Light-emitting element and display device

Abstract

A light-emitting element (1) according to the present disclosure comprises a substrate (2), a first electrode (10), a first light-emitting layer (20), a first charge generation layer (30), a conductive layer (40), a second charge generation layer (50), a second light-emitting layer (60), and a second electrode (70), in the given order. The widths of the conductive layer (40), the second charge generation layer (50), the second light-emitting layer (60), and the second electrode (70), respectively, in a second direction (X direction) orthogonal to a first direction (Z direction) from the first electrode (10) to the second electrode (70) are greater than the width of the light-emitting region (22) of the first light-emitting layer (20) in the second direction (X direction).

Description

Light-emitting element and display device

[0001] The present disclosure relates to a light-emitting element and a display device.

[0002] Patent Document 1 discloses a tandem-type light-emitting element.

[0003] US2018 / 0122873A1 (published on May 3, 2018)

[0004] In a tandem-type light-emitting element having two light-emitting layers, an upper layer and a lower layer, there is a problem that the luminance of the light-emitting layer in the upper layer, which is farther from the substrate than the lower layer close to the substrate, is likely to decrease.

[0005] A light-emitting element according to one aspect of the present disclosure includes a substrate, a first electrode, a second electrode with the first electrode positioned between the substrate and the second electrode, a first light-emitting layer positioned between the first electrode and the second electrode, a second light-emitting layer positioned between the first light-emitting layer and the second electrode, a first charge generation layer positioned between the first light-emitting layer and the second light-emitting layer and having one of electron transportability or hole transportability, a second charge generation layer positioned between the first charge generation layer and the second light-emitting layer and having the other of electron transportability or hole transportability, and a conductive layer positioned between the first charge generation layer and the second charge generation layer, and the widths in a second direction orthogonal to a first direction from the first electrode toward the second electrode of the conductive layer, the second charge generation layer, the second light-emitting layer, and the second electrode are each larger than the width in the second direction of the light-emitting region of the first light-emitting layer.

[0006] A display device according to one aspect of the present disclosure has a configuration including a plurality of light-emitting elements according to one aspect of the present disclosure.

[0007] According to one aspect of the present disclosure, it is possible to reduce the current density with respect to the upper layer of the tandem-type light-emitting element, reduce luminance degradation, and enhance the reliability of the element.

[0008] This is a cross-sectional view showing an example of the configuration of a light-emitting device according to Embodiment 1 of this disclosure. This is a cross-sectional view showing the configuration of a light-emitting device of a comparative example. This is a partial cross-sectional view showing an example of the stacked structure of a light-emitting element according to Embodiment 1 of this disclosure. This is a cross-sectional view showing an example of the configuration of a light-emitting device according to Embodiment 2 of this disclosure. This is a cross-sectional view showing an example of the configuration of a display device according to Embodiment 3 of this disclosure. This is another cross-sectional view showing an example of the configuration of a display device according to Embodiment 3 of this disclosure.

[0009] [Embodiment 1] (Configuration of Light-Emitting Device) Figure 1 is a cross-sectional view showing an example of the configuration of a light-emitting device according to Embodiment 1 of the present disclosure. As shown in Figure 1, the light-emitting device 1 according to the present disclosure comprises a substrate 2 and a laminated structure 3 provided on the substrate 2. The light-emitting device 1 may include a sealing layer 4 that covers the laminated structure 3.

[0010] The light-emitting element 1 comprises a substrate 2, a first electrode 10, and a second electrode 70, with the first electrode 10 positioned between the substrate 2 and the second electrode 70. The light-emitting element 1 further comprises a first light-emitting layer 20 located between the first electrode 10 and the second electrode 70, a second light-emitting layer 60 located between the first light-emitting layer 20 and the second electrode 70, a first charge-generating layer 30 located between the first light-emitting layer 20 and the second light-emitting layer 60 and having either electron-transporting or hole-transporting properties, a second charge-generating layer 50 located between the first charge-generating layer 30 and the second light-emitting layer 60 and having either electron-transporting or hole-transporting properties, and a conductive layer 40 located between the first charge-generating layer 30 and the second charge-generating layer 50. The width of the conductive layer 40, the second charge generation layer 50, the second light-emitting layer 60, and the second electrode 70 in the second direction (X direction in Figure 1) which is perpendicular to the first direction (Z direction in Figure 1) from the first electrode 10 to the second electrode 70 is greater than the width of the light-emitting region 22 of the first light-emitting layer 20 in the second direction (X direction).

[0011] In this disclosure, the width of a layer or region in a second direction (X direction) is the width of the layer or region in a second direction (X direction) when viewed from above. In this disclosure, a plan view is a plan view seen from a first direction (Z direction).

[0012] In this disclosure, the second charge generation layer 50 has hole transport properties when the first charge generation layer 30 has electron transport properties, and the second charge generation layer 50 has electron transport properties when the first charge generation layer 30 has hole transport properties. In a structure in which a conductive material is in contact with both an electron transport material and a hole transport material, by applying a reverse bias voltage between the electron transport material and the hole transport material, electron-hole pairs are generated in the conductive material, electrons move to the electron transport material, and holes move to the hole transport material. In this way, a charge carrier is generated by the reverse bias voltage. Generally, the entire stack from the electron transport material layer to the hole transport material layer is called a "charge generation layer". For example, in the configuration shown in Figure 1, the entire combination of the first charge generation layer 30, the conductive layer 40, and the second charge generation layer 50 is usually called a "charge generation layer". For convenience, in this disclosure, one of the electron-transporting material layer or the hole-transporting material layer will be referred to as the "first charge generation layer," the other as the "second charge generation layer," and the conductive material layer will be referred to as the "conductive layer."

[0013] The conductive layer 40 must have a sufficiently high transmittance to the light emitted from the first light-emitting layer. Furthermore, since the conductive layer 40 is a layer intended to reduce the current density to the second light-emitting layer 60, it is preferable that the surface resistivity of the conductive layer 40 is sufficiently smaller than that of the first charge generation layer 30 and the second charge generation layer 50, as described later. Based on these conditions, it is desirable that the conductive layer 40 be a thin film made of metal, or a film made of a transparent conductive oxide such as indium tin oxide (ITO) ITO. It is also desirable that the entire surface of the conductive layer 40, including its edges, be completely covered by a layer formed above the conductive layer 40, such as the second charge generation layer 50. By defining the size of the conductive layer 40, the conductive layer 40 is not exposed to the atmosphere, and deterioration inward due to water and oxygen is prevented. The light-emitting region of the second light-emitting layer 60 can be controlled. For example, in a plan view, it is desirable that at least the second charge generation layer 50 is formed such that its area is larger than the area of ​​the conductive layer 40 and completely covers the conductive layer 40.

[0014] Figure 2 is a cross-sectional view showing the configuration of a comparative example light-emitting element. As shown in Figure 2, the comparative example light-emitting element 101 comprises a substrate 102, a laminated structure 103 provided on the substrate 102, and a sealing layer 104 covering the laminated structure. The comparative example laminated structure 103 comprises a first electrode 110, a first light-emitting layer 120, a first charge generation layer 130, a second charge generation layer 150, a second light-emitting layer 160, and a second electrode 170 in this order. The comparative example light-emitting element 101 has the same configuration as the light-emitting element 1 shown in Figure 1, except that there is no conductive layer between the first charge generation layer 130 and the second charge generation layer 150.

[0015] The configuration according to this disclosure allows for a reduction in the driving voltage of the light-emitting element 1. In the light-emitting element 1 according to this disclosure (see Figure 1), electron-hole pairs are generated in the conductive layer 40. On the other hand, in the comparative example light-emitting element 101 (see Figure 2), electron-hole pairs are generated at the boundary between the first charge generation layer 130 and the second charge generation layer 150. Electron-hole pairs are more likely to be generated in conductive materials than at the boundary between electron-transporting materials and hole-transporting materials. Therefore, compared to the configuration of the comparative example, the configuration according to this disclosure requires a lower voltage for charge generation, and the driving voltage of the light-emitting element 1 can be reduced. By reducing the driving voltage, the reliability of the light-emitting element 1 can be improved.

[0016] The configuration according to this disclosure reduces or delays the decrease in brightness of the second light-emitting layer 60 and improves the reliability of the light-emitting element 1. In the light-emitting element 1 according to this disclosure (see Figure 1), the width in the second direction (X direction) of the conductive layer 40, the second charge generation layer 50, the second light-emitting layer 60, and the second electrode 70 is greater than the width in the second direction (X direction) of the light-emitting region 22 of the first light-emitting layer 20. When the current passes through the conductive layer 40, it can spread in the second direction (X direction). Spreading in the X direction includes spreading in the +X direction and spreading in the -X direction. Therefore, the current density of the current passing through the second light-emitting layer 60 is smaller than the current density of the current passing through the first light-emitting layer 20. On the other hand, in the comparative example light-emitting element 101 (see Figure 2), since there is no conductive layer between the first charge generation layer 130 and the second charge generation layer 150, the current density of the current passing through the second light-emitting layer 160 is the same as the current density of the current passing through the first light-emitting layer 120.

[0017] It is known that the expected lifetime LT of a certain light-emitting layer is inversely proportional to the Nth power of the current density Id of the current passing through the light-emitting layer, using a coefficient N (N > 0). That is, the following equation (1) is known to hold.

[0018] LT∝Id －Ｎ …(1) The smaller the current density Id, the larger the lifetime LT. Lifetime LT is an indicator of reliability, and the larger the lifetime LT, the higher the reliability. Therefore, the reliability of the second light-emitting layer 60 according to this disclosure is higher than that of the second light-emitting layer 160 of the comparative example. The second light-emitting layer 60, which is farther from the substrate 2, tends to degrade more easily than the first light-emitting layer 20, which is closer to the substrate 2. For this reason, improving the reliability of the second light-emitting layer 60 can increase the overall reliability of the light-emitting element 1.

[0019] The resistance of the conductive layer 40 in the second direction (X direction) is preferably smaller than the resistance of the conductive layer 40 in the first direction (Z direction) from the conductive layer 40 to the second electrode 70. This makes it easier for the current to spread in the second direction (X direction) through the conductive layer 40. The surface resistivity of the conductive layer 40 may be, for example, 100 kΩ / □ or less, preferably 1 kΩ / □ or less, and more preferably 100 Ω / □ or less. The conductive layer 40 is preferably a continuous film that spreads in the second direction (X direction).

[0020] The light transmittance of the conductive layer 40 in the first direction (Z direction) is preferably high, for example, it may be 30% or more. This makes it possible to increase the light extraction efficiency of the light-emitting element 1.

[0021] The conductive layer 40 may contain a light-transmitting conductive material. The light-transmitting conductive material may contain, for example, an indium-based transparent conductive oxide such as indium tin oxide (ITO), or a thin film or nanoparticles of a metal such as silver, gold, copper, or aluminum.

[0022] The area of ​​the substantial light-emitting region 62 of the second light-emitting layer 60 may be larger than the area of ​​the substantial light-emitting region 22 of the first light-emitting layer 20. In this disclosure, the area of ​​a region is the area measured along the shape of the region in a plan view.

[0023] Here, in order to simply explain the effects of this disclosure, we will ignore leakage current that does not pass through the light-emitting region of the light-emitting layer. When the area of ​​the substantial light-emitting region 62 of the second light-emitting layer 60 is x times (x > 1) the area of ​​the substantial light-emitting region 22 of the first light-emitting layer 20, the current density of the current passing through the light-emitting region 62 of the second light-emitting layer is 1 / x times the current density of the current passing through the light-emitting region 22 of the first light-emitting layer 20. Based on the law of exponents, the following equation (2) holds.

[0024] LT∝Id －Ｎ ...(1) (Id / x) －Ｎ =Id －Ｎ ×x Ｎ ... (2) When the current density Id decreases to 1 / x times, the lifetime LT is x based on the above equations (1) and (2). Ｎ It doubles. It is experimentally known that N is usually about 1.8, (1.1) １．８ ≈ 1.19. Therefore, when comparing the configuration according to this disclosure (see Figure 1), in which the area of ​​the substantial light-emitting region 62 of the second light-emitting layer 60 is 10% larger than the area of ​​the substantial light-emitting region 22 of the first light-emitting layer 20, with the configuration of a comparative example (see Figure 2), in which the area of ​​the substantial light-emitting region 162 of the second light-emitting layer 160 is equal to the area of ​​the substantial light-emitting region 122 of the first light-emitting layer 120, the lifespan of the second light-emitting layer 60 according to this disclosure is approximately 19% longer than the lifespan of the second light-emitting layer 160 according to the comparative example.

[0025] Therefore, the area of ​​the substantial light-emitting region 62 of the second light-emitting layer 60 may preferably be 10% or more larger than the area of ​​the substantial light-emitting region 22 of the first light-emitting layer 20. This can improve the reliability of the second light-emitting layer 60 by 19% or more.

[0026] The widths of the second charge generation layer 50, the second light-emitting layer 60, and the second electrode 70 in the second direction (X direction) may be greater than or equal to the width of the conductive layer 40 in the second direction (X direction). In a plan view, the conductive layer 40 is superimposed on the second charge generation layer 50, the second light-emitting layer 60, and the second electrode 70. This reduces the leakage current that flows between the conductive layer 40 and the second electrode 70 without passing through the second charge generation layer 50 and the second light-emitting layer 60. By reducing the leakage current, the internal quantum efficiency (IQE) of the light-emitting element 1 can be improved. At this time, the entire lower surface of the conductive layer 40 on the substrate 2 side is covered by the first charge generation layer 30 side. In addition, the entire upper surface of the conductive layer 40 opposite to the substrate 2, and the entire area between the lower and upper surfaces, are covered by the second charge generation layer 50 side.

[0027] The light-emitting element 1 may further include an edge cover 80 that covers at least a portion of the end face 16 of the first electrode 10. The edge cover 80 is preferably made of an insulating material. The first electrode 10 has a lower surface 12 on the substrate 2 side and an upper surface 14 on the opposite side of the substrate 2. The end face 16 of the first electrode 10 is located between the lower surface 12 and the upper surface 14. The edge cover 80 may cover up to the end region of the upper surface 14 that is near the end face 16 of the first electrode 10. In this case, the upper surface 14 of the first electrode 10 has an exposed region 14A that is exposed from the edge cover 80 and a covered region 14B that is covered by the edge cover 80.

[0028] The light-emitting region 22 of the first light-emitting layer 20 overlaps with the exposed region 14A of the first electrode 10 that is exposed from the edge cover 80 in a plan view. The region of the first light-emitting layer 20 that overlaps with the edge cover 80 tends to be less luminescent. Therefore, the width of the light-emitting region 22 of the first light-emitting layer 20 in the second direction (X direction) is approximately the same as the width of the exposed region 14A of the first electrode 10 in the second direction (X direction). For this reason, when the width of a certain layer in the second direction (X direction) is greater than the width of the exposed region 14A of the first electrode 10 in the second direction (X direction), the width of that layer in the second direction (X direction) is greater than the width of the light-emitting region 22 of the first light-emitting layer 20 in the second direction (X direction).

[0029] The edge cover 80 may have a forward-sloping surface 86 that surrounds the exposed area 14A of the first electrode 10 in a plan view. The edge cover 80 has a lower surface 82 on the substrate 2 side and an upper surface 84 on the opposite side of the substrate 2. Here, the lower surface 82 of the edge cover 80 on the substrate 2 side is a region that includes the substrate-side contact surface in which the edge cover 80 contacts the substrate 2 and the first electrode-side contact surface in contact with the upper surface 14 and end surface 16 of the first electrode 10. The upper surface 84 of the edge cover 80 is smaller than the lower surface 82, and the forward-sloping surface 86 is located between the lower surface 82 and the upper surface 84. In a plan view, the second light-emitting layer 60 may overlap with at least a portion of the forward-sloping surface 86. Similarly, the conductive layer 40, the second charge-generating layer 50, and the second electrode 70 may also overlap with at least a portion of the forward-sloping surface 86 in a plan view.

[0030] In this case, the light-emitting region 62 of the second light-emitting layer 60 has (i) a central flat portion 62A that overlaps with the exposed region 14A of the first electrode 10 in a plan view, and (ii) an inclined portion 62B that overlaps with at least a part of the forward-sloping surface 86 of the edge cover 80 in a plan view. The central flat portion 62A is substantially parallel to a flat surface perpendicular to the first direction (Z direction), and its substantial area is substantially the same as the area in a plan view. On the other hand, the inclined portion 62B is inclined with respect to a flat surface perpendicular to the first direction (Z direction), and its substantial area is larger than the area in a plan view by the amount of the inclination. As a result, the inclined portion 62B can improve the brightness of the light-emitting element 1 in the oblique direction (a direction oblique to the Z direction).

[0031] Furthermore, the second light-emitting layer 60 may superimpose on the entire forward-sloping surface 86 in a plan view. Similarly, the conductive layer 40, the second charge-generating layer 50, and the second electrode 70 may also superimpose on the entire forward-sloping surface 86 in a plan view.

[0032] In a plan view, the second light-emitting layer 60 may overlap with at least a portion of the upper surface 84 of the edge cover 80. Similarly, the conductive layer 40, the second charge-generating layer 50, and the second electrode 70 may also overlap with at least a portion of the upper surface 84 of the edge cover 80 in a plan view. In this case, the light-emitting region 62 of the second light-emitting layer 60 will have a peripheral flat portion 62C that overlaps with at least a portion of the upper surface 84 of the edge cover 80 in a plan view. The peripheral flat portion 62C is substantially parallel to a flat surface perpendicular to the first direction (Z direction), and its substantial area is substantially the same as the area in a plan view.

[0033] Figure 3 is a partial cross-sectional view showing an example of a stacked structure of a light-emitting element according to Embodiment 1 of the present disclosure. As shown in Figure 3, the light-emitting element 1 may be a quantum dot light-emitting diode (QLED). The first light-emitting layer 20 and the second light-emitting layer 60 may each contain a first quantum dot 26 and a second quantum dot 66. At least one of the first charge generation layer 30 or the second charge generation layer 50 may contain nanoparticles 36, 56, or both may contain nanoparticles 36, 56. At least one of the following may be that the first light-emitting layer 20 contains a first quantum dot 26, or the second light-emitting layer 60 contains a second quantum dot 66.

[0034] In QLEDs, moisture and / or oxygen can easily penetrate from the outside to the inside of the QLED through the gaps between quantum dots and nanoparticles. Therefore, layers closer to the outside tend to degrade more easily. Also, the shorter the emission wavelength, the more easily the light-emitting layer containing quantum dots degrades. For this reason, it has been necessary to consider the emission wavelength when determining the arrangement of light-emitting layers in a tandem type QLED. In the configuration according to this disclosure, the second light-emitting layer 60 is closer to the outside of the light-emitting element 1 than the first light-emitting layer 20 and tends to degrade more due to penetrating moisture and / or oxygen. On the other hand, as mentioned above, the current density of the current passing through the second light-emitting layer 60 is lower than that of the first light-emitting layer 20, and therefore tends to degrade less due to current. Therefore, the adverse effects of moisture and / or oxygen can be reduced. This improves the degree of freedom in arranging the light-emitting layers in a tandem type QLED.

[0035] The light-emitting element 1 may be an organic light-emitting diode (OLED). The first light-emitting layer 20 and the second light-emitting layer 60 may each contain an organic light-emitting material.

[0036] The light-emitting element 1 may optionally include one or more of the following: (i) a charge function layer K1 located between the first electrode 10 and the first light-emitting layer 20 and having the same polarity as the second charge generation layer 50; (ii) a charge function layer K2 located between the first light-emitting layer 20 and the first charge generation layer 30 and having the same polarity as the first charge generation layer 30; (iii) a charge function layer K3 located between the second charge generation layer 50 and the second light-emitting layer 60 and having the same polarity as the second charge generation layer 50; and (iv) a charge function layer K4 located between the second light-emitting layer 60 and the second electrode 70 and having the same polarity as the first charge generation layer 30. In the above, "same polarity" indicates that the corresponding charge generation layer and charge function layer both have electron transport properties, or both have hole transport properties. In this disclosure, each of the charge function layers K1 to K4 may include a charge transport layer and / or a charge injection layer. Each of the charge-functional layers K1 to K4 may contain nanoparticles or a continuous film.

[0037] If the light-emitting element 1 includes charge function layers K3 and K4, each of the charge function layers K3 and K4 overlaps with the exposed region 14A of the first electrode 10 in a plan view. Furthermore, the charge function layers K3 and K4 may overlap with at least a portion of the forward-sloping surface 86 of the edge cover 80, or with the entire forward-sloping surface 86, or with at least a portion of the upper surface 84 of the edge cover 80. The above-described matters concerning the width of the second charge generation layer 50 in the second direction (X direction) can be applied to the width of the charge function layers K3 and K4 in the second direction (X direction). Specifically, the width of each of the charge function layers K3 and K4 in the second direction (X direction) is greater than the width of the light-emitting region 22 of the first light-emitting layer 20 in the second direction (X direction). The width of each of the charge function layers K3 and K4 in the second direction (X direction) may be greater than or equal to the width of the conductive layer 40 in the second direction (X direction).

[0038] Regarding the second direction (X direction), what has been described above is applicable to any direction along the plane (XY plane) orthogonal to the first direction (Z direction) with respect to the so-called "in-plane direction". The in-plane direction can be expressed by combining the second direction and the third direction using the third direction (Y direction in FIG. 1) orthogonal to both the first direction (Z direction) and the second direction (X direction).

[0039] The light-emitting element 1 may have a normal structure. The first electrode 10 may be an anode, the first charge generation layer 30 may have electron-transporting properties, the second charge generation layer 50 may have hole-transporting properties, and the second electrode 70 may be a cathode.

[0040] The light-emitting element 1 may have an inverted structure. The first electrode 10 may be a cathode, the first charge generation layer 30 may have hole-transporting properties, the second charge generation layer 50 may have electron-transporting properties, and the second electrode 70 may be an anode.

[0041] The color of the light emitted by the second light-emitting layer 60 may be the same as the color of the light emitted by the first light-emitting layer 20. In the present disclosure, the colors of the lights being the same means that they may be substantially the same within the range visible to the human eye, and it is not required that the peaks of the light wavelengths are exactly the same in a strict sense. For example, if the emission peak wavelengths of the two light-emitting layers are within the wavelength ranges of the same color of 430 to 500 nm showing blue, 500 to 570 nm showing green, and 610 to 780 nm showing red, it is considered that the colors of the lights emitted by the two light-emitting layers are the same. Also, when the emission peaks of the two light-emitting layers overlap and are detected as one peak, the colors of the lights are considered to be the same.

[0042] The color of the light emitted by the second light-emitting layer 60 may be different from the color of the light emitted by the first light-emitting layer 20. For example, the first light-emitting layer 20 may emit yellow light and the second light-emitting layer 60 may emit blue light, and as a result, white light may be emitted from the light-emitting element 1. The light-emitting element 1 may include three or more light-emitting layers. The light-emitting element 1 may include, for example, a first light-emitting layer 20 that emits red light, a second light-emitting layer 60 that emits green light, and a third light-emitting layer that emits blue light.

[0043] (Example 1) The light-emitting device 1 according to Example 1 of the present disclosure was fabricated as follows, taking as an example the case where the light-emitting layer contains quantum dots (see FIG. 3) so as to have the configuration shown in FIG. 1.

[0044] A substrate 2 provided with a circuit for controlling the current applied to the first electrode 10 was prepared. On the substrate 2, an anode made of a conductive material such as indium tin oxide (ITO) or silver (Ag) was formed as the first electrode 10. On the substrate 2, a film made of an insulating material covering the end face 16 of the first electrode 10 was formed as the edge cover 80. On the first electrode 10 and the edge cover 80, a hole injection layer containing nickel oxide nanoparticles was formed, and on the hole injection layer, a hole transport layer containing TFB was formed.

[0045] Subsequently, a first light-emitting layer 20 containing the first quantum dots 26 was formed on the hole transport layer. On the first light-emitting layer 20, an electron transport layer containing zinc magnesium oxide nanoparticles was formed as the first charge generation layer 30. On the first charge generation layer 30, a conductive layer 40 containing an ITO film was formed. On the conductive layer 40, a hole injection layer containing nickel oxide nanoparticles was formed as the second charge generation layer 50. On the second charge generation layer 50, a hole transport layer containing TFB was formed.

[0046] Subsequently, a second light-emitting layer 60 containing the second quantum dots 66 was formed on the hole transport layer. The second quantum dots 66 in the second light-emitting layer 60 are the same as the first quantum dots 26 in the first light-emitting layer 20.

[0047] Subsequently, an electron transport layer containing zinc magnesium oxide nanoparticles was formed on the second light-emitting layer 60. On the electron transport layer, a cathode made of an ITO film was formed as the second electrode 70.

[0048] In the light-emitting device 1 according to Example 1, the widths in the second direction (X direction) and the third direction (Y direction) of the light-emitting region of the second light-emitting layer 60 were larger than the widths in the second direction (X direction) and the third direction (Y direction) of the light-emitting region of the first light-emitting layer 20.

[0049] [Embodiment 2] Figure 4 is a cross-sectional view showing an example of the configuration of a light-emitting device according to Embodiment 2 of the present disclosure. As shown in Figure 4, the light-emitting element 1 according to the present disclosure does not need to have an edge cover that covers the end face 16 of the first electrode 10. In this case, the light-emitting region 22 of the first light-emitting layer 20 superimposes the entire first electrode 10 in a plan view.

[0050] The configuration shown in Figure 4 is equivalent to the configuration shown in Figure 1, except for the edge cover. Therefore, according to the configuration of Embodiment 2 of this disclosure, the driving voltage of the light-emitting element 1 can be reduced, and the reliability of the second light-emitting layer 60 can be improved, similar to the configuration of Embodiment 1 described above.

[0051] In Embodiment 2, the light-emitting region 22 of the first light-emitting layer 20 overlaps with the entire first electrode 10 in a plan view. Therefore, the width of the light-emitting region 22 of the first light-emitting layer 20 in the second direction (X direction) is approximately equal to the width of the entire first electrode 10 in the second direction (X direction). For this reason, when the width of a certain layer in the second direction (X direction) is greater than the width of the entire first electrode 10 in the second direction (X direction), the width of that layer in the second direction (X direction) is greater than the width of the light-emitting region 22 of the first light-emitting layer 20 in the second direction (X direction).

[0052] [Embodiment 3] Figure 5 is a cross-sectional view showing an example of the configuration of a display device according to Embodiment 3 of the present disclosure. As shown in Figure 5, the display device DP comprises at least one light-emitting element 1 according to the present disclosure. The display device DP may comprise a plurality of light-emitting elements 1 according to the present disclosure. The display device DP may comprise a plurality of light-emitting elements of the same color, or it may comprise light-emitting elements that emit different colors. For example, the display device DP may comprise one or more red light-emitting elements 1R that emit red light, one or more green light-emitting elements 1G that emit green light, and one or more blue light-emitting elements 1B that emit blue light.

[0053] When a display device DP comprises multiple light-emitting elements 1 according to this disclosure, the conductive layers 40 of each of the multiple light-emitting elements 1 are separated from one another. By each having a separate conductive layer 40, the multiple light-emitting elements 1 are electrically isolated from one another, preventing unintended light emission from separate light-emitting elements due to crosstalk.

[0054] In a display device DP, the first charge generation layers 30, each possessed by a plurality of light-emitting elements 1, may be connected to one another. The resistance of the first charge generation layer 30 in the second direction (X direction) is greater than the resistance in the first direction (Z direction) from the conductive layer 40 to the first electrode 10. Therefore, even if the plurality of light-emitting elements 1 share a continuous first charge generation layer 30, they are substantially electrically isolated from each other. This configuration reduces the number of manufacturing steps and manufacturing costs of the display device DP compared to a configuration in which each of the plurality of light-emitting elements 1 has a separate first charge generation layer 30.

[0055] In a display device DP, the second charge generation layers 50 of each of the multiple light-emitting elements 1 may be connected to one another. The resistance of the second charge generation layer 50 in the second direction (X direction) is greater than the resistance in the first direction (Z direction) from the conductive layer 40 to the second electrode 70. Therefore, even if the multiple light-emitting elements 1 share a continuous second charge generation layer 50, they are substantially electrically isolated from each other. This configuration reduces the number of manufacturing steps and manufacturing costs of the display device DP compared to a configuration in which each of the multiple light-emitting elements 1 has a separate second charge generation layer 50.

[0056] In a display device DP, the first electrodes 10 of each of the multiple light-emitting elements 1 may be separated from each other, while the second electrodes 70 of each of the multiple light-emitting elements 1 may be connected to each other. By having each of the multiple light-emitting elements 1 have a separate first electrode 10, the display device DP can drive each of the multiple light-emitting elements 1 individually. By having the multiple light-emitting elements 1 share a continuous second electrode 70, the number of manufacturing steps and manufacturing costs of the display device DP can be reduced.

[0057] Figure 6 is another cross-sectional view showing an example of the configuration of a display device according to Embodiment 3 of the present disclosure. As shown in Figure 6, the display device DP may include a plurality of light-emitting elements 1 that emit light of the same color, and the light-emitting elements 1 that emit light of the same color may be adjacent to each other. Among the plurality of first light-emitting layers 20, the first light-emitting layers 20 that emit light of the same color may be connected to each other. Among the plurality of second light-emitting layers 60, the second light-emitting layers 60 that emit light of the same color may be connected to each other. The first light-emitting layers 20 and the second light-emitting layers 60 have high surface resistivity. Therefore, even if the plurality of light-emitting elements 1 share a continuous first light-emitting layer 20 and a continuous second light-emitting layer 60, they are substantially electrically isolated from each other.

[0058] 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.

[0059] 1. Light-emitting element 2. Substrate 10. First electrode 14A. Exposed area 20. First light-emitting layer 22. Light-emitting area 26. First quantum dot 30. First charge generation layer 36. Nanoparticles 40. Conductive layer 50. Second charge generation layer 56. Nanoparticles 60. Second light-emitting layer 62. Light-emitting area 66. Second quantum dot 70. Second electrode 80. Edge cover 86. Forward-sloping surface DP Display device

Claims

1. A light-emitting element comprising: a substrate; a first electrode; a second electrode in which the first electrode is located between the substrate and the second electrode; a first light-emitting layer located between the first electrode and the second electrode; a second light-emitting layer located between the first light-emitting layer and the second electrode; a first charge-generating layer located between the first light-emitting layer and the second light-emitting layer and having either electron-transporting or hole-transporting properties; a second charge-generating layer located between the first charge-generating layer and the second light-emitting layer and having either electron-transporting or hole-transporting properties; and a conductive layer located between the first charge-generating layer and the second charge-generating layer, wherein the width of the conductive layer, the second charge-generating layer, the second light-emitting layer, and the second electrode in a second direction perpendicular to the first direction from the first electrode to the second electrode is greater than the width of the light-emitting region of the first light-emitting layer in that second direction.

2. The light-emitting element according to claim 1, wherein the surface resistivity of the conductive layer is 100 kΩ / □ or less.

3. The light-emitting element according to claim 1 or 2, wherein the surface resistivity of the conductive layer is 1 kΩ / □ or less.

4. The light-emitting element according to any one of claims 1 to 3, wherein the surface resistivity of the conductive layer is 100 Ω / □ or less.

5. The light-emitting element according to any one of claims 1 to 4, wherein the light transmittance of the conductive layer in the first direction is 30% or more.

6. The light-emitting element according to any one of claims 1 to 5, wherein the conductive layer comprises a light-transmitting conductive material.

7. The light-emitting element according to any one of claims 1 to 5, wherein the conductive layer is made of a thin metal film or a transparent conductive oxide.

8. The light-emitting element according to any one of claims 1 to 7, wherein the area of ​​the light-emitting region of the second light-emitting layer in a plan view is larger than the area of ​​the light-emitting region of the first light-emitting layer in a plan view.

9. The light-emitting element according to claim 8, wherein the area of ​​the light-emitting region of the second light-emitting layer in a plan view is 10% or more larger than the area of ​​the light-emitting region of the first light-emitting layer in a plan view.

10. The light-emitting element according to any one of claims 1 to 9, wherein the width in the second direction of the second charge generating layer, the second light-emitting layer, and the second electrode is greater than or equal to the width in the second direction of the conductive layer.

11. The light-emitting element according to any one of claims 1 to 10, wherein the entire lower surface of the conductive layer on the substrate side is covered by the first charge generating layer, and the entire upper surface of the conductive layer opposite to the substrate, and the entire end face between the lower surface and the upper surface are covered by the second charge generating layer.

12. The light-emitting element according to any one of claims 1 to 11, further comprising an edge cover that covers at least a portion of the end face of the first electrode, wherein the light-emitting region of the first light-emitting layer superimposes, in a plan view, with the exposed region of the first electrode exposed from the edge cover.

13. The light-emitting element according to claim 12, wherein the edge cover has a forward-sloping surface that surrounds the exposed area of ​​the first electrode in a plan view, and the second light-emitting layer overlaps with at least a portion of the forward-sloping surface in a plan view.

14. The light-emitting region of the first light-emitting layer superimposes the entirety of the first electrode in a plan view, as described in any one of claims 1 to 11.

15. The light-emitting element according to any one of claims 1 to 14, wherein at least one of the first light-emitting layer or the second light-emitting layer includes quantum dots.

16. The light-emitting element according to any one of claims 1 to 15, wherein at least one of the first charge generation layer or the second charge generation layer comprises nanoparticles.

17. The light-emitting element according to any one of claims 1 to 16, wherein the first electrode is an anode, the first charge generation layer has electron transport properties, and the second charge generation layer has hole transport properties.

18. The light-emitting element according to any one of claims 1 to 16, wherein the first electrode is a cathode, the first charge generation layer has hole transport properties, and the second charge generation layer has electron transport properties.

19. The light-emitting element according to any one of claims 1 to 18, wherein the color of the light emitted by the second light-emitting layer is the same as the color of the light emitted by the first light-emitting layer.

20. The light-emitting element according to any one of claims 1 to 18, wherein the color of the light emitted by the second light-emitting layer is different from the color of the light emitted by the first light-emitting layer.

21. A display device comprising a plurality of light-emitting elements according to any one of claims 1 to 20.

22. The display device according to claim 21, wherein the conductive layers of each of the multiple light-emitting elements are separated from one another.

23. The display device according to claim 21 or 22, wherein the first charge generating layers of each of the multiple light-emitting elements are connected to one another.

24. The display device according to any one of claims 21 to 23, wherein the second charge generating layers of each of the multiple light-emitting elements are connected to one another.

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