Light-emitting element, display device, and production method for light-emitting element

Abstract

A light-emitting element (7) according to the present disclosure comprises: a light-emitting layer (5) that is disposed between an anode (EA) and a cathode (EC) and that includes a plurality of quantum dots (QD) and an inorganic matrix material (MX) which fills space between the plurality of quantum dots (QD); and a functional layer (6F) that is disposed between the anode (EA) and the cathode (EC) so as to be adjacent to the light-emitting layer (5) and that has the same constituent elements as the inorganic matrix material (MX) but has a different composition ratio.

Description

[Technical field]

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

[0002] In a light-emitting element having a light-emitting layer containing quantum dots as a light-emitting material, reactive current may occur when carriers pass through the light-emitting layer without being injected into the quantum dots. The generation of such reactive current not only reduces the light-emitting power efficiency of the light-emitting element, but also causes deterioration of the quantum dots and the charge transport layer, resulting in a decrease in the reliability of the light-emitting element. Patent Document 1 discloses a light-emitting element in which the light-emitting layer contains multiple quantum dots with shell thicknesses different from each other, thereby improving the confinement of carriers to the quantum dots. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. WO2015 / 056750 Summary of the Invention [Problem to be solved by the invention]

[0004] In the light-emitting device disclosed in Patent Document 1, since organic ligands exist between the quantum dots, it is difficult to reduce the reactive current flowing between the quantum dots and increase the light-emitting power efficiency. In addition, the organic ligands have a problem of reduced reliability due to degradation. [Means for solving the problem]

[0005] A light-emitting element according to one embodiment of the present disclosure comprises an anode and a cathode, a light-emitting layer disposed between the anode and the cathode and including a plurality of quantum dots and an inorganic matrix material filling spaces between the plurality of quantum dots, and a functional layer disposed between the anode and the cathode so as to be adjacent to the light-emitting layer and having the same constituent elements as the inorganic matrix material but a different composition ratio. Effect of the Invention

[0006] According to one aspect of the present disclosure, the light emitting power efficiency of a light emitting element is improved. [Brief description of the drawings]

[0007] [Figure 1] 1 is a cross-sectional view illustrating a configuration of a light-emitting element according to an embodiment. [Diagram 2] FIG. 2 is an example of a schematic band diagram of the light-emitting element shown in FIG. [Diagram 3] 10 is a cross-sectional view showing another configuration of the light-emitting device according to the embodiment. FIG. [Figure 4] FIG. 4 is an example of a schematic band diagram of the light-emitting element shown in FIG. [Diagram 5] 10 is a cross-sectional view showing another configuration of the light-emitting device according to the embodiment. FIG. [Figure 6] FIG. 6 is an example of a schematic band diagram of the light-emitting element shown in FIG. [Figure 7] 10 is a cross-sectional view showing another configuration of the light-emitting device according to the embodiment. FIG. [Figure 8] FIG. 8 is an example of a schematic band diagram of the light-emitting element shown in FIG. [Figure 9] 10 is a cross-sectional view showing another configuration of the light-emitting device according to the embodiment. FIG. [Figure 10] FIG. 10 is an example of a schematic band diagram of the light-emitting element shown in FIG. [Figure 11] 10 is a cross-sectional view showing another configuration of the light-emitting device according to the embodiment. FIG. [Figure 12] FIG. 12 is an example of a schematic band diagram of the light-emitting element shown in FIG. [Figure 13] 10 is a cross-sectional view showing another configuration of the light-emitting device according to the embodiment. FIG. [Figure 14] 4 is a flowchart showing a method for manufacturing a light-emitting device according to an embodiment. [Figure 15] 1A to 1C are cross-sectional schematic diagrams showing a method for forming a functional layer using a CBD method. [Figure 16A] 1A to 1C are schematic cross-sectional views showing examples of forming an inorganic matrix material. [Figure 16B]1A to 1C are schematic cross-sectional views showing examples of forming an inorganic matrix material. [Figure 17] FIG. 1 is a schematic diagram illustrating an example of a configuration of a display device according to an embodiment of the present invention. [Figure 18] 1 is a cross-sectional view showing an example of a configuration of a display device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Embodiment 1] (Configuration of light-emitting element) FIG. 1 is a cross-sectional view showing the configuration of a light-emitting element according to an embodiment. As shown in FIG. 1, the light-emitting element 7 according to this embodiment includes an anode EA and a cathode EC, an emission layer 5 disposed between the anode EA and the cathode EC and including a plurality of quantum dots QDs and an inorganic matrix material MX filling the spaces between the plurality of quantum dots QDs, and a functional layer 6F disposed between the anode EA and the cathode EC so as to be adjacent to the emission layer 5 and having the same constituent elements as the inorganic matrix material MX but a different composition ratio. The functional layer 6F and the inorganic matrix material MX may be chalcogenide metals of the same crystal type. The functional layer 6F may be an electron transport layer (ETL) disposed between the cathode EC and the emission layer 5. A hole transport layer (HTL) 4 may be disposed between the anode EA and the emission layer 5.

[0009] In the light-emitting element 7, the inorganic matrix material MX and the functional layer 6F, which have the same constituent elements, are homojunctionally joined, so that the potential barrier between the functional layer 6F and the inorganic matrix material MX is small. This facilitates charge injection (e.g., electron injection) from the functional layer 6F to the light-emitting layer 5, improving the light-emitting power efficiency (power consumption-brightness characteristics of the light-emitting element).

[0010] Inorganic Matrix Material MX terminates the surface defects of QDs and reduces non-radiative recombination in QDs, thereby improving the external luminescence efficiency (EQE). Material Since MX has superior durability compared to general organic ligands, the reliability of the light-emitting element 7 is improved.

[0011] Thus, the inorganic matrix Material Although the functional layer 6F is the same compound as MX (the constituent elements are the same), the functional layer 6F has a different composition. The functional layer 6F is formed adjacent to the light-emitting layer 5, and an inorganic matrix having a low defect density and can be formed at a low temperature. Material Using MX (eg, zinc sulfide, zinc selenide), the voltage for carrier injection can be reduced.

[0012] Each of the quantum dots QD may have a core 8 and a shell 9 whose constituent elements are the same as those of the inorganic matrix material MX. The composition ratio of the inorganic matrix material MX and the shell 9 may be the same or different. In this way, the light emission characteristics (voltage-luminance characteristics) can be reduced in voltage while maintaining the confinement effect of the shell 9.

[0013] Each of the functional layer 6F and the inorganic matrix material MX may contain a metal element and a nonmetal element, the metal element may be zinc, and the nonmetal element may be sulfur or selenium. The functional layer 6F may contain a hydroxyl group, and the functional layer 6F may contain a metal-hydroxyl group bond (described in detail below).

[0014] FIG. 2 is an example of a schematic band diagram of the light-emitting element shown in FIG. 1. In the following, closeness to the vacuum level VE (0 eV) is expressed as "shallow", and farthest from the vacuum level VE (0 eV) is expressed as "deep". CBM is the lower end of the conduction band, VBM is the upper end of the valence band, the band gap is the difference between the CBM and VBM, and FE is the Fermi level. As shown in FIG. 2, the inorganic matrix material MX may have a larger band gap than the multiple quantum dots QD. The band gap of the quantum dots QD may be the core band gap or the shell band gap.

[0015] When the functional layer 6F is an electron transport layer (ETL) disposed between the light-emitting layer 5 and the cathode EC, the functional layer 6F may have a conduction band minimum (CBM) shallower than that of the plurality of quantum dots QD and deeper than that of the inorganic matrix material MX. The CBM of the quantum dots QD may be the CBM of the core. In this way, by adjusting the CBM of the functional layer 6F, it is possible to adjust the amount of electron injection. Since the CBM is shallower than that of the quantum dots QD, the electron injection barrier from the functional layer 6F (electron transport layer) to the light-emitting layer 5 becomes smaller, and the luminous power efficiency increases. Also, since the CBM of the functional layer 6F is adjusted to be deeper than the CBM of the inorganic matrix Material MX, the electron injection into the inorganic matrix Material MX is suppressed. As a result, the light-emitting region moves closer to the functional layer 6F, and non-radiative recombination at the interface between the hole transport layer 4 and the light-emitting layer 5 can be suppressed. In the cases of FIGS. 1 and 2, the functional layer 6F (ETL) may have a CBM deeper than that of the shell 9 of the quantum dots QD.

[0016] By controlling the Fermi level of the functional layer 6F, a stepped potential can be formed, and the voltage for carrier injection (electron injection) can be reduced. The control of the Fermi level is possible, for example, by controlling the zinc element ratio in zinc sulfide and zinc selenide. When the zinc element is in excess, it becomes n-type conductive with sulfur defects and selenium defects as donors. Therefore, the functional layer 6F (ETL) may have a larger composition ratio of zinc than the inorganic matrix material MX. for example, When the functional layer 6F (ETL) is zinc x sulfide represented by Zn in the case of , the inorganic matrix material MX teeth Zn y sulfide represented by Zn For example, When the functional layer 6F (ETL) is zinc x selenide represented by Zn in the case of , the inorganic matrix material MX teeth Zn y selenide represented by Zn It becomes.

[0017] FIG. 3 is a cross-sectional view showing another configuration of the light-emitting device according to the embodiment. FIG. 4 is an example of a schematic band diagram of the light-emitting device shown in FIG. 3. As shown in FIG. 3, at least one of the multiple quantum dots QDs may be in contact with the functional layer 6F. That is, the light-emitting layer 5 includes quantum dots QDs having a portion exposed from the inorganic matrix material MX, and this exposed portion is in contact with the functional layer 6F. The functional layer 6F has a deeper CBM than the inorganic matrix material MX and has high carrier transportability, so that the light-emitting characteristics (voltage-luminance characteristics) can be achieved at a lower voltage. Furthermore, an inorganic matrix is ​​interposed between the exposed quantum dots QDs. Material Since MX is not present, the electron injection barrier is lowered, and the light emission characteristics (voltage-luminance characteristics) can be achieved at a lower voltage. The configuration of FIG. 3 can be formed, for example, by forming a light emission layer 5 containing an inorganic matrix material MX, and then etching the vicinity of the upper surface of the inorganic matrix material MX to expose a part of the quantum dots QD near the upper surface from the inorganic matrix material MX. As an example, by using a CBD (chemical bath deposition) method in which an inorganic layer (functional layer 6F) is grown using an alkaline aqueous solution, etching of the inorganic matrix material MX and growth of the functional layer 6F can be performed in the same simple aqueous solution process. In the functional layer 6F formed by the CBD method, OH groups (hydroxyl groups) are bonded to metal elements, thereby terminating dangling bonds of the metal elements, and thus non-light-emitting transition of carriers in the functional layer 6F can be suppressed. Furthermore, the mobility, which is one of the carrier transport characteristic indexes, is very high, reaching 1.0 [cm 2 / Vs)], it is possible to transport carriers at a smaller voltage.

[0018] FIG. 5 is a cross-sectional view showing another configuration of the light-emitting device according to the embodiment. FIG. 6 is an example of a schematic band diagram of the light-emitting device shown in FIG. 5. As shown in FIGS. 5 and 6, the functional layer 6F is a first electron transport layer, and a second electron transport layer 6S is disposed between the first electron transport layer 6F and the cathode EC. The second electron transport layer 6S may have the same constituent elements as the first electron transport layer 6F but a different composition ratio. The second electron transport layer 6S has a deeper CBM than the first electron transport layer 6F. By configuring the CBMs of the first electron transport layer 6F and the second electron transport layer 6S to form a stepped potential, the carrier injection voltage to the quantum dot QD can be lowered compared to the case of a single layer of the electron transport layer 6F.

[0019] In FIG. 5 and FIG. 6, the Fermi levels of the first and second electron transport layers 6F and 6S are controlled to form a stepped potential, which allows the voltage for carrier injection (electron injection) to be reduced. For example, when the first electron transport layer 6F is Zn x Zinc sulfide represented by S(x>1), the second electron transport layer 6S is Zn z The first electron transport layer 6F may be zinc sulfide represented by Zn x Zinc selenide represented by Se(x>1), the second electron transport layer 6S is Zn z It may be zinc selenide represented by Se(z>x).

[0020] Fig. 7 is a cross-sectional view showing another configuration of the light-emitting device according to the embodiment. Fig. 8 is an example of a schematic band diagram of the light-emitting device shown in Fig. 7. As shown in Figs. 7 and 8, the functional layer 6F is a first electron transport layer, and a second electron transport layer 6T is disposed between the first electron transport layer 6F and the cathode EC. The electron mobility of the first electron transport layer 6F is S1, the thickness is Da, the electron mobility of the second electron transport layer 6T is S2, the thickness is Db, and S1 / Da 3 ≧S2 / Db 3 It may be.

[0021] In order to increase the external luminous efficiency (EQE) of the light-emitting element 7, electrons and holes must be Quantum dotsIt is necessary to increase the efficiency of carrier injection into QDs. Furthermore, since excess carriers do not contribute to radiative recombination, it is effective to adjust the carrier balance, which is the ratio of the injected amount of electrons and holes. Therefore, as shown in Figure 7, by stacking the first electron transport layer 6F and the second electron transport layer 6T, which has a lower mobility than the first electron transport layer 6F, a bottleneck in the amount of electron injection is intentionally created, and the carrier balance can be adjusted to the hole side, which generally has a lower amount of carrier injection.

[0022] The amount of carrier injection is calculated by solving the Poisson equation, which takes into account the dielectric constant, mobility, carrier density, and film thickness of the ETL material. 2 / Vs or less, the space charge limited current (SCLC) is dominant over the ohmic current, and the amount of carrier injection is described according to Child's law with the dielectric constant, mobility, film thickness, and voltage as parameters. Here, if the dielectric constants of the first and second electron transport layers 6F and 6T are the same and the amount of electron injection at the same voltage is compared, the electron mobility of the first electron transport layer 6F is S1, the thickness is Da, and the electron mobility of the second electron transport layer 6T is S2, the thickness is Db, and S1 / Da 3 ≧S2 / Db 3 In this case, a bottleneck in electron injection can be intentionally created, improving the carrier balance and thus the external luminous efficiency (EQE).

[0023] Fig. 9 is a cross-sectional view showing another configuration of the light-emitting device according to the embodiment. Fig. 10 is an example of a schematic band diagram of the light-emitting device shown in Fig. 9. As shown in Figs. 9 and 10, a functional layer 4F (hole transport layer: HTL) having the same constituent elements as the inorganic matrix material MX but a different composition ratio is disposed between the light-emitting layer 5 and the anode EA. R The functional layer 4F may have a deeper VBM than the multiple quantum dots QD. The functional layer 4F may have a shallower VBM than the inorganic matrix material MX.

[0024] Zinc sulfide and zinc selenide exhibit p-type conductivity with zinc vacancies as acceptors when the atomic composition ratio shows a zinc deficiency. Therefore, the functional layer 4F (HTL) may have a smaller zinc composition ratio than the inorganic matrix material MX. for example, The functional layer 4F (HTL) is Zn x S( 0< zinc sulfide represented by x < 1) in the case of , the inorganic matrix material MX teeth Zn y S (0<x zinc sulfide represented by < y) For example, The functional layer 4F (HTL) is Zn x Se( 0< zinc selenide represented by x < 1) in the case of , the inorganic matrix material MX teeth Zn y Se (0<x zinc selenide represented by < y) It becomes.

[0025] In the light-emitting device 7, since the inorganic matrix material MX and the functional layer 4F (HTL) having the same constituent elements are homojunctioned, the potential barrier between the functional layer 4F and the inorganic matrix material MX becomes small. Therefore, hole injection from the functional layer 4F to the light-emitting layer 5 becomes easy, and the luminous power efficiency (power consumption-luminance characteristics of the light-emitting device) is improved. Further, since the functional layer 4F is configured with a deeper VBM than the plurality of quantum dots QD, the hole injection barrier from the functional layer 4F (hole transport layer) to the light-emitting layer 5 becomes small, and the luminous power efficiency increases.

[0026] FIG. 11 is a cross-sectional view showing another configuration of the light-emitting device according to the embodiment. FIG. 12 is an example of a schematic band diagram of the light-emitting device shown in FIG. 11. As shown in FIGS. 11 and 12, the functional layer 4F is a first hole transport layer, and a second hole transport layer 4S may be disposed between the first hole transport layer 4F and the anode EA. Let the hole mobility of the first hole transport layer 4F be S3, the thickness be Dc, the hole mobility of the second hole transport layer 4S be S4, and the thickness be Dd, then S3 / Dc 3 ≧S4 / Dd 3In this way, a bottleneck for hole injection can be intentionally created, and the carrier balance and thus the external luminous efficiency (EQE) can be improved.

[0027] FIG. 13 is a cross-sectional view showing another configuration of the light-emitting device according to the embodiment. As shown in FIG. 13, a functional layer 4F (HTL) having the same constituent elements as the inorganic matrix material MX but a different composition ratio may be disposed between the anode EA and the light-emitting layer 5, and a functional layer 6F (ETL) having the same constituent elements as the inorganic matrix material MX but a different composition ratio may be disposed between the cathode EC and the light-emitting layer 5. The inorganic matrix material MX and the functional layers 4F and 6F may be zinc chalcogenides (zinc sulfide, zinc selenide, etc.), and the functional layer 6F (ETL) may have a higher zinc composition ratio than the inorganic matrix material MX, and the functional layer 4F (HTL) may have a lower zinc composition ratio than the inorganic matrix material MX. In this way, the injection barrier due to the step-like potential can be reduced for both electrons and holes.

[0028] Fig. 14 is a flowchart showing a method for manufacturing a light-emitting device according to an embodiment. As shown in Fig. 1 and Fig. 14, the method for manufacturing a light-emitting device according to an embodiment includes a step S10 for forming a lower electrode (e.g., an anode EA), a step S20 for forming a light-emitting layer 5 including a plurality of quantum dots QD and an inorganic matrix material MX filling spaces between the plurality of quantum dots QD, a step S30 for forming a functional layer 6F having the same constituent elements as the inorganic matrix material MX but different in composition ratio on the light-emitting layer 5, and a step S40 for forming an upper electrode (e.g., a cathode EC).

[0029] 15 is a schematic cross-sectional view showing a method for forming a functional layer using the CBD method. For example, a laminate ST formed by laminating a substrate 13, an anode EA, a hole transport layer 4, and a light emitting layer 5 is immersed in an alkaline aqueous solution 10 containing a metal source and a chalcogen source at a predetermined temperature for a predetermined time in a state in which the lower surface BF and side surface SF of the laminate ST are covered with a mask MK, whereby a functional layer 6F can be grown on the laminate ST (so as to be in contact with the light emitting layer 5).

[0030] For example, zinc sulfate (ZnSO 4 ) at 0.16 mol / L, ammonia as an alkali source at 7.5 mol / L, and thiourea as a sulfur source at 0.6 mol / L are mixed to obtain an alkaline aqueous solution 10 with a pH of 11. The temperature of the alkaline aqueous solution 10 is adjusted to 80° C., and the laminate ST is immersed in it for 15 minutes to produce a zinc sulfide thin film (containing oxygen atoms and hydroxyl groups) with a thickness of 100 nm.

[0031] The quantum dot QD used in this embodiment may be a dot having a maximum width of 100 [nm] or less, and may be spherical or non-spherical in shape. The shape of the quantum dot QD is not limited to a spherical three-dimensional shape (circular cross-sectional shape) as long as it satisfies the maximum width. The maximum width may be 1.0 [nm] or more. The shape may be, for example, a polygonal cross-sectional shape, a rod-like three-dimensional shape, a branch-like three-dimensional shape, a three-dimensional shape with unevenness on the surface, or a combination thereof. The quantum dot QD may be composed of a semiconductor material, and may be an inorganic semiconductor nanocrystal. The semiconductor material may have a certain band gap and may be a material that generates electroluminescence. The wavelength region of the electroluminescence may be any of the red region, the green region, and the blue region.

[0032] The quantum dot QD may include at least one of crystals of II-VI group semiconductors such as MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, crystals of III-V group semiconductors such as GaAs, GaP, InN, InAs, InP, InSb, chalcogenide compound crystals, perovskite compound crystals, and crystals of IV group semiconductors such as Si and Ge. Note that the II-VI group compound means a compound containing a II group element and a VI group element, and the III-V group compound means a compound containing a III group element and a V group element. Additionally, Group II elements may include Group 2 and Group 12 elements, Group III elements may include Group 3 and Group 13 elements, Group V elements may include Group 5 and Group 15 elements, and Group VI elements may include Group 6 and Group 16 elements.

[0033] Chalcogenides are compounds that contain a Group VI A(16) element, such as CdS or CdSe. Chalcogenides may also include mixed crystals thereof.

[0034] Perovskite compounds are, for example, of the general formula CsPbX 3 The composition is represented by the following formula: The constituent element X includes at least one element selected from the group consisting of Cl, Br, and I, for example.

[0035] Here, the numbering of element families using Roman numerals is based on the old IUPAC (International Union of Pure and Applied Chemistry) system or the old CAS (Chemical Abstracts Service) system, while the numbering of element families using Arabic numerals is based on the current IUPAC system.

[0036] 16A and 16B are schematic cross-sectional views showing an example of the formation of an inorganic matrix material. As shown in FIG. 16A and FIG. 16B, the inorganic matrix material MX fills the region (space) JS between two adjacent quantum dots QD, and the inorganic matrix material MX is filled in the region JS. The region JS is defined by two straight lines (common circumscribing lines) tangent to the peripheries of two adjacent quantum dots QD in the cross section of the light-emitting layer 5 and a line (common circumscribing line) tangent to the peripheries of two adjacent quantum dots QD. D It is acceptable for the region to be surrounded by the quantum dots. As shown in FIG. 16B, even if two adjacent quantum dots are close to each other, a region JS exists, and the inorganic matrix material MX fills the region JS. For the inorganic matrix material filling the space between multiple quantum dots, it is sufficient to know that the inorganic matrix material is filled between at least two quantum dots QD. In other words, if it is known that the inorganic matrix material MX fills the region (space) JS between two adjacent quantum dots QD, it can be said that the inorganic matrix material MX fills the space between multiple quantum dots QD. In addition, another example of "filled" or "fulfilled" is "holding". In this case, two adjacent quantum dots QD may be held by the presence of an inorganic matrix material MX in the region JS. For example, if at least a part of the region JS is made of an inorganic matrix material MX, Material Two quantum dots (QDs) may be held together by being filled with MX.

[0037] The inorganic matrix material MX is mainly composed of an inorganic material (inorganic substance). The inorganic matrix material MX may be a component of the light-emitting layer containing a plurality of quantum dots QDs. The inorganic matrix material MX may be a member that is composed of an inorganic substance (for example, an inorganic semiconductor) and contains and holds other substances, and can be called a base material, a base material, or a filler. The inorganic matrix material MX may be solid at room temperature. The inorganic matrix material MX may contain a plurality of quantum dots QDs. The inorganic matrix material MX may fill the regions (spaces) other than the plurality of quantum dots QDs in the light-emitting layer (quantum dot layer), or may fill the spaces between the plurality of quantum dots QDs. The inorganic matrix material MX may fill the regions (spaces) other than the plurality of quantum dots QDs in the light-emitting layer. The inorganic matrix material MX may be partially or completely filled between the plurality of quantum dots QDs. The plurality of quantum dots QDs may be embedded in the inorganic matrix material MX at intervals. The inorganic matrix material MX may indicate a portion of the light-emitting layer other than the plurality of quantum dots QDs.

[0038] The inorganic matrix material MX may completely or incompletely fill the regions (spaces) other than the quantum dot group in the light-emitting layer. Here, three or more quantum dots QD are collectively referred to as a quantum dot group. In this disclosure, unless otherwise specified or contradictory, the structure of the inorganic matrix material MX, etc., only needs to be seen to have the desired configuration in a width of about 100 nm in cross-sectional observation of the light-emitting layer 5, and it is not necessary for the desired configuration to be observed in the entire light-emitting layer 5. The inorganic matrix material MX in the quantum dot layer is a material that is 1000 nm in width along the surface direction perpendicular to the layer thickness direction. 2The continuous film may be formed as a continuous film having an area of ​​100 mm or more. The continuous film means a film that is not divided by a material other than the material that constitutes the continuous film in one plane. The continuous film may be an integrated film that is connected without interruption by chemical bonds of the inorganic matrix material MX.

[0039] The outer periphery of the light-emitting layer may be made of an inorganic matrix material MX, and the quantum dots QD may be located away from the outer periphery. The outer periphery of the light-emitting layer does not have to be made of only the inorganic matrix material MX, and a part of the quantum dots QD may be exposed from the inorganic matrix material MX.

[0040] The inorganic matrix material MX may be the same material as the shell contained in each of the multiple quantum dots QDs. When the shell of the quantum dot QD and the inorganic matrix material MX cannot be distinguished, the shell may be considered as a part of the inorganic matrix material MX. The inorganic matrix material MX may contain a substance other than the inorganic compound (zinc sulfide, zinc selenide, etc.) that is the main component as an additive, impurity, or residue. When an emission layer containing the inorganic matrix material MX is analyzed, the carbon atom content may be 5 atomic % or less.

[0041] 17 is a schematic diagram showing an example of the configuration of a display device according to this embodiment. As shown in FIG. 17, the display device 20 includes a display section DA including a plurality of sub-pixels SP, a first driver X1 and a second driver X2 that drive the plurality of sub-pixels SP, and a display control section DC that controls the first driver X1 and the second driver X2. The sub-pixels SP include a light-emitting element 7 and a light-emitting element 7 and a pixel circuit PC connected to the scanning signal line GL, the data signal line DL, and the light emission control line EL. The scanning signal line GL and the light emission control line EL may be connected to a first driver X1, and the data signal line DL may be connected to a second driver X2.

[0042] FIG. 18 is a cross-sectional view showing an example of the configuration of the display device according to this embodiment. The display device 20 may include a substrate 13, a light emitting element layer 14, and a sealing layer 15. The substrate 13 may be a pixel circuit substrate including a support substrate 11 and a pixel circuit layer 12. A glass substrate, a resin substrate, or the like may be used for the support substrate 11. The support substrate 11 may be flexible. The pixel circuit layer 12 includes a plurality of pixel circuits PC arranged, for example, in a matrix. The pixel circuit PC may include a pixel capacitance to which a grayscale signal is written, a transistor that controls the current value of the light emitting element 7 according to the grayscale signal, a transistor connected to a scanning signal line GL and a data signal line DL, and a transistor connected to a light emission control line EL.

[0043] As shown in FIG. 18, the light-emitting element layer 14 may include, in order from the substrate 13 side, an anode EA, an edge cover film 2 covering the edge of the anode EA, a hole transport layer 4, a light-emitting layer 5, a functional layer 6F, and a cathode EC. The functional layer 6F may be an electron transport layer. The light-emitting element layer 14 may include a light-emitting element 7R(7) including a light-emitting layer 5R(5) that emits red light, a light-emitting element 7G(7) including a light-emitting layer 5G(5) that emits green light, and a light-emitting element 7B(7) including a light-emitting layer 5B(5) that emits blue light. The cathode EC may be located on the light extraction side. The sealing layer 15 includes an inorganic insulating film such as a silicon nitride film or a silicon oxide film, and prevents foreign matter (water, oxygen, etc.) from entering the light-emitting element layer 14.

[0044] The above-described embodiments are intended to be illustrative and explanatory, and are not intended to be limiting. Based on these examples and descriptions, it will be apparent to those skilled in the art that many variations are possible. [Explanation of symbols]

[0045] 4. Hole transport layer 4F Functional layer (hole transport layer) 5. Light-emitting layer 6 Electron transport layer 6F Functional layer (electron transport layer) 7 Light emitting element 8 cores 9. Shell EA Anode EC cathode QD Quantum dot MX Inorganic Matrix Materials

Claims

1. an anode and a cathode; a light-emitting layer disposed between the anode and the cathode, the light-emitting layer including a plurality of quantum dots and an inorganic matrix material; a functional layer that is disposed between the anode and the cathode so as to be adjacent to the light-emitting layer, and that has the same constituent elements as the inorganic matrix material but a different composition ratio;

2. The light-emitting device according to claim 1 , wherein each of the plurality of quantum dots has (i) a core and (ii) a shell having the same constituent elements as the inorganic matrix material but a different composition ratio or the same composition ratio.

3. The light-emitting device according to claim 1 , wherein at least one of the plurality of quantum dots is in contact with the functional layer.

4. The light-emitting device according to claim 1 , wherein the functional layer and the inorganic matrix material each contain a metal element and a non-metal element.

5. The light-emitting device according to claim 4 , wherein the metallic element is zinc, and the non-metallic element is sulfur or selenium.

6. The light-emitting device according to claim 5 , wherein the functional layer contains a hydroxyl group.

7. The light-emitting device according to claim 2 , wherein the inorganic matrix material has a band gap larger than that of the quantum dots.

8. 8. The light-emitting element according to claim 1, wherein the functional layer is disposed between the light-emitting layer and the cathode.

9. The light-emitting element according to claim 8 , wherein the functional layer has a shallower CBM than the plurality of quantum dots.

10. The light-emitting element according to claim 8 , wherein the functional layer has a deeper CBM than the inorganic matrix material.

11. each of the functional layer and the inorganic matrix material contains zinc and sulfur or selenium; The light-emitting element according to claim 8 , wherein the functional layer has a higher zinc composition ratio than the inorganic matrix material.

12. The light-emitting device according to claim 2 , wherein the material of the inorganic matrix material and the material of the shell are the same.

13. the functional layer is a first electron transport layer, a second electron transport layer disposed between the first electron transport layer and the cathode; The light-emitting device according to claim 8 , wherein the second electron transport layer has the same constituent elements as the first electron transport layer but a different composition ratio.

14. The light-emitting device according to claim 13 , wherein the second electron transport layer has a deeper CBM than the first electron transport layer.

15. the functional layer is a first electron transport layer, a second electron transport layer disposed between the first electron transport layer and the cathode; The electron mobility of the first electron transport layer is S1 and the thickness of the first electron transport layer is Da, The electron mobility of the second electron transport layer is S2 and the thickness is Db, S1 / Da ３ ≧S2 / Db ３ The light-emitting device according to claim 8 ,

16. The light-emitting device according to claims 1 to 2 and 7, wherein the functional layer is disposed between the light-emitting layer and the anode.

17. The light-emitting element according to claim 16 , wherein the functional layer has a deeper VBM than the plurality of quantum dots.

18. The light-emitting element according to claim 16 , wherein the functional layer has a shallower VBM than the inorganic matrix material.

19. the functional layer and the inorganic matrix material contain zinc and sulfur or selenium; The light-emitting element according to claim 16 , wherein the functional layer has a smaller zinc composition ratio than the inorganic matrix material.

20. the functional layer is a first hole transport layer, 17. The light-emitting device of claim 16, wherein a second hole transport layer is disposed between the first hole transport layer and the anode.

21. The hole mobility of the first hole transport layer is S3 and the thickness is Dc, The hole mobility of the second hole transport layer is S4 and the thickness is Dd, S3 / Dc ３ ≧S4 / Dd ３ The light-emitting device according to claim 20 ,

22. A display device comprising the light-emitting device according to any one of claims 1 to 2, 7 and 12.

23. The display device according to claim 22 , wherein the cathode is located on the light extraction side.

24. forming a lower electrode; forming a light-emitting layer including a plurality of quantum dots and an inorganic matrix material filling spaces between the plurality of quantum dots; forming a functional layer on the light-emitting layer, the functional layer having the same constituent elements as the inorganic matrix material but a different composition ratio; and forming an upper electrode.

25. The method for manufacturing a light-emitting element according to claim 24, wherein the functional layer is formed by using a CBD (chemical bath deposition) method.