Light-emitting element, light-emitting device, and method for aging electron hole-transport layer

Abstract

A light-emitting element (30) includes: a substrate (2); an anode (3) that is a lower electrode provided at a position near the substrate (2); a cathode (8) that is an upper electrode provided sandwiching the anode (3) on the opposite side from the substrate (2); a light-emitting layer (6) that is provided between the anode (3) and the cathode (8); an electron hole transport layer (5) that is provided between the anode (3) and the light-emitting layer (6); and one or more conductors (9) that are in contact with the electron hole transport layer (5).

Description

Light-emitting element, light-emitting device, and aging method for hole transport layer

[0001] This disclosure relates to a light-emitting element, a light-emitting device, and a method for aging a hole transport layer.

[0002] In recent years, various display devices have been developed using light-emitting elements, and in particular, display devices equipped with OLEDs (Organic Light Emitting Diodes) or QLEDs (Quantum Dot Light Emitting Diodes) have attracted considerable attention due to their ability to achieve low power consumption, thin design, and high image quality.

[0003] For example, Patent Document 1 describes a light-emitting element equipped with an organic hole transport layer made of polyvinylcarbazole.

[0004] Japanese Patent Application Publication No. 2011-61028

[0005] However, in light-emitting devices equipped with an organic hole transport layer and display devices that are light-emitting devices equipped with such light-emitting devices, there is a problem in that stable device characteristics cannot be obtained due to degradation specific to organic materials.

[0006] One aspect of this disclosure aims to provide a light-emitting element having stable element characteristics, a light-emitting device equipped with a light-emitting element having stable element characteristics, and a method for aging a hole transport layer to obtain a light-emitting element having stable element characteristics.

[0007] To solve the above problems, the light-emitting element of the present disclosure includes: a substrate; an anode which is a lower electrode provided near the substrate; a cathode which is an upper electrode provided on the opposite side of the substrate from the anode; a light-emitting layer provided between the anode and the cathode; a hole transport layer provided between the anode and the light-emitting layer; and one or more conductors in contact with the hole transport layer.

[0008] To solve the above problems, the light-emitting device of the present disclosure has a plurality of light-emitting elements, and is provided with terminals for electrically connecting a plurality of conductors included in the plurality of light-emitting elements, and the terminals are provided in a region that does not obstruct the light emitted from the plurality of light-emitting elements.

[0009] To solve the above problems, the hole transport layer aging method of the present disclosure comprises: a substrate; an anode which is a lower electrode provided near the substrate; a cathode which is an upper electrode provided on the opposite side of the substrate from the anode; an emitting layer provided between the anode and the cathode; a hole transport layer provided between the anode and the emitting layer; a first conductor in contact with the hole transport layer; and a second conductor in contact with the hole functional layer including the hole transport layer and electrically isolated from the first conductor, wherein a voltage is applied to the hole transport layer using the first conductor and the second conductor.

[0010] According to one aspect of this disclosure, it is possible to provide a light-emitting element having stable element characteristics, a light-emitting device equipped with a light-emitting element having stable element characteristics, and a method for aging a hole transport layer to obtain a light-emitting element having stable element characteristics.

[0011] Figure 1 illustrates the rapid degradation observed in a light-emitting element equipped with a hole transport layer containing an organic hole transport material. Figure 2 illustrates the slow degradation observed in a light-emitting element equipped with a hole transport layer containing an organic hole transport material shown in Figure 1. Figure 3 illustrates that the rapid degradation observed in a light-emitting element equipped with a hole transport layer containing an organic hole transport material shown in Figure 1 is caused by degradation specific to organic materials. Figure 4 illustrates the electrical properties of a hole transport layer containing an organic hole transport material. Figure 4 illustrates the reason for the change in the electrical properties of a hole transport layer containing an organic hole transport material. Figure 5 illustrates the schematic configuration of a light-emitting element of Embodiment 1 equipped with a conductor. Figure 6 illustrates an example of aging a hole transport layer containing an organic hole transport material using the conductor and anode provided in the light-emitting element of Embodiment 1 shown in Figure 6. Figure 7 illustrates the change in brightness over time of a light-emitting element that has undergone aging by applying a voltage to the hole transport layer containing an organic hole transport material using the conductor and anode provided in the light-emitting element of Embodiment 1, and the change in brightness over time of a comparative example light-emitting element whose hole transport layer containing an organic hole transport material has not been aged. Figure 6 is a plan view showing a schematic configuration of a display device, which is an example of a light-emitting device including a plurality of light-emitting elements of Embodiment 1. Figure 6 is a plan view showing a schematic configuration of a display device equipped with terminals for electrically connecting a plurality of conductors included in a plurality of light-emitting elements of Embodiment 1. Figure 16 is a cross-sectional view showing a schematic configuration of a light-emitting element, which is another example of Embodiment 1 equipped with a conductor. Figure 16 is a cross-sectional view showing a schematic configuration of a light-emitting element, which is yet another example of Embodiment 1 equipped with a conductor. Figure 16 is a diagram showing an example of materials constituting the light-emitting layer provided in the light-emitting element of Embodiment 1. Figure 16 is a diagram showing another example of materials constituting the light-emitting layer provided in the light-emitting element of Embodiment 1. Figure 16 is a diagram showing yet another example of materials constituting the light-emitting layer provided in the light-emitting element of Embodiment 1. Figure 16 is a cross-sectional view showing a schematic configuration of a light-emitting element of Embodiment 2 equipped with a first conductor and a second conductor.This is a plan view showing the schematic configuration of a display device comprising a first terminal for electrically connecting a plurality of first conductors included in a plurality of light-emitting elements of Embodiment 2, and a second terminal for electrically connecting a plurality of second conductors included in a plurality of light-emitting elements of Embodiment 2. This is a cross-sectional view showing the schematic configuration of a light-emitting element of Embodiment 3 in which a portion of the conductor is located inside a bank. This is a cross-sectional view showing the schematic configuration of a light-emitting element that is another example of Embodiment 3 in which the conductor is located inside a bank. This is a cross-sectional view showing the schematic configuration of a light-emitting element that is yet another example of Embodiment 3 in which the conductor is located inside a bank. This is a cross-sectional view showing the schematic configuration of a light-emitting element that is a modified example of the light-emitting element of Embodiment 3 shown in Figure 21. This is a cross-sectional view showing the schematic configuration of a light-emitting element of Embodiment 4 in which the first conductor and the second conductor are provided on the same plane as the anode.

[0012] The embodiments of this disclosure will be described below with reference to Figures 1 to 23. For the sake of convenience, in the following description, components having the same function as those described in a particular embodiment will be denoted by the same reference numerals, and their descriptions may be omitted.

[0013] [Embodiment 1] Figure 1 is a diagram illustrating the rapid degradation observed in a light-emitting element equipped with a hole transport layer containing an organic hole transport material. Figure 2 is a diagram illustrating the slow degradation observed in a light-emitting element equipped with a hole transport layer containing an organic hole transport material as shown in Figure 1. Figure 3 is a diagram illustrating that the rapid degradation observed in a light-emitting element equipped with a hole transport layer containing an organic hole transport material as shown in Figure 1 is caused by degradation specific to organic materials. Figure 4 is a diagram showing the electrical properties of the hole transport layer containing the organic hole transport material. Figure 5 is a diagram illustrating the reason for the change in the electrical properties of the hole transport layer containing the organic hole transport material as shown in Figure 4.

[0014] As shown in Figure 2, the time-dependent changes in the voltage and brightness of a light-emitting element were measured while keeping the current flowing through the element constant. The results show that in a light-emitting element equipped with a hole transport layer containing an organic hole transport material, the brightness decreases and the voltage required to maintain that constant current increases as time passes, exhibiting a typical degradation trend seen in light-emitting elements with organic layers. Furthermore, as shown in Figure 2, both brightness and voltage show large changes at the initial stage of energization, i.e., at the start of the constant current flow.

[0015] As can be seen from the voltage change rate and brightness change rate of the light-emitting element equipped with a hole transport layer containing an organic hole transport material shown in Figure 1, the rapid degradation during the rapid degradation period, which is within 10 minutes of the start of power application, has a major impact on the degradation of the element characteristics of the light-emitting element. On the other hand, after the rapid degradation period, which is within 10 minutes of the start of power application, the degradation of the light-emitting element changes to a slower degradation, and thereafter converges to a constant degradation rate.

[0016] To confirm that the rapid degradation during the rapid degradation period, which is the period within 10 minutes of the start of energization as described above, is due to the hole transport layer containing the organic hole transport material, the inventors of this disclosure performed PL (Photoluminescence) measurements on a light-emitting element equipped with a hole transport layer containing the organic hole transport material, in which an anode composed of a light-reflective electrode material, a hole transport layer containing the organic hole transport material, an emissive layer composed of blue light-emitting quantum dots, and a cathode composed of a light-transmitting electrode material were stacked in this order. A single element during reliability testing was identified, and the reliability test of that element was interrupted at predetermined elapsed times to perform PL measurements, and then the reliability test was resumed. This procedure was repeated to evaluate the change in PL characteristics. PL measurements were performed on the light-emitting element immediately after manufacturing (before continuous energization in Figure 3), after a constant current was passed through the element for 1 hour (after 1 hour of continuous energization in Figure 3), and after the constant current was passed through the element for 200 hours (after 200 hours of continuous energization in Figure 3), and then the reliability test was continued. For PL measurement excitation, the device should be irradiated with light shorter than the wavelength corresponding to the energy difference between the LUMO and HOMO of the hole transport layer (HTL) (for example, 390 nm). The intensity of the PL light emitted after absorbing the excitation light (PL intensity) was analyzed for each wavelength. The blue light-emitting quantum dots constituting the light-emitting layer of the light-emitting device described above did not degrade even when the constant current was passed for 200 hours. As shown in Figure 3, in the wavelength range of the PL light of the blue quantum dots (the region labeled QD in the figure), there was almost no decrease in PL intensity after passing the constant current for 1 hour (after 1 hour of continuous current in the figure) and after passing the constant current for 200 hours (after 200 hours of continuous current in the figure) compared to immediately after manufacturing (before continuous current is passed in the figure). On the other hand, the hole transport layer containing the organic hole transport material provided in the light-emitting element described above shows degradation even when the constant current is applied for 1 hour. As shown in Figure 3, in the wavelength region of the PL light of the hole transport layer containing the organic hole transport material (the region labeled HTL in the figure), it can be confirmed that the decrease in PL intensity after applying the constant current for 1 hour (1 hour after continuous energization in the figure) is greater than immediately after manufacturing (before continuous energization in the figure).The PL intensity after applying the constant current for 200 hours (200 hours of continuous energization in the figure) is lower than the PL intensity after applying the constant current for 1 hour (1 hour of continuous energization in the figure). However, the degree of decrease in PL intensity is smaller compared to the degree of decrease in PL intensity that occurs within 1 hour of continuous energization as described above.

[0017] Generally, the rate of degradation reflects the rate coefficient of the reaction involved in the degradation. For example, in inorganic devices such as typical semiconductor LEDs and semiconductor lasers, there are multiple degradation mechanisms, but the degradation rate corresponding to each degradation mechanism is constant, and it is known that the degradation rate is a combination of straight lines. On the other hand, in the light-emitting device dealt with in this disclosure, referring to the lower figure, which is an enlarged view of the first 0.5 hours in Figure 1, the rate of change up to approximately 0.2 hours is a curve, indicating that the degradation rate is changing continuously. After approximately 0.2 hours, it changes at a constant rate of change, resulting in a constant degradation rate. The degradation up to approximately 0.2 hours indicates that the reaction coefficient of the corresponding degradation mechanism is changing continuously, and such degradation is unique to organic materials.

[0018] From the above, it is thought that the hole transport layer containing organic hole transport material undergoes the most significant change in its properties during the rapid degradation period, which is within 10 minutes of the start of current application. This leads to a decrease in the hole injection characteristics into the light-emitting layer, resulting in a decrease in the brightness of the light-emitting element and an increase in the voltage required to maintain a constant current.

[0019] The inventors of this disclosure have confirmed that, for example, as shown in Figure 7 later, by applying a voltage (aging) to a hole transport layer 5 containing an organic hole transport material using the anode 3 and conductor 9 provided in the light-emitting element 30, the electrical characteristics (V-I characteristics) of the hole transport layer 5 containing the organic hole transport material approach space charge-limited current conduction, as shown by the solid line in Figure 4, from hopping conduction, as shown by the dotted line in Figure 4. The electrical properties of a hole transport layer 5 containing an organic hole transport material are described as hopping conduction if the current I flowing through the hole transport layer 5 containing the organic hole transport material is proportional to the value of the voltage V applied to the hole transport layer 5 raised to the power of m (3.0 ≤ m). The electrical properties of a hole transport layer 5 containing an organic hole transport material are described as space charge limited current conduction if the current I flowing through the hole transport layer 5 containing the organic hole transport material is proportional to the value of the voltage V applied to the hole transport layer 5 raised to the power of m (1.8 ≤ m ≤ 2.2). For reference, Figure 4 shows the case where the current I is proportional to the voltage V with a dashed line.

[0020] As shown on the left side of Figure 5, the hole current (I), which is the current value flowing through the hole transport layer 5, is V ｍ When proportional to (3.0 ≤ m), the current flowing through the hole transport layer is a hopping current that transports holes via isolated deep levels. In this case, the deep levels are thought to remain at a density similar to that of the injected carriers, and that density is 10 １５ ~10 １７ cm －３ This can be estimated to be the extent of the problem. This density is more than six orders of magnitude lower than the density of atoms constituting the hole transport layer, indicating that the polymerization or crosslinking reaction, viewed macroscopically, is almost complete, but there are still enough unbonded groups remaining to participate in the transport mechanism of the injected carriers. In this state, holes can hop through the defect levels by consuming voltage, so there is no accumulation of hole groups in the hole transport layer. This is an image of hole transport in the early stages of aging.

[0021] Next, when an electric current is applied to the hole transport layer to supply electrons, the residual unbonded groups are terminated by radical polymerization, and as shown in the middle of FIG. 5, the defect levels are decreased by radical polymerization due to the overflowed electrons. As such radical polymerization proceeds, the electrical characteristics of the hole transport layer converge such that the hole current (I) is proportional to V ｍ (1.8 ≤ m ≤ 2.2). At this time, since the defect levels have decreased sufficiently, holes are transported at the intrinsic mobility of the hole transport layer. The mobility of the hole transport layer including the organic hole transport material, which is an organic substance, is 10 －５ to 10 －６ cm ２ / V·sec, which is very low (but not zero). Therefore, holes injected from the anode stay in the hole transport layer and form a cloud of positive charges. This charge cloud creates an electric field in the direction that blocks holes injected from the anode, and in order for newly injected holes in the hole transport layer to reach the light-emitting layer, it is necessary to exceed the blocking electric field. Under such conditions, as shown on the right side of FIG. 5, the current flowing through the hole transport layer becomes a space charge limited current in which the current is proportional to the 1.8th to 2.2nd power of the voltage. From the above, if the relationship between the current and voltage flowing through the hole transport layer is such that the hole current (I) is proportional to V ｍ (1.8 ≤ m ≤ 2.2), it can be determined that the defect levels in the hole transport layer have decreased sufficiently and the radical polymerization of the hole transport layer that affects hole transport has terminated.

[0022] Therefore, in the present embodiment, as an aging method for the hole transport layer 5 including the organic hole transport material, a method is used in which a voltage is applied (aged) to the hole transport layer 5 until the current value I flowing through the hole transport layer 5 exhibits electrical characteristics proportional to the value of the m (1.8 ≤ m ≤ 2.2) power of the voltage V applied to the hole transport layer 5. However, the present invention is not limited to this, and the hole transport layer 5 including the organic hole transport material may be aged in a direction in which its electrical characteristics approach space charge limited current conduction from hopping conduction.

[0023] FIG. 6 is a cross-sectional view showing a schematic configuration of the light-emitting device 30 of Embodiment 1 including the conductor 9.

[0024] As shown in Figure 6, the light-emitting element 30 includes a substrate 2, an anode 3 which is a lower electrode located near the substrate 2, a cathode 8 which is an upper electrode located on the opposite side of the substrate 2 from the anode 3, a light-emitting layer 6 provided between the anode 3 and the cathode 8, a hole transport layer 5 provided between the anode 3 and the light-emitting layer 6, and one or more conductors 9 in contact with the hole transport layer 5. In this embodiment, as shown in Figure 6, the light-emitting element 30 is provided with two conductors 9 in contact with the hole transport layer 5, and the case in which the two conductors 9 are electrically connected will be described as an example. As shown in Figure 6, one of the two conductors 9 overlaps with the portion near the left end of the hole transport layer 5 in a plan view, and the other of the two conductors 9 overlaps with the portion near the right end of the hole transport layer 5 in a plan view. The invention is not limited to this, and for example, one of the conductors 9 superimposed on the left end portion of the hole transport layer 5 in a plan view and the conductor 9 superimposed on the right end portion of the hole transport layer 5 in a plan view may be provided on the front side in the depth direction of Figure 6, and the other may be provided on the back side in the depth direction of Figure 6. The conductors 9 are aging electrodes used when applying voltage to the hole transport layer 5 to promote aging.

[0025] Furthermore, multiple conductors 9 may be provided that overlap with the portion near the left end of the hole transport layer 5 in a plan view, and multiple conductors 9 may overlap with the portion near the right end of the hole transport layer 5 in a plan view. For example, one of the multiple conductors 9 that overlap with the portion near the left end of the hole transport layer 5 in a plan view and the multiple conductors 9 that overlap with the portion near the right end of the hole transport layer 5 in a plan view may be provided on the front side in the depth direction of Figure 6, and the other may be provided on the back side in the depth direction of Figure 6. Also, the other conductor 9 may be provided corresponding to the position between two adjacent conductors 9 of one of the multiple conductors 9 that overlap with the portion near the left end of the hole transport layer 5 in a plan view and the multiple conductors 9 that overlap with the portion near the right end of the hole transport layer 5 in a plan view.

[0026] In the present embodiment, a case where one conductor 9 overlapping a portion near the left end of the hole transport layer 5 in a plan view and one conductor 9 overlapping a portion near the right end of the hole transport layer 5 in a plan view are provided is taken as an example for explanation. However, the present invention is not limited to this. The number of conductors 9 overlapping a portion near the left end of the hole transport layer 5 in a plan view and the number of conductors 9 overlapping a portion near the right end of the hole transport layer 5 in a plan view may be different. For example, only one of the conductor 9 overlapping a portion near the left end of the hole transport layer 5 in a plan view and the conductor 9 overlapping a portion near the right end of the hole transport layer 5 in a plan view may be provided. For example, only a plurality of conductors 9 overlapping a portion near the left end of the hole transport layer 5 in a plan view may be provided, or only a plurality of conductors 9 overlapping a portion near the right end of the hole transport layer 5 in a plan view may be provided.

[0027] In the present embodiment, a case where the conductor 9 overlaps a portion near the left end of the hole transport layer 5 in a plan view or a portion near the right end of the hole transport layer 5 in a plan view is taken as an example for explanation. However, the present invention is not limited to this. If the conductor 9 is in contact with the hole transport layer 5, it may not overlap with any of the portion near the left end of the hole transport layer 5 and the portion near the right end of the hole transport layer 5 in a plan view.

[0028] In the present embodiment, a case where a plurality of conductors 9 are electrically connected to each other is taken as an example for explanation. However, if a voltage can be applied to the hole transport layer 5 using a plurality of conductors 9 and the anode 3, the plurality of conductors 9 may not be electrically connected to each other. In such a case, for example, each of the plurality of conductors 9 that are not electrically connected may be set to substantially the same potential.

[0029] In the present embodiment, since a voltage is applied to the hole transport layer 5 by utilizing the potential difference between the anode 3 and the conductor 9 that is electrically separated from the anode 3, at least one conductor 9 may be provided. In order to enhance the effect of aging due to the application of voltage to the hole transport layer 5, it is preferable to provide conductors 9 that contact more different-direction ends of the hole transport layer 5. As a method of providing conductors 9 that contact more different-direction ends of the hole transport layer 5, the shape of the conductor 9 may be optimized, or the number of conductors 9 may be increased. For example, as in the present embodiment, two conductors 9 that contact respectively two opposite ends of the hole transport layer 5 may be provided, or one conductor 9 having a shape that contacts the entire end of the hole transport layer 5 may be provided.

[0030] As shown in FIG. 6, the light-emitting element 30 includes a bank 4 provided so as to contact at least a part of the end of the anode 3, and at least a part of the conductor 9 is located on the bank 4. That is, in a plan view, at least a part of the conductor 9 overlaps with the bank 4.

[0031] In the present embodiment, the bank 4 includes a first bank that contacts a first end, which is the left end of the anode 3 in FIG. 6, and a second bank that contacts a second end, which is the right end of the anode 3 in FIG. 6 and faces the first end. A case where at least a part of the anode 3 is provided between the first bank and the second bank will be described as an example, but it is not limited thereto. For example, the bank 4 may be formed in a frame shape so as to surround the anode 3 in a plan view. In the present embodiment, a case where the light-emitting element 30 includes the bank 4 is described as an example, but the light-emitting element 30 may not include the bank 4.

[0032] As shown in FIG. 6, the bank 4 has an inclined surface that contacts the anode 3, and the hole transport layer 5 may extend on the inclined surface. According to such a configuration, the contact area between the conductor 9 located on the inclined surface of the bank 4 and the hole transport layer 5 can be increased.

[0033] It is preferable that the conductor 9 is electrically isolated from the light-emitting layer 6, electrically isolated from the cathode 8, and electrically isolated from the electron transport layer 7, or from the electron injection layer which may be provided between the cathode 8 and the electron transport layer 7. In this embodiment, the insulating layer 10 is used to electrically isolate the conductor 9 from the light-emitting layer 6, the electron transport layer 7, and the cathode 8, respectively. Note that electrically isolated means that they are insulated so that they do not conduct electricity.

[0034] Furthermore, as in this embodiment, the light-emitting element 30 is equipped with two conductors 9, and when applying a voltage to the hole transport layer 5 containing the organic hole transport material using the anode 3 and the conductors 9 to perform aging of the hole transport layer 5 containing the organic hole transport material, it is necessary to electrically isolate the conductors 9 from the anode 3. In this embodiment, electrical isolation of the conductors 9 from the anode 3 is achieved by placing the conductors 9 on the cathode 8 side, which is the upper surface side of the hole transport layer 5, and placing the anode 3 on the lower surface side of the hole transport layer 5.

[0035] The light-emitting element 30 shown in Figure 6 may be either a top-emission type or a bottom-emission type. The light-emitting element 30 shown in Figure 6 is a light-emitting element with a sequential structure in which the cathode 8 is positioned above the anode 3. In order to make such a sequential structure light-emitting element a top-emission type, the anode 3 should be formed from an electrode material that reflects visible light and the cathode 8 should be formed from an electrode material that transmits visible light. In order to make such a sequential structure light-emitting element a bottom-emission type, the anode 3 should be formed to transmit visible light and the cathode 8 should be formed to reflect visible light.

[0036] The electrodes that reflect visible light are not particularly limited as long as they are conductive, but examples include metallic materials such as Al, Mg, Li, and Ag, or alloys of the said metallic materials, or laminates of the said metallic material and transparent metal oxides (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.), or laminates of the said alloy and the said transparent metal oxide.

[0037] On the other hand, electrodes that transmit visible light are not particularly limited as long as they are conductive, but examples include thin films made of transparent metal oxides (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.) or metallic materials such as Al and Ag, or nanowires made of metallic materials such as Al and Ag.

[0038] The organic hole transport material contained in the hole transport layer 5 provided in the light-emitting element 30 shown in Figure 6 may be, for example, poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] (TFB), N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine (poly-TPD), or polyvinylcarbazole (PVK). In this embodiment, for example, the hole transport layer 5 was formed by coating a solution containing crosslinkable TFB, but the invention is not limited to this, and the hole transport layer 5 may also be formed using an inkjet method with a solution containing crosslinkable TFB. Organic materials are generally preferred as hole transport materials. The TFB, poly-TPD, and PVK mentioned above have HOMO (highest occupied orbital) levels close to the valence band upper edge (VBM) of the light-emitting layer 6, or, if the light-emitting layer 6 is composed of quantum dots, close to the valence band upper edge (VBM) of the quantum dots, thus enabling relatively efficient hole injection.

[0039] The light-emitting element 30 shown in Figure 6 may include a hole injection layer (HIL) between the anode 3 and the hole transport layer 5. If the light-emitting element 30 shown in Figure 6 includes a hole injection layer (HIL), the material used to form the hole injection layer (HIL) is not particularly limited as long as it is a hole injection material that can stabilize the injection of holes into the light-emitting layer 6. For example, nickel oxide (NiO) nanoparticles or a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT:PSS) can be used.

[0040] As shown in Figure 6, in this embodiment, the case in which the light-emitting element 30 is equipped with an electron transport layer 7 is described as an example, but the invention is not limited to this, and the light-emitting element 30 may further be equipped with an electron injection layer between the electron transport layer 7 and the cathode 8. Alternatively, the light-emitting element 30 may be equipped with only an electron injection layer between the light-emitting layer 6 and the cathode 8.

[0041] The electron transport material contained in the electron transport layer 7 provided in the light-emitting element 30 shown in Figure 6 may be an organic material such as 2,2',2"-(1,3,5-benzintriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi), or it may be an electron-transporting nanoparticle such as ZnO particles or oxide particles containing Zn and Mg.

[0042] If the light-emitting element 30 shown in Figure 6 is equipped with an electron injection layer (EIL), the material used to form the electron injection layer (EIL) is not particularly limited as long as it is an electron injection material that can stabilize the injection of electrons into the light-emitting layer 6. For example, alkali metals or alkaline earth metals such as aluminum, strontium, calcium, lithium, cesium, magnesium oxide, aluminum oxide, strontium oxide, lithium oxide, lithium fluoride, magnesium fluoride, strontium fluoride, calcium fluoride, barium fluoride, cesium fluoride, polymethyl methacrylate, sodium polystyrene sulfonate, alkali metals or alkaline earth metals, oxides of alkali metals or alkaline earth metals, fluorides of alkali metals or alkaline earth metals, or organic complexes of alkali metals can be used.

[0043] In each embodiment of this disclosure, the case in which the light-emitting layer 6 of the light-emitting element is a light-emitting layer containing quantum dots and the light-emitting element is a QLED (Quantum dot Light Emitting Diode) is described as an example, but the invention is not limited thereto. For example, the light-emitting element may be an OLED (Organic Light Emitting Diode) having a light-emitting layer containing an organic light-emitting material instead of a light-emitting layer containing quantum dots.

[0044] Quantum dots are semiconductor nanoparticles that emit light through the recombination of electrons and holes as the excitons lose energy, generating excitons from injected electrons and holes. A quantum dot may have a core / shell structure, for example, comprising a core and a shell covering at least a portion of the core's surface. The shell may be a single layer, a multi-layer shell containing different materials, or a giant shell with a thickness of 2 nm or more. In this case, the recombination of electrons and holes in the quantum dot primarily occurs in the core. The core of a quantum dot has a valence band level and a conduction band level, and emits light through the recombination of holes in the valence band level and electrons in the conduction band level. Because the emission from quantum dots has a narrow spectrum due to the quantum confinement effect, it is possible to obtain emission with relatively deep chromaticity. Furthermore, the shell has the function of suppressing the generation of defects or dangling bonds in the core and reducing carrier recombination through the deactivation process. From the viewpoint of efficiently obtaining the quantum confinement effect in quantum dots, the particle size of the quantum dot core may be approximately twice or less the exciton Bohr radius of the core material.

[0045] The quantum dot may include materials used for conventionally known core and shell materials in the core and shell materials, respectively. For example, the quantum dot may have a core / shell structure of a group I-III-V chalcopyrite material / ZnS including InP / ZnS, CdSe / ZnS, CdSe / ZnSe, CdSe / CdS, ZnSe / ZnS, or CuInGaS (CIGS). In addition, the quantum dot may contain InZnP, CdSeTe, or ZnSeTe. Furthermore, the core of the quantum dot may contain CuInZnS, CuInS, CuGaS, AgInS, or ZnAgInS. The shell may be formed from multiple layers containing multiple different materials.

[0046] The particle size of the quantum dots is approximately 1 to 100 nm. The quantum dots may be spherical or non-spherical in shape. In this disclosure, the particle size of the quantum dots may be measured by performing cross-sectional observation of the light-emitting layer 6 in the film thickness direction. In this cross-sectional observation, the particle size of each quantum dot may be considered to be the same as the diameter of a circle having the same area as its cross-sectional area. The particle size of the quantum dots may also be measured by measuring the particle size of 20 quantum dots in the cross-sectional observation and calculating the average. The cross-sectional observation may also be performed by analyzing images obtained by capturing cross-sectional images of each layer using a transmission electron microscope (TEM).

[0047] The light-emitting element 30 shown in Figure 6 was manufactured by the method described below. The substrate 2, which includes a thin-film transistor that serves as a drive circuit for driving the light-emitting element 30, may be formed in the same way as in the conventional method using the same materials. First, an anode 3, which is electrically connected to the drive circuit (not shown) included in the substrate 2, was formed, and then a bank 4 was formed. The bank 4 includes a first bank in contact with the first end, which is the left end of the anode 3 in Figure 6, and a second bank in contact with the second end, which is the right end of the anode 3 in Figure 6, opposite the first end, and is formed such that at least a part of the anode 3 is provided between the first bank and the second bank. The bank 4 can be formed, for example, by coating an organic material such as polyimide or acrylic and then patterning it by photolithography.

[0048] Subsequently, a hole transport layer 5 containing an organic hole transport material was formed on the inclined surface of bank 4 in contact with anode 3 and on anode 3. In the process of forming the hole transport layer 5 containing the organic hole transport material, a crosslinkable TFB may be applied or printed by inkjet. In particular, when the hole transport layer 5 is formed by application, the viscosity of the solution causes the hole transport layer 5 to crawl up onto the inclined surface of bank 4, but the crawled portion can be used for contact between the conductor 9 and the hole transport layer 5. Therefore, the contact area between the conductor 9 and the hole transport layer 5 can be increased.

[0049] When a hole injection layer (HIL) is provided, it is formed before the hole transport layer 5 is formed. The hole injection layer (HIL) can be made of NiO, for example, and may be formed by coating or printing a dispersed colloidal solution of NiO nanoparticles using an inkjet printer, or by forming a thin film using vacuum deposition or sputtering. A hole injection layer (HIL) of substantially uniform thickness can be formed using any of the coating, printing, or deposition methods.

[0050] Next, a conductor 9 is formed on bank 4. For example, a resist film having an opening in a desired region for forming the conductor 9 can be formed, then the conductor 9 can be formed on the opening and the resist film, and then the conductor 9 of a desired shape can be formed in the desired region by patterning using a lift-off method to peel off the resist film. In this embodiment, since the conductor 9 is positioned on bank 4, the conductor 9 is outside the light-emitting region and therefore does not need to be light-transmitting, and it is not a problem to form it as a thick film of several hundred nm or more. It may also be formed with a layer thickness suitable for patterning. The conductor 9 may be formed from a conductive material containing a metallic element or a metalloid element, for example. Examples of metalloid elements include B, Si, Ge, As, Sb, and Te. The conductor 9 may be formed from a metallic material or metal oxide material used for the anode and cathode of a light-emitting device, such as Ag, Al, and ITO (indium tin oxide), or from a semiconductor material such as polysilicon or an oxide semiconductor. The material used to form the conductor 9 is not particularly limited as long as it is a good conductor that can conduct electricity through the hole transport layer 5. The method for forming the conductor 9 on the bank 4 by patterning is not limited to the lift-off method described above. For example, a conductor 9 of a desired shape may be formed in the desired region by patterning by setting the holes of a metal mask, which has holes in positions corresponding to the desired region for forming the conductor 9, at the desired position on the bank 4, and then depositing a desired conductive material by a generally known means such as vapor deposition.

[0051] Subsequently, for example, a light-emitting layer 6 of a desired shape can be formed in the desired region by patterning using the lift-off method or a metal mask as described above. The light-emitting layer 6 may be formed, for example, by coating or printing a quantum dot dispersion with an inkjet printer, or, in the case of an organic light-emitting material, by vapor deposition.

[0052] Next, an insulating layer 10 is formed on the conductor 9, for example, by the lift-off method. If the conductor 9 and the light-emitting layer 6 come into contact, current will flow through the light-emitting layer during aging, potentially causing the excitons of the quantum dots contained in the light-emitting layer 6 to become inactive. Furthermore, if the conductor 9 and the cathode 8 come into contact, a short circuit will occur during aging, preventing current from flowing through the hole transport layer. In addition, if a voltage is applied between the cathode 8 and the anode 3 to make the light-emitting device emit light, the cathode 8 and the anode 3 will become conductive with the hole transport layer 5 in between, preventing electron injection into the light-emitting layer 6. The insulating layer 10 is a layer for electrically separating the conductor 9 from the light-emitting layer 6, the electron transport layer 7, and the cathode 8.

[0053] Next, the electron transport layer 7 and the cathode 8 were formed in this order using a conventional method.

[0054] In this embodiment, as described above, the case in which the conductor 9 is formed first, the light-emitting layer 6 is formed, and then the insulating layer 10 is formed was given as an example, but it is not limited to this. For example, the light-emitting layer 6 may be formed first, the conductor 9 may be formed, and then the insulating layer 10 may be formed, or the conductor 9 may be formed first, the insulating layer 10 may be formed, and then the light-emitting layer 6 may be formed.

[0055] Figure 7 shows an example of aging a hole transport layer 5 containing an organic hole transport material using the conductor 9 and anode 3 provided in the light-emitting element 30 of Embodiment 1 shown in Figure 6.

[0056] As shown in Figure 7, the light-emitting element 30 comprises a substrate 2, an anode 3 which is a lower electrode located near the substrate 2, a cathode 8 which is an upper electrode located on the opposite side of the substrate 2 from the anode 3, a light-emitting layer 6 provided between the anode 3 and the cathode 8, and a hole transport layer 5 provided between the anode 3 and the light-emitting layer 6. In this embodiment, as an aging method for the hole transport layer 5, the hole transport layer 5 is aged by applying a voltage to the hole transport layer 5 using a conductor 9 which is a first conductor in contact with the hole transport layer 5, and an anode 3 which is a second conductor in contact with the hole functional layer including the hole transport layer 5 and electrically isolated from the conductor 9 which is the first conductor. Here, in this embodiment, the hole functional layer including the hole transport layer 5 is described as consisting only of the hole transport layer 5 as an example, but it is not limited to this, and the hole injection layer and the hole transport layer 5 may be stacked in this order from the anode 3 side.

[0057] As shown in Figure 7, the power supply unit 50 is a device for supplying a constant current (constant current) between a first conductor, the conductor 9, and a second conductor, the anode 3, and includes a high-potential side terminal 51 from which a high-potential side power supply voltage is output, and a low-potential side terminal 52 from which a low-potential side power supply voltage is output. Furthermore, the power supply unit 50 may also include a current measuring unit 53 for measuring the constant current value. The hole transport layer 5 can be aged by electrically connecting the high-potential side terminal 51 of the power supply unit 50 to the anode 3 and the low-potential side terminal 52 of the power supply unit 50 to the conductor 9. The supply of current to the hole transport layer 5 is not polarity-dependent, so it is not limited to this, and the hole transport layer 5 can also be aged even if the high-potential side terminal 51 of the power supply unit 50 is electrically connected to the conductor 9 and the low-potential side terminal 52 of the power supply unit 50 is electrically connected to the anode 3.

[0058] As shown in Figure 7, the power supply 50 allows for monitoring a constant current value and the change in the voltage value required to maintain that constant current. This enables monitoring of the voltage-current relationship of the hole transport layer 5 during aging, i.e., the electrical characteristics of the hole transport layer 5. Therefore, in this embodiment, the aging method for the hole transport layer 5 containing the organic hole transport material is used, which involves aging the hole transport layer 5 until the current value I flowing through the hole transport layer 5 exhibits electrical characteristics proportional to the voltage V applied to the hole transport layer 5 raised to the power of m (1.8 ≤ m ≤ 2.2). However, the method is not limited to this, and the hole transport layer 5 containing the organic hole transport material only needs to be aged in a direction that moves its electrical characteristics from hopping conduction towards space charge-limited current conduction.

[0059] In addition to the above-described aging method for the hole transport layer 5, which monitors the change in the electrical characteristics of the hole transport layer 5, another aging method for the hole transport layer 5 may be used in which a voltage is applied to the hole transport layer 5 for a period of 4 / I (minutes), where I (mA) is the current value (a constant current value) flowing between the first conductor, the conductor 9, and the second conductor, the anode 3. In this method, the time is measured with a timer at the same time as the voltage is applied to the hole transport layer 5. For example, if the current value flowing between the first conductor, the conductor 9, and the second conductor, the anode 3, is 0.4 mA, then the amount of charge equivalent to 0.4 mA × 10 minutes (10 minutes is the time obtained from the above-described calculation formula 4 / I) is (= 1.5 × 10 １８ When [C]) is supplied, the application of voltage to the hole transport layer 5 is stopped. When the reliability test results of the light-emitting element are analyzed and the degradation rate is calculated, a strong correlation is observed between the energizing time (voltage application time) and the degradation rate of 1.5 × 10⁻⁶. １８ Since the degradation rate decreases with current equivalent to [C], it is thought that radical polymerization terminates when electrons of this charge overflow into the hole transport layer 5.

[0060] Figure 8 shows the change in brightness over time of a light-emitting element 30 that has been aged by applying a voltage to the hole transport layer 5 containing an organic hole transport material using the conductor 9 and anode 3 provided in the light-emitting element 30 of Embodiment 1, as shown in Figure 7, and the change in brightness over time of a comparative example light-emitting element in which the hole transport layer 5 containing the organic hole transport material has not been aged.

[0061] The inventors of this disclosure have found that by aging the hole transport layer 5 containing the organic hole transport material as described above before use of the light-emitting element or the display device which is a light-emitting device including the light-emitting element, the electrical characteristics of the hole transport layer 5 containing the organic hole transport material are changed from hopping conduction to space charge-limited current conduction, as shown in Figure 4, thereby suppressing a large decrease in brightness during use of the light-emitting element or the display device which is a light-emitting device including the light-emitting element, as shown in Figure 8. The sample of the light-emitting element labeled "HTL aging applied" in Figure 8 is the brightness transition of the light-emitting element 30 in which an aging voltage was applied in advance to the hole transport layer 5 containing the organic hole transport material, as shown in Figure 7, using the conductor 9 and anode 3 provided in the light-emitting element 30 of Embodiment 1, and then the light-emitting operation was performed. The sample of the light-emitting element labeled "HTL aging not applied" in Figure 8 is the brightness transition of a comparative example light-emitting element in which the light-emitting operation was performed without applying an aging voltage in advance to the hole transport layer 5 containing the organic hole transport material.

[0062] As described above, the light-emitting element 30 can suppress a significant decrease in brightness during use of the light-emitting element 30 and the display device 1 including the light-emitting element 30, thereby enabling the realization of a light-emitting element 30 with stable element characteristics and a display device 1 equipped with a light-emitting element 30 with stable element characteristics.

[0063] Furthermore, by using the aging method for the hole transport layer 5 described above, it is possible to obtain a light-emitting element 30 with stable element characteristics in which large changes in brightness occur during light emission operation are suppressed.

[0064] Figure 9 is a plan view showing a schematic configuration of a display device 1, which is an example of a light-emitting device including a plurality of light-emitting elements 30 of Embodiment 1 shown in Figure 6.

[0065] As shown in Figure 9, the display device 1 comprises a frame area NDA and a display area DA. The display area DA of the display device 1 is provided with a plurality of pixels PIX, and each pixel PIX includes a red subpixel RSP, a green subpixel GSP, and a blue subpixel BSP. In this embodiment, the case in which one pixel PIX is composed of a red subpixel RSP, a green subpixel GSP, and a blue subpixel BSP is described as an example, but it is not limited to this. For example, one pixel PIX may include subpixels of other colors in addition to the red subpixel RSP, green subpixel GSP, and blue subpixel BSP. In this embodiment, the display device 1 is provided with a red light-emitting element 30 having a red light-emitting layer as its light-emitting layer 6 in its red subpixel RSP, a green light-emitting element 30 having a green light-emitting layer as its light-emitting layer 6 in its green subpixel GSP, and a blue light-emitting element 30 having a blue light-emitting layer as its blue subpixel BSP, as an example, but the embodiment is not limited to this. In this embodiment, the display device 1 is used as an example to describe a light-emitting device that includes a plurality of light-emitting elements 30 of Embodiment 1 shown in Figure 6, but the light-emitting device that includes a plurality of light-emitting elements 30 of Embodiment 1 shown in Figure 6 may be, for example, an illumination device.

[0066] Figure 10 is a plan view showing a schematic configuration of a display device 1 equipped with terminals 9T that electrically connect a plurality of conductors 9 included in a plurality of light-emitting elements 30 of Embodiment 1.

[0067] As shown in Figure 10, the display device 1 has a plurality of light-emitting elements 30 and a terminal 9T that electrically connects a plurality of conductors 9 contained within the plurality of light-emitting elements 30. The terminal 9T is located in a region that does not obstruct the light emitted from the plurality of light-emitting elements 30, for example, in the frame region NDA. The electrical connection between the plurality of conductors 9 and the terminal 9T is made via wiring 9' that connects the plurality of conductors 9.

[0068] In this embodiment, as shown in Figure 10, the display device 1 is provided with an anode terminal 3T that electrically connects multiple anodes 3 contained in multiple light-emitting elements 30. Although not shown in the figure, the electrical connection between the multiple anodes 3 and the anode terminal 3T is made by multiple wires provided individually from the red subpixel RSP, green subpixel GSP, and blue subpixel BSP, respectively.

[0069] The method is not limited to this, and for example, a voltage may be applied to the anode 3 and the conductor 9 using terminal 9T and terminals electrically connected to the source electrodes of each of the multiple thin-film transistors included in the substrate 2.

[0070] Figure 11 is a cross-sectional view showing a schematic configuration of a light-emitting element 30a, which is another example of Embodiment 1 equipped with a conductor 9. Figure 12 is a cross-sectional view showing a schematic configuration of a light-emitting element 30b, which is yet another example of Embodiment 1 equipped with a conductor 9.

[0071] The light-emitting element 30 shown in Figure 6 is manufactured by forming a bank 4 after forming an anode 3, but the light-emitting element 30a shown in Figure 11 differs from the light-emitting element 30 shown in Figure 6 in that it is manufactured by forming an anode 3 after forming a bank 4. In the manufacturing process of the light-emitting element 30 shown in Figure 6, a different process, namely the process of forming a bank 4 which requires movement to another device, is included between the process of forming the anode 3 and the process of forming the hole transport layer 5. On the other hand, in the manufacturing process of the light-emitting element 30a shown in Figure 11, after the process of forming the bank 4 is performed first, layers such as the anode 3 and the hole transport layer 5 can be formed sequentially while switching the ink and the head of the inkjet device, so movement to another device is unnecessary, and the possibility of moisture intrusion and surface contamination that may occur when moving to another device can be suppressed. With such a light-emitting element 30a, it is possible to suppress a large decrease in brightness during use of the light-emitting element 30a and the display device 1 including the light-emitting element 30a, so a light-emitting element 30a with stable element characteristics and a display device 1 equipped with a light-emitting element 30a with stable element characteristics can be realized.

[0072] Furthermore, the light-emitting element 30 shown in Figure 6, described above, is equipped with an insulating layer 10 to electrically isolate the conductor 9 from the light-emitting layer 6, the electron transport layer 7, and the cathode 8, respectively. However, the light-emitting element 30b shown in Figure 12 differs from the light-emitting element 30 shown in Figure 6 in that it does not have an insulating layer 10. In cases where the conductor 9 can be electrically isolated structurally from the light-emitting layer 6, the electron transport layer 7, and the cathode 8, as in the light-emitting element 30b shown in Figure 12, the insulating layer 10 can be appropriately omitted. With such a light-emitting element 30b, it is possible to suppress a large decrease in brightness during use of the light-emitting element 30b and the display device 1 including the light-emitting element 30b, thereby realizing a light-emitting element 30b with stable element characteristics and a display device 1 equipped with a light-emitting element 30b with stable element characteristics.

[0073] Figure 13 shows an example of the material constituting the light-emitting layer 6 provided in the light-emitting element of Embodiment 1. Figure 14 shows another example of the material constituting the light-emitting layer 6 provided in the light-emitting element of Embodiment 1. Figure 15 shows yet another example of the material constituting the light-emitting layer 6 provided in the light-emitting element of Embodiment 1.

[0074] The light-emitting layer 6 provided in the light-emitting element of Embodiment 1 may include an adduct AD surrounding at least one quantum dot BQD, as shown in Figures 13 and 14, or a matrix MR as an adduct filling the space between at least two quantum dot BQDs, as shown in Figure 15. The adduct AD or the matrix MR as an adduct may have properties such as semiconductor or insulator. The adduct AD or the matrix MR as an adduct may include any of metal oxides, metalloid oxides, and metal sulfides. As shown in Figures 13, 14, and 15, the quantum dot BQD includes a core BQDC and a shell BQDS.

[0075] The adduct AD or matrix MR as an adduct is, for example, silicon oxide (SiO₂) ２ ), titanium oxide (TiO ２ ), aluminum oxide (Al ２ O ３ ), boron oxide (B ２ O３ ), phosphorus oxide (P ２ O ５ ), germanium oxide (GeO ２ ), hafnium oxide (HfO ２ ), zinc oxide (ZnO), zirconium oxide (ZrO ２ ), tellurium oxide (TeO ２ ), bismuth oxide (Bi ２ O ３ ), vanadium oxide (V ２ O ５ ), antimony oxide (Sb ２ O ５ It may also contain at least one of the following: ), lead oxide (PbO), and copper oxide (CuO). Here, the adduct AD or matrix MR as an adduct may be formed as a polymer. For example, if the adduct AD or matrix MR as an adduct contains silicon oxide as an oxide, it may also be a siloxane compound having siloxane bonds. Furthermore, the adduct AD or matrix MR as an adduct may contain, for example, zinc sulfide (ZnS) and magnesium zinc sulfide (ZnMgS, ZnMgS ２ ) may contain at least one of the following. Note that the chemical formula of the compound is a representative example, and the composition ratio indicated in the chemical formula may or may not be stoichiometric.

[0076] As shown in Figures 13 and 14, in the case where the adduct AD surrounds at least one quantum dot BQD, if the adduct AD occupies more than 90% of the periphery of the quantum dot BQD in the cross-section of the light-emitting layer 6 passing through the quantum dot BQD, then the quantum dot BQD may be considered to be covered by the adduct AD. The adduct AD is, for example, mainly composed of silicon oxide and may be arranged in contact with the surface of the quantum dot BQD, or with an organic ligand OL between the adduct AD and the quantum dot BQD.

[0077] As shown in Figure 15, when the matrix MR as an adduct is formed to fill the space between at least two quantum dots BQD, the matrix MR as an adduct has a thickness of 1000 nm in a direction perpendicular to the film thickness direction at any position in the film thickness direction of the light-emitting layer 6. ２ It may be formed as a continuous film having the above area. In addition, in the light-emitting layer 6, the quantum dots BQD may be embedded in a continuous film of matrix MR as an adduct. For example, if 60% or more of the surface of 80% or more of the quantum dots BQD constituting the light-emitting layer 6 is in contact with a continuous film of matrix MR as an adduct, then the quantum dots BQD contained in the light-emitting layer 6 can be said to be embedded in matrix MR as an adduct. Furthermore, when we say that matrix MR as an adduct fills the space between at least two quantum dots BQD, the space between the two quantum dots BQD may be filled only with matrix MR as an adduct, or it may be filled with matrix MR as an adduct and other materials. In addition to matrix MR as an adduct, a material such as a ligand different from matrix MR as an adduct may be included between the two quantum dots BQD. The material such as ligand may be an organic ligand that coordinates to the quantum dots BQD, or it may be an organic ligand that is separated from the quantum dots BQD. If the light-emitting layer 6 contains an organic ligand, for example, the weight ratio of the organic ligand to the total weight of the light-emitting layer 6 may be less than 5%. The weight ratio of the organic ligand can be measured, for example, using TOF-SIMS (time-of-flight secondary ion mass spectrometry). If the organic ligand is dispersed in the light-emitting layer 6, the organic ligand may contribute to the injection of holes and electrons into the quantum dot BQD.

[0078] In forming the light-emitting layer 6, first, a quantum dot dispersion is prepared. The quantum dot dispersion is a dispersion in which quantum dots BQD and a precursor of adduct AD or a precursor of matrix MR as an adduct are dispersed in a solvent. The precursor includes a material that is converted to adduct AD or matrix MR as an adduct through hydrolysis and dehydration condensation by performing a specific operation such as heating or light irradiation. The precursor may have a coordinating functional group that forms a coordination bond with the surface of the quantum dot BQD in the quantum dot dispersion. In this case, the precursor may coordinate to the quantum dot BQD in the quantum dot dispersion. The quantum dot dispersion may also contain a halide having a halogen atom (for example, zinc chloride (ZnCl)). ２ The material may also contain halogen atoms. By mixing a material having halogen atoms into the quantum dot dispersion, the halogen atoms can coat the surface of the quantum dot BQD independently of the adduct or the matrix MR as an adduct, thereby reducing defects on the surface of the quantum dot BQD. Therefore, by having halogen atoms in the adduct AD or the matrix MR as an adduct, each light-emitting device increases the coverage of the quantum dot BQD in the light-emitting layer 6, thereby improving the light-emitting properties.

[0079] A quantum dot dispersion may be prepared, for example, by stirring a dispersion containing quantum dots BQD and a dispersion containing a precursor to prepare a mixture, and then extracting a predetermined layer from the mixture. Here, the dispersion containing quantum dots BQD may contain an organic ligand that coordinates to the quantum dots BQD. In this case, for example, during the stirring for the preparation of the mixture, the ligand that coordinates to the quantum dots BQD may be replaced from the organic ligand with a part of a precursor such as 3-(mercaptopropyl)trimethoxysilane (MPS).

[0080] For example, if the adduct AD or the matrix MR as an adduct contains silicon oxide and the precursor has a coordination functional group, the precursor may contain 3-(trimethoxysilyl-1-propanechiol (TMSPT)). Also, if the adduct AD or the matrix MR as an adduct contains silicon oxide and the precursor does not have a coordination functional group, the precursor may contain diphenylsilanediol (DPSD). Furthermore, barium hydroxide (Ba(OH)) may be used as a catalyst. ２ ) may also be included. Furthermore, for example, if the adduct AD or the matrix MR as an adduct contains zinc sulfide, the precursor may also contain zinc xanthogenic acid, zinc thioureate, and zinc dithiocarboxylate, etc.

[0081] Next, the quantum dot dispersion is coated onto the lower layer of the light-emitting layer 6 to convert the precursor into an adduct AD or a matrix MR as an adduct. The conversion of the precursor into an adduct AD or a matrix MR as an adduct is carried out, for example, by heating the coated quantum dot dispersion to volatilize the solvent and convert the precursor into an adduct AD or a matrix MR as an adduct. For example, if the precursor contains diphenylsilanediol (DPSD) and 3-(trimethoxysilyl-1-propanediol (TMSPT), barium hydroxide (Ba(OH)) is used between diphenylsilanediol (DPSD) molecules, between 3-(trimethoxysilyl-1-propanediol (TMSPT) molecules, and between diphenylsilanediol (DPSD) and 3-(trimethoxysilyl-1-propanediol (TMSPT) molecules. ２ Dehydration condensation occurs using catalysts such as , thereby forming silicon oxide as adduct AD or matrix MR as an adduct. Alternatively, for example, if the precursor contains zinc xanthogenic acid, the zinc xanthogenic acid is decomposed to form zinc sulfide as adduct AD or matrix MR as an adduct. The conversion of the precursor to adduct AD or matrix MR as an adduct occurs sequentially around the quantum dots BQD in the quantum dot dispersion. By this method, a light-emitting layer 6 having adduct AD or matrix MR as an adduct can be formed.

[0082] As described above, in this embodiment, light-emitting elements 30, 30a, and 30b, each equipped with two electrically connected conductors 9, have been described as an example, but the embodiment is not limited thereto. For example, the first conductor 9a and the second conductor 9b provided in the light-emitting elements 30d, 30e, and 30f described later in Embodiment 3, a light-emitting element that is a modified version of the light-emitting element 30f, and the light-emitting element 30g described later in Embodiment 4 may be electrically connected.

[0083] [Embodiment 2] The light-emitting element 30c of this embodiment differs from the light-emitting elements 30, 30a, and 30b of Embodiment 1, which have two electrically connected conductors 9, in that it comprises an electrically isolated first conductor 9a and a second conductor 9b.

[0084] Figure 16 is a schematic cross-sectional view showing the configuration of an element-emitting element 30c of Embodiment 2, which comprises a first conductor 9a and a second conductor 9b. Figure 17 is a diagram showing an example of aging a hole transport layer 5 containing an organic hole transport material using the first conductor 9a and the second conductor 9b provided in the element-emitting element 30c of Embodiment 2 shown in Figure 16. Figure 18 is a plan view showing the schematic configuration of a display device 1a, which comprises a first terminal 9aT that electrically connects a plurality of first conductors 9a included in a plurality of element-emitting elements 30c of Embodiment 2, and a second terminal 9bT that electrically connects a plurality of second conductors 9b included in a plurality of element-emitting elements 30c of Embodiment 2.

[0085] As shown in Figure 16, the light-emitting element 30c comprises an electrically isolated first conductor 9a and a second conductor 9b.

[0086] As shown in Figure 16, it is preferable that the first contact portion where the first conductor 9a and the hole transport layer 5 are in contact, and the second contact portion where the second conductor 9b and the hole transport layer 5 are in contact, are separated by a distance greater than or equal to the distance between the two opposing ends of the light-emitting layer 6, that is, the distance between the right end and the left end of the light-emitting layer 6 in the figure.

[0087] As shown in Figure 17, the light-emitting element 30c comprises a substrate 2, an anode 3 which is a lower electrode located near the substrate 2, a cathode 8 which is an upper electrode located on the opposite side of the substrate 2 from the anode 3, a light-emitting layer 6 provided between the anode 3 and the cathode 8, and a hole transport layer 5 provided between the anode 3 and the light-emitting layer 6. In this embodiment, as an aging method for the hole transport layer 5, the hole transport layer 5 is aged by applying a voltage to the hole transport layer 5 using a first conductor 9a in contact with the hole transport layer 5 and a second conductor 9b in contact with the hole transport layer 5 and electrically isolated from the first conductor 9a. Except for the fact that the hole transport layer 5 is aged by applying a voltage to the hole transport layer 5 using the first conductor 9a and the second conductor 9b, this is the same as the aging method for the hole transport layer 5 in Embodiment 1 described above, so a detailed explanation is omitted.

[0088] As shown in Figure 18, the display device 1a has a plurality of light-emitting elements 30c, and includes a first terminal 9aT that electrically connects a plurality of first conductors 9a contained in the plurality of light-emitting elements 30c, and a second terminal 9bT that electrically connects a plurality of second conductors 9b contained in the plurality of light-emitting elements 30c. The first terminal 9aT and the second terminal 9bT are provided in a region that does not obstruct the light emitted from the plurality of light-emitting elements 30c, for example, in the frame region NDA. The electrical connection between the plurality of first conductors 9a and the first terminal 9aT is made via wiring 9a' connecting the plurality of first conductors 9a, and the electrical connection between the plurality of second conductors 9b and the second terminal 9bT is made via wiring 9b' connecting the plurality of second conductors 9b. Furthermore, the multiple first conductors 9a, the first terminal 9aT, and the wiring 9a' connecting the multiple first conductors 9a are electrically isolated from the multiple second conductors 9b, the second terminal 9bT, and the wiring 9b' connecting the multiple second conductors 9b. In the display device 1a shown in Figure 18, the first terminal 9aT and the second terminal 9bT are provided on one side (the upper side in the figure) of the frame area NDA of the display device 1a, as an example, but the explanation is not limited to this. For example, the first terminal 9aT can be placed above the frame area NDA of the display device 1a, and the second terminal 9bT can be placed below the frame area NDA of the display device. In this case, the first terminal 9aT and the second terminal 9bT can be formed on the same plane without overlapping in a plan view.

[0089] As described above, the light-emitting element 30c can suppress a significant decrease in brightness during use of the light-emitting element 30c and the display device 1a including the light-emitting element 30c, thereby enabling the realization of a light-emitting element 30 with stable element characteristics and a display device 1a equipped with a light-emitting element 30 with stable element characteristics.

[0090] Furthermore, according to the aging method of the hole transport layer 5 described above, a light-emitting element 30c with stable element characteristics can be obtained.

[0091] [Embodiment 3] Figure 19 is a cross-sectional view showing a schematic configuration of a light-emitting element 30d of Embodiment 3, in which a portion of the first conductor 9a and the second conductor 9b are located inside the bank. Figure 20 is a cross-sectional view showing a schematic configuration of a light-emitting element 30e, which is another example of Embodiment 3, in which the first conductor 9a and the second conductor 9b are located inside the bank. Figure 21 is a cross-sectional view showing a schematic configuration of a light-emitting element 30f, yet another example of Embodiment 3, in which the first conductor 9a and the second conductor 9b are located inside the bank. Figure 22 is a cross-sectional view showing a schematic configuration of a light-emitting element that is a modified example of the light-emitting element 30f, which is yet another example of Embodiment 3 shown in Figure 21.

[0092] The light-emitting elements 30d, 30e, and 30f of this embodiment, shown in Figures 19, 20, and 21, are equipped with a bank provided so as to be in contact with at least a portion of the end of the anode 3, and at least a portion of each of the first conductor 9a and the second conductor 9b is located inside the bank, which differs from the light-emitting elements 30, 30a, 30b, and 30c described above in Embodiments 1 and 2. In addition, in the light-emitting elements 30d, 30e, and 30f, the bank is composed of a lower bank 4b and an upper bank 4t.

[0093] On the other hand, in the light-emitting element which is a modified example of the light-emitting element 30f of this embodiment shown in Figure 22, the bank 4 is not divided into a lower bank 4b and an upper bank 4t, and is not in contact with at least a part of the end of the anode 3, but the first conductor 9a and the second conductor 9b are each located inside the bank 4.

[0094] Furthermore, as shown in Figures 19, 20, 21, and 22, it is preferable that the first contact portion where the first conductor 9a and the hole transport layer 5 are in contact, and the second contact portion where the second conductor 9b and the hole transport layer 5 are in contact, are separated by a distance greater than or equal to the distance between the two opposing ends of the light-emitting layer 6, that is, the distance between the right end and the left end of the light-emitting layer 6 in the figures.

[0095] The light-emitting element 30d shown in Figure 19 can be manufactured by performing the following steps in this order: forming a lower bank 4b, forming an anode 3, forming a hole transport layer 5 on the anode 3 and on a part of the lower bank 4b, forming a first conductor 9a and a second conductor 9b on the hole transport layer 5, forming an insulating layer 10 on the first conductor 9a and the second conductor 9b to electrically separate the first conductor 9a and the second conductor 9b from the light-emitting layer 6, forming an upper bank 4t such that a part of each of the first conductor 9a and the second conductor 9b is located inside the upper bank 4t, forming a light-emitting layer 6 on the hole transport layer 5, forming an electron transport layer 7 on the light-emitting layer 6, and forming a cathode 8 on the electron transport layer 7. In the case of the light-emitting element 30d, since the first conductor 9a and the second conductor 9b can be formed on the plane of the hole transport layer 5, the bonding between each of the first conductor 9a and the second conductor 9b and the hole transport layer 5 can be more reliably achieved.

[0096] The light-emitting element 30e shown in Figure 20 can be manufactured by performing the following steps in this order: forming a lower bank 4b, forming an anode 3, forming a first conductor 9a and a second conductor 9b on a part of the lower bank 4b, forming an upper bank 4t such that the first conductor 9a and the second conductor 9b can contact the hole transport layer 5 which is formed later and is located inside the upper bank 4t, forming a hole transport layer 5 on the anode 3, forming a light-emitting layer 6 on the hole transport layer 5, forming an electron transport layer 7 on the light-emitting layer 6, and forming a cathode 8 on the electron transport layer 7. In the case of the light-emitting element 30e, since the first conductor 9a and the second conductor 9b can be formed on the plane of the lower bank 4b, the bonding between the first conductor 9a and the second conductor 9b and the hole transport layer 5 can be more reliably achieved. In addition, the light-emitting element 30e has the advantage that it does not require the use of an insulating layer 10.

[0097] The light-emitting element 30f shown in Figure 21 can be manufactured by performing the following steps in this order: forming a lower bank 4b, forming an anode 3, forming a hole transport layer 5 on the anode 3 and on a part of the lower bank 4b, forming a first conductor 9a and a second conductor 9b on the hole transport layer 5, forming an upper bank 4t such that the first conductor 9a and the second conductor 9b are each located inside the upper bank 4t, forming a light-emitting layer 6 on the hole transport layer 5, forming an electron transport layer 7 on the light-emitting layer 6, and forming a cathode 8 on the electron transport layer 7. In the case of the light-emitting element 30f, since the first conductor 9a and the second conductor 9b can be formed on the plane of the hole transport layer 5, the bonding between the first conductor 9a and the second conductor 9b and the hole transport layer 5 can be achieved more reliably. In addition, the light-emitting element 30f has the advantage that it does not require the use of an insulating layer 10.

[0098] A modified light-emitting element, which is a modified light-emitting element 30f shown in Figure 22, can be manufactured by performing the following steps in this order: forming an anode 3; forming a hole transport layer 5 so as to cover the anode 3; forming a first conductor 9a and a second conductor 9b on the hole transport layer 5; forming a bank 4 such that the first conductor 9a and the second conductor 9b are each located inside the bank 4; forming a light-emitting layer 6 on the hole transport layer 5; forming an electron transport layer 7 on the light-emitting layer 6; and forming a cathode 8 on the electron transport layer 7. In the case of a modified light-emitting element, which is a modified light-emitting element 30f shown in Figure 22, the first conductor 9a and the second conductor 9b can be formed on the plane of the hole transport layer 5, thus more reliably achieving bonding between the first conductor 9a and the second conductor 9b and the hole transport layer 5. Furthermore, in the case of a modified light-emitting element, which is a modified light-emitting element 30f shown in Figure 22, there is the advantage that there is no need to use an insulating layer 10, and the advantage that the bank 4 can be formed in a single step without dividing it into a lower bank 4b and an upper bank 4t.

[0099] With the above-described light-emitting elements 30d, 30e, 30f and the light-emitting element that is a modified version of the light-emitting element 30f, it is possible to suppress a significant decrease in brightness during use of the light-emitting element or the display device containing the light-emitting element, thereby enabling the realization of a light-emitting element with stable element characteristics and a display device equipped with a light-emitting element with stable element characteristics.

[0100] [Embodiment 4] The light-emitting element 30g of this embodiment differs from the light-emitting elements 30, 30a, 30b, 30c, 30d, 30e, 30f and the modified light-emitting element 30f described above in Embodiments 1 to 3, in that the first conductor 9a and the second conductor 9b are each provided on the same plane as the anode 3.

[0101] Figure 23 is a cross-sectional view showing a schematic configuration of the light-emitting element 30g of Embodiment 4, in which the first conductor 9a and the second conductor 9b are arranged on the same plane as the anode 3.

[0102] As shown in Figure 23, it is preferable that the first contact portion CON1, where the first conductor 9a and the hole transport layer 5 are in contact, and the second contact portion CON2, where the second conductor 9b and the hole transport layer 5 are in contact, are separated by a distance DIS or greater from the two opposing ends of the light-emitting layer 6, that is, the distance between the right end and the left end of the light-emitting layer 6 in the figure.

[0103] The light-emitting element 30g shown in Figure 23 can be manufactured by performing the following steps in this order: forming an anode 3; forming a first conductor 9a and a second conductor 9b electrically separated from the anode 3; forming a hole transport layer 5 on the first conductor 9a, the second conductor 9b, and the anode 3, respectively; forming a bank 4 so as to overlap a part of the hole transport layer 5, the first conductor 9a, and the second conductor 9b in a plan view; forming a light-emitting layer 6 on the hole transport layer 5; forming an electron transport layer 7 on the light-emitting layer 6; and forming a cathode 8 on the electron transport layer 7. In this embodiment, the case in which the first conductor 9a and the second conductor 9b are formed after the anode 3 is described as an example, but the invention is not limited to this, and the anode 3 may be formed after the first conductor 9a and the second conductor 9b. In the case of the light-emitting element 30g, the first conductor 9a and the second conductor 9b can be formed on the plane of the substrate 2, thus more reliably achieving bonding between the first conductor 9a and the second conductor 9b and the hole transport layer 5. Furthermore, the light-emitting element 30g shown in Figure 23 has the advantage of not requiring the use of an insulating layer 10, and the advantage of being able to form the bank 4 in a single process without dividing it into a lower bank 4b and an upper bank 4t.

[0104] According to the above-described light-emitting element 30g, a significant decrease in brightness can be suppressed during use of the light-emitting element or a display device containing the light-emitting element, thereby enabling the realization of a light-emitting element with stable element characteristics and a display device equipped with a light-emitting element with stable element characteristics.

[0105] [Additional Notes] This disclosure is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of this disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0106] This disclosure can be used in light-emitting devices, light-emitting devices, and methods for aging hole transport layers.

[0107] 1, 1a Display device 2 Substrate 3 Anode 3T Anode terminal 4 Bank 4b Lower bank 4t Upper bank 5 Hole transport layer 6 Light-emitting layer 7 Electron transport layer 8 Cathode 9 Conductor 9' Wiring for electrically connecting conductors 9T Terminal 9a First conductor 9a' Wiring for electrically connecting the first conductor 9aT First terminal 9b Second conductor 9b' Wiring for electrically connecting the second conductor 9bT Second terminal 10 Insulating layer 30, 30a-30g Light-emitting element 50 Power supply 51 High-potential side terminal 52 Low-potential side terminal 53 Current measurement unit CON1 First contact part CON2 Second contact part DIS Distance between two opposing ends of the light-emitting layer BQD Quantum dot BQDC Quantum dot core BQDS Quantum dot shell AD Adductor OL Organic ligand MR Matrix PIX Pixel RSP Red subpixel GSP Green subpixel BSP Blue subpixel DA Display area NDA Border area

Claims

1. A light-emitting element comprising: a substrate; an anode which is a lower electrode provided near the substrate; a cathode which is an upper electrode provided on the opposite side of the substrate from the anode; a light-emitting layer provided between the anode and the cathode; a hole transport layer provided between the anode and the light-emitting layer; and one or more conductors in contact with the hole transport layer.

2. The light-emitting element according to claim 1, wherein the conductor is electrically isolated from the anode.

3. The light-emitting element according to claim 1 or 2, wherein the conductor is an aging electrode used for aging the hole transport layer.

4. The light-emitting element according to any one of claims 1 to 3, wherein the anode is electrically connected to a drive circuit included in the substrate.

5. The light-emitting element according to any one of claims 1 to 4, comprising a bank provided so as to be in contact with at least a portion of the end of the anode, wherein at least a portion of the conductor is located on the bank.

6. The light-emitting element according to any one of claims 1 to 4, comprising a bank provided so as to be in contact with at least a portion of the end of the anode, wherein at least a portion of the conductor is located inside the bank.

7. The light-emitting element according to claim 5 or 6, wherein the bank includes a first bank in contact with the first end of the anode and a second bank in contact with the second end of the anode facing the first end, and at least a portion of the anode is provided between the first bank and the second bank.

8. The light-emitting element according to claim 5 or 6, wherein the bank is formed in a frame shape so as to surround the anode in a plan view.

9. The light-emitting element according to any one of claims 5 to 8, wherein the bank has an inclined surface in contact with the anode, and the hole transport layer extends on the inclined surface.

10. The light-emitting element according to any one of claims 1 to 9, wherein the conductor is electrically isolated from the light-emitting layer.

11. The light-emitting element according to any one of claims 1 to 9, wherein the conductor is electrically isolated from the cathode.

12. The light-emitting element according to any one of claims 1 to 9, wherein an electron transport layer or an electron injection layer is provided between the cathode and the light-emitting layer, and the conductor is electrically isolated from the electron transport layer or the electron injection layer.

13. The light-emitting element according to any one of claims 1 to 12, wherein the conductor is provided as one, and the conductor is electrically isolated from the anode.

14. The light-emitting element according to any one of claims 1 to 12, wherein the conductor comprises two, and one of the two conductors, the first conductor, and the other of the two conductors, the second conductor, are electrically isolated.

15. The light-emitting element according to claim 14, wherein the first contact portion where the first conductor and the hole transport layer are in contact and the second contact portion where the second conductor and the hole transport layer are in contact are separated by a distance greater than or equal to the distance between two opposing ends of the light-emitting layer.

16. The light-emitting element according to any one of claims 1 to 15, wherein the light-emitting layer includes a plurality of quantum dots.

17. The light-emitting element according to claim 16, wherein an adduct exists around the quantum dot in the light-emitting layer.

18. The light-emitting element according to claim 17, wherein the adduct fills the space between at least two of the quantum dots, and the adduct contains a ligand.

19. A light-emitting device having a plurality of light-emitting elements according to any one of claims 1 to 18, and comprising terminals for electrically connecting a plurality of conductors included in the plurality of light-emitting elements, wherein the terminals are provided in a region that does not obstruct the light emitted from the plurality of light-emitting elements.

20. A method for aging a hole transport layer, comprising: a substrate; an anode which is a lower electrode provided near the substrate; a cathode which is an upper electrode provided on the opposite side of the substrate from the anode; a light-emitting layer provided between the anode and the cathode; a hole transport layer provided between the anode and the light-emitting layer; a first conductor in contact with the hole transport layer; and a second conductor in contact with the hole functional layer including the hole transport layer and electrically isolated from the first conductor, wherein a voltage is applied to the hole transport layer using the first conductor and the second conductor.

21. The method for aging a hole transport layer according to claim 20, wherein, when the current value flowing between the first conductor and the second conductor is I (mA), a voltage is applied to the hole transport layer for a period of 4 / I (minutes).

22. The method for aging a hole transport layer according to claim 20 or 21, wherein the high-potential terminal of a power supply device, which includes a high-potential terminal on which a high-potential power supply voltage is output and a low-potential terminal on which a low-potential power supply voltage is output, is electrically connected to one of the first conductor and the second conductor, and the low-potential terminal of the power supply device is electrically connected to the other of the first conductor and the second conductor.

23. A method for aging a hole transport layer according to any one of claims 20 to 22, wherein a voltage is applied to the hole transport layer until the current value I flowing through the hole transport layer exhibits electrical characteristics proportional to the value of the voltage V applied to the hole transport layer raised to the power of m (1.8 ≤ m ≤ 2.2).

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