Light-emitting device

Abstract

Light-emitting device comprising: a first electrode; a first light-emitting layer; a second light-emitting layer; and a second electrode, wherein the first light-emitting layer is arranged between the first electrode and the second light-emitting layer, wherein the second light-emitting layer is arranged between the first light-emitting layer and the second electrode, the first light-emitting layer comprises: a first phosphorescent compound; a first host material; and a first organic compound the second light-emitting layer comprises: a second phosphorescent compound; and a second host material, where the first host material and the first organic compound form an exciplex, where the light emitted by the second phosphorescent compound has a longer wavelength than the light emitted by the first phosphorescent compound, where a difference between an emission peak wavelength of a photoluminescence spectrum of the first phosphorescent compound and a wavelength of a peak on the side of the longest wavelength of a function ε(λ)λ 4 the second phosphorescent compound is 0.2 eV or less when the emission peak wavelength and the peak wavelength are converted into energy, where λ denotes a wavelength, and where ε(λ) denotes a molar absorption coefficient at wavelength λ.

Description

Technical field

[0001] The present invention relates to a light-emitting device which uses an organic compound as a light-emitting substance. State of the art

[0002] In recent years, intensive research and development has been conducted on light-emitting elements that utilize electroluminescence (EL). The basic structure of such a light-emitting element consists of a layer containing a light-emitting substance (an EL layer) positioned between a pair of electrodes. By applying a voltage to this element, light emission can be obtained from the light-emitting substance.

[0003] These light-emitting elements are self-illuminating and offer advantages over liquid crystal displays because they provide high pixel visibility and eliminate the need for backlighting. Therefore, they are considered suitable for flat panel displays. Displays incorporating these light-emitting elements are also particularly advantageous because they can be thin and lightweight. Furthermore, a fast response time is a key characteristic of these elements.

[0004] Since the light-emitting layers of these light-emitting elements can be manufactured in the form of a film or foil, it is possible to provide planar light emission. Therefore, elements with large surface areas can be easily produced. This characteristic is difficult to achieve with point light sources, such as incandescent lamps and LEDs, or with linear light sources, such as fluorescent lamps. Therefore, light-emitting elements have great potential as planar light sources suitable for lighting and similar applications.

[0005] In the case of an organic EL cell, where an organic compound is used as the light-emitting substance and the EL layer is provided between an electrode pair, applying a voltage between the electrode pair causes the injection of electrons from a cathode and holes from an anode into the light-emitting EL layer, thus generating a current. Recombination of the injected electrons and holes excites the light-emitting organic compound to a more energized state, enabling it to emit light.

[0006] It should be noted that the excited state formed by an organic compound comprises an excited singlet state and an excited triplet state, and the luminescence of the excited singlet state (S*) is called fluorescence, whereas the luminescence of the excited triplet state (T*) is called phosphorescence. Additionally, the statistical generation ratio of these in the light-emitting element is expected to be as follows: S*:T* = 1:3.

[0007] In a compound that emits light from the excited singlet state (hereinafter referred to as a fluorescent compound) at room temperature, light emission from the excited triplet state (phosphorescence) is generally not observed; only light emission from the excited singlet state (fluorescence) is observed. Therefore, the internal quantum efficiency (the ratio of photons produced to the injected carriers) of a light-emitting element employing a fluorescent compound is assumed to have a theoretical limit of 25%, based on the S* to T* ratio of 1:3.

[0008] In contrast, a compound that emits light from the excited triplet state (hereafter referred to as a phosphorescent compound) exhibits light emission from the excited triplet state (phosphorescence). Furthermore, since simple intersystem crossing (i.e., the transition from an excited singlet state to an excited triplet state) occurs in a phosphorescent compound, the internal quantum efficiency can theoretically be increased to 100%. That is, a higher emission efficiency can be achieved than when using a fluorescent compound. For this reason, light-emitting elements are now being actively developed using phosphorescent compounds to obtain highly efficient light-emitting elements.

[0009] Light-emitting devices are described in US 2008 / 0160345A1, US 2002 / 0182441A1, US 2004 / 0178720A1 and in "BALDO, Marc A. [et al.]: Very high-efficiency green organic light-emitting devices based on electrophosphorescence. In: Applied Physics Letters, Vol. 75, 1999, No. 1, pp. 4-6".

[0010] A white light-emitting element disclosed in patent document 1 comprises a light-emitting region containing a variety of types of light-emitting dopants which emit phosphorescence. Reference patent document

[0011] Patent document 1 Japanese translation of the international application PCT JP 2004 - 522 276 A Disclosure of the invention

[0012] Although an internal quantum efficiency of 100% is theoretically possible in a phosphorescent compound, such high efficiency can hardly be achieved without optimizing the element structure or its combination with another material. In particular, for a light-emitting element comprising a variety of phosphorescent compounds with different bands (different color emissions), such as light-emitting dopants, it is difficult to obtain highly efficient light emission without considering not only energy transfer but also optimizing the efficiency of that energy transfer. Indeed, in patent document 1, even when all light-emitting dopants of a light-emitting element are phosphorescent compounds, the external quantum efficiency is approximately 3% to 4%.It is assumed that, even when the light extraction efficiency is taken into account, the internal quantum efficiency is 20% or less, which is too low for a phosphorescent light-emitting element.

[0013] In a multicolor light-emitting element that uses dopants exhibiting different emission colors, it is necessary not only to improve emission efficiency but also to achieve a good balance between the light emissions from the dopants with their different emission colors. Maintaining a balance between the light emissions of the dopants while simultaneously achieving high emission efficiency is not easy.

[0014] In light of the above, one embodiment of the present invention relates to providing a light-emitting element which uses a variety of types of light-emitting dopants and has a high emission efficiency. Another embodiment of the present invention relates to providing a light-emitting device, a display device, an electronic device, and a lighting device, each with reduced power consumption, in which the above-mentioned light-emitting element is used.

[0015] The invention is defined by the claims.

[0016] In one embodiment of the present invention, the focus is on the Förster mechanism, which is a mechanism of intermolecular energy transfer. Effective energy transfer via the Förster mechanism is achieved by employing a combination of molecules that allow for an overlap between the emission spectrum of the energy-providing molecules and the peak of the longest wavelength side of a characteristic curve obtained by multiplying the absorption spectrum of the energy-receiving molecule by a wavelength raised to the fourth energy level. One of the characteristics of the above energy transfer is that the energy transfer is not a general energy transfer from a host to a dopant, but rather an energy transfer from one dopant to another.The light-emitting element of an embodiment of the present invention can be obtained by using such a combination of dopants between which energy can be effectively transferred and forming an element structure such that dopant molecules are suitably isolated.

[0017] That is to say, one embodiment of the present invention is a light-emitting element comprising, between a pair of electrodes, a first light-emitting layer in which a first phosphorescent compound is dispersed in a first host material; and a second light-emitting layer in which a second phosphorescent compound, which emits light with a longer wavelength than the light emitted by the first phosphorescent compound, is dispersed in a second host material. A wavelength on the long-wavelength side of a function ε(λ,)λ 4The spectrum of the second phosphorescent compound overlaps with the phosphorescence spectrum F(λ) of the first phosphorescent compound. It should be noted that ε(λ) represents the molar absorption coefficient of each of the phosphorescent compounds and is a function of a wavelength λ.

[0018] Another embodiment of the present invention is a light-emitting element comprising, between a pair of electrodes, a first light-emitting layer in which a first phosphorescent compound is dispersed in a first host material; and a second light-emitting layer in which a second phosphorescent compound is dispersed in a second host material, wherein the second phosphorescent compound emits light with a longer wavelength than the light emitted by the first phosphorescent compound. A band with a peak of a phosphorescence spectrum of the first phosphorescent compound overlaps with a band with a peak on the long-wavelength side of a function ε(λ)λ. 4of the second phosphorescent compound. It should be noted that ε(λ) represents a molar absorption coefficient of each of the phosphorescent compounds and is a function of a wavelength λ.

[0019] Another embodiment of the present invention is a light-emitting element with the above structure, wherein the first light-emitting layer further comprises a first organic compound, the first host material and the first organic compound form an exciplex, and the light emitted by the first phosphorescent compound has a longer wavelength than the light emitted by the exciplex.

[0020] Yet another embodiment of the present invention is a light-emitting element with the above structure, in which an emission spectrum of the exciplex with a wavelength of the peak on the long-wavelength side of a function ε(λ,)λ 4the first phosphorescent compound overlaps. It should be noted that ε(λ) represents a molar absorption coefficient of each of the phosphorescent compounds and is a function of the wavelength λ.

[0021] Yet another embodiment of the present invention is a light-emitting element with the above structure, wherein a band with a peak of the emission spectrum of the exciplex is combined with a band with the peak on the long-wavelength side of the function ε(λ,)λ 4 the first phosphorescent compound overlaps. It should be noted that ε(λ) represents a molar absorption coefficient of each of the phosphorescent compounds and is a function of a wavelength λ.

[0022] Yet another embodiment of the present invention is a light-emitting element with the above structure, wherein the first phosphorescent compound has a phosphorescence peak in a range of 500 nm to 600 nm and the second phosphorescent compound has a phosphorescence peak in a range of 600 nm to 700 nm.

[0023] Yet another embodiment of the present invention is a light-emitting element with the above structure, wherein a recombination region of an electron and a hole is present in the first light-emitting layer.

[0024] Yet another embodiment of the present invention is a light-emitting element with the above structure, wherein the first light-emitting layer is arranged closer to the anode than the second light-emitting layer and wherein at least in the second light-emitting layer an electron transport property is higher than a hole transport property.

[0025] Yet another embodiment of the present invention is a light-emitting element with the above structure, wherein the first light-emitting layer is arranged closer to the anode than the second light-emitting layer, and both the first host material and the second host material exhibit electron transport properties. It should be noted that a material with electron transport properties is preferably a material in which the electron transport property is higher than the hole transport property.

[0026] Yet another embodiment of the present invention is a light-emitting element with the above structure, wherein the first light-emitting layer is arranged closer to a cathode than the second light-emitting layer and at least in the second light-emitting layer a hole transport property is higher than an electron transport property.

[0027] Yet another embodiment of the present invention is a light-emitting element with the above structure, wherein the first light-emitting layer is arranged closer to the cathode than the second light-emitting layer, and both the first host material and the second host material exhibit hole transport properties. It should be noted that a material with hole transport properties is preferably a material in which the hole transport property is higher than the electron transport property.

[0028] Yet another embodiment of the present invention is a light-emitting element with the above structure, wherein the first light-emitting layer and the second light-emitting layer are stacked in contact with each other.

[0029] Yet another embodiment of the present invention is a light-emitting device, a light-emitting display device, an electronic device and a lighting device, each containing a light-emitting element with the above structure.

[0030] It should be noted that the light-emitting device described in this category includes an image display device using a light-emitting element. Furthermore, the category of light-emitting device described in this description includes a module in which a light-emitting element is provided with a connection, such as an anisotropic conductive film or a TCP (tape carrier package); a module in which the top side of the TCP is provided with a printed circuit board; and a module in which an IC (integrated circuit) is directly attached to a light-emitting element by a COG (chip-on-glass) process. The category also includes light-emitting devices used as lighting devices or the like.

[0031] One embodiment of the present invention provides a light-emitting element with high emission efficiency. By using the light-emitting element, another embodiment of the present invention provides a light-emitting device, a light-emitting display device, an electronic device, and a lighting device, each of which has reduced power consumption. Brief description of the drawings Fig. Figures 1A to 1C show conceptual diagrams of light-emitting elements. Fig. 2A and Fig. Figure 2B shows the energy transfer in light-emitting layers. Fig. 3A and Fig. 3B explain the forester energy transmission. Fig. 4A and Fig. Figure 4B shows conceptual diagrams of an active-matrix light-emitting device. Fig. 5A and Fig. Figure 5B shows conceptual diagrams of a passive matrix light-emitting device. Fig. 6A and Fig. Figure 6B shows conceptual diagrams of structures of an active-matrix light-emitting device. Fig. Figure 7 shows a conceptual diagram of an active matrix light-emitting device. Fig. 8A and Fig. Figure 8B shows conceptual diagrams of a lighting device. Fig. 9A, Fig. 9B1, Fig. 9B2, Fig. 9C and Fig. 9D shows electronic device. Fig. Figure 10 shows an electronic device. Fig. Figure 11 shows a lighting device. Fig. Figure 12 shows a lighting device and a display device. Fig. Figure 13 shows display devices which are attached in the motor vehicle and lighting device. Fig. Figures 14A to 14C show an electronic device. Fig. Figure 15 shows the luminance-current efficiency properties of a light-emitting element 1. Fig. Figure 16 shows the voltage-luminance properties of a light-emitting element 1. Fig. Figure 17 shows the luminance-external quantum efficiency properties of a light-emitting element 1. Fig. Figure 18 shows the luminance-power-efficiency characteristics of a light-emitting element 1. Fig. Figure 19 shows an emission spectrum of a light-emitting element 1. Fig. 20A and Fig. 20B explain the Förster energy transfer in a light-emitting element 1. Fig. 21A and Fig. 21B explains the Förster energy transfer in a light-emitting element 1. Fig. 22 explains the Förster energy transfer in a light-emitting element 1. Fig. Figure 23 shows PL spectra of 2mDBTPDBq-II, PCBA1BP and a mixed foil or film of these. Fig. Figure 24 shows the luminance-current efficiency properties of a light-emitting element 2. Fig. Figure 25 shows the voltage-luminance properties of a light-emitting element 2. Fig. Figure 26 shows the luminance-external quantum efficiency properties of a light-emitting element 2. Fig. Figure 27 shows the luminance-power efficiency characteristics of a light-emitting element 2. Fig. Figure 28 shows an emission spectrum of a light-emitting element 2. Fig. Figure 29 shows the result of a reliability study of a light-emitting element 2. Fig. Figure 30 shows the luminance-current efficiency properties of a light-emitting element 3. Fig. Figure 31 shows the voltage-luminance properties of a light-emitting element 3. Fig. Figure 32 shows the luminance-external quantum efficiency properties of a light-emitting element 3. Fig. Figure 33 shows the luminance-power efficiency characteristics of a light-emitting element 3. Fig. Figure 34 shows an emission spectrum of a light-emitting element 3. Fig. Figure 35 shows the luminance-current efficiency properties of a light-emitting element 4. Fig. Figure 36 shows the voltage-luminance properties of a light-emitting element 4. Fig. Figure 37 shows the luminance-external quantum efficiency properties of a light-emitting element 4. Fig. Figure 38 shows the luminance-power efficiency characteristics of a light-emitting element 4. Fig. Figure 39 shows an emission spectrum of a light-emitting element 4. Fig. Figure 40 shows the luminance-current efficiency properties of a light-emitting element 5. Fig. Figure 41 shows the voltage-luminance properties of a light-emitting element 5. Fig. Figure 42 shows the luminance-external quantum efficiency properties of a light-emitting element 5. Fig. Figure 43 shows the luminance-power efficiency characteristics of a light-emitting element 5. Fig. Figure 44 shows an emission spectrum of a light-emitting element 5. Fig. 45A and Fig. 45B explains the Förster energy transfer in a light-emitting element 4. Fig. 46 explains the Förster energy transfer in a light-emitting element 4. Fig. 47A and Fig. 47B explains the Förster energy transfer in a light-emitting element 5. Fig. 48A and Fig. 48B explain the Förster energy transfer in a light-emitting element 5. Fig. 49 explains the Förster energy transfer in a light-emitting element 5. Best way to implement the invention

[0032] The following section describes embodiments of the present invention in detail with reference to the drawings. It should be noted that the present invention is not limited to the description given below, and it is clear to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, the present invention should not be understood as being limited to the embodiments described below. Design 1

[0033] First, a functional principle of a light-emitting element of an embodiment of the present invention is described. The key aspect of the present invention is that a first phosphorescent compound and a second phosphorescent compound, which emits light with a longer wavelength than the light emitted by the first phosphorescent compound, are used, and both the first and second phosphorescent compounds emit light efficiently, thereby obtaining a multi-colored light-emitting element with high efficiency.

[0034] As a general method for obtaining a multi-colored light-emitting element containing a phosphorescent compound, a process can be described in which a variety of types of phosphorescent compounds with different emission colors are dispersed in a host material in a suitable ratio. In such a process, the phosphorescent compound emitting light with the longest wavelength simply emits light, making it extremely difficult to design and control a structure (especially the concentration of the phosphorescent compounds in the host material) to obtain polychromatic light.

[0035] Another method for obtaining a multi-colored light-emitting element is a tandem structure, in which light-emitting elements with different emission colors are stacked on top of each other. For example, a blue-light-emitting element, a green-light-emitting element, and a red-light-emitting element are stacked in that order and emit light simultaneously, thus easily producing polychromatic light (in this case, white light). The element structure can be built and controlled relatively easily because the blue-light-emitting element, the green-light-emitting element, and the red-light-emitting element can be optimized independently. However, stacking the three elements increases the number of layers, making the fabrication more complex.Furthermore, if there is a problem with the electrical contact at the connection areas between the elements (called intermediate layers), an increase in the drive voltage can occur, i.e., a current loss can be caused.

[0036] In contrast, in the light-emitting element of one embodiment of the present invention, the first light-emitting layer, in which the first phosphorescent compound is dispersed in the first host material, and the second light-emitting layer, in which the second phosphorescent compound, which emits light with a longer wavelength than that emitted by the first phosphorescent compound, is dispersed in the second host material, are stacked between the electrode pair. Unlike a tandem structure, the first and second light-emitting layers can be placed in contact with each other.

[0037] An element structure of the light-emitting element described above in an embodiment of the present invention is shown in the Fig. 1A to 1C shown schematically. Fig. Figure 1C shows a first electrode 101, a second electrode 102, and an EL layer 103. The EL layer 103 contains at least one light-emitting layer 113, and other layers can be provided if suitable. In the Fig. The structure shown in Figure 1C assumes that a hole injection layer 111, a hole transport layer 112, an electron transport layer 114, and an electron injection layer 115 are provided. It should be noted that the first electrode 101 is assumed to serve as an anode and the second electrode 102 as a cathode.

[0038] The Fig. 1A and Fig. Figure 1B shows enlarged views of the light-emitting layer 113 of the light-emitting element. In each of the Fig. 1A and Fig. 1B are represented as a first light-emitting layer 113a, a second light-emitting layer 113b, the light-emitting layer 113 which is a combination of the two layers, a first phosphorescent compound 113Da, a second phosphorescent compound 113Db, a first host material 113Ha and a second host material 113Hb. Fig. Figure 1B shows a schematic diagram illustrating the case where the first light-emitting layer 113a also contains a first organic compound 113A. In each case, the phosphorescent compounds (the first and second phosphorescent compounds) are dispersed in the host materials, so that the phosphorescent compounds are isolated from each other by the host materials. It should be noted that the first and second host materials can be the same or different. The first light-emitting layer 113a can be located on the anode side and the second light-emitting layer 113b can be located on the cathode side, or the first light-emitting layer 113a can be located on the cathode side and the second light-emitting layer 113b can be located on the anode side.

[0039] In this case, energy transfer between the phosphorescent compounds via electron exchange interaction (known as the Dexter mechanism) is suppressed. In other words, a phenomenon can be prevented in which, after the first phosphorescent compound 113Da has been excited, the excitation energy is transferred to the second phosphorescent compound 113Db via the Dexter mechanism. Therefore, a phenomenon in which the second phosphorescent compound 113Db, which emits light with the longest wavelength, predominantly emits light can be suppressed. It should be noted that the second phosphorescent compound 113Db emits light predominantly in the case where an exciton is generated directly in the second light-emitting layer 113b; therefore, it is preferable for a recombination region of the carriers to be present in the first light-emitting layer 113a (i.e.,mainly the first phosphorescent compound 113Da is excited).

[0040] It should be noted that if the energy transfer of the first phosphorescent compound 113Da is completely suppressed, no light emission can be obtained from the second phosphorescent compound 113Db. Therefore, in one embodiment of the present invention, the element design is such that the excitation energy of the first phosphorescent compound 113Da is partially transferred to the second phosphorescent compound 113Db. Such energy transfer between isolated molecules is made possible by the use of dipole-dipole interaction (Förster mechanism).

[0041] The Förster mechanism is described below. The molecules that release excitation energy and the molecules that absorb excitation energy are hereinafter referred to as energy donors and energy acceptors, respectively. That is, in one embodiment of the present invention, both the energy donor and the energy acceptor are phosphorescent compounds and are isolated from each other by the host materials.

[0042] In the Förster mechanism, direct intermolecular contact is not necessary for energy transfer. Energy transfer occurs through a resonance phenomenon of dipolar oscillation between an energy donor and an energy acceptor. This resonance phenomenon causes the energy donor to release energy to the energy acceptor; therefore, the energy donor relaxes from an excited state to a ground state, and the energy acceptor in a ground state is excited. The rate constant kF The energy transfer through the Förster mechanism is expressed by a formula (1). formula 1 kF=9000c4K2ϕln10128π5n4NτR6∫F(ν)ε(ν)ν4dν

[0043] In formula (1), v represents a frequency, F(v) represents a normalized emission spectrum of an energy donor (a fluorescence spectrum for energy transfer from an excited singlet state and a phosphorescence spectrum for energy transfer from an excited triplet state), ε(v) represents a molar absorption coefficient of an energy acceptor, N represents Avogadro's number, n represents a refractive index of a medium, R represents an intermolecular distance between the energy donor and the energy acceptor, τ represents a measured lifetime of an excited state (fluorescence lifetime or phosphorescence lifetime), c represents the speed of light, ϕ represents a luminescence quantum yield (a fluorescence quantum yield for energy transfer from an excited singlet state and a phosphorescence quantum yield for energy transfer from an excited triplet state), and K 2K gives a coefficient (0 to 4) of the orientation of a transition dipole moment between the energy donor and the energy acceptor. It should be noted that K 2 = 2 / 3 in statistical terms.

[0044] As formula (1) suggests, the following can be stated as necessary conditions for energy transfer by the Förster mechanism (Förster energy transfer): 1. the energy donor and the energy acceptor are not too far apart (in terms of the distance R); 2. the energy donor emits light (in terms of the luminescence quantum yield ϕ); and 3. an emission spectrum of the energy donor overlaps with an absorption spectrum of the energy acceptor (in terms of the integral part).

[0045] As already mentioned in relation to the Fig. As described in Figures 1A to 1C, the phosphorescent compounds (the first and second phosphorescent compounds) are dispersed in their respective host materials and isolated from each other by the host materials; therefore, the distance R is at least one molecule length or more (i.e., 1 nm or more). Consequently, the excitation energy generated in the first phosphorescent compound is not completely transferred to the second phosphorescent compound by the Förster mechanism. Förster energy transfer at the distance R can occur when R is less than approximately 10 nm to 20 nm or is equal to 10 nm to 20 nm. To ensure that the distance R is at least one molecule length or more between the first and second phosphorescent compounds, the mass of the phosphorescent compound dispersed in the host material is preferably adjusted to a specific mass or less.Based on this, the concentration of the phosphorescent compound in the light-emitting layer is 10 wt.% or less. If the concentration of the phosphorescent compound is too low, it is difficult to achieve desired properties; therefore, in this embodiment, the concentration of the phosphorescent compound is preferably 0.1 wt.% or more and 10 wt.% or less. In particular, it is preferred that the first phosphorescent compound is contained in the first light-emitting layer 113a at a concentration of 0.1 wt.% or more and 5 wt.% or less.

[0046] The Fig. 2A and Fig. Figure 2B schematically represents the Förster energy transfer between the phosphorescent compounds in the light-emitting layer of an embodiment of the present invention, wherein the first phosphorescent compound 113Da and the second phosphorescent compound 113Db, which emits light with a longer wavelength than the light emitted by the first phosphorescent compound, are included. In each of the Fig. 2A and Fig. Figure 2B shows a structure in which the first light-emitting layer 113a and a second light-emitting layer 113b are stacked between an electrode 10 and an electrode 11. It should be noted that one of the electrodes 10 and 11 serves as an anode and the other as a cathode. As shown in Fig. 2A shows that an excited singlet state is initially shown, which is in the first phosphorescent compound 113Da (S a) is formed by intersystem crossing into an excited triplet state (T a ) converted. In other words, an exciton in the first light-emitting layer 113a is essentially converted to T a brought.

[0047] Subsequently, the energy of the exciton can be transferred to the T a -state from which something is converted into light emission, partly via the Förster mechanism into the excited triplet state of the second phosphorescent compound 113Db (T b) are transferred. This follows from the fact that the first phosphorescent compound 113Da exhibits a light-emitting property (possesses a high phosphorescence quantum yield ϕ) and that direct absorption, corresponding to an electron transition from a singlet ground state to an excited triplet state, is observed in the second phosphorescent compound 113Db (an absorption spectrum of an excited triplet state exists). If these conditions are met, a triplet-triplet Förster energy transfer from T is possible. a to T b possible.

[0048] It should be noted that an excited singlet state of the second phosphorescent compound 113Db (S b ) in many cases possesses a higher energy than the excited triplet state of the first phosphorescent compound 113Da (T a) and therefore in many cases does not contribute much to the above energy transfer. For this reason, the description is omitted here. It is unnecessary to point out that if the excited singlet state of the second phosphorescent compound is 113Db (S b ) a lower energy than the excited triplet state of the first phosphorescent compound 113Da (T a ) exhibits, a similar energy transfer can occur. In this case, the energy is transferred to the excited singlet state of the second phosphorescent compound 113Db (S b ) energy transferred to the excited triplet state of the second phosphorescent compound 113Db (T b ) transmitted via intersystem crossing to contribute to light emission.

[0049] It should be noted that, in order for the Förster energy transfer described above to occur efficiently between the phosphorescent compounds serving as dopants and not to the host materials, it is preferred that the absorption spectra of the first and second host materials do not lie within the emission range of the first phosphorescent compound 113Da. If energy is transferred directly between dopants without being transferred through the host material (especially the second host material), the formation of an extra pathway for energy transfer can be suppressed, and a high emission efficiency can be achieved, which is preferred.

[0050] Furthermore, the first host material preferably has a triplet excitation energy that is higher than that of the first phosphorescent compound, in order to avoid quenching the first phosphorescent compound.

[0051] As described above, a fundamental concept of an embodiment of the present invention is an elemental structure in which the first phosphorescent compound, which emits light with a shorter wavelength, is primarily excited in a state where the first and second phosphorescent compounds are isolated from each other by means of the host materials and the stack layer structure. Since energy is partially transferred via the Förster mechanism over a certain distance (20 nm or less) in such an elemental structure, the excitation energy of the first phosphorescent compound is partially transferred to the second phosphorescent compound. As a result, light emission can be obtained from both the first and second phosphorescent compounds.

[0052] More importantly in one embodiment of the present invention, the materials and the element structure are selected taking into account the above energy transfer.

[0053] For Förster energy transfer to occur, the energy donor must have a high luminescence quantum yield ϕ. Regarding the luminescence quantum yield, there is no problem in one embodiment of the present invention, since a phosphorescent compound (in particular, a light-emitting compound with a phosphorescence quantum yield of 0.1 or more) is used. An important point is that the integral term of formula (1) is large, i.e., an emission spectrum F(v) of the energy donor overlaps suitably with the molar absorption coefficient ε(v) of the energy acceptor.

[0054] In general, it is assumed that the emission spectrum F(v) of the energy donor must simply overlap with a wavelength range in which the molar absorption coefficient ε(v) of the energy acceptor is large (i.e., the product of F(v) and ε(v) must simply be large). However, this does not necessarily hold true for the Förster mechanism, since the integral term in formula (1) is inversely proportional to the frequency v, which is raised to the fourth power to exhibit a wavelength dependence.

[0055] For easier understanding, formula (1) is transformed here. Since v = c / λ, where λ is a wavelength of light, formula (1) can be transformed into formula (2). Formula 2 kF=9000K2ϕln10128π5n4NτR6∫F(λ)ε(λ)λ4dλ

[0056] In other words, it becomes clear that the longer the wavelength λ, the larger the integral term. Put more simply, it suggests that energy transfer occurs more readily on the longer wavelength side. That is, it is not simply a matter of F(λ) overlapping with the wavelength range in which the molar absorption coefficient ε(λ) is large. It is necessary that F(λ) overlaps with a range in which ε(λ) ≤ λ. 4 is large.

[0057] Therefore, in order to increase the efficiency of energy transfer from the first phosphorescent compound 113Da in the light-emitting element of an embodiment of the present invention, a phosphorescent compound is used which enables a band with a maximum value of an emission spectrum of the first phosphorescent compound 113Da to be combined with a band with a peak on the long-wavelength side of the function ε(λ)λ. 4the second phosphorescent compound 113Db overlaps when the second phosphorescent compound 113Db is used.

[0058] It should be noted that the wavelength of the peak of the long-wavelength side of the function ε(λ)λ 4 The emission spectrum of the second phosphorescent compound preferably overlaps with a phosphorescence spectrum F(λ) of the first phosphorescent compound. Furthermore, it is more preferred that a wavelength range in which the band with the above maximum value of the emission spectrum of the first phosphorescent compound 113Da has half the intensity of the above maximum value overlaps with a wavelength range in which the band with the above peak of the function ε(λ)λ 4 the second phosphorescent compound exhibits half the intensity of the peak above, although in this case the overlap between the spectra may be greater.

[0059] In a light-emitting element with the structure described above, high emission efficiency can be achieved and the phosphorescent compound can provide light emissions in a good balance.

[0060] To better understand such structures of the phosphorescent compound, an explanation is given below with reference to specific examples. As an example, a case is described in which a compound (1), which is shown below (Bis[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato-κ) 2O,O')iridium(III) (abbreviation: Ir(tBuppm)2(acac))) is used as the first phosphorescent compound 113Da and a compound (2) which is shown below (Bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: Ir(tppr)2(dpm))) is used as the second phosphorescent compound 113Db which emits light with a longer wavelength than the light emitted by the first phosphorescent compound 113Da.

[0061] Fig. 3A shows a molar absorption coefficient ε(λ) and ε(λ,)λ 4 of compound (2), which is the second phosphorescent compound. The molar absorption coefficient ε(λ) decreases on the side of a longer wavelength, ε(λ,)λ 4 However, it exhibits the peak at approximately 550 nm (corresponding to a triplet MLCT absorption band of compound (2)). This example makes it clear that the expression λ 4 influenced, ε(λ,)λ 4the second phosphorescent compound has the peak in the absorption band (triplet MLCT absorption band), located on the long-wavelength side.

[0062] Fig. Figure 3B shows a photoluminescence (PL) spectrum F(λ) of compound (1) and ε(λ)λ 4 of compound (2). Compound (1) is the first phosphorescent compound and emits green light with an emission peak at approximately 545 nm. To measure the peak on the long-wavelength side of ε(λ)λ 4 The PL spectrum F(λ) of the second phosphorescent compound largely overlaps with ε(λ)λ of the first phosphorescent compound. 4The energy transfer from the first phosphorescent compound to the second phosphorescent compound occurs via the Förster mechanism. It should be noted that in this case, where the peak corresponds to the triplet MLCT absorption band, the energy transfer is the triplet-triplet Förster energy transfer (TFörster). a -T b -Energy transfer in the Fig. 2A and Fig. 2B). At this point, the difference between the emission peak wavelength of the PL spectrum F(λ) of the first phosphorescent compound and the wavelength of the peak on the long-wavelength side of ε(λ)λ 4 of the second phosphorescent compound preferably 0.2 eV or less, in which case energy transfer occurs efficiently. The emission peak wavelength of the PL spectrum F(λ) of compound (1) is 546 nm and the wavelength of the peak on the long-wavelength side of ε(λ)λ 4The distance between junction (2) is 543 nm, with a difference of 3 nm, corresponding to 0.01 eV. Therefore, it is evident that the energy transfer between junction (1) and junction (2) occurs very efficiently.

[0063] It should be noted that, according to the above, it is preferred that the absorption spectrum of the second phosphorescent compound shows direct absorption on the long-wavelength side, corresponding to an electron transition from a singlet ground state to an excited triplet state (e.g., triplet-MLCT absorption). Such a structure leads to a high efficiency of the triplet-triplet energy transition, which is present in the Fig. 2A and Fig. 2B is shown.

[0064] To obtain the recombination region described above, in the case where the first light-emitting layer 113a is arranged on the side of the anode, at least the second light-emitting layer 113b may preferably have an electron transport property, and both the first light-emitting layer 113a and the second light-emitting layer 113b may have an electron transport property. In the case where the first light-emitting layer 113a is arranged on the side of the cathode, at least the second light-emitting layer 113b may preferably have a hole transport property, and both the first light-emitting layer 113a and the second light-emitting layer 113b may have a hole transport property.

[0065] Additionally, in the first light-emitting layer 113a, it is preferred that a band with a peak of the photoluminescence (PL) spectrum F(λ) of the first host material 113Ha is clearly distinguished from a band with the peak on the long-wavelength side of the function ε(λ,)λ 4 overlaps the first phosphorescent compound.

[0066] In general, however, it is difficult to find an overlap between a band with a peak of a photoluminescence (PL) spectrum F(λ) of a host material and a band with the peak on the long-wavelength side of the function ε(λ)λ. 4to achieve a guest material (first phosphorescent compound 113Da). The reason for this is that the photoluminescence (PL) of the host material is generally fluorescence, i.e., light emission from a higher energy level than that of phosphorescence. Therefore, there is a high probability that a triplet excitation energy level of the guest material, whose fluorescence spectrum lies on the long-wavelength side of the guest material's absorption spectrum at a wavelength close to that of the guest material (an excited triplet state of the guest material), will be lower than a triplet excitation energy level of the host material. If the triplet excitation energy level of the guest material is lower than the triplet excitation energy level of the host material, the triplet excitation energy of the guest material will be transferred to the host material, resulting in a decrease in emission efficiency.

[0067] Therefore, in this embodiment, it is preferred that the first light-emitting layer 113a further contains the first organic compound 113A and that the first host material 113Ha and the first organic compound 113A form an exciplex (also referred to as an excited complex) 113Ec ( Fig. 1B and Fig. 2B). In the Fig. 2B denotes electrodes 10 and 11, one of which serves as the anode and the other as the cathode. It should be noted that in the drawings, an excited singlet state and an excited triplet state of Exciplex 113Ec are represented by S e and T e is represented as an excited singlet state and an excited triplet state of the first phosphorescent compound 113Da is represented by S a and T a represented and an excited singlet state and an excited triplet state of the second phosphorescent compound 113Db is represented by S b and T bdepicted.

[0068] In this case, at the time of recombination of the carriers (electrons and holes) in the first light-emitting layer 113a, the first organic compound 113A, and the first host material 113Ha form the exciplex 113Ec by absorbing energy as a result of the recombination of electrons and holes. Fluorescence of the exciplex 113Ec exhibits a spectrum on the long-wavelength side compared to a fluorescence spectrum of the first organic compound 113A alone and a fluorescence spectrum of the first host material 113Ha alone, and also possesses the property that the excited singlet state S e and the excited triplet state T e The energy levels of Exciplex 113Ec are extremely close together. Therefore, if a band with a peak of a PL spectrum F(λ), which shows light emission from the excited state of Exciplex 113Ec, is correlated with the band on the long-wavelength side of the function ε(λ)λ4 of the guest material (the first phosphorescent compound 113Da) (which exhibits an absorption spectrum of an excited triplet state T a (corresponding to the guest material) overlaps, both the energy transfer of S e to T a as well as the energy transfer of T e to T a to be increased as much as possible. In this case, a difference between an emission peak wavelength of the Exciplex 113Ec and a wavelength of a peak of ε(λ,)λ concerns 4 of the guest material (the first phosphorescent compound 113Da) preferably 0.2 eV or less, in which case energy transfer occurs efficiently. Furthermore, the triplet excitation energy levels of the first organic compound 113A and the first host material 113Ha are preferably kept higher than the triplet excitation energy level of the first phosphorescent compound 113Da.

[0069] Part of the energy that is transferred to the first phosphorescent compound 113Da is transferred to the second phosphorescent compound 113Db, as described above, so that both the first phosphorescent compound 113Da and the second phosphorescent compound 113Db efficiently emit light.

[0070] It should be noted that the energy transfer from the excited triplet state (T e The conversion of exciplex 113Ec to the first phosphorescent compound 113Da occurs efficiently via the Dexter mechanism. Energy transfer from the excited singlet state (S e ) occurs efficiently through the Förster mechanism described above, thereby achieving sufficient energy transfer as a whole.

[0071] There is no particular restriction regarding the first organic compound 113A and the first host material 113Ha, as long as they can form an exciplex; a combination of a compound that tends to accept electrons (a compound with an electron-capturing property) and a compound that tends to accept holes (a compound with a hole-capturing property) is preferably used.

[0072] The following are examples of compounds that tend to accept electrons: a metal complex such as Bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (abbreviation: BeBq2), Bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminium(III) (abbreviation: BAlq), Bis(8-quinolinola-to)zinc(II) (abbreviation: Znq), Bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO) or Bis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ); a heterocyclic compound with a polyazole skeleton, such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (abbreviation: TAZ), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (abbreviation: OXD-7), 9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation: CO11), 2,2',2"-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole) (abbreviation: TPBI) or 2-[3-(Dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole (abbreviation: mDBTBIm-II);a heterocyclic compound with a diazine skeleton, such as 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-[3'-(9H-Carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mCzBPDBq), 4,6-Bis[3-(phenanthren-9-yl)phenyl]pyrimidine (abbreviation: 4,6mPnP2Pm) or 4,6-Bis[3-(4-dibenzothienyl)phenyl]pyrimidine (abbreviation: 4,6mDBTP2Pm-II);and a heterocyclic compound with a pyridine backbone, such as 3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation: 35DCzPPy) or 1,3,5-tri[3-(3-pyridyl)phenyl]benzene (abbreviation: TmPyPB). Among the above materials, a heterocyclic compound with a diazine backbone and a heterocyclic compound with a pyridine backbone exhibit high reliability and are therefore preferred. In particular, a heterocyclic compound with a diazine (pyrimidine or pyrazine) backbone exhibits high electron transport properties, which contribute to a reduction in the drive voltage.

[0073] The following are examples of compounds that tend to take on holes: a compound with an aromatic amine skeleton, such as 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB), N,N-bis(3-methylphenyl)-N,N-diphenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviation: TPD), 4,4'-bis[N-(spiro-9,9'-bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB), 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP), 4-phenyl-3'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: mBPAFLP), 4-Phenyl-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), 4,4'-Diphenyl-4"-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBBi1BP), 4-(1-Naphthyl)-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBANB), 4,4'-Di(1-naphthyl)-4"-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB), 9,9-Dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-amine (abbreviation: PCBAF) or N-Phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]spiro-9,9'-bifluo-ren-2-amine (abbreviation: PCBASF); a compound with a carbazole skeleton, such as 1,3-bis(N-carbazolyl)benzene (abbreviation: mCP), 4,4'-di(N-carbazolyl)biphenyl (abbreviation: CBP), 3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviation: CzTP) or 3,3'-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP); a compound with a thiophene skeleton, such as 4,4',4"-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), 2,8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene (abbreviation: DBTFLP-III) or 4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene (abbreviation: DBTFLP-IV); and a compound with a furan skeleton, such as 4,4',4"-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviation: DBF3P-II) or 4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran (abbreviation: mmDBFFLBi-II). Among the above materials, a compound with an aromatic amine skeleton and a compound with a carbazole skeleton are preferred.because these connections are very reliable and have high hole transport properties, contributing to a reduction in the drive voltage.

[0074] The first organic compound 113A and the first host material 113Ha are not limited to the compounds as long as they can form an exciplex, the band with the peak of the photoluminescence (PL) spectrum F(λ) of the exciplex with the band with peak on the long-wavelength side of the function ε(λ,)λ 4 overlaps the first phosphorescent compound and the peak of an emission spectrum of the exciplex has a longer wavelength than a peak of the emission spectrum of the first phosphorescent compound 113Da.

[0075] It should be noted that in the case where a compound that tends to accept electrons and a compound that tends to accept holes are used as the first organic compound 113A and the first host material 113Ha, the carrier balance can be controlled by the mixing ratio of the compounds. In particular, the ratio of the first organic compound 113A to the first host material 113Ha is preferably from 1:9 to 9:1.

[0076] In this structure, the first host material 113Ha and the first organic compound 113A are selected such that an exciplex is formed which allows the band with the peak of the photoluminescence (PL) spectrum F(λ) of the exciplex to be combined with the band with the peak on the long-wavelength side of the function ε(λ,)λ 4 The first phosphorescent compound overlaps. It is preferred that the overlap between the bands be as large as possible.

[0077] It should be noted that a peak occurs on the long-wavelength side of the function ε(λ,)λ 4 The first phosphorescent compound preferably overlaps with the photoluminescence (PL) spectrum F(λ) of the exciplex. Furthermore, it is more preferred that a wavelength range in which the band with the peak of the photoluminescence (PL) spectrum F(λ) of the exciplex has half the intensity of the peak overlap above with a wavelength range in which the band with the peak of the function ε(λ,)λ 4 the first phosphorescent compound exhibits half the intensity of the peak above, although in this case the overlap between the spectra may be greater.

[0078] In the structure, energy can be effectively transferred from the exciplex, formed from the first host material 113Ha and the first organic compound 113A, to the first phosphorescent compound 113Da to increase energy transfer efficiency, thereby obtaining a light-emitting element with a higher external quantum efficiency. Design 2

[0079] In this embodiment, a detailed example of the structure of the light-emitting element, which is described in embodiment 1, is given below with reference to the Fig. Described in sections 1A to 1C.

[0080] In this embodiment, a light-emitting element comprises an EL layer containing a plurality of layers, located between a pair of electrodes. Specifically, the light-emitting element includes the first electrode 101, the second electrode 102, and the EL layer 103 positioned between the first electrode 101 and the second electrode 102. It should be noted that in this embodiment, the description is based on the assumption that the first electrode 101 acts as an anode and the second electrode 102 as a cathode. In other words, if a voltage is applied between the first electrode 101 and the second electrode 102 such that the potential of the first electrode 101 is higher than that of the second electrode 102, light emission can be obtained.

[0081] Since the first electrode 101 serves as the anode, it is preferably formed using metals, alloys, electrically conductive compounds with a high work function (in particular, a work function of 4.0 eV or more), mixtures thereof, and the like. In particular, examples include indium tin oxide (ITO), indium tin oxide containing silicon or silicon dioxide, indium zinc oxide, indium oxide containing tungsten oxide and zinc oxide (IWZO), and the like. Films or foils of these electrically conductive metal oxides are generally formed by a sputtering process, but can also be formed by a sol-gel process or the like. In one example of the manufacturing process, indium zinc oxide is deposited by a sputtering process using a target obtained by adding 1 wt.% to 20 wt.% zinc oxide to indium oxide.Furthermore, a film or foil of indium oxide containing tungsten oxide and zinc oxide (IWZO) can be formed by a sputtering process using a target in which tungsten oxide and zinc oxide are added to indium oxide at 0.5 wt% to 5 wt% and 0.1 wt% to 1 wt%, respectively. Other materials that can be used include gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), nitrides of metallic materials (e.g., titanium nitride), and the like. Graphene can also be used. It should be noted that if a composite material described later is used as a layer in contact with the first electrode 101 in the EL layer 103, an electrode material can be selected independently of the work function.

[0082] There is no particular restriction regarding the stacked layer structure of the EL layer 103, as long as the EL layer comprises the light-emitting layer 113, which has a structure similar to that described in embodiment 1. For example, the EL layer 103 can be formed by combining a hole injection layer, a hole transport layer, the light-emitting layer, an electron transport layer, an electron injection layer, a carrier blocking layer, an intermediate layer, and the like as appropriate. In this embodiment, the EL layer 103 has a structure in which the hole injection layer 111, the hole transport layer 112, the light-emitting layer 113, the electron transport layer 114, and the electron injection layer 115 are stacked on the first electrode 101 in that order. The materials contained in the layers are specified below.

[0083] The injection-molded layer is a layer containing a substance with high injection properties. Molybdenum oxide, vanadium oxide, ruthenium oxide, tungsten oxide, manganese oxide, or similar substances can be used. Alternatively, the hole injection layer 111 can be formed using a phthalocyanine-based compound such as phthalocyanine (abbreviation: H2Pc) or copper phthalocyanine (abbreviation: CuPc), an aromatic amine compound such as 4,4'-Bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation: DPAB) or N,N-Bis{ 4-[bis(3-methylphenyl)amino]phenyl}-N,N-diphenyl-(1,1'-biphenyl)-4,4'-diamine (abbreviation: DNTPD), a high molecular weight compound such as poly(ethylenedioxythiophene) / poly(styrenesulfonic acid) (PEDOT / PSS) or the like.

[0084] Alternatively, a composite material can be used for the hole injection layer 111, in which a substance with hole-transporting properties contains a substance with acceptor properties. It should be noted that the use of such a substance with hole-transporting properties, which contains a substance with acceptor properties, allows the selection of a material used to form an electrode, regardless of its work function. In other words, in addition to a material with a high work function, a material with a low work function can also be used as the first electrode 101. Examples of substances with acceptor properties include 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F4-TCNQ), chloranil, and the like. Transition metal oxides can also be mentioned.Oxides of metals belonging to groups 4 to 8 of the periodic table can be cited. In particular, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide are preferred because of their high electron-accepting properties. Among these, molybdenum oxide is especially preferred because it is stable in air, has low hygroscopic properties, and is easily processed.

[0085] Any of the many organic compounds, such as aromatic amines, carbazole derivatives, aromatic hydrocarbons, and high-molecular-weight compounds (e.g., oligomers, dendrimers, or polymers), can be used as the substance with hole transport properties for the composite material. It should be noted that the organic compound used for the composite material is preferably one with high hole transport properties. In particular, a substance with a hole mobility of 10 -6 cm 2 / Vs or more are preferably used. Organic compounds that can be used as the substance with hole transport properties in the composite material are specifically listed below.

[0086] Examples of aromatic amine compounds are N,N-Di(p-tolyl)-N,N-diphenyl-p-phenylenediamine (abbreviation: DTDPPA), 4,4'-Bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation: DPAB), N,N-Bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N-diphenyl-(1,1'-biphenyl)-4,4'-diamine (abbreviation: DNTPD), 1,3,5-Tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene (abbreviation: DPA3B) and the like.

[0087] Specific examples of the carbazole derivatives that can be used for the composite material are 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: PCzPCN1) and the like.

[0088] Other examples of carbazole derivatives that can be used for the composite material are 4,4'-Di(N-carbazolyl)biphenyl (abbreviation: CBP), 1,3,5-Tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB), 9-[4-(10-Phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA), 1,4-Bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene and the like.

[0089] Examples of aromatic hydrocarbons that can be used for the composite material are 2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA), 2-tert-butyl-9,10-di(1-naphthyl)anthracene, 9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA), 2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA), 9,10-di(2-naphthyl)anthracene (abbreviation: DNA), 9,10-diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene (abbreviation: t-BuAnth). 9,10-Bis(4-methyl-1-naphthyl)anthracene (abbreviation: DMNA), 2-tert-butyl-9,10-bis[2-(1-naphthyl)phenyl]anthracene, 9,10-bis[2-(1-naphthyl)phenyl]anthracene, 2,3,6,7-tetramethyl-9,1 0-di(1-naphthyl)anthracene, 2,3,6,7-tetramethyl-9,10-di(2-naphthyl)-anthracene, 9,9'-bianthryl, 10,10'-diphenyl-9,9'-bianthryl, 10,10'-bis(2-phenylphenyl)-9,9'-bianthryl, 10,10'-Bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9'-bianthryl, Anthracene, Tetracene, Rubrene, Perylene, 2,5,8,11-Tetra(tert-butyl)perylene and the like.Pentacene, coronene, or similar compounds can also be used. The aromatic hydrocarbon has a hole mobility of 1 x 10. -6 cm 2 A material with a value of / Vs or more and which has 14 to 42 carbon atoms is particularly preferred.

[0090] It should be noted that the aromatic hydrocarbons that can be used for the composite material may have a vinyl backbone. Examples of aromatic hydrocarbons with a vinyl group are 4,4'-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi), 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA), and the like.

[0091] A high molecular weight compound such as poly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA), poly[N-(4'-{N'-[4'-(4'-diphenylamino)phenyl]phenyl-N'-phenyl-amino}phenyl)methacrylamide] (abbreviation: PTPDMA) or poly[N,N'-bis(4'-butylphenyl)-N,N'-bis(phenyl)benzidine] (abbreviation: poly-TPD) can also be used.

[0092] By providing a hole injection layer, a high hole transport property can be achieved to allow a light-emitting element to have a low drive voltage.

[0093] The hole transport layer 112 is a layer which contains a substance with a hole transport property. Examples of substances with hole transport properties are aromatic amine compounds, such as 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB), N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviation: TPD), 4,4',4"-tris(N,N-diphenylamino)triphenylamine (abbreviation: TDATA), 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), 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP) and the like. The substances mentioned here exhibit high hole transport properties and are mainly those with a hole mobility of 10 -6 cm 2 / Vs or more. An organic compound, given as an example of the substance with hole-transporting properties in the composite material described above, can also be used for hole-transport layer 112. A high-molecular-weight compound, such as poly(N-vinylcarbazole) (abbreviation: PVK) or poly(4-vinyltriphenylamine) (abbreviation: PVTPA), can also be used. It should be noted that the layer containing a substance with hole-transporting properties is not limited to a single layer and can be a stack of two or more layers containing any of the above substances.

[0094] The light-emitting layer 113 is a layer containing the first phosphorescent compound and the second phosphorescent compound. Since the light-emitting layer 113 has a structure similar to that described in embodiment 1, the light-emitting element in this embodiment can exhibit extremely high emission efficiency. Reference is made to embodiment 1 for the main structures of the light-emitting layer 113.

[0095] There is no particular restriction on the materials used as the first and second phosphorescent compounds yyin of the light-emitting layer 1q13, as long as they exhibit the relationship described in embodiment 1. The following may be cited as examples of the first and second phosphorescent compounds.

[0096] The examples are an organometallic iridium complex with a 4H-triazole skeleton, such as Tris{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-κN 2]phenyl-κC}iridium(III) (abbreviation: Ir(mpptz-dmp)3), Tris(5-methyl-3,4-diphenyl-4H-1,2,4-triazolato)iridium(III) (abbreviation: Ir(Mptz)3) or Tris[4-(3-biphenyl)-5-isopropyl-3-phenyl-4H-1,2,4-triazolato]iridium(III) (abbreviation: Ir(iPrptz-3b)3); an organometallic iridium complex with a 1H-triazole skeleton, such as Tris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III) (abbreviation: Ir(Mptz1-mp)3) or Tris(1-methyl-5-phenyl-3-propyl-1H1,2,4-triazolato)iridium(III) (abbreviation: Ir(Prptz1-Me)3); an organometallic iridium complex with an imidazole skeleton, such as fac-Tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole]iridium(III) (abbreviation: Ir(iPrpmi)3) or Tris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato]iridium(III) (abbreviation: Ir(dmpimpt-Me)3); and an organometallic iridium complex in which a phenylpyridine derivative with an electron-withdrawing group is a ligand, such as Bis[2-(4',6'-difluorophenyl)pyridinato-N,C 2'Iiridium(III)tetrakis(1-pyrazolyl)borate (abbreviation: FIr6), Bis[2-(4',6'-difluorophenyl)pyridinato-N,C 2' Iiridium(III) picolinate (abbreviation: FIrpic), Bis{2-[3',5'-bis(trifluoromethyl)phenyl]pyridinato-N,C 2'}iridium(III)picolinate (abbreviation: Ir(CF3ppy)2(pic)) or Bis[2-(4',6'-difluorophenyl)pyridinato-N,C 2'Iridium(III) acetylacetonate (abbreviation: Flracac). These are compounds that emit blue phosphorescence and exhibit an emission peak at 440 nm to 520 nm. Among the compounds mentioned above, an organometallic iridium complex with a polyazole skeleton, such as a 4H-triazole skeleton, a 1H-triazole skeleton, or an imidazole skeleton, exhibits a high hole-trapping property.Therefore, it is preferred that each of these compounds, which is used as the first phosphorescent compound in the light-emitting element of an embodiment of the present invention, is positioned closer to the cathode than the second light-emitting layer, and that the second light-emitting layer has hole-transport properties (in particular, the second host material is a hole-transport material), in which case a recombination region of the supports can be easily controlled to be located in the first light-emitting layer. It should be noted that an organometallic iridium complex with a 4H-triazole framework exhibits excellent reliability and emission efficiency and is therefore particularly preferred.

[0097] Other examples include an organometallic iridium complex with a pyrimidine skeleton, such as tris(4-methyl-6-phenylpyrimidinato)iridium(III) (abbreviation: Ir(mppm)3), tris(4-t-butyl-6-phenyl-pyrimidinato)iridium(III) (abbreviation: Ir(tBuppm)3), (acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III) (abbreviation: Ir(mppm)2(acac)), (acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III) (abbreviation: Ir(tBuppm)2(acac)), (acetylacetonato)bis[6-(2-norbornyl)-4-phenylpyrimidinato]iridium(III) (abbreviation: Ir(nbppm)2(acac)). (Acetylacetonato)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinato]iridium(III) (abbreviation: Ir(mpmppm)2(acac)) or (Ace-tylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: Ir(dppm)2(acac));an organometallic iridium complex with a pyrazine skeleton, such as (acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III) (abbreviation: Ir(mppr-Me)2(acac)) or (acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III) (abbreviation: Ir(mppr-iPr)2(acac)); an organometallic iridium complex with a pyridine skeleton, such as Tris(2-phenylpyridinato-N,C; 2' )iridium(III) (abbreviation: Ir(ppy)3), Bis(2-phenylpyridinato-N,C 2' )iridium(III)acetylacetonate (abbreviation: Ir(ppy)2(acac)), Bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation: Ir(bzq)2(acac)), Tris(benzo[h]quinolinato)iridium(III) (abbreviation: Ir(bzq)3), Tris(2-phenylquinolinato-N,C 2' )iridium(III) (abbreviation: Ir(pq)3) or bis(2-phenylquinolinato-N, C 2Iridium(III) acetylacetonate (abbreviation: Ir(pq)₂(acac)); and a rare-earth metal complex, such as tris(acetylacetonato)(monophene-anthroline)terbium(III) (abbreviation: Tb(acac)₃(Phen)). These are mainly compounds that emit green phosphorescence and exhibit an emission peak at 500 nm to 600 nm. Among the above compounds, an organometallic iridium complex with a diazine framework, such as a pyrimidine or pyrazine framework, exhibits low hole-trapping and high electron-trapping properties.Therefore, it is preferred that each of these compounds be used as the first phosphorescent compound in the light-emitting element of an embodiment of the present invention, that the first light-emitting layer be positioned closer to the anode than the second light-emitting layer, and that the second light-emitting layer have electron-transport properties (in particular, that the second host material is an electron-transport material), whereby in this case a recombination region of the carriers can be easily controlled to be located in the first light-emitting layer. It should be noted that an organometallic iridium complex with a pyrimidine framework exhibits distinctively high reliability and emission efficiency and is therefore particularly preferred.

[0098] Other examples include an organometallic iridium complex with a pyrimidine skeleton, such as Bis[4,6-bis(3-methylphenyl)pyrimidinato](diisobutylylmethano)iridium(III) (abbreviation: Ir(5mdppm)2(dibm)), Bis[4,6-bis(3-methylphenyl)pyrimidinato](dipivaloylmethanato)iridium(III) (abbreviation: Ir(5mdppm)2(dpm)) or Bis[4,6-di(naphthalen-1-yl)pyrimidinato](dipivaloylmetha-nato)iridium(III) (abbreviation: Ir(d1npm)2(dpm)); an organometallic iridium complex with a pyrazine skeleton, such as (acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III) (abbreviation: Ir(tppr)2(acac)), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: Ir(tppr)2(dpm)) or (acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III) (abbreviation: Ir(Fdpq)2(acac)); an organometallic iridium complex with a pyridine skeleton, such as Tris(1-phenylisoquinolinato-N,C 2' )iridium(III) (abbreviation: Ir(piq)3) or Bis(1-phenylisoquinolina-to-N,C 2Iridium(III) acetylacetonate (abbreviation: Ir(piq)2(acac)); a platinum complex, such as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrinplatinum(II) (abbreviation: PtOEP); and a rare-earth metal complex, such as tris(1,3-diphenyl-1,3-propanedonato)(monophenanthroline)europium(III) (abbreviation: Eu(DBM)3(Phen)) or tris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III) (abbreviation: Eu(TTA)3(Phen)). These are compounds that emit red phosphorescence and exhibit an emission peak at 600 nm to 700 nm. Among the above materials, an organometallic iridium complex with a diazine framework, such as a pyrimidine framework or a pyrazine framework, exhibits a low hole simplicity property and a high electron capture property.Therefore, it is preferred that an organometallic iridium complex with a diazine framework is used as the second phosphorescent compound, that the first light-emitting layer is positioned closer to the cathode than the second light-emitting layer, and that the second light-emitting layer exhibits hole-transport properties (in particular, that the second host material is a hole-transport material), thereby allowing for easy control of the recombination region of the supports so that it is located in the first light-emitting layer. It should be noted that an organometallic iridium complex with a pyrimidine framework exhibits distinctively high reliability and emission efficiency and is therefore particularly preferred.Furthermore, since an organometallic iridium complex with a pyrazine framework can provide red light emission with preferred chromaticity, the use of the organometallic iridium complex in a white light-emitting element improves the color rendering property of the white light-emitting element.

[0099] It is also possible to select a first phosphorescent material and a second phosphorescent material, as described in relation to embodiment 1, from known phosphorescent materials in addition to the phosphorescent materials above.

[0100] It should be noted that instead of the phosphorescent compounds (the first phosphorescent compound 113a and the second phosphorescent compound 113b), materials exhibiting thermally activated delayed fluorescence, i.e., thermally activated delayed fluorescence (TADF) materials, can be used. Here, the term "delayed fluorescence" refers to light emission with a spectrum similar to that of normal fluorescence and an extremely long lifetime. The lifetime is 10 -6 Seconds or more, preferably 10 -3Seconds or more. Specific examples of thermally activated delayed-release fluorescent materials include a fullerene, a fullerene derivative thereof, an acridine derivative such as proflavin and eosin. Alternatively, a metal-containing porphyrin can be used, such as a porphyrin containing magnesium (Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium (In), or palladium (Pd). Examples of metal-containing porphyrins include a protoporphyrin tin fluoride complex (abbreviation: SnF2(Proto IX)), a mesoporphyrin tin fluoride complex (abbreviation: SnF2(Meso IX)), a hematoporphyrin tin fluoride complex (abbreviation: SnF2(Hemato IX)), a coproporphyrin tetramethyl ester tin fluoride complex (abbreviation: SnF2(Copro III-4Me)), an octaethylporphyrin tin fluoride complex (abbreviation: SnF2(OEP)), an etioporphyrin tin fluoride complex (abbreviation: SnF2(Etio I)), and an octaethylporphyrin platinum chloride complex (abbreviation: PtCl2(OEP)).Alternatively, a heterocyclic compound containing an n-electron-rich heteroaromatic ring and a π-electron-deficient heteroaromatic ring can be used, such as 2-(biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-a]carbazol-11-yl)-1,3,5-triazine (abbreviation: PIC-TRZ). It should be noted that a material in which the π-electron-rich heteroaromatic ring is directly bonded to the π-electron-deficient heteroaromatic ring is particularly preferred, since the donor property of the π-electron-rich heteroaromatic ring and the acceptor property of the π-electron-deficient heteroaromatic ring are both enhanced, and the energy difference between the S1 level and the T1 level becomes small.

[0101] There is no particular restriction on the materials that can be used as the first and second host materials; a variety of carrier transport materials can be selected and appropriately combined, so that a Fig. The element structure shown in 1A to 1C is obtained.

[0102] The following are examples of host material with an electron transport property: a metal complex such as Bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (abbreviation: BeBq2), Bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminium(III) (abbreviation: BAlq), Bis(8-quinolinola-to)zinc(II) (abbreviation: Znq), Bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO) or Bis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ); a heterocyclic compound with a polyazole skeleton, such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (abbreviation: TAZ), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (abbreviation: OXD-7), 9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation: CO11), 2,2',2"-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole) (abbreviation: TPBI) or 2-[3-(Dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole (abbreviation: mDBTBIm-II);a heterocyclic compound with a diazine skeleton, such as 2-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2m DBTPD Bq-li), 2-[3'-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), 2-[3'-(9H-Carbazol-9-yl)biphenyl-3-yl]dibenzo[fh]quinoxaline (abbreviation: 2mCzBPDBq), 4,6-Bis[3-(phenanthren-9-yl)phenyl]pyrimidine (abbreviation: 4,6mPnP2Pm) or 4,6-Bis[3-(4-dibenzothienyl)phenyl]pyrimidine (abbreviation: 4,6mDBTP2Pm-II);and a heterocyclic compound with a pyridine backbone, such as 3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation: 35DCzPPy) or 1,3,5-tri[3-(3-pyridyl)phenyl]benzene (abbreviation: TmPyPB). Among the above materials, a heterocyclic compound with a diazine backbone and a heterocyclic compound with a pyridine backbone exhibit high reliability and are therefore preferred. In particular, a heterocyclic compound with a diazine (pyrimidine or pyrazine) backbone exhibits high electron transport properties, contributing to a reduction in the drive voltage.

[0103] The following are examples of host material with hole transport properties: a compound with an aromatic amine skeleton, such as 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB), N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviation: TPD), 4,4'-bis[N-(spiro-9,9'-bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB), 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP), 4-phenyl-3'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: mBPAFLP), 4-Phenyl-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), 4,4'-Diphenyl-4"-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBBi1BP), 4-(1-Naphthyl)-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBANB), 4,4'-Di(1-naphthyl)-4"-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB), 9,9-Dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-amine (abbreviation: PCBAF) or N-Phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]spiro-9,9'-bifluo-ren-2-amine (abbreviation: PCBASF); a compound with a carbazole skeleton, such as 1,3-bis(N-carbazolyl)benzene (abbreviation: mCP), 4,4'-di(N-carbazolyl)biphenyl (abbreviation: CBP), 3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviation: CzTP) or 3,3'-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP); a compound with a thiophene skeleton, such as 4,4',4"-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), 2,8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene (abbreviation: DBTFLP-III), or 4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene (abbreviation: DBTFLP-IV); and a compound with a furan skeleton, such as 4,4',4"-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviation: DBF3P-II) or 4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran (abbreviation: mmDBFFLBi-II). Among the above materials, a compound with an aromatic amine skeleton and a compound with a carbazole skeleton are preferred.because these connections are very reliable and have high hole transport properties, contributing to a reduction in the drive voltage,

[0104] Host materials can be selected from known substances, including those listed above. It should be noted that the host materials should preferably be substances with a triplet energy level (energy gap between a ground state and an excited triplet state) that is larger than that of the phosphorescent compound. It is preferred that these host materials do not exhibit an absorption spectrum in the blue wavelength region. In particular, an absorption edge of the absorption spectrum is preferably located at 440 nm or below.

[0105] To form the light-emitting layer 113 with the structure described above, co-evaporation can be carried out using a vacuum evaporation process, or alternatively an inkjet process, a spin coating process, a dipping process or the like, using a mixed solution.

[0106] The electron transport layer 114 is a layer containing a substance with electron transport properties. For example, a layer containing a metal complex with a quinoline or benzoquinoline skeleton, such as tris(8-quinolinolato)aluminium (abbreviation: Alq), tris(4-methyl-8-quinolinolato)aluminium (abbreviation: Almq3), bis(10-hydroxyben-zo[h]quinolinato)beryllium (abbreviation: BeBq2), or bis(2-methyl-8-quinolinolato)(4-phenylphen-nolato)aluminium (abbreviation: BAlq), or the like, can be used. Alternatively, a metal complex with an oxal-based or thiazole-based ligand, such as Bis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation: Zn(BOX)2) or Bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation: Zn(BTZ)2) or the like, can be used.In addition to metal complexes such as 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-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (abbreviation: TAZ), bathophenanthroline (abbreviation: BPhen), bathocuproine (abbreviation: BCP), or similar compounds, the following substances can also be used. The substances mentioned here exhibit high electron transport properties and are primarily those with an electron mobility of 10. -6 cm 2 / Vs or more. It should be noted that any of the host materials with electron properties described above can be used for the electron transport layer 114.

[0107] Furthermore, the electron transport layer 114 is not limited to a single layer and can be a stack of two or more layers containing each of the above substances.

[0108] A layer that controls electron carrier transport can be placed between the electron transport layer and the light-emitting layer. This layer is formed by adding a small amount of a substance with high electron-capturing properties to a material with high electron transport properties, as described above. This layer is able to adjust the carrier balance by suppressing electron carrier transport. Such a structure is very effective in preventing problems (such as a reduction in the element's lifetime) that arise when electrons pass through the light-emitting layer.

[0109] Additionally, the electron injection layer 115 can be provided in contact with the second electrode 102 between the electron transport layer 114 and the second electrode 102. An alkali metal, an alkaline earth metal, or a compound thereof, such as lithium fluoride (LiF), cesium fluoride (CsF), or calcium fluoride (CaF₂), can be used for the electron injection layer 115. For example, a layer formed using a substance with electron transport properties and containing an alkali metal, an alkaline earth metal, or a compound thereof can be used. It should be noted that a layer formed using a substance with electron transport properties and containing an alkali metal or an alkaline earth metal is preferably used as the electron injection layer 115, in which case the electron injection from the second electrode 102 is carried out efficiently.

[0110] For the second electrode 102, any metal, alloy, electrically conductive compound, and mixtures thereof with a low work function (especially a work function of 3.8 eV or less) or the like can be used. Specific examples of such a cathode material are elements belonging to groups 1 and 2 of the periodic table, such as alkali metals (e.g., lithium (Li) and cesium (Cs)), magnesium (Mg), calcium (Ca), and strontium (Sr), alloys of these (e.g., MgAg and AlLi), rare-earth metals such as europium (Eu) and ytterbium (Yb), alloys of these, and the like. However, if the electron injection layer is provided between the second electrode 102 and the electron transport layer, a variety of conductive materials, such as Al, Ag, ITO, or indium oxide-tin oxide containing silicon or silicon oxide, can be used for the second electrode 102, regardless of the work function.Films of these electrically conductive materials can be formed by a sputtering process, an inkjet process, a spin coating process, or the like.

[0111] Furthermore, any of the many methods for forming the EL layer 103 can be used, regardless of whether it is a wet or dry process. For example, a vacuum evaporation process, an inkjet process, a spin coating process, or the like can be used. Different manufacturing processes can be used for the electrodes or the layers.

[0112] Additionally, the electrode can be produced using a wet process such as a sol-gel process or a wet process using a paste of a metallic material. Alternatively, the electrode can be produced using a dry process, such as sputtering or vacuum evaporation.

[0113] In the light-emitting element with the structure described above, current flows due to a potential difference between the first electrode 101 and the second electrode 102, and holes and electrons recombine in the light-emitting layer 113, which contains a substance with high light-emitting properties, thus emitting light. That is, a light-emitting region is formed in the light-emitting layer 113.

[0114] Light emission is extracted through one or both of the first electrode 101 and the second electrode 102. Therefore, one or both of the first electrode 101 and the second electrode 102 are transparent electrodes. If only the first electrode 101 is transparent, the light emission is extracted through the first electrode 101. If only the second electrode 102 is transparent, the light emission is extracted through the second electrode 102. If both the first electrode 101 and the second electrode 102 are transparent electrodes, the light emission is extracted through both the first electrode 101 and the second electrode 102.

[0115] The structure of the layers provided between the first electrode 101 and the second electrode 102 is not limited to the structure described above. Preferably, a light-emitting region in which holes and electrons recombine is arranged remotely from the first electrode 101 and the second electrode 102, so that quenching due to the proximity of the light-emitting region and a metal and support injection layers used for the electrodes can be prevented.

[0116] In order to suppress the transfer of energy from an exciton generated in the light-emitting layer, the hole transport layer and the electron transport layer, which are in contact with the light-emitting layer 113, in particular a carrier transport layer in contact with a side which is located closer to the light-emitting region in the light-emitting layer 113, are formed using a substance with a wider band gap than the light-emitting substance of the light-emitting layer or the emission center substance which is contained in the light-emitting layer.

[0117] In this embodiment, a light-emitting element is preferably produced on a substrate made of glass, plastic, or the like. As one method for stacking the layers on the substrate, the layers can be stacked successively from the side of the first electrode 101 or successively from the side of the second electrode 102. Although only one light-emitting element can be formed on a substrate, a plurality of light-emitting elements can be formed on a substrate in a light-emitting device. If a plurality of light-emitting elements are formed on a substrate as described above, a lighting device in which the elements are separate from one another or a passive-matrix light-emitting device can be produced.A light-emitting element can be formed on an electrode, electrically connected to a thin-film transistor (TFT) formed on a substrate of glass, plastic, or the like, thus creating an active-matrix light-emitting device in which the TFT controls the activation of the light-emitting element. It should be noted that there are no particular restrictions regarding the structure of the TFT, which can be a staggered TFT or an inverted staggered TFT. Furthermore, the crystallinity of the semiconductor used for the TFT is also not particularly restricted; an amorphous semiconductor or a crystalline semiconductor can be used. Additionally, a driver circuit formed on a TFT substrate can be created using an n-type TFT and a p-type TFT, or either an n-type TFT or a p-type TFT.

[0118] It should be noted that this embodiment can be combined with any other embodiment as appropriate. embodiment 3

[0119] This embodiment describes a light-emitting device using the light-emitting element described in embodiments 1 and 2.

[0120] In this embodiment, the light-emitting device, which uses the light-emitting element described in embodiments 1 and 2, is described with reference to Fig. 4A and Fig. 4B described. It should be noted that Fig. 4A is a view of the light-emitting device and Fig. 4B a cross-section along lines AB and CD in Fig. 4A. This light-emitting device comprises a source-line driver circuit 601, a pixel circuit 602, and a gate-line driver circuit 603, which control the light emission of the light-emitting element and are shown with dashed lines. Furthermore, reference numeral 604 denotes a sealing substrate; 625 a desiccant; 605 a sealing material; and 607 a space enclosed by the sealing material 605.

[0121] Reference numeral 608 denotes a wiring arrangement for transmitting signals input to the source-line driver circuit 601 and the gate-line driver circuit 603, and for receiving signals, such as a video signal, a time signal, a start signal, and a reset signal, from an FPC (flexible printed circuit board) 609, which serves as an external input terminal. Although only the FPC is shown here, a printed circuit board (PWB) may be attached to the FPC. In this category, the light-emitting device of this description includes not only the light-emitting device itself, but also the light-emitting device that is equipped with the FPC or PWB.

[0122] The following is a cross-sectional structure with reference to Fig. 4B described. The driver circuit area and the pixel area are formed on an element substrate 610; the source-line driver circuit 601, which is a driver circuit area, and one of the pixels in the pixel area 602 are shown here.

[0123] The source-line driver circuit 601 is a CMOS circuit in which an n-channel TFT 623 and a p-channel TFT 624 are combined. Additionally, the driver circuit can be formed with any of a variety of circuits, such as a CMOS circuit, a PMOS circuit, or an NMOS circuit. Although an integrated circuit in which the driver circuit is formed on the substrate is shown in this embodiment, the driver circuit does not necessarily have to be formed on the substrate and can be formed outside of it.

[0124] The pixel area 602 comprises a plurality of pixels, each of which has a switching TFT 611, a current-controlling TFT 612, and a first electrode 613, which is electrically connected to a drain of the current-controlling TFT 612. It should be noted that an insulator 614 is formed to cover one end region of the first electrode 613; for this insulator, a positive photosensitive acrylic resin film or foil is used.

[0125] To improve coverage, the insulator 615 is formed with a curved surface, the curvature being located at either the upper or lower end region. For example, if the positive photosensitive acrylic resin is used as the material for the insulator 614, only the upper end region of the insulator 614 preferably has a curved surface with a radius of curvature (0.2 µm to 3 µm). The insulator 614 can be made of either a negative or a positive photosensitive resin.

[0126] An EL layer 616 and a second electrode 617 are formed on the first electrode 613. The material used for the first electrode 613, which serves as an anode, is preferably a material with a high work function. For example, a single-layer foil or film made of an ITO film, an indium tin oxide film containing silicon, an indium oxide film containing zinc oxide with 2 wt.% to 20 wt.%, a titanium nitride film, a chromium film, a tungsten film, a zinc film, a platinum film, or the like, a stack of a titanium nitride film and a film containing aluminum as the main component, a stack of three layers of a titanium nitride film, a film containing aluminum as the main component and a titanium nitride film, or the like, can be used. The stacked layer structure enables low wiring resistance, a preferably ohmic contact, and function as an anode.

[0127] Additionally, the EL layer 616 is formed by any of a variety of processes, such as an evaporation process using an evaporation mask, an inkjet process, and a spin coating process. The EL layer 616 has a structure similar to that described in embodiments 1 and 2. Furthermore, any low-molecular-weight and high-molecular-weight compound (including oligomers and dendrimers) can be used as another material incorporated into the EL layer 616.

[0128] The material used for the second electrode 617, which is formed above the EL layer 616 and serves as a cathode, can preferably be a material with a low work function (e.g., Al, Mg, Li, Ca, or an alloy or compound thereof, such as MgAg, Mgl, or AlLi). In the case that light generated in the EL layer 616 is passed through the second electrode 617, a stack of a thin metal film or foil and a transparent conductive film (e.g., ITO, indium oxide containing 2 wt.% to 20 wt.% zinc oxide, indium tin oxide containing silicon, or zinc oxide (ZnO)) is preferably used for the second electrode 617.

[0129] It should be noted that the light-emitting element is formed by the first electrode 613, the EL layer 616, and the second electrode 617. The light-emitting element is the same as described in embodiments 1 and 2. In the light-emitting device of this embodiment, the pixel area, which comprises a plurality of light-emitting elements, can contain both the light-emitting element described in embodiments 1 and 2 and a light-emitting element with a different structure.

[0130] Furthermore, the sealing substrate 604 is attached to the element substrate 610 via the sealing material 605, such that a light-emitting element 618 is provided in the space 607, which is surrounded by the element substrate 610, the sealing substrate 604, and the sealing material 605. The space 607 can be filled with a filler, or it can be filled with an inert gas (such as nitrogen or argon) or the sealing material 605. It is preferred that the sealing substrate is provided with a recessed area and that the desiccant 625 is provided in the recessed area, so that deterioration due to the influence of moisture can be suppressed.

[0131] An epoxy-based resin or a glass frit is preferably used as the sealing material 605. It is preferred that such a material is as impermeable as possible to moisture or oxygen. The sealing substrate 604 can be a glass substrate, a quartz substrate, or a plastic substrate made of fiberglass-reinforced plastic (FRP), polyvinyl fluoride (PVF), polyester, acrylic resin, or the like.

[0132] As described above, the light-emitting device which uses the light-emitting element described in embodiments 1 and 2 can be obtained.

[0133] The light-emitting device in this embodiment is manufactured using the light-emitting element described in embodiments 1 and 2 and can therefore have advantageous properties. In particular, since the light-emitting element described in embodiments 1 and 2 has a high emission efficiency, the light-emitting device can have reduced power consumption. Since the light-emitting element also has a low drive voltage, the light-emitting device can be operated at a low voltage.

[0134] Although an active-matrix light-emitting device is described in this embodiment, as described above, a passive-matrix light-emitting device can also be manufactured. Fig. 5A and Fig. Figure 5B shows a passive matrix light-emitting device produced using the present invention. Fig. Figure 5A shows a perspective view of the light-emitting device and Fig. Figure 5B shows a cross-section along line XY in Fig. 5A. In the Fig. 5A and Fig. In 5B, an EL layer 955 is provided on a substrate 951 between an electrode 952 and an electrode 956. An end region of the electrode 952 is covered with an insulating layer 953. Additionally, a separating layer 954 is provided on the insulating layer 953. The side walls of the separating layer 954 are chamfered so that the distance between the two side walls gradually tapers towards the surface of the substrate. In other words, a cross-section along the direction of the short side of the separating layer 954 is trapezoidal, and the lower side (a side which runs in the same direction as a plane direction of the insulating layer 953 and is in contact with the insulating layer 953) is shorter than the upper side (a side which runs in the same direction as the plane direction of the insulating layer 953 and is not in contact with the insulating layer 953).The separating layer 954, as provided, can prevent defects in the light-emitting element due to static electricity or the like. The passive-matrix light-emitting device can also be operated with low power consumption, including the light-emitting element of embodiments 1 and 2, which can be operated at low voltage. Furthermore, the light-emitting device can exhibit high reliability by incorporating the light-emitting element described in embodiments 1 and 2.

[0135] Furthermore, to provide a full-color display, a color layer or a color-conversion layer can be provided in a light path through which the light is passed from the light-emitting element to the outside of the light-emitting device. An example of a light-emitting device in which a full-color display is achieved using a color layer and the like is shown in the Fig. 6A and Fig. 6B is shown. Fig. Figure 6A shows a substrate 1001, a base insulating film 1002, a gate insulating film 1003, gate electrodes 1006, 1007 and 1008, a first intermediate insulating film 1020, a second intermediate insulating film 1021, a peripheral area 1042, a pixel area 1040, a driver circuit area 1041, first electrodes 1024W, 1024R, 1024G and 1024B of the light-emitting elements, a partition 1025, an EL layer 1028, a second electrode 1029 of the light-emitting elements, a sealing substrate 1031 and sealing material 1032. Furthermore, color layers (a red color layer 1034R, a green color layer 1034G, and a blue color layer 1034B) are provided on a transparent base material 1033. Additionally, a black layer (a black matrix) 1035 can be provided.The transparent base material 1033, which is provided with color layers and a black layer, is arranged on and fixed to the substrate 1001. It should be noted that the color layers and the black layer are covered with an overlayer 1036. In this embodiment, light emitted by some of the light-emitting layers is not transmitted through the color layers, while light emitted by the other light-emitting layers is transmitted through the color layers. Since light that is not transmitted through the color layers is white, and light that is transmitted through one of the color layers is red, blue, or green, an image can be reproduced using pixels of the four colors.

[0136] The light-emitting device described above is a light-emitting device with a structure in which light is extracted from the side of the substrate 1001 on which the TFTs are formed (a bottom emission structure), but can also be a light-emitting device with a structure in which light is extracted from the side of the sealing substrate 1031 (a top or ceiling emission structure). Fig. Figure 7 shows a cross-section of a light-emitting device with a top-emission structure. In this case, an opaque substrate, substrate 1001, can be used. The process up to the step of forming a connecting electrode, which links the TFT and the anode of the light-emitting element, is carried out in a similar manner to that of the light-emitting device with a bottom-emission structure. Subsequently, a third interlayer insulating film 1037 is formed to cover an electrode 1022. The third interlayer insulating film 1037 can have a planarizing function. The third interlayer insulating film 1037 can be formed using a material similar to that of the second interlayer insulating film or, alternatively, using another known material.

[0137] The first electrodes 1024W, 1024R, 1024G and 1024B of the light-emitting elements serve here as an anode, but can also serve as a cathode. Furthermore, in the case of a light-emitting device with a top-emission structure, as in Fig. Figure 7 shows the first electrodes preferably being reflective electrodes. The EL layer 1028 is formed with a structure similar to that described in embodiments 1 and 2, whereby white light emission can be obtained. In the case where two EL layers are used, the following structures are employed to obtain white light emission: one in which blue light is obtained from a light-emitting layer in one of the EL layers and orange light is obtained from a light-emitting layer in the other EL layer; another in which blue light is obtained from a light-emitting layer in one of the EL layers and red and green light are obtained from light-emitting layers in the other EL layer; and so on.Furthermore, in the case where three EL layers are used, red light, green light, and blue light can be obtained from the respective light-emitting layers, so that the light-emitting element that emits white light can be obtained. It is unnecessary to state that the structure in which the emission of white light is obtained is not limited to this, as long as the structure described in embodiments 1 and 2 is used.

[0138] The color layers are each provided in a light path through which light is passed from the light-emitting element to the outside of the light-emitting device. In the case of the light-emitting device with a bottom emission structure, as in Fig. As shown in Figure 6A, the color layers 1034R, 1034G, and 1034B can be provided on the transparent base material 1033 and then attached to the substrate 1001. The color layers can be provided between the gate insulating film 1003 and the first intermediate insulating film 1020, as shown in Figure 6A. Fig. Figure 6B shows the following. In the case of a top emission structure, as in Fig. As shown in Figure 7, a seal can be created using the sealing substrate 1031, on which the color layers (the red color layer 1034R, the green color layer 1034G, and the blue color layer 1034B) are applied. The sealing substrate 1031 can be combined with the black layer (black matrix) 1035, which is positioned between the pixels. The color layers (the red color layer 1034R, the green color layer 1034G, and the blue color layer 1034B) and the black layer (black matrix) 1035 can be covered with an overlayer 1036. It should be noted that a translucent substrate is used as the sealing substrate 1031.

[0139] When a voltage is applied between the electrode pair of the organic light-emitting element thus obtained, a white light-emitting region of 1044W can be obtained. Additionally, using the color layers, a red light-emitting region of 1044W, a blue light-emitting region of 1044B, and a green light-emitting region of 1044G can be obtained. The light-emitting device of this embodiment comprises the light-emitting element described in embodiments 1 and 2; therefore, a low-power light-emitting device can be obtained.

[0140] Although an example is described here in which a full-color display is achieved using the four colors red, green, blue and white, there is no specific limitation and a full-color display using the three colors red, green and blue can also be achieved.

[0141] This embodiment can be freely combined with any other embodiment. Design 4

[0142] In this embodiment, an example is given in which the light-emitting element described in embodiments 1 and 2 is used for a lighting device, with reference to the Fig. 8A and Fig. 8B described. Fig. Figure 8B shows a top view of the lighting device and Fig. Figure 8A shows a cross-section along the line ef in Fig. 8B.

[0143] In the lighting device of this embodiment, a first electrode 401 is formed on a substrate 400, which is a support and has a translucent property. The first electrode 401 corresponds to the first electrode 101 in embodiment 3.

[0144] An auxiliary electrode 402 is provided on the first electrode 401. Since the light emission in the example described in this embodiment is extracted through the side of the first electrode 401, the first electrode 401 is formed using a material with a translucent property. The auxiliary electrode 402 is provided to compensate for the low conductivity of the translucent material and serves to suppress luminance unevenness in a light-emitting surface due to a voltage drop caused by the high resistance of the first electrode 401. The auxiliary electrode 402 is formed using a material that has at least a higher conductivity than the material of the first electrode 401 and is preferably formed using a material with high conductivity, such as aluminum.It should be noted that the other surfaces of the auxiliary electrode 402, as well as the area in contact with the first electrode 401, are preferably covered with an insulating layer. This serves to suppress light emission on the upper area of ​​the auxiliary electrode 402, which cannot be extracted, in order to reduce reactive current and to prevent a decrease in power efficiency. It should be noted that a pad 412 for applying a voltage to a second electrode 402 can be formed simultaneously with the formation of the auxiliary electrode 402.

[0145] An EL layer 403 is formed on the first electrode 401 and the auxiliary electrode 402. The EL layer 403 has the structure described in embodiments 1 and 2. Reference is made to these descriptions regarding the structure. It should be noted that the EL layer 403 is preferably formed to be somewhat larger than the first electrode 401 when viewed from above, so that in this case the EL layer 403 can also serve as an insulating layer that prevents a short circuit between the first electrode 401 and the second electrode 404.

[0146] The second electrode 404 is designed to cover the EL layer 403. The second electrode 404 corresponds to the second electrode 102 in embodiment 3 and has a similar structure. In this embodiment, it is preferred that the second electrode 404 be formed using a material with high reflectivity, since the light emission is extracted through the side of the first electrode 401. In this embodiment, the second electrode 404 is connected to the pad 412, thereby applying a voltage.

[0147] As described above, the lighting device described in this embodiment comprises a light-emitting element containing the first electrode 401, the EL layer 403, and the second electrode 404 (and the auxiliary electrode 402). Since the light-emitting element has high emission efficiency, the lighting device in this embodiment can be a lighting device with low power consumption. Furthermore, since the light-emitting element has high reliability, the lighting device of this embodiment can be a highly reliable lighting device.

[0148] The light-emitting element with the structure described above is attached to a sealing substrate 407 using sealing materials 405 and 406, and the seal is applied, thus completing the lighting device. It is possible to use only sealing material 405 or only sealing material 406. Additionally, the inner sealing material 406 can be mixed with a desiccant to absorb moisture and increase reliability.

[0149] If portions of the pad 412, the first electrode 401, and the auxiliary electrode 402 are extended to the outside of the sealing materials 405 and 406, the extended portions can serve as external input terminals. An IC chip 420, attached via a converter or the like, can be provided on the external input terminals.

[0150] As described above, the lighting device can be a low-power lighting device, since the lighting device described in this embodiment includes the light-emitting element described in embodiments 1 and 2. Furthermore, the lighting device can be a low-drive voltage lighting device. Additionally, the lighting device can be a high-reliability lighting device. Design 5

[0151] This embodiment describes examples of electronic devices, each containing the light-emitting element described in embodiments 1 and 2. The light-emitting element described in embodiments 1 and 2 exhibits high emission efficiency and reduced power consumption. As a result, the electronic device described in this embodiment can each have a light-emitting area with reduced power consumption. Additionally, the electronic device can be operated at a low voltage because the light-emitting element described in embodiments 1 and 2 has a low drive voltage.

[0152] Examples of electronic devices to which the above light-emitting element is applied include televisions (also called TVs or television receivers), computer monitors and the like, cameras such as digital cameras and digital video cameras, digital photo frames, mobile phones (also called cell phones or mobile telephones), portable game consoles, portable information terminals, audio playback devices, large gaming devices such as pachinko machines, and the like. Specific examples of these electronic devices are given below.

[0153] Fig. Figure 9A shows an example of a television. In this television, a display area 7103 is integrated into a housing 7101. The housing 7101 is supported by a stand 7105. Images can be displayed on the display area 7103, and the light-emitting elements described in embodiments 1 and 2 are arranged in a matrix within the light-emitting area 7103. The light-emitting elements can have high emission efficiency. Furthermore, the light-emitting elements can be operated at low voltage. Additionally, the light-emitting elements can have a long service life. Therefore, the television containing the display area 7103, which utilizes the light-emitting elements, can be a television with reduced power consumption. Furthermore, the television can be a television with high reliability.

[0154] The television can be operated using a control button on the housing 7101 or a separate remote control 7110. The control buttons 7109 on the remote control 7110 allow you to select channels and adjust the volume, as well as control images displayed on the screen 7103. Furthermore, the remote control 7110 can be equipped with a screen 7107 to display the data output by the remote control 7110.

[0155] It should be noted that the television is equipped with a receiver, a modem, and similar devices. Using the receiver, general television broadcasts can be received. Furthermore, if the television is connected to a communication network, with or without wires via the modem, one-way (from a transmitter to a receiver) or two-way (between a transmitter and a receiver, or between receivers) information communication can take place.

[0156] Fig. 9B1 represents a computer comprising a main body 7201, a housing 7202, a display area 7203, a keyboard 7204, an external connection port 7205, a pointing device 7206, and the like. It should be noted that this computer is manufactured using light-emitting elements arranged in a matrix within the display area 7203, the light-emitting elements being the same as those described in embodiment 2 or 3. The Fig. The computer shown in 9B1 can be in Fig. exhibit the structure shown in 9B2. The one in the Fig. The computer shown in Figure 9B2 is equipped with a second display area 7210 in place of the keyboard 7204 and the pointing device 7206. The second display area 7210 is a touchscreen, and input can be made by moving the display to input on the second display area 7210 using a finger or a suitable stylus. The second display area 7210 can also display images other than the input screen. The display area 7203 can also be a touchscreen. The connection of the two screens via a hinge serves as protection; for example, it prevents the screens from breaking or cracking while the computer is stored or carried. The light-emitting elements can have high emission efficiency. Therefore, this computer with the display area 7203, which is manufactured using the light-emitting elements, consumes less power.

[0157] Fig. Figure 9C shows a portable game console with two housings, a housing 7301 and a housing 7302, which are connected via a hinge area 7303 so that the portable game console can be opened and closed. The housing 7301 has a display area 7304 containing the light-emitting elements described in embodiments 1 and 2 and arranged in a matrix, and the housing 7302 contains a display area 7305. Additionally, the portable game console, which is described in Fig. 9C shows a loudspeaker area 7306, a recording medium insertion area 7307, an LED lamp 7308, input means (an operating button 7309, a connection terminal 7310, a sensor 7311 (a sensor with a function to measure force, displacement, position, velocity, acceleration, angular velocity, rotational frequency, distance, light, liquid, magnetism, temperature, chemical substance, noise, time, hardness, electric field, current, voltage, electrical power, radiation, flow rate, humidity, gradient, oscillation, odor or infrared rays) and a microphone 7312) and the like.It need not be pointed out that the structure of the portable game console is not limited to the above, as long as the display area, which contains the light-emitting elements described in embodiments 1 and 2 and is arranged in a matrix, is used for at least display area 7304 or display area 7305 or both, and the structure may include other elements if desired. The portable game console, which is described in . Fig. As shown in section 9C, it has a function to read a program or values ​​stored on a storage medium in order to display them on the screen, and a function to exchange information with other portable game consoles via wireless communication. It should be noted that the functions of the portable game console, which are shown in Fig. The features shown in 9C are not limited to this, and the portable game console can have various functions. Since the light-emitting elements used in the 7304 display area have high emission efficiency, the portable game console containing the 7304 display area described above can be a portable game console with reduced power consumption. Since the light-emitting elements used in the 7304 display area can be operated at low voltage, the portable game console can be a portable game console with a low drive voltage. Furthermore, since the light-emitting elements used in the 7304 display area have a long lifespan, the portable game console can be very reliable.

[0158] Fig. Figure 9D shows an example of a mobile phone. The mobile phone is equipped with a display area 7402, which is built into a housing 7401, control buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. It should be noted that the mobile phone 7400 has the display area 7402, which contains the light-emitting elements described in embodiments 1 and 2 and is arranged in a matrix. The light-emitting elements can have high emission efficiency. Furthermore, the light-emitting elements can be operated at a low voltage. Additionally, the light-emitting elements can have a long lifetime. Therefore, the mobile phone, comprising the display area 7402 formed using the light-emitting elements, can be a low-power mobile phone.Furthermore, the mobile phone can be a mobile phone with a low drive voltage. Furthermore, the mobile phone can be a mobile phone with high reliability.

[0159] If the display area 7402 of the mobile phone, which is in Fig. When the 9D display area is touched with a finger or similar device, data can be entered into the mobile phone. In this case, operations such as making a call or creating an email can be performed by touching the 7402 display area with a finger or similar device.

[0160] The 7402 display area has three main screen modes. The first mode is a display mode, primarily used for showing an image. The second mode is an input mode, primarily used for entering information such as text. The third mode is a combined display and input mode.

[0161] For example, when a call is being made or an email is being generated, a letter input mode, primarily for entering letters, is selected for display area 7402, so that the letters that can be entered are displayed on the screen. In this case, it is preferable to display a keyboard or number keys on almost the entire screen of display area 7402.

[0162] If a detection device containing a sensor for determining inclination, such as a gyroscope or an accelerometer, is provided inside the mobile phone, the display on the screen of the display area 7402 can be automatically changed by determining the orientation of the mobile phone (whether the mobile phone is held horizontally or vertically in landscape or portrait orientation).

[0163] The screen modes are changed by touching the display area 7402 or by using the control button 7403 on the housing 7401. The screen modes can be changed depending on the type of image displayed on the display area 7402. For example, if the signal of an image displayed on the screen area is a video signal, the screen mode switches to display mode. If the signal is text, the screen mode switches to input mode.

[0164] Furthermore, in input mode, if no input is made by touching the display area 7402 for a certain period of time while a signal is detected by an optical sensor in the display area 7402, the screen mode can be controlled to switch from input mode to display mode.

[0165] The 7402 display area can function as an image sensor. For example, an image of a handprint, fingerprint, or similar can be captured by touching the 7402 display area with the palm of the hand or a finger, thus enabling personal authentication. Furthermore, by providing backlighting or a scanning light source that emits near-infrared light into the display area, an image of a finger vein, hand vein, or similar can be captured.

[0166] The structure described in this embodiment can be combined with any structure described in embodiments 1 to 4, provided it is suitable.

[0167] As described above, the application range of the light-emitting device with the light-emitting element described in embodiments 1 and 2 is so broad that the light-emitting device can be applied to electronic devices in a wide variety of fields. Using the light-emitting element described in embodiments 1 and 2, an electronic device with reduced power consumption can be obtained.

[0168] Fig. Figure 10 provides an example of a liquid crystal display device which uses the light-emitting element described in embodiments 1 and 2 as a backlight. The in Fig. Figure 10 of the liquid crystal display device comprises a housing 910, a liquid crystal layer 902, a backlight unit 903, and a housing 904. The liquid crystal layer 902 is connected to a driver IC 905. The light-emitting element described in embodiments 1 and 2 is used as the backlight unit 903, to which current is supplied via a terminal 906.

[0169] The light-emitting element used in embodiments 1 and 2 serves as the backlight for the liquid crystal display device, thus enabling reduced power consumption of the backlight. Additionally, the use of the light-emitting element described in embodiment 2 allows for the fabrication of a planar emission illumination device, and furthermore, a planar emission illumination device with a larger area. Therefore, the backlight can be a larger area, and the liquid crystal display device can be a larger area device. Furthermore, the light-emitting device using the light-emitting element described in embodiment 2 can be thinner than a conventional one; consequently, the display device can also be made thinner.

[0170] Fig. Figure 11 presents an example in which the light-emitting element described in embodiments 1 and 2 is used as a table lamp, which is a lighting device. The table lamp, which is described in Fig. Figure 11 shows a housing 2001 and a light source 2002, and the light-emitting device described in embodiment 4 is used as the light source 2002.

[0171] Fig. Figure 12 shows an example in which the light-emitting element described in embodiments 1 and 2 is used as an interior lighting device 3001 and a display device 3002. Since the light-emitting element described in embodiments 1 and 2 has reduced power consumption, a lighting device with reduced power consumption can be obtained. Furthermore, since the light-emitting element described in embodiments 1 and 2 can have a large area, it can be used for a lighting device with a large area. Furthermore, since the light-emitting element described in embodiments 1 and 2 is thin, it can be used for a lighting device with reduced thickness.

[0172] The light-emitting element described in embodiments 1 and 2 can also be used as a motor vehicle windshield or motor vehicle dashboard. Fig. Figure 13 shows a mode in which the light-emitting elements described in embodiment 2 are used as a motor vehicle windshield and motor vehicle dashboard. Displays 5000 to 5005 each comprise the light-emitting elements described in embodiments 1 and 2.

[0173] Display 5000 and Display 5001 are display devices installed in the windshield of a motor vehicle, incorporating the light-emitting elements described in embodiments 1 and 2. The light-emitting element described in embodiments 1 and 2 can be formed into a so-called see-through display device, through which the opposite side can be seen. This is achieved by including a first electrode and a second electrode formed from electrodes with translucent properties. Such see-through display devices can even be installed in the windshield of a vehicle without obstructing the driver's view.It should be noted that if a transistor is provided for control, a transistor with a light-transmitting property, such as an organic transistor using an organic semiconductor material or a transistor using an oxide semiconductor, is preferably used.

[0174] Display 5002 is a display device provided in a pillar area and incorporating the light-emitting elements described in embodiments 1 and 2. Display 5002 can compensate for the obstruction of the view caused by the pillar area by displaying an image captured by a camera located in the vehicle body. Similarly, display 5003, provided in the instrument panel, can compensate for an obstruction of the view caused by the vehicle body by displaying an image captured by a camera located on the outside of the vehicle body, thereby avoiding blind spots and increasing safety. Displaying an image to compensate for an area the driver cannot see allows the driver to easily and conveniently confirm safety.

[0175] The 5004 and 5005 displays can provide a variety of information, such as navigation data, a speedometer, a odometer, a fuel gauge, a shift indicator, and climate control settings. The content or layout of the display can be freely modified by the user as needed. It should be noted that the information can also be displayed by the 5000 to 5003 displays. The 5000 to 5005 displays can also be used as lighting devices.

[0176] The light-emitting element described in embodiments 1 and 2 can exhibit higher emission efficiency and lower power consumption. Therefore, the load on the battery is low, even when a large number of screens, such as displays 5000 and 5005, are provided, thus enabling convenient use. For this reason, the light-emitting device and the lighting device, each containing the light-emitting element in embodiments 1 and 2, can be suitable for use as vehicle interior lighting and as a light-emitting device in the vehicle.

[0177] Fig. 14A and Fig. Figure 14B shows an example of a foldable tablet terminal. Fig. Figure 14A shows the tablet terminal, which is not folded. The tablet terminal comprises a housing 9630, a display area 9631a, a display area 9631b, a display mode switch 9034, an on / off switch 9035, a power-saving switch 9036, a closure 9033, and an operating switch 9038. It should be noted that in the tablet terminal, one or both of the display areas 9631a and the display area 9631b are formed using a light-emitting device which contains the light-emitting element described in embodiments 1 and 2.

[0178] Part of the display area 9631a can be a touchscreen area 9632a, and input can be made therein when a displayed control button 9637 is touched. Although only half of the display area 9631a has a display function and the other half a touchscreen function, one embodiment of the present invention is not limited to this structure. The entire display area 9631a can have a touchscreen function. For example, a keyboard can be displayed on the entire area of ​​the display area 9631a, so that the display area 9631a is used as a touchscreen; therefore, the display area 9631b can be used as a display screen.

[0179] Similar to display area 9631a, part of display area 9631b can be a touchscreen area 9632b. When a toggle button 9639 for showing / hiding a keyboard on the touchscreen is touched with a finger, stylus, or the like, the keyboard can be displayed on display area 9631b.

[0180] Touch input can be performed simultaneously in touchscreen area 9632a and touchscreen area 9632b.

[0181] The display mode switch 9034 can switch the display between portrait and landscape orientation, and between monochrome and color. The power-saving switch 9036 can control the display brightness according to the amount of external light when the tablet terminal is in use, as determined by an optical sensor built into the tablet terminal. In addition to the optical sensor, a further detection device, such as a gyroscope or accelerometer, can be built into the tablet terminal to determine tilt.

[0182] Although Fig. Figure 14A provides an example in which display area 9631a and display area 9631b have the same display area. However, an embodiment of the present invention is not limited to this example. Display area 9631a and display area 9631b can have different display areas and different display qualities. For example, higher-resolution images can be displayed on one of the display areas 9631a and 9631b.

[0183] Fig. Figure 14B shows the tablet terminal in its folded state. The tablet terminal in this embodiment comprises the housing 6930, a solar cell 6933, a charge and discharge control circuit 9634, a battery 9635, and a DC-to-DC converter 9636. As an example, Figure 14B shows... Fig. 14B the charge and discharge control circuit 9634, including the battery 9635 and the DC-to-DC converter 9636.

[0184] Since the tablet terminal is foldable, the housing 9630 can be closed when the tablet terminal is not in use. As a result, the display areas 9631a and 9631b can be protected, providing a highly durable and reliable tablet terminal for long-term use.

[0185] The tablet terminal, which is located in the Fig. 14A and Fig. As shown in Figure 14B, it may have other functions, such as a function to display different types of data (e.g., an image, a film, and text), a function to display a calendar, date, time, or the like on the display area, a function to operate or edit the data displayed on the display area by touch, and a function to control processing by different types of software (programs).

[0186] The solar cell 9633, which is provided on a surface of the tablet terminal, can supply power to the touchscreen, the display area, a video signal processing area, or the like. It should be noted that the solar cell 9633 can be provided on one or both surfaces of the housing 9630, so that the battery 9635 is charged efficiently.

[0187] The structure and operation of the charge and discharge control circuit 9634, which is located in Fig. 14B is shown with reference to a block diagram in Fig. 14C explained. Fig. Figure 14C shows the solar cell 9633, the battery 9635, the DC-to-DC converter 9636, a converter 9638, switches SW1 to SW3, and the display area 9631. The battery 9635, the DC-to-DC converter 9636, the converter 9638, and the switches SW1 to SW3 correspond to the charge and discharge control circuit 9634, which is located in the Fig. 14B is shown.

[0188] First, an example of operation is described, assuming the current is generated by solar cell 9633 using ambient light. The voltage of the current generated by the solar cell is increased or decreased by the DC-to-DC converter 9636 to achieve the voltage required to charge battery 9635. Then, when current from solar cell 9633 is used to operate display area 9631, switch SW1 is turned on, and the voltage of the current is increased or decreased by converter 9638 to achieve the voltage required for display area 9631. When no images are displayed on display area 9631, switch SW1 is turned off, and switch SW2 is turned on, thus charging battery 9635.

[0189] Although the solar cell 9633 is described as an example of power generation, power generation is not limited to this, and the battery 9635 can be charged by another power-generating device, such as a piezoelectric element or a thermoelectric conversion element (Peltier element). The battery 9635 can be charged by a contactless power transfer module capable of wirelessly transmitting and receiving power (without contact), or by any other charging device used in combination, and the power-generating devices do not necessarily need to be provided.

[0190] One embodiment of the present invention is not limited to a tablet terminal with the [missing information] in the Fig. The form shown in 14A to 14C is limited as long as the display area 9631 is included. Example 1

[0191] This example describes a method for producing a light-emitting element according to an embodiment of the present invention, which is described in embodiment 1 and embodiment 2, and its properties. The structural formulas of the organic compounds used in this example are shown below.

[0192] The following describes a method for producing the light-emitting element of this example.

[0193] First, a film or foil of indium tin oxide containing silicon dioxide (ITSO) was formed on a glass substrate by a sputtering process, thus creating the first electrode 101. This electrode had a thickness of 110 nm and an electrode area of ​​2 mm x 2 mm. Here, the first electrode 101 serves as the anode of the light-emitting element.

[0194] Subsequently, as a pretreatment to form the light-emitting element on the substrate, a UV ozone treatment was carried out for 370 seconds after a surface of the substrate was washed with water and the substrate was heated for one hour at 200°C.

[0195] The substrate was then transferred to a vacuum vapor deposition unit, where the pressure was increased to approximately 10 -4 The Pa had been reduced, and the substrate was heated in a vacuum at 170 °C for 30 minutes in a heating chamber of the vacuum steam device, and then cooled for approximately 30 minutes.

[0196] The substrate on which the first electrode 101 was formed was then attached to a substrate holder provided in the vacuum evaporation unit such that the surface on which the first electrode 101 was formed faced downwards. The pressure in the vacuum evaporation unit was set to approximately 10 -4Pa was reduced. Subsequently, 4,4',4"-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), represented by structural formula (i), and molybdenum(VI) oxide were deposited on the first electrode 101 by co-evaporation using a resistance heating process, thus forming the hole injection layer 111. The thickness of the hole injection layer 111 was adjusted to 33 nm, and the weight ratio of DBT3P-II to molybdenum oxide was adjusted to 4:2. It should be noted that the co-evaporation process is a process in which a variety of different substances are simultaneously deposited from different evaporation sources in a treatment chamber.

[0197] Subsequently, a film of 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP), represented by the structural formula (ii) with a thickness of 20 nm, was formed on the hole injection layer 111 to form the hole transport layer 112.

[0198] Furthermore, on the hole transport layer 112, 2-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), which is represented by structural formula (iii), 4-phenyl-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), which is represented by structural formula (iv), and bis[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato-κ 2O,O')iridium(III) (abbreviation: Ir(tBuppm)2(acac)), which is represented by the structural formula (v), deposited by Co vapor deposition with a thickness of 20 nm, wherein a mass ratio of 2mDBTPDBq-II to PCBA1BP and Ir(tBuppm)2(acac) was 0.8:0.2:0.05, so that the first light-emitting layer 113a was formed; Subsequently, 2mDBTPDBq-II and bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: Ir(tppr)2(dpm)), represented by structural formula (vi), were deposited by co-evaporation to a thickness of 20 nm, with a mass ratio of 2mDBTPDBq-II to Ir(tppr)2(dpm) of 1:0.06, thus forming the second light-emitting layer 113b. It should be noted that 2mDBTPDBq-II, which is a host material, and PCBA1BP form an exciplex.

[0199] Then the electron transport layer 114 was formed on the light-emitting layer 113 in such a way that a 15 nm thick film of 2mDBTPDBq-II was formed and a 15 nm thick film of bathophene anthroline (abbreviation: BPhen), which is represented by the structural formula (vii), was formed.

[0200] After the formation of the electron transport layer 114, lithium fluoride (LiF) was deposited by vapor deposition with a thickness of 1 nm, so that an electron injection layer 115 was formed.

[0201] Finally, aluminum was deposited by vapor deposition to a thickness of 200 nm to form the second electrode 102, which served as a cathode. In this way, a light-emitting element 1 was produced in this example.

[0202] It should be noted that in all of the above vapor deposition steps, the vapor deposition was carried out using a resistance heating process.

[0203] Table 1 shows an element structure of the light-emitting element 1 obtained as described above. [Table 1] Lochinjektionsschicht Lochtransportschicht Lichtemittierende Schicht Elektronentransportschicht Elektroneninjektionsschicht Erste lichtemittierende Schicht Zweite lichtemittierende Schicht DBT3P-II:MoO x 4:233 nm BPAFLP20 nm 2mDBTPDBq-II:PCBA1BP: Ir(tBuppm)2(acac)0,8:0,2:0,0520 nm 2mDBTPDBq-II:Ir(tppr)2(dpm )1:0,0620 nm 2mDBTPDBq-II15 nm Bphen15 nm LiF1 nm

[0204] The light-emitting element 1 was sealed in a glove compartment using a glass substrate, the glove compartment containing a nitrogen atmosphere to prevent exposure to air (in particular, a sealing material was applied to an outer edge of the element and a heat treatment at 80 °C for 1 hour was carried out at the time of sealing).

[0205] For light-emitting element 1, Ir(tBuppm)2(acac) and Ir(tppr)2(dpm) were used as the first phosphorescent compound 113Da and the second phosphorescent compound 113Db, respectively. A relationship is established between the PL spectrum of Ir(tBuppm)2(acac) and ε(λ)λ. 4described by Ir(tppr)2(dpm). It should be noted that λ represents a wavelength and ε(λ) represents a molar absorption coefficient.

[0206] Fig. Figure 20A shows curves of the molar absorption coefficient ε(λ) and ε(λ)λ. 4 of Ir(tppr)2(dpm). While the molar absorption coefficient ε(λ) showed no noticeable peak in a region on the long-wavelength side, the curve of ε(λ)λ 4 The image contains a peak with a local maximum value at 543 nm. This peak represents the triplet MLCT absorption of Ir(tppr)2(dpm). If this peak overlaps with an emission peak of the first phosphorescent compound 113Da, the energy transfer efficiency can be significantly increased.

[0207] Fig. Figure 20B shows the PL spectrum F(λ) of Ir(tBuppm)2(acac), which is the first phosphorescent compound 113Da, and the curve of ε(λ)λ 4of Ir(tppr)2(dpm), which is the second phosphorescent compound 113Db. The curve clearly shows that a band with a peak in the PL spectrum F(λ) of Ir(tBuppm)2(acac) differs significantly from the band with a peak on the long-wavelength side of ε(λ)λ. 4 overlaps with Ir(tppr)2(dpm), indicating that the combination enables extremely efficient energy transfer. Furthermore, Ir(tBuppm)2(acac), which is the first phosphorescent compound 113Da, exhibits an emission peak at 546 nm, and the spectrum, which ε(λ)λ 4 The waveform of Ir(tppr)2(dpm), which is the second phosphorescent compound 113Db, exhibits a local maximum on the long-wavelength side at 543 nm, resulting in a difference of 3 nm. The wavelengths of 546 nm and 543 nm correspond to 2.27 eV and 2.28 eV, respectively, so the difference is 0.01 eV, which is less than 0.2 eV; therefore, the peak positions also suggest the occurrence of efficient energy transfer.

[0208] Next, show Fig. 21A the curves of the molar absorption coefficient ε(λ) and ε(λ)λ 4 of Ir(tBuppm)2(acac), which is the first phosphorescent compound 113Da. While a peak in a region on the long-wavelength side has a lower intensity than a peak on the short-wavelength side of the molar absorption coefficient ε(λ) curve, the curve of ε(λ)λ 4 A high-intensity peak is observed at 494 nm. The peak exhibiting this phenomenon shows triplet MLCT absorption of Ir(tBuppm)2(acac). If this peak overlaps with an emission peak from an energy donor, the energy transfer efficiency can be significantly increased.

[0209] In this example, the light-emitting element 1, 2mDBTPDBq-II, which is the first host material, and PCBA1BP, which is the first organic compound, form the Exciplex 113Ec, and energy is transferred from the Exciplex 113Ec to the first phosphorescent compound 113Da. Fig. Figure 23 shows the PL spectra of 2mDBTPDBq-II, PCBA1BP, and a mixed film of these (a mass ratio of 2mDBTPDBq-II to PCBA1BP is 0.8:0.2), and it becomes clear that 2mDBTPDBq-II and PCBA1BP, which is the first organic compound, have formed the Exciplex 113Ec. Fig. Figure 21B shows a PL spectrum F(λ) of the exciplex and the curve of ε(λ)λ 4 Ir(tBuppm)2(acac) is a phosphorescent compound, 113Da. The curve clearly shows that a band with a peak in the PL spectrum F(λ) of the exciplex coincides with the band with a peak at the longest wavelength of ε(λ)λ. 4overlap of Ir(tBuppm)2(acac), indicating that the combination enables efficient energy transfer. Furthermore, the PL spectrum of the Exciplex exhibits a peak at 519 nm, and the spectrum that ε(λ)λ 4 Ir(tBuppm)2(acac), which is the first phosphorescent compound 113Da, exhibits a local maximum on the long-wavelength side at 494 nm, so the difference is 25 nm. The wavelengths 519 nm and 494 nm correspond to energies of 2.39 eV and 2.51 eV, respectively, so the difference is 0.12 eV, which is less than 0.2 eV; therefore, the positions of the peaks also suggest the occurrence of efficient energy transfer.

[0210] It should be noted that, as from Fig. As becomes clear in Figure 23, the PL spectrum of 2mDBTPDBq-II, which is the first host material 113Ha, exhibits a peak at 426 nm, which corresponds to an energy of 2.91 eV. Furthermore, the PL spectrum of PCBA1BP, which is the first organic compound 113A, exhibits a peak at 405 nm, which corresponds to an energy of 3.06 eV. The spectrum, which ε(λ)λ 4 The waveform of Ir(tBuppm)2(acac) shows a peak on the long-wavelength side at 494 nm, which corresponds to an energy of 2.51 eV. Therefore, the difference to 2mDBTPDBq-II, which is the first host material 113Ha, is 0.4 eV, and the difference to PCBA1BP, which is the first organic compound 113A, is 0.55 eV, each exceeding 0.2 eV; thus, energy is not transferred immediately from 2mDBTPDBq-II or PCBA1BP to Ir(tBuppm)2(acac).

[0211] Fig. Figure 22 shows the PL spectrum F(λ) of the exciplex, the PL spectrum F(λ) of Ir(tBuppm)2(acac), a PL spectrum F(λ) of Ir(tppr)2(dpm), ε(λ)λ 4 of Ir(tBuppm)2(acac) and ε(λ)λ 4 of Ir(tppr)2(dpm). It can be seen that energy is determined using the overlap between the PL spectrum of the exciplex and ε(λ)λ. 4 from Ir(tBuppm)2(acac) (around a peak A) is first transferred stepwise from the exciplex to Ir(tBuppm)2(acac) and then using the overlap between the PL spectrum of Ir(tBuppm)2(acac) and ε(λ)λ 4 Energy is transferred from Ir(tppr)2(dpm) (around peak B) from Ir(tBuppm)2(acac) to Ir(tppr)2(dpm). It should be noted that direct energy transfer from the exciplex to Ir(tppr)2(dpm), which is the second phosphorescent compound, is also possible. The reason for this is that, as shown in Fig. 22 becomes clear, ε(λ)λ 4Ir(tppr)2(dpm) also overlaps with the PL spectrum F(λ) of the Exciplex on a shorter wavelength side of the triplet MLCT absorption band (around peak B) of Ir(tppr)2(dpm).

[0212] The elemental properties of the light-emitting element were measured. It should be noted that the measurement was carried out at room temperature (in an atmosphere maintained at 25 °C).

[0213] Fig. Figure 15 shows the luminance-current efficiency characteristics of light-emitting element 1. Fig. 15 The horizontal axis represents the luminance (cd / m²). 2 ) and the vertical axis indicates the current output (cd / A). Fig. Figure 16 shows the voltage-luminance properties. Fig. 16. The horizontal axis indicates the voltage (V) and the vertical axis indicates the luminance (cd / m²). 2 ) on. Fig. Figure 17 shows the luminance-external quantum efficiency properties. Fig. 17, the horizontal axis represents the luminance (cd / m²). 2 ) and the vertical axis represents the external quantum efficiency (%). Fig. Figure 18 shows the luminance-power efficiency characteristics. Fig. 18, the horizontal axis gives the luminance (cd / m²). 2 ) and the vertical axis represents the power efficiency (Im / w).

[0214] From the above, it was evident that the light-emitting element 1 exhibited excellent element properties. In particular, the light-emitting element, as shown by the Fig. 15, Fig. 17 and Fig. 18 clearly shows an extremely high emission efficiency and possessed a high external quantum efficiency of no less than 20% at a practical luminance of approximately (1000 cd / m²). 2 Additionally, the current yield was approximately 60 cd / A and the power efficiency was approximately 60 Im / W, which are excellent values.

[0215] Fig. Figure 19 showed an emission spectrum of the light-emitting element 1, which was obtained when fluid flowed through the light-emitting element 1. Fig. 19 The horizontal axis indicates a wavelength (nm) and the vertical axis indicates the light emission intensity (arbitrary unit). Fig. 19 shows that the light-emitting element 1 exhibits a light emission spectrum, including light with a wavelength in a green wavelength range, which is from Bis[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato-κ 2 O,O')iridium(III) (abbreviation: Ir(tBuppm)2(acac)) originates, and light with a wavelength in a red wavelength range, which originates from Bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: Ir(tppr)2(dpm)), in a good balance.

[0216] It is evident from the above that the light-emitting element 1, which corresponded to an embodiment of the present invention, had a high emission efficiency and provided light from two types of emission center substances in a good balance. Example 2

[0217] This example describes a method for producing a light-emitting element corresponding to an embodiment described in embodiments 1 and 2, and outlines its properties. The structural formulas of the organic compounds used in this example are shown below.

[0218] The following describes a method for producing the light-emitting element of this example.

[0219] First, a film of indium tin oxide containing silicon dioxide (ITSO) was formed on a glass substrate by a sputtering process, creating the first electrode 101. This electrode had a thickness of 110 nm and an electrode area of ​​2 mm x 2 mm. The first electrode 101 serves as the anode of the light-emitting element.

[0220] Subsequently, as a pretreatment to form the light-emitting element on the substrate, a UV ozone treatment was carried out for 370 seconds after a surface of the substrate was washed with water and the substrate was heated for one hour at 200°C.

[0221] The substrate was then transferred to a vacuum vapor deposition unit, where the pressure was increased to approximately 10 -4 The Pa had been reduced, and the substrate was heated in a vacuum at 170 °C for 30 minutes in a heating chamber of the vacuum steam device, and then cooled for approximately 30 minutes.

[0222] The substrate on which the first electrode 101 was formed was then attached to a substrate holder provided in the vacuum evaporation unit such that the surface on which the first electrode 101 was formed faced downwards. The pressure in the vacuum evaporation unit was set to approximately 10 -4Pa was reduced. Subsequently, on the first electrode 101, 3-[4-(9-phenanthryl)phenyl]-9-phenyl-9H-carbazole (abbreviation: PCPPn), represented by structural formula (viii), and molybdenum(VI) oxide were deposited by co-evaporation using a resistance heating process, thus forming the hole injection layer 111. The thickness of the hole injection layer 111 was adjusted to 33.3 nm, and the weight ratio of PCPPn to molybdenum oxide was adjusted to 1:0.5. It should be noted that the co-evaporation process is an evaporation process in which a variety of different substances are simultaneously deposited from different evaporation sources in a treatment chamber.

[0223] Subsequently, a film of 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP), represented by the structural formula (ii) with a thickness of 20 nm, was formed on the hole injection layer 111 to form the hole transport layer 112.

[0224] Furthermore, on the hole transport layer 112, 2-[3'-(Dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), which is represented by the structural formula (ix), 4,4'-Di(1-naphthyl)-4"-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB), which is represented by the structural formula (x), and Bis[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato-κ 2O,O')iridium(III) (abbreviation: Ir(tBuppm)2(acac)), which is represented by the structural formula (v), deposited by Co vapor deposition with a thickness of 20 nm, wherein the mass ratio of 2mDBTBPDBq-II to PCBNBB and Ir(tBuppm)2(acac) is 0.8:0.2:0.06, so that the first light-emitting layer 113a was formed; Then, 2mDBTBPDBq-II and bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: Ir(tppr)2(dpm)), represented by structural formula (vi), were deposited by co-evaporation to a thickness of 20 nm, with a mass ratio of 2mDBTBPDBq-II to Ir(tppr)2(dpm) of 1:0.06, thus forming the second light-emitting layer 113b. It should be noted that 2mDBTBPDBq-II, which is a host material, and PCBNBB form an exciplex.

[0225] Then the electron transport layer 114 was formed on the light-emitting layer 113 in such a way that a 15 nm thick film of 2mDBTPDBq-II was formed and a 15 nm thick film of bathophene anthroline (abbreviation: BPhen), which is represented by the structural formula (vii), was formed.

[0226] After the formation of the electron transport layer 114, lithium fluoride (LiF) was deposited by vapor deposition with a thickness of 1 nm, so that an electron injection layer 115 was formed.

[0227] Finally, aluminum was deposited by vapor deposition to a thickness of 200 nm to form the second electrode 102, which served as a cathode. In this way, a light-emitting element 2 was produced in this example.

[0228] It should be noted that in all of the above vapor deposition steps, the vapor deposition was carried out using a resistance heating process.

[0229] Table 2 shows an element structure of the light-emitting element 1 obtained as described above. [Table 2] Hole injection layer Hole transport layer Light-emitting layer electron transport layer Electron injection layer First light-emitting layer Second light-emitting layer PCPP N :MoO x 4:233 nm BPAFLP20 nm 2mDBTPDBq-II:PCBNBB: Ir(tBuppm)2(acac)0.8:0.2:0.0620 nm 2mDBTPDBq-H:lr(tppr)2(dpm )1:0.0620 nm 2mDBTPDBq-II15 nm Bphen15 nm LiF1 nm

[0230] The light-emitting element 2 was sealed in a glove compartment using a glass substrate, the glove compartment containing a nitrogen atmosphere to prevent exposure to air (in particular, a sealing material was applied to an outer edge of the element and a heat treatment at 80 °C for 1 hour was carried out at the time of sealing).

[0231] For light-emitting element 2, Ir(tBuppm)2(acac) and Ir(tppr)2(dpm) were used as the first phosphorescent compound 113Da and the second phosphorescent compound 113Db, respectively. The relationship between a PL spectrum of Ir(tBuppm)2(acac) and ε(λ)λ is shown. 4The description of Ir(tppr)2(dpm) is the same as in the case of light-emitting element 1, and the description is not repeated. Reference is made to the description in relation to the Fig. 20A and Fig. Reference is made to 20B in Example 1. Accordingly, it is assumed that the energy transfer occurs efficiently between the first phosphorescent compound 113Da and the second phosphorescent compound 113Db in the light-emitting element 2.

[0232] The elemental properties of the light-emitting element were measured. It should be noted that the measurement was carried out at room temperature (in an atmosphere maintained at 25 °C).

[0233] Fig. Figure 24 shows the luminance-current efficiency properties of the light-emitting element 2. Fig. Figure 25 shows the voltage-luminance properties. Fig. Figure 26 shows the luminance-external quantum efficiency properties. Fig.Figure 27 shows the luminance-power efficiency characteristics.

[0234] The above shows that the light-emitting element 2 has excellent element properties. As can be seen in particular from the Fig. 24, Fig. 26 and Fig. As can be clearly seen in Figure 27, the light-emitting element exhibits a high emission efficiency and a high external quantum efficiency of no less than 20% at an approximately practical luminance (1000 cd / m²). 2 ). Additionally, the current yield was approximately 60 cd / A and the power efficiency was approximately 60 Im / W, which are excellent values.

[0235] Fig. Figure 28 shows an emission spectrum of the light-emitting element 2, which was obtained when a current of 0.1 mA flowed through the light-emitting element 1. Fig.28 shows that the light-emitting element exhibits an emission spectrum, including light with a wavelength in a green wavelength range, which is from Bis[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato-κ 2 O,O')iridium(III) (abbreviation: Ir(tBuppm)2(acac)) is derived from, and light with a wavelength in a red wavelength range, which is derived from Bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: Ir(tppr)2(dpm)) is in a good balance.

[0236] Furthermore, it shows Fig. 29 the results of a reliability study under conditions where the initial luminance was 5000 cd / m² 2 Assuming 100% and a constant current density, as shown... Fig. As becomes clear in section 29, the light-emitting element 2 maintained the initial luminance of 5000 cd / m², regardless of the reliability test. 296% of the initial luminance was retained after 70 hours, demonstrating that the light-emitting element had high reliability.

[0237] It is evident from the above that the light-emitting element 2, which corresponded to an embodiment of the present invention, exhibited high emission efficiency and provided light from two types of emission center substances in a good balance. It was also shown that the light-emitting element exhibited high reliability and a long lifetime. Example 3

[0238] This example describes a method for producing a light-emitting element corresponding to an embodiment described in embodiments 1 and 2, and outlines its properties. The structural formulas of the organic compounds used in this example are shown below.

[0239] The following describes a method for producing the light-emitting element of this example.

[0240] First, a film of indium tin oxide containing silicon dioxide (ITSO) was formed on a glass substrate by a sputtering process, creating the first electrode 101. This electrode had a thickness of 110 nm and an electrode area of ​​2 mm x 2 mm. The first electrode 101 serves as the anode of the light-emitting element.

[0241] Subsequently, as a pretreatment to form the light-emitting element on the substrate, a UV ozone treatment was carried out for 370 seconds after a surface of the substrate was washed with water and the substrate was heated for one hour at 200°C.

[0242] The substrate was then transferred to a vacuum vapor deposition unit, where the pressure was increased to approximately 10 -4The Pa had been reduced, and the substrate was heated in a vacuum at 170 °C for 30 minutes in a heating chamber of the vacuum steam device, and then cooled for approximately 30 minutes.

[0243] The substrate on which the first electrode 101 was formed was then attached to a substrate holder provided in the vacuum vapor deposition unit such that the surface on which the first electrode 101 was formed faced downwards. The pressure in the vacuum vapor deposition unit was set to approximately 10 -4Pa was reduced. Subsequently, 4,4',4"-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), represented by structural formula (i), and molybdenum(VI) oxide were deposited on the first electrode 101 by co-evaporation using a resistance heating process, thus forming the hole injection layer 111. The thickness of the hole injection layer 111 was adjusted to 40 nm, and the weight ratio of DBT3P-II to molybdenum oxide was adjusted to 4:2. It should be noted that the co-evaporation process is an evaporation process in which a variety of different substances are simultaneously deposited from different evaporation sources in a treatment chamber.

[0244] Subsequently, a film of 4,4',4"-Tri(N-carbazolyl)triphenylamine (abbreviation: TCTA), represented by the structural formula (xi) with a thickness of 10 nm, was formed on the hole injection layer 111 to form the hole transport layer 112.

[0245] Furthermore, TCTA and Bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: Ir(tppr)2(dpm)), which is represented by the structural formula (vi), were deposited on the hole transport layer 112 by co-evaporation with a thickness of 10 nm, wherein a mass ratio of TCTA to Bis Ir(tppr)2(dpm) was 1:0.1, so that the second light-emitting layer 113b was formed; Subsequently, 2-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), which is represented by structural formula (iii), 4-phenyl-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), which was represented by structural formula (iv), and bis[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato-κ 2Ir(tBuppm)2(acac) (abbreviation: Ir(tBuppm)2(acac)), represented by the structural formula (v), was deposited by cobalt vapor deposition to a thickness of 5 nm, with a mass ratio of 2mDBTPDBq-II to PCBA1BP and Ir(tBuppm)2(acac) of 0.8:0.2:0.05, thus forming the first light-emitting layer 113a. It should be noted that 2mDBTPDBq-II, which is a host material, and PCBA1BP form an exciplex.

[0246] Then the electron transport layer 114 on the light-emitting layer 113 was formed in such a way that 2mDBTPDBq-II and Ir(tBuppm)2(acac) were deposited by Co evaporation with a thickness of 20 nm, with a mass ratio of 2mDBTPDBq-II to Ir(tBuppm)2(acac) of 1:0.05, a 10 nm thick film of 2mDBTPDBq-II was formed, and a 20 nm thick film of bathophene anthroline (abbreviation: BPhen), which is represented by the structural formula (vii), was formed.

[0247] After the formation of the electron transport layer 114, lithium fluoride (LiF) was deposited by vapor deposition with a thickness of 1 nm, so that an electron injection layer 115 was formed.

[0248] Finally, aluminum was deposited by vapor deposition to a thickness of 200 nm to form the second electrode 102, which served as a cathode. In this way, a light-emitting element 3 was produced in this example.

[0249] It should be noted that in all of the above vapor deposition steps, the vapor deposition was carried out using a resistance heating process.

[0250] Table 3 shows an elemental structure of the light-emitting element 3 obtained as described above. The materials of the hole transport layer and the second host material of light-emitting element 3 differ significantly from those of light-emitting element 1 and light-emitting element 2. Additionally, there are also significant differences in the positions of the first and second light-emitting layers with respect to the electrode and the structure of the electron transport layer. [Table 3] Hole injection layer Hole transport layer Light-emitting layer electron transport layer Electron injection layer First light-emitting layer Second light-emitting layer DBT3P-II:MoO x 4:233 nm TCTA10 nm TCTA:Ir(tppr)2(dpm)1:0,110 nm 2mDBTPDBq-II:PCBA1BP: Ir(tBuppm)2(acac)0.8:0.2:0.055 nm 2mDBTPDBq-II:Ir(tBuppm)2(acac)0.8:0.0520 nm 2mDBTPDBq-II10 nm Bphen15 nm LiF1 nm

[0251] The light-emitting element 3 was sealed in a glove compartment using a glass substrate, the glove compartment containing a nitrogen atmosphere to prevent exposure to air (in particular, a sealing material was applied to an outer edge of the element and a heat treatment at 80 °C for 1 hour was carried out at the time of sealing).

[0252] For light-emitting element 3, as with light-emitting element 1, Ir(tBuppm)2(acac) and Ir(tppr)2(dpm) were used as the first phosphorescent compound 113Da and the second phosphorescent compound 113Db. The relationship between a PL spectrum of Ir(tBuppm)2(acac) and ε(λ)λ is shown. 4 The description of Ir(tppr)2(dpm) is the same as in the case of light-emitting element 1, and the description is not repeated. Reference is made to the description in relation to the Fig. 20A and Fig. Reference is made to 20B in Example 1. Accordingly, it is assumed that the energy transfer occurs efficiently between the first phosphorescent compound 113Da and the second phosphorescent compound 113Db in the light-emitting element 3.

[0253] The elemental properties of the light-emitting element were measured. It should be noted that the measurement was carried out at room temperature (in an atmosphere maintained at 25 °C).

[0254] Fig. Figure 30 shows the luminance-current efficiency properties of the light-emitting element 3. Fig. Figure 31 shows the voltage-luminance properties. Fig. Figure 32 shows the luminance-external quantum efficiency properties. Fig. Figure 33 shows the luminance-power efficiency characteristics.

[0255] The above shows that the light-emitting element 3 exhibits excellent element properties. This is particularly evident from the... Fig. 30, Fig. As can be clearly seen in Figure 32 and Figure 237, the light-emitting element exhibits a high emission efficiency and a high external quantum efficiency of no less than 20% at an approximately practical luminance (1000 cd / m²). 2). Additionally, the current yield was approximately 60 cd / A and the power efficiency was approximately 60 Im / W, which are excellent values.

[0256] Fig. Figure 34 shows an emission spectrum of the light-emitting element 3, which was obtained when a current of 0.1 mA flowed through the light-emitting element 3. Fig. 34 shows that the light-emitting element exhibits an emission spectrum, including light with a wavelength in a green wavelength range, which is from Bis[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato-κ 2 O,O')iridium(III) (abbreviation: Ir(tBuppm)2(acac)) originates, and light with a wavelength in a red wavelength range, which originates from Bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: Ir(tppr)2(dpm)), in a good balance.

[0257] It is evident from the above that the light-emitting element 3, which corresponded to an embodiment of the present invention, had a high emission efficiency and provided light from two types of emission center substances in a good balance, although the host material differed from that used in the light-emitting elements 1 and 2. Example 4

[0258] This example describes a method for producing a light-emitting element, corresponding to an embodiment described in embodiments 1 and 2, and its properties. The structural formulas of the organic compounds used in this example are shown below.

[0259] The following describes a method for producing the light-emitting element (a light-emitting element 4 and a light-emitting element 5) of this example.

[0260] First, a film of indium tin oxide containing silicon dioxide (ITSO) was formed on a glass substrate by a sputtering process, creating the first electrode 101. This electrode had a thickness of 110 nm and an electrode area of ​​2 mm x 2 mm. The first electrode 101 serves as the anode of the light-emitting element.

[0261] Subsequently, as a pretreatment to form the light-emitting element on the substrate, a UV ozone treatment was carried out for 370 seconds after a surface of the substrate was washed with water and the substrate was heated for one hour at 200°C.

[0262] The substrate was then transferred to a vacuum vapor deposition unit, where the pressure was increased to approximately 10 -4 The Pa had been reduced, and the substrate was heated in a vacuum at 170 °C for 30 minutes in a heating chamber of the vacuum steam device, and then cooled for approximately 30 minutes.

[0263] The substrate on which the first electrode 101 was formed was then attached to a substrate holder provided in the vacuum evaporation unit such that the surface on which the first electrode 101 was formed faced downwards. The pressure in the vacuum evaporation unit was set to approximately 10 -4Pa was reduced. Subsequently, 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP), represented by structural formula (ii), and molybdenum(VI) oxide were deposited on the first electrode 101 by co-evaporation using a resistance heating process, thus forming the hole injection layer 111. The thickness of the hole injection layer 111 was adjusted to 33.3 nm, and the weight ratio of BPAFLP to molybdenum oxide was adjusted to 1:0.5. It should be noted that the co-evaporation process is an evaporation process in which a variety of different substances are simultaneously deposited from different evaporation sources in a treatment chamber.

[0264] Subsequently, a BPAFLP film with a thickness of 20 nm was formed on the hole injection layer 111 to form the hole transport layer 112.

[0265] Des Weiteren wurde auf der Lochtransportschicht 112 2-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]chinoxalin (Abkürzung: 2mDBTPDBq-II) represented by Structural Formel (iii), 4-phenyl-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (Abkürzung: PCBA1BP) represented by Structural Formel (iv), and bis[2-(6-tert-butyl-4-pyrimidinyl-ĸN3)phenyl-ĸC](2,4-pentanedionato-x 2 O, O)iridium(IIl) (Abkürzung: Ir(tBuppm)2(acac)) represented by Structural Formel (v) were deposited by co-evaporation to a thickness of 20 nm with a mass ratio of 2mDBTPDBq-II to PCBA1BP and Ir(tBuppm)2(acac) being 0.8:0.2:0.06, so that the first light-emitting layer 113a was formed; then, 2mDBTPDBq-ll and bis{4,6-dimethyl-2-[3-(3,5-dimethylphenyl)-5-phenyl-2-pyrazinyl-κN]phenyl-κC}(2,6-dimethyl-3,5-heptanedionato-κ 2O,O')iridium(III) (Abbreviation: [Ir(dmdppr-P)2(dibm)]) represented by Structural Formula (xii) were deposited by co-evaporation to a thickness of 20 nm with a mass ratio of 2mDBTPDBq-II to [Ir(dmdppr-P)2(dibm)] being 1:0.06, so that the second light-emitting layer 113b was formed.

[0266] It should be noted that 2mDBTPDBq-II, which is a host material, and PCBA1BP form an Exciplex.

[0267] Then the electron transport layer 114 was formed on the light-emitting layer 113 in such a way that a 15 nm thick film of 2mDBTPDBq-II was formed and a 15 nm thick film of bathophene anthroline (abbreviation: BPhen), which is represented by the structural formula (vii), was formed.

[0268] After the formation of the electron transport layer 114, lithium fluoride (LiF) was deposited by vapor deposition with a thickness of 1 nm, so that an electron injection layer 115 was formed.

[0269] Finally, aluminum was deposited by vapor deposition to a thickness of 200 nm to form the second electrode 102, which served as a cathode. In this way, a light-emitting element 4 was produced in this example.

[0270] The light-emitting element 5 was prepared in the same way as the light-emitting element 4, except that the first light-emitting layer was used instead of [Ir(tBuppm)2(acac)] Tris[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC]iridium(III) (abbreviation: [Ir(tBuppm)3)]), which is represented by the structural formula (xiii).

[0271] It should be noted that in all of the above vapor deposition steps, the vapor deposition was carried out using a resistance heating process.

[0272] Tables 4 and 5 show element structures of the light-emitting elements 4 and 5 obtained as described above. [Table 4] Hole injection layer Hole transport layer Light-emitting layer electron transport layer Electron injection layer First light-emitting layer Second light-emitting layer BPAFLP:MoO x 4:233 nm BPAFLP20 nm 2mDBTPDBq-II:PCBA1BP: Ir(tBuppm)2(acac)0.8:0.2:0.0620 nm 2mDBTPDBq-II:Ir(tppr)2(dpm )1:0.0620 nm 2mDBTPDBq-II15 nm Bphen15 nm LiF1 nm [Table 5] Hole injection layer Hole transport layer Light-emitting layer electron transport layer Electron injection layer First light-emitting layer Second light-emitting layer BPAFLP:MoO x 4:233 nm BPAFLP20 nm 2mDBTPDBq-II:PCBA1BP: Ir(tBuppm)2(acac)0.8:0.2:0.0620 nm 2mDBTPDBq-II:Ir(tppr)2(dpm )1:0.0620 nm 2mDBTPDBq-ll15 nm Bphen15 nm LiF1 nm

[0273] The light-emitting elements 4 and 5 were sealed using a glass substrate in a glove compartment, the glove compartment containing a nitrogen atmosphere to prevent exposure to air (in particular, a sealing material was applied to an outer edge of the element and a heat treatment at 80 °C for 1 hour was carried out at the time of sealing).

[0274] For light-emitting element 4, Ir(tBuppm)₂(acac) and Ir(dmdppr-P)₂(dibm) were used as the first phosphorescent compound 113Da and the second phosphorescent compound 113Db, respectively. A relationship is established between the PL spectrum of Ir(tBuppm)₂(acac) and ε(λ)λ. 4 described by [Ir(dmdppr-P)2(dibm)]. It should be noted that λ represents a wavelength and ε(λ) represents a molar absorption coefficient.

[0275] Fig. Figure 45A shows curves of the molar absorption coefficient ε(λ) and ε(λ)λ. 4 of [Ir(dmdppr-P)2(dibm)]. While the molar absorption coefficient ε(λ) showed no noticeable peak in a region on the long-wavelength side, the curve of ε(λ)λ 4 The peak exhibits a local maximum at 509 nm and shoulders at approximately 550 nm and 505 nm. This peak represents the triplet MLCT absorption of [Ir(dmdppr-P)2(dibm)]. If this peak overlaps with an emission peak of the first phosphorescent compound 113Da, the energy transfer efficiency can be significantly increased.

[0276] Fig. Figure 45B shows the PL spectrum F(λ) of Ir(tBuppm)2(acac), which is the first phosphorescent compound 113Da in the light-emitting element 4, and the curve of ε(λ)λ 4of Ir(tppr)2(dpm), which is the second phosphorescent compound 113Db. The curve clearly shows that a band with a peak in the PL spectrum F(λ) of Ir(tBuppm)2(acac) differs significantly from the band with a peak on the long-wavelength side of ε(λ)λ. 4 overlaps with Ir(tppr)2(dpm), indicating that the combination enables extremely efficient energy transfer. Furthermore, Ir(tBuppm)2(acac), which is the first phosphorescent compound 113Da, exhibits an emission peak at 546 nm, and the spectrum, which ε(λ)λ 4 The waveform of Ir(tppr)2(dpm), which is the second phosphorescent compound 113Db, exhibits a local maximum on the long-wavelength side at 543 nm, resulting in a difference of 3 nm. The wavelengths of 546 nm and 543 nm correspond to 2.27 eV and 2.28 eV, respectively, so the difference is 0.01 eV, which is less than 0.2 eV; therefore, the peak positions also suggest the occurrence of efficient energy transfer.

[0277] For the light-emitting element 4, Ir(tBuppm)2(acac) and [Ir(dmdppr-P)2(dibm)] were used as the first phosphorescent compound 113Da and the second phosphorescent compound 113Db, respectively. Here, a relationship between a PL spectrum of Ir(tBuppm)2(acac) and ε(λ)λ is established. 4 described by [Ir(dmdppr-P)2(dibm)]. It should be noted that λ represents a wavelength and ε(λ) represents a molar absorption coefficient.

[0278] Fig. Figure 45A shows curves of the molar absorption coefficient ε(λ) and s(λ)λ 4 of [Ir(dmdppr-P)2(dibm)], which is the second phosphorescent compound 113Db in the light-emitting element 4. While the molar absorption coefficient ε(λ) does not show a distinct peak in a region on a long-wavelength side, the curve of ε(λ)λ 4The peak contains a local maximum at 509 nm and shoulders at approximately 550 nm and 605 nm. This peak exhibits triplet MLCT absorption of [Ir(dmdppr-P)2(dibm)]. When this peak overlaps with an emission peak of the first phosphorescent compound 113Da, the energy transfer efficiency can be significantly increased.

[0279] Fig. Figure 45B shows the PL spectrum F(λ) of Ir(tBuppm)2(acac), which is the first phosphorescent compound 113Da in the light-emitting element 4, and the curve of ε(λ)λ 4 of [Ir(dmdppr-P)2(dibm)], which is the second phosphorescent compound 113Db. As can be clearly seen from the curve, a band with a peak of the PL spectrum F(λ) of Ir(tBuppm)2(acac) overlaps significantly with the band with a peak on the long-wavelength side of (λ)λ. 4of [Ir(dmdppr-P)2(dibm)], which indicates that the combination enables extremely efficient energy transfer. Furthermore, Ir(tBuppm)2(acac), which is the first phosphorescent compound 113Da, exhibits an emission peak at 546 nm, and the spectrum, which ε(λ)λ 4 The equation for [Ir(dmdppr-P)2(dibm)], which shows that the second phosphorescent compound is 113Db, exhibits a local maximum on a long-wavelength side at 509 nm, so the difference is 37 nm. The wavelengths 546 nm and 509 nm correspond to 2.27 eV and 2.44 eV, respectively, so the difference is 0.17 eV, which is less than 0.2 eV; therefore, the peak positions also indicate the occurrence of efficient energy transfer. It should be noted that although the peak is on the long-wavelength side (peak C) in the ε(λ)λ 4The spectrum showing [Ir(dmdppr-P)2(dibm)] hardly overlaps with the spectrum F(λ) of Ir(tBuppm)2(acac), the band containing peak C in the spectrum which ε(λ)λ 4 The emission spectrum of [Ir(dmdppr-P)2(dibm)] exhibits a broad shape on the long-wavelength side, and shows a significant overlap with the emission spectrum F(λ) of Ir(tBuppm)2(acac) on the longer-wavelength side. Consequently, efficient energy transfer is achieved.

[0280] In light-emitting element 4, 2mDBTPDBq-II, which is the first host material, and PCBA1BP, which is the first organic compound, form an exciplex, so that energy is efficiently transferred to Ir(tBuppm)2(acac), which is the first phosphorescent compound 113Da. The relationship is similar to that of light-emitting element 1 and was described in detail in Example 1, so the description is not repeated here. Reference is made to the corresponding description in Example 1.

[0281] Fig. Figure 46 shows the PL spectrum F(λ) of the exciplex, the PL spectrum F(λ) of Ir(tBuppm)2(acac), a PL spectrum F(λ) of [Ir(dmdppr-P)2(dibm)], ε(λ)λ 4 of Ir(tBuppm)2(acac), and ε(λ)λ 4 of [Ir(dmdppr-P)2(dibm)]. It becomes clear that the energy is transferred stepwise from the exciplex to Ir(tBuppm)2(acac) by the overlap between the PL spectrum of the exciplex and ε(λ)λ 4from Ir(tBuppm)2(acac) (around peak A) is used, and then from Ir(tBuppm)2(acac) to [Ir(dmdppr-P)2(dibm)] by the overlap between the PL spectrum of Ir(tBuppm)2(acac) and ε(λ)λ 4 from [Ir(dmdppr-P)2(dibm)] (approximately a range from peak C to 650 nm). It should be noted that direct energy transfer from the exciplex to [Ir(dmdppr-P)2(dibm)], which is the second phosphorescent compound, is also possible. The reason for this is that, as shown from Fig. 46 becomes clear, ε(λ)λ 4 [Ir(dmdppr-P)2(dibm)] also overlaps with the PL spectrum F(λ) of the exciplex in the triplet MLCT absorption band (around peak C) of [Ir(dmdppr-P)2(dibm)].

[0282] For the light-emitting element 5, Ir(tBuppm)3 and [Ir(dmdppr-P)2(dibm)] were used as the first phosphorescent compound 113Da and the second phosphorescent compound 113Db, respectively. Here, a relationship between a PL spectrum of Ir(tBuppm)3 and ε(λ)λ is established. 4 described by [Ir(dmdppr-P)2(dibm)]. It should be noted that λ represents a wavelength and ε(λ) represents a molar absorption coefficient.

[0283] Fig. Figure 47A shows curves of the molar absorption coefficient ε(λ) and ε(λ)λ 4 of [Ir(dmdppr-P)2(dibm)], which is the second phosphorescent compound 113Db in the light-emitting element 5. While the molar absorption coefficient ε(λ) does not show a distinct peak in a region on the longer-wavelength side, the curve of ε(λ)λ 4The peak contains a local maximum at 509 nm and shoulders at approximately 550 nm and 605 nm. This peak exhibits triplet MLCT absorption of [Ir(dmdppr-P)2(dibm)]. If this peak overlaps with an emission peak of the first phosphorescent compound 113Da, the energy transfer efficiency can be significantly increased.

[0284] Fig. Figure 47B shows the PL spectrum F(λ) of Ir(tBuppm)3, which is the first phosphorescent compound 113Da in the light-emitting element 5, and the curve of ε(λ)λ 4 of [Ir(dmdppr-P)2(dibm)], which is the second phosphorescent compound 113Db. The curve clearly shows that a band with a peak in the PL spectrum F(λ) of Ir(tBuppm)3 is distinct from the band with the peak on the long-wavelength side of ε(λ)λ. 4overlaps with [Ir(dmdppr-P)2(dibm)], demonstrating that the combination enables extremely efficient energy transfer. Furthermore, Ir(tBuppm)3, which is the first phosphorescent compound 113Da, exhibits an emission peak at 540 nm, and the spectrum, which ε(λ)λ 4 [Ir(dmdppr-P)2(dibm)], which is the second phosphorescent compound 113Db, exhibits a local long-wavelength maximum at 509 nm, so the difference is 31 nm. The wavelengths 540 nm and 509 nm correspond to 2.30 eV and 2.44 eV, respectively, so the difference is 0.14 eV, which is less than 0.2 eV; therefore, the peak positions also suggest that efficient energy transfer occurs. It should be noted that although the local long-wavelength maximum (peak C) in the spectrum, ε(λ)λ 4 of [Ir(dmdppr-P)2(dibm)] shows, hardly overlaps with the spectrum F(λ) of Ir(tBuppm)3, the band containing the peak C in the spectrum that ε(λ)λ4 The spectrum of [Ir(dmdppr-P)2(dibm)] shows a broad shape on the long-wavelength side, and that the spectrum on the long-wavelength side exhibits a large overlap with the emission spectrum F(λ) of Ir(tBuppm)3. Consequently, extremely efficient energy transfer is achieved.

[0285] Fig. Figure 48A shows the curves of the molar absorption coefficient ε(λ) and ε(λ)λ 4 of Ir(tBuppm)3, which is the first phosphorescent compound 113Da in the light-emitting element 5. The curve of ε(λ)λ 4 The image exhibits high-intensity peaks at 409 nm and 465 nm, and a peak containing a shoulder at 494 nm. This peak shows triplet MLCT absorption of Ir(tBuppm)3. If this peak overlaps with a peak from an energy donor, energy transfer efficiency can be significantly increased.

[0286] In this example, the light-emitting element 5, 2mDBTPDBq-II, which is the first host material, and PCBA1BP, which is the first organic compound, form the exciplex 113Ec, and energy is transferred from the exciplex 113Ec to the first phosphorescent compound 113Da. Fig. Figure 23 shows PL spectra of 2mDBTPDBq-II, PCBA1BP and a mixed film of these (a mass ratio of 2mDBTPDBq-II to PCBA1BP is 0.8:0.2), and it becomes clear that 2mDBTPDBq-II and PCBA1BP, which is the first organic compound, form the Exciplex 113Ec. Fig. Figure 48B shows a PL spectrum F(λ) of the exciplex and the curve of ε(λ)λ 4of Ir(tBuppm)3, which is the first phosphorescent compound 113Da. The curve shows that part of a wavelength range where a band with a peak of the PL spectrum F(λ) of the exciplex has half the intensity of the peak overlaps part of the wavelength range where a band with a peak on the long-wavelength side of ε(λ)λ 4 Ir(tBuppm)3 exhibits half the intensity of the peak, demonstrating that the combination enables efficient energy transfer.

[0287] Fig. Figure 49 shows the PL spectrum F(λ) of the exciplex, the PL spectrum F(λ) of Ir(tBuppm)3, a PL spectrum F(λ) of [Ir(dmdppr-P)2(dibm)], ε(λ)λ 4 of Ir(tBuppm)3, and ε(λ)λ 4 from [Ir(dmdppr-P)2(dibm)]. It becomes clear that the energy is transferred stepwise first from the exciplex to Ir(tBuppm)3 by the overlap between the PL spectrum of the exciplex and ε(λ)λ 4is used from Ir(tBuppm)3 (around peak A), and then from Ir(tBuppm)3 to [Ir(dmdppr-P)2(dibm)] by the overlap between the PL spectrum of Ir(tBuppm)3 and ε(λ)λ 4 of [Ir(dmdppr-P)2(dibm)] (a region from peak C to 650 nm) is used. It should be noted that direct energy transfer from the exciplex to [Ir(dmdppr-P)2(dibm)], which is the second phosphorescent compound, is also possible. The reason for this is, as can be seen from the Fig. 49 becomes clear, ε(λ)λ 4 [Ir(dmdppr-P)2(dibm)] also overlaps with the PL spectrum F(λ) of the exciplex in the triplet MLCT absorption band (around peak C) of [Ir(dmdppr-P)2(dibm)].

[0288] The elemental properties of the light-emitting element were measured. It should be noted that the measurement was carried out at room temperature (in an atmosphere maintained at 25 °C).

[0289] Fig.Figure 35 shows the luminance-current efficiency properties of the light-emitting element 4. Fig. Figure 36 shows the voltage-luminance properties. Fig. Figure 37 shows the luminance-external quantum efficiency properties. Fig. Figure 38 shows the luminance-power efficiency characteristics.

[0290] The above showed that the light-emitting element 4 exhibited excellent elemental properties. In particular, it is shown that Fig. 35, Fig. 37 and Fig. 38 clearly shows that the light-emitting element has extremely high emission efficiency and a high external quantum efficiency of no less than 20% at a practical luminance (1000 cd / m²). 2 ). Additionally, the current yield was approximately 50 cd / A and the conduction efficiency was approximately 50 Im / W, which were excellent values.

[0291] Fig.Figure 39 shows an emission spectrum of the light-emitting element 4, which was obtained when a current of 0.1 mA flowed through the light-emitting element. Fig. 39, the horizontal axis indicates a wavelength (nm) and the vertical axis an arbitrary unit of light emission intensity. Fig. 39 states that the light-emitting element 4 exhibits an emission spectrum including light with a wavelength in a green wavelength range, which originates from [Ir(tBuppm)2(acac)], and light with a wavelength in a red wavelength range, which originates from [Ir(dmdppr-P)2(dibm)], in good balance.

[0292] Fig. Figure 40 shows the luminance-current efficiency properties of the light-emitting element 5. Fig. Figure 41 shows the voltage-luminance properties. Fig. Figure 42 shows the luminance-external quantum efficiency properties. Figure 438 shows the luminance-power efficiency properties.

[0293] The above showed that the light-emitting element 5 exhibited excellent elemental properties. In particular, it is shown that Fig. 40, Fig. 42 and Fig. 43 clearly shows that the light-emitting element has extremely high emission efficiency and a high external quantum efficiency of no less than 25% at a practical luminance (1000 cd / m²). 2 ). Additionally, the current yield was approximately 65 cd / A and the conduction efficiency was approximately 70 Im / W, which were excellent values.

[0294] Fig. Figure 44 shows an emission spectrum of the light-emitting element 5, which was obtained when a current of 0.1 mA flowed through the light-emitting element 5. Fig. 44, the horizontal axis indicates a wavelength (nm) and the vertical axis an arbitrary unit of light emission intensity. Fig.44 states that the light-emitting element 5 exhibits an emission spectrum including light with a wavelength in a green wavelength range, which originates from [Ir(tBuppm)2(acac)], and light with a wavelength in a red wavelength range, which originates from [Ir(dmdppr-P)2(dibm)], in good balance.

[0295] It is evident from the above that the light-emitting elements 4 and 5, each corresponding to an embodiment of the present invention, had a high emission efficiency and provided light from two types of emission center substances in a good balance. Reference example 1

[0296] Preparation of the organometallic complex Bis[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato-κ 2[Ir(tBuppm)2(acac)] (abbreviation: O,O')iridium(III) (abbreviation: [Ir(tBuppm)2(acac)]) is described, which is used in the above embodiment. The structure of [Ir(tBuppm)2(acac)] is shown below. (Step 1: Preparation of 4-tert-butyl-6-phenylpyrimidine (abbreviation: HtBuppm))

[0297] First, 22.5 g of 4,4-dimethyl-1-phenylpentane-1,3-dione and 50 g of formamide were placed in a round-bottom flask equipped with a reflux tube, and the air in the flask was replaced with nitrogen. This reaction vessel was heated so that the reacted solution refluxed for 5 hours. Subsequently, this solution was poured into an aqueous sodium hydroxide solution, and an organic layer was extracted with dichloromethane. The resulting organic layer was washed with water and a saturated salt solution and dried with magnesium sulfate. After drying, the solution was filtered. The solvent of this solution was distilled off, and the resulting residue was purified by silica gel column chromatography using hexane and ethyl acetate as mobile phases in a volume ratio of 10:1, yielding a pyrimidine derivative, HtBuppm (a colorless, oily substance, yield 14%).A synthesis scheme for step 1 is shown below. (Step 2: Preparation of di-µ-chlorobis[bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)] (abbreviation: [Ir(tBuppm)2Cl]2))

[0298] Subsequently, 15 ml of 2-ethoxyethanol, 5 ml of water, 1.49 g of HtBuppm obtained in step 1, and 1.04 g of iridium chloride hydrate (IrCl3·H2O) were introduced into a round-bottom flask equipped with a reflux tube, and the air in the flask was replaced with argon. Irradiation with microwaves (2.45 GHz, 100 W) was then carried out for one hour to initiate the reaction. The solvent was distilled off, and the resulting residue was filtered and washed with ethanol to obtain a dinuclear complex [Ir(tBuppm)2Cl]2 (yellow-green powder, yield 73%). A synthesis scheme for step 2 is shown below. (Step 3: Preparation of (Acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(tBuppm)2(acac)]))

[0299] Furthermore, 40 ml of 2-ethoxyethanol, 1.61 g of the dinuclear complex [Ir(tBuppm)2Cl]2 obtained in step 2, 0.36 g of acetylacetone, and 1.27 g of sodium carbonate were introduced into a round-bottom flask equipped with a reflux tube, and the air in the flask was replaced with argon. Microwave irradiation was then carried out for 60 minutes to initiate the reaction. The solvent was distilled off, and the resulting residue was filtered with ethanol and washed with water and ethanol. This solid was dissolved in dichloromethane, and the mixture was filtered through a filter aid consisting of Celite (manufactured by Wako Pure Chemical Industries, Ltd., catalog no. 531-16855), aluminum oxide, and Celite stacked in that order.The solvent was distilled off and the resulting solid was recrystallized with a mixed solvent of dichloromethane and hexane to obtain the desired substance as a yellow powder (yield 68%). A synthesis scheme for step 3 is shown below.

[0300] An analysis result by nuclear magnetic resonance spectroscopy ( 1 The ¹H NMR analysis of the yellow powder obtained in step 3 is described below. The result showed that the organometallic complex Ir(tBuppm)₂(acac) was obtained.

[0301] 1 H NMR. δ (CDCl3): 1.50 (s, 18H), 1.79 (s, 6H), 5.26 (s, 1H), 6.33 (d, 2H), 6.77 (t, 2H), 6.85 (t, 2H), 7.70 (d, 2H), 7.76 (s, 2H), 9.02 (s, 2H). Reference example 2

[0302] This reference example describes the synthesis of Bis{4,6-dimethyl-2-[3-(3,5-dimethylphenyl)-5-phenyl-2-pyrazinyl-κN]phenyl-κC}(2,6-dimethyl-3,5-heptanedionato-κ 2O,O')iridium(III) (abbreviation: [Ir(dmdppr-P)2(dibm)]), the iridium complex used in this organometallic example, is described. The structure of [Ir(dmdppr-P)2(dibm)] (abbreviation) is shown below. (Step 1: Preparation of 2,3-Bis(3,5-dimethylphenyl)pyrazine (abbreviation: Hdmdppr))

[0303] First, 5.00 g of 2,3-dichloropyrazine, 10.23 g of 3,5-dimethylphenylboronic acid, 7.19 g of sodium carbonate, 0.29 g of bis(triphenylphosphine)palladium(II) dichloride (abbreviation: Pd(PPh3)2Cl2), 20 ml of water, and 20 ml of acetonitrile were placed in a round-bottom flask equipped with a reflux tube, and the air in the flask was replaced with nitrogen. This reaction vessel was then subjected to microwave irradiation (2.45 GHz, 100 W) for 60 minutes to heat it. Furthermore, 2.55 g of 3,5-dimethylphenylboronic acid, 1.80 g of sodium carbonate, 0.070 g of Pd(PPh3)2Cl2, 5 ml of water and 5 ml of acetonitrile were added and irradiation with microwaves (2.45 GHz, 100 W) was carried out again for 60 minutes to heat the mixture.

[0304] Water was then added to this solution, and the organic layer was extracted with dichloromethane. The resulting organic layer was washed with a saturated aqueous sodium hydrogen solution, water, and a saturated sodium chloride solution, and dried with magnesium sulfate. After drying, the solution was filtered. The solvent was distilled off, and the residue was purified by flash column chromatography using hexane and ethyl acetate as a mobile phase in a 5:1 ratio. The solvent was then distilled off, and the residue was purified by flash column chromatography using dichloromethane and ethyl acetate as a mobile phase in a 10:1 volume ratio, yielding Hdmdppr (abbreviation), the pyrazine derivative to be prepared, as a white powder in a 44% yield.It should be noted that the microwave irradiation was performed using a microwave system (Discover, manufactured by CEM Corporation). A synthesis scheme for step 1 is shown in (a-1). (Step 2: Preparation of 2,3-Bis(3,5-dimethylphenyl)-5-phenylpyrazine (abbreviation: Hdmdppr-P))

[0305] First, 4.28 g of Hdmdppr (abbreviation), obtained in step 1, and 80 ml of dry THF were introduced into a three-necked flask, and the air in the flask was replaced with nitrogen. After cooling the flask with ice, 9.5 ml of phenyllithium (1.9 M phenyllithium solution in butyl ether) was added dropwise, and the mixture was stirred at room temperature for 23.5 hours. The reacted solution was poured into water, and the solution was extracted with chloroform. The resulting organic layer was washed with water and a saturated sodium chloride solution and dried with magnesium sulfate. Manganese oxide was added to the resulting mixture, and the mixture was stirred for 30 minutes. Subsequently, the solution was filtered, and the solvent was distilled off.The residue obtained was purified by silica gel column chromatography using dichloromethane as a mobile phase, yielding Hdmdppr-P (abbreviation), the pyrazine derivative to be prepared, as an orange oil in a yield of 26%. A synthesis scheme for step 2 is shown in (a-2). (Step 3: Preparation of di-µ-chlorotetrakis{4,6-dimethyl-2-[3-(3,5-dimethylphenyl)-5-phenyl-2-pyrazinyl-κN]phenyl-κC}diiridium(III) (abbreviation: [Ir(dmdppr-P)2Cl]2)〉

[0306] Subsequently, 15 ml of 2-ethoxyethanol, 5 ml of water, 1.40 g of Hdmdppr-P (abbreviation) obtained in step 2, and 0.51 g of iridium chloride hydrate (IrCl3·H2O) (prepared by Sigma-Aldrich Corporation) were introduced into a round-bottom flask equipped with a reflux tube, and the air in the flask was replaced with argon. Irradiation with microwaves (2.45 GHz, 100 W) was then carried out for 1 hour. The solvent was distilled off, and the resulting residue was filtered and washed with ethanol to obtain [Ir(dmdppr-P)2Cl]2 (abbreviation), a dinuclear complex, as a reddish-brown powder in a yield of 58%. A synthesis scheme for step 3 is shown in (a-3). (Step 4: Preparation of Bis{4,6-dimethyl-2-[3-(3,5-dimethylphenyl)-5-phenyl-2-pyrazinyl-κN]phenyl-κC}(2,6-dimethyl-3,5-heptanedionato-κ 2 O,O')iridium(III) (Abbreviation: [Ir(dmdppr-P)2(dibm)])〉

[0307] Furthermore, 30 ml of 2-ethoxyethanol, 0.94 g of [Ir(dmdppr-P)₂Cl]₂ (the dinuclear complex obtained in step 3), 0.23 g of diisobutyrylmethane (abbreviated Hdibm), and 0.52 g of sodium carbonate were introduced into a round-bottom flask equipped with a reflux tube, and the air in the flask was replaced with argon. Irradiation with microwaves (2.45 GHz, 120 W) was then carried out for 60 minutes. The solvent was distilled off, and the resulting residue was filtered with ethanol. The resulting solid was washed with water and ethanol, and recrystallization was carried out with a mixed solvent of dichloromethane and ethanol, such that [Ir(dmdppr-P)2(dibm)] (abbreviation), the organometallic complex in one embodiment of the present invention, was obtained as a dark red powder in a yield of 75%. A synthesis scheme of step 4 is shown below in (a-4).

[0308] An analysis result by nuclear magnetic resonance spectroscopy ( 1 The ¹H NMR analysis of the dark red powder obtained by the above-described procedure is described below. The results showed that the organometallic complex [Ir(dmdppr-P)₂(dibm)] (abbreviation) was obtained in this preparation example.

[0309] 1 H-NMR, δ(CDCl3): 0.79 (d, 6H), 0.96 (d, 6H), 1.41 (s, 6H), 1.96 (s, 6H), 2.24-2.28 (m, 2H), 2.41 (s, 12H), 5.08 (s, 1H), 6.46 (s, 2H), 6.82 (s, 2H), 7.18 (s, 2H), 7.39-7.50 (m, 10H), 8.03 (d, 4H), 8.76 (s, 2H). Reference sign

[0310] 10: Electrode, 11: Electrode, 101: First electrode, 102: Second electrode, 103: EL layer, 111: Hole injection layer, 112: Hole transport layer, 113: Light-emitting layer, 113a: First light-emitting layer, 113Da: First phosphorescent compound, 113Ha: First host material, 113b: Second light-emitting layer, 113Db: Second phosphorescent compound, 113Hb: Second host material, 113A: First organic compound, 113Ec: Exciplex, 114: Electron transport layer, 115: Electron injection layer, 400: Substrate, 401: First electrode, 402: Auxiliary electrode, 403: EL layer, 404: Second electrode, 405: Sealing material 406: Gasket material, 407: Gasket substrate, 412: Pad, 420: IC chip, 601: Driver circuit area (sourceline driver circuit), 602: Pixel area, 603: Driver circuit area (gateline driver circuit), 604: Gasket substrate, 605: Gasket material, 607: Space, 608: Wiring, 609: FPC (flexible printed circuit board), 610: Element substrate,611: Switching TFT, 612: Current-controlling TFT, 613: First electrode, 614: Insulator, 616: EL layer, 617: Second electrode, 618: Light-emitting element, 623: n-channel TFT, 624: p-channel TFT, 625: Desiccant, 901: Package, 902: Liquid crystal layer, 903: Background illumination unit, 904: Package, 905: Driver IC, 906: Terminal, 951: Substrate, 952: Electrode, 953: Insulating layer, 954: Separating layer, 955: EL layer, 956: Electrode, 1001: Substrate, 1002: Base insulating film, 1003: Gate insulating film, 1006: Gate electrode 1007: Gate electrode, 1008: Gate electrode, 1020: First intermediate insulating layer, 1021: Second intermediate insulating layer, 1022: Electrode, 1024W: First electrode of a light-emitting element, 1024R: First electrode of a light-emitting element, 1024G: First electrode of a light-emitting element, 1024B: First electrode of a light-emitting element, 1025: Partition, 1028: EL layer1029: second electrode of a light-emitting element, 1031: sealing substrate, 1032: sealant, 1033: transparent base material, 1034R: red color layer, 1034G: green color layer, 1034B: blue color layer, 1035: black layer (black matrix), 1036: top layer, 1037: third intermediate insulating film, 1040: pixel area, 1041: driver circuit area, 1042: peripheral area, 1044W: white light-emitting area, 1044R: red light-emitting area, 1044B: blue light-emitting area, 1044G: green light-emitting area, 2001: housing, 2002: light source, 3001: lighting device, 3002: Display device, 5000: Display, 5001: Display, 5002: Display, 5003: Display, 5004: Display, 5005: Display, 7101: Housing, 7103: Display area, 7105: Stand, 7107: Display area, 7109: Control button, 7110: Remote control, 7201: Main body, 7202: Housing, 7203: Display area, 7204: Keyboard, 7205: External connection port, 7206: Pointing device,7210: second display area, 7301: housing, 7302: housing, 7303: hinge area, 7304: display area, 7305: display area, 7306: speaker area, 7307: recording media slot area, 7308: LED lamp, 7309: control button, 7310: connection terminal, 7311: sensor, 7400: mobile phone, 7401: housing, 7402: display area, 7403: control button, 7404: external connection port, 7405: speaker, 7406: microphone, 9033: shutter, 9034: switch, 9035: on / off switch, 9036: switch, 9038: control switch, 9630: housing, 9631: display area, 9631a: Display area, 9631b: Display area, 9632a: Touchscreen area, 9632b: Touchscreen area, 9633: Solar cell, 9634: Charge and discharge control circuit, 9635: Battery, 9636: DC-to-DC converter, 9637: Control button, 9638: Converter, and 9639: Knob.

Claims

[1] Light-emitting device comprising: a first electrode; a first light-emitting layer; a second light-emitting layer; and a second electrode, wherein the first light-emitting layer is arranged between the first electrode and the second light-emitting layer, wherein the second light-emitting layer is arranged between the first light-emitting layer and the second electrode, the first light-emitting layer comprises: a first phosphorescent compound; a first host material; and a first organic compound the second light-emitting layer comprises: a second phosphorescent compound; and a second host material, where the first host material and the first organic compound form an exciplex, where the light emitted by the second phosphorescent compound has a longer wavelength than the light emitted by the first phosphorescent compound, where a difference between an emission peak wavelength of a photoluminescence spectrum of the first phosphorescent compound and a wavelength of a peak on the side of the longest wavelength of a function ε(λ)λ 4 the second phosphorescent compound is 0.2 eV or less when the emission peak wavelength and the peak wavelength are converted into energy, where λ denotes a wavelength, and where ε(λ) denotes a molar absorption coefficient at wavelength λ. [2] Light-emitting device comprising: a first electrode; a first light-emitting layer; a second light-emitting layer; and a second electrode, wherein the first light-emitting layer is arranged between the first electrode and the second light-emitting layer, wherein the second light-emitting layer is arranged between the first light-emitting layer and the second electrode, the first light-emitting layer comprises: a first phosphorescent compound; a first host material; and a first organic compound the second light-emitting layer comprises: a second phosphorescent compound; and a second host material, where the first host material and the first organic compound form an exciplex, where the light emitted by the second phosphorescent compound has a longer wavelength than the light emitted by the first phosphorescent compound, where a difference between an emission peak wavelength of a photoluminescence spectrum of the exciplex and a wavelength of a peak on the side of the longest wavelength of a function ε(λ)λ 4 the first phosphorescent compound is 0.2 eV or less when the emission peak wavelength and the peak wavelength are converted into energy, where a difference between an emission peak wavelength of a photoluminescence spectrum of the first phosphorescent compound and a wavelength of a peak on the side of the longest wavelength of a function ε(λ)λ 4 the second phosphorescent compound is 0.2 eV or less when the emission peak wavelength and the peak wavelength are converted into energy, where λ denotes a wavelength, and where ε(λ) denotes a molar absorption coefficient at wavelength λ. [3] Light-emitting device comprising: a first electrode; a first light-emitting layer; a second light-emitting layer; and a second electrode, wherein the first light-emitting layer is arranged between the first electrode and the second light-emitting layer, wherein the second light-emitting layer is arranged between the first light-emitting layer and the second electrode, the first light-emitting layer comprises: a first phosphorescent compound; a first connection; and a second connection the second light-emitting layer comprises: a second phosphorescent compound; and a host material, where the first and second connections form an exciplex, where the light emitted by the second phosphorescent compound has a longer wavelength than the light emitted by the first phosphorescent compound, where an emission spectrum of the exciplex with a peak on the side of the longest wavelength of a function ε(λ)λ 4 overlaps the first phosphorescent compound, where a difference between an emission peak wavelength of a photoluminescence spectrum of the first phosphorescent compound and a wavelength of a peak on the side of the longest wavelength of a function ε(λ)λ 4 the second phosphorescent compound is 0.2 eV or less when the emission peak wavelength and the peak wavelength are converted into energy, where λ denotes a wavelength, and where ε(λ) denotes a molar absorption coefficient at wavelength λ. [4] Light-emitting device according to any one of claims 1 to 3, wherein the first phosphorescent compound is a first iridium complex, and wherein the second phosphorescent compound is a second iridium complex. [5] Light-emitting device according to claim 3, wherein the first compound comprises an aromatic amine skeleton, a carbazole skeleton, a thiophene skeleton and a furan skeleton. [6] Light-emitting device according to any one of claims 1 to 4, wherein the first electrode is an anode and wherein the second electrode is a cathode. [7] Light-emitting device according to any one of claims 1 to 4, wherein the first light-emitting layer and the second light-emitting layer are in contact with each other. [8] Light-emitting device according to claim 4, the first iridium complex has three ligands, and where two of the three ligands are identical ligands and the other ligand of the three ligands differs from the two ligands. [9] Light-emitting device according to claim 4, the second iridium complex has three ligands, and where two of the three ligands are identical ligands and the other ligand of the three ligands differs from the two ligands.

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