Organic light-emitting diodes

Abstract

To provide an organic light-emitting device that improves the movement of carriers and triplet energy between stacked luminous layers, and has improved drive durability.SOLUTION: Luminous layers include a first luminous layer 4a and a second luminous layer 4b in contact with each other. The first luminous layer 4a includes a first organic compound, a first metal complex, and a second metal complex. The second luminous layer 4b includes a second organic compound and a third metal complex, and does not include the first metal complex. When the triplet energies of the first metal complex, second metal complex, and third metal complex are defined as T1D1, T1D2, and T1D3, respectively, the relationships of the following formulas [a] to [c] are satisfied. [a] T1D2>T1D1; [b] T1D3≥T1D2; [c] T1D2-T1D1>T1D3-T1D2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an organic light-emitting element and various devices having the organic light-emitting element. [Background technology]

[0002] An organic light-emitting element (hereinafter sometimes referred to as an "organic electroluminescent element" or "organic EL element") is an element that emits light by passing an electric current through an organic EL (electroluminescent) layer, which includes an anode, a cathode, and a light-emitting layer placed between these electrodes. In recent years, research and development of full-color displays using organic light-emitting elements has been actively pursued. Organic light-emitting elements are known to be broadly classified into fluorescent light-emitting elements and phosphorescent light-emitting elements depending on the type of compound contained in the light-emitting layer, and the design of an appropriate energy diagram for each is required. On the other hand, when manufacturing full-color displays, two methods are known: one in which the light-emitting layer is painted separately for each pixel (element), and another using an organic light-emitting element where the light-emitting layer emits white light and the color filter is painted separately for each pixel. Furthermore, when using a white light-emitting layer, it is known that the organic light-emitting element uses two or more types of light-emitting materials. Patent Document 1 discloses an organic light-emitting device in which an excited complex host and a light-emitting layer made of a phosphorescent material are laminated. Patent Document 2 discloses an organic light-emitting device in which a light-emitting layer made of a hole-transporting host and a phosphorescent material is laminated, and a light-emitting layer made of an electron-transporting host and a phosphorescent material is laminated. Patent Document 3 discloses an organic light-emitting device in which two light-emitting layers containing a blue phosphorescent material, a green phosphorescent material, and a red phosphorescent material are laminated. Patent Document 4 discloses an organic light-emitting device in which a light-emitting layer containing a blue phosphorescent material and a green phosphorescent material is laminated, and a light-emitting layer containing a red phosphorescent material is laminated. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2014-96557 [Patent Document 2] Japanese Patent Publication No. 2013-200939 [Patent Document 3] Japanese Patent Publication No. 2011-171269 [Patent Document 4] Japanese Patent Publication No. 2010-34484 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, the organic light-emitting element described in the above patent document was an organic light-emitting element that had room for improvement in its durability characteristics because carrier transfer and triplet energy transfer between the two light-emitting layers in contact with each other were difficult to occur. The present invention has been made in view of the above problems, and its objective is to provide an organic light-emitting element that improves carrier transfer and triplet energy transfer between two light-emitting layers in contact with each other, thereby improving driving durability. [Means for solving the problem]

[0005] This invention First The organic light-emitting element comprises a first electrode, a first light-emitting layer, a second light-emitting layer, and a second electrode. The first light-emitting layer and the second light-emitting layer are in contact with each other. The first light-emitting layer comprises a first organic compound, a first metal complex, and a second metal complex. The second light-emitting layer comprises a second organic compound and a third metal complex, but does not contain a first metal complex. When the triplet energies of the first metal complex, the second metal complex, and the third metal complex are T1D1, T1D2, and T1D3, respectively, the following relationships [a] to [c] hold: Chi, T1D2>T1D1 [a] T1D3≧T1D2 [b] T1D2-T1D1>T1D3-T1D2 [c] The first metal complex, the second metal complex, and the third metal complex are characterized by being compounds represented by the following general formula [I]. Ir(L) q(L’) r (L’’) s [I] [In general formula [1], L, L', and L'' each represent different bidentate ligands. q is an integer between 1 and 3, and r and s are integers between 0 and 2, respectively, where q + r + s = 3. When r is 2, the multiple L' elements may be the same or different. When s is 2, the multiple L'' elements may be the same or different. Substructure Ir(L) q This structure is represented by the following general formulas [Ir-5] to [Ir-16].

Chem.

Chem.

[0007] [Figure 1] This is a schematic cross-sectional view of an organic light-emitting element according to one embodiment of the present invention. [Figure 2] This is an energy diagram schematically representing the energy levels around the light-emitting layer of an organic light-emitting element according to one embodiment of the present invention. [Figure 3] This figure schematically represents the triplet energy levels of the metal complex contained in the light-emitting layer of an organic light-emitting device according to one embodiment of the present invention. [Figure 4] (a) A schematic diagram of a display device according to one embodiment of the present invention. (b) A schematic diagram of a display device according to one embodiment of the present invention. [Figure 5] This is a schematic diagram of a display device according to one embodiment of the present invention. [Figure 6] (a) A schematic diagram of an imaging device according to one embodiment of the present invention. (b) A schematic diagram of an electronic device according to one embodiment of the present invention. [Figure 7] (a) A schematic diagram of a display device according to one embodiment of the present invention. (b) A schematic diagram of a foldable display device according to one embodiment of the present invention. [Figure 8] (a) A schematic diagram of a lighting device according to one embodiment of the present invention. (b) A schematic diagram of an automobile having a vehicle light fixture according to one embodiment of the present invention. [Figure 9] (a) A schematic diagram showing an example of a wearable device according to one embodiment of the present invention. (b) A schematic diagram showing an example of a wearable device according to one embodiment of the present invention, which includes an imaging device. [Figure 10] This is a schematic diagram showing an example of an image forming apparatus according to one embodiment of the present invention and an example of its exposure light source. [Modes for carrying out the invention]

[0008] An organic light-emitting element according to one embodiment of the present invention comprises a first electrode, a laminated light-emitting layer consisting of a first light-emitting layer and a second light-emitting layer, and a second electrode. At least one of the first electrode and the second electrode may be a light-transmitting electrode, and either one may be a light-reflecting electrode. The first light-emitting layer and the second light-emitting layer are in contact, with one being the anode side and the other being the cathode side.

[0009] The first light-emitting layer contains a first organic compound, a first metal complex, and a second metal complex, while the second light-emitting layer contains a second organic compound and a third metal complex, but does not contain the first metal complex. That is, the first metal complex and the third metal complex are different metal complexes, and their triplet energies are different. Therefore, the first light-emitting layer and the second light-emitting layer exhibit different emission colors.

[0010] [Laminated light-emitting layer] An organic light-emitting element according to one embodiment of the present invention is characterized in that the following relationships [a] to [c] hold true. T1D2>T1D1 [a] T1D3≧T1D2 [b] T1D2-T1D1>T1D3-T1D2 [c] T1D1, T1D2, and T1D3 above represent the triplet energies of the first, second, and third metal complexes, respectively.

[0011] Equation [a] above shows that the first metal complex has a lower triplet energy than the second metal complex, and therefore, in the first luminescence layer, emission is mainly observed from the first metal complex. Equation [b] above shows that the triplet energy of the tertiary metal complex contained in the second emissive layer is greater than or equal to the triplet energy of the nitric metal complex contained in the first emissive layer. Furthermore, together with equation [a] above, this shows that the tertiary metal complex has a greater triplet energy than the nitric metal complex. Thus, it is shown that the second emissive layer is an emissive layer in which emission at shorter wavelengths is observed than that of the first emissive layer. Equation [c] above shows that the difference in triplet energies between the tertiary metal complex and the detertiary metal complex is smaller than the difference in triplet energies between the primary metal complex and the detertiary metal complex. As will be discussed later, this indicates that energy transfer is more likely to occur between the tertiary metal complex and the detertiary metal complex than between the tertiary metal complex and the primary metal complex.

[0012] Furthermore, since the tertiary and secondary metal complexes are metal complexes with a small or no difference in triplet energy, they have similar energy gaps. Therefore, the relative positions of their HOMO and LUMO energy levels are also close, indicating that carrier transfer is more likely to occur between the tertiary and secondary metal complexes than between the tertiary and primary metal complexes. As will be discussed later, this makes it easier to adjust the exciton density generated in the first and second light-emitting layers, thereby improving drive durability.

[0013] In this specification, triplet energy refers to the energy of the lowest excited triplet state, expressed in units of eV, with higher values ​​indicating higher energy. When converted to wavelength, higher energy corresponds to shorter wavelengths. In this specification, the energy gap refers to the energy gap between the energy level of the HOMO (highest occupied orbital) and the energy level of the LUMO (lowest unoccupied orbital), and is also called the band gap. The HOMO energy level and the LUMO energy level may also be written as "HOMO" or "HOMO level" and "LUMO" or "LUMO level," respectively.

[0014] Embodiments of the present invention will be described in more detail below with reference to Figures 1 to 3. Figure 1 is a schematic cross-sectional view of an organic light-emitting element according to this embodiment. In the organic light-emitting element shown in Figure 1, an anode 2, a hole transport layer 3, a first light-emitting layer 4a, a second light-emitting layer 4b, an electron transport layer 5, and a cathode 6 are arranged in this order on an insulating layer 1.

[0015] In this embodiment, the light-emitting layer refers to the light-emitting layer among the organic compound layers provided between the electrodes. Among the compounds contained in the light-emitting layer, the compound with the largest mass ratio is sometimes called the host, and the compound that contributes primarily to light emission is sometimes called the dopant or guest. More specifically, the host is a material contained in the light-emitting layer whose content in the light-emitting layer exceeds 50% by mass, and the dopant is a material contained in the light-emitting layer whose content in the light-emitting layer is less than 50% by mass. The concentration of the dopant in the light-emitting layer is preferably 0.1% by mass or more and 40% by mass or less, and furthermore, it is desirable to be 30% by mass or less in order to suppress concentration quenching. In this invention, the first organic compound and the second organic compound are the host, and the first metal complex and the third metal complex are the dopants.

[0016] Furthermore, among the compounds contained in the light-emitting layer, the assist material is a compound whose mass ratio is smaller than that of the host compound among the compounds constituting the light-emitting layer, and which assists the light emission of the guest compound. The assist material is also called the second host compound. Alternatively, if the guest compound is considered the first compound, the assist compound can be called the second compound. In this invention, the second metal complex is the assist material.

[0017] Figure 2 is an energy diagram schematically showing the energy levels around the light-emitting layer constituting the organic light-emitting device of the present invention. In the figure, HOMOD1, LUMOD1, HOMOD2, LUMOD2, HOMOD3, LUMOD3, HOMOH1, LUMOH1, HOMOH2, and LUMOH2 represent the HOMO and LUMO levels of the first metal complex, the HOMO and LUMO levels of the second metal complex, the HOMO and LUMO levels of the third metal complex, the HOMO and LUMO levels of the first host, and the HOMO and LUMO levels of the second host, respectively.

[0018] Figure 3 schematically shows the relationship between the triplet energy levels of metal complexes contained in the light-emitting layer constituting an organic light-emitting device according to one embodiment of the present invention. The vertical axis in Figure 3 represents the energy level, with higher energy being represented upwards. In the figure, D1, D2, and D3 represent the first, second, and third metal complexes, respectively, and T1D1, T1D2, and T1D3 represent the triplet energy levels of the first, second, and third metal complexes, respectively.

[0019] As shown in Figure 3, in the present invention, the following relationships [a] to [c] hold between the first metal complex and the second metal complex contained in the first light-emitting layer 4a and the third metal complex contained in the second light-emitting layer 4b.

[0020] T1D2>T1D1 [a] T1D3≧T1D2 [b] T1D2-T1D1>T1D3-T1D2 [c]

[0021] In this invention, the triplet energy of the metal complex may be obtained using either experimentally measured values ​​or values ​​obtained from molecular orbital calculations. The molecular orbital calculation method used for the metal complex in this specification employs the widely used Density Functional Theory (DFT). The functional used was B3PW91, and the basis set was LANL2DZ.In particular, the free-flowing spectroscopy is based on Gaussian09(Gaussian 09,Revision D.01, MJ Frisch, GWTrucks, HBSchlegel, GEScuseria, MARobb, JRCheeseman, G. Scalmani, V. Barone, B. Mennucci, GPetersson, H. Nakatsuji, M. Caricato, X. Li, HHPratchian, AFIzmaylov, J. Bloino, G. Zheng, JLSonne nberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nak ai,T.Vreven,JAMontgomery,Jr.,JEPeralta,F.Ogliaro,M.Bearpark,JJHeyd,E.Brothers,KNKudin,VNStar overov, T. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, JCBurant, SSIyengar, J. Thomas, M. Cossi, N. Rega, JMMillam, M. Klene, JEKnox, JBCross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, REStra p DJFox,Gaussian,Inc.,Wallingford CT,2013.) Then there is a lot of information The snow-white snowflakes are based on a snowstorm.

[0022] An organic light-emitting element according to one embodiment of the present invention has an element configuration having two or more light-emitting layers, and has the following configuration.

[0023] (1) Two luminescent layers are stacked, and each luminescent layer contains a metal complex that is a phosphorescent material exhibiting a different luminescence color, while one of the luminescent layers contains a metal complex that is an assisting material for triplet energy transfer. An organic light-emitting device according to one embodiment of the present invention has two stacked light-emitting layers, each of which has a phosphorescent metal complex. Each light-emitting layer exhibits a different emission wavelength. Phosphorescent emission is emission derived from triplet energy. That is, the triplet energies generated in each light-emitting layer are different, and a relative order exists. Therefore, energy transfer occurs from the light-emitting layer with higher triplet energy to the light-emitting layer with lower triplet energy. The first light-emitting layer and the second light-emitting layer may be stacked in the direction from the first electrode to the second electrode, and the first light-emitting layer may be positioned closer to the first electrode than the second light-emitting layer, or the first light-emitting layer may be positioned closer to the second electrode than the second light-emitting layer.

[0024] Here, the inventors have found that the durability of the device can be improved by rapidly transferring the excess triplet energy generated in a light-emitting layer with a higher triplet energy to an adjacent light-emitting layer with a lower triplet energy. More specifically, a metal complex having a triplet energy intermediate between the metal complexes contained in each light-emitting layer is included in the light-emitting layer to which the energy is transferred. With this configuration, energy transfer from the high-energy light-emitting layer to the adjacent low-energy light-emitting layer can be promoted. In other words, it can be said that the device includes an assisting material for triplet energy transfer.

[0025] Generally, phosphorescent light-emitting devices are prone to triplet-triplet annihilation (TTA) due to the long emission lifetime of the phosphorescent material. TTA occurs when excess triplet excitons that do not transition to the emission process collide with each other. The higher-order excited states resulting from TTA have high energy, which can lead to material degradation and worsen the device's durability.

[0026] The high energy generated by TTA is proportional to the triplet energy of the light-emitting layer. Therefore, in light-emitting layers with higher triplet energies, TTA generates higher-order excited states with even higher energies, thus increasing the risk of material degradation. Thus, it is thought that reducing TTA in higher-energy light-emitting layers and increasing TTA in lower-energy light-emitting layers can suppress material degradation.

[0027] In this invention, the relationships shown in formulas [a] and [b] above hold true. That is, in order to facilitate energy transfer from the second light-emitting layer containing a third metal complex having a higher triplet energy to the first light-emitting layer containing a first metal complex having a lower triplet energy, the first light-emitting layer contains a second metal complex having an intermediate energy level to promote triplet energy transfer. This reduces the TTA that may occur in the second light-emitting layer containing the third metal complex having a higher triplet energy, thereby suppressing material degradation. As a result, an organic light-emitting element with excellent durability can be obtained.

[0028] (2) The triplet energy of the assisting material that facilitates energy transfer is closer to the triplet energy of the luminescent material, which is the source of the energy transfer, than to the luminescent material, which is the destination of the energy transfer. As described above, the present invention is an organic light-emitting element having a multilayer light-emitting layer that can improve drive durability by promoting triplet energy transfer with an assisting material. Generally, energy transfer of triplet excitons is attributed to Dexter energy transfer. As shown in equation [A] below, the rate constant of Dexter energy transfer is proportional to the overlap between the emission spectrum of the energy source (donor) and the absorption spectrum of the energy destination (acceptor). It is also exponentially inversely proportional to the intermolecular distance between the donor and acceptor.

[0029]

number

[0030] Here, the inventors have found that the relationship shown in formula [c] above can promote Dexter energy transfer between the first and second light-emitting layers. That is, in the laminated light-emitting layer configuration according to the present invention, the triplet energy of the second metal complex, which is an assisting material that promotes energy transfer, is closer to the value of the third metal complex, which is the source of energy transfer, than that of the first metal complex, which is the destination of energy transfer, thereby promoting energy transfer.

[0031] In this invention, the assisting material, the second metal complex, is contained in the first light-emitting layer. On the other hand, the energy transfer source, the third metal complex, is contained in the second light-emitting layer. Therefore, the opportunity for contact between the donor (third metal complex) and the acceptor (second metal complex) is limited to the interface between the first and second light-emitting layers.

[0032] From the above formula [A], in Dexter energy transfer, energy transfer is easier when the intermolecular distance between the donor (third metal complex) and the acceptor (second metal complex) is short. Therefore, it is preferable that the distance between the donor (third metal complex) and the acceptor (second metal complex) is short. Accordingly, the inventors have found that by reducing the difference in triplet energies between the donor (third metal complex) and the acceptor (second metal complex), compatibility is increased and the intermolecular distance is shortened.

[0033] This is presumed to be because, as metal complexes, they have similar molecular structures, and because they are metal complexes, they have similar energies and their dipole moments tend to align, making it easier for the molecules to approach each other.

[0034] For example, when a second emissive layer is stacked after the formation of a first emissive layer containing acceptors (second metal complexes), donors (tertiary metal complexes) tend to accumulate around acceptors (second metal complexes), which are molecules with similar energy levels that are more energetically stable. As a result, the intermolecular distance between the donors (tertiary metal complexes) and acceptors (second metal complexes) decreases. Furthermore, because the difference in triplet energies between the donors (tertiary metal complexes) and acceptors (second metal complexes) is small, the overlap between the emission spectrum (phosphorescence) of the donors and the absorption spectrum of the acceptors becomes sufficiently large.

[0035] Therefore, the relationship shown in equation [c] above is necessary to shorten the intermolecular distance between the donor (third metal complex) and the acceptor (second metal complex), and the overlap between the emission spectrum of the donor and the absorption spectrum of the acceptor becomes sufficiently large, thus promoting Dexter energy transfer.

[0036] Furthermore, after energy transfer from the third metal complex to the second metal complex, energy transfer occurs from the second metal complex to the first metal complex within the first light-emitting layer, leading to the light-emitting process of the first metal complex. By creating a multilayer light-emitting layer that undergoes a continuous triplet energy transfer process in this way, it is expected that the accumulation of excess triplet excitons that do not reach the light-emitting process can be reduced. In other words, diffusion of triplet excitons in the multilayer light-emitting layer is more likely to occur. That is, the TTA itself, where excess triplet excitons collide with each other, can be reduced, and one of the features of this invention is that it can result in an organic light-emitting element with improved durability.

[0037] In addition to the above-mentioned (1) and (2), the organic light-emitting element according to one embodiment of the present invention preferably has the following configuration. <3> The concentration of the second metal complex in the first luminescent layer is higher than the concentration of the third metal complex in the second luminescent layer. <4> The concentration of the second metal complex in the first luminescent layer is higher than the concentration of the first metal complex. <5> The second metal complex and the third metal complex have at least one identical ligand. <6> The second and third metal complexes have a HOMO level difference of 0.2 eV or less and a LUMO level difference of 0.2 eV or less. <7> The first metal complex is a red phosphorescent material, and the third metal complex is a green phosphorescent material. <8> The second light-emitting layer has a second organic compound (assist material) that is not a metal complex. <9> The first electrode is the anode, the second electrode is the cathode, the first light-emitting layer is on the anode side, and the second light-emitting layer is on the cathode side. <10> The concentration of the tertiary metal complex in the second luminescence layer is higher than the concentration of the primary metal complex in the first luminescence layer. <11> The second metal complex and the third metal complex are the same compound. <12> The first organic compound (host of the first light-emitting layer) and the second organic compound (host of the second light-emitting layer) are the same compound. The following explains these points.

[0038] <3> The concentration of the second metal complex is higher than the concentration of the third metal complex. As described above, the opportunity for contact between the tertiary metal complex (donor) contained in the second light-emitting layer and the detertiary metal complex (acceptor) contained in the first light-emitting layer is limited to the interface between the first and second light-emitting layers. Here, by increasing the concentration of the detertiary metal complex (acceptor) compared to the tertiary metal complex (donor), energy transfer between the first and second light-emitting layers can be promoted. The detertiary metal complex that has accepted energy then needs to transfer that energy to the first metal complex. Here, if the concentration of the tertiary metal complex (donor) is higher, the detertiary metal complex (acceptor) accepts a large amount of triplet energy from the tertiary metal complex (donor), resulting in the detertiary metal complex (acceptor) having many triplet excitons before it can transfer energy to the first metal complex, which makes it more likely to generate TTA. If TTA is generated in the detertiary metal complex, energy transfer to the first metal complex becomes impossible, which is undesirable.

[0039] Therefore, it is preferable that the concentration of the second metal complex is higher than the concentration of the tertiary metal complex, and that the relationship shown in the following formula [d] holds. C1D2≧C1D3 [d] C1D2 and C1D3 represent the concentrations of the second metal complex in the first luminescence layer and the third metal complex in the second luminescence layer, respectively.

[0040] <4> The concentration of the second metal complex in the first luminescent layer is higher than the concentration of the first metal complex. A key feature of the organic light-emitting device of the present invention is that triplet energy transfer occurs continuously. Specifically, energy transfer occurs from the third metal complex to the second metal complex, and then from the second metal complex to the first metal complex. By creating a multilayer light-emitting layer that undergoes this continuous triplet energy transfer process, it is expected that the accumulation of excess triplet excitons that do not reach the light-emitting process can be reduced.

[0041] Here, it is preferable that the concentration of the second metal complex is higher than the concentration of the first metal complex. If the concentration of the first metal complex is high, the triplet energy transfer from the third metal complex will be transferred to the first metal complex instead of the second metal complex, making it difficult for the excitons to diffuse through the continuous energy transfer process described above.

[0042] Therefore, it is preferable that the concentration of the second metal complex is higher than the concentration of the first metal complex, and that the relationship shown in the following equation [e] holds. C1D2≧C1D1 [e] C1D1 and C1D2 represent the concentrations of the first and second metal complexes in the first luminescent layer, respectively.

[0043] <5> The second metal complex and the third metal complex have at least one identical ligand. As described above, the increased compatibility between the tertiary metal complex (donor) in the second light-emitting layer and the dizygous metal complex (acceptor) in the first light-emitting layer promotes energy transfer between the first and second light-emitting layers. Here, as a means of increasing the compatibility between the tertiary metal complex (donor) and the detertiary metal complex (acceptor), it is preferable that they have the same substructure in their molecules. Specifically, it is preferable that at least one of the ligands forming the metal complex has the same structure. This makes it easier for ligands with the same structure to approach each other, and as a result, it is expected that the intermolecular distance between the tertiary metal complex (donor) and the detertiary metal complex (acceptor) will be shortened. For example, it is preferable that the detertiary and tertiary metal complexes are metal complexes that simultaneously have one of the following molecular structures. The following example uses the phenylpyridine skeleton, pyridylpyridine skeleton, phenylpyrimidine skeleton, and phenylpyrazine skeleton, which are representative skeletons of bidentate ligands, and ligands with fused ring structures, monodentate ligands, tridentate ligands, and tetradentate ligands can be used. Note that in the following structural formulas, the two bonds between the ligand and the Ir metal are both represented by dotted lines, one being a covalent bond and the other a coordinate bond.

[0044] [ka]

[0045] <6> The second and third metal complexes have a HOMO level difference of 0.2 eV or less and a LUMO level difference of 0.2 eV or less. In Figure 2, the light-emitting layer 4a contains a host (first organic compound), an assisting material (second metal complex), and a dopant (first metal complex). The light-emitting layer 4b contains a host (second organic compound) and a dopant (third metal complex). Therefore, it is conceivable that the dopant or assisting material acts as a trapping level for moving carriers (holes and electrons) in the light-emitting layer.

[0046] Here, it is preferable that the HOMO level difference between the second and third metal complexes is within 0.2 eV and the LUMO level difference is within 0.2 eV. This relationship promotes carrier transfer between the first and second light-emitting layers. In other words, carrier transfer is promoted when the second metal complex, which is the carrier trap level of the first light-emitting layer, and the third metal complex, which is the carrier trap level of the second light-emitting layer, have similar HOMO and LUMO levels. If there is an extreme difference in the HOMO or LUMO levels between the second and third metal complexes, carriers will accumulate at the interface between the first and second light-emitting layers, causing a concentration of recombination regions, which is detrimental to luminescence efficiency and device durability. By promoting carrier transfer, unwanted charge accumulation is eliminated and exciton concentration is also eliminated, so TTA generation can be reduced and durability characteristics can be improved.

[0047] Therefore, it is preferable that the following relationships [f] and [g] hold. |LUMOD3-LUMOD2|≦0.2eV [f] |HOMOD3-HOMOD2|≦0.2eV [g] In [f] and [g], HOMOD2, LUMOD2, HOMOD3, and LUMOD3 represent the HOMO level and LUMO level of the second metal complex, and the HOMO level and LUMO level of the tertiary metal complex, respectively. Furthermore, the relationship between equations [f] and [g] above is also advantageous because it makes it easier to adjust the carrier balance between the first and second light-emitting layers.

[0048] <7> The first metal complex is a red phosphorescent material, and the third metal complex is a green phosphorescent material. From the viewpoint of maximizing the luminescence efficiency of the first and second light-emitting layers while satisfying the relationship between formulas [a] and [b], it is preferable that the first metal complex is a red phosphorescent material and the third metal complex is a green phosphorescent material. In the organic light-emitting element according to one embodiment of the present invention, the stacked structure is such that the recombination region is slightly biased towards the second light-emitting layer, allowing for efficient energy transfer to the first light-emitting layer, and making it easier to achieve a good balance of green and red light emission.

[0049] In this specification, a blue light-emitting material refers to a light-emitting material whose maximum peak wavelength in its emission spectrum is 430 nm to 480 nm. A green light-emitting material refers to a light-emitting material whose maximum peak wavelength in its emission spectrum is 500 nm to 570 nm. A red light-emitting material refers to a light-emitting material whose maximum peak wavelength in its emission spectrum is 580 nm to 680 nm. The emission spectrum is preferably obtained using a dilute toluene solution or the like to reduce the influence of other compounds and crystalline state.

[0050] Furthermore, yellow emission refers to a state where the main part of the emission spectrum is between 565 nm and 590 nm. For example, yellow emission can be obtained by mixing green emission and red emission. Similarly, cyan emission refers to a state where the main part of the emission spectrum is between 485 nm and 500 nm. For example, cyan emission can be obtained by mixing blue emission and green emission.

[0051] <8> The second light-emitting layer has an assisting material that is not a metal complex. As described above, in the organic light-emitting element according to one embodiment of the present invention, by slightly shifting the recombination region toward the second light-emitting layer, energy can be efficiently transferred to the first light-emitting layer, and as a result, well-balanced light emission can be obtained from each light-emitting layer.

[0052] Here, it is preferable that the second light-emitting layer contains a second organic compound, which is not a metal complex, as an assisting material. If the assisting material of the second light-emitting layer is also a phosphorescent metal complex, as described above, energy transfer between the third metal complex and the assisting material of the second light-emitting layer, i.e., energy transfer within the second light-emitting layer, is promoted, and energy transfer to the first light-emitting layer is inhibited, which is undesirable. The assisting material of the second light-emitting layer is preferably not a metal complex, and is a material that implants either hole or electron carriers into the light-emitting layer, thereby adjusting the recombination region slightly towards the center of the second light-emitting layer. Specifically, materials having one of the following skeletons—triarylamine, carbazole, azine ring, or xanthone—are preferred. These materials are preferred because they exhibit excellent electron-donating and electron-withdrawing properties, making it easier to adjust the HOMO and LUMO levels and promoting carrier injection from the surrounding layer.

[0053] <9> The first light-emitting layer is on the anode side, and the second light-emitting layer is on the cathode side. In addition to satisfying the above-mentioned condition <7>, it is preferable that the light-emitting layer 4a on the anode side contains a host (first organic compound), an assist material (second metal complex), and a dopant (first metal complex), as shown in Figure 2. Furthermore, it is preferable that the light-emitting layer 4b on the cathode side contains a host (second organic compound) and a dopant (third metal complex). In this case, the first metal complex, which is the red phosphorescent material, traps holes, and the third metal complex, which is the green phosphorescent material, traps electrons, resulting in a layered structure with the best carrier balance.

[0054] <10> The concentration of the tertiary metal complex in the second luminescence layer is higher than the concentration of the primary metal complex in the first luminescence layer. In addition to the above-mentioned condition <9>, it is preferable that the concentration of the tertiary metal complex be higher than that of the first metal complex. Because the first metal complex is a red phosphorescent material, it has a small band gap and therefore tends to have high carrier trapping properties. In this embodiment, hole trapping properties are high. Therefore, if the concentration of the first metal complex, which is a red phosphorescent material, is high, the hole concentration in the first light-emitting layer becomes localized, which is undesirable. Thus, the concentration of the first metal complex is kept low, and the role of hole transport in the first light-emitting layer is taken over by the second metal complex, which is an assisting material, to adjust the carrier balance. On the other hand, in the second light-emitting layer, the tertiary metal complex is responsible for electron transport, and as described above, smooth exchange of carriers with the second metal complex can be expected. Therefore, it is preferable that the concentration of the tertiary metal complex be higher than that of the first metal complex, and that the relationship shown in the following equation [h] holds. C1D3>C1D1 [h] C1D1 and C1D3 represent the concentration of the first metal complex in the first luminescence layer and the concentration of the tertiary metal complex in the second luminescence layer, respectively.

[0055] <11> The second metal complex and the third metal complex are the same compound. As described above, in embodiments of the present invention, it is preferable that carrier transfer and energy transfer between the first and second light-emitting layers are good. For this reason, it is preferable that the second metal complex and the third metal complex are the same compound. In this case, carrier transfer and energy transfer between the first and second light-emitting layers can be particularly promoted.

[0056] <12> The first organic compound and the second organic compound are the same compound. As described above, in embodiments of the present invention, it is preferable that carrier transfer and energy transfer between the first light-emitting layer and the second light-emitting layer are good. For this reason, it is preferable that the host (first organic compound) of the first light-emitting layer and the host (second organic compound) of the second light-emitting layer are the same compound. In this case, carrier transfer and energy transfer between the first light-emitting layer and the second light-emitting layer can be particularly promoted.

[0057] [First to Third Metal Complexes] Next, the first to third metal complexes used in one embodiment of the organic light-emitting device of the present invention will be specifically described. As the first to third metal complexes used in one embodiment of the present invention, compounds represented by the following general formula [I] are preferably used. Ir(L) q (L’) r (L’’) s [I] In general formula [1], L, L’, and L’’ each represent a different bidentate ligand. q is an integer from 1 to 3, and r and s are each an integer from 0 to 2. However, q + r + s = 3. When r is 2, the plurality of L’s may be the same or different from each other. When s is 2, the plurality of L’’s may be the same or different from each other. The partial structure Ir(L) q has a structure represented by the following general formulas [Ir-1] to [Ir-16].

[0058] [Chemical Formula]

[0059] [Chemical Formula]

[0060] In general formulas [Ir-1] to [Ir-16], Ar1 and Ar2 are each independently a deuterium atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted silyl group, or a cyano group. Specifically, Ar1 to Ar2 are preferably a deuterium atom, a fluorine atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, an aryl group having 6 to 10 carbon atoms, a silyl group substituted with an alkyl group, or a cyano group, and more preferably a methyl group, a tert-butyl group, or a phenyl group. p1 and p2 are each independently any integer from 0 to 4.

[0061] In general formulas [Ir-5] to [Ir-16], X is selected from oxygen atoms, sulfur atoms, C(R1)(R2), or NR3. R1 to R3 are independently selected from hydrogen atoms, deuterium atoms, halogen atoms, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkoxy groups, substituted or unsubstituted amino groups, substituted or unsubstituted aryloxy groups, substituted or unsubstituted aryl groups, substituted or unsubstituted heterocyclic groups, substituted or unsubstituted silyl groups, and cyano groups. R1 and R2 may bond to each other to form a ring. Specifically, R1 to R3 are preferably C1 to C3 alkyl groups or phenyl groups, and more preferably methyl groups.

[0062] Furthermore, as described above, the metal complex used in the present invention is a dopant or assist material, and it is particularly preferable that it has a skeleton that facilitates carrier transfer and energy transfer. Therefore, by using a highly planar compound having a fused ring structure in the ligand, the intermolecular distance is shortened. This is because highly planar substructures can easily come into close proximity to each other. As a result, energy transfer by the Dexter mechanism is more likely to occur, making it possible to provide an organic light-emitting element with high drive durability and highly efficient luminescence characteristics. Specifically, metal complexes represented by general formulas [Ir-5] to [Ir-16] are preferably used.

[0063] More specifically, it is even more preferable that the first to third metal complex has a triphenylene skeleton, phenanthrene skeleton, fluorene skeleton, benzofluorene skeleton, dibenzofuran skeleton, dibenzothiophene skeleton, benzoisoquinoline skeleton, or naphthoisoquinoline skeleton as a ligand. By using a metal complex having at least one of these skeletons as a ligand, the organic compound according to this embodiment can provide an organic light-emitting element with even better luminescence efficiency.

[0064] Specific examples of the first to third metal complexes according to this embodiment are shown below. However, the present invention is not limited to these. In the following structural formulas, the two bonds between the ligand and the iridium atom may both be represented by solid lines; in this case, one bond may be a covalent bond and the other a coordinate bond. On the other hand, when solid and dotted lines are mixed, the solid lines may represent covalent bonds and the dotted lines may represent coordinate bonds. Of the following specific examples, JJ1 to JJ30 are specific examples of general formulas [Ir-1] to [Ir-4], and the others are specific examples of general formulas [Ir-5] to [Ir-16].

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[0082] Among the organometallic complexes described above, the exemplary compounds belonging to groups AA and BB are compounds that have at least a phenanthrene skeleton as a ligand in the Ir complex, and are particularly stable compounds. Among the organometallic complexes mentioned above, the exemplary compounds belonging to the CC group are compounds that have at least a triphenylene skeleton as a ligand in the Ir complex, and are particularly stable compounds. Among the organometallic complexes described above, the exemplary compounds belonging to the DD group are those having at least a dibenzofuran skeleton or a dibenzothiophene skeleton as a ligand in the Ir complex. Because these compounds contain oxygen and sulfur atoms in their fused rings, the abundant lone pairs of electrons on these atoms can enhance charge transport. Therefore, they are particularly well-suited for adjusting carrier balance.

[0083] Among the organometallic complexes described above, the exemplary compounds belonging to the EE, FF, and GG groups are compounds that have at least a benzofluorene skeleton as a ligand of the Ir complex. These compounds further have a substituent at the 9-position of the fluorene ring. Therefore, because the substituent is oriented perpendicular to the in-plane direction of the fluorene ring, overlapping of fused rings can be particularly suppressed. As a result, these compounds exhibit particularly excellent sublimation properties.

[0084] Among the organometallic complexes described above, the exemplary compounds belonging to the HH group are compounds that have at least a benzoisoquinoline skeleton as a ligand in the Ir complex. Because these compounds contain nitrogen atoms in the fused ring, their charge transport properties can be enhanced by the lone pairs of electrons and high electronegativity of these atoms. Therefore, they are compounds that are particularly good at adjusting the carrier balance.

[0085] Among the organometallic complexes described above, the exemplary compounds belonging to Group II are those that have at least a naphthoisoquinoline skeleton as a ligand in the Ir complex. Because these compounds contain nitrogen atoms in the fused ring, their charge transport properties can be enhanced by the lone pairs of electrons and high electronegativity of these atoms. Therefore, they are particularly well-suited for adjusting the carrier balance.

[0086] In this embodiment, the light-emitting materials mainly involved in the light-emitting function include, in addition to the organometallic complexes represented by the general formulas [Ir-1] to [Ir-16] above, fused ring compounds (e.g., fluorene derivatives, naphthalene derivatives, pyrene derivatives, perylene derivatives, tetracene derivatives, anthracene derivatives, rubrene, etc.), quinacridone derivatives, coumarin derivatives, stilbene derivatives, organoaluminum complexes such as tris(8-quinolinolate)aluminum, iridium complexes, platinum complexes, rhenium complexes, copper complexes, europium complexes, ruthenium complexes, and polymer derivatives such as poly(phenylenevinylene) derivatives, poly(fluorene) derivatives, and poly(phenylene) derivatives.

[0087] The following are specific examples of compounds used as luminescent materials, but are not limited to these. In the following examples, BD9, GD10 to GD19, and RD3 to RD11 are metal complexes and can also be used as first to third metal complexes according to this embodiment. Furthermore, compounds other than metal complexes can be used as luminescent materials in combination with first and third metal complexes.

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[0091] [First and Second Organic Compounds] The embodiments of the present invention have a configuration that allows for good carrier transfer and energy transfer between the first and second light-emitting layers. For this reason, the first and second organic compounds used as the first and second hosts in the present invention are preferably compounds with excellent carrier transport ability. Therefore, as the first or second host, materials having one of the following skeletons—dibenzothiophene, dibenzofuran, triphenylene, or phenanthrene—are preferred. These materials have highly planar skeletons that can promote carrier movement between light-emitting layers, and thus, by using these materials, organic light-emitting devices with excellent luminescence efficiency can be obtained. When these host materials are combined with the device configuration according to the present invention, a good carrier balance can be achieved, and an organic light-emitting element with superior device durability can be provided.

[0092] [Third organic compound] The embodiment of the present invention has a configuration that allows for good carrier transfer and energy transfer between the first and second light-emitting layers. For this reason, the second light-emitting layer of the present invention preferably contains a third organic compound as an assisting material, and the assisting material is preferably a compound that easily adjusts the carrier balance. Specifically, materials having one of the following skeletons—triarylamine, carbazole, azine, or xanthone—are preferred. These materials exhibit excellent electron-donating and electron-withdrawing properties, making it easy to adjust the HOMO and LUMO levels and promoting carrier injection from the surrounding layer. Therefore, using these materials yields organic light-emitting devices with excellent luminescence efficiency. When these assist materials are combined with the device configuration according to the present invention, a good carrier balance can be achieved, and an organic light-emitting element with superior device durability can be provided.

[0093] In addition to the materials described above in [First and Second Organic Compounds] and [Third Organic Compound], other host materials or assist materials included in the light-emitting layer include aromatic hydrocarbon compounds or their derivatives, as well as carbazole derivatives, dibenzofuran derivatives, dibenzothiophene derivatives, organoaluminum complexes such as tris(8-quinolinolate)aluminum, and organoberylium complexes.

[0094] In particular, materials having a carbazole skeleton, materials having an azine ring, or materials having a xanthone skeleton are preferred as assisting materials. These materials have high electron-donating and electron-withdrawing properties, making it easy to adjust the HOMO and LUMO levels. Therefore, when these assisting materials are combined with the metal complex according to the present invention, a good carrier balance can be achieved. The following are specific examples of compounds used as host or assist materials in the light-emitting layer, but of course, they are not the only ones that can be used. Furthermore, among the specific examples below, materials having a carbazole skeleton are EM32 to EM38. Materials having an azine ring are EM35 to EM40. Materials having a xanthone skeleton are EM28 and EM30.

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[0097] [Other compounds] In the organic light-emitting element of this embodiment, a hole injection layer, a hole transport layer, an electron blocking layer, an electron injection layer, an electron transport layer, and a hole blocking layer can be arranged between the light-emitting layer and the electrode, as needed. For hole injection and transport layers, materials with high hole mobility are preferred to facilitate hole injection from the anode and transport the injected holes to the light-emitting layer. Furthermore, materials with a high glass transition temperature are preferred to suppress film quality degradation such as crystallization within the organic light-emitting element. Examples of low-molecular-weight and high-molecular-weight materials with hole injection and transport properties include triarylamine derivatives, arylcarbazole derivatives, phenylenediamine derivatives, stilbene derivatives, phthalocyanine derivatives, porphyrin derivatives, poly(vinylcarbazole), poly(thiophene), and other conductive polymers. These hole injection and transport materials are also suitable for use in electron blocking layers. The following are specific examples of compounds used as hole injection transport materials, but of course, they are not the only ones.

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[0099] Suitable electron transport materials for electron injection layers and electron transport layers can be arbitrarily selected from those capable of transporting electrons injected from the cathode to the light-emitting layer, taking into consideration the balance with the hole mobility of hole transport materials. Examples of materials with electron transport properties include oxadiazole derivatives, pyrazine derivatives, triazole derivatives, triazine derivatives, quinoline derivatives, quinoxaline derivatives, phenanthroline derivatives, organoaluminum complexes, and fused ring compounds (e.g., fluorene derivatives, naphthalene derivatives, chrysene derivatives, anthracene derivatives, etc.). Furthermore, the above electron transport materials are also suitably used in hole blocking layers. The following are specific examples of compounds used as electron transport materials, but of course, they are not the only ones.

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[0101] [Configuration of organic light-emitting diodes] The following describes the components other than the organic compound layer that constitute the organic light-emitting element of this embodiment. An organic light-emitting element is provided on a substrate by forming an insulating layer, a first electrode, an organic compound layer, and a second electrode. A protective layer, a color filter, a microlens, etc., may be provided on the second electrode. If a color filter is provided, a planarization layer may be provided between it and the protective layer. The planarization layer can be made of acrylic resin or the like. The same applies when a planarization layer is provided between the color filter and the microlens.

[0102] <substrate> Examples of substrates include quartz, glass, silicon wafers, resins, and metals. The substrate may also be equipped with switching elements such as transistors and wiring, and an insulating layer may be provided on top of them. The insulating layer can be made of any material that allows for the formation of contact holes between it and the first electrode, while ensuring insulation from wiring that is not connected. For example, resins such as polyimide, silicon oxide, and silicon nitride can be used.

[0103] <electrode> A pair of electrodes can be used. The pair of electrodes may be an anode and a cathode. When an electric field is applied in the direction in which the organic light-emitting element emits light, the electrode with the higher potential is the anode, and the other is the cathode. Alternatively, the electrode that supplies holes to the light-emitting layer can be the anode, and the electrode that supplies electrons can be the cathode.

[0104] For the anode, materials with the largest possible work function are preferable. For example, elemental metals such as gold, platinum, silver, copper, nickel, palladium, cobalt, selenium, vanadium, and tungsten, or mixtures containing these, or alloys combining them, as well as metal oxides such as tin oxide, zinc oxide, indium oxide, tin-indium oxide (ITO), and zinc-indium oxide can be used. Conductive polymers such as polyaniline, polypyrrole, and polythiophene can also be used. These electrode materials may be used individually or in combination of two or more types. Furthermore, the anode may consist of a single layer or multiple layers.

[0105] When used as a reflective electrode, materials such as chromium, aluminum, silver, titanium, tungsten, molybdenum, or alloys or laminates thereof can be used. It is also possible to use the above materials as a reflective film without serving as an electrode. Furthermore, when used as a transparent electrode, oxide transparent conductive layers such as indium tin oxide (ITO) or indium zinc oxide can be used, but are not limited to these. Photolithography can be used to form the electrodes.

[0106] On the other hand, materials with a small work function are preferred for the cathode. Examples include alkali metals such as lithium, alkaline earth metals such as calcium, and elemental metals or mixtures containing these, such as aluminum, titanium, manganese, silver, lead, and chromium. Alternatively, alloys combining these elemental metals can also be used. For example, magnesium-silver, aluminum-lithium, aluminum-magnesium, silver-copper, and zinc-silver can be used. Metal oxides such as indium tin oxide (ITO) can also be used. These electrode materials may be used individually or in combination of two or more. The cathode may also be a single-layer or multi-layer structure. Among these, silver is preferred, and a silver alloy is even more preferred to reduce silver aggregation. The alloy ratio is not important as long as silver aggregation is reduced. For example, the ratio of silver to other metals may be 1:1, 3:1, etc.

[0107] The cathode may be a top-emission element using an oxide conductive layer such as ITO, or a bottom-emission element using a reflective electrode such as aluminum (Al), and is not particularly limited. The method for forming the cathode is not particularly limited, but using DC and AC sputtering methods is more preferable because it provides good film coverage and makes it easier to reduce resistance.

[0108] <Organic compound layer> The organic compound layer according to this embodiment is disposed between the first electrode and the second electrode and comprises a laminated light-emitting layer consisting of the first light-emitting layer and the second light-emitting layer described above, and optionally a hole injection layer, a hole transport layer, an electron blocking layer, an electron injection layer, an electron transport layer, and a hole blocking layer. The organic compound layer is mainly composed of organic compounds, but may also contain inorganic atoms and inorganic compounds. For example, it may contain copper, lithium, magnesium, aluminum, iridium, platinum, molybdenum, zinc, etc.

[0109] Organic compound layers (hole injection layers, hole transport layers, electron blocking layers, light-emitting layers, hole blocking layers, electron transport layers, electron injection layers, etc.) can be formed by dry processes such as vacuum deposition, ionization deposition, sputtering, and plasma deposition. Alternatively, a wet process can be used instead of a dry process, in which the layer is formed by dissolving the compound in a suitable solvent and applying a known coating method (e.g., spin coating, dipping, casting, LB method, inkjet method, etc.). When layers are formed using methods such as vacuum deposition or solution coating, crystallization is less likely to occur, resulting in excellent stability over time. Furthermore, when forming films using coating methods, it is possible to combine the film with an appropriate binder resin.

[0110] Examples of the binder resins mentioned above include, but are not limited to, polyvinylcarbazole resin, polycarbonate resin, polyester resin, ABS resin, acrylic resin, polyimide resin, phenolic resin, epoxy resin, silicone resin, and urea resin. Furthermore, these binder resins may be used individually as homopolymers or copolymers, or as a mixture of two or more types. Additionally, known additives such as plasticizers, antioxidants, and UV absorbers may be used in combination as needed.

[0111] <Protective layer> A protective layer may be provided on the cathode. For example, by bonding glass with a desiccant to the cathode, the intrusion of water and other substances into the organic compound layer can be reduced, thereby reducing the occurrence of display defects. In another embodiment, a passivation film such as silicon nitride may be provided on the cathode to reduce the intrusion of water and other substances into the organic compound layer. For example, after forming the cathode, it may be transported to another chamber without breaking the vacuum and a silicon nitride film with a thickness of 2 μm may be formed by the CVD method to serve as a protective layer. A protective layer may also be provided using atomic deposition (ALD) after the film formation by the CVD method. The material of the film formed by the ALD method is not limited, but may be silicon nitride, silicon oxide, aluminum oxide, etc. Silicon nitride may be further formed on the film formed by the ALD method by the CVD method. The film formed by the ALD method may have a thinner film thickness than the film formed by the CVD method. Specifically, it may be 50% or less, or even 10% or less.

[0112] <Color Filter> A color filter may be provided on top of the protective layer. For example, a color filter that takes into account the size of the organic light-emitting element may be provided on a separate substrate and bonded to the substrate on which the organic light-emitting element is provided, or a color filter may be patterned on the protective layer as described above using photolithography technology. The color filter may be made of polymer.

[0113] <Planarization layer> A planarizing layer may be provided between the color filter and the protective layer. The planarizing layer is provided to reduce the unevenness of the layer below. It may also be called a material resin layer without limiting its purpose. The planarizing layer may be composed of an organic compound, which may be low molecular weight or high molecular weight, but high molecular weight is preferred.

[0114] The planarization layer may be provided above or below the color filter, and its constituent materials may be the same or different. Specifically, examples include polyvinylcarbazole resin, polycarbonate resin, polyester resin, ABS resin, acrylic resin, polyimide resin, phenolic resin, epoxy resin, silicone resin, urea resin, etc.

[0115] <Microlens> An organic light-emitting element may have optical components such as microlenses on its light-emitting side. Microlenses may be made of acrylic resin, epoxy resin, or the like. Microlenses may be used to increase the amount of light extracted from the organic light-emitting element or to control the direction of the extracted light. Microlenses may have a hemispherical shape. If they have a hemispherical shape, among the tangents tangent to the hemisphere, there is a tangent parallel to the insulating layer, and the point of contact between that tangent and the hemisphere is the vertex of the microlens. The vertex of the microlens can be similarly determined in any cross-sectional view. That is, among the tangents tangent to the semicircle of the microlens in the cross-sectional view, there is a tangent parallel to the insulating layer, and the point of contact between that tangent and the semicircle is the vertex of the microlens.

[0116] Furthermore, the midpoint of a microlens can also be defined. In the cross-section of a microlens, a line segment can be imagined from the point where one arc ends to the point where another arc ends, and the midpoint of this line segment can be called the midpoint of the microlens. The cross-section used to determine the vertices and midpoints may be a cross-section perpendicular to the insulating layer.

[0117] <Opposite substrate> A counter substrate may be provided on the planarized layer. The counter substrate is called a counter substrate because it is provided in a position corresponding to the aforementioned substrate. The constituent material of the counter substrate may be the same as that of the aforementioned substrate. The counter substrate may be the second substrate if the aforementioned substrate is referred to as the first substrate.

[0118] <Light-emitting device> An organic light-emitting element according to one embodiment of the present invention may be made into a light-emitting device by connecting a pixel circuit to it. The pixel circuit may be an active matrix type that independently controls the light emission of each of the multiple organic light-emitting elements. The active matrix type circuit may be voltage programmed or current programmed. The driving circuit has a pixel circuit for each pixel. The pixel circuit may have a light-emitting element, a transistor that controls the light emission brightness of the light-emitting element, a transistor that controls the light emission timing, a capacitor that holds the gate voltage of the transistor that controls the light emission brightness, and a transistor for connecting to GND without going through the light-emitting element.

[0119] The light-emitting device has a display area and a peripheral area arranged around the display area. The display area has a pixel circuit, and the peripheral area has a display control circuit. The mobility of the transistors constituting the pixel circuit may be smaller than the mobility of the transistors constituting the display control circuit.

[0120] The slope of the current-voltage characteristic of the transistors constituting the pixel circuit may be smaller than the slope of the current-voltage characteristic of the transistors constituting the display control circuit. The slope of the current-voltage characteristic can be measured using the so-called Vg-Ig characteristic. The transistors constituting the pixel circuit are transistors connected to organic light-emitting elements.

[0121] <Pixel> A plurality of organic light-emitting elements according to one embodiment of the present invention may be used to form a display device having a plurality of pixels. Each pixel has sub-pixels that emit light of a different color from the others. The sub-pixels may each have, for example, RGB light-emitting colors.

[0122] A pixel emits light in a region also called the pixel aperture. This region is the same as the first region. The pixel aperture may be 15 μm or less, or 5 μm or more. More specifically, it may be 11 μm, 9.5 μm, 7.4 μm, 6.4 μm, etc. The distance between subpixels may be 10 μm or less, and specifically, it may be 8 μm, 7.4 μm, 6.4 μm, etc.

[0123] Pixels can take on known arrangements in a plan view. For example, they may be in a stripe arrangement, delta arrangement, pentile arrangement, or Bayer arrangement. The shape of subpixels in a plan view may be any known shape. For example, rectangles, rhombuses, hexagons, etc. Of course, even if it is not a precise shape, if it is close to a rectangle, it is included in the category of rectangles. The shape of subpixels and the pixel arrangement can be used in combination.

[0124] [Applications of organic light-emitting diodes] An organic light-emitting element according to one embodiment of the present invention can be used as a component of a display device or lighting device. Other applications include exposure light sources for electrophotographic image forming apparatuses, backlights for liquid crystal display devices, and light-emitting devices with a color filter in a white light source.

[0125] The display device may also be an image information processing device that has an image input unit for receiving image information from an area CCD, linear CCD, memory card, etc., an information processing unit for processing the input information, and displays the input image on the display unit.

[0126] Furthermore, the display unit of the imaging device or inkjet printer may have a touch panel function. The driving method for this touch panel function may be infrared, capacitive, resistive, or electromagnetic induction, and is not particularly limited. The display device may also be used as the display unit of a multifunction printer.

[0127] Next, the display device according to this embodiment will be described with reference to the drawings. Figure 4(a) shows an example of a pixel, which is a component of the display device according to this embodiment. The pixel has sub-pixels 40. The sub-pixels are divided into 40R, 40G, and 40B based on their light emission. The light emission color is determined by the selective transmission or color conversion of the light emitted from the sub-pixel by a color filter. Each sub-pixel has a reflective electrode 32 which is the first electrode, an insulating layer 33 covering the end of the reflective electrode 32, an organic compound layer 34 covering the first electrode and the insulating layer, a transparent electrode 35, a protective layer 36, and a color filter 37 on an interlayer insulating layer 31.

[0128] The interlayer insulating layer 31 may have transistors and capacitive elements placed in the layer below or inside it. The transistor and the first electrode may be electrically connected via a contact hole or the like (not shown). The insulating layer 33 is also called a bank or pixel isolation layer. It covers the edge of the first electrode and surrounds the first electrode. The portion without the insulating layer is in contact with the organic compound layer 34 and forms the light-emitting region.

[0129] The protective layer 36 reduces the penetration of moisture into the organic compound layer. Although the protective layer is shown as a single layer, it may consist of multiple layers. Each layer may contain an inorganic compound layer and an organic compound layer. The color filters 37 are classified into 37R, 37G, and 37B according to their color. The color filters 37 may be formed on a planarization film (not shown). The color filters 37 may also have a resin protective layer (not shown). Furthermore, the color filters 37 may be formed on the protective layer 36, or they may be bonded together after being placed on an opposing substrate such as a glass substrate.

[0130] Figure 4(b) is a schematic cross-sectional view showing the configuration of an example of a display device having an organic light-emitting element according to one embodiment of the present invention and a transistor connected to the organic light-emitting element. The transistor is an example of an active element.

[0131] The display device 100 in Figure 4(b) shows an organic light-emitting element 26 and a TFT 18 as an example of a transistor. The organic light-emitting element 26 has an anode 21, a cathode 23, and an organic compound layer 22 placed between them. A substrate 11 made of glass, silicon, or the like is provided, with an insulating layer 12 on top of it. On the insulating layer 12 are the gate electrode 13, gate insulating film 14, and semiconductor layer 15 of the TFT 18. The TFT 18 is also composed of a semiconductor layer 15, a drain electrode 16, and a source electrode 17. An insulating film 19 is provided on top of the TFT 18. The anode 21 and the source electrode 17 constituting the organic light-emitting element 26 are connected via contact holes 20 provided in the insulating film 19.

[0132] Furthermore, the method of electrical connection between the electrodes (anode, cathode) included in the organic light-emitting element 26 and the electrodes (source electrode, drain electrode) included in the TFT is not limited to the configuration shown in Figure 4(b). In other words, it is sufficient if either the anode or cathode is electrically connected to either the source electrode or the drain electrode of the TFT 18. TFT refers to a thin-film transistor. In this embodiment, the luminescence brightness of the organic light-emitting element is controlled by a TFT, which is an example of a switching element, and by providing multiple organic light-emitting elements on the same plane, an image can be displayed using the luminescence brightness of each element. A first protective layer 24 and a second protective layer 25 are provided on the cathode 23 to reduce the degradation of the organic light-emitting element.

[0133] In the display device 100 shown in Figure 4(b), a transistor is used as the switching element, but other switching elements may be used instead.

[0134] Furthermore, the transistors used in the display device 100 in Figure 4(b) may be transistors using single-crystal silicon wafers, thin-film transistors having an active layer on the insulating surface of the substrate, transistors formed from low-temperature polysilicon, or active matrix drivers formed on a substrate such as a Si substrate. Examples of active layers include non-single-crystal silicon such as single-crystal silicon, amorphous silicon, and microcrystalline silicon, and non-single-crystal oxide semiconductors such as indium zinc oxide and indium gallium zinc oxide.

[0135] The transistors included in the display device 100 in Figure 4(b) may be formed within a substrate such as a Si substrate. Here, "formed within a substrate" means that the transistors are manufactured by processing the substrate itself, such as a Si substrate. In other words, having transistors within a substrate can be seen as the substrate and transistors being formed as a single unit. Whether to provide transistors within a substrate or to use TFTs is selected depending on the size of the display area; for example, if the size is about 0.5 inches, it is preferable to provide organic light-emitting elements on a Si substrate.

[0136] Figure 5 is a schematic diagram showing an example of a display device according to this embodiment. The display device 1000 has a touch panel 1003, a display panel 1005, a frame 1006, a circuit board 1007, and a battery 1008 between an upper cover 1001 and a lower cover 1009. Flexible printed circuits FPCs 1002 and 1004 are connected to the touch panel 1003 and the display panel 1005, respectively. Transistors are printed on the circuit board 1007. The battery 1008 does not need to be provided if the display device is not a portable device, or it may be provided in a different location even if it is a portable device.

[0137] The display device according to this embodiment may have a color filter having red, green, and blue colors, and the color filter may have the red, green, and blue colors arranged in a delta array.

[0138] The display device according to this embodiment may be used in the display unit of a mobile terminal. In that case, it may have both display and operation functions. Examples of mobile terminals include smartphones and other mobile phones, tablets, and head-mounted displays.

[0139] The display device according to this embodiment is used in the display unit of an imaging device having an optical unit with multiple lenses and an image sensor that receives light that has passed through the optical unit. The imaging device may have a display unit that displays information acquired by the image sensor, and the display unit may be a display unit exposed to the outside of the imaging device or a display unit located inside the viewfinder. The imaging device may be a digital camera or a digital video camera.

[0140] Figure 6(a) is a schematic diagram showing an example of an imaging device according to this embodiment. The imaging device 1100 includes a viewfinder 1101, a rear display 1102, an operation unit 1103, and a housing 1104. The viewfinder 1101 has a display device according to this embodiment, which may display not only the image to be captured, but also environmental information, imaging instructions, etc. Environmental information includes the intensity of ambient light, the direction of ambient light, the speed at which the subject is moving, and the possibility that the subject may be obscured by an obstruction.

[0141] Since the optimal timing for imaging is very short, it is best to display the information as quickly as possible. Therefore, display devices using organic light-emitting elements with a fast response speed can be suitably used in imaging devices and other applications where display speed is required.

[0142] The imaging device 1100 has an optical section (not shown). The optical section has multiple lenses that form an image on the image sensor housed in the housing 1104. The focus can be adjusted by adjusting the relative positions of the multiple lenses. This operation can also be performed automatically. The imaging device is also called a photoelectric converter. The photoelectric converter does not capture images sequentially, but may include imaging methods such as detecting the difference from the previous image or extracting from an image that is always being recorded.

[0143] Figure 6(b) is a schematic diagram showing an example of an electronic device according to this embodiment. The electronic device 1200 has a display unit 1201, an operation unit 1202, and a housing 1203. The display unit 1201 has an organic light-emitting element according to this embodiment. The housing 1203 may have a circuit, a printed circuit board having the circuit, a battery, and a communication unit. The operation unit 1202 may be a button or a touch panel type response unit. The operation unit may also be a biometric recognition unit that recognizes fingerprints to unlock or otherwise perform actions. An electronic device having a communication unit can also be called a communication device. The electronic device may further have a camera function by including a lens and an image sensor. Images captured by the camera function are displayed on the display unit. Examples of electronic devices include smartphones and laptop computers.

[0144] Figure 7 is a schematic diagram showing an example of a display device according to this embodiment. Figure 7(a) is a display device such as a television monitor or a PC monitor. The display device 1300 has a frame 1301 and a display unit 1302. The display unit 1302 has an organic light-emitting element according to this embodiment. It has a frame 1301 and a base 1303 that supports the display unit 1302. The base 1303 is not limited to the form shown in Figure 7(a). The bottom edge of the frame 1301 may also serve as the base. Furthermore, the frame 1301 and the display section 1302 may be curved. Their radius of curvature may be between 5000 mm and 6000 mm.

[0145] Figure 7(b) is a schematic diagram showing another example of the display device according to this embodiment. The display device 1310 in Figure 7(b) is configured to be foldable and is a so-called foldable display device. The display device 1310 has a first display unit 1311, a second display unit 1312, a housing 1313, and a bending point 1314. The first display unit 1311 and the second display unit 1312 have organic light-emitting elements according to this embodiment. The first display unit 1311 and the second display unit 1312 may be a single display device without seams, or they may be separated at a bending point. The first display unit 1311 and the second display unit 1312 may each display different images, or the first and second display units may together display a single image.

[0146] Figure 8(a) is a schematic diagram showing an example of a lighting device according to this embodiment. The lighting device 1400 includes a housing 1401, a light source 1402, a circuit board 1403, an optical filter 1404, and a light diffusion unit 1405. The light source has an organic light-emitting element according to this embodiment. The optical filter is a filter that improves the color rendering of the light source, and the light diffusion unit effectively diffuses the light from the light source, such as for lighting up, and can deliver light over a wide area. The optical filter and light diffusion unit are provided on the light-emitting side of the lighting, and a cover may be provided on the outermost part if necessary.

[0147] The lighting device is, for example, a device for illuminating a room. The lighting device may emit white light, daylight white light, or any other color from blue to red, and may have a dimming circuit to adjust the brightness of these colors. The lighting device has the organic light-emitting element of the present invention and a power supply circuit connected thereto. The power supply circuit is a circuit that converts AC voltage to DC voltage. White has a color temperature of 4200K, and daylight white has a color temperature of 5000K. The lighting device may have a color filter. Furthermore, the lighting device according to this embodiment may have a heat dissipation section, which releases heat from inside the device to the outside, and examples include metals with high specific heat, liquid silicon, etc.

[0148] Figure 8(b) is a schematic diagram of an automobile, which is an example of a mobile body according to this embodiment. The automobile has a taillight, which is an example of a lighting device. The automobile 1500 has a taillight 1501, and may be configured to illuminate when the brakes are applied or the like. The tail lamp 1501 has an organic light-emitting element according to this embodiment, and may have a protective member to protect the organic light-emitting element. The protective member has a reasonably high strength and is transparent, so the material is not limited, but it is preferably made of polycarbonate or the like, and the polycarbonate may be mixed with a flangic acid derivative, an acrylonitrile derivative, or the like.

[0149] The automobile 1500 has a body 1503 and windows 1502 attached thereto. The windows may be transparent displays, unless they are windows for checking the front and rear of the automobile. The transparent displays have organic light-emitting elements according to this embodiment. In this case, the constituent materials such as electrodes of the organic light-emitting element are made of transparent members.

[0150] The mobile body according to this embodiment may be a ship, aircraft, drone, etc. The mobile body may have a body and a lighting device provided on the body. The lighting device may emit light to indicate the position of the body. The lighting device has an organic light-emitting element according to this embodiment.

[0151] Referencing Figure 9, examples of applications of the display devices of each embodiment described above will be explained. The display device according to this embodiment can be applied to systems that can be worn as wearable devices such as smart glasses, HMDs, and smart contacts. The display device used in such an application example is an imaging display device having an imaging device capable of photoelectric conversion of visible light and a display device capable of emitting visible light.

[0152] Figure 9(a) illustrates a pair of glasses 1600 (smart glasses) according to one application example. An imaging device 1602, such as a CMOS sensor or SPAD, is provided on the front surface of the lens 1601 of the glasses 1600. In addition, the display devices of each embodiment described above are provided on the back surface of the lens 1601.

[0153] The eyeglasses 1600 further include a control device 1603. The control device 1603 functions as a power supply that provides power to the imaging device 1602 and the display device. The control device 1603 also controls the operation of the imaging device 1602 and the display device. The lens 1601 has an optical system formed therein for focusing light onto the imaging device 1602.

[0154] Figure 6(b) illustrates a pair of glasses 1610 (smart glasses) representing one application example. The glasses 1610 have a control device 1612, which is equipped with an imaging device corresponding to the imaging device 1602 in Figure 6(a) and a display device. The lens 1611 has an optical system formed therein for projecting light emitted from the imaging device and the display device within the control device 1612, and an image is projected onto the lens 1611. The control device 1612 functions as a power source that supplies power to the imaging device and the display device, and also controls the operation of the imaging device and the display device.

[0155] The control device 1612 may have a gaze detection unit that detects the wearer's gaze, and the gaze detection may use infrared light. The gaze detection unit using infrared light includes an infrared light emitter, which emits infrared light towards the user's eyeball that is fixated on the displayed image. An imaging unit having a light-receiving element detects the reflected light from the eyeball of the emitted infrared light, thereby obtaining an image of the eyeball. By having a reduction means that reduces the light from the infrared light emitter to the display unit in a planar view, the degradation of image quality is reduced. The user's gaze toward the displayed image is detected from the image of the eyeball obtained by imaging with infrared light.

[0156] Any known method can be applied to gaze detection using captured images of the eyeball. As an example, a gaze detection method based on the Purkinje image obtained by the reflection of irradiated light from the cornea can be used. More specifically, gaze detection processing based on the pupil-corneal reflection method is performed. Using the pupil-corneal reflection method, a gaze vector representing the orientation (rotation angle) of the eyeball is calculated based on the pupil image and the Purkinje image contained in the captured image of the eyeball, thereby detecting the user's gaze.

[0157] A display device according to one embodiment of the present invention includes an imaging device having a light-receiving element, and may control the display image of the display device based on the user's gaze information from the imaging device. Specifically, the display device determines a first field of view that the user is fixated on, and a second field of view other than the first field of view, based on gaze information. The first and second field of view may be determined by the control device of the display device, or they may be determined by an external control device and received by the display device. Within the display area of ​​the display device, the display resolution of the first field of view may be controlled to be higher than the display resolution of the second field of view. In other words, the resolution of the second field of view may be lower than that of the first field of view.

[0158] Furthermore, the display area has a first display area and a second display area different from the first display area, and based on gaze information, the area with higher priority is determined from the first display area and the second display area. The first and second view areas may be determined by the control device of the display device, or they may be determined by an external control device and received. The resolution of the high-priority area may be controlled to be higher than the resolution of the areas other than the high-priority area. In other words, the resolution of areas with relatively lower priority may be lower.

[0159] Furthermore, AI may be used to determine the primary field of view and high-priority areas. The AI ​​may be a model configured to estimate the angle of gaze and the distance to the target object at the end of the line of sight from the eyeball image, using the eyeball image and the direction the eye was actually looking in that image as training data. The AI ​​program may be installed in the display device, the imaging device, or an external device. If installed in an external device, it will be transmitted to the display device via communication.

[0160] When display control is based on visual detection, this method is preferably applicable to smart glasses that further include an imaging device for capturing images of the surrounding environment. The smart glasses can display the captured external information in real time.

[0161] Figure 10(a) is a schematic diagram showing an example of an image forming apparatus according to one embodiment of the present invention. The image forming apparatus is an electrophotographic image forming apparatus and includes a photoreceptor 1707, an exposure light source 1708, a charging unit 1706, a developing unit 1701, a transfer unit 1702, a transport roller 1703, and a fuser 1705. Light 1709 is irradiated from the exposure light source 1708, and an electrostatic latent image is formed on the surface of the photoreceptor 1707. This exposure light source 1708 has an organic light-emitting element according to this embodiment. The developing unit 1701 has toner or the like. The charging unit 1706 charges the photoreceptor 1707. The transfer unit 1702 transfers the developed image to a recording medium 1704. The transport roller 1703 transports the recording medium 1704. The recording medium 1704 is, for example, paper. The fuser 1705 fixes the image formed on the recording medium 1704.

[0162] Figures 10(b) and 10(c) are diagrams showing the exposure light source 1708, and are schematic diagrams showing how multiple light-emitting units 1710 having organic light-emitting elements according to this embodiment are arranged on a long substrate. Arrows 1711 indicate the column direction in which the organic light-emitting elements are arranged. This column direction is the same as the direction of the axis in which the photoreceptor 1707 rotates. This direction can also be called the long axis direction of the photoreceptor 1707. Figure 10(b) shows a configuration in which the light-emitting units 1710 are arranged along the long axis direction of the photoreceptor 1707. Figure 10(c) is a different configuration from Figure 10(b), in which the light-emitting units 1710 are arranged alternately in the column direction in the first and second columns, respectively. The first and second columns are arranged at different positions in the row direction. In the first column, multiple light-emitting units 1710 are arranged at intervals. In the second column, light-emitting units 1710 are located at positions corresponding to the intervals between the light-emitting units 1710 in the first column. In other words, multiple light-emitting units 1710 are also arranged at intervals in the row direction. The arrangement in Figure 10(c) can also be described as a grid arrangement, a houndstooth arrangement, or a checkerboard pattern.

[0163] As described above, by using the device employing the organic light-emitting element according to this embodiment, stable display with good image quality is possible even during long-term display.

[0164] [Included components] This embodiment includes the following configuration. (Configuration 1) An organic light-emitting element comprising a first electrode, a first light-emitting layer, a second light-emitting layer, and a second electrode, The first light-emitting layer and the second light-emitting layer are in contact with each other. The first light-emitting layer comprises a first organic compound, a first metal complex, and a second metal complex. The second light-emitting layer comprises a second organic compound and a third metal complex, but does not contain a first metal complex. An organic light-emitting element characterized in that, when the triplet energies of the first metal complex, the second metal complex, and the third metal complex are T1D1, T1D2, and T1D3, respectively, the following relationships [a] to [c] hold true.

[0165] T1D2>T1D1 [a] T1D3≧T1D2 [b] T1D2-T1D1>T1D3-T1D2 [c]

[0166] (Configuration 2) The organic light-emitting element according to Configuration 1, characterized in that when the concentration of the second metal complex in the first light-emitting layer and the concentration of the third metal complex in the second light-emitting layer are C1D2 and C1D3, respectively, the following relationship [d] holds. C1D2≧C1D3 [d]

[0167] (Configuration 3) The organic light-emitting element according to Configuration 1 or 2, characterized in that when the concentrations of the first metal complex and the second metal complex in the first light-emitting layer are C1D1 and C1D2, respectively, the following relationship [e] holds. C1D2≧C1D1 [e]

[0168] (Configuration 4) The organic light-emitting element according to any one of Configurations 1 to 3, characterized in that the second metal complex and the third metal complex have at least one identical ligand.

[0169] (Configuration 5) An organic light-emitting element according to any one of Configurations 1 to 4, characterized in that when the energy levels of the HOMO and LUMO of the second metal complex and the energy levels of the HOMO and LUMO of the third metal complex are HOMOD2, LUMOD2, HOMOD3, and LUMOD3, respectively, the following relationships [f] and [g] hold. |LUMOD3-LUMOD2|≦0.2eV [f] |HOMOD3-HOMOD2|≦0.2eV [g]

[0170] (Configuration 6) The organic light-emitting element according to any one of Configurations 1 to 5, characterized in that the first metal complex is a red phosphorescent material and the third metal complex is a green phosphorescent material. (Configuration 7) The organic light-emitting element according to any one of Configurations 1 to 6, characterized in that the second light-emitting layer has a third organic compound that is not a metal complex. (Configuration 8) The organic light-emitting element according to any one of Configurations 1 to 7, characterized in that the first electrode is an anode, the second electrode is a cathode, and the first light-emitting layer is positioned closer to the anode than the second light-emitting layer.

[0171] (Configuration 9) An organic light-emitting element according to any one of Configurations 1 to 8, characterized in that when the concentration of the first metal complex in the first light-emitting layer and the concentration of the third metal complex in the second light-emitting layer are C1D1 and C1D3, respectively, the following relationship [h] holds true. C1D3>C1D1 [h]

[0172] (Configuration 10) The organic light-emitting element according to any one of Configurations 1 to 9, characterized in that the second metal complex and the third metal complex are the same compound. (Configuration 11) The organic light-emitting element according to any one of Configurations 1 to 10, characterized in that the first organic compound and the second organic compound are the same compound. (Configuration 12) The organic light-emitting element according to any one of Configurations 1 to 11, characterized in that the light emission color obtained from the first light-emitting layer and the second light-emitting layer is yellow light emission.

[0173] (Configuration 13) A display device having a plurality of pixels, wherein at least one of the plurality of pixels has an organic light-emitting element according to any one of Configurations 1 to 12 and a transistor connected to the organic light-emitting element. (Configuration 14) An imaging device having an optical unit having a plurality of lenses, an imaging element that receives light that has passed through the optical unit, and a display unit that displays an image captured by the imaging element. The display unit has an organic light-emitting element according to any one of Configurations 1 to 12. (Configuration 15) An electronic device having a display unit having an organic light-emitting element according to any one of Configurations 1 to 12, a housing provided with the display unit, and a communication unit provided in the housing for communicating with the outside. (Configuration 16) A lighting device having a light source having an organic light-emitting element according to any one of Configurations 1 to 12 and a light diffusing unit or an optical filter that transmits light emitted by the light source. (Configuration 17) A moving body having a lighting fixture having an organic light-emitting element according to any one of Configurations 1 to 12 and a body provided with the lighting fixture. (Configuration 18) An exposure light source of an electrophotographic image forming apparatus having an organic light-emitting element according to any one of Configurations 1 to 12.

Example

[0174] (Example 1) <Evaluation of Triplet Energy> The T1 energy of the dopant was evaluated by the method shown below. The results are shown in Table 1. Using Hitachi F-4500, the photoluminescence (PL) measurement of a diluted toluene solution at 77K and an excitation wavelength of 300nm was performed by the built-in phosphorescence mode measurement. It was calculated from the maximum emission wavelength of the obtained emission spectrum. <s

[0175] <Evaluation of HOMO·LUMO> The HOMO level and LUMO level of the host and the dopant were evaluated by the method shown below. The results are shown in Table 1.

[0176] A) Method for evaluating HOMO levels 5 x 10 -4 A 30 nm thick vapor-deposited film was formed on an aluminum substrate under a vacuum of less than Pa, and this thin film was measured using an AC-3 (manufactured by Riken Keiki Co., Ltd.).

[0177] B) Method for evaluating LUMO levels 5 x 10 -4 Under a vacuum of less than Pa, a 30 nm thick vapor-deposited film was formed on a quartz substrate. The optical band gap (absorption edge) of this thin film was determined using a spectrophotometer (V-560, JASCO Corporation). The LUMO level was defined as the sum of this optical band gap value and the aforementioned HOMO level value. The results are shown in Table 1.

[0178] [Table 1]

[0179] (Example 2) An organic light-emitting device with a bottom-emission structure was fabricated on a substrate, in which an anode, hole injection layer, hole transport layer, electron blocking layer, light-emitting layer, hole blocking layer, electron transport layer, electron injection layer, and cathode were sequentially formed. First, an ITO film was deposited on a glass substrate, and an ITO electrode (anode) was formed by applying the desired patterning process. At this time, the film thickness of the ITO electrode was set to 100 nm. The substrate on which the ITO electrode was formed in this way was used as the ITO substrate in the following process. Next, 1.33 × 10 -4 Vacuum deposition was performed by resistance heating in a Pa vacuum chamber to continuously deposit the organic compound layer and electrode layer shown in Table 2 onto the ITO substrate. At this time, the electrode area of ​​the opposing electrodes (metal electrode layer, cathode) was 3 mm². 2 This was done. Afterwards, the substrate was moved to a glove box and sealed with a glass cap containing a desiccant in a nitrogen atmosphere to obtain an organic light-emitting element.

[0180] [Table 2]

[0181] The characteristics of the obtained organic light-emitting device were measured and evaluated. The organic light-emitting device emitted yellow light, and its maximum external quantum efficiency (EQE) was 18%. Furthermore, the current density is 100 mA / cm². 2 A continuous operation test was conducted, and the time it took for the brightness degradation rate to reach 5% was measured. When the time it took for the brightness degradation rate to reach 5% in Comparative Example 1 was set to 1.0, the brightness degradation ratio in this example was 2.3. In this embodiment, the measuring device specifically measured the current-voltage characteristics with a Hewlett-Packard 4140B micro-ammeter, and the luminous intensity with a Topcon BM7.

[0182] (Examples 3 to 20, Comparative Examples 1 to 7) Except for appropriately changing the compounds constituting the organic compound layer to those shown in Tables 3 and 4, organic light-emitting devices of Examples 3 to 20 and Comparative Examples 1 to 7 were fabricated in the same manner as in Example 2. The characteristics of the obtained organic light-emitting devices were measured and evaluated in the same manner as in Example 2. The measurement results are shown in Tables 3 and 4.

[0183] Furthermore, when the second light-emitting layer contains an assisting material, the mass ratio was adjusted so that the second host:assisting material:tertiary metal complex = 55:30:15.

[0184] [Table 3]

[0185] [Table 4]

[0186] From Tables 3 and 4, the E.Q.E. of Comparative Examples 1 to 7 were 18%, 7%, 12%, 15%, 15%, 13%, and 8%, respectively. Also, the luminance degradation ratios of Comparative Examples 1 to 7 were 1.0, 0.3, 0.8, 1.3, 1.1, 1.4, and 1.3, respectively. These are considered to be poor in light emission characteristics and durability characteristics because carrier transfer and energy transfer of triplet energy between the first light-emitting layer and the second light-emitting layer are unlikely to occur. On the other hand, the organic light-emitting device according to the present invention exhibited excellent luminous efficiency and excellent device lifetime. This is because the stacked light-emitting layer according to the present invention has a relationship in which carriers and energy are easily transferred.

[0187] Furthermore, by selecting a host material and a light-emitting material suitable for combination with the stacked light-emitting layer of the present invention, an organic light-emitting device particularly excellent in device lifetime could be obtained.

[0188] From the above, by using the organic compound according to the present invention, an organic light-emitting device excellent in luminous efficiency and device lifetime can be provided.

[0189] (Example 21) In Example 2, an organic light-emitting device was fabricated in the same manner as in Example 2, except that the film thickness of the first light-emitting layer was changed to 10 nm. The characteristics of the obtained organic light-emitting device were measured and evaluated in the same manner as in Example 2. The maximum external quantum efficiency (E.Q.E.) was 16%, and the luminance degradation ratio was 2.0.

[0190] (Example 22) In Example 2, an organic light-emitting device was fabricated in the same manner as in Example 2, except that the film thickness of the first light-emitting layer was changed to 10 nm and the film thickness of the second light-emitting layer was changed to 10 nm. The characteristics of the obtained organic light-emitting device were measured and evaluated in the same manner as in Example 2. The maximum external quantum efficiency (E.Q.E.) was 18%, and the luminance degradation ratio was 1.8.

[0191] (Example 23) In Example 2, an organic light-emitting element was fabricated using the same method as in Example 2, except that the mass ratio of the first light-emitting layer was changed to EM10:AA1:HH1=81:15:4 and the mass ratio of the second light-emitting layer was changed to EM14:AA2=85:15. The characteristics of the obtained organic light-emitting element were measured and evaluated in the same manner as in Example 2. The maximum external quantum efficiency (EQE) was 16%, and the brightness degradation ratio was 2.0.

[0192] (Example 24) In Example 2, an organic light-emitting element was fabricated using the same method as in Example 2, except that the mass ratio of the first light-emitting layer was changed to EM10:AA1:HH1=75:20:5 and the mass ratio of the second light-emitting layer was changed to EM14:AA2=95:5. The characteristics of the obtained organic light-emitting element were measured and evaluated in the same manner as in Example 2. The maximum external quantum efficiency (EQE) was 14%, and the brightness degradation ratio was 2.2. [Explanation of symbols]

[0193] 2: Anode, 4a: First light-emitting layer, 4b: Second light-emitting layer, 6: Cathode, 10: Display device, 18: Transistor, 1000: Display device, 1100: Imaging device, 1200: Electronic device, 1201: Display unit, 1203: Housing, 1300: Display device, 1310: Display device, 1313: Housing, 1400: Lighting device, 1401: Housing, 1402: Light source, 1404: Optical filter, 1405: Light diffusion unit, 1708: Exposure light source

Claims

1. An organic light-emitting element comprising a first electrode, a first light-emitting layer, a second light-emitting layer, and a second electrode, The first light-emitting layer and the second light-emitting layer are in contact with each other. The first light-emitting layer comprises a first organic compound, a first metal complex, and a second metal complex. The second light-emitting layer comprises a second organic compound and a third metal complex, but does not contain a first metal complex. When the triplet energies of the first metal complex, the second metal complex, and the third metal complex are T1D1, T1D2, and T1D3, respectively, the following relationships [a] to [c] hold: T1D2>T1D1 [a] T1D3≧T1D2 [b] T1D2-T1D1>T1D3-T1D2 [c] An organic light-emitting element characterized in that the first metal complex, the second metal complex, and the third metal complex are compounds represented by the following general formula [I]. Ir(L) q (L') r (L'') s [I] In general formula [1], L, L', and L'' each represent a different bidentate ligand. q is an integer between 1 and 3, and r and s are integers between 0 and 2, respectively, where q + r + s = 3. When r is 2, multiple L' elements may be the same or different from each other. When s is 2, multiple L'' elements may be the same or different from each other. The substructure Ir(L)q is a structure represented by the following general formulas [Ir-5] to [Ir-16]. 【Chemistry 1】 In general formulas [Ir-5] to [Ir-16], Ar1 and Ar2 are each independently a deuterium atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted silyl group, or a cyano group. p1 and p2 are each an integer between 0 and 4, independently of each other. X is selected from an oxygen atom, a sulfur atom, C(R1)(R2), or NR3. R1 to R3 are independently selected from hydrogen atoms, deuterium atoms, halogen atoms, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkoxy groups, substituted or unsubstituted amino groups, substituted or unsubstituted aryloxy groups, substituted or unsubstituted aryl groups, substituted or unsubstituted heterocyclic groups, substituted or unsubstituted silyl groups, and cyano groups. R1 and R2 may bond to each other to form a ring.

2. The organic light-emitting element according to claim 1, characterized in that when the concentration of the second metal complex in the first light-emitting layer and the concentration of the third metal complex in the second light-emitting layer are C1D2 and C1D3, respectively, the following relationship [d] holds true. C1D2≧C1D3 [d]

3. The organic light-emitting element according to claim 1, characterized in that when the concentrations of the first metal complex and the second metal complex in the first light-emitting layer are C1D1 and C1D2, respectively, the following relationship [e] holds true. C1D2≧C1D1 [e]

4. The organic light-emitting element according to claim 1, characterized in that the second metal complex and the third metal complex have at least one identical ligand.

5. The organic light-emitting element according to claim 1, characterized in that when the HOMO energy levels and LUMO energy levels of the second metal complex and the HOMO energy levels and LUMO energy levels of the third metal complex are denoted as HOMOD2, LUMOD2, HOMOD3, and LUMOD3, respectively, the following relationships [f] and [g] hold true. |LUMOD3-LUMOD2|≦0.2eV [f] |HOMOD3-HOMOD2|≦0.2eV [g]

6. The organic light-emitting element according to claim 1, characterized in that the first metal complex is a red phosphorescent material and the third metal complex is a green phosphorescent material.

7. The organic light-emitting element according to claim 1, characterized in that the second light-emitting layer has a third organic compound that is not a metal complex.

8. The organic light-emitting element according to claim 1, characterized in that the first electrode is an anode, the second electrode is a cathode, and the first light-emitting layer is positioned closer to the anode than the second light-emitting layer.

9. The organic light-emitting element according to claim 1, characterized in that when the concentration of the first metal complex in the first light-emitting layer and the concentration of the third metal complex in the second light-emitting layer are C1D1 and C1D3, respectively, the following relationship [h] holds true. C1D3>C1D1 [h]

10. The organic light-emitting device according to claim 1, characterized in that the second metal complex and the third metal complex are the same compound.

11. The organic light-emitting element according to claim 1, characterized in that the first organic compound and the second organic compound are the same compound.

12. The organic light-emitting element according to claim 1, characterized in that the emission color obtained from the first light-emitting layer and the second light-emitting layer is yellow emission.

13. An organic light-emitting element comprising a first electrode, a first light-emitting layer, a second light-emitting layer, and a second electrode, The first light-emitting layer and the second light-emitting layer are in contact with each other. The first light-emitting layer comprises a first organic compound, a first metal complex, and a second metal complex. The second light-emitting layer comprises a second organic compound and a third metal complex, but does not contain a first metal complex. When the triplet energies of the first metal complex, the second metal complex, and the third metal complex are T1D1, T1D2, and T1D3, respectively, the following relationships [a] to [c] hold: T1D2>T1D1 [a] T1D3≧T1D2 [b] T1D2-T1D1>T1D3-T1D2 [c] The first metal complex is selected from the group consisting of HH1, HH19, II8, II9, RD3, RD7, and RD10 as shown below. The aforementioned second metal complex is selected from the group consisting of AA1, AA21, BB21, CC1, CC21, FF11, JJ4, and JJ19 as shown below. The organic light-emitting element is characterized in that the third metal complex is selected from the group consisting of AA2, CC2, CC22, DD2, DD7, DD30, JJ2, JJ4, JJ14, JJ17, JJ19, JJ20, GD20, and GD11 as shown below. 【Chemistry 2】 【Transformation 3】 【Chemistry 4】

14. A display device having a plurality of pixels, wherein at least one of the plurality of pixels is an organic light-emitting element according to any one of claims 1 to 13, and a transistor connected to the organic light-emitting element.

15. It comprises an optical unit having multiple lenses, an image sensor that receives light that has passed through the optical unit, and a display unit that displays the image captured by the image sensor. The imaging apparatus is characterized in that the display unit has an organic light-emitting element as described in any one of claims 1 to 13.

16. An electronic device comprising: a display unit having an organic light-emitting element as described in any one of claims 1 to 13; a housing on which the display unit is provided; and a communication unit provided in the housing for communicating with the outside.

17. A lighting device comprising a light source having an organic light-emitting element as described in any one of claims 1 to 13, and a light-diffusing section or optical filter that transmits light emitted by the light source.

18. A mobile body characterized by comprising a lamp having an organic light-emitting element as described in any one of claims 1 to 13, and a body on which the lamp is provided.

19. An exposure light source for an electrophotographic image forming apparatus, characterized by having an organic light-emitting element according to any one of claims 1 to 13.

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