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

Abstract

A light-emitting element (30) includes: a substrate (2); a cathode (3) that is a lower electrode provided at a position near the substrate (2); an anode (8) that is an upper electrode provided sandwiching the cathode (3) on the opposite side from the substrate (2); a light-emitting layer (6) that is provided between the cathode (3) and the anode (8); an electron hole transport layer (7) that is provided between the light-emitting layer (6) and the anode (8); and one or more conductors (9) that are in contact with the electron hole transport layer (7).

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, a cathode which is a lower electrode provided near the substrate, an anode which is an upper electrode provided on the opposite side of the substrate from the cathode, a light-emitting layer provided between the cathode and the anode, a hole transport layer provided between the light-emitting layer and the anode, 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] The hole transport layer aging method of the present disclosure, in order to solve the above problems, comprises a substrate, a cathode which is a lower electrode provided near the substrate, an anode which is an upper electrode provided on the opposite side of the substrate with respect to the cathode, a light-emitting layer provided between the cathode and the anode, a hole transport layer provided between the light-emitting layer and the anode, 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 6 illustrates a schematic cross-sectional view showing the 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 illustrates a part of the manufacturing process of the light-emitting element of Embodiment 1 shown in Figure 6. This figure shows the remaining part of the manufacturing process for the light-emitting element of Embodiment 1 shown in Figure 6. This is a plan view showing the 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 shown in Figure 6. This figure shows an example of aging a hole transport layer containing an organic hole transport material using a conductor and an anode in a light-emitting device including a plurality of light-emitting elements of Embodiment 1 shown in Figure 6. This is a cross-sectional view showing the schematic configuration of a light-emitting element, which is another example of Embodiment 1 equipped with a conductor. This figure shows an example of the materials constituting the light-emitting layer provided in the light-emitting element of Embodiment 1. This figure shows another example of the materials constituting the light-emitting layer provided in the light-emitting element of Embodiment 1. This figure shows yet another example of the materials constituting the light-emitting layer provided in the light-emitting element of Embodiment 1. This is a cross-sectional view showing the schematic configuration of a light-emitting element of Embodiment 2 equipped with a first conductor and a second conductor. This figure shows an example of aging a hole transport layer containing an organic hole transport material using the first conductor and the second conductor provided in the light-emitting element of Embodiment 2 shown in Figure 17.Figure 17 shows an example of aging a hole transport layer containing an organic hole transport material using a first conductor and a second conductor in a light-emitting device including 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. This is a cross-sectional view showing the schematic configuration of another example of a light-emitting element of Embodiment 3. This is a cross-sectional view showing the schematic configuration of a light-emitting element of Embodiment 4. This is a cross-sectional view showing the schematic configuration of a light-emitting element of Embodiment 5. This is a cross-sectional view showing the schematic configuration of a light-emitting element of Embodiment 6.

[0012] The embodiments of this disclosure will be described below with reference to Figures 1 to 24. 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 coefficients of the reactions involved in 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 application, referring to the lower figure, which is an enlarged view of Figure 1, particularly the first 0.5 hours, 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, the rate of change changes to a constant level, indicating a constant degradation rate. The degradation up to approximately 0.2 hours indicates that the reaction coefficients of the corresponding degradation mechanisms are 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 7 containing an organic hole transport material using an anode 8 and a conductor 9 provided in a light-emitting element 30, the electrical characteristics (V-I characteristics) of the hole transport layer 7 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 7 containing an organic hole transport material are described as hopping conduction if the current I flowing through the hole transport layer 7 containing the organic hole transport material is proportional to the value of the voltage V applied to the hole transport layer 7 to the power of m (3.0 ≤ m). The electrical properties of a hole transport layer 7 containing an organic hole transport material are described as space charge limited current conduction if the current I flowing through the hole transport layer 7 containing the organic hole transport material is proportional to the value of the voltage V applied to the hole transport layer 7 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 7, 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 reduced 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, due to the sufficient reduction of the defect levels, holes are transported at the original 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, the 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 a direction that blocks the 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 where 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 been sufficiently reduced 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 7 including the organic hole transport material, a method is used in which the aging of the hole transport layer 7 is performed until the current value I flowing through the hole transport layer 7 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 7. However, it is not limited to this, and the hole transport layer 7 including the organic hole transport material only needs to 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 provided with the conductor 9.

[0024] As shown in Figure 6, the light-emitting element 30 includes a substrate 2, a cathode 3 which is a lower electrode located near the substrate 2, an anode 8 which is an upper electrode located on the opposite side of the substrate 2 from the cathode 3, a light-emitting layer 6 provided between the cathode 3 and the anode 8, a hole transport layer 7 provided between the light-emitting layer 6 and the anode 8, and one or more conductors 9 in contact with the hole transport layer 7. 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 7, and the case in which the two conductors 9 are electrically connected will be described as an example. As shown in Figure 6, a part of one of the two conductors 9 overlaps with the outer peripheral portion 7S of the hole transport layer 7, which is the part near the left end of the hole transport layer 7 in a plan view, and a part of the other of the two conductors 9 overlaps with the outer peripheral portion 7S of the hole transport layer 7, which is the part near the right end of the hole transport layer 7 in a plan view. However, this is not limited to this, and for example, one of the conductors 9 superimposed on the outer peripheral portion 7S of the hole transport layer 7, which is the portion near the left end of the hole transport layer 7 in a plan view, and the conductor 9 superimposed on the outer peripheral portion 7S of the hole transport layer 7, which is the portion near the right end of the hole transport layer 7 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. Note that the conductor 9 is an aging electrode used when applying voltage to the hole transport layer 7 to promote aging.

[0025] Furthermore, there may be multiple conductors 9 that overlap with the outer periphery 7S of the hole transport layer 7, which is the portion near the left end of the hole transport layer 7 in a plan view, and multiple conductors 9 that overlap with the outer periphery 7S of the hole transport layer 7, which is the portion near the right end of the hole transport layer 7 in a plan view. For example, one of the multiple conductors 9 that overlap with the outer periphery 7S of the hole transport layer 7, which is the portion near the left end of the hole transport layer 7 in a plan view, and the other of the multiple conductors 9 that overlap with the outer periphery 7S of the hole transport layer 7, which is the portion near the right end of the hole transport layer 7 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. Furthermore, in a plan view, a plurality of conductors 9 may be provided corresponding to the position between two adjacent conductors 9 of the outer periphery 7S of the hole transport layer 7, which is the portion near the left end of the hole transport layer 7, and the plurality of conductors 9 that are the portion near the right end of the hole transport layer 7, which is the portion near the right end of the hole transport layer 7, in a plan view.

[0026] In this embodiment, an example was described in which one conductor 9 overlaps with the outer peripheral portion 7S of the hole transport layer 7, which is the portion near the left end of the hole transport layer 7 in a plan view, and another conductor 9 overlaps with the outer peripheral portion 7S of the hole transport layer 7, which is the portion near the right end of the hole transport layer 7 in a plan view. However, the embodiment is not limited to this, and the number of conductors 9 overlapping with the outer peripheral portion 7S of the hole transport layer 7, which is the portion near the left end of the hole transport layer 7 in a plan view, and the number of conductors 9 overlapping with the outer peripheral portion 7S of the hole transport layer 7, which is the portion near the right end of the hole transport layer 7 in a plan view, may be different. For example, the conductor 9 may consist of only one of the following: a conductor 9 that overlaps with the outer peripheral portion 7S of the hole transport layer 7, which is the portion near the left end of the hole transport layer 7 in a plan view, and a conductor 9 that overlaps with the outer peripheral portion 7S of the hole transport layer 7, which is the portion near the right end of the hole transport layer 7 in a plan view. Alternatively, the conductor 9 may consist of only a plurality of conductors 9 that overlap with the outer peripheral portion 7S of the hole transport layer 7, which is the portion near the left end of the hole transport layer 7 in a plan view, or it may consist of only a plurality of conductors 9 that overlap with the outer peripheral portion 7S of the hole transport layer 7, which is the portion near the right end of the hole transport layer 7 in a plan view.

[0027] Also, in the present embodiment, as an example, the case where the conductor 9 overlaps with the outer peripheral portion 7S of the hole transport layer 7 which is a portion near the left end of the hole transport layer 7 in plan view or the outer peripheral portion 7S of the hole transport layer 7 which is a portion near the right end of the hole transport layer 7 in plan view has been described. However, the present invention is not limited to this. As long as the conductor 9 is in contact with the hole transport layer 7, it may not overlap with either the outer peripheral portion 7S of the hole transport layer 7 which is a portion near the left end of the hole transport layer 7 in plan view or the outer peripheral portion 7S of the hole transport layer 7 which is a portion near the right end of the hole transport layer 7 in plan view. As long as the conductor 9 is in contact with the hole transport layer 7, for example, it may overlap with the central portion 7C of the hole transport layer 7 in plan view. Note that the outer peripheral portion 7S of the hole transport layer 7 only needs to be located outside the central portion 7C. In the present embodiment, the case where the film thickness of the outer peripheral portion 7S is thinner than the film thickness of the central portion 7C is described as an example. However, the present invention is not limited to this. The film thickness of the outer peripheral portion 7S may be the same as the film thickness of the central portion 7C, or the film thickness of the outer peripheral portion 7S may be thicker than the film thickness of the central portion 7C.

[0028] Also, in the present embodiment, the case where a plurality of conductors 9 are electrically connected to each other has been described as an example. However, as long as a voltage can be applied to the hole transport layer 7 using a plurality of conductors 9 and the anode 8, the plurality of conductors 9 do not have to 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 7 by utilizing the potential difference between the anode 8 and the conductor 9 that is electrically separated from the anode 8, at least one conductor 9 may be provided. In order to enhance the aging effect due to the application of the voltage to the hole transport layer 7, it is preferable to provide conductors 9 that contact more different-direction ends of the hole transport layer 7. As a method of providing conductors 9 that contact more different-direction ends of the hole transport layer 7, 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 each of the two opposing ends of the hole transport layer 7 may be provided, or one conductor 9 having a shape that contacts the entire end of the hole transport layer 7 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 cathode 3, and at least a part of the conductor 9 overlaps the bank 4 in a plan view. That is, at least a part of the conductor 9 is located on the bank 4. In the present embodiment, as shown in FIG. 6, the entire conductor 9 overlaps the bank 4 in a plan view. Also, in the present embodiment, as shown in FIG. 6, the conductor 9 and the inclined surface 4K of the bank 4 come into contact more widely, and the adhesion between them can be made stronger.

[0031] In the present embodiment, the bank 4 includes a first bank that contacts a first end that is the left end of the cathode 3 in FIG. 6, and a second bank that contacts a second end that is the right end of the cathode 3 in FIG. that faces the first end. A case where at least a part of the cathode 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 cathode 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] Furthermore, in this embodiment, the case in which the bank 4 has an inclined surface 4K in contact with the hole transport layer 7 is described as an example, but the embodiment is not limited to this.

[0033] As shown in Figure 6, the hole transport layer 7 may include a central portion 7C and an outer peripheral portion 7S located outside the central portion 7C and having a thinner film thickness than the central portion 7C, and the conductor 9 may be in contact with the upper surface of the outer peripheral portion 7S of the hole transport layer 7.

[0034] In the case of the light-emitting element 30 shown in Figure 6, the entire outer periphery 7S of the hole transport layer 7 overlaps with the bank 4 in a plan view, and the conductor 9 is in contact with the outer periphery 7S. When the entire outer periphery 7S of the hole transport layer 7 and the conductor 9 are provided to overlap with the bank 4 in a plan view, as in the light-emitting element 30 shown in Figure 6, the conductor 9 only needs to be made of a conductive material, and may be made of a material that does not transmit visible light or a material that transmits visible light. As shown in Figure 6, the bank 4 provided in the light-emitting element 30 creates a bank formation region between the cathode 3 and the light-emitting layer 6, where the bank 4 is inserted in place of the electron transport layer 5. Since such a bank formation region may be a region where the supply of electrons from the cathode 3 to the light-emitting layer 6 is small, it is preferable to provide a part of the conductor 9 in the region that overlaps with the bank formation region in a plan view, instead of providing the anode 8.

[0035] Furthermore, in this embodiment, as shown in Figure 6, the case in which the film thickness of the outer peripheral portion 7S of the hole transport layer 7 is thinner than the film thickness of the central portion 7C of the hole transport layer 7 is given as an example for explanation, but as mentioned above, it is not limited to this.In addition, as shown in Figure 6, when the film thickness of the outer peripheral portion 7S of the hole transport layer 7 is thinner than the film thickness of the central portion 7C of the hole transport layer 7, the connection between the hole transport layer 7 and the conductor 9 can be easily made by utilizing the outer peripheral portion 7S of the hole transport layer 7 and a part of the conductor 9 that is in contact with the outer peripheral portion 7S, which are located in a region that overlaps with the bank formation region described above in a plan view.In addition, when the film thickness of the outer peripheral portion 7S of the hole transport layer 7 is thinner than the film thickness of the central portion 7C of the hole transport layer 7, as shown in Figure 6, the conductor 9 can also contact the side surface of the hole transport layer 7, so that current can flow not only from the surface of the hole transport layer 7 that is in contact with the conductor 9, but also from the side surface of the hole transport layer 7 that is in contact with the conductor 9. Furthermore, if the thickness of the outer peripheral portion 7S of the hole transport layer 7 is thinner than the thickness of the central portion 7C of the hole transport layer 7, as shown in Figure 6, the step created by the outer peripheral portion 7S and the central portion 7C of the hole transport layer 7 can more reliably avoid contact between the anode 8 and the conductor 9.

[0036] The conductor 9 is preferably electrically isolated from the light-emitting layer 6, preferably electrically isolated from the cathode 3, and preferably electrically isolated from the electron injection layer or electron transport layer 5, which may be provided between the electron transport layer 5 and the cathode 3.

[0037] In this embodiment, electrical isolation between the conductor 9 and the cathode 3, electron transport layer 5, and light-emitting layer 6 is achieved by placing the conductor 9 on the anode 8 side, which is the upper surface of the hole transport layer 7, and placing the cathode 3, electron transport layer 5, and light-emitting layer 6 on the cathode 3 side, which is the lower surface of the hole transport layer 7. Electrical isolation means that they are insulated so that they do not conduct electricity.

[0038] Furthermore, as in this embodiment, when the light-emitting element 30 is equipped with two conductors 9 that are electrically connected to each other, or when it is equipped with one conductor 9, when aging the hole transport layer 7, which is equipped with an organic hole transport material, by applying a voltage to the hole transport layer 7, which is equipped with an organic hole transport material, using the anode 8 and the conductor 9, it is necessary to electrically isolate the conductor 9 from the anode 8. In this embodiment, the electrical isolation between the conductor 9 and the anode 8 is achieved by separating the conductor 9 and the anode 8 by a predetermined distance or more.

[0039] The light-emitting element 30 shown in Figure 6 may be either a top-emission or bottom-emission type. The light-emitting element 30 shown in Figure 6 is an inverted-component light-emitting element in which the anode 8 is positioned above the cathode 3. To make such an inverted-component light-emitting element a top-emission type, the cathode 3 should be formed to reflect visible light and the anode 8 should be formed to transmit visible light. To make such an inverted-component light-emitting element a bottom-emission type, the cathode 3 should be formed to transmit visible light and the anode 8 should be formed to reflect visible light. Configurations that reflect visible light include, for example, using a material with high reflectivity itself, or alternately stacking two or more materials with different reflectivity or refractive indices as thin films, even if the materials have low reflectivity. Configurations that transmit visible light include, for example, using a material with high transmittance itself, or even if the transmittance is low, light transmission can be achieved if it is a thin film.

[0040] The electrode material that reflects visible light is not particularly limited as long as it can reflect visible light and is conductive, but examples include metallic materials such as Al, Mg, Li, and Ag, or alloys of the metallic materials, or laminates of the metallic material and transparent metal oxides (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.), or laminates of the alloy and the transparent metal oxide.

[0041] On the other hand, the electrode material that transmits visible light is not particularly limited as long as it can transmit visible light and is conductive, but examples include transparent metal oxides (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.), thin films made of metal materials such as Al and Ag, or nanowires made of metal materials such as Al and Ag.

[0042] Furthermore, if the light-emitting element 30 is a top-emission type light-emitting element, and for example, if the conductor 9 is also provided inside the bank-forming region described above, it is preferable that the conductor 9 is a thin metal film made of a metal material such as Al or Ag, or a transparent conductive film made of a transparent metal oxide (for example, indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.) that can transmit visible light.

[0043] As shown in Figure 6, in this embodiment, the case in which the light-emitting element 30 is equipped with an electron transport layer 5 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 5 and the cathode 3. Alternatively, the light-emitting element 30 may be equipped with only an electron injection layer between the light-emitting layer 6 and the cathode 3.

[0044] The electron transport material contained in the electron transport layer 5 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.

[0045] 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.

[0046] The organic hole transport material contained in the hole transport layer 7 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 7 was formed by coating a solution containing crosslinkable TFB, but the invention is not limited to this, and the hole transport layer 7 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.

[0047] The light-emitting element 30 shown in Figure 6 may include a hole injection layer (HIL) between the anode 8 and the hole transport layer 7. 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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).

[0052] Figure 7 shows an example of aging a hole transport layer 7 containing an organic hole transport material using the conductor 9 and anode 8 provided in the light-emitting element 30 of Embodiment 1 shown in Figure 6.

[0053] As shown in Figure 7, the light-emitting element 30 comprises a substrate 2, a cathode 3 which is a lower electrode located near the substrate 2, an anode 8 which is an upper electrode located on the opposite side of the substrate 2 from the cathode 3, a light-emitting layer 6 provided between the cathode 3 and the anode 8, and a hole transport layer 7 provided between the light-emitting layer 6 and the anode 8. In this embodiment, as an aging method for the hole transport layer 7, the hole transport layer 7 is aged by applying a voltage to the hole transport layer 7 using a conductor 9 which is a first conductor in contact with the hole transport layer 7, and an anode 8 which is a second conductor in contact with the hole functional layer including the hole transport layer 7 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 7 is described as consisting only of the hole transport layer 7 as an example, but is not limited to this, and may be a layer in which the hole injection layer and the hole transport layer 7 are stacked in this order from the anode 8 side.

[0054] 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 8, 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 7 can be aged by electrically connecting the high-potential side terminal 51 of the power supply unit 50 to the anode 8 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 7 is not polarity-dependent, so it is not limited to this, and the hole transport layer 7 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 8.

[0055] As shown in Figure 7, the power supply device 50 allows for monitoring a constant current value and the change in the voltage value required to supply that constant current. This enables monitoring of the voltage-current relationship of the hole transport layer 7 during aging, i.e., the electrical characteristics of the hole transport layer 7. Therefore, in this embodiment, the aging method for the hole transport layer 7 containing the organic hole transport material is used, which involves aging the hole transport layer 7 until the current value I flowing through the hole transport layer 7 exhibits electrical characteristics proportional to the voltage V applied to the hole transport layer 7 raised to the power of m (1.8 ≤ m ≤ 2.2). However, the method is not limited to this, and the hole transport layer 7 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.

[0056] In addition to the above-described aging method for the hole transport layer 7, which monitors the change in the electrical characteristics of the hole transport layer 7, another aging method for the hole transport layer 7 may be used in which a voltage is applied to the hole transport layer 7 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 8. In this method, the time is measured with a timer at the same time as the voltage is applied to the hole transport layer 7. For example, if the current value flowing between the first conductor, the conductor 9, and the second conductor, the anode 8, 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 7 is stopped. Analyzing the reliability test results of the light-emitting element and calculating the degradation rate, a strong correlation was found 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 7.

[0057] 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 7 containing an organic hole transport material using the conductor 9 and anode 8 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 7 containing the organic hole transport material has not been aged.

[0058] The inventors of this disclosure have found that by aging the hole transport layer 7 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 7 containing the organic hole transport material are changed from hopping conduction to approach 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 7 containing the organic hole transport material, as shown in Figure 7, using the conductor 9 and anode 8 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 7 containing the organic hole transport material.

[0059] 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.

[0060] Furthermore, by using the aging method for the hole transport layer 7 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.

[0061] Figure 9 is a diagram showing the manufacturing process of the light-emitting element 30 of Embodiment 1 shown in Figure 6. Figure 10 is a diagram showing the manufacturing process of the light-emitting element 30 of Embodiment 1 shown in Figure 6.

[0062] The light-emitting element 30 shown in Figure 6 can be manufactured, for example, using a manufacturing process that includes the manufacturing process for the light-emitting element 30 shown in Figure 9 and the manufacturing process for the light-emitting element 30 shown in Figure 10. 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 conventional materials. First, a cathode 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 around the cathode 3 in a plan view. The bank 4 can be formed, for example, by coating an organic material such as polyimide or acrylic and then patterning it by photolithography. Next, an electron transport layer 5 containing an electron transport material was formed on the cathode 3. In the process of forming the electron transport layer 5 containing the electron transport material, the electron transport layer 5 containing the electron transport material was formed by coating or printing with ink a colloidal solution in which oxide particles containing Zn and Mg, for example, ZnMgO nanoparticles, were dispersed. Then, similarly, a light-emitting layer 6 was formed on the electron transport layer 5 by coating or printing with ink a colloidal solution in which quantum dots were dispersed. Then, by applying a solution containing crosslinkable TFB, the lower part 7b of the hole transport layer 7, for example, having a thickness of about 5 nm, was formed on the light-emitting layer 6.

[0063] Subsequently, a process is performed to form a first resist layer RS1 on the outer peripheral portion 7S of the hole transport layer 7 in order to pattern a conductor 9 that contacts only the hole transport layer 7. In the process of forming the first resist layer RS1 on the lower part 7b of the hole transport layer 7 shown in Figure 9, the pattern was performed so that the first resist layer RS1 remains on the end side of the lower part 7b of the hole transport layer 7 as shown in Figure 9 (morphology S1). For example, as shown in Figure 9, in the process of forming the first resist layer RS1, one end of the first resist layer RS1 is in contact with the bank 4, and in a plan view, the other end of the first resist layer RS1 facing the one end is located outside the leading edge of the inclined surface of the bank 4 to which the one end of the first resist layer RS1 is in contact.

[0064] Then, in the step of forming the upper part 7t of the hole transport layer 7 shown in Figure 9, a solution containing crosslinkable TFB was applied or printed onto the lower part 7b of the hole transport layer 7 and the first resist layer RS1, and then the upper part 7t of the hole transport layer 7, having a film thickness of approximately 40 nm, was formed by thermal curing at a temperature of, for example, 80°C to 100°C (Form S2).

[0065] Next, in the step of lifting off the first resist layer RS1 shown in Figure 9, by lifting off the first resist layer RS1, the upper part 7t of the unnecessary hole transport layer 7 is removed, and as shown in Figure 6, the film thickness of the outer peripheral part 7S of the hole transport layer 7 can be made thinner than the film thickness of the central part 7C of the hole transport layer 7 (morphology S3).

[0066] Next, a process is performed to form a second resist layer RS2 on the stepped outer periphery of the hole transport layer 7 in order to reliably electrically separate the anode 8 and the conductor 9. In the process of forming the second resist layer RS2 on the hole transport layer 7 shown in Figure 10, the patterning was performed so that only the second resist layer RS2 on the outer periphery of the central part 7C of the hole transport layer 7 remained (morphology S4). When forming the second resist layer RS2 on the hole transport layer 7, it is preferable to determine the width in the left-right direction of the cross-section of the second resist layer RS2 shown in Figure 10, taking into consideration the points of ensuring electrical separation between the anode 8 and the conductor 9 and suppressing current concentration at the edges of the light-emitting region EMR that may occur when a voltage is applied to the hole transport layer 7 using the anode 8 and the conductor 9. If it is desired to secure a wider width in the left-right direction of the cross-section of the second resist layer RS2 shown in Figure 10, it is preferable to reduce the inclination angle of the bank 4.

[0067] Then, in the process of forming the transparent conductive film shown in Figure 10, for example, an ITO (indium tin oxide) film was formed by sputtering to a thickness of about 10 nm (morphology S5).

[0068] Subsequently, in the lift-off step of the second resist layer RS2 shown in Figure 10, the unnecessary transparent conductive film is removed by lifting off the second resist layer RS2, and both the electrically isolated anode 8 and conductor 9 can be formed simultaneously in a single step (morphology S6).

[0069] Figure 11 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.

[0070] As shown in Figure 11, 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.

[0071] Figure 12 shows an example of aging a hole transport layer 7 containing an organic hole transport material using a conductor 9 and an anode 8 in a light-emitting device including a plurality of light-emitting elements 30 of Embodiment 1 shown in Figure 6.

[0072] As shown in Figure 12, the multiple conductors 9 may be electrically connected by, for example, a connecting portion 9'. Also, as shown in Figure 12, the upper anode 8 and the lower anode 8 may be electrically connected by a connecting portion 8', and a row of anodes including the upper anode 8 and the lower anode 8 that are electrically connected by the connecting portion 8' may be electrically connected by a terminal 8T. In the case of a light-emitting device including multiple light-emitting elements 30 of Embodiment 1 shown in Figure 12, for example, the hole transport layer 7 can be aged by electrically connecting the high-potential side terminal 51 of the power supply 50 to a part of the conductor 9 and the low-potential side terminal 52 of the power supply 50 to terminal 8T. The current supply to the hole transport layer 7 is not polarity-dependent, so it is not limited to this, and the hole transport layer 7 may also be aged by electrically connecting the high-potential side terminal 51 of the power supply 50 to terminal 8T and the low-potential side terminal 52 of the power supply 50 to a part of the conductor 9.

[0073] This is not an exhaustive feature, and although not shown in the illustration, if there is no connecting portion 9' as shown in Figure 12 and each of the multiple conductors 9 is electrically isolated, then terminals for electrically connecting each of the multiple electrically isolated conductors 9 may be provided in a region that does not obstruct the light emitted from the multiple light-emitting elements 30, for example, in the frame region NDA.

[0074] Figure 13 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.

[0075] The light-emitting element 30 shown in Figure 6 above is a light-emitting element manufactured by forming a bank 4 after forming a cathode 3, but the light-emitting element 30a shown in Figure 13 differs from the light-emitting element 30 shown in Figure 6 in that it is a light-emitting element manufactured by forming a cathode 3 after forming a bank 4. With such a light-emitting element 30a, by performing aging on the hole transport layer 7 after manufacturing the element, 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, thereby realizing 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.

[0076] Figure 14 shows an example of the material constituting the light-emitting layer 6 provided on the light-emitting elements 30 and 30a of Embodiment 1. Figure 15 shows another example of the material constituting the light-emitting layer 6 provided on the light-emitting elements 30 and 30a of Embodiment 1. Figure 16 shows yet another example of the material constituting the light-emitting layer 6 provided on the light-emitting elements 30 and 30a of Embodiment 1.

[0077] The light-emitting layer 6 provided in the light-emitting elements 30 and 30a of Embodiment 1 may include an adduct AD surrounding at least one quantum dot BQD, as shown in Figures 14 and 15, or a matrix MR as an adduct filling the space between at least two quantum dot BQDs, as shown in Figure 16. In other words, an adduct may exist around the quantum dot BQD in the light-emitting layer 6. 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. Note that, as shown in Figures 14, 15, and 16, the quantum dot BQD includes a core BQDC and a shell BQDS.

[0078] 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 O ３ ), 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 ５It 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.

[0079] As shown in Figures 14 and 15, 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.

[0080] As shown in Figure 16, 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. ２It 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.

[0081] 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)). ２The 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.

[0082] 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).

[0083] 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.

[0084] 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.

[0085] As described above, in this embodiment, light-emitting elements 30 and 30a, each having two electrically connected conductors 9, have been described as an example, but the embodiment is not limited to this. For example, the first conductor 9a and the second conductor 9b provided in the light-emitting elements 30c and 30d described later in Embodiment 3, the light-emitting element 30e described later in Embodiment 4, the light-emitting element 30f described later in Embodiment 5, and the light-emitting element 30g described later in Embodiment 6 may be electrically connected.

[0086] [Embodiment 2] The light-emitting element 30b of this embodiment differs from the light-emitting elements 30 and 30a 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.

[0087] Figure 17 is a cross-sectional view showing a schematic configuration of a light-emitting element 30b of Embodiment 2, which comprises a first conductor 9a and a second conductor 9b. Figure 18 is a diagram showing an example of aging a hole transport layer 7 containing an organic hole transport material using the first conductor 9a and the second conductor 9b provided in the light-emitting element 30b of Embodiment 2 shown in Figure 17. Figure 19 is a diagram showing an example of aging a hole transport layer 7 containing an organic hole transport material using the first conductor 9a and the second conductor 9b in a light-emitting device that includes a plurality of light-emitting elements 30b of Embodiment 2 shown in Figure 17.

[0088] As shown in Figure 17, the light-emitting element 30b comprises an electrically isolated first conductor 9a and a second conductor 9b.

[0089] As shown in Figure 18, the light-emitting element 30b comprises a substrate 2, a cathode 3 which is a lower electrode located near the substrate 2, an anode 8 which is an upper electrode located on the opposite side of the substrate 2 from the cathode 3, a light-emitting layer 6 provided between the cathode 3 and the anode 8, and a hole transport layer 7 provided between the light-emitting layer 6 and the anode 8. In this embodiment, as an aging method for the hole transport layer 7, the hole transport layer 7 is aged by applying a voltage to the hole transport layer 7 using a first conductor 9a in contact with the hole transport layer 7 and a second conductor 9b in contact with the hole transport layer 7 and electrically isolated from the first conductor 9a. Except for the fact that the hole transport layer 7 is aged by applying a voltage to the hole transport layer 7 using the first conductor 9a and the second conductor 9b, this is the same as the aging method for the hole transport layer 7 in Embodiment 1 described above, so a detailed explanation is omitted.

[0090] As shown in Figure 19, the multiple first conductors 9a may be electrically connected, for example, by connecting portions 9a' of the first conductors 9a. In this embodiment, one second conductor 9b is provided as a common conductor for four adjacent light-emitting elements 30b. In the case of a light-emitting device including multiple light-emitting elements 30b of Embodiment 2 shown in Figure 17, for example, the hole transport layer 7 can be aged by electrically connecting the high-potential side terminal 51 of the power supply 50 to a part of the first conductor 9a and the low-potential side terminal 52 of the power supply 50 to a part of the second conductor 9b. The current supply to the hole transport layer 7 is not polarity-dependent, so it is not limited to this, and the hole transport layer 7 may also be aged by electrically connecting the high-potential side terminal 51 of the power supply 50 to a part of the second conductor 9b and the low-potential side terminal 52 of the power supply 50 to a part of the first conductor 9a.

[0091] The system is not limited to this, and although not shown in the figures, if there is no connecting portion 9a' as shown in Figure 19, and each of the multiple first conductors 9a is electrically isolated, and each of the second conductors 9b is also electrically isolated from each of the light-emitting elements 30b, then the system may include, for example, a frame region NDA in which the light emitted from the multiple light-emitting elements 30 is not obstructed, a first terminal that electrically connects each of the multiple electrically isolated first conductors 9a, and a second terminal that electrically connects each of the multiple electrically isolated second conductors 9b, and is electrically isolated from the first terminal.

[0092] According to the above-described light-emitting element 30b, by performing aging on the hole transport layer 7 after manufacturing the element, it is possible to suppress a significant decrease in brightness during use of the light-emitting element 30b and the display device containing the light-emitting element 30b, thereby realizing a light-emitting element 30b with stable element characteristics and a display device equipped with a light-emitting element 30b with stable element characteristics.

[0093] Furthermore, by using the aging method for the hole transport layer 7 described above, it is possible to obtain a light-emitting element 30b with stable element characteristics that can suppress a large decrease in brightness during display operation.

[0094] [Embodiment 3] The light-emitting elements 30c and 30d of this embodiment differ from the light-emitting elements 30, 30a, and 30b of embodiments 1 and 2 in that the hole transport layer 7 has a portion that creeps up onto the inclined surface 4K of the bank 4.

[0095] Figure 20 is a cross-sectional view showing a schematic configuration of the light-emitting element 30c of Embodiment 3. Figure 21 is a cross-sectional view showing a schematic configuration of the light-emitting element 30d, which is another example of Embodiment 3.

[0096] As shown in Figures 20 and 21, the light-emitting elements 30c and 30d are provided with a bank 4 having an inclined surface 4K that contacts the hole transport layer 7. A portion of the outer peripheral portion 7S of the hole transport layer 7 extends onto the inclined surface 4K. That is, the outer peripheral portion 7S of the hole transport layer 7 has a portion that creeps up onto the inclined surface 4K of the bank 4. The first conductor 9a and the second conductor 9b are in contact with at least the outer peripheral portion 7S that extends onto the inclined surface 4K. With this configuration, by utilizing the portion of the outer peripheral portion 7S of the hole transport layer 7 that extends onto the inclined surface 4K, contact between the first conductor 9a and the second conductor 9b and the hole transport layer 7 can be made more reliable.

[0097] Furthermore, the shape in which a portion of the outer peripheral portion 7S of the hole transport layer 7 extends onto the inclined surface 4K, that is, the portion of the outer peripheral portion 7S of the hole transport layer 7 that creeps up onto the inclined surface 4K of the bank 4, is formed, for example, in the process of forming the hole transport layer 7 containing an organic hole transport material, when a crosslinkable TFB is applied or formed by inkjet, the hole transport layer 7 creeps up onto the inclined surface 4K of the bank 4 due to the viscosity of the solution.

[0098] The light-emitting element 30c shown in Figure 20 can be manufactured by first forming a second resist layer RS2 on the hole transport layer 7 shown in Figure 10, patterning it so that only the second resist layer RS2 on the outer peripheral portion of the central part 7C of the hole transport layer 7 remains (morphology S4), then forming a transparent conductive film as shown in Figure 10, in which the anode 8, first conductor 9a, and second conductor 9b are each made of the same material (morphology S5), and finally lifting off the second resist layer RS2 shown in Figure 10 (morphology S6).

[0099] On the other hand, the light-emitting element 30d shown in Figure 21 can be manufactured by first patterning the hole transport layer 7 shown in Figure 10 so that the second resist layer RS2 remains on the outer peripheral portion of the central portion 7C of the hole transport layer 7 and on the flat portion of the outer peripheral portion 7S of the hole transport layer 7 (morphology S4), then forming the transparent conductive film shown in Figure 10, in which the anode 8, first conductor 9a, and second conductor 9b are each made of the same material (morphology S5), and finally lifting off the second resist layer RS2 shown in Figure 10 (morphology S6).

[0100] With the above-described light-emitting elements 30c and 30d, by performing aging on the hole transport layer 7 after manufacturing the elements, it is possible to suppress a significant decrease in brightness during use of the light-emitting elements 30c and 30d and the display device containing the light-emitting elements 30c and 30d. Therefore, it is possible to realize light-emitting elements 30c and 30d with stable element characteristics and a display device equipped with light-emitting elements 30c and 30d with stable element characteristics.

[0101] [Embodiment 4] The light-emitting element 30e of this embodiment differs from the light-emitting elements 30, 30a, 30b, 30c, and 30d of Embodiments 1 to 3 in that a portion of each of the first conductor 9a and the second conductor 9b is covered by the hole transport layer 7.

[0102] Figure 22 is a cross-sectional view showing the schematic configuration of the light-emitting element 30e of Embodiment 4.

[0103] Parts of the first conductor 9a and the second conductor 9b provided in the light-emitting element 30e shown in Figure 22 are covered by a hole transport layer 7. Electrical isolation between the light-emitting layer 6 and the first conductor 9a and the second conductor 9b is achieved by providing insulating layers 10 between the light-emitting layer 6 and the first conductor 9a and between the light-emitting layer 6 and the second conductor 9b. With this configuration, the contact area between the first conductor 9a and the second conductor 9b and the hole transport layer 7 can be increased, and electrical isolation between the first conductor 9a and the second conductor 9b and the anode 8 can be achieved more reliably.

[0104] In the light-emitting element 30e shown in Figure 22, the surface of the hole transport layer 7 on the anode 8 side is flat. With this configuration, it is possible to maintain a light-emitting area equivalent to that of the light-emitting element 30 in Figure 6, which is manufactured in the process shown in Figure 9 (morphologies S1 to S3). Furthermore, since the flat surface and part of the inclined surface of the first conductor 9a and the second conductor 9b are covered with the hole transport layer 7, the contact area between the first conductor 9a and the second conductor 9b and the hole transport layer 7 is increased, and the applied voltage during aging can be reduced.

[0105] The light-emitting element 30e shown in Figure 22 can be manufactured by following these steps in this order: forming the light-emitting layer 6, forming the insulating layer 10, forming the first conductor 9a and the second conductor 9b, forming the hole transport layer 7, and forming the anode 8. In the case of the light-emitting element 30e shown in Figure 22, the anode 8, the first conductor 9a, and the second conductor 9b cannot be formed in a single step, so the steps for forming the first conductor 9a and the second conductor 9b and the step for forming the anode 8 are separated.

[0106] According to the above-described light-emitting element 30e, by performing aging on the hole transport layer 7 after manufacturing the element, it is possible to suppress a significant decrease in brightness during use of the light-emitting element 30e and the display device containing the light-emitting element 30e, thereby realizing a light-emitting element 30e with stable element characteristics and a display device equipped with a light-emitting element 30e with stable element characteristics.

[0107] [Embodiment 5] The light-emitting element 30f of this embodiment differs from the light-emitting elements 30, 30a, 30b, 30c, 30d, and 30e of Embodiments 1 to 4 in that at least a portion of each of the first conductor 9a and the second conductor 9b is located inside the bank.

[0108] Figure 23 is a cross-sectional view showing the schematic configuration of the light-emitting element 30f of Embodiment 5.

[0109] The light-emitting element 30f shown in Figure 23 includes a bank provided so as to be in contact with at least a portion of the end of the cathode 3, and at least a portion of each of the first conductor 9a and the second conductor 9b is located inside the bank. With the light-emitting element 30f, the first conductor 9a and the second conductor 9b can each be formed only on a plane. In this embodiment, the bank is composed of a lower bank 4b and an upper bank 4t.

[0110] The light-emitting element 30f shown in Figure 23 can be manufactured by performing the following steps in this order: forming the lower bank 4b, forming the cathode 3, forming the electron transport layer 5, forming the light-emitting layer 6, forming the lower part 7b of the hole transport layer 7 shown in Figure 9, forming the first resist layer RS1 on the lower part 7b of the hole transport layer 7 shown in Figure 9 (morphology S1), forming the upper part 7t of the hole transport layer 7 shown in Figure 9 (morphology S2), lifting off the first resist layer RS1 shown in Figure 9 (morphology S3), forming the second resist layer RS2 on the hole transport layer 7 shown in Figure 10 (morphology S4), forming the transparent conductive film shown in Figure 10 (morphology S5), lifting off the second resist layer RS2 shown in Figure 10 (morphology S6), and forming the upper bank 4t.

[0111] With the above-described light-emitting element 30f, by performing aging on the hole transport layer 7 after manufacturing the element, it is possible to suppress a significant decrease in brightness during use of the light-emitting element 30f and the display device containing the light-emitting element 30f. Therefore, it is possible to realize a light-emitting element 30f with stable element characteristics and a display device equipped with a light-emitting element 30f with stable element characteristics.

[0112] [Embodiment 6] The light-emitting element 30g of this embodiment differs from the light-emitting elements 30, 30a, 30b, 30c, 30d, 30e, and 30f of Embodiments 1 to 5 in that a portion of each of the first conductor 9a and the second conductor 9b is covered by the hole transport layer 7, and a portion of each of the first conductor 9a and the second conductor 9b is located inside the bank.

[0113] Figure 24 is a cross-sectional view showing the schematic configuration of the light-emitting element 30g of Embodiment 6.

[0114] Parts of the first conductor 9a and the second conductor 9b provided in the light-emitting element 30g shown in Figure 24 are covered by a hole transport layer 7. Electrical isolation between the light-emitting layer 6 and the first conductor 9a and the second conductor 9b is achieved by providing insulating layers 10 between the light-emitting layer 6 and the first conductor 9a and between the light-emitting layer 6 and the second conductor 9b. With this configuration, the contact area between the first conductor 9a and the second conductor 9b and the hole transport layer 7 can be increased, and electrical isolation between the first conductor 9a and the second conductor 9b and the anode 8 can be achieved more reliably.

[0115] Furthermore, in the light-emitting element 30g shown in Figure 24, the surface of the hole transport layer 7 on the anode 8 side is flat. With this configuration, the hole transport layer 7 can be formed in a single step without performing the steps described above: forming the lower part 7b of the hole transport layer 7 shown in Figure 9, forming the first resist layer RS1 on the lower part 7b of the hole transport layer 7 shown in Figure 9 (Module S1), forming the upper part 7t of the hole transport layer 7 shown in Figure 9 (Module S2), and lifting off the first resist layer RS1 shown in Figure 9 (Module S3).

[0116] Furthermore, the light-emitting element 30g shown in Figure 24 is provided with a bank that is in contact with at least a portion of the end of the cathode 3, and a portion of each of the first conductor 9a and the second conductor 9b is located inside the bank. With the light-emitting element 30g, the first conductor 9a and the second conductor 9b can be formed only on a plane. In this embodiment, the bank is composed of a lower bank 4b and an upper bank 4t.

[0117] The light-emitting element 30g shown in Figure 24 can be manufactured by performing the following steps in this order: forming the lower bank 4b, forming the cathode 3, forming the electron transport layer 5, forming the light-emitting layer 6, forming the insulating layer 10, forming the first conductor 9a and the second conductor 9b, forming the upper bank 4t, forming the hole transport layer 7, and forming the anode 8. In the case of the light-emitting element 30g shown in Figure 24, the anode 8, the first conductor 9a, and the second conductor 9b cannot be formed in a single step, so the steps for forming the first conductor 9a and the second conductor 9b and the anode 8 are separated. Also, in the case of the light-emitting element 30g shown in Figure 24, the banks cannot be formed in a single step, so the steps for forming the lower bank 4b and the upper bank 4t are separated.

[0118] According to the above-described light-emitting element 30g, by performing aging on the hole transport layer 7 after manufacturing the element, it is possible to suppress a significant decrease in brightness during use of the light-emitting element 30g and the display device containing the light-emitting element 30g, thereby realizing a light-emitting element 30g with stable element characteristics and a display device equipped with a light-emitting element 30g with stable element characteristics.

[0119] [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.

[0120] This disclosure can be used in light-emitting devices, light-emitting devices, and methods for aging hole transport layers.

[0121] 1 Display device 2 Substrate 3 Cathode 4 Bank 4b Lower bank 4t Upper bank 4K Inclined surface in contact with hole transport layer 5 Electron transport layer 6 Light-emitting layer 7 Hole transport layer 7b Lower part of hole transport layer 7t Upper part of hole transport layer 7C Center of hole transport layer 7S Outer periphery of hole transport layer 8 Anode 8' Anode connection 8T Terminal 9 Conductor 9' Conductor connection 9a First conductor 9a' Connection of first conductor 9b Second conductor 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 BQD Quantum dot BQDC Quantum dot core BQDS Quantum dot shell AD Adductor OL Organic ligand MR Matrix RS1 First resist layer: RS2 Second resist layer: 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; a cathode which is a lower electrode provided near the substrate; an anode which is an upper electrode provided on the opposite side of the substrate from the cathode; a light-emitting layer provided between the cathode and the anode; a hole transport layer provided between the light-emitting layer and the anode; 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 for aging the hole transport layer.

4. The light-emitting element according to any one of claims 1 to 3, wherein the cathode 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, wherein the cathode is formed of an electrode material that reflects visible light, the anode is formed of an electrode material that transmits visible light, and the conductor is a thin metal film or a transparent conductive film.

6. The light-emitting element according to any one of claims 1 to 5, comprising a bank provided so as to be in contact with at least a portion of the end of the cathode, wherein at least a portion of the conductor is superimposed with the bank in a plan view.

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

8. The light-emitting element according to any one of claims 1 to 7, wherein the hole transport layer includes a central portion and an outer peripheral portion located outside the central portion, and the conductor is in contact with the outer peripheral portion.

9. The light-emitting element according to claim 6 or 7, wherein the hole transport layer includes a central portion and an outer peripheral portion located outside the central portion, the entire outer peripheral portion superimposed on the bank in a plan view, and the conductor is in contact with the outer peripheral portion.

10. The light-emitting element according to any one of claims 6, 7, or 9, wherein the bank has an inclined surface in contact with the hole transport layer, the hole transport layer includes a central portion and an outer peripheral portion located outside the central portion, a portion of the outer peripheral portion extends on the inclined surface, and the conductor is in contact with at least the outer peripheral portion extending on the inclined surface.

11. The light-emitting element according to any one of claims 8 to 10, wherein the film thickness of the outer periphery is thinner than the film thickness of the central part.

12. The light-emitting element according to any one of claims 1 to 9, wherein a portion of the conductor is covered by the hole transport layer.

13. The light-emitting element according to any one of claims 1 to 9, 12, wherein the anode-side surface of the hole transport layer is flat.

14. The light-emitting element according to any one of claims 1 to 13, wherein the conductor is electrically isolated from the light-emitting layer.

15. The light-emitting element according to any one of claims 1 to 13, wherein the conductor is electrically isolated from the cathode.

16. The light-emitting element according to any one of claims 1 to 13, 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.

17. The light-emitting element according to any one of claims 1 to 16, wherein the conductor is provided as one, and the conductor is electrically isolated from the anode.

18. The light-emitting element according to any one of claims 1 to 16, 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.

19. The light-emitting element according to any one of claims 1 to 18, wherein the light-emitting layer includes a plurality of quantum dots.

20. The light-emitting element according to claim 19, wherein an adduct exists around the quantum dot in the light-emitting layer.

21. The light-emitting element according to claim 20, wherein the adduct fills the space between at least two of the quantum dots, and the adduct contains a ligand.

22. A light-emitting device having a plurality of light-emitting elements according to any one of claims 1 to 21, and comprising terminals for electrically connecting a plurality of conductors included in the plurality of light-emitting elements, wherein the terminals are provided in an area that does not obstruct the light emitted from the plurality of light-emitting elements.

23. A method for aging a hole transport layer, comprising: a substrate; a cathode which is a lower electrode provided near the substrate; an anode which is an upper electrode provided on the opposite side of the substrate from the cathode; a light-emitting layer provided between the cathode and the anode; a hole transport layer provided between the light-emitting layer and the anode; 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.

24. The method for aging a hole transport layer according to claim 23, 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).

25. The method for aging a hole transport layer according to claim 23 or 24, 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.

26. A method for aging a hole transport layer according to any one of claims 23 to 25, wherein a voltage is applied to the hole transport layer until the current 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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