Light-emitting element, display device, and method for manufacturing a 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] This 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 device equipped with a light-emitting layer containing quantum dots as a light-emitting material, reactive current may be generated when carriers are not injected into the quantum dots but pass through the light-emitting layer. The generation of such reactive current not only reduces the light-emitting power efficiency of the light-emitting device but also causes degradation of the quantum dots and charge transport layer, leading to a decrease in the reliability of the light-emitting device. Patent Document 1 discloses a light-emitting device in which the light-emitting layer contains multiple quantum dots with different shell thicknesses, thereby improving carrier confinement to quantum dots. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International public access number WO2015 / 056750 [Overview of the project] [Problems that the invention aims to solve]

[0004] In the light-emitting device disclosed in Patent Document 1, the presence of organic ligands between quantum dots makes it difficult to reduce the reactive current flowing between quantum dots and thereby improve the luminous power efficiency. Furthermore, the organic ligands suffer from reliability degradation. [Means for solving the problem]

[0005] A light-emitting element according to one aspect 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 the spaces between the plurality of quantum dots; and a functional layer disposed between the anode and the cathode adjacent to the light-emitting layer and having the same constituent elements as the inorganic matrix material but with a different composition ratio. [Effect of the Invention]

[0006] According to one aspect of the present disclosure, the luminous power efficiency of the light-emitting element is improved. [Brief Description of the Drawings]

[0007] [Figure 1] It is a cross-sectional view showing the configuration of the light-emitting element according to the embodiment. [Figure 2] It is an example of a schematic band diagram of the light-emitting element shown in FIG. 1. [Figure 3] It is a cross-sectional view showing another configuration of the light-emitting element according to the embodiment. [Figure 4] It is an example of a schematic band diagram of the light-emitting element shown in FIG. 3. [Figure 5] It is a cross-sectional view showing another configuration of the light-emitting element according to the embodiment. [Figure 6] It is an example of a schematic band diagram of the light-emitting element shown in FIG. 5. [Figure 7] It is a cross-sectional view showing another configuration of the light-emitting element according to the embodiment. [Figure 8] It is an example of a schematic band diagram of the light-emitting element shown in FIG. 7. [Figure 9] It is a cross-sectional view showing another configuration of the light-emitting element according to the embodiment. [Figure 10] It is an example of a schematic band diagram of the light-emitting element shown in FIG. 9. [Figure 11] It is a cross-sectional view showing another configuration of the light-emitting element according to the embodiment. [Figure 12] It is an example of a schematic band diagram of the light-emitting element shown in FIG. 11. [Figure 13] It is a cross-sectional view showing another configuration of the light-emitting element according to the embodiment. [Figure 14] It is a flowchart showing a method for manufacturing a light-emitting element according to the embodiment. [Figure 15] It is a cross-sectional schematic view showing a method for forming a functional layer using the CBD method. [Figure 16A] It is a cross-sectional schematic view showing an example of forming an inorganic matrix material. [Figure 16B]It is a cross-sectional schematic view showing an example of the formation of an inorganic matrix material. [Figure 17] It is a schematic view showing an example of the configuration of a display device according to this embodiment. [Figure 18] It is a cross-sectional view showing an example of the configuration of a display device according to this embodiment.

Mode for Carrying Out the Invention

[0008] 〔Embodiment 1〕 (Configuration of the 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, a light-emitting layer 5 disposed between the anode EA and the cathode EC and including a plurality of quantum dots QD and an inorganic matrix material MX filling between the plurality of quantum dots QD, and a functional layer 6F disposed between the anode EA and the cathode EC adjacent to the light-emitting layer 5 and having the same constituent elements as the inorganic matrix material MX but different composition ratios. 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 light-emitting layer 5. A hole transport layer (HTL) 4 may be disposed between the anode EA and the light-emitting layer 5.

[0009] In the light-emitting element 7, since the inorganic matrix material MX and the functional layer 6F having the same constituent elements are homojunctioned, the potential barrier between the functional layer 6F and the inorganic matrix material MX becomes small. Therefore, charge injection (for example, electron injection) from the functional layer 6F to the light-emitting layer 5 becomes easy, and the luminous power efficiency (power consumption-luminance characteristics of the light-emitting element) is improved.

[0010] Inorganic matrix Material MX terminates the surface defects of the quantum dots QD and reduces non-radiative recombination in the quantum dots QD, so the external quantum efficiency (EQE) is improved. Inorganic matrix Material MX is excellent in durability compared with general organic ligands, so the reliability of the light-emitting element 7 is enhanced.

[0011] Thus, inorganic matrix Material By forming a functional layer 6F, which is the same compound (same constituent elements) as MX but has a different composition, adjacent to the light-emitting layer 5, an inorganic matrix that can be formed at low temperatures and has a low defect density is created. Material It is possible to lower the voltage for carrier injection while using MX (e.g., zinc sulfide, zinc selenide).

[0012] Each of the multiple quantum dots (QDs) 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 luminescence characteristics (voltage-luminance characteristics) can be reduced to a lower voltage while maintaining the confinement effect of the shell 9.

[0013] Functional layer 6F and inorganic matrix material MX may each contain a metallic element and a nonmetallic element, where the metallic element is zinc and the nonmetallic element is sulfur or selenium. Functional layer 6F may contain hydroxyl groups, and may contain metal-hydroxyl group bonds (details will be described later).

[0014] Figure 2 is an example of a schematic band diagram of the light-emitting device shown in Figure 1. Hereafter, a band close to the vacuum level VE(0eV) is described as "shallow," and a band far from the vacuum level VE(0eV) is described as "deep." CBM is the lower conduction band level, VBM is the upper valence band level, the band gap is the difference between CBM and VBM, and FE is the Fermi level. As shown in Figure 2, the inorganic matrix material MX may have a larger band gap than multiple quantum dots (QDs). The band gap of the quantum dots (QDs) 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, the amount of electron injection can be adjusted. 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. Thereby, the light-emitting region is closer to the functional layer 6F, and non-luminescent 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 lowered. The control of the Fermi level can be achieved, for example, by controlling the zinc element ratio in zinc sulfide and zinc selenide. When the zinc element is excessive, it becomes n-type conductivity with sulfur defects and selenium defects as donors. Therefore, the functional layer 6F (ETL) may have a larger zinc composition ratio than the inorganic matrix material MX. for example, 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 This is how it works. For example, 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 This is the result.

[0017] Figure 3 is a cross-sectional view showing another configuration of the light-emitting element according to the embodiment. Figure 4 is an example of a schematic band diagram of the light-emitting element shown in Figure 3. As shown in Figure 3, at least one of the plurality of quantum dots QD may be in contact with the functional layer 6F. That is, the light-emitting layer 5 includes quantum dots QD 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 higher carrier transport properties, so the light emission characteristics (voltage-luminance characteristics) can be reduced to a lower voltage. Furthermore, the inorganic matrix is ​​between the exposed quantum dots QD and the functional layer 6F. Material Since MX is not involved, the electron injection barrier is lowered, and the luminescence characteristics (voltage-luminance characteristics) can be reduced to lower voltages. The configuration shown in Figure 3 can be formed, for example, by forming a luminescence layer 5 containing the inorganic matrix material MX, then etching the vicinity of the top surface of the inorganic matrix material MX, exposing a portion of the quantum dots QD near the top surface from the inorganic matrix material MX. As an example, by using the CBD (Chemical Bath Deposition) method, in which the inorganic layer (functional layer 6F) is grown in an alkaline aqueous solution, the etching of the inorganic matrix material MX and the growth of the functional layer 6F can be performed in the same process using a simple aqueous solution. In the functional layer 6F formed by the CBD method, the OH groups (hydroxyl groups) bond with the metal element, terminating the unbonded hands (dangling bonds) of the metal element, thereby suppressing non-luminescent transitions of carriers in the functional layer 6F. Furthermore, the mobility, one of the indicators of carrier transport characteristics, is very high, at 1.0 [cm] 2 Since a functional layer 6F with a mobility greater than [Vs] can be obtained, carrier transport at a lower voltage becomes possible.

[0018] FIG. 5 is a cross-sectional view showing another configuration of the light-emitting element according to the embodiment. FIG. 6 is an example of a schematic band diagram of the light-emitting element 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 CBM deeper than that of 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 into the quantum dots QD can be lowered compared to the case of a single-layer electron transport layer 6F.

[0019] In FIGS. 5 and 6, a stepped potential can be formed by controlling the Fermi levels of the first and second electron transport layers 6F and 6S, and the voltage for carrier injection (electron injection) can be lowered. For example, the first electron transport layer 6F may be zinc sulfide represented by Zn x S(x>1), and the second electron transport layer 6S may be zinc sulfide represented by Zn z S(z>x). The first electron transport layer 6F may be zinc selenide represented by Zn x Se(x>1), and the second electron transport layer 6S may be zinc selenide represented by Zn z Se(z>x).

[0020] FIG. 7 is a cross-sectional view showing another configuration of the light-emitting element according to the embodiment. FIG. 8 is an example of a schematic band diagram of the light-emitting element 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. Let the electron mobility of the first electron transport layer 6F be S1 and the thickness be Da, and the electron mobility of the second electron transport layer 6T be S2 and the thickness be Db, then S1 / Da 3 ≧S2 / Db 3 may hold.

[0021] To increase the external quantum efficiency (EQE) of the light-emitting element 7, electrons and holes Quantum dotsIt is necessary to increase the carrier injection efficiency into the QD. Furthermore, if an excess of carriers is generated, it will not contribute to luminescence recombination, so it is effective to adjust the carrier balance, which is the ratio of electrons to holes injected. Therefore, as shown in Figure 7, by stacking a first electron transport layer 6F with a second electron transport layer 6T that has lower mobility, a bottleneck in the amount of electrons injected can be intentionally created, and the carrier balance can be adjusted to the hole side, which generally has a lower amount of carrier injection.

[0022] The carrier injection amount is calculated by solving Poisson's equation, which takes into account the dielectric constant, mobility, carrier density, and film thickness of the ETL material. However, when the layer thickness is 100 nm or less and the mobility is 1.0 [cm] 2 Below [ / Vs], the space charge limiting current (SCLC) is dominant over the ohmic current, and the amount of carrier injection is described by Child's law using dielectric constant, mobility, film thickness, and voltage as parameters. Here, assuming the dielectric constants of the first and second electron transport layers 6F and 6T are the same, and comparing the amount of electron injection at the same voltage, if the electron mobility of the first electron transport layer 6F is S1 and its thickness is Da, and the electron mobility of the second electron transport layer 6T is S2 and its thickness is Db, then S1 / Da 3 ≥S² / Db 3 In this case, an electron injection bottleneck can be intentionally created, improving carrier balance and, consequently, external luminescence efficiency (EQE).

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

[0024] Zinc sulfide and zinc selenide exhibit p-type conductivity with zinc vacancies as acceptors when the atomic composition ratio is zinc-deficient. 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) This is how it works. 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) This is the result.

[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 such that the VBM is deeper than that of 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 the 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 and the thickness be Dc, and the hole mobility of the second hole transport layer 4S be S4 and the thickness be Dd, then S3 / Dc 3 ≧S4 / Dd 3This is acceptable. This allows us to intentionally create a hole injection bottleneck, thereby improving carrier balance and, consequently, external luminescence efficiency (EQE).

[0027] Figure 13 is a cross-sectional view showing an alternative configuration of the light-emitting element according to the embodiment. As shown in Figure 13, a functional layer 4F(HTL) having the same constituent elements as the inorganic matrix material MX but with a different composition ratio may be placed 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 with a different composition ratio may be placed between the cathode EC and the light-emitting layer 5. The inorganic matrix material MX and functional layers 4F and 6F are 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, while the functional layer 4F(HTL) may have a lower zinc composition ratio than the inorganic matrix material MX. In this way, it becomes possible to reduce the injection barrier by a step-like potential for both electrons and holes.

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

[0029] Figure 15 is a schematic cross-sectional diagram showing a method for forming a functional layer using the CBD method. For example, a laminate ST consisting of a substrate 13, an anode EA, a hole transport layer 4, and a light-emitting layer 5 can be immersed for a predetermined time in an alkaline aqueous solution 10 containing a metal source and a chalcogen source at a predetermined temperature, with the bottom surface BF and side surface SF of the laminate ST covered with a mask MK, thereby allowing a functional layer 6F to grow on the laminate ST (in contact with the light-emitting layer 5).

[0030] For example, by mixing zinc sulfate (ZnSO4) as a zinc source at a concentration of 0.16 mol / L, ammonia as an alkali source at a concentration of 7.5 mol / L, and thiourea as a sulfur source at a concentration of 0.6 mol / L, an alkaline aqueous solution 10 with a pH of 11 is obtained. By adjusting the temperature of the alkaline aqueous solution 10 to 80°C and immersing the laminate ST for 15 minutes, a zinc sulfide thin film (containing oxygen atoms and hydroxyl groups) with a thickness of 100 nm is produced.

[0031] The quantum dots (QDs) used in this embodiment may be dots having a maximum width of 100 nm or less, and may be spherical or non-spherical in shape. The shape of the quantum dots (QDs) is not limited to a spherical three-dimensional shape (circular cross-sectional shape), as long as it satisfies the aforementioned 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-shaped three-dimensional shape, a branch-shaped three-dimensional shape, a three-dimensional shape with irregularities on the surface, or a combination thereof. The quantum dots (QDs) may be composed of a semiconductor material, and may be inorganic semiconductor nanocrystals. The semiconductor material may have a certain band gap and may be a material that exhibits electroluminescence. The wavelength range of the electroluminescence may be one of the red, green, or blue regions.

[0032] The quantum dot (QD) may contain at least one of the following: crystals of group II-VI 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 group III-V semiconductors such as GaAs, GaP, InN, InAs, InP, InSb; chalcogenide compound crystals; perovskite compound crystals; and crystals of group IV semiconductors such as Si and Ge. Note that a group II-VI compound means a compound containing group II and group VI elements, and a group III-V compound means a compound containing group III and group V elements. Furthermore, Group II elements include Group 2 and Group 12 elements, Group III elements include Group 3 and Group 13 elements, Group V elements include Group 5 and Group 15 elements, and Group VI elements may include Group 6 and Group 16 elements.

[0033] Chalcogenides are compounds containing group VI A(16) elements, such as CdS or CdSe. Chalcogenides may also contain mixed crystals of these elements.

[0034] Perovskite compounds have a composition represented by the general formula CsPbX3, for example. The constituent element X includes at least one selected from the group consisting of Cl, Br, and I.

[0035] Here, the Roman numeral notation for element group numbers is based on the old IUPAC (International Union of Pure and Applied Chemistry) system or the old CAS (Chemical Abstracts Service) system, while the Arabic numeral notation for element group numbers is based on the current IUPAC system.

[0036] Figures 16A and 16B are schematic cross-sectional diagrams showing examples of inorganic matrix material formation. As shown in Figures 16A and 16B, the inorganic matrix material MX fills the region (space) JS between two adjacent quantum dots QD, and the inorganic matrix material MX fills region JS. In the cross-section of the light-emitting layer 5, region JS is defined by two lines (common outer tangents) tangent to the outer circumference of two adjacent quantum dots QD, and the two adjacent quantum dots QD D It can be a region enclosed by two quantum dots. As shown in Figure 16B, even if two adjacent quantum dots are close together, the region JS still exists, and the inorganic matrix material MX fills the region JS. For an inorganic matrix material to fill the space between multiple quantum dots, it is sufficient to know that the inorganic matrix material fills the space 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, then it can be said that the inorganic matrix material MX fills the space between multiple quantum dots QD. In addition to "filling" or "being filled," there is also the case of "retention," where two adjacent quantum dots QD may be retained due to the presence of an inorganic matrix material MX in region JS. For example, if at least a part of region JS is an inorganic matrix Material The MX filling may hold two quantum dots (QDs).

[0037] The inorganic matrix material MX is mainly composed of inorganic materials (inorganic substances). The inorganic matrix material MX may be a component of an emissive layer containing multiple quantum dots (QD). The inorganic matrix material MX may be a component made of inorganic substances (e.g., inorganic semiconductors) that contains and holds other materials, and can be rephrased as a substrate, base material, or filler. The inorganic matrix material MX may be solid at room temperature. The inorganic matrix material MX may contain multiple quantum dots (QD). In the emissive layer (quantum dot layer), the inorganic matrix material MX may fill the areas (spaces) other than the multiple quantum dots (QD), or it may fill the spaces between the multiple quantum dots (QD). The inorganic matrix material MX may fill the areas (spaces) other than the multiple quantum dots (QD) in the emissive layer. The inorganic matrix material MX may partially or completely fill the spaces between the multiple quantum dots (QD). The multiple quantum dots (QD) may be embedded in the inorganic matrix material MX at intervals. The inorganic matrix material MX may refer to the portion of the emissive layer excluding the multiple quantum dots (QD).

[0038] The inorganic matrix material MX may completely or incompletely fill the regions (spaces) other than the quantum dot groups 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 observable in a cross-sectional view of the light-emitting layer 5 with a width of approximately 100 nm, and it is not necessary to observe the desired structure in the entire light-emitting layer 5. The inorganic matrix material MX in the quantum dot layer has a plane direction perpendicular to the layer thickness direction of 1000 nm. 2It may be formed as a continuous film having the above area. A continuous film means a film that is not interrupted by any material other than the material constituting the continuous film in a single plane. The continuous film may be a single film-like structure that is continuously connected by chemical bonds of the inorganic matrix material MX.

[0039] The outer periphery of the light-emitting layer may be composed of an inorganic matrix material MX, and the quantum dots QD may be positioned away from the outer edge. The outer edge of the light-emitting layer does not need to be formed solely of the inorganic matrix material MX; a portion 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). If the shell of the quantum dot (QD) and the inorganic matrix material MX cannot be distinguished, the shell may be considered as part of the inorganic matrix material MX. The inorganic matrix material MX may contain substances other than the main inorganic compound (zinc sulfide, zinc selenide, etc.) as additives, impurities, or residues. When the luminescent layer containing the inorganic matrix material MX is analyzed, the amount of carbon atoms it contains may be 5 atomic percent or less.

[0041] Figure 17 is a schematic diagram showing an example of the configuration of a display device according to this embodiment. As shown in Figure 17, the display device 20 includes a display unit DA including a plurality of subpixels SP, a first driver X1 and a second driver X2 that drive the plurality of subpixels SP, and a display control unit DC that controls the first driver X1 and the second driver X2. The subpixels SP include a light-emitting element 7 and a light-emitting element 7 It includes a pixel circuit PC connected to a scanning signal line GL, a data signal line DL, and a 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] Figure 18 is a cross-sectional view showing an example of the configuration of a 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 board including a support substrate 11 and a pixel circuit layer 12. The support substrate 11 can be a glass substrate, a resin substrate, or the like. The support substrate 11 may be flexible. The pixel circuit layer 12 includes, for example, a plurality of pixel circuits PC arranged in a matrix. The pixel circuit PC may include a pixel capacitance on 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 the scan signal line GL and the data signal line DL, and a transistor connected to the light emission control line EL.

[0043] As shown in Figure 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 also include a light-emitting element 7R(7) containing a light-emitting layer 5R(5) that emits red light, a light-emitting element 7G(7) containing a light-emitting layer 5G(5) that emits green light, and a light-emitting element 7B(7) containing 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 to prevent foreign matter (water, oxygen, etc.) from entering the light-emitting element layer 14.

[0044] The embodiments described above are for illustrative and explanatory purposes only, and not for limitation. It will be apparent to those skilled in the art that many variations are possible based on these examples and descriptions. [Explanation of Symbols]

[0045] 4. Hole transport layer 4F Functional layer (hole transport layer) 5. Emitting layer 6 Electron transport layer 6F Functional layer (electron transport layer) 7 Light-emitting elements 8 cores 9 Shells EA Anode EC Cathode QD Quantum Dots MX Inorganic Matrix Material

Claims

1. anode and cathode, Displaced between the anode and the cathode, the light-emitting layer includes a plurality of quantum dots and an inorganic matrix material, A light-emitting element comprising a functional layer disposed between the anode and the cathode adjacent to the light-emitting layer, the functional layer having the same constituent elements as the inorganic matrix material but a different composition ratio.

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

3. The light-emitting element according to claim 1 or 2, wherein at least one of the plurality of quantum dots is in contact with the functional layer.

4. The light-emitting element according to claim 1 or 2, wherein the functional layer and the inorganic matrix material each contain a metallic element and a non-metallic element.

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

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

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

8. The light-emitting element according to any one of claims 1 to 2 and 7, 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 (lower conduction band level) than the plurality of quantum dots.

10. The light-emitting element according to claim 8, wherein the functional layer has a CBM (lower end level of the conduction band) deeper than the inorganic matrix material.

11. Each of the functional layer and the inorganic matrix material comprises 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 element according to claim 2, wherein the material of the inorganic matrix and the material of the shell are the same.

13. The aforementioned functional layer is the first electron transport layer, A second electron transport layer is disposed between the first electron transport layer and the cathode. The light-emitting element 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 element according to claim 13, wherein the second electron transport layer has a deeper CBM (conduction band lower level) than the first electron transport layer.

15. The aforementioned functional layer is the first electron transport layer, A second electron transport layer is disposed between the first electron transport layer and the cathode. Let S1 be the electron mobility and Da be the thickness of the first electron transport layer. Let S2 be the electron mobility of the second electron transport layer and Db be its thickness. The light-emitting element according to claim 8, wherein S1 / Da3 ≥ S2 / Db3.

16. The light-emitting element 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 VBM (valence band upper level) deeper than the plurality of quantum dots.

18. The light-emitting element according to claim 16, wherein the functional layer has a shallower VBM (valence band upper level) 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 lower zinc composition ratio than the inorganic matrix material.

20. The functional layer is the first hole transport layer, The light-emitting element according to claim 16, wherein a second hole transport layer is disposed between the first hole transport layer and the anode.

21. Let S3 be the hole mobility and Dc be the thickness of the first hole transport layer. Let S4 be the hole mobility and Dd be the thickness of the second hole transport layer. S3 / Dc ３ ≥S4 / Dd ３ The light-emitting element according to claim 20.

22. A display device comprising a light-emitting element 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. The process of forming the lower electrode, A step of forming a light-emitting layer comprising a plurality of quantum dots and an inorganic matrix material filling the spaces between the plurality of quantum dots, A step of forming a functional layer on the light-emitting layer, which has the same constituent elements as the inorganic matrix material but a different composition ratio, A method for manufacturing a light-emitting element, comprising the step of forming an upper electrode.

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

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