JP7654874B2 - Light emitting element - Google Patents

Description

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

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

The light-emitting mechanism of a light-emitting element is said to be that, by applying a voltage to an EL layer containing a light-emitting body sandwiched between a pair of electrodes, electrons injected from the cathode and holes injected from the anode recombine at the luminescence center of the EL layer to form molecular excitons, which release energy when relaxing to the ground state, resulting in light emission. Singlet excitation and triplet excitation are known as excited states, and it is believed that light emission is possible through either excited state.

In order to improve the characteristics of such light-emitting elements, improvements to element structures and development of materials have been actively carried out (see, for example, Japanese Patent Application Laid-Open No. 2003-233663).

JP 2010-182699 A

However, the current light extraction efficiency of light-emitting elements is said to be about 20% to 30%, and even taking into account light absorption by reflective electrodes and transparent electrodes, the limit of the external quantum efficiency of light-emitting elements using phosphorescent compounds is thought to be about 25%.

In view of the above, one embodiment of the present invention provides a light-emitting element with high external quantum efficiency and a long lifetime.

One embodiment of the present invention is a light-emitting element having a light-emitting layer between a pair of electrodes (anode and cathode). The light-emitting layer contains at least a first light-emitting substance (guest material) that converts triplet excitation energy into light emission, a first organic compound (host material) that has an electron-transporting property, and a second organic compound (assist material) that has a hole-transporting property and is formed on the anode side. The light-emitting layer has a stacked structure of a first light-emitting layer and a second light-emitting layer that contains at least the second light-emitting substance (guest material) that converts triplet excitation energy into light emission, the first organic compound (host material) that has an electron-transporting property, and a third organic compound (assist material) that has a hole-transporting property. In the first light-emitting layer, the first organic compound (host material) and the second organic compound (assist material) form an exciplex. In the second light-emitting layer, the first organic compound (host material) and the third organic compound (assist material) form an exciplex.

Another embodiment of the present invention includes 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 a first light-emitting layer that contains at least a first light-emitting substance that converts triplet excitation energy into light emission, a first organic compound that has electron-transporting properties, and a second organic compound that has hole-transporting properties, and is formed in contact with the hole-transport layer. Another embodiment of the present invention includes a first light-emitting layer that contains at least a first light-emitting substance that converts triplet excitation energy into light emission, a first organic compound that has electron-transporting properties, and a second organic compound that has hole-transporting properties, and is formed in contact with the electron-transport layer. In the first light-emitting layer, the first organic compound (host material) and the second organic compound (assist material) are
In the second light-emitting layer, a first organic compound (host material) and a third organic compound (assist material) are combined to form an exciplex. In the second light-emitting layer, a first organic compound (host material) and a third organic compound (assist material) are combined to form an exciplex.

In each of the above structures, the emission wavelength of the exciplex formed by the first organic compound (host material) and the second organic compound (assist material) of the first light-emitting layer is equal to or longer than the emission wavelength (fluorescence wavelength) of each of the first organic compound (host material) and the second organic compound (assist material).
Since the emission wavelength of the exciplex is longer than that of the first organic compound (host material) and the second organic compound (assist material) in the second light-emitting layer, the emission wavelength of the exciplex formed by the first organic compound (host material) and the third organic compound (assist material) in the second light-emitting layer can be converted to an emission spectrum located on the longer wavelength side.
Since the fluorescence spectrum of the first organic compound (host material) and the fluorescence spectrum of the third organic compound (assist material) are on the longer wavelength side compared to the emission wavelengths (fluorescence wavelengths) of the first organic compound (host material) and the third organic compound (assist material), the formation of an exciplex can convert the fluorescence spectrum of the first organic compound (host material) and the fluorescence spectrum of the third organic compound (assist material) into emission spectra located on the longer wavelength side.

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

In the above structure, the first light-emitting layer and the second light-emitting layer each contain the same first organic compound (host material), and the second organic compound (assist material) contained in the first light-emitting layer has a higher highest occupied molecular orbital level (HOMO level) than a third organic compound (assist material) contained in the second light-emitting layer.

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

In the above-described structure, the first light-emitting substance and the second light-emitting substance are light-emitting substances that convert triplet excitation energy into light emission, and are phosphorescent compounds such as organometallic complexes, or materials that exhibit thermally activated delayed fluorescence (TADF).
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 third organic compound are mainly hole transporting materials having a hole mobility of 10 ⁻⁶ cm ² /Vs or more, specifically a π-excessive heteroaromatic compound or an aromatic amine compound.

One embodiment of the present invention includes not only a light-emitting device having a light-emitting element, but also an electronic device and a lighting device having a light-emitting device. Therefore, a light-emitting device in this specification refers to an image display device, a light-emitting device, or a light source (including a lighting device).
A connector, such as a flexible printed circuit (FPC), is attached to the light emitting device.
a module in which a TCP (Tape Carrier Package) or a TCP (Tape Carrier Package) is attached, a module in which a printed wiring board is provided at the end of the TCP, or a module in which a C
The light emitting device also includes all modules in which an IC (integrated circuit) is directly mounted by an OG (chip on glass) method.

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

In addition, in the light-emitting element which is one embodiment of the present invention, the above-described element structure allows the exciplex formed in the first light-emitting layer to have higher excitation energy than the exciplex formed in the second light-emitting layer. Therefore, by using a substance that exhibits emission of a shorter wavelength than that of the second light-emitting substance (guest material) contained in the second light-emitting layer, as the first light-emitting substance (guest material) that converts triplet excitation energy contained in the first light-emitting layer into light emission, light emission can be obtained from the first light-emitting layer and the second light-emitting layer at the same time. Furthermore, part of the excitation energy of the exciplex formed in the first light-emitting layer that has not contributed to light emission can be used as excitation energy for the second light-emitting substance (guest material) in the second light-emitting layer that converts triplet excitation energy into light emission. This makes it possible to further increase the light-emitting efficiency of the light-emitting element.

FIG. 1 illustrates a concept of one embodiment of the present invention. FIG. 1 illustrates a concept of one embodiment of the present invention. FIG. 13 shows calculation results according to one embodiment of the present invention. FIG. 13 shows calculation results according to one embodiment of the present invention. 1A to 1C are diagrams illustrating a structure of a light-emitting element. 1A to 1C are diagrams illustrating a structure of a light-emitting element. 1A and 1B are diagrams illustrating a light-emitting device. 1A and 1B are diagrams illustrating a light-emitting device. 1A to 1C are diagrams illustrating electronic devices. 1A to 1C are diagrams illustrating electronic devices. 1A and 1B are diagrams illustrating a lighting device. 1A to 1C are diagrams illustrating light-emitting elements. FIG. 13 shows current density vs. luminance characteristics of Light-emitting Element 1. FIG. 13 shows voltage-luminance characteristics of the light-emitting element 1. FIG. 13 shows luminance vs. current efficiency characteristics of Light-emitting Element 1. FIG. 13 shows voltage-current characteristics of the light-emitting element 1. FIG. 2 shows an emission spectrum of the light-emitting element 1. FIG. 13 shows an emission spectrum of a substance used in the light-emitting element 1. FIG. 13 shows an emission spectrum of a substance used in the light-emitting element 1.

Hereinafter, the embodiment of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and the form and details can be changed in various ways without departing from the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited to the description of the embodiment shown below.

(Elemental 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, a molecule that provides excitation energy will be referred to as a host molecule, and a molecule that receives excitation energy will be referred to as a guest molecule.

(1) An electron and a hole recombine in a guest molecule, causing the guest molecule to enter an excited state (direct recombination process).

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

(1-2) When the excited state of the guest molecule is a singlet excited state, the guest molecule in the singlet excited state undergoes intersystem crossing to a triplet excited state and emits phosphorescence.

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

(2) Electrons and holes recombine in the host molecule, causing the host molecule to enter an excited state (energy transfer process).

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

3H*+1G → 1H+3G* (2-1)

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

That is, as shown in the following formula (2-2A), energy is transferred from the singlet excited state (1H*) of the host molecule to the singlet excited state (1G*) of the guest molecule, and then the triplet excited state (3G*) of the guest molecule is generated by intersystem crossing. Alternatively, energy is transferred directly from the singlet excited state (1H*) of the host molecule to the triplet excited state (3G*) of the guest molecule as shown in the following formula (2-2B).

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 the singlet excitation energy of the host molecule are efficiently converted into the triplet excited state (3G*) of the guest molecule, enabling highly efficient light emission. Conversely, if the host molecule itself is deactivated by releasing the excitation energy as light or heat before the excitation energy is transferred from the host molecule to the guest molecule, the light emission efficiency will decrease.

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

The first mechanism, the Förster mechanism (dipole-dipole interaction), is a mechanism in which energy transfer does not require direct contact between molecules, but occurs through the resonance phenomenon of dipole vibration between a host molecule and a guest molecule. The host molecule transfers energy to a guest molecule through the resonance phenomenon of dipole vibration, and the host molecule becomes in a ground state and the guest molecule becomes in an excited state. The rate constant k _h*→g of the Förster mechanism is shown in Equation (1).

In the formula (1), ν represents a vibration frequency, f′ _h (ν) represents a normalized emission spectrum of the host molecule (a fluorescence spectrum when the energy transfer from a singlet excited state is considered, and a phosphorescence spectrum when the energy transfer from a triplet excited state is considered), and ε _g (
ν) represents the molar absorption coefficient of the guest molecule, N represents Avogadro's number, n represents the refractive index of the medium, R represents the intermolecular distance between the host molecule and the guest molecule, τ represents the lifetime of the excited state (fluorescence lifetime or phosphorescence lifetime) actually measured, c represents the speed of light, φ represents the luminescence quantum yield (fluorescence quantum yield when discussing energy transfer from a singlet excited state, and phosphorescence quantum yield when discussing energy transfer from a triplet excited state), 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. In the case of random orientation, K ² = 2/3.

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

In formula (2), h is Planck's constant, K' is a constant having the dimension of energy, v is the vibrational frequency, f' _h (v) is the normalized emission spectrum of the host molecule (fluorescence spectrum when discussing energy transfer from a singlet excited state, and phosphorescence spectrum when discussing energy transfer from a triplet excited state), ε' _g (v) is the normalized absorption spectrum of the guest molecule, L is the effective molecular radius, and R is 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 the mathematical formula (3). _kr represents the rate constant of the light-emitting process of the host molecule (fluorescence when discussing energy transfer from a singlet excited state, and phosphorescence when discussing energy transfer from a triplet excited state), _kn represents the rate constant of the non-light-emitting process of the host molecule (thermal deactivation and intersystem crossing), and τ represents the lifetime of the actually measured excited state of the host molecule.

From formula (3), it can be seen that in order to increase the energy transfer efficiency Φ _ET , the rate constant k _h*→g of energy transfer should be increased and the competing rate constant k _r +k _n (=1/τ) should be relatively small.

(Regarding the energy transfer efficiency of (2-1))
First, let us consider the energy transfer process of (2-1). In this case, since the Förster type (formula (1)) is forbidden, we need to consider only the Dexter type (formula (2)).
According to formula (2), in order to increase the rate constant k _h*→g , it is clear that the overlap between the emission spectrum of the host molecule (phosphorescence spectrum, since energy transfer from the triplet excited state is discussed) and the absorption spectrum of the guest molecule (absorption corresponding to direct transition from the singlet ground state to the triplet excited state) should be large.

In one embodiment of the present invention, a light-emitting substance (including a phosphorescent compound or a thermally activated delayed fluorescence (TADF) material) that converts triplet excitation energy into light emission is used as a guest material. In the absorption spectrum of a phosphorescent compound, absorption corresponding to a direct transition from a singlet ground state to a triplet excited state may be observed, and this is the absorption band that appears on the longest wavelength side. In particular, in a light-emitting iridium complex, the absorption band on the longest wavelength side often appears as a broad absorption band in the vicinity of 500 to 600 nm (of course, depending on the emission wavelength, it may appear on the shorter or longer wavelength side). This absorption band is mainly a triplet MLCT (Metal t
The absorption band is derived from the triplet π-π* transition and singlet MLCT transition. However, the absorption band also includes some absorptions derived from the triplet π-π* transition and the singlet MLCT transition, which are thought to overlap to form a broad absorption band on the longest wavelength side of the absorption spectrum. In other words, the difference between the lowest singlet excited state and the lowest triplet excited state is small, and the absorptions derived from these overlap to form a broad absorption band on the longest wavelength side of the absorption spectrum. Therefore, when an organometallic complex (especially an iridium complex) is used as the guest material, the broad absorption band on the longest wavelength side and the phosphorescence spectrum of the host material largely overlap in this way, so that the rate constant k _h*→g can be increased and the energy transfer efficiency can be improved.

Furthermore, since a fluorescent compound is usually used as the host material, the phosphorescence lifetime (τ) is very long, at least milliseconds ( _kr + _kn is small). This is because the transition from the triplet excited state to the ground state (singlet) is a forbidden transition. From formula (3), this means that the energy transfer efficiency Φ
This works in favor of _ET .

Considering the above, energy transfer from the triplet excited state of a host material to the triplet excited state of a guest material, i.e., the process of formula (2-1), tends to occur easily as long as the phosphorescence spectrum of the host material and the absorption spectrum corresponding to the direct transition from the singlet ground state to the triplet excited state of the guest material are overlapped.

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

When τ is eliminated from formula (1) and formula (3), it can be said that the higher the quantum yield φ (fluorescence quantum yield since energy transfer from a singlet excited state is discussed) is, the better the energy transfer efficiency _Φ ET is. However, in reality, as a more important factor, it is also necessary that the emission spectrum of the host molecule (fluorescence spectrum since energy transfer from a singlet excited state is discussed) and the absorption spectrum of the guest molecule (absorption corresponding to direct transition from a singlet ground state to a triplet excited state) overlap greatly (it is also preferable that the molar extinction coefficient of the guest molecule is high). This means that the fluorescence spectrum of the host material overlaps with the absorption band appearing on the longest wavelength side of the phosphorescent compound, which is the guest material.

However, it has been very difficult to achieve this in the past because:
This is because, in order to efficiently carry out both the above-mentioned steps (2-1) and (2-2), the host material must be designed so that not only its phosphorescent spectrum but also its fluorescent spectrum overlaps with the longest wavelength absorption band of the guest material, as discussed above. In other words, the host material must be designed so that its fluorescent spectrum is located at the same position as its phosphorescent 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 (the emission wavelength of fluorescence is < the emission wavelength of phosphorescence).
For example, in light-emitting devices using phosphorescent compounds, 4,
4'-di(N-carbazolyl)biphenyl (abbreviation: CBP) has a phosphorescence spectrum around 500 nm, but its fluorescence spectrum is around 400 nm, a difference of 100 nm. Considering this example, it is extremely difficult to design a host material such that its fluorescence spectrum is in the same position as its phosphorescence spectrum. Therefore, it is very important to improve the efficiency of energy transfer from the singlet excited state of the host material to the guest material.

Therefore, one aspect of the present invention provides a useful method for overcoming the problem of the efficiency of energy transfer from the singlet excited state of a host material to a guest material. Specific aspects of the method are described below.

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

The second organic compound (assist material) contained in the first light-emitting layer has a lower HOMO level than the third organic compound (assist material) contained in the second light-emitting layer, and therefore the excitation energy (E _A ) of the exciplex formed in the first light-emitting layer can be designed to be greater than the excitation energy (E _B ) of the exciplex formed in the second light-emitting layer.

The first light-emitting substance contained in the first light-emitting layer is a substance that emits light having 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 described with reference to FIG. 1(A).

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

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

The combination of the first organic compound (host material) 110 and the second organic compound (assist material) 111 in the first light-emitting layer 106a is characterized in that it is a combination that forms an exciplex. 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 on the longer wavelength side compared to the emission wavelengths (fluorescence wavelengths) of the first organic compound (host material) 110 and the second organic compound (assist material) 111, so that the fluorescence spectrum of the first organic compound (host material) 110 and the fluorescence spectrum of the second organic compound (assist material) 111 can be converted to an emission spectrum located on the longer wavelength side.

The same applies to the second light-emitting layer 106b.
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. 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 1/10 ...
Since the fluorescence spectrum of the first organic compound (host material) 110 and the fluorescence spectrum of the third organic compound (assist material) 112 are located on the longer wavelength side compared to the emission wavelengths (fluorescence wavelengths) of the first organic compound (host material) 110 and the third organic compound (assist material) 112, the fluorescence spectrum of the first organic compound (host material) 110 and the fluorescence spectrum of the third organic compound (assist material) 112 can be converted into emission spectra located on the longer wavelength side.

In the above structure, the triplet excitation energy level (T1 level) of each of the first organic compound (host material) 110 and the second organic compound (assist material) 111 is preferably higher than the T1 level of the first light-emitting substance (guest material) 109a that converts the triplet excitation energy into light emission. If the T1 level of the first organic compound 110 (or the second organic compound 111) is lower than the T1 level of the first light-emitting substance (guest material) 109a, the triplet excitation energy of the first light-emitting substance (guest material) 109a that contributes to light emission is quenched by the first organic compound 110 (or the second organic compound 111), resulting in a decrease in light-emitting 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 is preferably higher than the T1 level of the second light-emitting substance (guest material) 109b that converts the triplet excitation energy into light emission. When the T1 level of the first organic compound 110 (or the third organic compound 112) is lower than the T1 level of the second light-emitting substance (guest material) 109b, the triplet excitation energy of the second light-emitting substance (guest material) 109b that contributes to light emission is converted into light emission by the first organic compound 110 (
Alternatively, the third organic compound 112) is quenched, resulting in a decrease in luminous efficiency.

In addition, with regard to the ratio of the first organic compound (host material) 110 and the second organic compound (assist material) 111 contained in the first light-emitting layer 106a constituting the light-emitting layer 106, and the ratio of the first organic compound (host material) 110 and the third organic compound (assist material) 112 contained in the second light-emitting layer 106b constituting the light-emitting layer 106, either may be greater, and both cases are included in the present invention.

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

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

In addition, by using the above-mentioned element structure, an exciplex formed in the first light-emitting layer 106a has a higher excitation energy than an exciplex formed in the second light-emitting layer 106b. Therefore, a first exciplex that converts triplet excitation energy contained in the first light-emitting layer 106a into light emission can be obtained.
As the light-emitting substance (guest material) 109a in the first light-emitting layer 106b, a substance that emits light having a shorter wavelength than the second light-emitting substance (guest material) 109b that converts triplet excitation energy contained in the second light-emitting layer 106b into light emission is used.
Furthermore, a part of the excitation energy of the exciplex formed in the first light-emitting layer 106a that does not contribute to light emission can be used as excitation energy for the second light-emitting substance (guest material) 109b that converts the triplet excitation energy in the second light-emitting layer 106b into light emission, so that the light-emitting efficiency of the light-emitting element can be further increased.

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

Furthermore, it is considered that the difference between the singlet excitation energy and the triplet excitation energy of the exciplex is extremely small. In other words, the emission spectrum from the singlet state of the exciplex and the emission spectrum from the triplet state are extremely close to each other. Therefore, as described above, when the emission spectrum of the exciplex (generally, the emission spectrum from the singlet state of the exciplex) is designed to overlap with the absorption band located on the longest wavelength side of the luminescent substance 109 that converts triplet excitation energy into luminescence, 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) also overlaps with the absorption band located on the longest wavelength side of the luminescent substance 109 that converts triplet excitation energy into luminescence. In other words, not only the efficiency of the energy transfer from the singlet excited state ((2-2)) but also the efficiency of the energy transfer from the triplet excited state ((2-1)) is increased, and as a result, the energy from both the singlet and triplet excited states can be efficiently converted into luminescence.

In the following, whether or not an exciplex actually has such characteristics was verified by using molecular orbital calculations. In general, a combination of a heteroaromatic compound and an aromatic amine is a compound that is excited by the lowest unoccupied molecular orbital (LUMO) of the aromatic amine.
The LUMO level (the tendency for electrons to enter) of heteroaromatic compounds is deeper than the HOMO level of heteroaromatic compounds.
In many cases, an exciplex is formed due to the influence of the HOMO level (property that holes can easily enter) of aromatic amines, which is shallower than the LUMO level (most occupied molecular orbital) of the first organic compound 110 according to one embodiment of the present invention. Thus, dibenzo[f,h]quinoxaline (abbreviation: DBq), which has a typical skeleton constituting the LUMO level of a heteroaromatic compound, was used as a model for the first organic compound 110 according to one embodiment of the present invention, and triphenylamine (abbreviation: TPA), which has a typical skeleton constituting the HOMO level of an aromatic amine, was used as a model for the second organic compound 111 (or the third organic compound 112) according to one embodiment of the present invention, and these were combined for calculation.

First, the optimal molecular structures and excitation energies in the lowest excited singlet state (S1) and the lowest excited triplet state (T1) of one molecule of DBq (abbreviation) and one molecule of TPA (abbreviation) were calculated using the time-dependent density functional theory (TD-DFT).
The excitation energies of the dimer of

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 a function) of a one-electron potential expressed by electron density, so the calculation is fast and highly accurate. Here, the weights of each parameter related to the exchange and correlation energy are specified using the mixed functional B3LYP.

In addition, as the basis function, 6-311 (a triple split valence basis set using three contraction functions for each valence orbital) was applied to all atoms.

With the above-mentioned basis functions, for example, the 1s to 3s orbitals are considered for hydrogen atoms, and the 1s to 4s and 2p to 4p orbitals are considered for carbon atoms. Furthermore, to improve the accuracy of the calculation, the p function is used as a polarization basis set for hydrogen atoms, and the d
Added function.

The quantum chemical calculation program used was Gaussian 09. The calculations were performed using a high-performance computer (SGI, Altix 4700).

First, one molecule of DBq (abbreviation), one molecule of TPA (abbreviation), and a mixture of DBq (abbreviation) and TPA (
The HOMO level and LUMO level of the dimer of
The UMO level is shown in FIG. 3, and the distribution of the HOMO level and the LUMO level is shown in FIG.

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

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

Next, the excitation energies obtained from the optimal molecular structure at the S1 level and T1 level of one DBq (abbreviation) molecule are shown. Here, the excitation energies at the S1 level and T1 level correspond to the wavelengths of fluorescence and phosphorescence emitted by one DBq (abbreviation) molecule, respectively. The excitation energy at the S1 level of one DBq (abbreviation) molecule was 3.294 eV, and the fluorescence wavelength was 376.4 nm.
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 TPA (abbreviation) molecule. Here, the excitation energies at the S1 level and T1 level correspond to the wavelengths of fluorescence and phosphorescence emitted by one TPA (abbreviation) molecule, respectively. The excitation energy at the S1 level of one TPA (abbreviation) molecule was 3.508 eV, and the fluorescence wavelength was 353.4 nm.
The excitation energy of the T1 level of one molecule of TPA (abbreviation) was 2.610 eV, and the phosphorescence wavelength was 474.7 nm.

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

From the above, in either one molecule of DBq (abbreviation) or one molecule of TPA (abbreviation),
It can be seen that the phosphorescence wavelength is shifted to a longer wavelength by nearly 100 nm. This is due to the above-mentioned CBP
This shows a similar trend to (abbreviation) (actual measured value), and 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) is on the longer wavelength side compared to the fluorescence wavelength of one DBq (abbreviation) molecule and one TPA (abbreviation) molecule. 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 are almost the same wavelength.

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

In this manner, the light-emitting element according to one embodiment of the present invention can emit light by utilizing the overlap between the emission spectrum of the exciplex formed in the light-emitting layer and the absorption spectrum of a light-emitting substance (the guest material including the first light-emitting substance and the second light-emitting substance described above) that converts triplet excitation energy into light.
Since energy transfer occurs, the efficiency of energy transfer is high, and therefore a light-emitting element with high external quantum efficiency can be realized.

In addition, since exciplexes exist only in an excited state, they do not have a ground state in which they can absorb energy. Therefore, they are used as luminescent materials (guest materials) that convert triplet excitation energy into light emission.
In principle, it is believed that the phenomenon in which a light-emitting substance (guest material) that converts triplet excitation energy into light emission by energy transfer from the singlet excited state and triplet excited state of the above to the exciplex is deactivated before emitting light (i.e., the luminous efficiency is reduced) does not occur. This is also one of the reasons why the external quantum efficiency can be increased.

The above-mentioned exciplex is formed by interaction between different molecules in an excited state. It is generally known that an exciplex is easily formed between a material having a relatively deep LUMO level and a material having a shallow HOMO level.

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

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

In each light-emitting layer, when an exciplex is formed by two organic compounds (the first organic compound 110 and the second organic compound 111 in the first light-emitting layer 106a, and the first organic compound 110 and the third organic compound 112 in the second light-emitting layer 106b), the LUMO level of the exciplex in the first light-emitting layer 106a and the second light-emitting layer 106b is derived from the first organic compound (host material) 110, the HOMO level of the exciplex in the first light-emitting layer 106a is derived from the second organic compound (assist material) 111, and the HOMO level of the exciplex in the second light-emitting layer 106b is derived from the second organic compound (assist material) 112.
The HOMO level of the exciplex in the first light-emitting layer 106a 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 1/2 times the excitation energy (E _B ) of the exciplex in the second light-emitting layer 106b.
That is, by using a substance that emits light with a shorter wavelength than the second light-emitting substance 109b that converts triplet excitation energy contained in the second light-emitting layer into light as the first light-emitting substance 109a that converts triplet excitation energy contained in the first light-emitting layer into light, a light-emitting element with high emission efficiency can be formed. In addition, light-emitting materials with different emission wavelengths can be made to emit light efficiently at the same time.

Note that the exciplex may be formed through the following two processes 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 having carriers (specifically, cations).

In general, when electrons and holes are recombined in a host material, excitation energy is transferred from the excited host material to the guest material, and the guest material is excited and emits light. However, before the excitation energy is transferred from the host material to the guest material, the host material itself emits light, or the excitation energy becomes thermal energy, and a part of the excitation energy is deactivated. In particular, when the host material is in a singlet excited state, energy transfer is unlikely to occur as described in (2-2). Such deactivation of excitation energy is one of the factors that lead to a decrease in the life of a light-emitting element.

However, in one embodiment of the present invention, the first organic compound (host material) and the second organic compound (or the third organic compound) (assist material) form an exciplex from a state having a carrier (cation or anion), so that the formation of a singlet exciton in the first organic compound (host material) can be suppressed. In other words, there may be a process of directly forming an exciplex without forming a singlet exciton. This can also suppress the deactivation of the singlet excitation energy. Therefore, a light-emitting element with a long lifetime can be realized.

For example, when the first organic compound is an electron trapping compound (deep LUMO level) that has a property of easily trapping electrons (carriers) among electron transporting materials, and the second organic compound (or the third organic compound) is a hole trapping compound (shallow HOMO level) that has a property of easily trapping holes (carriers) among hole transporting materials, an exciplex is directly formed from the anion of the first organic compound and 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, the generation of a singlet excited state of the first organic compound (host material) is suppressed, and energy is transferred from the electroplex to a light-emitting substance (guest material) that converts triplet excitation energy into light emission, thereby obtaining a light-emitting element with high light-emitting efficiency. In this case, the first
The occurrence of the triplet excited state of the organic compound (host material) is also suppressed in the same way, and an exciplex is directly formed, and it is thought that energy is transferred from the exciplex to a light-emitting substance (guest material) that converts the triplet excitation energy into light emission.

The second formation process is an elementary process in which one of the first organic compound (host material), the second organic compound (assist material), or the third organic compound (assist material) forms a singlet exciton, and then interacts with the other in the ground state to form an exciplex. Unlike electroplexes, in this case, the singlet excited state of the first organic compound (host material), the second organic compound (assist material), or the third organic compound (assist material) is once generated, but this is quickly converted to an exciplex, so that deactivation of the singlet excitation energy can also be suppressed. Therefore, it is possible to suppress deactivation of the excitation energy of the first organic compound (host material), the second organic compound (assist material), or the third organic compound (assist material). In this case, it is considered that the triplet excited state of the host material is also quickly converted to an exciplex, and energy is transferred from the exciplex to a light-emitting substance (guest material) that converts the triplet excitation energy into light emission.

The first organic compound (host material) is an electron trapping compound, while the second
When the organic compound (or the third organic compound) (assist material) is a hole-trapping compound and there is a large difference between the HOMO levels and the LUMO levels of these compounds (specifically, the difference is 0.3 eV or more), electrons selectively enter the first organic compound (host material) and holes selectively enter the second organic compound (or the third organic compound) (assist material).
In this case, it is believed that the process of forming an electroplex takes precedence over the process of forming an exciplex via a singlet exciton.

In addition, the emission spectrum of the exciplex and the luminescent material 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 is preferably within 0.3 eV, more preferably within 0.2 eV, and most preferably within 0.1 eV.

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

In addition, when a light-emitting substance that converts triplet excitation energy into light emission is used as the first organic compound (host material) in the first light-emitting layer 106 a of the light-emitting element according to one embodiment of the present invention,
The organic compound (host material) itself becomes more likely to emit light, and the energy is less likely to be transferred to a light-emitting substance (guest material) that converts triplet excitation energy into light emission. In this case, it is sufficient for the first organic compound to emit light efficiently, but it is difficult to achieve high light emission efficiency because the host material has a problem of concentration quenching. Therefore, it is effective when at least one of the first organic compound (host material) and the second organic compound (or the third organic compound) (assist material) is a fluorescent compound (i.e., a compound that is likely to emit light or be thermally deactivated from a singlet excited state). Therefore, it is preferable that at least one of the first organic compound (host material) and the second organic compound (or the third organic compound) (assist material) is a fluorescent compound, and an exciplex is used as a medium for energy transfer.

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

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

The light-emitting element shown in this embodiment has a pair of electrodes (first electrode (anode) 2) as shown in FIG.
An EL layer 203 including a light-emitting layer 206 is sandwiched between a first electrode (cathode) 201 and a second electrode (cathode) 202. The EL layer 203 is formed to include a hole injection layer 204, a hole transport layer 205, an electron transport layer 207, an electron injection layer 208, and the like in addition to the light-emitting layer 206 having a laminated structure of a first light-emitting layer 206a and a second light-emitting layer 206b.

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

The second organic compound (assist material) contained in the first light-emitting layer has a lower HOMO level than the third organic compound (assist material) contained in the second light-emitting layer, and therefore the excitation energy (E _A ) of the exciplex formed in the first light-emitting layer can be designed to be greater than the excitation energy (E _B ) of the exciplex formed in the second light-emitting layer.

In the light-emitting layer 206 (the first light-emitting layer 206a and the second light-emitting layer 206b),
In the case of the first light-emitting layer 206a, a first light-emitting substance 209a that converts triplet excitation energy into light emission is dispersed 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 a first organic compound (host material) 210 and a third organic compound (assist material) 212.
In addition, it is possible to suppress concentration quenching caused by a high concentration of the light-emitting substance 209 (209a, 209b), thereby increasing the light-emitting efficiency of the light-emitting element.

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 first organic compound 210, the second organic compound 211, and the third organic compound 212 is preferably higher than the T1 level of the light-emitting material 209 (209a, 209b) that converts the triplet excitation energy into light emission.
The T1 level of 2 converts triplet excitation energy into light emission.
When the T1 level of the first organic compound 21 is lower than the T1 level of the first organic compound 21, the triplet excitation energy of the light-emitting substance 209 (209a, 209b) that converts the triplet excitation energy that contributes to light emission into light is converted into light.
This is because the emission of the compound 210 (or the second organic compound 211 or the third organic compound 212) is quenched, resulting in a decrease in the luminous efficiency.

In this embodiment, in the light-emitting layer 206, the first light-emitting layer 206a is formed by converting the first organic compound 210 into the second organic compound 210 when carriers (electrons and holes) injected from both electrodes are recombined.
An exciplex is formed from the first organic compound 210 and the second organic compound 211 in the first light-emitting layer 206a, and an exciplex is formed from the first organic compound 210 and the third organic compound 212 in the second light-emitting layer 206b. As a result, 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 to an emission spectrum of an exciplex located on the longer wavelength side, and 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 can be converted to an emission spectrum of an exciplex located on the longer wavelength side.
The emission spectrum of the exciplex located at a longer wavelength side can be converted. Therefore, in order to maximize the energy transfer from the singlet excited state, 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 so that the emission spectrum of the exciplex and the absorption spectrum of the light-emitting substance (guest material) 209 that converts triplet excitation energy into light emission are overlapped. That is, here, it is considered that energy transfer occurs from the exciplex, not from the host material, even with respect to the triplet excited state.

The light-emitting material 209 (first light-emitting material 20
The first organic compound (host material) 210 is preferably an electron transporting material. The second organic compound (assist material) 211 and the third organic compound (assist material) 212 are preferably a hole transporting material.

Examples of the organometallic complex include bis[2-(4',6'-difluorophenyl)pyridinato-N,C ^2' ]iridium(III) tetrakis(1-pyrazolyl)borate (abbreviation: FIr6), bis[2-(4',6'-difluorophenyl)pyridinato-N,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
iridium(III) acetylacetonate (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 3′ ]
C ^2' ) Iridium(III) acetylacetonate (abbreviation: Ir(piq) ₂ (aca
c)), (acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III) (abbreviation: Ir(Fdpq) ₂ (acac)), (acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III) (abbreviation: Ir(tppr) ₂ (acac)), 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II) (abbreviation: PtOEP), tris(
Acetylacetonato)(monophenanthroline)terbium(III) (abbreviation: Tb(a
cac) ₃ (Phen)), tris(1,3-diphenyl-1,3-propanedionato)
(Monophenanthroline)europium(III) (abbreviation: Eu(DBM) ₃ (Phen
)), tris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III) (abbreviation: Eu(TTA) ₃ (Phen)), and the like.

As the electron transporting material, a π-deficient heteroaromatic compound such as a nitrogen-containing heteroaromatic compound is preferable. For example, 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), 2-[3′-
(Dibenzothiophene-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
quinoxaline or dibenzoquinoxaline derivatives such as quinoxaline derivatives (TPDBq-II) and the like.

As the hole transport material, π-excess type heteroaromatic compounds (for example, carbazole derivatives and indole derivatives) and aromatic amine compounds are preferable. For example, 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
) are mentioned.

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

In addition, 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 mixture ratio.
The ratio is preferably in the range of up to 9:1.

The following describes a specific example of how to fabricate the light-emitting element shown in this embodiment.

The first electrode (anode) 201 and the second electrode (cathode) 202 can be made of a metal, an alloy, an electrically conductive compound, or a mixture thereof. Specifically, indium oxide-tin oxide (ITO), indium oxide-tin oxide containing silicon or silicon oxide, indium oxide-zinc oxide (ITO), and the like can be used.
nc Oxide), indium oxide containing tungsten oxide and zinc oxide, gold (A
In addition to platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), and titanium (Ti), elements belonging to the first or second group of the periodic table, namely lithium (Li),
i) and cesium (Cs), as well as magnesium (Mg), calcium (
Alkaline earth metals such as strontium (Sr) and alloys containing these metals (Mg
Examples of the usable materials include rare earth metals such as Ag, AlLi, europium (Eu), and ytterbium (Yb), alloys containing these metals, and graphene. The first electrode (anode) 201 and the second electrode (cathode) 202 can be formed by, for example, a sputtering method or a deposition method (including a vacuum deposition method).

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

Further, 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 other polymer compounds can also be used.

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

The light-emitting layers 206 (206a, 206b) are as described above. The first light-emitting layer 206a
The first light-emitting layer 206a has at least a first light-emitting substance 209a, a first organic compound (host material) 210, and a second organic compound (assist material) 211, and the second light-emitting layer 206b has at least a second light-emitting 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 a high electron transporting property.
_Alq3 , tris(4-methyl-8-quinolinolato)aluminum (abbreviation: _Almq3 )
, bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq ₂ ),
Metal complexes such as BAlq, Zn(BOX) ₂ , and bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation: Zn(BTZ) ₂ ) can be used.
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-tetramethylphenyl)
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 poly(2,5-pyridinediyl) (abbreviation: PPy) and poly[(9,9-dihexylfluorene-2,7-diyl)
Alternatively, a polymer compound such as poly[(9,9-dioctylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)] (abbreviation: PF-Py) or poly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2'-bipyridine-6,6'-diyl)] (abbreviation: PF-BPy) can be used. The substances described here are mainly substances having an electron mobility of 10 ^-6 cm ² /Vs or more. Note that substances other than those described above may be used as the electron transport layer 207 as long as they have a higher electron transporting property than holes.

The electron transport layer 207 may be a single layer or 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.
Lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride ( _CaF2 )
For the electron transport layer 207, an alkali metal, an alkaline earth metal, or a compound thereof, such as lithium oxide (LiOx), or a rare earth metal compound, such as erbium fluoride (ErF ₃ ), may be used. Alternatively, the above-mentioned material constituting the electron transport layer 207 may be used.

Alternatively, a composite material obtained by mixing an organic compound and an electron donor (donor) may be used for the electron injection layer 208. Such a composite material has excellent electron 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, the above-mentioned substances constituting the electron transport layer 207 (metal complexes, heteroaromatic compounds, etc.) can be used. The electron donor may be any substance that exhibits electron donating properties to the organic compound. Specifically, alkali metals, alkaline earth metals, and rare earth metals are preferred, and examples of such substances include lithium, cesium, magnesium, calcium, erbium, and ytterbium. Furthermore, alkali metal oxides and alkaline earth metal oxides are preferred, and examples of such substances include lithium oxide, calcium oxide, and barium oxide. Furthermore, a Lewis base such as magnesium oxide can also be used. Furthermore, an organic compound such as tetrathiafulvalene (abbreviation: TTF) can also be used.

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

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

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

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

In the case of an active matrix type light emitting device, the structure of the TFT is not particularly limited. For example, a staggered type or an inverted staggered type TFT may be used as appropriate.
The driving circuit formed on the FT substrate may be composed of N-type and P-type TFTs, or may be composed of only either N-type or P-type TFTs. Furthermore, the crystallinity of the semiconductor film used in the TFT is not particularly limited. For example, an amorphous semiconductor film, a crystalline semiconductor film, or an oxide semiconductor film may be used.

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

(Embodiment 3)
In this embodiment, a light-emitting element having a structure in which a charge generation layer is sandwiched between a plurality of EL layers (hereinafter referred to as a tandem-type 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 (first electrode 30) as shown in FIG.
A plurality of EL layers (first EL layer 302(1), second EL layer 302(2), and second EL layer 304) are disposed between the first EL layer 302(3), the second EL layer 302(4), and the second EL layer 304.
It is a tandem type light emitting device having an L layer 302(2).

In this embodiment, the first electrode 301 functions as an anode, and the second electrode 304 functions as a cathode. Note that the first electrode 301 and the second electrode 304 may have the same structure as in Embodiment 1.
The first 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, or either one may have the same structure. That is, the first EL layer 302(1) and the second EL layer 302(2) may have the same structure or different structures, and the same structure as that described in Embodiment 1 or 2 can be applied.

In addition, a charge generation layer (I) 305 is provided between the plurality of EL layers (the first EL layer 302(1) and the second EL layer 302(2)). The charge generation layer (I) 305 has a function of injecting electrons into one EL layer and injecting holes into the other EL layer when a voltage is applied between the first electrode 301 and the second electrode 304. In this embodiment, when a voltage is applied to the first electrode 301 so that the potential of the first electrode 301 is higher than that of the second electrode 304, the charge generation layer (I) 305 is injecting electrons into one EL layer and holes into the other EL layer.
Electrons are injected from the first EL layer 302(1) to the second EL layer 302(2) and holes are injected from the second EL layer 302(3) to the first EL layer 302(4).

From the viewpoint of light extraction efficiency, the charge generation layer (I) 305 is preferably transparent to visible light (specifically, the visible light transmittance of the charge generation layer (I) 305 is 40% or more).
It will function even with a conductivity lower than 0.4.

The charge generation layer (I) 305 may be a structure in which an electron acceptor is added to an organic compound having a high hole transporting property, or a structure in which an electron donor is added to an organic compound having a high electron transporting property, or a structure in which both of these structures are laminated.

In the case where an electron acceptor is added to an organic compound having a high hole transporting property, examples of the organic compound having a high hole transporting property include NPB, TPD, TDATA, and MTDATA.
and aromatic amine compounds such as 4,4'-bis[N-(spiro-9,9'-bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB) can be used. The substances described here are mainly substances having a hole mobility of 10 ^-6 cm ² /Vs or more. However, substances other than those mentioned above may be used as long as they are organic compounds that have a higher hole transporting property than electron transporting properties.

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

On the other hand, in the case where an electron donor is added to an organic compound having a high electron transporting property, examples of the organic compound having a high electron transporting property include Alq, Almq ₃ , BeBq ₂ , and B
Metal complexes having a quinoline skeleton or a 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. In addition to metal complexes, PBD, OXD-7, TAZ, BPhen, BCP, and the like can also be used. The substances described here are mainly substances having 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 having a higher electron transporting property than holes.

As the electron donor, an alkali metal, an alkaline earth metal, a rare earth metal, or a metal belonging to Group 13 of the periodic table, or an oxide or carbonate thereof can be used. Specifically, it is preferable to use lithium (Li), cesium (Cs), magnesium (Mg), calcium (Ca), ytterbium (Yb), indium (In), lithium oxide, cesium carbonate, etc. Also, an organic compound such as tetrathianaphthacene may be used as the electron donor.

By forming the charge generation layer (I) 305 using the above-mentioned material, an increase in driving voltage when an EL layer is laminated can be suppressed.

In this embodiment, a light-emitting element having two EL layers has been described, but the present invention can also be applied to a light-emitting element having n EL layers (n is 3 or more) stacked as shown in Fig. 6B. When a plurality of EL layers are provided between a pair of electrodes as in the light-emitting element according to this embodiment, a charge generation layer (I) is provided between the EL layers,
It is possible to emit light in a high brightness range while keeping the current density low. Since the current density can be kept low, it is possible to realize a long-life element. In addition, when applied to lighting, it is possible to reduce the voltage drop due to the resistance of the electrode material, making it possible to emit light uniformly over a large area. It is also possible to realize a light-emitting device that can be driven at a low voltage and consumes little power.

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

The same is true for a light-emitting element having three EL layers. For example, when the emission color of the first EL layer is red, the emission color of the second EL layer is green, and the emission color of the third EL layer is blue, the light-emitting element as a whole can emit white light.

Note that the structure described in this embodiment mode can be used in appropriate combination with structures described in other embodiment modes.

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

The light emitting device shown in this embodiment has a micro-optical resonator (microcavity) structure utilizing the optical resonance effect between a pair of electrodes.
The light-emitting element has a structure in which at least an EL layer 405 is provided between the electrode 401 and the semi-transmissive/semi-reflective electrode 402. The EL layer 405 is at least a light-emitting layer 405 which is a light-emitting region.
04 (404R, 404G, 404B), and may further include a hole injection layer, a hole transport layer, an electron transport layer, an electron injection layer, a charge generation layer (E), etc.
Each of (404R, 404G, and 404B) can include the structure of a light-emitting layer which is one embodiment of the present invention as described in Embodiments 1 and 2.

In this embodiment, a light emitting element having a different structure (first light emitting element (R) 4) is used as shown in FIG.
A light emitting device including a first light emitting element (10R), a second light emitting element (G) 410G, and a third light emitting element (B) 410B will be described.

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

In addition, the light emitting elements (first light emitting element (R) 410R, second light emitting element (G) 410G
In the third light-emitting element (B) 410B), a reflective electrode 401, an EL layer 405, a semi-transmissive
The semi-reflective electrode 402 is shared by both layers. The first light-emitting layer (B) 404B emits light (λ _B ) having a peak in the wavelength region of 420 nm or more and 480 nm or less. The second light-emitting layer (G)
The third light emitting layer (R) 404R emits light (λ _{R )} having a peak in the wavelength region of 500 nm or more and 550 nm or less. As a result, the first light emitting layer (B) 404B, the second light emitting layer (G) 404G, and the third light emitting layer (R) 404R emit light (λ R ) having a peak in the wavelength region of 600 nm or more and 760 nm or less.
) 404R are superimposed, that is, it is possible to emit broad light over the visible light region. From the above, it is assumed that the wavelengths have the relationship λ _B <λ _G <λ _R.

Each of the light-emitting elements shown in this embodiment has a reflective electrode 401 and a semi-transmissive/semi-reflective electrode 40
2, and the light emitted in all directions from each light-emitting layer contained in the EL layer 405 is resonated by the reflective electrode 401, which functions as a micro-optical resonator (microcavity), and the semi-transmissive and semi-reflective electrode 402. The reflective electrode 401 is formed of a conductive material having reflectivity, and the reflectivity of the film for visible light is 40% to 100%, preferably 70% to 100%, and the resistivity is 1×10
The ^semi -transmitting and semi-reflective electrode 402 is formed of a conductive material having reflectivity and a conductive material having optical transparency, and the reflectivity of the film to visible light is 20% to 80%, preferably 40% to 70%, and the resistivity is 1×10 ⁻
It is assumed that the film has a resistivity of ² Ωcm or less.

In the present embodiment, the transparent conductive layers (the first transparent conductive layer 403a, the second transparent conductive layer 403b) provided in the first light emitting element (R) 410R and the second light emitting element (G) 410G are
By changing the thickness of the transparent conductive layer 403b), the optical distance between the reflective electrode 401 and the semi-transmissive/semi-reflective electrode 402 is changed for each light-emitting element. In other words, the broad light emitted from each light-emitting layer of each light-emitting element is reflected by the reflective electrode 401 and the semi-transmissive/semi-reflective electrode 402.
Since it is possible to intensify light of a resonating wavelength and attenuate light of a non-resonating wavelength, it is possible to extract light of different wavelengths by changing the optical distance between the reflective electrode 401 and the semi-transparent/semi-reflective electrode 402 for each element.

The optical distance (also called the optical path length) is the actual distance multiplied by the refractive index, and in this embodiment, it is expressed by multiplying the actual film thickness by n (refractive index).
Optical distance=actual film thickness×n.

In the first light-emitting element (R) 410R, the reflective electrode 401 is connected to the semi-transmissive and semi-reflective electrode 404.
In the second light emitting element (G) 410G, the total thickness from the reflective electrode 401 to the semi-transmissive and semi-reflective electrode 402 is mλ _R /2 (where m is a natural number), and in the second light emitting element (G) 410G, the total thickness from the reflective electrode 401 to the semi-transmissive and semi-reflective electrode 402 is mλ _G /2 (where m is a natural number).
In the third light emitting element (B) 410B, the total thickness from the reflective electrode 401 to the semi-transmissive and semi-reflective electrode 402 is mλ _B /2 (where m is a natural number).

As a result, light (λ R ) emitted from the third light-emitting layer (R) 404R included in the EL layer 405 is extracted from the first light-emitting element (R) 410R, and the light (λ _R ) emitted from the second light-emitting element (G) 404R is extracted from the third light-emitting layer (R) 404R included in the EL layer 405.
From the third light-emitting element (B) 410B, light (λ _G ) emitted from the second light-emitting layer (G) 404G included in the EL layer 405 is mainly extracted.
The light (λ _B ) emitted from the first light emitting layer (B) 404B included in the first light emitting layer (B) 404B is extracted. The light extracted from each light emitting element is emitted from the semi-transmissive and semi-reflective electrode 402 side.

In the above configuration, the total thickness from the reflective electrode 401 to the semi-transmissive and semi-reflective electrode 402 can be said to be the total thickness from the reflective region of the reflective electrode 401 to the reflective region of the semi-transmissive and semi-reflective electrode 402.
Since it is difficult to precisely determine the position of the reflective region in 2, it is assumed that the above-mentioned effect can be sufficiently obtained by assuming any position of the reflective electrode 401 and the semi-transmissive and semi-reflective electrode 402 as the reflective region.

Next, in the first light-emitting element (R) 410R, the reflective electrode 401 is connected to the third light-emitting layer (R
The light emitted from the third light-emitting layer (R) 404R can be amplified by adjusting the optical distance from the reflective electrode 401 to a desired film thickness ((2m'+1)λ _R /4 (where m' is a natural number)). Of the light emitted from the third light-emitting layer (R) 404R, light reflected by the reflective electrode 401 and returned (first reflected light) interferes with light directly incident from the third light-emitting layer (R) 404R to the semi-transmissive and semi-reflective electrode 402 (first incident light). Therefore, by adjusting the optical distance from the reflective electrode 401 to the third light-emitting layer (R) 404R to a desired value ((2m'+1)λ _R /4 (where m' is a natural number)), the phases of the first reflected light and the first incident light can be matched, and the light emitted from the third light-emitting layer (R) 404R can be amplified.

In addition, the optical distance between the reflective electrode 401 and the third light-emitting layer (R) 404R can be strictly defined as the optical distance between the reflective region of the reflective electrode 401 and the light-emitting region of the third light-emitting layer (R) 404R.
Since it is difficult to precisely determine the position of the light-emitting region in the reflective electrode 40
It is assumed that the above-mentioned 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, the reflective electrode 401 is connected to the second light emitting layer (G
The light emitted from the second light-emitting layer (G) 404G can be amplified by adjusting the optical distance from the second light-emitting layer (G) 404G to a desired film thickness ((2m''+1)λ _G /4 (where m'' is a natural number). Of the light emitted from the second light-emitting layer (G) 404G, the light reflected back by the reflective electrode 401 (second reflected light) interferes with the light directly incident from the second light-emitting layer (G) 404G to the semi-transmissive and semi-reflective electrode 402 (second incident light).
to the second light emitting layer (G) 404G is set to a desired value ((2m''+1)λ _G /4(
However, by adjusting m″ to a natural number, the phases of the second reflected light and the second incident light can be matched, and the light emitted from the second light-emitting layer (G) 404G can be amplified.

In addition, the optical distance between the reflective electrode 401 and the second light-emitting layer (G) 404G can be strictly defined as the optical distance between the reflective region of the reflective electrode 401 and the light-emitting region of the second light-emitting layer (G) 404G.
Since it is difficult to precisely determine the position of the light emitting region in the reflective electrode 40
It is assumed that the above-mentioned effect can be sufficiently obtained by assuming that an arbitrary position of the first 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, the first light-emitting layer (B
) 404B is set to the desired film thickness ((2m'''+1)λ _B /4 (where m'''
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) interferes with the light directly incident from the first light-emitting layer (B) 404B to the semi-transmissive and semi-reflective electrode 402 (third incident light).
The optical distance from the first light emitting layer (B) 404B to the desired value ((2m'''+1)λ _B
/4 (where m''' is a natural number), the third reflected light and the third
By adjusting the phase of the incident light, the light emitted from the first light-emitting layer (B) 404B can be amplified.

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

In the above configurations, each of the light-emitting elements has a structure in which the EL layer has a plurality of light-emitting layers. However, the present invention is not limited to this. For example, a light-emitting element may be combined with the configuration of a tandem-type light-emitting element described in the third embodiment to sandwich a charge generating layer in one light-emitting element.
A single or multiple light-emitting layers may be formed in each EL layer.

The light-emitting device shown in this embodiment has a microcavity structure.
Even if the device has a layer, light of different wavelengths can be extracted for each light-emitting element, so there is no need to paint RGB separately. Therefore, it is advantageous in realizing full color because it is easy to achieve high definition. It can also be combined with a colored layer (color filter). In addition, it is possible to increase the emission intensity of a specific wavelength in the front direction, so that power consumption can be reduced. This configuration is particularly useful when applied to a color display (image display device) using pixels of three or more colors, but it may also be used for lighting and other purposes.

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

The light-emitting device may be a passive matrix light-emitting device or an active matrix light-emitting device. Note that the light-emitting element described in any of the other embodiment modes can be applied to the light-emitting device shown in this embodiment mode.

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

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

Further, on the element substrate 501, there are provided wirings 507 for connecting an external input terminal for transmitting signals (e.g., a video signal, a clock signal, a start signal, a reset signal, or the like) and potentials from the outside to the driver circuit portion 503 and the driver circuit portion 504.
An example is shown in which an FPC (flexible printed circuit) 508 is provided as an external input terminal. Although only an FPC is shown here, a printed wiring board (PWB) may be attached to this FPC. In this specification, the light emitting device includes not only the light emitting device itself, but also a state in which an FPC or PWB is attached to the light emitting device.

Next, the cross-sectional structure will be described with reference to FIG. 8B. A driver circuit portion and a pixel portion are formed on an element substrate 501. In this example, the driver circuit portion 503, which is a source line driver circuit,
5, a pixel portion 502 is shown.

The driver circuit section 503 is an example in which a CMOS circuit is formed by combining an n-channel TFT 509 and a p-channel TFT 510. The driver circuit section is formed by the following circuits:
It may be formed of various CMOS circuits, PMOS circuits, or NMOS circuits. In addition, in this embodiment, a driver integrated type in which a driving circuit is formed on a substrate is shown, but this is not necessarily required, and a driving circuit can be formed externally instead of on the substrate.

The pixel section 502 is formed of a plurality of pixels each 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.
An insulator 514 is formed to cover the end of the insulating film 13. Here, the insulating film 514 is formed by using a positive type photosensitive acrylic resin.

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

An EL layer 515 and a second electrode (cathode) 516 are stacked over a first electrode (anode) 513. The EL layer 515 includes at least a light-emitting layer, and the light-emitting layer has a stacked structure as described in Embodiment Mode 1. The EL layer 515 can include 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, in addition to the light-emitting layer.

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

Although only one light-emitting element 517 is shown in the cross-sectional view of FIG. 8B, a plurality of light-emitting elements are arranged in a matrix in the pixel portion 502.
02, a light-emitting element capable of obtaining three types of light emission (R, G, B) is selectively formed,
It is possible to form a light emitting device capable of full color display. In addition, a light emitting device capable of full color display may be formed by combining with a colored layer (color filter).

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

It is preferable to use epoxy resin, low melting point glass, or the like for the sealing material 505. It is also preferable that these materials are as impermeable to moisture and oxygen as possible. In addition, the sealing substrate 506 may be made of a glass substrate, a quartz substrate, or an FRP (Fiberglass).
For example, a plastic substrate made of, for example, Lass-Reinforced Plastics, PVF (polyvinyl fluoride), polyester, or acrylic can be used.

In this way, an active matrix type light emitting device can be obtained.

Note that the structure described in this embodiment mode can be used in appropriate combination with structures described in other embodiment modes.

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

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

FIG. 9A shows an example of a television device. The television device 7100 includes:
A display portion 7103 is incorporated in a housing 7101. The display portion 7103 can display an image, and a light-emitting device can be used for the display portion 7103. Here, the housing 7101 is supported by a stand 7105.

The television set 7100 can be operated using an operation switch provided on the housing 7101 or a separate remote control 7110. The channel and volume can be operated using operation keys 7109 provided on the remote control 7110, and an image displayed on the display portion 7103 can be operated. The remote control 7110 may be provided with a display portion 7107 that displays information output from the remote control 7110.

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

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 by using a light-emitting device for the display portion 7203.

9C shows a portable game machine, which is composed of two housings, a housing 7301 and a housing 7302, which are connected to each other by a connecting portion 7303 so as to be openable and closable. A display portion 7304 is incorporated in the housing 7301, and a display portion 7305 is incorporated in the housing 7302. The portable game machine shown in FIG. 9C also includes a speaker portion 7306, a recording medium insertion portion 7307, and a touch panel 7309.
, LED lamp 7308, input means (operation keys 7309, connection terminal 7310, sensor 73
11 (including a function for measuring force, displacement, position, speed, acceleration, angular velocity, rotation speed, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared), microphone 7312), etc. Of course, the configuration of the portable gaming machine is not limited to the above, and at least a display unit 73
A light-emitting device may be used for both or either of the display portion 7304 and the display portion 7305, and other auxiliary equipment may be appropriately provided. The portable gaming machine shown in Fig. 9C has a function of reading out a program or data recorded in a recording medium and displaying it on the display portion, and a function of sharing information with other portable gaming machines by wireless communication. Note that the functions of the portable gaming machine shown in Fig. 9C are not limited to these, and it may have various functions.

FIG. 9D shows an example of a mobile phone. The mobile phone 7400 has a housing 7401.
In addition to a display portion 7402 incorporated in the mobile phone 7400, the mobile phone 7400 includes operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like.

9D, information can be input by touching the display portion 7402 with a finger or the like. In addition, operations such as making a call or composing an e-mail can be performed by touching the display portion 7402 with a finger or the like.

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

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

In addition, by providing a detection device having a sensor for detecting the 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 of the display portion 7402 can be automatically switched.

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

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

The display unit 7402 can also function as an image sensor.
By touching the palm or fingers on 402 and capturing an image of a palm print, fingerprint, or the like, personal authentication can be performed.
Furthermore, if a backlight that emits near-infrared light or a sensing light source that emits near-infrared light is used for the display unit, finger veins, palm veins, etc. can also be captured.

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

A part of the display unit 9631a can be a touch panel area 9632a, and data can be input by touching the displayed operation keys 9637.
In the example of the display unit 96, half of the display area has a display function and the other half has a touch panel function, but the display unit 96 is not limited to this configuration.
The entire area of the display unit 931a may have a touch panel function.
The entire surface of the display portion 9631a can be used as a touch panel by displaying keyboard buttons, and the display portion 9631b can be used as a display screen.

Similarly to the display portion 9631a, part of the display portion 9631b can be used as a touch panel area 9632b. When a position on the touch panel where a keyboard display switch button 9639 is displayed is touched with a finger, a stylus, or the like, keyboard buttons can be displayed on the display portion 9631b.

In addition, touch input can be made simultaneously to touch panel area 9632a and touch panel area 9632b.

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

10A shows an example in which the display areas of the display portions 9631b and 9631a are the same, but this is not particularly limited, and the sizes of the display portions may be different from each other, and the display qualities may also be different. For example, one display panel may be capable of displaying images with higher resolution than the other.

FIG. 10B shows the tablet terminal in a closed state. The tablet terminal includes a housing 9630 and a solar cell 9
10B shows a battery 963 as an example of the charge/discharge control circuit 9634.
5. A configuration having a DC-DC converter 9636 is shown.

Note that the tablet terminal can be folded in half, and therefore the housing 9630 can be kept closed when not in use.
This makes it possible to provide a tablet device that is highly durable and reliable even when used for a long period of time.

In addition, the tablet terminals shown in Figures 10 (A) and 10 (B) can have a function to display various information (still images, videos, text images, etc.), a function to display a calendar, date or time on the display unit, a touch input function to perform touch input operations or edit the information displayed on the display unit, and a function to control processing using various software (programs), etc.

A solar cell 9633 attached to the surface of the tablet terminal can supply power to a touch panel, a display unit, a video signal processor, or the like. The solar cell 9633 can be provided on one side or both sides of the housing 9630, and can be configured to efficiently charge the battery 9635. The use of a lithium ion battery as the battery 9635 has the advantage of enabling miniaturization.

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

First, an example of operation in the case where power is generated by the solar cell 9633 using external light will be described. The power generated by the solar cell 9633 is stepped up or stepped down by a DC-DC converter 9636 so as to have a voltage for charging a battery 9635.
When power from the solar cell 9633 is used for the operation of the display unit 9631, the switch SW1 is turned on, and the converter 9638 increases or decreases the voltage to a voltage required for the display unit 9631. When no display is to be performed on the display unit 9631, the switch SW1 is turned off, and the switch SW
The configuration may be such that W2 is turned on to charge the battery 9635.

The solar cell 9633 is shown as an example of a power generating means, but is not limited thereto.
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, the battery 9635 may be charged by a non-contact power transmission module that transmits and receives power wirelessly (non-contact), or by combining with other charging means.

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

In the above manner, an electronic device can be obtained by using the light-emitting device which is one embodiment of the present invention. The light-emitting device has an extremely wide range of application and can be used in electronic devices in a variety of fields.

Note that the structure described in this embodiment mode can be used in appropriate combination with structures described in other embodiment modes.

(Seventh embodiment)
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 FIGS.

FIG. 11 shows an example in which the light-emitting device is used as an indoor lighting device 8001. Since the light-emitting device can be enlarged, a large-area lighting device can also be formed. In addition, by using a housing having a curved surface, a lighting device 8002 in which the light-emitting region has a curved surface can also be formed. The light-emitting element included in the light-emitting device shown in this embodiment mode is a thin film, and the housing has a high degree of freedom in design. Therefore, lighting devices with various elaborate designs can be formed. Furthermore, a large lighting device 8003 may be provided on the wall surface of the room.

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

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

The structure described in this embodiment mode can be used in appropriate combination with structures described in other embodiment modes.

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

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

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

Thereafter, the substrate was introduced into a vacuum deposition apparatus whose inside had been reduced in pressure to about 10 ⁻⁴ Pa, and vacuum baking was carried out at 170° C. for 30 minutes in a heating chamber in the vacuum deposition apparatus, and then the substrate 1100 was allowed to cool for about 30 minutes.

Next, the substrate 1100 was fixed to a holder provided in a vacuum deposition apparatus so that the surface on which the first electrode 1101 was formed was facing downward. In this example, the EL layer 1 was formed by vacuum deposition.
A case where 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 the element 102 are formed in this order will be described.

After reducing the pressure in the vacuum chamber to 10 ⁻⁴ Pa, 1,3,5-tri(dibenzothiophene-4
-yl)benzene (abbreviation: DBT3P-II) and molybdenum(VI) oxide were reacted with DBT3
A hole injection layer 1111 was formed on the first electrode 1101 by co-evaporation so that P-II (abbreviation):molybdenum oxide=4:2 (mass ratio). The film thickness was 20 nm. Note that co-evaporation is an evaporation method in which different substances are evaporated simultaneously from different evaporation sources.

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

Next, a light-emitting layer 1113 was formed on the hole-transporting layer 1112.
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)]) to 2mDBTBPDBq-II (abbreviation): PCBB
iF (abbreviation): [Ir(tBuppm) ₂ (acac)] (abbreviation) = 0.7:0.3:0
After forming the first light-emitting layer 1113a with a thickness of 20 nm by co-evaporation so that the ratio of the components was 0.05 (mass ratio), 2mDBTBPDBq-II (abbreviation), N,N'-bis(9,9-dimethylfluoren-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)])
-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 was formed to a thickness of 20 nm, thereby forming a light-emitting layer 1113 having a stacked structure.

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

Finally, aluminum was evaporated onto the electron injection layer 1115 to a thickness of 200 nm to form a second electrode 1103 serving as a cathode, thereby obtaining the light-emitting element 1. In the above-mentioned evaporation process, the evaporation was all performed using a resistance heating method.

The element structure of the light-emitting element 1 obtained as described above is shown in Table 1.

The fabricated light-emitting element 1 was sealed in a glove box with a nitrogen atmosphere so as not to be exposed to the air (a sealant was applied around the element, and the element was heat-treated at 80° C. for 1 hour during sealing).

<Operation characteristics of light-emitting element 1>
The operating characteristics of the fabricated light-emitting element 1 were measured. The measurements were carried out at room temperature (an atmosphere maintained at 25° C.).

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

15, it was found that the light-emitting element 1 of one embodiment of the present invention was a highly efficient element. Table 2 below shows main initial characteristic values of the light-emitting element 1 at around 1000 cd/ ^m2 .

From the above results, it is found that the light-emitting element 1 fabricated in this example exhibits high external quantum efficiency and therefore high luminous efficiency.

17 shows an emission spectrum when a current of 25 mA/cm ² is applied to the light-emitting element 1. As shown in FIG. 17, the emission spectrum of the light-emitting element 1 is 546 nm and 615 nm.
There are two peaks at around nm, which are phosphorescent organometallic iridium complexes [Ir(
It is suggested that this is due to the emission of [Ir(dmdppr-dmp) ₂ (divm)] and [Ir(tBuppm) ₂ (acac)].

In addition, from cyclic voltammetry measurement, the HOMO level of PCBBiF, which is the second organic compound having hole transport properties, was estimated to be −5.36 eV, and the HOMO level of FBi2P, which is the third organic compound having hole transport properties, was estimated to be −5.13 eV. Therefore, the HOMO level of the second organic compound is lower than that of the third organic compound.

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

18 and 19, since the emission wavelength of the mixed film is longer than the emission wavelength of the single film of each material, it can be seen that the first organic compound (2mDBTBPDBq-II) and the second organic compound (PCBBiF), and the first organic compound (2mDBTBPDBq-II) and the third organic compound (FBi2P) form exciplexes, respectively. In addition, the emission wavelength of the exciplex formed by the first organic compound (2mDBTBPDBq-II) and the second organic compound (PCBBiF) is 511 nm, while the emission wavelength of the exciplex formed by the first organic compound (2mDBTBPDBq-II) and the second organic compound (PCBBiF) is 521 nm.
Since the emission wavelength of the exciplex formed by BTBPDBq-II) and the third organic compound (FBi2P) is 553 nm, it is clear that the former has a higher energy.

101 First electrode 102 Second electrode 103 EL layer 104 Hole injection layer 105 Hole transport layer 106 Light-emitting layer 106a First light-emitting layer 106b Second light-emitting layer 107 Electron transport layer 108 Electron injection layer 109 Light-emitting substance 109a First light-emitting substance 109b that converts triplet excitation energy into light emission Second light-emitting substance 110 First organic compound 111 Second organic compound 112 Third organic compound 201 First electrode (anode)
202 Second electrode (cathode)
203 EL layer 204 Hole injection layer 205 Hole transport layer 206 Light-emitting layer 206a First light-emitting layer 206b Second light-emitting layer 207 Electron transport layer 208 Electron injection layer 209 Light-emitting substance 209a First light-emitting substance 209b that converts triplet excitation energy into light emission Second light-emitting substance 210 that converts triplet excitation energy into light emission First organic compound 211 Second organic compound 212 Third organic compound 301 First electrode 302(1) First EL layer 302(2) Second EL layer 302(n-1) (n-1)th EL layer 302(n) (n)th EL layer 304 Second electrode 305 Charge generation layer (I)
305(1) First charge generating layer (I)
305(2) Second charge generating layer (I)
305(n-2) (n-2)th charge generating layer (I)
305(n-1) (n-1)th charge generating layer (I)
401: Reflective electrode 402: Semi-transmissive/semi-reflective electrode 403a: First transparent conductive layer 403b: Second transparent conductive layer 404B: First light-emitting layer (B)
404G Second light-emitting layer (G)
404R Third light-emitting layer (R)
405 EL layer 410R First light-emitting element (R)
410G Second light-emitting element (G)
410B Third light-emitting element (B)
501: Element substrate 502: Pixel portion 503: Driver circuit portion (source line driver circuit)
504a, 504b Drive circuit section (gate line drive circuit)
505 Sealing material 506 Sealing substrate 507 Leading wiring 508 FPC (flexible printed circuit)
509 n-channel TFT
510 p-channel TFT
511 Switching TFT
512 Current control TFT
513 First electrode (anode)
514 Insulator 515 EL layer 516 Second electrode (cathode)
517 Light emitting element 518 Space 7100 Television device 7101 Housing 7103 Display section 7105 Stand 7107 Display section 7109 Operation key 7110 Remote control device 7201 Main body 7202 Housing 7203 Display section 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 7406 Microphone 8001 Illumination device 8002 Illumination device 8003 Illumination device 8004 Illumination device 9033 Fastener 9034 Display mode changeover switch 9035 Power switch 9036 Power saving mode changeover switch 9038 Operation switch 9630 Housing 9631 Display section 9631a Display section 9631b Display section 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 (6)

a first light-emitting layer and a second light-emitting layer in contact with the first light-emitting layer between a pair of electrodes;
the first light-emitting layer includes a first light-emitting substance and two kinds of organic compounds that form a first exciplex;
the second light-emitting layer includes a second light-emitting substance and two kinds of organic compounds that form a second exciplex;
a difference between an energy value of a peak in an emission spectrum of the first exciplex and an energy value of a peak in an absorption band on the lowest energy side in an absorption spectrum of the first luminescent material is within 0.2 eV;
the excitation energy of the first exciplex is greater than the excitation energy of the second exciplex;
The first light-emitting substance emits light having a shorter wavelength than the second light-emitting substance. a first light-emitting layer and a second light-emitting layer in contact with the first light-emitting layer between a pair of electrodes;
the first light-emitting layer includes a first light-emitting substance and two kinds of organic compounds that form a first exciplex;
the second light-emitting layer includes a second light-emitting substance and two kinds of organic compounds that form a second exciplex;
a difference between an energy value of a peak in an emission spectrum of the second exciplex and an energy value of a peak in an absorption band on the lowest energy side in an absorption spectrum of the second luminescent material is within 0.2 eV;
the excitation energy of the first exciplex is greater than the excitation energy of the second exciplex;
The first light-emitting substance emits light having a shorter wavelength than the second light-emitting substance. a first light-emitting layer and a second light-emitting layer in contact with the first light-emitting layer between a pair of electrodes;
the first light-emitting layer includes a first light-emitting substance and two kinds of organic compounds that form a first exciplex;
the second light-emitting layer includes a second light-emitting substance and two kinds of organic compounds that form a second exciplex;
a difference between a peak energy value of an emission spectrum of the first exciplex and a peak energy value of an absorption band on the lowest energy side of an absorption spectrum of the first luminescent material is within 0.2 eV;
a difference between an energy value of a peak in an emission spectrum of the second exciplex and an energy value of a peak in an absorption band on the lowest energy side in an absorption spectrum of the second luminescent material is within 0.2 eV;
the excitation energy of the first exciplex is greater than the excitation energy of the second exciplex;
The first light-emitting substance emits light having a shorter wavelength than the second light-emitting substance. a first light-emitting layer and a second light-emitting layer in contact with the first light-emitting layer between a pair of electrodes;
the first light-emitting layer includes a first organometallic complex and two kinds of organic compounds that form a first exciplex;
the second light-emitting layer includes a second organometallic complex and two kinds of organic compounds that form a second exciplex;
a difference between a peak energy value of an emission spectrum of the first exciplex and a peak energy value of an absorption band on the lowest energy side of an absorption spectrum of the first organometallic complex is within 0.2 eV;
the excitation energy of the first exciplex is greater than the excitation energy of the second exciplex;
The first organometallic complex emits light having a shorter wavelength than the second organometallic complex. a first light-emitting layer and a second light-emitting layer in contact with the first light-emitting layer between a pair of electrodes;
the first light-emitting layer includes a first organometallic complex and two kinds of organic compounds that form a first exciplex;
the second light-emitting layer includes a second organometallic complex and two kinds of organic compounds that form a second exciplex;
a difference between a peak energy value of an emission spectrum of the second exciplex and a peak energy value of an absorption band on the lowest energy side of an absorption spectrum of the second organometallic complex is within 0.2 eV;
the excitation energy of the first exciplex is greater than the excitation energy of the second exciplex;
The first organometallic complex emits light having a shorter wavelength than the second organometallic complex. a first light-emitting layer and a second light-emitting layer in contact with the first light-emitting layer between a pair of electrodes;
the first light-emitting layer includes a first organometallic complex and two kinds of organic compounds that form a first exciplex;
the second light-emitting layer includes a second organometallic complex and two kinds of organic compounds that form a second exciplex;
a difference between a peak energy value of an emission spectrum of the first exciplex and a peak energy value of an absorption band on the lowest energy side of an absorption spectrum of the first organometallic complex is within 0.2 eV;
a difference between a peak energy value of an emission spectrum of the second exciplex and a peak energy value of an absorption band on the lowest energy side of an absorption spectrum of the second organometallic complex is within 0.2 eV;
the excitation energy of the first exciplex is greater than the excitation energy of the second exciplex;
The first organometallic complex emits light having a shorter wavelength than the second organometallic complex.

Images