Lighting device

Abstract

The purpose of the present invention is to provide a lighting device provided with quantum dots and simultaneously satisfying manufacturing cost, reliability, and excellent color rendering properties. A lighting device according to the present invention is a thin plate-shaped lighting device having a light-emitting surface and a rear surface facing the light-emitting surface, wherein the length of one side of the light-emitting surface is larger than the thickness of the lighting device. The lighting device is characterized by including quantum dots that perform surface emission on the light-emitting surface and improve color rendering properties, and having an average color rendering index of 85 or more. In the present invention, the color rendering properties are preferably higher than those of the organic EL having the same configuration except for the light-emitting layer.

Description

lighting equipment

[0001] The present invention relates to a lighting device using quantum dots.

[0002] LED lighting uses light-emitting diodes made from inorganic semiconductors as its light source and is characterized by high reliability and excellent energy efficiency. Organic EL lighting, which uses organic EL made from organic semiconductors as its light source, is also expected to see further growth in the future. The following patent documents disclose inventions related to organic EL (organic electroluminescence).

[0003] An organic EL element is constructed by laminating an anode, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, and a cathode on a substrate. Such an organic EL element is made of an organic compound, and emits light by excitons generated by recombination of electrons and holes injected into the organic compound.

[0004] JP 2017-45650 A

[0005] Both LED lighting and organic EL have problems with color rendering. LEDs are limited in the semiconductor composition that can be selected, and while organic EL has more flexibility than LEDs, it is complicated to synthesize different organic materials for each emitted color. For these reasons, it has been difficult to satisfy color rendering requirements along with manufacturing costs and reliability.

[0006] The present invention has been made in view of the above points, and has as its object to provide a lighting device equipped with quantum dots that simultaneously satisfies requirements for manufacturing cost, reliability, and excellent color rendering properties.

[0007] An illumination device according to one aspect of the present invention is a thin-plate illumination device having a light-emitting surface and a back surface opposite the light-emitting surface, with the length of one side of the light-emitting surface being greater than the thickness of the device, the illumination device emitting light from the light-emitting surface, including quantum dots that improve color rendering, and having an average color rendering index of 90 or greater.

[0008] The lighting device of the present invention can simultaneously satisfy the requirements for manufacturing cost, reliability, and excellent color rendering properties.

[0009] 1 is a conceptual diagram of an illumination panel according to the present embodiment; FIG. 2 is a conceptual diagram showing an image of use of an illumination panel; FIG. 3 is a cross-sectional view of a light-emitting element constituting an illumination panel according to a first embodiment; FIG. 4 is an energy level diagram of each layer in the light-emitting element according to the first embodiment; FIG. 5 is a schematic diagram of quantum dots according to the present embodiment; FIG. 6 is a schematic diagram of quantum dots according to the present embodiment; FIG. 7 is a cross-sectional view of a light-emitting element constituting an illumination panel according to a second embodiment; FIG. 8 is an energy level diagram of each layer in the light-emitting element according to the second embodiment; FIG. 9 is a cross-sectional view showing an example of a practical structure of an illumination panel using the light-emitting element according to the present embodiment; FIG. 10 is a partial cross-sectional perspective view showing the light-emitting state within the illumination panel; FIG. 11 is an energy level diagram when quantum dots with a core-shell structure are used; FIG. 12 is an energy level diagram when quantum dots with a structure in which the core is not covered with a shell are used; FIG. 13 is a cross-sectional view showing an example of a layered structure of a light-emitting element that emits white light; FIG. 14 is a cross-sectional view of a hybrid light-emitting element; FIG. 15 is an example of a quantum dot layer (light-emitting layer) of a PL light-emitting element; FIG. 16 is a graph showing the relationship between wavelength and absorption coefficient for chalcopyrite quantum dots of an example and InP of a comparative example. 1 is a graph showing the relationship between wavelength and absorption coefficient in the chalcopyrite quantum dots of the example and InP of the comparative example. ＣＢ , the energy at the top of the valence band E ＶＢ ZnO used in the electron transport layer (ETL) Ｘ (Li) and ZnO Ｘ (K) UV data. ZnO used in the electron transport layer (ETL) Ｘ (Li) and ZnO Ｘ (K) PL data of ZnO used in the electron transport layer (ETL) Ｘ (Li) and ZnO Ｘ1 is PYS data for (K). ZnO synthesis flow. MgZnO synthesis flow. SnOx synthesis flow. NiOx synthesis flow. MnOx synthesis flow. Graph showing UV spectrum. Graph showing band gap energy. NiO synthesis flow. XRD of NiO. UV spectrum of NiO. Graph (Tauk plot) showing band gap energy of NiO. XANES spectrum in Ni valence evaluation. Graph showing the relationship between particle size and scattering intensity distribution in Examples 1 to 3. Graph showing the spectral intensity of general LED lighting. Graph showing the spectral intensity of organic EL lighting. Graph showing the standard radiant intensity spectrum of a lighting device using quantum dots.

[0010] An embodiment of the present invention (hereinafter abbreviated as "embodiment") will be described in detail below. Note that the present invention is not limited to the following embodiment, and various modifications can be made within the scope of the gist thereof.

[0011] FIG. 1A is a perspective view showing an image of an illumination panel (illumination device), and FIG. 1B is a conceptual diagram showing an image of how the illumination panel is used.

[0012] 1A, the lighting panel 1 is a thin plate having a light-emitting surface 1a on its front surface and a back surface opposite the light-emitting surface 1a. The light-emitting area is not limited, but can be 10 mm square or larger, preferably 50 mm square or larger, and more preferably 100 mm square or larger. In this embodiment, the quantum dot-containing material can be uniformly applied to a large substrate, thereby realizing a light-emitting surface 1a with a large area.

[0013] The thickness of the lighting panel 1 shown in FIG. 1A is 30 mm or less, preferably 20 mm or less, and more preferably 10 mm or less. The thickness of the lighting panel 1 is preferably smaller than the length of one side of the light-emitting surface 1a. The lighting panel 1 of this embodiment can be thin and lightweight. The lighting panel 1 includes a power supply circuit therein. Although not limited thereto, the weight of the lighting panel 1 is approximately 1.5 times or less the weight of the substrate 12 (panel substrate).

[0014] 1B, the lighting panel 1A of the present embodiment can be arranged as a large light on the ceiling surface 2 of a room, or as a curved light as shown in lighting panel 1B. In this way, the lighting panel 1 of the present embodiment is thin and light, and can also be formed into a curved shape, allowing for a high degree of freedom in placement.

[0015] Furthermore, the entire light-emitting surface 1a of the lighting panel 1 of this embodiment emits light. Therefore, unlike LED lighting, it is not dazzling when viewed directly and can achieve a natural light distribution that is less likely to create shadows.

[0016] Furthermore, the lighting panel 1 of the present embodiment can accommodate a variety of color rendering properties. For example, by having color reproducibility equivalent to that of sunlight, it is possible to realize lighting that gives the impression of light shining through a skylight.

[0017] Reproducing natural light emission in this way requires the design of an appropriate emission spectrum. However, the quantum dot material used in this embodiment can be made into a light-emitting material that emits light of different colors despite having the same composition by precisely controlling the particle size at the nanometer level during synthesis.

[0018] Quantum dot phosphors can be used as light-emitting materials that emit light when electrically excited (EL: Electro Luminescence), or as phosphors that emit light when excited by light (PL: Photo Luminescence).

[0019] In this embodiment, by appropriately combining the flexibility of quantum dots in selecting the emission color and the flexibility of the excitation method, it is possible to easily design an emission spectrum suitable for various applications. As such, the lighting panel 1 of this embodiment is advantageous over organic EL and LED lighting, which have limited color rendering properties. In other words, the lighting panel 1 of this embodiment has superior color rendering properties compared to organic EL that has the same configuration except for the light-emitting layer.

[0020] Furthermore, the lighting panel 1 of this embodiment consumes little power and generates almost no heat. Although not limited to this, the temperature of the light-emitting surface 1a of the lighting panel 1 is approximately 40°C or less. Therefore, even if the lighting panel 1 is placed near fresh food, paintings, or the like, it will not be thermally stressed. In this way, this embodiment is advantageous over LED lighting, which requires a heat dissipation mechanism.

[0021] Furthermore, the lighting panel 1 of this embodiment has a long product life and low manufacturing costs. The product life is comparable to that of organic EL, but the manufacturing costs can be significantly lower than that of organic EL. Also, because LED lighting is point-emitting, even if the price is low, the lighting panel 1 of this embodiment can be significantly cheaper when comparing lighting costs per unit area. The cross-sectional structure of the lighting panel 1 of this embodiment is not limited to, but can be exemplified by, for example, FIG. 2A.

[0022] FIG. 2A is a cross-sectional view of a light-emitting element constituting the lighting panel of the first embodiment, and FIG. 2B is an energy level diagram of each layer in the light-emitting element of the first embodiment.

[0023] As shown in FIG. 2A , the light-emitting element 10 includes a substrate 12, an anode 13 formed on the substrate, a hole transport layer (HTL: Hole Transport Layer) 14 formed on the anode 13, an emitter layer (EML: Emitter Layer) 15 formed on the hole transport layer 14, an electron transport layer (ETL: Electron Transport Layer) 16 formed on the emitter layer 15, and a cathode 17 formed on the electron transport layer 16.

[0024] When a voltage is applied to such a light-emitting element 10, holes are injected from the anode 13 and electrons are injected from the cathode 17. FIG. 2B shows energy level models of the hole transport layer 14, the light-emitting layer 15, and the electron transport layer 16. As shown in FIG. 2B, holes transported through the hole transport layer 14 are injected from the HOMO level of the hole transport layer 14 to the HOMO level of the light-emitting layer 15. Meanwhile, electrons transported from the electron transport layer 16 are injected from the LUMO level of the electron transport layer 16 to the LUMO level of the light-emitting layer 15. The holes and electrons then recombine in the light-emitting layer 15, causing the quantum dots in the light-emitting layer 15 to enter an excited state, and light can be emitted from the excited quantum dots.

[0025] In this embodiment, the light-emitting layer 15 is an inorganic layer containing quantum dots. In addition, in this embodiment, it is preferable that all layers from the anode 13 to the cathode 17 are formed of inorganic layers. That is, it is preferable that the anode 13, the hole transport layer 14, the light-emitting layer 15, the electron transport layer 16, and the cathode 17 are all formed of inorganic layers.

[0026] (Quantum Dots) The structure and material of the quantum dots are not limited, but for example, the quantum dots in this embodiment are nanoparticles having a particle size of about several nanometers to several tens of nanometers.

[0027] For example, quantum dots include CdS, CdSe, ZnS, ZnSe, ZnSeS, ZnTe, ZnTeS, InP, and AgInS. ２ , CuInS ２ , chalcopyrite-type semiconductors, etc. Because of the toxicity of Cd, its use is restricted in various countries, so it is preferable that the quantum dots do not contain Cd.

[0028] 3, it is preferable that a large number of organic ligands 21 are coordinated to the surface of the quantum dots 20. This makes it possible to suppress aggregation of the quantum dots 20, thereby enabling the desired optical properties to be exhibited. There are no particular limitations on the ligands that can be used in the reaction, but the following ligands are representative examples:

[0029] Aliphatic primary amine, oleylamine: C １８ H ３５ NH ２, stearyl(octadecyl)amine: C １８ H ３７ NH ２ , dodecyl(lauryl)amine: C １２ H ２５ NH ２ , decylamine: C １０ H ２１ NH ２ , octylamine: C ８ H １７ NH ２ Fatty acids, oleic acid: C １７ H ３３ COOH, stearic acid: C １７ H ３５ COOH, palmitic acid: C １５ H ３１ COOH, myristic acid: C １３ H ２７ COOH, lauryl (dodecanoic) acid: C １１ H ２３ COOH, decanoic acid: C ９ H １９ COOH, octanoic acid: C ７ H １５ COOH thiol, octadecanethiol: C １８ H ３７ SH, hexanedecanethiol: C １６ H ３３ SH, tetradecanethiol: C １４ H ２９ SH, dodecanethiol: C １２ H ２５ SH, decanethiol: C １０ H ２１ SH, octanethiol: C ８ H １７ SH phosphine system, trioctylphosphine: (C ８ H １７ ) ３ P, triphenylphosphine: (C ６ H ５ ) ３ P, tributylphosphine: (C ４ H ９ ) ３ P Phosphine oxide series, trioctylphosphine oxide: (C ８ H １７ )３ P═O, triphenylphosphine oxide: (C ６ H ５ ) ３ P═O, tributylphosphine oxide: (C ４ H ９ ) ３ P=O

[0030] The quantum dot 20 shown in FIG. 3B has a core-shell structure having a core 20a and a shell 20b coated on the surface of the core 20a. As shown in FIG. 3B, it is preferable that a large number of organic ligands 21 are coordinated to the surface of the quantum dot 20. The core 20a of the quantum dot 20 shown in FIG. 3B is the nanoparticle shown in FIG. 3A. Therefore, the core 20a is formed of, for example, one of the materials listed above. The material of the shell 20b is not particularly limited, but it may be formed of, for example, zinc sulfide (ZnS). Like the core 20a, it is preferable that the shell 20b does not contain cadmium (Cd).

[0031] The shell 20b may be in a state of being solid-solution-formed on the surface of the core 20a. In Fig. 3B, the boundary between the core 20a and the shell 20b is shown by a dotted line, but this means that it does not matter whether the boundary between the core 20a and the shell 20b can be confirmed by analysis or not.

[0032] (Light-emitting layer 15) The light-emitting layer 15 may be formed only with the quantum dots 20 described above, or may contain the quantum dots 20 and another fluorescent substance. In addition, since the light-emitting layer 15 can be formed by applying the quantum dots 20 dissolved in a solvent, the light-emitting layer 15 may contain a small amount of solvent component.

[0033] The quantum dots 20 contained in the light-emitting layer 15 include at least one of blue quantum dots that fluoresce in blue, red quantum dots that fluoresce in red, and green quantum dots that fluoresce in green. The light-emitting layer 15 may also include a plurality of quantum dots 20 with different fluorescence wavelengths, or may include quantum dots 20 and a phosphor other than quantum dots.

[0034] As mentioned above, the light-emitting layer 15 can be formed by applying the quantum dots 20 dissolved in a solvent (such as by spin coating), or by using an existing thin film formation method such as an inkjet method or a vacuum deposition method.

[0035] (Hole Transport Layer 14) The hole transport layer 14 is made of an inorganic or organic material having a function of transporting holes. The hole transport layer 14 is preferably made of an inorganic material, such as NiO or MoO. ３ , W.O. ３ The hole transport layer 14 is preferably made of an inorganic oxide such as NiO or MoO. ３ The hole transport layer 14 is preferably formed of nanoparticles of NiO. ２ O ３ The metal oxide may be doped with Li, Mg, Al, etc. The hole transport layer 14 may be made of an inorganic material other than an inorganic oxide.

[0036] Like the light-emitting layer 15, the hole transport layer 14 can be formed by spin coating a solvent containing nanoparticles, by a printing method such as an inkjet method, or by an existing thin film technology such as a vacuum deposition method.

[0037] (Electron Transport Layer 16) The electron transport layer 16 is made of an inorganic or organic material having the function of transporting electrons. The electron transport layer 16 is preferably made of an inorganic material, such as ZnO. ２ , TiO ２ , ZnO, SnO ２ , V ２ O ｘ , MoO ３ The electron transport layer 16 is preferably made of an inorganic oxide such as ZnO, MgZnO, or SnO. Two or more of these may be selected. ２ The electron transport layer 16 is preferably formed of nanoparticles of metal oxides. The metal oxides may be doped with Li, Mg, Al, Mn, etc. The electron transport layer 16 may also be formed of inorganic substances other than inorganic oxides (e.g., CsPbBr ３ etc.)

[0038] Like the light-emitting layer 15, the electron transport layer 16 can be formed by spin coating a solvent containing nanoparticles, by a printing method such as an inkjet method, or by an existing thin film technique such as a vacuum deposition method.

[0039] (Anode 13) In this embodiment, the material of the anode 13 is not limited. For example, the anode 13 may be made of an indium-tin composite oxide (ITO), a metal such as Au, or CuISnO ２ Preferably, the anode 13 is made of a conductive transparent material such as ITO or ZnO. Of these, the anode 13 is preferably made of ITO. The anode 13 can be formed as a thin film on the substrate 12 by vapor deposition, sputtering, or the like of these electrode materials.

[0040] The anode 13 must be a transparent electrode in a configuration in which light is extracted from the substrate 12 side, and is preferably made of the above-mentioned metal oxide or a very thin metal film.

[0041] (Cathode 17) In this embodiment, the material of the cathode 17 is not limited, but for example, a metal, an alloy, an electrically conductive compound, or a mixture thereof can be used as the electrode material for the cathode 17. Examples of the electrode material include Al, Mg, Li, and mixtures thereof. Of these, the cathode 17 is preferably formed of Al.

[0042] The cathode can be formed as a thin film of these electrode materials by vapor deposition, sputtering, or other methods.

[0043] (Substrate 12) In this embodiment, the material of the substrate 12 is not limited, but the substrate 12 can be formed of, for example, glass, plastic, etc. The substrate 12 is preferably a transparent substrate in a configuration in which light is extracted from the substrate 12 side. Examples of transparent substrates include glass, quartz, and transparent resin film.

[0044] The substrate 12 may be either a rigid substrate or a flexible substrate, but using a flexible substrate can impart flexibility to the light-emitting element 10. The transparent resin film may be, for example, polyester such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), polyethylene, polypropylene, cellophane, cellulose diacetate, cellulose triacetate (TAC), or the like.

[0045] In this embodiment, it is preferable that all layers from the anode 13 to the cathode 17, i.e., the anode 13, the hole transport layer 14, the light-emitting layer 15, the electron transport layer 16, and the cathode 17, are all formed of inorganic layers. By forming all layers from inorganic layers in this manner, the same coating / drying equipment can be used for film formation, simplifying the manufacturing process. Furthermore, the magnitude relationship of the HOMO levels from the anode 13 to the hole transport layer 14 and the light-emitting layer 15 can be optimized. Furthermore, the magnitude relationship of the LUMO levels from the cathode 17 to the electron transport layer 16 and the light-emitting layer 15 can be optimized. This improves carrier balance compared to when organic compounds are used, and hole injection layers and electron injection layers are not necessarily required. Therefore, by forming all layers from the anode 13 to the cathode 17 from inorganic layers, the number of layers can be reduced. However, in this embodiment, inorganic hole injection layers and electron injection layers can also be interposed between each electrode and each transport layer.

[0046] In this embodiment, the layer between the anode 13 and the light-emitting layer 15 is preferably a hole transport layer 14, a hole injection layer, a layer serving as both a hole injection layer and a hole transport layer, or a layer in which a hole transport layer and a hole injection layer are stacked (in such cases, the hole injection layer is formed on the anode 13 side, and the hole transport layer 14 is formed on the light-emitting layer 15 side).

[0047] In this embodiment, the layer between the cathode 17 and the light-emitting layer 15 is preferably the electron transport layer 16, or the electron injection layer, or a layer that serves as both the electron injection layer and the electron transport layer, or a layer in which the electron transport layer and the electron injection layer are stacked (in such cases, the electron injection layer is formed on the cathode 17 side, and the electron transport layer 16 is formed on the light-emitting layer 15 side).

[0048] FIG. 4A is a cross-sectional view of a light-emitting element 10 constituting an illumination device in the second embodiment, and FIG. 4B is an energy level diagram of each layer in the light-emitting element in the second embodiment.

[0049] The light-emitting element 10 shown in FIG. 4A has the reverse stacked structure of FIG. 2A. That is, from the substrate 12 side, a cathode 17, an electron transport layer 16, an emitting layer 15, a hole transport layer 14, and an anode 13 are stacked in this order. The electron transport layer 16, the emitting layer 15, and the hole transport layer 14 can be made of the materials listed above. The cathode 17 is preferably made of, for example, ITO, as used for the anode 13 in FIG. 2A. This allows the cathode 17, which is the electrode on the substrate 12 side, to be a transparent electrode, allowing light to be emitted from the substrate 12 side. The anode 13 shown in FIG. 4A can be made of the same material as the cathode 17 shown in FIG. 2A, for example, Al.

[0050] As described above, in the light-emitting element 10 shown in Fig. 4A, the light-emitting layer 15 is also formed of an inorganic layer containing quantum dots. It is also preferable that all layers from the cathode 17 to the anode 13 are formed of inorganic layers. In terms of the balance of the energy levels of each layer, the stacked structure shown in Fig. 2 is considered to be more preferable than that shown in Fig. 4.

[0051] In this embodiment, the hole transport layer 14, the light-emitting layer 15, and the electron transport layer 16 can all be inorganic layers formed of nanoparticles. In this case, each layer can be formed by spin coating or the like, and each layer can be easily formed with a uniform film thickness. This can effectively improve the luminous efficiency.

[0052] 5A is a cross-sectional view showing an example of an illumination panel 1 using the light-emitting element shown in FIG. 2A. As shown in FIG. 5, the substrate 12 faces the front, and the positive terminal of a power supply is connected to the anode 13 formed on the back surface of the substrate 12. It is preferable that each layer from the hole transport layer 14 to the cathode 17 be patterned, for example, to have a shape slightly smaller than the anode 13, making it easy to extract the positive terminal from the anode 13. The negative terminal of the power supply is connected to the cathode 17. In the illumination device 1 shown in FIG. 5A, the substrate 12 is a transparent glass substrate, and the anode 13 is made of ITO. Light L from quantum dots excited by the recombination of holes and electrons in the light-emitting layer 15 can be extracted from the substrate 12 side.

[0053] 5B, by providing sealing glass 18 on the back surface of cathode 17, light directed toward the back surface can be reflected by the sealing glass and efficiently extracted from the front surface. Therefore, in consideration of light emission efficiency, it is preferable to provide a sealing material on the back surface of the light-emitting element.

[0054] If the quantum dots used in the light-emitting layer 15 of this embodiment have a core-shell structure, the energy level diagram shown in Figure 6A will be obtained, and the energy level of the shell may act as a barrier to the recombination of holes and electrons. For this reason, it is preferable to use quantum dots whose core surfaces are not covered with a shell (i.e., the core surface is exposed: the material constituting the quantum dot is uniform from the center to the surface of the quantum dot), as shown in Figure 6B. This eliminates the energy barrier during recombination between holes and electrons, allowing for efficient recombination of holes and electrons, thereby improving luminous efficiency. In addition, to improve electron transport efficiency and hole transport efficiency, it is preferable to coordinate organic ligands 21 to the surface of the quantum dots 20, as shown in Figure 3A.

[0055] Furthermore, in the present embodiment, in a configuration including quantum dots with core-shell structures that have different fluorescence wavelengths, the energy levels of the shells of the quantum dots are matched to appropriately promote recombination. For this reason, it is preferable that the shell materials used for the quantum dots are the same.

[0056] To emit white light as a lighting device, three types of quantum dots must be used in the light-emitting layer: blue quantum dots, red quantum dots, and green quantum dots. In this case, the three types of quantum dots can be mixed in the same light-emitting layer, or the blue quantum dot layer, red quantum dot layer, and green quantum dot layer can be stacked separately. For example, as shown in FIG. 7 , a structure can be formed in which a red quantum dot layer 60, a green quantum dot layer 61, and a blue quantum dot layer 62 are stacked. This makes it possible to emit white light.

[0057] 8 , a stacked structure (tandem structure) may be formed of a quantum dot layer 65 containing a mixture of red and green quantum dots, a blue quantum dot layer 63, and an intermediate layer 64 between the quantum dot layer 65 and the blue quantum dot layer 63. The intermediate layer 64 may have an intermediate electrode or may have a stacked structure of layer A / intermediate electrode / layer B, layer A / intermediate electrode, or intermediate electrode / layer B. The layer A may be formed of an electron transport layer, an electron injection layer, or a stacked structure of an electron injection layer and an electron transport layer, and the layer B may be formed of a hole transport layer, a hole injection layer, or a stacked structure of a hole injection layer and a hole transport layer.

[0058] In the lighting device using quantum dots of this embodiment, they can be used as PL light emitters in parallel with EL light emitters. Furthermore, in lighting devices using quantum dots, a hybrid light-emitting element can be realized by stacking an EL light emitter and a PL light emitter. For example, a PL light emitter is stacked on the surface of an EL light emitter, and the quantum dots excited by the EL light emitter emit light, and the quantum dots contained in the PL light emitter can change the emission wavelength. The EL light emitter has a stacked structure of the above-mentioned light-emitting elements, and the PL light emitter is, for example, a sheet-like wavelength conversion material in which multiple quantum dots are dispersed in a resin. Such a hybrid configuration can be realized by using quantum dots. The PL light emitter preferably contains chalcopyrite quantum dots. Chalcopyrite quantum dots have a high absorption coefficient at 450 nm, so they can effectively attenuate the blue emission intensity.

[0059] Fig. 9 is a cross-sectional view of a hybrid light-emitting element. As shown in Fig. 9, a PL light-emitting element 30 is stacked on an EL light-emitting element 10. The EL light-emitting element 10 has, for example, the stacked structure described in Fig. 2A, but is not limited thereto. When a voltage is applied between the anode 13 and the cathode 17, the light-emitting layer 15 emits light. The PL light-emitting element 30 receives the light emitted from the EL light-emitting element 10 and emits fluorescence. The fluorescence can be extracted from the PL light-emitting element 30.

[0060] The PL light-emitting element 30 has a higher absorption coefficient wavelength than the light-emitting layer 15 of the EL light-emitting element 10. Both the PL light-emitting element 30 and the EL light-emitting element 10 can contain quantum dots, and the quantum dots used in the PL light-emitting element 30 have a longer emission peak wavelength than the quantum dots used in the light-emitting layer 15 of the EL light-emitting element 10.

[0061] 10 shows the structure of the quantum dot layer (light-emitting layer) 31 of the PL light-emitting element 30. For example, the EL light-emitting element 10 includes blue quantum dots, and the PL light-emitting element 30 includes red quantum dots and green quantum dots with different wavelengths. The quantum dot layer 31 of the PL light-emitting element 30 may be a mixed layer containing red quantum dots and green quantum dots, as shown in FIG. 10A , or may have a structure in which the red quantum dots and green quantum dots are separated into separate quantum dot layers 32 and 33 and stacked, as shown in FIG. 10B , or may have a structure in which the red quantum dots and green quantum dots are separated for each pixel 34 and 35, as shown in FIG. 10C .

[0062] As described above, in this embodiment, quantum dot phosphors are used as the light-emitting material for the lighting panel 1. This allows for illumination of any color depending on the application, and improves color rendering. Specifically, quantum dots allow for the low-cost production of phosphor materials with any emission wavelength. This allows for the creation of lighting devices with the appropriate spectral configuration for each application. In this embodiment, color rendering can be evaluated using the color rendering index (CRI). Color rendering indices include the general color rendering index (GRI) and the specific color rendering index (CRI). The GRI is the average value of the values ​​obtained by numerically evaluating the appearance of test colors R1 to R8 and is expressed in units of Ra. The specific color rendering index is not an average value, but rather each test color is individually evaluated to determine the difference from natural light. In Japan, seven colors have been standardized as JIS standards, including R9 (red), R10 (yellow), R11 (green), R12 (blue), R13 (skin color of Westerners), R14 (leaf color), and R15 (skin color of Japanese people), as defined by the International Commission on Illumination (CIE). In this embodiment, the general color rendering index (JIS Z 8726:1990) can be set to 90 or higher, and more preferably 95 or higher. In the case of organic electroluminescence (EL) and LEDs, Ra is less than 90. Furthermore, in this embodiment, the special color rendering index can be set to 75 or higher, preferably 80 or higher, and more preferably 85 or higher. Lighting devices using quantum dots can achieve any desired light emission and color rendering properties by adjusting the particle size of the quantum dots. In other words, lighting devices using quantum dots allow for more flexible control of color rendering properties and emitted light colors than organic electroluminescence (EL) and LED lighting.

[0063] The color temperature is about 2000K to 10000K, and in this embodiment, the color temperature can be freely controlled. ２ and continuously emit light, the brightness will decrease to the initial level of 3,000 cd / m due to deterioration. ２ to 2100 cd / m, which is 70% of the initial value. ２ The time required for the temperature to drop to 0°C (LT70) is approximately 12,000 hours or more.

[0064] For example, it will be possible to commercialize lighting devices such as lighting with color rendering properties equivalent to sunlight, lighting that is gentle on the eyes, light sources with colors that are highly visible, such as those required for brake lights, and lighting optimized for plant factories.

[0065] Furthermore, the lighting panel 1 of this embodiment is also suitable for curved light sources and flexible products depending on the selection of the substrate.

[0066] The effects of the present invention will be explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0067] <Quantum Dot Experiment> In this example, I-III-VI type chalcopyrite quantum dots containing no RoHS-regulated substances were fabricated as cadmium-free quantum dots. Specifically, Ag—Ga—S quantum dots were fabricated. As a comparative example, commercially available InP was used.

[0068] The graph shown in Figure 11A shows experimental results for green quantum dots, with the horizontal axis representing wavelength and the vertical axis representing absorption coefficient. As shown in Figure 13A, the chalcopyrite quantum dots of this example were found to have a higher absorption coefficient at 450 nm than InP. The absorption coefficient at 450 nm for this example was approximately 5 times, preferably approximately 6 times, and more preferably approximately 7 times, higher than that of the comparative example (in experiments, it was approximately 6 times, preferably approximately 7 times).

[0069] The graph shown in Figure 11B shows experimental results for red quantum dots, with the horizontal axis representing wavelength and the vertical axis representing absorption coefficient. As shown in Figure 11B, it was found that the chalcopyrite quantum dots of this example have a higher absorption coefficient at 450 nm than InP. The absorption coefficient at 450 nm for this example was approximately 1.5 times or more, preferably approximately 2 times or more, than that of the comparative example. The quantum dots used in this example are preferably quantum dots that emit green light with a peak wavelength of 520 to 560 nm and quantum dots that emit red light with a peak wavelength of 600 to 680 nm. However, it was found that the quantum dots of this example absorb blue light at 450 nm and have a higher absorption coefficient than InP, more effectively reducing the intensity of blue light emission.

[0070] <Experiment on Metal Oxides> FIG. 12 shows the energy band gap Eg and the conduction band minimum E of each layer in the light-emitting element used in the experiment. ＣＢ , the energy at the top of the valence band E ＶＢ 12 is a graph showing the energy level of each layer, and L2 is a graph showing the energy level of each layer. Ｘ (Li) was used. Here, Li may or may not be doped. Although not limited thereto, X is about 0.8 to 1.2. As shown in FIG. 12, ZnO used in the electron injection layer and electron transport layer (ETL) Ｘ ZnO Ｘ It was found that the band gap can be widened by using (Li). Ｘ PVK shown in FIG. 12 is a hole injection layer, B1, B2, G(H), G(I3), and R(F) are light-emitting layers (EL layers), and ZnO Ｘ , L2, and L4 are electron injection layers. When B1 or B2 is used in the light emitting layer, ZnO is used in the electron injection layer. Ｘ However, when G(H), G(I3), or R(F) is used in the light-emitting layer, it is preferable to use L2 or L4 in the electron injection layer. Ｘ (Li).

[0071] In particular, when a light-emitting layer (EL layer) with a shallow conduction band is used, ZnO Ｘ It is effective to apply (Li) to the electron injection layer or electron transport layer.

[0072] Including, but not limited to, ZnO Ｘ (Li) was obtained by stirring a zinc acetate-ethanol solution at a predetermined temperature for a predetermined time, followed by adding LiOH.4H ２ O-ethanol solution can be mixed and stirred, centrifuged, washed, etc. to produce the product.

[0073] 13 to 15 show ZnO applied to the electron transport layer (ETL). Ｘ (Li) and ZnO Ｘ (K) UV (bandgap), PL, and PYS data. Ｘ (K) is produced using KOH as a catalyst and is not doped with K or Li. Ｘ (Li) and ZnO Ｘ It was found that there was a discrepancy in the UV and PL data between PYS and ZnO (K). Ｘ (Li) and ZnO Ｘ It was found that there was almost no difference between (K) and (K), and the rising energy was almost the same.

[0074] In this way, ZnO with a controlled band gap by various particle sizes can be used as the electron injection / transport layer of an EL device using quantum dots. Ｘ By adding doping species, defect control and band gap control can be achieved. Ｘ can be proposed.

[0075] However, if the balance between the electrons and holes that generate light cannot be achieved, a thin insulating layer may be interposed between the EL layer and the electron injection layer, or ZnO Ｘ It is preferable to add a hole blocking function by integrating the molecules with the ZnO. ｘ and T2T (2,4,6-tris(biphenyl-3-yl)-1,3,5-triazine). Although not limited thereto, X is about 0.8 to 1.2.

[0076] Also, ZnO ｘ It has been found that ZnO can be used not only as an electron injection / transport layer but also as a hole injection / transport layer by performing ozone treatment or the like. ｘ It has been found that the hole transport capability is improved by performing ozone treatment on the electron transport layer. In this embodiment, the electron transport layer is formed of ZnO, MgZnO, or SnO. The synthesis flow of these metal oxides is described below.

[0077] Figure 16 shows the synthesis flow of ZnO. As shown in Figure 16, Zn(OAc) ２ ・2H ２ O (6.22 g, 28.3 mmmol) and 0.5 wt% hydrous methanol (198.8 g, 251 ml) were mixed and the temperature was raised to 60°C. Next, KOH / 0.5 wt% hydrous methanol was added to the flask at a rate of 13 ml per minute, and this addition was continued for 10 minutes. The temperature was then maintained at 60°C for 2 hours.

[0078] After cooling, the mixture was transferred to two centrifuge tubes and centrifuged at 7000 pm for 5 minutes. The supernatant was then removed from each tube, and the mixture was sonicated and centrifuged again at 7000 pm for 5 minutes. The process of removing the supernatant, sonicating, and centrifugation was repeated once more.

[0079] Then, the supernatant was removed and ultrasonication was performed, and between the removal of the supernatant and the ultrasonication, ethanol (5 ml) and aminoethanol (0.5 ml) were added to each centrifuge tube, and the tubes were then stored overnight in a dark place.

[0080] Next, the mixture was transferred to two other centrifuge tubes, and about 35 to 40 ml of ethyl acetate was added to each tube, followed by centrifugation at 5500 rpm for 5 minutes. The supernatant was then discarded from each tube, and the mixture was transferred to a G-BOX and dispersed using a vortex mixer.

[0081] Next, the solution was passed through a 0.54 μm filter and transferred to a 50 ml tube, from which 0.7 ml was taken, and the remainder was stored in a G-BOX. The concentration of the taken 0.7 ml was measured, and the concentration and dilution ratio were calculated. Based on this calculation, the dilution ratio was adjusted to the calculated value using dehydrated ethanol in the G-BOX. The completed G-BOX was then stored. A 1.6 ml aliquot was taken from this completed G-BOX, and DLS, UV value, PL value, and concentration were analyzed.

[0082] 17 shows the synthesis flow of MgZnO. As shown in FIG. 17, first, anhydrous ethanol (30 mL) was prepared, and Zn(OAc) ２ ・2H ２ O (560 mg, 2.55 mmol) and Mg (OAc) ２ ・4H ２ O (96.5 mg, 0.45 mmol) was added and stirred at room temperature for 30 minutes. Subsequently, KOH (309 mg, 5.5 mmol) / absolute ethanol (20 mL) was added. Then, stirring was continued at room temperature for 1 hour. Subsequently, hexane (80 mL) was added. This resulted in the mixture becoming cloudy white. Ethanolamine (1 mL) was added to this mixture until it dissolved, and further hexane was added to precipitate the solid, which was then dispersed in ethanol. This resulted in the production of MgZnO with a particle size of approximately 4.2 nm. The band gap energy E of MgZnO was ｇ was 3.79 eV.

[0083] Figure 18 shows the synthesis flow of SnOx. As shown in Figure 18, ethylene glycol (100 mL) was prepared, and SnCl ４ 5H ２ O (11.57 g, 0.33 mol), acetic acid (10 mL), and a 30% aqueous solution of tetramethylammonium hydroxide (25 mL) were mixed and stirred at 50°C for 30 minutes. The temperature was then raised to 160°C and stirring was continued for 4 hours. The mixture was then washed with ethanol-ethyl acetate, and 2 mL of ethanolamine was added, followed by dispersion in ethanol. In this embodiment, the hole transport layer 45 is formed from NiO or MoO. The synthesis flow for these metal oxides is described below.

[0084] Fig. 19 shows the synthesis flow of NiOx. As shown in Fig. 19, DMSO (100 mL) was prepared and Ni(NO ３ ) ２ ・6H ２ O (10 mmol) and KOH (673 mg, 12 mmol) in absolute ethanol (100 mL) were mixed and stirred at room temperature for 30 minutes. Subsequently, after washing with ethanol, DMSO (150 mL) was mixed and stirred at a temperature of 160°C for 4 hours. Next, it was washed with ethanol-ethyl acetate, and ethanolamine (0.2 mL) was added and dispersed in ethanol. A dark gray precipitate was obtained.

[0085] 20 shows the synthesis flow of MoOx. 1-octadecene and octanoic acid (total volume 60 mL, volume ratio of 1-octadecene:octanoic acid = 1:9) and MoOx were placed in a sealed tube. ２ (acac) ２ (244.62 mg, 0.75 mmol) and acetic acid (10 mL) were mixed and stirred at 50°C for 30 minutes. The temperature was then raised to 180°C and stirred for 40 minutes, and n-octane (250 mL) was added to obtain a dark blue precipitate. The precipitate was dispersed in ethanol.

[0086] According to the synthesis flow of this embodiment, a metal oxide free from oxidation defects can be obtained. Furthermore, by using the electron transport layer and hole transport layer of this embodiment, it is possible to effectively and sharply extend the absorption edge in the infrared region.

[0087] FIG. 21A is a graph showing the UV spectrum, and FIG. 21B is a graph showing the band gap energy. In the experiment, the amount of Mg doping in MgZnO was changed. The MgZnO used in the experiment was immediately after synthesis and dispersed in DEGME. As shown in FIG. 21 and Table 1, as the amount of Mg doping increased, the band gap energy E ｇ was found to increase.

[0088]

[0089] Fig. 22 shows a synthesis flow of NiO. Note that this is a synthesis flow different from that of Fig. 19. That is, as shown in Fig. 22, ３ ) ２ ・6H ２ O, dimethyl sulfoxide, and KOH / absolute ethanol solution were mixed and stirred at room temperature for 30 minutes. This resulted in a green precipitate. This was mixed with DMSO, kept at 160°C for 3 hours, and washed with ethanol / ethyl acetate. Ethanolamine was then added and dispersed in ethanol.

[0090] Figure 23 shows the XRD of NiO. The NiO used in the experiment was obtained using the synthesis flow shown in Figure 22. As shown in Figure 23, NiO was observed. However, Ni was not observed, indicating that the NiO was properly synthesized. Figure 24 shows the UV spectrum of NiO, and Figure 25 is a graph (Tauk plot) showing the band gap energy.

[0091] As shown in FIG. 25, the slope of the Tauch plot of the absorption edge was found to be greater than that of the bulk material. This indicated that the absorption edge could be sharply extended. As shown in FIG. 25, the nanoparticles showed a steeper rise in the Tauch plot than the bulk material, with a smaller tail. Because all of the electron transport materials in this example were semiconductors, the slope of the Tauch plot for all electron transport materials was greater than that of the bulk material. Furthermore, as shown in FIG. 25, it was found that the regions A and B enclosed by the tangent line indicating the slope, the plot curve, and the horizontal axis were smaller in region A of the nanoparticles than in region B of the bulk material. The smaller this region, the smaller the oxygen vacancy, proving that nanoparticles have smaller oxygen vacancies than bulk materials.

[0092] <Regarding Ni valence of NiO> Standard samples with known valence (NiO: divalent, LiNiO ２ A calibration curve of the rise position of the XANES spectrum and the Ni valence was created using the BL08W beamline and the transmission method for the measurement.

[0093] Next, the Ni valence was evaluated from the XANES spectrum of NiO prepared by the synthesis method of this example. The experimental results are shown in FIG.

[0094] As shown in Figure 26, it was found that the XANES spectrum shifted due to the change in valence. ２ Since the XANES spectrum of the example exists between the trivalent and trivalent states, the Ni valence of the NiO of the example is between 2 and 3, leaning toward divalent NiO. Therefore, it was found that the Ni valence of the example is greater than 2 and less than 2.5, preferably 2.1 or more and 2.4 or less. In the example of Figure 26, the Ni valence is predicted to be about 2.2. This proves that the NiO of the example is a hole carrier.

[0095] Furthermore, the polydispersity index of the metal oxide dispersion used in the electron transport layer of this example was less than 0.1 when measured by DLS. Dynamic light scattering (DLS) is applied to nanoparticles suspended and dispersed in a liquid. DLS measurement is a method for calculating particle diameter by measuring the diffusion rate of nanoparticles moving by Brownian motion.

[0096] The polydispersity index (PDI) is used to represent the width of the particle size distribution. In the experiments, ZnO particles were prepared as the metal oxide used in the electron transport layer. Figure 27 is a graph showing the relationship between particle size and scattering intensity distribution in each example. As shown in Table 2, the polydispersity index was less than 0.1 in each of Examples 1 to 3. This indicates that all particles measured in each example had approximately the same particle size.

[0097]

[0098] Metal oxides such as ZnO and NiO exist as a film in a display device. In this embodiment, the polydispersity index is set to less than 0.1 as described above to improve dispersibility, but the performance of the film can be defined as the surface roughness after film formation.

[0099] That is, the surface roughness Ra (arithmetic mean roughness) of the film is preferably less than 1.0 nm. The surface roughness (Ra) can be analyzed by AFM measurement or the like.

[0100] <Experiment on Color Rendering Properties> Fig. 28 is a graph showing the spectral intensity of a general LED light. Fig. 29 is a graph showing the spectral intensity of an organic EL light. Fig. 30 is a graph showing the standard radiation intensity spectrum of a lighting device using quantum dots.

[0101] As shown in Fig. 28, LED lighting produces a very strong blue light spectrum, but organic EL lighting suppresses the blue light spectrum intensity as shown in Fig. 29. However, the wavelength range of organic EL lighting is narrower than that of natural light (sunlight), and there are large fluctuations in the spectral intensity in the wavelength range of about 400 nm to 700 nm, which increases the difference with natural light and limits the color rendering properties and emitted color.

[0102] On the other hand, in lighting using quantum dots, by adjusting the particle size of the quantum dots, the spectral intensity can be made close to that of natural light, as shown in Figure 30, and the difference with natural light can be reduced. As a result, it was found that the color rendering properties and emitted color can be freely set over a wide wavelength range.

[0103] Thus, it has been found that lighting using quantum dots is superior to LEDs and organic EL in terms of color rendering properties and freedom of choice of emitted color.

[0104] According to the present invention, a large-sized lighting device containing quantum dots can be produced, and the lighting device has high color rendering properties and a high degree of freedom in shape, making it applicable to a variety of lighting applications.

[0105] This application is based on Japanese Patent Application No. 2023-211605, filed December 15, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. A thin-plate lighting device having a light-emitting surface and a back surface opposite to the light-emitting surface, with the length of one side of the light-emitting surface being greater than the thickness of the device, wherein the light-emitting surface emits light, the device contains quantum dots that improve color rendering, and the device has an average color rendering index of 90 or greater.

2. The lighting device according to claim 1, wherein the general color rendering index is 95 or greater.

3. The lighting device according to claim 1, characterized in that the special color rendering index is 75 or more.

4. The lighting device according to claim 1 or 2, characterized in that it has higher color rendering properties than an organic EL device having the same configuration except for the light-emitting layer.

5. The lighting device according to any one of claims 1 to 3, further comprising a sealing material on the rear surface that reflects light.

6. A lighting device as described in any one of claims 1 to 3, characterized in that a PL light emitter is overlaid on the surface of an EL light emitter, the EL light emitter and the PL light emitter have light emitting layers containing the quantum dots, and the emission wavelength is changed by the quantum dots contained in the PL light emitter due to light emission from excited quantum dots in the EL light emitter.

7. The lighting device according to claim 6, wherein the quantum dots contained in said PL emitter have a longer emission wavelength than the quantum dots contained in said EL emitter.

8. The lighting device according to claim 6, characterized in that the quantum dots contained in the PL luminescent material are of the chalcopyrite type.

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