JP6723421B2 - Light emitting element, light emitting device, electronic device and lighting device - Google Patents

Description

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

A light-emitting element using an organic compound as a light-emitting body, which has features such as thinness and lightness, high-speed response, and direct current low voltage driving, is expected to be applied to next-generation flat panel displays. In particular, a display device in which light emitting elements are arranged in a matrix is considered to be superior to a conventional liquid crystal display device in that it has a wide viewing angle and excellent visibility.

The light-emitting mechanism of the light-emitting element is such that electrons are injected from the cathode and holes are injected from the anode by re-applying at the emission center of the EL layer by applying a voltage with an EL layer containing a light-emitting body sandwiched between a pair of electrodes. It is said that they combine to form a molecular exciton, and when the molecular exciton relaxes to the ground state, it emits energy and emits light. Singlet excitation and triplet excitation are known as excited states, and it is considered that light emission is possible through either excited state.

With respect to such a light emitting element, in order to improve the element characteristics, improvement of the element structure, material development and the like have been actively carried out (for example, refer to Patent Document 1).

JP, 2010-182699, A

However, the light extraction efficiency of the light emitting device at present is said to be about 20% to 30%, and the external quantum efficiency of the light emitting device using the phosphorescent compound is considered even in consideration of light absorption by the reflective electrode or the transparent electrode. Is considered to be around 25%.

Therefore, in one embodiment of the present invention, a light-emitting element with high external quantum efficiency is provided. Further, one embodiment of the present invention provides a light-emitting element with a long life.

One embodiment of the present invention has a light-emitting layer between a pair of electrodes (anode and cathode), and the light-emitting layer has a first light-emitting substance (guest material) that converts triplet excitation energy into light emission and an electron-transporting property. A first light-emitting layer which is formed on the anode side and which contains at least a first organic compound (host material) and a second organic compound (assist material) having a hole transporting property, and triplet excitation energy. It is formed by including at least a second light-emitting substance (guest material) that converts to light emission, a third organic compound (host material) having an electron transporting property, and a second organic compound (assisting material) having a hole transporting property. In the first light emitting layer, the first organic compound (host material) and the second organic compound (assist material) are a combination forming an exciplex. The second light-emitting layer is a light-emitting device characterized in that the third organic compound (host material) and the second organic compound (assist material) are a combination that forms an exciplex.

Further, another embodiment of the present invention has a light-emitting layer between an anode and a cathode, a hole-transporting layer between the anode and the light-emitting layer, and an electron-transporting layer between the cathode and the light-emitting layer. The light emitting layer has a layer, and the light emitting layer contains at least a first light emitting substance that converts triplet excitation energy into light emission, a first organic compound having an electron transporting property, and a second organic compound having a hole transporting property. A first light-emitting layer containing and formed in contact with the hole-transporting layer, a second light-emitting substance that converts triplet excitation energy into light emission, a third organic compound having an electron-transporting property, and hole-transporting And a second light-emitting layer that is formed in contact with the electron-transporting layer and that includes at least a second organic compound having a property, and in the first light-emitting layer, the first organic compound (host material) is used. And the second organic compound (assist material),
And a second organic compound (host material) and a second organic compound (assist material) in the second light-emitting layer, which is a combination forming an exciplex. It is a light emitting element.

Note 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 (assist material) in the first light-emitting layer is the first organic compound (host Emission wavelength (fluorescence wavelength) of each of the material) and the second organic compound (assist material)
Since it exists on the long-wavelength side as compared with, 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 by forming an exciplex. It can be converted into an emission spectrum located on the wavelength side. In addition, the emission wavelength of the exciplex formed by the third organic compound (host material) and the second organic compound (assist material) in the second light emitting layer is the same as that of the third organic compound (host material) and the second organic compound (host material). Organic compounds (
Since they exist on the longer wavelength side compared to the respective emission wavelengths (fluorescence wavelengths) of the assist material), they form an exciplex to form the fluorescence spectrum of the third organic compound (host material) and the second organic compound. The fluorescence spectrum of the compound (assist material) can be converted into the emission spectrum located on the longer wavelength side.

Note that in each of the above structures, in the first light-emitting layer, the anion of the first organic compound and the second
Is characterized in that an exciplex is formed from the cation of the organic compound, and the exciplex is formed from the anion of the third organic compound and the cation of the second organic compound in the second light-emitting layer.

In the above structure, the first light-emitting layer and the second light-emitting layer each include the same second organic compound (assist material), and the first organic compound (host material) included in the first light-emitting layer. ) Is characterized by having a higher lowest unoccupied molecular orbital level (LUMO level) than the third organic compound (host material) contained in the second light emitting layer.

Further, in the above structure, the first light-emitting substance contained in the first light-emitting layer is a substance which emits light of a shorter wavelength than the second light-emitting substance contained in the second light-emitting layer. And

In the above structure, the first light-emitting substance and the second light-emitting substance are light-emitting substances that convert triplet excitation energy into light emission, and include phosphorescent compounds such as organometallic complexes and heat-activated delayed fluorescence. , Ie, thermally activated delayed fluorescence (TADF: Thermally A
Activated Delayed Fluorescence) material can be used. In addition, the first organic compound and the third organic compound are mainly 10 ⁻⁶ cm ² /V.
An electron transporting material having an electron mobility of s or more, specifically, a π-deficient heteroaromatic compound, and the second organic compound mainly has a hole mobility of 10 ⁻⁶ cm ² /Vs or more. A hole-transporting material, specifically, a π-excess type heteroaromatic compound or an aromatic amine compound.

Further, one embodiment of the present invention includes not only a light-emitting device having a light-emitting element but also an electronic device and a lighting device having the light-emitting device in its category. 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). Also,
The light emitting device has a connector, for example, an FPC (Flexible printed circuit).
it) or TCP (Tape Carrier Package) attached module, a module provided with a printed wiring board in front of TCP, or a light emitting element with C
It is assumed that the light emitting device includes all modules in which an IC (integrated circuit) is directly mounted by an OG (Chip On Glass) method.

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 included in the light-emitting layer; A highly efficient light emitting element can be realized.

In the light-emitting element which is one embodiment of the present invention, the exciplex formed in the first light-emitting layer has higher excitation energy than the exciplex formed in the second light-emitting layer with the above-described element structure. As a first light-emitting substance (guest material) that changes the triplet excitation energy contained in the first light-emitting layer into light emission, the triplet excitation energy contained in the second light-emitting layer becomes light emission. By using a substance that emits light having 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. Of the excitation energy of the exciplex formed in the second light-emitting layer, part of the energy that could not contribute to light emission is converted into triplet excitation energy in the second light-emitting layer into light emission. Since it can be used as the excitation energy for (1), the luminous efficiency of the light emitting element can be further improved.

7A to 7C each illustrate a concept of one embodiment of the present invention. 7A to 7C each illustrate a concept of one embodiment of the present invention. 6A and 6B are diagrams showing calculation results according to one embodiment of the present invention. 6A and 6B are graphs showing calculation results according to one embodiment of the present invention. 7A and 7B are diagrams illustrating a structure of a light-emitting element. 7A and 7B are diagrams illustrating a structure of a light-emitting element. FIG. 6 illustrates a light-emitting device. FIG. 6 illustrates a light-emitting device. 7A to 7C each illustrate an electronic device. 7A to 7C each illustrate an electronic device. FIG. 6 illustrates a lighting device. FIG. 6 illustrates a light-emitting element. FIG. 6 is a graph showing current density-luminance characteristics of Light-Emitting Element 1. FIG. 6 is a diagram showing voltage-luminance characteristics of the light-emitting element 1. FIG. 6 is a graph showing luminance-current efficiency characteristics of Light-Emitting Element 1. FIG. 6 is a diagram showing voltage-current characteristics of the light-emitting element 1. FIG. 8 shows an emission spectrum of the light-emitting element 1. FIG. 10 shows an emission spectrum of a substance used for a light-emitting element 1. FIG. 10 shows an emission spectrum of a substance used for a light-emitting element 1.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and its form and details can be variously modified without departing from the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited to the description of the embodiments below.

(About the elementary process of light emission in the light emitting element)
First, a general elementary process of light emission in a light-emitting element 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 will be described. In addition, here, a molecule that gives excitation energy is described as a host molecule, and a molecule that receives excitation energy is described as a guest molecule.

(1) When electrons and holes are recombined in the guest molecule and the guest molecule is in an excited state (direct recombination process).

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

(1-2) When the Excited State of the Guest Molecule is the Singlet Excited State The guest molecule in the singlet excited state intersystems with the triplet excited state to emit phosphorescence.

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

(2) When electrons and holes are recombined 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 the triplet excited state When the T1 level of the host molecule is higher than the T1 level of the guest molecule, the excitation energy is transferred from the host molecule to the guest molecule, and the guest molecule is It becomes a triplet excited state. The guest molecule in the triplet excited state emits phosphorescence. Note that energy transfer from the T1 level of the host molecule to the singlet excitation energy level of the guest molecule (S1 level) is forbidden unless the host molecule emits phosphorescence, and is not a main energy transfer process. It is 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 the singlet excited state When the S1 level of the host molecule is higher than the S1 level and T1 level of the guest molecule, the excitation energy is transferred from the host molecule to the guest molecule. The guest molecule is in a singlet excited state or a triplet excited state. The guest molecule in the triplet excited state emits phosphorescence. In addition, the guest molecule in the singlet excited state crosses the triplet excited state intersystem and emits phosphorescence.

That is, as shown in the following formula (2-2A), 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 triplet of the guest molecule is caused by intersystem crossing. Energy is directly transferred 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*). The process can be considered.

1H*+1G → 1H+1G* → (intersection crossing) → 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 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. On the contrary, if the host molecule itself emits its excitation energy as light or heat and deactivates before the excitation energy is transferred from the host molecule to the guest molecule, the luminous efficiency will be reduced.

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

First, the first mechanism, the Forster mechanism (dipole-dipole interaction), does not require direct contact between molecules for energy transfer, and causes resonance of dipole vibration between a host molecule and a guest molecule. It is a mechanism of energy transfer through a phenomenon. Due to the resonance phenomenon of the 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. The rate constant kh _*→g of the Forster mechanism is shown in Formula (1).

In Formula (1), ν represents a frequency, and f′ _h (ν) is a normalized emission spectrum of a host molecule (fluorescence spectrum, triplet excitation when discussing energy transfer from a singlet excited state). When discussing the energy transfer from a state, it represents a phosphorescence spectrum), and ε _g (
ν) represents the molar extinction coefficient of the guest molecule, N represents the Avogadro number, n represents the refractive index of the medium, R represents the intermolecular distance between the host molecule and the guest molecule, and τ is 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, triplet when discussing energy transfer from the singlet excited state). When discussing energy transfer from an excited state, it represents a phosphorescence quantum yield), and K ² is a coefficient (0 to 4) representing an orientation of a transition dipole moment of a host molecule and a guest molecule. In the case of random orientation, K ² =2/3.

Next, in the Dexter mechanism (electron exchange interaction), which is the second mechanism, the host molecule and the guest molecule approach the contact effective distance where orbital overlap occurs, and the electron of the excited host molecule and the guest molecule of the ground state are approached. Energy transfer occurs through the exchange of electrons. The rate constant kh _*→g of the Dexter mechanism is shown in Formula (2).

In Equation (2), h is Planck's constant, K 'is the constant with the dimension of energy, [nu denotes a frequency, f' _{h (ν)} is normalized host molecules Represents an emission spectrum (a fluorescence spectrum when discussing energy transfer from a singlet excited state, a phosphorescence spectrum when discussing energy transfer from a triplet excited state), and ε′ _g (ν) is the normalized value of the guest molecule. Represents the absorption spectrum, 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 Formula (3). k _r 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 k _n represents the host molecule. Represents the rate constant of the non-luminous process (heat deactivation or intersystem crossing), and τ represents the measured excited state lifetime of the host molecule.

From the equation (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 turns out that it is better if it becomes smaller.

(About the energy transfer efficiency of (2-1))
First, consider the energy transfer process of (2-1). In this case, the Forster type (Equation (1)) is forbidden, so only the Dexter type (Equation (2)) should be considered.
According to the equation (2), in order to increase the rate constant k _{h * →g} , the emission spectrum of the host molecule (phosphorescence spectrum because energy transfer from the triplet excited state is discussed) and the absorption spectrum of the guest molecule (single 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 or a thermally activated delayed fluorescence (TADF) material) that converts triplet excitation energy into light emission is used as a guest material. In some cases, absorption corresponding to the direct transition from the singlet ground state to the triplet excited state is observed, which is the absorption band appearing on the longest wavelength side. Particularly in the case of a luminescent iridium complex, 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 wavelength side or the longer wavelength side). In some cases). This absorption band is mainly due to triplet MLCT (Metal t
o Ligand Charge Transfer) transition. However, the absorption band partially includes absorption derived from triplet π-π* transition or singlet MLCT transition, and these are overlapped to form a broad absorption band on the longest wavelength side of the absorption spectrum. It is believed that 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 resulting from these overlap to form a broad absorption band on the longest wavelength side of the absorption spectrum. Therefore, the guest material, when using the organometallic complex (especially iridium complex), and absorption band broad present in this way the longest wavelength side by phosphorescence spectrum of the host material overlaps significantly, the rate constant k _{h *→g} can be increased to enhance energy transfer efficiency.

In addition, since a fluorescent compound is usually used as the host material, the phosphorescence lifetime (τ) is very long ( _{m r} +k _n is small) of milliseconds or more. This is because the transition from the triplet excited state to the ground state (singlet) is a forbidden transition. From the equation (3), this means that the energy transfer efficiency Φ
Works in favor of _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 the formula (2-1) is performed by the phosphorescence spectrum of the host material and the singlet of the guest material. As long as it overlaps with the absorption spectrum corresponding to the direct transition from the ground state to the triplet excited state, it generally tends to occur.

(About the energy transfer efficiency of (2-2))
Next, consider the energy transfer process of (2-2). In the process of formula (2-2A), the intersystem crossing efficiency of the guest material influences. Therefore, it is considered that the process of the formula (2-2B) is important for maximizing the luminous efficiency. In this case, Dexter type (mathematical formula (
2)) is forbidden, so it is only necessary to consider the Forster type (Equation (1)).

If τ is eliminated from the equations (1) and (3), the energy transfer efficiency Φ _ET has a higher quantum yield φ (fluorescent quantum yield because it discusses energy transfer from the singlet excited state). Can be said to be good. However, in reality, as an even more important factor, the emission spectrum of the host molecule (fluorescence spectrum because energy transfer from the singlet excited state is discussed) and the absorption spectrum of the guest molecule (singlet ground state to triplet excited state It is also necessary to have a large overlap with (absorption corresponding to the transition) (note that the guest molecule also has a higher molar extinction coefficient). This means that the fluorescence spectrum of the host material and the absorption band appearing on the longest wavelength side of the phosphorescent compound that is the guest material overlap.

However, it has been very difficult to realize this in the past. because,
In order to efficiently perform both the process (2-1) and the process (2-2) described above, from the above discussion, not only the phosphorescence spectrum of the host material but also the fluorescence spectrum of the guest material having the longest wavelength can be obtained. This is because it must be designed so as to overlap the absorption band on the side. In other words, the host material must be designed so that the fluorescence spectrum of the host material is in the same position as the phosphorescence spectrum.

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

Therefore, one embodiment of the present invention provides a useful method capable of overcoming a problem relating to energy transfer efficiency from a singlet excited state of a host material to a guest material. Below, the specific aspect is demonstrated.

(Embodiment 1)
In this embodiment, a concept for forming a light-emitting element which 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 is formed by sandwiching an EL layer including a light-emitting layer between a pair of electrodes (anode and cathode), and the light-emitting layer is a layer which converts triplet excitation energy into light emission. 1 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 (assist material), and formed on the anode side. And a second light-emitting substance (guest material) that converts triplet excitation energy into light emission, a third organic compound having an electron-transporting property (host material), and a hole-transporting property. It has a laminated structure with a second light-emitting layer formed to contain at least a second organic compound (assist material).

Note that the first organic compound (host material) contained in the first light-emitting layer has a lowest unoccupied molecular orbital level (LUMO level) than the third organic compound (host material) contained in the second light-emitting layer. Is high. Accordingly, the excitation energy of the exciplex formed in the first light-emitting layer (E _A)
Can be designed to be larger than the excitation energy (E _B ) of the exciplex formed in the second light emitting layer.

In addition, the first light-emitting substance contained in the first light-emitting layer is a substance which emits light having 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 will be described with reference to FIG.

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

The light-emitting layer 106 in one embodiment of the present invention has a first light-emitting substance (guest material) 109a which converts triplet excitation energy into light emission and a first electron-transporting substance as shown in FIG. Organic compound (host material) 110, and second organic compound having hole transporting property (
Assist material) 111 and at least a first light emitting layer 106a formed on the anode side.
And a second light-emitting substance (guest material) 109b that converts triplet excitation energy into light emission, a third organic compound (host material) 112 having an electron-transporting property, and a second organic compound having a hole-transporting property. Second light emitting layer 10 formed to include at least (assist material) 111
6b has a laminated structure, and as the first organic compound 110 and the third organic compound 112, an electron transporting material having an electron mobility of 10 ⁻⁶ cm ² /Vs or more is mainly used, and As the organic compound 111, a hole transporting material having a hole mobility of 10 ⁻⁶ cm ² /Vs or more is mainly used. In addition, in this specification, the first organic compound 110 and the third organic compound 112 are referred to as a host material, and the second organic compound 1
11 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 (also referred to as an exciplex). It is characterized by Furthermore, the emission wavelength of the exciplex formed by the first organic compound (host material) 110 and the second organic compound (assist 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 compared to the emission wavelength (fluorescence wavelength) of each (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 into the 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 third organic compound (host material) 112 and the second organic compound (assist material) 111 in 6b is characterized by forming an exciplex (also referred to as exciplex). Further, the emission wavelength of the exciplex formed by the third organic compound (host material) 112 and the second organic compound (assist material) 111 is the same as that of the third organic compound (host material) 112 and the second organic compound. (Assist material) 1
Since they exist on the longer wavelength side than the respective emission wavelengths (fluorescence wavelengths) of 11, the fluorescence spectrum of the third organic compound (host material) 112 and the fluorescence of the second organic compound (assist material) 111. The spectrum can be converted into an emission spectrum located on the longer wavelength side.

Note that in the above structure, 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. 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 that contributes to light emission This is because the first organic compound 110 (or the second organic compound 111) quenches (quenches) the triplet excitation energy of the (guest material) 109a, which leads to a decrease in light emission efficiency.

Similarly, the triplet excitation energy level (T1 level) of each of the third organic compound (host material) 112 and the second organic compound (assist material) 111 changes 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 third organic compound 112 (or the second organic compound 111) is lower than the T1 level of the second light emitting substance (guest material) 109b, the second light emitting substance that contributes to light emission (Guest material) 109b triplet excitation energy of the third organic compound 112 (
Alternatively, the second organic compound 111) is quenched (quenched), resulting in a decrease in luminous efficiency.

Further, in the first light emitting layer 106 a forming the light emitting layer 106, the ratio of the first organic compound (host material) 110 and the second organic compound (assist material) 111 included, and the first light emitting layer 106 a forming the light emitting layer 106. In the second light-emitting layer 106b, either of the third organic compound (host material) 112 and the second organic compound (assist material) 111 may be larger in proportion, and in the present invention, both cases are included. I will.

Note that the light emitting layer 106 having the above structure (the first light emitting layer 106a and the second light emitting layer 106b)
First organic compound (host material) 110 and second organic compound (assist material) in
A band diagram for explaining the energy relationship between the 111 and the third organic compound (host material) 112 is shown in FIG.

In the first light-emitting layer 106a, as shown in FIG. 1 (B), the first organic compound (host material) 110 and the excitation energy _{(E A} exciplex formed by the second organic compound (assist material) 111 ) Is the HOMO level of the second organic compound (assist material) 111,
It depends on the LUMO level of the first organic compound (host material) 110. In the second light-emitting layer 106b, the excitation energy (E _B ) of the exciplex formed by the third organic compound (host material) 112 and the second organic compound (assist material) 111 is the second organic compound. HOMO level of compound (assist material) 111 and third organic compound (host material) 1
Determined by 12 LUMO levels. Note that the first organic compound (host material) 110 included in the first light-emitting layer 106a has a higher LUMO level than the third organic compound (host material) 112 included in the second light-emitting layer 106b. Therefore, it can be designed so that the excitation energy (E _A ) of the exciplex formed in the first light-emitting layer 106a is larger than the excitation energy (E _B ) of the exciplex formed in the second light-emitting layer 106b. I understand.

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

The light-emitting element described in this embodiment has a structure in which an exciplex is formed in each of the light-emitting layer 106 (the first light-emitting layer 106a and the second light-emitting layer 106b). ) 110, the fluorescence spectrum of the third organic compound (host material) 112, or the fluorescence spectrum of the second organic compound (assist material) 111, can be converted into an emission spectrum located on the longer wavelength side. That is, as shown in FIG. 2, the first organic compound 110, the second organic compound 111, or the third organic compound 112 can be used.
Has a fluorescence spectrum that changes the triplet excitation energy into light emission (first light-emitting substance (guest material) 109a and second light-emitting substance (guest material) 109a).
The light-emitting substance 109 (first light-emitting substance (guest material) 109a, and second light-emitting substance 109, which is located on the short-wavelength side as compared with the absorption band on the longest-wavelength side of b) and 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), the overlap can be increased by forming an exciplex. Thereby, the energy transfer efficiency of the above-mentioned formula (2-2B) can be improved.

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

Therefore, whether or not the exciplex actually has such characteristics is verified below by using the molecular orbital calculation. In general, a combination of a heteroaromatic compound and an aromatic amine is obtained by using the lowest unoccupied molecular orbital (LUMO) of the aromatic amine.
The LUMO level of a heteroaromatic compound (a property that electrons easily enter) and the highest occupied molecular orbital of a heteroaromatic compound (HOMO: High)
Excited complexes are often formed under the influence of the HOMO level (a property that holes easily enter) of an aromatic amine, which is shallower than the est Occupied Molecular Orbital level. Thus, as a model of the first organic compound 110 (or the third organic compound 112) in one embodiment of the present invention, dibenzo[f,h]quinoxaline having a typical skeleton that constitutes the LUMO level of a heteroaromatic compound (Abbreviation: DBq) is used as a model of the second organic compound 111 in one embodiment of the present invention, and triphenylamine (abbreviation: TPA) having a typical skeleton that constitutes the HOMO level of an aromatic amine is used. The calculation was performed by combining.

First, the optimum molecular structures and excitation energies of one molecule of DBq (abbreviation) and one molecule of TPA (abbreviation) in the lowest excited singlet state (S1) and the lowest excited triplet state (T1) are determined by the time-dependent density functional method (TD). -DFT). Furthermore, DBq (abbreviation) and TPA (abbreviation)
The excitation energy was also calculated 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 complicated interactions between electrons. In the DFT, the exchange-correlation interaction is approximated by a one-electron-potential functional (meaning a function) expressed by electron density, and therefore 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 exchange and correlation energy.

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

According to the above-mentioned basis functions, for example, the orbits of 1s to 3s are considered for hydrogen atoms, and the orbits of 1s to 4s and 2p to 4p are considered for carbon atoms. Furthermore, in order to improve calculation accuracy, as a polarization basis system, a p-function is used for hydrogen atoms and d is used for other than hydrogen atoms.
Added function.

Gaussian 09 was used as the quantum chemical calculation program. The calculation was performed using a high performance computer (SGI, Altix4700).

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

FIG. 4A1 shows a distribution of LUMO levels of one molecule of DBq (abbreviation), FIG. 4A2 shows a distribution of HOMO levels of one molecule of DBq (abbreviation), and FIG. 4B1. , TPA (abbreviation)
FIG. 4 (abbreviation) (B2) shows the distribution of the HOMO level of one molecule, and FIG. 4 (C1) shows the distribution of the LUMO levels of DBq (abbreviation) and TPA (abbreviation). The distribution of the LUMO level of the dimer of (abbreviation) is shown, and the distribution of the HOMO level of the dimer of DBq (abbreviation) and TPA (abbreviation) is shown in FIG. 4C2.

As shown in FIG. 3, the dimer of DBq (abbreviation) and TPA (abbreviation) is L of TPA (abbreviation).
LUMO level (-1.99 eV) of DBq (abbreviation) deeper (lower) than the UMO level,
The HOMO level (-) of TPA (abbreviation), which is shallower (higher) than the HOMO level of DBq (abbreviation)
It is suggested that an exciplex of DBq (abbreviation) and TPA (abbreviation) is formed under the influence of 5.21 eV). 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, excitation energies obtained from optimum molecular structures at the S1 level and 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 molecule of DBq (abbreviation), respectively. The excitation energy of S1 level of one molecule of DBq (abbreviation) was 3.294 eV, and the fluorescence wavelength was 376.4 nm.
The excitation energy of T1 level of one molecule of DBq (abbreviation) was 2.460 eV, and the phosphorescence wavelength was 504.1 nm.

In addition, excitation energies obtained from the optimum molecular structures at the S1 level and the T1 level of one TPA (abbreviation) molecule 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 TPA (abbreviation) molecule, respectively. The excitation energy of the S1 level of one TPA (abbreviation) molecule was 3.508 eV, and the fluorescence wavelength was 353.4 nm.
The excitation energy of the T1 level of one TPA (abbreviation) molecule was 2.610 eV, and the phosphorescence wavelength was 474.7 nm.

Furthermore, the excitation energies obtained from the optimum molecular structures at the S1 level and the T1 level of the dimer of DBq (abbreviation) and TPA (abbreviation) are shown. The excitation energies of the S1 and T1 levels are
They correspond to the wavelengths of fluorescence and phosphorescence emitted by dimers of DBq (abbreviation) and TPA (abbreviation), respectively. The excitation energy of the S1 level of the dimer of DBq (abbreviation) and TPA (abbreviation) was 2.036.
It was eV, and the fluorescence wavelength was 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 61
It was 0.0 nm.

From the above, in both one molecule of DBq (abbreviation) and one molecule of TPA (abbreviation),
It can be seen that the phosphorescence wavelength is shifted by a long wavelength near 100 nm. This is the above-mentioned CBP
It has the same tendency as (abbreviation) (measured value) 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 a longer wavelength side than the fluorescence wavelength of one molecule of DBq (abbreviation) or one molecule of TPA (abbreviation). Further, 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 the wavelengths are almost the same.

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

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

Further, since the exciplex exists only in the excited state, there is no ground state capable of absorbing energy. Therefore, a light-emitting substance (guest material) that changes triplet excitation energy into light emission
Phenomenon in which a light-emitting substance (guest material) that changes triplet excitation energy into light emission by energy transfer from singlet and triplet excited states to an exciplex is deactivated (that is, light emission efficiency is impaired) before light emission Is considered not to occur in principle. This is also one of the reasons why the external quantum efficiency can be increased.

The exciplex described above is formed by the interaction between different kinds of molecules in the excited state. 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 the exciplex depends on the energy difference between the HOMO level and the LUMO level. As a general tendency, when the energy difference is large, the emission wavelength is short, and when the energy difference is small, the emission wavelength is long.

Therefore, the HOMO level and the LUMO level of the first organic compound (host material) 110, the second organic compound (assist material) 111, and the third organic compound (host material) 112 in this embodiment are 1(B) are different from each other. Specifically, the HOMO level of the first organic compound 110 and the HOMO level of the third organic compound 112 <the HOMO level of the second organic compound 111 <the LUMO level of the third organic compound 112 <the The energy levels differ in the order of LUMO level of the first organic compound 110 <LUMO level of the second organic compound 111.

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 third organic compound 112 in the second light emitting layer 106b) are used. And the second organic compound 111) form an exciplex, the HOMO level of the exciplex in the first light-emitting layer 106a and the second light-emitting layer 106b is the same as that of the second organic compound (assist material) 111. The LUMO level of the exciplex in the first light emitting layer 106a is derived from the first organic compound (host material) 110, and the second light emitting layer 1
The LUMO level of the exciplex in 06b is L of the third organic compound (host material) 112.
Derived from the UMO level. Therefore, the excitation energy (E _A ) of the exciplex in the first light-emitting layer 106a is higher than the excitation energy (E _B ) of the exciplex in the second light-emitting layer 106b. That is, as the first light-emitting substance 109a which converts the triplet excitation energy contained in the first light-emitting layer into light emission, the second light-emitting substance 109b which converts the triplet excitation energy contained in the second light-emitting layer into light emission. By using a substance that emits light with a shorter wavelength than that, a light-emitting element with high emission efficiency can be formed. In addition, light emitting materials having different emission wavelengths can efficiently emit light at the same time.

Note that the following two processes can be considered as the process of forming the exciplex in one embodiment of the present invention.

The first formation process is a formation process in which the second organic compound (assist material) has a carrier (specifically, a cation) to form an exciplex.

Generally, when electrons and holes (holes) are recombined in the host material, the excitation energy is transferred from the excited host material to the guest material, the guest material reaches the excited state, and light is emitted. 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 the singlet excited state, energy transfer is unlikely to occur as described in (2-2). Such deactivation of excitation energy is one of the factors leading to a reduction in the life of the light emitting device.

However, in one embodiment of the present invention, the first organic compound (or the third organic compound) (
Since the host material) and the second organic compound (assist material) form an exciplex from a state (cation or anion) having a carrier, the first organic compound (or third organic compound) (host material) The formation of singlet excitons can be suppressed. That is, there may be a process of directly forming an exciplex without forming singlet excitons. This can also suppress the deactivation of the singlet excitation energy. Therefore, a light emitting element having a long life can be realized.

For example, the first organic compound (or the third organic compound) is an electron-trapping compound having a property of easily trapping electrons (carriers) among electron transporting materials (having a deep LUMO level), When the organic compound of 2 is a hole trap compound having a property of easily capturing holes (carriers) among the hole transport materials (shallow HOMO level), the first organic compound (or The anion of the third organic compound) and the cation of the second organic compound directly form an exciplex. The exciplex formed in such a process is particularly referred to as an electroplex. In this way, a light-emitting substance (guest material) which suppresses the generation of a singlet excited state of the first organic compound (or the third organic compound) (host material) and changes triplet excitation energy from electroplex into light emission By transferring energy to the light emitting element, a light emitting element with high light emitting efficiency can be obtained. In this case, the generation of the triplet excited state of the first organic compound (or the third organic compound) (host material) is similarly suppressed, and a direct exciplex is formed, so that the triplet excitable state is generated from the exciplex. It is considered that energy is transferred to a light-emitting substance (guest material) that converts energy into light emission.

The second formation process is performed after any of the first organic compound (host material), the second organic compound (assist material), or the third organic compound (host material) forms singlet excitons. , Is an elementary process that interacts with the other ground state to form an exciplex. Unlike Electroplex, in this case, once the first organic compound (host material), the second organic compound (
The singlet excited state of the assist material) or the third organic compound (host material) is generated, but this is promptly converted into an exciplex, so that deactivation of the singlet excitation energy is also suppressed. You can Therefore, it is possible to suppress the deactivation of the excitation energy of the first organic compound (host material), the second organic compound (assist material), or the third organic compound (host material). In this case, it is considered that the triplet excited state of the host material is similarly rapidly converted into an exciplex and energy is transferred from the exciplex to a light-emitting substance (guest material) that converts triplet excitation energy into light emission.

Note that the first organic compound (or the third organic compound) (host material) is a compound having an electron trapping property, while the second organic compound (assisting material) is a compound having a hole trapping property. When the difference in the HOMO level and the difference in the LUMO level are large (specifically, the difference is 0.3 eV or more), the electrons selectively emit the first organic compound (or the third organic compound) (host material). ), and the holes selectively enter the second organic compound (assist material).
In this case, it is considered that the process of forming the electroplex is prioritized over the process of forming the exciplex through the singlet excitons.

Note that the emission spectrum of the exciplex and the luminescent substance that converts triplet excitation energy into luminescence (
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 must be 0.3 eV or less. 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 the light-emitting substance (guest material) that changes triplet excitation energy into light emission, and the emission from the exciplex is substantially It is preferably not observed. Therefore, it is preferable that the light-emitting substance that converts triplet excitation energy into light emission by transferring energy through the exciplex to the light-emitting substance that changes triplet excitation energy into light emission emits light. Note that the light-emitting substance that converts triplet excitation energy into light emission is preferably a phosphorescent compound (such as an organometallic complex) or a thermally activated delayed fluorescence (TADF) material.

In the first light-emitting layer 106a of the light-emitting element which is one embodiment of the present invention, triplet excitation occurs in the first organic compound (the third organic compound in the case of the second light-emitting layer 106b) (host material). When a light-emitting substance that converts energy into light emission is used, the first organic compound (the second light-emitting layer 10
In the case of 6b, the third organic compound) (host material) itself easily emits light, and energy is less likely to be transferred to the light-emitting substance (guest material) that converts triplet excitation energy into light emission.
In this case, the first organic compound (the third organic compound in the case of the second light-emitting layer 106b) may emit light efficiently, but the host material has a problem of concentration quenching, so that high emission efficiency is obtained. Difficult to achieve. Therefore, at least one of the first organic compound (third organic compound in the case of the second light-emitting layer 106b) (host material) and the second organic compound (assist material) is a fluorescent compound (that is, singlet). It is effective when the compound is a compound that easily emits light or thermally deactivates from the excited state. Therefore, at least one of the first organic compound (the third organic compound in the case of the second light-emitting layer 106b) (host material) and the second organic compound (assist material) is a fluorescent compound, and the exciplex Is preferably used as an energy transfer medium.

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

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

The light-emitting element described in this embodiment has a pair of electrodes (first electrode (anode) 2 as shown in FIG.
01 and the second electrode (cathode) 202 sandwiches an EL layer 203 including a light emitting layer 206. The EL layer 203 has a laminated structure of a first light emitting layer 206a and a second light emitting layer 206b. In addition to the light-emitting layer 206 included therein, a hole (or a hole) injection layer 204, a hole (or a hole) transport layer 205, an electron transport layer 207, an electron injection layer 208, or the like is 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 20.
6b, the first light-emitting layer 206a of the light-emitting layer 206 has a first light-emitting substance (guest material) 209a that converts triplet excitation energy into light and a first light-emitting substance having an electron-transporting property. One organic compound (host material) 210 and a second organic compound (assist material) 211 having a hole-transporting property 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 third organic compound (host material) 212 having an electron-transporting property, and a second organic compound (having a hole-transporting property (
Assist material) 211 is included.

Note that the first organic compound (host material) contained in the first light-emitting layer has a lowest unoccupied molecular orbital level (LUMO level) than the third organic compound (host material) contained in the second light-emitting layer. Is high. Accordingly, the excitation energy of the exciplex formed in the first light-emitting layer (E _A)
Can be designed to be larger than the excitation energy (E _B ) of the exciplex formed in the second light emitting layer.

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, the first light-emitting substance 209a that converts triplet excitation energy into light emission is placed in the first organic compound (host material) 210 and the second organic compound (assist material) 211. In the case of the second light-emitting layer 206b that is dispersed, the second light-emitting substance 209b that converts triplet excitation energy into light emission is used as the third organic compound (host material) 212 and the second organic compound (assist material). ) 211 to disperse the light emitting layer 20.
6 (first light emitting layer 206a and second light emitting layer 206b) can be suppressed from being crystallized. Further, 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
It is preferable that the triplet excitation energy level (T1 level) of each of 12 is higher than the T1 level of the light-emitting substance 209 (209a, 209b) that converts the triplet excitation energy into light emission. First organic compound 210, second organic compound 211, and third organic compound 21
The luminescent substance 209 (209a, 20) in which the T1 level of 2 converts triplet excitation energy into luminescence
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 that contributes to light emission into light emission is changed to the first organic compound 21.
This is because 0 (or the second organic compound 211 or the third organic compound 212) is quenched (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, the first organic compound 210 is recombined when carriers (electrons and holes) injected from both electrodes are recombined.
And an exciplex is formed from the second organic compound 211, and an exciplex is formed from the third organic compound 212 and the second organic compound 211 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 third organic compound 212 and the fluorescence spectrum of the second organic compound 211 in the second light-emitting layer 206b are
It can be converted into the emission spectrum of the exciplex located 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 changes the triplet excitation energy into light emission should have a large overlap. , The first organic compound 210 and the second organic compound 211 are selected in the first light emitting layer 206a, and the third organic compound 212 and the second organic compound 211 are selected in the second light emitting layer 206b. And That is, here, it is considered that the triplet excited state also causes energy transfer from the exciplex rather than the host material.

Note that the light-emitting substance 209 that converts triplet excitation energy into light emission (the first light-emitting substance 20
9a and the second light-emitting substance 209b) are preferably a phosphorescent compound (organic metal complex or the like), a thermally activated delayed fluorescence (TADF) material, or the like. Further, as the first organic compound (host material) 210 and the third organic compound (host material) 212, it is preferable to use an electron transporting material. In addition, as the second organic compound (assist material) 211,
It is preferable to use a hole transporting material.

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,C2 ^' ]iridium(III) picolinate (abbreviation: FIrpic), bis[2-
(3 ', 5'-bis-trifluoromethylphenyl) pyridinato -N, C ^2'] iridium (III) picolinate _{(abbreviation: Ir (CF 3 ppy) 2} (pic)), bis [2- (4
',6'-Difluorophenyl)pyridinato-N,C2 ^' ]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,C2 ^' }iridium(III) acetylacetonate (abbreviation: Ir(p-PF-ph) ₂ (acac)
), bis(2-phenylbenzothiazolato-N,C2 ^' )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(2,2) 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-propanedionate)
(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.

Further, as the electron transporting material, a π-deficient heteroaromatic compound such as a nitrogen-containing heteroaromatic compound is preferable, and for example, 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f, h]quinoxaline (abbreviation: 2mDBTPDBq-II), 2-[3'-
(Dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), 2-[4-(3,6-diphenyl-9H-
Carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 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)
Examples include quinoxaline or dibenzoquinoxaline derivatives such as TPDBq-II).

The hole transporting material is preferably a π-excess type heteroaromatic compound (for example, a carbazole derivative or an indole derivative) or an aromatic amine compound.
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
) Is mentioned.

However, a light-emitting substance (guest material) 209 that converts the above triplet excitation energy into light emission
(First light-emitting substance 209a, second light-emitting substance 209b), first organic compound (host material) 210, second organic compound (assist material) 211, and third organic compound (host material) The material that can be used for each 212 is not limited to these,
It is a combination that can form an exciplex, and the emission spectrum of the exciplex is such that a luminescent substance (guest material) 209 (first luminescent substance 209a or second luminescent substance 209b) that changes triplet excitation energy into luminescence The peak of the emission spectrum of the exciplex that overlaps with the absorption spectrum and changes triplet excitation energy into light emission is a light-emitting substance (guest material) 209 (first).
Any substance having a wavelength longer than the peak of the absorption spectrum of the light-emitting substance 209a or the second light-emitting substance 209b) may be used.

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, the first organic compound 210:the second organic compound 211=1:9
It is preferably in the range of ˜9:1.

Specific examples for manufacturing the light-emitting element described in this embodiment are described below.

For the first electrode (anode) 201 and the second electrode (cathode) 202, a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like can be used. Specifically, indium oxide-tin oxide (ITO: indium tin oxide), indium oxide-tin oxide containing silicon or silicon 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 ( In addition to Ti), elements belonging to Group 1 or 2 of the periodic table of the elements, namely, lithium (L
i) and alkali metals such as cesium (Cs), and magnesium (Mg), calcium (
Ca), alkaline earth metals such as strontium (Sr), and alloys containing these (Mg
Rare earth metals such as Ag, AlLi), europium (Eu), and ytterbium (Yb), alloys containing these, and other graphene can be used. Note that the first electrode (anode) 201 and the second electrode (cathode) 202 can be formed by, for example, a sputtering method, an evaporation method (including a vacuum evaporation method), or the like.

Examples of the substance having a high hole-transporting property used for the hole-injecting layer 204 and the hole-transporting layer 205 include, for example, 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB). Or α-NPD) or 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:
A carbazole derivative such as TCPB) or 9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA) can be used. The substances described here are mainly substances having a hole mobility of 10 ⁻⁶ cm ² /Vs or higher. However, a substance other than these substances may be used as long as it has a property of transporting more holes than electrons.

Further, poly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA), poly[N-(4-{N'-[4-(4-diphenylamino)) Phenyl]phenyl-N'-phenylamino}phenyl)methacrylamide]
A high molecular compound such as (abbreviation: PTPDMA) or poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation: Poly-TPD) can also be used.

As an acceptor substance that can be used for the hole-injection layer 204, a transition metal oxide or an oxide of a metal belonging to Groups 4 to 8 in the periodic table can be given. Specifically, molybdenum oxide is particularly preferable.

The light emitting layer 206 (206a, 206b) is 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. The second light-emitting layer 206b has a second light-emitting property. It is formed by including at least the substance 209b, the third organic compound (host material) 212, and the second organic compound (assist material) 211.

The electron-transport layer 207 is a layer containing a substance having a high electron-transport property. 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 ),
A metal complex such as BAlq, Zn(BOX) ₂ , or 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 described here are mainly substances having an electron mobility of 10 ⁻⁶ cm ² /Vs or higher. 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 property of transporting more electrons than holes.

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

The electron-injection layer 208 is a layer containing a substance having a high electron-injection property. The electron injection layer 208 includes
Lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF ₂ )
, An alkali metal such as lithium oxide (LiOx), an alkaline earth metal, or a compound thereof can be used. Further, a rare earth metal compound such as erbium fluoride (ErF ₃ ) can be used. In addition, the above-described substances forming the electron-transporting layer 207 can also be used.

Alternatively, for the electron injection layer 208, a composite material formed by mixing an organic compound and an electron donor (donor) may be used. Such a composite material is excellent in electron injection property and electron transport property 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, and specifically, for example, the substance (metal complex, heteroaromatic compound, or the like) forming the electron transport layer 207 described above is used. Can be used. The electron donor may be any substance that exhibits an electron donating property with respect to the organic compound. Specifically, alkali metals, alkaline earth metals and rare earth metals are preferable, and examples thereof include lithium, cesium, magnesium, calcium, erbium and ytterbium. In addition, alkali metal oxides and alkaline earth metal oxides are preferable, and lithium oxide, calcium oxide, barium oxide and the like can be mentioned. It is also possible to use a Lewis base such as magnesium oxide. Alternatively, an organic compound such as tetrathiafulvalene (abbreviation: TTF) can be used.

In addition, the hole injection layer 204, the hole transport layer 205, and the light emitting layer 206 (206a, 20a) described above.
6b), the electron transport layer 207, and the electron injection layer 208 can be formed by methods such as a vapor deposition method (including a vacuum vapor deposition method), an inkjet method, and a coating method.

Light emitted from the light emitting layer 206 of the above-described light emitting element 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 is a light-transmitting electrode.

In the light-emitting element described in this embodiment, energy transfer efficiency is increased by energy transfer utilizing overlap between an emission spectrum of an exciplex and an absorption spectrum of a light-emitting substance (guest material) that changes 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 particularly characterized by the structure of the light-emitting layer. Therefore, by applying the structure described in this embodiment, a passive matrix light-emitting device, an active matrix light-emitting device, or the like can be manufactured, and these are all included in the present invention. ..

In the case of an active matrix 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 driving circuit formed on the FT substrate may be composed of N-type and P-type TFTs, or may be composed of only one of N-type TFTs and P-type TFTs. 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 combined with any of the structures described in the other embodiments as appropriate.

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

A light-emitting element described in this embodiment mode has a pair of electrodes (first electrode 30) as shown in FIG.
A plurality of EL layers (a first EL layer 302(1) and a second E layer) are provided between the first and second electrodes 304).
A tandem light emitting element having an L layer 302(2).

In this embodiment, the first electrode 301 is an electrode functioning as an anode and the second electrode 304 is an electrode functioning as a cathode. Note that the first electrode 301 and the second electrode 304 can have a structure similar to that in Embodiment 1. In addition, a plurality of EL layers (first
The EL layer 302(1) and the second EL layer 302(2) may have the same structure as the EL layer described in Embodiment 1 or 2, but one of them is the same. It may be configured. That is, the first EL layer 302(1) and the second EL layer 302(2) may have the same structure or different structures, and the structure is the same as that in Embodiment 1 or Embodiment 2. The same can be applied.

A charge generation layer (I) 305 is provided between the 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 injecting holes into the other EL layer when voltage is applied to the first electrode 301 and the second electrode 304. Have. In this embodiment mode, 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 is generated.
Electrons are injected into the first EL layer 302(1) from 5, and holes are injected into the second EL layer 302(2).

Note that the charge generation layer (I) 305 has a property of transmitting visible light in terms 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 on the first electrode 301 and the second electrode 3
Even a conductivity lower than 04 will work.

Although 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-transporting property, an electron donor (donor) is added to the organic compound having a high electron-transporting property. It may be configured. Also, both of these configurations may be laminated.

In the case where 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.
An aromatic amine compound such as 4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB) can be used. The substances described here are mainly substances having a hole mobility of 10 ⁻⁶ cm ² /Vs or higher. However, a substance other than the above substances may be used as long as it is an organic compound having a property of transporting more holes than electrons.

Examples of the electron acceptor include 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F4-TCNQ) and chloranil.
Moreover, a transition metal oxide can be mentioned. Further, oxides of metals belonging to Groups 4 to 8 in the periodic table can be given. Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide are preferable because they have high electron accepting properties. Among them, molybdenum oxide is particularly preferable because it is stable in the air, has low hygroscopicity, and is easy to handle.

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

As the electron donor, an alkali metal, an alkaline earth metal, a rare earth metal, a metal belonging to Group 13 of the periodic table, or an oxide or carbonate 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. Also, an organic compound such as tetrathianaphthacene may be used as an electron donor.

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

Although a light-emitting element having two EL layers is described in this embodiment, a light-emitting element in which n layers (where n is 3 or more) of EL layers are stacked as illustrated in FIG. , Can be similarly applied. When a plurality of EL layers are provided between a pair of electrodes as in the light-emitting element according to this embodiment, by disposing the charge generation layer (I) between the EL layers,
It is possible to emit light in a high brightness region while keeping the current density low. Since the current density can be kept low, a long-life element can be realized. Further, in the case of using illumination as an application example, the voltage drop due to the resistance of the electrode material can be reduced, so that uniform light emission in a large area becomes possible. Further, a light emitting device which can be driven at low voltage and consumes low power can be realized.

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

The same applies to the case of a light emitting element having three EL layers, for example, the first EL layer has a red emission color, the second EL layer has a green emission color, and the third EL layer has a third emission color. When the emission color of is blue, white emission can be obtained as the entire light emitting element.

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

(Embodiment 4)
In this embodiment, a light-emitting device which 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. As illustrated in FIG. Electrode 4
01 and the semi-transmissive/semi-reflective electrode 402), at least the EL layer 405 is provided. Further, the EL layer 405 is at least the light emitting layer 4 serving as a light emitting region.
04 (404R, 404G, 404B), and may further include a hole injection layer, a hole transport layer, an electron transport layer, an electron injection layer, a charge generation layer (E), and the like. Note that the light emitting layer 404
(404R, 404G, 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 mode, as shown in FIG. 7, light emitting elements having different structures (first light emitting element (R) 4
A light emitting device configured to include 10R, the second light emitting element (G) 410G, and the third light emitting element (B) 410B will be described.

The first light emitting element (R) 410R includes a first transparent conductive layer 403a on the reflective electrode 401,
The first light emitting layer (B) 404B, the second light emitting layer (G) 404G, and the third light emitting layer (R) 404.
It has a structure in which an EL layer 405 partially including R and a semi-transmissive/semi-reflective electrode 402 are sequentially stacked. In addition, the second light emitting element (G) 410G includes the second transparent conductive layer 4 on the reflective electrode 401.
03b, the EL layer 405, and the semi-transmissive/semi-reflective electrode 402 are sequentially stacked. 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 above light emitting element (first light emitting element (R) 410R, second light emitting element (G) 410G)
, The third light-emitting element (B) 410B), the reflective electrode 401, the EL layer 405, the semi-transmissive
The semi-reflective electrode 402 is common. In the first light-emitting layer (B) 404B, light (λ _B ) having a peak in a wavelength region of 420 nm to 480 nm is emitted, and the second light-emitting layer (G) is emitted.
The 404G emits light (λ _G ) having a peak in the wavelength range of 500 nm to 550 nm, and the third light-emitting layer (R) 404R emits light having a peak in the wavelength range of 600 nm to 760 nm (λ _R ). Light up. Thereby, in any of the light emitting elements (the first light emitting element (R) 410R, the second light emitting element (G) 410G, and the third light emitting element (B) 410B), the first light emitting layer (B) 404B, The second light emitting layer (G) 404G and the third light emitting layer (R)
) The light emitted from 404R is superposed, that is, broad light can be emitted over the visible light region. From the above, it is assumed that the wavelength lengths have a relationship of λ _B <λ _G <λ _R.

Each of the light-emitting elements described in this embodiment includes a reflective electrode 401 and a semi-transmissive/semi-reflective electrode 40.
2 has a structure in which an EL layer 405 is sandwiched between the two, and light emitted from all the light emitting layers included in the EL layer 405 in all directions functions as a micro optical resonator (micro cavity). Resonance is caused by the reflective electrode 401 having the and the semi-transmissive/semi-reflective electrode 402. The reflective electrode 401 is formed of a conductive material having reflectivity, has a visible light reflectance of 40% to 100%, preferably 70% to 100%, and a resistivity of 1×. 10
^-2 Ωcm or less. The semi-transmissive/semi-reflective electrode 402 is formed of a conductive material having reflectivity and a conductive material having light transmissivity, and has a visible light reflectance of 20% to 80%, preferably 40%. % To 70%, and the resistivity is 1×10 ^−.
It is assumed that the film is ² Ωcm or less.

Further, in this embodiment, in each light emitting element, the transparent conductive layers (the first transparent conductive layer 403a, the first transparent conductive layer 403a, and the first light emitting element (R) 410R and the second light emitting element (G) 410G, respectively. Two
The optical distance between the reflective electrode 401 and the semi-transmissive/semi-reflective electrode 402 is changed for each light emitting element by changing the thickness of the transparent conductive layer 403b). That is, the broad light emitted from each light emitting layer of each light emitting element is generated between the reflective electrode 401 and the semi-transmissive/semi-reflective electrode 402.
Light of a wavelength that resonates can be strengthened and light of a wavelength that does not resonate can be attenuated. Therefore, by changing the optical distance between the reflective electrode 401 and the semi-transmissive/semi-reflective electrode 402 for each element, light of different wavelengths can be generated. You can take it out.

Note that an optical distance (also referred to as an optical path length) is a value obtained by multiplying an actual distance by a refractive index, and in this embodiment, an actual film thickness is multiplied by n (refractive index). .. That is, "
Optical distance=actual film thickness×n”.

In the first light emitting element (R) 410R, the reflective electrode 401 to the semi-transmissive/semi-reflective electrode 4 are used.
02 is mλ _R /2 (where m is a natural number), and in the second light emitting element (G) 410G, the total thickness from the reflective electrode 401 to the semi-transmissive/semi-reflective electrode 402 is mλ _G /2( 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 from the third light-emitting layer (R) 404R mainly included in the EL layer 405 is extracted from the first light-emitting element (R) 410R and the second light-emitting element (G) is extracted. ) 4
Light (λ _G ) emitted from the second light emitting layer (G) 404G included in the EL layer 405 is extracted mainly from 10G, and the EL layer 405 is mainly extracted from the third light emitting element (B) 410B.
The light (λ _B ) emitted from the first light-emitting layer (B) 404B included in is extracted. 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 region of the reflective electrode 401 to the reflective region of the semi-transmissive/semi-reflective electrode 402. it can. However, the reflective electrode 401 and the semi-transmissive/semi-reflective electrode 40
Since it is difficult to determine the position of the reflection area in 2 exactly, it is possible to obtain the above effect sufficiently by assuming an arbitrary position of the reflection electrode 401 and the semi-transmissive/semi-reflective electrode 402 as the reflection area. It should be possible.

Next, in the first light emitting element (R) 410R, from the reflective electrode 401 to the third light emitting layer (R).
) Amplification of light emitted from the third light emitting layer (R) 404R by adjusting the optical distance to 404R to a desired film thickness ((2m′+1)λ _R /4 (where m′ is a natural number)). Can be made. Of the light emitted from the third light emitting layer (R) 404R, the light reflected by the reflective electrode 401 and returning (first reflected light) is semi-transmissive/semi-reflective from the third light emitting layer (R) 404R. Since the light that directly enters the electrode 402 (first incident light) is interfered with, 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 (however, m′ is a natural number) is adjusted so that the first reflected light and the first incident light are in phase with each other and the light emitted from the third light emitting layer (R) 404R is amplified. be able to.

The optical distance between the reflective electrode 401 and the third light emitting layer (R) 404R is strictly 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. You can However, the reflective region of the reflective electrode 401 and the third light emitting layer (R)
Since it is difficult to precisely determine the position of the light emitting region at 404R, the reflective electrode 40
It is assumed that the above effect can be sufficiently obtained by assuming that an arbitrary position of 1 is a reflection region and an arbitrary position of the third light emitting layer (R) 404R is a light emitting region.

Next, in the second light emitting element (G) 410G, the reflective electrode 401 to the second light emitting layer (G)
) Light emission from the second light emitting layer (G) 404G is adjusted by adjusting the optical distance to 404G to a desired film thickness ((2m″+1)λ _G /4 (where m″ is a natural number)). Can be amplified. Of the light emitted from the second light emitting layer (G) 404G, the light reflected by the reflective electrode 401 and returning (second reflected light) is semi-transmissive/semi-reflective from the second light emitting layer (G) 404G. Since it interferes with the light (second incident light) directly incident on the electrode 402, the reflective electrode 401
To the second light emitting layer (G) 404G from the desired value ((2m″+1)λ _G /4(
However, by adjusting m″ to a natural number)), the phases of the second reflected light and the second incident light are matched with each other, and the light emission from the second light emitting layer (G) 404G is amplified. You can

The optical distance between the reflective electrode 401 and the second light emitting layer (G) 404G is strictly 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. You can However, the reflective region of the reflective electrode 401 and the second light emitting layer (G)
Since it is difficult to precisely determine the position of the light emitting region in 404G, the reflective electrode 40
It is assumed that the above-described effect can be sufficiently obtained by assuming that the arbitrary position of 1 is the reflection region and the arbitrary position of the second light emitting layer (G) 404G is the light emitting region.

Next, in the third light emitting element (B) 410B, from the reflective electrode 401 to the first light emitting layer (B
) The optical distance to 404B is set to the desired film thickness ((2m′″+1)λ _B /4 (where m′″
Is a natural number)), whereby 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 returning (third reflected light) is semi-transmitted/semi-reflected from the first light-emitting layer (B) 404B. Since it interferes with the light (third incident light) that is directly incident on the electrode 402, the reflective electrode 4
The optical distance from 01 to the first light emitting layer (B) 404B is set to a desired value ((2m′″+1)λ _B
/4 (however, m''' is a natural number), and the third reflected light and the third reflected light are provided.
The light emitted from the first light-emitting layer (B) 404B can be amplified by matching the phase with the incident light.

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 the reflection region of the reflective electrode 401 and the light emission of the first light emitting layer (B) 404B. It can be said to be the optical distance to the area. However, it is difficult to precisely determine the position of the reflective region of the reflective electrode 401 or the light emitting region of the first light emitting layer (B) 404B. Therefore, an arbitrary position of the reflective electrode 401 is defined as the reflective region and the first light emission. It is assumed that the above effect can be sufficiently obtained by assuming an arbitrary position of the layer (B) 404B as a light emitting region.

Note that in the above structure, each light-emitting element has a structure in which a plurality of light-emitting layers is included in the EL layer, but the present invention is not limited to this, and for example, the tandem-type light emitting element described in Embodiment Mode 3 can be used. In combination with the structure of the light emitting element, a plurality of ELs are sandwiched by one light emitting element with a charge generation layer interposed therebetween.
A layer may be provided and a single or a plurality of light emitting layers may be formed in each EL layer.

The light-emitting device described in this embodiment has a microcavity structure and has the same EL structure.
Even if it has a layer, it is possible to extract light of different wavelengths for each light emitting element, so that it is not necessary to separately paint RGB. Therefore, it is advantageous in realizing full-color display because it is easy to realize 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 be used for applications such as lighting.

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

The light emitting device may be a passive matrix type light emitting device or an active matrix type light emitting device. Note that the light-emitting element described in any of the above embodiments can be applied to the light-emitting device described in this embodiment.

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

Note that FIG. 8A is a top view illustrating the light-emitting device, and FIG. 8B is a dashed line A- of 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).
The pixel portion 502, the driving circuit portion 503, and the driving circuit portion 504 are separated by the sealant 505.
It is sealed between the element substrate 501 and the sealing substrate 506.

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

Next, a cross-sectional structure will be described with reference to FIG. Although 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 is shown.

The driving circuit portion 503 shows an example in which a CMOS circuit in which an n-channel TFT 509 and a p-channel TFT 510 are combined is formed. The circuit forming the drive circuit unit is
It may be formed by various CMOS circuits, PMOS circuits, or NMOS circuits. In addition, although a driver integrated type in which a driver circuit is formed over a substrate is described in this embodiment, the driver circuit is not necessarily required and the driver circuit can be formed outside the substrate.

The pixel portion 502 includes a plurality of pixels each including a switching TFT 511, a current control TFT 512, and a first electrode (anode) 513 electrically connected to a wiring (source electrode or drain electrode) of the current control TFT 512. Is formed by. The first electrode (anode) 5
An insulator 514 is formed so as to cover the end portion of 13. Here, it is formed by using a positive photosensitive acrylic resin.

Further, in order to improve the coverage of the film formed over and over, it is preferable that a curved surface with curvature be formed at the upper end portion or the lower end portion of the insulator 514. 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 have 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, and not only an organic compound but also an inorganic compound such as silicon oxide or silicon oxynitride.
Both can be used.

An EL layer 515 and a second electrode (cathode) 516 are stacked and formed 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 1. In addition to the light-emitting layer, the EL layer 515 can be provided with a hole-injection layer, a hole-transport layer, an electron-transport layer, an electron-injection layer, a charge-generation layer, or the like as appropriate.

Note that the light-emitting element 517 is formed with a stacked structure of the first electrode (anode) 513, the EL layer 515, and the second electrode (cathode) 516. First electrode (anode) 513, EL layer 515
As the material used for the second electrode (cathode) 516, the material described in Embodiment Mode 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 in FIG. 8B, it is assumed that a plurality of light emitting elements are arranged in matrix in the pixel portion 502. Pixel part 5
In 02, light-emitting elements capable of obtaining three types (R, G, B) of light emission 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 formed by combining with a colored layer (color filter).

Further, 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 formed. ing. Note that the space 518 includes a structure filled with an inert gas (nitrogen, argon, or the like) and a structure filled with a sealant 505.

Note that it is preferable to use epoxy resin, low melting point glass, or the like for the sealant 505. Further, it is desirable that these materials are materials that are as impermeable to moisture and oxygen as possible. Further, as a material used for the sealing substrate 506, in addition to a glass substrate or a quartz substrate, FRP (Fiber
A plastic substrate made of, for example, last-reinforced plastics, PVF (polyvinyl fluoride), polyester or acrylic 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 the other embodiments as appropriate.

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

Examples of electronic devices to which the light-emitting device is applied include a television device (also referred to as a television or a television receiver), a monitor for a computer, a digital camera, a digital video camera, a digital photo frame, a mobile phone (a mobile phone, a mobile phone). Also called a telephone device),
Examples include a portable game machine, a portable information terminal, a sound reproducing device, and a large game machine such as a pachinko machine. Specific examples of these electronic devices are shown in FIGS.

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

The television device 7100 can be operated with an operation switch included in the housing 7101 or a separate remote controller 7110. The operation key 7109 included in the remote controller 7110 can be used to operate a channel and volume, and an image 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 provided with 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, it can be unidirectional (sender to receiver) or bidirectional (sender).
It is also possible to perform information communication between the sender and the receiver, or between the receivers).

FIG. 9B illustrates a computer, which includes 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 by using the light-emitting device for the display portion 7203.

FIG. 9C illustrates a portable game machine including two housings, a housing 7301 and a housing 7302, which are connected with a joint portion 7303 so that the portable game machine can be opened or folded. 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 illustrated in FIG. 9C includes a speaker portion 7306, a recording medium insertion portion 7307, and the like.
, LED lamp 7308, input means (operation key 7309, connection terminal 7310, sensor 73)
11 (force, displacement, position, velocity, acceleration, angular velocity, rotation speed, distance, light, liquid, magnetism, temperature, chemical substance, voice, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, It has a function of measuring inclination, vibration, odor or infrared rays), a microphone 7312) and the like. Of course, the configuration of the portable game machine is not limited to the above, and at least the display portion 73
The light emitting device may be used for both or one of the display device 04 and the display portion 7305, and other accessory equipment can be provided as appropriate. The portable game machine illustrated in FIG. 9C has a function of reading a program or data recorded in a recording medium and displaying the program or data on the display portion or performing wireless communication with another portable game machine to share information. Have a function. Note that the function of the portable game machine illustrated in FIG. 9C is not limited to this and can have various functions.

FIG. 9D illustrates an example of a mobile phone. The mobile phone 7400 has a housing 7401.
In addition to a display portion 7402 incorporated in the device, an operation button 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like are provided. Note that the mobile phone 7400 is manufactured by 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. Further, operations such as making a call and composing a mail can be performed by touching the display portion 7402 with a finger or the like.

The screen of the display portion 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 display mode and input mode are mixed.

For example, in the case of making a call or composing a mail, the display portion 7402 may be set to a character input mode mainly for inputting characters and input operation of characters displayed on the screen may be performed. In this case, it is preferable to display a keyboard or number buttons on most of the screen of the display portion 7402.

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

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

In addition, in the input mode, a signal detected by the optical sensor of the display portion 7402 is detected, and when input by touch operation of the display portion 7402 is not performed for a certain period, the screen mode is switched from the input mode to the display mode. You may control.

The display portion 7402 can also function as an image sensor. For example, the display unit 7
By touching 402 with a palm or a finger and capturing an image of a palm print, a fingerprint, or the like, personal authentication can be performed.
Further, by using a backlight that emits near-infrared light or a sensing light source that emits near-infrared light in the display portion, an image of a finger vein, a palm vein, or the like can be taken.

10A and 10B show a tablet terminal that can be folded in two. Figure 10 (A
) Is an open state, and the tablet terminal has 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. With. Note that the tablet terminal is manufactured by using the light-emitting device for one or both of the display portion 9631a and the display portion 9631b.

A part of the display portion 9631a can be a touch panel region 9632a, and data can be input by touching the displayed operation keys 9637. The display unit 96
In FIG. 31a, as an example, a configuration in which half the region has a display-only function and the other half region has the touch panel function is shown, but the configuration is not limited to this. Display unit 96
All the regions of 31a may have a touch panel function. For example, the display unit 9
A keyboard button can be displayed over the entire surface of 631a to serve as a touch panel, and the display portion 9631b can be used as a display screen.

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

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

Further, the display mode changeover switch 9034 can change the display direction such as vertical display or horizontal display, and can select switching between monochrome display and color display. The power-saving mode changeover switch 9036 can optimize the display brightness in accordance with the amount of external light in use detected by an optical sensor incorporated in the tablet terminal. The tablet terminal may include not only the optical sensor but also other detection devices such as a sensor for detecting the inclination such as a gyro and an acceleration sensor.

10A illustrates an example in which the display area of the display portion 9631b is the same as that of the display portion 9631a, the size of the display portion 9631b and the display portion 9631a may be different from each other and the display quality may be different. May be different. For example, one may be a display panel that can display a higher definition than the other.

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

Since the tablet terminal can be folded in two, the housing 9630 can be closed when not in use. Therefore, since the display portion 9631a and the display portion 9631b can be protected,
It is possible to provide a tablet terminal having excellent durability and excellent reliability from the viewpoint of long-term use.

In addition to this, the tablet terminal shown in FIGS. 10A and 10B has 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 portion, a touch input function of performing touch input operation or editing of information displayed on the display portion, a function of controlling processing by various software (programs), and the like.

Electric power can be supplied to the touch panel, the display portion, the video signal processing portion, or the like by the solar cell 9633 attached to the surface of the tablet terminal. Note that the solar cell 9633 can be provided on one side or both sides of the housing 9630, and the battery 9635 can be efficiently charged. When a lithium ion battery is used as the battery 9635, there are advantages such as downsizing.

In addition, the structure and operation of the charge and discharge control circuit 9634 illustrated in FIG.
A block diagram is shown in FIG. In FIG. 10C, a solar cell 9633, a battery 9
635, DCDC converter 9636, converter 9638, switches SW1 to SW3
, A display portion 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 illustrated in FIG.

First, an example of operation in the case where power is generated by the solar cell 9633 by external light is described. Electric power generated by the solar cell 9633 is stepped up or down by the DCDC converter 9636 so that it has a voltage for charging the battery 9635. Then, the display portion 9631
When the electric power from the solar cell 9633 is used for the above operation, the switch SW1 is turned on, and the converter 9638 steps up or down the voltage required for the display portion 9631. When the display portion 9631 does not display, the switch SW1 is turned off and the switch S
The battery 9635 may be charged by turning on W2.

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

Needless to say, the electronic device shown in FIG. 10 is not particularly limited 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 applicable range of the light emitting device is extremely wide, and the light emitting device can be applied to electronic devices in various fields.

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

(Embodiment 7)
In this embodiment, an example of a lighting device to which the light-emitting device including the 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 the light emitting device is used as an indoor lighting device 8001. Since the light-emitting device can have a large area, a large-area lighting device can be formed. Alternatively, by using a housing having a curved surface, the lighting device 8002 having a curved light emitting region can be formed. The light-emitting element included in the light-emitting device described in this embodiment has a thin film shape and has a high degree of freedom in designing the housing. Therefore, a lighting device with various designs can be formed. Further, a large lighting device 8003 may be provided on the wall surface in the room.

Further, by using the light emitting device on the surface of the table, a lighting device 8004 having a function as a table can be obtained. Note that a lighting device having a function as furniture can be obtained by using a light-emitting device for part of other 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.

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

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

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

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

After that, the substrate is introduced into a vacuum vapor deposition apparatus whose internal pressure is reduced to about 10 ⁻⁴ Pa, and vacuum baking is performed at 170° C. for 30 minutes in a heating chamber in the vacuum vapor deposition apparatus, and then the substrate 1100 is performed for about 30 minutes. I let it cool.

Next, the substrate 1100 was fixed to a holder provided in a vacuum evaporation apparatus so that the surface on which the first electrode 1101 was formed faces downward. In this embodiment, the EL layer 1 is formed by the vacuum deposition method.
A case will be described in which 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 that form the element 102 are sequentially formed.

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 oxide (VI), DBT3
The hole injection layer 1111 was formed over the first electrode 1101 by co-evaporation so that P-II (abbreviation):molybdenum oxide=4:2 (mass ratio). The film thickness was 20 nm. Note that co-evaporation is an evaporation method in which a plurality of different substances are simultaneously evaporated from different evaporation sources.

Next, 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP) was evaporated to a thickness of 20 nm, so that the hole-transporting layer 1112 was formed.

Next, the light emitting layer 1113 was formed on the hole transporting layer 1112. 4,6-bis[3-(9H
-Carbazol-9-yl)phenyl]pyrimidine (abbreviation: 4,6mCzP2Pm), N
-(1,1'-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation) :
PCBBiF), tris(2-phenylpyridinato)iridium(III) (abbreviation: [I
r(ppy) ₃ ]) to 4,6mCzP2Pm (abbreviation): PCBBiF (abbreviation): [Ir
(Ppy) ₃ ] (abbreviation)=0.7:0.3:0.05 (mass ratio), so that the first light emitting layer 1113a is formed with a thickness of 20 nm, and then 2-[ 3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2 mD
BTBPDBq-II), PCBBiF (abbreviation), bis{4,6-dimethyl-2-[5-]
(2,6-Dimethylphenyl)-3-(3,5-dimethylphenyl)-2-pyrazinyl-
κN]phenyl-κC}(2,8-dimethyl-4,6-nonandionato-κ ² O,O′)
Iridium (III) (abbreviation: [Ir(dmdppr-dmp) ₂ (divm)])
2mDBTBPDBq-II (abbreviation): PCBBiF (abbreviation): [Ir(dmdppr-
dmp) ₂ (divm)] (abbreviation)=0.9:0.1:0.05 (mass ratio) by co-evaporation to form the second light-emitting layer 1113b with a thickness of 20 nm. A light emitting layer 1113 having a laminated structure was formed.

Next, 2 mDBTBPDBq-II (abbreviation) was deposited to 15 nm on the light-emitting layer 1113, and bathophenanthroline (abbreviation: Bphen) was deposited to 10 nm to form an electron-transport layer 1114. Further, lithium fluoride was evaporated to a thickness of 1 nm on the electron-transporting layer 1114 to form an electron-injecting layer 1115.

Lastly, aluminum was vapor-deposited on the electron-injection layer 1115 so as to have a thickness of 200 nm to form the second electrode 1103 serving as a cathode, whereby the light-emitting element 1 was obtained. Note that in the above evaporation process, evaporation was all performed by a resistance heating method.

Table 1 shows the element structure of the light-emitting element 1 obtained as described above.

Further, the manufactured 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-treated at 80° C. for 1 hour at the time of sealing).

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

First, FIG. 13 shows current density-luminance characteristics of the light emitting element 1. Note that in FIG. 13, the vertical axis represents luminance (cd/m ² ) and the horizontal axis represents current density (mA/cm ² ). In addition, FIG. 14 shows voltage-luminance characteristics of the light-emitting element 1. Note that in FIG. 14, the vertical axis represents luminance (cd/m ² ),
The horizontal axis represents voltage (V). 15 shows luminance-current efficiency characteristics of the light-emitting element 1. Note that in FIG. 15, the vertical axis represents current efficiency (cd/A) and the horizontal axis represents luminance (cd/m ² ). In addition, FIG. 16 shows voltage-current characteristics of the light-emitting element 1. Note that in FIG. 16, the vertical axis represents current (mA) and the horizontal axis represents voltage (V).

From FIG. 15, it was found 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 the light-emitting element 1 around 1000 cd/m ² .

From the above results, it is found that the light-emitting element 1 manufactured in this example has high external quantum efficiency and thus high emission efficiency.

17 shows an emission spectrum of the light-emitting element 1 which was obtained by applying a current at a current density of 25 mA/cm ² . As shown in FIG. 17, the emission spectrum of the light-emitting element 1 is 519 nm and 615.
It has two peaks near nm, and each has a phosphorescent organometallic iridium complex [Ir(
It is suggested that they are derived from the light emission of [ppy] ₃ ] and [Ir(dmdppr-dmp) ₂ (divm)].

According to cyclic voltammetry measurement, the LUMO level of 4,6mCzP2Pm, which is the first organic compound having an electron-transporting property, is -2.88 eV, and 2mDBTBPDBq, which is the third organic compound having an electron-transporting property, is obtained. The LUMO level of -II was estimated to be -2.94 eV. Therefore, the LUMO of the first organic compound is better than that of the third organic compound.
It has a high level structure.

Here, in FIG. 18, 4,6mCzP2Pm which is a first organic compound having an electron-transporting property is shown.
2 shows an emission spectrum of a thin film of the above, an emission spectrum of a thin film of PCBBiF which is a second organic compound having a hole transporting property, and an emission spectrum of a mixed film (co-deposited film) of 4,6mCzP2Pm and PCBBiF. In addition, in FIG. 19, a third organic compound having an electron-transporting property 2
Emission spectrum of thin film of mDBTBPDBq-II, emission spectrum of thin film of PCBBiF which is a second organic compound having a hole transporting property, and 2mDBTBPDBq-II and PC
3 shows an emission spectrum of a mixed film of BBiF (co-deposited film).

18 and 19, since the emission wavelength of the mixed film is located at a longer wavelength than the emission wavelength of the single film of each material, the first organic compound (4,6mCzP2Pm) and the second organic compound (P
It can be seen that CBBiF), the third organic compound (2mDBTBPDBq-II) and the second organic compound (PCBBiF) each form an exciplex.

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 light-emitting substance that converts triplet excitation energy into light emission 109b Second light-emitting substance that converts triplet excitation energy into light emission 110 First organic compound 111 Second organic compound 112 Third organic compound 201 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 Luminescent substance 209a Triplet Excitation energy converted into light emission First light-emitting substance 209b Second light-emitting substance 210 that converts triplet excitation energy into light emission First organic compound 211 Second organic compound 212 Third organic compound 301 First electrode 302(1) First EL layer 302(2) Second EL layer 302(n-1) (n-1) EL layer 302(n) (n) 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)th (n−2)th charge generation layer (I)
305(n−1)th (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 section 503 drive circuit section (source line drive circuit)
504a, 504b drive circuit section (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 portion 7105 stand 7107 display portion 7109 operation keys 7110 remote controller 7201 main body 7202 housing 7203 display portion 7204 keyboard 7205 external connection port 7206 pointing device 7301 housing 7302 housing 7303 connection part 7304 display part 7305 display part 7306 speaker part 7307 recording medium insertion part 7308 LED lamp 7309 operation key 7310 connection terminal 7311 sensor 7312 microphone 7400 mobile phone 7401 housing 7402 display part 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 portion 9631a Display portion 9631b Display portion 9632a Touch panel area 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 (5)

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 light-emitting substance that converts triplet excitation energy into light emission, a first organic compound, and a second organic compound,
The second light-emitting layer includes a second light-emitting substance that converts triplet excitation energy into light emission, the second organic compound, and a third organic compound,
The first organic compound has a higher lowest unoccupied molecular orbital level (LUMO level) than the third organic compound,
The first luminescent material emits light of a shorter wavelength than the second luminescent material,
The first organic compound is a π-deficient heteroaromatic compound,
The third organic compound is a π-deficient heteroaromatic compound,
The second organic compound is a π-excess type heteroaromatic compound or an aromatic amine compound,
The T1 level of the first organic compound is higher than the T1 level of the first light-emitting substance,
The T1 level of the second organic compound is higher than the T1 level of the first light-emitting substance,
The T1 level of the third organic compound is higher than the T1 level of the second light-emitting substance,
The T1 level of the second organic compound is higher than the T1 level of the second light-emitting substance. In claim 1,
The first luminescent material is a phosphorescent compound or a heat-activated delayed fluorescent material,
The second light emitting material is a light emitting device which is a phosphorescent compound or a heat activated delayed fluorescent material. A light emitting device comprising the light emitting element according to claim 1. An electronic device comprising the light emitting device according to claim 3. An illumination device comprising the light emitting device according to claim 3.