RQD2 and is composed of, for example, ZnS or MgS. The inorganic matrix MR can physically fix the inorganic additives 11, halogens, and organic ligands around the red-emitting quantum dots RQD1 and RQD2. This can further improve the reliability of the red-emitting layer REM″. Note that the shortest distance D4 shown in FIG. 10 is the shortest distance from the outermost surface of the shell of the first red-emitting quantum dot RQD1 to the outermost surface of the shell of the second red-emitting quantum dot RQD2, which is located closest to the first red-emitting quantum dot RQD1. Note that, although not shown, the blue light-emitting layer of the blue light-emitting element provided in the display device 1 of embodiment 1 may also include an inorganic matrix MR.

[0077] FIG. 11 is a diagram illustrating a process for forming the light-emitting layers of the red light-emitting element, the green light-emitting element 10G, and the blue light-emitting element provided in the display device 1 of the first embodiment.

[0078] Here, as an example, a process for forming a light-emitting layer including quantum dots, an inorganic additive 11 that protects the quantum dots, and an inorganic matrix MR, such as the green light-emitting layer GEM'' shown in FIG. 7 and the red light-emitting layer REM'' shown in FIG. 10, will be described. As shown in FIG. 11, the process for forming a light-emitting layer including quantum dots, an inorganic additive 11 that protects the quantum dots, and an inorganic matrix MR includes a step (S1) of applying a first mixed solution including a plurality of quantum dots, a precursor of the inorganic additive 11, a precursor of the inorganic matrix MR, and a solvent, and a heat treatment step (S2).

[0079] On the other hand, although not shown, the process of forming a light-emitting layer including quantum dots and an inorganic additive 11 that protects the quantum dots, such as the green light-emitting layers GEM and GEM' shown in FIGS. 5 and 6 and the red light-emitting layers REM and REM' shown in FIGS. 8 and 9, includes a process of applying a second mixed solution of a plurality of quantum dots, a precursor of the inorganic additive 11, and a solvent, and a process of heat treatment.

[0080] Here, the inorganic additive 11 is silicon oxide (e.g., SiO ２ ) and the inorganic matrix MR is made of ZnS, which is a metal sulfide, will be described as an example.

[0081] In this embodiment, as an example, a case will be described in which (3-mercaptopropyl)trimethoxysilane, which is an example of a molecule containing a Si element, three alkoxy groups, and a group capable of coordinating to quantum dots, is used as a precursor of the inorganic additive 11 contained in the first mixed solution used in the step of applying the first mixed solution, which is step S1 in FIG. 11 . However, the present invention is not limited to this, and other examples include tetraalkoxysilane (Si(OR) ４ Inorganic oxide precursors containing alkoxy groups (OR) (where R is an alkyl group), such as M(OR) may also be used, ｎIt is also possible to use a precursor of an inorganic oxide containing an alkoxy group (OR) (where M is a metal element or a metalloid element, R is an alkyl group, and n is an integer) such as the above. When (3-mercaptopropyl)trimethoxysilane is used as the precursor of the inorganic additive 11, the propyl group coordinates to the quantum dots via a thiol group, which is a group capable of coordinating to the quantum dots, and this part is the organic conjugate OL described above, and silicon oxide (for example, SiO ２ The network portion of the Si—O bonds in the above-mentioned polymer becomes the inorganic additive 11 .

[0082] In this embodiment, zinc xanthate is used as a precursor of the inorganic matrix MR contained in the first mixed solution used in the step S1 of applying the first mixed solution in FIG. 11 , but the present invention is not limited thereto. For example, a metal sulfide precursor may be used as the precursor of the inorganic matrix MR contained in the first mixed solution. The metal sulfide precursor may comprise a metal source and a sulfur source. The metal source may be one or more selected from metal acetates, metal nitrates, and metal halides. The sulfur source may be one or more selected from thiourea, N-methylthiourea, 1,3-dimethylthiourea, N,N′-dimethylthiourea, tetramethylthiourea, and thioacetamide. Furthermore, the metal sulfide precursor may be a metal complex in which one or more selected from thiourea, N-methylthiourea, 1,3-dimethylthiourea, N,N′-dimethylthiourea, tetramethylthiourea, thioacetamide, and xanthogenic acid are coordinated to a metal atom. Furthermore, the precursor of the inorganic matrix MR may be, for example, tetraalkoxysilane (Si(OR) ４ Inorganic oxide precursors containing alkoxy groups (OR) (where R is an alkyl group), such as M(OR) may also be used, ｎ A precursor of an inorganic oxide containing an alkoxy group (OR) (wherein M is a metal element or a semimetal element, R is an alkyl group, and n is an integer) such as the following may also be used.

[0083] In addition, when the inorganic matrix MR is configured by a mixture of an inorganic oxide and a metal sulfide, the precursor of the inorganic matrix MR contained in the first mixed solution used in the step S1 of applying the first mixed solution in FIG. 11 may be, for example, a mixture of zinc xanthate and tetraalkoxysilane (Si(OR) ４ Inorganic oxide precursors containing alkoxy groups (OR) (where R is an alkyl group), such as M(OR) ｎ It is possible to use a precursor of an inorganic oxide containing an alkoxy group (OR) (wherein M is a metal element or a metalloid element, R is an alkyl group, and n is an integer) such as the following.

[0084] When the inorganic matrix MR contains both an inorganic oxide containing a metal element or a metalloid element and a metal sulfide, the number of moles of the metal sulfide contained in a unit volume of the inorganic matrix MR is preferably 0.05 times or more and 2 times or less the number of moles of the inorganic oxide contained in the inorganic matrix MR in the unit volume. For example, when the inorganic matrix MR contains silicon oxide (e.g., SiO ２ ) and ZnS as a metal sulfide, each quantum dot is silicon oxide (e.g., SiO ２ ) are protected by a network of Si—O bonds, so that, for example, ligands arranged on or near the surface of the quantum dots can be prevented from detaching from the quantum dots, ensuring high reliability. In addition, ZnS, which is a metal sulfide, can be easily protected by a silicon oxide (e.g., SiO ２ ) and has a lattice constant close to that of ZnSe or InP, which are preferably used for quantum dots. Therefore, when the inorganic matrix MR contains such a metal sulfide, defects due to lattice mismatch can be reduced, and a decrease in luminous efficiency can be suppressed.

[0085] By appropriately adjusting the mixing ratio of inorganic oxide to metal sulfide in the inorganic matrix MR as described above, it is possible to realize a light-emitting element and a display device that combine good current injection characteristics into quantum dots with high reliability.

[0086] As described above, when the mixing ratio of the inorganic oxide and the metal sulfide in the inorganic matrix MR is appropriately adjusted, the mixing ratio may be adjusted using a metal sulfide containing one or more elements selected from Zn, Mg, Ga, and Te, and an inorganic oxide containing one or more elements selected from Si, Be, B, Al, Ca, Sc, Ti, Mn, Ni, Ge, As, Sr, Y, Zr, Nb, Mo, In, Sn, Sb, Ba, Ce, Eu, Hf, Ta, and Th, or the mixing ratio may be adjusted using a metal sulfide containing one or more elements selected from Zn and Te, and an inorganic oxide containing one or more elements selected from Si, Be, B, Mg, Al, Ca, Sc, Ti, Mn, Ni, Ga, Ge, As, Sr, Y, Zr, Nb, Mo, In, Sn, Sb, Ba, Ce, Eu, Hf, Ta, and Th.

[0087] Furthermore, the mixing ratio may be adjusted by using zinc sulfide (e.g., ZnS) which is a metal sulfide and an inorganic oxide which is any one of silicon oxide, beryllium oxide, boron oxide, magnesium oxide, aluminum oxide, calcium oxide, scandium oxide, titanium oxide, manganese oxide, nickel oxide, gallium oxide, germanium oxide, arsenic oxide, strontium oxide, yttrium oxide, zirconium oxide, niobium oxide, molybdenum oxide, indium oxide, tin oxide, antimony oxide, barium oxide, cerium oxide, europium oxide, hafnium oxide, tantalum oxide, and thorium oxide. As described above, the mixing ratio may be adjusted by using zinc sulfide (e.g., ZnS) which is a metal sulfide and silicon oxide (e.g., SiO ２ ) may be used to adjust the mixing ratio.

[0088] In addition, in this embodiment, it is preferable that the solvent contained in the first mixed solution used in the step of applying the first mixed solution, which is step S1 of FIG. 11, contains one or more selected from toluene, chlorobenzene, methanol, ethanol, propanol, butanol, N,N-dimethylformamide, and dimethyl sulfoxide.

[0089] [Additional Notes] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of 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. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0090] The present disclosure can be used in light-emitting devices and display devices.

[0091] 1 Display device 2 Anode 3 First charge transport layer 4 Second charge transport layer 5 Cathode 10G Green light-emitting element 11 Inorganic additive OL Organic junction MR Inorganic matrix GEM, GEM', GEM'' Green light-emitting layer REM, REM', REM'' Red light-emitting layer GQD, GQD1, GQD2 Green light-emitting quantum dot GQDC Core part of green light-emitting quantum dot GQDS Shell part of green light-emitting quantum dot RQD, RQD1, RQD2 Red light-emitting quantum dot RQDC Core part of red light-emitting quantum dot RQDS Shell part of red light-emitting quantum dot PIX Pixel RSP Red sub-pixel GSP Green sub-pixel BSP Blue sub-pixel DA Display area NDA Frame area D1 to D4 Shortest distance between quantum dots

Claims

1. A light-emitting device comprising: an anode; a cathode; and a light-emitting layer provided between the anode and the cathode, wherein the light-emitting layer contains a plurality of quantum dots, at least a portion of whose surface is protected with an inorganic additive, the quantum dots being stacked in a thickness direction of the light-emitting layer, and wherein, where D is the average particle size of the quantum dots, the thickness of the light-emitting layer is greater than 1.6 × D and not greater than 3.2 × D + 4 nm.

2. A light-emitting device comprising: an anode; a cathode; and a light-emitting layer provided between the anode and the cathode, wherein the light-emitting layer comprises a plurality of quantum dots, at least a portion of whose surface is protected with an inorganic additive; the quantum dots are stacked in a thickness direction of the light-emitting layer; and in a cross section cut along the thickness direction of the light-emitting layer, the shortest distance between a first quantum dot that is one of the plurality of quantum dots and a second quantum dot that is located closest to the first quantum dot is greater than 0 nm and equal to or less than 2 nm.

3. A light-emitting device comprising: an anode; a cathode; and a light-emitting layer provided between the anode and the cathode, wherein the light-emitting layer comprises a plurality of quantum dots, at least a portion of whose surface is protected with an inorganic additive; the quantum dots are stacked in a thickness direction of the light-emitting layer; and in a cross section cut along the thickness direction of the light-emitting layer, (total area of ​​the plurality of quantum dots / area of ​​the cross section) x 100% is 50% or more.

4. The light-emitting element according to claim 2 or 3, wherein the light-emitting layer is a green light-emitting layer, and the thickness of the light-emitting layer is 20 nm or less.

5. The light-emitting element according to claim 2 or 3, wherein the light-emitting layer is a red light-emitting layer, and the thickness of the light-emitting layer is 29.6 nm or less.

6. The light-emitting element according to claim 2 or 3, wherein the light-emitting layer is a blue light-emitting layer, and the thickness of the light-emitting layer is 29.6 nm or less.

7. The light-emitting device according to any one of claims 1 to 6, wherein the inorganic additive comprises an insulating material.

8. The light-emitting device according to any one of claims 1 to 7, wherein the light-emitting layer further contains at least one of a halogen element and an organic ligand.

9. The light-emitting element according to any one of claims 1 to 8, wherein the light-emitting layer contains an organic material, and the content of the organic material is 10 wt% or less with respect to the weight of the light-emitting layer.

10. The light-emitting device according to any one of claims 1 to 9, wherein the light-emitting layer contains an organic ligand, and the organic ligand contains 10 or less carbon atoms.

11. The light-emitting element according to any one of claims 1 to 10, wherein the light-emitting layer contains a halogen element, and in the light-emitting layer, (the number of the halogen elements / the number of elements contained in the light-emitting layer) x 100% is 1% or more.

12. The light-emitting device according to any one of claims 1 to 11, wherein the inorganic additive comprises one selected from silicon oxide, boron oxide, phosphorus oxide, germanium oxide, beryllium fluoride, arsenic sulfide, silicon selenide, germanium sulfide, titanium oxide, tellurium oxide, aluminum oxide, bismuth oxide, vanadium oxide, antimony oxide, lead oxide, copper oxide, zirconium fluoride, aluminum fluoride, indium fluoride, zinc chloride, zinc bromide, and silicon nitride.

13. The light-emitting device according to any one of claims 1 to 11, wherein the inorganic additive is silicon oxide.

14. The light-emitting element according to any one of claims 1 to 13, wherein the light-emitting layer includes an inorganic matrix that fills spaces between the plurality of quantum dots, and the inorganic matrix includes a metal sulfide.

15. A light-emitting device according to any one of claims 1 to 13, wherein the light-emitting layer includes an inorganic matrix filling spaces between the plurality of quantum dots, and the inorganic matrix includes a mixture of both an inorganic oxide containing a metal element or a semi-metal element and a metal sulfide.

16. The light-emitting element according to claim 14 or 15, wherein the metal sulfide contains one or more metal elements selected from the group consisting of Zn, Mg, and Ga.

17. The light-emitting element according to claim 14 or 15, wherein the metal sulfide is any one of zinc sulfide, zinc magnesium sulfide, gallium sulfide, zinc tellurium sulfide, magnesium sulfide, and zinc gallium sulfide.

18. A display device comprising a light-emitting element according to any one of claims 1 to 17.

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