Light-emitting element, light-emitting device, electronic device and lighting device

Abstract

Light-emitting element, comprising: a pair of electrodes; and a first light-emitting layer and a second light-emitting layer between the pair of electrodes, where the second light-emitting layer is in contact with the first light-emitting layer, wherein the first light-emitting layer comprises a first phosphorescent compound, a first organic compound and a second organic compound, wherein the second light-emitting layer comprises a second phosphorescent compound, the first organic compound and the second organic compound, wherein the first organic compound and the second organic compound form an exciplex, the first organic compound is a nitrogen-containing heteroaromatic compound, where the second organic compound is a π-electron-rich heteroaromatic compound or an aromatic amine compound, where a peak of an emission spectrum of the first phosphorescent compound has a shorter wavelength than a peak of an emission spectrum of the second phosphorescent compound, and where the difference between the energy of a peak in an emission spectrum of the exciplex and the energy of a peak in an absorption band on the longest wavelength side in an absorption spectrum of the first phosphorescent compound is 0.2 eV or less.

Description

Technical field

[0001] One embodiment of the present invention relates to a light-emitting element in which an organic compound capable of emitting light by the application of an electric field is arranged between a pair of electrodes, and also relates to a light-emitting device, an electronic device and a lighting device, each comprising such a light-emitting element. State of the art

[0002] Light-emitting elements (LEDs) containing an organic compound as a phosphor, and exhibiting characteristics such as thinness, lightness, fast response time, and low-voltage DC operation, are expected to be used in next-generation flat panel displays. In particular, displays in which LEDs are arranged in a matrix are anticipated to offer advantages over conventional liquid crystal displays, such as a wide viewing angle and high visibility.

[0003] A light-emitting element is said to have the following light emission mechanism: when a voltage is applied between a pair of electrodes, with an EL layer containing a phosphor between them, electrons injected from the cathode and holes injected from the anode recombine in the light emission center of the EL layer to form molecular excitons, and energy is released and light is emitted when the molecular excitons return to the ground state. A singlet excitation state and a triplet excitation state are known as excitation states, and it is thought that light emission can be obtained from either of these excitation states.

[0004] To improve the elemental properties of such light-emitting elements, improvements to the elemental structure, the development of a material, and the like are actively carried out (see, for example, patent documents 1 and 2, as well as non-patent documents 1 and 2). [References] [Patent Document 1] JP 2010 - 182 699 A1 [Patent document 2] DE 11 2012 000 831 B4 [Non-patent document 1] M. Kondakova et al., Journal of Applied Physics 2008, 104(9), 094501-1. [Non-Patent Document 2] X. Gong et al., Journal of Applied Physics 2004, 95(3), 948-953. Disclosure of the invention

[0005] However, it is said that the light extraction efficiency of a light-emitting element is currently around 20% to 30%. When light absorption by a reflective electrode and a transparent electrode is also taken into account, the external quantum yield of a light-emitting element containing a phosphorescent compound has a limit of at most around 25%.

[0006] In one embodiment of the present invention, a light-emitting element with high external quantum yield is provided. In another embodiment of the present invention, a light-emitting element with a long lifetime is provided.

[0007] One embodiment of the present invention is a light-emitting element comprising a light-emitting layer between a pair of electrodes. The light-emitting layer contains at least one phosphorescent compound, a first organic compound (host material) with electron transport properties, and a second organic compound (auxiliary material) with hole transport properties. The light-emitting layer has a stacked structure comprising a first light-emitting layer and a second light-emitting layer, the second light-emitting layer being in contact with the first light-emitting layer, wherein the first light-emitting layer comprises a first phosphorescent compound, a first organic compound, and a second organic compound, and wherein the second light-emitting layer comprises a second phosphorescent compound.comprising the first organic compound and the second organic compound, wherein the first organic compound is a nitrogen-containing heteroaromatic compound, wherein the second organic compound is a π-electron-rich heteroaromatic compound or an aromatic amine compound, wherein a peak of an emission spectrum of the first phosphorescent compound has a shorter wavelength than a peak of an emission spectrum of the second phosphorescent compound, and wherein a difference between an energy of a peak of an emission spectrum of the exciplex and an energy of a peak of an absorption band on the longest wavelength side in an absorption spectrum of the first phosphorescent compound is 0.2 eV or less. In the light-emitting layer (the first light-emitting layer and the second light-emitting layer), a combination of the first organic compound and the second organic compound forms an exciplex.

[0008] Another embodiment of the present invention is a light-emitting element comprising a light-emitting layer between a pair of electrodes and a first light-emitting layer and a second light-emitting layer between the pair of electrodes, wherein the second light-emitting layer is in contact with the first light-emitting layer, wherein the first light-emitting layer comprises a first phosphorescent compound, a first organic compound and a second organic compound, wherein the second light-emitting layer comprises a second phosphorescent compound, the first organic compound and the second organic compound, wherein a peak of an emission spectrum of a mixture film of the first organic compound and the second organic compound has a longer wavelength than a peak of an emission spectrum of a film of the first organic compound.wherein the peak of the emission spectrum of the mixture film has a longer wavelength than a peak of an emission spectrum of a film of the second organic compound, wherein the first organic compound is a nitrogen-containing heteroaromatic compound, wherein the second organic compound is a π-electron-rich heteroaromatic compound or an aromatic amine compound, wherein a peak of an emission spectrum of the first phosphorescent compound has a shorter wavelength than a peak of an emission spectrum of the second phosphorescent compound, and wherein a difference between an energy of the peak of the emission spectrum of the mixture film and an energy of a peak of an absorption band on the longest wavelength side in an absorption spectrum of the first phosphorescent compound is 0.2 eV or less,

[0009] It should be noted that in each of the above embodiments, the emission wavelength of the exciplex formed by the first organic compound (host material) and the second organic compound (auxiliary material) lies on the longer wavelength side than the emission wavelength (fluorescence wavelength) of each of the first and second organic compounds (host and auxiliary materials). Therefore, by forming the exciplex, the fluorescence spectrum of the first organic compound (host material) and the fluorescence spectrum of the second organic compound (auxiliary material) can be transformed into an emission spectrum that lies on the longer wavelength side.

[0010] Consequently, according to one embodiment of the present invention, the light-emitting element can transfer energy by forming the exciplex in the light-emitting layer, exploiting an overlap between the emission spectrum of the exciplex on the longer wavelength side than the emission wavelength (fluorescence wavelength) of each of the first and second organic compounds and the absorption spectrum of the phosphorescent compound (guest material); thus, the light-emitting element can achieve high energy transfer efficiency and high external quantum yield.

[0011] It should be noted that in the foregoing embodiments, the first light-emitting layer and the second light-emitting layer contain different phosphorescent compounds, wherein light emitted by the first light-emitting layer has a shorter wavelength than light emitted by the second light-emitting layer.

[0012] It should be noted that in the above embodiments, the exciplex can be formed from an anion of the first organic compound and a cation of the second organic compound.

[0013] In the foregoing embodiments, the phosphorescent compound can be a metal-organic complex, and the first organic compound can be mainly an electron transport material with an electron mobility of 10 -6 cm 2 / Vs or more, in particular a π-electron-deficient heteroaromatic compound, and the second organic compound can mainly be a hole transport material with a hole mobility of 10 -6 cm 2 / Vs or more, in particular a π-electron-rich heteroaromatic compound or aromatic amine compound.

[0014] Furthermore, the present invention comprises electronic devices and lighting devices that include light-emitting devices, in addition to light-emitting devices that include light-emitting elements. The light-emitting device in this description refers to an image display device and a light source (e.g., a lighting device). The light-emitting device further comprises all of the following modules: a module in which a connector, such as a flexible printed circuit (FPC) or a tape carrier package (TCP), is attached to a light-emitting device; a module in which a printed circuit board is provided at the end of a TCP; and a module in which an integrated circuit (IC) is mounted directly onto a light-emitting element by a chip-on-glass (COG) method.

[0015] It should be noted that according to one embodiment of the present invention, the light-emitting element can transfer energy thanks to the formation of the exciplex in the light-emitting layer by exploiting an overlap between the emission spectrum of the exciplex on the longer wavelength side than the emission wavelength (fluorescence wavelength) of each of the first and second organic compounds and the absorption spectrum of the phosphorescent compound (guest material); thus, the light-emitting element can achieve high energy transfer efficiency and high external quantum yield.

[0016] Furthermore, in one embodiment of the present invention, the light-emitting layer has a stacked structure consisting of the first light-emitting layer and the second light-emitting layer. The first light-emitting layer and the second light-emitting layer each contain the first organic compound (host material) with electron transport properties and the second organic compound (auxiliary material) with hole transport properties, with the first light-emitting layer containing a higher proportion of the second organic compound (auxiliary material) than the second light-emitting layer. Consequently, charge carriers (holes and electrons) can be well balanced in the light-emitting layer, and excitons generated in the light-emitting layer can be distributed at the interface between the first light-emitting layer and the second light-emitting layer.As a result, it can be prevented that the light-emitting layer is degraded as a result of a local increase in exciton density. Brief description of the drawings Fig. 1A and Fig. Figure 1B shows a concept of an embodiment of the present invention. Fig. Figure 2 shows calculation results according to one embodiment of the present invention. Fig. 3A1, Fig. 3A2, Fig. 3B1, Fig. 3B2, Fig. 3C1 and Fig. Figures 3C2 show calculation results according to one embodiment of the present invention. Fig. Figure 4 shows energy levels of an Exciplex applied to an embodiment of the present invention. Fig. Figure 5 shows the structure of a light-emitting element. Fig. 6A and Fig. Figure 6B each shows a structure of a light-emitting element. Fig. Figure 7 shows a light-emitting device. Fig. 8A and Fig. Figure 8B shows a light-emitting device. Fig. 9A to Fig. 9D shows electronic devices. Fig. 10A to Fig. 10C shows an electronic device. Fig. Figure 11 shows lighting devices. Fig. Figure 12 shows a structure of a light-emitting element 1. Fig. Figure 13 shows the current density-luminance properties of the light-emitting element 1. Fig. Figure 14 shows the voltage-luminance properties of the light-emitting element 1. Fig. Figure 15 shows luminance-current efficiency properties of light-emitting element 1. Fig. Figure 16 shows the voltage-current properties of the light-emitting element 1. Fig. Figure 17 shows an emission spectrum of the light-emitting element 1. Fig. Figure 18 shows the reliability of the light-emitting element 1. Fig. Figure 19 shows current density-luminance properties of a light-emitting element 2. Fig. Figure 20 shows the voltage-luminance properties of the light-emitting element 2. Fig. Figure 21 shows luminance-current efficiency properties of the light-emitting element 2. Fig. Figure 22 shows the voltage-current properties of the light-emitting element 2. Fig. Figure 23 shows an emission spectrum of the light-emitting element 2. Fig. Figure 24 shows a structure of a light-emitting element 3. Fig. Figure 25 shows current density-luminance properties of the light-emitting element 3. Fig. Figure 26 shows the voltage-luminance properties of the light-emitting element 3. Fig. Figure 27 shows luminance-current efficiency properties of the light-emitting element 3. Fig. Figure 28 shows voltage-current properties of the light-emitting element 3. Fig. Figure 29 shows an emission spectrum of the light-emitting element 3. Fig. Figure 30 shows current density-luminance properties of a light-emitting element 4. Fig. Figure 31 shows the voltage-luminance properties of the light-emitting element 4. Fig. Figure 32 shows luminance-current efficiency properties of the light-emitting element 4. Fig. Figure 33 shows voltage-current properties of the light-emitting element 4. Fig. Figure 34 shows an emission spectrum of the light-emitting element 4. Fig. 35 shows reliability of the light-emitting element 4. Fig. Figure 36 shows current density-luminance properties of a light-emitting element 5. Fig. Figure 37 shows the voltage-luminance properties of the light-emitting element 5. Fig. Figure 38 shows luminance-current efficiency properties of the light-emitting element 5. Fig. Figure 39 shows voltage-current properties of the light-emitting element 5. Fig. Figure 40 shows an emission spectrum of the light-emitting element 5. Fig. 41 shows reliability of the light-emitting element 5. Fig. Figure 42 shows current density-luminance properties of a light-emitting element 6. Fig. Figure 43 shows the voltage-luminance properties of the light-emitting element 6. Fig. Figure 44 shows luminance-current efficiency properties of the light-emitting element 6. Fig. Figure 45 shows voltage-current properties of the light-emitting element 6. Fig. Figure 46 shows an emission spectrum of the light-emitting element 6. Fig. 47 shows reliability of the light-emitting element 6. Best way to implement the invention

[0017] Embodiments of the present invention are described below with reference to the drawings. It should be noted that the present invention is not limited to the following description and that various changes and modifications can be made without departing from the inventive concept. Therefore, the present invention should not be interpreted as being limited to the description of the following embodiments. (Basic process of light emission in a light-emitting element)

[0018] First, general basic processes of light emission in a light-emitting element that uses a phosphorescent substance as a host material are described. It should be noted that a molecule that releases excitation energy is called the host molecule, while a molecule that receives the excitation energy is called the guest molecule.

[0019] (1) The case in which an electron and a hole recombine in a guest molecule and in which the guest molecule is excited (direct recombination process).

[0020] (1-1) If the excitation state of the guest molecule is a triplet excitation state, the guest molecule emits phosphorescence.

[0021] (1-2) If the excitation state of the guest molecule is a singlet excitation state, the guest molecule in the singlet excitation state undergoes intersystem crossing into a triplet excitation state and emits phosphorescence.

[0022] In other words, the direct recombination process in (1) can achieve high emission efficiency as long as the intersystem crossing efficiency and the phosphorescence quantum yield of the guest molecule are high. It should be noted that the T1 level of the host molecule is preferably higher than the T1 level of the guest molecule.

[0023] (2) The case in which an electron and a hole recombine in a host molecule and in which the host molecule is brought into an excited state (energy transfer process).

[0024] (2-1) If the excitation state of the host molecule is a triplet excitation state and the T1 level of the host molecule is higher than the T1 level of the guest molecule, the excitation energy is transferred from the host molecule to the guest molecule, and therefore the guest molecule is brought into a triplet excitation state. The guest molecule in the triplet excitation state emits phosphorescence. It should be noted that energy transfer from the T1 level of the host molecule to a singlet excitation energy level (S1 level) of the guest molecule is forbidden, except when the host molecule emits phosphorescence, and that it is unlikely to be a major energy transfer process. Therefore, a description of it is omitted here.In other words, energy transfer from the host molecule in the triplet excitation state (3H*) to the guest molecule in the triplet excitation state (3G*) is important, as represented by the following formula (2-1) (where 1G represents the singlet ground state of the guest molecule, and 1H represents the singlet ground state of the host molecule). 3H*+1G→1H+3G*

[0025] (2-2) If the excitation state of the host molecule is a singlet excitation state and the S1 level of the host molecule is higher than the S1 level and the T1 level of the guest molecule, the excitation energy is transferred from the host molecule to the guest molecule, and therefore the guest molecule is converted to a singlet or triplet excitation state. The guest molecule in the triplet excitation state emits phosphorescence. Additionally, the guest molecule in the singlet excitation state undergoes intersystem crossing into a triplet excitation state and emits phosphorescence.

[0026] In other words, there can be a process in which energy is transferred from the host molecule in the singlet excitation state (1H*) to the guest molecule in the singlet excitation state (1G*) and then the guest molecule is brought into the triplet excitation state (3G*) by intersystem crossing, as represented by formula (2-2A) below, and a process in which energy is transferred directly from the host molecule in the singlet excitation state (1H*) to the guest molecule in the triplet excitation state (3G*), as represented by formula (2-2B) below. 1H*+1G→1H+1G*→(Intersystem Crossing)→1H+3G* 1H*+1G→1H+3G*

[0027] If all of the energy transfer processes described above in (2) occur efficiently, both the triplet excitation energy and the singlet excitation energy of the host molecule are efficiently converted into the triplet excitation state (3G*) of the guest molecule. Therefore, highly efficient light emission is possible. In contrast, the emission efficiency decreases if the host molecule itself is deactivated by the emission of the excitation energy as light or heat before the excitation energy of the host molecule is transferred to the guest molecule.

[0028] Next, factors that control the intermolecular energy transfer processes between the host molecule and the guest molecule described above are described. The following two mechanisms of intermolecular energy transfer are identified.

[0029] One mechanism is the Förster mechanism (dipole-dipole interaction), in which energy transfer does not require direct contact between molecules and is transferred through a resonance phenomenon of dipole vibration between a host molecule and a guest molecule. Through this resonance phenomenon, the host molecule provides energy to the guest molecule, thus bringing the host molecule to a ground state and the guest molecule to an excited state. It should be noted that the rate constant k h*→g the Förster mechanism is represented by a formula (1). [Formula 1] kh∗→g=9000c4K2ϕln 10128π5n4NτR6∫f'h(ν)εg(ν)ν4dν

[0030] In formula (1) ν denotes a frequency, f' h(ν) denotes a normalized emission spectrum of a host molecule (a fluorescence spectrum for energy transfer from a singlet excitation state and a phosphorescence spectrum for energy transfer from a triplet excitation state), ε g (ν) denotes a molar absorption coefficient of a guest molecule, N denotes Avogadro's number, n denotes a refractive index of a medium, R denotes an intermolecular distance between the host molecule and the guest molecule, τ denotes a measured lifetime of an excitation state (fluorescence lifetime or phosphorescence lifetime), c denotes the speed of light, ϕ denotes a luminescence quantum yield (a fluorescence quantum yield for energy transfer from a singlet excitation state and a phosphorescence quantum yield for energy transfer from a triplet excitation state), and K 2denotes a coefficient (0 to 4) of the orientation of a transition dipole moment between the host molecule and the guest molecule. It should be noted that in the case of random orientation K 2 = 2 / 3 is fulfilled.

[0031] The other is the Dexter mechanism (electron exchange interaction), in which a host molecule and a guest molecule are located near a contact-inducing region where their orbitals overlap, and the host molecule in an excited state and the guest molecule in a ground state exchange electrons, resulting in energy transfer. It should be noted that the rate constant k h*→g the Dexter mechanism is represented by a formula (2). [Formula 2] kh∗→g=(2πh)K'2exp(−2RL)∫f'h(ν)ε'g(ν)dν

[0032] In formula (2), h denotes a Planck constant, K' denotes a constant with an energy dimension, v denotes a frequency, f'h (ν) denotes a normalized emission spectrum of a host molecule (a fluorescence spectrum for energy transfer from a singlet excitation state and a phosphorescence spectrum for energy transfer from a triplet excitation state), ε g (ν) denotes a normalized absorption spectrum of a guest molecule, L denotes an effective molecular radius, and R denotes an intermolecular distance between the host molecule and the guest molecule.

[0033] Here, the efficiency of energy transfer from the host molecule to the guest molecule (energy transfer efficiency Φ) is to be determined. ET ) can be expressed by a formula (3). In the formula, k denotes r a rate constant of a light emission process (fluorescence during energy transfer from a singlet excitation state and phosphorescence during energy transfer from a triplet excitation state) of a host molecule, k ndenotes a rate constant of a non-light emission process (thermal deactivation or intersystem crossing) of a host molecule, and τ denotes a measured lifetime of an excitation state of a host molecule. [Formula 3] ΦET=kh∗→gkr+kn+kh∗→g=kh∗→g(1τ)+kh∗→g

[0034] According to formula (3), the energy transmission efficiency Φ is found to be... ET by increasing the rate constant k h*→g for energy transfer can be increased, so that another competing rate constant k r + k n (= 1 / τ) becomes relatively small. (Energy transmission efficiency in (2-1))

[0035] First, the energy transfer process in (2-1) is considered. Since the Förster mechanism (formula (1)) is forbidden in this case, only the Dexter mechanism (formula (2)) will be considered. To determine the rate constant k h*→gTo increase the effect, according to formula (2) it is preferred that an emission spectrum of a host molecule (a phosphorescence spectrum here because it is energy transfer from a triplet excitation state) largely overlaps an absorption spectrum of a guest molecule (absorption corresponding to a direct transition from a singlet ground state to a triplet excitation state).

[0036] In one embodiment of the present invention, a phosphorescent compound is used as the guest material. In the absorption spectrum of the phosphorescent compound, absorption corresponding to a direct transition from a singlet ground state to a triplet excitation state is observed in some cases, which is an absorption band on the longest wavelength side. In particular, light-emitting iridium complexes have a broad absorption band at approximately 500 nm to 600 nm as the absorption band on the longest wavelength side (in fact, the broad absorption band can be located on a shorter or longer wavelength side depending on the emission wavelengths). This absorption band is based mainly on a triplet MLCT (metal-ligand charge-transfer) transition.It should be noted that the absorption band is assumed to also include absorptions based on a triplet π-π* transition and a singlet MLCT transition, and that these absorptions overlap to form a broad absorption band on the longest wavelength side of the absorption spectrum. In other words, the difference between the lowest singlet excitation state and the lowest triplet excitation state is small, and absorptions based on these states overlap to form a broad absorption band on the longest wavelength side of the absorption spectrum. Therefore, when a metal-organic complex (especially an iridium complex) is used as the guest material, the broad absorption band on the longest wavelength side largely overlaps the phosphorescence spectrum of the host material, as described above. This allows the rate constant k to be determined. h*→gcan be increased, and energy transmission efficiency can be improved.

[0037] Furthermore, a fluorescent compound is generally used as the host material. Therefore, a phosphorescence lifetime (τ) is one millisecond or longer, which is extremely long (i.e., k). r + k n is low). This is because the transition from the triplet excitation state to the ground state (singlet) is a forbidden transition. Equation (3) shows that this is low for the energy transfer efficiency Φ. ET which is advantageous.

[0038] The foregoing description also suggests that energy transfer from the host material in the triplet excitation state to the guest material in the triplet excitation state, i.e. the process in formula (2-1), generally promises to occur as long as the phosphorescence spectrum of the host material overlaps the absorption spectrum corresponding to the direct transition of the guest material from the singlet ground state to the triplet excitation state. (Energy transmission efficiency in (2-2))

[0039] Next, the energy transfer process in (2-2) is considered. The process in equation (2-2A) is influenced by the efficiency of intersystem crossing of the guest material. To maximize emission efficiency, the process in equation (2-2B) is therefore considered important. Since the Dexter mechanism (equation (2)) is forbidden in this case, only the Förster mechanism (equation (1)) will be considered.

[0040] When τ is eliminated from formula (1) and formula (3), it can be said that the energy transfer efficiency Φ ETThe yield is higher when the quantum yield ϕ (a fluorescence quantum yield here because it involves energy transfer from a singlet excitation state) is higher. However, a more important factor is as follows: the emission spectrum of the host molecule (a fluorescence spectrum here because it involves energy transfer from a singlet excitation state) largely overlaps the absorption spectrum of the guest molecule (absorption corresponding to the direct transition from the singlet ground state to the triplet excitation state) (it should be noted that the molar absorption coefficient of the guest molecule is also preferably high). This means that the fluorescence spectrum of the host material overlaps the absorption band along the longest wavelength side of the phosphorescent compound used as the guest material.

[0041] However, this is usually very difficult to achieve. The reason for this is as follows: in order to efficiently enable both of the processes (2-1) and (2-2) described above, it is clear from the preceding discussion that the host material must be designed such that not only its phosphorescence spectrum but also its fluorescence spectrum overlaps the absorption band of the guest material located on the longest wavelength side. In other words, the host material must be designed such that its fluorescence spectrum lies in a position close to that of its phosphorescence spectrum.

[0042] The S1 level, however, generally differs significantly from the T1 level (S1 level > T1 level), and therefore the fluorescence emission wavelength also differs significantly from the phosphorescence emission wavelength (fluorescence emission wavelength < phosphorescence emission wavelength). For example, 4,4'-Di(N-carbazolyl)biphenyl (abbreviation: CBP), which is conventionally used as a host material in a light-emitting element containing a phosphorescent compound, exhibits a phosphorescence spectrum at approximately 500 nm and a fluorescence spectrum at approximately 400 nm, which differ significantly by about 100 nm. This example also demonstrates that it is extremely difficult to form a host material whose fluorescence spectrum is located in a similar position to the phosphorescence spectrum.Therefore, it is very important to improve the efficiency of energy transfer from the host material in the singlet excitation state to the guest material.

[0043] Consequently, one embodiment of the present invention offers a useful technique that can overcome such a problem of the efficiency of energy transfer from the host material in the singlet excitation state to the guest material. Specific embodiments thereof are described below. (Version 1)

[0044] In this embodiment, a structural concept of a light-emitting element in one embodiment of the present invention and a specific structure of the light-emitting element are described. It should be noted that in one embodiment of the present invention, the light-emitting element is configured such that an EL layer, which includes a light-emitting layer, is provided between a pair of electrodes, and the light-emitting layer contains a guest material, which is a phosphorescent compound, a first organic compound, and a second organic compound.

[0045] First, an elemental structure of a light-emitting element, which is an example of the present invention, is described using Fig. 1A described.

[0046] In the element structure that is in Fig. As shown in Figure 1A, an EL layer 103, which includes a light-emitting layer 106, is provided between a pair of electrodes (an anode 101 and a cathode 102), and the EL layer 103 has a structure in which a hole injection layer 104, a hole transport layer 105, the light-emitting layer 106 (106a and 106b), an electron transport layer 107, an electron injection layer 108 and the like are sequentially stacked over the anode 101.

[0047] The light-emitting layer 106 in one embodiment of the present invention contains a phosphorescent compound 109 as a guest material, a first organic compound 110 and a second organic compound 111, as shown in Fig. Figure 1A shows an electron transport material with an electron mobility of 10. -6 cm 2 / Vs or more is mainly used as the first organic compound 110, and a hole transport material with a hole mobility of 10 -6 cm 2 / Vs or more is mainly used as the second organic compound 111. In this description, the first organic compound 110 is referred to as the host material, and the second organic compound 111 is referred to as the auxiliary material.

[0048] It should be noted that in the above structure, it is preferred that the triplet excitation energy level (T1 level) of each of the first and second organic compounds (host and auxiliary materials) 110 and 111 is higher than the T1 level of the phosphorescent compound (guest material) 109. This is because if the T1 level of the first organic compound 110 (or the second organic compound 111) is lower than the T1 level of the phosphorescent compound 109, the triplet excitation energy of the phosphorescent compound 109, which contributes to light emission, is quenched by the first organic compound 110 (or the second organic compound 111), leading to a reduction in emission efficiency.

[0049] A feature of the light-emitting layer 106 in one embodiment of the present invention is that light-emitting layers containing the second organic compound (auxiliary material) 111 in different proportions are stacked within the light-emitting layer 106. In particular, as shown in Fig. Figure 1A shows that the light-emitting layer 106 is a stacked structure consisting of a first light-emitting layer 106a and a second light-emitting layer 106b, and the proportion of the second organic compound (auxiliary material) 111 in the first light-emitting layer 106a is higher than the proportion of the second organic compound (auxiliary material) 111 in the second light-emitting layer 106b. The first light-emitting layer 106a comprises a first phosphorescent compound, and the second light-emitting layer 106b comprises a second phosphorescent compound, wherein a peak of an emission spectrum of the first phosphorescent compound has a shorter wavelength than a peak of an emission spectrum of the second phosphorescent compound.

[0050] Furthermore, in each of the first light-emitting layer 106a and the second light-emitting layer 106b, either the first organic compound (host material) 110 or the second organic compound (auxiliary material) 111 can be present in a higher proportion in the light-emitting layer 106. The present invention encompasses both cases.

[0051] It should be noted that if, in the above structure, the proportion of the second organic compound (auxiliary material) 111, which is a hole transport material, is low in the first light-emitting layer 106a, a light-emitting region forms locally on the anode side (on the side of the hole transport layer 105) in the first light-emitting layer 106a. Conversely, charge carriers (both holes and electrons) tend to pass through the light-emitting layer 106 if the proportion of the second organic compound (auxiliary material) 111 in both the first light-emitting layer 106a and the second light-emitting layer 106b is too high, leading to a reduction in recombination efficiency. However, if the structure is based on Fig. In the structure described in Figure 1A, used in an embodiment of the present invention, the hole transport property of the first light-emitting layer 106a is relatively increased compared to the hole transport property of the second light-emitting layer 106, while the electron transport property is decreased. As a result, excitons can be distributed within the light-emitting layer 106 without local formation, primarily at or near the interface between the first light-emitting layer 106a and the second light-emitting layer 106b. Consequently, the formation of excitons within the light-emitting layer 106 and the degradation of the light-emitting layer 106 due to an increase in exciton density can be prevented. Furthermore, high emission efficiency can be maintained because charge carriers can be prevented from passing through the light-emitting layer 106.

[0052] One characteristic is as follows: a combination of the first organic compound (host material) 110 and the second organic compound (auxiliary material) 111 in each of the first and second light-emitting layers 106a and 106b forms an exciplex (also called an excited complex). Furthermore, the emission wavelength of the exciplex lies on the longer wavelength side than the emission wavelength (fluorescence wavelength) of each of the first and second organic compounds (host and auxiliary materials) 110 and 111. Therefore, the fluorescence spectrum of the first organic compound (host material) 110 and the fluorescence spectrum of the second organic compound (auxiliary material) 111 can be transformed into an emission spectrum that lies on the longer wavelength side.

[0053] This means that, as in Fig. As shown in 1B, even if the fluorescence spectrum of the first organic compound 110 (or the second organic compound 111) lies on the shorter wavelength side than the absorption band of the phosphorescent compound (guest material) 109, which lies on the longest wavelength side, and does not overlap with the absorption band of the phosphorescent compound (guest material) 109, which lies on the longest wavelength side, the emission spectrum of the exciplex and the absorption band can exhibit a large overlap. Consequently, the energy transfer efficiency in the above formula (2-2B) can be increased.

[0054] Furthermore, it is considered that the exciplex exhibits a very small difference between singlet and triplet excitation energies. In other words, the emission spectrum of the exciplex from the singlet state and its emission spectrum from the triplet state are very close to each other. Consequently, in the case where a design is used in which, as described above, the emission spectrum of the exciplex (generally the emission spectrum of the exciplex from the singlet state) overlaps the absorption band of the phosphorescent compound on the longest wavelength side, the emission spectrum of the exciplex from the triplet state (which is not observed at room temperature and in many cases not even at low temperatures) also overlaps the absorption band of the phosphorescent compound located on the longest wavelength side.In other words, not only the efficiency of energy transfer from the singlet excitation state ((2-2)), but also the efficiency of energy transfer from the triplet excitation state ((2-1)) can be increased, and as a result, energy from both the singlet and triplet excitation states can be efficiently converted into light emission.

[0055] Therefore, molecular orbital calculations were performed as follows to determine whether an exciplex actually exhibits such properties. In general, a combination of a heteroaromatic compound and an aromatic amine often forms an exciplex under the influence of the lowest unoccupied molecular orbital (LUMO) level of the heteroaromatic compound, which is lower than the LUMO level of the aromatic amine (the property of readily accepting electrons), and the highest occupied molecular orbital (HOMO) level of the aromatic amine, which is less deep than the HOMO level of the heteroaromatic compound (the property of readily accepting holes).Therefore, calculations were performed using a combination of dibenzo[f,h]quinoxaline (abbreviation: DBq), which is a typical scaffold forming the LUMO level of a heteroaromatic compound and is a model of the first organic compound 110 in an embodiment of the present invention, and triphenylamine (abbreviation: TPA), which is a typical scaffold forming the HOMO level of an aromatic amine and is a model of the second organic compound 111 in an embodiment of the present invention.

[0056] First, the optimal molecular structures and excitation energies of a molecule of DBq (abbreviation) and a molecule of TPA (abbreviation) in the lowest singlet excitation state (S1) and the lowest triplet excitation state (T1) were calculated using time-dependent density functional theory (TD-DFT). Furthermore, the excitation energy of a dimer of DBq (abbreviation) and TPA (abbreviation) was also calculated.

[0057] In DFT (Density Functional Theory), total energy is represented as the sum of potential energy, electrostatic energy between electrons, electronic kinetic energy, and exchange-correlation energy, including all complex interactions between electrons. Furthermore, in DFT, an exchange-correlation interaction is approximated by a functional (a function of another function) of an electron potential expressed in terms of the electron density to enable high-speed, high-precision calculations. Here, B3LYP, a hybrid functional, was used to specify the importance of each parameter with respect to an exchange-correlation energy.

[0058] Additionally, the basic function 6-311 (a basic function of a triple-split valence basis set using three contraction functions for each valence orbital) was applied to all atoms.

[0059] The basic function above considers, for example, 1s to 3s orbitals in the case of hydrogen atoms, while 1s to 4s and 2p to 4p orbitals are considered in the case of carbon atoms. To further improve the accuracy of the calculation, the p function and the d function were also added as polarization basis sets for hydrogen atoms and atoms other than hydrogen atoms, respectively.

[0060] It should be noted that Gaussian 09 was used as a quantum chemical computer program. A high-performance computer (Altix 4700, manufactured by SGI Japan, Ltd.) was used for the calculations.

[0061] First, the HOMO levels and the LUMO levels of a molecule of DBq (abbreviation), a molecule of TPA (abbreviation) and a dimer of DBq (abbreviation) and TPA (abbreviation) were calculated. Fig. Figure 2 shows the HOMO levels and the LUMO levels, and Fig. 3A1, Fig. 3A2, Fig. 3B1, Fig. 3B2, Fig. 3C1 and Fig. 3C2 shows HOMO and LUMO distributions.

[0062] Fig. 3A1 shows the LUMO distribution of a molecule of DBq (abbreviation); Fig. 3A2, the HOMO distribution of a molecule of DBq (abbreviation); Fig. 3B1, the LUMO distribution of a molecule of TPA (abbreviation); Fig. 3B2, the HOMO distribution of a molecule of TPA (abbreviation); Fig. 3C1, the LUMO distribution of the dimer of DBq (abbreviation) and TPA (abbreviation); and Fig. 3C2, the HOMO distribution of the dimer of DBq (abbreviation) and TPA (abbreviation).

[0063] As in Fig. Figure 2 suggests that the dimer of DBq (abbreviation) and TPA (abbreviation) forms an exciplex of DBq (abbreviation) and TPA (abbreviation) under the influence of the LUMO level (-1.99 eV) of DBq (abbreviation), which is lower than the LUMO level of TPA (abbreviation), and the HOMO level (-5.21 eV) of TPA (abbreviation), which is less low (higher) than the HOMO level of DBq (abbreviation). It is actually from Fig. 3C1 and Fig. 3C2 clearly states that the LUMO of the dimer of DBq (abbreviation) and TPA (abbreviation) is distributed on the DBq (abbreviation) side, and its HOMO level is distributed on the TPA (abbreviation) side.

[0064] Next, excitation energies obtained from the optimal molecular structures of a molecule of DBq (abbreviation) at S1 and T1 levels are shown. Here, the excitation energies at the S1 and T1 levels correspond to the fluorescence and phosphorescence wavelengths, respectively, obtained from a molecule of DBq (abbreviation). The excitation energy at the S1 level of a molecule of DBq (abbreviation) is 3.294 eV, and the fluorescence wavelength is 376.4 nm. The excitation energy at the T1 level of a molecule of DBq (abbreviation) is 2.460 eV, and the phosphorescence wavelength is 504.1 nm.

[0065] Additionally, excitation energies obtained from the optimal molecular structures of a TPA molecule (abbreviation) at S1 and T1 levels are shown. These excitation energies correspond to the fluorescence and phosphorescence wavelengths, respectively, obtained from a single TPA molecule. The excitation energy at the S1 level of a TPA molecule is 3.508 eV, and the fluorescence wavelength is 353.4 nm. The excitation energy at the T1 level of a TPA molecule is 2.610 eV, and the phosphorescence wavelength is 474.7 nm.

[0066] Furthermore, excitation energies obtained from the optimal molecular structures of the DBq (abbreviation) and TPA (abbreviation) dimer at S1 and T1 levels are shown. These excitation energies correspond to the fluorescence and phosphorescence wavelengths, respectively, obtained from the DBq (abbreviation) and TPA (abbreviation) dimer. The excitation energy at the S1 level of the DBq (abbreviation) and TPA (abbreviation) dimer is 2.036 eV, and the fluorescence wavelength is 609.1 nm. The excitation energy at the T1 level of the DBq (abbreviation) and TPA (abbreviation) dimer is 2.030 eV, and the phosphorescence wavelength is 610.0 nm.

[0067] From the above description, it can be seen that each of the phosphorescence wavelengths of a molecule of DBq (abbreviation) and a molecule of TPA (abbreviation) shifts towards the longer wavelength side by approximately 100 nm. This result shows a trend similar to that of the CBP (abbreviation) (measured values) described above and confirms the validity of the calculations.

[0068] On the other hand, it is found that the fluorescence wavelength of the dimer of DBq (abbreviation) and TPA (abbreviation) lies on the longer wavelength side than the fluorescence wavelengths of a single molecule of DBq (abbreviation) and a single molecule of TPA (abbreviation). It is also found that the difference between the fluorescence wavelength and the phosphorescence wavelength of the dimer of DBq (abbreviation) and TPA (abbreviation) is only 0.9 nm, and that these wavelengths are essentially the same.

[0069] These results show that the exciplex can combine the singlet and triplet excitation energies into essentially the same energy. Therefore, as shown above, it is suggested that the exciplex can efficiently transfer energy to the phosphorescent compound from both the singlet and triplet states.

[0070] In one embodiment of the present invention, the light-emitting element transfers energy by utilizing an overlap between the emission spectrum of the exciplex formed in the light-emitting layer and the absorption spectrum of the phosphorescent substance (guest material), and therefore exhibits high energy transfer efficiency. Consequently, the light-emitting element can achieve a high external quantum yield.

[0071] Furthermore, the exciplex exists only in one excited state and therefore has no ground state that can absorb energy. For this reason, it is assumed that a phenomenon in which the phosphorescent compound (guest material) 109 is deactivated before light emission by energy transfer from the phosphorescent substance (guest material) in the singlet and triplet excited states to the exciplex (i.e., the emission efficiency decreases) does not occur in principle. This also contributes to improving the external quantum yield.

[0072] It should be noted that the exciplex described above is formed by an interaction between dissimilar molecules in excited states. It is generally known that the exciplex is readily formed between a material with a relatively low LUMO level and a material with a relatively shallow HOMO level.

[0073] The emission wavelength of the exciplex depends on the energy difference between the HOMO and LUMO levels. Generally, the emission wavelength is short when the energy difference is large and long when the energy difference is small.

[0074] Therefore, the HOMO and LUMO levels of the first organic compound (host material) 110 and the second organic compound (auxiliary material) 111 differ from each other in this embodiment. In particular, the energy levels vary in the following order: the HOMO level of the first organic compound 110 < the HOMO level of the second organic compound 111 < the LUMO level of the first organic compound 110 < the LUMO level of the second organic compound 111 (see Fig. 4).

[0075] When the exciplex is formed from these two organic compounds, the LUMO level and the HOMO level of the exciplex originate from the first organic compound (host material) 110 and the second organic compound (auxiliary material) 111, respectively (see Fig. 4) Therefore, the energy difference of the exciplex is smaller than the energy difference of the first organic compound (host material) 110 and the energy difference of the second organic compound (auxiliary material) 111. In other words, the emission wavelength of the exciplex is longer than the emission wavelengths of the first organic compound (host material) 110 and the second organic compound (auxiliary material) 111.

[0076] It should be noted that the process of forming an exciplex in one embodiment of the present invention can be either of the following two processes.

[0077] The formation process is as follows: an exciplex is formed by the first organic compound (host material) and the second organic compound (auxiliary material) with charge carriers (cation or anion).

[0078] In general, when an electron and a hole recombine in a host material, excitation energy is transferred from the host material in an excited state to a guest material, thereby exciting the guest material to emit light. Before the excitation energy is transferred from the host material to the guest material, the host material itself emits light, or the excitation energy is converted into heat energy, resulting in the deactivation of some of the excitation energy. In particular, if the host material is in a singlet excited state, energy transfer does not occur readily, as described in (2-2). Such deactivation of excitation energy is one of the causes of a decrease in the lifetime of a light-emitting element.

[0079] However, in one embodiment of the present invention, an exciplex is formed between the first organic compound (host material) and the second organic compound (auxiliary material) with charge carriers (cation or anion). Therefore, the formation of a singlet exciton in the first organic compound (host material) can be suppressed. In other words, a process can occur in which an exciplex is formed directly without the formation of a singlet exciton. Consequently, the deactivation of the singlet excitation energy can be prevented. As a result, a light-emitting element with a long lifetime can be obtained.

[0080] For example, if the first organic compound 110 is an electron-capturing compound with the property of readily trapping electrons (charge carriers) (with a low LUMO level) under electron transport materials, and the second organic compound 111 is a hole-capturing compound with the property of readily trapping holes (charge carriers) (with a shallow HOMO level) under hole transport materials, an exciplex is formed directly from an anion of the first organic compound and a cation of the second organic compound. An exciplex formed in such a process is specifically called an electroplex.A light-emitting element with high emission efficiency can be obtained by suppressing the generation of the singlet excitation state of the first organic compound (host material) and by transferring energy from an electroplex to the phosphorescent compound (guest material) in the manner described above. It should be noted that in this case, the generation of the triplet excitation state of the first organic compound (host material) is suppressed in a similar way, and an exciplex is formed directly. Therefore, it is assumed that energy is transferred from the exciplex to the phosphorescent compound (guest material).

[0081] The other formation process is a fundamental process in which one of the first and second organic compounds (host and auxiliary materials) forms a singlet exciton and then interacts with the other in its ground state to form an exciplex. Unlike an electroplex, a singlet excitation state of the first organic compound (host material) or the second organic compound (auxiliary material) is temporarily generated in this case, but it is quickly converted into an exciplex, thus preventing the deactivation of the singlet excitation energy. Consequently, it is possible to prevent the deactivation of the excitation energy of either the first organic compound (host material) or the second organic compound (auxiliary material).It should be noted that in this case it is assumed that the triplet excitation state of the host material is converted into an exciplex at a similar rate, and that energy is transferred from the exciplex to the phosphorescent compound (guest material).

[0082] It should be noted that if the first organic compound (host material) is an electron-capturing compound, the second organic compound (auxiliary material) is a hole-capturing compound, and the difference between the HOMO levels and the difference between the LUMO levels of these compounds is large (especially 0.3 eV or more), electrons are selectively injected into the first organic compound (host material) and holes are selectively injected into the second organic compound (auxiliary material). In this case, the process by which an electroplex is formed is assumed to have priority over the process by which an exciplex is formed by a singlet exciton.

[0083] To ensure sufficient overlap between the emission spectrum of the exciplex and the absorption spectrum of the phosphorescent compound (guest material), the difference between the energy of a peak in the emission spectrum and the energy of a peak in the absorption band on the side of the lowest energy in the absorption spectrum is 0.2 eV or less, preferably 0.1 eV or less.

[0084] In the light-emitting element of one embodiment of the present invention, it is also preferred that the excitation energy of the exciplex is sufficiently transferred to the phosphorescent compound (guest material), and that light emission from the exciplex is essentially not observed. Therefore, the energy is preferably transferred by the exciplex to the phosphorescent compound (guest material) so that the phosphorescent compound (guest material) emits phosphorescence. It should be noted that the phosphorescent compound (guest material) is preferably a metal-organic complex.

[0085] In an embodiment of the present invention where a phosphorescent compound is used as the first organic compound (host material) in the light-emitting element, the first organic compound (host material) itself readily emits light and does not readily transfer energy to the phosphorescent compound (guest material). In this case, it would be preferable for the first organic compound to be able to emit light efficiently, but achieving high emission efficiency is difficult because the host material causes concentration quenching. Therefore, it is more effective if the first organic compound (host material) and / or the second organic compound (auxiliary material) are fluorescent compounds (i.e., compounds that readily undergo light emission or thermal deactivation from the singlet excitation state).Therefore, it is preferred that the first organic compound (host material) and / or the second organic compound (auxiliary material) is a fluorescent compound.

[0086] For this reason, it is preferred that the first organic compound (host material) is a fluorescent compound, and that an exciplex is used as the medium for energy transfer.

[0087] It should be noted that the structure described in this embodiment can be appropriately combined with one of the structures described in the other embodiments. (Version 2)

[0088] In this embodiment, an example of a light-emitting element in an embodiment of the present invention is given by reference to Fig. 5 described.

[0089] The light-emitting element described in this embodiment is, as in Fig. 5 an EL layer 203, which includes a light-emitting layer 206, is provided between a pair of electrodes (a first electrode (anode) 201 and a second electrode (cathode) 202), and the EL layer 203 includes a hole injection layer 204, a hole transport layer 205, an electron transport layer 207, an electron injection layer 208 and the like, in addition to the light-emitting layer 206, having a stacked structure comprising a first light-emitting layer 206a and a second light-emitting layer 206b.

[0090] It should be noted that the light-emitting layer 206 (each of the first and second light-emitting layers 206a and 206b) described in this embodiment contains a phosphorescent compound 209 as a guest material, a first organic compound 210 as a host material, and a second organic compound 211 as an auxiliary material. It should be noted that in this embodiment, the proportion of the first organic compound 210 in the light-emitting layer 206 (each of the first and second light-emitting layers 206a and 206b) is higher than that of the second organic compound 211.

[0091] The light-emitting layer 206 in this embodiment has the stacked structure of the first light-emitting layer 206a and the second light-emitting layer 206b, and the proportion of the second organic compound (auxiliary material) 211 in the first light-emitting layer 206a is higher than the proportion of the second organic compound (auxiliary material) 211 in the second light-emitting layer 206b.

[0092] When a structure is used in which the phosphorescent compound 209 is distributed within the first organic compound (host material) 210 and the second organic compound (auxiliary material) 211 in the light-emitting layer 206 (the first light-emitting layer 206a and the second light-emitting layer 206b), crystallization of the light-emitting layer 206 can be suppressed. Furthermore, it is possible to suppress concentration quenching resulting from a high concentration of the phosphorescent compound 209, and therefore the light-emitting element can exhibit higher emission efficiency.

[0093] It is preferred that the triplet excitation energy level (T1 level) of each of the first and second organic compounds 210 and 211 is higher than the T1 level of the phosphorescent compound 209. This is because if the T1 level of the first organic compound 210 (or the second organic compound 211) is lower than the T1 level of the phosphorescent compound (guest material) 209, the triplet excitation energy of the phosphorescent compound (guest material) 209, which contributes to light emission, is quenched by the first organic compound 210 (or the second organic compound 211), leading to a reduction in emission efficiency.

[0094] In the light-emitting layer 206 of this embodiment, the first organic compound 210 and the second organic compound 211 form an exciplex at the time of recombination of charge carriers (electrons and holes) injected from the corresponding electrodes. Accordingly, the fluorescence spectrum of the first organic compound 210 and that of the second organic compound 211 in the light-emitting layer 206 can be converted into an emission spectrum of the exciplex, which lies on a longer wavelength side. Therefore, the first organic compound 210 and the second organic compound 211 are selected such that the emission spectrum of the exciplex largely overlaps the absorption spectrum of the phosphorescent compound (guest material) 209, in order to maximize energy transfer from a singlet excitation state.It should be noted that this assumes energy transfer from the exciplex, not from the host material, even in the case of a triplet excitation state.

[0095] It should be noted that the phosphorescent compound 209 is preferably a metal-organic complex. An electron transport material is preferably used as the first organic compound (host material) 210. A hole transport material is preferably used as the second organic compound (auxiliary material) 211.

[0096] It should be noted that examples of the organometallic complex include: Bis[2-(4',6'-difluorophenyl)pyridinato-N,C 2' ]iridium(III)tetrakis(1-pyrazolyl)borate (abbreviation: FIr6), Bis[2-(4',6'-difluorophenyl)pyridinato-N,C 2' ]iridium(III)picolinate (abbreviation: Flrpic), Bis[2-(3',5'-bistrifluoromethylphenyl)pyridinato-N,C 2']Iridium(III)picolinate (abbreviation: Ir(CF3ppy)2(pic)), Bis[2-(4',6'-difluorophenyl)pyridinato-N,C 2' ]iridium(III)acetylacetonate (abbreviation: Flracac), Tris(2-phenylpyridinato)iridium(III) (abbreviation: Ir(ppy)3), Bis(2-phenylpyridinato)iridium(III)acetylacetonate (abbreviation: Ir(ppy)2(acac)), Bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation: Ir(bzq)2(acac)), Bis(2,4-diphenyl-1,3-oxazolato-N,C 2') iridium(III)acetylacetonate (abbreviation: Ir(dpo)2(acac)), Bis{2-[4'-(perfluorophenyl)phenyl]pyridinato-N,C 2'}iridium(III)acetylacetonate (abbreviation: Ir(p-PF-ph)2(acac)), Bis(2-phenylbenzothiazolato-N,C 2') iridium(III)acetylacetonate (abbreviation: Ir(bt)2(acac)), Bis[2-(2'-benzo[4,5-α]thienyl)pyridinato-N,C 3' ]Iridium(III)acetylacetonate (abbreviation: Ir(btp)2(acac)), Bis(1-phenylisoquinolinato-N,C 2')iridium(III)acetylacetonate (abbreviation: Ir(piq)2(acac)), (Acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III) (abbreviation: Ir(Fdpq)2(acac)), (Acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III) (abbreviation: Ir(tppr)2(acac)), 2,3,7,8,12,13,17,18-Octaethyl-21H,23H-porphyrin platinum(II) (abbreviation: PtOEP), Tris(acetylacetonato)(monophenanthroline)terbium(III) (abbreviation: Tb(acac)3(Phen)), Tris(1,3-diphenyl-1,3-propandionato)(monophenanthroline)europium(III) (abbreviation: Eu(DBM)3(Phen)), Tris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III) (abbreviation: Eu(TTA)3(Phen)) and the like.

[0097] A nitrogen-containing heteroaromatic compound is used as the electron transport material, and examples include quinoxaline and dibenzoquinoxaline derivatives such as 2-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), 2-[3'-(Dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), 2-[4-(3,6-Diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2CzPDBq-III), 7-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[fh]quinoxaline (abbreviation: 7mDBTPDBq-II) and 6-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 6mDBTPDBq-II).

[0098] A π-electron-rich heteroaromatic compound (e.g., a carbazole derivative or an indole derivative) or an aromatic amine compound is used as the hole transport material, and examples include 4-phenyl-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), 4,4'-di(1-naphthyl)-4"-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB), 3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole (abbreviation: PCzPCN1), 4,4',4"-tris[N-(1-naphthyl)-N-phenylamino]triphenylamine (abbreviation: 1'-TNATA), 2,7-Bis[N-(4-diphenylaminophenyl)-N-phenylamino]-spiro-9,9'-bifluorene (abbreviation: DPA2SF), N,N'-Bis(9-phenylcarbazol-3-yl)-N,N'-diphenylbenzene-1,3-diamine (abbreviation: PCA2B), N-(9,9-Dimethyl-2-diphenylamino-9H-fluoren-7-yl)diphenylamine (abbreviation: DPNF), N,N',N"-Triphenyl-N,N',N"-tris(9-phenylcarbazol-3-yl)benzene-1,3,5-triamine (abbreviation: PCA3B), 2-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]spiro-9,9'-bifluorene (abbreviation: PCASF),2-[N-(4-Diphenylaminophenyl)-N-phenylamino]spiro-9,9'-bifluorene (abbreviation: DPASF), N,N'-Bis[4-(carbazol-9-yl)phenyl]-N,N'-diphenyl-9,9-dimethylfluorene-2,7-diamine (abbreviation: YGA2F), 4,4'-Bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (abbreviation: TPD), 4,4'-Bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation: DPAB), N-(9,9-Dimethyl-9H-fluoren-2-yl)-N-{9,9-dimethyl-2-[N'-phenyl-N'-(9,9-dimethyl-9H-fluoren-2-yl)amino]-9H-fluoren-7-yl}phenylamine (abbreviation: DFLADFL), 3-[N-(9-Phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA1), 3-[N-(4-Diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzDPA1), 3,6-Bis[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzDPA2), 4,4'-Bis(N-{4-[N'-(3-methylphenyl)-N'-phenylamino]phenyl}-N-phenylamino)biphenyl (abbreviation: DNTPD), 3,6-Bis[N-(4-diphenylaminophenyl)-N-(1-naphthyl)amino]-9-phenylcarbazole (abbreviation: PCzTPN2) and 3,6-Bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA2).,

[0099] It should be noted that the combination of materials that can be used for the phosphorescent compound 209, the first organic compound (host material) 210 and the second organic compound (auxiliary material) 211, such that an exciplex can be formed, that the emission spectrum of the exciplex overlaps the absorption spectrum of the phosphorescent compound 209, and that the peak of the emission spectrum of the exciplex has a longer wavelength than the peak of the absorption spectrum of the phosphorescent compound 209.

[0100] In the case where an electron transport material is used as the first organic compound 210 and a hole transport material is used as the second organic compound 211, the charge carrier equilibrium can be controlled by the mixing ratio of the compounds. In particular, the ratio of the first organic compound 210 to the second organic compound 211 is preferably 1:9 to 9:1.

[0101] A specific example in which the light-emitting element described in this embodiment is manufactured is described below.

[0102] For the first electrode (anode) 201 and the second electrode (cathode) 202, a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like may be used. In particular, indium tin oxide (ITO), indium tin oxide containing silicon or silicon oxide, indium zinc oxide, indium oxide containing tungsten oxide and zinc oxide, gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), or titanium (Ti) may be used. Furthermore, an element belonging to Group 1 or Group 2 of the periodic table may be used, such as an alkali metal like lithium (Li) or cesium (Cs), an alkaline earth metal like... B. Magnesium (Mg), Calcium (Ca) or Strontium (Sr), an alloy containing such an element (e.g. MgAg or AlLi), a rare earth metal such as e.g.Europium (Eu) or ytterbium (Yb), an alloy containing such an element, graphene, or the like may be used. The first electrode (anode) 201 and the second electrode (cathode) 202 may, for example, be formed by a sputtering process, an evaporation process (including a vacuum evaporation process), or the like.

[0103] Examples of substances with high hole transport properties used for the hole injection layer 204 and the hole transport layer 205 include aromatic amine compounds such as... B. 4,4'-Bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB or α-NPD), N,N'-Bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviation: TPD), 4,4',4"-Tris(carbazol-9-yl)triphenylamine (abbreviation: TCTA), 4,4',4"-Tris(N,N-diphenylamino)triphenylamine (abbreviation: TDATA), 4,4',4"-Tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (abbreviation: MTDATA) and 4,4'-Bis[N-(spiro-9,9'-bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB), 3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA1), 3,6-Bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA2), and 3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole (abbreviation: PCzPCN1). Other examples include carbazole derivatives such as...4,4'-Di(N-carbazolyl)biphenyl (abbreviation: CBP), 1,3,5-Tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB), and 9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA). The substances mentioned here are mainly substances that have a hole mobility of 10. -6 cm 2 exhibiting / Vs or more. It should be noted that, in addition to these substances, any substance that has the property of transporting more holes than electrons can be used.

[0104] Other examples include high-molecular-weight compounds such as poly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA), poly[N-(4-{N'-[4-(4-diphenylamino)phenyl]phenyl-N'-phenylamino}phenyl)metha crystalline] (abbreviation: PTPDMA) and poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] (abbreviation: poly-TPD).

[0105] Further examples of an acceptor substance that can be used for the hole injection layer 204 include oxides of transition metals, oxides of metals belonging to groups 4 to 8 of the periodic table, and the like. Specifically, molybdenum oxide is particularly preferred.

[0106] The light-emitting layer 206 (206a and 206b) contains, as described above, the phosphorescent compound 209, the first organic compound (host material) 210 and the second organic compound (auxiliary material) 211.

[0107] The electron transport layer 207 is a layer containing a substance with high electron transport properties. A metal complex can be used for the electron transport layer 207, such as Alq3, Tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq3), Bis(10-hydroxybenzo[h]-quinolinato)beryllium (abbreviation: BeBq2), BAlq, Zn(BOX)2, or Bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation: Zn(BTZ)2). Alternatively, a heteroaromatic compound can be used, such as... B. 2-(4-Biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 1,3-Bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (abbreviation: OXD-7), 3-(4-tert-Butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole (abbreviation: TAZ), 3-(4-tert-Butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole (abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: Bphen), bathocuproine (abbreviation: BCP) or 4,4'-Bis(5-methylbenzoxazol-2-yl)stilbene (abbreviation: BzOs).Alternatively, a high-molecular-weight compound can be used, such as poly(2,5-pyridine-diyl) (abbreviation: PPy), poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)] (abbreviation: PF-Py), or poly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2'-bipyridine-6,6'-diyl)] (abbreviation: PF-BPy). The substances mentioned here are mainly substances with an electron mobility of 10. -6 cm 2 / Vs or more. It should be noted that, in addition to these substances, a substance which has the property of transporting more electrons than holes can be used for the electron transport layer 207.

[0108] The electron transport layer 207 is not limited to a single layer and can be a stack of two or more layers containing each of the aforementioned substances.

[0109] The electron injection layer 208 is a layer containing a substance with high electron injection properties. Examples of substances that can be used for the electron injection layer 208 include alkali metals, alkaline earth metals, and compounds thereof, such as lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF₂), and lithium oxide (LiO₂). x ), and rare earth metal compounds such as erbium fluoride (ErF3). Alternatively, the substances described above can also be used to form the electron transport layer 207.

[0110] Alternatively, a composite material in which an organic compound and an electron donor (a donor) are mixed can be used for the electron injection layer 208. Such a composite material, in which electrons are generated in the organic compound by the electron donor, exhibits high electron injection and electron transport properties. The organic compound is preferably a material that efficiently transports the generated electrons, and in particular, one of the substances mentioned above (such as metal complexes and heteroaromatic compounds) can be used for the electron transport layer 207. A substance that exhibits electron-donating properties with respect to the organic compound can be used as the electron donor. In particular, alkali metals, alkaline earth metals, and rare earth metals are preferred, and lithium, cesium, magnesium, calcium, erbium, ytterbium, and the like are suitable.Any of the alkali metal oxides and alkaline earth metal oxides is preferred, and examples of them are lithium oxide, calcium oxide, barium oxide and the like, and a Lewis base such as magnesium oxide or an organic compound such as tetrathiafulvalene (abbreviation: TTF) can be used.

[0111] It should be noted that the hole injection layer 204, the hole transport layer 205, the light-emitting layer 206 (206a and 206b), the electron transport layer 207 and the electron injection layer 208 described above can each be formed by a process such as an evaporation process (including a vacuum evaporation process), an inkjet process or a coating process.

[0112] Light emission from the light-emitting layer 206 of the light-emitting element described above is extracted to the outside through the first electrode 201 and / or the second electrode 202. The first electrode 201 and / or the second electrode 202 in this embodiment are therefore electrodes with a translucent property.

[0113] In the light-emitting element described in this embodiment, the energy transfer efficiency can be improved thanks to an energy transfer mechanism that exploits an overlap between the emission spectrum of an exciplex and the absorption spectrum of a phosphorescent compound. Consequently, a high external quantum yield of the light-emitting element can be achieved.

[0114] It should be noted that the light-emitting element described in this embodiment is an embodiment of the present invention and is characterized in particular by the structure of the light-emitting layer. Therefore, when the structure described in this embodiment is used, a light-emitting passive matrix device, a light-emitting active matrix device, and the like can be produced. These light-emitting devices are included in the present invention.

[0115] It should be noted that when fabricating the light-emitting active-matrix device, there are no particular restrictions regarding the structure of the TFT. For example, a staggered TFT or an inverted staggered TFT can be used. Furthermore, a driver circuit formed on top of a TFT substrate can be implemented using either an n-type TFT or a p-type TFT, or either an n-type TFT or a p-type TFT. Additionally, there are no particular restrictions regarding the crystallinity of the semiconductor film used for the TFT. For example, an amorphous semiconductor film, a crystalline semiconductor film, an oxide semiconductor film, or the like can be used.

[0116] It should be noted that the structure described in this embodiment can be appropriately combined with one of the structures described in the other embodiments. (Version 3)

[0117] In this embodiment, an embodiment of the present invention is described as a light-emitting element (hereinafter referred to as a light-emitting tandem element) in which a charge-generating layer is arranged between a plurality of EL layers.

[0118] The light-emitting element described in this embodiment is a light-emitting tandem element comprising a plurality of EL layers (a first EL layer 302(1) and a second EL layer 302(2)) between a pair of electrodes (a first electrode 301 and a second electrode 304), as shown in Fig. 6A shown.

[0119] In this embodiment, the first electrode 301 serves as the anode, and the second electrode 304 serves as the cathode. It should be noted that the first electrode 301 and the second electrode 304 may have structures similar to those described in embodiment 1. Furthermore, any or all of the plurality of EL layers (the first EL layer 302(1) and the second EL layer 302(2)) may have structures similar to those described in embodiment 1 or 2. In other words, the structures of the first EL layer 302(1) and the second EL layer 302(2) may be the same or different from each other and may be similar to those of the EL layers described in embodiment 1 or 2.

[0120] A charge-generating layer (I) 305 is further arranged between the plurality of EL layers (the first EL layer 302(1) and the second EL layer 302(2)). The charge-generating layer (I) 305 has a function of injecting electrons into one of the EL layers and injecting holes into the other of the EL layers when a voltage is applied between the first electrode 301 and the second electrode 304. In this embodiment, when a voltage is applied such that the potential of the first electrode 301 is higher than that of the second electrode 304, the charge-generating layer (I) 305 injects electrons into the first EL layer 302(1) and holes into the second EL layer 302(2).

[0121] It should be noted that, with regard to light extraction efficiency, the charge-generating layer (I) 305 preferably has a visible light transmittance (specifically, the charge-generating layer (I) 305 preferably has a visible light transmittance of 40% or more). Furthermore, the charge-generating layer (I) 305 functions even if it has a lower conductivity than the first electrode 301 or the second electrode 304.

[0122] The charge-generating layer (I) 305 can have either a structure in which an electron acceptor (acceptor) is added to an organic compound with high hole transport properties, or a structure in which an electron donor (donor) is added to an organic compound with high electron transport properties. Alternatively, both of these structures can be stacked.

[0123] In the case where the electron acceptor is added to the organic compound with high hole transport properties, examples of organic compounds with high hole transport properties include aromatic amine compounds such as NPB, TPD, TDATA, MTDATA, and 4,4'-bis[N-(spiro-9,9'-bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB) and the like. The substances mentioned here are mainly substances that exhibit a hole mobility of 10 -6 cm 2 exhibiting / Vs or more. It should be noted that, apart from these substances, any organic compound that has the property of transporting more holes than electrons can be used.

[0124] Examples of electron acceptors include 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F4-TCNQ), chloranil, oxides of transition metals, and oxides of metals belonging to groups 4 to 8 of the periodic table. Vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide are particularly preferred due to their high electron-accepting properties. Among these, molybdenum oxide is especially preferred because it is stable in air, has low hygroscopic properties, and is easy to handle.

[0125] On the other hand, if the electron donor is added to an organic compound with high electron transport properties, examples of suitable organic compounds with high electron transport properties include metal complexes with a quinoline or benzoquinoline framework, such as Alq, Almq3, BeBq2, and BAlq, and the like. Other examples are metal complexes with an oxazole-based or thiazole-based ligand, such as Zn(BOX)2 and Zn(BTZ)2. Besides metal complexes, PBD, OXD-7, TAZ, BPhen, BCP, or the like can be used. The substances mentioned here are mainly substances with an electron mobility of 10 -6 cm 2 / Vs or more. It should be noted that, apart from these substances, any organic compound that has the property of transporting more electrons than holes can be used.

[0126] Examples of electron donors that can be used include alkali metals, alkaline earth metals, rare earth metals, metals belonging to group 13 of the periodic table, and oxides or carbonates thereof. Lithium (Li), cesium (Cs), magnesium (Mg), calcium (Ca), ytterbium (Yb), indium (In), lithium oxide, cesium carbonate, and the like are particularly favored. An organic compound, such as tetrathianaphthacene, can also be used as an electron donor.

[0127] It should be noted that the formation of the charge-generating layer (I) 305 using one of the above materials can suppress an increase in operating voltage caused by the stack of EL layers.

[0128] Although this embodiment shows the light-emitting element with two EL layers, the present invention can be similarly applied to a light-emitting element having n EL layers (where n is 3 or more) (302(1), 302(2), ... , 302(n-1), 302(n)) as shown in Fig. 6B are stacked. In the case where a plurality of EL layers are contained between a pair of electrodes, as in the light-emitting element according to this embodiment, by providing charge-generating layers (I) (305(1), 305(2), ... , 305(n-2), 305(n-1)) between the EL layers, light emission in a high luminance range can be obtained while keeping the current density low. Since the current density can be kept low, the element can have a long lifetime. When the light-emitting element is applied to illumination, a voltage drop due to the resistance of an electrode material can be reduced, which enables uniform light emission over a large area. Furthermore, a light-emitting device that can be operated at a low voltage and consumes little power can be obtained.

[0129] Furthermore, by making the emission colors of the EL layers different, light of a desired color can be obtained from the light-emitting element as a whole. For example, the emission colors of the first and second EL layers in a light-emitting element with two EL layers are complementary, so that the light-emitting element as a whole can emit white light. It should be noted that the term "complementary" refers to the color relationship in which an achromatic color is obtained when the colors are mixed. That is, the emission of white light can be obtained by mixing light emitted by substances whose emission colors are complementary colors.

[0130] The same principle can be applied to a light-emitting element with three EL layers. For example, the light-emitting element as a whole can emit white light if the emission color of the first EL layer is red, the emission color of the second EL layer is green, and the emission color of the third EL layer is blue.

[0131] It should be noted that the structure described in this embodiment can be appropriately combined with one of the structures described in the other embodiments. (Version 4)

[0132] In this embodiment, a light-emitting device according to an embodiment of the present invention is described.

[0133] A light-emitting device described in this embodiment has an optical microresonator (microcavity) structure in which a light resonance effect between a pair of electrodes is utilized. The light-emitting device includes a plurality of light-emitting elements, each having at least one EL layer 405 between a pair of electrodes (a reflective electrode 401 and a semi-transparent and semi-reflective electrode 402), as shown in Fig. Figure 7 shows that the EL layer 405 also includes at least light-emitting layers 404 (404R, 404G and 404B), each serving as a light-emitting region, and may further include a hole injection layer, a hole transport layer, an electron transport layer, an electron injection layer, a charge generation layer (E) and the like.

[0134] In this embodiment, a light-emitting device is described which includes light-emitting elements (a first light-emitting element (R) 410R, a second light-emitting element (G) 410G and a third light-emitting element (B) 410B) with different structures as shown in Fig. 7 is included.

[0135] The first light-emitting element (R) 410R has a structure in which a first transparent conductive layer 403a; an EL layer 405, which partially incorporates a first light-emitting layer (B) 404B, a second light-emitting layer (G) 404G, and a third light-emitting layer (R) 404R; and a semi-transparent and semi-reflective electrode 402 are stacked successively over a reflective electrode 401. The second light-emitting element (G) 410G has a structure in which a second transparent conductive layer 403b, the EL layer 405, and the semi-transparent and semi-reflective electrode 402 are stacked successively over the reflective electrode 401. The third light-emitting element (B) 410B has a structure in which the EL layer 405 and the semi-transparent and semi-reflective electrode 402 are stacked successively over the reflective electrode 401.

[0136] It should be noted that the reflective electrode 401, the EL layer 405, and the semi-transparent and semi-reflective electrode 402 are identical in the light-emitting elements (in the first light-emitting element (R) 410R, the second light-emitting element (G) 410G, and the third light-emitting element (B) 410B). The first light-emitting layer (B) 404B emits light (λ B ) with a peak in a wavelength range of 420 nm to 480 nm. The second light-emitting layer (G) 404G emits light (λ G ) with a peak in a wavelength range of 500 nm to 550 nm. The third light-emitting layer (R) 404R emits light (λ R) with a peak in a wavelength range from 600 nm to 760 nm. In each of the light-emitting elements (in the first light-emitting element (R) 410R, the second light-emitting element (G) 410G, and the third light-emitting element (B) 410B), light emitted from the first light-emitting layer (B) 404B, light emitted from the second light-emitting layer (G) 404G, and light emitted from the third light-emitting layer (R) 404R therefore overlap. In this way, light with a broad emission spectrum covering a range of visible light can be emitted. It should be noted that the aforementioned wavelengths satisfy the condition λ. B < λ G < λ R fulfill.

[0137] Each of the light-emitting elements described in this embodiment has a structure in which the EL layer 405 is arranged between the reflective electrode 401 and the semi-transparent and semi-reflective electrode 402. Light emitted in all directions from the light-emitting layers in the EL layer 405 is brought into resonance by the reflective electrode 401 and the semi-transparent and semi-reflective electrode 402, which serve as an optical microresonator (microcavity). It should be noted that the reflective electrode 401 is formed using a conductive material with reflectivity and that it is a film that reflects visible light to 40% to 100%, preferably to 70% to 100%, and has a resistivity of 1 × 10⁻⁶ Ω. -2Ωcm or lower, is used. Furthermore, the semi-transparent and semi-reflective electrode 402 is formed using a conductive material with reflectivity and a conductive material that is transparent, and a film that reflects visible light to 20% to 80%, preferably to 40% to 70%, and has a resistivity of 1 × 10 -2 If the product has Ωcm or lower, it is used.

[0138] In this embodiment, the thicknesses of the transparent conductive layers (the first transparent conductive layer 403a and the second transparent conductive layer 403b) contained in the first light-emitting element (R) 410R and the second light-emitting element (G) 410G, respectively, are different between the light-emitting elements, so that the optical path length from the reflecting electrode 401 to the semi-transparent and semi-reflective electrode 402 is different between the light-emitting elements.In other words, in light with a broad emission spectrum emitted from the light-emitting layers of each of the light-emitting elements, light with a wavelength that is brought into resonance between the reflecting electrode 401 and the semi-transparent and semi-reflective electrode 402 can be amplified, while light with a wavelength that is not brought into resonance between them can be attenuated. Therefore, if the optical path length from the reflecting electrode 401 to the semi-transparent and semi-reflective electrode 402 differs between the elements, light with different wavelengths can be extracted.

[0139] It should be noted that the optical path length (also called optical distance) is represented as the product of an actual distance and a refractive index, and in this embodiment, it is the product of an actual thickness and n (refractive index). That is, the following applies: optical path length = actual thickness × n.

[0140] Furthermore, the total thickness from the reflective electrode 401 to the semi-transparent and semi-reflective electrode 402 is measured in mλ. R / 2 (m is a natural number) at the first light-emitting element (R) 410R. The total thickness from the reflecting electrode 401 to the semi-transparent and semi-reflective electrode 402 is set to mλ. G / 2 (m is a natural number) at the second light-emitting element (G) 410G. The total thickness from the reflecting electrode 401 to the semi-transparent and semi-reflective electrode 402 is set to mλ.B / 2 (m is a natural number) set at the third light-emitting element (B) 410B.

[0141] In this way the light (λ) R ), which is emitted from the third light-emitting layer (R) 404R in the EL layer 405, mainly taken from the first light-emitting element (R) 410R, the light (λ G ), which is emitted from the second light-emitting layer (G) 404G in the EL layer 405, is mainly taken from the second light-emitting element (G) 410G, and the light (λ B The light emitted from the first light-emitting layer (B) 404B in the EL layer 405 is mainly taken from the third light-emitting element (B) 410B. It should be noted that the light taken from each of the light-emitting elements is emitted from the side of the semi-transparent and semi-reflective electrode 402.

[0142] Furthermore, strictly speaking, the total thickness from the reflective electrode 401 to the semi-transparent and semi-reflective electrode 402 can be the total thickness from a reflective region in the reflective electrode 401 to a reflective region in the semi-transparent and semi-reflective electrode 402. However, it is difficult to precisely determine the positions of the reflective regions in the reflective electrode 401 and in the semi-transparent and semi-reflective electrode 402. Therefore, it can be assumed that the previously described effect can be achieved sufficiently regardless of where the reflective regions are located in the reflective electrode 401 and the semi-transparent and semi-reflective electrode 402.

[0143] In the first light-emitting element (R) 410R, the optical path length from the reflecting electrode 401 to the third light-emitting layer (R) 404R is next adjusted to a desired thickness ((2m'+1)λ). R / 4, where m' is a natural number); light emitted from the third light-emitting layer (R) 404R can thus be amplified. Regarding the light emitted from the third light-emitting layer (R) 404R, light (first reflected light) reflected from the reflecting electrode 401 interferes with light (first incident light) that enters the semi-transparent and semi-reflective electrode 402 directly from the third light-emitting layer (R) 404R. By controlling the optical path length from the reflecting electrode 401 to the third light-emitting layer (R) 404R to the desired value ((2m'+1)λ) R / 4, where m' is a natural number) therefore the phases of the first reflected light and the first incident light can be adjusted to each other, and the light emission from the third light-emitting layer (R) 404R can be enhanced.

[0144] It should be noted that, strictly speaking, the optical path length from the reflecting electrode 401 to the third light-emitting layer (R) 404R can be the optical path length from a reflective region in the reflecting electrode 401 to a light-emitting region in the third light-emitting layer (R) 404R. However, it is difficult to precisely determine the positions of the reflective region in the reflecting electrode 401 and the light-emitting region in the third light-emitting layer (R) 404R. Therefore, it can be assumed that the effect described above can be sufficiently achieved regardless of where the reflective region and the light-emitting region are located in the reflecting electrode 401 and the third light-emitting layer (R) 404R, respectively.

[0145] Next, for the second light-emitting element (G) 410G, the optical path length from the reflecting electrode 401 to the second light-emitting layer (G) 404G is adjusted to a desired thickness ((2m"+1)λ. G / 4, where m" is a natural number). Thus, light emitted from the second light-emitting layer (G) 404G can be amplified. Regarding the light emitted from the second light-emitting layer (G) 404G, light (second reflected light) reflected from the reflecting electrode 401 interferes with light (second incident light) that enters the semi-transparent and semi-reflective electrode 402 directly from the second light-emitting layer (G) 404G. By controlling the optical path length from the reflecting electrode 401 to the second light-emitting layer (G) 404G to the desired value ((2m"+1)λ G / 4, where m" is a natural number) therefore the phases of the second reflected light and the second incident light can be adjusted to each other, and the light emission from the second light-emitting layer (G) 404G can be enhanced.

[0146] It should be noted that, strictly speaking, the optical path length from the reflecting electrode 401 to the second light-emitting layer (G) 404G can be the optical path length from a reflective region in the reflecting electrode 401 to a light-emitting region in the second light-emitting layer (G) 404G. However, it is difficult to precisely determine the positions of the reflective region in the reflecting electrode 401 and the light-emitting region in the second light-emitting layer (G) 404G. Therefore, it can be assumed that the effect described above can be sufficiently achieved regardless of where the reflective region and the light-emitting region are located in the reflecting electrode 401 and the second light-emitting layer (G) 404G, respectively.

[0147] In the third light-emitting element (B) 410B, the optical path length from the reflecting electrode 401 to the first light-emitting layer (B) 404B is next adjusted to a desired thickness ((2m'''+1)λ). B / 4, where m''' is a natural number); light emitted from the first light-emitting layer (B) 404B can thus be amplified. Regarding the light emitted from the first light-emitting layer (B) 404B, light (third reflected light) reflected from the reflecting electrode 401 interferes with light (third incident light) that enters the semi-transparent and semi-reflective electrode 402 directly from the first light-emitting layer (B) 404B. By controlling the optical path length from the reflecting electrode 401 to the first light-emitting layer (B) 404B to the desired value ((2m'''+1)λ B / 4, where m''' is a natural number) therefore the phases of the third reflected light and the third incident light can be adjusted to each other, and the light emission from the first light-emitting layer (B) 404B can be enhanced.

[0148] It should be noted that, strictly speaking, the optical path length from the reflecting electrode 401 to the first light-emitting layer (B) 404B in the third light-emitting element can be the optical path length from a reflective region in the reflecting electrode 401 to a light-emitting region in the first light-emitting layer (B) 404B. However, it is difficult to precisely determine the positions of the reflective region in the reflecting electrode 401 and the light-emitting region in the first light-emitting layer (B) 404B. Therefore, it can be assumed that the effect described above can be sufficiently achieved regardless of where the reflective region and the light-emitting region are located in the reflecting electrode 401 and the first light-emitting layer (B) 404B, respectively.

[0149] It should be noted that although each of the light-emitting elements in the structure mentioned above includes a plurality of light-emitting layers in the EL layer, the present invention is not limited thereto. For example, the structure of the light-emitting tandem element described in embodiment 3 can be combined, in which case a plurality of EL layers and an intervening charge-generating layer are arranged in a single light-emitting element, and one or more light-emitting layers are formed in each of the EL layers.

[0150] The light-emitting device described in this embodiment has a microcavity structure from which light with wavelengths differing between the light-emitting elements can be extracted, even if they contain the same EL layers, thus eliminating the need to manufacture light-emitting elements for the colors R, G, and B. The above structure is therefore advantageous for a full-color display due to the ease with which higher display resolutions or similar features can be achieved. Additionally, the emission intensity at a predetermined wavelength can be increased towards the front, thereby reducing power consumption. The above structure is particularly useful when used for a color display (an image display device) that has pixels for three or more colors, and it can also be used for illumination or similar applications. (Version 5)

[0151] In this embodiment, a light-emitting device comprising a light-emitting element according to an embodiment of the present invention is described.

[0152] The light-emitting device can be either a passive-matrix light-emitting device or an active-matrix light-emitting device. It should be noted that any of the light-emitting elements described in the other embodiments can be applied to the light-emitting device described in this embodiment.

[0153] In this embodiment, a light-emitting active matrix device is used based on Fig. 8A and Fig. 8B described.

[0154] It should be noted that Fig. 8A is a top view showing a light-emitting device, and Fig. 8B a cross-sectional view along the dashed-dotted line AA' in Fig. 8A. The light-emitting active-matrix device according to this embodiment comprises a pixel section 502 provided above an element substrate 501, a driver circuit section (a source line driver circuit) 503, and driver circuit sections (gate line driver circuits) 504 (504a and 504b). The pixel section 502, the driver circuit section 503, and the driver circuit sections 504 are sealed with a sealant 505 between the element substrate 501 and a sealing substrate 506.

[0155] Additionally, a lead wiring 507 is provided above the element substrate 501. The lead wiring 507 is provided to connect an external input terminal through which a signal (e.g., a video signal, a clock signal, a start signal, or a reset signal) or a potential is sent from outside to the driver circuit section 503 and the driver circuit sections 504. An example is shown here in which a flexible printed circuit (FPC) 508 is provided as the external input terminal. Although only the FPC is shown here, the FPC can be equipped with a printed circuit board (PWB). The light-emitting device in this description includes, in its category, not only the light-emitting device as such, but also the light-emitting device equipped with the FPC or the PWB.

[0156] Next, a cross-sectional structure will be created based on... Fig. 8B described. The driver circuit sections and the pixel section are formed above the element substrate 501; here, the driver circuit section 503, which is the source line driver circuit, and the pixel section 502 are shown.

[0157] The driver circuit section 503 is an example in which a CMOS circuit is formed, which is a combination of an n-channel TFT 509 and a p-channel TFT 510. It should be noted that a circuit included in the driver circuit section can be formed using one of various circuits, such as a CMOS circuit, a PMOS circuit, or an NMOS circuit. In this embodiment, a driver-integrated type is described in which a driver circuit is formed on top of the substrate; however, the present invention is not limited to this type, and the driver circuit can also be formed outside the substrate.

[0158] The pixel section 502 comprises a plurality of pixels, each containing a TFT 511 for switching, a TFT 512 for current control, and a first electrode (anode) 513 electrically connected to a conductor (a source electrode or a drain electrode) of the TFT 512 for current control. It should be noted that an insulator 514 is provided to cover end regions of the first electrode (anode) 513. In this embodiment, the insulator 514 is formed using a positive photosensitive acrylic resin.

[0159] The insulator 514 preferably has a curved surface with a curvature in its upper end region or its lower end region to achieve good coverage by a film stacked over the insulator 514. For example, if a positive photosensitive acrylic resin is used as the material for the insulator 514, the insulator 514 preferably has a curved surface with a radius of curvature (0.2 µm to 3 µm) in its upper end region. The insulator 514 can be formed using a negative photosensitive resin or a positive photosensitive resin. It is possible to use either an organic compound or an inorganic compound, such as silicon dioxide or silicon oxynitride, without restriction to an organic compound.

[0160] An EL layer 515 and a second electrode (cathode) 516 are stacked above the first electrode (anode) 513. At least one light-emitting layer is provided in the EL layer 515. The light-emitting layer has a stacked structure as described in embodiment 1. In addition to the light-emitting layer, a hole injection layer, a hole transport layer, an electron transport layer, an electron injection layer, a charge generation layer, and the like may also be appropriately arranged in the EL layer 515.

[0161] The stacked structure, comprising the first electrode (anode) 513, the EL layer 515, and the second electrode (cathode) 516, forms a light-emitting element 517. The materials described in embodiment 2 can be used for the first electrode (anode) 513, the EL layer 515, and the second electrode (cathode) 516. The second electrode (cathode) 516, although not shown, is electrically connected to the FPC 508, which serves as an external input terminal.

[0162] The cross-sectional view in Fig. Although 8B shows only one light-emitting element 517, pixel section 502 contains a matrix of multiple light-emitting elements. Light-emitting elements emitting three types of light (R, G, and B) are optionally configured in pixel section 502, thus creating a light-emitting device suitable for full-color display. Alternatively, a light-emitting device suitable for full-color display can be created in combination with color filters.

[0163] The sealing substrate 506 is further attached to the element substrate 501 by the sealing agent 505, such that the light-emitting element 517 is provided in a space 518 enclosed by the element substrate 501, the sealing substrate 506, and the sealing agent 505. The space 518 can be filled with an inert gas (such as nitrogen or argon) or with the sealing agent 505.

[0164] An epoxy-based resin or low-melting-point glass is preferably used for the sealant 505. It is preferred that such a material be as impermeable as possible to moisture or oxygen. The sealant substrate 506 can be a glass substrate, a quartz substrate, or a plastic substrate made of fiberglass-reinforced plastic (FRP), polyvinyl fluoride (PVF), polyester, acrylic, or the like.

[0165] A light-emitting active matrix device can be obtained in the manner described above.

[0166] It should be noted that the structure described in this embodiment can be appropriately combined with one of the structures described in the other embodiments. (Version 6)

[0167] In this embodiment, examples of various electronic devices completed using a light-emitting device are shown by means of Fig. 9A to Fig. 9D and Fig. 10A to Fig. 10C described. The light-emitting device is manufactured using a light-emitting element which is an embodiment of the present invention.

[0168] Examples of electronic devices to which the light-emitting device is applied include television sets (also called TVs or television receivers), computer monitors and the like, cameras such as digital cameras and digital video cameras, digital photo frames, mobile phones (also called mobile phone devices), portable game consoles, portable information terminals, audio playback devices, large gaming devices such as pinball machines and the like. Specific examples of these electronic devices are in Fig. 9A to Fig. 9D shown.

[0169] Fig. Figure 9A shows an example of a television set. In a television set 7100, a display section 7103 is installed in a housing 7101. The display section 7103 is capable of displaying images, and a light-emitting device can be used for the display section 7103. Additionally, the housing 7101 is supported by a stand 7105.

[0170] The television 7100 can be operated via a control switch on the housing 7101 or a separate remote control 7110. The remote control 7110's control buttons 7109 allow for channel selection and volume control, as well as control of the images displayed on the screen 7103. Furthermore, the remote control 7110 can be equipped with a display area 7107 to show the data output by the remote control 7110.

[0171] It should be noted that the 7100 television is equipped with a receiver, a modem, and similar components. A general television program can be received via the receiver. Furthermore, if the 7100 television is connected to a communication network via a wired or wireless connection through the modem, data communication can take place in one direction (from a transmitter to a receiver) or in two directions (between a transmitter and a receiver, between receivers, etc.).

[0172] Fig. Figure 9B shows a computer comprising a main body 7201, a case 7202, a display section 7203, a keyboard 7204, an external connection port 7205, a pointing device 7206, and the like. It should be noted that this computer is manufactured using a light-emitting device for the display section 7203.

[0173] Fig. Figure 9C shows a portable game console comprising two enclosures, namely enclosure 7301 and enclosure 7302, connected by a hinge 7303 so that the portable game console can be opened or closed. A display section 7304 is built into enclosure 7301, and a display section 7305 is built into enclosure 7302. The portable game console also includes Fig. 9C a speaker section 7306, a recording media insertion section 7307, an LED lamp 7308, input means (an operating button 7309, a connection port 7310, a sensor 7311 (a sensor with a function to measure force, displacement, position, velocity, acceleration, angular velocity, rotational speed, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, electric current, voltage, electric power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared rays) and a microphone 7312) and the like. Of course, the structure of the portable game console is not limited to the above structure, as long as a light-emitting device is used for the display section 7304 and / or the display section 7305, and may appropriately include other accessories. The portable game console in Fig. The 9C has a function for reading a program or data stored on a storage medium in order to display it on the screen, and a function for sharing information with another portable game console via wireless communication. It should be noted that the portable game console in Fig. 9C can have various functions without being limited to the functions mentioned above.

[0174] Fig. Figure 9D shows an example of a mobile phone. A 7400 mobile phone includes a display section 7402, which is built into a housing 7401, operating buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. It should be noted that the 7400 mobile phone is manufactured using a light-emitting device for the display section 7402.

[0175] If the display section 7402 of the mobile phone 7400 is in Fig. When 9D is touched with a finger or similar object, data can be entered into the 7400 mobile phone. Furthermore, operations such as making calls and writing emails can be performed by touching the display section 7402 with a finger or similar object.

[0176] The 7402 display section has three main screen modes. The first mode is a display mode, primarily for showing images. The second mode is an input mode, primarily for entering information such as text. The third mode is a combined display and input mode.

[0177] For example, when making calls or writing emails, a text input mode, where text is the primary input, is selected for display section 7402, allowing input of text displayed on the screen. In this case, it is preferable to display a keyboard or number keys covering almost the entire screen of display section 7402.

[0178] If a detector device with a sensor for detecting inclination, such as a gyroscope or an accelerometer, is provided inside the 7400 mobile phone, the display on the screen of the display section 7402 can be automatically switched by determining the direction of the 7400 mobile phone (whether the mobile phone is positioned horizontally or vertically for landscape or portrait orientation).

[0179] The screen modes are switched by touching the display section 7402 or by operating the control buttons 7403 on the housing 7401. Alternatively, the screen modes can be switched depending on the type of images displayed on the display section 7402. For example, if the signal for an image displayed on the display section is data from moving images, then the screen mode switches to display mode. If the signal is text data, then the screen mode switches to input mode.

[0180] Furthermore, if a signal detected by an optical sensor in the display section 7402 is detected in input mode and no touch input is received via the display section 7402 for a certain period of time, then the screen mode can be set to switch from input mode to display mode.

[0181] The display section 7402 can serve as an image sensor. For example, an image of a handprint, fingerprint, or the like can be taken by touching the display section 7402 with the hand or finger, thus enabling personal identification. Furthermore, if a backlight or a scanning light source emitting near-infrared light is provided in the display section, an image of a finger vein, palm vein, or the like can also be taken.

[0182] Fig. 10A and Fig. Figure 10B shows a foldable tablet computer. The tablet computer is in Fig. 10A opened. The tablet computer includes a housing 9630, a display section 9631a, a display section 9631b, a display mode switch 9034, a power switch 9035, a power-saving switch 9036, a clip 9033, and an operating switch 9038. The tablet computer is manufactured using the light-emitting device for the display section 9631a and / or the display section 9631b.

[0183] Part of the display section 9631a can be a touchscreen area 9632a, and data can be entered when a displayed control button 9637 is touched. Although a structure is shown as an example where one half of the display section 9631a has only a display function and the other half also has a touchscreen function, the display section 9631a is not limited to this structure. The entire area of ​​the display section 9631a can have a touchscreen function. For example, the display section 9631a can display keyboard buttons in the entire area that is intended to be a touchscreen, and the display section 9631b can be used as a display screen.

[0184] As with display section 9631a, part of display section 9631b can be a touchscreen area 9632b. When a button 9639 for switching a keyboard display, which is shown on the touchscreen, is touched with a finger, a stylus or the like, a keyboard can be displayed on display section 9631b.

[0185] Touch input can be performed simultaneously in touchscreen area 9632a and touchscreen area 9632b.

[0186] The display mode switch 9034, for example, can switch the display between portrait, landscape, and other orientations, and between monochrome and color display. The power-saving switch 9036 can control the display brightness according to the amount of ambient light detected by an optical sensor in the tablet computer when it is in use. In addition to the optical sensor, another detector device, such as a gyroscope or accelerometer, can be installed in the tablet computer to detect tilt.

[0187] Fig. Figure 10A shows an example where display section 9631a and display section 9631b have the same display area. However, without limitation, one of the display sections may differ from the other in terms of size and display quality. For example, one display section may show an image with a higher resolution than the other display section.

[0188] The tablet computer is in Fig. 10B closed. The tablet computer includes the housing 9630, a solar cell 9633, a charge and discharge control circuit 9634, a battery 9635 and a DC-DC converter 9636. In Fig. 10B is a structure that includes the battery 9635 and the DC voltage converter 9636, shown as an example of the charge and discharge control circuit 9634.

[0189] Since the tablet computer is foldable, the housing 9630 can be closed when the tablet computer is not in use. Consequently, the display section 9631a and the display section 9631b can be protected. Therefore, a tablet computer with excellent durability and reliability for long-term use can be provided.

[0190] Furthermore, the tablet computer can be used in Fig. 10A and Fig. 10B shall have a function for displaying various types of data (e.g., a still image, a moving image, and a text image), a function for displaying a calendar, date, time, or the like on the display section, a touch input function for operating or editing the data displayed on the display section, a function for controlling processing by means of various types of software (programs), and the like.

[0191] The solar cell 9633 on a surface of the tablet computer can supply power to the touchscreen, the display section, an image signal processing section, or the like. It should be noted that the solar cell 9633 can be provided on one or both surfaces of the housing 9630 so that the battery 9635 can be efficiently charged. The use of a lithium-ion battery as the battery 9635 is advantageous for miniaturization or the like.

[0192] The structure and operation of the charging and discharging control circuit 9634, which is in Fig. As shown in 10B, a block diagram is used in Fig. 10C described. The solar cell 9633, the battery 9635, the DC-DC converter 9636, a converter 9638, switches SW1 to SW3 and a display section 9631 are in Fig. 10C shown, and the battery 9635, the DC-DC converter 9636, the converter 9638 and the switches SW1 to SW3 correspond to the charging and discharging control circuit 9634 in Fig. 10B.

[0193] First, an example of operation is described in the case where power is generated by the solar cell 9633 using external light. The voltage of the power generated by the solar cell 9633 is increased or decreased by the DC-DC converter 9636 so that the power has a voltage required to charge the battery 9635. Then, when the power from the solar cell 9633 is used to operate the display section 9631, switch SW1 is turned on, and the voltage associated with the power is increased or decreased by the converter 9638 so that it corresponds to a voltage required for the display section 9631. Furthermore, when there is no display on the display section 9631, switch SW1 is turned off, and switch SW2 is turned on so that the battery 9635 can be charged.

[0194] It should be noted that although the solar cell 9633 is described as an example of a means of power generation, the battery 9635 can also be charged, without limitation, by any other means of power generation, such as a piezoelectric element or a thermoelectric converter element (Peltier element). For example, a contactless power transfer module that wirelessly (without contact) transmits and receives power can be used to charge the battery 9635, or a combination of the solar cell 9633 and another means of charging can be used.

[0195] Of course, one embodiment of the present invention is not limited to the electronic device that is in Fig. 10A to Fig. 10C is shown, limited as long as the display section described in the preceding embodiment is included therein.

[0196] As described above, the electronic devices can be obtained by using the light-emitting device, which is an embodiment of the present invention. The light-emitting device has a very wide range of applications and can be used on electronic devices in various fields.

[0197] It should be noted that the structure described in this embodiment can be combined, where appropriate, with one of the structures described in the other embodiments. (Version 7)

[0198] In this embodiment, examples of lighting devices are given based on Fig. 11 described. A light-emitting device comprising a light-emitting element according to an embodiment of the present invention is used for lighting devices.

[0199] Fig. Figure 11 shows an example in which a light-emitting device is used for an interior lighting device 8001. Since the light-emitting device can have a larger area, a lighting device with a large area can also be designed. Furthermore, a lighting device 8002, in which a light-emitting area has a curved surface, can also be obtained using a housing with a curved surface. A light-emitting element in the light-emitting device described in this embodiment is in the form of a thin film, which allows for a more flexible design of the housing. Consequently, the lighting device can be constructed in various elaborate ways. In addition, a wall of the room can be provided with a large lighting device 8003.

[0200] Furthermore, if the light-emitting device is used for a table by serving as the surface of a table, a lighting device 8004 with a function as a table can be obtained. If the light-emitting device is used as part of other furniture, a lighting device with a function as furniture can be obtained.

[0201] In this way, various lighting devices can be obtained to which the light-emitting device is applied. It should be noted that such lighting devices are also embodiments of the present invention.

[0202] The structure described in this embodiment can be combined, where appropriate, with one of the structures described in the other embodiments. Examples 1 and 3 to 6 listed below are comparative examples. [Example 1]

[0203] In this example, a light-emitting element 1 is described using... Fig. 12 described. Chemical formulas of the materials used in this example are shown below. <<Herstellung des Licht emittierenden Elements 1> >

[0204] First, a film of indium tin oxide containing silicon oxide (ITSO) was formed over a glass substrate 1100 by a sputtering process, thus forming a first electrode 1101, which served as the anode. It should be noted that the thickness was set to 110 nm and that the electrode area was set to 2 mm × 2 mm.

[0205] Next, as a pretreatment to produce the light-emitting element 1, a UV ozone treatment was carried out over the substrate 1100 for 370 seconds after a surface of the substrate had been washed with water and baked at 200 °C for one hour.

[0206] The substrate was then transferred to a vacuum evaporation unit, in which the pressure was reduced to approximately 10 -4 Pa was reduced, and was subjected to vacuum baking at 170 °C for 30 minutes in a heating chamber of the vacuum evaporation device, and then the substrate 1100 was cooled for approximately 30 minutes.

[0207] The substrate 1100 was next attached to a holder in the vacuum evaporation apparatus such that a surface on which the first electrode 1101 was formed faced downwards. This example describes a case in which a hole injection layer 1111, a hole transport layer 1112, a light-emitting layer 1113, an electron transport layer 1114, and an electron injection layer 1115, contained in the EL layer 1102, are formed successively using a vacuum evaporation process.

[0208] The pressure in the vacuum evaporation unit was set to approximately 10 -4 Pa was reduced. Then, 1,3,5-tri(dibenzothiophen-4-yl)benzene (abbreviation: DBT3P-II) and molybdenum(VI) oxide were co-evaporated, with a mass ratio of DBT3P-II to molybdenum oxide of 4:2. This formed the hole injection layer 1111 over the first electrode 1101. The thickness of the hole injection layer 1111 was 40 nm. It should be noted that co-evaporation is an evaporation process in which several different substances are simultaneously evaporated from corresponding different evaporation sources.

[0209] Next, the hole transport layer 1112 was formed to a thickness of 20 nm by evaporation of 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP).

[0210] Next, the light-emitting layer 1113 was formed above the hole transport layer 1112. The light-emitting layer 1113 with a stacked structure was formed as follows.A first light-emitting layer 1113a with a thickness of 15 nm was formed by co-evaporation of 2-[3'-(Dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), 4,4'-Di(1-naphthyl)-4"-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB) and (Acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(tBuppm)2(acac)]), wherein the mass ratio of 2mDBTBPDBq-II (abbreviation) to PCBNBB (abbreviation) and [Ir(tBuppm)2(acac)] (abbreviation) was 0.7:0.3:0.05. and then a second light-emitting layer 1113b with a thickness of 25 nm was formed by co-evaporation of 2mDBTBPDBq-II (abbreviation), PCBNBB (abbreviation) and [Ir(tBuppm)2(acac)] (abbreviation), wherein the mass ratio of 2mDBTBPDBq-II (abbreviation) to PCBNBB (abbreviation) and [Ir(tBuppm)2(acac)] (abbreviation) was 0.8:0.2:0.05.

[0211] Next, the electron transport layer 1114 was formed above the light-emitting layer 1113 in such a way that by

[0212] A film of 2mDBTBPDBq-II (abbreviation) with a thickness of 10 nm was formed by evaporation, and then a film of bathophenanthroline (abbreviation: BPhen) with a thickness of 20 nm was formed by evaporation. A film of lithium fluoride with a thickness of 1 nm was further formed over the electron transport layer 1114 by evaporation, forming the electron injection layer 1115.

[0213] Finally, an aluminum film 200 nm thick was formed over the electron injection layer 1115 by evaporation to create a second electrode 1103, which served as the cathode; in this way, the light-emitting element 1 was produced. It should be noted that in all the above evaporation steps, the evaporation was carried out by a resistance heating process.

[0214] Table 1 shows an elemental structure of the light-emitting element 1, which was obtained as described above. [Table 1] erste Elektrode Lochinjektionsschicht Lochtransport- -schicht Licht emittierendeSchicht Elektronentransportschicht Elektro-schicht zweite Elektrode Lichtemittierendes Element 1 ITSO(110nm) DBT3P-II:MoOx(4:2 40nm) BPAFLP(20nm) * ** 2mDBTBPDBq-II(10nm) BPhen(20nm) LiF (1nm) Al (200nm) * 2mDBTBPDBq-II:PCBNBB:Ir(tBuppm)2acac (0,7:0.3:0,05 15nm) ** 2mDBTBPDBq-I:PCBNBB:Ir(tBuppm)2acac (0,8:0,2:0,05 25nm)

[0215] The manufactured light-emitting element 1 was sealed in a glove box containing a nitrogen atmosphere to prevent it from being exposed to air (in particular, a sealant was applied to an outer edge of the element, and a heat treatment was carried out for 1 hour at 80 °C at the time of sealing). <<Betriebseigenschaften des Licht emittierenden Elements 1> >

[0216] The operating characteristics of the manufactured light-emitting element 1 were measured. It should be noted that the measurements were carried out at room temperature (in an atmosphere maintained at 25 °C).

[0217] First shows Fig. 13. The current density-luminance properties of the light-emitting element. 1. In Fig. 13 The vertical axis represents the luminance (cd / m²). 2 ) represents the and the horizontal axis represents the current density (mA / cm²). 2 ) dar. Fig. Figure 14 shows the voltage-luminance properties of light-emitting element 1. Fig. 14 The vertical axis represents the luminance (cd / m²). 2 ) represents the voltage (V), and the horizontal axis represents the voltage (V). Fig. Figure 15 shows the luminance-current efficiency properties of light-emitting element 1. Fig. 15 The vertical axis represents the power efficiency (cd / A), and the horizontal axis represents the luminance (cd / m²). 2 ) dar. Fig. Figure 16 shows the voltage-current properties of light-emitting element 1. Fig. 16 The vertical axis represents the current (mA), and the horizontal axis represents the voltage (V).

[0218] Fig. Figure 14 shows the high efficiency of the light-emitting element 1. Table 2 shows initial values ​​of the main properties of the light-emitting element 1 at a luminance of approximately 1000 cd / m². 2 . [Table 2] Spannung (V) Strom(mA) Current density (mA / cm³) 2 ) Farbart(x,y) Luminance (cd / m²) 2 ) Stromeffizienz(cd / A) Leistungseffizienz (lm / W;) external quantum yield (%) Light-emitting element 1 2.9 0,045 1,1 (0,44;0,55) 1000 90 97 25

[0219] The results above show that the light-emitting element 1 produced in this example has a high external quantum yield, meaning that its emission efficiency is high. Regarding color purity, it can further be stated that the light-emitting element emits yellow-green light with high color purity.

[0220] Fig. Figure 17 shows an emission spectrum at the time of application of a current at a current density of 25 mA / cm². 2 to the light-emitting element 1. Fig. Figure 17 shows that the emission spectrum of the light-emitting element 1 has a peak at approximately 550 nm, which suggests that the peak of emission originates from the phosphorescent organometallic iridium complex [Ir(tBuppm)2(acac)].

[0221] Fig. Figure 18 shows the results of a reliability test on the light-emitting element 1. Fig.Figure 18 shows the vertical axis representing the normalized luminance (%) with an initial luminance of 100%, and the horizontal axis represents the operating time (h) of the element. For comparison, a light-emitting reference element was fabricated by forming a light-emitting layer 40 nm thick by co-evaporation, with a mass ratio of 2mDBTBPDBq-II (abbreviation) to PCBNBB (abbreviation) and [Ir(tBuppm)2(acac)] (abbreviation) of 0.8:0.2:0.05, and the other components being formed in a similar manner to light-emitting element 1. The light-emitting reference element was subjected to a reliability test in a similar manner. It should be noted that in the reliability tests, light-emitting element 1 and the light-emitting reference element were operated under conditions where the initial luminance was set to 5000 cd / m². 2The current density was set to a constant value. As a result, after 500 hours, light-emitting element 1 showed approximately 90% of its initial luminance, while the light-emitting comparison element showed approximately 85% of its initial luminance after 500 hours.

[0222] Thus, the reliability tests indicated that the light-emitting element 1 has high reliability and a long service life.

[0223] It should be noted that a film of 2mDBTBPDBq-II (abbreviation), a film of PCBNBB (abbreviation), and a mixed film of 2mDBTBPDBq-II (abbreviation) and PCBNBB (abbreviation) were formed, and the photoluminescence (PL) of each film was measured. The results are as follows: the photoluminescence (PL) peak wavelength of the evaporated film of 2mDBTBPDBq-II (abbreviation) was 428 nm, and the PL peak wavelength of the evaporated film of PCBNBB (abbreviation) was 428 nm, while the PL peak wavelength of the mixed film formed by co-evaporation of these substances was 501 nm and was significantly shifted towards the longer wavelength side. Therefore, it can be found that the combination of 2mDBTBPDBq-II (abbreviation) and PCBNBB (abbreviation) forms an exciplex. [Example 2]

[0224] In this example, a light-emitting element 2 according to an embodiment of the present invention is described. It should be noted that in the description of the light-emitting element 2 in this example Fig. 12, which was used to describe the light-emitting element 1 in Example 1, is used. Chemical formulas of the materials used in this example are given below. <<Herstellung des Licht emittierenden Elements 2> >

[0225] First, a film of indium tin oxide containing silicon oxide (ITSO) was formed over a glass substrate 1100 by a sputtering process, thus forming a first electrode 1101, which served as the anode. It should be noted that the thickness was set to 110 nm and that the electrode area was set to 2 mm × 2 mm.

[0226] Next, as a pretreatment to produce the light-emitting element 2, a UV ozone treatment was carried out over the substrate 1100 for 370 seconds after a surface of the substrate had been washed with water and baked at 200 °C for one hour.

[0227] The substrate was then transferred to a vacuum evaporation unit, in which the pressure was reduced to approximately 10 -4 Pa was reduced, and was subjected to vacuum baking at 170 °C for 30 minutes in a heating chamber of the vacuum evaporation device, and then the substrate 1100 was cooled for approximately 30 minutes.

[0228] The substrate 1100 was then attached to a holder in the vacuum evaporation apparatus such that a surface on which the first electrode 1101 had been formed faced downwards. This example describes a case in which a hole injection layer 1111, a hole transport layer 1112, a light-emitting layer 1113, an electron transport layer 1114, and an electron injection layer 1115, contained within an EL layer 1102, are successively formed using a vacuum evaporation process.

[0229] The pressure in the vacuum evaporation unit was set to approximately 10 -4Pa was reduced. Then, 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP) and molybdenum(VI) oxide were co-evaporated, with a mass ratio of BPAFLP to molybdenum oxide of 1:0.5. This formed the hole injection layer 1111 over the first electrode 1101. The thickness of the hole injection layer 1111 was 50 nm. It should be noted that co-evaporation is an evaporation process in which several different substances are simultaneously evaporated from corresponding different evaporation sources.

[0230] Next, the hole transport layer 1112 was formed to a thickness of 20 nm by evaporation of BPAFLP (abbreviation).

[0231] Next, the light-emitting layer 1113 was formed above the hole transport layer 1112. The light-emitting layer 1113 with a stacked structure was formed as follows.A first light-emitting layer 1113a with a thickness of 20 nm was formed by co-evaporation of 2-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[fh]quinoxaline (abbreviation: 2mDBTPDBq-II), 4-phenyl-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP) and (acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(mppm)2(acac)]), wherein the mass ratio of 2mDBTPDBq-II (abbreviation) to PCBA1BP (abbreviation) and [Ir(mppm)2(acac)] (abbreviation) was 0.7:0.3:0.06, and then a second light-emitting layer 1113b with a thickness of 20 nm by co-evaporation of 2mDBTPDBq-II (abbreviation), PCBA1BP (abbreviation) and Bis(2,3,5-triphenylpyradinato)(dipivaloylmethanato)iridium(III) (abbreviation: [Ir(tppr)2(dpm)]), wherein the mass ratio of 2mDBTPDBq-II (abbreviation) to PCBA1BP (abbreviation) and [Ir(tppr)2(dpm)] (abbreviation) was 0.8:0.2:0.03.

[0232] Next, the electron transport layer 1114 was formed over the light-emitting layer 1113 by evaporating a 15 nm thick film of 2mDBTPDBq-II, followed by evaporating a 15 nm thick film of bathophene anthroline. A 1 nm thick film of lithium fluoride was then evaporated over the electron transport layer 1114, forming the electron injection layer 1115.

[0233] Finally, an aluminum film 200 nm thick was formed over the electron injection layer 1115 by evaporation to create a second electrode 1103, which served as the cathode; in this way, the light-emitting element 2 was produced. It should be noted that in all the above evaporation steps, the evaporation was carried out by a resistance heating process.

[0234] Table 3 shows an elemental structure of the light-emitting element 2, which was obtained as described above. [Table 3] first electrode Hole injection layer Hole transport layer light-emitting layer electron transport layer electron layer second electrode Light-emitting element 2 ITSO (110nm) BPAFLP:MoOx(1:0.5 50nm) BPAFLP(20nm) * ** 2mDBTPDBq-II(15nm) BPhen(15nm) LiF (1nm) Al (200nm) * 2mDBTPDBq-I[PCBA1BP:[Ir(mppm)2acac] (0.7:0.3:0.06 20nm) ** 2mDBTPDBq-I:PCBA1BP:[Ir(tppr)2dpm] (0.8:0.2:0.03 20nm)

[0235] The manufactured light-emitting element 2 was sealed in a glove box containing a nitrogen atmosphere to prevent it from being exposed to air (in particular, a sealant was applied to an outer edge of the element, and a heat treatment was carried out for 1 hour at 80 °C at the time of sealing). <<Betriebseigenschaften des Licht emittierenden Elements 2> >

[0236] The operating characteristics of the manufactured light-emitting element 2 were measured. It should be noted that the measurements were carried out at room temperature (in an atmosphere maintained at 25 °C).

[0237] First shows Fig. 19 the current density-luminance properties of the light-emitting element 2. In Fig. 19 The vertical axis represents the luminance (cd / m²). 2 ) represents the and the horizontal axis represents the current density (mA / cm²). 2 ) dar. Fig. Figure 20 shows the voltage-luminance properties of the light-emitting element 2. Fig. 20 The vertical axis represents the luminance (cd / m²). 2 ) represents the voltage (V), and the horizontal axis represents the voltage (V). Fig. Figure 21 shows the luminance-current efficiency properties of light-emitting element 2. Fig. 21 The vertical axis represents the power efficiency (cd / A), and the horizontal axis represents the luminance (cd / m²). 2 ) dar. Fig. Figure 22 shows the voltage-current characteristics of the light-emitting element 2. Fig. 22 the vertical axis represents the current (mA), and the horizontal axis represents the voltage (V).

[0238] Fig.Figure 21 shows the high efficiency of the light-emitting element 2, which is an embodiment of the present invention. Table 4 shows initial values ​​of the main properties of the light-emitting element 2 at a luminance of about 1000 cd / m². 2 . [Table 4] Voltage (V) Current (mA) Current density (mA / cm³) 2 ) Color type(x;y) Luminance (cd / m²) 2 ) Power efficiency (cd / A) Energy efficiency (lm / W) external quantum yield (%) Light-emitting element 2 3,6 0,100 2,6 (0,55;0,45) 1100 44 38 21

[0239] The results above show that the light-emitting element 2 produced in this example has a high external quantum yield, which means that its emission efficiency is high.

[0240] Fig. Figure 23 shows an emission spectrum at the time of application of a current with a current density of 25 mA / cm². 2 to the light-emitting element 2. Fig.Figure 23 shows that the emission spectrum of the light-emitting element has two peaks at approximately 550 nm and 620 nm, which suggests that the peaks of emission originate from the phosphorescent organometallic iridium complexes [Ir(mppm)2(acac)] (abbreviation) and [Ir(tppr)2(dpm)] (abbreviation).

[0241] It should be noted that a film of 2mDBTPDBq-II (abbreviation), a film of PCBA1BP (abbreviation), and a mixed film of 2mDBTPDBq-II (abbreviation) and PCBA1BP (abbreviation) were formed, and the photoluminescence (PL) of each film was measured. The results are as follows: the photoluminescence (PL) peak wavelength of the evaporated film of 2mDBTPDBq-II (abbreviation) was 426 nm, and the PL peak wavelength of the evaporated film of PCBA1BP (abbreviation) was 416 nm, while the PL peak wavelength of the mixed film formed by co-evaporation of these substances was 519 nm and was significantly shifted towards the longer wavelength side. Therefore, it can be found that the combination of 2mDBTPDBq-II (abbreviation) and PCBA1BP (abbreviation) forms an exciplex. [Example 3]

[0242] In this example, a light-emitting element 3, which is in Fig.The light-emitting element 3 shown in Figure 24 was fabricated, and its operating characteristics and reliability were measured. It should be noted that the light-emitting element 3 fabricated in this example is a light-emitting element (hereinafter referred to as the light-emitting tandem element) in which a charge-generating layer is arranged between a plurality of EL layers, as described in embodiment 3. Chemical formulas of the materials used in this example are given below. <<Herstellung des Licht emittierenden Elements 3> >

[0243] First, a film of indium tin oxide containing silicon oxide (ITSO) was formed over a glass substrate 3000 by a sputtering process, thus forming a first electrode 3001, which served as the anode. It should be noted that the thickness was set to 110 nm and that the electrode area was set to 2 mm × 2 mm.

[0244] Next, as a pretreatment to produce the light-emitting element 3, a UV ozone treatment was carried out over the substrate 3000 for 370 seconds after a surface of the substrate had been washed with water and baked at 200 °C for one hour.

[0245] The substrate was then transferred to a vacuum evaporation unit, in which the pressure was reduced to approximately 10 -4The Pa was reduced and subjected to vacuum baking at 170 °C for 30 minutes in a heating chamber of the vacuum evaporation device, and then the substrate 3000 was cooled for approximately 30 minutes.

[0246] The substrate 3000 was next attached to a holder in the vacuum evaporation device in such a way that a surface on which the first electrode 3001 was formed faced downwards. This example describes a case in which a first hole injection layer 3011a, a first hole transport layer 3012a, a light-emitting layer (A) 3013a, a first electron transport layer 3014a and a first electron injection layer 3015a, contained in a first EL layer 3002a, are successively formed by a vacuum evaporation process, a charge generation layer 3004 is formed, and then a second hole injection layer 3011b, a second hole transport layer 3012b, a light-emitting layer (B) 3013b, a second electron transport layer 3014b and a second electron injection layer 3015b, contained in a second EL layer 3002b, are successively formed by a vacuum evaporation process.

[0247] The pressure in the vacuum evaporation unit was set to approximately 10 -4 Pa was reduced. Then, 9-[4-(9-phenylcarbazol-3-yl)]phenyl-10-phenylanthracene (abbreviation: PCzPA) and molybdenum(VI) oxide were co-evaporated, with a mass ratio of PCzPA to molybdenum oxide of 1:0.5. This formed the first hole injection layer 3011a over the first electrode 3001. The thickness of the first hole injection layer 3011a was set to 90 nm. It should be noted that co-evaporation is an evaporation process in which several different substances are simultaneously evaporated from corresponding different evaporation sources.

[0248] Next, the first hole transport layer 3012a was formed by evaporating PCzPA (abbreviation) to a thickness of 30 nm.

[0249] The light-emitting layer (A) 3013a was then formed over the first hole transport layer 3012a. The light-emitting layer (A) 3013a was formed by co-evaporation of 9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA) and N,N'-bis(3-methylphenyl)-N,N'-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyren-1,6-diamine (abbreviation: 1.6mMemFLPAPrn), where the mass ratio of CzPA (abbreviation) to 1.6mMemFLPAPrn (abbreviation) was 1:0.05. The thickness of the light-emitting layer (A) 3013a was 30 nm.

[0250] Next, the first electron transport layer 3014a was formed over the light-emitting layer (A) 3013a by evaporating a 5 nm thick film of CzPA (abbreviation CzPA), followed by evaporating a 15 nm thick film of bathophenanthroline (abbreviation BPhen). A 0.1 nm thick film of lithium oxide (Li₂O) was then evaporated over the first electron transport layer 3014a, forming the first electron injection layer 3015a.

[0251] Subsequently, copper phthalocyanine (abbreviation: CuPc) was evaporated to a thickness of 2 nm over the first electron injection layer 3015a, thereby forming the charge generation layer 3004.

[0252] Subsequently, 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP) and molybdenum(VI) oxide were co-evaporated, with a mass ratio of BPAFLP to molybdenum oxide of 1:0.5, forming the second hole injection layer 3011b above the charge generation layer 3004. The thickness of the second hole injection layer 3011b was 60 nm.

[0253] Then the second hole transport layer 3012b was formed by evaporation of BPAFLP (abbreviation) to a thickness of 20 nm.

[0254] Next, the light-emitting layer (B) 3013b was formed above the second hole transport layer 3012b. The light-emitting layer (B) 3013b with a stacked structure was formed as follows.A first light-emitting layer 3013(b1) with a thickness of 10 nm was formed by co-evaporation of 2-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[fh]quinoxaline (abbreviation: 2mDBTPDBq-II), 4-phenyl-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP) and (acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(mppm)2(acac)]), wherein the mass ratio of 2mDBTPDBq-II (abbreviation) to PCBA1BP (abbreviation) and [Ir(mppm)2(acac)] (abbreviation) was 0.6:0.4:0.06, and then a second light-emitting layer 3013(b2) was formed in a thickness of 30 nm is formed by co-evaporation of 2mDBTPDBq-II (abbreviation), PCBA1BP (abbreviation) and (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: [Ir(dppm)2(acac)]), wherein the mass ratio of 2mDBTPDBq-II (abbreviation) to PCBA1BP (abbreviation) and [Ir(dppm)2(acac)] (abbreviation) was 0.8:0.2:0.06.

[0255] Next, the second electron transport layer 3014b was formed over the light-emitting layer (B) 3013b by evaporating a 15 nm thick film of 2mDBTPDBq-II (abbreviation), followed by evaporating a 15 nm thick film of BPhen (abbreviation). A 1 nm thick film of lithium fluoride was then evaporated over the second electron transport layer 3014b, forming the second electron injection layer 3015b.

[0256] Finally, an aluminum film was formed over the second electron injection layer 3015b by evaporation to a thickness of 200 nm, forming a second electrode 3003 that served as the cathode. This produced the light-emitting element 3. It should be noted that in all of the above evaporation steps, the evaporation was carried out by a resistance heating process.

[0257] Table 5 shows an elemental structure of the light-emitting element 3, which was obtained as described above.

[0258] The manufactured light-emitting element 3 was sealed in a glove box containing a nitrogen atmosphere to prevent it from being exposed to air (in particular, a sealant was applied to an outer edge of the element, and a heat treatment was carried out for 1 hour at 80 °C at the time of sealing). <<Betriebseigenschaften des Licht emittierenden Elements 3> >

[0259] The operating characteristics of the manufactured light-emitting element 3 were measured. It should be noted that the measurements were carried out at room temperature (in an atmosphere maintained at 25 °C).

[0260] First shows Fig. 25 the current density-luminance properties of the light-emitting element 3. In Fig.25 represents the vertical axis, the luminance (cd / m²). 2 ) represents the and the horizontal axis represents the current density (mA / cm²). 2 ) dar. Fig. Figure 26 shows the voltage-luminance properties of the light-emitting element 3. Fig. 26 the vertical axis represents the luminance (cd / m²). 2 ) represents the voltage (V), and the horizontal axis represents the voltage (V). Fig. Figure 27 shows the luminance-current efficiency properties of light-emitting element 3. Fig. 27 The vertical axis represents the power efficiency (cd / A), and the horizontal axis represents the luminance (cd / m²). 2 ) dar. Fig. Figure 28 shows the voltage-current characteristics of the light-emitting element 3. Fig. 28 the vertical axis represents the current (mA), and the horizontal axis represents the voltage (V).

[0261] Fig.Figure 27 shows the high efficiency of the light-emitting element 3. Table 6 shows initial values ​​of the main properties of the light-emitting element 3 at a luminance of approximately 1000 cd / m². 2 . [Table 6] Voltage (V) Current (mA) Current density (mA / cm³) 2 ) Color type (x,y) Luminance (cd / m²) 2 ) Power efficiency (cd / A) Energy efficiency (lm / W) external quantum yield (%) Light-emitting element 3 6 0,044 1.1 (0,44;0,38) 850 77 41 31

[0262] The results above show that the light-emitting element 3 produced in this example has a high external quantum yield, which means that its emission efficiency is high.

[0263] Fig. Figure 29 shows an emission spectrum at the time of application of a current with a current density of 25 mA / cm². 2 to the light-emitting element 3. Fig. Figure 29 shows that the emission spectrum of the light-emitting element has 3 peaks at 467 nm and 587 nm, suggesting that the emission peaks originate from the phosphorescent organometallic iridium complexes contained in the light-emitting layers.

[0264] It should be noted that the combination of 2mDBTPDBq-II (abbreviation) and PCBA1BP (abbreviation) forms an exciplex, as described in the preceding Example 2. [Example 4]

[0265] In this example, a light-emitting element 4 is used based on Fig. 12 described. Chemical formulas of the materials used in this example are shown below. <<Herstellung des Licht emittierenden Elements 4> >

[0266] First, a film of indium tin oxide containing silicon oxide (ITSO) was formed over a glass substrate 1100 by a sputtering process, thus forming a first electrode 1101, which served as the anode. It should be noted that the thickness was set to 110 nm and that the electrode area was set to 2 mm × 2 mm.

[0267] Next, as a pretreatment to produce the light-emitting element 4, a UV ozone treatment was carried out over the substrate 1100 for 370 seconds after a surface of the substrate had been washed with water and baked at 200 °C for one hour.

[0268] The substrate was then transferred to a vacuum evaporation unit, in which the pressure was reduced to approximately 10 -4 Pa was reduced, and was subjected to vacuum baking for 30 minutes at 170 °C in a heating chamber of the vacuum evaporation device, and then the substrate 1100 was cooled for approximately 30 minutes.

[0269] The substrate 1100 was then attached to a holder in the vacuum evaporation apparatus such that a surface on which the first electrode 1101 was formed faced downwards. This example describes a case in which a hole injection layer 1111, a hole transport layer 1112, a light-emitting layer 1113, an electron transport layer 1114, and an electron injection layer 1115, contained within an EL layer 1102, are successively formed using a vacuum evaporation process.

[0270] The pressure in the vacuum evaporation unit was set to approximately 10 -4Pa was reduced. Then, 1,3,5-tri(dibenzothiophen-4-yl)benzene (abbreviation: DBT3P-II) and molybdenum(VI) oxide were co-evaporated, with a mass ratio of DBT3P-II to molybdenum oxide of 4:2, forming the hole injection layer 1111 over the first electrode 1101. The thickness of the hole injection layer 1111 was 20 nm. It should be noted that co-evaporation is an evaporation process in which several different substances are simultaneously evaporated from different evaporation sources.

[0271] Next, the hole transport layer 1112 was formed to a thickness of 20 nm by evaporation of 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP).

[0272] Next, the light-emitting layer 1113 was formed above the hole transport layer 1112. The light-emitting layer 1113 with a stacked structure was formed as follows. A first light-emitting layer 1113a was formed to a thickness of 20 nm by co-evaporation of 2-[3'-(Dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), 4,4'-Di(1-naphthyl)-4"-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB) and (Acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: [Ir(dppm)2(acac)]), wherein the mass ratio of 2mDBTBPDBq-II (abbreviation) to PCBNBB (abbreviation) and [Ir(dppm)2(acac)] (abbreviation) was 0.7:0.3:0.05, and then a second light-emitting layer was formed. Emitting layer 1113b in a thickness of 20 nm was formed by co-evaporation, wherein the mass ratio of 2mDBTBPDBq-II (abbreviation) to PCBNBB (abbreviation) and [Ir(dppm)2(acac)] (abbreviation) was 0.8:0.2:0.05.

[0273] Then, the electron transport layer 1114 was formed over the light-emitting layer 1113 by evaporating a 20 nm thick film of 2mDBTBPDBq-II, followed by evaporating a 20 nm thick film of bathophene anthroline. A 1 nm thick film of lithium fluoride was then evaporated over the electron transport layer 1114, forming the electron injection layer 1115.

[0274] Finally, an aluminum film 200 nm thick was formed over the electron injection layer 1115 by evaporation, forming a second electrode 1103 that served as the cathode. Thus, the light-emitting element 4 was produced. It should be noted that in all the above evaporation steps, the evaporation was carried out by a resistance heating process.

[0275] Table 7 shows an elemental structure of the light-emitting element 4, which was obtained as described above. [Table 7] first electrode Hole injection layer Hole transport layer light-emitting layer electron transport layer electron layer second electrode Light-emitting element 4 ITSO (110nm) DBT3P-II :MoOx (4:220nm) BPAFLP(20nm) * ** 2mDBTBPDBq-II(20nm) BPhen(20nm) LiF (1 nm) Al (200nm) * 2mDBTBPDBq-II:PCBNBB:Ir(dppm)2acac (0.7:0.3.0.05 20nm) ** 2mDBTBPDBq-II:PCBNBB:Ir(dppm)2acac (0.8:0.2:0.05 20nm)

[0276] The manufactured light-emitting element 4 was sealed in a glove box containing a nitrogen atmosphere to prevent it from being exposed to air (in particular, a sealant was applied to an outer edge of the element, and a heat treatment was carried out for 1 hour at 80 °C at the time of sealing). <<Betriebseigenschaften des Licht emittierenden Elements 4> >

[0277] The operating characteristics of the fabricated light-emitting element 4 were measured. It should be noted that the measurements were carried out at room temperature (in an atmosphere maintained at 25 °C).

[0278] First shows Fig. 30 the current density-luminance properties of the light-emitting element 4. In Fig. 30 represents the vertical axis, the luminance (cd / m²). 2 ) represents the and the horizontal axis represents the current density (mA / cm²). 2 ) dar. Fig. Figure 31 shows the voltage-luminance properties of the light-emitting element 4. Fig. 31 represents the vertical axis, the luminance (cd / m²). 2 ) represents the voltage (V), and the horizontal axis represents the voltage (V). Fig. Figure 32 shows the luminance-current efficiency properties of light-emitting element 4. Fig. 32 The vertical axis represents the power efficiency (cd / A), and the horizontal axis represents the luminance (cd / m²). 2 ) dar. Fig. Figure 33 shows the voltage-current properties of the light-emitting element 4. Fig. 33 The vertical axis represents the current (mA), and the horizontal axis represents the voltage (V).

[0279] Fig.Figure 32 shows the high efficiency of the light-emitting element 4. Table 8 shows initial values ​​of the main properties of the light-emitting element 4 at a luminance of approximately 1000 cd / m². 2 . [Table 8] Voltage (V) Current (mA) Current density (mA / cm³) 2 ) Color type (x,y) Luminance (cd / m²) 2 ) Power efficiency (cd / A) Energy efficiency (lm / W) external quantum yield (%) Light-emitting element 4 3 0,051 1,3 (0,57;0.43) 1000 79 81 31

[0280] The results above show that the light-emitting element 4 produced in this example exhibits a high external quantum yield, meaning that its emission efficiency is high. Regarding color purity, it can also be found that the light-emitting element emits orange light with high color purity.

[0281] Fig. Figure 34 shows an emission spectrum at the time of application of a current at a current density of 25 mA / cm². 2 to the light-emitting element 4. Fig.Figure 34 shows that the emission spectrum of the light-emitting element 4 has a peak at 586 nm, which suggests that the peak originates from an emission of the phosphorescent organometallic iridium complex [Ir(dppm)2(acac)] (abbreviation).

[0282] Fig. Figure 35 shows the results of a reliability test on the light-emitting element 4. Fig. Figure 35 represents the normalized luminance (%) with an initial luminance of 100%, and the horizontal axis represents the operating time (h) of the element. It should be noted that in the reliability test, the light-emitting element 4 was operated such that the initial luminance was 5000 cd / m². 2 The current density was kept constant. As a result, after 1610 hours, light-emitting element 4 still showed approximately 94% of its initial luminance.

[0283] In this way, the reliability test proved that the light-emitting element 4 has high reliability and a long service life.

[0284] It should be noted that the combination of 2mDBTBPDBq-II (abbreviation) and PCBNBB (abbreviation) forms an exciplex, as described in the preceding Example 1. [Example 5]

[0285] In this example, a light-emitting element 5 is described using the following: Fig. 12 described. Chemical formulas of the materials used in this example are shown below. <<Herstellung des Licht emittierenden Elements 5> >

[0286] First, a film of indium tin oxide containing silicon oxide (ITSO) was formed over a glass substrate 1100 by a sputtering process, thus forming a first electrode 1101, which served as the anode. It should be noted that the thickness was set to 110 nm and that the electrode area was set to 2 mm × 2 mm.

[0287] Next, as a pretreatment to produce the light-emitting element 5, a UV ozone treatment was carried out over the substrate 1100 for 370 seconds after a surface of the substrate had been washed with water and baked at 200 °C for one hour.

[0288] The substrate was then transferred to a vacuum evaporation unit, in which the pressure was reduced to approximately 10 -4Pa was reduced, and was subjected to vacuum baking for 30 minutes at 170 °C in a heating chamber of the vacuum evaporation device, and then the substrate 1100 was cooled for approximately 30 minutes.

[0289] The substrate 1100 was then attached to a holder in the vacuum evaporation apparatus such that a surface on which the first electrode 1101 was formed faced downwards. This example describes a case in which a hole injection layer 1111, a hole transport layer 1112, a light-emitting layer 1113, an electron transport layer 1114, and an electron injection layer 1115, contained within an EL layer 1102, are successively formed using a vacuum evaporation process.

[0290] The pressure in the vacuum evaporation unit was set to approximately 10 -4Pa was reduced. Then, 1,3,5-tri(dibenzothiophen-4-yl)benzene (abbreviation: DBT3P-II) and molybdenum(VI) oxide were co-evaporated, with a mass ratio of DBT3P-II to molybdenum oxide of 4:2, forming the hole injection layer 1111 over the first electrode 1101. The thickness of the hole injection layer 1111 was 20 nm. It should be noted that co-evaporation is an evaporation process in which several different substances are simultaneously evaporated from different evaporation sources.

[0291] Next, the hole transport layer 1112 was formed to a thickness of 20 nm by evaporation of 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP).

[0292] Next, the light-emitting layer 1113 was formed above the hole transport layer 1112. The light-emitting layer 1113 with a stacked structure was formed as follows. A first light-emitting layer 1113a with a thickness of 20 nm was formed by co-evaporation of 2-[3'-(Dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), N-(1,1'-Biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluorene-2-amine (abbreviation: PCBBiF) and (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: [Ir(dppm)2(acac)]), wherein the mass ratio of 2mDBTBPDBq-II (abbreviation) to PCBBiF (abbreviation) and [Ir(dppm)2(acac)] (abbreviation) 0.7:0.3:0.05, and then a second light-emitting layer 1113b was formed in a thickness of 20 nm by co-evaporation, the mass ratio of 2mDBTBPDBq-II (abbreviation) to PCBBiF (abbreviation) and [Ir(dppm)2(acac)] (abbreviation) being 0.8:0.2:0.05.

[0293] Then, the electron transport layer 1114 was formed above the light-emitting layer 1113 by evaporating a 20 nm thick film of 2mDBTBPDBq-III (abbreviation) and then a 20 nm thick film of bathophene anthroline (abbreviation: BPhen) by evaporation. A 1 nm thick film of lithium fluoride was then evaporated above the electron transport layer 1114, forming the electron injection layer 1115.

[0294] Finally, an aluminum film 200 nm thick was formed over the electron injection layer 1115 by evaporation, forming a second electrode 1103 that served as the cathode. Thus, the light-emitting element 5 was produced. It should be noted that in all the above evaporation steps, the evaporation was carried out by a resistance heating process.

[0295] Table 9 shows an elemental structure of the light-emitting element 5, which was obtained as described above. [Table 9] first electrode Hole injection layer Hole transport layer light-emitting layer electron transport layer Electron injection layer second electrode Light-emitting element 5 ITSO (110nm) DBT3P-I:MoOx (4:220nm) BPAFLP(20nm) * ** 2mDBTBPDBq-II (20nm) BPhen(20nm) LiF (1 nm) Al (200nm) * 2mDBTBPDBq-II.PCBBiF:Ir(dppm)2acac (0.7:0.3:0.05 20nm) ** 2mDBTBPDBq-II:PCBBiF:Ir(dppm)2acac (0.8:0.2:0.05 20nm)

[0296] The manufactured light-emitting element 5 was sealed in a glove box containing a nitrogen atmosphere to prevent it from being exposed to air (in particular, a sealant was applied to an outer edge of the element, and a heat treatment was carried out for 1 hour at 80 °C at the time of sealing). <<Betriebseigenschaften des Licht emittierenden Elements 5> >

[0297] The operating characteristics of the fabricated light-emitting element 5 were measured. It should be noted that the measurements were carried out at room temperature (in an atmosphere maintained at 25 °C).

[0298] First shows Fig. 36 the current density-luminance properties of the light-emitting element 5. In Fig. 36 The vertical axis represents the luminance (cd / m²). 2 ) represents the and the horizontal axis represents the current density (mA / cm²). 2 ) dar. Fig. Figure 37 shows the voltage-luminance properties of the light-emitting element 5. Fig. 37 represents the vertical axis, the luminance (cd / m²). 2 ) represents the voltage (V), and the horizontal axis represents the voltage (V). Fig. Figure 38 shows the luminance-current efficiency properties of light-emitting element 5. Fig. 38 The vertical axis represents the power efficiency (cd / A), and the horizontal axis represents the luminance (cd / m²). 2 ) dar. Fig. Figure 39 shows the voltage-current properties of the light-emitting element 5. Fig. 39 the vertical axis represents the current (mA), and the horizontal axis represents the voltage (V).

[0299] Fig.Figure 38 shows the high efficiency of the light-emitting element 5. Table 10 shows initial values ​​of the main properties of the light-emitting element 5 at a luminance of approximately 1000 cd / m². 2 . [Table 10] Voltage (V) Current (mA) Current density (mA / cm³) 2 ) Color type (x,y) Luminance (cd / m²) 2 ) Power efficiency (cd / A) Energy efficiency (lm / W) external quantum yield (%) Light-emitting element 5 2.8 0,047 1.2 (0.56;0.44) 1000 85 95 31

[0300] The results above show that the light-emitting element 5 produced in this example exhibits a high external quantum yield, meaning that its emission efficiency is high. Regarding color purity, it can also be found that the light-emitting element emits orange light with high color purity.

[0301] Fig. Figure 40 shows an emission spectrum at the time of application of a current with a current density of 25 mA / cm². 2 to the light-emitting element 5. Fig.Figure 40 shows that the emission spectrum of the light-emitting element 5 has a peak at 583 nm, which suggests that the peak originates from an emission of the phosphorescent organometallic iridium complex [Ir(dppm)2(acac)].

[0302] Fig. Figure 41 shows the results of a reliability test on the light-emitting element 5. Fig. Figure 41 shows the vertical axis representing the normalized luminance (%) with an initial luminance of 100%, and the horizontal axis represents the operating time (h) of the element. It should be noted that in the reliability test, the light-emitting element 5 was operated such that the initial luminance was 5000 cd / m². 2 The current density was constant. As a result, after 1980 hours, light-emitting element 5 still showed approximately 92% of its initial luminance.

[0303] In this way, the reliability test proved that the light-emitting element 5 has high reliability and a long service life.

[0304] It should be noted that a film of 2mDBTBPDBq-II (abbreviation), a film of PCBBiF (abbreviation), and a mixed film of 2mDBTBPDBq-II (abbreviation) and PCBBiF (abbreviation) were formed, and the photoluminescence (PL) of each film was measured. The results are as follows: the photoluminescence (PL) peak wavelength of the evaporated film of 2mDBTBPDBq-II (abbreviation) was 428 nm, and the PL peak wavelengths of the evaporated film of PCBBiF (abbreviation) were 415 nm and 436 nm, while the PL peak wavelength of the mixed film formed by co-evaporation of these substances was 512 nm and was significantly shifted towards the longer wavelength side. Therefore, it can be found that the combination of 2mDBTBPDBq-II (abbreviation) and PCBBiF (abbreviation) forms an Exciplex. [Example 6]

[0305] In this example, a light-emitting element 6 is described using the following: Fig. 12 described. Chemical formulas of the materials used in this example are shown below. <<Herstellung des Licht emittierenden Elements 6> >

[0306] First, a film of indium tin oxide containing silicon oxide (ITSO) was formed over a glass substrate 1100 by a sputtering process, thus forming a first electrode 1101, which served as the anode. It should be noted that the thickness was set to 110 nm and that the electrode area was set to 2 mm × 2 mm.

[0307] Next, as a pretreatment to produce the light-emitting element 6, a UV ozone treatment was carried out over the substrate 1100 for 370 seconds after a surface of the substrate had been washed with water and baked at 200 °C for one hour.

[0308] The substrate was then transferred to a vacuum evaporation unit, in which the pressure was reduced to approximately 10 -4 Pa was reduced, and was subjected to vacuum baking for 30 minutes at 170 °C in a heating chamber of the vacuum evaporation device, and then the substrate 1100 was cooled for approximately 30 minutes.

[0309] The substrate 1100 was then attached to a holder in the vacuum evaporation apparatus such that a surface on which the first electrode 1101 was formed faced downwards. This example describes a case in which a hole injection layer 1111, a hole transport layer 1112, a light-emitting layer 1113, an electron transport layer 1114, and an electron injection layer 1115, contained within an EL layer 1102, are successively formed using a vacuum evaporation process.

[0310] The pressure in the vacuum evaporation unit was set to approximately 10 -4Pa was reduced. Then, 1,3,5-tri(dibenzothiophen-4-yl)benzene (abbreviation: DBT3P-II) and molybdenum(VI) oxide were co-evaporated, with a mass ratio of DBT3P-II to molybdenum oxide of 4:2, forming the hole injection layer 1111 over the first electrode 1101. The thickness of the hole injection layer 1111 was 20 nm. It should be noted that co-evaporation is an evaporation process in which several different substances are simultaneously evaporated from different evaporation sources.

[0311] Next, the hole transport layer 1112 was formed to a thickness of 20 nm by evaporation of 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP).

[0312] Next, the light-emitting layer 1113 was formed above the hole transport layer 1112. The light-emitting layer 1113 with a stacked structure was formed as follows.A first light-emitting layer 1113a with a thickness of 20 nm was formed by co-evaporation of 2-{3-[3-(6-phenyldibenzothiophen-4-yl)phenyl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-IV), N-(1,1'-Biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluorene-2-amine (abbreviation: PCBBiF) and (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: [Ir(dppm)2(acac)]), wherein the mass ratio of 2mDBTBPDBq-IV (abbreviation) to PCBBiF (abbreviation) and [Ir(dppm)2(acac)] (Abbreviation) 0.7:0.3:0.05, and then a second light-emitting layer 1113b was formed in a thickness of 20 nm by co-evaporation, the mass ratio of 2mDBTBPDBq-IV (abbreviation) to PCBBiF (abbreviation) and [Ir(dppm)2(acac)] (abbreviation) being 0.8:0.2:0.05.

[0313] Then, the electron transport layer 1114 was formed above the light-emitting layer 1113 by evaporating a 20 nm thick film of 2mDBTBPDBq-IV (abbreviation) and then a 20 nm thick film of bathophene anthroline (abbreviation: BPhen) by evaporation. A 1 nm thick film of lithium fluoride was then evaporated above the electron transport layer 1114, forming the electron injection layer 1115.

[0314] Finally, an aluminum film 200 nm thick was formed over the electron injection layer 1115 by evaporation, forming a second electrode 1103 that served as the cathode. Thus, the light-emitting element 6 was produced. It should be noted that in all the above evaporation steps, the evaporation was carried out by a resistance heating process.

[0315] Table 11 shows an elemental structure of the light-emitting element 6, which was obtained as described above. [Table 11] first electrode Hole injection layer Hole transport layer light-emitting layer electron transport layer Elactrene injection layer Second electrode Light-emitting element 6 ITSO{(110nm) DBT3P- II:MoOx(4:2 20nm) BPAFLP(20nm) * ** 2mDBTBPDBq-II(20nm) BPhen(20nm) LiF (Inm) Al (200 nm) * 2mDBTBPDBq-[V:PCBBiF:] [Ir(dppm)2(acac)] 0.7:0.3:0.05 20nm) ** 2mDBTBPDBq-IV:PCBBiF:] [Ir(dppm)2(acac)] 0.8:0.2:0.05 20nm)

[0316] The manufactured light-emitting element 6 was sealed in a glove box containing a nitrogen atmosphere to prevent it from being exposed to air (in particular, a sealant was applied to an outer edge of the element, and a heat treatment was carried out for 1 hour at 80 °C at the time of sealing). <<Betriebseigenschaften des Licht emittierenden Elements 6> >

[0317] The operating characteristics of the fabricated light-emitting element 6 were measured. It should be noted that the measurements were carried out at room temperature (in an atmosphere maintained at 25 °C).

[0318] First shows Fig. 42 the current density-luminance properties of the light-emitting element 6. In Fig. 42 The vertical axis represents the luminance (cd / m²). 2 ) represents the and the horizontal axis represents the current density (mA / cm²). 2 ) dar. Fig. Figure 43 shows the voltage-luminance properties of the light-emitting element 6. Fig. 43 The vertical axis represents the luminance (cd / m²). 2 ) represents the voltage (V), and the horizontal axis represents the voltage (V). Fig. Figure 44 shows the luminance-current efficiency properties of light-emitting element 6. Fig. 44 The vertical axis represents the power efficiency (cd / A), and the horizontal axis represents the luminance (cd / m²). 2 ) dar. Fig. Figure 45 shows the voltage-current properties of the light-emitting element 6. Fig. 45 The vertical axis represents the current (mA), and the horizontal axis represents the voltage (V).

[0319] Fig.Figure 44 shows the high efficiency of the light-emitting element 6. Table 12 shows initial values ​​of the main properties of the light-emitting element 6 at a luminance of approximately 1000 cd / m². 2 . [Table 12] Voltage (V) Current (mA) Current density (mA / cm³) 2 ) Color type (x;y) Luminance (cd / m²) 2 ) Power efficiency (cd / A) Energy efficiency (lm / W) external quantum yield (%) Light-emitting element 6 3 0.04 0,99 (0,57;0,43) 1000 76 80 31

[0320] The results above show that the light-emitting element 6 produced in this example has a high external quantum yield, meaning that its emission efficiency is high. Regarding color purity, the light-emitting element emits orange light with high color purity.

[0321] Fig. Figure 46 shows an emission spectrum at the time of application of a current with a current density of 25 mA / cm². 2 to the light-emitting element 6. Fig.Figure 46 shows that the emission spectrum of the light-emitting element 6 has a peak at approximately 587 nm, which suggests that the peak originates from an emission of the phosphorescent organometallic iridium complex [Ir(dppm)2(acac)].

[0322] Fig. Figure 47 shows the results of a reliability test on the light-emitting element 6. Fig. Figure 47 shows that the vertical axis represents the normalized luminance (%) with an initial luminance of 100%, and the horizontal axis represents the operating time (h) of the element. It should be noted that in the reliability test, the light-emitting element 6 was operated such that the initial luminance was 5000 cd / m². 2 The current density was constant. As a result, after 833 hours, light-emitting element 6 still showed approximately 91% of its initial luminance.

[0323] In this way, the reliability test proved that the light-emitting element 6 has high reliability and a long service life. Explanation of reference symbols

[0324] 101: Anode, 102: Cathode, 103: EL layer, 104: Hole injection layer, 105: Hole transport layer, 106: Light-emitting layer, 106a: First light-emitting layer, 106b: Second light-emitting layer, 107: Electron transport layer, 108: Electron injection layer, 109: Phosphorescent compound, 110: First organic compound, 111: Second organic compound, 201: First electrode (anode), 202: Second electrode (cathode), 203: EL layer, 204: Hole injection layer, 205: Hole transport layer, 206: Light-emitting layer, 206a: First light-emitting layer, 206b: Second light-emitting layer, 207: Electron transport layer, 208: Electron injection layer 301: first electrode, 302(1): first EL layer, 302(2): second EL layer, 304: second electrode, 305: charge generation layer (I), 305(1): first charge generation layer (I), 305(2): second charge generation layer (II), 401: reflecting electrode,402: semi-transparent and semi-reflective electrode, 403a: first transparent conductive layer, 403b: second transparent conductive layer, 404B: first light-emitting layer (B), 404G: second light-emitting layer (G), 404R: third light-emitting layer (R), 405: EL layer, 410R: first light-emitting element (R), 410G: second light-emitting element (G), 410B: third light-emitting element (B), 501: element substrate, 502: pixel section, 503: driver circuit section (source line driver circuit), 504a, 504b: driver circuit section (gate line driver circuit), 505: sealant, 506: sealant substrate, 507: connecting lead, 508: flexible printed circuit (flexible printed circuit (FPC), 509: n-channel TFT, 510: p-channel TFT, 511: switching TFT, 512: current-control TFT, 513: first electrode (anode), 514: insulator, 515: EL layer, 516: second electrode (cathode), 517: light-emitting element, 518: space, 1100: substrate,1101: first electrode, 1102: EL layer, 1103: second electrode, 1111: hole injection layer, 1112: hole transport layer, 1113: light-emitting layer, 1114: electron transport layer, 1115: electron injection layer, 3000: substrate, 3001: first electrode, 3002a: first EL layer, 3002b: second EL layer, 3011a: first hole injection layer, 3011b: second hole injection layer, 3012a: first hole transport layer, 3012b: second hole transport layer, 3013a: light-emitting layer (A), 3013b: light-emitting layer (B), 3014a: first electron transport layer, 3014b: second electron transport layer, 3015a: first Electron injection layer, 3015b: second electron injection layer, 3003: second electrode, 3004: charge generation layer, 7100: television set, 7101: housing, 7103: display section, 7105: stand, 7107: display section, 7109: control button, 7110: remote control, 7201: main body, 7202: housing, 7203: display section, 7204: keyboard,7205: External connection port, 7206: Pointing device, 7301: Housing, 7302: Housing, 7303: Hinge part, 7304: Display section, 7305: Display section, 7306: Speaker section, 7307: Recording media insertion section, 7308: LED lamp, 7309: Control button, 7310: Connection port, 7311: Sensor, 7312: Microphone, 7400: Mobile phone, 7401: Housing, 7402: Display section, 7403: Control knob, 7404: External connection port, 7405: Speaker, 7406: Microphone, 8001: Lighting device, 8002: Lighting device, 8003: Lighting device, 8004: Lighting device, 9033: Clip 9034: Display mode switch, 9035: Circuit breaker, 9036: Power saving switch, 9038: Operating switch, 9630: Housing, 9631: Display section, 9631a: Display section, 9631b: Display section, 9632a: Touchscreen area, 9632b: Touchscreen area, 9633: Solar cell, 9634: Charge and discharge control circuit, 9635: Battery, 9636: DC-DC converter, 9637: Operating button9638: Converter and 9639: Button.

Claims

[1] Light-emitting element, comprising: a pair of electrodes; and a first light-emitting layer and a second light-emitting layer between the pair of electrodes, where the second light-emitting layer is in contact with the first light-emitting layer, wherein the first light-emitting layer comprises a first phosphorescent compound, a first organic compound and a second organic compound, wherein the second light-emitting layer comprises a second phosphorescent compound, the first organic compound and the second organic compound, wherein the first organic compound and the second organic compound form an exciplex, the first organic compound is a nitrogen-containing heteroaromatic compound, where the second organic compound is a π-electron-rich heteroaromatic compound or an aromatic amine compound, where a peak of an emission spectrum of the first phosphorescent compound has a shorter wavelength than a peak of an emission spectrum of the second phosphorescent compound, and where the difference between the energy of a peak in an emission spectrum of the exciplex and the energy of a peak in an absorption band on the longest wavelength side in an absorption spectrum of the first phosphorescent compound is 0.2 eV or less. [2] Light-emitting element, comprising: a pair of electrodes; and a first light-emitting layer and a second light-emitting layer between the pair of electrodes, where the second light-emitting layer is in contact with the first light-emitting layer, wherein the first light-emitting layer comprises a first phosphorescent compound, a first organic compound and a second organic compound, wherein the second light-emitting layer comprises a second phosphorescent compound, the first organic compound and the second organic compound, wherein a peak of an emission spectrum of a mixture film of the first organic compound and the second organic compound has a longer wavelength than a peak of an emission spectrum of a film of the first organic compound, where the peak of the emission spectrum of the mixture film has a longer wavelength than a peak of an emission spectrum of a film of the second organic compound, the first organic compound is a nitrogen-containing heteroaromatic compound, where the second organic compound is a π-electron-rich heteroaromatic compound or an aromatic amine compound, where a peak of an emission spectrum of the first phosphorescent compound has a shorter wavelength than a peak of an emission spectrum of the second phosphorescent compound, and where the difference between the energy of the peak of the emission spectrum of the mixture film and the energy of a peak of an absorption band on the longest wavelength side in an absorption spectrum of the first phosphorescent compound is 0.2 eV or less. [3] Light-emitting element according to claim 1 or 2, where a level of triplet excitation energy of the first organic compound is higher than a level of triplet excitation energy of the first phosphorescent compound, and where the level of a triplet excitation energy of the second organic compound is higher than the level of a triplet excitation energy of the first phosphorescent compound. [4] Light-emitting element according to claim 1 or 2, where the first phosphorescent compound is a first iridium complex, and where the second phosphorescent compound is a second iridium complex. [5] Light-emitting element according to claim 1 or 2, which further comprises a third light-emitting layer between the pair of electrodes, wherein the third light-emitting layer comprises a light-emitting material which has blue emission. [6] Light-emitting device comprising the light-emitting element according to claim 1 or 2. [7] Electronic device comprising the light-emitting device according to claim 6. [8] Lighting device comprising the light-emitting device according to claim 6.

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