Light-emitting element and display device

Abstract

A light-emitting element (10) comprises: an anode (3) and a cathode (8); an auxiliary electrode (9) that does not overlap the cathode (8) in plan view; and a light-emitting layer (5) that overlaps the anode (3) and the cathode (8) in plan view and includes quantum dots. The auxiliary electrode (9) overlaps the anode (3) and the light-emitting layer (5) in plan view, and the cathode (8) and the auxiliary electrode (9) have different constituent materials.

Description

Light-emitting element, display device

[0001] The present disclosure relates to a light-emitting device and the like.

[0002] Patent Document 1 discloses a configuration in which a cathode is laminated in a light-emitting element having a light-emitting layer containing quantum dots.

[0003] Japanese Patent Publication "Patent Publication No. 2022-516211"

[0004] Conventional light-emitting elements have a problem of low luminous efficiency.

[0005] A light-emitting element according to the present disclosure includes an anode and a cathode, an auxiliary electrode that does not overlap the cathode in a planar view, and a light-emitting layer that overlaps the anode and the cathode in a planar view and contains quantum dots, wherein the auxiliary electrode overlaps the anode and the light-emitting layer in a planar view, and the cathode and the auxiliary electrode are made of different materials.

[0006] The luminous efficiency can be improved.

[0007] 18 is a cross-sectional view showing an example of the configuration of a light-emitting element according to the present embodiment; FIG. 19 is a cross-sectional view showing an example of the configuration of a light-emitting layer; FIG. 19 is a band diagram of a light-emitting element; FIG. 19 is a schematic diagram showing an example of driving the light-emitting element according to the present embodiment; FIG. 20 is a band diagram showing the operating principle of the light-emitting element; FIG. 21 is a schematic diagram showing an example of driving the light-emitting element; FIG. 21 is a graph showing change in luminance versus drive time of a conventional light-emitting element; FIG. 22 is a graph showing change in luminance versus drive time of a light-emitting element according to the present embodiment; FIG. 22 is a graph showing external quantum efficiency of a light-emitting element according to the present embodiment; FIG. 23 is a flowchart showing a method for manufacturing a light-emitting element; FIG. 24 is a plan view showing an example of the shape of a cathode and an auxiliary electrode; FIG. 25 is a graph showing the in-plane luminance distribution of a light-emitting layer; FIG. 26 is a graph showing the in-plane luminance distribution of a light-emitting layer; FIG. 27 is a plan view showing an example of the shape of a cathode and an auxiliary electrode; FIG. 28 is a plan view showing an example of the shape of a cathode and an auxiliary electrode; FIG. 29 is a plan view showing an example of the shape of a cathode and an auxiliary electrode; FIG. 29 is a cross-sectional view showing an example of the configuration of a light-emitting element; FIG. 21 is a cross-sectional view showing an example of the configuration of a light-emitting element; FIG. 22 is a band diagram of the light-emitting element of FIG. 18; FIG. 23 is a schematic diagram showing an example of the configuration of a display device according to the present embodiment;

[0008] FIG. 1 is a cross-sectional view showing an example of the configuration of a light-emitting element according to this embodiment. FIG. 2 is a cross-sectional view showing an example of the configuration of a light-emitting layer. FIG. 3 is a band diagram of the light-emitting element. As shown in FIGS. 1 and 2 , a light-emitting element 10 according to this embodiment includes an anode 3, a cathode 8, an auxiliary electrode 9 that does not overlap the cathode 8 in a planar view, and a light-emitting layer 5 that overlaps the anode 3 and the cathode 8 in a planar view and contains quantum dots Q. The auxiliary electrode 9 overlaps the anode 3 and the light-emitting layer 5 in a planar view, and the cathode 8 and the auxiliary electrode 9 are made of different materials. The cathode 8 and the auxiliary electrode 9 may be electrically insulated, and the material of the auxiliary electrode 9 may have a smaller work function (the energy difference (absolute value) between the vacuum level and the Fermi level at absolute zero) than the material of the cathode 8. This suppresses electron injection from the cathode 8 into the light-emitting layer 5, reduces trion Auger (non-radiative recombination) within the quantum dots, and allows electrons remaining between the light-emitting layer 5 and the cathode 8 to escape to the auxiliary electrode 9, thereby improving the luminous efficiency of the light-emitting element 10. The cathode 8 and the auxiliary electrode 9 may be formed in the same layer so as to be insulated from each other.

[0009] The cathode 8 and the auxiliary electrode 9 may be composed of a plurality of materials. For example, when the auxiliary electrode 9 is composed of a plurality of materials, it is preferable that at least one of the plurality of materials contained in the auxiliary electrode 9 has a work function smaller than that of the material constituting the cathode 8. In this case, the composition ratio of the material having a work function smaller than that of the material constituting the cathode 8 may exceed 50% in the composition ratio of the plurality of materials contained in the auxiliary electrode 9.

[0010] When the constituent material of the cathode 8 includes a plurality of materials, it is preferable that at least one of the plurality of materials included in the cathode 8 has a work function greater than that of the constituent material of the auxiliary electrode 9. In this case, the composition ratio of the material having a work function greater than that of the constituent material of the auxiliary electrode 9 may exceed 50% in the composition ratio of the plurality of materials included in the cathode 8.

[0011] In this way, even when the constituent materials of the cathode 8 and the auxiliary electrode 9 are composed of a plurality of materials, the above-described configuration can suppress electron injection from the cathode 8 into the light-emitting layer 5, reduce trion Auger (non-radiative recombination) within the quantum dots, and allow electrons remaining between the light-emitting layer 5 and the cathode 8 to escape to the auxiliary electrode 9, thereby improving the luminous efficiency of the light-emitting element 10.

[0012] In the present disclosure, the phrase "the cathode 8 and the auxiliary electrode 9 are made of different materials" may be interpreted to include an embodiment in which the composition ratios of the materials common to the cathode 8 and the auxiliary electrode 9 are different. In such a configuration, it is preferable to make the material of the auxiliary electrode 9 have a smaller work function than the material of the cathode 8 (the material of the cathode 8 has a larger work function than the material of the auxiliary electrode 9) by making the composition ratios of the corresponding materials (the materials common to the cathode 8 and the auxiliary electrode 9) different between the cathode 8 and the auxiliary electrode 9.

[0013] An anode 3 may be disposed on a substrate 1, a hole transport layer 4 (HTL) may be disposed between the anode 3 and an emitting layer 5, and an electron transport layer 7 (ETL) may be disposed between the emitting layer 5 and a cathode 8 and an auxiliary electrode 9 located in the same layer. A hole injection layer (HIL) may be provided between the anode 3 and the hole transport layer 4, and an electron injection layer (EIL) may be provided between the emitting layer 5 and the electron transport layer 7. A light emitting element layer 6 may be formed on a pixel circuit substrate 2 so as to include the anode 3, the emitting layer 5, the cathode 8, and the auxiliary electrode 9.

[0014] 1 to 3, the auxiliary electrode 9 may contain aluminum (Al) and the cathode 8 may contain nickel (Ni). The material constituting the cathode 8 may have a work function smaller than that of Ag, and the auxiliary electrode 9 may be an Al film or an Ag film and the cathode 8 may be a Ni film.

[0015] The light-emitting layer 5 may include a plurality of quantum dots Q and a matrix material MX located at least partially between adjacent quantum dots Q. The matrix material MX may be a continuous film having a band gap larger than that of the quantum dots Q.

[0016] 4 is a schematic diagram showing an example of driving the light-emitting element. The anode 3 may be connected to an anode voltage source PA via a switching element SA. As shown in FIG. 4 , the auxiliary electrode 9 may be grounded via a switching element SD. During the light-emitting element 10's on period (the on period of the switching element SA), the switching element SD may be turned OFF to electrically disconnect the auxiliary electrode 9 from ground (GND), and during the light-emitting element 10's off period (the off period of the switching element SA), the switching element SD may be turned ON to electrically connect the auxiliary electrode 9 to ground (GND) (the auxiliary electrode 9 may be grounded). The ground (GND) refers to a ground power supply provided in the pixel circuit substrate 2.

[0017] In this way, trion Auger (non-radiative recombination) is reduced in the light-emitting layer 5 during the light-emitting period, promoting the radiative recombination of electrons E and holes H, while electrons remaining between the light-emitting layer 5 and the cathode 8 (particularly near the interface between the light-emitting layer 5 and the electron transport layer 7) can be released from the auxiliary electrode 9 to ground (GND) during the light-off period.

[0018] When the light emitting element 10 is applied to a sub-pixel of a display device (described later), each frame period may include an off period (for example, a period during which the switching element SA, which is a light emission control transistor, is turned off).

[0019] 4, a switching element SC may be provided between the cathode 8 and the cathode power supply PL, and the switching element SC may be turned OFF during the extinction period. That is, the light-emitting element 10 is in an extinction state during the ground period when the switching element SD is ON, and no power is supplied to the cathode 8 during the ground period. This allows electrons to escape to ground (GND) more quickly.

[0020] A light emitting device or a display device can also be configured including the light emitting element 10, the switching elements SA and SD, the anode voltage source PA, the cathode power source PL, and the ground (GND).

[0021] 5 is a band diagram illustrating the operating principle of this light-emitting device. As shown in Fig. 5, electrons remaining at the interface between the light-emitting layer 5 and the electron transport layer 7 are unlikely to cross the spike barrier of the electron transport layer 7 (e.g., the electron transport layer) even when the switching element SC is turned OFF (even when the cathode 8 is disconnected from the cathode power supply PL). However, when the switching element SD is turned ON, the electrons are released to ground (GND) via the auxiliary electrode 9.

[0022] That is, a spike-shaped electron barrier exists in the direction from the electron transport layer 7 to the cathode 8, but a sloping band appears and no electron barrier exists in the direction from the electron transport layer 7 to the auxiliary electrode 9. Therefore, by disconnecting the cathode 8 from the external power supply and connecting the auxiliary electrode 9 to ground (GND), the electrons accumulated at the interface (on the electron transport layer 7 side) between the light-emitting layer 5 and the electron transport layer 7 are easily released.

[0023] 6 and 7 are schematic diagrams showing examples of driving the light-emitting device. As shown in Fig. 6, the cathode 8 and the auxiliary electrode 9 may each be connected to a cathode power supply PL, or as shown in Fig. 7, the cathode 8 may be connected to the cathode power supply PL and the auxiliary electrode 9 may be connected to a power supply PX of a different voltage from the cathode power supply PL. To reduce the risk of short-circuiting between the cathode 8 and the auxiliary electrode 9 due to a shift in switching timing (the timing of carrier injection and release overlapping), diodes may be connected in antiparallel to both switching circuits.

[0024] FIG. 8 is a graph showing the change in luminance versus drive time of a conventional light-emitting element. FIG. 9 is a graph showing the change in luminance versus drive time of a light-emitting element according to this embodiment. FIG. 10 is a graph showing the external quantum efficiency of a light-emitting element according to this embodiment. As shown in FIGS. 8 and 9, it can be seen that the decrease in luminance of the light-emitting element 10 is significantly improved for both intermittent drive (lighting on every hour) and continuous drive (for example, continuous light on including periodic extinction at 60 Hz), and reliability is improved. As shown in FIG. 10, the light-emitting element according to this embodiment also has a significantly improved external quantum efficiency EQE compared to conventional elements.

[0025] The cathode 8 and the auxiliary electrode 9 may be light-transmitting. The ratio of the area of ​​the auxiliary electrode 9 to the area of ​​the cathode 8 may be 0.6 to 1.0. The cathode 8 and the auxiliary electrode 9 may each contain an elemental metal or an alloy. The cathode 8 may contain at least one of Au, W, Cr, Co, Ni, Pt, and Cu. The auxiliary electrode 9 may be an Ag film or an Al film, or a metal compound film containing any one of B, Ca, and La.

[0026] The thickness of each of the cathode 8 and the auxiliary electrode 9 may be equal to or less than a threshold value, and this threshold value may be expressed as (extinction coefficient of aluminum / extinction coefficient of cathode) × 10 [nm]. The thickness of each of the cathode 8 and the auxiliary electrode 9 may be equal to or greater than 0.5 [nm]. The thickness of each of the cathode 8 and the auxiliary electrode 9 may be equal to or less than 20 [nm]. This ensures the light transmittance of the cathode 8 and the auxiliary electrode 9 required for a top-emission device.

[0027] The electron transport layer 7 may be an electron transport layer (ETL) in contact with the cathode 8 and the auxiliary electrode 9, and may contain any one of ZnO, ZnMgO, ZnS, and ZnMgS. The thickness of the electron transport layer may be 5.0 nm to 40 nm.

[0028] 11 is a flowchart showing a method for manufacturing a light-emitting element. As shown in FIGS. 1, 2, and 11, in step S10, an anode 3 and a bank BK that covers the edge of the anode 3 and separates the elements are formed on the TFT substrate 1. The anode 3 is formed, for example, by film formation using a sputtering method or a vacuum deposition method and patterning using a photolithography method. A resin material such as polyimide may be used for the bank BK.

[0029] Next, a hole injection layer (HIL) such as a NiO layer is formed on the anode 3. The NiO layer can be formed by applying and heating a colloidal solution of dispersed nanoparticles. The particle size of the NiO nanoparticles is preferably approximately 6 nm or more, so that the quantum size effect does not occur. The NiO layer can also be formed by a sputtering method, a vacuum deposition method, or the like. Either method can form a NiO layer of approximately uniform thickness over the entire panel, including the slopes of the banks BK.

[0030] In step S20, a hole transport layer 4 (HTL) is formed on the hole injection layer. For example, a cross-linkable TFB is applied to a NiO layer and cross-linked to form the hole transport layer 4. The hole transport layer 4 is preferably made of a material such as TFB, PVK, or p-TPD, which has a HOMO not significantly different from the VBM of the quantum dots and a LUMO shallower than the CBM of the quantum dots. The HOMO of the hole transport layer 4 is used to lower the hole injection barrier, and the LUMO is used as a barrier to suppress electron overflow from the quantum dots.

[0031] In step S30, a colloidal solution containing quantum dots Q is applied to the hole transport layer 4 and heated to form the light-emitting layer 5. The light-emitting layer 5 may contain an organic ligand, or the organic ligand may be removed and the quantum dots Q may be protected with an inorganic substance such as a semiconductor or silica. General techniques can be used to remove the ligand and protect the quantum dots Q with an inorganic substance (forming a matrix material MX).

[0032] In step S40, a colloidal solution containing particles such as ZnO or ZnMgO is applied to the light-emitting layer 5 and heated to form the electron transport layer 7 (ETL). As with the NiO layer, the particle size of the ZnO or ZnMgO particles should be such that quantum size effects do not occur. Generally, when the particle size is less than twice the Bohr radius, exciton confinement occurs, resulting in the formation of quantum levels in the valence and conduction bands. The effective mass of the semiconductor material contained in the light-emitting layer 5, HTL 4, or ETL 7 is often greater than that of holes, and the quantum level difference between the VBM and CBM and the conduction band is greater than that of the valence band, resulting in a significant quantum size effect in the conduction band. When exciton confinement due to the quantum size effect becomes significant, the probability of trion Auger generation increases. Therefore, when using particulate materials in layers other than the light-emitting layer 5, it is desirable to set the particle size to greater than twice the exciton Bohr radius of the particulate material.

[0033] In step S50, the cathode 8 is formed by sputtering or vacuum deposition and patterning by photolithography. In step S60, the auxiliary electrode 9 is formed by sputtering or vacuum deposition and patterning by photolithography using a material different from that of the cathode 8. In steps S50 and S60, the cathode 8 and the auxiliary electrode 9 are sequentially formed in separate formation regions so as not to contact each other.

[0034] The quantum dots Q in FIG. 2 may be dots (particles) with a maximum width of 100 nm or less. The shape of the quantum dots Q is not particularly limited as long as it satisfies the above-mentioned maximum width, and is not limited to a spherical three-dimensional shape (circular cross-sectional shape). For example, the quantum dots Q may have a polygonal cross-sectional shape, a rod-like three-dimensional shape, a branch-like three-dimensional shape, or a three-dimensional shape with an uneven surface, or a combination thereof. The quantum dots Q may be semiconductor single crystals and may have a particle size of 1.0 nm to 50 nm. The quantum dots Q may have at least one of a crystal of a II-VI group semiconductor compound such as MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, a crystal of a III-V group semiconductor compound such as GaAs, GaP, InN, InAs, InP, InSb, and a crystal of a group IV semiconductor compound such as Si or Ge.

[0035] The quantum dots Q may be, for example, a core-shell type in which the above crystal is used as a core and the core is overcoated with a shell material having a high band gap, or may be a shell-less type consisting of only the core.

[0036] 2 may be an inorganic insulator (e.g., silicon oxide). The matrix material MX (inorganic medium) is not limited to an inorganic insulator and may be a semiconductor such as zinc sulfide. The matrix material MX may be located in the gaps between the quantum dots Q.

[0037] Materials for the hole transport layer 4 or the hole injection layer include metal oxides such as nickel oxide (NiO), as well as poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] (abbreviated as "TFB"), poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (abbreviated as "Poly-TPD"), polyvinylcarbazole (abbreviated as "PVK"), and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (abbreviated as "PTAA"). These materials may be used alone or in combination of two or more. An inorganic material such as a metal oxide may be used for the HIL on the anode 3, and an organic material may be used for the hole transport layer 4 located on the HIL and in contact with the light-emitting layer 5. Nanoparticles of metal oxides such as nickel oxide may also be used in the hole injection layer or hole transport layer 4 .

[0038] The electron transport layer 7 may be made of zinc oxide (ZnO), magnesium zinc oxide (MgZnO), titanium oxide (TiO ２ In addition to metal oxides such as zinc oxide, compounds or complexes containing one or more nitrogen-containing heterocycles such as an oxadiazole ring, a triazole ring, a triazine ring, a quinoline ring, a phenanthroline ring, a pyrimidine ring, a pyridine ring, an imidazole ring, or a carbazole ring may be used in the electron transport layer 7.

[0039] FIG. 12 is a plan view showing an example of the shape of the cathode and auxiliary electrode. FIGS. 13 and 14 are graphs showing the in-plane luminance distribution of the light-emitting layer. As shown in FIG. 12, the cathode 8 may have a comb-like shape including multiple comb teeth 8a, 8b, and 8c, and the auxiliary electrode 9 may have a comb-like shape including multiple comb teeth 9a and 9b that mesh with the cathode 8 (8a to 8c). In this case, as shown in FIG. 13, uniform in-plane luminance is obtained with almost no change in luminance in the direction of the comb teeth. Note that when a rectangular cathode 8 and auxiliary electrode 9 are arranged above the light-emitting layer 5, a slight decrease in luminance is observed in the region below the auxiliary electrode 9, as shown in FIG. 14.

[0040] 15 to 17 are plan views showing examples of the shapes of the cathode and auxiliary electrode. As shown in FIG. 15, the cathode 8 has a double-tooth comb shape, and the auxiliary electrode 9 has a first region 9X including comb teeth 9c that mesh with the comb teeth on one side of the cathode 8 and a second region 9Y including comb teeth 9d that mesh with the comb teeth on the other side of the cathode 8, and the tooth width of the cathode 8 may be smaller than the tooth width of the auxiliary electrode 9. As shown in FIG. 16, the cathode 8 may have a shape that surrounds three sides of the rectangular auxiliary electrode 9. As shown in FIG. 17, the cathode 8 may have a shape that surrounds four sides of the rectangular auxiliary electrode 9.

[0041] 18 and 19 are cross-sectional views showing exemplary configurations of a light-emitting device. As shown in FIG. 18 , a cathode 8 and an auxiliary electrode 9 are located on an electron transport layer 7, and the light-emitting device 10 may include an insulating layer ZL located between the light-emitting layer 5 and the electron transport layer 7. The insulating layer ZL may be located between the auxiliary electrode 9 and the electron transport layer 7. The insulating layer ZL may be in contact with the upper surface of the electron transport layer 7. As shown in FIG. 19 , the insulating layer ZL may be provided inside the electron transport layer 7. In a plan view, the insulating layer ZL may not overlap the cathode 8 but may overlap the auxiliary electrode 9. At least the insulating layer ZL overlaps the auxiliary electrode 9 in a plan view. In FIG. 18 , a structure is shown in which the region directly below the auxiliary electrode 9 is insulated from the light-emitting layer 5 (quantum dot layer). FIG. 20 shows a band diagram of this structure, and it can be seen from FIG. 20 that electron injection from the cathode 8 to the quantum dots Q is effectively suppressed. The insulating layer ZL may be located between the light-emitting layer 5 and the electron transport layer 7. In this case, because of the structure in which electrons are accumulated near the interface between the insulating layer ZL and the electron transport layer 7 (on the ETL side), electron injection can be suppressed regardless of the quantum dots Q and the CBM of the electron transport layer 7.

[0042] For example, following the formation of the light-emitting layer 5, the insulating layer ZL is formed only in the region directly below the auxiliary electrode 9 by photolithography using the same mask as that used for the auxiliary electrode 9. The insulating layer ZL can be formed by vapor deposition, sputtering, or the like, but the insulating layer ZL can also be formed by coating or printing if the insulating material can be made into nanoparticles.

[0043] The insulating material used for the insulating layer ZL is SiO ２ , Al ２O ３ Examples of suitable insulating layers include inorganic materials such as SiO2 and SiN, as well as insulating resins such as PVC and polyimide. The insulating layer ZL is preferably thick enough to prevent electron tunneling (for example, 5 nm or thicker) in order to prevent excessive electron injection into the light-emitting layer 5. On the other hand, a thickness of 10 nm or less is desirable in order to reduce the risk of the electron transport layer 7 on the insulating layer ZL peeling off or cracking of the ETL 7 around the insulating layer ZL.

[0044] 21 is a schematic diagram showing an example of the configuration of a display device according to this embodiment. The display device 20 includes a display unit DA, a first driver circuit X1 (e.g., a data signal line drive circuit) and a second driver circuit X2 (e.g., a scanning signal line drive circuit and a light-emitting control line drive circuit) that drive the display unit DA, and a control circuit CL that controls the first driver circuit X1 and the second driver circuit X2. The display unit DA may include a substrate (pixel circuit substrate) 1 and a light-emitting element layer 6 ( FIG. 1 ). The light-emitting element layer 6 may include a light-emitting element 10R (10) that emits red light, a light-emitting element 10G (10) that emits green light, and a light-emitting element 10B (10) that emits blue light, and the light-emitting elements 10R, 10G, and 10B may each be connected to a pixel circuit PC formed in the pixel circuit layer.

[0045] [Notes] The above-described embodiments are for the purpose of illustration and description, 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.

[0046] REFERENCE SIGNS LIST 1 Substrate (pixel circuit substrate) 3 Anode 4 Hole transport layer (HTL) 5 Light-emitting layer 7 Electron transport layer (ETL) 8 Cathode 9 Auxiliary electrode 10 Light-emitting element 20 Display device E Electron H Hole Q Quantum dot SC Switching element SD Switching element

Claims

1. A light-emitting element comprising an anode and a cathode, an auxiliary electrode that does not overlap the cathode in a planar view, and a light-emitting layer that overlaps the anode and the cathode in a planar view and contains quantum dots, wherein the auxiliary electrode overlaps the anode and the light-emitting layer in a planar view, and the cathode and the auxiliary electrode are made of different materials.

2. The light-emitting device according to claim 1, wherein said cathode and said auxiliary electrode are electrically insulated.

3. The light-emitting device according to claim 1 or 2, wherein the material of said auxiliary electrode has a work function smaller than that of the material of said cathode.

4. The light-emitting element according to claim 1 or 2, wherein at least one of the cathode and the auxiliary electrode includes a plurality of constituent materials.

5. The light-emitting element according to claim 4, wherein the cathode comprises a plurality of constituent materials, at least one of the plurality of constituent materials of the cathode has a work function greater than that of the constituent material of the auxiliary electrode, and the composition ratio of the constituent material having a work function greater than that of the constituent material of the auxiliary electrode in the cathode exceeds 50%.

6. The light-emitting element according to claim 4, wherein the auxiliary electrode comprises a plurality of constituent materials, at least one of the plurality of constituent materials of the auxiliary electrode has a work function smaller than that of the constituent material of the cathode, and the composition ratio of the constituent material having a work function smaller than that of the constituent material of the cathode in the auxiliary electrode exceeds 50%.

7. The light-emitting device according to any one of claims 1 to 6, wherein the auxiliary electrode is grounded via a switching element.

8. The light-emitting device according to any one of claims 1 to 7, wherein the material of the cathode has a work function smaller than that of Ag.

9. The light-emitting element according to any one of claims 1 to 8, wherein the cathode and the auxiliary electrode are formed in the same layer.

10. The light-emitting element according to claim 7, which is turned off during a ground period in which the switching element is turned on.

11. The light-emitting element according to claim 10, wherein no power is supplied to the cathode during the ground period.

12. The light-emitting element according to any one of claims 1 to 11, wherein the cathode and the auxiliary electrode are light-transmitting.

13. The light-emitting device according to any one of claims 1 to 12, further comprising an electron transport layer in contact with the cathode and the auxiliary electrode.

14. The light-emitting device of claim 13, wherein the cathode and the auxiliary electrode are located on the electron transport layer.

15. The light-emitting device of claim 13, further comprising an insulating layer located between the light-emitting layer and the electron-transporting layer.

16. The light-emitting device of claim 13, further comprising an insulating layer located within the electron transport layer.

17. The light-emitting device according to claim 15, wherein the insulating layer is located between the auxiliary electrode and the electron transport layer.

18. The light-emitting element according to any one of claims 1 to 17, wherein the cathode has a comb-like shape.

19. The light-emitting device according to claim 18, wherein the auxiliary electrode has a comb-like shape that interdigitates with the cathode, and the cathode has a tooth width that is smaller than that of the auxiliary electrode.

20. The light-emitting element according to any one of claims 1 to 17, wherein the cathode is shaped to surround the auxiliary electrode.

21. The light-emitting device according to any one of claims 1 to 20, wherein the ratio of the area of ​​said auxiliary electrode to the area of ​​said cathode is 0.6 to 1.

0.

22. The light-emitting device according to any one of claims 1 to 21, wherein the cathode and the auxiliary electrode each comprise an elemental metal or an alloy.

23. The light-emitting device according to any one of claims 1 to 22, wherein the cathode comprises at least one of Au, W, Cr, Co, Ni, Pt, and Cu.

24. The light-emitting element according to any one of claims 1 to 23, wherein the auxiliary electrode is an Ag film, an Al film, or a metal compound film containing any one of B, Ca, and La.

25. A light-emitting element according to any one of claims 1 to 24, wherein the thickness of each of the cathode and the auxiliary electrode is equal to or less than a threshold value, and the threshold value is expressed as (extinction coefficient of aluminum / extinction coefficient of cathode) x 10 [nm].

26. The light-emitting device according to any one of claims 1 to 25, wherein the thickness of each of the cathode and the auxiliary electrode is 0.5 nm or more.

27. The light-emitting device according to any one of claims 1 to 26, wherein the thickness of each of the cathode and the auxiliary electrode is 20 nm or less.

28. The insulating layer is made of SiO ２ , SiN, Al ２ O ３ 18. The light-emitting device according to claim 15, comprising one of MgO and MgO.

29. The light-emitting element according to any one of claims 15 to 17, wherein the insulating layer has a thickness of 5.0 nm or more.

30. The light-emitting element according to claim 17, wherein the insulating layer does not overlap the cathode in a plan view.

31. The light-emitting device according to claim 13, wherein the electron transport layer includes any one of ZnO, ZnMgO, ZnS, and ZnMgS.

32. The light-emitting device according to claim 13, wherein the thickness of the electron transport layer is 5.0 nm to 40 nm.

33. A display device comprising a light-emitting element according to any one of claims 1 to 32.

34. The display device according to claim 33, further comprising a switching element, the auxiliary electrode being grounded via the switching element, and the switching element being turned ON during a period when the light-emitting element is turned off.

35. A method for driving a light-emitting element comprising an anode and a cathode, an auxiliary electrode that does not overlap the cathode in a planar view, and a light-emitting layer that overlaps the anode and the cathode in a planar view and includes quantum dots, wherein the auxiliary electrode overlaps the anode and the light-emitting layer in a planar view, the cathode and the auxiliary electrode are made of different materials, the auxiliary electrode is grounded via a switching element, and the switching element is turned ON during an extinguishing period of the light-emitting element.

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