Patent ID: 12200953

DESCRIPTION OF EMBODIMENTS

First Embodiment

Hereinafter, an embodiment of the disclosure will be described. In addition, a “lower layer” means a layer that is formed in a process prior to that of a comparison layer, and an “upper layer” means a layer that is formed in a process after that of a comparison layer.

FIG.1is a diagram schematically illustrating an example of a layered structure of a light-emitting device100according to the present embodiment.

As illustrated inFIG.1, the light-emitting device100includes an array substrate1as a support body, and a plurality of types of light-emitting elements10, each having a light emission peak wavelength in a different wavelength band. The light-emitting device100has a structure in which each layer of the light-emitting element10is layered on the array substrate1in which a thin film transistor (TFT; not illustrated) is formed. Note that, in the disclosure, a direction from the array substrate1side toward the light-emitting element10side is referred to as “upward”, and a direction from the light-emitting element10side toward the array substrate1side is referred to as “downward”.

The light-emitting device100is a display device (QLED display) including, as light-emitting elements10, quantum dot light-emitting diodes (hereinafter referred to as “QLED”) that use quantum dots (semiconductor nanoparticles) QD as a light-emitting material. The light-emitting device100includes a plurality of pixels P, and includes the light-emitting element10corresponding to the pixel P for each of the pixels P.

The light-emitting element10includes an anode2, a light-emitting layer (hereinafter referred to as “EML”)5, and a cathode7, in this order. Between the anode2and EML5, a hole transport layer (hereinafter referred to as “HTL”)3is provided as a layer having hole transport properties and including a metal chalcogenide. Between the HTL3and the EML5, an insulating layer (hereinafter referred to as “IL”)4including an organic material is provided as an intermediate layer between the HTL3and the EML5. Note that, between the EML5and the cathode7, an electron transport layer (hereinafter referred to as “ETL”)6may be provided as a layer having electron transport properties.

The light-emitting element10illustrated inFIG.1includes the anode2, the HTL3, the IL4, the EML5, the ETL6, and the cathode7in this order from the array substrate1side (that is, lower layer side).

The anode2, the HTL3, the IL4, and the EML5are each separated into an island shape for each pixel P by a bank (not illustrated). As a result, in the light-emitting device100, a plurality of the QLEDs are provided correspondingly to the pixels P as the light-emitting elements10.

The bank described above functions as a pixel separation wall as well as an edge cover covering each edge of anodes2R,2G,2B. An insulating material such as an acrylic resin or a polyimide resin, for example, is used in the bank described above.

The light-emitting device100illustrated inFIG.1includes a pixel RP that is red, a pixel GP that is green, and a pixel BP that is blue as the pixels P. In the pixel RP, a light-emitting element10R that emits red light (red light-emitting element) is provided as the light-emitting element10. In the pixel GP that is green, a light-emitting element10G that emits green light (green light-emitting element) is provided as the light-emitting element10. In the pixel BP that is blue, a light-emitting element10B that emits blue light (blue light-emitting element) is provided as the light-emitting element10.

Hereafter, the anodes2having island shapes separated from each other in a corresponding manner to the pixel RP, the pixel GP, and the pixel BP by the bank described above are respectively referred to as the anode2R, the anode2G, and the anode2B. Similarly, the HTLs3having island shapes separated from each other in a corresponding manner to the pixel RP, the pixel GP, and the pixel BP by the bank described above are respectively referred to as an HTL3R, an HTL3G, and an HTL3B. The ILs4having island shapes separated from each other in a corresponding manner to the pixel RP, the pixel GP, and the pixel BP by the bank described above are respectively referred to as an IL4R, an IL4G, and an IL4B. The EMLs5having island shapes separated from each other in a corresponding manner to the pixel RP, the pixel GP, and the pixel BP by the bank described above are respectively referred to as an EML5R, an EML5G, and an EML5B. Note that the ETL6and the cathode7are not separated by the bank described above, and are formed in solid-like shapes in a display region as common layers common to all pixels P.

The light-emitting element10R is formed by the anode2R, the HTL3R, the IL4R, and the EML5R, each having an island shape, and the ETL6and the cathode7, each being a common layer. The light-emitting element10G is formed by the anode2G, the HTL3G, the IL4G, and the EML5G, each having an island shape, and the ETL6and the cathode7, each being a common layer. The light-emitting element10B is formed by the anode2B, the HTL3B, the IL4B, and the EML5B, each having an island shape, and the ETL6and the cathode7, each being a common layer.

The anodes2R,2G,2B, which are lower electrodes formed on the array substrate1, are pattern anodes provided for each pixel P and are respectively electrically connected to the TFTs of the array substrate1. On the other hand, the cathode7, which is an upper electrode, is a common cathode common to all pixels P.

Each layer of the light-emitting elements10R,10G,10B may be formed of the same material in layers corresponding to one another in the light-emitting elements10R,10G,10B, with the exception of the EMLs5R,5G,5B.

The EML5R includes, as the quantum dot QD, a quantum dot QR that emits red light. The EML5G includes, as the quantum dot QD, a quantum dot QG that emits green light. The EML5B includes, as the quantum dot QD, a quantum dot QB that emits blue light.

Note that, in the disclosure, the red light refers to light having a light emission peak wavelength in a wavelength band from 600 nm to 780 nm. The green light refers to light having a light emission peak wavelength in a wavelength band from 500 nm to 600 nm. The blue light refers to light having a light emission peak wavelength in a wavelength band from 400 nm to than 500 nm.

The light-emitting element10R preferably has a light emission peak wavelength in a wavelength band from 620 nm to 650 nm. The light-emitting element10G preferably has a light emission peak wavelength in a wavelength band from 520 nm to 540 nm. The light-emitting element10B preferably has a light emission peak wavelength in a wavelength band from 440 nm to 460 nm.

However, the configuration described above is an example, and the configuration of the light-emitting device100is not necessarily limited to the configuration described above. The light-emitting device100may include, as the light-emitting element10, a light-emitting element that emits light having a light emission peak wavelength in a wavelength band other than the wavelength bands described above. The ETL6may be separated into an island shape for each pixel P by the bank described above. The layered order from the anode2to the cathode7may be reversed. Accordingly, the light-emitting element10may include the anode2, the HTL3, the IL4, the EML5, the ETL6, and the cathode7in this order from the upper layer side. In a case in which the cathode7is the lower electrode formed on the array substrate1, the cathode7is electrically connected to the TFT of the array substrate1as a pattern cathode. On the other hand, the anode2serving as the upper electrode is used as a common anode common to all pixels P. Hereinafter, a case in which the light-emitting device100has the configuration illustrated inFIG.1will be described as an example.

Note that, when there is no need to distinguish the light-emitting elements10R,10G,10B from one another, these light-emitting elements10R,10G,10B are collectively referred to simply as the “light-emitting element10” as described above. Similarly, when there is no need to distinguish the pixels RP, GP, BP from one another, these pixels RP, GP, BP are collectively referred to simply as the “pixel P”. When there is no need to distinguish the anodes2R,2G,2B from one another, these anodes2R,2G,2B are collectively referred to simply as the “anode2”. When there is no need to distinguish the HTLs3R,3G,3B from one another, these HTLs3R,3G,3B are collectively referred to simply as the “HTL3”. When there is no need to distinguish the ILs4R,4G,4B from one another, these ILs4R,4G,4B are collectively referred to simply as the “IL4”. When there is no need to distinguish the EMLs5R,5G,5B from one another, these EMLs5R,5G,5B are collectively referred to simply as the “EML5”. When there is no need to distinguish the quantum dots QR, QG, QB from one another, these quantum dots QR, QG, QB are collectively referred to simply as the “quantum dot QD”.

The anode2is formed of a conductive material, and has a function as a hole injection layer (hereinafter referred to as “HIL”) for injecting a positive hole into the HTL3. The cathode7is formed of a conductive material and has a function as an electron injection layer (hereinafter referred to as “EIL”) for injecting an electron into the ETL6.

One of the anode2and the cathode7is made of a light-transmissive material. Note that one of the anode2and the cathode7may be formed of a light-reflective material. In a case in which the light-emitting device100is a top-emitting-type light-emitting device, the cathode7being an upper layer is formed of a light-transmissive material, and the anode2being a lower layer is formed of a light-reflective material. In a case in which the light-emitting device100is a bottom-emitting-type light-emitting device, the cathode7being an upper layer is formed of a light-reflective material, and the anode2being a lower layer is formed of a light-transmissive material.

As the light-transmissive material, a transparent conductive material can be used, for example. Specifically, for example, indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO2), or fluorine-doped tin oxide (FTO) can be used as the light-transmissive material. These materials have a high transmittance of visible light, and thus luminous efficiency is improved.

As the light-reflective material, a metal material can be used, for example. Specifically, for example, aluminum (Al), silver (Ag), copper (Cu), or gold (Au) can be used as the light-reflective material. These materials have a high reflectivity of visible light, and thus luminous efficiency is improved.

Further, an electrode having light reflectivity obtained by making either one of the anode2or the cathode7a layered body including a light-transmissive material and a light-reflective material may be used.

The anode2and the cathode7can be formed using various methods known as the related art as formation methods of the anode2and the cathode7, such as sputtering or a vacuum vapor deposition technique, for example.

The ETL6transports electrons to the EML5. Note that the ETL6may have a function of inhibiting the transport of positive holes. Further, the ETL6may also serve as an EIL that promotes the injection of electrons from the cathode7into the EML5. In a case in which a layer having electron transport properties is provided between the cathode7and the EML5, the light-emitting element10may include the EIL and the ETL6in this order from the cathode7side, or may include only the ETL6.

A known electron transport material can be used for the ETL6. Examples of the electron transport material include zinc oxide (for example, ZnO), titanium oxide (for example, TIO2), and strontium oxide titanium (for example, SrTiO3). One type of these electron transport materials may be used, or two or more types thereof may be mixed and used as appropriate. Further, nanoparticles may be used for the electron transport material described above.

The HTL3transports positive holes to the EML5via the IL4. Note that the HTL3may have a function of inhibiting the transport of electrons. Further, the HTL3may also serve as an HIL that promotes the injection of positive holes from the anode2into the EML5.

The HTL3is a layer having hole transport properties and including a metal chalcogenide, as previously described. Note that the HTL3mainly includes a metal chalcogenide, but may further include other materials. Metal chalcogenides have particularly high durability, even among inorganic materials. Examples of metal chalcogenides include nickel oxide (for example, NiO), copper oxide (for example, Cu2O), and copper sulfide (for example, CuS). One type of these metal chalcogenides may be used, or two or more types thereof may be mixed and used as appropriate. Accordingly, the metal chalcogenide described above is at least one type selected from the group consisting of nickel oxide, copper oxide, and copper sulfide.

The HTL3can be formed by, for example, a sol-gel method, sputtering, chemical vapor deposition (CVD), or a spin coating method (application method).

The IL4is provided between the HTL3and the EML5, in contact with the HTL3and the EML5. Note that the IL4mainly includes an organic material, but may further include other materials.

The IL4is formed using an insulating material capable of being uniformly layered in a manufacturing process without any loss due to dissolution of the lower layer or any trouble such as repelling during material application to the lower layer. As the insulating material described above, an organic material that is not a good conductor is desirable, and an organic material that does not include a hydroxyl group is even more desirable. Further, to suppress an overflow of electrons from the EML5to the HTL3, an electron affinity value of the IL4is preferably smaller than an electron affinity value of the EML5by 0.5 eV or greater. Furthermore, an ionization potential value of the IL4is desirably greater than a value obtained by subtracting 0.5 eV from an ionization potential value of the EML5because such a value facilitates the injection of positive holes from the HTL3into the EML5.

That is, given EAILas the electron affinity of the IL4and EAEMLas the electron affinity of the EML5, then preferably EAIL≤EAEML−0.5 eV. Further, given IPILas the ionization potential of the IL4and IPEMLas the ionization potential of the EML5, then preferably IPIL≥IPEML−0.5 eV.

Examples of such an insulating material include polymethyl methacrylate (abbreviation: PMMA), polyvinyl pyrrolidone (abbreviation: PVP), and poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (abbreviation: PFN). One type of these insulating materials may be used, or two or more types thereof may be mixed and used as appropriate. Accordingly, the IL4may be formed of at least one type of insulating material selected from the group consisting of PMMA, PVP, and PFN.

As an example, the electron affinities, the ionization potentials, and band gaps of the PMMA, PVP, and PFN are shown in Table 1. The band gap corresponds to the difference between the ionization potential and the electron affinity of the layer.

TABLE 1Electron affinityIonization potentialBand gapMaterialEAIL(eV)IPIL(eV)(eV)PMMA2.65.83.2PVA2.05.93.9PFN2.15.63.5

The IL4can be formed by, for example, a spin coating method (application method), a dip coating method, or an ink-jet method.

As mentioned above, metal chalcogenides have durability. Further, as described above, a light-emitting device that uses the quantum dots QD in the EML, unlike a light-emitting device that uses an organic EL in the EML, can be manufactured at low cost by a manufacturing process that does not use a high-vacuum device. Nevertheless, when a metal chalcogenide is used for the HTL and a light-emitting device that uses the quantum dots QD as described above is manufactured by a manufacturing process that does not use a high-vacuum device, the metal chalcogenide surface may be exposed by a gas containing moisture. When the metal chalcogenide surface is even slightly exposed to a gas containing moisture, a hydroxyl group is presumably adsorbed on the metal chalcogenide surface.

In particular, from the perspective of versatility of a manufacturing apparatus, desirably the manufacturing apparatuses of each layer in the light-emitting element10are separated from each other. Accordingly, desirably the manufacturing apparatus of the HTL3and the film formation apparatus used in the next process (that is, manufacturing apparatus of the layer formed on the HTL3) are separated from each other. Nevertheless, when the HTL3is formed and subsequently the substrate on which the HTL3is formed is transported to the manufacturing apparatus separated from the manufacturing apparatus of the HTL3, the substrate on which the HTL3is formed is exposed to the atmosphere between the two manufacturing apparatuses.

Thus, although the manufacturing process of the light-emitting device100includes a process in which the metal chalcogenide surface of the HTL3is exposed to a gas containing moisture, from the standpoint of the versatility of the manufacturing apparatus, desirably the manufacturing apparatuses of each layer in the light-emitting element10are separated from each other. Then, in the process in which the metal chalcogenide surface of the HTL3is exposed to a gas containing moisture, the hydroxyl group is presumably adsorbed on the surface of the metal chalcogenide. Accordingly, the manufacturing process of the light-emitting device100including a process in which the metal chalcogenide surface of the HTL3is exposed to a gas containing moisture presumably means that the manufacturing process of the light-emitting device100includes a process in which a hydroxyl group is adsorbed on the surface of the metal chalcogenide.

The IL4suppresses charging of the quantum dots QD by the hydroxyl group on the metal chalcogenide surface, and suppresses a decrease in light-emission characteristics caused by the charging of the quantum dots QD.

Further, the IL4has the effect of controlling the transport of positive holes from the HTL3to the EML5and inhibiting the transport of electrons injected from cathode7. This makes it possible to increase a recombination efficiency of the positive holes and the electrons within the EML5and thus improve luminous efficiency.

The EML5is a layer that includes a light-emitting material and emits light due to the occurrence of recombination between electrons transported from the cathode7and positive holes transported from the anode2. The light-emitting device100includes, in each pixel P, the quantum dots QD layered in a plurality of layers as a light-emitting material.

The method of forming the EML5is not particularly limited, but a solvolysis method is suitably used instead of, for example, crystal growth. The EML5can be formed by applying a dispersion of the quantum dots QD in a solvent (dispersant) to an upper surface of the layer that is a lower layer of the EML5to form a coating film containing the quantum dots QD, and subsequently volatilizing the solvent described above to solidify (cure) the coating film described above. As the solvent described above, water or an organic solvent such as hexane or toluene can be used. The dispersion described above is separately patterned for each pixel P using a spin coating method, an ink-jet method, or the like. Note that the dispersion may be mixed with a dispersion material such as thiol and amine.

The dispersion described above is a colloidal solution including the quantum dots QD, ligands adsorbed (coordinated) on the surfaces of the quantum dots QD with the quantum dots QD as receptors, and the solvent described above. The ligand is a surface-modifying group that modifies the surface of the quantum dot QD. The surface of the quantum dot QD is protected by the ligand.

The EML5thus formed by the solvolysis method includes the quantum dots QD, each having a spherical shape, and the ligands. The quantum dot QD of the application type thus formed by the solvolysis method has a spherical shape instead of an island shape (lens shape) such as when formed by crystal growth, making it possible to reduce the polarization characteristics of light emission. Further, with the EML5including ligands, it is possible to suppress aggregation of the quantum dots QD during formation of an applied film including the quantum dots QD and favorably disperse the quantum dots QD.

The light-emitting device100includes the quantum dots QD of a plurality of types, and includes the quantum dots QD of the same type in the same pixel P. The EML5R has a configuration in which a plurality of the quantum dots QR are layered, for example. The EML5G has a configuration in which a plurality of the quantum dots QG are layered, for example. The EML5B has a configuration in which a plurality of the quantum dots QB are layered, for example.

FIG.2is a cross-sectional view schematically illustrating an overall configuration of the quantum dots QR, QG, QB and ligands LR, LG, LB included in the EMLs5R,5G,5B of the light-emitting device100.

The quantum dots QR, QG, QB as receptors used in the present embodiment are core-shell type quantum dots (core-shell particles), and are each a core-shell type quantum dot (core-shell particle) including a core and a shell covering the core.

As illustrated inFIG.2, the quantum dot QR includes a core CR and a shell SR covering the core CR. Similarly, the quantum dot QG includes a core CG and a shell SG covering the core CG. The quantum dot QB includes a core CB and a shell SB covering the core CB.

Further, the EML5R includes the ligand LR adsorbed on the surface of the quantum dot QR. The EML5G includes the ligand LG adsorbed on the surface of the quantum dot QG. The EML5B includes the ligand LB adsorbed on the surface of the quantum dot QB.

The quantum dots QR, QG, QB each may include, for example, at least one type of semiconductor material formed of an element of at least one type selected from the group consisting of cadmium (Cd), sulfur (S), tellurium (Te), selenium (Se), zinc (Zn), indium (In), nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), aluminum (Al), gallium (Ga), lead (Pb), silicon (Si), germanium (Ge), and magnesium (Mg).

As the shells SR, SG, SB, zinc sulfide (ZnS) is used, for example. As materials of the shells SR, SG, SB, materials having lattice constants similar to those of the cores CR, CG, CB covered by the shells SR, SG, SB are suitably used. In a case in which the lattice constants of the cores CR, CG, CB are compatible with the lattice constants of the shells SR, SG, SB covering the cores CR, CG, CB, a number of defects in the crystalline body can be reduced. Further, as the materials of the shells SR, SG, SB, desirably a shell material having a larger band gap than that of the material of the cores CR, CG, CB covered by the shells SR, SG, SB is used. By using such a material, it is possible to increase a photoluminescence quantum yield (PLQY) and thus protect an excited state. ZnS satisfies these requirements. However, the material of the shells SR, SG, SB is not limited to ZnS, and other suitable materials may be used.

Examples of combinations (core/shell) of the cores CR, CG, CB and the shells SR, SG, SB in each quantum dot QR, QG, QB include cadmium selenide (CdSe)/zinc selenide (ZnSe), CdSe/ZnS, cadmium sulfide (CdS)/ZnSe, CdS/ZnS, ZnSe/ZnS, indium phosphide (InP)/ZnS, or zinc oxide (ZnO)/magnesium oxide (MgO).

The ligands LR, LG, LB each consist of an adsorption group adsorbed (coordinated) on the surface of each quantum dot QR, QG, QB, and an alkyl group bonded to the adsorption group. Examples of the adsorption group described above include an amino group, a phosphine group, a carboxyl group, a hydroxyl group, and a thiol group. Further, examples of the alkyl group described above include an alkyl group having from 2 to 50 carbons.

Examples of the ligands LR, LG, LB include hexadecylamine, oleylamine, octylamine, hexadecanthiol, dodecanthiol, trioctylphosphine, trioctylphosphine oxide, myristic acid, and oleic acid. The ligands LR, LG, LB also serve as dispersing agents that improve a dispersibility of the quantum dots QR, QG, QB in the dispersions.

As a feature of the core-shell type quantum dot QD, a wavelength of light emitted by the core-shell type quantum dot QD is dependent on a particle size of the core that is a light-emitting portion and is independent of a particle size of the shell. A wavelength of light emitted by the quantum dots QR, QG, QB can be controlled according to the particle size of the cores CR, CG, CB of the quantum dots QR, QG, QB.

The quantum dot QD tends to lengthen in light emission wavelength as the particle size of the core that is the light-emitting portion is increased, and tends to shorten in the light emission wavelength as the particle size of the core is decreased.

As illustrated inFIG.2, given d1as the particle size (diameter size) of the core CR, d11as the particle size (diameter size) of the core CG, and d21as the particle size (diameter size) of the core CB, then d1>d11>d21. The particle sizes (hereinafter referred to as “core diameters”) d1, d11, d21of these cores CR, CG, CB need only be set as appropriate to obtain the desired light emission wavelengths depending on the materials of the cores CR, CG, CB, and are not particularly limited. These core diameters d1, d11, d21can be set as in the related art.

The core diameters d1, d11, d21described above are, for example, from 1 nm to 10 nm. The quantum dots QR, QG, QB emit light having a wavelength corresponding to the band gap (prohibited band width) and quantum level (excitation level) thereof. As described above, the quantum dots QR, QG, QB according to the present embodiment have spherical shapes and substantially uniform particle sizes. The quantum dots QR, QG, QB emit light having wavelengths corresponding to the core diameters d1, d11, d21of the respective cores CR, CG, CB, which are the light-emitting portions.

Further, given d3as an outermost particle size of the quantum dot QR including the shell SR, d13as an outermost particle size of the quantum dot QG including the shell SG, and d23as an outermost particle size of the quantum dot QB including the shell SB, these outermost particle sizes d3, d13d23are from 2 nm to 20 nm, for example. Layer thicknesses of the EMLs5R,5G,5B are preferably about several times the outermost particle sizes d3, d13, d23of each quantum dots QR, QG, QB, and a number of overlapping layers of each quantum dot QR, QG, QB in the EMLs5R,5G,5B is from 1 to 9 layers, for example.

The core diameters d1, d11, d21described above can be calculated from a quantum size effect by analyzing the materials of the cores CR, CG, CB. Further, the outermost particle sizes d43, d13, d23described above can be measured from transmission electron microscope (TEM) images of cross sections of the EMLs5R,5G,5B. Note that thicknesses of the shells SR, SG, SB and lengths of the ligands LR, LG, LB will be described below.

In the light-emitting elements10R,10G,10B according to the present embodiment, layer thicknesses of layers other than the ILs4R,4G,4B can be set as in light-emitting elements of the related art.

Table 2 shows the layer thickness of each layer in the light-emitting elements10R,10G,10B according to the present embodiment. In Table 2, the layer thicknesses in parentheses indicate suitable ranges for the layer thickness of each layer. Further, the layer thicknesses outside the parentheses are the specific layer thicknesses of each layer in the light-emitting elements10R,10G,10B used in the present embodiment and indicate examples of combinations of the layer thickness of each layer in the light-emitting elements10R,10G,10B.

TABLE 2Layer thickness of eachlayer (nm)Anode electrodeR: 100 (from 20 to 200)G: 100 (from 20 to 200)B: 100 (from 20 to 200)HTLR: 50 (from 20 to 150)(Metal chalcogenide layer)G: 50 (from 20 to 150)B: 50 (from 20 to 150)ILR: 6 (from 0 to 12)G: 6 (from 0 to 12)B: 8 (from 0.5 to 12.5)EMLR: 40 (from 15 to 80)G: 40 (from 15 to 80)B: 40 (from 15 to 80)ETL50 (from 20 to 150)Cathode electrode100 (from 50 to 200)

As shown in Table 2, layer thicknesses of the anodes2R,2G,2B are preferably from 20 nm to 200 nm. Further, layer thicknesses of the HTLs3R,3G,3B are preferably from 20 nm to 150 nm. A layer thickness of the IL4R and a layer thickness of the IL4G are preferably not greater than 12 nm. A layer thickness of the IL4B is preferably from 0.5 nm to 12.5 nm. However, the ILs4R,4G,4B are set so that the layer thickness of the IL4B is greater than the layer thickness of the IL4R and the layer thickness of the IL4B is greater than the layer thickness of the IL4G. The layer thicknesses of the EMLs5R,5G,5B are preferably from 15 nm to 80 nm. A layer thickness of the ETL6is preferably from 20 nm to 150 nm. A layer thickness of the cathode7is preferably from 50 nm to 200 nm.

In the following, an example of a manufacturing method of the light-emitting elements10R,10G,10B and the light-emitting device100according to the present embodiment will be described with reference toFIG.1and Table 2.

In the present embodiment, first, the array substrate1as a support body was prepared, and an ITO layer having a layer thickness of 100 nm was formed in a matrix shape on the array substrate1as the anodes2R,2G,2B by sputtering (anode formation process).

Next, a bank having a lattice pattern (not illustrated) was formed as a pixel separation wall and edge cover, covering each edge of the anodes2R,2G,2B (bank formation process).

Next, NiO layers having a layer thickness of 50 nm were respectively formed as the HTLs3R,3G,3B by respectively spin coating NiO on the anodes2R,2G,2B, and subsequently applying heat in the atmosphere (HTL formation process).

Next, PMMA layers were respectively formed as the ILs4R,4G,4B on the HTLs3R,3G,3B using a solution of PMMA dissolved in acetone by a spin coating method (IL formation process). Note that films were formed using a mask in areas other than the film formation area, and the layer thicknesses of the ILs4R,4G,4B were adjusted by changing the concentration of the PMMA in the solution described above, the number of revolutions during spin coating, and the like. Thus, a PMMA layer having a layer thickness of 8 nm was formed as the IL4B, and PMMA layers having a layer thickness of 6 nm were each formed as the IL4R and the IL4G.

Next, quantum dot QD layers having a layer thickness of 40 nm were formed as the EMLs5R,5G,5B on the ILs4R,4G,4B, respectively, by a spin coating method (EML formation process).

Next, a ZnO layer having a layer thickness of 50 nm and consisting of ZnO—NPs (nanoparticles) was formed as the ETL6, covering the EMLs5R,5G,5B and the bank described above as a common layer common to each pixel P by a spin coating method (ETL formation process). According to the present embodiment, by thus forming the ETL6using the same electron transport material in at least a portion of the light-emitting elements10R,10G,10B, it is possible to make the ETL6a common layer in at least the portion of the light-emitting elements described above. According to the present embodiment, the ETL6can be formed more easily by making the material of the ETL6common to the light-emitting elements10R,10G,10B as described above.

Next, an Al layer having a layer thickness of 100 nm was formed as the cathode7on the ETL6as a common layer common to each pixel P by a vacuum vapor deposition technique (cathode formation process).

In this manner, the light-emitting elements10R,10G,10B according to the present embodiment were manufactured. The light-emitting device100according to the present embodiment is manufactured by sealing the light-emitting elements10R,10G,10B by a sealing layer (not illustrated) after the cathode formation process described above.

Next, an effect of the light-emitting device100according to the present embodiment will be described.

As described above, in NPL 1, the distance from the carrier transport layer to the quantum dot core is shortened to improve the characteristics of the light-emitting element. On the other hand, in NPL 2, contrary to NPL 1, the distance from the carrier transport layer to the quantum dot core is lengthened to improve the characteristics of the light-emitting element.

For this reason, the inventors of the present application conducted extensive studies, which lead to the following conclusions. As described above, NPL 1 uses a common organic material for the hole injection layer and the hole transport layer. The reason for shortening the distance from the carrier transport layer to the quantum dot core in such a light-emitting element is presumably because it is more difficult for carriers to be injected from the carrier transport layer into the quantum dot core in blue quantum dots compared to red quantum dots and green quantum dots.

On the other hand, NPL 2 uses NiO for the hole transport layer as described above. NiO is a type of metal chalcogenide. The reason for lengthening the distance from the carrier transport layer to the quantum dot core in such a light-emitting element is presumably because the presence of a hydroxyl group on the metal chalcogenide surface charges the quantum dots, which degrades the characteristics of the light-emitting element.

However, according to the studies of the inventors of the present application, when a metal chalcogenide is used in a layer having hole transport properties and the thickness of the quantum dot shell of each light-emitting element differing in light emission wavelength is increased, the luminance of the light-emitting element that emits light in a wavelength band having the shortest light emission peak wavelength lowers, as described above.

Therefore, the inventors of the present application conducted further extensive studies. As a result, the inventors of the present application found that the problem described above can be solved by making the layer thickness of the intermediate layer between the EML and the layer composed of a metal chalcogenide in the light-emitting element that emits light in a wavelength band having the shortest light emission peak wavelength greater than the layer thicknesses of the corresponding intermediate layers of the other light-emitting elements. Therefore, in the present embodiment, the layer thicknesses of the ILs4R,4G,4B are each set so that the layer thickness of the IL4B is greater than the layer thickness of the IL4R, and the layer thickness of the IL4B is greater than the layer thickness of the IL4G, as described above. The reason for the above will be described in more detail below with reference toFIG.2toFIG.5.

FIG.3toFIG.5illustrate the energy bands and layer thicknesses of each layer in the light-emitting elements10R,10G,10B according to the present embodiment manufactured by the method described above.FIG.3illustrates the energy band and the layer thickness of each layer in the light-emitting element10R.FIG.4illustrates the energy band and the layer thickness of each layer in the light-emitting element10G.FIG.5illustrates the energy band and the layer thickness of each layer in the light-emitting element10B.

As illustrated inFIG.3toFIG.5, the ITO layer as the anodes2R,2G,2B has a Fermi level (hereinafter referred to as “EF1”) of 4.7 eV, and the Al layer as the cathode7has a Fermi level (hereinafter referred to as “EF2”) of 4.3 eV. Further, the NiO layer as the HTLs3R,3G,3B has an electron affinity (hereinafter referred to as “EAHTL”) of 1.9 eV and an ionization potential (hereinafter referred to as “IPHTL”) of 5.4 eV. Further, the ZnO layer as the ETL6has an electron affinity (hereinafter referred to as “EAETL”) of 4.0 eV and an ionization potential (hereinafter referred to as “IPETL”) of 7.5 eV. Further, the quantum dot QD layer as the EML5R has an electron affinity (hereinafter referred to as “EAEMLR”) of 5.9 eV and an ionization potential (hereinafter referred to as “IPEMLR”) of 3.9 eV. The quantum dot QD layer as the EML5G has an electron affinity (hereinafter referred to as “EAEMLG”) of 5.9 eV, and an ionization potential (hereinafter referred to as “IPEMLG”) of 3.2 eV. The quantum dot QD layer as the EML5B has an electron affinity (hereinafter referred to as “EAEMLB”) of 5.9 eV, and an ionization potential (hereinafter referred to as “IPEMLB”) of 3.2 eV. Further, the PMMA as the ILs4R,4G,4B has an electron affinity EAILof 2.6 eV, and an ionization potential IPILof 5.8 eV, as shown in Table 1.

The electron affinity EAHTLcorresponds to an energy difference between a vacuum level (not illustrated) and a conduction band minimum (CBM) of the HTLs3R,3G,3B. The ionization potential IPHTLcorresponds to an energy difference between the vacuum level described above and a valence band maximum (VBM) of the HTLs3R,3G,3B. The electron affinity EAILcorresponds to an energy difference between the vacuum level described above and the CBM of the ILs4R,4G,4B. The ionization potential IPILcorresponds to an energy difference between the vacuum level described above and the VBM of the ILs4R,4G,4B. The electron affinity EAEMLRcorresponds to an energy difference between the vacuum level described above and the CBM of the EML5R. The ionization potential IPEMLRcorresponds to an energy difference between the vacuum level described above and the VBM of the EML5R. The electron affinity EAEMLGcorresponds to an energy difference between the vacuum level described above and the CBM of the EML5G. The ionization potential IPEMLGcorresponds to an energy difference between the vacuum level described above and the VBM of the EML5G. The electron affinity EAEMLBcorresponds to an energy difference between the vacuum level described above and the CBM of the EML5B. The ionization potential IPEMLBcorresponds to an energy difference between the vacuum level described above and the VBM of the EML5B. The electron affinity EAETLcorresponds to an energy difference between the vacuum level described above and the CBM of the ETL6R. The ionization potential IPETLcorresponds to an energy difference between the vacuum level described above and the VBM of the ETL6.

As illustrated inFIG.3toFIG.5, when a potential difference is applied between the cathode7and the anodes2R,2G,2B in the light-emitting device100, electrons are injected from the cathode7and positive holes are injected from the anodes2R,2G,2B toward the EMLs5R,5G, SB, respectively. As illustrated inFIG.3toFIG.5by e, the electrons from the cathode7reach the EMLs SR,5G,5B via the ETL6. On the other hand, as illustrated inFIG.3toFIG.5by h+, the positive holes from the anodes2R,2G,2B reach the EMLs5R,5G,5B via the HTLs3R,3G,3B and the ILs4R,4G,4B. The positive holes and the electrons that have reached the EMLs SR,5G,5B are recombined at the quantum dots QR, QG, QB in the respective pixels RP, GP, BP to emit light. Light emitted from the quantum dots QR, QG, QB is, for example, reflected by the cathode7, which is a metal electrode, transmitted through the anodes2R,2G,2B, which are transparent electrodes, and irradiated outside of the light-emitting device100.

In the light-emitting elements10R,10G,10B, in a case in which the layer thicknesses of the ILs4R,4G,4B are sufficiently thin, the positive holes move through the ILs4R,4G,4B by tunneling.

A hole injection barrier from the HTL3R to the EML5R is indicated by an energy difference between the ionization potential IPEMLRof the EML5R and the ionization potential IPETLof the HTL3R (IPEMLR−IPETL). Similarly, a hole injection barrier from the HTL3G to the EML5G is indicated by an energy difference between the ionization potential IPEMLGof the EML5G and the ionization potential IPETLof the HTL3R (IPEMLG−IPETL). A hole injection barrier from the HTL3B to the EML5B is indicated by an energy difference between the ionization potential IPEMLBof the EML5B and the ionization potential IPETLof the HTL3B (IPEMLB−IPETL).

As illustrated inFIG.3toFIG.5, in a case in which the same material is used, the VBMs of the quantum dot QD layers generally do not vary by the light emission wavelength of the quantum dots QD used as the quantum dots QR, QG, QB. Therefore, in a case in which the same material is used, the ionization potentials IPEMLR, IPEMLG, IPEMLBare substantially the same. This is because of the following reasons. For the quantum dots QR, QG, QB, the smaller the atomic number of the elements that make up the cores CR, CG, CB of these quantum dots QR, QG, QB, the fewer the closed-shell orbitals and the less likely the nuclei are shielded by the closed-shell orbitals. Therefore, the valence electrons of the quantum dots QR, QG, QB are readily affected by the electric fields created by the nuclei and tend to remain at a certain energy level.

Accordingly, in a case in which the same material is used, the quantum dot QD layers have substantially the same ionization potential, and the hole injection efficiencies into the quantum dot QD layers are independent of the light emission wavelength. In particular, in the examples illustrated inFIG.3toFIG.5the hole injection barriers from the HTLs3R,3G,3B to the EMLs5R,5G,5B are each small at 0.5 eV or less, and the hole injection efficiencies from the HTLs3R,3G,3B into the EMLs SR,5G, SB are high.

Nevertheless, as illustrated inFIG.3toFIG.5, the CBMs of the quantum dot QD layers generally differ, depending on the light emission wavelength. Particularly, in a case in which the same material is used, the conduction band level of the quantum dots QD used as the quantum dots QR, QG, QB has a deeper energy level as a wavelength of light emitted from the quantum dots QD is longer, and has a lower energy level as a wavelength of light emitted from the quantum dots QD is shorter. This is because the quantum dots QD with a smaller band gap have a deeper conduction band level.

Accordingly, among the light-emitting elements10R,10G,10B, the light-emitting element10B that emits light in a wavelength band having the shortest light emission peak wavelength has a larger electron injection barrier than those of the other light-emitting elements10R,10G.

The electron injection barrier from the ETL6to the EML5R is indicated by an energy difference between the electron affinity EAETLof the ETL6and the electron affinity EAEMLRof the EML5R (EAETL−EAEMLR). The electron injection barrier from the ETL6to the EML5G is indicated by an energy difference between the electron affinity EAETLof the ETL6and the electron affinity EAEMLGof the EML5G (EAETL−EAEMLG). The electron injection barrier from the ETL6to the EML5B is indicated by an energy difference between the electron affinity EAETLof the ETL6and the electron affinity EAEMLBof the EML5B (EAETL−EAEMLB).

In the examples illustrated inFIG.3toFIG.5, the electron injection barriers from the ETL6to the EML5R, the EML5G, and the EML5B are, in order, 0.1 eV, 0.5 eV, and 0.8 eV, and injection of the electrons increases in difficulty in the order R→G→B. In particular, in the examples illustrated inFIG.3toFIG.5, the electron injection barrier from the ETL6to the EML5R and the EML5G are each small at 0.5 eV or less, and the electron injection transport from the ETL6to the EMLs5R,5G is high. On the other hand, the electron injection barrier from the ETL6to the EML5B is greater than 0.5 eV, and the light-emitting element10B has a low electron injection efficiency compared to those of the other light-emitting elements10R,10G.

When the CBM of the EML5B is thus shallower than the CBMs of the EMLs5R,5G, the injection of electrons into the light-emitting element10B is more difficult than the injection of electrons into the other light-emitting elements10R,10G.

Therefore, in the present embodiment, the layer thickness of the IL4B is made greater than the layer thickness of the ILs4R,4G, thereby suppressing the injection of positive holes into the EML5B. Thus, in the light-emitting element10B, a carrier balance between positive holes and electrons can be achieved, and the recombination probability of the positive holes and the electrons can be improved. As a result, the equivalent luminance can be obtained in the light-emitting element10B as in the other light-emitting elements10R,10G.

Thus, according to the present embodiment, even when a metal chalcogenide is used in the HTL3as described above, it is possible to suppress equivalent charging in the light-emitting element10B and the other light-emitting elements10R,10G. Further, a balance in luminance can be achieved between the light-emitting element10B and the other light-emitting elements10R,10G.

Further, according to the present embodiment, by making the layer thickness of the IL4B larger than the layer thicknesses of the ILs4R,4G, it is possible to achieve the equivalent carrier balance in the light-emitting element10B as in the other light-emitting elements10R,10G. Thus, according to the present embodiment, it is not necessary to change the CBM of the ETL6by changing the material of the ETL6depending on the light-emitting element10, and the ETL6can be made common.

Further, according to the present embodiment, with the IL4being provided as an intermediate layer between the HTL3and the EML5as described above, it is not necessary to consider the hole transport properties of the IL4, making it possible to easily manage the hole transport properties of the light-emitting elements10R,10G,10B during manufacture.

As described above, the layer thickness of the IL4R and the layer thickness of the IL4G are preferably not greater than 12 nm. The layer thickness of the IL4B is preferably from 0.5 nm to 12.5 nm.

With the layer thickness of the IL4B being no less than 0.5 nm, the IL4B can be formed uniformly, and an in-plane variation of hole injection in the IL4B can be suppressed. Further, when the layer thickness of the IL4is excessively thick, positive holes can no longer be transported from the HTL3to the EML5by tunneling. By making the layer thickness of the IL4B having a layer thickness thicker than those of the IL4R and the IL4G 12.5 nm or less, it is possible to effectively inject positive holes into the EML5B by tunneling, even with the IL4B.

Further, in the present embodiment, in the light-emitting device100, a difference between the layer thickness of the IL4B in the light-emitting element10B that emits light in a wavelength band having the shortest light emission peak wavelength, and the layer thicknesses of the ILs4R,4G of the other light-emitting elements10R,10G is desirably from 0.5 nm to 12.5 nm.

That is, given TILR, TILG, TILBas the layer thickness of the IL4R, the layer thickness of the IL4G, and the layer thickness of the IL4B in this order, then desirably (TILR+0.5 nm)≤TILB≤(TILR+12.5 nm) and (TILG+0.5 nm)≤TILB≤(TILG+12.5 nm).

Thus, by making the difference between the layer thicknesses of the IL4B and the ILs4R,4G 0.5 nm or greater, it is possible to form the IL4with a significant difference between the light-emitting element10B and the light-emitting elements10R,10G other than the light-emitting element10B. That is, in the above formula, (TILR+0.5 nm) and (TILG+0.5 nm) are uniform films and indicate values of the lowest limit allowing film formation with a significant difference. Further, as described above, by making the difference in layer thickness between the IL4B and the ILs4R,4G 12.5 nm or less, it is possible to effectively inject positive holes by tunneling from the HTL3B into the EML5B. That is, in the above formula, (TILR+12.5 nm) and (TILG+12.5 nm) indicate values of the desired upper limit allowing effective tunneling by the positive holes.

Note that, as described above, the layer thickness TILBof the IL4B is greater than the layer thickness TILRof the IL4R and the layer thickness TILGof the IL4G. Accordingly, the difference in layer thickness between the IL4B and the ILs4R,4G is indicated by TILB−TILR(where TILB>TILR) Or TILB−TILG(where TILB>TILG).

Further, as described above, in the IL4, preferably EAIL≤EAEML−0.5 eV. Further, in the IL4, preferably IPIL≥IPEML−0.5 eV. In other words, given EAILBas the electron affinity of the IL4B and IPILBas the ionization potential of the IL4B, then preferably, in the IL4B, EAILB≤EAEMLB−0.5 eV and IPILB≥IPEMLB−0.5 eV. Further, given EAILRas the electron affinity of the IL4R and IPILRas the ionization potential of the IL4R, then preferably, in the IL4R, EAILR≤EAEMLR−0.5 eV and IPILR≥IPEMLR−0.5 eV. Further, given EAILGas the electron affinity of the IL4G and IPILGas the ionization potential of the IL4G, then preferably, in the IL4G, EAILG≤EAEMLG−0.5 eV and IPILG≥IPEMLG−0.5 eV.

The ILs4R,4G,4B described above satisfy all conditions described above.

Further, as illustrated inFIG.2, given d2as a shell thickness of the shell SR, d12as a shell thickness of the shell SG, and d22as a shell thickness of the shell SB, then desirably these shell thicknesses d2, d12, d22satisfy d22<d2and/or d22<d12. That is, the shell thickness d22of the quantum dot QB in the light-emitting element10B that emits light in a wavelength band having the shortest light emission peak wavelength is desirably thinner than the shell thicknesses d2, d12of the quantum dots QR, QG in the other light-emitting elements10R,10G. As illustrated inFIG.2, d2=d3−(d1×2). Similarly, d12=d13−(d11×2), and d22=d23−(d21×2). Thus, the shell thicknesses d2, d12, d22can be easily calculated by subtracting the core diameters d1, d11, d21from the outermost particle sizes d3, d13, d23.

Further, given d4as a ligand length of the ligand LR, d14as a ligand length of the ligand LG, and d24as a ligand length of the ligand LB, then desirably the ligand lengths d4, d14, d24satisfy d24<d4and/or d24<d14. That is, the ligand length d24of the quantum dot QB in the light-emitting element10B that emits light in a wavelength band having the shortest light emission peak wavelength is desirably shorter than the ligand lengths d4, d14in the other light-emitting elements10R,10G. The ligand lengths d4, d14, d24can be measured by determining a distance between the quantum dots QD adjacent to each other in the same pixel P from TEM images of the cross sections of the EMLs5R,5G,5B.

Table 3 summarizes the shell thicknesses d2, d12, d22and the ligand lengths d4, d14, d24for each of the quantum dots QR, QG, QB. In Table 3, the values in parentheses indicate suitable ranges for the shell thicknesses d2, d12, d22and the ligand lengths d4, d14, d24. Further, the values outside the parentheses are the specific values of the shell thicknesses d2, d12, d22and the ligand lengths d4, d14, d24used in the present embodiment, and are examples of combinations of the shell thicknesses d2, d12, d22and the ligand lengths d4, d14, d24.

TABLE 3QuantumQuantumQuantumdot QRdot QGdot QBShell thickness152.40.8(nm)(from 1.5 to 5.0)(from 1.5 to 5.0)(from 0.5 to 3.0)Ligand length2.32.31.2(nm)(from 1.5 to 2.5)(from 1.5 to 2.5)(from 0.5 to 1.5)

As shown in Table 3, the shell thicknesses d2, d12of the quantum dots QR, QG are preferably from 1.5 nm to 5.0 nm, and the shell thickness d22of the quantum dot QB is preferably from 0.5 nm to 3.0 nm. Further, the ligand lengths d4, d14of the quantum dots QR, QG are preferably from 1.5 nm to 2.5 nm, and the ligand length d24of the quantum dot QB is preferably from 0.5 nm to 1.5 nm.

To suppress the degradation of the characteristics of the quantum dot QD caused by the charging of the quantum dot QD by the presence of a hydroxyl group on the surface of the metal chalcogenide in the HTL3, it is desirable to increase a distance from the HTL3to the core of quantum dot QD.

Nevertheless, as described above, the light-emitting element10B has a low electron injection efficiency compared to those of the light-emitting elements10R,10G. Thus, in the present embodiment, the layer thickness TILBof the IL4B is made larger than the layer thickness TILRof the IL4R and the layer thickness TILGof the IL4G, thereby suppressing positive hole injection into the EML5B and achieving carrier balance in the EML5B. Therefore, the quantum dots QB of light-emitting element10B are less likely to be injected by the carriers from the IL4and the ETL6in comparison to the quantum dots QR, QG of other light-emitting elements10R,10G.

Therefore, as described above, when the shell thickness d22of the quantum dot QB is made thinner than the shell thicknesses d2, d12of the quantum dots QR, QG, distances from the IL4B and the ETL6to the core CB of the quantum dot QB can be shortened. Thus, it is possible to achieve the equivalent effective carrier injection into the quantum dot QB as into the quantum dots QR, QB, making it possible to improve light-emission characteristics.

Further, as described above, in a case in which the ligand length d24of the quantum dot QB is made shorter than the ligand lengths d4, d14of the quantum dots QR, QG as well, the distances from the IL4B and the ETL6to the core CB of the quantum dot QB can be shortened. Accordingly, in this case as well, it is possible to achieve the equivalent effective carrier injection into the quantum dot QB as into the quantum dots QR, QB, making it possible to improve light-emission characteristics.

Modified Example

Note that, in the present embodiment, a case in which the ILs4R,4G,4B are respectively provided to the light-emitting elements10R,10G,10B has been described as an example. Nevertheless, as long as the IL4B is provided, the IL4R and the IL4G need not necessarily be provided, and at least one of the layer thickness TILRof the IL4R and the layer thickness TILGof the IL4G may be 0 nm, as shown in Table 2.

That is, in the present embodiment, the layer thickness TILRof the IL4R can be rephrased as a distance between the HTL3R, which is the layer including the metal chalcogenide, and the EML5R in the light-emitting element10R. Accordingly, the layer thickness TILRof the IL4R being 0 nm indicates that the distance between the HTL3R and the EML5R is 0 nm, and the HTL3R and the EML5R are in contact with each other.

Further, the layer thickness TILGof the IL4G can be rephrased as a distance between the HTL3G, which is the layer including the metal chalcogenide, and the EML5G in the light-emitting element10G. Accordingly, the layer thickness TILGof the IL4G being 0 nm indicates that the distance between the HTL3G and the EML5G is 0 nm, and the HTL3G and the EML5G are in contact with each other.

Similarly, in the description above, the layer thickness TILBof the IL4B can be rephrased as a distance between the HTL3B, which is the layer including the metal chalcogenide, and the EML5B in the light-emitting element10B.

Accordingly, the difference in layer thickness between the IL4B and the IL4R can be rephrased as a difference between the above-described distance between the HTL3B and the EML5B in the light-emitting element10B and the above-described distance between the HTL3R and the EML5R in the light-emitting element10R. Similarly, the difference in layer thickness between the IL4B and the IL4G can be rephrased as a difference between the above-described distance between the HTL3B and the EML5B in the light-emitting element10B and the above-described distance between the HTL3G and the EML5G in the light-emitting element10G.

Note that, as described above, in order to suppress the degradation of the characteristics of the quantum dot QD caused by the charging of the quantum dot QD when a metal chalcogenide is used for the HTL3, the distance from the HTL3to the core of the quantum dot QD need only be lengthened. Accordingly, for the quantum dots QR, QG, at least one of the shell thicknesses d2, d12of the quantum dots QR, QG and the ligand lengths d4, d14of quantum dots QR, QG need only be set to the values within the numerical ranges shown in Table 3, for example. This makes it possible to suppress the degradation of characteristics in the quantum dots QR, QG caused by charging, unlike the quantum dot QB. Further, as described above, the quantum dots QR, QG, unlike the quantum dot QB, have high hole injection efficiency and electron injection efficiency. Accordingly, the IL4R and the IL4G need not necessarily be provided.

Further, as described above, in the present embodiment, a case in which the layer thickness TILBof the IL4B is greater than the layer thickness TILGof the IL4G that is equal to the layer thickness TILRof the IL4R was described as an example. Nevertheless, as described above, the injection of electrons increases in difficulty in the order of R→G→B. Accordingly, the layer thicknesses of the ILs4R,4G,4B are set so that the layer thickness TILBof the IL4B is greater than the layer thickness TILGof the IL4G that is greater than the layer thickness TILRof the IL4R.

Second Embodiment

Differences from the first embodiment will be described in the present embodiment. Note that, for convenience of description, components having the same function as the components described in the first embodiment are designated by the same reference numbers, and descriptions thereof are omitted.

FIG.6is a diagram schematically illustrating an example of a layered structure of the light-emitting device100according to the present embodiment.

The light-emitting element10and the light-emitting device100according to the present embodiment have the same configuration as those of the light-emitting element10and the light-emitting device100according to the first embodiment, except for the following points.

The light-emitting device100according to the present embodiment is provided with a hole injection layer (hereinafter referred to as “HIL”)11as a layer having hole transport properties and including a metal chalcogenide between the anode2and the EML5. Between the HIL11and the EML5, an HTL12including an organic material is provided as an intermediate layer between the HIL11and the EML5. Note that the HIL11mainly includes a metal chalcogenide, but may further include other materials. Further, the HTL12mainly includes an organic material, but may further include other materials.

The light-emitting element10illustrated inFIG.6includes the anode2, the HIL11, the HTL12, the IL4, the EML5, the ETL6, and the cathode7in this order from the array substrate1side (that is, lower layer side).

The anode2, the HIL11, the HTL12, and the EML5are each separated into an island shape for each pixel P by a bank (not illustrated).

The light-emitting element10R is formed by the anode2R, an HIL11R, an HTL12R, and the EML5R, each having an island shape, and the ETL6and the cathode7, each being a common layer. The light-emitting element10G is formed by the anode2G, an HIL11G, an HTL12G, and the EML5G, each having an island shape, and the ETL6and the cathode7, each being a common layer. The light-emitting element10B is formed by the anode2B, an HIL11B, an HTL12B, and the EML5B, each having an island shape, and the ETL6and the cathode7, each being a common layer.

However, in the present embodiment as well, the configuration described above is an example, and the configuration of the light-emitting device100is not necessarily limited to the configuration described above. In the present embodiment as well, the light-emitting device100may include, as the light-emitting element10, a light-emitting element that emits light having a light emission peak wavelength in a wavelength band other than the wavelength bands described in the first embodiment. The ETL6may be separated into an island shape for each pixel P by the bank described above. The layered order from the anode2to the cathode7may be reversed. Accordingly, the light-emitting element10may include the anode2, the HIL11, the HTL12, the EML5, the ETL6, and the cathode7in this order from the upper layer side. Hereinafter, a case in which the light-emitting device100has the configuration illustrated inFIG.6will be described as an example.

Note that, in the following description, when there is no need to distinguish the HILs11R,11G,11B from one another, these HILs11R,11G,11B are collectively referred to simply as the “HIL11”. Further, when there is no need to distinguish the HTLs12R,12G,12B from one another, these HTLs12R,12G,12B are collectively referred to simply as the “HTL12”.

In the present embodiment, the anode2injects positive holes into the HIL11. The HIL11injects positive holes into the HTL12.

The HIL11is a layer having hole transport properties and mainly including a metal chalcogenide, as previously described. As the metal chalcogenide, the same material as that of the HTL3according to the first embodiment can be used. Further, the HIL11can be formed using the same method as that for the HTL3according to the first embodiment.

Specific examples of the metal chalcogenide described above include nickel oxide (for example, NiO), copper oxide (for example, Cu2O), and copper sulfide (for example, CuS). One type of these metal chalcogenides may be used, or two or more types thereof may be mixed and used as appropriate. Accordingly, the metal chalcogenide described above is at least one type selected from the group consisting of nickel oxide, copper oxide, and copper sulfide.

The HIL11can be formed by, for example, a sol-gel method, sputtering, chemical vapor deposition (CVD), or a spin coating method (application method).

The HTL12is a layer that transports positive holes to the EML5. The HTL12is provided between the HIL11and the EML5, in contact with the HIL11and the EML5.

The HTL12mainly contains organic materials having hole transport properties, such as poly(N-vinylcarbazole) (abbreviation: PVK) and poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-4-sec-butylphenyl))diphenylamine)] (abbreviation: TFB), for example. One type of these organic materials may be used, or two or more types thereof may be mixed and used as appropriate. Accordingly, the HTL12may include at least one type of organic hole transport material selected from the group consisting of PVK and TFB.

The HTL12can be formed by, for example, an application method (method of dissolving the organic hole transport material described above in a solvent, and spin coating and then drying the solvent) or a dip coating method.

Note that, in the present embodiment as well, from the perspective of the versatility of a manufacturing apparatus, desirably the manufacturing apparatuses of each layer in the light-emitting element10are separated from each other. Accordingly, desirably the manufacturing apparatus of the HIL11and the film formation apparatus used in the next process (that is, manufacturing apparatus of the layer formed on the HIL11) are separated from each other. Nevertheless, when the HIL11is formed and subsequently the substrate on which the HIL11is formed is transported to the manufacturing apparatus separated from the manufacturing apparatus of the HIL11, the substrate on which the HIL11is formed is exposed to the atmosphere between the two manufacturing apparatuses.

Thus, although the manufacturing process of the light-emitting device100includes a process in which the metal chalcogenide surface of the HIL11is exposed to a gas containing moisture, from the standpoint of the versatility of the manufacturing apparatus, desirably the manufacturing apparatuses of each layer in the light-emitting element10are separated from each other. Then, in the process in which the metal chalcogenide surface of the HIL11is exposed to a gas containing moisture, the hydroxyl group is presumably adsorbed on the surface of the metal chalcogenide. Accordingly, the manufacturing process of the light-emitting device100including a process in which the metal chalcogenide surface of the HIL11is exposed to a gas containing moisture presumably means that the manufacturing process of the light-emitting device100includes a process in which a hydroxyl group is adsorbed on the surface of the metal chalcogenide.

The HTL12suppresses the charging of the quantum dots QD by the hydroxyl group on the metal chalcogenide surface, and suppresses a decrease in light-emission characteristics caused by the charging of the quantum dots QD.

In the light-emitting elements10R,10G,10B according to the present embodiment, the layer thicknesses of the layers other than the HTLs12R,12G,12B can be set as in light-emitting elements of the related art.

Table 4 shows the layer thickness of each layer in the light-emitting elements10R,10G,10B according to the present embodiment. In Table 4, the layer thicknesses in parentheses indicate suitable ranges for the layer thickness of each layer. Further, the layer thicknesses outside the parentheses are the specific layer thicknesses of each layer in the light-emitting elements10R,10G,10B used in the present embodiment and indicate examples of combinations of the layer thickness of each layer in the light-emitting elements10R,10G,10B.

TABLE 4Layer thickness of eachlayer (nm)Anode electrodeR: 100 (from 20 to 200)G: 100 (from 20 to 200)B: 100 (from 20 to 200)HILR: 15 (from 5 to 50)(Metal chalcogenide layer)G: 15 (from 5 to 50)B: 15 (from 5 to 50)HTLR: 30 (from 30 to 59.5)G: 30 (from 30 to 59.5)B: 40 (from 30.5 to 60)EMLR: 40 (from 15 to 80)G: 40 (from 15 to 80)B: 40 (from 15 to 80)ETL50 (from 20 to 150)Cathode electrode100 (from 50 to 200)

As shown in Table 4, layer thicknesses of the HILs11R,11G,11B are preferably from 5 nm to 50 nm. Further, layer thicknesses of the HTLs12R,12G are preferably from 30 nm to 59.5 nm. The layer thickness of the HTL12B is preferably from 30.5 nm to 60 nm. However, the HTLs12R,12G,12B are set so that the layer thickness of the HTL12B is greater than the layer thickness of the HTL12R and the layer thickness of the HTL12B is greater than the layer thickness of the HTL12G.

In the following, an example of a manufacturing method of the light-emitting elements10R,10G,10B and the light-emitting device100according to the present embodiment will be described with reference toFIG.6and Table 4.

In the present embodiment, the processes up to formation of the bank having a lattice pattern are the same as those in the first embodiment. In the present embodiment as well, as in the first embodiment, ITO layers having a layer thickness of 100 nm were formed as the anodes2R,2G,2B on the array substrate1, and subsequently the bank having a lattice pattern was formed.

In the present embodiment, next, NiO layers having a layer thickness of 15 nm were respectively formed as the HILs11R,11G,11B by respectively spin coating NiO on the anodes2R,2G,2B, and subsequently applying heat in the atmosphere (HIL formation process).

Next, PVK layers were respectively formed as the HTLs12R,12G,12B on the HILs11R,11G,11B by dissolving PVK in a solvent and spin coating and drying the solvent (HTL formation process). Note that, films were deposited using a mask in areas other than the film formation area, and the layer thicknesses of the HTLs12R,12G,12B were adjusted by changing the concentration of the PVK with respect to the solvent described above, the number of revolutions during spin coating, and the like. Thus, a PVK layer having a layer thickness of 40 nm was formed as the HTL12B, and PVK layers having a layer thickness of 30 nm were formed as the HTL12R and the HTL12G.

Next, quantum dot QD layers having a layer thickness of 40 nm were formed on the HTLs12R,12G,12B as the EMLs5R,5G,5B in the same manner as in the first embodiment.

Subsequently, in the same manner as in the first embodiment, the ZnO layer composed of ZnO—NP and having a layer thickness of 50 nm, and the Al layer having a layer thickness of 100 nm were formed in this order, layering the ETL6and the cathode7common to each pixel P in this order. In this manner, the light-emitting elements10R,10G,10B according to the present embodiment were manufactured. Note that, in the present embodiment as well, the light-emitting device100is manufactured by sealing the light-emitting elements10R,10G,10B by a sealing layer (not illustrated) after formation of the cathode7described above.

FIG.7toFIG.9illustrate the energy bands and layer thicknesses of each layer in the light-emitting elements10R,10G,10B according to the present embodiment, thus manufactured.FIG.7illustrates the energy band and the layer thickness of each layer in the light-emitting element10R.FIG.8illustrates the energy band and the layer thickness of each layer in the light-emitting element10G.FIG.9illustrates the energy band and the layer thickness of each layer in the light-emitting element10B.

As illustrated inFIG.7toFIG.9, the difference between the light-emitting elements10R,10G,10B according to the present embodiment and the light-emitting elements10R,10G,10B according to the first embodiment is only the layers between the anodes2R,2G,2B and the EMLs5R,5B,5B. In the present embodiment, as illustrated inFIG.7toFIG.9, the HILs11R,11G,11B and the HTLs12R,12G,12B are provided in this order between the anodes2R,2G,2B and the EMLs SR,5G,5B. The NiO layers as the HILs11R,11G,11B have an electron affinity (hereinafter referred to as “EAHTL”) of 1.9 eV, and an ionization potential (hereinafter referred to as “IPHTL”) of 5.4 eV. Further, the PVK layers as the HTLs12R,12G,12B have an electron affinity EAHTLof 2.2 eV, and an ionization potential IPHTLof 5.8 eV.

The electron affinity EAHILcorresponds to an energy difference between a vacuum level (not illustrated) and the CBM of the HILs11R,11G,11B. The ionization potential IPHILcorresponds to an energy difference between the vacuum level described above and the VBM of the HILs11R,11G,11B. Further, in the present embodiment, the electron affinity EAHTLcorresponds to an energy difference between a vacuum level (not illustrated) and the CBM of the HTLs12R,12G,12B. The ionization potential IPHTLcorresponds to an energy difference between the vacuum level described above and the VBM of the HTLs12R,12G,12B.

In the present embodiment, as indicated by h+ inFIG.7toFIG.9, positive holes from the anodes2R,2G,2B reach the EMLs5R,5G,5B via the HILs11R,11G,11B and the HTLs12R,12G,12B.

As described in the first embodiment, in a case in which the same material is used, the conduction band level of the quantum dots QD used as the quantum dots QR, QG, QB has a deeper energy level as a wavelength of light emitted from the quantum dots QD is longer, and has a lower energy level as a wavelength of light emitted from the quantum dots QD is shorter.

Then, when the CBM of the EML5B is shallower than the CBMs of the EMLs5R,5G, the injection of electrons into the light-emitting element10B is more difficult than the injection of electrons into the other light-emitting elements10R,10G.

Therefore, as illustrated inFIG.7toFIG.9, in the present embodiment as well, among the light-emitting elements10R,10G,10B, the light-emitting element10B that emits light in a wavelength band having the shortest light emission peak wavelength has a larger electron injection barrier than those of the other light-emitting elements10R,10G.

Therefore, in the present embodiment, as described above, the layer thickness of the HTL12B is greater than the layer thicknesses of the HTLs12R,12G. A hole mobility of organic materials is lower than a hole mobility of inorganic materials (metal chalcogenides). Therefore, the layer thickness of the HTL12B is greater than the layer thicknesses of the HTLs12R,12G, making it possible to suppress the injection of positive holes into the EML5B. Accordingly, in the present embodiment as well, in the light-emitting element10B, a carrier balance between positive holes and electrons can be achieved, and the recombination probability between the positive holes and the electrons can be improved. As a result, the equivalent luminance can be obtained in the light-emitting element10B as in the other light-emitting elements10R,10G.

Thus, according to the present embodiment, even when a metal chalcogenide is used in the HIL11as described above, it is possible to suppress equivalent charging between the light-emitting element10B and the other light-emitting elements10R,10G. Further, a balance in luminance can be achieved between the light-emitting element10B and the other light-emitting elements10R,10G.

Further, according to the present embodiment, by making the layer thickness of the HTL12B larger than the layer thicknesses of the HTLs12R,12G, the same carrier balance can be achieved in the light-emitting element10B as in the other light-emitting elements10R,10G. Thus, in the present embodiment as well, it is not necessary to change the CBM of the ETL6by changing the material of the ETL6depending on the light-emitting element10, and the ETL6can be made common.

Further, according to the present embodiment, the HTL12is provided as an intermediate layer between the HIL11and the EML5as described above, making it is possible to easily control the layer thickness during the manufacture of the HTL12.

As described above, the layer thicknesses of the HTLs12R,12G are preferably from 30 nm to 59.5 nm. The layer thickness of the HTL12B is preferably from 30.5 nm to 60 nm.

The suitable layer thickness of the HTL12is several tens of nm or greater, and favorable hole transport properties can be obtained by setting the lower limit of the layer thicknesses of the HTLs12R,12G, which is the lower limit of the layer thickness of the HTL12, to 30 nm. Further, to suppress an increase in power consumption of the light-emitting device100, a drive voltage is preferably 15 V or less. For example, when the layer thickness of the HTL12is increased by 12 nm, the voltage to obtain the same luminance is 3 V higher. Therefore, the upper limit of the layer thickness of the HTL12, which is the upper limit of the layer thickness of the HTL12B, is desirably 60 nm.

Further, in the present embodiment, in the light-emitting device100, a difference between the layer thickness of the HTL12B in the light-emitting element10B that emits light in a wavelength band having the shortest light emission peak wavelength, and the layer thicknesses of the HTLs12R,12G of the other light-emitting elements10R,10G is desirably from 0.5 nm to 30 nm.

That is, given THTLR, THTLG, THTLBas the layer thickness of the HTL12R, the layer thickness of the HTL12G, and the layer thickness of the HTL12B in this order, then desirably (THTLR+0.5 nm)≤THTLB≤(THTLR+30 nm) and (THTLG+0.5 nm)≤THTLB≤(THTLG+30 nm).

Thus, by making the difference between the layer thicknesses of the HTL12B and the HTLs12R,12G 0.5 nm or greater, it is possible to form the HTL12with a significant difference between the light-emitting element10B and the light-emitting elements10R,10G other than the light-emitting element10B. That is, in the above formula, (THTLR+0.5 nm) and (THTLG+0.5 nm) are uniform films, and indicate values of the lowest limit allowing film formation with a significant difference. On the other hand, as described above, by making the difference in layer thickness between the HTL12B and the HTLs12R,12G 30 nm or less, it is possible to effectively transport positive holes from the HIL11B to the EML5B. That is, in the above formula, (THTLR+30 nm) and (THTLG+30 nm) indicate the values of the desired upper limits allowing achievement of favorable hole transport properties.

Note that, as described above, the layer thickness THTLBof the HTL12B is greater than the layer thickness THTLRof the HTL12R and the layer thickness THILGof the HTL12G. Accordingly, the difference in layer thickness between the HTL12B and the HTLs12R.12G is indicated by THTLB−THTLR(where THTLB>THTLR) OF THTLB−THILG(where THTLB>THTLG).

Modified Example

As described above, in the present embodiment, a case in which the layer thickness THTLBof the HTL12B is greater than the layer thickness THTLGof the HTL12G that is equal to the layer thickness THTLRof the HTL12R was described as an example. Nevertheless, as described above, the injection of electrons increases in difficulty in the order of R→G→B. Accordingly, the layer thicknesses of the HTLs12R,12G,12B are set so that the layer thickness THTLBof the HTL12B is greater than the layer thickness THTLGof the HTL12G that is greater than the layer thickness THTLRof the HTL12R.

Note that, in the present embodiment, the layer thickness THTLBof the HTL12B can be rephrased as a distance between the HIL11B, which is the layer including the metal chalcogenide, and the EML5B in the light-emitting element10B. Further, the layer thickness THTLRof the HTL12R can be rephrased as a distance between the HIL11R, which is the layer including the metal chalcogenide, and the EML5R in the light-emitting element10R. Similarly, the layer thickness THTLGof the HTL12G can be rephrased as a distance between the HIL11G, which is the layer including the metal chalcogenide, and the EML5G in the light-emitting element10G.

Further, the difference in layer thickness between the HTL12B and the HTL12R can be rephrased as a difference between the above-described distance between the HIL11B and the EML5B in light-emitting element10B and the above-described distance between the HIL11R and the EML5R in light-emitting element10R. Similarly, the difference in layer thickness between the HTL12B and the HTL12G can be rephrased as a difference between the above-described distance between the HIL11B and the EML5in the light-emitting element10B and the above-described distance between the HIL11G and the EML5G in the light-emitting element10G.

The disclosure is not limited to the embodiments described above, and various modifications may be made within the scope of the claims. Embodiments obtained by appropriately combining technical approaches disclosed in the different embodiments also fall within the technical scope of the disclosure. Furthermore, novel technical features can be formed by combining the technical approaches disclosed in each of the embodiments.