JP7321321B2 - Light-emitting elements, light-emitting devices, electronic devices and lighting devices - Google Patents

Description

One embodiment of the present invention relates to a light-emitting element in which an organic compound that emits light when an electric field is applied is sandwiched between a pair of electrodes, a light-emitting device, an electronic device, and a lighting device each having such a light-emitting element.

A light-emitting device using an organic compound as a light-emitting body is expected to be applied to next-generation flat-panel displays. In particular, display devices in which light-emitting elements are arranged in a matrix are considered to be superior to conventional liquid crystal display devices in that they have a wide viewing angle and excellent visibility.

The light-emitting mechanism of a light-emitting element is to sandwich an EL layer containing a light-emitting material between a pair of electrodes and apply a voltage. It is said that they combine to form a molecular exciton that releases energy and emits light when the molecular exciton relaxes to the ground state. Singlet excitation and triplet excitation are known as excited states, and it is believed that light emission is possible through either excited state.

In order to improve the characteristics of such light-emitting devices, improvements in device structures and development of materials have been actively carried out (see, for example, Patent Document 1).

JP 2010-182699 A

However, the light extraction efficiency of current light-emitting devices is said to be about 20% to 30%. is considered to be about 25%.

Thus, one embodiment of the present invention provides a light-emitting element with high external quantum efficiency. Another embodiment of the present invention provides a long-life light-emitting element.

One embodiment of the present invention has a light-emitting layer between a pair of electrodes (anode and cathode), and the light-emitting layer includes a first light-emitting substance (guest material) that converts triplet excitation energy into light emission, and a second organic compound having a hole-transporting property (assisting material) and formed on the anode side; It contains at least a second light-emitting substance (guest material) that converts light to light, a first organic compound (host material) that has electron-transport properties, and a third organic compound (assist material) that has hole-transport properties. In the first light-emitting layer, the first organic compound (host material) and the second organic compound (assist material) are combined to form an exciplex. In the second light-emitting layer, the first organic compound (host material) and the third organic compound (assist material) are combined to form an exciplex.

In another aspect of the present invention, a light-emitting layer is provided between an anode and a cathode, a hole-transport layer is provided between the anode and the light-emitting layer, and an electron-transport layer is provided between the cathode and the light-emitting layer. The light-emitting layer includes at least a first light-emitting substance that converts triplet excitation energy into light emission, a first organic compound that has an electron-transport property, and a second organic compound that has a hole-transport property. a first light-emitting layer comprising and formed in contact with a hole-transporting layer, a second light-emitting substance that converts triplet excitation energy into light emission, a first organic compound having an electron-transporting property, and a hole-transporting layer and a second light-emitting layer formed in contact with the electron-transporting layer, wherein the first light-emitting layer contains the first organic compound (host material). and the second organic compound (assist material) are
It is a combination that forms an exciplex, and in the second light-emitting layer, the first organic compound (host material) and the third organic compound (assist material) are a combination that forms an exciplex. It is a light-emitting element that

In each of the above structures, the emission wavelength of the exciplex formed by the first organic compound (host material) and the second organic compound (assisting material) in the first light-emitting layer is the same as that of the first organic compound (host material). material) and the emission wavelength (fluorescence wavelength) of each of the second organic compound (assisting material)
Therefore, by forming an exciplex, the fluorescence spectrum of the first organic compound (host material) and the fluorescence spectrum of the second organic compound (assist material) can be made longer. It can be converted into an emission spectrum located on the wavelength side. Further, the emission wavelength of the exciplex formed by the first organic compound (host material) and the third organic compound (assisting material) in the second light-emitting layer is of organic compounds (
(assisting material) exists on the longer wavelength side than the respective emission wavelengths (fluorescence wavelengths) of the first organic compound (host material). The fluorescence spectrum of the compound (assisting material) can be converted into an emission spectrum positioned on the longer wavelength side.

In each of the above structures, in the first light-emitting layer, the anion of the first organic compound and the second
An exciplex is formed from the cation of the organic compound in (1), and an exciplex is formed in the second light-emitting layer from the anion of the first organic compound and the cation of the third organic compound.

In the above structure, each of the first light-emitting layer and the second light-emitting layer contains the same first organic compound (host material), and the second organic compound (assisting material) contained in the first light-emitting layer ) is characterized in that the highest occupied molecular orbital level (HOMO level) is lower than that of the third organic compound (assisting material) contained in the second light-emitting layer.

Furthermore, in the above structure, the first light-emitting substance contained in the first light-emitting layer is a substance that emits light having a shorter wavelength than the second light-emitting substance contained in the second light-emitting layer. and

In the above configuration, the first luminescent substance and the second luminescent substance are luminescent substances that convert triplet excitation energy into luminescence, and include phosphorescent compounds such as organometallic complexes, thermally activated delayed fluorescence, and the like. , namely thermally activated delayed fluorescence (TADF: Thermally A
activated Delayed Fluorescence) material can be used. Further, the first organic compound is mainly an electron-transporting material having an electron mobility of 10 ⁻⁶ cm ² /Vs or more, specifically a π-deficient heteroaromatic compound, and the second organic compound and the second The organic compound of 3 is mainly a hole-transporting material having a hole mobility of 10 ⁻⁶ cm ² /Vs or more, specifically a π-excessive heteroaromatic compound or an aromatic amine compound. do.

Further, one embodiment of the present invention includes not only a light-emitting device including a light-emitting element but also an electronic device and a lighting device including a light-emitting device. Therefore, the light-emitting device in this specification refers to an image display device, a light-emitting device, or a light source (including a lighting device). again,
A connector such as an FPC (flexible printed circuit) is connected to the light emitting device.
it) or a module with a TCP (Tape Carrier Package) attached, a module with a printed wiring board at the end of the TCP, or a C
All modules in which an IC (integrated circuit) is directly mounted by the OG (Chip On Glass) method are included in the light emitting device.

Note that in the light-emitting element which is one embodiment of the present invention, an exciplex can be formed in each of the first light-emitting layer and the second light-emitting layer which constitute the light-emitting layer; A light-emitting element with high efficiency can be realized.

Further, in the light-emitting element which is one embodiment of the present invention, the excitation energy of the exciplex formed in the first light-emitting layer is higher than that of the exciplex formed in the second light-emitting layer by using the above element structure. Therefore, the triplet excitation energy contained in the second light-emitting layer is used as the first light-emitting substance (guest material) that converts the triplet excitation energy contained in the first light-emitting layer into light emission. By using a substance that emits light with a shorter wavelength than the second light-emitting substance (guest material) to be changed, light emission from the first light-emitting layer and the second light-emitting layer can be obtained at the same time. A second light-emitting substance (guest material ), the luminous efficiency of the light-emitting device can be further increased.

1A and 1B illustrate a concept of one embodiment of the present invention; FIG. 1A and 1B illustrate a concept of one embodiment of the present invention; FIG. 4A and 4B are diagrams showing calculation results according to one embodiment of the present invention; FIG. 4A and 4B are diagrams showing calculation results according to one embodiment of the present invention; FIG. 4A and 4B illustrate the structure of a light-emitting element; 4A and 4B illustrate the structure of a light-emitting element; 4A and 4B illustrate a light-emitting device; 4A and 4B illustrate a light-emitting device; 4A and 4B illustrate electronic devices; 4A and 4B illustrate electronic devices; 4A and 4B illustrate a lighting device; 4A and 4B illustrate a light-emitting element; FIG. 3 is a graph showing current density-luminance characteristics of Light-Emitting Element 1; FIG. 3 is a diagram showing voltage-luminance characteristics of Light-Emitting Element 1; FIG. 4 is a diagram showing luminance-current efficiency characteristics of Light-Emitting Element 1; FIG. 4 is a diagram showing voltage-current characteristics of the light-emitting element 1; FIG. 2 shows an emission spectrum of Light-Emitting Element 1; 4A and 4B show emission spectra of substances used for Light-Emitting Element 1. FIG. 4A and 4B show emission spectra of substances used for Light-Emitting Element 1. FIG.

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 various changes in form and detail can be made without departing from the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited to the descriptions of the embodiments shown below.

(Regarding Elementary Process of Light Emission in Light Emitting Element)
First, a general elementary process of light emission in a light-emitting device using a light-emitting substance (including a phosphorescent compound and a thermally activated delayed fluorescence (TADF) material) that converts triplet excitation energy into light emission as a guest material will be described. Note that here, a molecule that gives excitation energy is referred to as a host molecule, and a molecule that receives excitation energy is referred to as a guest molecule.

(1) When electrons and holes recombine in guest molecules and the guest molecules are in an excited state (direct recombination process).

(1-1) When the excited state of the guest molecule is a triplet excited state The guest molecule emits phosphorescence.

(1-2) When the Excited State of the Guest Molecule is a Singlet Excited State A guest molecule in a singlet excited state intersystem crosses to a triplet excited state and emits phosphorescence.

That is, in the direct recombination process (1) above, high luminous efficiency can be obtained as long as the intersystem crossing efficiency of the guest molecules and the phosphorescence quantum yield are high. Note that T1 of the host molecule
The level is preferably higher than the T1 level of the guest molecule.

(2) When electrons and holes recombine in the host molecule and the host molecule is in an excited state (energy transfer process).

(2-1) When the excited state of the host molecule is a triplet excited state When the T1 level of the host molecule is higher than the T1 level of the guest molecule, excitation energy is transferred from the host molecule to the guest molecule, and the guest molecule It becomes a triplet excited state. The guest molecule in the triplet excited state emits phosphorescence. Note that the energy transfer from the T1 level of the host molecule to the singlet excitation energy level (S1 level) of the guest molecule is prohibited unless the host molecule emits phosphorescence, and is unlikely to be the main energy transfer process. omitted here. That is, as shown in the following formula (2-1), energy transfer from the triplet excited state (3H*) of the host molecule to the triplet excited state (3G*) of the guest molecule is important (wherein 1G is the guest singlet ground state of the molecule, 1H represents the singlet ground state of the host molecule).

3H*+1G → 1H+3G* (2-1)

(2-2) When the excited state of the host molecule is a singlet excited state When the S1 level of the host molecule is higher than the S1 and T1 levels of the guest molecule, excitation energy is transferred from the host molecule to the guest molecule. , the guest molecule becomes a singlet excited state or a triplet excited state. The guest molecule in the triplet excited state emits phosphorescence. Further, the guest molecule in the singlet excited state undergoes intersystem crossing to the triplet excited state and emits phosphorescence.

That is, as shown in the following formula (2-2A), the energy is transferred from the singlet excited state (1H*) of the host molecule to the singlet excited state (1G*) of the guest molecule, and then the triplet of the guest molecule by intersystem crossing. Direct energy transfer from the singlet excited state (1H*) of the host molecule to the triplet excited state (3G*) of the guest molecule as shown in the following formula (2-2B) and the process of generating the excited state (3G*) process can be considered.

1H*+1G → 1H+1G* → (intersystem crossover) → 1H+3G* (2-2A)
1H*+1G → 1H+3G* (2-2B)

If all the energy transfer processes described in (2) above occur efficiently, both the triplet excitation energy and the singlet excitation energy of the host molecule are efficiently converted to the triplet excited state (3G*) of the guest molecule. Therefore, highly efficient light emission is possible. Conversely, if the host molecule itself emits its excitation energy as light or heat and is deactivated before the excitation energy is transferred from the host molecule to the guest molecule, the luminous efficiency will decrease.

Next, the factors governing the above-described intermolecular energy transfer process between the host molecule and the guest molecule will be described. The following two mechanisms have been proposed as mechanisms of intermolecular energy transfer.

First, the Förster mechanism (dipole-dipole interaction), which is the first mechanism, does not require direct contact between molecules for energy transfer, and resonance of dipole vibrations between host and guest molecules It is the mechanism by which energy transfer occurs through phenomena. Due to the resonance phenomenon of dipole vibration, the host molecule transfers energy to the guest molecule, the host molecule becomes the ground state, and the guest molecule becomes the excited state. Note that the rate constant k _h*→g of the Förster mechanism is shown in Equation (1).

In equation (1), ν represents the vibration frequency, f′ _h (ν) is the normalized emission spectrum of the host molecule (fluorescence spectrum when discussing energy transfer from the singlet excited state, triplet excitation represents the phosphorescence spectrum when discussing energy transfer from a state, and ε _g (
ν) represents the molar absorption coefficient of the guest molecule, N represents Avogadro's number, n represents the refractive index of the medium, R represents the intermolecular distance between the host molecule and the guest molecule, and τ represents the measured value. represents the lifetime of the excited state (fluorescence lifetime or phosphorescence lifetime), c represents the speed of light, and φ represents the emission quantum yield (fluorescence quantum yield when discussing energy transfer from the singlet excited state, triplet When discussing energy transfer from an excited state, ^K2 represents the phosphorescence quantum yield), and K2 is a coefficient (0-4) representing the orientation of the transition dipole moments of the host and guest molecules. In the case of random orientation, K ² =2/3.

Next, in the second mechanism, the Dexter mechanism (electron exchange interaction), the host molecule and the guest molecule approach the contact effective distance that causes orbital overlap, and the electrons of the host molecule in the excited state and the guest molecule in the ground state Energy transfer occurs through the exchange of electrons in Note that the rate constant k _h*→g of the Dexter mechanism is shown in Equation (2).

In equation (2), h is Planck's constant, K′ is a constant with the dimension of energy, ν represents the vibrational frequency, and f′ _h (ν) is the normalized represents the emission spectrum (fluorescence spectrum when discussing energy transfer from the singlet excited state, phosphorescence spectrum when discussing energy transfer from the triplet excited state), and ε′ _g (ν) is the normalized value of the guest molecule. L represents the effective molecular radius, and R represents the intermolecular distance between the host molecule and the guest molecule.

Here, the energy transfer efficiency Φ _ET from the host molecule to the guest molecule is considered to be represented by Equation (3). _kr represents the rate constant of the emission process of the host molecule (fluorescence when discussing energy transfer from the singlet excited state, phosphorescence when discussing energy transfer from the triplet excited state), and _kn is the host molecule represents the rate constant of the non-radiative process (thermal deactivation and intersystem crossing) of , and τ represents the measured lifetime of the excited state of the host molecule.

From formula (3), in order to increase the energy transfer efficiency Φ _ET , the energy transfer rate constant k _{h * → g} is increased, and the other competing rate constants k _r + k _n (= 1/τ) are relative It can be seen that the smaller the size, the better.

(Regarding (2-1) energy transfer efficiency)
First, consider the energy transfer process of (2-1). In this case, the Förster type (formula (1)) is prohibited, so only the Dexter type (formula (2)) should be considered.
According to the formula (2), in order to increase the rate constant _kh*→g, the emission spectrum of the host molecule (phosphorescence spectrum because we are discussing energy transfer from the triplet excited state) and the absorption spectrum of the guest molecule (singleton It can be seen that the larger the overlap with the absorption corresponding to the direct transition from the term ground state to the triplet excited state, the better.

In one embodiment of the present invention, a light-emitting substance (including a phosphorescent compound and a thermally activated delayed fluorescence (TADF) material) that converts triplet excitation energy into light emission is used as a guest material. , an absorption corresponding to a direct transition from the singlet ground state to the triplet excited state may be observed, which is the absorption band appearing at the longest wavelength. Especially in luminescent iridium complexes, the absorption band on the longest wavelength side often appears as a broad absorption band near 500 to 600 nm (of course, depending on the emission wavelength, it appears on the shorter or longer wavelength side. In some cases). This absorption band is mainly the triplet MLCT (Metal t
o Ligand Charge Transfer) transition. However, the absorption band also includes some absorption derived from triplet π-π* transitions and singlet MLCT transitions, and these overlap to form a broad absorption band on the longest wavelength side of the absorption spectrum. It is thought that there are In other words, it is considered that the difference between the lowest singlet excited state and the lowest triplet excited state is small, and the absorptions derived from these overlap to form a broad absorption band on the longest wavelength side of the absorption spectrum. Therefore, when an organometallic complex (especially an iridium complex) is used as the guest material, the broad absorption band present on the longest wavelength side overlaps greatly with the phosphorescence spectrum of the host material, resulting in a rate constant of k _{h *→g} can be increased to increase energy transfer efficiency.

Furthermore, since a fluorescent compound is usually used as the host material, the phosphorescence lifetime (τ) is as long as milliseconds or more (k _r +k _n is small). This is because the transition from the triplet excited state to the ground state (singlet) is a forbidden transition. From equation (3), this means that the energy transfer efficiency Φ
Favors _ET .

Considering the above, the energy transfer from the triplet excited state of the host material to the triplet excited state of the guest material, that is, the process of formula (2-1) can be explained by the phosphorescence spectrum of the host material and the singlet of the guest material. As long as the absorption spectrum corresponding to the direct transition from the ground state to the triplet excited state is superimposed, it tends to occur generally.

(Regarding (2-2) energy transfer efficiency)
Next, consider the energy transfer process of (2-2). The process of formula (2-2A) is affected by the intersystem crossing efficiency of the guest material. Therefore, it is considered that the process of formula (2-2B) is important for maximizing the luminous efficiency. In this case, the dexter type (formula (
2)) is prohibited, so only the Förster type (formula (1)) should be considered.

Eliminating τ from equations (1) and (3), the energy transfer efficiency Φ _ET can be expressed as I can say good. In practice, however, more important factors are the emission spectrum of the host molecule (fluorescence spectrum, since we are discussing energy transfer from the singlet excited state) and the absorption spectrum of the guest molecule (direct transfer from the singlet ground state to the triplet excited state). It is also necessary to have a large overlap with the absorption corresponding to the transition (in addition, it is preferable that the molar absorption coefficient of the guest molecule is also high). This means that the fluorescence spectrum of the host material overlaps with the absorption band appearing on the longest wavelength side of the phosphorescent compound as the guest material.

However, it has been very difficult in the past to achieve this. because,
When trying to efficiently perform both the above-mentioned process (2-1) and process (2-2), from the above discussion, not only the phosphorescence spectrum of the host material but also the fluorescence spectrum is the longest wavelength of the guest material. This is because it must be designed so as to overlap with the side absorption bands. In other words, the host material must be designed so that the fluorescence spectrum of the host material is positioned similarly to the phosphorescence spectrum.

However, since the S1 level and the T1 level are generally significantly different (S1 level>T1 level),
The fluorescence emission wavelength and the phosphorescence emission wavelength are also significantly different (fluorescence emission wavelength<phosphorescence emission wavelength).
For example, 4, which is often used as a host material in a light-emitting device using a phosphorescent compound,
4′-di(N-carbazolyl)biphenyl (abbreviation: CBP) has a phosphorescence spectrum around 500 nm, while a fluorescence spectrum is around 400 nm, separated by as much as 100 nm. Considering this example, it is extremely difficult to design the host material so that the fluorescence spectrum of the host material is located at the same position as the phosphorescence spectrum. Therefore, improving the efficiency of energy transfer from the singlet excited state of the host material to the guest material is very important.

Accordingly, one aspect of the present invention provides a useful technique that can overcome such problems related to efficiency of energy transfer from the singlet excited state of the host material to the guest material. Specific aspects thereof will be described below.

(Embodiment 1)
In this embodiment, a concept for forming a light-emitting element that is one embodiment of the present invention and a specific structure of the light-emitting element will be described. Note that the light-emitting element which is one embodiment of the present invention includes an EL layer including a light-emitting layer sandwiched between a pair of electrodes (an anode and a cathode). The light-emitting layer converts triplet excitation energy into light emission. containing at least one light-emitting substance (guest material), a first organic compound having an electron-transporting property (host material), and a second organic compound having a hole-transporting property (assisting material), and formed on the anode side a first light-emitting layer, a second light-emitting substance (guest material) that converts triplet excitation energy into light emission, a first organic compound (host material) that has an electron-transport property, and a hole-transport property It has a layered structure with a second light-emitting layer containing at least a third organic compound (assisting material).

Note that the second organic compound (assisting material) contained in the first light-emitting layer has a lower HOMO level than the third organic compound (assisting material) contained in the second light-emitting layer. Therefore, the excitation energy (E _A ) of the exciplex formed in the first light-emitting layer can be designed to be higher than the excitation energy (E _B ) of the exciplex formed in the second light-emitting layer. .

The first light-emitting substance contained in the first light-emitting layer is a substance that emits light with a shorter wavelength than the second light-emitting substance contained in the second light-emitting layer.

First, an element structure of a light-emitting element which is an example of the present invention is described with reference to FIG.

In the element structure shown in FIG. 1A, a light-emitting layer 10 is placed between a pair of electrodes (an anode 101 and a cathode 102).
6 is sandwiched therebetween, and the EL layer 103 includes, from the anode 101 side, a hole injection layer 104, a hole transport layer 105, a light emitting layer 106 (106a, 106b),
It has a structure in which an electron transport layer 107, an electron injection layer 108, and the like are sequentially laminated.

In addition, as shown in FIG. 1A, the light-emitting layer 106 in one embodiment of the present invention includes a first light-emitting substance (guest material) 109a that converts triplet excitation energy into light emission, and a first electron-transporting substance 109a. An organic compound (host material) 110 and a second organic compound having a hole-transport property (
first light-emitting layer 106a containing at least assist material 111 and formed on the anode side
, a second light-emitting substance (guest material) 109b that converts triplet excitation energy into light emission, a first organic compound (host material) 110 having an electron-transporting property, and a third organic compound having a hole-transporting property. Second light-emitting layer 10 containing at least (assisting material) 112
6b has a laminated structure, and as the first organic compound 110, mainly 10 ⁻⁶ cm
An electron-transporting material having an electron mobility of ² /Vs or more is used, and as the second organic compound 111 and the third organic compound 112, a positive electrode having a hole mobility of 10 ⁻⁶ cm ² /Vs or more is mainly used. A hole-transporting material will be used. Also, in this specification, the first organic compound 110 is referred to as a host material, and the second organic compound 111 and the third organic compound 1 are referred to as host materials.
12 is called an assist material.

The combination of the first organic compound (host material) 110 and the second organic compound (assist material) 111 in the first light-emitting layer 106a is a combination that forms an exciplex. characterized by being Furthermore, the emission wavelength of the exciplex formed by the first organic compound (host material) 110 and the second organic compound (assisting material) 111 is the same as that of the first organic compound (host material) 110 and the second organic compound. Since it exists on the longer wavelength side than the respective emission wavelengths (fluorescence wavelengths) of the (assist material) 111, the fluorescence spectrum of the first organic compound (host material) 110 and the second organic compound (assist material) The fluorescence spectrum of 111 can be converted to an emission spectrum located on the longer wavelength side.

This also applies to the second light emitting layer 106b. Therefore, the second light-emitting layer 10
The combination of the first organic compound (host material) 110 and the third organic compound (assist material) 112 in 6b is characterized by forming an exciplex. Furthermore, the emission wavelength of the exciplex formed by the first organic compound (host material) 110 and the third organic compound (assist material) 112 is the same as that of the first organic compound (host material) 110 and the third organic compound. (assist material) 1
12, the fluorescence spectrum of the first organic compound (host material) 110 and the fluorescence spectrum of the third organic compound (assisting material) 112. The spectrum can be converted to an emission spectrum located on the longer wavelength side.

In the above configuration, the triplet excitation energy level (T1 level) of each of the first organic compound (host material) 110 and the second organic compound (assist material) 111 emits triplet excitation energy. is higher than the T1 level of the first light-emitting substance (guest material) 109a to be changed to . When the T1 level of the first organic compound 110 (or the second organic compound 111) is lower than the T1 level of the first light-emitting substance (guest material) 109a, the first light-emitting substance contributes to light emission. This is because the triplet excitation energy of the (guest material) 109a is quenched by the first organic compound 110 (or the second organic compound 111), resulting in a decrease in luminous efficiency.

Similarly, the triplet excitation energy level (T1 level) of each of the first organic compound (host material) 110 and the third organic compound (assist material) 112 converts the triplet excitation energy into light emission. It is preferably higher than the T1 level of the second light-emitting substance (guest material) 109b. When the T1 level of the first organic compound 110 (or the third organic compound 112) is lower than the T1 level of the second light-emitting substance (guest material) 109b, the second light-emitting substance contributes to light emission. (Guest material) The triplet excitation energy of 109b is converted to the first organic compound 110 (
Alternatively, the third organic compound 112) is quenched, resulting in a decrease in luminous efficiency.

In addition, the first organic compound (host material) 110 and the second organic compound (assist material) 111 are contained in the first light emitting layer 106a constituting the light emitting layer 106. In the second light-emitting layer 106b, either of the first organic compound (host material) 110 and the third organic compound (assisting material) 112 may be included in a higher proportion, and in the present invention, both cases are included. It is assumed that

Note that the light-emitting layer 106 having the above structure (the first light-emitting layer 106a and the second light-emitting layer 106b)
, the first organic compound (host material) 110, the second organic compound (assist material)
FIG. 1B shows a band diagram for explaining the energy relationship between 111 and the third organic compound (assisting material) 112 .

As shown in FIG. 1B, in the first light-emitting layer 106a, the excitation energy (E _A ) is the HOMO level of the second organic compound (assisting material) 111,
It is determined by the LUMO level of the first organic compound (host material) 110 . Further, in the second light-emitting layer 106b, the excitation energy (E _B ) of the exciplex formed by the first organic compound (host material) 110 and the third organic compound (assist material) 112 is HOMO level of compound (assist material) 112 and first organic compound (host material) 1
It is determined by 10 LUMO levels. Note that the second organic compound (assisting material) 111 contained in the first light-emitting layer 106a is the same as the third organic compound (assisting material) contained in the second light-emitting layer 106b.
Since the HOMO level is lower than that of the assist material) 112, the excitation energy (E A ) of the exciplex formed in the first light-emitting layer 106a is the excitation energy (E _A ) of the exciplex formed in the second light-emitting layer 106b. It can be seen that it can be designed to be larger than E _B ).

Note that with the above element structure, the exciplex formed in the first light-emitting layer 106a has higher excitation energy than the exciplex formed in the second light-emitting layer 106b. The first
As the light-emitting substance (guest material) 109a, a substance that emits light with a shorter wavelength than the second light-emitting substance (guest material) 109b that converts the triplet excitation energy contained in the second light-emitting layer 106b into light emission is used. At the same time, the first light-emitting layer 106a and the second light-emitting layer 10
Emission from 6b can be obtained. Further, part of the excitation energy of the exciplex formed in the first light-emitting layer 106a, which could not contribute to light emission, is converted into light emission by the triplet excitation energy in the second light-emitting layer 106b. Since it can be used as excitation energy for the light emitting substance (guest material) 109b, the light emission efficiency of the light emitting element can be further increased.

The light-emitting element described in this embodiment has a structure in which an exciplex is formed in each of the light-emitting layers 106 (the first light-emitting layer 106a and the second light-emitting layer 106b). ) 110, the fluorescence spectrum of the second organic compound (assisting material) 111, or the fluorescence spectrum of the third organic compound (assisting material) 112 can be converted into an emission spectrum positioned on the longer wavelength side. This means that as shown in FIG. 2, the first organic compound 110, the second organic compound 111, or the third organic compound 11
The fluorescence spectrum of 2 is even higher than that of the luminescent material 109 (
First luminescent substance (guest material) 109a and second luminescent substance (guest material) 10
9b), which is located on the shorter wavelength side than the absorption band located on the longest wavelength side of 9b), and which converts triplet excitation energy into light emission. This means that even if there is no overlap with the absorption band located on the longest wavelength side of the light-emitting substance (guest material) 109b) of , the overlap can be increased by forming an exciplex. As a result, the energy transfer efficiency of formula (2-2B) described above can be enhanced.

Furthermore, exciplexes are considered to have a very small difference between singlet and triplet excitation energies. In other words, the emission spectrum from the singlet state and the emission spectrum from the triplet state of the exciplex are very close to each other. Therefore, as described above, the emission spectrum of the exciplex (generally, the emission spectrum from the singlet state of the exciplex) is the absorption band located on the longest wavelength side of the light-emitting substance 109 that converts the triplet excitation energy into light emission. , the emission spectrum from the triplet state of the exciplex (which is often not observed at room temperature and is often not observed at low temperatures) is also the longest wavelength of the luminescent substance 109 that converts triplet excitation energy into light emission. It will overlap with the absorption band located on the side. In other words, not only the energy transfer from the singlet excited state ((2-2)), but also the efficiency of energy transfer from the triplet excited state ((2-1)) is increased, and as a result, singlet/triplet Energy from both excited states can be efficiently converted into luminescence.

Therefore, in the following, molecular orbital calculations were used to verify whether the exciplex actually has such characteristics. In general, the combination of a heteroaromatic compound and an aromatic amine is the lowest unoccupied molecular orbital (LUMO) of the aromatic amine.
The LUMO level of heteroaromatic compounds (property where electrons easily enter) and the highest occupied orbital of heteroaromatic compounds (HOMO: High
An exciplex is often formed under the influence of the HOMO level of aromatic amines (the property that holes easily enter) that is shallower than the (est Occupied Molecular Orbital) level. Therefore, dibenzo[f,h]quinoxaline (abbreviation: DBq), which is a typical skeleton constituting the LUMO level of a heteroaromatic compound, is used as a model of the first organic compound 110 in one embodiment of the present invention. As a model of the second organic compound 111 (or the third organic compound 112) in one embodiment, triphenylamine (abbreviation: TPA), which is a representative skeleton constituting the HOMO level of the aromatic amine, is used, and these were calculated in combination.

First, the optimal molecular structures and excitation energies in the lowest excited singlet state (S1) and the lowest excited triplet state (T1) of one molecule of DBq (abbreviation) and one molecule of TPA (abbreviation) were analyzed by time-dependent density functional theory (TD). -DFT). In addition, DBq (abbreviation) and TPA (abbreviation)
We also calculated the excitation energy for the dimer of

The total energy of DFT (Density Functional Theory) is represented by the sum of potential energy, electrostatic energy between electrons, kinetic energy of electrons, and exchange-correlation energy including all complex interactions between electrons. In DFT, since the exchange-correlation interaction is approximated by a functional of one-electron potential expressed by electron density, the calculation is fast and highly accurate. Here, B3LYP, which is a mixed functional, is used to define the weight of each parameter related to the exchange and correlation energies.

As a basis function, 6-311 (a basis function of a triple split valence basis set using three shortening functions for each valence orbital) was applied to all atoms.

According to the basis functions described above, for example, 1s to 3s orbitals are considered for hydrogen atoms, and 1s to 4s and 2p to 4p orbitals are considered for carbon atoms. Furthermore, in order to improve the calculation accuracy, the polarization basis set is a p-function for hydrogen atoms and a d-function for non-hydrogen atoms.
added a function.

Gaussian 09 was used as a quantum chemical calculation program. Calculations were performed using a high-performance computer (SGI Altix4700).

First, DBq (abbreviation) one molecule, TPA (abbreviation) one molecule, and DBq (abbreviation) and TPA (
The HOMO level and the LUMO level were calculated for the dimer of (abbreviation). HOMO level and L
FIG. 3 shows the UMO level, and FIG. 4 shows the distribution of the HOMO level and the LUMO level.

4A1 shows the LUMO level distribution of one DBq (abbreviation) molecule, FIG. 4A2 shows the HOMO level distribution of one DBq (abbreviation) molecule, and FIG. , TPA (abbreviation)
4 (abbreviation) (B2) shows the HOMO level distribution of one molecule of TPA (abbreviation), and FIG. 4 (C1) shows DBq (abbreviation) and TPA ( FIG. 4C2 shows the HOMO level distribution of the dimer of DBq (abbreviation) and TPA (abbreviation).

As shown in FIG. 3, the dimer of DBq (abbreviation) and TPA (abbreviation) is L
A DBq (abbreviation) LUMO level (−1.99 eV) that is deeper (lower) than the UMO level,
The HOMO level of TPA (abbreviation) (-
5.21 eV), it is suggested that an exciplex of DBq (abbreviation) and TPA (abbreviation) is formed. Actually, as can be seen from FIG. 4, the LUMO level of the dimer of DBq (abbreviation) and TPA (abbreviation) is distributed on the DBq (abbreviation) side, and the HOMO level is distributed on the TPA (abbreviation) side.

Next, the excitation energies obtained from the optimum molecular structure at the S1 level and the T1 level of one molecule of DBq (abbreviation) are shown. Here, the excitation energies of the S1 level and the T1 level correspond to the wavelengths of fluorescence and phosphorescence emitted by one DBq (abbreviation) molecule, respectively. The excitation energy of the S1 level of one DBq (abbreviation) molecule was 3.294 eV, and the fluorescence wavelength was 376.4 nm.
In addition, the excitation energy of the T1 level of one molecule of DBq (abbreviation) was 2.460 eV, and the phosphorescence wavelength was 504.1 nm.

In addition, the excitation energy obtained from the optimum molecular structure at the S1 level and T1 level of one molecule of TPA (abbreviation) is shown. Here, the excitation energies of the S1 level and the T1 level respectively correspond to the wavelengths of fluorescence and phosphorescence emitted by one molecule of TPA (abbreviation). The excitation energy of the S1 level of one molecule of TPA (abbreviation) was 3.508 eV, and the fluorescence wavelength was 353.4 nm.
In addition, the excitation energy of the T1 level of one molecule of TPA (abbreviation) was 2.610 eV, and the phosphorescence wavelength was 474.7 nm.

Furthermore, the excitation energies obtained from the optimal molecular structures at the S1 and T1 levels of the dimer of DBq (abbreviation) and TPA (abbreviation) are shown. The excitation energies of the S1 level and the T1 level are
These correspond to the wavelengths of fluorescence and phosphorescence emitted by dimers of DBq and TPA levels, respectively. DBq
(abbreviation) and TPA (abbreviation) dimer had an excitation energy of S1 level of 2.036 eV and a fluorescence wavelength of 609.1 nm. The excitation energy of the T1 level of the dimer of DBq (abbreviation) and TPA (abbreviation) is 2.030 eV, and the phosphorescence wavelength is 610.0 n.
was m.

From the above, in either one molecule of DBq (abbreviation) or one molecule of TPA (abbreviation),
It can be seen that the phosphorescence wavelength is shifted to a longer wavelength by approximately 100 nm. This is the CBP
(Abbreviation) This is the same trend as (actual measurement), and is a result that supports the validity of the calculation.

On the other hand, it can be seen that the fluorescence wavelength of the dimer of DBq (abbreviation) and TPA (abbreviation) exists on the longer wavelength side than the fluorescence wavelengths of one molecule of DBq (abbreviation) and one molecule of TPA (abbreviation). In addition, the difference between the fluorescence wavelength and the phosphorescence wavelength of the dimer of DBq (abbreviation) and TPA (abbreviation) is only 0.9n.
m, and it can be seen that they have almost the same wavelength.

From this result, it can be said that the exciplex has almost the same singlet excitation energy and triplet excitation energy. Thus, as mentioned above, the exciplex can be in its singlet state,
and triplet states, it was suggested that energy can be efficiently transferred to a light-emitting substance (guest material including the above-described first light-emitting substance and second light-emitting substance) that converts triplet excitation energy into light emission. .

As described above, the light-emitting element of one embodiment of the present invention includes a light-emitting substance (the first light-emitting substance and the second light-emitting substance described above) that converts the emission spectrum and triplet excitation energy of an exciplex formed in the light-emitting layer into light emission. Using the overlap with the absorption spectrum of the guest material including the light-emitting substance),
Energy transfer efficiency is high. Therefore, a light-emitting device with high external quantum efficiency can be realized.

Also, since an exciplex exists only in an excited state, there is no ground state that can absorb energy. Therefore, a luminescent substance (guest material) that converts triplet excitation energy into luminescence
A phenomenon in which a light-emitting substance (guest material) that converts triplet excitation energy into light emission by energy transfer from singlet and triplet excited states to an exciplex is deactivated before light emission (i.e., loss of light emission efficiency) is considered not to occur in principle. This is also one of the reasons why the external quantum efficiency can be increased.

Note that the above-described exciplex is formed by interaction between different molecules in an excited state. Further, it is generally known that an exciplex is easily formed between a material having a relatively deep LUMO level and a material having a shallow HOMO level.

The emission wavelength of an exciplex depends on the energy difference between the HOMO and LUMO levels. As a general trend, the larger the energy difference, the shorter the emission wavelength, and the smaller the energy difference, the longer the emission wavelength.

Therefore, the HOMO level and LUMO level of the first organic compound (host material) 110, the second organic compound (assisting material) 111, and the third organic compound (assisting material) 112 in this embodiment are shown in FIG. Each is different as shown in 1(B). Specifically, the HOMO level of the first organic compound 110 < the HOMO level of the second organic compound 111 and the HOMO level of the third organic compound 112 < the LUMO level of the first organic compound 110 < the HOMO level of the third organic compound 112 The energy levels differ in the order of the LUMO level of the second organic compound 111 and the LUMO level of the third organic compound 112 .

Then, in each light-emitting layer, two organic compounds (the first organic compound 110 and the second organic compound 111 in the first light-emitting layer 106a, and the first organic compound 110 in the second light-emitting layer 106b) and the third organic compound 112), the LUMO level of the exciplex in the first light-emitting layer 106a and the second light-emitting layer 106b is equal to that of the first organic compound (host material) 110 The HOMO level of the exciplex in the first light-emitting layer 106 a is derived from the second organic compound (assisting material) 111 , and the second light-emitting layer 1
The HOMO level of the exciplex in 06 b is derived from the HOMO level of the third organic compound (assisting material) 112 . Therefore, the excitation energy (E _A ) of the exciplex in the first light-emitting layer 106a is equal to the excitation energy (E _B ) of the exciplex in the second light-emitting layer 106b
be larger than That is, the first luminescent substance 109a that converts the triplet excitation energy contained in the first luminescent layer into luminescence is the second luminescent substance 109b that converts the triplet excitation energy contained in the second luminescent layer into luminescence. A light-emitting element with high emission efficiency can be formed by using a substance that emits light with a shorter wavelength than the light-emitting element. In addition, light-emitting materials with different emission wavelengths can be efficiently emitted at the same time.

Note that the formation process of an exciplex in one embodiment of the present invention includes the following two processes.

The first formation process is a formation process in which an exciplex is formed from a state in which the second organic compound (assisting material) and the third organic compound (assisting material) have carriers (specifically, cations). be.

In general, when electrons and holes recombine in the host material, excitation energy is transferred from the host material in an excited state to the guest material, and the guest material becomes excited and emits light. Before the excitation energy is transferred to the guest material, the host material itself emits light or the excitation energy becomes thermal energy, so that part of the excitation energy is deactivated. In particular, when the host material is in a singlet excited state, energy transfer is difficult to occur as described in (2-2). Such deactivation of excitation energy is one of the factors leading to shortening of the life of the light-emitting element.

However, in one aspect of the present invention, the first organic compound (host material) and the second organic compound (or third organic compound) (assist material) have carriers (cations or anions), Since an exciplex is formed, formation of singlet excitons in the first organic compound (host material) can be suppressed. That is, there may be a process of forming an exciplex directly without forming a singlet exciton. As a result, deactivation of the singlet excitation energy can also be suppressed. Therefore, a long-life light-emitting element can be realized.

For example, the first organic compound is an electron-trapping compound (having a deep LUMO level) that easily traps electrons (carriers) among electron-transporting materials, and the second organic compound (or third organic compound) is a hole-trapping compound (shallow HOMO level) having a property of easily trapping holes (carriers) among hole-transporting materials, the anion of the first organic compound and the cation of the second organic compound (or the third organic compound) directly form an exciplex. An exciplex formed in such a process is particularly called an electroplex. Thus, by suppressing the generation of the singlet excited state of the first organic compound (host material) and transferring energy from the electroplex to the light-emitting substance (guest material) that converts the triplet excitation energy into light emission, A light-emitting element with high luminous efficiency can be obtained. In this case, the first
The generation of the triplet excited state of the organic compound (host material) is similarly suppressed, and the exciplex is formed directly, so energy transfer from the exciplex to the luminescent substance (guest material) that converts the triplet excitation energy into light emission It is thought that

The second formation process occurs after either the first organic compound (host material), the second organic compound (assist material), or the third organic compound (assist material) forms a singlet exciton. , interacting with the other ground state to form an exciplex. Unlike electroplex, in this case, once the singlet excited state of the first organic compound (host material), second organic compound (assist material), or third organic compound (assist material) is generated, However, since this is rapidly converted to an exciplex, deactivation of singlet excitation energy can be suppressed. Therefore, it is possible to suppress deactivation of the excitation energy of the first organic compound (host material), the second organic compound (assist material), or the third organic compound (assist material). In this case, the triplet excited state of the host material is also rapidly converted to an exciplex, and energy is transferred from the exciplex to a light-emitting substance (guest material) that converts the triplet excitation energy into light emission.

Note that the first organic compound (host material) is an electron-trapping compound, while the second
The organic compound (or third organic compound) (assisting material) of is a hole-trapping compound, and the difference in HOMO level and LUMO level of these compounds is large (specifically, the difference is 0 .3 eV or higher), electrons preferentially enter the first organic compound (host material) and holes preferentially enter the second organic compound (or third organic compound) (assist material).
In this case, it is considered that the process of forming an electroplex takes precedence over the process of forming an exciplex via singlet excitons.

The emission spectrum of the exciplex and the luminescent substance that converts the triplet excitation energy into light emission (
In order to sufficiently overlap the absorption spectra of the guest material), the difference between the energy value of the peak of the emission spectrum and the energy value of the peak of the absorption band on the lowest energy side of the absorption spectrum should be within 0.3 eV. preferable. It is more preferably within 0.2 eV, and most preferably within 0.1 eV.

In the light-emitting element which is one embodiment of the present invention, the excitation energy of the exciplex is sufficiently transferred to a light-emitting substance (guest material) that converts triplet excitation energy into light emission, and light emission from the exciplex is substantially preferably unobserved. Therefore, it is preferable that energy is transferred to a luminescent substance that converts triplet excitation energy into luminescence via an exciplex, and that the luminescent substance that converts triplet excitation energy into luminescence emits light. The light-emitting substance that converts triplet excitation energy into light emission is preferably a phosphorescent compound (organometallic complex, etc.), a thermally activated delayed fluorescence (TADF) material, or the like.

Further, in the first light-emitting layer 106a of the light-emitting element which is one embodiment of the present invention, when a light-emitting substance that converts triplet excitation energy into light emission is used as the first organic compound (host material), the first
The organic compound (host material) itself easily emits light, and energy is less likely to be transferred to a light-emitting substance (guest material) that converts triplet excitation energy into light emission. In this case, the first organic compound should emit light efficiently, but the problem of concentration quenching occurs in the host material, making it difficult to achieve high luminous efficiency. Therefore, at least one of the first organic compound (host material) and the second organic compound (or third organic compound) (assisting material) is a fluorescent compound (that is, light emission or heat deactivation from a singlet excited state). is likely to occur) is effective. Therefore, at least one of the first organic compound (host material) and the second organic compound (or the third organic compound) (assisting material) is a fluorescent compound, and an exciplex is used as an energy transfer medium. is preferably

Note that the structure described in this embodiment can be used in combination with any of the structures described in other embodiments as appropriate.

(Embodiment 2)
In this embodiment, an example of a light-emitting element that is one embodiment of the present invention will be described with reference to FIGS.

As shown in FIG. 5, the light-emitting element described in this embodiment includes a pair of electrodes (first electrode (anode) 2
An EL layer 203 including a light-emitting layer 206 is sandwiched between the electrode (cathode) 202 and a second electrode (cathode) 202). In addition to the light emitting layer 206, a hole (or hole) injection layer 204, a hole (or hole) transport layer 205, an electron transport layer 207, an electron injection layer 208, and the like are formed.

Note that the light-emitting layer 206 described in this embodiment includes the first light-emitting layer 206a and the second light-emitting layer 206a.
In the first light-emitting layer 206a of the light-emitting layers 206, a first light-emitting substance (guest material) 209a that converts triplet excitation energy into light emission, a first light-emitting substance (guest material) 209a that converts triplet excitation energy into light emission, and an electron-transporting first light-emitting layer 206a. 1 organic compound (host material) 210 and a second hole-transporting organic compound (assisting material) 211 are included, and the second light-emitting layer 206b converts triplet excitation energy into light emission. A second light-emitting substance (guest material) 209b, a first organic compound (host material) 210 having an electron-transporting property, and a third organic compound having a hole-transporting property (
assist material) 212 is included.

Note that the second organic compound (assisting material) contained in the first light-emitting layer has a lower HOMO level than the third organic compound (assisting material) contained in the second light-emitting layer. Therefore, the excitation energy (E _A ) of the exciplex formed in the first light-emitting layer can be designed to be higher than the excitation energy (E _B ) of the exciplex formed in the second light-emitting layer. .

Note that in the light-emitting layer 206 (the first light-emitting layer 206a and the second light-emitting layer 206b),
In the case of the first light-emitting layer 206a, a first light-emitting substance 209a that converts triplet excitation energy into light emission is contained in a first organic compound (host material) 210 and a second organic compound (assist material) 211. In the case of the second light-emitting layer 206b, a second light-emitting material 209b, which converts triplet excitation energy into light emission, is combined with a first organic compound (host material) 210 and a third organic compound (assist material). ) 212, the light-emitting layer 20
6 (the first light-emitting layer 206a and the second light-emitting layer 206b) can be suppressed. In addition, concentration quenching due to the high concentration of the light-emitting substance 209 (209a, 209b) can be suppressed, and the light-emitting efficiency of the light-emitting element can be increased.

In addition, the first organic compound 210, the second organic compound 211, and the third organic compound 2
Each of the 12 triplet excitation energy levels (T1 level) is preferably higher than the T1 level of the luminescent materials 209 (209a, 209b) that convert triplet excitation energy into luminescence. First organic compound 210, second organic compound 211, and third organic compound 21
The T1 level of 2 converts triplet excitation energy into light emission 209 (209a, 20
9b) is lower than the T1 level, the triplet excitation energy of the light-emitting substance 209 (209a, 209b) that converts the triplet excitation energy contributing to light emission into light emission is transferred to the first organic compound 21
This is because 0 (or the second organic compound 211 or the third organic compound 212) is quenched, resulting in a decrease in luminous efficiency.

In this embodiment mode, in the light-emitting layer 206, in the first light-emitting layer 206a, when carriers (electrons and holes) injected from both electrodes recombine, the first organic compound 210
and the second organic compound 211 form an exciplex, and the first organic compound 210 and the third organic compound 212 form an exciplex in the second light-emitting layer 206b. Accordingly, the fluorescence spectrum of the first organic compound 210 and the fluorescence spectrum of the second organic compound 211 in the first light-emitting layer 206a can be converted into the emission spectrum of the exciplex located on the longer wavelength side. , the fluorescence spectrum of the first organic compound 210 and the fluorescence spectrum of the third organic compound 212 in the second light-emitting layer 206b are
It can be converted into an emission spectrum of an exciplex positioned on the longer wavelength side. Therefore, in order to maximize the energy transfer from the singlet excited state, the emission spectrum of the exciplex and the absorption spectrum of the light-emitting substance (guest material) 209 that converts the triplet excitation energy into light emission should overlap. , the first organic compound 210 and the second organic compound 211 in the first light emitting layer 206a, and the first organic compound 210 and the third organic compound 212 in the second light emitting layer 206b. and That is, here, it is considered that energy transfer occurs not from the host material but from the exciplex even in the triplet excited state.

Note that the luminescent substance 209 (the first luminescent substance 20
9a and second light-emitting substance 209b) are preferably phosphorescent compounds (organometallic complexes, etc.), thermally activated delayed fluorescence (TADF) materials, and the like. As the first organic compound (host material) 210, an electron-transporting material is preferably used. As the second organic compound (assisting material) 211 and the third organic compound (assisting material) 212, it is preferable to use hole-transporting materials.

Examples of the organometallic complex include bis[2-(4′,6′-difluorophenyl)pyridinato-N,C ^2′ ]iridium (III) tetrakis(1-pyrazolyl)borate (abbreviation: FIr6), bis[2-(4′,6′-difluorophenyl)pyridinato-N,C ^2′ ]iridium(III) picolinate (abbreviation: FIrpic), bis[2-
(3′,5′-bistrifluoromethylphenyl)pyridinato-N,C ^2′ ]iridium(III) picolinate (abbreviation: Ir(CF ₃ ppy) ₂ (pic)), bis[2-(4
',6'-difluorophenyl)pyridinato-N,C ^2' ]iridium (III) acetylacetonate (abbreviation: FIracac), tris(2-phenylpyridinato)iridium (III) (abbreviation: Ir(ppy) ₃ ), bis(2-phenylpyridinato)iridium(III) acetylacetonate (abbreviation: Ir(ppy) ₂ (acac)), bis(benzo[h]quinolinato)iridium(III) acetylacetonate (abbreviation: Ir (bzq
) ₂ (acac)), bis(2,4-diphenyl-1,3-oxazolato-N,C ^2′ )
iridium (III) acetylacetonate (abbreviation: Ir(dpo) ₂ (acac)),
Bis{2-[4′-(perfluorophenyl)phenyl]pyridinato-N,C ^2′ }iridium(III) acetylacetonate (abbreviation: Ir(p-PF-ph) ₂ (acac)
), bis(2-phenylbenzothiazolato-N,C ^2′ ) iridium (III) acetylacetonate (abbreviation: Ir(bt) ₂ (acac)), bis[2-(2′-benzo[4,
5-α]thienyl)pyridinato-N,C ^3′ ]iridium (III) acetylacetonate (abbreviation: Ir(btp) ₂ (acac)), bis(1-phenylisoquinolinato-N,
C ^2′ ) iridium (III) acetylacetonate (abbreviation: Ir(piq) ₂ (aca
c)), (acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III) (abbreviation: Ir(Fdpq) ₂ (acac)), (acetylacetonato)bis(2, 3,5-triphenylpyrazinato)iridium (III) (abbreviation: Ir(tppr) ₂ (acac)), 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin Platinum (II) (abbreviation: PtOEP), Tris (
Acetylacetonato)(monophenanthroline)terbium(III) (abbreviation: Tb(a
cac) ₃ (Phen)), tris(1,3-diphenyl-1,3-propanedionato)
(Monophenanthroline) Europium (III) (abbreviation: Eu(DBM) ₃ (Phen
)), tris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline) europium (III) (abbreviation: Eu(TTA) ₃ (Phen)), and the like.

As the electron-transporting material, a π-deficient heteroaromatic compound such as a nitrogen-containing heteroaromatic compound is preferable. h]quinoxaline (abbreviation: 2mDBTPDBq-II), 2-[3′-
(Dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), 2-[4-(3,6-diphenyl-9H-
Carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2CzP
DBq-III), 7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[
f,h]quinoxaline (abbreviation: 7mDBTPDBq-II) and 6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 6mDB
and quinoxaline or dibenzoquinoxaline derivatives such as TPDBq-II).

Further, as the hole-transporting material, π-excessive heteroaromatic compounds (eg, carbazole derivatives and indole derivatives) and aromatic amine compounds are preferable.
Phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), 4,4′-di(1-naphthyl)-4″-(9-phenyl-
9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB), 3-[N
-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole (abbreviation: PCzPCN1), 4,4′,4″-tris[N-(1-naphthyl) —N-phenylamino]triphenylamine (abbreviation: 1′-TNATA), 2,
7-bis[N-(4-diphenylaminophenyl)-N-phenylamino]-spiro-9
,9′-bifluorene (abbreviation: DPA2SF), N,N′-bis(9-phenylcarbazol-3-yl)-N,N′-diphenylbenzene-1,3-diamine (abbreviation: PCA2
B), N-(9,9-dimethyl-2-diphenylamino-9H-fluoren-7-yl)
Diphenylamine (abbreviation: DPNF), N,N',N''-triphenyl-N,N',N
''-Tris(9-phenylcarbazol-3-yl)benzene-1,3,5-triamine (abbreviation: PCA3B), 2-[N-(9-phenylcarbazol-3-yl)-N-phenylamino] Spiro-9,9′-bifluorene (abbreviation: PCASF), 2-[N-(4
-diphenylaminophenyl)-N-phenylamino]spiro-9,9'-bifluorene (abbreviation: DPASF), N,N'-bis[4-(carbazol-9-yl)phenyl]-
N,N'-diphenyl-9,9-dimethylfluorene-2,7-diamine (abbreviation: YGA
2F), 4,4′-bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (abbreviation: TPD), 4,4′-bis[N-(4-diphenylaminophenyl)-N- Phenylamino]biphenyl (abbreviation: DPAB), N-(9,9-dimethyl-9H-fluoren-2-yl)-N-{9,9-dimethyl-2-[N'-phenyl-N'-(9 , 9-
Dimethyl-9H-fluoren-2-yl)amino]-9H-fluoren-7-yl}phenylamine (abbreviation: DFLADFL), 3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino] -9-phenylcarbazole (abbreviation: PCzPCA1), 3
-[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzDPA1), 3,6-bis[N-(4-diphenylaminophenyl)-N-phenylamino]- 9-phenylcarbazole (abbreviation: PCzDPA2), 4
, 4′-bis(N-{4-[N′-(3-methylphenyl)-N′-phenylamino]phenyl}-N-phenylamino)biphenyl (abbreviation: DNTPD), 3,6-bis[N -
(4-diphenylaminophenyl)-N-(1-naphthyl)amino]-9-phenylcarbazole (abbreviation: PCzTPN2), 3,6-bis[N-(9-phenylcarbazole-
3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA2
).

However, the light-emitting substance (guest material) 209 that converts the above-described triplet excitation energy into light emission
(first luminescent substance 209a, second luminescent substance 209b), first organic compound (host material) 210, second organic compound (assisting material) 211, and third organic compound (assisting material) Materials that can be used for 212 are not limited to these, but are combinations that can form an exciplex, and the emission spectrum of the exciplex is a light-emitting substance (guest material) 209 that converts triplet excitation energy into light emission. It overlaps with the absorption spectrum of (the first luminescent substance 209a or the second luminescent substance 209b), and the peak of the emission spectrum of the exciplex is the luminescent substance (guest material) 209 (the second luminescent substance) that converts triplet excitation energy into light emission. The wavelength may be longer than the peak of the absorption spectrum of the first luminescent substance 209a or the second luminescent substance 209b).

When an electron-transporting material is used for the first organic compound 210 and a hole-transporting material is used for the second organic compound 211, the carrier balance can be controlled by the mixing ratio. Specifically, first organic compound 210:second organic compound 211=1:9
A range of ~9:1 is preferred.

A specific example of manufacturing the light-emitting element described in this embodiment is described below.

Metals, alloys, electrically conductive compounds, mixtures thereof, and the like can be used for the first electrode (anode) 201 and the second electrode (cathode) 202 . Specifically, indium oxide-tin oxide (ITO: Indium Tin Oxide), indium oxide containing silicon or silicon oxide-tin oxide, indium oxide-zinc oxide (Indium Zi
nc oxide), indium oxide containing tungsten oxide and zinc oxide, gold (A
u), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), titanium ( Ti), as well as elements belonging to Group 1 or Group 2 of the periodic table, that is, lithium (L
i) and alkali metals such as cesium (Cs), magnesium (Mg), calcium (
Ca), alkaline earth metals such as strontium (Sr), and alloys containing these (Mg
Ag, AlLi), europium (Eu), ytterbium (Yb) and other rare earth metals, alloys containing these, graphene, and the like can be used. The first electrode (anode) 201 and the second electrode (cathode) 202 can be formed by, for example, a sputtering method, a vapor deposition method (including a vacuum vapor deposition method), or the like.

Examples of the highly hole-transporting substance used for the hole-injecting layer 204 and the hole-transporting layer 205 include 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB or α-NPD), N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine (abbreviation: TPD), 4,4 '，
4″-tris(carbazol-9-yl)triphenylamine (abbreviation: TCTA), 4
,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbreviation: TD
ATA), 4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (abbreviation: MTDATA), 4,4′-bis[N-(spiro-9 ，
9′-bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB)
aromatic amine compounds such as 3-[N-(9-phenylcarbazol-3-yl)-N-
Phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA1), 3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA2), 3 -[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole (abbreviation: PCzPC
N1) and the like. In addition, 4,4'-di(N-carbazolyl)biphenyl (abbreviation:
CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation:
TCPB), 9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA) and other carbazole derivatives, and the like can be used. The substances mentioned here are mainly substances having a hole mobility of 10 ⁻⁶ cm ² /Vs or more. However, other substances may be used as long as they have a higher hole-transport property than electron-transport property.

Furthermore, 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) and poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] (abbreviation: Poly-TPD) can also be used.

Examples of acceptor substances that can be used for the hole-injection layer 204 include transition metal oxides and oxides of metals belonging to Groups 4 to 8 of the periodic table. Specifically, molybdenum oxide is particularly preferred.

The light-emitting layers 206 (206a, 206b) are as described above, and the first light-emitting layer 206a
has at least a first light-emitting substance 209a, a first organic compound (host material) 210, and a second organic compound (assist material) 211, and a second light-emitting layer 206b comprises a second light-emitting layer It is formed having at least a substance 209 b , a first organic compound (host material) 210 and a third organic compound (assist material) 212 .

The electron-transporting layer 207 is a layer containing a highly electron-transporting substance. In the electron transport layer 207,
Alq ₃ , tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq ₃ )
, bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq ₂ ),
Metal complexes such as BAlq, Zn(BOX) ₂ and bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation: Zn(BTZ) ₂ ) can be used. Also, 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-te
rt-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole (abbreviation: TAZ), 3-(4-tert-butylphenyl)-4-(4-ethylphenyl) -5-(4-biphenylyl)-1,2,4-triazole (abbreviation: p-EtT
AZ), bathophenanthroline (abbreviation: BPhen), bathocuproine (abbreviation: BCP
), 4,4′-bis (5-methylbenzoxazol-2-yl) stilbene (abbreviation: B
Heteroaromatic compounds such as zOs) can also be used. In addition, poly(2,5-pyridinediyl) (abbreviation: PPy), poly[(9,9-dihexylfluorene-2,7-diyl)
-co-(pyridine-3,5-diyl)] (abbreviation: PF-Py), poly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2'-bipyridine-6, 6′-diyl)] (abbreviation: PF-BPy) can also be used. The substances mentioned here are mainly substances having an electron mobility of 10 ⁻⁶ cm ² /Vs or more. Note that a substance other than the above substances may be used for the electron-transport layer 207 as long as the substance has a higher electron-transport property than hole-transport property.

Further, the electron transport layer 207 is not limited to a single layer, and may be a laminate of two or more layers made of the above substances.

The electron injection layer 208 is a layer containing a substance with high electron injection properties. In the electron injection layer 208,
Lithium fluoride (LiF), Cesium fluoride (CsF), Calcium fluoride ( _CaF2 )
, lithium oxide (LiOx), etc., alkaline earth metals, or compounds thereof can be used. Also, rare earth metal compounds such as erbium fluoride (ErF ₃ ) can be used. In addition, the substance constituting the electron transport layer 207 described above can also be used.

Alternatively, a composite material obtained by mixing an organic compound and an electron donor (donor) may be used for the electron injection layer 208 . Such a composite material has excellent electron-injecting and electron-transporting properties because electrons are generated in the organic compound by the electron donor. In this case, the organic compound is preferably a material that is excellent in transporting the generated electrons. can be used. As the electron donor, any substance can be used as long as it exhibits an electron donating property with respect to an organic compound. Specifically, alkali metals, alkaline earth metals, and rare earth metals are preferred, and examples include lithium, cesium, magnesium, calcium, erbium, and ytterbium. Further, alkali metal oxides and alkaline earth metal oxides are preferred, and examples thereof include lithium oxide, calcium oxide and barium oxide. Lewis bases such as magnesium oxide can also be used. An organic compound such as tetrathiafulvalene (abbreviation: TTF) can also be used.

Note that the above-described hole injection layer 204, hole transport layer 205, light emitting layer 206 (206a, 20
6b), the electron-transporting layer 207 and the electron-injecting layer 208 can be formed by a vapor deposition method (including a vacuum vapor deposition method), an inkjet method, a coating method, or the like.

Light emitted from the light-emitting layer 206 of the light-emitting element described above is extracted to the outside through one or both of the first electrode 201 and the second electrode 202 . Therefore, one or both of the first electrode 201 and the second electrode 202 in this embodiment mode are translucent electrodes.

The light-emitting element described in this embodiment increases the efficiency of energy transfer by utilizing the overlap between the emission spectrum of an exciplex and the absorption spectrum of a light-emitting substance (guest material) that converts triplet excitation energy into light emission. Therefore, a light-emitting element with high external quantum efficiency can be realized.

Note that the light-emitting element described in this embodiment is one embodiment of the present invention, and is characterized in particular by the structure of the light-emitting layer. Therefore, by applying the structure described in this embodiment mode, a passive matrix light-emitting device, an active matrix light-emitting device, or the like can be manufactured, and both of these devices are included in the present invention. .

Note that in the case of an active matrix type light emitting device, the structure of the TFT is not particularly limited. For example, a staggered TFT or an inverted staggered TFT can be used as appropriate. Also, T
The drive circuit formed on the FT substrate may also be composed of N-type and P-type TFTs, or may be composed of only one of the N-type TFT and the P-type TFT. Furthermore, the crystallinity of the semiconductor film used for the TFT is not particularly limited. For example, an amorphous semiconductor film, a crystalline semiconductor film, an oxide semiconductor film, or the like can be used.

Note that the structure described in this embodiment can be used in combination with any of the structures described in other embodiments as appropriate.

(Embodiment 3)
In this embodiment, as one embodiment of the present invention, a light-emitting element having a structure in which a plurality of EL layers are provided with a charge-generating layer interposed therebetween (hereinafter referred to as a tandem light-emitting element) will be described.

The light-emitting element described in this embodiment includes a pair of electrodes (first electrode 30
1 and second electrode 304), a plurality of EL layers (first EL layer 302(1), second E
It is a tandem type light emitting device having an L layer 302(2)).

In this embodiment mode, the first electrode 301 is an electrode that functions as an anode, and the second electrode 304 is an electrode that functions as a cathode. Note that the first electrode 301 and the second electrode 304 can have structures similar to those in Embodiment Mode 1. FIG. In addition, multiple EL layers (first
The EL layer 302(1) and the second EL layer 302(2)) may have a structure similar to that of the EL layer described in Embodiment 1 or 2; It may be a configuration. That is, the first EL layer 302(1) and the second EL layer 302(2) may have the same structure or a different structure from that in Embodiment 1 or 2. Similar can be applied.

A charge generation layer (I) 305 is provided between a plurality of EL layers (the first EL layer 302(1) and the second EL layer 302(2)). The charge generation layer (I) 305 has a function of injecting electrons into one EL layer and holes into the other EL layer when a voltage is applied to the first electrode 301 and the second electrode 304 . have. In the case of this embodiment, when a voltage is applied to the first electrode 301 so that the potential is higher than that of the second electrode 304, the charge generation layer (I) 30
5, electrons are injected into the first EL layer 302(1) and holes are injected into the second EL layer 302(2).

Note that the charge generation layer (I) 305 is transparent to visible light from the viewpoint of light extraction efficiency (specifically, the visible light transmittance of the charge generation layer (I) 305 is 40% or more) is preferable. In addition, the charge generation layer (I) 305 is formed between the first electrode 301 and the second electrode 3
Conductivities lower than 04 will also work.

Even if the charge generation layer (I) 305 has a structure in which an electron acceptor (acceptor) is added to an organic compound having a high hole transport property, an electron donor (donor) is added to an organic compound having a high electron transport property. It may be a configuration that is Also, both of these configurations may be stacked.

When an electron acceptor is added to an organic compound having a high hole-transporting property, examples of the organic compound having a high hole-transporting property include NPB, TPD, TDATA, and MTDATA.
, 4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB) and the like. The substances mentioned here are mainly substances having a hole mobility of 10 ⁻⁶ cm ² /Vs or more. However, a substance other than the above may be used as long as it is an organic compound having a higher hole-transport property than an electron-transport property.

Examples of electron acceptors include 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F4-TCNQ) and chloranil.
Moreover, a transition metal oxide can be mentioned. In addition, 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 preferred because it is stable even in the atmosphere, has low hygroscopicity, and is easy to handle.

On the other hand, in the case where an electron donor is added to an organic compound having a high electron transport property, examples of the organic compound having a high electron transport property include Alq, Almq ₃ , BeBq ₂ , B
A metal complex having a quinoline skeleton or a benzoquinoline skeleton, such as Alq, or the like can be used. In addition, metal complexes having oxazole-based or thiazole-based ligands such as Zn(BOX) ₂ and Zn(BTZ) ₂ can also be used. In addition to metal complexes, PBD, OXD-7, TAZ, BPhen, BCP, etc. can also be used. The substances mentioned here are mainly substances having an electron mobility of 10 ⁻⁶ cm ² /Vs or more. Note that any substance other than the above may be used as long as it is an organic compound having a higher electron-transport property than hole-transport property.

Further, as the electron donor, alkali metals, alkaline earth metals, rare earth metals, metals belonging to group 13 in the periodic table, oxides, and carbonates thereof can be used. Specifically, it is preferable to use lithium (Li), cesium (Cs), magnesium (Mg), calcium (Ca), ytterbium (Yb), indium (In), lithium oxide, cesium carbonate, or the like. Alternatively, an organic compound such as tetrathianaphthacene may be used as an electron donor.

Note that by forming the charge-generating layer (I) 305 using the above material, an increase in driving voltage when EL layers are stacked can be suppressed.

Although a light-emitting element having two EL layers is described in this embodiment mode, a light-emitting element in which n layers (where n is 3 or more) of EL layers are stacked as shown in FIG. , can be similarly applied. In the case where a plurality of EL layers are provided between a pair of electrodes as in the light-emitting element according to this embodiment, the charge-generating layer (I) is arranged between the EL layers to
It is possible to emit light in a high luminance region while keeping the current density low. Since the current density can be kept low, a long life device can be realized. In addition, when lighting is used as an application, the voltage drop due to the resistance of the electrode material can be reduced, so uniform light emission over a large area becomes possible. In addition, a light-emitting device that can be driven at low voltage and consumes low power can be realized.

In addition, by making the respective EL layers emit light of different colors, light of a desired color can be obtained from the light-emitting element as a whole. For example, in a light-emitting element having two EL layers, the emission color of the first EL layer and the emission color of the second EL layer are in a complementary color relationship, so that the entire light-emitting element emits white light. It is also possible to obtain Complementary colors refer to the relationship between colors that become achromatic when mixed. In other words, white light emission can be obtained by mixing complementary colors with light obtained from a substance that emits light.

The same applies to a light-emitting element having three EL layers. For example, the first EL layer emits red light, the second EL layer emits green light, and the third EL layer emits red light. When the emission color of is blue, the entire light-emitting element can emit white light.

Note that the structure described in this embodiment can be combined with any of the structures described in other embodiments as appropriate.

(Embodiment 4)
In this embodiment, a light-emitting device that is one embodiment of the present invention will be described.

The light-emitting device described in this embodiment mode has a micro optical resonator (microcavity) structure that utilizes the resonance effect of light between a pair of electrodes, and as shown in FIG. electrode 4
01 and a semi-transmissive/semi-reflective electrode 402). In addition, the EL layer 405 includes at least the light-emitting layer 4 serving as a light-emitting region.
04 (404R, 404G, 404B), and may also include a hole injection layer, a hole transport layer, an electron transport layer, an electron injection layer, a charge generation layer (E), and the like. Note that the light emitting layer 404
(404R, 404G, and 404B) can include the structure of the light-emitting layer which is one embodiment of the present invention as described in Embodiments 1 and 2.

In this embodiment, as shown in FIG. 7, a light-emitting element having a different structure (first light-emitting element (R) 4
10R, a second light emitting element (G) 410G, and a third light emitting element (B) 410B).

The first light emitting element (R) 410R includes a first transparent conductive layer 403a on the reflective electrode 401,
First light-emitting layer (B) 404B, second light-emitting layer (G) 404G, third light-emitting layer (R) 404
It has a structure in which an EL layer 405 partly containing R and a semi-transmissive/semi-reflective electrode 402 are sequentially laminated. In addition, the second light emitting element (G) 410G has the second transparent conductive layer 4 on the reflective electrode 401.
03b, an EL layer 405, and a semi-transmissive/semi-reflective electrode 402 are stacked in this order. Also, the third light emitting element (B) 410B has a structure in which an EL layer 405 and a semi-transmissive/semi-reflective electrode 402 are sequentially stacked on a reflective electrode 401 .

Note that the light emitting elements (the first light emitting element (R) 410R and the second light emitting element (G) 410G
, the third light-emitting element (B) 410B), the reflective electrode 401, the EL layer 405, the transflective/
The semi-reflective electrode 402 is common. Further, the first light-emitting layer (B) 404B emits light (λ _B ) having a peak in a wavelength region of 420 nm or more and 480 nm or less, and the second light-emitting layer (G)
404G emits light (λ _G ) having a peak in a wavelength region of 500 nm or more and 550 nm or less, and the third light emitting layer (R) 404R emits light (λ _R ) having a peak in a wavelength region of 600 nm or more and 760 nm or less. light up. As a result, in any of the light emitting elements (first light emitting element (R) 410R, second light emitting element (G) 410G, third light emitting element (B) 410B), A second light-emitting layer (G) 404G, and a third light-emitting layer (R
) 404R is superimposed, that is, broad light over the visible light region can be emitted. From the above, it is assumed that the length of the wavelength satisfies the relationship of λ _B <λ _G <λ _R.

Each light-emitting element shown in this embodiment includes a reflective electrode 401 and a semi-transmissive/semi-reflective electrode 40 .
2, and light emitted in all directions from each light-emitting layer included in the EL layer 405 functions as a micro optical resonator (microcavity). Resonance is caused by the reflective electrode 401 and the semi-transmissive/semi-reflective electrode 402. The reflective electrode 401 is made of a reflective conductive material, and has a visible light reflectance of 40% to 100%, preferably 70% to 100%, and a resistivity of 1×. 10
It is assumed that the film is ^-2 Ωcm or less. The semi-transmissive/semi-reflective electrode 402 is formed of a reflective conductive material and a light-transmissive conductive material, and the visible light reflectance of the film is 20% to 80%, preferably 40%. % to 70% and its resistivity is 1×10 ⁻
Assume that the film has a resistance of ² Ωcm or less.

In addition, in this embodiment mode, the transparent conductive layers (the first transparent conductive layer 403a, the second transparent conductive layer 403a, the 2
By changing the thickness of the transparent conductive layer 403b), the optical distance between the reflective electrode 401 and the semi-transmissive/semi-reflective electrode 402 is changed for each light emitting element. In other words, broad light emitted from each light-emitting layer of each light-emitting element is distributed between the reflective electrode 401 and the semi-transmissive/semi-reflective electrode 402.
Since it is possible to intensify light of resonating wavelengths and attenuate light of non-resonating wavelengths, light of different wavelengths can be emitted by changing the optical distance between the reflective electrode 401 and the semi-transmissive/semi-reflective electrode 402 for each element. can be taken out.

The optical distance (also referred to as optical path length) is the actual distance multiplied by the refractive index, and in the present embodiment, it represents the actual film thickness multiplied by n (refractive index). . That is, "
Optical distance=actual film thickness×n”.

In addition, in the first light emitting element (R) 410R, from the reflective electrode 401 to the semi-transmissive/semi-reflective electrode 4
02 is mλ _R /2 (where m is a _natural number). However, m
is a natural number), and in the third light emitting element (B) 410B, the total thickness from the reflective electrode 401 to the semi-transmissive/semi-reflective electrode 402 is mλ _B /2 (where m is a natural number).

As described above, the light (λ R ) emitted mainly by the third light emitting layer (R) 404R included in the EL layer 405 is extracted from the first light emitting element ( _R ) 410R, and the second light emitting element (G ) 4
10G mainly extracts light (λ _G ) emitted from the second light emitting layer (G) 404G included in the EL layer 405, and from the third light emitting element (B) 410B, mainly the EL layer 405
The light (λ _B ) emitted by the first light-emitting layer (B) 404B included in is taken out. The light extracted from each light emitting element is emitted from the semi-transmissive/semi-reflective electrode 402 side.

In the above configuration, the total thickness from the reflective electrode 401 to the semi-transmissive/semi-reflective electrode 402 is strictly the total thickness from the reflective area of the reflective electrode 401 to the reflective area of the semi-transmissive/semi-reflective electrode 402. can. However, the reflective electrode 401 and the semi-transmissive/semi-reflective electrode 40
Since it is difficult to strictly determine the position of the reflective area in 2, it is possible to sufficiently obtain the above effect by assuming that an arbitrary position of the reflective electrode 401 and the semi-transmissive/semi-reflective electrode 402 is the reflective area. It shall be possible.

Next, in the first light emitting element (R) 410R, from the reflective electrode 401 to the third light emitting layer (R
) 404R to the desired film thickness ((2m′+1)λ _R /4 (where m′ is a natural number)) to amplify the light emitted from the third light emitting layer (R) 404R. can be made Of the light emitted from the third light-emitting layer (R) 404R, the light reflected by the reflective electrode 401 and returned (first reflected light) is semi-transmissive/semi-reflected from the third light-emitting layer (R) 404R. In order to cause interference with the light (first incident light) directly incident on the electrode 402, the optical distance from the reflective electrode 401 to the third light-emitting layer (R) 404R is set to a desired value ((2m′+1)λ _R / 4 (where m′ is a natural number)) to match the phases of the first reflected light and the first incident light and amplify the light emitted from the third light emitting layer (R) 404R. be able to.

Strictly speaking, the optical distance between the reflective electrode 401 and the third light-emitting layer (R) 404R is the optical distance between the reflective region of the reflective electrode 401 and the light-emitting region of the third light-emitting layer (R) 404R. can be done. However, the reflective region in the reflective electrode 401 and the third light emitting layer (R)
Since it is difficult to strictly determine the position of the light emitting region in 404R, the reflective electrode 40
By assuming an arbitrary position of 1 as a reflective region and an arbitrary position of the third light emitting layer (R) 404R as a light emitting region, the above effect can be obtained sufficiently.

Next, in the second light-emitting element (G) 410G, from the reflective electrode 401 to the second light-emitting layer (G
) 404G to a desired film thickness ((2m″+1)λ _G /4 (where m″ is a natural number)), light emission from the second light emitting layer (G) 404G can be amplified. Of the light emitted from the second light-emitting layer (G) 404G, the light reflected by the reflective electrode 401 and returned (second reflected light) is semi-transmissive/half-reflected from the second light-emitting layer (G) 404G. In order to cause interference with light (second incident light) directly incident on the electrode 402, the reflective electrode 401
to the second light-emitting layer (G) 404G to the desired value ((2m''+1)λ _G /4(
However, by adjusting m'' to be a natural number)), the phases of the second reflected light and the second incident light are matched, and the light emitted from the second light emitting layer (G) 404G is amplified. can be done.

Strictly speaking, the optical distance between the reflective electrode 401 and the second light-emitting layer (G) 404G is the optical distance between the reflective region of the reflective electrode 401 and the light-emitting region of the second light-emitting layer (G) 404G. can be done. However, the reflective region in the reflective electrode 401 and the second light-emitting layer (G)
Since it is difficult to strictly determine the position of the light emitting region in 404G, the reflective electrode 40
By assuming that an arbitrary position of 1 is a reflective region and an arbitrary position of the second light-emitting layer (G) 404G is a light-emitting region, the above effects can be sufficiently obtained.

Next, in the third light emitting element (B) 410B, from the reflective electrode 401 to the first light emitting layer (B
) 404B to the desired film thickness ((2m'''+1)λ _B /4, where m'''
is a natural number)), the light emission from the first light-emitting layer (B) 404B can be amplified. Of the light emitted from the first light-emitting layer (B) 404B, the light reflected by the reflective electrode 401 and returned (third reflected light) is semi-transmissive/semi-reflected from the first light-emitting layer (B) 404B. In order to cause interference with the light (third incident light) directly incident on the electrode 402, the reflective electrode 4
01 to the first light-emitting layer (B) 404B to the desired value ((2m'''+1) _λB
/4 (where m''' is a natural number)), the third reflected light and the third
can be in phase with the incident light from the first light-emitting layer (B) 404B, and the light emitted from the first light-emitting layer (B) 404B can be amplified.

In the third light-emitting element, strictly speaking, the optical distance between the reflective electrode 401 and the first light-emitting layer (B) 404B is It can be said that it is an optical distance to the area. However, since it is difficult to strictly determine the positions of the reflective region in the reflective electrode 401 and the light-emitting region in the first light-emitting layer (B) 404B, an arbitrary position of the reflective electrode 401 is the reflective region and the first light-emitting region. By assuming that an arbitrary position of the layer (B) 404B is the light emitting region, the above effect can be sufficiently obtained.

Note that in the above structure, each of the light-emitting elements has a structure in which a plurality of light-emitting layers are provided in the EL layer; however, the present invention is not limited to this. In combination with the structure of the light-emitting element, a plurality of ELs with a charge generation layer interposed in one light-emitting element
A structure in which layers are provided and one or more light-emitting layers are formed in each EL layer may be employed.

The light-emitting device described in this embodiment has a microcavity structure and has the same EL.
Even if there are layers, different wavelengths of light can be extracted from each light-emitting element, so separate RGB colors are unnecessary. Therefore, it is advantageous in realizing full-color display because it is easy to achieve high definition. A combination with a colored layer (color filter) is also possible. In addition, since it is possible to increase the emission intensity of the specific wavelength in the front direction, it is possible to reduce power consumption. This configuration is particularly useful when applied to a color display (image display device) using pixels of three or more colors, but may also be used for applications such as illumination.

(Embodiment 5)
In this embodiment, a light-emitting device including a light-emitting element that is one embodiment of the present invention will be described.

Further, the light emitting device may be a passive matrix light emitting device or an active matrix light emitting device. Note that the light-emitting elements described in other embodiments can be applied to the light-emitting device described in this embodiment.

In this embodiment mode, an active matrix light-emitting device will be described with reference to FIGS.

Note that FIG. 8A is a top view showing a light-emitting device, and FIG. 8B shows FIG.
It is sectional drawing cut|disconnected by A'. The active matrix light-emitting device according to this embodiment includes a pixel portion 502 provided over an element substrate 501 and a driver circuit portion (source line driver circuit) 50 .
3 and a driving circuit portion (gate line driving circuit) 504 (504a and 504b).
A pixel portion 502, a driver circuit portion 503, and a driver circuit portion 504 are separated by a sealing material 505.
It is sealed between the element substrate 501 and the sealing substrate 506 .

In addition, on the element substrate 501, an external input terminal for transmitting an external signal (for example, a video signal, a clock signal, a start signal, or a reset signal) or a potential to the driver circuit portion 503 and the driver circuit portion 504 is provided. A routing wiring 507 is provided for connection. here,
An example of providing an FPC (flexible printed circuit) 508 as an external input terminal is shown. Although only the FPC is shown here, a printed wiring board (PWB) may be attached to the FPC. The light emitting device in this specification includes not only the main body of the light emitting device but also the state in which the FPC or PWB is attached thereto.

Next, a cross-sectional structure will be described with reference to FIG. A driver circuit portion and a pixel portion are formed over the element substrate 501. Here, a driver circuit portion 503 which is a source line driver circuit is formed.
, and a pixel portion 502 are shown.

A driving circuit portion 503 shows an example in which a CMOS circuit is formed by combining an n-channel TFT 509 and a p-channel TFT 510 . It should be noted that the circuit forming the drive circuit section is
It may be formed by various CMOS circuits, PMOS circuits or NMOS circuits. In addition, in this embodiment mode, a driver integrated type in which a driver circuit is formed over a substrate is shown, but this is not always necessary, and a driver circuit can be formed outside instead of over the substrate.

In addition, the pixel portion 502 includes a plurality of pixels including a switching TFT 511, a current controlling TFT 512, and a first electrode (anode) 513 electrically connected to a wiring (source electrode or drain electrode) of the current controlling TFT 512. Formed by Note that the first electrode (anode) 5
An insulator 514 is formed over the end of 13 . Here, it is formed by using a positive photosensitive acrylic resin.

In addition, in order to improve the coverage of the film laminated on the upper layer, it is preferable that the insulator 514 has a curved surface having a curvature at the upper end portion or the lower end portion thereof. For example, when a positive photosensitive acrylic resin is used as the material of the insulator 514, it is preferable that the upper end portion of the insulator 514 has a curved surface with a radius of curvature (0.2 μm to 3 μm). As the insulator 514, either a negative photosensitive resin or a positive photosensitive resin can be used.
can be used.

An EL layer 515 and a second electrode (cathode) 516 are stacked on the first electrode (anode) 513 . The EL layer 515 is provided with at least a light-emitting layer, and the light-emitting layer has a stacked-layer structure as described in Embodiment Mode 1. FIG. In addition to the light-emitting layer, the EL layer 515 can be appropriately provided with a hole-injection layer, a hole-transport layer, an electron-transport layer, an electron-injection layer, a charge generation layer, and the like.

Note that a light-emitting element 517 is formed with a stacked structure including a first electrode (anode) 513 , an EL layer 515 , and a second electrode (cathode) 516 . First electrode (anode) 513 and EL layer 515
As a material for the second electrode (cathode) 516, the material described in Embodiment 2 can be used. Although not shown here, the second electrode (cathode) 516 is electrically connected to the FPC 508 which is an external input terminal.

Although only one light-emitting element 517 is illustrated in the cross-sectional view of FIG. 8B, a plurality of light-emitting elements are arranged in matrix in the pixel portion 502 . Pixel unit 5
In 02, light emitting elements capable of emitting light of three types (R, G, B) are selectively formed,
A light-emitting device capable of full-color display can be formed. Further, a light-emitting device capable of full-color display may be obtained by combining with a colored layer (color filter).

Furthermore, by bonding the sealing substrate 506 to the element substrate 501 with the sealing material 505, a structure in which a light emitting element 517 is provided in a space 518 surrounded by the element substrate 501, the sealing substrate 506, and the sealing material 505 is obtained. ing. Note that the space 518 may be filled with the sealing material 505 in addition to the case where the space 518 is filled with an inert gas (nitrogen, argon, or the like).

Note that epoxy resin, low-melting glass, or the like is preferably used for the sealing material 505 . In addition, it is desirable that these materials be materials that do not transmit moisture and oxygen as much as possible. Materials used for the sealing substrate 506 include a glass substrate, a quartz substrate, FRP (fiber
A plastic substrate made of glass-reinforced plastics), PVF (polyvinyl fluoride), polyester, acrylic, or the like can be used.

As described above, an active matrix light-emitting device can be obtained.

Note that the structure described in this embodiment can be combined with any of the structures described in other embodiments as appropriate.

(Embodiment 6)
In this embodiment, examples of various electronic devices completed using a light-emitting device manufactured using a light-emitting element that is one embodiment of the present invention will be described with reference to FIGS.

Examples of electronic devices to which light-emitting devices are applied include television devices (also referred to as televisions or television receivers), monitors for computers, digital cameras, digital video cameras, digital photo frames, mobile phones (mobile phones, mobile phones, etc.). (also called telephone equipment),
Portable game machines, personal digital assistants, sound reproducing devices, large game machines such as pachinko machines, and the like. Specific examples of these electronic devices are shown in FIG.

FIG. 9A shows an example of a television device. The television device 7100 is
A display portion 7103 is incorporated in a housing 7101 . Images can be displayed on the display portion 7103 , and the light-emitting device can be used for the display portion 7103 . Further, here, a structure in which the housing 7101 is supported by a stand 7105 is shown.

The television apparatus 7100 can be operated using operation switches provided in the housing 7101 or a separate remote controller 7110 . Channels and volume can be operated with operation keys 7109 included in the remote controller 7110, and images displayed on the display portion 7103 can be operated. Further, the remote controller 7110 may be provided with a display portion 7107 for displaying information output from the remote controller 7110 .

Note that the television device 7100 is configured to include a receiver, a modem, and the like. The receiver can receive general television broadcasts, and by connecting to a wired or wireless communication network via a modem, one-way (from the sender to the receiver) or two-way (
It is also possible to communicate information between a sender and a receiver, or between receivers, etc.).

FIG. 9B shows a computer including a main body 7201, a housing 7202, a display portion 7203, a keyboard 7204, an external connection port 7205, a pointing device 7206, and the like. Note that the computer is manufactured using the light-emitting device for the display portion 7203 .

FIG. 9C shows a portable game machine including two housings, a housing 7301 and a housing 7302, which are connected by a connecting portion 7303 so as to be openable and closable. A display portion 7304 is incorporated in the housing 7301 and a display portion 7305 is incorporated in the housing 7302 . In addition, the portable game machine shown in FIG. 9C includes a speaker portion 7306 and a recording medium insertion portion 7307.
, LED lamp 7308, input means (operation key 7309, connection terminal 7310, sensor 73
11 (force, displacement, position, speed, acceleration, angular velocity, number of rotations, distance, light, liquid, magnetism, temperature, chemical substances, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, including a function to measure inclination, vibration, smell or infrared rays), a microphone 7312), etc. Of course, the configuration of the portable game machine is not limited to the one described above, and at least the display section 73
04 and the display portion 7305, or one of which may be a light-emitting device, and other accessories may be provided as appropriate. The portable game machine shown in FIG. 9(C) has a function of reading out a program or data recorded in a recording medium and displaying it on a display unit, and performing wireless communication with other portable game machines to share information. have a function. Note that the functions of the portable game machine shown in FIG. 9C are not limited to this, and can have various functions.

FIG. 9D shows an example of a mobile phone. A mobile phone 7400 includes a housing 7401
In addition to a display unit 7402 incorporated in the device, it includes operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. Note that the mobile phone 7400 is manufactured using a light-emitting device for the display portion 7402 .

Information can be input to the mobile phone 7400 illustrated in FIG. 9D by touching the display portion 7402 with a finger or the like. An operation such as making a call or composing an email can be performed by touching the display portion 7402 with a finger or the like.

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

For example, in the case of making a call or composing an e-mail, the display portion 7402 is set to a character input mode in which characters are mainly input, and characters displayed on the screen can be input. In this case, it is preferable to display a keyboard or number buttons on most of the screen of the display portion 7402 .

In addition, by providing a detection device having a sensor such as a gyro or an acceleration sensor for detecting inclination inside the mobile phone 7400, the orientation (vertical or horizontal) of the mobile phone 7400 can be determined,
The screen display of the display portion 7402 can be automatically switched.

Switching of the screen mode is performed by touching the display portion 7402 or operating the operation button 7403 of the housing 7401 . Further, switching can be performed according to the type of image displayed on the display portion 7402 . For example, if the image signal to be displayed on the display unit is moving image data, the mode is switched to the display mode, and if the image signal is text data, the mode is switched to the input mode.

In the input mode, a signal detected by the optical sensor of the display portion 7402 is detected, and if there is no input by a touch operation on the display portion 7402 for a certain period of time, the screen mode is switched from the input mode to the display mode. may be controlled.

The display portion 7402 can also function as an image sensor. For example, the display unit 7
Personal authentication can be performed by touching the device 402 with a palm or a finger and taking an image of a palm print, a fingerprint, or the like.
Further, when a backlight that emits near-infrared light or a light source for sensing that emits near-infrared light is used for the display portion, an image of a finger vein, a palm vein, or the like can be captured.

FIGS. 10A and 10B show a tablet terminal that can be folded in half. Figure 10 (A
) is an open state, and the tablet terminal includes a housing 9630, a display portion 9631a, a display portion 9631b, a display mode switching switch 9034, a power switch 9035, a power saving mode switching switch 9036, a fastener 9033, and an operation switch 9038. , has Note that the tablet terminal is manufactured using a light-emitting device for one or both of the display portion 9631a and the display portion 9631b.

Part of the display portion 9631a can be a touch panel region 9632a, and data can be input by touching a displayed operation key 9637. FIG. Note that the display unit 96
In 31a, as an example, a configuration in which half of the area has only a display function and a configuration in which the other half of the area has a touch panel function is shown, but the configuration is not limited to this. Display unit 96
The entire area of 31a may have a touch panel function. For example, the display unit 9
The entire surface of 631a can be used as a touch panel by displaying keyboard buttons, and the display portion 9631b can be used as a display screen.

Further, in the display portion 9631b, part of the display portion 9631b can be used as a touch panel region 9632b, similarly to the display portion 9631a. Further, a keyboard button can be displayed on the display portion 9631b by touching a position where the keyboard display switching button 9639 of the touch panel is displayed with a finger, a stylus, or the like.

Further, touch input can be performed simultaneously on the touch panel region 9632a and the touch panel region 9632b.

A display mode switching switch 9034 can switch the orientation of display such as vertical display or horizontal display, and can select switching between black-and-white display and color display. The power saving mode switching switch 9036 can optimize display luminance according to the amount of external light during use detected by an optical sensor incorporated in the tablet terminal. The tablet terminal may incorporate not only the optical sensor but also other detection devices such as a sensor for detecting inclination such as a gyro and an acceleration sensor.

Further, FIG. 10A shows an example in which the display areas of the display portion 9631b and the display portion 9631a are the same; however, there is no particular limitation. can be different. For example, one of them may be a display panel capable of displaying with higher definition than the other.

FIG. 10B shows a closed state, and the tablet terminal includes a housing 9630, a solar cell 9
633, a charge/discharge control circuit 9634, a battery 9635, and a DCDC converter 9636. Note that the battery 963 is an example of the charge/discharge control circuit 9634 in FIG.
5, a configuration with a DCDC converter 9636 is shown.

Note that since the tablet terminal can be folded in half, the housing 9630 can be closed when not in use. Therefore, since the display portions 9631a and 9631b can be protected,
It is possible to provide a tablet terminal that is highly durable and highly reliable from the standpoint of long-term use.

In addition, the tablet terminals shown in FIGS. 10(A) and 10(B) have a function of displaying various information (still images, moving images, text images, etc.), a calendar, a date or time, and the like. It can have a function of displaying on the display unit, a touch input function of performing a touch input operation or editing information displayed on the display unit, a function of controlling processing by various software (programs), and the like.

A solar cell 9633 attached to the surface of the tablet terminal can supply power to a touch panel, a display portion, a video signal processing portion, or the like. Note that the solar cell 9633 can be provided on one side or both sides of the housing 9630 so that the battery 9635 can be efficiently charged. Note that use of a lithium ion battery as the battery 9635 has an advantage such as miniaturization.

Also, the configuration and operation of the charge/discharge control circuit 9634 shown in FIG.
C) shows a block diagram for explanation. In FIG. 10C, a solar cell 9633 and a battery 9
635, DCDC converter 9636, converter 9638, switches SW1 to SW3
, a display unit 9631, a battery 9635, a DCDC converter 963
6. The converter 9638 and the switches SW1 to SW3 correspond to the charge/discharge control circuit 9634 shown in FIG. 10B.

First, an example of operation in the case where the solar cell 9633 generates power with external light is described. The power generated by the solar cell 9633 is stepped up or down in a DCDC converter 9636 so as to have a voltage for charging the battery 9635 . And the display part 9631
When the power from the solar battery 9633 is used for the operation of , the switch SW1 is turned on, and the converter 9638 steps up or down the voltage necessary for the display portion 9631 . When not displaying on the display unit 9631, the switch SW1 is turned off and the switch S is turned off.
A configuration in which W2 is turned on and the battery 9635 is charged may be employed.

Although the solar cell 9633 is shown as an example of power generation means, it is not particularly limited.
The battery 9635 may be charged by other power generation means such as a piezoelectric element (piezo element) or a thermoelectric conversion element (Peltier element). For example, a non-contact power transmission module that transmits and receives power wirelessly (non-contact) for charging may be used in combination with other charging means.

Further, it goes without saying that the electronic device is not particularly limited to the electronic device shown in FIG. 10 as long as it has the display unit described in the above embodiment.

As described above, an electronic device can be obtained by applying the light-emitting device which is one embodiment of the present invention. The application range of the light-emitting device is extremely wide and can be applied to electronic devices in all fields.

Note that the structure described in this embodiment can be combined with any of the structures described in other embodiments as appropriate.

(Embodiment 7)
In this embodiment, an example of a lighting device to which a light-emitting device including a light-emitting element of one embodiment of the present invention is applied will be described with reference to FIGS.

FIG. 11 shows an example in which a light-emitting device is used as an indoor lighting device 8001 . Note that since the light-emitting device can have a large area, a large-area lighting device can be formed. Alternatively, by using a housing with a curved surface, the lighting device 8002 having a light-emitting region with a curved surface can be formed. The light-emitting element included in the light-emitting device described in this embodiment is thin film, and the housing has a high degree of freedom in design. Therefore, it is possible to form lighting devices with various elaborate designs. Further, a large lighting device 8003 may be provided on the wall surface of the room.

By using the light-emitting device on the surface of the table, the lighting device 8004 can function as a table. By using the light-emitting device as part of other furniture, the lighting device can function as furniture.

As described above, various lighting devices to which the light-emitting device is applied can be obtained. Note that these lighting devices are included in one embodiment of the present invention.

Further, the structure described in this embodiment can be combined with any of the structures described in other embodiments as appropriate.

Example 1 In this example, a light-emitting element 1 which is one embodiment of the present invention will be described with reference to FIGS. Chemical formulas of materials used in this example are shown below.

<<Production of Light-Emitting Element 1>>
First, indium tin oxide containing silicon oxide (ITSO) was deposited over a substrate 1100 made of glass by a sputtering method to form a first electrode 1101 functioning as an anode. The film thickness was set to 110 nm, and the electrode area was set to 2 mm×2 mm.

Next, as a pretreatment for forming the light emitting element 1 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.

After that, the substrate is introduced into a vacuum deposition apparatus whose inside is evacuated to about 10 ⁻⁴ Pa, and vacuum baked at 170° C. for 30 minutes in a heating chamber in the vacuum deposition apparatus. Allow to cool.

Next, the substrate 1100 was fixed to a holder provided in a vacuum deposition apparatus so that the surface on which the first electrode 1101 was formed faced downward. In this embodiment, the EL layer 1 is formed by a vacuum evaporation method.
A case where the hole injection layer 1111, the hole transport layer 1112, the light emitting layer 1113, the electron transport layer 1114, and the electron injection layer 1115 which constitute 102 are sequentially formed will be described.

After reducing the pressure in the vacuum apparatus to 10 ⁻⁴ Pa, 1,3,5-tri(dibenzothiophene-4
-yl)benzene (abbreviation: DBT3P-II) and molybdenum (VI) oxide, DBT3
A hole-injection layer 1111 was formed over the first electrode 1101 by co-evaporating P-II (abbreviation): molybdenum oxide at a ratio of 4:2 (mass ratio). The film thickness was set to 20 nm. Note that co-evaporation is a vapor deposition method in which a plurality of different substances are simultaneously evaporated from different evaporation sources.

Next, a hole transport layer 1112 was formed by vapor-depositing 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP) to a thickness of 20 nm.

Next, a light-emitting layer 1113 was formed over the hole-transport layer 1112 . 2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation:
2mDBTBPDBq-II), N-(1,1′-biphenyl-4-yl)-N-[4-
(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H
-fluorene-2-amine (abbreviation: PCBBiF), (acetylacetonato)bis(6-
tert-butyl-4-phenylpyrimidinato)iridium (III) (abbreviation: [Ir (
tBuppm) ₂ (acac)]) to 2mDBTBPDBq-II (abbreviation): PCBB
iF (abbreviation): [Ir(tBuppm) ₂ (acac)] (abbreviation) = 0.7:0.3:0
. 05 (mass ratio) to form a first light-emitting layer 1113a with a thickness of 20 nm, then 2mDBTBPDBq-II (abbreviation), N,N′-bis(9,9-dimethylfluorene-2 -yl)-N,N'-di(biphenyl-4-yl)-1,4-phenylenediamine (abbreviation: FBi2P), bis{4,6-dimethyl-2-[5-(2,6-dimethylphenyl) )-3-(3,5-dimethylphenyl)-2-pyrazinyl-κN]phenyl-κC
}(2,8-dimethyl-4,6-nonanedionato-κ ² O,O′)iridium (III)
(Abbreviation: [Ir (dmdppr-dmp) ₂ (divm)]), 2mDBTBPDBq
-II (abbreviation): FBi2P (abbreviation): [Ir (dmdppr-dmp) ₂ (divm)
] (abbreviation)=0.8:0.2:0.05 (mass ratio), and the second light-emitting layer 1113b is formed to have a thickness of 20 nm, thereby forming a light-emitting layer having a laminated structure. 1113 was formed.

Next, 2mDBTBPDBq-II (abbreviation) was vapor-deposited over the light-emitting layer 1113 to a thickness of 15 nm, and then bathophenanthroline (abbreviation: Bphen) was vapor-deposited to a thickness of 10 nm to form an electron-transporting layer 1114 . Furthermore, an electron injection layer 1115 was formed on the electron transport layer 1114 by evaporating lithium fluoride to a thickness of 1 nm.

Finally, aluminum was vapor-deposited on the electron injection layer 1115 to a thickness of 200 nm to form a second electrode 1103 serving as a cathode, whereby a light-emitting element 1 was obtained. In addition, in the vapor deposition process described above, the resistance heating method was used for all the vapor depositions.

Table 1 shows the element structure of Light-Emitting Element 1 obtained as described above.

In addition, the fabricated light-emitting element 1 was sealed in a glove box in a nitrogen atmosphere so as not to be exposed to the atmosphere (a sealing material was applied around the element, and heat treatment was performed at 80° C. for 1 hour during sealing).

<<Operating Characteristics of Light-Emitting Element 1>>
The operating characteristics of the manufactured light-emitting element 1 were measured. The measurement was performed at room temperature (atmosphere maintained at 25°C).

First, FIG. 13 shows the current density-luminance characteristics of Light-Emitting Element 1. In FIG. In FIG. 13, the vertical axis indicates luminance (cd/m ² ) and the horizontal axis indicates current density (mA/cm ² ). FIG. 14 shows the voltage-luminance characteristics of Light-Emitting Element 1. FIG. In FIG. 14, the vertical axis represents luminance (cd/m ² ),
The horizontal axis indicates voltage (V). FIG. 15 shows luminance-current efficiency characteristics of Light-Emitting Element 1. In FIG. In FIG. 15, the vertical axis represents current efficiency (cd/A) and the horizontal axis represents luminance (cd/m ² ). FIG. 16 shows the voltage-current characteristics of Light-Emitting Element 1. FIG. In FIG. 16, the vertical axis indicates current (mA) and the horizontal axis indicates voltage (V).

FIG. 15 shows that the light-emitting element 1 which is one embodiment of the present invention is a highly efficient element. Table 2 below shows main initial characteristic values of Light-Emitting Element 1 at around 1000 cd/m ² .

From the above results, it can be seen that Light-Emitting Element 1 manufactured in this example exhibits high external quantum efficiency and thus high emission efficiency.

FIG. 17 shows an emission spectrum obtained when a current was applied to the light-emitting element 1 at a current density of 25 mA/cm ² . As shown in FIG. 17, the emission spectrum of the light-emitting element 1 is 546 nm and 615 nm.
It has two peaks in the vicinity of nm, each of which corresponds to the phosphorescent organometallic iridium complex [Ir(
tBuppm) ₂ (acac)] and [Ir(dmdppr-dmp) ₂ (divm)].

According to cyclic voltammetry measurements, the HOMO level of PCBBiF, which is the second organic compound having hole-transporting properties, is −5.36 eV, and FBi2P, which is the third organic compound having hole-transporting properties, is −5.36 eV. The HOMO level of was estimated to be −5.13 eV. Therefore, the HOMO level of the second organic compound is lower than that of the third organic compound.

Here, FIG. 18 shows 2mDBTBPDBq, which is the first organic compound having an electron-transport property.
-II thin film emission spectrum, PCBBi, a second organic compound with hole-transport properties
Emission spectra of thin films of F and mixed films of 2mDBTBPDBq-II and PCBBiF (
Co-evaporated film) shows the emission spectrum. Further, FIG. 19 shows the emission spectrum of a thin film of 2mDBTBPDBq-II, which is the first organic compound having an electron-transporting property, the emission spectrum of a thin film of FBi2P, which is the third organic compound having a hole-transporting property, and 2mDBTBPDBq-.
The emission spectrum of a mixed film (co-deposited film) of II and FBi2P is shown.

From FIGS. 18 and 19, the emission wavelength of the mixed film is positioned longer than the emission wavelength of the single film of each material, so the first organic compound (2mDBTBPDBq-II) and the second organic compound (PCBBBiF ), and the first organic compound (2mDBTBPDBq-II) and the third organic compound (FBi2P) each form an exciplex. Further, the emission wavelength of the exciplex formed by the first organic compound (2mDBTBPDBq-II) and the second organic compound (PCBBiF) is 511 nm, whereas the first organic compound (2mD
Since the emission wavelength of the exciplex formed by BTBPDBq-II) and the third organic compound (FBi2P) is 553 nm, the former has higher energy.

101 First electrode 102 Second electrode 103 EL layer 104 Hole-injection layer 105 Hole-transport layer 106 Light-emitting layer 106a First light-emitting layer 106b Second light-emitting layer 107 Electron-transport layer 108 Electron-injection layer 109 Light-emitting substance 109a First luminescent substance 109b that converts triplet excitation energy into luminescence Second luminescent substance 110 that converts triplet excitation energy into luminescence First organic compound 111 Second organic compound 112 Third organic compound 201 Second 1 electrode (anode)
202 second electrode (cathode)
203 EL layer 204 hole-injection layer 205 hole-transport layer 206 light-emitting layer 206a first light-emitting layer 206b second light-emitting layer 207 electron-transport layer 208 electron-injection layer 209 light-emitting substance 209a first layer that converts triplet excitation energy into light emission 1 luminescent material 209b converts triplet excitation energy into luminescence second luminescent material 210 first organic compound 211 second organic compound 212 third organic compound 301 first electrode 302(1) first electrode EL layer 302(2) Second EL layer 302(n-1) (n-1)th EL layer 302(n) (n)th EL layer 304 second electrode 305 charge generation layer (I)
305(1) First charge generation layer (I)
305(2) Second charge generation layer (I)
305(n-2) the (n-2)th charge generation layer (I)
305(n-1) the (n-1)th charge generation layer (I)
401 Reflective electrode 402 Semi-transmissive/semi-reflective electrode 403a First transparent conductive layer 403b Second transparent conductive layer 404B First light-emitting layer (B)
404G second light-emitting layer (G)
404R third light-emitting layer (R)
405 EL layer 410R First light emitting element (R)
410G Second light emitting element (G)
410B Third light emitting element (B)
501 element substrate 502 pixel portion 503 driver circuit portion (source line driver circuit)
504a, 504b drive circuit unit (gate line drive circuit)
505 sealing material 506 sealing substrate 507 routing wiring 508 FPC (flexible printed circuit)
509 n-channel TFT
510 p-channel TFT
511 Switching TFT
512 current control TFT
513 first electrode (anode)
514 insulator 515 EL layer 516 second electrode (cathode)
517 Light-emitting element 518 Space 7100 Television device 7101 Housing 7103 Display unit 7105 Stand 7107 Display unit 7109 Operation keys 7110 Remote controller 7201 Main unit 7202 Housing 7203 Display unit 7204 Keyboard 7205 External connection port 7206 Pointing device 7301 Housing 7302 Housing 7303 connecting portion 7304 display portion 7305 display portion 7306 speaker portion 7307 recording medium insertion portion 7308 LED lamp 7309 operation key 7310 connection terminal 7311 sensor 7312 microphone 7400 mobile phone 7401 housing 7402 display portion 7403 operation button 7404 external connection port 7405 speaker 7406 microphone 8001 lighting device 8002 lighting device 8003 lighting device 8004 lighting device 9033 fastener 9034 display mode switching switch 9035 power switch 9036 power saving mode switching switch 9038 operation switch 9630 housing 9631 display section 9631a display section 9631b display section 9632a touch panel region 9632b touch panel area 9633 solar cell 9634 charge/discharge control circuit 9635 battery 9636 DCDC converter 9637 operation key 9638 converter 9639 button

Claims (8)

having a light-emitting layer between the anode and the cathode;
The light-emitting layer has a first light-emitting layer and a second light-emitting layer,
the first light-emitting layer is located between the anode and the second light-emitting layer;
the first light-emitting layer includes a first organometallic complex, a first organic compound, and a second organic compound;
the second light-emitting layer includes a second organometallic complex, the first organic compound, and a third organic compound;
The highest occupied molecular orbital level (HOMO level) of the second organic compound is lower than the highest occupied molecular orbital level (HOMO level) of the third organic compound,
The first organic compound is a π-deficient heteroaromatic compound,
the second organic compound is a π-excessive heteroaromatic compound or an aromatic amine compound;
the third organic compound is a π-excessive heteroaromatic compound or an aromatic amine compound,
the first organic compound and the second organic compound are a combination that forms a first exciplex;
the first organic compound and the third organic compound are a combination that forms a second exciplex;
Light emission in which the difference between the energy value of the peak of the emission spectrum of the first exciplex and the energy value of the peak of the absorption band on the lowest energy side of the absorption spectrum of the first organometallic complex is within 0.2 eV. element. having a light-emitting layer between the anode and the cathode;
The light-emitting layer has a first light-emitting layer and a second light-emitting layer,
the first light-emitting layer is located between the anode and the second light-emitting layer;
the first light-emitting layer includes a first organometallic complex, a first organic compound, and a second organic compound;
the second light-emitting layer includes a second organometallic complex, the first organic compound, and a third organic compound;
The highest occupied molecular orbital level (HOMO level) of the second organic compound is lower than the highest occupied molecular orbital level (HOMO level) of the third organic compound,
The first organic compound is a π-deficient heteroaromatic compound,
the second organic compound is a π-excessive heteroaromatic compound or an aromatic amine compound;
the third organic compound is a π-excessive heteroaromatic compound or an aromatic amine compound,
the first organic compound and the second organic compound are a combination that forms a first exciplex;
the first organic compound and the third organic compound are a combination that forms a second exciplex;
Light emission in which the difference between the energy value of the peak of the emission spectrum of the second exciplex and the energy value of the peak of the absorption band on the lowest energy side of the absorption spectrum of the second organometallic complex is within 0.2 eV. element. having a light-emitting layer between the anode and the cathode;
The light-emitting layer has a first light-emitting layer and a second light-emitting layer,
the first light-emitting layer is located between the anode and the second light-emitting layer;
the first light-emitting layer includes a first organometallic complex, a first organic compound, and a second organic compound;
the second light-emitting layer includes a second organometallic complex, the first organic compound, and a third organic compound;
The highest occupied molecular orbital level (HOMO level) of the second organic compound is lower than the highest occupied molecular orbital level (HOMO level) of the third organic compound,
The first organic compound is a π-deficient heteroaromatic compound,
the second organic compound is a π-excessive heteroaromatic compound or an aromatic amine compound;
the third organic compound is a π-excessive heteroaromatic compound or an aromatic amine compound,
the first organic compound and the second organic compound are a combination that forms a first exciplex;
the first organic compound and the third organic compound are a combination that forms a second exciplex;
the difference between the energy value of the peak of the emission spectrum of the first exciplex and the energy value of the peak of the absorption band on the lowest energy side of the absorption spectrum of the first organometallic complex is within 0.2 eV;
Light emission in which the difference between the energy value of the peak of the emission spectrum of the second exciplex and the energy value of the peak of the absorption band on the lowest energy side of the absorption spectrum of the second organometallic complex is within 0.2 eV. element. In any one of claims 1 to 3,
The T1 level of the first organic compound is higher than the T1 level of the first organometallic complex,
A light-emitting element in which the T1 level of the second organic compound is higher than the T1 level of the first organometallic complex. In any one of claims 1 to 4,
The T1 level of the first organic compound is higher than the T1 level of the second organometallic complex,
A light-emitting element in which the T1 level of the third organic compound is higher than the T1 level of the second organometallic complex. A light-emitting device comprising the light-emitting element according to claim 1 . An electronic device comprising the light-emitting device according to claim 6 . A lighting device comprising the light emitting device according to claim 6 .

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