Light-emitting element and display device

Abstract

A light-emitting element (10) includes an anode (E1), a cathode (E2), and a light-emitting layer (EL) between the anode and the cathode, the light-emitting layer including a plurality of quantum dots (QD) and a host material (Mx) having a p-type semiconductor (Mp) portion and filling between the plurality of quantum dots.

Description

Technical Field

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

[0002] Patent Document 1 discloses a hole transport layer containing a metal oxide and a carbon element whose content is adjusted to a predetermined ratio. Prior art literature Patent Literature

[0003] Patent Document 1: WO2020 / 065944 (International Publication on April 2, 2020) Summary of the Invention Technical problems to be solved by the present invention

[0004] Existing light-emitting elements have the problem of low luminous efficiency. Technical solutions to technical problems

[0005] A light-emitting element according to one embodiment of the present invention includes an anode, a cathode, and a light-emitting layer located between the anode and the cathode. The light-emitting layer includes a plurality of quantum dots and a host material. The host material has a p-type semiconductor portion and fills spaces between the plurality of quantum dots. Beneficial effects

[0006] According to one embodiment of the present disclosure, luminous efficiency can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 This is a cross-sectional view showing a configuration example of a light-emitting element according to one embodiment. Figure 2 It shows Figure 1 Schematic diagram of an example of the region between quantum dots shown. Figure 3 It shows Figure 1 Schematic diagram of another example of the region between quantum dots shown. Figure 4 It is a cross-sectional view of a configuration example of a light emitting element of a comparative example. Figure 5 It shows Figure 1 Schematic diagram of an example of the energy band structure of the light-emitting layer of the present disclosure. Figure 6 It shows Figure 4 Schematic diagram of the energy band structure of the light-emitting layer of the comparative example shown. Figure 7 It shows Figure 1 Flowchart of an example of a method for manufacturing a light-emitting element shown. Figure 81 is a cross-sectional view showing an example of a process for forming a light-emitting layer according to an embodiment of the present disclosure. Figure 9 1 is a cross-sectional view showing an example of a process for forming a light-emitting layer according to an embodiment of the present disclosure. Figure 10 It shows Figure 1 FIG. 1 is a flow chart of another example of a method for manufacturing a light-emitting element. Figure 11 1 is a cross-sectional view showing an example of a process for forming a light-emitting layer according to an embodiment of the present disclosure. Figure 12 This is a cross-sectional view for explaining the replacement process. Figure 13 It is a schematic diagram showing a quantum dot dispersion. Figure 14 This is a cross-sectional view showing a modified example of the structure of the light-emitting element according to the above-described embodiment. Figure 15 This is a cross-sectional view showing a modified example of the structure of the light-emitting element according to the above-described embodiment. Figure 16 This is a cross-sectional view showing a configuration example of a light-emitting element according to one embodiment. Figure 17 Schematic diagram illustrating an example of a process for forming a light-emitting layer according to one embodiment of the present invention. Figure 18 It is a plan view showing a configuration example of a display device according to one embodiment of the present disclosure. DETAILED DESCRIPTION

[0008] [Implementation Method 1] (Cross-sectional structure of light-emitting element) Figure 1 : is a cross-sectional view showing a configuration example of a light emitting element according to one embodiment of the present disclosure. Figure 1 As shown, the light-emitting element 10 according to this embodiment includes an anode E1 and a cathode E2 facing each other, and a light-emitting layer EL located between the anode E1 and the cathode E2. The light-emitting layer EL includes a plurality of quantum dots QD located between the anode E1 and the cathode E2, and a matrix material Mx filling the spaces between the quantum dots QD. The matrix material Mx includes a p-type semiconductor portion Mp and an i-type semiconductor portion Mi. The matrix material Mx can change from the i-type semiconductor portion Mi to the p-type semiconductor portion Mp continuously or in stages. The matrix material Mx can also be composed of an inorganic semiconductor.

[0009] The light-emitting element 10 may further include one or both of a charge functional layer F1 positioned between the anode E1 and the light-emitting layer EL and a charge functional layer F2 positioned between the cathode E2 and the light-emitting layer EL. The charge functional layer F1 may include one or more of a hole injection layer HIL, a hole transport layer HTL, and an electron shielding layer. The charge functional layer F2 may include one or more of an electron injection layer, an electron transport layer ETL, and a hole blocking layer. The current flowing in the light-emitting layer EL flows through the quantum dots QD and includes current I1 that contributes to light emission and current I2 that avoids the quantum dots QD and does not contribute to light emission.

[0010] The matrix material Mx refers to a component that contains other substances and holds them, and can be called a substrate, a base material, or a filling material. The matrix material Mx can also be a solid at room temperature. The matrix material Mx can also be an inorganic matrix material composed of an inorganic material (such as an inorganic semiconductor). The matrix material Mx can also be a component that contains and holds a plurality of quantum dots QD. The matrix material Mx can also be a constituent element of the light-emitting layer EL that contains a plurality of quantum dots QD.

[0011] Figure 2 as well as Figure 3 They are shown respectively Figure 1 Schematic diagram of an example of the region between the quantum dots shown. The matrix material Mx can also be filled in the light-emitting layer EL. Figure 1 As shown, the matrix material Mx can also satisfy the region (space) outside the plurality of quantum dots QD in the light-emitting layer EL. We can also focus on two quantum dots QD among the plurality of quantum dots QD, and the matrix material Mx satisfies the region (space) K between the two quantum dots QD. These two quantum dots QD are called the first quantum dot QD1 and the second quantum dot QD2. Figure 2 and Figure 3 As shown in the cross-sectional view, region K is an area surrounded by two straight lines (common tangent lines) that circumscribe the peripheries of the first and second quantum dots QD1 and QD2 and the relative peripheries of the first and second quantum dots QD1 and QD2. Figure 3 As shown, even if the first quantum dot QD1 is located near the second quantum dot QD2, there may still be a region K. “Filling the space between multiple quantum dots” may be as follows: Figure 2 (or Figure 3 The matrix material Mx filling the region K may be the p-type semiconductor portion Mp, the i-type semiconductor portion Mi, or both the p-type semiconductor portion Mp and the i-type semiconductor portion Mi.

[0012] The matrix material Mx may also fill the region (space) outside the quantum dot group in the light-emitting layer EL. Here, three or more quantum dots QD are collectively referred to as a quantum dot group. The matrix material Mx may fill the region (space) outside the plurality of quantum dots QD in the light-emitting layer EL.

[0013] The outer edge (upper and lower surfaces) of the light-emitting layer EL can be covered by a matrix material Mx. Alternatively, the matrix material Mx can be provided from the outer edge of the light-emitting layer EL, and the quantum dots QD can be located away from the outer edge. The outer edge of the light-emitting layer EL does not have to be formed solely of the matrix material Mx, and a portion of the quantum dots QD can be exposed from the matrix material Mx. The matrix material Mx can be a portion of the light-emitting layer EL excluding a plurality of quantum dots QD. The matrix material Mx covering the outer edge of the light-emitting layer EL can be a p-type semiconductor portion Mp, an i-type semiconductor portion Mi, or both a p-type semiconductor portion Mp and an i-type semiconductor portion Mi.

[0014] The matrix material Mx may also contain multiple quantum dots QD. The matrix material Mx may also be formed to fill the spaces between the multiple quantum dots QD. The multiple quantum dots QD may also be embedded in the matrix material Mx at intervals. The matrix material Mx may also partially or completely fill the spaces between the multiple quantum dots QD.

[0015] The matrix material Mx may also include a continuous film having a thickness of 1000 nm along the plane direction perpendicular to the film thickness direction. 2 A continuous film is a film that is not separated on a plane by any material other than the material that constitutes the continuous film. A portion of the continuous film may be a p-type semiconductor portion Mp, and the remaining portion may be an i-type semiconductor portion Mi.

[0016] The matrix material Mx can also be the same material as the shell contained in each of the multiple quantum dots QD. In this case, the average distance between adjacent cores (internuclear distance) can be more than 3nm, or more than 5nm. Alternatively, the average distance between the above-mentioned adjacent cores can also be more than 0.5 times the average core diameter. The internuclear distance is the distance after averaging the shortest distance between 20 adjacent cores. The internuclear distance can be kept wider than the distance in the case where the shell contacts each other. The average core diameter is obtained by averaging the core diameters of 20 adjacent cores in cross-section observation. The core diameter can be set to the diameter of a circle with the same area as the core area in cross-section observation.

[0017] The concentration of the matrix material Mx in the light-emitting layer EL can be greater than 0.1% and less than 79.0%. For example, the concentration can be determined based on the area ratio in image processing during cross-sectional observation. When the quantum dot QD has a core-shell structure, the concentration of the shell can be greater than 0.1% and less than 39%. The shell and the matrix material Mx are made of the same material (same composition), and when the shell and the matrix material Mx cannot be distinguished, the concentration of the area as the total of the shell and the matrix material Mx can be greater than 0.1% and less than 99.9%. In this way, when the shell and the matrix material Mx cannot be distinguished, the shell can also be regarded as a part of the matrix material Mx.

[0018] The light-emitting layer EL may also be composed of a plurality of quantum dots QD and a host material Mx. When analyzing the light-emitting layer EL, the intensity of the carbon element detected by the chain structure can be lower than the noise.

[0019] The band gap of the constituent material of the preferred matrix material Mx is wider than the constituent material (e.g., core material) of the quantum dot QD. As the material constituting the matrix material Mx, a semiconductor or an insulator can be used. Examples of constituent materials of the matrix material Mx include metal sulfides and / or metal oxides. Metal sulfides can be, for example, zinc sulfide (ZnS), zinc magnesium sulfide (ZnMgS, ZnMgS2), gallium sulfide (GaS, Ga2S3), zinc tellurium sulfide (ZnTeS), magnesium sulfide (MgS), zinc gallium sulfide (ZnGa2S4), and magnesium sulfide (MgGa2S4). Metal oxides can be zinc oxide (ZnO), titanium oxide (TiO2), tin oxide (SnO2), tungsten oxide (WO3), and zirconium oxide (ZrO2). It should be noted that the chemical formula recorded in brackets after the compound name is a representative example. In addition, with respect to the composition ratio recorded in the chemical formula, it is ideal as long as the composition of the actual compound is stoichiometric as shown in the chemical formula, but it is not necessarily stoichiometric.

[0020] The structure of the matrix material Mx is sufficient to be observed in a cross-section of the light-emitting layer EL over a width of approximately 100 nm. The structure does not need to be observed throughout the entire light-emitting layer EL. The matrix material Mx may contain a substance different from the main material (e.g., an inorganic substance such as an inorganic semiconductor) as an additive.

[0021] Figure 4 : is a cross-sectional view showing a configuration example of a light emitting element of a comparative example. Figure 4 As shown, the host material Mx in the light-emitting element 110 of the comparative example does not have a p-type semiconductor portion but has an i-type semiconductor portion Mi.

[0022] (p-type semiconductor portion and i-type semiconductor portion) The p-type semiconductor portion Mp is the portion where the inorganic semiconductor constituting the matrix material Mx is a p-type semiconductor. On the other hand, the i-type semiconductor portion Mi is the portion where the inorganic semiconductor constituting the matrix material Mx is an i-type semiconductor. This difference in inorganic semiconductor type can be achieved by doping the inorganic semiconductor or adjusting the inorganic semiconductor composition ratio.

[0023] The matrix material Mx comprises, for example, a Group IV semiconductor. An i-type Group IV semiconductor refers to an inorganic semiconductor containing one or more Group XIV elements. In this disclosure, element group numbers using Roman numerals are based on the old IUPAC notation, while those using Arabic numerals are based on the new IUPAC notation. The matrix material Mx can contain one or more elements selected from carbon (C), silicon (Si), germanium (Ge), and tin (Sn).

[0024] When the matrix material Mx includes a Group IV semiconductor, the p-type semiconductor portion Mp may include a p-type Group IV semiconductor, and the i-type semiconductor portion Mi may include an i-type Group IV semiconductor. The p-type Group IV semiconductor may be a Group IV semiconductor doped with a Group III element. That is, the p-type semiconductor portion Mp may include a Group III element, for example, one or more elements selected from boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Tl).

[0025] The matrix material Mx includes, for example, a Group III-V semiconductor. An i-type Group III-V semiconductor refers to an inorganic semiconductor containing a Group III element and a Group V element in a composition ratio of approximately 1:1. The matrix material Mx may include one or more elements selected from boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Tl), and one or more elements selected from nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi).

[0026] When the matrix material Mx comprises a Group III-V semiconductor, the p-type semiconductor portion Mp may comprise a p-type Group III-V semiconductor, and the i-type semiconductor portion Mi may comprise an i-type Group III-V semiconductor. The p-type Group III-V semiconductor may be a Group III-V semiconductor doped with a Group II element, and / or may be a Group III-V semiconductor containing a Group V element in a ratio greater than 1:1 relative to the Group III element. That is, the p-type semiconductor portion Mp may contain a Group II element, for example, one or more elements selected from magnesium (Mg), zinc (Zn), cadmium (Cd), and mercury (Hg). Furthermore, / or, the p-type semiconductor portion Mp may contain a Group V element in a ratio greater than 1:1 relative to the Group III element. A Group III-V semiconductor containing a Group V element in a ratio greater than 1:1 relative to the Group III element is also referred to as a "Group V-rich" Group III-V semiconductor.

[0027] The matrix material Mx includes, for example, a Group II-VI semiconductor. An i-type Group II-VI semiconductor refers to an inorganic semiconductor containing a Group II element and a Group VI element in a composition ratio of approximately 1:1. The matrix material Mx may include one or more elements selected from magnesium (Mg), zinc (Zn), cadmium (Cd), and mercury (Hg), and one or more elements selected from oxygen (O), sulfur (S), selenium (Se), and tellurium (Te).

[0028] When the matrix material Mx comprises a Group II-VI semiconductor, the p-type semiconductor portion Mp may comprise a p-type Group II-VI semiconductor, and the i-type semiconductor portion Mi may comprise an i-type Group II-VI semiconductor. The p-type Group II-VI semiconductor may be a Group II-VI semiconductor doped with a Group IV element, and / or may be a Group II-VI semiconductor containing a Group V element in a ratio greater than 1:1 relative to the Group II element. That is, the p-type semiconductor portion Mp may contain a Group IV element, and in particular, a Group IV element, for example, one or more elements selected from carbon (C), silicon (Si), germanium (Ge), and tin (Sn). In particular, the p-type semiconductor portion Mp may contain carbon (C). Furthermore, / or, the p-type semiconductor portion Mp may contain a Group VI element in a ratio greater than 1:1 relative to the Group II element. A Group II-VI semiconductor containing a Group VI element in a ratio greater than 1:1 relative to the Group II element is also referred to as a "Group VI-rich" Group II-VI semiconductor.

[0029] (Band structure of the light-emitting layer) Figure 5 Yes Figure 1 Schematic diagram of an example of the band structure of the light-emitting layer of the present invention is shown. Figure 6 Yes Figure 4 Schematic diagram of the energy band structure of the light-emitting layer of the comparative example shown. Figure 5 and Figure 6 Rectangles represent the HOMO (highest occupied molecular orbital), LUMO (lowest unoccupied molecular orbital), and the band gaps between them for the hole transport layer (HTL), the matrix material (Mx), the quantum dots (QD), and the electron transport layer (ETL). The upper side of the rectangle corresponds to the LUMO, and the lower side corresponds to the HOMO.

[0030] like Figure 5 As shown by the solid arrows, in the configuration example of the present invention, electrons cross the energy barrier of the p-type semiconductor portion Mp and are injected from the electron transport layer ETL into the quantum dot QD. Figure 6As indicated by the solid arrows in the middle, in the comparative example, electrons are injected from the electron transport layer ETL into the quantum dot QD, overcoming the energy barrier of the i-type semiconductor portion Mi. The energy barrier formed by the p-type semiconductor portion Mp is greater than the energy barrier formed by the i-type semiconductor portion Mi. Therefore, the electron injection efficiency into the light-emitting layer EL of the present invention is lower than that of the comparative example.

[0031] Furthermore, in the configuration example according to the present invention, electrons traversing the light-emitting layer EL pass through both the p-type semiconductor portion Mp and the i-type semiconductor portion Mi. On the other hand, in the configuration of the comparative example, electrons traversing the light-emitting layer EL pass only through the i-type semiconductor portion Mi. The electron mobility of the p-type semiconductor portion Mp is lower than that of the i-type semiconductor portion Mi. Therefore, the electron mobility in the light-emitting layer EL of the present invention is lower than that of the comparative example.

[0032] The light-emitting layer EL of the comparative example suffers from poor carrier balance. Light-emitting layers EL comprising inorganic semiconductors tend to have higher electron injection efficiency than light-emitting layers comprising organic ligands, leading to an excess of electrons being injected into the light-emitting layer EL. Furthermore, compared to organic ligands, inorganic semiconductors tend to have greater electron mobility, making it easier for electrons to cross the light-emitting layer EL and recombine with holes at or near the boundary between the hole transport layer HTL and the light-emitting layer EL. Consequently, the light-emitting element 110 of the comparative example exhibits a low EQE (external quantum efficiency).

[0033] In contrast, the light-emitting layer EL according to the present disclosure has lower electron injection efficiency and electron mobility than the comparative example as described above. Therefore, the carrier balance of the light-emitting layer EL according to the present invention is improved, and the EQE of the light-emitting element 10 is high.

[0034] In order to improve the carrier balance, the hole carrier concentration in the p-type semiconductor portion Mp is preferably about 10 16 cm -3 In addition, in order to not exceed the so-called "doping concentration" range, the hole carrier concentration in the p-type semiconductor portion Mp is preferably about 10 21 cm -3 Below. The matrix material Mx only needs to have about 10 16 cm -3 More than and about 10 21 cm -3 The portion with the following hole carrier concentration is sufficient. This portion functions as the p-type semiconductor portion Mp, and has the effect of improving the EQE of the light-emitting element 10. When the matrix material Mx contains a II-VI semiconductor and the p-type semiconductor portion Mp contains carbon (C) as an example, the carbon concentration in the p-type semiconductor portion Mp is preferably about 10 16 cm -3 Above and 10 21 cm -3When converted to the concentration of the light-emitting layer EL containing quantum dots QD, the carbon concentration is preferably 10 12 cm -3 above 10 21 cm -3 The same also applies when the host material Mx includes a Group II-VI semiconductor and the p-type semiconductor portion Mp includes silicon (Si), germanium (Ge), and tin (Sn) as an example.

[0035] As described above, the current flowing in the light emitting layer EL includes the current I1 that flows through the quantum dots QD and contributes to light emission, and the current I2 that flows away from the quantum dots QD and does not contribute to light emission. The maximum value of the hole carrier concentration in the p-type semiconductor portion Mp is 10 19 cm -3 When the current I2 that does not contribute to light emission is small due to carrier compensation, the resistance of the p-type semiconductor portion Mp is large. Therefore, the current I1 that contributes to light emission is large. In order to improve the light emission efficiency of the light emitting element 10, the maximum value of the hole carrier concentration in the p-type semiconductor portion Mp is preferably 10 19 cm -3 Above and 10 21 cm -3 When the matrix material Mx includes a II-VI semiconductor and the p-type semiconductor portion Mp includes carbon (C), the maximum value of the carbon concentration in the p-type semiconductor portion Mp is preferably about 10 19 cm -3 Above and 10 21 cm -3 the following.

[0036] (Manufacturing method 1) In the following, the case where the p-type semiconductor portion Mp includes zinc sulfide (ZnS) doped with carbon (C) is discussed. Figure 1 The following description will describe a method for manufacturing the light emitting element 10. The following description will explain a method for manufacturing the light emitting element 10 in a case other than the case where the p-type semiconductor portion Mp includes zinc sulfide doped with carbon, and therefore, the description thereof will be omitted.

[0037] Figure 7 Yes Figure 1 Flowchart of an example of a method for manufacturing a light-emitting element shown in FIG. Figure 7 As shown, a substrate is prepared (step S1), an anode E1 is formed on the substrate (step S2), and a charge functional layer F1 is formed on the anode E1 (step S3). Then, a light-emitting layer EL is formed on the charge functional layer F1 (step S4), a charge functional layer F2 is formed on the light-emitting layer EL (step S5), and a cathode E2 is formed on the charge functional layer F2 (step S6).

[0038] Figure 8: is a cross-sectional view showing an example of a process for forming a light-emitting layer in this embodiment. Figure 7 , in the case of executing in order from step S1 to step S6, as Figure 8 As shown, the light-emitting layer EL can be formed. In step S4, first, a quantum dot dispersion L is applied to the charge functional layer F1. The quantum dot dispersion L contains a precursor J of the matrix material Mx, a plurality of quantum dots QD, and a solvent S. Then, by firing, the solvent S evaporates and / or decomposes from the applied quantum dot dispersion L. Subsequently, or simultaneously and in parallel, the precursor J is converted to the matrix material Mx by firing. This coating and firing forms a lower layer L1 comprising quantum dots QD and the i-type semiconductor portion Mi.

[0039] The solvent S includes, for example, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N-methylformamide (NMF), formamide, N,N'-dimethylpropyleneurea, dimethylacetamide, N-methylpyrrolidone, γ-butyrolactone, propylene carbonate, acetonitrile, 2-methoxyethanol, methyl acetate, ethyl acetate, ethyl formate, methyl formate, tetrahydrofuran, diethyl ether, tetrahydrothiophene, diethyl sulfide, and the like. When the matrix material Mx is zinc sulfide, the precursor J may include, for example, at least one of a metal acetate, a metal nitrate, or a metal halide as a metal source, and may also include at least one of thiourea, N-methylthiourea, 1,3-dimethylthiourea, N,N'-dimethylthiourea, tetramethylthiourea, or thioacetamide as a sulfur source. Alternatively, the precursor J may also include a metal complex in which thiourea, N-methylthiourea, 1,3-dimethylthiourea, N,N′-dimethylthiourea, tetramethylthiourea or thioacetamide is coordinated to the metal atom.

[0040] The i-type semiconductor portion Mi in the lower layer L1 is formed by firing the quantum dot dispersion L at a high temperature. High-temperature firing fully decomposes the organic compound, leaving no carbon (C) in the substrate Mx. Furthermore, the content ratio in the precursor J is adjusted so that the composition ratio of the inorganic semiconductor constituting the matrix material Mx is not biased. Furthermore, the matrix material Mx is not doped with carbon or other acceptors. Here, the high-temperature firing is preferably performed at a temperature of 125 degrees Celsius or higher and 500 degrees Celsius or lower, for a period of 1 minute or higher and 24 hours or lower.

[0041] like Figure 8As shown, the quantum dot dispersion L is then coated and fired on the lower layer L1 to form an upper layer L2 containing quantum dots QD and a p-type semiconductor portion Mp. The p-type semiconductor portion Mp in the upper layer L2 is formed by firing the quantum dot dispersion L at a low temperature. As a by-product of the decomposition of the solvent S and the modification of the precursor J, carbon (C) may remain in the light-emitting layer EL. By firing the quantum dot dispersion L at a low temperature, the decomposition of the organic compound becomes insufficient. As a result, the organic compound remains in a partially decomposed state or a completely decomposed state, and carbon remains. Carbon (C) acts as an acceptor in zinc sulfide (ZnS) to form a p-type semiconductor portion Mp. Here, the low-temperature firing is preferably above 60 degrees Celsius and below 125 degrees Celsius, and is above 1 minute and below 24 hours.

[0042] The light emitting layer EL is not limited to the two layers of the lower layer L1 and the upper layer L2 , and may be formed to include three or more layers.

[0043] (Manufacturing method 2) Figure 9 1 is a cross-sectional view showing another example of the process of forming the light-emitting layer of this embodiment. Figure 7 , in the case of executing in order from step S1 to step S6, as Figure 9 As shown, the light-emitting layer EL can be formed. In step S4, the quantum dot dispersion L is first applied and fired onto the charge functional layer F1 to form a layer L3 containing quantum dots QD and an i-type semiconductor portion Mi. Then, only in the upper portion of layer L3, the i-type semiconductor portion Mi is converted to a p-type semiconductor portion Mp. For example, only the upper portion of the substrate Mx is doped with a carbon-containing material Dp.

[0044] (Manufacturing method 3) Figure 10 It shows Figure 1 Flowchart of another example of a method for manufacturing a light emitting element shown in FIG. Figure 10 As shown, a substrate is prepared (step S1), a cathode E2 is formed on the substrate (step S6), and a charge functional layer F2 is formed on the cathode E2 (step S5). Then, a light-emitting layer EL is formed on the charge functional layer F2 (step S4), a charge functional layer F1 is formed on the light-emitting layer EL (step S3), and an anode E1 is formed on the charge functional layer F1 (step S2).

[0045] Figure 11 1 is a cross-sectional view showing another example of the process of forming the light-emitting layer of this embodiment. Figure 10 , in the case of executing in order from step S1 and step S6 to step S2, as Figure 11As shown, a light-emitting layer EL can be formed. In step S4, the quantum dot dispersion L is applied to the charge functional layer F1 and fired to form the light-emitting layer EL. Carbon (C) tends to remain, so it is more likely to be distributed on the lower side of the matrix material Mx than on the upper side. As a result, a p-type semiconductor portion Mp is formed on the lower side of the matrix material Mx, and an i-type semiconductor portion Mi is formed on the upper side. Here, firing is preferably performed at a temperature of 60°C to 125°C for 1 minute to 24 hours.

[0046] (Quantum Dot Dispersion) In this embodiment, the quantum dot dispersion L is, for example, a solution containing quantum dots QD coordinated with halide ions 16H. Therefore, in this embodiment, for example, a step of obtaining quantum dots QD coordinated with halide ions 16H is performed as a pre-step before synthesizing the quantum dot dispersion L containing quantum dots QD. More specifically, a replacement step is performed to replace the ligands coordinated to the quantum dots QD.

[0047] Figure 12 This is a cross-sectional view used to illustrate the replacement process. Figure 12 As shown on the left side of FIG, in the replacement process, first, a first solution 20 containing dissolved halide ions 16H and a second solution 22 containing dispersed quantum dots QD coordinated by carbon chains CC serving as organic ligands are injected into a container 18. The first solution 20 contains a first solvent S in which the halide ions 16H are soluble, and the second solution 22 contains a second solvent 26 in which the carbon chains CC are soluble. For example, the polarity of the second solvent 26 is different from that of the first solvent S, and the specific gravity is lighter than that of the first solvent S. In order to more clearly distinguish the boundary between the first solution 20 and the second solution 22, a separation liquid 28 having a specific gravity and polarity between the first solvent S and the second solvent 26 may be injected into the container 18.

[0048] The first solvent S allows the quantum dots QD coordinated with the halide ions 16H to be well dispersed together with the precursor of the matrix material Mx. In addition, the first solvent S can also be a polar solvent with a greater polarity than the second solvent 26. The second solvent 26 is preferably a non-polar solvent that is immiscible with the first solvent S.

[0049] The carbon chain CC can generally be a carbon chain used as a ligand for quantum dots QD. The second solvent 26 is a solvent in which the carbon chain CC is soluble, so the quantum dots QD coordinated by the carbon chain CC are easily dispersed in the second solution 22. In addition, an excess of halide ions 16H exceeding the amount of halide ions 16H that can be coordinated to the quantum dots QD is dissolved in the first solution 20. The halide ion concentration of the first solvent S is preferably 0.01 mol / l or greater, more preferably 0.1 mol / l or greater.

[0050] Next, the container 18 containing the first solution 20 and the second solution 22 is vibrated at high speed by a stirrer to stir the first solution 20 and the second solution 22. In order to improve the stirring efficiency, a stirrer may be added to the container 18. In other words, the process of stirring the first solution 20 and the second solution 22 is a process of treating the quantum dots QD with halide ions 16H, and in particular, a process of generating quantum dots QD coordinated with halide ions 16H.

[0051] Here, as described above, the first solution 20 contains an excess of halide ions 16H. Generally, when a solution containing dispersed quantum dots QD contains two or more ligands, the ligands coordinated to the quantum dots QD are in equilibrium with the ligands in the solution. Therefore, when the first solution 20 and the second solution 22 are stirred, at least a portion of the ligands coordinated to the quantum dots QD are replaced by halide ions 16H from the carbon chains CC.

[0052] For example, the solution in container 18 is stirred for at least one minute. Alternatively, stirring of the solution in container 18 can be performed at a temperature of 25 degrees Celsius and a vibration frequency of 10 times per minute for one hour. Under these conditions, the probability that the ligands coordinated to the quantum dots QD in container 18 are replaced by halide ions 16H is sufficiently high. Furthermore, stirring of the solution in container 18 is preferably performed under an atmosphere of nitrogen or argon to prevent water or oxygen in the atmosphere from mixing with the solution in container 18.

[0053] Therefore, by the above stirring, as Figure 12 As shown on the right side of FIG, a fourth solution 30 in which halide ion 16H-coordinated quantum dots QD are dispersed in the first solvent S and a fourth solution 32 in which carbon chain CC is dissolved in the second solvent 26 are obtained in container 18. Thus, halide ion 16H-coordinated quantum dots QD are obtained in the third solution 30. Alternatively, the above-mentioned stirring may be completed at the stage where the liquid in container 18 is irradiated with ultraviolet light, for example, and the luminescent liquid layer is confirmed to have moved from the upper portion to the lower portion of container 18.

[0054] Next, a quantum dot dispersion in which the quantum dots QD coordinated with the halide ions 16H are dispersed is synthesized. Figure 13 , the quantum dot dispersion involved in this embodiment is described in detail. Figure 13 For example, after the above stirring, only the third solution 30 is extracted from the container 18 by dripping, etc., and injected into the container 18. Figure 13 In the container 34 shown.

[0055] Here, a solution in which the precursor J of the matrix material Mx is dispersed in the first solvent S can also be injected into the container 18. Figure 13As shown, a quantum dot dispersion L in which quantum dots QD coordinated with halide ions 16H and a precursor J are dispersed in a first solvent S is synthesized.

[0056] (Evaluation of impurity concentration) The carbon concentration of the light-emitting layer EL is measured by using any one of SIMS (Secondary Ion Mass Spectrometry), AES (Auger Electron Spectroscopy), GCMS (Gas Chromatograph Mass Spectrometry), FTIR (Fourier Transform Infrared Spectroscopy), XPS (X-ray Photoelectron Spectroscopy), and EDX (Energy Dispersive X-ray Analyzer) or a combination of two or more.

[0057] If all of the above instruments are available and have comparable accuracy, SIMS is most preferred. AES is second most preferred, followed by GCMS, FTIR, XPS, and EDX in that order. The order of preference for measurement results follows the same order of preference.

[0058] The carbon concentration in the light-emitting layer EL containing quantum dots QD can also be converted into the carbon concentration in the matrix material Mx that does not contain quantum dots QD. Using TEM (transmission electron microscope, Transmission Electron Microscope), the particle size of the quantum dots QD, the shape of the quantum dots QD, and the number of quantum dots QD per unit cross-sectional area of ​​the light-emitting layer EL can be measured. The distribution of quantum dots QD in the light-emitting layer EL is random. Through geometric calculations based on these, the volume ratio of quantum dots QD relative to the light-emitting layer EL can be calculated, and the volume ratio of the matrix material Mx can be calculated.

[0059] Furthermore, it is preferable to confirm that the quantum dots QD contain no carbon before converting the carbon concentration. Furthermore, even when the p-type semiconductor portion Mp contains impurities other than carbon, dopants, or acceptors, the impurity concentration can be similarly measured and converted. It is preferable to confirm that the quantum dots QD contain no impurities beforehand. Example 1

[0060] The light emitting element 10 of Example 1 was used Figure 1 The matrix material Mx contains ZnS, and the p-type semiconductor portion Mp contains C (carbon element). The carbon concentration in the p-type semiconductor portion Mp is 10 19 cm-3 Above and 10 21 cm -3 the following.

[0061] (Variation) like Figure 1 As shown, the p-type semiconductor portion Mp can be distributed with a uniform thickness, can be distributed continuously, or can be distributed so as to cover the upper surface of the light-emitting layer EL. However, the distribution of the p-type semiconductor portion Mp is not limited to this and can be any distribution. The following describes variations of the configuration of the light-emitting element of this embodiment.

[0062] Figure 14 and Figure 15 Each of them is a cross-sectional view showing a modified example of the structure of the light emitting element of this embodiment. Figure 14 As shown in FIG. 1 , the p-type semiconductor portion Mp may be distributed with a non-uniform thickness or may be distributed so as to cover the lower surface of the light emitting layer EL. Figure 15 As shown, the p-type semiconductor portion Mp may be distributed intermittently or may be distributed inside the light emitting layer EL.

[0063] combination Figure 1 , Figure 14 , Figure 15 As an example, the p-type semiconductor portion Mp may be continuously distributed with an uneven thickness so as to cover the upper surface of the light-emitting layer EL, or may be discontinuously distributed so as to cover the upper surface of the light-emitting layer EL. Furthermore, for example, the p-type semiconductor portion Mp may be continuously distributed with a uniform thickness so as to cover the lower surface of the light-emitting layer EL, or may be discontinuously distributed so as to cover the lower surface of the light-emitting layer EL. Furthermore, for example, the p-type semiconductor portion Mp may be continuously distributed with a uniform thickness within the light-emitting layer EL, or may be continuously distributed with an uneven thickness within the light-emitting layer EL.

[0064] In the light-emitting layer EL, it is preferred that the p-type semiconductor portion Mp is located on the cathode E2 side of the matrix material Mx, and the i-type semiconductor portion Mi is located on the anode E1 side of the matrix material Mx. In other words, it is preferred that the hole carrier concentration of the portion on the cathode E2 side of the matrix material Mx is greater than the hole carrier concentration of the portion on the anode E1 side of the matrix material Mx. According to this configuration, the carrier balance in the light-emitting layer EL is further improved. In addition, the accumulation of holes at the boundary between the light-emitting layer EL and the electron transport layer ETL can be reduced. When the matrix material Mx contains a II-VI semiconductor and the p-type semiconductor portion Mp contains carbon (C) as an example, it is preferred to adopt a structure in which the carbon concentration of the portion on the cathode E2 side of the matrix material Mx is greater than the carbon concentration of the portion on the anode E1 side of the matrix material Mx. The hole carrier concentration or carbon concentration in the matrix material Mx can change in stages or continuously. The same applies when the matrix material Mx contains a II-VI semiconductor and the p-type semiconductor portion Mp contains silicon (Si), germanium (Ge) and tin (Sn) as an example.

[0065] [Implementation Method 2] For the sake of convenience, components having the same functions as those described in the above embodiments are denoted by the same reference numerals and their description will not be repeated.

[0066] Figure 16 1 is a cross-sectional view showing a configuration example of a light emitting element according to one embodiment. Figure 16 As shown, the configuration of the second embodiment is the same as that of the first embodiment except that the entire host material Mx is a p-type semiconductor portion Mp.

[0067] (Manufacturing Method) In the following, the case where the p-type semiconductor portion Mp includes zinc sulfide (ZnS) doped with carbon (C) is discussed. Figure 16 The following describes a method for manufacturing the light-emitting element 10. The description of the manufacturing method for cases other than when the host material Mx includes zinc sulfide doped with carbon is omitted.

[0068] Figure 17 1 is a cross-sectional view showing an example of a process for forming a light-emitting layer in this embodiment. Figure 7 , in the case of executing in order from step S1 to step S6, refer again to Figure 10 , when the steps S1 and S6 are executed in order to step S1, as shown in FIG. Figure 17 In step S4 , first, the quantum dot dispersion L is applied and fired on the charge functional layer F1 or the charge functional layer F2 to form the light emitting layer EL including the quantum dots QD and the p-type semiconductor portion Mp.

[0069] The p-type semiconductor portion Mp is formed by low-temperature firing of the quantum dot dispersion L. Alternatively, the i-type semiconductor portion Mi may be formed by high-temperature firing and converted into the p-type semiconductor portion Mp.

[0070] [Embodiment 3] Other embodiments of the present disclosure are described below.

[0071] Figure 18 1 is a top view showing a configuration example of a display device according to an embodiment of the present disclosure. Figure 18 As shown, the display device 100 includes a display unit 15 including a plurality of sub-pixels X and a driving circuit 25 for driving the display unit 15. For example, the sub-pixel X includes the light-emitting element 10 and the pixel circuit 5 described in Embodiment 1 or 2 above.

[0072] The present disclosure is not limited to the above-described embodiments. Various modifications can be made within the scope of the claims. Embodiments obtained by appropriately combining the technical solutions 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 methods disclosed in the various embodiments. Description of Reference Numerals

[0073] 10 light-emitting elements 100 Display device E1 anode E2 cathode K area Mp p-type semiconductor department Mx matrix material QD Quantum Dots QD1, the first quantum dot QD2 second quantum dot

Claims

1. A light emitting element, characterized in that: include: an anode, a cathode and a light-emitting layer between the anode and the cathode, The light emitting layer includes a plurality of quantum dots and a matrix material, wherein the matrix material has a p-type semiconductor portion and fills spaces between the plurality of quantum dots.

2. The light emitting element according to claim 1, characterized in that In a cross-sectional view of the light-emitting layer, the matrix material fills a region surrounded by two straight lines tangent to the peripheries of a first quantum dot and a second quantum dot among the plurality of quantum dots and the peripheries facing the first quantum dot and the second quantum dot.

3. The light emitting element according to claim 1 or 2, characterized in that: The matrix material comprises a Group IV semiconductor, The p-type semiconductor portion contains a Group III element.

4. The light emitting element according to claim 3, characterized in that The matrix material contains one or more elements selected from carbon C, silicon Si, germanium Ge and tin Sn, The p-type semiconductor portion contains one or more elements selected from the group consisting of boron B, aluminum Al, gallium Ga, indium In, and thallium Tl.

5. The light emitting element according to claim 1 or 2, characterized in that: The matrix material includes a Group III-V semiconductor, and the p-type semiconductor portion includes a Group II element.

6. The light emitting element according to claim 5, characterized in that The p-type semiconductor portion contains one or more elements selected from the group consisting of magnesium Mg, zinc Zn, cadmium Cd, and mercury Hg.

7. The light emitting element according to claim 1 or 2, characterized in that: The matrix material includes a Group III-V semiconductor, and the p-type semiconductor portion includes a Group V element in a ratio greater than 1:1 with respect to a Group III element.

8. The light emitting element according to any one of claims 5 to 7, characterized in that: The matrix material includes one or more elements selected from boron B, aluminum Al, gallium Ga, indium In and thallium Tl and one or more elements selected from nitrogen N, phosphorus P, arsenic As, antimony Sb and bismuth Bi.

9. The light emitting element according to claim 1 or 2, characterized in that: The matrix material comprises a II-VI semiconductor, The p-type semiconductor portion contains a Group IV element.

10. The light emitting element according to claim 9, characterized in that The p-type semiconductor portion contains one or more elements selected from the group consisting of carbon C, silicon Si, germanium Ge, and tin Sn.

11. The light emitting element according to claim 1 or 2, characterized in that: The matrix material includes a Group II-VI semiconductor, and the p-type semiconductor portion includes a Group VI element in a ratio greater than 1:1 with respect to a Group II element.

12. The light emitting element according to any one of claims 9 to 11, characterized in that: The matrix material contains one or more elements selected from magnesium Mg, zinc Zn, cadmium Cd, and mercury Hg, and one or more elements selected from oxygen O, sulfur S, selenium Se, and tellurium Te.

13. The light emitting element according to any one of claims 1 to 12, characterized in that: The hole carrier concentration in the p-type semiconductor portion is 10 16 cm -3 Above and 10 21 cm -3 the following.

14. The light emitting element according to any one of claims 1 to 13, characterized in that: The maximum value of the hole carrier concentration in the p-type semiconductor portion is 10 19 cm -3 Above and 10 21 cm -3 the following.

15. The light emitting element according to any one of claims 1 to 14, characterized in that: The p-type semiconductor portion is located on the cathode side in the matrix material.

16. The light emitting element according to any one of claims 1 to 15, characterized in that: The hole carrier concentration of the portion of the matrix material on the cathode side is greater than the hole carrier concentration of the portion of the matrix material on the anode side.

17. The light emitting element according to claim 9 or 10, characterized in that: The p-type semiconductor portion includes carbon C.

18. The light emitting element according to claim 17, characterized in that: The carbon concentration in the p-type semiconductor portion is 10 16 cm -3 Above and 10 21 cm -3 the following.

19. The light emitting element according to claim 17 or 18, characterized in that: The maximum carbon concentration in the p-type semiconductor portion is 10 19 cm -3 Above and 10 21 cm -3 the following.

20. The light emitting element according to any one of claims 17 to 19, characterized in that: The carbon concentration of the portion of the matrix material on the cathode side is greater than the carbon concentration of the portion of the matrix material on the anode side.

21. A display device, characterized in that: It comprises the light-emitting element according to any one of claims 1 to 20.

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