Light-emitting element, production method therefor, and display device

Abstract

This invention achieves control of a wavelength of light emitted from a light-emitting element with a simple configuration between electrode layers in the light-emitting element. This light-emitting element (1) is configured such that a first electrode layer (11), a light-emitting function layer (10), and a second electrode layer (14) are laid on one another in this order. The light-emitting function layer (10) contains a refractive index change material and expresses a specific refractive index determined according to an optical path length of light emitted from the light-emitting function layer (10) in the light-emitting element (1) and the wavelength of light emitted from the light-emitting element (1).

Description

Light-emitting element, its manufacturing method and display device

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

[0002] Conventionally, in light-emitting elements, techniques for controlling the optical path of emitted light have been considered in order to adjust the wavelength of the emitted light, and one known technique for this is to arrange a refractive index adjustment layer on the light-emitting element.

[0003] One known technique is a light-emitting device having three overlapping electrode layers, a light-emitting layer disposed between the first and second electrode layers, and an electric-field-induced refractive-index-change layer disposed between the second and third electrode layers. In this light-emitting device, a voltage is applied to the electric-field-induced refractive-index-change layer independently of the light-emitting layer, thereby adjusting the optical path of light emitted from the light-emitting layer and controlling the emission wavelength of the light-emitting device (see, for example, Patent Document 1).

[0004] Another known technology is a light-emitting device having a first electrode layer, a light-emitting layer, and a second electrode layer stacked in this order, which further includes a refractive index change layer formed in the optical path of light emitted from the light-emitting layer. In this light-emitting device, the light emitted from the light-emitting layer is reflected at the interface between the portions of the refractive index change layer that have different refractive indices, thereby controlling the direction of the light. As a result, the visibility of the light-emitting device is improved (see, for example, Patent Document 2).

[0005] International Publication No. 2018 / 072454 Japanese Patent Application Laid-Open No. 2002-164180

[0006] In the technology described in Patent Document 1, an electric-field-induced refractive index change layer is disposed separately from the light-emitting functional layer between the electrode layers. In the technology described in Patent Document 2, the refractive index change layer controls the direction of light emitted from the light-emitting element by reflection at the interface due to the refractive index difference, but is not used to control the wavelength of the emitted light. As such, the conventional technology leaves room for further study from the perspective of realizing control of the wavelength of light emitted from the light-emitting element by the refractive index of the layer between the electrode layers of the light-emitting element.

[0007] An object of one aspect of the present disclosure is to realize control of the wavelength of light emitted from a light-emitting element with a simple configuration between electrode layers of the light-emitting element.

[0008] In order to solve the above-mentioned problems, the light-emitting element of the present disclosure is a light-emitting element having a first electrode layer, a light-emitting functional layer that emits light upon application of a voltage, and a second electrode layer stacked in this order, wherein the light-emitting functional layer contains a refractive index-changing material and exhibits a specific refractive index that is determined according to the optical path length of light emitted from the light-emitting functional layer in the light-emitting element and the wavelength of light emitted from the light-emitting element.

[0009] In addition, in order to solve the above-mentioned problems, the method for manufacturing a light-emitting element in the present disclosure is a method for manufacturing the above-mentioned light-emitting element, and includes the steps of preparing the first electrode layer, fabricating the light-emitting functional layer overlapping the first electrode layer, and fabricating the second electrode layer overlapping the first electrode layer and the light-emitting functional layer.

[0010] Furthermore, in order to solve the above-mentioned problems, a display device according to the present disclosure includes a substrate and the above-mentioned light-emitting element disposed on the substrate.

[0011] According to one aspect of the present disclosure, it is possible to control the wavelength of light emitted from a light-emitting element with a simple configuration between electrode layers of the light-emitting element.

[0012] FIG. 1 is a plan view schematically showing a configuration of a display device according to an embodiment of the present disclosure; FIG. 2 is a cross-sectional view schematically showing a configuration of a display region in a display device according to an embodiment of the present disclosure; FIG. 3 is a diagram schematically showing an example of a configuration of a light-emitting element according to an embodiment of the present disclosure; FIG. 4 is a diagram schematically showing a first example of a configuration of a light-emitting element according to the present disclosure; FIG. 5 is a diagram schematically showing a second example of a configuration of a light-emitting element according to the present disclosure; FIG. 6 is a diagram schematically showing a third example of a configuration of a light-emitting element according to the present disclosure; FIG. 7 is a diagram schematically showing a fourth example of a configuration of a light-emitting element according to the present disclosure; FIG. 8 is a flowchart showing an example of a process flow of a method for manufacturing a light-emitting element according to the present disclosure; FIG. 9 is a flowchart showing an example of a process flow of a refractive index adjustment layer in the method for manufacturing a light-emitting element according to the present disclosure; FIG. 10 is a diagram schematically showing a first state in the method for manufacturing a light-emitting element according to the present disclosure; FIG. 11 is a diagram schematically showing a second state in the method for manufacturing a light-emitting element according to the present disclosure; FIG. 12 is a diagram schematically showing a third state in the method for manufacturing a light-emitting element according to the present disclosure; FIG. 13 is a diagram schematically showing a fourth state in the method for manufacturing a light-emitting element according to the present disclosure; FIG. 14 is a diagram schematically showing a fifth state in the method for manufacturing a light-emitting element according to the present disclosure;

[0013] Embodiments of the present disclosure will be described below. In the following description of the embodiments, for the sake of convenience, the same reference numerals will be used to designate components having the same functions, and the description thereof will not be repeated.

[0014] [Display Device] The display device of the present disclosure has a substrate and a light-emitting element disposed on the substrate. The display device of the present disclosure can be configured in the same manner as a known display device having a known light-emitting element, except that it has the light-emitting element described below. The light-emitting element in the present disclosure will be described in detail later. The display device of the present disclosure will be described in more detail below with reference to the drawings.

[0015] [Display Device] Fig. 1 is a plan view schematically illustrating the configuration of a display device according to an embodiment of the present disclosure. As shown in Fig. 1, the display device 100 includes a frame region NDA and a display region DA. The display region DA of the display device 100 includes a plurality of pixels PIX, each of which includes a red sub-pixel RSP, a green sub-pixel GSP, and a blue sub-pixel BSP.

[0016] The pixel configuration of the display device of the present disclosure is not limited to the above configuration. In the display device of the present disclosure, 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. Note that in this specification, configurations of different colors among similar basic configurations are indicated by adding a symbol indicating the color to the symbol of the basic configuration. For example, a configuration related to red is indicated by adding a symbol R, a configuration related to green is indicated by adding a symbol G, and a configuration related to blue is indicated by adding a symbol B.

[0017] 2 is a cross-sectional view schematically illustrating the configuration of a display area in a display device according to an embodiment of the present disclosure. As shown in Fig. 2, in the display area DA of the display device 100, a barrier layer 120, a thin-film transistor layer 130 including a transistor TR, red light-emitting elements 1R, green light-emitting elements 1G, blue light-emitting elements 1B, a bank (transparent resin layer) 40, a sealing layer 140, and a functional film 150 are formed on a substrate 110.

[0018] The structure in which the substrate 110, the barrier layer 120, and the thin film transistor layer 130 shown in FIG. 2 are provided in this order from the substrate 110 side is also called an "active matrix substrate."

[0019] The red sub-pixel RSP includes a red light-emitting element 1R, the green sub-pixel GSP includes a green light-emitting element 1G, and the blue sub-pixel BSP includes a blue light-emitting element 1B. The light-emitting elements 1 of each color have the same configuration except for the materials of the light-emitting layers. The configuration of the light-emitting element 1 will be described later.

[0020] The substrate 110 may be, for example, a resin substrate made of a resin material such as polyimide, or may be a glass substrate.

[0021] The barrier layer 120 is a layer that prevents foreign substances such as water and oxygen from penetrating into the transistor TR, the red light emitting element 1R, the green light emitting element 1G, and the blue light emitting element 1B. The barrier layer 120 can be made of, for example, a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a laminated film of these, formed by a CVD method.

[0022] The thin-film transistor layer 130 has a portion including a transistor TR and a portion not including a transistor TR. The portion of the thin-film transistor layer 130 other than the transistor TR portion is configured by inorganic insulating films 131 to 133 and a planarization film 134 stacked in this order from the substrate 110 side. The transistor TR portion of the thin-film transistor layer 130 is configured by a semiconductor film SEM, an inorganic insulating film 131, a gate electrode G, an inorganic insulating film 132, an inorganic insulating film 133, a source electrode S and a drain electrode D, and the planarization film 134. The semiconductor film SEM includes a drain region SEM2 and a source region SEM3 doped with impurities such as phosphorus, and a channel region SEM1 between the drain region SEM2 and the source region SEM3.

[0023] The inorganic insulating films 131 to 133 can be formed, for example, by a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a laminated film of these films, which are formed by a CVD method. The inorganic insulating films 131 to 133 may be of the same type or different types.

[0024] The planarization film 134 can be made of a coatable organic material such as polyimide or acrylic.

[0025] The semiconductor film SEM is made of, for example, low-temperature polysilicon (LTPS), but may also be made of an oxide semiconductor (for example, an In—Ga—Zn—O-based semiconductor). In this embodiment, the transistor TR has, for example, a top-gate structure. Note that in the present disclosure, the transistor TR may also have a bottom-gate structure.

[0026] The gate electrode G and the source and drain electrodes S and D may each be formed of a single layer or a multilayer film of a metal, examples of which include aluminum, tungsten, molybdenum, tantalum, chromium, titanium, and copper.

[0027] The thin film transistor layer 130 is provided with a control circuit including a transistor TR for controlling the red light emitting element 1R, the green light emitting element 1G, and the blue light emitting element 1B, respectively, for each of the red sub-pixel RSP, the green sub-pixel GSP, and the blue sub-pixel BSP.

[0028] The red light-emitting element 1R has, in this order in the stacking direction, a first electrode layer 11R above the planarization film 134, a light-emitting functional layer 10R including a red light-emitting layer, and a second electrode layer 14. Similarly, the green light-emitting element 1G has, in this order in the stacking direction, a first electrode layer 11G above the planarization film 134, a light-emitting functional layer 10G including a green light-emitting layer, and a second electrode layer 14. The blue light-emitting element 1B also has, in this order in the stacking direction, a first electrode layer 11B above the planarization film 134, a light-emitting functional layer 10B including a blue light-emitting layer, and a second electrode layer 14.

[0029] The sealing layer 140 is a light-transmitting film, and can be composed of, for example, an inorganic sealing film 141 that covers the second electrode layer 14, an organic film 142 that is above the inorganic sealing film 141, and an inorganic sealing film 143 that is above the organic film 142. The sealing layer 140 prevents foreign substances such as water and oxygen from penetrating into the red light-emitting element 1R, the green light-emitting element 1G, and the blue light-emitting element 1B.

[0030] Here, the inorganic sealing films 141 and 143 are each an inorganic film, and can be composed of a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a laminate film of these. The inorganic film is formed by, for example, a CVD method. The organic film 142 is a light-transmitting organic film with a planarizing effect, and can be composed of a coatable organic material such as acrylic.

[0031] The functional film 150 is a film having at least one function selected from the group consisting of, for example, an optical compensation function, a touch sensor function, and a protection function.

[0032] [Light-emitting element] Fig. 3 schematically shows an example of the configuration of a light-emitting element 1 according to an embodiment of the present disclosure. The light-emitting element 1 is a QLED. As shown in Fig. 3, the light-emitting element 1 has a first electrode layer 11, a second electrode layer 14, and a light-emitting functional layer 10, which is any one of a light-emitting functional layer 10R, a light-emitting functional layer 10G, and a light-emitting functional layer 10B, provided between the first electrode layer 11 and the second electrode layer 14.

[0033] 2, the light-emitting element 1 is formed on a thin-film transistor layer 130, which is formed on a barrier layer 120, which is formed on a substrate 110. The banks 40 are arranged on the thin-film transistor layer 130 so as to separate the light-emitting functional layers 10 when viewed in plan.

[0034] The bank 40 is disposed on the thin film transistor layer 130 and is made of a transparent resin. Examples of the transparent resin include polyimide and acrylic resin. The bank 40 can be fabricated by applying ink containing the transparent resin to a plane and then patterning the ink by photolithography.

[0035] The light-emitting functional layer 10 has a hole injection layer 17, a hole transport layer 15, a light-emitting layer 12 which is either a red light-emitting layer, a green light-emitting layer, or a blue light-emitting layer, and an electron transport layer 16, and these layers are stacked and arranged in this order from the thin-film transistor layer 130 side.

[0036] In this embodiment, the first electrode layer 11 is also referred to as an anode. The first electrode layer 11 is conductive and has optical properties, for example, of reflecting part of visible light and transmitting the rest. The first electrode layer 11 includes both an electrode material that reflects visible light and an electrode material that transmits visible light.

[0037] Examples of electrode materials that reflect visible light include metal materials such as Al, Mg, Li, and Ag, alloys of these metal materials, and stacks (e.g., ITO / Ag / ITO) of these metal materials or their alloys with transparent metal oxides (e.g., indium tin oxide (ITO), indium zinc oxide, indium gallium zinc oxide, etc.).

[0038] Examples of electrode materials that transmit visible light include transparent metal oxides, thin films made of metal materials such as Al and Ag, and nanowires made of the metal materials.

[0039] The first electrode layer 11 can be formed by a general electrode formation method. Examples of methods for forming the first electrode layer 11 include physical vapor deposition (PVD) and chemical vapor deposition (CVD), and examples of physical vapor deposition include vacuum deposition, sputtering, electron beam (EB) deposition, and ion plating. Examples of physical vapor deposition (PVD) methods, such as CVD, or chemical vapor deposition (CVD) methods, can be used. Examples of methods for patterning the first electrode layer 11 include photolithography and inkjet printing.

[0040] The hole injection layer (HIL) 17 is composed of a hole-injecting material that can stabilize the injection of holes into the light-emitting layer 34. Examples of hole-injecting materials include poly(3,4-ethylenedioxythiophene):polystyrenesulfonic acid (PEDOT:PSS), NiO, and CuSCN.

[0041] The hole transport layer (HTL) 15 is composed of a hole transporting material that can stabilize the transport of holes into the light-emitting layer 12. Examples of hole transporting materials include poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] (TFB) and poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] (poly-TPD).

[0042] The light-emitting layer (EML) 12 is composed of, for example, quantum dots (QDs). QDs refer to dots with a maximum width of 100 nm or less. The shape of the QDs may be spherical (circular cross-sectional shape), or may be, for example, polygonal cross-sectional shape, rod-like shape, branch-like shape, or a three-dimensional shape with an uneven surface, or a combination thereof.

[0043] The QDs may have a core structure, a core / shell structure, a core / shell / shell structure, or a core / shell structure with a continuously varying core / shell ratio. The QDs may have a ligand, and if the QD has a core structure, the ligand may be provided on the surface of the core structure, or if the QD has a shell structure, the ligand may be provided on the surface of the shell structure.

[0044] Materials that make up the core structure of QDs include, if they are unicomponent, Si and C. If they are binary, they include CdSe, CdS, CdTe, InP, GaP, InN, ZnSe, ZnS, and ZnTe. If they are ternary, they include CdSeTe, GaInP, and ZnSeTe. If they are quaternary, they include AIGS.

[0045] Binary materials that make up the shell structure of QDs include CdS, CdTe, CdSe, ZnS, ZnSe, and ZnTe, and ternary materials include CdSSe, CdTeSe, CdSTe, ZnSSe, ZnSTe, ZnTeSe, and AIP.

[0046] The electron transport layer (ETL) 16 is composed of an electron transport material that can stabilize the transport of electrons into the light-emitting layer 34. In this embodiment, it is composed of MgZnO-PVP nanoparticles (MgZnO-PVP-NPs). MgZnO-PVP-NPs have a nanometer-order particle size, with a core structure of MgZnO as the electron transport material and a shell structure of PVP. MgZnO-PVP-NPs correspond to the composite material nanoparticles described above. Examples of electron transport materials include nanoparticles containing one or more elements selected from the group consisting of Zn, Mg, Ti, Si, Sn, W, Ta, Ba, Zr, Al, Y, and Hf, in addition to MgZnO.

[0047] In this embodiment, the second electrode layer 14 is also referred to as a cathode. The second electrode layer 14 has, for example, electrical conductivity and visible light transparency. Examples of electrode materials constituting the second electrode layer 14 include ITO and Ag nanowires (NW). The second electrode layer 14 can be composed of the electrode material described above for the first electrode layer 11 and can be fabricated by the method described above for the first electrode layer 11 depending on the electrode material. The second electrode layer 14 is formed on the entire surface of the light-emitting element 1 opposite the first electrode layer 11 across the light-emitting functional layer 10, and covers the electron transport layer 16, the bank 40, and the thin-film transistor layer 130.

[0048] In the light-emitting element 1, the light-emitting functional layer 10 has a refractive index adjusting function, which will be described later. For example, the light-emitting functional layer 10 further includes a refractive index adjusting layer, or at least one layer included in the light-emitting functional layer 10 also serves as a refractive index adjusting layer. Therefore, in the display device 100, the wavelength of light emitted from the light-emitting functional layer 10 in the light-emitting element 1 is appropriately controlled by a simple configuration between the electrodes.

[0049] The light-emitting device of the present disclosure having a light-emitting functional layer that exhibits a specific refractive index will be described in more detail below.

[0050] [Embodiment 1] Fig. 4 is a diagram schematically illustrating a first example of the configuration of a light-emitting element according to the present disclosure. As shown in Fig. 4, the light-emitting element 1 has a first electrode layer 11, a light-emitting layer 12, a refractive index adjustment layer 13, and a second electrode layer 14. These layers are stacked in this order. The light-emitting layer 12 and the refractive index adjustment layer 13 correspond to the light-emitting functional layer 10 described above. The light-emitting element 1 is formed on, for example, an active matrix substrate.

[0051] The light-emitting element 1 may be a top-emission type or a bottom-emission type, and may be an organic light-emitting diode (OLED) or a quantum dot light-emitting diode (QLED).

[0052] The first electrode layer 11 is made of a conductive material. The electrode material can be appropriately selected from electrode materials that transmit visible light and electrode materials that reflect visible light depending on the type of the light-emitting element 1. The first electrode layer 11 is made of, for example, a conductive electrode material that reflects visible light.

[0053] The light-emitting layer 12 is a layer that emits light when a voltage is applied. The light-emitting layer 12 may be one type or more types. For example, the light-emitting layer 12 may be a layer that emits monochromatic light, or may be composed of multiple types of light-emitting layers that each emit monochromatic light and are arranged in a planar direction. Examples of the light-emitting layer 12 include a red light-emitting layer, a green light-emitting layer, a blue light-emitting layer, and a combination of two or more of these. The light-emitting layer of each color may be a light-emitting layer other than the layer composed of QDs exemplified above, and may be prepared by a known manufacturing method using a known light-emitting layer material that emits light of the desired color wavelength.

[0054] Similar to the first electrode layer 11, the second electrode layer 14 can be produced by a known method for producing an electrode layer using an electrode material appropriate for the type of the light-emitting element 1. The second electrode layer 14 is produced, for example, from a conductive electrode material that transmits visible light.

[0055] The refractive index adjustment layer 13 is disposed between the first electrode layer 11 and the second electrode layer 14 and in the optical path of light emitted from the light emitting layer 12. In the light emitting element 1, the light emitted from the light emitting layer 12 is emitted upward in FIG. 4 , i.e., via the second electrode layer 14. In the light emitting element 1, the refractive index adjustment layer 13 is formed between the light emitting layer 12 and the second electrode layer 14.

[0056] The refractive index adjustment layer 13 has a specific refractive index that is determined according to the optical path length of light emitted from the light-emitting functional layer in the light-emitting element and the wavelength of the light emitted from the light-emitting element. If the wavelength of the light emitted from the light-emitting element 1 is "λ", the optical path length in the light-emitting element of the light emitted from the light-emitting functional layer is "d", and the refractive index exhibited by the light-emitting functional layer is "n", the relationship between these is expressed by the following formula. In the following formula, "m" is any odd number. [Formula] nd=mλ / 4 (m=1, 3, 5, ...)

[0057] In the microcavity method, device parameters (film thickness or refractive index) are designed to generate constructive interference in the light extraction direction (the direction in which light generated in the light-emitting functional layer is emitted from the light-emitting element) from the perspective of the light-emitting molecules. In particular, it is known that the increase in radiant intensity due to the interference effect is greatest when the distance d between the reflective surface of the metal reflective layer and the light-emitting position of the light-emitting layer satisfies the condition d = iλ / (4n) (i = 1, 3, 5, ...). i is the interference order, λ is the peak wavelength in vacuum of the PL spectrum of the light-emitting molecules, and n corresponds to the effective refractive index between the light-emitting point and the metal reflective layer.

[0058] 4, light generated in the light-emitting layer 12 is emitted from the second electrode layer 14. Therefore, the optical path length d in the light-emitting element 1 in FIG. 4 is the distance from the center of the light-emitting layer 12 in the thickness direction to the interface between the light-emitting layer 12 and the first electrode layer 11.

[0059] The refractive index adjusting layer 13 is a layer containing a refractive index changing material. The refractive index adjusting layer 13 may be composed of only the refractive index changing material, or may be composed of a binder resin phase composed of a transparent resin or the like and refractive index changing material particles bound by the binder resin phase. The refractive index changing material is a material that exhibits a refractive index according to the application of energy, for example, a material whose refractive index increases when irradiated with electromagnetic waves.

[0060] The refractive index changing material may be an inorganic material or an organic material, and may be one or more types. The electromagnetic wave may be an electron beam that changes the refractive index of the refractive index changing material. From the viewpoint of stabilizing the refractive index of the refractive index adjusting layer 13 of the light emitting element 1, it is preferable that the electromagnetic wave be an electron beam having a sufficiently high energy compared to the emitted light of the light emitting element.

[0061] Examples of inorganic refractive index change materials include GaAs and GeO ２ , B ２ O ３ or P ２ O ５ Silica glass doped with As ２ S ３ , As ４０ S ２５ Se ２５ Ge １０, MAPbBr ３ or Mg-doped LiNbO ３ The refractive index changing material is not particularly limited, but may be a general photorefractive material.

[0062] Alternatively, the refractive index changing material may be a photopolymer for hologram recording, which may have a molecular structure of a polymerization reaction product of a composition containing a monomer, a photopolymerization initiator, a sensitizer, and a binder as main components.

[0063] Examples of the monomer include a monomer having at least one ethylenically unsaturated double bond in one molecule, and a photopolymerizable or photocrosslinkable monomer, oligomer, prepolymer, and mixtures thereof. More specifically, examples of the monomer include unsaturated carboxylic acids and their salts, esters of unsaturated carboxylic acids and aliphatic polyhydric alcohol compounds, and amides of unsaturated carboxylic acids and aliphatic polyhydric amine compounds.

[0064] Examples of the photopolymerization initiator / sensitizer include known components that are applied in the photopolymerization or photocrosslinking reaction of a monomer.

[0065] Examples of binders include polymethacrylic acid esters and partial hydrolyzates thereof, polyvinyl acetate and hydrolyzates thereof, polystyrene, polyvinyl butyral, polychloroprene, polyvinyl chloride, chlorinated polyethylene, chlorinated polypropylene, poly-N-vinylcarbazole and derivatives thereof, poly-N-vinylpyrrolidone and derivatives thereof, copolymers of styrene and maleic anhydride and half esters thereof, and copolymers of copolymerizable monomers, such as acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, acrylamide, and acrylonitrile.

[0066] Examples of the organic refractive index changing material include spiropyran, spirooxazine, naphthoquinone diazide derivatives described in JP-A-11-60803, triazine ring-containing polymers described in JP-A-6970926, and diarylethene derivatives described in JP-A-2003-322887.

[0067] Examples of electromagnetic waves include ultraviolet light, electron beams, and high-pressure mercury lamps. From the viewpoint of suppressing changes in the refractive index of the refractive index-adjusting layer due to light emitted from the light-emitting layer and external light, the electromagnetic waves are preferably electromagnetic waves other than visible light.

[0068] The refractive index of the refractive index-matching layer 13 can be adjusted appropriately depending on the refractive index-changing material and the mechanism of the refractive index change. For example, when the refractive index-matching material is the naphthoquinone diazide derivative, the refractive index of the refractive index-matching layer 13 can be adjusted by the content of the refractive index-matching material in the refractive index-matching layer 13, the wavelength of the electromagnetic wave irradiated to the refractive index-matching layer 13, or the irradiation time of the electromagnetic wave.

[0069] The adjustment of the refractive index of the refractive index adjustment layer 13 can be performed at any time after the refractive index adjustment layer 13 is formed during the production of the light-emitting element 1. For example, the refractive index adjustment layer 13 may be formed on the light-emitting layer 12, and the refractive index of the refractive index adjustment layer 13 may be adjusted by irradiating the refractive index adjustment layer 13 with electromagnetic waves before the second electrode layer 14 is formed. Alternatively, the refractive index of the refractive index adjustment layer 13 may be adjusted by irradiating the light-emitting element 1 with electromagnetic waves from the second electrode layer 14 side after the second electrode layer 14 is formed and the light-emitting element 1 is completed. If the refractive index of the refractive index adjustment layer 13 before adjustment (before electromagnetic wave irradiation) is n1, the refractive index of the refractive index adjustment layer 13 is adjusted to n2 (n2>n1), which is higher than n1, by the irradiation of electromagnetic waves.

[0070] In the light-emitting element 1, the light-emitting layer 12 emits light through an electroluminescence source when a voltage is applied to the light-emitting layer 12 from the first electrode layer 11 and the second electrode layer 14. Since the first electrode layer 11 is formed of an electrode material that reflects visible light and the second electrode layer 14 is formed of an electrode material that transmits visible light, light emitted from the light-emitting layer 12 is emitted from the light-emitting element 1 in the direction of the arrow in the figure, i.e., through the refractive index adjustment layer 13 and the second electrode layer 14.

[0071] The wavelength of light emitted from the light-emitting layer 12 is determined by the light-emitting layer material and is a value specific to the light-emitting layer 12. When the refractive index of the refractive index-matching layer 13 is n1, the wavelength of light emitted from the light-emitting element 1 is expressed as n1×d×4 / m.

[0072] After the refractive index of the refractive index-adjusting layer 13 is adjusted from n1 to n2, the wavelength of the light emitted from the light-emitting element 1 is n2 × d × 4 / m, where n2 is greater than n1. Therefore, the wavelength of the light emitted from the light-emitting element 1 shifts to a longer wavelength side than the wavelength of the light emitted from the light-emitting layer 12. The magnitude of the shift increases as the amount of change in the refractive index of the refractive index-adjusting layer 13 before and after the refractive index adjustment (i.e., the amount of change from n1 to n2) increases. The light emitted from the light-emitting element 1 usually has substantially the same wavelength as the light emitted from the light-emitting layer 12, but in this embodiment, the wavelength is longer than the light emitted from the light-emitting layer 12. In this way, the refractive index-adjusting layer 13 adjusts the wavelength of the light emitted from the light-emitting element 1 by having the specific refractive index described above.

[0073] A configuration in which the refractive index adjustment layer 13 is provided between the light-emitting layer 12 and the second electrode layer 14, as in the light-emitting element 1, is expected to improve electrical properties compared to a configuration in which the refractive index adjustment layer 13 described below is provided between the light-emitting layer 12 and the first electrode layer 11, when the electron mobility of the material in the refractive index adjustment layer 13 is higher than the hole mobility.

[0074] [Embodiment 2] Figure 5 is a diagram schematically illustrating a second example of the configuration of a light-emitting element according to the present disclosure. As shown in Figure 5, in the light-emitting element 2, the order of the light-emitting layer 12 and the refractive index adjustment layer 13 in the stacking direction is reversed. The light-emitting layer 12 and the refractive index adjustment layer 13 correspond to the light-emitting functional layer 10 described above. Furthermore, the light-emitting element 2 has a second electrode layer 24 instead of the second electrode layer 14. The second electrode layer 24 is an electrode layer that reflects a portion of the light emitted from the light-emitting layer 12 and transmits the remainder. The second electrode layer 24 is composed of, for example, a laminate of a metal thin film and a transparent electrode material. Otherwise, the light-emitting element 2 has the same configuration as the light-emitting element 1 described above.

[0075] Hereinafter, for the light emitting element 2 of this embodiment, the change in wavelength of the emitted light from the light emitting element due to the refractive index adjustment layer will be described based on more specific conditions.

[0076] [Specific Example] A light-emitting element A having the configuration shown in Figure 5 is constructed. In the light-emitting element A, m is 3, and the sum d (nm) of the thickness of the light-emitting layer 12 at the center in the thickness direction and the thickness of the refractive index adjustment layer 13 is 200 nm. The light-emitting layer is a blue light-emitting layer. The refractive index adjustment layer 13 is made of a coating film of a transparent polymer composition containing approximately 40% by mass of the naphthoquinoazide derivative described in the aforementioned Japanese Patent Laid-Open Publication No. 1-60803. The refractive index of the refractive index adjustment layer 13, which is not irradiated with ultraviolet light, is 1.8. The wavelength of light emitted from the light-emitting element A is 480 nm, as n x d = m / 4 x λ, and the emitted color of the light-emitting element A is sky blue.

[0077] Next, the refractive index of the refractive index adjustment layer 13 is changed to 1.72 by irradiating the light-emitting element A with ultraviolet light having a wavelength of 380 to 500 nm. The light-emitting element after changing the refractive index of the refractive index adjustment layer 13 is designated as light-emitting element B. The wavelength of light emitted from light-emitting element B is 458.7 nm, as calculated by n×d=m / 4×λ, and the emitted color of light-emitting element B is deep blue.

[0078] From the above results, it can be seen that by changing the refractive index of the refractive index-adjusting layer by irradiating it with electromagnetic waves after its formation, the emission color of the light-emitting element can be adjusted to any color, for example, a color between sky blue and deep blue, after the light-emitting element is fabricated.

[0079] [Embodiment 3] Fig. 6 is a diagram schematically illustrating a third example of the configuration of a light-emitting element according to the present disclosure. As shown in Fig. 6, the light-emitting element 3 has a refractive index adjustment layer 33 instead of the refractive index adjustment layer 13, and has electrical functional layers such as a hole transport layer 15 and an electron transport layer 16. The electron transport layer 16, the light-emitting layer 12, the hole transport layer 15, and the refractive index adjustment layer 33 correspond to the light-emitting functional layer 10.

[0080] The refractive index adjusting layer 33 further contains a hole injection material in addition to the refractive index adjusting material. Thus, the refractive index adjusting layer 33 further contains an electrically functional material that supplies holes to the light-emitting layer upon application of a voltage from the first electrode layer 11 and the second electrode layer 24. As a result, the refractive index adjusting layer 33 has the ability to inject holes into the light-emitting layer in addition to adjusting the refractive index described above, and also serves as a hole injection layer in the light-emitting element 3. The hole injection material is a material that has the property of stabilizing the injection of holes into the light-emitting layer 12, and may be one or more types. Examples of hole injection materials include poly(3,4-ethylenedioxythiophene):polystyrenesulfonic acid (PEDOT:PSS), NiO, and CuSCN.

[0081] The hole transport layer 15 is a layer containing a hole transport material. The hole transport material is a material that has the property of stabilizing the transport of holes into the light-emitting layer 12, and may be one or more types. Examples of the hole transport material include poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] (poly-TPD), polyvinylcarbazole (PVK), and poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] (TFB).

[0082] The electron transport layer 16 is a layer containing an electron transport material. The electron transport material is a material that has the property of stabilizing the transport of electrons into the light-emitting layer 12, and may be one or more types. Examples of electron transport materials include nanoparticles with electron transport properties, and examples of nanoparticles with electron transport properties include nanoparticles containing at least one of Zn, Mg, Ti, Si, Sn, W, Ta, Ba, Zr, Al, Y, and Hf. Examples of nanoparticles with electron transport properties include ZnO nanoparticles.

[0083] 6 is expressed as the distance from the center (light-emitting position) of the light-emitting layer 12 in the thickness direction to the interface between the refractive index adjusting layer 33 and the first electrode layer 11. The light-emitting element 3 further includes various electrical functional layers, one of which functions as both an electrical functional layer and a refractive index adjusting layer. Therefore, compared to the light-emitting element 2 described above, the light-emitting element 3 is more advantageous in terms of achieving higher luminous efficiency and a longer life.

[0084] [Embodiment 4] Figure 7 is a diagram schematically illustrating a fourth example of the configuration of a light-emitting element according to the present disclosure. As shown in Figure 7, the light-emitting element 4 has a refractive index adjustment layer 43 instead of the refractive index adjustment layer 33, does not have the hole transport layer 15, and has a light-emitting layer 42 instead of the light-emitting layer 12, but has the same configuration as the light-emitting element 3 described above. The light-emitting layer 42 and the refractive index adjustment layer 43 correspond to the light-emitting functional layer 10 described above. As shown in Figure 7, the optical path length d in the light-emitting element 4 is expressed as the distance from the center (light-emitting position) of the light-emitting layer 42 in the thickness direction to the interface between the refractive index adjustment layer 43 and the first electrode layer 11.

[0085] The light-emitting layer 42 includes a red light-emitting layer 421, a green light-emitting layer 422, and a blue light-emitting layer 423. For example, the light-emitting layers of each color form a sub-pixel, and one set of light-emitting layers of each color corresponds to one pixel. In this way, the light-emitting layer 42 includes multiple light-emitting regions that emit light of different wavelengths.

[0086] Like the refractive index matching layer 33, the refractive index matching layer 43 contains a hole transport material in addition to a refractive index changing material and also functions as a hole transport layer. The refractive index matching layer 43 includes three regions: a first refractive index region 431, a second refractive index region 432, and a third refractive index region 433. In the stacking direction, the first refractive index region 431 is a region in the refractive index matching layer 43 that overlaps with the red light-emitting layer 421, and the second refractive index region 432 is a region in the refractive index matching layer 43 that overlaps with the green light-emitting layer 422. The third refractive index region 433 is a region in the refractive index matching layer 43 that overlaps with the blue light-emitting layer 423. In this way, the refractive index matching layer 43 has multiple types of refractive index regions corresponding to the above-mentioned light-emitting regions.

[0087] The first refractive index region 431 has a refractive index n1. The second refractive index region 432 includes regions of two refractive indexes in the thickness direction. The region of the second refractive index region 432 facing the first electrode layer 11 has a refractive index n1, and the region of the second refractive index region 432 facing the light-emitting layer 42 has a refractive index n2. The third refractive index region 433 has a refractive index n2.

[0088] The refractive index n1 of the first refractive index region 431 is set to a value that satisfies the above-mentioned formula depending on the optical path length d and the wavelength λr of the light emitted from the red light-emitting layer 421. That is, n1 is set to a value that satisfies the relationship n1 × d = mλr / 4. Similarly, the refractive index n2 of the third refractive index region 433 is set to a value that satisfies the relationship n2 × d = mλb / 4, and the refractive index n12 of the second refractive index region 432, represented by the refractive indices n1 and n2, is set to a value that satisfies the relationship n12 × d = mλg / 4. The refractive index n12 is adjusted, for example, by the thickness of the region of refractive index n1 and the thickness of the region of refractive index n2. In this way, each of the above refractive index regions has a specific refractive index corresponding to the corresponding light-emitting region.

[0089] The refractive index can be set based on calculated values ​​obtained by computer simulation, etc. Alternatively, the refractive index can be set based on measured values ​​of luminous intensity when the refractive index of the refractive index-adjusting layer is changed in various ways in a light-emitting element produced on a trial basis.

[0090] In the light-emitting element 4, light emitted from the red light-emitting layer 421 passes through the first refractive index region 431 and is multiple-reflected between the first electrode layer 11 and the second electrode layer 24. The first refractive index region 431 is adjusted to have a refractive index n1 such that the light emitted from the red light-emitting layer 421 satisfies the above-mentioned formula. Therefore, the wavelength distribution of the red light emitted from the red light-emitting layer 421 and emitted from the second electrode layer 14 becomes sharper. Similarly, the wavelength distribution of the green light emitted from the green light-emitting layer 422 and emitted from the second electrode layer 14 also becomes sharper, and the wavelength distribution of the blue light emitted from the blue light-emitting layer 423 and emitted from the second electrode layer 14 also becomes sharper.

[0091] In this way, in the light-emitting element 4, an appropriate optical path length corresponding to the light emitted from each of the light-emitting layers of multiple colors is realized by the refractive index adjustment layer 43, which has the same thickness between electrode layers at a certain distance. Conventionally, in top-emission light-emitting elements, the film thickness of the electrical functional layer in the region corresponding to each color is individually set and precisely painted using a fine metal mask, thereby achieving an optical path length corresponding to each color. Based on the above-mentioned formula, n is constant, and the optical path length is achieved by individually adjusting L. In the light-emitting element 4, the above-mentioned optical path length corresponding to each color is achieved by forming regions that exhibit specific refractive indices in the refractive index adjustment layer 43. The regions with specific refractive indices are formed by irradiation with electromagnetic waves, as described below, and therefore can be formed more easily than by painting inks.

[0092] [Method for manufacturing light-emitting element] A method for manufacturing a light-emitting element according to the present disclosure will be described. Fig. 8 is a flowchart showing an example of the flow of steps in the method for manufacturing a light-emitting element according to the present disclosure, and Fig. 9 is a flowchart showing an example of the flow of steps for forming a refractive index adjusting layer in the method for manufacturing a light-emitting element according to the present disclosure.

[0093] 8, in the manufacturing process of the light-emitting device of the present disclosure, a first electrode layer is first prepared (step S501). The first electrode layer can be produced by selecting an electrode material according to the type of the light-emitting device and using a known method according to the electrode material.

[0094] Next, a refractive index adjustment layer is formed to overlap the first electrode layer (step S502).

[0095] In the process of producing the refractive index adjustment layer, when a material whose refractive index changes when irradiated with electromagnetic waves is used as the refractive index changing material, ink containing the refractive index changing material is first uniformly applied to a plane (step S601), as shown in Fig. 9. Here, the "plane" refers to a semi-finished light-emitting element to be coated with the ink, such as the aforementioned light-emitting element that has been fabricated up to the first electrode layer.

[0096] The ink can be prepared as a solution or dispersion depending on the type of refractive index changing material. The content of the refractive index changing material in the ink can be determined appropriately depending on the desired refractive index of the refractive index adjusting layer, taking into account the type of refractive index changing material and the electromagnetic wave irradiation conditions, as necessary. The ink application method can be determined appropriately from known methods depending on the properties of the ink and the precision of the area to be formed.

[0097] Next, the ink coating film prepared in step S601 is irradiated with electromagnetic waves (step S602). The electromagnetic waves are irradiated onto the coating film through a mask. This adjusts the refractive index at a desired position in the coating film. Irradiating the coating film with electromagnetic waves can be performed by the simple process of aligning the mask and irradiating the electromagnetic waves. The electromagnetic waves can be irradiated at any timing within a range in which the refractive index of the refractive index changing material in the coating film can be changed by irradiation with the electromagnetic waves. For example, the irradiation may be performed before the coating film dries or after the coating film has solidified. A refractive index adjustment layer is prepared through step S602.

[0098] Next, a light-emitting layer is formed on the refractive index adjustment layer (step S503). The light-emitting layer can be appropriately formed using known materials and known manufacturing methods. In this manner, a light-emitting functional layer including the refractive index adjustment layer and the light-emitting layer is formed on the first electrode layer.

[0099] Next, a second electrode layer is formed on the light-emitting layer (step S504). Like the light-emitting layer, the second electrode layer can also be appropriately formed using known materials and known methods. In this manner, a light-emitting device is manufactured in which the first electrode layer, the refractive index adjustment layer, the light-emitting layer, and the second electrode layer are stacked in this order.

[0100] The refractive index adjusting layer that also serves as the electrical functional layer can be produced by using the ink described above that further contains an electrical functional material. The electrical functional layer that does not also serve as the refractive index adjusting layer can be produced appropriately using a known material and a known method. Furthermore, depending on the stacking order, step S502 for producing the refractive index adjusting layer and step S503 for producing the light-emitting layer can be interchanged.

[0101] Next, a method for manufacturing a light-emitting device having a refractive index adjusting layer including the above-mentioned plurality of refractive index regions will be described using the light-emitting device 4 shown in Fig. 7 as an example. Figs. 10 to 14 are diagrams schematically showing the first to fifth states in the manufacturing method, respectively.

[0102] First, as shown in FIG. 10 , ink containing a refractive index changing material is applied to the first electrode layer 11 to form a coating film 71 of the refractive index changing material. The refractive index of the coating film at this time is defined as n1. Then, as indicated by the arrow in the upper right corner of FIG. 10 , one end of the coating film 71, consisting of one end, a central portion, and the other end, is irradiated with electromagnetic waves such as ultraviolet light. The coating film 71 becomes the refractive index adjustment layer 43, for example, by drying and solidifying. As a result, as shown in FIG. 11 , the refractive index of the end irradiated with the electromagnetic waves changes from n1 to n2. In this way, a region 43a with a refractive index of n1 and a region 43b with a refractive index of n2 are formed in the refractive index adjustment layer 43.

[0103] Next, as shown in FIG. 12 , ink containing a refractive index changing material is applied to the refractive index adjusting layer 43 to form a coating film 72 of the refractive index changing material. Then, as shown by the arrows at the upper right and center of FIG. 12 , electromagnetic waves are irradiated onto one end and the center of the coating film 72. As a result, as shown in FIG. 13 , the refractive index of the end and the center irradiated with the electromagnetic waves changes from n1 to n2. Thus, a region 43a with a refractive index of n1 and a region 43b with a refractive index of n2 are formed in the refractive index adjusting layer 43. More specifically, the refractive index adjusting layer 43 has one end formed by a region with a refractive index of n2, a central region formed by a region where the lower layer has a refractive index of n1 and the upper layer has a refractive index of n2, and the other end formed by a region with a refractive index of n1. The coating film 72 dries and solidifies to become the refractive index adjusting layer 43, and is integrated with the lower refractive index adjusting layer 43.

[0104] Next, as shown in FIG. 14 , a light-emitting layer 42 is fabricated on the refractive index matching layer 43 fabricated in two stages. For example, a red light-emitting layer 421 is fabricated on the other end portion, a green light-emitting layer 422 is fabricated on the central portion, and a blue light-emitting layer 423 is fabricated on the one end portion. In this manner, the other end portion, the central portion, and the one end portion correspond to the first refractive index region 431, the second refractive index region 432, and the third refractive index region 433, respectively. An electron transport layer 16 and a second electrode layer 24 are fabricated in this order on the light-emitting layer 42, thereby producing a light-emitting device 4 as shown in FIG. 7 .

[0105] [Embodiment 5] Fig. 15 is a diagram schematically illustrating a fifth example of the configuration of a light-emitting element according to the present disclosure. As shown in Fig. 15, the light-emitting element 5 has a refractive index adjustment layer 53 instead of the refractive index adjustment layer 43, and a light-emitting layer 52 instead of the light-emitting layer 42, but has the same configuration as the light-emitting element 4 described above. The light-emitting layer 52 and the refractive index adjustment layer 53 correspond to the light-emitting functional layer 10 described above. As shown in Fig. 15, the optical path length d in the light-emitting element 5 is expressed as the distance from the center (light-emitting position) of the light-emitting layer 52 in the thickness direction to the interface between the refractive index adjustment layer 53 and the first electrode layer 11.

[0106] The light-emitting layer 52 is a light-emitting layer that emits light of a single color (preferably white) having luminous intensities in at least two or more wavelength bands.

[0107] The refractive index matching layer 53 has a first refractive index region 531, a second refractive index region 532, and a third refractive index region 533. For example, each refractive index region constitutes a sub-pixel, and a set of three refractive index regions corresponds to one pixel. The first refractive index region 531 has a refractive index n1, the second refractive index region 532 has a refractive index n2, and the third refractive index region 533 has a refractive index n3. The magnitude of the refractive indices is n3 > n2 > n1.

[0108] Such a refractive index region is produced by irradiating electromagnetic waves as described above. As described above, first, ink containing a refractive index changing material is applied to the first electrode layer 11 to produce a coating film 71 with a refractive index n1. Next, the coating film is irradiated with electromagnetic waves (e.g., ultraviolet light) at an irradiation dose I2 at the position of the second refractive index region 532, and then the coating film is irradiated with electromagnetic waves at an irradiation dose I3 at the position of the third refractive index region 533. The magnitude of the irradiation dose is I3 > I2. In this way, it is possible to produce different refractive indices between the refractive index regions by varying the irradiation dose.

[0109] Although the light emitted from the light-emitting layer 52 is of a single color, the emitted light passes through regions with different refractive indices for each subpixel. As a result, light of a color corresponding to the refractive index n1 to n3 of each subpixel is emitted from each subpixel. For example, the subpixel in the first refractive index region 531 emits light of color C1 (e.g., red), the subpixel in the second refractive index region 532 emits light of color C2 (e.g., green), and the subpixel in the third refractive index region 533 emits light of color C3 (e.g., blue).

[0110] The light-emitting element of this embodiment is capable of emitting light of different colors for each sub-pixel from a single-color light-emitting layer. The color change for each sub-pixel is set by the amount of electromagnetic wave irradiation to a coating film of a uniform thickness. As such, this embodiment does not require different coatings of the light-emitting layer for each sub-pixel, which is advantageous in further simplifying the manufacture of the light-emitting element.

[0111] [Uses of Light-Emitting Element] The light-emitting element of the present disclosure is applied to a display device. The display device includes the light-emitting element of the present disclosure. The display element can be configured in the same manner as a known display device including a known light-emitting element, so long as it includes the light-emitting element of the present disclosure. Since the wavelength of the light emitted from the light-emitting element can be adjusted after the light-emitting element is manufactured, the display device can appropriately adjust the color of the light emitted from the light-emitting element or display a clear image with enhanced color emission from the light-emitting element.

[0112] [Modification] In the display element of the present disclosure, the light-emitting layer may contain a refractive index changing material, that is, the light-emitting layer may also serve as a refractive index adjusting layer.

[0113] In the display element of the present disclosure, the refractive index changing material may be any material that exhibits a refractive index according to the application of energy, and may be, for example, a material whose refractive index decreases when irradiated with electromagnetic waves.

[0114] The display element of the present disclosure may have a layer other than the electrical functional layer, for example, an electron injection layer. The electron injection layer may be a layer containing the electron transport material. The electron injection layer may be disposed on the second electrode layer side of the electron transport layer, and is preferably disposed adjacent to both the electron transport layer and the second electrode layer in the stacking direction.

[0115] When the refractive index adjusting layer also serves as an electrical functional layer, the electrical functional layer that the refractive index adjusting layer also serves as may be a layer other than the hole injection layer described above, and may be a hole transport layer, an electron transport layer, or an electron injection layer. The refractive index adjusting layer also serves as an electron injection layer contains a refractive index changing material and an electron injection material. The electrical functional layer that the refractive index adjusting layer also serves as may be of multiple types. In this case, the refractive index changing material in the refractive index adjusting layer (each electrical functional layer) may be the same in all electrical functional layers, or may be different for each electrical functional layer.

[0116] Furthermore, the refractive index adjusting layer is disposed between the electrode layers, and within the scope of the effects of the present disclosure, it may be a single layer as shown in embodiment 1, or may be a layer that also serves as a layer other than the electrical functional layer. Examples of such other layers include an intermediate layer and a buffer layer that are disposed between two adjacent layers in the stacking direction among the above-mentioned electrode layers, electrical functional layers, and light-emitting layers.

[0117] In addition, in the fourth embodiment, the refractive index adjustment layer 43 may be configured with three or more stages of coating films. In this case, the refractive index region in each stage can be appropriately set within a range in which electromagnetic waves that change the refractive index can be irradiated.

[0118] In the method for manufacturing a light-emitting element, when the refractive index adjustment layer includes a refractive index region having a constant refractive index in the thickness direction of the refractive index adjustment layer, the irradiation of electromagnetic waves to form the refractive index region may be performed after a layer to be disposed in a position overlapping the refractive index adjustment layer, such as a second electrode layer, is fabricated. In this case, the refractive index region can be set so that the refractive index adjustment layer exhibits an appropriate refractive index while monitoring the actual light emitted from the light-emitting element.

[0119] [Summary] As is clear from the above description, the light-emitting element (1) of a first aspect of the present disclosure is a light-emitting element having a first electrode layer (11), a light-emitting functional layer (10) that emits light upon application of a voltage, and a second electrode layer (11) stacked in this order, wherein the light-emitting functional layer contains a refractive index-changing material and exhibits a specific refractive index determined according to the optical path length of light emitted from the light-emitting functional layer in the light-emitting element and the wavelength of the light emitted from the light-emitting element. The first aspect makes it possible to control the wavelength of light emitted from the light-emitting element with a simple configuration of a light-emitting functional layer between the electrode layers of the light-emitting element.

[0120] In the light-emitting element of the second aspect of the present disclosure, in the first aspect, the first electrode layer may be a layer that reflects light emitted from the light-emitting layer, and the second electrode layer may be a layer that reflects a part of the light emitted from the light-emitting layer and transmits the rest. The second aspect is even more effective from the viewpoint of increasing the color purity and luminous intensity of the light emitted from the light-emitting element by multiple reflections between the electrode layers.

[0121] In the light-emitting element of the third aspect of the present disclosure, in the first or second aspect, the light-emitting functional layer includes a light-emitting layer (12) that emits light upon application of a voltage, and a refractive index adjusting layer (13) that contains a refractive index changing material and exhibits a specific refractive index, and the refractive index adjusting layer may further contain an electric functional material that supplies one or both of holes and electrons to the light-emitting layer upon application of a voltage to the first electrode layer and the second electrode layer. The third aspect is even more effective from the viewpoint of increasing the luminous efficiency of the light-emitting element.

[0122] In a light-emitting element according to a fourth aspect of the present disclosure, in any one of the first to third aspects, the light-emitting layer may have a plurality of light-emitting regions each having a different wavelength of emitted light, and the refractive index-adjusting layer may have a plurality of refractive index regions each having a specific refractive index corresponding to the light-emitting region. The fourth aspect is even more effective in terms of easily adjusting the optical path length of the emitted light, since the optical path length of the emitted light from the light-emitting layer can be adjusted for each emitted color without adjusting the film thickness by applying ink.

[0123] In the light-emitting element of a fifth aspect of the present disclosure, in any one of the first to fourth aspects, the refractive index changing material may be a material whose refractive index changes upon irradiation with electromagnetic waves. The fifth aspect is even more effective from the viewpoint of easily and precisely expressing the specific refractive index in the refractive index adjusting layer, since the refractive index adjusting layer exhibits a specific refractive index upon irradiation with electromagnetic waves.

[0124] A sixth aspect of the present disclosure provides a method for manufacturing a light-emitting element according to any one of the first to fifth aspects, including the steps of preparing a first electrode layer, fabricating a light-emitting functional layer overlapping the first electrode layer, and fabricating a second electrode layer overlapping the first electrode layer and the light-emitting functional layer. The sixth aspect enables control of the wavelength of light emitted from the light-emitting element with a simple configuration of a refractive index adjustment layer between the electrode layers of the light-emitting element.

[0125] In the method for manufacturing a light-emitting element according to a seventh aspect of the present disclosure, in the sixth aspect, the step of forming a refractive index adjusting layer overlapping the first electrode layer may include a step of uniformly applying, onto a plane, an ink containing a refractive index changing material whose refractive index increases when irradiated with electromagnetic waves, and a step of irradiating the ink coating with electromagnetic waves. The seventh aspect is even more effective from the viewpoint of easily forming the refractive index adjusting layer.

[0126] A display device according to an eighth aspect of the present disclosure includes a substrate and a light-emitting element according to any one of the first to fifth aspects disposed on the substrate. As with the first aspect, the eighth aspect allows for control of the wavelength of light emitted from the light-emitting element with a simple configuration.

[0127] 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.

[0128] According to the configuration of the present disclosure, the optical path length of light emitted from the light-emitting layer or the wavelength of light emitted from the light-emitting element can be appropriately and easily adjusted regardless of the layer thickness, which is expected to make it possible to provide high-quality display devices more simply and inexpensively, and to contribute to the achievement of the Sustainable Development Goals (SDGs) related to education, welfare, lifestyles, and industry, for example.

[0129] 1 to 5 Light-emitting element 10 Light-emitting functional layer 11 First electrode layer 12, 42, 52 Light-emitting layer 13, 33, 43, 53 Refractive index adjusting layer 14, 24 Second electrode layer 15 Hole transport layer 16 Electron transport layer 43a Region where refractive index is n1 43b Region where refractive index is n2 71, 72 Coating of refractive index changing material 100 Display device 110 Substrate 120 Barrier layer 130 Thin-film transistor layer 131 to 133 Inorganic insulating film 134 Planarization film 140 Sealing layer 141, 143 Inorganic sealing film 142 Organic film 150 Functional film 421 Red light-emitting layer 422 Green light-emitting layer 423 Blue light-emitting layer 431, 531 First refractive index region 432, 532 Second refractive index region 433, 533 Third refractive index region DA Display area NDA Frame area PIX Pixel RSP Red subpixel GSP Green subpixel BSP Blue subpixel SEM Semiconductor film SEM1 Channel region SEM2 Drain region SEM3 Source region

Claims

1. A light-emitting device having a first electrode layer, a light-emitting functional layer that emits light upon application of a voltage, and a second electrode layer, which are stacked in this order, wherein the light-emitting functional layer contains a refractive-index changing material and exhibits a specific refractive index determined according to the optical path length of the light emitted from the light-emitting functional layer in the light-emitting device and the wavelength of the light emitted from the light-emitting device.

2. The light-emitting device according to claim 1, wherein the first electrode layer is a layer that reflects light emitted from the light-emitting functional layer, and the second electrode layer is a layer that reflects a part of the light emitted from the light-emitting functional layer and transmits the remainder.

3. The light-emitting functional layer includes a light-emitting layer that emits light upon application of a voltage and a refractive-index adjustment layer that contains the refractive-index changing material and exhibits the specific refractive index, and the refractive-index adjustment layer further contains an electrofunctional material that supplies one or both of holes and electrons to the light-emitting layer upon application of a voltage to the first electrode layer and the second electrode layer. The light-emitting device according to claim 1 or 2.

4. The light-emitting layer has a plurality of light-emitting regions having different wavelengths of emitted light, the refractive-index adjustment layer has a plurality of refractive-index regions corresponding to the light-emitting regions, and each of the refractive-index regions has a specific refractive index corresponding to the corresponding light-emitting region. The light-emitting device according to claim 3.

5. The light-emitting device according to claim 3 or 4, wherein the refractive-index changing material is a material whose refractive index changes upon irradiation with electromagnetic waves.

6. A method for manufacturing the light-emitting device according to any one of claims 1 to 5, including a step of preparing the first electrode layer, a step of fabricating the light-emitting functional layer that overlaps the first electrode layer, and a step of fabricating the second electrode layer that overlaps the first electrode layer and the light-emitting functional layer. A method for manufacturing a light-emitting device.

7. The step of fabricating the light-emitting functional layer includes a step of uniformly applying an ink containing a refractive-index changing material whose refractive index increases upon irradiation with electromagnetic waves onto a plane, and a step of irradiating the ink coating film with electromagnetic waves. The method for manufacturing a light-emitting device according to claim 6.

8. A display device having a substrate and the light-emitting device according to any one of claims 1 to 5 disposed on the substrate.

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