JP2019062240A - Light-emitting device, electronic apparatus, and lighting device - Google Patents

Abstract

To provide a light-emitting element having high external quantum efficiency, and to provide a light-emitting element having a long service life.SOLUTION: The light-emitting element has a light-emitting layer between an anode and a cathode. The light-emitting layer is a laminate of: a first light-emitting layer which contains at least a first luminescent substance converting triplet excitation energy into light emission, a first organic compound having electron transportability, and a second organic compound having hole transportability and is formed on the anode side; and a second light-emitting layer which is formed containing at least a second luminescent substance converting triplet excitation energy into light emission, the first organic compound, and a third organic compound having hole transportability. The second organic compound has a lower HOMO level than the third organic compound. The first luminescent substance exhibits light emission of a shorter wavelength than the second luminescent substance. The first organic compound and the second organic compound, and the first organic compound and the third organic compound form exciplexes, respectively.SELECTED DRAWING: None

Description

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

A light emitting element using an organic compound having characteristics such as thin and light weight, high speed response, direct current low voltage drive, etc. as a light emitter is expected to be applied to the next generation flat panel display. In particular, a display device in which light emitting elements are arranged in a matrix is considered to be superior to a conventional liquid crystal display device in that the viewing angle is wide and the visibility is excellent.

In the light emission mechanism of the light emitting element, by applying a voltage across the EL layer containing a light emitter between a pair of electrodes, electrons injected from the cathode and holes injected from the anode are read again at the light emission center of the EL layer. They combine to form molecular excitons, which are said to emit light and emit light when the molecular excitons relax to the ground state. Singlet excitation and triplet excitation are known as excited states, and light emission is considered to be possible through either of the excited states.

With regard to such a light emitting element, in order to improve the element characteristics, improvement of the element structure, material development and the like are actively performed (see, for example, Patent Document 1).

JP, 2010-182699, A

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

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

One embodiment of the present invention has a light-emitting layer between a pair of electrodes (anode and cathode), and the light-emitting layer is a first light-emitting substance (guest material) that converts triplet excitation energy into light emission; And a first light-emitting layer formed on the anode side, containing at least a first organic compound (host material) and a second organic compound (assist material) having hole transportability, and a triplet excitation energy At least formed by including at least a second light-emitting substance (guest material) for converting into light emission, a first organic compound having an electron transporting property (host material), and a third organic compound having a hole transporting property (assist material) In the first light emitting layer, the first organic compound (host material) and the second organic compound (assist material) are a combination forming an exciplex. , The second light In the first organic compound (host material) and the third organic compound (assist material) but is a light-emitting element which is a combination of forming an exciplex.

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

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 the first organic compound (host Emission wavelength (fluorescent wavelength) of the material) and the second organic compound (assist material)
Since it exists on the long wavelength side compared with the above, the fluorescence spectrum of the first organic compound (host material) and the fluorescence spectrum of the second organic compound (assist material) are longer by forming an exciplex. It can be converted into an emission spectrum located on the wavelength side. The emission wavelength of the exciplex formed by the first organic compound (host material) and the third organic compound (assist material) of the second light emitting layer is the same as that of the first organic compound (host material) and the third organic compound (host material). Organic compounds
The fluorescence spectrum of the first organic compound (host material) or the third organic material is formed by forming an exciplex because it exists on the long wavelength side compared to the respective emission wavelengths (fluorescent wavelengths) of the assist materials). The fluorescence spectrum of the compound (assist material) can be converted into an emission spectrum located on the longer wavelength side.

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

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

Furthermore, in the above configuration, the first light-emitting substance contained in the first light-emitting layer is a substance that emits light of a wavelength shorter than that of the second light-emitting substance contained in the second light-emitting layer. I assume.

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, a phosphorescent compound such as an organometallic complex, or thermal activation delayed fluorescence A material that shows heat, that is, thermally activated delayed fluorescence (TADF: Thermally A
ctivated delayed fluorescence) materials can be used. The first organic compound is mainly an electron transporting material having an electron mobility of 10 ⁻⁶ cm ² / Vs or more, specifically a π-deficient heteroaromatic compound, and the second organic compound and the second organic compound The organic compound 3 is characterized in that it is mainly a hole transporting material having a hole mobility of 10 ⁻⁶ cm ² / Vs or more, specifically a π excess heteroaromatic compound or an aromatic amine compound. Do.

Further, one embodiment of the present invention includes, in its category, not only a light-emitting device having a light-emitting element but also an electronic device and a lighting device each having a light-emitting device. Accordingly, a light emitting device in the present specification refers to an image display device, a light emitting device, or a light source (including a lighting device). Also,
A connector for the light emitting device, for example, FPC (Flexible printed circu
It) or a module attached with TCP (Tape Carrier Package), a module provided with a printed wiring board ahead of TCP, or a light emitting element
It is assumed that all modules in which an IC (integrated circuit) is directly mounted by an OG (Chip On Glass) method are included in the light emitting device.

Note that since the light emitting element which is one embodiment of the present invention can form an exciplex in each of the first light emitting layer and the second light emitting layer which form the light emitting layer, the energy transfer efficiency is high, and the external quantum A light emitting element with high efficiency can be realized.

In addition, in the light-emitting element which is one embodiment of the present invention, an excitation energy which is higher than that of an excitation complex which is formed in the first light-emitting layer by using the above-described element structure is higher than that in the second light-emitting layer. As a first light-emitting substance (guest material) for converting the triplet excitation energy contained in the first light-emitting layer into light emission, the triplet excitation energy contained in the second light-emitting layer is emitted. By using a substance which emits light of a wavelength shorter than that of the second light-emitting substance (guest material) to be changed, light emission from the first light-emitting layer and the second light-emitting layer can be obtained simultaneously. A second light-emitting substance that converts a part of the excitation energy of the exciplex formed in the light-emitting layer into a light emission that causes triplet excitation energy in the second light-emitting layer to emit light It is possible to use as excitation energy to strike the material), it is possible to enhance the luminous efficiency of the light emitting element.

FIG. 6 illustrates the concept of one embodiment of the present invention. FIG. 6 illustrates the concept of one embodiment of the present invention. FIG. 18 shows calculation results of one embodiment of the present invention. FIG. 18 shows calculation results of one embodiment of the present invention. 5A to 5C illustrate structures of light-emitting elements. 5A to 5C illustrate structures of light-emitting elements. FIG. 7 illustrates a light-emitting device. FIG. 7 illustrates a light-emitting device. 5A to 5C illustrate electronic devices. 5A to 5C illustrate electronic devices. The figure explaining a lighting installation. 5A to 5C illustrate light-emitting elements. FIG. 19 shows current density-luminance characteristics of the light-emitting element 1; FIG. 16 shows voltage-luminance characteristics of the light-emitting element 1; FIG. 16 shows luminance-current efficiency characteristics of the light-emitting element 1; FIG. 18 shows voltage-current characteristics of the light-emitting element 1; FIG. 16 shows an emission spectrum of the light-emitting element 1; FIG. 16 shows emission spectra of substances used in the light-emitting element 1; FIG. 16 shows emission spectra of substances used in the light-emitting element 1;

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

(Basic process of light emission in light emitting element)
First, a general elementary process of light emission in a light-emitting element using a light-emitting substance (including a phosphorescent compound and a thermally activated delayed fluorescence (TADF) material) which changes triplet excitation energy to light emission as a guest material will be described. Here, a molecule to which excitation energy is given is referred to as a host molecule, and a molecule which receives excitation energy is referred to as a guest molecule.

(1) The case where electrons and holes (holes) recombine in the guest molecule and the guest molecule is in an excited state (direct recombination process).

(1-1) When the Excited State of the Guest Molecule is 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 intersystem-crosses to a triplet excited state to emit phosphorescence.

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

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

(2-1) When the excited state of the host molecule is a triplet excited state If 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 It becomes a triplet excited state. The guest molecule in the triplet excited state emits phosphorescence. Note that energy transfer from the T1 level of the host molecule to the singlet excitation energy level of the guest molecule (S1 level) is prohibited as long as the host molecule does not emit phosphorescence, and the main energy transfer process is unlikely to occur. It is omitted here. That is, energy transfer from the triplet excited state (3H *) of the host molecule to the triplet excited state (3G *) of the guest molecule is important as shown in the following formula (2-1) (wherein 1 G is a guest Singlet ground state of molecule, 1 H represents singlet ground state of 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 The guest molecule becomes singlet excited state or triplet excited state. The guest molecule in the triplet excited state emits phosphorescence. In addition, the guest molecule in the singlet excited state crosses the term in the triplet excited state and emits phosphorescence.

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

1H * + 1G → 1H + 1G * → (intersection crossing) → 1H + 3G * (2-2A)
1H * + 1G to 1H + 3G * (2-2B)

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

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

First, the first mechanism, the Forster mechanism (dipole-dipole interaction), does not require direct contact between molecules for energy transfer, and the resonance of the dipole vibration between the host molecule and the guest molecule It is a mechanism by which energy transfer occurs through phenomena. The host molecule transfers energy to the guest molecule by the resonance phenomenon of dipole vibration, the host molecule becomes ground state, and the guest molecule becomes excited state. The velocity constant kh _{* → g} of the Forster mechanism is shown in Formula (1).

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

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

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

Here, the energy transfer efficiency _{ET ET} from the host molecule to the guest molecule is considered to be expressed by Formula (3). k _r represents the rate constant of the light emission process of the host molecule (fluorescence when discussing energy transfer from singlet excited states, and phosphorescence when discussing energy transfer from triplet excited states), and k _n is the host molecule Represents the rate constant of the non-emission process (thermal deactivation and intersystem crossing), and .tau. Represents the lifetime of the measured excited state of the host molecule.

From equation (3), in order to increase the energy transfer efficiency 、 _ET , the energy transfer rate constant k _{h * → g} is increased and the other competing rate constants k _r + k _n (= 1 / τ) are relative. It turns out that it should be as small as possible.

(About the energy transfer efficiency of (2-1))
Let us first consider the energy transfer process of (2-1). In this case, since the Forster type (Formula (1)) is prohibited, it is sufficient to consider only the Dexter type (Formula (2)).
According to Equation (2), to increase the rate constant kh _{* → g} , the emission spectrum of the host molecule (phosphorescence spectrum because energy transfer from the triplet excited state is discussed) and the absorption spectrum of the guest molecule (singlet It can be seen that the larger the overlap with the term (the absorption corresponding to the direct transition from the term ground state to the triplet excited state), the better.

In one embodiment of the present invention, a light-emitting substance (including a phosphorescent compound and a thermally activated delayed fluorescence (TADF) material) which converts triplet excitation energy into light emission is used as a guest material, but in the absorption spectrum of the phosphorescent compound An absorption corresponding to a direct transition from a singlet ground state to a triplet excited state may be observed, which is an absorption band appearing at the longest wavelength side. In particular, in the case of a luminescent iridium complex, the absorption band at the longest wavelength side often appears as a broad absorption band around 500 to 600 nm (Of course, depending on the emission wavelength, it appears at a shorter wavelength side or a longer wavelength side) In some cases). This absorption band is mainly formed by triplet MLCT (Metal t
o Derived from the Ligand Charge Transfer) transition. However, the absorption band partially includes absorption derived from triplet π-π * transition and singlet MLCT transition, and these overlap to form a broad absorption band on the longest wavelength side of the absorption spectrum. It is thought that In other words, the difference between the lowest singlet excited state and the lowest triplet excited state is small, and it is considered that the absorptions derived from them overlap to form a broad absorption band on the longest wavelength side of the absorption spectrum. Therefore, when using an organometallic complex (particularly, an iridium complex) as a guest material, the rate constant k _{h is} obtained by largely overlapping the broad absorption band existing on the longest wavelength side with the phosphorescence spectrum of the host material. _The energy transfer efficiency can be enhanced by increasing _{* → g} .

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

Taking the above into consideration, the energy transfer from the triplet excited state of the host material to the triplet excited state of the guest material, that is, the process of the equation (2-1) is the phosphorescence spectrum of the host material and the singlet of the guest material As long as the absorption spectrum corresponding to the direct transition from the ground state to the triplet excited state is overlapped, it is generally easy to occur.

(About the energy transfer efficiency of (2-2))
Next, consider the energy transfer process of (2-2). The process of equation (2-2A) is influenced by the intersystem crossing efficiency of the guest material. Therefore, it is considered that the process of Formula (2-2B) is important in order to increase the luminous efficiency to the limit. In this case, the Dexter type
2) is prohibited, so it is sufficient to consider only the Forster type (equation (1)).

If τ is eliminated from Equation (1) and Equation (3), the energy transfer efficiency _{ET ET} has a higher quantum yield ((the energy transfer from the singlet excited state is discussed, so the higher the fluorescence quantum yield) It can be said that it is good. However, in fact, as more important factors, the emission spectrum of the host molecule (the fluorescence spectrum because energy transfer from the singlet excited state is discussed) and the absorption spectrum of the guest molecule (direct from the singlet ground state to the triplet excited state) It is also necessary that the overlap with the absorption (corresponding to the transition) is large (note that the molar extinction coefficient of the guest molecule is preferably high). This means that the fluorescence spectrum of the host material and the absorption band appearing on the longest wavelength side of the guest compound phosphorescent compound overlap with each other.

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

However, in general, the S1 level and the T1 level are largely different (S1 level> T1 level),
The emission wavelength of fluorescence and the emission wavelength of phosphorescence are also largely different (emission wavelength of fluorescence <emission wavelength of phosphorescence).
For example, it is often used as a host material in a light emitting element using a phosphorescent compound4,
4'-di (N-carbazolyl) biphenyl (abbreviation: CBP) has a phosphorescence spectrum around 500 nm, while the fluorescence spectrum is around 400 nm and may be separated by as much as 100 nm. Even considering this example, it is extremely difficult to design the host material so that the fluorescence spectrum of the host material is in the same position as the phosphorescence spectrum. Therefore, improvement of the energy transfer efficiency from the singlet excited state of the host material to the guest material is very important.

Therefore, one aspect of the present invention is to provide a useful method that can overcome the problems related to the energy transfer efficiency from such a singlet excited state of the host material to the guest material. Below, the specific aspect is demonstrated.

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

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

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

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

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

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

In addition, the combination of the first organic compound (host material) 110 and the second organic compound (assist material) 111 in the first light emitting layer 106 a is a combination forming an exciplex (also referred to as exciplex). It is characterized by Furthermore, the emission wavelength of the exciplex formed by the first organic compound (host material) 110 and the second organic compound (assist material) 111 is the same as that of the first organic compound (host material) 110 and the second organic compound (Assist material) The fluorescence spectrum of the first organic compound (host material) 110 and the second organic compound (assist material), because they exist on the longer wavelength side than the respective emission wavelengths (fluorescence wavelength) of the (assist material) 111 The fluorescence spectrum of 111 can be converted to an emission spectrum located on the longer wavelength side.

The same applies to the second light emitting layer 106 b. Therefore, the second light emitting layer 10
The combination of the first organic compound (host material) 110 and the third organic compound (assist material) 112 in 6 b is characterized in that it is a combination forming an exciplex (also referred to as exciplex). Furthermore, the emission wavelength of the exciplex formed by the first organic compound (host material) 110 and the third organic compound (assist material) 112 is the first organic compound (host material) 110 and the third organic compound. (Assist material) 1
The fluorescence spectrum of the first organic compound (host material) 110 and the fluorescence of the third organic compound (assist material) 112 because they exist on the long wavelength side as compared to the respective emission wavelengths (fluorescence wavelength) of 12 The spectrum can be converted to an emission spectrum located on the longer wavelength side.

Note that in the above configuration, the level (T1 level) of the triplet excitation energy of each of the first organic compound (host material) 110 and the second organic compound (assist material) 111 emits triplet excitation energy. Is preferably higher than the T1 level of the first light-emitting substance (guest material) 109a. 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 first light-emitting substance contributing to light emission This is because the first organic compound 110 (or the second organic compound 111) quenches (trips) triplet excitation energy of the (guest material) 109a and causes a decrease in light emission efficiency.

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

Further, in the first light emitting layer 106 a constituting the light emitting layer 106, a ratio in which the first organic compound (host material) 110 and the second organic compound (assist material) 111 are contained, and the light emitting layer 106 The ratio in which the first organic compound (host material) 110 and the third organic compound (assist material) 112 are included in the second light emitting layer 106b may be either large, and in the present invention, both cases are included. To be.

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

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

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

Although the light-emitting element described in this embodiment has a structure in which an exciplex is formed in each of the light-emitting layer 106 (the first light-emitting layer 106 a and the second light-emitting layer 106 b), the first organic compound (host material Conversion of the fluorescence spectrum of 110), the fluorescence spectrum of the second organic compound (assist material) 111, or the fluorescence spectrum of the third organic compound (assist material) 112 into an emission spectrum located on the longer wavelength side As shown in FIG. 2, the first organic compound 110, the second organic compound 111, or the third organic compound 11 can be used.
The light emission substance 109 (the fluorescence spectrum of 2 changes the triplet excitation energy into light emission,
First light-emitting substance (guest material) 109a and second light-emitting substance (guest material) 10
A luminescent substance 109 (a first luminescent substance (guest material) 109a, and a second luminescent substance (guest material) 109a, which is located on a shorter wavelength side than the absorption band located on the longest wavelength side of 9b) and converts triplet excitation energy into light emission Even if there is no overlap with the absorption band located on the longest wavelength side of the light-emitting substance (guest material) 109b), it means that the overlap can be increased by forming an exciplex. By this, the energy transfer efficiency of Formula (2-2B) mentioned above can be improved.

Furthermore, it is considered that the exciplex has a very small difference between singlet excitation energy and triplet excitation energy. In other words, the emission spectrum from the singlet state of the exciplex and the emission spectrum from the triplet state are in close proximity. Therefore, as described above, the absorption band located on the longest wavelength side of the light-emitting substance 109, which converts triplet excitation energy into light emission, of the emission spectrum of the exciplex (generally, the emission spectrum from the singlet state of the exciplex) The emission spectrum from the triplet state of the exciplex (in many cases not observed at normal temperature, often not observed at low temperature) is also the longest wavelength of the light-emitting substance 109 that converts triplet excitation energy into light emission. It will overlap the absorption band located on the side. That is, not only energy transfer from the singlet excited state ((2-2)) but also the efficiency of energy transfer from the triplet excited state ((2-1)) is increased, resulting in singlet and triplet. Energy from both of the excited states can be efficiently converted to light emission.

Therefore, with regard to whether or not the exciplex actually has such properties, in the following, it was verified using molecular orbital calculation. Generally, the combination of heteroaromatic compound and aromatic amine is the lowest unoccupied molecular orbital of the aromatic amine (LUMO: Lowest Unoccupied
LUMO level (property easy to enter electrons) of the heteroaromatic compound deeper than the Molecular Orbital level and the highest occupied orbital (HOMO: High) of the heteroaromatic compound
Excitation complexes are often formed under the influence of the HOMO level (the property of holes being easily inserted) of a shallow aromatic amine compared to the est Occupied Molecular Orbital level. Therefore, the present invention uses dibenzo [f, h] quinoxaline (abbreviation: DBq) as a model of the first organic compound 110 in one embodiment of the present invention, which is a typical skeleton constituting the LUMO level of a heteroaromatic compound. As a model of the second organic compound 111 (or the third organic compound 112) in one embodiment of the present invention, triphenylamine (abbreviation: TPA) having a typical skeleton constituting the HOMO level of an aromatic amine is used. The calculation was performed combining.

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

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

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

By the above basis function, for example, in the case of a hydrogen atom, the orbit of 1s to 3s is considered, and in the case of a carbon atom, the orbits of 1s to 4s and 2p to 4p are considered. Furthermore, for the purpose of improving calculation accuracy, as a polarization basis system, p function for hydrogen atoms and d for hydrogen atoms other than hydrogen atoms
Added a function.

Note that Gaussian 09 was used as a quantum chemistry calculation program. The calculation was performed using a high performance computer (SGI, Altix 4700).

First, one molecule of DBq (abbreviation), one molecule of TPA (abbreviation), and DBq (abbreviation) and TPA (
HOMO level and LUMO level were calculated regarding the dimer of (abbreviation). HOMO level and L
The UMO levels are shown in FIG. 3, and the distributions of the HOMO and LUMO levels are shown in FIG. 4, respectively.

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

As shown in FIG. 3, the dimer of DBq (abbreviation) and TPA (abbreviation) is L of TPA (abbreviation)
LUMO level (-1.99 eV) of DBq (abbreviation) deeper (lower) than UMO level,
HOMO level (-) of shallow (high) TPA (abbreviation) compared to the HOMO level of DBq (abbreviation)
The influence of 5.21 eV) suggests that DBq (abbreviation) and TPA (abbreviation) form an exciplex. Actually, as can be seen from FIG. 4, the LUMO levels of the dimer of DBq (abbreviation) and TPA (abbreviation) are distributed on the DBq (abbreviation) side, and the HOMO levels are distributed on the TPA (abbreviation) side.

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

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

Furthermore, it shows the excitation energy obtained from the optimum molecular structure at the S1 level and T1 level of the dimer of DBq (abbreviation) and TPA (abbreviation). The excitation energies of the S1 and T1 levels are
It corresponds to the fluorescence and phosphorescence wavelengths emitted by the dimer of the DBq level and the TPA level, respectively. DBq
The excitation energy of the S1 level of the dimer of (abbreviation) and TPA (abbreviation) was 2.036 eV, and the fluorescence wavelength was 609.1 nm. In addition, the excitation energy of the T1 level of the dimer of DBq (abbreviation) and TPA (abbreviation) is 2.030 eV, and the phosphorescence wavelength is 610.0 n.
It was m.

From the above, in any of DBq (abbreviation) one molecule and TPA (abbreviation) one molecule,
It can be seen that the phosphorescence wavelength is shifted by a long wavelength close to 100 nm. This is the CBP mentioned above
This is a tendency similar to (abbreviation) (measured value), which is a result supporting the validity of the calculation.

On the other hand, it is understood that the fluorescence wavelength of the dimer of DBq (abbreviation) and TPA (abbreviation) exists on the longer wavelength side than the fluorescence wavelength of DBq (abbreviation) one molecule or TPA (abbreviation) molecule. Also, the difference between the fluorescence and phosphorescence wavelengths of DBq (abbreviation) and TPA (abbreviation) dimers is only 0.9 n.
It can be seen that m is substantially the same wavelength.

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

Thus, in the light-emitting element which is one embodiment of the present invention, the light-emitting substance which changes the emission spectrum of the exciplex formed in the light-emitting layer and the triplet excitation energy into light emission (the first light-emitting substance and the second Taking advantage of the overlap with the absorption spectrum of the guest material (containing the luminescent material),
Energy transfer efficiency is high because of energy transfer. Therefore, a light emitting element with high external quantum efficiency can be realized.

In addition, since the exciplex exists only in the excited state, there is no ground state capable of absorbing energy. Therefore, a luminescent substance (guest material) that converts triplet excitation energy into luminescence
Is a phenomenon that a light emitting substance (guest material) that converts triplet excitation energy into light emission by emission of energy from singlet excited state and triplet excited state to an excited complex is deactivated (that is, light emission efficiency is impaired) Is considered not to occur in principle. This is also one factor that can increase the external quantum efficiency.

The above-mentioned exciplex is formed by the interaction between different molecules in the excited state. Also, it is generally known that exciplexes are easily formed between a material having a relatively deep LUMO level and a material having a shallow HOMO level.

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

Therefore, the HOMO level and the LUMO level of the first organic compound (host material) 110, the second organic compound (assist material) 111, and the third organic compound (assist material) 112 in this embodiment are shown in FIG. As shown in 1 (B), they are different. Specifically, the HOMO level of the first organic compound 110 <the HOMO level of the second organic compound 111 and the HOMO level of the third organic compound 112 <the LUMO level of the first organic compound 110 < The energy levels differ in the order of the LUMO level of organic compound 111 of 2 and the LUMO level of third organic compound 112.

Then, in each light emitting layer, two organic compounds (in the first light emitting layer 106a, the first organic compound 110 and the second organic compound 111, and in the second light emitting layer 106b, the first organic compound 110) The LUMO level of the exciplex in the first light emitting layer 106 a and the second light emitting layer 106 b is the same as that of the first organic compound (host material) 110 in the case where the exciplex is formed by And the HOMO level of the exciplex in the first light emitting layer 106 a is derived from the second organic compound (assist material) 111, and the second light emitting layer 1
The HOMO level of the exciplex in 06 b is derived from the HOMO level of the third organic compound (assist material) 112. Accordingly, the excitation energy _{(E A)} of the exciplex in the first light-emitting layer 106a, the excitation energy of the exciplex in the second light-emitting layer 106b _(E B)
It becomes bigger than. That is, as the first light-emitting substance 109a which changes the triplet excitation energy contained in the first light-emitting layer into light emission, the second light-emitting substance 109b which changes the triplet excitation energy contained in the second light-emitting layer into light emission By using a substance that emits light with a wavelength shorter than that of the light-emitting element, a light-emitting element with high emission efficiency can be formed. In addition, light-emitting materials with different emission wavelengths can be efficiently emitted at the same time.

The following two processes can be considered as the formation process of the exciplex in one aspect 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 carrier-carrying state (specifically, a cation). is there.

Generally, when electrons and holes (hole) recombine in the host material, excitation energy is transferred from the excited host material to the guest material, and the guest material reaches the excited state to emit light, but from the host material Before the excitation energy is transferred to the guest material, the host material itself emits light, or the excitation energy becomes thermal energy, thereby deactivating part of the excitation energy. In particular, when the host material is in a singlet excited state, energy transfer hardly occurs as described in (2-2). Deactivation of such excitation energy is one of the factors leading to a decrease in the lifetime of the light emitting element.

However, in one aspect of the present invention, from the state (cation or anion) in which the first organic compound (host material) and the second organic compound (or third organic compound) (assist material) have a carrier, In order to form an exciplex, formation of singlet excitons of the first organic compound (host material) can be suppressed. That is, there may be a process of directly forming an exciplex without forming a singlet exciton. Thereby, the deactivation of the singlet excitation energy can also be suppressed. Therefore, a light emitting element with a long lifetime can be realized.

For example, the first organic compound is a compound having electron trapping properties (deep LUMO level) that has the property of easily trapping electrons (carriers) among electron transporting materials, and the second organic compound (or third compound) Of the organic compound of (1) is an anion of the first organic compound when it is a hole-transporting compound having a property of easily capturing holes (carriers) among hole transporting materials (a shallow HOMO level). And the cation of the second organic compound (or the third organic compound) directly form an exciplex. An exciplex formed in such a process is particularly called an electroplex. Thus, by suppressing the generation of the singlet excited state of the first organic compound (host material) and performing energy transfer from the electroplex to the light emitting substance (guest material) that converts the triplet excitation energy into light emission, A light emitting element with high luminous efficiency can be obtained. In this case, the first
The generation of the triplet excited state of the organic compound (host material) is similarly suppressed, and the direct excitation complex is formed, so that the energy transfer from the exciplex to the light emitting substance (guest material) that converts the triplet excitation energy into light emission It is thought that.

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

Note that the first organic compound (host material) is an electron trapping compound, and on the other hand, the second organic compound
The organic compound (or third organic compound) (assist material) is a hole trapping compound, and the difference between the HOMO levels of these compounds and the difference between the LUMO levels are large (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 third organic compound) (assist material).
In this case, the process in which the electroplex is formed is considered to be prioritized over the process in which the exciplex is formed through singlet excitons.

Note that a luminescent substance that changes the emission spectrum of an exciplex and the triplet excitation energy into light emission (
In order to sufficiently overlap the absorption spectrum of the guest material), the difference between the energy value of the peak of the emission spectrum and the energy value of the peak of the absorption band at the lowest energy side of the absorption spectrum is within 0.3 eV preferable. More preferably, it is within 0.2 eV, and most preferably within 0.1 eV.

In the light-emitting element which is one embodiment of the present invention, the excitation energy of the exciplex is sufficiently energy-transferred to a light-emitting substance (guest material) that converts triplet excitation energy into light emission, and light emission from the exciplex is substantially Preferably not observed. Therefore, it is preferable that light is emitted by a light emitting substance that transfers energy to a light emitting substance that converts triplet excitation energy into light emission via an exciplex and that converts triplet excitation energy into light emission. Note that as a light-emitting substance which converts triplet excitation energy into light emission, a phosphorescent compound (organic metal complex or the like), a thermally activated delayed fluorescence (TADF) material, or the like is preferable.

In the first light-emitting layer 106a of the light-emitting element which is one embodiment of the present invention, a light-emitting substance which changes triplet excitation energy to light emission is used as the first organic compound (host material).
The organic compound (host material) itself easily emits light, and energy transfer to the light-emitting substance (guest material) that converts triplet excitation energy into light emission becomes difficult. In this case, although the first organic compound may emit light efficiently, the host material has a problem of concentration quenching, so it is difficult to achieve high emission efficiency. Therefore, at least one of the first organic compound (host material) and the second organic compound (or third organic compound) (assist material) is a fluorescent compound (that is, light emission or thermal deactivation from a singlet excited state) The compound is effective when it is a compound in which Therefore, a configuration in which at least one of the first organic compound (host material) and the second organic compound (or third organic compound) (assist material) is a fluorescent compound, and the exciplex is used as a medium for energy transfer Is preferred.

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

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

The light-emitting element described in this embodiment includes a pair of electrodes (a first electrode (anode) 2) as shown in FIG.
The EL layer 203 including the light emitting layer 206 is sandwiched between the electrode 01 and the second electrode (cathode) 202), and the EL layer 203 has a laminated structure of the first light emitting layer 206a and the second light emitting layer 206b. In addition to the light emitting layer 206, the light emitting layer 206 is formed to include a hole (or hole) injection layer 204, a hole (or hole) transport layer 205, an electron transport layer 207, an electron injection layer 208, and the like.

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

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

Note that in the light emitting layer 206 (the first light emitting layer 206 a and the second light emitting layer 206 b),
In the case of the first light emitting layer 206 a, the first light emitting substance 209 a for converting triplet excitation energy into light emission is contained in the first organic compound (host material) 210 and the second organic compound (assist material) 211. In the case of the second light-emitting layer 206b, the second light-emitting substance 209b which disperses the triplet excitation energy into light emission is a first organic compound (host material) 210 and a third organic compound (assist material) Light emitting layer 20 by dispersing the light
It is possible to suppress crystallization of 6 (the first light emitting layer 206a and the second light emitting layer 206b). In addition, concentration quenching due to the high concentration of the light-emitting substance 209 (209a, 209b) can be suppressed, and the light emission efficiency of the light-emitting element can be increased.

In addition, the first organic compound 210, the second organic compound 211, and the third organic compound 2
The level of each triplet excitation energy (T1 level) of 12 is preferably higher than the T1 level of the light-emitting substance 209 (209a, 209b) that converts the triplet excitation energy into light emission. First organic compound 210, second organic compound 211, and third organic compound 21
A light-emitting substance 209 (209a, 20) in which the T1 level of 2 changes triplet excitation energy into light emission.
9b), the triplet excitation energy of the light-emitting substance 209 (209a, 209b) which changes the triplet excitation energy contributing to light emission to light emission is the first organic compound 21.
This is because 0 (or the second organic compound 211 or the third organic compound 212) is quenched (quenched) to cause a decrease in light emission efficiency.

In this embodiment mode, in the light emitting layer 206, in the first light emitting layer 206a, when the carriers (electrons and holes) injected from the both electrodes are recombined, the first organic compound 210 is used.
An exciplex (exciplex) is formed from the second organic compound 211, and an exciplex is formed from the first organic compound 210 and the third organic compound 212 in the second light emitting layer 206b. Thus, the fluorescence spectrum of the first organic compound 210 and the fluorescence spectrum of the second organic compound 211 in the first light emitting layer 206a can be converted into the emission spectrum of an exciplex located on the longer wavelength side. The fluorescence spectrum of the first organic compound 210 in the second light emitting layer 206 b and the fluorescence spectrum of the third organic compound 212 are as follows:
It can be converted to the emission spectrum of an exciplex located on the longer wavelength side. Therefore, in order to maximize energy transfer from the singlet excited state, the overlap between 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 is increased. In the first light emitting layer 206a, select the first organic compound 210 and the second organic compound 211, and in the second light emitting layer 206b, select the first organic compound 210 and the third organic compound 212, respectively. I assume. That is, here, it is considered that energy transfer from the exciplex as well as the host material occurs in the triplet excited state.

Note that a light-emitting substance 209 (first light-emitting substance 20) that converts triplet excitation energy into light emission
The 9a and the second light emitting substance 209b) are preferably a phosphorescent compound (organic metal complex or the like), a thermally activated delayed fluorescence (TADF) material, or the like. In addition, as the first organic compound (host material) 210, an electron transporting material is preferably used. As the second organic compound (assist material) 211 and the third organic compound (assist material) 212, it is preferable to use a hole transportable 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)
', 6'-Difluorophenyl) pyridinato-N, C ^2' ] iridium (III) acetylacetonate (abbreviation: FIracac), tris (2-phenyl pyridinato) iridium (III) (abbreviation: Ir (ppy) ₃ ), Bis (2-phenylpyridinato) iridium (III) acetylacetonate (abbreviation: Ir (ppy) ₂ (acac)), bis (benzo [h] quinolinato) iridium (III) acetylacetonate (abbreviation: Ir) (Bzq
) ₂ (acac)), bis (2,4-diphenyl-1,3-oxazolato-N, C ^{2 ′} )
Iridium (III) acetylacetonate (abbreviation: Ir (dpo) ₂ (acac)),
Bis {2- [4 ′-(perfluorophenyl) phenyl] pyridinato-N, C ^{2 ′} } iridium (III) acetylacetonate (abbreviation: Ir (p-PF-ph) ₂ (acac)
), Bis (2-phenylbenzothiazolato-N, C ^{2 ′} ) iridium (III) acetylacetonate (abbreviation: Ir (bt) ₂ (acac)), bis [2- (2′-benzo [4 ,,
5-α] thienyl) pyridinato-N, C3 ^′ ] iridium (III) acetylacetonate (abbreviation: Ir (btp) ₂ (acac)), bis (1-phenylisoquinolinato-N,
C ^{2 ′} ) iridium (III) acetylacetonate (abbreviation: Ir (piq) ₂ (aca
c)) (Acetylacetonato) bis [2,3-bis (4-fluorophenyl) quinoxarinato] 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, 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.

The electron transporting material is preferably a π-deficient heteroaromatic compound such as a nitrogen-containing heteroaromatic compound, for example, 2- [3- (dibenzothiophen-4-yl) phenyl] dibenzo [f, h] quinoxaline (abbreviation: 2mDBTPDBq-II), 2- [3'-
(Dibenzothiophen-4-yl) biphenyl-3-yl] dibenzo [f, h] quinoxaline (abbreviation: 2mDBTBPDBq-II), 2- [4- (3,6-diphenyl-9H-)
Carbazol-9-yl) phenyl] dibenzo [f, h] quinoxaline (abbreviation: 2CzP)
DBq-III), 7- [3- (dibenzothiophen-4-yl) phenyl] dibenzo [
f, h] quinoxaline (abbreviation: 7mDBTPDBq-II), and 6- [3- (dibenzothiophen-4-yl) phenyl] dibenzo [f, h] quinoxaline (abbreviation: 6mDB)
Examples include quinoxalines and dibenzoquinoxaline derivatives such as TPDB q-II).

In addition, as the hole transporting material, a π excess heteroaromatic compound (for example, a carbazole derivative or an indole derivative) or an aromatic amine compound is 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, 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)
Can be mentioned.

However, the light-emitting substance (guest material) 209 that converts the above-described triplet excitation energy into light emission
(First light-emitting substance 209a, second light-emitting substance 209b), first organic compound (host material) 210, second organic compound (assist material) 211, and third organic compound (assist material) The materials that can be used for each of 212 are combinations that can form an exciplex without being limited thereto, and a luminescent substance (guest material) 209 in which the emission spectrum of the exciplex converts triplet excitation energy into luminescence. A light-emitting substance (guest material) 209 (the first one which overlaps with the absorption spectrum of the first light-emitting substance 209a or the second light-emitting substance 209b) and the peak of the emission spectrum of the exciplex converts triplet excitation energy into light emission 1 if it has a wavelength longer than the peak of the absorption spectrum of the first light-emitting substance 209a or the second light-emitting substance 209b). .

When an electron transporting material is used for the first organic compound 210 and a hole transporting material is used for the second organic compound 211, the carrier balance can be controlled by the mixing ratio. Specifically, the first organic compound 210: the second organic compound 211 = 1: 9.
It is preferable to set it as -9: 1.

  Hereinafter, specific examples of manufacturing the light-emitting element described in this embodiment will be described.

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

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

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

Further, as an acceptor substance which can be used for the hole injecting layer 204, a transition metal oxide or an oxide of a metal belonging to Groups 4 to 8 in the periodic table can be given. Specifically, molybdenum oxide is particularly preferred.

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

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

The electron-transporting layer 207 is not limited to a single layer, and two or more layers containing the above substances may be stacked.

The electron injection layer 208 is a layer containing a substance having a high electron injection property. The electron injection layer 208
Lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF ₂ )
Alkali metals such as lithium oxide (LiOx) and the like, alkaline earth metals, or compounds thereof can be used. Alternatively, a rare earth metal compound such as erbium fluoride (ErF ₃ ) can be used. Alternatively, the above-described substance that forms the electron transport layer 207 can be used.

Alternatively, for the electron injection layer 208, a composite material in which an organic compound and an electron donor (donor) are mixed may be used. Such a composite material is excellent in electron injectability and electron transportability because electrons are generated in the organic compound by the electron donor. In this case, the organic compound is preferably a material excellent in transportation of generated electrons, and specifically, for example, the above-described substance (metal complex, heteroaromatic compound, etc.) constituting the electron transport layer 207 may be used. It can be used. As the electron donor, any substance may be used as long as it exhibits an electron donating property to the organic compound. Specifically, alkali metals, alkaline earth metals and rare earth metals are preferable, and lithium, cesium, magnesium, calcium, erbium, ytterbium and the like can be mentioned. Further, alkali metal oxides and alkaline earth metal oxides are preferable, and lithium oxide, calcium oxide, barium oxide and the like can be mentioned. Also, Lewis bases such as magnesium oxide can be used. Alternatively, an organic compound such as tetrathiafulvalene (abbreviation: TTF) can also be used.

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

Light emitted from the light-emitting layer 206 of the light-emitting element described above is extracted outside through one or both of the first electrode 201 and the second electrode 202. Therefore, any one 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 mode improves energy transfer efficiency by energy transfer utilizing overlap of the emission spectrum of an exciplex and the absorption spectrum of a light-emitting substance (guest material) that converts triplet excitation energy into light emission. Thus, a light-emitting element with high external quantum efficiency can be realized.

Note that the light-emitting element described in this embodiment is an embodiment of the present invention, and is particularly characterized in the structure of a 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, which are all included in the present invention. .

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

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

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

The light-emitting element described in this embodiment includes a pair of electrodes (a first electrode 30 as shown in FIG. 6A).
Between the first and second electrodes 304), a plurality of EL layers (first EL layer 302 (1), second E
It is a tandem type light emitting element which has L layer 302 (2).

In this embodiment, the first electrode 301 is an electrode functioning as an anode, and the second electrode 304 is an electrode functioning as a cathode. Note that the first electrode 301 and the second electrode 304 can have the same structure as in Embodiment 1. In addition, multiple EL layers (first
The EL layer 302 (1) and the second EL layer 302 (2)) may have the same structure as the EL layer described in Embodiment 1 or Embodiment 2, but either is the same. It may be a configuration. That is, the first EL layer 302 (1) and the second EL layer 302 (2) may have the same configuration or different configurations, and the configuration is the same as Embodiment 1 or Embodiment 2. Similar things can be applied.

Further, 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 of the EL layers and injecting holes into the other of the EL layers when voltage is applied to the first electrode 301 and the second electrode 304. Have. In the case of this embodiment, when a voltage is applied to the first electrode 301 so that the potential is higher than that of the second electrode 304, the charge generation layer (I) 30 can be used.
Electrons are injected from the fifth to the first EL layer 302 (1), and holes are injected to the second EL layer 302 (2).

The charge generation layer (I) 305 is translucent to visible light in terms of light extraction efficiency (specifically, the visible light transmittance to the charge generation layer (I) 305 is 40% or more) is preferable. In addition, the charge generation layer (I) 305 includes the first electrode 301 and the second electrode 3.
Even conductivity lower than 04 works.

In the charge generation layer (I) 305, even if the electron acceptor (acceptor) is added to the organic compound having high hole transportability, the electron donor (donor) is added to the organic compound having high electron transportability. The configuration may be modified. Also, both of these configurations may be stacked.

When an electron acceptor is added to an organic compound having high hole transportability, examples of the organic compound having high hole transportability 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 mentioned here are mainly ones having a hole mobility of 10 ⁻⁶ cm ² / Vs or more. However, any substance other than the above may be used as long as it is an organic compound having a hole transportability higher than that of electrons.

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

On the other hand, when an electron donor is added to an organic compound having a high electron transporting property, examples of the organic compound having a high electron transporting property include Alq, Almq ₃ , BeBq ₂ , and B.
A metal complex having a quinoline skeleton or a benzoquinoline skeleton, such as Alq, can be used. Besides these, metal complexes having an oxazole type such as Zn (BOX) ₂ and Zn (BTZ) ₂ and a thiazole type ligand can also be used. Furthermore, other than metal complexes, PBD, OXD-7, TAZ, BPhen, BCP and the like can also be used. The substances mentioned here are mainly ones having an electron mobility of 10 ⁻⁶ cm ² / Vs or more. Note that a substance other than the above may be used as long as it is an organic compound having electron transportability higher than that of holes.

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

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

Although a light emitting element having two EL layers is described in this embodiment, as shown in FIG. 6B, a light emitting element in which n EL layers (where n is 3 or more) are stacked as shown in FIG. , Can be applied as well. In the case where a plurality of EL layers are provided between a pair of electrodes as in the light-emitting element according to this embodiment, the charge generation layer (I) is disposed between the EL layer and the EL layer;
It is possible to emit light in a high luminance region while keeping the current density low. Since the current density can be kept low, a long-life element can be realized. Further, in the case of application to illumination, the voltage drop due to the resistance of the electrode material can be reduced, so that uniform light emission over a large area can be achieved. In addition, a light-emitting device which can be driven at low voltage and consumes low power can be realized.

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

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

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

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

The light emitting device described in this embodiment has a micro optical resonator (micro cavity) structure utilizing the resonance effect of light between a pair of electrodes, and as shown in FIG. Electrode 4
A plurality of light emitting elements, which are structures having at least an EL layer 405 between the light emitting element 01 and the semi-transmissive semi-reflective electrode 402). In addition, the EL layer 405 is at least a light emitting layer 4 to be a light emitting region.
04 (404R, 404G, 404B), and may further include a hole injection layer, a hole transport layer, an electron transport layer, an electron injection layer, a charge generation layer (E), and the like. Note that the light emitting layer 404
(404R, 404G, 404B) can include the structure of the light-emitting layer which is one embodiment of the present invention as described in Embodiment 1 or 2.

In this embodiment, as shown in FIG. 7, light emitting elements having different structures (a first light emitting element (R) 4
A light emitting device configured to include the 10R, the second light emitting element (G) 410G, and the third light emitting element (B) 410B will be described.

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

In addition, the light emitting element (the first light emitting element (R) 410R, the second light emitting element (G) 410G)
In the third light emitting element (B) 410B), the reflective electrode 401, the EL layer 405,
The semireflective electrode 402 is common. In the first light emitting layer (B) 404B, light (λ _B ) having a peak in a wavelength region of 420 nm to 480 nm is emitted, and a second light emitting layer (G)
In 404G, light (λ _G ) having a peak in the wavelength range of 500 nm to 550 nm is emitted, and in the third light emitting layer (R) 404R, light having a peak in the wavelength range of 600 nm to 760 nm (λ _R ) To make it glow. Thereby, in any light emitting element (the first light emitting element (R) 410R, the second light emitting element (G) 410G, and the third light emitting element (B) 410B), the first light emitting layer (B) 404B, Second light emitting layer (G) 404G, and third light emitting layer (R
The light from 404R can be superimposed, that is, broad light can be emitted over the visible light region. From the above, it is assumed that the length of the wavelength has a relationship of λ _B <λ _G <λ _R.

Each light emitting element shown in this embodiment includes a reflective electrode 401 and a semitransparent / semireflective electrode 40 respectively.
The light emission emitted in all directions from each light emitting layer included in the EL layer 405 has a function as a micro optical resonator (micro cavity). And the semi-transmissive and semi-reflective electrode 402 resonate. The reflective electrode 401 is formed of a conductive material having reflectivity, and the reflectance of visible light to the film is 40% to 100%, preferably 70% to 100%, and the resistivity is 1 × 10
It is assumed that the film is ⁻² Ωcm or less. The semi-transmissive and semi-reflective electrode 402 is formed of a conductive material having reflectivity and a conductive material having light permeability, and the visible light reflectance of the film is 20% to 80%, preferably 40. % To 70%, and its resistivity is 1 × 10 ⁻
It is assumed that the film is ² Ωcm or less.

In this embodiment mode, transparent conductive layers (a first transparent conductive layer 403 a and a first conductive layer 403 a) provided on the first light emitting element (R) 410 R and the second light emitting element (G) 410 G in each light emitting element. 2
The optical distance between the reflective electrode 401 and the semi-transmissive and semi-reflective electrode 402 is changed for each light emitting element by changing the thickness of the transparent conductive layer 403 b). That is, the broad light emitted from each light emitting layer of each light emitting element is between the reflective electrode 401 and the semi-transmissive and semi-reflective electrode 402,
Since it is possible to intensify the light of the resonating wavelength and attenuate the light of the non-resonance wavelength, the light of different wavelengths is changed by changing the optical distance between the reflective electrode 401 and the semi-transmissive and semi-reflective electrode 402 for each element. It can be taken out.

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

In the first light emitting element (R) 410 R, the reflective electrode 401 transmits the semi-transmissive and semi-reflective electrode 4.
M [lambda a total thickness of up to 02 _R / 2 (provided that, m is a natural number), the second light emitting element (G) 410G, m [lambda the total thickness from the reflective electrode 401 to the semi-transmissive and semi-reflective electrode 402 _G / 2 ( However, m
In the third light emitting element (B) 410B, the total thickness from the reflective electrode 401 to the semi-transmissive / semi-reflective electrode 402 is mλ _B / 2 (where m is a natural number).

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

Further, in the above configuration, the total thickness from the reflective electrode 401 to the semi-transmissive semi-reflective electrode 402 may be exactly the total thickness from the reflective region in the reflective electrode 401 to the reflective region in the semi-transmissive semi-reflective electrode 402 it can. However, the reflective electrode 401 or the semi-transmissive and semi-reflective electrode 40
Since it is difficult to precisely determine the position of the reflective area in 2, it is sufficient to obtain the above effect by assuming any position of the reflective electrode 401 and the semitransparent / semireflective electrode 402 as the reflective area. It shall be possible.

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

Strictly speaking, the optical distance between the reflective electrode 401 and the third light emitting layer (R) 404R is the optical distance between the reflective region in the reflective electrode 401 and the light emitting region in the third light emitting layer (R) 404R. Can. However, the reflective region in the reflective electrode 401 or the third light emitting layer (R)
Since it is difficult to precisely determine the position of the light emitting region in 404 R, the reflective electrode 40
It is assumed that the above effect can be sufficiently obtained by assuming an arbitrary position of 1 as a reflection area and an arbitrary position of the third light emitting layer (R) 404R as a light emission area.

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

Note that the optical distance between the reflective electrode 401 and the second light emitting layer (G) 404G is, strictly speaking, the optical distance between the reflective region in the reflective electrode 401 and the light emitting region in the second light emitting layer (G) 404G. Can. However, the reflective region in the reflective electrode 401 and the second light emitting layer (G)
Since it is difficult to precisely determine the position of the light emitting region in 404 G, the reflective electrode 40
Assuming that an arbitrary position of 1 is a reflection area, and an arbitrary position of the second light emitting layer (G) 404G is a light emission area, the above effect can be sufficiently obtained.

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

In the third light emitting element, the optical distance between the reflective electrode 401 and the first light emitting layer (B) 404B is strictly the light emission from the reflective region of the reflective electrode 401 and the first light emitting layer (B) 404B It can be said to be the optical distance from the area. However, it is difficult to determine the position of the reflective region in the reflective electrode 401 and the position of the light emitting region in the first light emitting layer (B) 404B strictly, so any position of the reflective electrode 401 is the reflective region, the first light emission Assuming that an arbitrary position of the layer (B) 404B is a light emitting region, the above effect can be sufficiently obtained.

In the above structure, each light emitting element has a structure in which a plurality of light emitting layers are provided in the EL layer, but the present invention is not limited to this. For example, the tandem type described in Embodiment 3 In combination with the configuration of the light emitting element, a plurality of ELs sandwiching the charge generation layer in one light emitting element
A layer may be provided and one or more light emitting layers may be formed in each EL layer.

The light emitting device described in this embodiment has a microcavity structure, and the same EL
Even when the light emitting element has a layer, light of different wavelengths can be extracted for each light emitting element, so that the different coloring of RGB is not necessary. Therefore, it is advantageous in realizing full color since it is easy to realize high definition. In addition, the combination with a colored layer (color filter) is also possible. In addition, since it is possible to intensify the light emission intensity in the front direction of the specific wavelength, 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 may be used for applications such as illumination.

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

The light emitting device may be either 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 embodiments can be applied to the light-emitting device described in this embodiment.

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

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

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

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

The driver circuit portion 503 is an example in which a CMOS circuit in which an n-channel TFT 509 and a p-channel TFT 510 are combined is formed. The circuit that forms the drive circuit unit is
It may be formed of various CMOS circuits, PMOS circuits or NMOS circuits. Further, although the driver integrated type in which the drive circuit is formed on the substrate is shown in this embodiment mode, the driver circuit is not necessarily required, and the drive circuit can be formed not on the substrate but outside.

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

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

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

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

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

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

Note that an epoxy resin, low melting point glass, or the like is preferably used as the sealant 505. In addition, it is desirable that these materials do not transmit moisture and oxygen as much as possible. In addition to glass and quartz substrates as materials used for the sealing substrate 506, FRP (Fiberg)
A plastic substrate made of lass-Reinforced Plastics, PVF (polyvinyl fluoride), polyester, acrylic or the like can be used.

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

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

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

As an electronic device to which a light emitting device is applied, for example, a television device (also referred to as a television or a television receiver), a monitor for a computer, a digital camera, a digital video camera, a digital photo frame, a mobile phone (mobile phone, mobile phone Also called telephone equipment),
Examples include large game machines such as portable game machines, portable information terminals, sound reproduction devices, and pachinko machines. A specific example of these electronic devices is shown in FIG.

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

The television set 7100 can be operated by an operation switch of the housing 7101 or a separate remote controller 7110. Channels and volume can be controlled with an operation key 7109 of the remote controller 7110, and an image displayed on the display portion 7103 can be manipulated. Further, the remote control 7110 may be provided with a display portion 7107 for displaying information output from the remote control 7110.

Note that the television set 7100 is provided with a receiver, a modem, and the like. The receiver can receive general television broadcasts, and can connect to a wired or wireless communication network via a modem to be unidirectional (sender to receiver) or bidirectional (bidirectional).
It is also possible to communicate information between the sender and the receiver, or between the receivers, etc.).

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

FIG. 9C illustrates a portable game machine, which includes two housings, a housing 7301 and a housing 7302, which are connected to be openable / closable by a connection portion 7303. 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 and a recording medium insertion portion 7307.
, LED lamp 7308, input means (operation key 7309, connection terminal 7310, sensor 73
11 (force, displacement, position, velocity, acceleration, angular velocity, number of rotations, distance, light, liquid, magnetism, temperature, chemical, voice, time, hardness, electric field, current, voltage, power, radiation, flow, humidity, (Including the function of measuring inclination, vibration, smell or infrared), microphone 7312) and the like. Of course, the configuration of the portable game machine is not limited to that described above, and at least the display unit 73
The light-emitting device may be used for both or one of the display portion 7305 and the display portion 7305, and other additional facilities can be provided as appropriate. The portable game machine illustrated in FIG. 9C has a function of reading out a program or data recorded in a recording medium and displaying the program or data on the display portion and performing wireless communication with another portable game machine to share information. It has a function. Note that the portable game machine illustrated in FIG. 9C can have various functions without limitation to the above.

FIG. 9D illustrates an example of a mobile phone. The mobile phone 7400 has a housing 7401
In addition to the display portion 7402 incorporated in the camera, the operation button 7403, the external connection port 7404, the speaker 7405, the microphone 7406, and the like are provided. Note that the cellular phone 7400 is manufactured using the light-emitting device for the display portion 7402.

Information can be input to the mobile phone 7400 illustrated in FIG. 9D by touching the display portion 7402 with a finger or the like. Further, operations such as making a call and creating an e-mail can be performed by touching the display portion 7402 with a finger or the like.

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

For example, in the case of making a call or text messaging, the display portion 7402 may be in a text input mode mainly for text input, and text input operation can be performed on the screen. In this case, it is preferable to display a keyboard or a number button on most of the screen of the display portion 7402.

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

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

In the input mode, a signal detected by the light sensor of the display portion 7402 is detected, and when there is no input by a touch operation on the display portion 7402, the screen mode is switched from the input mode to the display mode. You may control.

The display portion 7402 can also function as an image sensor. For example, the display unit 7
Person's authentication can be performed by touching the finger 402 with a palm or a finger to capture a palm print, a fingerprint, or the like.
In addition, when a backlight which emits near-infrared light or a sensing light source which emits near-infrared light is used for the display portion, an image of a finger vein, a palm vein, or the like can be taken.

FIGS. 10A and 10B illustrate a foldable tablet terminal. Figure 10 (A
Is open, and the tablet terminal includes the housing 9630, the display portion 9631a, the display portion 9631b, the display mode switching switch 9034, the power switch 9035, the power saving mode switching switch 9036, the clasp 9033, and the operation switch 9038. And. Note that the tablet terminal is manufactured by using a light-emitting device for one or both of the display portion 9631 a and the display portion 9631 b.

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

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

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

Further, the display mode switching switch 9034 can switch the display orientation such as vertical display or horizontal display, and can select switching between black and white display and color display. The power saving mode switching switch 9036 can optimize the display brightness in accordance with the amount of external light at the time of use detected by the light sensor incorporated in the tablet type terminal. The tablet type terminal may incorporate not only an optical sensor but also other detection devices such as a sensor for detecting inclination of a gyro, an acceleration sensor or the like.

10A shows an example in which the display areas of the display portions 9631 b and 9631 a are the same, but the present invention is not particularly limited, and one size may be different from the other size, and the display quality is also shown. It may be different. For example, a display panel in which one can perform higher definition display than the other may be used.

The tablet terminal is closed in FIG. 10B and the housing 9630 and the solar battery 9 are illustrated in FIG.
And 633, a charge and discharge control circuit 9634, a battery 9635, and a DCDC converter 9636. Note that in FIG. 10B, the battery 963 is an example of the charge and discharge control circuit 9634.
5 shows a configuration having a DCDC converter 9636.

Note that since the tablet terminal can be folded in half, the housing 9630 can be closed when not in use. Therefore, the display portion 9631 a and the display portion 9631 b can be protected.
It is excellent in durability, and can provide a tablet type terminal excellent in reliability also from the viewpoint of long-term use.

In addition to this, the tablet type terminal shown in FIGS. 10A and 10B has a function of displaying various information (still image, moving image, text image, etc.), calendar, date or time, etc. A function of displaying on the display portion, a touch input function of performing touch input operation or editing of information displayed on the display portion, a function of controlling processing by various software (programs), and the like can be provided.

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

In addition, the structure and operation of the charge and discharge control circuit 9634 illustrated in FIG.
C) and a block diagram will be described. In FIG. 10C, a solar cell 9633 and a battery 9 are shown.
635, DC-DC converter 9636, converter 9638, switches SW1 to SW3
, The display portion 9631, the battery 9635, the DCDC converter 963
6, the converter 9638, and the switches SW1 to SW3 correspond to the charge / discharge control circuit 9634 shown in FIG. 10B.

First, an example of operation in the case where electric power is generated by the solar battery 9633 by external light will be described. The electric power generated by the solar cell 9633 is boosted or lowered by the DCDC converter 9636 to a voltage for charging the battery 9635. And, the display portion 9631
When the power from the solar cell 9633 is used for the operation of the switch 913, the switch SW1 is turned on, and the converter 9638 boosts or steps down the voltage required for the display portion 9631. In addition, when display on the display portion 9631 is not performed, the switch SW1 is turned off, and the switch S1 is turned off.
It may be configured to charge the battery 9635 with W2 turned on.

Although the solar cell 9633 is shown as an example of the power generation means, it is not particularly limited,
The battery 9635 may be charged by another power generation unit such as a piezoelectric element (piezo element) or a thermoelectric conversion element (Peltier element). For example, a non-contact power transmission module that transmits and receives power wirelessly (without contact) to charge the battery, or another charging unit may be combined.

Needless to say, the electronic device illustrated in FIG. 10 is not particularly limited as long as the display unit described in the above embodiment is included.

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

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

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

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

In addition, by using a light emitting device for the surface of a table, the lighting device 8004 can have a function as a table. Note that by using a light-emitting device for part of other furniture, the lighting device can have a function as furniture.

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

The structure described in this embodiment can be used in appropriate combination with the structure described in any of the other embodiments.

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

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

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

After that, the substrate is introduced into a vacuum evaporation apparatus whose inside is depressurized to about 10 ^-4 Pa, and vacuum baking is performed at 170 ° C. for 30 minutes in a heating chamber in the vacuum evaporation apparatus. It was allowed to cool.

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

After reducing the pressure in the vacuum device to 10 ^-4 Pa, 1,3,5-tri (dibenzothiophene-4)
-Yl) benzene (abbreviation: DBT3P-II) and molybdenum oxide (VI) with DBT3
The hole injection layer 1111 was formed over the first electrode 1101 by co-evaporation such that P-II (abbreviation): molybdenum oxide = 4: 2 (mass ratio). The film thickness was 20 nm. Co-evaporation is an evaporation method in which a plurality of different substances are simultaneously evaporated from different evaporation sources.

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

Next, the light emitting layer 1113 was formed over the hole transporting layer 1112. 2- [3 ′-(dibenzothiophen-4-yl) biphenyl-3-yl] dibenzo [f, h] quinoxaline (abbreviation:
2mDBTBPDB q-II), N- (1,1'-biphenyl-4-yl) -N- [4-]
(9-phenyl-9H-carbazol-3-yl) phenyl] -9,9-dimethyl-9H
-Fluoren-2-amine (abbreviation: PCBBiF), (acetylacetonato) bis (6-)
tert-Butyl-4-phenylpyrimidinato) iridium (III) (abbreviation: [Ir (
tBuppm) ₂ (acac)]), 2mDBTBPDBq-II (abbreviation): PCBB
iF (abbreviation): [Ir (tBuppm) ₂ (acac)] (abbreviation) = 0.7: 0.3: 0
. After co-evaporation to be 05 (mass ratio) to form a first light emitting layer 1113 a with a thickness of 20 nm, 2m DBTBPDB q-II (abbreviation), N, N′-bis (9,9-dimethylfluorene-2 -Yl) -N, N'-di (biphenyl-4-yl) -1,4-phenylenediamine (abbreviation: FBi2P), bis {4,6-dimethyl-2- [5- (2,6-dimethylphenyl) ) -3- (3,5-Dimethylphenyl) -2-pyrazinyl-κN] phenyl-κC
} (2,8-Dimethyl-4,6-nonandionato-κ ² O, O ') iridium (III)
(Abbreviation: [Ir (dmdppr-dmp) ₂ (divm)]), 2mDBTBPDBq
-II (abbreviation): FBi2P (abbreviation): [Ir (dmdppr-dmp) ₂ (divm)
(Abbr.) = 0.8: 0.2: 0.05 (mass ratio) by co-evaporation to form a second light emitting layer 1113 b with a thickness of 20 nm; thus, a light emitting layer having a laminated structure 1113 was formed.

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

Lastly, aluminum was vapor-deposited to a thickness of 200 nm over the electron injection layer 1115 to form a second electrode 1103 to be a cathode, whereby a light-emitting element 1 was obtained. In the above-mentioned vapor deposition process, all vapor deposition used resistance heating.

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

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

«Operational Characteristics of Light-Emitting Element 1»
The operating characteristics of the manufactured light emitting element 1 were measured. The measurement was performed at room temperature (in the atmosphere kept at 25 ° C.).

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

According to FIG. 15, it was found that the light-emitting element 1 which is one embodiment of the present invention is a highly efficient element. Also, Table 2 below shows initial values of main characteristics of the light-emitting element 1 at around 1000 cd / ^{m 2.}

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

In addition, a light emission spectrum when current is supplied to the light-emitting element 1 at a current density of 25 mA / cm ² is shown in FIG. As shown in FIG. 17, the emission spectrum of the light emitting element 1 is 546 nm and 615 nm.
It has two peaks in the vicinity of nm, and each of them is a phosphorescent organometallic iridium complex [Ir (
It is suggested that it originates in the light emission of tBuppm) ₂ (acac)] and [Ir (dmdppr-dmp) ₂ (divm)].

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

Here, in FIG. 18, 2mDBTBPDBq which is a first organic compound having an electron transporting property.
Emission spectrum of a thin film of II-II, PCBBi which is a second organic compound having a hole transportability
Emission spectrum of thin film of F, and mixed film of 2mDBTBPDBq-II and PCBBiF (
The emission spectrum of the co-deposited film is shown. Further, FIG. 19 shows an emission spectrum of a thin film of 2mDBTBPDBq-II which is a first organic compound having an electron transporting property, an emission spectrum of a thin film of FBi2P which is a third organic compound having a hole transporting property, and 2mDBTBPDBq-
The emission spectrum of the mixed film (coevaporation film | membrane) of II and FBi2P is shown.

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

101 First electrode 102 Second electrode 103 EL layer 104 Hole injection layer 105 Hole transport layer 106 Light emitting layer 106 a First light emitting layer 106 b 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 that converts triplet excitation energy into light emission First organic compound 111 Second organic compound 112 Third organic compound 201 1 electrode (anode)
202 Second electrode (cathode)
203 EL layer 204 hole injecting layer 205 hole transporting layer 206 light emitting layer 206 a first light emitting layer 206 b second light emitting layer 207 electron transporting layer 208 electron injecting layer 209 light emitting substance 209 a third element for converting triplet excitation energy into light emission 1 light emitting substance 209 b second triplet for converting 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) nth (n-1) EL layer 302 (n) nth (n) EL layer 304 second electrode 305 charge generation layer (I)
305 (1) first charge generation layer (I)
305 (2) Second charge generation layer (I)
305 (n-2) The (n-2) th charge generation layer (I)
305 (n-1) th (n-1) charge generation layer (I)
401 Reflective electrode 402 Semi-transmissive / semi-reflective electrode 403 a First transparent conductive layer 403 b Second transparent conductive layer 404 B 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 drive circuit portion (source line drive circuit)
504a, 504b drive circuit unit (gate line drive circuit)
505 sealing material 506 sealing substrate 507 lead wiring 508 FPC (flexible printed circuit)
509 n-channel TFT
510 p-channel TFT
511 TFT for switching
512 TFT for current control
513 1st electrode (anode)
514 insulator 515 EL layer 516 second electrode (cathode)
517 light emitting element 518 space 7100 television apparatus 7101 housing 7103 display 7107 stand 7107 display 7109 operation keys 7110 remote control 720 main body 7202 housing 7203 display 7204 keyboard 7205 external connection port 7206 pointing device 7301 housing 7302 housing 7303 connecting unit 7304 display unit 7305 display unit 7306 speaker unit 7307 recording medium insertion unit 7308 LED lamp 7309 operation key 7310 connection terminal 7311 sensor 7312 microphone 7400 mobile phone 7401 housing 7402 display unit 7403 operation button 7404 external connection port 7405 speaker 7406 microphone 7406 8001 lighting system 8002 lighting system 8003 lighting system 8004 lighting system 9033 fastener 90 4 Display mode switching switch 9035 Power switch 9036 Power saving mode switching switch 9038 Operation switch 9630 Case 9631 Display area 9631a Display area 9631b Display area 9632a Touch panel area 9632b Touch panel area 9633 Solar battery 9634 Charge and discharge control circuit 9635 Battery 9636 DCDC converter 9637 operation key 9638 converter 9639 button

Claims (3)

Has a light emitting layer between the anode and the cathode,
The light emitting layer has a first light emitting layer and a second light emitting layer,
The first light emitting layer is located between the anode and the second light emitting layer,
The first light emitting layer includes a first material exhibiting thermally activated delayed fluorescence, a first organic compound, and a second organic compound.
The second light emitting layer includes a second material exhibiting thermally activated delayed fluorescence, the first organic compound, and a third organic compound.
The second organic compound has a lower highest occupied orbital level (HOMO level) than the third organic compound,
The first organic compound is a π-deficient heteroaromatic compound,
The second organic compound is a π excess heteroaromatic compound or an aromatic amine compound,
The light emitting device, wherein the third organic compound is a π excess heteroaromatic compound or an aromatic amine compound.   An electronic device comprising the light emitting device according to claim 1.   A lighting device comprising the light emitting device according to claim 1.