Light-emitting element and display device

Abstract

A light-emitting element (1) is provided with an anode (11), a cathode (15), and a light-emitting layer (13). At least part of the light-emitting layer (13) is positioned between the anode (11) and the cathode (15). The light-emitting element (1) is provided with a light-emitting transport layer (HY) adjacent to the at least part of the light-emitting layer (13) in the thickness direction of the light-emitting element. The light-emitting transport layer (HY) emits first light (L1) having a first wavelength. The light-emitting layer (13) emits second light (L2) having a second wavelength longer than the first wavelength by absorbing the first light (L1).

Description

Light-emitting element and display device

[0001] The following disclosure relates to light-emitting devices.

[0002] Various technologies have been proposed for light-emitting elements. For example, Patent Document 1 listed below discloses an example of the configuration of an organic electroluminescence (EL) device aimed at improving the performance of the device.

[0003] Japan Special Publication No. 2020-513158

[0004] An object of one embodiment of the present disclosure is to improve the performance of a light-emitting element by using a configuration different from conventional ones.

[0005] A light-emitting element according to one aspect of the present disclosure is a light-emitting element comprising an anode, a cathode, and an emitting layer, wherein at least a portion of the emitting layer is located between the anode and the cathode, and the light-emitting element comprises a luminescent transport layer adjacent to at least a portion of the luminescent layer in a thickness direction of the light-emitting element, wherein the luminescent transport layer emits first light having a first wavelength, and the luminescent layer absorbs the first light to emit second light having a second wavelength longer than the first wavelength.

[0006] According to one aspect of the present disclosure, it is possible to improve the performance of a light-emitting element by using a configuration different from conventional configurations.

[0007] 1 shows an example of the configuration of a light-emitting device in embodiment 1. FIG. 2 is a diagram illustrating a light-emitting device in embodiment 2. FIG. 3 is a diagram illustrating a light-emitting device in embodiment 3. FIG. 4 is a diagram illustrating a light-emitting device in embodiment 4. FIG. 5 shows an example of the configuration of a luminescent transport layer in a light-emitting device in embodiment 5. FIG. 6 shows an example of an energy diagram corresponding to the above example of the configuration of embodiment 5. FIG. 7 shows an example of the configuration of a light-emitting device in embodiment 6. FIG. 8 shows a schematic diagram of a composite electric field obtained by a metal mirror surface in the light-emitting device of embodiment 6. FIG. 9 shows an example of the configuration of a display device in embodiment 7.

[0008] [Embodiment 1] Embodiment 1 will be described below. For convenience of explanation, components having the same functions as those described in embodiment 1 will be denoted by the same reference numerals in the following embodiments, and their descriptions will not be repeated. For simplicity, descriptions of well-known technical matters will be omitted as appropriate. Unless otherwise specified, the components, materials, and numerical values ​​described in this specification are merely examples. Therefore, for example, unless otherwise specified, the positional relationship of each component is not limited to the example in each figure. Furthermore, each figure is not necessarily drawn to scale.

[0009] (Configuration example of light-emitting element 1) Fig. 1 shows a configuration example of the light-emitting element 1 in embodiment 1. Fig. 1 schematically shows the layered structure of the light-emitting element 1. In the example of Fig. 1, the light-emitting element 1 includes an anode 11, a hole transport layer 12, a light-emitting layer 13, an electron transport layer 14, and a cathode 15, in this order from the bottom. The hole transport layer 12 in embodiment 1 is an example of the light-emitting transport layer HY described later.

[0010] For convenience of explanation, the present specification introduces an orthogonal coordinate system (XYZ coordinate system) shown in FIG. 1 . The Z direction in FIG. 1 is the thickness direction of each part of the light-emitting element 1. The Z direction in FIG. 1 is defined as the normal direction of the surface SS of the substrate 90 of the light-emitting element 1. In the example of the first embodiment, the surface SS of the substrate 90 is the horizontal plane of the substrate 90.

[0011] In this specification, the positive direction of the Z direction will be described as the upward direction. Therefore, the negative direction of the Z direction is the downward direction. In the example of FIG. 1, the downward direction is defined as the direction toward the substrate 90. The X direction and Y direction in FIG. 1 are examples of directions that intersect with the Z direction. In this specification, of the two directions that intersect with the Z direction, the X direction will be mainly focused on.

[0012] In the example of Fig. 1, each part of the light-emitting element 1 is supported by a substrate 90. In the example of Fig. 1, the anode 11 is the lower electrode, and the cathode 15 is the upper electrode. Therefore, in the example of Fig. 1, the distance between the anode 11 and the substrate 90 is smaller than the distance between the cathode 15 and the substrate 90. However, unlike the example of Fig. 1, the anode 11 may be the upper electrode, and the cathode 15 may be the lower electrode.

[0013] The light-emitting element 1 is configured so that light emitted from the light-emitting layer 13 can be extracted to the outside of the light-emitting element 1. Therefore, in the light-emitting element 1, at least one of the anode 11 and the cathode 15 may be a light-transmitting electrode. Either the anode 11 or the cathode 15 may be a light-reflecting electrode.

[0014] It is sufficient that at least a part of the light-emitting layer 13 is located between the anode 11 and the cathode 15. Fig. 1 illustrates a case in which the entire light-emitting layer 13 is located between the anode 11 and the cathode 15. In the example of Fig. 1, the entire light-emitting layer 13 is located between the hole transport layer 12 and the electron transport layer 14.

[0015] The light-emitting layer 13 in the example of FIG. 1 includes QDs (Quantum Dots) 130. The QDs 130 in FIG. 1 are an example of an EL material. The QDs 130 emit EL light upon recombination of holes supplied from the anode 11 and electrons transported from the cathode 15. Therefore, EL light can be generated in the light-emitting layer 13 by applying a forward voltage between the anode 11 and the cathode 15. For this reason, the light-emitting layer 13 may also be referred to as an EL light-emitting layer.

[0016] 1 is an example of an inorganic EL material. However, the light-emitting layer 13 in embodiment 1 may contain an organic EL material. The light-emitting layer 13 may be configured to generate EL light.

[0017] The hole transport layer 12 is located between the light-emitting layer 13 and the anode 11. In the example of FIG. 1 , the hole transport layer 12 is adjacent to the light-emitting layer 13 in the Z direction. The hole transport layer 12 may contain any hole transport material. As an example, the hole transport layer 12 may contain a hole transport material as a main material. In this specification, the term "main material of a certain layer" means a material that occupies 50% or more of the volume ratio of the layer.

[0018] The electron transport layer 14 is located between the light-emitting layer 13 and the cathode 15. In the example of Figure 1, the electron transport layer 14 is adjacent to the light-emitting layer 13 in the Z direction. The electron transport layer 14 may include any electron transport material. As an example, the electron transport layer 14 may include an electron transport material as a main material.

[0019] The light-emitting element 1 in embodiment 1 includes a luminescent transport layer HY. The luminescent transport layer HY may be configured to emit a first light L1 having a first wavelength. In this specification, the first wavelength is denoted as λ1. As an example, the luminescent transport layer HY may be configured to emit the first light L1 as EL light. Therefore, the luminescent transport layer HY may contain any EL material. For this reason, the luminescent transport layer HY may be referred to as an EL luminescent transport layer.

[0020] The luminescent transport layer HY may be any layer as long as it is a carrier transport layer. Therefore, the luminescent transport layer HY may be either a hole transport layer 12 or an electron transport layer 14. The luminescent transport layer HY may be adjacent to at least a part of the luminescent layer 13 in the Z direction. In embodiment 1, a case where the luminescent transport layer HY is a hole transport layer 12 is exemplified.

[0021] As shown in FIG. 1 , first light L1 emitted from the luminescent transport layer HY can enter the luminescent layer 13. Therefore, the luminescent layer 13 can absorb the first light L1 and emit second light L2 having a second wavelength longer than the first wavelength. In this specification, the second wavelength is referred to as λ2. Specifically, the QDs 130 in the luminescent layer 13 can absorb the first light L1 and emit second light L2 having the second wavelength λ2.

[0022] Thus, the QDs 130 in the first embodiment can also emit light by photoluminescence (PL). In the example shown in Figure 1, the second light L2 is PL light. By appropriately setting the band gap of the QDs 130, it is possible to realize a QD 130 that absorbs the first light L1 and emits the second light L2 having a second wavelength λ2.

[0023] (Effects of Light-Emitting Element 1) In a general light-emitting element, carrier overflow may occur. Since carrier overflow can lead to a decrease in the light-emitting efficiency of the light-emitting element, some kind of countermeasure is desired.

[0024] Patent Document 1 discloses a technical idea of ​​providing an electron blocking layer in an organic EL device and optimizing the energy level of the electron blocking layer to improve the carrier balance (in other words, reduce carrier overflow).

[0025] In response to this, the inventors of the present application have discovered a new technical idea that is completely different from that of Patent Document 1, namely, "actively utilizing the overflow of carriers in a light-emitting element." Light-emitting element 1 is created based on this new technical idea. Specifically, light-emitting element 1 is provided with a light-emitting transport layer HY to utilize the overflowed carriers.

[0026] In the light-emitting element 1, the overflowed carriers flow into the light-emitting transport layer HY. As a result, the overflowed carriers generate a first light L1 as electroluminescent light in the light-emitting transport layer HY. Next, the light-emitting layer 13 receives the first light L1, and generates a second light L2 as photoluminescent light in the light-emitting layer 13.

[0027] In this way, the light-emitting layer 13 in the light-emitting element 1 emits PL light in addition to EL light. The PL light (i.e., the second light L2) improves the luminous efficiency of the light-emitting element 1. In addition, the second light L2 is caused by carrier overflow. As described above, the light-emitting element 1 can improve the performance of light-emitting elements using a configuration different from conventional configurations.

[0028] As an example, from the viewpoint of improving the color purity of the light extracted to the outside of the light-emitting element 1, it is preferable that the first light L1 be invisible light. Therefore, for example, the luminescent transport layer HY may be configured to emit the first light L1 as UV light. As an example, the luminescent transport layer HY may be configured to emit the first light L1 with λ1 = 365 nm. In this case, the luminescent layer 13 may be configured to emit the second light L2 having a wavelength peak in the range of 440 nm to 650 nm, for example.

[0029] (Example of a Method for Producing a Luminescent Transport Layer HY) As an example, the luminescent transport layer HY can be obtained by introducing luminescent defects into an inorganic semiconductor layer. For example, inorganic semiconductors such as ZnO, MgZnOm, and AlZnO emit light due to oxygen vacancies. Furthermore, the number of oxygen vacancies can be increased by UV (ultra-violet) exposure.

[0030] As another example, a luminescent transport layer HY can be obtained by mixing a luminescent material into the carrier transport layer. In this example, the luminescent material refers to a material having a higher luminous efficiency than the carrier transport material that is the main material of the carrier transport layer. As an example, the luminescent transport layer HY can be obtained by mixing QDs into the carrier transport layer. In this case, it is preferable that the QDs be as small as possible in order to improve the film formation properties of the luminescent transport layer HY.

[0031] The concentration of the luminescent material in the luminescent transport layer HY may be reduced by mixing a material having a wider bandgap than the luminescent material in the carrier transport layer. This reduces the risk of concentration quenching in the luminescent transport layer HY. As a result, the luminous efficiency of the luminescent transport layer HY can be increased.

[0032] Furthermore, the luminescent transport layer HY may be formed after removing quenching impurities contained in the material of the luminescent transport layer HY by purification. In this case, too, the luminescent efficiency of the luminescent transport layer HY can be increased. Any method such as reprecipitation or sublimation purification can be used as the purification method.

[0033] (Additional information regarding the luminescent transport layer HY) As an example, the luminescent transport layer HY may be configured so that the energy corresponding to the peak wavelength of the first light L1 is smaller than the main band gap of the luminescent transport layer HY. The "main band gap of the luminescent transport layer HY" is defined as, for example, the "band gap of the main material of the luminescent transport layer HY."

[0034] The above-described luminescent transport layer HY allows for more efficient use of overflowed carriers in the light-emitting element 1. In addition, since the energy of the first light L1 emitted from the luminescent transport layer HY is relatively small, damage caused by the first light L1 to each layer of the light-emitting element 1 can also be reduced.

[0035] The luminescent transport layer HY may comprise an oxide semiconductor covered by an oxide insulator. ２ The material may include MZO (Magnesium-Zinc-Oxide) covered with SiO ２ is an example of an oxide insulator, and MZO is an example of an oxide semiconductor.

[0036] The above-described luminous transport layer HY also enables more efficient use of overflowed carriers in the light emitting element 1. In addition, the luminous efficiency of the luminous transport layer HY can be improved.

[0037] [Embodiment 2] Fig. 2 is a diagram illustrating a light-emitting element 1 according to embodiment 2. Fig. 2 shows a virtual line IL that is inclined with respect to a normal line to the surface SS of the substrate 90. In embodiment 2, the inclination angle with respect to the normal line is represented as θ. In Fig. 2, the virtual line IL is shown to indicate θ. θ in the example of Fig. 2 represents the inclination angle in the X direction with respect to the normal line.

[0038] In the example of the second embodiment, when θ=0°, the direction of the virtual line IL coincides with the Z direction. On the other hand, when θ=90°, the direction of the virtual line IL coincides with the X direction. In the second embodiment, the direction of θ=0° (i.e., the Z direction) is referred to as the front direction. On the other hand, the direction of 0°<θ<90° is referred to as the oblique direction.

[0039] The optical path length of the first light L1 traveling in an oblique direction through the thickness of the light-emitting layer 13 is longer than the optical path length of the first light L1 traveling in the front direction. Therefore, the first light L1 traveling in an oblique direction is more easily absorbed by the light-emitting layer 13 than the first light L1 traveling in the front direction. Therefore, by emitting the first light L1 in an oblique direction, the light-emitting efficiency of the light-emitting element 1 can be further improved.

[0040] Therefore, θ will be considered below. In this specification, the radiance of the first light L1 at θ due to PL is denoted as RM1(θ), while the radiance of the second light L2 at θ due to PL is denoted as RM2(θ).

[0041] The wavelength of the excitation light of the PL may be shorter than the wavelength of the first light L1. For example, the wavelength of the excitation light of the PL may be 320 nm.

[0042] In this specification, the thickness of the luminescent transport layer HY is denoted as T1. In the example of Figure 2, T1 is the thickness of the hole transport layer 12. On the other hand, in this specification, the thickness of the luminescent layer 13 is denoted as T2.

[0043] In this specification, the first index value INDEX1 is determined by the following equation (1): INDEX1=RM1(θ) / T1 (1) That is, INDEX1 is determined as a value obtained by dividing RM1(θ) by T1.

[0044] Next, a second index value INDEX2 is determined by the following equation (2): INDEX2=RM2(θ) / T2 (2) That is, INDEX2 is determined as a value obtained by dividing RM2(θ) by T2.

[0045] By realizing a luminescent transport layer HY with high luminous efficiency, RM1(θ) becomes large. Therefore, in the light-emitting element 1, for example, there may be a θ that satisfies the following formula (3): INDEX1≧0.3×INDEX2 ... (3). That is, there may be a θ where the first index value is 0.3 times or more the second index value. As an example, when the internal quantum efficiency of the luminescent transport layer HY is 0.3 or more, formula (3) may hold.

[0046] [Embodiment 3] Fig. 3 is a diagram illustrating a light-emitting device 1 according to embodiment 3. In embodiment 3, RM1(θ) will be further considered. As shown in Fig. 3, the radiance of the first light L1 may have angle dependence. For example, by appropriately designing the resonator structure (described later) in the light-emitting device 1, the radiance of the first light L1 traveling in an oblique direction can be made greater than the radiance of the first light L1 traveling in a frontal direction.

[0047] For this reason, in the light-emitting element 1, for example, θ that satisfies the following formula (4): RM1(θ)≧1.5×RM1(0°) (4) can exist when θ≧20°. That is, when θ≧20°, θ can exist where RM1(θ) is 1.5 times or more of RM1(0°).

[0048] As can be seen from equation (4), the radiance of the first light L1 in the front direction can be set to be relatively small in the light-emitting element 1. By reducing the radiance of the first light L1 in the front direction, the color purity of the light extracted to the outside of the light-emitting element 1 in the front direction can be increased.

[0049] (Additional Information Regarding Radiance in the Front Direction) As an example, when observed from the front direction, the radiance of the first light L1 PL can be 1 / 10 or less of the radiance of the light emitted from the light-emitting layer 13. Note that this observation should be made after eliminating the influence of optical members (e.g., color filters) external to the light-emitting element 1.

[0050] (Example of resonator structure in light-emitting element 1) The light-emitting element 1 may have a resonator structure that strengthens the second light L2 in the Z direction (front direction) and weakens the first light L1 in the Z direction. This resonator structure can improve the color purity of the light extracted to the outside of the light-emitting element 1 in the front direction, and can also improve the luminous efficiency of the light-emitting element 1.

[0051] 1 and the like, there may be a plurality of boundary surfaces with different refractive indices that can serve as reflective surfaces between the light-emitting element 1 and the outside of the light-emitting element 1. In this specification, the boundary surface with the highest reflectance among the plurality of boundary surfaces of the light-emitting element 1 located on the negative side in the Z direction (the side of the substrate 90) is referred to as the first reflective surface. On the other hand, the boundary surface with the highest reflectance among the plurality of boundary surfaces of the light-emitting element 1 located on the positive side in the Z direction (the side opposite to the substrate 90) is referred to as the second reflective surface.

[0052] As an example, consider a case where the first and second reflecting surfaces are flat and parallel to each other, in which the resonator structure of the light-emitting element 1 is formed in the region between the first and second reflecting surfaces.

[0053] When the resonator structure in the light-emitting element 1 completely intensifies light, the following formula (5) is satisfied: holds true.

[0054] On the other hand, if the resonator structure completely attenuates the light, then the following equation (6) is satisfied: The formula (6) is a counterpart to the formula (5).

[0055] In equations (5) and (6), m represents the order of resonance. θD represents the phase shift of light due to reflection at the first reflecting surface. θU represents the phase shift of light due to reflection at the second reflecting surface. λ represents the peak wavelength of light. n represents the refractive index of the layer located between the first reflecting surface and the second reflecting surface. d represents the distance between the first reflecting surface and the second reflecting surface.

[0056] As an example, when the distance d is positive, θD and θU may be set so that the order m in equation (5) is a natural number. θD and θU may be set so that

[0057] In this specification, the value of the distance d when equation (5) is true for order m is denoted as Dm, while the value of the distance d when equation (6) is true for order m is denoted as dm.

[0058] In a resonator structure that intensifies light of a peak wavelength λ, it is preferable that the following formula (8-1) holds, it is more preferable that the following formula (8-2) holds, and it is even more preferable that the following formula (8-3) holds. When formulas (8-1) to (8-3) are generalized using a natural number k, the following formula (8-4) is obtained.

[0059] Equations (8-1), (8-2), and (8-3) correspond to the cases of k = 1, k = 2, and k = 4 in equation (8-4), respectively. As can be understood from this, in a resonator structure that intensifies light, it is preferable that equation (8-4) holds true for a larger k.

[0060] On the other hand, in a resonator structure that weakens light of peak wavelength λ, it is preferable that the following formula (9-1) holds, it is more preferable that the following formula (9-2) holds, and it is even more preferable that the following formula (9-3) holds. When formulas (9-1) to (9-3) are generalized using a natural number k, the following formula (9-4) is obtained. Formula (9-4) is a paired formula with formula (8-4).

[0061] Equations (9-1), (9-2), and (9-3) correspond to the cases of k = 1, k = 2, and k = 4 in equation (9-4), respectively. As can be understood from this, in a resonator structure that weakens light, it is preferable that equation (9-4) holds for a larger k.

[0062] As described above, the second wavelength λ2, which is the wavelength of the second light L2, is different from the first wavelength λ1, which is the wavelength of the first light L1. Therefore, for example, based on equations (8-4) and (9-4), a resonator structure may be designed that strengthens the second light L2 in the Z direction and weakens the first light L1 in the Z direction.

[0063] 4 is a diagram illustrating a light-emitting element 1 according to embodiment 4. In the light-emitting element 1, the anode 11 or the cathode 15, whichever is located on the same side as the light-emitting layer 13 when the light-emitting transport layer HY is used as a reference, may have a metal mirror surface MF.

[0064] As in the above-described embodiments, Fig. 4 also illustrates a case where the hole transport layer 12 is a light-emitting transport layer HY. Therefore, in the example of Fig. 4, the cathode 15 has a metal mirror surface MF. The cathode 15 in the example of Fig. 4 may be any metal electrode. The metal mirror surface MF in the example of Fig. 4 is the lower surface of the cathode 15.

[0065] In the example of embodiment 3, the average refractive index between the luminescent transport layer HY and the metal mirror surface MF of the light-emitting element 1 is denoted as RI. The average refractive index in this specification is given as the optical path length divided by the geometric distance.

[0066] In the third embodiment, the distance D(K) corresponding to an integer K is defined as follows: D(K)=(2K+1)×λ1 / (4RI) (10).

[0067] In the example of Figure 4, a portion of the first light L1 traveling from the light-emitting transport layer HY toward the light-emitting layer 13 is reflected by the metal mirror surface MF, generating the reflected first light L1_RF. The reflected first light L1_RF travels toward the light-emitting layer 13. The metal mirror surface MF allows fixed-end reflection of the first light L1. Therefore, the position of the metal mirror surface MF is the position of a node of the composite wave (composite electric field) of the first light L1 and the reflected first light L1_RF. Therefore, a position a distance D (K) away from the metal mirror surface MF is the position of an antinode of the composite wave.

[0068] Therefore, as shown in Fig. 4, in the fourth embodiment, it is preferable that a portion of the light-emitting layer 13 is located at a distance D (K) from the metal mirror surface MF in the Z direction. In this case, since a portion of the light-emitting layer 13 is located at the antinode of the composite wave, more of the first light can be absorbed by the light-emitting layer 13. In this way, the configuration shown in Fig. 4 can increase the absorptance of the first light by the light-emitting layer 13. As a result, the luminous efficiency of the light-emitting element 1 can be increased.

[0069] [Embodiment 5] In embodiment 5, another configuration example of the luminescent transport layer HY will be described. Fig. 5 shows a configuration example of the hole transport layer 12 as the luminescent transport layer HY in the light-emitting element 1 of embodiment 5. For convenience of explanation, Fig. 5 also shows the luminescent layer 13.

[0070] The emissive transport layer HY in the example of Figure 5 includes QDs 120 and organic material 125. QDs 120 are an example of an EL material. The organic material 125 can be any hole transport material. In the example of Figure 5, holes are transported by the organic material 125. Therefore, current can be effectively passed through the emissive layer 13.

[0071] 5 is a core-shell QD. The QD 120 has a QD core 121 and a QD shell 122 that covers the QD core 121. For example, the QD shell 122 may be an oxide insulator. Examples of oxide insulators include SiO ２ Examples include:

[0072] The QD shells made of oxide insulators may individually surround the outer periphery of the QD core. For example, the QD core and the QD shell surrounding the QD core may be directly bonded. For another example, there may be an air gap between the QD core and the QD shell surrounding the QD core.

[0073] As yet another example, a material other than the QD core and the QD shell may be interposed between the QD core and the QD shell. For example, the QD core and the QD shell may be bonded to each other by an organic material.

[0074] Fig. 6 shows an example of an energy diagram corresponding to the configuration example of Fig. 5. In Fig. 6, the notation "HTL" represents the hole transport layer 12 as the luminescent transport layer HY, and the notation "EML" represents the luminescent layer 13. Furthermore, the notation "FRET" in Fig. 6 represents the Förster transition.

[0075] In the example of the fifth embodiment, the frequency of the first light L1 emitted from the HTL is denoted as vHTL. vHTL corresponds to the reciprocal of the first wavelength λ1. As shown in FIG. 6, the energy of the first light L1 is expressed by the product of Planck's constant h and vHTL.

[0076] In Figure 6, the energy band of the QD 120 is represented by a dotted line. As shown in Figure 6, the band gap of the QD shell 122 is larger than that of the QD core 121. This prevents the presence of the HTL from increasing carrier overflow in the light-emitting device 1. Therefore, the configuration of embodiment 4 also improves the luminous efficiency of the luminous transport layer HY.

[0077] 7 shows an example of the configuration of a light-emitting device according to embodiment 6. The light-emitting device in Fig. 7 is referred to as light-emitting device 2. Unlike light-emitting device 1 in each of the above-described embodiments, light-emitting device 2 has a sloped structure.

[0078] 7 indicates the light-emitting region of the light-emitting element 2. The light-emitting region REG refers to a region in the light-emitting element 2 where EL light is emitted from the light-emitting layer 13 upon receiving carrier injection from the anode 11 and the cathode 15. In the light-emitting region REG, the above-mentioned carrier overflow may occur. Therefore, as shown in FIG. 7 , the first light L1 is emitted from the hole transport layer 12 serving as the light-emitting transport layer HY.

[0079] The light-emitting element 2 includes a first insulating film IS1 located on a side of the light-emitting region REG. In the sixth embodiment, the X direction is used as an example of the direction representing the "side." In the example of FIG. 7, the first insulating film IS1 covers a part of the anode 11. Therefore, the light-emitting region REG in the example of FIG. 7 does not overlap with the first insulating film IS1 when viewed from the Z direction.

[0080] 7, the first insulating film IS1 is a bank of the light-emitting element 2. More specifically, the first insulating film IS1 is a light-transmitting bank. Therefore, a part of the first light L1 emitted from the light-emitting transport layer HY passes through the first insulating film IS1 and travels toward the slope structure described below.

[0081] 7, the light-emitting element 2 has a sloped structure located further to the side of the first insulating film IS1. In other words, in the light-emitting element 2, the light-emitting region REG and the sloped structure are separated by the first insulating film IS1.

[0082] The inclined structure has, from the bottom up, a second insulating film IS2, an inclined portion 22, a light-emitting layer 13, an electron transport layer 14, and a cathode 15. The inclined structure does not have an anode 11. Therefore, in the inclined structure, EL light emission does not occur in the light-emitting layer 13. The inclined structure also does not have a hole transport layer 12 as a light-emitting transport layer HY.

[0083] 7, each portion of the inclined structure forms an inclination angle φ with respect to the surface SS of the substrate 90 (i.e., with respect to the X direction). φ is preferably set to a relatively small angle. In the example of the fifth embodiment, φ is set so that 0°<φ≦15°.

[0084] The inclined portion 22 may be formed of any metal material. The inclined portion 22 has a metal mirror surface MF2. Therefore, the metal mirror surface MF2 reflects the first light L1 arriving from the light-emitting region REG, generating the reflected first light L1_RF. The metal mirror surface MF2 can direct the reflected first light L1_RF toward the light-emitting layer 13 belonging to the inclined structure. Therefore, a larger amount of the first light can be absorbed by the light-emitting layer 13 belonging to the inclined structure.

[0085] In this specification, the distance between the inclined portion 22 inside the inclined structure and the light-emitting layer 13 is referred to as DS. From the viewpoint of allowing the light-emitting layer 13 belonging to the inclined structure to absorb as much of the first light as possible, it is preferable that DS be set as small as possible.

[0086] As an example, in the light-emitting element 2, DS is preferably set so that 0 nm≦DS<50 nm. In the example of Fig. 7, inside the sloped structure, the sloped portion 22 and the light-emitting layer 13 are in contact with each other. Therefore, in the example of Fig. 7, DS=0 nm.

[0087] As described above, the metal mirror surface MF2 forms a relatively small inclination angle φ with respect to the X direction. The inclined portion 22 is located to the side of the light-emitting region REG. Therefore, the first light L1 arriving from the light-emitting region REG can be incident on the metal mirror surface MF2 at a relatively large angle of incidence. As a result, as described below, a relatively large electric field can be obtained as a composite electric field of the first light L1 and the reflected first light L1_RF.

[0088] Fig. 8 shows a schematic diagram of a composite electric field obtained by the metal mirror surface MF2. In the example of Fig. 8, the incident wave corresponds to the first light L1, and the outgoing wave corresponds to the first light L1_RF after reflection. Fig. 8 shows the composite electric field of the incident wave and the outgoing wave. Point P in Fig. 8 is the point of incidence of the first light L1 on the metal mirror surface MF2.

[0089] 8, when the first light L1 is incident on point P at a relatively large incident angle, a relatively large combined electric field is generated in the normal direction of the metal mirror surface MF2 at point P. Therefore, according to the inclined structure of the light-emitting element 2 in FIG. 7, a larger amount of the first light can be absorbed by the light-emitting layer 13 belonging to the inclined structure.

[0090] As a result, in the light-emitting element 2, the second light L2 can be generated even in the light-emitting layer 13 belonging to the sloped structure. As described above, the light-emitting element 2 can also improve the luminous efficiency of the light-emitting element.

[0091] Seventh Embodiment Fig. 9 shows a configuration example of a display device 300 according to a seventh embodiment. The display device 300 may include a light-emitting element (e.g., light-emitting element 1) according to one aspect of the present disclosure. In the example of Fig. 9, the display device 300 includes, as the light-emitting element 1, a first light-emitting element 1-1, a second light-emitting element 1-2, and a third light-emitting element 1-3. As an example, the first light-emitting element 1-1 is a blue light-emitting element, the second light-emitting element 1-2 is a green light-emitting element, and the third light-emitting element 1-3 is a red light-emitting element.

[0092] 9 , the display device 300 includes a display unit DA including a plurality of subpixels SP, a first driver X1 and a second driver X2 that drive the plurality of subpixels SP, and a display controller DC that controls the first driver X1 and the second driver X2. Each subpixel SP includes a light-emitting element 1 and a pixel circuit PC connected to the light-emitting element 1.

[0093] As an example, the pixel circuit PC is connected to a scanning signal line GL, a data signal line DL, and a light-emission control line ELL. The scanning signal line GL and the light-emission control line ELL are connected to a first driver X1. The data signal line DL is connected to a second driver X2.

[0094] [Additional Notes] One aspect of the present disclosure is not limited to the above-described embodiments, 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 one aspect of the present disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0095] 1, 2 Light-emitting element 1-1 First light-emitting element 1-2 Second light-emitting element 1-3 Third light-emitting element 11 Anode 12 Hole transport layer 13 Light-emitting layer 14 Electron transport layer 15 Cathode HY Light-emitting transport layer 22 Sloped portion 90 Substrate 120 QD (QD in light-emitting transport layer) 121 QD core 122 QD shell 125 Organic material 300 Display device MF1 Metal mirror surface (metal mirror surface of anode or cathode) MF2 Metal mirror surface (metal mirror surface of sloped portion)

Claims

1. A light-emitting device comprising an anode and a cathode; and a light-emitting layer, wherein at least a portion of the light-emitting layer is located between the anode and the cathode; the light-emitting device further comprises a light-emitting transport layer adjacent to at least a portion of the light-emitting layer in a thickness direction of the light-emitting device; the light-emitting transport layer emits first light having a first wavelength; and the light-emitting layer absorbs the first light to emit second light having a second wavelength longer than the first wavelength.

2. The light-emitting element of claim 1, wherein the anode, the cathode, the light-emitting layer, and the light-emitting transport layer are supported by a surface of a substrate, and an inclination angle of the substrate with respect to a normal to the surface is denoted as θ, the radiance of the first light at θ is denoted as RM1(θ), and the radiance of the second light at θ is denoted as RM2(θ), and a value obtained by dividing RM1(θ) by the thickness of the light-emitting transport layer is defined as a first index value, and a value obtained by dividing RM2(θ) by the thickness of the light-emitting layer is defined as a second index value, there exists an angle θ at which the first index value is 0.3 times or more of the second index value.

3. The light-emitting device according to claim 1 or 2, wherein the internal quantum efficiency of said light-emitting transport layer is 0.3 or more.

4. A light-emitting device according to any one of claims 1 to 3, wherein the anode, the cathode, the light-emitting layer, and the light-emitting transport layer are supported by a surface of a substrate, and wherein, when the tilt angle of the substrate with respect to a normal to the surface is denoted as θ and the radiance of the first light at θ is denoted as RM1(θ), there exists a θ such that RM1(θ) is 1.5 times or more of RM1(0°) for θ≧20°.

5. A light-emitting element according to any one of claims 1 to 4, wherein one of the anode and the cathode, which is located on the same side as the light-emitting layer when the light-emitting transport layer is used as a reference, has a metal mirror surface, and when the average refractive index between the light-emitting transport layer of the light-emitting element and the metal mirror surface is denoted as RI, the first wavelength is denoted as λ1, and a distance D(K) corresponding to an integer K is defined as D(K) = (2K + 1) × λ1 / (4RI), a part of the light-emitting layer is located at a position D(K) away from the metal mirror surface in the thickness direction.

6. A light-emitting element according to any one of claims 1 to 5, having a resonator structure that strengthens the second light in a normal direction relative to a horizontal plane of a substrate of the light-emitting element and weakens the first light in the normal direction.

7. The light-emitting device according to any one of claims 1 to 6, wherein the energy corresponding to the peak wavelength of said first light is smaller than the main band gap of said luminescent transport layer.

8. The light-emitting device of claim 7, wherein the emissive transport layer comprises an oxide semiconductor covered by an oxide insulator.

9. The light-emitting element according to claim 7, wherein the light-emitting transport layer contains an organic material and a quantum dot (QD).

10. The light-emitting device of claim 9, wherein the QDs in the luminescent transport layer are core-shell QDs, the core-shell QDs have a QD core and a QD shell covering the QD core, and the QD shell is an oxide insulator.

11. A light-emitting element according to any one of claims 1 to 10, wherein the anode, the cathode, the light-emitting layer, and the light-emitting transport layer are supported by a surface of a substrate, the light-emitting element has an inclined portion having a metal mirror surface on one side of the light-emitting region, the inclined portion forms an inclination angle with the surface of the substrate that is greater than 0° and not greater than 15°, and the distance between the inclined portion and the light-emitting layer located on the other side of the light-emitting region is greater than 0 nm and less than 50 nm.

12. The light-emitting element according to any one of claims 1 to 11, wherein the light-emitting transport layer contains a hole transport material as a main material.

13. The light-emitting device according to any one of claims 1 to 11, wherein the light-emitting transport layer contains an electron transport material as a main material.

14. A display device comprising a light-emitting element according to any one of claims 1 to 13.

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