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

Abstract

To provide a light-emitting element which uses a fluorescent material as a light-emitting substance and has higher luminous efficiency.SOLUTION: Provided is a light-emitting element which includes a mixture of a thermally activated delayed fluorescent substance and a fluorescent material. The thermally activated delayed fluorescent substance is a material capable of generating a singlet excited state (S1) by reverse intersystem crossing from a triplet excited state (T1), by thermal activation. While the thermally activated delayed fluorescent substance may be composed of one kind of material, use of an excited complex (exciplex) of two kinds of materials is particularly preferable. By making the emission spectrum of the thermally activated delayed fluorescent substance overlap with an absorption band on the longest wavelength side in absorption at an S1 level of the fluorescent material, energy at an S1 of the thermally activated delayed fluorescent substance can be transferred to the S1 of the fluorescent material. Alternatively, it is also possible that the S1 of the thermally activated delayed fluorescent substance is generated from part of the energy at a T1 level of the thermally activated delayed fluorescent substance, and is transferred to the S1 of the fluorescent material.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a light-emitting device using an organic compound as a light-emitting substance.

Background Art

[0002] In recent years, research and development of light-emitting devices using electroluminescence (EL) have been actively carried out. The basic configuration of these light-emitting devices is such that a layer containing a light-emitting substance (EL layer) is sandwiched between a pair of electrodes. By applying a voltage to this device, light emission from the light-emitting substance can be obtained.

[0003] Since such a light-emitting device is self-luminous, it has advantages such as higher visibility of pixels compared to liquid crystal displays and the absence of a need for a backlight, and is suitable as a flat panel display device. Also, a display using such a light-emitting device can be fabricated to be thin and lightweight, which is also a great advantage. Furthermore, it is also characterized by a very fast response speed.

[0004] Since these light-emitting devices can form the light-emitting layer in a film shape, light emission can be obtained in a planar manner. Therefore, a large-area light source can be easily formed. This is a characteristic that is difficult to obtain with point light sources typified by incandescent bulbs and LEDs, or line light sources typified by fluorescent lamps, and thus it also has high utility value as a planar light source applicable to lighting and the like.

[0005] In the case of an organic EL device using an organic compound as the light-emitting substance and provided with an EL layer containing the light-emitting substance between a pair of electrodes, by applying a voltage between the pair of electrodes, electrons are injected from the cathode and holes are injected from the anode into the light-emitting EL layer, respectively, and a current flows. Then, the injected ​ When electrons and holes recombine, a luminescent organic compound is excited to an excited state and light emission can be obtained from the excited luminescent organic compound.

[0006] The types of excited states formed by organic compounds include singlet excited states and triplet excited states. The light emission from the singlet excited state (S1) is called fluorescence, and the light emission from the triplet excited state (T1) is called phosphorescence. Also, the statistical generation ratio in the light-emitting device is considered to be S1:T1 = 1:3. Therefore, in recent years, the development of light-emitting devices using a luminescent compound capable of converting the triplet excited state into light emission has been actively carried out.

[0007] However, on the other hand, most of the currently used phosphorescent compounds are complexes with rare metals such as iridium as the central metal, and there are concerns about their cost and supply stability.

[0008] For this reason, research on materials that can convert a part of the triplet excited state into light emission without using rare metals has also been conducted. In materials that emit delayed fluorescence, a singlet excited state is generated from the triplet excited state by reverse intersystem crossing, and the singlet excited state is converted into light emission.

[0009] In Patent Document 1 and Patent Document 2, materials that emit thermally activated delayed fluorescence (TADF) are disclosed.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

[0011] However, in order to improve the luminous efficiency of a light-emitting element, not only generating a singlet excited state from a triplet excited state but also efficiently obtaining light emission from the singlet excited state, that is, having a high fluorescence quantum efficiency is important. Therefore, in the configurations of the above Patent Document 1 etc., in order to further improve the luminous efficiency, a material that emits TADF and has a high fluorescence quantum yield is necessary, but designing a material that satisfies both of these is very difficult.

[0012] Therefore, one aspect of the present invention aims to provide a light-emitting element having higher luminous efficiency, in which a material that emits fluorescence is used as a light-emitting substance. [Means for Solving the Problems]

[0013] In order to achieve the above object, in one aspect of the present invention, the function of generating a singlet excited state from a triplet excited state and the function of efficiently obtaining light emission from the singlet excited state are assigned to different materials.

[0014] More specifically, in the light-emitting layer, a material capable of generating a singlet excited state from a triplet excited state and a material capable of efficiently obtaining light emission from the singlet excited state are mixed and used.

[0015] As the material capable of generating a singlet excited state from a triplet excited state, a thermally activated delayed phosphor is applied. ​​​​​​​​​

[0016] In this specification and the like, a thermally activated delayed phosphor refers to a material that can generate a singlet excited state from a triplet excited state by reverse intersystem crossing due to thermal activation. A thermally activated delayed phosphor may include, for example, a material that can generate a singlet excited state from a triplet excited state by reverse intersystem crossing alone, such as a material that emits TADF. It may also include a combination of two materials that form an exciplex. A thermally activated delayed phosphor can also be said to be a material in which the triplet excited state and the singlet excited state are close. More specifically, a material with an energy difference between the triplet excited state and the singlet excited state within 0.2 eV is preferred. That is, in a material that can generate a singlet excited state from a triplet excited state by reverse intersystem crossing alone, such as a material that emits TADF, the energy difference between the triplet excited state and the singlet excited state is within 0.2 eV, or the energy difference between the triplet excited state and the singlet excited state in the exciplex is preferably within 0.2 eV. As a material that can efficiently obtain light emission from the singlet excited state, known fluorescent materials are applied. Among them, materials with a high fluorescence quantum yield, for example, materials with a fluorescence quantum yield of 50% or more, are preferably used. As described above, one aspect of the present invention provides a light-emitting device using a thermally activated delayed phosphor as an energy donor and a fluorescent material as an energy acceptor. With such a configuration, by overlapping the emission spectrum of the thermally activated delayed phosphor with the absorption band on the longest wavelength side of the absorption of the singlet excited state of the fluorescent material, the singlet excited state of the thermally activated delayed phosphor

[0017]

[0018]

[0019] ​​​​​​​​​​​​​The energy can be transferred to the singlet excited state of the material that emits fluorescence. Also, From a part of the energy of the triplet excited state of the thermally activated delayed phosphor, a singlet excited state of the thermally activated delayed phosphor can be generated and transferred to the singlet excited state of the material that emits fluorescence.

[0020] For example, in the case of a configuration using a material that emits TADF as an energy acceptor, in order to increase the emission efficiency, a material that emits TADF and has a high fluorescence quantum yield is required. However, as described above, by using a thermally activated delayed phosphor as the energy donor in the configuration, regardless of the presence or absence of TADF, a material with a high fluorescence quantum yield can be selected as the energy acceptor.

[0021] Therefore, the singlet excited state of the thermally activated delayed phosphor and the singlet excited state of the thermally activated delayed phosphor generated from a part of the energy of the triplet excited state of the thermally activated delayed phosphor can be more efficiently converted into light emission through the singlet excited state of the material that emits fluorescence. As a result, a light-emitting device with higher luminous efficiency can be obtained.

[0022] One aspect of the present invention is a light-emitting device having a pair of electrodes and an EL layer sandwiched between the pair of electrodes, the EL layer having at least a light-emitting layer, and the light-emitting layer including at least a thermally activated delayed phosphor and a material that emits fluorescence.

[0023] Also, in the above, the thermally activated delayed phosphor preferably contains a first organic compound and a second organic compound, and the first organic compound and the second organic compound form a combination that forms an exciplex.

[0024] In addition, in the above, it is preferable that the absorption band on the lowest energy side of the material that emits fluorescence overlaps with the emission of the thermally activated delayed phosphor.

[0025] In addition, in the above, the energy conversion value difference between the peak wavelength of the absorption band on the lowest energy side of the material that emits fluorescence and the peak wavelength of the emission of the thermally activated delayed phosphor is preferably 0.2 eV or less. It is preferable.

[0026] In addition, in the above, the difference between the peak wavelength of the emission of the thermally activated delayed phosphor and the peak wavelength of the emission of the material that emits fluorescence is preferably within 30 nm. It is preferable.

[0027] In addition, in the above, it is preferable that one of the first organic compound and the second organic compound is a material having electron transporting properties and the other is a material having hole transporting properties.

[0028] In addition, in the above, it is preferable that one of the first organic compound and the second organic compound is a π-electron deficient hetero aromatic and the other is a π-electron rich heteroaromatic or aromatic amine.

Advantages of the Invention

[0029] According to one aspect of the present invention, in a light-emitting device using a material that emits fluorescence as a light-emitting substance, a light-emitting device with higher light emission efficiency can be provided.

Brief Description of the Drawings

[0030]

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Mode for Carrying Out the Invention

[0031] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and its form and details can be It is easily understood by those skilled in the art that various modifications can be made. Therefore, the present invention is not construed as being limited to the description of the embodiments shown below. It is not construed as being limited to the description of the embodiments shown below.

[0032] (Embodiment 1) In a light-emitting device in which a thermally activated delayed phosphor and a material that emits fluorescence are mixed and used, light emission occurs through the following energy process.

[0033] (1) When electrons and holes (holes) recombine in a material that emits fluorescence and the material that emits fluorescence becomes an excited state (direct recombination process).

[0034] (1-1) When the excited state of the material that emits fluorescence is a singlet excited state: Fluorescence is emitted. (1-2) When the excited state of the material that emits fluorescence is a triplet excited state: Thermal deactivation occurs.

[0035] In the direct recombination process of (1) above, if the fluorescence quantum efficiency is high, a high luminous efficiency can be obtained. Note that the level of the singlet excited state of the thermally activated delayed phosphor is preferably higher than the level of the singlet excited state of the material that emits fluorescence. Note that the level of the singlet excited state of the thermally activated delayed phosphor is preferably higher than the level of the singlet excited state of the material that emits fluorescence.

[0036] (2) When electrons and holes (holes) recombine in a thermally activated delayed phosphor and the thermally activated delayed phosphor becomes an excited state (energy transfer process).

[0037] (2-1) When the excited state of the thermally activated delayed phosphor is a singlet excited state When the level of the singlet excited state of the thermally activated delayed phosphor is higher than the level of the singlet excited state of the material that emits fluorescence, excitation energy is transferred from the thermally activated delayed phosphor to the material that emits fluorescence, and the material that emits fluorescence becomes a singlet excited state. When the material that emits fluorescence becomes a singlet excited state. The material emits fluorescence. Note that the energy transfer from the singlet excited state level of the thermally activated delayed phosphor to the triplet excited state level of the material that emits fluorescence is not the main energy transfer process because the direct transition from the singlet ground state to the triplet excited state in the material that emits fluorescence is forbidden, so it is omitted here. That is, as shown in the following formula (2-1), the energy transfer from the singlet excited state ( 1 H * ) of the thermally activated delayed phosphor to the singlet excited state ( 1 G * ) of the material that emits fluorescence is important (in the formula, 1 G is the singlet ground state of the material that emits fluorescence, 1 H represents the singlet ground state of the thermally activated delayed phosphor). The energy transfer from the singlet excited state level of the thermally activated delayed phosphor to the triplet excited state level of the material that emits fluorescence is not the main energy transfer process because the direct transition from the singlet ground state to the triplet excited state in the material that emits fluorescence is forbidden, so it is omitted here. That is, as shown in the following formula (2-1), the energy transfer from the singlet excited state ( 1 H * ) of the thermally activated delayed phosphor to the singlet excited state ( 1 G * ) of the material that emits fluorescence is important (in the formula, 1 G is the singlet ground state of the material that emits fluorescence, 1 H represents the singlet ground state of the thermally activated delayed phosphor). The energy transfer from the singlet excited state level of the thermally activated delayed phosphor to the triplet excited state level of the material that emits fluorescence is not the main energy transfer process because the direct transition from the singlet ground state to the triplet excited state in the material that emits fluorescence is forbidden, so it is omitted here. That is, as shown in the following formula (2-1), the energy transfer from the singlet excited state ( 1 H * ) of the thermally activated delayed phosphor to the singlet excited state ( 1 G * ) of the material that emits fluorescence is important (in the formula, 1 G is the singlet ground state of the material that emits fluorescence, 1 H represents the singlet ground state of the thermally activated delayed phosphor). The energy transfer from the singlet excited state level of the thermally activated delayed phosphor to the triplet excited state level of the material that emits fluorescence is not the main energy transfer process because the direct transition from the singlet ground state to the triplet excited state in the material that emits fluorescence is forbidden, so it is omitted here. That is, as shown in the following formula (2-1), the energy transfer from the singlet excited state ( 1 H * ) of the thermally activated delayed phosphor to the singlet excited state ( 1 G * ) of the material that emits fluorescence is important (in the formula, 1 G is the singlet ground state of the material that emits fluorescence, 1 H represents the singlet ground state of the thermally activated delayed phosphor). The energy transfer from the singlet excited state level of the thermally activated delayed phosphor to the triplet excited state level of the material that emits fluorescence is not the main energy transfer process because the direct transition from the singlet ground state to the triplet excited state in the material that emits fluorescence is forbidden, so it is omitted here. That is, as shown in the following formula (2-1), the energy transfer from the singlet excited state ( 1 H * ) of the thermally activated delayed phosphor to the singlet excited state ( 1 G * ) of the material that emits fluorescence is important (in the formula, 1 G is the singlet ground state of the material that emits fluorescence, 1 H represents the singlet ground state of the thermally activated delayed phosphor). 1 H * The energy transfer from the singlet excited state level of the thermally activated delayed phosphor to the triplet excited state level of the material that emits fluorescence is not the main energy transfer process because the direct transition from the singlet ground state to the triplet excited state in the material that emits fluorescence is forbidden, so it is omitted here. That is, as shown in the following formula (2-1), the energy transfer from the singlet excited state ( 1 H * ) of the thermally activated delayed phosphor to the singlet excited state ( 1 G * ) of the material that emits fluorescence is important (in the formula, 1 G is the singlet ground state of the material that emits fluorescence, 1 H represents the singlet ground state of the thermally activated delayed phosphor). 1 G * The energy transfer from the singlet excited state level of the thermally activated delayed phosphor to the triplet excited state level of the material that emits fluorescence is not the main energy transfer process because the direct transition from the singlet ground state to the triplet excited state in the material that emits fluorescence is forbidden, so it is omitted here. That is, as shown in the following formula (2-1), the energy transfer from the singlet excited state ( 1 H * ) of the thermally activated delayed phosphor to the singlet excited state ( 1 G * ) of the material that emits fluorescence is important (in the formula, 1 G is the singlet ground state of the material that emits fluorescence, 1 H represents the singlet ground state of the thermally activated delayed phosphor). 1 G is the singlet ground state of the material that emits fluorescence , 1 H represents the singlet ground state of the thermally activated delayed phosphor).

[0038] 1 H * + 1 G → 1 H+ 1 G * (2-1)

[0039] (2-2) When the excited state of the thermally activated delayed phosphor is the triplet excited state When the singlet excited state level of the thermally activated delayed phosphor is higher than the singlet excited state level of the material that emits fluorescence, the following process occurs for luminescence. First, the excitation energy moves from the triplet excited state level of the thermally activated delayed phosphor to the singlet excited state level of the thermally activated delayed phosphor by reverse intersystem crossing. Then, the excitation energy moves from the singlet excited state level of the thermally activated delayed phosphor to the singlet excited state level of the material that emits fluorescence, and the material that emits fluorescence becomes the singlet excited state. The material that emits fluorescence in the singlet excited state emits fluorescence. When the singlet excited state level of the thermally activated delayed phosphor is higher than the singlet excited state level of the material that emits fluorescence, the following process occurs for luminescence. First, the excitation energy moves from the triplet excited state level of the thermally activated delayed phosphor to the singlet excited state level of the thermally activated delayed phosphor by reverse intersystem crossing. Then, the excitation energy moves from the singlet excited state level of the thermally activated delayed phosphor to the singlet excited state level of the material that emits fluorescence, and the material that emits fluorescence becomes the singlet excited state. The material that emits fluorescence in the singlet excited state emits fluorescence. When the singlet excited state level of the thermally activated delayed phosphor is higher than the singlet excited state level of the material that emits fluorescence, the following process occurs for luminescence. First, the excitation energy moves from the triplet excited state level of the thermally activated delayed phosphor to the singlet excited state level of the thermally activated delayed phosphor by reverse intersystem crossing. Then, the excitation energy moves from the singlet excited state level of the thermally activated delayed phosphor to the singlet excited state level of the material that emits fluorescence, and the material that emits fluorescence becomes the singlet excited state. The material that emits fluorescence in the singlet excited state emits fluorescence. When the singlet excited state level of the thermally activated delayed phosphor is higher than the singlet excited state level of the material that emits fluorescence, the following process occurs for luminescence. First, the excitation energy moves from the triplet excited state level of the thermally activated delayed phosphor to the singlet excited state level of the thermally activated delayed phosphor by reverse intersystem crossing. Then, the excitation energy moves from the singlet excited state level of the thermally activated delayed phosphor to the singlet excited state level of the material that emits fluorescence, and the material that emits fluorescence becomes the singlet excited state. The material that emits fluorescence in the singlet excited state emits fluorescence. When the singlet excited state level of the thermally activated delayed phosphor is higher than the singlet excited state level of the material that emits fluorescence, the following process occurs for luminescence. First, the excitation energy moves from the triplet excited state level of the thermally activated delayed phosphor to the singlet excited state level of the thermally activated delayed phosphor by reverse intersystem crossing. Then, the excitation energy moves from the singlet excited state level of the thermally activated delayed phosphor to the singlet excited state level of the material that emits fluorescence, and the material that emits fluorescence becomes the singlet excited state. The material that emits fluorescence in the singlet excited state emits fluorescence. When the singlet excited state level of the thermally activated delayed phosphor is higher than the singlet excited state level of the material that emits fluorescence, the following process occurs for luminescence. First, the excitation energy moves from the triplet excited state level of the thermally activated delayed phosphor to the singlet excited state level of the thermally activated delayed phosphor by reverse intersystem crossing. Then, the excitation energy moves from the singlet excited state level of the thermally activated delayed phosphor to the singlet excited state level of the material that emits fluorescence, and the material that emits fluorescence becomes the singlet excited state. The material that emits fluorescence in the singlet excited state emits fluorescence.

[0040] That is, as shown in the following formula (2-2), the triplet excited state of the thermally activated delayed phosphor ( 3 H * ) undergoes inverse intersystem crossing to generate the singlet excited state of the thermally activated delayed phosphor ( 1 H * 1 ), and then the energy is transferred to the singlet excited state ( * G 3 ) of the material that emits fluorescence. ) of the material that emits fluorescence.

[0041] 3 H * + 1 G → (inverse intersystem crossing) → 1 H * + 1 G→ 1 H+ 1 G * (2-2)

[0042] If all the energy transfer processes described in (2) above occur efficiently, both the triplet excitation energy and the singlet excitation energy of the thermally activated delayed phosphor are efficiently converted into the singlet excited state ( 1 G * ) of the material that emits fluorescence, enabling highly efficient light emission. Conversely, if the thermally activated delayed phosphor ) of the material that emits fluorescence, enabling highly efficient light emission. Conversely, if the thermally activated delayed phosphor itself emits and loses its excitation energy as light or heat before the excitation energy is transferred to the material that emits fluorescence from the thermally activated delayed phosphor, the light emission efficiency will decrease. decrease.

[0043] Next, the governing factors of the intermolecular energy transfer process between the above-mentioned thermally activated delayed phosphor and the material that emits fluorescence will be explained. As the mechanism of intermolecular energy transfer, two mechanisms, the Förster mechanism (dipole-dipole interaction) and the Dexter mechanism, have been proposed. (dipole-dipole interaction) and the Dexter mechanism, have been proposed.

[0044] First, the first mechanism, the Förster mechanism (dipole-dipole interaction), is an energy The mechanism in which energy transfer occurs through the resonance phenomenon of dipole vibration between a thermally activated delayed phosphor and a fluorescent material without the need for direct contact between molecules during movement. Through the resonance phenomenon of dipole vibration, the thermally activated delayed phosphor transfers energy to the fluorescent material, causing the thermally activated delayed phosphor to return to the ground state and the fluorescent material to enter the excited state. Note that the rate constant k of the Förster mechanism is shown in Equation (1). In the resonance phenomenon of dipole vibration, the thermally activated delayed phosphor transfers energy to the fluorescent material, causing the thermally activated delayed phosphor to return to the ground state and the fluorescent material to enter the excited state. Note that the rate constant k of the Förster mechanism is shown in Equation (1). In the resonance phenomenon of dipole vibration, the thermally activated delayed phosphor transfers energy to the fluorescent material, causing the thermally activated delayed phosphor to return to the ground state and the fluorescent material to enter the excited state. Note that the rate constant k of the Förster mechanism is shown in Equation (1). In the resonance phenomenon of dipole vibration, the thermally activated delayed phosphor transfers energy to the fluorescent material, causing the thermally activated delayed phosphor to return to the ground state and the fluorescent material to enter the excited state. Note that the rate constant k of the Förster mechanism is shown in Equation (1). In the resonance phenomenon of dipole vibration, the thermally activated delayed phosphor transfers energy to the fluorescent material, causing the thermally activated delayed phosphor to return to the ground state and the fluorescent material to enter the excited state. Note that the rate constant k of the Förster mechanism is shown in Equation (1). h*→g In the resonance phenomenon of dipole vibration, the thermally activated delayed phosphor transfers energy to the fluorescent material, causing the thermally activated delayed phosphor to return to the ground state and the fluorescent material to enter the excited state. Note that the rate constant k of the Förster mechanism is shown in Equation (1).

[0045]

Equation

[0046] In Equation (1), ν represents the frequency, f’(ν) represents the normalized emission spectrum of the thermally activated delayed phosphor (fluorescence spectrum when discussing energy transfer from the singlet excited state, phosphorescence spectrum when discussing energy transfer from the triplet excited state), ε(ν) represents the molar extinction coefficient of the fluorescent material, N represents Avogadro's number, n represents the refractive index of the medium, R represents the intermolecular distance between the thermally activated delayed phosphor and the fluorescent material, τ represents the measured lifetime of the excited state (fluorescence lifetime or phosphorescence lifetime), φ represents the emission quantum yield (fluorescence quantum yield when discussing energy transfer from the singlet excited state, phosphorescence quantum yield when discussing energy transfer from the triplet excited state), and K represents the coefficient (0 - 4) representing the orientation of the transition dipole moments of the thermally activated delayed phosphor and the fluorescent material. Note that in the case of random orientation, K = 2 / 3. h In Equation (1), ν represents the frequency, f’(ν) represents the normalized emission spectrum of the thermally activated delayed phosphor (fluorescence spectrum when discussing energy transfer from the singlet excited state, phosphorescence spectrum when discussing energy transfer from the triplet excited state), ε(ν) represents the molar extinction coefficient of the fluorescent material, N represents Avogadro's number, n represents the refractive index of the medium, R represents the intermolecular distance between the thermally activated delayed phosphor and the fluorescent material, τ represents the measured lifetime of the excited state (fluorescence lifetime or phosphorescence lifetime), φ represents the emission quantum yield (fluorescence quantum yield when discussing energy transfer from the singlet excited state, phosphorescence quantum yield when discussing energy transfer from the triplet excited state), and K represents the coefficient (0 - 4) representing the orientation of the transition dipole moments of the thermally activated delayed phosphor and the fluorescent material. Note that in the case of random orientation, K = 2 / 3. In Equation (1), ν represents the frequency, f’(ν) represents the normalized emission spectrum of the thermally activated delayed phosphor (fluorescence spectrum when discussing energy transfer from the singlet excited state, phosphorescence spectrum when discussing energy transfer from the triplet excited state), ε(ν) represents the molar extinction coefficient of the fluorescent material, N represents Avogadro's number, n represents the refractive index of the medium, R represents the intermolecular distance between the thermally activated delayed phosphor and the fluorescent material, τ represents the measured lifetime of the excited state (fluorescence lifetime or phosphorescence lifetime), φ represents the emission quantum yield (fluorescence quantum yield when discussing energy transfer from the singlet excited state, phosphorescence quantum yield when discussing energy transfer from the triplet excited state), and K represents the coefficient (0 - 4) representing the orientation of the transition dipole moments of the thermally activated delayed phosphor and the fluorescent material. Note that in the case of random orientation, K = 2 / 3. In Equation (1), ν represents the frequency, f’(ν) represents the normalized emission spectrum of the thermally activated delayed phosphor (fluorescence spectrum when discussing energy transfer from the singlet excited state, phosphorescence spectrum when discussing energy transfer from the triplet excited state), ε(ν) represents the molar extinction coefficient of the fluorescent material, N represents Avogadro's number, n represents the refractive index of the medium, R represents the intermolecular distance between the thermally activated delayed phosphor and the fluorescent material, τ represents the measured lifetime of the excited state (fluorescence lifetime or phosphorescence lifetime), φ represents the emission quantum yield (fluorescence quantum yield when discussing energy transfer from the singlet excited state, phosphorescence quantum yield when discussing energy transfer from the triplet excited state), and K represents the coefficient (0 - 4) representing the orientation of the transition dipole moments of the thermally activated delayed phosphor and the fluorescent material. Note that in the case of random orientation, K = 2 / 3. In Equation (1), ν represents the frequency, f’(ν) represents the normalized emission spectrum of the thermally activated delayed phosphor (fluorescence spectrum when discussing energy transfer from the singlet excited state, phosphorescence spectrum when discussing energy transfer from the triplet excited state), ε(ν) represents the molar extinction coefficient of the fluorescent material, N represents Avogadro's number, n represents the refractive index of the medium, R represents the intermolecular distance between the thermally activated delayed phosphor and the fluorescent material, τ represents the measured lifetime of the excited state (fluorescence lifetime or phosphorescence lifetime), φ represents the emission quantum yield (fluorescence quantum yield when discussing energy transfer from the singlet excited state, phosphorescence quantum yield when discussing energy transfer from the triplet excited state), and K represents the coefficient (0 - 4) representing the orientation of the transition dipole moments of the thermally activated delayed phosphor and the fluorescent material. Note that in the case of random orientation, K = 2 / 3. g In Equation (1), ν represents the frequency, f’(ν) represents the normalized emission spectrum of the thermally activated delayed phosphor (fluorescence spectrum when discussing energy transfer from the singlet excited state, phosphorescence spectrum when discussing energy transfer from the triplet excited state), ε(ν) represents the molar extinction coefficient of the fluorescent material, N represents Avogadro's number, n represents the refractive index of the medium, R represents the intermolecular distance between the thermally activated delayed phosphor and the fluorescent material, τ represents the measured lifetime of the excited state (fluorescence lifetime or phosphorescence lifetime), φ represents the emission quantum yield (fluorescence quantum yield when discussing energy transfer from the singlet excited state, phosphorescence quantum yield when discussing energy transfer from the triplet excited state), and K represents the coefficient (0 - 4) representing the orientation of the transition dipole moments of the thermally activated delayed phosphor and the fluorescent material. Note that in the case of random orientation, K = 2 / 3. In Equation (1), ν represents the frequency, f’(ν) represents the normalized emission spectrum of the thermally activated delayed phosphor (fluorescence spectrum when discussing energy transfer from the singlet excited state, phosphorescence spectrum when discussing energy transfer from the triplet excited state), ε(ν) represents the molar extinction coefficient of the fluorescent material, N represents Avogadro's number, n represents the refractive index of the medium, R represents the intermolecular distance between the thermally activated delayed phosphor and the fluorescent material, τ represents the measured lifetime of the excited state (fluorescence lifetime or phosphorescence lifetime), φ represents the emission quantum yield (fluorescence quantum yield when discussing energy transfer from the singlet excited state, phosphorescence quantum yield when discussing energy transfer from the triplet excited state), and K represents the coefficient (0 - 4) representing the orientation of the transition dipole moments of the thermally activated delayed phosphor and the fluorescent material. Note that in the case of random orientation, K = 2 / 3. In Equation (1), ν represents the frequency, f’(ν) represents the normalized emission spectrum of the thermally activated delayed phosphor (fluorescence spectrum when discussing energy transfer from the singlet excited state, phosphorescence spectrum when discussing energy transfer from the triplet excited state), ε(ν) represents the molar extinction coefficient of the fluorescent material, N represents Avogadro's number, n represents the refractive index of the medium, R represents the intermolecular distance between the thermally activated delayed phosphor and the fluorescent material, τ represents the measured lifetime of the excited state (fluorescence lifetime or phosphorescence lifetime), φ represents the emission quantum yield (fluorescence quantum yield when discussing energy transfer from the singlet excited state, phosphorescence quantum yield when discussing energy transfer from the triplet excited state), and K represents the coefficient (0 - 4) representing the orientation of the transition dipole moments of the thermally activated delayed phosphor and the fluorescent material. Note that in the case of random orientation, K = 2 / 3. In Equation (1), ν represents the frequency, f’(ν) represents the normalized emission spectrum of the thermally activated delayed phosphor (fluorescence spectrum when discussing energy transfer from the singlet excited state, phosphorescence spectrum when discussing energy transfer from the triplet excited state), ε(ν) represents the molar extinction coefficient of the fluorescent material, N represents Avogadro's number, n represents the refractive index of the medium, R represents the intermolecular distance between the thermally activated delayed phosphor and the fluorescent material, τ represents the measured lifetime of the excited state (fluorescence lifetime or phosphorescence lifetime), φ represents the emission quantum yield (fluorescence quantum yield when discussing energy transfer from the singlet excited state, phosphorescence quantum yield when discussing energy transfer from the triplet excited state), and K represents the coefficient (0 - 4) representing the orientation of the transition dipole moments of the thermally activated delayed phosphor and the fluorescent material. Note that in the case of random orientation, K = 2 / 3. In Equation (1), ν represents the frequency, f’(ν) represents the normalized emission spectrum of the thermally activated delayed phosphor (fluorescence spectrum when discussing energy transfer from the singlet excited state, phosphorescence spectrum when discussing energy transfer from the triplet excited state), ε(ν) represents the molar extinction coefficient of the fluorescent material, N represents Avogadro's number, n represents the refractive index of the medium, R represents the intermolecular distance between the thermally activated delayed phosphor and the fluorescent material, τ represents the measured lifetime of the excited state (fluorescence lifetime or phosphorescence lifetime), φ represents the emission quantum yield (fluorescence quantum yield when discussing energy transfer from the singlet excited state, phosphorescence quantum yield when discussing energy transfer from the triplet excited state), and K represents the coefficient (0 - 4) representing the orientation of the transition dipole moments of the thermally activated delayed phosphor and the fluorescent material. Note that in the case of random orientation, K = 2 / 3. 2 In Equation (1), ν represents the frequency, f’(ν) represents the normalized emission spectrum of the thermally activated delayed phosphor (fluorescence spectrum when discussing energy transfer from the singlet excited state, phosphorescence spectrum when discussing energy transfer from the triplet excited state), ε(ν) represents the molar extinction coefficient of the fluorescent material, N represents Avogadro's number, n represents the refractive index of the medium, R represents the intermolecular distance between the thermally activated delayed phosphor and the fluorescent material, τ represents the measured lifetime of the excited state (fluorescence lifetime or phosphorescence lifetime), φ represents the emission quantum yield (fluorescence quantum yield when discussing energy transfer from the singlet excited state, phosphorescence quantum yield when discussing energy transfer from the triplet excited state), and K represents the coefficient (0 - 4) representing the orientation of the transition dipole moments of the thermally activated delayed phosphor and the fluorescent material. Note that in the case of random orientation, K = 2 / 3. In Equation (1), ν represents the frequency, f’(ν) represents the normalized emission spectrum of the thermally activated delayed phosphor (fluorescence spectrum when discussing energy transfer from the singlet excited state, phosphorescence spectrum when discussing energy transfer from the triplet excited state), ε(ν) represents the molar extinction coefficient of the fluorescent material, N represents Avogadro's number, n represents the refractive index of the medium, R represents the intermolecular distance between the thermally activated delayed phosphor and the fluorescent material, τ represents the measured lifetime of the excited state (fluorescence lifetime or phosphorescence lifetime), φ represents the emission quantum yield (fluorescence quantum yield when discussing energy transfer from the singlet excited state, phosphorescence quantum yield when discussing energy transfer from the triplet excited state), and K represents the coefficient (0 - 4) representing the orientation of the transition dipole moments of the thermally activated delayed phosphor and the fluorescent material. Note that in the case of random orientation, K = 2 / 3. In Equation (1), ν represents the frequency, f’(ν) represents the normalized emission spectrum of the thermally activated delayed phosphor (fluorescence spectrum when discussing energy transfer from the singlet excited state, phosphorescence spectrum when discussing energy transfer from the triplet excited state), ε(ν) represents the molar extinction coefficient of the fluorescent material, N represents Avogadro's number, n represents the refractive index of the medium, R represents the intermolecular distance between the thermally activated delayed phosphor and the fluorescent material, τ represents the measured lifetime of the excited state (fluorescence lifetime or phosphorescence lifetime), φ represents the emission quantum yield (fluorescence quantum yield when discussing energy transfer from the singlet excited state, phosphorescence quantum yield when discussing energy transfer from the triplet excited state), and K represents the coefficient (0 - 4) representing the orientation of the transition dipole moments of the thermally activated delayed phosphor and the fluorescent material. Note that in the case of random orientation, K = 2 / 3. 2 In Equation (1), ν represents the frequency, f’(ν) represents the normalized emission spectrum of the thermally activated delayed phosphor (fluorescence spectrum when discussing energy transfer from the singlet excited state, phosphorescence spectrum when discussing energy transfer from the triplet excited state), ε(ν) represents the molar extinction coefficient of the fluorescent material, N represents Avogadro's number, n represents the refractive index of the medium, R represents the intermolecular distance between the thermally activated delayed phosphor and the fluorescent material, τ represents the measured lifetime of the excited state (fluorescence lifetime or phosphorescence lifetime), φ represents the emission quantum yield (fluorescence quantum yield when discussing energy transfer from the singlet excited state, phosphorescence quantum yield when discussing energy transfer from the triplet excited state), and K represents the coefficient (0 - 4) representing the orientation of the transition dipole moments of the thermally activated delayed phosphor and the fluorescent material. Note that in the case of random orientation, K = 2 / 3.

[0047] Next, in the Dexter mechanism (electron exchange interaction), which is the second mechanism, thermally activated delayed fluorescence The thermally activated delayed fluorescence emitter and the material emitting fluorescence approach the contact effective distance where orbital overlap occurs, and energy transfer occurs through the exchange of electrons between the electrons of the thermally activated delayed phosphor in the excited state and the electrons of the material emitting fluorescence in the ground state. Note that the rate constant k of the Dexter mechanism is shown in Equation (2). h*→g Shown in mathematical formula (2).

[0048]

Equation

[0049] In Equation (2), h is Planck's constant, K is a constant with the dimension of energy and ν represents frequency, and f’ h (ν) represents the normalized emission spectrum of the thermally activated delayed phosphor (fluorescence spectrum when discussing energy transfer from the singlet excited state, phosphorescence spectrum when discussing energy transfer from the triplet excited state), ε’ g (ν) g (ν) represents the normalized absorption spectrum of the material emitting fluorescence, L represents the effective molecular radius , and R represents the intermolecular distance between the thermally activated delayed phosphor and the material emitting fluorescence.

[0050] Here, the energy transfer efficiency Φ ET from the thermally activated delayed phosphor to the material emitting fluorescence is considered to be represented by Equation (3). k r represents the rate constant of the emission process of the thermally activated delayed phosphor (fluorescence when discussing energy transfer from the singlet excited state, phosphorescence when discussing energy transfer from the triplet excited state), k n n represents the rate constant of the non-emission process (thermal deactivation and intersystem crossing) of the thermally activated delayed phosphor, and τ represents the measured excited state lifetime of the thermally activated delayed phosphor Represents the lifespan.

[0051]

Number

[0052] From Equation (3), to increase the energy transfer efficiency Φ ET it can be seen that the rate of energy transfer constant k h*→g should be increased, and the other competing rate constant k r +k n (=1 / τ) should be relatively small for this to be the case.

[0053] In both of the energy transfer processes of (2-1) and (2-2) above, the energy transfer from the singlet excited state of the thermally activated delayed phosphor ( 1 H * ) to the material that emits fluorescence is such that energy transfer by both the Förster mechanism (Equation (1)) and the Dexter mechanism (Equation (2)) is considered. Energy transfer by both mechanisms is considered.

[0054] First, consider the energy transfer by the Förster mechanism. Eliminating τ from Equation (1) and Equation (3), the energy transfer efficiency Φ it can be said that it is better for the quantum yield φ (since we are discussing energy transfer from the singlet excited state, the fluorescence quantum yield) to be high. However, in reality, ET more importantly, as a factor, it is also necessary for the emission spectrum of the thermally activated delayed phosphor (since we are discussing energy transfer from the singlet excited state, the fluorescence spectrum) and the absorption spectrum of the material that emits fluorescence to have a large overlap (note that it is also preferable for the molar absorption coefficient of the material that emits fluorescence to be high). This means that the emission spectrum of the thermally activated delayed phosphor and the absorption spectrum of the material that emits fluorescence should have a large overlap (since we are discussing energy transfer from the singlet excited state, the fluorescence spectrum) and the absorption spectrum of the material that emits fluorescence (corresponding to the absorption from the singlet ground state to the singlet excited state) is large (it is also preferable for the molar absorption coefficient of the material that emits fluorescence to be high). This is the emission spectrum of the thermally activated delayed phosphor and the longest wavelength side of the material that emits fluorescence It means that the absorption bands overlap.

[0055] Next, consider the energy transfer by the Dexter mechanism. According to Equation (2), to increase the rate constant k h *→g it is better for the emission spectrum of the thermally activated delayed phosphor (fluorescence spectrum, since we are discussing energy transfer from the singlet excited state) to have a large overlap with the absorption spectrum of the material that emits fluorescence (absorption corresponding to the transition from the singlet ground state to the singlet excited state). Since we are discussing energy transfer from the singlet excited state, it is the fluorescence spectrum. It can be seen that a larger overlap is better between the emission spectrum of the thermally activated delayed phosphor and the absorption band that appears on the longest wavelength side of the material that emits fluorescence (absorption corresponding to the transition from the singlet ground state to the singlet excited state). From the above, in any of the processes (2-1) and (2-2), the optimization of the energy transfer efficiency is achieved by the overlap between the emission spectrum of the thermally activated delayed phosphor and the absorption band that appears on the longest wavelength side of the material that emits fluorescence.

[0056] However, in order to increase the emission efficiency of the light-emitting device, it is important not only for the thermally activated delayed phosphor to generate the singlet excited state from the triplet excited state, but also for the fluorescence quantum yield of the material that emits fluorescence to be high. However, designing a material that can generate the singlet excited state from the triplet excited state and has a high fluorescence quantum yield is very difficult. It is important that the fluorescence quantum yield of the material that emits fluorescence is high.

[0057] However, designing a material that can generate the singlet excited state from the triplet excited state and has a high fluorescence quantum yield is very difficult. Moreover, for the light-emitting device to have high emission efficiency, it is not only necessary for the thermally activated delayed phosphor to generate the singlet excited state from the triplet excited state, but also for the fluorescence quantum yield of the material that emits fluorescence to be high. It is important that the fluorescence quantum yield of the material that emits fluorescence is high.

[0058] However, designing a material that can generate the singlet excited state from the triplet excited state and has a high fluorescence quantum yield is very difficult. Designing a material that can generate the singlet excited state from the triplet excited state and has a high fluorescence quantum yield is very difficult.

[0059] In addition, it is preferable that the proportion of the energy transfer process in (2) is large and the proportion of the direct recombination process in (1) is small, because the heat deactivation process in (1-2) can be reduced. Therefore, it is preferable that the concentration of the material that emits fluorescence is 5 wt% or less, and more preferably 1 wt% or less. it is preferable that the concentration of the material that emits fluorescence is 5 wt% or less, and more preferably 1 wt% or less.

[0060] Therefore, one aspect of the present invention is to overcome the problems related to the energy transfer efficiency from the triplet excited state of a thermally activated delayed phosphor to a material that emits fluorescence when using a fluorescent material as the luminescent substance, and the fluorescence quantum efficiency of the singlet excited state of the fluorescent material. A useful method is provided. The specific embodiments thereof will be described below. When a fluorescent material is used as the luminescent substance, the energy transfer efficiency from the triplet excited state of the thermally activated delayed phosphor to the material that emits fluorescence, and the problems related to the fluorescence quantum efficiency of the singlet excited state of the fluorescent material can be overcome. A useful method is provided. The specific embodiments thereof will be described below.

[0061] In one aspect of the present invention, a light-emitting device using a thermally activated delayed phosphor is provided as an energy donor capable of efficiently transferring energy to a fluorescent material. The thermally activated delayed phosphor has the characteristic that its singlet excited state and triplet excited state are close to each other. Therefore, the thermally activated delayed phosphor easily undergoes a transition from the triplet excited state to the singlet excited state. Further, among the absorptions of the singlet excited state of the fluorescent material that is the energy acceptor, the absorption band on the longest wavelength side (the absorption corresponding to the transition from the singlet ground state to the singlet excited state), by overlapping the emission spectrum of the thermally activated delayed phosphor, the energy transfer efficiency from the triplet excited state and singlet excited state of the thermally activated delayed phosphor to the singlet excited state of the fluorescent material can be increased. Furthermore, by assigning the function of generating the singlet excited state from the triplet excited state and the function of efficiently obtaining light emission from the singlet excited state to different materials, a material with a high fluorescence quantum yield (for example, a material with a fluorescence quantum yield of 50% or more) can be selected regardless of whether it has thermally activated delay as the luminescent substance. Moreover, by overlapping the emission spectrum of the thermally activated delayed phosphor with the absorption band on the longest wavelength side (the absorption corresponding to the transition from the singlet ground state to the singlet excited state) of the absorption of the singlet excited state of the fluorescent material that is the energy acceptor, the energy transfer efficiency from the triplet excited state and singlet excited state of the thermally activated delayed phosphor to the singlet excited state of the fluorescent material can be increased. The energy transfer efficiency from the triplet excited state and singlet excited state of the thermally activated delayed phosphor to the singlet excited state of the fluorescent material can be increased. The energy transfer efficiency from the triplet excited state and singlet excited state of the thermally activated delayed phosphor to the singlet excited state of the fluorescent material can be increased.

[0062] In addition, by assigning the function of generating the singlet excited state from the triplet excited state and the function of efficiently obtaining light emission from the singlet excited state to different materials, a material with a high fluorescence quantum yield (for example, a material with a fluorescence quantum yield of 50% or more) can be selected regardless of whether it has thermally activated delay as the luminescent substance. A material with a high fluorescence quantum yield (for example, a material with a fluorescence quantum yield of 50% or more) can be selected regardless of whether it has thermally activated delay as the luminescent substance.

[0063] As a result, the energy of the triplet excited state and singlet excited state of the thermally activated delayed phosphor can be more efficiently converted into light emission through the singlet excited state of the fluorescent material. The energy of the triplet excited state and singlet excited state of the thermally activated delayed phosphor can be more efficiently converted into light emission through the singlet excited state of the fluorescent material. It becomes possible to obtain a light-emitting element with high luminous efficiency.

[0064] In the light-emitting element having the above-described configuration, energy transfer occurs efficiently as shown in FIG. 2. In FIG. 2, a state where a light-emitting layer 113 is provided between an electrode 101 and an electrode 102 is described. Any layer may exist between each electrode and the light-emitting layer 113. Thermally activated delayed phosphor 113D's singlet excited state S D transfers energy to the singlet excited state of the light-emitting substance 113A S A Also, the triplet excited state T of the thermally activated delayed phosphor 113D D intersystem crosses to the singlet excited state S of the thermally activated delayed phosphor 113D D and then transfers energy to the singlet excited state S of the light-emitting substance 113A. And light emission occurs from the singlet excited state S of the light-emitting substance 113A A . Thus, in the light-emitting element of the present embodiment, the function of generating a singlet excited state from a triplet excited state and the function of efficiently emitting light A from the singlet excited state are assigned to different materials, so that energy transfer and light emission can each be performed well, and a light-emitting element with high luminous efficiency can be provided.

[0065] FIG. 1 shows a conceptual diagram of the light-emitting element in the present embodiment. FIG. 1(A) is a diagram of the light-emitting element, and FIGS. 1(B) and 1(C) are diagrams showing an enlarged view of only the light-emitting layer 113.

[0066] The light-emitting element has an EL layer 10 3 sandwiched between a pair of electrodes, a first electrode 101 and a second electrode 102, and the EL layer 103 contains an organic compound as a light-emitting substance. Also, the EL layer emits light It has layer 113, and the luminescent material is contained at least in the light-emitting layer 113. For the layers other than the layer outside the light-emitting layer 113, there is no limitation, so any layer may be used for the other layers. As a typical laminated structure, there are a hole injection layer 111, a hole transport layer 112, an electron transport layer 114 , an electron injection layer 115, etc. In addition, a carrier blocking layer or the like may be provided, or a plurality of light-emitting layers may be provided.

[0067] The light-emitting layer 113 contains a thermally activated delayed phosphor 113D and a luminescent material 113A. As shown in FIG. 1(B), the thermally activated delayed phosphor 113D may be composed of a material that can generate a singlet excited state from a triplet excited state by reverse intersystem crossing alone. Also, the thermally activated delayed phosphor 113D may be composed of a plurality of types of materials. Among them, as shown in FIG. 1(C), it is preferably composed of two types of materials, a first organic compound 113D1 and a second organic compound 113D2, and these form a combination that forms an exciplex. Since the exciplex has a property that the difference in energy levels between the singlet excited state and the triplet excited state is very likely to be small, energy transfer from the triplet excited state level to the singlet excited state level is likely to occur. Therefore, the thermally activated delayed phosphor composed of a combination of the first organic compound and the second organic compound that forms an exciplex is optimal as the thermally activated delayed phosphor in one aspect of the present invention. Also, among the first organic compound and the second organic compound, when one is a hole-transporting material and the other is an electron-transporting material, by adjusting the mixing ratio of the first organic compound and the second organic compound, it is easy to optimize the carrier balance between holes and electrons in the light-emitting layer. Therefore, from the viewpoints of not only luminous efficiency but also reliability, it is optimal as the thermally activated delayed phosphor in one aspect of the present invention. Also, among the first organic compound and the second organic compound, when one is a hole-transporting material and the other is an electron-transporting material, by adjusting the mixing ratio of the first organic compound and the second organic compound, it is easy to optimize the carrier balance between holes and electrons in the light-emitting layer. Therefore, from the viewpoints of not only luminous efficiency but also reliability, it is optimal. is also preferable. In the light-emitting element of the present embodiment, the inclusion of other substances in the light-emitting layer 113 is not excluded.

[0068] The thermally activated delayed phosphor is in a state where its singlet excited state and triplet excited state are close to each other However, it is particularly preferable that the energy difference between the singlet excited state and the triplet excited state is 0 eV or more and 0.2 eV or less is.

[0069] Furthermore, the thermally activated delayed phosphor and the material that emits fluorescence are a combination in which the emission of the thermally activated delayed phosphor and the absorption band on the longest wavelength side of the light-emitting substance 113A overlap as described above is preferable. As a result, energy is efficiently transferred from the singlet excited state of the thermally activated delayed phosphor to the singlet excited state of the material that emits fluorescence.

[0070] Examples of the material that can emit fluorescence and can be used as the light-emitting substance 113A include, for example, the following. 5,6-bis[4-(10-phenyl-9-anthryl) phenyl]-2,2'-bipyridine (abbreviation: PAP2BPy), 5,6-bis[4'-( 10-phenyl-9-anthryl)biphenyl-4-yl]-2,2'-bipyridine (abbreviation: PAPP2BPy), N,N'-bis[4-(9-phenyl-9H-fluorene-9 -yl)phenyl]-N,N'-diphenyl-pyrene-1,6-diamine (abbreviation: 1,6 FLPAPrn), N,N'-bis[4-(9H-carbazol-9-yl)phenyl] -N,N'-diphenylstilbene-4,4'-diamine (abbreviation: YGA2S), 4-( 9H-carbazol-9-yl)-4'-(10-phenyl-9-anthryl)triphenyl ​​​Nilamine (abbreviation: YGAPA), 4-(9H-carbazol-9-yl)-4'-(9 ,10-diphenyl-2-anthryl) triphenylamine (abbreviation: 2YGAPPA), N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H -carbazole-3-amine (abbreviation: PCAPA), perylene, 2,5,8,11-tet ra-tert-butylperylene (abbreviation: TBP), 4-(10-phenyl-9-anthry l)-4'-(9-phenyl-9H-carbazol-3-yl) triphenylamine (abbreviation: PCBAPA), N,N''-(2-tert-butylanthracene-9,10-di yl-di-4,1-phenylene) bis[N,N',N'-triphenyl-1,4-phenylenediamine](abbreviation: DPABPA), N,9-diphenyl-N-[4-(9,10-di phenyl-2-anthryl)phenyl]-9H-carbazole-3-amine (abbreviation: 2P CAPPA), N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N, N',N'-triphenyl-1,4-phenylenediamine (abbreviation: 2DPAPPA), N ,N,N',N',N'',N'',N''',N'''-octaphenyldibenzo[g ,p]chrysene-2,7,10,15-tetraamine (abbreviation: DBC1), coumarin 30 , N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carb azole-3-amine (abbreviation: 2PCAPA), N-[9,10-bis(1,1'-biphe nyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazole-3- amine (abbreviation: 2PCABPhA), N-(9,10-diphenyl-2-anthryl)- N,N',N'-triphenyl-1,4-phenylenediamine (abbreviation: 2DPAPA), N,N,N',N',N'',N'',N''',N'''-octaphenyldibenzo[g N-[9,10-Bis(1,1'-biphenyl-2-yl)-2-anthryl]-N,N ',N'-triphenyl-1,4-phenylenediamine (abbreviation: 2DPABPhA), 9 ,10-bis(1,1'-biphenyl-2-yl)-N-[4-(9H-carbazol- 9-yl)phenyl]-N-phenylanthracen-2-amine (abbreviation: 2YGABPh A), N,N,9-triphenylanthracen-9-amine (abbreviation: DPhAPhA) cl marin 545T, N,N'-diphenylquinacridone, (abbreviation: DPQd), rubrene, 5,12-bis(1,1'-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT), 2-(2-{2-[4-(dimethylamino)phenyl]ethenyl}- 6-methyl-4H-pyran-4-ylidene)propanedinitrile (abbreviation: DCM1), 2 -{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[i j]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinit ril (abbreviation: DCM2), N,N,N',N'-tetrakis(4-methylphenyl)tet racene-5,11-diamine (abbreviation: p-mPhTD), 7,14-diphenyl-N,N ,N',N'-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene -3,10-diamine (abbreviation: p-mPhAFD), 2-{2-isopropyl-6- [2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H- benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}pro panedinitrile (abbreviation: DCJTI), 2-{2-tert-butyl-6-[2-(1, 1,7,7-Tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCJTB), 2-(2,6-bis{2-[4-(dimethylamino)phenyl ethenyl}-4H-pyran-4-ylidene)propanedinitrile (abbreviation: BisDCM ), 2-{2,6-bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3 ,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl -4H-pyran-4-ylidene}propanedinitrile (abbreviation: BisDCJTM), etc. are mentioned.

[0071] The concentration of the above-mentioned material that emits fluorescence in the light-emitting layer 113 is preferably 5 wt% or less, and more preferably 1 wt% or less. By setting the concentration in this way, the ratio of the energy transfer process in (2) can be increased, the ratio of the direct recombination process in (1) can be decreased, and the heat deactivation process in (1-2) can be reduced .

[0072] As the thermally activated delayed phosphor, for example, when it is composed of one kind of material, the following can be used .

[0073] First, fullerenes and their derivatives, acridine derivatives such as proflavine, eosin, etc. are mentioned . Also, metal-containing porphyrins containing magnesium (Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium (In), or palladium (Pd), etc. are mentioned. As the metal-containing porphyrin, for example, the protoporphyrin-tin fluoride complex (SnF2(Proto IX)) shown by the following structural formula, mesoporph phyrin, etc. are shown Phyllin-tin fluoride complex (SnF2(Meso IX)), hematoporphyrin-tin fluoride complex (SnF2(Hemato IX)), coproporphyrin tetramethyl ester-tin fluoride complex (SnF2(Copro III-4Me)), octaethylporphyrin-tin fluoride complex (SnF2(OEP)), etioporphyrin-tin fluoride complex (SnF2(Etio I)), octaethylporphyrin-platinum chloride complex (PtCl 2OEP), etc. can also be mentioned.

[0074]

Chem.

[0075] In addition, as a thermally activated delayed phosphor composed of one kind of material, those represented by the following structural formula 2-(Biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-a] carbazol-11-yl)-1,3,5-triazine (PIC-TRZ), etc., heterocyclic compounds having a π-electron excess type heteroaromatic ring and a π-electron deficient type heteroaromatic ring can also be used. Since the heterocyclic compound has a π-electron excess type heteroaromatic ring and a π-electron deficient type heteroaromatic ring , it has high electron transporting property and hole transporting property, which is preferable. Note that a substance in which a π-electron excess type heteroaromatic ring and a π-electron deficient type heteroaromatic ring are directly bonded has both strong donor property of the π-electron excess type heteroaromatic ring and π-electron acceptor property of the deficient type heteroaromatic ring, and the difference in energy levels between the singlet excited state and the triplet excited state becomes small, so it is particularly preferable.

[0076]

Chem.

[0077] As the thermally activated delayed phosphor, a combination of two organic compounds, i.e., a first organic compound and a second organic compound, which form an excited complex, can be used. In this case, known carrier transport materials can be appropriately used. However, in order to efficiently form an excited complex, a compound that easily accepts electrons (a material having electron transporting properties) and a compound that easily accepts holes (a material having hole transporting properties) are particularly preferably combined.

[0078] This is because by combining a material having electron transporting properties and a material having hole transporting properties and using them as a thermally activated delayed phosphor, and adjusting the mixing ratio of the material having electron transporting properties and the material having hole transporting properties, it becomes easy to optimize the carrier balance between holes and electrons in the light emitting layer. By optimizing the carrier balance between holes and electrons in the light emitting layer, it is possible to suppress the deviation of the region where recombination of electrons and holes occurs in the light emitting layer. By suppressing the deviation of the region where recombination occurs, the reliability of the light emitting device can be improved.

[0079] As the compound that easily accepts electrons (a material having electron transporting properties), π - electron - deficient heteroaromatics, metal complexes, etc. can be used. Specifically, bis(10 - hydroxybenzo [h]quinolinato)beryllium(II) (abbreviation: BeBq2), bis(2 - methyl - 8 - quinolinolato)(4 - phenylphenolato)aluminum(III) (abbreviation: BAlq) , bis(8 - quinolinolato)zinc(II) (abbreviation: Znq), bis[2 - (2 - benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO), bis[2 - (2 - benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ) and other metal complexes, 2 - ( [[ID=�6]] ​​​​​​​4-Biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadia zole (abbreviation: PBD), 3-(4-biphenylyl)-4-phenyl-5-(4-ter t-butylphenyl)-1,2,4-triazole (abbreviation: TAZ), 1,3-bis[5 -(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (abbreviation: OXD-7), 9-[4-(5-phenyl-1,3,4-oxadiazol -2-yl)phenyl]-9H-carbazole (abbreviation: CO11), 2,2’,2’’- (1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole) (abbreviation: TPBI), 2-[3-(dibenzothiophen-4-yl)phenyl]-1-f enyl-1H-benzimidazole (abbreviation: mDBTBIm-II), etc. polyazole heterocyclic compounds having a skeleton, and 2-[3-(dibenzothiophen-4-yl)phenyl] dibenz[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), 2-[3’-( dibenzothiophen-4-yl)biphenyl-3-yl]dibenz[f,h]quinoxali ne (abbreviation: 2mDBTBPDBq-II), 2-[3’-(9H-carbazol-9-i l)biphenyl-3-yl]dibenz[f,h]quinoxaline (abbreviation: 2mCzBPDB q), 4,6-bis[3-(phenanthren-9-yl)phenyl]pyrimidine (abbreviation: 4,6mPnP2Pm), 4,6-bis〔3-(4-dibenzothienyl)phenyl〕pyr imidine (abbreviation: 4,6mDBTP2Pm-II), etc. heterocyclic compounds having a diazine skeleton, and 3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation : 35DCzPPy), 1,3,5-tri[3-(3-pyridyl)phenyl]benzene( : 35DCzPPy), 1,3,5-tri[3-(3-pyridyl)phenyl]benzene( Abbreviations: Heterocyclic compounds having a pyridine skeleton such as TmPyPB can be mentioned. Among the above-mentioned Among them, heterocyclic compounds having a diazine skeleton and heterocyclic compounds having a pyridine skeleton are preferred because of their good reliability. In particular, heterocyclic compounds having a diazine (pyrimidine or pyrazine) skeleton have high electron transport properties and contribute to reducing the driving voltage.

[0080] As a compound that easily accepts holes (a material having hole transport properties), a π-electron-excessive heterocyclic aromatic or aromatic amine can be preferably used. Specifically, 2-[N-(9- phenylcarbazol-3-yl)-N-phenylamino]spiro-9,9'-bifluoro rene (abbreviation: PCASF), 4,4'-bis[N-(1-naphthyl)-N-phenylamino biphenyl (abbreviation: NPB), N,N'-bis(3-methylphenyl)-N,N'- diphenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviation: TPD), 4,4 '-bis[N-(spiro-9,9'-bifluorene-2-yl)-N-phenylamino] biphenyl (abbreviation: BSPB), 4-phenyl-4'-(9-phenylfluoren-9- yl)triphenylamine (abbreviation: BPAFLP), 4-phenyl-3'-(9-phenyl fluoren-9-yl)triphenylamine (abbreviation: mBPAFLP), 4-phenyl -4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), 4,4'-diphenyl-4''-(9-phenyl-9H-carbazolo l-3-yl)triphenylamine (abbreviation: PCBBi1BP), 4-(1-naphthyl) -4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBANB), 4,4'-di(1-naphthyl)-4''-(9-phenyl-9H-carbamoyl) PCBNBB, 9,9-dimethyl- N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl] -Fluoren-2-amine (abbreviation: PCBAF), N-phenyl-N-[4-(9-phenyl (9H-carbazol-3-yl)phenyl]-spiro-9,9'-bifluorene- Compounds with aromatic amine skeletons such as 2-amine (abbreviated as PCBASF) and 1,3- Bis(N-carbazolyl)benzene (abbreviation: mCP), 4,4'-di(N-carbazolyl) ) biphenyl (abbreviation: CBP), 3,6-bis(3,5-diphenylphenyl)-9-phenyl CzTP, 9-phenyl-9H-3-(9-phenyl-9 Carbazole skeleton such as H-carbazol-3-yl)carbazole (abbreviation: PCCP) and compounds having 4,4',4''-(benzene-1,3,5-triyl)tri(dibenzyl) benzothiophene) (abbreviation: DBT3P-II), 2,8-diphenyl-4-[4-(9- (phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene (abbreviation: DBT FLP-III), 4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl ]-6-phenyldibenzothiophene (abbreviated as DBTFLP-IV) and other thiophene skeletons Compounds with 4,4',4''-(benzene-1,3,5-triyl)tri(diphenyl) benzofuran) (abbreviation: DBF3P-II), 4-{3-[3-(9-phenyl-9H- Fluoren-9-yl)phenyl]phenyl}dibenzofuran (abbreviation: mmDBFFLB Among the above, aromatic amino compounds such as i-II) and furan compounds are preferred. Compounds having a fluorene skeleton or compounds having a carbazole skeleton have good reliability and are also preferable because they have high hole transportability and contribute to reducing the driving voltage.

[0081] The first organic compound and the second organic compound are not limited to these, and are a combination that can transport carriers and form an exciplex, and the emission of the exciplex overlaps with the absorption band on the longest wavelength side in the absorption spectrum of the light-emitting material (absorption corresponding to the transition from the singlet ground state to the singlet excited state of the light-emitting material), and other known materials may be used. The absorption band on the longest wavelength side in the absorption spectrum of the light-emitting material (absorption corresponding to the transition from the singlet ground state to the singlet excited state of the light-emitting material), and it is sufficient if they overlap, and other known materials may be used. It is okay. That is fine.

[0082] When the first organic compound and the second organic compound are composed of a material having electron transporting properties and a material having hole transporting properties, the carrier balance can be controlled by the mixing ratio. Specifically, the range of the first organic compound: the second organic compound = 1:9 to 9:1 is preferable. Specifically, the range of the first organic compound: the second organic compound = 1:9 to 9:1 is preferred. That is preferable.

[0083] Here, each compound (the first organic compound 113D1 and the second organic compound 113D2) forming the exciplex and the exciplex will be described in a little more detail. Here, each compound (the first organic compound 113D1 and the second organic compound 113D2) forming the exciplex and the exciplex will be described in a bit more detail.

[0084] In FIGS. 10(A) and 10(B), the emission spectra of four organic compounds alone and the emission spectra of the exciplexes formed therefrom are shown. In the figure, Compound 1 is 2-[4-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzoimidazole (abbreviation: DBTBIm-II), Compound 2 is 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), and the compound (abbreviation: DBTBIm-II), Compound 2 is 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), and the compound (abbreviation: DBTBIm-II), Compound 2 is 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), and the compound (abbreviation: DBTBIm-II), Compound 2 is 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), and the compound The substance 3 is 4,4’,4’’-tris[N-(1-naphthyl)-N-phenylamino]triphenylamine (abbreviation: 1’-TNATA), and the compound 4 is 2,7-bis[N-(4-diphenylaminophenyl)-N-phenylamino]-spiro-9,9’-bifluorene (abbreviation: DPA2SF). The exciplex 1 is the exciplex of compound 1 and compound 3, the exciplex 2 is the exciplex of compound 2 and compound 3, the exciplex 3 is the exciplex of compound 2 and 4,4’-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB), and the exciplex 4 is the spectrum of the exciplex of compound 2 and compound 4. The structural formulas of each compound are shown below.

Chemical formula

[0085]

[0086]

[0087]

[0088] Figure 10(A) shows the emission spectra of the exciplexes 1 and 2, and compounds 1 to 3. The spectrum represented by the exciplex 1 shows the result of measuring the emission of a material with a small amount of compound 3 added based on compound 1, and the spectrum represented by the exciplex 2 shows the result of measuring the emission of a material with a small amount of compound 3 added based on compound 2. That is, in the sample for measuring the exciplex 1, either compound 1 or compound 3 corresponds to the first organic compound 113D1, and the other corresponds to the second organic compound 113D2. Also, in the sample for measuring the exciplex 2, either compound 2 or compound 3 corresponds to the first organic compound 113D1, and the other corresponds to the second organic compound 113D2.​​​​​​​​​​​​​As can be seen from Fig. 10(A), even if the minor component, compound 3, is the same, the emissions of exciplex 1 and exciplex 2 have a difference of more than 100 nm. That is, by changing the base material in this way, the emission wavelength of the exciplex can be easily adjusted.

[0089] Since the peak wavelength of the emission spectrum of exciplex 1 is about 520 nm, the thermally activated delayed phosphor containing compound 1 and compound 3 can be preferably used by mixing with a material that emits blue-green to red fluorescence.

[0090] Also, since the peak wavelength of the emission spectrum of exciplex 2 is about 610 nm, the thermally activated delayed phosphor containing compound 2 and compound 3 can be preferably used by mixing with a material that emits red fluorescence.

[0091] In Fig. 10(B), in addition to exciplex 3 and exciplex 4, the emission spectra of compound 2 and compound 4 are shown. The spectrum represented by exciplex 3 shows the result of measuring the emission of the material with a small amount of NPB added based on compound 2, and the spectrum represented by exciplex 4 shows the result of measuring the emission of the material with a small amount of compound 4 added based on compound 2. That is , in the sample for measuring exciplex 3, either compound 2 or NPB corresponds to the first organic compound 113D1, and the other corresponds to the second organic compound 113D2. Also, , in the sample for measuring exciplex 4, either compound 2 or compound 4 corresponds to the first organic compound 113D1, and the other corresponds to the second organic compound 113D2. As can be seen from Fig. 10(B), even if the base materials are the same, exciplex 3 and exciplex

[0092] 4 ​​​​There is a difference of nearly 100 nm in the emission of 4. That is, even by changing the substance which is a minor component, it is possible to easily adjust the emission wavelength of the exciplex.

[0093] Since the peak wavelength of the emission spectrum of the exciplex 3 is about 520 nm, the thermally activated delayed phosphor containing Compound 2 and NPB can be suitably used by mixing with a material that emits fluorescence from blue-green to red.

[0094] Also, since the peak wavelength of the emission spectrum of the exciplex 4 is about 580 nm, the thermally activated delayed phosphor containing Compound 2 and Compound 4 can be suitably used by mixing with a material that emits fluorescence from orange to red.

[0095] The light-emitting element having the above configuration has high energy transfer efficiency to the material that emits fluorescence, and is a light-emitting element with good luminous efficiency.

[0096] In addition, it is also preferable that when two kinds of organic compounds in a combination that forms an exciplex are used as the thermally activated delayed phosphor, the driving voltage of the light-emitting element can be lowered. By lowering the driving voltage, it is possible to obtain a light-emitting element with low power consumption. The reason why the driving voltage of the light-emitting element can be lowered by using an exciplex will be explained below.

[0097] When using a combination of organic compounds that form an exciplex as the thermally activated delayed phosphor, the voltage threshold at which the exciplex is formed by the recombination of carriers (or singlet excitons) is determined by the energy of the peak of the emission spectrum of the exciplex. For example, if the peak of the emission spectrum of the exciplex is 620 nm (2.0 eV), the exciplex is electrically energized. If the peak of the emission spectrum is 620 nm (2.0 eV), the exciplex is electrically energized. The threshold voltage required to form a exciplex is also about 2.0V.

[0098] Here, if the energy of the peak of the emission spectrum of the exciplex is too high (the wavelength is too short) the threshold voltage at which the exciplex is formed also increases. In this case, in order to transfer energy from the exciplex to the material that emits fluorescence and cause the material that emits fluorescence to emit light, a larger voltage is required, which consumes extra energy, so it is not preferable. From this point of view, it is preferable that the lower the energy of the peak of the emission spectrum of the exciplex (the longer the wavelength), the lower the threshold voltage of the voltage. Therefore, if the peak wavelength of the emission spectrum of the exciplex is set to be equal to or longer than the peak wavelength of the absorption band located on the longest wavelength side of the absorption spectrum of the material that emits fluorescence, a light-emitting element with a low driving voltage

[0099] can be obtained. Even in this case, since energy transfer is possible by utilizing the overlap between the emission spectrum of the exciplex and the absorption band located on the longest wavelength side of the absorption spectrum of the material that emits fluorescence, a high luminous efficiency can be obtained. In this way, by reducing the driving voltage while obtaining a high luminous efficiency (external quantum efficiency), a high power efficiency can be realized.

[0100] The threshold voltage at which the exciplex is formed by carrier recombination is lower than the threshold voltage at which the material that emits fluorescence starts to emit light due to carrier recombination. That is, even if the voltage applied to the light-emitting element is less than the threshold voltage at which the material that emits fluorescence starts to emit light, carriers recombine to form an exciplex, and a recombination current starts to flow through the light-emitting element. Therefore, a light-emitting element with a lower driving voltage (better voltage-current characteristics) is realized. ​​​It can be done.

[0101] Also, when the threshold voltage at which the material that emits fluorescence starts to emit light is reached, light emission There are a sufficient number of carriers in the layer, and recombination of carriers that can contribute to the light emission of the material that emits fluorescence Occurs smoothly and frequently. Therefore, near the threshold voltage (light emission start voltage) of the material that emits fluorescence, the luminance increases rapidly. That is, since the rise near the light emission start voltage of the voltage-luminance characteristics can be made steep, the driving voltage required to obtain a desired luminance can also be lowered. Moreover, in order to obtain a practical luminance, since it is driven at a voltage equal to or higher than the threshold voltage (light emission start voltage) of the material that emits fluorescence, the light emission of the material that emits fluorescence is dominant, The light-emitting element can also achieve high current efficiency. (Emission start voltage) and above, the light emission of the material that emits fluorescence is dominant, The light-emitting element can also achieve high current efficiency.

[0102] The effect of the above voltage reduction is significantly observed in the region where the peak of the emission spectrum of the exciplex is within +30 nm of the peak of the emission spectrum of the material that emits fluorescence, or the difference in the energy conversion value between the peak wavelength of the emission spectrum of the exciplex and The peak wavelength of the emission spectrum of the material that emits fluorescence is +0.2 eV or less. Also, if the peak of the emission spectrum of the exciplex is within -30 nm of the peak of the emission spectrum of the material that emits fluorescence, or the difference in the energy conversion value between the peak wavelength of the emission spectrum of the exciplex and The peak wavelength of the emission of the material that emits fluorescence is -0.2 eV or more, a relatively high emission efficiency can also be maintained. The peak of the emission spectrum of the exciplex is within -30 nm of the peak of the emission spectrum of the material that emits fluorescence, or the difference in the energy conversion value between the peak wavelength of the emission spectrum of the exciplex and The peak wavelength of the emission of the material that emits fluorescence is -0.2 eV or more, a relatively high emission efficiency can also be maintained. The peak wavelength of the emission of the material that emits fluorescence is -0.2 eV or more, a relatively high emission efficiency can also be maintained. If it is in the region above, a relatively high emission efficiency can also be maintained.

[0103] (Embodiment 2) In this embodiment, an example of the detailed structure of the light-emitting element described in Embodiment 1 will be described below with reference to FIG. 1. It will be described below.

[0104] The light-emitting element in this embodiment has an EL layer composed of a plurality of layers between a pair of electrodes. In this embodiment, the light-emitting element is composed of a first electrode 101, a second electrode 102, and an EL layer 103 provided between the first electrode 101 and the second electrode 102. In addition, in this embodiment, the first electrode 101 functions as an anode, and the second electrode 102 functions as a cathode, and the following description will be made. That is, when a voltage is applied to the first electrode 101 and the second electrode 102 such that the potential of the first electrode 101 is higher than that of the second electrode 102, light emission can be obtained. Since the first electrode 101 functions as an anode, it is preferably formed using a metal, alloy, conductive compound, or a mixture thereof having a large work function (specifically, 4.0 eV or more). Specifically, for example, indium tin oxide (ITO: Indium Tin Oxide), indium tin oxide containing silicon or silicon oxide, indium zinc oxide, indium oxide containing tungsten oxide and zinc oxide (IWZO), etc. can be mentioned. These conductive metal oxide films are usually formed by sputtering, but may also be produced by applying a sol-gel method or the like. As an example of the production method, indium zinc oxide can be formed by sputtering using a target in which 1 to 20 wt% of zinc oxide is added to indium oxide. In addition, indium oxide containing tungsten oxide and zinc oxide (IWZO) can also be formed by sputtering using a target containing 0.5 to 5 wt% of tungsten oxide and 0.1 to 1 wt% of zinc oxide with respect to indium oxide. In addition, gold (Au), platinum (P

[0105] oxide), indium tin oxide containing silicon or silicon oxide, indium zinc oxide, indium oxide containing tungsten oxide and zinc oxide (IWZO), etc. can be mentioned. These conductive metal oxide films are usually formed by sputtering, but may also be produced by applying a sol-gel method or the like. As an example of the production method, indium zinc oxide can be formed by sputtering using a target in which 1 to 20 wt% of zinc oxide is added to indium oxide. In addition, indium oxide containing tungsten oxide and zinc oxide (IWZO) can also be formed by sputtering using a target containing 0.5 to 5 wt% of tungsten oxide and 0.1 to 1 wt% of zinc oxide with respect to indium oxide. In addition, gold (Au), platinum (P oxide), indium tin oxide containing silicon or silicon oxide, indium zinc oxide, indium oxide containing tungsten oxide and zinc oxide (IWZO), etc. can be mentioned. These conductive metal oxide films are usually formed by sputtering, but may also be produced by applying a sol-gel method or the like. As an example of the production method, indium zinc oxide can be formed by sputtering using a target in which 1 to 20 wt% of zinc oxide is added to indium oxide. In addition, indium oxide containing tungsten oxide and zinc oxide (IWZO) can also be formed by sputtering using a target containing 0.5 to 5 wt% of tungsten oxide and 0.1 to 1 wt% of zinc oxide with respect to indium oxide. In addition, gold (Au), platinum (P oxide), indium tin oxide containing silicon or silicon oxide, indium zinc oxide, indium oxide containing tungsten oxide and zinc oxide (IWZO), etc. can be mentioned. These conductive metal oxide films are usually formed by sputtering, but may also be produced by applying a sol-gel method or the like. As an example of the production method, indium zinc oxide can be formed by sputtering using a target in which 1 to 20 wt% of zinc oxide is added to indium oxide. In addition, indium oxide containing tungsten oxide and zinc oxide (IWZO) can also be formed by sputtering using a target containing 0.5 to 5 wt% of tungsten oxide and 0.1 to 1 wt% of zinc oxide with respect to indium oxide. In addition, gold (Au), platinum (P oxide), indium tin oxide containing silicon or silicon oxide, indium zinc oxide, indium oxide containing tungsten oxide and zinc oxide (IWZO), etc. can be mentioned. These conductive metal oxide films are usually formed by sputtering, but may also be produced by applying a sol-gel method or the like. As an example of the production method, indium zinc oxide can be formed by sputtering using a target in which 1 to 20 wt% of zinc oxide is added to indium oxide. In addition, indium oxide containing tungsten oxide and zinc oxide (IWZO) can also be formed by sputtering using a target containing 0.5 to 5 wt% of tungsten oxide and 0.1 to 1 wt% of zinc oxide with respect to indium oxide. In addition, gold (Au), platinum (P oxide), indium tin oxide containing silicon or silicon oxide, indium zinc oxide, indium oxide containing tungsten oxide and zinc oxide (IWZO), etc. can be mentioned. These conductive metal oxide films are usually formed by sputtering, but may also be produced by applying a sol-gel method or the like. As an example of the production method, indium zinc oxide can be formed by sputtering using a target in which 1 to 20 wt% of zinc oxide is added to indium oxide. In addition, indium oxide containing tungsten oxide and zinc oxide (IWZO) can also be formed by sputtering using a target containing 0.5 to 5 wt% of tungsten oxide and 0.1 to 1 wt% of zinc oxide with respect to indium oxide. In addition, gold (Au), platinum (P oxide), indium tin oxide containing silicon or silicon oxide, indium zinc oxide, indium oxide containing tungsten oxide and zinc oxide (IWZO), etc. can be mentioned. These conductive metal oxide films are usually formed by sputtering, but may also be produced by applying a sol-gel method or the like. As an example of the production method, indium zinc oxide can be formed by sputtering using a target in which 1 to 20 wt% of zinc oxide is added to indium oxide. In addition, indium oxide containing tungsten oxide and zinc oxide (IWZO) can also be formed by sputtering using a target containing 0.5 to 5 wt% of tungsten oxide and 0.1 to 1 wt% of zinc oxide with respect to indium oxide. In addition, gold (Au), platinum (P oxide), indium tin oxide containing silicon or silicon oxide, indium zinc oxide, indium oxide containing tungsten oxide and zinc oxide (IWZO), etc. can be mentioned. These conductive metal oxide films are usually formed by sputtering, but may also be produced by applying a sol-gel method or the like. As an example of the production method, indium zinc oxide can be formed by sputtering using a target in which 1 to 20 wt% of zinc oxide is added to indium oxide. In addition, indium oxide containing tungsten oxide and zinc oxide (IWZO) can also be formed by sputtering using a target containing 0.5 to 5 wt% of tungsten oxide and 0.1 to 1 wt% of zinc oxide with respect to indium oxide. In addition, gold (Au), platinum (P oxide), indium tin oxide containing silicon or silicon oxide, indium zinc oxide, indium oxide containing tungsten oxide and zinc oxide (IWZO), etc. can be mentioned. These conductive metal oxide films are usually formed by sputtering, but may also be produced by applying a sol-gel method or the like. As an example of the production method, indium zinc oxide can be formed by sputtering using a target in which 1 to 20 wt% of zinc oxide is added to indium oxide. In addition, indium oxide containing tungsten oxide and zinc oxide (IWZO) can also be formed by sputtering using a target containing 0.5 to 5 wt% of tungsten oxide and 0.1 to 1 wt% of zinc oxide with respect to indium oxide. In addition, gold (Au), platinum (P oxide), indium tin oxide containing silicon or silicon oxide, indium zinc oxide, indium oxide containing tungsten oxide and zinc oxide (IWZO), etc. can be mentioned. These conductive metal oxide films are usually formed by sputtering, but may also be produced by applying a sol-gel method or the like. As an example of the production method, indium zinc oxide can be formed by sputtering using a target in which 1 to 20 wt% of zinc oxide is added to indium oxide. In addition, indium oxide containing tungsten oxide and zinc oxide (IWZO) can also be formed by sputtering using a target containing 0.5 to 5 wt% of tungsten oxide and 0.1 to 1 wt% of zinc oxide with respect to indium oxide. In addition, gold (Au), platinum (P oxide), indium tin oxide containing silicon or silicon oxide, indium zinc oxide, indium oxide containing tungsten oxide and zinc oxide (IWZO), etc. can be mentioned. These conductive metal oxide films are usually formed by sputtering, but may also be produced by applying a sol-gel method or the like. As an example of the production method, indium zinc oxide can be formed by sputtering using a target in which 1 to 20 wt% of zinc oxide is added to indium oxide. In addition, indium oxide containing tungsten oxide and zinc oxide (IWZO) can also be formed by sputtering using a target containing 0.5 to 5 wt% of tungsten oxide and 0.1 to 1 wt% of zinc oxide with respect to indium oxide. In addition, gold (Au), platinum (P oxide), indium tin oxide containing silicon or silicon oxide, indium zinc oxide, indium oxide containing tungsten oxide and zinc oxide (IWZO), etc. can be mentioned. These conductive metal oxide films are usually formed by sputtering, but may also be produced by applying a sol-gel method or the like. As an example of the production method, indium zinc oxide can be formed by sputtering using a target in which 1 to 20 wt% of zinc oxide is added to indium oxide. In addition, indium oxide containing tungsten oxide and zinc oxide (IWZO) can also be formed by sputtering using a target containing 0.5 to 5 wt% of tungsten oxide and 0.1 to 1 wt% of zinc oxide with respect to indium oxide. In addition, gold (Au), platinum (P oxide), indium tin oxide containing silicon or silicon oxide, indium zinc oxide, indium oxide containing tungsten oxide and zinc oxide (IWZO), etc. can be mentioned. These conductive metal oxide films are usually formed by sputtering, but may also be produced by applying a sol-gel method or the like. As an example of the production method, indium zinc oxide can be formed by sputtering using a target in which 1 to 20 wt% of zinc oxide is added to indium oxide. In addition, indium oxide containing tungsten oxide and zinc oxide (IWZO) can also be formed by sputtering using a target containing 0.5 to 5 wt% of tungsten oxide and 0.1 to 1 wt% of zinc oxide with respect to indium oxide. In addition, gold (Au), platinum (P t), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), or nitrides of metal materials (e.g., titanium nitride), etc. can be mentioned. Graphene can also be used. Note that by using the composite material described later for the layer in contact with the first electrode 101 in the EL layer 103, regardless of the work function, the electrode material can be selected.

[0106] Regarding the laminated structure of the EL layer 103, as long as the light-emitting layer 113 has the configuration as shown in Embodiment 1, the others are not particularly limited. For example, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, a carrier blocking layer, an intermediate layer, etc. can be appropriately combined and configured. In this embodiment, the EL layer 103 will be described with a configuration having a hole injection layer 111, a hole transport layer 112, a light-emitting layer 113, an electron transport layer 114, and an electron injection layer 115 laminated in order on the first electrode 101. The materials constituting each layer will be specifically shown below.

[0107] The hole injection layer 111 is a layer containing a material with high hole injection properties. Molybdenum oxide, vanadium oxide, ruthenium oxide, tungsten oxide, manganese oxide, etc. can be used. In addition, phthalocyanine (abbreviation: H2Pc), copper phthalocyanine (CuPC), etc. phthalocyanine-based compounds, 4,4'-bis[N-(4-diphenylaminophenyl) -N-phenylamino]biphenyl (abbreviation: DPAB), N,N'-bis{4-[bis( (3-methylphenyl)amino]phenyl}-N,N'-diphenyl-(1,1'-biphe nyl)-4,4'-diamine (abbreviation: DNTPD), etc. aromatic amine compounds, or poly (Ethylenedioxythiophene) / poly(styrenesulfonic acid) (PEDOT / PSS) The hole injection layer 111 can also be formed by polymers such as these.

[0108] Also, as the hole injection layer 111, a composite material in which an acceptor substance is contained in a material having hole transporting properties can be used. Note that by using a material in which an acceptor substance is contained in a hole transporting substance, a material for forming an electrode can be selected regardless of the work function of the electrode. That is, not only a material with a large work function but also a material with a small work function can be used as the first electrode 101. Examples of the acceptor substance include 7,7,8,8 - tetracyano - 2,3,5,6 - tetrafluoroquinodimethane (abbreviation: F4 - TCNQ), chloranil, etc. Also, transition metal oxides can be mentioned. Also, oxides of metals belonging to Groups 4 to 8 in the periodic table can be mentioned. Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide are preferable because they have high electron accepting properties. Among them, molybdenum oxide is particularly preferable because it is stable in the air, has low hygroscopicity, and is easy to handle. ,8,8 - tetracyano - 2,3,5,6 - tetrafluoroquinodimethane (abbreviation: F4 - TCNQ), chloranil, etc. can be mentioned. Also, transition metal oxides can be mentioned. Also, oxides of metals belonging to Groups 4 to 8 in the periodic table can be mentioned. Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide are preferable because they have high electron accepting properties. Among them, molybdenum oxide is particularly preferable because it is stable in the air, has low hygroscopicity, and is easy to handle.

[0109] Examples of the hole transporting substance used in the composite material include aromatic amine compounds, carbazole derivatives, aromatic hydrocarbons, and various organic compounds such as polymer compounds (oligomers, dendrimers, polymers, etc.). Note that as the organic compound used in the composite material, it is preferable that the organic compound has high hole transporting properties. Specifically, 10 cm / Vs or more -6 cm 2 / Vs or more ​​​​​​​Preferably, it is a substance having a hole mobility. Hereinafter, hole transport in the composite material Specifically, organic compounds that can be used as substances with hole transport properties in the composite material are listed.

[0110] For example, as aromatic amine compounds, N,N'-di(p-tolyl)-N,N'-diphe nyl-p-phenylenediamine (abbreviation: DTDPPA), 4,4'-bis[N-(4-di phenylaminophenyl)-N-phenylamino]biphenyl (abbreviation: DPAB), N, N'-bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N'-diphe nyl-(1,1'-biphenyl)-4,4'-diamine (abbreviation: DNTPD), 1,3, 5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene ( abbreviation: DPA3B), etc. can be mentioned.

[0111] Specific examples of carbazole derivatives that can be used in the composite material include 3-[N-( 9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazo le (abbreviation: PCzPCA1), 3,6-bis[N-(9-phenylcarbazol-3- yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA2), 3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]- 9-phenylcarbazole (abbreviation: PCzPCN1), etc. can be mentioned.

[0112] In addition, other carbazole derivatives that can be used in the composite material include 4,4'-di (N-carbazolyl)biphenyl (abbreviation: CBP), 1,3,5-tris[4-(N-ca rbazolyl)phenyl]benzene (abbreviation: TCPB), 9-[4-(10-phenyl-9 -Anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA), 1,4-bis [4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene, etc. can be used.

[0113] In addition, examples of aromatic hydrocarbons that can be used in composite materials include 2-tert- butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA), 2-t ert-butyl-9,10-di(1-naphthyl)anthracene, 9,10-bis(3,5 -diphenylphenyl)anthracene (abbreviation: DPPA), 2-tert-butyl-9, 10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA), 9,10 -di(2-naphthyl)anthracene (abbreviation: DNA), 9,10-diphenylanthrac ene (abbreviation: DPAnth), 2-tert-butylanthracene (abbreviation: t-BuAnt h), 9,10-bis(4-methyl-1-naphthyl)anthracene (abbreviation: DMNA), 2-tert-butyl-9,10-bis[2-(1-naphthyl)phenyl]anthracene , 9,10-bis[2-(1-naphthyl)phenyl]anthracene, 2,3,6,7-tetra methyl-9,10-di(1-naphthyl)anthracene, 2,3,6,7-tetramethyl -9,10-di(2-naphthyl)anthracene, 9,9’-bianthryl, 10,10 ’-diphenyl-9,9’-bianthryl, 10,10’-bis(2-phenylphenyl ))-9,9’-bianthryl, 10,10’-bis[(2,3,4,5,6-penta phenyl)phenyl]-9,9’-bianthryl, anthracene, tetracene, rubrene, pery lene, 2,5,8,11-tetra(tert-butyl)perylene, etc. Also , in addition, pentacene, coronene, etc. can also be used. Thus, it is more preferable to use an aromatic hydrocarbon having a hole mobility of 1×10 -6 c m 2 / Vs or more and having 14 to 42 carbon atoms. This is more preferable.

[0114] Note that the aromatic hydrocarbon that can be used for the composite material may have a vinyl skeleton . Examples of the aromatic hydrocarbon having a vinyl group include 4,4'-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi), 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA), and the like.

[0115] In addition, high molecular 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]methacrylamide (abbreviation: PTPDMA), poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] (abbreviation: Poly-TPD), etc. can also be used.

[0116] By forming the hole injection layer 111, the injection property of holes becomes good, and it becomes possible to obtain a light-emitting element with a small driving voltage.

[0117] The hole transport layer 112 is a layer containing a material having hole transport properties. Examples of the hole transport material include, for example, 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB), N,N'-bis(3-methylphenyl)-N,N'-diphenyl- ​​​​​​​​1,1'-Biphenyl]-4,4'-diamine (abbreviation: TPD), 4,4',4''-tris (N,N-diphenylamino)triphenylamine (abbreviation: TDATA), 4,4' ,4''-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (abbreviation: MTDATA), 4,4'-bis[N-(spiro-9,9'-bifluorene -2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB), 4-phenyl-4 '-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP) and other aromatic amine compounds can be used. The substances described here have high hole transportability and are mainly substances having a hole mobility of 10 -6 cm 2 / Vs or more. Also, the organic compounds listed as hole transportable substances in the above composite materials can also be used for the hole transport layer 112 . In addition, polymer compounds such as poly(N-vinylcarbazole) (abbreviation: PVK) and poly(4-vinyl triphenylamine) (abbreviation: PVTPA) can also be used. . Note that the layer containing the hole transportable substance may be not only a single layer but also a laminate of two or more layers made of the above substances . .

[0118] The light-emitting layer 113 is a layer containing at least a light-emitting substance and a thermally activated delayed phosphor. Since the light-emitting layer 113 has the configuration as described in Embodiment 1, the light-emitting device in this embodiment can be a light-emitting device with very good luminous efficiency. For the main configuration of the light-emitting layer 113, refer to the description in Embodiment 1 . .

[0119] The light-emitting layer 113 having the above configuration can be co-evaporated by a vacuum evaporation method or as a mixed solution It can be produced by forming a film using an inkjet method, a spin coating method, a dip coating method, or the like. It can be achieved.

[0120] The electron transport layer 114 is a layer containing a material having electron transport properties. For example, tris(8-quinolinolato)aluminum (abbreviation: Alq), tris(4-methyl-8-quinolinolato) aluminum (abbreviation: Almq3), bis(10-hydroxybenzo[h]quinolinato) beryllium (abbreviation: BeBq2), bis(2-methyl-8-quinolinolato)(4-phenyl phenolato)aluminum (abbreviation: BAlq), etc., are layers composed of metal complexes having a quinoline skeleton or a benzoquinoline skeleton. In addition, other metal complexes such as bis[2-(2-hydroxy phenyl)benzoxazolato]zinc (abbreviation: Zn(BOX)2), bis[2-(2-hydroxy phenyl)benzothiazolato]zinc (abbreviation: Zn(BTZ)2), etc., having oxazole -based or thiazole-based ligands can also be used. Furthermore, in addition to metal complexes, 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-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl yl)-1,2,4-triazole (abbreviation: TAZ), bathophenanthroline (abbreviation: BP hen), bathocuproin (abbreviation: BCP), etc., can also be used. The substances described here have high electron transport properties and mainly have an electron mobility of 10 cm -6 / Vs or more. 2 It is a substance having the above properties. Yes. Note that the above-described electron-transporting thermally activated delayed phosphor may be used for the electron transport layer 114. Yes.

[0121] In addition, the electron transport layer 114 may be not only a single layer but also a layer in which two or more layers made of the above substances are laminated. Yes.

[0122] Also, a layer for controlling the movement of electrons may be provided between the electron transport layer and the light-emitting layer. This is a layer in which a small amount of a substance with high electron trapping property is added to a material with high electron transport property as described above. By suppressing the movement of electron carriers, it becomes possible to adjust the carrier balance. Such a configuration has a great effect on suppressing problems (for example, a decrease in the device lifetime) caused by electrons passing through the light-emitting layer. Yes. Yes. (For example, a decrease in device lifetime).

[0123] Also, an electron injection layer 115 may be provided between the electron transport layer 114 and the second electrode 102 in contact with the second electrode 102. As the electron injection layer 115, an alkali metal or an alkaline earth metal such as lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF2), or a compound thereof can be used. For example, a layer containing an alkali metal or an alkaline earth metal or a compound thereof in a layer made of a substance having electron transport properties can be used. Note that as the electron injection layer 115, by using a layer containing an alkali metal or an alkaline earth metal in a layer made of a substance having electron transport properties, electron injection from the second electrode 102 is more preferably performed efficiently. Yes. Yes. Yes. Yes. Yes. Yes. Yes.

[0124] As the material for forming the second electrode 102, a material with a small work function (specifically, less than 3.8 eV) For the lower layer, metals, alloys, electrically conductive compounds, and mixtures thereof can be used. Specific examples of such cathode materials include alkali metals such as lithium (Li) and cesium (Cs), and elements belonging to Group 1 or Group 2 of the periodic table such as magnesium (Mg), calcium (Ca), strontium (Sr), and alloys containing these (MgAg, AlLi), rare earth metals such as europium (Eu) and ytterbium (Yb), and alloys containing these. However, by providing an electron injection layer between the second electrode 102 and the electron transport layer, regardless of the work function, various conductive materials such as Al, Ag, ITO, indium tin oxide containing silicon or silicon oxide can be used as the second electrode 102. These conductive materials can be formed into films using methods such as sputtering, inkjet, or spin coating.

[0125] Also, as a method for forming the EL layer 103, various methods can be used regardless of whether it is a dry method or a wet method. For example, methods such as vacuum evaporation, inkjet, or spin coating can be used. Moreover, different film formation methods can be used for each electrode or each layer.

[0126] Regarding the electrodes, they can be formed by a wet method using the sol-gel method, or by a wet method using a paste of a metal material. Also, they can be formed by a dry method such as sputtering or vacuum evaporation.

[0127] In the light-emitting element having the above configuration, a current flows due to the potential difference generated between the first electrode 101 and the second electrode 102, and holes and electrons are generated in the light-emitting layer 113, which is a layer containing a light-emitting substance. recombine and emit light. That is, a light-emitting region is formed in the light-emitting layer 113 It has such a configuration.

[0128] The light emission is taken out to the outside through either one or both of the first electrode 101 and the second electrode 102. Therefore, either one or both of the first electrode 101 and the second electrode 102 are electrodes having translucency. When only the first electrode 101 is an electrode having translucency, the light emission is taken out through the first electrode 101. Also, when only the second electrode 102 is an electrode having translucency, the light emission is taken out through the second electrode 102. When both the first electrode 101 and the second electrode 102 are electrodes having translucency, the light emission is taken out from both through the first electrode 101 and the second electrode 102. Note that the configuration of the layer provided between the first electrode 101 and the second electrode 102 is not limited to the above. However, in order to suppress quenching caused by the proximity of the light-emitting region to the electrodes or the metal used in the carrier injection layer, a configuration in which a light-emitting region where holes and electrons recombine is provided at a site away from the first electrode 101 and the second electrode 102 is preferable.

[0129] Also, the hole transport layer or electron transport layer in contact with the light-emitting layer 113, particularly the carrier transport layer in contact with the light-emitting region in the light-emitting layer 113, is preferably composed of a material having a band gap larger than the band gap of the light-emitting substance in order to suppress energy transfer from the excitons generated in the light-emitting layer. The light-emitting element in the present embodiment is provided on a substrate made of glass, plastic, metal, etc.

[0130]

[0131] ​ The substrate through which the light from the light-emitting element passes has high translucency in the visible light region. It is used. As the order of fabrication on the substrate, they may be laminated in order from the side of the first electrode 101, or in order from the side of the second electrode 102. The light-emitting device may have one light-emitting element formed on one substrate, but a plurality of light-emitting elements may also be formed. By fabricating a plurality of such light-emitting elements on one substrate, an element-divided lighting device or a passive matrix type light-emitting device can be fabricated. Further, for example, a thin film transistor (TFT) may be formed on a substrate made of glass, plastic, etc., and a light-emitting element may be fabricated on an electrode electrically connected to the TFT. Thus, an active matrix type light-emitting device in which the driving of the light-emitting element is controlled by the TFT can be fabricated. Note that the structure of the TFT is not particularly limited. It may be a staggered type TFT or an inverted staggered type TFT. Also, the crystallinity of the semiconductor used for the TFT is not particularly limited, and an amorphous semiconductor or a crystalline semiconductor may be used. Further, the driving circuit formed on the TFT substrate may also be composed of N-type and P-type TFTs, or may consist of only either an N-type TFT or a P-type TFT. Note that this embodiment can be appropriately combined with other embodiments.

[0132]

[0133] (Embodiment 3) In this embodiment, an example in which the light-emitting element described in Embodiment 1 or Embodiment 2 is used as a lighting device will be described with reference to FIG. 3. FIG. 3(B) is a top view of the lighting device, and FIG. 3(A) is a cross-sectional view taken along the line e-f in FIG. 3(B).

[0134] In the lighting device according to this embodiment, a first electrode 401 is formed on a translucent substrate 400 that is a support. The first electrode 401 corresponds to the first electrode 10 in Embodiment 2.

[0135] An auxiliary electrode 402 is provided on the first electrode 401. In this embodiment, since an example of extracting light from the first electrode 401 side is shown, the first electrode 401 is formed of a translucent material . The auxiliary electrode 402 is provided to compensate for the low conductivity of the translucent material, and has a function of suppressing unevenness in luminance within the light-emitting surface caused by voltage drop due to the high resistance of the first electrode 401. The auxiliary electrode 402 is formed using a material having a higher conductivity than at least the material of the first electrode 401, and preferably formed using a material having a high conductivity such as aluminum . It is preferable that the surface of the auxiliary electrode 402 other than the portion in contact with the first electrode 401 is covered with an insulating layer. This is to suppress light emission from above the auxiliary electrode 402 that cannot be extracted, reduce the idle current, and suppress a decrease in power efficiency . Incidentally, a pad 412 for supplying a voltage to the second electrode 404 may be formed simultaneously with the formation of the auxiliary electrode 402 . .

[0136] An EL layer 403 is formed on the first electrode 401 and the auxiliary electrode 402. The EL layer 403 has the configuration described in Embodiment 1 or Embodiment 2. Incidentally, it is preferable to form the EL layer 403 slightly larger in plan view than the first electrode 401, because it can also serve as an insulating layer for suppressing a short circuit between the first electrode 401 and the second electrode 404 .

[0137] The second electrode 404 is formed to cover the EL layer 403. The second electrode 404 corresponds to the second electrode 102 in Embodiment 2 and has a similar configuration. In this embodiment, since light emission is taken out from the first electrode 401 side, the second electrode 404 is preferably formed of a material with high reflectivity. In this embodiment, it is assumed that voltage is supplied to the second electrode 404 by connecting it to the pad 412. This is equivalent to the second electrode 102 in Embodiment 2 and has a similar configuration. In this embodiment, since light emission is taken out from the first electrode 401 side, the second electrode 404 is preferably formed of a material with high reflectivity. This is equivalent to the second electrode 102 in Embodiment 2 and has a similar configuration. In this embodiment, since light emission is taken out from the first electrode 401 side, the second electrode 404 is preferably formed of a material with high reflectivity. This is equivalent to the second electrode 102 in Embodiment 2 and has a similar configuration. In this embodiment, since light emission is taken out from the first electrode 401 side, the second electrode 404 is preferably formed of a material with high reflectivity. This is equivalent to the second electrode 102 in Embodiment 2 and has a similar configuration. In this embodiment, since light emission is taken out from the first electrode 401 side, the second electrode 404 is preferably formed of a material with high reflectivity.

[0138] As described above, the lighting device in this embodiment includes a light-emitting element having the first electrode 401, the EL layer 403, and the second electrode 404 (and the auxiliary electrode 402). Since the light-emitting element is a light-emitting element with high luminous efficiency, the lighting device in this embodiment can be a lighting device with low power consumption. As described above, the lighting device in this embodiment includes a light-emitting element having the first electrode 401, the EL layer 403, and the second electrode 404 (and the auxiliary electrode 402). Since the light-emitting element is a light-emitting element with high luminous efficiency, the lighting device in this embodiment can be a lighting device with low power consumption. As described above, the lighting device in this embodiment includes a light-emitting element having the first electrode 401, the EL layer 403, and the second electrode 404 (and the auxiliary electrode 402). Since the light-emitting element is a light-emitting element with high luminous efficiency, the lighting device in this embodiment can be a lighting device with low power consumption. As described above, the lighting device in this embodiment includes a light-emitting element having the first electrode 401, the EL layer 403, and the second electrode 404 (and the auxiliary electrode 402). Since the light-emitting element is a light-emitting element with high luminous efficiency, the lighting device in this embodiment can be a lighting device with low power consumption.

[0139] The lighting device is completed by fixing and sealing the sealing substrate 407 using the sealing materials 405 and 406 for the light-emitting element having the above configuration. Either of the sealing materials 405 and 406 may be used. Also, a desiccant can be mixed into the inner sealing material 406, which can adsorb moisture and lead to an improvement in reliability. The lighting device is completed by fixing and sealing the sealing substrate 407 using the sealing materials 405 and 406 for the light-emitting element having the above configuration. Either of the sealing materials 405 and 406 may be used. Also, a desiccant can be mixed into the inner sealing material 406, which can adsorb moisture and lead to an improvement in reliability. The lighting device is completed by fixing and sealing the sealing substrate 407 using the sealing materials 405 and 406 for the light-emitting element having the above configuration. Either of the sealing materials 405 and 406 may be used. Also, a desiccant can be mixed into the inner sealing material 406, which can adsorb moisture and lead to an improvement in reliability. The lighting device is completed by fixing and sealing the sealing substrate 407 using the sealing materials 405 and 406 for the light-emitting element having the above configuration. Either of the sealing materials 405 and 406 may be used. Also, a desiccant can be mixed into the inner sealing material 406, which can adsorb moisture and lead to an improvement in reliability.

[0140] Also, a part of the pad 412, the first electrode 401, and the auxiliary electrode 402 can be extended outside the sealing materials 405 and 406 to serve as external input terminals. Also, an IC chip 420 with a converter or the like mounted thereon may be provided. Also, a part of the pad 412, the first electrode 401, and the auxiliary electrode 402 can be extended outside the sealing materials 405 and 406 to serve as external input terminals. Also, an IC chip 420 with a converter or the like mounted thereon may be provided. Also, a part of the pad 412, the first electrode 401, and the auxiliary electrode 402 can be extended outside the sealing materials 405 and 406 to serve as external input terminals. Also, an IC chip 420 with a converter or the like mounted thereon may be provided.

[0141] As described above, since the lighting device described in this embodiment has the light-emitting element described in Embodiment 1 or Embodiment 2 for the EL element, it can be a lighting device with high luminous efficiency and low power consumption. As described above, since the lighting device described in this embodiment has the light-emitting element described in Embodiment 1 or Embodiment 2 for the EL element, it can be a lighting device with high luminous efficiency and low power consumption. As described above, since the lighting device described in this embodiment has the light-emitting element described in Embodiment 1 or Embodiment 2 for the EL element, it can be a lighting device with high luminous efficiency and low power consumption.

[0142] (Embodiment 4) In this embodiment, a passive matrix type light-emitting device manufactured by applying the light-emitting element described in Embodiment 1 or Embodiment 2 will be described with reference to FIG. 4. FIG. 4(A) is a perspective view showing the light-emitting device, and FIG. 4(B) is a cross-sectional view obtained by cutting FIG. 4(A) along the X-Y plane. In FIG. 4, an EL layer 955 is provided between an electrode 952 and an electrode 956 on a substrate 951. The end of the electrode 952 is covered with an insulating layer 953. Then, a partition layer 954 is provided on the insulating layer 953. The side walls of the partition layer 954 have an inclination such that the distance between one side wall and the other side wall becomes narrower as it approaches the substrate surface. That is, the cross-section of the partition layer 954 in the short side direction is trapezoidal, and the bottom side (the side facing the same direction as the surface direction of the insulating layer 953 and in contact with the insulating layer 953) is shorter than the upper side (the side facing the same direction as the surface direction of the insulating layer 953 and not in contact with the insulating layer 953). By providing the partition layer 954 in this way, it is possible to prevent defects in the light-emitting element caused by static electricity or the like. Also, in the passive matrix type light-emitting device, by having the light-emitting element described in Embodiment 1 or Embodiment 2, it is possible to obtain an illumination device with high luminous efficiency and low power consumption.

[0143] (Embodiment 5) In this embodiment, an active matrix type light-emitting device manufactured by applying the light-emitting element described in Embodiment 1 or Embodiment 2 will be described with reference to FIG. 5.

[0144] FIGS. 5(A) and 5(B) show a light-emitting device that has been made full-color by providing a coloring layer or the like. This is an example. FIG. 5(A) shows a substrate 1001, an underlying insulating film 1002, a gate insulating film 1003 , gate electrodes 1006, 1007, 1008, a first interlayer insulating film 1020, a second interlayer insulating film 1021, a peripheral portion 1042, a pixel portion 1040, a driving circuit portion 1041, a first electrode 1024W of a light-emitting element, a first electrode 1024R, a first electrode 1024G, a first electrode 1024 B, a partition wall 1025, an EL layer 1028, a second electrode 1029 of the light-emitting element, a sealing substrate 1031 , sealing materials 1032a, 1032b, etc. are shown. A desiccant can also be mixed into the sealing material 1032b . Further, a colored layer (a red colored layer 1034R, a green colored layer 1034G, a blue colored layer 1034B) is provided on a transparent substrate 1033. Also, a black layer (black matrix) 1035 may be further provided. The transparent substrate 1033 on which the colored layer and the black layer are provided is aligned and fixed to the substrate 1001. Note that the colored layer and the black layer are covered with an overcoat layer 1036. Also, in this embodiment, there are a light-emitting layer in which light does not pass through the colored layer and exits to the outside, and a light-emitting layer in which light passes through the colored layers of each color and exits to the outside . Light that does not pass through the colored layer is white, and light that passes through the colored layer is red, blue, and green. Therefore, an image can be expressed with four-color pixels . . .

[0145] In addition, in the light-emitting device described above, a light-emitting device having a structure (bottom emission type) that extracts light from the side of the substrate 1001 on which the TFT is formed has been described. However, a light-emitting device having a structure (top emission type) that extracts light from the side of the sealing substrate 1031 may also be used . A cross-sectional view of a top emission type light-emitting device is shown in FIG. 6. In this case, the substrate 1001 uses a substrate that does not transmit light . . It is possible. Until a connection electrode connecting the TFT and the anode of the light-emitting element is formed, it is formed in the same manner as the bottom-emission type light-emitting device. After that, a third interlayer insulating film 1037 is formed to cover the electrode 1022. This insulating film may serve as a planarization layer. The third interlayer insulating film 1037 can be formed using the same material as the second interlayer insulating film 1021, as well as other known materials. In the case of a top-emission type light-emitting device as shown in FIG. 6, it is preferable that the first electrode is a reflective electrode. The configuration of the EL layer 1028 is the same as the configuration described in Embodiment 1 or Embodiment 2, and the element structure is such that white light emission can be obtained. As a configuration for obtaining white light emission, when two EL layers are used, a configuration in which blue light is obtained from the light-emitting layer in one EL layer and orange light is obtained from the light-emitting layer in the other EL layer, or a configuration in which blue light is obtained from the light-emitting layer in one EL layer and red and green lights are obtained from the light-emitting layer in the other EL layer, etc. can be considered. Also, when three EL layers are used, a light-emitting element that exhibits white light emission can be obtained by causing red, green, and blue light emissions to be obtained from the respective light-emitting layers. Of course, the configuration for obtaining white light emission is not limited to this if the configuration shown in Embodiment 1 or Embodiment 2 is applied. The first electrodes 1024W, 1024R, 1024G, and 1024B of the light-emitting element are anodes here, but they may be cathodes. The colored layer is provided on the optical path through which the light from the light-emitting element exits to the outside. In the case of a bottom-emission type light-emitting device as shown in FIG. 5(A), colored layers 1034R and 1034G are provided on the transparent substrate 1033. It can be formed.

[0146] The first electrodes 1024W, 1024R, 1024G, and 1024B of the light-emitting element are anodes here, but they may be cathodes. In the case of a top-emission type light-emitting device as shown in FIG. 6, it is preferable that the first electrode is a reflective electrode. The configuration of the EL layer 1028 is the same as the configuration described in Embodiment 1 or Embodiment 2, and the element structure is such that white light emission can be obtained. As a configuration for obtaining white light emission, when two EL layers are used, a configuration in which blue light is obtained from the light-emitting layer in one EL layer and orange light is obtained from the light-emitting layer in the other EL layer, or a configuration in which blue light is obtained from the light-emitting layer in one EL layer and red and green lights are obtained from the light-emitting layer in the other EL layer, etc. can be considered. Also, when three EL layers are used, a light-emitting element that exhibits white light emission can be obtained by causing red, green, and blue light emissions to be obtained from the respective light-emitting layers. Of course, the configuration for obtaining white light emission is not limited to this if the configuration shown in Embodiment 1 or Embodiment 2 is applied. The first electrodes 1024W, 1024R, 1024G, and 1024B of the light-emitting element are anodes here, but they may be cathodes. The colored layer is provided on the optical path through which the light from the light-emitting element exits to the outside. In the case of a bottom-emission type light-emitting device as shown in FIG. 5(A), colored layers 1034R and 1034G are provided on the transparent substrate 1033. The first electrodes 1024W, 1024R, 1024G, and 1024B of the light-emitting element are anodes here, but they may be cathodes. In the case of a top-emission type light-emitting device as shown in FIG. 6, it is preferable that the first electrode is a reflective electrode. The configuration of the EL layer 1028 is the same as the configuration described in Embodiment 1 or Embodiment 2, and the element structure is such that white light emission can be obtained. As a configuration for obtaining white light emission, when two EL layers are used, a configuration in which blue light is obtained from the light-emitting layer in one EL layer and orange light is obtained from the light-emitting layer in the other EL layer, or a configuration in which blue light is obtained from the light-emitting layer in one EL layer and red and green lights are obtained from the light-emitting layer in the other EL layer, etc. can be considered. Also, when three EL layers are used, a light-emitting element that exhibits white light emission can be obtained by causing red, green, and blue light emissions to be obtained from the respective light-emitting layers. Of course, the configuration for obtaining white light emission is not limited to this if the configuration shown in Embodiment 1 or Embodiment 2 is applied. The first electrodes 1024W, 1024R, 1024G, and 1024B of the light-emitting element are anodes here, but they may be cathodes. In the case of a top-emission type light-emitting device as shown in FIG. 6, it is preferable that the first electrode is a reflective electrode. The configuration of the EL layer 1028 is the same as the configuration described in Embodiment 1 or Embodiment 2, and the element structure is such that white light emission can be obtained. As a configuration for obtaining white light emission, when two EL layers are used, a configuration in which blue light is obtained from the light-emitting layer in one EL layer and orange light is obtained from the light-emitting layer in the other EL layer, or a configuration in which blue light is obtained from the light-emitting layer in one EL layer and red and green lights are obtained from the light-emitting layer in the other EL layer, etc. can be considered. Also, when three EL layers are used, a light-emitting element that exhibits white light emission can be obtained by causing red, green, and blue light emissions to be obtained from the respective light-emitting layers. Of course, the configuration for obtaining white light emission is not limited to this if the configuration shown in Embodiment 1 or Embodiment 2 is applied. The first electrodes 1024W, 1024R, 1024G, and 1024B of the light-emitting element are anodes here, but they may be cathodes. In the case of a top-emission type light-emitting device as shown in FIG. 6, it is preferable that the first electrode is a reflective electrode. The configuration of the EL layer 1028 is the same as the configuration described in Embodiment 1 or Embodiment 2, and the element structure is such that white light emission can be obtained. As a configuration for obtaining white light emission, when two EL layers are used, a configuration in which blue light is obtained from the light-emitting layer in one EL layer and orange light is obtained from the light-emitting layer in the other EL layer, or a configuration in which blue light is obtained from the light-emitting layer in one EL layer and red and green lights are obtained from the light-emitting layer in the other EL layer, etc. can be considered. Also, when three EL layers are used, a light-emitting element that exhibits white light emission can be obtained by causing red, green, and blue light emissions to be obtained from the respective light-emitting layers. Of course, the configuration for obtaining white light emission is not limited to this if the configuration shown in Embodiment 1 or Embodiment 2 is applied. The first electrodes 1024W, 1024R, 1024G, and 1024B of the light-emitting element are anodes here, but they may be cathodes. In the case of a top-emission type light-emitting device as shown in FIG. 6, it is preferable that the first electrode is a reflective electrode. The configuration of the EL layer 1028 is the same as the configuration described in Embodiment 1 or Embodiment 2, and the element structure is such that white light emission can be obtained. As a configuration for obtaining white light emission, when two EL layers are used, a configuration in which blue light is obtained from the light-emitting layer in one EL layer and orange light is obtained from the light-emitting layer in the other EL layer, or a configuration in which blue light is obtained from the light-emitting layer in one EL layer and red and green lights are obtained from the light-emitting layer in the other EL layer, etc. can be considered. Also, when three EL layers are used, a light-emitting element that exhibits white light emission can be obtained by causing red, green, and blue light emissions to be obtained from the respective light-emitting layers. Of course, the configuration for obtaining white light emission is not limited to this if the configuration shown in Embodiment 1 or Embodiment 2 is applied.

[0147] The colored layer is provided on the optical path through which the light from the light-emitting element exits to the outside. In the case of a bottom-emission type light-emitting device as shown in FIG. 5(A), colored layers 1034R and 1034G are provided on the transparent substrate 1033. The first electrodes 1024W, 1024R, 1024G, and 1024B of the light-emitting element are anodes here, but they may be cathodes. It can be provided by providing 1034B and fixing it to the substrate 1001. Also, As shown in FIG. 5(B), a colored layer may be provided between the gate insulating film 1003 and the first interlayer insulating film 1020. In the case of a top emission structure as shown in FIG. 6, a sealing substrate 1031 provided with a colored layer (red colored layer 1034R, green colored layer 1034G, blue colored layer 1034B) can also be used for sealing. A black layer (black matrix) 1035 may be provided on the sealing substrate 1031 so as to be located between pixels. The colored layer (red colored layer 1034R, green colored layer 1034G, blue colored layer 1034B) and the black layer (black matrix) may be covered with an overcoat layer 1036. The sealing substrate 1031 shall use a substrate having translucency. matrix) When a voltage is applied between a pair of electrodes of the light-emitting element thus obtained, a white light-emitting region 1044W is obtained. Also, by combining with the colored layer, a red light-emitting region 1044R, a blue

[0148] light-emitting region 1044B, and a green light-emitting region 1044G are obtained. Since the light-emitting device of this embodiment uses the light-emitting element described in Embodiment 1 or Embodiment 2, it is possible to realize a light-emitting device with a low driving voltage and low power consumption. light-emitting region 1044B, and a green light-emitting region 1044G are obtained. Since the light-emitting device of this embodiment uses the light-emitting element described in Embodiment 1 or Embodiment 2, it is possible to realize a light-emitting device with a low driving voltage and low power consumption. light-emitting region 1044B, and a green light-emitting region 1044G are obtained. Since the light-emitting device of this embodiment uses the light-emitting element described in Embodiment 1 or Embodiment 2, it is possible to realize a light-emitting device with a low driving voltage and low power consumption. device uses the light-emitting element described in Embodiment 1 or Embodiment 2, it is possible to realize a light-emitting device with a low driving voltage and low power consumption. device uses the light-emitting element described in Embodiment 1 or Embodiment 2, it is possible to realize a light-emitting device with a low driving voltage and low power consumption.

[0149] Also, although an example of full-color display using four colors of red, green, blue, and white has been shown here, it is not particularly limited and full-color display may be performed using three colors of red, green, and blue.

[0150] Also, this embodiment can be freely combined with other embodiments.

[0151] (Embodiment 6) In this embodiment, a light-emitting element including the light-emitting element described in Embodiment 1 or 2 as a part thereof is used. An example of a child device will be described. The light emitting device described in the first or second embodiment has a light emitting efficiency. As a result, the light-emitting element described in this embodiment has high efficiency and reduced power consumption. The device may be an electronic device having a light emitting portion with reduced power consumption.

[0152] As an electronic device to which the light-emitting element is applied, for example, a television set (television or television) (also called revision receivers), monitors for computers, digital cameras, digital Video cameras, digital photo frames, mobile phones (also called mobile phones or mobile phone devices) ), portable game machines, personal digital assistants, audio playback devices, large game machines such as pachinko machines, etc. Specific examples of these electronic devices are listed below.

[0153] 7A shows an example of a television device. The television device includes a housing 710 A display unit 7103 is built into the housing 1. The display unit 7103 displays images. The display portion 7103 can be formed using the light-emitting element described in Embodiment 1 or 2. The light emitting element is configured by arranging elements in a matrix. Therefore, the display portion 7103 including the light-emitting element can be used as a The television set can be a television set with reduced power consumption.

[0154] The television device can be operated using the operation switches on the housing 7101 or a separate remote control. This can be done by the operation key 7109 provided on the remote control operation device 7110. Thus, operations such as channel selection and volume adjustment can be performed, and the video displayed on the display unit 7103 can be operated. Further, the remote control operation unit 7110 may be configured to include a display unit 7107 for displaying information output from the remote control operation unit 7110.

[0155] FIG. 7(B1) shows a computer, which includes a main body 7201, a housing 7202, a display unit 7203, a keyboard 7204, an external connection port 7205, a pointing device 7206, etc. Note that this computer is manufactured by arranging light emitting elements in a matrix and using them for the display unit 7203, similar to those described in Embodiment 1 or Embodiment 2. FIG. 7( B1) shows a computer, which may be in the form shown in FIG. 7(B2). The computer shown in FIG. 7(B2) is provided with a second display unit 7210 instead of the keyboard 7204 and the pointing device 7206. The second display unit 7210 is a touch panel type, and input can be performed by operating the input display shown on the second display unit 7210 with a finger or a dedicated pen. Further, the second display unit 7210 can display not only input displays but also other images. The display unit 7203 may also be a touch panel. By connecting the two screens with a hinge, it is possible to prevent problems such as damage or breakage of the screens during storage or transportation. Note that this computer is manufactured by arranging light emitting elements in a matrix and using them for the display unit 7203, similar to those described in Embodiment 1 or Embodiment 2. The light emitting element is a light emitting element with good luminous efficiency. Thus, a display unit 7203 composed of the light emitting element can be obtained. The computer can be a computer with reduced power consumption.

[0156] FIG. 7(C) is a portable game machine, which is composed of two casings, a casing 7301 and a casing 7302, and is connected so as to be openable and closable by a connecting portion 7303. In the casing 7301, a display portion 7304 is incorporated, which is produced by arranging the light-emitting elements described in Embodiment 1 or Embodiment 2 in a matrix, and a display portion 7305 is incorporated in the casing 7302. Further, the portable game machine shown in FIG. 7(C) further includes a speaker portion 7306, a recording medium insertion portion 7307, an LED lamp 7308, input means (operation keys 7309, connection terminals 7310, sensors 73 11 (capable of measuring force, displacement, position, speed, acceleration, angular velocity, rotational speed, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor or infrared rays), a microphone 7312), etc. Of course, the configuration of the portable game machine is not limited to the above, and at least both or one of the display portion 73 04 and the display portion 7305 may use a display portion produced by arranging the light-emitting elements described in Embodiment 1 or Embodiment 2 in a matrix, and other accessory equipment can be provided as appropriate. The portable game machine shown in FIG. 7(C) has a function of reading a program or data recorded on a recording medium and displaying it on the display portion, and a function of performing wireless communication with other portable game machines to share information. Note that the functions of the portable game machine shown in FIG. 7(C) are not limited to this, and it can have various functions. A portable game machine having a display portion 7304 as described above uses the light-emitting elements used in the display portion 7304 FIG. 7(C) is a portable game machine, which is composed of two casings, a casing 7301 and a casing 7302, and is connected so as to be openable and closable by a connecting portion 7303. In the casing 7301, a display portion 7304 is incorporated, which is produced by arranging the light-emitting elements described in Embodiment 1 or Embodiment 2 in a matrix, and a display portion 7305 is incorporated in the casing 7302. Further, the portable game machine shown in FIG. 7(C) further includes a speaker portion 7306, a recording medium insertion portion 7307, Since the child has good luminous efficiency, it can be made into a portable game machine with reduced power consumption. Also, since the light-emitting element used in the display unit 7304 can be driven at a low driving voltage, it can be made into a portable game machine with a small driving voltage. Further, since the light-emitting element used in the display unit 7304 is a light-emitting element with a long lifespan, it can be made into a highly reliable portable game machine.

[0157] FIG. 7(D) shows an example of a mobile phone. The mobile phone includes, in addition to a display unit 7402 incorporated in a housing 7401, operation buttons 7403, an external connection port 7404, a speaker 74 05, a microphone 7406, and the like. Note that the mobile phone 7400 has a display unit 7402 manufactured by arranging the light-emitting elements described in Embodiment 1 or Embodiment 2 in a matrix form. The light-emitting element can be a light-emitting element with good luminous efficiency. Also, it can be a light-emitting element with a small driving voltage. Further, it can be a light-emitting element with a long lifespan. Therefore, the mobile phone having the display unit 7402 constituted by the light-emitting element can be made into a mobile phone with reduced power consumption. Also, it can be made into a mobile phone with a small driving voltage. Further, it can be made into a highly reliable mobile phone. .

[0158] The mobile phone shown in FIG. 7(D) can also be configured such that information can be input by touching the display unit 7402 with a finger or the like. In this case, operations such as making a call or creating an email can be performed by touching the display unit 7402 with a finger or the like.

[0159] The screen of the display unit 7402 mainly has three modes. The first is the display mode mainly for displaying images, the second is the input mode mainly for inputting information such as characters. The third is the display + input mode in which the two modes of the display mode and the input mode are mixed.

[0160] For example, when making a phone call or creating an email, the display unit 7402 may be set to the character input mode mainly for character input, and an input operation on the characters displayed on the screen may be performed. In this case , it is preferable to display a keyboard or number buttons on most of the screen of the display unit 7402.

[0161] In addition, by providing a detection device having sensors for detecting inclination such as a gyro and an acceleration sensor inside the mobile phone, the orientation (vertical or horizontal) of the mobile phone can be determined, and the screen display of the display unit 7402 can be automatically switched.

[0162] Also, the switching of the screen mode is performed by touching the display unit 7402 or operating the operation button 7403 of the housing 7401. It can also be switched according to the type of image displayed on the display unit 7402. For example, if the image signal displayed on the display unit is video data, it is switched to the display mode, and if it is text data, it is switched to the input mode.

[0163] In addition, in the input mode, the signal detected by the optical sensor of the display unit 7402 is detected, and when there is no input by the touch operation of the display unit 7402 for a certain period, the screen mode may be controlled to be switched from the input mode to the display mode.

[0164] The display unit 7402 can also function as an image sensor. For example, the display unit 74​​​​​​ By touching the palm or fingers on 02 and imaging the palm prints, fingerprints, etc., personal authentication can be performed. Also by using a backlight that emits near-infrared light or a light source for sensing that emits near-infrared light on the display unit, it is also possible to image finger veins, palm veins, etc.

[0165] Note that the configuration shown in this embodiment can be used by appropriately combining the configurations shown in Embodiments 1 to 5.

[0166] The electric stand 2003 shown in Fig. 8(A) is an example in which the light-emitting element described in Embodiment 1 or Embodiment 2 is used in an illumination device. The electric stand 2003 has a housing 2001 and a light source 2 002, and as the light source 2002, the light-emitting elements described in Embodiment 1 and Embodiment 2 are used. Fig. 8(B) is an example in which the light-emitting elements described in Embodiment 1 and Embodiment 2 are used as the indoor lighting device 3001 and the television device 3002. By using the light-emitting elements described in Embodiment 1 or Embodiment 2 in these lighting devices, it is possible to use them as lighting devices with reduced power consumption, or large-area lighting devices, or thin lighting devices.

[0167] The light-emitting elements described in Embodiment 1 or Embodiment 2 can also be mounted on the windshield or dashboard of an automobile. Fig. 9(A) shows an aspect in which the light-emitting elements described in Embodiment 1 and Embodiment 2 are used on the windshield or dashboard of an automobile.

[0168] The displays 5000 and 5001 are display devices equipped with the light-emitting elements described in Embodiment 1 or Embodiment 2 provided on the windshield of an automobile. Embodiment 1 or Embodiment 2 The light-emitting element described in can be used to make a so-called see-through display device where the opposite side can be seen through. In the case of a see-through display, even if it is installed on the windshield of an automobile, it can be installed without obstructing the view. When providing transistors or the like for driving, it is advisable to use transistors with light-transmitting properties, such as organic transistors made of organic semiconductor materials or transistors using oxide semiconductors.

[0169] Display 5002 is a display device equipped with the light-emitting element described in Embodiment 1 or Embodiment 2 provided in the pillar portion. By projecting the video from the imaging means provided on the vehicle body onto Display 5002, the view blocked by the pillar can be complemented. Similarly, Display 5003 provided in the dashboard portion can compensate for the view blocked by the vehicle body by projecting the video from the imaging means provided outside the vehicle, thereby making up for the blind spot and enhancing safety. By projecting the video to complement the invisible part, safety confirmation can be performed more naturally without a sense of discomfort.

[0170] Displays 5004 and 5005 can provide various other information, such as navigation information, speedometers, tachometers, driving distance, fuel supply amount, gear state, air conditioner settings, etc. The display can appropriately change its display items and layout according to the user's preference. In addition, this information can also be provided on Displays 5000 to 5003. Moreover, Displays 5000 to 5005 can also be used as lighting devices.

[0171] Also, as shown in Fig. 9(B), the light-emitting element described in Embodiment 1 or Embodiment 2 may be applied to the display portion of the license plate 5011. Thereby, the visibility of the license plate 501 1 can be improved.

[0172] Also, as shown in Fig. 9(C), the light-emitting element described in Embodiment 1 or Embodiment 2 may be mounted on the hands 5021 and the display portion 5022 of the wristwatch. Thereby, without using radioactive substances such as tritium as in the conventional luminous wristwatch, the visibility in the dark can be improved and.

[0173] As described above, the application range of the light-emitting device provided with the light-emitting element described in Embodiment 1 or Embodiment 2 is extremely wide, and this light-emitting device can be applied to electronic devices in all fields. By using the light-emitting element described in Embodiment 1 or Embodiment 2, an electronic device with low power consumption can be obtained .

Example

[0174] In this example, the results of actually fabricating and comparing a light-emitting element using a mixture of a thermally activated delayed phosphor and a material that emits fluorescence for the light-emitting layer, and a comparative light-emitting element using a mixture of a material that does not emit thermally activated delayed fluorescence and a material that emits fluorescence for the light-emitting layer will be described with reference to Figs. 11 to 15 . Hereinafter, the light-emitting element 1 is a light-emitting element using a mixture of a thermally activated delayed phosphor and a material that emits fluorescence for the light-emitting layer. Also, the comparative light-emitting element 1 is a light-emitting element using a mixture of a material that does not have thermally activated delayed fluorescence and a material that emits fluorescence for the light-emitting layer .

[0175] Hereinafter, the light-emitting element 1 is a light-emitting element in which a thermally activated delayed phosphor and a material that emits fluorescence are mixed and used in the light-emitting layer. Also, the comparative light-emitting element 1 is a light-emitting element in which a material that does not have thermally activated delayed fluorescence and a material that emits fluorescence are mixed and used in the light-emitting layer .

[0176] ​​​The materials that emit fluorescence used in the light-emitting element 1 and the comparative light-emitting element 1 are 5,6,11,12-tetra triphenylnaphthacene (common name: rubrene).

[0177] In the light-emitting element 1, as a thermally activated delayed phosphor, two kinds of organic compounds that form an exciplex were used. Specifically, as the first organic compound, 2-[3-(dibenzothiophen- 4-yl)phenyl]dibenz[f,h]quinoxaline (abbreviation: 2mDBTPDBq-I I) was used, and as the second organic compound, 2-[N-(9-phenylcarbazol-3-yl )-N-phenylamino]spiro-9,9'-bifluorene (abbreviation: PCASF) was used .

[0178] In the comparative light-emitting element 1, as a material that does not emit thermally activated delayed fluorescence, 2-[3-(dibenzothio phen-4-yl)phenyl]dibenz[f,h]quinoxaline (abbreviation: 2mDBTPD Bq-II) was used. That is, as a material that does not emit thermally activated delayed fluorescence, only the first organic compound in the light-emitting element 1 was used.

[0179] The chemical formulas of the materials used in this example are shown below.

[0180] [Chemical formula]

[0181] The manufacturing methods of the light-emitting element 1 and the comparative light-emitting element 1 are shown below.

[0182] (Light-emitting element 1) First, indium tin oxide (ITSO) containing silicon oxide was formed on the glass substrate 1100 by sputtering to form a first electrode 1101 that functions as an anode. Note that The film thickness was set to 110 nm, and the electrode area was set to 2 mm × 2 mm (see Fig. 11).

[0183] Next, as a pretreatment for forming a light-emitting element on the substrate 1100, the substrate surface was washed with water , baked at 200 °C for 1 hour, and then subjected to UV ozone treatment for 370 seconds.

[0184] Thereafter, the substrate was introduced into a vacuum evaporation apparatus whose interior was evacuated to about 10 -4 Pa, and vacuum baking was performed at 170 °C for 30 minutes in the heating chamber of the vacuum evaporation apparatus. Then, the substrate 1100 was allowed to cool for about 3 0 minutes.

[0185] Next, with the surface on which the first electrode 1101 was formed facing downward, the substrate 1100 on which the first electrode 1101 was formed was fixed to a substrate holder provided in the vacuum evaporation apparatus, and after evacuating to about 10 Pa, 1,3,5-tri(dibenzothiophen-4-yl)-benzene (abbreviation: DBT3P-II) and molybdenum oxide were co-evaporated on the first electrode 1101 -4 P to form a hole injection layer 1111. The film thickness was set to 40 nm, and the ratio of DBT3P-II to molybdenum oxide was adjusted to a mass ratio of 1:0.5 (= DBT3P-II: molybdenum oxide) . The ratio of DBT3P-II to molybdenum oxide was adjusted to a mass ratio of 1:0.5 (= DBT3P-II: molybdenum oxide).

[0186] Next, BPAFLP (abbreviation) was formed into a film with a film thickness of 20 nm on the hole injection layer 1111 to form a hole transport layer 1112.

[0187] Furthermore, 2mDBTPDBq-II (abbreviation), PCASF (abbreviation), and rubrene were co-evaporated to form a light-emitting layer 1113 on the hole transport layer 1112. Here, the weight ratio of 2mDBTPDB q-II, PCASF, and rubrene was 0.8:0.2:0.01 (= 2m​ It was adjusted so that it became DBTPDBq-II:PCASF:rubrene). Also, the light-emitting layer 1 The film thickness of 113 was 30 nm.

[0188] Next, 2mDBTPDBq-II (abbreviation) was formed into a film with a film thickness of 20 nm on the light-emitting layer 1113 to form the first electron transport layer 1114a.

[0189] Next, bathophenanthroline (abbreviation: BPhen) was formed into a film with a film thickness of 20 nm on the first electron transport layer 1114a to form the second electron transport layer 1114b.

[0190] Furthermore, lithium fluoride (LiF) was vapor-deposited with a film thickness of 1 nm on the second electron transport layer 1114b to form the electron injection layer 1115.

[0191] Finally, as the second electrode 1103 functioning as a cathode, aluminum was vapor-deposited with a film thickness of 200 nm to fabricate the light-emitting device 1 of this example.

[0192] (Comparative light-emitting device 1) The light-emitting layer 1113 of the comparative light-emitting device 1 was formed by co-vapor deposition of 2mDBTPDBq-II (abbreviation) and rubrene Here, the weight ratio of 2mDBTPDBq-II (abbreviation) and rubrene was adjusted so that it became 1:0.01 (=2mDBTPDBq-II:rubrene). Also, the film thickness of the light-emitting layer 1113 was 30 nm. Except for the light-emitting layer 1113, the light-emitting device was fabricated in the same manner as the light-emitting device 1. In addition, in the above-described vapor deposition process, all vapor depositions used the resistance heating method.

[0193] The device structures of the light-emitting device 1 and the comparative light-emitting device 1 obtained as described above are shown in Table 1.

[0194] The device structures of the light-emitting device 1 and the comparative light-emitting device 1 obtained as described above are shown in Table 1.

[0195]

Table 1

[0196] These light-emitting elements were sealed in a glove box under a nitrogen atmosphere so that the light-emitting elements were not exposed to the air, and then the operating characteristics of the light-emitting elements were measured. Note that the measurement was performed at room temperature (atmosphere maintained at 25°C).

[0197] The voltage-luminance characteristics of Light-Emitting Element 1 and Comparative Light-Emitting Element 1 are shown in FIG. 12. In FIG. 12, the horizontal axis represents the voltage (V), and the vertical axis represents the luminance (cd / m 2 ²). Also, the luminance-current efficiency characteristics are shown in FIG. 1 3. In FIG. 13, the horizontal axis represents the luminance (cd / m 2 ²), and the vertical axis represents the current efficiency (cd / A ). Also, the luminance-power efficiency characteristics are shown in FIG. 14. In FIG. 14, the horizontal axis represents the luminance (cd / m 2 ²), and the vertical axis represents the power efficiency (lm / W). Also, the luminance-external quantum efficiency is shown in FIG. 15 . In FIG. 15, the horizontal axis represents the luminance (cd / m 2 ²), and the vertical axis represents the external quantum efficiency (%).

[0198] Also, the voltage (V), current density (mA / cm 2 ²), CIE chromaticity coordinates (x, y), current efficiency (cd / A ), power efficiency (lm / W), and external quantum efficiency (%) near a luminance of 1000 cd / m 2 ² for Light-Emitting Element 1 and Comparative Light-Emitting Element 1 are shown in Table 2.

[0199]

Table 2

[0200] As shown in Table 2, at a luminance of 1000 cd / m 2 ​​The CIE chromaticity coordinates of the light-emitting element 1 at around are (x , y) = (0.47, 0.52), and the comparative light-emitting element 2 1 at around a luminance of 1000 cd / m had CIE chromaticity coordinates of (x, y) = (0.46, 0.50). From this result, it was found that the light-emitting element 1 and the comparative light-emitting element 1 obtained yellow light emission derived from rubrene.

[0201] As can be seen from Table 2 and FIGS. 12 to 15, the light-emitting element 1 had a lower threshold voltage (light emission start voltage) for starting light emission compared with the comparative light-emitting element 1, and showed high values in current efficiency, power efficiency, and external quantum efficiency. Since 2mDBTPDBq-II and PC ASF used in the light-emitting layer 1113 form an exciplex, a singlet excited state of the exciplex is generated from a part of the triplet excited state of the exciplex in the light-emitting layer 1113. The energy of this singlet excited state of the exciplex moves to the singlet excited state of the material that emits fluorescence, which is considered to lead to an improvement in light emission efficiency. Also, it is considered that the light emission start voltage decreased due to the influence of the formation of this exciplex.

Example

[0202] In this example as well, in the same manner as in Example 1, a light-emitting element using a mixture of a thermally activated delayed phosphor and a material that emits fluorescence in the light-emitting layer, and a comparative light-emitting element using a mixture of a material that does not emit thermally activated delayed fluorescence and a material that emits fluorescence in the light-emitting layer were actually fabricated and compared, and the results will be described with reference to FIGS. 1 6 to 22.

[0203] Hereinafter, the light-emitting element 2 is a light-emitting element using a mixture of a thermally activated delayed phosphor and a material that emits fluorescence in the light-emitting layer. Also, the comparative light-emitting element 2 is a material that does not have thermally activated delayed fluorescence and emits fluorescence ​​​​​​​​ It is made into a light-emitting element used for a light-emitting layer by mixing with a material to be used.

[0204] The material that emits fluorescence used in the light-emitting element 2 and the comparative light-emitting element 2 is 5,6,11,12-tetra triphenylnaphthacene (common name: rubrene).

[0205] In the light-emitting element 2, as a thermally activated delayed phosphor, two kinds of organic compounds forming an exciplex were used. Specifically, 4,6-bis[3-(9H-carbazol-9-yl)phenyl]pyrimidine (abbreviation: 4,6mCzP2Pm) was used as the first organic compound, and N-(1,1'-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluorene-2-amine (abbreviation: PCBBiF) was used as the second organic compound.

[0206] In the comparative light-emitting element 2, 4,6-bis[3-(9H-carbazol-9-yl)phenyl]pyrimidine (abbreviation: 4,6mCzP2Pm) was used as a material that does not emit thermally activated delayed fluorescence. That is, only the first organic compound in the light-emitting element 2 was used as a material that does not emit thermally activated delayed fluorescence.

[0207]

[0208] The chemical formulas of the materials used in this example are shown below.

[0208]

Chemical formula

[0209] The manufacturing methods of the light-emitting element 2 and the comparative light-emitting element 2 are shown below.

[0210] (Light-emitting element 2) First, on a glass substrate 1100, under the same materials and conditions as the light-emitting element 1, a first electrode 11 01, a hole injection layer 1111, and a hole transport layer 1112 were formed.

[0211] Next, 4,6mCzP2Pm (abbreviation), PCBBiF (abbreviation), and rubrene were co-evaporated to form a light-emitting layer 1113 on the hole transport layer 1112. Here, the weight ratio of 4,6mCzP2Pm, PCBBiF, and rubrene was adjusted to 0.8:0.2:0.0075 (= 4,6mC zP2Pm:PCBBiF:rubrene). Also, the film thickness of the light-emitting layer 1113 was set to 40 nm.

[0212] Next, 4,6mCzP2Pm (abbreviation) was formed into a film with a film thickness of 10 nm on the light-emitting layer 1113 to form a first electron transport layer 1114a.

[0213] Next, on the first electron transport layer 1114a, bathophenanthroline (abbreviation: BPhen) was formed into a film with a film thickness of 15 nm to form a second electron transport layer 1114b.

[0214] Furthermore, under the same materials and conditions as the light-emitting element 1, an electron injection layer 1115 and a second electrode were formed to fabricate the light-emitting element 2 of this example.

[0215] (Comparative light-emitting element 2) The light-emitting layer 1113 of the comparative light-emitting element 2 was formed by co-evaporating 4,6mCzP2Pm (abbreviation) and rubrene. Here, the weight ratio of 4,6mCzP2Pm and rubrene was adjusted to 1 :0.005 (= 4,6mCzP2Pm:rubrene). Also, the film thickness of the light-emitting layer 1113 was set to 40 nm. Except for the light-emitting layer 1113, it was fabricated in the same manner as the light-emitting element 2.

[0216] In the above-described deposition process, the deposition was all carried out by resistance heating.

[0217] The element structures of the thus obtained light-emitting element 2 and comparative light-emitting element 2 are shown in Table 3.

[0218] [Table 3]

[0219] These light emitting devices were placed in a glove box with a nitrogen atmosphere, and the light emitting devices were exposed to the atmosphere. After sealing the device to prevent leakage, the operating characteristics of the light-emitting device were measured. The measurements were carried out at room temperature (atmosphere maintained at 25°C).

[0220] FIG. 16 shows the voltage-luminance characteristics of the light-emitting element 2 and the comparative light-emitting element 2. The vertical axis represents voltage (V) and the vertical axis represents brightness (cd / m 2 ) and the luminance-current efficiency characteristics are shown in Figure 1. 7. In FIG. 17, the horizontal axis represents luminance (cd / m 2 ) and the vertical axis is the current efficiency (cd / A) The voltage-current characteristics are shown in Figure 18. In Figure 18, the horizontal axis represents voltage (V), The vertical axis represents the current (mA). The luminance vs. power efficiency characteristics are shown in Figure 19. , the horizontal axis is luminance (cd / m 2 ) and the vertical axis shows the power efficiency (lm / W). The photoelectric efficiency is shown in Figure 20. In Figure 20, the horizontal axis represents the luminance (cd / m 2 ) and the vertical axis is the external quantum Efficiency (%) is shown.

[0221] Furthermore, the luminance of the light-emitting element 2 and the comparative light-emitting element 2 was 1000 cd / m 2 Electricity when nearby Voltage (V), current density (mA / cm 2) CIE chromaticity coordinates (x, y), current efficiency (cd / A ) Power efficiency (lm / W), and external quantum efficiency (%) are shown in Table 4.

[0222]

Table 4

[0223] As shown in Table 4, the CIE chromaticity coordinates of the light-emitting element 2 near a luminance of 1000 cd / m 2 are (x, y ) = (0.47, 0.52), and the CIE chromaticity coordinates of the comparative light-emitting 2 element 2 at the time of luminance near 1000 cd / m were (x, y) = (0.47, 0.50).

[0224] Also, the emission spectra of the light-emitting element 2 and the comparative light-emitting element 2 when a current of 0.1 mA was passed through them are shown in Fig. 21. In Fig. 21, the vertical axis represents the emission intensity (in arbitrary units), and the horizontal axis represents the wavelength (nm). . The emission intensity is shown as a relative value with the maximum emission intensity set to 1. As shown in Fig. 21, the emission spectra of the light-emitting element 2 and the comparative light-emitting element 2 have a spectrum derived from rubrene with a maximum emission wavelength near 558 nm. Combined with the results in Table 4, it was found that the light-emitting element 2 and the comparative light-emitting element 2 are light-emitting elements that exhibit yellow emission.

[0225] Also, with the initial luminance set to 5000 cd / m 2 and under the condition of constant current density, the light-emitting element 2 and the comparative light-emitting element 2 were driven, and the results of the reliability test are shown in Fig. 22. In Fig. 22, the change in the normalized luminance with the initial luminance set to 100% is shown.

[0226] From the results of Table 4 and Figs. 16 to 22, the light-emitting element 2 starts emitting light earlier than the comparative light-emitting element 2. The turn-on threshold voltage (light emission start voltage) is low, and high values are shown in terms of current efficiency, power efficiency, and external quantum efficiency. Furthermore, it was found to be a light-emitting element with good reliability and a small decrease in luminance with driving time.

[0227] Since 4,6mCzP2Pm and PCBBiF used in the light-emitting layer 1113 form an exciplex, the singlet excited state of the exciplex is generated from a part of the triplet excited state of the exciplex in the light-emitting layer 1113. It is considered that the energy of the singlet excited state of this exciplex is transferred to the singlet excited state of the material that emits fluorescence, leading to an improvement in light emission efficiency. Also, due to the influence of the formation of this exciplex, the light emission start voltage is considered to have decreased.

Example

[0228] Also in this example, similar to Example 1, a light-emitting element using a mixture of a thermally activated delayed phosphor and a material that emits fluorescence in the light-emitting layer, and a comparative light-emitting element using a mixture of a material that does not emit thermally activated delayed fluorescence and a material that emits fluorescence in the light-emitting layer were actually fabricated and compared. The results will be described with reference to FIGS. 2 3 to 29.

[0229] Hereinafter, the light-emitting element 3 is a light-emitting element using a mixture of a thermally activated delayed phosphor and a material that emits fluorescence in the light-emitting layer. Also, the comparative light-emitting element 3 is a light-emitting element using a mixture of a material that does not have thermally activated delayed fluorescence and a material that emits fluorescence in the light-emitting layer.

[0230] The material that emits fluorescence used in the light-emitting element 3 and the comparative light-emitting element 3 is coumarin 6 (common name).

[0231] In the light-emitting element 3, as the thermally activated delayed phosphor, the same combination that forms an exciplex as in Example 2 is used. ​​​​​​​​Two types of organic compounds were used. Specifically, as the first organic compound, 4,6-bis[3- (9H-carbazol-9-yl)phenyl]pyrimidine (abbreviation: 4,6mCzP2Pm ) was used, and as the second organic compound, N-(1,1'-biphenyl-4-yl)-N-[4 -(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9 H-fluorene-2-amine (abbreviation: PCBBiF) was used.

[0232] In Comparative Light-Emitting Device 3, as a material that does not emit thermally activated delayed fluorescence, the same 4,6-bis [3-(9H-carbazol-9-yl)phenyl]pyrimidine (abbreviation: 4,6mCz P2Pm) as in Example 2 was used. That is, as a material that does not emit thermally activated delayed fluorescence, only the first organic compound in Light-Emitting Device 3 was used.

[0233] For the chemical formulas of the materials used in this example, refer to the chemical formulas of Example 2.

[0234] The manufacturing methods of Light-Emitting Device 3 and Comparative Light-Emitting Device 3 are shown below.

[0235] (Light-Emitting Device 3) First, on a glass substrate 1100, a first electrode 11 01, a hole injection layer 1111, and a hole transport layer 1112 were formed using the same materials and conditions as in Light-Emitting Device 1.

[0236] Next, 4,6mCzP2Pm (abbreviation), PCBBiF (abbreviation), and coumarin 6 were co-evaporated to form a light-emitting layer 1113 on the hole transport layer 1112. Here, the weight ratio of 4,6mCzP2Pm , PCBBiF, and coumarin 6 was adjusted to 0.8:0.2:0.005 (= 4,6m CzP2Pm:PCBBiF:coumarin 6). Also, the thickness of the light-emitting layer 111 The film thickness of 3 was set to 40 nm.

[0237] Next, 4,6mCzP2Pm (abbreviation) was formed into a film on the light-emitting layer 1113 with a film thickness of 10 nm to form the first electron transport layer 1114a.

[0238] Next, on the first electron transport layer 1114a, bathophenanthroline (abbreviation: BPhen) was formed into a film with a film thickness of 15 nm to form the second electron transport layer 1114b.

[0239] Furthermore, with the same materials and conditions as the light-emitting element 1, an electron injection layer 1115 and a second electrode were formed to fabricate the light-emitting element 3 of this example.

[0240] (Comparative light-emitting element 3) The light-emitting layer 1113 of the comparative light-emitting element 3 was formed by co-evaporating 4,6mCzP2Pm (abbreviation) and coumarin 6. Here, the weight ratio of 4,6mCzP2Pm and coumarin 6 was adjusted to 1:0.005 (= 4,6mCzP2Pm: coumarin 6). Also the film thickness of the light-emitting layer 1113 was set to 40 nm. Except for the light-emitting layer 1113, it was fabricated in the same manner as the light-emitting element 3 and fabricated.

[0241] In the evaporation process described above, all evaporation was performed using the resistance heating method.

[0242] The element structures of the light-emitting element 3 and the comparative light-emitting element 3 obtained as described above are shown in Table 5.

[0243]

Table 5

[0244] These light-emitting elements were placed in a glove box under a nitrogen atmosphere where the light-emitting elements were exposed to the atmosphere After performing the operation of sealing so as not to allow it, the operating characteristics of the light-emitting element were measured. Note that the measurement was performed at room temperature (atmosphere maintained at 25°C).

[0245] The voltage-luminance characteristics of the light-emitting element 3 and the comparative light-emitting element 3 are shown in FIG. 23. In FIG. 23, the horizontal axis represents voltage (V), and the vertical axis represents luminance (cd / m 2 ²). Also, the luminance-current efficiency characteristics are shown in FIG. 2 4. In FIG. 24, the horizontal axis represents luminance (cd / m 2 ²), and the vertical axis represents current efficiency (cd / A ). Also, the voltage-current characteristics are shown in FIG. 25. In FIG. 25, the horizontal axis represents voltage (V), and the vertical axis represents current (mA). Also, the luminance-power efficiency characteristics are shown in FIG. 26. In FIG. 26 , the horizontal axis represents luminance (cd / m 2 ²), and the vertical axis represents power efficiency (lm / W). Also, the luminance-external quantum efficiency is shown in FIG. 27. In FIG. 27, the horizontal axis represents luminance (cd / m 2 ²), and the vertical axis represents external quantum efficiency (%).

[0246] Also, the voltage (V), current density (mA / cm 2 ²), CIE chromaticity coordinates (x, y), current efficiency (cd / A ), power efficiency (lm / W), and external quantum efficiency (%) of the light-emitting element 3 and the comparative light-emitting element 3 at around a luminance of 1000 cd / m 2 ² are shown in Table 6. ) and power efficiency (lm / W) and external quantum efficiency (%) are shown in Table 6.

[0247]

Table 6

[0248] As shown in Table 6, the CIE chromaticity coordinates of the light-emitting element 3 around a luminance of 1000 cd / m 2 ² are (x, y ) = (0.28, 0.60), and at the luminance around 1000 cd / m 2 ² of the comparative light-emitting The CIE chromaticity coordinates of the element 3 were (x, y) = (0.26, 0.58).

[0249] In addition, the emission spectra of the light-emitting element 3 and the comparative light-emitting element 3 when a current of 0.1 mA was passed through them are shown in Fig. 28. In Fig. 28, the vertical axis represents the emission intensity (in arbitrary units), and the horizontal axis represents the wavelength (nm). The emission intensity is shown as a relative value with the maximum emission intensity being 1. As shown in Fig. 28, the emission spectra of the light-emitting element 3 and the comparative light-emitting element 3 had a maximum emission wavelength near 500 nm and exhibited a spectrum derived from Chlorophyll 6. Combined with the results in Table 6, it was found that the light-emitting element 3 and the comparative light-emitting element 3 are light-emitting elements that exhibit green emission.

[0250] Also, with the initial luminance being 5000 cd / m 2 and under the condition of constant current density, the results of driving the light-emitting element 3 and the comparative light-emitting element 3 and conducting a reliability test are shown in Fig. 29. Fig. 29 shows the change in the normalized luminance with the initial luminance set to 100%.

[0251] From the results of Table 6 and Figs. 23 to 29, the light-emitting element 3 has a lower threshold voltage (emission start voltage) for starting emission compared to the comparative light-emitting element 3, and shows high values in terms of current efficiency, power efficiency, and external quantum efficiency. Furthermore, it was found that the light-emitting element 3 is a light-emitting element with good reliability and a small decrease in luminance with driving time.

[0252] Since 4,6mCzP2Pm and PCBBiF used in the light-emitting layer 1113 form an exciplex, a singlet excited state of the exciplex is generated from a part of the triplet excited state of the exciplex in the light-emitting layer 1113. The energy of this singlet excited state of the exciplex is that of the singlet It is considered that moving to the excited state leads to an improvement in luminous efficiency. Also, due to the influence of the formation of this excited complex, it is considered that the turn-on voltage of luminescence has decreased.

Example

[0253] Also in this example, in the same manner as in Example 1, a light-emitting element using a mixture of a thermally activated delayed phosphor and a material that emits fluorescence for the light-emitting layer, and a comparative light-emitting element using a mixture of a material that does not emit thermally activated delayed fluorescence and a material that emits fluorescence for the light-emitting layer were actually fabricated and compared, and the results will be described with reference to FIGS. 30 to 35.

[0254] Hereinafter, the light-emitting element 4 is a light-emitting element using a mixture of a thermally activated delayed phosphor and a material that emits fluorescence for the light-emitting layer. Also, the comparative light-emitting element 4 is a light-emitting element using a mixture of a material that does not have thermally activated delayed fluorescence and a material that emits fluorescence for the light-emitting layer.

[0255] The material that emits fluorescence used in the light-emitting element 3 and the comparative light-emitting element 3 is {2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCJTB).

[0256] In the light-emitting element 4, as the thermally activated delayed phosphor, two kinds of organic compounds in a combination that forms the same excited complex as in Example 2 were used. Specifically, as the first organic compound, 4,6-bis[3-(9H-carbazol-9-yl)phenyl]pyrimidine (abbreviation: 4,6mCzP2Pm) was used, and as the second organic compound, N-(1,1'-biphenyl-4-yl)-N-[4 ​​​​​​​​​​​​-[(9-Phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9 H-fluorene-2-amine (abbreviation: PCBBiF) was used.

[0257] In Comparative Light-Emitting Element 4, as a material that does not emit thermally activated delayed fluorescence, the same 4,6-bis [3-(9H-carbazol-9-yl)phenyl]pyrimidine (abbreviation: 4,6mCz P2Pm) was used. That is, as a material that does not emit thermally activated delayed fluorescence, only the first organic compound in Light-Emitting Element 4 was used.

[0258] Regarding the chemical formulas of the materials used in this example, refer to the chemical formulas in Example 2.

[0259] The manufacturing methods of Light-Emitting Element 4 and Comparative Light-Emitting Element 4 are shown below.

[0260] (Light-Emitting Element 4) First, on a glass substrate 1100, a first electrode 11 01, a hole injection layer 1111, and a hole transport layer 1112 were formed under the same materials and conditions as in Light-Emitting Element 1.

[0261] Next, 4,6mCzP2Pm (abbreviation), PCBBiF (abbreviation), and DCJTB (abbreviation) were co-evaporated to form a light-emitting layer 1113 on the hole transport layer 1112. Here, the weight ratio of 4,6mCz P2Pm, PCBBiF, and DCJTB was adjusted to 0.8:0.2:0.005 (= 4,6mCzP2Pm:PCBBiF:DCJTB). Also, the film thickness of the light-emitting layer 1113 was set to 40 nm.

[0262] Next, 4,6mCzP2Pm (abbreviation) was formed into a film with a film thickness of 10 nm on the light-emitting layer 1113 to form a first electron transport layer 1114a.

[0263] Next, bathophenanthroline (abbreviation: BPhen) was formed on the first electron transport layer 1114a to form a film with a thickness of 15 nm, thereby forming the second electron transport layer 1114b.

[0264] Furthermore, an electron injection layer 1115 and a second electrode were formed under the same materials and conditions as those of the light-emitting element 1, thereby fabricating the light-emitting element 4 of this example.

[0265] (Comparative light-emitting element 4) The light-emitting layer 1113 of the comparative light-emitting element 3 was formed by co-evaporating 4,6mCzP2Pm (abbreviation) and DCJTB ( abbreviation). Here, the weight ratio of 4,6mCzP2Pm and DCJTB was adjusted to be 1:0.0 ( =4,6mCzP2Pm:DCJTB). Also, the thickness of the light-emitting layer 1113 was set to 40 nm. Except for the light-emitting layer 1113, the comparative light-emitting element 3 was fabricated in the same manner as the light-emitting element 4.

[0266] In the above-described evaporation process, all evaporations were performed using the resistance heating method.

[0267] The element structures of the light-emitting element 4 and the comparative light-emitting element 4 obtained as described above are shown in Table 7.

[0268]

Table 7

[0269] After these light-emitting elements were sealed in a glove box under a nitrogen atmosphere so that the light-emitting elements were not exposed to the air, the operating characteristics of the light-emitting elements were measured. Note that the measurement was performed at room temperature (atmosphere maintained at 25°C).

[0270] The voltage-luminance characteristics of the light-emitting element 3 and the comparative light-emitting element 3 are shown in FIG. 30. In FIG. 30, the horizontal ​​The horizontal axis represents voltage (V), and the vertical axis represents luminance (cd / m 2 ). The luminance-current efficiency characteristics are shown in FIG. 3 1. In FIG. 31, the horizontal axis represents luminance (cd / m 2 ), and the vertical axis represents current efficiency (cd / A) . The voltage-current characteristics are shown in FIG. 32. In FIG. 32, the horizontal axis represents voltage (V), and the vertical axis represents current (mA). The luminance-power efficiency characteristics are shown in FIG. 33. In FIG. 33 , the horizontal axis represents luminance (cd / m 2 ), and the vertical axis represents power efficiency (lm / W). The luminance-external quantum efficiency is shown in FIG. 34. In FIG. 34, the horizontal axis represents luminance (cd / m 2 ), and the vertical axis represents external quantum efficiency (%).

[0271] Also, the voltage (V), current density (mA / cm 2 ), CIE chromaticity coordinates (x, y), current efficiency (cd / A ), power efficiency (lm / W), and external quantum efficiency (%) of the light-emitting element 4 and the comparative light-emitting element 4 when the luminance is around 1000 cd / m 2 are shown in Table 8.

[0272]

Table 8

[0273] As shown in Table 8, the CIE chromaticity coordinates of the light-emitting element 4 around a luminance of 1000 cd / m 2 are (x, y ) = (0.57, 0.43), and the CIE chromaticity coordinates of the comparative light-emitting 2 element 4 at a luminance around 1000 cd / m are (x, y) = (0.56, 0.41).

[0274] Also, the emission spectra when a current of 0.1 mA is passed through the light-emitting element 4 and the comparative light-emitting element 4 ​is shown in Fig. 35. In Fig. 35, the vertical axis represents the emission intensity (arbitrary unit), and the horizontal axis represents the wavelength (nm). . The emission intensity is shown as a relative value with the maximum emission intensity being 1. As shown in Fig. 35, the emission spectra of the light-emitting element 4 and the comparative light-emitting element 4 had a maximum emission wavelength near 595 nm and exhibited a spectrum derived from D CJTB, and in combination with the results in Table 8, it was found that the light-emitting element 4 and the comparative light-emitting element 4 are light-emitting elements that exhibit yellow emission.

[0275] Also, with the initial luminance being 5000 cd / m 2 , the light-emitting element 4 and the comparative light-emitting element 4 were driven under the condition of constant current density, and the results of the reliability test are shown in Fig. 36. In Fig. 36, the change in the normalized luminance with the initial luminance being set to 100% is shown.

[0276] From the results in Table 8 and Figs. 30 to 36, the light-emitting element 4 has a lower threshold voltage (light emission start voltage) for starting emission compared to the comparative light-emitting element 4, and shows high values in terms of current efficiency, power efficiency, and external quantum efficiency. Furthermore, it was found that the light-emitting element has good reliability with a small decrease in luminance over the driving time.

[0277] Since 4,6mCzP2Pm and PCBBiF used in the light-emitting layer 1113 form an exciplex, a singlet excited state of the exciplex is generated from a part of the triplet excited state of the exciplex in the light-emitting layer 1113. It is considered that the energy of this singlet excited state of the exciplex is transferred to the singlet excited state of the material that emits fluorescence, leading to an improvement in the light emission efficiency. Also, it is considered that the light emission start voltage decreased due to the influence of the formation of this exciplex.

Explanation of symbols

[0278] 101 Electrode​​​​​​​ 102 Electrode 103 EL layer 111 Hole injection layer 112 Hole transport layer 113 Light-emitting layer 113A Luminescent substance 113D Thermally activated delayed phosphor 113D1 Organic compound 113D2 Organic compound 114 Electron transport layer 115 Electron injection layer 400 Substrate 401 Electrode 402 Auxiliary electrode 403 EL layer 404 Electrode 405 Sealing material 406 Sealing material 407 Sealing substrate 412 Pad 420 IC chip 951 Substrate 952 Electrode 953 Insulating layer 954 Partition layer 955 EL layer 956 Electrode 1001 Substrate 1002 Underlying insulating film 1003 Gate insulating film 1006 Gate electrode 1007 Gate electrode 1008 Gate electrode 1020 Interlayer insulating film 1021 Interlayer insulating film 1022 Electrode 1024R Electrode 1024G Electrode 1024B Electrode 1024W Electrode 1025 Partition 1028 EL layer 1029 Electrode 1031 Sealing substrate 1032a Sealing material 1032b Sealing material 1033 Substrate material 1034B Color layer 1034G Color layer 1034R Color layer 1036 Overcoat layer 1037 Interlayer insulating film 1040 Pixel section 1041 Driving circuit section 1042 Peripheral section 1044B Light-emitting region 1044G Light-emitting region 1044R Light-emitting region 1044W Light-emitting region 1100 Substrate 1101 Electrode 1103 Electrode 1111 Hole injection layer 1112 Hole transport layer 1113 Light-emitting layer 1114a Electron transport layer 1114b Electron transport layer 1115 Electron injection layer 2001 Housing 2002 Light source 2003 Electric stand 3001 Lighting device 5000 Display 5001 Display 5002 Display 5003 Display 5004 Display 5005 Display 5021 Needle 5022 Display section 7101 Housing 7103 Display section 7105 Fixture 7107 Display section 7109 Operation key 7110 Remote control operation unit 7201 Main body 7202 Housing 7203 Display section 7204 Keyboard 7205 External connection port 7206 Pointing device 7210 Display unit 7301 Housing 7302 Housing 7303 Connecting part 7304 Display unit 7305 Display unit 7306 Speaker unit 7307 Recording medium insertion part 7308 LED lamp 7309 Operation key 7310 Connection terminal 7311 Sensor 7312 Microphone 7400 Mobile phone 7401 Housing 7402 Display unit 7403 Operation button 7404 External connection port 7405 Speaker 7406 Microphone

Claims

1. A light-emitting element having a light-emitting layer between a pair of electrodes, wherein the light-emitting layer includes a first material which is a thermally activated delayed phosphor and a second material which emits fluorescence, and a difference between a peak wavelength of an emission spectrum of the first material and a peak wavelength of an emission spectrum of the second material is within 30 nm.

2. A light-emitting element having a light-emitting layer between a pair of electrodes, wherein the light-emitting layer includes a first material which is a thermally activated delayed phosphor and a second material which emits fluorescence, and a difference between an energy conversion value of a peak wavelength of an emission spectrum of the first material and an energy conversion value of a peak wavelength of an emission spectrum of the second material is 0.2 eV or less.

3. The light-emitting element according to Claim 1 or Claim 2, wherein the first material has a π-electron-excessive heteroaromatic ring.

4. The light-emitting element according to Claim 3, wherein the π-electron-excessive heteroaromatic ring has any one of a carbazole skeleton, a thiophene skeleton, and a furan skeleton.

5. The light-emitting element according to any one of Claims 1 to 4, wherein the first material has a π-electron-deficient heteroaromatic ring.

6. The light-emitting element according to Claim 5, wherein the π-electron-deficient heteroaromatic ring has any one of a polyazole skeleton, a diazine skeleton, and a pyridine skeleton.

7. The light-emitting element according to any one of Claims 1 to 6, wherein the second material is a material having a fluorescence quantum yield of 50% or more.

8. A light-emitting device having the light-emitting element according to any one of Claims 1 to 7.

9. An illumination device having the light-emitting element according to any one of Claims 1 to 7.

10. An electronic device having the light-emitting element according to any one of Claims 1 to 7.

Images