JP2023129582A - Light-emitting element - Google Patents

Abstract

To provide a light-emitting element having high external quantum efficiency and also to provide a light-emitting element having a long lifespan.SOLUTION: A light-emitting element includes a light-emitting layer between an anode and a cathode. The light-emitting layer is a stack comprising: a first light-emitting layer containing at least a first light-emitting material for converting triplet excitation energy into light emission, a first organic compound having electron transportability, and a second organic compound having hole transportability, the light-emitting layer being formed on an anode side; and a second light-emitting layer formed by containing at least a second light-emitting material for converting triplet excitation energy into light emission, the first organic compound, and a third organic compound having hole transportability. The second organic compound has a HOMO level lower than that of the third organic compound, the first light-emitting material represents light emission of wavelengths that are shorter than that of the second light-emitting material, and the first and second organic compounds and the first and third organic compounds separately form an excitation complex.SELECTED DRAWING: None

Description

One embodiment of the present invention relates to a light-emitting element in which an organic compound that 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 including such a light-emitting element.

Light-emitting devices using organic compounds as light emitters are expected to be applied to next-generation flat panel displays, and have characteristics such as thinness, lightness, high-speed response, and low DC voltage drive. In particular, display devices in which light-emitting elements are arranged in a matrix are considered to have an advantage over conventional liquid crystal display devices in that they have a wide viewing angle and excellent visibility.

The light emitting mechanism of a light emitting device is that by applying a voltage to a pair of electrodes with an EL layer containing a light emitter sandwiched between them, electrons injected from the cathode and holes injected from the anode are regenerated at the light emitting center of the EL layer. It is said that they combine to form molecular excitons, and when the molecular excitons relax to the ground state, they release energy and emit light. Singlet excitation and triplet excitation are known as excited states, and it is thought that light emission is possible through either of the excited states.

Regarding such light emitting elements, in order to improve the device characteristics, improvements in the device structure, material development, etc. are actively being carried out (see, for example, Patent Document 1).

Japanese Patent Application Publication No. 2010-182699

However, the current light extraction efficiency of light emitting devices is said to be around 20% to 30%, and even considering light absorption by reflective electrodes and transparent electrodes, the external quantum efficiency of light emitting devices using phosphorescent compounds is The limit is thought to be around 25%.

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

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

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

In each of the above configurations, the emission wavelength of the exciplex formed by the first organic compound (host material) and the second organic compound (assist material) of the first light emitting layer is different from that of the first organic compound (host material). each emission wavelength (fluorescence wavelength) of the material) and the second organic compound (assist material)
By forming an exciplex, the fluorescence spectrum of the first organic compound (host material) and the fluorescence spectrum of the second organic compound (assist material) can be made longer. It can be converted to an emission spectrum located on the wavelength side. Furthermore, the emission wavelength of the exciplex formed by the first organic compound (host material) and the third organic compound (assist material) of the second light-emitting layer is different from that of the first organic compound (host material) and the third organic compound (assist material). Organic compounds (
Since it exists on the long wavelength side compared to the respective emission wavelengths (fluorescence wavelengths) of the assist materials, by forming an exciplex, the fluorescence spectrum of the first organic compound (host material) and the third organic compound The fluorescence spectrum of the compound (assist material) can be converted to an emission spectrum located on the longer wavelength side.

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

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

Furthermore, in the above structure, the first luminescent substance contained in the first luminescent layer is a substance that emits light with a shorter wavelength than the second luminescent substance contained in the second luminescent layer. shall be.

In the above configuration, the first luminescent substance and the second luminescent substance are luminescent substances that convert triplet excitation energy into luminescence, and include phosphorescent compounds such as organometallic complexes, thermally activated delayed fluorescence, etc. Thermal activated delayed fluorescence (TADF)
activated Delayed Fluorescence) materials can be used. Further, the first organic compound is mainly an electron transporting material having an electron mobility of 10 ⁻⁶ cm ² /Vs or more, specifically a π-deficient heteroaromatic compound, and the second organic compound and the The organic compound of No. 3 is mainly a hole transport material having a hole mobility of 10 ⁻⁶ cm ² /Vs or more, specifically a π-excess type heteroaromatic compound or an aromatic amine compound. do.

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 each having a light-emitting device. Therefore, the light-emitting device in this specification refers to an image display device, a light-emitting device, or a light source (including a lighting device). Also,
A connector such as FPC (Flexible printed circuit) is attached to the light emitting device.
it) or a module with a TCP (Tape Carrier Package) attached, a module with a printed wiring board installed at the end of the TCP, or a module with a C on the light emitting element.
All modules in which ICs (integrated circuits) are directly mounted using the OG (Chip On Glass) method are also included in the light emitting device.

Note that in the light-emitting element that is one embodiment of the present invention, an exciplex can be formed in each of the first and second light-emitting layers that constitute the light-emitting layer, so energy transfer efficiency is high and external quantum A highly efficient light emitting element can be realized.

Further, in the light-emitting element that is one embodiment of the present invention, the above-described element structure allows the exciplex formed in the first light-emitting layer to have a higher excitation energy than the exciplex formed in the second light-emitting layer. Therefore, as a first luminescent substance (guest material) that converts the triplet excitation energy contained in the first luminescent layer into luminescence, it converts the triplet excitation energy contained in the second luminescent layer into luminescence. By using a substance that emits light at a shorter wavelength than the second light-emitting substance (guest material) to be changed, it is possible to obtain light emission from the first light-emitting layer and the second light-emitting layer at the same time. A second luminescent substance (guest material ), the luminous efficiency of the light emitting element can be further improved.

FIG. 2 is a diagram illustrating the concept of one embodiment of the present invention. FIG. 2 is a diagram illustrating the concept of one embodiment of the present invention. FIG. 3 is a diagram showing calculation results according to one embodiment of the present invention. FIG. 3 is a diagram showing calculation results according to one embodiment of the present invention. FIG. 3 is a diagram illustrating the structure of a light emitting element. FIG. 3 is a diagram illustrating the structure of a light emitting element. FIG. 2 is a diagram illustrating a light emitting device. FIG. 2 is a diagram illustrating a light emitting device. A diagram explaining an electronic device. A diagram explaining an electronic device. FIG. 3 is a diagram illustrating a lighting device. FIG. 3 is a diagram illustrating a light emitting element. FIG. 3 is a diagram showing current density-luminance characteristics of the light emitting element 1. FIG. 3 is a diagram showing voltage-luminance characteristics of the light emitting element 1. FIG. 3 is a diagram showing the luminance-current efficiency characteristics of the light emitting element 1. FIG. FIG. 3 is a diagram showing voltage-current characteristics of the light emitting element 1. FIG. FIG. 3 is a diagram showing the emission spectrum of the light emitting element 1. FIG. 3 is a diagram showing the emission spectrum of a substance used in the light emitting element 1. FIG. 3 is a diagram showing the emission spectrum of a substance used in the light emitting element 1.

Hereinafter, embodiments of the present invention will be described in detail using the drawings. However, the present invention is not limited to the following description, and the form and details thereof may be variously changed without departing from the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited to the contents described in the embodiments shown below.

(About the elementary process of light emission in light emitting elements)
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 as a guest material will be described. Note that here, the molecule that gives excitation energy is referred to as a host molecule, and the molecule that receives excitation energy is referred to as a guest molecule.

(1) When electrons and holes recombine in a guest molecule and the guest molecule becomes excited (direct recombination process).

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

(1-2) When the excited state of the guest molecule is the singlet excited state The guest molecule in the singlet excited state intersystem-crosses to the triplet excited state and emits phosphorescence.

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

(2) When electrons and holes recombine in a host molecule and the host molecule becomes excited (energy transfer process).

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

3H*+1G → 1H+3G* (2-1)

(2-2) When the excited state of the host molecule is a singlet excited state If the S1 level of the host molecule is higher than the S1 level and T1 level of the guest molecule, excitation energy transfers from the host molecule to the guest molecule. , the guest molecule becomes a singlet excited state or a triplet excited state. The guest molecule in the triplet excited state emits phosphorescence. Furthermore, the guest molecule in the singlet excited state intersystemically crosses into the triplet excited state and emits phosphorescence.

In other words, 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 the triplet state of the guest molecule is transferred by intersystem crossing. The process of generating an excited state (3G*) and direct energy transfer from the singlet excited state (1H*) of the host molecule to the triplet excited state (3G*) of the guest molecule, as shown in equation (2-2B) below. The process can be considered.

1H*+1G → 1H+1G* → (intersystem 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 will be efficiently converted to the triplet excited state (3G*) of the guest molecule. This makes it possible to emit light with high efficiency. Conversely, if the host molecule itself releases its excitation energy as light or heat and is deactivated before the excitation energy is transferred from the host molecule to the guest molecule, the luminous efficiency will decrease.

Next, the controlling factors of the above-mentioned intermolecular energy transfer process between the host molecule and the guest molecule will be explained. The following two mechanisms have been proposed as mechanisms for energy transfer between molecules.

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

In formula (1), ν represents the vibration frequency, and f' _h (ν) is the normalized emission spectrum of the host molecule (fluorescence spectrum when discussing energy transfer from the singlet excited state, triplet excited state). When discussing energy transfer from a state, it is expressed as phosphorescence spectrum) and ε _g (
ν) represents the molar extinction coefficient of the guest molecule, N represents Avogadro's number, n represents the refractive index of the medium, R represents the intermolecular distance between the host molecule and the guest molecule, and τ represents the actual measurement c is the speed of light, and φ is the emission quantum yield (fluorescence quantum yield when discussing energy transfer from the singlet excited state, triplet When discussing energy transfer from an excited state, it represents the phosphorescence quantum yield), and K ² is a coefficient (0 to 4) representing the orientation of the transition dipole moment of the host molecule and the guest molecule. Note that in the case of random orientation, K ² =2/3.

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

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

Here, the energy transfer efficiency Φ _ET from the host molecule to the guest molecule is considered to be expressed by formula (3). k _r represents the rate constant of the light emission process of the host molecule (fluorescence when discussing energy transfer from a singlet excited state, phosphorescence when discussing energy transfer from a triplet excited state), and k _n is the rate constant of the host molecule represents the rate constant of non-luminescent processes (thermal deactivation and intersystem crossing), and τ represents the actually measured lifetime of the excited state of the host molecule.

From formula (3), in order to increase the energy transfer efficiency Φ _ET , the energy transfer rate constant k _h*→g should be increased, and the other competing rate constants k _r +k _n (=1/τ) should be It turns out that the smaller the size, the better.

(About energy transfer efficiency in (2-1))
First, let's consider the energy transfer process (2-1). In this case, since the Förster type (formula (1)) is prohibited, only the Dexter type (formula (2)) needs to be considered.
According to formula (2), in order to increase the rate constant _kh 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 luminescent substance (including a phosphorescent compound and a thermally activated delayed fluorescence (TADF) material) that converts triplet excitation energy into light emission is used as a guest material. , absorption corresponding to a direct transition from the singlet ground state to the triplet excited state may be observed, and this is the absorption band that appears on the longest wavelength side. Especially in luminescent iridium complexes, the absorption band on the longest wavelength side often appears as a broad absorption band around 500 to 600 nm (of course, depending on the emission wavelength, it appears on the shorter wavelength side or longer wavelength side). In some cases). This absorption band is mainly caused by triplet MLCT (Metal t
o Ligand Charge Transfer) transition. However, this absorption band also includes some absorption derived from triplet π-π* transition and singlet MLCT transition, and these overlap to form a broad absorption band on the longest wavelength side of the absorption spectrum. It is thought that there are. In other words, it is considered that the difference between the lowest singlet excited state and the lowest triplet excited state is small, and the absorptions derived from these overlap to form a broad absorption band on the longest wavelength side of the absorption spectrum. Therefore, when an organometallic complex (particularly an iridium complex) is used as a guest material, the rate constant _{kh *→g} can be increased to increase energy transfer efficiency.

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

Considering the above, the energy transfer from the triplet excited state of the host material to the triplet excited state of the guest material, that is, the process of formula (2-1), is based on the phosphorescence spectrum of the host material and the singlet excited state of the guest material. As long as the absorption spectrum corresponding to the direct transition from the ground state to the triplet excited state is overlapped, it tends to occur more easily.

(About energy transfer efficiency in (2-2))
Next, let's consider the energy transfer process in (2-2). The process expressed by equation (2-2A) is affected by the intersystem crossing efficiency of the guest material. Therefore, in order to increase the luminous efficiency to the maximum, the process expressed by equation (2-2B) is considered to be important. In this case, Dexter type (formula (
2)) is prohibited, so only the Förster type (Equation (1)) needs to be considered.

If we eliminate τ from equations (1) and (3), the energy transfer efficiency Φ _ET becomes the higher the quantum yield φ (fluorescence quantum yield, since we are discussing energy transfer from the singlet excited state). I can say it's good. However, in reality, even more important factors are the emission spectrum of the host molecule (fluorescence spectrum since we are discussing energy transfer from the singlet excited state) and the absorption spectrum of the guest molecule (the direct transfer from the singlet ground state to the triplet excited state). It is also necessary that the molar absorption coefficient of the guest molecule is also high. 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 extremely difficult to achieve this in the past. because,
If we try to efficiently carry out both the processes (2-1) and (2-2) above, from the above discussion, we can see that not only the phosphorescence spectrum of the host material but also the fluorescence spectrum of the guest material has the longest wavelength. This is because it must be designed to overlap with the side absorption bands. In other words, the host material must be designed so that the fluorescence spectrum of the host material is at a similar position to the phosphorescence spectrum.

However, in general, the S1 level and the T1 level are significantly different (S1 level>T1 level), so
The emission wavelength of fluorescence and the emission wavelength of phosphorescence are also significantly different (emission wavelength of fluorescence < emission wavelength of phosphorescence).
For example, 4, which is often used as a host material in light-emitting devices using phosphorescent compounds,
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 this example, it is extremely difficult to design a host material so that its fluorescence spectrum is at a similar position to its phosphorescence spectrum. Therefore, improving the efficiency of energy transfer from the singlet excited state of the host material to the guest material is very important.

Therefore, one aspect of the present invention provides a useful method that can overcome such problems regarding the efficiency of energy transfer from the singlet excited state of the host material to the guest material. The specific aspects thereof will be explained below.

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

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

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

First, the element structure of a light emitting element which is an example of the present invention will be explained with reference to FIG. 1(A).

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

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

Further, 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 exciplex). characterized by something. 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 different from that of the first organic compound (host material) 110 and the second organic compound (Assist material) 111 exists on the long wavelength side compared to each emission wavelength (fluorescence wavelength), so the fluorescence spectrum of the first organic compound (host material) 110 and the second organic compound (assist material) The fluorescence spectrum of 111 can be converted to an emission spectrum located on the longer wavelength side.

This also applies to the second light emitting layer 106b. Therefore, the second light emitting layer 10
The combination of the first organic compound (host material) 110 and the third organic compound (assist material) 112 in 6b is characterized in that it is a combination that forms an exciplex (also referred to as exciplex). Furthermore, the emission wavelength of the exciplex formed by the first organic compound (host material) 110 and the third organic compound (assist material) 112 is different from that of the first organic compound (host material) 110 and the third organic compound (assist material) 112. (Assist material) 1
12, the fluorescence spectrum of the first organic compound (host material) 110 and the fluorescence of the third organic compound (assist material) 112 are different from each other. The spectrum can be converted to an emission spectrum located on the longer wavelength side.

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

Similarly, the triplet excitation energy level (T1 level) of each of the first organic compound (host material) 110 and the third organic compound (assist material) 112 converts triplet excitation energy into light emission. It is preferable that the T1 level is higher than the T1 level of the second luminescent substance (guest material) 109b. When the T1 level of the first organic compound 110 (or the third organic compound 112) is lower than the T1 level of the second luminescent substance (guest material) 109b, the second luminescent substance contributing to light emission (Guest material) The triplet excitation energy of 109b is transferred to the first organic compound 110 (
Alternatively, the third organic compound 112) may be quenched, leading to a decrease in luminous efficiency.

In addition, the ratio of the first organic compound (host material) 110 and the second organic compound (assist material) 111 in the first light-emitting layer 106a constituting the light-emitting layer 106, and In the second light emitting layer 106b, the proportion of the first organic compound (host material) 110 and the third organic compound (assist material) 112 may be greater than any other, and in the present invention, both cases are included. That's it.

Note that the light emitting layer 106 having the above structure (first light emitting layer 106a and second light emitting layer 106b)
The first organic compound (host material) 110, the second organic compound (assist material)
A band diagram illustrating the energy relationship between 111 and the third organic compound (assist material) 112 is shown in FIG. 1(B).

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

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

The light-emitting element described in this embodiment has a structure in which exciplexes are formed in each of the light-emitting layers 106 (first light-emitting layer 106a, second light-emitting layer 106b); ) 110, the fluorescence spectrum of the second organic compound (assist material) 111, or the fluorescence spectrum of the third organic compound (assist material) 112, into an emission spectrum located on the longer wavelength side. This means that the first organic compound 110, the second organic compound 111, or the third organic compound 11 can be
Even if the fluorescence spectrum of 2 is a luminescent substance 109 (
First luminescent substance (guest material) 109a and second luminescent substance (guest material) 10
A luminescent substance 109 (first luminescent substance (guest material) 109a, and second This means that even if there is no overlap with the absorption band located on the longest wavelength side of the luminescent substance (guest material) 109b), the overlap can be increased by forming an exciplex. This makes it possible to improve the energy transfer efficiency of the above equation (2-2B).

Furthermore, in exciplexes, the difference between singlet excitation energy and triplet excitation energy is considered to be extremely small. 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 emission spectrum of the exciplex (generally, the emission spectrum from the singlet state of the exciplex) is changed to the absorption band located on the longest wavelength side of the luminescent substance 109 that converts triplet excitation energy into luminescence. When designed to be superimposed on the exciplex, the emission spectrum from the triplet state of the exciplex (which is not observed at room temperature and is often not observed even at low temperatures) is also the longest wavelength of the luminescent substance 109 that converts triplet excitation energy into luminescence. It overlaps with the absorption band located on the side. In other words, the efficiency of not only the energy transfer from the singlet excited state ((2-2)) but also the energy transfer from the triplet excited state ((2-1)) increases, and as a result, the singlet/triplet Energy from both excited states can be efficiently converted into light emission.

Therefore, in the following, molecular orbital calculations were used to verify whether exciplexes actually have such properties. In general, the combination of a heteroaromatic compound and an aromatic amine is based on the lowest unoccupied molecular orbital (LUMO) of the aromatic amine.
The LUMO level (characteristic in which electrons can easily enter) of heteroaromatic compounds, which is deeper than the Molecular Orbital) level, and the highest occupied orbital (HOMO: High
Excited complexes are often formed due to the HOMO level of aromatic amines, which is shallower than the Occupied Molecular Orbital) level (a property in which holes easily enter). Therefore, dibenzo[f,h]quinoxaline (abbreviation: DBq), which has a typical skeleton constituting the LUMO level of a heteroaromatic compound, is used as a model of the first organic compound 110 in one embodiment of the present invention, and the present invention In one embodiment, triphenylamine (abbreviation: TPA), which has a typical skeleton constituting the HOMO level of aromatic amine, is used as a model of the second organic compound 111 (or third organic compound 112). The calculation was performed by combining the

First, the optimal molecular structure and excitation energy in the lowest excited singlet state (S1) and lowest excited triplet state (T1) of one molecule of DBq (abbreviation) and one molecule of TPA (abbreviation) are determined using time-dependent density functional theory (TD). -DFT). Furthermore, DBq (abbreviation) and TPA (abbreviation)
The excitation energy was also calculated for the dimer.

The total energy of DFT (density functional theory) is expressed as the sum of potential energy, electrostatic energy between electrons, kinetic energy of electrons, and exchange-correlation energy including all complex interactions between electrons. In DFT, the exchange-correlation interaction is approximated by a functional (meaning a function of functions) of one-electron potential expressed by electron density, so calculation is fast and highly accurate. Here, the weight of each parameter related to exchange and correlation energy was defined using B3LYP, which is a mixed functional.

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

According to the above-mentioned basis functions, for example, in the case of a hydrogen atom, orbitals of 1s to 3s are taken into consideration, and in the case of a carbon atom, orbitals of 1s to 4s and 2p to 4p are taken into consideration. Furthermore, in order to improve calculation accuracy, we use the p function for hydrogen atoms and d for non-hydrogen atoms as polarization basis sets.
Added functions.

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

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

Figure 4 (A1) shows the distribution of the LUMO level of one molecule of DBq (abbreviation), Figure 4 (A2) shows the distribution of the HOMO level of one molecule of DBq (abbreviation), and Figure 4 (B1) shows the distribution of the HOMO level of one molecule of DBq (abbreviation). , TPA (abbreviation)
Figure 4 (abbreviation) (B2) shows the distribution of the HOMO level of one molecule of TPA (abbreviation), and Figure 4 (C1) shows the distribution of LUMO level of one molecule of DBq (abbreviation) and TPA (abbreviation). Figure 4 (C2) shows the HOMO level distribution of the dimer of DBq (abbreviation) and TPA (abbreviation).

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

Next, the excitation energy obtained from the optimal molecular structure at the S1 level and T1 level of one molecule of DBq (abbreviation) is 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 the S1 level of one molecule of DBq (abbreviation) was 3.294 eV, and the fluorescence wavelength was 376.4 nm.
Further, the excitation energy of the T1 level of one molecule of DBq (abbreviation) was 2.460 eV, and the phosphorescence wavelength was 504.1 nm.

Also shown is the excitation energy obtained from the optimal molecular structure at the S1 level and T1 level of one molecule of TPA (abbreviation). 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 TPA (abbreviation), respectively. The excitation energy of the S1 level of one molecule of TPA (abbreviation) was 3.508 eV, and the fluorescence wavelength was 353.4 nm.
Further, the excitation energy of the T1 level of one molecule of TPA (abbreviation) was 2.610 eV, and the phosphorescence wavelength was 474.7 nm.

Furthermore, the excitation energy obtained from the optimal molecular structure at the S1 level and T1 level of the dimer of DBq (abbreviation) and TPA (abbreviation) is shown. The excitation energy of S1 level and T1 level is
This corresponds to the wavelengths of fluorescence and phosphorescence emitted by dimers at the DBq level and TPA level, respectively. DBq
The excitation energy of the S1 level of the dimer of (abbreviation) and TPA (abbreviation) was 2.036 eV, and the fluorescence wavelength was 609.1 nm. Furthermore, the excitation energy of the T1 level of the dimer of DBq (abbreviation) and TPA (abbreviation) is 2.030eV, and the phosphorescence wavelength is 610.0n.
It was m.

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 nearly 100 nm. This is the CBP mentioned above.
(abbreviation) (actual measurement value), and this result supports the validity of the calculation.

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

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

As described above, a light-emitting element that is an embodiment of the present invention combines the emission spectrum of an exciplex formed in a light-emitting layer and a light-emitting substance (the above-mentioned first light-emitting substance and second light-emitting substance) that converts triplet excitation energy into light emission. Utilizing the overlap with the absorption spectrum of guest materials (including luminescent substances),
Because it transfers energy, it has high energy transfer efficiency. Therefore, a light emitting element with high external quantum efficiency can be realized.

Furthermore, since exciplexes exist only in excited states, there is no ground state that can absorb energy. Therefore, a luminescent substance (guest material) that converts triplet excitation energy into luminescence
A phenomenon in which a luminescent substance (guest material) that converts triplet excitation energy into luminescence by transferring energy from the singlet excited state and triplet excited state to the exciplex is deactivated before emitting light (that is, impairing luminous efficiency) is considered not to occur in principle. This is also one of the reasons why the external quantum efficiency can be increased.

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

The emission wavelength of an exciplex depends on the energy difference between the HOMO level and the LUMO level. As a general tendency, when the energy difference is large, the emission wavelength becomes short, and when the energy difference is small, the emission wavelength becomes long.

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

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, the first organic compound 110 and the second organic compound 111 in the second light emitting layer 106b) and the third organic compound 112), the LUMO level of the exciplex in the first light-emitting layer 106a and the second light-emitting layer 106b is the same as that of the first organic compound (host material) 110. The HOMO level of the exciplex in the first light emitting layer 106a originates from the second organic compound (assist material) 111, and the HOMO level of the exciplex in the first light emitting layer 106a originates from the second organic compound (assist material) 111.
The HOMO level of the exciplex in 06b is derived from the HOMO level of the third organic compound (assist material) 112. Therefore, the excitation energy (E _A ) of the exciplex in the first light emitting layer 106a is equal to the excitation energy (E _B ) of the exciplex in the second light emitting layer 106b.
becomes larger than That is, as a first luminescent substance 109a that converts triplet excitation energy contained in the first luminescent layer into luminescence, a second luminescent substance 109b which converts triplet excitation energy contained in the second luminescent layer into luminescence. By using a substance that emits light at a shorter wavelength than the above, it is possible to form a light emitting element with high luminous efficiency. Furthermore, luminescent materials having different emission wavelengths can be made to emit light simultaneously and efficiently.

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

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

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

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

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

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

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

In addition, 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 materials, 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 within 0.3 eV. preferable. It is more preferably within 0.2 eV, and most preferably within 0.1 eV.

Furthermore, in the light-emitting element that is one embodiment of the present invention, the excitation energy of the exciplex is sufficiently transferred to the luminescent substance (guest material) that converts triplet excitation energy into light emission, and the light emission from the exciplex is substantially reduced. Preferably, it is not observed. Therefore, it is preferable that the luminescent substance that converts triplet excitation energy into luminescence emits light by transferring energy to the luminescent substance that converts triplet excitation energy into luminescence via an exciplex. Note that the luminescent substance that converts triplet excitation energy into luminescence is preferably a phosphorescent compound (organometallic complex, etc.), a thermally activated delayed fluorescence (TADF) material, or the like.

Further, in the first light-emitting layer 106a of the light-emitting element which is one embodiment of the present invention, when a light-emitting substance that converts triplet excitation energy into light emission is used as the first organic compound (host material), the first
The organic compound (host material) itself becomes easier to emit light, and energy is less likely to be transferred to the luminescent substance (guest material) that converts triplet excitation energy into light emission. In this case, the first organic compound only needs to emit light efficiently, but the host material suffers from the problem of concentration quenching, making it difficult to achieve high luminous efficiency. Therefore, at least one of the first organic compound (host material) and the second organic compound (or third organic compound) (assist material) is a fluorescent compound (i.e., emit light from a singlet excited state or undergo thermal deactivation). This is effective when the compound is a compound that is likely to cause Therefore, at least one of the first organic compound (host material) and the second organic compound (or third organic compound) (assist material) is a fluorescent compound, and an exciplex is used as an energy transfer medium. It is preferable that

Note that the structure shown in this embodiment can be used in combination with the structures shown in 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 FIG.

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

Note that the light-emitting layer 206 shown in this embodiment mode has a first light-emitting layer 206a and a second light-emitting layer 20.
Among the light-emitting layers 206, the first light-emitting layer 206a includes a first light-emitting substance (guest material) 209a that converts triplet excitation energy into light emission, and a first light-emitting substance (guest material) 209a having an electron transport property. The second light-emitting layer 206b includes a first organic compound (host material) 210 and a second organic compound (assist material) 211 having a hole transport property, and the second light-emitting layer 206b converts triplet excitation energy into light emission. A second light emitting substance (guest material) 209b, a first organic compound (host material) 210 having an electron transporting property, and a third organic compound having a hole transporting property (
Assist material) 212 is included.

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

Note that in the light emitting layer 206 (first light emitting layer 206a and second light emitting layer 206b),
In the case of the first light-emitting layer 206a, a first light-emitting substance 209a that converts triplet excitation energy into light emission is contained in a first organic compound (host material) 210 and a second organic compound (assist material) 211. In the case of the second light-emitting layer 206b, a second light-emitting substance 209b that converts triplet excitation energy into light emission is dispersed in the first organic compound (host material) 210 and the third organic compound (assist material). ) 212, the light emitting layer 20
6 (the first light-emitting layer 206a and the second light-emitting layer 206b) can be suppressed. Further, concentration quenching due to a high concentration of the luminescent substance 209 (209a, 209b) can be suppressed, and the luminous 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
The triplet excitation energy level (T1 level) of each of the 12 is preferably higher than the T1 level of the luminescent substance 209 (209a, 209b) that converts triplet excitation energy into light emission. First organic compound 210, second organic compound 211, and third organic compound 21
Luminescent substances 209 (209a, 20
9b), the triplet excitation energy of the luminescent substance 209 (209a, 209b) that converts the triplet excitation energy contributing to light emission into light emission is transferred to the first organic compound 21.
This is because 0 (or the second organic compound 211 or the third organic compound 212) is quenched, resulting in a decrease in luminous efficiency.

In this embodiment, in the light emitting layer 206, in the first light emitting layer 206a, when carriers (electrons and holes) injected from both electrodes are recombined, the first organic compound 210
An exciplex is formed from the first organic compound 210 and the second organic compound 211, and an exciplex is formed from the first organic compound 210 and the third organic compound 212 in the second light emitting layer 206b. Thereby, the fluorescence spectrum of the first organic compound 210 and the fluorescence spectrum of the second organic compound 211 in the first light emitting layer 206a can be converted into the emission spectrum of the exciplex located on the longer wavelength side. , the fluorescence spectrum of the first organic compound 210 and the fluorescence spectrum of the third organic compound 212 in the second light emitting layer 206b are as follows:
It can be converted to 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 luminescent substance (guest material) 209 that converts triplet excitation energy into luminescence should be increased. , the first organic compound 210 and the second organic compound 211 are selected in the first light emitting layer 206a, and the first organic compound 210 and the third organic compound 212 are selected in the second light emitting layer 206b. shall be. In other words, it is assumed here that energy transfer occurs from the exciplex rather than from the host material also regarding the triplet excited state.

Note that a luminescent substance 209 (first luminescent substance 20
9a, second luminescent substance 209b) is preferably a phosphorescent compound (organometallic complex, etc.), a thermally activated delayed fluorescence (TADF) material, or the like. Further, as the first organic compound (host material) 210, it is preferable to use an electron transporting material. Further, as the second organic compound (assist material) 211 and the third organic compound (assist material) 212, it is preferable to use a hole transporting material.

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

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).

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

However, the luminescent substance (guest material) 209 that converts the triplet excitation energy into luminescence.
(first luminescent substance 209a, second luminescent substance 209b), first organic compound (host material) 210, second organic compound (assist material) 211, and third organic compound (assist material) Materials that can be used for each of the materials 212 are not limited to these, but are combinations that can form an exciplex, and include luminescent substances (guest materials) 209 in which the emission spectrum of the exciplex changes triplet excitation energy into luminescence. (first luminescent substance 209a or second luminescent substance 209b), the peak of the emission spectrum of the exciplex overlaps with the absorption spectrum of the luminescent substance (guest material) 209 (guest material) that converts triplet excitation energy into luminescence. Any material having a wavelength longer than the peak of the absorption spectrum of the first luminescent substance 209a or the second luminescent substance 209b) may be used.

Further, 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 thereof. Specifically, first organic compound 210:second organic compound 211=1:9
The ratio is preferably in the range of 9:1 to 9:1.

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

For the first electrode (anode) 201 and the second electrode (cathode) 202, metals, alloys, electrically conductive compounds, mixtures thereof, and the like can be used. Specifically, indium oxide-tin oxide (ITO), indium oxide-tin oxide containing silicon or silicon oxide, indium oxide-zinc oxide (Indium Zi oxide), etc.
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 Group 2 of the periodic table, namely lithium (L
i) and alkali metals such as cesium (Cs), as well as magnesium (Mg) and calcium (
Alkaline earth metals such as Ca), strontium (Sr), and alloys containing these (Mg
Rare earth metals such as Ag, AlLi), europium (Eu), and ytterbium (Yb), alloys containing these metals, and other materials such as 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, a vapor deposition method (including a vacuum vapor deposition method), or the like.

As a material with high hole transport properties used for the hole injection layer 204 and the hole transport layer 205, for example, 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB or α-NPD), N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviation: TPD), 4,4 ',
4''-tris(carbazol-9-yl)triphenylamine (abbreviation: TCTA), 4
,4',4''-tris(N,N-diphenylamino)triphenylamine (abbreviation: TD
ATA), 4,4',4''-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (abbreviation: MTDATA), 4,4'-bis[N-(spiro-9 ，
9'-bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB)
Aromatic amine compounds such as 3-[N-(9-phenylcarbazol-3-yl)-N-
phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA1), 3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA2), 3 -[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole (abbreviation: PCzPC
N1), etc. Others, 4,4'-di(N-carbazolyl)biphenyl (abbreviation:
CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation:
TCPB), carbazole derivatives such as 9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA), and the like. The substances described here mainly have a hole mobility of 10 ⁻⁶ cm ² /Vs or more. However, materials other than these may be used as long as they have a higher transportability for holes than for electrons.

Furthermore, poly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA), poly[N-(4-{N'-[4-(4-diphenylamino) phenyl]phenyl-N'-phenylamino}phenyl) methacrylamide]
(abbreviation: PTPDMA), poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] (abbreviation: Poly-TPD), and the like can also be used.

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

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

The electron transport layer 207 is a layer containing a substance with high electron transport properties. The electron transport layer 207 includes
Alq ₃ , tris(4-methyl-8-quinolinolato) aluminum (abbreviation: Almq ₃ )
, bis(10-hydroxybenzo[h]quinolinato) beryllium (abbreviation: BeBq ₂ ),
Metal complexes such as BAlq, Zn(BOX) ₂ , 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, A polymer compound such as 6'-diyl) (abbreviation: PF-BPy) can also be used. The substances mentioned here mainly have an electron mobility of 10 ⁻⁶ cm ² /Vs or more. Note that any material other than those mentioned above may be used as the electron transport layer 207 as long as it has a higher ability to transport electrons than holes.

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

The electron injection layer 208 is a layer containing a substance with high electron injection properties. The electron injection layer 208 includes
Lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF ₂ )
, lithium oxide (LiOx), etc., alkaline earth metals, or compounds thereof can be used. Also, rare earth metal compounds such as erbium fluoride (ErF ₃ ) can be used. Moreover, the substance constituting the electron transport layer 207 described above can also be used.

Alternatively, a composite material made of a mixture of an organic compound and an electron donor may be used for the electron injection layer 208. Such a composite material has excellent electron injection and electron transport properties because electrons are generated in the organic compound by the electron donor. In this case, the organic compound is preferably a material that is excellent in transporting the generated electrons, and specifically, for example, a material (such as a metal complex or a heteroaromatic compound) constituting the electron transport layer 207 described above is used as the organic compound. Can be used. The electron donor may be any substance that exhibits electron-donating properties to organic compounds. Specifically, alkali metals, alkaline earth metals, and rare earth metals are preferred, and examples include lithium, cesium, magnesium, calcium, erbium, and ytterbium. Moreover, alkali metal oxides and alkaline earth metal oxides are preferable, and examples thereof include lithium oxide, calcium oxide, barium oxide, and the like. Additionally, Lewis bases such as magnesium oxide can also be used. Moreover, organic compounds such as tetrathiafulvalene (abbreviation: TTF) can also be used.

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

The light emitted from the light emitting layer 206 of the light emitting element described above is extracted to the outside through either or both of the first electrode 201 and the second electrode 202. Therefore, either one or both of the first electrode 201 and the second electrode 202 in this embodiment is an electrode having light-transmitting properties.

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

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

Note that in the case of an active matrix type light emitting device, the structure of the TFT is not particularly limited. For example, a staggered TFT or an inverted staggered TFT can be used as appropriate. Also, T
The driving circuit formed on the FT substrate may also be composed of N-type and P-type TFTs, or may be composed of only one of N-type TFTs or P-type TFTs. Furthermore, there are no particular limitations on the crystallinity of the semiconductor film used in the TFT. For example, an amorphous semiconductor film, a crystalline semiconductor film, an oxide semiconductor film, or the like can be used.

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

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

The light-emitting element shown in this embodiment has a pair of electrodes (a first electrode 30
A plurality of EL layers (first EL layer 302(1), second EL layer 302(1), second EL layer 302(1),
This is a tandem light emitting element having an L layer 302(2)).

In this embodiment, the first electrode 301 is an electrode that functions as an anode, and the second electrode 304 is an electrode that functions as a cathode. Note that the first electrode 301 and the second electrode 304 can have the same configuration as in Embodiment 1. In addition, multiple 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; It may be a configuration. In other words, the first EL layer 302(1) and the second EL layer 302(2) may have the same structure or different structures, and the structure may be the same as that of Embodiment 1 or 2. The same can be applied.

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

Note that the charge generation layer (I) 305 is transparent to visible light in terms of light extraction efficiency (specifically, the transmittance of visible light to the charge generation layer (I) 305 is as follows: 40% or more) is preferable. Further, the charge generation layer (I) 305 is connected to the first electrode 301 and the second electrode 3.
It works even if the conductivity is lower than 04.

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

In the case where an electron acceptor is added to an organic compound with a high hole transport property, examples of the organic compound with a high hole transport property include NPB, TPD, TDATA, and MTDATA.
, 4,4'-bis[N-(spiro-9,9'-bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB), etc. can be used. The substances described here mainly have a hole mobility of 10 ⁻⁶ cm ² /Vs or more. However, any substance other than the above may be used as long as it is an organic compound that transports holes better than electrons.

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

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

Further, as the electron donor, an alkali metal, an alkaline earth metal, a rare earth metal, a metal belonging to Group 13 in the periodic table of elements, and their oxides and carbonates 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. Additionally, organic compounds such as tetrathianaphthacene may be used as electron donors.

Note that by forming the charge generation layer (I) 305 using the above-mentioned material, it is possible to suppress an increase in driving voltage when EL layers are stacked.

Although a light-emitting element having two EL layers has been described in this embodiment, a light-emitting element having n EL layers (where n is 3 or more) stacked as shown in FIG. 6B can also be described. , can be similarly applied. When the light emitting element according to this embodiment has a plurality of EL layers between a pair of electrodes, 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, long-life devices can be realized. Furthermore, when applied to lighting, the voltage drop due to the resistance of the electrode material can be reduced, making it possible to emit light uniformly over a large area. Furthermore, a light emitting device that can be driven at low voltage and consumes low power can be realized.

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

The same applies to a light emitting element having three EL layers; for example, the first EL layer emits red light, the second EL layer emits green light, and the third EL layer emits red light. When the emitted light color is blue, the light emitting element as a whole can emit white light.

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

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

The light-emitting device shown in this embodiment has a micro-optical resonator (micro-cavity) structure that utilizes the resonance effect of light between a pair of electrodes, and as shown in FIG. Electrode 4
01 and semi-transparent/semi-reflective electrodes 402), the light emitting element has a structure including at least an EL layer 405. In addition, the EL layer 405 includes at least a light emitting layer 4 serving as a light emitting region.
04 (404R, 404G, 404B), and may also include a hole injection layer, a hole transport layer, an electron transport layer, an electron injection layer, a charge generation layer (E), etc. 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 Embodiment Modes 1 and 2.

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

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

Each light emitting element shown in this embodiment mode has a reflective electrode 401 and a semi-transparent/semi-reflective electrode 40.
It has a structure in which an EL layer 405 is sandwiched between the EL layer 405 and the EL layer 405, and the light emitted from each light emitting layer included in the EL layer 405 in all directions functions as a micro optical resonator (micro cavity). The reflection electrode 401 and the semi-transmissive/semi-reflective electrode 402 resonate. The reflective electrode 401 is formed of a reflective conductive material, and has a visible light reflectance of 40% to 100%, preferably 70% to 100%, and a resistivity of 1×. 10
Assume that the film is ^-2 Ωcm or less. Further, the semi-transparent/semi-reflective electrode 402 is formed of a conductive material having a reflective property and a conductive material having a light transmitting property, and the reflectance of visible light to the film is 20% to 80%, preferably 40%. % to 70%, and its resistivity is 1×10 ⁻
It is assumed that the film has a resistance of ² Ωcm or less.

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

Note that the optical distance (also referred to as optical path length) is the actual distance multiplied by the refractive index, and in this embodiment, it represents the actual film thickness multiplied by n (refractive index). . In other words, “
Optical distance=actual film thickness×n”.

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

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

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

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

Note that the optical distance between the reflective electrode 401 and the third light emitting layer (R) 404R is, strictly speaking, the optical distance between the reflective region in the reflective electrode 401 and the light emitting region in the third light emitting layer (R) 404R. I can do it. However, the reflective region in 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 in 404R, the reflective electrode 40
It is assumed that the above effect can be sufficiently obtained by assuming that an arbitrary position of the third light emitting layer (R) 404R is a reflective 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, from the reflective electrode 401 to the second light emitting layer (G)
) 404G to the desired film thickness ((2m''+1)λ _G /4 (where m'' is a natural number)), light emission from the second light emitting layer (G) 404G can be amplified. Of the light emitted from the second light-emitting layer (G) 404G, the light reflected by the reflective electrode 401 and returned (second reflected light) is semi-transmitted and semi-reflected from the second light-emitting layer (G) 404G. In order to cause interference with the light directly incident on the electrode 402 (second incident light), the reflective electrode 401
to the second light emitting layer (G) 404G to the desired value ((2m''+1)λ _G /4(
However, by adjusting m'' to a natural number), the phase of the second reflected light and the second incident light can be matched and the light emission from the second light emitting layer (G) 404G can be amplified. I can do it.

Note that the optical distance between the reflective electrode 401 and the second light emitting layer (G) 404G is, strictly speaking, the optical distance between the reflective region in the reflective electrode 401 and the light emitting region in the second light emitting layer (G) 404G. I can do it. However, the reflective region in the reflective electrode 401 and the second light emitting layer (G)
Since it is difficult to accurately determine the position of the light emitting region in 404G, the reflective electrode 40
It is assumed that the above-mentioned effects can be sufficiently obtained by assuming that an arbitrary position of the second light-emitting layer (G) 404G is a reflective region and an arbitrary position of the second light-emitting layer (G) 404G is a light-emitting region.

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

Note that in the third light emitting element, the optical distance between the reflective electrode 401 and the first light emitting layer (B) 404B is strictly speaking the optical distance between the reflective area in the reflective electrode 401 and the light emission in the first light emitting layer (B) 404B. It can be said to be the optical distance to the area. However, since it is difficult to precisely determine the position of the reflective region in the reflective electrode 401 and the light emitting region in the first light emitting layer (B) 404B, any position of the reflective electrode 401 can be set as the reflective region and the first light emitting layer. It is assumed that the above-mentioned effect can be sufficiently obtained by assuming that an arbitrary position of the layer (B) 404B is a light emitting region.

Note that in the above structure, each light-emitting element has a structure in which the EL layer has a plurality of light-emitting layers, but the present invention is not limited to this. For example, the tandem type described in Embodiment 3 In combination with the structure of the light emitting element, multiple ELs can be formed in one light emitting element with a charge generation layer sandwiched between them.
It is also possible to have a structure in which layers are provided and each EL layer has one or more light emitting layers.

The light-emitting device shown in this embodiment has a microcavity structure, and the same EL
Even if it has layers, it is possible to extract light of different wavelengths for each light emitting element, so there is no need to separate RGB colors. Therefore, it is advantageous in realizing full color because it is easy to realize high definition. Note that a combination with a colored layer (color filter) is also possible. Further, since it is possible to increase the intensity of light emitted from the front direction at a specific wavelength, it is possible to reduce power consumption. This configuration is particularly useful when applied to a color display (image display device) using pixels of three or more colors, but may also be used for purposes 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.

Further, 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 elements described in other embodiments can be applied to the light-emitting device shown in this embodiment.

In this embodiment, an active matrix light-emitting device will be described with reference to FIG. 8.

Note that FIG. 8(A) is a top view showing the light emitting device, and FIG. 8(B) shows FIG. 8(A) along the chain line A-
It is a sectional view taken along A'. The active matrix light emitting device according to this embodiment includes a pixel portion 502 provided on an element substrate 501 and a drive circuit portion (source line drive circuit) 50.
3, and a drive circuit section (gate line drive circuit) 504 (504a and 504b).
The pixel portion 502, the drive circuit portion 503, and the drive circuit portion 504 are sealed by the sealant 505.
It is sealed between the element substrate 501 and the sealing substrate 506.

Further, on the element substrate 501, external input terminals for transmitting external signals (for example, a video signal, a clock signal, a start signal, a reset signal, etc.) and potential to the drive circuit section 503 and the drive circuit section 504 are provided. A routing wiring 507 for connection is provided. here,
An example is shown in which an FPC (flexible printed circuit) 508 is provided as an external input terminal. Note that although only the FPC is illustrated here, a printed wiring board (PWB) may be attached to the FPC. In this specification, the light emitting device includes not only the light emitting device main body but also a state in which an FPC or PWB is attached to the light emitting device.

Next, the cross-sectional structure will be explained using FIG. 8(B). A drive circuit section and a pixel section are formed on the element substrate 501, but here, a drive circuit section 503 which is a source line drive circuit is formed.
and a pixel portion 502 are shown.

The drive circuit section 503 shows an example in which a CMOS circuit is formed by combining an n-channel type TFT 509 and a p-channel type TFT 510. Note that the circuit forming the drive circuit section is
It may be formed using various CMOS circuits, PMOS circuits, or NMOS circuits. Furthermore, although this embodiment shows a driver-integrated type in which a drive circuit is formed on a substrate, this is not necessarily necessary, and the drive circuit can be formed externally instead of on the substrate.

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

Further, in order to improve the coverage of the film laminated on the upper layer, it is preferable that a curved surface having a curvature is formed at the upper end or the lower end of the insulator 514. For example, when a positive photosensitive acrylic resin is used as the material for the insulator 514, it is preferable that the upper end of the insulator 514 have a curved surface with a radius of curvature (0.2 μm to 3 μm). Further, as the insulator 514, either a negative photosensitive resin or a positive photosensitive resin can be used, and not only organic compounds but also inorganic compounds such as silicon oxide, silicon oxynitride, etc.
Both can be used.

On the first electrode (anode) 513, an EL layer 515 and a second electrode (cathode) 516 are laminated. The EL layer 515 is provided with at least a light-emitting layer, and the light-emitting layer has a stacked structure as shown in Embodiment Mode 1. Further, 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, and the like as appropriate.

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

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

Furthermore, by bonding the sealing substrate 506 to the element substrate 501 using the sealant 505, a structure is created 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 sealant 505. ing. Note that in addition to the case where the space 518 is filled with an inert gas (such as nitrogen or argon), the space 518 also includes a structure where it is filled with the sealing material 505.

Note that it is preferable to use epoxy resin, low melting point glass, or the like as the sealing material 505. Further, it is desirable that these materials are as impervious to moisture and oxygen as possible. In addition to glass substrates and quartz substrates, materials used for the sealing substrate 506 include FRP (Fiberg
A plastic substrate made of lass-reinforced plastics, PVF (polyvinyl fluoride), polyester, acrylic, or the like can be used.

In the manner described above, an active matrix type light emitting device can be obtained.

Note that the structure shown in this embodiment can be used in appropriate combination with the structures shown in other embodiments.

(Embodiment 6)
In this embodiment, examples of various electronic devices completed using a light-emitting device manufactured using a light-emitting element that is one embodiment of the present invention will be described with reference to FIGS. 9 and 10.

Electronic devices to which light-emitting devices are applied include, for example, television devices (also called televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, and mobile phones (mobile phones, mobile phones, etc.). (also called telephone equipment)
Examples include portable game machines, personal digital assistants, audio playback devices, and large game machines such as pachinko machines. Specific examples of these electronic devices are shown in FIG.

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

The television device 7100 can be operated using an operation switch included in the housing 7101 or a separate remote controller 7110. An operation key 7109 included in the remote controller 7110 can be used to control the channel and volume, and can also control the image displayed on the display section 7103. Further, the remote control device 7110 may be provided with a display section 7107 that displays information output from the remote control device 7110.

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

FIG. 9B shows 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 using a light-emitting device for the display portion 7203.

FIG. 9C shows a portable gaming machine, which is composed of two housings, a housing 7301 and a housing 7302, which are connected by a connecting portion 7303 so as to be openable and closable. A display portion 7304 is built into the casing 7301, and a display portion 7305 is built into the casing 7302. In addition, the portable gaming machine shown in FIG. 9(C) also includes a speaker section 7306, a recording medium insertion section 7307,
, 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 substances, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, (includes the function of measuring tilt, vibration, odor, or infrared rays), a microphone 7312), etc. Of course, the configuration of the portable gaming machine is not limited to that described above, and at least the display section 73
04 and the display section 7305, or a light emitting device may be used for one of them, and other auxiliary equipment may be provided as appropriate. The portable gaming machine shown in FIG. 9(C) has a function of reading out a program or data recorded on a recording medium and displaying it on a display unit, and sharing information by wirelessly communicating with other portable gaming machines. Has a function. Note that the functions of the portable gaming machine shown in FIG. 9(C) are not limited to these, and can have various functions.

FIG. 9(D) shows an example of a mobile phone. The mobile phone 7400 has a housing 7401
In addition to a display section 7402 built into the , it is equipped with operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. Note that the mobile phone 7400 is manufactured using a light-emitting device for the display portion 7402.

In the mobile phone 7400 shown in FIG. 9(D), information can be input by touching the display portion 7402 with a finger or the like. Further, operations such as making a call or composing an email can be performed by touching the display portion 7402 with a finger or the like.

The screen of the display section 7402 mainly has three modes. The first is a display mode that mainly displays images, and the second is an input mode that mainly inputs information such as characters. The third mode is a display+input mode, which is a mixture of two modes: a display mode and an input mode.

For example, when making a phone call or composing an email, the display unit 7402 may be set to a character input mode that mainly inputs characters, and the user may input the characters displayed on the screen. In this case, it is preferable to display a keyboard or number buttons on most of the screen of the display section 7402.

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

Further, switching of the screen mode is performed by touching the display portion 7402 or operating the operation button 7403 on the housing 7401. Further, it is also possible to switch depending on the type of image displayed on the display section 7402. For example, if the image signal to be displayed on the display section is video data, the mode is switched to display mode, and if it is text data, the mode is switched to input mode.

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

The display portion 7402 can also function as an image sensor. For example, display section 7
By touching 402 with the palm or fingers and capturing an image of a palm print, fingerprint, etc., the person can be authenticated.
Furthermore, if a backlight that emits near-infrared light or a sensing light source that emits near-infrared light is used in the display section, it is also possible to image finger veins, palm veins, and the like.

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

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

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

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

Further, a display mode changeover switch 9034 can switch the display orientation such as portrait display or landscape display, and can select switching between black and white display and color display. The power saving mode changeover switch 9036 can optimize the brightness of the display according to the amount of external light during use, which is detected by an optical sensor built into the tablet terminal. The tablet terminal may include not only a light sensor but also other detection devices such as a sensor that detects tilt, such as a gyro or an acceleration sensor.

Further, although FIG. 10A shows an example in which the display area of the display portion 9631b and the display portion 9631a are the same, this is not particularly limited, and the size of one and the other may be different, and the quality of the display may also be affected. May be different. For example, one display panel may be capable of displaying higher definition than the other.

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

Note that since the tablet terminal can be folded in two, the housing 9630 can be kept in a closed state 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 device that is highly durable and highly reliable from the standpoint of long-term use.

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

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

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

First, an example of the operation when the solar cell 9633 generates power using external light will be described. The power generated by the solar cell 9633 is boosted or stepped down by a DC/DC converter 9636 so that it becomes a voltage for charging a battery 9635. And display section 9631
When the power from the solar cell 9633 is used for the operation, the switch SW1 is turned on, and the converter 9638 steps up or steps down the voltage necessary for the display section 9631. Also, when not displaying on the display section 9631, switch SW1 is turned off and switch SW1 is turned off.
The configuration may be such that the battery 9635 is charged by turning on W2.

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

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

In the above manner, an electronic device can be obtained by applying a light-emitting device that is one embodiment of the present invention. The scope of application of light emitting devices is extremely wide, and they can be applied to electronic devices in all fields.

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

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

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

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

As described above, various lighting devices using light emitting devices can be obtained. Note that these lighting devices are included in one embodiment of the present invention.

Further, the structure shown in this embodiment can be used in combination with the structures shown in other embodiments as appropriate.

In this example, a light emitting element 1 that is one embodiment of the present invention will be described with reference to FIG. 12. The chemical formulas of the materials used in this example are shown below.

<<Fabrication of light emitting element 1>>
First, a film of indium tin oxide containing silicon oxide (ITSO) was formed on a glass substrate 1100 by sputtering to form a first electrode 1101 functioning as an anode. Note that the film thickness was 110 nm, and the electrode area was 2 mm x 2 mm.

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

Thereafter, the substrate 1100 was introduced into a vacuum evaporation apparatus whose internal pressure was reduced to about 10 ^-4 Pa, and vacuum baking was performed at 170° C. for 30 minutes in the heating chamber of the vacuum evaporation apparatus. It was left to 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 faced downward. In this example, the EL layer 1 is
A case will be described in which a hole injection layer 1111, a hole transport layer 1112, a light emitting layer 1113, an electron transport layer 1114, and an electron injection layer 1115 that constitute 102 are sequentially formed.

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

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

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

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

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

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 with 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 during sealing).

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

First, FIG. 13 shows the 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 ). Further, the voltage-luminance characteristics of the light emitting element 1 are shown in FIG. Note that in FIG. 14, the vertical axis represents luminance (cd/m ² );
The horizontal axis indicates voltage (V). Further, the luminance-current efficiency characteristics of the light emitting element 1 are shown in FIG. Note that in FIG. 15, the vertical axis represents current efficiency (cd/A), and the horizontal axis represents brightness (cd/m ² ). Further, the voltage-current characteristics of the light emitting element 1 are shown in FIG. 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. Further, the main initial characteristic values of the light emitting element 1 at around 1000 cd/m ² are shown in Table 2 below.

From the above results, it can be seen that the light emitting element 1 manufactured in this example exhibits high external quantum efficiency, and thus exhibits high luminous efficiency.

Further, FIG. 17 shows an emission spectrum when a current is passed through the light emitting element 1 at a current density of 25 mA/cm ² . As shown in FIG. 17, the emission spectrum of light emitting element 1 is 546 nm and 615 nm.
It has two peaks near nm, each of which is a phosphorescent organometallic iridium complex [Ir(
It is suggested that the emission is derived from the luminescence of [tBuppm) ₂ (acac)] and [Ir(dmdppr-dmp) ₂ (divm)].

Furthermore, according to cyclic voltammetry measurement, the HOMO level of PCBBiF, which is the second organic compound with hole transporting properties, is -5.36 eV, and FBi2P, which is the third organic compound with hole transporting properties, is -5.36 eV. The HOMO level of was estimated to be -5.13 eV. Therefore, the second organic compound has a lower HOMO level than the third organic compound.

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

From FIG. 18 and FIG. 19, the emission wavelength of the mixed film is located at a longer wavelength than that of the single film of each material. ), and the first organic compound (2mDBTBPDBq-II) and the third organic compound (FBi2P) each form an exciplex. Furthermore, the emission wavelength of the exciplex formed by the first organic compound (2mDBTBPDBq-II) and the second organic compound (PCBBiF) is 511 nm, whereas the emission wavelength of the exciplex formed by the first organic compound (2mD
Since the emission wavelength of the exciplex formed by BTBPDBq-II) and the third organic compound (FBi2P) is 553 nm, it can be seen that the former has higher energy.

101 First electrode 102 Second electrode 103 EL layer 104 Hole injection layer 105 Hole transport layer 106 Light emitting layer 106a First light emitting layer 106b Second light emitting layer 107 Electron transport layer 108 Electron injection layer 109 Luminescent substance 109a First luminescent substance that converts triplet excitation energy into luminescence 109b Second luminescent substance that converts triplet excitation energy into luminescence 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 Light emitting substance 209a A first light emitting layer 206a that converts triplet excitation energy into light emission 1 luminescent substance 209b 2nd luminescent substance 210 that converts triplet excitation energy into luminescence 1st organic compound 211 2nd organic compound 212 3rd organic compound 301 1st electrode 302 (1) 1st luminescent substance 209b EL layer 302 (2) Second EL layer 302 (n-1) (n-1)th EL layer 302 (n) (n)th EL layer 304 Second electrode 305 Charge generation layer (I)
305(1) First charge generation layer (I)
305(2) Second charge generation layer (I)
305(n-2)th (n-2)th charge generation layer (I)
305(n-1)th (n-1)th charge generation layer (I)
401 Reflective electrode 402 Semi-transparent/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 board 507 Routing wiring 508 FPC (flexible printed circuit)
509 n-channel TFT
510 p channel type 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 control unit 7201 Main body 7202 Housing 7203 Display portion 7204 Keyboard 7205 External connection port 7206 Pointing device 7301 Housing 7302 housing 7303 Connection section 7304 Display section 7305 Display section 7306 Speaker section 7307 Recording medium insertion section 7308 LED lamp 7309 Operation key 7310 Connection terminal 7311 Sensor 7312 Microphone 7400 Mobile phone 7401 Housing 7402 Display section 7403 Operation button 7404 External connection port 7405 Speaker 7 406 Microphone 8001 Lighting device 8002 Lighting device 8003 Lighting device 8004 Lighting device 9033 Fastener 9034 Display mode changeover switch 9035 Power switch 9036 Power saving mode changeover 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 (2)

having a first light emitting layer and a second light emitting layer in contact with the first light emitting layer between the pair of electrodes,
The excitation energy of the first exciplex formed in the first light-emitting layer is greater than the excitation energy of the second exciplex formed in the second light-emitting layer,
A light emitting element, wherein a first light emitting substance included in the first light emitting layer emits light with a shorter wavelength than a second light emitting substance contained in the second light emitting layer. having a first light emitting layer and a second light emitting layer in contact with the first light emitting layer between the pair of electrodes,
The excitation energy of the first exciplex formed in the first light-emitting layer is greater than the excitation energy of the second exciplex formed in the second light-emitting layer,
A light emitting element, wherein the first organometallic complex included in the first light emitting layer emits light with a shorter wavelength than the second organometallic complex contained in the second light emitting layer.

Images